Melatonin and health: an umbrella review of health outcomes and biological mechanisms of action

Melatonin improves quality and longevity of chronic neural recording

The chronic performance of implantable neural electrodes is hindered by inflammatory brain tissue responses, including microglia activation, glial scarring, and neuronal loss. Melatonin (MT) has shown remarkable neuroprotective and neurorestorative effects in treating central nervous system (CNS) injuries and degeneration by inhibiting caspase-1, -3, and -9 activation and mitochondrial cytochrome c release, as well as reducing oxidative stress and neuroinflammation. This study examined the effect of MT administration on the quality and longevity of neural recording from an implanted microelectrode in the visual cortex of mice for 16 weeks. MT (30 mg/kg) was administered via daily intraperitoneal injection for acute (3 days before and 14 days post-implantation) and chronic (3 days before and 16 weeks post-implantation) exposures. During the first 4 weeks, both MT groups showed significantly higher single-unit (SU) yield, signal-to-noise ratio (SNR), and amplitude compared to the vehicle control group. However, after 4 weeks of implantation, the SU yield of the acute treatment group dropped to the same level as the control group, while the chronic treatment group maintained significantly higher SU yield compared to both acute (week 5-16) and control (week 0-16) mice. Histological studies revealed a significant increase in neuronal viability and decrease in neuronal apoptosis around the implanted electrode at week 16 in the chronic group in comparison to control and acute subjects, which is correlated with reduced oxidative stress and increased number of pro-regeneration arginase-1 positive microglia cells. These results demonstrate the potent effect of MT treatment in maintaining a high-quality electrode-tissue interface and suggest that MT promotes neuroprotection possibly through its anti-apoptotic, anti-inflammatory, and anti-oxidative properties.

Use of melatonin as adjunctive therapy in neonatal sepsis: A systematic review and meta-analysis

BACKGROUND

Sepsis remains one of the major causes of neonatal mortality and morbidity. Increased production of free radicals and pro-inflammatory cytokines, combined with the innately low levels of plasma antioxidants in neonates, have been implicated in the pathogenesis and complications of neonatal sepsis. To date, few clinical trials on the beneficial effects of exogenous melatonin on improvement of clinical outcomes in septic neonates have been conducted.

METHODS

The electronic databases including PubMed, Embase, and Cochrane Central Register of Controlled Trials were systematically searched on July 2017 for clinical studies that reported the effects of melatonin as an adjuvant therapy in neonatal sepsis. Serum levels of C-reactive protein (CRP) as biomarker endpoint and recovery of sepsis as clinical endpoint were used to compare treatment responses between groups. The Risk of Bias Assessment tool for Non-Randomized Studies (RoBANS) and the Cochrane Collaboration Risk of Bias tool were used to assess the quality of included studies.

RESULTS

Three studies with a total of 120 participants were included in the systematic review and meta-analysis. Pooled analysis revealed statistically significant mean differences in CRP serum levels (mg/L) between groups at 24 h post-adjunctive therapy with melatonin (-1.739 mg/L; 95% CI: -3.205 to -0.273; P = 0.020). Additionally, adjunctive therapy with melatonin significantly improved clinical condition of sepsis in neonates from the intervention group, compared to the control group, within 3 days of therapy (RR: 2.212; 95% CI: 1.452 to 3.371; P < 0.0005).

CONCLUSIONS

Findings showed that administration of melatonin as adjunctive therapy significantly reduced an inflammatory biomarker and improved sepsis status in neonate. Larger scale studies with higher validity are needed to demonstrate clear clinical benefits of the therapy.