Hypothesis related to the regulation of inducible nitric oxide synthase during carotid endarterectomy.

Sudden occlusion of an artery caused by a thrombus or emboli is the most frequent cause of acute brain ischemia (ABI). Carotid endarterectomy (CEA) represents the gold standard for preventing strokes of carotid origin. However, neuronal damage caused by ischemia and/or reperfusion may contribute to a poor clinical outcome after CEA. In response to shear stress caused by hypoxic-ischemic conditions in patients undergoing CEA, stimulation of the hypothalamic-pituitaryadrenal axis leads to biological responses known as hypermetabolic stress, characterized by hemodynamic, metabolic, inflammatory and immunological changes. These changes maintain homeostasis and assist recovery, but an unregulated inflammatory response could lead to further tissue damage and death of neurons. Nitric oxide (NO) is an important signaling molecule involved in several physiological and pathological processes, including ABI. However, an excess of NO could have detrimental effects. We hypothesized that the hypoxic-ischemic state induced by carotid clamping leads to overexpression of inducible NO synthase and that uncontrolled production of NO could adversely affect outcome after CEA.

17ß-estradiol inhibits hepatic iNOS via the activation of the estrogen receptor ER-α and inhibition of erk1/2-mir-221 axis.

17ß-Estradiol (E2) is known to negatively regulate inducible nitric oxide (NO) synthase (iNOS) expression via estrogen receptor alpha (ER-α) activation in aortic vascular smooth muscle cells.Therefore, we sought to determine whether E2 can inhibit iNOS in vivo in hepatic tissue via the activation of ER-α and whether extracellular signal-regulated kinases 1/2 (ERK1/2)-miR-221 axis is involved in this process. Male Wistar rats were treated with a bolus injection of E2 intraperitoneally (40 µg/kg), and 24 hours after treatment the animals were sacrificed and the livers excised. The protein levels of iNOS, p50 and p65 subunits of nuclear factor κB (NFκB), ERα, ERK1/2 and protein kinase B (Akt), as well as the association of ERα/Src in liver lysates were assessed by Western blot. The expression of hepatic miR-221 was analyzed by qRT-PCR. Results show that E2 reduced hepatic iNOS protein expression (p less than 0.01), the protein level of ERα (p less than 0.05), ERK1/2 (p less than 0.05), Akt phosphorylation (p less than 0.001) and miR-221 expression (p less than 0.05). In contrast, hepatic ERα/Src kinase association level (p less than 0.05) increased after E2 treatment. Our results indicate that E2 inhibits hepatic iNOS via molecular mechanisms involving the activation of the ER-α and inhibition of ERK1/2-miR-221 axis.