Are Changes in Composition in Response to Treatment of a Mouse Model of Osteogenesis Imperfecta Sex-dependent?

Abstract

Background Osteogenesis imperfecta (OI) is a genetic disease characterized by skeletal fragility and deformity. There is extensive debate regarding treatment options in adults with OI. Antiresorptive treatment reduces the number of fractures in growing oim/oim mice, an animal model that reproducibly mimics the moderate-to-severe form of OI in humans. Effects of long-term treatments with antiresorptive agents, considered for treatment of older patients with OI with similar presentation (moderate-tosevere OI) are, to date, unknown. Questions/purposes Fourier transform infrared (FTIR) imaging, which produces a map of the spatial variation in chemical composition in thin sections of bone, was used to address the following questions: (1) do oim/oim mice show a sex dependence in compositional properties at 6.5 months of age; (2) is there a sex-dependent response to treatment with antiresorptive agents used in the treatment of OI in humans; and (3) are any compositional parameters in oim/oim mice corrected to wild-type (WT) values after treatment? Methods FTIR imaging data were collected from femurs from four to five mice per sex per genotype per treatment. Treatments were 24 weeks of saline, alendronate, or RANKFc; and 12 weeks of saline + 12 weeks RANK-Fc and 12 weeks of alendronate + RANK-Fc. FTIR imaging compositional parameters measured in cortical and cancellous bones were mineral-to-matrix ratio, carbonate-to-mineral ratio, crystal size/perfection, acid phosphate substitution, collagen maturity, and their respective distributions (heterogeneities). Because of the small sample size, nonparametric statistics (Mann-Whitney U-and Kruskal-Wallis tests with Bonferroni correction) were used to compare saline-treated male and female mice of different genotypes and treatment effects by sex and genotype, respectively. Statistical significance was defined as p \ 0.05.One or more of the authors (CLR) has received research funding from Amgen (Thousand Oaks, CA, USA) in partial support of this study in an amount less than USD 10,000. One or more of the authors (ALB) owns stock in Amgen (Thousand Oaks, CA) in an amount less than USD 10,000 and in Merck (Kenilworth, NJ, USA) in an amount less than USD 10,000. Results At 6.5 months, saline-treated male cortical oim/ oim bone had increased mineral-to-matrix ratio (p = 0.016), increased acid phosphate substitution (p = 0.032), and decreased carbonate-to-mineral ratio (p = 0.016) relative to WT. Cancellous bone in male oim/oim also had increased mineral-to-matrix ratio (p = 0.016) relative to male WT. Female oim/oim mouse bone composition for all cortical and cancellous bone parameters was comparable to WT (p [ 0.05). Only the female WT mice showed a response of mean compositional properties to treatment, increasing mineral-to-matrix after RANK-Fc treatment in cancellous bone (p = 0.036) compared with saline-treated mice. Male oim/oim increased mineral-to-matrix cortical and cancellous bone heterogeneity in response to all long-term treatments except for saline + RANK-Fc (p...

Splenomegaly, myeloid lineage expansion and increased osteoclastogenesis in osteogenesis imperfecta murine

“…In contrast, surprisingly only females showed significantly elevated levels of TNFα and IL1α in serum. We also observed a tendency toward higher fracture rate in OIM males, a trend that has been reported in previous studies as well as in a human cohort [40, 41]. The sexual dimorphism in the OIM phenotype is therefore more prevalent during early adulthood, but some differences are already evident by 5 weeks of age prior to sexual maturation.…”

“…Some studies in OIM have pooled mice of both genders for evaluation of treatment approaches [42], and many have used animals of one gender only [24, 26, 43–45]. As noted in other recent studies, there are indications of sex-related differences in OI that may affect response to treatment that should be taken into account in future studies, particularly those targeting adolescents and adults [41, 46]. …”

Bone mineral properties in growing Col1a2+/G610C mice, an animal model of osteogenesis imperfecta

“…The amide I band, used as the denominator to assess the matrix contribution, is influenced by the environment in which the vibrating carbonyl-bonds sit, and hence any change in the association of noncollagenous proteins 33 can alter the position and intensity of this band. The collagen cross-link maturity, which is also elevated in other OI models 14, 32, 37 , may suggest disorganization and/or over-modification of abnormal mutant collagen fibrils. This parameter, although controversial 34 is widely used to study bone material properties and has been shown to correlate to enzymatic cross-links determined by HPLC 17 .…”

“…Three separate regions from three different sections of each type of bone were analyzed resulting in 9 images/bone type. Isys4 software (Spectral Dimensions, MD, USA) was used to subtract the embedding media (PMMA), and the infrared images were analyzed to determine 5 FTIR outcome parameter: (1) mineral-to-matrix ratio (area ratio of [917–1180 cm −1 ]/[1588–1712 cm −1 ] peaks), which characterizes tissue mineral content based on the presence of phosphate and is directly related to ash weight 16 ; (2) carbonate-to-phosphate peak area ratio ([852–890 cm −1 ]/[917–1180 cm −1 ]), which, as detailed elsewhere 14 , characterizes the extent of carbonate substitution into the hydroxyapatite lattice; (3) collagen cross-link intensity ratio (1660 cm −1 /1690 cm −1 ), which is related to the ratio of non-reducible to reducible enzymatic collagen cross-links as determined by HPLC 17 ; (4) mineral crystallinity intensity ratio (1030 cm −1 /1020 cm −1 ), which is linked to crystal size and perfection of the hydroxyapatite crystals 16 ; and (5) acid phosphate substitution intensity ratio (1128 cm −1 /1096cm −1 ), which characterizes the extent of acid phosphate substitution into the mineral lattice 18 .…”

Response to Comment on Strontium Ranelate Reduces the Fracture Incidence in a Growing Mouse Model of Osteogenesis Imperfecta

“…The first reason is that there may exist sex-dependent differences in response to pharmaceutical intervention in several mouse models of OI, which is what Raggio and colleagues mentioned. (8) Another reason why we did not include the male mice is that the male mice usually show more activity, sometimes even fighting and biting each other, which may cause fractures resulting from the bone fragility in this severe mouse model of OI. Because our primary goal was to evaluate the effect of strontium ranelate on the fracture reduction in OI, we thought that the male mice might not be suitable for the study.…”