THU0262 LEVELS OF OSTEOCALCIN AND PROCOLLAGEN TYPE I C-TERMINAL PROPEPTIDE IN PATIENTS WITH SYSTEMIC LUPUS ERYTHEMATOSUS, THEIR ASSOCIATION WITH BONE MINERAL DENSITY AND LEVEL OF INTERLEUKIN-6
Authors: S. Shevchuk, L. Denyshchych
Journal: Annals of the Rheumatic Diseases (2020)

Background: Osteoporosis and fractures associated with it are considered to be one of the most severe complications of systemic lupus erythematosus (SLE). The role of a systemic inflammatory process, vitamin D deficiency, hypogonadism and peculiarities of disease treatment in reduced bone mineral density (BMD) is being discussed. Even though the frequency of osteoporosis in patients with SLE is being studied extensively by scientists from different countries, data on the peculiarities of bone tissue metabolism and the factors that provoke disorders of bone remodeling in such individuals are quite limited. The association between markers of bone tissue metabolism and BMD, and how they change during an inflammatory process is poorly studied. Objectives: The objective of our research is to study the levels of osteocalcin (OC) and procollagen type I C-terminal propeptide (PICP) in patients with systemic lupus erythematosus and to estimate their association with BMD and inflammatory activity based on the levels of interleukin-6 (IL-6). Methods: A total of 58 women with SLE (the average age was 45.11 ± 1.03 years old) and 29 individuals from the control group (the average age was 46.79 ± 2.30 years old) were examined. The diagnosis of SLE was established on the basis of 2019 EULAR/ACR classification criteria for SLE. Levels of IL-6, OC and PICP in serum were determined by enzyme immunoassay. Changes in BMD of the lumbar spine at the level of L1-L4 and the proximal femur were determined by dual-energy X-ray absorptiometry. In postmenopausal women, the diagnosis of osteoporosis was established by the T-score ≤ -2.5 SD. Osteopenia met T-score from -1 to -2.5 SD. In women of reproductive age, the Z-score was used to determine BMD. Values of the Z-score ≤ -2.0 SD were considered as “below expected range for age”. Results: The average OC level in serum of practically healthy individuals equaled 17.64 ± 0,59 ng/ml, and in patients with SLE it was 13.96 ± 0.40 ng/ml, i.e. it was 20.9% lower. The average PICP level in the control group equaled 107.8 ± 4.28 ng/ml, in the main group it was 92.9 ± 5.01 ng/ml, i.e. 16% lower. Overall, the decrease in the bone turnover markers (PICP and/or OC) was noticed in 28 patients with SLE (48.3%) and only in 4 practically healthy individuals (13.8%). In women with decreased bone turnover markers, the T-score of the lumbar spine and hip was 2.3-2.6 times lower (p &lt; 0.05) than in the group with adequate levels of bone turnover markers. Z-score was also lower among patients with decreased levels of OC and PICP. In this group, the average BMD level was 0.81 ± 0.05 g/cm 2 and was 13.8% lower than in the group of patients with no signs of bone tissue metabolism disorder – 0.94 ± 0.02 g/cm 2 . Among the group of women with signs of suppression of biosynthetic processes in bone tissue, there were twice more individuals with decreased BMD. In patients with critically high levels of IL-6 (above 20.0 ng/L), OC level was lower than in patients with high (12.5-20.0 ng/L) and adequate (&lt; 12.5 ng/L) levels of IL-6 (by 17.3 and 19% respectively). The proportion of individuals with low OC levels increased from 31.2% in the last group to 70.6% among patients with critically high levels of IL-6. PICP level was also lower (38.1% and 39.7% respectively) in case of critically high IL-6 levels compared to its high and adequate levels. The proportion of individuals with low PICP levels increased from 6.3% in the group with adequate IL-6 level to 58.8% in the group with critically high IL-6 level. Conclusion: Women with SLE have bone tissue metabolism disorder in the form of decreased bone turnover markers (procollagen type I C-terminal propeptide and osteocalcin) associated with the inflammatory activity. In the group of patients with the signs of suppression of biosynthetic processes in the bone tissue, there were more individuals with decreased BMD. Disclosure of Interests: Sergii Shevchuk Grant/research support from: Celltrion, Inc, Liudmyla Denyshchych: None declared