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As a final common pathway of renal injuries, renal fibrosis leads to chronic kidney disease (CKD). Currently, there is no safe and effective therapy to prevent the progression of renal fibrosis to CKD. Inhibition of transforming growth factor-β1 (TGF-β1) pathway is proposed as one of the most promising approaches for anti-renal fibrosis therapies. This study aimed to identify novel anti-fibrotic agents using the TGF-β1-induced fibrosis in renal proximal tubule epithelial cells (RPTEC) and characterize their mechanism of action as well as in vivo efficacy. By screening 362 natural product-based compounds for their ability to reduce collagen accumulation assessed by picro-sirius red (PSR) staining in RPTEC cells, a chalcone derivative AD-021 was identified as an anti-fibrotic agent with IC50 of 14.93 μM. AD-021 suppressed TGF-β1-induced collagen production, expression of pro-fibrotic proteins (fibronectin and α-smooth muscle actin (αSMA)), and Smad-dependent and Smad-independent signaling pathways via suppression of TGF-β receptor II (TGFβRII) phosphorylation in RPTEC cells. Furthermore, TGF-β1-induced mitochondrial fission in RPTEC cells was ameliorated by AD-021 via mechanisms involving inhibition of Drp1 phosphorylation. In a mouse model of unilateral ureteral obstruction (UUO)-induced renal fibrosis, AD-021 reduced plasma TGF-β1, ameliorated renal fibrosis and improved renal function. Collectively, AD-021 represents a novel class of natural product-based anti-fibrotic agent that has therapeutic potential in the prevention of fibrosis-associated renal disorders including CKD.

Colistin is a last-resort polypeptide antibiotic widely used to treat against multidrug-resistant Gram-negative bacterial infections. However, this treatment is associated with nephrotoxicity. The aim of this study was to examine the potential protective effect of panduratin A, a bioactive compound of Boesenbergia rotunda, on colistin-induced nephrotoxicity in both in vivo and in vitro models. Intraperitoneal injection of 15 mg/kg colistin for 7 days markedly promoted renal tubular degeneration, increased blood urea nitrogen (BUN) levels, and upregulated the expression of renal injury biomarker and apoptosis proteins. In addition, treatment with colistin increased oxidative stress and apoptosis in mice kidney tissues. Interestingly, these defects were attenuated when co-administered of colistin with panduratin A (2.5 or 25 mg/kg). The underlying mechanisms of panduratin A attenuating colistin toxicity was investigated in human renal proximal tubular cells (RPTEC/TERT1). The mechanisms by which colistin-triggered cytotoxicity was determined by analysis of cell death, reactive oxygen species (ROS) levels, mitochondria function as well as the expression of proteins related to apoptosis pathway. Colistin treatment (200 µg/ml) significantly increased cell apoptosis, elevated ROS production, reduced mitochondrial membrane potential, and decreased anti-apoptotic protein (Bcl-2) expression. These effects were notably suppressed by co-treatment with panduratin A (5 μM). Collectively, panduratin A exerts as a novel nephroprotective agent to protect against colistin-induced renal injury by attenuating mitochondrial damage and renal cell apoptosis.

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. Keywords: Uric acid, Urate, Fractional excretion of uric acid, Urate under-excretion animal model, Calcium channel blocker

L-type amino acid transporter 1 (LAT1, SLC7A5) incorporates essential amino acids into cells. Recent studies have shown that LAT1 is a predominant transporter in various human cancers. However, the function of LAT1 in thymic carcinoma remains unknown. Here we demonstrate that LAT1 is a critical transporter for human thymic carcinoma cells. LAT1 was strongly expressed in human thymic carcinoma tissues. LAT1-specific inhibitor significantly suppressed leucine uptake and growth of Ty82 human thymic carcinoma cell lines, suggesting that thymic carcinoma takes advantage of LAT1 as a quality transporter and that LAT1-specific inhibitor might be clinically beneficial in therapy for thymic carcinoma.

We analyzed the functional properties of five nonsynonymous single nucleotide polymorphisms (SNPs) in the sodium-phosphate transporter NPT4 gene (SLC17A3) using the Xenopus oocyte expression system. NPT4 variants carrying SNP V257F, G279R, or P378L exhibited reduced transport of [14C]para-aminohippurate, [3H]bumetanide, [3H]estrone sulfate, and [14C]urate, when each variant clone was expressed in the plasma membrane of oocytes. This study suggests the possibility that the genetic variation of NPT4 contributes to inter-individual differences in disposition of anionic drugs such as diuretics as well as certain endogenous organic anions such as urate. Keywords:: single nucleotide polymorphism, diuretic, urate

Abstract.: In the present study, we investigated the transport of nephrotoxic mycotoxin ochratoxin A (OTxA) by a novel human organic anion transporter hNPT4 using the Xenopus oocyte expression system. hNPT4 mediated time- and concentration-dependent uptake of OTxA (Km: 802.8 μM) in a pH- and voltage-sensitive manner. Cis-inhibition experiments suggest that the substrate selectivity of hNPT4 is similar to that of hOAT4. The fact that the Km of OTxA for the efflux transporter hNPT4 was much higher than those for the uptake transporters hOAT1 and hOAT3 may favor the accumulation of OTxA in the tubular cell and lead to nephrotoxicity. Keywords:: ochratoxin A, organic anion transporter, nephrotoxicity

Endothelial cell proliferation supporting angiogenesis requires sufficient nutrient supply because of facilitated intracellular metabolism. However, little is known about the mechanism for the promotion of nutrient incorporation in proliferating endothelial cells. Here we show that L-type amino acid transporter 1 (LAT1) is a major transporter of essential amino acids in human umbilical vein endothelial cells (HUVECs). Growing HUVECs express a certain level of LAT1. A LAT1-specific inhibitor suppressed leucine uptake, cell proliferation, and tube formation of HUVECs. Therefore, LAT1 acts to support effective uptake of amino acids, which is critical for the optimal function of HUVECs for angiogenesis. Keywords:: LAT1, amino acid transporter, HUVEC

Hyperuricemia is currently recognized as a risk factor for cardiovascular diseases. It has been reported that the angiotensin II–receptor blocker (ARB) losartan decreases serum uric acid level. In this study, the effects of another ARB, irbesartan, on [14C]uric acid–transport activity of renal uric acid reabsorptive transporters URAT1 and URATv1 were examined with Xenopus oocytes expressing each transporter. The results showed that irbesartan (100 – 500 μM) inhibited the uptake of uric acid via both transporters. The inhibitory effects of irbesartan exceeded those of losartan and other ARBs, and the results suggest that irbesartan can reduce serum uric acid level. Keywords:: angiotensin II–receptor blocker, transporter, uric acid

Renal organic anion transporters play an important role in the handling of a number of endogenous and exogenous anionic substances in the kidney. In this study, we investigated prostaglandin E2 (PGE2) transport properties and intrarenal localization of mouse organic anion transporter 3 (mOat3). When expressed in Xenopus oocytes, mOat3 mediated the time- and concentration-dependent transport of PGE2 (Km: 1.48 µM). PGE2 transport mediated by mOat3 was trans-stimulated by intracellular glutarate injected into the oocytes. PGE2 efflux via mOat3 was also trans-stimulated by extracellular glutarate. Thus, mOat3 was shown to mediate the bidirectional transport of PGE2, partly coupled to the dicarboxylate exchange mechanism. Immunohistochemical study revealed that mOat3 protein was localized at the basolateral membrane of renal proximal and distal tubules. Furthermore, diffuse expression of mOat3, including expression in the basolateral membrane in macula densa (MD) cells, was observed. These results indicate that mOat3 plays an important role as a basolateral transport pathway of PGE2 in the distal nephron including MD cells that may constitute one of the indispensable steps for renin release and regulation of the tubuloglomerular feedback mechanism. Keywords:: organic anion transporter, OAT, prostaglandin E2, glutarate, macula densa

Human organic anion transporter OAT4 is expressed in the kidney and placenta and mediates high-affinity transport of estrone-3-sulfate (E1S). Because a previous study demonstrated no trans-stimulatory effects by E1S, the mode of organic anion transport via OAT4 remains still unclear. In the present study, we examined the driving force of OAT4 using mouse proximal tubular cells stably expressing OAT4 (S2 OAT4). OAT4-mediated E1S uptake was inhibited by glutarate (GA) (IC50: 1.25 mM) and [14C]GA uptake via S2 OAT4 was significantly trans-stimulated by unlabeled GA (5 mM) (P