Myricetin: a potential plant-derived anticancer bioactive compound-an updated overview

The globe is currently confronting a global fight against the deadliest cancer sickness. Chemotherapy, hormonal therapy, surgery, and radiation therapy are among cancer treatment options. Still, these treatments can induce patient side effects, including recurrence, multidrug resistance, fever, and weakness. As a result, the scientific community is always working on natural phytochemical substances. Numerous phytochemical compounds, including taxol analogues, vinca alkaloids such as vincristine and vinblastine, and podophyllotoxin analogues, are currently undergoing testing and have shown promising results against a number of the deadliest diseases, as well as considerable advantages due to their safety and low cost. According to research, secondary plant metabolites such as myricetin, a flavonoid in berries, herbs, and walnuts, have emerged as valuable bio-agents for cancer prevention. Myricetin and its derivatives have antiinflammatory, anticancer, apoptosis-inducing, and anticarcinogenic properties and can prevent cancer cell proliferation. Multiple studies have found that myricetin has anticancer characteristics in various malignancies, including colon, breast, prostate, bladder, and pancreatic cancers. Current knowledge of the anticancer effects of myricetin reveals its promise as a potentially bioactive chemical produced from plants for the prevention and treatment of cancer. This review aimed to study the numerous bioactivities, mode of action, and modification of several cellular processes that myricetin possesses to impede the spread of cancer cells. This review also addresses the challenges and future prospects of using myricetin as a anticancer drug.

Ursolic acid: a pentacyclic triterpenoid that exhibits anticancer therapeutic potential by modulating multiple oncogenic targets

The world is currently facing a global challenge against neoplastic diseases. Chemotherapy, hormonal therapy, surgery, and radiation therapy are some approaches used to treat cancer. However, these treatments are frequently causing side effects in patients, such as multidrug resistance, fever, weakness, and allergy, among others side effects. As a result, current research has focused on phytochemical compounds isolated from plants to treat deadly cancers. Plants are excellent resources of bioactive molecules, and many natural molecules have exceptional anticancer properties. They produce diverse anticancer derivatives such as alkaloids, terpenoids, flavonoids, pigments, and tannins, which have powerful anticancer activities against various cancer cell lines and animal models. Because of their safety, eco-friendly, and cost-effective nature, research communities have recently focused on various phytochemical bioactive molecules. Ursolic acid (UA) and its derivative compounds have anti-inflammatory, anticancer, apoptosis induction, anti-carcinogenic, and anti-breast cancer proliferation properties. Ursolic acid (UA) can improve the clinical management of human cancer because it inhibits cancer cell viability and proliferation, preventing tumour angiogenesis and metastatic activity. Therefore, the present article focuses on numerous bioactivities of Ursolic acid (UA), which can inhibit cancer cell production, mechanism of action, and modulation of anticancer properties via regulating various cellular processes.

Vacuum epidural cyst with acute neurological presentation. A case report

The widespread use of MRI in the assessment of low back pain has led to increased detection of degenerative cysts of the spine, which was essentially a surgical diagnosis earlier. The awareness of degenerative cysts, the significance of their role in the etiology of radicular and back pain and their effective management is evolving. We describe a case of bilateral, gas-filled lumbar facet synovial/ ganglion cysts causing focal arachnoid inflammation and lateral lumbar canal stenosis.

Distribution of malignant neoplasms reported at different pathology centers and hospitals in Jaipur, Rajasthan

BACKGROUND

Cancer data from Rajasthan are limited. Only two studies, one from Western Rajasthan, and the other from Eastern Rajasthan have been published by Sharma et al. in 1992 and 1996.

AIMS

To put the cancer profile from this region in proper perspective, we conducted the present study on the patterns of various malignancies in Jaipur region, i.e., Eastern Rajasthan. SETTING AND DESIGN AND MATERIAL AND METHODS: The study spans over one and half decade (1990-2004) and is based on a retrospective six-year sample analysis of approximately 200,000 histopathological and cytological reports for the years 1990, 1991, 1996, 1999, 2001 and 2004.

RESULTS

A total of 21,868 cancers were recorded in the six sample years. There were 59.11% (12,926) males and 40.89% (8942) females, with the male to female ratio being 1.45:1. Organ wise, lung (8.45%), prostate (7.12%), brain (6.04%), urinary bladder (5.31%), esophagus (4.67%) and tongue (4.60%) are most common sites involved in males with regard to frequency, whereas breast (20.44%), cervix (14.99%), ovary (4.35%), brain (3.80%), esophagus (3.67%), uterus (3.01%) and rectum (2.80%) are common sites for malignancies in females.

CONCLUSIONS

Significant findings were a higher frequency of cancers of the prostate, urinary bladder, and brain in males along with gall bladder cancers in females. Our figures have been compared with the national data.

Genetic typing of bovine viral diarrhoea virus isolates from India

Thirteen BVDV isolates collected in four geographic regions of India between 2000 and 2002 were typed in 5'-UTR. To confirm results of genetic typing, selected viruses were also analysed in the N(pro) region. Phylogenetic analysis revealed that all Indian BVDV isolates belong to BVDV-1b (Osloss-like group). Despite a long distance between the farms from which the viruses were isolated there was no correlation between the origin of viral isolates and their position in a phylogenetic tree. Higher genetic similarity of Indian BVDV isolates was observed most probably due to the uncontrolled movement of cattle as well as the uncontrolled use of semen from bulls for breeding of local and farm cattle in different states of India.

Affinity labeling of rat cytochrome P450C24 (CYP24) and identification of Ser57 as an active site residue

25-hydroxyvitamin D(3)- or 1alpha,25-dihydroxyvitamin D(3)-24R-hydroxylase (cytochromeP450C24 or CYP24) has a dual role of removing 25-OH-D(3) from circulation and excess 1,25(OH)(2)D(3) from kidney. As a result, CYP24 is an important multifunctional regulatory enzyme that maintains essential tissue-levels of Vitamin D hormone. As a part of our continuing interest in structure-function studies characterizing various binding proteins in the Vitamin D endocrine system, we targeted recombinant rat CYP24 with a radiolabeled 25-OH-D(3) affinity analog, and showed that the 25-OH-D(3)-binding site was specifically labeled by this analog. An affinity labeled sample of CYP24 was subjected to MS/MS analysis, which identified Ser57 as the only amino acid residue in the entire length of the protein that was covalently modified by this analog. Site-directed mutagenesis was conducted to validate the role of Ser57 towards substrate-binding. S57A mutant displayed significantly lower binding capacity for 25-OH-D(3) and 1,25(OH)(2)D(3). On the other hand, S57D mutant strongly enhanced binding for the substrates and conversion of 1,25(OH)(2)D(3) to calcitroic acid. The affinity probe was anchored via the 3-hydroxyl group of 25-OH-D(3). Therefore, these results suggested that the 3-hydroxyl group (of 25-OH-D(3) and 1,25(OH)(2)D(3)) in the S57D mutant could be stabilized by hydrogen bonding or a salt bridge leading to enhanced substrate affinity and metabolism.

Baculovirus-expressed vitamin D-binding protein-macrophage activating factor (DBP-maf) activates osteoclasts and binding of 25-hydroxyvitamin D(3) does not influence this activity

Vitamin D-binding protein (DBP) is a multi-functional serum protein that is converted to vitamin D-binding protein-macrophage activating factor (DBP-maf) by post-translational modification. DBP-maf is a new cytokine that mediates bone resorption by activating osteoclasts, which are responsible for resorption of bone. Defective osteoclast activation leads to disorders like osteopetrosis, characterized by excessive accumulation of bone mass. Previous studies demonstrated that two nonallelic mutations in the rat with osteopetrosis have independent defects in the cascade involved in the conversion of DBP to DBP-maf. The skeletal defects associated with osteopetrosis are corrected in these mutants with in vivo DBP-maf treatment. This study evaluates the effects of various forms of DBP-maf (native, recombinant, and 25-hydroxyvitamin D(3) bound) on osteoclast function in vitro in order to determine some of the structural requirements of this protein that relate to bone resorbing activities. Osteoclast activity was determined by evaluating pit formation using osteoclasts, isolated from the long bones of newborn rats, incubated on calcium phosphate coated, thin film, Ostologic MultiTest Slides. Incubation of osteoclasts with ex vivo generated native DBP-maf resulted in a dose dependent, statistically significant, activation of the osteoclasts. The activation was similar whether or not the vitamin D binding site of the DBP-maf was occupied. The level of activity in response to DBP-maf was greater than that elicited by optimal doses of other known stimulators (PTH and 1,25(OH(2)D(3)) of osteoclast function. Furthermore, another potent macrophage activating factor, interferon--gamma, had no effect on osteoclast activity. The activated form of a full length recombinant DBP, expressed in E. coli showed no activity in the in vitro assay. Contrary to this finding, baculovirus-expressed recombinant DBP-maf demonstrated significant osteoclast activating activity. The normal conversion of DBP to DBP-maf requires the selective removal of galactose and sialic acid from the third domain of the protein. Hence, the differential effects of the two recombinant forms of DBP-maf is most likely related to glycosylation; E. coli expressed recombinant DBP is non-glycosylated, whereas the baculovirus expressed form is glycosylated. These data support the essential role of glycosylation for the osteoclast activating property of DBP-maf.

Why do we need a three-dimensional architecture of the ligand-binding domain of the nuclear 1alpha,25-dihydroxyvitamin D(3) receptor?

Highly specific binding of 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) by vitamin D receptor (VDR), a nuclear transcriptional factor, activates a genomic mechanism that is manifested in the multiple biologic properties of 1alpha,25(OH)(2)D(3). Numerous synthetic analogs of 1alpha,25(OH)(2)D(3) have been employed to study the interaction between 1alpha,25(OH)(2)D(3) and VDR, and to identify structural markers in 1alpha,25(OH)(2)D(3) that are important for VDR-binding. On the other hand the three-dimensional structure of VDR remained elusive till very recently. In the present study we employed affinity labeling (by 1alpha,25-dihydroxyvitamin D(3)-3-bromoacetate, 1alpha,25(OH)(2)D(3)-3-BE) of VDR to identify C(288) as the anchoring residue for the 3-hydroxyl group of 1alpha,25(OH)(2)D(3) inside the ligand-binding domain of VDR (VDR-LBD). In addition we carried out mutation/hormone-binding analyses to determine the importance of M(284) and W(286) toward hormone binding. We incorporated this information with the three-dimensional structure of the LBD of progesterone receptor to develop a homology-extension model of VDR-LBD. This model identified several amino acid residues as ligand-contact points inside the LBD. Mutational and hormone-binding analyses of these residues verified the structure-functional authenticity of this model, in comparison with the crystal structure of VDR, bound to 1alpha,25(OH)(2)D(3).

Molecular modeling, affinity labeling, and site-directed mutagenesis define the key points of interaction between the ligand-binding domain of the vitamin D nuclear receptor and 1 alpha,25-dihydroxyvitamin D3

We have combined molecular modeling and classical structure-function techniques to define the interactions between the ligand-binding domain (LBD) of the vitamin D nuclear receptor (VDR) and its natural ligand, 1alpha,25-dihydroxyvitamin D(3) [1alpha,25-(OH)(2)D(3)]. The affinity analogue 1alpha,25-(OH)(2)D(3)-3-bromoacetate exclusively labeled Cys-288 in the VDR-LBD. Mutation of C288 to glycine abolished this affinity labeling, whereas the VDR-LBD mutants C337G and C369G (other conserved cysteines in the VDR-LBD) were labeled similarly to the wild-type protein. These results revealed that the A-ring 3-OH group docks next to C288 in the binding pocket. We further mutated M284 and W286 (separately creating M284A, M284S, W286A, and W286F) and caused severe loss of ligand binding, indicating the crucial role played by the contiguous segment between M284 and C288. Alignment of the VDR-LBD sequence with the sequences of nuclear receptor LBDs of known 3-D structure positioned M284 and W286 in the presumed beta-hairpin of the molecule, thereby identifying it as the region contacting the A-ring of 1alpha, 25-(OH)(2)D(3). From the multiple sequence alignment, we developed a homologous extension model of the VDR-LBD. The model has a canonical nuclear receptor fold with helices H1-H12 and a single beta hairpin but lacks the long insert (residues 161-221) between H2 and H3. We docked the alpha-conformation of the A-ring into the binding pocket first so as to incorporate the above-noted interacting residues. The model predicts hydrogen bonding contacts between ligand and protein at S237 and D299 as well as at the site of the natural mutation R274L. Mutation of S237 or D299 to alanine largely abolished ligand binding, whereas changing K302, a nonligand-contacting residue, to alanine left binding unaffected. In the "activation" helix 12, the model places V418 closest to the ligand, and, consistent with this prediction, the mutation V418S abolished ligand binding. The studies together have enabled us to identify 1alpha,25-(OH)(2)D(3)-binding motifs in the ligand-binding pocket of VDR.

Development of an affinity-driven cross-linker: isolation of a vitamin D receptor associated factor

A vitamin D analogue containing an affinity and a photoaffinity probe (affinity-driven cross-linker, Double Label) was synthesized. An unknown factor, associated with vitamin D receptor (VDR), was isolated from rat liver nuclear extract using a GST-VDR-ligand-binding domain fusion protein (GST-VDR-LBD), affinity labeled with Double Label, and protein-protein cross-linking by photolysis.

Probing the vitamin D sterol-binding pocket of human vitamin D-binding protein with bromoacetate affinity labeling reagents containing the affinity probe at C-3, C-6, C-11, and C-19 positions of parent vitamin D sterols

The multiple physiological properties of vitamin D-binding protein (DBP) include organ-specific transportation of vitamin D(3) and its metabolites, manifested by its ability to bind vitamin D sterols with high affinity. In the present investigation we probed the vitamin D sterol-binding pocket of human DBP with affinity labeling analogs of 25-hydroxyvitamin D(3) ¿25-OH-D(3) and 1, 25-dihydroxyvitamin D(3) ¿1,25(OH)(2)D(3) containing bromoacetate alkylating probe at C-3 (A-ring), C-6 (triene), C-11 (C-ring), and C-19 (exocyclic methylene) of the parent sterol. Competitive binding assays with DBP showed approximately 22-, 68-, and 2000-fold decrease in the binding of 1,25(OH)(2)-D(3)-11-BE, 25-OH-D(3)-3-BE, and 25-OH-D(3)-6-BE, respectively, compared to that seen with 25-OH-D(3), while there was no significant difference in the DBP-binding affinity of 25-OH-D(3)-19-BE and 25-OH-D(3). Surprisingly, ¿(14)C25-OH-D(3)-11-BE and ¿(14)C1, 25(OH)(2)-D(3)-19-BE failed to label DBP despite high-affinity DBP-binding, indicating the absence of any nucleophilic amino acid in the vicinity of their bromoacetate moiety to form a covalent bond, while these analogs are inside the binding pocket. In contrast, ¿(14)C25-OH-D(3)-6-BE and ¿(14)C25-OH-D(3)-3-BE specifically labeled DBP. BNPS-skatole digestion of DBP labeled with ¿(14)C25-OH-D(3)-3-BE or ¿(14)C25-OH-D(3)-6-BE produced two peptides (M(r) 17,400 and 33,840), with radioactivity associated with the N- and C-terminal peptides, respectively, raising the possibility that either different areas of the same vitamin D sterol-binding pocket, or different domains of DBP might be labeled by these analogs. Successful affinity labeling of recombinant domain I (1-203) of DBP with both reagents indicated that different areas of the same vitamin D-binding pocket (domain I) were labeled. These affinity analogs are potentially useful for "mapping" the vitamin D sterol-binding pocket and developing a functional model.

Cervical subarachnoid hematoma of unknown origin: case report

OBJECTIVE AND IMPORTANCE

Spontaneous spinal subarachnoid hematoma is rare, having been reported in the English literature in only seven other cases. We describe the first case of spontaneous subarachnoid hematoma located in the cervical spinal cord of a 43-year-old man. The pathologic examination showed no apparent source of bleeding, but there was evidence of cervical spondylotic myelopathy.

CLINICAL PRESENTATION

The patient presented with a 10-day history of severe neck pain, followed by the onset of quadriparesis that was more evident on the left side, urinary retention, and sensory loss below C5. His medical history included hypertension. Magnetic resonance imaging showed a massive hemorrhage in the cervical spinal canal.

INTERVENTION

A C4-C5 subarachnoid hematoma was removed. The patient died due to respiratory distress and uncontrollable hypotension on day 6 after surgery. Surgical exploration, neuroradiologic examinations, and autopsy showed no evidence of vascular malformations, tumors, or other possible sources of bleeding.

CONCLUSION

After excluding more common causes of spontaneous subarachnoid hematoma in this patient, we suggest that chronic spinal cord compression (spondylotic myelopathy) and arterial hypertension in this patient may have caused the pathogenesis of this rare clinical entity. Experimental data supporting this hypothesis are discussed.

Mechanistic studies to evaluate the enhanced antiproliferation of human keratinocytes by 1alpha,25-dihydroxyvitamin D(3)-3-bromoacetate, a covalent modifier of vitamin D receptor, compared to 1alpha,25-dihydroxyvitamin D(3)

1alpha,25-Dihydroxyvitamin D(3)-3-bromoacetate (1, 25(OH)(2)D(3)-3-BE), an affinity labeling analog of 1alpha, 25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), displayed stronger antiproliferative activities than 1,25(OH)(2)D(3) at 10(-10)-10(-6) M dose levels in cultured human keratinocytes (CHK). Additionally, preincubation of the cells with 10(-6) M 1,25(OH)(2)D(3), followed by treatment with various doses of 1,25(OH)(2)D(3)-3-BE, resulted in a significantly stronger antiproliferative activity by the mixture than individual reagents at every dose level. To search for a mechanism of this observation, we determined that [(14)C]1, 25(OH)(2)D(3)-3-BE covalently labeled human recombinant 1alpha, 25-dihydroxyvitamin D(3) receptor (reVDR) swiftly (<1 min) with a 1:1 stoichiometry and induced conformational changes (in VDR) that are different from 1,25(OH)(2)D(3), by limited tryptic digestion. Furthermore, a protein band, corresponding to reVDR, was specifically labeled by [(14)C]1,25(OH)(2)D(3)-3-BE in CHK extract, indicating that VDR is the main target of [(14)C]1, 25(OH)(2)D(3)-3-BE. The above-mentioned observations suggest that a rapid covalent labeling of VDR in CHK might alter the interaction between the holo-VDR and 1,25(OH)(2)D(3)-controlled genes. Furthermore, we observed that 1,25(OH)(2)D(3)-3-BE significantly decreased the binding of VDR to human osteocalcin vitamin D responsive element (hOCVDRE), as well as the dissociation rate of VDR from hOCVDRE, compared with 1,25(OH)(2)D(3) in COS-1 cells, transiently transfected with a VDR construct. Additionally, 1, 25(OH)(2)D(3)-3-BE was found to be more potent in inducing 1alpha, 25-dihydroxyvitamin D(3)-24-hydroxylase (24-OHase) promoter activity and mRNA expression in keratinocytes. The accumulation of 24-OHase message was also prolonged by the analog. Collectively these results indicated that rapid covalent labeling of VDR in keratinocytes (by 1, 25(OH)(2)D(3)-3-BE) might result in the conversion of apo-VDR to a holo-form, with a conformation that is different from that of the 1, 25(OH)(2)D(3)-VDR complex. This resulted in an enhanced stability of the 1,25(OH)(2)D(3)-3-BE/VDR-VDRE complex and contributed to the amplified antiproliferative effect of 1,25(OH)(2)D(3)-3-BE in keratinocytes.

Synthesis and estrogen receptor binding affinity of a porphyrin-estradiol conjugate for targeted photodynamic therapy of cancer

A tetraphenylporphyrin-C11-beta-estradiol conjugate has been synthesized. Competitive binding assay of the conjugate with estrogen receptor (ER)-ligand-binding domain showed that the conjugate binds specifically to the protein with high affinity. Potential use of this conjugate to selectively deliver cytotoxic porphyrins to ER-positive cells in various carcinomas is discussed.

C-6 functionalized analogs of 25-hydroxyvitamin D3 and 1alpha,25-dihydroxyvitamin D3: synthesis and binding analysis with vitamin D-binding protein and vitamin D receptor

In this article, we describe the development of a general synthetic strategy to functionalize the C-6 position of vitamin D3 and its biologically important metabolites, i.e. 25-hydroxyvitamin D3 (25-OH-D3) and 1alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3]. We employed Mazur's cyclovitamin D method to synthesize vitamin D3 analogs with several functionalities at the C-6 position. In addition, we synthesized 6-(3-hydroxypropyl) and 6-[(2-bromoacetoxy)propyl] derivatives of 25-OH-D3 15 and 16, respectively, and 6-(3-hydroxypropyl) derivative of 1,25(OH)2D3 17. Competitive binding assays of 15-17 with human serum vitamin D-binding protein showed that all these analogs specifically bound to this protein, although with significantly lower affinity than the 25-OH-D3, the strongest natural binder, but with comparable affinity with 1,25(OH)2D3, the hormone. On the other hand, 6-[3-hydroxypropyl], 1alpha,25-dihydroxyvitamin D3 17 did not show any specific binding for recombinant nuclear vitamin D receptor. These results indicated that the region containing the C-6 position of the parent seco-steroid [1,25(OH)2D3] may be an important recognition marker towards vitamin D receptor binding. Information, delineated in this article, will be important for evaluating structure-activity relationship in synthetic analogs of vitamin D and its metabolites.

Vitamin D receptor interacts with DnaK/heat shock protein 70: identification of DnaK interaction site on vitamin D receptor

Vitamin D receptor (VDR) regulates the expression of vitamin D-dependent genes upon binding to its cognate ligand, 1alpha, 25-dihydroxyvitamin D3 (1,25(OH)2D3). This process represents a complex interaction of ligand-bound VDR with nuclear proteins like retinoid X receptor, nuclear accessory factors, and regulatory elements of the target gene. Expression of full-length VDR in Escherichia coli revealed that VDR binds DnaK, a member of heat-shock protein (Hsp) family, with high affinity. By systematic N-terminal truncation of VDR, the interaction site of DnaK on VDR was localized within a 17-amino-acid segment (105-122) representing the "hinge region" between the DNA-binding and hormone-binding domains of VDR. The putative DnaK-binding site was further localized between residues 105 to 109 of VDR by using binding-energy-minimization studies. The interaction of DnaK with VDR did not influence the binding of 1,25(OH)2D3 or nuclear accessory factor(s) to VDR. Furthermore, bovine brain Hsp 70, similar to DnaK, interacted with VDR-ligand-binding domain (105-427). These results suggest that DnaK/Hsp 70 may interact with VDR prior to the activation of the latter by 1,25(OH)2D3-binding.

Identification of the subdomain in the nuclear receptor for the hormonal form of vitamin D3, 1 alpha,25-dihydroxyvitamin D3, vitamin D receptor, that is covalently modified by an affinity labeling reagent

Multiple physiological actions of the hormonal form of vitamin D3, 1 alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3), are mediated by a genomic pathway which is initiated by the highly specific recognition and binding by its cognate receptor (vitamin D receptor, VDR) in the target cells. Thus, knowledge of the three-dimensional geometries of the ligand, i.e., 1,25(OH)2D3, and the 1,25(OH)2D3-binding domain of VDR is crucial for a better understanding of diverse physiological roles of this hormone. Recently our laboratory has developed 1 alpha,25-dihydroxyvitamin D3-3 beta-bromoacetate (1,25(OH)2 D3-3-BE) as an affinity labeling reagent for covalently modifying the hormone binding domain of native VDRs from calf thymus and rat osteosarcoma cells and baculovirus-expressed recombinant human VDR (hVDR). In the present report, we report affinity labeling of the hormone binding domain of hVDR, expressed in Escherichia coli as a glutathione S-transferase fusion partner, site-specific cleavage of the affinity-labeled VDR with 3-bromo-3-methyl-2-(2-nitrophenylmercapto)- 3H-indole, and identification of the C-terminal subdomain of human VDR containing the putative hormone binding site.

Roles of the structure and orientation of ligands and ligand mimics inside the ligand-binding pocket of the vitamin D-binding protein

1alpha,25-Dihydroxyvitamin D3, the vitamin D hormone, manifests its diverse biological properties by specifically binding to the vitamin D sterol-binding pockets of vitamin D-binding protein (DBP) and vitamin D receptor. In the past, several affinity, photoaffinity, and chemical modification studies have been carried out to probe the vitamin D sterol-binding pocket of DBP and to evaluate the relationship between the structure of this pocket and the functions of the protein. In the present study, we examined the steric requirements inside this pocket by considering conformational structures of various bromoacetate derivatives of 25-hydroxyvitamin D3 and 1alpha,25-dihydroxyvitamin D3 and their abilities to covalently and specifically modify this pocket. We observed that, although 25-hydroxyvitamin D3 3beta-bromoacetate (25-OH-D3-3-BE), 1alpha,25-dihydroxyvitamin D3 3beta-bromoacetate [1alpha,25(OH)2D3-3-BE], 1alpha,25-dihydroxyvitamin D3 1alpha-bromoacetate [1alpha,25(OH)2D3-1-BE], and 1alpha,25-dihydroxyvitamin D3 1alpha,3beta-dibromoacetate [1alpha,25(OH)2D3-1,3-di-BE] bound DBP in a specific manner, only [3H]-25-OH-D3-3-BE and [3H]-1alpha,25(OH)2D3-3-BE affinity labeled the protein. BNPS-skatole cleavages of [3H]-25-OH-D3-3-BE- and 3H-1alpha,25(OH)2D3-3-BE-labeled DBP samples produced the same labeled peptide (N-terminal), demonstrating the specificity of labeling by these analogs. Energy-minimized conformational structures of these bromoacetate derivatives indicated significant changes in the A-ring conformations of these analogs. These structural changes were invoked to explain the inability of [3H]-1alpha,25(OH)2D3-1-BE and [3H]-1alpha,25(OH)2D3-1,3-di-BE to affinity label DBP. Overall, these studies suggested that the vitamin D sterol-binding pocket in DBP is sterically quite restrictive. This information could be potentially important in designing future vitamin D-based drugs for several diseases.

Bacterial expression of human vitamin D-binding protein (Gc2) in functional form

In this report, we report the first expression of human vitamin D-binding protein (hDBP), a serum protein with several functions and a multidomained structure, in Escherichia coli. The recombinant protein (reDBP) was expressed as a fusion partner of glutathione S-transferase in order to facilitate proper folding of the reDBP; E. coli-expressed DBP was found to be fully functional with respect to vitamin D sterol binding, interaction with actin, and cross-reactivity with anti-DBP antibody. Furthermore, both natural DBP and reDBP were affinity-labeled with 25-hydroxyvitamin D3-3-bromo[1-14C]acetate in a similar fashion. Availability of an expression system for hDBP in functional form provides opportunity to develop mutants and truncated DBPs to study multiple ligand-binding properties of this protein in relationship with its structure.

Affinity labeling of rat serum vitamin D binding protein

Vitamin D binding protein (DBP) plays an essential role in the vitamin D hormone endocrine system in sequestering vitamin D3 and its metabolites with high affinity, and transporting them to various target organs and tissues. In the present investigation, 25-hydroxyvitamin D3-3 beta-(1,2-epoxypropyl)ether (25-OH-D3-epoxide) and 25-hydroxyvitamin D3-3 beta-bromoacetate (25-OH-D3-BE), synthetic analogs of 25-hydroxyvitamin D3 (25-OH-D3), were developed as affinity alkylating reagents for the covalent modification of the 25-OH-D3-binding site in rat vitamin D binding protein (rDBP). Competitive radioligand binding assays of 25-OH-D3-BE and 25-OH-D3-epoxide with affinity-purified rDBP demonstrated that these analogs displaced 25-hydroxy[26(27)-3H]vitamin D3 (3H-25-OH-D3), specifically bound to rDBP, in a dose-dependent fashion. Incubation of rDBP samples with radiolabeled versions of these analogs, i.e., 3H-25-OH-D3-epoxide and 3H-25-OH-D3-BE, resulted in the covalent labeling of rDBP. This labeling was largely prevented when incubations were carried out in the presence of an excess of 25-OH-D3, the natural ligand for rDBP. Labeling-specificity by these analogs was further demonstrated by the covalent labeling, inhibited by coincubation with a large excess of 25-OH-D3, of a single protein band, upon incubating rat serum Cohn IV fraction with 3H-25-OH-D3-epoxide and 3H-25-OH-D3-BE. Collectively, these results strongly suggested that 3H-25-OH-D3-epoxide and 3H-25-OH-D3-BE covalently modified the 25-OH-D3-binding site in rDBP. The reagents described in this report could be important in mapping the 25-OH-D3-binding pocket in rDBP.

Affinity labeling of the 1 alpha,25-dihydroxyvitamin D3 receptor

Genomic actions of the calciotropic hormone 1 alpha, 25-dihydroxyvitamin D3 (1,25(OH)2D3) involves a multistep process that is triggered by the highly specific binding of 1,25(OH)2D3 to 1 alpha, 25-dihydroxyvitamin D3 receptor, VDR. In order to study this key step in the cascade, we synthesized 1 alpha,25-dihydroxy[26(27)-3H]vitamin D3-3-deoxy-3 beta-bromoacetate (1,25(OH)2[3H]D3-BE) and 1 alpha,25-dihydroxyvitaminD3-3 beta-[1-14C]bromoacetate(1,25(OH)2D3-[14C]BE) binding-site directed analogs of 1,25(OH)2D3, and affinity-labeled baculovirus-expressed recombinant human VDR (with 1,25(OH)2[3H]D3-BE), and naturally occurring VDRs in cytosols from calf thymus homogenate and rat osteosarcoma (ROS 17/2.8) cells (with 1,25(OH)2D3-[14C]BE). In each case, specificity of labeling was demonstrated by the drastic reduction in labeling when the incubation was carried out in the presence of an excess of nonradioactive 1 alpha,25(OH)2D3. These results strongly suggested that 1,25(OH)2[3H]D3-BE and 1,25(OH)2D3-[14C]BE covalently modified the 1,25(OH)2D3-binding sites in baculovirus-expressed recombinant human VDR and naturally occurring calf thymus VDR and rat osteosarcoma VDR, respectively.

25-Hydroxy[26,27-methyl-3H]vitamin D3-3 beta-(1,2-epoxypropyl)ether: an affinity labeling reagent for human vitamin D-binding protein

Vitamin D-binding protein (DBP) is primarily involved in the binding and transportation of vitamin D3 and its various metabolites to target organs and tissues. This is manifested by the ability of DBP to bind vitamin D3 and its metabolites with high affinity. In the present study we developed 25-hydroxyvitamin D3-3 beta-(1,2-epoxypropyl)ether (25-OH-D3-epoxide) as an affinity labeling reagent of human DBP (hDBP). Competitive radioligand binding assays of 25-OH-D3-epoxide with hDBP demonstrated that the binding affinity of this analog was similar to that of 25-hydroxyvitamin D3 (25-OH-D3). Incubation of 25-hydroxy[26(27)-3H]-vitamin D3-3 beta-(1,2-epoxypropyl)ether [[3H]25-OH-D3-epoxide] with hDBP covalently labeled the protein. When the incubation was carried out in the presence of a large excess of 25-OH-D3, labeling was removed completely. When human Cohn IV fraction, containing hDBP, was incubated with [3H]25-OH-D3-epoxide a single protein band, corresponding to hDBP, was labeled. Labeling was completely obliterated in the presence of a large amount of 25-OH-D3. However, an equivalent amount of 7-dehydrocholesterol had no effect on labeling. These results demonstrated that [3H]25-OH-D3-epoxide most probably labeled the vitamin D sterol-binding domain of hDBP.

Affinity purification of human plasma vitamin D-binding protein

During the course of our studies to probe the vitamin D ligand-binding domains of vitamin D-binding protein and vitamin D receptor, we developed a synthetic procedure to modify the 3 beta-hydroxyl group of vitamin D3 and its 25-hydroxy- and 1,25-dihydroxy metabolites with a 3'-aminopropylether group. In the present study we have coupled 25-hydroxyvitamin D3-3 beta-3'-aminopropylether to an activated Sepharose matrix. Using this stable and reusable affinity matrix we have purified human vitamin D-binding protein from human plasma to homogeneity.

Trp-145 is essential for the binding of 25-hydroxyvitamin D3 to human serum vitamin D-binding protein

Chemical modification of specific amino acid residues in a protein has been a valuable tool in identifying amino acid residues that are responsible for ligand binding of a protein. In the present investigation, we targeted Trp and His residues in human serum vitamin D-binding protein (hDBP) by modifying them with specific chemical modifiers. We also evaluated the results of these modifications in the binding of 25-hydroxy[26(27)-3H]vitamin D3 ([3H]25-OH-D3) to hDBP. We observed a dose-dependent loss of binding activity by N-bromosuccinimide (specific for Trp). Similar results were observed with diethylpyrocarbonate (specific for His). Furthermore, loss of [3H]25-OH-D3-binding was protected by preincubation of hDBP samples with an excess of 25-hydroxyvitamin D3. These results strongly emphasized the importance of Trp (single residue at position 145) and 1 His residue (out of a total of 6) in the vitamin D sterol-binding by vitamin D-binding protein.

Functional diseases of the esophagus: role of endoscopy

The use of endoscopic procedures in the evaluation of primary motor disorders, or functional diseases, of the esophagus is filled with both risks and benefits. Since both flexible and open-tube esophagoscopy carry a significant risk factor, it is necessary to have a clear concept of the indications and value of endoscopy in the management of functional diseases of the esophagus. A review of the literature reveals very little documentation on the value of endoscopy in diagnosing esophageal functional diseases other than Zenker's diverticulum and achalasia. Based on the current literature and the experience of the authors, observations and recommendations concerning the role of endoscopy in functional diseases of the esophagus are presented. These are: 1) In Phase I or upper esophageal sphincter dysfunctions, endoscopy contributes little to their understanding, is difficult to perform, and may be hazardous. In this group, esophagoscopy should be reserved for indications beyond the dysfunction itself. If endoscopy has to be performed, open-tube esophagoscopy should be performed by an experienced endoscopist. 2) In functional diseases of the esophageal body or Phase II dysfunction, endoscopy is frequently valuable. In spastic disorders, it helps to differentiate between primary spasm of neuromuscular origin and spasm secondary to esophagitis or an obstructive process. In scleroderma and pulsion diverticulum, endoscopy helps to identify such unsuspected complications as esophagitis, hiatal hernia, and carcinoma. 3) In Phase III or however esophageal sphincter dysfunctions, endoscopic examination is essential both to rule out organic lesions that stimulate functional disorders, and to determine the presence and extent of esophagitis.

Esophageal spasm: clinical and manometric response to nitroglycerine and long acting nitrites

The effect of nitroglycerine and long acting nitrites was studied in a group of 8 normal control subjects and 12 patients with esophageal spasm. The objective response of the esophagus to these drugs was recorded by obtaining esophageal manometric studies and was correlated with response in clinical symptoms. In 7 patients who had significant gastroesophageal reflux associated with spasm, the response to nitroglycerine was unpredictable. But in the group of 5 patients with diffuse esophageal spasm without gastroesophageal reflux, the response was uniformly good. All of the patients who responded to nitroglycerine also responded to long acting nitrites. These 5 patients, who were placed on long term management with long acting nitrites, remained symptom-free from 6 months to 4 years. None of them had recurrence of symptoms while they were on long acting nitrite therapy. The study suggests that if esophageal spasm is associated with reflux, the use of nitrites is less effective in controlling spasm than it is in those who do not show this association, and that diffuse esophageal spasm can be effectively managed with long acting nitrites on a long term basis in the absence of reflux. If there is esophageal spasm associated with reflux esophagitis, nitrites may be beneficial as an adjunct to antireflux therapy.