Renal transport and metabolism of mercapturic acids and their precursors

In vivo multiphoton imaging of mitochondrial structure and function during acute kidney injury

Mitochondrial dysfunction has been implicated in the pathogenesis of acute kidney injury due to ischemia and toxic drugs. Methods for imaging mitochondrial function in cells using confocal microscopy are well established; more recently, it was shown that these techniques can be utilized in ex vivo kidney tissue using multiphoton microscopy. We extended this approach in vivo and found that kidney mitochondrial structure and function can be imaged in anesthetized rodents using multiphoton excitation of endogenous and exogenous fluorophores. Mitochondrial nicotinamide adenine dinucleotide increased markedly in rat kidneys in response to ischemia. Following intravenous injection, the mitochondrial membrane potential-dependent dye TMRM was taken up by proximal tubules; in response to ischemia, the membrane potential dissipated rapidly and mitochondria became shortened and fragmented in proximal tubules. In contrast, the mitochondrial membrane potential and structure were better maintained in distal tubules. Changes in mitochondrial structure, nicotinamide adenine dinucleotide, and membrane potential were found in the proximal, but not distal, tubules after gentamicin exposure. These changes were sporadic, highly variable among animals, and were preceded by changes in non-mitochondrial structures. Thus, real-time changes in mitochondrial structure and function can be imaged in rodent kidneys in vivo using multiphoton excitation of endogenous and exogenous fluorophores in response to ischemia-reperfusion injury or drug toxicity.

Occupational hydrocarbon exposure and chronic nephropathy

This review aims at discussing the questions raised by the hydrocarbon-related chronic nephropathy and its possible consequence, the hydrocarbon-related chronic renal failure. It has been attempted to adopt the point of view of the clinician. Therefore, the most important part of the review is devoted to a presentation and an analysis of the available data on humans. The main features of the available studies on human subjects are presented, their conclusions discussed in the light of the possible methodological flaws, and practical conclusions drawn. After a discussion of the main difficulties encountered for selecting the suitable exposure indicator, the studies are discussed in order of decreasing quality of the study design (cohort, case-control, cross-sectional studies, and the case reports). It is concluded that a great deal of controversies about chronic hydrocarbon-related nephropathy is explained by differences in the study design and that hydrocarbon-induced nephropathy is probably more than a mere hypothesis, although a causal relationship has not yet been proven. Finally, some practical consequences for dealing with a hydrocarbon-exposed patient diagnosed with a kidney disease and the need for further research are discussed.

Cytosolic C-S lyase activity in human kidney samples-relevance for the nephrotoxicity of halogenated alkenes in man

Human renal cortex cytosolic samples were screened for C-S lyase (EC 4.4.1.13) activity using cysteine conjugates of halogenated aliphatic and aromatic hydrocarbons as substrates. Cystosolic activity was greatest with S-(1,2-dichlorovinyl)-L-cysteine (DCVC) and S-(1,1,2,2-tetrafluoroethyl)-L-cysteine (TFEC) (72.0 +/- 26.8 and 74.4 +/- 38.3 nmol pyruvate formed/mg protein/120 min. respectively). Less than five fold inter-individual variation was observed. In contrast to the low C-S lyase activity detectable in rat cytosol, no cleavage of the aromatic conjugates S-(2-benzothiazolyl)-L-cysteine (BTC), S-(2,3,5,6-tetrachlorophenyl)-L-cysteine (TCPC) and S-(4-bromophenyl)-L-cysteine (4-BPC) was detectable in human cytosol. Structure-activity relationships showed that increasing the fluorinated carbon chain length of the halogenated hydrocarbon species decreased conjugate cleavage by C-S lyase. The position and number of fluorine and chlorine atoms on the parent hydrocarbon determined the extent of cysteine conjugate C-S cleavage. Activity increased with an increase in fluorine and chlorine substitution and shortening of carbon chain length in the rat, although in human cytosol an increase in chlorine substitution resulted in decreased activity.

Comparative metabolism of the cysteine and homocysteine conjugates of propachlor by in situ perfused kidneys of rats

1. 14C-Cysteinyl- and homocysteinylpropachlor were metabolized to their respective mercapturic acids by rat kidneys in situ. First-pass elimination of 14C in urine was 47.5% for the cysteine conjugate and 36% for the homocysteine conjugate. 2. About half of the perfused 14C-labelled material isolated from urine from kidneys perfused with homocysteinylpropachlor was unchanged homocysteinylpropachlor and about half was the corresponding mercapturic acid. However, only the corresponding mercapturic acid and the S-oxide of this mercapturic acid (31.4% and 1.7% of the dose) were found in urine from kidneys perfused with cysteinylpropachlor, indicating that rat kidneys more efficiently acetylated the natural substrate, the cysteine conjugate.

Determination of mercapturic acid excretions in exposure control to toxicants

Toxicants can be converted in vivo by a variety of biotransformation reactions into substances that are more, equally, or less noxious than the parent compound. Although conjugation with glutathione is a process that usually results in less harmful products, these products might subsequently form new metabolites that exert more toxicity than the parent compound. These conjugation reactions are catalyzed by several classes of glutathione-S-transferase isoenzymes and thus result in the urinary or biliary excretion of N-acetyl-L-cysteine-S-conjugates (mercapturic acids). Inasmuch as GSH-S-transferase activity varies among different tissues, urinary excretion of mercapturic acids might reflect tissue-specific toxicity. Urinary mercapturic acids are biomarkers of internal and, in some cases, effective dose. The utility of these markers is, however, limited to times shortly after exposure. Studies on possible human deficiencies in some GSH-S-transferases might help us better understand interindividual variations in susceptibility to different toxicants and thus the differences in the pathway of mercapturic acid excretion pattern.