Approaching virtual osteoid volume estimation and in-depth tissue characterization in patients with tumor-induced osteomalacia

Recombinant ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) decreases vascular calcification and prevents osteomalacia in a rat model of chronic kidney disease

Chronic kidney disease (CKD) impacts a large percentage of the global population. Chronic kidney disease-mineral bone disorder (MBD) is the broad term describing alterations in key circulating factors involved in mineralization, ectopic calcification, and bone abnormalities. Cardiovascular complications, involving vascular calcification are one of the leading causes of death in this patient population. Plasma levels of pyrophosphate, a potent inhibitor of ectopic mineralization, are low in CKD and end-stage kidney disease patients. These data suggest that the correction of pyrophosphate levels could stand out as a crucial therapeutic goal to mitigate vascular calcifications and reduce cardiovascular mortality. The primary enzyme responsible for the generation of plasma pyrophosphate is ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1). We therefore evaluated INZ-701, a recombinant human ENPP1-Fc fusion protein, in an adenine-induced rat model of CKD. Our investigation revealed that INZ-701 administration resulted in significantly lower levels of calcification in the vasculature and soft tissues. Moreover, INZ-701 treatment significantly prevented the osteoid volume increase observed in vehicle-treated rats, addressing another critical clinical manifestation of CKD-MBD. These results underscore the potential of INZ-701 to reduce vascular calcification and bone mineralization abnormalities in CKD.

In-depth clinical characterization of intravenous iron infusion-induced hypophosphatemic osteomalacia and its resolution

Iron deficiency anemia is treated by iron supplementation. Increasing evidence has shown that the carbohydrate components in iron infusions can cause hypophosphatemia and subsequent osteomalacia due to excess intact fibroblast growth factor 23 (iFGF23). We here undertook an in-depth characterization of 13 patients with iron infusion-induced osteomalacia (IIIO). Patients were characterized (monocentric institutional practice) by means of laboratory, bone density, HR-pQCT, and virtual osteoid volume estimation. We additionally report a patient who was treated with burosumab because iron infusions had to be continued despite osteomalacia. All 13 patients received ferric carboxymaltose (FCM) infusions and presented with low phosphate levels. Stopping the FCM infusions and supportive treatment by substitution of phosphate, calcium, native, and/or active Vitamin D was the chosen therapeutic approach. Pain, mobility, and biochemical data, such as serum phosphate levels, BMD, bone microstructure, and virtual osteoid volume, were the main outcome measures. Our results indicate biochemical normalization (eg, phosphate levels pre: 0.50 mmol/L ± 0.23 mmol/L, post: 0.93 mmol/L ± 0.32 mmol/L, p<.001) after stopping the FCM infusion and establishing supportive treatment. Additionally, pain levels on the visual analog scale (VAS) decreased (VASpre 7.31 ± 1.22, VASpost 2.73 ± 1.27, p<.0001) and areal BMD (expressed by T-score) improved significantly (T-scorepre: -1.85 ± 1.84, T-scorepost: -0.91 ± 2.13, p<.05). One patient requiring ongoing FCM infusions experienced significant additional benefits from burosumab treatment. In conclusion, our results highlight the importance of monitoring phosphate in patients treated with FCM infusions. Stopping FCM infusions is effective in addressing the excess of iFGF23 and thereby phosphate wasting. Supportive therapy enables quick recovery of the musculoskeletal system and improves pain levels in these patients.