Gene polymorphisms involved in the regulation of bone quality

An update on therapies for the treatment of diabetes-induced osteoporosis

Introduction: Currently, 424 million people aged between 20 and 79 years worldwide are diabetic. More than 25% of adults aged over 65 years in North America have Type 2 diabetes mellitus (DM). Diabetes-induced osteoporosis (DM-OS) is caused by chronic hyperglycemia, advanced glycated end products and oxidative stress. The increase in the prevalence of DM-OS has prompted researchers to develop new biological therapies for the management of DM-OS. Areas covered: This review covered the current and novel biological agents used in the management of DM-OS. Data were retrieved from PubMed, Scopus, American Diabetes Association and International Osteoporosis Foundation websites, and ClinicalTrials.gov. The keywords for the search included: DM, osteoporosis, and management. Expert opinion: Several biological molecules have been examined in order to find efficient drugs for the treatment of DM-OS. These biological agents include anti-osteoporosis drugs: net anabolics (parathyroid hormone/analogs, androgens, calcilytics, anti-sclerostin antibody), net anti-resorptive osteoporosis drugs (calcitonin, estrogen, selective estrogen receptor modulators, bisphosphonates, RANKL antibody) and anti-diabetic drugs (alpha glucosidase inhibitors, sulfonylureas, biguanides, meglitinides, thiazolidinediones, GLP-1 receptor agonists, dipeptidylpeptidase-4 inhibitors, sodium glucose co-transporter-2 inhibitors, insulin). Biological medications that effectively decrease hyperglycemia and, at the same time, maintain bone health would be an ideal drug/drug combination for the treatment of DM-OS.

Characteristics of particulate and non-particulate corticosteroids. Indications for their use in chronic pain treatments

Corticosteroids been used frequently in pain treatments since the middle of last century (1952). Due to a review of the complications as a result of their application in epidural injections, the United States of America Food and Drug Administration (FDA) issued an «alert controversy» requesting that a warning label should be added to injectable corticosteroids, where risks must be described (loss of sight, brain damage, paralysis and death) when administering by this route. It must be mentioned that there are different types of corticosteroids with diverse characteristics, which as a result, may produce different side-effects. Due to the aforementioned developments, the controversies that have arisen, and the lack of well-conducted studies on the use of steroids in epidural injections, we must begin by reviewing their indications in different pain conditions.

Bone morphogenetic protein-2 activity is regulated by secreted phosphoprotein-24 kd, an extracellular pseudoreceptor, the gene for which maps to a region of the human genome important for bone quality

The material properties of bone are the sum of the complex and interrelated anabolic and catabolic processes that modulate formation and turnover. The 2q33-37 region of the human genome contains quantitative trait loci important in determining the broadband ultrasound attenuation (an index of trabecular microarchitecture, bone elasticity, and susceptibility to fracture) of the calcaneus, but no genes of significance to bone metabolism have been identified in this domain. Secreted phosphoprotein-24 kd (SPP24 or SPP2) is a novel and relatively poorly characterized growth hormone-regulated gene that maps to 2q37. The purpose of this review is to summarize the status of research related to spp24 and how it regulates bone morphogenetic protein (BMP) bioactivity in bone. SPP24 codes for an extracellular matrix protein that contains a high-affinity BMP-2-binding transforming growth factor-beta receptor II homology 1 loop similar to those identified in fetuin and the receptor itself. SPP24 is transcribed primarily in the liver and bone. High levels of spp24 (a hydroxyapatite-binding protein) are found in bone, and small amounts are found in fetuin-mineral complexes. Full-length secretory spp24 inhibits ectopic bone formation, and overexpression of spp24 reduces murine bone mass and density. Spp24 is extremely labile to proteolysis, a process that regulates its bioactivity in vivo. For example, an 18.5-kd degradation product of spp24, designated spp18.5, is pro-osteogenic. A synthetic cyclized Cys(1)-to-Cys(19) disulfide-bonded peptide (BMP binding peptide) corresponding to the transforming growth factor-beta receptor II homology 1 domain of spp24 and spp18.5 binds BMP-2 and increases the rate and magnitude of BMP-2-mediated ectopic bone formation. Thus, the mechanism of action of spp18.5 and spp24 may be to regulate the local bioavailability of BMP cytokines. SPP24 is regulated by growth hormone and 3 major families of transcription factors (nuclear factor of activated T cells, CCAAT/enhancer-binding protein, Cut/Cux/CCAAT displacement protein) that regulate mesenchymal cell proliferation, embryonic patterning, and terminal differentiation. The gene contains at least 2 single nucleotide polymorphisms. Given its mechanism of action and sequence variability, SPP24 may be an interesting candidate for future studies of the genetic regulation of bone mass, particularly during periods of BMP-mediated endochondral bone growth, development, and fracture healing.

Type I collagen alpha1 Sp1 polymorphism and the risk of cruciate ligament ruptures or shoulder dislocations

BACKGROUND

Cruciate ligament ruptures and shoulder dislocations are often caused by trauma, but predisposing intrinsic factors might also influence the risk. These injuries are more common in those with a previously injured sibling, an observation that might indicate a genetic predisposition. It is well known that polymorphisms in the collagen I gene are associated not only with osteoporosis and osteoporotic fracture risk, but also with osteoarthritis.

HYPOTHESIS

Because collagen I is abundant in ligaments and tendons, the authors hypothesized that collagen I alpha1 Sp1 polymorphism also was related to the occurrence of cruciate ligament ruptures and shoulder dislocations.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

A total of 358 patients and 325 randomly selected population-based female controls were included in the study. Of the cases, 233 had a cruciate ligament rupture and 126 had had a shoulder dislocation. Age-adjusted odds ratios (ORs) with 95% confidence intervals (CIs) estimated by unconditional logistic regression were used as measures of association.

RESULTS

Compared with the homozygous SS category, the heterozygous participants displayed a similar risk (OR, 1.06; 95% CI, 0.76-1.49), whereas the ss genotype was underrepresented in the injured population compared with the controls (OR, 0.15; 95% CI, 0.03-0.68). This latter estimate was similar for both cruciate ligament ruptures and shoulder dislocations, and was furthermore not modified by general joint laxity.

CONCLUSION

The authors found a substantially decreased risk of these injuries associated with collagen type I alpha1 Sp1 polymorphism. The study might encourage other investigators to consider further research in the area of genes and soft tissue injuries.

Vitamin D and its implications for musculoskeletal health in women: an update

Vitamin D is a hormone that controls phosphorus, calcium, and bone metabolism and neuromuscular function. Vitamin D synthesis is a process in which the skin, liver, and kidney are sequentially involved. The vitamin D pool is completed by the amount taken with food and supplements. Vitamin D deficiency causes osteopenia, precipitates and exacerbates osteoporosis, causes a painful disease, osteomalacia, and increases muscle weakness, which worsens the risk of falls and fractures. A high prevalence of vitamin D insufficiency exists in the apparently healthy population, osteoporotic patients, and patients with prior fractures. Factors contributing to low vitamin D levels include low sunlight exposure, decreased skin synthesis and intestinal absorption, and inadequate diet. The simplest way to correct hypovitaminosis is adequate nutrition and supplements. However, few patients with osteoporosis and/or fractures, receive adequate supplements. Vitamin D insufficiency may alter the regulatory mechanisms of parathyroid hormone and may induce a secondary hyperparathyroidism that increases the risk of osteoporosis and fractures, although the necessary degree of this is not established. Monitoring of serum 25-hydroxyvitamin D levels is the only way to assess vitamin D status. The ideal healthy blood levels of 25-hydroxyvitamin D are controversial, although a range from 30 to 60ng/mL is widely accepted. The role of vitamin D supplementation is to provide humans with the nutrient in an amount closer to the biological norm for our species. This amount of vitamin D results in optimal function of many aspects of health, including balance and muscle strength, thus reducing the risk of fracture beyond what is possible via the quality and quantity of bone itself.

An application of bioinformatics and text mining to the discovery of novel genes related to bone biology

The treatment and management of complex genetic diseases such as osteoporosis can greatly benefit from the integration of relevant research across many different disciplines. We created a text mining tool that analyzes the PubMed literature database and integrates the available genomic information to provide a detailed mapping of the genes and their interrelationships within a particular network such as osteoporosis. The results obtained from our text mining program show that existing genomic data within the PubMed database can effectively be used to predict potentially novel target genes for osteoporosis research that have not previously been reported in the literature. To filter the most significant findings, we developed a ranking system to rate our predicted novel genes. Some of our predicted genes ranked higher than those currently studied, suggesting that they may be of particular interest from a therapeutic standpoint. A preliminary analysis of the current biomedical literature in our research area using our tool suggests that S100A12, as well as a group of SMAD genes previously unstudied in relation to osteoporosis, may be highly relevant to the mechanism of action of bisphosphonates, that the function of osteocytes may be influenced by a family of important interleukins and interleukin-related molecules, and that the FYN oncogene may play an important role in regulating the apoptosis of bone cells in the context of degenerative bone diseases. An evaluation of our tool's predictive ability with an analysis of PubMed literature published before the year 2000 in the area of osteoporosis research shows that many of its top-rated novel target genes from that analysis were later studied and shown to be relevant to osteoporosis in the period between 2000 and 2006. We believe that our tool will be beneficial to researchers in the field of orthopaedics seeking to identify novel target genes in their research area, and it will allow them to delve deeper into the complex interplay between genes, biological systems and diseases.

Association between SNP and haplotypes in PPARGC1 and adiponectin genes and bone mineral density in Chinese nuclear families

AIM

To assess the contribution of single nucleotide polymorphisms (SNP) and haplotypes in the peroxisome proliferators-activated receptor-gamma co-activator-1 (PPARGC1) and adiponectin genes to normal bone mineral density (BMD) variation in healthy Chinese women and men.

METHODS

We performed population-based (ANOVA) and family-based (quantitative trait locus transmission disequilibrium test) association studies of PPARGC1 and adiponectin genes. SNP in the 2 genes were genotyped. BMD was measured using dual-energy X-ray absorptiometry in the lumbar spine and hip in 401 nuclear families with a total of 1260 subjects, including 458 premenopausal women, 20-40 years of age; 401 postmenopausal women (mothers), 43-74 years of age; and 401 men (fathers), 49-76 years of age.

RESULTS

Significant within-family association was found between the Thr394Thr polymorphism in the PPGAGC1 gene and peak BMD in the femoral neck (P=0.026). Subsequent permutations were in agreement with this significant within-family association result (P=0.016), but Thr394Thr SNP only accounted for 0.7% of the variation in femoral neck peak BMD. However, no significant within-family association was detected between each SNP in the adiponectin gene and peak BMD. Although no significant association was found between BMD and SNP in the PPARGC1 and adiponectin genes in both men and postmenopausal women, haplotype 2 (T-T) in the adiponectin gene was associated with lumbar spine BMD in postmenopausal women (P=0.019).

CONCLUSION

Our findings suggest that Thr394Thr SNP in the PPARGC1 gene was associated with peak BMD in the femoral neck in Chinese women. Confirmation of our results is needed in other populations and with more functional markers within and flanking the PPARGC1 or adiponectin genes region.

Vitamin D: the secosteroid hormone and human reproduction

Vitamin D is a secosteroid with an endocrine mechanism of action which is sequentially synthesized in humans in the skin, liver and kidneys. The active hormone, 1alpha,25-dihydrocholecalciferol [1,25(OH)2D3], is often considered only in terms of its role in controlling calcium and phosphorus homeostasis. However, cumulative evidence points to the presence of vitamin D receptors in many tissues. The present article summarizes key points regarding the participation of vitamin D in pregnancy and breastfeeding. During pregnancy, sufficient vitamin D concentrations are needed not only to address the growing demand for calcium on the part of the fetus, but also to participate in fetal growth, development of the nervous system, lung maturation and fetal immune system function. Hypovitaminosis D has been related to the development of diabetes, pre-eclampsia and fetal neurological disorders. During pregnancy and lactation, calcium from the maternal skeleton is mobilized, with a rise in bone turnover and a reduction in bone mass. It is advisable for pregnant and nursing women to maintain adequate levels of vitamin D, through small doses of solar exposure to facilitate natural formation of the hormone or by ingesting appropriate vitamin supplements. Further studies are needed to clarify the many gaps in knowledge and elucidate the role of vitamin D in the context of reproduction. Confirmation of experimental observations relating to the risks of hypovitaminosis D would have important public health implications.