Reduced number of circulating monocytes after institution of insulin therapy--relevance for development of atherosclerosis in diabetics?

Diabetes propels the risk for cardiovascular disease: sweet monocytes becoming aggressive?

Diabetes strongly predisposes to cardiovascular disease (CVD), the leading cause of mortality in these patients, as well as in the entire population. Hyperglycemia is an important cardiovascular risk factor as shown by the observation that even transient periods of hyperglycemia, despite return to normoglycemia during follow-up, increase the risk for CVD, a phenomenon termed 'hyperglycemic memory'. The molecular mechanisms underlying this phenomenon remain largely unknown. As inflammation plays an important role in the pathogenesis of atherosclerosis, we propose that long-term functional reprogramming of monocytes and macrophages, induced by hyperglycemia, plays an important role in the phenomenon of hyperglycemic memory leading to cardiovascular complications in patients with diabetes. In this review, we discuss recent insights showing that innate immune cells possess the capacity to reprogram their function through epigenetically mediated rewiring of gene transcription, a process termed 'trained immunity'. The long-term reprogramming of monocytes can be induced by microbial as well as metabolic products, and involves a shift in cellular metabolism from oxidative phosphorylation to aerobic glycolysis. We hypothesize that hyperglycemia in diabetes patients induces long-term activation of monocytes and macrophages through similar mechanisms, thereby contributing to plaque development and subsequent macrovascular complications.

Disordered haematopoiesis and athero-thrombosis

Atherosclerosis, the major underlying cause of cardiovascular disease, is characterized by a lipid-driven infiltration of inflammatory cells in large and medium arteries. Increased production and activation of monocytes, neutrophils, and platelets, driven by hypercholesterolaemia and defective high-density lipoproteins-mediated cholesterol efflux, tissue necrosis and cytokine production after myocardial infarction, or metabolic abnormalities associated with diabetes, contribute to atherogenesis and athero-thrombosis. This suggests that in addition to traditional approaches of low-density lipoproteins lowering and anti-platelet drugs, therapies directed at abnormal haematopoiesis, including anti-inflammatory agents, drugs that suppress myelopoiesis, and excessive platelet production, rHDL infusions and anti-obesity and anti-diabetic agents, may help to prevent athero-thrombosis.

Hyperglycemia promotes myelopoiesis and impairs the resolution of atherosclerosis

Diabetes is a major risk factor for atherosclerosis. Although atherosclerosis is initiated by deposition of cholesterol-rich lipoproteins in the artery wall, the entry of inflammatory leukocytes into lesions fuels disease progression and impairs resolution. We show that diabetic mice have increased numbers of circulating neutrophils and Ly6-C(hi) monocytes, reflecting hyperglycemia-induced proliferation and expansion of bone marrow myeloid progenitors and release of monocytes into the circulation. Increased neutrophil production of S100A8/S100A9, and its subsequent interaction with the receptor for advanced glycation end products on common myeloid progenitor cells, leads to enhanced myelopoiesis. Treatment of hyperglycemia reduces monocytosis, entry of monocytes into atherosclerotic lesions, and promotes regression. In patients with type 1 diabetes, plasma S100A8/S100A9 levels correlate with leukocyte counts and coronary artery disease. Thus, hyperglycemia drives myelopoiesis and promotes atherogenesis in diabetes.

Blood pressure reactions to insulin treatment in patients with type 2 diabetes

BACKGROUND

The initiation of insulin therapy may be easy and uncomplicated in some patients with type 2 diabetes, but in others, mainly in obese patients, problems often arise (ie, poor compliance, worsening B-cell function and/or insulin resistance).

METHODS

As a substudy of a broader investigation concerning hemorheological effects of insulin treatment in insufficiently controlled type 2 diabetes, blood pressure was recorded in 12 patients at baseline, after two months and after four months on insulin.

RESULTS

After two months on insulin, analyses of triglycerides, high-density lipoprotein cholesterol and total cholesterol indicated metabolic improvement (P<0.05 to 0.001) and a surprisingly uniform increase of blood pressure values (P<0.05 to 0.01) was found. At the same time, the serum sodium concentration increased (P<0.01) and was positively correlated to both systolic and diastolic blood pressure (P<0.01). After four months on insulin, blood pressure returned to pretreatment values or lower (P<0.05 to 0.01). Serum sodium also decreased to pretreatment values. No significant changes of the flow behaviour of blood were seen after the initiation of insulin.

CONCLUSIONS

The number of patients was small and the study was not primarily designed to examine blood pressure. The preliminary conclusion from the present study, however, is that the initiation of insulin treatment in poorly controlled type 2 diabetes causes a temporary and possibly clinically significant elevation of blood pressure. A change in renal treatment of sodium caused by insulin may be one of several possible explanations of the results, but further studies are warranted to confirm the findings.

Effect of hyperketonemia on blood monocytes in type-I diabetic patients and apoptosis in cultured U937 monocytes

Recent studies have proposed a role for a reduced number of circulating monocytes in the development of atherosclerosis and circulatory diseases in diabetes. Ketosis is frequently encountered in type-I diabetics. This study was undertaken to test the hypothesis that hyperketonemia can lower blood monocyte count in type-I diabetic patients. Blood monocyte count was significantly lower (p < 0.05) in diabetics (n = 27) compared with age-matched normal siblings (n = 22). Blood levels of acetoacetate (AA) and triglycerides were significantly higher in diabetics compared with normals. To examine whether hyperketonemia can directly alter the monocyte count in diabetics, we studied the effect of ketone bodies AA and beta-hydroxybutyrate (BHB) on U937 cells, a human-derived promonocytic cell line as an in vitro model. The cell culture studies showed a dose-dependent growth inhibition and induction of apoptosis as a result of treatment with AA in U937 cells. Furthermore, there was a significant decrease in GSH and increase in lipid peroxidation products in AA-treated U937 cells. Taken together, this study suggests that elevated levels of ketone body AA can result in oxidative damage, accelerated apoptosis, and inhibition of cell growth in monocytes, which in turn can lower monocyte count in the blood of type-I diabetic patients.