Reduction of NO production in LPS-stimulated primary rat microglial cells by Bromelain

Microglia, the sentries of the brain, is highly implicated in neurodegeneration as in neuroprotection. Chronic microglial activation endangers neuronal survival through the release of various potentially neurotoxicmediators including Nitric Oxide (NO). Thus, negative regulators of microglial activation have beenconsidered as potential therapeutic candidates to target neurodegeneration, such as those in Alzheimer’s and Parkinson’s diseases and even in chronic epileptic syndromes. Bromelain, a mixture of cysteine proteases, derived from pineapple stem, has been reported to have anti-inflammatory and immunomodulatory effects.Neonatal rat primary microglial cells were isolated from the brain according to the Floden’s method. Thepurity of the cultures was determined by immunostaining with an OX-42 antibody which showed a purity greater than 95%.The activation profile of microglia was investigated by determining the effects of Bromelain(1, 10, 20, 30, 40 and 50 μg/ml) on the level of neurotoxin, NO, mitochondrial activity and morphologicalchanges in treated microglia with lipopolysaccharide (LPS) (1μg/ml), as an endotoxin. Our results showed thatpretreatment of primary rat microglia with bomelain (30 μg/ml), decreased the production of NO induced by LPS (1μg/ml) treatment in a dose-dependent manner, which prevented the deramification of microglia and its phagocytic morphology. Moreover, bromelain does not show cytotoxicity at any of the applied doses,suggesting that the anti-inflammatory effects of bromelain are not due to the cell death. In conclusion, Bromelain reduces the NO synthesis in vitro by potentially exerting its anti-inflammatory effects. Bromelain naturally found in pineapple stem, can be considered as a useful agent for neuroprotection and alleviation of symptoms in neurodegenerative diseases.

Keywords:

Microglia , Bromelain , CNS inflammation , NO , Neurodegeneration