Dietary supplementation of ß-hydroxy-ß-methylbutyrate in animals - a review.

The leucine metabolite ß-hydroxy-ß-methylbutyrate (HMB) has been studied by many researchers over the last two decades. In particular, the utility of HMB supplementation in animals has been shown in numerous studies, which have demonstrated enhanced body weight gain and carcass yield in slaughter animals; positive immunostimulatory effect; decreased mortality; attenuation of sarcopenia in elderly animals; and potential use in pathological conditions such as glucocorticoid-induced muscle loss. The aim of this study was to summarize the body of research on HMB supplementation in animals and to examine possible mechanisms of HMB action. Furthermore, while the safety of HMB supplementation in animals is well documented, studies demonstrating efficacy are less clear. The possible reasons for differences in these findings will also be examined.

A clinical informaticist to support primary care decision making.

OBJECTIVES: To develop and evaluate an information service in which a "clinical informaticist" (a GP with training in evidence-based medicine) provided evidence-based answers to questions posed by GPs and nurse practitioners. DESIGN: Descriptive pilot study with systematic recording of the process involved in searching for and critically appraising literature. Evaluation by questionnaire and semi-structured interview. SETTING: General practice. PARTICIPANTS: 34 clinicians from two London primary care groups (Fulham and Hammersmith). MAIN OUTCOME MEASURES: Number and origin of questions; process and time involved in producing summaries; satisfaction with the service. RESULTS: All 100 clinicians in two primary care groups were approached. Thirty four agreed to participate, of whom 22 asked 60 questions over 10 months. Participants were highly satisfied with the summaries they received. For one third of questions the clinicians stated they would change practice in the index patient, and for 55% the participants stated they would change practice in other patients. Answering questions thoroughly was time consuming (median 130 minutes). The median turnaround time was 9 days; 82% of questions were answered within the timeframe specified by the questioner. Without the informaticist, one third of questions would not have been pursued. CONCLUSION: The clinical informaticist service increased access to evidence for busy clinicians. Satisfaction was high among users and clinicians stated that changes in practice would occur. However, uptake of the service was lower than expected (22% of those offered the service). Further research is needed into how this method of increasing access to evidence compares with other strategies, and whether it results in improved health outcomes for patients.

Influence of HMB (beta-hydroxy-beta-methylbutyrate) on antibody secreting cells (ASC) after in vitro and in vivo immunization with the anti-Yersinia ruckeri vaccine of rainbow trout (Oncorhynchus mykiss).

In practice, protection of fish against disease by immunization is of limited effectiveness. Therefore, research is concentrated on how to improve the potency and efficacy of vaccines and how to optimally activate the cell-mediated immunity and the specific antibody response. In the present study, the influence of HMB (beta-Hydroxy-beta-methylbutyrate) on the antibody secreting cells (ASC) after both in vitro and in vivo immunization of rainbow trout (Oncorhynchus mykiss) with the anti-yersiniosis vaccine was studied. For in vitro immunization, the spleens from 160 fish were sampled and placed each in 35 mm sterile wells with medium containing HMB at concentrations of 0, 0.1, 1, 5, 10, 25, 50 or 100 microg/mL of medium. The spleens from 80 fish were injected with the vaccine and incubated at 14 degrees C for 10 days. For the in vivo study, fish were fed pellets containing HMB at doses of 0, 10, 25 and 50 mg/kg bw per day. After 2 weeks of HMB supplementation, the fish were immunized by intraperitoneal injection of the vaccine. At 7, 14, 18, 21, 28 and 35 days after immunization, pronephros were taken from 10 fish in each group for testing. When analyzed by the ELISPOT assay, HMB increased the number of splenic ASC after in vitro immunization at concentrations between 10 and 100 microg/mL (P < 0.05). Dietary HMB also increased the number of total and specific ASC when the fish were vaccinated in vivo. In conclusion, the results of the present study showed that HMB increases the levels of specific ASC after both in vitro and in vivo immunization of rainbow trout with the anti-Yersinia ruckeri vaccine.

In vitro effects of beta-hydroxy-beta-methylbutyrate (HMB) on cell-mediated immunity in fish.

beta-Hydroxy-beta-methyl butyrate(HMB) has been shown to counteract many of the negative effects of intensive animal production methods and results in increased growth and protection against diseases. In the present study, the effect of HMB on the immunocompetence cell activity in rainbow trout (Oncorhynchus mykiss) and carp (Cyprinus carpio) was examined. Pronephric phagocytes and lymphocytes were isolated from the fish and grown in culture medium (RPMI-1640) containing either 0, 0.1, 1, 5, 10, 25, 50 or 100 microg HMB/ml of medium. The effects of HMB on the respiratory burst activity (RBA) stimulated by phorbol myristate acetate (PMA), the potential killing activity (PKA) and lymphocyte proliferation stimulated by either concanavalin A (Con-A) or lipopolysaccharide (LPS) were examined. The addition of HMB to the culture medium increased the RBA by up to 84% (p<0.01) over that of cells grown without HMB. Similarly, the PKA of the phagocytes was also increased with HMB addition to the medium by up to 140% (p<0.01) over that of cells grown without HMB. Lymphocyte proliferation stimulated by both ConA and LPS was also increased approximately two-fold (p<0.01) when HMB was added to the culture medium at concentrations between 10 and 100 microg HMB/ml in both rainbow trout and carp. The greatest effects of HMB on RBA and PKA activities were observed at a concentration >50 microg HMB/ml while lymphocyte proliferation was maximally stimulated at 25 microg HMB/ml. In conclusion, the current study shows that HMB could potentially improve immunocompetence cell activity in fish through increased cell proliferation and functionality.

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.

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.

Use of 18O-labelled leucine and phenylalanine to measure protein turnover in muscle cell cultures and possible futile cycling during aminoacylation.

Amino acids labelled with 18(O) on both carboxy oxygen atoms have the potential for use as non-recyclable tracers to measure protein turnover. During protein synthesis one of the labelled oxygen atoms is removed, and thus release of the mono-labelled amino acid could be used to determine proteolysis. Primary cultures of embryonic-chick skeletal-muscle cells were used to test the use of 18(O2)-labelled Leu to measure proteolysis. For 9-day cultures, prelabelled on days 2-8 with medium containing one-half the Leu as [18O2]Leu and one-half as [2H3]Leu, release of [18(O)]Leu was less than 50% that of [2H]Leu over 24 h, suggesting a loss of the 18O label by a mechanism other than protein synthesis. Medium containing [18(O2)]Leu, [2H3]Leu, [18O2]Phe and [13C]Phe was then incubated with 9-day cultures to compare the rate of loss of the 18(O)-label from Leu and Phe with the rate of uptake of the non-carboxy-oxygen-labelled amino acids. Results for Leu demonstrated an 81% loss of the 18(O) label compared with a 33% decrease in [2H]Leu over 12 h. Loss of the 18(O) label was four times as great for Leu as for Phe. Loss of the 18(O) label was not decreased by addition of cycloheximide or by addition of a 3-fold excess of Ile, Val and Tyr; thus the loss of label was not due to protein synthesis alone or to misbinding to incorrect tRNAs. Infusion of the isotopes into pigs showed that the 18(O) label of Leu was not lost during transamination to alpha-ketoisocaproate (alpha-oxoisohexanoate). The most probable explanation is that the 18(O) label is lost as a result of the enzymic deacylation of tRNA, that this process is substantially faster for Leu than for Phe, and that this represents a potentially costly futile cycle for Leu.