Expression of slc5a8 in Kidney and Its Role in Na+-coupled Transport of Lactate

Uric acid in health and disease: From physiological functions to pathogenic mechanisms

Owing to renal reabsorption and the loss of uricase activity, uric acid (UA) is strictly maintained at a higher physiological level in humans than in other mammals, which provides a survival advantage during evolution but increases susceptibility to certain diseases such as gout. Although monosodium urate (MSU) crystal precipitation has been detected in different tissues of patients as a trigger for disease, the pathological role of soluble UA remains controversial due to the lack of causality in the clinical setting. Abnormal elevation or reduction of UA levels has been linked to some of pathological status, also known as U-shaped association, implying that the physiological levels of UA regulated by multiple enzymes and transporters are crucial for the maintenance of health. In addition, the protective potential of UA has also been proposed in aging and some diseases. Therefore, the role of UA as a double-edged sword in humans is determined by its physiological or non-physiological levels. In this review, we summarize biosynthesis, membrane transport, and physiological functions of UA. Then, we discuss the pathological involvement of hyperuricemia and hypouricemia as well as the underlying mechanisms by which UA at abnormal levels regulates the onset and progression of diseases. Finally, pharmacological strategies for urate-lowering therapy (ULT) are introduced, and current challenges in UA study and future perspectives are also described.

Exploring monocarboxylate transporter inhibition for cancer treatment

Cells are separated from the environment by a lipid bilayer membrane that is relatively impermeable to solutes. The transport of ions and small molecules across this membrane is an essential process in cell biology and metabolism. Monocarboxylate transporters (MCTs) belong to a vast family of solute carriers (SLCs) that facilitate the transport of certain hydrophylic small compounds through the bilipid cell membrane. The existence of 446 genes that code for SLCs is the best evidence of their importance. In-depth research on MCTs is quite recent and probably promoted by their role in cancer development and progression. Importantly, it has recently been realized that these transporters represent an interesting target for cancer treatment. The search for clinically useful monocarboxylate inhibitors is an even more recent field. There is limited pre-clinical and clinical experience with new inhibitors and their precise mechanism of action is still under investigation. What is common to all of them is the inhibition of lactate transport. This review discusses the structure and function of MCTs, their participation in cancer, and old and newly developed inhibitors. Some suggestions on how to improve their anticancer effects are also discussed.

Adaptive metabolic response to short-term intensive fasting

BACKGROUND & AIMS

Short-term intensive fasting (STIF), known as beego in Chinese phonetic articulation, has been practiced for more than two thousand years. However, the potential risk of STIF and the body's response to the risk have not been adequately evaluated. This study aims to address this issue, focusing on the STIF-triggered metabolic response of the liver and kidney.

METHODS

The STIF procedure in the clinical trial includes a 7-day water-only intensive fasting phase and a 7-day gradual refeeding phase followed by a regular diet. The intensive fasting in humans was assisted with psychological induction. To gain insights not available in the clinical trial, we designed a STIF program for mice that resulted in similar phenotypes seen in humans. Plasma metabolic profiling and examination of gene expression as well as liver and kidney function were performed by omics, molecular, biochemical and flow cytometric analyses. A human cell line model was also used for mechanistic study.

RESULTS

Clinically significant metabolites of fat and protein were found to accumulate during the fasting phase, but they were relieved after gradual refeeding. Metabolomics profiling revealed a universal pattern in the consumption of metabolic intermediates, in which pyruvate and succinate are the two key metabolites during STIF. In the STIF mouse model, the accumulation of metabolites was mostly counteracted by the upregulation of catabolic enzymes in the liver, which was validated in a human cell model. Kidney filtration function was partially affected by STIF but could be recovered by refeeding. STIF also reduced oxidative and inflammatory levels in the liver and kidney. Moreover, STIF improved lipid metabolism in mice with fatty liver without causing accumulation of metabolites after STIF.

CONCLUSIONS

The accumulation of metabolites induced by STIF can be relieved by spontaneous upregulation of catabolic enzymes, suggesting an adaptive and protective metabolic response to STIF stress in the mammalian body.

Sex and Cross-Sex Testosterone Treatment Alters Gamma-Hydroxybutyrate Acid Toxicokinetics and Toxicodynamics in Rats

Γ-hydroxybutyric acid (GHB) is widely abused due to its sedative/hypnotic and euphoric effects. In recent years, GHB use has witnessed a notable rise within the LGBTQ+ community. GHB is a substrate of monocarboxylate transporters (MCTs) and exhibits nonlinear toxicokinetics, characterized by saturable metabolism, absorption, and renal reabsorption. This study investigates the impact of exogenous testosterone administration on GHB toxicokinetics and toxicodynamics, exploring the potential of MCT1 inhibition as a strategy to counteract toxicity. Ovariectomized (OVX) females and castrated (CST) male Sprague Dawley rats were treated with testosterone or placebo for 21 days. GHB was administered at two doses (1000 mg/kg or 1500 mg/kg i.v.), and the MCT1 inhibitor AR-C 155858 (1 mg/kg i.v.) was administered 5 min after GHB (1500 mg/kg i.v.) administration. Plasma and urine were collected up to 8 h post-dose, and GHB concentrations were quantified via a validated LC/MS/MS assay. Sleep time (sedative/hypnotic effect) was utilized as the toxicodynamic endpoint. Testosterone treatment significantly affected GHB toxicokinetics and toxicodynamics. Testosterone-treated CST rats exhibited significantly lower renal clearance, higher AUC, and increased sedative effect, while testosterone-treated OVX rats demonstrated higher metabolic clearance. AR-C 155858 treatment led to an increase in GHB renal and total clearance together with an improvement in sedative/hypnotic effect. In conclusion, exogenous testosterone treatment induces significant alterations in GHB toxicokinetics and toxicodynamics, and MCT inhibition can serve as a potential therapeutic strategy for GHB overdose in both cisgender and transgender male populations.

Synergistic and antagonistic interactions of oxybenzone and ocean acidification: new insight into vulnerable cellular processes in non-calcifying anthozoans

Cnidarians face significant threats from ocean acidification (OA) and anthropogenic pollutants such as oxybenzone (BP-3). The convergence of threats from multiple stressors is an important area to investigate because of potential significant synergistic or antagonistic interactions. Real-time quantitative PCR was performed to characterize the expression profiles of twenty-two genes of interest (GOI) in sea anemones (Exaiptasia diaphana) exposed to one of four treatments: 1) 96 h of OA conditions followed by a 4 h exposure to 20 ppb BP-3; 2) Exposure to 4 h 20 ppb BP-3 without 96 h of OA; 3) Exposure to 96 h of OA alone; or 4) laboratory conditions with no exposure to BP-3 and/or OA. These 22 GOIs represent cellular processes associated with proton-dependent transport, sodium-dependent transport, metal cation binding/transport, extracellular matrix, amino acid metabolism/transport, immunity, and/or steroidogenesis. These 22 GOIs provide new insight into vulnerable cellular processes in non-calcifying anthozoans exposed to OA and BP-3. Expression profiles were categorized as synergistic, antagonistic, or additive of BP-3 in the presence of OA. Two GOIs were synergistic. Fifteen GOIs were antagonistic and the remaining five GOIs were additive in response to BP-3 in acidified seawater. A subset of these GOIs appear to be candidate biomarkers for future in situ investigations. In human health, proton-dependent monocarboxylate transporters (MCTs) are promising pharmacological targets and recognized as potential biomarkers. By comparison, these same MCTs appear to be targets of xenobiotic chemical pollutants in cnidarian physiology. In the presence of BP-3, a network of collagen synthesis genes are upregulated and antagonistic in their expression profiles. Cytochrome b561 is a critical protein required for collagen synthesis and in silico modeling demonstrates BP-3 binds in the pocket of cytochrome b561. Understanding the underlying molecular mechanisms of "drug-like" compounds such as BP-3 may lead to a more comprehensive interpretation of transcriptional expression profiles. The collective antagonistic responses of GOIs associated with collagen synthesis strongly suggests these GOIs should be considered candidate biomarkers of effect. GOIs with synergistic and additive responses represent candidate biomarkers of exposure. Results show the effects of OA and BP-3 are interactive with respect to their impact on cnidarians. This investigation offers mechanistic data that supports the expression profiles and underpins higher order physiological responses.

Key enzyme in charge of ketone reabsorption of renal tubular SMCT1 may be a new target in diabetic kidney disease

OBJECTIVE

A ketogenic diet or mildly increased ketone body levels are beneficial for diabetic kidney disease (DKD) patients. Our previous study has found that sodium-coupled monocarboxylate transporter 1 (SMCT1), a key enzyme in charge of ketone reabsorption, possesses beneficial effects on the function of renal tubular epithelial cells (TECs) in energy crisis. Our present study is to investigate whether SMCT1 is important in maintaining the physiological function of renal tubular and plays a role in DKD.

METHODS

We tested the expression of SMCT1 in kidney tissues from DKD patients receiving kidney biopsy as well as diabetes mice. We compared the difference of β-hydroxybutyrate (β-HB) levels in serum, urine and kidney tissues between diabetic mice and control. Using recombinant adeno-associated viral vector containing SMCT1 (encoded by Slc5a8 gene), we tested the effect of SMCT1 upregulation on microalbuminuria as well as its effects on mitochondrial energy metabolism in diabetic mice. Then we investigated the role of SMCT1 and its β-HB reabsorption function in maintaining the physiological function of renal tubular using renal tubule-specific Slc5a8 gene knockout mice. Transcriptomes and proteomics analysis were used to explore the underlying mechanism.

RESULTS

SMCT1 downregulation was found in DKD patients as well as in diabetic mice. Moreover, diabetic mice had a decreased renal β-HB level compared with control, and SMCT1 upregulation could improve microalbuminuria and mitochondrial energy metabolism. In renal tubule-specific Slc5a8 gene knockout mice, microalbuminuria occurred early at 24 weeks of age, accompanied by ATP shortage and metabolic reprogramming in the kidney; however, supplementation with β-HB precursor substance 1,3-butanediol in food alleviated kidney damage as well as energy metabolic reprogramming.

CONCLUSIONS

Decreased SMCT1 expression and its ketone reabsorption function play an important role in the occurrence of DKD. SMCT1 may be a new promising target in treating DKD.

Role of hypermethylated SLC5A8 in follicular thyroid cancer diagnosis and prognosis prediction

OBJECTIVE

Thyroid cancer is one of the most frequently reported endocrine system malignancies. It is difficult to distinguish follicular thyroid cancer (FTC) from follicular thyroid adenoma (FTA) during pathological diagnosis in patients without lymph nodes or distant metastases. Therefore, we conducted a retrospective study to investigate the significance of SLC5A8 methylation and expression in the diagnosis and prognosis of FTC.

METHODS

We used 165 tissue samples, including FTC (n = 58), thyroid tumors of uncertain malignant potential (TT-UMP, n = 40), and FTA (n = 67), to explore the differences in SLC5A8 methylation and mRNA transcription in different pathological types. Survival analysis was conducted to evaluate the recurrence rate at a 5-year follow-up.

RESULTS

The SLC5A8 methylation positive rate was higher in patients with thyroglobulin ≥ 40 μg/l and Chol ≥ 5.17 mmol/l, and it was higher in patients with FTC (n = 42, 72.4%) than those with FTA (n = 27, 40.3%) and TT-UMP (n = 23, 57.5%). The relative concentration of SLC5A8 mRNA was lower in patients with FTC than in those with FTA (p < 0.05). At 5-year follow-ups, patients who were SLC5A8 methylation-positive had a higher recurrence rate than those who were methylation-negative.

CONCLUSIONS

Our current study indicates that SLC5A8 gene methylation occurs more commonly in patients with FTC than in those with FTA. The differences in SLC5A8 methylation and expression among FTA, FTC, and TT-UMP provide an important basis for further exploration of epigenetic changes in the occurrence, development, and prognosis of thyroid cancer. Our findings need to be further validated in larger populations with long-term follow-up in the future.

GHB toxicokinetics and renal monocarboxylate transporter expression are influenced by the estrus cycle in rats

BACKGROUND

The illicit use and abuse of gamma-hydroxybutyric acid (GHB) occurs due to its sedative/hypnotic and euphoric effects. Currently, there are no clinically available therapies to treat GHB overdose, and care focuses on symptom treatment until the drug is eliminated from the body. Proton- and sodium-dependent monocarboxylate transporters (MCTs (SLC16A) and SMCTs (SLC5A)) transport and mediate the renal clearance and distribution of GHB. Previously, it has been shown that MCT expression is regulated by sex hormones in the liver, skeletal muscle and Sertoli cells. The focus of the current study is to evaluate GHB toxicokinetics and renal monocarboxylate transporter expression over the estrus cycle in females, and in the absence of male and female sex hormones.

METHODS

GHB toxicokinetics and renal transporter expression of MCT1, SMCT1 and CD147 were evaluated in females over the estrus cycle, and in ovariectomized (OVX) female, male and castrated (CST) male rats. GHB was administered iv bolus (600 and 1000 mg/kg) and plasma and urine samples were collected for six hours post-dose. GHB concentrations were quantified using a validated LC/MS/MS assay. Transporter mRNA and protein expression was quantified by qPCR and Western Blot.

RESULTS

GHB renal clearance and AUC varied between sexes and over the estrus cycle in females with higher renal clearance and a lower AUC in proestrus females as compared to males (intact and CST), and OVX females. We demonstrated that renal MCT1 membrane expression varies over the estrus cycle, with the lowest expression observed in proestrus females, which is consistent with the observed changes in GHB renal clearance.

CONCLUSIONS

Our results suggest that females may be less susceptible to GHB-induced toxicity due to decreased exposure resulting from increased renal clearance, as a result of decreased renal MCT1 expression.

Analytical and therapeutic profiles of DNA methylation alterations in cancer; an overview of changes in chromatin arrangement and alterations in histone surfaces

DNA methylation is the most important epigenetic element that activates the inhibition of gene transcription and is included in the pathogenesis of all types of malignancies. Remarkably, the effectors of DNA methylation are DNMTs (DNA methyltransferases) that catalyze de novo or keep methylation of hemimethylated DNA after the DNA replication process. DNA methylation structures in cancer are altered, with three procedures by which DNA methylation helps cancer development which are including direct mutagenesis, hypomethylation of the cancer genome, and also focal hypermethylation of the promoters of TSGs (tumor suppressor genes). Conspicuously, DNA methylation, nucleosome remodeling, RNA-mediated targeting, and histone modification balance modulate many biological activities that are essential and indispensable to the genesis of cancer and also can impact many epigenetic changes including DNA methylation and histone modifications as well as adjusting of non-coding miRNAs expression in prevention and treatment of many cancers. Epigenetics points to heritable modifications in gene expression that do not comprise alterations in the DNA sequence. The nucleosome is the basic unit of chromatin, consisting of 147 base pairs (bp) of DNA bound around a histone octamer comprised of one H3/H4 tetramer and two H2A/H2B dimers. DNA methylation is preferentially distributed over nucleosome regions and is less increased over flanking nucleosome-depleted DNA, implying a connection between nucleosome positioning and DNA methylation. In carcinogenesis, aberrations in the epigenome may also include in the progression of drug resistance. In this report, we report the rudimentary notes behind these epigenetic signaling pathways and emphasize the proofs recommending that their misregulation can conclude in cancer. These findings in conjunction with the promising preclinical and clinical consequences observed with epigenetic drugs against chromatin regulators, confirm the important role of epigenetics in cancer therapy.

Associations of circulating proteins with lipoprotein profiles: proteomic analyses from the OmniHeart randomized trial and the Atherosclerosis Risk in Communities (ARIC) Study

BACKGROUND

Within healthy dietary patterns, manipulation of the proportion of macronutrient can reduce CVD risk. However, the biological pathways underlying healthy diet-disease associations are poorly understood. Using an untargeted, large-scale proteomic profiling, we aimed to (1) identify proteins mediating the association between healthy dietary patterns varying in the proportion of macronutrient and lipoproteins, and (2) validate the associations between diet-related proteins and lipoproteins in the Atherosclerosis Risk in Communities (ARIC) Study.

METHODS

In 140 adults from the OmniHeart trial, a randomized, cross-over, controlled feeding study with 3 intervention periods (carbohydrate-rich; protein-rich; unsaturated fat-rich dietary patterns), 4,958 proteins were quantified at the end of each diet intervention period using an aptamer assay (SomaLogic). We assessed differences in log2-transformed proteins in 3 between-diet comparisons using paired t-tests, examined the associations between diet-related proteins and lipoproteins using linear regression, and identified proteins mediating these associations using a causal mediation analysis. Levels of diet-related proteins and lipoprotein associations were validated in the ARIC study (n = 11,201) using multivariable linear regression models, adjusting for important confounders.

RESULTS

Three between-diet comparisons identified 497 significantly different proteins (protein-rich vs. carbohydrate-rich = 18; unsaturated fat-rich vs. carbohydrate-rich = 335; protein-rich vs. unsaturated fat-rich dietary patterns = 398). Of these, 9 proteins [apolipoprotein M, afamin, collagen alpha-3(VI) chain, chitinase-3-like protein 1, inhibin beta A chain, palmitoleoyl-protein carboxylesterase NOTUM, cathelicidin antimicrobial peptide, guanylate-binding protein 2, COP9 signalosome complex subunit 7b] were positively associated with lipoproteins [high-density lipoprotein (HDL)-cholesterol (C) = 2; triglyceride = 5; non-HDL-C = 3; total cholesterol to HDL-C ratio = 1]. Another protein, sodium-coupled monocarboxylate transporter 1, was inversely associated with HDL-C and positively associated with total cholesterol to HDL-C ratio. The proportion of the association between diet and lipoproteins mediated by these 10 proteins ranged from 21 to 98%. All of the associations between diet-related proteins and lipoproteins were significant in the ARIC study, except for afamin.

CONCLUSIONS

We identified proteins that mediate the association between healthy dietary patterns varying in macronutrients and lipoproteins in a randomized feeding study and an observational study.

TRIAL REGISTRATION

NCT00051350 at clinicaltrials.gov.

The effect of dietary approaches to stop hypertension and ketogenic diets intervention on serum uric acid concentration: a systematic review and meta-analysis of randomized controlled trials

Hyperuricemia as a risk factor for metabolic diseases is proved to be profoundly modified by dietary approaches. This systematic review and meta-analysis of randomized control trials (RCT) was conducted to investigate the effect of two nutritional interventions; dietary approaches to stop hypertension (DASH) diet and ketogenic diet (KD) on serum uric acid (UA) concentrations. Our systematic search was for RCTs in which KD or DASH diet were assigned to adults for at least 2 weeks or more. Until March 2023 in Embase, Web of Science, PubMed, and Scopus databases, 10 eligible RCTs that intervened with DASH diet (n = 4) or KD (n = 6) and had provided laboratory data on serum UA were found. Summary effect was calculated by random-effects model. Results from the meta-analysis of the 4 DASH diet RCTs with a total of 590 participants revealed significant decrease in serum UA after at least 4 weeks of interventions (mean difference (MD) = ‒0.25; 95% CI ‒0.4 to ‒0.1 mg/dL; p < 0.01; I² = 0%). The pooled meta-analysis of the 6 included RCTs of KD reporting data of 267 participants showed no significant changes in serum UA (MD = 0.26; 95% CI ‒0.47 to 0.98 mg/dL, I² = 95.32%). However, a non-significant reduction of UA in the subgroup analysis of very low-calorie KD (VLCKD) studies (MD = ‒0.04; 95% CI ‒0.29 to 0.22, I² = 0%) was obtained. DASH diet has an ameliorating effect on serum UA and may be recommended for hyperuricemia states such as gout. In addition, we have shown that serum UA level following KD remained unchanged. Although, in view of the heterogeneity across the studies, further investigations are needed to determine the effect of KD and VLKD on serum UA concentrations.

PCK1 is a key regulator of metabolic and mitochondrial functions in renal tubular cells

Phosphoenolpyruvate carboxykinase 1 (PCK1 or PEPCK-C) is a cytosolic enzyme converting oxaloacetate to phosphoenolpyruvate, with a potential role in gluconeogenesis, ammoniagenesis, and cataplerosis in the liver. Kidney proximal tubule cells display high expression of this enzyme, whose importance is currently not well defined. We generated PCK1 kidney-specific knockout and knockin mice under the tubular cell-specific PAX8 promoter. We studied the effect of PCK1 deletion and overexpression at the renal level on tubular physiology under normal conditions and during metabolic acidosis and proteinuric renal disease. PCK1 deletion led to hyperchloremic metabolic acidosis characterized by reduced but not abolished ammoniagenesis. PCK1 deletion also resulted in glycosuria, lactaturia, and altered systemic glucose and lactate metabolism at baseline and during metabolic acidosis. Metabolic acidosis resulted in kidney injury in PCK1-deficient animals with decreased creatinine clearance and albuminuria. PCK1 further regulated energy production by the proximal tubule, and PCK1 deletion decreased ATP generation. In proteinuric chronic kidney disease, mitigation of PCK1 downregulation led to better renal function preservation. PCK1 is essential for kidney tubular cell acid-base control, mitochondrial function, and glucose/lactate homeostasis. Loss of PCK1 increases tubular injury during acidosis. Mitigating kidney tubular PCK1 downregulation during proteinuric renal disease improves renal function.NEW & NOTEWORTHY Phosphoenolpyruvate carboxykinase 1 (PCK1) is highly expressed in the proximal tubule. We show here that this enzyme is crucial for the maintenance of normal tubular physiology, lactate, and glucose homeostasis. PCK1 is a regulator of acid-base balance and ammoniagenesis. Preventing PCK1 downregulation during renal injury improves renal function, rendering it an important target during renal disease.

Segment-Dependent Gene Expression Profiling of the Cartilaginous Fish Nephron Using Laser Microdissection for Functional Characterization of Nephron at Segment Levels

For adaptation to a high salinity marine environment, cartilaginous fishes have evolved a ureosmotic strategy. They have a highly elaborate "four-loop nephron" in the kidney, which is considered to be important for reabsorption of urea from the glomerular filtrate to maintain a high concentration of urea in the body. However, the function and regulation, generally, of the "four-loop nephron" are still largely unknown due to the complicated configuration of the nephron and its many subdivided segments. Laser microdissection (LMD) followed by RNA-sequencing (RNA-seq) analysis is a powerful technique to obtain segment-dependent gene expression profiles. In the present study, using the kidney of cloudy catshark, Scyliorhinus torazame, we tested several formaldehyde-free and formaldehyde-based fixatives to optimize the fixation methods. Fixation by 1% neutral buffered formalin for 15 min resulted in sufficient RNA and structural integrities, which allowed LMD clipping of specific nephron segments and subsequent RNA-seq analysis. RNA-seq from the LMD samples of the second-loop, the fourth-loop, and the five tubular segments in the bundle zone revealed a number of specific membrane transporter genes that can characterize each segment. Among them, we examined expressions of the Na ⁺ -coupled cotransporters abundantly expressed in the second loop samples. Although the proximal II segment of the second loop is known for the elimination of excess solutes, the present results imply that the PII segment is also crucial for reabsorption of valuable solutes. Looking ahead to future studies, the segment-dependent gene expression profiling will be a powerful technique for unraveling the renal mechanisms and regulation in euryhaline elasmobranchs.

Evolution and developmental expression of the sodium-iodide symporter (NIS, slc5a5) gene family: Implications for perchlorate toxicology

The vertebrate sodium-iodide symporter (NIS or SLC5A5) transports iodide into the thyroid follicular cells that synthesize thyroid hormone. The SLC5A protein family includes transporters of vitamins, minerals, and nutrients. Disruption of SLC5A5 function by perchlorate, a pervasive environmental contaminant, leads to human pathologies, especially hypothyroidism. Perchlorate also disrupts the sexual development of model animals, including threespine stickleback (Gasterosteus aculeatus) and zebrafish (Danio rerio), but the mechanism of action is unknown. To test the hypothesis that SLC5A5 paralogs are expressed in tissues necessary for the development of reproductive organs, and therefore are plausible candidates to mediate the effects of perchlorate on sexual development, we first investigated the evolutionary history of Slc5a paralogs to better understand potential functional trajectories of the gene family. We identified two clades of slc5a paralogs with respect to an outgroup of sodium/choline cotransporters (slc5a7); these clades are the NIS clade of sodium/iodide and lactate cotransporters (slc5a5, slc5a6, slc5a8, slc5a8, and slc5a12) and the SGLT clade of sodium/glucose cotransporters (slc5a1, slc5a2, slc5a3, slc5a4, slc5a10, and slc5a11). We also characterized expression patterns of slc5a genes during development. Stickleback embryos and early larvae expressed NIS clade genes in connective tissue, cartilage, teeth, and thyroid. Stickleback males and females expressed slc5a5 and its paralogs in gonads. Single-cell transcriptomics (scRNA-seq) on zebrafish sex-genotyped gonads revealed that NIS clade-expressing cells included germ cells (slc5a5, slc5a6a, and slc5a6b) and gonadal soma cells (slc5a8l). These results are consistent with the hypothesis that perchlorate exerts its effects on sexual development by interacting with slc5a5 or its paralogs in reproductive tissues. These findings show novel expression domains of slc5 genes in stickleback and zebrafish, which suggest similar functions across vertebrates including humans, and provide candidates to mediate the effects of perchlorate on sexual development.

An evaluation method for uric acid uptake inhibition using primary human proximal tubule epithelial cells treated with insulin

The effects of uricosuric agents have been evaluated in vitro with indices of uric acid uptake into human urate transporter 1 (URAT1)-overexpressed oocytes or cells. In the present study, we evaluated a method using primary human renal proximal tubule epithelial cells (RPTECs). Pretreatment of RPTECs with insulin significantly increased the uptake of uric acid into these cells. The uric acid uptake was inhibited in a concentration-dependent manner by the URAT1 inhibitors benzbromarone and dotinurad. Therefore, effects of uricosuric agents can be evaluated by the novel method, which is closer to the physiological system compared with previous methods.

Enterotoxigenic Escherichia coli Heat-Stable Toxin and Ebola Virus Delta Peptide: Similarities and Differences

Enterotoxigenic Escherichia coli (ETEC) STb toxin exhibits striking structural similarity to Ebola virus (EBOV) delta peptide. Both ETEC and EBOV delta peptide are enterotoxins. Comparison of the structural and functional similarities and differences of these two toxins illuminates features that are important in induction of pathogenesis by a bacterial and viral pathogen.

The effect of valproic acid on SLC5A8 expression in gonad-intact and gonadectomized rat thymocytes

BACKGROUND

Valproic acid (VPA) pharmacological mechanisms are related to the anti-inflammatory and anti-viral effects. VPA is a histone deacetylases inhibitor and serves a role in its immunomodulatory impacts. VPA has complex effects on immune cell's mitochondrial metabolism. The SLC5A8 transporter of short fatty acids has an active role in regulating mitochondrial metabolism. The study aimed to investigate whether SLC5A8 expresses the sex-related difference and how SLC5A8 expression depends on gonadal hormones, VPA treatment, and NKCC1 expression in rat thymocytes.

METHODS

Control groups and VPA-treated gonad-intact and gonadectomized Wistar male and female rats were investigated (n = 6 in a group). The VPA 300 mg/kg/day in drinking water was given for 4 weeks. The SLC5A8 (Slc5a8 gene) and NKCC1 (Slc12a2 gene) RNA expressions were determined by the RT-PCR method.

RESULTS

The higher Slc5a8 expression was found in the gonad-intact males than respective females (p = 0.004). VPA treatment decreased the Slc5a8 expression in gonad-intact and castrated males (p = 0.02 and p = 0.03, respectively), and increased in gonad-intact female rats compared to their control (p = 0.03). No significant difference in the Slc5a8 expression between the ovariectomized female control and VPA-treated females was determined (p > 0.05). VPA treatment alters the correlation between Slc5a8 and Slc12a2 gene expression in thymocytes of gonad-intact rats.

CONCLUSION

VPA effect on the Slc5a8 expression in rat thymocytes is gender- and gonadal hormone-dependent.

Structure and mechanism of the SGLT family of glucose transporters

Glucose is a primary energy source in living cells. The discovery in 1960s that a sodium gradient powers the active uptake of glucose in the intestine¹ heralded the concept of a secondary active transporter that can catalyse the movement of a substrate against an electrochemical gradient by harnessing energy from another coupled substrate. Subsequently, coupled Na⁺/glucose transport was found to be mediated by sodium-glucose cotransporters^2,3 (SGLTs). SGLTs are responsible for active glucose and galactose absorption in the intestine and for glucose reabsorption in the kidney⁴, and are targeted by multiple drugs to treat diabetes⁵. Several members within the SGLT family transport key metabolites other than glucose². Here we report cryo-electron microscopy structures of the prototypic human SGLT1 and a related monocarboxylate transporter SMCT1 from the same family. The structures, together with molecular dynamics simulations and functional studies, define the architecture of SGLTs, uncover the mechanism of substrate binding and selectivity, and shed light on water permeability of SGLT1. These results provide insights into the multifaceted functions of SGLTs.

Starvation Ketosis and the Kidney

BACKGROUND

The remarkable ability of the body to adapt to long-term starvation has been critical for survival of primitive man. An appreciation of these processes can provide the clinician better insight into many clinical conditions characterized by ketoacidosis.

SUMMARY

The body adapts to long-term fasting by conserving nitrogen, as the brain increasingly utilizes keto acids, sparing the need for glucose. This shift in fuel utilization decreases the need for mobilization of amino acids from the muscle for purposes of gluconeogenesis. Loss of urinary nitrogen is initially in the form of urea when hepatic gluconeogenesis is dominant and later as ammonia reflecting increased glutamine uptake by the kidney. The carbon skeleton of glutamine is utilized for glucose production and regeneration of consumed HCO3-. The replacement of urea with NH4+ provides the osmoles needed for urine flow and waste product excretion. Over time, the urinary loss of nitrogen is minimized as kidney uptake of filtered ketone bodies becomes more complete. Adjustments in urine Na+ serve to minimize kidney K+ wasting and, along with changes in urine pH, minimize the likelihood of uric acid precipitation. There is a sexual dimorphism in response to starvation. Key Message: Ketoacidosis is a major feature of common clinical conditions to include diabetic ketoacidosis, alcoholic ketoacidosis, salicylate intoxication, SGLT2 inhibitor therapy, and calorie sufficient but carbohydrate-restricted diets. Familiarity with the pathophysiology and metabolic consequences of ketogenesis is critical, given the potential for the clinician to encounter one of these conditions.

Function of Uric Acid Transporters and Their Inhibitors in Hyperuricaemia

Disorders of uric acid metabolism may be associated with pathological processes in many diseases, including diabetes mellitus, cardiovascular disease, and kidney disease. These diseases can further promote uric acid accumulation in the body, leading to a vicious cycle. Preliminary studies have proven many mechanisms such as oxidative stress, lipid metabolism disorders, and rennin angiotensin axis involving in the progression of hyperuricaemia-related diseases. However, there is still lack of effective clinical treatment for hyperuricaemia. According to previous research results, NPT1, NPT4, OAT1, OAT2, OAT3, OAT4, URAT1, GLUT9, ABCG2, PDZK1, these urate transports are closely related to serum uric acid level. Targeting at urate transporters and urate-lowering drugs can enhance our understanding of hyperuricaemia and hyperuricaemia-related diseases. This review may put forward essential references or cross references to be contributed to further elucidate traditional and novel urate-lowering drugs benefits as well as provides theoretical support for the scientific research on hyperuricemia and related diseases.

Renal Sensing of Bacterial Metabolites in the Gut-kidney Axis

Seminal works have now revealed the gut microbiota is connected with several diseases, including renal disorders. The balance between optimal and dysregulated host-microbiota interactions has completely changed our understanding of immunity and inflammation. Kidney injury is associated with accumulation of uremic toxins in the intestine, augmented intestinal permeability, and systemic inflammation. Intestinal bacteria can signal through innate receptors and induce immune cell activation in the lamina propria and release of inflammatory mediators into the bloodstream. But the gut microbiota can also modulate immune functions through soluble products as short-chain fatty acids (SCFAs). The three most common SCFAs are propionate, butyrate, and acetate, which can signal through specific G-protein coupled receptors (GPCRs), such as GPR43, GPR41, and GPR109a, expressed on the surface of epithelial, myeloid, endothelial, and immune cells, among others. The triggered signaling can change cell metabolism, immune cell activation, and cell death. In this study, we reviewed the gut-kidney axis, how kidney cells can sense SCFAs, and its implication in kidney diseases.

Dissecting the Interplay Mechanism between Epigenetics and Gut Microbiota: Health Maintenance and Disease Prevention

The gut microbiota exists throughout the full life cycle of the human body, and it has been proven to have extensive impacts on health and disease. Accumulating evidence demonstrates that the interplay between gut microbiota and host epigenetics plays a multifaceted role in health maintenance and disease prevention. Intestinal microflora, along with their metabolites, could regulate multiple epigenetic pathways; e.g., DNA methylation, miRNA, or histone modification. Moreover, epigenetic factors can serve as mediators to coordinate gut microbiota within the host. Aiming to dissect this interplay mechanism, the present review summarizes the research profile of gut microbiota and epigenetics in detail, and further interprets the biofunctions of this interplay, especially the regulation of intestinal inflammation, the improvement of metabolic disturbances, and the inhibition of colitis events. This review provides new insights into the interplay of epigenetics and gut microbiota, and attempts to reveal the mysteries of health maintenance and disease prevention from this new perspective.

Control of lymphocyte functions by gut microbiota-derived short-chain fatty acids

A mounting body of evidence indicates that dietary fiber (DF) metabolites produced by commensal bacteria play essential roles in balancing the immune system. DF, considered nonessential nutrients in the past, is now considered to be necessary to maintain adequate levels of immunity and suppress inflammatory and allergic responses. Short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, are the major DF metabolites and mostly produced by specialized commensal bacteria that are capable of breaking down DF into simpler saccharides and further metabolizing the saccharides into SCFAs. SCFAs act on many cell types to regulate a number of important biological processes, including host metabolism, intestinal functions, and immunity system. This review specifically highlights the regulatory functions of DF and SCFAs in the immune system with a focus on major innate and adaptive lymphocytes. Current information regarding how SCFAs regulate innate lymphoid cells, T helper cells, cytotoxic T cells, and B cells and how these functions impact immunity, inflammation, and allergic responses are discussed.

Critical transporters of methionine and methionine hydroxyl analogue supplements across the intestine: What we know so far and what can be learned to advance animal nutrition

DL-methionine (DL-Met) and its analogue DL-2-hydroxy-4-(methylthio) butanoic acid (DL-methionine hydroxyl analogue or DL-MHA) have been used as nutritional supplements in the diets of farmed raised animals. Knowledge of the intestinal transport mechanisms involved in these products is important for developing dietary strategies. This review provides updated information of the expression, function, and transport kinetics in the intestine of known Met-linked transporters along with putative MHA-linked transporters. As a neutral amino acid (AA), the transport of DL-Met is facilitated by multiple apical sodium-dependent/-independent high-/low-affinity transporters such as ASCT2, B⁰AT1 and rBAT/b^0,+AT. The basolateral transport largely relies on the rate-limiting uniporter LAT4, while the presence of the basolateral antiporter y⁺LAT1 is probably necessary for exchanging intracellular cationic AAs and Met in the blood. In contrast, the intestinal transport kinetics of DL-MHA have been scarcely studied. DL-MHA transport is generally accepted to be mediated simply by the proton-dependent monocarboxylate transporter MCT1. However, in-depth mechanistic studies have indicated that DL-MHA transport is also achieved through apical sodium monocarboxylate transporters (SMCTs). In any case, reliance on either a proton or sodium gradient would thus require energy input for both Met and MHA transport. This expanding knowledge of the specific transporters involved now allows us to assess the effect of dietary ingredients on the expression and function of these transporters. Potentially, the resulting information could be furthered with selective breeding to reduce overall feed costs.

γ-Hydroxybutyric Acid: Pharmacokinetics, Pharmacodynamics, and Toxicology

Gamma-hydroxybutyrate (GHB) is a short-chain fatty acid present endogenously in the brain and used therapeutically for the treatment of narcolepsy, as sodium oxybate, and for alcohol abuse/withdrawal. GHB is better known however as a drug of abuse and is commonly referred to as the "date-rape drug"; current use in popular culture includes recreational "chemsex," due to its properties of euphoria, loss of inhibition, amnesia, and drowsiness. Due to the steep concentration-effect curve for GHB, overdoses occur commonly and symptoms include sedation, respiratory depression, coma, and death. GHB binds to both GHB and GABAB receptors in the brain, with pharmacological/toxicological effects mainly due to GABAB agonist effects. The pharmacokinetics of GHB are complex and include nonlinear absorption, metabolism, tissue uptake, and renal elimination processes. GHB is a substrate for monocarboxylate transporters, including both sodium-dependent transporters (SMCT1, 2; SLC5A8; SLC5A12) and proton-dependent transporters (MCT1-4; SLC16A1, 7, 8, and 3), which represent significant determinants of absorption, renal reabsorption, and brain and tissue uptake. This review will provide current information of the pharmacology, therapeutic effects, and pharmacokinetics/pharmacodynamics of GHB, as well as therapeutic strategies for the treatment of overdoses. Graphical abstract.

Urinary ketone body loss leads to degeneration of brain white matter in elderly SLC5A8-deficient mice

SLC5A8 is a sodium-coupled monocarboxylate and ketone transporter expressed in various epithelial cells. A putative role of SLC5A8 in neuroenergetics has been also hypothesized. To clarify this issue, we studied the cerebral phenotype of SLC5A8-deficient mice during aging. Elderly SLC5A8-deficient mice presented diffuse leukoencephalopathy characterized by intramyelinic oedema without demyelination suggesting chronic energetic crisis. Hypo-metabolism in the white matter of elderly SLC5A8-deficient mice was found using ^99mTc-hexamethylpropyleneamine oxime (HMPAO) single-photon emission CT (SPECT). Since the SLC5A8 protein could not be detected in the mouse brain, it was hypothesized that the leukoencephalopathy of aging SLC5A8-deficient mice was caused by the absence of slc5a8 expression in a peripheral organ, i.e. the kidney, where SLC5A8 is strongly expressed. A hyper-excretion of the ketone β-hydroxybutyrate (BHB) in the urine of SLC5A8-deficient mice was observed and showed that SLC5A8-deficient mice suffered a cerebral BHB insufficiency. Elderly SLC5A8-deficient mice also presented altered glucose metabolism. We propose that the continuous renal loss of BHB leads to a chronic energetic deficiency in the brain of elderly SLC5A8-deficient mice who are unable to counterbalance their glucose deficit. This study highlights the importance of alternative energetic substrates in neuroenergetics especially under conditions of restricted glucose availability.

Characterization of the segmental transport mechanisms of DL-methionine hydroxy analogue along the intestinal tract of rainbow trout with an additional comparison to DL-methionine

The aim of this study was to identify the unknown transport mechanism of the extensively used monocarboxylate methionine feed supplement DL-methionine hydroxy analogue (DL-MHA) in rainbow trout intestine. Transport across the pyloric caeca (PC), midgut (MG), and hindgut (HG) regions were kinetically studied in Na⁺- and H⁺-dependent manners. Gene expression of monocarboxylate (MCTs) and sodium monocarboxylate transporters (SMCTs) were assessed. Results demonstrated that DL-MHA transport from 0.2-20 mM was Na⁺-dependent and obeyed Michaelis-Menten kinetics with low affinity in PC & MG in apical/basal pH of 7.7/7.7. Changes in apical/basal pH (6.0/6.0, 6.0/7.7, and 7.7/8.7) had insignificant effects on kinetics. In contrast, HG flux kinetics were only obtained in pH 7.7/8.7 or in the presence of lactate with medium affinity. Additionally, DL-MHA transport from 0-150 μM demonstrated the presence of a Na⁺-dependent high-affinity transporter in PC & MG. Conclusively, two distinct carrier-mediated DL-MHA transport mechanisms along the trout gut were found: 1) in PC & MG: apical transport was regulated by Na⁺-requiring systems that possibly contained low- and high-affinity transporters, and basolateral transport was primarily achieved through a H⁺-independent transporter; 2) in HG: uptake was apically mediated by a Na⁺-dependent transporter with medium affinity, and basolateral exit was largely controlled by an H⁺-dependent transporter. Finally, two major methionine feed supplements, DL-MHA and DL-methionine (DL-Met) were compared to understand the differences in their bioefficacy. Flux rates of DL-MHA were only about 42.2-66.0% in PC and MG compared to DL-Met, suggesting intestinal transport of DL-MHA was lower than DL-Met.

Lactate: the ugly duckling of energy metabolism

Lactate, perhaps the best-known metabolic waste product, was first isolated from sour milk, in which it is produced by lactobacilli. Whereas microbes also generate other fermentation products, such as ethanol or acetone, lactate dominates in mammals. Lactate production increases when the demand for ATP and oxygen exceeds supply, as occurs during intense exercise and ischaemia. The build-up of lactate in stressed muscle and ischaemic tissues has established lactate's reputation as a deleterious waste product. In this Perspective, we summarize emerging evidence that, in mammals, lactate also serves as a major circulating carbohydrate fuel. By providing mammalian cells with both a convenient source and sink for three-carbon compounds, circulating lactate enables the uncoupling of carbohydrate-driven mitochondrial energy generation from glycolysis. Lactate and pyruvate together serve as a circulating redox buffer that equilibrates the NADH/NAD ratio across cells and tissues. This reconceptualization of lactate as a fuel-analogous to how Hans Christian Andersen's ugly duckling is actually a beautiful swan-has the potential to reshape the field of energy metabolism.

Recent approaches to gout drug discovery: an update

INTRODUCTION

Inflammation induced by urate deposition in joints causes gout. Healthy individuals maintain serum levels of urate by balancing urate production/excretion, whereas a production/excretion imbalance increases urate levels. Hyperuricemia is diagnosed when the serum urate level is continuously above 7 mg/dl as the solubility limit, and urate accumulates in the kidneys and joints. Because hyperuricemia increases the risk of gout, therapies aim to eliminate urate deposition to prevent gouty arthritis and kidney injury.

AREAS COVERED

This review discusses the mechanism underlying hyperuricemia with respect to urate production and urate transport, along with urate-lowering therapeutics, including urate synthesis inhibitors, uricolytic enzymes, and uricosuric agents. The authors asses published data on relevant commercial therapy development projects and clinical trials.

EXPERT OPINION

Available treatment options for hyperuricemia are limited. Allopurinol, a urate synthesis inhibitor, is generally administered at a reduced dosage to patients with renal impairment. Some URAT1 inhibitors have an unfavorable side effect profile. A promising strategy for treatment is the use of uricosuric agents that inhibit transporters (e.g. URAT1, URATv1/GLUT9, OAT10) which reabsorb urate from the urine.

Pharmacologic inducers of the uric acid exporter ABCG2 as potential drugs for treatment of gouty arthritis

Uric acid is the end product of purine catabolism and its plasma levels are maintained below its maximum solubility in water (6–7 mg/dl). The plasma levels are tightly regulated as the balance between the rate of production and the rate of excretion, the latter occurring in urine (kidney), bile (liver) and feces (intestinal tract). Reabsorption in kidney is also an important component of this process. Both excretion and reabsorption are mediated by specific transporters. Disruption of the balance between production and excretion leads to hyperuricemia, which increases the risk of uric acid crystallization as monosodium urate with subsequent deposition of the crystals in joints causing gouty arthritis. Loss-of-function mutations in the transporters that mediate uric acid excretion are associated with gout. The ATP-Binding Cassette exporter ABCG2 is important in uric acid excretion at all three sites: kidney (urine), liver (bile), and intestine (feces). Mutations in this transporter cause gout and these mutations occur at significant prevalence in general population. However, mutations that are most prevalent result only in partial loss of transport function. Therefore, if the expression of these partially defective transporters could be induced, the increased number of the transporter molecules would compensate for the mutation-associated decrease in transport function and hence increase uric acid excretion. As such, pharmacologic agents with ability to induce the expression of ABCG2 represent potentially a novel class of drugs for treatment of gouty arthritis.

Targeting L-Lactate Metabolism to Overcome Resistance to Immune Therapy of Melanoma and Other Tumor Entities

Although immunotherapy plays a significant role in tumor therapy, its efficacy is impaired by an immunosuppressive tumor microenvironment. A molecule that contributes to the protumor microenvironment is the metabolic product lactate. Lactate is produced in large amounts by cancer cells in response to either hypoxia or pseudohypoxia, and its presence in excess alters the normal functioning of immune cells. A key enzyme involved in lactate metabolism is lactate dehydrogenase (LDH). Elevated baseline LDH serum levels are associated with poor outcomes of current anticancer (immune) therapies, especially in patients with melanoma. Therefore, targeting LDH and other molecules involved in lactate metabolism might improve the efficacy of immune therapies. This review summarizes current knowledge about lactate metabolism and its role in the tumor microenvironment. Based on that information, we develop a rationale for deploying drugs that target lactate metabolism in combination with immune checkpoint inhibitors to overcome lactate-mediated immune escape of tumor cells.

Learning Physiology From Inherited Kidney Disorders

The identification of genes causing inherited kidney diseases yielded crucial insights in the molecular basis of disease and improved our understanding of physiological processes that operate in the kidney. Monogenic kidney disorders are caused by mutations in genes coding for a large variety of proteins including receptors, channels and transporters, enzymes, transcription factors, and structural components, operating in specialized cell types that perform highly regulated homeostatic functions. Common variants in some of these genes are also associated with complex traits, as evidenced by genome-wide association studies in the general population. In this review, we discuss how the molecular genetics of inherited disorders affecting different tubular segments of the nephron improved our understanding of various transport processes and of their involvement in homeostasis, while providing novel therapeutic targets. These include inherited disorders causing a dysfunction of the proximal tubule (renal Fanconi syndrome), with emphasis on epithelial differentiation and receptor-mediated endocytosis, or affecting the reabsorption of glucose, the handling of uric acid, and the reabsorption of sodium, calcium, and magnesium along the kidney tubule.

Promoter Methylation of Four Tumor Suppressor Genes in Human Papillary Thyroid Carcinoma

BACKGROUND & OBJECTIVE

Papillary thyroid cancer (PTC) is considered to be the most common type of thyroid malignancies. Epigenetic alteration, in which the chromatin conformation and gene expression change without changing the sequence of DNA, can occur in some tumor suppressor genes and oncogenes. Methylation is the most common type of epigenetic alterations that can be an excellent indicator of PTC invasive behavior.

METHODS

In this research, we determined the promoter methylation status of four tumor suppressor genes (SLC5A8, RASSF1, MGMT, and DNMT1) and compared the results of 55 PTC cases with 40 goiter patients. For methylation, we used the methylation-sensitive high resolution melting (MS-HRM) assay technique. The resulting graphs of each run were compared with those of 0%, 50%, and 100% methylated controls.

RESULTS

Our data showed that the promoter methylation of SLC5A8, Ras association domain family member 1(RASSF1), and MGMT were significantly different between PTC tissue and goiter with P-value less than 0.05. The most significant differences were observed in RASSF1; 77.2% of hyper-methylated PTC patients versus 15.6% hyper-methylated goiter samples (P<0.001).

CONCLUSION

RASSF1 promoter methylation can be a PTC genetic marker. RASSF1 promoter methylation is under the impact of the methyltransferase genes (DNMT1 and MGMT), protein expression, and promoter methylation.

Sodium-coupled monocarboxylate transporter 1 interacts with the RING finger- and PDZ domain-containing protein PDZRN3

Sodium-coupled monocarboxylate transporter SMCT1 (SLC5A8) mediates monocarboxylate transport in the proximal tubule of the kidney. We have identified PDZK1 and PDZ domain-containing RING finger 3 (PDZRN3) as potent binding partners of SMCT1, which has a PDZ motif (Thr-Arg-Leu), by yeast two-hybrid screening and revealed that PDZK1 enhances the transport activity of SMCT1. In this study, we aimed to characterize the interaction between SMCT1 and PDZRN3 as well as to examine how PDZRN3 regulates SMCT1 function. An interaction between SMCT1 and PDZRN3 through the PDZ motif was observed in a co-immunoprecipitation assay and yeast two-hybrid assay. A transport assay showed that PDZRN3 abolished the enhancing effect of PDZK1 on nicotinate uptake via SMCT1. Our results suggest that SMCT1 interacts with PDZRN3 and that PDZRN3 may regulate SMCT1 function by interfering with the interaction between SMCT1 and PDZK1.

Identification of the multivalent PDZ protein PDZK1 as a binding partner of sodium-coupled monocarboxylate transporter SMCT1 (SLC5A8) and SMCT2 (SLC5A12)

Sodium-coupled monocarboxylate transporters SMCT1 (SLC5A8) and SMCT2 (SLC5A12) mediate the high- and low-affinity transport of lactate in the kidney, but their regulatory mechanism is still unknown. Since these two transporters have the PDZ-motif at their C-terminus, the function of SMCTs may be modulated by a protein-protein interaction. To investigate the binding partner(s) of SMCTs in the kidney, we performed yeast two-hybrid (Y2H) screenings of a human kidney cDNA library with the C-terminus of SMCT1 (SMCT1-CT) and SMCT2 (SMCT2-CT) as bait. PDZK1 was identified as a partner for SMCTs. PDZK1 coexpression in SMCT1-expressing HEK293 cells enhanced their nicotinate transport activity. PDZK1, SMCT1, and URAT1 in vitro assembled into a single tri-molecular complex and their colocalization was confirmed in the renal proximal tubule in vivo by immunohistochemistry. These results indicate that the SMCT1-PDZK1 interaction thus plays an important role in both lactate handling as well as urate reabsorption in the human kidney.

Urinary metabolites predict prolonged duration of delayed graft function in DCD kidney transplant recipients

Extending kidney donor criteria, including donation after circulatory death (DCD), has resulted in increased rates of delayed graft function (DGF) and primary nonfunction. Here, we used Nuclear Magnetic Resonance (NMR) spectroscopy to analyze the urinary metabolome of DCD transplant recipients at multiple time points (days 10, 42, 180, and 360 after transplantation). The aim was to identify markers that predict prolonged duration of functional DGF (fDGF). Forty-seven metabolites were quantified and their levels were evaluated in relation to fDGF. Samples obtained at day 10 had a different profile than samples obtained at the other time points. Furthermore, at day 10 there was a statistically significant increase in eight metabolites and a decrease in six metabolites in the group with fDGF (N = 53) vis-à-vis the group without fDGF (N = 22). In those with prolonged fDGF (≥21 days) (N = 17) urine lactate was significantly higher and pyroglutamate lower than in those with limited fDGF (<21 days) (N = 36). In order to further distinguish prolonged fDGF from limited fDGF, the ratios of all metabolites were analyzed. In a logistic regression analysis, the sum of branched-chain amino acids (BCAAs) over pyroglutamate and lactate over fumarate, predicted prolonged fDGF with an AUC of 0.85. In conclusion, kidney transplant recipients with fDGF can be identified based on their altered urinary metabolome. Furthermore, two ratios of urinary metabolites, lactate/fumarate and BCAAs/pyroglutamate, adequately predict prolonged duration of fDGF.

Transcriptome analysis identifies activated signaling pathways and regulated ABC transporters and solute carriers after hyperosmotic stress in renal MDCK I cells

Hyperosmolality is found under physiological conditions in the kidneys, whereas hyperosmolality in other tissues may be associated with pathological conditions. In such tissues an association between inflammation and hyperosmolality has been suggested. During hyperosmotic stress, an important phenomenon is upregulation of solute carriers (SLCs). We hypothesize that hyperosmolality affects the expression of many SLCs as well as ABC transporters. Through RNA-sequencing and topological pathway analysis, the cell cycle, the cytokine-cytokine receptor interaction pathway, and the chemokine-signaling pathway were significantly activated in MDCK I cells after hyperosmotic treatment (Δ200 mOsm) with raffinose or NaCl. 9065, 8052 and 5018 genes were significantly regulated by raffinose, NaCl or urea supplementation (500 mOsm), respectively, compared to control (300 mOsm). Cytokines, that have not previously been associated with hyperosmolality, were identified. We further provide an overview of transport proteins that could be of relevance in tissues exposed to hyperosmolality. Especially Slc5a8 was found highly up-regulated.

Involvement of butyrate in electrogenic K+ secretion in rat rectal colon

Short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, are synthesized from dietary carbohydrates by colonic bacterial fermentation. These SCFAs supply energy, suppress cancer, and affect ion transport. However, their roles in ion transport and regulation in the intracellular environment remain unknown. In order to elucidate the roles of SCFAs, we measured short-circuit currents (I_SC) and performed RT-PCR and immunohistochemical analyses of ion transporters in rat rectal colon. The application of 30 mM butyrate shifted I_SC in a negative direction, but did not attenuate the activity of epithelial Na⁺ channels (ENaC). The application of bumetanide, a Na⁺-K⁺-2Cl⁻ cotransporter inhibitor, to the basolateral side reduced the negative I_SC shift induced by butyrate. The application of XE991, a KCNQ-type K⁺ channel inhibitor, to the apical side decreased the I_SC shift induced by butyrate in a dose-dependent manner. The I_SC shift was independent of HCO₃⁻ and insensitive to ibuprofen, an SMCT1 inhibitor. The mucosa from rat rectal colon expressed mRNAs of H⁺-coupled monocarboxylate transporters (MCT1, MCT4, and MCT5, also referred to as SLC16A1, SLC16A3, and SLC16A4, respectively). RT-PCR and immunofluorescence analyses demonstrated that KCNQ2 and KCNQ4 localized to the apical membrane of surface cells in rat rectal colon. These results indicate that butyrate, which may be transported by H⁺-coupled monocarboxylate transporters, activates K⁺ secretion through KCNQ-type K⁺ channels on the apical membrane in rat rectal colon. KCNQ-type K⁺ channels may play a role in intestinal secretion and defense mechanisms in the gastrointestinal tract.

The uricosuric effects of dihydropyridine calcium channel blockers in vivo using urate under-excretion animal models

The purpose of this study was to create novel urate under-excretion animal models using pyrazinamide and to evaluate whether dihydropyridine calcium channel blockers (CCBs) have uricosuric effects in vivo. Adult male ICR mice were treated with pyrazinamide, vehicle (dimethyl sulfoxide: DMSO), or tap water. Thirty minutes later, pyrazinamide-treated mice were given benzbromarone, losartan, nilvadipine, nitrendipine, nifedipine or azelnidipine. Six hours after the second administration, urine (by urinary bladder puncture) and plasma were collected to measure uric acid and creatinine levels, and fractional excretion of uric acid (FEUA) and creatinine clearance (Ccr) were calculated and evaluated. There was no significant difference in the levels of plasma uric acid, plasma creatinine, Ccr, urinary N-acetyl-β-d-glucosaminidase (NAG) and urinary NAG-creatinine ratio between water, DMSO, and pyrazinamide-treated mice. But the FEUA of pyrazinamide-treated mice was significantly lower than water mice. The FEUA was significantly higher in mice taking the dihydropyridine CCBs (nilvadipine, nitrendipine, nifedipine, and high-dose azelnidipine) than in pyrazinamide-treated mice. There was no significant difference in Ccr. Thus, a novel animal model created with PZA administration was useful as a urate under-excretion animal model that was probably URAT1-mediated, and the uricosuric effects of dihydropyridine CCBs were confirmed in vivo.

Short-Chain Fatty Acid Transporters: Role in Colonic Homeostasis

Short-chain fatty acids (SCFA; acetate, propionate, and butyrate) are generated in colon by bacterial fermentation of dietary fiber. Though diffusion in protonated form is a significant route, carrier-mediated mechanisms constitute the major route for the entry of SCFA in their anionic form into colonic epithelium. Several transport systems operate in cellular uptake of SCFA. MCT1 (SLC16A1) and MCT4 (SLC16A3) are H+-coupled and mediate electroneutral transport of SCFA (H+: SCFA stoichiometry; 1:1). MCT1 is expressed both in the apical membrane and basolateral membrane of colonic epithelium whereas MCT4 specifically in the basolateral membrane. SMCT1 (SLC5A8) and SMCT2 (SLC5A12) are Na+-coupled; SMCT1-mediated transport is electrogenic (Na+: SCFA stoichiometry; 2:1) whereas SMCT2-mediated transport is electroneutral (Na+: SCFA stoichiometry; 1:1). SMCT1 and SMCT2 are expressed exclusively in the apical membrane. An anion-exchange mechanism also operates in the apical membrane in which SCFA entry in anionic form is coupled to bicarbonate efflux; the molecular identity of this exchanger however remains unknown. All these transporters are subject to regulation, notably by their substrates themselves; this process involves cell-surface receptors with SCFA as signaling molecules. There are significant alterations in the expression of these transporters in ulcerative colitis and colon cancer. The tumor-associated changes occur via transcriptional regulation by p53 and HIF1α and by promoter methylation. As SCFA are obligatory for optimal colonic health, the transporters responsible for the entry and transcellular transfer of these bacterial products in colonic epithelium are critical determinants of colonic function under physiological conditions and in disease states. © 2018 American Physiological Society. Compr Physiol 8:299-314, 2018.

Meta-analysis of promoter methylation in eight tumor-suppressor genes and its association with the risk of thyroid cancer

Promoter methylation in a number of tumor-suppressor genes (TSGs) can play crucial roles in the development of thyroid carcinogenesis. The focus of the current meta-analysis was to determine the impact of promoter methylation of eight selected candidate TSGs on thyroid cancer and to identify the most important molecules in this carcinogenesis pathway. A comprehensive search was performed using Pub Med, Scopus, and ISI Web of Knowledge databases, and eligible studies were included. The methodological quality of the included studies was evaluated according to the Newcastle Ottawa scale table and pooled odds ratios (ORs); 95% confidence intervals (CIs) were used to estimate the strength of the associations with Stata 12.0 software. Egger's and Begg's tests were applied to detect publication bias, in addition to the "Metatrim" method. A total of 55 articles were selected, and 135 genes with altered promoter methylation were found. Finally, we included eight TSGs that were found in more than four studies (RASSF1, TSHR, PTEN, SLC5A, DAPK, P16, RARβ2, and CDH1). The order of the pooled ORs for these eight TSGs from more to less significant was CDH1 (OR = 6.73), SLC5 (OR = 6.15), RASSF1 (OR = 4.16), PTEN (OR = 3.61), DAPK (OR = 3.51), P16 (OR = 3.31), TSHR (OR = 2.93), and RARβ2 (OR = 1.50). Analyses of publication bias and sensitivity confirmed that there was very little bias. Thus, our findings showed that CDH1 and SCL5A8 genes were associated with the risk of thyroid tumor genesis.

Ketosis and diabetic ketoacidosis in response to SGLT2 inhibitors: Basic mechanisms and therapeutic perspectives

Inhibitors of the sodium-glucose cotransporter SGLT2 are a new class of antihyperglycemic drugs that have been approved for the treatment of type 2 diabetes mellitus (T2DM). These drugs inhibit glucose reabsorption in the proximal tubules of the kidney thereby enhancing glucosuria and lowering blood glucose levels. Additional consequences and benefits include a reduction in body weight, uric acid levels, and blood pressure. Moreover, SGLT2 inhibition can have protective effects on the kidney and cardiovascular system in patients with T2DM and high cardiovascular risk. However, a potential side effect that has been reported with SGLT2 inhibitors in patients with T2DM and particularly during off-label use in patients with type 1 diabetes is diabetic ketoacidosis. The US Food and Drug Administration recently warned that SGLT2 inhibitors may result in euglycemic ketoacidosis. Here, we review the basic metabolism of ketone bodies, the triggers of diabetic ketoacidosis, and potential mechanisms by which SGLT2 inhibitors may facilitate the development of ketosis or ketoacidosis. This provides the rationale for measures to lower the risk. We discuss the role of the kidney and potential links to renal gluconeogenesis and uric acid handling. Moreover, we outline potential beneficial effects of modestly elevated ketone body levels on organ function that may have therapeutic relevance for the observed beneficial effects of SGLT2 inhibitors on the kidney and cardiovascular system.

Metabiotics: One Step ahead of Probiotics; an Insight into Mechanisms Involved in Anticancerous Effect in Colorectal Cancer

Colorectal cancer is closely associated with environment, diet and lifestyle. Normally it is treated with surgery, radiotherapy or chemotherapy but increasing systemic toxicity, resistance and recurrence is prompting scientists to devise new potent and safer alternate prophylactic or therapeutic strategies. Among these, probiotics, prebiotics, synbiotics, and metabiotics are being considered as the promising candidates. Metabiotics or probiotic derived factors can optimize various physiological functions of the host and offer an additional advantage to be utilized even in immunosuppressed individuals. Interestingly, anti colon cancer potential of probiotic strains has been attributable to metabiotics that have epigenetic, antimutagenic, immunomodulatory, apoptotic, and antimetastatic effects. Thus, it's time to move one step further to utilize metabiotics more smartly by avoiding the risks associated with probiotics even in certain normal/or immuno compromised host. Here, an attempt is made to provide insight into the adverse effects associated with probiotics and beneficial aspects of metabiotics with main emphasis on the modulatory mechanisms involved in colon cancer.

Transport of haloacids across biological membranes

Haloacids are considered to be environmental pollutants, but some of them have also been tested in clinical research. The way that haloacids are transported across biological membranes is important for both biodegradation and drug delivery purposes. In this review, we will first summarize putative haloacids transporters and the information about haloacids transport when studying carboxylates transporters. We will then introduce MCT1 and SLC5A8, which are respective transporter for antitumor agent 3-bromopyruvic acid and dichloroacetic acid, and monochloroacetic acid transporters Deh4p and Dehp2 from a haloacids-degrading bacterium. Phylogenetic analysis of these haloacids transporters and other monocarboxylate transporters reveals their evolutionary relationships. Haloacids transporters are not studied to the extent that they deserve compared with their great application potentials, thus future inter-discipline research are desired to better characterize their transport mechanisms for potential applications in both environmental and clinical fields.

Gut microbiota in renal physiology: focus on short-chain fatty acids and their receptors

A number of recent studies have begun to explore a new and exciting area: the interaction between the gut microbiome and renal physiology. In particular, multiple studies have focused on the role of microbially produced short chain fatty acids, which are generally thought to promote health. This review will focus on what is known to date regarding the influence of the microbiome on renal function, with emphasis on the cell biology, physiology, and clinical implications of short chain fatty acids and short chain fatty acid receptors. It is clear that microbe-host interactions are an exciting and ever-expanding field, which has implications for how we view diseases such as hypertension, acute kidney injury, and chronic kidney disease. However, it is important to recognize that although the potential promise of this area is extremely enticing, we are only the very edge of this new field.

Histological characterization of orphan transporter MCT14 (SLC16A14) shows abundant expression in mouse CNS and kidney

BACKGROUND

MCT14 (SLC16A14) is an orphan member of the monocarboxylate transporter (MCT) family, also known as the SLC16 family of secondary active transmembrane transporters. Available expression data for this transporter is limited, and in this paper we aim to characterize MCT14 with respect to tissue distribution and cellular localization in mouse brain.

RESULTS

Using qPCR, we found that Slc16a14 mRNA was highly abundant in mouse kidney and moderately in central nervous system, testis, uterus and liver. Using immunohistochemistry and in situ hybridization, we determined that MCT14 was highly expressed in excitatory and inhibitory neurons as well as epithelial cells in the mouse brain. The expression was exclusively localized to the soma of neurons. Furthermore, we showed with our phylogenetic analysis that MCT14 most closely relate to the aromatic amino acid- and thyroid-hormone transporters MCT8 (SLC16A2) and MCT10 (SLC16A10), in addition to the carnitine transporter MCT9 (SLC16A9).

CONCLUSIONS

We provide here the first histological mapping of MCT14 in the brain and our data are consistent with the hypothesis that MCT14 is a neuronal aromatic-amino-acid transporter.