Ultrastructural aspects of streptozotocin cytotoxicity on rat pancreatic islets in vitro. Test of a protective effect of zinc

Morphological and gene expression analysis in mouse primary cultured hepatocytes exposed to streptozotocin

Streptozotocin (SZ) is known to exert toxic effects not only on pancreatic islet beta cells but also on other organs including the liver. For analyzing direct effects of SZ on hepatocytes, we performed morphological analysis and DNA microarray analysis on mouse primary cultured hepatocytes. Hepatocytes were taken from non-treated Crj:CD-1(ICR) mice. The primary cultured hepatocytes were treated with SZ at concentrations of 0, 1, 3, 10, 30 and 100 mM. After the treatment for about 6 or 24h, cell survival assay using tetrazolium salt (WST-1), light microscopic/electron microscopic analysis and gene expression analysis were performed. For the gene expression analysis, target (labeled cRNA) prepared from total RNA of the hepatocytes was hybridized to the GeneChip Murine Genome U74A V.2 (Affymetrix). The signal intensity calculation and scaling were performed using Microarray Suite Software Ver 5.0. IC50 of the cell survival assay was around 62 mM at 6 h exposure and 7 mM at 24 h exposure. Marked chromatin margination was observed in nuclei of the hepatocytes treated with SZ at concentrations of 3 or 10mM. Gene expression analysis revealed similar expression changes to those of in vivo, i.e. up-regulation in cell proliferation/ apoptosis related genes, and down-regulation of lipid metabolism related genes. These results potently supported the hypothesis that many of the hepatic alteration including histopathological and gene expression changes are induced by direct effect of SZ rather than by the secondary effect of the hyperglycemia or hypoinsulinemia.

Decrease in insulin-containing secretory granules and mitochondrial gene expression in mouse pancreatic islets maintained in culture following streptozotocin exposure

We have previously described a preferential reduction in the secretory response to nutrient secretagogues in pancreatic mouse islets maintained in culture after in vitro exposure to streptozotocin (SZ). This reduction was associated with an impaired substrate metabolism at the mitochondrial level. To further clarify this issue, mouse pancreatic islets were exposed in vitro to 2.2 mM SZ for 30 min. At 4 h after SZ treatment ultrastructural changes were apparent in the endoplasmic reticulum and Golgi areas of the B-cells. However, 2 and 6 days following SZ exposure the B-cells appeared well preserved, except for a marked decrease in the number of insulin-containing secretory granules. A morphometric analysis of the B-cells 6 days after SZ exposure showed a normal B-cell size and a normal volume fraction of B-cell mitochondria. However, there was a decrease in total islet size and a 13% decrease in the volume fraction of B-cells in the islets. These mouse islets exhibited a decreased content of the mitochondrial DNA-encoded cytochrome b mRNA, as evaluated by dot-blot analysis. As a whole, the data obtained indicate that SZ treatment does not induce a decrease in the number of mitochondria or long-lasting ultrastructural damage to this organelle. However, there is a clear decrease in the cytochrome b mRNA, suggesting that SZ can induce damage to the mitochondrial DNA.