Alteration of collagen synthesis and cross-link profile by beta-adrenergic agonists

在人类医学中，广泛使用β-肾上腺素能激动剂（β-AA）（例如克伦特罗）作为支气管扩张剂来控制哮喘和慢性肺阻塞性疾病的症状。长期（大于或等于一天）使用与肌肉细胞中胶原蛋白积累增加有关，并可能导致心脏和骨骼肌组织疾病。这不仅是人类医学关注的问题，也是动物农业关注的问题，因为 β-AA 盐酸莱克多巴胺 (RAC) 和盐酸齐帕特罗 (ZIL) 已被批准在加拿大用作生长促进剂和重新分配剂，以提高牛的瘦肉产量和饲料效率。 RAC 和 ZIL 有可能影响肌内胶原蛋白，这表明它们也可能影响肉食质量，因为胶原蛋白的数量及其成熟、热稳定的交联的密度与韧性的增加有关。申请人最近的研究表明，在牛日粮中添加RAC不会增加牛肌肉中的总胶原蛋白，但确实降低了摩尔上热稳定胶原蛋白交联吡啶啉(PYR)的密度(0.23和0.17摩尔PYR/摩尔胶原蛋白，对照与RAC，P<0.001)和每克生肌肉(2.86与2.60nmol PYR/g生肌肉，对照)与 RAC 相比，P < 0.05）。申请人和她的团队的进一步研究表明，给肉牛植入雌激素-孕激素生长促进剂（HGP）也没有改变臀中肌（GM，上牛腰肉）中的总胶原蛋白浓度，但确实增加了臼齿上另一种成熟胶原蛋白交联艾氏色原（EC）的浓度（0.38至0.43 mol EC/mol胶原蛋白，对照与治疗组，P < 0.05）和每克原始肌肉基础（4.34 至 4.78 nmol/g 原始肌肉，对照与治疗组，P < 0.05）。此外，随着 HGP 的使用，PYR 的浓度有从 0.18（对照）增加到 0.21 mol PYR/mol 胶原蛋白的趋势（P < 0.1）。这些结果表明，胶原蛋白对熟牛肉韧性的贡献可能会随着β-AA的施用而降低，但随着类固醇生长促进剂的使用而增加。肉牛行业广泛使用市售生长促进物质，尽管它们对体重增加、饲料效率和胴体成分的影响众所周知，但它们对肌内胶原蛋白的影响却鲜为人知。这些结果首次表明，β-AA 和 HGP 的施用可以影响肌内成熟胶原蛋白交联的密度，并改变胶原蛋白对熟牛肉韧性的贡献。 HGP 和 ß-AA 在骨骼肌胶原蛋白中产生不同的结构修饰，表明响应这些生长促进剂的胶原蛋白合成和周转机制明显不同；因此，拟议研究的短期目标是阐明 ß-AA 和 HGP 影响胶原蛋白交联的生化途径。这些目标是长期研究计划的下一个逻辑步骤，该计划致力于研究控制胶原蛋白合成和交联的机制及其对肉品质的影响。这项研究对于系统地全面了解胶原蛋白合成的控制机制至关重要，不仅在动物生产方面具有广泛的应用，而且在人类损伤或疾病治疗过程中预防组织纤维化方面也具有广泛的应用，并将有助于培训六名高素质人才。

The use of beta-adrenergic agonists (ß-AA) such as clenbuterol as bronchial dilators in human medicine to control the symptoms of asthma and chronic pulmonary obstructive disease is widespread. Long-term (greater than or equal to one day) use is associated with increased accumulation of collagen in muscle cells, and can lead to both cardiac and skeletal muscle tissue diseases. This is a concern not only to human medicine but to animal agriculture as well because the ß-AA ractopamine hydrochloride (RAC) and zilpaterol hydrochloride (ZIL) are approved for use in Canada as growth promotants and re-partitioning agents to increase lean meat yield and feed efficiency in cattle. That RAC and ZIL have the potential to affect intramuscular collagen suggests that they may also affect meat eating quality because the quantity of collagen and the density of its mature, heat-stable crosslinks have been linked to increased toughness. Recent research by the applicant indicated that supplementation of cattle diets with RAC did not increase the total collagen in the muscles of cattle, but did decrease the density of the heat-stable collagen crosslink pyridinoline (PYR) on a molar (0.23 and 0.17 mole PYR/mole collagen, control versus RAC, P < 0.001) and per gram raw muscle (2.86 versus 2.60 nmol PYR/g raw muscle, control versus RAC, P < 0.05) basis. Further research by the applicant and her team showed that the implantation of beef cattle with estrogen-progesterone hormone growth promotants (HGP) also did not change total collagen concentration in the gluteus medius muscle (GM, top sirloin), but it did increase the concentration of another mature collagen crosslink Ehrlich's Chromogen (EC) on a molar (0.38 to 0.43 mol EC/mol collagen, control versus treated, P < 0.05) and per gram raw muscle basis (4.34 to 4.78 nmol/g raw muscle, control versus treated, P < 0.05). Additionally, there was a trend for the concentration of PYR to increase with HGP use from 0.18 (control) to 0.21 mol PYR/mol collagen (P < 0.1). These results suggested that the contribution of collagen to cooked beef toughness may decrease with ß-AA administration but increase with the use of steroidal growth promotants. The use of commercially available growth promoting substances in the beef industry is widespread and although their effects on body weight gain, feed efficiency and carcass composition are well known, their impact on intramuscular collagen is not. These results are the first to indicate that administration of ß-AA and HGP can affect the density of intramuscular mature collagen crosslinks and change the contribution of collagen to cooked beef toughness. That HGP and ß-AA produced different structural modifications in skeletal muscle collagen indicated that the mechanisms of collagen synthesis and turnover in response to these growth promotants were markedly different; consequently, the short term objectives of the proposed research are to elucidate the biochemical pathways by which ß-AA and HGP affect collagen crosslinking. These objectives are the next logical steps in a long term research program devoted to investigating the mechanisms controlling the synthesis and crosslinking of collagen and its impact on meat quality. This research is fundamental to fully understand the control mechanisms of collagen synthesis systemically and will have broad applications not only for animal production but for the prevention of tissue fibrosis during the treatment of human injury or disease and will contribute to the training of six highly qualified personnel.