Interleukin 6 signal transduction in a human hepatoma cell line (Hep G2)

Isoflavones are safe compounds for therapeutical applications - evaluation of in vitro data

Isoflavone-rich food and food supplements have gained increasing popularity also in the Western world. Their weak estrogenic effect has been considered as a potential risk, although all epidemiological studies and clinical trials show a significant cancer protection and decreased risk of cardiovascular diseases. In vitro data suggest that the concerted action of the isoflavones and their metabolites show antiproliferative behaviour, reduce angiogenesis, reduce tumor progression and exert antiinflammatory effects. For the evaluation of the biological effects, special emphasis has to be put on the concerted action between the isoflavones and their metabolites. For instance, while isolated genistein shows some growth promoting effect at low concentrations, the metabolite equol or soy extract show growth retardation as well as higher concentrations of genistein do. The isoflavones have multiple affinities to other members of the steroid hormone receptor superfamily. The beneficial effect on metabolic diseases and weight reduction by isoflavone consumption can be partly explained by its affinity for the PPAR family. In light of the in vitro experiments, together with the epidemiological observations and the clinical experience, isoflavones can be considered as safe compounds and their consumption as food and food supplements has to be promoted.

Anticancer therapeutic potential of soy isoflavone, genistein

Genistein (4'5, 7-trihydroxyisoflavone) occurs as a glycoside (genistin) in the plant family Leguminosae, which includes the soybean (Glycine max). A significant correlation between the serum/plasma level of genistein and the incidence of gender-based cancers in Asian, European and American populations suggests that genistein may reduce the risk of tumor formation. Other evidence includes the mechanism of action of genistein in normal and cancer cells. Genistein inhibits protein tyrosine kinase (PTK), which is involved in phosphorylation of tyrosyl residues of membrane-bound receptors leading to signal transduction, and it inhibits topoisomerase II, which participates in DNA replication, transcription and repair. By blocking the activities of PTK, topoisomerase II and matrix metalloprotein (MMP9) and by down-regulating the expression of about 11 genes, including that of vascular endothelial growth factor (VEGF), genistein can arrest cell growth and proliferation, cell cycle at G2/M, invasion and angiogenesis. Furthermore, genistein can alter the expression of gangliosides and other carbohydrate antigens to facilitate their immune recognition. Genistein acts synergistically with drugs such as tamoxifen, cisplatin, 1,3-bis 2-chloroethyl-1-nitrosourea (BCNU), dexamethasone, daunorubicin and tiazofurin, and with bioflavonoid food supplements such as quercetin, green-tea catechins and black-tea thearubigins. Genistein can augment the efficacy of radiation for breast and prostate carcinomas. Because it increases melanin production and tyrosinase activity, genistein can protect melanocytes of the skin of Caucasians from UV-B radiation-induced melanoma. Genistein-induced antigenic alteration has the potential for improving active specific immunotherapy of melanoma and carcinomas. When conjugated to B43 monoclonal antibody, genistein becomes a tool for passive immunotherapy to target B-lineage leukemias that overexpress the target antigen CD19. Genistein is also conjugated to recombinant EGF to target cancers overexpressing the EGF receptor. Although genistein has many potentially therapeutic actions against cancer, its biphasic bioactivity (inhibitory at high concentrations and activating at low concentrations) requires caution in determining therapeutic doses of genistein alone or in combination with chemotherapy, radiation therapy, and/or immunotherapies. Of the more than 4500 genistein studies in peer-reviewed primary publications, almost one fifth pertain to its antitumor capabilities and more than 400 describe its mechanism of action in normal and malignant human and animal cells, animal models, in vitro experiments, or phase I/II clinical trials. Several biotechnological firms in Japan, Australia and in the United States (e.g., Nutrilite) manufacture genistein as a natural supplement under quality controlled and assured conditions.

Protein kinase C alpha protein expression is necessary for sustained erythropoietin production in human hepatocellular carcinoma (Hep3B) cells exposed to hypoxia

Although protein kinase C (PKC) has been implicated as an effector of erythropoietin (EPO) production, its exact role is still uncertain. Hep3B human hepatocellular carcinoma cells were used for this study and were depleted of PKC in three different ways: long-term treatment with phorbol 12-myristate 13-acetate (PMA), selective inhibition with calphostin C, and treatment with PKCalpha antisense oligonucleotides. When EPO-producing Hep3B cells were incubated in 1% O2 (hypoxia) for 24 h, PMA treatment resulted in significant decreases in medium levels of EPO in Hep3B cell cultures at concentrations higher than 10 nM. The specific PKC inhibitor, calphostin C, significantly inhibited medium levels of EPO and EPO mRNA levels in Hep3B cells exposed to 1% O2. Western blot analysis revealed that Hep3B cells express the classical PKCalpha and gamma isoforms, as well as novel PKCepsilon and delta and the atypical zeta isoform. Preincubation with PMA for 6 h specifically down-regulated PKCalpha protein expression. Phosphorothioate modified antisense oligonucleotides specific for PKCalpha also decreased EPO production in Hep3B cells exposed to hypoxia for 20 h when compared to PKCalpha sense treatment. The translocation of PKCalpha from the soluble to particulate fractions was increased in Hep3B cells incubated under hypoxia compared with normoxia (21% O2) controls. These results suggest that the PKCalpha isoform plays an important role in sustaining hypoxia-regulated EPO production.