Production and release of carboxylic acids during oxic and anoxic metabolism by the pulmonate snail Biomphalaria glabrata (Say)

Metabolomic Investigations of the Temporal Effects of Exposure to Pharmaceuticals and Personal Care Products and Their Mixture in the Eastern Oyster (Crassostrea virginica)

The eastern oyster (Crassostrea virginica) supports a large aquaculture industry and is a keystone species along the Atlantic seaboard. Native oysters are routinely exposed to a complex mixture of contaminants that increasingly includes pharmaceuticals and personal care products (PPCPs). Unfortunately, the biological effects of chemical mixtures on oysters are poorly understood. Untargeted gas chromatography-mass spectrometry metabolomics was utilized to quantify the response of oysters exposed to fluoxetine, N,N-diethyl-meta-toluamide, 17α-ethynylestradiol, diphenhydramine, and their mixture. Oysters were exposed to 1 µg/L of each chemical or mixture for 10 d, followed by an 8-d depuration period. Adductor muscle (n = 14/treatment) was sampled at days 0, 1, 5, 10, and 18. Trajectory analysis illustrated that metabolic effects and class separation of the treatments varied at each time point and that, overall, the oysters were only able to partially recover from these exposures post-depuration. Altered metabolites were associated with cellular energetics (i.e., Krebs cycle intermediates), as well as amino acid metabolism and fatty acids. Exposure to these PPCPs also affected metabolic pathways associated with anaerobic metabolism, osmotic stress, and oxidative stress, in addition to the physiological effects of each chemical's postulated mechanism of action. Following depuration, fewer metabolites were altered, but none of the treatments returned them to their initial control values, indicating that metabolic disruptions were long-lasting. Interestingly, the mixture did not directly cluster with individual treatments in the scores plot from partial least squares discriminant analysis, and many of its affected metabolic pathways were not well predicted from the individual treatments. The present study highlights the utility of untargeted metabolomics in developing exposure biomarkers for compounds with different modes of action in bivalves. Environ Toxicol Chem 2020;39:419-436. © 2019 SETAC.

Role of antioxidant defenses during estivation and anoxia exposure in the freshwater snailBiomphalaria tenagophila(Orbigny, 1835)

The effects of 24 h of exposure to underwater anoxia and 15 days of estivation (at 26–27°C) on the enzymatic antioxidant system of the hepatopancreas of the freshwater snail Biomphalaria tenagophila (Planorbidae) are described. The effect of 24 h of recovery was also investigated. Catalase activity dropped by 31% during 24 h of anoxia, and superoxide dismutase (SOD) activity was reduced by 43% during the 15 days of estivation. This is consistent with the overall decrease in metabolic rate during estivation or anoxia. Indeed, the heartbeat diminished by 28–36% during estivation (determination was possible for only 4 days) and by 66% after 24 h of anoxia. On the other hand, selenium-dependent glutathione peroxidase (Se-GPX) activity increased during anoxia (from 10 to 14 mU/mg protein) and estivation (by 14%). Glutathione S-transferase (GST) and glutathione reductase activities remained unchanged during estivation and anoxia. Glucose 6-phosphate dehydrogenase activity was unchanged during estivation and recovery. Recovery restored SOD activity. Catalase, Se-GPX, and GST activities during recovery were significantly lower than those of the respective controls. Lipid peroxidation, determined as the level of thiobarbituric acid-reactive substances, was unchanged in the hepatopancreas after 15 days of estivation and 26 h of recovery from estivation. It is possible that the increase in Se-GPX activity during anoxia and estivation, and the maintenance of GST activity, are relevant in minimizing the effects of reactive oxygen species that can be formed upon resumption of aerobic metabolism. Thus, B. tenagophila may have a biochemical strategy of preparation for oxidative stress such as that observed in several other species of anoxia/hypoxia-tolerant animals.

Uptake and assimilation of short chain carboxylic acids by Biomphalaria glabrata (Say), the freshwater pulmonate snail host of Schistosoma mansoni (Sambon)

The use of radiolabelling and high performance liquid chromatography (h. p. l. c. ) has shown that the freshwater pulmonate snail Biomphalaria glabrata can achieve a net uptake of short chain carboxylic acid (C 2 -C 4 ) from the medium, and also metabolize them. This appears to be the first time that this phenomenon has been reported for a freshwater invertebrate. The uptake characteristics for acetate and butanoate conform to the Michaelis-Menten model. The transport constants,V max (in micromole equivalents per gram of wet mass per hour) and K s (in micromoles per litre) for acetate (1005 and 2.29 respectively) and butanoate (129 and 1.29 respectively) are similar to those obtained by other workers for marine, detritivorous, polychaete worms. Evidence is given that the carboxylic acids are transported through the body wall, and not taken up to any significant extent by microorganisms or absorbed on the surface mucus. The acids are metabolized by the snail after accumulation, as shown by the appearance of label in respiratory CO 2 and the decline in the mass-specific accumulation rates (m. s. a. r. ), in micromole equivalents per gram of mass per hour, to an asymptote during the course of a 4 h incubation period. Differences in m.s.a.r. values for [1- 14 C]- and [2- 14 C]acetate probably reflect the different fates of the two carbons during metabolism. The m. s. a. r. values are influenced by the metabolic state of the snails. Thus they increase in response to food deprivation and decrease under anoxic conditions. However, as snails continue to accumulate acetate from the medium, even when well fed, or ‘preloaded ’ with acetate, it is clear that this acid is not being used solely as a food supplement. Estimates of the contributions that C 2 and C 4 acids might make to the basal metabolism of the snails have been made using the following param eters: (i) the range of concentrations of these acids in microhabitats, such as the interstitial waters in surface sediments, and an experimentally decayed macrophyte, Lemna paucicostata (ii) transport constants of the carboxylic acids taken up by the snails; (iii) the respiration rates of the snails. It was calculated that the acetate in interstitial waters can contribute only a negligible amount (less than 6%) of the snail’s basal metabolic rate (b. m. r. ). However, if the snails encountered the concentrations of 2250 μm and 400 μm of acetate and butanoate respectively found in supernatant from laboratory decaying Lemna , then each acid could provide more than 50% of the snails’ b. m. r. The significance of these results to the behavioural and chemical ecology of the snails is discussed.