Abstract
Background Ezetimibe, as a lipid-lowering agent, inhibits the intestinal absorption of cholesterol and decreases low-density lipoprotein cholesterol (LDL-C) level in serum. It also up-regulates hepatic cholesterol biosynthesis and, by contrast to statins, increases serum mevalonate levels. Statins and biphosphonates decrease osteoclastic activity through the same mechanisms by inhibiting the mevalonate pathway. We therefore tested the effect of ezetimibe on bone turnover in hypercholesterolemic patients.
Subject and Methods In an open-label clinical trial, 54 hypercholesterolemic patients included in the study underwent 12 months of treatment with ezetimibe at a dosage of 10 mg/d. Before and after the 1-year ezetimibe treatment, bone mineral density (BMD) was measured by dual-energy x-ray absorptiometry and serum samples taken for measurements of levels of total cholesterol (TC), triglyceride, high-density lipoprotein cholesterol and LDL-C, serum calcium (Ca), serum phosphate, total and bone alkaline phosphatases (ALPs), and carboxyterminal fragment of type 1 collagen in the serum.
Results The hypercholesterolemic patients showed a significant reduction with respect to baseline TC and LDL-C serum levels: 20% for TC (270.18 [38.58]−214.46 [38] mg/dL) and 24% for LDL-C (189.57 [38.58]−144 [32.05] mg/dL). Biochemical markers of both bone formations (total ALP level, 65.50 [21.33]−66.27 [21.017] IU/L and bone ALP level, 55.93 [7.92]−56.25 [7.49] IU/L) and bone resorption (β-CTx, 0.44 [0.24]−0.46 [0.21] ng/mL) increased but did not show any significant change for the whole study period. At the end of 1 year, both BMD-lumbar spine (0.90 [0.12]−0.89 [0.08] g/cm2) and BMD-total femur (0.93 [0.12]−0.92 [0.12] g/cm2) showed a negative trend but without reaching statistical significance.
Conclusions Our study results showed a negative trend but did not demonstrate statistically significant changes of BMD and metabolic markers with the treatment of ezetimibe.
Statins are well established as lipid-lowering drugs that reduce the risk of cardiovascular events including myocardial infarction. They are also known to have pleiotropic effects such as improvement of endothelial function, increased nitric oxide and antioxidant properties, inhibition of inflammatory responses, and immunomodulatory actions.1,2It has also been suggested that 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors directly affect osteoclastic activity through mechanisms analogous to those of biphosphonates by inhibiting the same mevalonate pathway and increase bone mineral density (BMD) with increased expression of bone morphogenetic protein 2 (BMP-2) gene in bone cells.3-5As a member of a new class of lipid-lowering agents, ezetimibe inhibits the intestinal absorption of cholesterol by binding Niemann-Pick C1-like 1 (NPC1L1) located on the brush border of the jejunum. Although ezetimibe decreases low-density lipoprotein cholesterol (LDL-C) level in serum, it also up-regulates hepatic cholesterol biosynthesis and, by contrast to statins, increases serum mevalonate level.6Owing to controversial effects of statins and ezetimibe on mevalonate pathway, ezetimibe may affect osteoclastic activity different than statins and may decrease BMD (Fig. 1).
The purpose of our study was to examine and assess the effects of ezetimibe on bone turnover in hypercholesterolemic patients during the 1-year treatment.
SUBJECTS AND METHODS
Subjects
In an open-label clinical trial, 60 consecutive hypercholesterolemic patients (45 women and 15 men) who attended our outpatient clinic and consented to be enrolled in the research were included in the study. Tenets of the current version of the Declaration of Helsinki were followed, institutional ethical committee approval was granted, and the nature of the trial and possible adverse effects of the drug were explained to the patients.
Subjects with slight to moderate hypercholesterolemia who only needed a diet were excluded. Patients with secondary hyperlipidemia and endocrinologic and systemic diseases and those receiving steroids, hormone replacement therapy, thiazides, biphosphonates, calcium, vitamin D, or any lipid-lowering drugs for the past 6 months were also excluded.
The 60 hypercholesterolemic patients underwent 12 months of treatment with ezetimibe at a dosage of 10 mg/d. Serum creatine phosphokinase and hepatic aminotransferase (aspartate and alanine aminotransferases) levels were measured before and after 4 weeks of ezetimibe treatment and then at 3-month intervals throughout the study period. A liver enzyme increment to more than 3 times the upper limit of the reference range or an increase of the creatine phosphokinase level with clinical symptoms and signs of muscle involvement, drug intolerance, or noncompliance among patients were also exclusion criteria.
During the follow-up period, 2 patients were excluded from the study because of vitamin D and calcium use. In addition, 1 patient was lost to follow-up, and 3 patients refused to continue the study. The remaining 54 subjects completed the study.
METHODS
In all subjects, after an overnight fast, venous blood samples were drawn at baseline and after 12 months for the measurement of levels of total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol and LDL-C, serum calcium (Ca), serum phosphate (P), total and bone alkaline phosphatases (T- and B-ALPs), and carboxyterminal fragment of type 1 collagen in the serum.
Levels of lipid parameters, serum P, T-ALP, and serum Ca, were measured using calorimetric methods. Bone ALP level was measured using heat inactivation method at 57°C and bone resorption marker β-CrossLaps (β-CTx) by chemiluminescence method.
In all subjects, BMD was measured at baseline and after 12 months by dual energy x-ray absorptiometry on the lumbar spine (L-S; from the first to the fourth lumbar vertebra) and on the total femur (F-total). In our institution, in vitro coefficient variation (precision), performed on manufacturer's phantom, was 1% for the spine and F-total.
STATISTICAL ANALYSIS
On the basis of previous estimates of SD of 2.5 and accounting for paired t test comparisons, we calculated that 51 patients would be required to provide the study with 80% power to detect (2-sided α, 0.05) a mean difference in BMD from baseline of 1 g/cm2. The sample size was calculated 60 with expected rate of nonevaluable patients of 15%. Parameters are reported as mean (SD); statistical testing of differences between groups was made by paired t test. Statistical tests were considered significant when P < 0.05, and analysis was carried out using SPSS 11.0 (SPSS Inc., Chicago, IL).
RESULTS
Table 1 shows the lipid parameters and Table 2 the BMD and bone markers of the patients at the beginning of the study and after 12 months of treatment with 10-mg/d ezetimibe.
As expected, the hypercholesterolemic patients on treatment with 10-mg/d ezetimibe showed significant reduction with respect to baseline in TC and in LDL-C serum levels, which at the end of the study were 20% for TC (270.18 [38.58]−214.46 [38] mg/dL; P < 0.001) and 24% for LDL-C (189.57 [38.58]−144 [32.05] mg/dL; P < 0.001). High-density lipoprotein cholesterol and TG levels did not show any significant changes (P > 0.05).
Biochemical markers of both bone formations (T- and B-ALPs) and bone resorption (β-CTx) increased but did not show any significant change for the whole study period (P > 0.05). The mean BMD change from the baseline for a 1-year period is shown in Table 2. At the end of 1 year, both BMD L-S and F-total levels showed a negative trend but without reaching the statistical significance (P > 0.05).
DISCUSSION
To our knowledge, the present study is the first study investigating the changes in both bone remodeling parameters and BMD in hypercholesterolemic patients treated with ezetimibe. Our results showed that during the 1 year of treatment, ezetimibe caused a nonsignificant decrease in BMD. The levels of the bone resorption marker β-CTx and the bone formation marker B-ALP were increased without reaching statistically significant levels.
In previous years, observational, retrospective, and prospective studies examining the effects of statins on BMD in patients with hypercholesterolemia showed an increase of BMD.3,7,8One of the suggested mechanisms of statins on bone metabolism include inhibition of mevalonate pathway analogous to those of biphosphonates by inhibiting the HMG-CoA reductase thus causing decreased prenylation of key regulatory guanosine 5'-triphosphate-binding proteins that inhibit osteoclast activity and eventually induce osteoclast apoptosis as seen in Figure 1. Statins also stimulate BMP-2 production in osteoblasts that induce bone formation. The stimulation of BMP-2 is thought to be due to inhibition of mevalonate synthesis from HMG-CoA. In several studies, it has been shown that addition of mevalonate blocks the effects of statins on BMP-2 production.1,5
Ezetimibe, as a member of a new class of lipid-lowering drugs, differs from statins by its actions on cholesterol metabolism. It decreases intestinal absorbtion of cholesterol by binding to the polytopic transmembrane protein NPC1L1 that plays a critical role in cholesterol absorption.9,10Due to decreased absorbtion of cholesterol form in intestinal mucosa, ezetimibe up-regulates hepatic cholesterol biosynthesis indirectly. Thus, unlike statins, it has been shown that ezetimibe increases mevalonate synthesis from HMG-CoA.6As the mechanism of action of statins and ezetimibe differs especially on the mevalonate pathway, BMD decreases and β-CTx level increases may be expected with ezetimibe treatment.
In the present study, no significant decrease could be observed in BMD after 1 year of ezetimibe treatment. However, long-term treatment with high doses of ezetimibe may exert more pronounced effect on BMD. Moreover, in the present study, the included subjects were not osteopenic. As osteopenia is a risk factor for osteoporosis, it may be possible that ezetimibe may have more prominent effect on BMD among subjects with osteopenia.11
In conclusion, although there was a negative trend on BMD, no statistically significant BMD and bone metabolism marker changes were seen with the 1 year of ezetimibe treatment. Further studies with large population groups and longer periods of follow-up would be helpful to clarify the effect of ezetimibe on bone mineral metabolism.