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1 대한내과학회지 : 제 71 권제 3 호 2006 강직성척추염환자에서골다공증의발생과혈청 RANKL/OPG의불균형 건국대학교의과대학내과학교실, 가톨릭대학교의과대학내과학교실 2 김해림 홍지현 2 김동림 김호연 2 이상헌 =Abstract= Development of osteoporosis and the imbalance of RANKL/OPG in ankylosing spondylitis Hae-Rim Kim, M.D., Ji-Hyun Hong, M.D., 2 Dong Lim Kim, M.D., Ho-Youn Kim, M.D., 2 and Sang-Heon Lee, M.D. Department of Internal Medicine, Konkuk University School of Medicine, Seoul, Korea; Department of Internal Medicine, The Catholic University of Korea College of Medicine, Seoul, Korea 2 Background : To determine the bone mineral density (BMD), serum soluble receptor activator of the nuclear factors κb ligand (srankl) and the osteoprotegerin (OPG) levels in patients with ankylosing spondylitis (AS), and to determine their relationship with disease activity indexes. Methods : The disease activity was evaluated by the Bath Ankylosing Spondylitis Disease Activity Score Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), Bath Ankylosing Spondylitis Metrology Index (BASMI) and Bath Ankylosing Spondylitis Patient Global Score (BAS-G). The BMD was measured by dual energy X-ray absorptiometry. Serum levels of srankl and OPG were measured by the sandwich enzyme-linked immunosorbent assay. Results : Osteoporosis and osteopenia of the femoral neck were found in 33% and 41%, respectively. BMD of femoral neck showed a negative correlation with disease activities. The serum levels of srankl were higher in patients with AS than in controls, and the ratio of srankl to OPG was also elevated in AS, but had no correlation with disease activity. The srankl/opg ratio tended to be higher in patients with lower BMD. Conclusions : BMD was reduced in 79% of AS patients and reflected disease status. The srankl/opg ratio was upregulated in patients with AS and it appears to be related to BMD and radiological changes. These results suggest that the imbalance between RANKL and OPG might be involved in the pathogenesis and clinical courses of AS.(Korean J Med 71: , 2006) Key Words : Ankylosing spondylitis, Osteoporosis, Receptor activator of nuclear factors κb ligand, Osteoprotegerin Received : Accepted : Correspondence to : Sang-Heon Lee, M.D., Department of Internal Medicine, Konkuk University School of Medicine, #4-12 Hwayang-dong, Gwangjin-gu, Seoul , Korea shlee@kuh.ac.kr *This work was supported by grant (R ) from Korea Science & Engineering Foundation through the RhRC at Catholic University of Korea and from the Catholic medical center research foundation made in the program year of

2 -Hae-Rim Kim, et al : Osteoporosis and elevated srankl/opg in AS - 서론강직성척추염은축성골격을주로침범하는원인불명의염증성질환으로양쪽엉치엉덩관절염 (bilateral sacroiliitis) 이특징이나말초관절염이나관절외조직을침범하기도한다. 대표적인관절외증상중하나가골다공증인데, 강직성척추염환자에서나이와성별에부합하지않게골다공증과그에의한비외상성골절이흔하게나타나지만그원인과기전은아직명확히밝혀지지않았다 1, 2). 강직성척추염에서골다공증의정도가질환의활성도와관련이있다는연구결과들이있는데, 대퇴경부의골밀도가 Schober index에기초한질병의활성도와관련이있는것으로보이는반면, 요추골밀도의경우질환초기에는감소하지만질환이진행되면서골밀도가증가하는데이는 syndesmophyte의형성과인대의골화로인해골밀도가증가된것처럼보이는것이기때문에요추보다는대퇴골의골밀도측정이보다정확하고유용하다 1, 3). 또한골교체표지자의농도가혈중 C-반응단백질과방사선소견과양의상관관계를보이는것으로보아질환의활성도가높고상태가더심한경우에골다공증의발생이더흔한것으로알려져있다 4). Receptor activator of nuclear factors κb ligand (RANKL) 는파골세포의세포막에존재하는수용체인 receptor activator of nuclear factors κb (RANK) 에결합하여파골세포가뼈흡수과정을수행하게하는대표적인파골세포자극물질이다. 반면 osteoprotegerin (OPG) 은 RANKL에대한가용성유인수용체 (soluble decoy receptor) 로 RANKL 이 RANK에결합하는것을방해하여파골세포의성숙과활성화를차단함으로써뼈흡수를억제하는물질이다. 이러한 RANKL/RANK와 OPG의균형이뼈의재형성 (bone remodelling) 과소실을조절하는데매우중요한요소이기때문에 5) 골다공증, 만성염증성관절염이나악성종양의골전이등뼈의파괴와소실에관련된질환의병인에직접적으로관여한다 6-8). 류마티스관절염과강직성척추염환자에서조직내 RANKL과 OPG의발현을살펴보면, 면역염색결과류마티스관절염과강직성척추염의활동성활막염조직에서 RANKL의발현이정상인에비해상당히증가된것을알수있다 9). OPG의경우활동성류마티스관절염환자의활막조직에서는발현이현저하게감소하였으나 강직성척추염에서는그러한 OPG의감소가보이지않아두질환간의 RANKL/OPG 균형과상호작용에차이가있음을예상할수있다 10). 아직까지의연구에서강직성척추염환자의혈중 OPG의농도에대해서는증가또는감소했다는상반된결과가존재하고있고, RANKL 과의관계, 즉균형유지여부가확인된연구는없는상태로이질환과골다공증의발생기전을이해함에있어보다깊은연구가필요한실정이다 11-13). 이에저자들은강직성척추염환자에서골다공증의빈도와임상양상, 가용성 RANKL (soluble RANKL, srankl) 과 OPG의혈중농도를조사하고, 이들과질환의활성도사이의관계를알아보고자이연구를수행하였다. 대상및방법 1. 대상환자연구참여에동의한강직성척추염환자 60명을대상으로하였고, 강직성척추염의진단은 1984년개정된 modified New York criteria 를따랐다 14). 폐경기여성, 당뇨, 갑상선질환, 부갑상선질환, 뇌하수체질환, 만성간질환또는신질환환자는대상에서제외하였다. 혈청 C-반응단백질과적혈구침강속도를측정하였고, Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) 15), Bath Ankylosing Spondylitis Functional Index (BASFI) 16), Bath Ankylosing Spondylitis Metrology Index (BASMI) 17) 와 Bath Ankylosing Spondylitis Patient Global Score (BAS-G) 18) 를산출하였다. 2. 방사선적검사척추의방사선학적분류는 syndesmophyte의존재유무로환자를구분하기위해 M-SASSS (Modified Stoke Ankylosing Spondylitis Spine Score) 를응용하여경추부터요추의방사선소견을 0= 정상, 1= 골미란 (erosion), 경화 (sclerosis), 또는사각화 (squaring), 2=syndesmophyte, 3=bridging syndesmophyte로분류하여가장높은점수를나타낸부위의점수를따랐다 19). 엉치엉덩관절의방사선학적분류는 New York criteria for sacroiliitis에따라 0= 정상, 1= 의심은되나명확한변화는없는경우, 2= 최소한의엉치엉덩관절염 ( 관절의가장자리의소실, 관절곁경화증, 최소한의미란, 관절강의협착이있는경우 ), 3= 중등도의엉치엉덩관절염 ( 양측의뚜렷한경화증, 가

3 - 대한내과학회지 : 제 71 권제 3 호통권제 553 호 장자리의흐려짐과불명확성, 미란, 관절강소실 ), 4= 심한엉치엉덩관절염 ( 관절의완전한교합과강직 ) 으로분류한뒤양측의평균값을계산하였다 19). 3. 골밀도측정골밀도는이중에너지방사선흡수계측법 (dual energy X-ray absorptiometry, DEXA, Hologic QDR-4500A) 을이용하였으며 1번에서 4번요추의전후면과우측대퇴경부의골밀도를측정하였다. 골밀도는골량 (g/cm 2 ) 과 T 값으로표시하였고, 골밀도측정기의정밀도는요추와대퇴골의변동계수가각각 1% 와 1.2 % 였다. 세계보건기구의기준에따라골다공증은 T 값이 -2.5 표준편차미만인경우로, 골감소증은 T 값이 -1.0에서 -2.5 표준편차이내로감소한경우로정의하였다 20). 4. 혈청 srankl, OPG, TNF-α 와 IL-17의측정대상환자로부터말초혈액을채취한후즉시원심분리하여혈청을얻었고, 측정시까지 -20 냉동고에보관하였다. 혈청내 srankl, OPG, interleukin (IL)-17, tumor necrosis factor (TNF)-α의농도는 sandwich 효소면역측정법 (enzyme- linked immonosorbent assay, ELISA) 으로측정하였다. 간략히설명하면, sandwich ELISA 용 96 well plate (NUNC, Denmark) 에 capture monoclonal IL-17, TNF-α antibodies (R&D, Minneapolis, MN, USA) 4 ug/ml, OPG antibody (R&D) 2 ug/m 와 srankl antibody (PIERCE, USA) 1 ug/ml를각각 50 ul/well 씩넣고 4 에서밤새반응시킨후차단용액 (1% 소혈청알부민이포함된인산염완충식염수 ) 을 200 ul/well 씩넣고실온에서 2시간반응시켰다. 기준 (standard) 으로는재조합인간 IL-17, TNF-α, OPG (R&D) 와 srankl (PIERCE, USA) 을이용하여 10 ng/ml~15.6 pg/ml 농도로사용하였다. 기준물질과환자의혈청을 50 ul/well씩넣고실온에서 2시간반응시킨후세척용액 (0.05% Tween20이포함된인산염완충식염수 ) 으로 4번세척하였다. 이후 biotin 이표지된 anti-human IL-17과 OPG antibodies (R&D, USA) 100 ng/ml, anti-human TNF-α antibody (R&D, USA) 200 ng/ml 그리고 anti-human srankl antibody (PIERCE, USA) 500 ng/ml를각 well 당 50 ul씩넣어실온에서 2시간반응시킨후 4번세척하였다. 마지막으로 IL-17, TNF-α와 OPG는 ExtraAvidin-Alkaline Phosphatase conjugate (SIGMA, St. Louis, MO, USA) 를 1:2000으로, srankl (PIERCE, USA) 은 ExtraAvidin- Horseradish Peroxidase (SIGMA) 를 1:1000으로희석하여 50 ul/well 씩넣고실온에서 2시간반응시키고세척후 IL-17, TNF-α, OPG는 PNPP (Fluka, Phosphate Disodium Salt Hexahydrate) /DEA 용액 (Diethanolamine 97 ml, NaN g, MgCl 26H 2O 0.1 g, 1차증류수 800 ml) 을 1 mg/ml 농도로녹여 50 ul/well 씩넣어 20~30분후 0.2 N NaOH로반응을멈추고 405 nm파장에서흡광도를측정하였다. srankl 은 TMB system (KPL, USA) 의용액 1, 2를같은비율로혼합하고 50 ul/well씩넣은후 10분후 1N H 2SO 4 로반응을멈추고 450 nm 파장에서흡광도를측정하였다. 5. 통계적분석통계처리는 Windows 용 SPSS 11.5 프로그램 (SPSS, Chicago, IL, USA) 을이용하였다. 측정수치는산술평균표준오차로표시하였고, 환자와정상대조군간혈청사이토카인농도는 student t-test를이용하여비교하였고, 각지표들의상관관계는 Spearman's correlation coefficient를이용하여조사하였다. p값이 0.05 이하일때통계적으로유의하다고판정하였다. 결과 1. 환자의임상적특징총 60명의강직성척추염환자를대상으로임상적특징을알아보았다. 성별은남자가 51명, 여자가 9명이었고, 평균연령은 32.1±1.2세, 유병기간은평균 5.5±0.9 년이었다. BASDAI 는평균 3.7±0.3점, BASFI 는평균 1.8±0.3점, BASMI 는평균 1.5±0.3점, BAS-G 는평균 4.2±0.4 점이었다. 적혈구침강속도는평균 17.7±2.2 mm/hour, 혈청 C-반응단백질농도 1.1±0.2 mg/dl이었고, HLA-B27 양성인환자는 50명 (83%) 이었다 ( 표 1). New York criteria for sacroiliitis에따라분류한엉치엉덩관절염의정도는 1등급이 6명, 2등급이 11명, 3등급이 29명, 4등급은 14명이었고, M-SASSS를응용한척추의변화정도는 0점이 22명, 1점이 22명, 2점이 13명, 3점이 3명으로 syndesmophyte가없는군이 44명, 있는군이 16명이었다

4 - 김해림외 4 인 : 강직성척추염에서골다공증과 srankl/opg 의불균형 - Table 1. Clinical characteristics of sixty patients with ankylosing spondylitis Age (mean±sem, year) 32.1±1.2 Sex Male 51 (85%) Female 9 (15%) HLA B27 (+) 50 (83%) Disease duration (year) 5.5±0.9 BASDAI 3.7±0.3 BASFI 1.8±0.3 BASMI 1.5±0.3 BAS-G 4.2±0.4 ESR (mm/hour) 17.7±2.2 CRP (mg/dl) 1.1±0.2 SEM, standard error mean; BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; BASFI, Bath Ankylosing Spondylitis Functional Index; BASMI, Bath Ankylosing Spondylitis Metrologic Index; BAS- G, Bath Ankylosing Spondylitis Patient Global Score; ESR, Erythrocyte sedimentation rate; CRP, C-reactive protein A Figure 1. Bone mineral density of patients with ankylosing spondylitis. (A) Femoral neck and (B) lumbar spine. Osteoporosis mean T score <-2.5 standard deviation (SD) and osteopenia means -2.5<T score<-1.0 SD. B 2. 골다공증결과 강직성척추염환자의골밀도측정결과, 1-4번요추골의평균골량은 0.97±0.03 g/cm 2, T 값은 -0.93±0.25 이었고, 대퇴골경부의평균골량은 0.77±0.03 g/cm 2, T 값은 -1.78±0.24 이었다. 대상환자의요추에서 19% 가골다공증, 37% 가골감소증을대퇴골에서 33% 가골다공증, 41% 가골감소증을보여전체환자의 79.1% 에서골 Figure 2. The difference of bone mineral density according to radiological findings. Striped bars indicate T scores of the femoral neck of patients based on the New York criteria for sacroiliitis (NYS) score 1~2; the black bar indicates that of patients with NYS score 3~4; the open bar indicates the T score of the femoral neck of patients with the highest modified Stoke Ankylosing Spondylitis Spine Score (M-SASSS) 0~1; the gray bar indicates that of the patients with the highest M-SASSS 2~3, *, p<0.05 and NS, not significant. A B Figure 3. (A) Concentrations of serum soluble receptor activator of nuclear factors κb ligand (srankl) and osteoprotegerin (OPG) in ankylosing spondylitis (AS) and healthy controls (HC) were measured by sandwich ELISA. Open bars indicate the serum levels of AS patients and solid bars indicate the serum levels of controls. Serum levels of srankl was significantly higher in AS patients than in the controls; (B) srankl:opg ratio was also higher in AS patients than in the controls. *, p<

5 -The Korean Journal of Medicine : Vol. 71, No. 3, 경부의골량이적을수록강직성척추염의활성도가높았고 (BASDAI 는 r=-0.43, p=0.006, BASFI 는 r=-0.41, p=0.008, BASMI 는 r=-0.52, p=0.001, BAS-G 는 r=-0.44, p=0.004) 적혈구침강속도와혈청 C-반응단백질의농도가높았다 ( 각각 r=-0.45, p=0.003과 r=-0.39, p=0.01). 그러나요추부평균골량과임상소견간의뚜렷한관련성은나타나지않았다. 또한요추와엉치엉덩관절염의방사선적등급이나유병기간과골량간의뚜렷한관련성이보이지않았다. 다만대퇴부 T 값이 New York criteria for sacroiliitis에따라분류한엉치엉덩관절염등급이 0-2인군에서 -0.95±0.34, 3-4인군에서 -1.73± 0.19로엉치엉덩관절의방사선적진행이심한군에서보다낮은 T 값을보였다 (p=0.04)( 그림 2). Figure 4. The relationship between radiological findings to the srankl:opg ratio. The open bar indicates the srankl:opg ratio in patients with the highest modified Stoke Ankylosing Spondylitis Spine Score (M-SASSS) 0~1, the gray bar indicates the srankl:opg ratio in patients with the highest M-SASSS 2~3, the striped bar indicates the srankl:opg ratio in patients with New York criteria for sacroiliitis (NYS) score 1~2, and the black bar indicates the srankl:opg ratio in patients with NYS score 3~4. *, p<0.05 and NS, not significant. 다공증이나골감소증등골밀도감소소견을보였고, 나이나성별에따른골밀도의차이는없었다 ( 그림 1). 골밀도와임상검사와의상관관계를살펴보면, 대퇴골 3. srankl 과 OPG의혈청농도강직성척추염환자의혈청 srankl 농도는 ±419.0 pg/ml 인반면정상대조군은 301.0±110.3 pg/ml 로환자군에서상당히증가된소견을보였다 (p=0.045). 반면혈청 OPG 농도는강직성척추염환자는 928.4±61.7 pg/ml 이고, 정상대조군이 ±266.1 pg/ml 로환자군에서낮은경향을보였으나통계학적유의한차이를보이지않았다. 또한 srankl:opg 비는강직성척추염환자군이 1.49±0.5로 0.34±0.1를보인정상대조군에비해유의하게높았다 (p=0.033)( 그림 3). A Figure 5. Correlation between serum soluble receptor activator of the nuclear factor κb ligand (srankl) and proinflammatory cytokines. (A) Serum srankl levels were positively correlated with serum tumor necrosis factor-α (TNF-α) levels (r=0.49, p<0.001) and (B) with interleukin (IL)-17 levels (r=0.30, p=0.02). B

6 -Hae-Rim Kim, et al : Osteoporosis and elevated srankl/opg in AS - Table 2. Correlation between clinical data and bone mineral density (g/cm 2 ) in patients with ankylosing spondylitis BMD of lumbar spine BMD of femoral neck BASDAI r=-0.22 r=-0.43 * BASFI r=-0.17 r=-0.41 * BASMI r=0.04 r=-0.52 * BAS-G r=-0.25 r=-0.44 * ESR (mm/hour) r=-0.27 r=-0.45 * CRP (mg/dl) r=-0.14 r=-0.39 * BMD, bone mineral density; BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; BASFI, Bath Ankylosing Spondylitis Functional Index; BASMI, Bath Ankylosing Spondylitis Metrology Index; BAS-G, Bath Ankylosing Spondylitis Patient Global Score; ESR, erythrocyte sedimentation rate; CRP, C-reactive protein. * means p< srankl 과 OPG의혈청농도와임상소견과의관계강직성척추염환자의방사선소견과 srankl:opg 비의상관관계를알아본결과, M-SASSS를응용한척추의방사선적변화점수가 0-1점인군에서 2점이상을보인 syndesmophyte가형성된군에비해 srankl: OPG 비가유의하게증가되어있었다 (2.0±0.7 Vs 0.2± 0.03, p=0.01). New York criteria for sacroiliitis에따라분류한엉치엉덩관절염등급에따른 srankl:opg 비의경우등급이 0-2인군에서 1.0±0.4, 3-4인군에서 2.7 ±1.5로방사선적진행이심한군에서더높은경향을보였으나통계적으로유의한차이는보이지않았다 ( 그림 4). 반면혈청 C-반응단백질과적혈구침강속도, BASDAI, BASFI, BASMI, BAS-G 등과 srankl:opg 비간에유의한관련성이존재하지않았다. 또한연령이나성별, 유병기간에따른 srankl 과 OPG의혈청농도의차이도보이지않았다. 5. srankl 의혈청농도와골밀도의관계 srankl 과 OPG의혈청농도, srankl/opg 비와평균골량이나 T 값상호간의유의한관련성은관찰되지않았다. 다만골다공증이나골감소증을보이는환자군에서정상골밀도를보이는군에비해 srankl/opg 비가상승되어있었으나통계적으로유의하지는않았다 (2.09±0.94 Vs 1.21±0.71, p>0.05). 6. srankl 과 TNF-α, IL-17 과의관계 RANKL의강력한유도물질이며염증성관절염에서면역반응의촉진과관절파괴를발생시키는 TNF-α와 IL-17과 srankl 의혈청농도의관련성을알아보았다. 그결과 TNF-α와 IL-17 모두강직성척추염환자에서대조군에비해유의하게높았으며 ( 결과생략 ), srankl 의혈청농도와유의한양의상관관계를나타냈다 ( 각각 r=0.49, p<0.001, r=0.30, p=0.02)( 그림 5). 고찰강직성척추염은엉치엉덩관절에서시작하는축성골격관절의염증과부착부위염 (enthesitis) 을특징으로하는질환으로, 만성염증이있는부위의골소실과더불어새로운뼈의생성을동반하는역설적특성을가지고있는질환이다 21). 국소적인골밀도저하외에전신적골다공증도흔하게관찰되어골다공증이나골감소증의빈도가척추는 41~62%, 대퇴골은 46~86% 까지발생비율이매우높고, 이에따른비외상성골절의빈도가약 10~40% 에이른다 3, 22-24). 골밀도감소의정도와유병기간과의관계에서는질환의초기보다오랜기간진행된경우골밀도가더감소하는경향을보이나, 척추의 syndesmophyte 생성과인대의석회화와골화로인해진행된강직성척추염환자에서골밀도가더높게측정되어결과의해석에오류를범할수있다 25). 골밀도와질병활성도간의관계를보면, 척추의운동성이감소될수록골밀도가저하되고 11), 골교체표지자 ( 소변의 pyridinoline, deoxypyridinoline 과 C-telopeptide) 의농도가혈중 C-반응단백질, 방사선소견과유의한상관관계를보이는것으로보아질환의활성도가높고상태가더심한경우에골다공증이더욱흔하게발생하는것으로예측되고있다 4, 11, 26). 류마티스관절염과강직성척추염등염증성관절질

7 - 대한내과학회지 : 제 71 권제 3 호통권제 553 호 환의흔한합병증의하나인골다공증의정확한기전과병인은아직밝혀지지않았지만, 염증반응으로인한파골세포의활성화, 장기간의관절부동, 스테로이드의사용, 골교체표지자의증가, 성호르몬의이상, 유전적원인등으로인한전신적또는국소적골소실로인한것으로추정되고있다 21, 26). 이중류마티스관절염에서골소실이발생하는기전을살펴보면, 면역세포와염증성사이토카인에의한파골세포의활성화가가장중요한병인이되는데, 활성화된 T 세포와활막세포에서 RANKL 을생산, 분비하여직접적으로파골세포를활성화시키고그전구세포의분화를유도한다 27, 28). RANK는파골세포뿐아니라수지상세포, 성숙한 T 세포, 연골세포등에서도발현되어 RANKL/RANK의부착이수지상세포의생존, CD40 발현, IL-12 등의분비를유도하여면역반응에참여한다 8). 또한활성화된 T 세포는 IL-1β, TNFα와 IL-17 등을분비함으로써간접적인경로로파골세포를활성화시키기도한다 29, 30). OPG는이러한 RANKL 매개성파골세포의활성화와골파괴를억제하는작용을하여뼈의재형성과정에서 RANKL/RANK와반대측면에서균형을이루게된다. 정상적으로는혈청 OPG 농도는연령이증가함에따라그농도가증가한다. 폐경후여성에서에스트로겐의감소에의한 OPG의생산감소로골다공증이발생하는것으로보이나 31), 실제로는골다공증이있는여성에서정상여성에비해그혈청농도가더높으며, 골교체율이높은여성에서더욱높은농도를보이는것으로알려져있다 6, 32, 33). 이러한현상은골밀도가감소함에따라 OPG가보상적으로증가하나그증가가불충분하여결과적으로는골다공증이발생하는것으로설명된다. 그러나임상적으로혈청 OPG 농도가골밀도의정도와관련성이있는지의여부는연구자마다서로다른결과를보이고있다 6, 34, 35). 반면 RANKL의경우연령이나성별, 폐경여부에따른혈청농도의차이는없으나, 그농도가낮을수록비외상성골절의위험도가증가한다고알려져있다 36). 또한한국인남성을대상으로한연구에서혈청 OPG 농도와 RANKL/OPG 비가혈청 osteocalcin 농도와의미있는상관관계를보이고요추골밀도의예측인자가됨을확인하여혈중 OPG-RANKL 체계가남성의골대사에도중요함이시사되고있다 37). 본연구에서강직성척추염환자의골밀도소견을보면대퇴경부의경우환자의대부분, 즉 79% 의환자에서 골다공증과골감소증등골밀도저하소견을보였다. 그러나요추에서는대퇴부에비해골밀도저하빈도가적고방사선적진행소견과부합하지않았는데이것은요추의 syndesmophyte 형성과인대의골화로인해골밀도가실제보다높게측정되었기때문으로보인다. 그러므로강직성척추염환자에서골밀도검사를시행할때요추부보다는대퇴부에서시행하는것이오류가적고, 요추의전후면보다는측면촬영이보다정확하며, 척추의진행된강직을보이는경우엔 single energy quantitative computed tomography (SE-QCT) 를이용한골밀도측정이도움이될것으로생각된다 38, 39). 류마티스관절염환자에서활동성활막염을보이는조직내 RANKL의발현이매우증가되어있고 OPG의발현이감소되어있어이두물질의불균형이이질환의골소실에중요한역할을한다는것은정립된사실이다 9, 10). 하지만골미란, 관절주위골다공증과골파괴등골소실만을보이는류마티스관절염과는달리강직성척추염의경우골소실뿐아니라새로운뼈의생성이나타나기때문에골대사에있어서로다른기전이존재할것이고, RANKL과 OPG의발현과상호작용의차이가두질환사이의차이점이유발하는것으로추정된다. 아직강직성척추염에서두물질의관계와질환과의관련성에대해서는연구결과가미비한데, 면역염색결과활동성활막염조직에서 RANKL 의발현은역시증가되어있으나 OPG 발현의감소는보이지않는다는보고가있으나 10), 환자의혈중 OPG 농도에대해서는연구자에따라그혈중농도가증가또는감소했다는상반된연구결과가있다 11-13). 본연구에서강직성척추염환자의혈중 OPG 농도가정상인과크게다르지않으나약간감소한경향을보였고, 상대적으로 RANKL:OPG의비는훨씬증가된것으로보아각각의농도보다는두물질의불균형이이질환에서골밀도저하의중요한병인임을알수있다. 그리고흥미로운결과중하나는요추의방사선소견이비교적초기일때는 RANKL:OPG의비가증가하나진행되면감소하는경향을보였다는것이다. 이러한현상이발생하는원인으로질환의초기에는염증반응의결과그비율이커져골미란과골소실이발생하는경향을보이다가, 질환이진행하면그비율이역전되면서반대로 syndesmophyte의형성과인대의골화등새로운뼈의생성이유도되었을가능성을예측해볼수있다. 하

8 - 김해림외 4 인 : 강직성척추염에서골다공증과 srankl/opg 의불균형 - 지만강직성척추염에서관절과뼈의변화가모든관절에서동일하게일어나는것이아니라각관절마다다른단계의변화를보일수있으므로혈중농도가아닌관절염세포나조직에서의연구가더필요할것으로보인다. 본연구에서는기존의연구에비해골밀도정도와질환의활동성의관계를보다자세하게분석하였다는것에주목할필요가있다. 아직까지의연구결과는골밀도와임상적인질병활성도와의관계를조사할때단순히척추의운동성 11), C-반응단백질, 방사선소견과의연관성을별개로조사한것에비해본연구에서는강직성척추염의다양한질병평가방법을이용하여비교, 분석하였다는장점이있다. 객관적인평가방법으로척추운동성과강직정도를도량적으로수치화한 BASMI 17) 와혈청 C-반응단백질, 적혈구침강속도를측정하였을뿐아니라, 주관적인평가방법으로환자자신의통증평가와일상생활수행능력의지표인 BASDAI 15) 와 BASFI 16), 그리고 BAS-G 18) 를산출하여골밀도와비교를하였다. 그결과골밀도가객관적인임상지표뿐아니라주관적인지표들과모두유의한상관관계를나타내강직성척추염의활성도가높을수록대퇴골경부의골량이적다는것을알수있었다. 이러한사실은질병의활성도를알아보는데있어골밀도검사가간접적인지표가될수있는중요한검사요소임을시사하는것이라고생각된다. 마지막으로 RANKL의유도물질로알려진 TNF-α 와 IL-17과의관계를알아보았는데, TNF-α는강직성척추염의병인에깊이관여하여최근그차단제를이용한치료가좋은효과를보이고있어이질환에서중요한사이토카인으로인식되고있다 39). 또한, 아직 IL-17과이질환의관계는알려진것이없으나류마티스관절염환자의관절액에서높은농도로존재하면서파골세포가뼈재흡수를수행하게하는강력한유도물질로알려져있다 30). 본연구에서강직성척추염에서두사이토카인의혈청농도가정상인에비해상승되어있었으며, srankl 의농도와도좋은상관관계를보였다. 특히강직성척추염환자에서 IL-17의혈청농도가상승되어있다는것을최초로규명하였으나이농도와질환의활성도및골밀도결과를비교해본결과특별한관련성은찾을수없었다 ( 결과생략 ). 이상으로본연구는 60명의강직성척추염환자를대상으로골밀도변화의양상과혈청 RANKL 과 OPG의농도를측정하고임상소견과의관련성을조사하는목 적으로수행되었다. 그결과대상환자의 79% 에서골밀도가감소하였고, 이러한골량의감소는질환의활성도와관련이있으며, 방사선변화와도어느정도관련성이있었다. 또한 srankl:opg 의비가강직성척추염환자에서증가된것으로보아 RANKL과 OPG의불균형이강직성척추염에서골다공증이유발되는중요한병인중하나임을확인하였다. 그러므로임상진료에서강직성척추염등혈청음성척추관절증환자를관리함에있어나이와성별에무관하게질환자체가골다공증의하나의중요한위험요소이며질환의활성도를간접적으로나타낸다는사실을상기하여이에대한조기진단과적절한치료로이질환의주요이환과사망원인인병적인골절의발생을줄이도록노력해야할것이다. 요약목적 : 강직성척추염에서연령과성별에부합하지않는골다공증이흔한합병증이지만그원인과기전은명확히밝혀지지않았다. 이에저자들은강직성척추염환자에서골밀도저하의양상을알아보고혈청 soluble receptor activator of nuclear factors κb ligand (srankl) 와 OPG (osteoprotegerin) 농도를측정하여이들과골밀도, 질환활성도와의관계를규명하고자연구를하였다. 방법 : 총 60명의강직성척추염환자를대상으로 sandwich 효소면역측정법을이용하여혈청 srankl 과 OPG의농도를측정하였다. Bath Ankylosing Spondylitis Disease Activity Score Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), Bath Ankylosing Spondylitis Metrology Index (BASMI) 와 Bath Ankylosing Spondylitis Patient Global Score (BAS-G) 를이용하여강직성척추염의활성도를파악하였고, 적혈구침강속도와 C-반응단백질의농도와척추와엉치엉덩관절의방사선촬영을시행하였다. 이중에너지방사선흡수계측법을이용하여요추부와대퇴경부의골밀도를측정하였다. 결과 : 강직성척추염환자의골다공증이 33%, 골감소증이 41% 로나타났다. 대퇴경부의골량은질환활성도점수, 적혈구침강속도, C-반응단백질농도와반비례하였다. 강직성척추염환자의혈청 srankl 농도가정상대조군에비해높았고, OPG는두군간차이가없었으나 srankl:opg 비는환자군에서높았다. 골밀도

9 -The Korean Journal of Medicine : Vol. 71, No. 3, 가저하되고방사선적변화가심한군에서그비가높은경향을보였다. 결론 : 79% 의강직성척추염환자에서낮은골밀도를보였고, 이는질환활성도와관련이있었다. srankl: OPG 비는강직성척추염환자군에서높았고, 골밀도와방사선소견과부합하는경향을보였다. srankl 과 OPG의불균형이강직성척추염과그합병증인골다공증의병인에관여하는것으로보여이에대한보다깊은연구가필요할것으로생각된다. 중심단어 : 강직성척추염, 골다공증, 파골세포관련인자 REFERENCES 1) Reid DM, Nicoll JJ, Kennedy NS, Smith MA, Tothill P, Nuki G. Bone mass in ankylosing spondylitis. J Rheumatol 13: , ) Will R, Palmer R, Bhalla AK, Ring F, Calin A. Osteoporosis in early ankylosing spondylitis: a primary pathological event? Lancet 2: , ) Donnelly S, Doyle DV, Denton A, Rolfe I, McCloskey EV, Spector TD. Bone mineral density and vertebral compression fracture rates in ankylosing spondylitis. Ann Rheum Dis 53: , ) el Maghraoui A, Borderie D, Cherruau B, Edouard R, Dougados M, Roux C. Osteoporosis, body composition, and bone turnover in ankylosing spondylitis. J Rheumatol 26: , ) Bolon B, Shalhoub V, Kostenuik PJ, Campagnuolo G, Morony S, Boyle WJ, Zack D, Feige U. Osteoprotegerin, an endogenous antiosteoclast factor for protecting bone in rheumatoid arthritis. Arthritis Rheum 46: , ) Yano K, Tsuda E, Washida N, Kobayashi F, Goto M, Harada A, Ikeda K, Higashio K, Yamada Y. Immunological characterization of circulating osteoprotegerin/osteoclastogenesis inhibitory factor: increased serum concentrations in postmenopausal women with osteoporosis. J Bone Miner Res 14: , ) Hofbauer LC, Neubauer A, Heufelder AE. Receptor activator of nuclear factor-kappa B ligand and osteoprotegerin: potential implications for the pathogenesis and treatment of malignant bone diseases. Cancer 92: , ) Jones DH, Kong YY, Penninger JM. Role of RANKL and RANK in bone loss and arthritis. Ann Rheum Dis 61(Suppl 2):ii32-ii39, ) Crotti TN, Smith MD, Weedon H, Ahern MJ, Findlay DM, Kraan M, Tak PP, Haynes DR. Receptor activator NF-kappaB ligand (RANKL) expression in synovial tissue from patients with rheumatoid arthritis, spondyloarthropathy, osteoarthritis, and from normal patients: semiquantitative and quantitative analysis. Ann Rheum Dis 61: , ) Haynes DR, Barg E, Crotti TN, Holding C, Weedon H, Atkins GJ, Zannetino A, Ahern MJ, Coleman M, Roberts-Thomson PJ, Kraan M, Tak PP, Smith MD. Osteoprotegerin expression in synovial tissue from patients with rheumatoid arthritis, spondyloarthropathies and osteoarthritis and normal controls. Rheumatology 42: , ) Franck H, Meurer T, Hofbauer LC. Evaluation of bone mineral density, hormones, biochemical markers of bone metabolism, and osteoprotegerin serum levels in patients with ankylosing spondylitis. J Rheumatol 31: , ) Grisar J, Bernecker PM, Aringer M, Redlich K, Sedlak M, Wolozcszuk W, Spitzauer S, Grampp S, Kainberger F, Ebner W, Smolen JS, Pietschmann P. Ankylosing spondylitis, psoriatic arthritis, and reactive arthritis show increased bone resorption, but differ with regard to bone formation. J Rheumatol 29: , ) Golmia RP, Sousa BD, Scheinberg MA. Increased osteoprotegerin and decreased pyridinoline levels in patients with ankylosing spondylitis: comment on the article by Gratacos et al. Arthritis Rheum 46: , ) van der Linden S, Valkenburg HA, Cats A. Evaluation of diagnostic criteria for ankylosing spondylitis: a proposal for modification of the New York criteria. Arthritis Rheum 27: , ) Garrett S, Jenkinson T, Kennedy LG, Whitelock H, Gaisford P, Calin A. A new approach to defining disease status in ankylosing spondylitis: the Bath Ankylosing Spondylitis Disease Activity Index. J Rheumatol 21: , ) Calin A, Garrett S, Whitelock H, Kennedy LG, O'Hea J, Mallorie P, Jenkinson T. A new approach to defining functional ability in ankylosing spondylitis: the development of the Bath Ankylosing Spondylitis Functional Index. J Rheumatol 21: , ) Jenkinson TR, Mallorie PA, Whitelock HC, Kennedy LG, Garrett SL, Calin A. Defining spinal mobility in ankylosing spondylitis (AS): the Bath AS Metrology Index. J Rheumatol 21: , ) Jones SD, Steiner A, Garrett SL, Calin A. The Bath Ankylosing Spondylitis Patient Global Score

10 -Hae-Rim Kim, et al : Osteoporosis and elevated srankl/opg in AS - (BAS-G). Br J Rheumatol 35:66-71, ) Wanders AJ, Landewe RB, Spoorenberg A, Dougados M, van der Linden S, Mielants H, van der Tempel H, van der Heijde DM. What is the most appropriate radiologic scoring method for ankylosing spondylitis?: a comparison of the available methods based on the Outcome Measures in Rheumatology Clinical Trials filter. Arthritis Rheum 50: , ) World Health Organization. Assessment of fracture risk and its application to screening for postmenopausal osteoporosis: report of a WHO Study Group. World Health Organ Tech Rep Ser 843:1-129, ) Wendling D. Bone loss in ankylosing spondylitis: can we put the puzzle together? J Rheumatol 32: , ) Karberg K, Zochling J, Sieper J, Felsenberg D, Braun J. Bone loss is detected more frequently in patients with ankylosing spondylitis with syndesmophytes. J Rheumatol 32: , ) Meirelles ES, Borelli A, Camargo OP. Influence of disease activity and chronicity on ankylosing spondylitis bone mass loss. Clin Rheumatol 18: , ) Sivri A, Kilinc S, Gokce-Kutsal Y, Ariyurek M. Bone mineral density in ankylosing spondylitis. Clin Rheumatol 15:51-54, ) Capaci K, Hepguler S, Argin M, Tas I. Bone mineral density in mild and advanced ankylosing spondylitis. Yonsei Med J 44: , ) el Maghraoui A. Osteoporosis and ankylosing spondylitis. Joint Bone Spine 71: , ) Kong YY, Feige U, Sarosi I, Bolon B, Tafuri A, Morony S, Capparelli C, Li J, Elliott R, McCabe S, Wong T, Campagnuolo G, Moran E, Bogoch ER, Van G, Nguyen LT, Ohashi PS, Lacey DL, Fish E, Boyle WJ, Penninger JM. Activated T cells regulate bone loss and joint destruction in adjuvant arthritis through osteoprotegerin ligand. Nature 402: , ) Takayanagi H, Iizuka H, Juji T, Nakagawa T, Yamamoto A, Miyazaki T, Koshihara Y, Oda H, Nakamura K, Tanaka S. Involvement of receptor activator of nuclear factor kappab ligand/osteoclast differentiation factor in osteoclastogenesis from synoviocytes in rheumatoid arthritis. Arthritis Rheum 43: , ) Hofbauer LC, Lacey DL, Dunstan CR, Spelsberg TC, Riggs BL, Khosla S. Interleukin-1beta and tumor necrosis factor-alpha, but not interleukin-6, stimulate osteoprotegerin ligand gene expression in human osteoblastic cells. Bone 25: , ) Kotake S, Udagawa N, Takahashi N, Matsuzaki K, Itoh K, Ishiyama S, Saito S, Inoue K, Kamatani N, Gillespie MT, Martin TJ, Suda T. IL-17 in synovial fluids from patients with rheumatoid arthritis is a potent stimulator of osteoclastogenesis. J Clin Invest 103: , ) Hofbauer LC, Khosla S, Dunstan CR, Lacey DL, Spelsberg TC, Riggs BL. Estrogen stimulates gene expression and protein production of osteoprotegerin in human osteoblastic cells. Endocrinology 140: , ) Grigorie D, Neacsu E, Marinescu M, Popa O. Circulating osteoprotegerin and leptin levels in postmenopausal women with and without osteoporosis. Rom J Intern Med 41: , ) Indridason OS, Franzson L, Sigurdsson G. Serum osteoprotegerin and its relationship with bone mineral density and markers of bone turnover. Osteoporos Int 16: , ) Jorgensen HL, Kusk P, Madsen B, Fenger M, Lauritzen JB. Serum osteoprotegerin (OPG) and the A163G polymorphism in the OPG promoter region are related to peripheral measures of bone mass and fracture odds ratios. J Bone Miner Metab 22: , ) Browner WS, Lui LY, Cummings SR. Associations of serum osteoprotegerin levels with diabetes, stroke, bone density, fractures, and mortality in elderly women. J Clin Endocrinol Metab 86: , ) Schett G, Kiechl S, Redlich K, Oberhollenzer F, Weger S, Egger G, Mayr A, Jocher J, Xu Q, Pietschmann P, Teitelbaum S, Smolen J, Willeit J. Soluble RANKL and risk of nontraumatic fracture. JAMA 291: , ) Oh KW, Rhee EJ, Lee WY, Kim SW, Baek KH, Kang MI, Yun EJ, Park CY, Ihm SH, Choi MG, Yoo HJ, Park SW. Circulating osteoprotegerin and receptor activator of NF-kappaB ligand system are associated with bone metabolism in middle-aged males. Clin Endocrinol 62:92-98, ) Gilgil E, Kacar C, Tuncer T, Butun B. The association of syndesmophytes with vertebral bone mineral density in patients with ankylosing spondylitis. J Rheumatol 32: , ) Lange U, Kluge A, Strunk J, Teichmann J, Bachmann G. Ankylosing spondylitis and bone mineral density: what is the ideal tool for measurement? Rheumatol Int 26: ,