The Health Influences of Puberty (HIP) Study

Specific Aims:

Pediatric insulin resistance and related disorders, such as type 2 diabetes mellitus (T2DM), are increasing in prevalence, and portend significant end-organ and cardiovascular morbidity and mortality. Thus, measures aimed at understanding its causes and preventing its onset are critical. The physiologic decrease in insulin sensitivity in all adolescents during puberty is well-established. It is also known that obese adolescents start out less insulin sensitive at the onset of puberty than lean adolescents, and that their insulin sensitivity worsens as puberty progresses. While there are both longitudinal and cross-sectional data confirming the natural recovery of pre-pubertal insulin sensitivity in normal weight adolescents after puberty is completed, it is unknown whether obese adolescents recover their pre-pubertal insulin sensitivity. Failure to regain pre-pubertal insulin sensitivity at the end of puberty, and failure of compensatory insulin secretion, may accelerate progression from obesity to insulin resistance to T2DM in at-risk youth and contribute to long-term cardiovascular risk.

In addition, obesity and insulin resistance are associated with earlier onset of puberty and premature adrenarche in females. Insulin resistance also contributes to the gonadal dysfunction of polycystic ovarian disease in fully pubertal females and is associated with hypogonadism in older adult males. Little is known about effects of obesity and insulin resistance on gonadal function in young males. However, persistent metabolic changes at the end of puberty may contribute to gonadal dysfunction in obese youth. Currently, there are few longitudinal studies in either sex that evaluate the interactions among obesity, insulin resistance and gonadal function during puberty.

The investigators' long-term goal is to better understand the metabolic changes that occur during puberty, their underlying mechanisms, and their potential contribution to adult disease. The overall aim is to evaluate the effects of obesity on the evolution of insulin sensitivity and gonadal function during puberty. In addition, because improvement in insulin action during puberty may slow β-cell deterioration, the investigators will evaluate whether compensatory insulin secretion is also affected in obese adolescents and whether treatment with metformin improves β-cell response.

HYPOTHESES:

• Obese adolescents will show decreased improvement in insulin sensitivity from Tanner stage 2/3 to Tanner 5 when compared with lean counterparts.
• Obese adolescents treated with metformin will have greater improvement in insulin sensitivity from Tanner stage 2/3 to Tanner 5 vs. those treated with placebo. (See hypothesis schematics below)

To test these hypotheses, we propose to address the following Specific Aims:

SPECIFIC AIM 1 (Observational Arm):

• To compare longitudinal changes in insulin sensitivity and secretion and their correlates in obese and normal weight adolescents during puberty.

• Primary outcome: Change in insulin sensitivity (Si), as measured by frequently sampled intravenous glucose tolerance test (IVGTT), from early puberty to puberty completion in obese and normal weight adolescents.
• Secondary outcomes: Change in insulin secretion (AIR) and disposition index (DI) as measured by IVGTT, body composition, fat distribution, markers of gonadal function, and inflammatory markers over time in these groups.

SPECIFIC AIM 2 (Treatment Arm):

• To compare longitudinal changes in insulin sensitivity and secretion and their correlates in obese adolescents treated with metformin or placebo during puberty.

• Primary outcome: Change in Si from early puberty to puberty completion in obese controls and obese adolescents treated with metformin.
• Secondary outcome: Change in AIR and DI, body composition, fat distribution, markers of gonadal function, and inflammatory markers over time in these groups.

Inclusion criteria

• BMI ≥ 95th percentile
• At least Tanner 2, but no more than Tanner 3
• Age ≥ 9 years
• Absence of impaired glucose tolerance (IGT), impaired fasting glucose (IFG) or Type 2 diabetes mellitus (T2DM)

Exclusion criteria

• Presence of T2DM, IGT or IFG
• Any disorder or medication known to effect glucose tolerance;
• Hypertension or hyperlipidemia requiring pharmacological intervention;
• Weight >300lbs. due to limits of imaging tables.
• Chronic illness