Antiproliferative and Apoptosis-Inducing Effects of Hemin in Hepatoma Cells

Amoebal pathogens as emerging causal agents of pneumonia

Despite using modern microbiological diagnostic approaches, the aetiological agents of pneumonia remain unidentified in about 50% of cases. Some bacteria that grow poorly or not at all in axenic media used in routine clinical bacteriology laboratory but which can develop inside amoebae may be the agents of these lower respiratory tract infections (RTIs) of unexplained aetiology. Such amoebae-resisting bacteria, which coevolved with amoebae to resist their microbicidal machinery, may have developed virulence traits that help them survive within human macrophages, i.e. the first line of innate immune defence in the lung. We review here the current evidence for the emerging pathogenic role of various amoebae-resisting microorganisms as agents of RTIs in humans. Specifically, we discuss the emerging pathogenic roles of Legionella-like amoebal pathogens, novel Chlamydiae (Parachlamydia acanthamoebae, Simkania negevensis), waterborne mycobacteria and Bradyrhizobiaceae (Bosea and Afipia spp.).

Involvement of PKC in TPA-potentiated apoptosis induction during hemin-mediated erythroid differentiation in K562 cells

Triggering differentiation has been employed as a strategy to inhibit cell proliferation and accelerate apoptosis in malignant cells. To better understand the mechanisms underlying differentiation-mediated regulation of apoptosis, we have studied the effects of PKC pathway with an activator of the protein kinase C, 12-O-tetradecanoylphorbol-13-acetate (TPA), during hemin-induced erythroid differentiation of K562 erythroleukemia cells. K562 cell line has been used as a model of common progenitor of erythroblasts and magakaryocytes and can be differentiated into erythroid and megakaryocytic lineages by hemin and TPA, respectively. TPA induced almost complete loss of proliferation during megakaryocytic differentiation in K562 cells. However, upon hemin-mediated erythroid differentiation, the growth rate was slightly decreased at the subtoxic concentrations. Cotreatment with TPA at the hemin-treated K562 cells produced a concentration-dependent increase in cell injuries with apoptotic changes and significantly diminished the erythroid phenotype. To better understand the events implicated, we have used the PKC inhibitors such as bisindolylmaleimide II, RO318220, and the PKCbeta inhibitor. Our data showed that TPA-potentiated apoptosis in hemin-treated K562 cells was rescued by the application of the PKC inhibitors. Taken together, our results suggested the involvement of PKC in TPA-potentiated apoptosis induction during hemin-mediated erythroid differentiation in K562 cells.

Inhibition of vascular smooth muscle cell proliferation by chronic hemin treatment

Hemin, an oxidized form of heme, is an essential regulator of gene expression and cell cycle progression. Our laboratory previously reported (34) that chronic hemin treatment of spontaneously hypertensive rats reversed the eutrophic inward remodeling of small peripheral arteries. Whether long-term treatment of cultured vascular smooth muscle cells (VSMCs) with hemin alters the proliferation status of these cells has been unknown. In the present study, hemin treatment at 5 muM for 4, 7, 14, and 21 days significantly inhibited the proliferation of cultured rat aortic VSMCs (A-10 cells) by arresting cells at G0/G1 phases so as to decelerate cell cycle progression. Heme oxygenase (HO) activity and inducible HO-1 protein expression were significantly increased by hemin treatment. HO inhibitor tin protoporphyrin IX (SnPP) abolished the effects of hemin on cell proliferation and HO activity. Interestingly, hemin-induced HO-1 expression was further increased in the presence of SnPP. Hemin treatment had no significant effect on the expression of constitutive HO-2. Expression of p21 protein and the level of reactive oxygen species (ROS) were decreased by hemin treatment, which was reversed by application of SnPP. After removal of hemin from culture medium, inhibited cell proliferation and increased HO-1 expression in VSMCs were returned to control level within 1 wk. Transfection with HO-1 small interfering RNA significantly knocked down HO-1 expression and decreased HO activity, but had no effect on HO-2 expression, in cells treated with or without hemin for 7 days. The inhibitory effect of hemin on cell proliferation was abolished in HO-1 silenced cells. It is concluded that induction of HO-1 and, consequently, increased HO activity are responsible for the chronic inhibitory effect of hemin on VSMC proliferation. Changes in the levels of p21 and ROS might also participate in the cellular effects of hemin.

Apoptotic activity of frog Bombina maxima skin albumin

Albumin, the most abundant protein components of blood plasma, is synthesized and secreted by liver cells in vertebrates. Recently, it was demonstrated that frog Bombina maxima albumin is also expressed in skin. Both B. maxima albumins from skin and serum (BmA-skin and BmA-serum) have similar biochemical characteristics except that the former contains haem b. Present studies showed that BmA-skin exhibited cytotoxic activity on H9 and C8166 cells. Pretreated with hemin to induce erythroid differentiation, K562 cells lost their resistance to cytotoxicity of BmA-skin. After treating cells with BmA-skin for 48 h, 50 percentage cytotoxic concentrations (CC(50)) of BmA-skin on H9, C8166 and hemin-treated K562 cells were 1.31+/-0.09, 1.59+/-0.08 and 2.28+/-0.06 microM, respectively. The cell death induced by BmA-skin was mediated by apoptosis of the tested cell lines, as demonstrated by nuclear morphological changes, DNA fragmentation and DNA hypodiploidy of apoptosis cells. At BmA-skin concentration of 2 microM, 27.3%, 19.7% and 17.8% of H9, C8166 and hemin-treated K562 cells were found to be apoptotic. In contrast, BmA-serum possessed no cytotoxic and apoptosis-inducing activity on all the cell lines tested, even with concentration used up to 15 microM. These results indicated that bound haem b in BmA-skin contributed significantly to its cytotoxic and apoptosis-inducing activity on the cell lines assayed.