1H NMR metabolomics and lipidomics analysis of neutrophils reveals biomarkers of ageing, inflammageing and frailty

Neutrophil function declines with age, but little is known about the changes in neutrophil metabolism that take place in older people and people with frailty. We used 1H-NMR spectroscopy to investigate the metabolomic and lipidomic profiles of blood neutrophils from healthy younger (HY) and older (HO) people and older people with frailty (FR), to identify metabolites and metabolic pathways altered with healthy ageing and ageing with frailty. We also compared FR metabolites to rheumatoid arthritis (RA) neutrophils to identify markers of inflammation in FR neutrophils. We identified 17 significantly different polar metabolites across the participant groups (ANOVA adj. p<0.05). Three polar metabolites were significantly different in FR vs HO neutrophils, with NADP being higher in FR and lysine and choline being lower. NADP was uniquely elevated in FR compared to HO, HY and RA neutrophils. Seven metabolites were significantly different between HO and HY neutrophils, and only two metabolites were different between FR and RA neutrophils, identifying underlying similarities between FR and RA that may be driven by inflammation. Four lipid peaks were significantly different between FR and HY neutrophils. These were attributed to total cholesterol and omega 6 fatty acids. This is the first study of polar and lipid metabolism in neutrophils from people with frailty, providing evidence that metabolic signalling pathways involved in neutrophil activation, oxidative stress and lipid metabolism are altered during healthy ageing and ageing with frailty, and we identify NADP as a unique biomarker of altered neutrophil function in people with frailty.