Genetic polymorphisms and other risk factors associated with bisphosphonate induced osteonecrosis of the jaw

Pharmacogenomics of osteoporotic fractures

Osteoporosis is a prevalent disease that typically reduces bone strength and predisposes to fractures. It is a multifactorial disorder resulting from the interaction of genetic and acquired factors. Candidate gene studies and, more recently, genome-wide studies have identified a number of polymorphisms significantly associated with bone mass and fractures. Anti-resorptive drugs, which inhibit the differentiation and activity of osteoclasts, are frequently used to treat patients with osteoporosis.Several candidate gene studies have explored the association of genetic factors with drug response, including some common polymorphisms of the gene encoding FDPS (Farnesyl diphosphate synthase), an enzyme that is the main target of aminobisphosphonates. Although scarce data are available, interesting opportunities are open for a better understanding of the pharmacogenetics of osteoporosis and osteoporotic fractures. They include the reanalysis of data already available from epidemiological studies and clinical trials, as well as obtaining pharmacogenetic data in new studies. However, based upon the experience with previous genome-wide association studies, large collaborative efforts would be likely needed to obtain meaningful results.

Hyperbaric oxygen therapy suppresses osteoclast formation and bone resorption

The cellular and molecular mechanism through which hyperbaric oxygen therapy (HBO) improves osteonecrosis (ON) is unclear. The present study therefore examined the effect of HBO, pressure and hyperoxia on RANKL-induced osteoclast formation in RAW 264.7 cells and human peripheral blood monocytes (PBMC). Daily exposure to HBO (2.4 ATA, 97% O2 , 90 min), hyperbaric pressure (2.4 ATA, 8.8% O2 , 90 min) or normobaric hyperoxia (1 ATA, 95% O2 , 90 min) significantly decreased RANKL-induced osteoclast formation and bone resorption in normoxic conditions. HBO had a more pronounced anti-osteoclastic effect than hyperoxia or pressure alone and also directly inhibited osteoclast formation and resorption in hypoxic conditions a hallmark of many osteolytic skeletal disorders. The suppressive action of HBO was at least in part mediated through a reduction in RANK, NFATc1, and Dc-STAMP expression and inhibition of hypoxia-induced HIF-1α mRNA and protein expression. This data provides mechanistic evidence supporting the use of HBO as an adjunctive therapy to prevent osteoclast formation and bone loss associated with low oxygen partial pressure.

Pharmacogenetics of osteoporosis: towards novel theranostics for personalized medicine?

Osteoporosis is a complex multifactorial bone disorder with a strong genetic basis. It is the most common, severe, progressive skeletal illness that has been increasing, particularly in developed countries. Osteoporosis will no doubt constitute a serious clinical burden in healthcare management in the coming decades. The genetics of osteoporosis should be analyzed from both the disease susceptibility and the pharmacogenetic treatment perspectives. The former has been widely studied and discussed, while the latter still requires much more information and research. This article provides a synthesis of the literature on the genetics of osteoporosis and an update on progress made in pharmacogenetics of osteoporosis in recent years, specifically regarding the new molecular targets for antiresorptive drugs. In-depth translation of osteoporosis pharmacogenetics approaches to clinical practice demands a new vision grounded on the concept of "theranostics," that is, the integration of diagnostics for both disease susceptibility testing, as well as for prediction of health intervention outcomes. In essence, theranostics signals a broadening in the scope of inquiry in diagnostics medicine. The upcoming wave of theranostics medicine also suggests more distributed forms of science and knowledge production, both by experts and end-users of scientific products. Both the diagnosis and personalized treatment of osteoporosis could conceivably benefit from the emerging postgenomics field of theranostics.

Osteopontin gene SNPs (rs9138, rs11730582) mediate susceptibility to external root resorption in orthodontic patients

OBJECTIVE

External apical root resorption (EARR) is a frequent iatrogenic effect of orthodontic treatment. Substantial variability in responses to postorthodontic EARR has been observed among patients even when similar treatment protocols were used. This observation suggests that environmental and/or genetic variations between individuals may confer susceptibility or resistance to developing EARR. The objective of this study is to determine whether variants in the osteopontin gene, an essential mediator in the odontoclast fusion and attachment process, are positively/negatively associated with postorthodontic EARR.

MATERIALS AND METHODS

Genetic screening of eighty-seven orthodontic patients was performed for two polymorphisms in the osteopontin gene cluster (rs9138 and rs11730582). Subjects were divided into groups, according to the presence or absence of EARR (>2 mm). Genotype distributions and allelic frequencies were calculated using the chi-square test. Logistic regression analysis was used to assess the extent to which clinical-related parameters interfered with the EARR. Odds ratios (OR) and 95% confidence intervals were also calculated.

RESULTS

Data from this study show that subjects heterozygous and homozygous for the most frequent allele of the osteopontin gene at position 89261521 [OR: 0.035 (P = 0.035*) (allele A)] and 89253600 [OR: 0.20 (P = 0.025*) (allele T)], respectively, are protected against postorthodontic EARR. Nevertheless, a highly significant association was found in the comparative analysis of homozygous subjects [2/2 (CC)] for the osteopontin gene (rs9138), resulting in an increased risk of suffering postorthodontic EARR[OR: 4.10; P = 0.045*; CI: 95%]. Subjects who were homozygous [2/2 (CC)] for the osteopontin gene (rs11730582) were more likely, and to a greater extent, to be affected with EARR [OR: 11.68; P < 0.039*; CI: 95%] compared with other genotypes.

CONCLUSION

Variations in the osteopontin gene (rs9138 and rs11730582) are determinants of a genetic predisposition to suffer EARR secondary to orthodontic treatment.

Genetic polymorphism of the OPG gene associated with breast cancer

Background

The receptor activator of NF-κB (RANK), its ligand (RANKL) and osteoprotegerin (OPG) have been reported to play a role in the pathophysiological bone turnover and in the pathogenesis of breast cancer. Based on this we investigated the role of single nucleotide polymorphisms (SNPs) within RANK, RANKL and OPG and their possible association to breast cancer risk.

Methods

Genomic DNA was obtained from Caucasian participants consisting of 307 female breast cancer patients and 396 gender-matched healthy controls. We studied seven SNPs in the genes of OPG (rs3102735, rs2073618), RANK (rs1805034, rs35211496) and RANKL (rs9533156, rs2277438, rs1054016) using TaqMan genotyping assays. Statistical analyses were performed using the χ²-tests for 2 x 2 and 2 x 3 tables.

Results

The allelic frequencies (OR: 1.508 CI: 1.127-2.018, p=0.006) and the genotype distribution (p=0.019) of the OPG SNP rs3102735 differed significantly between breast cancer patients and healthy controls. The minor allele C and the corresponding homo- and heterozygous genotypes are more common in breast cancer patients (minor allele C: 18.4% vs. 13.0%; genotype CC: 3.3% vs. 1.3%; genotype CT: 30.3% vs. 23.5%). No significantly changed risk was detected in the other investigated SNPs. Additional analysis showed significant differences when comparing patients with invasive vs. non-invasive tumors (OPG rs2073618) as well as in terms of tumor localization (RANK rs35211496) and body mass index (RANKL rs9533156 and rs1054016).

Conclusions

This is the first study reporting a significant association of the SNP rs3102735 (OPG) with the susceptibility to develop breast cancer in the Caucasian population.

Bisphosphonate-related osteonecrosis of the jaws. A severe side effect of bisphosphonate therapy

Bisphosphonates (BP) are potent inhibitors of bone resorption used mainly in the treatment of metastatic bone disease and osteoporosis. By inhibiting bone resorption, they prevent complications as pathological fracture, pain, tumor-induced hypercalcemia. Even though patient's benefit of BP therapy is huge, various side effects may develop. Bisphosphonate-related osteonecrosis of the jaws (BRONJ) is among the most serious ones. Oncologic patients receiving high doses of BP intravenously are at high risk of BRONJ development. BPs impair bone turnover leading to compromised bone healing which may result in the exposure of necrotic bone in the oral cavity frequently following tooth extraction or trauma of the oral mucosa. Frank bone exposure may be complicated by secondary infection leading to osteomyelitis development with various symptoms and radiological findings. In the management of BRONJ, conservative therapy aiming to reduce the symptoms plays the main role. In patients with extensive bone involvement resective surgery may lead to complete recovery, provided that the procedure is correctly indicated. Since the treatment of BRONJ is difficult, prevention is the main goal. Therefore in high risk patients dental preventive measures should be taken prior to bisphosphonate administration. This requires adequate communication between the prescribing physician, the patient and the dentist.

Pharmacogenomics of adverse drug reactions

Considerable progress has been made in identifying genetic risk factors for idiosyncratic adverse drug reactions in the past 30 years. These reactions can affect various tissues and organs, including liver, skin, muscle and heart, in a drug-dependent manner. Using both candidate gene and genome-wide association studies, various genes that make contributions of varying extents to each of these forms of reactions have been identified. Many of the associations identified for reactions affecting the liver and skin involve human leukocyte antigen (HLA) genes and for reactions relating to the drugs abacavir and carbamazepine, HLA genotyping is now in routine use prior to drug prescription. Other HLA associations are not sufficiently specific for translation but are still of interest in relation to underlying mechanisms for the reactions. Progress on non-HLA genes affecting adverse drug reactions has been less, but some important associations, such as those of SLCO1B1 and statin myopathy, KCNE1 and drug-induced QT prolongation and NAT2 and isoniazid-induced liver injury, are considered. Future prospects for identification of additional genetic risk factors for the various adverse drug reactions are discussed.

Association between CYP2C8 (rs1934951) polymorphism and bisphosphonate-related osteonecrosis of the jaws in patients on bisphosphonate therapy: a meta-analysis

AIMS

Bisphosphonate-related osteonecrosis of the jaws (BONJ) is a severe complication in patients on bisphosphonate therapy. The study was conducted to verify the association between CYP2C8 (rs1934951) polymorphism and BONJ predisposition.

METHODS

The relative epidemiologic studies were identified in PubMed and Embase to conduct a meta-analysis using STATA.

RESULTS

In the pooled analysis with multiple cancer types, patients carrying the CYP2C8 rs1934951 AA or AG genotype showed no significantly increased BONJ susceptibility compared with those carrying the wild GG genotype [dominant: odds ratio (OR) = 2.05, 95% confidence interval (CI) = 0.67-6.29, p = 0.209; recessive: OR = 1.88, 95% CI = 0.23-15.6, p = 0.560; AG vs. GG: OR = 2.07, 95% CI = 0.80-5.32, p = 0.133, and AA vs. GG: OR = 1.34, 95% CI = 0.48-3.74, p = 0.578]. A significant association between AA and AG genotypes of CYP2C8 (rs1934951) and BONJ risk was found in the subgroup analysis of multiple myeloma (dominant: OR = 5.77, 95% CI = 1.21-27.63, p = 0.028; AG vs. GG: OR = 5.02, 95% CI = 2.06-12.23, p = 0.001, and AA vs. GG: OR = 16.23, 95% CI = 1.72-78.7, p = 0.015).

CONCLUSION

The results indicated that AA and AG genotypes of CYP2C8 (rs1934951) might be predictors for multiple myeloma patients at high risk to develop BONJ.

Pharmacogenomics of osteoporosis: a pathway approach

Osteoporosis is frequent in postmenopausal women and old men. As with other prevalent disorders, it is the consequence of complex interactions between genetic and acquired factors. Candidate gene and genome-wide association studies have pointed to several genes as determinants of the risk of osteoporosis. Some of them were previously unsuspected and may help to find new therapeutic targets. Several drugs already available are very effective in increasing bone mass and decreasing fracture risk. However, not all patients respond properly and some of them suffer fragility fractures despite therapy. Investigators have tried to identify the genetic features influencing the response to antiosteoporotic therapy. In this article we will review recent data providing insight into new genes involved in osteoporosis and the pharmacogenetic data currently available.

Emerging concepts in the management and treatment of osteonecrosis of the jaw

Since the first description of bone necrosis in patients receiving bisphosphonate therapy in 2004, there have been multiple retrospective, prospective, and case-control studies that have served to characterize the diagnosis, associated risk factors, and treatment of this new complication. Bisphosphonate-related osteonecrosis of the jaw is at present associated with several risk factors that are identified across several disciplines in medicine and dentistry. With this level of broad-based recognition, new clinical and basic science research initiatives have begun and are likely to elucidate the etiopathogenesis of this disease process, significantly improving the level of disease management and prevention.

Lack of association between TNF-α promoter polymorphisms and multiple myeloma: a meta-analysis

Results of available literatures, which concerned the association between TNF-α promoter -238/-308 gene polymorphisms and multiple myeloma (MM), are of great controversy. A review was performed in studies reporting on the association between them. Odds ratios (ORs) with 95% confidence interval (CI) were used to evaluate the association. The pooled ORs indicated that there was no association between TNF-α -238/-308 polymorphisms and MM susceptibility in overall population. Sub-group analysis also confirmed that no evidence supported the relevance of TNF-α promoter -238/-308 gene polymorphisms with MM. Studies with large sample size and multi-ethnics may be needed to further explore the association between them.

Osteoporosis genetics: year 2011 in review

Increased rates of osteoporotic fractures represent a worldwide phenomenon, which result from a progressing aging in the population around the world and creating socioeconomic problems. This review will focus mostly on human genetic studies identifying genomic regions, genes and mutations associated with osteoporosis (bone mineral density (BMD) and bone loss) and related fractures, which were published during 2011. Although multiple genome-wide association studies (GWAS) were performed to date, the genetic cause of osteoporosis and fractures has not yet been found, and only a small fraction of high heritability of bone mass was successfully explained. GWAS is a successful tool to initially define and prioritize specific chromosomal regions showing associations with the desired traits or diseases. Following the initial discovery and replication, targeted sequencing is needed in order to detect those rare variants which GWAS does not reveal by design. Recent GWAS findings for BMD included WNT16 and MEF2C. The role of bone morphogenetic proteins in fracture healing has been explored by several groups, and new single-nucleotide polymorphisms present in genes such as NOGGIN and SMAD6 were found to be associated with a greater risk of fracture non-union. Finding new candidate genes, and mutations associated with BMD and fractures, also provided new biological connections. Thus, candidates for molecular link between bone metabolism and lactation (for example, RAP1A gene), as well as possible pleiotropic effects for bone and muscle (ACTN3 gene) were suggested. The focus of contemporary studies seems to move toward whole-genome sequencing, epigenetic and functional genomics strategies to find causal variants for osteoporosis.