On the Mechanism Underlying (23S)-25-Dehydro-1α(OH)-vitamin D3-26,23-lactone Antagonism of hVDRwt Gene Activation and Its Switch to a Superagonist

(23S)-25-Dehydro-1α(OH)-vitamin D3-26,23-lactone (MK) is an antagonist of the 1α,25(OH)2-vitamin D3 (1,25D)/human nuclear vitamin D receptor (hVDR) transcription initiation complex, where the activation helix (i.e. helix-12) is closed. To study the mode of antagonism of MK an hVDR mutant library was designed to alter the free molecular volume in the region of the hVDR ligand binding pocket occupied by the ligand side-chain atoms (i.e. proximal to helix-12). The 1,25D-hVDR structure-function studies demonstrate that 1) van der Waals contacts between helix-12 residues Leu-414 and Val-418 and 1,25D enhance the stability of the closed helix-12 conformer and 2) removal of the side-chain H-bonds to His-305(F) and/or His-397(F) have no effect on 1,25D transactivation, even though they reduce the binding affinity of 1,25D. The MK structure-function results demonstrate that the His-305, Leu-404, Leu-414, and Val-418 mutations, which increase the free volume of the hVDR ligand binding pocket, significantly enhance MK antagonist potency. Surprisingly, the H305F and H305F/H397F mutations turn MK into a VDR superagonist (EC50 ∼ 0.05 nm) but do not concomitantly alter MK binding affinity. Molecular modeling studies demonstrate that MK antagonism stems from its side chain energetically preferring a pose in the VDR ligand binding pocket where its terminal C26-methylene atom is far removed from helix-12. MK superagonism results from an energetically favored increase in interaction between Leu-404/Val-418 and C26, resulting in an increase in the stability and population of the closed, helix-12 conformer. Finally, the results/model generated, coupled with application of a VDR ensemble allosterics model, provide an understanding for the species specificity of MK

Examining the potential clinical value of curcumin in the prevention and diagnosis of Alzheimer’s disease

Curcumin derived from turmeric is well documented for its anti-carcinogenic, antioxidant and anti-inflammatory properties. Recent studies show that curcumin also possesses neuroprotective and cognitive-enhancing properties that may help delay or prevent neurodegenerative diseases, including Alzheimer’s disease (AD). Currently, clinical diagnosis of AD is onerous, and it is primarily based on the exclusion of other causes of dementia. In addition, phase III clinical trials of potential treatments have mostly failed, leaving disease-modifying interventions elusive. AD can be characterised neuropathologically by the deposition of extracellular ß amyloid (Aß) plaques and intracellular accumulation of tau-containing neurofibrillary tangles. Disruptions in Aß metabolism/clearance contribute to AD pathogenesis. In vitro studies have shown that Aß metabolism is altered by curcumin, and animal studies report that curcumin may influence brain function and the development of dementia, because of its antioxidant and anti-inflammatory properties, as well as its ability to influence Aß metabolism. However, clinical studies of curcumin have revealed limited effects to date, most likely because of curcumin’s relatively low solubility and bioavailability, and because of selection of cohorts with diagnosed AD, in whom there is already major neuropathology. However, the fresh approach of targeting early AD pathology (by treating healthy, pre-clinical and mild cognitive impairment-stage cohorts) combined with new curcumin formulations that increase bioavailability is renewing optimism concerning curcumin-based therapy. The aim of this paper is to review the current evidence supporting an association between curcumin and modulation of AD pathology, including in vitro and in vivo studies. We also review the use of curcumin in emerging retinal imaging technology, as a fluorochrome for AD diagnostics