Brain metabolism in hepatic encephalopathy and hyperammonemia

Exploratory investigation on nitro- and phospho-proteome cerebellum changes in hyperammonemia and hepatic encephalopathy rat models

Hepatic encephalopathy (HE) is a neurological disease associated with hepatic dysfunction. Current knowledge suggests that hyperammonemia, related to liver failure, is a main factor contributing to the cerebral alterations in HE and that hyperammonemia might impair signal transduction associated with post-translational modification of proteins such as tyrosine-nitration and phosphorylation. However, the molecular bases of the HE remain unclear and very little is known about the occurrence of post-translational modification on in vivo proteins. In this exploratory study we look for evidence of post-translation modifications of proteins in the cerebellum of experimental HE rat models using a proteomic approach. For the first time we showed that hyperammonemia without liver failure (HA rats) and experimental HE with liver failure due to portacaval shunt (PCS rats) lead to a reduced protein nitration in rat cerebellum, where the undernitrated proteins were involved in energy metabolism and cytoskeleton remodelling. Moreover we showed that tyrosine nitration loss of these proteins was not necessarily associated to a change in their phosphorylation state as result of the disease. Interestingly the rat cerebellum phosphoproteome was mainly perturbed in PCS rats, whereas HA rats did not shown appreciable changes in their phosphoprotein profile. Since the protein nitration level decreased similarly in the cerebellum of both HA and PCS rats, this implies that the two disease models share common effects but also present some differential signalling effects in the cerebellum of the same animals. This study highlights the interest for studying the concerted action of multiple signalling pathways in HE development.

Chronic alcoholics without Wernicke-Korsakoff syndrome or cirrhosis do not lose serotonergic neurons in the dorsal raphe nucleus

Despite the considerable evidence that alcoholics have perturbation of serotonergic function, there is little pathological evidence for alcohol directly affecting the nervous system. The present study aims to assess neuronal loss that occurs as a consequence of alcohol neurotoxicity in the serotonergic dorsal raphe nucleus (DRN). To that end, the brains of eight alcoholics and eight age-matched control cases were carefully screened to eliminate serious liver disease, the sequela of thiamine deficiency, Wernicke-Korsakoff syndrome (WKS), and other pathological abnormalities. Brains were formalin-fixed for 2 weeks, cut, and then immunohistochemically stained using a monoclonal PH8 antibody specific for the rate-limiting enzyme of serotonin synthesis, tryptophan hydroxylase. The morphology of the serotonin-synthesizing neurons and their average size was similar in all cases. However, there was a reduction in the staining intensity of the reaction product in the DRN serotonergic neurons of most alcoholics. Neuronal counts on spaced serial sections revealed that there were an estimated average total of 106,100 +/- 19,500 serotonergic neurons in the DRN of alcoholics and 108,300 +/- 11,800 in the DRN of controls, indicating that in most alcoholics there is no reduction in the number of these neurons. Therefore, the effect of chronic alcohol consumption on the serotonergic system, in the absence of WKS or liver disease, seems to be functional rather than neuropathological.