Metabolic stability of 3-epi-1α,25-dihydroxyvitamin D3 over 1 α 25-dihydroxyvitamin D3: metabolism and molecular docking studies using rat CYP24A1.

3-epi-1α,25-dihydroxyvitamin D3 (3-epi-1α,25(OH)2D3), a natural metabolite of 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3), exhibits potent vitamin D receptor (VDR)-mediated actions such as inhibition of keratinocyte growth or suppression of parathyroid hormone secretion. These VDR-mediated actions of 3-epi-1α,25(OH)2D3 needed an explanation as 3-epi-1α,25(OH)2D3, unlike 1α,25(OH)2D3, exhibits low affinity towards VDR. Metabolic stability of 3-epi-1α,25(OH)2D3 over 1α,25(OH)2D3 has been hypothesized as a possible explanation.

1α,25(OH)2-3-epi-vitamin D3, a natural physiological metabolite of vitamin D3: its synthesis, biological activity and crystal structure with its receptor.

Background: The 1α,25-dihydroxy-3-epi-vitamin-D3 (1α,25(OH)2-3-epi-D3), a natural metabolite of the seco-steroid vitamin D3, exerts its biological activity through binding to its cognate vitamin D nuclear receptor (VDR), a ligand dependent transcription regulator. In vivo action of 1α,25(OH)2-3-epi-D3 is tissue-specific and exhibits lowest calcemic effect compared to that induced by 1α,25(OH)2D3. To further unveil the structural mechanism and structure-activity relationships of 1α,25(OH)2-3-epi-D3 and its receptor complex, we characterized some of its in vitro biological properties and solved its crystal structure complexed with human VDR ligand-binding domain (LBD).

Interactions of natural polyamines with mammalian proteins.

The ubiquitously expressed natural polyamines putrescine, spermidine, and spermine are small, flexible cationic compounds that exert pleiotropic actions on various regulatory systems and, accordingly, are essentially involved in diverse life functions. These roles of polyamines result from their capability to interact with negatively charged regions of all major classes of biomolecules, which might act in response by changing their structures and functions. The present review deals with polyamine-protein interactions, thereby focusing on mammalian proteins.

A new insight into the role of rat cytochrome P450 24A1 in metabolism of selective analogs of 1α,25-dihydroxyvitamin D₃.

We examined the metabolism of two synthetic analogs of 1α,25-dihydroxyvitamin D₃ (1), namely 1α,25-dihydroxy-16-ene-23-yne-vitamin D₃ (2) and 1α,25-dihydroxy-16-ene-23-yne-26,27-dimethyl-vitamin D₃ (4) using rat cytochrome P450 24A1 (CYP24A1) in a reconstituted system. We noted that 2 is metabolized into a single metabolite identified as C26-hydroxy-2 while 4 is metabolized into two metabolites, identified as C26-hydroxy-4 and C26a-hydroxy-4. The structural modification of adding methyl groups to the side chain of 1 as in 4 is also featured in another analog, 1α,25-dihydroxy-22,24-diene-24,26,27-trihomo-vitamin D₃ (6).

Cytochromes P450 are essential players in the vitamin D signaling system.

From earliest development on, the vitamin D receptor (VDR) is expressed in most cells of the mammalian body. The VDR is a nuclear, ligand-induced transcription factor that regulates in complex with hormonally active vitamin D the expression of more than 900 genes involved in a wide array of physiological functions (e.g.

Polyamines: naturally occurring small molecule modulators of electrostatic protein-protein interactions.

Modulations of protein-protein interactions are a key step in regulating protein function, especially in networks. Modulators of these interactions are supposed to be candidates for the development of novel drugs. Here, we describe the role of the small, polycationic and highly abundant natural polyamines that could efficiently bind to charged spots at protein interfaces as modulators of such protein-protein interactions.

Sterol 14alpha-demethylase as a potential target for antitrypanosomal therapy: enzyme inhibition and parasite cell growth.

Sterol 14alpha-demethylases (CYP51) serve as primary targets for antifungal drugs, and specific inhibition of CYP51s in protozoan parasites Trypanosoma brucei (TB) and Trypanosoma cruzi (TC) might provide an effective treatment strategy for human trypanosomiases. Primary inhibitor selection is based initially on the cytochrome P450 spectral response to ligand binding. Ligands that demonstrate strongest binding parameters were examined as inhibitors of reconstituted TB and TC CYP51 activity in vitro.

Inhibition of cytochromes p450: existing and new promising therapeutic targets.

Mammalian cytochromes P450 have been shown to play highly important roles in the metabolism of drugs and xenobiotics as well as in the biosynthesis of a variety of endogenous compounds, many of them displaying hormonal function. The role of P450s as therapeutic targets is still inadequately recognized although several P450 inhibitors became efficient drugs that even reached blockbuster status. Here, we try to give a comprehensive overview on cytochromes P450s, which are already well-established targets - particularly focussing on the treatment of infectious diseases, metabolic disorders and cancer - and on those, which have a high potential to become successful targets.

Selective inhibitors of vitamin D metabolism--new concepts and perspectives.

Background: Levels of active vitamin D (VD) are controlled by synthesis via CYP27B1 and self-induced metabolism by CYP24A1. Unbalanced high CYP24A1 expression due to induction by diverse endogenous compounds and xenobiotics, and amplification found in various tumours, might lead to local VD deficiency, thereby causing/reinforcing disorders.

Materials And Methods: Using primary human keratinocytes, CYP24A1 expression was examined at the mRNA level by dot-blot and Northern blot hybridization, and at the enzyme activity level by analysing HPLC profiles from incubations with 3H-labelled VD metabolites.

C-25 hydroxylation of 1alpha,24(R)-dihydroxyvitamin D3 is catalyzed by 25-hydroxyvitamin D3-24-hydroxylase (CYP24A1): metabolism studies with human keratinocytes and rat recombinant CYP24A1.

Recently, 25-hydroxyvitamin D3-24-hydroxylase (CYP24A1) has been shown to catalyze not only hydroxylation at C-24 but also hydroxylations at C-23 and C-26 of the secosteroid hormone 1alpha, 25-dihydroxyvitamin D3 (1alpha,25(OH)2D3). It remains to be determined whether CYP24A1 has the ability to hydroxylate vitamin D3 compounds at C-25. 1alpha,24(R)-dihydroxyvitamin D3 (1alpha,24(R)(OH)2D3) is a non-25-hydroxylated synthetic vitamin D3 analog that is presently being used as an antipsoriatic drug.

Induction of apoptosis by vitamin D metabolites and analogs in a glioma cell line.

Gliomas are the most common malignant tumors in brain. Recent studies demonstrate the capacity of 1alpha,25(OH)2D3 to specifically induce cell death (apoptosis) in model glioma cell lines and in primary cultures from tumor tissue, but not in primary astrocytes. In spite of this promising activity, a broad therapeutic application of vitamin D metabolites and analogs is still restricted because of their poor bioavailability and their hypercalcemic actions.

Combination of vitamin D metabolites with selective inhibitors of vitamin D metabolism.

1alpha,25(OH)2D3 exerts antiproliferative, differentiating effects on many cell types, including cancer tissues. In most of its target cells, levels of 1alpha,25(OH)2D3 are regulated by local synthesis via CYP27B and metabolism via CYP24. Rapidly induced by vitamin D, CYP24 repeatedly hydroxylates the vitamin D side chain and ultimately terminates hormonal activity.

Inhibitors of vitamin D hydroxylases: structure-activity relationships.

Aiming at new drugs to efficiently treat diseases, in which either increased or decreased levels of active vitamin D are desirable, we have designed some 400 structurally different azole-type inhibitors and examined their capacity to selectively block vitamin D metabolism by CYP24 or synthesis by CYP27B, in human keratinocytes. Based on resulting data, we built pharmacophore models of the active sites using commercial software. The overlay of potent selective compounds indicated similar docking modes in the two-substrate pockets and allowed for identification of bioactive conformations.