Postmenopausal osteoporosis represents an interaction between estrogen scarcity and augmented immune reactivity. T cells are the IL-17 source, while its receptor is expressed on fibroblasts, osteoblasts, chondrocytes, macrophages, dendritic, as well as on endothelial, and most parenchymal cells [14]. IL-17 is one of contributor of bone deterioration in long-established auto-immune inflammatory disorders associated with bone loss including psoriasis, rheumatoid arthritis, systemic sclerosis, and systemic lupus erythematosus [6, 9, 15].
This study aimed to evaluate the levels of IL-17 and estrogen in relation to bone mineral density and risk of fracture in postmenopausal women with and without osteoporosis.
In the present study, IL-17 levels were significantly higher and estradiol levels were significantly lower in the osteoporotic group compared to the non-osteoporotic group (P value ≤ 0.01).
Our results agree with Molnar et al. [16, 17] who investigated serum IL-17A, rank ligand, OPG levels and (BMDs) in 18 pre- and 72 postmenopausal women and reported that IL-17A were elevated in osteoporotic women than in osteopenic ones. They also conveyed the connection between estrogen deficiency and elevated IL-17 level in post-menopausal females.
Same results were also reported by AL-Tai [18] who evaluated IL-17 in 84 postmenopausal females and concluded that serum IL-17 was significantly high-up in osteoporotic postmenopausal when compared to healthy postmenopausal women. Furthermore, Zhao et al. [19] reported higher serum concentrations of IL-17, with increased IL-17-producing CD4+ T cells, as well as mRNA levels of IL-17 in CD4+ T cells in osteoporotic postmenopausal women than postmenopausal healthy controls. Similarly, Waliullah et al. [20] also conveyed a higher level of IL-17 in post-menopausal females with estrogen deficiency.
This is because E2 preserves bone by boosting osteoclasts apoptosis attributed by increased assembly of TGF-β. In an estrogen shortage, the osteoclasts are enhanced by amplified action of proinflammatory cytokines, as IL-1, IL-6, IL-17, and TNF-α, which are adversely operated by estrogen [21]. IL-17 bone loss effect is triggered through RANK ligand-mediated osteoclastogenesis, to generate MCSF and RANKL in osteoblasts and mesenchymal stem cells to boost the growth of bone-resorbing osteoclasts from monocyte/macrophage precursors. Moreover, Th17 cells (RANKL-expressing T cells) reinforce osteoclastogenesis [22].
De Selm et al. [23] observed that blocking IL-17 signaling prevents estrogen deficiency-mediated osteoporosis by inhibiting osteoclastogenesis in an animal model. Additionally, there was an upsurge in IL-17A producing T helper 17 cells in BM after ovariectomy of mice, and on providing them with neutralizing IL-17 antibodies; bone loss was no longer deteriorating. While another study established that mice missing the core IL-17 receptor (IL-17RA) or its downstream effector protein, Act1, were guarded from the skeletal impacts of ovariectomy [5].
In our study, IL-17was inversely correlated to estrogen level and had a highly significant statistical negative correlation with bone mineral density (DEXA score) as well as a highly significant positive one with FRAX index. These results are in harmony with Molnar et al. [17], Zhang et al. [24], and Waliullah et al. [20], who stated that serum IL-17A levels were higher in postmenopausal patients with osteoporosis, with a significant negative correlation between IL-17A levels and BMD further highlighting the influential role of IL-17 in the pathogenesis of postmenopausal OP.
On performing ROC statistical analysis, IL-17 serum level was able to diagnose osteoporosis at a cutoff level of > 80 pg/mL with 100% sensitivity, 100% specificity, 100% PPV, and 100% NPV. To our limited knowledge, this is the earliest study to investigate the diagnostic performance of IL-17 using ROC curve to discriminate osteoporotic from non-osteoporotic postmenopausal females.
In the present study, DEXA score diagnosed osteoporosis at a cutoff level of ≤ 0.875, with 100% sensitivity, 100% specificity, 100% PPV, and 100% NPV and an AUC of 1.0.
As for the FRAX, it can be used to diagnose osteoporosis at a cutoff level of > 0.4, with 93.33% sensitivity, 80% specificity, 82.4% PPV, and 92.3% NPV and an AUC of 0.92.
Kripa et al. [25] in their study evaluate various screening tools in determining the risk of osteoporosis in 2000 postmenopausal women concluded that the performance of FRAX® was suboptimal as it was devised to foresee fractures not osteoporosis. They found that at a cutoff level of ≥ 0.7%, AUC of 0.736, FRAX® had a sensitivity of 72.7% and an acceptable specificity 60.5%. Thus, the utilization of straightforward evaluating methods for the spotting of osteoporosis helps in the early distinguishing of women in danger of fracture.