Melatonin as a potential treatment for sepsis: metabolomic consequences of high oral dosing

Abstract

Sepsis is a life-threatening dysregulated host response to infection, and kills over 40 000 people in the UK each year. Mitochondrial dysfunction driven by oxidative stress features and antioxidants that specifically protect mitochondria may offer a therapeutic strategy. Melatonin is a potent antioxidant and can be administered exogenously. It protects against mitochondrial damage in models of sepsis. Exogenous melatonin appears to be very safe, and clinical trials are underway. However, the metabolic consequences of exogenous melatonin are unknown. We undertook a metabolomic analysis of serum samples from the DAMSEL1 Phase I dose escalation trial.1 Briefly, cohorts of five subjects received a single oral dose of melatonin 20–100 mg, and blood samples were obtained over 6 h. Serum samples were extracted into chloroform/methanol/water at 4°C and stored at –80°C until transfer to the University of Glasgow Polyomics Centre. Hydrophilic interaction liquid chromatography (HILIC) was carried out using a zwitterionic-pHILIC column at 30°C. The samples were eluted with a linear gradient (ammonium carbonate/acetonitrile) over 26 min at 0.3 ml min–1. Mass spectrometry operated in polarity switching mode was then undertaken. Data were exported into a custom Excel template for processing of metabolomics to annotated and hyperlinked metabolite (IDentification and Evaluation of Metabolomics Data from LC-MS), and were processed with an mzMatch/XCMS pipeline. Authentic standards were run with each batch to identify metabolites according to the Metabolomics Standards Initiative with verification against the Kyoto Encyclopedia of Genes and Genomes database. Differences in metabolites were identified and relevant pathways interrogated to find changes across connected metabolites. Minor changes did not show recurrent patterns at different doses, showing that the melatonin administration did not affect the overall metabolic processes. Melatonin and its major metabolite 6-hydroxymelatonin had a dose–response pattern consistent with previous analysis patterns. No potential for bioactivation or macromolecule adducts was identified. Metabolomics can identify and quantify thousands of metabolites to define changes in biochemical pathways after administration of drugs. This work confirms the excellent safety profile of this drug. The authors thank the Chief Scientist Office (CSO) for funding the original Dose Assessment of Melatonin in Sepsis Trial 1 (DAMSEL1), and the Glasgow Polyomics Centre for the metabolomic analysis.