Glucose impairs B-1 cell function in diabetes

B-1 lymphocytes produce natural immunoglobulin (Ig)M, among which a large proportion is directed against apoptotic cells and altered self-antigens, such as modified low-density lipoprotein (LDL). Thereby, natural IgM maintains homeostasis in the body and is also protective against atherosclerosis. Diabetic patients have an increased risk of developing certain infections as well as atherosclerosis compared with healthy subjects, but the underlying reason is not known. The aim of this study was to investigate whether diabetes and insulin resistance affects B-1 lymphocytes and their production of natural IgM. We found that diabetic db/db mice had lower levels of peritoneal B-1a cells in the steady state-condition compared to controls. Also, activation of B-1 cells with the Toll-like receptor (TLR)-4 agonist Kdo2-Lipid A or immunization against Streptococcus pneumoniae led to a blunted IgM response in the diabetic db/db mice. In-vitro experiments with isolated B-1 cells showed that high concentrations of glucose, but not insulin or leptin, caused a reduced secretion of total IgM and copper-oxidized (CuOx)-LDL- and malondialdehyde (MDA)-LDL-specific IgM from B-1 cells in addition to a decreased differentiation into antibody-producing cells, proliferation arrest and increased apoptosis. These results suggest that metabolic regulation of B-1 cells is of importance for the understanding of the role of this cell type in life-style-related conditions.

Increased lipolysis by secretory phospholipase A(2) group V of lipoproteins in diabetic dyslipidaemia

BACKGROUND

Lipolysis of lipoproteins by secretory phospholipase A(2) group V (sPLA(2)-V) promotes inflammation, lipoprotein aggregation and foam cell formation--all considered as atherogenic mechanisms.

OBJECTIVE

In this study, we compared the susceptibility to sPLA(2)-V lipolysis of VLDL and LDL from individuals with type 2 diabetes and the metabolic syndrome (T2D-MetS) and from healthy controls. Design. VLDL and LDL were isolated from 38 T2D-MetS subjects and 38 controls, treated pair-wise. Extent of sPLA(2)-V lipolysis was measured as release of nonesterified free fatty acids (NEFA). In a subset of the subjects, lipoprotein composition was determined as a relationship between lipid and apolipoprotein components.

RESULTS

Mean paired increase in sPLA(2)-V lipolysis after 1 h for T2D-MetS versus control was 2.0 micromol NEFA l(-1) for VLDL (P = 0.004) and 0.75 micromol NEFA l(-1) for LDL (P = 0.001). There were also substantial differences in lipoprotein composition between the groups. T2D-MetS VLDL had higher triglyceride and cholesterol contents than control VLDL. T2D-MetS LDL was smaller and contained more triglycerides and less cholesterol than control LDL. Both VLDL and LDL from T2D-MetS subjects also contained more apolipoprotein CIII per particle.

CONCLUSION

VLDL and LDL from T2D-MetS individuals were more susceptible to sPLA(2)-V lipolysis than those from control individuals. This may result in elevated levels of NEFA and lysophosphatidylcholine, both in circulation and in LDL, possibly contributing to the elevated inflammatory state and increased risk of cardiovascular diseases seen in these individuals.