• Journal of Microbiology and Biotechnology
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• v.29 no.9
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• pp.1470-1477
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• 2019

${\beta}_2$-adrenergic receptor (${\beta}_2-AR$) was expressed efficiently using Bac-to-Bac Baculovirus Expression System in Sf9 cells as a bio-recognition element for multianalyte screening of ${\beta}$-agonist residues in pork. Sf9 cells were selected as the expression system, and codon optimization of wild-type nucleic acid sequence and time-dependent screening of expression conditions were then carried out for enhancing expression level and biological activity. Under optimum conditions of multiplicity of infection (MOI) = 5 and 48 h post transfection, the protein yield was up to 1.23 mg/ml. After purification by chromatographic techniques, the purified recombinant protein was applied to develop a direct competitive enzyme-linked receptor assay (ELRA) and the efficiency and reliability of the assay was determined. The IC50 values of clenbuterol, salbutamol, and ractopamine were 28.36, 50.70, and $59.57{\mu}g/l$, and clenbuterol showed 47.61% and 55.94% cross-reactivities with ractopamine and salbutamol, respectively. The limit of detection (LOD) was $3.2{\mu}g/l$ and the relevant recoveries in pork samples were in the range of 73.0-91.2%, 69.4-84.6%, and 63.7-80.2%, respectively. The results showed that it had better performance compared with other present nonradioactive receptorbased assays, indicating that the genetically modified ${\beta}_2-AR$ would have great application potential in detection of ${\beta}$-agonist residues.

• Asian-Australasian Journal of Animal Sciences
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• v.11 no.5
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• pp.566-572
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• 1998

The present study examined the effects of excessive dietary protein and energy on growth response to clenbuterol in broilers. The chicks were allocated into 6 groups at 14d old, and used for a $3{\times}2$ factorial experiment. Birds were fed six diets, the control diet containing 21% crude protein (CP) and 3,100 kcal of metabolizable energy ME/kg, a high protein (30% CP) or a high energy (3,500 kcal/ ME/kg) diet, with or without 1 ppm clenbuterol, for 18 d. Clenbuterol feeding markedly decreased (p < 0.05) body weight gain by 23% in the high energy group. Feed intake was also decreased (p < 0.05) by clenbuterol administration across diet treatments. Abdominal fat weight was reduced (p < 0.05) by clenbuterol only when chickens were fed the high energy diet. Clenbuterol increased (p < 0.05) leg muscle weight in the control diet group, but decreased (p < 0.05) it in the high energy group. Muscle protein concentration was increased by 11 % in leg muscle only of the birds at the high energy level. In leg muscle, clenbuterol enhanced the protein/DNA ratio by 18%, except for the high protein group. These results indicate that feeding a diet containing excessive amounts of protein and more energy than normal did not necessarily improve growth response to clenbuterol.

• BMB Reports
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• v.40 no.4
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• pp.525-531
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• 2007

As a $\beta_2$-adrenergic agonist, clenbuterol decreases body fat, but the molecular mechanism underlying this process is unclear. In the present study, we treated 293T and L-02 cells with clenbuterol and found that clenbuterol downregulates SREBP-1c expression and upregulates CREB1 expression. Considering SREBP-1c has the function of regulating the transcription of several lipogenic enzymes, we considered that the downregulation of SREBP-1c is responsible for body fat reduction by clenbuterol. Many previous studies have found that clenbuterol markedly increases intracellular cAMP levels, therefore, we also investigated whether CREB1 is involved in this process. The data from our experiments indicate that CREB1 overexpression inhibits SREBP-1c transcription, and that this action is antagonized by CREB2, a competitive inhibitor of CREB1. Furthermore, since PPARs are able to repress SREBP-1c transcription, we investigated whether clenbuterol and CREB1 function via a pathway involving PPAR activation. However, our results showed that clenbuterol or CREB1 overexpression suppressed PPARs transcription in 293T and L-02 cells, which suggested that they impair SREBP-1c expression in other ways.

• Asian-Australasian Journal of Animal Sciences
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• v.12 no.5
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• pp.788-793
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• 1999

To determine the interrelationship between thyroid status and the reparitioning action of clenbuterol (CLE) in broilers, two-week-old female chickens were fed diets containing an antithyroid substance, propylthiouracil (PTU, 0 or 0.3%), CLE (0 to 1 mg/kg), or both for 18 days in a $2{\times}2$ factorial design experiment. Muscle weights (breast muscle, gastrocnemius and peroneus longus) increased only in the normal chickens fed CLE. As absolute mass, protein of leg muscle quantitatively increased in the CLE-fed normal birds. In contrast, inhibition of the CLE-induced protein accretion, especially of peroneus longus, occurred in the PTU group. A quantitative increase in DNA was observed in leg muscles of the normal chickens, but no DNA response to CLE was shown in the PTU-treated chickens. The decreased RNA in leg muscles of the PTU group was more reduced by CLE feeding. Although not statistically significant, the reduced degradation rate of whole muscle protein in normal chickens fed CLE was not confirmed in the PTU-fed group. The present study, therefore, concluded that metabolic action of thyroid hormones was a prerequisite for the hypertrophic effect of ${\beta}$-agonist in broilers.

• Asian-Australasian Journal of Animal Sciences
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• v.16 no.6
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• pp.903-909
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• 2003

For the last two decades, energy utilization of growing chicks has been studied more and more. This paper focuses on the energy utilization estimated by the metabolizable energy (ME) values and the efficiency at which ME is used for growth of chicks under various nutritional environment. Degree of saturation of dietary fats is responsible for nitrogen-corrected apparent metabolizable energy (AMEn) of fats. The effect of dietary fat sources on heat production depends on the kind of unsaturated fatty acids as well as the degree of saturation. Medium chain triglyceride shows lower AME and net energy than long chain triglyceride. Phytase as feed additives increases the AME values of the diet along with improvement of the phosphorous utilization. Ostriches have higher ability to metabolize the energy of fiber-rich foodstuffs than fowls. Their higher ability seems to be associated with fermentation of fiber in the hindgut. Proportions of macronutrients in the diets have influenced not only the gain of body protein and energy but also the oxidative phosphorylation of the chicken liver. Essential amino acids deficiency reduces ME/GE (energy metabolizability) little, if any. Growing chicks respond to a deficiency of single essential amino acids with the reduction of energy retained as protein and increased energy retained as fat. Thus, energy retention is proportional to ME intake despite deficiency, and efficiency of ME utilization is not affected by deficiency of amino acids. Effect of oral administration of clenbuterol, a beta-adrenergic agonist, on the utilization of ME varies with the dose of the agents. Although the heat production related to eating behavior has been estimated less than 5% of ME, tube-feeding diets decreases HI by about 30%.