The Potentials of Melatonin in the Prevention and Treatment of Bacterial Meningitis Disease

Melatonin: A potential protective multifaceted force for sepsis-induced cardiomyopathy

Sepsis is a life-threatening condition manifested by organ dysfunction caused by a dysregulated host response to infection. Lung, brain, liver, kidney, and heart are among the affected organs. Sepsis-induced cardiomyopathy is a common cause of death among septic patients. Sepsis-induced cardiomyopathy is characterized by an acute and reversible significant decline in biventricular both systolic and diastolic function. This is accompanied by left ventricular dilatation. The pathogenesis underlying sepsis-induced cardiomyopathy is multifactorial. Hence, targeting an individual pathway may not be effective in halting the extensive dysregulated immune response. Despite major advances in sepsis management strategies, no effective pharmacological strategies have been shown to treat or even reverse sepsis-induced cardiomyopathy. Melatonin, namely, N-acetyl-5-methoxytryptamine, is synthesized in the pineal gland of mammals and can also be produced in many cells and tissues. Melatonin has cardioprotective, neuroprotective, and anti-tumor activity. Several literature reviews have explored the role of melatonin in preventing sepsis-induced organ failure. Melatonin was found to act on different pathways that are involved in the pathogenesis of sepsis-induced cardiomyopathy. Through its antimicrobial, anti-inflammatory, and antioxidant activity, it offers a potential role in sepsis-induced cardiomyopathy. Its antioxidant activity is through free radical scavenging against reactive oxygen and nitrogen species and modulating the expression and activity of antioxidant enzymes. Melatonin anti-inflammatory activities control the overactive immune system and mitigate cytokine storm. Also, it mitigates mitochondrial dysfunction, a major mechanism involved in sepsis-induced cardiomyopathy, and thus controls apoptosis. Therefore, this review discusses melatonin as a promising drug for the management of sepsis-induced cardiomyopathy.

Oral GSH Exerts a Therapeutic Effect on Experimental Salmonella Meningitis by Protecting BBB Integrity and Inhibiting Salmonella-induced Apoptosis

Bacterial meningitis (BM) is the main cause of the central nervous system (CNS) infection and continues to be an important cause of mortality and morbidity. Glutathione (GSH), an endogenous tripeptide antioxidant, has been proved to exert crucial role in reducing superoxide radicals, hydroxyl radicals and peroxynitrites. The purpose of this study is to expand the application scope of GSH via exploring its therapeutic effect on BM caused by Salmonella typhimurium SL1344 and then provide a novel approach for the treatment of BM. The results suggested that intragastric administration of GSH could significantly increase median survival and improve experimental autoimmune encephalomyelitis score of BM model mice. However, exogenous GSH did not affect the adhesion, invasion and cytotoxicity of SL1344 to C6, BV2 and primary microglia. Due to the contradiction between the therapeutic and bactericidal effects of GSH, the effect of GSH on blood-brain barrier (BBB) was investigated to explore its action target for the treatment of meningitis. GSH was found to repair the damage of BBB and then prevent the leakage of SL1344 from the brain to the blood circulation. The repaired BBB could also effectively reduce the entry of macrophages and neutrophils into the brain, and significantly reverse the microglia activation induced by SL1344. More importantly, exogenous GSH was proved to reduce mouse brain cell apoptosis by inhibiting the activation of caspase-8 followed by caspase-3, and reversing the up-regulation of ICAD and PARP-1 caused by SL1344.

Melatonin Is Neuroprotective in Escherichia coli Meningitis Depending on Intestinal Microbiota

Avian meningitis Escherichia coli (E. coli) can cause acute bacterial meningitis which threatens poultry health, causes great economic losses in the poultry industry, and has recently been speculated as a potential zoonotic pathogen. Melatonin can counteract bacterial meningitis-induced disruption of the blood-brain barrier (BBB), neuroinflammation, and reduce mortality. There are increasing data showing that melatonin's beneficial effects on bacterial meningitis are associated with intestinal microbiota. In this study, our data showed that melatonin alleviated neurological symptoms, enhanced survival rate, protected the integrity of the BBB, reduced the bacterial load in various tissues and blood, and inhibited inflammation and neutrophil infiltration of brain tissue in an APEC TW-XM-meningitis mice model. The results of 16S rRNA showed that melatonin pretreatment significantly maintained the composition of intestinal microbiota in APEC-meningitis mice. The abundance and diversity of intestinal microbiota were disturbed in APEC TW-XM-meningitis mice, with a decreased ratio of Firmicutes to Bacteroides and an increased the abundance of Proteobacteria. Melatonin pretreatment could significantly improve the composition and abundance of harmful bacteria and alleviate the decreased abundance of beneficial bacteria. Importantly, melatonin failed to affect the meningitis neurologic symptoms caused by APEC TW-XM infection in antibiotic-pretreated mice. In conclusion, the results suggest that melatonin can effectively prevent meningitis induced by APEC TW-XM infection in mice, depending on the intestinal microbiota. This finding is helpful to further explore the specific target mechanism of melatonin-mediated intestinal microbiota in the prevention of and protection against Escherichia coli meningitis.

Melatonin: A mitochondrial resident with a diverse skill set

Melatonin is an ancient molecule that originated in bacteria. When these prokaryotes were phagocytized by early eukaryotes, they eventually developed into mitochondria and chloroplasts. These new organelles retained the melatonin synthetic capacity of their forerunners such that all present-day animal and plant cells may produce melatonin in their mitochondria and chloroplasts. Melatonin concentrations are higher in mitochondria than in other subcellular compartments. Isolated mouse oocyte mitochondria form melatonin when they are incubated with serotonin, a necessary precursor. Oocyte mitochondria subsequently give rise to these organelles in all adult vertebrate cells where they continue to synthesize melatonin. The enzymes that convert serotonin to melatonin, i.e., arylalkylamine-N-acetyltransferase (AANAT) and acetylserotonin-O-methyltransferase, have been identified in brain mitochondria which, when incubated with serotonin, also form melatonin. Melatonin is a potent antioxidant and anti-cancer agent and is optimally positioned in mitochondria to aid in the maintenance of oxidative homeostasis and to reduce cancer cell transformation. Melatonin stimulates the transfer of mitochondria from healthy cells to damaged cells via tunneling nanotubes. Melatonin also regulates the major NAD⁺-dependent deacetylase, sirtuin 3, in the mitochondria. Disruptions of mitochondrial melatonin synthesis may contribute to a number of mitochondria-related diseases, as discussed in this review.