Intracellular distribution of thiols and disulfides: assay of mitochondrial glutathione transport

Mitochondrial glutathione transport: physiological, pathological and toxicological implications

Although most cellular glutathione (GSH) is in the cytoplasm, a distinctly regulated pool is present in mitochondria. Inasmuch as GSH synthesis is primarily restricted to the cytoplasm, the mitochondrial pool must derive from transport of cytoplasmic GSH across the mitochondrial inner membrane. Early studies in liver mitochondria primarily focused on the relationship between GSH status and membrane permeability and energetics. Because GSH is an anion at physiological pH, this suggested that some of the organic anion carriers present in the inner membrane could function in GSH transport. Indeed, studies by Lash and colleagues in isolated mitochondria from rat kidney showed that most of the transport (>80%) in that tissue could be accounted for by function of the dicarboxylate carrier (DIC, Slc25a10) and the oxoglutarate carrier (OGC, Slc25a11), which mediate electroneutral exchange of dicarboxylates for inorganic phosphate and 2-oxoglutarate for other dicarboxylates, respectively. The identity and function of specific carrier proteins in other tissues is less certain, although the OGC is expressed in heart, liver, and brain and the DIC is expressed in liver and kidney. An additional carrier that transports 2-oxoglutarate, the oxodicarboxylate or oxoadipate carrier (ODC; Slc25a21), has been described in rat and human liver and its expression has a wide tissue distribution, although its potential function in GSH transport has not been investigated. Overexpression of the cDNA for the DIC and OGC in a renal proximal tubule-derived cell line, NRK-52E cells, showed that enhanced carrier expression and activity protects against oxidative stress and chemically induced apoptosis. This has implications for development of novel therapeutic approaches for treatment of human diseases and pathological states. Several conditions, such as alcoholic liver disease, cirrhosis or other chronic biliary obstructive diseases, and diabetic nephropathy, are associated with depletion or oxidation of the mitochondrial GSH pool in liver or kidney.

Role of glutathione in reproductive tract secretions on mouse preimplantation embryo development

We investigated the hypothesis that glutathione (GSH) in reproductive tract secretions (RTS) protects the preimplantation embryo from endogenous reactive oxygen species and is important for normal development during the embryo's sensitive period when it is incapable of synthesizing GSH de novo. Mice were administered buthionine sulfoximine (BSO) to inhibit GSH synthesis and decrease GSH concentration in RTS. Embryos were then allowed to develop either in vivo or in vitro in the presence of RTS and the GSH concentration of the embryos was quantified by HPLC and embryonic development was recorded. GSH concentration in RTS did not differ over the phases of the estrous cycle, but there were significant decreases in GSH concentration on Day 2 of gestation and due to BSO treatment. Embryos allowed to develop in vivo and in vitro in RTS with decreased GSH concentration did not exhibit decreased development or GSH concentration. Oocytes exposed to BSO during maturation in vivo experienced a significant decrease in GSH concentration and an increase in percent of degenerate embryos when compared with control. These data suggest that most of the GSH in RTS does not play a critical role in normal preimplantation embryo development but that GSH stored in the oocyte during maturation has an important role in subsequent embryo development. Our studies do not exclude the possibility that GSH in RTS plays an important role in protection of the preimplantation embryo during exposure to some toxicants.

Tumor cytotoxicity by endothelial cells. Impairment of the mitochondrial system for glutathione uptake in mouse B16 melanoma cells that survive after in vitro interaction with the hepatic sinusoidal endothelium

High GSH content associates with high metastatic activity in B16-F10 melanoma cells cultured to low density (LD B16M). GSH homeostasis was investigated in LD B16M cells that survive after adhesion to the hepatic sinusoidal endothelium (HSE). Invasive B16M (iB16M) cells were isolated using anti-Met-72 monoclonal antibodies and flow cytometry-coupled cell sorting. HSE-derived NO and H(2)O(2) caused GSH depletion and a decrease in gamma-glutamylcysteine synthetase activity in iB16M cells. Overexpression of gamma-glutamylcysteine synthetase heavy and light subunits led to a rapid recovery of cytosolic GSH, whereas mitochondrial GSH (mtGSH) further decreased during the first 18 h of culture. NO and H(2)O(2) damaged the mitochondrial system for GSH uptake (rates in iB16M were approximately 75% lower than in LD B16M cells). iB16M cells also showed a decreased activity of mitochondrial complexes II, III, and IV, less O(2) consumption, lower ATP levels, higher O(2) and H(2)O(2) production, and lower mitochondrial membrane potential. In vitro growing iB16M cells maintained high viability (>98%) and repaired HSE-induced mitochondrial damages within 48 h. However, iB16M cells with low mtGSH levels were highly susceptible to TNF-alpha-induced oxidative stress and death. Therefore depletion of mtGSH levels may represent a critical target to challenge survival of invasive cancer cells.

In vivo monitoring of hepatic glutathione in anesthetized rats by 13C NMR

A method for in vivo (13)C NMR monitoring of hepatic glutathione (GSH) in intact, anesthetized rats has been developed. Studies were conducted using a triple-tuned, surgically implanted surface coil designed for this animal model. The coil permitted complete decoupling and sufficient resolution in the (13)C NMR spectrum to monitor the time course of hepatic (13)C-metabolites of intravenously administered 2-(13)C-glycine, particularly GSH at 44.2 ppm and serine signals at 61.1 and 57.2 ppm, respectively. It further allowed concomitant monitoring of high-energy phosphagens and intracellular pH by (31)P NMR. To confirm in vivo NMR peak assignments, we compared high-resolution 2D (1)H[(13)C] heteronuclear multiple quantum coherence and 1D (13)C spectra of hepatic perchloric acid extracts to those of authentic standards. The fractional isotopic enrichment of hepatic (13)C-glycine increased exponentially at a rate of 1.68 h(-1) and reached its plateau level of 81% in 2 h. The (13)C fractional isotopic enrichment of GSH increased exponentially at a rate of 0.316 h(-1) and reached 55% after 4 h of 2-(13)C-glycine infusion, but without achieving a plateau. To confirm that the resonance at 44.2 ppm resulted from GSH, a rat was given an intravenous dose of 2-oxothiazolidine-4-carboxylic acid (OTC), a cysteine precursor that increases intracellular GSH. As expected, with OTC administration the hepatic (13)C GSH-to-glycine peak area increased more than sevenfold.

The antioxidants of legume nodule mitochondria

The mitochondria of legume root nodules are critical to sustain the energy-intensive process of nitrogen fixation. They also generate reactive oxygen species at high rates and thus require the protection of antioxidant enzymes and metabolites. We show here that highly purified mitochondria from bean nodules (Phaseolus vulgaris L. cv. Contender x Rhizobium leguminosarum bv. phaseoli strain 3622) contain ascorbate peroxidase primarily in the inner membrane (with lesser amounts detected occasionally in the matrix), guaiacol peroxidases in the outer membrane and matrix, and manganese superoxide dismutase (MnSOD) and an ascorbate-regenerating system in the matrix. This regenerating system relies on homoglutathione (instead of glutathione) and pyridine nucleotides as electron donors and involves the enzymes monodehydroascorbate reductase, dehydroascorbate reductase, and homoglutathione reductase. Homoglutathione is synthesized in the cytosol and taken up by the mitochondria and bacteroids. Although bacteroids synthesize glutathione, it is not exported to the plant in significant amounts. We propose a model for the detoxification of peroxides in nodule mitochondria in which membrane-bound ascorbate peroxidase scavenges the peroxide formed by the electron transport chain using ascorbate provided by L-galactono-1,4-lactone dehydrogenase in the inner membrane. The resulting monodehydroascorbate and dehydroascorbate can be recycled in the matrix or cytosol. In the matrix, the peroxides formed by oxidative reactions and by MnSOD may be scavenged by specific isozymes of guaiacol peroxidase, ascorbate peroxidase, and catalase.

Measurement of glutathione transport

This unit provides methods for analyzing uptake in rat kidney proximal tubule cells and rat kidney cortical mitochondria, preparation of proximal tubule cells and cortical mitochondria, and HPLC analysis of glutathione and related compounds.

Mitochondrial glutathione depletion by glutamine in growing tumor cells

The effect of L-glutamine (Gln) on mitochondrial glutathione (mtGSH) levels in tumor cells was studied in vivo in Ehrlich ascites tumor (EAT)-bearing mice. Tumor growth was similar in mice fed a Gln-enriched diet (GED; where 30% of the total dietary nitrogen was from Gln) or a nutritionally complete elemental diet (SD). As compared with non-tumor-bearing mice, tumor growth caused a decrease of blood Gln levels in mice fed an SD but not in those fed a GED. Tumor cells in mice fed a GED showed higher glutaminase and lower Gln synthetase activities than did cells isolated from mice fed an SD. Cytosolic glutamate concentration was 2-fold higher in tumor cells from mice fed a GED ( approximately 4 mM) than in those fed an SD. This increase in glutamate content inhibited GSH uptake by tumor mitochondria and led to a selective depletion of mitochondrial GSH (mtGSH) content (not found in mitochondria of normal cells such as lymphocytes or hepatocytes) to approximately 57% of the level found in tumor mitochondria of mice fed an SD. In tumor cells of mice fed a GED, 6-diazo-5-norleucine- or L-glutamate-gamma-hydrazine-induced inhibition of glutaminase activity decreased cytosolic glutamate content and restored GSH uptake by mitochondria to the rate found in EAT cells of mice fed an SD. The partial loss of mtGSH elicited by Gln did not affect generation of reactive oxygen intermediates (ROIs) or mitochondrial functions (e.g., intracellular peroxide levels, O(2)(-)(*) generation, mitochondrial membrane potential, mitochondrial size, adenosine triphosphate and adenosine diphosphate contents, and oxygen consumption were found similar in tumor cells isolated from mice fed an SD or a GED); however, mitochondrial production ROIs upon TNF-alpha stimulation was increased. Our results demonstrate that glutamate derived from glutamine promotes an inhibition of GSH transport into mitochondria, which may render tumor cells more susceptible to oxidative stress-induced mediators.