Toxicity And Transport Of Three Synthesized Mercury-Thiol-Complexes In Isolated Rabbit Renal Proximal Tubule Suspensions

Abstract

Previous work has suggested that endogenous sulfhydryls, such as glutathione (GSH) and cysteine, are involved in the uptake and toxicity of HgCl2. To study this possibility, uptake and toxicity of synthesized Hg(SG)2, Hg(cysteinylglycine)2 [Hg(CYS-GLY)2] and Hg(CYS)2 were investigated in rabbit renal proximal tubule suspensions (RPT). The intracellular K+ was used as a toxicity indicator, and the mercury content in the tubules was measured by proton induced x-ray emission analysis. The toxicity rank order of the three synthesized mercury-thiol-complexes from the highest to the lowest was: Hg(CYS)2 > Hg(CYS-GLY)2 > Hg(SG)2. However, no significant difference among the mercury contents in the tubules exposed to these synthesized mercury-thiol-complexes was detected. Acivicin (0.25 mM), an inhibitor of gamma-glutamyltranspeptidase (GGT), decreased the toxicity of Hg(SG)2 in a manner that did not decrease the uptake of mercury in the tubules. This suggests that the toxicity of Hg(SG)2 requires processing to Hg(CYS-GLY)2 or Hg(CYS)2, while Hg(SG)2 may be taken up by the tubules via Na(+)-dependent GSH transporter since 10 mM acivicin, an inhibitor of this transporter dramatically decreased the uptake of Hg(SG)2. Organic anion transporter plays a minor role, if any, in the toxicity and uptake of Hg(SG)2 and Hg(CYS)2 since p-aminohippuric acid (PAH), an inhibitor of organic anion transporter, did not have significant effect on their uptake and toxicity. L-phenylalanine, an inhibitor of the neutral amino acid decreased the uptake of mercury, but to a lesser extent. This suggested that neutral amino acid transporter seemed to play a role, in part, in the toxicity and uptake of synthesized Hg(CYS)2. In summary, the data suggested that basolateral transport is important for the toxicity of the three synthesized mercury-thiol-complexes, and a variety of mechanisms are involved in the toxicity and uptake of these complexes in isolated rabbit RPT.

A study of the glutathione metaboloma peptides by energy‐resolved mass spectrometry as a tool to investigate into the interference of toxic heavy metals with their metabolic processes

“…Transposing the mass spectrometric results (i.e. a reactivity study of molecules performed on isolated gas‐phase ions) to their aimed biochemical meaning of reactivity in water solution, this finding stands with the indirect evidence56 that biochemically formed or exogenously administered bis‐ S ‐glutathionyl‐mercury (II) is also a substrate of γ‐glutamyl‐transferase, able to undergo enzymatic loss of the pyroglutamic acid residue in full analogy with GSH adducts of xenobiotics, here represented by GS‐Me, which are catabolized in vitro and ex vivo to the final S ‐methylcysteine and S ‐methylmercapturic acid urinary metabolites.…”

“…The fragmentation pathways of the analysed GSH metaboloma closely mimic well‐known biochemical transformations of GSH metabolites into the excreted end products, as in particular, exemplified by the energy‐resolved mass spectrometric study of the process leading to loss of the C ‐terminal, γ‐linked residue of glutamic acid as pyroglutamic acid ( or 5‐oxo‐proline). In analogy with the mass spectrometric fragmentation of GSSG, the fragmentation of the GSH‐mercury conjugate closely resembles that occurring by enzymatic cleavage in ex vivo preparations of rabbit renal tubules,56 mainly represented by removal of the N ‐terminal γ‐glutamic acid residue by γ‐glutamyl transferase. It is worth noting that 5‐oxo‐proline is a known catabolite of the GSH metaboloma, which is excreted in the urine in large amounts in human subjects with a congenital defect of the oxoprolinase enzyme 57, 58…”

Molecular characterization of homo- and heterodimeric mercury(II)-bis-thiolates of some biologically relevant thiols by electrospray ionization and triple quadrupole tandem mass spectrometry

“…Standard samples of some symmetrical mercury(II)thiol compounds were prepared by reacting 0.2 M Hg(II) nitrate with two equivalents of the considered thiols (0.4 M) in nitrogen-purged deionized water and isolated according to published procedures [9,11]. The asymmetrical Hg(II)-thiol compounds were prepared by mixing equal volumes of 0.1 mM water solutions of different thiols and adding a stoichiometric amount of Hg 2ϩ to yield a solution which was infused into the mass spectrometer source.…”

“…Thiol compounds of Hg 2ϩ with glutathione are the transport form of the metal into the bile of experimental model animals [8]; also, the mercury(II)-bis-thiolato compounds of glutathione, cysteinyl-glycine, and cysteine were recently proposed as accumulation and transport forms of the metal into kidney cells [9].…”

Molecular and ionic mimicry and the transport of toxic metals

“…Indeed, studies in brush-border membrane vesicles (isolated from the renal cortex and outer stripe of the outer medulla of rats) indicate that mercuric ions are taken up more readily when they are in the form of Cys-S-Hg-S-Cys than when they are in the form of G-S-Hg-S-G or mercuric conjugates of 2,3-dimercaptopropane-1-sulfonate (DMPS; Zalups and Lash, 1997b). Moreover, studies in suspensions of rabbit proximal tubules (Wei et al, 1999;Zalups et al, 1993) and isolated perfused proximal tubules from rabbits (Cannon et al, 2000(Cannon et al, , 2001 have provided additional evidence for the luminal uptake of Cys-S-Hg-S-Cys. Since this conjugate is similar structurally to the amino acid cystine, our laboratory hypothesized that Cys-S-Hg-S-Cys can serve as a mimic of cystine at the site of one or more transporters (of this amino acid) located in the luminal plasma membrane of proximal tubular epithelial cells.…”