Indolo[3,2-b]carbazole inhibits gap junctional intercellular communication in rat primary hepatocytes and acts as a potential tumor promoter

Abstract

Indole-3-carbinol (I3C) is a naturally occurring substance that shows anti-carcinogenic properties in animal models. Besides its clear anti-carcinogenic effects, some studies indicate that I3C may sometimes act as a tumor promoter. Indolo[3,2-b]carbazole (ICZ), which is formed in the acidic environment of the stomach after intake of I3C, has a similar structure to, and shares biological effects with, the well-known tumor promoter 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Therefore, we hypothesized that ICZ could be responsible for the potential tumor-promoting activity of I3C. The aim of the present study was to investigate the effect of ICZ on gap junctional intercellular communication (GJIC) in primary cultured rat hepatocytes co-cultured with the rat liver epithelial cell line WB-F344. Indolo[3,2-b]carbazole inhibited GJIC in the rat hepatocytes in a dose- and time-dependent manner. Significant inhibition was observed after 8 and 12 h of treatment with 1 and 0.1 micro M ICZ, respectively. Maximum GJIC inhibition (cell-cell communication only 5% of control values) was observed after 24-48 h of ICZ treatment. Continued exposure to 1 micro M ICZ suppressed GJIC until approximately 120 h. Both ICZ and TCDD treatment reduced the Cx32 mRNA level as well as the plasma membrane Cx32 staining. Indolo[3,2-b]carbazole increased the Cyp1a1, Cyp1a2 and Cyp1b1 mRNA levels concurrently with an increase in 7-ethoxyresorufin O-deethylase (EROD) activities. Maximum EROD activity and Cyp1a1 mRNA levels were observed after approximately 12 h, whereas Cyp1a2 and Cyp1b1 mRNA levels peaked after 48 h. This study shows that ICZ may possess tumor promoter activity down-regulating GJIC by mechanisms, which seem to include activation of the Ah receptor and/or Cyp1 activity. Further studies are needed in order to clarify the anticarcinogenic/carcinogenic effects of I3C and ICZ before high doses of I3C may be recommended as a dietary supplement.

Malassezia Yeasts Produce a Collection of Exceptionally Potent Activators of the Ah (Dioxin) Receptor Detected in Diseased Human Skin

“…The corresponding, AhR mediated local metabolic and immune aberrations have been proposed as the pathophysiological background of the suggested Malassezia indoles and basal cell carcinoma association (Gaitanis et al, 2011). It is noteworthy that ICZ, like TCDD, has been considered as a tumor promoter (Herrmann et al, 2002). Another interesting issue that rises from our findings is the impact these indoles could have on the local induction of P450 enzymes that metabolize antifungal azoles.…”

Physiological effects of broccoli consumption

“…Although animal studies find protection against cancer with broccoli diets or broccoli sprouts extracts (Canene-Adams et al 2007;Dinkova-Kostova et al 2006, and although clinical studies find dietary I3C (50-400 mg/day for 28 days) to be safe (Wong et al 1997) there remains considerable concern about whether dietary I3C prevents or enhances carcinogenesis (Stoner et al 2002). Recent work with an alternative I3C metabolite to DIM, indolo 3,2b-carbazole, may have identified this compound as responsible for enhancement of carcinogenesis by I3C (Herrmann et al 2002;Agerbirk et al 2008). Studies are needed to understand how to minimize indolo 3,2b-carbazone formation.…”

Pharmacological Exploitation of Indole-3-Carbinol to Develop Potent Antitumor Agents

“…Among them, DIM induces apoptosis and cell cycle arrest through the modulation of signaling targets similar to those affected by indole-3-carbinol, including Akt, NF-B, endoplasmic reticulum stress, and nuclear receptors, such as ER and arylhydrocarbon receptor (AhR) [35][36][37][38][39][40][41][42][43][44][45][46][47]. In contrast, the functions of the oligomers ICZ, LTr1, and CTr are mainly associated with ER and AhR [48,49], while the tetrameric product CTet suppressed breast cancer growth by inhibiting the expression of cyclin-dependent kinase (CDK)6 and other cell cycle regulatory proteins with fivefold higher potency than indole-3-carbinol [50].…”