Circulating dipeptidyl peptidase-4 activity correlates with measures of hepatocyte apoptosis and fibrosis in non-alcoholic fatty liver disease in type 2 diabetes mellitus and obesity: A dual cohort cross-sectional study

Diabetes as a risk factor for MASH progression

Non-alcoholic (now: metabolic) steatohepatitis (MASH) is the progressive inflammatory form of metabolic dysfunction-associated steatotic liver disease (MASLD), which often coexists and mutually interacts with type 2 diabetes (T2D), resulting in worse hepatic and cardiovascular outcomes. Understanding the intricate mechanisms of diabetes-related MASH progression is crucial for effective therapeutic strategies. This review delineates the multifaceted pathways involved in this interplay and explores potential therapeutic implications. The synergy between adipose tissue, gut microbiota, and hepatic alterations plays a pivotal role in disease progression. Adipose tissue dysfunction, particularly in the visceral depot, coupled with dysbiosis in the gut microbiota, exacerbates hepatic injury and insulin resistance. Hepatic lipid accumulation, oxidative stress, and endoplasmic reticulum stress further potentiate inflammation and fibrosis, contributing to disease severity. Dietary modification with weight reduction and exercise prove crucial in managing T2D-related MASH. Additionally, various well-known but also novel anti-hyperglycemic medications exhibit potential in reducing liver lipid content and, in some cases, improving MASH histology. Therapies targeting incretin receptors show promise in managing T2D-related MASH, while thyroid hormone receptor-β agonism has proven effective as a treatment of MASH and fibrosis.

Targeting cluster of differentiation 26 / dipeptidyl peptidase 4 (CD26/DPP4) in organ fibrosis

Cluster of differentiation 26 (CD26)/dipeptidyl peptidase 4 (DPP4) is an exopeptidase that is expressed as a transmembrane protein in many organs but also present in a circulating soluble form. Beyond its enzymatic and costimulatory activity, CD26/DPP4 is involved in the pathogenesis of chronic fibrotic diseases across many organ types, such as liver cirrhosis, kidney fibrosis and lung fibrosis. Organ fibrosis is associated with a high morbidity and mortality, and there are no causative therapies that can effectively attenuate the progress of the disease. Growing evidence suggests that inhibiting CD26/DPP4 can modulate the profibrotic tissue microenvironment and thus reduce fibrotic changes within affected organs. This review summarizes the role of CD26/DPP4 in fibroproliferative disorders and highlights new opportunities for an antifibrotic treatment by CD26/DPP4 inhibition. As a major advantage, CD26/DPP4 inhibitors have been in safe and routine clinical use in type 2 diabetes for many years and thus qualify for repurposing to repurpose as a promising therapeutic against fibrosis. LINKED ARTICLES: This article is part of a themed issue on Translational Advances in Fibrosis as a Therapeutic Target. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.22/issuetoc.

Pharmacotherapies of NAFLD: updated opportunities based on metabolic intervention

Non-alcoholic fatty liver disease (NAFLD) is a chronic liver disease that is becoming increasingly prevalent, and it ranges from simple steatosis to cirrhosis. However, there is still a lack of pharmacotherapeutic strategies approved by the Food and Drug Administration, which results in a higher risk of death related to carcinoma and cardiovascular complications. Of note, it is well established that the pathogenesis of NAFLD is tightly associated with whole metabolic dysfunction. Thus, targeting interconnected metabolic conditions could present promising benefits to NAFLD, according to a number of clinical studies. Here, we summarize the metabolic characteristics of the development of NAFLD, including glucose metabolism, lipid metabolism and intestinal metabolism, and provide insight into pharmacological targets. In addition, we present updates on the progresses in the development of pharmacotherapeutic strategies based on metabolic intervention globally, which could lead to new opportunities for NAFLD drug development.

Hepatocyte-derived DPP4 regulates portal GLP-1 bioactivity, modulates glucose production, and when absent influences NAFLD progression

Elevated circulating dipeptidyl peptidase-4 (DPP4) is a biomarker for liver disease, but its involvement in gluconeogenesis and metabolic associated fatty liver disease progression remains unclear. Here, we identified that DPP4 in hepatocytes but not TEK receptor tyrosine kinase-positive endothelial cells regulates the local bioactivity of incretin hormones and gluconeogenesis. However, the complete absence of DPP4 (Dpp4-/-) in aged mice with metabolic syndrome accelerates liver fibrosis without altering dyslipidemia and steatosis. Analysis of transcripts from the livers of Dpp4-/- mice displayed enrichment for inflammasome, p53, and senescence programs compared with littermate controls. High-fat, high-cholesterol feeding decreased Dpp4 expression in F4/80+ cells, with only minor changes in immune signaling. Moreover, in a lean mouse model of severe nonalcoholic fatty liver disease, phosphatidylethanolamine N-methyltransferase mice, we observed a 4-fold increase in circulating DPP4, in contrast with previous findings connecting DPP4 release and obesity. Last, we evaluated DPP4 levels in patients with hepatitis C infection with dysglycemia (Homeostatic Model Assessment of Insulin Resistance > 2) who underwent direct antiviral treatment (with/without ribavirin). DPP4 protein levels decreased with viral clearance; DPP4 activity levels were reduced at long-term follow-up in ribavirin-treated patients; but metabolic factors did not improve. These data suggest elevations in DPP4 during hepatitis C infection are not primarily regulated by metabolic disturbances.

Dipeptidyl peptidase IV inhibition delays developmental programming of obesity and metabolic disease in male offspring of obese mothers

Maternal obesity programs the offspring to metabolic diseases later in life; however, the mechanisms of programming are yet unclear, and no strategies exist for addressing its detrimental transgenerational effects. Obesity has been linked to dipeptidyl peptidase IV (DPPIV), an adipokine, and treatment of obese individuals with DPPIV inhibitors has been reported to prevent weight gain and improve metabolism. We hypothesized that DPPIV plays a role in maternal obesity-mediated programming. We measured plasma DPPIV activity in human maternal and cord blood samples from normal-weight and obese mothers at term. We found that maternal obesity increases maternal and cord blood plasma DPPIV activity but only in male offspring. Using two non-human primate models of maternal obesity, we confirmed the activation of DPPIV in the offspring of obese mothers. We then created a mouse model of maternal high-fat diet (HFD)-induced obesity, and found an early-life increase in plasma DPPIV activity in male offspring. Activation of DPPIV preceded the progression of obesity, glucose intolerance and insulin resistance in male offspring of HFD-fed mothers. We then administered sitagliptin, DPPIV inhibitor, to regular diet (RD)- and HFD-fed mothers, starting a week prior to breeding and continuing throughout pregnancy and lactation. We found that sitagliptin treatment of HFD-fed mothers delayed the progression of obesity and metabolic diseases in male offspring and had no effects on females. Our findings reveal that maternal obesity dysregulates plasma DPPIV activity in males and provide evidence that maternal inhibition of DPPIV has potential for addressing the transgenerational effects of maternal obesity.

Dipeptidyl Peptidase 4 (DPP4) as A Novel Adipokine: Role in Metabolism and Fat Homeostasis

Dipeptidyl peptidase 4 (DPP4) is a molecule implicated in the regulation of metabolic homeostasis and inflammatory processes, and it exerts its main action through its enzymatic activity. DPP4 represents the enzyme most involved in the catabolism of incretin hormones; thus, its activity impacts appetite, energy balance, and the fine regulation of glucose homeostasis. Indeed, DPP4 inhibitors represent a class of antidiabetic agents widely used for the treatment of Type 2 diabetes mellitus (T2DM). DPP4 also acts as an adipokine and is mainly secreted by the adipose tissue, mostly from mature adipocytes of the visceral compartment, where it exerts autocrine and paracrine activities. DPP4 can disrupt insulin signaling within the adipocyte and in other target cells and tissues, where it also favors the development of a proinflammatory environment. This is likely at the basis of the presence of elevated circulating DPP4 levels in several metabolic diseases. In this review, we summarize the most recent evidence of the role of the DPP4 as an adipokine-regulating glucose/insulin metabolism and fat homeostasis, with a particular focus on clinical outcomes associated with its increased secretion in the presence of adipose tissue accumulation and dysfunction.

Inhibition of dipeptidyl peptidase-4 averts free fatty acids deposition in the hearts of oral estrogen-progestin contraceptive-induced hyperinsulinemic female rats

Free fatty acid (FFA) deposition in non-adipose tissues such as the heart is a characteristic of insulin resistant states which feature hyperinsulinemia and dipeptidyl peptidase-4 (DPP-4) activation. Estrogen-progestin oral contraceptives (OC) treatment reportedly increased DPP-4 activity in rat tissue, and DPP-4 inhibitors have anti-diabetic and anti-inflammatory properties. This study aims to investigate the effects of DPP-4 inhibition on cardiac FFA deposition in estrogen-progestin-treated female rats. From our data, estrogen-progestin OC exposure in female rats led to elevated plasma insulin, cardiac DPP-4 activity, FFA and triglyceride (TG) accumulation, TG/high-density lipoprotein cholesterol (TG/HDL-C) ratio, adenosine deaminase/xanthine oxidase/uric acid pathway (ADA/XO/UA), lipid peroxidation, glycogen synthase activity, and alanine phosphatase; whereas cardiac glucose-6-phosphate dehydrogenase, Na+/K+-ATPase and nitric oxide (NO) were decreased. However, DPP-4 inhibition resulted in decreased plasma insulin, cardiac DPP-4 activity, FFA, TG, TG/HDL-C ratio, and alkaline phosphatase. These were accompanied by reduced ADA/XO/UA pathway, lipid peroxidation, and augmented NO and Na+/K+-ATPase in estrogen-progestin OC-treated rats. DPP-4 inhibition attenuated cardiac lipid deposition accompanied by reduced activity in the ADA/XO/UA pathway in estrogen-progestin OC-treated female rats. DPP-4 is therefore a plausible therapeutic target in cardiometabolic disorders.

Dipeptidyl Peptidase Inhibition Enhances CD8 T Cell Recruitment and Activates Intrahepatic Inflammasome in a Murine Model of Hepatocellular Carcinoma

Simple Summary

This study reported, for the first time, on the expression and activity of the dipeptidyl peptidase 4 (DPP4) family during the development of hepatocellular carcinoma (HCC). We also demonstrated that the pan-DPP inhibitory compound ARI-4175 significantly reduced the number of macroscopic liver nodules in a mouse HCC model. ARI-4175 increased intrahepatic inflammatory cell infiltration, CD8⁺ T cell numbers and caspase-1-mediated inflammasome activation in the HCC-bearing liver. Thus, this study provides promising data on the efficacy of ARI-4175 in the treatment of early-stage HCC. Targeting the DPP4 family may be a novel and effective approach to promote anti-tumour immunity in HCC via caspase-1 activation.

Abstract

The mRNA expression of the dipeptidyl peptidase 4 (DPP4) gene family is highly upregulated in human hepatocellular carcinoma (HCC) and is associated with poor survival in HCC patients. Compounds that inhibit the DPP4 enzyme family, such as talabostat and ARI-4175, can mediate tumour regression by immune-mediated mechanisms that are believed to include NLRP1 activation. This study investigated the expression and activity of the DPP4 family during the development of HCC and evaluated the efficacy of ARI-4175 in the treatment of early HCC in mice. This first report on this enzyme family in HCC-bearing mice showed DPP9 upregulation in HCC, whereas intrahepatic DPP8/9 and DPP4 enzyme activity levels decreased with age. We demonstrated that ARI-4175 significantly lowered the total number of macroscopic liver nodules in these mice. In addition, ARI-4175 increased intrahepatic inflammatory cell infiltration, including CD8⁺ T cell numbers, into the HCC-bearing livers. Furthermore, ARI-4175 activated a critical component of the inflammasome pathway, caspase-1, in these HCC-bearing livers. This is the first evidence of caspase-1 activation by a pan-DPP inhibitor in the liver. Our data suggest that targeting the DPP4 enzyme family may be a novel and effective approach to promote anti-tumour immunity in HCC via caspase-1 activation.

SARS-CoV-2 and diabetes: A potential therapeutic effect of dipeptidyl peptidase 4 inhibitors in diabetic patients diagnosed with COVID-19

COVID-19 is caused by severe acute respiratory syndrome coronavirus 2 and has become an urgent economic and health challenge. Dipeptidyl peptidase 4 (DPP4), also mentioned as a cluster of differentiation 26 (CD26) is a serine exopeptidase found in two arrangements: a soluble form (sDPP-4) and a plasma membrane-bound form. Because other coronaviruses enter the cells by binding to DPP-4, it has been speculated that DPP-4 inhibitors may exert activity against COVID-19. Therefore, this review aimed to summarize the potential therapeutic effect of dipeptidyl peptidase 4 inhibitors in diabetic patients diagnosed with COVID-19. To include different studies, publications related to Dipeptidyl peptidase-4 inhibitor use and clinical outcomes from COVID-19 were searched from the databases such as Web of Science, PubMed, Medline, Elsevier, Google Scholar, and SCOPUS, via English key terms. A direct engrossment of DPP4 in COVID-19 needs to be elucidated, there is also evidence confirming that DPP4 inhibitors exert anti-fibrotic and modulate inflammation activity. Thus, the use of DPP-4 inhibitors could reduce mortality due to COVID-19 or improve the progression of COVID-19; this evidence may support the management of diabetic patients diagnosed with COVID-19; however more well-designed investigation is urgently required.

Emerging therapeutic approaches for the treatment of NAFLD and type 2 diabetes mellitus

Non-alcoholic fatty liver disease (NAFLD) has emerged as the most prevalent liver disease in the world, yet there are still no approved pharmacological therapies to prevent or treat this condition. NAFLD encompasses a spectrum of severity, ranging from simple steatosis to non-alcoholic steatohepatitis (NASH). Although NASH is linked to an increased risk of hepatocellular carcinoma and cirrhosis and has now become the leading cause of liver failure-related transplantation, the majority of patients with NASH will ultimately die as a result of complications of type 2 diabetes mellitus (T2DM) and cardiometabolic diseases. Importantly, NAFLD is closely linked to obesity and tightly interrelated with insulin resistance and T2DM. Thus, targeting these interconnected conditions and taking a holistic attitude to the treatment of metabolic disease could prove to be a very beneficial approach. This Review will explore the latest relevant literature and discuss the ongoing therapeutic options for NAFLD focused on targeting intermediary metabolism, insulin resistance and T2DM to remedy the global health burden of these diseases.

Circulating dipeptidyl peptidase-4 is independently associated with the presence and severity of NAFLD/NASH in individuals with and without obesity and metabolic disease

INTRODUCTION

Dipeptidyl peptidase 4 (DPP4) levels are associated to metabolic and cardiovascular diseases in humans; initial evidence reported a relationship between DPP4 and chronic liver diseases. Aim of this study was to investigate hepatic and systemic DPP4 levels/activity in relation to NAFLD/NASH in individuals with and without metabolic disease.

METHODS

We recruited fifty-two obese individuals undergoing bariatric surgery and intra-operative liver biopsy at Sapienza University, Rome, Italy. The association between DPP4 levels/activity and NAFLD was also evaluated in 126 non-obese individuals recruited in the same setting.

RESULTS

NAFLD patients had significantly higher circulating DPP4 activity than no-NAFLD in both the obese and non-obese cohorts; plasma DPP4 activity and levels linearly correlated with steatosis grade and inflammation at the liver biopsy. Hepatic DPP4 mRNA was not associated to either its circulating levels/activity or NAFLD. In the multivariate logistic regression analysis on all the study participants (n = 178), higher circulating DPP4 activity was associated with NAFLD independently of potential confounders with OR (95% CI): 3.5 (1.2-10.21), p = 0.022.

CONCLUSIONS

This study demonstrates the coexistence of increased plasma DPP4 levels and activity in NAFLD. Circulating DPP4 measurement may represent a novel cost-effective strategy for NAFLD/NASH risk stratification and a potential tool for monitoring disease's progression in established NAFLD.

Serum levels of soluble dipeptidyl peptidase-4 in type 2 diabetes are associated with severity of liver fibrosis evaluated by transient elastography (FibroScan) and the FAST (FibroScan-AST) score, a novel index of non-alcoholic steatohepatitis with significant fibrosis

AIM

To investigate the relationship in people with type 2 diabetes between serum soluble dipeptidyl peptidase-4 (sDDP-4) and degree of liver fibrosis assessed as the liver stiffness measurement (LSM) and FAST (FibroScan-AST) score, both of which were measured by transient elastography (FibroScan).

SUBJECTS AND METHODS

In this cross-sectional study, we examined 115 patients with type 2 diabetes. With transient elastography (FibroScan), we assessed the controlled attenuation parameter (CAP) and liver stiffness measurement (LSM) as measures of hepatic steatosis and liver fibrosis, respectively. We calculated the FAST score, which identifies progressive non-alcoholic steatohepatitis (NASH), from CAP, LSM, and the serum aspartate aminotransferase level. Significant hepatic steatosis was defined as CAP ≥280 dB/m; and significant liver fibrosis, as LSM ≥ 8.0 kPa. LSM was divided into 3 severity levels: significant fibrosis (8.0 to <9.7 kPa); advanced fibrosis, (9.7 to <13.0 kPa); and liver cirrhosis (≥ 13.0 kPa).

RESULTS

Serum sDPP-4 correlated positively with liver enzymes, CAP, LSM, and FAST score. Multivariate analysis showed that LSM remained to be an independent factor for serum sDDP-4. Serum sDPP-4 was significantly higher in patients with LSM ≥ 8.0 kPa than in those with LSM <8.0 kPa and was significantly elevated in patients who are at risk for non-alcoholic steatohepatitis (NASH) with fibrosis (FAST score ≥ 035 or 0.67). Patients with both hepatic steatosis and liver fibrosis had the highest serum sDPP-4.

CONCLUSION

Serum sDPP-4 was strongly associated with severity of liver fibrosis evaluated by LSM and the FAST score and was markedly elevated in diabetic patients with LSM ≥ 13.0 kPa indicating probable cirrhosis.

Effects of the Combination of Evogliptin and Leucine on Insulin Resistance and Hepatic Steatosis in High-Fat Diet-Fed Mice

In this study, we aimed to investigate the effects of 8 weeks of treatment with a combination of evogliptin and leucine, a branched-chain amino acid, in mice with high-fat diet (HFD)-induced diabetes. Treatment with evogliptin alone or in combination with leucine reduced the body weight of the mice, compared to the case for those from the HFD control group. Long-term treatment with evogliptin alone or in combination with leucine resulted in a significant reduction in glucose intolerance; however, leucine alone did not affect postprandial glucose control, compared to the case for the mice from the HFD control group. Furthermore, the combination of evogliptin and leucine prevented HFD-induced insulin resistance, which was associated with improved homeostasis model assessment for insulin resistance, accompanied by markedly reduced liver fat deposition, hepatic triglyceride content, and plasma alanine aminotransferase levels. The combination of evogliptin and leucine increased the gene expression levels of hepatic peroxisome proliferator-activated receptor alpha, whereas those of the sterol regulatory element-binding protein 1 and stearoyl-CoA desaturase 1 were not altered, compared to the case in the HFD-fed mice (p<0.05). Thus, our results suggest that the combination of evogliptin and leucine may be beneficial for treating patients with type 2 diabetes and hepatic steatosis; however, further studies are needed to delineate the molecular mechanisms underlying the action of this combination.

Decrease of dipeptidyl peptidase 4 activity is associated with weight loss after bariatric surgery

Purpose

Dipeptidyl peptidase 4 (DPP4) is expressed and secreted by adipocytes. DPP4 induces insulin resistance independently of its effect on glucagon-like peptide 1, thus it is conceivable that DPP4 directly contributes to metabolic dysfunction in patients with morbid obesity. The aim of this study was to investigate the impact of weight loss induced by bariatric surgery on DPP4 activity, and whether these changes are associated with improvements in markers of metabolic dysfunction and fatty liver disease.

Materials and Methods

We included 68 non-diabetic patients who underwent bariatric surgery. Serum DPP4 activity was measured using a fluorogenic substrate before and after surgery.

Results

Results: After a median follow-up period of 12 (IQR 11-17) months, median serum DPP4 activity decreased from 230 (IQR: 194-273) to 193 (164-252) pmol/min (p=0.012). The decrease in DPP4 activity was significantly correlated with decreases in BMI, improved cholesterol levels, reduced hepatic injury markers as well as improved post-prandial insulin sensitivity. After multivariable adjustment, ΔDPP4 activity remained significantly associated with Δcholesterol (beta=0.341, p=0.025), ΔLDL cholesterol (beta=0.350, p=0.019), Δgamma-glutamyltransferase (beta=0.323, p=0.040) and ΔMatsuda index (beta=-0.386, p=0.045).

Conclusion

We demonstrated that weight loss induced by bariatric surgery results in decreased circulating DPP4 activity beyond the initial phase of weight loss. The associations between decreased DPP4 activity and improved cholesterol levels as well as hepatic injury markers point towards pleiotropic effects of DPP4 beyond glucose metabolism which warrant further investigation.

COVID-19 and comorbidities: A role for dipeptidyl peptidase 4 (DPP4) in disease severity?

The coronavirus disease 2019 (COVID-19) pandemic is caused by a novel betacoronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), similar to SARS-CoV and Middle East respiratory syndrome (MERS-CoV), which cause acute respiratory distress syndrome and case fatalities. COVID-19 disease severity is worse in older obese patients with comorbidities such as diabetes, hypertension, cardiovascular disease, and chronic lung disease. Cell binding and entry of betacoronaviruses is via their surface spike glycoprotein; SARS-CoV binds to the metalloprotease angiotensin-converting enzyme 2 (ACE2), MERS-CoV utilizes dipeptidyl peptidase 4 (DPP4), and recent modeling of the structure of SARS-CoV-2 spike glycoprotein predicts that it can interact with human DPP4 in addition to ACE2. DPP4 is a ubiquitous membrane-bound aminopeptidase that circulates in plasma; it is multifunctional with roles in nutrition, metabolism, and immune and endocrine systems. DPP4 activity differentially regulates glucose homeostasis and inflammation via its enzymatic activity and nonenzymatic immunomodulatory effects. The importance of DPP4 for the medical community has been highlighted by the approval of DPP4 inhibitors, or gliptins, for the treatment of type 2 diabetes mellitus. This review discusses the dysregulation of DPP4 in COVID-19 comorbid conditions; DPP4 activity is higher in older individuals and increased plasma DPP4 is a predictor of the onset of metabolic syndrome. DPP4 upregulation may be a determinant of COVID-19 disease severity, which creates interest regarding the use of gliptins in management of COVID-19. Also, knowledge of the chemistry and biology of DPP4 could be utilized to develop novel therapies to block viral entry of some betacoronaviruses, potentially including SARS-CoV-2.

DPP4 and ACE2 in Diabetes and COVID-19: Therapeutic Targets for Cardiovascular Complications?

COVID-19 outbreak, caused by severe acute respiratory syndrome (SARS)-CoV-2 coronavirus has become an urgent health and economic challenge. Diabetes is a risk factor for severity and mortality of COVID-19. Recent studies support that COVID-19 has effects beyond the respiratory tract, with vascular complications arising as relevant factors worsening its prognosis, then making patients with previous vascular disease more prone to severity or fatal outcome. Angiotensin-II converting enzime-2 (ACE2) has been proposed as preferred receptor for SARS-CoV-2 host infection, yet specific proteins participating in the virus entry are not fully known. SARS-CoV-2 might use other co-receptor or auxiliary proteins allowing virus infection. In silico experiments proposed that SARS-CoV-2 might bind dipeptidyl peptidase 4 (DPP4/CD26), which was established previously as receptor for MERS-CoV. The renin-angiotensin-aldosterone system (RAAS) component ACE2 and DPP4 are proteins dysregulated in diabetes. Imbalance of the RAAS and direct effect of soluble DPP4 exert deleterious vascular effects. We hypothesize that diabetic patients might be more affected by COVID-19 due to increased presence ACE2 and DPP4 mediating infection and contributing to a compromised vasculature. Here, we discuss the role of ACE2 and DPP4 as relevant factors linking the risk of SARS-CoV-2 infection and severity of COVID-19 in diabetic patients and present an outlook on therapeutic potential of current drugs targeted against RAAS and DPP4 to treat or prevent COVID-19-derived vascular complications. Diabetes affects more than 400 million people worldwide, thus better understanding of how they are affected by COVID-19 holds an important benefit to fight against this disease with pandemic proportions.

A Systematic Review of Newer Antidiabetic Agents in the Treatment of Nonalcoholic Fatty Liver Disease

OBJECTIVE

To evaluate glucagon-like peptide 1 receptor agonists (GLP-1 RAs), dipeptidyl-peptidase IV (DPP-4) inhibitors, and sodium-glucose cotransporter 2 (SGLT) inhibitors to treat nondiabetic and type 2 diabetes mellitus (T2DM) nonalcoholic fatty liver disease (NAFLD) as it relates to improvement in hepatosteatosis (HS) or steatohepatitis (SH).

DATA SOURCES

MEDLINE and CINAHL were searched from inception through May 1, 2020. Search terms included nonalcoholic steatohepatitis, nonalcoholic fatty liver disease, fatty liver, dipeptidyl-peptidase IV inhibitors, glucagon-like peptide-1 receptor agonists, and sodium-glucose transporter 2 inhibitors.

STUDY SELECTION AND DATA EXTRACTION

Full-text observational and randomized controlled studies in English were included. Patients diagnosed with NAFLD, treated with GLP-1 RAs, DPP-4 inhibitors, and SGLT2 inhibitors, with measures to evaluate HS or SH were evaluated.

DATA SYNTHESIS

Eight GLP-1 RA trials were reviewed; 7 GLP-1 RA trials showed improvement in HS. Two studies demonstrated improvement in liver histology in patients with SH. Seven SGLT2 inhibitor studies were reviewed; 6 studies demonstrated improvements in NAFLD. Five studies showed improvements in HS, whereas 1 displayed improvement in liver histology in NASH. Six studies that included DPP-4 inhibitors were evaluated, and only 2 demonstrated improvement in NASH.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Based on evidence reviewed, GLP-1 RAs and SGLT2 inhibitors decreased HS and SH in NAFLD patients, whereas DPP-4 inhibitor therapy was not effective for patients with HS.

CONCLUSIONS

Based on study data utilizing imaging studies and biopsy results, GLP-1 RAs or SGLT2 inhibitors can benefit NAFLD T2DM patients. Clinical trials with larger patient populations may augment these results.

Germacrone cooperates with dexmedetomidine to alleviate high-fat diet-induced type 2 diabetes mellitus via upregulating AMPKα1 expression

The aim of the present study was to investigate the effects of germacrone (GM) and dexmedetomidine (DEX) in treating type 2 diabetes mellitus (T2DM). A high-fat diet (HFD)-induced T2DM rat model was established. The experimental rats were divided into the control group, HFD group, GM treatment group, DEX treatment group and GM + DEX treatment group. In addition, adenosine monophosphate-activated protein kinase (AMPK) inhibitor compound C (CC) was used to inhibit AMPKα1 expression. All rats received their respective treatment daily for 21 days. Blood glucose and lipid levels, apoptosis of hepatic cells, and levels of inflammatory factors and oxidative stress indicators in serum samples were evaluated. Protein expression of AMPKα1 and its downstream targets were also investigated. Results demonstrated that blood glucose concentration, blood lipid indicators (endothelin, total cholesterol, triglyceride and low density lipoprotein cholesterol), cell apoptosis in liver tissues, total oxidant status, malondialdehyde, interleukin (IL)-6, tumor necrosis factor-α (TNF-α) and IL-1β levels in serum were increased in the high-fat group compared to the control but decreased following GM and/or DEX treatment. By contrast, high-density lipoprotein cholesterol and antioxidative stress indicator superoxide dismutase (SOD) were decreased in the high-fat group but increased following GM and/or DEX treatment. Protein expression of AMPKα1 and the catabolic genes carnitine palmitoyltransferase-1, peroxisome proliferator-activated receptor-α and acyl coenzyme A were decreased whilst anabolic genes, including sterol regulatory element binding protein-1c, fatty acid synthase and diacylglycerol acyltransferase-2, were increased in the HFD group. These effects were attenuated by GM and/or DEX treatment. AMPKα1 inhibition resulted in decreased SOD and increased cell apoptosis in liver tissues as well as increased IL-6, TNF-α and IL-1β levels compared with the HFD group. However, these effects were abolished following treatment with CC, GM and DEX together. Taken together these results indicated that GM worked synergistically with DEX to attenuate symptoms of high-fat-induced T2DM, with the effect potentially involving an increase in AMPKα1 expression.

Greater circulating DPP4 activity is associated with impaired flow-mediated dilatation in adults with type 2 diabetes mellitus

BACKGROUND AND AIM

Dipeptidyl peptidase 4 (DPP4) is a key enzyme involved in the regulation of the incretin system exerted by cleaving the glucagon-like peptide 1 (GLP-1); the blockage of DPP4, exerted by the antidiabetic agents DPP4-inhibitors (DPP4-I), results in greater GLP-1 concentration and improved glycaemic control. DPP4 acts also as a pro-inflammatory molecule and mediates vascular damage in experimental models. The relationship between DPP4 activity and endothelial function in diabetes has not been explored yet. Aim of this study was to investigate systemic plasma DPP4 activity in relation to endothelial function in patients with type 2 diabetes mellitus (T2DM).

METHODS AND RESULTS

Sixty-two T2DM individuals were recruited in our Diabetes outpatient clinics, Sapienza University, Rome, Italy. All participants underwent complete clinical work-up; endothelial function was evaluated by flow-mediated dilatation (FMD) test; plasma DPP4 activity was assessed by measuring the 7-amino-4-methylcoumarin (AMC) cleavage rate from the synthetic substrate H-glycyl-prolyl-AMC and compared with DPP4 activity measured in sixty-two age-, sex-, BMI-matched non-diabetic subjects. Patients with T2DM had significantly higher DPP4 activity than non-diabetic individuals (211,466 ± 87657 vs 158,087 ± 60267 nmol/min/ml, p < 0.001); in T2DM patients, greater DPP4 activity significantly correlated with lower FMD whereas was not associated with BMI and metabolic control. Greater systemic DPP4 activity was an independent predictor of reduced FMD after adjusting for age, gender and other confounders.

CONCLUSIONS

Circulating DPP4 activity is increased in individuals with T2DM and associated with signs of endothelial dysfunction such as impaired FMD. DPP4 may negatively affect endothelial function through mechanisms beyond glucose homeostasis and metabolic control.

Circulating Levels of Soluble Dipeptidyl Peptidase-4 Are Dissociated from Inflammation and Induced by Enzymatic DPP4 Inhibition

Dipeptidyl peptidase-4 (DPP-4) controls glucose homeostasis through enzymatic termination of incretin action. We report that plasma DPP-4 activity correlates with body weight and fat mass, but not glucose control, in mice. Genetic disruption of adipocyte Dpp4 expression reduced plasma DPP-4 activity in older mice but did not perturb incretin levels or glucose homeostasis. Knockdown of hepatocyte Dpp4 completely abrogated the obesity-associated increase in plasma DPP-4 activity, reduced liver cytokine expression, and partially attenuated inflammation in adipose tissue without changes in incretin levels or glucose homeostasis. In contrast, circulating levels of soluble DPP4 (sDPP4) were dissociated from inflammation in mice with endothelial-selective or global genetic inactivation of Dpp4. Remarkably, inhibition of DPP-4 enzymatic activity upregulated circulating levels of sDPP4 originating from endothelial or hematopoietic cells without inducing systemic or localized inflammation. Collectively, these findings reveal unexpected complexity in regulation of soluble versus enzymatic DPP-4 and control of inflammation and glucose homeostasis.

Lecithin nano-liposomal particle as a CRISPR/Cas9 complex delivery system for treating type 2 diabetes

BACKGROUND

Protein-based Cas9 in vivo gene editing therapeutics have practical limitations owing to their instability and low efficacy. To overcome these obstacles and improve stability, we designed a nanocarrier primarily consisting of lecithin that can efficiently target liver disease and encapsulate complexes of Cas9 with a single-stranded guide RNA (sgRNA) ribonucleoprotein (Cas9-RNP) through polymer fusion self-assembly.

RESULTS

In this study, we optimized an sgRNA sequence specifically for dipeptidyl peptidase-4 gene (DPP-4) to modulate the function of glucagon-like peptide 1. We then injected our nanocarrier Cas9-RNP complexes directly into type 2 diabetes mellitus (T2DM) db/db mice, which disrupted the expression of DPP-4 gene in T2DM mice with remarkable efficacy. The decline in DPP-4 enzyme activity was also accompanied by normalized blood glucose levels, insulin response, and reduced liver and kidney damage. These outcomes were found to be similar to those of sitagliptin, the current chemical DPP-4 inhibition therapy drug which requires recurrent doses.

CONCLUSIONS

Our results demonstrate that a nano-liposomal carrier system with therapeutic Cas9-RNP has great potential as a platform to improve genomic editing therapies for human liver diseases.

Dipeptidyl peptidase-4 inhibition protects the liver of insulin-resistant female rats against triglyceride accumulation by suppressing uric acid

Dipeptidyl peptidase-4 (DPP-4) inhibition has been shown to exert beneficial effects against insulin resistance (IR) and type 2 diabetes. Combined oral contraceptive (COC) treatment is associated with impaired glucose and lipid metabolism but the mechanisms are elusive. We therefore, hypothesized that DPP-4 inhibition ameliorates COC-induced glucose dysregulation and hepatic triglyceride (TG) accumulation through adenosine deaminase (ADA) /xanthine oxidase (XO) /uric acid-dependent pathway. Female Wistar rats received (po) vehicle and COC (1.0 μg ethinylestradiol plus 5.0 μg levonorgestrel; po) with or without DPP-4 inhibitor (sitagliptin; 100 mg/kg; po) for 8 weeks (n = 6/group). Glucose dysmetabolism was assessed by elevated fasting blood glucose, impaired oral glucose tolerance test and homeostatic model assessment of IR. Treatment with COC led to increased plasma fasting glucose, triglyceride-glucose index, 1-h postload glucose response, insulin, free fatty acid, IR and impaired glucose tolerance. COC treatment also resulted in increased plasma and hepatic TG, TG/HDL-cholesterol ratio, malondialdehyde, uric acid (plasma; 25.2 ± 0.6 mg/dl; hepatic 128.9 ± 8.0 mg/100 mg tissue), lactate dehydrogenase, DPP-4, ADA and XO (plasma;10.5 ± 1.1 U/L; hepatic 21.2 ± 1.4 U/g protein) activities. Likewise, COC led to reduction in nitric oxide level. However, DPP-4 inhibition significantly ameliorated these alterations induced by COC treatment through suppression of uric acid (plasma; 15.1 ± 1.0 mg/dl, hepatic; 75.6 ± 5.0 mg/100 mg tissue), XO (plasma; 4.1 ± 0.9 U/L, hepatic; 8.7 ± 0.4 U/g protein), ADA and DPP-4 activities suggesting their involvement in glucose dysregulation and hepatic TG accumulation induced by COC treatment. Therefore, DPP-4 inhibition would impact positively on cardiometabolic disorders, at least in part, through XO, ADA and uric acid suppression.

Effect of Radix isatidis polysaccharide on alleviating insulin resistance in type 2 diabetes mellitus cells and rats

OBJECTIVES

The objective of this paper was to explore the effects of Radix isatidis polysaccharide (RIP) extracted from Radix isatis on alleviating insulin resistance.

METHODS

The insulin resistance models of 3T3-L1 preadipocytes and type 2 diabetic rats were established to evaluate the insulin resistance activity of RIP.

KEY FINDINGS

Radix isatidis polysaccharide within the concentration range of 25-100 μg/ml could reduce cell supernatant glucose and TNF-α levels (P < 0.01) and increase the expression of PI-3K P85, Glut4, IRS-1 and Akt protein in symptoms of IR 3T3-L1 preadipocytes. In the meantime, RIP contributed to relieve the weight loss of diabetic rats whose liver weight and liver index were decreased due to the effects of RIP. Experiments in rats also showed that RIP had capacity in reduced serum TC, TG, LDL-C, FFA, FBG, FINS, MDA, ALT, AST activities and increased serum HDL-C, SOD, ISI (P < 0.05 or 0.01). In addition, the oral glucose tolerance in rats was improved (P < 0.05) and liver damage was restored due to RIP.

CONCLUSIONS

Radix isatidis polysaccharide significantly alleviates insulin resistance in 3T3-L1 preadipocytes and type 2 diabetic rats. These beneficial effects of RIP may associate with their roles in improving the glucose metabolism, lipid metabolism and oxidative stress.

Sodium acetate improves disrupted glucoregulation and hepatic triglyceride content in insulin-resistant female rats: involvement of adenosine deaminase and dipeptidyl peptidase-4 activities

Combined oral contraceptive (COC) treatment has been shown to be associated with glucose deregulation and increased triglyceride levels, but the mechanisms are elusive. Soluble dipeptidyl peptidase-4 (sDPP-4) and adenosine deaminase (ADA) are involved in the initiation and/or progression of cardiometabolic disorders. We therefore, hypothesized that increased DPP-4 and ADA activities are involved in glucose deregulation and hepatic triglyceride accumulation induced by COC treatment. This study also investigated whether short-chain fatty acid, acetate, would protect against COC-induced dysmetabolic effects. Female Wistar rats received (p.o.) vehicle and COC (1.0 μg ethinylestradiol plus 5.0 μg levonorgestrel) with or without sodium acetate (ACE; 200 mg) for 8 weeks. Treatment with COC led to increased plasma triglyceride-glucose index, 1-h postload glucose response, insulin, free fatty acid, insulin resistance, and impaired glucose tolerance. COC treatment also resulted in increased plasma and hepatic triglycerides (TG), TG/HDL-cholesterol ratio, malondialdehyde, uric acid, lactate dehydrogenase, DPP-4, ADA, and xanthine oxidase (XO) activities. On the other hand, COC led to reduction in nitric oxide level. However, ACE significantly ameliorated the alterations induced by COC treatment, but XO activity remains elevated during COC treatment. This result also demonstrates that increased DPP-4 and ADA activities are at least in part involved in glucose deregulation and hepatic TG accumulation induced by COC treatment. Therefore, sodium acetate would impact positively on cardiometabolic disorders, at least in part, by inhibition of DPP-4 and ADA activities.

Apoptosis and non-alcoholic fatty liver diseases

The number of patients with nonalcoholic fatty liver diseases (NAFLD) including nonalcoholic steatohepatitis (NASH), has been increasing. NASH causes cirrhosis and hepatocellular carcinoma (HCC) and is one of the most serious health problems in the world. The mechanism through which NASH progresses is still largely unknown. Activation of caspases, Bcl-2 family proteins, and c-Jun N-terminal kinase-induced hepatocyte apoptosis plays a role in the activation of NAFLD/NASH. Apoptotic hepatocytes stimulate immune cells and hepatic stellate cells toward the progression of fibrosis in the liver through the production of inflammasomes and cytokines. Abnormalities in glucose and lipid metabolism as well as microbiota accelerate these processes. The production of reactive oxygen species, oxidative stress, and endoplasmic reticulum stress is also involved. Cell death, including apoptosis, seems very important in the progression of NAFLD and NASH. Recently, inhibitors of apoptosis have been developed as drugs for the treatment of NASH and may prevent cirrhosis and HCC. Increased hepatocyte apoptosis may distinguish NASH from NAFLD, and the improvement of apoptosis could play a role in controlling the development of NASH. In this review, the association between apoptosis and NAFLD/NASH are discussed. This review could provide their knowledge, which plays a role in seeing the patients with NAFLD/NASH in daily clinical practice.

Elevated hepatic DPP4 activity promotes insulin resistance and non-alcoholic fatty liver disease

OBJECTIVE

Increased hepatic expression of dipeptidyl peptidase 4 (DPP4) is associated with non-alcoholic fatty liver disease (NAFLD). Whether this is causative for the development of NAFLD is not yet clarified. Here we investigate the effect of hepatic DPP4 overexpression on the development of liver steatosis in a mouse model of diet-induced obesity.

METHODS

Plasma DPP4 activity of subjects with or without NAFLD was analyzed. Wild-type (WT) and liver-specific Dpp4 transgenic mice (Dpp4-Liv-Tg) were fed a high-fat diet and characterized for body weight, body composition, hepatic fat content and insulin sensitivity. In vitro experiments on HepG2 cells and primary mouse hepatocytes were conducted to validate cell autonomous effects of DPP4 on lipid storage and insulin sensitivity.

RESULTS

Subjects suffering from insulin resistance and NAFLD show an increased plasma DPP4 activity when compared to healthy controls. Analysis of Dpp4-Liv-Tg mice revealed elevated systemic DPP4 activity and diminished active GLP-1 levels. They furthermore show increased body weight, fat mass, adipose tissue inflammation, hepatic steatosis, liver damage and hypercholesterolemia. These effects were accompanied by increased expression of PPARγ and CD36 as well as severe insulin resistance in the liver. In agreement, treatment of HepG2 cells and primary hepatocytes with physiological concentrations of DPP4 resulted in impaired insulin sensitivity independent of lipid content.

CONCLUSIONS

Our results give evidence that elevated expression of DPP4 in the liver promotes NAFLD and insulin resistance. This is linked to reduced levels of active GLP-1, but also to auto- and paracrine effects of DPP4 on hepatic insulin signaling.

Association between Serum Dipeptidyl Peptidase-4 Concentration and Obesity-related Factors in Health Screen Examinees

Background

Dipeptidyl peptidase-4 (DPP-4) is an aminopeptidase that inhibits the enzymatic degradation of glucagon-like peptide-1, glucose-dependent insulinotropic polypeptides, neuropeptides, and various chemokines. Recent studies reported that serum DPP-4 concentration is correlated with clinical parameters of obesity. However, research on these correlations has never been conducted in Korea. Therefore, we investigated the relationship between serum DPP-4 concentration and various clinical parameters of obesity in the Korean population.

Methods

Patients who visited the Health Promotion Center at Keimyung University Dongsan Medical Center for a regular medical examination between January 2013 and March 2013 and consented to participate in this study were included. We measured and analyzed parameters of obesity. In addition, serum DPP-4 concentration was determined using an enzyme-linked immunosorbent assay kit.

Results

Serum DPP-4 concentration was positively correlated with lean body mass, total cholesterol level, and creatinine level. Serum DPP-4 concentration was higher in the obese group than in the normal body mass index (BMI) group. No significant difference in serum DPP-4 concentration was found between the metabolically healthy group and metabolically unhealthy group.

Conclusion

Serum DPP-4 concentration was higher in the obesity group than in the normal BMI group, which was associated with obesity-related factors.

Dipeptidyl Peptidase-4, Wound Healing, Scarring, and Fibrosis

Scarring and fibrosis are an enormous public health concern, resulting in excessive morbidity and mortality in addition to countless lost health care dollars. Recent advances in cell and developmental biology promise a better understanding of scarring and fibrosis and may translate to new clinical therapies.

High circulating plasma dipeptidyl peptidase- 4 levels in non-obese Asian Indians with type 2 diabetes correlate with fasting insulin and LDL-C levels, triceps skinfolds, total intra-abdominal adipose tissue volume and presence of diabetes: a case-control study

AIM

To evaluate circulating plasma dipeptidyl peptidase-4 (DPP4) levels in non-obese Asian Indians with type 2 diabetes mellitus (T2DM), and to correlate these with metabolic profile and measures of anthropometry, skinfolds, abdominal adipose tissue depots, pancreatic volume, and liver span.

METHODOLOGY

Non-obese (body mass index (BMI) <25 kg/m²) patients with T2DM (cases, n=93), diagnosed within 1 year from recruitment, on metformin therapy and BMI-matched, and non-diabetic subjects (controls, n=40) were compared. Measurements of blood glucose, glycosylated hemoglobin, plasma insulin levels, lipid profile, hepatic transaminases and plasma DPP4 levels, and quantification of abdominal fat depots, pancreatic volume and liver span (MRI scan), were done.

RESULTS

Significantly higher (p<0.001) circulating plasma DPP4 levels were observed in cases as compared to controls. Specifically, in patients with T2DM with non-alcoholic fatty liver disease (NAFLD) (n=48), the mean plasma DPP4 level (52.6±27.8 ng/mL) was significantly higher (p<0.05) as compared with those without NAFLD (n=43; 47±28.3 ng/mL). Significant positive correlation was observed for circulating plasma DPP4 levels with waist-to-hip ratio, total intra-abdominal adipose volume, and liver span. Fasting serum insulin, low-density lipoprotein cholesterol (LDL-C), triceps skinfolds, total intra-abdominal adipose tissue volume and presence of T2DM were significant determinants of circulating plasma DPP4 levels.

CONCLUSION

Non-obese Asian Indian patients with T2DM and on metformin therapy have significantly higher circulating plasma DPP4 levels as compared to non-obese non-diabetic controls, and these levels correlate with fasting insulin and LDL-C levels, upper limb subcutaneous adipose tissue, intra-abdominal adiposity and presence of diabetes.

Circulating fibroblast activation protein and dipeptidyl peptidase 4 in rheumatoid arthritis and systemic sclerosis

AIM

To quantify circulating fibroblast activation protein (cFAP) and dipeptidyl peptidase 4 (cDPP4) protease activities in patients with rheumatoid arthritis (RA), systemic sclerosis (SSc), and a control group with mechanical back pain and to correlate plasma levels with disease characteristics.

METHODS

Plasma was collected from patients with RA (n = 73), SSc (n = 37) and control subjects (n = 26). DPP4 and FAP were quantified using specific enzyme activity assays.

RESULTS

Median cDPP4 was significantly lower in the RA group (P = 0.02), and SSc group (P = 0.002) compared with controls. There were no significant differences in median cFAP between the three groups. DPP4 and FAP demonstrated a negative correlation with inflammatory markers and duration of disease. There were no associations with disease subtypes in RA, including seropositive and erosive disease. Decreased cDPP4 was found in SSc patients with myositis. Plasma FAP was lower in RA patients receiving prednisone (P = 0.001) or leflunomide (P = 0.04), but higher with biologic agents (P = 0.01). RA patients receiving leflunomide also had decreased cDPP4 (P = 0.014). SSc patients receiving prednisone (P = 0.02) had lower cDPP4 but there was no association with cFAP.

CONCLUSIONS

No association was found between cFAP and RA or SSc. Plasma DPP4 was decreased in RA and SSc when compared with controls. cDPP4 and cFAP correlated negatively with inflammatory markers and there were no significant correlations with disease characteristics in this RA cohort.

The pro-fibrotic role of dipeptidyl peptidase 4 in carbon tetrachloride-induced experimental liver injury

Liver fibrosis is a progressive pathological process involving inflammation and extracellular matrix deposition. Dipeptidyl peptidase 4 (DPP4), also known as CD26, is a cell surface glycoprotein and serine protease. DPP4 binds to fibronectin, can inactivate specific chemokines, incretin hormone and neuropeptides, and influences cell adhesion and migration. Such properties suggest a pro-fibrotic role for this peptidase but this hypothesis needs in vivo examination. Experimental liver injury was induced with carbon tetrachloride (CCl₄) in DPP4 gene knockout (gko) mice. DPP4 gko had less liver fibrosis and inflammation and fewer B cell clusters than wild type mice in the fibrosis model. DPP4 inhibitor-treated mice also developed less liver fibrosis. DNA microarray and PCR showed that many immunoglobulin (Ig) genes and some metabolism-associated transcripts were differentially expressed in the gko strain compared with wild type. CCl₄-treated DPP4 gko livers had more IgM⁺ and IgG⁺ intrahepatic lymphocytes, and fewer CD4⁺, IgD⁺ and CD21⁺ intrahepatic lymphocytes. These data suggest that DPP4 is pro-fibrotic in CCl₄-induced liver fibrosis and that the mechanisms of DPP4 pro-fibrotic action include energy metabolism, B cells, NK cells and CD4⁺ cells.

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.

Linagliptin alleviates fatty liver disease in diabetic db/db mice

AIM

To study the effects of linagliptin on the structural signs of non-alcoholic fatty liver disease (NAFLD) in db/db mice.

METHODS

Male diabetic db/db mice (BKS.Cg-Dock7^m+/⁺Lepr^db/J) aged 10 wk received the dipeptidyl peptidase 4 (DPP4) inhibitor linagliptin (10 mg/kg) or saline as a placebo once per day by gavage for 8 wk. Intact db/db mice served as controls. Structural changes in the liver were analyzed from light and electron microscopic images of sections from intact, placebo-treated and linagliptin-treated animals. We estimated the changes in hepatocytes, sinusoidal cells, liver microvasculature and lymphatic roots. Hepatic staining for lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) was assessed by immunohistochemistry.

RESULTS

In 18-wk-old diabetic mice, liver steatosis (predominantly microvesicular and mediovesicular steatosis) was accompanied by dilation of the roots of the lymphatic system, interlobular blood vessels and bile canaliculi. Compared to saline-treated mice, linagliptin-treated mice exhibited a reduction in the mean numeral densities of hepatocytes with lipid droplets (92.4% ± 1.7% vs 64.9% ± 5.8% per field of view, P = 0.0002) and a lower proportion of hepatocytes with a high density of lipid droplets (20.7% ± 3.6% vs 50.4% ± 3.1%, P = 0.0007). We observed heterogeneous hepatocytes and relatively preserved cell structures in the linagliptin group. Dilation of blood and lymphatic vessels, as well as ultrastructural changes in the hepatocyte endoplasmic reticulum and mitochondria, were alleviated by linagliptin treatment. In intact and placebo-treated mice, immunohistochemical staining for LYVE-1 was observed in the endothelial cells of interlobular lymphatic vessels and on the membranes of some endothelial sinusoidal cells. We observed an enlarged LYVE-1 reaction area in linagliptin-treated mice compared to intact and placebo-treated mice. The improvement in the structural parameters of the liver in linagliptin-treated mice was independent to changes in the plasma glucose levels.

CONCLUSION

The DPP4 inhibitor linagliptin alleviates liver steatosis and structural changes in the hepatic microvasculature and lymphatic roots in a model of NAFLD in diabetic db/db mice.

Differentiation of human foreskin fibroblast-derived induced pluripotent stem cells into hepatocyte-like cells

The aim of this study was to investigate the differentiation potential of induced pluripotent stem cells (iPSCs) derived from human foreskin fibroblasts (HFFs) into hepatocyte-like cells (HLCs). The iPSCs were firstly induced by transduction of OCT4, SOX2, KLF4, and c-MYC into HFFs using retrovirus. Afterwards, expressions of pluripotency factors were identified by semiquantitative reverse transcription-polymerase chain reaction and immunofluorescence staining, and karyotype, embryoid, and teratoma were observed by microscope. Then, iPSCs were gradually differentiated into endoderm cells, hepatic progenitor cells, and mature HLCs by special culture medium. During this process, differentiation efficiency into each kind of cells was evaluated by detecting SOX17, HNF4a, and ALB using flow cytometry, respectively. Besides, enzyme-linked immunosorbent assay was conducted to detect the secretion of ALB in iPSC-induced HLCs and quantitative reverse transcription-polymerase chain reaction was performed to detect the expression levels of hepatocyte-specific genes. The iPSCs were successfully induced by HFFs, which exhibited typical embryonic stem cells morphology, positive alkaline phosphatase staining, normal diploid karyotype, and positive expression of various pluripotency factors. Meanwhile, spherical embryoid and teratoma with 3 germ layers were formed by iPSCs. The iPSCs were consecutively induced into endoderm cells, hepatic progenitor cells and mature HLCs, and the differentiation efficiency was 55.7 ± 2.9%, 45.7 ± 4.8%, and 35.0 ± 3.9%, respectively. Besides, the secretion of ALB and expression of various hepatocyte-specific genes was highly detected in iPSC-induced HLCs. The iPSCs were successfully derived from HFFs and then differentiated into HLCs, which proved a new source for hepatocyte transplantation.

HIGHLIGHTS

HFFs were successfully induced into iPSCs by transduction of OCT4, SOX2, KLF4, and c-MYC. Positive expressions of various pluripotency factors were exhibited in HFFs-induced iPSCs. The iPSCs were consecutively induced into endoderm cells, hepatic progenitor cells, and mature HLCs. Various hepatocyte-specific genes were highly expressed in iPSC-induced HLCs.

Non-alcoholic fatty liver disease and diabetes

Non-alcoholic fatty liver disease (NAFLD) and type 2 diabetes (T2DM) are common conditions that regularly co-exist and can act synergistically to drive adverse outcomes. The presence of both NAFLD and T2DM increases the likelihood of the development of complications of diabetes (including both macro- and micro- vascular complications) as well as augmenting the risk of more severe NAFLD, including cirrhosis, hepatocellular carcinoma and death. The mainstay of NAFLD management is currently to reduce modifiable metabolic risk. Achieving good glycaemic control and optimising weight loss are pivotal to restricting disease progression. Once cirrhosis has developed, it is necessary to screen for complications and minimise the risk of hepatic decompensation. Therapeutic disease modifying options for patients with NAFLD are currently limited. When diabetes and NAFLD co-exist, there are published data that can help inform the clinician as to the most appropriate oral hypoglycaemic agent or injectable therapy that may improve NAFLD, however most of these data are drawn from observations in retrospective series and there is a paucity of well-designed randomised double blind placebo controlled studies with gold-standard end-points. Furthermore, given the heterogeneity of inclusion criteria and primary outcomes, as well as duration of follow-up, it is difficult to draw robust conclusions that are applicable across the entire spectrum of NAFLD and diabetes. In this review, we have summarised and critically evaluated the available data, with the aim of helping to inform the reader as to the most pertinent issues when managing patients with co-existent NAFLD and T2DM.

Hepatocellular carcinoma: Mouse models and the potential roles of proteases

Primary liver cancer is the second most common cause of mortality from cancer. The most common models of hepatocellular carcinoma, which use a chemical and/or metabolic insult, xenograft, or genetic manipulation, are discussed in this review. In the tumour microenvironment lymphocytes, fibroblasts, endothelial cells and antigen presenting cells are important determinants of cell fate. These cells make a range of proteases that modify the biological activity of other proteins, particularly extracellular matrix proteins that alter cell migration of tumour cells, fibroblasts and leucocytes, and chemokines that alter leucocyte migration. The DPP4 family of post-proline peptidase enzymes modifies cell movement and the activities of many bioactive molecules including growth factors and chemokines.

Mitochondrial Molecular Pathophysiology of Nonalcoholic Fatty Liver Disease: A Proteomics Approach

Nonalcoholic fatty liver disease (NAFLD) is a chronic liver condition that can progress to nonalcoholic steatohepatitis, cirrhosis and cancer. It is considered an emerging health problem due to malnourishment or a high-fat diet (HFD) intake, which is observed worldwide. It is well known that the hepatocytes’ apoptosis phenomenon is one of the most important features of NAFLD. Thus, this review focuses on revealing, through a proteomics approach, the complex network of protein interactions that promote fibrosis, liver cell stress, and apoptosis. According to different types of in vitro and murine models, it has been found that oxidative/nitrative protein stress leads to mitochondrial dysfunction, which plays a major role in stimulating NAFLD damage. Human studies have revealed the importance of novel biomarkers, such as retinol-binding protein 4, lumican, transgelin 2 and hemoglobin, which have a significant role in the disease. The post-genome era has brought proteomics technology, which allows the determination of molecular pathogenesis in NAFLD. This has led to the search for biomarkers which improve early diagnosis and optimal treatment and which may effectively prevent fatal consequences such as cirrhosis or cancer.

Neuropeptide Y is a physiological substrate of fibroblast activation protein: Enzyme kinetics in blood plasma and expression of Y2R and Y5R in human liver cirrhosis and hepatocellular carcinoma

Fibroblast activation protein (FAP) is a dipeptidyl peptidase (DPP) and endopeptidase that is weakly expressed in normal adult human tissues but is greatly up-regulated in activated mesenchymal cells of tumors and chronically injured tissue. The identities and locations of target substrates of FAP are poorly defined, in contrast to the related protease DPP4. This study is the first to characterize the physiological substrate repertoire of the DPP activity of endogenous FAP present in plasma. Four substrates, neuropeptide Y (NPY), peptide YY, B-type natriuretic peptide and substance P, were analyzed by mass spectrometry following proteolysis in human or mouse plasma, and by in vivo localization in human liver tissues with cirrhosis and hepatocellular carcinoma (HCC). NPY was the most efficiently cleaved substrate of both human and mouse FAP, whereas all four peptides were efficiently cleaved by endogenous DPP4, indicating that the in vivo degradomes of FAP and DPP4 differ. All detectable DPP-specific proteolysis and C-terminal processing of these neuropeptides was attributable to FAP and DPP4, and plasma kallikrein, respectively, highlighting their combined physiological significance in the regulation of these neuropeptides. In cirrhotic liver and HCC, NPY and its receptor Y2R, but not Y5R, were increased in hepatocytes near the parenchymal-stromal interface where there is an opportunity to interact with FAP expressed on nearby activated mesenchymal cells in the stroma. These novel findings provide insights into the substrate specificity of FAP, which differs greatly from DPP4, and reveal a potential function for FAP in neuropeptide regulation within liver and cancer biology.

Antidiabetic Effect of Galantamine: Novel Effect for a Known Centrally Acting Drug

The cholinergic anti-inflammatory pathway is one of the putative biochemical pathways that link diabetes with Alzheimer disease. Hence, we aimed to verify the potential antidiabetic effect of galantamine, unveil the possible mechanisms and evaluate its interaction with vildagliptin. The n5-STZ rat model was adopted and the diabetic animals were treated with galantamine and/or vildagliptin for 4 weeks. Galantamine lowered the n5-STZ-induced elevation in body weight, food/water intake, serum levels of glucose, fructosamine, and ALT/AST, as well as AChE in the tested organs. Moreover, it modulated successfully the lipid profile assessed in serum, liver, and muscle, and increased serum insulin level, as well as % β-cell function, in a pattern similar to that of vildagliptin. Additionally, galantamine confirmed its antioxidant (Nrf2, TAC, MDA), anti-inflammatory (NF-κB, TNF-α, visfatin, adiponectin) and anti-apoptotic (caspase-3, cytochrome c) capabilities by altering the n5-STZ effect on all the aforementioned parameters. On the molecular level, galantamine/vildagliptin have improved the insulin (p-insulin receptor, p-Akt, GLUT4/GLUT2) and Wnt/β-catenin (p-GSK-3β, β-catenin) signaling pathways. On almost all parameters, the galantamine effects surpassed that of vildagliptin, while the combination regimen showed the best effects. The present results clearly proved that galantamine modulated glucose/lipid profile possibly through its anti-oxidant, -apoptotic, -inflammatory and -cholinesterase properties. These effects could be attributed partly to the enhancement of insulin and Wnt/β-catenin signaling pathways. Galantamine can be strongly considered as a potential antidiabetic agent and as an add-on therapy with other oral antidiabetics.