Effect of sulfur-containing compounds on experimental diabetes. X. The transport of SH and S-S compounds into red blood cells

Abstract

The transport of glutathione (GSH) and 2-mercaptopropionylglycine (MPG) was studied in vitro with red blood cells of normal and alloxan diabetic rats. 1) About 30% of MPG was incorporated into red blood cells. The amount equivalent to one-tenth the incorporated MPG was trapped as oxidized MPG in red blood cells but not the oxidized MPG itself. 2) MPG incorporated into red blood cells and oxidized MPG formed in red blood cells were rapidly released into the medium (60% disappeared in 5 min). 3) Only a small amount of GSH and oxidized GSH were incorporated into red blood cells. 4) The amount of non-protein thiol and disulfide in red blood cells was larger in normal than in diabetic rats but MPG uptake into red blood cells was larger in alloxan diabetic rats : (MPG 0.370±0.008, oxidized MPG 0.026±0.002) than in normal ones (MPG : 0.357±0.009, oxidized MPG 0.019±0.003). 5) Uptake of MPG into red blood cells increased when SH groups of the RBC membrane were inhibited by SH inhibitors (NEM, PCMB, PCMBS). 6) Treatment of red blood cells with insulin showed no effect on transport of MPG into normal red blood cells but decreased the transport into the blood cells of diabetic rats to the normal level. The present results indicated that the amount of MPG incorporated into red blood cells was larger in alloxan diabetic rats than in normal rats and that it increased when normal red blood cells was inhibited by SH inhibitors. This suggests that SH groups in the epithelial layer of red blood cell membrane have previously been inhibited in diabetic rats. Since it is known that transport of glucose into red blood cells is decreased when SH groups of the cell membrane are inhibited by SH inhibitors, it seems that SH groups of RBC have previously been inhibited and utilization of sugar has been influenced in diabetic state.