Effect of cysteine dosage on erythrocyte glutathione synthesis rate in a patient with cystathionine beta synthase deficiency

Reduced Production of Hydrogen Sulfide and Sulfane Sulfur Due to Low Cystathionine β-Synthase Levels in Brain Astrocytes of Stroke-Prone Spontaneously Hypertensive Rats

Stroke-prone spontaneously hypertensive rats (SHRSP/Izm; SHRSP) develop severe hypertension and die of cerebral stroke. However, the genetic mechanisms underlying their stroke susceptibility have not been clarified yet. In this study, we used astrocytes from the newborn brain cortex of spontaneously hypertensive rats (SHR/Izm; SHR) and SHRSP to find the difference of genetic characteristics. Astrocytes are known to have functions of vasodilation and nutrient uptake for neurons in the brain. The continuous generation of hydrogen peroxide (H₂O₂) dose-dependently causes cell death in astrocytes, and SHRSP was more vulnerable than SHR. We found that the total thiols decreased in SHRSP astrocytes but the total glutathione (GSH) did not change. Hydrogen sulfide (H₂S), which is known to protect cells through anti-oxidant and vasodilatory effects, is produced by cystathionine β-synthase (CBS) in astrocytes. We found that H₂S production was significantly decreased in SHRSP as compared to SHR. This was caused by the decreasing expression of mRNA, protein and enzyme activity of CBS in astrocytes. We also found that astrocyte cell death from oxidative stress could be prevented by GYY4137 H₂S donor. H₂S is also known to cause protein S-sulfhydration to modify enzyme activity. Sulfane sulfur in astrocytes was significantly lower in SHRSP and decreased by CBS inhibitor. We showed that astrocytes in SHRSP vulnerable to oxidative stress may be caused by reduction of H₂S through lower expression and activity of CBS.

Activation of transsulfuration pathway by salvianolic acid a treatment: a homocysteine-lowering approach with beneficial effects on redox homeostasis in high-fat diet-induced hyperlipidemic rats

Background

Elevated homocysteine is a cardiovascular risk factor in hyperlipidemia. Transsulfuration pathway provides an endogenous pathway for homocysteine conversion to antioxidant glutathione (GSH). Salvianolic acid A (Sal A) contains two molecules of caffeic acid and one molecule of danshensu that is capable of enhancing homocysteine transsulfuration, which led to the hypothesis that Sal A has activatory effect on transsulfuration pathway and this effect may have beneficial effects on both homocysteine and redox status in hyperlipidemia.

Methods and results

To test this hypothesis, we developed a rat model of hyperlipidemia induced by high-fat diet for 16 weeks, during which rats were treated with 1 mg/kg salvianolic acid A (Sal A) for the final 4 weeks. Activities of key enzymes and metabolite profiling in the transsulfuration pathway revealed that hyperlipidemia led to elevated plasma homocysteine levels after 16-week dietary treatment, which was associated with reduced activities of homocysteine transsulfuration enzymes, cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE). The impaired transsulfuration pathway prevented homocysteine transsulfuration to cysteine, resulting in cysteine deficiency and subsequent reduction in GSH pool size. The redox status was altered in the setting of hyperlipidemia as indicated by GSH/GSSG ratio. Sal A treatment increased hepatic CBS and CSE activities, which was associated with reduced accumulation in circulating homocysteine levels and attenuated decline in hepatic cysteine content in hyperlipidemic rats. Sal A also led to an increase in GSH pool size, which subsequently caused a restored GSH/GSSG ratio. The activatory effect of Sal A on CBS was also observed in normal rats and in in vitro experiment.

Conclusion

Our results suggest that activation of transsulfuration pathway by Sal A is a promising homocysteine-lowering approach that has beneficial effects on redox homeostasis in hyperlipidemic settings.

Erythrocyte glutathione concentration and production during hyperinsulinemia, hyperglycemia, and endotoxemia in healthy humans

In diabetes mellitus and sepsis, low erythrocyte glutathione (GSH) concentrations are found. Whether this is caused by lowered GSH production has not been clarified. To obtain insight in the relationship between erythrocyte GSH concentrations and GSH production, GSH kinetics were measured in healthy male volunteers during 4 different clamps (low-dose or medium-dose insulin [100 or 400 pmol/L] and euglycemia or hyperglycemia [5 or 12 mmol/L]) in a control setting (n = 6; all 4 clamps in the same subject) or after systemic administration of lipopolysaccharide (to mimic sepsis) (4 groups of n = 6; each clamp in a different subject). Hyperinsulinemia decreased erythrocyte GSH concentration (P = .042), but did not affect fractional synthetic rate (FSR) of GSH. Hyperglycemia did not affect erythrocyte GSH concentration, but decreased FSR of GSH (P = .025). Lipopolysaccharide decreased erythrocyte GSH concentration (P < .001), but increased FSR of erythrocyte GSH (P = .035). Depending on the metabolic circumstances, we found either stable GSH concentrations with lower production rates or decreased levels with either no change or an increase in production rate. Based upon these data, it seems inappropriate to infer conclusions about changes in synthesis rate of GSH from changes in its concentration.

Vitamin B-6 restriction tends to reduce the red blood cell glutathione synthesis rate without affecting red blood cell or plasma glutathione concentrations in healthy men and women

BACKGROUND

Glutathione plays various protective roles in the human body. Vitamin B-6 as pyridoxal-5'-phosphate (PLP) is required as the coenzyme in the formation of glutathione precursors. Despite this obligatory role of PLP, previous studies from this laboratory showed that vitamin B-6 deficiency caused elevated glutathione concentrations in rat liver and human plasma.

OBJECTIVE

Our aim was to determine the effect of marginal vitamin B-6 deficiency (plasma PLP 20-30 nmol/L) on the rate of red blood cell (RBC) glutathione synthesis.

DESIGN

We measured plasma and RBC glutathione concentrations and the fractional and absolute synthesis rates of RBC glutathione using the stable-isotope-labeled glutathione precursor [1,2-(13)C(2)]glycine in 13 healthy volunteers aged 21-39 y.

RESULTS

Dietary vitamin B-6 restriction did not significantly affect the glutathione concentration in plasma (6.9 +/- 1.9 compared with 6.7 +/- 1.1 micromol/L) or RBCs (2068 +/- 50 compared with 2117 +/- 48 micromol/L). For RBC glutathione, the mean fractional synthesis rates were 54 +/- 5%/d and 43 +/- 4%/d (P = 0.10), and the absolute synthesis rates were 1116 +/- 100 and 916 +/- 92 micromol . L(-1) . d(-1) (P = 0.14) before and after vitamin B-6 restriction, respectively.

CONCLUSIONS

Marginal vitamin B-6 deficiency tended to decrease mean RBC glutathione synthesis with no effect on RBC glutathione concentration, but the responses varied widely among individuals. Because the cysteine concentration in plasma and RBC did not change during vitamin B-6 restriction, we conclude that the effects of marginal vitamin B-6 deficiency on glutathione synthesis are not caused by altered precursor concentrations.