High daily insulin exposure in patients with type 2 diabetes is associated with increased risk of cardiovascular events.

AIMS: Intensive glucose control, often involving insulin treatment, failed to improve cardiovascular outcomes in several clinical trials. Observational studies reported an association between insulin use and cardiovascular disease (CVD) risk. It has therefore been suggested that insulin adversely affects CVD risk. To investigate the feasibility of this hypothesis, we studied the association between insulin dose and CVD risk in type 2 diabetes. METHODS: A case-control study was conducted of new users of oral antidiabetics who were prescribed insulin, using the Dutch Pharmo database. Cases were hospitalized for a cardiovascular event (CVE) and matched 1:2 to patients who were not hospitalized for a CVE, by sex, age, duration of diabetes and type of oral antidiabetic. Patients were divided into tertiles according to mean daily insulin dose. Conditional logistic regression analyses were used to explore the association between insulin exposure and CVE risk. RESULTS: We included 836 patients (517 (62%) male, mean age 66 years). After adjusting for available potential confounders, including HbA1c and triglycerides, insulin exposure was positively related to CVE risk (odds ratios for high (≥53.0 U/day) and intermediate (24.3-52.9 U/day) vs. low exposure (≤24.2 U/day): 3.00 [95% confidence interval (CI) 1.70 to 5.28] and 2.03 [95% CI 1.17 to 3.52]. CONCLUSION: Our findings are in line with the suggestion that high-dose insulin therapy adversely affects CVD risk, but need to be interpreted with caution due to the observational nature of the study. The role of particularly high-dose insulin in the progression of CVD warrants further investigation.

Loss of function in heparan sulfate elongation genes EXT1 and EXT 2 results in improved nitric oxide bioavailability and endothelial function.

BACKGROUND: Heparanase is the major enzyme involved in degradation of endothelial heparan sulfates, which is associated with impaired endothelial nitric oxide synthesis. However, the effect of heparan sulfate chain length in relation to endothelial function and nitric oxide availability has never been investigated. We studied the effect of heterozygous mutations in heparan sulfate elongation genes EXT1 and EXT2 on endothelial function in vitro as well as in vivo. METHODS AND RESULT: Flow-mediated dilation, a marker of nitric oxide bioavailability, was studied in Ext1(+/-) and Ext2(+/-) mice versus controls (n=7 per group), as well as in human subjects with heterozygous loss of function mutations in EXT1 and EXT2 (n=13 hereditary multiple exostoses and n=13 controls). Endothelial function was measured in microvascular endothelial cells under laminar flow with or without siRNA targeting EXT1 or EXT2. Endothelial glycocalyx and maximal arteriolar dilatation were significantly altered in Ext1(+/-) and Ext2(+/-) mice compared to wild-type littermates (glycocalyx: wild-type 0.67±0.1 µm, Ext1(+/-) 0.28±0.1 µm and Ext2(+/-) 0.25±0.1 µm, P<0.01, maximal arteriolar dilation during reperfusion: wild-type 11.3±1.0%), Ext1(+/-) 15.2±1.4% and Ext2(+/-) 13.8±1.6% P<0.05). In humans, brachial artery flow-mediated dilation was significantly increased in hereditary multiple exostoses patients (hereditary multiple exostoses 8.1±0.8% versus control 5.6±0.7%, P<0.05). In line, silencing of microvascular endothelial cell EXT1 and EXT2 under flow led to significant upregulation of endothelial nitric oxide synthesis and phospho-endothelial nitric oxide synthesis protein expression. CONCLUSIONS: Our data implicate that heparan sulfate elongation genes EXT1 and EXT2 are involved in maintaining endothelial homeostasis, presumably via increased nitric oxide bioavailability.