Relation between triketone structure, generation of reactive oxygen species, and selective toxicity of the diabetogenic agent alloxan.

The diabetogenic agent alloxan is a triketone that selectively destroys pancreatic beta cells. To investigate the importance of the triketone structure of alloxan for its cytotoxic potency, alloxan was compared with ninhydrin, also a triketone, and the amino derivative of alloxan uramil, which is not a triketone, because the 5-keto group of the alloxan is replaced by an amino group. Both compounds are cytotoxic but not diabetogenic. Ninhydrin was capable of generating cytotoxic reactive oxygen species (ROS) through redox cycling with dithiols, and uramil could also generate cytotoxic ROS. Both ninhydrin and uramil could not redox cycle with glutathione (GSH) and were not selectively toxic to beta cells; their structure does not allow selective cellular uptake via the GLUT2 glucose transporter. Thus, the results show that the 5-keto group in the pyrimidine ring structure of the triketone alloxan is crucially important for its ability to be selectively taken up into the beta cells via the specific glucose transporter GLUT2. The 5-keto group of the molecule enables redox cycling of alloxan through reaction with glutathione (GSH), thereby generating the cytotoxic ROS. Thus, the unique combination of these two properties confers on alloxan the beta cell-selective toxicity and diabetogenicity. Replacement of the 5-keto group by an amino group, as in uramil, abolishes selective beta cell toxicity because of the loss of the glucose analogue structure and the capability to generate ROS via redox cycling with GSH and cysteine.

[Ninhydrin permeability tests of common packaging materials in the field of fingerprint examination]. / Untersuchung zur Ninhydrinpermeabilität von Verpackungen in der daktyloskopischen Spurensicherung.

With a simple experimental set-up, common packaging materials were tested for their ninhydrin permeability. The packaging material was loaded with a ninhydrin treated paper on the inside and covered with an amino acid treated paper on the outside. If ninhydrin penetrates through the packaging film, "Ruhemann's purple" will form on the amino acid treated paper. In all, 28 packaging materials were tested over a period of 24 weeks. It turned out that all the films made of polyethylene (PE) showed ninhydrin permeability. With one exception, this permeability occurred after three days already. All packages made of other film material were not permeable to ninhydrin.

Comparative toxicity of alloxan, N-alkylalloxans and ninhydrin to isolated pancreatic islets in vitro.

The in vitro toxicity of the diabetogenic agent alloxan as documented by the induction of beta cell necrosis was studied in isolated ob/ob mouse pancreatic islets. The effect of alloxan has been compared with that of a number of N-alkyl alloxan derivatives and with that of the structurally related compound, ninhydrin. Alloxan and its derivatives were selectively toxic to pancreatic beta cells, with other endocrine cells and exocrine parenchymal cells being well preserved, even at high concentration. In contrast, ninhydrin was selectively toxic to pancreatic beta cells only at comparatively low concentration, destroying all islet cell types at high concentrations. The ultrastructural changes induced by all the test compounds in pancreatic beta cells in vitro were very similar to those observed during the development of alloxan diabetes in vivo. The relative toxicity of the various compounds to pancreatic beta cells in vitro was not, however, related to their ability to cause diabetes in vivo. Indeed, the non-diabetogenic substances ninhydrin, N-butylalloxan and N-isobutylalloxan were very much more toxic to isolated islets than the diabetogenic compounds alloxan and N-methylalloxan. These results suggest that the differences in diabetogenicity among alloxan derivatives are not due to intrinsic differences in the susceptibility of the pancreatic beta cells to their toxicity, but may reflect differences in distribution or metabolism. High concentrations of glucose protected islets against the harmful effects of alloxan and its derivatives, but not those of ninhydrin. Low levels of glucose, and non-carbohydrate nutrients, afforded little protection, indicating that the effect of glucose is not due to the production of reducing equivalents within the cell, 3-O-Methylglucose, which protects against alloan diabetes in vivo, did not protect against alloxan toxicity in vitro. Since 3-O-methylglucose is known to prevent uptake of alloxan by pancreatic beta cells, it appears that uptake of alloxan by the cell is not a prerequisite for the induction of beta cell necrosis.

Tumour-promoting activity of ninhydrin on mouse skin.

Ninhydrin (2,2-dihydroxy-1,3-indanedione; CAS No. 485-47-2) is widely used as a reagent for the detection of free amino and carboxyl groups in proteins and peptides. It is an irritant to mammalian skin. Various toxic effects of ninhydrin have been reported in laboratory animals; however, so far there has been no evaluation of its carcinogenic and co-carcinogenic potential in laboratory animals by long-term in vivo bioassay. Ninhydrin was found to induce the activity of gamma-glutamyl transpeptidase (GGT) in mouse skin but it failed to alter the activity of the enzyme ornithine decarboxylase when compared with animals treated with standard tumour promoter 12-O-tetradecanoyl phorbol-13-acetate (TPA). In the present investigations, the tumour-promoting activity of ninhydrin (including both stage I and stage II of tumour promotion) was tested on Swiss albino mice in a multistage mouse skin model of carcinogenesis. The animals were initiated with a single topical application of 7,12-dimethylbenz-anthracene followed by four topical applications of ninhydrin biweekly as stage I promoter for 2 wk. Stage II promotion was twice weekly through topical application of mezerein. The results revealed that ninhydrin is a strong stage I tumour promoter and its efficacy was comparable with that of TPA at the dose level used in the experiment. However, ninhydrin failed to produce tumours when tested as a stage II or complete tumour promoter on mouse skin.