A new method for quantification of islets by measurement of zinc content

The ability to quantify the yield of pancreatic islet tissue after isolation is important for interlaboratory comparisons and for the assessment of islet yield prior to clinical transplantation. Because pancreatic islets contain a much higher concentration of zinc than other tissues, we investigated the analysis of zinc as a measure of islet tissue yield. Rat islets of standard diameter 250 microns were handpicked into samples containing 10-80 islets. The zinc content was measured by EAAS and showed a linear correlation with islet number. A zinc binding fluorescent dye, TSQ, was investigated as a way of simplifying the zinc measurement for routine use. Samples of 10-80 islets of 250 microns were sonicated in 3 ml zinc-free water, 0.18 mumol TSQ was added, and the TSQ-zinc fluorescence was measured at 480 nm. A linear correlation was observed. Exocrine contamination up to 50% barely affected the results. Islet zinc content also was shown to be correlated linearly with islet number for freshly isolated human islets. Measurement of zinc by TSQ fluorescence is a rapid, cheap, and objective measure of islet tissue content.