Effect of Metformin on Vascular and Mitochondrial Function in Type 1 Diabetes

Determine the effect of metformin on insulin sensitivity in T1D. Reported measure is glucose infusion rate during hyperinsulinemic euglycemic clamp normalized to total body weight. For this measure, insulin was infused at 40 mU/m2 surface area. Blood sugar wass checked every 5 minutes and glucose infusion adjusted to maintain glucose level at 90 mg/dL for 2 hours. The glucose infusion rate for the final 30 minutes is reported as GIR (aka M-value or glucose disposal rate) in mg glucose/kg*min. A higher value corresponds to greater sensitivity to insulin. There is no strictly defined normal range.

Measure of endothelial function by brachial ultrasound of the percent dilation after 5 minutes of occlusion.

Pulse wave velocity by Sphygmacor as a measure of aortic stiffness in m/sec.

Augmentation index by Sphygmacor is a measure of aortic arterial stiffness. AI@75 is the ratio of augmented pressure/pulse pressure adjusted to a heart rate of 75.

Oxygen consumption rate with various substrates and max uncoupled O2 consumption.

Measure is performed on permeabilized muscle fibers from biopsy tissue from the vastus lateralis using the Oroboros OxygraphO2k high resolution respirometer. State 3 is full coupled oxygen flux using PMG or PMGS (pyruvate, malate, glutamate, +/- succinate) or OCMS (octanyl carnitine, malate, +/- succinate) as substrates. state 4 is after addition of oligomycin to inhibit the ATP synthase and thus corresponds to the maximum leak state where O2 consumption is limited by the buildup of the proton gradient and can only proceed as fast as the protons can leak back across the membrane. FCCP is added as an uncoupler, allowing free leakage of protons across the inner membrane, and thus measures maximum possible O2 flux. There are no defined normal ranges, but higher state 3 and uncoupled flux indicate better mitochondrial function, while state 4 is needed to correct state 3 to the fully coupled flux.

Mito content by Western Blotting of electron transport chain complexes I, II, III, and V. complex 1 utilizes NADH from pyruvate/malate/glutamate while complex II utilizes FADH from succinate. complex III is the cytochrome c reductase while complex V is the ATP synthase.

hsCRP (mg/L) by Beckman Coulter assay

measure of autonomic function: ratio of fastest to slowest heart rate during valsalva maneuver

Mean Glucose & Glucose Standard Deviation (Glycemic Variability) by Dexcom CGM

Percent of time less than 70 mg/dL during the final week of each phase by Dexcom CGM.

Glucagon (pg/ml); baseline on AM of each phase final study visit.

Glucose (mg/dL), triglycerides (mg/dL), cholesterol (mg/dL) at baseline after each phase

fatty acids (microeq/L) at baseline after each phase in the AM of the final visit

glycerol (micromol/L) at baseline after each phase in the AM of the final phase visit

insulin (microIU/ml) at baseline after each phase in the AM of the final phase visit

lactate (mmol/L) at baseline after each phase in the AM of the final phase visit

adiponection (microg/ml) at baseline after each phase in the AM of the final phase visit

endothelin-1 at baseline after each phase in the AM of the final phase visit by peninsula labs radioimmunoassay

Measured by 31P-mass spec. This ratio measures mitochondrial efficiency. The higher the ratio, the more efficiently the individual converts metabolic substrates into ATP, with the ATP then available for energy-demanding cellular processes such as protein synthesis and biomass production

Measured by 31P-mass spec. ADP time constant and phosphocreatine time constant. ADP time constant is a measure of the time required to convert ADP → ATP and is a measure of muscle mitochondrial health (energy metabolism). A faster recovery is a better outcome; a slower recovery is a worse outcome. Similarly for phosphocreatine.

Measured by 31P-mass spec. For each measure, a higher value indicates better mitochondrial function. All re calculated from multiple measures from the MRS spectra. These are relatively new research measures and normal values are not known or generally accepted.

• QMax is theoretical maximum activity.
• VPCr measures the rate at which PCr is regenerated.

Measured by 31P-mass spec. A higher value indicates better mitochondrial function. All re calculated from multiple measures from the MRS spectra. These are relatively new research measures and normal values are not known or generally accepted. Oxidative Phosphorylation measures the rate at which electron transport activity generates phosphorylated energy sources (ATP and PCr)

Measured by 31P-mass spec. Anaerobic glycolysis measures the amount of anaerobic ATP generation for energy. It is generally felt that a higher value here reflects impaired mitochondrial function necessitating greater reliance on anaerobic metabolism.

Cardiac output

PAI-1 exploratory thromobotic marker.

ICAM

TBARs, GSSG:GSH ratio

oxidant generation

IL6, TNF alpha

exploratory measure looking at H2O2 production. not performed due to equipment not available.