Serum amyloid A: a marker of adiposity-induced low-grade inflammation but not of metabolic status

Abstract

Objective: Adipocytes secrete a series of acute phase proteins including serum amyloid A (SAA); the link with metabolic status is unknown. We studied the variations of expression of the SAA gene in adipose and liver tissues and of SAA serum levels, as well as their relationships with metabolic features during weight loss.

Research methods and procedures: Plasmatic variations of SAA, inflammatory markers (high sensitivity C-reactive protein, interleukin-6, fibrinogen, and orosomucoid), and adipokines (adiponectin, leptin) were studied in 60 morbidly obese patients before and after gastric surgery. For 10 subjects, SAA mRNA expression was measured at baseline in subcutaneous white adipose tissue (scWAT) and visceral white adipose tissue (vWAT) and in the liver. The evolution of SAA mRNA expression was also studied after surgery in scWAT.

Results: SAA serum concentration displayed a significant reduction 3 months after surgery and remained stable beyond 6 months. mRNA expression of inducible SAA isoforms (SAA 1 and 2) in scWAT was higher than in vWAT (p = 0.01) and the liver (p < 0.01) and correlated significantly with BMI, SAA, and high sensitivity C-reactive protein serum concentrations but not with metabolic markers (glucose, insulin, lipid parameters, adiponectin). SAA serum level and its variation during weight loss significantly correlated with adiposity markers (BMI and adipocyte volume, p < 0.01) and inflammatory markers but not with variations of metabolic parameters. The variations of SAA expression in scWAT after surgery correlated with changes in BMI and SAA protein serum levels (p < 0.05).

Discussion: SAA can be considered as a marker of adiposity-induced low-grade inflammation but not of the metabolic status of obese subjects.