The effects of pro-inflammatory cytokines and glutamate on <sc>l</sc>-arginine transport in a human microglial cell line (HMC-3)

Abstract

Purpose Neuroinflammation and microglial activation are the key factors in neurodegenerative motor neuron diseases. Microglial activation has been link to disease progression in humans. This study investigated the transport and potential effects of l-arginine under pathological conditions in a human microglial cell line.Methods Transport study was performed using [H-3]l-arginine isotope and uptake was measured in the human microglial clone 3 (HMC-3) cell line. MTT assay was performed for cell viability analysis. mRNA expression of cationic amino acid transporter-1 (CAT-1) was also determined.Results The transport of l-arginine was time- and concentration-dependent in HMC-3 cell lines. Kinetic parameters revealed carrier-mediated arginine transport via CAT-1, with high affinity and low capacity at high-affinity sites and low affinity and high capacity at low-affinity sites. HMC-3 cells pretreated with glutamate exhibited decreased viability. [H-3]l-arginine uptake increased markedly with glutamate pretreatment, whereas co-treatment with arginine further increased the uptake. After tumor necrosis factor alpha and lipopolysaccharide pretreatment, [H-3]l-arginine uptake significantly increased. In contrast, the uptake was significantly decreased after co-treatment of the cells with unlabeled l-arginine. The mRNA expression of CAT-1 showed a similar uptake pattern. Various pharmacological drugs including donepezil, quinidine, verapamil and tramadol significantly inhibited the uptake of [H-3]l-arginine in HMC-3 cell line.Conclusion These results suggest that l-arginine supplementation may play an effective role against inflammatory states in neurodegenerative diseases.