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

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 µCT, 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.

Evaluation of urinary pyridinium crosslink excretion as a marker of bone resorption in the rat.

The aim of this study was to evaluate the value of the urinary excretion of the pyridinium crosslinks, pyridinoline (Pyr) and deoxypyridinoline (D-Pyr), as markers of bone resorption in the rat. The excretion of the crosslinks was compared with that of urinary [3H]tetracycline ([3H]TC) excretion from chronically [3H]TC-prelabeled animals, a technique established to monitor bone resorption in the rat. Bone resorption was modulated by Ca restriction, infusion of PTH, thyroparathyroidectomy, and administration of different bisphosphonates. Furthermore, the urinary crosslinks were assessed in three different osteopetrotic mutations in the rat. We found a delayed response of Pyr and D-Pyr excretion to acute changes in bone resorption compared with [3H]TC excretion. This delay was 1 day after Ca restriction and longer after other treatments, such as PTH administration or bisphosphonate treatment, with which it was more than 3 weeks. In contrast, chronic states with stimulation or inhibition of bone resorption showed similar changes in excretion of the urinary crosslinks and [3H]TC, except after PTH administration. The excretion of the crosslinks was greatly reduced in osteopetrotic rats (op/op, tl/tl, and ia/ia) and increased to normal levels in tl/tl rats after stimulation of bone resorption by M-CSF administration. These results suggest that, in rats, urinary excretion of the pyridinium crosslinks reflects bone resorption in chronic but not always in acute conditions. The cause of this discrepancy is still unclear.

Congenital erythropoietic porphyria: skeletal manifestations and effect of pamidronate treatment.

Congenital erythropoietic porphyria (CEP) is a rare disorder of heme biosynthesis. Skeletal abnormalities have been described in patients with this disease. We report a 25-year-old woman with osteodystrophy from CEP. On examination, mild hepatosplenomegaly, multiple hyperpigmented scars, hypertrichosis, erythrodontia and red coloration of urine were found. Biochemical studies showed increased serum levels of alkaline phosphatase, fasting and total 24-h urinary calcium excretion. Serum 250H vitamin-D concentration was low due to avoidance of sun exposure. Skeletal radiographs disclosed marked vertical and horizontal trabecular pattern and biconcavity of most of the dorsal and lumbar vertebral bodies. Several round sclerotic lesions (1-3 cm in diameter) were seen in the skull, pelvis and one lumbar vertebrae. The sclerotic lesions were augmented in size and number compared to X-rays obtained 8 years before. Bone mineral density (evaluated by DEXA) was markedly reduced at the spine and moderately diminished at the proximal femur and total skeleton. Treatment for 11 months with pamidronate (and the addition of hydrochlorotiazide for the last 6 months) reduced to normal values the serum levels of alkaline phosphatase and fasting urinary calcium. The 24-h urinary excretion of calcium and hydroxyproline were also decreased. The BMD increased in all the skeletal areas with presumably hyperactive bone marrow: spine, head, ribs and pelvis (and total skeleton), but did not change at the extremities and diminished at the femoral neck. Patients with CEP may present osteodystrophy characterized by sclerotic lesions and osteopenia, most likely due to accelerated bone turnover in areas of active bone marrow.(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant human interferon gamma therapy for osteopetrosis.

A defect in leukocytic superoxide formation has been demonstrated in patients with congenital osteopetrosis. This leukocyte defect appears to be related to defective bone resorption. Because recombinant human interferon gamma therapy enhances superoxide production in patients with chronic granulomatous disease, we sought to determine whether a similar strategy could reverse the osteopetrotic condition. Interferon gamma, 1.5 micrograms/kg three times a week, was administered by subcutaneous injection for 6 months to eight patients with osteopetrosis. Urinary hydroxyproline and urinary calcium excretion increased markedly during therapy in parallel with a significant decrease in trabecular bone volume. Bone marrow scans demonstrated increased bone marrow production. The hemoglobin concentration, platelet count, and leukocyte production of superoxide increased significantly. No serious infections were encountered during the therapy. These data suggest that interferon gamma administration enhances bone resorption and leukocyte function in patients with osteopetrosis.

Triiodothyronine stimulates urinary excretion of calcium and hydroxyproline in autosomal dominant osteopetrosis.

Six patients with autosomal dominant osteopetrosis were treated orally with 100 mcg. triiodothyronine (T3) daily for seven days. The effect of T3 on bone remodelling was monitored. T3 treatment increased serum T3 from day 1 to 7 (p less than 0.02) with a corresponding fall in serum T4 (p less than 0.01) and serum TSH (p less than 0.02). The levels of thyroid hormones returned to initial levels within the observation period. The renal excretion of calcium and hydroxyproline increased significantly (p less than 0.05) on day 7 and 14 respectively, while there was no significant increase in phosphate excretion. No significant changes were observed in serum calcium, phosphate, or osteocalcin during the study. The observed changes suggest that bone resorption in autosomal dominant osteopetrosis is stimulated by exogenous administration of T3.

Abnormal urinary excretion of glycosaminoglycans in Albers-Schönberg disease.

Abnormal urinary excretion of acid mucopolysaccharides in two children affected with Albers-Schönberg disease is described. The urine specimens were first checked for their acid glycosaminoglycan (AGAG) content by a screening test. The AGAGs were then evaluated by uronic acid determination using the carbazole method, and the ratio between high molecular mass and low molecular mass AGAGs was determined. Qualitative characterization, before and after enzymatic digestion with chondroitinases AC (ChAC) and ABC (ChABC), of the total AGAGs contained in the specimen and of each AGAG separated with Dowex 1X2 was also performed by electrophoresis. The pattern of the urinary mucopolysaccharides in the two patients showed an abnormal quantity of heparan sulphate (HS) and a smaller quantity of dermatan sulphate (DS). Such abnormal urinary AGAGs excretion should confirm the assumption of some authors that malignant infantile osteopetrosis may be caused by a deficiency in the lysosomal enzymatic activity, or by some anomaly in the cell membrane function.