osteoprotegerin and Phenylketonurias

Phenylketonuria (PKU) is a rare inborn error of metabolism often complicated by a progressive bone impairment of uncertain etiology, as documented by both ionizing and non- ionizing techniques.. Peripheral blood mononuclear cell (PBMC) cultures were performed to study osteoclastogenesis, in the presence or absence of recombinant human monocyte-colony stimulating factor (M-CSF) and receptor activator of NFκB ligand (RANKL). Flow cytometry was utilized to analyze osteoclast precursors (OCPs) and T cell phenotype. Tumour necrosis factor α (TNF-α), RANKL and osteoprotegerin (OPG) were quantified in cell culture supernatants by ELISA. The effects of RANKFc and anti-TNF-α antibodies were also investigated to determine their ability to inhibit osteoclastogenesis. In addition, bone conditions and phenylalanine levels in PKU patients were clinically evaluated.. Several in vitro studies in PKU patients' cells identified a potential mechanism of bone formation inhibition commonly associated with this disorder. First, PKU patients disclosed an increased osteoclastogenesis compared to healthy controls, both in unstimulated and M-CSF/RANKL stimulated PBMC cultures. OCPs and the measured RANKL/OPG ratio were higher in PKU patients compared to healthy controls. The addition of specific antagonist RANKFc caused osteoclastogenesis inhibition, whereas anti-TNF-α failed to have this effect. Among PBMCs isolated from PKU patients, activated T cells, expressing CD69, CD25 and RANKL were identified. Confirmatory in vivo studies support this proposed model. These in vivo studies included the analysis of osteoclastogenesis in PKU patients, which demonstrated an inverse relation to bone condition assessed by phalangeal Quantitative Ultrasound (QUS). This was also directly related to non-compliance to therapeutic diet reflected by hyperphenylalaninemia.. Our results indicate that PKU spontaneous osteoclastogenesis depends on the circulating OCP increase and the activation of T cells. Osteoclastogenesis correlates with clinical parameters, suggesting its value as a diagnostic tool for an early assessment of an increased bone resorption in PKU patients.

Topics: Adolescent; Bone and Bones; Bone Density; Bone Resorption; Cell Differentiation; Cells, Cultured; Child; Enzyme-Linked Immunosorbent Assay; Female; Flow Cytometry; Humans; Leukocytes, Mononuclear; Lymphocyte Activation; Macrophage Colony-Stimulating Factor; Male; Osteoclasts; Osteoprotegerin; Phenylalanine; Phenylketonurias; RANK Ligand; T-Lymphocytes; Tumor Necrosis Factor-alpha; Young Adult

Non-invasive biochemical markers which show global skeletal activity have lately been developed and validated for the assessment of bone formation and bone resorption processes. Among them, osteocalcin (OC) and collagen type I cross-linked C-telopeptide (CTX) are considered to be clinically useful. Recently the novel cytokine osteoprotegerin (OPG), belonging to the tumour necrosis factor receptor family, has been established as an endogenous inhibitor of osteoclastogenesis and resorption processes. Some authors have observed decreased bone mineral density and osteopenia in patients suffering from phenylketonuria (PKU). The aim of the study was to assess osteoprotegerin and some bone formation and resorption markers concentrations in phenylketonuric patients.. We measured OPG, OC and CTX in 112 patients with PKU treated at the Department of Pediatrics of the Institute of Mother and Child in Warsaw. Healthy subjects in the same age range sent to our laboratory for routine analytical control were the reference group. Serum bone metabolism markers were determined by an immunoenzymatic assays.. Mean serum level of OPG was significantly lower in PKU patients than in controls: in prepubertal and postpubertal subjects by about 15% and in adolescents by 35% respectively. Serum OC and CTX in prepubertal children with PKU compared to the control group was lower by 20-25%. In adolescents both markers were slightly lower (by about 10%) and in postpubertal subjects OC was lower by 25% and CTX by 15% compared to the age-matched controls.. Our results indicate that in phenylketonuric patients an imbalance between bone formation and degradation processes occurred and they are at risk for osteopenia and osteoporosis in later life.

Topics: Adolescent; Adult; Biomarkers; Bone Diseases, Metabolic; Bone Resorption; Child; Child, Preschool; Collagen Type I; Female; Humans; Male; Osteocalcin; Osteogenesis; Osteoporosis; Osteoprotegerin; Peptides; Phenylketonurias