The Effects of Age and Adiposity on Casein Digestibility and Tissue Protein Synthesis in Rats

Objectives Age and adiposity can impact the digestibility of dietary proteins and the metabolic response to their ingestion. The objective was to evaluate the effects of age and adiposity on casein digestibility and protein synthesis in tissues and organs. Methods Wistar rats of 1 month (n = 15) and 10 months (n = 15) at their arrival were fed ad libitum with a standard diet or High Fat diet to obtain rats of normal and high adiposity levels. Four groups were constituted (n = 7/8): 2 months/normal adiposity, 2 months/high adiposity, 11 months/normal adiposity and 11 months/high adiposity. At the end of the dietary intervention, they were fed the standard diet for 1 week before the test meal. The rats consumed a 4g meal containing 15N-labeled casein (Prodiet® 85B). Six hours after meal ingestion, the rats were euthanized. Intravenous injection of a massive dose of 13C-valine prior to euthanasia was used to determine protein synthesis rate in liver, kidneys, skin and muscle. Body composition was evaluated and digestive contents were collected to measure casein digestibility. Results No weight difference between rats of the same age was observed. However, a significant difference in adiposity was noted, with a surge in body fat of 3% in young rats and 7% in older rats. Digestibility increased with a higher adiposity level (P = 0.04). In young rats, it was 94.1 ± 1.1% in lean rats and 95.2 ± 1.7% in fat rats. In older rats, it was 94.5 ± 2.2% and 95.8 ± 0.7%, in lean and fat rats respectively. Significant effects of age (P < 0.01) and adiposity (P < 0.01) were observed in the muscle fractional synthesis rate (FSR), with age decreasing it and adiposity increasing it. In young rats, FSR was 10.1 ± 2.1%/day and 12.0 ± 3.0%/day in lean and fat rats, respectively, these values being 6.2 ± 1.5%/day and 10.6 ± 2.0%/day in older rats. In the skin, younger rats exhibited a higher FSR (P < 0.01) as it was 11.1 ± 2.6%/day and 12.6 ± 3.7%/day in lean and fat rats respectively, and 8.3 ± 2.3%/day and 8.2 ± 2.7%/day in older rats. No differences were found for the liver and kidneys. Conclusions Protein synthesis in muscle decreased with age while adiposity increased it. This is consistent with an improvement in ribosomal activity at an intermediate state of obesity. The surge in casein digestibility with higher adiposity, although moderate, could have contributed to the improvement in muscle anabolism response. Funding Sources Ingredia.

Exercise Plus Presleep Protein Ingestion Increases Overnight Muscle Connective Tissue Protein Synthesis Rates in Healthy Older Men

Protein ingestion and exercise stimulate myofibrillar protein synthesis rates. When combined, exercise further increases the postprandial rise in myofibrillar protein synthesis rates. It remains unclear whether protein ingestion with or without exercise also stimulates muscle connective tissue protein synthesis rates. The authors assessed the impact of presleep protein ingestion on overnight muscle connective tissue protein synthesis rates at rest and during recovery from resistance-type exercise in older men. Thirty-six healthy, older men were randomly assigned to ingest 40 g intrinsically L-[1-13C]-phenylalanine and L-[1-13C]-leucine-labeled casein protein (PRO, n = 12) or a nonprotein placebo (PLA, n = 12) before going to sleep. A third group performed a single bout of resistance-type exercise in the evening before ingesting 40 g intrinsically-labeled casein protein prior to sleep (EX+PRO, n = 12). Continuous intravenous infusions of L-[ring-2H5]-phenylalanine and L-[1-13C]-leucine were applied with blood and muscle tissue samples collected throughout overnight sleep. Presleep protein ingestion did not increase muscle connective tissue protein synthesis rates (0.049 ± 0.013 vs. 0.060 ± 0.024%/hr in PLA and PRO, respectively; p = .73). Exercise plus protein ingestion resulted in greater overnight muscle connective tissue protein synthesis rates (0.095 ± 0.022%/hr) when compared with PLA and PRO (p < .01). Exercise increased the incorporation of dietary protein-derived amino acids into muscle connective tissue protein (0.036 ± 0.013 vs. 0.054 ± 0.009 mole percent excess in PRO vs. EX+PRO, respectively; p < .01). In conclusion, resistance-type exercise plus presleep protein ingestion increases overnight muscle connective tissue protein synthesis rates in older men. Exercise enhances the utilization of dietary protein-derived amino acids as precursors for de novo muscle connective tissue protein synthesis during overnight sleep.

Interactions of deoxynivalenol and lipopolysaccharides on tissue protein synthesis in pigs

Possible interactions between the Fusarium toxin deoxynivalenol and lipopolysaccharides on in vivo protein synthesis were investigated in selected porcine tissues. A total of 36 male castrated pigs (initial weight of 26 kg) were used. 24 pigs were fed a control diet and 12 a Fusarium-contaminated diet (chronic oral deoxynivalenol, 3.1 mg/kg diet) for 37 days. Tissue protein synthesis was measured in pigs fed control diet after intravenous infusion of deoxynivalenol (100 µg/kg live weight/h), lipopolysaccharides (7.5 µg/kg live weight/h) or a combination of both compounds on the day of the measurements, while six pigs from the chronic oral deoxynivalenol group were intravenously treated with lipopolysaccharides (7.5 µg/kg live weight/h). Deoxynivalenol challenge alone failed to alter protein synthesis parameters. Fractional protein synthesis rates were exclusively reduced in liver, spleen and small intestine of lipopolysaccharides-treated pigs. Intravenous deoxynivalenol co-exposure enhanced the impacts of lipopolysaccharides on protein synthesis parameters in the spleen and the small intestine to some extent, while a chronic oral pre-exposure with deoxynivalenol relieved its effects in the spleen. Whether these interactions occur in other tissues and under other study conditions, especially toxin doses and route of entry into the body, needs to be examined further.

Protein synthesis in gilthead sea bream: response to partial fishmeal replacement

The present study aimed to measure tissue protein synthesis in sea bream fed isonitrogenous diets that contained 63, 55 and 50 % fishmeal; in the latter two diets, 16 and 27 % of the fishmeal protein was replaced with plant protein. Over a 35 d period, there were no differences in feed intake, growth or feed efficiency among the three diets. Protein metabolism was then measured in the liver and white muscle tissue as rates of protein synthesis and as the capacity for protein synthesis before feeding (0 h) and at different times after feeding (4–48 h). Diet did not have a significant effect on protein synthesis or on the capacity for protein synthesis in either tissue. The capacity for protein synthesis was not affected by time after feeding, and overall mean values were 81·02 (se 1·68) and 4·07 (se 0·94) mg RNA/g protein for the liver and white muscle, respectively. Liver and white muscle fractional rates of protein synthesis were significantly higher at 4–8 h, intermediate at 12 h and were not different among pre-feeding (0 h), 24 and 48 h. Overall, the indices of protein metabolism measured at various times over 48 h following feeding were closely aligned with measurements of feeding, growth and growth efficiency established over a longer time scale.