Khan Mushfiquddin, Shunmugavel Anandakumar, Dhammu Tajinder S, Matsuda Fumiyo, Singh Avtar K, Singh Inderjit
Department of Pediatrics, Medical University of South Carolina, Charleston, SC, 29425, USA.
School of Health Science, Kagoshima University, Kagoshima, Japan.
J Neuroinflammation. 2015 May 15;12:94. doi: 10.1186/s12974-015-0311-y.
Phospholipase A2 (PLA2)-derived proinflammatory lipid mediators such as prostaglandin E2 (PGE2), leukotrienes B4 (LTB4), lysophosphatidylcholine (LPC), and free fatty acids (FFA) are implicated in spinal cord injury (SCI) pathologies. Reducing the levels of these injurious bioactive lipid mediators is reported to ameliorate SCI. However, the specific role of the group IVA isoform of PLA2 cytosolic PLA2 (cPLA2) in lumbar spinal canal stenosis (LSS) due to cauda equina compression (CEC) injury is not clear. In this study, we investigated the role of cPLA2 in a rat model of CEC using a non-toxic cPLA2-preferential inhibitor, arachidonyl trifluoromethyl ketone (ATK).
LSS was induced in adult female rats by CEC procedure using silicone blocks within the epidural spaces of L4 to L6 vertebrae. cPLA2 inhibitor ATK (7.5 mg/kg) was administered by oral gavage at 2 h following the CEC. cPLA2-derived injurious lipid mediators and the expression/activity of cPLA2, 5-lipoxygenase (5-LOX), and cyclooxygenase-2 (COX-2) were assessed. ATK-treated (CEC + ATK) were compared with vehicle-treated (CEC + VEH) animals in terms of myelin levels, pain threshold, and motor function.
ATK treatment of CEC animals reduced the phosphorylation of cPLA2 (pcPLA2) determined by Western blot, improved locomotor function evaluated by rotarod task, and reduced pain threshold evaluated by mechanical hyperalgesia method. Levels of FFA and LPC, along with PGE2 and LTB4, were reduced in CEC + ATK compared with CEC + VEH group. However, ATK treatment reduced neither the activity/expression of 5-LOX nor the expression of COX-2 in CEC + VEH animals. Increased cPLA2 activity in the spinal cord from CEC + VEH animals correlated well with decreased spinal cord as well as cauda equina fiber myelin levels, which were restored after ATK treatment.
The data indicate that cPLA2 activity plays a significant role in tissue injury and pain after LSS. Reducing the levels of proinflammatory and tissue damaging eicosanoids and the deleterious lipid mediator LPC shows therapeutic potential. ATK inhibits cPLA2 activity, thereby decreasing the levels of injurious lipid mediators, reducing pain, improving functional deficits, and conferring protection against LSS injury. Thus, it shows potential for preclinical evaluation in LSS.
磷脂酶A2（PLA2）衍生的促炎脂质介质，如前列腺素E2（PGE2）、白三烯B4（LTB4）、溶血磷脂酰胆碱（LPC）和游离脂肪酸（FFA），与脊髓损伤（SCI）病理过程有关。据报道，降低这些有害生物活性脂质介质的水平可改善脊髓损伤。然而，胞质型磷脂酶A2（cPLA2）的IVA亚型在马尾神经受压（CEC）损伤导致的腰椎管狭窄（LSS）中的具体作用尚不清楚。在本研究中，我们使用无毒的cPLA2优先抑制剂花生四烯酰三氟甲基酮（ATK），研究了cPLA2在CEC大鼠模型中的作用。
通过在L4至L6椎体硬膜外间隙使用硅胶块进行CEC手术，在成年雌性大鼠中诱导LSS。在CEC后2小时，通过口服灌胃给予cPLA2抑制剂ATK（7.5mg/kg）。评估cPLA2衍生的有害脂质介质以及cPLA2、5-脂氧合酶（5-LOX）和环氧化酶-2（COX-2）的表达/活性。将接受ATK治疗的（CEC + ATK）动物与接受载体治疗的（CEC + VEH）动物在髓鞘水平疼痛阈值和运动功能方面进行比较。
对CEC动物进行ATK治疗可降低通过蛋白质印迹法测定的cPLA2磷酸化（pcPLA2），改善通过转棒试验评估的运动功能，并降低通过机械性痛觉过敏法评估的疼痛阈值。与CEC + VEH组相比，CEC + ATK组中FFA和LPC以及PGE2和LTB4的水平降低。然而，ATK治疗并未降低CEC + VEH动物中5-LOX的活性/表达或COX-2的表达。CEC + VEH动物脊髓中cPLA2活性增加与脊髓以及马尾神经纤维髓鞘水平降低密切相关，ATK治疗后这些水平得以恢复。
数据表明，cPLA2活性在LSS后的组织损伤和疼痛中起重要作用。降低促炎和组织损伤性类花生酸以及有害脂质介质LPC的水平显示出治疗潜力。ATK抑制cPLA2活性，从而降低有害脂质介质的水平，减轻疼痛，改善功能缺陷，并对LSS损伤提供保护。因此，它在LSS的临床前评估中显示出潜力。
