Carbon monoxide and sepsis: is a toxic gas good for your liver?

Dobutamine Improves Liver Function after Hemorrhagic Shock through Induction of Heme Oxygenase-1

RATIONALE

Induction of heme oxygenase-1 (HO-1) protects the liver against reperfusion injury after hemorrhagic shock. Previous data suggest that the beta(1)-adrenoceptor agonist dobutamine induces HO-1 in hepatocytes.

OBJECTIVES

To investigate the functional significance of dobutamine pretreatment for liver function after hemorrhagic shock in vivo.

METHODS

Anesthetized rats received either Ringer's (Vehicle/Shock), 10 microg/kg/min of the beta(1)-adrenoceptor agonist dobutamine (Dob/Shock), or 10 microg/kg/min dobutamine and 500 microg/kg/min of the beta(1)-adrenoceptor antagonist esmolol (Dob/Esmolol/Shock) for 6 h. Hemorrhagic shock was induced thereafter (mean arterial pressure, 35 mm Hg for 90 min). Animals were resuscitated with shed blood and Ringer's. In addition, the HO pathway was blocked after dobutamine pretreatment with 10 micromol/kg tin-mesoporphyrin-IX (Dob/SnMP/Shock) or animals received 100 mg/kg of the carbon monoxide donor dichloromethane (DCM/Shock).

MEASUREMENTS

Hepatocellular metabolism and liver blood flow were measured by plasma disappearance rate of indocyanine green (PDR(ICG)) as a sensitive marker of liver function.

MAIN RESULTS

Pretreatment with dobutamine induced HO-1 in pericentral hepatocytes and improved PDR(ICG) (Vehicle/Shock: 11.7 +/- 8.12%/min vs. Dob/Shock: 19.7 +/- 2.46%/min, p = 0.006). Blockade of the HO pathway after preconditioning and the combined pretreatment with dobutamine and esmolol decreased PDR(ICG) (Dob/SnMP/Shock: 12.6 +/- 4.24%/min, p = 0.011; Dob/Esmolol/Shock: 10.2 +/- 4.34%/min, p = 0.008). Pretreatment with a carbon monoxide donor improved PDR(ICG) (DCM/Shock: 18 +/- 3.19%/min, p = 0.022) compared with Vehicle/Shock.

CONCLUSIONS

These results suggest a beta(1)-adrenoceptor-dependent hepatic up-regulation of HO-1 and a better maintained hepatocellular function after hemorrhagic shock in animals pretreated with dobutamine. The improved hepatocellular function may be in part mediated by carbon monoxide because of up-regulation of HO-1. Pretreatment with dobutamine might be a potential means of pharmacologic preconditioning before ischemia-reperfusion of the liver.

Liver in sepsis and systemic inflammatory response syndrome

In patients with sepsis and SIRS, the liver has two opposing roles: a source of inflammatory mediators and a target organ for the effects of the inflammatory mediators. The liver is pivotal in modulating the systemic response to severe infection, because it contains the largest mass of macrophages (Kupffer cells) in the body; these macrophages can clear the endotoxin and bacteria that initiate the systemic inflammatory response. This article summarizes the functional changes that take place in the liver during sepsis and systemic inflammatory response syndrome and discusses the cellular and molecular mechanisms that underlie clinical outcomes.

Organ design for generation and reception of CO: lessons from the liver

Carbon monoxide (CO) is synthesized in vivo by heme oxygenase. Although for many years CO had been regarded as potentially toxic waste, recent studies have indicated that it is a signaling molecule with important physiological functions. Nitric oxide (NO), another diatomic diffusible gas, is regarded as an established signaling molecule. Structural similarities between CO and NO have led many investigators to draw analogies between the two gaseous mediators. Whereas the NO signaling system has been well defined as to its receptor molecule, soluble guanylate cyclase, the CO system has been conceived to require further tuning with respect to identifying its receptor molecules and its downstream effectors. Furthermore, there has been little quantitative information to argue for a physiological role of CO in vivo. This review, therefore, focuses on recent developments on both physiologic and pathophysiologic roles of CO in the model of isolated perfused liver of rats where endogenous production of CO is actually estimated. This model has revealed that CO acts as an endogenous vasorelaxant in the liver and that effects of CO are at least in part cyclic GMP-dependent. It has also provided answers to many questions of hepatobiliary functions that had not been resolved because of the complexity introduced by the interplay between NO and CO.

Mechanisms of liver injury relevant to pediatric hepatology

Hepatocyte injury and necrosis from many causes may result in pediatric liver disease. Influenced by other cell types in the liver, by its unique vascular arrangements, by lobular zonation, and by contributory effects of sepsis, reactive oxygen species and disordered hepatic architecture, the hepatocyte is prone to injury from exogenous toxins, from inborn errors of metabolism, from hepatotrophic viruses, and from immune mechanisms. Experimental studies on cultured hepatocytes or animal models must be interpreted with caution. Having discussed general concepts, this review describes immune mechanisms of liver injury, as seen in autoimmune hepatitis, hepatitis B and C infection, the anticonvulsant hypersensitivity syndrome, and autoimmune polyendocrinopathy. Of the monogenic disorders causing significant liver injury in childhood, alpha-1 antitrypsin deficiency and Niemann-Pick C disease demonstrate the effect of endoplasmic or endosomal retention of macromolecules. Tyrosinemia illustrates how understanding the biochemical defect leads to understanding cell injury, extrahepatic porphyric effects, oncogenesis, pharmacological intervention, and possible stem cell therapy. Pathogenesis of cirrhosis in galactosemia remains incompletely understood. In hereditary fructose intolerance, phosphate sequestration causes ATP depletion. Recent information about mitochondrial disease, NASH, disorders of glycosylation, Wilson's disease, and the progressive familial intrahepatic cholestases is discussed.