Interferon Gamma, but not Calcitriol Improves the Osteopetrotic Phenotypes in ADO2 Mice

Abstract

ADO2 is a heritable osteosclerotic disorder that usually results from heterozygous missense dominant negative mutations in the chloride channel 7 gene (CLCN7). ADO2 is characterized by a wide range of features and severity, including multiple fractures, impaired vision due to secondary bony overgrowth and/or the lack of the optical canal enlargement with growth, and osteonecrosis/ osteomyelitis. The disease is presently incurable, although anecdotal evidence suggests that calcitriol and interferon gamma-1b (IFN-G) may have some beneficial effects. To identify the role of these drugs for the treatment of ADO2, we utilized a knock-in (G213R mutation in Clcn7) ADO2 mouse model that resembles the human disease. Six-week-old ADO2 heterozygous mice were administered vehicle (PBS) or calcitriol or IFN-G 5 times per week for 8 weeks. We determined bone phenotypes using DXA and mCT, and analyzed serum biochemistry and bone resorption markers. ADO2 mice treated with all doses of IFN-G significantly (p<0.05) attenuated the increase of whole body aBMD and distal femur BV/TV gain in both male and female compared to the vehicle group. In contrast, mice treated with low and medium doses of calcitriol showed a trend of higher aBMD and BV/TV whereas high dose calcitriol significantly (p<0.05) increased bone mass compared to the vehicle group. The calcium and phosphorus levels did not differ between vehicle and IFN-G or calcitriol treated mice; however, we detected significantly (p<0.05) elevated levels of CTX/ TRAP5b ratio in IFN-G treated mice. Our findings indicate that while IFN-G at all doses substantially improved the osteopetrotic phenotypes in ADO2 heterozygous mice, calcitriol treatment at any dose did not improve the phenotype and at high dose further increased bone mass. Thus, use of high dose calcitriol therapy in ADO2 patients merits serious reconsideration. Importantly, our data support the prospect of a clinical trial of IFN-G in ADO2 patients.

Clcn7F318L/+ as a new mouse model of Albers-Schönberg disease

“…It has previously been reported that IFN-G therapy benefitted some patients with autosomal recessive forms of osteopetrosis [13] as well as the Clcn7 G213R/+ mouse model of Albers-Schönberg disease [14]. IFN-G is only FDA approved for the treatment of autosomal recessive malignant osteopetrosis, but it may be used “off-label” in patients with Albers-Schönberg disease.…”

“…IFN-G is only FDA approved for the treatment of autosomal recessive malignant osteopetrosis, but it may be used “off-label” in patients with Albers-Schönberg disease. Therefore, we treated Clcn7 F318L/+ mice from 4 to 12 weeks of age, using an agent and dosing schedule that improved skeletal properties and markers of bone turnover in Clcn7 G213R/+ mice [14]. We confirmed the bioavailability of IFN-G by measuring serum levels 2 hours after subcutaneous injection.…”

“…Since interferon gamma (IFN-G) has been reported to benefit some patients with recessive forms of osteopetrosis [13], this therapy was evaluated in Clcn7 G213R/+ mice. Thrice weekly IFN-G injection in Clcn7 G213R/+ mice on the 129S1 background, from 4 to 12 weeks of age, significantly reduced trabecular bone BV/TV; one reason for this improvement seemed to be improved osteoclast function as indicated by increase in the serum CTX/TRAPc5b ratio [14]. …”

Interferon γ-1b in chronic granulomatous disease and severe malignant osteopetrosis: a guide to its use in the USA

“…In a recent mouse model of autosomal dominant heterozygous osteopetrosis, substantial improvements in osteopetrotic phenotypes were shown with all doses of interferon c-1b; in contrast, calcitriol (at any dose) did not improve osteopetrotic phenotypes, and high doses were associated with additional increases in bone mass [31].…”

“…1 Most commonly reported treatment-emergent adverse events in a randomized, double-blind trial of subcutaneous interferon c-1b three times weekly (n = 63) vs. placebo (n = 65) in patients with chronic granulomatous disease [24]. *p = 0.01, **p = 0.001. h indicates zero dominant osteopetrosis in which substantial improvements in osteopetrotic phenotypes were shown with interferon c1b, but not with calcitriol [31]. Although calcitriol (generally in combination with a low calcium diet) has been shown to indirectly stimulate bone resorption in some patients with osteopetrosis, it provides little to no benefits with regard to improving the immunological defects associated with the disease [8].…”