Activation of Neuronal Nitric Oxide Synthase in Cerebellum of Chronic Hepatic Encephalopathy Rats is Associated with Up-regulation of NADPH-Producing Pathway Santosh Singh & Surendra K. Trigun Published online: 20 April 2010 # Springer Science+Business Media, LLC 2010 Abstract Cerebellum-associated functions get affected during mild hepatic encephalopathy (MHE) in patients with chronic liver failure (CLF). Involvement of nitrosative and antioxidant factors in the pathogenesis of chronic hepatic encephalopathy is an evolving concept and needs to be defined in a true CLF animal model. This article describes profiles of NADPH-dependent neuronal nitric oxide synthase (nNOS) and those of glutathione peroxidase and glutathione reductase (GR) vis-a-vis regulation of NADPH-producing pathway in the cerebellum of CLF rats induced by administration of thioacetamide (100 mg kg -1 b.w., i.p.) up to 10 days and confirming MHE on Morris water maze tests. Significant increases in the expression of nNOS protein and nitric oxide (NOx) level coincided with a similar increment in NADPH–diaphorase activity in the cerebellum of CLF rats. Glutathione peroxidase and GR utilize NADPH to regenerate reduced glutathione (GSH) in the cells. Both these enzymes and GSH level were found to be static and thus suggested efficient turnover of GSH in the cerebellum of MHE rats. Relative levels of glucose-6- phosphate dehydrogenase (G6PD) vs. phosphofructokinase 2 (PFK2) determine the rate of pentose phosphate pathway (PPP) responsible to synthesize NADPH. The cerebellum of CLF rats showed overactivation of G6PD with a significant decline in the expression of PFK2 and thus suggested activation of PPP in the cerebellum during MHE. It is concluded that concordant activations of PPP and nNOS in cerebellum of MHE rats could be associated with the implication of NOx in the pathogenesis of MHE. Keywords Cerebellum . Hepatic encephalopathy . NADPH–diaphorase . nNOS . Nitric oxide . G6PD/PFK2 Introduction Hepatic encephalopathy (HE) is a serious nervous system disorder developed due to liver dysfunctions. The symp- toms and severity of the disease vary with different grades of liver failure and hyperammonemia (HA) in the patients [1]. Studies related to the changes in cerebral chemistry during overt end-stage HE suggest overactivation of NMDA receptor followed by alterations in a number of biochemical events in the brain [2], including induction of nitrosative and oxidative stress as important factors [3–5]. Moreover, as compared to the acute and end-stage HE, low mild-grade HE is prevalent in the patients with chronic liver failure (CLF) [6]. This is because viral hepatitis, alcoholism, drug intoxication, and long-term drug abuses are the main inducers of liver diseases in any population, and all of them cause CLF. Importantly, ∼60% to 80% of liver cirrhotic patients have been reported to show minimal overt HE symptoms with serious consequences in their daily life [7, 8]. Therefore, there is a need to redefine neurobiochemical alterations associated with the pathogen- esis of mild-grade HE (MHE) in a suitable CLF model. As prolonged CLF may lead into acute type HE, such studies would also help in understanding the mechanistic transition from chronic to acute HE, which is of much current interest for therapeutic management of end-stage HE. A mild-grade chronic type persistent HE is characterized by the impairment in motor functions [9, 10] and, thus, indicates derangements of cerebellar functions [11, 12]. Cerebellum is likely to produce high amount of reactive oxygen species (ROS) [13] and, therefore, speculated to be S. Singh : S. K. Trigun (*) Biochemistry and Molecular Biology Laboratory, Centre of Advanced Studies in Zoology, Banaras Hindu University, Varanasi 221005, India e-mail: sktrigun@sify.com Cerebellum (2010) 9:384–397 DOI 10.1007/s12311-010-0172-y