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

Microbial Modulation of Digoxin Bioavailability: A Pharmacomicrobiome Perspective on Eggerthella lenta's Role in Steroid-Like Drug Metabolism and Precision Therapeutics

Digoxin is a cardiac glycoside used to treat heart failure and atrial fibrillation, but its narrow therapeutic index makes precise dosing critical. The effectiveness of digoxin is influenced by individual variations in drug metabolism, with recent studies showing that gut microbiota, particularly Eggerthella lenta (E. lenta), plays a key role. E. lenta can convert digoxin into its inactive form, dihydrodigoxin, potentially reducing its therapeutic efficacy. This paper explores how E. lenta affects the biotransformation of digoxin and other drugs like L-dopa and resveratrol. The aim is to investigate how the presence of E. lenta in the gut influences drug metabolism and therapeutic outcomes. The review also examines the broader implications of microbiome-driven drug interactions and highlights the need for precision dosing strategies based on an individual's microbiome composition which is also essential for patients with high E. lenta colonization. Further research into microbiome-driven drug and sterol interactions is needed to optimize treatment strategies, ensuring personalized and effective patient care.

An Unusual Cause of Hypokalemia to Consider

Apparent mineralocorticoid excess syndrome is a rare disorder that can be acquired through inhibition of the enzyme 11 β-hydroxysteroid dehydrogenase type 2 by various substances such as bile acids. We report the case of a 61-year-old woman presenting with painless jaundice. Computed tomography demonstrated a pulmonary as well as a pancreatic tumor, with multiple metastases and dilated bile ducts. Laboratory findings showed persistent hypokalemia despite aggressive enteral and parenteral supplementation, as well as hypertension, metabolic alkalosis, and elevated cholestasis enzymes. Urinary potassium excretion was inappropriately high. Plasma aldosterone concentration was 0.97 ng/dL (26.91 pmol/L) (reference range, 2.21-25.30 ng/dL [61.31-701.82 pmol/L]) and direct renin concentration was 3.9 mIU/L (2.1 ng/L) (reference range, 4.4-46.1 mIU/L [2.53-27.42 ng/L]). Endogenous hypercortisolism was ruled out. After the placement of a metal biliary stent via endoscopic retrograde cholangiopancreatography and the subsequent decrease in cholestasis enzyme levels, potassium levels, hypertension, and metabolic alkalosis gradually normalized. The case was ultimately diagnosed as apparent mineralocorticoid excess syndrome resulting from 11 β-hydroxysteroid dehydrogenase type 2 inhibition caused by elevated bile acids secondary to malignant obstruction of the biliary tract.

Update on Low-Renin Hypertension: Current Understanding and Future Direction

Low-renin hypertension is common and affects 1 in 4 people with hypertension. Understanding the different causes and management of low-renin hypertension is becoming increasingly relevant as renin measurements are more widely ordered in clinical practice. Importantly, many people with low-renin hypertension do not fit traditional definitions of known causes, and the approach to management of these people is not unclear. This review provides an overview of our evolving understanding of the causes of low-renin hypertension, the expanding spectrums of pathophysiology, key differentiating characteristics, distinct management strategies, and highlights our knowledge gaps. It is important to distinguish the underlying pathophysiology of an individual with low-renin hypertension to individualize treatment.

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.