Hamilton R F, Iyer L L, Holian A
Department of Internal Medicine, University of Texas Medical School, Houston 77030, USA.
Am J Physiol. 1996 Nov;271(5 Pt 1):L813-9. doi: 10.1152/ajplung.1996.271.5.L813.
Asbestos refers to a group of fibrous minerals implicated in the development of several lung diseases, including fibrosis (asbestosis), cancer, and malignant mesothelioma. Although major health risks exist in occupationally exposed individuals, low-level exposures of asbestos may still contribute to health problems. The mechanism by which asbestos causes lung disease is not clearly understood but has been proposed to involve the alveolar macrophage (AM). We propose that asbestos induces apoptosis of AM, resulting in the development of an inflammatory state. In this study, we examined two forms of asbestos, chrysotile (CHR) and crocidolite (CRO), along with a control fiber, wollastonite (WOL), to characterize their relative cytotoxicity and ability to stimulate apoptosis in vitro. AM were cultured for 24 h with these particulates and examined for cell viability (trypan blue exclusion) and apoptosis (morphology, levels of cytosolic oligonucleosomal DNA fragments, and DNA ladder). In the absence of a decrease in cell viability, both CHR and CRO produced changes in cell morphology consistent with apoptosis. In addition, levels of cytoplasmic oligonucleosomal DNA (Cell Death Detection enzyme-linked immunosorbent assay) were significantly enhanced for CHR (3-25 micrograms/ml) and CRO (25-75 micrograms/ml) in a dose-dependent manner (a process that was inhibitable by 10 microM Z-Val-Ala-Asp fluoromethyl ketone, an interleukin-converting enzyme inhibitor). In contrast, WOL (up to 400 micrograms/ml) produced no significant DNA fragmentation in a 24-h culture. Neither CHR nor CRO caused DNA ladder formation in 24-h cell cultures. However, in 48-h cell cultures, both CHR- and CRO-exposed cells, but not WOL, resulted in the formation of DNA ladders characteristic of apoptosis. In summary, these results suggest that, unlike nonfibrogenic particulates, low doses of asbestos fibers cause apoptosis in cultured human AM that may be an early step in the development of lung fibrosis.
石棉是指一类纤维状矿物质，与包括纤维化（石棉肺）、癌症和恶性间皮瘤在内的多种肺部疾病的发生有关。虽然职业暴露人群存在重大健康风险，但低水平接触石棉仍可能导致健康问题。石棉导致肺部疾病的机制尚不清楚，但有人提出其涉及肺泡巨噬细胞（AM）。我们认为石棉诱导AM凋亡，从而导致炎症状态的发展。在本研究中，我们检测了两种石棉形式，温石棉（CHR）和青石棉（CRO），以及一种对照纤维硅灰石（WOL），以表征它们在体外的相对细胞毒性和刺激凋亡的能力。将AM与这些颗粒一起培养24小时，并检测细胞活力（台盼蓝排斥法）和凋亡情况（形态学、胞质寡核小体DNA片段水平和DNA梯带）。在细胞活力未降低的情况下，CHR和CRO均产生了与凋亡一致的细胞形态变化。此外，CHR（3 - 25微克/毫升）和CRO（25 - 75微克/毫升）的胞质寡核小体DNA水平（细胞死亡检测酶联免疫吸附测定）以剂量依赖方式显著升高（该过程可被10微摩尔Z - 缬氨酰 - 丙氨酰 - 天冬氨酸氟甲基酮抑制，一种白细胞介素转化酶抑制剂）。相比之下，WOL（高达400微克/毫升）在24小时培养中未产生显著的DNA片段化。CHR和CRO在24小时细胞培养中均未导致DNA梯带形成。然而，在48小时细胞培养中，CHR和CRO处理的细胞（而非WOL处理的细胞）导致了凋亡特征性的DNA梯带形成。总之，这些结果表明，与非致纤维化颗粒不同，低剂量石棉纤维可导致培养的人AM凋亡，这可能是肺纤维化发展的早期步骤。
