Nicotinamide Restores the Reduction of Parvalbumin in Cerebral Ischemic Injury

Abstract

ABSTRACT. The aim of this study investigated whether nicotinamide affects parvalbumin expression in focal cerebral ischemic injury. Rats were treated with vehicle or nicotinamide (500 mg/kg) 2 hr after middle cerebral artery occlusion (MCAO), and cerebral cortex tissues were collected 24 hr after MCAO. Nicotinamide significantly decreases the volume of infarct areas in the cerebral cortex. A proteomic approach revealed that MCAO induces decreases of parvalbumin levels, while nicotinamide treatment prevents injury-induced decreases in parvalbumin. RT-PCR and Western blot analyses demonstrated that nicotinamide restores injury-induced decreases in parvalbumin. Moreover, immunohistochemical staining confirmed that the numbers of parvalbumin-positive cells were decreased in vehicle-treated animals with MCAO, and that nicotinamide averted this decrease. In cultured hippocampal cells, nicotinamide treatment prevents the glutamate exposure-induced increase in intracellular Ca 2+ concentration and decrease in parvalbumin expression. These results suggest the fact that the maintenance of parvalbumin expression is mediated to the neuroprotective function of nicotinamide against ischemic brain injury. Nicotinamide is an essential precursor of nicotinamide adenine dinucleotide (NAD+) that acts as a poly-ADP ribose polymerase (PARP) inhibitor. Nicotinamide protects against oxidative stress and neurotoxicity, and exerts neuroprotective effects in neurodegenerative conditions such as Alzheimer's disease and stroke [1,6]. Nicotinamide attenuates infarct volumes following focal cerebral ischemia and prevents neuronal cell death by enhancing survival pathways and inhibiting apoptotic signaling pathways [8,17].Parvalbumin, a calcium sensor protein, is predominately expressed in brain tissues including the hippocampus, cortex and cerebellum [2,3]. Parvalbumin is involved in intracellular calcium buffering by binding to Ca 2+ molecules released into the cytoplasm [3,4]. Parvalbumin plays an important role in modulating calcium homeostasis of the central nervous system [4]. Increases in intracellular Ca 2+ concentration induce neuronal cell death and result in nervous system disorders [15]. Therefore, parvalbumin is considered to mediate neuroprotective function by attenuating increases of intracellular Ca 2+ . Although previous studies elucidated the neuroprotective mechanism of nicotinamide, more information is needed to understand its neuroprotective effects. This study hypothesizes that nicotinamide contributes to the regulation of parvalbumin in cerebral ischemia. However, few data are available regarding the effects of nicotinamide on parvalbumin expression in ischemic brain injury. The present paper describes the effect of nicotinamide on parvalbumin during focal cerebral ischemia.All experimental procedures for animals were approved by Institutional Animals Care and Use Committee at Gyeongsang National University. Sprague-Dawley rats (male, 220-230 g, n=60) were randomly divided into four groups, vehicle + sham group, nicotin...