Chitosan oligosaccharide mitigates kidney injury in prediabetic rats by improving intestinal barrier and renal autophagy

Consumption of a high-fat diet (HFD) not only increases the risk of metabolic syndrome but also initiates kidney injury. Lipid accumulation-induced systemic low-grade inflammation is an upstream mechanism of kidney injury associated with prediabetes. Chitosan oligosaccharide (COS) provides potent anti-obesity effects through several mechanisms including fecal lipid excretion. In this study, we investigated the effects of COS on the prevention of obesity-related complications and its ability to confer renoprotection in a prediabetic model. Rats fed on a HFD developed obesity, glucose intolerance and kidney dysfunction. COS intervention successfully ameliorated these conditions (p < 0.05) by attenuating intestinal lipid absorption and the renal inflammation-autophagy-apoptosis axis. A novel anti-inflammatory effect of COS had been demonstrated by the strengthening of intestinal barrier integrity via calcium-sensing receptor (p < 0.05). The use of COS as a supplement may be useful in reducing prediabetic complications especially renal injury and the risk of type 2 diabetes.

The combination of dapagliflozin and statins ameliorates renal injury through attenuating the activation of inflammasome-mediated autophagy in insulin-resistant rats

Long-term use of a high-fat diet with high-fructose (HFF) intake could promote insulin resistance and induce lipid accumulation leading to kidney injury possibly via impairment of the autophagy process and enhancement of the inflammasome pathway. We investigated whether dapagliflozin as a monotherapy or combined with atorvastatin could restore kidney autophagy impairment and reduce inflammasome activation associated with kidney injury induced by HFF consumption. Male Wistar rats were given an HFF for 16 weeks and then treated with dapagliflozin with or without atorvastatin for 4 weeks. Impaired glucose tolerance, dyslipidemia, renal lipid accumulation along with impaired renal autophagy and activated inflammasome pathway promoted renal injury were exhibited in HFF rats. Dapagliflozin with or without atorvastatin treatment could partially restore disrupted metabolic parameters and reduce kidney injury. In particular, the combination treatment group showed significant amelioration of inflammasome activation and autophagy impairment. In conclusion, the combination therapy of dapagliflozin and atorvastatin has a positive effect on renal injury associated with autophagy and inflammasome activation induced by HFF in insulin-resistant rats. This study is the first report demonstrating the underlying mechanism associated with a combination treatment of dapagliflozin and atorvastatin on autophagy and inflammasome pathways in an insulin-resistant condition. Therefore, dapagliflozin in combination with atorvastatin may be a further preventive or therapeutic strategy for chronic kidney disease in an insulin-resistant or diabetic condition.

A chalcone derivative retards renal cyst enlargement by inhibiting fluid secretion and cell proliferation in an in vitro model of polycystic kidney disease

BACKGROUND

Renal bilateral fluid filled-cyst in polycystic kidney disease (PKD) is associated with abnormal epithelial cell proliferation and transepithelial fluid secretion which leads to end-stage renal disease (ESRD). A chalcone derivative, isoliquiritigenin (ISLQ), has been shown to have various pharmacological properties. Since several studies have shown that ISLQ could inhibit CFTR channel activity, it is interesting to see whether it can inhibit renal cyst enlargement. The present study was aimed to determine an inhibitory effect and the mechanism of chalcone derivatives on MDCK cyst progression and Pkd1 mutant cells.

METHODS

MDCK cyst growth and cyst formation experiments, MTT assay, Ussing chamber experiment, BrdU cell proliferation assay and western blot analysis were performed in this study.

RESULTS

Among four compounds of chalcone derivatives tested, CHAL-005 (100 µM) was found to inhibit MDCK cyst growth in a dose-dependent manner without cytotoxicity. It inhibited short-circuit current of chloride secretion as well as CFTR protein expression in MDCK cells. CHAL-005 significantly suppressed cell proliferation. In addition, CHAL-005 strongly reduced phosphorylation ERK1/2 and phosphorylation S6 kinase in MDCK and Pkd1 mutant cells. Interestingly, CHAL-005 activated phosphorylation of AMP kinase protein expression in MDCK and Pkd1 mutant cells.

CONCLUSION

CHAL-005 slowed MDCK cyst progression by inhibiting CFTR expression and reducing ERK1/2 and mTOR/S6K signaling pathways as well as activating AMPK expression. Therefore, a chalcone derivative could represent as a promising drug candidate for polycystic kidney disease intervention.

Farnesoid X Receptor Activation Stimulates Organic Cations Transport in Human Renal Proximal Tubular Cells

Farnesoid X receptor (FXR) is a ligand-activated transcription factor highly expressed in the liver and kidneys. Activation of FXR decreases organic cation transporter (OCT) 1-mediated clearance of organic cation compounds in hepatocytes. The present study investigated FXR regulation of renal clearance of organic cations by OCT2 modulation and multidrug and toxin extrusion proteins (MATEs). The role of FXR in OCT2 and MATEs functions was investigated by monitoring the flux of ³H-MPP⁺, a substrate of OCT2 and MATEs. FXR agonists chenodeoxycholic acid (CDCA) and GW4064 stimulated OCT2-mediated ³H-MPP⁺ uptake in human renal proximal tubular cells (RPTEC/TERT1 cells) and OCT2-CHO-K1 cells. The stimulatory effect of CDCA (20 µM) was abolished by an FXR antagonist, Z-guggulsterone, indicating an FXR-dependent mechanism. CDCA increased OCT2 transport activity via an increased maximal transport rate of MPP⁺. Additionally, 24 h CDCA treatment increased MATEs-mediated ³H-MPP⁺ uptake. Moreover, CDCA treatment increased the expression of OCT2, MATE1, and MATE2-K mRNA compared with that of the control. OCT2 protein expression was also increased following CDCA treatment. FXR activation stimulates renal OCT2- and MATE1/2-K-mediated cation transports in proximal tubules, demonstrating that FXR plays a role in the regulation of OCT2 and MATEs in renal proximal tubular cells.

Mitigation of renal inflammation and endoplasmic reticulum stress by vildagliptin and statins in high-fat high-fructose diet-induced insulin resistance and renal injury in rats

Dyslipidemia and insulin resistance in obesity can lead to lipotoxicity and cellular damage. Renal lipotoxicity in association with an impairment of lipid metabolism induces renal damage through the activation of inflammation, ER stress, fibrosis and apoptosis. We investigated the effects of a combination treatment of the DPP-4 inhibitor vildagliptin and atorvastatin on renal lipotoxicity related to renal dysfunction and injury in a high-fat high-fructose diet (HFF)-induced insulin resistant condition. Male Wistar rats were fed on a high-fat diet and were given drinking water with 10% fructose for 16 weeks. After that, rats were divided into: no treatment (HFF), treatment with vildagliptin, atorvastatin and vildagliptin plus atorvastatin for 4 weeks. The results demonstrated that the combination treatment prominently improved insulin resistance, dyslipidemia and kidney morphological changes induced by HFF. These changes correlated well with the increased expression of nephrin and podocin and decreased urine protein. Notably, the combined treatment produced greater improvement in renal lipid metabolism through increasing fatty acid oxidation with the decreases in fatty acid transporters and fatty acid synthesis, thereby reducing renal lipid accumulation in HFF rats. The reduction in renal lipotoxicity via diminishing renal inflammation, ER stress, fibrosis and apoptosis was also more significant in the combined treatment group than in the other groups in which the drug was used as a monotherapy. In conclusion, the combination therapy produced synergistic beneficial effects on metabolic parameters, lipid metabolism and accumulation related to renal lipid accumulation-induced lipotoxicity and kidney injury in the HFF-induced insulin resistant model with improved outcomes.

Dapagliflozin attenuates renal gluconeogenic enzyme expression in obese rats

The kidneys release glucose into the systemic circulation through glucose reabsorption and renal gluconeogenesis. Currently, the significance of renal glucose release in pathological conditions has become a subject of interest. We examined the effect of sodium-dependent glucose cotransporter 2 inhibitor (SGLT2i) on renal gluconeogenic enzyme expression in obese rats. Male Wistar rats (180-200 g) were fed either a normal diet (ND, n = 6) or a high-fat diet. At 16 weeks, after confirming the degree of glucose intolerance, high-fat diet-fed rats were randomly subdivided into three groups (n = 6/group): untreated group (HF), treated with dapagliflozin 1 mg/kg/day (HFSG) and treated with metformin 30 mg/kg/day (HFM). The treatment was continued for 4 weeks. We observed that dapagliflozin or metformin mitigated the enhanced expression of renal gluconeogenic enzymes, PEPCK, G6Pase and FBPase, as well as improved glucose tolerance and renal function in obese rats. Dapagliflozin downregulated the elevated expression of gluconeogenic transcription factors p-GSK3β, p-CREB and coactivator PGC1α in the renal cortical tissue. Metformin reduced the expression levels of renal cortical FOXO1 and CREB. Furthermore, reduced renal insulin signaling was improved and renal oxidative stress was attenuated by either dapagliflozin or metformin treatment in obese rats. We concluded that glucose tolerance was improved by dapagliflozin in obese prediabetic rats by suppressing renal glucose release from not only glucose reabsorption but also renal gluconeogenesis through improving renal cortical insulin signaling and oxidative stress. The efficacy of dapagliflozin in improving renal insulin signaling, oxidative stress and renal function was greater than that of metformin.

Atorvastatin attenuates obese-induced kidney injury and impaired renal organic anion transporter 3 function through inhibition of oxidative stress and inflammation

An excessive consumption of high-fat diet can lead to the alterations of glucose and lipid metabolism, impaired insulin signaling and increased ectopic lipid accumulation resulting in renal lipotoxicity and subsequent renal dysfunction. Atorvastatin is a lipid-lowering drug in clinical treatment. Several studies have reported that atorvastatin has several significant pleiotropic effects including anti-inflammatory, antioxidant, and anti-apoptotic effects. However, the effects of atorvastatin on metabolic disturbance and renal lipotoxicity in obesity are not fully understood. In this study, obesity in rat was developed by high-fat diet (HFD) feeding for 16 weeks. After that, the HFD-fed rats were received either a vehicle (HF), atorvastatin (HFA) or vildagliptin (HFVIL), by oral gavage for 4 weeks. We found that HF rats showed insulin resistance, visceral fat expansion and renal lipid accumulation. Impaired renal function and renal organic anion transporter 3 (Oat3) function and expression were also observed in HF rats. The marked increases in MDA level, renal injury and NF-κB, TGF-β, NOX-4, PKC-α expression were demonstrated in HF rats. Atorvastatin or vildagliptin treatment attenuated insulin resistance and renal lipid accumulation-induced lipotoxicity in HFA and HFVIL rats. Moreover, the proteins involved in renal inflammation, fibrosis, oxidative stress and apoptosis were attenuated leading to improved renal Oat3 function and renal function in the treated groups. Interestingly, atorvastatin showed higher efficacy than vildagliptin in improving insulin resistance, renal lipid accumulation and in exerting renoprotective effects in obesity-induced renal injury and impaired renal Oat3 function.

High affinity of 4-(4-(dimethylamino)styryl)-N-methylpyridinium transport for assessing organic cation drugs in hepatocellular carcinoma cells

Human organic cation transporter 1 (hOCT1) and human organic cation transporter 3 (hOCT3) are highly expressed in hepatocytes and play important roles in cationic drug absorption, distribution, and elimination. A previous study demonstrated that downregulation of hOCT1 and hOCT3 mRNA was related to hepatocellular carcinoma (HepG2) prognosis and severity. Whether these transporters expressed in HepG2 cells serve for cationic drug delivery has not been investigated. Besides radioactive transport, options for assessing hOCTs in hepatocytes are limited. This study clarified the significant roles of hOCTs in HepG2 by comparing cationic fluorescent 4-(4-(dimethylamino)styryl)-N-methylpyridinium (ASP⁺ ) with traditional [³ H]-1-methyl-4-phenylpyridinium (MPP⁺ ). The results showed ASP⁺ was preferably transported into HepG2 compared to [³ H]-MPP⁺ with high affinity and a high maximal transport rate. Selective transport of ASP⁺ mediated by hOCTs was influenced by extracellular pH, temperature, and membrane depolarization, corresponding to hOCT1 and hOCT3 expressions. Furthermore, transport of cationic drugs, metformin, and paclitaxel in HepG2 cells was blunted by OCT inhibitors, suggesting that hOCT1 and hOCT3 expressed in HepG2 cells exhibit notable impacts on cationic drug actions. The fluorescent ASP⁺ -based in vitro model may also provide a rapid and powerful analytical tool for further screening of cationic drug actions and interactions with hOCTs, particularly hOCT1 and hOCT3 in hepatocellular carcinoma.

Exhaustive exercise decreases renal organic anion transporter 3 function

This study aimed to investigate the effects of various types of exercise on organic anion transporter 3 (Oat3) function, a major transporter that plays a role in the secretion of a variety of drugs and endogenous compounds. Male Wistar rats were randomly allocated to non-exercise, exhaustive, acute and training exercise groups. The function of Oat3 was assessed by the uptake of [3H]-estrone sulfate ([3H]-ES) into rat renal cortical slices. Acute and training exercises had no effect on [3H]-ES uptake whereas a marked reduction in [3H]-ES uptake occurred immediately after exhaustive exercise. However, the reduction in Oat3 function was gradually recovered at 6 and 24 h after the exercise session. Importantly, the impairment of Oat3 function was associated with a decrease in renal Oat3 protein expression. Our results indicate that exhaustive exercise produces a significant impact on renal organic anion transport function, which in turn could alter the plasma level of drugs and compounds in the body.

Activation of constitutive androstane receptor inhibits intestinal CFTR-mediated chloride transport

Constitutive androstane receptor (CAR) belonging to the nuclear receptor superfamily plays an important role in the xenobiotic metabolism and disposition. It has been reported that CAR regulates the expression of the ATP-binding cassette (ABC) transporters in the intestine, such as multidrug resistance protein 1 (MDR1) and multidrug resistance-associated protein 2/3 (MRP2 and MRP3). In this study, we investigated the role of CAR in the regulation of cystic fibrosis transmembrane conductance regulator (CFTR)-mediated chloride transport in T84 human colonic epithelial cells and mouse intestinal tissues. Treatments of T84 cell monolayers with specific CAR agonists (CITCO and phenytoin at concentrations of 1 μM and 5 μM, respectively) for 24 h decreased transepithelial Cl^- secretion in response to cAMP-dependent agonist. This inhibition was abolished by coincubation of CITCO with a CAR antagonist, CINPA1. We confirmed that an inhibitory effect of CAR agonists was not due to their cytotoxicity. Basolateral membrane permeabilization experiments also revealed that activation of CAR decreased apical Cl^- current stimulated by both CPT-cAMP and genistein (a direct CFTR activator). Such activation also reduced both mRNA and protein expression of CFTR. Furthermore, CITCO decreased cholera toxin (CT)-induced Cl^- secretion across T84 cell monolayers. In ICR mice, administration of TCPOBOP (3 mg/kgBW), a murine-specific CAR agonist, for 7 days produced significant decreases in CFTR mRNA and protein expressions in intestinal tissues. Interestingly, TCPOBOP also inhibited CT-induced intestinal fluid accumulation in mice. This is the first evidence showing that CFTR was downregulated by CAR activation in the intestine. Our findings suggest that CAR has potential as a new drug target for treatment of condition with hyperactivity/ hyperfunction of CFTR especially secretory diarrheas.

Dapagliflozin, a sodium-glucose co-transporter-2 inhibitor, slows the progression of renal complications through the suppression of renal inflammation, endoplasmic reticulum stress and apoptosis in prediabetic rats

AIM

To evaluate the renoprotective roles of dapagliflozin in prediabetic rats in order to elucidate the effects of this sodium-glucose co-transporter-2 (SGLT2) inhibitor on the renal complications associated with metabolic dysfunction in diet-induced obesity.

METHODS

Obesity was induced by feeding a high-fat diet (HFD) to male Wistar rats for 16 weeks. HFD-fed rats were treated with dapagliflozin (1 mg/kg/d) or metformin (30 mg/kg/d) by oral gavage for 4 weeks after insulin resistance had been established. The metabolic characteristics and renal function associated with lipid accumulation, inflammation, fibrosis, endoplasmic reticulum (ER) stress and apoptosis in the renal tissue were examined.

RESULTS

The results showed that HFD-fed rats developed both obesity and impaired renal function, along with increased renal triglyceride accumulation. Importantly, dapagliflozin had greater efficacy in improving renal function and reducing both body weight and visceral fat accumulation than metformin treatment. Dapagliflozin and metformin were found to have similar effects regarding the suppression of renal triglycerides, superoxide dismutase (SOD) expression and malondialdehyde (MDA) levels, subsequently leading to a decrease in renal inflammation and fibrosis. Renal ER stress and apoptosis were increased in HFD-fed rats and were effectively reduced after administration of dapagliflozin. The expression of renal SGLT2 was not affected by administration of dapagliflozin or metformin.

CONCLUSION

Collectively, these findings indicate that dapagliflozin exerts renoprotective effects by alleviating obesity-induced renal inflammation, fibrosis, ER stress, apoptosis and lipid accumulation in the prediabetic condition.

Molecular signaling mechanisms of renal gluconeogenesis in nondiabetic and diabetic conditions

The kidneys are as involved as the liver in gluconeogenesis which can significantly contribute to hyperglycemia in the diabetic condition. Substantial evidence has demonstrated the overexpression of rate-limiting gluconeogenic enzymes, especially phosphoenolpyruvate carboxykinase and glucose 6 phosphatase, and the accelerated glucose release both in the isolated proximal tubular cells and in the kidneys of diabetic animal models and diabetic patients. The aim of this review is to provide an insight into the mechanisms that accelerate renal gluconeogenesis in the diabetic conditions and the therapeutic approaches that could affect this process in the kidney. Increase in gluconeogenic substrates, reduced insulin concentration or insulin resistance, downregulation of insulin receptors and insulin signaling, oxidative stress, and inappropriate activation of the renin-angiotensin system are likely to participate in enhancing renal gluconeogenesis in the diabetic milieu. Several studies have suggested that controlling glucose metabolism at the renal level favors effective overall glycemic control in both type 1 and type 2 diabetes. Therefore, renal gluconeogenesis may be a promising target for effective glycemic control as a therapeutic strategy in diabetes.

An agonist of a zinc-sensing receptor GPR39 enhances tight junction assembly in intestinal epithelial cells via an AMPK-dependent mechanism

Intestinal barrier function depends on integrity of tight junctions, which serve as barriers to transepithelial influx of noxious substances/microorganisms from gut lumen. The G-protein coupled receptor 39 (GPR39) is a zinc-sensing receptor, which is expressed in several cell types including intestinal epithelial cells (IECs). The main objective of this study was to investigate the effect of GPR39 activation on tight junction assembly in IECs. Treatment with TC-G 1008 (1 μM -10 μM), a GPR39 agonist, and zinc (10 μM -100 μM) increased tight junction assembly in T84 cells. This effect was suppressed by pretreatment with compound C, an inhibitor of AMP-activated protein kinase (AMPK). In addition, western blot analysis revealed that treatment with TC-G 1008 induced AMPK activation in time- and concentration-dependent manners. Interestingly, inhibitors of phospholipase C (PLC) and calcium/calmodulin-dependent protein kinase kinase β (CaMKKβ) abrogated the effect of TC-G 1008 on inducing AMPK activation, tight junction assembly and zonula occludens-1 re-organization. Collectively, this study reveals a novel role of GPR39 in enhancing tight junction assembly in IECs via PLC-CaMKKβ-AMPK pathways. GPR39 agonists may be beneficial in the treatment of diseases associated impaired intestinal barrier function.

GPR40 receptor activation promotes tight junction assembly in airway epithelial cells via AMPK-dependent mechanisms

Tight junctions play key roles in the regulation of airway epithelial barrier function and promotion of tight junction integrity is beneficial to lung health. G-protein coupled receptor (GPR) 40 has been identified as a receptor of polyunsaturated fatty acids. This study aimed to investigate the function of GPR40 in regulating tight junction assembly in human airway epithelial cells (Calu-3 cells) using GW9508, a GPR40 agonist. Immunoblotting and immunofluorescence analyses showed that Calu-3 cells expressed both types of polyunsaturated fatty acid receptors including GPR40 and GPR120. Intracellular Ca²⁺ measurements confirmed that GW9508 stimulated GPR40, but not GPR120. In Ca²⁺ switch assays, GW9508 promoted the recovery of transepithelial electrical resistance and re-localization of zonula occludens (ZO)-1 to intercellular areas. These effects were suppressed by inhibitors of GPR40 and phospholipase C (PLC). Interestingly, GW9508 enhanced tight junction assembly in an AMP-activated protein kinase (AMPK)-dependent manner. The effect of GW9508 on inducing tight junction assembly was also confirmed in 16HBE14o- cells. Our results indicate that GPR40 stimulation by GW9508 leads to AMPK activation via calcium/calmodulin-dependent protein kinase kinase β (CaMKKβ). Collectively, this study reveals an unprecedented role of GPR40 in facilitating airway epithelial tight junction assembly via PLC-CaMKKβ-AMPK pathways. GPR40 represents a novel regulator of airway epithelial integrity and its stimulation may be beneficial in the treatment of airway diseases.

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.

Steviol slows renal cyst growth by reducing AQP2 expression and promoting AQP2 degradation

Overexpression of aquaporin 2 (AQP2) was observed and suggested to be involved in fluid secretion leading to cyst enlargement in polycystic kidney disease (PKD). The cyst expansion deteriorates the renal function and, therefore, therapies targeting cyst enlargement are of clinical interest. Of note, inhibition of vasopressin function using vasopressin 2 receptor (V2R) antagonist which decreased cAMP production along with AQP2 production and function can slow cyst growth in ADPKD. This finding supports the role of AQP2 in cyst enlargement. Steviol, a major metabolite of the sweetening compound stevioside, was reported to retard MDCK cyst growth and enlargement by inhibiting CFTR activity. Interestingly, its efficacy was found to be higher than that of CFTR_inh-172. Since steviol was also found to produce diuresis in rodent, it is likely that steviol might have an additional effect in retarding cyst progression, such as inhibition of AQP2 expression and function. Here, we investigated the effect of steviol on AQP2 function and on cyst growth using an in vitro cyst model (MDCK and Pkd1^-/- cells). We found that steviol could markedly inhibit cyst growth by reducing AQP2 expression in both Pkd1^-/- and MDCK cells. Real-time PCR also revealed that steviol decreased AQP2 mRNA expression level as well. Moreover, a proteasome inhibitor, MG-132, and the lysosomotropic agent, hydroxychloroquine (HCQ) were found to abolish the inhibitory effect of steviol in Pkd1^-/- cells. Increased lysosomal enzyme marker (LAMP2) expression following steviol treatment clearly confirmed the involvement of lysosomes in steviol action. In conclusion, our finding showed for the first time that steviol slowed cyst growth, in part, by reducing AQP2 transcription, promoted proteasome, and lysosome-mediated AQP2 degradation. Due to its multiple actions, steviol is a promising compound for further development in the treatment of PKD.

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.

Diacerein alleviates kidney injury through attenuating inflammation and oxidative stress in obese insulin-resistant rats

A link between inflammation with obesity and metabolic syndrome has been found in patients with chronic kidney disease (CKD). Diacerein is an anthraquinone used to treat osteoarthritis that exerts anti-inflammatory action by inhibiting the synthesis and activity of proinflammatory cytokines. This study aimed to investigate the protective effect of diacerein on renal function and renal organic anion transporter 3 (Oat3) function in obese insulin-resistant condition. Obese insulin-resistant rats were induced by feeding a high-fat diet in male Wistar rats for 16 weeks. Diacerein or metformin (positive control) (30mg/kg/day) was administered orally for 4 weeks after insulin resistance had been confirmed. Obese insulin-resistant rats showed an impaired renal function as indicated by the increased serum creatinine and microalbuminuria along with the decreased renal Oat3 function and expression. Importantly, diacerein treatment not only improved insulin resistance but also restored renal function. The decreased renal malondialdehyde level, expressions of PKCα, angiotensin 1 receptor (AT1R), Nrf2, and HO-1, and increased expression of SOD2 were observed in diacerein treatment group, indicating the attenuation of renal oxidative stress condition. Moreover, renal inflammation and renal damage were also alleviated in diacerein-treated rats. Our results demonstrated for the first time that diacerein was effective to improve renal function and renal Oat3 function in obese insulin-resistance condition mediated by suppressing renal oxidative stress and inflammation. These findings suggest that anti-inflammatory agents can be used therapeutically to improve metabolic disorder and prevent organ dysfunctions in pre-diabetic condition.

Activation of liver X receptor inhibits OCT2-mediated organic cation transport in renal proximal tubular cells

Liver X receptor (LXR) is transcriptional factor that plays an important role in the regulation of energy metabolism such as cholesterol, lipid, and glucose metabolism as well as membrane transporters and channels. Using both in vitro and in vivo models, LXR regulation of the expression and function of renal organic cation transporter 2 (OCT2) was observed. Synthetic LXR agonist (GW3965) and endogenous LXR agonist (22R-hydroxycholesterol) significantly reduced the uptake of ³H-MPP⁺, a prototypic substrate of OCT2, in both OCT2- Chinese hamster ovary K1 and human renal proximal tubular cells (RPTEC/TERT1). GW3965 decreased transport activity of OCT2 via a reduction of the maximal transport rate of MPP⁺ without affecting transporter affinity. The inhibitory effect of GW3965 was attenuated by co-treatment with LXR antagonist (fenofibrate) indicating the inhibition was LXR-dependent mechanism. In addition, co-treatment with a retinoic X receptor (RXR) ligand, 9-cis retinoic acid enhanced the inhibitory effect of GW3965, indicating negative regulation of OCT2 transport activity by the LXR/RXR complex. Treatment RPTEC/TERT1 cells with GW3965 significantly reduced OCT2 protein expression without changing mRNA expression. In parallel, the effect of LXR activation on OCT2 function was investigated in intact mouse kidney. Treating mice with 50 mg/kg BW T0901317 for 14 days significantly decreased ³H-MPP⁺ uptake into renal cortical slices, correlating with decreased OCT2 protein expression in renal cortex without changes in mRNA expression levels. Taken together, LXR/RXR activation downregulates the protein expression and function of OCT2 in renal proximal tubule, suggesting LXR might affect the total profile of renal excretion of cationic compounds.

Cellular mechanisms underlying the inhibitory effect of flufenamic acid on chloride secretion in human intestinal epithelial cells

Intestinal Cl^- secretion is involved in the pathogenesis of secretory diarrheas including cholera. We recently demonstrated that flufenamic acid (FFA) suppressed Vibrio cholerae El Tor variant-induced intestinal fluid secretion via mechanisms involving AMPK activation and NF-κB-suppression. The present study aimed to investigate the effect of FFA on transepithelial Cl^- secretion in human intestinal epithelial (T84) cells. FFA inhibited cAMP-dependent Cl^- secretion in T84 cell monolayers with IC₅₀ of ∼8 μM. Other fenamate drugs including tolfenamic acid, meclofenamic acid and mefenamic acid exhibited the same effect albeit with lower potency. FFA also inhibited activities of CFTR, a cAMP-activated apical Cl^- channel, and KCNQ1/KCNE3, a cAMP-activated basolateral K⁺ channel. Mechanisms of CFTR inhibition by FFA did not involve activation of its negative regulators. Interestingly, FFA inhibited Ca²⁺-dependent Cl^- secretion with IC₅₀ of ∼10 μM. FFA inhibited activities of Ca²⁺-activated Cl^- channels and K_Ca3.1, a Ca²⁺-activated basolateral K⁺ channels, but had no effect on activities of Na⁺-K⁺-Cl^- cotransporters and Na⁺-K⁺ ATPases. These results indicate that FFA inhibits both cAMP and Ca²⁺-dependent Cl^- secretion by suppressing activities of both apical Cl^- channels and basolateral K⁺ channels. FFA and other fenamate drugs may be useful in the treatment of secretory diarrheas.

Anthocyanin-rich Riceberry bran extract attenuates gentamicin-induced hepatotoxicity by reducing oxidative stress, inflammation and apoptosis in rats

Liver plays an important role in the detoxification and metabolic elimination of various drugs and harmful substances. The damaging effects on the liver tissue treated with gentamicin are multi-factorial and their mechanisms remain unclear. This study aimed to investigate the possible protective effects of anthocyanin-rich Riceberry bran extract on gentamicin-induced hepatotoxicity in rats. Riceberry bran extract was given by oral administration 30min before gentamicin injection for 15 consecutive days. Serum levels of liver marker enzymes, AST and ALT, were significantly elevated and the total serum protein level was markedly reduced in gentamicin-treated rats. Gentamicin injection led to the significant increase in hepatic MDA level and decrease SOD expression. Liver inflammation and apoptosis were observed in gentamicin-treated rats as indicated by the increases in NF-κB, TNF-αR1, COX2, and iNOS, caspase-3, Bax, and decrease in Bcl-XL expressions. Riceberry bran extract significantly prevented gentamicin-induced the elevations of serum AST, ALT and the reduction of serum total protein. These were related to the inhibition of oxidative stress, inflammation and apoptosis in Riceberry bran extract treatment. These findings suggest that anthocyanin-rich Riceberry bran extract can prevent liver dysfunction and damage induced by gentamicin, possibly through its antioxidant, anti-inflammatory and anti-apoptotic effects.

Effect of Exercise Training on Signaling of Interleukin-6 in Skeletal Muscles of Type 2 Diabetic Rats

OBJECTIVES

Diabetes and exercise training have been shown to involve interleukin 6 (IL-6) signaling in muscle. However, the relationship between the actions of these two stimuli on muscle IL-6 and their downstream components is still unknown. Thus, the effect of endurance training on the key components of muscle IL-6 signaling transduction was investigated in a rat model of type 2 diabetes.

METHODS

Diabetes was induced by streptozotocin (STZ) in male Wistar rats fed a high-fat diet, with normal rats acting as controls. The animals were left to conduct their normal activities or assigned to endurance training in a treadmill. At the end of 8 weeks, blood biochemical profiles, exercise performance, muscle oxidative capacity, glucose transporter 4 (GLUT4) protein distribution, and expressions of IL-6 and its downstream proteins were determined.

RESULTS

Blood biochemical profiles of the diabetic rats were altered compared to normal rats, whereas endurance training improved blood chemistry and exercise performance. It also increased muscle oxidative capacity, and promoted GLUT4 subcellular localization to the membrane in muscles. Furthermore, protein expression of IL-6 receptor (IL-6Rα) was increased in both normal and diabetic rats after endurance training, but no significant changes in IL-6, phosphorylated signal transducer and activator of transcription 3 (p-STAT3), or suppressor of cytokine signaling 3 (SOC3) were observed in muscles of normal and diabetic rats.

CONCLUSIONS

IL-6 signaling pathway mediating muscle response to endurance training was conserved in type 2 diabetes. There was no link between training-induced IL-6 downstream targets in skeletal muscles and IL-6-induced type 2 diabetes.

Riceberry bran extract prevents renal dysfunction and impaired renal organic anion transporter 3 (Oat3) function by modulating the PKC/Nrf2 pathway in gentamicin-induced nephrotoxicity in rats

PURPOSE

This study investigated the protective effects of Riceberry bran extract (RBBE) on renal function, and the function and expression of renal organic anion transporter 3 (Oat3) in gentamicin-induced nephrotoxicity in rats and explored the mechanisms for its protective effects.

MATERIAL AND METHODS

Male Sprague Dawley rats (n= 42) were divided into six groups to receive normal saline, gentamicin (100mg/kg), co-treatment of gentamicin and RBBE (at dose of 250, 500 and 1000mg/kg), and RBBE (at dose of 1000mg/kg) only, for consecutive fifteen days. Renal function, oxidative and antioxidative markers, the function and expression of Oat3 and histological changes in the kidney were evaluated.

RESULTS

Elevation of BUN, serum creatinine levels and reduction in urine creatinine and creatinine clearance indicated decreased renal function in the gentamicin-treated rats. The decrease of [³H]ES uptake in the renal cortical slices of these rats, reflecting the attenuation of Oat3 transport function that was accompanied by decreased expression of Oat3. Moreover, increased MDA level and reduced superoxide dismutase (SOD) and glutathione (GSH) activities were found in gentamicin-treated rats compared to the control group. These changes were associated with the upregulated PKCα, Nrf-2, Keap 1, NQO-1 and HO-1 expressions in kidneys. RBBE treatment improved the renal function and Oat3 transport function and expression in gentamicin-treated rats. The oxidative status was also restored by RBBE treatment.

CONCLUSION

RBBE protects kidney injury by its antioxidant effect, subsequently leading to modulation of the PKC/Nrf2 antioxidant defense pathway.

Chitosan oligosaccharide: Biological activities and potential therapeutic applications

Chitosan oligosaccharide (COS) is an oligomer of β-(1➔4)-linked d-glucosamine. COS can be prepared from the deacetylation and hydrolysis of chitin, which is commonly found in the exoskeletons of arthropods and insects and the cell walls of fungi. COS is water soluble, non-cytotoxic, readily absorbed through the intestine and mainly excreted in the urine. Of particular importance, COS and its derivatives have been demonstrated to possess several biological activities including anti-inflammation, immunostimulation, anti-tumor, anti-obesity, anti-hypertension, anti-Alzheimer's disease, tissue regeneration promotion, drug and DNA delivery enhancement, anti-microbial, anti-oxidation and calcium-absorption enhancement. The mechanisms of actions of COS have been found to involve the modulation of several important pathways including the suppression of nuclear factor kappa B (NF-κB) and mitogen-activated protein kinases (MAPK) and the activation of AMP-activated protein kinase (AMPK). This review summarizes the current knowledge of the preparation methods, pharmacokinetic profiles, biological activities, potential therapeutic applications and safety profiles of COS and its derivatives. In addition, future research directions are discussed.

Amelioration of Renal Inflammation, Endoplasmic Reticulum Stress and Apoptosis Underlies the Protective Effect of Low Dosage of Atorvastatin in Gentamicin-Induced Nephrotoxicity

Gentamicin is a commonly used aminoglycoside antibiotic. However, its therapeutic use is limited by its nephrotoxicity. The mechanisms of gentamicin-induced nephrotoxicity are principally from renal inflammation and oxidative stress. Since atorvastatin, 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, exerts lipid-lowering effects, antioxidant, anti-inflammatory as well as anti-apoptotic effects, this study aimed to investigate the protective effects of atorvastatin against gentamicin-induced nephrotoxicity. Male Sprague Dawley rats were used and nephrotoxicity was induced by intraperitoneal injection of gentamicin, 100 mg/kg/day, for 15 days. Atorvastatin, 10 mg/kg/day, was administered by orally gavage 30 min before gentamicin injection on day 1 to 15 (pretreatment) or on day 10 to15 (delayed treatment). For only atorvastatin treatment group, it was given on day 1 to 15. At the end of the experiment, kidney weight, blood urea nitrogen and serum creatinine as well as renal inflammation (NF-κB, TNFαR1, IL-6 and iNOS), renal fibrosis (TGFβ1), ER stress (calpain, GRP78, CHOP, and caspase 12) and apoptotic markers (cleaved caspase-3, Bax, and Bcl-2) as well as TUNEL assay were determined. Gentamicin-induced nephrotoxicity was confirmed by marked elevations in serum urea and creatinine, kidney hypertrophy, renal inflammation, fibrosis, ER stress and apoptosis and attenuation of creatinine clearance. Atorvastatin pre and delayed treatment significantly improved renal function and decreased renal NF-κB, TNFαR1, IL-6, iNOS and TGFβ1 expressions. They also attenuated calpain, GRP78, CHOP, caspase 12, Bax, and increased Bcl-2 expressions in gentamicin-treated rat. These results indicate that atorvastatin treatment could attenuate gentamicin-induced nephrotoxicity in rats, substantiated by the reduction of inflammation, ER stress and apoptosis. The effect of atorvastatin in protecting from renal damage induced by gentamicin seems to be more effective when it beginning given along with gentamicin or pretreatment.

Chitosan oligosaccharide suppresses synovial inflammation via AMPK activation: An in vitro and in vivo study

Synovial inflammation plays an important role in the early pathogenesis of osteoarthritis (OA). Chitosan oligosaccharide (COS) has been shown to activate AMPK and suppress inflammatory responses in intestinal epithelial cells. This study aimed to investigate the effect of COS on AMPK activation and synovial inflammation using both primary cultures of synoviocytes and a rabbit model of anterior cruciate ligament (ACL) transection-induced OA. COS induced AMPK activation in both rabbit and human synoviocytes. The mechanism of COS-induced AMPK activation involves an increase in the ADP/ATP ratio but not calcium/calmodulin-dependent protein kinase kinase beta (CaMKKβ). Interestingly, COS suppressed the TNFα-induced iNOS and COX-2 expression via an AMPK-dependent mechanism in both rabbit and human synoviocytes. Importantly, oral administration of COS (10mg/kg/day) induced AMPK activation and alleviated signs of inflammation including COX-2 expression in the synovium of a rabbit ACL transection model. Taken together, our results indicate that COS suppresses synovial inflammation in vitro and in vivo via AMPK activation. COS may be useful in the prevention of OA.

Pinocembrin attenuates gentamicin-induced nephrotoxicity in rats

Oxidative stress mediated apoptosis of renal tubular cells is a major pathology of gentamicin-induced nephrotoxicity, which is one of the prevailing causes of acute renal failure. Pinocembrin is a major flavonoid found in rhizomes of fingerroot (Boesenbergia pandurata). It has pharmacological and biological activities including antimicrobial, anti-inflammatory, and antioxidant effects. Preclinical studies have suggested that pinocembrin protects rat brain and heart against oxidation and apoptosis induced by ischemia–reperfusion. The aim of the current study was to investigate the mechanisms of renoprotection elicited by pinocembrin in gentamicin-induced nephrotoxicity. Nephrotoxicity was induced in rats by intraperitoneal injection (i.p.) of gentamicin, and pinocembrin was administered via i.p. 30 min before gentamicin treatment for 10 days. Gentamicin-induced nephrotoxicity was indicated by the reduced renal function and renal Oat3 function and expression. Gentamicin treatment also stimulated Nrf2, HO-1, and NQO1, as well as the pro-apoptotic proteins Bax and caspase-3, concomitant with the attenuation of Bcl-XL expression in the renal cortical tissues. Pinocembrin pretreatment improved renal function and renal Oat3 function and reduced oxidative stress and apoptotic conditions. These findings indicate that pinocembrin has a protective effect against gentamicin-induced nephrotoxicity, which may be due in part to its antioxidant and anti-apoptotic effects, subsequently leading to improved renal function.

Pathophysiological mechanisms of diarrhea caused by the Vibrio cholerae O1 El Tor variant: an in vivo study in mice

Cholera is caused by infection with Vibrio cholerae. This study aimed to investigate the pathophysiology of diarrhea caused by the V. cholerae O1 El Tor variant (EL), a major epidemic strain causing severe diarrhea in several regions. In the ligated ileal loop model of EL-induced diarrhea in the ICR mice, a cystic fibrosis transmembrane conductance regulator (CFTR) inhibitor and a calcium-activated chloride channel (CaCC) inhibitor similarly inhibited intestinal fluid secretion. In addition, barrier disruption and NF-κB-mediated inflammatory responses, e.g., iNOS and COX-2 expression, were observed in the infected ileal loops. Interestingly, intestinal fluid secretion and barrier disruption were suppressed by NF-κB and COX-2 inhibitors, whereas an iNOS inhibitor suppressed barrier disruption without affecting fluid secretion. Furthermore, EP2 and EP4 PGE2 receptor antagonists ameliorated the fluid secretion in the infected ileal loops. The amount of cholera toxin (CT) produced in the ileal loops by the EL was ∼2.4-fold of the classical biotype. The CT transcription inhibitor virstatin, a toll-like receptor-4 (TLR-4) antibody and a CT antibody suppressed the EL-induced intestinal fluid secretion, barrier disruption and COX-2 expression. The CT at levels detected during EL infection induced mild intestinal barrier disruption without inducing inflammatory responses in mouse intestine. Collectively, this study indicates that CT-induced intestinal barrier disruption and subsequent TLR-4-NF-κB-mediated COX-2 expression are involved in the pathogenesis of EL-induced diarrhea and represent promising novel therapeutic targets of cholera.

Losartan and Sodium Nitroprusside Effectively Protect against Renal Impairments after Ischemia and Reperfusion in Rats

Ischemia and subsequent reperfusion are known to impair renal function. We examined several agents that might prevent renal impairment or enhance the recovery of renal function after ischemia/reperfusion injury in rats. Different degrees of preventive effects were observed in rats treated with captopril, BQ-123 (endothelin type A receptor antagonist), sodium nitroprusside (SNP, a nitric oxide donor), and losartan (angiotensin II type 1 receptor antagonist). Only minimal changes in renal morphology were observed after treatment with losartan, SNP, captopril, and BQ-123 compared with control animals. On the other hand, lesions were prominent in the N(G)-nitro-L-arginine-methyl ester (L-NAME)- and L-arginine-treated rats. The Na(+)-K(+) ATPase activity of ischemic kidneys was, however, preserved in all treatment groups, except in those treated with L-arginine and L-NAME, which showed a marked reduction in Na(+)-K(+) ATPase activity. Our post-treatment data suggest that losartan and SNP have the greatest potential for therapeutic use to mitigate post-ischemic renal damage and functional impairment.

Chitosan oligosaccharide suppresses tumor progression in a mouse model of colitis-associated colorectal cancer through AMPK activation and suppression of NF-κB and mTOR signaling

Novel, effective and safe agents are needed for the chemoprevention of colorectal cancer (CRC). This study investigated the effects of chitosan oligosaccharides (COS) on CRC progression and their underlying mechanisms and safety profiles in mice. Using a mouse model of colitis-associated CRC, we found that oral administration of COS (500mg/kg/day) resulted in a ∼60% reduction of tumor size and tumor numbers/sectioning. In addition, COS treatment increased AMPK activity, suppressed the NF-κB-mediated inflammatory response and reduced the expressions of cyclin D1, phosphorylated ribosomal protein S6, and MMP-9 in the colon tissues of these mice. Importantly, administration of COS (500mg/kg/day; 50 days) had no adverse effects on renal or liver functions. Our results indicate that COS suppressed CRC progression via AMPK activation and the suppression of NF-κB and mTOR signaling. COS may be of potential utility in the chemoprevention of CRC.

Nutraceutical for Autosomal Dominant Polycystic Kidney Disease Therapy

Autosomal dominant polycystic kidney disease (ADPKD) is the most common inherited renal disorder caused by mutations of either PKD1 or PKD2 gene. Cyst formation initiates from a combination of abnormal cell proliferation along with enhanced fluid secretion. ADPKD is characterized by the progressive enlargement of cysts which destroy the renal parenchymal cells, resulting in renal failure. Currently, there is no effective treatment for this disease. Interestingly, several relevant therapeutic effects of herbal medicine relevant to pathogenic process of ADPKD have urged the researchers to search for potential candidate herb as nutraceutical for ADPKD therapy. Up to now, several natural compounds, such as triptolide, curcumin, ginkolide B, and steviol (stevia extract) have been shown to be able to retard cyst progression in ADPKD. The detailed mechanism of these compounds showed that triptolide enhanced calcium restoration, curcumin inhibited ERK & p-STAT3 pathways, ginkolide B inhibited Ras/MAPK pathway, and steviol activated AMPK, which inhibited CFTR channel and mTOR pathway in cell and mouse models of PKD. In addition, they are currently inpreclinical and clinical studies, respectively. This review focuses on the pathophysiology of ADPKD and the recent therapeutic approaches, especially a potential use of nutraceutical for the treatment of autosomal dominant polycystic kidney disease.

Inhibition of intestinal chloride secretion by piperine as a cellular basis for the anti-secretory effect of black peppers

Piperine is the principal alkaloid in black peppers (Piper nigrum L.), which is a commonly included spice in anti-diarrheal formulations. Piperine has antispasmodic activities, but its anti-secretory effect is not known. Therefore, this study investigated the anti-secretory effect of piperine and its underlying mechanism. Piperine inhibited cAMP-mediated Cl- secretion in human intestinal epithelial (T84) cells, similar to black pepper extract. Intraluminal administration of piperine (2 μg/loop) suppressed cholera toxin-induced intestinal fluid accumulation by ∼85% in mice. The anti-secretory mechanism of piperine was investigated by evaluating its effects on the activity of transport proteins involved in cAMP-mediated Cl- secretion. Notably, piperine inhibited CFTR Cl- channel activity (IC50#8'6#10 μM) without affecting intracellular cAMP levels. The mechanisms of piperine-induced CFTR inhibition did not involve MRP4-mediated cAMP efflux, AMPK or TRPV1. Piperine also inhibited cAMP-activated basolateral K+ channels, but it had no effect on Na+-K+-Cl- cotransporters or Na+-K+ ATPases. Piperine suppressed Ca2+-activated Cl- channels (CaCC) without affecting intracellular Ca2+ concentrations or Ca2+-activated basolateral K+ channels. Collectively, this study indicates that the anti-secretory effect of piperine involves the inhibition of CFTR, CaCC and cAMP-activated basolateral K+ channels. Piperine represents a novel class of drug candidates for the treatment of diarrheal diseases caused by the intestinal hypersecretion of Cl-.

Antidiabetic and renoprotective effects of Cladophora glomerata Kützing extract in experimental type 2 diabetic rats: a potential nutraceutical product for diabetic nephropathy

Cladophora glomerata extract (CGE) has been shown to exhibit antigastric ulcer, anti-inflammatory, analgesic, hypotensive, and antioxidant activities. The present study investigated antidiabetic and renoprotective effects of CGE in type 2 diabetes mellitus (T2DM) rats. The rats were induced by high-fat diet and streptozotocin and supplemented daily with 1 g/kg BW of CGE for 12 weeks. The renal transport function was assessed by the uptake of para-aminohippurate mediated organic anion transporters 1 (Oat1) and 3 (Oat3), using renal cortical slices. These two transporters were known to be upregulated by insulin and PKCζ while they were downregulated by PKCα activation. Compared to T2DM, CGE supplemented rats had significantly improved hyperglycaemia, hypertriglyceridemia, insulin resistance, and renal morphology. The baseline uptake of para-aminohippurate was not different among experimental groups and was correlated with Oat1 and 3 mRNA expressions. Nevertheless, while insulin-stimulated Oat1 and 3 functions in renal slices were blunted in T2DM rats, they were improved by CGE supplementation. The mechanism of CGE-restored insulin-stimulated Oat1 and 3 functions was clearly shown to be associated with upregulated PKCζ and downregulated PKCα expressions and activations. These findings indicate that CGE has antidiabetic effect and suggest it may prevent diabetic nephropathy through PKCs in a T2DM rat model.

Inhibition of cAMP-activated intestinal chloride secretion by diclofenac: cellular mechanism and potential application in cholera

Cyclic AMP-activated intestinal Cl⁻ secretion plays an important role in pathogenesis of cholera. This study aimed to investigate the effect of diclofenac on cAMP-activated Cl⁻ secretion, its underlying mechanisms, and possible application in the treatment of cholera. Diclofenac inhibited cAMP-activated Cl⁻ secretion in human intestinal epithelial (T84) cells with IC₅₀ of ∼20 µM. The effect required no cytochrome P450 enzyme-mediated metabolic activation. Interestingly, exposures of T84 cell monolayers to diclofenac, either in apical or basolateral solutions, produced similar degree of inhibitions. Analyses of the apical Cl⁻ current showed that diclofenac reversibly inhibited CFTR Cl⁻ channel activity (IC₅₀∼10 µM) via mechanisms not involving either changes in intracellular cAMP levels or CFTR channel inactivation by AMP-activated protein kinase and protein phosphatase. Of interest, diclofenac had no effect on Na⁺-K⁺ ATPases and Na⁺-K⁺-Cl⁻ cotransporters, but inhibited cAMP-activated basolateral K⁺ channels with IC₅₀ of ∼3 µM. In addition, diclofenac suppressed Ca²⁺-activated Cl⁻ channels, inwardly rectifying Cl⁻ channels, and Ca²⁺-activated basolateral K⁺ channels. Furthermore, diclofenac (up to 200 µM; 24 h of treatment) had no effect on cell viability and barrier function in T84 cells. Importantly, cholera toxin (CT)-induced Cl⁻ secretion across T84 cell monolayers was effectively suppressed by diclofenac. Intraperitoneal administration of diclofenac (30 mg/kg) reduced both CT and Vibrio cholerae-induced intestinal fluid secretion by ∼70% without affecting intestinal fluid absorption in mice. Collectively, our results indicate that diclofenac inhibits both cAMP-activated and Ca²⁺-activated Cl⁻ secretion by inhibiting both apical Cl⁻ channels and basolateral K⁺ channels in intestinal epithelial cells. Diclofenac may be useful in the treatment of cholera and other types of secretory diarrheas resulting from intestinal hypersecretion of Cl⁻.

Diarrhea in cholera results from stimulation of cAMP-mediated intestinal Cl⁻ secretion by cholera toxin (CT). This study demonstrates that diclofenac, a widely used non-steroidal anti-inflammatory drug (NSAID), inhibited cAMP-activated Cl⁻ secretion in human intestinal epithelial (T84) cells by inhibiting both apical Cl⁻ channels (i.e. CFTR) and cAMP-activated basolateral K⁺ channels (i.e. KCNQ1/KCNE3). The mechanism by which CFTR was inhibited did not involve changes in intracellular cAMP levels and activation of negative regulators of CFTR activity including AMP-activated protein kinase (AMPK) and protein phosphatase. In addition, diclofenac suppressed two other types of apical Cl⁻ channels, namely, Ca²⁺-activated Cl⁻ channels and inwardly rectifying Cl⁻ channels, and Ca²⁺-activated basolateral K⁺ channels (i.e. K_Ca3.1) without affecting Na⁺-K⁺ ATPase and Na⁺-K⁺-Cl⁻ cotransporter activities. Of particular importance, diclofenac at 30 mg/kg, which is the human equivalent dose for treatment of pain and inflammation (∼2 mg/kg in human), exhibited anti-secretory efficacy in mouse closed-loop models of cholera induced by either CT or V. cholerae. This study provides a rational basis for further development of diclofenac and related compounds as anti-diarrheal therapy for cholera and other types of diarrheas resulting from Cl⁻ transport-driven intestinal fluid secretion.

Impaired insulin signaling affects renal organic anion transporter 3 (Oat3) function in streptozotocin-induced diabetic rats

Organic anion transporter 3 (Oat3) is a major renal Oats expressed in the basolateral membrane of renal proximal tubule cells. We have recently reported decreases in renal Oat3 function and expression in diabetic rats and these changes were recovered after insulin treatment for four weeks. However, the mechanisms by which insulin restored these changes have not been elucidated. In this study, we hypothesized that insulin signaling mediators might play a crucial role in the regulation of renal Oat3 function. Experimental diabetic rats were induced by a single intraperitoneal injection of streptozotocin (65 mg/kg). One week after injection, animals showing blood glucose above 250 mg/dL were considered to be diabetic and used for the experiment in which insulin-treated diabetic rats were subcutaneously injected daily with insulin for four weeks. Estrone sulfate (ES) uptake into renal cortical slices was examined to reflect the renal Oat3 function. The results showed that pre-incubation with insulin for 30 min (short term) stimulated [3H]ES uptake into the renal cortical slices of normal control rats. In the untreated diabetic rats, pre-incubation with insulin for 30 min failed to stimulate renal Oat3 activity. The unresponsiveness of renal Oat3 activity to insulin in the untreated diabetic rats suggests the impairment of insulin signaling. Indeed, pre-incubation with phosphoinositide 3-kinase (PI3K) and protein kinase C zeta (PKCζ) inhibitors inhibited insulin-stimulated renal Oat3 activity. In addition, the expressions of PI3K, Akt and PKCζ in the renal cortex of diabetic rats were markedly decreased. Prolonged insulin treatment in diabetic rats restored these alterations toward normal levels. Our data suggest that the decreases in both function and expression of renal Oat3 in diabetes are associated with an impairment of renal insulin-induced Akt/PKB activation through PI3K/PKCζ/Akt/PKB signaling pathway.

Steviol retards renal cyst growth through reduction of CFTR expression and inhibition of epithelial cell proliferation in a mouse model of polycystic kidney disease

Cyst enlargement in autosomal dominant polycystic kidney disease (ADPKD) is associated with cAMP-activated proliferation of cyst-lining epithelial cells and transepithelial fluid secretion into the cyst lumen via cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel leading to renal failure for which no effective treatment is currently available. We previously reported that steviol retards Madin-Darby canine kidney (MDCK) cyst enlargement by inhibiting CFTR channel activity and promoting proteasomal-mediated CFTR degradation. It is imperative to examine the effect of steviol in animal models of ADPKD. Therefore, we examined the effect of steviol on renal cyst growth in an orthologous mouse model of human ADPKD (Pkd1(flox/flox):Pkhd1-Cre). The results showed that daily treatment with both 200mg/kg BW of steviol and 1000mg/kg BW of stevioside for 14 days markedly decreased kidney weight and cystic index in these mice. However, only steviol markedly reduced blood urea nitrogen and creatinine values. Steviol also reduced cell proliferation but had no effect on cell apoptosis. In addition, steviol suppressed CFTR and mTOR/S6K expression in renal cyst-lining epithelial cells. Interestingly, steviol was found to stimulate AMP-activated protein kinase (AMPK). Our findings indicate that steviol slows cyst progression in ADPKD mouse model, in part, through the activation of AMPK which subsequently inhibits CFTR chloride channel expression and inhibits renal epithelial cell proliferation via mTOR/S6K pathway. Most importantly, steviol could markedly improve kidney function in a mouse model of ADPKD. Steviol thus has potential application for further development as a therapeutic compound for the treatment of polycystic kidney disease.