Although there is no HbA1c threshold for cardiovascular risk, the American Diabetic Association-recommended goal of HbA1c < 7.0% appears to be unacceptably high. To achieve an optimal HbA1c level goal of 6.0% or less, a high dosage of sulfonylureas and insulin would be required; the trade-off would be the common adverse effects of hypoglycemia and weight gain. In contrast, hypoglycemia is uncommon with insulin sensitizers and GLP-1 analogs, allowing the physician to titrate these drugs to maximum dosage to reduce HbA1c levels below 6.0% and they have been shown to preserve β-cell function. Lastly, weight gain is common with sulfonylurea and insulin therapy, whereas GLP-1 analogs induce weight loss and offset the weight gain associated with TZDs. A treatment paradigm shift is recommended in which combination therapy is initiated with diet/exercise, metformin (which has antiatherogenic effects and improves hepatic insulin sensitivity), a TZD (which improves insulin sensitivity and preserves β-cell function with proven durability), and a GLP-1 analog (which improves β, α-cell function and promotes weight loss) or a dipeptidyl peptidase IV inhibitor in patients with type 2 diabetes mellitus.
Diabetes mellitus; Glucagon-like peptide 1; Metformin; Thiazolidinediones
AIM: To assess the efficacy and safety of vildagliptin/pioglitazone combination therapy in Korean patients with type 2 diabetes mellitus (T2DM).
METHODS: This was a post hoc analysis in Korean patients, from a 24-wk, randomized, active-controlled, double-blind, parallel-group, multicenter study. Eligible patients were aged between 18 and 80 years, drug naive, and had been diagnosed with T2DM [hemoglobin A1c (HbA1c): 7.5%-11.0% and fasting plasma glucose (FPG): < 270 mg/dL (< 15 mmol/L)]. Patients were randomized (1:1:1:1) to receive the vildagliptin/pioglitazone combination at 100/30 mg q.d. (high-dose) or 50/15 mg q.d. (low-dose), vildagliptin 100 mg q.d., or pioglitazone 30 mg q.d. monotherapies. The primary outcome measure was change in HbA1c from baseline to endpoint.
RESULTS: The distribution of baseline demographic and clinical parameters was well balanced between treatment groups. The overall mean age, body mass index, HbA1c, FPG, and duration of disease were 50.8 years, 24.6 kg/m2, 8.6%, 10.1 mmol/L, and 2.2 years, respectively. Adjusted mean changes (± standard error) in HbA1c from baseline (~8.7%) to week 24 endpoint were -2.03% ± 0.16% (high-dose, N = 34), -1.88% ± 0.15% (low-dose, N = 34), -1.31% ± 0.21% (vildagliptin, N = 36), and -1.52% ± 0.16% (pioglitazone, N = 36). The high-dose combination therapy demonstrated greater efficacy than monotherapies [vildagliptin (P = 0.029) and pioglitazone (P = 0.027)]. Percentage of patients achieving HbA1c < 7% and ≤ 6.5% was the highest in the high-dose group (76% and 68%) followed by low-dose (58% and 47%), vildagliptin (59% and 37%), and pioglitazone (53% and 28%) groups. The overall incidence of adverse events was comparable.
CONCLUSION: In Korean patients, first-line treatment with high-dose combination therapy improved glycemic control compared to pioglitazone and vildagliptin monotherapies, consistent with results published for the overall study population.
Type 2 diabetes mellitus; Vildagliptin; Pioglitazone
Several studies have suggested a cancer risk reduction in statin users although the evidence remains weak for stomach cancer. The purpose of this study was to use an exact-matching case–control design to examine the risk of gastric cancer associated with the use of statins in a cohort of patients with diabetes.
Cases were defined as patients with incident gastric cancer identified by International Classification of Diseases 16.0 ~ 16.9 recorded at Samsung Medical Center database during the period of 1999 to 2008, at least 6 months after the entry date of diabetes code. Each gastric cancer case patient was matched with one control patient from the diabetes patient registry in a 1:1 fashion, blinded to patient outcomes.
A total of 983 cases with gastric cancer and 983 controls without gastric cancer, matched by age and sex, were included in the analysis. The presence of prescription for any statin was inversely associated with gastric cancer risk in the unadjusted conditional logistic regression model (OR: 0.18; 95% CI: 0.14 – 0.24; P < .0001). Multivariate analysis using conditional logistic regression with Bonferroni’s correction against aspirin indicated a significant reduction in the risk of gastric cancer in diabetes patients with statin prescriptions (OR: 0.21; 95% CI: 0.16 – 0.28; P < .0001). After adjustment for aspirin use, a longer duration of statin use was associated with reduced risk of gastric cancer, with statistical significance (P<.0001).
A strong inverse association was found between the risk of gastric adenocarcinoma and statin use in diabetic patients.
Gastric cancer; Statins; Risk
To evaluate whether there is a difference in the association between nonalcoholic fatty liver disease (NAFLD) and incident diabetes based on the presence of impaired fasting glucose.
RESEARCH DESIGN AND METHODS
A total of 7,849 individuals (5,409 men and 2,440 women) without diabetes, who underwent comprehensive health check-ups annually for 5 years, were categorized into four groups by the presence of impaired fasting glucose and NAFLD at baseline. The association between NAFLD and incident diabetes was evaluated separately in groups with normal and impaired fasting glucose.
For 4 years, the incidence of diabetes in the NAFLD group was 9.9% compared with 3.7% in the non-NAFLD group, with multivariable-adjusted hazard ratio of 1.33 (95% CI 1.07–1.66). However, this higher risk for diabetes only existed in the impaired fasting glucose group.
Our study suggests that NAFLD has an independent and additive effect on the development of diabetes under conditions of impaired insulin secretion.
Diabetes self-management education and reinforcement are important for effective management of the disease. We investigated the effectiveness of interactive small-group education on glycemic, blood pressure, and lipid levels.
For this study, 207 type 2 diabetes patients with suboptimal glycemic control (HbA1c levels >6.5%) were enrolled. The conventional education group received an existing education program from April to November in 2006, and the interactive education group received a new small-group education program from December 2006 to July 2007. The two groups were comparatively analyzed for changes in blood sugar, glycated hemoglobin, lipid, and blood pressure at baseline, 3, 6, and 12 months and the proportion of patients achieving target goals at 12 months.
After 12 months of follow-up, HbA1c levels in the interactive education group were significantly lower than in the conventional education group (6.7% vs. 6.4%, P<0.001). Fasting and 2 hour postprandial glucose concentrations, total cholesterol, and low density lipoprotein cholesterol were significantly lower in the interactive education group than in the conventional education group. The proportion of patients that achieved target goals was significantly higher in the interactive education group.
The small-group educational method improved and re-established the existing group educational method. This finding suggests that the importance of education appears to be related to the method by which it is received rather than the education itself. Thus, the use of small-group educational methods to supplement existing educational methods established for diverse age levels should be considered in the future.
Achievement; Diabetes mellitus; Education
To investigate the clinical results of sitagliptin (SITA) and the characteristics of the treatment failure group or of low responders to SITA.
A retrospective study of type 2 diabetic patients reviewed 99 cases, including 12 treatment failure cases, who stopped SITA because of worsening patients' condition, and 87 cases, who continued treatment over five visits (total 9.9±10.1 months) after receiving the prescription of SITA from December 2008 to June 2009. Subjects were classified as five groups administered SITA as an initial combination with metformin (MET), add-on to metformin or sulfonylurea, and switching from sulfonylurea or thiazolidinedione. The changes in HbA1c level from the first to last visit (ΔHbA1c) in treatment maintenance group were subanalyzed.
The HbA1c level was significantly reduced in four groups, including initial coadministration of SITA with metformin (ΔHbA1c=-1.1%, P<0.001), add-on to MET (ΔHbA1c=-0.6%, P=0.017), add-on to sulfonylurea (ΔHbA1c=-0.5%, P<0.001), and switching from thiazolidinedione (ΔHbA1c=-0.3%, P=0.013). SITA was noninferior to sulfonlyurea (ΔHbA1c=-0.2%, P=0.63). There was no significant adverse effect. The treatment failure group had a longer diabeties duration (P=0.008), higher HbA1c (P=0.001) and fasting plasma glucose (P=0.003) compared to the maintenance group. Subanalysis on the tertiles of ΔHbA1c showed that low-response to SITA (tertile 1) was associated with a longer diabetes duration (P=0.009) and lower HbA1c (P<0.001).
SITA was effective and safe for use in Korean type 2 diabetic patients. However, its clinical responses and long-term benefit-harm profile is yet to be established.
Diabetes mellitus, type 2; Sitagliptin; Treatment outcome
We performed a retrospective longitudinal study on the effects of changes in weight, body composition, and homeostasis model assessment (HOMA) indices on glycemic progression in subjects without diabetes during a four-year follow-up period in a community cohort without intentional intervention.
From 28,440 non-diabetic subjects who participated in a medical check-up program in 2004, data on anthropometric and metabolic parameters were obtained after four years in 2008. Body composition analyses were performed with a bioelectrical impedance analyzer. Skeletal muscle index (SMI, %) was calculated with lean mass/weight×100. Subjects were divided into three groups according to weight change status in four years: weight loss (≤-5.0%), stable weight (-5.0 to 5.0%), weight gain (≥5.0%). Progressors were defined as the subjects who progressed to impaired fasting glucose or diabetes.
Progressors showed worse baseline metabolic profiles compared with non-progressors. In logistic regression analyses, the increase in changes of HOMA-insulin resistance (HOMA-IR) in four years presented higher odds ratios for glycemic progression compared with other changes during that period. Among the components of body composition, a change in waist-hip ratio was the strongest predictor, and SMI change in four years was a significant negative predictor for glycemic progression. Changes in HOMA β-cell function in four years was a negative predictor for glycemic progression.
Increased interval changes in HOMA-IR, weight gain and waist-hip ratio was associated with glycemic progression during a four-year period without intentional intervention in non-diabetic Korean subjects.
Glycemic progression; Prediabetes; Skeletal muscle index; Visceral obesity; Weight change
Acute postprandial hyperglycemia is an important affector for atherosclerosis in subjects with glucose intolerance. We analyzed the relationship of brachial-ankle pulse wave velocity (baPWV) with fasting and post-challenge plasma glucose levels according to different time points during oral glucose tolerance test (OGTT).
In 663 subjects with fasting hyperglycemia, 75 g OGTT were performed to confirm the glucose tolerant status, and fasting, post-challenge 30-minute and 120-minute glucose levels were measured. Anthropometric measurements were done, and fasting lipid profiles were measured. baPWV were measured in all subjects and the relationship between fasting, 30- and 120-minute post-challenge glucose levels and baPWV were analyzed.
Among the participants, 62.9% were prediabetes and 31.7% were diabetes. Mean baPWV value was significantly higher in subjects with diabetes compared with prediabetes group. In bivariate correlation analyses, age, blood pressure, total cholesterol, low density lipoprotein cholesterol, 30-minute and 120-minute post-challenge glucose levels showed significant positive correlation with baPWV value. In multiple regression analysis, 30-minute post-challenge glucose level was a weak but significant determinant for mean baPWV value even after adjustment for other confounding variables.
Postprandial hyperglycemia, especially 30-minute glucose levels showed significant correlation with baPWV in subjects with fasting hyperglycemia. These results can imply the deleterious effect of acute hyperglycemic excursion on arterial stiffness in subjects with glucose intolerance.
Arterial stiffness; Oral glucose tolerance test; Postprandial hyperglycemia; Pulse wave analysis
Community-associated methicillin resistant Staphylococcus aureus (CA-MRSA) infections are increasing. Although gentamicin (GEN) is usually susceptible against CA-MRSA, GEN is rarely considered for treatment as monotherapy. We employed an in vitro pharmacodynamic model (IVPDM) to compare efficacies of GEN against CA-MRSA with two dosing regimens [thrice-daily (TD), once-daily (OD)].
Materials and Methods
Using two strains of CA-MRSA, we adopted IVPDM comprised of two-compartments with a surface-to-volume ratio of 5.34 cm-1. GEN regimens were simulated with human pharmacokinetic data of TD and OD. Experiments were performed over 48 hours in triplicate for each strain and dosing regimen.
MICs of GEN for YSSA1 and YSSA15 were 1 and 2 mg/L, respectively. In OD, indices of peak/MIC were > 8.6 at least, in contrast to < 6.4 in TD. A ≥ 3-log10 reduction in CFU/mL was demonstrated prior to 4 hours in TD and OD, and continued until 8 hours for both strains. However, reductions in the colony counts at 24 and 48 hours were significantly larger for OD compared to TD in both strains (p < 0.001). During TD, resistance developed in YSSA1 and small colony variants (SCVs) were documented in YSSA15. No resistance or SCVs were observed during OD in both strains.
TD and OD showed the same killing slopes until 8 hours. After the 24 hours of experiments, OD of GEN would be advantageous not only in having more reductions in colony counts, but also suppressing the development of resistance or SCVs for 48 hours.
Methicillin-Resistant Staphylococcus aureus; gentamicin; pharmacodynamics; once-daily treatment
We investigated the relationships of adiponectin/leptin (A/L) ratio with cardiovascular risk factors, insulin resistance index, and metabolic syndrome (MS) in apparently healthy Korean male adults.
Sixty-eight male subjects were enrolled among the participants of an annual health check-up program (mean age, 55.1 years). Percent body fat (%) was measured using a bioelectric impedance analyzer. Serum leptin level was measured via radioimmunoassay, and adiponectin level was measured using an enzyme-linked immunosorbent assay. Homeostasis model assessment (HOMA)-insulin resistance (IR) index was calculated, and the presence of metabolic syndrome was assessed.
Adiponectin, leptin, and A/L ratio showed significant correlations with percent body fat, lipid profile, and HOMA-IR. Mean leptin and HOMA-IR levels were significantly higher, while A/L ratio was significantly lower in subjects with MS. With increasing number of MS components, the mean values of leptin and HOMA-IR increased and the A/L ratio decreased. In multiple regression analysis, HOMA-IR was significantly correlated with triglyceride, fasting glucose, and A/L ratio, while A/L ratio was significantly correlated with body mass index and HOMA-IR. HOMA-IR and A/L ratio were significant predictors for each other after adjustment for other factors.
A/L ratio correlated well with lipid profile, HOMA-IR, and the presence and number of MS components in Korean male subjects.
Adiponectin/leptin ratio; Insulin resistance; Metabolic syndrome
The aflatoxin B1 degrading abilities of two different ruminants were compared in this study. One set of experiments evaluated the aflatoxin B1 degradation ability of different rumen fluid donors (steers vs. goats) as well as the rumen fluid filtration method (cheese cloth filtered vs. 0.45 µm Millipore) in a 2 × 2 factorial arrangement. Additional studies examined aflatoxin B1 degradation by collecting rumen fluid at different times (0, 3, 6, 9 and 12 h) after feeding. Cannulated Holstein steers (740 ± 10 kg bw) and Korean native goats (26 ± 3 kg bw) were fed a 60% timothy and 40% commercial diet with free access to water. Rumen fluid from Korean native goats demonstrated higher (p < 0.01) aflatoxin B1 degradability than Holstein steers. However, filtration method had no significant influence on degradability. In addition, aflatoxin degradation did not depend upon rumen fluid collection time after feeding, as no significant differences were observed. Finally, a comparison of two types of diet high in roughage found aflatoxin degradability in goats was higher with timothy hay opposed to rice straw, although individual variation existed. Thus, our findings showed the aflatoxin degradability is comparatively higher in goats compared to steers.
aflatoxin B1; degradation; ELISA; rumen
Studies on the molecular epidemiologic characteristics of methicillin-resistant Staphylococcus aureus (MRSA) strains have demonstrated their genetic and geographical diversity. In addition, it has been reported that there are genetic differences between community-associated (CA) and health care-associated (HA) MRSA strains. Therefore, we investigated the major epidemiologic characteristics of CA MRSA isolates in South Korea and compared them with those of HA MRSA strains. Distributions of staphylococcal chromosome cassette mec (SCCmec) types and other molecular features, including the Panton-Valentine leukocidin (PVL) gene, were studied in 138 invasive MRSA isolates. Multiplex type IVA SCCmec was identified as the major CA MRSA infection type (53.1%), with a significantly higher prevalence than in HA MRSA (P < 0.001). One major group of type IVA strains carried a larger atypical class B mec element and new subtypes of ccrA2 (96% amino acid homology). The PVL gene was detected in one USA300-like isolate only. Seven major clone types determined by combinational grouping (genetic background SCCmec typing) showed representative patterns of antimicrobial susceptibilities. We concluded that less multi-drug-resistant strains of clone types B-I and D-1 (genetic background, B and D complexes; type IVA SCCmec) predominate in CA MRSA and that international PVL-positive strains have not spread in South Korea as yet.
It has been suggested that the haplotypic relationship between microsatellite markers and single nucleotide polymorphisms (SNPs) is of considerable importance, as microsatellite markers can potentially be incorporated into haplotypes containing SNPs to increase marker density across a region of interest. However, SNPs and microsatellite markers have different mutation rates and durations, and it is conceivable that the linkage disequilibrium (LD) patterns between the genetic markers may considerably differ. We assessed the LD patterns using 1,661 SNPs and 65 microsatellite markers along chromosome 22 and investigated whether common patterns of LD between the two genetic markers are deduced from the results. The results demonstrated that the patterns of LD among microsatellite markers varied considerably and the LD runs of SNPs and microsatellite markers showed distinct patterns. Microsatellite markers have a much higher mutation rate and the evolution of microsatellite markers is a more complex process which has distinct mutation properties from those of SNPs. We consider that these might contribute to the different LD patterns between the two genetic markers. Therefore, it would seem inadvisable to make assumptions about persistence of LD across even a relatively small genetic distance among microsatellite markers and to construct mixed marker haplotypes/LD maps employing microsatellite markers.
Single Nucleotide Polymorphisms; Microsatellite Markers; Linkage Disequilibrium
To validate the prevalence rate of symptoms of asthma produced by the phase I ISAAC (International Study of Asthma and Allergies in Childhood) study, hypertonic saline challenge test was carried out during the phase II study at a year after the phase I study. For the phase II study, six middle schools from three cities in the phase I study were selected. Finally, 499 children who responded to both studies were analyzed. All subjects were asked to complete the written questionnaire (WQ) first, followed by a video questionnaire (AVQ 3.0) during the phase I study. Of the 499 children, only 19 (3.8%) were positive to the hypertonic saline bronchial challenge test. The degree of agreement between responses to the two corresponding questions "wheezing at rest" and "nocturnal wheeze" in the AVQ 3.0 and WQ were moderate and weak with a Kappa indices of 0.45 and 0.23, respectively. The question on "severe wheeze" in the AVQ 3.0 had the highest Youden's index among the five questions related to asthma symptoms in the previous 12 months, but its specificity was low whereas its sensitivity was 1.0. There was no consistency of priority between the two questionnaires in predicting bronchial hyperreactivity in a group of Korean schoolchildren. Therefore we need to develop more appropriate WQ or AVQ to compare the prevalences of asthma to other countries.
Loss of bone mass is usually detected after bone marrow transplantation (BMT) during the early post-transplant period. However, little is known about the long-term effects of BMT on bone metabolism. We have prospectively investigated 11 patients undergoing BMT. Bone mineral density (BMD) was measured before BMT, and 1, 2, and 3 yr after BMT. Serum markers of bone turnover were serially measured before BMT and 1, 2, 3, 4, and 12 weeks, 6 months, and 1 yr after BMT. The mean change in the lumbar spine (L2-4) BMD, calculated as the percent change from the baseline to the level at 1, 2, and 3 yr was -4.7% (NS), -1.1% (NS), and +6.4% (p<0.05), respectively. The mean change in the total proximal femur BMD from the baseline to the level at 1, 2, and 3 yr was -8.5% (p<0.01), -8.7% (p<0.05) and -5.6% (p<0.05), respectively. In summary, there was little decline in lumbar BMD at 1 yr following BMT and gradual recovery until 3 yr. In contrast, femoral BMD decreased much more than the lumbar area at 1 yr and did not recover until 3 yr. The mechanism of skeletal site-selective differences in the changes of BMD needs to be elucidated.
It is generally agreed that euthyroid sick syndromes (ESS) are associated with an increased production of cytokines. However, there has been scarce data on the relationship thyroid hormone changes and cytokines among the patients undergoing bone marrow transplantation (BMT). Because interleukin-8 (IL-8) has been identified as a potent proinflammatory and interleukin-10 (IL-10) as an antiinflammatory cytokine, we studied the relation between thyroid hormone parameters and these cytokines following BMT. We studied 80 patients undergoing allogeneic BMT. Serum T3 decreased to nadir at post-BMT 3 weeks. Serum T4 was the lowest at the post-BMT 3 months. Serum TSH sharply decreased to nadir at 1 week and gradually recovered. Serum free T4 significantly increased during 3 weeks and then returned to basal level. Mean levels of serum IL-8 significantly increased at 1 week after BMT. Mean levels of serum IL-10 significantly increased until 4 weeks after BMT. No significant correlation was found between serum thyroid hormone parameters and cytokines (IL-8, IL-10) after adjusting steroid doses during the entire study period. In conclusion, ESS developed frequently following allogeneic BMT and cytokine levels were increased in post-BMT patients. However, no significant correlation was found between serum thyroid hormone parameters and these cytokines.
Double high-dose chemotherapy (HDCT) was applied to 18 patients with highrisk neuroblastoma including 14 patients who could not achieve complete response (CR) even after the first HDCT. In 12 patients, successive double HDCT was rescued with peripheral blood stem cells collected during a single round of leukaphereses and in 6 patients, second or more rounds of leukaphereses were necessary after the first HDCT to rescue the second HDCT. The median interval between the first and second HDCT (76 days; range, 47-112) in the single harvest group was shorter than that (274.5 days; range, 83-329) in the double harvest group (p<0.01). Hematologic recovery was slow in the second HDCT. Six (33.3%) treatment-related mortalities (TRM) occurred during the second HDCT but were not related to the shorter interval. Disease-free survival rates at 2 years with a median follow-up of 24 months (range, 6-46) in the single and double harvest group were 57.1% and 33.3%, respectively. These results suggest that successive double HDCT using the single harvest approach may improve the survival of high-risk patients, especially who could not achieve CR after the first HDCT despite delayed hematologic recovery and high rate of TRM during the second HDCT.
We evaluated the association of regular physical exercise with the presence of non-alcoholic fatty liver disease (NAFLD) and liver enzymes in relation to obesity and insulin resistance.
A cross-sectional analysis was conducted in 72,359 healthy Korean adults without diabetes who participated in a comprehensive health check-up. Subjects who have been exercising regularly (more than 3 times per week, at least for 30 minutes each time and for consecutive 3 month) were categorized into exercise group. All subjects were categorized into deciles based on their body mass index (BMI) and we estimated the odds ratios (ORs) for having NAFLD according to exercise regularity in each decile. The diagnosis of NAFLD was based on ultrasonography findings. Individuals with NAFLD (n = 19,921) were analyzed separately to evaluate ORs for having elevated liver enzymes based on regularity of exercise. The risk for NAFLD was significantly reduced in exercise group with age- and sex-adjusted ORs of 0.53–0.72 for all BMI deciles except at BMI categories of <19.6 and 20.7–21.6 kg/m2. While no difference was seen in BMI between subjects in exercise and non-exercise group across the BMI deciles, the values of body fat percentage and metabolic risk factors differed. Among NAFLD patients, subjects in exercise group had a lower risk for having elevated liver enzymes with multivariable adjusted OR of 0.85 (95% CI 0.74–0.99, for AST) and 0.74 (95% CI 0.67–0.81, for ALT) than did subjects in non-exercise group.
Regular exercise was associated with a reduced risk for having NAFLD and decreased liver enzymes in patients with NAFLD, and this relationship was also independent of obesity.
The effects of exendin-4 on Sirt1 expression as a mechanism of reducing fatty liver have not been previously reported. Therefore, we investigated whether the beneficial effects of exendin-4 treatment on fatty liver are mediated via Sirt1 in high-fat (HF) diet-induced obese C57BL/6J mice and related cell culture models. Exendin-4 treatment decreased body weight, serum free fatty acid (FA), and triglyceride levels in HF-induced obese C57BL/6J mice. Histological analysis showed that exendin-4 reversed HF-induced hepatic accumulation of lipids and inflammation. Exendin-4 treatment increased mRNA and protein expression of Sirt1 and its downstream factor, AMPK, in vivo and also induced genes associated with FA oxidation and glucose metabolism. In addition, a significant increase in the hepatic expression of Lkb1 and Nampt mRNA was observed in exendin-4-treated groups. We also observed increased expression of phospho-Foxo1 and GLUT2, which are involved in hepatic glucose metabolism. In HepG2 and Huh7 cells, mRNA and protein expressions of GLP-1R were increased by exendin-4 treatment in a dose-dependent manner. Exendin-4 enhanced protein expression of Sirt1 and phospho-AMPKα in HepG2 cells treated with 0.4 mM palmitic acid. We also found that Sirt1 was an upstream regulator of AMPK in hepatocytes. A novel finding of this study was the observation that expression of GLP-1R is proportional to exendin-4 concentration and exendin-4 could attenuate fatty liver through activation of Sirt1.
Sirt6 has been implicated in the regulation of hepatic lipid metabolism and the development of hepatic steatosis. The aim of this study was to address the potential role of Sirt6 in the protective effects of rosiglitazone (RGZ) on hepatic steatosis.
To investigate the effect of RGZ on hepatic steatosis, rats were treated with RGZ (4 mg·kg−1·day−1) by stomach gavage for 6 weeks. The involvement of Sirt6 in the RGZ's regulation was evaluated by Sirt6 knockdown in AML12 mouse hepatocytes.
RGZ treatment ameliorated hepatic lipid accumulation and increased expression of Sirt6, peroxisome proliferator-activated receptor gamma coactivtor-1-α (Ppargc1a/PGC1-α) and Forkhead box O1 (Foxo1) in rat livers. AMP-activated protein kinase (AMPK) phosphorylation was also increased by RGZ, accompanied by alterations in phosphorylation of LKB1. Interestingly, in free fatty acid-treated cells, Sirt6 knockdown increased hepatocyte lipid accumulation measured as increased triglyceride contents (p = 0.035), suggesting that Sirt6 may be beneficial in reducing hepatic fat accumulation. In addition, Sirt6 knockdown abolished the effects of RGZ on hepatocyte fat accumulation, mRNA and protein expression of Ppargc1a/PGC1-α and Foxo1, and phosphorylation levels of LKB1 and AMPK, suggesting that Sirt6 is involved in RGZ-mediated metabolic effects.
Our results demonstrate that RGZ significantly decreased hepatic lipid accumulation, and that this process appeared to be mediated by the activation of the Sirt6-AMPK pathway. We propose Sirt6 as a possible therapeutic target for hepatic steatosis.