Geeta Kala

The MRP2/cMOAT transporter and arsenic-glutathione complex formation are required for biliary excretion of arsenic

Worldwide, millions of people are exposed to arsenic in drinking water that exceeds the World Health Organization standard of 10 μg/liter by as much as 50–300-fold, yet little is known about the molecular basis for arsenic excretion. Here we show that transport of arsenic into bile depends on the MRP2/cMOAT transporter and that glutathione is obligatory for such transport. Using reversed phase liquid chromatography/mass spectrometry, we demonstrate that two arsenic-glutathione complexes not previously identified in vivo, arsenic triglutathione and methylarsenic diglutathione, account for most of the arsenic in the bile. The structure of the compounds was also confirmed by nuclear magnetic resonance spectroscopy. Our findings may help explain the increased susceptibility of malnourished human populations to arsenic.

Neuronal-astrocytic and cytosolic-mitochondrial metabolite trafficking during brain activation, hyperammonemia and energy deprivation.

A novel concept is described, according to which both neurons and astrocytes are capable of metabolizing glucose all the way to CO(2) and water, but in addition interact metabolically in a process generating glutamate from glucose, and subsequently, metabolizing excess glutamate to CO(2) and water Hertz, L., Dringen, R., Schousboe, A., Robinson, S.R., 1999. Astrocytes: Glutamate producers for neurons (Journal of Neuroscience Research 57, 417-428). The proposed metabolic degradation of glucose via glutamate serves the purpose of adjusting transmitter pools of glutamate to the demands for glutamatergic transmission, and it must account for a major fraction of glucose utilization. Evidence in favor of this concept is presented and a multitude of in vivo data are interpreted in the context of metabolic trafficking between neurons and astrocytes. In addition, intracellular trafficking occurs between cytosol and mitochondria during synthesis of transmitter glutamate, partly explaining a robust quantitative correlation between glutamine synthesis, as a measure of release of transmitter glutamate, and glucose utilization, reported by several authors. Both intracellular and intercellular metabolic trafficking may be affected during pathological conditions, as evidenced by effects of hyperammonemia (mimicking hepatic encephalopathy) and energy deprivation (mimicking stroke). It is suggested that neuronal-astrocytic interactions may also be impaired during degenerative dementing diseases.

Reproductive defects in γ-glutamyl transpeptidase-deficient mice

Mice deficient in gamma-glutamyl transpeptidase (GGT) are growth retarded as a result of cysteine deficiency secondary to excessive glutathione excretion in urine and display coat color defects and cataracts. Although GGT is widely expressed throughout the mouse reproductive axis, little is known about its role in reproduction. Here, we present an analysis of the reproductive phenotypes of GGT-deficient mice. Mutant male mice have reduced testis and seminal vesicle size and suppressed serum insulin-like growth factor I and FSH levels and are infertile. Although these mice are severely oligospermic, histological analysis of testes reveals grossly normal stages of spermatogenesis, including late stage spermatids, but the tubule diameter is reduced. GGT-deficient female mice are also hypogonadal and infertile. At 6 weeks of age, the ovaries of mutant mice are histologically indistinguishable from those of its wild-type counterpart. However, the absence of antral follicles and corpora lutea and follicular degeneration are apparent by 11-13 weeks. In addition, immature female mutant mice (at 21-23 days) are insensitive to exogenous gonadotropin administration and fail to superovulate, suggesting an intraovarian defect. Consistent with these mutant phenotypes, HPLC analysis of adult mutant testes and ovaries showed a reduction in intracellular cysteine levels. Administration of N-acetylcysteine in the drinking water beginning on day 21 to mutant mice for 2 weeks restored testis, seminal vesicle, and ovary sizes to values comparable to those in wild-type mice. Furthermore, N-acetylcysteine-fed (continuously) mutant male and female mice were fertile and produced normal numbers of offspring when mated to wild-type control mice. These results demonstrate that GGT itself is not necessary for reproductive function. However, GGT plays an important role in cysteine homeostasis within the mouse reproductive axis.

Reproductive Defects in γ-Glutamyl Transpeptidase-Deficient Mice1

Mice deficient in g-glutamyl transpeptidase (GGT) are growth retarded as a result of cysteine deficiency secondary to excessive glutathione excretion in urine and display coat color defects and cataracts. Although GGT is widely expressed throughout the mouse reproductive axis, little is known about its role in reproduction. Here, we present an analysis of the reproductive phenotypes of GGT-deficient mice. Mutant male mice have reduced testis and seminal vesicle size and suppressed serum insulin-like growth factor I and FSH levels and are infertile. Although these mice are severely oligospermic, histological analysis of testes reveals grossly normal stages of spermatogenesis, including late stage spermatids, but the tubule diameter is reduced. GGT-deficient female mice are also hypogonadal and infertile. At 6 weeks of age, the ovaries of mutant mice are histologically indistinguishable from those of its wild-type counterpart. However, the absence of antral follicles and corpora lutea and follicular degeneration are apparent by 11‐13 weeks. In addition, immature female mutant mice (at 21‐23 days) are insensitive to exogenous gonadotropin administration and fail to superovulate, suggesting an intraovarian defect. Consistent with these mutant phenotypes, HPLC analysis of adult mutant testes and ovaries showed a reduction in intracellular cysteine levels. Administration of N-acetylcysteine in the drinking water beginning on day 21 to mutant mice for 2 weeks restored testis, seminal vesicle, and ovary sizes to values comparable to those in wild-type mice. Furthermore, N-acetylcysteine-fed (continuously) mutant male and female mice were fertile and produced normal numbers of offspring when mated to wild-type control mice. These results demonstrate that GGT itself is not necessary for reproductive function. However, GGT plays an important role in cysteine homeostasis within the mouse reproductive axis. (Endocrinology 141: 4270 ‐ 4277, 2000)

Accumulation of DNA damage in the organs of mice deficient in γ- glutamyltranspeptidase

Abstract We have used a differential alkaline single cell gel electrophoresis assay of DNA (“omet assay” at pH 13 and 12.3) to evaluate DNA damage as a function of age in mice with an inherited defect in gluthathione (GSH) metabolism. The mice are homozygous null for γ-glutamyltranspeptidase (GGT), the enzyme responsible for initiating the catabolism of GSH, and paradoxically have reduced levels of GSH and cysteine in many organs. We found an accumulation of DNA damage in lung, liver and kidney in these mice as a function of age. The largest differences were in assays run at pH 13, suggesting that the accumulation of apurinic/apryrimidinic (AP) sites and oxidative damage of DNA was largely responsible. In contrast, little if any accumulation of these lesions was detected in wild-type mice. Although these findings do not allow a precise analysis of the molecular basis of damage accumulation in GGT-deficient mice, they implicate low GSH and cysteine levels as a cause of accumulative DNA damage in the intact mammal.

Oxygen-Induced Pulmonary Injury in g-Glutamyl Transpeptidase-Deficient Mice

We used mice with a targeted disruption in g-glutamyl transpeptidase (GGT-deficient mice) to study the role of glutathione (GSH) in protection against oxygen-induced lung injury. These mice had reduced levels of lung GSH and restricted ability to synthesize GSH because of low levels of cysteine. When GGT-deficient mice were exposed to 80% oxygen, they developed diffuse pulmonary injury and died within eight days. Ten of 12 wild-type mice were alive after 18 days. Administration of N-acetylcysteine (NAC) to GGT-deficient mice corrected GSH values and prevented the development of severe pulmonary injury and death. Oxygen exposure induced an increase in lung GSH levels in both wild-type and GGT-deficient mice, but induced levels in the mutant mice were <50% of those in wild-type mice. Cysteine levels were approximately 50-fold lower than GSH levels the lungs of both wild-type and GGT-deficient mice. Levels of lung RNA coding for the heavy subunit of g-glutamyl cysteine synthetase rose three- to fourfold after oxygen exposure in both wild-type and GGT-deficient mice. In contrast, oxygen exposure failed to provoke increases in glutathione synthetase, glutathione peroxidase, glutaredoxin, or thioredoxin.

Erratum to “Accumulation of DNA damage in the organs of mice deficient in γ-glutamyltranspeptidase” [Mutat. Res. 447 (2000) 305–316] ☆

Erratum Erratum to “Accumulation of DNA damage in the organs of mice deficient in g-glutamyltranspeptidase” [Mutat. Res. 447 (2000) 305–316] Emilio Rojas a,∗, Mahara Valverde a, Subbarao V. Kala b, Geeta Kala b, Michael W. Lieberman b a UNAM, Departmento de Genetica y Toxicoloǵa Ambiental, Instituto de Investigaciones Biomedicas, P.O. Box 70228, Ciudad Universitaria 04510, Mexico, D.F., Mexico b Department of Pathology, Baylor College of Medicine, Houston, TX 77030, USA

Response from lieberman and colleagues

Respond on comments on Liebermans article: Cyclosiloxanes Produce Fatal Liver and Lung Damage in Mice. Environ Health Perspect 107:161-165