In vitro alteration of macrophage phenotype and function by serum lipids

Diabetes (type I and type II) affects approximately 13 million people in th e United States. Delayed and incomplete healing of wounds can be a major pr oblem for diabetic patients. Macrophages are an important cell in the compl ex process of wound repair representing the major source of cytokines throu ghout the wound-healing process. Cytokines mediate many of the cellular res ponses critical to timely wound repair. It has been suggested that diabetes impairs wound heating through disruption of local cytokine production. Our previous in vivo studies in rats demonstrated that diabetes-induced and di et-induced hyperlipidemia cause changes in macrophage phenotype and functio n (Iacopino 1995; Doxey et al. 1998), suggesting that alterations in macrop hage cytokine profiles represent the cellular/molecular mechanism responsib le for delayed wound healing. The purpose of this study was to investigate how monocyte maturation/differentiation and cytokine production were altere d by serum lipids in an in vitro system using human cells. Commercially pre pared purified human monocytes were cultured and exposed to serum lipids. P henotypic analysis of differentiated macrophages was then performed by flow cytometry and fluorescent microscopy using surface antigens specific for v arious macrophage subsets. Selected cytokines in conditioned medium were as sayed using commercial human enzyme-linked immunosorbent assay (ELISA) kits . We demonstrate that serum lipids cause an increase in monocytic different iation leading to an inflammatory macrophage phenotype rather than a repara tive/proliferative phenotype. We also show that serum lipids cause a genera lized decrease in macrophage cytokine production using interleukin-1 beta ( IL-1 beta), tumor necrosis factor alpha (TNF-alpha), platelet-derived growt h factor (PDGF), and transforming growth factor beta 1 (TGF-beta 1) as mark er cytokines. Our present in vitro results using human cells confirm our pr evious in vivo studies in the rat and support the hypothesis that diabetes- induced hyperlipidemia alters the monocyte differentiation process resultin g in changes of macrophage subsets and cytokine release at the wound site, ultimately impairing the wound-healing process.