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Standardized assessment of islet quality is imperative for clinical islet transplantation. We have previously shown that the increment in oxygen consumption rate stimulated by glucose (∆OCR glc ) can predict in vivo efficacy of islet transplantation in mice. To further evaluate the approach, we studied three factors: islet specificity, islet composition and agreement between results obtained by different groups. Equivalent perifusion systems were set up at the City of Hope and the University of Washington and the values of ∆OCR glc obtained at both institutions were compared. Islet specificity was determined by comparing ∆OCR glc in islet and nonislet tissue. The ∆OCR glc ranged from 0.01 to 0.19 nmol/min/100 islets (n = 14), a wide range in islet quality, but the values obtained by the two centers were similar. The contribution from nonislet impurities was negligible (∆OCR glc was 0.12 nmol/min/100 islets vs. 0.007 nmol/min/100 nonislet clusters). The ∆OCR glc was statistically independent of percent beta cells, demonstrating that ∆OCR glc is governed more by islet quality than by islet composition. The ∆OCR glc , but not the absolute level of OCR, was predictive of reversal of hyperglycemia in diabetic mice. These demonstrations lay the foundation for testing ∆OCR glc as a measurement of islet quality for human islet transplantation.

Increased dietary fructose may produce insulin insensitivity and elevate blood pressure in rats. It is possible that the reduced magnesium content of the high-fructose commercial diet used in some studies may play a role in these abnormalities because it is known that magnesium deficiency can produce insulin insensitivity and increased angiotensin II action in humans. To study this, we maintained rats for 9 weeks on either a normal control diet, a standard high-fructose diet, or the same high-fructose diet supplemented with magnesium. Glucose uptake was assessed using a perfused rat hindquarter preparation sequentially with 0, 900, and 120,000 pmol/L of added insulin. Basal serum glucose, plasma insulin, and basal glucose uptake in the absence of insulin were similar among all three groups. However, insulin sensitivity, defined as glucose uptake in the presence of 900 pmol/L insulin minus basal, was depressed in the high-fructose compared with the control group (1.02 +/- 0.38 to 1.77 +/- 0.57 mumol/g per hour, P < .05). In contrast, the high-fructose group supplemented with normal magnesium had similar insulin sensitivity as the control group (2.09 +/- 0.69 mumol/g per hour). Total serum magnesium was reduced in the high-fructose group compared with control or high-fructose plus magnesium-supplemented groups. Blood pressure and fasting insulin levels were also lower in the magnesium-supplemented group. These results suggest that magnesium deficiency and not fructose ingestion per se leads to insulin insensitivity in skeletal muscle and changes in blood pressure.

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