NO blockade results in a rise in arterial pressure and restored the effects of catecholamines. Overall, beneficial effects have been observed with selective iNOS inhibitors, whereas high doses of nonselective NOS inhibitors have been shown to be detrimental (5,7). Indeed, it has been demonstrated that nonselective NO inhibitors decrease blood flow, tissue oxygenation, and survival (5). Our results confirmed the effects of nonselective NOS inhibitors increasing the animal mortality. On the other hand, the beneficial effects of selective iNOS inhibitors were shown by the attenuation of circulatory failure, renal, hepatic, and pancreatic dysfunction, and improvement of survival in rats submitted to endotoxemia (5,19–21). The present data show that inhibition of HMG-CoA reductase with simvastatin is similar to treatment with aminoguanidine by restoring response to phenylephrine and reducing NO production without affecting the survival rate.
In endotoxic shock, multiple cellular processes are involved and many humoral cascades are triggered, so that the blocking a single component may be insufficient to arrest the inflammatory process. The statins have a strong protective effect against sepsis by the diverse anti-inflammatory properties that are independent of their lipid-lowering ability (14). Most of these effects are mediated by the inhibition of isoprenoid synthesis (14,22–25). HMG-CoA reductase inhibitor interrupts the isoprenylation of small G proteins (e.g., Ras and Rho) by decreasing FPP and GGPP level, leading to the accumulation of inactive small G proteins in the cytoplasm. The reduction of cellular isoprenoid, as well as the lowering membrane levels and activity of Ras/Rho proteins, may be important mechanisms mediating the direct cellular effects of statins on the vascular wall (22).
The present data show that simvastatin reestablished the pressor response to phenylephrine during endotoxic shock. The smooth muscle contraction elicited by most vasoconstrictor agents is regulated by an increase in cytosolic calcium levels from intracellular stores or by calcium influx through calcium channels located in the cell membrane. Phenylephrine, an α-adrenergic receptor agonist causes vasoconstriction through opening of receptor-operated membrane calcium channels with a resulting influx of extracellular calcium; activation of phospholipase C and hydrolysis of phosphatidyl inositol biphosphate to diacyl glycerol, which activates myosin light-chain kinase through protein kinase C; and production of inositol 1,4,5-triphosphate (IP3), which in turn causes calcium release from intracellular stores in the endoplasmic reticulum (31). A possible interference of the NO in these signal transduction mechanisms has previously been suggested by Ji and collaborators (32), who reported that NO selectively inhibits IP3-induced intracellular calcium release in aortic smooth muscle of rats. NO was also shown to inhibit calcium-permeable cation channels and suppress the increase in intracellular calcium levels in vascular smooth muscle (33). Endotoxemia is accompanied by a generalized contractile defect secondary to a decrease in the influx of calcium into the cell and reduction of release of calcium from intracellular stores (34). The dominant mechanism involved in this impairment might be the activation of iNOS by endotoxin and the subsequent overproduction of NO (3). In the present model, simvastatin reduces NO production, leading to the recovery to vasoconstrictor agent effect during the endotoxemia. In fact, a significant decrease in mortality rates was recently reported among patients with bacteremia who were receiving statins (35).
In conclusion, this work shows that simvastatin reduces the production of NO and reverts the impaired vascular responsiveness observed in endotoxin shock. These results suggest a possible therapeutic benefit and provide insight into putative mechanisms involved in the pathophysiology of endotoxic shock. A comprehensive understanding of the cellular mechanisms involved in the induction of iNOS and cytokines should help to identify novel targets for therapeutic intervention of NO-mediated changes in inflammatory diseases. The potential role of statins as adjuvant drugs in the treatment of septic shock and other inflammatory states remains to be defined.
The authors are grateful to Marina Holanda, Maria Valci Silva, and Wagner L. Reis for their excellent technical support. This research was supported by grants from FAPESP, CNPq, and PRONEX.
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