Uptake of DL-2-hydroxy-4-methylthio-butanoic acid (DL-HMB) in the broiler liver in vivo

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.

Selenium source and level on performance, selenium retention and biochemical responses of young broiler chicks

Background

Selenium (Se) has been recognized as an essential micronutrient for nearly all forms of life. In recent decades, broiler responses to dietary Se supplemental levels and sources have received considerable attention. On environmental grounds, organic trace mineral utilization in practical broiler feeds has been defended due to its higher bioavailability. In such feeds, trace minerals are provided simultaneously in the same supplement as inorganic salts or organic chelates, a fact commonly ignored in assays conducted to validate organic trace mineral sources. The current assay aimed to investigate growth and biochemical responses, as well as Se retention of growing chicks fed diets supplemented with organic and inorganic Se levels and where the trace minerals (zinc, copper, manganese, and iron) were provided as organic chelates or inorganic salts according to Se source assessed. In so doing, a 2 × 5 factorial arrangement was used to investigate the effects of sodium selenite (SS) and selenium-yeast (SY) supplemented in feeds to provide the levels of 0, 0.08, 0.16, 0.24, and 0.32 mg Se/kg.

Results

Chicks fed selenium-yeast diets had body weight (BW), and average daily gain (ADG) maximized at 0.133 and 0.130 mg Se/kg, respectively. Both Se sources linearly increased (P < 0.05) the glutathione peroxidase (GSH-Px) activity in chick blood but higher values were observed in sodium selenite fed chicks (P < 0.05). Both Se sources influenced thyroid hormone serum concentrations (P < 0.05). Chicks fed SY exhibited greater retention of Se in the feathers (P < 0.05). Relative bioavailability of selenium yeast compared with SS for the Se content in carcass, feathers, total and Se retention were, 126, 116, 125 and 125%, respectively. SY supplementation resulted in lower liver Se concentration as Se supplementation increased (P < 0.05).

Conclusions

Based on performance traits, the supplemental level of organic Se as SY in organic trace minerals supplement to support the maximal growth of broiler chicks is 0.133 mg Se/kg.

Dietary methionine source and level affect hepatic sulfur amino acid metabolism of broiler breeder hens

A study was carried out to investigate the effects of dietary methionine source and level on plasma free amino acids patterns and the expression of genes involved in hepatic methionine metabolism in broiler breeders. A total of 2184 broiler breeders were assigned to 13 dietary treatments, with eight replicates per treatment. The 13 treatments included one control group and 12 additional treatments employing two sources and six levels (0.05, 0.10, 0.15, 0.20, 0.25 and 1.00%). Higher plasma methionine concentration was measured for DL-methionine (DLM) treated hens. Plasma alanine concentration was linearly increased as DLM or 2-hydroxy-4-(methylthio) butanoic acid (HMTBA) supplementation level increased. There was a linear increase in concentrations of tyrosine, valine, glycine and serine as dietary DLM supplementation level increased. Hens treated with DLM had higher relative expression of ADA than those fed HMTBA. The expression of MS, ADA, SAHH and MAT2A changed quadratically as HMTBA supplementation level increased, while the expression of GNMT and SAHH changed quadratically as DLM supplementation level increased. In conclusion, the effects of HMTBA on plasma free amino acid patterns and the expression of hepatic genes involved with methionine are different from DLM.

Conversion of the Methionine Hydroxy Analogue dl-2-Hydroxy-(4-Methylthio) Butanoic Acid to Sulfur-Containing Amino Acids in the Chicken Small Intestine

dl-Methionine or its corresponding hydroxy analogue, DL-2-hydroxy-(4-methylthio) butanoic acid (DLHMB), are commonly added to commercial animal diets to satisfy the TSAA requirement. The utilization of DLHMB as a supplementary source of Met begins with its conversion to L-Met via a 2-step mediated process. L-Methionine can then be transsulfurated to L-Cys, which, in turn, can be catabolized to taurine (TAU). In the present study, the capacity of the chicken small intestine to convert DLHMB to L-Met and to use this amino acid as a source for L-Cys and TAU production was evaluated. The appearance of Met in the serosal compartment of everted sacs incubated with DLHMB is higher in the presence of an H(+) gradient (mucosal pH 5.5 vs. 7.4). Serosal Cys and TAU concentration was compared in everted sacs incubated at a mucosal pH of 5.5 with DLHMB or L-Met, and the results show significantly higher values after incubation with the hydroxy analogue. Regional comparisons indicate no significant differences in the appearance of serosal Met and Cys, although lower values were obtained for TAU in the duodenum than in the jejunum and ileum. The profile of non-S amino acids was also determined and revealed no significant differences between DLHMB- and L-Met-incubated sacs. In conclusion, Cys and TAU content in chicken enterocytes is higher when DLHMB is used as a Met source.

Effects of dietary supplementation of DL-methionine or 2-hydroxy-4-(methylthio)-butanoic acid on food intake, nutrient digestibility, nitrogen balance, and urinary and blood metabolites in healthy, growing dogs

The aim of this study was to evaluate effects on nutritional responses of supplemental DL-methionine and 2-hydroxy-4-(methylthio) butanoic acid (HMTBA) in a commercial-type diet in growing dogs. A nitrogen balance study was conducted as a randomized complete block design using 30 Pointer puppies (72-d-old; 5.5 kg). A corn and poultry byproduct meal based diet was supplemented with 0.1 or 0.2% DL-methionine or HMTBA on an equimolar basis. Organic matter and gross energy tended (p < 0.10) to be less digestible by dogs fed the 0.1% HMTBA diet compared with the 0.2% DL-methionine diet, but other nutrients were unaffected. Postprandial urinary calcium tended (p < 0.10) to be lower for the basal and HMTBA treatments. Fecal ammonia tended (p < 0.10) to be lower for the 0.1% HMTBA diet than for the 0.2% DL-methionine diet. At the levels tested, DL-methionine and HMTBA appear to act similarly when included in a corn and poultry by-product meal diet fed to young dogs.

Absorption and Digestive Tract Metabolism of 2-Hydroxy-4-Methylthiobutanoic Acid in Lambs

Anabolic availability of the hydroxyl methionine analog, 2-hydroxy-4-methylthiobutanoic acid (HMTBA), given as oral doses to lambs, was quantified both directly as appearance in the portal vein and as synthesis to Met by digestive tract tissues. Eight lambs, prepared with vascular catheters in the mesenteric and portal veins plus the aorta, received twice daily for 7 d either 0.46 g or 2 g of HMTBA. On d 7, [1-13C]HMTBA was supplied as 1 oral dose while [methyl-2H3]Met was infused into the jugular vein. Peak absorption as HMTBA occurred 70 to 90 min after the oral dose. All digestive tract tissues converted HMTBA to Met, equivalent to 24% of the Met provided by the diet for the larger HMTBA dose. Overall, total availability of HMBTA averaged 17.9% of the dose (range 10.6 to 27.9%), with 12.5% (range 7 to 22%) as absorbed HMBTA and the remainder as Met synthesized by digestive tract tissues. Release of 13CO2 into the portal vein accounted for another 23% of the dose. In all digestive tract tissues, the d-isomer was present in a smaller proportion than in the dose. In terms of whole-body kinetics, HMTBA loss from the plasma followed first-order kinetics, with a mean biological half-life of 76 min. Using this value, a simple model was devised to estimate HMTBA absorption based on peripheral plasma samples. When compared with direct measures of absorption, the model gave a slope of 0.81 (R2 = 0.68) and offers a practical means to test HMTBA availability to animals.

Absorption of 2-Hydroxy-4-Methylthiobutyrate and Conversion to Methionine in Lambs

Absorption and metabolism of the Met hydroxy analog 2-hydroxy-4-methylthiobutyrate (HMTBA) was examined using stable isotopes. In the first trial, Dl[1-13C]HMTBA was infused for 6 h (7.4 micromol/min) into the abomasum, and [2H3]Met was infused into the mesenteric vein, of 4 lambs prepared with vascular catheters across the splanchnic bed. Daily, lambs were offered 35 g of a mixed forage-concentrate feed/kg. Recovery of HMTBA at the portal vein was 87%, and of this, 63% bypassed the liver. In contrast, hepatic extraction of Met equaled or exceeded net absorption. Only small quantities of Met synthesized from HMTBA were exported from either the digestive tract or liver, but there was substantial and significant input from posthepatic tissues. In a second experiment, 3 of the lambs were killed following 4-h infusions of DL[1-13C]HMTBA and [2H3]Met with enrichments monitored in 15 tissues. Only kidney showed [1-13C]Met enrichment higher than plasma, which suggests that it must be a primary source of plasma Met derived from HMTBA. Based on comparison of plasma and intracellular [1-13C]:[2H3]Met enrichments, all tissues synthesized Met from HMTBA but to significantly different extents. The lowest values were for muscle, skin, brain, and lung; intermediate conversions occurred in rumen, omasum, abomasum, duodenum, jejunum, ileum, and cecum; and the greatest synthesis, equivalent to 22 to 24% of Met entry into cells, was observed for liver and kidney. Therefore, although liver and kidney both converted HMTBA to Met, it was retained by the former and exported by the latter. Under these experimental conditions, synthesis of Met from HMTBA completely eliminated use of dietary Met.

Hepatic Metabolism of 2-Hydroxy-4-Methylthiobutyrate in Growing Lambs

This study was undertaken to determine how, and where, 2-hydroxy-4-methylthiobutyrate (HMTBA) can augment Met metabolism in lambs. Four lambs (initial body weight of 50 kg, SE = 2, and 6 mo of age) prepared with catheters in the mesenteric, portal, hepatic, and jugular veins plus the aorta, were fed at 1.5x maintenance on a grass hay, barley, fish meal, molasses/pre-mix (5:3:1:1, as fed) diet, supplied as hourly meals. Lambs were infused for 10 h with [methyl-2H3]Met (0.11 mmol/h) in a jugular vein and p-aminohippurate into the mesenteric vein. From 1 h onwards, successive 3-h infusions of saline (control), 0.55 mg/min (3.67 micromol/min), and 4.44 mg/min (29.6 micromol/min) of HMTBA were also infused into the mesenteric vein. Plasma, sampled continuously, was collected every 20 min during the last 60 min of each infusion. All infused HMTBA was recovered at the portal vein with 25% extracted subsequently by the liver. Portal appearance of total Cys and Met was unaltered by HMTBA infusion, but net splanchnic appearance of Cys increased (0.04, 0.08, 0.23 mmol/h, SEM = 0.05), whereas Met decreased (0.14, -0.01, -0.21 mmol/h, SED = 0.05). Despite this, arterial Met increased (27.0, 30.7, 51.5 microM, SEM = 2.1) as did Met irreversible loss rate (27.6, 28.7, 40.1 micromol/h, SEM = 0.51), equivalent to 40% of the HMTBA reentering the plasma after conversion to Met. These data indicate that, in ruminants, HMTBA is probably converted to Met within peripheral tissues; that is, where the metabolic need for Met exists.

The hepatic extraction of plasma free amino acids and response to hepatic portal venous infusion of methionine sources in anesthetized SCWL males (Gallus domesticus)

This study was conducted to investigate the hepatic extraction of plasma free amino acids in anesthetized Single Comb White Leghorn (SCWL) males (Gallus domesticus). SCWL males were anesthetized and implanted with cannulae in the carotid artery, hepatic vein, hepatic portal vein and the left hepatic duct. Free amino acids in plasma and bile were determined before, during and after 30-min infusions of Saline (control), DL-Methionine (DL-Met) or DL-2-hydroxy-4-methylthio-butanoic acid (DL-HMB) into the hepatic portal vein. Hepatic extraction rates (HER) of amino acids were calculated based on the concentration of amino acids in plasma multiplied by estimations of blood flow in the hepatic portal vein, hepatic artery and hepatic vein. For the non-essential amino acids, alanine had the highest HER (46%). The liver also removed more than 20% of hepatic inflow of tyrosine and asparagine with substantial extraction (14-18%) of serine, glycine and glutamine, also. In contrast, less than 5% of hepatic inflow of glutamate and cystine were removed by liver. For the essential amino acids, HER for methionine, histidine and phenylalanine were 30, 14 and 17%, respectively, with less than 5% for branched-chain amino acids, lysine, arginine and threonine. Biliary secretion of amino acids represented a small percentage (<0.2%) of total hepatic extraction turnover of the amino acids. Infusion of methionine sources, DL-Met and DL-HMB, had no effect on hepatic metabolism of amino acids other than methionine. The results demonstrated for the first time, the hepatic extraction of circulating free amino acids in avian species in vivo.