A systematic review of metabolism of methionine sources in animals: One parameter does not convey a comprehensive story.

The goal of this review article, based on a systematic literature search, is to critically assess the state of knowledge and experimental methodologies used to delineate the conversion and metabolism of the 2 methionine (Met) sources DL-methionine (DL-Met) and DL-2-hydroxy-4-(methylthio) butanoic acid (HMTBa). The difference in the chemical structures of HMTBa and DL-Met indicates that these molecules are absorbed and metabolized differently in animals. This review explores the methodologies used to describe the 2-step enzymatic conversion of the 3 enantiomers (D-HMTBa, L-HMTBa and D-Met) to L-Met, as well as the site of conversion at the organ and tissue levels. Extensive work was published documenting the conversion of HMTBa and D-Met into L-Met and, consequently, the incorporation into protein using a variety of in vitro techniques, such as tissue homogenates, cell lines, primary cell lines, and everted gut sacs of individual tissues. These studies illustrated the role of the liver, kidney, and intestine in the conversion of Met precursors into L-Met. A combination of in vivo studies using stable isotopes and infusions provided evidence of the wide conversion of HMTBa to L-Met by all tissues and how some tissues are net users of HMTBa, whereas others are net secreters of L-Met derived from HMTBa. Conversion of D-Met to L-Met in organs other than the liver and kidney is poorly documented. The methodology cited in the literature to determine conversion efficiency ranged from measurements of urinary, fecal, and respiratory excretion to plasma concentration and tissue incorporation of isotopes after intraperitoneal and oral infusions. Differences observed between these methodologies reflect differences in the metabolism of Met sources rather than differences in conversion efficiency. The factors affecting conversion efficiency are explored in this paper and are mostly associated with extreme dietary conditions, such as noncommercial crystalline diets that are very deficient in total sulfur amino acids with respect to requirements. Implications in the diversion of the 2 Met sources toward transsulfuration over transmethylation pathways are discussed. The strengths and weaknesses of some methodologies used are discussed in this review. From this review, it can be concluded that due to the inherent differences in conversion and metabolism of the 2 Met sources, the experimental methodologies (e.g., selecting different organs at different time points or using diets severely deficient in Met and cysteine) can impact the conclusions of the study and may explain the apparent divergences of conclusion found in the literature. It is recommended when conducting studies or reviewing the literature to properly select the experimental models that allow for differences in how the 2 Met precursors are converted to L-Met and metabolized by the animal to enable a proper comparison of their bioefficacy.

Correction: da Silva et al. Increased Sulphur Amino Acids Consumption as OH-Methionine or DL-Methionine Improves Growth Performance and Carcass Traits of Growing-Finishing Pigs Fed under Hot Conditions. Animals 2022, 12, 2159.

In the original publication [...].

New statistical approach shows that hydroxy-methionine is noninferior to DL-Methionine in 35-day-old broiler chickens.

The efficacy of a new molecule is assessed in the pharmaceutical industry through noninferiority tests to establish that it is not unacceptably less efficient than the reference. This method was proposed to compare DL-Methionine (DL-Met) as reference and DL-Hydroxy-Methionine (OH-Met) as alternative, in broiler chickens. The research hypothesized that OH-Met is inferior to DL-Met. Noninferiority margins were determined using 7 datasets comparing broiler growth response between a sulfur amino acid deficient and adequate diet from 0 to 35 d. The datasets were selected from the literature and internal records of the company. The noninferiority margins were then fixed as the largest loss of effect (inferiority) acceptable when OH-Met is compared to DL-Met. Three corn/soybean meal-based experimental treatments were offered to 4,200 chicks (35 replicates of 40 birds). Birds received from 0 to 35 d 1) a negative control diet deficient in Met and Cys; the negative control treatment supplemented on equimolar basis with 2) DL-Met or 3) OH-Met in amounts allowing to reach Aviagen Met+Cys recommendations. The three treatments were adequate in all other nutrients. Growth performance, which was analysed with one-way ANOVA, showed no significant difference between DL-Met and OH-Met. The supplemented treatments improved (P < 0.0001) the performance parameters compared to the negative control. The lower limits of the confidence intervals of the difference between means for the feed intake [-1.34; 1.41], body weight [-57.3; 9.8] and daily growth [-1.64; 0.28], did not exceed the noninferiority margins. This demonstrates that OH-Met was non-inferior to DL-Met.

Absorption of methionine sources in animals-is there more to know?

This literature review evaluates the absorption of methionine (Met) sources such as 2-hydroxy-4-methylthiobutyric acid (HMTBa), its calcium salts (HMTBa-Ca), and DL-methionine (DL-Met) by focusing on the state of knowledge regarding the absorption mechanism, experimental methodology, and factors affecting their absorption. The 2 Met sources differ in mechanism and site of absorption due to differences in their chemical characteristics and enzymatic conversion. This review addresses diffusion- and transport-mediated absorption systems for amino acids and carboxylic compounds, best elucidated by in vitro, ex vivo, and in vivo experimental models. Opportunities and limitations in the use of radioisotopes to depict absorption sites as well as host and microbial metabolism are described. Physiological and environmental conditions that lead to changes in gut absorptive capacity and the impact of Met source absorption are also evaluated. This review concludes that any comparison between HMTBa and DL-Met should consider their different behaviors during the absorption phase. Hence, the chemical characteristics of these 2 molecules entail different absorption sites and mechanisms, from passive absorption in the case of HMTBa and HMTBa-Ca to active transporters for DL-Met, HMTBa, and HMTBa-Ca. In addition, the different conversion modes of these 2 molecules further differentiate their absorption modes. Considering these important differences, it is easier to understand the apparent divergence between the conclusions of existing publications. When comparing these 2 molecules, it is recommended to properly adapt to the conditions under which the absorption of Met sources is evaluated.

Increased Sulphur Amino Acids Consumption as OH-Methionine or DL-Methionine Improves Growth Performance and Carcass Traits of Growing-Finishing Pigs Fed under Hot Conditions.

This study aimed to evaluate the impact of DL-Methionine (DL-Met) or OH-Methionine (OH-Met) when supplemented beyond the usually accepted requirements in sulfur amino acids (SAA) on the performance and carcass traits of growing-finishing pigs. Two hundred mixed sex pigs were distributed in a randomized block (body weight and sex), under a 2 × 2 factorial design with two methionine sources, DL-methionine, or OH-Methionine and two methionine doses (100% SAA or 120% of the SAA level present in the control). Diets were formulated to meet amino acids recommendations of the Brazilian Tables for Poultry and Swine (2017), except for SAA, which varied with the methionine doses. Daily feed intake, daily weight gain, and feed conversion were evaluated. Moreover, the carcasses were measured electronically for fat thickness (FT), longissimus dorsi muscle depth (LD), and lean meat (%). During the growing phase II (92 till 122 days of age), daily feed intake (p < 0.001) and daily weight gain (p < 0.05) increased with the high SAA levels. High SAA levels also provided greater daily weight gain during the entire period of the trial (0.90 versus 0.86 kg; p < 0.05) No significant interaction was observed between the methionine source and the SAA level for any carcass traits. However, animals that received OH-Met had greater (p < 0.05) loin depth (58.37 versus 55.21 mm) and those that received higher doses of methionine presented heavier (p < 0.05) carcass weight (78.16 versus 74.70 kg), and more (p < 0.05) lean meat weight (43.69 versus 41.90 kg). Taken together, these results demonstrated that supplementation of high sulfur amino acids levels under hot conditions provided heavier carcasses and more lean meat.

Evaluating growth response of broiler chickens fed diets supplemented with synthetic DL-methionine or DL-hydroxy methionine: a meta-analysis.

Methionine (Met) is the first limiting amino acid in corn and soybean meal-based diets (containing L-Met) in broiler chickens, which are often supplemented with synthetic DL-Met or DL-Hydroxy Met (OH-Met). Our objective was to quantitatively assess the efficacy of synthetic Met sources and determine differences in growth rate of broilers fed at or below requirements in response to Met intake. A systematic literature search resulted in building a database containing 480 treatment means from 39 articles published between 1985 and 2019 globally. The database was divided into starter, grower, and finisher subsets based on the age of the broilers. For each subset, linear-plateau and quadratic-plateau models were fitted to determine Met or sulfur amino acid (SAA; Met + Cysteine) requirements using average daily gain as a response variable. For each phase, 4 new subsets were obtained by only retaining records with digestible Met or SAA intake at or below requirement by linear-plateau or quadratic-plateau models. Then, a linear model (without plateau) was fitted for all new subsets for each rearing phase using supplemental digestible synthetic Met or SAA intake (basal Met intake was subtracted from total Met intake) as independent variables. The basal diet was made of only raw materials without supplementation of any synthetic Met source. Finally, the models were extended to evaluate source of synthetic Met effects on the slope parameter. At all stages of model fitting, the inclusion of a random study effect was evaluated for each parameter. All models were fitted within a Bayesian framework, for which minimally informative priors were used. The best models, that is, the most accurate inclusion of random effects, were selected based on at least 10-point difference in leave-one-out cross-validation information criterion. Model selection criteria did not consistently favor either of the linear- and quadratic-plateau models to determine Met or SAA requirements across broiler growth phases. Extending models with covariates (e.g., dietary energy and amino acids) did not improve any model fit. Body weight gain response of broiler chickens to the 2 sources was not different when fed at or below Met requirements for any of the growth phases.

Increased Ingestion of Hydroxy-Methionine by Both Sows and Piglets Improves the Ability of the Progeny to Counteract LPS-Induced Hepatic and Splenic Injury with Potential Regulation of TLR4 and NOD Signaling.

Methionine, as an essential amino acid, play roles in antioxidant defense and the regulation of immune responses. This study was designed to determine the effects and mechanisms of increased consumption of methionine by sows and piglets on the capacity of the progeny to counteract lipopolysaccharide (LPS) challenge-induced injury in the liver and spleen of piglets. Primiparous sows (n = 10/diet) and their progeny were fed a diet that was adequate in sulfur amino acids (CON) or CON + 25% total sulfur amino acids as methionine from gestation day 85 to postnatal day 35. A total of ten male piglets were selected from each treatment and divided into 2 groups (n = 5/treatment) for a 2 × 2 factorial design [diets (CON, Methionine) and challenge (saline or LPS)] at 35 d old. After 24 h challenge, the piglets were euthanized to collect the liver and spleen for the histopathology, redox status, and gene expression analysis. The histopathological results showed that LPS challenge induced liver and spleen injury, while dietary methionine supplementation alleviated these damages that were induced by the LPS challenge. Furthermore, the LPS challenge also decreased the activities of GPX, SOD, and CAT and upregulated the mRNA and(or) protein expression of TLR4, MyD88, TRAF6, NOD1, NOD2, NF-kB, TNF-α, IL-8, p53, BCL2, and COX2 in the liver and (or) spleen. The alterations of GPX and SOD activities and the former nine genes were prevented or alleviated by the methionine supplementation. In conclusion, the maternal and neonatal dietary supplementation of methionine improved the ability of piglets to resist LPS challenge-induced liver and spleen injury, potentially through the increased antioxidant capacity and inhibition of TLR4 and NOD signaling pathway.

Methionine Protects Mammary Cells against Oxidative Stress through Producing S-Adenosylmethionine to Maintain mTORC1 Signaling Activity.

The mechanistic target of rapamycin complex 1 (mTORC1) signaling plays pivotal roles in cell growth and diseases. However, it remains mechanistically unclear about how to maintain mTORC1 activity during mammary glands development. Here we showed that mammary glands suffered from aggravated oxidative stress as pregnancy advanced and was accompanied by an increase in H2O2 levels, while the consumption for methionine and S-adenosylmethionine (SAM) rather than S-adenosylhomocysteine (SAH) were promoted in vivo. Likewise, H2O2 promoted SAM synthesis and reduced SAM utilization for methylation depending on H2O2 levels and treatment time in vitro. H2O2 inhibited phosphorylation of S6 kinase Thr 389 (p-S6K1 (T389)), 4E-BP1 Thr 37/46 and ULK1 Ser 757, the downstream of mTORC1, in mammary epithelial cells. However, methionine and SAM were shown to activate mTORC1 under H2O2-exposed condition. Moreover, this effect was not disabled by SGI-1027 which inhibits SAM transmethylation. In conclusion, methionine appeared to protect mammary cells against oxidative stress through producing SAM to maintain mTORC1 signaling activity.

Increased Consumption of Sulfur Amino Acids by Both Sows and Piglets Enhances the Ability of the Progeny to Adverse Effects Induced by Lipopolysaccharide.

This study determined the effects of increased consumption of sulfur amino acids (SAA), as either DL-Met or Hydroxy-Met (OH-Met), by sows and piglets on their performance and the ability of the progeny to resist a lipopolysaccharide (LPS) challenge. Thirty primiparous sows were fed a diet adequate in SAA (CON) or CON + 25% SAA, either as DL-Met or OH-Met from gestation day 85 to postnatal day 21. At 35 d old, 20 male piglets from each treatment were selected and divided into 2 groups (n = 10/treatment) for a 3 × 2 factorial design [diets (CON, DL-Met or OH-Met) and challenge (saline or LPS)]. OH-Met and/or DL-Met supplementation increased (p ≤ 0.05) piglets' body weight gain during day 0-7 and day 7-14. Sow's milk quality was improved in the supplemented treatments compared to the CON. The LPS challenge decreased (p ≤ 0.05) piglets' performance from 35 to 63 d and increased (p ≤ 0.05) the levels of aspartate aminotransferase, total bilirubin, IL-1ß, IL-6, TNF-a, and malondialdehyde. Plasma albumin, total protein, total antioxidant capacity and glutathione peroxidase decreased post-challenge. The results were better with OH-Met than DL-Met. The increase of Met consumption, particularly as OH-Met increased piglets' growth performance during the lactation phase and the challenging period.

Improving pork quality traits by a short-term dietary hydroxy methionine supplementation at levels above growth requirements in finisher pigs.

The effects of dietary methionine (Met) supplies above growth requirements on tissue biology and pork quality were studied. At 70 kg, 45 crossbred pigs were fed a control (CONT) diet adequate in Met (0.22% Met) up to 105 kg. For the last 14 days before slaughter, pigs were fed with the CONT diet or with diets where the Met level was increased to Met3 (0.66% Met) or Met5 (1.10% Met). Growth performance and carcass composition did not change with the treatment. Pigs fed the Met5 treatment displayed lower TBARS and higher glutathione levels (P ≤ .05), along with higher ultimate pH (P < .01) and lower drip, lightness and hue (P ≤ .10) in the longissimus muscle, compared to the CONT and Met3 pigs. Extra-dietary Met improved ham's technological quality in the Met3 and Met5 groups (P ≤ .05). Thus, dietary Met supplementation improves pork quality without impairing growth or carcass traits.

Efficacy of 2-hydroxy-4-methylthiobutanoic acid compared to DL-Methionine on growth performance, carcass traits, feather growth, and redox status of Cherry Valley ducks.

The objective of this study was to compare the bio-efficacy of 2-hydroxy-4-methylthiobutanoic acid (DL-HMTBA) with that of DL-methionine (DLM) as sources of methionine in terms of the growth performance, carcass traits, feather growth, and redox statuses of Cherry Valley ducks. Six hundred and thirty male ducks were randomly allotted to 9 dietary treatment groups with 7 replicates of 10 birds each. The first group received a basal diet (BD) without methionine addition that was deficient in the total number of sulfur amino acids. In Groups 2 to 5 and Groups 6 to 9, the BD was supplemented with 4 increasing doses of methionine as either DLM or DL-HMTBA. The trial was run from ages 1 to 42 d. Dietary supplementation with DLM and DL-HMTBA improved body weight gain and feed intake as well as weights of carcasses, breast meat, and feathers compared with the BD. No significant difference was observed between the 2 methionine sources on growth performance, carcass traits, and feather growth. Concentrations of some redox markers in the pectoralis major muscle were improved by addition of methionine to the BD. However, a significant difference was observed between DLM and DL-HMTBA in this respect, as the supplementation of DL-HMTBA significantly increased the total antioxidant capacity, the activities of glutathione peroxidase, and the concentration of reduced glutathione in the pectoralis major muscle, compared with DLM. No significant difference between methionine sources was found with regard to the concentrations of oxidized glutathione and malondialdehyde in the pectoralis major muscle. Both DLM and DL-HMTBA increased malondialdehyde concentrations in the pectoralis major muscle compared with the BD. In conclusion, these results indicated that DLM and DL-HMTBA have equal biological value for the growth performance, carcass traits, and feather growth of Cherry Valley duck. Moreover, the improved antioxidant capacity observed with DL-HMTBA makes this a better candidate than DLM for lowering the oxidation process in the meat during post-mortem storage and thereby contributes to a better duck meat quality.