Xian C J, Shoubridge C A, Read L C
Cooperative Research Centre for Tissue Growth and Repair, Women's and Children's Hospital, North Adelaide, Australia.
J Endocrinol. 1995 Aug;146(2):215-25. doi: 10.1677/joe.0.1460215.
To investigate the potential of IGF-I peptides as therapeutics in the gut, the survival profiles of a bolus of 125I-labelled IGF-I (8.6 ng) in vivo in various ligated gut segments of fasted adult rats have been examined. The intactness of IGF-I tracer in the flushed luminal contents was estimated by trichloroacetic acid precipitation, antibody and receptor binding assays. It was found that IGF-I was degraded very rapidly in duodenum and ileum segments with a half-life (t1/2) of 2 min by all three methods. IGF-I was slightly more stable in the stomach (t1/2 = 8, 5 and 2.5 min by the above three methods), and considerably more stable in the colon (t1/2 = 38, 33 and 16 min as judged by the three methods). Rates of degradation in gut flushings in vitro were similar to the in vivo rates except for the colon, where IGF-I was proteolysed more rapidly in vivo. As a means of developing gut-stable and active forms of IGF-I, several approaches were examined for their effectiveness in prolonging IGF-I survival in the upper gut. It was found that the extension peptide on the analogue, LR3IGF-I did not protect IGF-I, nor did association with IGF-binding protein-3. However, an IGF-I antiserum was effective in prolonging IGF-I half-life in duodenum fluid by 28-fold. Charge interaction between IGF-I and heparin could also protect IGF-I in the stomach but not in duodenum flushings. Furthermore, casein (a non-specific dietary protein) and to a lesser extent, BSA and lactoferrin, were effective in preserving IGF-I structural integrity and receptor binding activity in both stomach and duodenum fluids. It can be concluded that IGF-I cannot be expected to retain bioactivity if delivered orally because of rapid proteolysis in the upper gut, but the use of IGF antibodies and casein could represent useful approaches for IGF-I protection in oral formulae.
为了研究胰岛素样生长因子-I（IGF-I）肽作为肠道治疗药物的潜力，我们检测了禁食成年大鼠不同结扎肠段内125I标记的IGF-I（8.6 ng）团注物的体内存活情况。通过三氯乙酸沉淀、抗体和受体结合试验评估冲洗后的肠腔内容物中IGF-I示踪剂的完整性。结果发现，在十二指肠和回肠段，IGF-I通过这三种方法测得的半衰期（t1/2）均为2分钟，降解非常迅速。IGF-I在胃中稳定性稍高（上述三种方法测得的t1/2分别为8、5和2.5分钟），而在结肠中稳定性更高（三种方法判断t1/2分别为38、33和16分钟）。除结肠外，体外肠冲洗液中的降解速率与体内速率相似，在结肠中IGF-I在体内的蛋白水解速度更快。作为开发肠道稳定且有活性的IGF-I形式的一种手段，我们研究了几种方法延长IGF-I在上消化道中存活时间的有效性。结果发现，类似物LR3IGF-I上的延伸肽不能保护IGF-I，与IGF结合蛋白-3结合也无此作用。然而，一种IGF-I抗血清可有效将十二指肠液中IGF-I的半衰期延长28倍。IGF-I与肝素之间的电荷相互作用也可在胃中保护IGF-I，但在十二指肠冲洗液中无此作用。此外，酪蛋白（一种非特异性膳食蛋白）以及程度稍轻的牛血清白蛋白和乳铁蛋白，可有效保持胃和十二指肠液中IGF-I的结构完整性和受体结合活性。可以得出结论，由于在上消化道中迅速被蛋白水解，口服IGF-I无法预期保留生物活性，但使用IGF抗体和酪蛋白可能是在口服制剂中保护IGF-I的有用方法。
