Circulating Lipocalin-2 Predicts Changes in Lumbar Spine Bone Mineral Density After Parathyroidectomy in Primary Hyperparathyroidism

Lipocalin-2(LCN2), known as neutrophil gelatinase-associated lipocalin is known to a regulator of bone homeostasis. Upregulation of LCN2 in mice reduces osteoblast differentiation and stimulates the NF-kB pathway, promoting osteoclastogenesis. High serum LCN2 level was associated with elevated risk of fracture-related hospitalization in elderly women. Bone mineral density(BMD) of primary hyperparathyroidism(PHPT) patients tends to recover after parathyroidectomy, but with different extent. Whether circulating LCN2 can predict the extent of BMD recovery after parathyroidectomy in PHPT remains unclear. Clinical data and preoperative serum samples obtained from 35 PHPT patients (women n=30) who underwent parathyroidectomy at Severance hospital, Seoul, Korea between 2016 and 2019 were analyzed. Among 35 patients, 25 patients underwent BMD before surgery and two years after surgery. LCN2 was measured using enzyme-linked immunosorbent assay kit (DLCN20, R&D Systems, USA). Primary outcome was two-year lumbar spine BMD change (%). Mean age of study subjects was 57±13 years. Calcium and parathyroid hormone (PTH) levels restored to normal range after parathyroidectomy in all subjects (calcium [mean 8.7±0.4mg/dL]; PTH [median 33.3], 25.9 to 47.4 pg/mL). Baseline BMD of lumbar spine(LS), femoral neck(FN), and total hip(TH) were 0.776±0.177 g/cm(2), 0.578±0.138 g/cm(2), and 0.695±0.150 g/cm(2), respectively. At 1 year after parathyroidectomy, BMD increased up to 5.5%, 6.1%, and 4.5% at LS, FN, and TH, respectively. At 2 years after parathyroidectomy, BMD increased up to 8.6%, 7.6%, and 7.2% at LS, FN, and TH, respectively. Log-transformed LCN2 at baseline showed positive correlation with LS BMD changes (%) after 2 years (β Coefficient = 3.46, 95% CI = 0.83 to 6.10, p-value = 0.012). In multiple linear regression model, one log-unit increment in LCN2 was associated with 4.7 percent point increase in LSBMD at two years after parathyroidectomy (adjusted β=4.72, 95% CI = 1.62 to 7.82, p-value = 0.005) after adjustment of PTH, creatinine level, and body mass index. This result remained robust for 3 year change in LSBMD (in subgroup, n=14; adjusted β=4.70, 95% CI = 0.9 to 8.5, p-value = 0.021). In conclusion, preoperative high circulating LCN2 level was associated with more LSBMD gain after parathyroidectomy in patients with PHPT.