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1.  Zonula occludens toxin synthetic peptide derivative AT1002 enhances in vitro and in vivo intestinal absorption of low molecular weight heparin 
Journal of drug targeting  2006;14(5):321-329.
Zonula occludens toxin (Zot) is an enterotoxin obtained from the bacterium vibrio cholerae that has been shown to reversibly and safely open the tight junctions and enhance paracellular transport. AT1002 is a novel synthetic hexapeptide derived from Zot. The hypothesis to be tested in this study is that AT1002 enhances the oral absorption of ardeparin, a low molecular weight heparin (LMWH). To test this hypothesis, drug transport through Caco-2 cell monolayers was monitored in the presence and absence of AT1002. Regional permeability studies using rat intestine were performed. Cell viability in the presence of various concentrations of enhancer was determined. The absorption of ardeparin after oral administration in rats was measured by anti-factor Xa assay. Furthermore, the eventual mucosal and epithelial damage was histologically evaluated. Higher ardeparin permeability (~2-fold) compared to control was observed in the presence of 0.025% of AT1002. Regional permeability studies revealed that the permeability of ardeparin across the duodenal membrane was improved by the AT1002. Cell viability studies showed no significant cytotoxicity below 0.0028% of AT1002. In the presence of 100 μg/kg of AT1002, ardeparin oral bioavailability was significantly increased (Frelative/s.c ~ 20.5%). Furthermore, AT1002 at a dose of 100 μg/kg did not induce any observable morphological damage on gastrointestinal (GI) tissues in vivo. These in vivo and in vitro results suggest that the co-administration of LMWH with AT1002 may be a useful delivery strategy to increase its permeability and hence oral absorption.
PMCID: PMC1994914  PMID: 16882552
AT1002; low molecular weight heparin; enhancer; oral delivery; zonula occludens toxin
2.  Modulation of gastrointestinal permeability of low-molecular-weight heparin by l-arginine: in-vivo and in-vitro evaluation 
l-Arginine is the principal physiological precursor of nitric oxide (NO, a key neurotransmitter) that plays a versatile role in the physiology of the gastrointestinal tract. In this study, the efficacy of l-arginine in enhancing intestinal absorption of ardeparin, a low-molecular-weight heparin (LMWH) was investigated in Caco-2 cell monolayers and a rat model. Regional permeability studies using rat intestine were performed using a modified Ussing chamber. Cell viability in the presence of various concentrations of enhancer was determined by MTT assay. Furthermore, the eventual mucosal epithelial damage was histologically evaluated. LMWH formulated with l-arginine was administered orally to mate Sprague-Dawley rats and the absorption of LMWH was determined by measuring plasma anti-factor Xa activity. Higher ardeparin in-vitro permeability (~3 fold) compared with control was observed in the presence of 2% l-arginine. Regional permeability studies indicated predominant absorption in the colon region. Cell viability studies showed no significant cytotoxicity below 0.8% l-arginine. The oral bioavailability of ardeparin formulated with l-arginine (250 mg kg−1) was increased by ~2 fold compared with control. The formulation was well tolerated by the rats and no abnormal histopathological findings were observed in intestinal tissues of rats exposed to l-arginine. These results suggest that l-arginine may be useful in enhancing the intestinal absorption of LMWHs.
PMCID: PMC1557380  PMID: 16640827
3.  Oral delivery of low-molecular-weight heparin using sodium caprate as absorption enhancer reaches therapeutic levels 
Journal of drug targeting  2005;13(10):573-583.
The primary objective of this study was to evaluate sodium caprate as an oral penetration enhancer for low molecular weight heparin (LMWH), ardeparin. In vitro studies using Caco-2 cell monolayer indicated that 0.0625% of sodium caprate gave approximately 2-fold enhancement of ardeparin compared to negative control with almost 100% cell survival as evaluated by MTT cytotoxicity assay. In vivo studies in rats with ardeparin (1200 IU/kg) and sodium caprate (100 mg/kg) led to a relative bioavailability of 27% with plasma anti-factor Xa levels within the therapeutic range (> 0.2 IU/ml). Moreover, under these conditions, histological examination provided evidence that there was no damage to the gastrointestinal wall. Regional permeability studies using rat intestine indicated the colon as the region of maximum permeation. These results suggest that, at the dose administered, sodium caprate acts as a relatively safe and efficient absorption enhancer in the quest for alternatives for the oral delivery of LMWH.
PMCID: PMC1993550  PMID: 16390818
Sodium caprate; low molecular weight heparin; Caco-2 cell monolayer; absorption enhancer; ardeparin; oral absorption
4.  Positively Charged Polyethylenimines Enhance Nasal Absorption of the Negatively Charged Drug, Low Molecular Weight Heparin 
This study tests the hypothesis that positively charged polyethylenimines (PEIs) enhance nasal absorption of low molecular weight heparin (LMWH) by reducing the negative surface charge of the drug molecule. Physical interactions between PEIs and LMWH were studied by Fourier transform infrared (FTIR) spectroscopy, particle size analysis, conductivity measurements, zeta potential analysis, and azure A assay. The efficacy of PEIs in enhancing nasal absorption of LMWH was studied by administering LMWH formulated with PEI into the nose of anesthetized rats and monitoring drug absorption by measuring plasma anti-factor Xa activity. The metabolic stability of LMWH was evaluated by incubating the drug in rat nasal mucosal homogenates. FTIR spectra of the LMWH-PEI formulation showed a shift in peak position compared to LMWH or PEI alone. Decreases in conductivity, zeta potential and the amount of free LMWH in the PEI-LMWH formulation, as revealed by azure A assay, suggest that PEIs possibly neutralize the negative surface charge of LMWH. The efficacy of PEI in enhancing the bioavailability of nasally administered LMWH can be ranked as PEI-1000 KDa ≥ PEI-750 KDa > PEI-25 KDa. When PEI-1000 KDa was used at a concentration of 0.25%, there was a 4-fold increase in both the absolute and relative bioavailabilities of LMWH compared to the control formulation. Overall, these results indicate that polyethylenimines can be used as potential carriers for nasally administered LMWHs.
PMCID: PMC1847392  PMID: 17023085
low molecular weight heparin; polyethylenimine; nasal absorption; enoxaparin; conductivity
5.  Inhalable Lactose-Based Dry Powder Formulations of Low Molecular Weight Heparin 
Currently low molecular weight heparin (LMWH) is administered as subcutaneous injection. This study sought to investigate the feasibility of LMWH as an inhalable dry powder (DPI) formulation and evaluate the interaction of the drug with lactose when used as a carrier. The study also compares the extent of pulmonary absorption of LMWH administered as a dry powder with that administered as an aerosolized aqueous solution.
The formulations were prepared by mixing LMWH in an aqueous solution of lactose followed by lyophilization of the resulting solution. The lyophilized preparation was then ground and sieved. Physical characterization of the formulations was performed by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), particle size analysis, and determination of aerodynamic diameter. For in vivo studies, formulations were administered to anesthetized rats, and drug absorption was monitored by measuring plasma antifactor Xa activity.
Results and Conclusions
In the FTIR scan, all characteristic peaks of lactose and LMWH were observed, suggesting that there was no strong interaction between lactose and LMWH. Although the aerodynamic diameter of the formulation (DPI-2) that was sieved through 170- and 230-mesh screens was similar to that of the formulation (DPI-1) sieved through 120- and 170-mesh screens, the particle sizes of the two formulations were significantly different. Dry powder formulations of LMWH were better absorbed compared to an inhalable solution of LMWH. One of the dry powder formulations (DPI-2) produced an almost 1.5-fold increase in the relative bioavailability (41.6%) compared to the liquid formulation of LMWH (32.5%). Overall, the data presented here suggest that lactose does not adversely affect the physical-chemical characteristics of the drug, and that lactose can be used as a carrier for pulmonary delivery of LMWH.
PMCID: PMC3196062  PMID: 19778265
LMWH; inhalation; dry powder; pulmonary absorption
6.  Increasing Oral Absorption of Polar Neuraminidase Inhibitors: A Prodrug Transporter Approach Applied to Oseltamivir Analogue 
Molecular pharmaceutics  2013;10(2):512-522.
Poor oral absorption is one of the limiting factors in utilizing the full potential of polar antiviral agents. The neuraminidase target site requires a polar chemical structure for high affinity binding, thus limiting oral efficacy of many high affinity ligands. The aim of this study was to overcome this poor oral absorption barrier, utilizing prodrug to target the apical brush border peptide transporter 1 (PEPT1). Guanidine oseltamivir carboxylate (GOCarb) is a highly active polar antiviral agent (prodrug) with insufficient oral bioavailability (4%) to be an effective therapeutic agent. In this report we utilize a carrier-mediated targeted prodrug approach to improve the oral absorption of GOCarb.
Acyloxy(alkyl) ester based amino acid linked prodrugs were synthesized and evaluated as potential substrates of mucosal transporters e.g. PEPT1. Prodrugs were also evaluated for their chemical and enzymatic stability. PEPT1 transport studies included [3H]Gly-Sar uptake inhibition and cellular uptake experiments using HeLa cells over-expressing PEPT1. The intestinal membrane permeability of the selected prodrugs and the parent drug were then evaluated for epithelial cell transport across Caco-2 monolayers, and in the in-situ rat intestinal jejunal perfusion model.
Prodrugs exhibited a pH dependent stability with higher stability at acidic pHs. Significant inhibition of uptake (IC50 <1mM) was observed for L-valyl and L-isoleucyl amino acid prodrugs in competition experiments with [3H]Gly-Sar, indicating a 3–6 times higher affinity for PEPT1 compared to valacyclovir; a well-known PEPT1 substrate and >30 fold increase in affinity compared to GOCarb. The L-valyl prodrug exhibited significant enhancement of uptake in PEPT1/HeLa cells, and compared favorably with the well absorbed valacyclovir. Transepithelial permeability across Caco-2 monolayers showed that these amino acid prodrugs have a 2–5 fold increase in permeability as compared to the parent drug and showed that the L-valyl prodrug (Papp = 1.7×10−6 cm/sec) has the potential to be a rapidly transported across the epithelial cell apical membrane. Significantly, only the parent drug (GOCarb) appeared in the basolateral compartment, indicating complete activation (hydrolysis) during transport. Intestinal rat jejunal permeability studies showed that L-valyl and L-isoleucyl prodrugs are highly permeable compared to the orally well absorbed metoprolol, while the parent drug had essentially zero permeability in the jejunum, consistent with its known poor low absorption.
Prodrugs were rapidly converted to parent in cell homogenates suggesting their ability to be activated endogenously in the epithelial cell, consistent with the transport studies. Additionally, L-valyl prodrug was found to be a substrate for valacyclovirase (Km=2.37 mM) suggesting a potential cell activation mechanism.
Finally we determined the oral bioavailability of our most promising candidate, GOC-L-Val, in mice to be 23% under fed conditions and 48% under fasted conditions.
In conclusion, GOC-L-Val prodrug was found to be a very promising antiviral agent for oral delivery. These findings indicate that the carrier-mediated prodrug approach is an excellent strategy for improving oral absorption of polar neuraminidase inhibitors. These promising results demonstrates that the oral peptide transporter-mediated prodrug strategy has enormous promise for improving the oral mucosal cell membrane permeability of polar, poorly absorbed antiviral agents and treating influenza via the oral route of administration.
PMCID: PMC3572763  PMID: 23244438
Prodrugs; valacyclovirase; PEPT1; influenza; neuraminidase; oral absorption; intestinal permeability; antiviral; oseltamivir; transporter; stability; caco-2 permeability; glysar; rat perfusion
7.  Enhanced regenerative healing efficacy of a highly skin-permeable growth factor nanocomplex in a full-thickness excisional mouse wound model 
Exogenous administration of growth factors has potential benefits in wound healing; however, limited percutaneous absorption, inconsistent efficacy, and the need for high doses have hampered successful clinical use. To overcome these restrictions, we focused on the development of a topical formulation composed of highly skin-permeable multimeric nanocomplex of growth factors. In the present study, we fused low-molecular-weight protamine (LMWP) with epidermal growth factor (EGF), insulin-like growth factor 1 (IGF-I), and platelet-derived growth factor A ligand (PDGF-A) (producing recombinant [r]LMWP-EGF, rLMWP-IGF-I, and rLMWP-PDGF-A, respectively) via genetic modification. Then, we used in vitro cell proliferation studies to assess the biological activity and the benefits of the combination. The LMWP-conjugated growth factors were complexed with low-molecular-weight heparin (LMWH) and formulated with Poloxamer 188 as a delivery vehicle. After confirming the enhanced skin permeability, in vivo studies were performed to assess whether the LMWP-conjugated growth factor nanocomplex formulations accelerated the healing of full-thickness wounds in mice. The LMWP-conjugated growth factors were biologically equivalent to their native forms, and their combination induced greater fibroblast proliferation. rLMWP-EGF showed significantly enhanced permeability and cumulative permeation, and the rates for rLMWP-IGF-I and rLMWP-PDGF-A, across excised mouse skin, were 124% and 164% higher, respectively, than for the native forms. The LMWP-fused growth factors resulted in formation of nanocomplexes (23.51±1.12 nm in diameter) in combination with LMWH. Topical delivery of growth factors fused with LMWP accelerated wound re-epithelialization significantly, accompanied by the formation of healthy granulation tissue within 9 days compared with a free–growth factor complex or vehicle. Thus, the LMWP-conjugated growth factor nanocomplex can induce rapid, comprehensive healing and may be a candidate wound-healing therapeutic.
PMCID: PMC4184407  PMID: 25288883
epidermal growth factor; insulin-like growth factor; platelet-derived growth factor
8.  Enabling the Intestinal Absorption of Highly Polar Anti-Viral Agents: Ion-Pair Facilitated Membrane Permeation of Zanamivir Heptyl Ester and Guanidino Oseltamivir 
Molecular pharmaceutics  2010;7(4):1223-1234.
Anti-viral drugs often suffer from poor intestinal permeability, preventing their delivery via the oral route. The goal of this work was to enhance the intestinal absorption of the low-permeability anti-viral agents zanamivr heptyl ester (ZHE) and guanidino oseltamivir (GO) utilizing an ion-pairing approach, as a critical step toward making them oral drugs. The counterion 1-hydroxy-2-napthoic acid (HNAP) was utilized to enhance the lipophilicity and permeability of the highly polar drugs. HNAP substantially increased the log P of the drugs by up to 3.7 log units. Binding constants (K11aq) of 388 M−1 for ZHE-HNAP and 2.91 M−1 for GO.-HNAP were obtained by applying a quasi-equilibrium transport model to double-reciprocal plots of apparent octanol-buffer distribution coefficients versus HNAP concentration. HNAP enhanced the apparent permeability (Papp) of both compounds across Caco-2 cell monolayers in a concentration-dependent manner, as substantial Papp (0.8 – 3.0 × 10−6 cm/s) was observed in the presence of 6–24 mM HNAP, whereas no detectable transport was observed without counterion. Consistent with a quasi-equilibrium transport model, a linear relationship with slope near 1 was obtained from a log-log plot of Caco-2 Papp versus HNAP concentration, supporting the ion-pair mechanism behind the permeability enhancement. In the rat jejunal perfusion assay, the addition of HNAP failed to increase the effective permeability (Peff) of GO. However, the rat jejunal permeability of ZHE was significantly enhanced by the addition of HNAP in a concentration-dependent manner, from essentially zero without HNAP to 4.0 × 10−5 cm/s with 10 mM HNAP, matching the Peff of the high-permeability standard metoprolol. The success of ZHE-HNAP was explained by its >100-fold stronger K11aq versus GO-HNAP, making ZHE-HNAP less prone to dissociation and ion-exchange with competing endogenous anions and able to remain intact during membrane permeation. Overall, this work presents a novel approach to enable the oral delivery of highly polar anti-viral drugs, and provides new insights into the underlying mechanisms governing the success or failure of the ion-pairing strategy to increase oral absorption.
PMCID: PMC3496398  PMID: 20536260
ion-pair; membrane transport; anti-viral; membrane permeability; oral absorption
9.  Design and Evaluation of Self-Emulsifying Drug Delivery System (SEDDS) Of Carvedilol to Improve the Oral Absorption 
Self-emulsifying drug delivery system is an isotropic mixture of natural or synthetic oils, non-ionic surfactants or, one or more hydrophilic solvent and co-solvents/surfactant and polymer that improve bioavailability and increase solubility of poorly-soluble drugs.
This study was aimed to prepare and develop a stable formulation for self-emulsifying drug delivery system to enhance the solubility, release rate, and oral absorption of the poorly-soluble drug, carvedilol.
Materials and Methods:
The prepared self-emulsifying drug delivery system formulations were evaluated regarding their particle size, refractory index (RI), emulsifying efficiency, drug release, and rat intestine permeability.
The results showed oleic acid as oil with Labrafil as surfactant and Labrafac PG (propylene glycol dicaprylocapraye) as co-surfactant with hydroxypropyl methylcellulose and Poloxamer as polymer prepared stable emulsions with a refractive index higher than acidic medium and water. The particle size of formulations was influenced by the type of polymer so that the mean particle size in the self-emulsifying drug delivery system formulations containing hydroxypropyl methylcellulose have a higher particle size compared to Poloxamer formulations. The percentage of drug release after 24 hours (R24) for Poloxamer and hydroxypropyl methylcellulose formulations were 61.24-70.61% and to 74.26-91.11%, respectively. The correlation between percentages of drug released after 24 hours with type of polymer was significant. In permeation studies, a significant and direct correlation existed between P4 and surfactant/co-surfactant ratio. The self-emulsifying drug delivery system formulations showed drug permeability through the rat intestine 2.76 times more, compared with the control.
This study demonstrated that physicochemical properties, in vitro release and rat intestine permeability were dependent upon the contents of S/C, water and oil percentage in formulations.
PMCID: PMC4165178  PMID: 25237644
Carvedilol; Self-Emulsifying Drug Delivery Systems; Oral Absorption
10.  Enhanced Permeability of Etoposide across Everted Sacs of Rat Small Intestine by Vitamin E-TPGS  
Etoposide, a widely used anticancer drug, exhibits low and variable oral bioavailability mainly because of being substrate for the efflux transporter, P-glycoprotein (P-gp). Therefore, the present study was aimed to investigate the effect of D-α-tocopherol polyethylene glycol 1000 succinate (TPGS) and PEG 400 as P-gp inhibitors on the intestinal absorption of etoposide. Everted sacs of rat small intestine were incubated in Krebs buffer solution which contained etoposide in the absence or presence of various concentrations of TPGS or PEG 400. The effect of verapamil as a known P-gp inhibitor on the absorption of drug was also studied.
The absorptive transport of etoposide was significantly enhanced (p < 0.001) in the presence of verapamil (100 μg/mL) and TPGS (over the concentration range of 0.002- 0.1 mg/mL), suggesting that the inhibition of P-gp located in the intestine may be involved in the enhancement of etoposide absorption. However, the addition of PEG 400 at various concentrations (0.05, 0.1 and 0.5% w/v) had no effect on the etoposide transport. No significant difference was found between the permeability values in the absence and presence of the maximum concentration of TPGS for two transport markers, lucifer yellow and imipramine, indicating that the enhancement in etoposide permeability in the presence of TPGS was not due to the compromise in tight junctions or membrane integrity of epithelial cells.
The results of the study suggest that the use of TPGS as a safe excipient in etoposide formulations may enhance the oral bioavailability of etoposide and result in a predictable oral absorption.
PMCID: PMC3813364  PMID: 24250670
Etoposide; Vitamin E-TPGS; Everted gut sac; Permeability; P-glycoprotein
11.  Enhancing the Intestinal Membrane Permeability of Zanamivir: A Carrier Mediated Prodrug Approach 
Molecular Pharmaceutics  2011;8(6):2358-2367.
The purpose of this study was to improve the membrane permeability and oral absorption of the poorly permeable anti-influenza agent, zanamivir. The poor oral bioavailability is attributed to the high polarity (cLogP~-5) resulting from the polar and zwitterionic nature of zanamivir. In order to improve the permeability of zanamivir, prodrugs with amino acids were developed to target the intestinal membrane transporter, hPepT1. Several acyloxy ester prodrugs of zanamivir conjugated with amino acids were synthesized and characterized. The prodrugs were evaluated for their chemical stability in buffers at various pHs and for their transport and tissue activation by enzymes. The acyloxy ester prodrugs of zanamivir were shown to competitively inhibit [3H]Gly-Sar uptake in Caco-2 cells (IC50: 1.19±0.19mM for L-valyl prodrug of zanamivir). The L-valyl prodrug of zanamivir exhibited ~3 fold higher uptake in transfected HeLa/hPepT1 cells compared to wild type HeLa cells, suggesting, at least in part, carrier mediated transport by the hPepT1 transporter. Further, enhanced transcellular permeability of prodrugs across Caco-2 monolayer compared to the parent drug (Papp= 2.24E-06 ± 1.33E-07 cm/sec for L-valyl prodrug of zanamivir), with only parent zanamivir appearing in the receiver compartment, indicates that the prodrugs exhibited both enhanced transport and activation in intestinal mucosal cells. Most significantly several of these prodrugs exhibited high intestinal jejunal membrane permeability, similar to metoprolol, in the in situ rat intestinal perfusion system, a system highly correlated with human jejunal permeability.
In summary, this mechanistic targeted prodrug strategy, to enhance oral absorption via intestinal membrane carriers such as hPepT1, followed by activation to parent drug (active pharmaceutical ingredient or API) in the mucosal cell, significantly improves the intestinal epithelial cell permeability of zanamivir and has the potential to provide the high oral bioavailability necessary for oral zanamivir therapy.
PMCID: PMC3304100  PMID: 21905667
Prodrugs; carrier-mediated transport; hPepT1; zanamivir
12.  Zanamivir Oral Delivery: Enhanced Plasma and Lung Bioavailability in Rats 
Biomolecules & Therapeutics  2013;21(2):161-169.
The objective of this study was to enhance the oral bioavailability (BA) of zanamivir (ZMR) by increasing its intestinal permeability using permeation enhancers (PE). Four different classes of PEs (Labrasol®, sodium cholate, sodium caprate, hydroxypropyl β-cyclodextrin) were investigated for their ability to enhance the permeation of ZMR across Caco-2 cell monolayers. The flux and Papp of ZMR in the presence of sodium caprate (SC) was significantly higher than other PEs in comparison to control, and was selected for further investigation. All concentrations of SC (10-200 mM) demonstrated enhanced flux of ZMR in comparison to control. The highest flux (13 folds higher than control) was achieved for the formulation with highest SC concentration (200 mM). The relative BA of ZMR formulation containing SC (PO-SC) in plasma at a dose of 10 mg/kg following oral administration in rats was 317.65% in comparison to control formulation (PO-C). Besides, the AUC0-24 h of ZMR in the lungs following oral administration of PO-SC was 125.22 ± 27.25 ng hr ml-1 with a Cmax of 156.00 ± 24.00 ng/ml reached at 0.50±0.00 h. But, there was no ZMR detected in the lungs following administration of control formulation (PO-C). The findings of this study indicated that the oral formulation PO-SC containing ZMR and SC was able to enhance the BA of ZMR in plasma to an appropriate amount that would make ZMR available in lungs at a concentration higher (>10 ng/ml) than the IC50 concentration of influenza virus (0.64-7.9 ng/ml) to exert its therapeutic effect.
PMCID: PMC3762309  PMID: 24009875
Zanamivir oral delivery; Permeation enhancer; Bioavailability enhancement; Sodium caprate; Influenza
13.  Enhanced absorption of hydroxysafflor yellow A using a self-double-emulsifying drug delivery system: in vitro and in vivo studies 
Hydroxysafflor yellow A (HSYA), the main active ingredient of the safflower plant (Carthamus tinctorius L.), is a hydrophilic drug with low oral bioavailability. Water-in-oil-in-water (w/o/w) double emulsions may enhance the oral absorption of HSYA. In this study, we prepared a self-double-emulsifying drug delivery system (SDEDDS) to improve the absorption of HSYA. SDEDDS consists of water in oil emulsions and hydrophilic surfactants that can self-emulsify into w/o/w double emulsions in the aqueous gastrointestinal environment. Confocal laser scanning micrographs showed that spherical droplets were uniformly distributed in the dispersion medium with narrow particle size distribution and could form fine w/o/w double emulsions upon dilution in dispersion medium with gentle stirring. The dispersed oil droplets contained small dispersed aqueous droplets consistent with the characteristics of double emulsions. Furthermore, in vitro cellular experiments were performed to study the mechanism of the absorption promoting effect of SDEDDS. The accumulation of rhodamine-123 in Caco-2 cells was used to evaluate the efflux transport of p-glycoprotein inhibitor. Histopathologic studies on the rat intestine showed that SDEDDS can cause mucosal damage to a certain degree of toxicity, however this was not serious. These results suggest that SDEDDS can greatly improve the oral absorption of HSYA. Given the toxicity demonstrated to the small intestine, the formulation prescription should be improved to enhance security in the future.
PMCID: PMC3415323  PMID: 22888246
self-double-emulsifying drug delivery system; hydroxysafflor yellow A; Caco-2 cells; bioavailability; histopathologic studies
14.  The Use of Low Molecular Weight Protamine Chemical Chimera to Enhance Monomeric Insulin Intestinal Absorption 
Biomaterials  2013;34(31):7733-7743.
Although oral delivery of insulin offers a number of unmatched advantages, it nevertheless is beset by the poor permeability of insulin molecules through the epithelial cell membranes of the intestinal mucosal layer. We previously reported the development of low molecular weight protamine (LMWP) as a nontoxic yet potent cell penetrating peptide, of which via covalent linkage was capable of translocating protein cargos through the membranes of almost all cell types. It is therefore hypothesized that LMWP could be practically employed as a safe and effective tool to deliver insulin across the intestinal mucosal membrane, thereby augmenting its absorption through the GI tract. However, formulating 1:1 monomeric insulin/LMWP conjugate presents a tall order of challenge, as the acidic insulin and basic LMWP would automatically form tight aggregates through electrostatic interactions. In this paper, we developed an innovative conjugation strategy to solve this problem, by using succinimidyl-[(N-maleimidopropionamido)-polyethyleneglycol] ester (NHS-PEG-MAL) as an intermediate cross-linker during the coupling process. Both SDS-PAGE and MALDI-TOF mass spectroscopy confirmed the formation of a homogeneous, monomeric (1:1 ratio) insulin/LMWP conjugate without encountering the conventional problem of substrate aggregation. Cell culture studies demonstrated that transport of the Insulin-PEG-LMWP conjugate across the intestinal mucosal monolayer was augmented by almost five folds compared to native insulin. Furthermore, results from the in situ loop absorption tests in rats showed that systemic pharmacological bioavailability of insulin was significantly enhanced after its conjugation with LMWP. Overall, the presented chemical conjugation with LMWP could offer a reliable and safe means to improve the intestinal permeability of therapeutic peptides/proteins, shedding light of the possibility for their effective oral delivery.
PMCID: PMC3766633  PMID: 23863452
Cell-penetrating peptide; intestinal absorption; low molecular weight protamine; insulin; monomeric conjugation; permeation enhancement
15.  Nonlinear Absorption Kinetics of Self-Emulsifying Drug Delivery Systems (SEDDS) Containing Tocotrienols as Lipophilic Molecules: In Vivo and In Vitro Studies 
The AAPS Journal  2013;15(3):684-695.
Self-emulsifying drug delivery systems (SEDDS) have been broadly used to promote the oral absorption of poorly water-soluble drugs. The purpose of the current study was to evaluate the in vivo oral bioavailability of vitamin E isoforms, δ-tocotrienol (δ-T3) and γ-tocotrienol (γ-T3) administered as SEDDS, as compared to commercially available UNIQUE E® Tocotrienols capsules. Results from studies in rats showed that low dose treatment with δ-T3 (90%) and γ-T3 (10%) formulated SEDDS showed bioavailability of 31.5% and 332%, respectively. However, bioavailability showed a progressive decrease with increased treatment dose that displayed nonlinear absorption kinetics. Additional in vitro studies examining cellular uptake studies in Caco 2 cells revealed that the SEDDS formulation increased passive permeability of δ-T3 and γ-T3 by threefold as compared to the commercial capsule formulation. These studies also showed that free surfactants decreased δ-T3 and γ-T3 absorption. Specifically, combined treatment cremophor EL or labrasol with tocotrienols caused a 60–85% reduction in the cellular uptake of δ-T3 and γ-T3 and these effects appear to result from surfactant-induced inhibition of the δ-T3 and γ-T3 transport protein Niemann–Pick C1-like 1 (NPC1L1). In summary, results showed that SEDDS formulation significantly increases the absorption and bioavailability δ-T3 and γ-T3. However, this effect is self-limiting because treatment with increasing doses of SEDDS appears to be associated with a corresponding increase in free surfactants levels that directly and negatively impact tocotrienol transport protein function and results in nonlinear absorption kinetics and a progressive decrease in δ-T3 and γ-T3 absorption and bioavailability.
Electronic supplementary material
The online version of this article (doi:10.1208/s12248-013-9481-7) contains supplementary material, which is available to authorized users.
PMCID: PMC3691427  PMID: 23572242
cremophor EL; labrasol; NPC1L1; SEDDS; tocotrienols
16.  Effects of polymer molecular weight on relative oral bioavailability of curcumin 
Polylactic-co-glycolic acid (PLGA) nanoparticles have been used to increase the relative oral bioavailability of hydrophobic compounds and polyphenols in recent years, but the effects of the molecular weight of PLGA on bioavailability are still unknown. This study investigated the influence of polymer molecular weight on the relative oral bioavailability of curcumin, and explored the possible mechanism accounting for the outcome.
Curcumin encapsulated in low (5000–15,000) and high (40,000–75,000) molecular weight PLGA (LMw-NPC and HMw-NPC, respectively) were prepared using an emulsification-solvent evaporation method. Curcumin alone and in the nanoformulations was administered orally to freely mobile rats, and blood samples were collected to evaluate the bioavailability of curcumin, LMw-NPC, and HMw-NPC. An ex vivo experimental gut absorption model was used to investigate the effects of different molecular weights of PLGA formulation on absorption of curcumin. High-performance liquid chromatography with diode array detection was used for quantification of curcumin in biosamples.
There were no significant differences in particle properties between LMw-NPC and HMw-NPC, but the relative bioavailability of HMw-NPC was 1.67-fold and 40-fold higher than that of LMw-NPC and conventional curcumin, respectively. In addition, the mean peak concentration (Cmax) of conventional curcumin, LMw-NPC, and HMw-NPC was 0.028, 0.042, and 0.057 μg/mL, respectively. The gut absorption study further revealed that the HMw-PLGA formulation markedly increased the absorption rate of curcumin in the duodenum and resulted in excellent bioavailability compared with conventional curcumin and LMw-NPC.
Our findings demonstrate that different molecular weights of PLGA have varying bioavailability, contributing to changes in the absorption rate at the duodenum. The results of this study provide the rationale for design of a nanomedicine delivery system to enhance the bioavailability of water-insoluble pharmaceutical compounds and functional foods.
PMCID: PMC3384366  PMID: 22745556
absorption; duodenum; molecular weight; poly(lactic-co-glycolic acid); PLGA; relative oral bioavailability
17.  Surface-modified solid lipid nanoparticles for oral delivery of docetaxel: enhanced intestinal absorption and lymphatic uptake 
Docetaxel is a potent anticancer drug, but development of an oral formulation has been hindered mainly due to its poor oral bioavailability. In this study, solid lipid nanoparticles (SLNs) surface-modified by Tween 80 or D-alpha-tocopheryl poly(ethylene glycol 1000) succinate (TPGS 1000) were prepared and evaluated in terms of their feasibility as oral delivery systems for docetaxel. Tween 80-emulsified and TPGS 1000-emulsified tristearin-based lipidic nanoparticles were prepared by a solvent-diffusion method, and their particle size distribution, zeta potential, drug loading, and particle morphology were characterized. An in vitro release study showed a sustained-release profile of docetaxel from the SLNs compared with an intravenous docetaxel formulation (Taxotere®). Tween 80-emulsified SLNs showed enhanced intestinal absorption, lymphatic uptake, and relative oral bioavailability of docetaxel compared with Taxotere in rats. These results may be attributable to the absorption-enhancing effects of the tristearin nanoparticle. Moreover, compared with Tween 80-emulsified SLNs, the intestinal absorption and relative oral bioavailability of docetaxel in rats were further improved in TPGS 1000-emulsified SLNs, probably due to better inhibition of drug efflux by TPGS 1000, along with intestinal lymphatic uptake. Taken together, it is worth noting that these surface-modified SLNs may serve as efficient oral delivery systems for docetaxel.
PMCID: PMC3894956  PMID: 24531717
solid lipid nanoparticles; vitamin E TPGS; docetaxel; lymphatic uptake; bioavailability; toxicity
International Journal of Pharmaceutics  2012;434(1-2):315-324.
A majority of studies involving prodrugs are directed to overcome low bioavailability of the parent drug. The aim of this study is to increase the bioavailability of acyclovir (ACV) by designing a novel prodrug delivery system which is more lipophilic, and at the same time site specific. In this study, a lipid raft has been conjugated to the parent drug molecule to impart lipophilicity. Simultaneously a targeting moiety that can be recognized by a specific transporter/receptor in the cell membrane has also been tethered to the other terminal of lipid raft. Targeted lipid prodrugs i.e., biotin-ricinoleicacid-acyclovir (B-R-ACV) and biotin-12hydroxystearicacid-acyclovir (B-12HS-ACV) were synthesized with ricinoleicacid and 12hydroxystearicacid as the lipophilic rafts and biotin as the targeting moiety. Biotin-ACV (B-ACV), ricinoleicacid-ACV (R-ACV) and 12hydroxystearicacid-ACV (12HS-ACV) were also synthesized to delineate the individual effects of the targeting and the lipid moieties. Cellular accumulation studies were performed in confluent MDCK-MDR1 and Caco-2 cells. The targeted lipid prodrugs B-R-ACV and B-12HS-ACV exhibited much higher cellular accumulation than B-ACV, R-ACV and 12HS-ACV in both cell lines. This result indicates that both the targeting and the lipid moiety act synergistically towards cellular uptake. The biotin conjugated prodrugs caused a decrease in the uptake of [3H] biotin suggesting the role of sodium dependent multivitamin transporter (SMVT) in uptake. The affinity of these targeted lipid prodrugs towards SMVT was studied in MDCK-MDR1 cells. Both the targeted lipid prodrugs B-R-ACV (20.25 ± 1.74 µM) and B-12HS-ACV (23.99 ± 3.20 µM) demonstrated higher affinity towards SMVT than B-ACV (30.90 ± 4.19 µM). Further, dose dependent studies revealed a concentration dependent inhibitory effect on [3H] biotin uptake in the presence of biotinylated prodrugs. Transepithelial transport studies showed lowering of [3H] biotin permeability in the presence of biotin and biotinylated prodrugs, further indicating a carrier mediated translocation by SMVT. Overall, results from these studies clearly suggest that these biotinylated lipid prodrugs of ACV possess enhanced affinity towards SMVT. These prodrugs appear to be potential candidates for the treatment of oral and ocular herpes virus infections, because of higher expression of SMVT on intestinal and corneal epithelial cells. In conclusion we hypothesize that our novel prodrug design strategy may help in higher absorption of hydrophilic parent drug. Moreover, this novel prodrug design can result in higher cell permeability of hydrophilic therapeutics such as genes, siRNA, antisense RNA, DNA, oligonucleotides, peptides and proteins.
PMCID: PMC3401275  PMID: 22692074
acyclovir; targeted lipid prodrugs; biotin; SMVT; affinity; drug delivery
19.  Enhanced uptake and transport of (+)-catechin and (−)-epigallocatechin gallate in niosomal formulation by human intestinal Caco-2 cells 
The aim of this study was to evaluate (+)-catechin and (−)-epigallocatechin gallate (EGCG) cellular uptake and transport across human intestinal Caco-2 cell monolayer in both the absence and presence of niosomal carrier in variable conditions. The effect of free drugs and drug-loaded niosomes on the growth of Caco-2 cells was studied. The effects of time, temperature, and concentration on drug cellular uptake in the absence or presence of its niosomal delivery systems were investigated. The intestinal epithelial membrane transport of the drug-loaded niosomes was examined using the monolayer of the human Caco-2 cells. The kinetics of transport, and the effect of temperature, adenosine triphosphate inhibitor, permeability glycoprotein inhibitor, multidrug resistance-associated protein 2 inhibitor, and the absorption enhancer on transport mechanism were investigated. It was found that the uptake of catechin, EGCG, and their niosomes by Caco-2 cells was 1.22±0.16, 0.90±0.14, 3.25±0.37, and 1.92±0.22 μg/mg protein, respectively (n=3). The apparent permeability coefficient values of catechin, EGCG, and their niosomes were 1.68±0.16, 0.88±0.09, 2.39±0.31, and 1.42±0.24 cm/second (n=3) at 37°C, respectively. The transport was temperature- and energy-dependent. The inhibitors of permeability glycoprotein and multidrug resistance-associated protein 2 and the absorption enhancer significantly enhanced the uptake amount. Compared with the free drugs, niosomal formulation significantly enhanced drug absorption. Additionally, drug-loaded niosomes exhibited stronger stability and lower toxicity. These findings showed that the oral absorption of tea flavonoids could be improved by using the novel drug delivery systems.
PMCID: PMC4020900  PMID: 24855353
niosomes; formulation; bioavailability; stability
20.  Intestinal absorption of forsythoside A in in situ single-pass intestinal perfusion and in vitro Caco-2 cell models 
Acta Pharmacologica Sinica  2012;33(8):1069-1079.
To investigate the mechanisms underlying the intestinal absorption of the major bioactive component forsythoside A (FTA) extracted from Forsythiae fructus.
An in vitro Caco-2 cell model and a single-pass intestinal perfusion in situ model in SD rats were used.
In the in vitro Caco-2 cell model, the mean apparent permeability value (Papp-value) was 4.15×10-7 cm/s in the apical-to-basolateral (AP-BL) direction. At the concentrations of 2.6–10.4 μg/mL, the efflux ratio of FTA in the bi-directional transport experiments was approximately 1.00. After the transport, >96% of the apically loaded FTA was retained on the apical side, while >97% of the basolaterally loaded FTA was retained on the basolateral side. The Papp-values of FTA were inversely correlated with the transepithelial electrical resistance. The paracellular permeability enhancers sodium caprate and EDTA, the P-gp inhibitor verapamil and the multidrug resistance related protein (MRP) inhibitors cyclosporine and MK571 could concentration-dependently increase the Papp-values, while the uptake (OATP) transporter inhibitors diclofenac sodium and indomethacin could concentration-dependently decrease the Papp-values. The intake transporter SGLT1 inhibitor mannitol did not cause significant change in the Papp-values. In the in situ intestinal perfusion model, both the absorption rate constant (Ka) and the effective permeability (Peff-values) following perfusion of FTA 2.6, 5.2 and 10.4 μg/mL via the duodenum, jejunum and ileum had no significant difference, although the values were slightly higher for the duodenum as compared to those in the jejunum and ileum. The low, medium and high concentrations of verapamil caused the largest increase in the Peff-values for duodenum, jejunum and ileum, respectively. Sodium caprate, EDTA and cyclosporine resulted in concentration-dependent increase in the Peff-values. Diclofenac sodium and indomethacin caused concentration-dependent decrease in the Peff-values. Mannitol did not cause significant change in the Papp-values for the duodenum, jejunum or ileum.
The results suggest that the intestinal absorption of FTA may occur through passive diffusion, and the predominant absorption site may be in the upper part of small intestine. Paracellular transport route is also involved. P-gp, MRPs and OATP may participate in the absorption of FTA in the intestine. The low permeability of FTA contributes to its low oral bioavailability.
PMCID: PMC4011322  PMID: 22773077
forsythoside A; in situ intestinal perfusion; Caco-2 cells; intestinal absorption; pharmacokinetics; P-gp; multidrug resistance related protein; uptake (OATP) transporter
21.  Improvement of colchicine oral bioavailability by incorporating eugenol in the nanoemulsion as an oil excipient and enhancer 
The effect of eugenol on colchicine transport across an isolated rat intestinal membrane was studied using an in vitro diffusion chamber system. We found that eugenol increased the absorptive transport of the drug efficiently. The effect of eugenol on intestinal absorption of colchicine in an oral administrative nanoemulsion formulation was also demonstrated in vivo. The colchicine nanoemulsion was prepared with isopropyl myristate, eugenol, Tween80, ethanol and water, and eugenol was used as an oil phase in the formulation; an average particle size of this nanoemulsion was 41.2 ± 7.2 nm. The permeation of colchicine in the nanoemulsion across the intestinal membrane was significantly different from that of the control group (0.2 mM colchicine). Finally, co-administration of eugenol in colchicine nanoemulsion to enhance the colchicine bioavailability was investigated by an oral administration method. After oral administration of colchicine (8 mg/kg) in the form of either the nanoemulsion or in free colchicine solution, the relative bioavailability of nanoemulsion and eugenol–nanoemulsion were enhanced by about 1.6- and 2.1-fold, respectively, compared with free colchicine solution. The procedure indicated that the intestinal absorption of colchicine was enhanced significantly by eugenol in the tested nanoemulsion. All the results suggested that eugenol is an efficient component in an oral administrative formulation for improving the intestinal absorption of colchicine.
PMCID: PMC3131190  PMID: 21753875
intestinal absorption; nanoemulsion; absorption enhancement; eugenol
22.  Improvement of Intestinal Absorption of Forsythoside A and Chlorogenic Acid by Different Carboxymethyl Chitosan and Chito-oligosaccharide, Application to Flos Lonicerae - Fructus Forsythiae Herb Couple Preparations 
PLoS ONE  2013;8(5):e63348.
The current study aims to investigate the effect of chitosan derivatives on the intestinal absorption and bioavailabilities of forsythoside A (FTA) and Chlorogenic acid (CHA), the major active components in Flos Lonicerae - Fructus Forsythiae herb couple. Biopharmaceutics and pharmacokinetics properties of the two compounds have been characterized in vitro, in situ as well as in rats. Based on the identified biopharmaceutics characteristics of the two compounds, the effect of chitosan derivatives as an absorption enhancer on the intestinal absorption and pharmacokinetics of FTA and CHA in pure compound form as well as extract form were investigated in vitro, in situ and in vivo. Both FTA and CHA demonstrated very limited intestinal permeabilities, leading to oral bioavailabilities being only 0.50% and 0.13% in rats, respectively. Results from both in vitro, in situ as well as in vivo studies consistently indicated that Chito-oligosaccharide (COS) at dosage of 25 mg/kg could enhance intestinal permeabilities significantly as well as the in vivo bioavailabilities of both FTA and CHA than CMCs in Flos Lonicerae - Fructus Forsythiae herb couple preparations, and was safe for gastrointestine from morphological observation. Besides, treatment with Flos Lonicerae - Fructus Forsythiae herb couple preparations with COS at the dosage of 25 mg/kg prevented MDCK damage after influenza virus propagation, which was significantly better than control. The current findings not only identified the usefulness of COS for the improved delivery of Flos Lonicerae - Fructus Forsythiae preparations but also demonstrated the importance of biopharmaceutical characterization in the dosage form development of traditional Chinese medicine.
PMCID: PMC3652823  PMID: 23675483
23.  Oral Delivery of Lipophilic Drugs: The Tradeoff between Solubility Increase and Permeability Decrease When Using Cyclodextrin-Based Formulations 
PLoS ONE  2013;8(7):e68237.
The purpose of this study was to investigate the impact of oral cyclodextrin-based formulation on both the apparent solubility and intestinal permeability of lipophilic drugs. The apparent solubility of the lipophilic drug dexamethasone was measured in the presence of various HPβCD levels. The drug’s permeability was measured in the absence vs. presence of HPβCD in the rat intestinal perfusion model, and across Caco-2 cell monolayers. The role of the unstirred water layer (UWL) in dexamethasone’s absorption was studied, and a simplified mass-transport analysis was developed to describe the solubility-permeability interplay. The PAMPA permeability of dexamethasone was measured in the presence of various HPβCD levels, and the correlation with the theoretical predictions was evaluated. While the solubility of dexamethasone was greatly enhanced by the presence of HPβCD (K1∶1 = 2311 M−1), all experimental models showed that the drug’s permeability was significantly reduced following the cyclodextrin complexation. The UWL was found to have no impact on the absorption of dexamethasone. A mass transport analysis was employed to describe the solubility-permeability interplay. The model enabled excellent quantitative prediction of dexamethasone’s permeability as a function of the HPβCD level. This work demonstrates that when using cyclodextrins in solubility-enabling formulations, a tradeoff exists between solubility increase and permeability decrease that must not be overlooked. This tradeoff was found to be independent of the unstirred water layer. The transport model presented here can aid in striking the appropriate solubility-permeability balance in order to achieve optimal overall absorption.
PMCID: PMC3712970  PMID: 23874557
24.  Role of different biodegradable polymers on the permeability of ciprofloxacin 
Since permeability across biological membranes is a key factor in the absorption and distribution of drugs, drug permeation characteristics of three oral suspensions of ciprofloxacin were designed and compared. The three suspensions of ciprofloxacin were prepared by taking biodegradable polymers such as carbopol 934, carbopol 940, and hydroxypropyl methylcellulose (HPMC). The permeability study was performed by using a Franz diffusion cell through both synthetic cellulose acetate membrane and excised goat gastrointestinal membranes in acidic as well as alkaline pH. To know the permeability of drug from control/formulations through different membranes in acidic/alkaline pH, cumulative percentage drug permeation, apparent permeability (Papp), flux, and enhancement ratio (ER) were calculated. Considering Papp and flux values of all formulations, it is evident that formulation containing HPMC was the most beneficial for improving permeation and diffusivity of ciprofloxacin even after 16 h. Hence, this preparation may be considered as the most suitable formulation to obtain prolonged release action of the drug. The ER values of all formulations, through excised goat intestinal mucosal membrane in alkaline pH, were higher than those formulations through goat stomach mucosal membrane in acidic pH. Enhancement ratio values of those formulations indicate that the permeability of the drug was more enhanced by the polymers in the intestinal part, leading to more bioavailability and prolonged action in that portion of the gastrointestinal tract. It may also be concluded from our results that HPMC containing formulation was the best suspension, which may show effective controlled release action. Even carbopol containing formulations might also produce controlled release action.
PMCID: PMC4131405  PMID: 25126536
C934; C940; ciprofloxacin; hydroxypropyl methylcellulose; permeability
25.  A novel drug–phospholipid complex enriched with micelles: preparation and evaluation in vitro and in vivo 
Mixed micelles are widely used to increase solubility and bioavailability of poorly soluble drugs. One promising antitumor drug candidate is 20(S)-protopanaxadiol (PPD), although its clinical application is limited by low water solubility and poor bioavailability after oral administration. In this study, we developed mixed micelles consisting of PPD–phospholipid complexes and Labrasol® and evaluated their potential for oral PPD absorption. Micelles were prepared using a solvent-evaporation method, and their physicochemical properties, including particle size, zeta potential, morphology, crystal type, drug loading, drug entrapment efficiency, and solubility, were characterized. Furthermore, in vitro release was investigated using the dialysis method, and transport and bioavailability of the mixed micelles were investigated through a Caco-2 cell monolayer and in vivo absorption studies performed in rats. Compared with the solubility of free PPD (3 μg/mL), the solubility of PPD in the prepared mixed micelles was 192.41 ± 1.13 μg/mL in water at room temperature. The in vitro release profiles showed a significant difference between the more rapid release of free PPD and the slower and more sustained release of the mixed micelles. At the end of a 4-hour transport study using Caco-2 cells, the apical-to-basolateral apparent permeability coefficients (Papp) increased from (1.12 ± 0.21) × 106 cm/s to (1.78 ± 0.16) × 106 cm/s, while the basolateral-to-apical Papp decreased from (2.42 ± 0.16) × 106 cm/s to (2.12 ± 0.32) × 106. In this pharmacokinetic study, compared with the bioavailability of free PPD (area under the curve [AUC]0–∞), the bioavailability of PPD from the micelles (AUC0–∞) increased by approximately 216.36%. These results suggest that novel mixed micelles can significantly increase solubility, enhance absorption, and improve bioavailability. Thus, these prepared micelles might be potential carriers for oral PPD delivery in antitumor therapies.
PMCID: PMC3575161  PMID: 23431115
20(S)-protopanaxadiol; phospholipid complex; Labrasol; mixed micelles; Caco-2 cell monolayer; bioavailability

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