The support of steroid aromatization by mitochondrial metabolic activities of the human placenta

Regulation of aromatase expression: Potential therapeutic insight into breast cancer treatment

Estrogen signaling has been implicated in hormone-dependent breast cancer which constitutes >75% of breast cancer diagnosis and other malignancies. Aromatase, the key enzyme involved in the synthesis of estrogen, is often dysregulated in breast cancers. This has led to the administration of aromatase-inhibitors (AIs), commonly used for hormone-dependent breast cancers. Unfortunately, the increasing development of acquired resistance to the current AIs and modulators of estrogen receptors, following initial disease steadiness, has posed a serious clinical challenge in breast cancer treatment. In this review we highlight historical and recent advances on the transcriptional and post-translational regulation of aromatase in both physiological and pathological contexts. We also discuss the different drug combinations targeting various tumor promoting cell signaling pathways currently being developed and tested both in laboratory settings and in the clinic.

Aromatisation of steroids in the bivalve Mytilus trossulus

In this study, we demonstrated the presence of the enzymatic complex able to perform aromatization (estrogen synthesis) in both, the microsomal and mitochondrial fractions of gills and gonads from Mytilus trossulus. Based on in vitro experiments, we highlighted the importance of temperature as the limiting factor of aromatisation efficiency (AE) in mussels. After testing range of temperatures (4–23 °C), the highest AE was found during incubation at 8 °C and pH 7.6 (41.66 pmol/h/mg protein in gills and 58.37 pmol/h/mg protein in gonads). The results were confirmed during field studies where the most efficient aromatisation occurred in bivalves collected in spring while the least effective in those collected in winter. During in vitro studies, AE turned out to be more intensive in female gonads than in male gonads. The process was also more intensive in mitochondrial fraction than in microsomal one (62.97 pmol/h/mg protein in male gills and 73.94 pmol/h/mg protein in female gonads). Enzymatic complex (aromatase-like enzyme) catalysing aromatisation in mussels was found to be insensitive to inhibitory effect of selective inhibitors of mammalian aromatase such as letrozole and anastrazole, suggesting its different structure from vertebrate aromatase. Further in vivo studies using ¹³C-labeled steroids at 8 °C temperature window confirmed that bivalves are able to uptake testosterone and androstenedione from the ambient environment and metabolise them to estrone and 17β-estradiol thus confirming endogenous estrogen’ synthesis.

The expression and environmental regulation of P450 enzymes in human placenta

The human placenta oxidizes several xenobiotics, although the spectrum of substrates and metabolic activities when compared with the liver appears somewhat restricted. Maternal cigarette smoking or PCB exposure increases the expression of CYP1A1. This induced activity is able to catalyze the activation of benzo(a)pyrene (B(a)P) into DNA-bound products, both in vitro and in vivo. Studies on adult human liver bolster the concept that CYP1A1 and -1A2 are differentially expressed in hepatic and extrahepatic tissues. Studies with cDNA probe or enzyme specific antibodies and substrates for CYP2A, -2B, -2C, -2D, and -2E gene products have yielded negative results. There are only minimal activities that can be found in substantial quantities in placentas without maternal smoking; one example is 7-ethoxycoumarin O-deethylase (ECOD). Aromatase and cholesterol side-chain cleaving P450 mRNAs, proteins, and activities are measurable in human placentas and do not seem to be affected by maternal cigarette smoking.