https://pubs.rsc.org/en/content/articlepdf/2019/NP/C8NP00092A

Marine natural products.

The chemical diversity and distribution of glucosinolates and isothiocyanates among plants

Our appreciation of the physiological functions of estrogens and the mechanisms through which estrogens bring about these functions has changed during the past decade. Just as transgenic mice were produced in which estrogen receptors had been inactivated and we thought that we were about to understand the role of estrogen receptors in physiology and pathology, it was found that there was not one but two distinct and functional estrogen receptors, now called ERα and ERβ. Transgenic mice in which each of the receptors or both the receptors are inactive have revealed a much broader role for estrogens in the body than was previously thought. This decade also saw the description of a male patient who had no functional ERα and whose continued bone growth clearly revealed an important function of estrogen in men. The importance of estrogen in both males and females was also demonstrated in the laboratory in transgenic mice in which the aromatase gene was inactivated. Finally, crystal structures of the estrogen r...

Mechanisms of Estrogen Action

The induction of expression of genes for xenobiotic metabolizing enzymes in response to chemical insult is an adaptive response found in most organisms. In vertebrates, the AhR is one of several chemical/ligand-dependent intracellular receptors that can stimulate gene transcription in response to xenobiotics. The ability of the AhR to bind and be activated by a range of structurally divergent chemicals suggests that the AhR contains a rather promiscuous ligand binding site. In addition to synthetic and environmental chemicals, numerous naturally occurring dietary and endogenous AhR ligands have also been identified. In this review, we describe evidence for the structural promiscuity of AhR ligand binding and discuss the current state of knowledge with regards to the activation of the AhR signaling pathway by naturally occurring exogenous and endogenous ligands.

Activation of the aryl hydrocarbon receptor by structurally diverse exogenous and endogenous chemicals.

The heterorneric unliga nded aryl hydrocarbon receptor complex (AHRC) con­ ta ins the aryl hydrocarbon receptor monomer (AHR). Binding of polycyclic or ha loge nated aromatic hydrocarbon (PAH and HAH) ligand causes release of AHR, which then associates with the AHR nuclear translocator protein (ARNT) to generate the heterodimeric "transformed" AHRC, AHR and ARNT belong to a novel subclass of basic helix-loop-helix -containing transcription factors. The transformed AHRC binds xenobiotic responsive elements in re­ sponsive genes and turns on their transcr iption, Certain of these genes encode enzymes involved in the metabol ic activation of PAHs to mutagenic deriva­ tives. HAHs are not genotoxic: Their pathogen icity depends on the AHRC but not on their metab olism. Current rese arch includes investigations dir ected towards delineating the pathways of HAH pathogenesis, ascer taining whether AHR can mediate signal transduction independently of DNA binding, under­ standing the mechanism of transcriptional activation, and investigating the potential roles of AHR and ARNT in development.

The aryl hydrocarbon receptor complex.

Indole-3-carbinol (I3C) is a secondary plant metabolite produced in vegetables of the Brassica genus, including cabbage, cauliflower, and brussels sprouts. I3C is both an anti-initiator and a promoter of carcinogenesis. Consumption of I3C by humans and rodents can lead to marked increases in activities of cytochrome P-450-dependent monooxygenases and in a variety of phase II drug-metabolizing enzymes. We have reported previously that the enzyme-inducing activity of I3C is mediated through a mechanism requiring exposure of the compound to the low-pH environment of the stomach. We report here the aromatic hydrocarbon responsiveness-receptor Kd values (22 nM-90 nM), determined with C57BL/6J mouse liver cytosol and the in vitro- and in vivo-molar yields (0.1-6%) of the major acid condensation products of I3C. We also show that indolo[3,2-b]carbazole (ICZ) is produced from I3C in yields on the order of 0.01% in vitro and, after oral intubation, in vivo. ICZ has a Kd of 190 pM for aromatic hydrocarbon responsiveness-receptor binding and an EC50 of 269 nM for induction of cytochrome P4501A1, as measured by ethoxyresorufin O-deethylase activity in murine hepatoma Hepa 1c1c7 cells. The binding affinity of ICZ is only a factor of 3.7 x 10(-2) lower than that of the highly toxic environmental contaminant and cancer promoter 2,3,7,8-tetrachlorodibenzo-p-dioxin. ICZ and related condensation products appear responsible for the enzyme-inducing effects of dietary I3C.

https://www.pnas.org/content/pnas/88/21/9543.full.pdf

Aromatic hydrocarbon responsiveness-receptor agonists generated from indole-3-carbinol in vitro and in vivo: comparisons with 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Christopher A. Bradfield

Papers

Aromatic hydrocarbon responsiveness-receptor agonists generated from indole-3-carbinol in vitro and in vivo: comparisons with 2,3,7,8-tetrachlorodibenzo-p-dioxin.