Betaine and arginine supplementation of low protein diets improves plasma lipids but does not affect hepatic fatty acid composition and related gene expression profiling in pigs

Dietary Amino Acid Source Elicits Sex-Specific Metabolic Response to Diet-Induced NAFLD in Mice

SCOPE

Non-alcoholic fatty liver disease (NAFLD) is a sexually dimorphic disease influenced by dietary factors. Here, the metabolic and hepatic effects of dietary amino acid (AA) source is assessed in Western diet (WD)-induced NAFLD in male and female mice.

METHODS AND RESULTS

The AA source is either casein or a free AA mixture mimicking the composition of casein. As expected, males fed a casein-based WD display glucose intolerance, fasting hyperglycemia, and insulin-resistance and develop NAFLD associated with changes in hepatic gene expression and microbiota dysbiosis. In contrast, males fed the AA-based WD show no steatosis, a similar gene expression profile as males fed a control diet, and a distinct microbiota composition compared to males fed a casein-based WD. Females are protected against WD-induced liver damage, hepatic gene expression, and gut microbiota changes regardless of the AA source.

CONCLUSIONS

Free dietary AA intake prevents the unhealthy metabolic outcomes of a WD preferentially in male mice.

Effects of Dietary Protein Restriction on Colonic Microbiota of Finishing Pigs

This study is aimed at the effects of low-protein diets with four amino acids balanced on serum biochemical parameters and colonic microflora of finishing pigs. Fifty-four healthy (Duroc × Landrace × Yorkshire) hybrid barrows with an average body weight of 70.12 ± 4.03 kg were randomly assigned to one of three dietary treatments with three barrows per pen and six pens per treatment. The barrows were fed a normal protein diet (NP), a low-protein diet (LP), and a very low-protein diet (VLP). Compared with the NP diet, reduced dietary protein did not influence serum biochemical parameters (p > 0.05). The valeric acid was significantly increased with the VLP diet (p < 0.05). Compared with the NP diets, the abundance of Terrisporobacter (13.37%) Clostridium_sensu_stricto_1 (23.37%) and Turicibacter (2.57%) increased to 21.04, 33.42 and 13.68% in LP diets and 16.72, 43.71 and 14.61% in VLP diets, while the abundance of Lactobacillus (9.30%) and Streptococcus (25.26%) decreased to 3.57 and 14.50% in LP diets and 1.86 and 4.07% in VLP diets. Turicibacter and Clostridium_sensu_stricto_6 had a powerful negative correlation with the content of valeric acid (p < 0.01), while Peptococcus and Clostridia_UCG-014 had a very solid positive correlation (p < 0.01). In conclusion, reducing dietary protein level can improve colon microbiota composition, especially reducing the abundance of bacteria related to nitrogen metabolism, but has no significant effect on SCFA except valeric acid. In addition, reduction in the dietary protein level by 5.48% had more different flora than that of 2.74% reduction in dietary CP level.

Preventive and therapeutic role of betaine in liver disease: A review on molecular mechanisms

Betaine is a kind of water-soluble quaternary amine-type alkaloid widely existing in food, such as wheat germ, beet, spinach, shrimp and wolfberry. As an important methyl donor and osmotic pressure regulator in human body, betaine plays an important role in a variety of physiological activities. In recent years, a large number of literatures have shown that betaine has good preventive and therapeutic effects on many liver diseases, including chemical or drug-induced liver injury, nonalcoholic fatty liver disease, alcoholic fatty liver disease, liver fibrosis, hepatitis B and hepatitis C. Therefore, by searching the databases of Web of Science, PubMed, SciFinder and CNKI, this paper has summarized the molecular mechanisms of betaine in improving liver diseases. The results show that the improvement of liver diseases by betaine is closely related to a variety of molecular mechanisms, including inhibition of inflammatory response, improvement of insulin resistance, reduction of endoplasmic reticulum stress, alleviation of liver oxidative stress, increase of autophagy, remodeling of intestinal flora and regulation of epigenetic modification. More importantly, nuclear transcription factor kappa (NF-κB), AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor α/γ (PPAR-α/γ), liver X receptor α (LXRα), protein kinase B (Akt), toll-like receptor 4 (TLR4) and cysteinyl aspartate specific proteinase-3 (Caspase-3) signaling pathways are considered as important molecular targets for betaine to improve liver diseases. These important findings will provide a direction and basis for further exploring the pathogenesis of various liver diseases and tapping the potential of betaine in the clinical treatment.

Soares B, Pimpão C, M. A. Pinto R, Costa T, Freire JPB, Corrent E, Chalvon-Demersay T, Prates JAM, Lopes PA, Soveral G. Glutamine and cystine-enriched diets modulate aquaporins gene expression in the small intestine of piglets

The regulation of glycerol permeability in the gastrointestinal tract is crucial to control fat deposition, lipolysis and gluconeogenesis. Knowing that the amino acid glutamine is a physiological regulator of gluconeogenesis, whereas cystine promotes adiposity, herein we investigated the effects of dietary supplementation with glutamine and cystine on the serum biochemical parameters of piglets fed on amino acid-enriched diets, as well as on the transcriptional profile of membrane water and glycerol channels aquaporins (AQPs) in the ileum portion of the small intestine and its impact on intestinal permeability. Twenty male piglets with an initial body weight of 8.8 ± 0.89 kg were allocated to four dietary treatments (n = 5) and received, during a four week-period, a basal diet without supplementation (control) or supplemented with 8 kg/ton of glutamine (Gln), cystine (Cys) or the combination of the two amino acids in equal proportions (Gln + Cys). Most biochemical parameters were found improved in piglets fed Gln and Cys diet. mRNA levels of AQP3 were found predominant over the others. Both amino acids, individually or combined, were responsible for a consistent downregulation of AQP1, AQP7 and AQP10, without impacting on water permeability. Conversely, Cys enriched diet upregulated AQP3 enhancing basolateral membranes glycerol permeability and downregulating glycerol kinase (GK) of intestinal cells. Altogether, our data reveal that amino acids dietary supplementation can modulate intestinal AQPs expression and unveil AQP3 as a promising target for adipogenesis regulation.

Dietary protein insufficiency: an important consideration in fatty liver disease?

Dietary protein insufficiency has been linked to excessive TAG storage and non-alcoholic fatty liver disease (NAFLD) in developing countries. Hepatic TAG accumulation following a low-protein diet may be due to altered peroxisomal, mitochondrial and gut microbiota function. Hepatic peroxisomes and mitochondria normally mediate metabolism of nutrients to provide energy and substrates for lipogenesis. Peroxisome biogenesis and activities can be modulated by odd-chain fatty acids (OCFA) and SCFA that are derived from gut bacteria, for example, propionate and butyrate. Also produced during amino acid metabolism by peroxisomes and mitochondria, propionate and butyrate concentrations correlate inversely with risk of obesity, insulin resistance and NAFLD. In this horizon-scanning review, we have compiled available evidence on the effects of protein malnutrition on OCFA production, arising from loss in mitochondrial, peroxisomal and gut microbiota function, and its association with lipid accumulation in the liver. The methyl donor amino acid composition of dietary protein is an important contributor to liver function and lipid storage; the presence and abundance of dietary branched-chain amino acids can modulate the composition and metabolic activity of the gut microbiome and, on the other hand, can affect protective OCFA and SCFA production in the liver. In preclinical animal models fed with low-protein diets, specific amino acid supplementation can ameliorate fatty liver disease. The association between low dietary protein intake and fatty liver disease is underexplored and merits further investigation, particularly in vulnerable groups with dietary protein restriction in developing countries.