Romare A, Lundholm C E
Department of Pharmacology, Faculty of Health Sciences, University of Linköping, Sweden.
Arch Toxicol. 1999 Jun-Jul;73(4-5):223-8. doi: 10.1007/s002040050610.
The mechanisms by which cadmium (Cd) causes skeletal impairment have not been fully clarified. Release of calcium from neonatal mouse calvaria in organ culture is stimulated by submicromolar concentrations of Cd, an effect that is associated with increased production of prostaglandin E2 (PGE2). The prostaglandin-synthesising enzyme cyclooxygenase (cox) exists in two forms, one constitutive (cox-1) and the other inducible (cox-2). Cox-2 can be induced by mitogenic stimuli and inflammatory cytokines, such as parathyroid hormone (PTH), interleukin-1alpha and tumour necrosis factor-alpha. Cd potently activates protein kinase C (PKC). which in turn induces cox-2 production in several cell types. Our aim was to determine whether Cd-induced Ca release and PGE2 production in neonatal mouse calvaria involve induction of cox-2 and, if so, to ascertain whether that effect is mediated by activation of PKC. Cd dose-dependently stimulated Ca release from cultured neonatal mouse calvaria, with a maximal effect at 0.4-0.8 microM. Different sensitivity was observed to Cd-induced Ca release between two breeds of mice suggesting that the susceptibility to Cd may be genetically determined. Dexamethasone (10 microM) added to the culture medium abolished the Ca releasing effect of Cd, an effect not overcome by addition of arachidonic acid (10 microM). The cox-2-selective inhibitors NS-398 and DFU and the less selective inhibitor meloxicam, potently impeded Cd-induced Ca release (IC50 of 1 nM, 41 nM and 7 nM, respectively) and calvarial production of PGE2. Cd-induced and phorbol 12-myristate 13-acetate (PMA; 20 nM)-induced Ca release was inhibited by the PKC inhibitor calphostin C (0.5 microM) and by NS-398. The effects of PMA and Cd on Ca release were not additive, suggesting that both operated via the PKC pathway. We suggest that Cd-induced Ca release from neonatal mouse calvaria in culture depends on induction of cox-2 that occurs via the PKC signalling pathway.
镉（Cd）导致骨骼损伤的机制尚未完全阐明。在器官培养中，亚微摩尔浓度的Cd可刺激新生小鼠颅骨释放钙，这一效应与前列腺素E2（PGE2）生成增加有关。前列腺素合成酶环氧化酶（cox）有两种形式，一种是组成型（cox - 1），另一种是诱导型（cox - 2）。Cox - 2可由促有丝分裂刺激和炎性细胞因子诱导产生，如甲状旁腺激素（PTH）、白细胞介素 - 1α和肿瘤坏死因子 - α。Cd能有效激活蛋白激酶C（PKC），进而在多种细胞类型中诱导cox - 2的产生。我们的目的是确定Cd诱导新生小鼠颅骨释放钙和产生PGE2是否涉及cox - 2的诱导，如果是，确定该效应是否由PKC的激活介导。Cd剂量依赖性地刺激培养的新生小鼠颅骨释放钙，在0.4 - 0.8微摩尔时达到最大效应。观察到两种品系小鼠对Cd诱导的钙释放敏感性不同，这表明对Cd的易感性可能由基因决定。添加到培养基中的地塞米松（10微摩尔）消除了Cd的钙释放效应，添加花生四烯酸（10微摩尔）无法克服这一效应。cox - 2选择性抑制剂NS - 398和DFU以及选择性较低的抑制剂美洛昔康有效抑制了Cd诱导的钙释放（IC50分别为1纳摩尔、41纳摩尔和7纳摩尔）以及颅骨中PGE2的产生。Cd诱导的和佛波醇12 - 肉豆蔻酸酯13 - 乙酸酯（PMA；20纳摩尔）诱导的钙释放被PKC抑制剂钙泊三醇C（0.5微摩尔）和NS - 398抑制。PMA和Cd对钙释放的作用不是相加的，这表明两者均通过PKC途径起作用。我们认为，培养的新生小鼠颅骨中Cd诱导的钙释放依赖于通过PKC信号通路发生的cox - 2的诱导。
