Bolaffi J L, Nagamatsu S, Harris J, Grodsky G M
Endocrinology. 1987 May;120(5):2117-22. doi: 10.1210/endo-120-5-2117.
It has been suggested that a result of streptozotocin (Sz)-initiated damage to beta-cell DNA is activation of the repair enzyme nuclear poly-ADP-ribose (p-ADPR) synthetase and subsequent depletion of cellular NAD. This reduction of NAD is presumed responsible for the impaired islet function. Using freshly isolated rat pancreatic islets, we have examined the ability of p-ADPR synthetase inhibitors, in particular the previously not studied thymidine, to block Sz-induced damage to the B cell. Islets were incubated in 2 mM glucose and 2 mM Sz with or without p-ADPR synthetase inhibitor and then challenged for 1 h with 25 mM glucose plus 25 microM forskolin or 100 nM phorbol ester without glucose. Sz treatment inhibited insulin secretion about 90% even when stimulated by the non-glucose-containing challenge, indicating that Sz caused a rapid and generalized lesion past glucose-specific signals. Thymidine maintained the insulin secretory response to glucose plus forskolin from Sz-treated islets as, or more, effectively than nicotinamide. In a dose-dependent manner, thymidine protected Sz-treated islets to 87% of normal islet secretion at the highest thymidine dose (20 mM). However, even protected islets could not sustain normal secretion; insulin secretion was significantly diminished in thymidine-protected islets challenged with a second consecutive 1-h glucose plus forskolin stimulus. As expected, the acute depletion of islet NAD content (approximately 50%, 1 h after Sz) was reversed to 90% of normal by thymidine. However, even in unprotected Sz-treated islets, NAD content gradually recovered over 48 h of culture in standard RPMI, although insulin secretion remained suppressed. Thus, thymidine may be a useful protective agent against chemically induced islet cell damage. Furthermore, a sustained suppression of NAD content does not explain Sz's permanent inhibition of islet secretory response. Other aspects of inhibited nuclear p-ADP-ribosylation are considered to explain protection against Sz damage to the beta-cell.
有人提出，链脲佐菌素（Sz）引发的β细胞DNA损伤的一个结果是修复酶核多聚ADP - 核糖（p - ADPR）合成酶的激活以及随后细胞内NAD的消耗。NAD的这种减少被认为是胰岛功能受损的原因。我们使用新鲜分离的大鼠胰岛，研究了p - ADPR合成酶抑制剂，特别是之前未研究过的胸腺嘧啶核苷，阻断Sz诱导的B细胞损伤的能力。胰岛在含2 mM葡萄糖和2 mM Sz的培养基中培养，添加或不添加p - ADPR合成酶抑制剂，然后用25 mM葡萄糖加25 μM福斯高林或不含葡萄糖的100 nM佛波酯刺激1小时。即使在不含葡萄糖的刺激下，Sz处理也会抑制胰岛素分泌约90%，这表明Sz导致了一种超越葡萄糖特异性信号的快速且普遍的损伤。胸腺嘧啶核苷维持了经Sz处理的胰岛对葡萄糖加福斯高林的胰岛素分泌反应，其效果与烟酰胺相同或更有效。胸腺嘧啶核苷以剂量依赖的方式保护经Sz处理的胰岛，在最高胸腺嘧啶核苷剂量（20 mM）时，胰岛素分泌达到正常胰岛分泌的87%。然而，即使受到保护的胰岛也无法维持正常分泌；在用连续第二个1小时的葡萄糖加福斯高林刺激的胸腺嘧啶核苷保护的胰岛中，胰岛素分泌显著减少。正如预期的那样，胸腺嘧啶核苷将胰岛NAD含量的急性消耗（Sz处理后1小时约50%）逆转至正常水平的90%。然而，即使在未受保护的经Sz处理的胰岛中，在标准RPMI培养基中培养48小时后，NAD含量也会逐渐恢复，尽管胰岛素分泌仍受到抑制。因此，胸腺嘧啶核苷可能是一种针对化学诱导的胰岛细胞损伤的有用保护剂。此外，NAD含量的持续抑制并不能解释Sz对胰岛分泌反应的永久性抑制。核p - ADP - 核糖基化受抑制的其他方面被认为可以解释对Sz对β细胞损伤的保护作用。
