RESUMO
Because of the relative lack of understanding of the neurobiological mechanisms that drive toxic effects of cadmium in bone, the purpose of this study was to characterize a preclinical model of chronic cadmium exposure. Adult male C57BL/6 J mice were exposed to cadmium 25 mg/L (as CdCl2) in drinking water for 16 weeks. During this time, pain-related behaviors including hindpaw mechanical sensitivity and vertical rears were evaluated every four weeks. We assessed changes in bone microarchitecture at the femoral neck and L5 vertebra by microcomputed tomography and quantified the density of nerve fibers expressing PGP 9.5 (a pan-neuronal marker) and CGRP (a marker of sensory nerve fibers subfamily) at the femoral neck and glabrous skin of the hindpaw using immunohistochemistry. Cadmium exposure produced mechanical hypersensitivity in both hindpaws along with decreased rearing activity (surrogate for musculoskeletal-related pain) without affecting the horizontal activity (a measure of locomotor behavior) in comparison to the control group. Intraperitoneal acute treatment with morphine and gabapentin reversed pain-related behaviors in cadmium-exposed mice. Furthermore, exposure to cadmium resulted in significant trabecular bone deterioration at the femoral neck and L5 vertebra. We also observed a significant reduction in the density of both CGRP+ and PGP 9.5+ nerve fibers in the femoral neck, but not in the hindpaw glabrous skin, suggesting tissue-dependent neurotoxicity. This model may help in developing a mechanism-based understanding of the factors that generate and maintain musculoskeletal pain and bone loss caused by chronic cadmium exposure and in translating these findings into new therapies for treating cadmium-induced bone toxicity.
Assuntos
Cádmio , Colo do Fêmur , Animais , Cádmio/toxicidade , Colo do Fêmur/fisiologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Dor , Microtomografia por Raio-XRESUMO
Recent in vitro studies have shown a role for the peptidyl-arginine deiminases (PADs) in bone resorption. However, it is unknown whether these enzymes are involved in bone loss in vivo. Thus, we evaluated the antiresorptive effect of a pan-PAD inhibitor in two murine models of osteoporosis: (a) primary osteoporosis induced by ovariectomy (OVX); and (b) secondary osteoporosis associated to Type-1 diabetes induced by streptozotocin (STZ, 50 mg/kg, i.p., five daily administrations). Five weeks after OVX and 15 weeks after injections of STZ, mice received daily administrations of Cl-amidine (3 or 10 mg/kg, i.p.) or vehicle for 30 consecutive days. At the end of the treatment, femur and vertebra were harvested for microCT analysis. Blood samples were collected for determination of antibodies against cyclic citrullinated peptides (anti-CCP) by enzyme-linked immunosorbent assay. Serum levels of anti-CCP antibodies from diabetic mice were not significantly different compared to control mice. However, a significant loss of both trabecular bone at the femoral neck and cortical bone at the femoral diaphysis was found in diabetic mice, and Cl-amidine did not reverse the diabetes-induced bone loss. Mice with OVX had significantly lower serum levels of anti-CCP compared to mice with sham surgery. OVX resulted in significant loss of both trabecular bone at the L5 vertebra and distal femoral metaphysis. Cl-amidine did not block the OVX-induced bone loss. Our results suggest that chronic treatment with Cl-amidine at the doses and period of time administered is not long enough to inhibit bone loss in two different murine models of osteoporosis.
Assuntos
Diabetes Mellitus Experimental/complicações , Ornitina/análogos & derivados , Osteoporose/tratamento farmacológico , Ovariectomia/efeitos adversos , Administração Oral , Animais , Modelos Animais de Doenças , Feminino , Fêmur/diagnóstico por imagem , Fêmur/efeitos dos fármacos , Camundongos , Ornitina/administração & dosagem , Ornitina/farmacologia , Osteoporose/diagnóstico por imagem , Osteoporose/etiologia , Coluna Vertebral/diagnóstico por imagem , Coluna Vertebral/efeitos dos fármacos , Estreptozocina , Resultado do Tratamento , Microtomografia por Raio-XRESUMO
Type-1 diabetes mellitus (T1DM) results in loss of innervation in some tissues including epidermis and retina; however, the effect on bone innervation is unknown. Likewise, T1DM results in pathological bone loss and increased risk of fracture. Thus, we quantified the density of calcitonin gene-related peptide (CGRP+) sensory and tyrosine hydroxylase (TH+) sympathetic nerve fibers and determined the association between the innervation density and microarchitecture of trabecular bone at the mouse femoral neck. Ten weeks-old female mice received 5 daily administrations of streptozocin (i.p. 50mg/kg) or citrate (control group). Twenty weeks later, femurs were analyzed by microCT and processed for immunohistochemistry. Confocal microscopy analysis revealed that mice with T1DM had a significant loss of both CGRP+ and TH+ nerve fibers in the bone marrow at the femoral neck. Likewise, microCT analysis revealed a significant decrease in the trabecular bone mineral density (tBMD), bone volume/total volume ratio (BV/TB), trabecular thickness (Tb.Th), trabecular number (Tb.N) and trabecular separation (Tb.Sp) in mice with T1DM as compared to control mice. Analysis of correlation revealed a positive and significant association between density of CGRP+ or TH+ nerve fibers with tBMD, BV/TV, Tb.Th and Tb.Sp, but not with trabecular number (there was a positive association only for CGRP+) and degree of anisotropy (DA). This study suggests an interaction between sensory and sympathetic nervous system and T1DM-induced bone loss. Identification of the factors involved in the loss of CGRP+ sensory and TH+ sympathetic fibers and how they regulate bone loss may result in new avenues to treat T1DM-related osteoporosis.