Bile acid sequestrants: glucose-lowering mechanisms and efficacy in type 2 diabetes

Elucidating the glucose-lowering effect of the bile acid sequestrant sevelamer

AIM

Bile acid sequestrants are cholesterol-lowering drugs, which also improve glycaemic control in people with type 2 diabetes. The mechanism behind the glucose-lowering effect is unknown but has been proposed to be mediated by increased glucagon-like peptide-1 (GLP-1) secretion. Here, we investigated the glucose-lowering effects of sevelamer including any contribution from GLP-1 in people with type 2 diabetes.

MATERIALS AND METHODS

In a randomized, double-blind, placebo-controlled, crossover study, 15 people with type 2 diabetes on metformin monotherapy underwent two 17-day treatment periods with the bile acid sequestrant sevelamer and placebo, respectively, in a randomized order and with an interposed wash-out period of minimum 6 weeks. On days 15 and 17 of each treatment period, participants underwent experimental days with 4-h liquid meal tests and application of concomitant infusion of exendin(9-39)NH2 or saline.

RESULTS

Compared with placebo, sevelamer improved insulin sensitivity (assessed by homeostatic model assessment of insulin resistance) and beta-cell sensitivity to glucose and lowered fasting and postprandial plasma glucose concentrations. In both treatment periods, exendin(9-39)NH2 increased postprandial glucose excursions compared with saline but without absolute or relative difference between the two treatment periods. In contrast, exendin(9-39)NH2 abolished the sevelamer-induced improvement in beta-cell glucose sensitivity.

CONCLUSIONS

The bile acid sequestrant sevelamer improved insulin sensitivity and beta-cell sensitivity to glucose, but using the GLP-1 receptor antagonist exendin(9-39)NH2 we were not able to detect a GLP-1-mediated glucose-lowering effect of sevelamer in individuals with type 2 diabetes. Nevertheless, the sevelamer-induced improvement of beta-cell sensitivity to glucose was shown to be GLP-1-dependent.

Polymethoxyflavones in citrus extract has a beneficial effect on hypercholesterolemia rats by promoting liver cholesterol metabolism

ETHNOPHARMACOLOGICAL RELEVANCE

Hyperlipidemia is characterized by the disorder of lipid metabolism accompanied by oxidative stress damage, and low-grade inflammation, with the pathway of cholesterol and bile acid metabolic are an important triggering mechanism. Polymethoxyflavones (PMFs) are the active constituents of Aurantii Fructus Immaturus, which have many biological effects, including anti-inflammatory, antioxidant activities, anti-obesity, suppressing adipogenesis in adipocytes, and ameliorate type 2 diabetes, with potential roles for regulation of lipid metabolism. However, its associated mechanisms on hyperlipidemia remain unclear.

AIM OF THE STUDY

This study aims to identify the anti-hypercholesterolemia effects and mechanisms of PMFs in a hypercholesterolemia model triggered by high-fat compounds in an excessive alcohol diet (HFD).

MATERIALS AND METHODS

A hypercholesterolemia rat model was induced by HFD, and PMFs was intragastric administered at 125 and 250 mg/kg daily for 16 weeks. The effects of PMFs on hypercholesterolemia were assessed using serum lipids, inflammatory cytokines, and oxidative stress levels. Hematoxylin & eosin (H&E) and Oil Red O staining were performed to evaluate histopathological changes in the rat liver. The levels of total cholesterol (TC) and total bile acid (TBA) in the liver and feces were determined to evaluate lipid metabolism. RAW264.7 and BRL cells loaded with NBD-cholesterol were used to simulate the reverse cholesterol transport (RCT) process in vitro. The signaling pathway of cholesterol and bile acid metabolic was evaluated by Western Blotting (WB) and qRT-PCR.

RESULTS

Lipid metabolism disorders, oxidative stress injury, and low-grade inflammation in model rats were ameliorated by PMFs administration. Numerous vacuoles and lipid droplets in hepatocytes were markedly reduced. In vitro experiments results revealed decreased NBD-cholesterol levels in RAW264.7 cells and increased NBD-cholesterol levels in BRL cells following PMFs intervention. PMFs upregulated the expression of proteins associated with the RCT pathway, such as LXRα, ABCA1, LDLR, and SR-BI, thereby promoting TC entry into the liver. Meanwhile, the expression of proteins associated with cholesterol metabolism and efflux pathways such as CYP7A1, CYP27A1, CYP7B1, ABCG5/8, ABCB1, and BSEP were regulated, thereby promoting cholesterol metabolism. Moreover, PMFs treatment regulated the expression of proteins related to the pathway of enterohepatic circulation of bile acids, such as ASBT, OSTα, NTCP, FXR, FGF15, and FGFR4, thereby maintaining lipid metabolism.

CONCLUSIONS

PMFs might ameliorate hypercholesterolemia by promoting the entry of cholesterol into the liver through the RCT pathway, followed by excretion via metabolism pathways of cholesterol and bile acid. These findings provide a promising therapeutic potential for PMFs to treat hypercholesterolemia.

Development of New Genome Editing Tools for the Treatment of Hyperlipidemia

Hyperlipidemia is a medical condition characterized by high levels of lipids in the blood. It is often associated with an increased risk of cardiovascular diseases such as heart attacks and strokes. Traditional treatment approaches for hyperlipidemia involve lifestyle modifications, dietary changes, and the use of medications like statins. Recent advancements in genome editing technologies, including CRISPR-Cas9, have opened up new possibilities for the treatment of this condition. This review provides a general overview of the main target genes involved in lipid metabolism and highlights the progress made during recent years towards the development of new treatments for dyslipidemia.

Association of CYP7A1 and CYP2E1 Polymorphisms with Type 2 Diabetes in the Chinese Han Populations

Background

Type 2 diabetes mellitus (T2DM) is caused by diverse environmental and genetic risk factors. Previous studies have reported that cytochrome P450 (CYP) is a promising gene for T2DM. Therefore, we aimed to determine the effects of CYP7A1 and CYP2E1 polymorphisms on T2DM susceptibility among the Chinese Han population.

Methods

A case-control study was conducted to assess the potential relationship of four polymorphisms (rs8192879, rs12542233, rs2070672 and rs2515641) with T2DM susceptibility in the Chinese population, involving 512 T2DM patients and 515 age- and gender-matched healthy individuals. We used the Agena MassARRAY platform to detect CYP7A1 and CYP2E1 polymorphisms. The relationship between genetic polymorphisms and T2DM risk was evaluated using odds ratios (ORs) and 95% confidence intervals (CIs) in various genetic models.

Results

After adjusting for age and gender, rs12542233 in the CYP7A1 gene was significantly associated with decreased T2DM risk (recessive: OR = 0.67, 95% CI = 0.49–0.91, p = 0.012; after FDR correction, p = 0.048). The CYP7A1 rs12542233 was associated with a reduced risk of T2DM in people over 59 years of age (p = 0.010). In the population with BMI ≤ 24 kg/m², CYP7A1 rs12542233 was associated with an increased risk of T2DM (p < 0.05). In the population with BMI > 24 kg/m², CYP2E1 rs2515641 can significantly reduce the risk of T2DM (p < 0.05). And rs8192879, rs2070672 and rs2515641 could significantly increase the risk of diabetes retinopathy in T2DM patients (p < 0.05). Furthermore, the T_rs8192879C_rs12542233 haplotype was significantly associated with T2DM (p = 0.019).

Conclusion

CYP7A1 and CYP2E1 polymorphisms may contribute to T2DM susceptibility in the Chinese Han population, especially in stratified analysis.

Bile Acid Sequestrants for Hypercholesterolemia Treatment Using Sustainable Biopolymers: Recent Advances and Future Perspectives

Bile acids, the endogenous steroid nucleus containing signaling molecules, are responsible for the regulation of multiple metabolic processes, including lipoprotein and glucose metabolism to maintain homeostasis. Within our body, they are directly produced from their immediate precursors, cholesterol C (low-density lipoprotein C, LDL-C), through the enzymatic catabolic process mediated by 7-α-hydroxylase (CYP7A1). Bile acid sequestrants (BASs) or amphiphilic resins that are nonabsorbable to the human body (being complex high molecular weight polymers/electrolytes) are one of the classes of drugs used to treat hypercholesterolemia (a high plasma cholesterol level) or dyslipidemia (lipid abnormalities in the body); thus, they have been used clinically for more than 50 years with strong safety profiles as demonstrated by the Lipid Research Council-Cardiovascular Primary Prevention Trial (LRC-CPPT). They reduce plasma LDL-C and can slightly increase high-density lipoprotein C (HDL-C) levels, whereas many of the recent clinical studies have demonstrated that they can reduce glucose levels in patients with type 2 diabetes mellitus (T2DM). However, due to higher daily dosage requirements, lower efficacy in LDL-C reduction, and concomitant drug malabsorption, research to develop an "ideal" BAS from sustainable or natural sources with better LDL-C lowering efficacy and glucose regulations and lower side effects is being pursued. This Review discusses some recent developments and their corresponding efficacies as bile removal or LDL-C reduction of natural biopolymer (polysaccharide)-based compounds.

The Role of the Gut Microbiota in the Pathogenesis of Diabetes

Diabetes mellitus is a significant clinical and therapeutic problem because it can lead to serious long-term complications. Its pathogenesis is not fully understood, but there are indications that dysbiosis can play a role in the development of diabetes, or that it appears during the course of the disease. Changes in microbiota composition are observed in both type 1 diabetes (T1D) and type 2 diabetes (T2D) patients. These modifications are associated with pro-inflammation, increased intestinal permeability, endotoxemia, impaired β-cell function and development of insulin resistance. This review summarizes the role of the gut microbiota in healthy individuals and the changes in bacterial composition that can be associated with T1D or T2D. It also presents new developments in diabetes therapy based on influencing the gut microbiota as a promising method to alter the course of diabetes. Moreover, it highlights the lacking data and suggests future directions needed to prove the causal relationship between dysbiosis and diabetes, both T1D and T2D.

Gut microbiota influence in type 2 diabetes mellitus (T2DM)

A strong and expanding evidence base supports the influence of gut microbiota in human metabolism. Altered glucose homeostasis is associated with altered gut microbiota, and is clearly associated with the development of type 2 diabetes mellitus (T2DM) and associated complications. Understanding the causal association between gut microbiota and metabolic risk has the potential role of identifying susceptible individuals to allow early targeted intervention.

Bile acid sequestrants: a review of mechanism and design

OBJECTIVE

Bile acid sequestrants (BAS) are used extensively in the treatment of hypercholesterolaemia. This brief review aimed to describe the design and evaluation of three types of BAS: amphiphilic copolymers, cyclodextrin/poly-cyclodextrin and molecular imprinted polymers. The mechanisms underlying the action of BAS are also discussed.

KEY FINDINGS

BAS could lower plasma cholesterol, improve glycemic control in patients with type 2 diabetes and regulate balance energy metabolism via receptors or receptor-independent mediated mechanisms. Different types of BAS have different levels of ability to bind to bile acids, different stability and different in-vivo activity.

CONCLUSIONS

A growing amount of evidence suggests that bile acids play important roles not only in lipid metabolism but also in glucose metabolism. The higher selectivity, specificity, stability and in-vivo activity of BAS show considerable potential for lipid-lowering therapy.

Prevention of the rise in plasma cholesterol and glucose levels by kaki-tannin and characterization of its bile acid binding capacity

BACKGROUND

Bile acid-binding agents, such as cholestyramine and colesevelam, improve both cholesterol and glucose metabolism. Kaki-tannin, a polymerized condensed tannin derived from persimmon (Diospyros kaki), has been shown to have bile acid-binding capacity and a hypocholesterolemic effect. However, its effects on glucose metabolism have not been well studied, and the binding selectivity of kaki-tannin to bile acid molecules has not been reported.

RESULTS

In vivo experiments using mice with high-fat diet-induced obesity showed that kaki-tannin intake (20 g kg^-1 of the diet) increased fecal bile acid excretion by 2.3-fold and prevented a rise in plasma cholesterol levels and fasting plasma glucose levels. Kaki-tannin also suppressed the development of impaired glucose tolerance. To characterize the bile acid-binding capacity of kaki-tannin, we investigated its capacity to bind to eight types of bile acid and cholesterol in vitro. Kaki-tannin showed strong capacity to bind to lithocholic acid (85.5%), which has one hydroxy group. It also showed moderate capacity to bind to bile acids with two hydroxy groups (53.3%), followed by those with three hydroxy groups (39.0%), but kaki-tannin did not show binding capacity to cholesterol. These results suggest that the binding capacity of kaki-tannin to bile acids tends to decrease as the number of hydroxy groups increases. Interestingly, the binding capacity of kaki-tannin correlated with that of cholestyramine (correlation coefficient: r = 0.900).

CONCLUSION

Our findings indicate that kaki-tannin binds preferentially to bile acids with fewer hydroxy groups and has beneficial effects on glucose metabolism as well as cholesterol metabolism. © 2020 Society of Chemical Industry.

Physiology and Physical Chemistry of Bile Acids

Bile acids (BAs) are facial amphiphiles synthesized in the body of all vertebrates. They undergo the enterohepatic circulation: they are produced in the liver, stored in the gallbladder, released in the intestine, taken into the bloodstream and lastly re-absorbed in the liver. During this pathway, BAs are modified in their molecular structure by the action of enzymes and bacteria. Such transformations allow them to acquire the chemical-physical properties needed for fulling several activities including metabolic regulation, antimicrobial functions and solubilization of lipids in digestion. The versatility of BAs in the physiological functions has inspired their use in many bio-applications, making them important tools for active molecule delivery, metabolic disease treatments and emulsification processes in food and drug industries. Moreover, moving over the borders of the biological field, BAs have been largely investigated as building blocks for the construction of supramolecular aggregates having peculiar structural, mechanical, chemical and optical properties. The review starts with a biological analysis of the BAs functions before progressively switching to a general overview of BAs in pharmacology and medicine applications. Lastly the focus moves to the BAs use in material science.

Improving glucose and lipids metabolism: drug development based on bile acid related targets

Bariatric surgery is one of the most effective treatment options for severe obesity and its comorbidities. However, it is a major surgery that poses several side effects and risks which impede its clinical use. Therefore, it is urgent to develop alternative safer pharmacological approaches to mimic bariatric surgery. Recent studies suggest that bile acids are key players in mediating the metabolic benefits of bariatric surgery. Bile acids can function as signaling molecules by targeting bile acid nuclear receptors and membrane receptors, like FXR and TGR5 respectively. In addition, the composition of bile acids is regulated by either the hepatic sterol enzymes such as CYP8B1 or the gut microbiome. These bile acid related targets all play important roles in regulating metabolism. Drug development based on these targets could provide new hope for patients without the risks of surgery and at a lower cost. In this review, we summarize the most updated progress on bile acid related targets and development of small molecules as drug candidates based on these targets.

The Novel Phosphate and Bile Acid Sequestrant Polymer SAR442357 Delays Disease Progression in a Rat Model of Diabetic Nephropathy

As a gut-restricted, nonabsorbed therapy, polymeric bile acid sequestrants (BAS) play an important role in managing hyperlipidemia and hyperglycemia. Similarly, nonabsorbable sequestrants of dietary phosphate have been used for the management of hyperphosphatemia in end-stage renal disease. To evaluate the potential utility of such polymer sequestrants to treat type 2 diabetes (T2D) and its associated renal and cardiovascular complications, we synthesized a novel polymeric sequestrant, SAR442357, possessing optimized bile acid (BA) and phosphate sequestration characteristics. Long-term treatment of T2D obese ^cZucker fatty/Spontaneously hypertensive heart failure F1 hybrid (ZSF1) with SAR442357 resulted in enhanced sequestration of BAs and phosphate in the gut, improved glycemic control, lowering of serum cholesterol, and attenuation of diabetic kidney disease (DKD) progression. In comparison, colesevelam, a BAS with poor phosphate binding properties, did not prevent DKD progression, whereas losartan, an angiotensin II receptor blocker that is widely used to treat DKD, showed no effect on hyperglycemia. Analysis of hepatic gene expression levels of the animals treated with SAR442357 revealed upregulation of genes responsible for the biosynthesis of cholesterol and BAs, providing clear evidence of target engagement and mode of action of the new sequestrant. Additional hepatic gene expression pathway changes were indicative of an interruption of the enterohepatic BA cycle. Histopathological analysis of ZSF1 rat kidneys treated with SAR442357 further supported its nephroprotective properties. Collectively, these findings reveal the pharmacological benefit of simultaneous sequestration of BAs and phosphate in treating T2D and its associated comorbidities and cardiovascular complications. SIGNIFICANCE STATEMENT: A new nonabsorbed polymeric sequestrant with optimum phosphate and bile salt sequestration properties was developed as a treatment option for DKD. The new polymeric sequestrant offered combined pharmacological benefits including glucose regulation, lipid lowering, and attenuation of DKD progression in a single therapeutic agent.

Bile Acids: Key Regulators and Novel Treatment Targets for Type 2 Diabetes

Type 2 diabetes mellitus (T2DM), characterized by insulin resistance and unclear pathogenesis, is a serious menace to human health. Bile acids are the end products of cholesterol catabolism and play an important role in maintaining cholesterol homeostasis. Furthermore, increasing studies suggest that bile acids may regulate glucose tolerance, insulin sensitivity, and energy metabolism, suggesting that bile acids may represent a potential therapeutic target for T2DM. This study summarizes the metabolism of bile acids and, more importantly, changes in their concentrations, constitution, and receptors in diabetes. Furthermore, we provide an overview of the mechanisms underlying the role of bile acids in glucose and lipid metabolism, as well as the occurrence and development of T2DM. Bile acid-targeted therapy may represent a valid approach for T2DM treatment.

New Avenues in the Regulation of Gallbladder Motility-Implications for the Use of Glucagon-Like Peptide-Derived Drugs

CONTEXT

Several cases of cholelithiasis and cholecystitis have been reported in patients treated with glucagon-like peptide 1 (GLP-1) receptor agonists (GLP-1RAs) and GLP-2 receptor agonists (GLP-2RAs), respectively. Thus, the effects of GLP-1 and GLP-2 on gallbladder motility have been investigated. We have provided an overview of the mechanisms regulating gallbladder motility and highlight novel findings on the effects of bile acids and glucagon-like peptides on gallbladder motility.

EVIDENCE ACQUISITION

The articles included in the present review were identified using electronic literature searches. The search results were narrowed to data reporting the effects of bile acids and GLPs on gallbladder motility.

EVIDENCE SYNTHESIS

Bile acids negate the effect of postprandial cholecystokinin-mediated gallbladder contraction. Two bile acid receptors seem to be involved in this feedback mechanism, the transmembrane Takeda G protein-coupled receptor 5 (TGR5) and the nuclear farnesoid X receptor. Furthermore, activation of TGR5 in enteroendocrine L cells leads to release of GLP-1 and, possibly, GLP-2. Recent findings have pointed to the existence of a bile acid-TGR5-L cell-GLP-2 axis that serves to terminate meal-induced gallbladder contraction and thereby initiate gallbladder refilling. GLP-2 might play a dominant role in this axis by directly relaxing the gallbladder. Moreover, recent findings have suggested GLP-1RA treatment prolongs the refilling phase of the gallbladder.

CONCLUSIONS

GLP-2 receptor activation in rodents acutely increases the volume of the gallbladder, which might explain the risk of gallbladder diseases associated with GLP-2RA treatment observed in humans. GLP-1RA-induced prolongation of human gallbladder refilling may explain the gallbladder events observed in GLP-1RA clinical trials.

Impact of lipid-lowering therapy on glycemic control and the risk for new-onset diabetes mellitus

Lipid-lowering therapy is used very commonly nowadays not only for the optimization of the lipid profile but also to reduce cardiovascular risk. However, some studies have linked the use of certain lipid-lowering agents with an increased risk for impaired glycemic control and new-onset diabetes mellitus, a condition well established as an important risk factor for cardiovascular disease. On the other hand, some other lipid-lowering agents have been shown to have a beneficial effect on glucose metabolism. Profound knowledge of these differences would enable the clinician to choose the right lipid-lowering medication for each individual patient, so that the benefits would outweigh the risk of side effects. This review aims to present and discuss the clinical and scientific data pertaining to the impact of lipid-lowering therapy on glycemic control and the risk for new-onset diabetes mellitus.

In Vitro Bile Acid Binding Capacities of Red Leaf Lettuce and Cruciferous Vegetables

In the present study, we tested the bile acid binding capacity of red leaf lettuce, red cabbage, red kale, green kale, and Brussels sprouts through in vitro digestion process by simulating mouth, gastric, and intestinal digestion using six bile acids at physiological pH. Green and red kale exhibited significantly higher (86.5 ± 2.9 and 89.7 ± 0.9%, respectively) bile acid binding capacity compared to the other samples. Further, three different compositions of bile acids were tested to understand the effect on different health conditions. To predict the optimal dose for bile acid binding, we established a logistic relationship between kale dose and bile acid binding capacity. The results indicated that kale showed significantly higher bile acid binding capacity (82.5 ± 2.9% equivalent to 72.06 mg) at 1.5 g sample and remained constant up to 2.5 g. In addition, minimally processed (microwaved 3 min or steamed 8 min) green kale showed significantly enhanced bile acid binding capacity (91.1 ± 0.3 and 90.2 ± 0.7%, respectively) compared to lyophilized kale (85.5 ± 0.24%). Among the six bile acids tested, kale preferentially bound hydrophobic bile acids chenodeoxycholic acid and deoxycholic acid. Therefore, regular consumption of kale, especially minimally processed kale, can help excrete more bile acids and, thus, may lower the risk of hypercholesterolemia.

ANMCO/ISS/AMD/ANCE/ARCA/FADOI/GICR-IACPR/SICI-GISE/SIBioC/SIC/SICOA/SID/SIF/SIMEU/SIMG/SIMI/SISA Joint Consensus Document on cholesterol and cardiovascular risk: diagnostic-therapeutic pathway in Italy

Atherosclerotic cardiovascular disease still represents the leading cause of death in Western countries. A wealth of scientific evidence demonstrates that increased blood cholesterol levels have a major impact on the outbreak and progression of atherosclerotic plaques. Moreover, several cholesterol-lowering pharmacological agents, including statins and ezetimibe, have proved effective in improving clinical outcomes. This document focuses on the clinical management of hypercholesterolaemia and has been conceived by 16 Italian medical associations with the support of the Italian National Institute of Health. The authors discuss in detail the role of hypercholesterolaemia in the genesis of atherosclerotic cardiovascular disease. In addition, the implications for high cholesterol levels in the definition of the individual cardiovascular risk profile have been carefully analysed, while all available therapeutic options for blood cholesterol reduction and cardiovascular risk mitigation have been explored. Finally, this document outlines the diagnostic and therapeutic pathways for the clinical management of patients with hypercholesterolaemia.

Bile acid sequestrants for glycemic control in patients with type 2 diabetes: A systematic review with meta-analysis of randomized controlled trials

AIM

To evaluate the effects of bile acid sequestrants (BASs) versus placebo, no intervention or active comparators on glycemic control in type 2 diabetes.

METHODS

Data were retrieved and a systematic review with meta-analyses was performed. We evaluated bias control and subgroup and sensitivity analyses were performed to evaluate heterogeneity and bias.

RESULTS

We included 17 trials with a total of 2950 patients randomized to BASs (colesevelam or colestimide) versus placebo, no intervention, statins or sitagliptin. Random-effects meta-analysis showed that patients randomized to BASs had a lower hemoglobin A_1c at the end of treatment compared with the control group (mean difference-0.55%; 95% confidence interval-0.64 to -0.46). Analysis of trials with low risk of bias in all domains confirmed the findings. Data on adverse events were limited. There were no differences between trials stratified by the control group and no evidence of publication bias or small study effects.

CONCLUSIONS

Our analyses found that BAS treatment improves glycemic control. The size of the effect was clinically relevant and despite limited safety data, our findings support the inclusion of BASs in current diabetes management algorithms for type 2 diabetes.

Indolepropionic acid and novel lipid metabolites are associated with a lower risk of type 2 diabetes in the Finnish Diabetes Prevention Study

Wide-scale profiling technologies including metabolomics broaden the possibility of novel discoveries related to the pathogenesis of type 2 diabetes (T2D). By applying non-targeted metabolomics approach, we investigated here whether serum metabolite profile predicts T2D in a well-characterized study population with impaired glucose tolerance by examining two groups of individuals who took part in the Finnish Diabetes Prevention Study (DPS); those who either early developed T2D (n = 96) or did not convert to T2D within the 15-year follow-up (n = 104). Several novel metabolites were associated with lower likelihood of developing T2D, including indole and lipid related metabolites. Higher indolepropionic acid was associated with reduced likelihood of T2D in the DPS. Interestingly, in those who remained free of T2D, indolepropionic acid and various lipid species were associated with better insulin secretion and sensitivity, respectively. Furthermore, these metabolites were negatively correlated with low-grade inflammation. We replicated the association between indolepropionic acid and T2D risk in one Finnish and one Swedish population. We suggest that indolepropionic acid, a gut microbiota-produced metabolite, is a potential biomarker for the development of T2D that may mediate its protective effect by preservation of β-cell function. Novel lipid metabolites associated with T2D may exert their effects partly through enhancing insulin sensitivity.

Improved glucose metabolism following bariatric surgery is associated with increased circulating bile acid concentrations and remodeling of the gut microbiome

Clinical studies have indicated that circulating bile acid (BA) concentrations increase following bariatric surgery, especially following malabsorptive procedures such as Roux-en-Y gastric bypasses (RYGB). Moreover, total circulating BA concentrations in patients following RYGB are positively correlated with serum glucagon-like peptide-1 concentrations and inversely correlated with postprandial glucose concentrations. Overall, these data suggest that the increased circulating BA concentrations following bariatric surgery - independently of calorie restriction and body-weight loss - could contribute, at least in part, to improvements in insulin sensitivity, incretin hormone secretion, and postprandial glycemia, leading to the remission of type-2 diabetes (T2DM). In humans, the primary and secondary BA pool size is dependent on the rate of biosynthesis and the enterohepatic circulation of BAs, as well as on the gut microbiota, which play a crucial role in BA biotransformation. Moreover, BAs and gut microbiota are closely integrated and affect each other. Thus, the alterations in bile flow that result from anatomical changes caused by bariatric surgery and changes in gut microbiome may influence circulating BA concentrations and could subsequently contribute to T2DM remission following RYGB. Research data coming largely from animal and cell culture models suggest that BAs can contribute, via nuclear farnezoid X receptor (FXR) and membrane G-protein-receptor (TGR-5), to beneficial effects on glucose metabolism. It is therefore likely that FXR, TGR-5, and BAs play a similar role in glucose metabolism following bariatric surgery in humans. The objective of this review is to discuss in detail the results of published studies that show how bariatric surgery affects glucose metabolism and subsequently T2DM remission.

Lipid Management in Diabetes with a Focus on Emerging Therapies

We reviewed the current and potential future management of dyslipidemia in patients with diabetes, with a focus on reduction of risk for macrovascular disease. We considered novel dyslipidemia therapies, in particular, inhibitors of proprotein convertase subtilisin kexin 9 (PCSK9), which have been approved in Canada for reducing low-density lipoprotein (LDL) cholesterol in certain patient groups. We searched for English-language randomized clinical trials (RCTs) of lipid-lowering modalities, mainly since 2012, that included patients with diabetes. The results from some RCTs may have future impacts on the approach to patients with diabetes. In particular, ezetimibe added to statins in the context of acute coronary syndromes seems to have particular benefits in patients with diabetes. Also, patients with diabetes show no differences, so far, from patients without diabetes with respect to efficacy of PCSK9 inhibitors in LDL cholesterol reduction and also in the frequency of adverse effects. RCTs of clinical outcomes with PCSK9 inhibitors performed exclusively in patients with diabetes are desirable, but approval of these agents for use in Canada has occurred before the availability of such results. Clinicians will have to gauge whether certain subjects with diabetes might benefit from this therapy, such as those with superimposed familial dyslipidemia, those with recurrent cardiovascular events and recalcitrant LDL cholesterol levels despite maximally tolerated statin therapy and those with high cardiovascular risk who cannot tolerate any dose of statins.

Endocrine effects of duodenal-jejunal exclusion in obese patients with type 2 diabetes mellitus

Duodenal-jejunal bypass liner (DJBL) is an endoscopically implantable device designed to noninvasively mimic the effects of gastrointestinal bypass operations by excluding the duodenum and proximal jejunum from the contact with ingested food. The aim of our study was to assess the influence of DJBL on anthropometric parameters, glucose regulation, metabolic and hormonal profile in obese patients with type 2 diabetes mellitus (T2DM) and to characterize both the magnitude and the possible mechanisms of its effect. Thirty obese patients with poorly controlled T2DM underwent the implantation of DJBL and were assessed before and 1, 6 and 10months after the implantation, and 3months after the removal of DJBL. The implantation decreased body weight, and improved lipid levels and glucose regulation along with reduced glycemic variability. Serum concentrations of fibroblast growth factor 19 (FGF19) and bile acids markedly increased together with a tendency to restoration of postprandial peak of GLP1. White blood cell count slightly increased and red blood cell count decreased throughout the DJBL implantation period along with decreased ferritin, iron and vitamin B12 concentrations. Blood count returned to baseline values 3months after DJBL removal. Decreased body weight and improved glucose control persisted with only slight deterioration 3months after DJBL removal while the effect on lipids was lost. We conclude that the implantation of DJBL induced a sustained reduction in body weight and improvement in regulation of lipid and glucose. The increase in FGF19 and bile acids levels could be at least partially responsible for these effects.

Intestinally-targeted TGR5 agonists equipped with quaternary ammonium have an improved hypoglycemic effect and reduced gallbladder filling effect

TGR5 activation of enteroendocrine cells increases glucagon-like peptide 1 (GLP-1) release, which maintains glycemic homeostasis. However, TGR5 activation in the gallbladder and heart is associated with severe side effects. Therefore, intestinally-targeted TGR5 agonists were suggested as potential hypoglycemic agents with minimal side effects. However, until now no such compounds with robust glucose-lowering effects were reported, especially in diabetic animal models. Herein, we identify a TGR5 agonist, 26a, which was proven to be intestinally-targeted through pharmacokinetic studies. 26a was used as a tool drug to verify the intestinally-targeted strategy. 26a displayed a robust and long-lasting hypoglycemic effect in ob/ob mice (once a day dosing (QD) and 18-day treatment) owing to sustained stimulation of GLP-1 secretion, which suggested that robust hypoglycemic effect could be achieved with activation of TGR5 in intestine alone. However, the gallbladder filling effect of 26a was rather complicated. Although the gallbladder filling effect of 26a was decreased in mice after once a day dosing, this side effect was still not eliminated. To solve the problem above, several research strategies were raised for further optimization.

Partial ileal bypass affords protection from onset of type 2 diabetes

BACKGROUND

Partial ileal bypass (PIB) in the National Institutes of Health-sponsored Program on the Surgical Control of the Hyperlipidemias (POSCH) randomized controlled trial was found to reduce plasma cholesterol, in particular low density lipoprotein cholesterol, with concomitant retardation of atherosclerotic cardiovascular disease and increased life expectancy. Glucagon-like peptide-1, related to amelioration of type 2 diabetes, is increased over 5-fold after PIB. We hypothesized that PIB, in addition to its action on cholesterol metabolism, may also prevent type 2 diabetes.

METHODS

We surveyed by telephone inquiry of former POSCH patients the 30+year posttrial incidence of type 2 diabetes or prediabetes, the presence of which was a trial exclusion criteria. We were able to contact 17.4% (n = 838) of the original POSCH population.

RESULTS

Of 66 control responders, 17 contracted type 2 diabetes (25.8%); of 80 PIB responders, 8 contracted type 2 diabetes (10%). The difference between groups was significant (P = .015 by Fisher exact test) with an odds ratio of .320 for the PIB group and an over 2-fold (2.6) increase in the incidence of type 2 diabetes in the controls. Including borderline type 2 diabetes (prediabetic) patients, these values were 22 of 66 controls (33.3%) and 10 of 80 PIB patients (12.5%), with an odds ratio of .286 and a P<.004, and again an over 2-fold (2.7) increase in the incidence of type 2 diabetes in the control patients.

CONCLUSION

PIB appears to afford partial protection from the onset of type 2 diabetes for over 30 years.

Effect of chenodeoxycholic acid and the bile acid sequestrant colesevelam on glucagon-like peptide-1 secretion

AIM

To evaluate the effects of the primary human bile acid, chenodeoxycholic acid (CDCA), and the bile acid sequestrant (BAS) colesevelam, instilled into the stomach, on plasma levels of glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide, glucose, insulin, C-peptide, glucagon, cholecystokinin and gastrin, as well as on gastric emptying, gallbladder volume, appetite and food intake.

METHODS

On four separate days, nine patients with type 2 diabetes, and 10 matched healthy control subjects received bolus instillations of (i) CDCA, (ii) colesevelam, (iii) CDCA + colesevelam or (iv) placebo. At baseline and for 180 min after instillation, blood was sampled.

RESULTS

In both the type 2 diabetes group and the healthy control group, CDCA elicited an increase in GLP-1 levels compared with colesevelam, CDCA + colesevelam and placebo, respectively (p < 0.05). The interventions did not affect plasma glucose, insulin or C-peptide concentrations in any of the groups. CDCA elicited a small increase in plasma insulin : glucose ratio compared with colesevelam, CDCA + colesevelam and placebo in both groups. Compared with colesevelam, CDCA + colesevelam and placebo, respectively, CDCA increased glucagon and delayed gastric emptying in both groups.

CONCLUSIONS

CDCA increased GLP-1 and glucagon secretion, and delayed gastric emptying. We speculate that bile acid-induced activation of TGR5 on L cells increases GLP-1 secretion, which, in turn, may result in amplification of glucose-stimulated insulin secretion. Furthermore our data suggest that colesevelam does not have an acute effect on GLP-1 secretion in humans.

Inflammation Meets Metabolic Disease: Gut Feeling Mediated by GLP-1

Chronic diseases, such as obesity and diabetes, cardiovascular, and inflammatory bowel diseases (IBD) share common features in their pathology. Metabolic disorders exhibit strong inflammatory underpinnings and vice versa, inflammation is associated with metabolic alterations. Next to cytokines and cellular stress pathways, such as the unfolded protein response (UPR), alterations in the enteroendocrine system are intersections of various pathologies. Enteroendocrine cells (EEC) have been studied extensively for their ability to regulate gastrointestinal motility, secretion, and insulin release by release of peptide hormones. In particular, the L-cell-derived incretin hormone glucagon-like peptide 1 (GLP-1) has gained enormous attention due to its insulinotropic action and relevance in the treatment of type 2 diabetes (T2D). Yet, accumulating data indicate a critical role for EEC and in particular for GLP-1 in metabolic adaptation and in orchestrating immune responses beyond blood glucose control. EEC sense the lamina propria and luminal environment, including the microbiota via receptors and transporters. Subsequently, mediating signals by secreting hormones and cytokines, EEC can be considered as integrators of metabolic and inflammatory signaling. This review focuses on L cell and GLP-1 functions in the context of metabolic and inflammatory diseases. The effects of incretin-based therapies on metabolism and immune system are discussed and the interrelation and common features of metabolic and immune-mediated disorders are highlighted. Moreover, it presents data on the impact of inflammation, in particular of IBD on EEC and discusses the potential role of the microbiota as link between nutrients, metabolism, immunity, and disease.

Metabolic effects of bile acid sequestration: impact on cardiovascular risk factors

PURPOSE OF REVIEW

This article discusses the impact of bile acid sequestrants (BAS) on cardiovascular risk factors (CVRFs), on the basis of recent (pre)clinical studies assessing the metabolic impact of modulation of enterohepatic bile acid signaling via the bile acid receptors farnesoid X receptor (FXR) and Takeda G-protein-coupled receptor 5 (TGR5).

RECENT FINDINGS

BAS decrease low-density lipoprotein-cholesterol by stimulating de novo hepatic bile acid synthesis and lowering intestinal lipid absorption, and improve glucose homeostasis in type 2 diabetes mellitus, at least in part by increasing GLP-1 production, via intestinal TGR5- and FXR-dependent mechanisms. Intestinal and peripheral FXR and TGR5 modulation also affects peripheral tissues, which can contribute to the reduction of CVRFs.

SUMMARY

Bile acids are regulators of metabolism acting in an integrated interorgan manner via FXR and TGR5. Modulation of the bile acid pool size and composition, and selective interference with their receptors could, therefore, be a therapeutic approach to decrease CVRFs. Even though clinical cardiovascular outcome studies using BAS are still lacking, the existing data point to BAS as an efficacious pharmacological approach to reduce CVRFs.

The Influence of Bariatric Surgery on Serum Bile Acids in Humans and Potential Metabolic and Hormonal Implications: a Systematic Review

Recent research suggests a mechanistic role for bile acids (BA) in the metabolic improvement following bariatric surgery. It is believed that the hormonal and metabolic effects associated with changes in systemic BAs may be related to the farnesoid X receptor (FXR) and a G-protein coupled receptor (TGR5). This systematic review examines changes in systemic BAs following bariatric procedures. Studies were included if they reported the measurement of systemic BAs in humans at at least one time point after bariatric surgery. Eleven papers were identified that met the inclusion criteria. Seven studies reported the effect of Roux-en-Y gastric bypass (RYGB) on fasting BAs. The majority (6/7) reported that fasting BAs increased after RYGB. Data regarding fasting BAs after vertical sleeve gastrectomy (VSG) and laparoscopic gastric banding (LAGB) are inconsistent. Data regarding post-prandial BA changes after RYGB, VSG, and LAGB are also inconsistent. More research is needed to investigate the connection between BAs and the metabolic improvement seen after bariatric surgery.

Emerging treatments for post-transplantation diabetes mellitus

Post-transplantation diabetes mellitus (PTDM), also known as new-onset diabetes mellitus (NODM), occurs in 10-15% of renal transplant recipients and is associated with cardiovascular disease and reduced lifespan. In the majority of cases, PTDM is characterized by β-cell dysfunction, as well as reduced insulin sensitivity in liver, muscle and adipose tissue. Glucose-lowering therapy must be compatible with immunosuppressant agents, reduced glomerular filtration rate (GFR) and severe arteriosclerosis. Such therapy should not place the patient at risk by inducing hypoglycaemic episodes or exacerbating renal function owing to adverse gastrointestinal effects with hypovolaemia. First-generation and second-generation sulphonylureas are generally avoided, and caution is currently advocated for the use of metformin in patients with GFR <60 ml/min/1.73 m(2). DPP-4 inhibitors do not interact with immunosuppressant drugs and have demonstrated safety in small clinical trials. Other therapeutic options include glinides and glitazones. Evidence-based treatment regimens used in patients with type 2 diabetes mellitus cannot be directly implemented in patients with PTDM. Studies investigating the latest drugs are required to direct the development of improved treatment strategies for patients with PTDM. This Review outlines the modern principles of glucose-lowering treatment in PTDM with specific reference to renal transplant recipients.

Sevelamer in a diabetologist's perspective: a phosphate-binding resin with glucose-lowering potential

Sevelamer is a calcium-free and metal-free phosphate-binding oral drug used in the management of hyperphosphataemia in chronic kidney disease. Preclinical and clinical trials have shown glucose and lipid-lowering effects of sevelamer, thereby giving rise to a potential role of the drug in the treatment of patients with type 2 diabetes. These 'novel' effects are most probably derived from the bile acid-binding properties of sevelamer. The proposed potential is supported by the approval of the bile acid sequestrant colesevelam in the United States for the treatment of type 2 diabetes and hypercholesterolaemia. This article offers a brief review on the effects of sevelamer and a perspective on the potential mechanisms behind the glucose-lowering effect of the drug.

Intestinal microbiota and type 2 diabetes: From mechanism insights to therapeutic perspective

The incidence of type 2 diabetes (T2DM) is rapidly increasing worldwide. However, the pathogenesis of T2DM has not yet been well explained. Recent evidence suggests that the intestinal microbiota composition is associated with obesity and T2DM. In this review, we provide an overview about the mechanisms underlying the role of intestinal microbiota in the pathogenesis of T2DM. There is clear evidence that the intestinal microbiota influences the host through its effect on body weight, bile acid metabolism, proinflammatory activity and insulin resistance, and modulation of gut hormones. Modulating gut microbiota with the use of probiotics, prebiotics, antibiotics, and fecal microbiota transplantation may have benefits for improvement in glucose metabolism and insulin resistance in the host. Further studies are required to increase our understanding of the complex interplay between intestinal microbiota and the host with T2DM. Further studies may be able to boost the development of new effective therapeutic approaches for T2DM.