The Endogenous Inhibitor of CETP, apoC1, Remains Ineffective In Vivo after Correction of Hyperglycemia in People with Type 1 Diabetes

Abstract

ApolipoproteinC1 (apoC1) is the main physiological inhibitor of the cholesterol ester transfer protein (CETP). Increased CETP activity is associated with macrovascular complications in patients with type 1 diabetes (T1D). ApoC1 has lost its ability to inhibit CETP in patients with T1D, and in vitro glycation of apoC1 increases CETP activity, suggesting that hyperglycemia could be a factor implicated in the loss of the inhibitory effect of apoC1 on CETP. Thus, we aimed to see whether improvement of glycemic control might restore apoC1 inhibitory effect on CETP. We studied 98 patients with T1D and HbA1c > 9% at baseline and 3 months after improvement of glycemic control by a medical intervention (insulin introduction or changes in multi-injection therapy or pump therapy introduction/therapeutic education for all patients). CETP activity was assessed by a radioactive method and plasma apoC1 levels were measured by ELISA. The different isoforms of apoC1 were determined by mass spectrometry. CETP activity was not significantly modified after improvement of glycemic control, despite a significant reduction in mean HbA1c (8.7 ± 1.7 vs. 10.8 ± 2, p < 0.0001). No association between plasma apoC1 and CETP activity was observed in patients with T1D at baseline, nor at 3 months, even in the subgroup of patients with optimal control (3-month HbA1c < 7%). We did not find any glycated form of apoC1 using mass spectrometry in people with T1D. Hyperglycemia in vivo does not seem to be a major factor implicated in the loss of apoC1 ability to inhibit CETP activity observed in T1D. Other factors, such as qualitative abnormalities of lipoproteins, could be involved. Our data emphasize the fact that hyperglycemia is not the only factor involved in lipid abnormalities and macrovascular complications in T1D. Clinical trial reg. no. NCT02816099 ClinicalTrials.gov.

Keywords

• type 1 diabetes
• hyperglycemia
• apolipoprotein C1
• CETP
• glycation