Serum Metabolomic Profile of Critical Limb-Threatening Ischemia Patients

Abstract

Despite a high prevalence of 10% to 20% in the elderly population, peripheral artery disease (PAD) is often undiagnosed in the primary care setting as over 50% of patients are asymptomatic. Some patients experience variable and unpredicTable progression to the severe, end-stage form known as critical limb-threatening ischemia (CLTI). A better understanding of this progression can reduce delays in surgical interventions, reduce amputations and decrease mortality. With the help of metabolomics, we aim to investigate PAD and CLTI at the metabolites level. Non-PAD, PAD, and CLTI patients were recruited for this study (ethics application number REB #16-375). Patients with diabetes, history of cancer, deep vein thrombosis, and acute coronary syndrome were excluded. Nontargeted metabolite screening of serum was conducted using three operation modes of multisegment injection-capillary electrophoresis-mass spectrometry with full-scan data acquisition, where a total of 90 authentic metabolites were consistently detected in the majority of samples after a stringent process of data filtering and quality control. A total of 60 patients were recruited and stratified based on the Rutherford Classification for chronic limb ischemia into CLTI (n = 20), PAD (n = 20) and non-PAD controls (n = 20). Compared with controls, patients with CLTI showed lower serum concentrations of creatine, lysine, histidine, linoleic and eicosadienoic acids, as well as higher concentrations of creatinine and phenylacetylglutamine that satisfied a false discovery rate adjustment (q < 0.05) (Figure). All identified serum metabolites were also correlated with the ankle-brachial index (r = ± 0.35 – 0.44; P = .01-.0001). Reduced creatine/creatinine ratios in circulation likely indicates a perturbation in energy metabolism within skeletal muscle, which may be specific to CLTI as compared to coronary artery disease. Lower serum levels of linoleic acid is indicative of increased atherosclerotic processes in CLTI patients, whereas phenylacetylglutamine is a uremic toxin that is an independent risk factor for overall mortality and cardiovascular disease. Also, decreased serum levels of the antioxidant histidine in the diseased state can contribute to reduced protection of vascular tissue from increased free radical production in CLTI patients. This work provides novel biochemical insights into the pathophysiology of CLTI and offers a new foundation for possible metabolic markers that can be used for PAD and CLTI screening and monitoring.