Vitamin D sites and mechanisms of action: a histochemical perspective. Reflections on the utility of autoradiography and cytopharmacology for drug targeting

Association of vitamin D and functional dyspepsia: a case-control study

Background

Vitamin D plays a key role in responses of brain-gut axis. It has been suggested that functional dyspepsia (FD) may be associated with decreased levels of vitamin D. Hence this study wished to find the association between vitamin D in patients with FD.

Materials and methods

This case-control study was done at a tertiary care hospital with 150 cases and 150 controls. FD was diagnosed by the ROME IV criteria. Demographic profile and serum vitamin D levels including Perceived Stress Score (PSS) and salivary amylase were determined for both cases and controls.

Results

Majority of the FD cases were males (57.3%). Post-prandial distress syndrome represented the major type of FD cases (69.3%). A higher mean BMI was found among the control group (23.2 vs. 21.2, P<0.05) and higher percentage of obese individuals in the control group (42.7% vs. 29.3%, P= 0.05). Majority of the cases are from rural background (89.3% vs. 74%, P<0.001). Comparison of PSS showed that cases had significantly higher grades of PSS than control (P<0.001). However, no significant association was found in the levels of salivary amylase between the groups (P=0.728). Hypovitaminosis D (<30 ng/ml) was found significantly more among cases than controls (73.3% vs. 60%; P<0.05) with an odds ratio of 1.833 (CI 95%= 1.126-2.985). After adjustment of age, place of residence and BMI, vitamin D levels were significantly associated with FD in the regression analysis.

Conclusion

This study shows significant association of vitamin D deficiency in FD patients. It also opens up new avenues for further research into the role of vitamin D supplementation to further improve the management of such cases.

Safety Assessment of Vitamin D and Its Photo-Isomers in UV-Irradiated Baker's Yeast

Vitamin D deficiency due to, e.g., nutritional and life style reasons is a health concern that is gaining increasing attention over the last two decades. Vitamin D₃, the most common isoform of vitamin D, is only available in food derived from animal sources. However, mushrooms and yeast are rich in ergosterol. This compound can be converted into vitamin D₂ by UV-light, and therefore act as a precursor for vitamin D. Vitamin D₂ from UV-irradiated mushrooms has become an alternative source of vitamin D, especially for persons pursuing a vegan diet. UV-irradiated baker’s yeast (Saccharomyces cerevisiae) for the production of fortified yeast-leavened bread and baked goods was approved as a Novel Food Ingredient in the European Union, according to Regulation (EC) No. 258/97. The Scientific Opinion provided by the European Food Safety Authority Panel on Dietetic Products, Nutrition, and Allergies has assessed this Novel Food Ingredient as safe under the intended nutritional use. However, recent findings on the formation of side products during UV-irradiation, e.g., the photoproducts tachysterol and lumisterol which are compounds with no adequate risk assessment performed, have only been marginally considered for this EFSA opinion. Furthermore, proceedings in analytics can provide additional insights, which might open up new perspectives, also regarding the bioavailability and potential health benefits of vitamin D-fortified mushrooms and yeast. Therefore, this review is intended to give an overview on the current status of UV irradiation in mushrooms and yeast in general and provide a detailed assessment on the potential health effects of UV-irradiated baker’s yeast.

A Narrative Role of Vitamin D and Its Receptor: With Current Evidence on the Gastric Tissues

Vitamin D is a major steroid hormone that is gaining attention as a therapeutic molecule. Due to the general awareness of its importance for the overall well-being, vitamin D deficiency (VDD) is now recognized as a major health issue. The main reason for VDD is minimal exposure to sunlight. The vitamin D receptor (VDR) is a member of the steroid hormone receptors that induces a cascade of cell signaling to maintain healthy Ca²⁺ levels that serve to regulate several biological functions. However, the roles of vitamin D and its metabolism in maintaining gastric homeostasis have not yet been completely elucidated. Currently, there is a need to increase the vitamin D status in individuals worldwide as it has been shown to improve musculoskeletal health and reduce the risk of chronic illnesses, including some cancers, autoimmune and infectious diseases, type 2 diabetes mellitus, neurocognitive disorders, and general mortality. The role of vitamin D in gastric homeostasis is crucial and unexplored. This review attempts to elucidate the central role of vitamin D in preserving and maintaining the overall health and homeostasis of the stomach tissue.

Role of vitamin D and vitamin D receptor (VDR) in oral cancer

Oral cancer is known as one of the most common cancers, with a poor prognosis, related to delayed clinical diagnosis, either due to the lack of particular biomarkers related to the disease or costly therapeutic alternatives. Vitamin D executes its functions by interacting with the vitamin D receptor (VDR), both in healthy and diseased individuals, including oral cancer. This review discusses the role of vitamin D and VDR on tumorigenesis, emphasizing on oral cancer. Furthermore, regulation of VDR expression, mechanisms of anticancer effects of calcitriol, oral cancer chemoresistance and its relation with VDR and polymorphisms of VDR gene will be discussed. The manuscript is prepared mainly using the information collected from PubMed and MEDLINE.

Direct vitamin D3 actions on rhesus macaque follicles in three-dimensional culture: assessment of follicle survival, growth, steroid, and antimüllerian hormone production

OBJECTIVE

To investigate the direct actions of active 1,25-dihydroxy vitamin D3 (VD3) upon primate follicular development at specific stages of folliculogenesis.

DESIGN

Secondary preantral follicles were isolated from rhesus monkeys ovaries, encapsulated in alginate, and cultured for 40 days. Follicles were randomly assigned to experimental groups of control, low-dose VD3 (LVD3; 25 pg/mL), and high-dose VD3 (HVD3; 100 pg/mL).

SETTING

National primate research center.

ANIMAL(S)

Adult, female rhesus macaques (Macaca mulatta).

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Follicle survival and growth, as well as oocyte size, were assessed. Progesterone (P₄), androstenedione (A₄), E₂, and antimüllerian hormone (AMH) concentrations in culture media were measured.

RESULT(S)

Compared with the control group, LVD3 increased preantral follicle survival at week 2 by >66%, while HVD3 increased antral follicle diameters at week 5. Follicles with diameters ≥500 μm at week 5 were categorized as fast-growing follicles. Higher percentages of fast-growing follicles were obtained after HVD3 treatment. Although P₄, A₄, and E₂ production by antral follicles was not altered by VD3, AMH concentrations were 36% higher in the LVD3 group relative to controls at week 5. Oocytes with larger diameters were retrieved from antral follicles developed in both LVD3 and HVD3 groups compared with controls.

CONCLUSION(S)

The addition of LVD3 increased preantral follicle survival and maintained AMH production by antral follicles, while HVD3 improved antral follicle growth. VD3 supplement promoted oocyte growth in in vitro-developed follicles. Direct actions of VD3 on the primate follicle appear to be both dose and stage dependent.

Neurotransmitter receptor localization: from autoradiography to imaging mass spectrometry

Autoradiography is used to determine the anatomical distribution of biological molecules in human tissue and experimental animal models. This method is based on the analysis of the specific binding of radiolabeled compounds to locate neurotransmitter receptors or transporters in fresh frozen tissue slices. The anatomical resolution obtained by quantification of the radioligands has allowed the density of receptor proteins to be mapped over the last 40 years. The data yielded by autoradiography identify the receptors at their specific microscopic localization in the tissues and also in their native microenvironment, the intact cell membrane. Furthermore, in functional autoradiography, the effects of small molecules on the activity of G protein-coupled receptors are evaluated. More recently, autoradiography has been combined with membrane microarrays to improve the high-throughput screening of compounds. These technical advances have made autoradiography an essential analytical method for the progress of drug discovery. We include the future prospects and some preliminary results for imaging mass spectrometry (IMS) as a useful new method in pharmacodynamic and pharmacokinetic studies, complementing autoradiographic studies. IMS results could also be presented as density maps of molecules, proteins, and metabolites in tissue sections that can be identified, localized, and quantified, with the advantage of avoiding any labeling of marker molecules. The limitations and future developments of these techniques are discussed here.

Associations of serum 25-hydroxyvitamin D concentrations with quality of life and self-rated health in an older population

CONTEXT

Vitamin D deficiency has been associated with impaired physical functioning, depression, and several chronic diseases and might thereby affect quality of life and self-rated health.

OBJECTIVE

The aim of this study was to assess relationships of serum 25-hydroxyvitamin D [25(OH)D] with quality of life and self-rated health and to examine whether physical performance, depressive symptoms, and number of chronic diseases mediate these relationships.

DESIGN

We analyzed data from the Longitudinal Aging Study Amsterdam, an ongoing population-based cohort study of older Dutch individuals.

MAIN OUTCOME MEASURES

Serum 25(OH)D was classified into the following categories: less than 25, 25-50, and 50 nmol/L or greater. We assessed quality of life (QOL) using the Short Form-12 Health Survey (SF-12; n = 862) and self-rated health (SRH) with a single question, dichotomized into good vs poor SRH (n = 1248).

RESULTS

Individuals with serum 25(OH)D less than 25 nmol/L scored lower on the physical component score of the SF-12 and had a lower odds on good SRH score compared with individuals with serum 25(OH)D greater than 50 nmol/L (β (95% confidence interval) -3.9 (-6.5 to -1.3) for SF-12, and odds ratio [95% confidence interval) 0.50 (0.33-0.76) for SRH]. Physical performance, depressive symptoms, and the number of chronic diseases were associated with vitamin D status, QOL, and SRH. Adding all these potential mediators to regression models attenuated associations of 25(OH)D less than 25 nmol/L with QOL with 78% and SRH with 32%.

CONCLUSION

Lower 25(OH)D status is related to lower scores on QOL and SRH. A large part of the association with QOL can statistically be explained by physical performance, depressive symptoms, and the number of chronic diseases.

Vitamin D and adipose tissue-more than storage

The pandemic increase in obesity is inversely associated with vitamin D levels. While a higher BMI was causally related to lower 25-hydroxyvitamin D (25(OH)D), no evidence was obtained for a BMI lowering effect by higher 25(OH)D. Some of the physiological functions of 1,25(OH)₂D₃ (1,25-dihydroxycholecalciferol or calcitriol) via its receptor within the adipose tissue have been investigated such as its effect on energy balance, adipogenesis, adipokine, and cytokine secretion. Adipose tissue inflammation has been recognized as the key component of metabolic disorders, e.g., in the metabolic syndrome. The adipose organ secretes more than 260 different proteins/peptides. However, the molecular basis of the interactions of 1,25(OH)₂D₃, vitamin D binding proteins (VDBPs) and nuclear vitamin D receptor (VDR) after sequestration in adipose tissue and their regulations are still unclear. 1,25(OH)₂D₃ and its inactive metabolites are known to inhibit the formation of adipocytes in mouse 3T3-L1 cell line. In humans, 1,25(OH)₂D₃ promotes preadipocyte differentiation under cell culture conditions. Further evidence of its important functions is given by VDR knock out (VDR^−/−) and CYP27B1 knock out (CYP27B1 ^−/−) mouse models: Both VDR^−/− and CYP27B1^−/− models are highly resistant to the diet induced weight gain, while the specific overexpression of human VDR in adipose tissue leads to increased adipose tissue mass. The analysis of microarray datasets from human adipocytes treated with macrophage-secreted products up-regulated VDR and CYP27B1 genes indicating the capacity of adipocytes to even produce active 1,25(OH)₂D₃. Experimental studies demonstrate that 1,25(OH)₂D₃ has an active role in adipose tissue by modulating inflammation, adipogenesis and adipocyte secretion. Yet, further in vivo studies are needed to address the effects and the effective dosages of vitamin D in human adipose tissue and its relevance in the associated diseases.

Whole-body and microscopic autoradiography to determine tissue distribution of biopharmaceuticals -- target discoveries with receptor micro-autoradiography engendered new concepts and therapies for vitamin D

Information about the distribution of biopharmaceuticals is basic for understanding their actions. Tissue and cellular localization is a key to function. Autoradiography with radiolabeled compounds has provided valuable information with both low resolution whole-body macro-autoradiography and high resolution microscopic autoradiography (micro-autoradiography). Whole-body macro-autoradiography is a uniform and expedient single method approach, providing convenient dose- and time-related overviews with data similar to those obtained with conventional bioassays - and therefore widely used. However, whole-body macro-autoradiography, like common bioassays, has limitations. High specificity-low capacity sites of binding and deposition frequently remain unrecognized. Lack of cellular resolution can cause false negatives and provide misleading results (e.g., false blood-brain barrier). For micro-autoradiography, different methods are advertised in the literature. Most of them are, however, unsuited for drug localization because of inadequate resolution and frequent artifacts. Most drugs interact with their receptors non-covalently by weak electrostatic forces. Therefore, translocation and loss can occur during tissue preparation. This has complicated the use of micro-autoradiography. Receptor micro-autoradiography has overcome these complications and is a method of choice. It has been validated through several diffusible compounds with known localization, extensively applied. It has contributed numerous discoveries, followed by new concepts and therapies. Pictorial evidence in this review indicates that cellular information is essential, a 'sine qua non' for meaningful drug distribution studies. High resolution cellular microscopic information obtained from autoradiography requires tissue dissection and the necessary precautions for preserving pristine in vivo drug deposition. Receptor micro-autoradiography fulfils these requirements. It reveals crucial information at the subcellular level that cannot currently be obtained with any other type of autoradiography or spectrometric imaging.

The world epidemic of sleep disorders is linked to vitamin D deficiency

An observation of sleep improvement with vitamin D supplementation led to a 2 year uncontrolled trial of vitamin D supplementation in 1500 patients with neurologic complaints who also had evidence of abnormal sleep. Most patients had improvement in neurologic symptoms and sleep but only through maintaining a narrow range of 25(OH) vitamin D3 blood levels of 60-80 ng/ml. Comparisons of brain regions associated with sleep-wake regulation and vitamin D target neurons in the diencephalon and several brainstem nuclei suggest direct central effects of vitamin D on sleep. We propose the hypothesis that sleep disorders have become epidemic because of widespread vitamin D deficiency. The therapeutic effects together with the anatomic-functional correspondence warrant further investigation and consideration of vitamin D in the etiology and therapy of sleep disorders.

Vitamin D deficiency and psychotic features in mentally ill adolescents: a cross-sectional study

BACKGROUND

Vitamin D deficiency is a re-emerging epidemic, especially in minority populations. Vitamin D is crucial not only for bone health but for proper brain development and functioning. Low levels of vitamin D are associated with depression, seasonal affective disorder, and schizophrenia in adults, but little is known about vitamin D and mental health in the pediatric population.

METHODS

One hundred four adolescents presenting for acute mental health treatment over a 16-month period were assessed for vitamin D status and the relationship of 25-OH vitamin D levels to severity of illness, defined by presence of psychotic features.

RESULTS

Vitamin D deficiency (25-OH D levels <20 ng/ml) was present in 34%; vitamin D insufficiency (25-OH D levels 20-30 ng/ml) was present in 38%, with a remaining 28% in the normal range. Adolescents with psychotic features had lower vitamin D levels (20.4 ng/ml vs. 24.7 ng/ml; p=0.04, 1 df). The association for vitamin D deficiency and psychotic features was substantial (OR 3.5; 95% CI 1.4-8.9; p <0.009). Race was independently associated with vitamin D deficiency and independently associated with psychosis for those who were Asian or biracial vs. white (OR=3.8; 95% CI 1.1‒13.4; p<0.04). Race was no longer associated with psychosis when the results were adjusted for vitamin D level.

CONCLUSIONS

Vitamin D deficiency and insufficiency are both highly prevalent in adolescents with severe mental illness. The preliminary associations between vitamin D deficiency and presence of psychotic features warrant further investigation as to whether vitamin D deficiency is a mediator of illness severity, result of illness severity, or both. Higher prevalence of vitamin D deficiency but no greater risk of psychosis in African Americans, if confirmed, may have special implications for health disparity and treatment outcome research.

Where is the vitamin D receptor?

The vitamin D receptor (VDR) is a member of the nuclear receptor superfamily and plays a central role in the biological actions of vitamin D. VDR regulates the expression of numerous genes involved in calcium/phosphate homeostasis, cellular proliferation and differentiation, and immune response, largely in a ligand-dependent manner. To understand the global function of the vitamin D system in physiopathological processes, great effort has been devoted to the detection of VDR in various tissues and cells, many of which have been identified as vitamin D targets. This review focuses on the tissue- and cell type-specific distribution of VDR throughout the body.

Drugs in the brain--cellular imaging with receptor microscopic autoradiography

For cell and tissue localization of drugs, receptor microscopic autoradiography is reviewed, including its development history, multiple testing, extensive applications and significant discoveries. This sensitive high-resolution imaging method is based on the use of radiolabeled compounds (esp. tagged with (3)H or (125)I), preservation through freezing of in vivo localization of tissue constituents, cutting thin frozen sections, and close contact with the recording nuclear emulsion. After extensive testing of the utility of this method, the distribution of radiolabeled compounds has been identified and characterized for estradiol, progestagens, adrenal steroids, thyroid hormone, ecdysteroids, vitamin D, retinoic acid, metabolic indicators glucose and 2-deoxyglucose, as well as extracellular space indicators. Target cells and associated tissues have been characterized with special stains, fluorescing compounds, or combined autoradiography-immunocytochemistry with antibodies to dopamine-beta-hydroxylase, GABA, enkephalin, specific receptor proteins, or other cellular products. Blood-brain barrier and brain entries via capillary endothelium, ependyma, or circumventricular recess organs have been visualized for (3)H-dexamethasone, (210)Pb lead, and (3)H-1,25(OH)(2) vitamin D(3). With this histopharmacologic approach, cellular details and tissue integrative overviews can be assessed in the same preparation. As a result, information has been gained that would have been difficult or impossible otherwise. Maps of brain drug distribution have been developed and relevant target circuits have been recognized. Examples include the stria terminalis that links septal-amygdaloid-thalamic-hypothalamic structures and telencephalic limbic system components which extend as the periventricular autonomic-neuroendocrine ABC (Allocortex-Brainstem-Circuitry) system into the mid- and hindbrain. Discoveries with radiolabeled substances challenged existing paradigms, engendering new concepts and providing seminal incentives for further research toward understanding drug actions. Most notable are discoveries made during the 1980s with vitamin D in the brain together with over 50 target tissues that challenged the century-old doctrine of vitamin D's main role as 'the calcitropic hormone', when the new data made it apparent that the main biological function of this multifunctional sunshine hormone rather is maintenance of life and adapting vital functions to the solar environment. In the brain, vitamin D, in close relation to sex and adrenal steroids, participates in the regulation of the secretion of neuro-endocrines, such as, serotonin, dopamine, nerve growth factor, acetyl choline, with importance in prophylaxis and therapy of neuro-psychiatric disorders. Histochemical imaging with high cellular-subcellular resolution is necessary for obtaining detailed information, as this review indicates. New spectrometric methods, like MALDI-MSI, are unlikely to furnish the same information as receptor microautoradiography does, but can provide important correlative molecular information.

Association between low serum 25-hydroxyvitamin D and depression in a large sample of healthy adults: the Cooper Center longitudinal study

OBJECTIVE

To investigate the association between serum vitamin D levels and depression in a large database of patients from the Cooper Clinic.

PATIENTS AND METHODS

We conducted a cross-sectional study of 12,594 participants seen at the Cooper Clinic from November 27, 2006, to October 4, 2010. Serum 25-hydroxyvitamin D [25(OH)D] was analyzed, and depression was defined as a Center for Epidemiologic Studies Depression Scale (CES-D) score of 10 or more. Those with and those without a history of depression represented 2 distinct populations with respect to CES-D scores; accordingly, they were analyzed separately.

RESULTS

In the total sample, higher vitamin D levels were associated with a significantly decreased risk [odds ratio, 0.92 (95% confidence interval, 0.87-0.97)] of current depression based on CES-D scores. The finding was stronger in those with a prior history of depression [odds ratio, 0.90 (95% confidence interval, 0.82-0.98)] and not significant in those without a history of depression [odds ratio, 0.95 (95% confidence interval, 0.89-1.02)].

CONCLUSION

We found that low vitamin D levels are associated with depressive symptoms, especially in persons with a history of depression. These findings suggest that primary care patients with a history of depression may be an important target for assessment of vitamin D levels.

Minireview: Vitamin D: is there a role in extraskeletal health?

In recent years, vitamin D has received increased attention due to the resurgence of vitamin D deficiency and rickets in developed countries together with the identification of extraskeletal vitamin D receptor-mediated actions, suggesting unexpected benefits of vitamin D in health and diseases. Although there is increased awareness of the importance of vitamin D, the role of vitamin D in extraskeletal health has been a matter of debate. In this review, we will summarize what is known and indicate the questions that remain and need to be addressed.

Is the vitamin d receptor found in muscle?

The active form of vitamin D, 1α,25-dihydroxyvitamin D(3), is critical for the regulation of serum calcium and phosphorus levels that in turn support bone mineralization and neuromuscular activity. It is well known that vitamin D deficiency causes rachitic/osteomalacic myopathy and cardiac disorder and the provision of vitamin D can reverse the symptoms. However, the underlying mechanisms remain unclear. The question of whether the vitamin D receptor is found in muscle has been debated but not settled. We recently studied all available antibodies against the vitamin D receptor and found that most antibodies used detect proteins other than the vitamin D receptor, and therefore, the utility of these antibodies may generate the false-positive results. Using antibodies that do not detect proteins in tissues from vitamin D receptor null mice, we have developed a specific and sensitive immunohistochemical assay. The results from this investigation show that the vitamin D receptor is undetectable in skeletal, cardiac, and smooth muscle, suggesting that the function of vitamin D on muscle is either of an indirect nature or does not involve the known receptor.

Relationship between vitamin D levels and depressive symptoms in older residents from a national survey population

OBJECTIVE

To investigate the association between vitamin D deficiency and depressive symptoms in a national community sample of older people. Vitamin D deficiency is common in older people with potential effects on mood.

METHODS

Data were analyzed from 2070 participants aged ≥65 years who had participated in the 2005 Health Survey for England. Serum 25-hydroxy vitamin D (25(OH)D) levels and depressive symptoms (Geriatric Depression Scale) had been measured. Covariates included age, sex, social class, season of examination, and physical health status.

RESULTS

Depressive symptoms were associated with clinical vitamin D deficiency (25(OH)D levels <10 ng/mL; present in 9.8%) independent of other covariates but not with broader deficiency states. This association was not modified by season of examination.

CONCLUSION

Vitamin D deficiency is associated with late-life depression in northern latitudes.

Identification of a highly specific and versatile vitamin D receptor antibody

The active form of vitamin D, 1alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) is critical for regulation of serum calcium and phosphorus levels and for proper maintenance of bone mineralization and neuromuscular function. Biological effects of 1,25(OH)2D3 are mediated through a nuclear steroid hormone receptor, known as the vitamin D receptor (VDR). The discovery of VDR in a number of different cell and tissue types, suggests that the physiological role of vitamin D may extend beyond the regulation of calcium homeostasis and bone function. Unfortunately, identification of tissues expressing VDR has been controversial due to low abundance of the receptor and quality of the antibodies used. Therefore, we elected to characterize a panel of commercially available VDR antibodies in order to identify antibodies with high specificity and sensitivity. To address these objectives, we have used multiple immunoassays to determine VDR expression in tissues from several organs from multiple species employing tissues from VDR knockout mice as critical negative controls. Many of the antibodies tested showed nonspecific binding that can account for divergent reports. However, one antibody, identified as D-6, is highly specific and extremely sensitive. The specificity, sensitivity, and versatility of this antibody make it the preferred antibody for identifying VDR expression in target tissues using immunological methods.

Involvement of Vitamin D receptor in the intestinal induction of human ABCB1

ABCB1 (P-glycoprotein) is an efflux transporter that limits the cellular uptake levels of various drugs in intestine, brain, and other tissues. The expression of human ABCB1 has recently been reported to be under the control of nuclear receptor NR1I subfamily members, pregnane X receptor (PXR, NR1I2) and constitutive androstane receptor (CAR, NR1I3). Here, we have investigated the involvement of another NR1I member, vitamin D receptor (VDR, NR1I1), in ABCB1 expression. In the human colorectal adenocarcinoma cell line LS174T, which abundantly expresses VDR, both 1alpha,25-dihydroxyvitamin D(3) (1,25-VD3) and lithocholic acid (LCA) increased ABCB1 mRNA levels. Reporter gene assays in LS174T cells with constructs containing various lengths of the ABCB1 regulatory region revealed that the region containing multiple nuclear receptor binding motifs located at -7.8 kilobases [termed nuclear receptor-responsive module (NURREM)], to which PXR and CAR also bind, is essential for the VDR-mediated ABCB1 transactivation. Further reporter assays with constructs containing truncated NURREM and gel shift assays suggested simultaneous binding of multiple VDR/retinoid X receptor alpha heterodimers to NURREM. Furthermore, knockdown of VDR expression in LS174T cells blocked the LCA- and the 1,25-VD3-induced transcription of ABCB1 reporter genes. In human hepatoma HepG2 cells, in contrast with LS174T cells, 1,25-VD3 activated the ABCB1 transcription only in the presence of ectopically expressed VDR. These results suggest that the NR1I subfamily members regulate the ABCB1 expression sharing the binding sites within NURREM and that the physiologically produced LCA and 1,25-VD3 may modulate the ABCB1 expression in human intestines, possibly associated with interindividual variations of ABCB1 expression.

Is this D vitamin to worry about? Vitamin D insufficiency in an inpatient sample

OBJECTIVE

The aim of the present study was to investigate the relationship between reduced serum vitamin D levels and psychiatric illness.

METHOD

This study was an audit of serum 25-hydroxyvitamin D (25-OHD) levels measured routinely in a sample of 53 inpatients in a private psychiatric clinic. These levels were compared with those of controls without psychiatric illness.

RESULTS

The median levels of serum 25-OHD were 43.0 nmol L(-1) (range 20-102 nmol L(-1)) in the patient population, 46.0 nmol L(-1) (range 20-102 nmol L(-1)) in female patients (n =33) and 41.5 nmol L(-1) (range 22-97 nmol L(-1)) in male patients (n =20). The proportion of vitamin D insufficiency (serum 25-OHD < or =50 nmol L(-1)) in this patient population was 58%. Furthermore, 11% had moderate deficiency (serum 25-OHD < or =25 nmol L(-1)). There was a 29% difference between mean levels in the patient population and control sample (geometric mean age- and season-adjusted levels: 46.4 nmol L(-1) (95% confidence interval (CI) =38.6-54.9 nmol L(-1)) vs 65.3 nmol L(-1) (95%CI =63.2-67.4 nmol L(-1)), p <0.001).

CONCLUSION

Low levels of serum 25-OHD were found in this patient population. These data add to the literature suggesting an association between vitamin D insufficiency and psychiatric illness, and suggest that routine monitoring of vitamin D levels may be of benefit given the high yield of clinically relevant findings.

Salivary glands epithelial and myoepithelial cells are major vitamin D targets

Receptor binding with 3H-1,25(OH)2 vitamin D3 (vitamin D) and its oxygen analog 3H-OCT is demonstrated in rat, hamster, and mice submandibular, sublingual and parotid glands, using receptor microautoradiography high-resolution imaging. Nuclear uptake and retention of radiolabeled compound exist strongest in epithelial cells of striated ducts, granular convoluted tubules and in myoepithelial cells throughout, scattered in epithelial cells of intercalated ducts and relatively low in cells of serous and mucous acini. Deposition and retention of radiolabeled compound is also observed in interstitial spaces. The specific nuclear localization with vitamin D and its analogue OCT, which is absent with 3H-(OH) vitamin D3 and in competition with excess non-radioactive vitamin D, indicates involvement of vitamin D in the multi-hormonal regulation of salivary gland secretion, excretion, and cell proliferation. These data--together with previously recognized similar receptor binding in esophagus, gastric glands, entero-endocrine cells, pyloric muscle, and generative and absorptive epithelium of the small intestine and colon, point to the importance of vitamin D for the digestive system regulation of functions and maintenance with related therapeutic potentials.

Contemporary diagnosis and treatment of vitamin D-related disorders

Plasma 25(OH)D has emerged as a valuable biomarker for the many varied health-related effects of vitamin D in the clinic mainly because of the recognition of the importance of the enzyme, CYP27B1, or the 25(OH)D-alpha-hydroxylase in the extrarenal, target cell production of calcitriol. This review briefly assesses current methodology for plasma 25(OH)D assay focusing mainly on currrent controversies surrounding the definition of the normal range and performance characteristics of the assay, separate measurement of both 25(OH)D(2) and 25(OH)D(3), and quality assurance tesing of laboratories offering the test. Clinicians have two main types of 25(OH)D assay based on either high-performance liquid chromatography with UV or mass detection or higher throughput kits based on protein (competitive protein binding assay or radioimmunoassay) binding. Based on 30 yr of experience with measuring 25(OH)D levels, it is concluded that, in the hands of appropriately trained experts, both types of assay provide reliable and accurate results, but all laboratories providing 25(OH)D data need frequent external quality assurance service to ensure that this performance is maintained.

Expanding role for vitamin D in chronic kidney disease: importance of blood 25-OH-D levels and extra-renal 1alpha-hydroxylase in the classical and nonclassical actions of 1alpha,25-dihydroxyvitamin D(3)

Recent advances in the understanding of vitamin D have revolutionized our view of this old nutritional factor and suggested that it has much wider effects on the body than ever believed before. In addition to its well-known effects on calcium/phosphate homeostasis, vitamin D, through its hormonal form, 1alpha,25-dihydroxyvitamin D(3) or calcitriol, is a cell differentiating factor and anti-proliferative agent with actions on a variety of tissues around the body (e.g., skin, muscle, immune system). By influencing gene expression in multiple tissues, calcitriol influences many physiological processes besides calcium/phosphate homeostasis including muscle and keratinocyte differentiation, insulin secretion, blood pressure regulation, and the immune response. The incidence of various diseases including epithelial cancers, multiple sclerosis, muscle weakness as well as bone-related disorders has been correlated with vitamin D deficiency/insufficiency and has led to a re-evaluation of recommended daily intakes both in the normal subject and CKD patient. Critical developments have been the emergence of the value of blood 25-OH-D measurement as a tool in predicting vitamin D-related problems and this has in turn emphasized the importance of the extra-renal version of the 1alpha-hydroxylase, the enzyme responsible for the final step in vitamin D activation. The widespread expression of this extra-renal enzyme supports the view that it exists to boost intracellular concentrations of calcitriol within some target tissues in order to modulate a unique set of genes specifically in those tissues, a process which is therefore dependent upon circulating 25-OH-D. For CKD patients with their tendency to vitamin D substrate insufficiency coupled with their documented loss of the renal 1alpha-hydroxylase in late stages, this new information has profound implications. Physicians must start to manage the vitamin D insufficiency by vitamin D supplements throughout stages 1-5 whilst continuing to provide calcitriol replacement therapy, in the form of calcitriol or its analogs, in stages 3-5.

Sweat gland epithelial and myoepithelial cells are vitamin D targets

Nuclear receptor binding of 1,25(OH)(2)-vitamin D(3) (vitamin D) in skin keratinocytes of epidermis, hair sheaths and sebaceous glands was discovered through receptor microscopic autoradiography. Extended experiments with (3)H-1,25(OH)(2)-vitamin D(3) and its analog (3)H-oxacalcitriol (OCT) now demonstrate nuclear receptor binding in sweat gland epithelium of secretory coils and ducts as well as in myoepithelial cells, as studied in paws of nude mice after i.v. injection. The results suggest genomic regulation of cell proliferation and differentiation, as well as of secretory and excretory functions, indicating potential therapies for impaired secretion as in hypohidrosis of aged and diseased skin.

The dose makes the medicine

Dose and time considerations in the development and use of a drug are important for assessing actions and side effects, as well as predictions of safety and toxicity. This article deals with epistemological aspects of dose selection by probing into the linguistic and cultural roots for the measure of medicine mediated by the medical doctor. Because toxicity is related to dose, historic and recent views suggest that less can be more. At low, medium and high dose levels, effects can differ not only quantitatively but also qualitatively. Dose-related target activation and recognition of enantiodromic thresholds between beneficial and toxic effects require elucidation of underlying events. Such studies, including hormesis and microdosing, call for extended ADME procedures with high-resolution methods in addition to the current low-resolution approaches. Improved information of drug logistics and target pharmacokinetics enables effective drug selection, dose determination and prediction. It also allows considerations of systems biology [i.e. integral (gestalt) pharmacology] exemplified by the drug homunculus, as in the case of vitamin D, that might lead to new paradigms and drug design.

Drug localization and targeting with receptor microscopic autoradiography

This review is an argument in favor of better drug target identification. It presents the many merits and feasibilities of drug localization and target identification through the use of a suitable technique: receptor microautoradiography. Studies of drug targets and target bioavailability require methods with high resolution and sensitivity to gain information for understanding mechanisms of action, sound modeling, prediction of effects, and toxicity. For in vivo localization of drugs in tissues and cells, receptor microautoradiography was specifically designed to preserve both tissue structure and deposition of noncovalently bound diffusible compounds and to enable microscopic viewing, quantitative analysis, and characterization of target sites. This method and its applications are explained here. Pictorial and quantitative data are provided together with a discussion of identified targets that document the utility of receptor microautoradiography. For example, when applied to quantitative studies of vitamin D compounds, pharmacokinetic data of blood differed from those of target tissues and even among target tissues. Many of the target tissues discovered and characterized with receptor microautoradiography remained unrecognized with common ADME procedures, radioassay-HPLC, and whole-body autoradiography. For a visual overview of the multiple vitamin D targets, a drug homunculus has been composed. Such a drug or target homunculus may be created for any drug, dose, and time to aid in documenting and fingerprinting. Receptor microautoradiography also is a sensitive method. It can be used for the study of low-dose stimulatory actions of toxic substances to show relationships of receptor binding to dose-dependent reversal of effects, known as hormesis. In addition, a combination of autoradiography and immunocytochemistry with radiolabeled drug and antibodies to receptor or other cellular product permits further target characterization. In its own league, receptor microautoradiography provides unique information. Through greater detail and certainty, it can validate and complement less-sensitive approaches, decrease the failure rates of current ADMET predictions, and serve as a diagnostic tool and guide for biochemical, functional, and clinical follow-up in drug research and development.

Receptor microscopic autoradiography for the study of percutaneous absorption, in vivo skin penetration, and cellular-intercellular deposition

INTRODUCTION

Microscopic autoradiography with cellular resolution and preservation of in vivo conditions is potentially the method of choice to gain detailed information about sites of deposition and retention in the epidermis and of penetration to the dermis after topical application of drugs. We tested this using (3)H-Maxacalcitol.

METHODS

Dorsal skin of adult rats was treated in vivo with ointment containing 1 or 40 microg/kg body weight of the vitamin D analogue (3)H-Maxacalcitol for periods of 0.5, 2, 8, 24, 48, or 168 h. Samples of skin exposed to the ointment and control samples remote from the treatment site were excised and freeze-mounted, and 4-microm frozen sections were exposed to nuclear emulsion.

RESULTS

Two penetration routes to the dermis could be distinguished: one via epidermal cell layers and the other via hair follicles. Highest uptake and retention of radiolabeled steroid was observed in stratum corneum and in intercellular spaces of stratum granulosum. By contrast, cell boundaries and intercellular spaces in the stratum spinosum and basale contained low levels of radioactivity. Keratinocytes in these layers showed high concentration in the cytoplasm at early time intervals, when surrounding radioactivity levels were high, but high nuclear and low or no cytoplasmic concentration at late time intervals, when surrounding radioactivity levels were low.

DISCUSSION

The autoradiographic method provides detailed information on time- and dose-related distribution of radiolabeled compound at the cellular level that is not obtainable with common radioassays and biochemical procedures. A sustained concentration and retention of radiolabeled steroid in the stratum corneum and intercellular space of the stratum granulosum indicate a selective deposition in components of secreted-membrane-coating granules and suggest a temporary barrier and depot for slow release. The differential cytoplasmic-nuclear distribution in the stratum Malpighi suggests functional correlation to a toxic-hormetic reversal of action on cell proliferation, from high-dose inhibitory effects associated with high extranuclear concentration as utilized in the treatment of psoriasis, to low-dose stimulatory effects associated with high nuclear and low cytoplasmic concentration as applicable in wound healing.

Effects of 1α,25 dihydroxyvitamin D3 on the expression of HO-1 and GFAP in glial cells of the photothrombotically lesioned cerebral cortex

In ischemic cerebral injuries a cascade of degenerative mechanisms, all participating in the development of oxidative stress, influence the condition of the tissue. The survival of viable tissue affected by secondary injury largely depends on the balance between endogenous protective mechanisms and the ongoing degenerative processes. The inducible enzyme, heme oxygenase-1 metabolizes and thus detoxifies free heme to the powerful endogenous antioxidants biliverdin and bilirubin therefore enhancing neuroprotection. The secosteroid 1alpha,25-dihydroxyvitamin D3 (1,25-D3) is a modulator of the immune system and also exhibits a strong potential for neuroprotection as recently shown in the MCAO model of cerebral ischemia. We studied the effects of 1,25-D3 treatment on heme oxygenase-1 expression following focal cortical ischemia elicited by photothrombosis. Postlesional treatment with 1,25-D3 (4 microg/kg body weight) resulted in a transient, but significant upregulation of glial heme oxygenase-1 immunoreactivity concomitant with a reduction in glial fibrillary acidic protein immunoreactivity in remote cortical regions affected by a secondary spread of injury, whereas the size of the lesion's core remained unaffected. 1,25-D3 did not produce a temporal shift or extension of injury-related heme oxygenase-1 responses, indicating that 1,25-D3 did not prolong ischemia-related heme oxygenase-1 expression. In contrast to glial heme oxygenase-1 upregulation, glial fibrillary acidic protein, a sensitive marker for reactive gliosis, was significantly reduced. These findings support an additional protective action of 1,25-D3 at the cellular level in regions affected by secondary injury-related responses.

Inhibition of peroxisome proliferator-activated receptor α signaling by vitamin D receptor

Peroxisome proliferator-activated receptors (PPARs) are nuclear fatty acid receptors that have been implicated to play an important role in lipid and glucose homeostasis. PPARalpha potentiates fatty acid catabolism in the liver and is activated by the lipid-lowering fibrates, whereas PPARgamma is essential for adipocyte differentiation. Here we report that nuclear vitamin D(3) receptor (VDR) represses the transcriptional activity of PPARalpha but not PPARgamma in a 1,25(OH)(2)D(3)-dependent manner. The analysis using chimeric receptors revealed that ligand binding domain of PPARalpha and VDR was involved in the molecular basis of this functional interaction and that the DNA binding domain of VDR was not required for the suppression, suggesting a novel mechanism that might involve protein-protein interactions rather than a direct DNA binding. Furthermore, the treatment of rat hepatoma H4IIE cells with 1,25(OH)(2)D(3) diminishes the induction of AOX mRNA by PPARalpha ligands, Wy14,643. VDR signaling might be considered as a factor regulating lipid metabolism via PPARalpha pathway. We report here the novel action of VDR in controlling gene expression through PPARalpha signaling.

Localization of a negative vitamin D response sequence in the human growth hormone gene

1,25-Dihydroxyvitamin D(3) [1,25(OH)(2) D(3)] exerts its biological effects by binding to the vitamin D receptor (VDR), which binds in turn to the vitamin D response elements located in the target gene's promoter. We have previously demonstrated that VDR binds in vitro with high affinity to the 5'-flanking sequence of the human growth hormone (hGH) gene. In this study, we analyzed the response to 1,25(OH)(2) D(3) of hGH-promoter constructs introduced by transfection into the MCF-7 human adenocarcinoma cell line. We found that the transcriptional activity of some of these constructs was markedly reduced by 1,25(OH)(2) D(3). Deletion analyses revealed that a 34-bp sequence located between positions -62 and -29 upstream of the transcription start site is sufficient for this repressive response. This conclusion was also confirmed by gel mobility shift assays. Our results indicate that vitamin D inhibits hGH gene transcription, directly or by interference with other transcription factors.

Transcriptional control of intestinal cytochrome P-4503A by 1alpha,25-dihydroxy vitamin D3

It was previously shown that CYP3A4 is induced in the human intestinal Caco-2 cell model by treatment with 1alpha,25-dihydroxy vitamin D3 (1,25-D3). We demonstrate the vitamin D analog, 19-nor-1alpha,25-dihydroxy vitamin D2, is also an effective inducer of CYP3A4 in Caco-2 cells, but with half the potency of 1,25-D3. We report that treatment of LS180 cells, a human intestinal cell line, with 1 to 10 nM 1,25-D3 dose dependently increased CYP3A4 protein and CYP3A4 mRNA expression. CYP3A4- and CYP3A23-promoter-Luciferase reporter constructs transiently transfected into LS180 cells were transcriptionally activated in a dose-dependent manner by 1,25-D3, whereas mutation of the nuclear hormone receptor binding motif (ER6) in the CYP3A4 promoter abrogated 1,25-D3 activation of CYP3A4. Although the CYP3A4 ER6 promoter element has been shown to bind the pregnane X receptor (PXR), this receptor does not mediate 1,25-D3 induction of CYP3A4 because a) PXR is not expressed in Caco-2 cells; b) PXR mRNA expression is not induced by 1,25-D3 treatment of LS180 cells; and c) the ligand binding domain of human PXR was not activated by 1,25-D3. 1,25-D3 uses the vitamin D receptor to induce CYP3A4 because a) the vitamin D receptor (VDR)-retinoid X receptor (RXR) heterodimer binds specifically to the CYP3A4 ER6; b) selective mutation of the CYP3A4 ER6 disrupted the binding of VDR-RXR; and c) reporter constructs containing only three copies of the CYP3A4 ER6 linked to a TK-CAT reporter were activated by 1,25-D3 only in cells cotransfected with a human VDR expression plasmid. These data support the hypothesis that 1,25-D3 and VDR induce expression of intestinal CYP3A by binding of the activated VDR-RXR heterodimer to the CYP3A PXR response element and promoting gene transcription.

Effect of a vitamin D3-based nutritional supplement ('Videchol') on carbohydrate metabolism of rats following chronic low dose-rate irradiation

In this study we evaluated the effects of the administration of a vitamin D3 preparation 'Videchol' to chronically irradiated rats (1 cGy day(-1)) by the assessment of the activities of several glycolytic enzymes: lactic dehydrogenase (LDH) (EC 1.1.1.28), pyruvate kinase (PK) (EC 2.7.1.40) and hexokinase (HK) (EC 2.7.1.1), in populations of erythroid and myeloid bone marrow cells. Videchol treatment of irradiated rats led to the normalisation of HK and LDH activity at cumulative doses of around 30 cGy in granulocyte-monocyte cells and to normalisation of LDH and PK activities in erythroid cells starting at 20 cGy in comparison with irradiated rats who did not receive Videchol. The reaction kinetic parameters of LDH in erythrocytes changed according to the redistribution pattern of the isozymes throughout the different stages of the experiment. The administration of Videchol to irradiated rats led to a rearrangement of the LDH isozymes ratio characterised by kinetic properties more comparable to those of the controls. Thus, vitamin D3 appears to induce a normalisation of carbohydrate metabolism in rats chronically irradiated with low dose-rate ionising radiation.

Histochemistry and cytochemistry of nuclear receptors

Receptors of steroid hormones, thyroid hormones and several kinds of vitamins have been shown to act as nuclear transcription factors and to form a nuclear receptor (NR) family. Histochemical techniques including autoradiography using radio-labeled ligands, immunohistochemistry and in situ hybridization histochemistry, have displayed that target cells of these receptors are distributed not only in the classical target organs but also widely in a variety of tissues; these techniques can demonstrate the presence of receptor proteins and mRNAs, even though they are expressed in a small cell population of tissues. On the other hand, many studies have been performed to demonstrate the interaction between NRs and nuclear and cytoplasmic proteins, and to clarify the mechanism of transcriptional regulation through NRs in artificial conditions which are created in gene transfer experiments or under cell-free conditions. Some data coincide with those obtained from histochemical techniques, however, some histochemical data do not support the results of studies in vitro. This review focuses on the following topics: histochemical methodologies to detect NRs, the distribution and function of NRs in the tissues, the intracellular and intranuclear localization of NRs, roles of gonadal steroid receptors and their ligands on developing tissues including cell communications such as mesenchymal-stromal interaction, and the interaction between other cellular components and NRs. In addition, the agreement and disagreement between the results of histochemical studies and those from the experiments in the model systems or in vitro are discussed.

Evidence of functional vitamin D receptors in rat hippocampus

The steroid hormone vitamin D has important biological roles in calcium transport, cell growth, and cell differentiation. Its cellular activities are mediated by high affinity interaction with the vitamin D receptor. In brain, autoradiographic, immunohistologic, and messenger RNA expression studies implicate a number of neuronal systems, including the hippocampus, as potential targets of vitamin D. However, cellular distribution and protein expression, and binding of the receptor to vitamin D response elements have yet to be established in hippocampus. This investigation was undertaken to characterize the vitamin D receptor in rat hippocampus with western blot, immunocytochemistry, and gel shift analyses. The presence of the receptor protein in hippocampus extracts was revealed with western blotting using an anti-rat vitamin D receptor antiserum. In vivo and in vitro immunocytochemical results confirmed the presence of vitamin D receptor in neuronal and glial cells. In the hippocampus, the receptor was localized in pyramidal and granule cell layers, CA1, CA2, and CA3 subfields and in the dentate gyrus. Double labeling for the vitamin D receptor and glial fibrillary acidic protein revealed that glia also expressed the receptor protein. Gel shift analyses evaluated with the murine osteopontin vitamin D response element indicated a specific, bound receptor-containing complex from hippocampal extracts. Altogether, these findings clearly document the localization of vitamin D receptor in rat hippocampus and that hippocampus contains vitamin D receptors capable of specifically binding to DNA. In combination with reports of a neuroprotective role for vitamin D in hippocampal cell survival, these data suggest that the endogenous vitamin D receptor may mitigate processes related to cellular homeostasis, perhaps through a calcium buffering mechanism.

Vitamin D is an important factor in estrogen biosynthesis of both female and male gonads

In the present study, the role of vitamin D in the regulation of estrogen synthesis in gonads was investigated. Vitamin D receptor null mutant mice showed gonadal insufficiencies. Uterine hypoplasia and impaired folliculogenesis were observed in the female, and decreased sperm count and decreased motility with histological abnormality of the testis were observed in the male. The aromatase activities in these mice were low in the ovary, testis, and epididymis at 24%, 58%, and 35% of the wild-type values, respectively. The gene expression of aromatase was also reduced in these organs. Elevated serum levels of LH and FSH revealed hypergonadotropic hypogonadism in these mice. The gene expressions of estrogen receptor alpha and beta were normal in gonads in these mice. Supplementation of estradiol normalized histological abnormality in the male gonads as well as in the female. Calcium supplementation increased aromatase activity and partially corrected the hypogonadism. When the serum calcium concentration was kept in the normal range by supplementation, the aromatase activity in the ovary increased to 60% of the wild-type level, but LH and FSH levels were still elevated. These results indicated that vitamin D is essential for full gonadal function in both sexes. The action of vitamin D on estrogen biosynthesis was partially explained by maintaining calcium homeostasis; however, direct regulation of the expression of the aromatase gene should not be neglected.