Multiple sclerosis: Effects of fixed-dose combination of dimethyl fumarate and NADPH oxidase inhibitor on oxidative stress markers and neurobehavioral activity in mice model of cuprizone-induced demyelination

Background Motor coordination (MC) and long-term recognition memory (LRM) are affected in people with multiple sclerosis (MS). The exact mechanism underlying the pathogenesis of MS is still unknown. However, oxidative stress is one of the underlying mechanisms of the pathogenesis of MS that is detrimental to myelin due to an imbalance in the levels of antioxidants. Dimethyl fumarate (DMF) is a first-line treatment for relapsing-remitting multiple sclerosis (RRMS). Since OS plays a significant role in MS, in addition to DMF treatment, inhibition of NADPH oxidases (NOXs) may provide surplus glutathione (GSH) to prevent myelin loss. Hence, the objective of this study was to test the effect of a fixed dose of apocynin (50 mg/kg) combined with a fixed-dose DMF (30 mg/kg) on antioxidants, MC, and LRM in cuprizone (CUP)-induced mice model of demyelination. Methods The MC and LRM were evaluated by narrow beam and novel object recognition tests, catalase and superoxide dismutase activity by the degradation of hydrogen peroxide and nitroblue tetrazolium method; malondialdehyde by thiobarbituric acid assay, GSH by high-performance liquid chromatography, and presence of myelin by modified luxol fast blue staining. Results The combination therapy with DMF plus APO in CUP-fed mice preserved LRM and MC with a significant increase in catalase activity (1.15 ± 0.04 U/mg protein; p<0.001), superoxide dismutase activity (9.25 ± 0.10 U/mg protein; p<0.0001), and GSH (195.25 ± 22.75 nmol/mg protein, \**\*|\*p <0.0001) of the cerebral cortex versus disease control (98.52 ± 8.85 nmol/mg protein). APO plus DMF30 in CUP-fed mice also preserved myelin (p<0.001) at the corpus callosum of mice brains. Conclusions We conclude that APO combination with DMF might have protected myelin by modulating (increasing) the levels of antioxidants to act against CUP-induced oxidative stress and thereby preserved MC and LRM in the cuprizone-induced mice model of demyelination. ### Competing Interest Statement The authors have declared no competing interest. * MS : Motor coordination LRM : Long-term recognition memory MS : Multiple sclerosis APO : Apocynin DMF : Dimethyl fumarate RRMS : Relapsing and remitting multiple sclerosis OS : Oxidative stress NADPH : Nicotinamide adenine dinucleotide phosphate NOX : NADPH Oxidase TBA : Thiobarbituric acid TCEP : Tris (2-carboxyethyl)phosphine hydrochloride ABD-F : 4-aminosulfonyl-7fluoro-2,1,3-benzoxadiazole HPLC : High-performance liquid chromatography GSH : Glutathione MDA : Malondialdehyde SOD : Superoxide dismutase TET : Total exploration time RI : Recognition index DI : Discrimination index