The roles of NADPH-oxidase and nNOS for the increased oxidative stress and the oxygen consumption in the diabetic kidney.
BACKGROUND
Sustained hyperglycaemia induces increased renal oxygen consumption resulting in reduced oxygen availability in the diabetic kidney. We investigated the roles of the nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase and the neuronal nitric oxide synthase (nNOS) for the increased oxygen consumption in streptozotocin-diabetic rats.


METHODS
Oxygen consumption was measured in isolated proximal tubular cells (PTC) from streptozotocin-induced diabetic rats (n = 7-9 per group) with and without chronic treatment with apocynin, a NADPH-oxidase inhibitor, or S-methyl-L-thiocitrulline (SMTC), a selective nNOS inhibitor, or a combination of the two and the results were compared to normoglycaemic controls (n = 10). Oxidative stress was estimated from thiobarbituric acid reactive substances and protein expression measured by Western blot.


RESULTS
Proximal tubular cells from untreated diabetic rats had increased oxygen consumption compared to controls (40.6 +/- 7.9 versus 10.9 +/- 2.0 nmol/mg protein/min). All treatments reduced the diabetes-induced increase in oxygen consumption (apocynin 10.5 +/- 1.7, SMTC 19.7 +/- 3.0 and apocynin + SMTC 21.6 +/- 3.6 nmol/mg protein/min). Neither apocynin nor SMTC had any effect on the oxygen consumption in cells pre-incubated with ouabain, an inhibitor of active electrolyte transport. Oxidative stress was elevated in the diabetic kidney and inhibited by all treatments. The increased oxygen consumption by diabetic proximal tubular cells correlated with increased protein expressions of p47(phox) and nNOS and the treatments prevented these increases.


CONCLUSIONS
Diabetes induces oxidative stress, which increases oxygen consumption in proximal tubular cells. Inhibition of either NADPH-oxidase or nNOS prevented the increased oxygen consumption. The effect of blocking both these enzymes was less than additive suggesting overlapping pathways which warrant further studies.
Edlund
Jenny
J
Department of Medical Cell Biology, Division of Integrative Physiology, Uppsala University, Uppsala, Sweden.
Fasching
Angelica
A
Liss
Per
P
Hansell
Peter
P
Palm
Fredrik
F
D000098:Acetophenones / Q000494:pharmacology; D000818:Animals; D002956:Citrulline / Q000031:analogs & derivatives / Q000494:pharmacology; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D003928:Diabetic Nephropathies / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism; D015227:Lipid Peroxidation / Q000187:drug effects; D008297:Male; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000502:physiology*; D052248:Nitric Oxide Synthase Type I / Q000037:antagonists & inhibitors / Q000502:physiology*; D018384:Oxidative Stress / Q000187:drug effects*; D010101:Oxygen Consumption / Q000187:drug effects*; D051381:Rats; D011920:Rats, Inbred WF; D013890:Thiourea / Q000031:analogs & derivatives / Q000494:pharmacology
D000098:Acetophenones; D002956:Citrulline; C056165:acetovanillone; D052248:Nitric Oxide Synthase Type I; D019255:NADPH Oxidases; D013890:Thiourea; C086717:S-methylthiocitrulline