H.p.l.c. analysis of di- and tri-carboxylic porphyrins in porphyric patients.

New h.p.l.c. methods have been developed for the quantitative determination of di- and tri-carboxylic porphyrin methyl esters, and applied to the analysis of faecal extracts from patients with four different types of porphyria.     

Alterations in renal cellular glutathione metabolism after in vivo administration of a subtoxic dose of mercuric chloride

Renal cellular concentration of glutathione (GSH) increases after exposure to a subtoxic dose of inorganic mercury (Hg²⁺). In the present study, we tested the hypothesis that the increase in renal cellular concentration of GSH after exposure to a subtoxic dose of Hg²⁺ (0.5 μmol HgCl₂/kg body wt) is due to induction of GSH synthesis. Rats were treated in vivo with HgCl₂, and renal proximal tubular (PT) and distal tubular (DT) cells were isolated 24 hours later. PT cells were studied as the presumed target site for Hg²⁺, and DT cells were investigated as a nontarget cell population. γ-Glutamylcysteine synthetase activity increased after exposure to Hg²⁺ in PT cells when expressed on a per cell basis. Increases in activities of glutathione disulfide (GSSG) reductase, GSH peroxidase, and several enzymes involved in cellular energetics occurred after exposure to Hg²⁺. Many of these increases were observed in both PT and DT cells, indicating that the responses to Hg²⁺ were not restricted to the PT cells. These results are consistent with the hypothesis that in vivo exposure to a subtoxic dose of Hg²⁺ is also associated with induction of GSH synthesis and other key cellular enzymes. Early changes in GSH metabolism associated with exposure to Hg²⁺ appear to occur both in the primary target cell population and in more distal nephron sites. © 1996 John Wiley & Sons, Inc.     

Metabolism of analogues of coproporphyrinogen-III with modified side chains: implications for binding at the active site of coproporphyrinogen oxidase

Porphyrinogens with modified propionate side chains bearing methyl substituents were found to be modest substrates for coproporphyrinogen oxidase; the results indicate that alteration of the substituents involved in secondary binding interactions has a comparable affect to modifying the side chain that undergoes degradation at the catalytic site.     

Alterations of oxidative stress biomarkers due to in utero and neonatal exposures of airborne manganese

Neonatal rats were exposed to airborne manganese sulfate (MnSO₄) (0, 0.05, 0.5, or 1.0 mg Mn/m³) during gestation (d 0–19) and postnatal days (PNDs) 1–18. On PND19, rats were killed, and we assessed biochemical end points indicative of oxidative stress in five brain regions: cerebellum, hippocampus, hypothalamus, olfactory bulb, and striatum. Glutamine synthetase (GS) and tyrosine hydroxylase (TH) protein levels, metallothionein (MT), TH and GS mRNA levels, and reduced and oxidized glutathione (GSH and GSSG, respectively) levels were determined for all five regions. Mn exposure (all three doses) significantly (p=0.0021) decreased GS protein levels in the cerebellum, and GS mRNA levels were significantly (p=0.0008) decreased in the striatum. Both the median and high dose of Mn significantly (p=0.0114) decreased MT mRNA in the striatum. Mn exposure had no effect on TH protein levels, but it significantly lowered TH mRNA levels in the olfactory bulb (p=0.0402) and in the striatum (p=0.0493). Mn eposure significantly lowered GSH levels at the median dose in the olfactory bulb (p=0.032) and at the median and high dose in the striatum (p=0.0346). Significantly elevated (p=0.0247) GSSG, which can be indicative of oxidative stress, was observed in the cerebellum of pups exposed to the high dose of Mn. These data reveal that alterations of oxidative stress biomarkers resulting from in utero and neonatal exposures of airborne Mn exist. Coupled with our previous study in which similarly exposed rats were allowed to recover from Mn exposure for 3 wk, it appears that many of these changes are reversible. It is important to note that the doses of Mn utilized represent levels that are a hundred- to a thousand-fold higher than the inhalation reference concentration set by the United States Environmental Protection Agency.     

S-(1,2-dichlorovinyl)-L-homocysteine-induced cytotoxicity in isolated rat kidney cells

Incubation of isolated, rat kidney cells with S-(1,2-dichlorovinyl)-L-homocysteine (DCVHC) caused time-dependent cell death. Cytotoxicity of DCVHC was potentiated by addition of alpha-ketobutyrate, indicating the involvement of pyridoxal phosphate-dependent enzymes. A second addition of DCVHC to cells produced increased cytotoxicity, indicating that the bioactivating ability is not lost after exposure to the conjugate. DCVHC decreased cellular glutathione concentrations by 52% and substantially inhibited glutathione biosynthesis from precursors. In contrast, the cysteine analog S-(1,2-dichlorovinyl)-L-cysteine (DCVC) failed to decrease cellular glutathione concentrations and only partially inhibited glutathione biosynthesis. As with DCVC, DCVHC did not increase cellular glutathione disulfide concentrations and did not initiate lipid peroxidation, indicating that it does not produce an oxidative stress. DCVHC and DCVC produced similar alterations in mitochondrial function: Cellular ATP concentrations were decreased by 57% and cellular ADP and AMP concentrations were increased twofold, thereby decreasing the ATP/ADP ratio from 2.8 to 0.6 and the cellular energy charge from 0.80 to 0.56; DCVHC was a potent inhibitor of succinate-dependent oxygen consumption, but had little effect on respiration linked to oxidation of glutamate + malate or ascorbate + N,N,N'N'-tetramethyl-p-phenylenediamine. DCVHC was a potent inhibitor of mitochondrial Ca2+ sequestration and, in contrast to DCVC, also inhibited microsomal Ca2+ sequestration. These DCVHC-induced alterations in cellular metabolism were prevented by addition of propargylglycine or aminooxyacetic acid, and the alpha-methyl analog S-(1,2-dichlorovinyl)-DL-alpha-methylhomocysteine was not toxic. These results support a role for pyridoxal phosphate-dependent bioactivation of DCVHC and indicate that the greater nephrotoxic potency of DCVHC as compared to DCVC is partially due to the presence of both mitochondrial and extramitochondrial targets for DCVHC.     

Purification and properties of the membranal thiol oxidase from porcine kidney

A thiol oxidase was purified from porcine kidney cortex by chromatography of detergent-solubilized plasma membranes on cysteinylsuccinamidopropyl-glass beads, hydroxyapatite, and Sephacryl S-200. The oxidase was purified 2600-fold; 28% recovery of activity was obtained. With glutathione as substrate, the apparent Km was 0.73 mM and the V max was a 4.4 U/mg protein. The reaction catalyzed was 2 RSH + O2----RSSR + H2O2, and superoxide production was not detected during the reaction. Other low molecular weight thiols, including cysteine, dithiothreitol, N-acetylcysteine, and cysteamine, were substrates for the oxidase; 2-mercaptoethanol, reductively denatured ribonuclease A, and chymotrypsinogen A were not substrates. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed one band corresponding to 70 kDa; gel filtration on a Sephacryl column produced a single elution of activity with a protein corresponding to 120 kDa, indicating that the functional form is a dimer. On a high-pressure gel permeation column the protein eluted at 70 kDa under dilute conditions but at greater than 200 kDa at high concentrations, indicating that the protein also aggregates into larger multimers. Activity was inhibited by copper chelators, L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid (acivicin), H2O2, and N-ethylmaleimide, suggesting the presence of copper and a sulfhydryl group at the active site. Following treatment with metal chelators, enzyme activity was reconstituted with CuSO4, but not with FeSO4. The purified enzyme contained 1 mol copper per subunit which was undetectable by electron paramagnetic resonance, suggesting that the copper is in a binuclear complex.     

Expression of type X collagen mRNA levels in embryonic chick sternum during development

Embryonic chick sternum cartilage exhibits profound spatial and temporal changes in Type X collagen biosynthesis during development. Production of this collagen is confined to the presumptive calcification region and its expression is not acquired until stage 43. To examine the mechanisms responsible for regulation of developmental changes in biosynthetic expression of Type X collagen, we determined the levels of translatable Type X procollagen mRNA employing a cell-free translation system. We found that mRNA capable of directing Type X collagen synthesis was present exclusively in cartilage destined to undergo calcification and that its levels were nearly equivalent at all stages of development. These findings suggest that expression of Type X collagen in embryonic chick sternum is determined at the translational level.