PULSATILE STRETCH STIMULATES SUPEROXIDE PRODUCTION IN HUMAN AORTIC ENDOTHELIAL-CELLS

Background Free radicals such as superoxide and nitric oxide (NO) play a key role in the pathophysiology of atherosclerosis. Mechanical forc es such as pulsatile stretch may be involved in free radical productio n. We studied superoxide production by pulsatile stretch in human endo thelial cells. Methods and Results Human cultured aortic endothelial c ells were exposed to pulsatile stretch up to 24 hours, and superoxide production was examined. Short-term stretch for 1 hour (10% average el ongation, 50 cycles per minute) increased superoxide production Z.2-fo ld. This effect was reduced by diphenyleneiodonium chloride, an NADPH oxidase inhibitor, but not by the xanthine oxidase inhibitor oxypurino l or the cyclooxygenase inhibitor indomethacin. Prolonged stretch up t o 6 hours increased superoxide production, but it returned to near the control level after 24 hours of stretch. However. after blockade of N O production, 24 hours of stretch did increase superoxide production 2 .4-fold compared with 24 hours of stretch alone. Moreover, 24-hour str etch doubled NO synthase (NOS) (III) protein and mRNA expression. The tetrahydrobiopterin synthesis inhibitor 2,4-diamino-6-hydroxyprimidine had no effect on unstretched cells but doubled superoxide production compared with 24-hour stretch alone; this increase was halved by cotre atment with 6-methyl-5,6,7,8-tetrahydropterine, a lipid-soluble form o f tetrahydrobiopterine. Conclusions Short-term stretch increased super oxide production from human aortic endothelial cells via NADPH oxidase and NOS (III), whereas prolonged stretch increased both superoxide an d NO production. The increase in NOS (III) protein with prolonged stre tch acts as a scavenger mechanism whereby NO inactivates superoxide. T etrahydrobiopterin determines the balance of superoxide and NO product ion from NOS (III) after prolonged stretch in which NOS (III) level is upregulated.