Methionine deficiency does not increase polyamine turnover through depletion of hepatic S-adenosylmethionine in juvenile Atlantic salmon

Abstract

During the last few decades, plant protein ingredients such as soya proteins have replaced fishmeal in the diets of aquacultured species. This may affect the requirement and metabolism of methionine as soya contains less methionine compared with fishmeal. To assess whether methionine limitation affects decarboxylated S-adenosylmethionine availability and polyamine status, in the present study, juvenile Atlantic salmon were fed a methionine-deficient plant protein-based diet or the same diet supplemented with DL-methionine for 8 weeks. The test diets were compared with a fishmeal-based control diet to assess their effects on the growth performance of fish. Methionine limitation reduced growth and protein accretion, but when fish were fed the DL-methionine-supplemented diet their growth and protein accretion equalled those of fish fed the fishmeal-based control diet. Methionine limitation reduced free methionine concentrations in the plasma and muscle, while those in the liver were not affected. S-adenosylmethionine (SAM) concentrations were higher in the liver of fish fed the methionine-deficient diet, while S-adenosylhomocysteine concentrations were not affected. Putrescine concentrations were higher and spermine concentrations were lower in the liver of fish fed the methionine-deficient diet, while the gene expression of SAM decarboxylase (SAMdc) and the rate-limiting enzyme of polyamine synthesis ornithine decarboxylase (ODC) was not affected. Polyamine turnover, as assessed by spermine/spermidine acetyltransferase (SSAT) abundance, activity and gene expression, was not affected by treatment. However, the gene expression of the cytokine TNF-a increased in fish fed the methionine-deficient diet, indicative of stressful conditions in the liver. Even though taurine concentrations in the liver were not affected by treatment, methionine and taurine concentrations in muscle decreased due to methionine deficiency. Concomitantly, liver phospholipid and cholesterol concentrations were reduced, while NEFA concentrations were elevated. In conclusion, methionine deficiency did not increase polyamine turnover through depletion of hepatic SAM, as assessed by SSAT activity and abundance.

Atlantic salmon fed a nutrient package of surplus methionine, vitamin B12, folic acid and vitamin B6 improved growth and reduced the relative liver size, but when in excess growth reduced

“…There were no differences in phospholipids or cholesterol between fish fed the three diets in the current trial. No differences in phospholipids are in line with Espe et al () in adult salmon, but not in juvenile salmon where phospholipids increased following increased dietary methionine (Espe et al, ). We were unable to detect any changes in the current trial, this might be due to the relative high variation present between tanks in the current study or simply due to having enough of the vitamins and methionine in the diets to prevent the development of fatty liver.…”

“…Espe et al () reported increased TAG accumulation in liver of adult salmon fed low methionine diets (6.7 g methionine per kilo diet) of which disappeared when salmon were fed diets containing 9 g methionine per kg diet. On the other hand, juvenile Atlantic salmon fed diets containing low methionine or a methionine‐supplemented diet did not accumulate liver TAG (Espe et al, ), though having a higher relative liver weight and reduced growth are in line with the current trial. The lower protein growth, the elevated FCR and lower retention of indispensable amino acids in the presmolts as compared to postsmolts indicate that presmolt salmon used more of the dietary amino acids for energy purposes than on deposition of muscle protein.…”

“…In the current trial, the vitamin levels at the low 1C diet were similar to the levels suggested by Hemre et al (), while methionine is according to required levels (Espe et al, ; NRC, ) then added at two surplus levels. We previously reported that juvenile Atlantic salmon showed better protein accretion and growth when fed 11.4 g methionine per kilo diet as compared to salmon fed 7.9 g methionine per kilo diet (Espe et al, ). Espe et al () reported increased TAG accumulation in liver of adult salmon fed low methionine diets (6.7 g methionine per kilo diet) of which disappeared when salmon were fed diets containing 9 g methionine per kg diet.…”

“…RNA was extracted from liver and muscle ( n = 5 individual fish per tank) using the BioRobot EZ1 and EZ1 RNA Universal Tissue kit (Qiagen) according to the manufacture's descriptions. Quality and quantity of RNA were analysed as described elsewhere (Espe et al, ). Reverse transcription followed by quatitative real‐time PCR (RT‐qPCR) as earlier described (Skjaerven, Olsvik, Finn, Holen, & Hamre, ).…”

Elucidation of the roles and requirements of sulphur amino acids in the diet of barramundi (Lates calcarifer)

“…SAM is a major donor of methyl groups for transmethylation reactions involving nucleic acids and proteins (Lieber and Packer, 2002) as well as aminopropyl groups for the synthesis of polyamines (Espe et al, 2014) which are critical for a range of metabolic processes such as cell proliferation and differentiation . Increased levels of circulating SAM, is likely to provide an advantage in maintaining a rapid rate of growth as seen in those fish in the MetADQ treatment relative to the MetDEF treatment fish in .…”