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NADPH plays a central role in reductive biosynthesis of membrane lipids, maintenance of cell integrity, protein synthesis and redox balance maintenance. Hence, NADPH is involved in the growth and proliferation processes. In addition, it has been shown that changes in nutritional conditions produced changes in NADPH levels and growth rate. Maslinic acid (MA), a pentacyclic triterpene of natural origin, is able to stimulate NADPH production, through regulation of the two oxidative phase dehydrogenases of the pentose phosphate pathway. Our main objective was to study the effects of MA on the kinetic behaviour and on the molecular expression of two NADPH-generating systems, NADP-dependent isocitrate dehydrogenase (NADP-IDH) and malic enzyme (ME), in the liver and white muscle of gilthead sea bream (Sparus aurata). Four groups of 12g of a mean body mass were fed for 210days in a fish farm, with diets containing 0 (control), and 0.1g of MA per kg of diet. Two groups were fed ad libitum (C-AL and MA-AL) and another's two, with restricted diet of 1% of fish weight (C-R and MA-R). Results showed that MA significantly increased the main kinetic parameter of the NADPH-forming enzymes (NADP-IDH and ME). In this sense, specific activity, maximum velocity, catalytic efficiency and activity ratio values were higher in MA conditions than control groups. Moreover, these changes were observed in both feeding regimen, AL and R. Meanwhile, the Michaelis constant changed mainly in groups fed with the MA and restricted diet, these changes are related to the best substrate affinity by enzyme. Moreover, in the Western-blot result, we found that MA increased both protein levels studied, this behaviour being consistent with the regulation of the number of enzyme molecules. All results, indicate that MA, independently of the fed regimen, could potentially be a nutritional additive for fish as it improved the metabolic state of fish, as consequence of increased activity and expression of NADP-IDH and ME enzymes., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Maslinic acid (MA) is a pentacyclic triterpene used as a feed additive to stimulate growth, protein-turnover rates, and hyperplasia in fish. To further our understanding of cellular mechanisms underlying the action of MA, we have used 2-DE coupled with MS to identify proteins differentially expressed in the livers of juvenile gilthead sea bream (Sparus aurata) grown under fish-farm conditions and fed with a 100 mg/kg MA-enriched diet (MA(100)). After the comparison of the protein profiles from MA(100) fed fish and from control, 49 protein spots were found to be altered in abundance (≥2-fold). Analysis by MALDI-TOF/TOF allowed the unambiguous identification of 29 spots, corresponding to 19 different proteins. These proteins were: phosphoglucomutase, phosphoglucose isomerase, S-adenosyl methionine-dependent methyltransferase class I, aldehyde dehydrogenase, catalase, 6-phosphogluconate dehydrogenase, fumarylacetoacetate hydrolase, 4-hydroxyphenylpyruvic dioxygenase, methylmalonate-semialdehyde dehydrogenase, lysozyme, urate oxidase, elongation factor 2, 60 kDa heat-shock protein, 58 kDa glucose-regulated protein, cytokeratin E7, type-II keratin, intermediate filament proteins, 17-β-hydroxysteroid dehydrogenase type 4, and kinase suppressor of Ras1. Western blot analysis of kinase suppressor of Ras1, glucose 6-phosphate dehydrogenase, elongation factor 2, 60 kDa heat-shock protein, and catalase supported the proteome evidence. Based on the changes found in the protein-expression levels of these proteins, we proposed a cellular-signalling pathway to explain the hepatic-cell response to the intake of a diet containing MA., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Maslinic acid is a triterpene present in a considerable proportion in solid residues from olive-oil production. In the present work the effects of maslinic acid on growth, protein-turnover rates and nucleic-acid concentration on liver were investigated in the rainbow trout. Five groups of 120 fish of a mean body mass of 20 g were fed for 225 days with diets containing 0, 1, 5, 25 and 250 mg of maslinic acid per kg diet. At the end of the experiment, whole-body and liver weight and growth rate of trout fed with maslinic acid were higher than controls. The highest weight increase was registered for the group fed 250 mg kg(-1), representing a 29% increase over controls. The total hepatic DNA or liver cell hyperplasia levels in trout fed with 25 and 250 mg of maslinic acid kg(-1) were 37% and 68% higher than controls. Also in these same groups of trout, fractional and absolute hepatic protein-synthesis rates were significantly higher than in control, and significant increments in hepatic protein-synthesis efficiency and protein-synthesis capacity were reported. In close agreement with these results, microscopy studies showed that trout fed on 25 and 250 mg kg(-1) hepatocytes appeared to be more compact, with a larger rough-endoplasmic reticulum and larger glycogen stores than controls. These results suggest that maslinic acid can act as a growth factor when added to trout diet.

Little is known about the way in which carnivorous fish such as salmonids mobilise and metabolise dietary carbohydrates, which are essential to lipid metabolism. Thus we have studied changes caused by the absence of dietary carbohydrates to the kinetics and molecular behaviour of the four cellular NADPH-production systems [glucose 6-phosphate dehydrogenase (G6PDH); 6-phosphogluconate dehydrogenase (6PGDH); malic enzyme (ME); and isocitrate dehydrogenase NADP-dependent (NADP-IDH)] in the liver and adipose tissue of rainbow trout (Oncorhynchus mykiss). We used spectrophotometry to study enzyme kinetics and nucleic acid concentrations, and immunoblot analysis to determine specific protein concentrations. The absence of carbohydrate reduced specific enzyme activity, maximum rate and catalytic efficiency by almost 65% in G6PDH and 6PGDH, by more than 50% in ME, and by almost 25% in NADP-IDH but caused no significant changes in the K(m) values or activity ratios in any of these hepatic enzymes. Molecular analysis clearly showed that this kinetic behaviour reflected concomitant changes in intracellular enzyme concentrations, produced by protein-induction/repression processes rather than changes in the activity of pre-existing enzymes. We conclude that the absence of carbohydrates significantly reduces intracellular concentrations of G6PDH, ME and NADP-IDH in trout liver in percentages similar to those recorded for enzyme activity. We found no such variations in the concentrations of any of these enzymes in adipose tissue and no change in the levels of their activity, suggesting that the liver and adipose tissues are subject to different regulation systems with regard to carbohydrates and play distinct roles in lipid metabolism.

We have determined the protein-turnover rates and nucleic-acid concentrations in the liver of trout (Oncorhynchus mykiss) fed on two different isocaloric diets: low-protein/high-fat and non-carbohydrate/high-fat. Compared to controls, the partial replacement of protein with fat significantly decreased the protein accumulation rate and protein-retention efficiency in the liver whilst increasing the fractional protein-synthesis and protein-degradation rates as well as protein-synthesis efficiency. The complete replacement of carbohydrates with fat significantly lowered the protein-accumulation rate and protein-retention efficiency, but enhanced both the protein-synthesis and protein-degradation rates as well as protein-synthesis capacity. The protein:DNA and RNA:DNA ratios decreased considerably on both diets. Total DNA decreased in fish on a low-protein/high-fat diet but did not change in those on a non-carbohydrate/high-fat diet. The absolute protein-synthesis rate registered no significant change under any of the nutritional conditions. Both the experimental diets did however raise the fractional protein-synthesis rate significantly, due to enhanced protein-synthesis efficiency when protein was partially replaced with fat and to enhanced protein-synthesis capacity when carbohydrates were completely replaced with fat. Our results show the capacity of the liver to adapt its turnover rates and conform to different nutritional conditions. They also point to the possibility of controlling fish growth by dietary means.

We report upon the effects of a cycle of long-term starvation followed by re-feeding on the liver-protein turnover rates and nature of protein growth in the rainbow trout (Oncorhynchus mykiss). We determined the protein-turnover rate and its relationship with the nucleic-acid concentrations in the livers of juvenile trout starved for 70 days and then re-fed for 9 days. During starvation the total hepatic-protein and RNA contents decreased significantly and the absolute protein-synthesis rate (A(S)) also fell, whilst the fractional protein-synthesis rate (K(S)) remained unchanged and the fractional protein-degradation rate (K(D)) increased significantly. Total DNA content, an indicator of hyperplasia, and the protein:DNA ratio, an indicator of hypertrophy, both fell considerably. After re-feeding for 9 days the protein-accumulation rates (K(G), A(G)) rose sharply, as did K(S), A(S), K(D)), protein-synthesis efficiency (K(RNA)) and the protein-synthesis rate/DNA unit (K(DNA)). The total hepatic protein and RNA contents increased but still remained below the control values. The protein:DNA and RNA:DNA ratios increased significantly compared to starved fish. These changes demonstrate the high response capacity of the protein-turnover rates in trout liver upon re-feeding after long-term starvation. Upon re-feeding hypertrophic growth increased considerably whilst hyperplasia remained at starvation levels.

Herein we report on the kinetic and protein expression of glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase, and malic enzyme (ME) in the liver of the trout (Oncorhynchus mykiss) during a long-term starvation-refeeding cycle. Starvation significantly depressed the activity of these enzymes by almost 60%, without changing the Michaelis constant. The time response to this nutritional stimulus increased with fish weight. The sharp decline in G6PDH and ME activities was due to a specific protein-repression phenomenon, as demonstrated by molecular and immunohistochemical analyses. Also, the dimeric banding pattern of liver G6PDH shifted from the fully reduced and partially oxidized forms, predominant in control, to a fully oxidized form, more sensitive to proteolytic inactivation. Refeeding caused opposite effects in both protein concentration and enzyme activities of about twice the control values in the first stages, later reaching the normal enzyme activity levels. Additionally, the partially oxidized form of G6PDH increased. The kinetics of these enzymes were examined in relation to the various metabolic roles of NADPH. These results clearly indicate that trout liver undergoes protein repression-induction processes under these two contrasting nutritional conditions.

In fish, metabolic changes and qualitative responses during different nutritional situations are highly controversial in the scientific literature, and for this reason the objective of this work has been to probe deeper into the adaptive behaviour of two important amino acid-metabolising enzymes, glutamate dehydrogenase (GDH) and alanine aminotransferase (AAT) of liver and kidney in trout. In the present study, we examined the long-term effects of endogenous or exogenous proteins--generated, respectively, by a prolonged starvation or by feeding a high-protein diet--on the kinetics of liver and kidney GDH and AAT. Feeding on a high-protein diet significantly increased the liver (100%) and kidney (49%) GDH Vmax and catalytic efficiency; the same kinetic parameters of AAT increased by 65% only in the liver enzyme, without changing the Km and activity ratio values. Starvation registered a significant increase of both enzymes, Vmax and catalytic efficiency in the liver, but activity was unaltered in the kidney. In addition, no significant changes were found in the Km or activity ratio. All enzyme kinetics showed a Michaelian behaviour without any evidence of sigmoidicity. The experimental results show strong adaptive responses in the kinetic behaviour of the enzymes of both tissues. With the exception of renal AAT, the remainder of the enzymes presented a marked influence in their kinetic parameters by an excess of protein. The results are discussed in terms of the possible adaptive role of enzyme kinetics to amino acid availability.

The nutritional and metabolic effects of the use of Hansenula anomala yeast as the only protein source were studied in the trout. Food intake, weight and length increments significantly decreased in trout fed on yeast diet. Hepatosomatic index did not suffer any change. Soluble protein content in liver and kidney rose significantly. Liver alkaline phosphatase activity increased significantly. Liver lactate dehydrogenase (LDH) activity did not change in the experimental conditions. Glutamic-oxalacetic transaminase (GOT) activity appeared as the most affected parameter in both organs, increasing significantly in those trout fed on yeast diet.

The effect of diets with different fatty acids composition on muscular and hepatic fatty acids of rainbow trout (Salmo gairdnerii) was studied. The effect was higher on muscular fatty acids than on hepatic ones. The lack of correlation between dietary and liver fatty acids in diets with a high level of linoleic acid, showed a better utilization of this acid by the liver. The change in muscular fatty acids pattern was observed within a week of diet change, showing a significant tendency to approach the new dietary fatty acids pattern.