Links between cardiovascular disease and osteoporosis in postmenopausal women: serum lipids or atherosclerosis per se?

INTRODUCTION AND HYPOTHESIS: Epidemiological observations suggest links between osteoporosis and risk of acute cardiovascular events and vice versa. Whether the two clinical conditions are linked by common pathogenic factors or atherosclerosis per se remains incompletely understood. We investigated whether serum lipids and polymorphism in the ApoE gene modifying serum lipids could be a biological linkage. METHODS: This was an observational study including 1176 elderly women 60-85 years old. Women were genotyped for epsilon (epsilon) allelic variants of the ApoE gene, and data concerning serum lipids (total cholesterol, triglycerides, HDL-C, LDL-C, apoA1, ApoB, Lp(a)), hip and spine BMD, aorta calcification (AC), radiographic vertebral fracture and self-reported wrist and hip fractures, cardiovascular events together with a wide array of demographic and lifestyle characteristics were collected. RESULTS: Presence of the ApoE epsilon 4 allele had a significant impact on serum lipid profile, yet no association with spine/hip BMD or AC could be established. In multiple regression models, apoA1 was a significant independent contributor to the variation in AC. However, none of the lipid components were independent contributors to the variation in spine or hip BMD. When comparing the women with or without vertebral fractures, serum triglycerides showed significant differences. This finding was however not applicable to hip or wrist fractures. After adjustment for age, severe AC score (>or=6) and/or manifest cardiovascular disease increased the risk of hip but not vertebral or wrist fractures. CONCLUSION: The contribution of serum lipids to the modulators of BMD does not seem to be direct but rather indirect via promotion of atherosclerosis, which in turn can affect bone metabolism locally, especially when skeletal sites supplied by end-arteries are concerned. Further studies are needed to explore the genetic or environmental risk factors underlying the association of low triglyceride levels to vertebral fractures.

Radiographic measure of aorta calcification is a site-specific predictor of bone loss and fracture risk at the hip.

OBJECTIVE: To investigate whether aorta calcification (AC) - a surrogate marker of atherosclerosis - is an independent indicator of low bone mass density (BMD), accelerated bone loss, and risk of future fractures in postmenopausal women. DESIGN: A prospective epidemiological study. Follow-up period was 7.5 years. SETTING: Community-based sample followed by a research institute. SUBJECTS: A total of 2662 generally healthy postmenopausal women with a mean age of 65.0 +/- 7.1 years at baseline. MAIN OUTCOME MEASURES: Annual rate of changes in BMD (DEXA) and AC (X-rays), vertebral fractures (X-rays), hip fractures (questionnaire). RESULTS: Advanced AC at baseline was significantly associated with lower BMD and accelerated bone loss from the proximal femur. In a multivariate logistic regression model, age (OR 1.1, 95% CI 1.0-1.2, P = 0.02), body mass index (BMI; OR 0.9, 95% CI 0.8-1.0, P = 0.03) and the severity of AC (OR 2.3, 95% CI 1.1-4.8, P = 0.03) were independent predictors of hip fractures. Adjusted OR for vertebral fracture was 1.2 (95% CI 1.0-1.5, P = 0.12). CONCLUSIONS: Aorta calcification seems to independently contribute to the development of osteoporosis in the proximal femur. Further studies are needed to clarify whether effective atherosclerosis prevention lowers hip fracture risk.

The long-term impact of 2-3 years of hormone replacement therapy on cardiovascular mortality and atherosclerosis in healthy women.

OBJECTIVE: The effect of hormone replacement therapy (HRT) on cardiovascular risk is intensely debated. The aim of this study was to investigate the long-term effects of HRT given for a few years on all-cause and cardiovascular mortality and the severity of atherosclerosis. METHODS: This analysis was based on a cohort of 1,458 postmenopausal women (55.8 +/- 6.1 years old) who previously participated in a number of randomized, placebo-controlled, clinical trials assessing the efficacy of 2-3 years of therapy with various estrogen plus progestin combinations for preventing bone loss. Women were followed on average for 9.8 years and came for a follow-up visit. Outcome variables were all-cause and cardiovascular mortality and the severity of atherosclerosis, as estimated by semi-quantitative scoring of vascular calcification in the lumbar aorta on lateral radiographs. RESULTS: A total of 174 women died during the observation period. All-cause mortality was decreased by 30% in the HRT+ group compared with the HRT- group (hazard ratio (HR) 0.70; 95% confidence interval (CI) 0.50-0.97) after adjusting for age, body mass index and smoking. Under the same conditions, similar results characterized mortality from cardiovascular disease (n = 61 deaths; 35.1% of all deaths) and coronary heart disease (n = 39 deaths; 22.4% of all deaths), which were decreased by 46% (HR 0.54, 95% CI 0.29-0.98, p = 0.045) and 53% (HR 0.47, 95% CI 0.21-1.03, p = 0.062), respectively. Furthermore, the mean severity score of aortic calcification at follow-up was significantly lower in hormone-treated compared to non-treated women (p < 0.0001). CONCLUSION: Women who receive 2-3 years of HRT after menopause do not have increased all-cause mortality, and results of the present study suggest relative cardiovascular benefits compared to those who had not used hormones.

Calcitonin directly attenuates collagen type II degradation by inhibition of matrix metalloproteinase expression and activity in articular chondrocytes.

OBJECTIVE: Calcitonin was recently reported to counter progression of cartilage degradation in an experimental model of osteoarthritis, and the effects were primarily suggested to be mediated by inhibition of subchondral bone resorption. We investigated direct effects of calcitonin on chondrocytes by assessing expression of the receptor and pharmacological effects on collagen type II degradation under ex vivo and in vivo conditions. METHODS: Localization of the calcitonin receptor on articular chondrocytes was investigated by immunohistochemistry, and the expression by reverse transcriptase polymerase chain reaction (RT-PCR). In bovine articular cartilage explants, cartilage degradation was investigated by release of C-terminal telopeptides of collagen type II (CTX-II), induced by tumor necrosis factor-alpha (TNF-alpha) [20 ng/ml] and oncostatin M (OSM) [10 ng/ml], with salmon calcitonin [0.0001-1 microM]. In vivo, cartilage degradation was investigated in ovariectomized (OVX) rats administered with oral calcitonin [2 mg/kg calcitonin] for 9 weeks. RESULTS: The calcitonin receptor was identified in articular chondrocytes by immunohistochemistry and RT-PCR. Calcitonin concentration-dependently increased cAMP levels in isolated chondrocytes. Explants cultured with TNF-alpha and OSM showed a 100-fold increase in CTX-II release compared to vehicle-treated controls (P<0.001). The degradation of type II collagen in these explants was concentration-dependently inhibited by calcitonin, 65% protection at 10 nM calcitonin (P<0.01). TNF-alpha and OSM induced a pronounced increase in matrix metalloproteinase (MMP) activity, which was strongly inhibited by calcitonin. In vivo, administration of salmon calcitonin to OVX rats resulted in significant (P<0.001) decrease in CTX-II levels. CONCLUSION: These results are the first evidence of calcitonin receptor expression on articular chondrocytes and that the chondroprotective effects of calcitonin might involve the inhibition of MMP expression.

Low bone mineral density in the hip as a marker of advanced atherosclerosis in elderly women.

Previous studies indicate that low bone mineral density (BMD) in the hip is a useful predictor of cardiovascular mortality among the elderly. The objective of this study was to investigate whether low hip BMD is directly associated with the severity of atherosclerosis. The per-protocol population consisted of 963 women aged 60-85 years. Study variables were aortic calcification (AC) graded on lateral lumbar radiographs, BMD at various anatomic sites (distal radius, lumbar spine, proximal femur) measured by DXA, information on various risk factors, and medical history. After adjustment for age, BMD at the proximal femur, but not at the radius or spine BMD, showed statistically significant association with the severity of AC (r = -0.12-17, P < 0.001). Age, years since menopause, BMI, level of education, current and previous smoking, and weekly fitness activity were significant common risk factors (all P < 0.05) with contrasting influence on AC and hip BMD. In a multiple regression model, AC contributed significantly and independently to the variation in hip BMD (beta = -0.10, P = 0.004). Impaired blood flow represented by 40 women with documented history of intermittent claudication was not an independent contributor and did not alter the association between AC and hip BMD. However, AC and demineralization in the hip was particularly severe in women with intermittent claudication accompanied by a higher prevalence of coronary heart disease compared with age-matched controls (all P < 0.001). In conclusion, severe osteoporosis in the hip may indicate advanced atherosclerosis and thereby an increased risk for not only hip fractures but also for coronary heart disease. The results further emphasize that osteoporosis in the hip and peripheral vascular disease are linked by common risk factors and pathomechanisms.

Does serum cholesterol contribute to vertebral bone loss in postmenopausal women?

Recent in vitro and animal studies suggest that cholesterol and its metabolites inhibit the functional activity of osteoblasts and thereby induce reduced bone mineralization. However, scant information is available on the clinical implication of these findings with special regard to postmenopausal bone loss. Therefore, the aim of the present study was to investigate cross-sectional and longitudinal associations between serum cholesterol, bone mineral density (BMD), and bone turnover in 340 postmenopausal women aged 50-75 years (mean 59 years), who were followed for 8.3 +/- 1.1 years. BMD in the lumbar spine, distal forearm, and total hip was measured by dual energy X-ray absorptiometry. Other study variables were physical measures, serum cholesterol, serum markers of bone turnover, and self-reported information on various risk factors for osteoporosis. At baseline, serum cholesterol showed significant negative correlation with BMD at the lumbar spine (r = -0.21, P < 0.0001) and distal forearm (r = -0.14, P = 0.013), but not at the hip. No associations of serum cholesterol with serum osteocalcin (r = 0.054, P = 0.317) and CTX (r = -0.027, P = 0.623) were, however, noted. After adjustment for age and BMI, the negative correlation remained significant at the lumbar spine (r = -0.16, P = 0.004), but not at the distal forearm (r = -0.018, P = 0.738). At the end of the 8-year follow-up, the correlation between serum cholesterol and spine BMD was not observed. Those with the largest increases in serum cholesterol, however, showed the greatest decreases in spine BMD independently of the changes in BMI (r = -0.16, P = 0.004). The correlation between the changes in serum cholesterol and the simultaneous changes in osteocalcin (r = 0.081, P = 0.140) and CTX (r = 0.042, P = 0.441) were statistically insignificant. Thus, our results suggest that the weak associations between spine BMD and serum cholesterol can be explained by the fact that both variables are simultaneously affected by estrogen deficiency rather than by a direct influence of serum cholesterol on osteoblast function.

No major effect of estrogen receptor gene polymorphisms on bone mineral density or bone loss in postmenopausal Danish women.

The polymorphisms of the estrogen receptor (ER) gene defined by the restriction enodonucleases PvuII and XbaI have recently been reported to be associated with bone mineral density (BMD) in postmenopausal women. To investigate the possible relation of the PvuII and XbaI restriction fragment-length polymorphisms of the ER gene with BMD in Danish postmenopausal women, two studies were undertaken: 1) a cross-sectional study of 499 postmenopausal women, where the ER genotypes and alleles were related to BMD of the hip, spine, and lower forearm; and 2) a longitudinal study of 101 postmenopausal women followed up for 18 years. In the latter study, late postmenopausal bone loss in the hip and spine was determined over a period of 6 years in women (mean age of 63 to 69 years), and long-term postmenopausal bone loss in the lower forearm was determined over a period of 18 years in women (mean age of 51 to 69 years). Genotyping was performed through the restriction cleavage of polymerase chain reaction-amplified genomic DNA with the two restriction enzymes, PvuII and XbaI. Restriction fragment-length polymorphisms were represented as P or p (PvuII) and X or x (XbaI), with the lower case letters signifying the presence of the restriction site. The frequencies of the ER genotypes were similar to previously published genotype frequencies in Caucasian and Asian populations. No significant effect of the ER genotypes or alleles on BMD was found at any site, nor was there a relation between ER genotypes and the rate of bone loss either in the hip and spine over 6 years, or in the lower forearm over 18 years. In conclusion, we could not demonstrate any major effect of the ER gene polymorphisms on BMD or rate of bone loss in healthy postmenopausal Danish women.

Vitamin D receptor and estrogen receptor gene polymorphisms in postmenopausal Danish women: no relation to bone markers or serum lipoproteins.

OBJECTIVE: To investigate the polymorphisms of the vitamin D receptor (VDR) and estrogen receptor (ER) genes in relation to biochemical markers of bone turnover (serum osteocalcin and urinary collagen type I degradation products (CrossLaps), and to study ER genotypes in relation to serum lipoproteins, blood pressure, or changes in these parameters after 2 years of hormone replacement therapy (HRT) in 499 Danish postmenopausal women. METHODS: The VDR gene polymorphisms were determined by means of the three restriction enzymes, i.e. BsmI, ApaI and TaqI, while the ER gene polymorphisms were determined by means of the PvuII and XbaI restriction enzymes. Serum osteocalcin, urinary CrossLaps and the lipoproteins were also assessed. Body mass index was recorded. RESULTS: The VDR or ER genotypes did not differ significantly with respect to age, age at menopause or body mass index. No significant effect of VDR or ER genotype on bone turnover was found. Furthermore, we were unable to find any relationship between ER genotype and lipoproteins or blood pressure at baseline, or changes in these parameters during HRT. CONCLUSION: A clinically significant relationship between VDR and ER genotypes and biochemical markers of bone turnover or serum lipoproteins could not be demonstrated in healthy Danish postmenopausal women.

Monoclonal antibodies against Yersinia enterocolitica common antigen produced by immunization with immunoprecipitates.

Crossed immunoelectrophoresis was applied to purify Y. enterocolitica common antigen by precipitation with monospecific rabbit anti-P. aeruginosa CA antibody. Monoclonal antibodies against Y. enterocolitica CA were then raised by immunization of mice with these immunoprecipitates. This method provides the possibility of producing a panel of anti-CA monoclonal antibodies from a large number of bacterial species.