Incretin Hormones: The Link between Glycemic Index and Cardiometabolic Diseases

An extended minimal model of OGTT: estimation of α- and β-cell dysfunction, insulin resistance, and the incretin effect

Loss of insulin sensitivity, α- and β-cell dysfunction, and impairment in incretin effect have all been implicated in the pathophysiology of type 2 diabetes (T2D). Parsimonious mathematical models are useful in quantifying parameters related to the pathophysiology of T2D. Here, we extend the minimum model developed to describe the glucose-insulin-glucagon dynamics in the isoglycemic intravenous glucose infusion (IIGI) experiment to the oral glucose tolerance test (OGTT). The extended model describes glucose and hormone dynamics in OGTT including the contribution of the incretin hormones, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide-1 (GLP-1), to insulin secretion. A new function describing glucose arrival from the gut is introduced. The model is fitted to OGTT data from eight individuals with T2D and eight weight-matched controls (CS) without diabetes to obtain parameters related to insulin sensitivity, β- and α-cell function. The parameters, i.e., measures of insulin sensitivity, a1, suppression of glucagon secretion, k1, magnitude of glucagon secretion, γ2, and incretin-dependent insulin secretion, γ3, were found to be different between CS and T2D with P values < 0.002, <0.017, <0.009, <0.004, respectively. A new rubric for estimating the incretin effect directly from modeling the OGTT is presented. The average incretin effect correlated well with the experimentally determined incretin effect with a Spearman rank test correlation coefficient of 0.67 (P < 0.012). The average incretin effect was found to be different between CS and T2D (P < 0.032). The developed model is shown to be effective in quantifying the factors relevant to T2D pathophysiology.NEW & NOTEWORTHY A new extended model of oral glucose tolerance test (OGTT) has been developed that includes glucagon dynamics and incretin contribution to insulin secretion. The model allows the estimation of parameters related to α- and β-cell dysfunction, insulin sensitivity, and incretin action. A new function describing the influx of glucose from the gut has been introduced. A new rubric for estimating the incretin effect directly from the OGTT experiment has been developed. The effect of glucose dose was also investigated.

Obesity and its comorbidities, current treatment options and future perspectives: Challenging bariatric surgery?

Obesity and its comorbidities, including type 2 diabetes mellitus, cardiovascular disease, heart failure and non-alcoholic liver disease are a major health and economic burden with steadily increasing numbers worldwide. The need for effective pharmacological treatment options is strong, but, until recently, only few drugs have proven sufficient efficacy and safety. This article provides a comprehensive overview of obesity and its comorbidities, with a special focus on organ-specific pathomechanisms. Bariatric surgery as the so far most-effective therapeutic strategy, current pharmacological treatment options and future treatment strategies will be discussed. An increasing knowledge about the gut-brain axis and especially the identification and physiology of incretins unfolds a high number of potential drug candidates with impressive weight-reducing potential. Future multi-modal therapeutic concepts in obesity treatment may surpass the effectivity of bariatric surgery not only with regard to weight loss, but also to associated comorbidities.

Mechanism of preventive effects of exendin-4 and des-fluoro-sitagliptin in a murine model of fructose-induced prediabetes

Protective effects of exendin-4 (glucagon-like peptide-1 -GLP-1- receptor agonist) and des-fluoro-sitagliptin (dipeptidyl peptidase-4 inhibitor) on fructose-induced hepatic disturbances were evaluated in prediabetic rats. Complementary, a possible direct effect of exendin-4 in human hepatoblastoma-derived cell line HepG2 incubated with fructose in presence/absence of exendin-9-39 (GLP-1 receptor antagonist) was investigated. In vivo, after 21 days of fructose rich diet, we determined: glycemia, insulinemia, and triglyceridemia; hepatic fructokinase, AMP-deaminase, and G-6-P dehydrogenase (G-6-P DH) activities; carbohydrate-responsive element-binding protein (ChREBP) expression; triglyceride content and lipogenic gene expression (glycerol-3-phosphate acyltransferase -GPAT-, fatty acid synthase -FAS-, sterol regulatory element-binding protein-1c -SREBP-1c); oxidative stress and inflammatory markers expression. In HepG2 cells we measured fructokinase activity and triglyceride content. Hypertriglyceridemia, hyperinsulinemia, enhanced liver fructokinase, AMP-deaminase, and G-6-P DH activities, increased ChREBP and lipogenic genes expression, enhanced triglyceride level, oxidative stress and inflammatory markers recorded in fructose fed animals, were prevented by co-administration of either exendin-4 or des-fluoro-sitagliptin. Exendin-4 prevented fructose-induced increase in fructokinase activity and triglyceride contain in HepG2 cells. These effects were blunted co-incubating with exendin-9-39. The results demonstrated for the first time that exendin-4/des-fluro-sitagliptin prevented fructose-induced endocrine-metabolic oxidative stress and inflammatory changes probably acting on the purine degradation pathway. Exendin 9-39 blunted in vitro protective exendin-4 effects, thereby suggesting a direct effect of this compound on hepatocytes through GLP-1 receptor. Direct effect on fructokinase and AMP-deaminase activities, with a key role in the pathogenesis of liver dysfunction induced by fructose, suggests purine degradation pathway constitute a potential therapeutic objective for GLP-1 receptor agonists.

GLP-1 Receptor Agonists in Non-Alcoholic Fatty Liver Disease: Current Evidence and Future Perspectives

To date, non-alcoholic fatty liver disease (NAFLD) is the most frequent liver disease, affecting up to 70% of patients with diabetes. Currently, there are no specific drugs available for its treatment. Beyond their anti-hyperglycemic effect and the surprising role of cardio- and nephroprotection, GLP-1 receptor agonists (GLP-1 RAs) have shown a significant impact on body weight and clinical, biochemical and histological markers of fatty liver and fibrosis in patients with NAFLD. Therefore, GLP-1 RAs could be a weapon for the treatment of both diabetes mellitus and NAFLD. The aim of this review is to summarize the evidence currently available on the role of GLP-1 RAs in the treatment of NAFLD and to hypothesize potential future scenarios.

The Glycemic Index and Human Health with an Emphasis on Potatoes

Diabetes and obesity are associated with the excessive intake of high-glycemic index (GI) carbohydrates, increased glycemic load (GL) foods, and inactive lifestyles. Carbohydrate-rich diets affect blood glucose levels. GI is an indicator of the impact of a specific food on blood glucose, while GL represents the quantity and quality of carbohydrates in the overall diet and their interactions. There are in vitro and in vivo methods for estimating GI and GL. These values are useful human health markers for conditions such as diabetes, obesity, and pregnancy. Potato is a major starchy vegetable, which is consumed widely and is the fourth most important crop globally. However, the GI of diets rich in starchy vegetables such as potatoes has not been studied in detail. The GI values in potatoes are affected by external and internal factors, such as methods of cooking, methods of processing, resistant starches, cultivation methods, mixed meals and food additions, and hormone levels. This review summarizes how these factors affect the GI and GL associated with diets containing potatoes. Understanding the impacts of these factors will contribute to the development of new and improved potato varieties with low GI values. The consumption of low-GI foods will help to combat obesity. The development of low-GI potatoes may contribute to the development of meal plans for individuals living with diabetes and obesity.

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.

Non-Alcoholic Fatty Liver Disease: From Pathogenesis to Clinical Impact

Non-Alcoholic Fatty Liver Disease (NAFLD) is caused by the accumulation of fat in over 5% of hepatocytes in the absence of alcohol consumption. NAFLD is considered the hepatic manifestation of metabolic syndrome (MS). Recently, an expert consensus suggested as more appropriate the term MAFLD (metabolic-associated fatty liver disease). Insulin resistance (IR) plays a key role in the development of NAFLD, as it causes an increase in hepatic lipogenesis and an inhibition of adipose tissue lipolysis. Beyond the imbalance of adipokine levels, the increase in the mass of visceral adipose tissue also determines an increase in free fatty acid (FFA) levels. In turn, an excess of FFA is able to determine IR through the inhibition of the post-receptor insulin signal. Adipocytes secrete chemokines, which are able to enroll macrophages inside the adipose tissue, responsible, in turn, for the increased levels of TNF-α. The latter, as well as resistin and other pro-inflammatory cytokines such as IL-6, enhances insulin resistance and correlates with endothelial dysfunction and an increased cardiovascular (CV) risk. In this review, the role of diet, intestinal microbiota, genetic and epigenetic factors, low-degree chronic systemic inflammation, mitochondrial dysfunction, and endoplasmic reticulum stress on NAFLD have been addressed. Finally, the clinical impact of NAFLD on cardiovascular and renal outcomes, and its direct link with type 2 diabetes have been discussed.

Associations between Dietary Glycemic Index and Glycemic Load Values and Cardiometabolic Risk Factors in Adults: Findings from the China Health and Nutrition Survey

Studies investigating the associations between dietary glycemic index (GI) and glycemic load (GL) values and cardiometabolic risk factors (CMRF) among Chinese populations are strikingly limited. To assess the associations between dietary GI and GL values and CMRF, including dyslipidemia, hyperglycemia, and hyperuricemia in Chinese adults, we extracted data of 7886 apparently healthy adults from the 2009 wave of the China Health and Nutrition Survey. Dietary GI and GL values were calculated using data collected from three consecutive 24 h dietary recalls. Fasting lipid, glucose, and uric acid concentrations were measured and CMRF were defined on the basis of established criteria. There were no significant associations between dietary GI values and CMRF, and analyzing the data by age, sex, body mass index (BMI), and region did not alter these results. Dietary GL values were positively associated with prevalence of hyperuricemia in all participants (Q4 compared with Q1: odds ratio (OR) = 1.46; 95% CI: 1.14, 1.87; p-trend = 0.0030) and prevalence of hypercholesterolemia in participants ≥ 60 years old (Q5 compared with Q1: OR = 1.72; 95% CI: 1.11, 2.68; p-trend < 0.0010). Higher dietary GL but not GI values were associated with increased prevalence of hyperuricemia in apparently healthy Chinese adults and hypercholesterolemia in older Chinese adults. Further studies are required to confirm the public health implication of these findings.

Effects of Anthocyanins in Composite Meals on Cardiometabolic Outcomes-A Systematic Review of Randomized Controlled Feeding Trials

Accumulating epidemiological evidence suggests that anthocyanin intake is associated with reduced risks of cardiometabolic disorders, highlighting the importance of incorporating the phytochemical in our diets. Numerous food-based intervention studies have examined, in controlled meal settings, the role of anthocyanin on cardiometabolic health; but their effects have not been systematically summarized. This study aims to systematically review and summarize the effects of anthocyanin consumption with composite meals on cardiometabolic health from randomized controlled feeding trials. A systematic literature search for relevant human nutritional intervention studies was performed using PubMed, Embase, Cochrane Library, CINAHL Plus with Full Text, and Scopus databases. The Cochrane Risk of Bias tool was used to assess the study quality. Eighteen articles involving 371 participants were included in this review. Consistent improvements from anthocyanin intake were found in glycemic, gastric inhibitory peptide (GIP), interleukin-6 (IL-6), and oxygen radical absorbance capacity (ORAC) responses. Anthocyanin intake did not significantly affect other markers of energy metabolism, vascular functions, oxidative stress and antioxidant status, as well as inflammatory responses. Inconsistencies in successful outcomes between epidemiological studies and included interventions were largely attributed to matrix effects, which may impede the bioaccessibility of anthocyanins and consequently, limiting its health benefits when co-delivered with some foods.

Sitagliptin/Metformin: A New Medical Treatment in Polycystic Ovary Syndrome

Metformin has long been used in the treatment of polycystic ovarian syndrome (PCOS). Recently, sitagliptin has been reported to improve ovarian cycles and ovulation in PCOS. We suggest that a combination of sitagliptin and metformin can be more effective than either treatment alone in improving different aspects of PCOS.

Comparing the effect of sitagliptin and metformin on the oocyte and embryo quality in classic PCOS patients undergoing ICSI

BACKGROUND

Insulin resistance plays a major role in the pathogenesis of polycystic ovary syndrome (PCOS). Therefore, there is a growing interest in the use of insulin sensitizer drugs in the treatment of PCOS. Research in recent years has shown that sitagliptin has been reported to improve ovarian cycles and ovulation in PCOS patients.

AIMS

We aimed to compare the effects of metformin and sitagliptin on PCOS individuals undergoing ICSI.

METHODS

Sixty PCOS patients were divided into 3 groups: metformin, sitagliptin, and placebo group. Treatment was carried out 2 months before the start of the ovulation cycle and continued until the day of oocyte aspiration. The serum levels of total testosterone, estradiol, and fasting insulin along with the total number of retrieved, normal and abnormal MII, and fertilized oocytes, the number of transferred embryos (grades I, II and III), and biochemical and clinical pregnancy rates as well as the ovarian hyperstimulation syndrome (OHSS) were evaluated.

RESULTS

There was a significant reduction in the serum levels of Insulin and total testosterone in the treated groups compared with the placebo. The number of mature and normal MII oocytes increased significantly in the treated groups compared with the placebo. Moreover, the number of immature oocytes decreased significantly and the number of grade I embryos increases significantly in the sitagliptin group compared with the placebo group.

CONCLUSION

We conclude that sitagliptin can improve the maturation of oocytes and embryos' quality more effectively than metformin, in PCOS patients undergoing ICSI.

TRIAL REGISTRATION

Trial registration is NCT04268563 ( https://clinicaltrials.gov ).