Melatonin inhibits amphetamine-induced nitric oxide synthase mRNA overexpression in microglial cell lines

Amphetamine (AMPH) derivatives are the most commonly abused drugs. Chronic or intermittent AMPH abuse may create temporary or permanent disturbances in the dopaminergic system of the brain that may predispose individuals to Parkinsonism. AMPH induces a massive release of dopamine from synaptic vesicles and then generates reactive oxygen species (ROS). Furthermore, nitric oxide (NO), produced in the central nervous system (CNS) mediated by the activation of microglia, appears to play a critical role in stress-induced brain damage. In the present study, we examined the involvement of NO in the neurotoxic effects of AMPH, to investigate the hypothesis that altered nitric oxide synthase (NOS) function was involved. AMPH at a concentration of 0.4-3.2mM has a cytotoxic effect on highly aggressively proliferating immortalized (HAPI) cells, a rat microglial cell line. The effect of AMPH on increasing inducible NOS (iNOS) mRNA in HAPI microglial cells is concentration-dependent. Pretreatment with either S-methylisothiourea (S-MT), a selective iNOS inhibitor, or melatonin, a major secretory product of pineal gland, counteracted the over expression of iNOS induced by AMPH in a concentration-dependent manner. The induction of iNOS by AMPH in microglial cells could be an important source of NO in CNS inflammatory disorders associated with the death of neurons and oligodendrocytes. Administration of exogenous melatonin will be beneficial, as it reduces iNOS mRNA expression, and may, therefore, be able to be used as a neuroprotective agent in toxicity induced by AMPH or other immunogens.     

Upregulation of colonic ion channels in APC Min/+ mice

The adenomatous polyposis coli (APC) tumor suppressor gene is mutated in almost all human colonic cancers. Disturbances in Na⁺ absorption have been observed in colonic cancer, and ion channels such as ether a go-go (Eag) or Ca²⁺-sensitive BK channels have been recognized for their oncogenic potential. APC ^Min/+ mice have reduced APC expression and develop multiple intestinal neoplasias (Min). Ion channels in the colonic epithelium were examined using electrophysiology and molecular techniques. APC ^Min/+ mice developed intestinal neoplasia and experienced a significant weight loss. Due to intestinal bleedings, the hematocrit was largely reduced and plasma aldosterone levels were enhanced. Rectal potential measurements in vivo indicated an increase in amiloride-sensitive Na⁺ absorption in APC ^Min/+ mice. Quantitative Ussing chamber studies demonstrated enhanced Na⁺ absorption via epithelial Na⁺ channels (ENaC) and suggested enhanced activity of oncogenic BK and Eag-1 channels. Patch clamp and fluorescence measurements on isolated crypts suggested enhanced K⁺ channel activity in the surface epithelium. ENaC-mRNA and membrane protein expression was enhanced in colonic surface epithelial cells. The data suggest that reduced expression of the APC gene with upregulation of the downstream proteins Akt and mTOR and subsequent hyperaldosteronism is paralleled by upregulation of oncogenic potassium channels and enhanced colonic Na⁺ absorption. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.