This study is designed to investigate the effects of metformin, a commonly prescribed first line medication for diabetes and recommended for prediabetes, on the levels of the potentially tissue damaging reactive product (MG) in the blood and its cleared counterpart in the urine (IMZ). The study will involve patients with elevated HbA1c randomized to receive either metformin or a similar inactive placebo pill and a group of sex and age matched volunteers without diabetes. Study participants will be recruited from the University of Arizona Medical Center, South Campus clinics (Endocrine clinic, family medicine clinic and general medicine clinic). Eighty patients with HbA1c >6.0% will be randomized to receive either metformin or a similar inactive placebo for 6 weeks. The response of these patients will be compared to 40 patients normal HbA1c <5.6% who will not receive either study medication. Investigators will compare the plasma MG and urine IMZ concentration/content between the 3 groups before and after the 6-week intervention. It is hypothesized that plasma MG level in the metformin treatment group will be less than in the group taking the placebo pills, while there will be no significant difference in MG level between the metformin treatment group and the volunteers without diabetes.

A prospective randomized controlled clinical trial of 120 adult patients will be conducted from June 2015 to June 2017 (2 years). Study participants will be recruited from the University of Arizona Medical Center, South Campus clinics (Endocrine clinic, family medicine clinic and general medicine clinic).

Eighty patients with HbA1c* >6.0% will be randomized to receive either metformin or a similar inactive placebo for 6 weeks. The response of these patients will be compared to 40 patients with normal HbA1c <5.6% who will not receive either study medication.

Twenty four-hour urine samples will be analyzed to measure metformin-MG adducted product (IMZ) at baseline (D0) and at the end of the study period (D42). Blood sample will be analyzed at the baseline to measure the plasma methylglyoxal concentration (baseline MG concentration- D0) and re-measure it at the end of the study period(D42). Mass spectrometry will be performed for samples analysis to detect the plasma methylglyoxal (MG) level. Metformin-MG adducted product (IMZ) will be measured using Multiple Reaction Method (MRM). Also, Mass spectrometry will be performed to detect plasma protein modifications at baseline and at the end of the study period (after 6 weeks). Investigators will measure the concentrations of IMZ and MG in the human urine and plasma of our cohort in the nM and μM range, respectively via mass spectrometry. Investigators will be normalizing these values by specific gravity.

A logbook will be provided to each participant to record their blood sugar measurements at home. Investigators will provide glucometer (One Touch glucometer), strips and lancets to patients who never had glucometer before enrolling to our study. Participants taking metformin or placebo will be asked to perform an 4-point self-measured blood sugar profile with measurements taken as indicated in the table (once a week). Investigators will contact study participants (treatment and placebo group only) by phone at the mid of the study period (D21) to follow up on the recorded fasting blood glucose levels and development of side effects. The results of the blood sugar measurements will help the study physicians to adjust diabetes therapy (metformin or the other concomitant diabetes medications) in order that the study subjects maintain appropriate blood glucose control (target pre-meal and bedtime glucose between 90-180 mg/dL).

The participants in the non-diabetic group, they will not receive either metformin hydrochloride or placebo. Their fasting blood glucose, plasma MG level and urine IMZ level will be measured during the study. They will not be required to perform 4 point testing. They will have all the same clinic visits and lab orders as diabetic patients except receiving the study medication.

It is hypothesized that plasma MG level in the metformin treatment group will be less than in the group taking the placebo pills, while there will be no significant difference in MG level between the metformin treatment group and the volunteers without diabetes.

Inclusion Criteria:

• Elevated HbA1c > 6.0% (patients with type 2 diabetes mellitus or prediabetes), HbA1C < 9.0%
• For matched non-diabetic patients: HbA1C ≤ 5.6%
• Serum creatinine (SCr) < 1.5 mg/dL in males or < 1.4 mg/dL in females,
• Calculated glomerular filtration rate (GFR) > 60 ml/min/1.73m2,
• Body mass index (BMI) 25-40 kg/m2,
• Glycosylated hemoglobin A1C (HA1C) < 9%,
• No known intolerance to metformin
• Has not taken metformin previous 3 months

Exclusion Criteria:

• Patients on thiazolidinediones (TZD)
• Patients with history of metformin intolerance (gastrointestinal side effects or poor renal function; Serum Cr > 1.5mg/dL in males or > 1.4 mg/dL in females or calculated GFR < 60 mL/min/1.73m2
• Patients with active (symptomatic or unstable) cardiovascular disease
• Patients requiring home oxygen
• Patients with end-stage liver disease (cirrhosis)
• Patients on oral glucocorticoids within the past 30 days (equivalent to prednisone > 5mg/day)
• Excessive alcohol intake (The Substance Abuse and Mental Health Services Administration (SAMHSA) defines heavy drinking as drinking 5 or more drinks on the same occasion on each of 5 or more days in the past 30 days) 29
• Pregnancy