Renal organic cation and nucleoside transport

We previously reported that the rat organic cation transporter rOCT1 could transport the nucleoside analog deoxytubercidin (dTub) (Chen R, Nelson JA. Biochem Pharmacol 2000;60:215-9). The cationic form of dTub (dTub(+)) appeared to be the true substrate of rOCT1. We also reported that although rOCT2 is similar to rOCT1, it does not transport dTub at pH 7.4. In this study, we measured the K(m) and V(max) values of dTub(+) uptake at a reduced pH (pH 5.4) for both rOCT1 and rOCT2. The difference in substrate activity appears due, in large part, to a poor affinity of rOCT2 for dTub(+). The transport efficiency estimated by V(max)/K(m) values for rOCT2 was only 6% that of rOCT1. Chimeras constructed between rOCT1 and rOCT2 revealed that the difference in dTub binding lies within transmembrane domains 2-7. To evaluate the potential of OCT1 in the renal secretion of dTub, tissue distribution and urinary excretion of dTub in OCT1 knockout mice were measured. No significant difference was observed in renal elimination, plasma level, and tissue distribution of dTub between the knockout and the wild-type mice. Therefore, dTub is a good substrate for OCT1; however, OCT1 does not appear to be necessary for its renal secretion.     

Analysis of Spermatozoa from Seven ICSI Males with Constitutional Sex Chromosomal Abnormalities by Fluorescent In Situ Hybridization

Purpose: The objective was to estimate the risk for subfertilemales with a constitutional sex chromosomal abnormalityof transmitting such a chromosome abnormality to theirchildren, conceived by intracytoplasmic sperm injection(ICSI). Methods: Semen samples were obtained from seven severelyoligospermic ICSI candidates. Six of them had a numericalsex chromosomal abnormality, including mosaic 45,X/46,XY,mosaic 46,XY/47, XXY, 47,XXY (Klinefelter's syndrome), and47,XYY. One male had a structural abnormality, namely, aninversion of the Y chromosome. The semen was studied bythree-color fluorescent in situ hybridization (FISH) withprobes specific for chromosomes 18,X, and Y. Results: Chromosomal aneuploidy rates of any of the threechromosomes were significantly higher than the aneuploidyrates observed in three control samples but comparable tothe rates observed in 10 ICSI candidates witholigoasthenoteratozoospermia (OAT) and a normal constitutionalkaryotype. Conclusions: Our data indicate that males with (mosaic) sexchromosomal abnormalities have no higher risk of producingoffspring with a sex chromosomal abnormality by ICSI thanOAT males with a normal karyotype.     

Micronutrient and Urate Transport in Choroid Plexus and Kidney: Implications for Drug Therapy

Abstract With application of molecular biology techniques, there has been rapid progress in understanding how many drugs and micronutrients (e.g., vitamins) are transferred across the choroid plexus (CP), the main transport locus of the blood–cerebrospinal fluid (CSF) barrier, and the renal tubular epithelial cells. In many cases, these molecules are transported by separate, specific carriers or receptors on the apical and/or basal side of the CP or renal epithelial cells. This commentary focuses on four micronutrient transport systems in CP (ascorbic acid, folate, inositol, and riboflavin), all of which have been recently cloned, expressed and for which knockout mice models were developed and transporter localization studies performed. Also reviewed is the recently cloned uric acid transport system in human kidney in which there exists a human “knockout” model. The implications of these transport systems for drug therapy of central nervous system and renal disorders are discussed, especially with regard to methods to circumvent the blood–brain and blood–CSF barriers to deliver drugs to the brain.     

Impact of curcumin on the pharmacokinetics of rosuvastatin in rats and dogs based on the conjugated metabolites

1. Plasma concentrations of curcumin-O-glucuronide (COG) and curcumin-O-sulfate (COS) significantly increased after Sprague-Dawley rats dealt with the Oatp inhibitor rifampicin, with the C_max ascending 2.9 and 6.7 times, and the AUC_0–∞ ascending 4.4 and 10.8 times, respectively. When pretreated with the Oat inhibitor probenecid, the C_max increased 4.4 and 20 times, and the AUC_0–∞ increased 3.2 and 13.9 times, respectively. The results suggested that COG and COS may be the substrates of Oatp and Oat.

2. The accumulation of curcumin significantly increased in organic anion transporting polypeptide (OATP)- and organic anion transporter (OAT)-transfected human embryonic kidney (HEK) 293 systems, which suggested that curcumin was a substrate of OATP1B1, OATP1B3, OATP2B1, OAT1, and OAT3; and COG was a substrate of OATP1B1, OATP1B3, and OAT3.

3. Inhibition study using rosuvastatin as the substrate in OATP1B1- and OATP1B3-transfected cells indicated that curcumin was an OATP1B1 and 1B3 inhibitor, with IC₅₀ at 5.19?±?0.05 and 3.68?±?0.05?μM, respectively; the data for COG were 1.04?±?0.01 and 1.08?±?0.02?μM, respectively. COS was speculated to be an inhibitor of hepatic OATP1B1 as calculated using the ADMET Predictor.

4. COG and COS are substrates and inhibitors of OATP/Oatp. Co-administration of curcumin significantly increased rosuvastatin concentration in rat and dog plasma.     

Role of gemfibrozil as an inhibitor of CYP2C8 and membrane transporters

Introduction: Cytochrome P450 (CYP) 2C8 is a drug metabolizing enzyme of major importance. The lipid-lowering drug gemfibrozil has been identified as a strong inhibitor of CYP2C8 in vivo. This effect is due to mechanism-based inhibition of CYP2C8 by gemfibrozil 1-O-β-glucuronide. In vivo, gemfibrozil is a fairly selective CYP2C8 inhibitor, which lacks significant inhibitory effect on other CYP enzymes. Gemfibrozil can, however, have a smaller but clinically meaningful inhibitory effect on membrane transporters, such as organic anion transporting polypeptide 1B1 and organic anion transporter 3.

Areas covered: This review describes the inhibitory effects of gemfibrozil on CYP enzymes and membrane transporters. The clinical drug interactions caused by gemfibrozil and the different mechanisms contributing to the interactions are reviewed in detail.

Expert opinion: Gemfibrozil is a useful probe inhibitor of CYP2C8 in vivo, but its effect on membrane transporters has to be taken into account in study design and interpretation. Moreover, gemfibrozil could be used to boost the pharmacokinetics of CYP2C8 substrate drugs. Identification of gemfibrozil 1-O-β-glucuronide as a potent mechanism-based inhibitor of CYP2C8 has led to recognition of glucuronide metabolites as perpetrators of drug-drug interactions. Recently, also acyl glucuronide metabolites of clopidogrel and deleobuvir have been shown to strongly inhibit CYP2C8.     

Safety issues in assisted reproduction technology: Should men undergoing ICSI be screened for chromosome abnormalities in their sperm?

The incidence of aneuploidy in gametes of men undergoing ICSI has raised the prospect of there being risks associated with ICSI and the question of whether or not to screen men for sperm aneuploidy before treatment. We report results of a questionnaire undertaken to address how IVF staff perceive this problem, whether ICSI men are already being screened for sperm aneuploidy and the extent to which IVF specialists feel that there is merit in such a test. The results suggest that this is seen as a problem but most feel the risks outweigh the benefits. Most claimed their clinics do not screen sperm for aneuploidy but feel that there is merit in doing so. There are considerable benefits to screening i.e. couples would get additional information about the genetic repercussions of ICSI and could make informed decisions before treatment; screening would also facilitate the design of a large research study to give clearer answers on the safety of ICSI. However, we acknowledge counter arguments i.e. families would not necessarily benefit as most would have the ICSI procedure regardless of screen results; sex chromosome trisomies clinically are not severe enough to worry about in this context and there are other potential risks of ICSI that screening would not address.     

猫须草水提物对痛风性肾病大鼠肾脏URAT1、OAT1及病理的影响

目的探讨猫须草水提物对痛风性肾病大鼠肾脏尿酸盐转运体1(URAT1),有机阴离子转运蛋白1(OAT1)及病理的影响。方法采用酵母粉+腺嘌呤法建立大鼠痛风性肾病模型,测定其血尿酸、血肌酐、血尿素氮、尿尿酸、尿肌酐、24 h尿液排泄量及尿酸分级排泄率,光镜下观察肾组织病理变化,免疫组化法检测肾组织URAT1、OAT1蛋白表达。结果与模型组比较,猫须草水提物高、中剂量组大鼠血尿酸、血肌酐、血尿素氮水平及URAT1蛋白表达降低,而尿尿酸、尿肌酐水平,尿酸分级排泄率,OAT1蛋白表达升高;高、中、低剂量组大鼠24 h尿液排泄量升高程度无明显变化。结论猫须草水提物可能通过上调OAT1蛋白表达促进尿酸排泄、下调URAT1蛋白表达抑制尿酸重吸收的双重调节功能来促进尿酸在肾脏中的排泄,并减轻尿酸对肾脏的病理损伤。     

Reversal of cystoid macular edema in gyrate atrophy patients

Purpose: This study reports the presentation of two families with gyrate atrophy (GA). The aim of this study was to characterize the potential effect of therapeutic regimens on macular edema.

Methods: Two unrelated patients with GA were studied for the potential effect of low protein diet (≤ 0.8 g/kg/d), and oral administration of pyridoxine (500 mg/day), on serum ornithine levels, best corrected visual acuity (BCVA), slit-lamp, OCT, and auto-fluorescence findings. Blood samples for DNA, mRNA, and exons of the OAT gene were screened for mutations and splicing effect when relevant.

Results: At presentation, both patients manifested typical ophthalmic features of GA including cystoid macular edema (CME). One patient also exhibited optic nerve head hamartoma. Following treatment ornithine levels have lessened, BCVA improved, and central macular thickness (CMT) markedly decreased in all four studied eyes. The molecular pathologic features included a novel splice site mutation (c.900+1G>A).

Conclusions: We have identified a novel mutation and two formerly described mutations in patients with GA. Of them, one patient comprised an unusual phenotype including bilateral astrocytic hamartomas. We have recognized for the first time improvement in CME following treatment with low protein intake and pyridoxine supplement. This finding may have significance in the understanding of treatment options for macular edema regardless of underlying etiology.     

Cilastatin protects against imipenem-induced nephrotoxicity via inhibition of renal organic anion transporters (OATs)

Imipenem is a carbapenem antibiotic. However, Imipenem could not be marketed owing to its instability and nephrotoxicity until cilastatin, an inhibitor of renal dehydropeptidase-I (DHP-I), was developed. In present study, the potential roles of renal organic anion transporters (OATs) in alleviating the nephrotoxicity of imipenem by cilastatin were investigated in vitro and in rabbits. Our results indicated that imipenem and cilastatin were substrates of hOAT1 and hOAT3. Cilastatin inhibited hOAT1/3-mediated transport of imipenem with IC₅₀ values comparable to the clinical concentration, suggesting the potential to cause a clinical drug–drug interaction (DDI). Moreover, imipenem exhibited hOAT1/3-dependent cytotoxicity, which was alleviated by cilastatin and probenecid. Furthermore, cilastatin and probenecid ameliorated imipenem-induced rabbit acute kidney injury, and reduced the renal secretion of imipenem. Cilastatin and probenecid inhibited intracellular accumulation of imipenem and sequentially decreased the nephrocyte toxicity in rabbit primary proximal tubule cells. Renal OATs, besides DHP-I, was also the target of interaction between imipenem and cilastatin, and contributed to the nephrotoxicity of imipenem. This therefore gives in part the explanation about the mechanism by which cilastatin protected against imipenem-induced nephrotoxicity. Thus, OATs can potentially be used as a therapeutic target to avoid the renal adverse reaction of imipenem in clinic.     

Anti-hyperuricemic and nephroprotective effects of Modified Simiao Decoction in hyperuricemic mice

Ethnopharmacological relevance

Modified Simiao Decoction (MSD), based on clinical experience, has been used for decades and famous for its efficiency in treating hyperuricemic and gouty diseases.

Aim of the study

To investigate the effects of MSD on anti-hyperuricemic and nephroprotective effects are involved in potassium oxonate-induced hyperuricemic mice.

Materials and methods

The effects of MSD were investigated in hyperuricemic mice induced by potassium oxonate. MSD were fed to hyperuricemic mice daily at a dose of 0.45, 0.90, 1.80 g/kg for 10 days, and allopurinol (5 mg/kg) was given as a positive control. Serum and urine levels of uric acid and creatinine, and fractional excretion of uric acid (FEUA) were determined by colorimetric method. Its nephroprotective effects were evaluated by determining a panel of oxidative stress markers after the intervention in hyperuricemic mice. Simultaneously, protein levels of urate transporter 1 (URAT1) and organic anion transporter 1 (OAT1) in the kidney were analyzed by Western blotting.

Results

MSD could inhibit XOD activities in serum and liver, decrease levels of serum uric acid, serum creatinine and BUN, and increased levels of urine uric acid, urine creatinine, FEUA dose-dependently through down-regulation of URAT1 and up-regulation of OAT1 protein expressions in the renal tissue of hyperuricemic mice. It also effectively reversed oxonate-induced alterations on renal MDA levels and SOD activities in this model.

Conclusion

MSD processes uricosuric and nephroprotective actions by regulating renal urate transporters and enhancing antioxidant enzymes activities to improve renal dysfunction in hyperuricemic mice.