Novel insights into the effects of inducible nitric oxide synthase inhibition during sepsis*:

Applying gases for microcirculatory and cellular oxygenation in sepsis: effects of nitric oxide, carbon monoxide, and hydrogen sulfide

PURPOSE OF REVIEW

Nitric oxide, carbon monoxide, and hydrogen sulfide (H2S) are gases that have received attention as signaling molecules regulating many biological processes. All of them were reported to have beneficial effects in inflammatory states, in particular for microcirculatory perfusion and tissue energy balance. Thus, this review will highlight the most important results with a focus on resuscitated, clinically relevant experimental models and, if available, human studies.

RECENT FINDINGS

There is ample evidence that nitric oxide, carbon monoxide, and H2S may exert cytoprotective effects in shock states due to their vasomotor, antioxidant, and anti-inflammatory properties as well as their potential to induce a hibernation-like metabolic state called 'suspended animation' resulting from inhibition of cytochrome-c-oxidase. It must be emphasized, however, that the three molecules may also be cytotoxic, not only because of their inhibition of cellular respiration but also because of their marked pro-inflammatory effects.

SUMMARY

It is still a matter of debate whether manipulating nitric oxide, carbon monoxide, or H2S tissue concentrations, either by using the inhaled gas itself or by administering donor molecules or inhibitors of their endogenous production, is a useful therapeutic approach to improve microcirculatory blood flow, tissue oxygenation, and cellular respiration. This is mainly due to their 'friend and foe character' documented in various experimental models, but also to the paucity of data from long-term, resuscitated large animal experiments that fulfil the criteria of clinically relevant models.

L-NIL prevents renal microvascular hypoxia and increase of renal oxygen consumption after ischemia-reperfusion in rats

Even though renal hypoxia is believed to play a pivotal role in the development of acute kidney injury, no study has specifically addressed the alterations in renal oxygenation in the early onset of renal ischemia-reperfusion (I/R). Renal oxygenation depends on a balance between oxygen supply and consumption, with the nitric oxide (NO) as a major regulator of microvascular oxygen supply and oxygen consumption. The aim of this study was to investigate whether I/R induces inducible NO synthase (iNOS)-dependent early changes in renal oxygenation and the potential benefit of iNOS inhibitors on such alterations. Anesthetized Sprague-Dawley rats underwent a 30-min suprarenal aortic clamping with or without either the nonselective NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) or the selective iNOS inhibitor L-N(6)-(1-iminoethyl)lysine hydrochloride (L-NIL). Cortical (CmicroPo(2)) and outer medullary (MmicroPo(2)) microvascular oxygen pressure (microPo(2)), renal oxygen delivery (Do(2ren)), renal oxygen consumption (Vo(2)(ren)), and renal oxygen extraction (O(2)ER) were measured by oxygen-dependent quenching phosphorescence techniques throughout 2 h of reperfusion. During reperfusion renal arterial resistance and oxygen shunting increased, whereas renal blood flow, CmicroPo(2), and MmicroPo(2) (-70, -42, and -42%, respectively, P < 0.05), Vo(2)(ren), and Do(2ren) (-70%, P < 0.0001, and -28%, P < 0.05) dropped. Whereas L-NAME further decreased Do(2ren), Vo(2)(ren), CmicroPo(2), and MmicroPo(2) and deteriorated renal function, L-NIL partially prevented the drop of Do(2ren) and microPo(2), increased O(2)ER, restored Vo(2)(ren) and metabolic efficiency, and prevented deterioration of renal function. Our results demonstrate that renal I/R induces early iNOS-dependent microvascular hypoxia in disrupting the balance between microvascular oxygen supply and Vo(2)(ren), whereas endothelial NO synthase activity is compulsory for the maintenance of this balance. L-NIL can prevent ischemic-induced renal microvascular hypoxia.