No abstract

The mechanisms leading to hepatic venoocclusive dis-Little is known about the causal mechanisms of heease (HVOD) remain largely unknown. Azathioprine and patic venoocclusive disease (HVOD). There has been monocrotaline were studied as part of a series of studies speculation as to whether hepatocytes or endothelial looking at a variety of toxins that induce HVOD to find cells might be the initial target, 1-4 but with little evicommon features that might be of pathogenic signifi-dence to support any of the contentions. Biopsy and cance. In a previous study, dacarbazine showed selective autopsy material demonstrate damage to both hepatoin vitro toxicity to sinusoidal endothelial cells (SEC) cytes or sinusoidal endothelial cells (SEC) early on. 1,2 compared with hepatocytes and a key role for SEC gluta-However morphology does not allow continuous monithione (GSH) was demonstrated. Murine SEC and hepatoring of changes and does not provide information on tocytes were isolated and studied in culture. Azathiosublethal damage that might lead to other events. Thus prine and monocrotaline were found to be selectively more toxic to SEC than to hepatocytes. The relative re-it is currently unknown why a variety of insults lead sistance of hepatocytes to azathioprine was due to en-to HVOD rather than to another manifestation of liver hanced GSH defense: hepatocytes exposed to azathio-toxicity. prine maintained intracellular GSH levels better thanOur approach to HVOD has been to study a number SEC, particularly when supplemental GSH precursors of chemically diverse compounds to search for common were added, and hepatocyte resistance was completely characteristics in an in vitro model. The first compound overcome by depletion of intracellular GSH. In contrast, studied, dacarbazine, demonstrated selective toxicity monocrotaline toxicity in hepatocytes was largely unaf-to SEC rather than to hepatocytes. 5 These studies also fected by depletion of GSH, which suggests that selectivdemonstrated that glutathione (GSH) plays a major ity of monocrotaline for SEC may be attributable to difrole in dacarbazine detoxification in the SEC. Based ferences in metabolic activation. Both compounds are on these findings, we have postulated that SEC GSH detoxified by GSH in SEC, as demonstrated by enhanced toxicity in the presence of buthionine sulfoximine (BSO) status may be a major determinant of susceptibility to and attenuation of toxicity with exogenous GSH. SEC this toxicity. In the current study, the characteristics of GSH levels were more than 70% to 80% depleted by mo-azathioprine and monocrotaline were studied in vitro. nocrotaline and azathioprine, respectively, before cell Azathioprine has been linked to multiple different death. Azathioprine and monocrotaline are selectively liver lesions in patients on long-term immunosupprestoxic to SEC; the mechanism of toxicity in the SEC may sion after kidney or liver transplantation: HVOD, sinube caused by profound GSH depletion. (HEPATOLOGY soidal dilatation, sinusoidal fibrosis, peliosis hepati...

Information on the origin of brain glutathione and the possibility of its transport from blood to brain is limited. We found a substantial uptake of f3Slabeled glutathione by the rat brain using the carotid artery injection technique. The brain uptake index of glutathione with and without an irreversible gammaglutamyl transpeptidase inhibitor, acivicin, was similar. No sign t differences in the regional uptake of labeled giutathione were found in rats pretreated with acivicin. The brain uptake index of tracer glutathione was similar to that of cysteine tracer and was lower than that of phenylalanine. The transport of oxidized glutathione (glutathione disulfide) across the blood-brain barrier was not significantly different from that of sucrose, an impermeable marker. Brain radioactivity 15 s after carotid artery injection of labeled glutathione to rats pretreated with acivicin was predominantly in the form of giutathione. The in vivo giutathione uptake was saturable with an apparent K., of 5.84 mM. Amino acids, amino acid analogues, and other compounds Icysteine, phenylalanine, glutathione disulfide, gamma-glutamylglutamate, gamma-glutamyl p-nitroanilide, 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid (BCH)] did not affect glutathione transport. Our data suggest that glutathione is transported across the blood-brain barrier by a saturable and specific mechanism. (J. Clin.-Invest. 1990.

We have shown previously that plating primary cultures of rat hepatocytes under low density, which stimulates hepatocytes to shift from the G 0 to the G 1 phase of the cell cycle, resulted in increased levels of glutathione (GSH) and cysteine, and increased activity of ␥-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in GSH synthesis (Lu et al., Am. J. Physiol. 1992;263:C1181-C1189). In the current work we examined changes in GSH homeostasis after two-thirds partial hepatectomy (PH). Male SpragueDawley rats underwent two-thirds PH or sham operation. GSH, oxidized glutathione (GSSG), cysteine, GSH efflux, DNA synthesis, changes in GCS subunit messenger RNA (mRNA), and protein levels were measured 12 and 24 hours after PH. Both liver GSH and cysteine levels were doubled at 12 hours and remained elevated at 24 hours after PH. GSSG levels also increased, but the ratio of GSH to GSSG levels remained unchanged. The increase in GSH and cysteine levels preceded the increase in DNA synthesis. Sinusoidal GSH efflux was unchanged after two-thirds PH, but biliary GSH efflux decreased. However, total GSH efflux was minimally altered after two-thirds PH. The increase in GSH can be largely accounted for by the increase in both cysteine availability and the activity of GCS. The steadystate mRNA and protein levels of the GCS heavy subunit were increased at 12 hours after PH. The mRNA level of the GCS light subunit was unchanged. In summary, early in the course of liver regeneration the steady-state hepatic GSH levels double because of an increase in the biosynthesis of GSH. (HEPATOLOGY 1998;27:147-153.)