Study of the influence of tributyrin-supplemented diets on the gut bacterial communities of rainbow trout (Oncorhynchus mykiss).

Dietary supplementation with triglyceride tributyrin (TBT), a butyrate precursor, has been associated with beneficial effects on fish health and improvements in the ability of carnivorous fish to tolerate higher levels of plant-based protein. In this study, we aimed to investigate the effects of a plant-based diet supplemented with TBT on the structural diversity and putative function of the digesta-associated bacterial communities of rainbow trout (Oncorhynchus mykiss). In addition to this, we also assessed the response of fish gut digestive enzyme activities and chyme metabolic profile in response to TBT supplementation. Our results indicated that TBT had no significant effects on the overall fish gut bacterial communities, digestive enzyme activities or metabolic profile when compared with non-supplemented controls. However, a more in-depth analysis into the most abundant taxa showed that diets at the highest TBT concentrations (0.2% and 0.4%) selectively inhibited members of the Enterobacterales order and reduced the relative abundance of a bacterial population related to Klebsiella pneumoniae, a potential fish pathogen. Furthermore, the predicted functional analysis of the bacterial communities indicated that increased levels of TBT were associated with depleted KEGG pathways related to pathogenesis. The specific effects of TBT on gut bacterial communities observed here are intriguing and encourage further studies to investigate the potential of this triglyceride to promote pathogen suppression in the fish gut environment, namely in the context of aquaculture.

Effect of glycerol feed-supplementation on seabass metabolism and gut microbiota.

Dietary glycerol supplementation in aquaculture feed is seen as an alternative and inexpensive way to fuel fish metabolism, attenuate metabolic utilization of dietary proteins and, subsequently, reduce nitrogen excretion. In this study, we evaluated the impact of dietary glycerol supplementation on nitrogen excretion of European seabass (Dicentrarchus labrax) and its effects on metabolite profile and bacterial community composition of gut digesta. These effects were evaluated in a 60-day trial with fish fed diets supplemented with 2.5% or 5% (w/w) refined glycerol and without glycerol supplementation. Nuclear magnetic resonance spectroscopy and high-throughput 16S rRNA gene sequencing were used to characterize the effects of glycerol supplementation on digesta metabolite and bacterial community composition of 6-h postprandial fish. Our results showed that ammonia excretion was not altered by dietary glycerol supplementation, and the highest glycerol dosage was associated with significant increases in amino acids and a decrease of ergogenic creatine in digesta metabolome. Concomitantly, significant decreases in putative amino acid degradation pathways were detected in the predicted metagenome analysis, suggesting a metabolic shift. Taxon-specific analysis revealed significant increases in abundance of some specific genera (e.g., Burkholderia and Vibrio) and bacterial diversity. Overall, our results indicate glycerol supplementation may decrease amino acid catabolism without adversely affecting fish gut bacterial communities.Key points• Glycerol can be an inexpensive and energetic alternative in fish feed formulations.• Glycerol did not affect nitrogen excretion and gut bacteriome composition.• Glycerol reduced uptake of amino acids and increased uptake of ergogenic creatine.• Glycerol reduced putative amino acid degradation pathways in predicted metagenome.

Hypoxia and the metabolic phenotype of prostate cancer cells.

Many cancer cells have an unusual ability to grow in hypoxia, but the origins of this metabolic phenotype remain unclear. We compared the metabolic phenotypes of three common prostate cancer cell models (LNCaP, DU145, PC3), assessing energy metabolism, metabolic gene expression, and the response to various culture contexts (in vitro and xenografts). LNCaP cells had a more oxidative phenotype than PC3 and DU145 cells based upon respiration, lactate production, [ATP], metabolic gene expression, and sensitivity of these parameters to hypoxia. PC3 and DU145 cells possessed similar Complex II and mtDNA levels, but lower Complex III and IV activities, and were unresponsive to dinitrophenol or dichloroacetate, suggesting that their glycolytic phenotype is due to mitochondrial dysfunction rather than regulation. High passage under normoxia converted LNCaP from oxidative to glycolytic cells (based on respiration and lactate production), and altered metabolic gene expression. Though LNCaP-derived cells differed from the parental line in mitochondrial enzyme activities, none differed in mitochondrial content (assessed as cardiolipin levels). When LNCaP-derived cells were grown as xenografts in immunodeficient mice, there were elements of a hypoxic response (e.g., elevated VEGF mRNA) but line-specific changes in expression of select glycolytic, mitochondrial and fatty acid metabolic genes. Low oxygen in vitro did not influence the mRNA levels of SREBP axis, nor did it significantly alter triglyceride production in any of the cell lines suggesting that the pathway of de novo fatty acid synthesis is not directly upregulated by hypoxic conditions. Collectively, these studies demonstrate important differences in the metabolism of these prostate cancer models. Such metabolic differences would have important ramifications for therapeutic strategies involving metabolic targets.

Glucagon effects on brain carbohydrate and ketone body metabolism of rainbow trout.

The levels of glycogen in brain, lactate and acetoacetate in brain and plasma, glucose in plasma and the activities of brain key enzymes of glycogen metabolism (glycogen phosphorylase, GPase, glycogen synthetase, GSase), gluconeogenesis (fructose 1,6-bisphosphatase, FBPase), and glycolysis (6-phosphofructo 1-kinase, PFK) were evaluated in rainbow trout, Oncorhynchus mykiss, from 0.5 to 3 hr after intraperitoneal injection of 1 ml/kg(-1) body weight of saline alone (controls) or containing bovine glucagon at three different doses: 10, 50, and 100 ng/g(-1) body weight. The results obtained demonstrate, for the first time in a teleost fish, the existence of changes in brain carbohydrate and ketone body metabolism following peripheral glucagon treatment. A clear stimulation of brain glycogenolytic potential was observed after glucagon treatment, as judged by the time- and dose-dependent changes observed in brain glycogen levels (up to 88% decrease), and GPase (up to 30% increase) and GSase (up to 42% decrease) activities. In addition, clear time- and dose-dependent increased and decreased levels were observed in brain of glucagon-treated rainbow trout for lactate (up to 60% increase) and acetoacetate (up to 67% decrease), respectively. In contrast, no significant changes were observed after glucagon treatment in those parameters related to glycolytic/gluconeogenic capacity of rainbow trout brain. Altogether, these in vivo results suggest that glucagon may play a role (direct or indirect) in the regulation of carbohydrate and ketone body metabolism in brain of rainbow trout.

Branchial carbonic anhydrase (CA) of gills of Chasmagnathus granulata (Crustacea Decapoda).

The occurrence, localization and response to environmental salinity of carbonic anhydrase (CA) activity were studied in all of the gills of the euryhaline crab Chasmagnathus granulata from Mar Chiquita coastal lagoon (Buenos Aires Province, Argentina). CA activity in all gills appeared to be dependent on salinity. The pattern of distribution of CA activity among gills was different upon transition of C. granulata from osmoionoconformity (more uniform distribution) to hyperregulation (highest activity in posterior gills 6-8). Upon abrupt salinity change a differential response of CA activity occurred among gills which could suggest a differential role of CA in ion transport process in different gills of this crab. Furthermore, CA activity in anterior and posterior gills was found in cytosolic and microsomal fractions, although highest activity appeared to be membrane-associated. Both pools of CA were also strongly influenced by salinity and very sensitive to sulfonamide acetazolamide. The results suggest a differential participation of branchial CA in ionoregulatory mechanisms of C. granulata.