The furan fatty acid metabolite CMPF is elevated in diabetes and induces β cell dysfunction

The SLC22 Transporter Family: A Paradigm for the Impact of Drug Transporters on Metabolic Pathways, Signaling, and Disease

The SLC22 transporter family consists of more than two dozen members, which are expressed in the kidney, the liver, and other tissues. Evolutionary analysis indicates that SLC22 transporters fall into at least six subfamilies: OAT (organic anion transporter), OAT-like, OAT-related, OCT (organic cation transporter), OCTN (organic cation/carnitine transporter), and OCT/OCTN-related. Some-including OAT1 [SLC22A6 or NKT (novel kidney transporter)] and OAT3 (SLC22A8), as well as OCT1 (SLC22A1) and OCT2 (SLC22A2)-are widely studied drug transporters. Nevertheless, analyses of knockout mice and other data indicate that SLC22 transporters regulate key metabolic pathways and levels of signaling molecules (e.g., gut microbiome products, bile acids, tricarboxylic acid cycle intermediates, dietary flavonoids and other nutrients, prostaglandins, vitamins, short-chain fatty acids, urate, and ergothioneine), as well as uremic toxins associated with chronic kidney disease. Certain SLC22 transporters-such as URAT1 (SLC22A12) and OCTN2 (SLC22A5)-are mutated in inherited metabolic diseases. A new systems biology view of transporters is emerging. As proposed in the remote sensing and signaling hypothesis, SLC22 transporters, together with other SLC and ABC transporters, have key roles in interorgan and interorganism small-molecule communication and, together with the neuroendocrine, growth factor-cytokine, and other homeostatic systems, regulate local and whole-body homeostasis.

Mitochondrial Activity and Skeletal Muscle Insulin Resistance in Kidney Disease

Insulin resistance is a key feature of the metabolic syndrome, a cluster of medical disorders that together increase the chance of developing type 2 diabetes and cardiovascular disease. In turn, type 2 diabetes may cause complications such as diabetic kidney disease (DKD). Obesity is a major risk factor for developing systemic insulin resistance, and skeletal muscle is the first tissue in susceptible individuals to lose its insulin responsiveness. Interestingly, lean individuals are not immune to insulin resistance either. Non-obese, non-diabetic subjects with chronic kidney disease (CKD), for example, exhibit insulin resistance at the very onset of CKD, even before clinical symptoms of renal failure are clear. This uraemic insulin resistance contributes to the muscle weakness and muscle wasting that many CKD patients face, especially during the later stages of the disease. Bioenergetic failure has been associated with the loss of skeletal muscle insulin sensitivity in obesity and uraemia, as well as in the development of kidney disease and its sarcopenic complications. In this mini review, we evaluate how mitochondrial activity of different renal cell types changes during DKD progression, and discuss the controversial role of oxidative stress and mitochondrial reactive oxygen species in DKD. We also compare the involvement of skeletal muscle mitochondria in uraemic and obesity-related muscle insulin resistance.

Application of Ion Chromatography Coupled with Mass Spectrometry for Human Serum and Urine Metabolomics

Biomarkers that indicate the presence or severity of organ damage caused by diseases and toxicities are useful diagnostic tools. Metabolomics platforms using chromatography coupled with mass spectrometry (MS) have been widely used for biomarker screening. In this study, we aimed to establish a novel metabolomics platform using ion chromatography coupled with MS (IC-MS) for human biofluids. We found that ethylenediaminetetraacetic acid (EDTA) plasma is not suitable for IC-MS metabolomics platforms because of the desensitization of MS. IC-MS enabled detection of 131 polar metabolites in human serum and urine from healthy volunteers. Pathway analysis demonstrated that the metabolites detectable using our platform were composed of a broad spectrum of organic acids with carboxylic moieties. These metabolites were significantly associated with pathways such as the tricarboxylic acid (TCA) cycle; glyoxylate and dicarboxylate metabolism; alanine, aspartate, and glutamate metabolism; butanoate metabolism; and the pentose phosphate pathway. Moreover, comparison of serum and urine samples showed that four metabolites (4-hydroxybutyric acid, aspartic acid, lactic acid, and γ-glutamyl glutamine) were abundant in serum, whereas 62 metabolites, including phosphoric acid, vanillylmandelic acid, and N-tiglylglycine, were abundant in urine. In addition, allantoin and uric acid were abundant in male serum, whereas no gender-associated differences were found for polar metabolites in urine. Our results demonstrate that the present established IC-MS metabolomics platform can be applied for analysis of human serum and urine as well as detection of a broad spectrum of polar metabolites in human biofluids.

Uraemic syndrome of chronic kidney disease: altered remote sensing and signalling

Uraemic syndrome (also known as uremic syndrome) in patients with advanced chronic kidney disease involves the accumulation in plasma of small-molecule uraemic solutes and uraemic toxins (also known as uremic toxins), dysfunction of multiple organs and dysbiosis of the gut microbiota. As such, uraemic syndrome can be viewed as a disease of perturbed inter-organ and inter-organism (host-microbiota) communication. Multiple biological pathways are affected, including those controlled by solute carrier (SLC) and ATP-binding cassette (ABC) transporters and drug-metabolizing enzymes, many of which are also involved in drug absorption, distribution, metabolism and elimination (ADME). The remote sensing and signalling hypothesis identifies SLC and ABC transporter-mediated communication between organs and/or between the host and gut microbiota as key to the homeostasis of metabolites, antioxidants, signalling molecules, microbiota-derived products and dietary components in body tissues and fluid compartments. Thus, this hypothesis provides a useful perspective on the pathobiology of uraemic syndrome. Pathways considered central to drug ADME might be particularly important for the body's attempts to restore homeostasis, including the correction of disturbances due to kidney injury and the accumulation of uraemic solutes and toxins. This Review discusses how the remote sensing and signalling hypothesis helps to provide a systems-level understanding of aspects of uraemia that could lead to novel approaches to its treatment.

Serum 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid is associated with lipid profiles and might protect against non-alcoholic fatty liver disease in Chinese individuals

AIMS/INTRODUCTION

High plasma 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) levels are significantly associated with type 2 diabetes mellitus, which is usually accompanied by metabolic syndrome and non-alcoholic fatty liver disease (NAFLD) with increased triglyceride levels. Thus, we hypothesized that elevated CMPF levels might be related to lipid metabolism and NAFLD risk.

MATERIALS AND METHODS

Serum CMPF levels were determined using an enzyme-linked immunosorbent assay in a total of 466 individuals, including 116 controls with no NAFLD or type 2 diabetes mellitus, 53 individuals with NAFLD but no type 2 diabetes mellitus, 151 individuals with type 2 diabetes mellitus but no NAFLD, and 146 individuals with both NAFLD and type 2 diabetes mellitus. The associations with age, blood pressure, lipid profiles, body mass index and liver injury marker levels were examined, and a meta-analysis of non-diabetic and diabetic groups was carried out to detect the combined effects.

RESULTS

The CMPF concentration in NAFLD patients was significantly lower than individuals without NAFLD in both the non-diabetic group (P < 0.05) and diabetic group (P < 0.01), and correlated negatively with several parameters of liver function and the adiposity index. Meta-analysis showed that serum CMPF levels was associated with decreased risk of NAFLD after combining the results (odds ratio 0.677, 95% confidence interval 0.552-0.831, P < 0.001). Additionally, the CMPF concentration was independently negatively associated with triglycerides and high-density lipoprotein cholesterol in the meta-analysis. Multiple stepwise regression analysis showed that body mass index, high-density lipoprotein cholesterol, triglyceride level, age, sex and fasting plasma glucose were independently associated with CMPF (all P < 0.05).

CONCLUSIONS

The results suggest that serum CMPF levels are negatively related to lipid metabolism and could be used to predict NAFLD development.

The discovery of novel predictive biomarkers and early-stage pathophysiology for the transition from gestational diabetes to type 2 diabetes

AIMS/HYPOTHESIS

Gestational diabetes mellitus (GDM) affects up to 20% of pregnancies, and almost half of the women affected progress to type 2 diabetes later in life, making GDM the most significant risk factor for the development of future type 2 diabetes. An accurate prediction of future type 2 diabetes risk in the early postpartum period after GDM would allow for timely interventions to prevent or delay type 2 diabetes. In addition, new targets for interventions may be revealed by understanding the underlying pathophysiology of the transition from GDM to type 2 diabetes. The aim of this study is to identify both a predictive signature and early-stage pathophysiology of the transition from GDM to type 2 diabetes.

METHODS

We used a well-characterised prospective cohort of women with a history of GDM pregnancy, all of whom were enrolled at 6-9 weeks postpartum (baseline), were confirmed not to have diabetes via 2 h 75 g OGTT and tested anually for type 2 diabetes on an ongoing basis (2 years of follow-up). A large-scale targeted lipidomic study was implemented to analyse ~1100 lipid metabolites in baseline plasma samples using a nested pair-matched case-control design, with 55 incident cases matched to 85 non-case control participants. The relationships between the concentrations of baseline plasma lipids and respective follow-up status (either type 2 diabetes or no type 2 diabetes) were employed to discover both a predictive signature and the underlying pathophysiology of the transition from GDM to type 2 diabetes. In addition, the underlying pathophysiology was examined in vivo and in vitro.

RESULTS

Machine learning optimisation in a decision tree format revealed a seven-lipid metabolite type 2 diabetes predictive signature with a discriminating power (AUC) of 0.92 (87% sensitivity, 93% specificity and 91% accuracy). The signature was highly robust as it includes 45-fold cross-validation under a high confidence threshold (1.0) and binary output, which together minimise the chance of data overfitting and bias selection. Concurrent analysis of differentially expressed lipid metabolite pathways uncovered the upregulation of α-linolenic/linoleic acid metabolism (false discovery rate [FDR] 0.002) and fatty acid biosynthesis (FDR 0.005) and the downregulation of sphingolipid metabolism (FDR 0.009) as being strongly associated with the risk of developing future type 2 diabetes. Focusing specifically on sphingolipids, the downregulation of sphingolipid metabolism using the pharmacological inhibitors fumonisin B1 (FB1) and myriocin in mouse islets and Min6 K8 cells (a pancreatic beta-cell like cell line) significantly impaired glucose-stimulated insulin secretion but had no significant impact on whole-body glucose homeostasis or insulin sensitivity.

CONCLUSIONS/INTERPRETATION

We reveal a novel predictive signature and associate reduced sphingolipids with the pathophysiology of transition from GDM to type 2 diabetes. Attenuating sphingolipid metabolism in islets impairs glucose-stimulated insulin secretion.

Maternal metabolites during pregnancy are associated with newborn outcomes and hyperinsulinaemia across ancestries

AIMS/HYPOTHESIS

We aimed to determine the association of maternal metabolites with newborn adiposity and hyperinsulinaemia in a multi-ethnic cohort of mother-newborn dyads.

METHODS

Targeted and non-targeted metabolomics assays were performed on fasting and 1 h serum samples from a total of 1600 mothers in four ancestry groups (Northern European, Afro-Caribbean, Mexican American and Thai) who participated in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study, underwent an OGTT at ~28 weeks gestation and whose newborns had anthropometric measurements at birth.

RESULTS

In this observational study, meta-analyses demonstrated significant associations of maternal fasting and 1 h metabolites with birthweight, cord C-peptide and/or sum of skinfolds across ancestry groups. In particular, maternal fasting triacylglycerols were associated with newborn sum of skinfolds. At 1 h, several amino acids, fatty acids and lipid metabolites were associated with one or more newborn outcomes. Network analyses revealed clusters of fasting acylcarnitines, amino acids, lipids and fatty acid metabolites associated with cord C-peptide and sum of skinfolds, with the addition of branched-chain and aromatic amino acids at 1 h.

CONCLUSIONS/INTERPRETATION

The maternal metabolome during pregnancy is associated with newborn outcomes. Maternal levels of amino acids, acylcarnitines, lipids and fatty acids and their metabolites during pregnancy relate to fetal growth, adiposity and cord C-peptide, independent of maternal BMI and blood glucose levels.

3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) prevents high fat diet-induced insulin resistance via maintenance of hepatic lipid homeostasis

AIM

Omega-3 fatty acid ethyl ester supplements, available by prescription, are common in the treatment of dyslipidaemia in humans. Recent studies show that 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF), a metabolite formed from fish oil supplementation, was able to prevent and reverse high fat diet (HFD)-induced fatty liver in mice. In the present study, we investigated the underlying molecular mechanisms responsible for CMPF's hepatic lipid-lowering effects.

MATERIALS AND METHODS

CD1 male mice were i.p. injected with CMPF (dosage, 6 mg/kg) for 7 days, followed by 5 weeks of a 60% HFD to induce a fatty liver phenotype. Metabolic parameters, liver morphology, lipid content, protein expression and microarray analysis were assessed. We also utilized primary hepatocytes, an in vitro model, to further investigate the direct effects of CMPF on hepatic lipid utilization and biosynthesis.

RESULTS

CMPF-treated mice display enhanced hepatic lipid clearance while hepatic lipid storage is prevented, thereby protecting against liver lipid accumulation and development of HFD-induced hepatic insulin resistance. Mechanistically, as CMPF enters the liver, it acts as an allosteric acetyl-coA carboxylase (ACC) inhibitor, which directly induces both fatty acid oxidation and hepatic production of fibroblast growth factor 21 (FGF21). A feed-back loop is initiated by CMPF, which exists between ACC inhibition, fatty acid oxidation and production of FGF21. As a consequence, an adaptive decrease in Insig2/SREBP-1c/FAS protein expression results in priming of the liver to prevent a HFD-induced fatty liver phenotype.

CONCLUSION

CMPF is a potential driver of hepatic lipid metabolism, preventing diet-induced hepatic lipid deposition and insulin resistance in the long term.

Changes of urine metabolites in response to n-3 fatty acid supplements and their correlation with metabolic risk factors in patients with type 2 diabetes

The present study aimed to investigate the effects of n-3 fatty acid supplements on urine metabolite profiling and their correlation with metabolic risk factors in Chinese T2D patients.

Metabolomics activity screening for identifying metabolites that modulate phenotype

Metabolomics, in which small-molecule metabolites (the metabolome) are identified and quantified, is broadly acknowledged to be the omics discipline that is closest to the phenotype. Although appreciated for its role in biomarker discovery programs, metabolomics can also be used to identify metabolites that could alter a cell's or an organism's phenotype. Metabolomics activity screening (MAS) as described here integrates metabolomics data with metabolic pathways and systems biology information, including proteomics and transcriptomics data, to produce a set of endogenous metabolites that can be tested for functionality in altering phenotypes. A growing literature reports the use of metabolites to modulate diverse processes, such as stem cell differentiation, oligodendrocyte maturation, insulin signaling, T-cell survival and macrophage immune responses. This opens up the possibility of identifying and applying metabolites to affect phenotypes. Unlike genes or proteins, metabolites are often readily available, which means that MAS is broadly amenable to high-throughput screening of virtually any biological system.

Metabolomic correlates of aerobic capacity among elderly adults

BACKGROUND

Aerobic capacity is a powerful predictor of cardiovascular disease and all-cause mortality, and it declines with advancing age.

HYPOTHESIS

Since physical activity alters body metabolism, metabolism markers will likely differ between subjects with high vs low aerobic capacities.

METHODS

Community-based participants without physician-diagnosed heart disease, stroke or cancer underwent same-day multimodal assessment of cardiovascular function (by echocardiography and magnetic resonance feature tracking of left atrium) and aerobic capacity by peak oxygen uptake (VO₂ ) metrics. Associations between VO₂ and cardiovascular and metabolomics profiles were studied in adjusted models including standard covariates.

RESULTS

We studied 141 participants, of whom 82 (58.2%) had low VO₂ , while 59 (41.8%) had high VO₂ . Compared to participants with high VO₂ , participants with low VO₂ had more adverse cardiovascular parameters, such as lower ratio of peak velocity flow in early diastole to peak velocity flow in late diastole by atrial contraction of >0.8 (76% vs 35%, adjusted odd ratio [OR] = 4.1, 95% confidence interval [CI] [1.7-9.5], P = 0.001) and lower left atrial conduit strain (11.3 ± 4.0 vs 15.6 ± 6.1%, adjusted OR = 1.1, 95% CI [1.002-1.3], P = 0.045). High VO₂ was associated with lower accumulation of wide-spectrum acyl-carnitines (OR = 0.6, 95% CI [0.4-0.9], P = 0.013), alanine (OR = 0.1, 95% CI [0.01-0.9], P = 0.044) and glutamine /glutamate (OR = 0.1, 95% CI [0.01-0.5], P = 0.007), compared to low VO_2. CONCLUSION: Elderly adults with low VO₂ have adverse cardiovascular and metabolic parameters compared to their counterparts with high VO₂ . Combined cardiac and metabolomics phenotyping may be a promising tool to provide insights into physiological states, useful for tracking future interventions related to physical activity among community cohorts.

GABA promotes β-cell proliferation, but does not overcome impaired glucose homeostasis associated with diet-induced obesity

γ-Aminobutyric acid (GABA) administration has been shown to increase β-cell mass, leading to a reversal of type 1 diabetes in mice. Whether GABA has any effect on β cells of healthy and prediabetic/glucose-intolerant obese mice remains unknown. In the present study, we show that oral GABA administration ( ad libitum) to mice indeed increased pancreatic β-cell mass, which led to a modest enhancement in insulin secretion and glucose tolerance. However, GABA treatment did not further increase insulin-positive islet area in high fat diet-fed mice and was unable to prevent or reverse glucose intolerance and insulin resistance. Mechanistically, whether in vivo or in vitro, GABA treatment increased β-cell proliferation. In vitro, the effect was shown to be mediated via the GABA_A receptor. Single-cell RNA sequencing analysis revealed that GABA preferentially up-regulated pathways linked to β-cell proliferation and simultaneously down-regulated those networks required for other processes, including insulin biosynthesis and metabolism. Interestingly, single-cell differential expression analysis revealed GABA treatment gave rise to a distinct subpopulation of β cells with a unique transcriptional signature, including urocortin 3 ( ucn3), wnt4, and hepacam2. Taken together, this study provides new mechanistic insight into the proliferative nature of GABA but suggests that β-cell compensation associated with prediabetes overlaps with, and negates, its proliferative effects.-Untereiner, A., Abdo, S., Bhattacharjee, A., Gohil, H., Pourasgari, F., Ibeh, N., Lai, M., Batchuluun, B., Wong, A., Khuu, N., Liu, Y., Al Rijjal, D., Winegarden, N., Virtanen, C., Orser, B. A., Cabrera, O., Varga, G., Rocheleau, J., Dai, F. F., Wheeler, M. B. GABA promotes β-cell proliferation, but does not overcome impaired glucose homeostasis associated with diet-induced obesity.

Metabolomic Analysis Identifies Lactate as an Important Pathogenic Factor in Diabetes-associated Cognitive Decline Rats

Diabetes mellitus causes brain structure changes and cognitive decline, and it has been estimated that diabetes doubles the risk for dementia. Until now, the pathogenic mechanism of diabetes-associated cognitive decline (DACD) has remained unclear. Using metabolomics, we show that lactate levels increased over time in the hippocampus of rats with streptozotocin-induced diabetes, as compared with age-matched control rats. Additionally, mRNA levels, protein levels, and enzymatic activity of lactate dehydrogenase-A (LDH-A) were significantly up-regulated, suggesting increased glycolysis activity. Importantly, by specifically blocking the glycolysis pathway through an LDH-A inhibitor, chronic diabetes-induced memory impairment was prevented. Analyzing the underlying mechanism, we show that the expression levels of cAMP-dependent protein kinase and of phosphorylated transcription factor cAMP response element-binding proteins were decreased in 12-week diabetic rats. We suggest that G protein-coupled receptor 81 mediates cognitive decline in the diabetic rat. In this study, we report that progressively increasing lactate levels is an important pathogenic factor in DACD, directly linking diabetes to cognitive dysfunction. LDH-A may be considered as a potential target for alleviating or treating DACD in the future.

Maternal β-Cell Adaptations in Pregnancy and Placental Signalling: Implications for Gestational Diabetes

Rates of gestational diabetes mellitus (GDM) are on the rise worldwide, and the number of pregnancies impacted by GDM and resulting complications are also increasing. Pregnancy is a period of unique metabolic plasticity, during which mild insulin resistance is a physiological adaptation to prioritize fetal growth. To compensate for this, the pancreatic β-cell utilizes a variety of adaptive mechanisms, including increasing mass, number and insulin-secretory capacity to maintain glucose homeostasis. When insufficient insulin production does not overcome insulin resistance, hyperglycemia can occur. Changes in the maternal system that occur in GDM such as lipotoxicity, inflammation and oxidative stress, as well as impairments in adipokine and placental signalling, are associated with impaired β-cell adaptation. Understanding these pathways, as well as mechanisms of β-cell dysfunction in pregnancy, can identify novel therapeutic targets beyond diet and lifestyle interventions, insulin and antihyperglycemic agents currently used for treating GDM.

Uncommon Fatty Acids and Cardiometabolic Health

Cardiovascular disease (CVD) is a major cause of mortality. The effects of several unsaturated fatty acids on cardiometabolic health, such as eicosapentaenoic acid (EPA) docosahexaenoic acid (DHA), α linolenic acid (ALA), linoleic acid (LA), and oleic acid (OA) have received much attention in past years. In addition, results from recent studies revealed that several other uncommon fatty acids (fatty acids present at a low content or else not contained in usual foods), such as furan fatty acids, n-3 docosapentaenoic acid (DPA), and conjugated fatty acids, also have favorable effects on cardiometabolic health. In the present report, we searched the literature in PubMed, Embase, and the Cochrane Library to review the research progress on anti-CVD effect of these uncommon fatty acids. DPA has a favorable effect on cardiometabolic health in a different way to other long-chain n-3 polyunsaturated fatty acids (LC n-3 PUFAs), such as EPA and DHA. Furan fatty acids and conjugated linolenic acid (CLNA) may be potential bioactive fatty acids beneficial for cardiometabolic health, but evidence from intervention studies in humans is still limited, and well-designed clinical trials are required. The favorable effects of conjugated linoleic acid (CLA) on cardiometabolic health observed in animal or in vitro cannot be replicated in humans. However, most intervention studies in humans concerning CLA have only evaluated its effect on cardiometabolic risk factors but not its direct effect on risk of CVD, and randomized controlled trials (RCTs) will be required to clarify this point. However, several difficulties and limitations exist for conducting RCTs to evaluate the effect of these fatty acids on cardiometabolic health, especially the high costs for purifying the fatty acids from natural sources. This review provides a basis for better nutritional prevention and therapy of CVD.

Metabolic Abnormalities in Diabetes and Kidney Disease: Role of Uremic Toxins

PURPOSE OF REVIEW

Chronic kidney disease (CKD) is characterized by the accumulation of uremic retention solutes (URS) and is associated with perturbations of glucose homeostasis even in absence of diabetes. The underlying mechanisms of insulin resistance, β cell failure, and increase risk of diabetes in CKD, however, remain unclear. Metabolomic studies reported that some metabolites are similar in CKD and diabetic kidney disease (DKD) and contribute to the progression to end-stage renal disease. We attempted to discuss the mechanisms involved in the disruption of carbohydrate metabolism in CKD by focusing on the specific role of URS.

RECENT FINDINGS

Recent clinical data have demonstrated a defect of insulin secretion in CKD. Several studies highlighted the direct role of some URS (urea, trimethylamine N-oxide (TMAO), p-cresyl sulfate, 3-carboxylic acid 4-methyl-5-propyl-2-furan propionic (CMPF)) in glucose homeostasis abnormalities and diabetes incidence. Gut dysbiosis has been identified as a potential contributor to diabetes and to the production of URS. The complex interplay between the gut microbiota, kidney, pancreas β cell, and peripheral insulin target tissues has brought out new hypotheses for the pathogenesis of CKD and DKD. The characterization of intestinal microbiota and its associated metabolites are likely to fill fundamental knowledge gaps leading to innovative research, clinical trials, and new treatments for CKD and DKD.

Characteristics of Colon-Derived Uremic Solutes

BACKGROUND AND OBJECTIVES

Colon microbial metabolism produces solutes that are normally excreted in the urine and accumulate in the plasma when the kidneys fail. This study sought to further identify and characterize human colon-derived uremic solutes.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Colon-derived solutes normally excreted in the urine were identified by comparing urine from controls (n=17) and patients with total colectomies (n=12), using an established metabolomic platform. Colon-derived solutes that accumulate in kidney failure were then identified by comparing the plasma of the control patients with that of patients on dialysis (n=14).

RESULTS

Ninety-one urinary solutes were classified as colon-derived on the basis of the finding of a urine excretion rate at least four-fold higher in control patients than in patients with total colectomies. Forty-six were solutes with known chemical structure, 35 of which had not previously been identified as colon-derived. Sixty of the colon-derived solutes accumulated in the plasma of patients with ESKD to a degree greater than urea and were therefore classified as uremic. The estimated urinary clearance for 27 out of the 32 colon-derived solutes for which clearance could be calculated exceeded that of creatinine, consistent with tubular secretion. Sulfatase treatment revealed that 42 out of the 91 colon-derived solutes detected were likely conjugates.

CONCLUSIONS

Metabolomic analysis identified numerous colon-derived solutes that are normally excreted in human urine. Clearance by tubular secretion limits plasma levels of many colon-derived solutes.

Glucolipotoxic conditions induce β-cell iron import, cytosolic ROS formation and apoptosis

Type 2 diabetes (T2D) arises when the pancreatic beta-cell fails to compensate for increased insulin needs due to insulin resistance. Glucolipotoxicity (GLT) has been proposed to induce beta-cell dysfunction in T2D by formation of reactive oxygen species (ROS). Here, we examined if modeling glucolipotoxic conditions by high glucose-high free fatty acid (FFA) exposure (GLT) regulates beta-cell iron transport, by increasing the cytosolic labile iron pool (LIP). In isolated mouse islets, the GLT-induced increase in the LIP catalyzed cytosolic ROS formation and induced apoptosis. We show that GLT-induced ROS production is regulated by an increased LIP associated with elevated expression of genes regulating iron import. Using pharmacological and transgenic approaches, we show that iron reduction and decreased iron import protects from GLT-induced ROS production, prevents impairment of the mitochondrial membrane potential (MMP) and inhibits apoptosis. This study identifies a novel pathway underlying GLT-induced apoptosis involving increased iron import, generation of hydroxyl radicals from hydrogen peroxide through the Fenton reaction in the cytosolic compartment associated with dissipation of the MMP and beta-cell apoptosis.

Probiotic Lactobacillus paracasei HII01 protects rats against obese-insulin resistance-induced kidney injury and impaired renal organic anion transporter 3 function

The relationship between gut dysbiosis and obesity is currently acknowledged to be a health topic which causes low-grade systemic inflammation and insulin resistance and may damage the kidney. Organic anion transporter 3 (Oat3) has been shown as a transporter responsible for renal handling of gut microbiota products which are involved in the progression of metabolic disorder. The present study investigated the effect of probiotic supplementation on kidney function, renal Oat3 function, inflammation, endoplasmic reticulum (ER) stress, and apoptosis in obese, insulin-resistant rats. After 12 weeks of being provided with either a normal or a high-fat diet (HF), rats were divided into normal diet (ND); ND treated with probiotics (NDL); HF; and HF treated with probiotic (HFL). Lactobacillus paracasei HII01 1 × 108 colony forming unit (CFU)/ml was administered to the rats daily by oral gavage for 12 weeks. Obese rats showed significant increases in serum lipopolysaccharide (LPS), plasma lipid profiles, and insulin resistance. Renal Oat 3 function was decreased along with kidney dysfunction in HF-fed rats. Obese rats also demonstrated the increases in inflammation, ER stress, apoptosis, and gluconeogenesis in the kidneys. These alterations were improved by Lactobacillus paracasei HII01 treatment. In conclusion, probiotic supplementation alleviated kidney inflammation, ER stress, and apoptosis, leading to improved kidney function and renal Oat3 function in obese rats. These benefits involve the attenuation of hyperlipidemia, systemic inflammation, and insulin resistance. The present study also suggested the idea of remote sensing and signaling system between gut and kidney by which probiotic might facilitate renal handling of gut microbiota products through the improvement of Oat3 function.

Effects of acute exposure to a high-fat, high-sucrose diet on gestational glucose tolerance and subsequent maternal health in mice

Gestational diabetes mellitus (GDM) is a common obstetric complication. Half of women who have GDM will go on to develop type 2 diabetes. Understanding the mechanisms by which this occurs requires an animal model of GDM without ongoing diabetes at conception. C57Bl/6J mice react acutely to a high-fat, high-sucrose (HFHS) challenge. Here, we hypothesized that a periconceptional HFHS challenge will induce glucose intolerance during gestation. C57Bl/6J female mice were placed on an HFHS either 1 or 3 weeks prior to mating and throughout pregnancy. Intraperitoneal glucose tolerance tests, insulin measurements, and histological analysis of pancreatic islets were used to assess the impact of acute HFHS. C57Bl/6J females fed HFHS beginning 1 week prior to pregnancy became severely glucose intolerant, with reduced insulin response to glucose, and decreased pancreatic islet expansion during pregnancy compared to control mice. These GDM characteristics did not occur when the HFHS diet was started 3 weeks prior to mating, suggesting the importance of acute metabolic stress. Additionally, HFHS feeding resulted in only mild insulin resistance in nonpregnant females. When the diet was discontinued at parturition, symptoms resolved within 3 weeks. However, mice that experienced glucose intolerance in pregnancy became glucose intolerant more readily in response to a HFHS challenge later in life than congenic females that experienced a normal pregnancy, or that were fed the same diet outside of pregnancy. Thus, acute HFHS challenge in C57Bl/6 mice results in a novel, nonobese, animal model that recapitulates the long-term risk of developing type 2 diabetes following GDM.

Increased serum 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) levels are associated with glucose metabolism in Chinese pregnant women

PURPOSE

Previous studies have found that 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) was associated with diabetes. This study aimed to investigate the relationship between abnormal increased CMPF levels and gestational diabetes mellitus (GDM).

METHODS

We recruited 828 pregnant women, and all of them underwent an oral glucose tolerance test (OGTT). We screened out 141 GDM patients and 230 pregnant women with normal glucose tolerance as controls. The serum CMPF concentration in participants was measured, and the relationship between the serum CMPF concentration and various parameters and biochemical indices was analyzed.

RESULTS

Compared with the serum levels in pregnant women with normal glucose tolerance, GDM patients exhibited markedly higher serum CMPF levels. The serum CMPF concentration showed an independent positive correlation with the blood glucose levels, glycated hemoglobin A1c(HbA1c), and the area under the glucose-time curve from the 2-h OGTT (AUC for glucose). Moreover, the CMPF concentration was independently negatively correlated with insulin secretion. However, CMPF was not significantly associated with lipid metabolism.

CONCLUSIONS

Elevated serum CMPF levels are detrimental to the development of hyperglycemia and islet β-cell functional failure in patients with GDM, which may promote the development of GDM.

Is 3-Carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF) a Clinically Relevant Uremic Toxin in Haemodialysis Patients?

3-Carboxy-4-methyl-5-propyl-2-furanpropionate (CMPF) is a metabolite of furan fatty acid and a marker of fish oil intake. CMPF is described as a protein-bound uremic toxin and interacts with free oxygen radicals, which can induce cell damages. However, the clinical consequences of CMPF accumulation in haemodialysis patients remain poorly documented. The aims of this study are to investigate potential association between CMPF levels and (i) biochemical and nutritional parameters; (ii) cardiovascular events and (iii) mortality. Two hundred and fifty-two patients undergoing maintenance haemodialysis were included. Routine clinical biochemistry tests and assay for CMPF by HPLC technique were performed at the inclusion. Body composition parameters were measured using a bioimpedance spectroscopy method. The enrolled patients were prospectively monitored for cardiovascular events and mortality. CMPF level was positively correlated with nutritional parameters and lean mass and is significantly higher in patients without protein-energy wasting. However, the multivariate linear regression analysis indicated that CMPF level was not independently associated with albumin, prealbumin, creatinemia and body mass index. Elevated serum CMPF was not associated with mortality and cardiovascular morbidity. Our results indicate that CMPF is not a relevant uremic toxin in haemodialysis and in contrast could be a marker of healthy diet and omega 3 intakes.

Metabolomic profiling of women with gestational diabetes mellitus and their offspring: Review of metabolomics studies

BACKGROUND

Gestational diabetes mellitus (GDM) reflects an increased risk of developing type 2 diabetes (T2D) after pregnancy in women. Offspring born to mothers with GDM are at an elevated risk of obesity and T2D at a young age. Currently, there are lack of ways for identifying women in early pregnancy who are at risk of developing GDM. As a result, both mothers and fetus are not treated until late in the second trimester when GDM is diagnosed. The recent advance in metabolomics, a new approach of systematic investigation of the metabolites, provides an opportunity for early detection of GDM, and classifying the risk of subsequent chronic diseases among women and their offspring.

METHODS

We reviewed the literatures published in the past 20 years on studies using high-throughput metabolomics technologies to investigate women with GDM and their offspring.

CONCLUSIONS

Despite the inconsistent results, previous studies have identified biomarkers that involved in specific metabolite groups and several pathways, including amino acid metabolism, steroid hormone biosynthesis, glycerophospholipid metabolism, and fatty acid metabolism. However, most studies have small sample sizes. Further research is warranted to determine if metabolomics will result in new indicators for the diagnosis, management, and prognosis of GDM and related complications.

Elevated Medium-Chain Acylcarnitines Are Associated With Gestational Diabetes Mellitus and Early Progression to Type 2 Diabetes and Induce Pancreatic β-Cell Dysfunction

Specific circulating metabolites have emerged as important risk factors for the development of diabetes. The acylcarnitines (acylCs) are a family of metabolites known to be elevated in type 2 diabetes (T2D) and linked to peripheral insulin resistance. However, the effect of acylCs on pancreatic β-cell function is not well understood. Here, we profiled circulating acylCs in two diabetes cohorts: 1) women with gestational diabetes mellitus (GDM) and 2) women with recent GDM who later developed impaired glucose tolerance (IGT), new-onset T2D, or returned to normoglycemia within a 2-year follow-up period. We observed a specific elevation in serum medium-chain (M)-acylCs, particularly hexanoyl- and octanoylcarnitine, among women with GDM and individuals with T2D without alteration in long-chain acylCs. Mice treated with M-acylCs exhibited glucose intolerance, attributed to impaired insulin secretion. Murine and human islets exposed to elevated levels of M-acylCs developed defects in glucose-stimulated insulin secretion and this was directly linked to reduced mitochondrial respiratory capacity and subsequent ability to couple glucose metabolism to insulin secretion. In conclusion, our study reveals that an elevation in circulating M-acylCs is associated with GDM and early stages of T2D onset and that this elevation directly impairs β-cell function.

Improvement in insulin resistance after gastric bypass surgery is correlated with a decline in plasma 2-hydroxybutyric acid

BACKGROUND

Gastric bypass surgery for weight reduction often corrects dysglycemia in diabetic patients, but a full understanding of the underlying biochemical pathways continues to be investigated.

OBJECTIVES

To explore the effects of weight loss by surgical and dietary interventions on plasma metabolites using both targeted and discovery-oriented metabolomics platforms.

SETTING

An academic medical center in the United States.

METHODS

Improvement in homeostatic model assessment for insulin resistance (HOMA-IR), as an index of insulin resistance, was compared at 6 months in 11 patients that underwent Roux-en-Y gastric bypass against 11 patients that were matched for weight loss in the Weight Loss Maintenance (WLM) program. Metabolites in plasma were evaluated by nontargeted gas chromatography/mass spectrometry for the potential detection of >1100 biochemical markers.

RESULTS

Among multiple metabolites detected, 2-hydroxybutyric acid (2-HBA) declined most significantly after 6 months in comparing patients that underwent Roux-en-Y gastric bypass with those in WLM (P < .001), corresponding with declines in HOMA-IR (P = .025). Baseline levels of 2-HBA for all patients were correlated with preintervention levels of HOMA-IR (R² = .565, P < .001). Moreover, the changes in 2-HBA after 6 months were correlated with changes in HOMA-IR (R² = .399, P = .0016).

CONCLUSIONS

Correlation between insulin resistance and 2-HBA suggests the utility of the latter as an excellent biomarker for tracking glycemic improvement, and offers further insight into the pathways that control diabetes. This is the first report of a decline in 2-HBA in response to bariatric surgery.

Prebiotic prevents impaired kidney and renal Oat3 functions in obese rats

Obesity is health issue worldwide, which can lead to kidney dysfunction. Prebiotics are non-digestible foods that have beneficial effects on health. This study aimed to investigate the effects of xylooligosaccharide (XOS) on renal function, renal organic anion transporter 3 (Oat3) and the mechanisms involved. High-fat diet was provided for 12 weeks in male Wistar rats. After that, the rats were divided into normal diet (ND); normal diet treated with XOS (NDX); high-fat diet (HF) and high-fat diet treated with XOS (HFX). XOS was given daily at a dose of 1000 mg for 12 weeks. At week 24, HF rats showed a significant increase in obesity and insulin resistance associated with podocyte injury, increased microalbuminuria, decreased creatinine clearance and impaired Oat3 function. These alterations were improved by XOS supplementation. Renal MDA level and the expression of AT1R, NOX4, p67^phox, 4-HNE, phosphorylated PKCα and ERK1/2 were significantly decreased after XOS treatment. In addition, Nrf2-Keap1 pathway, SOD2 and GCLC expression as well as renal apoptosis were also significantly reduced by XOS. These data suggest that XOS could indirectly restore renal function and Oat3 function via the reduction of oxidative stress and apoptosis through the modulating of AT1R-PKCα-NOXs activation in obese insulin-resistant rats. These attenuations were instigated by the improvement of obesity, hyperlipidemia and insulin resistance.

Renal outcomes with sodium glucose cotransporter 2 (SGLT2) inhibitor, dapagliflozin, in obese insulin-resistant model

A growing body of evidence indicates that obesity and insulin resistance contribute to the progression of renal disease. This study was performed to determine the effects of dapagliflozin, a novel sodium glucose cotransporter 2 (SGLT2) inhibitor, on renal and renal organic anion transporter 3 (Oat3) functions in high-fat diet fed rats, a model of obese insulin-resistance. Twenty-four male Wistar rats were divided into two groups, and received either a normal diet (ND) (n = 6) or a high-fat diet (HFD) (n = 18) for 16 weeks. At week 17, the HFD-fed rats were subdivided into three subgroups (n = 6/subgroup) and received either a vehicle (HFD), dapagliflozin (HFDAP; 1.0 mg/kg/day) or metformin (HFMET; 30 mg/kg/day), by oral gavage for four weeks. Metabolic parameters, renal function, renal Oat3 function, renal oxidative stress, and renal morphology were determined. The results showed that obese insulin-resistant rats induced by HFD feeding had impaired renal function and renal Oat3 function together with increased renal oxidative injury. Dapagliflozin or metformin treatment decreased insulin resistance, hypercholesterolemia, creatinine clearance and renal oxidative stress leading to improved renal function. However, dapagliflozin treatment decreased blood pressure, serum creatinine, urinary microalbumin and increased glucose excretions, and showed a greater ability to ameliorate impaired renal insulin signaling and glomerular barrier damage than metformin. These data suggest that dapagliflozin had greater efficacy than metformin for attenuating renal dysfunction and improving renal Oat3 function, at least in part by reducing renal oxidative stress and modulating renal insulin signaling pathways, and hence ameliorating renal injury.

Biochemical and Clinical Impact of Organic Uremic Retention Solutes: A Comprehensive Update

In this narrative review, the biological/biochemical impact (toxicity) of a large array of known individual uremic retention solutes and groups of solutes is summarized. We classified these compounds along their physico-chemical characteristics as small water-soluble compounds or groups, protein bound compounds and middle molecules. All but one solute (glomerulopressin) affected at least one mechanism with the potential to contribute to the uremic syndrome. In general, several mechanisms were influenced for each individual solute or group of solutes, with some impacting up to 7 different biological systems of the 11 considered. The inflammatory, cardio-vascular and fibrogenic systems were those most frequently affected and they are one by one major actors in the high morbidity and mortality of CKD but also the mechanisms that have most frequently been studied. A scoring system was built with the intention to classify the reviewed compounds according to the experimental evidence of their toxicity (number of systems affected) and overall experimental and clinical evidence. Among the highest globally scoring solutes were 3 small water-soluble compounds [asymmetric dimethylarginine (ADMA); trimethylamine-N-oxide (TMAO); uric acid], 6 protein bound compounds or groups of protein bound compounds [advanced glycation end products (AGEs); p-cresyl sulfate; indoxyl sulfate; indole acetic acid; the kynurenines; phenyl acetic acid;] and 3 middle molecules [β₂-microglobulin; ghrelin; parathyroid hormone). In general, more experimental data were provided for the protein bound molecules but for almost half of them clinical evidence was missing in spite of robust experimental data. The picture emanating is one of a complex disorder, where multiple factors contribute to a multisystem complication profile, so that it seems of not much use to pursue a decrease of concentration of a single compound.

CMPF, a Metabolite Formed Upon Prescription Omega-3-Acid Ethyl Ester Supplementation, Prevents and Reverses Steatosis

Prescription ω-3 fatty acid ethyl ester supplements are commonly used for the treatment of hypertriglyceridemia. However, the metabolic profile and effect of the metabolites formed by these treatments remain unknown. Here we utilized unbiased metabolomics to identify 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) as a significant metabolite of the ω-3-acid ethyl ester prescription Lovaza™ in humans. Administration of CMPF to mice before or after high-fat diet feeding at exposures equivalent to those observed in humans increased whole-body lipid metabolism, improved insulin sensitivity, increased beta-oxidation, reduced lipogenic gene expression, and ameliorated steatosis. Mechanistically, we find that CMPF acutely inhibits ACC activity, and induces long-term loss of SREBP1c and ACC1/2 expression. This corresponds to an induction of FGF21, which is required for long-term steatosis protection, as FGF21KO mice are refractory to the improved metabolic effects. Thus, CMPF treatment in mice parallels the effects of human Lovaza™ supplementation, revealing that CMPF may contribute to the improved metabolic effects observed with ω-3 fatty acid prescriptions.

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CMPF is an abundant metabolite resultant from supplementation with the ω-3-acid ethyl ester prescription Lovaza™ in humans

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Treatment with CMPF reverses hepatic lipid accumulation in diet-induced and genetically obese mouse models

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CMPF treatment prior to high fat diet feeding prevents development of steatosis through an FGF21-dependent mechanism

Fish oil is commonly prescribed for treating dyslipidemia and metabolic syndrome. Here, we identify CMPF as a significant metabolite in humans supplemented with ω-3-acid ethyl esters. CMPF treatment reversed liver lipid accumulation and improved insulin sensitivity in obese mice, while treatment of lean mice prior to high fat diet feeding prevented the development of fatty liver and insulin resistance. We find that CMPF acutely enhances fatty acid utilization and decreases lipid synthesis in the liver, while the preventative action is dependent on FGF21, which potentiates a feedback loop activated by CMPF. Thus, CMPF may contribute to the improved metabolic effects associated with fish oil supplementation.

Higher blood urea nitrogen is associated with increased risk of incident diabetes mellitus

Experimental evidence suggests that higher levels of urea may increase insulin resistance and suppress insulin secretion. However, whether higher levels of blood urea nitrogen (BUN) are associated with increased risk of incident diabetes mellitus in humans is not known. To study this, we built a national cohort of 1,337,452 United States Veterans without diabetes to characterize the association of BUN and risk of incident diabetes. Over a median follow-up of 4.93 years, there were 172,913 cases of incident diabetes. In joint risk models of estimated glomerular filtration rate (eGFR) and BUN. there was no association between eGFR and the risk of incident diabetes in those with a BUN of 25 mg/dl or less. However, the risk was significantly increased in those with a BUN over 25 mg/dl at all eGFR levels, even in those with an eGFR of 60 ml/min/1.73m² or more (hazard ratio 1.27; confidence interval 1.24-1.31). The risk of incident diabetes was highest in those with BUN over 25 mg/dL and an eGFR under 15 ml/min/1.73m² (1.68; 1.51-1.87). Spline analyses of the relationship between BUN and risk of incident diabetes showed that risk was progressively higher as BUN increased. In models where eGFR was included as a continuous covariate, compared to a BUN of 25 mg/dl or less, a BUN over 25 mg/dl was associated with increased risk of incident diabetes (1.23; 1.21-1.25). Every 10 ml/min/1.73m² decrease in eGFR was not associated with risk of incident diabetes (1.00; 1.00-1.01). Two-stage residual inclusion analyses showed that, independent of the impact of eGFR, every 10 mg/dL increase in BUN concentration was associated with increased risk of incident diabetes (1.15; 1.14-1.16). Thus, higher levels of BUN are associated with increased risk of incident diabetes mellitus.

Biomarkers of food intake and nutrient status are associated with glucose tolerance status and development of type 2 diabetes in older Swedish women

Background: Diet is frequently associated with both the development and prevention of type 2 diabetes (T2D), but there is a lack of objective tools for assessing the relation between diet and T2D. Biomarkers of dietary intake are unconfounded by recall and reporting bias, and using multiple dietary biomarkers could help strengthen the link between a healthy diet and the prevention of T2D.Objective: The objective of this study was to explore how diet is related to glucose tolerance status (GTS) and to future development of T2D irrespective of common T2D and cardiovascular disease risk factors by using multiple dietary biomarkers.Design: Dietary biomarkers were measured in plasma from 64-y-old Swedish women with different GTS [normal glucose tolerance (NGT; n = 190), impaired glucose tolerance (IGT; n = 209), and diabetes (n = 230)]. The same subjects were followed up after 5 y to determine changes in glucose tolerance (n = 167 for NGT, n = 174 for IGT, and n = 159 for diabetes). ANCOVA and logistic regression were used to explore baseline data for associations between dietary biomarkers, GTS, and new T2D cases at follow-up (n = 69).Results: Of the 10 dietary biomarkers analyzed, β-alanine (beef) (P-raw < 0.001), alkylresorcinols C17 and C19 (whole-grain wheat and rye) (P-raw = 0.003 and 0.011), eicosapentaenoic acid (fish) (P-raw = 0.041), 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) (fish) (P-raw = 0.002), linoleic acid (P-raw < 0.001), oleic acid (P-raw = 0.003), and α-tocopherol (margarine and vegetable oil) (P-raw < 0.001) were associated with GTS, and CMPF (fish) (OR: 0.72; 95% CI: 0.56, 0.93; P-raw = 0.013) and α-tocopherol (OR: 0.71; 95% CI: 0.51, 0.98; P-raw = 0.041) were inversely associated with future T2D development.Conclusions: Several circulating dietary biomarkers were strongly associated with GTS after correction for known T2D risk factors, underlining the role of diet in the development and prevention of T2D. To our knowledge, this study is the first to use multiple dietary biomarkers to investigate the link between diet and disease risk.

Furan fatty acids - Beneficial or harmful to health?

Furan fatty acids are found in plants, algae, and fish, and reported to have some positive health benefits, including anti-oxidant and anti-inflammatory activities, and inhibition of non-enzymatic lipid peroxidation. A major metabolite of furan fatty acids, 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF), has been reported to be increased in patients who progress from prediabetes to type 2 diabetes, although CMPF is not necessarily associated with impaired glucose metabolism. Other studies report that CMPF levels are lower in subjects with diabetes than control subjects. Plasma CMPF levels increase in subjects who consume fish or fish oil, and in patients with renal failure. It is not known where furan fatty acids are converted to CMPF and it is speculated that this might be a result of microbiome activity. The plasma levels reported for CMPF in healthy, diabetic and patients with renal disease vary by factors of more than 100-fold within each of these three groups, so measurement error appears to be limiting the ability to interpret studies. This review explores these controversies and raises questions about whether CMPF is a marker for healthy diets or indeed associated with diabetes and renal health. The review concludes that, on balance, furan fatty acids are beneficial for health.

Using binding competitors of albumin to promote the removal of protein-bound uremic toxins in hemodialysis: Hope or pipe dream?

Chronic kidney disease is associated with the accumulation of a large range of uremic retention solutes as referred to as uremic toxins. Some of these compounds belong to the group of Protein Bound Uremic Toxins (PBUT) due to their tight interactions with plasma proteins and especially serum albumin. These PBUT therefore exist in the bloodstream into two forms: a major bound (and non-diffusible) fraction and a minor free fraction. As a result, these compounds are poorly removed by most of the renal replacement therapies (such as hemodialysis) and their concentration can hardly be decreased in end-stage renal disease patients. An increase of the free fraction of PBUT could be achieved using chemical displacers that could compete with PBUT for binding to serum albumin. This review summarizes and discusses the interest of chemicals displacers as a valuable option to enhance PBUT removal in CKD patients.

Concentrations, Stability, and Isolation of the Furan Fatty Acid 9-(3-Methyl-5-pentylfuran-2-yl)-nonanoic Acid from Disposable Latex Gloves

Because of their antioxidant properties, furan fatty acids (furan-FAs) are valuable minor compounds with a widespread occurrence in all living matter. Unfortunately, pure standards are not readily available, because they usually contribute only 1% to the lipid fraction. A known exception of this is the milky fluid of Hevea brasiliensis, commonly known as latex, in which the furan-FA 9-(3-methyl-5-pentylfuran-2-yl)-nonanoic acid (9M5) contributes about 90% to the triacylglycerides. In this study, we investigated the content of 9M5 in 30 different disposable latex gloves, which ranged from 0.7 to 8.2 mg/g of glove. The light degradability of 9M5 in latex gloves was investigated, and different amounts of 9M5 in disposable latex gloves were attributed to varying exposure time to light. Additionally, over 100 mg of the methyl or ethyl ester of 9M5 (purity of >98%) could be extracted from disposable latex gloves, employing cold extraction and silver ion chromatography. With this method, standards for the quantitation of furan-FAs are obtained easily and rapidly in all laboratories.

The drug transporter OAT3 (SLC22A8) and endogenous metabolite communication via the gut-liver-kidney axis

The organic anion transporters OAT1 (SLC22A6) and OAT3 (SLC22A8) have similar substrate specificity for drugs, but it is far from clear whether this holds for endogenous substrates. By analysis of more than 600 metabolites in the Oat3KO (Oat3 knockout) by LC/MS, we demonstrate OAT3 involvement in the movement of gut microbiome products, key metabolites, and signaling molecules, including those flowing through the gut-liver-kidney axis. Major pathways affected included those involved in metabolism of bile acids, flavonoids, nutrients, amino acids (including tryptophan-derivatives that are uremic toxins), and lipids. OAT3 is also critical in elimination of liver-derived phase II metabolites, particularly those undergoing glucuronidation. Analysis of physicochemical features revealed nine distinct metabolite groups; at least one member of most clusters has been previously validated in transport assays. In contrast to drugs interacting with the OATs, endogenous metabolites accumulating in the Oat1KO (Oat1 knockout) versus Oat3KO have distinct differences in their physicochemical properties; they are very different in size, number of rings, hydrophobicity, and molecular complexity. Consistent with the Remote Sensing and Signaling Hypothesis, the data support the importance of the OAT transporters in inter-organ and inter-organismal remote communication via transporter-mediated movement of key metabolites and signaling molecules (e.g. gut microbiome-to-intestine-to-blood-to-liver-to-kidney-to-urine). We discuss the possibility of an intimate connection between OATs and metabolite sensing and signaling pathways (e.g. bile acids). Furthermore, the metabolomics and pathway analysis support the view that OAT1 plays a greater role in kidney proximal tubule metabolism and OAT3 appears relatively more important in systemic metabolism, modulating levels of metabolites flowing through intestine, liver, and kidney.

A wellness study of 108 individuals using personal, dense, dynamic data clouds

Personal data for 108 individuals were collected during a 9-month period, including whole genome sequences; clinical tests, metabolomes, proteomes, and microbiomes at three time points; and daily activity tracking. Using all of these data, we generated a correlation network that revealed communities of related analytes associated with physiology and disease. Connectivity within analyte communities enabled the identification of known and candidate biomarkers (e.g., gamma-glutamyltyrosine was densely interconnected with clinical analytes for cardiometabolic disease). We calculated polygenic scores from genome-wide association studies (GWAS) for 127 traits and diseases, and used these to discover molecular correlates of polygenic risk (e.g., genetic risk for inflammatory bowel disease was negatively correlated with plasma cystine). Finally, behavioral coaching informed by personal data helped participants to improve clinical biomarkers. Our results show that measurement of personal data clouds over time can improve our understanding of health and disease, including early transitions to disease states.

Key Role for the Organic Anion Transporters, OAT1 and OAT3, in the in vivo Handling of Uremic Toxins and Solutes

In vitro data indicates that the kidney proximal tubule (PT) transporters of uremic toxins and solutes (e.g., indoxyl sulfate, p-cresol sulfate, kynurenine, creatinine, urate) include two “drug” transporters of the organic anion transporter (OAT) family: OAT1 (SLC22A6, originally NKT) and OAT3 (SLC22A8). Here, we have examined new and prior metabolomics data from the Oat1KO and Oat3KO, as well as newly obtained metabolomics data from a “chemical double” knockout (Oat3KO plus probenecid). This gives a picture of the in vivo roles of OAT1 and OAT3 in the regulation of the uremic solutes and supports the centrality of these “drug” transporters in independently and synergistically regulating uremic metabolism. We demonstrate a key in vivo role for OAT1 and/or OAT3 in the handling of over 35 uremic toxins and solutes, including those derived from the gut microbiome (e.g., CMPF, phenylsulfate, indole-3-acetic acid). Although it is not clear whether trimethylamine-N-oxide (TMAO) is directly transported, the Oat3KO had elevated plasma levels of TMAO, which is associated with cardiovascular morbidity in chronic kidney disease (CKD). As described in the Remote Sensing and Signaling (RSS) Hypothesis, many of these molecules are involved in interorgan and interorganismal communication, suggesting that uremia is, at least in part, a disorder of RSS.

miR‑433 protects pancreatic β cell growth in high‑glucose conditions

Pancreatic β cell dysfunction is a key characteristic in the pathogenesis of diabetes mellitus (DM). MicroRNAs (miRNAs) have been identified to serve a role in DM pathogenesis, but how specific miRNAs regulate glucose-stimulated β cell functions remain unclear. The present study aimed to explore the effects of miR-433 on cell growth under high-glucose culture conditions and to determine the possible mechanisms involved. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis was performed to detect the expression levels of miRNAs in Min-6 pancreatic β cells cultured in high-glucose medium, which revealed that miR-433 was significantly downregulated. Results from in vitro Cell Counting Kit-8, colony formation and flow cytometry analyses indicated that overexpression of miR-433 may enhance cell viability and proliferation by promoting cell cycle progression and suppressing apoptosis. Furthermore, bioinformatics prediction and luciferase analysis demonstrated that miR-433 was able to inhibit the expression of cyclooxygenase 2 (COX2) through targeting its 3′-UTR. Moreover, knockdown of COX2 expression alleviated the inhibition of cell growth induced by high glucose, similar to overexpression of miR-433. In conclusion, the present results suggested that miR-433 may protect pancreatic β cells cultured in high glucose, which suggests that miR-433 may have beneficial effects in preventing and treating DM.

Circulating 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) levels are associated with hyperglycemia and β cell dysfunction in a Chinese population

Several recent clinical studies have suggested that the levels of circulating 3-carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) are significantly higher in patients with gestational diabetes mellitus (GDM), impaired glucose tolerance (IGT), and type 2 diabetes mellitus (T2DM). This study recruited a total of 516 participants. The following patient populations were enrolled: 99 newly diagnosed cases with T2DM, 219 cases with prediabetes [82 with isolated impaired glucose tolerance (I − IGT), 66 with isolated impaired fasting glucose (I − IFG) and 71 with impaired glucose tolerance and impaired fasting glucose (IGT + IFG)], and 198 cases with normal glucose tolerance [NGT, including 99 first-degree relatives of type 2 diabetes patients (FDRs) and 99 non-FDRs]. We investigated the circulating CMPF levels in subjects with different glucose metabolism statuses and examined the potential link between CMPF and β cell function. Our results indicate that the serum CMPF levels were elevated in the prediabetes, T2DM, and FDRs groups compared to the NGT group. Additionally, the serum CMPF concentrations were independently and negatively associated with the triglyceride levels and Stumvoll first-phase insulin secretion index. Cumulatively, our findings suggest that the circulating CMPF levels can predict glycolipid metabolism disorders. Furthermore, elevated serum CMPF concentrations may determine hyperglycemia and β cell dysfunction.

Impaired "Glycine"-mia in Type 2 Diabetes and Potential Mechanisms Contributing to Glucose Homeostasis

The onset and/or progression of type 2 diabetes (T2D) can be prevented if intervention is early enough. As such, much effort has been placed on the search for indicators predictive of prediabetes and disease onset or progression. An increasing body of evidence suggests that changes in plasma glycine may be one such biomarker. Circulating glycine levels are consistently low in patients with T2D. Levels of this nonessential amino acid correlate negatively with obesity and insulin resistance. Plasma glycine correlates positively with glucose disposal, and rises with interventions such as exercise and bariatric surgery that improve glucose homeostasis. A role for glycine in the regulation of glucose, beyond being a potential biomarker, is less clear, however. Dietary glycine supplementation increases insulin, reduces systemic inflammation, and improves glucose tolerance. Emerging evidence suggests that glycine, a neurotransmitter, also acts directly on target tissues that include the endocrine pancreas and the brain via glycine receptors and as a coligand for N-methyl-d-aspartate glutamate receptors to control insulin secretion and liver glucose output, respectively. Here, we review the current evidence supporting a role for glycine in glucose homeostasis via its central and peripheral actions and changes that occur in T2D.

Synthesis and Characterization of Urofuranoic Acids: In Vivo Metabolism of 2-(2-Carboxyethyl)-4-methyl-5-propylfuran-3-carboxylic Acid (CMPF) and Effects on in Vitro Insulin Secretion

CMPF (2-(2-carboxyethyl)-4-methyl-5-propylfuran-3-carboxylic acid) is a metabolite that circulates at high concentrations in type 2 and gestational diabetes patients. Further, human clinical studies suggest it might have a causal role in these diseases. CMPF inhibits insulin secretion in mouse and human islets in vitro and in vivo in rodents. However, the metabolic fate of CMPF and the relationship of structure to effects on insulin secretion have not been significantly studied. The syntheses of CMPF and analogues are described. These include isotopically labeled molecules. Study of these materials in vivo has led to the first observation of a metabolite of CMPF. In addition, a wide range of CMPF analogues have been prepared and characterized in insulin secretion assays using both mouse and human islets. Several molecules that influence insulin secretion in vitro were identified. The molecules described should serve as interesting probes to further study the biology of CMPF.

Patent highlights August-September 2016

A snapshot of noteworthy recent developments in the patent literature of relevance to pharmaceutical and medical research and development.

Metabolomics and Metabolic Diseases: Where Do We Stand?

Metabolomics, or the comprehensive profiling of small molecule metabolites in cells, tissues, or whole organisms, has undergone a rapid technological evolution in the past two decades. These advances have led to the application of metabolomics to defining predictive biomarkers for incident cardiometabolic diseases and, increasingly, as a blueprint for understanding those diseases' pathophysiologic mechanisms. Progress in this area and challenges for the future are reviewed here.

New Roles of Syntaxin-1A in Insulin Granule Exocytosis and Replenishment

In type-2 diabetes (T2D), severely reduced islet syntaxin-1A (Syn-1A) levels contribute to insulin secretory deficiency. We generated β-cell-specific Syn-1A-KO (Syn-1A-βKO) mice to mimic β-cell Syn-1A deficiency in T2D. Glucose tolerance tests showed that Syn-1A-βKO mice exhibited blood glucose elevation corresponding to reduced blood insulin levels. Perifusion of Syn-1A-βKO islets showed impaired first- and second-phase glucose-stimulated insulin secretion (GSIS) resulting from reduction in readily releasable pool and granule pool refilling. To unequivocally determine the β-cell exocytotic defects caused by Syn-1A deletion, EM and total internal reflection fluorescence microscopy showed that Syn-1A-KO β-cells had a severe reduction in the number of secretory granules (SGs) docked onto the plasma membrane (PM) at rest and reduced SG recruitment to the PM after glucose stimulation, the latter indicating defects in replenishment of releasable pools required to sustain second-phase GSIS. Whereas reduced predocked SG fusion accounted for reduced first-phase GSIS, selective reduction of exocytosis of short-dock (but not no-dock) newcomer SGs accounted for the reduced second-phase GSIS. These Syn-1A actions on newcomer SGs were partly mediated by Syn-1A interactions with newcomer SG VAMP8.