Methionine limitation results in increased hepatic FAS activity, higher liver 18:1 to 18:0 fatty acid ratio and hepatic TAG accumulation in Atlantic salmon, Salmo salar

Abstract

The current experiment aimed to study whether interactions with lipid metabolism possibly might explain the relative increased liver weight obtained in fish fed sub-optimal methionine levels. A basal diet based on a blend of plant proteins which is low in methionine (1.6 g Met/16 g N) was compared to a methionine adequate diet (2.2 g Met/16 g N) prepared by adding DL-methionine (2.4 g/kg) to the basal diet in the expense of wheat grain. Fish oil was used as the lipid source. The diets were balanced in all nutrients except methionine. The diets were fed to Atlantic salmon (500 g BW) for a period of 3 months. Feed intake did not differ, rendering the intake of all nutrients except methionine equal. Fish fed the low methionine diet had an increased liver size relative to body weight, indicating fat deposition in the liver. Fish given the sub-optimal methionine diet showed about six times higher fatty acid synthase (FAS) activity as compared to the fish fed the adequate methionine diet, indicating a higher de novo lipogenesis. A significant rise in the liver 18:1 to 18:0 fatty acid ratios also supported storage of lipids over fatty acid oxidation. Indeed, methionine limitation resulted in significantly higher TAG concentrations in the liver. Sub-optimal dietary methionine also resulted in lower hepatic taurine concentrations and the total bile acids concentrations were reduced in faeces and tended to be reduced in plasma. Taken together, our data show that salmon fed sub-optimal methionine levels had increased relative liver weight and developed signs commonly described in the early stage of non-alcoholic fatty liver disease in rodent models (increased FAS activity, changed fatty acid ratios and TAG accumulation).

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

“…The increased cystathionine and the stable methionine in liver from fish fed the higher methionine diets are in line with our previous reports feeding adult or juvenile salmon increasing methionine (Espe et al, , , ). Espe and co‐workers sampled tissues 6 hr postfeeding while the current trial sampled 24 hr postfeeding.…”

“…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.…”

“…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. 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.…”

Adult Atlantic salmon (Salmo salarL.) adapts to long-term surplus dietary arginine supplementation

“…Plasma was analysed for bile acids, phospholipids, triglycerides and creatinine concentrations using a clinical bioanalyzer (Maxmat PL analyser; erba Diagnostics, Montpellier, France) according to the standardized procedures, reagents and controls as described by Espe et al . (). Polyamines were measured using high‐pressure liquid chromatography (HPLC) as described by Liaset & Espe () in pooled samples of muscle, liver and plasma after homogenization in 0.4 M perchloric acid with along with an internal standard.…”

Minor lipid metabolic perturbations in the liver of Atlantic salmon (Salmo salar L.) caused by suboptimal dietary content of nutrients from fish oil

“…Atlantic salmon liver TAG accumulation has also been linked to high intake of the n-6 FA LA (Alvheim et al 2013), use of plant ingredients (Jordal et al 2007;Kjaer et al 2008;Torstensen et al 2011), methionine limitation (Espe et al 2010), low water temperature (Ruyter et al 2006), low dietary levels of saturated fats and a high dietary phytosterol/cholesterol ratio (Liland 2014;Miller et al 2008). In the present study, there were no significant effects on liver TAG in the analysis of lipid class composition of all diet groups.…”