Non-systemic drugs: a critical review

Cryptosporidium PI(4)K inhibitor EDI048 is a gut-restricted parasiticidal agent to treat paediatric enteric cryptosporidiosis

Diarrhoeal disease caused by Cryptosporidium is a major cause of morbidity and mortality in young and malnourished children from low- and middle-income countries, with no vaccine or effective treatment. Here we describe the discovery of EDI048, a Cryptosporidium PI(4)K inhibitor, designed to be active at the infection site in the gastrointestinal tract and undergo rapid metabolism in the liver. By using mutational analysis and crystal structure, we show that EDI048 binds to highly conserved amino acid residues in the ATP-binding site. EDI048 is orally efficacious in an immunocompromised mouse model despite negligible circulating concentrations, thus demonstrating that gastrointestinal exposure is necessary and sufficient for efficacy. In neonatal calves, a clinical model of cryptosporidiosis, EDI048 treatment resulted in rapid resolution of diarrhoea and significant reduction in faecal oocyst shedding. Safety and pharmacological studies demonstrated predictable metabolism and low systemic exposure of EDI048, providing a substantial safety margin required for a paediatric indication. EDI048 is a promising clinical candidate for the treatment of life-threatening paediatric cryptosporidiosis.

The Use of Systemically Absorbed Drugs to Explore An In Vitro Bioequivalence Approach For Comparing Non-Systemically Absorbed Active Pharmaceutical Ingredients in Drug Products For Use in Dogs

PURPOSE

Currently, for veterinary oral formulations containing one or more active pharmaceutical ingredient (API) that are not systemically absorbed and act locally within the gastrointestinal (GI) tract, the use of terminal clinical endpoint bioequivalence (BE) studies is the only option for evaluating product BE. This investigation explored the use of a totality of evidence approach as an alternative to these terminal studies.

METHODS

Three formulations of tablets containing ivermectin plus praziquantel were manufactured to exhibit distinctly different in vitro release characteristics. Because these APIs are highly permeable, plasma drug concentrations served as a biomarker of in vivo dissolution. Tablets were administered to 27 healthy Beagle dogs (3-way crossover) and the rate and extent of exposure of each API for each formulation was compared in a pairwise manner. These results were compared to product relative in vitro dissolution profiles in 3 media. In vivo and in vitro BE predictions were compared.

RESULTS

In vivo/in vitro inconsistencies in product relative performance were observed with both compounds when considering product performance across the 3 dissolution media. Formulation comparisons flagged major differences that could explain this outcome.

CONCLUSIONS

The finding of an inconsistent in vivo/in vitro relationship confirmed that in vitro dissolution alone cannot assure product BE for veterinary locally acting GI products. However, when combined with a comparison of product composition and manufacturing method, this totality of evidence approach can successfully alert scientists to potential therapeutic inequivalence, thereby supporting FDA's efforts to Replace, Reduce, and/or Refine terminal animal studies.

Trust Your Gut: Strategies and Tactics for Intestinally Restricted Drugs

Non-absorbable small-molecule drugs targeted to the gut represent an alternative approach to safe, non-systemic therapeutics. Such drugs remain confined to the gastrointestinal tract upon oral dosing by virtue of their limited passive permeability, increasing the local concentration at the site of action while minimizing exposure elsewhere in the body. Herein we review the latest advances in the field of gut-restricted therapeutics, highlighting the different strategies and tactics that medicinal chemists have employed in pursuit of drugs with minimal intestinal absorption.

Small molecule inhibitors of intestinal epithelial anion exchanger SLC26A3 (DRA) with a luminal, extracellular site of action

The anion exchanger protein SLC26A3 (down-regulated in adenoma, DRA) is expressed in the luminal membrane of intestinal epithelial cells in colon, where it facilitates the absorption of Cl^- and oxalate. We previously identified a 4,8-dimethylcoumarin class of SLC26A3 inhibitors that act from the SLC26A3 cytoplasmic surface, and demonstrated their efficacy in mouse models of constipation and hyperoxaluria. Here, screening of 50,000 new compounds and 1740 chemical analogs of active compounds from the primary screen produced five novel classes of SLC26A3-selective inhibitors (1,3-dioxoisoindoline-amides; N-(5-sulfamoyl-1,3,4-thiadiazol-2-yl)acetamides; thiazolo-pyrimidin-5-ones; 3-carboxy-2-phenylbenzofurans and benzoxazin-4-ones) with IC₅₀ down to 100 nM. Kinetic washout and onset of action studies revealed an extracellular site of action for the thiazolo-pyrimidin-5-one and 3-carboxy-2-phenylbenzofuran inhibitors. Molecular docking computations revealed putative binding sites for these inhibitors. In a loperamide model of constipation in mice, orally administered 7-(2-chloro-phenoxymethyl)-3-phenyl-thiazolo [3,2-a]pyrimidin-5-one (3a) significantly increased stool weight, pellet number and water content. SLC26A3 inhibitors with an extracellular site of action offer the possibility of creating non-absorbable, luminally acting inhibitors with minimal systemic exposure following oral administration. Our findings also suggest that inhibitors of related SLC26 anion transporters with an extracellular site of action might be identified for pharmacological modulation of selected epithelial ion transport processes.

Design, Synthesis, and Biological Evaluation of a Novel Series of 4-Guanidinobenzoate Derivatives as Enteropeptidase Inhibitors with Low Systemic Exposure for the Treatment of Obesity

To discover a novel series of potent inhibitors of enteropeptidase, a membrane-bound serine protease localized to the duodenal brush border, 4-guanidinobenzoate derivatives were evaluated with minimal systemic exposure. The 1c docking model enabled the installation of an additional carboxylic acid moiety to obtain an extra interaction with enteropeptidase, yielding 2a. The oral administration of 2a significantly elevated the fecal protein output, a pharmacodynamic marker, in diet-induced obese (DIO) mice, whereas subcutaneous administration did not change this parameter. Thus, systemic exposure of 2a was not required for its pharmacological effects. Further optimization focusing on the in vitro IC₅₀ value and T_1/2, an indicator of dissociation time, followed by enhanced in vivo pharmacological activity based on the ester stability of the compounds, revealed two series of potent enteropeptidase inhibitors, a dihydrobenzofuran analogue ((S)-5b, SCO-792) and phenylisoxazoline (6b), which exhibited potent anti-obesity effects despite their low systemic exposure following their oral administration to DIO rats.

First-in-Human Evaluation of Oral Denatonium Acetate (ARD-101), a Potential Bitter Taste Receptor Agonist: A Randomized, Double-Blind, Placebo-Controlled Phase 1 Trial in Healthy Adults

Preclinical studies in animal models of obesity and inflammation have shown that oral administration of ARD-101, a potential TAS2R agonist, reduced food intake and body weight and downregulated inflammatory cytokines. We present results from a first-in-human phase 1 randomized, placebo-controlled trial that evaluated safety, pharmacokinetics, and pharmacodynamics of single or multiple ascending doses of oral ARD-101 (40, 100, and 240 mg) in healthy adults. A total of 43 subjects were randomly assigned and dosed to ARD-101 or placebo with 42 subjects completing the study treatment. ARD-101 was found to be >99% restricted to the gut with minimal systemic exposure, demonstrated a favorable safety profile, and was well tolerated at all dose levels. Blood samples taken 1 hour after administration showed that subjects dosed with 240 mg of ARD-101 had elevated circulating levels of several gut peptide hormones. It is postulated that ARD-101 activates enteroendocrine cells to achieve its effects regulating metabolism and inflammation. The phase 1 clinical results demonstrated safety of ARD-101 and indicated activation of gut peptide hormone release in healthy adults. Further clinical trials will evaluate ARD-101 in patients with metabolic and inflammatory disorders.

Exploratory studies with NX-13: oral toxicity and pharmacokinetics in rodents of an orally active, gut-restricted first-in-class therapeutic for IBD that targets NLRX1

Nucleotide-binding oligomerization domain, leucine rich repeat containing X1 (NLRX1) is an emerging therapeutic target for a spectrum of human diseases. NX-13 is a small molecule therapeutic designed to target and activate NLRX1 to induce immunometabolic changes resulting in lower inflammation and therapeutic responses in inflammatory bowel disease (IBD). This study investigates the safety of NX-13 in a seven-day, repeat-dose general toxicity study in male and female Sprague Dawley rats at oral doses of 500 and 1000 mg/kg. Weights, clinical signs, functional observational battery, clinical pathology and histopathology were used for evaluation. Daily oral dosing of NX-13 up to 1000 mg/kg did not result in any changes in weight, abnormal clinical signs or behavior. No significant differences were observed between treated and control rats in hematology or blood biochemistry. Histopathological evaluation of 12 tissues demonstrated no differences between controls and treated rats. There were no changes in weights of brain, heart, kidney, liver or spleen. Pharmacokinetic analysis of a single oral dose of NX-13 at 10 mg/kg in Sprague Dawley rats provided a maximum plasma concentration of 57 ng/mL at 0.5 h post-dose. Analysis of colon tissue after oral dosing with 1 and 10 mg/kg indicated high peak concentrations (10 and 100 µg/g, respectively) that scale in a dose-proportional manner. These experiments suggest that NX-13 is safe and well-tolerated in rats given oral doses as high as 1000 mg/kg with a favorable gastrointestinal localized pharmacokinetic profile, confirming NX-13 as a promising therapeutic for Crohn's disease and ulcerative colitis.

Molecular Design in Practice: A Review of Selected Projects in a French Research Institute That Illustrates the Link between Chemical Biology and Medicinal Chemistry

Chemical biology and drug discovery are two scientific activities that pursue different goals but complement each other. The former is an interventional science that aims at understanding living systems through the modulation of its molecular components with compounds designed for this purpose. The latter is the art of designing drug candidates, i.e., molecules that act on selected molecular components of human beings and display, as a candidate treatment, the best reachable risk benefit ratio. In chemical biology, the compound is the means to understand biology, whereas in drug discovery, the compound is the goal. The toolbox they share includes biological and chemical analytic technologies, cell and whole-body imaging, and exploring the chemical space through state-of-the-art design and synthesis tools. In this article, we examine several tools shared by drug discovery and chemical biology through selected examples taken from research projects conducted in our institute in the last decade. These examples illustrate the design of chemical probes and tools to identify and validate new targets, to quantify target engagement in vitro and in vivo, to discover hits and to optimize pharmacokinetic properties with the control of compound concentration both spatially and temporally in the various biophases of a biological system.

In Silico Prediction, Molecular Docking and Dynamics Studies of Steroidal Alkaloids of Holarrhena pubescens Wall. ex G. Don to Guanylyl Cyclase C: Implications in Designing of Novel Antidiarrheal Therapeutic Strategies

The binding of heat stable enterotoxin (STa) secreted by enterotoxigenic Escherichia coli (ETEC) to the extracellular domain of guanylyl cyclase c (ECD_GC-C) causes activation of a signaling cascade, which ultimately results in watery diarrhea. We carried out this study with the objective of finding ligands that would interfere with the binding of STa on ECD_GC-C. With this view in mind, we tested the biological activity of a alkaloid rich fraction of Holarrhena pubescens against ETEC under in vitro conditions. Since this fraction showed significant antibacterial activity against ETEC, we decided to test the screen binding affinity of nine compounds of steroidal alkaloid type from Holarrhena pubescens against extracellular domain (ECD) by molecular docking and identified three compounds with significant binding energy. Molecular dynamics simulations were performed for all the three lead compounds to establish the stability of their interaction with the target protein. Pharmacokinetics and toxicity profiling of these leads demonstrated that they possessed good drug-like properties. Furthermore, the ability of these leads to inhibit the binding of STa to ECD was evaluated. This was first done by identifying amino acid residues of ECD_GC-C binding to STa by protein-protein docking. The results were matched with our molecular docking results. We report here that holadysenterine, one of the lead compounds that showed a strong affinity for the amino acid residues on ECD_GC-C, also binds to STa. This suggests that holadysenterine has the potential to inhibit binding of STa on ECD and can be considered for future study, involving its validation through in vitro assays and animal model studies.

Larazotide acetate: a pharmacological peptide approach to tight junction regulation

Larazotide acetate (LA) is a single-chain peptide of eight amino acids that acts as a tight junction regulator to restore intestinal barrier function. LA is currently being studied in phase III clinical trials and is orally administered to adult patients with celiac disease as an adjunct therapeutic to enhance intestinal barrier function that has been disrupted by gliadin-induced immune reactivity. Mechanistically, LA is thought to act as a zonulin antagonist to reduce zonulin-induced increases in barrier permeability and has been associated with the redistribution and rearrangement of tight junction proteins and actin filaments to restore intestinal barrier function. More recently, LA has been linked to inhibition of myosin light chain kinase, which likely reduces tension on actin filaments, thereby facilitating tight junction closure. Small (rodent) and large (porcine) animal studies have been conducted that demonstrate the importance of LA as a tight junction regulatory peptide in conditions other than celiac disease, including collagen-induced arthritis in mice and intestinal ischemic injury in pigs.

Effect of the Phosphate Binders Sevelamer Carbonate and Calcium Acetate on the Pharmacokinetics of Roxadustat After Concomitant or Time-Separated Administration in Healthy Individuals

PURPOSE

Roxadustat, a hypoxia-inducible factor prolyl hydroxylase inhibitor, treats anemia in chronic kidney disease. Hyperphosphatemia, a common complication in chronic kidney disease, is treated with phosphate binders (PBs). This study in healthy individuals investigated the effect of 2 PBs, sevelamer carbonate and calcium acetate, on the pharmacokinetic properties of a single oral dose of roxadustat administered concomitantly or with a time lag.

METHODS

This 2-part, Phase I study was conducted with an open-label, randomized, 3-way (part 1) or 5-way (part 2) crossover design, with 5-day treatment periods. On day 1 of each period, participants received 200 mg roxadustat administered alone or (1) concomitantly with sevelamer carbonate (2400 mg) or calcium acetate (1900 mg) (part 1) or (2) 1 hour before or 1, 2, or 3 hours after sevelamer carbonate (part 2A) or calcium acetate (part 2B); 5 additional PB doses were administered during 2 days. In both parts, PBs were administered with meals. Primary pharmacokinetic variables were AUC_0-∞ and C_max. FINDINGS: Twenty-four individuals were randomized in part 1; 60 individuals were randomized in part 2 (part 2A, n = 30; part 2B, n = 30). All participants completed the study in part 1; 28 and 27 individuals completed the study in part 2A and part 2B, respectively. Compared with roxadustat alone, concomitant sevelamer carbonate and calcium acetate administration reduced roxadustat's AUC_0-∞ by 67% (90% CI, 63.5%-69.3%) and 46% (90% CI, 41.7%-50.9%), respectively, and reduced roxadustat's C_max by 66% (90% CI, 61.6%-69.4%) and 52% (90% CI, 46.2%-57.2%), respectively. This effect was attenuated when roxadustat and PB administration occurred with a time lag. Roxadustat's AUC_0-∞ was reduced by 41% and 22% to 25%, respectively, when roxadustat was administered 1 hour before or 1 to 3 hours after sevelamer carbonate and by 31% and 14% to 18%, respectively, when administered 1 hour before or 1 to 3 hours after calcium acetate. Roxadustat's C_max was reduced by 26% and 12%, respectively, when roxadustat was administered 1 hour before and 1 hour after sevelamer carbonate; it was reduced by 19% when administered 1 hour before calcium acetate and was not affected when administered 1 hour after. Roxadustat was well tolerated.

IMPLICATIONS

Concomitant administration of roxadustat with sevelamer carbonate or calcium acetate reduced exposure to roxadustat in healthy individuals. This effect was attenuated when roxadustat was administered ≥1 hour before or after either PB. Results from this study helped inform dosing and administration guidelines aimed at reducing interactions between roxadustat and these PBs. (Clin Ther. 2021;XX:XXX-XXX) © 2021 Elsevier HS Journals, Inc.

Synthetic Approaches to the New Drugs Approved during 2019

New drugs introduced to the market are privileged structures having affinities for biological targets implicated in human diseases and conditions. These new chemical entities (NCEs), particularly small molecules and antibody-drug conjugates, provide insight into molecular recognition and simultaneously function as leads for the design of future medicines. This review is part of a continuing series presenting the most likely process-scale synthetic approaches to 40 NCEs approved for the first time anywhere in the world in 2019.

Beyond the Rule of 5: Impact of PEGylation with Various Polymer Sizes on Pharmacokinetic Properties, Structure-Properties Relationships of mPEGylated Small Agonists of TGR5 Receptor

PEGylation of therapeutic agents is known to improve the pharmacokinetic behavior of macromolecular drugs and nanoparticles. In this work, we performed the conjugation of polyethylene glycols (220-5000 Da) to a series of non-steroidal small agonists of the bile acids receptor TGR5. A suitable anchoring position on the agonist was identified to retain full agonistic potency with the conjugates. We describe herein an extensive structure-properties relationships study allowing us to finely describe the non-linear effects of the PEG length on the physicochemical as well as the in vitro and in vivo pharmacokinetic properties of these compounds. When appending a PEG of suitable length to the TGR5 pharmacophore, we were able to identify either systemic or gut lumen-restricted TGR5 agonists.

Inhibition of sodium-proton-exchanger subtype 3-mediated sodium absorption in the gut: A new antihypertensive concept

Arterial hypertension is one of the main contributors to cardiovascular diseases, including stroke, heart failure, and coronary heart disease. Salt plays a major role in the regulation of blood pressure and is one of the most critical factors for hypertension and stroke. At the individual level, effective salt reduction is difficult to achieve and available methods for managing sodium balance are lacking for many patients. As part of the ingested food, salt is absorbed in the gastrointestinal tract by the sodium proton exchanger subtype 3 (NHE3 also known as Slc9a3), influencing extracellular fluid volume and blood pressure. In this review, we discuss the beneficial effects of pharmacological inhibition of NHE3-mediated sodium absorption in the gut and focus on the effect on blood pressure and end-organ damage.

Bioformulative concepts on intracellular organ specific bioavailability

Bioavailability is an ancient but effective terminology by which the entire therapeutic efficacy of a drug directly or indirectly relays. Despite considering general plasma bioavailability, specific organ/tissue bioavailability will pave the path to broad spectrum dose calculation. Clear knowledge and calculative vision on bioavailability can improve the research and organ-targeting phenomenon. This article comprises a detailed introduction on bioavailability along with regulatory aspects, kinetic data and novel bioformulative approaches to achieve improved organ specific bioavailability, which may not be readily related to blood plasma bioavailability.

Lead optimization and efficacy evaluation of quinazoline-based BET family inhibitors for potential treatment of cancer and inflammatory diseases

Extensive optimization of quinazoline-based lead 8 is described. The structure-activity relationship studies indicate the S-configuration is preferred for the phenylmorpholine substitution. Together with incorporation of a (2-hydroxyl-2-methylpropyl)pyrazole moiety at the 2-position leads to analogs with comparable potency and marked improvement in the pharmacokinetic profile over our previously reported lead compounds. Further in vivo efficacy studies in Kasumi-1 xenograft mouse model demonstrates that the selected inhibitors are well tolerated and highly efficacious in the inhibition of tumor growth. Additionally, the representative analog 19 also demonstrated significant improvement of arthritis severity in a collagen-induced arthritis (CIA) mouse model. These results indicate potential use of these quinazoline-based BET inhibitors for treatment of cancer and inflammatory diseases. A brief discussion of the co-crystallized structure of 19 with BRD4 (BD1) is also highlighted.

Identification of novel small molecule inhibitors for solute carrier SGLT1 using proteochemometric modeling

Sodium-dependent glucose co-transporter 1 (SGLT1) is a solute carrier responsible for active glucose absorption. SGLT1 is present in both the renal tubules and small intestine. In contrast, the closely related sodium-dependent glucose co-transporter 2 (SGLT2), a protein that is targeted in the treatment of diabetes type II, is only expressed in the renal tubules. Although dual inhibitors for both SGLT1 and SGLT2 have been developed, no drugs on the market are targeted at decreasing dietary glucose uptake by SGLT1 in the gastrointestinal tract. Here we aim at identifying SGLT1 inhibitors in silico by applying a machine learning approach that does not require structural information, which is absent for SGLT1. We applied proteochemometrics by implementation of compound- and protein-based information into random forest models. We obtained a predictive model with a sensitivity of 0.64 ± 0.06, specificity of 0.93 ± 0.01, positive predictive value of 0.47 ± 0.07, negative predictive value of 0.96 ± 0.01, and Matthews correlation coefficient of 0.49 ± 0.05. Subsequent to model training, we applied our model in virtual screening to identify novel SGLT1 inhibitors. Of the 77 tested compounds, 30 were experimentally confirmed for SGLT1-inhibiting activity in vitro, leading to a hit rate of 39% with activities in the low micromolar range. Moreover, the hit compounds included novel molecules, which is reflected by the low similarity of these compounds with the training set (< 0.3). Conclusively, proteochemometric modeling of SGLT1 is a viable strategy for identifying active small molecules. Therefore, this method may also be applied in detection of novel small molecules for other transporter proteins.

Pharmacodynamics, Safety, and Tolerability of the NHE3 Inhibitor Tenapanor: Two Trials in Healthy Volunteers

Background

Tenapanor, a small molecule with minimal systemic availability, is a first-in-class sodium/hydrogen exchanger 3 (NHE3) inhibitor that acts in the gut. Here, we evaluate the pharmacodynamics and safety of tenapanor in healthy adults.

Methods

Two phase I, single-center, randomized, double-blind, placebo-controlled studies were performed. The first study assessed single-ascending oral tenapanor doses of 10, 50, 150, 450, and 900 mg (n = 8 per group; six tenapanor, two placebo) and multiple ascending doses over 7 days of 3, 10, 30, and 100 mg q.d. (n = 10 per group; eight tenapanor, two placebo). In the second study, different tenapanor regimens were evaluated over 7 days (n = 15 per group; 12 tenapanor, three placebo): 15 mg twice daily (b.i.d.), 30 mg once daily (q.d.), 30 mg b.i.d., 30 mg three times daily (t.i.d.), 60 mg b.i.d., escalating b.i.d. dose (daily total 30–90 mg), 30 mg b.i.d. with psyllium.

Results

Tenapanor produced generally dose-dependent increases in stool sodium excretion and decreases in urinary sodium excretion versus placebo; in addition, twice-daily dosing appeared to have a greater effect on sodium absorption than once-daily dosing with an equivalent daily dose. Tenapanor softened stool consistency and increased stool frequency and weight from baseline versus placebo. Tenapanor concentrations were below the quantification limit (0.5 ng/ml) in 98.5% of 895 plasma samples. Adverse events were mild or moderate in severity, and were typically gastrointestinal in nature. There were no clinically relevant changes in serum electrolytes.

Conclusions

Tenapanor was well tolerated and resulted in reduced intestinal sodium absorption and softer stool consistency versus placebo. Systemic exposure to tenapanor was minimal. These results support potential use of tenapanor in patients who could benefit from modification of gastrointestinal sodium balance.

ClinicalTrials.gov identifiers

NCT02819687, NCT02796131.

Electronic supplementary material

The online version of this article (10.1007/s40261-017-0614-0) contains supplementary material, which is available to authorized users.

Polymeric bile acid sequestrants: Review of design, in vitro binding activities, and hypocholesterolemic effects

Polymeric bile acid sequestrants (BAS) have recently attracted much attention as lipid-lowering agents. These non-absorbable materials specifically bind bile acids (BAs) in the intestine, preventing bile acid (BA) reabsorption into the blood through enterohepatic circulation. Therefore, it is important to understand the structure-property relationships between the polymer sequestrant and its ability to bind specific BAs molecules. In this review, we describe pleiotropic effects of bile acids, and we focus on BAS with various molecular architectures that result in different mechanisms of BA sequestration. Here, we present 1) amphiphilic polymers based on poly(meth)acrylates, poly(meth)acrylamides, polyalkylamines and polyallylamines containing quaternary ammonium groups, 2) cyclodextrins, and 3) BAS prepared via molecular imprinting methods. The synthetic approaches leading to individual BAS preparation, as well as results of their in vitro BA binding activities and in vivo lipid-lowering activities, are discussed.

Development and Characterization of a Human and Mouse Intestinal Epithelial Cell Monolayer Platform

We describe the development and characterization of a mouse and human epithelial cell monolayer platform of the small and large intestines, with a broad range of potential applications including the discovery and development of minimally systemic drug candidates. Culture conditions for each intestinal segment were optimized by correlating monolayer global gene expression with the corresponding tissue segment. The monolayers polarized, formed tight junctions, and contained a diversity of intestinal epithelial cell lineages. Ion transport phenotypes of monolayers from the proximal and distal colon and small intestine matched the known and unique physiology of these intestinal segments. The cultures secreted serotonin, GLP-1, and FGF19 and upregulated the epithelial sodium channel in response to known biologically active agents, suggesting intact secretory and absorptive functions. A screen of over 2,000 pharmacologically active compounds for inhibition of potassium ion transport in the mouse distal colon cultures led to the identification of a tool compound.

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Epithelial cell monolayer growth conditions developed for all intestinal segments

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Monolayer gene expression is consistent with tissue from each intestinal segment

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Ion transport, secretory, and absorptive functions match intestinal physiology

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Compound screen identified inhibitor of mouse distal colon potassium transport

Advances in bumped kinase inhibitors for human and animal therapy for cryptosporidiosis

Improvements have been made to the safety and efficacy of bumped kinase inhibitors, and they are advancing toward human and animal use for treatment of cryptosporidiosis. As the understanding of bumped kinase inhibitor pharmacodynamics for cryptosporidiosis therapy has increased, it has become clear that better compounds for efficacy do not necessarily require substantial systemic exposure. We now have a bumped kinase inhibitor with reduced systemic exposure, acceptable safety parameters, and efficacy in both the mouse and newborn calf models of cryptosporidiosis. Potential cardiotoxicity is the limiting safety parameter to monitor for this bumped kinase inhibitor. This compound is a promising pre-clinical lead for cryptosporidiosis therapy in animals and humans.

Identification of potent, nonabsorbable agonists of the calcium-sensing receptor for GI-specific administration

Modulation of gastrointestinal nutrient sensing pathways provides a promising a new approach for the treatment of metabolic diseases including diabetes and obesity. The calcium-sensing receptor has been identified as a key receptor involved in mineral and amino acid nutrient sensing and thus is an attractive target for modulation in the intestine. Herein we describe the optimization of gastrointestinally restricted calcium-sensing receptor agonists starting from a 3-aminopyrrolidine-containing template leading to the identification of GI-restricted agonist 19 (GSK3004774).

Comparative Pharmacokinetic Study for Linezolid and Two Novel Antibacterial Oxazolidinone Derivatives in Rabbits: Can Differences in the Pharmacokinetic Properties Explain the Discrepancies between Their In Vivo and In Vitro Antibacterial Activities?

This is a comparative pharmacokinetics study of linezolid (Lzd), and two novel oxazolidinone antibacterial agents—PH027 and PH051—in rabbits to determine if the discrepancy between the in vitro and in vivo activities of the novel compounds is due to pharmacokinetic factors. The pharmacokinetics after IV and oral administration, plasma protein binding and tissue distribution for the three compounds were compared. The elimination half-lives were 52.4 ± 6.3, 68.7 ± 12.1 and 175 ± 46.1 min for Lzd, PH027 and PH051, respectively. The oral bioavailability for Lzd, PH027 and PH051 administered as suspension were 38.7%, 22.1% and 4.73%, which increased significantly when administered as microemulsion to 51.7%, 72.9% and 13.9%. The plasma protein binding were 32–34%, 37–38% and 90–91% for Lzd, PH027 and PH051. The tissue distribution for PH027 and PH051 in all investigated tissues were higher than that for Lzd. It can be concluded that the lower bioavailability of PH027 and PH051 compared to Lzd when administered as suspension is the main cause of their lower in vivo activity, despite their comparable in vitro activity. Differences in the other pharmacokinetic characteristics cannot explain the lower in vivo activity. The in vivo activity of the novel compounds should be re-evaluated using formulations with good oral bioavailability.

Topical Intestinal Aminoimidazole Agonists of G-Protein-Coupled Bile Acid Receptor 1 Promote Glucagon Like Peptide-1 Secretion and Improve Glucose Tolerance

The role of the G-protein-coupled bile acid receptor TGR5 in various organs, tissues, and cell types, specifically in intestinal endocrine L-cells and brown adipose tissue, has made it a promising therapeutical target in several diseases, especially type-2 diabetes and metabolic syndrome. However, recent studies have shown deleterious on-target effects of systemic TGR5 agonists. To avoid these systemic effects while stimulating glucagon-like peptide-1 (GLP-1) secreting enteroendocrine L-cells, we have designed TGR5 agonists with low intestinal permeability. In this article, we describe their synthesis, characterization, and biological evaluation. Among them, compound 24 is a potent GLP-1 secretagogue, has low effect on gallbladder volume, and improves glucose homeostasis in a preclinical murine model of diet-induced obesity and insulin resistance, making the proof of concept of the potential of topical intestinal TGR5 agonists as therapeutic agents in type-2 diabetes.

Obesity: Current and potential pharmacotherapeutics and targets

Obesity is a global epidemic that contributes to a number of health complications including cardiovascular disease, type 2 diabetes, cancer and neuropsychiatric disorders. Pharmacotherapeutic strategies to treat obesity are urgently needed. Research over the past two decades has increased substantially our knowledge of central and peripheral mechanisms underlying homeostatic energy balance. Homeostatic mechanisms involve multiple components including neuronal circuits, some originating in hypothalamus and brain stem, as well as peripherally-derived satiety, hunger and adiposity signals that modulate neural activity and regulate eating behavior. Dysregulation of one or more of these homeostatic components results in obesity. Coincident with obesity, reward mechanisms that regulate hedonic aspects of food intake override the homeostatic regulation of eating. In addition to functional interactions between homeostatic and reward systems in the regulation of food intake, homeostatic signals have the ability to alter vulnerability to drug abuse. Regarding the treatment of obesity, pharmacological monotherapies primarily focus on a single protein target. FDA-approved monotherapy options include phentermine (Adipex-P®), orlistat (Xenical®), lorcaserin (Belviq®) and liraglutide (Saxenda®). However, monotherapies have limited efficacy, in part due to the recruitment of alternate and counter-regulatory pathways. Consequently, a multi-target approach may provide greater benefit. Recently, two combination products have been approved by the FDA to treat obesity, including phentermine/topiramate (Qsymia®) and naltrexone/bupropion (Contrave®). The current review provides an overview of homeostatic and reward mechanisms that regulate energy balance, potential therapeutic targets for obesity and current treatment options, including some candidate therapeutics in clinical development. Finally, challenges in anti-obesity drug development are discussed.

Gut hormones and gut microbiota: implications for kidney function and hypertension

Increased blood pressure (BP) and chronic kidney disease are two leading risk factors for cardiovascular disease. Increased sodium intake is one of the most important risk factors for development of hypertension. Recent data have shown that gut influences kidney function and BP by variety of mechanisms. Various hormones and peptides secreted from gut such as gastrin, glucocorticoids, Glucagon-like peptide-1 impact on kidney function and BP especially influencing sodium absorption from gut. These findings stimulate scientist to find new therapeutic options such as tenapanor for treatment of hypertension by blocking sodium absorption from gut. The gastrointestinal tract is also occupied by a huge community of microbes (microbiome) that under normal condition has a symbiotic relationship with the host. Alterations in the structure and function of the gut microbiota have been shown to play a key role in the pathogenesis and complications of numerous diseases including hypertension. Based on these data, in this review, we provide a summary of the available data on the role of gut and gut microbiota in regulation of BP and kidney function.

Preclinical and Healthy Volunteer Studies of Potential Drug-Drug Interactions Between Tenapanor and Phosphate Binders

Tenapanor (RDX5791, AZD1722), a first‐in‐class small molecule with minimal systemic availability, is an inhibitor of the sodium/hydrogen exchanger isoform 3. Tenapanor acts locally in the gut, where it reduces absorption of sodium and phosphate. It is being studied in patients with chronic kidney disease requiring dialysis, who are often administered phosphate binders such as sevelamer to help control hyperphosphatemia. We investigated whether coadministration of tenapanor with phosphate binders (sevelamer or calcium‐based binders) impacts the pharmacodynamic effects of tenapanor. In vitro studies suggested a binding interaction between tenapanor and sevelamer, but this did not translate into altered pharmacodynamic effects in rats. An open‐label, 2‐way crossover study was then conducted in healthy volunteers (NCT02346890). This showed that 4 days’ treatment with tenapanor hydrochloride (15 mg twice daily) with or without sevelamer carbonate (800 mg 3 times daily) resulted in comparable 24‐hour stool and urinary sodium and phosphorus levels. Stool frequency, consistency, and weight were also comparable between the treatments. These results suggest that the binding between sevelamer and tenapanor observed in vitro does not translate into altered pharmacodynamic effects in humans.

A Way Forward for Cancer Chemoprevention: Think Local

As cells progress through carcinogenesis, the associated exponential expansion of genetic and molecular aberrations and resultant heterogeneity make therapeutic success increasingly unattainable. Therapeutic intervention at early stages of carcinogenesis that occurs within the primary organ and in the face of a lower burden of molecular aberrations, constitutes a basic tenet of cancer chemoprevention, and provides a situation that favors a greater degree of therapeutic efficacy compared with that of advanced cancer. A longstanding barrier to chemoprevention relates to the requirement for essentially no systemic toxicity, and the fact that when large numbers of people are treated, the emergence of systemic toxicity is almost universal. A rational means to address this in fact relates to a second basic tenet of the chemopreventive strategy: the focus of therapeutic intervention is to disrupt a process that is in essence localized to a single organ. Based upon this consideration, a strategy which is based upon local delivery of therapeutics to an at-risk organ will achieve therapeutic efficacy while avoiding systemic delivery and its associated toxicity. This article will review the rationale for undertaking such an approach, describe successful clinical achievements based on this strategy, describe ongoing efforts to expand the impact of this approach, and together will highlight the high impact that this approach has already had on the field as well as its extremely high potential for future impact. Cancer Prev Res; 10(1); 14-35. ©2016 AACR.

Intestinal phospholipid and lysophospholipid metabolism in cardiometabolic disease

PURPOSE OF REVIEW

Phospholipids are major constituents in the intestinal lumen after meal consumption. This article highlights current literature suggesting the contributory role of intestinal phospholipid metabolism toward cardiometabolic disease manifestation.

RECENT FINDINGS

Group 1b phospholipase A2 (PLA2g1b) catalyzes phospholipid hydrolysis in the intestinal lumen. The digestive product lysophospholipid, particularly lysophosphatidylcholine (LPC), has a direct role in mediating chylomicron assembly and secretion. The LPC in the digestive tract is further catabolized into lysophosphatidic acid and choline via autotaxin-mediated and autotaxin-independent mechanisms. The LPC and lysophosphatidic acid absorbed through the digestive tract and transported to the plasma directly promote systemic inflammation and cell dysfunction, leading to increased risk of cardiovascular disease and obesity/diabetes. The choline moiety generated in the digestive tract can also be used by gut bacteria to generate trimethylamine, which is subsequently transported to the liver and oxidized into trimethylamine-N-oxide that also enhances atherosclerosis and cardiovascular abnormalities.

SUMMARY

Products of phospholipid metabolism in the intestine through PLA2g1b and autotaxin-mediated pathways directly contribute to cardiometabolic diseases through multiple mechanisms. The implication of these studies is that therapeutic inhibition of PLA2g1b and autotaxin in the digestive tract may be a viable approach for cardiovascular and metabolic disease intervention.

Cryptosporidiosis Drug Discovery: Opportunities and Challenges

The apicomplexan parasite Cryptosporidium is the second most important diarrheal pathogen causing life-threatening diarrhea in children, which is also associated with long-term growth faltering and cognitive deficiency. Cryptosporidiosis is a parasitic disease of public health concern caused by Cryptosporidium parvum and Cryptosporidium hominis. Currently, nitazoxanide is the only approved treatment for cryptosporidium infections. Unfortunately, it has limited efficacy in the most vulnerable patients, thus there is an urgent need for a safe and efficacious cryptosporidiosis drug. In this work, we present our current perspectives on the target product profile for novel cryptosporidiosis therapies and the perceived challenges and possible mitigation plans at different stages in the cryptosporidiosis drug discovery process.

Identification of nonabsorbable inhibitors of the scavenger receptor-BI (SR-BI) for tissue-specific administration

The identification of a low-permeability scavenger receptor BI (SR-BI) inhibitor starting from the ITX-5061 template is described. Structure-activity and structure-permeability relationships were assessed for analogs leading to the identification of compound 8 as a potent and nonabsorbable SR-BI inhibitor.

Folate Receptor-Targeted Polymeric Micellar Nanocarriers for Delivery of Orlistat as a Repurposed Drug against Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a recalcitrant malignancy with no available targeted therapy. Off-target effects and poor bioavailability of the FDA-approved antiobesity drug orlistat hinder its clinical translation as a repurposed new drug against TNBC. Here, we demonstrate a newly engineered drug formulation for packaging orlistat tailored to TNBC treatment. We synthesized TNBC-specific folate receptor-targeted micellar nanoparticles (NP) carrying orlistat, which improved the solubility (70-80 μg/mL) of this water-insoluble drug. The targeted NPs also improved the delivery and bioavailability of orlistat to MDA-MB-231 cells in culture and to tumor xenografts in a nude mouse model. We prepared HEA-EHA copolymer micellar NPs by copolymerization of 2-hydroxyethylacrylate (HEA) and 2-ethylhexylacrylate (EHA), and functionalized them with folic acid and an imaging dye. Fluorescence-activated cell sorting (FACS) analysis of TNBC cells indicated a dose-dependent increase in apoptotic populations in cells treated with free orlistat, orlistat NPs, and folate-receptor-targeted Fol-HEA-EHA-orlistat NPs in which Fol-HEA-EHA-orlistat NPs showed significantly higher cytotoxicity than free orlistat. In vitro analysis data demonstrated significant apoptosis at nanomolar concentrations in cells activated through caspase-3 and PARP inhibition. In vivo analysis demonstrated significant antitumor effects in living mice after targeted treatment of tumors, and confirmed by fluorescence imaging. Moreover, folate receptor-targeted Fol-DyLight747-orlistat NP-treated mice exhibited significantly higher reduction in tumor volume compared to control group. Taken together, these results indicate that orlistat packaged in HEA-b-EHA micellar NPs is a highly promising new drug formulation for TNBC therapy. Mol Cancer Ther; 15(2); 221-31. ©2015 AACR.

Cation Exchange Resins and colonic perforation. What surgeons need to know

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Cation Exchange Resins have been the mainstream treatment for chronic hyperkalemia.

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In 1987 the first case series of uremic patients with colonic perforations associated with the use of sodium polystyrene sulfonate was reported.

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The pathologic damage of Cation Exchange Resin in gastrointestinal tract goes from mucosal edema, ulcers, pseudomembranes, and the most severe transmural necrosis.

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Surgeons must avoid therapies with intestinal osmotic challenge implication in patients presenting gastrointestinal adverse reactions derived from Cation Exchange Resins.

Introduction

Since 1961 the use of Cation Exchange Resins has been the mainstream treatment for chronic hyperkalemia. For the past 25 years different kind of complications derived from its clinical use have been recognized, being the colonic necrosis the most feared and lethal of all.

Presentation of case

We report a case of a 72-year-old patient with chronic kidney disease, treated with calcium polystyrene sulfonate for hyperkalemia treatment who presented in the emergency department with constipation treated with hypertonic cathartics. With clinical deterioration 48 h later progressed with colonic necrosis requiring urgent laparotomy, sigmoidectomy and open abdomen management with subsequent rectal stump perforation and dead. The histopathology finding: calcium polystyrene sulfonate embedded in the mucosa, consistent with the cause of perforation.

Discussion

Lillemoe reported the first case series of five uremic patients with colonic perforation associated with the use of SPS in sorbitol in 1987 and in 2009 the FDA removed from the market the SPS containing 70% of sorbitol.

The pathophysiologic change of CER goes from mucosal edema, ulcers, pseudomembranes, and the most severe case transmural necrosis.

Up to present day, some authors have questioned the use of CER in the setting of lowering serum potassium. Despite its worldwide use in hyperkalemia settings, multiple studies have not demonstrated a significant potassium excretion by CER.

Conclusion

Despite the low incidence of colonic complication and lethal colonic necrosis associated with the CER clinical use, the general surgeon needs a high index of suspicion when dealing with patients treated with CER and abdominal pain.

Gastrointestinal localization of metronidazole by a lactobacilli-inspired tetramic acid motif improves treatment outcomes in the hamster model of Clostridium difficile infection

OBJECTIVES

Metronidazole, a mainstay treatment for Clostridium difficile infection (CDI), is often ineffective for severe CDI. Whilst this is thought to arise from suboptimal levels of metronidazole in the colon due to rapid absorption, empirical validation is lacking. In contrast, reutericyclin, an antibacterial tetramic acid from Lactobacillus reuteri, concentrates in the gastrointestinal tract. In this study, we modified metronidazole with reutericyclin's tetramic acid motif to obtain non-absorbed compounds, enabling assessment of the impact of pharmacokinetics on treatment outcomes.

METHODS

A series of metronidazole-bearing tetramic acid substituents were synthesized and evaluated in terms of anti-C. difficile activities, gastric permeability, in vivo pharmacokinetics, efficacy in the hamster model of CDI and mode of action.

RESULTS

Most compounds were absorbed less than metronidazole in cell-based Caco-2 permeability assays. In hamsters, lead compounds compartmentalized in the colon rather than the bloodstream with negligible levels detected in the blood, in direct contrast with metronidazole, which was rapidly absorbed into the blood and was undetectable in caecum. Accordingly, four leads were more efficacious (P < 0.05) than metronidazole in C. difficile-infected animals. Improved efficacy was not due to an alternative mode of action, as the leads retained the mode of action of metronidazole.

CONCLUSIONS

This study provides the clearest empirical evidence that the high absorption of metronidazole lowers treatment outcomes for CDI and suggests a role for the tetramic acid motif for colon-specific drug delivery. This approach also has the potential to lower systemic toxicity and drug interactions of nitroheterocyclic drugs for treating gastrointestine-specific diseases.

Current developments in pharmacological therapeutics for chronic constipation

Chronic constipation is a common gastrointestinal disease severely affecting the patient׳s quality of life. The traditional treatment of constipation is the use of laxatives. Recently, several new drugs including lubiprostone, linaclotide and prucalopride have been approved for treatment of chronic constipation. However, a significant unmet medical need still remains, particularly among those patients achieving poor results by current therapies. The 5-HT4 receptor modulators velusetrag and naronapride, the guanylate cyclase C agonist plecanatide and the ileal bile acid transporter inhibitor elobixibat are recognized as the most promising drugs under investigation. Herein, we give a comprehensive review on the pharmacological therapeutics for the treatment of chronic constipation, with the purpose of reflecting the drug development trends in this field.

Tenapanor hydrochloride for the treatment of constipation-predominant irritable bowel syndrome

INTRODUCTION

Constipation-predominant irritable bowel syndrome (IBS-C) is a common functional gastrointestinal (GI) disorder characterized by recurrent abdominal pain and prolonged GI transit. The pathogenesis of IBS-C has still not been established; therefore, drugs currently in use in IBS-C act mainly symptomatically, whereas novel pharmacological targets are urgently needed. Tenapanor is a potent inhibitor of Na(+)/H(+) exchanger 3 [NHE3], localized in the apical membrane of intestinal epithelial cells. NHE3 participates in the uptake of sodium ions and water from the intestinal lumen.

AREAS COVERED

In this review, the authors discuss pharmacodynamics and pharmacokinetics of tenapanor, focusing on animal models and in vitro studies. They also summarize clinical trials on tenapanor's safety and efficacy in view of its potential role in IBS-C therapy.

EXPERT OPINION

Tenapanor possesses an excellent preclinical safety profile and, as of now, there are no serious concerns about its side effects. The non-systemic action of tenapanor constitutes a significant advantage, as it minimizes possible adverse effects or drug-drug interactions. However, Phase III clinical trials are still needed to confirm results obtained in earlier phases and optimize the dose-response for tenapanor, whereas limiting diarrhea, its major adverse effect.

The importance of intake: a gut feeling

Limiting enteric sodium absorption is an attractive option when renal sodium excretion is disturbed. An effective approach in the gut appears to be inhibition of the electroneutral Na(+)/H(+) exchangers (NHE), in particular NHE3. Recently, fluid retention, blood pressure and target organ injury were limited in rats with cardiorenal syndrome when treated with the NHE3 inhibitor tenapanor. The downside was that the osmotic fecal load leads to watery feces. Tenapanor also induced marked reductions in enteric phosphorus absorption in rats with cardiorenal syndrome on a high phosphorus intake and resulted in marked reductions in renal injury and practically prevented vascular calcification. We have yet to discover the clinical relevance in volume terms and vascular calcifications in patients in relation to the tolerated dose. However, even if the tenapanor-induced reduction in sodium adsorption is limited in humins, combination of tenapanor therapy with diuretics may be an interesting option in selected patients.

Discovery of Intestinal Targeted TGR5 Agonists for the Treatment of Type 2 Diabetes

Activation of TGR5 stimulates intestinal glucagon-like peptide-1 (GLP-1) release, but activation of the receptors in gallbladder and heart has been shown to cause severe on-target side effects. A series of low-absorbed TGR5 agonists was prepared by modifying compound 2 with polar functional groups to limit systemic exposure and specifically activate TGR5 in the intestine. Compound 15c, with a molecular weight of 1401, a PSA value of 223 Å(2), and low permeability on Caco-2 cells, exhibited satisfactory potency both in vitro and in vivo. Low levels of 15c were detected in blood, bile, and gallbladder tissue, and gallbladder-related side effects were substantially decreased compared to the absorbed small-molecule TGR5 agonist 2.

Role of NPT2b in health and chronic kidney disease

PURPOSE OF REVIEW

Maintaining phosphate homeostasis is essential and any deviation can lead to several acute and chronic disease states. To maintain normal physiological levels, phosphate needs to be tightly regulated. This is achieved through a complex relationship of organ cross-talk via hormonal regulation of the type II sodium-dependent phosphate co-transporters. This editorial provides evidence of the importance of intestinal NPT2b in health and chronic kidney disease (CKD).

RECENT FINDINGS

The advent of the different Npt2b knockout mice has increased our understanding of how the intestinal phosphate co-transporter contributes to the regulation of systemic phosphate. In addition, these studies have suggested that Npt2b may participate in the phosphate-sensing machinery important for organ cross-talk. Studies using Drosophila have expanded our knowledge of phosphate sensing mechanisms and may provide a foundation for delineating these pathways in humans. Several preclinical studies using different agents to modulate Npt2b, and clinical studies using nicotinamide, have provided evidence that Npt2b is a viable therapeutic target for the management of hyperphosphatemia.

SUMMARY

Over the last couple of years, new experimental approaches have increased our understanding of the important role of Npt2b in maintaining phosphate homeostasis. In addition, several clinical studies have associated the detrimental effects of elevated phosphate with cardiovascular events, and decreased lifespan. Although several key questions about intestinal phosphate transport remain to be answered, it is clear that the intestine is an important player, with current evidence suggesting that it is a prime target for regulating phosphate uptake and improving health outcomes in CKD.

Intestinal inhibition of the Na+/H+ exchanger 3 prevents cardiorenal damage in rats and inhibits Na+ uptake in humans

The management of sodium intake is clinically important in many disease states including heart failure, kidney disease, and hypertension. Tenapanor is an inhibitor of the sodium-proton (Na(+)/H(+)) exchanger NHE3, which plays a prominent role in sodium handling in the gastrointestinal tract and kidney. When administered orally to rats, tenapanor acted exclusively in the gastrointestinal tract to inhibit sodium uptake. We showed that the systemic availability of tenapanor was negligible through plasma pharmacokinetic studies, as well as autoradiography and mass balance studies performed with (14)C-tenapanor. In humans, tenapanor reduced urinary sodium excretion by 20 to 50 mmol/day and led to an increase of similar magnitude in stool sodium. In salt-fed nephrectomized rats exhibiting hypervolemia, cardiac hypertrophy, and arterial stiffening, tenapanor reduced extracellular fluid volume, left ventricular hypertrophy, albuminuria, and blood pressure in a dose-dependent fashion. We observed these effects whether tenapanor was administered prophylactically or after disease was established. In addition, the combination of tenapanor and the blood pressure medication enalapril improved cardiac diastolic dysfunction and arterial pulse wave velocity relative to enalapril monotherapy in this animal model. Tenapanor prevented increases in glomerular area and urinary KIM-1, a marker of renal injury. The results suggest that therapeutic alteration of sodium transport in the gastrointestinal tract instead of the kidney--the target of current drugs--could lead to improved sodium management in renal disease.

Sevelamer revisited: pleiotropic effects on endothelial and cardiovascular risk factors in chronic kidney disease and end-stage renal disease

Endothelial dysfunction underlies multiple cardiovascular consequences of chronic kidney disease (CKD) and antecedent diabetes or hypertension. Endothelial insults in CKD or end-stage renal disease (ESRD) patients include uremic toxins, serum uric acid, hyperphosphatemia, reactive oxygen species, and advanced glycation endproducts (AGEs). Sevelamer carbonate, a calcium-free intestinally nonabsorbed polymer, is approved for hyperphosphatemic dialysis patients in the US and hyperphosphatemic stage 3-5 CKD patients in many other countries. Sevelamer has been observed investigationally to reduce absorption of AGEs, bacterial toxins, and bile acids, suggesting that it may reduce inflammatory, oxidative, and atherogenic stimuli in addition to its on-label action of lowering serum phosphate. Some studies also suggest that noncalcium binders may contribute less to vascular calcification than calcium-based binders. Exploratory sevelamer carbonate use in patients with stages 2-4 diabetic CKD significantly reduced HbA1c, AGEs, fibroblast growth factor (FGF)-23, and total and low-density lipoprotein (LDL) cholesterol versus calcium carbonate; inflammatory markers decreased and defenses against AGEs increased. Sevelamer has also been observed to reduce circulating FGF-23, potentially reducing risk of left ventricular hypertrophy. Sevelamer but not calcium-based binders in exploratory studies increases flow-mediated vasodilation, a marker of improved endothelial function, in patients with CKD. In contrast, lanthanum carbonate and calcium carbonate effects on FMV did not differ in hemodialysis recipients. The recent independent-CKD randomized trial compared sevelamer versus calcium carbonate in predialysis CKD patients (investigational in the US, on-label in European participants); sevelamer reduced 36-month mortality and the composite endpoint of mortality or dialysis inception. Similarly, independent-HD in incident dialysis patients showed improved survival with 24 months of sevelamer versus calcium-based binders. This review discusses recent exploratory evidence for pleiotropic effects of sevelamer on endothelial function in CKD or ESRD. Endothelial effects of sevelamer may contribute mechanistically to the improved survival observed in some studies of CKD and ESRD patients.

Group 1B phospholipase A₂ inactivation suppresses atherosclerosis and metabolic diseases in LDL receptor-deficient mice

OBJECTIVE

Previous studies have shown that inactivation of the group 1B phospholipase A2 (Pla2g1b) suppresses diet-induced obesity, hyperglycemia, insulin resistance, and hyperlipidemia in C57BL/6 mice. A possible influence of Pla2g1b inactivation on atherosclerosis has not been addressed previously. The current study utilized LDL receptor-deficient (Ldlr(-/-)) mice with plasma lipid levels and distribution similar to hyperlipidemic human subjects as a preclinical animal model to test the effectiveness of Pla2g1b inactivation on atherosclerosis.

METHODS AND RESULTS

The Pla2g1b(+/+)Ldlr(-/-) and Pla2g1b(-/-)Ldlr(-/-) mice were fed a low fat chow diet or a hypercaloric diet with 58.5 kcal% fat and 25 kcal% sucrose for 10 weeks. Minimal differences were observed between Pla2g1b(+/+)Ldlr(-/-) and Pla2g1b(-/-)Ldlr(-/-) mice when the animals were maintained on the low fat chow diet. However, when the animals were maintained on the hypercaloric diet, the Pla2g1(+/+)Ldlr(-/-) mice showed the expected body weight gain but the Pla2g1b(-/-)Ldlr(-/-) mice were resistant to diet-induced body weight gain. The Pla2g1b(-/-)Ldlr(-/-) mice also displayed lower fasting glucose, insulin, and plasma lipid levels compared to the Pla2g1b(+/+)Ldlr(-/-) mice, which displayed robust hyperglycemia, hyperinsulinemia, and hyperlipidemia in response to the hypercaloric diet. Importantly, atherosclerotic lesions in the aortic roots were also reduced 7-fold in the Pla2g1b(-/-)Ldlr(-/-) mice.

CONCLUSION

The effectiveness of Pla2g1b inactivation to suppress diet-induced body weight gain and reduce diabetes and atherosclerosis in LDL receptor-deficient mice suggests that pharmacological inhibition of Pla2g1b may be a viable strategy to decrease diet-induced obesity and the risk of diabetes and atherosclerosis in humans.