Uptake of Labeled Alloxan in Mouse Organs and Mitochondriain Vivoandin Vitro*

Abstract

[14C]2-Alloxan was administered in vivo and in vitro for study of the uptake of alloxan in different organs and their mitochondia of mice. After in vivo administration, radioactivity was demonstrated in all organs investigated, with quantitative differences: endocrine pancreas greater than liver greater than exocrine pancreas and heart. No significant difference was found between the iv and ip routes of injection. An in vivo uptake of alloxan was also found in mitochondria, with significant quantitative differences as to the origin of the organelles: endocrine pancreas greater than liver greater than exocrine pancreas and heart. Pretreatment with D-glucose caused significantly decreased uptake in liver, exocrine pancreas, and heart, but significantly increased uptake in endocrine pancreas, whereas the uptake was significantly decreased in the mitochondria from all of these organs. In vitro uptake was observed in all kinds of mitochondria studied. This uptake was higher than the in vivo uptake in mitochondria from liver, exocrine pancreas, and heart, whereas the uptake in vivo was higher than the in vitro uptake in islet mitochondria. The presence of D-glucose did not affect the in vitro uptake of alloxan in mitochondria. The findings show that in vivo, alloxan passes across plasma membranes and is taken up by mitochondria, and data obtained with mitochondrial subfractions may also indicate a passage across mitochondrial membranes. D-Glucose protection against alloxan diabetogenicity may be associated with prevention of mitochondrial uptake of alloxan. This prevention seems to be dependent on the metabolism of glucose.

The mechanisms of alloxan- and streptozotocin-induced diabetes

“…2) the GLUT2 glucose transporter in the beta cell plasma membrane accepts this glucomimetic and transports it into the cytosol [25,26]. Alloxan does not inhibit the function of the transporter [27], and can therefore selectively enter beta cells in an unrestricted manner [28][29][30]. It is therefore not toxic to insulin-producing cells that do not express this transporter [27,31].…”

Alloxan effects on mitochondria: study of oxygen consumption, fluxes of Mg2+, Ca2+, K+ and adenine nucleotides, membrane potential and volume change in vitro

“…It is of interest that loss of Ca 2+ and swelling are induced by alloxan in isolated mitochondria, since qualitative and quantitative electron microscopy and X-ray microanalysis of islet fl cells from alloxan-treated mice show dislocation of Ca 2+ from mitochondria to cytosol, and volume increases in mitochondria very early during the development of alloxan diabetes [2,3]. Furthermore, study in vivo has demonstrated that alloxan passes across plasma membranes and is taken up in mitochondria inter alia of islet fl cells and hepatocytes [17].…”

“…The pancreatic islets were isolated using the collagenase technique, and the islet mitochondria were isolated as described previously [17] in a medium containing mannitol (190mmol/1), sucrose (60 nmol/1), N-tris(hydroxymethyl)methyl-2-aminoethane sulphonic acid (5 mmol/1), and EDTA (0.5 mmol/1), pH 7.4, with 0.5% bovine serum albumin. The same medium was used in pilot studies for isolation of liver mitochondria for comparison with those isolated in the conventional medium.…”

“…Liver mitochondria were used in these experiments since they are much more easily obtained in sufficient amount than mitochondria from the endocrine pancreas. Also, there is an uptake of alloxan in liver mitochondria both in vivo and in vitro [17], and our preceding work has demonstrated that alloxan affects ion transport in isolated liver mitochondria [18,19]. Recent studies by others, not specifically directed to mitochondria, have verified a considerable, rapid accumulation [20] and cytotoxicity [21] of alloxan in hepatocytes.…”

“…Recent studies by others, not specifically directed to mitochondria, have verified a considerable, rapid accumulation [20] and cytotoxicity [21] of alloxan in hepatocytes. However, mitochondria from mouse endocrine pancreas can be isolated [17], and, to facilitate the interpretation of the data with regard to diabetogenicity of alloxan, some additional experiments were carried out on mitochondria from the endocrine pancreas.…”