Membrane Transporters in Drug Disposition

Many clinically used drugs and their metabolites as well as a variety of environmental toxins are organic cations at physiologic pH. Secretion in the renal proximal tubule constitutes a major pathway in the elimination of organic cations. In this report, the results of studies recently performed in this laboratory are presented. First, the molecular cloning of a novel splice variant of organic cation transporter from rat kidney (rOCTIA) is described. The functional characteristics of the transporter are discussed along with the implications of RNA splicing in enhancing transporter diversity. Second, the molecular cloning of the first human organic cation transporter (hOCTI) is described. Distinct interspecies differences in the tissue distribution and function of this transporter is presented. These studies have paved the way for elucidating molecular structure function relationships of organic cation transporters and for determining their physiologic role in drug absorption and elimination. The cloned transporters can be used in mammalian expression systems for screening candidate compounds identified during drug discovery and development and in the in vivo prediction of the pharmacokinetics of therapeutic agents.     

Living kidney transplantation between spouses: Results in 100 cases

Abstract The use of unrelated living donors in kidney transplantation is still controversial but many transplant centres have accepted this procedure. The main argument against this approach is usually an ethical one. Because of this, at our institution we accept biologically unrelated donors only if they have an emotional closeness to the recipient. From January 1983 to October 1993, out of 654 kidney transplantations we performed at our institution, 364 kidney allografts were from living donors. Of these living donors, 245 were first-degree relatives of the recipient (LRD) while 119 were unrelated (LURD); 100 cases were spouses-wife to husband in 76 cases and husband to wife in 24 cases Statistical analysis of the results (chisquare) revealed actuarial patient and graft survival rates of 89.8% and 86.8% at 1 year, 82.9% and 72.3% at 5 years and 12.3% and 60.3% at 9 years, respectively. In our series, the result of living donor kidney transplantation in this group were similar to those obtained in the LRD group, while they were significantly better than those from cadaver donors (P = 0.003). In conclusion, cadaver organs given the shortage of kidney transplantation between spouses may be a good alternative and can be performed successfully, providing a "gift of life" for both the patient and the family.     

Handling of asymmetrical dimethylarginine and symmetrical dimethylarginine by the rat kidney under basal conditions and during endotoxaemia.

BACKGROUND: Asymmetrical dimethylarginine (ADMA) is capable of inhibiting nitric oxide synthase enzymes, whereas symmetrical dimethylarginine (SDMA) competes with arginine transport. The potential role of inflammation in the metabolism of ADMA has been elucidated in an in vitro model using tumour necrosis factor-alpha, resulting in a decreased activity of the ADMA-degrading enzyme dimethylarginine dimethylaminohydrolase (DDAH). The kidney probably plays a crucial role in the metabolism of ADMA by both urinary excretion and degradation by DDAH. We aimed to further elucidate the role of the kidney in a rat model under basal conditions and during endotoxaemia. METHODS: Twenty-five male Wistar rats weighing 275-300 g were used for this study. The combination of arteriovenous concentration differences and kidney blood flow allowed calculation of net organ fluxes. Blood flow was measured using radiolabelled microspheres according to the reference sample method. Concentrations of ADMA, SDMA and arginine were measured by high-performance liquid chromatography. RESULTS: The kidney showed net uptake of both ADMA and SDMA and fractional extraction rates were 35% and 31%, respectively. Endotoxaemia resulted in a lower systemic ADMA concentration (P = 0.01), which was not explained by an increased net renal uptake. Systemic SDMA concentrations increased during endotoxaemia (P = 0.007), which was accompanied by increased creatinine concentrations. CONCLUSIONS: The rat kidney plays a crucial role in the regulation of concentrations of dimethylarginines, as both ADMA and SDMA were eliminated from the systemic circulation in substantial amounts. Furthermore, evidence for the role of endotoxaemia in the metabolism of dimethylarginines was obtained as plasma levels of ADMA were significantly lower in endotoxaemic rats.     

Effects of different perfusates on functional parameters of isolated perfused dog kidneys.

BACKGROUND: The isolated perfused canine kidney has been established as a valid model for conducting both renal physiology and transplantation research. This model is of particular importance for developing new strategies to improve graft function after renal transplantation. In the present study, a newly developed method using isolated haemoperfused porcine kidneys was adapted for use in canine kidneys. In contrast to haemoperfusion, synthetic perfusion media can be standardized and can prevent the initiation of blood-mediated reperfusion reactions. Thus, an additional aim was to determine whether blood could be replaced by synthetic cell-free perfusion solutions. METHODS: Canine kidneys (n = 30) were harvested from donors euthanized in veterinary practices for causes unrelated to the present study. The kidneys were isolated and perfused with autologous blood or cell-free synthetic electrolyte buffer (Tyrode solution). During perfusion, we monitored renal perfusate flow (RPF), glomerular filtration rate (GFR), electrolyte and glucose reabsorption, oxygen consumption and urine concentration. RESULTS: Changes in perfusion medium did not affect the RPF. In contrast, GFR, urine concentration and oxygen consumption were significantly higher, whereas fractional excretion of sodium and glucose were significantly lower in blood- than in Tyrode-perfused kidneys. CONCLUSIONS: This system offers a simple model for studying whole-organ functional alterations after acute renal ischaemia. Renal function indicators were below values reported during in vivo physiological conditions. These functions were better conserved when kidneys were perfused with autologous blood than with Tyrode.     

猪肾近端小管的超微结构

目的 研究猪肾近端小管的超微结构。方法 树脂包埋一超薄切片、透射电子显微镜技术。结果 猪肾近端小管可分S1、S2、S3和S4段构成，其中S1、S2段构成了近端小管曲部，S3、S4段构成了近端小管直部。本文对各段细胞超微结构特点进行详细的描述。结论 猪肾近端小管的超微结构与人肾近端小管最接近。     

肾移植2,3,5年患者的免疫抑制用药分析

目的：分析肾移植后免疫抑制剂对长期存活的影响，寻找移植后不同时间合适的免疫抑制用药方案及其用药剂量。 方法：对肾移植一年以上、肾功能正常的４９７例患者进行５年连续随访。根据移植后２、３、５年的不同免疫抑制用药将患者分为三联、二联、传统二联治疗三组。统计各组的排异发生率，排异和无排异患者免疫抑制用药的种类、剂量及ＣｓＡ浓度，对排异患者追踪排异发生前１２个月内的药物更动情况。 结果：肾移植后２、３、５     

A model of sterile vesicoureteric reflux in the sheep

Eighteen Coopworth ewe lambs were divided into three groups based on the initial cystourethrogram and cystometry findings at 5 – 7 weeks of age: group 1, 6 lambs with spontaneous low-pressure bilateral vesicoureteric reflux (VUR) on bladder filling were used to study the natural history of reflux; group 2, 5 lambs with no VUR detected were used to establish an experimental model of bilateral VUR using an unroofing surgical procedure; group 3, 7 lambs with spontaneous VUR detected during micturition had the same surgical procedure to increase the degree of VUR. All three animal groups were followed for 4 – 10 months. Spontaneous VUR was demonstrated in 13 of 18 lambs (25/36 ureters). The presence and severity of spontaneously occurring reflux in group 1 lambs diminished with increasing age. VUR was created successfully in group 2 and increased in degree in group 3 animals. The only significant histological finding in all three animal groups with grades II and III VUR was distal renal tubular dilatation. The sheep is a useful and readily available animal for studying VUR. During 4 – 10 months of follow-up, sterile reflux without bladder outflow obstruction resulted in distal renal tubular dilatation, but no renal parenchymal damage. Received April 17, 1997; received in revised form August 5, 1997; accepted August 21, 1997     

Polycystic kidney disease genes and polycystins

Conclusion The past decade has seen extraordinary progress in the study of autosomal-dominant polycystic kidney disease. The 2 major genes for this disorder have been identified. Animal models of ADPKD have been produced. The molecular basis of the disease has been characterized. ADPKD is a “second-hit” disease, much like many cancer predisposition syndromes. This has profound implications for our understanding. The progression of ADPKD in individual patients is likely related more to their individual rate of acquisition of second hits at thePKD1 orPKD2 locus than to the inherited germ line mutation itself. Therapeutic approaches will perhaps now be considered, which will include interventions that may limit the rate at which somatic mutations occur in the kidney. The major focus of research at present is to elucidate the normal functions ofPKD1 andPKD2. Protein binding partners are being sought for both proteins. The possible calcium channel function ofPKD2 is being investigated. The downstream effects of cellular deficiency of either protein are likely to yield many clues. Modifying genetic factors that may independently affect disease progression are likely to be identified using the several mouse models. Perhaps the next decade will bring great strides in understanding and in potential therapy for this common disease. This paper was presented at the 2nd International Forum “The Frontiers of Nephrology,” Tokyo, May 10, 1998.