Molecular aspects of microcystin-induced hepatotoxicity and hepatocarcinogenesis.

It is known that microcystin (MC) is a cyanotoxin that is a potent environmental inhibitor of eucariotic protein serine/threonine phosphatase 1 and 2A, both in vitro and in vivo. Consequently, these cyanobacterial toxins (MC-IARC group 2B carcinogen, MC extracts-group 3) are potent tumor promoters and there is an indication that they may also act as tumor initiators. The ability of microcystin-LR (MC-LR) to act as a tumor initiator is based on fact that it can induce DNA damage either by direct interaction with DNA or by indirect mechanisms through formation of reactive oxygen species (ROS). Both acute and chronic exposures, to either low or high doses of MC-LR, can activate apoptotic pathways. Chronic exposure to low concentrations of MC-LR contributes to increased risk for cancer development. Epidemiological studies, in certain areas of China, have suggested that MC is one of the risk factors for the high incidence of primary liver cancer (PLC). Recently, we have reported a correlation between PLC and cyanobacterial "blooms" in reservoirs used as a source for drinking water supply in central Serbia. It appears that the combination of acute and chronic exposures to both high and low doses of MC can lead to PLC initiation and promotion. Based on this, we propose that the requirement for the co-factors such as aflatoxin B1 and other mycotoxins, HBV, HCV, alcohol, etc. is not needed for initiation and promotion of PLC by MC-LR as was suggested earlier. The possible mechanisms of the genotoxicity of MC and its role as a hepatocarcinogen are outlined in this review. Furthermore, we show that the exposure of hepatocytes to MC can lead either to malignant proliferation or apoptosis.

In vitro cytotoxicity of cyanobacteria from water ecosystems of Serbia.

PURPOSE: The purpose of this study was to investigate whether water samples from water ecosystems of Serbia, unknown so far with regard to cyanotoxin levels, are the source of toxic compounds originating from the biological activity of cyanobacteria. MATERIALS AND METHODS: The growth inhibition activity was evaluated using in vitro toxicity assay in Neuro-2a (mouse neuroblastoma) and MRC-5 (human fetal lung) cell lines, after 48 h of exposure time. Cell growth was evaluated by the colorimetric sulforhodamine B (SRB) assay. RESULTS: Our experiments revealed that some of the investigated water samples are toxigenic and alter cell growth of Neuro-2 and MRC-5 cell lines in vitro. CONCLUSION: Neuro-2a and MRC-5 cell lines responded to the presence of secondary metabolites of cyanobacteria. Significant cytotoxic effects were detected in the samples from lakes (Ludos and Palic), reservoirs (Zobnatica) and rivers (Krivaja).

[Goals and scientific achievements of the Institute of Oncology]. / Stremljenja i strucno-naucna dostignuca Instituta za onkologiju.

The Institute of oncology represents an oncological center which renders the measures of prevention, early detection and diagnostic of tumours and multidisciplinary strategy for antitumour treatment, including rehabilitation of patients suffering from tumours. To fulfil the above mentioned aims the Institute is organized in ten completely operative units and several functional centres and committees. The paper presents only few aspects of diagnostic and treatment of tumour, and the implementation of the programmes and targets of individual organizational units within the Institute. This orientation is particularly actual now when epidemiological studies show an increase of disease and mortality incidence in the region of Vojvodina.

Ovarian carcinoma: modification of T4 lymphocytes after surgery and during chemotherapy.

OBJECTIVE: To examine the values of helper/inducer lymphocytes (T4), preoperatively, and during the chemotherapy, 1 and 3 months postoperatively in a prospective randomized study of women with cancer. The study included 30 surgically-treated patients with ovarian cancer at the Department of Obstetrics and Gynecology in Novi Sad, Yugoslavia. In the control group, 20 patients had no malignant ovarian tumor. Patients with ovarian cancer, besides surgical treatment, were treated with chemotherapy (CP protocol). Helper/inducer lymphocytes were defined by monoclonal antibody--CD4, conducted by laser flow cytometry. The average values of T4 lymphocytes in relation to control group (1.09 +/- 0.50), in IIIa, IIIb and IIIc stage of ovarian cancer decreased preoperatively (0.55 +/- 0.26), but increased in stages Ia and Ic (1.12 +/- 0.57) and in stage IV (0.31 +/- 0.51). Post surgery treatment (1 and 3 months) and during chemotherapy (CP protocol), the average values of T4 lymphocytes were lowered in relation to preoperative values.

Artificial reversion of acute myeloid leukemia cells into normal phenotype.

1. Induction of tumor cell differentiation could reverse transformed cells into normal, mature cells. Important question is whether these malignant-to-normal reversed cells are really normal ones. 2. We have developed an experimental model based on the examination of three different levels of human acute myeloid leukemia cell properties before and after induction of differentiation: morphological (percentage of undifferentiated blast cells), functional (DNA ploidy, Fc receptors, phagocytic activity, clonogenic assay in soft agar, oxidative metabolism which accompanies phagocytosis in mature granulocytes) and genetical (expression of oncogene p53). 3. Several inducers have been employed: dimethylsulfoxide (DMSO) granulocyte-macrophage colony stimulating factor (GM-CSF); tunicamycin, interferon gamma, tumor necrosis factor and lipopolysaccharide. 4. Our results indicate that the reversion of leukemic cells into mature normal ones with some inducers (DMSO, GM-CSF) could be a complete process.

Detection of cross-reacting idiotypes in sera of lymphoma patients by inverse monoclonal radioimmunoassay.

An anti-idiotypic IgG1 kappa murine monoclonal antibody (MoAb) Y7 against purified monoclonal IgM lambda 1, derived from a patient with Waldenström's macroglobulinemia, has been generated. This antibody cross-reacted with the tumor-derived idiotypes of patients with B cell non Hodgkin's lymphoma as measured by competitive inverse solid radioimmunoassay using unpurified serum samples. Our results with the inhibition curves of 10 sera of normal donors and 60 sera of lymphoma patients indicate that 21 lymphoma patients revealed cross-reactivities greater than 7%, the mean value observed in normal donors. Of these, 5 sera cross-reacted strongly, in the range of 43-163%, revealing a frequency of positive cross-reactivity for MoAb Y7 of 1/12 sera of lymphoma patients. The generation of a panel of anti-idiotypic antibodies which cross-react with different tumor-derived Ig in serum may be valuable for monitoring the disease in a high proportion of NHL patients.

Growth factors in human tumors.

Various human tumor tissues contain different growth factors. In some cases progression of tumors is paralleled by elevated levels of these substances in blood or in tumor tissue. There is evidence that these growth promoting peptides might stimulate tumor growth. The growth of most tumors was associated with insulin-like substances (MW 45,000). We isolated and purified a substance immunologically cross-reactive with insulin (SICRI) from human melanoma. We found the molecular weight of affinity purified SICRI to be approximately 120,000. Our in vitro experiments with human renal carcinoma cells and growth factors suggest an important role of these molecules in tumor progression.

Elevated levels of substances immunologically cross-reactive with insulin in blood of patients with malignant and nonmalignant pulmonary tissue proliferation.

Results of a survey of concentrations of substances immunologically cross-reactive with insulin (SICRI), glucose and growth hormone in preprandially drawn blood of 84 patients suffering from bronchial epidermoid, microcellular and adenocarcinomas and 22 patients from sarcoidosis, tuberculosis and obstructive bronchitis are presented. In all these diseases, tissue proliferation takes place. Supranormal SICRI concentrations were frequently associated with these diseases, whereas concentrations of glucose and growth hormone remained unaffected; this shows that physiological effects of SICRI in these diseases differ from the effects in patients suffering from some lympho-proliferative and solid tumors. These results indicate that elevated levels of circulating substances detectable by insulin-specific radioimmunoassay can accompany both malignant and nonmalignant proliferation in lungs.