Sepsis, leukocytes, and nitric oxide (NO): an intricate affair

Tacrolimus modulates liver and pancreas nitric oxide synthetase and heme-oxygenase isoforms and cytokine production after endotoxemia

Cytoprotective effects of tacrolimus are due to its unspecific anti-inflammatory and anti-oxidant properties. Neither the exact mechanisms nor if there is any organ-specificity or dose-dependent response have not been yet elucidated. Our aim was to evaluate the effect of tacrolimus on oxidative stress and mediator production in liver and pancreatic tissue secondary to endotoxemia. Wistar rats were pretreated with intraperitoneal injection of tacrolimus (0.07, 0.15, and 0.3mg/kg) 24h before Escherichia coli LPS was administrated. Animals were sacrificed 24h after LPS administration and iNOS, eNOS, and nNOS and type 1 and 2 heme-oxygenase (HO) expression were measured. TNF-α and IL-1 tissue expression and plasmatic NO, CO, TNF-α, and IL-1 were also determined. LPS exposure increased iNOS expression in both organs, eNOS did not show variations and liver nNOS expression was significantly lower. Tacrolimus diminished both pancreas and liver iNOS and nNOS expression. Both liver and pancreatic eNOS expression augmented when tacrolimus was administrated. High doses of tacrolimus were correlated with ameliorated liver HO-1 plus HO-2 and pancreas HO-1 expression after LPS stimulation. Tacrolimus treatment diminished TNF-α but not IL-1 expression increase after LPS challenge in hepatic tissue. Pancreatic TNF-α and IL-1 values diminished partially when high doses were employed. Plasmatic NO, CO, TNF-α, and IL-1 concentrations increase after LPS challenge was diminished when highest doses of tacrolimus were given. In conclusion, tacrolimus exerts a protective effect on commonly observed harmful phenomena after LPS stimulation by modulating liver and pancreas oxidative enzyme expression and cytokine production.

Regulation of endothelial cell tetrahydrobiopterin pathophysiological and therapeutic implications

Tetrahydrobiopterin (BH(4)) is a critical cofactor for the nitric oxide synthases. In the absence of BH(4), these enzymes become uncoupled, fail to produce nitric oxide, and begin to produce superoxide and other reactive oxygen species (ROS). BH(4) levels are modulated by a complex biosynthetic pathway, salvage enzymes, and by oxidative degradation. The enzyme GTP cyclohydrolase-1 catalyzes the first step in the de novo synthesis of BH(4) and new evidence shows that this enzyme is regulated by phosphorylation, which reduces its interaction with its feedback regulatory protein (GFRP). In the setting of a variety of common diseases, such as atherosclerosis, hypertension, and diabetes, reactive oxygen species promote oxidation of BH(4) and inhibit expression of the salvage enzyme dihydrofolate reductase (DHFR), promoting accumulation of BH(2) and NOS uncoupling. There is substantial interest in therapeutic approaches to increasing tissue levels of BH(4), largely by oral administration of this agent. BH(4) treatment has proved effective in decreasing atherosclerosis, reducing blood pressure, and preventing complications of diabetes in experimental animals. While these basic studies have been very promising, there are only a few studies showing any effect of BH(4) therapy in humans in treatment of these common problems. Whether BH(4) or related agents will be useful in treatment of human diseases needs additional study.