| 摘要: | 牙周病是最常見的慢性發炎性疾病 (chronic inflammatory diseases) 之一。牙周病菌以及其內毒素 (主要成份為脂多糖 (lipopolysaccharide, LPS) 可經由牙周囊袋之潰瘍進入體循環，並釋放促炎性細胞激素 (pro-inflammatory cytokines)，如介白素 (IL-1β, IL-6) 和腫瘤壞死因子 (TNF-α) 等，導致局部性和全身多數器官的發炎反應。牙周病所引致的系統性發炎反應 (systemic inflammation) 已被證實與心臟疾病 (cardiac diseases)、糖尿病 (diabetes)、腎臟疾病 (renal diseases)、新生兒體重過低 (low birth weight) 與阿茲海默症 (Alzheimer’s disease) 等之病理衍生過程有密切關連。帕金森氏症 (Parkinson’s disease) 為一慢性退化性疾病，位於黑質 (substantia nigra) 的多巴胺神經元 (dopaminergic neurons) 長期發炎為導致該症的重要原因之一。先前的研究已證實，於腦室內注射脂多糖可巨幅活化微膠細胞 (microglial activation)，大量提升促炎性細胞激素的濃度，並誘使黑質多巴胺神經元出現神經退化等病徵。藥理學的研究亦報導，長期服用抗發炎藥物可有效降低帕金森氏症之發病率，進一步證明慢性發炎反應為帕金森氏症之潛在導因。然而，縱使發炎反應在牙周病與帕金森氏症之病理衍生過程中，皆扮演相當重要的角色，然截至目前為止，由牙周病所引致之系統性發炎反應是否與帕金森氏症之誘發間具有潛在關聯，迄今仍無任何研究加以探討。另一方面，施加具有抗發炎能力與神經保護功效之褪黑激素 (melatonin)，是否可有效改善牙周病引致之系統性發炎與神經功能缺失，亦亟待進一步研究加以闡明。緣此，本研究之目的乃在積極探討：
(1) 利用牙周病動物模式之建立與分析，釐清牙周病是否與帕金森氏症之病理衍生過程具有潛在關聯。研究利用直接於牙周纏線或牙髓腔給予牙周菌等動物模式，探討牙周病與帕金森氏症病理衍生之潛在關連。
(2) 藉由褪黑激素的施加，深度評估褪黑激素是否可有效抑低牙周病所導致的系統性與神經性發炎、保護神經細胞，並具有改善臨床病徵之神經保護功效。
本實驗證實利用牙周纏線確實可有效誘發牙周病，導致促炎性細胞激素 (IL-1-β, IL-6) 濃度巨幅上升與全身性發炎反應。研究進一步審視牙周病動物大腦區域後發現，其黑質區域出現活化的星狀膠細胞與微膠細胞，多巴胺神經元死亡與 型突觸核蛋白 (-synuclein) 大量聚積等帕金森氏症之病理表徵。除此之外，牙周病菌亦會大量堆積在皮質與中腦，並抑低海馬回環磷腺苷反應元件結合蛋白 (CREB) 的磷酸化表現，此一抑低現象極有可能為帕金森氏症認知功能缺失之潛在導因。透過物體辨識、焦慮與抑鬱等行為測試的結果也顯示，牙周病確實會對認知功能造成破壞性影響，其中抑鬱行為最為嚴重。利用穿透式電子顯微鏡 (transmission electron microscope) 的觀察亦發現，牙周病動物之血腦障蔽 (blood-brain barrier)結構亦明顯受損。綜合上述生化學、免疫組織化學、行為學與超微結構等結果分析，本研究已清楚闡明牙周病與帕金森氏症的誘發之間，具有極為密切的因果關連。
根據上述成果，研究進一步利用此動物模型探討褪黑激素是否能有效治療牙周病，並抑制牙周病所引發之神經性發炎反應，進而達到神經保護功效。實驗結果顯示，牙周病動物給予褪黑激素治療後，其牙周病病徵明顯改善，其系統性發炎因子濃度與調控發炎相關之分子訊息傳遞路徑活性也顯著下降。研究觀察其大腦區域後發現，接受褪黑激素治療後，黑質區域之微膠細胞活化明顯降低，多巴胺神經元與海馬回相關蛋白之表現量漸趨正常，認知功能也顯著獲得改善。綜合上述成果，本研究進一步證明施加褪黑激素不僅可有效改善牙周病，更可保護神經功能，防止因牙周病引致帕金森氏症之神經功能受損。
藉由本研究的進行，已詳實提供牙周病引致帕金森氏症之功能解剖學證據，其所得結果除對社會上宣導口腔衛生的重要性外，尚對臨床上使用褪黑激素用以治療牙周病或其引致帕金森氏症之神經功能缺失，有顯著之參考價值與貢獻。
Periodontitis is one of the most prevalent chronic inflammatory diseases, which affects the supporting tissues of the teeth. Numerous periodontal pathogens and their endotoxin (mainly lipopolysaccharide, LPS) may enter the systemic circulation through the oral ulcerations in periodontal pocket, and exacerbate the production of pro-inflammatory cytokines (such as IL-1β, IL-6, and TNF-α) that causes systemic inflammation not only to local tissue but also to a variety of visceral organs. This increased inflammatory burden would form the basis for the proposed link between periodontitis and various systemic diseases such as cardiac diseases, diabetes, renal diseases, low birth weight as well as Alzheimer disease.
Parkinson’s disease is a chronic progressive neurodegenerative disorder in which persisted inflammatory reaction in dopaminergic neurons of the substantia nigra (SN) may contribute to the aetiology and pathogenesis of this disease. Previous studies have indicated that intra-ventricular injection of LPS could induce strong microglial activation and increase the pro-inflammatory cytokine levels, which could selectively lead to the neurodegeneration of dopaminergic neurons. Pharmacological results also demonstrated that subjects on regular anti-inflammatory drugs have a reduced risk of Parkinson’s disease, which further highlights the importance of inflammatory reaction in initiation and progression of this disorder. However, although chronic inflammation is consistently associated with the pathophysiology of Parkinson’s disease, so far, there is no direct evidence implicating the potential effect of periodontitis in the induction or development of Parkinson’s disease.
Therefore, the aim of the present research is to
(1) Clarify the potential impact of periodontitis on the induction or development of Parkinson’s disease through in vivo analysis. The pathological changes as well as the related neurochemical expressions in the SN will be extensively determined by employing two animal models of tightly encompassing the periodontium with retentive silk and/or dental infection by periodontal pathogen (porphyromonas gingivalis).
(2) Investigate whether melatonin that bears the anti-inflammatory and neuroprotective effects will serve as an effective therapeutic strategy to counteract the neurological deficits resulted from the periodontitis-induced Parkinson’s disease.
In this study, we have firstly verified that ligature model could successfully cause periodontitis and lead to systemic inflammation through the enhanced release of IL-1β, and IL-6. Secondly, we further found that increased astrocyte and microglia activation, enhanced -synuclein expression, reduced tyrosine hydroxylase immunoreactivity, and significant loss of dopaminergic neurons were detected in the SN; which are all pathological features of Parkinson’s disease. Thirdly, we also found that periodontitis would drastically suppress hippocampal pCREB expression, which indicates that periodontitis may play an important role in the pathogenesis of Pakinson’s disease-related cognitive deficiency. In this regard, several cognitive tests have been performed to assess the memorial function, anxiety, and depressive behavior following the current model of periodontitis. The behavioral results showed that although no significant difference was detected in the performance of object recognition between normal untreated and periodontitis animals, noticeable anxiety-like and depression-like behaviors were seen in animals subjected to periodontitis. Moreover, by the use of transmission electron microscopy, we have successfully detected the destruction of blood brain barrier (BBB) in the cortex of periodontitis animals, which strongly supports the distribution of periodontal pathogen in numerous brain regions. Based on these above findings, we conclude that periodontitis-induced systemic inflammation would play an essential role in the induction or trigger the pathogenesis of Parkinson’s disease and the subsequent Parkinson’s disease related cognitive deficiency.
In the next step, we further investigated the protective effect of melatonin on the suppression of periodontitis and the periodontitis-induced neuronal deficiency. The results indicated that melatonin treatment not only effectively suppress the pathogenesis of periodontitis, but also depress the activation of microglia, prevent the dopaminergic neuronal loss, and ameliorate the cognitive dysfunctions.
With regard to these findings, we suggest that keeping or maintaining the oral hygiene by regular use of melatonin may serve as a valuable therapeutic strategy to prevent periodontal problems as well as to decrease the risk of periodontitis-induced neuronal injury. |
