Adolescents ages 12–19 years were recruited through posted advertisements or through contact with primary care providers. Interested participants were invited to a screening visit at which time a family history, physical exam, and fasting laboratory evaluation were obtained. Participants who had fasting insulin level >25 microunits/ml or HOMA (Homeostasis model assessment: fasting insulin in microunits/ml × fasting glucose in millimoles/liter/22.5) > 3.5 and 2 out of 3 risk factors (presence of acanthosis nigricans, obesity (BMI >95% for age), or family history of T2DM) were invited to participate in the study. Exclusion criteria included pre-existing diabetes, pregnancy, heart disease, serum gamma-glutamyl transferase (GGT) over 1.5 times the upper limit of normal, or creatinine > 1.5 mg/dl.
We utilized a randomized, placebo controlled double blind design. The protocol was approved by the Colorado Multiple Institutional Review Board (COMIRB). Eligible subjects were invited to the Pediatric (Clinical Translational Research Center CTRC) at the Children’s Hospital in Denver, CO after an overnight fast of at least 10 hours. At this first visit, samples were drawn for insulin, glucose, lipid panel [cholesterol, high density lipoprotein (HDL), low density lipoprotein (LDL), and triglycerides], creatinine, and GGT or (in the last 50 subjects) aspartate aminotransferase (AST) and alanine aminotransferase (ALT). Female subjects not practicing adequate contraception had a urine pregnancy test. Age, race, BMI, blood pressure (BP), sexual history, alcohol consumption, exercise history, and family history of diabetes were recorded. Subjects then underwent a 2-hour oral glucose tolerance test with a 75 gram glucose load.
Subjects completed a food frequency questionnaire and received written information about symptoms of diabetes from a study physician. They watched a video that emphasized modest calorie reduction, decreased fat and simple sugar consumption, increased fiber, fruit and vegetable intake, and regular aerobic exercise. Subjects then worked with a dietician or study investigator to choose 3 goals for themselves, related to dietary or exercise changes. They were assisted in choosing very specific goals that were attainable in a 1-month period, for example decreasing soda intake from 3 daily to 1 daily. All subjects were encouraged to choose at least one goal related to exercise. They were given a calendar and instructed to record progress on their goals and record if they took the medication.
Upon completion of the baseline visit, subjects were randomized 2:1 by the CTRC pharmacist to receive metformin or placebo. Randomization was stratified by race (AA or other) and fasting insulin level (greater than or less than 40 IU/ml). Subjects were started on metformin or placebo 500 mg once daily. At one month, the dose increased to 500 mg twice daily, followed by an increase to 850 mg twice daily at 2 months. If gastrointestinal side effects persisted for more than 2 weeks, the dose was lowered to the previously tolerated dose.
Subjects were seen monthly for measurement of weight and BP, urine pregnancy test if indicated, assessment of adherence to goals, contraception, alcohol consumption, and adherence with and tolerability of treatment. The research assistant met subjects at a convenient location chosen by the subject; the only requirement being the presence of a scale. The majority of follow-up visits were conducted at schools. A pill count was to be completed at each visit; however, most pill counts were estimated by subjects, as they were unable to carry medications at school. In this population of largely indigent patients followed at school-based health centers subjects were considered adherent if 4 or more medication bottles were dispensed over the 6th month study. With this cut-off, subjects should have taken the maximum dose of metformin for at least 2 months. Subjects were allowed to modify their personal goals at each visit. The research assistant was trained by the study dietician to assess whether subjects had been adherent with their goals and to encourage change to more or less difficult goals if necessary.
At 6 months, the subjects returned to the Pediatric CTRC after a 10 hour fast. Outcome measures obtained included fasting insulin, fasting and 2-hour glucose, lipid panel, BMI, and BP. Subjects again completed a food frequency questionnaire. Subjects were also interviewed regarding lifestyle changes they had made during the 6-month study period. The interview was conducted in a motivational style to promote continued healthy lifestyle changes by an interviewer unaware of group assignment. Responses per subject could be multiple. Subject responses were grouped into categories based on similar themes.
All laboratory assays, except serum insulin, were performed by standard clinical laboratory procedure at the Children’s Hospital in Denver. Insulin assay was performed by microparticle enzyme immunoassay (Diagnostic Systems Lab) at the Core Laboratory of the General Clinical Research Center at the University of Colorado at Denver and Health Sciences Center. The sensitivity of the assay is 3 microunits/ml . Within day precision is 5.2 microunits/ml; between-day precision is 9.8 microunits/ml.
T-tests and stepwise logistic regression analysis were performed to analyze the relationship between selected variables (sex, medication group, and specific goal type including increase in exercise, decrease in portion size, increase in positive dietary choices, and decrease in negative dietary choices) to a decrease in BMI of >5% or more. All statistical analyses were performed using SPSS/PC (version 14; 2006[H1]).