OC19 - Bone turnover markers in arginine vasopressin deficiency: a cross-sectional comparison with primary polydipsia and healthy controls

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Abstract Background/Introduction Arginine vasopressin (AVP) and oxytocin (OXT) are neurohypophyseal hormones known to exert opposing effects on bone metabolism. Based on animal models, AVP has been shown to reduce bone formation and promote resorption via AVP V1a receptor signaling, whereas OXT promotes osteoblast differentiation and activity. Despite the well-established cellular actions of these hormones on osteoblasts and osteoclasts in preclinical studies, data from human studies are lacking, particularly regarding bone metabolism in populations with a deficiency of AVP and possibly OXT, such as individuals with AVP deficiency (AVP-D, previously referred to as central diabetes insipidus). This study aimed to evaluate bone turnover markers in patients with AVP-D compared to individuals with primary polydipsia (PP) and healthy controls (HC). Methods This was a secondary analysis of a prospective trial that included adult HC and patients diagnosed with either PP or AVP-D, all of whom underwent a novel copeptin stimulation test with urea. Laboratory assessments were performed at baseline and included markers for bone resorption (C-terminal telopeptide of type I collagen, CTX) and bone formation (N-terminal propeptide of type I procollagen, P1NP), as well as 25OH vitamin D, serum calcium, and phosphate. Patients on chronic steroid therapy (except budesonide and corticosteroid replacement therapy), those with a history of osteoporotic fractures, or those receiving long-term treatment with antiresorptive agents were excluded from the analysis. Results A total of 47 subjects (HC=22, AVP-D=12, PP=13) were included. Serum calcium, phosphate, and 25OH vitamin D levels did not differ significantly among the three groups. Median (IQR) CTX levels were significantly lower in AVP-D patients (0.376 [0.295-0.580] ng/ml) compared to HC (0.592 [0.427-0.729] ng/ml, p=0.036), with no significant difference observed between AVP-D and PP (0.514 [0.411-0.618] ng/ml, p=0.225). In contrast, P1NP levels were comparable across all groups (AVP-D: 65.4 [49.2-84.7] ng/ml; PP: 65.5 [55.7-72.7] ng/ml; HC: 76.8 [53.8-87.2] ng/ml). Conclusion Patients with AVP-D exhibit reduced CTX levels compared to HC but not compared to patients with PP, and no differences were observed in P1NP levels across the three groups. Overall, these findings do not provide clear evidence of altered bone metabolism in AVP-D.

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