Human islet oxygen consumption rate and DNA measurements predict diabetes reversal in nude mice

Abstract

There is a need for simple, quantitative and prospective assays for islet quality assessment that are predictive of islet transplantation outcome. The current state-of-the-art athymic nude mouse bioassay is costly, technically challenging and retrospective. In this study, we report on the ability of 2 parameters characterizing human islet quality: (1) oxygen consumption rate (OCR), a measure of viable volume; and (2) OCR/DNA, a measure of fractional viability, to predict diabetes reversal in nude mice. Results demonstrate that the probability for diabetes reversal increases as the graft's OCR/DNA and total OCR increase. For a given transplanted OCR dose, diabetes reversal is strongly dependent on OCR/DNA. The OCR and OCR/DNA (the 'OCR test') data exhibit 89% sensitivity and 77% specificity in predicting diabetes reversal in nude mice (n = 86). We conclude that the prospective OCR test can effectively replace the retrospective athymic nude mouse bioassay in assessing human islet quality prior to islet transplantation.

Figure 1. Blood glucose (BG) levels and rates of diabetes reversal (DR) in athymic nude mice transplanted with 5 OCR doses

Data in the left column were obtained with islets from a preparation with low OCR/DNA, while data in the right column were obtained with islets from a preparation with a higher OCR/DNA. Asterisk (*) denotes DR rates that do not take into account mice that were excluded from the analysis either (a) because of insufficient pre-transplant hyperglycemia (left panel, OCR dose of 2.5 nmol/min) or (b) because of postnephrectomy normoglycemia in cases of DR post-transplant (right panel, OCR dose of 1 nmol/min). Time of nephrectomy is shown with a dashed line when follow-up postnephrectomy was conducted. When transplanted mice were hyperglycemic before nephrectomy, follow-up post-nephrectomy was not necessary and was not conducted.

Figure 2. Rates of diabetes reversal (DR) in athymic nude mice for 3 OCR dose groups (low, 0.5–1.5 nmol/min; medium, 2–2.5 nmol/min; and high, 5–7.5 nmol/min) when transplanted islets were of low (OCR/DNA <125 nmol/min—mg DNA) or higher viability (OCR/DNA >125 nmol/min—mg DNA)

N.S. = nonsignificant.

Figure 3. Probability of diabetes reversal (DR) in the athymic nude mouse bioassay (NMB) as a function of transplanted OCR (a measure of the transplanted viable tissue volume) and OCR/DNA (a measure of islet fractional viability)

The model was based on outcomes from 86 mouse transplants. The model equation and optimization parameters are provided in the text.

Figure 4. Islet fractional viability (FV) based on OCR/DNA plotted against islet FV based on FDA/PI for 43 human islet preparations

OCR/DNA shows a high level of variability in FV among preparations that is not reflected in FDA/PI measurements clustered around 90%.