Glucose-lowering effects and mechanisms of the bile acid-sequestering resin sevelamer

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.

Colesevelam has no acute effect on postprandial GLP-1 levels but abolishes gallbladder refilling

OBJECTIVE

Colesevelam, a bile acid sequestrant approved for the treatment of hypercholesterolaemia, improves glycaemic control in type 2 diabetes. We hypothesised that single-dose colesevelam increases postprandial GLP-1 secretion, thus, reducing postprandial glucose excursions in individuals with type 2 diabetes. Further, we explored the effects of single-dose colesevelam on ultrasonography-assessed postprandial gallbladder motility, paracetamol absorption (proxy for gastric emptying), and circulating factors known to affect gallbladder motility.

METHODS

In a randomised, double-blind, placebo-controlled crossover study, 12 individuals with type 2 diabetes (mean ± SD: age 61 ± 8.8 years; body mass index 29.8 ± 3.0 kg/m2) were subjected to 4 mixed meal tests on separate days; 2 with orally administered colesevelam (3.75 g) and 2 with placebo, with intravenous infusion of the GLP-1 receptor antagonist exendin(9-39)NH2 or saline.

RESULTS

Single-dose colesevelam had no effect on postprandial concentrations of glucose (P = .786), C-peptide (P = .440), or GLP-1 (P = .729), and exendin(9-39)NH2 administration revealed no GLP-1-mediated effects of colesevelam. Colesevelam did not affect gallbladder emptying but abolished gallbladder refilling (P = .001), increased postprandial cholecystokinin (CCK) secretion (P = .010), and decreased postprandial serum concentrations of fibroblast growth factor 19 (FGF19) (P = .035) and bile acids (P = .043).

CONCLUSION

Single-dose colesevelam had no effect on postprandial GLP-1 responses or glucose tolerance but disrupted postprandial gallbladder refilling by increasing CCK secretion and reducing circulating concentrations of FGF19 and bile acids. These findings leave the antidiabetic actions of colesevelam unresolved but provide mechanistic insights into its effect on gallbladder motility.

Sevelamer Use and Mortality in People with Chronic Kidney Disease Stages 4 and 5 Not on Dialysis

Rationale and objective: Data suggest that non-calcium-based binders, and specifically sevelamer, may lead to lower rates of death when compared with calcium-based binders in end-stage renal disease (ESRD) patients. However, the association between sevelamer use and mortality for those with non-dialysis-dependent chronic kidney disease (NDD-CKD) patients has been uncertain. Study design: Our research is presented in a prospective cohort study. Setting and participants: A total of 966 participants with NDD-CKD stages 4-5 were enrolled in the PECERA study from 12 centers in Spain. Exposure: The participants were treated with sevelamer. Outcome: This study yielded all-cause and cardiovascular mortality outcomes. Analytical approach: We conducted an association analysis between mortality and sevelamer use with time-dependent Cox proportional hazards models. Results: After a median follow-up of 29 months (IQR: 13-36 months), death occurred in 181 participants (19%), with cardiovascular (n = 95, 53%) being the leading cause of death. In a multivariable model, the adjusted hazard ratios (HRs) for patients under sevelamer treatment were 0.44 (95% CI, 0.22 to 0.88) and 0.37 (95% CI, 0.18 to 0.75) for all-cause and cardiovascular mortality, respectively, compared with those of untreated patients. Limitations: Some limitations include potential confusion via indication bias; causal statements about these associations cannot be made due to the observational nature of this study. Conclusions: In this prospective NDD-CKD cohort study, the administration of sevelamer was independently associated with lower all-cause and cardiovascular mortality, suggesting that non-calcium-based phosphate binders might be the first-line therapy for phosphate lowering in this population. Further interventional studies clarifying the risks and benefits of phosphate binders in NDD-CKD are warranted.

An Updated Perspective on the Dual-Track Model of Enterocyte Fat Metabolism

The small intestinal epithelium has classically been envisioned as a conduit for nutrient absorption, but appreciation is growing for a larger and more dynamic role for enterocytes in lipid metabolism. Considerable gaps remain in our knowledge of this physiology, but it appears that the enterocyte's structural polarization dictates its behavior in fat partitioning, treating fat differently based on its absorption across the apical versus the basolateral membrane. In this review, we synthesize existing data and thought on this dual-track model of enterocyte fat metabolism through the lens of human integrative physiology. The apical track includes the canonical pathway of dietary lipid absorption across the apical brush-border membrane, leading to packaging and secretion of those lipids as chylomicrons. However, this track also reserves a portion of dietary lipid within cytoplasmic lipid droplets for later uses, including the "second-meal effect," which remains poorly understood. At the same time, the enterocyte takes up circulating fats across the basolateral membrane by mechanisms that may include receptor-mediated import of triglyceride-rich lipoproteins or their remnants, local hydrolysis and internalization of free fatty acids, or enterocyte de novo lipogenesis using basolaterally absorbed substrates. The ultimate destinations of basolateral-track fat may include fatty acid oxidation, structural lipid synthesis, storage in cytoplasmic lipid droplets, or ultimate resecretion, although the regulation and purposes of this basolateral track remain mysterious. We propose that the enterocyte integrates lipid flux along both of these tracks in order to calibrate its overall program of lipid metabolism.

MiR-203 is an anti-obese miRNA by targeting ASBT

Obesity is characterized by excessive fat deposition within the body. Bile acids (BA) are important regulators for controlling the absorption of lipid. Here we show that miR-203 exerts weight-loss and lipid-lowering effects by increasing total BA excretion in obese rodents. miR-203 overexpression transgenic mice are resistant to high-fat diet (HFD)-induced obesity and dyslipidemia. Moreover, the knockdown of miR-203 deteriorates metabolic disorders. ASBT plays important role in regulating BA homeostasis and is a direct target of miR-203. In human intestinal epithelial cells, overexpression of miR-203 decreases the cellular uptake of BA by inhibiting ASBT. Furthermore, TCF7L2 is downregulated in obese mice and acts as a transcription factor of miR-203. The ASBT mRNA level was positively correlated with the body mass index (BMI) of population, while the miR-203 level was negatively associated with BMI. Taken together, these data suggest miR-203 could be a new therapeutic BA regulator for obesity and dyslipidemia.

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miR-203 is downregulated in obese rodents and overweight/obese population

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ASBT is a direct target of miR-203 in obesity

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TCF7L2 acts as an upstream activator of miR-203 in obesity

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miR-203 ameliorates obesity and dyslipidemia by increasing TBAs and lipids excretion

Pharmacomicrobiomics in Western Medicine and Traditional Chinese Medicine in Type 2 Diabetes

Pharmacomicrobiomics refers to the interactions between foreign compounds and the gut microbiome resulting in heterogeneous efficacy, side effects, and toxicity of the compound concerned. Glucose lowering drugs reduce blood glucose by modulating insulin secretion and its actions as well as redistributing energy disposal. Apart from genetic, ecological, and lifestyle factors, maintaining an equilibrium of the whole gut microbiome has been shown to improve human health. Microbial fingerprinting using faecal samples indicated an 'invisible phenotype' due to different compositions of microbiota which might orchestrate the interactions between patients' phenotypes and their responses to glucose-lowering drugs. In this article, we summarize the current evidence on differences in composition of gut microbiota between individuals with type 2 diabetes (T2D) and healthy individuals, the disruption of the balance of beneficial and pathogenic microbiota was shown in patients with T2D and how Western Medicine (WM) and Traditional Chinese Medicine (TCM) might re-shape the gut microbiota with benefits to the host immunity and metabolic health. We particularly highlighted the effects of both WM and TCM increase the relative abundance of health promoting bacteria, such as, Akkermansia muciniphila, Blautia, and Bifidobacterium adolescentis, and which have been implicated in type 2 diabetes (T2D). Several lines of evidence suggested that TCM might complement the efficacy of WM through alteration of microbiota which warrants further investigation in our pursuit of prevention and control of T2D.

Systematic review and meta-analysis of potential pleiotropic effects of sevelamer in chronic kidney disease: Beyond phosphate control

Sevelamer, has been shown to have many pleiotropic actions on lipid panel, various inflammatory markers, and blood glucose levels in chronic kidney disease patients. We conducted a systematic review and meta-analysis to compare these pleiotropic effects of sevelamer to other phosphate binders used in chronic kidney disease patients. The relevant randomized controlled trials published from 1 January 2001 to 31 November 2019 on the following databases: Cochrane Central Register of Controlled Trials published in The Cochrane Library, PubMed, Scopus and Google Scholar were identified. All the included studies were independently assessed for eligibility and risk of bias. The modified data extraction form of Cochrane was used. This review included 44 studies for qualitative analysis and 28 reports for quantitative analysis. A meta-analysis of three studies (n = 180) showed that glycated haemoglobin had significantly decreased in sevelamer-treated patients (MD: 0.5%; p = <.001). Compared with calcium-based phosphate binders, sevelamer showed a significant reduction in low-density lipoprotein (MD: -19.43 mg/dL; p = <.001) and total cholesterol (MD: -19.98 mg/dL; p < .001). A significant increase in high-density lipoprotein (MD: 1.29 mg/dL; p = .05) was also prominent in sevelamer treated patients. However, we were not able to observe a significant change in other biochemical parameters such as TG, CRP, hs-CRP, FGF-23, IL-6 and albumin as, no statistically significant difference was observed.

The Impact of Microbial Composition on Postprandial Glycaemia and Lipidaemia: A Systematic Review of Current Evidence

Postprandial hyperglycaemia is associated with increased risk of cardiovascular disease. Recent studies highlight the role of the gut microbiome in influencing postprandial glycaemic (PPG) and lipidaemic (PPL) responses. The authors of this review sought to address the question: “To what extent does individual gut microbiome diversity and composition contribute to PPG and PPL responses?”. CINAHL Plus, PubMed, Web of Science, and the Cochrane Central Register of Controlled Trials (CENTRAL) databases were searched from January 2010 to June 2020. Following screening, 22 studies were eligible to be included in the current review. All trials reported analysis of gut microbiome diversity and composition and PPG and/or PPL. Results were reported according to the ‘Preferred Reporting Items for Systematic Reviews and Meta-Analysis’ (PRISMA) statement. Individual microbiota structure was found to play a key role in determining postprandial metabolic responses in adults and is attributed to a complex interplay of diet, microbiota composition, and metagenomic activity, which may be predicted by metagenomic analysis. Alterations of gut microbiota, namely relative abundance of bacterial phylum Actinobacteria and Proteobacteria, along with Enterobacteriaceae, were associated with individual variation in postprandial glycaemic response in adults. The findings of the current review present new evidence to support a personalised approach to nutritional recommendations and guidance for optimal health, management, and treatment of common metabolic disorders. In conclusion, personalised nutrition approaches based on individual microbial composition may improve postprandial regulation of glucose and lipids, providing a potential strategy to ameliorate cardiometabolic health outcomes.

Phosphate, Microbiota and CKD

Phosphate is a key uremic toxin associated with adverse outcomes. As chronic kidney disease (CKD) progresses, the kidney capacity to excrete excess dietary phosphate decreases, triggering compensatory endocrine responses that drive CKD-mineral and bone disorder (CKD-MBD). Eventually, hyperphosphatemia develops, and low phosphate diet and phosphate binders are prescribed. Recent data have identified a potential role of the gut microbiota in mineral bone disorders. Thus, parathyroid hormone (PTH) only caused bone loss in mice whose microbiota was enriched in the Th17 cell-inducing taxa segmented filamentous bacteria. Furthermore, the microbiota was required for PTH to stimulate bone formation and increase bone mass, and this was dependent on bacterial production of the short-chain fatty acid butyrate. We review current knowledge on the relationship between phosphate, microbiota and CKD-MBD. Topics include microbial bioactive compounds of special interest in CKD, the impact of dietary phosphate and phosphate binders on the gut microbiota, the modulation of CKD-MBD by the microbiota and the potential therapeutic use of microbiota to treat CKD-MBD through the clinical translation of concepts from other fields of science such as the optimization of phosphorus utilization and the use of phosphate-accumulating organisms.

Impact drugs targeting cardiometabolic risk on the gut microbiota

PURPOSE OF REVIEW

Alterations in the gut microbiome composition or function are associated with risk factors for cardiometabolic diseases, including hypertension, hyperlipidemia and hyperglycemia. Based on recent evidence that also oral medications used to treat these conditions could alter the gut microbiome composition and function and, vice versa, that the gut microbiome could affect the efficacy of these treatments, we reviewed the literature on these observed interactions.

RECENT FINDINGS

While the interaction of metformin with the gut microbiome has been studied most, other drugs that target cardiometabolic risk are gaining attention and often showed associations with alterations in microbiome-related features, including alterations in specific microbial taxa or pathways, microbiome composition or microbiome-derived metabolites, while the gut microbiome was also involved in drug metabolism and drug efficacy. As for metformin, for some of them even a potential therapeutic effect via the gut microbiome is postulated. However, exact mechanisms remain to be elucidated.

SUMMARY

There is growing interest in clarifying the interactions between the gut microbiome and drugs to treat hypertension, hyperlipidemia and hyperglycemia as well as the first pass effect of microbiome on drug efficacy. While mostly analysed in animal models, also human studies are gaining more and more traction. Improving the understanding of the gut microbiome drug interaction can provide clinical directions for therapy by optimizing drug efficacy or providing new targets for drug development.

Effects of Manipulating Circulating Bile Acid Concentrations on Postprandial GLP-1 Secretion and Glucose Metabolism After Roux-en-Y Gastric Bypass

BACKGROUND

Altered bile acid (BA) turnover has been suggested to be involved in the improved glucose regulation after Roux-en-Y gastric bypass (RYGB), possibly via stimulation of GLP-1 secretion. We investigated the role of exogenous as well as endogenous BAs for GLP-1 secretion after RYGB by administering chenodeoxycholic acid (CDCA) and the BA sequestrant colesevelam (COL) both in the presence and the absence of a meal stimulus.

METHODS

Two single-blinded randomized cross-over studies were performed. In study 1, eight RYGB operated participants ingested 200 ml water with 1) CDCA 1.25 g or 2) CDCA 1.25 g + colesevelam 3.75 g on separate days. In study 2, twelve RYGB participants ingested on separate days a mixed meal with addition of 1) CDCA 1.25 g, 2) COL 3.75 g or 3) COL 3.75 g × 2, or 4) no additions.

RESULTS

In study 1, oral intake of CDCA increased circulating BAs, GLP-1, C-peptide, glucagon, and neurotensin. Addition of colesevelam reduced all responses. In study 2, addition of CDCA enhanced meal-induced increases in plasma GLP-1, glucagon and FGF-19 and lowered plasma glucose and C-peptide concentrations, while adding colesevelam lowered circulating BAs but did not affect meal-induced changes in plasma glucose or measured gastrointestinal hormones.

CONCLUSION

In RYGB-operated persons, exogenous CDCA enhanced meal-stimulated GLP-1 and glucagon secretion but not insulin secretion, while the BA sequestrant colesevelam decreased CDCA-stimulated GLP-1 secretion but did not affect meal-stimulated GLP-1, C-peptide or glucagon secretion, or glucose tolerance. These findings suggest a limited role for endogenous bile acids in the acute regulation of postprandial gut hormone secretion or glucose metabolism after RYGB.

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 Acid Sequestrant, Sevelamer Ameliorates Hepatic Fibrosis with Reduced Overload of Endogenous Lipopolysaccharide in Experimental Nonalcoholic Steatohepatitis

Despite the use of various pharmacotherapeutic strategies, fibrosis due to nonalcoholic steatohepatitis (NASH) remains an unsatisfied clinical issue. We investigated the effect of sevelamer, a hydrophilic bile acid sequestrant, on hepatic fibrosis in a murine NASH model. Male C57BL/6J mice were fed a choline-deficient, L-amino acid-defined, high-fat (CDHF) diet for 12 weeks with or without orally administered sevelamer hydrochloride (2% per diet weight). Histological and biochemical analyses revealed that sevelamer prevented hepatic steatosis, macrophage infiltration, and pericellular fibrosis in CDHF-fed mice. Sevelamer reduced the portal levels of total bile acid and inhibited both hepatic and intestinal farnesoid X receptor activation. Gut microbiome analysis demonstrated that sevelamer improved a lower α-diversity and prevented decreases in Lactobacillaceae and Clostridiaceae as well as increases in Desulfovibrionaceae and Enterobacteriaceae in the CDHF-fed mice. Additionally, sevelamer bound to lipopolysaccharide (LPS) in the intestinal lumen and promoted its fecal excretion. Consequently, the sevelamer treatment restored the tight intestinal junction proteins and reduced the portal LPS levels, leading to the suppression of hepatic toll-like receptor 4 signaling pathway. Furthermore, sevelamer inhibited the LPS-mediated induction of fibrogenic activity in human hepatic stellate cells in vitro. Collectively, sevelamer inhibited the development of murine steatohepatitis by reducing hepatic LPS overload.

GIP and GLP-1 Receptor Antagonism During a Meal in Healthy Individuals

CONTEXT

The actions of both endogenous incretin hormones during a meal have not previously been characterized.

OBJECTIVE

Using specific receptor antagonists, we investigated the individual and combined contributions of endogenous glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) to postprandial glucose metabolism, energy expenditure, and gallbladder motility.

DESIGN

Randomized, double-blinded, placebo-controlled, crossover design.

SETTING

On four separate days, four liquid mixed meal tests (1894 kJ) over 270 minutes (min).

PATIENTS OR OTHER PARTICIPANTS

Twelve healthy male volunteers.

INTERVENTIONS

Infusions of the GIP receptor antagonist GIP(3-30)NH2 (800 pmol/kg/min), the GLP-1 receptor antagonist exendin(9-39)NH2 (0-20 min: 1000 pmol/kg/min; 20-270 min: 450 pmol/kg/min), GIP(3-30)NH2+exendin(9-39)NH2, or placebo/saline.

MAIN OUTCOME MEASURE

Baseline-subtracted area under the curve (bsAUC) of C-peptide.

RESULTS

Infusion of GIP(3-30)NH2+exendin(9-39)NH2 significantly increased plasma glucose excursions (bsAUC: 261 ± 142 mmol/L × min) during the liquid mixed meals compared with GIP(3-30)NH2 (180 ± 141 mmol/L × min; P = 0.048), exendin(9-39)NH2 (171 ± 114 mmol/L × min; P = 0.046), and placebo (116 ± 154 mmol/L × min; P = 0.015). Correspondingly, C-peptide:glucose ratios during GIP(3-30)NH2+exendin(9-39)NH2 infusion were significantly lower than during GIP(3-30)NH2 (P = 0.0057), exendin(9-39)NH2 (P = 0.0038), and placebo infusion (P = 0.014). GIP(3-30)NH2 resulted in significantly lower AUCs for glucagon than exendin(9-39)NH2 (P = 0.0417). Gallbladder ejection fraction was higher during GIP(3-30)NH2 compared with placebo (P = 0.004). For all interventions, energy expenditure and respiratory quotient were similar.

CONCLUSIONS

Endogenous GIP and GLP-1 lower postprandial plasma glucose excursions and stimulate insulin secretion but only endogenous GIP affects gallbladder motility. The two incretin hormones potentiate each other's effects in the control of postprandial glycemia in healthy men.

Changes in oxidative nucleic acid modifications and inflammation following one-week treatment with the bile acid sequestrant sevelamer: Two randomised, placebo-controlled trials

AIMS

Sevelamer has been reported to have anti-oxidative and anti-inflammatory effects as well as effects on glycaemic control and plasma lipids. The aim of this study was to determine the effects of one-week treatment with sevelamer on oxidative nucleic acid modifications and inflammation markers.

METHODS

Two double-blinded studies including 30 patients with type 2 diabetes (T2D) and 20 healthy individuals were conducted. Participants were randomised to one week of treatment with sevelamer (1600 mg three times daily) or placebo. RNA and DNA oxidation, measured by urinary excretion of 8-oxo-7,8-dihydroguanosine(8-oxoGuo) and (8-oxo-7,8-dihydro-2'-deoxyguanosine(8-oxodG), and markers of inflammation were determined before and after the intervention.

RESULTS

In patients with T2D there was no significant placebo-corrected reduction in 8-oxoGuo or 8-oxodG. However, a reduction in 8-oxoGuo was observed within the group treated with sevelamer (∆8-oxoGuo/creatinine (median[IQR]): -0.04 [-0.24; 0.01] nmol/mmol, p = 0.02). A sevelamer-mediated reduction in interleukin-2 (p = 0.04) and a trend towards reduction in interleukin-6 (p = 0.053) were found in patients with T2D.

CONCLUSIONS

This study reveals a potential effect of sevelamer treatment on inflammation and possible oxidative RNA modifications. The potential protective effects of sevelamer in terms of cardiovascular disease in patients with T2D need further investigation.

Gluco-Metabolic Effects of Pharmacotherapy-Induced Modulation of Bile Acid Physiology

CONTEXT

The discovery and characterization of the bile acid specific receptors farnesoid X receptor (FXR) and Takeda G protein-coupled receptor 5 (TGR5) have facilitated a wealth of research focusing on the link between bile acid physiology and glucose metabolism. Modulation of FXR and TGR5 activation have been demonstrated to affect the secretion of glucagon-like peptide 1, insulin, and glucagon as well as energy expenditure and gut microbiota composition, with potential beneficial effects on glucose metabolism.

EVIDENCE ACQUISITION

A search strategy based on literature searches in on PubMed with various combinations of the key words FXR, TGR5, agonist, apical sodium-dependent bile acid transporter (ASBT), bile acid sequestrant, metformin, and glucose metabolism has been applied to obtain material for the present review. Furthermore, manual searches including scanning of reference lists in relevant papers and conference proceedings have been performed.

EVIDENCE SYNTHESIS

This review provides an outline of the link between bile acid and glucose metabolism, with a special focus on the gluco-metabolic impact of treatment modalities with modulating effects on bile acid physiology; including FXR agonists, TGR5 agonists, ASBT inhibitors, bile acid sequestrants, and metformin.

CONCLUSIONS

Any potential beneficial gluco-metabolic effects of FXR agonists remain to be established, whereas the clinical relevance of TGR5-based treatment modalities seems limited because of substantial safety concerns of TGR5 agonists observed in animal models. The glucose-lowering effects of ASBT inhibitors, bile acid sequestrants, and metformin are at least partly mediated by modulation of bile acid circulation, which might allow an optimization of these bile acid-modulating treatment modalities. (J Clin Endocrinol Metab XX: 00-00, 2019).

Phosphate Binders and Nonphosphate Effects in the Gastrointestinal Tract

Phosphate binders are commonly prescribed in patients with end-stage kidney disease to prevent and treat hyperphosphatemia. These binders are usually associated with gastrointestinal distress, may bind molecules other than phosphate, and may alter the gut microbiota, altogether having systemic effects unrelated to phosphate control. Sevelamer is the most studied of the available binders for nonphosphate-related effects including binding to bile acids, endotoxins, gut microbiota-derived metabolites, and advanced glycation end products. Other binders (calcium- and noncalcium-based binders) may bind vitamins, such as vitamin K and folic acid. Moreover, the relatively new iron-based phosphate binders may alter the gut microbiota, as some of the iron or organic ligands may be used by the gastrointestinal bacteria. The objective of this narrative review is to provide the current evidence for the nonphosphate effects of phosphate binders on gastrointestinal function, nutrient and molecule binding, and the gut microbiome.

Strategies for Phosphate Control in Patients With CKD

Hyperphosphatemia is a common complication in patients with chronic kidney disease (CKD), particularly in those requiring renal replacement therapy. The importance of controlling serum phosphate has long been recognized based on observational epidemiological studies that linked increased phosphate levels to adverse outcomes and higher mortality risk. Experimental data further supported the role of phosphate in the development of bone and cardiovascular diseases. Recent advances in our understanding of the mechanisms involved in phosphate homeostasis have made it clear that the serum phosphate concentration depends on a complex interplay among the kidneys, intestinal tract, and bone, and is tightly regulated by a complex endocrine system. Moreover, the source of dietary phosphate and the use of phosphate-based additives in industrialized foods are additional factors that are of particular importance in CKD. Not surprisingly, the management of hyperphosphatemia is difficult, and, despite a multifaceted approach, it remains unsuccessful in many patients. An additional issue is the fact that the supposedly beneficial effect of phosphate lowering on hard clinical outcomes in interventional trials is a matter of ongoing debate. In this review, we discuss currently available treatment approaches for controlling hyperphosphatemia, including dietary phosphate restriction, reduction of intestinal phosphate absorption, phosphate removal by dialysis, and management of renal osteodystrophy, with particular focus on practical challenges and limitations, and on potential benefits and harms.