This was a cross-sectional study of children with and without TID between the ages of 13-20 years who were either of normal weight or were overweight. Subjects with TID were mainly recruited from our diabetes clinics and non-diabetic subjects were recruited through recruitment fliers and campus wide emails. A total of 77 children were enrolled, and 68 completed the study. Data from 2 participants were not included in the analysis: one subject was on oral contraceptive pills (inadvertently consented and screened, despite having an exclusion criterion per protocol, and the other because of markedly abnormal lipid data suggesting a possible genetic mutation in lipoprotein metabolism, also an exclusion criterion). Study subjects were defined as being overweight if their body mass index (BMI) was above the 85th percentile for age and gender and normal weight if their BMI was between the 3rd to 85th percentile for age and gender. The research protocol was approved by the Institutional Review Board at University of Oklahoma Health Sciences Center and all subjects signed an assent form prior to testing.
Inclusion criteria for children with T1D included a diagnosis of type 1 diabetes for more than 3 years and an average HbA1c between 6.5 to 10.7% for the past 6 months. To control for potentially independent effects of extreme hyperglycemia, a cut-off HbA1c level of 10.7% was selected, which represents one standard deviation above the mean HbA1c achieved in the adolescent population during the DCCT. To control for the well-described changes in the rates of diabetic complications after puberty, children who were prepubertal or early pubertal (Tanner 1 and 2) were excluded. Children were excluded from the study if they had any other coexisting endocrine, genetic or metabolic disease, if they were on any medications, including those that could affect substrate metabolism (excluding insulin), psychotropic medications, weight loss medications, and oral contraceptives for female subjects. Inclusion criteria for Tanner stage and ages were identical for non-T1D children. Children were excluded from the study if they had impaired fasting glucose or had diabetes based on fasting glucose values. Additional exclusion criteria were otherwise identical to those listed above for the group with T1D. Two children with coexisting hypothyroidism and 1 child with Addison’s disease, all well-controlled on physiological replacement hormonal therapy, were included in the study. Three diabetic participants treated for urinary microalbuminuria with angiotensin converting enzyme inhibitors (for an average of three years prior to entry into the study) were included.
After obtaining appropriate consent and assent, each child underwent a history and physical exam by a board certified pediatrician. Height and weight were used to calculate BMI, waist and hip circumference were obtained on each subject, and the presence and degree of acanthosis nigricans were noted if present. Then they underwent testing for body composition, vascular elasticity indices and a blood draw for lipid profile and apolipoprotein values. All testing was done in the morning after an overnight fast and was done by an experienced nurse assigned to the study at the General Clinical Research Center at the University of Oklahoma.
Body composition was measured using dual energy x-ray absorptiometry scan (DXA; Hologic QDR 4500, Waltham, MA). Pulse wave analysis determination was made by HDI/Pulsewave CR-2000, Hypertension Diagnostics, Eagan, MN8
. This technique uses a modified Windkessel model to derive information on proximal and distal arteries by analyzing the diastolic part of the arterial wave form 9
. Testing was done in fasting subjects when rested in the supine position. An average of three readings was calculated to derive the mean small artery elasticity index and large artery elasticity index. Age related norms for small artery and large artery compliance have recently been published 8
Blood was analyzed for fasting lipids, apolipoprotein B, and apolipoprotein C-III levels. Total cholesterol, triglycerides and HDL-cholesterol were measured by standardized enzymatic procedure. VLDL-cholesterol and LDL-cholesterol were estimated by Freidewald formula and non HDL-cholesterol was calculated as total cholesterol-HDL-cholesterol.
Blood was frozen for later analysis of apolipoprotein levels. Apolipoprotein levels were measured by immunoturbidimetry as described previously10
. Since heparin-manganese has a high affinity for apoB, apoC-III in the heparin manganese precipitate (HP) is apoC-III bound to apoB-containing lipoproteins, and apoC-III in the heparin-manganese supernate (HS) is apoC-III bound to apoA-containing lipoproteins. ApoC-III is measured in the total plasma sample and in the precipitate following reconstitution to the original volume to obtain apoC-III HP. The value for apoC-III HS was derived by subtracting apoC-III HP from total plasma apoC-III.