Background Methylene blue (MB) is used endoscopically to demarcate tumors and as a photosensitizer in photodynamic therapy (PDT). However, there are few in vivo studies about its toxicity in healthy stomach tissue. We performed sequential in vitro and in vivo analyses of MB-induced phototoxicity. Methods We performed in vitro experiments using the AGS human gastric cancer cell line treated with light-emitting diode (LED) irradiation (3.6 J/cm2) and MB. Cytotoxicity was evaluated using terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) assay. In vivo toxicity was evaluated in the stomach of beagles using the same dose of fiber-optic LED via gastroscopy, after spraying 0.1% and 0.5% MB solutions. Stomach tissue was also evaluated using the TUNEL assay. Results In vitro, increased concentrations of MB led to higher TUNEL scores. However, cell viability was significantly lower after MB plus LED irradiation than after treatment with MB alone (P < 0.001). In vivo, the TUNEL score was highest immediately after treatment with 0.1% or 0.5% MB plus light irradiation, and the score was significantly higher in the LED illumination plus MB group than in the control group (P < 0.05). The elevated TUNEL score was maintained for 3 days in the MB plus light irradiation group but returned to normal levels on day 10. Conclusions : Endoscopic light application with MB 0.5% concentration to the stomach may be regarded as a safe procedure despite some DNA injuries in the early period.

中文翻译：

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亚甲蓝诱导的胃粘膜体外和体内光毒性。

背景 亚甲蓝 (MB) 在内窥镜下用于划定肿瘤并用作光动力疗法 (PDT) 中的光敏剂。然而，关于其对健康胃组织的毒性的体内研究很少。我们对 MB 诱导的光毒性进行了连续的体外和体内分析。方法 我们使用经发光二极管 (LED) 照射 (3.6 J/cm2) 和 MB 处理的 AGS 人胃癌细胞系进行体外实验。使用末端脱氧核苷酸转移酶 dUTP 缺口末端标记 (TUNEL) 测定评估细胞毒性。在喷洒 0.1% 和 0.5% MB 溶液后，通过胃镜检查使用相同剂量的光纤 LED 在比格犬的胃中评估体内毒性。还使用 TUNEL 测定评估了胃组织。结果 在体外，增加的 MB 浓度导致更高的 TUNEL 分数。然而，与单独使用 MB 处理后相比，MB 加 LED 照射后的细胞活力显着降低 (P < 0.001)。在体内，TUNEL 评分在 0.1% 或 0.5% MB 加光照处理后即刻最高，且 LED 照明加 MB 组的评分显着高于对照组（P < 0.05）。升高的 TUNEL 评分在 MB 加光照射组中维持了 3 天，但在第 10 天恢复到正常水平。结论：尽管 DNA 损伤在胃中，但内窥镜光照射 0.5% 浓度的 MB 可能被认为是一种安全的手术早期。1%或0.5%MB加光照，LED光照加MB组评分显着高于对照组（P < 0.05）。升高的 TUNEL 评分在 MB 加光照射组中维持了 3 天，但在第 10 天恢复到正常水平。结论：尽管 DNA 损伤在胃中，但内窥镜光照射 0.5% 浓度的 MB 可能被认为是一种安全的手术早期。1%或0.5%MB加光照，LED光照加MB组评分显着高于对照组（P < 0.05）。升高的 TUNEL 评分在 MB 加光照射组中维持了 3 天，但在第 10 天恢复到正常水平。结论：尽管 DNA 损伤在胃中，但内窥镜光照射 0.5% 浓度的 MB 可能被认为是一种安全的手术早期。