Different actions of vitamin D2 and D3 on bone metabolism in patients treated with phenobarbitone/phenytoin

Vitamin D: sources, physiological role, biokinetics, deficiency, therapeutic use, toxicity, and overview of analytical methods for detection of vitamin D and its metabolites

Vitamin D has a well-known role in the calcium homeostasis associated with the maintenance of healthy bones. It increases the efficiency of the intestinal absorption of dietary calcium, reduces calcium losses in urine, and mobilizes calcium stored in the skeleton. However, vitamin D receptors are present ubiquitously in the human body and indeed, vitamin D has a plethora of non-calcemic functions. In contrast to most vitamins, sufficient vitamin D can be synthesized in human skin. However, its production can be markedly decreased due to factors such as clothing, sunscreens, intentional avoidance of the direct sunlight, or the high latitude of the residence. Indeed, more than one billion people worldwide are vitamin D deficient, and the deficiency is frequently undiagnosed. The chronic deficiency is not only associated with rickets/osteomalacia/osteoporosis but it is also linked to a higher risk of hypertension, type 1 diabetes, multiple sclerosis, or cancer. Supplementation of vitamin D may be hence beneficial, but the intake of vitamin D should be under the supervision of health professionals because overdosing leads to intoxication with severe health consequences. For monitoring vitamin D, several analytical methods are employed, and their advantages and disadvantages are discussed in detail in this review.

Association of vitamin D2 and D3 with type 2 diabetes complications

AIMS

Vitamin D measurement is a composite of vitamin D₂ (25(OH)D₂) and D₃ (25(OH)D₃) levels, and its deficiency is associated with the development of type 2 diabetes (T2DM) and diabetic complications; vitamin D deficiency may be treated with vitamin D₂ supplements. This study was undertaken to determine if vitamin D₂ and D₃ levels differed between those with and without T2DM in this Middle Eastern population, and the relationship between diabetic microvascular complications and vitamin D₂ and vitamin D₃ levels in subjects with T2DM_. METHODS: Four hundred ninety-six Qatari subjects, 274 with and 222 without T2DM participated in the study. Plasma levels of total vitamin D₂ and D₃ were measured by LC-MS/MS analysis.

RESULTS

All subjects were taking vitamin D₂ and none were taking D₃ supplements. Vitamin D₂ levels were higher in diabetics, particularly in females, and higher levels were associated with hypertension and dyslipidemia in the diabetic subjects (p < 0.001), but were not related to diabetic retinopathy or nephropathy. Vitamin D₃ levels measured in the same subjects were lower in diabetics, particularly in females (p < 0.001), were unrelated to dyslipidemia or hypertension, but were associated with retinopathy (p < 0.014). Neither vitamin D₂ nor vitamin D₃ were associated with neuropathy. For those subjects with hypertension, dyslipidemia, retinopathy or neuropathy, comparison of highest with lowest tertiles for vitamin D₂ and vitamin D₃ showed no difference.

CONCLUSIONS

In this Qatari cohort, vitamin D₂ was associated with hypertension and dyslipidemia, whilst vitamin D₃ levels were associated with diabetic retinopathy. Vitamin D₂ levels were higher, whilst vitamin D₃ were lower in diabetics and females, likely due to ingestion of vitamin D₂ supplements.

Vitamin D supplementation for bone health in adults with epilepsy: A systematic review

OBJECTIVE

Several antiepileptic drugs (AEDs) have been associated with a detrimental effect on bone health through a reduction in serum vitamin D. Subsequently, several studies have investigated the effect of vitamin D supplementation in persons with epilepsy being treated with AEDs. The present systematic review of published literature was conducted to determine the effect of vitamin D intervention on bone health in adults with epilepsy.

METHODS

The following databases were searched using keywords including but not limited to epilepsy, bone, and vitamin D: PubMed, Medline, Embase, Scopus, Cochrane Clinical Trials, International Pharmaceutical Abstracts, Health Canada Clinical Trials Database, ClinicalTrials.gov, EU Clinical Trials, and Google. Studies were eligible if there was an epilepsy diagnosis, participants were adults (18+ years old), and vitamin D treatment and bone outcome were provided. Articles were screened independently by 2 reviewers. Methodological quality was assessed using the Cochrane Collaboration's tool and a modified Newcastle Ottawa Scale for nonrandomized studies.

RESULTS

Nine studies were found to be eligible for this review. After vitamin D treatment, there appeared to be positive changes in bone turnover markers; 3 of 8 studies found the increase in serum calcium to be significant, 6 of 8 studies found the decrease in alkaline phosphatase to be significant, and 2 of 4 studies found the decrease in parathyroid hormone to be significant. All 6 studies that investigated bone mineralization had significant findings; however, due to varying methodologies, the impact of vitamin D on bone mineralization was inconclusive.

SIGNIFICANCE

Vitamin D does appear to have some benefit to bone health in adults with epilepsy, and therefore supplementation could potentially be a requisite to using some AEDs. To clarify the role of vitamin D supplementation to manage the adverse effect of AEDs on bone health in adults with epilepsy, long-term trials that use higher doses (>1800 IU) and measure bone mineral density are necessary.

Vitamin D bioavailability: state of the art

There has been renewed interest in vitamin D since numerous recent studies have suggested that besides its well-established roles in bone metabolism and immunity, vitamin D status is inversely associated with the incidence of several diseases, e.g., cancers, cardio-vascular diseases, and neurodegenerative diseases. Surprisingly, there is very little data on factors that affect absorption of this fat-soluble vitamin, although it is acknowledged that dietary vitamin D could help to fight against the subdeficient vitamin D status that is common in several populations. This review describes the state of the art concerning the fate of vitamin D in the human upper gastrointestinal tract and on the factors assumed to affect its absorption efficiency. The main conclusions are: (i) ergocalciferol (vitamin D2), the form mostly used in supplements and fortified foods, is apparently absorbed with similar efficiency to cholecalciferol (vitamin D3, the main dietary form), (ii) 25-hydroxyvitamin D (25OHD), the metabolite produced in the liver, and which can be found in foods, is better absorbed than the nonhydroxy vitamin D forms cholecalciferol and ergocalciferol, (iii) the amount of fat with which vitamin D is ingested does not seem to significantly modify the bioavailability of vitamin D3, (iv) the food matrix has apparently little effect on vitamin D bioavailability, (v) sucrose polyesters (Olestra) and tetrahydrolipstatin (orlistat) probably diminish vitamin D absorption, and (vi) there is apparently no effect of aging on vitamin D absorption efficiency. We also find that there is insufficient, or even no data on the following factors suspected of affecting vitamin D bioavailability: (i) effect of type and amount of dietary fiber, (ii) effect of vitamin D status, and (iii) effect of genetic variation in proteins involved in its intestinal absorption. In conclusion, further studies are needed to improve our knowledge of factors affecting vitamin D absorption efficiency. Clinical studies with labeled vitamin D, e.g., deuterated or (13)C, are needed to accurately and definitively assess the effect of various factors on its bioavailability.

Cytochrome P450-mediated metabolism of vitamin D

The vitamin D signal transduction system involves a series of cytochrome P450-containing sterol hydroxylases to generate and degrade the active hormone, 1α,25-dihydroxyvitamin D3, which serves as a ligand for the vitamin D receptor-mediated transcriptional gene expression described in companion articles in this review series. This review updates our current knowledge of the specific anabolic cytochrome P450s involved in 25- and 1α-hydroxylation, as well as the catabolic cytochrome P450 involved in 24- and 23-hydroxylation steps, which are believed to initiate inactivation of the vitamin D molecule. We focus on the biochemical properties of these enzymes; key residues in their active sites derived from crystal structures and mutagenesis studies; the physiological roles of these enzymes as determined by animal knockout studies and human genetic diseases; and the regulation of these different cytochrome P450s by extracellular ions and peptide modulators. We highlight the importance of these cytochrome P450s in the pathogenesis of kidney disease, metabolic bone disease, and hyperproliferative diseases, such as psoriasis and cancer; as well as explore potential future developments in the field.

Serum 25-hydroxyvitamin D levels in vitamin D-insufficient hip fracture patients after supplementation with ergocalciferol and cholecalciferol

Vitamin D insufficiency is commonly associated with hip fracture. However, the equipotency of ergocalciferol and cholecalciferol supplementation in this patient group has not been studied in a randomized trial using high-performance liquid chromatography (HPLC) measurement of serum 25-hydroxyvitamin D (25OHD). The objective of this study was to determine if ergocalciferol and cholecalciferol are equipotent therapies in vitamin D-insufficient hip fracture patients. Ninety five hip fracture inpatients with vitamin D insufficiency (25OHD<50 nmol/L) were randomized, double-blind, to treatment with ergocalciferol 1000 IU/day (n=48) or cholecalciferol 1000 IU/day (n=47) for three months. All participants were also given a placebo matching the alternative treatment to maintain blinding of treatment allocation. The primary endpoint was total serum 25OHD measured by HPLC. Secondary endpoints included 25OHD measured by radioimmunoassay (RIA), intact parathyroid hormone (iPTH), and bioactive (1-84) whole PTH (wPTH). Seventy patients (74%) completed the study with paired samples for analysis. Cholecalciferol supplementation resulted in a 31% greater increase in total HPLC-measured 25OHD (p=0.010) and 52% greater rise in RIA-measured 25OHD (p<0.001) than supplementation with an equivalent dose of ergocalciferol. Changes in iPTH and wPTH were not significantly different between calciferol treatments (p>0.05). In vitamin D-insufficient hip fracture patients, supplementation with cholecalciferol 1000 IU/day for three months was more effective in increasing serum 25OHD than an equivalent dose of ergocalciferol. However, the lack of difference in PTH lowering between calciferol treatments raises questions about the biological importance of this observation.

Vitamins for epilepsy

BACKGROUND

Vitamins have been reported to be effective in controlling certain types of seizures and to prevent some of the harmful effects of antiepileptic drugs (AEDs). In this review we will summarize evidence from randomized controlled trials.

OBJECTIVES

To assess if vitamins improve seizure control, reduce adverse effects of AEDs or improve the quality of life in people with epilepsy.

SEARCH STRATEGY

We searched MEDLINE from 1966 to 2004, the Cochrane Epilepsy Group trials register (December 2004), CENTRAL (the Cochrane Controlled Trials Register) (TheCochraneLibrary Issue 4, 2004), and cross-references from identified studies.

SELECTION CRITERIA

Randomized or quasi-randomized studies investigating the effects of one or more vitamins given alone or in addition to AEDs to people of any age with any type of epilepsy.

DATA COLLECTION AND ANALYSIS

Both reviewers assessed the trials for inclusion and extracted the data. Outcomes assessed included seizure frequency, gingival hyperplasia, neuropathy, changes in bone mineral content, serum calcium, alkaline phosphatase, hemogram, serum levels of AEDs, neuropsychological and quality of life outcomes. Primary analyses were by intention to treat.

MAIN RESULTS

Fifteen studies met our inclusion criteria and were of poor methodological quality. None described randomization methods and most enrolled small numbers of participants. Nine studies (331 participants) investigated folic acid. Two studies (75 participants) found no effect for the outcome 50% or greater reduction in seizure frequency (OR 0.96; 95% CI 0.32 to 2.29). Also, no evidence was found for an effect on gingival health, intelligence, behavior, mental health or personality, or measures of red blood volume and hemoglobin content. Folic acid was not associated with any consistent changes in serum phenytoin or phenobarbitone levels or improvement in the mean motor conduction velocities of peripheral nerves. One small study (72 participants) found that thiamine improves neuropsychological functions related to psychomotor speed, visuospatial abilities, selective attention and verbal abstracting ability. One study (226 participants) found a significantly higher bone mineral content (BMC) among patients with epilepsy taking AEDs with vitamin D supplementation compared to controls who were not given supplementation (OR 3.6; 95% CI 2.48 to 4.72; p < 0.00001). The studies found no significant effects on serum calcium, alkaline phosphatase or general well-being. One small study (24 participants) found a significant decrease in seizure frequency in those treated with vitamin E compared to placebo (p = 0.00005; Peto OR 26.73; 95% CI 5.46 to 130.92).

AUTHORS' CONCLUSIONS

In view of methodological deficiencies and limited number of individual studies, we have found no reliable evidence to support the routine use of vitamins in patients with epilepsy. Further trials are needed, especially to assess the utility of vitamin D supplementation to prevent osteomalacia and the role of vitamin E on seizures and thiamine in improving cognitive functions.

Hypovitaminosis D in acutely injured pediatric burn patients

PROBLEM

The prevalence of vitamin D insufficiency, its etiology, and associated sequelae among acutely injured burn patients is unknown.

OBJECTIVE

This study assessed vitamin D and endocrine status, as well as the effect of anabolic agents, in pediatric patients who had sustained burns in excess of 25% total body surface area (TBSA).

SUBJECTS

Sixty-nine patients with a mean TBSA burn of 50.6+/-2.2% (range 27% to 94%) and full thickness injury of 41.3+/-3.0% (range 0% to 94%) were studied. Subjects ranged in age from 0.6 to 18 years (mean, 5.8+/-0.6 years). Main outcome measures Blood samples were obtained for serum 25-hydroxyvitamin D (D25), 1,25-dihydroxyvitamin D (D1,25), albumin, cortisol, triiodothyronine (T3), tetraiodothyronine (T(4)), thyroid stimulating hormone (TSH), and parathormone (PTH).

RESULTS

Two hundred eighty morning blood samples of D25 and D1,25 demonstrated that 45% and 26.2% were low and 8.9% and 11% were very low, respectively. At least one low D25 or D1,25 level occurred in 62.3% of all subjects. Very low levels were noted in 23.2% of all patients. There was an increased incidence of hyperparathyroidism in patients with very low serum D25. Vitamin D25 and D1,25 levels were lower in subjects with larger burns or inhalation injury, as well as those treated with thyroxine or oxandrolone. Serum albumin, cortisol, T(4), and TSH were not correlated with concentration of vitamin D.

CONCLUSIONS

Demonstration of a high incidence of low serum vitamin D indicates vitamin D status may be significantly compromised in burned children. It is unclear why vitamin D deficiency exists in this population. The most effective way to improve vitamin D status remains elusive at this time.

Four-Year Review of Burns as an Etiologic Factor in the Development of Long Bone Fractures in Pediatric Patients

Reduced bone density has been documented in children after burns. This loss of bone may place children at heightened risk for fractures. The medical records of all acutely injured patients with burns in excess of 40% TBSA burn admitted to our institution between January 1, 1997, through December 31, 2000, were reviewed for fracture incidence. Patients with fractures sustained during the course of initial trauma were not included in the review. One hundred four records were reviewed. These patients had a mean age of 6.7 +/- 0.51 years, (range, 0.2 to 18.0) and a mean %TBSA burn of 59.9 +/- 1.60 (range, 40 to 98) with a mean full-thickness %burn of 51.7 +/- 2.16 (range, 0 to 95). Fifteen long bone fractures were documented in six patients during the review time frame. All fractures were initially suspected by physical therapy personnel upon regularly scheduled therapy sessions and subsequently verified by x-ray. All fractures identified by this review occurred in children less than 3 years of age. Most fractures were noted during the rehabilitation phase of injury (range, 73 to 283 days after burn) once wounds were more than 95% healed, except for one child, who sustained multiple fractures during the acute recovery phase at a referring hospital. A 5.8% incidence of fractures was noted in patients with burns in excess of 40% (6 of 104 admissions). The etiology of the fractures is unknown, although the hormonal milieu postburn, depressed vitamin D status, inadequate protein intake, and decreased weight-bearing activity are potential contributory factors. In addition, infants and toddlers tend to provide more resistance to therapy because of an inherent lack of cognition. This may account for the increased breaks in this population.

Changes in bone turnover and deoxypyridinoline levels in epileptic patients

In this study, we evaluated bone turnover in 52 epileptic patients receiving chronic anticonvulsant therapy and in 39 healthy volunteers whose ages matched those of the patients. We determined serum osteocalcin and total and bone alkaline phosphatase levels as markers of bone formation, and urinary deoxypyridinoline and urinary calcium levels as markers of bone resorption. Statistical comparison of the levels of these markers between sexes in epileptic patients and their control groups revealed that total alkaline phosphatase levels were significantly increased in patients from both sexes compared with those of their controls. Urinary deoxypyridinoline levels of male epileptic patients were significantly increased compared with those of their controls. On the other hand, 25-hydroxyvitamin D levels of the male patients were significantly reduced compared with those of their controls. Serum osteocalcin, bone alkaline phosphatase, and urinary calcium levels of epileptic patients were not statistically different from those of the controls. We found that urinary deoxypyridinoline levels of male epileptic patients were increased, however, we observed no difference in serum osteocalcin and bone alkaline phosphatase levels. The lack of difference may be attributed to the fact that only the resorption phase of bone turnover is affected during chronic anticonvulsant therapy.

Isolation and identification of 4,25-dihydroxyvitamin D2: a novel A-ring hydroxylated metabolite of vitamin D2

Vitamin D2 is less toxic in rats when compared to vitamin D3. Our laboratory has been involved in research projects which were directed towards identifying the possible mechanisms responsible for the toxicity differences between vitamins D2 and D3 in rats. The present research project was designed to isolate and identify new metabolites of vitamin D2 from serum of rats which were fed toxic doses of vitamin D2. Hypervitaminosis D2 was induced in 30 rats by feeding each rat with 1000 nmol of vitamin D2/day x 14 days. The rats were sacrificed on the 15th day and obtained 180 ml of serum. The lipid extract of the serum was directly analyzed by a straight phase HPLC system. The various vitamin D2 metabolites were monitored by their ultraviolet (UV) absorbance at 254 nm. One of the UV absorbing peaks did not comigrate with any of the known vitamin D2 metabolites. This unknown metabolite peak was further purified by HPLC and was then subjected to UV absorption spectrophotometry and mass spectrometry. The structure assignment of the new metabolite was established to be 4,25-dihydroxyvitamin D2 [4,25(OH)2D2] by the techniques of UV absorption spectrophotometry and mass spectrometry and by the new metabolite's susceptibility to sodium metaperiodate oxidation. At present the biological activity of this unique 'A-ring' hydroxylated vitamin D2 metabolite is not known. As this new metabolite is isolated from the serum of rats intoxicated with vitamin D2, we speculate that 4,25(OH)2D2 may be playing an important role in the deactivation of vitamin D2.

Physiological significance of C-28 hydroxylation in the metabolism of 1alpha,25-dihydroxyvitamin D(2)

In our previous study, we indicated for the first time that C-28 hydroxylation plays a significant role in the metabolism of 1alpha, 25-dihydroxyvitamin D(2) [1alpha,25(OH)(2)D(2)] by identifying 1alpha,24(S),25,28-tetrahydroxyvitamin D(2) [1alpha,24(S),25, 28(OH)(4)D(2)] as a major renal metabolite of 1alpha,25(OH)(2)D(2) [G. S. Reddy and K-Y. Tserng Biochemistry 25, 5328-5336, 1986]. The present study was performed to establish the physiological significance of C-28 hydroxylation in the metabolism of 1alpha, 25(OH)(2)D(2). We perfused rat kidneys in vitro with 1alpha, 25(OH)(2)[26,27-(3)H]D(2) (5 x 10(-10)M) and demonstrated that 1alpha,24(R),25-trihydroxyvitamin D(2) [1alpha,24(R),25(OH)(3)D(2)] and 1alpha,24(S),25,28(OH)(4)D(2) are the only two major physiological metabolites of 1alpha,25(OH)(2)D(2). In the same perfusion experiments, we also noted that there is no conversion of 1alpha,25(OH)(2)D(2) into 1alpha,25,28-trihydroxyvitamin D(2 )[1alpha,25,28(OH)(3)D(2)]. Moreover, 1alpha,24(S),25,28(OH)(4)D(2) is not formed in the perfused rat kidney when synthetic 1alpha,25, 28(OH)(3)D(2) is used as the starting substrate. This finding indicates that C-28 hydroxylation of 1alpha,25(OH)(2)D(2) occurs only after 1alpha,25(OH)(2)D(2) is hydroxylated at C-24 position. At present the enzyme responsible for the C-28 hydroxylation of 1alpha, 24(R),25(OH)(3)D(2) in rat kidney is not known. Recently, it was found that 1alpha,25(OH)(2)D(3)-24-hydroxylase (CYP24) can hydroxylate carbons 23, 24, and 26 of various vitamin D(3) compounds. Thus, it may be speculated that CYP24 may also be responsible for the C-28 hydroxylation of 1alpha,24(R),25(OH)(3)D(2) to form 1alpha, 24(S),25,28(OH)(4)D(2). The biological activity of 1alpha,24(S),25, 28(OH)(4)D(2), determined by its ability to induce intestinal calcium transport and bone calcium resorption in the rat, was found to be almost negligible. Also, 1alpha,24(S),25,28(OH)(4)D(2) exhibited very low binding affinity toward bovine thymus vitamin D receptor. These studies firmly establish that C-28 hydroxylation is an important enzymatic reaction involved in the inactivation of 1alpha,25(OH)(2)D(2) in kidney under physiological conditions.

Effects of increasing doses of 1 alpha-hydroxyvitamin D2 on calcium homeostasis in postmenopausal osteopenic women

This study is the first reported administration of 1 alpha-hydroxyvitamin D2 (1 alpha-OHD2) to human subjects. A total of 15 postmenopausal osteopenic women were given increasing oral doses of 1 alpha-OHD2, beginning with a low dose of 0.5 microgram/day. In 15 subjects, the doses were raised at weekly intervals to 1.0, 2.0, 4.0, and 5.0 micrograms/day, and in 5 of these subjects, the dose was further increased to 8.0 or 10.0 micrograms/day. Mean urine calcium +/- SEM showed a dose-related increase from 134 +/- 17 mg/24 h on 0.5 microgram/day to 198 +/- 21 mg/24 h on 4.0 micrograms/day (p < 0.05) and to 241 +/- 35 mg/24 h on 5.0 micrograms/day (p < 0.05). No subjects had hypercalciuria (> 350 mg/24 h, the upper limit of the laboratory normal range) at doses less than 5.0 micrograms/day; 5 subjects had hypercalciuria at or above 5.0 micrograms/day (3 at 5.0 micrograms/day, 1 at 8.0 micrograms/day, and 1 at 10.0 micrograms/day). Mean serum calcium increased slightly on the 4.0 micrograms dose only (p < 0.05) but remained well within the normal range. Mean creatinine clearance and BUN, used as measures of renal function, showed no significant changes. Routine blood and urine assays also showed no significant changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of vitamin D2 and vitamin D3 in patients on anticonvulsant therapy

We examined the effect of short-term treatment with pharmacological doses of vitamin D2 or vitamin D3 on the serum concentration of 1,25(OH)2D metabolites in epileptic patients on chronic anticonvulsant drug therapy. Nine patients were studied before and after treatment with vitamin D2 4000 IU daily for 24 weeks and 10 before and after treatment with vitamin D3 in the same dose. Before treatment the serum concentrations of 1,25(OH)2D and 25(OH)D were significantly lower in epileptics than in normal subjects (P less than 0.01). Vitamin D2 treatment increased the serum concentration of 1,25(OH)2D2, but a corresponding decrease in 1,25(OH)2D3 resulted in an unchanged serum concentration of total 1,25(OH)2D. The serum concentration of 25(OH)D2 and 25(OH)D increased significantly, whereas there was a small decrease in 25(OH)D3. Vitamin D3 treatment did not change the serum concentration of 1,25(OH)2D3 whereas serum 25(OH)D3 increased significantly. The correlation between the serum ratio of 1,25(OH)2D2/1,25(OH)2D3 and 25(OH)D2/25(OH)D3 estimated on vitamin D2-treated epileptic patients and normal subjects was highly significant (P less than 0.01). The data indicate that the serum concentration of 1,25(OH)2D2 and 1,25(OH)2D3 are directly proportional to the amount of their precursors 25(OH)D2 and 25(OH)D3 and that the concentration of total 1,25(OH)2D is tightly regulated.

Comparisons between two receptor assays for 1,25-dihydroxyvitamin D

We present a competitive protein binding assay (CPBA) for 1,25(OH)2D employing 1,25(OH)2D receptor from calf thymus, which was compared with a CPBA-employing receptor from rachitic chick intestine. The thymus receptor assay was more sensitive, specific and precise than the intestinal receptor assay. The thymus receptor assay measured both 1,25(OH)2D2 and 1,25(OH)2D3 with equal affinity, whereas 1,25(OH)2D2 was 1.1 times less potent than 1,25(OH)2D3 in the displacement from the chick intestinal receptor. Mean serum values of 1,25(OH)2D in normal subjects, post-menopausal women, pregnant women, and patients with chronic renal failure measured by the two assay systems did not differ. Furthermore, both assays showed that 1,25(OH)2D was unchanged in post-menopausal women after treatment with vitamin D2 or vitamin D3, 4000 IU/day for 8 weeks. We conclude that the high sensitivity of the thymus receptor and the equal affinity for the D2 and D3 analogue make the thymus receptor assay a reliable alternative to the chick intestinal receptor assay.

Action and metabolism of dihydrotachysterol2

Dihydrotachysterol2 (DHT2) is a synthetic analogue of vitamin D2. DHT2 is used extensively in the treatment of renal osteodystrophy and hypoparathyroidism. It is equally efficacious as 1 alpha,25-dihydroxyvitamin D3 and 1 alpha-hydroxyvitamin D3. Moreover, it offers interesting therapeutical advantages and it is surprising that until recently little was known of its metabolism and sites of action. This paper deals with studies on the pharmacology of DHT2 in rats. Following the synthesis of [3H]DHT2 and oral administration, evidence was obtained that DHT2 is metabolized extensively; three of the major metabolites could be identified as 25-hydroxy-DHT2, 1 alpha,25- and 1 beta,25-dihydroxy-DHT2.

Maternal compared with infant vitamin D supplementation

Vitamin D metabolites were studied in mother-infant pairs at delivery and eight and 15 weeks after that to evaluate the possibility of vitamin D supplementation of infant through the mother. Healthy mothers (n = 49) delivering in January received daily either 2000 IU (group 1), 1000 IU (group 2), or no (group 3) vitamin D. Their infants were exclusively breast fed, and those in group 3 received 400 IU of vitamin D a day. After eight weeks of lactation the infantile vitamin D concentrations were similar in groups 1 and 3 but significantly lower in group 2. The serum 24,25-dihydroxyvitamin D and 1,25-dihydroxyvitamin D concentrations were also lower in group 2. The mean mineral, parathyroid hormone, and alkaline phosphatase values showed no intergroup differences at any point. No infants showed any clinical or biochemical signs of rickets, and their growth was equal. In conclusion, a daily postpartum maternal supplementation with 2000 IU of vitamin D, but not with 1000 IU, seems to normalise the vitamin D metabolites of breast fed infants in winter. Maternal safety with such supplementation over prolonged periods, however, should be examined.

Isolation and identification of 1,24,25-trihydroxyvitamin D2, 1,24,25,28-tetrahydroxyvitamin D2, and 1,24,25,26-tetrahydroxyvitamin D2: new metabolites of 1,25-dihydroxyvitamin D2 produced in rat kidney

Three new metabolites of vitamin D2 were produced in vitro by perfusing isolated rat kidneys with 1,25-dihydroxyvitamin D2. They were isolated and purified from the kidney perfusate by the techniques of methanol-methylene chloride lipid extraction and high-performance liquid chromatography. By means of ultraviolet absorption spectrophotometry, mass spectrometry, and specific chemical reactions, the metabolites were identified as 1,24,25-trihydroxyvitamin D2, 1,24,25,28-tetrahydroxyvitamin D2, and 1,24,25,26-tetrahydroxyvitamin D2. Both 1,24,25,28-tetrahydroxyvitamin D2 and 1,24,25,26-tetrahydroxyvitamin D2 were also produced when a kidney was perfused with 1,24,25-trihydroxyvitamin D2. Thus, it becomes clear that 1,25-dihydroxyvitamin D2 is first hydroxylated at C-24 to form 1,24,25-trihydroxyvitamin D2, which is then further hydroxylated at C-28 and C-26 to form 1,24,25,28-tetrahydroxyvitamin D2 and 1,24,25,26-tetrahydroxyvitamin D2, respectively. From several recent studies, it has been well established that 1,25-dihydroxyvitamin D3 is converted into various further metabolites in the kidney as a result of chemical reactions such as C-23, C-24, and C-26 hydroxylations, C-24 ketonization, and C-23:C-26 lactonization. From our study it is obvious that 1,25-dihydroxyvitamin D2 does not undergo all of the aforementioned chemical reactions except C-24 and C-26 hydroxylations. Also, our study indicates that C-28 hydroxylation plays a significant role in the further metabolism of 1,25-dihydroxyvitamin D2. Thus, for the first time, we describe a novel further metabolic pathway for 1,25-dihydroxyvitamin D2 in a mammalian kidney.

Representativity of regional to total bone mineral in healthy subjects and 'anticonvulsive treated' epileptic patients. Measurements by single and dual photon absorptiometry

Dual photon (153Gd) and single photon (125I) absorptiometry were used to measure the regional bone mineral content (BMC) and density (BMD), as well as the total body mineral content (TBBM) and density (TBBD), in sixty-nine healthy subjects and in twenty-three epileptics on phenobarbitone. The BMCs (and BMDs) of all regions were significantly correlated to each other and to the TBBM (and TBBD). No difference in the ability to discriminate between the different study groups was found for the various regions, excepting the BMD of the head. The relationship between the forearm BMC and TBBM was highly significant, and identical in the five groups. The relationships between spinal BMC and forearm BMC, and TBBM differed in the five groups. It is concluded that some local measurement may be used as estimates of the total body bone mineral in some groups of patients with minor metabolic bone disease and healthy subjects.

Different metabolism of vitamin D2/D3 in epileptic patients treated with phenobarbitone/phenytoin

Serum concentrations of vitamin D metabolites were measured before and during treatment with either vitamin D2 or vitamin D3, 4000 IU per day for 24 weeks, in 22 epileptic outpatients receiving phenobarbitone/phenytoin. The serum concentration of total 1,25(OH)2D did not change during the treatment period in any of the treatment groups. On the other hand, in the vitamin D2 group, serum 25(OH)D2, total 25(OH)D, and 24,25(OH)2D increased significantly during the trial, whereas serum concentrations of the vitamin D3 metabolites were unchanged. In the vitamin D3 group, serum concentrations of the vitamin D3 metabolites increased significantly, whereas the vitamin D3 metabolite levels remained unchanged. However, vitamin D3 treatment resulted in a 2-4-fold greater increase in serum concentrations compared to vitamin D2 treatment. Treatment with vitamin D2 and vitamin D3 in the same dose in IU results in considerably different serum concentrations of the vitamin D metabolites.

Irreversible bone loss in osteomalacia. Comparison of radial photon absorptiometry with iliac bone histomorphometry during treatment

We examined the relationships between the changes in bone mineral deficit in the radius, determined by single-energy photon absorptiometry at standard proximal and distal sites, and in the ilium, determined by bone histomorphometry, during the treatment of osteomalacia of diverse etiology in 28 patients. In the ilium, relative osteoid volume decreased by 75-80% in both cortical bone (from 6.0% to 1.5%) and trabecular bone (from 30.1% to 6.6%) during a mean treatment duration of 2 yr. There was also a significant fall in iliac cortical porosity from 10.3% to 7.8%. As a result, mineralized bone volume increased by 7.5% in cortical and by 40.1% in trabecular bone; the cortical and trabecular increments were correlated (r = 0.69, P less than 0.001). The properly weighted increase for the entire tissue sample was 18.6%. By contrast, there was no change in bone mineral at either radial site, although there was a 2% increase at both sites when allowance was made for age-related bone loss during treatment. The proximal and distal age-adjusted increments was correlated (r = 0.76, P less than 0.001), but there was no correlation between the changes in any photon absorptiometric and any histomorphometric index. In that iliac cortical bone turnover in normal subjects was 7.2%/yr, we estimated the rate of bone turnover to be less than 2%/yr at both proximal and distal radial sites, including any trabecular bone present at the distal site. Compared to appropriate control subjects, the bone mineral deficits fell during treatment from 19.2% to 17.1% at the proximal radius (greater than 95% cortical bone) and from 20.5% to 18.5% at the distal radius (greater than 75% cortical bone). In the ilium the deficits, assuming attainment of normal values for osteoid volume and cortical porosity, fell from 41.7% to 36.1% in cortical and from 31.5% to 6.3% in trabecular bone, the properly weighted combined deficit falling from 38.6% to 27.7%. The irreversible iliac cortical deficit was entirely due to cortical thinning because of increased net endosteal resorption; the resultant expansion of the marrow cavity offset the modest loss of fractional trabecular mineralized bone. We conclude: in osteomalacia there is a large irreversible and a small reversible bone mineral deficit at both proximal and distal radial sites, in similar proportion to the iliac cortex but of smaller magnitude; the anatomic basis of the irreversible bone mineral deficit at all three sites that persists despite correction of the mineralization defect by appropriate treatment is thinning of cortical bone, most likely owing to prolonged secondary hyperparathyroidism; (c) there is no evidence that the proportion of trabecular bone in the distal radius at any site proximal to the radioulnar joint has any relevance to the interpretation of measurements made at that site; (d) there are at least three functional subdivisions of trabecular bone depending on proximity to hematopoietic marrow, fatty marrow, or synovium; and (e) single photon absorptiometry of the radius is an excellent method for measuring cortical bone mass in the appendicular skeleton, but is of little value for the assessment of changes in trabecular bone status.

Different metabolism of vitamin D2 and vitamin D3 in epileptic patients on carbamazepine

Serum concentrations of vitamin D metabolites were measured in 30 epileptic outpatients on monotherapy with carbamazepine before and during treatment with either vitamin D2 or vitamin D3, 4000 IU per day for 24 weeks. Vitamin D2 treatment increased the serum concentration of 25OHD2, but a corresponding decrease in 25OHD3 resulted in an unchanged serum value of total 25OHD. Vitamin D3 treatment increased the serum concentration of 25OHD3. The resulting serum level of 25OHD was consequently twice the level of that in the D2-treated group. The serum concentrations of the dihydroxy metabolites showed a similar difference between the 2 treatment groups. We conclude that treatment with vitamins D2 and D3 in the same doses produces considerably different serum concentrations of vitamin D metabolites. If the present findings can be extrapolated to normal subjects, it is important to consider more carefully which D-vitamin should be used, both with regard to therapy and supplementation.