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Tissue inflammation is a major component of the acne process. Leukotriene B4 (LTB4) is considered to be a major player in the development of tissue inflammation. Synthesis of LTB4 is controlled by the enzyme 5-lipoxygenase. Since Zileuton blocks the activity of 5-lipoxygenase, experimental and clinical studies have been conducted to test mode of function, as well as efficacy and safety of this compound in the treatment of acne vulgaris. Human SZ95 sebocytes and inflammatory cells in vitro express the enzymes of the leukotriene pathway at mRNA and protein levels and enzymes involved in the biosynthesis of LTB4 are activated in sebaceous glands of acne lesions. Pre-treatment of SZ95 sebocytes with Zileuton partially prevented short-term arachidonic acid-induced effects, such as induction of LTB4, increase of neutral lipid content and stimulation of interlekin-6 release. Long-term treatment with Zileuton directly reduced the content of neutral lipids and interleukin-6 release from SZ95 seb ocytes. PPAR mRNA levels were not regulated by Zileuton. In a first pilot clinical study with 10 patients with papulopustular acne Zileuton 4 × 600 mg/d p.o. for 3 months decreased the acne severity index in a time-dependent manner being 41% of the initial score at week 12 (p < 0.05). This was mostly due to a decrease of the number of inflammatory lesions of 29% (p < 0.01). In addition, total sebum lipids significantly decreased (35%, p < 0.05) and the pro-inflammatory free fatty acids (22%) and lipoperoxides (26%) were markedly diminished in patients’ sebum under treatment. The magnitude of clinical improvement strongly correlated with the reduction of total sebum lipids (p = 0.0009, r2 = 0.81) and free fatty acids (p = 0.0003, r2 = 0.82). In a further study, a 40-year-old female with mild disseminated sebaceous gland hyperplasia and seborrhea, responded with normalization of the casual skin surface lipids and similar reduction of facial sebum synthesis under treatment with Zileuton over 2weeks and—after a wash-out phase—low-dose isotretinoin (10 mg/2nd d) over 5 weeks. These data are in agreement with a phase II multicenter, clinical study in 101 patients with mild to moderate inflammatory facial acne conducted in the US, which showed a significant efficacy of Zileuton in a subset of patients with moderate acne, whereas those patients treated with Zileuton showed a significant mean decrease in inflammatory lesions compared to the placebo group. In all clinical studies, Zileuton was found to be safe and well tolerated.
Tissue inflammation is a major component in the process of the development of acne lesions.1–4 Patients with severe acne have been shown to benefit by a treatment with anti-inflammatory agents.5–9 On the other hand, enzymes involved in the biosynthesis of the proinflammatory lipids leukotriene (LT)-B4 and prostaglandin-E2 are activated in sebaceous glands of acne lesions.10
LTB4 is a 5-lipoxygenase (LOX)/LTA4 hydrolase product of arachidonic acid (AA) metabolism.11,12 AA induces LTB4 and interleukin (IL)-6 release and enhances lipid synthesis in cultured human sebocytes.5,13 Interestingly, LTB4 is also a natural ligand for peroxisome proliferator-activated receptor (PPAR)-α.14,15 PPARs, ligand-activated transcription factors belonging to the nuclear receptor superfamily, are activated by fatty-acid derivatives and can regulate lipid and lipoprotein metabolism, cell proliferation, differentiation and apoptosis of various cell types,16,17 including sebaceous gland cells.10,18 Especially, PPAR-α can modulate the inflammatory response in various cell types by inhibiting the expression of proinflammatory genes such as cytokines, metalloproteinases and acute-phase proteins.15,19
Since 5-LOX catalyzes LTB4 production, inhibition of 5-LOX provides an attractive target for downregulation of inflammatory processes in the sebaceous gland.20 Zileuton [(±)-1-(1-benzo[b] thien-2-ylethyl)-1-hydroxyurea], is an orally active and selective 5-LOX inhibitor been approved in the US for the treatment of asthma (Zyflo™).21 We have conducted experimental22 and clinical studies23,24 to test mode of function, as well as efficacy and safety of this compound in the treatment of acne vulgaris.
The maximum non-cytotoxic concentration evaluated for AA was 4 × 10−4 M at 24 h, whereas up to 5 × 10−5 M Zileuton was not cytotoxic at 24 h. Long-term treatment with AA (14 d) increased intracellular neutral (sebaceous) lipids in SZ95 sebocytes (19 ± 2%; p < 0.001), as previously described.13 Interruption of AA treatment (switch from 13 d AA treatment to 24 h no treatment) led to reduction of neutral lipids (minus 30 ± 1%; p < 0.001; Fig. 1A). Long-term treatment with Zileuton reduced neutral lipids in SZ95 sebocytes (minus 17 ± 2%; p < 0.001). In addition, pre-treatment with Zileuton prevented the AA-induced increase of neutral lipids in SZ95 sebocytes (minus 35 ± 3%; p < 0.001).
AA did not affect polar (cell membrane) lipids of SZ95 sebocytes. Long-term and short-term (24 h) treatment with Zileuton slightly reduced polar lipids (comparison of AA + Zileuton treatment with switch of Zileuton treatment to Zileuton + AA; minus 43 ± 2%; p < 0.001).
The long-term AA + Zileuton treatment increased polar lipids (19 ± 2%; p < 0.01), which are cell membrane lilpids and, therefore, indicate an increase of sebocyte number. The latter was confirmed by the cell number-associated FDA AFU increase (8 ± 2%; p < 0.01) (Fig. 1A). The concomitant increase of neutral lipids (36 ± 4%; p < 0.01) under this treatment is, thereafter, probably due to the increased cell number detected.
AA induced a marked LTB4 generation in SZ95 sebocytes both after long-term (14 d; 656 ± 35%; p < 0.001) and short-term (24 h; control→AA; 800 ± 120%; p < 0.001) treatment (Fig. 1B). Discontituation of AA treatment quickly attenuated LTB4 production (minus 94 ± 4%; p < 0.001). While long-term maintenance of SZ95 sebocytes in AA + Zileuton did not influence the marked LTB4 production as compared with AA alone, pre-treatment with Zileuton reduced the short-term AA-induced LTB4 generation (minus 34 ± 22%; p < 0.05).
Short-term but not long-term treatment with AA resulted in increased release of IL-6 by SZ95 sebocytes (41 ± 1%; p < 0.001), whereas interruption of AA treatment reduced quickly IL-6 cell release (24 h; switch of AA treatment to no treatment; minus 35 ± 2%; p < 0.001; Fig. 1C). Long-term treatment with Zileuton reduced IL-6 release from SZ95 sebocytes (minus 42 ± 1%; p < 0.001).
In contrast, AA, Zileuton and their combination did not affect IL-8 release by SZ95 sebocytes.
Zileuton did not affect the PPARα, PPARδ, PPARγ1 and PPARγ2 mRNA levels of SZ95 sebocytes treated with AAs.
A gradual and time-related reduction in inflammatory lesions and acne severity was shown under the treatment with Zileuton (Fig. 2). This was already significant by two weeks compared to baseline. The mean reduction in inflammatory lesions was 71% at 12 weeks (95% CI 54–89%; median reduction 75%; p = 0.007). Likewise, the acne severity index was suppressed at 12 weeks (mean suppression 59%, 95% CI 28–75%; median 63%; p = 0.01). There was a trend in reduction of non-inflammatory lesions (mean reduction 36%, 95% CI 6–66% at 12 weeks; median 14%; p = 0.076). Total sebum lipids were also significantly suppressed, showing a mean reduction of 65% at 12 weeks (95% CI 29–100%, median 47%; p = 0.038). Free fatty acids [mean reduction 78% (95% CI 65–90%), median 58%] and hydroperoxides [mean 74% (95% CI 53–95%), median 72%] in sebum were markedly, but not significantly decreased at week 12. LTB4 levels in blood were not affected by the treatment. The reduction of inflammatory lesions strongly correlated with the reduction of total sebum lipids (p = 0.0009, r2 = 0.81) and free fatty acids in sebum (p = 0.0003, r2 = 0.82).
In the patient with the disseminated sebaceous gland hyperplasia and seborrhea CSSL were normalized under treatment with Zileuton and NSS decreased (Fig. 3). Six weeks after discontinuation of treatment CSSL were found increased again and average NSS had returned to baseline. Subsequently, low-dose oral Isotretinoin 10 mg/2nd day was administered over five weeks leading to normalzation of NSSL and to decreased NSS after two and five weeks.
Immortalized human facial SZ95 sebocytes, been shown to conserve the major characteristics of normal sebocytes25 were cultured in Sebomed® medium with 10% heat-inactivated fetal calf serum, 5 ng/ml human recombinant epidermal growth factor, 1 mM CaCl2 and 50 µg/ml gentamicin at 37°C in a 5% CO2 atmosphere. After leaving the cells to attach for 24 h, the culture medium (and compounds to be tested) was replaced thrice, namely every 2nd day. Cells were subcultured once weekly.
A first panel of SZ95 sebocytes were treated for 14 d with AA (10−5 M), Zileuton (5 × 10−5 M) or AA (10−5 M) + Zileuton (5 × 10−5 M) dissolved in dimethyl sulfoxide (DMSO) with a final DMSO concentration of 0.2% in medium. Untreated cultures in medium supplemented with 0.2% DMSO served as controls. A second panel of identical SZ95 sebocyte cultures were washed twice with phosphate-buffered saline without Ca2+ and Mg2+ (PBS) after 13 d and were subsequently further treated with or without AA and/or Zileuton for 24 h.
For detection of cytotoxicity, SZ95 sebocytes were cultured for 24 h, washed with PBS and treated with AA (10−9 to 10−4 M) or zileuton (10−7 to 5 × 10−5 M). Lactate dehydrogenase (LDH) release was measured in supernatants at 4 and 24 h with a LDH assay kit.13
For cell quantification, SZ95 sebocytes were treated with the compounds mentioned above for 24 h and assessed by the fluorescein diacetate assay (FDA).25
The detection of intracellular lipids was performed in parallel wells with SZ95 sebocytes incubated with 100 µl of a 1 µg/ml nile red solution at 37°C for 20 min.25
For LTB4 detection, SZ95 sebocytes were treated with the compounds mentioned above for 24 h. The culture supernatants were assayed for LTB4 by a colorimetric enzyme immunoassay.22 IL (interleukin)-6 and IL-8 levels were determined in the same supernatants using ELISA kits.
PPAR mRNA levels were assessed by quantitative RT-PCR. SZ95 sebocytes were treated with the compounds mentioned above for 24 h. mRNA was extracted and reverse transcribed to cDNA. The following primers and probes were used: PPARα sense 5′-GTA GCG TAT GGA AAT GGG TTT ATA ACT-3′, antisense 5′-CCT TAG GCT TTT TAG GAA TTC ACG A-3′; PPARδ sense 5′-ACC AGG TGA CCC TCC TCA AGT A-3′, antisense 5′-GCA TGG CAA AGA TGG CCT-3′; PPARγ1 sense 5′-TCG AGG ACA CCG GAG AGG-3′, antisense 5′-TTG TAT ATT GGT GGT TTA GTG TCG G-3′; PPARγ2 sense 5′-GTG TGA ATT ACA GCA AAC CCC TAT T-3′, antisense 5′-TCC CAG AGT TTC ACC CAT AAC A-3′. Primers for the L27 ribosomal protein gene and probe serving as internal control were added in the thermal cycling procedure as reference controls.
An open-label drug, ethic committee-approved, industry-independent study in a small cohort of 10 consecutive patients (4 female, 6 male; median age 17 years) moderate inflammatory acne was conducted to evaluate efficacy and safety of Zileuton (4 × 600 mg/d p.o. over 3 months).23 All patients provided written consent, had been off all topical and oral acne therapy for at least 1 month, and none had received oral isotretinoin or anabolic steroids. The use of cleansers and personal care products were prohibited during the study. Patients who had atypical disease such as Gram-negative folliculitis were not included, nor were patients with any other disease, pregnant or breast feeding females, any patients taking any other medications or females using any form of hormonal contraception.
The acne was assessed by counting inflammatory lesions, being the primary outcome measure, and non-inflammatory lesions on the entire face and upper chest and back. Acne severity was determined by the method of Allen and Smith.26 Patients were photographed before and at the end of treatment. To obtain sebum samples patients were always invited at 4 p.m., a defined central area of the forehead was wiped twice with ethanol and sebum samples (500 µl) were obtained one hour later, were suspended in 600 µl Ch3Cl/CH3OH 2:1 and were split into aliquots. Total lipids and free fatty acids in sebum were measured by gas chromatography-mass spectrometry, hydroperoxides in sebum by a photometrical method based on the use of N,N-diethyl-1,4-phenylene-diamine after comparison to the reaction of the reference standard compound cumene hydroperoxide, and LTB4 in blood by a commercial LTB4 enzyme immunoassay system. Clinical assessments performed at the same time of the day were made at baseline, 2, 4, 8 and 12 weeks. Laboratory assessments were made at baseline and 12 weeks. Although the study was not double-blind the assessor did not have access to the previous or other visit data until the study was completed.
In another case study, a 40-year-old female with histologically confirmed, mild, disseminated sebaceous gland hyperplasia and seborrhea on face, scalp and neck since puberty was treated with Zileuton (4 × 600 mg/d o.o. over 3 weeks) after receiving written consent.24 Casual skin surface lipids (CSSL) of the central forehead were measured at 4 p.m. using a computerized photometric devise. To determine new sebum synthesis (NSS), defined areas of the central forehead and the left temple were wiped twice with ethanol after measuring CSSL. NSS was detected 1 h later using the device as described above.
The involvement of products of the LT pathway in inflammatory skin diseases is well established.12 5-LOX and the other enzymes which are involved in the LT pathway form a family of lipid peroxidation enzymes and generate lipid mediators.10 On the other hand, LT are leukocyte chemotactic mediators with LTB4 being the most potent among them.4 It increases neutrophil adherence, as well as lysosomal release and generation of superoxide radicals. In addition, it activates complement and induces interleukin production by neutrophils. Intradermal injection of LTB4 provokes the local attraction of neutrophils and monocytes.
There is increasing evidence that acne is a genuine inflammatory disorder.1–4 Since 5-LOX catalyzes the first step in AA metabolism towards LTB4, we have considered the application of 5-LOX inhibitors as a definitive step for modulation of LT effects in acne patients. Our pilot clinical study with systemic administration of Zileuton in 10 patients with inflammatory acne has detected anti-inflammatory and lipid reducing effects of the compound.23 Searching for the primary effect, we have observed that Zileuton inhibited the synthesis of sebaceous lipids in a patient with no inflammatory signs.24 Inhibition of lipid synthesis, especially of pro-inflammatory lipids, is likely to be the major effect of Zileuton on sebaceous glands followed by reduction of inflammatory lesions in acne.23 The direct effect of Zileuton on the synthesis of sebaceous lipids was confirmed in the in vitro study. This effect was associated with the ability of Zileuton to reduce IL-6 release from SZ95 sebocytes. In addition, pre-treatment with Zileuton partially antagonised the short-term AA-induced induction of LTB4 release, increase of sebaceous lipids, and stimulation of IL-6 release. Zileuton ability to inhibit LTB4 formation in the present study is in agreement with published data on inflammatory cells.21 On the other hand, 5-LOX inhibitors may also down-regulate the inflammatory activity of locally involved lymphocytes and macrophages27 leading to the anti-inflammatory activity which is clinically observed.
Finally, a phase II multicenter, clinical study in 101 patients with mild to moderate inflammatory facial acne conducted in the US showed a significant efficacy of Zileuton in a subset of patients with moderate acne (baseline inflammatory lesions ≥30), whereas those patients treated with Zileuton (n = 26) showed a mean decrease in inflammatory lesions of 41.6% compared to 26.2% in the placebo group (p = 0.025).28
In all clinical studies, Zileuton was found to be safe and well tolerated.
In summary, Zileuton directly inhibits lipogenesis in human sebocytes and prevents the activation of the leukotriene pathway by AA. Zileuton inhibited sebum synthesis to a similar level with that of low-dose Isotretinoin.24 This is probably the most intriguing aspect of our work and may seem difficult to explain. However, an effect on PPARs can be implicated.28 LTB4 is a natural ligand for PPAR-α. The latter is shown to regulate lipid and lipoprotein metabolism, inflammatory response, cell proliferation, differentiation and apoptosis of various cell types, including sebaceous gland cells,29 providing a comprehensive link towards the introduction of Zileuton in the treatment of sebaceous gland diseases, and especially of acne.
I thank my co-workers and scientific collaborators at this project Y.D. Adler, T. Alestas, A. Boschnakow, E. Camera, W.J. Cunliffe, S. Nestoris, C.E. Orfanos, M. Orth, M. Picardo, A. Saborowski, and H. Seltmann. I also thank the group of Prof. W. Wahli (Center for Integrative Genomics, Lausanne, Switzerland) for the quantification of PPAR mRNA in the sebocyte samples. We are grateful to Dr. S. Pattabhiraman and Dr. A. Hossini for friendly advice and support.
Previously published online as a Dermato-Endocrinology E-publication: http://www.landesbioscience.com/journals/dermatoendocrinology/article/8368