Increased superoxide production in hypertensive patients with diabetes mellitus: role of nitric oxide synthase.
BACKGROUND
Hypertension and diabetes are important independent risk factors for increased oxidative stress and increased cardiovascular risk. The combination of hypertension and diabetes results in a dramatic increase in cardiovascular risk. Enhanced oxidative stress in hypertension and diabetes is linked to decreased nitric oxide (NO) bioavailability because of its interaction with vascular superoxide (O(2)(*-)), derived predominantly from NAD(P)H-dependent oxidases. When uncoupled from essential cofactors, NO synthase III (NOS III) can also produce O(2)(*-). We studied platelet superoxide production in patients with hypertension alone and in patients with coexistent diabetes mellitus, investigating the contribution of NOS III uncoupling to platelet superoxide production.


RESULTS
Gel-filtered platelets were obtained and were stimulated with Phorbol 12-myristate 13-acetate, and O(2)(*-) production was detected using lucigenin-enhanced chemiluminescence. Superoxide production was significantly higher in patients with diabetes and hypertension (6.4 +/- 1.6 pmol/min/10(8) platelets) than in patients with hypertension (1.6 +/- 0.6 pmol/min/10(8) platelets) (P < .04). After incorporation of N(omega)-nitro-l-arginine methyl ester (L-NAME, 1 mmol/L), O(2)(*-) detection increased in 40% of patients with diabetes and hypertension and in 87% of patients with hypertension. This expected response results from L-NAME inhibition of NO production preventing NO scavenging of O(2)(*-). A reduction in O(2)(*-) production in response to L-NAME occurred in the remaining patients and indicates O(2)(*-) production by the uncoupled NOS III enzyme.


CONCLUSIONS
This study provides first published evidence that NOS III can reside in the uncoupled state in patients with hypertension and, to a greater extent, in patients with coexisting hypertension and diabetes, and that it contributes significantly to increased superoxide production in these disease states.
Dixon
Lana J
LJ
Department of Therapeutics and Pharmacology, The Queen's University of Belfast, Belfast, Northern Ireland.
Hughes
Sinead M
SM
Rooney
Keith
K
Madden
Aine
A
Devine
Adrian
A
Leahey
William
W
Henry
Welby
W
Johnston
G Dennis
GD
McVeigh
Gary E
GE
D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D001713:Biphenyl Compounds / Q000494:pharmacology; D001792:Blood Platelets / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood* / Q000150:complications; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D006973:Hypertension / Q000097:blood* / Q000150:complications; D066298:In Vitro Techniques; D008163:Luminescent Measurements; D008297:Male; D008875:Middle Aged; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D052250:Nitric Oxide Synthase Type III; D009861:Onium Compounds / Q000494:pharmacology; D018384:Oxidative Stress / Q000502:physiology*; D011796:Quinacrine / Q000494:pharmacology; D013481:Superoxides / Q000378:metabolism*
D015415:Biomarkers; D001713:Biphenyl Compounds; D004791:Enzyme Inhibitors; D009861:Onium Compounds; C031291:diphenyliodonium; D013481:Superoxides; C496314:NOS3 protein, human; D019001:Nitric Oxide Synthase; D052250:Nitric Oxide Synthase Type III; D011796:Quinacrine; D019331:NG-Nitroarginine Methyl Ester