Role of Nitric Oxide Synthesis Inhibitors in Iron-Induced Nigral Neurotoxicity: A Mechanistic Exploration

Blocking of L-type calcium channels protects hippocampal and nigral neurons against iron neurotoxicity. The role of L-type calcium channels in iron-induced neurotoxicity

Iron plays an important role in maintaining normal brain function. However, iron overload and enhanced hydroxyl radical formation have been implicated as the causative factors of some neurodegenerative disorders such as Parkinson's and Alzheimer's diseases. Calcium is also required for diverse physiological process including secretion of neurotransmitters, synaptic plasticity, gene expression and axonal growth. Iron and calcium are essential for neuronal function but, when present in excessive level, they induce neuronal damage and may even cause neuronal death. Some reports suggest that voltage gated calcium channels (VGCCs) are an alternate route for iron entry into neuronal cell lines under conditions of iron overload. The aim of the present study was to investigate the effects of L-type VGCCs on iron-induced neurotoxicity. Iron neurotoxicity was generated by intracerebroventricular FeCl₃ injection. Nicardipine treatment (10 mg/kg/d) was applied to block L-type VGCCs for 10 d. Rats were perfused intracardially under deep urethane anaesthesia after treatment period. Removed brains were processed using the standard histological techniques. The numbers of neurons in hippocampus and substantia nigra of all rats were estimated by stereological techniques. Results of present study show that nicardipine decreased hippocampal and nigral neuron loss from 43.9% to 18.4% and 41.0% to 12.1%, respectively. Outcomes of the present study propose that blocking of L-type VGCCs may reduce the neurotoxic effects of iron by inhibiting the cellular influx of excessive calcium and/or iron ions.

Alpha-tocopherol decreases iron-induced hippocampal and nigral neuron loss

There are many studies about iron-induced neuronal hyperactivity and oxidative stress. Some reports also showed that iron levels rise in the brain in some neurodegenerative diseases such as Parkinson's (PD) and Alzheimer's disease (AD). It has been suggested that excessive iron level increases oxidative stress and causes neuronal death. Tocopherols act as a free radical scavenger when phenoxylic head group encounters a free radical. We have aimed to identify the effect of alpha-tocopherol (Vitamin E) on iron-induced neurotoxicity. For this reason, rats were divided into three groups as control, iron, and iron + alpha-tocopherol groups. Iron chloride (200 mM in 2.5 microl volume) was injected into brain ventricle of iron and iron + alpha-tocopherol group rats. Same volume of saline (2.5 microl) was given to the rats belonging to control group. Rats of iron + alpha-tocopherol group received intraperitoneally (i.p.) alpha-tocopherol (100 mg/kg/day) for 10 days. After 10 days, rats were perfused intracardially under deep urethane anesthesia. Removed brains were processed using standard histological techniques. The numbers of neurons in hippocampus and substantia nigra of all rats were estimated by stereological techniques. Results of present study show that alpha-tocopherol decreased hippocampal and nigral neuron loss from 51.7 to 12.1% and 41.6 to 17.8%, respectively. Findings of the present study suggest that alpha-tocopherol may have neuroprotective effects against iron-induced hippocampal and nigral neurotoxicity and it may have a therapeutic significance for neurodegenerative diseases involved iron.