Experimental hyperhomocysteinemia reduces bone quality in rats

Nutrition and Bone Marrow Adiposity in Relation to Bone Health

Bone remodeling is energetically demanding process. Energy coming from nutrients present in the diet contributes to function of different cell type including osteoblasts, osteocytes and osteoclasts in bone marrow participating in bone homeostasis. With aging, obesity and osteoporosis the function of key building blocks, bone marrow stromal cells (BMSCs), changes towards higher accumulation of bone marrow adipose tissue (BMAT) and decreased bone mass, which is affected by diet and sex dimorphism. Men and women have unique nutritional needs based on physiological and hormonal changes across the life span. However, the exact molecular mechanisms behind these pathophysiological conditions in bone are not well-known. In this review, we focus on bone and BMAT physiology in men and women and how this approach has been taken by animal studies. Furthermore, we discuss the different diet interventions and impact on bone and BMAT in respect to sex differences. We also discuss the future perspective on precision nutrition with a consideration of sex-based differences which could bring better understanding of the diet intervention in bone health and weight management.

Increased bone resorption that outpaces increased bone formation: An important pathology of rapidly destructive coxarthrosis

Rapid joint destruction caused by rapidly destructive coxarthrosis (RDC) can increase surgical complexity and intraoperative blood loss. This single-center retrospective study investigates osteoporosis-related biomarkers for early RDC diagnosis and explores new treatment targets. We included 398 hip joints from patients who underwent total hip arthroplasty, examining medical records for preoperative patient demographics, bone mineral density of the hip and lumbar spine from dual-energy X-ray absorptiometry scans, and osteoporosis-related biomarkers including TRACP-5b, total P1NP, intact parathyroid hormone, and homocysteine. We compared RDC and osteoarthritis (OA) patients, and univariate analysis showed that RDC patients were older (p < 0.001) and had lower serum levels of albumin (p < 0.001) and higher serum levels of TRACP-5b, total P1NP (p < 0.001), and homocysteine (p = 0.006). Multivariable analysis showed that the ratio of serum TRACP-5b to total P1NP had a more significant difference in RDC patients than in OA patients (p = 0.04). Serum TRACP-5b levels were negatively correlated with the time between RDC onset and blood collection, and Japanese Orthopedic Association pain score. Receiver operating characteristic curve analysis revealed that the ratio of serum TRACP-5b to total P1NP had the highest area under the curve value. This study is the first to demonstrate that the ratio of serum TRACP-5b to total P1NP-increased bone resorption that outpaces increased bone formation-is significantly elevated in patients with RDC and that TRACP-5b is higher in the early stages of RDC. Inhibiting serum levels of TRACP-5b, activated osteoclasts, during early RDC may suppress disease progression.

Different methionine to cysteine supplementation ratios altered bone quality of broilers with or without Eimeria challenge assessed by dual energy X-ray absorptiometry and microtomography

Despite the acknowledged significance of nutrition in bone development, effects of methionine (Met) and cysteine (Cys) on bone quality remain under-researched, particularly during Eimeria challenge. We investigated the effects of different supplemental Met to Cys ratios (MCR) on bone quality of broilers under Eimeria challenge. A total of 720 fourteen-day old Cobb500 broilers were allocated into a 5 × 2 factorial arrangement. Five diets with Met and Cys supplemented at MCR of 100:0, 75:25, 50:50, 25:75, and 0:100 were fed to the birds with or without Eimeria challenge. Body composition was measured by dual energy x-ray absorptiometry, and the femur bone characteristics were assessed by microtomography. Data were analyzed by two-way ANOVA and orthogonal polynomial contrast. The results reaffirmed the detrimental effects of Eimeria challenge on bone quality. On 9 d post inoculation (DPI), significant interaction effects were found for whole body bone mineral content (BMC), lean tissue weight, and body weight (P < 0.05); in the nonchallenged group (NCG), these parameters linearly decreased as MCR decreased (P < 0.05). In the challenged group (CG), body weight and lean tissue weight were unaffected by MCR, and BMC linearly increased as MCR decreased (P < 0.05). For the cortical bone of femoral metaphysis on 6 DPI, bone mineral density (BMD) linearly increased as MCR decreased (P < 0.05). Bone volume to tissue volume ratio (BV/TV) in the CG linearly increased as MCR decreased (P < 0.05). On 9 DPI, BMC and TV linearly increased as MCR decreased (P < 0.05) in the NCG. BMD and BV/TV changed quadratically as MCR decreased (P < 0.05). For the trabecular bone of femoral metaphysis on 9 DPI, BV/TV, and trabecular number linearly increased as MCR decreased (P < 0.05) in the NCG. For the femoral diaphysis, BV, TV, BMC on 6 DPI, and BMD on 9 DPI linearly increased as MCR decreased (P < 0.05). In conclusion, this study showed that both Eimeria challenge and varying supplemental MCR could influence bone quality of broilers.

Association of osteoporosis and high serum homocysteine levels with intraoperative periprosthetic fracture during total hip arthroplasty: a propensity-score matching analysis

INTRODUCTION

Intraoperative periprosthetic fracture, one of the most frequent complications of total hip arthroplasty, is a very important factor that affects rehabilitation, hospitalization time, and cost of treatment. Osteoporosis is common in total hip arthroplasty patients and likely contributes to the increasing incidence of periprosthetic fracture. Despite this awareness, preoperative and postoperative osteoporosis evaluations remain insufficient. The purpose of this study was to evaluate the relationships between the occurrence of intraoperative periprosthetic fractures and both bone mineral density (BMD) and osteoporosis-related biomarkers.

MATERIALS AND METHODS

This single-center retrospective study included a total of consecutive 487 hip joints of patients with a mean age of 65.5 ± 11.8 years who underwent total hip arthroplasty between July 2017 and December 2020. Patients with low BMD defined as T-score < -1.0 versus those with normal BMD were matched by a 1:1 propensity score to balance for patient baseline characteristics, and outcome was analyzed by a modified Poisson regression model. Our primary outcome was the incidence of intraoperative periprosthetic fracture during surgery. We also investigated the effect modification of osteoporosis-related biomarkers, including tartrate-resistant acid phosphatase 5b (TRACP-5b), total procollagen type 1 amino-terminal propeptide (total P1-NP), intact parathyroid hormone (intact PTH), and homocysteine, on osteoporosis and outcomes.

RESULTS

After matching, 250 patients were analyzed. The risk of fracture was significantly higher in patients with low BMD than in normal BMD patients (Incidence rate ratio 5.00 [95% CI 1.11-22.43], p = 0.036). We also observed significant effect of high serum homocysteine on the occurrence of intraoperative fractures (Incidence rate ratio 8.38 × 106 [95% C; 3.44 × 106-2.01 × 107], p < 0.01).

CONCLUSION

Preoperative osteoporosis and high serum homocysteine levels were risk factors for intraoperative periprosthetic fractures.

LEVEL OF EVIDENCE

III, A single-center retrospective study.

Folate ameliorates homocysteine-induced osteoblast dysfunction by reducing endoplasmic reticulum stress-activated PERK/ATF-4/CHOP pathway in MC3T3-E1 cells

INTRODUCTION

Homocysteine (Hcy) is considered a newly identified risk factor for osteoporosis. Nevertheless, the underlying mechanism of folate (FA), a key factor in the metabolism of Hcy, in protection against osteoblast dysfunction remains unclear. The purpose of this study was to investigate the mechanism by which FA attenuates Hcy-induced osteoblast damage.

MATERIALS AND METHODS

The Hcy-induced MC3T3-E1 cells were treated with different concentrations of FA. Cell morphology, cell density, cell proliferation ability, alkaline phosphatase (ALP) activity and mineralization capacity were observed and determined; the gene expression of B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X protein (BAX) and ERS-associated factors, including glucose-regulated protein 78 (GRP-78), activating transcription factor 4 (ATF-4) and growth arrest and DNA damage inducible gene 153 (CHOP/GADD153), were assessed by RT-PCR; and protein levels of GRP-78 and ATF-4 were analyzed by western blotting.

RESULTS

Hcy suppressed the proliferation, differentiation and mineralization ability of MC3T3-E1 cells in a concentration-dependent manner and activated the ERS signaling pathway. After intervention with different concentrations of FA, the cell viability and density, ALP activity, number of mineralized nodules, calcium content and Bcl-2 gene expression were all significantly increased, whereas the gene expression of GRP-78, CHOP/GADD153, ATF-4 and Bax was markedly downregulated, and protein levels of GRP-78 and ATF-4 were also markedly decreased.

CONCLUSION

The adverse effects of Hcy on osteoblast differentiation are dose dependent. FA not only protects against osteoblasts apoptosis but also has a direct osteogenic effect on Hcy-induced osteoblasts, which could be partially mediated by inhibition of the PERK-activated ERS pathway.

Vitamin B12 status is a risk factor for bone fractures among vegans

Several studies consistently showed vegans having a higher risk of bone fractures compared to individuals from other diet groups. While researchers have focused on several factors as possible explanation of these findings, both dietary (e.g. calcium) and non-dietary (e.g. weight/BMI status), the widespread inadequate vitamin B12 (B12) status among vegans as a risk factor for bone fractures has not received adequate scrutiny. The detrimental impact of inadequate B12 status on bone tissue is both direct, via the impairment of the insulin-like growth hormone 1 and taurine synthesis, and indirect, induced through its hyperhomocysteinemic effect, via at least the following mechanisms: 1) reducing bone mineral content and density by accumulating in the extracellular matrix, 2) reducing osteoblasts and increasing osteoclasts function, 3) reducing blood flow to bone tissue, 4) inducing apoptosis via the reactive oxygen-species-mediated mitochondrial pathway, and 5) obstructing the formation of collagen cross-links, impeding lyslyl oxidase, and hampering insolubility of fibrils. Considering the widespread B12 deficiency prevalence among vegans, its role in bone fracture risk should not be overlooked.

Causal effects of homocysteine levels on the changes of bone mineral density and risk for bone fracture: A two-sample mendelian randomization study

BACKGROUND & AIMS

Observational studies have demonstrated the relations of homocysteine (HCY) with bone mineral density (BMD) and bone fracture risk, but yielding contradictory results. The present study was conducted to evaluate whether the genetically predicted plasma HCY levels were causally associated with the change of BMD and the risk of bone fracture.

METHODS

Genetic summary statistics were extracted from genome-wide association study (GWAS) meta-analysis of plasma HCY levels (n = 44,147), GWAS meta-analyses of measured forearm (FA), femoral neck (FN) and lumbar spine (LS) BMD (n = up to 32,735), UK Biobank estimated heel BMD (eBMD) (n = 426,824) and fracture (n = 426,795) GWAS data. Two Sample Mendelian Randomization (TSMR) analysis was performed to assess the causal effects of genetically determined plasma HCY on the BMD and bone fractures.

RESULTS

The MR analysis indicated that, genetically decreased plasma HCY was associated with the increased FA-BMD based on the inverse variance weighting (IVW) method (standard deviation [SD] = 0.348, 95% CI: 0.146 to 0.550, P = 7 × 10^-4). However, there were no significant associations of genetically decreased plasma HCY with FN-BMD, LS-BMD, eBMD and the risk for bone fracture (SD = -0.041, 95% CI: -0.189 to 0.106, P = 0.582; SD = -0.053, 95% CI: -0.238 to 0.131, P = 0.572; SD = -0.030, 95% CI: -0.090 to 0.030, P = 0.328, odds ratio [OR]: 1.03, 95% CI: 0.94 to 1.13, P = 0.562, respectively). Moreover, the results also found that genetically determined HCY increase was not correlated with the changes of BMD and the risk for bone fracture.

CONCLUSION

Our study revealed that genetically decreased plasma HCY was associated with increase of FA-BMD.

Association between plasma total homocysteine level within normal range and bone mineral density in adults

BACKGROUND

Growing evidence indicates that homocysteine is a noteworthy marker for general health status. However, research regarding plasma total homocysteine (tHcy) levels and bone mineral density (BMD) is sparse and controversial. Hence, we aimed to investigate the association between plasma tHcy level within normal range and lumbar BMD in adults.

METHODS

In this cross-sectional study, using the National Health and Nutrition Examination Survey database, data on 10748 adults aged between 30 and 85 years were analyzed. The weighted multiple logistic regression analyses were conducted to evaluate the association between plasma tHcy level and lumbar BMD. The fitted smoothing curves were performed to explore potential non-linear relationships. When non-linearity was detected, we further calculated the inflection point using a recursive algorithm and constructed a weighted two-piecewise linear regression model.

RESULTS

After adjusting for all the covariates, the association between plasma tHcy and lumbar BMD was different in various age groups (adults aged 30-49 years: β = -0.0004, 95% CI -0.0025, 0.0018; adults aged 50-69 years: β = 0.0001, 95% CI -0.0025, 0.0026; adults aged 70-85 years: β = 0.0050, 95% CI 0.0008, 0.0092). In the subgroup analysis stratified by gender, this association also differed based on gender. There was a negative trend in females (aged 30-49 years: β = -0.0022, 95% CI -0.0054, 0.0011; aged 50-69 years: β = -0.0028, 95% CI -0.0062, 0.0007), and a positive trend in males (aged 30-49 years: β = 0.0018, 95% CI -0.0012, 0.0048; aged 50-69 years: β = 0.0027, 95% CI -0.0009, 0.0063) in both 30-49 years group and 50-69 years group. In the 70-85 years group, this association was significantly positive in males (β = 0.0136, 95% CI 0.0068, 0.0204), but was not significantly different in females (β = 0.0007, 95% CI -0.0046, 0.0060).

CONCLUSION

The correlation between plasma tHcy level within the normal range and lumbar BMD differs by age and gender.

Factors Influencing Serum Homocysteine Levels in Postmenopausal Osteoporotic Females - Comparison to Urinary Collagen Crosslinks

Purpose: The correlation between serum levels of homocysteine and bone mineral density remains controversial. The aim of this study was to identify the potential factors associated with the levels of serum total homocysteine (S-Hcy) and urinary N-terminal telopeptide of type I collagen (U-NTX) in female osteoporotic patients. Materials and Methods: This cross-sectional study included 163 female osteoporotic patients, aged between 48 and 91 years, who had never been treated with anti-osteoporosis therapy. Background data including spine and hip bone mineral density, ongoing therapy for the metabolic disease, aortic calcification score as evaluated by lateral lumbar X-ray film, and recent fragility fracture history were obtained. S-Hcy, U-NTX levels, and creatinine clearance were measured. Results: Multiple linear regression analysis revealed a significant correlation between S-Hcy levels and aortic calcification score (p = 0.022), creatinine clearance (p = 0.004), and recent fracture history (within 1 year after fracture) (p = 0.028); conversely, U-NTX levels correlated significantly with total hip bone mineral density (p < 0.0001) and recent fracture history (p = 0.0007). Conclusions: S-Hcy levels had no correlation with bone mineral density, but were associated with the degree of aortic calcification, renal function, and fracture events. These confounding factors should be taken into consideration when the relationship between S-Hcy and bone mineral density is discussed.

The Effects of Homocysteine on the Skeleton

PURPOSE OF REVIEW

Homocystinuria is a congenital metabolic disorder in which cystathionine β-synthase deficiency results in a prominent increase in homocysteine (serum levels > 100 μM), causing mental retardation, atherosclerotic cerebral infarction, and osteoporosis accompanied by fragility fractures. Encountering a case with excessive homocysteinemia such as that seen in hereditary homocystinuria is unlikely during usual medical examinations. However, in individuals who have vitamin B or folate deficiency, serum homocysteine concentrations are known to increase. These individuals may also have a polymorphism in methylenetetrahydrofolate reductase, MTHFR (C677T: TT type), which regulates homocysteine metabolism. These changes in homocysteine levels may elicit symptoms resembling those of homocystinuria (e.g., Alzheimer's disease, atherosclerosis, osteoporosis).

RECENT FINDINGS

High serum homocysteine has been shown to have detrimental effects on neural cells, vascular endothelial cells, osteoblasts, and osteoclasts. Homocysteine is also known to increase oxidative stress, disrupt cross-linking of collagen molecules, and increase levels of advanced glycation end products, which results in reduced bone strength through a mechanism that goes beyond low bone density and increased bone resorption. Therefore, high serum homocysteine may be regarded as a factor that can reduce both bone mass and impair bone quality. In this review, we outline the epidemiology and pathophysiology of osteoporosis associated with hyperhomocysteinemia.

Hydrogen sulfide epigenetically mitigates bone loss through OPG/RANKL regulation during hyperhomocysteinemia in mice

Hydrogen sulfide (H2S) is a novel gasotransmitter produced endogenously in mammalian cells, which works by mediating diverse physiological functions. An imbalance in H2S metabolism is associated with defective bone homeostasis. However, it is unknown whether H2S plays any epigenetic role in bone loss induced by hyperhomocysteinemia (HHcy). We demonstrate that diet-induced HHcy, a mouse model of metabolite induced osteoporosis, alters homocysteine metabolism by decreasing plasma levels of H2S. Treatment with NaHS (H2S donor), normalizes the plasma level of H2S and further alleviates HHcy induced trabecular bone loss and mechanical strength. Mechanistic studies have shown that DNMT1 expression is higher in the HHcy condition. The data show that activated phospho-JNK binds to the DNMT1 promoter and causes epigenetic DNA hyper-methylation of the OPG gene. This leads to activation of RANKL expression and mediates osteoclastogenesis. However, administration of NaHS could prevent HHcy induced bone loss. Therefore, H2S could be used as a novel therapy for HHcy mediated bone loss.

Homocysteine as a Pathological Biomarker for Bone Disease

In the last few decades, perturbation in methyl-group and homocysteine (Hcy) balance have emerged as independent risk factors in a number of pathological conditions including neurodegenerative disease, cardiovascular dysfunction, cancer development, autoimmune disease, and kidney disease. Recent studies report Hcy to be a newly recognized risk factor for osteoporosis. Elevated Hcy levels are known to modulate osteoclastgenesis by causing detrimental effects on bone via oxidative stress induced metalloproteinase-mediated extracellular matrix degradation and decrease in bone blood flow. Evidence from previous studies also suggests that the decreased chondrocytes mediated bone mineralization in chick limb-bud mesenchymal cells and during the gestational period of ossification in rat model. However, Hcy imbalance and its role in bone loss, regression in vascular invasion, and osteoporosis, are not clearly understood. More investigations are required to explore the complex interplay between Hcy imbalance and onset of bone disease progression. This article reviews the current body of knowledge on regulation of Hcy mediated oxidative stress and its role in bone remodeling, vascular blood flow and progression of bone disease. J. Cell. Physiol. 232: 2704-2709, 2017. © 2016 Wiley Periodicals, Inc.

Bazedoxifene Ameliorates Homocysteine-Induced Apoptosis and Accumulation of Advanced Glycation End Products by Reducing Oxidative Stress in MC3T3-E1 Cells

Elevated plasma homocysteine (Hcy) level increases the risk of osteoporotic fracture by deteriorating bone quality. However, little is known about the effects of Hcy on osteoblast and collagen cross-links. This study aimed to investigate whether Hcy induces apoptosis of osteoblastic MC3T3-E1 cells as well as affects enzymatic and nonenzymatic collagen cross-links and to determine the effects of bazedoxifene, a selective estrogen receptor modulator, on the Hcy-induced apoptosis and deterioration of collagen cross-links in the cells. Hcy treatments (300 μM, 3 mM, and 10 mM) increased intracellular reactive oxygen species (ROS) production in a dose-dependent manner. Propidium iodide staining showed that 3 and 10 mM Hcy induced apoptosis of MC3T3-E1 cells. Moreover, the activities of caspases-8, 9, and 3 were increased by 3 mM Hcy. The detrimental effects of 3 mM Hcy on apoptosis and ROS production were partly reversed by bazedoxifene and 17β estradiol. In addition, real-time PCR, immunostaining and Western blot showed that 300 μM Hcy decreased the expression of lysyl oxidase (Lox). Furthermore, 300 μM Hcy increased extracellular accumulation of pentosidine, an advanced glycation end product. Treatment with bazedoxifene ameliorated Hcy-induced suppression of Lox expression and increase in pentosidine accumulation. These findings suggest that high-dose Hcy induces apoptosis of osteoblasts by increasing oxidative stress, and low-dose Hcy decreases enzymatic collagen cross-links and increases pentosidine accumulation, resulting in the deterioration of bone quality. Bazedoxifene treatment effectively prevents the Hcy-induced detrimental reactions of osteoblasts. Thus, bazedoxifene may be a potent therapeutic drug for preventing Hcy-induced bone fragility.

Activation of AMP-activated protein kinase protects against homocysteine-induced apoptosis of osteocytic MLO-Y4 cells by regulating the expressions of NADPH oxidase 1 (Nox1) and Nox2

BACKGROUND

Elevated plasma homocysteine (Hcy) level is associated with the risk of osteoporotic fracture. While Hcy increases oxidative stress, AMP-activated protein kinase (AMPK) activation ameliorates it. This study aimed to investigate whether Hcy induces apoptosis of osteocytic MLO-Y4 cells through regulating expressions of oxidant and anti-oxidant enzymes and determine the effects of AMPK activation by 5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside (AICAR) and metformin on the Hcy-induced apoptosis of the cells.

RESULTS

DNA fragment ELISA and TUNEL staining assays showed that Hcy treatments (0.1-5.0 mM) induced apoptosis of MLO-Y4 cells in a dose-dependent manner. The detrimental effect of Hcy was partly but significantly reversed by an antioxidant (N-acetylcysteine) and NADPH oxidase (Nox) inhibitors (apocynin and diphenyleneiodonium). In addition, treatment with AICAR (0.05-0.1 mM) and metformin (10-100 μM) ameliorated Hcy-induced apoptosis of the cells. The favorable effect of metformin on Hcy-induced apoptosis was completely canceled by an AMPK inhibitor Ara-A. Hcy increased the expression levels of Nox1 and Nox2, while it had no effects on the expressions of Nox4 or the anti-oxidant enzymes, superoxide dismutase 1 and 2. Hcy-induced increases in the expressions of Nox1 and Nox2 decreased significantly by treatments with AICAR.

CONCLUSION

These findings suggest that Hcy induces apoptosis of osteocytes by increasing the expressions of Nox1 and Nox2, and AMPK activation by AICAR and metformin effectively prevents the detrimental reactions. Thus, AMPK activation may be a potent therapeutic candidate for preventing Hcy-induced osteocyte apoptosis and the resulting bone fragility.

The role of homocysteine in bone remodeling

Bone remodeling is a very complex process. Homocysteine (Hcy) is known to modulate this process via several known mechanisms such as increase in osteoclast activity, decrease in osteoblast activity and direct action of Hcy on bone matrix. Evidence from previous studies further support a detrimental effect on bone via decrease in bone blood flow and an increase in matrix metalloproteinases (MMPs) that degrade extracellular bone matrix. Hcy binds directly to extracellular matrix and reduces bone strength. There are several bone markers that can be used as parameters to determine how high levels of plasma Hcy (hyperhomocysteinemia, HHcy) affect bone such as: hydroxyproline, N-terminal collagen 1 telopeptides. Mitochondrion serves an important role in generating reactive oxygen species (ROS). Mitochondrial abnormalities have been identified during HHcy. The mechanism of Hcy-induced bone remodeling via the mitochondrial pathway is largely unknown. Therefore, we propose a mitochondrial mechanism by which Hcy can contribute to alter bone properties. This may occur both through generations of ROS that activate MMPs and could be extruded into matrix to degrade bone matrix. However, there are contrasting reports on whether Hcy affects bone density, with some reports in favour and others not. Earlier studies also found an alteration in bone biomechanical properties with deficiencies of vitamin B12, folate and HHcy conditions. Moreover, existing data opens speculation that folate and vitamin therapy act not only via Hcy-dependent pathways but also via Hcy-independent pathways. However, more studies are needed to clarify the mechanistic role of Hcy during bone diseases.

Homocysteine alters the osteoprotegerin/RANKL system in the osteoblast to promote bone loss: pivotal role of the redox regulator forkhead O1

In this study we determined the molecular mechanisms of how homocysteine differentially affects receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) synthesis in the bone. The results showed that oxidative stress induced by homocysteine deranges insulin-sensitive FOXO1 and MAP kinase signaling cascades to decrease OPG and increase RANKL synthesis in osteoblast cultures. We observed that downregulation of insulin/FOXO1 and p38 MAP kinase signaling mechanisms due to phosphorylation of protein phosphatase 2A (PP2A) was the key event that inhibited OPG synthesis in homocysteine-treated osteoblast cultures. siRNA knockdown experiments confirmed that FOXO1 is integral to OPG and p38 synthesis. Conversely homocysteine increased RANKL synthesis in osteoblasts through c-Jun/JNK MAP kinase signaling mechanisms independent of FOXO1. In the rat bone milieu, high-methionine diet-induced hyperhomocysteinemia lowered FOXO1 and OPG expression and increased synthesis of proresorptive and inflammatory cytokines such as RANKL, M-CSF, IL-1α, IL-1β, G-CSF, GM-CSF, MIP-1α, IFN-γ, IL-17, and TNF-α. Such pathophysiological conditions were exacerbated by ovariectomy. Lowering the serum homocysteine level by a simultaneous supplementation with N-acetylcysteine improved OPG and FOXO1 expression and partially antagonized RANKL and proresorptive cytokine synthesis in the bone milieu. These results emphasize that hyperhomocysteinemia alters the redox regulatory mechanism in the osteoblast by activating PP2A and deranging FOXO1 and MAPK signaling cascades, eventually shifting the OPG:RANKL ratio toward increased osteoclast activity and decreased bone quality.

High serum total homocysteine levels accelerate hip bone loss in healthy premenopausal women and men

INTRODUCTION

Despite extensive evidence demonstrating the direct, detrimental role of homocysteine on bone metabolism, the effects of serum total homocysteine (tHcy) on bone loss are still equivocal. In the present study, we performed a longitudinal study on healthy participants of various ages of both sexes in order to investigate the association between serum tHcy concentrations and annualized changes in bone mineral density (BMD).

METHODS

A total of 460 Koreans ≥ 30 years of age received comprehensive, routine health examinations for an average period of 3 years. The BMD at proximal femur sites was measured with dual-energy X-ray absorptiometry using the same equipment at baseline and follow-up.

RESULTS

After adjusting for potential confounders, the rates of bone loss at the proximal femur sites were significantly accelerated in a dose-response fashion across increasing tHcy concentrations in premenopausal women and men, but not in postmenopausal women. Consistently, compared with subjects in the lowest tHcy quartile, premenopausal women in the third and/or highest tHcy quartile and men in the highest tHcy quartile showed significantly higher rates of bone loss at all proximal femur sites (p=0.015-0.048) and at the total femur and femur neck (p=0.008-0.013), respectively. In contrast, there were no differences in terms of bone loss among the tHcy quartiles for postmenopausal women.

CONCLUSION

These data provide the first clinical evidence that increased tHcy levels could be an independent risk factor for the future deterioration of bone mass in premenopausal women and men.

The contribution of collagen crosslinks to bone strength

Collagen crosslinking is a major post-translational modification of collagen which has important roles in determining the biomechanical competence of bone. Crosslinks can be divided into enzymatic lysil oxidase-mediated and non-enzymatic glycation-induced (advanced glycation end products, AGE) molecules. In addition, collagen in bone can also undergo spontaneous isomerization and racemization of the aspartic acid residues with the C-telopeptide (CTX), leading to the formation of two isomers namely α (newly formed collagen) and β (matured isomerized collagen) CTX. Several in vitro and ex vivo studies, relating the bone content of these crosslinks with bone strength, have shown that they contributed to the mechanical competence of trabecular and cortical bone-mainly on the post-yield properties-in part independent of the bone mineral content. In addition, AGEs such as pentosidine have been reported to alter the formation and propagation of microdamage by making the bone more brittle. The bone content of AGEs and isomerization can also be modified by antiresorptive and anabolic therapies. They may thus explain part of the antifracture efficacy of these treatments. The main challenge consists in the transposition of these in vitro/ex vivo studies to clinical applications for the development of a non-invasive biomarker, as none of currently identified collagen crosslinks (both enzymatic and nonenzymatic) is bone specific. Nevertheless, serum or urine levels of pentosidine and the ratio of α/β CTX have been reported to predict fracture risk in postmenopausal women, in men and in patients with type 2 diabetes.

Role of B₁₂ and homocysteine status in determining BMD and bone turnover in young Indians

Vitamin B(12) (B(12)) deficiency and hyperhomocysteinemia (HHcy) are independent risk factors for low bone mineral density (BMD) and fracture risk. We studied the role of HHcy and B(12) deficiency in determining the peak bone mass in Indians. Randomly selected 151 healthy young adult subjects (females 100, mean age: 26 yr) underwent evaluation of dietary intake of calcium and B(12); sun exposure; estimation of BMD by dual-energy X-ray absorptiometry at total hip, forearm, and lumbar spine; serum 25(OH)D(3); intact parathyroid hormone; B(12); homocysteine (Hcy); and bone turnover markers (BTMs) serum crosslaps, N-mid osteocalcin, and bone-specific alkaline phosphatase. Hypovitaminosis D (serum 25OHD(3)<20 ng/mL) and serum ALP level >150 IU/L were seen in 83% and 27%, respectively. Median serum B(12) and Hcy levels were 140 pg/mL (interquartile range [IQR]: 72-230 pg/mL) and 18 μmol/L (IQR 14-32 μmol/L); B(12) deficiency (serum B(12)<200 pg/mL) and HHcy (serum Hcy>30 μmol/L) were present in 71% and 68%, respectively. Low BMD (Z-score <-2.0) was present in 17% of subjects. There was no significant correlation between serum Hcy, folate, B(12), BTM, and BMD. BMD was predicted by height, weight, and body mass index. Young Indian healthy adults have high prevalence of hypovitaminosis D, B(12) deficiency, and HHcy. There is no correlation of serum B(12), folate, and Hcy status with BTMs and BMD in young, healthy, vegetarian Indian adults. Anthropometric variables predict BMD in young Indians.

Involvement of endoplasmic reticulum stress in homocysteine-induced apoptosis of osteoblastic cells

Hyperhomocysteinemia has been shown to increase the incidence of osteoporosis and osteoporotic fractures. Endoplasmic reticulum (ER) stress was recently shown to be associated with apoptosis in several types of cells. In this study, we determined the effect of homocysteine (Hcy) on the apoptosis of osteoblastic cells and investigated whether ER stress participates in Hcy-induced osteoblast apoptosis. Human osteoblastic cells were incubated with Hcy. Hcy dose-dependently decreased cell viability and increased apoptosis in osteoblastic cells. Osteoblastic cells are more susceptible to Hcy-mediated cell death than other cell types. Expression of cleaved caspase-3 was significantly increased by Hcy, and pretreatment with caspase-3 inhibitor rescued the cell viability by Hcy. Hcy treatment led to an increase in release of mitochondrial cytochrome c. It also triggered ER stress by increased expression of glucose-regulated protein 78, inositol-requiring transmembrane kinase and endonuclease 1α (IRE-1α), spliced X-box binding protein, activating transcription factor 4, and C/EBP homologous protein. Silencing IRE-1α expression by small interfering RNA effectively suppressed Hcy-induced apoptosis of osteoblastic cells. Our results suggest that hyperhomocysteinemia induces apoptotic cell death in osteoblasts via ER stress.

Influence of methionine and vitamin E on fluoride concentration in bones and teeth of rats exposed to sodium fluoride in drinking water

Increased exposure to fluorine-containing compounds leads to accumulation of fluorides in hard tissues of bones and teeth, which may result in numerous skeletal and dental disorders. This study evaluates the influence of methionine and vitamin E on fluoride concentration in bones and teeth of rats subjected to long-term exposure to sodium fluoride in drinking water. The study was conducted in 30 3-month-old female Wistar FL rats. The animals were divided into five groups, six rats per group. The control group consisted of rats receiving only distilled water as drinking water. All other groups received NaF in the amount of 10 mg/kg of body mass/day in their drinking water. In addition, respective animal groups received: NaF + Met group--10 mg of methionine/kg of body mass/day, NaF + Met + E group--10 mg of methionine/kg of body mass/day and 3 mg of vitamin E (tocopheroli acetas)/rat/day and NaF + E group--3 mg of vitamin E/rat/day. Femoral bones and incisor teeth were collected for the study, and the fluoride concentration was determined using a fluoride ion-selective electrode. Fluoride concentration in both bones and teeth was found to be higher in the NaF and NaF + Met groups compared to the control group. In groups NaF + Met + E and NaF + E, the study material contained much lower fluoride concentration compared to the NaF group, while the effect was more prominent in the NaF + E group. The results of the studies indicate that methionine and vitamin E have opposite effects on accumulation of fluorides in hard tissue in rats. By stimulating fluoride accumulation, methionine reduces the adverse effect of fluorides on soft tissue, while vitamin E, which prevents excessive accumulation of fluorides in bones and teeth, protects these tissues from fluorosis. Therefore, it seems that combined application of both compounds would be optimal for the prevention of the adverse effects of chronic fluoride intoxication.

Effect of excessive methionine on the development of the cranial growth plate in newborn rats

OBJECTIVE

Methionine is an essential amino acid and pivotal for normal growth and development. However, previous animal studies have shown that excessive maternal intake of methionine causes growth restrictions, organ damages, and abnormal growth of the mandible in newborn animals. However, the effect of excessive methionine on the development of the cranial growth plate is unknown. This study investigated histological alterations of the cranial growth plate induced by high methionine administration in newborn rats.

DESIGN

Twenty pregnant dams were divided into a control and an experimental group. The controls received a diet for rats and the experimental group was fed from the 18th gestational day with a special manufactured high methionine diet for rats. The high methionine diet was maintained until the end of the lactation phase (day 20). The offspring of both groups were killed at day 10 or 20 postnatally and their spheno-occipital synchondroses were collected for histological analysis.

RESULTS

The weight of the high-dose methionine treated experimental group was considerably reduced in comparison to the control group at day 10 and 20 postnatally. The cartilaginous area of the growth plate and the height of the proliferative zone were markedly reduced at postnatal day 10 in the experimental group.

CONCLUSIONS

In summary, the diet-induced hypermethioninemia in rat dams resulted in growth retardations and histomorphological changes of the spheno-occipital synchondrosis, an important craniofacial growth centre in newborns. This finding may elucidate facial dysmorphoses reported in patients suffering from hypermethioninemia.

Hyperhomocysteinemia is not associated with reduced bone quality in humans with hip osteoarthritis

BACKGROUND

Recent clinical and animal studies suggest that increased serum homocysteine (HCY) concentrations may be a risk factor for osteoporosis. In vitro studies showed that increasing HCY concentrations stimulate the activity of human osteoclasts. However, there is no data demonstrating that circulating HCY is related to structural and biomechanical properties of human bones. This study investigated the relationship between morphological as well as biomechanical bone properties and HCY serum concentrations in humans suffering from hip osteoarthritis (OA).

METHODS

Fasting blood samples and femoral heads were obtained from 94 males and females who underwent hip arthroplasty due to OA. Bones were assessed by dual energy X-ray absorptiometry (DXA), biomechanical testing (indentation method), and histomorphometry. Blood was collected for measurement of HCY, folate, vitamin B6, and vitamin B12. Subjects were classified as hyperhomocysteinemic (>12 micromol/L, n=47) and normohomocysteinemic (<12 micromol/L, n=47) according to their serum HCY concentrations.

RESULTS

Folate and vitamin B6, but not vitamin B12, were significantly lower in hyperhomocysteinemic subjects compared with controls. However, DXA, biomechanical testing, and histomorphometry did not reveal significant differences in bone quality between hyperhomocysteinemic subjects and controls.

CONCLUSIONS

The results of the present study do not indicate a significant relationship between circulating HCY concentrations and morphological or biomechanical bone properties in humans with OA of the hip.

Deficiencies of folate and vitamin B12 do not affect fracture healing in mice

PURPOSE

Recently, hyperhomocysteinemia has been shown to be associated with impaired fracture healing in mice. The main causes for hyperhomocysteinemia are deficiencies of folate and vitamin B12. However, there is no information on whether deficiencies of these B vitamins are affecting bone repair, too.

METHODS

We used two groups of mice to investigate the impact of folate and vitamin B12 deficiency on fracture healing: mice of the first group were fed a folate- and vitamin B12-deficient diet (n=14), while mice of the second group received an equicaloric control diet (n=13). Four weeks after stabilizing a closed femur fracture, bone repair was analyzed by histomorphometry and biomechanical testing. In addition, serum concentrations of homocysteine, folate, vitamin B12, the bone formation marker osteocalcin (OC), and the bone resorption marker collagen I C-terminal crosslaps (CTX) were measured.

RESULTS

Serum analyses revealed significantly decreased concentrations of folate and vitamin B12 in animals fed the folate- and vitamin B12-deficient diet when compared to controls. This was associated with a moderate hyperhomocysteinemia in folate- and vitamin B12-deficient mice, while no hyperhomocysteinemia was found in controls. Three-point bending tests showed no significant differences in callus stiffness between bones of folate- and vitamin B12-deficient animals and those of control animals. In accordance, the histomorphometric analysis demonstrated a comparable size and tissue composition of the callus, and also serum markers of bone turnover did not differ significantly between the two groups.

CONCLUSIONS

We conclude that folate and vitamin B12 deficiency does not affect bone repair in mice.

Effects of hyperhomocysteinemia during the gestational period on ossification in rat embryo

Severe hyperhomocysteinemia, as seen in classic homocystinuria, is associated with several skeletal malformations and osteopenia. Moreover, hyperhomocysteinemia during pregnancy has been associated with multiple developmental defects in the fetus. This study was undertaken to determine whether offspring of hyperhomocysteinemic mothers have demonstrable changes in bone volume and the epiphyseal growth plate. Ten adult female Sprague-Dawley rats were randomly assigned to the control or experimental group. The experimental group received 100 mg/kg/day of homocysteine in their drinking water for 3 weeks before mating and for the total duration of pregnancy. In each group, three pups per mother were randomly selected. The histomorphometric properties of tibial, radial and vertebral growth plates of newborn rats and the volume fraction of bone were compared between groups. The plasma homocysteine concentration at the end of study was significantly higher in dams in the experimental group (16.42+/-1.5 vs. 4.7+/-1.7 mumol/L, P<0.05). In offspring born to dams given the homocysteine supplement, the volume fraction of bone in the tibia (30.7+/-1.5% vs. 36.8+/-1.9%, P<0.05), radius (29.6+/-1.1% vs. 37.4+/-2%, P<0.05) and vertebra (34.4+/-1.8% vs. 41+/-1.9%, P<0.05) were significantly decreased whereas vertical heights of proliferative (423+/-25.1 vs. 301.8+/-28.1 microm for radius and 131.9+/-5.9 vs. 107.8+/-3.5 microm for vertebra) and hypertrophic zones (213.1+/-12 vs. 163.3+/-7.5 microm for tibia, 153.2+/-7.7 vs. 121.1+/-7.9 microm for radius and 112+/-9.9 vs. 88.4+/-10.1 microm for the vertebra) were increased (P<0.05). The results showed that the administration of homocysteine caused osteopenia in newborn rats. In addition, these data suggest that hyperhomocysteinemia may induce disruption of normal development of epiphyseal cartilage in the rat embryo.

Serum N-terminal-pro-brain natriuretic peptide (NT-pro-BNP) and homocysteine levels in type 2 diabetic patients with asymptomatic left ventricular diastolic dysfunction

AIMS

: The aim of this study was to determine serum NT-proBNP and plasma Hcy levels and to explore the relationship between serum NT-proBNP and plasma Hcy levels in type 2 diabetic patients with and without asymptomatic LVDD.

METHODS

: NT-proBNP and Hcy levels were measured 31 patients with type 2 diabetes mellitus. According to echocardiographic data, diabetic patients were divided into two groups: normal LV function or LV diastolic dysfunction.

RESULTS

: Serum NT-proBNP levels in diabetic patients with LVDD were significantly higher than in diabetic patients with normal LV function and controls. The area under the receiver-operating characteristic (ROC) curve for NT-proBNP to separate normal vs. diastolic dysfunction was 0.96 in type 2 diabetic patients. Plasma Hcy levels were significantly higher in both diabetic groups than in controls. Positive correlation was noted between NT-proBNP and Hcy levels in diabetic patients with LVDD (r=0.881, p=0.0001).

CONCLUSIONS

: The correlation between elevated NT-proBNP and Hcy levels in diabetic patients with LVDD suggest an association between homocysteinemia and increased NT-proBNP secretion. Our data indicate that NT-proBNP may be a simple screening tool to select diabetic patients with LVDD requiring further examination with echocardiography.

Hyperhomocysteinemia is associated with impaired fracture healing in mice

Hyperhomocysteinemia (HHCY) has been shown to disturb bone metabolism and to increase the incidence of osteoporosis and osteoporotic fractures. However, there is a complete lack of information on whether these metabolic alterations affect bone repair. The aim of this study was to analyze the impact of HHCY on fracture healing. One group of mice was fed a homocystine-supplemented diet (n = 12), whereas another group received the accordant standard diet for control (n = 13). Four weeks after the stable fixation of a closed femoral fracture, animals were killed to prepare bones for histomorphometric and biomechanical analyses. In addition, blood samples were obtained to evaluate serum concentration of homocysteine (HCY). Quantitative analysis of blood samples revealed severe HHCY as indicated by significantly increased serum concentrations of HCY in animals fed the homocystine-supplemented diet (102.2 +/- 64.5 micromol/l) compared to controls (2.8 +/- 1.5 micromol/l). Biomechanical evaluation of bone repair revealed significantly decreased bending stiffness of the femora of homocystine-fed animals (45.5 +/- 18.2 N/mm) compared with controls (64.6 +/- 15.8 N/mm). Histomorphometric analysis demonstrated a slightly smaller callus diameter in HHCY animals but no significant differences in the tissue composition of the callus. In conclusion, the homocystine-supplemented diet leads to severe HHCY, which is associated with an impaired biomechanical quality of the healing bone.

The relation of plasma homocysteine to radiographic knee osteoarthritis

OBJECTIVE

Homocysteine has been implicated in multiple diseases that involve changes in structural tissue. In vitro studies have found that it alters the structure of collagen cross-linking thus affecting stability and mineralization such as that occurring in bone tissue. In the present study we considered the possible relationship between plasma homocysteine levels and the development and progression of knee osteoarthritis (OA).

METHODS

The study question was posed in 691 men and 966 women from the original and offspring cohorts of the Framingham Osteoarthritis Study. We divided individuals into three groups according to plasma homocysteine levels and compared their risk for the development of new and progression of existing OA. We adjusted for potential confounders including age, body mass index, weight change, and physical activity.

RESULTS

In the crude analysis, men in the middle homocysteine tertile were found to be at a greater risk than men in the lowest tertile for incident OA [odds ratios of 1.9 (1.1-3.5)]. This result persisted after adjusting for covariates [odds: 2.0, (1.1-3.8)]. No significant correlation was seen in women for the development of OA. In the evaluation of progression no significant trends were seen for both men and women.

CONCLUSIONS

Although cellular and molecular studies of homocysteine-related pathophysiology suggest a possible correlation between plasma homocysteine levels and OA, the present clinical study did not conclusively demonstrate such an association. However, further research is needed to explore the role of homocysteine in specific aspects of OA etiopathogenesis.

Hyperhomocysteinemia induces a tissue specific accumulation of homocysteine in bone by collagen binding and adversely affects bone

BACKGROUND

Recently, hyperhomocysteinemia (HHCY) has been suggested to have adverse effects on bone. This study investigated if an experimental HHCY in rats induces an accumulation of homocysteine (HCY) in bone tissue that is accompanied by bone loss and reduced bone strength.

MATERIAL AND METHODS

HHCY was induced in healthy rats by either a methionine (Meth)- or a homocystine (Homo)-enriched diet and compared with controls. Homocystine is the product of two disulfide linked HCY molecules. Tissue and plasma concentrations of HCY, S-adenosylhomocysteine (SAH) and S-adenosylmethionine (SAM) were measured. Bones were assessed by biomechanical testing, histomorphometry, microCT and the measurement of biochemical bone turnover markers in plasma.

RESULTS

Meth and Homo animals developed a significant HHCY that was accompanied by a tissue specific accumulation of HCY (1300 to 2000% vs. controls). 65% of HCY in bone was bound to collagen of the extracellular matrix. The SAH / SAM-ratio in bone and plasma of Meth and Homo animals exhibited a tissue specific increase indicating a reduced methylation capacity. Accumulation of HCY in bone was characterized by a distinct reduction of cancellous bone (proximal femur: -25 to -35%; distal femur -56 to -58%, proximal tibia: -28 to -43%). Accordingly, bone strength was significantly reduced (-9 to -12%).

CONCLUSION

A tissue specific accumulation of HCY in bone may be a promising mechanism explaining adverse effects of HHCY on bone. A reduced methylation capacity of bone cells might be another relevant pathomechanism.

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.

Stimulation of osteoblast activity by homocysteine

Homocysteine (HCY) has recently been linked to fragility fractures. Moreover, HCY activates osteoclasts. Little is known about the effect of HCY on activity of human osteoblasts (OBs). We hypothesized that HCY decreases the activity of OBs. Osteoblasts obtained from tra-becular human bone specimens of eight donors were cultured with conditioned medium. Culture medium was adjusted to 0, 100, 500, 1000 and 2000 μM HCY. After 14 days alkaline phosphatase (AP) activity, pro-collagen type I N-terminal peptide (PINP) and osteocalcin (OC) secretion in the supernatant were measured. After 20 days the formation of mineralized matrix was analyzed. HCY-stimulated AP activity gradually (100 μM HCY: 118%, P= 0.006; 500 μM HCY: 125%, P < 0.001). At 1000 and 2000 μM HCY the increase of AP activity was reversible (1000 μM HCY: 106%, P= 0.317; 2000 μM HCY: 102%, P < 0.737). The PINP secretion was also stimulated by HCY reaching a maximum of 260 ± 154 μg/l at 500 μmol/l versus 205 ± 94 μ,g/l in controls. After 20 days of culture the formation of bone matrix was increased at 100 and 500 μM HCY. OC secretion was not significantly changed. The results of the present study consistently demonstrate a moderate stimulation of primary human OB activity by increasing concentrations of HCY. However, the magnitude of this effect seems to be less pronounced than recent observations on primary human osteoclasts, suggesting a dysbalance between OBs and osteoclasts in favour of osteoclasts

Is hyperhomocysteinemia a risk factor for osteoporosis?

Hyperhomocysteinemia (HHCY) has been accepted as a risk factor not only for cardiovascular diseases (CVDs) but also for osteoporosis. Furthermore, clinical data suggest that HHCY also increases fracture risk, but have no or only minor effects on bone mineral density (BMD). Measurement of biochemical bone turnover markers indicates a shift of bone metabolism toward bone resorption. Animal studies confirm these observations showing a reduced bone quality and stimulation of bone resorption in hyperhomocysteinemic animals. In addition, homocysteine (HCY) has been found to accumulate in bone tissue by collagen binding. These results indicate a causal involvement of HHCY in osteoporosis. The first experimental studies revealed that several pathomechanisms might be involved. Cell culture studies demonstrate that high HCY and low vitamin B levels stimulate osteoclasts but not osteoblasts, indicating again a shift of bone metabolism toward bone resorption. In addition, HHCY seems to have adverse affects on extracellular bone matrix by disturbing collagen crosslinking. Well-performed large cell culture studies confirm the results obtained with exogenous HCY administration. In conclusion, existing data suggest that HHCY (and possibly vitamin B deficiencies) adversely affects bone quality by a stimulation of bone resorption and disturbance of collagen crosslinking.

The effect of B-vitamins on biochemical bone turnover markers and bone mineral density in osteoporotic patients: a 1-year double blind placebo controlled trial

BACKGROUND

Hyperhomocysteinemia is a new risk factor for osteoporosis. This study analyzed the effect of a homocysteine (HCY)-lowering treatment in osteoporotic individuals.

METHODS

Osteoporotic subjects (n=47, 55-82 years) were treated with either a combination of 2.5 mg folate, 0.5 mg vitamin B(12) and 25 mg vitamin B(6) or placebo. Bone mineral density (BMD) at lumbar spine and hip was measured at baseline and after 1 year. Urinary desoxypyridinoline cross-links (DPD) and plasma levels of tartrate resistant acid phosphatase (TRAP), C-terminal cross-links of collagen I (CTx), pro-collagen type I N-terminal peptide (PINP) and osteocalcin (OC) were measured after 0, 4, 8 and 12 months.

RESULTS

B-vitamin supplementation significantly reduced HCY (0 vs. 12 months: 13.6+/-4.8 vs. 8.9+/-2.4 micromol/L). Placebo treatment had no effect on HCY (0 vs. 12 months: 12.0+/-3.4 vs. 12.7+/-3.9 micromol/L). BMD, TRAP, CTx, OC and PINP did not change throughout the study in both groups. Vitamin treatment decreased urinary DPD by -13% (p<0.01) after 8 and 12 months. In a sub-group analysis of hyperhomocysteinemic subjects (HCY>15 mumol/L, n=8), B-vitamin treatment tended to increase BMD at the lumbar spine, with a t-score from -2.7 to -1.7, and to decrease OC and PINP by approximately 50%.

CONCLUSIONS

B-vitamin supplementation had no consistent effects on bone turnover or BMD. However, the situation may be different in patients with hyperhomocysteinemia.

The role of hyperhomocysteinemia and B-vitamin deficiency in neurological and psychiatric diseases

Hyperhomocysteinemia (HHcy) is related to central nervous system diseases. Epidemiological studies show a positive, dose-dependent relationship between plasma total homocysteine (tHcy) concentration and neurodegenerative disease risk. tHcy is a marker of B-vitamin (folate, B(12), B(6)) status. Hypomethylation, caused by low B-vitamin status and HHcy, is linked to key pathomechanisms of dementia; B-vitamin supplementation could potentially reduce neurological damage. In retrospective studies, the association between tHcy and cognition is impressive; there is also evidence that tHcy-lowering treatment could be effective in primary and secondary stroke prevention. Increased tHcy and low serum folate occur in patients with Parkinson's disease, especially those receiving L-dopa. There is also an association between HHcy and multiple sclerosis, and between B-vitamin status and depression. Studies also confirm a causal role for tHcy in epilepsy, and certain anti-epileptics enhance HHcy. B-vitamin status should be optimized by ensuring sufficient intake in patients with neuropsychiatric diseases. HHcy occurs commonly in the elderly and can contribute to age-related neurodegeneration. Treatment with folic acid, B(12) and B(6) lowers tHcy. For secondary and primary prevention from several neuropsychiatric disorders, it seems prudent to actively identify deficient subjects and ensure sufficient vitamin intake.

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.

Accumulation of homocysteine by decreasing concentrations of folate, vitamin B12 and B6 does not influence the activity of human osteoblasts in vitro

BACKGROUND

Homocysteine (HCY) has recently been linked to fragility fractures. Elevated circulating HCY is mainly caused by folate, vitamin B12 and B6 deficiencies. However, little is known about the effect of these vitamins on the activity of osteoblasts. We hypothesized that decreasing concentrations of folate, vitamin B12 and B6 decrease osteoblasts activity by accumulation of HCY.

METHODS

Osteoblasts obtained from trabecular human bone specimens of 8 donors were cultured with decreasing concentrations of folate, vitamin B12 and B6. Vitamin concentrations were modified in combination or one vitamin only (8 repetitions x 8 donors, n=64). After 14 days alkaline phosphatase (AP) activity, pro-collagen type I N-terminal peptide (PINP) and osteocalcin secretion in the supernatant was measured. After 20 days, the formation of mineralized matrix was analyzed.

RESULTS

Decreasing B-vitamin concentrations induced a significant accumulation of HCY in the supernatant reaching up to 160%. The increase in HCY was not accompanied by changes of AP, osteocalcin and PINP. Moreover, mineralized matrix formation was not affected.

CONCLUSION

Accumulation of HCY by decreasing concentrations of folate, vitamin B12 and B6 does not affect the activity of human osteoblasts. Consequently, other mechanisms have to be responsible for the reduced bone quality in hyperhomocysteinemic subjects.

Homocysteine, brain natriuretic peptide and chronic heart failure: a critical review

Chronic heart failure (CHF) is a major public health problem causing considerable morbidity and mortality. Recently, plasma homocysteine (HCY) has been suggested to be significantly increased in CHF patients. This article reviews the relation between hyperhomocysteinemia (HHCY) and CHF. Clinical data indicate that HHCY is associated with an increased incidence, as well as severity, of CHF. In addition, HCY correlates with brain natriuretic peptide (BNP), a modern biochemical marker of CHF, which is used for diagnosis, treatment guidance and risk assessment. Animal studies showed that experimental HHCY induces systolic and diastolic dysfunction, as well as an increased BNP expression. Moreover, hyperhomocysteinemic animals exhibit an adverse cardiac remodeling characterized by accumulation of interstitial and perivascular collagen. In vitro superfusion experiments with increasing concentrations of HCY in the superfusion medium stimulated myocardial BNP release independent from myocardial wall stress. Thus, clinical and experimental data underline a correlation between HHCY and BNP supporting the role of HHCY as a causal factor for CHF. The mechanisms leading from an elevated HCY level to reduced pump function and adverse cardiac remodeling are a matter of speculation. Existing data indicate that direct effects of HCY on the myocardium, as well as nitric oxide independent vascular effects, are involved. Preliminary data from small intervention trials have initiated the speculation that HCY lowering therapy by micronutrients may improve clinical as well as laboratory markers of CHF.

In conclusion, HHCY might be a potential etiological factor in CHF. Future studies need to explore the pathomechanisms of HHCY in CHF. Moreover, larger intervention trials are needed to clarify whether modification of plasma HCY by B-vitamin supplementation improves the clinical outcome in CHF patients.

Clin Chem Lab Med 2007;45:1633–44.