Decreased Circulating Lactoferrin in Insulin Resistance and Altered Glucose Tolerance as a Possible Marker of Neutrophil Dysfunction in Type 2 Diabetes

Context: Lactoferrin is an innate immune system protein with multiple beneficial health activities. Objective: To gain insight in the interaction between innate immune system and metabolic disturbances (obesity and insulin resistance), we investigated the relationship between circulating lactoferrin and chronic inflammation-associated insulin resistance according glucose tolerance status in Caucasian population. Design, Setting, Participants, and Main Outcome Measures: Circulating nonstressed lactoferrin (ELISA), metabolic variables, and inflammatory markers were measured in 229 men, 94 with normal (NGT) and 135 with altered glucose tolerance (AGT). Lactoferrin secretion by neutrophil was investigated in whole-blood culture (four young NGT subjects, four older NGT subjects, and four patients with type 2 diabetes) under microbial lipopolysaccharide (LPS) with IL-6 and rosiglitazone treatment. We also tested the lactoferrin action in THP-1 cells under LPS stimulus. Results: Circulating lactoferrin was significantly decreased in patients with AGT (431.5 +/- 187.5 vs. 493.5 +/- 238.9 ng/ml, P = 0.02). In addition, circulating lactoferrin was negatively associated with hyperglycemia and obesity measures and positively with insulin sensitivity. Lactoferrin was negatively related to inflammatory markers, especially in AGT subjects. In ex vivo experiments, we found a significant decrease in LPS-induced lactoferrin release from neutrophils in subjects with type 2 diabetes. IL-6 coincubation decreased LPS-induced lactoferrin release in NGT subjects (P < 0.001). Finally, rosiglitazone treatment led to increased lactoferrin secretion (398 +/- 193 vs. 280.1 +/- 104.9 ng/ml, P < 0.0001). Lactoferrin decreased nuclear factor-kappa beta activation and IL-6, IL-8, and macrophage chemoattractant protein-1 expression under LPS challenge. Conclusions: Decreased circulating lactoferrin levels may play a role in chronic low level inflammation-associated insulin resistance. (J Clin Endocrinol Metab 94: 4036-4044, 2009)