<scp>1H NMR</scp> 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 robust older people and older people with frailty. We used ¹H-NMR spectroscopy to investigate the metabolomic and lipidomic profiles of blood neutrophils from healthy younger (HY, n = 21, mean age 22Y) and robust older (RO, n = 24, mean age 66Y) people and older people with frailty (FR, n = 31, mean age 84Y), to identify metabolites and metabolic pathways altered with ageing with and without frailty. We also compared FR metabolites to rheumatoid arthritis (RA, n = 16, mean age 55Y) neutrophils to identify inflammation markers in FR neutrophils. Seventeen polar metabolites were significantly different between the participant groups (ANOVA adj. P < 0.05). NADP was uniquely elevated in FR compared with RO, HY and RA neutrophils, and lysine and choline were lower in FR vs. RO. Seven metabolites were significantly different between RO 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.