Identification of a mechanism by which the methylmercury antidotes N-acetylcysteine and dimercaptopropanesulfonate enhance urinary metal excretion:: Transport by the renal organic anion transporter-1
Identification of a mechanism by which the methylmercury antidotes N-acetylcysteine and dimercaptopropanesulfonate enhance urinary metal excretion:: Transport by the renal organic anion transporter-1
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DOI：
10.1124/mol.62.4.921
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发表时间：
2002-10-01
影响因子：
3.6
通讯作者：
Ballatori, N
中科院分区：
文献类型：
--
作者：
Koh, AS;Simmons-Willis, TA;Ballatori, N
N-乙酰半胱氨酸（NAC）和二巯基丙磺酸盐（DMPS）是含巯基的化合物，其在中毒动物中产生尿甲基汞（MeHg）排泄的急剧加速，但这种作用的分子机制尚不清楚。NAC和DMPS本身以高浓度经尿液排泄。本研究测试的假设，甲基汞和这些阴离子螯合剂之间形成的复合物从血液运输到近端小管细胞的基底外侧膜有机阴离子转运蛋白（燕麦）1和燕麦3。非洲爪蟾卵母细胞表达大鼠燕麦1表现出增加摄取[C-14]甲基汞时，无论是NAC或DMPS复合，但不与L-半胱氨酸，谷胱甘肽，二巯基琥珀酸，青霉胺，或γ-谷氨酰半胱氨酸复合。与此相反，这些甲基汞复合物都没有被Oat 3表达卵母细胞转运。Oat 1介导的转运的表观Km值对于MeHg-NAC为31 +/- 2 μ M，对于MeHg-DMPS为9 +/- 2 μ M，表明这些是相对高亲和力的底物。Oat 1介导的[C-14] MeHg-NAC和[C-14] MeHg-DMPS的摄取被Oat 1的原型底物抑制，包括对氨基马尿酸盐（PAH），并且当卵母细胞预先加载2 mM戊二酸盐而不是谷氨酸盐时被反式刺激。相反，[H-3] PAH从Oat 1-表达卵母细胞的流出被戊二酸、PAH、NAC、DMPS、MeHg-NAC、MeHg-DMPS和巯基尿酸反式刺激，表明这些是转运溶质。[H-3]PAH摄取被NAC（Ki为2.0 +/- 0.3 mM）和DMPS（Ki为0.10 +/- 0.02 mM）竞争性抑制，进一步证明这些螯合剂是Oat 1的底物。这些结果表明，甲基汞解毒剂NAC和DMPS和它们的硫醇盐络合物被Oat 1转运，但对Oat 3来说是相对较差的底物。这是第一个分子鉴定的运输机制，这些解毒剂可能会增加有毒金属的尿排泄。
N-Acetylcysteine (NAC) and dimercaptopropanesulfonate (DMPS) are sulfhydryl-containing compounds that produce a dramatic acceleration of urinary methylmercury (MeHg) excretion in poisoned animals, but the molecular mechanism for this effect is unknown. NAC and DMPS are themselves excreted in urine in high concentrations. The present study tested the hypothesis that the complexes formed between MeHg and these anionic chelating agents are transported from blood into proximal tubule cells by the basolateral membrane organic anion transporters (Oat) 1 and Oat3. Xenopus laevis oocytes expressing rat Oat1 showed increased uptake of [C-14] MeHg when complexed with either NAC or DMPS but not when complexed with L-cysteine, glutathione, dimercaptosuccinate, penicillamine, or gamma-glutamylcysteine. In contrast, none of these MeHg complexes were transported by Oat3-expressing oocytes. The apparent K-m values for Oat1-mediated transport were 31 +/- 2 muM for MeHg-NAC and 9 +/- 2 muM for MeHg-DMPS, indicating that these are relatively high-affinity substrates. Oat1-mediated uptake of [C-14] MeHg-NAC and [C-14] MeHg-DMPS was inhibited by prototypical substrates for Oat1, including p-aminohippurate (PAH), and was trans-stimulated when oocytes were preloaded with 2 mM glutarate but not glutamate. Conversely, efflux of [H-3] PAH from Oat1-expressing oocytes was trans-stimulated by glutarate, PAH, NAC, DMPS, MeHg-NAC, MeHg-DMPS, and a mercapturic acid, indicating that these are transported solutes. [H-3] PAH uptake was competitively inhibited by NAC (K-i of 2.0 +/- 0.3 mM) and DMPS (K-i of 0.10 +/- 0.02 mM), providing further evidence that these chelating agents are substrates for Oat1. These results indicate that the MeHg antidotes NAC and DMPS and their mercaptide complexes are transported by Oat1 but are comparatively poor substrates for Oat3. This is the first molecular identification of a transport mechanism by which these antidotes may enhance urinary excretion of toxic metals.