Thelle K, Christensen E I, Vorum H, Ørskov H, Birn H
Department of Cell Biology, Institute of Anatomy, University of Aarhus, Aarhus, Denmark.
Kidney Int. 2006 Apr;69(8):1333-40. doi: 10.1038/sj.ki.5000272.
Intravenous infusion of basic amino acids is used experimentally and pharmacologically to prevent renal proximal tubular uptake of filtered proteins. Intravenously injected L-lysine is rapidly cleared from plasma and the effect on tubular protein reabsorption is transient. To obtain a more sustained effect, we developed a model of oral L-lysine administration and characterized this model by analyzing urinary protein excretion and proximal tubule uptake of filtered proteins. Rats placed in metabolic cages were treated with 20 mmol/kg/6 h of L-lysine, glycine, or water. Urines were analyzed for proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotting, and radioimmunoassay. Proximal tubule uptake of proteins and expression of apical membrane receptors were investigated by immunocytochemistry. In vitro uptake and receptor expression were studied using a yolk sac cell line. L-lysine administration produced increased urinary excretion of a large number of proteins while the effect on tubular accumulation of selected proteins was variable. L-lysine treatment induced changes in the localization of two receptors responsible for tubular endocytosis of filtered proteins. In conclusion, oral L-lysine treatment induced proteinuria, in particular albuminuria, as efficiently as previous reports on intravenous infusion. The effect on tubular protein accumulation was variable suggesting differential effects on tubular reabsorption and degradation of filtered proteins. Changes in tubular protein handling were accompanied by changes in the localization of the endocytic receptors, megalin, and cubilin. In vitro experiments supported the in vivo observations. The findings suggest that L-lysine may affect receptor trafficking in addition to possible effects on the direct binding of ligands to the receptors.
实验和药理学上使用静脉输注碱性氨基酸来防止肾近端小管对滤过蛋白的摄取。静脉注射的L-赖氨酸可迅速从血浆中清除，对肾小管蛋白重吸收的作用是短暂的。为了获得更持久的效果，我们建立了口服L-赖氨酸给药模型，并通过分析尿蛋白排泄和近端小管对滤过蛋白的摄取来表征该模型。将置于代谢笼中的大鼠用20 mmol/kg/6 h的L-赖氨酸、甘氨酸或水进行处理。通过十二烷基硫酸钠-聚丙烯酰胺凝胶电泳、免疫印迹和放射免疫测定法分析尿液中的蛋白质。通过免疫细胞化学研究近端小管对蛋白质的摄取和顶端膜受体的表达。使用卵黄囊细胞系研究体外摄取和受体表达。给予L-赖氨酸导致大量蛋白质的尿排泄增加，而对所选蛋白质的肾小管蓄积的影响则各不相同。L-赖氨酸处理诱导了负责滤过蛋白肾小管内吞作用的两种受体的定位变化。总之，口服L-赖氨酸治疗诱导蛋白尿，尤其是白蛋白尿，其效果与先前关于静脉输注的报道一样有效。对肾小管蛋白蓄积的影响各不相同，表明对滤过蛋白的肾小管重吸收和降解有不同的影响。肾小管蛋白处理的变化伴随着内吞受体、巨膜蛋白和立方蛋白定位的变化。体外实验支持了体内观察结果。这些发现表明，L-赖氨酸除了可能影响配体与受体的直接结合外，还可能影响受体运输。
