Sensitivity to pentamidine but resistance to streptozotocin of tumoral insulin-producing cells (RINm5F line)

Effect of cimetidine on pentamidine induced hyperglycemia in rats

The antiprotozoal agent pentamidine, used for the treatment of Pneumocystis jirovecii pneumonia (PCP), is known to cause abnormalities in blood glucose homeostasis, such as hypoglycemia and hyperglycemia. Pentamidine has been reported to be a substrate of organic cation transporter 1 (OCT1). We investigated the combination effects of cimetidine, an OCT1 inhibitor, on the pharmacokinetics of pentamidine and on pentamidine-induced hyperglycemia. Pentamidine was infused intravenously to rats for 20 min at a dose of 7.5 or 15 mg/kg and serum samples were obtained periodically. The serum concentration of glucose did not change significantly after pentamidine infusion at 7.5mg/kg, while it increased with pentamidine at 15 mg/kg, and the maximal concentration of glucose was 167 ± 36 mg/dl, 30 min after the start of pentamidine infusion. Cimetidine (50mg/kg) enhanced the pentamidine-induced elevation of glucose concentration and the maximal concentration of glucose was 208 ± 33 mg/dl in the pentamidine 15 mg/kg treated group. Cimetidine combination significantly reduced total body clearance of pentamidine and increased pentamidine concentrations in the liver, kidneys, and lungs. A significant correlation was found between changes in serum glucose concentrations and serum concentrations of pentamidine 30 min after the start of pentamidine infusion. These results suggest that the hyperglycemic effect of pentamidine is dependent on the concentration of pentamidine and can be enhanced by cimetidine combination.

Cytotoxic action of 2-deoxy-D-glucose tetraacetate in tumoral pancreatic islet cells

Tumoral insulin-producing cells of the RINm5F line were cultured for 8-96 h in the absence or presence of 2-deoxy-D-glucose (0.15-0.80 mM) or its tetraacetate ester (0.08-0.80 mM). Despite the fact that over a short incubation of 120 min the utilization of D-[5-3H]glucose and oxidation of D-[U-14C]glucose were not more markedly decreased by 2-deoxy-D-glucose tetraacetate than by the unesterified glucose analogue, the growth of the tumoral cells, as assessed by either the generation of formazan from 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide or direct cell counting, was more severely affected by the ester than by 2-deoxy-D-glucose. At a high concentration (0.80 mM), the ester even decreased the cell number below its initial value. No restoration of cell growth was observed when the cells were exposed for only 8 h to 2-deoxy-D-glucose tetraacetate (0.80 mM) and then further cultured for 64 h in the absence of the ester. These findings indicate that such an ester acts as a powerful cytostatic and cytotoxic agent in this tumoral cell line.

Effect of beta-cell toxins on genetically engineered insulin-secreting cells

The betacyte is a genetically engineered insulin-secreting liver cell line that is glucose responsive. Whether this cell is affected by specific beta-cell toxins is unknown. To explore this possibility we exposed these cells and those from the NIT-1 beta-cell line (positive controls) to the toxins streptozotocin (STZ, 2.5-20 mM), alloxan (ALL, 2.5-20 mM), and pentamidine (PENT, 10(-6)-1 mM). STZ and ALL were added for 1 h and pentamidine for 24 h. Insulin secretion from betacytes during a period of 5 h after removal of the toxin was inhibited only by pentamidine; all agents were inhibitory to NIT-1 cells. Glucose metabolism, as determined by a colorimetric MTT reduction assay, was adversely affected in betacytes by ALL (20 mM) and PENT (1 mM), and in NIT-1 cells by STZ (20 mM) as well as by ALL (2.5 mM) and PENT (1 mM). The magnitude of inhibition was less for the betacytes-58 v. 99%. Confluence of cells in culture wells and cell viability as assessed by the fluorochromes propidium iodide and acridine orange was reduced to a lesser extent for the betacytes than for the NIT-1 cells. The metabolic and microscopic effects of the toxins were unchanged in the betacyte from those in the liver cell line, HEP G2, from which the betacyte was engineered. These results of general resistance of the betacyte to beta-cell toxins with differing modes of action offer hope that this cell, or cells created in a similar manner from primary hepatocytes, may be at least partly resistant to the adverse effect of beta-cell toxins involved in autoimmune destruction of the pancreas. This increases the potential of the use of these cells for reversal of diabetes.