Zinc Potentiates Lipopolysaccharide-induced Nitric Oxide Production in Cultured Primary Rat Astrocytes

Zn2+ plays a crucial role in the CNS where it accumulates in synaptic vesicles and is released during neurotransmission. Synaptically released Zn2+ is taken up by neurons and astrocytes. The majority of previous work has focused on neuronal damage caused by excess Zn2+. However, its effect on astrocyte function is not well understood. We examined the effect of extracellularly applied Zn2+ on nitric oxide (NO) production in primary cultured rat astrocytes, which were experimentally activated by lipopolysaccharide (LPS). Zn2+, at a concentration up to 125 mu M, augmented LPS-induced NO production without affecting cell viability. LPS induced expression of both mRNA and protein of inducible NO synthase; this expression was enhanced by 125 mu M Zn2+. Zn2+ also increased LPS-induced production of intracellular reactive oxygen species. Zn2+ enhanced the phosphorylation of p38-mitogen-activated protein kinase (MAPK) at 1-6 h after LPS treatment. The LPS-induced nuclear factor-kappaB (NF kappa B) activation was sustained for 6 h by Zn2+. Intracellular Zn2+ chelation with N, N, N', N'-tetrakis(2-pyridylmethyl) ethylenediamine (TPEN) or inhibition of p38-MAPK diminished the Zn2+ enhancement of LPS-induced NO production. These findings suggest that activation of MAPK and NF kappa B is important for mediating Zn2+ enhancement of LPS-induced NO production in astrocytes. Such changes may exacerbate glial and neuronal damage during neuroinflammation.