Metabolism of aldrin to dieldrin by rat skin following topical application

Impact of dieldrin on liver morphological and biochemical parameters of rats

The current study deals with the effect of the organochlorine insecticide on the liver of Wistar rats. The dieldrin effect on rats was tested after a single intraperitoneal (i.p.) injection of two doses: 3 and 6 mg/kg and observations were made 4 days later. Animals showed a significant dose-dependent increase in relative liver weight. Elevations of transaminases (aspartate aminotransferase [AST], alanine aminotransferase [ALT]), bilirubin and total activity of lactate dehydrogenase (LDH) were recorded in the sera of treated rats. Serum LDH-5 isoenzyme activity increases in a dose-dependent manner. In contrast, LDH-1 activity does not show any significant variations with respect to controls. Histological examination of the liver of dieldrin-treated animals revealed cytoplasmic vacuolation, focal necrosis and nuclear enlargement of hepatocytes. This study suggests that biochemical assessment (transaminases, LDH and bilirubin activity) and LDH (LDH-1 & LDH-5) isoenzyme profiles can be very helpful in defining the border of the liver injury, dieldrin damaged liver would be a valuable addition to histological analysis in evaluating histopathological liver changes.

From Knowledge Generation to Knowledge Archive. A General Strategy Using TOPS-MODE with DEREK To Formulate New Alerts for Skin Sensitization

A general strategy for knowledge flow concerning skin sensitization based on the combined use of TOPS-MODE and DEREK expert system is proposed. TOPS-MODE is used as a knowledge generator, while DEREK represents the knowledge archive. A TOPS-MODE classification model allows the identification of structural fragments and groups responsible for strong/moderate skin sensitization. These structural contributions are sorted, analyzed, and graphically displayed in an appropriate way allowing the identification of several structural alerts for skin sensitization. Nine structural alerts already implemented in DEREK are identified using this strategy. They comprise, among others, alkyl halides, aldehydes, alpha,beta-unsaturated compounds, aromatic amines, phenols, hydroquinone, isothiazolinone, and alkyl sulfonates. Four new hypotheses are generated using TOPS-MODE structural contributions to skin sensitization, which are not recognized as structural alerts by DEREK. They include the reduction of aromatic nitro groups and epoxidation reaction of double bonds as metabolic activation steps that can lead to reactive haptens which can trigger the skin sensitization mechanism. Another new alert is based on 1,2,5-thiadiazole-1,1-dioxide for which we have identified a possible mechanism explaining its strong skin sensitization profile. It is based on the existence of a tautomeric equilibrium and further reaction with nucleophiles, which are both supported by experimental evidence. Finally, we have identified a possible new mechanism for the skin sensitization of nonreactive compounds, which involves the formation of noncovalent complexes with proteins in a processing- and metabolism-independent way.

The influence of various methods of cold storage of skin on the permeation of melatonin and nimesulide

The purpose of this study was to investigate the influence of different methods of skin preservation on the percutaneous permeation of two drugs with varied physicochemical properties (melatonin and nimesulide). Hairless rat skin was freshly excised and immediately stored at three different storage conditions: (a). 4 degrees C in minimal essential medium eagle (MEM), (b). frozen at -22 degrees C and (c) frozen at -22 degrees C in 10% glycerol (as a cryoprotective agent). The permeation of melatonin and nimesulide from saturated solutions was studied using the skin stored at various cold storage conditions for 6 months. At 4 degrees C, the flux of melatonin was similar to fresh skin for up to 7 days (P>0.05) and increased 2.4-fold at 14 days (P<0.001). The flux of melatonin was similar to fresh skin for 14 days with skin at -22 degrees C (P>0.05) and then steadily increased from 30 days onwards and at 180 days, the flux was 5-fold greater than fresh skin (P<0.001). Freezing of skin at -22 degrees C with 10% glycerol showed similar flux values for melatonin up to 60 days and at 180 days the flux increased 2.2-fold as compared to fresh skin (P<0.001). In the case of nimesulide, the skin stored for 2 days at 4 degrees C showed similar flux as compared to fresh skin (P>0.05) and increased steadily from 4 days onwards and at 14 days the flux was 3.5-fold higher than fresh skin (P<0.001). The skin frozen at -22 degrees C with or without 10% glycerol showed no difference in flux up to 4 days which however increased from 7 days onwards. At 180 days, the skin at -22 degrees C showed 2.5-fold increase in the flux (P<0.001) whereas the skin frozen with 10% glycerol showed 2-fold increase in the flux (P<0.001) as compared to fresh skin. The results of the present study demonstrate that the permeability of the drugs across the stored skin was dependent on the storage condition, the length of storage and the physicochemical properties of the drug under study. Overall, the freezing of skin at -22 degrees C with 10% glycerol was found to be very helpful for the long-term storage of skin for percutaneous permeation studies.

Distribution of aldrin and its epoxide (dieldrin) in egg-forming tissues and eggs of laying hens following an oral application

Laying hens were treated orally with a single dose of aldrin (1,2,3,4,10,10-hexachloro-1,4,4a,5,8,8a-hexahydro-1,4:5,8-dimethanonaphthalene, AD) 1 mg kg(-1) bw. Concentrations (microg g(-1)) of AD or its epoxide, dieldrin (1,2,3,4,10,10-hexachloro-6,7-epoxy-1,4,4a,5,6,7,8,8a-octahydroendo-,exo-1,4:5,8-dimetha-nonaphthalene, DD), in the main tissues involved in egg formation (blood, liver, ovary, and oviducts) and egg yolk, collected at 1 day after AD dosing, were determined by normal-phase high-performance liquid chromatography. The limits of determination were 0.07 microg g(-1) for AD and 0.08 microg g(-1) for DD, respectively. In extractable fats from the above tissues and egg yolk, AD was found in the egg yolk; however, no AD was found in tissues involved in egg formation. DD was found in all tissues examined here. The DD level was highest in the liver and was lowest in the blood (P<0.01). These results suggest that the epoxidation of AD to DD occurred rapidly in the hen.