Dipeptidyl Peptidase IV Inhibitor Improves Insulin Resistance and Steatosis in a Refractory Nonalcoholic Fatty Liver Disease Patient: A Case Report

Prolonged effects of DPP-4 inhibitors on steato-hepatitic changes in Sprague-Dawley rats fed a high-cholesterol diet

OBJECTIVE

Sitagliptin and other dipeptidyl peptidase (DPP)-4 inhibitors/gliptins are antidiabetic drugs known to improve lipid profile, and confer anti-inflammatory and anti-fibrotic effects, which are independent of their hypoglycemic effects. However, in our previous short-term (35 days) studies, we showed that sitagliptin accentuates the hepato-inflammatory effects of high dietary cholesterol (Cho) in male Sprague-Dawley rats. Since most type 2 diabetics also present with lipid abnormalities and use DPP-4 inhibitors for glucose management, the present study was conducted to assess the impact of sitagliptin during long-term (98 days) feeding of a high Cho diet. An additional component of the present investigation was the inclusion of other gliptins to determine if hepatic steatosis, necro-inflammation, and fibrosis were specific to sitagliptin or are class effects.

METHODS

Adult male Sprague-Dawley rats were fed control or high Cho (2.0%) diets, and gavaged daily (from day 30 through 98) with vehicle or DPP-4 inhibitors (sitagliptin or alogliptin or saxagliptin). On day 99 after a 4 h fast, rats were euthanized. Blood and liver samples were collected to measure lipids and cytokines, and for histopathological evaluation, determination of hepatic lesions (steatosis, necrosis, inflammation, and fibrosis) using specific staining and immunohistochemical methods.

RESULTS

Compared to controls, the high Cho diet produced a robust increase in NASH like phenotype that included increased expression of hepatic (Tnfa, Il1b, and Mcp1) and circulatory (TNFα and IL-1β) markers of inflammation, steatosis, necrosis, fibrosis, and mononuclear cell infiltration. These mononuclear cells were identified as macrophages and T cells, and their recruitment in the liver was facilitated by marked increases in endothelium-expressed cell adhesion molecules. Importantly, treatment with DPP-4 inhibitors (3 tested) neither alleviated the pathologic responses induced by high Cho diet nor improved lipid profile.

CONCLUSIONS

The potential lipid lowering effects of DPP-4 inhibitors were diminished by high Cho (a significant risk factor for inducing liver damage). The robust inflammatory responses induced by high Cho feeding in long-term experiment were not exacerbated by DPP-4 inhibitors and a consistent hepatic inflammatory environment persisted, implying a prospective physiological adaptation.

Efficacy of Sitagliptin on Nonalcoholic Fatty Liver Disease in High-fat-diet-fed Diabetic Mice

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) is a common cause of clinical liver dysfunction and an important prepathological change of liver cirrhosis. Central obesity, type 2 diabetes mellitus, dyslipidemia, and metabolic syndrome are the major risk factors for NAFLD. Sitagliptin (Sig) is a novel hypoglycemic agent that improves blood glucose levels by increasing the level of active incretin. Sig has been shown to prevent the development of fatty livers in mice on a fructose-rich diet. The purpose of this study was to observe the efficacy of Sig on NAFLD in type 2 diabetic mice.

METHODS

The diet-induced obesity mouse model was established, and the diabetic mice were screened by an intraperitoneal glucose tolerance trial. The mice were randomly divided into four groups for 8 weeks of intervention: high-fat diet (HFD) group, Sig group, metformin (Met) group, and Sig+Met group. After the intervention, the liver function indexes as well as the blood glucose and blood lipid levels of the mice were measured. In addition, the wet weight of the liver was measured; the pathological sections of the liver tissues were stained to observe the hepatocyte fatty degeneration, inflammation, necrosis, and fibrosis; and the hepatic histological injury was recorded as the NAFLD activity score (NAS).

RESULTS

Compared with the normal control group, the body weight, liver weight, blood glucose level, insulin resistance (IR), blood lipid level, and transaminase level of the mice in the HFD group were significantly increased, showing typical metabolic syndrome. After treatment with Sig and/or Met, the mice gained less weight, had lower levels of blood glucose, triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), and transaminase, and had improved IR compared with the HFD group. The liver pathological NASs in the Sig group (P=0.01), Met group (P=0.028), and Sig+Met group (P<0.001) were lower than those in the HFD group (P<0.05), suggesting that the use of the two drugs alone or in combination can improve the state of liver inflammation. In terms of fibrosis, there was no fibrosis in the control group but there was significant fibrosis in the HFD group (P<0.001). There was no significant difference between the drug intervention groups and the HFD group, indicating that the drug therapy (Sig and/or Met) did not significantly improve the pre-existing fibrosis.

CONCLUSION

Our experiment proved that Sig can improve NAFLD, including improvement of the serum transaminase level, hepatic pathological inflammation level, and hepatocyte adiposis, suggesting that Sig may play a role by improving glucose and lipid metabolism, reducing the body weight and liver weight, improving insulin sensitivity, and inhibiting fatty liver inflammation. Sig may be a new direction for the treatment of patients with a nonalcoholic fatty liver and diabetes, delaying the progression of NAFLD.

Potential Effect of DPP-4 Inhibitors Towards Hepatic Diseases and Associated Glucose Intolerance

Dipeptidyl-peptidase-4 (DPP-4) is an enzyme having various properties and physiological roles in lipid accumulation, resistance to anticancer agents, and immune stimulation. DPP-4 includes membrane-bound peptidases and is a kind of enzyme that cleaves alanine or proline-containing peptides such as incretins, chemokines, and appetite-suppressing hormones (neuropeptide) at their N-terminal dipeptides. DPP-4 plays a role in the final breakdown of peptides produced by other endo and exo-peptidases from nutritious proteins and their absorption in these tissues. DPP-4 enzyme activity has different modes of action on glucose metabolism, hunger regulation, gastrointestinal motility, immune system function, inflammation, and pain regulation. According to the literature survey, as DPP-4 levels increase in individuals with liver conditions, up-regulation of hepatic DPP-4 expression is likely to be the cause of glucose intolerance or insulin resistance. This review majorly focuses on the cleavage of alanine or proline-containing peptides such as incretins by the DPP-4 and its resulting conditions like glucose intolerance and cause of DPP-4 level elevation due to some liver conditions. Thus, we have discussed the various effects of DPP-4 on the liver diseases like hepatitis C, non-alcoholic fatty liver, hepatic regeneration and stem cell, hepatocellular carcinoma, and the impact of elevated DPP-4 levels in association with liver diseases as a cause of glucose intolerance and their treatment drug of choices. In addition, the effect of DPP-4 inhibitors on obesity and their negative aspects are also discussed in brief.

Systematic analysis of the pharmacological function of Schisandra as a potential exercise supplement

[Purpose] Exercise can prevent conditions such as atrophy and degenerative brain diseases. However, owing to individual differences in athletic ability, exercise supplements can be used to improve a person’s exercise capacity. Schisandra chinensis (SC) is a natural product with various physiologically active effects. In this study, we analyzed SC using a pharmacological network and determined whether it could be used as an exercise supplement.[Methods] The active compounds of SC and target genes were identified using the Traditional Chinese Medicine Database and Analysis Platform (TCMSP). The active compound and target genes were selected based on pharmacokinetic (PK) conditions (oral bioavailability (OB) ≥ 30%, Caco-2 permeability (Caco-2) ≥ -0.4, and drug-likeness (DL) ≥ 0.18). Gene ontology (GO) was analyzed using the Cytoscape software.[Results] Eight active compounds were identified according to the PK conditions. Twenty-one target genes were identified after excluding duplicates in the eight active compounds. The top 10 GOs were analyzed using GO-biological process analysis. GO was subsequently divided into three representative categories: postsynaptic neurotransmitter receptor activity (53.85%), an intracellular steroid hormone receptor signaling pathway (36.46%), and endopeptidase activity (10%). SC is related to immune function.[Conclusion] According to the GO analysis, SC plays a role in immunity and inflammation, promotes liver metabolism, improves fatigue, and regulates the function of steroid receptors. Therefore, we suggest SC as an exercise supplement with nutritional and anti-fatigue benefits.

Selenium cleome droserifolia nanoparticles (Se-CNPs) and it's ameliorative effects in experimentally induced diabetes mellitus

Diabetes mellitus is a group of metabolic disorders with great challenge in its treatment due to its pathological complication. In recent decade, there is extensive use of applying nanotechnology to medicinal plants as a trend in diabetes treatment due to phytochemical constituents. The present study aimed to evaluate the hypoglycemic effect of selenium cleome droserifolia nanoparticles (Se-CNPs) and/or Galvus met® treatment on streptozotocin induced diabetes mellitus in male rats. Fifty male Wistar rats were divided equally into five groups: control group, control diabetic group, diabetic group treated with Se-CNPs, diabetic group treated with Galvus met® and diabetic group treated with Se-CNPs plus Galvus met®. Glucose and insulin levels, Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST), Total Cholesterol (TC), Triacylglycerols (TG), High Density Lipoprotein (HDL-c), Very Low Density Lipoprotein cholesterol (VLDL-c), Low Density Lipoprotein cholesterol (LDL-c) and (NEFAs), urea and creatinine were evaluated. Also, histopathological changes in pancreatic tissue were examined. The results showed significant elevation in serum glucose concentration, ALT and AST activities, TG, LDL-c, VLDL-c and Non Esterified Fatty Acids (NEFAs), urea and creatinine levels while a significant decrease in serum insulin and HDL-c concentration in untreated diabetic rats when compared with control. Meanwhile, daily administration of Se-CNPs and/or Galvus met® to diabetic rats showed significant amelioration of these parameters.

Activity and selectivity cliffs for DPP-IV inhibitors: Lessons we can learn from SAR studies and their application to virtual screening

The inhibition of dipeptidyl peptidase-IV (DPP-IV) has emerged over the last decade as one of the most effective treatments for type 2 diabetes mellitus, and consequently (a) 11 DPP-IV inhibitors have been on the market since 2006 (three in 2015), and (b) 74 noncovalent complexes involving human DPP-IV and drug-like inhibitors are available at the Protein Data Bank (PDB). The present review aims to (a) explain the most important activity cliffs for DPP-IV noncovalent inhibition according to the binding site structure of DPP-IV, (b) explain the most important selectivity cliffs for DPP-IV noncovalent inhibition in comparison with other related enzymes (i.e., DPP8 and DPP9), and (c) use the information deriving from this activity/selectivity cliff analysis to suggest how virtual screening protocols might be improved to favor the early identification of potent and selective DPP-IV inhibitors in molecular databases (because they have not succeeded in identifying selective DPP-IV inhibitors with IC₅₀ ≤ 100 nM). All these goals are achieved with the help of available homology models for DPP8 and DPP9 and an analysis of the structure-activity studies used to develop the noncovalent inhibitors that form part of some of the complexes with human DPP-IV available at the PDB.

Treatment options for alcoholic and non-alcoholic fatty liver disease: A review

Alcoholic liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD) are serious health problems worldwide. These two diseases have similar pathological spectra, ranging from simple steatosis to hepatitis to cirrhosis and hepatocellular carcinoma. Although most people with excessive alcohol or calorie intake display abnormal fat accumulation in the liver (simple steatosis), a small percentage develops progressive liver disease. Despite extensive research on understanding the pathophysiology of both these diseases there are still no targeted therapies available. The treatment for ALD remains as it was 50 years ago: abstinence, nutritional support and corticosteroids (or pentoxifylline as an alternative if steroids are contraindicated). As for NAFLD, the treatment modality is mainly directed toward weight loss and co-morbidity management. Therefore, new pathophysiology directed therapies are urgently needed. However, the involvement of several inter-related pathways in the pathogenesis of these diseases suggests that a single therapeutic agent is unlikely to be an effective treatment strategy. Hence, a combination therapy towards multiple targets would eventually be required. In this review, we delineate the treatment options in ALD and NAFLD, including various new targeted therapies that are currently under investigation. We hope that soon we will be having an effective multi-therapeutic regimen for each disease.

Prevention and treatment effect of evogliptin on hepatic steatosis in high-fat-fed animal models

Dipeptidyl peptidase 4 (DPP4) is an adipokine that interrupts insulin signaling. The resulting insulin resistance exacerbates hepatic steatosis. We previously reported that the novel DPP4 inhibitor evogliptin improves insulin resistance. This study aimed to verify the therapeutic potential of evogliptin for fatty liver. Evogliptin treatment was initiated simultaneously with a high-fat diet (HFD) feeding in normal mice and in a post-24 week HFD-fed rats. In a prevention study, insulin sensitivity was preserved in evogliptin-treated mice after a 16-week treatment. Overall plasma lipid levels stayed lower and hepatic lipid accumulation was drastically suppressed by evogliptin treatment. Evogliptin reduced hepatic expression of Srebf1, a key transcriptional factor for lipogenesis. Additionally, DPP4 inhibitor-treated mice showed less weight gain. In a treatment study, after evogliptin treatment for 14 weeks in pre-established HFD-fed obese rats, weight loss was marginal, while hepatic lipid accumulation and liver damage assessed by measuring plasma aminotransferase levels were completely resolved, suggesting weight loss-independent beneficial effects on fatty liver. Moreover, reduction in plasma non-esterified fatty acids supported the improvement of insulin resistance by evogliptin treatment. Conclusively, our findings suggest that evogliptin treatment ameliorates fatty liver by increasing insulin sensitivity and suppressing lipogenesis.

Combination of Vildagliptin and Pioglitazone in Experimental Type 2 Diabetes in Male Rats

Preclinical Research The majority of studies on vildagliptin and pioglitazone have focused on their combination in glycemic control. The aim of the present study was to investigate their effects in combination on (i) hyperglycemia-induced oxidative stress and inflammation and (ii) on organs involved in the pathophysiology of diabetes, pancreas, kidney and liver. Type 2 diabetes was induced using low-dose streptozotocin in male Wistar rats. Diabetic rats were treated for 4 weeks, with vildagliptin (10 mg/kg/day), pioglitazone (10 mg/kg/day) and their combination. Diabetic rats showed elevated fasting serum glucose, fasting serum insulin, serum transaminases together with a deleterious lipid profile and elevated serum creatinine and urea concentrations. Serum levels of the inflammatory markers tumor necrosis factor-α (TNF-α) and nitrite/nitrate were also elevated compared to normal rats. Oxidative stress was manifested by lowered hepatic reduced glutathione (GSH) and increased malondialdehyde (MDA) levels. Pancreatic sections from diabetic rats showed degenerated islets with poorly maintained architecture that was prevented by drug treatment. Pioglitazone was generally more effective than vildagliptin in the studied parameters except for the lipid profile where the effect of both drugs was comparable and for the liver enzymes and renal parameters where vildagliptin was more effective. The combination of vildagliptin and pioglitazone produced superior effects than either drug alone. Drug Dev Res 77 : 251-257, 2016. © 2016 Wiley Periodicals, Inc.

DPP-4 inhibitors in diabetic complications: role of DPP-4 beyond glucose control

Dipeptidyl peptidase-4 (DPP-4) inhibitors (gliptins) are an emerging class of antidiabetic drugs that constitutes approximately fifty percent of the market share of the oral hypoglycemic drugs. Its mechanism of action for lowering blood glucose is essentially via inhibition of the rapid degradation of incretin hormones, such as glucagon-like peptide (GLP)-1 and gastric inhibitory polypeptide (GIP), thus the plasma concentration of GLP-1 increases, which promotes insulin secretion from the pancreatic β cells and suppresses glucagon secretion from the α cells. In addition to the direct actions on the pancreas, GLP-1 exhibits diverse actions on different tissues through its action on GLP-1 receptor, which is expressed ubiquitously. Moreover, DPP-4 has multiple substrates besides GLP-1 and GIP, including cytokines, chemokines, neuropeptides, and growth factors, which are involved in many pathophysiological conditions. Recently, it was suggested that DPP-4 is a new adipokine secreted from the adipose tissue, which plays an important role in the regulation of the endocrine function in obesity-associated type 2 diabetes. Consequently, DPP-4 inhibitors have been reported to exhibit cytoprotective functions against various diabetic complications affecting the liver, heart, kidneys, retina, and neurons. This review outlines the current understanding of the effect of DPP-4 inhibitors on the complications associated with type 2 diabetes, such as liver steatosis and inflammation, dysfunction of the adipose tissue and pancreas, cardiovascular diseases, nephropathy, and neuropathy in preclinical and clinical studies.

Effect of sitagliptin on epicardial fat thickness in subjects with type 2 diabetes and obesity: a pilot study

The aim of the study was to assess the effect of sitagliptin addition on the epicardial adipose tissue (EAT) thickness in subjects with type 2 diabetes mellitus inadequately controlled on metformin monotherapy. This was a 24-week interventional pilot study in 26 consecutive type 2 diabetic patients, 14 females and 12 males average age of 43.8 ± 9.0 years, with Hemoglobin A1c (HbA1c) ≥ 7% on metformin monotherapy. Subjects who met the inclusion criteria were added on sitagliptin and started on sitagliptin/metformin combination at the dosage of 50 mg/1000 mg twice daily. EAT and visceral and total body fat were measured, respectively, with echocardiography and bioelectrical impedance analysis at baseline and after 24 weeks of sitagliptin/metformin treatment in each subject. HbA1c and plasma lipids were also measured. EAT decreased significantly from 9.98 ± 2.63 to 8.10 ± 2.11 mm, p = 0.001, accounting for a percentage of reduction (∆%) of -15% after 24 weeks of sitagliptin addition, whereas total body fat percentage, visceral fat, and body mass index (BMI), decreased by 8, 12, and 7%, respectively (p = 0.001 for all). After 6 month, EAT ∆% was significantly correlated with ∆% of visceral fat (r = 0.456; p = 0.01), whereas no correlation with either BMI ∆% (r = 0.292; p = 0.147) or HbA1c ∆% was found. The addition of Sitagliptin produced a significant and rapid reduction of EAT, marker of organ-specific visceral fat, in overweight/obese individuals with type 2 diabetes inadequately controlled on metformin monotherapy. EAT as measured with ultrasound can serve as no invasive and accurate marker of visceral fat changes during pharmaceutical interventions targeting the fat.

Epicardial fat: a new cardiovascular therapeutic target

Epicardial fat is the visceral fat depot of the heart. Given its rapid metabolism, organ fat specificity and simple objective measurability, epicardial fat can serve as target for pharmaceutical agents targeting the adipose tissue. Epicardial fat has shown to significantly respond to thiazolidinediones, glucagon like peptide 1 receptor agonists, dipeptidyl peptidase-4 inhibitors and statins. Epicardial fat may represent a measurable risk factor and modifiable therapeutic target. Targeted pharmaceutical interventions may allow the epicardial fat to resume its physiological role. A drug-induced browning effect on epicardial fat suggests the development of pharmacological strategies to increase energy consumption. The potential of modulating the epicardial fat transcriptome with targeted pharmacological agents can open new avenues in the pharmacotherapy of cardio-metabolic diseases.

Hepatic role in an early glucose-lowering effect by a novel dipeptidyl peptidase 4 inhibitor, evogliptin, in a rodent model of type 2 diabetes

Although multiple dipeptidyl peptidase 4 (DPP4) inhibitors have shown glucose-lowering effects by preserving pancreatic cells in high-fat diet (HFD)/streptozotocin (STZ)-induced diabetic mice, the hepatic role in regulation of glucose homeostasis by DPP4 inhibitors in HFD/STZ mice remains elusive. In herein study, parallel comparison of effects on the liver (expression of gluconeogenic genes and the linked signaling molecules) and pancreas (islet morphology and relative area of alpha or beta cells) in combination with glucose-lowering effects were made at the end of 2- and 10-week of evogliptin treatment in HFD/STZ mice. Significant control of hyperglycemia was observed from the second week and persisted during 10-week treatment of 0.3% evogliptin in HFD/STZ mice. This effect was accompanied by increased level of plasma glucagon-like peptide-1 and preserved pancreas islet structure. Furthermore, the hepatic increases in gluconeogenic gene expression in HFD/STZ mice was significantly reduced by evogliptin treatment, which was accompanied by the suppression of cAMP response element-binding protein (CREB) phosphorylation and expression of transducer of regulated CREB protein 2. This hepatic effect of evogliptin treatment was reproduced in 2-week study, however, pancreatic beta-cell area was not altered yet although the expression of pancreatic and duodenal homeobox protein 1 was increased. We conclude that the suppression of hepatic gluconeogenesis by evogliptin is followed by preservation of pancreatic islet, leading to remarkable and persistent glucose-lowering effect in HFD/STZ mice. Our findings provide further insight for the hepatic role in DPP4 inhibitor-mediated glucose control in diabetes.

Prevention and treatment of nonalcoholic fatty liver disease in patients with type 2 diabetes mellitus

Nonalcoholic fatty liver disease (NAFLD) is frequently seen in the type 2 diabetes mellitus (T2DM) population. Insulin resistance is the pathophysiologic bridge which links T2DM and NAFLD. Coexistence of both diseases indicates more severe diseases and higher risk of death. As a result, it is urgent to effectively control NAFLD in patients with T2DM. The advent of glucagon like peptide-1 (GLP-1) agonists and dipeptidyl peptidase-4 (DPP-4) inhibitors brings new hope for effectively managing NAFLD in T2DM patients. Bariatric surgery provides obese T2DM patients with a powerful means to treat NAFLD. The discovery of adipokines such as adiponectin and fibroblast growth factor 21 (FGF21) may point to a new research direction for NAFLD. In this paper, we present therapeutic options currently available for NAFLD in T2DM patients as well as the present research progress in NAFLD with T2DM, with regards to epidemiology and pathophysiologic links between them.

DPP4 in Diabetes

Dipeptidyl-peptidase 4 (DPP4) is a glycoprotein of 110 kDa, which is ubiquitously expressed on the surface of a variety of cells. This exopeptidase selectively cleaves N-terminal dipeptides from a variety of substrates, including cytokines, growth factors, neuropeptides, and the incretin hormones. Expression of DPP4 is substantially dysregulated in a variety of disease states including inflammation, cancer, obesity, and diabetes. Since the incretin hormones, glucagon-like peptide-1 and glucose-dependent insulinotropic polypeptide (GIP), are major regulators of post-prandial insulin secretion, inhibition of DPP4 by the gliptin family of drugs has gained considerable interest for the therapy of type 2 diabetic patients. In this review, we summarize the current knowledge on the DPP4–incretin axis and evaluate most recent findings on DPP4 inhibitors. Furthermore, DPP4 as a type II transmembrane protein is also known to be cleaved from the cell membrane involving different metalloproteases in a cell-type-specific manner. Circulating, soluble DPP4 has been identified as a new adipokine, which exerts both para- and endocrine effects. Recently, a novel receptor for soluble DPP4 has been identified, and data are accumulating that the adipokine-related effects of DPP4 may play an important role in the pathogenesis of cardiovascular disease. Importantly, circulating DPP4 is augmented in obese and type 2 diabetic subjects, and it may represent a molecular link between obesity and vascular dysfunction. A critical evaluation of the impact of circulating DPP4 is presented, and the potential role of DPP4 inhibition at this level is also discussed.

Non-alcoholic fatty liver disease in 2015

There is worldwide epidemic of non-alcoholic fatty liver disease (NAFLD). NAFLD is a clinical entity related to metabolic syndrome. Majority of the patients are obese but the disease can affect non-obese individuals as well. Metabolic factors and genetics play important roles in the pathogenesis of this disorder. The spectrum of disorders included in NAFLD are benign macrovesicular hepatic steatosis, non-alcoholic steatohepatitis, hepatic fibrosis, cirrhosis of liver and hepatocellular carcinoma. Although the disease remains asymptomatic most of the time, it can slowly progress to end stage liver disease. It will be the most common indication of liver transplantation in the future. It is diagnosed by abnormal liver chemistry, imaging studies and liver biopsy. As there are risks of potential complications during liver biopsy, many patients do not opt for liver biopsy. There are some noninvasive scoring systems to find out whether patients have advanced hepatic fibrosis. At the present time, there are limited treatment options which include lifestyle modification to loose weight, vitamin E and thioglitazones. Different therapeutic agents are being investigated for optimal management of this entity. There are some studies done on incretin based therapies in patients with NAFLD. Other potential agents will be silent information regulator protein Sirtuin and antifibrotic monoclonal antibody Simtuzumab against lysyl oxidase like molecule 2. But they are still in the investigational phase.

Non-alcoholic fatty liver disease in 2015

There is worldwide epidemic of non-alcoholic fatty liver disease (NAFLD). NAFLD is a clinical entity related to metabolic syndrome. Majority of the patients are obese but the disease can affect non-obese individuals as well. Metabolic factors and genetics play important roles in the pathogenesis of this disorder. The spectrum of disorders included in NAFLD are benign macrovesicular hepatic steatosis, non-alcoholic steatohepatitis, hepatic fibrosis, cirrhosis of liver and hepatocellular carcinoma. Although the disease remains asymptomatic most of the time, it can slowly progress to end stage liver disease. It will be the most common indication of liver transplantation in the future. It is diagnosed by abnormal liver chemistry, imaging studies and liver biopsy. As there are risks of potential complications during liver biopsy, many patients do not opt for liver biopsy. There are some noninvasive scoring systems to find out whether patients have advanced hepatic fibrosis. At the present time, there are limited treatment options which include lifestyle modification to loose weight, vitamin E and thioglitazones. Different therapeutic agents are being investigated for optimal management of this entity. There are some studies done on incretin based therapies in patients with NAFLD. Other potential agents will be silent information regulator protein Sirtuin and antifibrotic monoclonal antibody Simtuzumab against lysyl oxidase like molecule 2. But they are still in the investigational phase.

Review on the effect of glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors for the treatment of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is a common liver disease and it represents the hepatic manifestation of metabolic syndrome, which includes type 2 diabetes mellitus (T2DM), dyslipidemia, central obesity and hypertension. Glucagon-like peptide-1 (GLP-1) analogues and dipeptidyl peptidase-4 (DPP-4) inhibitors were widely used to treat T2DM. These agents improve glycemic control, promote weight loss and improve lipid metabolism. Recent studies have demonstrated that the GLP-1 receptor (GLP-1R) is present and functional in human and rat hepatocytes. In this review, we present data from animal researches and human clinical studies that showed GLP-1 analogues and DPP-4 inhibitors can decrease hepatic triglyceride (TG) content and improve hepatic steatosis, although some effects could be a result of improvements in metabolic parameters. Multiple hepatocyte signal transduction pathways and mRNA from key enzymes in fatty acid metabolism appear to be activated by GLP-1 and its analogues. Thus, the data support the need for more rigorous prospective clinical trials to further investigate the potential of incretin therapies to treat patients with NAFLD.

Pharmacokinetics in patients with chronic liver disease and hepatic safety of incretin-based therapies for the management of type 2 diabetes mellitus

Patients with type 2 diabetes mellitus have an increased risk of chronic liver disease (CLD) such as non-alcoholic fatty liver disease and steatohepatitis, and about one-third of cirrhotic patients have diabetes. However, the use of several antidiabetic agents, such as metformin and sulphonylureas, may be a concern in case of hepatic impairment (HI). New glucose-lowering agents targeting the incretin system are increasingly used for the management of type 2 diabetes. Incretin-based therapies comprise oral inhibitors of dipeptidyl peptidase-4 (DPP-4) (gliptins) or injectable glucagon-like peptide-1 (GLP-1) receptor agonists. This narrative review summarises the available data regarding the use of both incretin-based therapies in patients with HI. In contrast to old glucose-lowering agents, they were evaluated in specifically designed acute pharmacokinetic studies in patients with various degrees of HI and their hepatic safety was carefully analysed in large clinical trials. Only mild changes in pharmacokinetic characteristics of DPP-4 inhibitors were observed in patients with different degrees of HI, presumably without major clinical relevance. GLP-1 receptor agonists have a renal excretion rather than liver metabolism. Specific pharmacokinetic data in patients with HI are only available for liraglutide. No significant changes in liver enzymes were reported with DPP-4 inhibitors or GLP-1 receptor agonists, alone or in combination with various other glucose-lowering agents, in clinical trials up to 2 years in length. On the contrary, preliminary data suggested that incretin-based therapies may be beneficial in patients with CLD, more particularly in the presence of non-alcoholic fatty liver disease. Nevertheless, caution should be recommended, especially in patients with advanced cirrhosis, because of a lack of clinical experience with incretin-based therapies in these vulnerable patients.

Pilot study of liraglutide effects in non-alcoholic steatohepatitis and non-alcoholic fatty liver disease with glucose intolerance in Japanese patients (LEAN-J)

AIM

Non-alcoholic fatty liver disease (NAFLD), a hepatic manifestation of metabolic syndrome, is associated with an increased risk of developing lifestyle-related diseases including type 2 diabetes, cardiovascular disease and cerebral vessel disease. No current drug therapy provides the ideal effects of decreasing hepatic inflammation while simultaneously improving liver fibrosis. Liraglutide is a glucagon-like peptide-1 receptor agonist that affects the histological findings in patients with non-alcoholic steatohepatitis (NASH). This study was conducted to evaluate the effect and action of liraglutide for biopsy-proven NASH.

METHODS

After lifestyle modification intervention for 24 weeks, subjects whose hemoglobin A1c levels failed to improve to less than 6.0% and/or whose alanine aminotransferase levels were not lower than baseline, received liraglutide at 0.9 mg/body per day for 24 weeks.

RESULTS

Of 27 subjects, 26 completed the lifestyle modification intervention. Nineteen subjects received liraglutide therapy for 24 weeks. Body mass index, visceral fat accumulation, aminotransferases and glucose abnormalities improved significantly. Repeated liver biopsy was performed in 10 subjects who continued liraglutide therapy for 96 weeks. Six subjects showed decreased histological inflammation as determined by NASH activity score and stage determined by Brunt classification. We saw no significant adverse events during therapy with liraglutide.

CONCLUSION

Our pilot study demonstrated that treatment with liraglutide had a good safety profile and significantly improved liver function and histological features in NASH patients with glucose intolerance.

Comparative analysis of therapeutic efficiency and costs (experience in Bulgaria) of oral antidiabetic therapies based on glitazones and gliptins

Type 2 diabetes mellitus is a serious, chronic, progressive and widespread disease. Metformin is the most commonly prescribed initial therapy, but combination with other antidiabetic agents usually becomes necessary due to the progression of the disease. Pioglitazone is recommended as a second-line therapy because of its strong antihyperglycemic effect and its ability to reduce insulin resistance. Treatment with pioglitazone is associated with a significantly lower risk of cardiovascular complications and hypoglycemia, while simultaneously improving the lipid profile and the symptomatic and histological changes in the liver. Gliptins (sitagliptin and vildagliptin) are a new class of oral antidiabetic drugs which reduce glycated hemoglobin by a different mechanism. Although the efficacy of sitagliptin and vildagliptin is close to that of pioglitazone, the lack of long-term safety data and the higher price question their predominant use. The objective of this review is to highlight the advantages of mono- and combination therapy with pioglitazone in comparison with gliptins and to underline the inconsistencies in the medicinal and reimbursement policy in Bulgaria.

Non-alcoholic fatty liver disease and type 2 diabetes mellitus: The liver disease of our age?

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease that might affect up to one-third of the adult population in industrialised countries. NAFLD incorporates histologically and clinically different non-alcoholic entities; fatty liver (NAFL, steatosis hepatis) and steatohepatitis (NASH-characterised by hepatocyte ballooning and lobular inflammation ± fibrosis) might progress to cirrhosis and rarely to hepatocellular cancer. NAFL increasingly affects children (paediatric prevalence is 4.2%-9.6%). Type 2 diabetes mellitus (T2DM), insulin resistance (IR), obesity, metabolic syndrome and NAFLD are particularly closely related. Increased hepatic lipid storage is an early abnormality in insulin resistant women with a history of gestational diabetes mellitus. The accumulation of triacylglycerols in hepatocytes is predominantly derived from the plasma nonesterified fatty acid pool supplied largely by the adipose tissue. A few NAFLD susceptibility gene variants are associated with progressive liver disease, IR, T2DM and a higher risk for hepatocellular carcinoma. Although not approved, pharmacological approaches might be considered in NASH patients.

Incretin based therapies: A novel treatment approach for non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease is considered a hepatic manifestation of metabolic syndrome (MS). The current treatment of non-alcoholic fatty liver disease (NAFLD) principally includes amelioration of MS components by lifestyle modifications but the lack of success in their implementation and sustainment arises the need for effective pharmacological agent in fatty liver treatment. Incretins are gut derived hormones secreted into the circulation in response to nutrient ingestion that enhances glucose-stimulated insulin secretion. Glucagon-like peptide-1 (GLP-1) is the most important incretin. Its receptor agonist and inhibitors of dipeptidyl peptidase-4 (DPP-4) are used in treatment of type 2 diabetes mellitus. DPP-4 serum activity and hepatic expression are shown to be elevated in several hepatic diseases. There are several experimental and clinical trials exploring the efficacy of incretin based therapies in NAFLD treatment. They suggest that GLP-1 analogues might have beneficial effect on hepatic steatosis acting as insulin sensitizers and directly by stimulating GLP-1 receptors expressed on hepatocytes. The use of DPP-4 inhibitors also results in hepatic fat reduction but the mechanism of action remains unclear. There is growing evidence that incretin based therapies have beneficial effects on hepatocytes, however further study analysis are needed to assess the long term effect of incretin based therapies on NAFLD.

Linagliptin: from bench to bedside

PURPOSE

The nature of biomedical research affords a broad range of investigational topics at the preclinical stage, not all of which may be explored in subsequent clinical studies. To provide a comprehensive perspective on the physiologic effects of the dipeptidyl peptidase-4 inhibitor linagliptin, this review will discuss the results of both preclinical and clinical research, summarizing data describing outcomes associated with its use.

SUMMARY

Clinical studies demonstrate an overall favorable safety profile, low risk for hypoglycemia, weight neutrality, primarily nonrenal clearance, and efficacy for glycosylated hemoglobin reduction, typically ranging from 0.6% to 0.8% depending on baseline levels. In addition to these characteristics, preclinical research on linagliptin has yielded several interesting findings such as improved wound healing, reduced hepatic fat content, decreased infarct size following myocardial infarction or intracranial stroke, and improved vascular function with decreased oxidative stress. In accordance with its preclinical profile, linagliptin is unique among available dipeptidyl peptidase-4 compounds because it does not require dose adjustment when used in patients with renal dysfunction. Reduction of albuminuria with linagliptin on top of inhibitors of the renin-angiotensin-aldosterone system in both preclinical and post hoc clinical analysis serves as the foundation for ongoing clinical trials.

CONCLUSION

In addition to its efficacy for glycemic control, current literature points to other potential opportunities associated with linagliptin therapy. These results warrant further investigation and underscore the importance of translational study based on findings from preclinical research. Moving forward, we can expect that future research on linagliptin and other incretin-based therapies will continue to expand their applications beyond the maintenance of glycemic control in patients with type 2 diabetes.

Pharmacokinetic and toxicological considerations for the treatment of diabetes in patients with liver disease

INTRODUCTION

Patients with type 2 diabetes have an increased risk of chronic liver disease (CLD) such as non-alcoholic fatty liver disease and steatohepatitis and about one-third of cirrhotic patients have diabetes. However, the use of several antidiabetic agents may be a cause for concern in the case of hepatic impairment (HI).

AREAS COVERED

An extensive literature search was performed to analyze the influence of HI on the pharmacokinetics (PK) of glucose-lowering agents and the potential consequences for clinical practice as far as the efficacy/safety balance of their use in diabetic patients with CLD is concerned.

EXPERT OPINION

Almost no PK studies have been published regarding metformin, sulfonylureas, thiazolidinediones and α-glucosidase inhibitors in patients with HI. Only mild changes in PK of glinides, dipeptidyl peptidase-4 inhibitors and sodium glucose cotransporters type 2 inhibitors were observed in dedicated PK studies in patients with various degrees of HI, presumably without major clinical relevance although large clinical experience is lacking. Glucagon-like peptide-1 receptor agonists have a renal excretion rather than liver metabolism. Rare anecdotal case reports of hepatotoxicity have been described with various glucose-lowering agents contrasting with numerous reassuring data. Nevertheless, caution should be recommended, especially in patients with advanced cirrhosis, including with the use of metformin.

Nonalcoholic Fatty liver: a possible new target for type 2 diabetes prevention and treatment

Non-alcoholic fatty liver disease (NAFLD) is the most common liver disorder worldwide. Several lines of evidence have indicated a pathogenic role of insulin resistance, and a strong association with type 2 diabetes (T2MD) and metabolic syndrome. Importantly, NAFLD appears to enhance the risk for T2MD, as well as worsen glycemic control and cardiovascular disease in diabetic patients. In turn, T2MD may promote NAFLD progression. The opportunity to take into account NAFLD in T2MD prevention and care has stimulated several clinical studies in which antidiabetic drugs, such as metformin, thiazolidinediones, GLP-1 analogues and DPP-4 inhibitors have been evaluated in NAFLD patients. In this review, we provide an overview of preclinical and clinical evidences on the possible efficacy of antidiabetic drugs in NAFLD treatment. Overall, available data suggest that metformin has beneficial effects on body weight reduction and metabolic parameters, with uncertain effects on liver histology, while pioglitazone may improve liver histology. Few data, mostly preclinical, are available on DPP4 inhibitors and GLP-1 analogues. The heterogeneity of these studies and the small number of patients do not allow for firm conclusions about treatment guidelines, and further randomized, controlled studies are needed.

Dipeptidyl peptidase-4: A key player in chronic liver disease

Dipeptidyl peptidase-4 (DPP-4) is a membrane-associated peptidase, also known as CD26. DPP-4 has widespread organ distribution throughout the body and exerts pleiotropic effects via its peptidase activity. A representative target peptide is glucagon-like peptide-1, and inactivation of glucagon-like peptide-1 results in the development of glucose intolerance/diabetes mellitus and hepatic steatosis. In addition to its peptidase activity, DPP-4 is known to be associated with immune stimulation, binding to and degradation of extracellular matrix, resistance to anti-cancer agents, and lipid accumulation. The liver expresses DPP-4 to a high degree, and recent accumulating data suggest that DPP-4 is involved in the development of various chronic liver diseases such as hepatitis C virus infection, non-alcoholic fatty liver disease, and hepatocellular carcinoma. Furthermore, DPP-4 occurs in hepatic stem cells and plays a crucial role in hepatic regeneration. In this review, we described the tissue distribution and various biological effects of DPP-4. Then, we discussed the impact of DPP-4 in chronic liver disease and the possible therapeutic effects of a DPP-4 inhibitor.