硫酸鎂抗血小板凝集作用之機轉探討

Mechanisms involved in the Antiplatelet Activity of Magnesium Sulfate

陳藝文(Yi-Wen Chen)

指導教授 ： 許準榕

臺北醫學大學/醫學院/醫學科學研究所/碩士(2001年)

摘要

Magnesium Sulfate (MgSO4)在臨床上注射用於抗痙攣(anticonvulsant)及抗心律不整(antiarrhythemic) (Parra et al., 2001)。鎂離子(Mg2+)為必需的微量元素，在人體神經肌肉功能及能量代謝上扮演一輔助因子 (cofactor)的角色。正常濃度的鎂離子會減少血液凝集 (Gawaz et al.,1994)。對人體的病生理上機轉並不清楚。本篇論文的研究目的是進一步探討硫酸鎂在人類血小板上的作用。 在人類血小板懸浮液中，MgSO4 (0.6-3.0 mM)會隨著濃度的增加，而抑制collagen (1 mg/l)， thrombin (0.02 IU/ml)，及ADP (0.02 mM)所引起的血小板的凝集及ATP的釋放反應。所以，我們懷疑MgSO4是否是作用在血小板凝集最後的共同路徑上(Santoro et al., 1989)；也就是纖維蛋白原(fibrinogen)與血小板細胞膜上的glycoprotein IIb/IIIa complex的結合，進而抑制血小板凝集反應。實驗發現MgSO4不會影響FITC標定的triflavin結合到細胞膜上glycoprotein IIb/IIIa complex；triflavin是一種含Arg-Gly-Asp (RGD)的蛇毒蛋白，已證實為一種glycoprotein IIb/IIIa complex的拮抗劑。 另外，MgSO4 在3.0 mM下能抑制collagen (1 mg/l)所引起的phosphoinositol (PI)的分解，細胞內鈣離子的增加，及抑制thromboxane B2的形成，但在1.5 mM時，並不會有意義的抑制thromboxane B2的形成。 在偵測細胞流動性的實驗中，MgSO4 (1.5及3.0 mM)會直接影響diphylhexatriene (DPH)標定到細胞膜的程度，暗示著MgSO4會影響血小板細胞膜的流動性。此外，MgSO4會有意義的增加血小板內cyclic AMP的含量，且會提高cyclic GMP在血小板濃度。 綜合以上結果，MgSO4對血小板的抑制作用機轉可能有以下二點：(一) MgSO4直接改變血小板細胞膜的流動性，進而影響一些嵌在細胞膜上蛋白質的作用，如phospholipase C (PLC)，使得phosphoinositides (PI)分解後產生inositol-1,4,5,-trisphosphate (IP3)與1,2-diacylglycerol (DG)的含量減少，IP3的減少會降低細胞內鈣離子的濃度，進而抑制血小板的凝集及釋放作用，而DG減少則會進一步抑制47 kDa protein phosphorylation。(二) MgSO4使得血小板內cyclic AMP及cyclic GMP的含量增加，而抑制血小板的凝集。

關鍵字

血小板 ； 硫酸鎂

並列摘要

Magnesium Sulfate (MgSO4) used in human medicine as an injectable solution as an an anticonvulsant and an antiarrhythemic(Parra et al., 2001). As essential element, Magnesium (Mg2+) plays a role of cofactor for many enzymes in human neuromuscular function and energy metabolism. Although concentrations of Mg2+ above the normal range have been shown to reduce platelet aggregation (Gawaz et al.,1994), the underlying pathophysiological mechanisms are still poorly understood. The aim of this thesis is to further investigate the mechanisms of MgSO4 in human platelets. In human platelet suspension, we found that MgSO4 (0.6-3.0 mM) dise dependently potentiated platelet aggregation and ATP release by collagen (1 mg/l), thrombin (0.02 IU/ml), and ADP (0.02 mM). This may imply that whether MgSO4 inhibits platelet aggregation through directly interfering with fibrinogen binding to fibrinogen receptor associated with the glycoprotein IIb/IIIa complex(Santoro et al., 1989). We found that MgSO4 did not significantly affect the FITC-triflavin binding to the glycoprotein IIb/IIIa complex；Triflavin, an Arg-Gly-Asp (RGD) containing antiplatelet peptide, was purified from Trimeresurus flavoviridis snake venom. In addition, MgSO4 (3.0 mM) inhibited the phosphoinositide breakdown and [Ca2+]i mobilization and thromboxane B2 formation in human platelet suspension stimulated by collagen (1 mg/l). At 1.5 mM, MgSO4 did not inhibit thromboxane B2 formation. Measurememt of the platelet membrane fluidity, we found that MgSO4 (1.5-3.0 mM)capable of direct interaction with platelet membrane fluidity tragged with diphenylhexatriene (DPH). On the other hand, MgSO4 (1.5-3.0 mM) did significantly affect cyclic AMP and cyclic GMP levels. Therefore, based on the above observation, we suggested that there are two passibilities involving in the antiplatelet activity of MgSO4：(1) MgSO4 influenced the platelet membrane fluidity is the primary mechanism, followed by the inhibition of phospholipase C activity, thereby leading to the inhibition of [Ca2+]i mobilization and platelet aggregation induced by agonist. (2) MgSO4 increased the cyclic AMP and cyclic GMP levels resulting in inhibitory platelet aggregation.

並列關鍵字

platelet ； magnesium sulfate ； Mg2+ ； cyclic AMP ； cyclic GMP ； TxA2 ； GP IIb/IIIa

參考文獻

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