ESPE Abstracts

Background: X-linked hypophosphatemia (XLH) is a rare genetic disorder caused by mutations in PHEX gene and characterized by low phosphate levels and impaired bone mineralization. Burosumab, a monoclonal antibody targeting fibroblast growth factor 23 (FGF23), has emerged as a crucial therapy for XLH management, increasing serum phosphate levels and improving bone health. Recent studies indicate that inflammation may play a crucial role in the XLH complications, often resulting in severe pain. However, it remains uncertain whether Burosumab may also influence inflammatory pathways and offer potential benefits. Central to the body’s inflammatory response are macrophages that can adopt pro-inflammatory (M1) or anti-inflammatory (M2) state. Alterations in Iron metabolism, with its accumulation in macrophages, may tip this balance towards a pro-inflammatory state, highlighting a significant link between iron dysregulation and inflammation. In addition, Transient Receptor Potential Vanilloid 1 (TRPV1), expressed by macrophages, also plays a key role in inflammation and pain transmission. Understanding Burosumab’s effects on macrophages and inflammation is crucial for comprehensive XLH treatment strategies.

Methods: We isolated macrophages from children with XLH, both untreated (n = 3) and under treatment with Burosumab (n = 7), and from healthy donors (n = 4). In these three groups of subjects, western blot was performed to assess the polarization of macrophages by evaluating the protein levels of M1 (CCR7, CD86, iNOS) and M2 (CD206 and p-STAT6) markers. Iron metabolism was assessed by DMT1 and TfR1 expression and iron assay. In addition, TRPV1 expression was examined to understand its role in XLH-related pain.

Results: Our findings revealed that XLH macrophages of untreated patients predominantly exhibit a M1 pro-inflammatory phenotype, and a disrupted iron metabolism characterized by increased expression of TfR1 and DMT1 proteins with elevated intracellular iron concentrations. Notably, TRPV1 protein levels were significantly higher in these patients compared to healthy donors. Interestingly, macrophages isolated from XLH patients under Burosumab treatment showed M2 polarization, a restoring iron metabolism and a reduction of TRPV1 expression.

Conclusion: In untreated XLH patients, the prevalence of pro-inflammatory M1 macrophages, disrupted iron metabolism, and elevated TRPV1 expression contribute to chronic inflammation and pain development. In contrast, treatment with Burosumab promotes the polarization of anti-inflammatory M2 phenotype and normalizes iron metabolism, thereby reducing chronic inflammation. Additionally, Burosumab appears to modulate TRPV1 expression potentially alleviating pain. These findings suggest that Burosumab provides significant clinical benefits, not only in improving bone health but also in managing inflammation and associated pain symptoms.