Homocysteine as a predictive factor for hip fracture in stroke patients

Relationship between Bone Mineral Density and Selected Parameters of Calcium-Phosphate Economy with Dietary Management and Metabolic Control in Polish Pediatric Patients with Classical Homocystinuria-A Preliminary Study

BACKGROUND

Classical homocystinuria (HCU) is an inborn defect of methionine metabolism caused by a deficiency of the enzyme cystathionine β-synthase (CBS). The main symptoms of classical homocystinuria are lens subluxation, bone lesions, vascular disease and developmental delay/intellectual disability. The treatment method for HCU is a methionine-poor diet supplemented with amino acid preparations. The aim of the study was to examine the relationship of dietary factors, metabolic compensation and selected skeletal parameters in patients with HCU.

METHODS

Bone mineral density measurements (DXA) were performed in pediatric patients with HCU, and blood levels of selected amino acids, minerals and vitamins, as well as dietary nutritional value, were analyzed.

RESULTS

A total of 11 patients with HCU whose median age was 9.3 years were enrolled in the study. The median DXA total body less head of HCU patients was -0.4 z-score, and the lumbar spine was -1.4 z-score. Despite supplementation, calcium intake was below the age norm. Average vitamin D3 intake was in line with recommendations, but 36% of patients had reduced blood levels. Bone mineral density depended on blood levels of 25-hydroxyvitamin D, homocysteine and methionine, as well as on BMI, age and intake of natural protein (R2 = 98.5%, p = 0.015; R2 = 86.7%, p = 0.0049) and protein from an amino acid preparation (r = 0.69, p = 0.026).

CONCLUSION

The results of the study indicate the need for regular densitometry in patients with HCU and also the use of additional calcium and vitamin D3 supplementation. It is also necessary to perform a comprehensive analysis of the diet and metabolic controls.

The association of homocysteine, folate, vitamin B12, and vitamin B6 with fracture incidence in older adults: a systematic review and meta-analysis

Background

Diverse conclusions have been drawn regarding the association of homocysteine (HCY) deficiency and supplements of B vitamins with fracture incidence in older adults. The aim of this meta-analysis was to investigate the association of HCY and B vitamins (folate, vitamin B12, and B6) with fracture incidence in older adults and whether supplements of B vitamins reduce the risk of fracture.

Methods

The PubMed, Embase, and Cochrane library databases were systematically searched from their inception dates to 1 July 2019 to identify relevant published articles. Meta-analysis was performed to pool hazard ratios (HRs) or risk ratios (RRs) and 95% confidence intervals (CIs) using a random effects model.

Results

A total of 28 studies fulfilled the inclusion criteria. High serum HCY was an independent risk factor for fractures in older persons (HR =1.25, 95% CI: 1.12 to 1.40), but only at the highest quartile level (>15 µmol/L) (HR =1.71, 95% CI: 1.37 to 2.12), rather than the second and third quartile. Multiple sensitivity and subgroup analyses supported the consistency and stability of this result. A severe deficiency of folate, instead of vitamin B12 and B6, was found to increase the risk of fracture in older adults (HR =1.46, 95% CI: 1.06 to 2.02; 1.24, 95% CI: 0.79 to 1.95; 1.36, 95% CI: 0.90 to 2.06, respectively). For the interventional effect, there was no significant association of combined folate and vitamin B12, combined folate, vitamin B12 and B6, or single vitamin B6 supplementation with the decrease of fracture risk.

Discussion

This meta-analysis revealed that significantly elevated serum level of HCY is positively associated with fracture incidence in older adults, yet the necessity and threshold for intervention by B vitamins require further large-scale high-quality clinical trials to validate.

PROSPERO identifier

CRD42019122586.

Risk of hip fracture following stroke, a meta-analysis of 13 cohort studies

This study systematically reviews prospective and retrospective cohort studies evaluating the risk of hip fracture following stroke. Stroke survivors are at high risk of hip fracture and had a 1.5-fold increased risk compared to stroke-free men and women of the same age. Hip fracture often occurs in ageing and female stroke patients. We performed a meta-analysis to summarize evidence from prospective and retrospective cohort studies about the risk of hip fracture following stroke. We identified English and non-English publications in MEDLINE and EMBASE using stroke and fracture as keywords to 31 December 2015. The data of the incidence of hip fracture were extracted to calculate raw incident rate in stroke survivors as well as risk of hip fractures in strokes comparing populations using a random-effects model. Subgroup analyses were performed to identify the potential influence of some factors. Six prospective and seven retrospective cohort studies were included, involving 512,214 stroke patients with 22,559 hip fractures. The pooled prevalence of hip fractures was 4.87 % (95 % CI, 4.05 to 5.68 %) in stoke patients. We conducted subgroup analysis according to sex, age, duration of follow-up, study design, and region, which showed that female (vs. male) stroke patients older than 70 years (vs. those less than 70 years) and duration of follow-up more than 2 years (vs. those less than 2 years) have higher proportions of hip fractures. Four studies showed that stroke patients had a significantly higher risk of hip fracture compared with the general population, while the other study had a non-significant higher risk. The overall prevalence of hip fracture was 3.28 % (3431 of 104,646) in stroke patients and 2.83 % (36,493 of 1,287,726) in general population, respectively, and the unadjusted combined relative risk of hip fracture was 1.54 (95 % CI, 1.06-2.25). Hip fractures often occur in ageing and female stroke patients.

Low bone mineral density is a common finding in patients with homocystinuria

Homocystinuria (HCU) due to deficiency of cystathionine beta-synthetase is associated with increased plasma levels of homocysteine and methionine and is characterized by developmental delay, intellectual impairment, ocular defects, thromboembolism and skeletal abnormalities. HCU has been associated with increased risk for osteoporosis in some studies, but the natural history of HCU-related bone disease is poorly understood. The objective of this study was to characterize bone mineral density (BMD) measured by dual energy X-ray absorptiometry (DXA) in a multi-center, retrospective cohort of children and adults with HCU. We identified 19 subjects (9 males) aged 3.5 to 49.2 years who had DXA scans performed as a part of routine clinical care from 2002-2010. The mean lumbar spine (LS) BMD Z-score at the time of first DXA scan in this cohort was -1.2 (± SD of 1.3); 38% of participants had low BMD for age (as defined by a Z-score ≤-2). Homocysteine and methionine were positively associated with LS BMD Z-score in multiple linear regression models. Our findings suggest that low BMD is common in both children and adults with HCU and that routine assessment of bone health in this patient population is warranted. Future studies are needed to clarify the relationship between HCU and BMD.

Preventing Hip Fracture After Stroke

Hip fracture after stroke is a frequently occurring and costly complication. The bone quality of stroke survivors is affected by decreased mobility, asymmetric weight bearing, and impaired vitamin D stores. Simultaneously, the risk of falling after stroke is often increased by various impairments. Yet, attempts to limit falls are not enough to prevent fractures. Closer attention to bone health is also needed. Bone markers, which reflect the dynamics of bone remodeling, are becoming more available. Activity is necessary for bone health, but there are no clear guidelines for the type and amount of therapeutic exercise. New metrics for studying bone mineral density and exercise are on the horizon. Finally, there appears to be a role for bisphosphonate prophylaxis in a yet-to-be-defined at-risk population of stroke survivors. The purpose of this review is to discuss the setting for hip fracture after stroke and assess emerging treatments and technologies that may be used to combat the problem.

Vitamin B12, folic acid, and bone

Vitamin B12 and folic acid deficiency are associated with a higher serum concentration of homocysteine. A high serum homocysteine is a risk factor for fractures. Both vitamins play a role in the remethylation of homocysteine to methionine. The pathophysiology from a high serum homocysteine to fractures is not completely clear, but might involve bone mineral density, bone turnover, bone blood flow, DNA methylation, and/or physical function and fall risk. Genetic variation, especially polymorphisms of the gene encoding for methylenetetrahydrofolate reductase may play a role in homocysteine metabolism and fracture risk. It is uncertain whether supplementation with vitamin B12 and folate can decrease fracture incidence. One double blind clinical trial in post-stroke patients showed that these B vitamins could decrease hip fracture incidence, but the results of further clinical trials should be awaited before a definite conclusion can be drawn.

Homocysteine level and risk of fracture: A meta-analysis and systematic review

AIMS

Previous studies have reported inconsistent findings regarding the association between elevated plasma Hcy levels and fracture risk. We investigated this association between homocysteine (Hcy) levels in patients with fracture and unaffected controls by conducting a meta-analysis and systematic review.

METHODS

We conducted a systematic literature search (up to April 2012) of the PubMed database and Embase. We selected observational studies that evaluated Hcy levels in subjects with fracture compared to unaffected controls. We also included randomized clinical trials (RCTs) on the effect of Hcy-lowering therapy in fracture patients. Criteria for inclusion were the assessment of baseline Hcy and risk of fracture as an outcome. The results were presented as relative risk (RR) and corresponding 95% confidence intervals (CI) comparing fracture patients to the control subjects or the highest Hcy quartile group to the lowest Hcy quartile group.

RESULTS

Nine studies with 14,863 participants were identified and analyzed. The pooled RR from a random effect model of participants with all fractures compared with the control subjects was 1.59 (95% CI 1.30-1.96). The pooled RR from a random model for hip fractures in the highest Hcy quartile group compared with the lowest Hcy quartile group was 1.67 (95% CI 1.17-2.38). The effect of Hcy-lowering therapy on fracture was tested in two clinical trials, but clinically important end points were not reported in a consistent way.

CONCLUSIONS

This meta-analysis and systematic review suggested that Hcy significantly increased the risk of fracture, and the increase was independent of risk factors.

Homocysteine, folate, and vitamin B12 levels and vertebral fracture risk in postmenopausal women

The objective of this study was to examine the influence of homocysteine, vitamin B(12), and folate on the prevalence of asymptomatic osteoporotic vertebral fractures (VFs) using vertebral fracture assessment (VFA) in postmenopausal women. The study cohort consisted of 188 consecutive postmenopausal women (mean age, weight, and body mass index of 57.9 ± 8.5 [41-91]yr, 74.4 ± 13.5 [38-150]kg, and 30.4 ± 5.2 [17.1-50.7]kg/m(2), respectively). Lateral VFA images and scans of the lumbar spine and proximal femur were obtained using a Lunar Prodigy Vision densitometer (GE Healthcare Inc., Waukesha, WI). VFs were defined using a combination of Genant's semiquantitative approach and morphometry. Fifty-eight (30.9%) patients had densitometric osteoporosis. VFs were identified using VFA in 76 (40.4%) patients: 61 women had grade 1 VFs and 15 had grade 2 or 3 VFs. No statistical difference was shown between the 3 groups (absence of VFs, VFs grade 1, and VFs grade 2/3) concerning the biological parameters. Comparison of patients according to quartiles of homocysteine levels showed that women in the highest quartile were older and had a lower bone mineral density (BMD); however, the prevalence of VFs was not statistically different from that of women in the other quartile groups. Stepwise regression analysis showed that homocysteine was not independently associated with the presence of VFs, which was mainly related to the osteoporotic status. Although a weak association was observed between hyperhomocysteinemia and low BMD and a trend to higher prevalence of grade 2/3 VFs was observed, our study did not confirm that homocysteine, vitamin B(12), and folate status are important determinants of prevalent asymptomatic VFs in postmenopausal women.

The skeletal subsystem as an integrative physiology paradigm

Homeostatic bone remodeling depends on precise regulation of osteoblast-osteoclast coupling through intricate endocrine, immune, neuronal, and mechanical factors. The osteoblast-osteoclast model of bone physiology with layers of regulatory complexity can be investigated as a component of a local skeletal subsystem or as a part of a complete whole-body system. In this review, we flip the traditional investigative paradigm of scientific experimentation ("bottom-top research") to a "top-bottom" approach using systems biology. We first establish the intricacies of the two-cell model at the molecular signaling level. We then provide, on a systems level, an integrative physiologic approach involving many recognized organ-level subsystems having direct and/or indirect effects on bone remodeling. Lastly, a hypothetical model of bone remodeling based on frequency and amplitude regulatory mechanisms is presented. It is hoped that by providing a thorough model of skeletal homeostasis, future progress can be made in researching and treating skeletal morbidities.

Homocysteine-lowering therapy or antioxidant therapy for bone loss in Parkinson's disease

We investigated whether homocysteine (Hcy)- lowering therapy or an antioxidant prevented bone loss in Parkinson's disease (PD) patients taking levodopa. Forty-two PD patients with low bone mineral density (BMD) taking levodopa were randomly assigned to Hcy-lowering therapy (5 mg folate and 1500 microg vitamin B(12) daily), alpha-lipoic acid (alpha-LA) therapy (1200 mg daily), or control groups. Primary outcomes were BMD changes from baseline to 12 months. Secondary outcomes were changes in Hcy level, and C-telopeptide (CTX) levels at 12 months. Forty-one patients completed the study. Hcy-lowering therapy resulted in significantly greater BMD changes at the lumbar spine (4.4%), total femur (2.8%), and femur shaft (2.8%) than control (P = 0.005-0.023). BMD changes in the alpha-LA therapy group were similar to those of the control group, but changes at the trochanter (4.6%) were significantly greater in the alpha-LA therapy group than in the control group after adjustment for body mass index changes. Hcy concentrations decreased to 35.2% +/- 13.4% in the Hcy-lowering therapy group, but increased in other groups. Serum CTX levels at 12 months tended to be lower in the Hcy-lowering group (0.442 +/- 0.024 ng/mL) than control group (0.628 +/- 0.039 ng/mL) (P = 0.159). This small trial suggests that Hcy-lowering therapy may prevent bone loss in PD patients taking levodopa.

Differential effects of homocysteine and beta aminopropionitrile on preosteoblastic MC3T3-E1 cells

Compounds, like beta-aminopropionitrile (bAPN) and homocysteine (hcys), are known to inhibit a stable matrix formation. Osteoblast-synthesized collagen matrix regulates the differentiation of precursor cells into mature osteoblasts. They express lysyl oxidase, an enzyme involved in the collagen cross-linking process. Lately, plasma hcys levels have recently been strongly correlated with fracture in humans. We have previously shown that bAPN not only disturbs collagen cross-links but also affects osteoblastic differentiation in a cell culture system. The aim of the present study was to investigate the effects of bAPN and hcys on collagen cross-links and gene expression at the mRNA level by FTIR and quantitative RT-PCR, respectively. We found that bAPN and hcys down-regulated cell multiplication. While bAPN also down-regulated the metabolic activity of MC3T3-E1 cells, hcys down-regulated it by lower concentrations but up-regulated it by higher; both substances up-regulated alkaline phosphatase activity. The substances increased the ratio of pyr/divalent cross-links of collagen, and down-regulated mRNA expression of lysyl hydroxylase (Plod2) and lysyl oxidase (Lox), genes which play an important role in the formation of a stable matrix. Furthermore, we demonstrate that both substances stimulated the expression of Runx2, an indispensable regulator of osteoblastic differentiation. However, analysis of genome wide mRNA expression suggests that hcys and bAPN have differential effects on genes involved in osteoblastic differentiation and phenotype regulation. The results indicate that although both bAPN and hcys affect collagen cross-link post-translational modifications in a similar manner as far as pyr and divalent cross-links are concerned, they have differential effects on the monitored genes expression at the mRNA level, with hcys exerting a broader effect on the genome wide mRNA expression.

Bone tissue and hyperhomocysteinemia

Bone tissue quality is determined not only by multiple architectural variables, but also by the mechanical properties of collagen type 1. Homocysteinuria is a genetic disease whose manifestations include severe hyperhomocysteinemia and decreased bone strength. The effects of smaller homocysteine elevations on bone tissue are difficult to demonstrate in clinical studies. Studies in animals and in humans suggest that homocysteine may weaken collagen crosslinks and, if present in large amounts, interfere with bone remodeling. Whether routine homocysteine assays should be performed to detect bone frailty remains unclear. In clinical practice, the focus should be on identifying patients with potential causes of homocysteine elevation (e.g., medications), who should then be given vitamin D and folic acid supplementation if needed. This approach may improve not only bone health, but also vascular and general health.

Collagen cross-linking influences osteoblastic differentiation

Osteoblasts synthesize collagen matrix, which itself regulates the differentiation of precursor cells into mature osteoblasts. They express lysyl oxidase (LOX), which is involved in the collagen cross-linking process. Lathyrogens, like ss-aminopropionitrile (ssAPN), inhibit the formation of a stable matrix. The aim of the present study was to investigate the influence of cross-linking on osteoblastic differentiation. MC3T3-E1 cells were seeded and treated with or without 400 muM ssAPN for 1 week. Thereafter, living cells were removed and, on this extracellular matrix, new MC3T3-E1 cells were seeded and cultured for 1 week without ssAPN. RNA was isolated, and expression of specific marker genes was determined by quantitative reverse transcription-polymerase chain reaction. Changes in specific cross-links after ssAPN treatment were measured with Fourier-transform infrared spectroscopy. The collagen matrix that formed showed a significant reduction of two major cross-links of bone collagen, deH-DHLNL and pyr, compared to control cultures. Gene expression studies showed an increase of collagen alpha1 (I) (COL1A1) to 150%. Expression of LOX and osteocalcin (OCN) mRNA was significantly downregulated to about 75%. When fresh MC3T3-E1 cells were seeded on this altered matrix without ssAPN, COL1A1 mRNA expression was upregulated (140%), OCN was downregulated (60%), and LOX mRNA expression remained unaffected. These results indicate that ssAPN treatment not only disrupts collagen cross-link formation but also affects osteoblastic activity and expression. In conclusion, the disrupted matrix produced in the presence of lathyrogen influences, even in its absence, the expression of osteoblastic genes.

The role of hyperhomocysteinemia as well as folate, vitamin B(6) and B(12) deficiencies in osteoporosis: a systematic review

Hyperhomocysteinemia (HHCY) has been suggested as a new risk factor for osteoporosis. Recent epidemiological, clinical and experimental studies provide a growing body of data, which is reviewed in this article. Epidemiological and (randomized) clinical trials suggest that HHCY increases fracture risk, but has minor effects on bone mineral density. Measurement of biochemical bone turnover markers indicates a shift of bone metabolism towards bone resorption. Animal studies confirm these observations showing a reduced bone quality and stimulation of bone resorption in hyperhomocysteinemic animals. Homocysteine (HCY) has been found to accumulate in bone by collagen binding. Cell culture studies demonstrate that high HCY levels stimulate osteoclasts but not osteoblasts, indicating again a shift of bone metabolism towards bone resorption. Regarding B-vitamins, only a few in vivo studies with equivocal results have been published. However, two large cell culture studies confirm the results obtained with exogenous HCY administration. In addition, HHCY seems to have adverse affects on extracellular bone matrix by disturbing collagen crosslinking. In conclusion, existing data suggest that HHCY (and possibly B-vitamin deficiencies) adversely affects bone quality by a stimulation of bone resorption and disturbance of collagen crosslinking.

Relation of folates, vitamin B12 and homocysteine to vertebral bone mineral density change in postmenopausal women. A five-year longitudinal evaluation

Elevation of homocysteine is associated with an increased risk for bone fractures. Whether the risk is due to homocysteine or to the reduced levels of cofactors necessary for its metabolisation, such as folates or vitamin B12, is not completely clear. In this study we wanted to determine whether in postmenopausal women, levels of folates, homocysteine or vitamin B12 are predictive of the rate of vertebral bone mineral density (BMD) change. The study was conducted at the centre for the menopause of our university hospital. Between September 2001 and March 2002, 161 healthy postmenopausal women volunteered for a cross-sectional evaluation of BMD and levels of serum folates, homocysteine and vitamin B12. Women were recalled for a second evaluation of vertebral BMD after about 5 years. Women having used anti-resorptive therapies for more than 1 year were excluded. The analysis was possible in 117 postmenopausal women. The annual rate of vertebral BMD change was independently related to levels of folates (coefficient of regression (CR): 2.040; 95%CI: 0.483, 3.596; p=0.011), and initial BMD values (CR: -0.060; 95%CI: -0.117, -0.003; p=0.040). No significant relation was found between the change of vertebral BMD and homocysteine or vitamin B12. BMD values at the first (r=0.225; p=0.016) and the second (r=0.206; p=0.027) evaluation were related to levels of folates, but not of homocysteine or of vitamin B12. These data suggest an important role for folates deficiency in the vertebral BMD decline of postmenopausal women.

Calcifications in the abdominal aorta predict fractures in men: MINOS study

In a cohort of 781 men >or=50 yr of age followed up for 10 yr, extended calcifications in the abdominal aorta were associated with a 2- to 3-fold increase in the risk of osteoporotic fractures regardless of BMD and falls.

INTRODUCTION

Cardiovascular disease and osteoporotic fractures are public health problems that frequently coexist.

MATERIALS AND METHODS

We assessed the relation of the severity of aortic calcifications with BMD and the risk of fracture in 781 men >or=50 yr of age. During a 10-year follow-up, 66 men sustained incident clinical fractures. Calcifications in the abdominal aorta expressed as an aortic calcification score (ACS) were assessed by a semiquantitative method. BMD was measured at the lumbar spine, hip, whole body, and distal forearm.

RESULTS

ACS > 2 was associated with a 2-fold increase in the mortality risk after adjustment for age, weight, smoking, comorbidity, and medications. After adjustment for age, body mass index (BMI), smoking, and comorbidity, men in the highest quartile of ACS (>6) had lower BMD of distal forearm, ultradistal radius, and whole body than men in the lower quartiles. Log-transformed ACS predicted fractures when adjusted for age, BMI, age by BMI interaction, prevalent fractures, BMD, and history of two or more falls (e.g., hip BMD; OR = 1.44; p < 0.02). ACS, BMD at all the skeletal sites, and history of two or more falls were independent predictors of fracture. Men with ACS > 6 had a 2- to 3-fold increased risk of fracture after adjustment for confounding variables (OR = 2.54-3.04; p < 0.005-0.001 according to the site).

CONCLUSIONS

This long-term prospective study showed that elevated ACS (>6) is a robust and independent risk factor for incident fracture in older men regardless of age, BMI, BMD, prevalent fractures, history of two or more falls, comorbidities, and medications.

Biochemical assessment of bone turnover and bone fragility in men

Osteoporosis in men is less studied than in women. Few data concern biochemical bone turnover markers (BTM) in men and their potential use.

METHODOLOGY

We evaluated papers concerning BTM in men cited on Medline. Selection of studies were based on the number of subjects, age range, group homogeneity, follow-up duration, number of BTM.

RESULTS

BTM levels are high in young men, then decrease with age. In elderly men, bone resorption increases with age more than bone formation. Variability of individual values is high and their significance is unclear. In elderly men, BTM levels correlate negatively with bone mineral density suggesting that accelerated bone turnover underlies age-related bone loss. Data on the prediction of accelerated bone loss and fractures by BTM in men are scant. Testosterone treatment induces a decrease in bone resorption followed by a decrease in bone formation. Bisphosphonates and calcitonin decrease BTM levels in osteoporotic men. Parathyroid hormone 1-34 and growth hormone induce a rapid increase in bone turnover followed by a progressive slowdown.

CONCLUSIONS

Few studies concern BTM in men. Currently available data are not sufficient to suggest guidelines for the practical use of BTM in the clinical management of the osteoporosis in elderly men.

Homocysteine and fracture risk in postmenopausal women: the OFELY study

Homocysteine has recently been described as an independent risk factor for osteoporotic fractures in the elderly. We prospectively followed 671 postmenopausal women belonging to the OFELY study, mean age 62 years, during a mean follow-up of 10 years. After adjustment for age, there was no significant relation between the plasma level of homocysteine and the subsequent risk of fracture.

INTRODUCTION

Plasma homocysteine increases with age. Recent studies have described homocysteine as an independent risk factor for osteoporotic fractures in elderly. We investigated the role of plasma homocysteine in the subsequent risk of fractures in healthy ambulatory postmenopausal women.

METHODS

Homocysteine was measured at baseline in 671 postmenopausal women from the OFELY cohort (mean age 62.2 +/- 9 years). Incident clinical fractures were recorded during annual follow-up and vertebral fractures were evaluated with radiographs every four years. A cox proportional hazards model based on time to first fracture was used to calculate hazard ratios for quartiles of homocysteine values.

RESULTS

Mean homocysteine was 10.6 +/- 3.4 mumol/l, increasing with age. After adjustment for age, homocysteine was significantly associated with physical activity, calcium intake, serum albumin and serum creatinine but not with bone turnover markers and bone mineral density. During a mean follow-up of 10 years, 183 fractures occurred among 134 women. After adjustment for age, the overall relative risk of fracture for each 1 SD increment of homocysteine was 1.03 (95%CI 0.87-1.31). Fracture risk was higher in women with homocysteine in the highest quartile without adjustment but no longer after adjustment for age.

CONCLUSIONS

Homocysteine is not an independent risk factor of osteoporotic fractures in healthy postmenopausal women from the OFELY cohort with a broad age range.

Homocysteine enhances apoptosis in human bone marrow stromal cells

INTRODUCTION

High plasma homocysteine (Hcy) levels have been associated with increased risk of fracture. Since Hcy has been shown to induce apoptosis in many cell types, including vascular endothelial cells, we hypothesized that Hcy would have a similar apoptotic effect on osteoblasts, leading to osteoporosis by reducing bone formation.

MATERIALS AND METHODS

Using primary human bone marrow stromal cells (hBMSC) and HS-5 cell line (human bone marrow stromal cell line), we investigated the effects of Hcy on these cells by cell viability assay and analysis of cytoplasmic histone-associated DNA fragments. Caspase activity assay, Western blots, and electrophoresis mobility shift assay (EMSA) were performed to find the mechanism of apoptosis. Intracellular reactive oxygen species (ROS) were measured by spectrometry using dichlorofluorescein diacetate, and cellular total glutathione level was determined by a commercially available kit. N-acetylcysteine (NAC) and pyrrolidine dithiocarbamate (PDTC) were used as tools for investigating the role of ROS and nuclear factor-kappaB (NF-kappaB), respectively.

RESULTS

Hcy induced apoptosis in primary human bone marrow stromal cells and the HS-5 cell line, and this apoptotic effect was caspase-dependent. In addition, Hcy increased cytochrome c release into the cytosol, and activated caspase-9 and caspase-3, but not caspase-8, indicating that Hcy induces apoptosis via the mitochondria pathway. Hcy increased ROS, and NAC inhibited the apoptotic effect of Hcy. Western blot and EMSA showed that Hcy activated the NF-kappaB pathway. PDTC blocked Hcy-induced caspase-3 activation and apoptosis.

CONCLUSION

These results suggest that Hcy induces apoptosis via the ROS-mediated mitochondrial pathway and NF-kappaB activation in hBMSCs, and that Hcy may contribute to the development of osteoporosis by reducing bone formation. Antioxidants may have a role in preventing bone loss in individuals with hyperhomocysteinemia.