Intergenotypic effect of isopropanol ingestion in the further detoxification of ethanol and isopropanol in Drosophila melanogaster

A MULTILEVEL APPROACH TO THE SIGNIFICANCE OF GENETIC VARIATION IN ALCOHOL DEHYDROGENASE OF DROSOPHILA

Prior studies showed that differences in alcohol dehydrogenase (ADH) activity across genotypes of Drosophila are decisive for the outcome of selection by ethanol. In the present paper, the effect on ADH activity and egg-to-adult survival of combinations of ethanol, propan-2-ol, and acetone in naturally occurring concentrations is examined. Propan-2-ol is converted into acetone by ADH in vitro. Acetone is considered a competitive inhibitor of ethanol for the ADH enzymes. The melanogaster-ADH-S allozyme is two times more sensitive towards inhibition by acetone than either simulans-ADH or melanogaster-ADH-F. The physiological implications of these in vitro differences for larvae were studied in short-term in vivo and long-term exposure experiments. No major differences in acetone accumulation or fitness parameters were found between the strains in response to ecologically relevant concentrations of acetone or propan-2-ol. Ethanol, however, strongly decreased egg-to-pupal survival in both Drosophila simulans strains and increased developmental time in four out of the five strains tested. Therefore, under physiological conditions only ethanol was shown to act as a selective agent on the ADH polymorphism during egg-to-pupa development in Drosophila.

Of flies and man: Drosophila as a model for human complex traits

Understanding the genetic and environmental factors affecting human complex genetic traits and diseases is a major challenge because of many interacting genes with individually small effects, whose expression is sensitive to the environment. Dissection of complex traits using the powerful genetic approaches available with Drosophila melanogaster has provided important lessons that should be considered when studying human complex traits. In Drosophila, large numbers of pleiotropic genes affect complex traits; quantitative trait locus alleles often have sex-, environment-, and genetic background-specific effects, and variants associated with different phenotypic are in noncoding as well as coding regions of candidate genes. Such insights, in conjunction with the strong evolutionary conservation of key genes and pathways between flies and humans, make Drosophila an excellent model system for elucidating the genetic mechanisms that affect clinically relevant human complex traits, such as alcohol dependence, sleep, and neurodegenerative diseases.

Inhibition of alcohol dehydrogenase after 2-propanol exposure in different geographic races of Drosophila mojavensis: lack of evidence for selection at the Adh-2 locus

High frequencies of the fast allele of alcohol dehydrogenase-2 (Adh-2F) are found in populations of Drosophila mojavensis that inhabit the Baja California peninsula (race BII) whereas the slow allele (Adh-2S) predominates at most other localities within the species' geographic range. Race BII flies utilize necrotic tissue of pitaya agria cactus (Stenocereus gummosus) which contains high levels of 2-propanol, whereas flies from most other localities utilize different cactus hosts in which 2-propanol levels are low. To test if 2-propanol acts as a selective force on Adh-2 genotype, or whether some other yet undetermined genetic factor is responsible, mature males of D. mojavensis lines derived from the Grand Canyon (race A) and Santa Catalina Island (race C), each with individuals homozygous for Adh-2F and Adh-2S, were exposed to 2-propanol for 24 h and ADH-2 specific activity was then determined on each genotype. Flies from five other localities homozygous for either the fast or slow allele also were examined. Results for all reported races of D. mojavensis were obtained. 2-propanol exposure inhibited ADH-2 specific activity in both genotypes from all localities, but inhibition was significantly less in two populations of race BII flies homozygous for Adh-2F. When F/F and S/S genotypes in flies from the same locality were compared, both genotypes showed high 2-propanol inhibition that was not statistically different, indicating that the F/F genotype alone does not provide a benefit against the inhibitory effects of 2-propanol. ADH-1 activity in female ovaries was inhibited less by 2-propanol than ADH-2. These results do not support the hypothesis that 2-propanol acts as a selective factor favoring the Adh-2F allele.

Tolerance to 1-pentene-3-ol and to 1-pentene-3-one in relation to alcohol dehydrogenase (ADH) and aldo keto reductase (AKR) activities in Drosophila melanogaster

The detoxification of 1-pentene-3-ol (pentenol) and 1-pentene-3-one (pentenone) by Drosophila melanogaster adult flies has been studied in two homozygous lines for the AdhF and AdhS alleles (LRC lines), in their respective lines selected for tolerance to ethanol (LRSe lines) and in a homozygous strain for the Adhn4 null allele. For each line, the genotype and sex LDs50 of both compounds were estimated. Then, in order to explain the differences in LD50, both alcohol dehydrogenase (ADH) and aldo keto reductase (AKR) activities were assayed. In addition, the effects of pentenone on AKR activity were also studied. Our results show that ADH-positive flies exhibit a much higher sensitivity to pentenol than ADH-null flies. However, both ADH-positive and ADH-null flies show a similar tolerance to pentenone. Our results show that flies selected for improving tolerance to ethanol also have increased tolerance to pentenol (FF and SS flies) and pentenone (SS flies). However, this improved ability to tolerate pentenol and/or pentenone cannot be explained by changes in ADH or AKR activities. On the other hand, we have observed a beneficial effect of pentenol, but not of pentenone, in n4 flies. We also show that AKR activity is not modified by the administration of pentenone. These results suggest that, in the absence of ADH activity, pentenol may be transformed into a compound that is less toxic than pentenone and that pentenone itself might also be transformed into a less toxic compound.

ADH activity and ethanol tolerance in third chromosome substitution lines in Drosophila melanogaster

In vitro ADH activity and ethanol tolerance were studied in males of a series of third chromosome substitution lines in Drosophila melanogaster. The lines were divided into those with a random third chromosome from a vineyard population (VO lines) and those with a selected third chromosome from males obtained after an egg-to-adult ethanol survival test on the F4 of the previous population (VE lines). Both ADH activity and ethanol tolerance varied significantly among the lines, but the characters showed no significant correlation. Ethanol tolerance (at the higher ethanol concentrations) was higher in the selected lines (VE lines) but ADH activity was not. In our lines, the in vitro ADH activity variability, linked to the regulatory genes (located on the third chromosome) and unrelated to the polymorphism of the Adh locus (located on the second chromosome), is not involved in the ethanol tolerance variability. The data suggest that in this population ethanol tolerance was acquired in nature, at least partially, by means other than increasing ADH activity.

Participation of Drosophila melanogaster alcohol dehydrogenase (ADH) in the detoxification of 1-pentene-3-ol and 1-pentene-3-one

The participation of the ADH enzymes in the detoxification by D. melanogaster of 1-pentene-3-ol (also called pentenol) and its oxidized product, 1-pentene-3-one (usually known as ethyl-vinyl-ketone or pentenone) have been studied using the LR lines. For this purpose flies of AdhS AdhS (SS) and AdhF AdhF (FF) genotypes were independently pretreated with a 2 per cent isopropanol (2-propanol) solution and the survivors exposed to water, to a 0.0075 per cent pentenol solution or to a 0.00375 per cent pentenone solution. After one day in these solutions, the ability to tolerate both compounds was checked and the ADH activity of the surviving flies was measured and compared with those of control flies not pretreated with isopropanol. Additionally, the effects of pentenone on ADH enzymes have been studied by comparing them with those of acetone. Our results show that, in contrast to acetone, pentenone neither reduced significantly the ADH activity in vivo nor altered the normal proportion of ADH isozymes of either SS or FF flies. Our findings also demonstrate that the isopropanol pretreatment implied a considerable decrease in sensitivity not only to pentenol (60 and 91 per cent for SS and FF flies, respectively) but also to pentenone (72 and 80 per cent for SS and FF flies, respectively). After isopropanol pretreatment, FF flies continued exhibiting higher ADH activities than SS ones. However, FF pretreated flies displayed higher tolerance to pentenol and a similar tolerance to pentenone than SS animals. Our results suggest that pentenol (unsaturated secondary alcohol) and isopropanol (saturated secondary alcohol) may be detoxified by slightly different processes (both ADH-activity-dependent), and that pentenone could not be accumulated in the fly but transformed into another compound(s) by means of some ADH-independent mechanism(s).