Melatonin plays a protective role in postburn rodent gut pathophysiology.
Melatonin plays a protective role in postburn rodent gut pathophysiology.
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DOI：
10.7150/ijbs.6.282
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发表时间：
2010-05-17
影响因子：
9.2
通讯作者：
Fazal N
中科院分区：
文献类型：
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作者：
Al-Ghoul WM;Abu-Shaqra S;Park BG;Fazal N
褪黑素可能是烧伤后肠道病理生理动态过程中的一种保护剂。我们在一个具有明确肠道炎症并发症特征的大鼠严重热损伤模型中，研究了内源性产生的褪黑素与外源性给予的褪黑素所起的作用。我们的理论依据是，了解褪黑素在正常和发炎组织中的体内作用机制，将增进我们对其作为一种安全的抗炎/抗氧化治疗替代物潜力的认识。为此，我们验证了这样一个假设：肠道既是褪黑素的来源也是其作用靶点，并且在体表面积30%以上三度热水烫伤的大鼠严重热损伤后，肠系膜褪黑素起到抗炎作用。我们评估肠道作为褪黑素来源的方法包括：通过酶联免疫吸附测定（ELISA）测量全身和肠系膜循环中的血浆褪黑素，以及通过逆转录聚合酶链反应（rtPCR）测量假手术组和烧伤后第3天大鼠空肠和回肠末端褪黑素合成酶芳基烷基胺N - 乙酰转移酶（AA - NAT）和5 - 羟色胺 - O - 甲基转移酶（HIOMT）的表达。我们的褪黑素ELISA结果显示，肠系膜循环中的褪黑素含量远高于全身循环，并且在严重热损伤3天后，肠系膜和全身的褪黑素水平均升高。我们的rtPCR结果与ELISA数据相互补充，表明褪黑素合成酶AA - NAT和HIOMT在回肠和空肠中表达，并且在严重热损伤3天后这种表达增加。有趣的是，rtPCR数据还显示了褪黑素的负反馈作用，因为以7.43毫克（32微摩尔/千克）的剂量补充外源性褪黑素，但以1.86毫克/千克（8微摩尔/千克）的剂量补充时则不会，会显著抑制AA - NAT mRNA的表达。我们的方法还包括利用计算机化免疫组织化学测量来评估肠道作为褪黑素作用靶点的情况，以量化外源性褪黑素补充对烧伤后肠道黏膜屏障炎症特征的影响。在此，我们的结果显示，烧伤后每天以1.86毫克/千克（8微摩尔/千克）的剂量腹腔注射褪黑素，可分别通过Gr - 1和硝基酪氨酸免疫组织化学检测显著抑制中性粒细胞浸润和酪氨酸亚硝基化。总之，我们的结果支持肠系膜褪黑素水平较高以及肠道动态从头合成褪黑素这两种情况，它们在严重热损伤时内源性增加，但似乎不足以消除烧伤后过度的炎症反应。此外，外源性褪黑素补充可显著抑制肠道炎症，从而证实褪黑素对烧伤后炎症具有保护作用。
Melatonin is a possible protective agent in postburn gut pathophysiological dynamics. We investigated the role of endogenously-produced versus exogenously-administered melatonin in a major thermal injury rat model with well-characterized gut inflammatory complications. Our rationale is that understanding in vivo melatonin mechanisms in control and inflamed tissues will improve our understanding of its potential as a safe anti-inflammatory/antioxidant therapeutic alternative. Towards this end, we tested the hypothesis that the gut is both a source and a target for melatonin and that mesenteric melatonin plays an anti-inflammatory role following major thermal injury in rats with 3rd degree hot water scald over 30% TBSA. Our methods for assessing the gut as a source of melatonin included plasma melatonin ELISA measurements in systemic and mesenteric circulation as well as rtPCR measurement of jejunum and terminal ileum expression of the melatonin synthesizing enzymes arylalkylamine N-acetyltransferase (AA-NAT) and 5-hydroxyindole-O-methyltransferase (HIOMT) in sham versus day-3 postburn rats. Our melatonin ELISA results revealed that mesenteric circulation has much higher melatonin than systemic circulation and that both mesenteric and systemic melatonin levels are increased three days following major thermal injury. Our rtPCR results complemented the ELISA data in showing that the melatonin synthesizing enzymes AA-NAT and HIOMT are expressed in the ileum and jejunum and that this expression is increased three days following major thermal injury. Interestingly, the rtPCR data also revealed negative feedback by melatonin as exogenous melatonin supplementation at a dose of 7.43 mg (32 μmole/kg), but not 1.86 mg/kg (8 μmole/kg) drastically suppressed AA-NAT mRNA expression. Our methods also included an assessment of the gut as a target for melatonin utilizing computerized immunohistochemical measurements to quantify the effects of exogenous melatonin supplementation on postburn gut mucosa barrier inflammatory profiles. Here, our results revealed that daily postburn intraperitoneal melatonin administration at a dose of 1.86 mg/kg (8 μmole/kg) significantly suppressed both neutrophil infiltration and tyrosine nitrosylation as revealed by Gr-1 and nitrotyrosine immunohistochemistry, respectively. In conclusion, our results provide support for high mesenteric melatonin levels and dynamic de novo gut melatonin production, both of which increase endogenously in response to major thermal injury, but appear to fall short of abrogating the excessive postburn hyper-inflammation. Moreover, supplementation by exogenous melatonin significantly suppresses gut inflammation, thus confirming that melatonin is protective against postburn inflammation.