Influences of dietary vitamin D restriction on bone strength, body composition and muscle in rats fed a high-fat diet: involvement of mRNA expression of MyoD in skeletal muscle

Effects of vitamin D3 supplementation on strength of lower and upper extremities in athletes: an updated systematic review and meta-analysis of randomized controlled trials

Background

Coaches and athletes are increasingly interested in understanding athletes' serum vitamin D levels, their impact on strength, physical performance, and athletic outcomes. Previous meta-analyses were reported with limited sample size and no significant overall effect was found. Hence, it is crucial to conduct a thorough and up-to-date systematic examination and meta-analysis to elucidate the potential advantages of supplementing with vitamin D3 in enhancing muscle strength for athletes.

Methods

We performed a thorough investigation, spanning three databases (PubMed, EBSCO, and Cochrane Library), seeking randomized controlled trials (RCTs) in all languages. These trials delved into the influence of vitamin D3 supplementation on the changes of pre- and post-intervention muscle strength in healthy athletes. Our systematic examination and meta-analysis took into account serum 25(OH)D levels exceeding 30 ng/mL as a marker of adequacy.

Results

Ten RCTs, comprising 354 athletes (185 in the vitamin D3 group and 169 in the placebo group), fulfilled the inclusion criteria. During the study, 36 athletes were lost to follow-up, leaving 318 athletes (166 in the vitamin D3 group and 152 in the placebo group) with documented complete results. In comparison with the placebo group, there is a significant increase between the changes of pre- and post-intervention serum 25(OH)D levels among athletes following a period of vitamin D3 supplementation (MD 14.76, 95% CI: 8.74 to 20.77, p < 0.0001). Overall effect of four strength measurements including handgrip, one repetition maximum Bench Press (1-RM BP), vertical jump, and quadriceps contraction was not significantly improved (SMD 0.18, 95% CI: -0.02 to 0.37, p = 0.08), but there was a significant increase in quadriceps contraction (SMD 0.57, 95% CI: 0.04 to 1.11, p = 0.04).

Conclusion

This updated meta-analysis indicates the potential benefits of vitamin D supplementation for enhancing muscle strength in athletes when analyzing its quantitatively synthesized effects. With limited available studies for the quantitative synthesis, it cannot warrant significant overall enhancements in muscle strength when athletes attain adequate serum 25(OH)D levels through supplementation.

A low-intensity lifelong exercise routine changes miRNA expression in aging and prevents osteosarcopenic obesity by modulating inflammation

Osteosarcopenic obesity (OSO) has been associated with increase immobility, falls, fractures, and other dysfunctions, which could increase mortality risk during aging. However, its etiology remains unknown. Recent studies revealed that sedentarism, fat gain, and epigenetic regulators are critical in its development. One effective intervention to prevent and treat OSO is exercise. Therefore, in the present study, by keeping rats in conditions of sedentarism and others under a low-intensity exercise routine, we established an experimental model of OSO. We determined the degree of sarcopenia, obesity, and osteopenia at different ages and analyzed the miRNA expression during the lifespan using miRNA microarrays from gastrocnemius muscle. Interestingly microarrays results showed that there is a set of miRNAs that changed their expression with exercise. The pathway enrichment analysis showed that these miRNAs are strongly associated with immune regulation. Further inflammatory profiles with IL-6/IL-10 and TNF-α/IL-10 ratios showed that exercised rats presented a lower pro-inflammatory profile than sedentary rats. Also, the body fat gain in the sedentary group increased the inflammatory profile, ultimately leading to muscle dysfunction. Exercise prevented strength loss over time and maintained skeletal muscle functionality over time. Differential expression of miRNAs suggests that they might participate in this process by regulating the inflammatory response associated with aging, thus preventing the development of OSO.

Calcitriol increases MBNL1 expression and alleviates myotonic dystrophy phenotypes in HSALR mouse models

BACKGROUND

Myotonic dystrophy type 1 (DM1), one of the most common forms of adult-onset muscular dystrophy, is caused by abnormally expanded CTG repeats in the 3' untranslated region of the DMPK gene. The CUG repeats transcribed from the expanded CTG repeats sequestrate a splicing factor, MBNL1, causing the clinical symptoms in DM1. Nowadays, only symptomatic treatments are available for DM1, and no rational therapy is available. Recently, upregulation of MBNL1 expression has been found to be one of the promising therapies for DM1.

METHODS

All experiments were conducted in the C2C12 myoblasts and HSA^LR mice, a DM1 mouse model. Real-time PCR and western blot were used to detect the mRNA and protein level, respectively. The rotarod exercise, grip strength and hanging time were used to evaluate the muscle strength of mice.

RESULTS

In this study, we demonstrated that calcitriol, an active form of vitamin D3, increased MBNL1 in C2C12 mouse myoblasts as well as in HSA^LR mice model for DM1. In HSA^LR mice model, calcitriol improved muscle strength, and corrected aberrant splicing in skeletal muscle. Besides, calcitriol reduced the number of central nuclei, and improved muscle histopathology in HSA^LR mice. In addition, we identified that calcitriol upregulated MBNL1 expression via activating the promoter of Mbnl1 in C2C12 myogenic cells.

CONCLUSION

Our study suggests that calcitriol is a potential pharmacological strategy for DM1 that enhances MBNL1 expression.

Effects of Vitamin D on Satellite Cells: A Systematic Review of In Vivo Studies

The non-classical role of vitamin D has been investigated in recent decades. One of which is related to its role in skeletal muscle. Satellite cells are skeletal muscle stem cells that play a pivotal role in skeletal muscle growth and regeneration. This systematic review aims to investigate the effect of vitamin D on satellite cells. A systematic search was performed in Scopus, MEDLINE, and Google Scholar. In vivo studies assessing the effect of vitamin D on satellite cells, published in English in the last ten years were included. Thirteen in vivo studies were analyzed in this review. Vitamin D increases the proliferation of satellite cells in the early life period. In acute muscle injury, vitamin D deficiency reduces satellite cells differentiation. However, administering high doses of vitamin D impairs skeletal muscle regeneration. Vitamin D may maintain satellite cell quiescence and prevent spontaneous differentiation in aging. Supplementation of vitamin D ameliorates decreased satellite cells' function in chronic disease. Overall, evidence suggests that vitamin D affects satellite cells' function in maintaining skeletal muscle homeostasis. Further research is needed to determine the most appropriate dose of vitamin D supplementation in a specific condition for the optimum satellite cells' function.

Correlation between the Positive Effect of Vitamin D Supplementation and Physical Performance in Young Male Soccer Players

The aim of this study was to determine whether supplementation with vitamin D during eight weeks of high-intensity training influences muscle power and aerobic performance in young soccer players. A total of 25 athletes were divided into two groups: the supplemented group (GS; n = 12; vitamin D 20,000 IU, twice a week) and the non-supplemented group (GN; n = 13). A set of measurements, including sprint tests, explosive power test, maximal oxygen uptake (VO2max), and serum 25(OH)D concentration, were obtained before (T1) and after (T2) the intervention. A significant group x time interaction was found in the 25(OH)D serum levels (p = 0.002; ES = 0.36, large). A significant improvement in VO2max was found in the TG (p = 0.0004) and the GS (p = 0.031). Moreover, a positive correlation between 25(OH)D and VO2max (R = 0.4192, p = 0.0024) was calculated. The explosive power tests revealed insignificant time interactions in the average 10-jump height and average 10-jump power (p = 0.07, ES = 0.13; p = 0.10, ES = 0.11, respectively). A statistically insignificant trend was observed only in the group-by-time interaction for the sprint of 10 m (p = 0.05; ES = 0.15, large). The present study provides evidence that vitamin D supplementation has a positive but trivial impact on the explosive power and locomotor skills of young soccer players, but could significantly affect their aerobic performance.

A high-fat diet in the presence of vitamin D deficiency status is associated with a negative influence on calcaneal quantitative ultrasound parameters in young adults: a cross-sectional study

Vitamin D deficiency and a high-fat diet are considered health problems worldwide. The aims of this study were to examine the prevalence of vitamin D deficiency/insufficiency in young adults, factors related to the vitamin D status, and the influence of vitamin D deficiency and/or a high-fat diet on bone parameters. Here, we investigated the hypothesis that a high-fat diet in the presence of a vitamin D-deficient status would have a more negative influence on bone parameters than a normal-fat diet with such a status. In the present study, we targeted young Japanese adults aged 21-23 (n = 175). We conducted a diet survey based on 3-day food records, biochemical examination of serum, and quantitative ultrasound measurements at the calcaneus. As a result, the rates of vitamin D deficiency {serum 25-hydroxyvitamin D₃ [25(OH)D] concentration less than 20 ng/mL} and insufficiency [serum 25(OH)D concentration less than 30 ng/mL but not less than 20 ng/mL] were 60.6 and 30.9%, respectively. A positive correlation was observed between the serum 25(OH)D level and serum bone-specific alkaline phosphatase level, which is a serum marker of bone formation (r = 0.253, P< .01) or the speed of sound (SOS) as an index of bone density (r = 0.259, P< .01). A negative correlation was observed between the ratio of fat intake to total energy intake (%E) and serum 25(OH)D levels (r = -0.206, P< .01). Furthermore, we revealed that a high-fat diet in the presence of a vitamin D deficient status reduced the SOS parameter compared with a normal-fat diet with a vitamin D-deficient status (P< .05).

The role of serum levels of vitamin D in children's muscle strength: A systematic review

This review aims to investigate the different levels of vitamin D and its role in muscle strength in healthy children and non-athletes. A search conducted in three databases (PubMed, Scopus, and Psycinfo) resulted in 655 articles, which were systematically analyzed and selected based on the following criteria: (a) original cross-sectional studies and clinical trials; (b) healthy children aged 5-11 years; (c) no language restriction or year of publication; and (d) studies that assessed the possible relationship between vitamin D levels and muscle strength. Six studies were included because they met all the inclusion criteria. According to the findings of this review, factors such as sex, skin color, and vitamin D supplementation early in life modulate the levels of vitamin D in the body, and there is a relationship between muscle strength and vitamin D levels. Interestingly, vitamin D supplementation is not always significantly associated with increased muscle grip strength. However, there is a scarcity of studies that aim to analyze the possible effects of different levels of vitamin D on muscle function and neuromuscular variables in physically inactive children and non-athletes without previously diagnosed disease. Further studies are warranted in the future to address the gap in the literature.

High Salt Diet Impacts the Risk of Sarcopenia Associated with Reduction of Skeletal Muscle Performance in the Japanese Population

The World Health Organization has recommended 5 g/day as dietary reference intakes for salt. In Japan, the averages for men and women were 11.0 g/day and 9.3 g/day, respectively. Recently, it was reported that amounts of sodium accumulation in skeletal muscles of older people were significantly higher than those in younger people. The purpose of this study was to investigate whether the risk of sarcopenia with decreased muscle mass and strength was related to the amount of salt intake. In addition, we investigated its involvement with renalase. Four groups based on age and salt intake ("younger low-salt," "younger high-salt," "older low-salt," and "older high-salt") were compared. Stratifying by age category, body fat percentage significantly increased in high-salt groups in both younger and older people. Handgrip strength/body weight and chair rise tests of the older high-salt group showed significant reduction compared to the older low-salt group. However, there was no significant difference in renalase concentrations in plasma. The results suggest that high-salt intake may lead to fat accumulation and muscle weakness associated with sarcopenia. Therefore, efforts to reduce salt intake may prevent sarcopenia.

Bone tissue engineering gelatin-hydroxyapatite/graphene oxide scaffolds with the ability to release vitamin D: fabrication, characterization, and in vitro study

Developing smart scaffolds with drug release capability is one of the main approaches to bone tissue engineering. The current study involves the fabrication of novel gelatin (G)-hydroxyapatite (HA)-/vitamin D (VD)-loaded graphene oxide (GO) scaffolds with different concentrations through solvent-casting method. Characterizations confirmed the successful synthesis of HA and GO, and VD was loaded in GO with 36.87 ± 4.87% encapsulation efficiency. Physicochemical characterizations showed that the scaffold containing 1% VD-loaded GO had the best mechanical properties and its porosity percentage and density was in the range of natural spongy bone. All scaffolds were degraded after 1-month, subjecting to phosphate buffer saline. The release profile of VD did not match any mathematical kinetics model, porosities and the degradation rate of the scaffolds were dominant controlling factors of release behavior. Studies on the bioactivity of scaffolds immersed in simulated body fluid indicated that VD and HA could encourage the formation of secondary apatite crystals in vitro. Buccal fat pad-derived stem cells (BFPSCs) were seeded on the scaffolds, MTT assay, alkaline phosphatase activity as an indicator of osteoconductivity, and cell adhesion were conducted in order to evaluate in vitro biological responses. All scaffolds highly supported cell adhesion, MTT assay indicated better cell viability in 0.5% VD-loaded GO containing scaffold, and the scaffold enriched with 2% VD-loaded GO performed the most ALP activity. The results demonstrated the potential of these scaffolds to induce bone regeneration. Developing smart scaffolds with drug release capability is one of the main approaches to bone tissue engineering. The current study involves the fabrication of novel gelatin (G)-hydroxyapatite (HA)-/vitamin D (VD)-loaded graphene oxide (GO) scaffolds with different concentrations through solvent-casting method. Characterizations confirmed the successful synthesis of HA and GO, and VD was loaded in GO with 36.87 ± 4.87% encapsulation efficiency. Physicochemical characterizations showed that the scaffold containing 1% VD-loaded GO had the best mechanical properties and its porosity percentage and density was in the range of natural spongy bone. All scaffolds were degraded after 1-month, subjecting to phosphate buffer saline. The release profile of VD did not match any mathematical kinetics model, porosities and the degradation rate of the scaffolds were dominant controlling factors of release behavior. Studies on the bioactivity of scaffolds immersed in simulated body fluid indicated that VD and HA could encourage the formation of secondary apatite crystals in vitro. Buccal fat pad-derived stem cells (BFPSCs) were seeded on the scaffolds, MTT assay, alkaline phosphatase activity as an indicator of osteoconductivity, and cell adhesion were conducted in order to evaluate in vitro biological responses. All scaffolds highly supported cell adhesion, MTT assay indicated better cell viability in 0.5% VD-loaded GO containing scaffold, and the scaffold enriched with 2% VD-loaded GO performed the most ALP activity. The results demonstrated the potential of these scaffolds to induce bone regeneration.

Vitamin D and Skeletal Muscle: Emerging Roles in Development, Anabolism and Repair

This special issue article will focus on morphologic and functional roles of vitamin D in muscle, from strength to contraction to development and ageing and will characterise the controversy of VDR's expression in skeletal muscle, central to our understanding of vitamin D's effects on this tissue.

Effects of vitamin D3 supplementation on serum 25(OH)D concentration and strength in athletes: a systematic review and meta-analysis of randomized controlled trials

Background

The purpose of this systematic review and meta-analysis is to investigate the effects of vitamin D3 supplementation on skeletal muscle strength in athletes. Vitamin D3 supplements or vitamin D3 fortified foods always have claims for bringing people health benefits including bone and muscle health. An up-to-date rigorous systematic review and meta-analysis is important to better understand the effect of vitamin D3 supplementation on muscle strength.

Methods

English written randomized controlled trials (RCTs) that looked at effects of vitamin D3 supplementation on muscle strength in healthy athletes were searched using three databases (PubMed, Embase and Cochrane Library). Serum 25(OH)D above 30 ng/mL is considered to be sufficient in this systematic review and meta-analysis.

Results

Five RCTs with 163 athletes (vitamin D3 n = 86, placebo n = 77) met inclusion criteria. Fourteen athletes were lost to follow-up and 149 athletes (vitamin D3 n = 80, placebo n = 69) were documented with complete result. Among athletes with baseline serum 25(OH)D values suggesting insufficiency, vitamin D3 daily dosage at 5000 IU for over 4 weeks led to a serum 25(OH)D concentration of 31.7 ng/mL. Athletes with sufficient serum 25(OH)D level at baseline were recruited in only one study, and the participants of which were assigned to either vitamin D3 at a daily dosage of 3570 IU or placebo for 12 weeks, their serum 25(OH)D sufficiency (VD: 37.2 ± 7.6 vs. 45.6 ± 7.6; PL: 38 ± 6.8 vs. 32 ± 8.4) was well maintained above the cut-off boundary. One repetition maximum Bench Press (1-RM BP) was not improved significantly (SMD 0.07, 95% CI: − 0.32 to 0.47, P = 0.72) and there was no significant increase in maximal quadriceps contraction (SMD -2.14, 95% CI: − 4.87 to 0.59, P = 0.12). Furthermore, there was no significant overall effect of vitamin D3 intervention on muscle strength in this meta-analysis (SMD -0.75, 95% CI: − 1.82 to 0.32, P = 0.17).

Conclusion

Although, serum 25(OH)D concentrations after supplementation reached sufficiency was observed, muscle strength did not significantly improve at this point of current meta-analysis. Additional well-designed RCTs with large number of participants examined for the effect of vitamin D3 supplementation on serum 25(OH)D concentrations, muscle strength in a variety of sports, latitudes and diverse multicultural populations are needed.

Effects of vitamin D on primary human skeletal muscle cell proliferation, differentiation, protein synthesis and bioenergetics

The active form of Vitamin D (1,25(OH)2D), has been suggested to have a regulatory role in skeletal muscle function and metabolism, however, the effects and mechanisms of vitamin D (VitD) action in this tissue remain to be fully established. In this study, we have used primary human skeletal muscle myoblast (HSMM) cells that display typical characteristics of human skeletal muscle function and protein levels, to investigate the effects of the active form of VitD on proliferation, differentiation, protein synthesis and bioenergetics. Myoblast cells were treated with 100 nM of VitD for 24 h, 48 h, 72 h and five days (cells were differentiated into myotubes) and then analyses were performed. We report that VitD inhibits myoblast proliferation and enhances differentiation by altering the expression of myogenic regulatory factors. In addition, we found that protein synthesis signaling improved in myotubes after VitD treatment in the presence of insulin. We also report an increase in oxygen consumption rate after 24 h of treatment in myoblasts and after 5 days of treatment in myotubes after VitD exposure. VitD significantly impacted HSMM myogenesis, as well as protein synthesis in the presence of insulin.

Mechanisms of vitamin D action in skeletal muscle

Vitamin D receptor expression and associated function have been reported in various muscle models, including C2C12, L6 cell lines and primary human skeletal muscle cells. It is believed that 1,25-hydroxyvitamin D3 (1,25(OH)2D3), the active form of vitamin D, has a direct regulatory role in skeletal muscle function, where it participates in myogenesis, cell proliferation, differentiation, regulation of protein synthesis and mitochondrial metabolism through activation of various cellular signalling cascades, including the mitogen-activated protein kinase pathway(s). It has also been suggested that 1,25(OH)2D3 and its associated receptor have genomic targets, resulting in regulation of gene expression, as well as non-genomic functions that can alter cellular behaviour through binding and modification of targets not directly associated with transcriptional regulation. The molecular mechanisms of vitamin D signalling, however, have not been fully clarified. Vitamin D inadequacy or deficiency is associated with muscle fibre atrophy, increased risk of chronic musculoskeletal pain, sarcopenia and associated falls, and may also decrease RMR. The main purpose of the present review is to describe the molecular role of vitamin D in skeletal muscle tissue function and metabolism, specifically in relation to proliferation, differentiation and protein synthesis processes. In addition, the present review also includes discussion of possible genomic and non-genomic pathways of vitamin D action.

Changes of serum 25(OH) D3 and IGF-1 levels in patients with thyroid nodules

BACKGROUND

The present study aimed to study the relationship between serum 25 hydroxyvitamin D3(25(OH)D3) and insulin-like growth factor-1 (IGF-1) and thyroid nodules.

METHODS

Two hundred eighty-nine cases with thyroid nodules and 109 health subjects (control group) who admitted to the Hebei General Hospital during June 2016 to December 2016 were included in the study. Basic clinical information (age, sex, thyroid function, liver and kidney function, hypertension history, etc.) of patients were collected. Serum 25(OH) D3 and Serum IGF-1 were detected by electrochemiluminescence and radioimmunoassay methods, respectively. The relationship between the above-mentioned factors and thyroid nodules was statistically analyzed.

RESULTS

Serum 25(OH)D3, IGF-1, fasting blood glucose (FBG), total cholesterol (TC), waist circumference (WC), total triiodothyronine (TT3), total thyroxine (TT4), hypertension history, and drinking history were significantly different between the nodules group and the control group (P < 0.05). Logistic regression analysis showed that there was a negative correlation between thyroid nodules and levels of 25(OH)D3, IGF-1, TT3, as well as a positive correlation with FBG, TC, TT4, and hypertension. There was a positive correlation between IGF-1 and serum 25(OH)D3 in thyroid nodules (P < 0.05). After correcting the aforementioned factors, high-level of serum 25(OH)D3 was significantly correlated with the decreased incidence of thyroid nodules.

CONCLUSIONS

The incidence of thyroid nodules is relatively lower in a high-level of serum 25(OH)D3, and serum 25(OH)D3 may be a direct protective factor for thyroid nodules. Serum IGF-1 can be one of the indirect protective factors for thyroid nodules as well.

Impact of Western and Mediterranean Diets and Vitamin D on Muscle Fibers of Sedentary Rats

Background: The metabolic syndrome is associated with sarcopenia. Decreased serum levels of Vitamin D (VitD) and insulin-like growth factor (IGF)-1 and their mutual relationship were also reported. We aimed to evaluate whether different dietary profiles, containing or not VitD, may exert different effects on muscle molecular morphology. Methods: Twenty-eight male rats were fed for 10 weeks in order to detect early defects induced by different dietary regimens: regular diet (R); regular diet with vitamin D supplementation (R-DS) and regular diet with vitamin D restriction (R-DR); high-fat butter-based diets (HFB-DS and HFB-DR) with 41% energy from fat; high-fat extra-virgin olive oil-based diets (HFEVO-DS and HFEVO-DR) with 41% energy from fat. IL-1β, insulin-like growth factor (IGF)1, Dickkopf-1 (DKK-1), and VitD-receptor (VDR) expressions were evaluated by immunohistochemistry. Muscle fiber perimeter was measured by histology and morphometric analysis. Results: The muscle fibers of the HEVO-DS rats were hypertrophic, comparable to those of the R-DS rats. An inverse correlation existed between the dietary fat content and the perimeter of the muscle fibers (p < 0.01). In the HFB-DR rats, the muscle fibers appeared hypotrophic with an increase of IL-1β and a dramatic decrease of IGF-1 expression. Conclusions: High-fat western diet could impair muscle metabolism and lay the ground for subsequent muscle damage. VitD associated with a Mediterranean diet showed trophic action on the muscle fibers.

Vitamin D and muscle trophicity

PURPOSE OF REVIEW

We review recent findings on the involvement of vitamin D in skeletal muscle trophicity.

RECENT FINDINGS

Vitamin D deficiencies are associated with reduced muscle mass and strength, and its supplementation seems effective to improve these parameters in vitamin D-deficient study participants. Latest investigations have also evidenced that vitamin D is essential in muscle development and repair. In particular, it modulates skeletal muscle cell proliferation and differentiation. However, discrepancies still exist about an enhancement or a decrease of muscle proliferation and differentiation by the vitamin D. Recently, it has been demonstrated that vitamin D influences skeletal muscle cell metabolism as it seems to regulate protein synthesis and mitochondrial function. Finally, apart from its genomic and nongenomic effects, recent investigations have demonstrated a genetic contribution of vitamin D to muscle functioning.

SUMMARY

Recent studies support the importance of vitamin D in muscle health, and the impact of its deficiency in regard to muscle mass and function. These 'trophic' properties are of particular importance for some specific populations such as elderly persons and athletes, and in situations of loss of muscle mass or function, particularly in the context of chronic diseases.

Supplementation with 2000 IU of Cholecalciferol Is Associated with Improvement of Trabecular Bone Mineral Density and Muscle Power in Pediatric Patients with IBD

BACKGROUND

Inflammatory bowel diseases (IBD) are associated with altered bone health and increased risk for fractures. Vitamin D deficiency is frequently found in IBD; however, the effect of vitamin D supplementation on bone health of children with IBD is poorly understood. We aimed to observe the changes in volumetric bone density and dynamic muscle functions after vitamin D substitution in a cohort of pediatric patients with IBD.

METHODS

This was a prospective observational study of 55 patients (aged 5-19 years) with IBD. Bone quality was assessed using peripheral quantitative computed tomography and muscle functions by jumping mechanography at baseline and after a median of 13.8 (interquartile range, 12.0-16.0) months of daily substitution of 2000 IU of cholecalciferol.

RESULTS

Median serum levels of 25-hydroxyvitamin D increased from 58 nmol/L at the baseline visit to 85 nmol/L at the last follow-up visit (P < 0.001); no signs of overdose were reported. The Z-scores of trabecular bone mineral density, cortical bone cross-sectional area, and maximal muscle power improved significantly during the follow-up period (+0.5, P = 0.001, +0.3, P = 0.002 and +0.5, P = 0.002, respectively). Cholecalciferol substitution was positively associated with trabecular bone mineral density and maximal muscle power (estimates 0.26, 95% confidence interval 0.14-0.37, P < 0.0001 and 0.60, 95% confidence interval 0.32-0.85, P < 0.0001, respectively) but not with the Strength-Strain Index or maximal muscle force (Fmax).

CONCLUSIONS

We observed an improvement in bone and muscle parameters after cholecalciferol substitution in pediatric patients with IBD. Therefore, vitamin D substitution can be considered in such patients.

[AGE AND SEX FEATURES OF BONE MINERAL DENSITY IN RATS]

In vivo assessment of bone mineral density (BMD) and bone mineral content (BMC) indices gives an objective description of the possible rates of bone loss during aging and various diseases, as well as response to treatment by various drugs, affecting bone metabolism. This study was conducted on 376 Wistar rats of both genders, divided into 12 age groups using the method of dual-energy X-ray absorptiometry. Studying the parameters of BMD and BMC depending on age and sex has found no bone mass opeak) in rats of both sexes. Bone mineral density indices were increased in both male and female rats during growing, more pronounced in males. These differences are noted in all age groups of animals. Moreover, we have established age and gender particularities of BMC indices in different parts of the skeleton. In female rats, a significant increase of BMD and BMC parameters have been detected in age from 1.5 to 2 months (33%), from 2 to 3 months - by 12.5%. In males, the increase of BMD indices was found to happen 1 month later and it was less pronounced (from 2 to 3 months - 27%, from 4 to 5 months - 5%). In other age periods, the dynamics of BMD indices had only an upward trend, but significant differences different groups were not established. Our results of BMD and BMC indices and their age and gender features can be used for further research in osteology as reference data for modeling of experimental osteoporosis in rats and study of response to the use of different antiosteoporotic drugs.

Histochemical examination of the effects of high-dose 1,25(OH)2D3 on bone remodeling in young growing rats

Vitamin D has an anabolic effect on bone developmental processes and is involved in maintaining skeletal integrity. In recent years, pediatric cases of vitamin D intoxication have attracted attention. Therefore, the aim of this study was to investigate the influence of long-term administration of physiologically-high-dose calcitriol (1,25(OH)2D3) on bone remodeling in young developing rats. Neonatal rats received once-daily subcutaneous injection of calcitriol (250 ng/kg body weight), or PBS only as a control, for 3 weeks. At 1, 2 and 4 weeks' post-administration, rats were sacrificed and fixed by transcardial perfusion with 4 % paraformaldehyde, following which tibiae were extracted for histochemical analysis. Compared with the control group, the number of tartrate-resistant acid phosphatase- and Cathepsin K-positive osteoclasts were significantly increased, and the expression of alkaline phosphatase in osteoblasts was decreased in trabecular bone of rats administered high-dose 1,25(OH)2D3, leading to decreased trabecular bone volume. In addition, the expression of receptor activator of nuclear factor kappa-B ligand (RANKL) was increased, while that of osteoprotegerin was weaker in osteoblasts in the experimental group compared with the control group. Moreover, there was weaker immunoreactivity for EphrinB2 in osteoclasts and EphB4 in osteoblasts of trabecular bone in the experimental group compared with the control group. These findings suggest that long-term use of physiologically-high dose calcitriol may result in bone loss through RANKL/RANK/osteoprotegerin and EphrinB2-EphB4 signaling pathways, and that these negative effects could continue after drug withdrawal. Therefore, optimal limits for vitamin D administration need to be established for children and adolescents.