The toxicities of short-chain primary alcohols and the accumulation of storage bodies in the larval fat body of Drosophila melanogaster.

In terms of the LD50 values for alcohols, third-instar wild-type larvae of Drosophila melanogaster had a greater tolerance to ethanol, n-propanol and n-butanol than alcohol dehydrogenase (ADH)-deficient larvae. The tolerances of the two strains to methanol were similar. Methanol, ethanol, n-propanol and n-butanol all induced higher ADH activity in wild-type larvae. Ethanol, n-propanol, methanol and n-butanol slowed the growth for ADH-deficient larvae, whereas only methanol had this effect on wild-type larvae. The proportion of wild-type pupae to eclose was increased by n-butanol, n-propanol and ethanol. Cytometric methods to measure the densities of storage bodies--glycogen rosettes, protein bodies and lipid droplets--in fat body cells indicated that all of the test alcohols exerted some negative influence on the accumulation of at least one type of storage body. Analyses of total protein, glycogen and acylglycerols indicated that ethanol and n-butanol were associated with an accumulation of acylglycerols in both wild-type and ADH-deficient larvae; whereas, the other test alcohols resulted in low glycogen and protein concentrations in both test strains. The short-chain primary alcohols may in part be toxic to larvae because of disruptions in metabolism that lead to reductions in one or more kinds of storage bodies in the larval fat body.

At high dietary levels ethanol alters the structure of mid- and hindgut epithelial cells of Drosophila melanogaster larvae.

The midgut of Drosophila melanogaster is a site of alcohol dehydrogenase (ADH) activity, the enzyme that catalyzes the first step in the major pathway for ethanol degradation. The effects of different levels of dietary ethanol on the ultrastructures of the guts of larvae of the Canton-S wild-type strain and the ADH-deficient, Adhn2, strain were ascertained. In wild-type larvae fed an ethanol-free, defined medium, the foregut epithelium was characterized by few glycogen rosettes and sparse microvilli that protruded into the gut's thick lumen lining. The midgut epithelium was typical of cells involved in absorption and active transport with abundant microvilli on the apical surface and membrane infoldings on the basal surface. In place of microvilli, the apical surface of the hindgut had membrane infoldings. The apical surfaces of both the mid- and hindgut epithelium were covered by a thick, electron-dense peritrophic membrane consisting of chitin. In both strains the subcellular damage that was correlated with ethanol levels in the diet was confined to the midgut and hindgut regions. Damage to gut cells in the form of disrupted mitochondria, dilated rough endoplasmic reticulum, low densities of glycogen rosettes and protein granules, high numbers of autophagic vacuoles, and the presence of myelin whirls was extensive in Canton-S strain larvae fed a high ethanol diet. A low dietary concentration of ethanol induced changes in gut ultrastructure of Adhn2 larvae similar to the changes that were observed in wild-type larvae fed the higher ethanol concentrations, but the basal infoldings were more dilated in the Adhn2 larvae. At high dietary concentrations the disruption of mid- and hindgut cells by ethanol appeared great enough to interfere with the digestion and absorption of nutrients.

Alcohol dehydrogenase and ethanol tolerance at the cellular level in Drosophila melanogaster.

Exposure of early third instar larvae of Drosophila melanogaster to a nonlethal dose of ethanol was detrimental to larvae lacking alcohol dehydrogenase (ADH) but beneficial to wild-type larvae in terms of surviving a later ethanol tolerance test, indicating that one of the important functions of the ADH system is to supply derivatives of ethanol to larvae that in turn promote ethanol tolerance. High intracellular concentrations of ethanol in ADH-deficient (Adhn2) larvae fed ethanol were accompanied by a decrease in the cell membrane infoldings of fat body cells, suggesting that the capacities to absorb and release molecules were reduced. Marked effects of ethanol on the endoplasmic reticulum and mitochondria of ADH-deficient larvae were also evident. The absence of similar changes in wild-type larvae that were fed moderate levels of ethanol showed that the ADH system kept the intracellular level of ethanol at a concentration low enough to avoid cell damage. A cytometric analysis of electron micrographs showed that there were ethanol-induced reductions in glycogen, lipid, and protein stores in the fat body cells of ADH-deficient larvae fed 1.25% ethanol (v/v) compared with null larvae fed an ethanol-free diet. This finding implied that the capacities to synthesize or store these compounds may be limited by high intracellular concentrations of ethanol. The cytometric analysis also revealed that the consumption of diets containing 2.5% and 4.5% ethanol by Canton-S wild-type larvae for 3 days after 4 days of feeding on an ethanol-free diet resulted in decreases in glycogen and protein deposits in fat body cells, but increased the amount of lipid deposits compared to larvae fed an ethanol-free diet. This observation, coupled with the greater weight of wild-type adults that were fed a growth-limiting concentration of ethanol compared with control adults, suggested that a metabolic defense mechanism in larvae is to convert toxic ethanol to nontoxic storage products. Dietary ethanol alone and in combination with isopropanol stimulated an increase in the size of the NAD-pool in larvae, a condition that may favor the activity of ADH. A low dietary level of isopropanol (1%) completely blocked glycogen deposition in wild-type larvae, whereas ethanol did not. Thus ethanol and isopropanol exert some different toxic effects on larval fat bodies.