Changes in serum amyloid A, plasma high-density lipoprotein cholesterol and apolipoprotein A-I as useful biomarkers for Mycobacterium tuberculosis infection

Introduction. In recent years, cholesterol has received interest in the study of infection due to evidence of a relationship between low plasma cholesterol levels and tuberculosis (TB).Hypothesis/Gap Statement. Plasma lipid profiles of serum amyloid A (SAA), apolipoprotein A-I and high-density lipoprotein cholesterol (HDL-C) are biomarkers associated with symptomatic TB patients.Objective. We aimed to evaluate plasma lipid profiles of apolipoprotein A-I, SAA and the size of HDL as biomarkers to diagnose symptomatic TB patients.Methodology. Patients with TB symptoms attending the Instituto Brasileiro para a Investigação da Tuberculose/Fundação José Silveira (IBIT/FJS) between September 2015 and August 2016 for diagnosis of TB were studied. From 129 patients, 97 were classified as pulmonary TB and 32 as negative-bacilloscopy (non-TB group). Medical history, fasting serum and plasma were obtained. Total cholesterol (TC), HDL-C, apolipoprotein A-I and SAA were measured by enzymatic or immunochemical reaction assays. HDL size was measured by laser light-scattering.Results. In TB patients, TC (147.0±37 vs. 168±44 mg dL-1), HDL-C (37±14 vs. 55±18 mg dL-1) and apolipoprotein A-I (102±41 vs. 156±47 mg dL-1) concentrations were lower (P<0.0001), while HDL particle size (10.16±1.02 vs. 9.62±0.67 nm) and SAA levels (280±36 vs. 19±8 mg L-1) were higher (P<0.0001). Using receiver-operating characteristic curve analysis for predicting TB, the cutoff values were <83.85 mg L-1 for SAA (sensitivity=96.88 %, specificity=78.43 %, P<0.0001), >44.50 mg dL-1 for HDL-C (sensitivity=75 %, specificity=72.16 %, P<0.001) and >118.5 mg dL-1 for apolipoprotein A-I (sensitivity=83.83 %, specificity=72.22 %, P<0.001).Conclusion. SAA, HDL-C and apolipoprotein A-I are associated with TB infection and could be used as laboratory biomarkers, especially in patients who are negative for alcohol-acid-resistant bacilli.