The Effects of Hypoglycaemia on Inflammation and Atherosclerosis.

Hypoglycaemia is associated with cardiovascular (CV) events in diabetes. The mechanisms through which hypoglycaemia may increase CV risk, however, remain to be elucidated. I hypothesised that hypoglycaemia induces activation of the innate immune system, through: monocyte mobilisation and activation, increased platelet reactivity and platelet-leukocyte interactions and therefore accelerates pre-established atherosclerosis through inflammatory pathways. I conducted studies in both man and mouse. In a novel human experimental model of combined hypoglycaemia and low-dose endotoxin challenge, I studied 24 healthy participants that underwent either a hyperinsulinaemic-hypoglycaemic (2.5 mmol/l) (n=8), euglycaemic (6.0 mmol/l) (n=8) or sham-saline clamp (n=8) (normoglycaemic conditions). To determine if antecedent hypoglycaemia modified innate immune responses, all participants then received a low dose (0.3 ng/kg) intravenous endotoxin challenge 48 hours later. I studied in vivo monocyte mobilisation and monocyte-platelet interactions. In comparison to controls, hypoglycaemia increased total leukocytes and significantly mobilised pro-inflammatory CD16+ monocytes. Platelet aggregation to agonist, and formation of monocyte-platelet aggregates, increased following hypoglycaemia with significant aggregation of CD16+ monocytes and platelets. Compared to euglycaemia, hypoglycaemia caused greater leukocyte mobilisation in response to endotoxin stimulation 48 hours later. In mice, I developed a unique model of recurrent insulin induced hypoglycaemia (n=10) or sham-saline injection (n=10) in high fat diet fed Apolipoprotein E deficient mice (ApoE -/-) that had pre-established atherosclerotic plaques. I show that 8 episodes of a modest recurrent hypoglycaemic stimulus over 4 weeks compared to sham-saline injection resulted in a trend towards increased total atherosclerotic burden in whole aortae. I conclude that hypoglycaemia mobilises monocytes, increases platelet reactivity, promotes interaction between platelets and pro-inflammatory monocyte subsets, and changes the subsequent immune response to endotoxin in humans. In mice, data suggest pro-atherosclerotic effects of recurrent hypoglycaemia that abolish anti-atherogenic effects of insulin. Collectively, these data highlight mechanisms whereby hypoglycaemia may increase CV risk.