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Mitochondrial dysfunction and oxidative stress are extensively linked to Parkinson’s disease (PD) pathogenesis. Melatonin is a pleiotropic molecule with antioxidant and neuroprotective effects. The aim of this study was to evaluate the effect of melatonin on oxidative stress markers, mitochondrial complex 1 activity, and mitochondrial respiratory control ratio in patients with PD. A double-blind, cross-over, placebo-controlled randomized clinical trial study was conducted in 26 patients who received either 25 mg of melatonin or placebo at noon and 30 min before bedtime for three months. At the end of the trial, in patients who received melatonin, we detected a significant diminution of lipoperoxides, nitric oxide metabolites, and carbonyl groups in plasma samples from PD patients compared with the placebo group. Conversely, catalase activity was increased significantly in comparison with the placebo group. Compared with the placebo group, the melatonin group showed significant increases of mitochondrial complex 1 activity and respiratory control ratio. The fluidity of the membranes was similar in the melatonin group and the placebo group at baseline and after three months of treatment. In conclusion, melatonin administration was effective in reducing the levels of oxidative stress markers and restoring the rate of complex I activity and respiratory control ratio without modifying membrane fluidity. This suggests that melatonin could play a role in the treatment of PD.

The COVID-19 pandemic has proven to be a challenge for healthcare systems, especially in terms of the care of patients with Alzheimer’s disease (AD). Age is one of the major risk factors for severe forms of COVID-19, most probably due to the presence of comorbidities and inflammations. It is known that SARS-CoV-2 invades nerve endings and olfactory nerves through the binding of the spike protein to the angiotensin-converting enzyme 2 (ACE2) receptor. This interaction triggers an inflammatory cascade that results in cognitive impairment. In turn, the isoform of apolipoprotein-E4 (APOE-4ε) in AD is a risk factor for increased neuroinflammation through microglia activation, increased oxidative stress, and neurodegeneration. AD and SARS-CoV-2 are associated with increases in levels of inflammatory markers, as well as increases in levels of APOE-4ε, ACE2 and oxidative stress. Thus, there is a synergistic relationship between AD and SARS-CoV-2. In addition, the social isolation and other health measures resulting from the pandemic have led to a higher level of anxiety and depression among AD patients, a situation which may lead to a decline in cognitive function. Therefore, there is a need to develop strategies for keeping the patient calm but active.