Effects of cyclophosphamide and a metabolite, acrolein, on Naegleria fowleri in vitro and in vivo

Efficient Liquid Media for Encystation of Pathogenic Free-Living Amoebae

Pathogenic Naegleria fowleri, Acanthamoeba castellanii, and Acanthamoeba polyphaga, are distributed worldwide. They are causative agents of primary amoebic meningoencephalitis or acanthamoebic keratitis in humans, respectively. Trophozoites encyst in unfavorable environments, such as exhausted food supply and desiccation. Until recently, the method of N. fowleri encystation used solid non-nutrient agar medium supplemented with heat-inactivated Escherichia coli; however, for the amoebic encystment of Acanthamoeba spp., a defined, slightly modified liquid media is used. In this study, in order to generate pure N. fowleri cysts, a liquid encystment medium (buffer 1) modified from Page’s amoeba saline was applied for encystation of N. fowleri. N. fowleri cysts were well induced after 24 hr with the above defined liquid encystment medium (buffer 1). This was confirmed by observation of a high expression of differential mRNA of nfa1 and actin genes in trophozoites. Thus, this liquid medium can replace the earlier non-nutrient agar medium for obtaining pure N. fowleri cysts. In addition, for cyst formation of Acanthamoeba spp., buffer 2 (adjusted to pH 9.0) was the more efficient medium. To summarize, these liquid encystment media may be useful for further studies which require axenic and pure amoebic cysts.

Biology and pathogenesis of Naegleria fowleri

Naegleria fowleri is a protist pathogen that can cause lethal brain infection. Despite decades of research, the mortality rate related with primary amoebic meningoencephalitis owing to N. fowleri remains more than 90%. The amoebae pass through the nose to enter the central nervous system killing the host within days, making it one of the deadliest opportunistic parasites. Accordingly, we present an up to date review of the biology and pathogenesis of N. fowleri and discuss needs for future research against this fatal infection.

Naegleria fowleri after 50 years: is it a neglected pathogen?

It has been 50 years since the first case of primary amoebic meningoencephalitis (PAM), an acute and rapidly fatal disease of the central nervous system (CNS), was reported in Australia. It is now known that the aetiological agent of PAM is Naegleria fowleri, an amoeba that is commonly known as 'the brain-eating amoeba'. N. fowleri infects humans of different ages who are in contact with water contaminated with this micro-organism. N. fowleri is distributed worldwide and is found growing in bodies of freshwater in tropical and subtropical environments. The number of PAM cases has recently increased, and the rate of recovery from PAM has been estimated at only 5 %. Amphotericin B has been used to treat patients with PAM. However, it is important to note that there is no specific treatment for PAM. Moreover, this amoeba is considered a neglected micro-organism. Researchers have exerted great effort to design effective drugs to treat PAM and to understand the pathogenesis of PAM over the past 50 years, such as its pathology, molecular and cellular biology, diagnosis and prevention, and its biological implications, including its pathogenic genotypes, its distribution and its ecology. Given the rapid progression of PAM and its high mortality rate, it is important that investigations continue and that researchers collaborate to gain better understanding of the pathogenesis of this disease and, consequently, to improve the diagnosis and treatment of this devastating infection of the CNS.

Aldo-keto reductase 1B10 protects human colon cells from DNA damage induced by electrophilic carbonyl compounds

Electrophilic carbonyl compounds are highly cytotoxic and genotoxic. Aldo-keto reductase 1B10 (AKR1B10) is an enzyme catalyzing reduction of carbonyl compounds to less toxic alcoholic forms. This study presents novel evidence that AKR1B10 protects colon cells from DNA damage induced by electrophilic carbonyl compounds. AKR1B10 is specifically expressed in epithelial cells of the human colon, but this study found that AKR1B10 expression was lost or markedly diminished in colorectal cancer, precancerous tissues, and a notable portion of normal adjacent tissues (NAT). SiRNA-mediated silencing of AKR1B10 in colon cancer cells HCT-8 enhanced cytotoxicity of acrolein and HNE, whereas ectopic expression of AKR1B10 in colon cancer cells RKO prevented the host cells against carbonyl cytotoxicity. Furthermore, siRNA-mediated AKR1B10 silencing led to DNA breaks and activation of γ-H2AX protein, a marker of DNA double strand breaks, particularly in the exposure of HNE (10 μM). In the AKR1B10 silenced HCT-8 cells, hypoxanthine-guanine phosphoribosyl transferase (HPRT) mutant frequency increased by 26.8 times at basal level and by 33.5 times in the presence of 10 μM HNE when compared to vector control cells. In these cells, the cyclic acrolein-deoxyguanosine adducts levels were increased by over 10 times. These findings were confirmed by pharmacological inhibition of AKR1B10 activity by Epalrestat. Taken together, these data suggest that AKR1B10 is a critical protein that protects host cells from DNA damage induced by electrophilic carbonyl compounds. AKR1B10 deficiency in the colon may be an important pathogenic factor in disease progression and carcinogenesis. © 2016 Wiley Periodicals, Inc.

Immunotoxicity of nitrobenzene in female B6C3F1 mice

Nitrobenzene (NBZ) is primarily employed as an oxidizing agent in the synthesis of analine and benzene compounds. It produces myelotoxic effects and effects on erythrocytes in both animal models and man. Reported hepatosplenomegaly and effects on the bone marrow are indicators that NBZ may be immunotoxic. In these studies, female B6C3F1 mice were exposed to 30, 100 and 300 mg/kg of NBZ in corn oil by gavage for 14 consecutive days. To assess the immunotoxic potential of NBZ, body and organ weights were determined and selected immunologic and host resistance responses were studied. In these studies, the liver and spleen appeared to be the primary target organs. Both liver and spleen weights were dose dependently increased. Gross histopathologic examinations revealed significant changes in the spleen, consisting of severe congestion of the red pulp areas with erythrocytes and reticulocytes. Serum chemistry profiles showed increases in alanine aminotransferase and aspartate aminotransferase activities, indicating liver toxicity. Hematologic studies showed a decrease in erythrocyte number and a concomitant increase in mean corpuscular hemoglobin and mean corpuscular volume. A dose-dependent increase in peripheral reticulocytes was also seen. DNA synthesis was enhanced, as was the number of formed elements and the number of monocyte/granulocyte stem cells in the bone marrow of treated mice. IgM responses were decreased and the phagocytic activity of macrophages in the liver was dose dependently increased with a concomitant decrease in the activities in the spleen and lung. Other immunological parameters examined were unchanged. Host resistance to microbial or viral infection was not markedly altered by NBZ; however, there were trends towards increased susceptibility where T-cell function contributes to host defense. These data indicate that NBZ-induced hemolysis and liver injury are linked to the observed alterations in bone marrow activity.