Different behavior of myeloperoxidase in two rodent amoebic liver abscess models

The protozoan Entamoeba histolytica is the etiological agent of amoebiasis, which can spread to the liver and form amoebic liver abscesses. Histological studies conducted with resistant and susceptible models of amoebic liver abscesses (ALAs) have established that neutrophils are the first cells to contact invasive amoebae at the lesion site. Myeloperoxidase is the most abundant enzyme secreted by neutrophils. It uses hydrogen peroxide secreted by the same cells to oxidize chloride ions and produce hypochlorous acid, which is the most efficient microbicidal system of neutrophils. In a previous report, our group demonstrated that myeloperoxidase presents amoebicidal activity in vitro. The aim of the current contribution was to analyze in vivo the role of myeloperoxidase in a susceptible (hamsters) and resistant (Balb/c mice) animal models of ALAs. In liver samples of hamsters and mice inoculated intraportally with Entamoeba histolytica trophozoites, the number of neutrophils in ALAs was determined by enzymatic activity. The presence of myeloperoxidase was observed by staining, and its expression and activity were quantified in situ. A significant difference existed between the two animal models in the number of neutrophils and the expression and activity of myeloperoxidase, which may explain the distinct evolution of amoebic liver abscesses. Hamsters and mice were treated with an MPO inhibitor (4-aminobenzoic acid hydrazide). Hamsters treated with ABAH showed no significant differences in the percentage of lesions or in the percentage of amoebae damaged compared with the untreated hamsters. ABAH treated mice versus untreated mice showed larger abscesses and a decreased percentage of damaged amoebae in these lesion at all stages of evolution. Further studies are needed to elucidate the host and amoebic mechanisms involved in the adequate or inadequate activation and modulation of myeloperoxidase.

溶组织内阿米巴（Entamoeba histolytica）是阿米巴病的致病因子，该病原体可侵袭肝脏并形成阿米巴肝脓肿（amoebic liver abscesses, ALAs）。针对阿米巴肝脓肿的易感与抵抗模型开展的组织学研究证实，中性粒细胞是病灶部位最先接触侵袭性阿米巴的细胞。髓过氧化物酶（myeloperoxidase, MPO）是中性粒细胞分泌的含量最丰富的酶类，它可利用自身细胞分泌的过氧化氢氧化氯离子，生成次氯酸——这是中性粒细胞最有效的杀菌系统。本团队此前的研究已证实，髓过氧化物酶在体外具备抗阿米巴活性。本研究旨在通过易感（仓鼠）与耐受（Balb/c小鼠）两种阿米巴肝脓肿动物模型，分析髓过氧化物酶在体内的作用。在经门静脉接种溶组织内阿米巴滋养体的仓鼠与小鼠肝脏样本中，研究人员通过酶活性检测确定了阿米巴肝脓肿病灶内的中性粒细胞数量；通过染色法观测到髓过氧化物酶的存在，并原位定量了其表达水平与活性。两种动物模型在中性粒细胞数量、髓过氧化物酶的表达与活性方面均存在显著差异，这或可解释阿米巴肝脓肿病程的显著差异。研究人员使用髓过氧化物酶抑制剂4-氨基苯甲酰肼（4-aminobenzoic acid hydrazide, ABAH）对两组动物进行处理。与未处理的仓鼠相比，经ABAH处理的仓鼠在病灶占比或受损阿米巴占比方面均未出现显著变化；而经ABAH处理的小鼠，其病灶体积更大，且各病程阶段病灶内受损阿米巴的占比均有所降低。未来仍需开展进一步研究，以阐明宿主与阿米巴双方参与髓过氧化物酶激活与调控的具体机制。