Modulation of 11β-hydroxysteroid dehydrogenase functions by the cloud of endogenous metabolites in a local microenvironment: The glycyrrhetinic acid-like factor (GALF) hypothesis

Melatonin, BAG-1 and cortisol circadian interactions in tumor pathogenesis and patterned immune responses

A dysregulated circadian rhythm is significantly associated with cancer risk, as is aging. Both aging and circadian dysregulation show suppressed pineal melatonin, which is indicated in many studies to be linked to cancer risk and progression. Another independently investigated aspect of the circadian rhythm is the cortisol awakening response (CAR), which is linked to stress-associated hypothalamus-pituitary-adrenal (HPA) axis activation. CAR and HPA axis activity are primarily mediated via activation of the glucocorticoid receptor (GR), which drives patterned gene expression via binding to the promotors of glucocorticoid response element (GRE)-expressing genes. Recent data shows that the GR can be prevented from nuclear translocation by the B cell lymphoma-2 (Bcl-2)-associated athanogene 1 (BAG-1), which translocates the GR to mitochondria, where it can have diverse effects. Melatonin also suppresses GR nuclear translocation by maintaining the GR in a complex with heat shock protein 90 (Hsp90). Melatonin, directly and/or epigenetically, can upregulate BAG-1, suggesting that the dramatic 10-fold decrease in pineal melatonin from adolescence to the ninth decade of life will attenuate the capacity of night-time melatonin to modulate the effects of the early morning CAR. The interactions of pineal melatonin/BAG-1/Hsp90 with the CAR are proposed to underpin how aging and circadian dysregulation are associated with cancer risk. This may be mediated via differential effects of melatonin/BAG-1/Hsp90/GR in different cells of microenvironments across the body, from which tumors emerge. This provides a model of cancer pathogenesis that better integrates previously disparate bodies of data, including how immune cells are regulated by cancer cells in the tumor microenvironment, at least partly via the cancer cell regulation of the tryptophan-melatonin pathway. This has a number of future research and treatment implications.

In vitro methods to assess 11β-hydroxysteroid dehydrogenase type 2 activity

11β-Hydroxysteroid dehydrogenase type 2 (11β-HSD2) converts active 11β-hydroxyglucocorticoids to their inactive 11-keto forms, fine-tuning the activation of mineralocorticoid and glucocorticoid receptors. 11β-HSD2 is expressed in mineralocorticoid target tissues such as renal distal tubules and cortical collecting ducts, and distal colon, but also in placenta where it acts as a barrier to reduce the amount of maternal glucocorticoids that reach the fetus. Disruption of 11β-HSD2 activity by genetic defects or inhibitors causes the syndrome of apparent mineralocorticoid excess (AME), characterized by hypernatremia, hypokalemia and hypertension. Secondary hypertension due to 11β-HSD2 inhibition has been observed upon consumption of excessive amounts of licorice and in patients treated with the azole fungicides posaconazole and itraconazole. Furthermore, inhibition of 11β-HSD2 during pregnancy with elevated exposure of the fetus to cortisol can cause neurological complications with a lower intelligence quotient, higher odds of attention deficit and hyperactivity disorder as well as metabolic reprogramming with an increased risk of cardio-metabolic disease in adulthood. This chapter describes in vitro methods for the determination of 11β-HSD2 activity that can be applied to identify inhibitors that may cause secondary hypertension and characterize the enzyme's activity in disease models. The included decision tree and the list of methods with their advantages and disadvantages aim to enable the reader to select and apply an in vitro method suitable for the scientific question and the equipment available in the respective laboratory.