Ethanol and Isopropanol detoxification associated with the Adh locus of Drosophila melanogaster

Alcohol dehydrogenase activities and ethanol tolerance in Anastrepha (Diptera, Tephritidae) fruit-fly species and their hybrids

The ADH (alcohol dehydrogenase) system is one of the earliest known models of molecular evolution, and is still the most studied in Drosophila. Herein, we studied this model in the genus Anastrepha (Diptera, Tephritidae). Due to the remarkable advantages it presents, it is possible to cross species with different Adh genotypes and with different phenotype traits related to ethanol tolerance. The two species studied here each have a different number of Adh gene copies, whereby crosses generate polymorphisms in gene number and in composition of the genetic background. We measured certain traits related to ethanol metabolism and tolerance. ADH specific enzyme activity presented gene by environment interactions, and the larval protein content showed an additive pattern of inheritance, whilst ADH enzyme activity per larva presented a complex behavior that may be explained by epistatic effects. Regression models suggest that there are heritable factors acting on ethanol tolerance, which may be related to enzymatic activity of the ADHs and to larval mass, although a pronounced environmental effect on ethanol tolerance was also observed. By using these data, we speculated on the mechanisms of ethanol tolerance and its inheritance as well as of associated traits.

Differences in the effect of ethanol on fertility and viability components among laboratory strains of Drosophila melanogaster

We studied the effect of ethanol on several fitness components in six Drosophila melanogaster strains. Mating success, fecundity, egg-to-larva, egg-to-pupa and egg-to-adult survival and the number of emerging adults were estimated in a single series of experiments. The strains either had different combinations of genetic background and Adh genotypes with identical OdhF genotype or different Adh-Odh two-locus genotypes with similar genetic background. Ethanol had the greatest effect on mating success and fecundity, while its influence was lower on survival. When the experimental conditions were contrasted to the natural environment of the flies the most significant results were the ones related to fecundity and larval survival. Ethanol had the highest selective effect on fecundity. The genetic factors contributed substantially to the variation in the fertility and viability components. The Adh locus hardly influenced mating success while it had a sizable effect on fecundity and on all survival components. The influence of Adh on fecundity greatly depended on the other genetic factors. Genetic background had the largest influence on the different survival components. The influence of the Odh locus was mostly observed through the Adh-Odh interaction.

Strains of Drosophila melanogaster differ in alcohol tolerance

The influence of environmental ethanol on different fitness components and the larval activities of some enzymes were studied in three strains of Drosophila melanogaster. All three strains carried the AdhS-alphaGpdhF allele combination on their second chromosomes while they had unique allele combinations at the Odh and Aldox loci on their third chromosomes (strain 1: OdhS-AldoxF; strain 2: OdhF-AldoxS; strain 3: OdhS-AldoxS). Normal lines and exposure lines, kept on 5% ethanol supplemented medium for at least 20 generations, were established from each strain and the responses of the two lines to different ethanol concentrations were compared. Two survival components were estimated in the juvenile life history stages. In addition, the weights of the emerging adult males were measured at various concentrations of ethanol. The changes in the activities of two enzymes (ADH and alpha GPDH) were also surveyed in the larvae after the different ethanol treatments. Strain-specific differences were observed in the responses of all investigated traits to ethanol. OdhS-AldoxF larvae seemed to be more tolerant to ethanol than the larvae of the other two strains while the utilisation of ethanol as energy source appeared to be the least effective in this strain. Larvae of the exposure lines had significantly higher tolerance to ethanol, and the adult males were heavier, than the ones from the normal lines. The enzymatic responses of the two lines to the ethanol treatments were also different. ADH activity, fresh male weight, and pupa-to-adult survival seemed only to be associated under short-term exposure to ethanol. Ethanol tolerance appeared to be independent of the utilisation of ethanol in the larva-to-pupa stage.

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.

Fitness components at the octanol dehydrogenase locus in Drosophila melanogaster

Experiments were performed to study the fitness at the Odh locus in Drosophila melanogaster. Populations previously treated with alcohol (5% in the medium) were transferred to media containing more (10%) or no alcohol. Odh genotype frequencies of second instar larvae and mature adults were determined in each generation. Selection appeared at a significant level in both experimental populations. Net fitness and larva-to-adult survival were investigated. To interpret our results the constant and frequency-dependent models of selection were tested. Both larva-to-adult survival and net fitness were found to be significantly correlated with genotype frequencies. Thus the frequency-dependence of net fitness was due to the larva-to-adult survival.

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).

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

The effect of isopropanol ingestion on a further tolerance to ethanol and isopropanol, and its relationship with the Adh locus, have been studied using Drosophila melanogaster selected for tolerance to ethanol. For this purpose, AdhF AdhF, AdhF AdhS and AdhS AdhS flies were independently pretreated with 2 per cent isopropanol and then further exposed to solutions of 10 per cent ethanol or of 2 per cent isopropanol. Afterwards, the ability to tolerate both alcohols, and the ADH activities of the surviving flies were compared with those of flies not pretreated with isopropanol. After isopropanol ingestion, the flies of all three Adh genotypes shown much higher sensitivity to ethanol than to isopropanol although the opposite results were observed in flies not pretreated with isopropanol. Isopropanol treatment decreased the ADH activity in flies of all three genotypes within a range varying from 73 per cent (females FF) to 93 per cent (males FS), the remaining ADH activity being between 2 to 3 times higher in FF than in FS and SS flies. The reduction in ADH activity was associated with the phenomenon of ADH isozyme interconversion. After the isopropanol pretreatment, the most isopropanol tolerant flies (FF) were also the most ADH active ones. Therefore, the adaptative significance of the isozyme conversion is questioned.

Relation between tolerance to ethanol and alcohol dehydrogenase (ADH) activity in Drosophila melanogaster: selection, genotype and sex effects

The suggestion of Oakeshott et al. (1984) that selection at the Adh locus, as a response to ethanol, is restricted to D. melanogaster laboratory-adapted populations, is tested in this paper with the "Lagar de los Reyes" (LR) lines. For this purpose, homozygous lines for the AdhF and the AdhS alleles were maintained on food supplemented with ethanol. After the selection, the ethanol tolerance and the ADH activity of the selected flies (LRSeF and LRSeS) were determined and compared with those of the control flies (LRCF and LRCS), maintained on standard medium. Then, the effects of the selection, genotype and sex, and the relation between ethanol tolerance and ADH activity were analysed. Our results fail to show a consistent correlation between ethanol tolerance and ADH activity in the adults of LR lines. Our findings also indicate that adaptation of D. melanogaster to ethanol-containing food could be accomplished without significant changes on the ADH activity in the adults. The possibility that the adaptation of D. melanogaster to environmental ethanol could be independent of the Adh locus is discussed.