Hyperglycemic levels of glucose inhibit interleukin 1 release from RAW 264.7 murine macrophages by activation of protein kinase C.

Diabetic patients with hyperglycemia (high blood glucose) have frequent and persistent bacterial infections linked to significantly diminished bactericidal activity and macrophage function. Interleukin-1 (IL-1), released primarily from activated macrophages, is a key mediator of effective host defense against microorganisms. We observe that hyperglycemic levels of D-glucose (8-20 mM) inhibit the release of IL-1 by lipopolysaccharide-stimulated RAW 264.7 murine macrophage cells. An inhibitor of glucose transport and metabolism, 2-deoxyglucose, prevents this inhibition of IL-1 release. High levels (8-20 mM) of fructose and mannose (but not galactose or L-glucose) also inhibit the release of IL-1 activity, suggesting that metabolism is required for IL-1 inhibition. Immunoprecipitation and activity measurements demonstrate that high glucose levels block the release of IL-1 but do not inhibit IL-1 production. High glucose levels (20 mM) increase protein kinase C (PKC) activity, and inhibitors of PKC block the inhibitory effects of glucose. Phorbol 12-myristate 13-acetate, an agonist of PKC, mimics glucose-induced inhibition of IL-1 release. These results demonstrate that high glucose levels inhibit IL-1 release (but not production) by RAW 264. 7 murine macrophages, and this inhibition is mediated by PKC activation. These studies suggest that persistent infections in hyperglycemic patients may be due to an inhibition of IL-1 release from macrophages.