Synthesis of an Endogenous Steroidal Na Pump Inhibitor Marinobufagenin, Implicated in Human Cardiovascular Diseases, Is Initiated by CYP27A1 via Bile Acid Pathway

Abstract

Background The bioactive steroid, marinobufagenin (MBG), is an endogenous Na/K-ATPase bufadienolide inhibitor that is synthetized by adrenocortical and placental cells. MBG binding to Na/K-ATPase initiates pro-fibrotic cell signaling, and heightened MBG levels are implicated in the pathogenesis of hypertension, preeclampsia and chronic kidney disease. Steroids are derived from cholesterol through the “traditional” steroidogenesis pathway initiated by enzyme CYP11A1, and via the “acidic” bile acid pathway, which is controlled by enzyme CYP27A1. The mechanism of MBG biosynthesis in mammals however remains unknown. Methods and Results Here we show that post-transcriptional silencing of the CYP27A1 gene in human trophoblast and rat adrenocortical cells reduced the expression of CYP27A1 mRNA by 70%, reduced total bile acids 2-fold, and MBG levels by 67%, compared to non-treated cells or cells transfected with non-targeting siRNA. In contrast, silencing of the CYP11A1 gene did not affect MBG production in either cell culture, but suppressed production of progesterone 2-fold in human trophoblast cells, and of corticosterone by 90% in rat adrenocortical cells, compared to cells transfected with non-targeting siRNA. In vivo, in a high salt administration experiment, male and female Dahl-S rats became hypertensive after 4 weeks on a high NaCl diet, their plasma MBG levels doubled, and adrenocortical CYP27A1 mRNA and protein increased 1.6-fold and 2.0-fold. Conclusions Therefore, the endogenous steroidal Na/K-ATPase inhibitor, MBG, is synthesized in mammalian placenta and adrenal cortex from cholesterol through the novel “acidic” bile acid pathway. These findings will help to understand the role of MBG in highly prevalent human cardiovascular diseases.

Multifactorial Effects on Different Types of Brain Cells Contribute to Ammonia Toxicity

“…Ammonia detoxification recently been studied by Fedorova et al [192] in adrenocortical and placental cells and found to occur from cholesterol via the acidic bile acid pathway, which is controlled by enzyme mitochondrial sterol 27-hydroxylase (CYP27A1). In macrophages the needed cholesterol trafficking from the outer to the inner mitochondrial membrane is mediated by a highly regulated multimeric protein complex.…”

Associations between abnormal vitamin D metabolism pathway function and non‑small cell lung cancer

“…However, the identification of specific biomarkers for the early diagnosis and prognosis of lung cancer is still required (17). The most bioactive metabolite of vitamin D, 1α,25(OH) 2 D 3 has been confirmed to contribute various non-endocrine functions in addition to maintaining calcium stability; including anti-proliferative activity, induction of cell differentiation, promotion of cell cycle stagnation and apoptosis, inhibiting cytopoiesis and regulating tumor occurrence and development (18,19). Vitamin D generates 1α,25(OH) 2 CYP27A1, CYP27B1, and CYP24A1 belong to the cytochrome P450 (CYP450) family.…”

Genetic Control of Serum Marinobufagenin in the Spontaneously Hypertensive Rat and the Relationship to Blood Pressure

“…Also, it has provided evidence that material with MBG properties can be detected and is related to cholesterol metabolism in adrenocortical cells. Specifically, we and others have shown that production of immunologically detected MBG is independent of cholesterol side chain cleavage, can be interrupted by blockade of de novo cholesterol synthesis, and appears to involve modification of the cholesterol side chain by a pathway known to be involved in bile acid synthesis …”

“…An important area where increased knowledge is needed is identification of genes involved in the regulation and biosynthesis of this proposed endocrine material. At present, there is evidence that the CSs that can be detected in mammals by several indirect assays (functional and immunologic) may have an endogenous origin from steroid biosynthesis and may involve modification of the cholesterol side chain by CYP27A1 . However, studies to investigate the genetic control of circulating CS have not been reported.…”

“…However, numerous independent investigations, including those using the most modern analytical chemistry methods, have shown that ouabain is not present in humans . We and others have developed evidence in support of similarity between CS and the vertebrate steroid, marinobufagenin (MBG) . MBG is a CS aglycone synthesized by members of the Bufonidae family of true toads .…”