Formation of beta-hydroxyisovalerate by an alpha-ketoisocaproate oxygenase in human liver

Superior bioavailability of the calcium salt form of β-hydroxy-β-methylbutyrate compared with the free acid form

We investigated the bioavailability of the calcium salt (HMB-Ca) and the free acid (HMB-FA) forms of β-hydroxy-β-methylbutyrate (HMB). Sixteen young individuals received the following treatments on three different occasions in a counterbalanced crossover fashion: (1) HMB-FA in clear capsules; (2) HMB-Ca in gelatine capsules; (3) HMB-Ca dissolved in water. All treatments provided 1 g of HMB. Blood samples were taken before and on multiple time points following ingestion. The following parameters were calculated: peak plasma (Cmax), time to peak (Tmax), slope of HMB appearance in blood, area under the curve (AUC), half-life time (t1/2) and relative bioavailability (HMB-Ca in water set as reference). All treatments led to rapid and large increases in plasma HMB. HMB-Ca in capsules and in water showed similar plasma HMB values across time (p = 0.438). HMB-FA resulted in lower concentrations vs. the other treatments (both p < 0.001). AUC (HMB-Ca in capsules: 50,078 ± 10,507; HMB-Ca in water: 47,871 ± 10,783; HMB-FA: 29,130 ± 12,946 µmol L-1 × 720 min), Cmax (HMB-Ca in capsules: 229.2 ± 65.9; HMB-Ca in water: 249.7 ± 49.7; HMB-FA: 139.1 ± 67.2 µmol L-1) and relative bioavailability (HMB-Ca in capsules: 104.8 ± 14.9%; HMB-FA: 61.5 ± 17.0%) were lower in HMB-FA vs. HMB-Ca (all p < 0.001). HMB-Ca in water resulted in the fastest Tmax (43 ± 22 min) compared to HMB-Ca in capsules (79 ± 40 min) and HMB-FA (78 ± 21 min) (all p < 0.05), while t1/2 was similar between treatments. To conclude, HMB-Ca exhibited superior bioavailability compared to HMB-FA, with HMB-Ca in water showing faster absorption. Elimination kinetics were similar across all forms, suggesting that the pharmaceutical form of HMB affects the absorption rates, but not its distribution or elimination.

Isobutene production in Synechocystis sp. PCC 6803 by introducing α-ketoisocaproate dioxygenase from Rattus norvegicus

Cyanobacteria can be utilized as a platform for direct phototrophic conversion of CO₂ to produce several types of carbon-neutral biofuels. One promising compound to be produced photobiologically in cyanobacteria is isobutene. As a volatile compound, isobutene will quickly escape the cells without building up to toxic levels in growth medium or get caught in the membranes. Unlike liquid biofuels, gaseous isobutene may be collected from the headspace and thus avoid the costly extraction of a chemical from culture medium or from cells. Here we investigate a putative synthetic pathway for isobutene production suitable for a photoautotrophic host. First, we expressed α-ketoisocaproate dioxygenase from Rattus norvegicus (RnKICD) in Escherichia coli. We discovered isobutene formation with the purified RnKICD with the rate of 104.6 ​± ​9 ​ng (mg protein)^-1 min^-1 using α-ketoisocaproate as a substrate. We further demonstrate isobutene production in the cyanobacterium Synechocystis sp. PCC 6803 by introducing the RnKICD enzyme. Synechocystis strain heterologously expressing the RnKICD produced 91 ​ng ​l⁻¹ OD₇₅₀⁻¹ ​h⁻¹. Thus, we demonstrate a novel sustainable platform for cyanobacterial production of an important building block chemical, isobutene. These results indicate that RnKICD can be used to further optimize the synthetic isobutene pathway by protein and metabolic engineering efforts.

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Photosynthetic isobutene production is demonstrated in a cyanobacterium.

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A Synechocystis strain capable of continuous direct conversion of CO₂ to isobutene.

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α-ketoisocaproate dioxygenase from R. norvegicus (RnKICD) is determined to form isobutene.

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RnKICD can convert α-ketoisocaproate to isobutene both in vitro and in vivo.

Mechanism of Action and the Effect of Beta-Hydroxy-Beta-Methylbutyrate (HMB) Supplementation on Different Types of Physical Performance - A Systematic Review

Beta-hydroxy-beta-methylbutyrate (HMB) has been used extensively as a dietary supplement for athletes and physically active people. HMB is a leucine metabolite, which is one of three branched chain amino acids. HMB plays multiple roles in the human body of which most important ones include protein metabolism, insulin activity and skeletal muscle hypertrophy. The ergogenic effects of HMB supplementation are related to the enhancement of sarcolemma integrity, inhibition of protein degradation (ubiquitin pathway), decreased cell apoptosis, increased protein synthesis (mTOR pathway), stimulation of the growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis and enhancement of muscle stem cells proliferation and differentiation. HMB supplementation has been carried out with various groups of athletes. In endurance and martial arts athletes, HMB supplementation revealed positive effects on specific aerobic capacity variables. Positive results were also disclosed in resistance trained athletes, where changes in strength, body fat and muscle mass as well as anaerobic performance and power output were observed. The purpose of this review was to present the main mechanisms of HMB action, especially related to muscle protein synthesis and degradation, and ergogenic effects on different types of sports and physical activities.

Transport Mechanisms for the Nutritional Supplement β-Hydroxy-β-Methylbutyrate (HMB) in Mammalian Cells

PURPOSE

β-Hydroxy-β-methylbutyrate (HMB), a nutritional supplement, elicits anabolic activity in muscle. Here we investigated the mechanism of HMB uptake in muscle cells.

METHODS

Murine muscle cells (C2C12) and human mammary epithelial cells (MCF7) were used for uptake. As HMB is a monocarboxylate, focus was on monocarboxylate transporters, monitoring interaction of HMB with H⁺-coupled lactate uptake, and influence of H⁺ directly on HMB uptake. Involvement of MCT1-4 was studied using selective inhibitors and gene silencing. Involvement of human Na⁺/monocarboxylate transporter SMCT1 was also assessed using Xenopus oocytes.

RESULTS

H⁺-coupled lactate uptake was inhibited by HMB in both mammalian cells. HMB uptake was H⁺-coupled and inhibited by lactate. C2C12 cells expressed MCT1 and MCT4; MCF7 cells expressed MCT1-4; undifferentiated C2C12 cells expressed SMCT1. SMCT1 mediated Na⁺-coupled HMB transport. Inhibitors of MCT1/4, siRNA-mediated gene silencing, and expression pattern showed that MCT1-4 were responsible only for a small portion of HMB uptake in these cells.

CONCLUSION

HMB uptake in C2C12 and MCF7 cells is primarily H⁺-coupled and inhibited by lactate, but MCT1-4 are only partly responsible for HMB uptake. SMCT1 also transports HMB, but in a Na⁺-coupled manner. Other, yet unidentified, transporters mediate the major portion of HMB uptake in C2C12 and MCF7 cells.

A Review of the Effects of Leucine Metabolite (β-Hydroxy-β-methylbutyrate) Supplementation and Resistance Training on Inflammatory Markers: A New Approach to Oxidative Stress and Cardiovascular Risk Factors

β-hydroxy β-methylbutyrate (HMB) is a bioactive metabolite formed from the breakdown of the branched-chain amino acid, leucine. Given the popularity of HMB supplements among different athletes, specifically, those who participate in regular resistance training, this review was performed to summarize current literature on some aspects of HMB supplementation that have received less attention. Because of the small number of published studies, it has not been possible to conclude the exact effects of HMB on cardiovascular parameters, oxidative stress, and inflammatory markers. Thus, the interpretation of outcomes should be taken cautiously. However, the data presented here suggest that acute HMB supplementation may attenuate the pro-inflammatory response following an intense bout of resistance exercise in athletes. Also, the available findings collectively indicate that chronic HMB consumption with resistance training does not improve cardiovascular risk factors and oxidative stress markers greater than resistance training alone. Taken together, there is clearly a need for further well-designed, long-term studies to support these findings and determine whether HMB supplementation affects the adaptations induced by resistance training associated with the body’s inflammatory condition, antioxidative defense system, and cardiovascular risk factors in humans.

A metabolite of leucine (β-hydroxy-β-methylbutyrate) given to sows during pregnancy alters bone development of their newborn offspring by hormonal modulation

The effects of dietary β-hydroxy-β-methylbutyrate (HMB) supplementation during gestation on bone, growth plate, and articular cartilage in newborns were determined. Thermal analysis of articular cartilage was performed to examine the structural changes in collagen. At day 70 of gestation, a total of 12 sows (Large White Polish breed, at the second parity) were randomly assigned to two groups, with each group receiving either a basal diet or the same diet supplemented with 0.2 g/day HMB until the 90^th day. Maternal HMB supplementation enhanced body weight, bone length, and diameter in males. It also improved geometric and mechanical properties contributing to increased bone morphology and endurance. In turn, alteration of the length was only observed in females. The positive effects were mediated by increased serum concentrations of insulin-like growth factor-1 and leptin. HMB-treatment enhanced the concentration of FSH, LH, estradiol, and testosterone. Serum TAP was enhanced by the HMB-treatment by 34% in females and 138% in males. Beneficial effects of the HMB-treatment on trabecular bone and content of proteoglycans in articular cartilage were shown. The HMB-treatment significantly changed the collagen structure in cartilages, especially in the females, which was demonstrated by the PSR analysis. Differences between the HMB-supplemented and the control females in the calorimetric peak temperatures were presumably related to different collagen fibril density in the articular cartilage structure. In summary, maternal HMB supplementation in the mid-gestation period significantly improved general growth and mechanical endurance of long bones by the influence on the somatotropic and pituitary-gonadal axes in the offspring.

Determination of β-hydroxy-β-methylbutyrate concentration and enrichment in human plasma using chemical ionization gas chromatography tandem mass spectrometry

Our objective was to develop a quick and simplified method for the determination of β-Hydroxy-β-methylbutyrate (HMB) and ɑ-ketoisocaproic acid (KIC) concentrations and enrichments by GC/MS/MS to determine the turnover rate of HMB in humans. In experiment 1, we provided a pulse of L-[5,5,5-²H₃]leucine to younger adults in the postabsorptive state then collected blood samples over a 4h time period. In experiment 2, we provided a pulse of [3,4,methyl-¹³C₃]HMB to older adults in the postabsorptive state then collected blood samples over a 3h time period. Plasma concentrations of KIC and HMB and MPE of KIC and HMB were determined by GC/MS/MS. Plasma enrichment of leucine was determined by LC/MS/MS. To determine plasma enrichment of [5,5,5-²H₃]HMB and [3,4,methyl-¹³C₃]HMB, samples were derivatized using pentafluorobenzyl bromide and analyzed using chemical ionization mode. The final methods used included multiple reaction monitoring of transitions 117.3>59.3 for M+0 and 120.3>59.3 for M+3. In experiment 1, peak MPE of Leu peaked at 9.76% generating a peak MPE of KIC at 2.67% and a peak HMB MPE of 0.3%. In experiment 2, the rate of appearance for HMB was  0.66μmol/kg ffm/h. We calculated that production of HMB in humans accounts for 0.66% of total leucine turnover.

Enteral β-hydroxy-β-methylbutyrate supplementation increases protein synthesis in skeletal muscle of neonatal pigs

Many low-birth weight infants are at risk for poor growth due to an inability to achieve adequate protein intake. Administration of the amino acid leucine stimulates protein synthesis in skeletal muscle of neonates. To determine the effects of enteral supplementation of the leucine metabolite β-hydroxy-β-methylbutyrate (HMB) on protein synthesis and the regulation of translation initiation and degradation pathways, overnight-fasted neonatal pigs were studied immediately (F) or fed one of five diets for 24 h: low-protein (LP), high-protein (HP), or LP diet supplemented with 4 (HMB4), 40 (HMB40), or 80 (HMB80) μmol HMB·kg body wt(-1)·day(-1) Cell replication was assessed from nuclear incorporation of BrdU in the longissimus dorsi (LD) muscle and jejunum crypt cells. Protein synthesis rates in LD, gastrocnemius, rhomboideus, and diaphragm muscles, lung, and brain were greater in HMB80 and HP and in brain were greater in HMB40 compared with LP and F groups. Formation of the eIF4E·eIF4G complex and S6K1 and 4E-BP1 phosphorylation in LD, gastrocnemius, and rhomboideus muscles were greater in HMB80 and HP than in LP and F groups. Phosphorylation of eIF2α and eEF2 and expression of SNAT2, LAT1, MuRF1, atrogin-1, and LC3-II were unchanged. Numbers of BrdU-positive myonuclei in the LD were greater in HMB80 and HP than in the LP and F groups; there were no differences in jejunum. The results suggest that enteral supplementation with HMB increases skeletal muscle protein anabolism in neonates by stimulation of protein synthesis and satellite cell proliferation.

Effects of amino acid derivatives on physical, mental, and physiological activities

Nutritional ergogenic aids have been in use for a long time to enhance exercise and sports performance. Dietary components that exhibit ergogenic activity are numerous and their consumption is common and popular among athletes. They often come under scrutiny by legal authorities for their claimed benefits and safety concerns. Amino acid derivatives are propagated as being effective aids to enhance physical and mental performance in many ways, even though studies have pointed out that individuals who are deficient are more likely to benefit from dietary supplementation of amino acid derivatives than normal humans. In this review, some of the most common and widely used amino acids derivatives in sports and athletics namely creatine, tyrosine, carnitine, HMB, and taurine have been discussed for their effects on exercise performance, mental activity as well as body strength and composition. Creatine, carnitine, HMB, and taurine are reported to delay the onset of fatigue, improve exercise performance, and body strength. HMB helps in increasing fat-free mass and reduce exercise induced muscle injury. Taurine has been found to reduce oxidative stress during exercise and also act as an antihypertensive agent. Although, studies have not been able to find any favorable effect of tyrosine administration on exercise performance, it has been proved to be very effective in fighting stress, improving mood and cognitive performance particularly in sleep-deprived subjects. While available data from published studies and findings are equivocal about the efficacy of creatine, tyrosine, and HMB, more comprehensive researches on carnitine and taurine are necessary to provide evidence for the theoretical basis of their ergogenic role in nutritional modification and supplementation.

Simultaneous quantification of salivary 3-hydroxybutyrate, 3-hydroxyisobutyrate, 3-hydroxy-3-methylbutyrate, and 2-hydroxybutyrate as possible markers of amino acid and fatty acid catabolic pathways by LC-ESI-MS/MS

We have developed a highly sensitive and specific method for quantification of salivary 3-hydroxybutyrate (3HB), 3-hydroxyisobutyrate (3HIB), 3-hydroxy-3-methylbutyrate (3HMB) and 2-hydroxybutyrate (2HB), which could be new non-invasive biomarkers for catabolic pathways of fatty acids/ketogenic amino acids, valine, leucine, and methionine/threonine/α-ketobutyrate, respectively. The four hydroxybutyrates (3HB, 3HIB, 3HMB, and 2HB) were extracted from 5 µl of saliva, converted to 2-pyridylmethyl (2PM) ester derivatives, and measured by liquid chromatography–tandem mass spectrometry in positive electrospray ionization mode. [¹³C₄]3HB was used as an internal standard. The detection limits for the 2PM esters were <1 pg (7.9–9.6 fmol) on-column (signal-to-noise ratio = 3). Reproducibilities and recoveries of the hydroxybutyrates were validated according to one-way layout and polynomial equation, respectively. The variances between sample preparations and between measurements were calculated to be 0.45–5.28 and 0.54–3.45 %, respectively. Experiments performed using 5 µl of saliva spiked with 3.8–154.4 pmol of the four hydroxybutyrates gave recoveries of 98.5 to 108.8 %, with a mean recovery of 104.1 %. In vitro experiments in hepatocytes or skeletal muscle cells showed that addition of palmitic acid, valine, leucine or α-ketobutyrate to culture medium markedly increased the targeted hydroxybutyrate concentrations. The salivary concentration of each targeted hydroxybutyrate was positively correlated with that in serum, and the salivary levels were elevated in patients with liver cirrhosis, which is characterized by upregulated catabolism of lipids and amino acids. The proposed method is useful for quantification of salivary 3HB, 3HIB, 3HMB, and 2HB for monitoring of catabolic activities of amino acids and fatty acids.

The relative bioavailability of the calcium salt of β-hydroxy-β-methylbutyrate is greater than that of the free fatty acid form in rats

BACKGROUND

β-Hydroxy-β-methylbutyrate (HMB) supplementation has been demonstrated to enhance muscle protein synthesis and attenuate loss of muscle mass by multiple pathways. The beneficial effects of HMB have been studied by using either the calcium salt, monohydrate, of HMB (CaHMB) or the free acid form (FAHMB).

OBJECTIVE

The present study was designed to compare the pharmacokinetics and relative bioavailability of the 2 forms of HMB administered as a liquid suspension in male Sprague-Dawley rats.

METHODS

CaHMB at 30, 100, and 300 mg/kg and equivalent doses of FAHMB at 24.2, 80.8, and 242 mg/kg were administered orally as a liquid suspension to male Sprague-Dawley rats. A single i.v. dose of 5 mg/kg CaHMB, corresponding to an equivalent dose of 4.04 mg/kg FAHMB, was also administered. Plasma concentrations of HMB were analyzed by liquid chromatography tandem mass spectrometry, and pharmacokinetic variables and relative bioavailability of the 2 forms of HMB were determined.

RESULTS

After oral administration, the area under the plasma concentration time curve (AUC) from time 0 to time t (0-t) and from time 0 to infinity (0-∞) and the maximum (peak) plasma concentration (Cmax) for CaHMB were significantly greater than for FAHMB, whereas the time to reach Cmax did not differ from that of FAHMB. The relative bioavailability of CaHMB was 49%, 54%, and 27% greater than that of FAHMB for the 3 respective oral doses tested. After i.v. administration, the AUCs 0-t and 0-∞ of the calcium salt were significantly greater than those of FAHMB. The relative bioavailability of CaHMB was 80% greater than that of FAHMB. The higher relative bioavailability of CaHMB may be attributable to its low systemic clearance compared with FAHMB.

CONCLUSIONS

This study demonstrates the enhanced relative bioavailability of CaHMB compared with FAHMB. Further studies are warranted to understand the physiologic mechanisms contributing to the differences in systemic clearance.

Protein synthesis in skeletal muscle of neonatal pigs is enhanced by administration of β-hydroxy-β-methylbutyrate

Many low-birth-weight infants experience failure to thrive. The amino acid leucine stimulates protein synthesis in skeletal muscle of the neonate, but less is known about the effects of the leucine metabolite β-hydroxy-β-methylbutyrate (HMB). To determine the effects of HMB on protein synthesis and the regulation of translation initiation and degradation pathways, overnight-fasted neonatal pigs were infused with HMB at 0, 20, 100, or 400 μmol·kg body wt(-1)·h(-1) for 1 h (HMB 0, HMB 20, HMB 100, or HMB 400). Plasma HMB concentrations increased with infusion and were 10, 98, 316, and 1,400 nmol/ml in the HMB 0, HMB 20, HMB 100, and HMB 400 pigs. Protein synthesis rates in the longissimus dorsi (LD), gastrocnemius, soleus, and diaphragm muscles, lung, and spleen were greater in HMB 20 than in HMB 0, and in the LD were greater in HMB 100 than in HMB 0. HMB 400 had no effect on protein synthesis. Eukaryotic initiation factor (eIF)4E·eIF4G complex formation and ribosomal protein S6 kinase-1 and 4E-binding protein-1 phosphorylation increased in LD, gastrocnemius, and soleus muscles with HMB 20 and HMB 100 and in diaphragm with HMB 20. Phosphorylation of eIF2α and elongation factor 2 and expression of system A transporter (SNAT2), system L transporter (LAT1), muscle RING finger 1 protein (MuRF1), muscle atrophy F-box (atrogin-1), and microtubule-associated protein light chain 3 (LC3-II) were unchanged. Results suggest that supplemental HMB enhances protein synthesis in skeletal muscle of neonates by stimulating translation initiation.

β-Hydroxy-β-methylbutyrate (HMβ) supplementation stimulates skeletal muscle hypertrophy in rats via the mTOR pathway

β-Hydroxy-β-methylbutyrate (HMβ) supplementation is used to treat cancer, sepsis and exercise-induced muscle damage. However, its effects on animal and human health and the consequences of this treatment in other tissues (e.g., fat and liver) have not been examined. The purpose of this study was to evaluate the effects of HMβ supplementation on skeletal muscle hypertrophy and the expression of proteins involved in insulin signalling. Rats were treated with HMβ (320 mg/kg body weight) or saline for one month. The skeletal muscle hypertrophy and insulin signalling were evaluated by western blotting, and hormonal concentrations were evaluated using ELISAs. HMβ supplementation induced muscle hypertrophy in the extensor digitorum longus (EDL) and soleus muscles and increased serum insulin levels, the expression of the mammalian target of rapamycin (mTOR) and phosphorylation of p70S6K in the EDL muscle. Expression of the insulin receptor was increased only in liver. Thus, our results suggest that HMβ supplementation can be used to increase muscle mass without adverse health effects.

Prenatal programming of skeletal development in the offspring: effects of maternal treatment with beta-hydroxy-beta-methylbutyrate (HMB) on femur properties in pigs at slaughter age

Alteration in fetal growth and development in response to prenatal environmental conditions such as nutrition has long-term or permanent effects during postnatal life. The aim of this study was to investigate effects of beta-hydroxy-beta-methylbutyrate (HMB) treatment of sows during the last 2 weeks of pregnancy on programming of skeletal development in the offspring. The study was performed on 141 pigs born by 12 sows of Polish Landrace breed. Two weeks before delivery, pregnant sows were divided into two groups. The first group consisted of control sows (N=6) that were treated with placebo. Sows that were orally treated with beta-hydroxy-beta-methylbutyrate (N=6) at the dosage of 0.05 g/kg of body weight per day belonged to the second group. Newborn piglets were weighed and subjected to blood collection for determination of serum levels of growth hormone (GH), insulin-like growth factor-1 (IGF-1), insulin, leptin, glucose and bone alkaline phosphatase (BAP) activity and lipid profile. At the age of 6 months, the piglets were slaughtered, their femur was isolated for analysis and assessment of lean meat content of carcasses was performed. The effects of maternal administration with HMB on skeletal properties in the offspring were evaluated in relation to bone mineral density and geometrical and mechanical properties. Maternal treatment with HMB increased serum levels of GH, IGF-1 and BAP activity in the newborns by 38.0%, 20.0% and 26.0%, respectively (P<0.01). HMB administration significantly increased volumetric bone mineral density of the trabecular and cortical bone of femur in the offspring at the age of 6 months (P<0.001). The weight of femur and geometrical parameters such as cross-sectional area, second moment of inertia, mean relative wall thickness and cortical index were significantly increased after HMB treatment (P<0.05). HMB induced higher values of maximum elastic strength and ultimate strength of femur (P<0.01). Furthermore, lean meat content of carcass was significantly increased in the females born by HMB-treated sows (P<0.05). The obtained results showed that maternal administration with HMB has positive long-term effects on bone tissue and improves volumetric bone mineral density, geometrical and mechanical properties of femur in the offspring. These effects were connected with increased level of GH and IGF-1 in the newborns indicating involvement of improved somatotrophic axis function in prenatal programming of skeletal development in pigs.

Effects of in ovo feeding of carbohydrates and beta-hydroxy-beta-methylbutyrate on the development of chicken intestine

Early development of the digestive tract is crucial for achieving maximal growth and development of chickens. Because the late-term embryo naturally consumes the amniotic fluids, insertion of a nutrient solution into the embryonic amniotic fluid [in ovo (IO) feeding] may enhance development. This study examined the effect of IO feeding on d 17.5 of incubation of carbohydrates (CHO) and beta-hydroxy-beta-methylbutyrate (HMB) on small intestinal development of chickens during the pre and posthatch periods. Results shows that 48 h post-IO feeding procedure all IO feeding treatments exhibited increased villus width and surface area compared with the control group. At d 3 posthatch the surface area of an average villi was increased by 45% for the HMB IO group and by 33% for the CHO and CHO+HMB IO groups compared with controls (noninjected fertile eggs). The activity of jejunal sucrase-isomaltase (SI) was higher (P < 0.05) 48 h after IO feeding in all the IO fed embryos, whereas at day of hatch and at d 3 the CHO+HMB IO group had the highest maltase activity (P < 0.05), which was approximately 50% greater than control embryos. These observations indicated that small intestines of IO fed hatchlings were functionally at a similar stage of development as a conventionally fed 2-d-old chick. Body weight of all IO fed hatchlings was greater than controls, and these differences (P < 0.05) were sustained until the end of the experiment (10 d). At d 10 chicks that were IO fed with CHO had BW that were 2.2% higher, whereas HMB and CHO+HMB IO fed chicks showed 5 to 6.2% BW increase, respectively, compared with controls. The current study shows that the administration of exogenous nutrients into the amnion enhanced intestinal development by increasing the size of the villi and by increasing the intestinal capacity to digest disaccharides. This advantage probably leads to higher BW in IO fed chicks.

The alpha-ketoisocaproate catabolism in human and rat livers

Catabolism of alpha-ketoisocaproate in liver is mediated by cytosolic alpha-ketoisocaproate dioxygenase (KICD) and mitochondrial branched-chain alpha-keto acid dehydrogenase complex (BCKDC). The latter is believed to be involved in the main pathway of the KIC catabolism. In the present study, we measured the activities of KICD and BCKDC in human and rat livers. The KICD activity in human liver was 0.9 mU/g tissue, which was 14.2% of the total activity of BCKDC, and that in rat liver was 4.2 mU/g tissue, which was only 1.0% of the total activity, suggesting that KICD in human liver plays a relatively important role in the alpha-ketoisocaproate catabolism. The KICD activity in human liver was significantly increased by cirrhosis. In rat liver, the enzyme activity was markedly increased by physical training and streptozotocin-induced diabetes, but not by feeding of a diet rich in branched-chain amino acids, although BCKDC activity was increased by feeding of the diet.

beta-hydroxy-beta-methylbutyrate (HMB) supplementation in humans is safe and may decrease cardiovascular risk factors

The leucine metabolite, beta-hydroxy-beta-methylbutyrate (HMB) enhances the effects of exercise on muscle size and strength. Although several reports in animals and humans indicate that HMB is safe, quantitative safety data in humans have not been reported definitively. The objective of this work was to summarize safety data collected in nine studies in which humans were fed 3 g HMB/d. The studies were from 3 to 8 wk in duration, included both males and females, young and old, exercising or nonexercising. Organ and tissue function was assessed by blood chemistry and hematology; subtle effects on emotional perception were measured with an emotional profile test (Circumplex), and tolerance of HMB was assessed with a battery of 32 health-related questions. HMB did not adversely affect any surrogate marker of tissue health and function. The Circumplex emotion profile indicated that HMB significantly decreased (improved) one indicator of negative mood (Unactivated Unpleasant Affect category, P < 0.05). No untoward effects of HMB were indicated. Compared with the placebo, HMB supplementation resulted in a net decrease in total cholesterol (5.8%, P < 0.03), a decrease in LDL cholesterol (7.3%, P < 0.01) and a decrease in systolic blood pressure (4.4 mm Hg, P < 0.05). These effects of HMB on surrogate markers of cardiovascular health could result in a decrease in the risk of heart attack and stroke. In conclusion, the objective data collected across nine experiments indicate that HMB can be taken safely as an ergogenic aid for exercise and that objective measures of health and perception of well-being are generally enhanced.

Enhancement of cellular and humoral immunity in young broilers by the dietary supplementation of beta-hydroxy-beta-methylbutyrate

As a dietary supplement, beta-Hydroxy-beta-Methylbutyrate (HMB), a catabolite of leucine, has been shown to reduce broiler mortality. In a series of experiments, male broilers (Experiments 1 and 2, n = 576) were grown for 21 days on diets that contained HMB at 0, 0.01. 0.05, and 0.10% of diet. In Experiment 3 (n = 240), chicks were fed diets containing 0, 0.05, 0.075, and 0.10% HMB. HMB dietary supplementation did not significantly affect broiler weight gain in any experiment. However, a trend toward increased mean broiler weight gain per bird was observed in Experiments 1 and 3 when HMB was consumed at 0.10% of the diet. Mean feed to gain ratio was not affected by the inclusion of HMB in broiler diets. In Experiment 3, HMB supplemented diets did not affect bursa of Fabricius, thymus, and spleen weights at 21 days of age. Cutaneous basophilic hypersensitivity response against pokeweek mitogen was higher (P < or = 0.05) at 48 and 72 hours post-injection in chicks on 0.05% dietary HMB (Experiment 1). In Experiment 2, this increase occurred 24 hours post-injection in chicks fed HMB at 0.01% of the diet. On the contrary, the T-cell mediated response against PHA-P mitogen was comparable between all dietary treatments in multiple experiments. Macrophage function profiles were determined at 21 days of age. All chicks in experiments 1 and 2 on HMB supplemented diets showed an increase in the recruitment of Sephadex-G50-elicited abdominal exudate cells (AEC). A 2-fold increase in AEC numbers occurred at the 0.10% HMB level (Experiment 1, P < or = 0.05). Although HMB supplementation did not significantly affect the phagocytic potential of the abdominal macrophages, nitrite levels in the macrophage culture supernatants were higher in 0.01% and 0.05% treatment groups as compared to the controls (Experiment 2, P < or = 0.04; Experiment 3, P < or = 0.05). HMB supplementation did not alter the bird's ability to clear Escherichiacoli or Salmonella arizona from the bloodstream. Beginning 7 days post-hatch, chicks were injected i.v. with a 7% sheep red blood cells suspension. Serum samples were collected to determine the primary and secondary antibody response. Chicks receiving the 0.1% HMB diet in Experiments 1 and 2 exhibited increased IgG and total anti-sheep red blood cell (SRBC) antibody levels during the primary response. During the secondary response, birds consuming the 0.10% HMB diet had elevated IgM levels as well as increased total anti-SRBC levels over the controls in Experiments 1 and 3. These studies show that HMB supplementation improves several immunological functions in young broilers, and such improvement may result in decreased mortality.

In vitro exposure with beta-hydroxy-beta-methylbutyrate enhances chicken macrophage growth and function

Beta-hydroxy-beta-methylbutyrate (HMB), a leucine catabolite, has been shown to decrease broiler mortality. One possible target of HMB action may be the cells of the immune system. Macrophages from a chicken macrophage cell line, MQ-NCSU, were exposed to 0, 10, 20, 40, 80, and 100 microg of HMB per 5 x l0(4) cells in a 96-well culture plate. After 24 h of exposure, macrophage proliferation was quantitated by an MTT bioassay. In duplicate experiments, HMB stimulated growth over control (p < or = 0.05) at a wide range of doses. Macrophages were exposed to 20 and 80 microg of HMB and the culture supernatant fractions tested for the presence of nitrite. HMB exposure (20 microg) increased nitrite production by 44.1% over the controls (Experiment 1, p< or =0.035). To determine the phagocytic potential of macrophages after HMB exposure, MQ-NCSU cell line and Sephadex-G50-elicited abdominal macrophages were incubated with fluorescent latex beads (1:40, macrophage to beads ratio) for I h and then analyzed by flow cytometry. When exposed to 40 microg HMB, the phagocytic potential of MQ-NCSU macrophages was significantly higher (31.7%) than that of the controls (p < or = 0.0006). Sephadex-elicited macrophages exhibited 14.4% increased phagocytosis over controls when treated with 80 microg HMB (p < or = 0.0016). When MQ-NCSU macrophages were exposed to HMB, Fc-receptor expression was significantly elevated over the controls (p < or = 0.0001). These data demonstrate that HMB exposure induces proliferation of macrophages in culture as well as enhances macrophage effector functions, such as nitrite production and phagocytosis. The findings of these studies imply that HMB can be used as a possible dietary immunomodulator.

Conversion of beta-methylbutyric acid to beta-hydroxy-beta-methylbutyric acid by Galactomyces reessii

beta-Hydroxy-beta-methylbutyric acid (HMB) has been shown to increase strength and lean mass gains in humans undergoing resistance-exercise training. HMB is currently marketed as a calcium salt of HMB, and thus, environmentally sound and inexpensive methods of manufacture are being sought. This study investigates the microbial conversion of beta-methylbutyric acid (MBA) to HMB by cultures of Galactomyces reessii. Optimal concentrations of MBA were in the range of 5 to 20 g/liter for HMB production. Preliminary shake flask experiments indicated that HMB yields were sensitive to dissolved oxygen levels and that cell growth decreased significantly as MBA concentrations increased. Degradation of HMB was faster at acidic pH, and pH 7.0 was optimal for HMB production. Resting cells obtained from media without MBA could efficiently convert MBA to HMB. Thus, a two-step, fed-batch fermentation procedure in which biomass was first produced, followed by coaddition of MBA and glucose, while dissolved oxygen was maintained at 20% of saturation, was designed. A maximum HMB concentration of 38 g/liter was obtained after 136 h, and the molar conversion yield was more than 0.50 mol of HMB/mol of MBA during the fermentation.

Effect of leucine metabolite beta-hydroxy-beta-methylbutyrate on muscle metabolism during resistance-exercise training

The effects of dietary supplementation with the leucine metabolite beta-hydroxy-beta-methylbutyrate (HMB) were studied in two experiments. In study 1, subjects (n = 41) were randomized among three levels of HMB supplementation (0, 1.5 or 3.0 g HMB/day) and two protein levels (normal, 117 g/day, or high, 175 g/day) and weight lifted for 1.5 h 3 days/wk for 3 wk. In study 2, subjects (n = 28) were fed either 0 or 3.0 g HMB/day and weight lifted for 2-3 h 6 days/wk for 7 wk. In study 1, HMB significantly decreased the exercise-induced rise in muscle proteolysis as measured by urine 3-methylhistidine during the first 2 wk of exercise (linear decrease, P < 0.04). Plasma creatine phosphokinase was also decreased with HMB supplementation (week 3, linear decrease, P < 0.05). Weight lifted was increased by HMB supplementation when compared with the unsupplemented subjects during each week of the study (linear increase, P < 0.02). In study 2, fat-free mass was significantly increased in HMB-supplemented subjects compared with the unsupplemented group at 2 and 4-6 wk of the study (P < 0.05). In conclusion, supplementation with either 1.5 or 3 g HMB/day can partly prevent exercise-induced proteolysis and/or muscle damage and result in larger gains in muscle function associated with resistance training.

The effect of beta-hydroxy-beta-methylbutyrate on growth, mortality, and carcass qualities of broiler chickens

Experiments were conducted to determine whether the leucine catabolite beta-hydroxy-beta-methylbutyrate (HMB) could influence protein metabolism in broilers. In Experiment 1, HMB was fed at either .01 or .05% of the diet. beta-Hydroxy-beta-methylbutyrate did not improve feed conversion or BW gain; however, broilers fed HMB at .01% in a diet formulated to meet NRC (1984) recommendations had no mortality (P < .03) from 0 to 21 d of age. In Experiment 2, HMB fed at .003, .01, .03, and .09% of the diet had no significant affect on growth or carcass yield of the broilers when compared with control-fed broilers. In Experiment 3, HMB fed at .001, .003, and .01% of the diet had no effect on broiler growth. In Experiment 4, HMB was fed at .01% of the diet in combination with an antibiotic and coccidiostat (GP). Use of GP increased (P < .01) BW, feed conversion, and carcass yield when compared with the control broilers. In Experiment 5, HMB was fed at .1% of the diet, and effects of sex and GP were examined. beta-Hydroxy-beta-methylbutyrate decreased (P < .01) mortality by 72% in the male broilers. In a combined analysis, HMB fed at .01% of the diet (Experiments 1, 2, and 3) increased breast yield (P < .05) and reduced mortality by 56% (P < .04) from 0 to 21 d of age. In a combined analysis, HMB fed at .003% of the diet (Experiments 2 and 3) increased 42-d BW (P < .02) and hot (P < .04) and chilled (P < .05) carcass yields. In conclusion, across all HMB dosages mortality of male broilers was decreased from 6.37 to 4.39% (-31%, P < .04) by feeding HMB, with the pattern of death suggesting that HMB decreased the incidence of sudden death syndrome in these broilers.

Oxidation of leucine and alpha-ketoisocaproate to beta-hydroxy-beta-methylbutyrate in vivo

The oxidation of alpha-ketoisocaproate (KIC) to beta-hydroxy-beta-methylbutyrate (HMB) by the enzyme KIC dioxygenase has been previously described in rat and human liver; however, the importance of this pathway in normal leucine metabolism has not yet been assessed. A series of experiments was conducted in young lambs and pigs to determine whether HMB is produced from KIC in vivo and to estimate the importance of this pathway in leucine metabolism. In the first study, lambs were fed a bolus of KIC, and the change in plasma HMB concentration was monitored over a 24-h period. Administration of KIC increased plasma HMB from basal concentrations of 2 to approximately 7 microM 4 h after the supplementation. In the second experiment, lambs were infused with [6,6,6-2H3]KIC into the duodenum, and the appearance of labeled [2H3]HMB was measured. Under basal conditions, a minimum of 18% of the HMB was derived from KIC, but when unlabeled KIC was infused into the duodenum at a rate of 1.6 mumol.kg-1.min-1, plasma HMB concentration doubled, and essentially 100% of the HMB present was derived from KIC. In a third experiment, young pigs were infused with [6,6,6-2H3]leucine. At steady state, [2H3]-leucine and HMB enrichments were nearly identical, indicating that plasma HMB is derived solely from leucine. In a fourth experiment, both lambs and pigs were injected intravenously with 600 mg of HMB daily, and urinary HMB excretion was quantitated.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of beta-hydroxy-beta-methyl butyrate in plasma by gas chromatography and mass spectrometry

A method for measuring the branched chain hydroxy acid beta-hydroxy-beta-methyl butyrate (HMB, a product of leucine catabolism) has been described. A [2H6]HMB internal standard was added to plasma and standards, and samples were extracted with diethyl ether, backextracted into neutral phosphate, dried, and derivatized for gas chromatography and mass spectrometry. The natural HMB was monitored at 175 amu and the deuterated HMB was monitored at 181 amu. Standard curves were linear to at least 25 microns and were quantitatively recovered from plasma. Basal concentrations of plasma HMB were from 1 to 2 microM in sheep and increased three- to fourfold when leucine's alpha-ketoacid (alpha-ketoisocaproate, KIC) was fed to lambs. This method can also be adapted to quantitate KIC and other branched chain ketoacids in plasma during the same run.

Increased urinary excretion of beta-hydroxyisovaleric acid in ketotic and non-ketotic type II diabetes mellitus

To evaluate the catabolism of leucine in diabetes mellitus, the urinary excretion of beta-hydroxyisovaleric acid, a by-product of leucine catabolism, in 21 nonproteinuric type II diabetic patients with and without ketosis and 21 control subjects was measured using gas chromatography-mass spectrometry. Urinary beta-hydroxyisovaleric acid and serum leucine concentrations were higher in the 9 ketotic diabetic patients than in the 12 nonketotic diabetic patients (p less than 0.005, p less than 0.01, respectively) or in the control subjects (p less than 0.01, p less than 0.01, respectively). The serum leucine concentrations in the nonketotic diabetic patients and control subjects did not differ significantly (p greater than 0.05), but urinary beta-hydroxyisovaleric acid concentrations were significantly greater in the former (p less than 0.01). These data suggest that in type II diabetic patients the catabolism of leucine is accelerated even in the absence of ketosis and that the urinary beta-hydroxyisovaleric acid concentration is a useful marker of short-term metabolic control in these patients.

New conjugated urinary metabolites in intermediate type maple syrup urine disease

N-Lactylvaline, N-lactylleucine, N-lactylisoleucine and the N-2-hydroxyisovaleryl conjugates of glycine, valine, leucine and isoleucine have been identified in urine from a patient with the intermediate type of maple syrup urine disease.

Metabolism of leucine in fibroblasts from patients with deficiencies in each of the major catabolic enzymes: branched-chain ketoacid dehydrogenase, isovaleryl-CoA dehydrogenase, 3-methylcrotonyl-CoA carboxylase, 3-methylglutaconyl-CoA hydratase, and 3-hydroxy-3-methylglutaryl-CoA lyase

The metabolism of leucine was studied in cultured human fibroblasts derived from patients with defects in each of the major steps in the catabolism of the amino acid. Intact fibroblasts were incubated with [U-14C]leucine and the organic acid products were isolated by liquid partition chromatography. In control fibroblasts the major product of leucine was 3-hydroxyisovaleric acid. This was also the case for fibroblasts with deficiency of 3-hydroxy-3-methylglutaryl-CoA lyase, 3-methylcrotonyl-CoA carboxylase and 3-methylglutaconyl-CoA hydratase. There was little or no accumulation of the compound with fibroblasts from patients with maple syrup urine disease and isovaleric acidemia.