Redox regulation of diabetic nephropathy
Abstract
Diabetes is a disease with many microvascular complications. Diabetic nephropathy is one of the severe complications. We hypothesized that (1) glutathione (GSH) regulation would be altered during diabetes; (2) oxidative stress results in mitochondrial dysfunction; (3) proximal tubular cells are more susceptible to oxidant challenge in diabetes. We used a STZ-diabetic rat model. Rats with a blood glucose level > 250 mg/dl were regarded as diabetic and were kept for 1 month or 3 months. Proteinuria and albuminuria were significantly increased as early as 1-month in STZ-diabetic rats, and were more severe in 3-month diabetic rats. Mesangial expansion was detected as early as 1-month in STZ-diabetic rats, and was more profound in 3-month STZ-diabetic rats. Renal mitochondria from 1-month STZ-diabetic rats had a significant increase in complex II respiratory function. Renal mitochondria from 1-month STZ-diabetic rats were much more susceptible to the oxidants tert-butyl hydroperoxide (tBH) and methyl vinyl ketone (MVK). Renal homogenate and renal mitochondrial GSH content were significantly increased in 1-month diabetic rats versus control rats. Activity of glutathione peroxidase and glutathione S-transferase in renal mitochondria from 1-month STZ-diabetic rats were significantly increased versus control rats. Proximal tubular (PT) cells from 1-month diabetic rats had a much higher basal level of ROS, and an elevated mitochondrial membrane potential versus control. Cytosolic and mitochondrial GSH contents were significantly higher in PT cells from 1-month STZ-diabetic rats versus control. Antimycin A (AA) caused an increase in ROS in PT cells from both 1-month diabetic rats and control rats, and N-acetylcysteine (NAC) and catalase protected against this increase in ROS. tBH and MVK caused a much greater increase in ROS production in PT cells from 1-month diabetic rats. tBH and an additional 300 mg/dl glucose in the medium caused a greater decrease in mitochondrial membrane potential in PT cells from 1-month diabetic rats. tBH and MVK altered the morphology of PT cells from both 1-month control and diabetic rats, and NAC pretreatment completely prevented the change in cell morphology except with 200 μM tBH treatment. MVK caused higher apoptosis in PT cells from 1-month diabetic rats. We conclude that renal mitochondrial GSH content and mitochondrial GSH content of PT cells are higher in 1-month diabetic rats. Renal mitochondrial respiratory function is increased in 1-month diabetic rats. PT cells from 1-month diabetic rats exist in a high-ROS environment and maintain a higher mitochondrial membrane potential. Oxidant challenges produce more damage to renal mitochondria and PT cells in 1-month diabetic rats. The higher mitochondrial GSH level may be the results of a higher concentration gradient between cytoplasm and mitochondria, and/or increased activities of potential GSH carriers located in the inner mitochondria membrane. Even though GSH content increased in diabetic status, renal mitochondria and proximal tubular cells still were more susceptible to oxidant challenge. There must be more ROS or GSSG in the cells or damage to other antioxidant systems, which led to decreased capacity of antioxidants in diabetic status. The protection by NAC holds promise as a future therapy to delay the development of diabetic nephropathy.
Recommended Citation
Qing Zhong,
"Redox regulation of diabetic nephropathy"
(January 1, 2009).
ETD Collection for Wayne State University.
Paper AAI3341581.
http://digitalcommons.wayne.edu/dissertations/AAI3341581
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