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Microglia play a dual role in neuroprotection as well as in neurodegeneration and thus occupy the focal interest in neurodegenerative disease research. In vitro studies either by using cell lines or neonatal mouse primary microglia correlated xenobiotic induced microglial activation and neuronal death. However, these in vitro studies cannot portray the in vivo scenario. Therefore, environmental pollutant induced in vivo alteration in microglial function can be best assessed by ex vivo analysis, which is not in use because of limitations in the isolation procedure. Therefore, in the first part of the study we describe an optimized isolation procedure and characterization of isolated cells. The second part of the study demonstrates the utility of the isolated cells in evaluation of immunotoxicological alterations following arsenic, as a model xenobiotic, exposure. Purity of the isolated microglia was checked by immunostaining of microglial (CD11b and CD68) and nonmicroglial (GFAP) markers. Immunostaining of activation marker Iba1 proves that cells were not activated during the isolation procedure. Microglia yield and viability from the treated group shows no significant alterations compared to that of the control group. Proinflammatory cytokines (IL-6 and TNF-α) were upregulated following arsenic treatment as in the case of the LPS stimulated group without alterations in anti-inflammatory IL-10. Phagocytic potential was affected significantly following arsenic exposure without alteration in viability. Thus, our protocol can be proficiently used for quick isolation of primary microglia from adult mouse brain without altering their activation status, and most importantly, the isolated cells can be of aid to the ex vivo evaluation of immunotoxicological alterations.

Zinc oxide nanoparticle (ZnO-NP) is one of the most widely used engineered nanoparticles. Upon exposure, nanoparticle can eventually reach the brain through various routes, interact with different brain cells, and alter their activity. Microglia is the fastest glial cell to respond to any toxic insult. Nanoparticle exposure can activate microglia and induce neuroinflammation. Simultaneous to activation, microglial death can exacerbate the scenario. Therefore, we focused on studying the effect of ZnO-NP on microglia and finding out the pathway involved in the microglial death. The present study showed that the 24 h inhibitory concentration 50 (IC) of ZnO-NP for microglia is 6.6 μg/ml. Early events following ZnO-NP exposure involved increase in intracellular calcium level as well as reactive oxygen species (ROS). Neither of NADPH oxidase inhibitors, apocynin, (APO) and diphenyleneiodonium chloride (DPIC) were able to reduce the ROS level and rescue microglia from ZnO-NP toxicity. In contrary, N-acetyl cysteine (NAC) showed opposite effect. Exogenous supplementation of superoxide dismutase (SOD) reduced ROS significantly even beyond control level but partially rescued microglial viability. Interestingly, pyruvate supplementation rescued microglia near to control level. Following 10 h of ZnO-NP exposure, intracellular ATP level was measured to be almost 50 % to the control. ZnO-NP-induced ROS as well as ATP depletion both disturbed mitochondrial membrane potential and subsequently triggered the apoptotic pathway. The level of apoptosis-inducing proteins was measured by western blot analysis and found to be upregulated. Taken together, we have deciphered that ZnO-NP induced microglial apoptosis by NADPH oxidase-independent ROS as well as ATP depletion.