The combined use of thymoquinone and metformin provides more effective neuroprotection in a mouse model of MPTP-induced Parkinson's disease.

Thymoquinone (TQ) is known for its antioxidant properties, and although metformin (MM) is known as an antidiabetic drug, it is suggested that it reduces neurodegeneration. The study aimed to investigate the neuroprotective effects of TQ and MM, particularly when used together, in relation to Parkinson's disease (PD). In the study, sixty-eight male C57BL/6 mice weighing 25-30 g were divided into five groups as follows: control, MPTP, MPTP+TQ, MPTP+MM, and MPTP+TQ+MM. MM (500 mg/kg, orally) and TQ (5 mg/kg, i.p.) were administered for 21 days. Motor coordination and locomotor activities were evaluated by the pole test. TOS and TAS analyses were conducted to determine oxidative stress levels in the substantia nigra. Dopaminergic degeneration in the substantia nigra was evaluated by analyzing Tyrosine hydroxylase (TH). To evaluate the apoptotic pathway, the expression levels of iNOS, BDNF, Complex 1, Bax, Bcl-2, Cytochrome C, AIF, and Caspase-3 were examined immunohistochemically. Compared to the MPTP-treated group, TQ, MM and MM+TQ treatment provided significant improvement in locomotor activity in mice, significantly increased antioxidant activity, significantly reduced the expression levels of iNOS, Bax, Cytochrome C, Caspase-3, and AIF, significantly increased BDNF, Bcl-2, and Complex 1 expressions, and significantly increased the number of TH positive cells. The separate use of TQ and MM exhibits neuroprotective activity, however, we showed that using TQ and MM in combination may be more effective. This may provide preclinical evidence supporting the therapeutic potential of their combined use for treating PD.