Diğer

Are Bioactive and Free Sex Steroids Associated with Bone Mineral Density and Bone Turnover Markers in Middle Aged Men? - Original Investigation

  • Melek Sezgin
  • Burak Çimen
  • Handan Çamdeviren Ankarali
  • Ismet As
  • Neslihan Erçetin
  • Özlem Bölgen Çimen
  • Günsah Sahin

Turk J Osteoporos 2009;15(3):-

SummaryAim: To investigate whether bioactive and free sex steroids are associated with bone mineral density (BMD) and bone turnover markers in middle aged men. Material and Methods: One hundred and fifteen out of 165 volunteers aged 35-65 years presenting to our outpatient clinic were included in the study. Serum albumin, total testosterone (T), total estradiol (E2), SHBG, osteocalcin (OC) and C-terminal telopeptide (CTx) levels were measured. Free and bioactive sex steroids, free androgen index (FAI) and free estrogen index (FEI) were calculated. BMD in the lumbar spine and the hip was measured in all participants and effects of sex steroids on BMD and bone turnover markers were investigated. Results: The mean age and the mean body mass index (BMI) in all participants were 52.4±7.8 years and 26.1±3.4 kg/m2 respectively. There was no significant difference in sex hormone levels and bone turnover markers between the individuals with osteoporosis and osteopenia and the individuals with normal BMD (p>0.05). There was a significant relation between age and FAI (r=-0.23, p=0.01), but there was no significant relation between age and bioactive and free sex steroids, FEI and SHBG. However, there was a positive correlation between BMI and bioactive E2 (r=0.35, p:0001), free E2 (r=0.29, p:0.002) and FEI (r=0.39, p=0.0001). After an adjustment for variables effective on BMD was made; no relation was found between BMD measures from the lumbar spine and the hip and serum bioactive sex steroids, free sex steroids, FAI, FEI and SHBG (p>0.05). However, there was a weak positive relation between serum bioactive T, FEI and OC, CTx levels (p=0.05). Conclusion: We think that bioactive and free sex steroids are not independent variables effective on BMD in the spine and the hip in middle aged men and that further studies are needed to elucidate the pathophysiology of idiopathic male osteoporosis. (From the World of Osteoporosis 2009;15:59-65)Key words: Male osteoporosis, bioactive sex steroids, free sex steroids, bone mineral density, bone turnover markersÖzetAmaç: Orta yasli erkeklerde biyoaktif ve serbest seks steroidlerinin kemik mineral yogunlugu (KMY) ve kemik döngüsü belirteçleri ile iliskili olup olmadigini arastirmak.Gereç ve Yöntemler: Çalismaya poliklinigimize basvuran, 35 ile 65 yaslari arasindaki 165 gönüllü arasindan 115 erkek alindi. Serum albumin, total testosteron (T), total östradiol (E2), SHBG, osteokalsin (OC), C-terminal telopeptid (CTx) seviyeleri ölçüldü. Serbest ve biyoaktif seks steroidleri, serbest androjen indeksi (SAI) ve serbest östrojen indeksi (SÖI) hesaplandi. Çalisma grubunun bel ve kalçalarindan KMY’u ölçüldükten sonra seks steroidlerinin, KMY ve kemik döngüsü belirteçleri üzerine etkisi arastirildi.Bulgular: Çalisma grubunun yas ve vucüt kitle indekslerinin ortalamalari sirasiyla 52,4±7,8 yil ve 26,1±3,4 kg/m2’di. Osteoporozlu ve osteopenik bireylerin hem seks hormonu düzeyleri hem de kemik döngüsü belirteçleri KMY normal olan bireylerden farkli degildi (p>0,05). Yas ile, SAI hariç (r=-0,23, p=0,01), biyoaktif ve serbest seks steroidleri, SÖI ve SHBG arasinda iliski yoktu. Ancak VKI ile biyoaktif E2 (r=0,35, p=0001), serbest E2 (r=0,29, p=0,002) ve SÖI (r=0,39, p=0,0001) arasinda pozitif korelasyon vardi. KMY üzerine etkili degiskenler için düzeltme yapildiktan sonra, serum biyoaktif seks steroidleri, serbest seks steroidleri, SAI, SÖI ve SHBG seviyelerinin ne bel ne de kalça KMY ölçümleri ile iliskisi tesbit edilmedi (p>0,05). Ancak serum biyoaktif T, SÖI ile OC ve CTx seviyeleri arasinda sinirda iliski vardi (p=0,05). Sonuç: Biz, orta yasli erkeklerde biyoaktif ve serbest seks steroidlerinin bel ve kalça KMY’na etkili bagimsiz degiskenler olmadiklari ve idiopatik erkek osteoporozunun patofizyolojisini açiklayacak yeni çalismalara ihtiyaç oldugu kanisindayiz. (Osteoporoz Dünyasindan 2009;15:59-65)Anahtar kelimeler: Erkek osteoporozu, biyoaktif seks steroidleri, serbest seks steroidleri, kemik mineral yogunlugu, kemik döngüsü belirteçleri

Introduction

Osteoporosis is a disease characterized by low bone mineral density (BMD) and increased risk of fracture (1). Male osteoporosis has been the subject of growing interest over the past few years on account of its frequency and cost. In the last few years, there have been several studies suggesting that about 30% of all hip fractures occur in men and that the incidence of vertebral fractures in men is approximately one-half of that in women (2-4). Moreover, the mortality rate after hip fracture is even higher in men than in women (5) and is estimated at 10% to 14% (6).A major cause or etiological factor of male osteoporosis has been evidenced in only 30% to 50% of the cases. In the remainder of the patients, the etiology is unclear and is termed “primary” or “idiopathic osteoporosis” (7). In recent years several factors, particularly insulin-like growth factor-1 (IGF-1) and sex hormones have been claimed to play important roles in the pathogenesis of idiopathic bone loss in men. In humans, studies have showed age-related declines in circulating IGF-1 as well as IGF-1 stored in the cortical and trabecular bone, and significant correlations between serum IGF-1 levels and BMD in men with idiopathic osteoporosis (8-13). However, other studies have showed no correlation between IGF-1 and BMD after adjusting for potential confounding variables (14,15). Likewise, in our previous study, we found a significant relation between serum IGF-1 levels and BMD only in the lumbar spine after adjusting for potential confounding variables in a Turkish male population (16). Sex steroids play an important role in the skeletal growth and maintenance both in females and in males. Estrogen (E) deficiency is a major risk factor for postmenopausal osteoporosis in women (17,18). Despite the fact that men do not have the equivalent of menopause and that serum total testosterone (T) and total E levels decline only marginally with age, there are substantial age-related bone losses in men (19,20). The previous studies assessing the relationship of serum total and/or free T and E levels with BMD have generally revealed conflicting results (21-25). Thus, it has been difficult to attribute bone loss in aging men to either T or/and E deficiency. However, measurements of total T or total E levels do not accurately reflect the actual levels of these steroids available to tissues because the fraction bound to sex hormone-binding globulin (SHBG) does not freely pass to target tissues. Besides, free T and E levels constitute only 1-3% of the total sex steroids and the proportions available to target tissues are underestimated (26,27). Bioavailable sex steroids comprise the fractions that are free or bound to albumin in the circulation, and in contrast to the fraction bound to SHBG, it is these fractions that have rapid access to target tissues (26,27). Ferrini et al. were the first to show that bioavailable T and E levels decline significantly principally in response to marked age-related increases in serum SHBG levels in men (28). Thereafter, Khosla et al. found that bioavailable T and E levels were positively correlated with BMD and negatively correlated with bone resorption marker in men (29).To our knowledge, there have not been any studies on the effects of bioavailable sex steroids on BMD in Turkish males. For this reason, we attempted to determine the roles of bioavailable and free sex steroids in BMD at various skeletal sites in middle aged Turkish men. In addition, we investigated the relationship between sex steroids and bone turnover markers.


Results

Of 165 volunteering men, fifty volunteers did not meet the study criteria and were excluded from the study after physical and laboratory examinations. The mean age and BMI of the subjects included in the study were 52.4±7.8 years and 26.1±3.4 kg/m2 respectively. The measurements of sex steroids, bone turnover markers and BMD of the study population are shown in Table 1. Twenty-two subjects (19.2%) were found to have BMD T scores of ≤-2.5 SD (osteoporosis) in at least one skeletal site tested. Fifty-one subjects (44.3%) were found to have BMD T scores of -2.5 SD (osteopenia), while the rest had bone density T scores of ≥-1 SD (normal). The definition of low BMD used in this study was based on the WHO diagnostic criteria (31). There was no significant difference in serum levels of sex hormones and bone turnover markers between the subjects with osteoporosis or osteopenia and the subjects with normal BMD (p>0.05, Table 2, Figure 1 a and b). While age had significantly negative effects on femoral neck and Ward’s triangle BMD (r=-0.26, p=0.007 and r=-0.29, p:0.004 respectively), BMI had significantly positive effects on BMD of the lumbar spine (r=0.32, p=0.002), the femoral neck (r=0.29, p=0.004), the trochanter (r=0.35, p=0.001), and the Ward’s triangle (r=0.21, p=0.03). Age was positively correlated with FSH (r=0.27, p=0.003), LH (r=0.33, p=0.0001) and total E2 (r=0.21, p=0.02), but negatively correlated with FAI (r=-0.23, p=0.01). There was no significant relation between age and SHBG, bioavailable T, free T, total T, bioavailable E2, free E2, FEI (p>0.05, Figure 2 a and b). BMI was negatively correlated with total T (r=-0.30, p=0.001) and SHBG (r=-0.21, p=0.02), but positively correlated with bioavailable E2 (r=0.35, p=0.0001), free E2 (r=0.29, p=0.002), FEI (r=0.39, p=0.0001) and total E2 (r=0.18, p=0.04, Table 3). After age and BMI were adjusted, the relations between sex hormones and BMD were determined with multiple linear regression analysis. There was no significant relation between all BMD measurements and levels of serum bioavailable T, free T, bioavailable E2, free E2, and SHBG (p>0.05, Table 4). Also, there was no significant relation between all BMD measurements and FAI, FEI, total T, and total E2 (p>0.05).When the relation between sex hormones levels and bone turnover markers was investigated, there were weak positive relations between serum OC levels and FEI (r=0.92, p=0.05) and between serum CTx levels and FEI and bioavailable T (r=0.86, p=0.05 and r=0.72, p=0.05 respectively).


Discussion

In the present study, we found that age was positively correlated with FSH, LH and total E2, and negatively correlated with FAI. However, we did not find any correlations between age and bioavailable T, free T, bioavailable E2, free E2, FEI and SHBG levels. First Ferrini et al. and then Szulc et al. reported that free T, bioavailable T, and FAI as well as bioavailable E2 concentrations decreased and SHBG levels increased with age (28,29,30,31,32). The results of this study are not consistent with their results. It may be that this study only included middle aged men, that is, the men aged 35-65 years, but that prior studies included the men over 65.All E2 measurements were positively correlated with BMI, but total T and SHBG were negatively correlated with BMI. We determined that age had a significantly negative effect on hip BMD, whereas BMI had a significantly positive effect on all BMD measures. After age and BMI were adjusted, neither serum bioavailable sex steroids levels nor serum free sex steroids levels were associated with BMD at the hip and the lumbar spine.Previously, Khosla et al. in their study on 346 men aged 23-90 yr showed that serum bioavailable T and total and bioavailable E2 levels were significantly correlated with BMD at various sites. The correlation was considerably stronger for bioavailable E2 as opposed to total E (29). Likewise, in 534 community-dwelling men aged 50-89 yrs, Greendale et al. reported that bioavailable E2 and T were significantly associated with BMD at the forearm, the spine and the hip, whereas total T was not associated with BMD measurements (22). Van den Beld et al. found that bioavailable and free T were more strongly related to hip BMD than total T in elderly men (33). Recently, in a longitudinal study, Khosla et al. showed significant associations between bioavailable sex steroid levels and rates of changes in BMD only at the forearm sites, but not at the total hip or the mid lateral spine in subjects over the age of 60. On the other hand, in middle-aged subjects, only ulnar BMD was significantly correlated with bioavailable E2 (34). Unlike the previous studies, we did not measure BMD at the forearm. This is a limitation of this study, which may explain the lack of association between bioavailable sex hormones and BMD.In addition, we found no significant relation between FEI, FAI, total E2, total T, SHBG and BMD at the lumbar spine and the hip. However, in a prior study on 14 elderly Turkish men, Gürlek et al. showed that total T levels were associated with forearm and hip BMD and that total E2 levels were associated with forearm BMD (35). Thereafter, Keles et al. showed that neither total T nor total E2 was associated with any BMD measurements in 174 healthy Turkish men (36). They found a significant relation between free T and only distal radius BMD even though many early studies had revealed correlations between hip and forearm BMD and free T and FAI (25). Drinka et al. failed to find any correlation between free T and BMD measured at the lumbar spine, the hip and the radius (24). Likewise, Rapado et al. in their study on a group of elderly healthy men did not find any significant relation between androgens or SHBG values and BMD measured at any sites (40). In this study, the osteoporotic and the osteopenic subjects regarding the levels of total, free and bioavailable sex steroids, SHBG and bone turnover markers were not different from the subjects with normal BMD. There have been conflicting results in the literature regarding levels of sex steroids, SHBG and bone turnover markers between osteoporotic patients and normal individuals. Gillberg et al. reported that the men with idiopathic osteoporosis had significantly lower estradiol levels, FEI and FAI and higher SHBG levels than the normal healthy men (41). However, others did not find any difference in the levels of testosterone and estradiol, bone remodelling markers between patients with osteoporosis and controls, but they showed higher SHBG plasma levels in the osteoporotic patients than in the controls. Moreover, this carrier protein was negatively correlated with BMD at the femoral neck and at the lumbar spine (42,43). Likewise, Rucker et al. suggested that SHBG was a significant predictor for BMD at the total hip and the femoral trochanter (44). Our results showed positive correlations between bioavailable T and FEI with bone resorption (serum CTx) and/or bone formation (serum OC) markers. Therefore, we thought that both E2 and T may contribute to the bone turnover in middle aged men. Likewise, Lormeau et al. showed significant positive correlations between E2 and FEI and bone formation (bone alkaline phosphatase) and resorption (serum CTx) markers (44). In addition, several studies revealed that levels of bone turnover markers were significantly higher in men with the lowest concentration of bioavailable E2 and FEI or with bioavailable E2 levels below 40 pmol/L (11pg/ml). They suggested that E2 played a dominant role in the regulation of bone resorption in elderly men although T may have smaller contributions (32,33,33,34,35,36,37,38,39,40,41,42).This study has some limitations. First, 115 adult men referring to our outpatient clinic were included in the present study. This type of recruitment cannot exclude the possibility of bias in the results. Second, the sample size was small and BMD in the forearm was not measured. Third, this study had a cross-sectional design. Despite these limitations, this is the first study in the literature performed to determine whether bioavailable T, bioavailable E2 and SHBG levels were associated with BMD and bone turnover markers in a Turkish male population. Most of the prior studies included elderly subjects as well. Unlike those studies, we included only middle aged men into this study. All above limitations might have caused failure to determine a relation between BMD measures and sex hormones and SHBG levels. In conclusion, we found that bioavailable and free sex steroids did not have any impact on hip and lumbar spine BMD measures in a middle aged Turkish male population. We think that further studies are needed to elucidate the etiology of idiopathic osteoporosis in middle aged males.