The expanding incretin universe: from basic biology to clinical translation.

Incretin hormones, principally glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1(GLP-1), potentiate meal-stimulated insulin secretion through direct (GIP + GLP-1) and indirect (GLP-1) actions on islet ß-cells. GIP and GLP-1 also regulate glucagon secretion, through direct and indirect pathways. The incretin hormone receptors (GIPR and GLP-1R) are widely distributed beyond the pancreas, principally in the brain, cardiovascular and immune systems, gut and kidney, consistent with a broad array of extrapancreatic incretin actions. Notably, the glucoregulatory and anorectic activities of GIP and GLP-1 have supported development of incretin-based therapies for the treatment of type 2 diabetes and obesity. Here we review evolving concepts of incretin action, focusing predominantly on GLP-1, from discovery, to clinical proof of concept, to therapeutic outcomes. We identify established vs uncertain mechanisms of action, highlighting biology conserved across species, while illuminating areas of active investigation and uncertainty that require additional clarification.

Honokiol activates the LKB1-AMPK signaling pathway and attenuates the lipid accumulation in hepatocytes.

Honokiol is a bioactive neolignan compound isolated from the species of Magnolia. This study was designed to elucidate the cellular mechanism by which honokiol alleviates the development of non-alcoholic steatosis. HepG2 cells were treated with honokiol for 1h, and then exposed to 1mM free fatty acid (FFA) for 24h to simulate non-alcoholic steatosis in vitro. C57BL/6 mice were fed with a high-fat diet for 28days, and honokiol (10mg/kg/day) was daily treated. Honokiol concentration-dependently attenuated intracellular fat overloading and triglyceride (TG) accumulation in FFA-exposed HepG2 cells. These effects were blocked by pretreatment with an AMP-activated protein kinase (AMPK) inhibitor. Honokiol significantly inhibited sterol regulatory element-binding protein-1c (SREBP-1c) maturation and the induction of lipogenic proteins, stearoyl-CoA desaturase-1 (SCD-1) and fatty acid synthase (FAS) in FFA-exposed HepG2 cells, but these effects were blocked by pretreatment of an AMPK inhibitor. Honokiol induced AMPK phosphorylation and subsequent acetyl-CoA carboxylase (ACC) phosphorylation, which were inhibited by genetic deletion of liver kinase B1 (LKB1). Honokiol stimulated LKB1 phosphorylation, and genetic deletion of LKB1 blocked the effect of honokiol on SREBP-1c maturation and the induction of SCD-1 and FAS proteins in FFA-exposed HepG2 cells. Honokiol attenuated the increases in hepatic TG and lipogenic protein levels and fat accumulation in the mice fed with high-fat diet, while significantly induced LKB1 and AMPK phosphorylation. Taken together, our findings suggest that honokiol has an anti-lipogenic effect in hepatocytes, and this effect may be mediated by the LKB1-AMPK signaling pathway, which induces ACC phosphorylation and inhibits SREBP-1c maturation in hepatocytes.

Genetic variations of superoxide dismutase 2 and cytochrome P450 2E1 in non-alcoholic steatohepatitis.

BACKGROUND & AIMS: Non-alcoholic fatty liver disease is the most prevalent liver disease in the world. However, the exact mechanisms that lead to development of advanced non-alcoholic steatohepatitis (NASH) are unknown. Oxidative stress may be an important pathogenic factor in NASH. Manganese superoxide dismutase (SOD2) is an important antioxidant phase 2 enzyme that can reduce reactive oxidative substances and protect hepatocytes. In contrast, cytochrome P450 2E1 (CYP2E1) has pro-oxidant activity and may enhance oxidative stress and counteract the effect of SOD2. Little is known regarding the associations of genetic variants of these enzymes with the risk of NASH. We aimed to investigate the association of genetic variants of SOD2 and CYP2E1 with susceptibility to NASH. METHODS: Data from 100 patients with NASH, 31 patients with non-alcoholic steatosis (NAS) and 90 healthy controls were analysed. Their DNA was retrieved for genotyping SOD2 47T>C and CYP2E1 -1053C>T variation by polymerase chain reaction. RESULTS: There was no statistical difference in the frequency distributions of SOD2 and CYP2E1 genotypes among the NASH, NAS and control groups. However, the frequency of the SOD2 C variant was significantly higher in the NASH group than in the NAS and control groups (22% vs. 14.5% and 11.1%, respectively; P = 0.015). After adjustment for confounders, the SOD2 C/C and C/T genotypes remained associated with the risk of NASH (odds ratio, 2.81; 95% confidence interval, 1.37-5.76; P = 0.005). CONCLUSIONS: The anti-oxidative SOD2 47T>C genetic variant might increase susceptibility to NASH in Chinese. Individuals with the SOD2 C variant may have a higher risk for NASH.

Progress in the search for circulating biomarkers of nonalcoholic fatty liver disease.

CONTEXT: The definitive standard for the diagnosis of nonalcoholic fatty liver disease (NAFLD) is clinico-pathological correlation, but frequently the only laboratory abnormality is an elevation of serum aminotransferases. OBJECTIVE: This has resulted in the search for more specific laboratory biomarkers. METHODS: The literature was searched for novel plasma/serum markers of NAFLD. RESULTS: Studies reviewed here included histologically-confirmed patients presenting some stage of NAFLD and monitored one or more novel serum/plasma biomarkers. CONCLUSION: The most promising application of some of these novel biomarkers for the detection and quantification of NAFLD and particularly NASH appears to be in the combination of several into diagnostic panels.

Glucagon-like Peptide-1 Receptor-based Therapeutics for Metabolic Liver Disease.

Glucagon-like peptide-1 (GLP-1) controls islet hormone secretion, gut motility, and body weight, supporting development of GLP-1 receptor agonists (GLP-1RA) for the treatment of type 2 diabetes (T2D) and obesity. GLP-1RA exhibit a favorable safety profile and reduce the incidence of major adverse cardiovascular events in people with T2D. Considerable preclinical data, supported by the results of clinical trials, link therapy with GLP-RA to reduction of hepatic inflammation, steatosis, and fibrosis. Mechanistically, the actions of GLP-1 on the liver are primarily indirect, as hepatocytes, Kupffer cells, and stellate cells do not express the canonical GLP-1R. GLP-1RA reduce appetite and body weight, decrease postprandial lipoprotein secretion, and attenuate systemic and tissue inflammation, actions that may contribute to attenuation of metabolic-associated fatty liver disease (MAFLD). Here we discuss evolving concepts of GLP-1 action that improve liver health and highlight evidence that links sustained GLP-1R activation in distinct cell types to control of hepatic glucose and lipid metabolism, and reduction of experimental and clinical nonalcoholic steatohepatitis (NASH). The therapeutic potential of GLP-1RA alone, or in combination with peptide agonists, or new small molecule therapeutics is discussed in the context of potential efficacy and safety. Ongoing trials in people with obesity will further clarify the safety of GLP-1RA, and pivotal studies underway in people with NASH will define whether GLP-1-based medicines represent effective and safe therapies for people with MAFLD.

Are the Protean Effects of Pentoxifylline in the Therapy of Diabetes and Its Complications Still Relevant?

Pentoxifylline (Px) has protean effects that can be utilized in the therapy of diabetes and its complications. There have been well-documented but often inconclusive improvements in peripheral arterial disease, foot ulcers, peripheral neuropathy, nephropathy, retinopathy, ischemic heart disease and cerebrovascular disease. In addition, non-alcoholic steatosis and steatohepatitis, which are closely associated with insulin resistance and type 2 diabetes, have been shown to improve with pentoxifylline. Surprisingly, pentoxifylline modestly improves insulin resistance through improvements in capillary blood flow as well as beta cell function and decreased hepatic glucose production. The therapeutic effects of pentoxifylline are complementary to the effects of drugs such as blockers of the renin-angiotensin-aldosterone system when utilized in the therapy of diabetic nephropathy.

The Root of Polygonum multiflorum Thunb. Alleviates Non-Alcoholic Steatosis and Insulin Resistance in High Fat Diet-Fed Mice.

Non-alcoholic steatosis and insulin resistance are critical health problems and cause metabolic complications worldwide. In this study, we investigated the molecular mechanism of Polygonum multiflorum Thunb. (PM) against hepatic lipid accumulation and insulin resistance by using in vitro and in vivo models. PM extract significantly attenuated the accumulation of lipid droplets and hepatic triglyceride in free fatty acid (FFA)-exposed HepG2 cells. PM extract increased the AMPK and ACC phosphorylation and GLUT4 expression, whose levels were downregulated in FFA-exposed cells. PM extract also decreased precursor and mature forms of SREBP-1 in FFA-exposed cells. C57BL/6 mice fed with normal diet (ND) or high-fat diet (HFD) were administered PM extract (100 mg/kg) or vehicle orally for 16 weeks. PM extract attenuated the increases of the epididymal and perirenal fats on HFD feeding. PM extract markedly reduced hepatic lipid accumulation and fasting glucose levels, and improved glucose and insulin sensitivity in HFD-fed mice. HFD-fed mice decreased the AMPK and ACC phosphorylation and GLUT4 expression, and increased precursor and mature forms of SREBP-1; these changes were significantly restored by PM extract. In conclusion, PM extract alleviates non-alcoholic steatosis and insulin resistance through modulating the expression of proteins on lipid metabolism and glucose transport in the liver.

Non-alcoholic steatohepatitis associated with Netherton syndrome.

A 21-year-old man with Netherton syndrome underwent investigation of a persistently elevated serum alanine transaminase, detected on routine monitoring. He drank no alcohol, was not diabetic or overweight (body mass index 23 kg/m2) and had no clinical features of liver dysfunction. A FibroScan yielded an elevated result of 9.3 kPa. An ultrasound guided liver biopsy showed histological features consistent with non-alcoholic steatohepatitis, with activity score of 4 and fibrosis stage of 3. The patient was started on vitamin E supplementation and remains under surveillance.

High-dose steroids as a therapeutic option in the management of spur cell haemolytic anaemia.

Spur cell haemolytic anaemia (SCA) is a form of anaemia that can be seen in patients with severely impaired liver function or advanced cirrhosis. It is associated with high mortality. The treatment options for SCA secondary to cirrhosis are limited. Our patient is a middle-aged man who developed SCA and was not a candidate for liver transplantation or splenectomy. High-dose steroids helped ameliorate haemolysis and improve anaemia and general condition of our patient.

Association between rice, bread, and noodle intake and the prevalence of non-alcoholic fatty liver disease in Japanese middle-aged men and women.

BACKGROUND & AIMS: Prevention of non-alcoholic fatty liver disease (NAFLD) through lifestyle modification is an important public health issue. Carbohydrate intake from soft drinks has received particular interest. Owing to differences in dietary habits, however, major contributors to the intake of dietary carbohydrates, such as rice, bread, and noodles, might have more influence on NAFLD prevalence in East Asian countries than consumption of soft drinks. We examined the relationship of the intake of rice, bread, and noodles, as well as overall carbohydrate intake, with NAFLD prevalence in middle-aged Japanese. METHODS: This is a cross-sectional study of 977 men and 1467 women aged 40-69 y. Dietary information was obtained using a validated self-administered diet history questionnaire. Diagnosis of NAFLD was based on the following criteria: presence of steatosis on abdominal ultrasound, alcohol intake <20 g/day in women and <30 g/day in men, and exclusion of other liver diseases. Logistic regression was performed as multivariate analysis. RESULTS: The presence of NAFLD was 34.9% (n = 341) in men and 11.7% (n = 171) in women. Carbohydrate intake was positively associated with NAFLD prevalence in women (p for trend = 0.008). There was also a positive association between rice intake and NAFLD prevalence in women; the multi-adjusted odds ratio for the highest versus the lowest quartiles of rice intake was 1.87 (95% CI: 1.03, 3.41; p for trend = 0.006). These associations were not observed in men. No association was observed between bread and noodle intake and the prevalence of NAFLD in either sex. CONCLUSIONS: Consumption of carbohydrates and rice was positively associated with NAFLD prevalence in middle-aged Japanese women.

Impact of high cholesterol and endoplasmic reticulum stress on metabolic diseases: An updated mini-review.

Endoplasmic reticulum (ER) is the major site of protein folding and calcium storage. Beside the role of ER in protein homeostasis, it controls the cholesterol production and lipid-membrane biosynthesis as well as surviving and cell death signaling mechanisms in the cell. It is well-documented that elevated plasma cholesterol induces adverse effects in cardiovascular diseases (CVDs), liver disorders, such as non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatosis hepatitis (NASH), and metabolic diseases which are associated with oxidative and ER stress. Recent animal model and human studies have showed high cholesterol and ER stress as an emerging factors involved in the development of many metabolic diseases. In this review, we will summarize the crucial effects of hypercholesterolemia and ER stress response in the pathogenesis of CVDs, NAFLD/NASH, diabetes and obesity which are major health problems in western countries.

Enfermedad hepática grasa. Aspectos patológicos / Pathological aspects of fatty liver disease

En el hígado humano normal aproximadamente un 5% de su masa está compuesta por lípidos. Cuando tenemos aumento del depósito de grasa el término más utilizado es el de hígado graso o esteatosis e incluye el hígado graso no alcohólico (HGNA) y el hígado graso de etiología alcohólica (HGA), siendo aún la biopsia hepática considerada como el patrón de oro para determinar la severidad del daño hepático en cualquiera de estas entidades.