Population pharmacokinetic and pharmacodynamic modeling for assessing risk of bisphosphonate-related osteonecrosis of the jaw

Bisphosphonate-Related Osteonecrosis of the Jaw and Oral Microbiome: Clinical Risk Factors, Pathophysiology and Treatment Options

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) represents a serious health condition, impacting the lives of many patients worldwide. The condition challenges clinical care due to its complex etiology and limited therapeutic options. A thorough understanding of the pathophysiological and patient-related factors that promote disease development is essential. Recently, the oral microbiome has been implicated as a potential driver and modulating factor of BRONJ by several studies. Modern genomic sequencing methods have provided a wealth of data on the microbial composition of BRONJ lesions; however, the role of individual species in the process of disease development remains elusive. A comprehensive PubMed search was conducted to identify relevant studies on the microbiome of BRONJ patients using the terms "microbiome", "osteonecrosis of the jaws", and "bisphosphonates". Studies focusing on symptoms, epidemiology, pathophysiology, risk factors, and treatment options were included. The principal risk factors for BRONJ are tooth extraction, surgical procedures, and the administration of high doses of bisphosphonates. Importantly, the oral microbiome plays a significant role in the progression of the disease. Several studies have identified alterations of microbial composition in BRONJ lesions. However, there is no consensus regarding bacterial species that are associated with BRONJ across studies. The bacterial genera typically found include Actinomyces, Fusobacterium, and Streptococcus. It is postulated that these microbes contribute to the pathogenesis of BRONJ by promoting inflammation and disrupting normal bone remodeling processes. Current therapeutic approaches are disease-stage-specific and the necessity for more effective treatment strategies remains. This review examines the potential causes of and therapeutic approaches to BRONJ, highlighting the link between microbial colonization and BRONJ development. Future research should seek to more thoroughly investigate the interactions between bisphosphonates, the oral microbiome, and the immune system in order to develop targeted therapies.

Mechanistic PK-PD model of alendronate treatment of postmenopausal osteoporosis predicts bone site-specific response

Alendronate is the most widely used drug for postmenopausal osteoporosis (PMO). It inhibits bone resorption, affecting osteoclasts. Pharmacokinetics (PK) and pharmacodynamics (PD) of alendronate have been widely studied, but few mathematical models exist to simulate its effect. In this work, we have developed a PK model for alendronate, valid for short- and long-term treatments, and a mechanistic PK-PD model for the treatment of PMO to predict bone density gain (BDG) at the hip and lumbar spine. According to our results, at least three compartments are required in the PK model to predict the effect of alendronate in both the short and long terms. Clinical data of a 2-year treatment of alendronate, reproduced by our PK-PD model, demonstrate that bone response is site specific (hip: 7% BDG, lumbar spine: 4% BDG). We identified that this BDG is mainly due to an increase in tissue mineralization and a decrease in porosity. The difference in BDG between sites is linked to the different loading and dependence of the released alendronate on the bone-specific surface and porosity. Osteoclast population diminishes quickly within the first month of alendronate treatment. Osteoblast population lags behind but also falls due to coupling of resorption and formation. Two dosing regimens were studied (70 mg weekly and 10 mg daily), and both showed very similar BDG evolution, indicating that alendronate accumulates quickly in bone and saturates. The proposed PK-PD model could provide a valuable tool to analyze the effect of alendronate and to design patient-specific treatments, including drug combinations.

Bisphosphonates in dentistry: Historical perspectives, adverse effects, and novel applications

Studies of the potential role of bisphosphonates in dentistry date back to physical chemical research in the 1960s, and the genesis of the discovery of bisphosphonate pharmacology in part can be linked to some of this work. Since that time, parallel research on the effects of bisphosphonates on bone metabolism continued, while efforts in the dental field included studies of bisphosphonate effects on dental calculus, caries, and alveolar bone loss. While some utility of this drug class in the dental field was identified, leading to their experimental use in various dentrifice formulations and in some dental applications clinically, adverse effects of bisphosphonates in the jaws have also received attention. Most recently, certain bisphosphonates, particularly those with strong bone targeting properties, but limited biochemical effects (low potency bisphosphonates), are being studied as a local remedy for the concerns of adverse effects associated with other more potent members of this drug class. Additionally, low potency bisphosphonate analogs are under study as vectors to target active drugs to the mineral surfaces of the jawbones. These latter efforts have been devised for the prevention and treatment of oral problems, such as infections associated with oral surgery and implants. Advances in the utility and mechanistic understanding of the bisphosphonate class may enable additional oral therapeutic options for the management of multiple aspects of dental health.

On the pharmacological evaluation of bisphosphonates in humans

One of the key parameters for a successful treatment with any drug is the use of an optimal dose regimen. Bisphosphonates (BPs) have been in clinical use for over five decades and during this period clinical pharmacokinetic (PK) and pharmacodynamic (PD) evaluations have been instrumental for the identification of optimal dose regimens in patients. Ideal clinical PK and PD studies help drug developers explain variability in responses and enable the identification of a dose regimen with an optimal effect. PK and PD studies of the unique and rather complex pharmacological properties of BPs also help determine to a significant extent ideal dosing for these drugs. Clinical PK and PD evaluations of BPs preferably use study designs and assays that enable the assessment of both short- (days) and long-term (years) presence and effect of these drugs in patients. BPs are mainly used for metabolic bone diseases because they inhibit osteoclast-mediated bone resorption and the best way to quantify their effects in humans is therefore by measuring biochemical markers of bone resorption in serum and urine. In these very same samples BP concentrations can also be measured. Short-term serum and urine data after both intravenous (IV) and oral administration enable the assessment of oral bioavailability as well as the amount of BP delivered to the skeleton. Longer-term data provide information on the anti-resorptive effect as well as the elimination of the BP from the skeleton. Using PK-PD models to mathematically link the anti-resorptive action of the BPs to the amount of BP at the skeleton provides a mechanism-based explanation of the pattern of bone resorption during treatment. These models have been used successfully during the clinical development of BPs. Newer versions of such models, which include systems pharmacology and disease progression models, are more comprehensive and include additional PD parameters such as BMD and fracture risk. Clinical PK and PD studies of BPs have been useful for the identification of optimal dose regimens for metabolic bone diseases. These analyses will also continue to be important for newer research directions, such as BP use in the delivery of other drugs to the bone to better treat bone metastases and bone infections, as well as the potential benefit of BPs at non-skeletal targets for the prevention and treatments of soft tissue cancers, various fibroses, and other cardiovascular and neurodegenerative diseases, and reduction in mortality and extension of lifespan.

In Vitro Investigation of the Antimicrobial Effect of Three Bisphosphonates Against Different Bacterial Strains

PURPOSE

Since the first descriptions of medication-related osteonecrosis of the jaw (MRONJ) in 2003, the pathogenesis has remained unanswered. Recent histomorphometric studies have found several microorganisms, including Actinomyces, Bacillus, Fusobacterium, Staphylococcus, Streptococcus, Selenomonas, Treponema, and Candida albicans in necrotic bone. Polymerase chain reaction studies have recently confirmed the occurrence of 48 genera. Only a few studies have examined the antimicrobial effect of bisphosphonates (BPs). The influence of bacterial growth on the etiology remains unclear. The aim of the present study was the in vitro investigation of the antimicrobial effect of 3 BPs against different bacterial strains.

MATERIALS AND METHODS

The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of 48 strains from 40 species were determined in microdilution assays against pamidronic, ibandronic, and zoledronic acid.

RESULTS

Growth of gram-positive oral microbiota, which account for most microorganisms in MRONJ, was present for 2 of 22 species; 6 of 26 gram-negative species and 9 of 13 anaerobes were inhibited. The MIC values were compared with the BP bone concentrations from previous reports. Of the 48 strains, 9 had an MIC or MBC less than the bone concentrations.

CONCLUSIONS

The results of the present study have demonstrated that BPs have an inhibitory effect on selected bacterial species and might inhibit the growth of some relevant pathogens in osteonecrosis. However, most of the species tested were unaffected at the concentration levels assumed present in the human jawbone. The clinical relevance of these in vitro data will better be clarified with reliable data on the BP concentrations in the human jawbone. The present study has provided a first approach toward the assessment of the interaction of oral bacteria and BPs.

Design, Synthesis, and Antimicrobial Evaluation of a Novel Bone-Targeting Bisphosphonate-Ciprofloxacin Conjugate for the Treatment of Osteomyelitis Biofilms

Osteomyelitis is a major problem worldwide and is devastating due to the potential for limb-threatening sequelae and mortality. Osteomyelitis pathogens are bone-attached biofilms, making antibiotic delivery challenging. Here we describe a novel osteoadsorptive bisphosphonate-ciprofloxacin conjugate (BV600022), utilizing a "target and release" chemical strategy, which demonstrated a significantly enhanced therapeutic index versus ciprofloxacin for the treatment of osteomyelitis in vivo. In vitro antimicrobial susceptibility testing of the conjugate against common osteomyelitis pathogens revealed an effective bactericidal profile and sustained release of the parent antibiotic over time. Efficacy and safety were demonstrated in an animal model of periprosthetic osteomyelitis, where a single dose of 10 mg/kg (15.6 μmol/kg) conjugate reduced the bacterial load by 99% and demonstrated nearly an order of magnitude greater activity than the parent antibiotic ciprofloxacin (30 mg/kg, 90.6 μmol/kg) given in multiple doses. Conjugates incorporating a bisphosphonate and an antibiotic for bone-targeted delivery to treat osteomyelitis biofilm pathogens constitute a promising approach to providing high bone-antimicrobial potency while minimizing systemic exposure.

Assessing the utility of serum C-telopeptide cross-link of type 1 collagen as a predictor of bisphosphonate-related osteonecrosis of the jaw: A systematic review and meta-analysis

BACKGROUND

The authors of this systematic review and meta-analysis assessed the utility of serum C-telopeptide cross-link of type 1 collagen (sCTX), a biomarker of bone resorption, as a predictor of the development of bisphosphonate-related osteonecrosis of the jaw (BRONJ).

TYPES OF STUDIES REVIEWED

The authors searched for studies involving adult participants, written in English, and published through January 20, 2016, using the following electronic databases: the Cochrane Library, MEDLINE via PubMed, and Web of Science. They also searched Google Scholar and the reference lists of all eligible trials and reviews. They identified 16 articles that met their inclusion criteria (9 controlled studies and 7 case series). They applied the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines for systematic reviews and meta-analyses. They independently extracted data in duplicate, including the characteristics of study participants, risk factors, control groups, and outcomes. They assessed risk of bias, and they resolved any disagreements between review authors through discussion.

RESULTS

A meta-analysis with 9 controlled studies revealed no significant difference in mean sCTX values between patients with BRONJ and control participants (difference in means, -31.417; 95% confidence interval [CI], -91.560 to 28.726; P = .306). A second meta-analysis with 4 studies showed no significant difference in risk of having an sCTX value below 150 picograms per milliliter for patients with BRONJ compared with control participants (risk ratio, 1.892; 95% CI, 0.636-5.626; P = .251).

CONCLUSIONS AND PRACTICAL IMPLICATIONS

A systematic review of the literature with meta-analysis does not support the use of sCTX levels as a predictor of the development of BRONJ. Further prospective large sample studies are needed to understand the role of sCTX as a predictor for BRONJ.

Role of microcracks in the pathogenesis of bisphosphonate-related osteonecrosis of the jaw

OBJECTIVES

The aim of this study was to investigate the potential role of microcrack accumulation in the pathogenesis of bisphosphonate-related osteonecrosis of the jaw (ONJ) through an animal model.

MATERIALS AND METHODS

Twenty-four ovariectomized rats were randomly divided into a bisphosphonate group (n = 19) and control group (n = 5) and weekly injected with zoledronic acid and normal saline, respectively. After 6 weeks, surgical intervention was performed, and the injections were continued for eight additional weeks. Then, the animals were sacrificed, and ONJ lesions were inspected for the presence of microcracks using scanning electron microscopy. Measurements included bone dimension, number of cracks, crack length, and normalized indices; crack density (Cr.Dn) and crack surface density (Cr.S.Dn) were used for group comparison.

RESULTS

Both number of cracks and crack length in the bisphosphonate group were greater than those in the control group (P < 0.05). Of the 19 rats injected with bisphosphonates, 13 rats (68.4 %) were classified into the ONJ group. Cr.Dn and Cr.S.Dn were significantly greater in the ONJ group than in the non-ONJ group, indicating accumulation of unrepaired microcracks (P < 0.05). Seventy-two percent of microcracks in the ONJ group conformed to the defined length that was considered significant according to a previous literature (30-80 μm); whereas 12 % of microcracks in the non-ONJ group were considered significant (P < 0.05).

CONCLUSION

Accumulation of unrepaired microcracks was significantly associated with the development of bisphosphonate-related ONJ. Further research is required to determine the role of microcracks in the pathogenesis of bisphosphonate-related ONJ.

CLINICAL RELEVANCE

Long-term bisphosphonates use may deteriorate the biomechanical and physiological bone integrity, contributing to the pathogenesis of bisphosphonate-related ONJ.

Biomarkers for Bisphosphonate-Related Osteonecrosis of the Jaw

PURPOSE

The aim of this study was to investigate a possible biomarker for bisphosphonate-related osteonecrosis of the jaw (BRONJ) in an animal model.

MATERIALS AND METHODS

Forty-eight Sprague-Dawley rats were randomly divided into the bisphosphonate group (n = 36), who were injected once a week with zoledronic acid, and the control group (n = 12), who were injected once a week with saline. After 6 weeks, surgical intervention was performed, and injections were continued up to 8 weeks. Rats in the bisphosphonate group were then further classified to the ONJ group, and the non-ONJ group, and biomarkers, including CTx, Glu-OC, TRACP 5b, RANKL, and OPG, were assessed at baseline (T0), at surgical intervention (T1), and at sacrifice (T2). Histomorphometric analysis for quantification of osteoclasts was performed.

RESULTS

Repeated measures analysis of variance revealed that TRACP 5b levels and the RANKL/OPG ratio were significantly decreased over time in the ONJ group compared with the non-ONJ group (p < .05). At T2, the area under the curve was 0.807 for TRACP 5b (sensitivity: 88.9%, specificity 66.7% at cutoff) and 0.765 for the RANKL/OPG ratio (sensitivity: 77.8%, specificity 62.9% at cutoff). TRACP 5b showed a lower least significant change (29.6%) with lower intra-assay coefficient of variability (CV; 6.32%) and interassay CV (11.20%) compared with those of the RANKL/OPG ratio (39.27%) and showed a higher signal-to-noise ratio (2.76) than that of the RANKL/OPG ratio (1.62). N.Oc/T.Ar and N.Oc/B.Ar demonstrated significantly decreased number of osteoclasts in ONJ group versus non-ONJ group.

CONCLUSIONS

These results show that serum TRACP 5b and the RANKL/OPG ratio were possible biomarkers for BRONJ. These data may provide useful additional information for future ONJ research. Further studies are needed to validate these results in humans with ONJ.

Oral microbiota and host innate immune response in bisphosphonate-related osteonecrosis of the jaw

Bacterial biofilms have emerged as potential critical triggers in the pathogenesis of bisphosphonate (BP)-related osteonecrosis of the jaw (ONJ) or BRONJ. BRONJ lesions have shown to be heavily colonized by oral bacteria, most of these difficult to cultivate and presents many clinical challenges. The purpose of this study was to characterize the bacterial diversity in BRONJ lesions and to determine host immune response. We examined tissue specimens from three cohorts (n=30); patients with periodontal disease without a history of BP therapy (Control, n=10), patients with periodontal disease having history of BP therapy but without ONJ (BP, n=5) and patients with BRONJ (BRONJ, n=15). Denaturing gradient gel electrophoresis of polymerase chain reaction (PCR)-amplified 16S rRNA gene fragments revealed less bacterial diversity in BRONJ than BP and Control cohorts. Sequence analysis detected six phyla with predominant affiliation to Firmicutes in BRONJ (71.6%), BP (70.3%) and Control (59.1%). Significant differences (P<0.05) in genera were observed, between Control/BP, Control/BRONJ and BP/BRONJ cohorts. Enzyme-linked immunosorbent assay (ELISA) results indicated that the levels of myeloperoxidase were significantly lower, whereas interleukin-6 and tumor necrosis factor-alpha levels were moderately elevated in BRONJ patients as compared to Controls. PCR array showed significant changes in BRONJ patients with downregulation of host genes, such as nucleotide-binding oligomerization domain containing protein 2, and cathepsin G, the key modulators for antibacterial response and upregulation of secretory leukocyte protease inhibitor, proteinase 3 and conserved helix-loop-helix ubiquitous kinase. The results suggest that colonization of unique bacterial communities coupled with deficient innate immune response is likely to impact the pathogenesis of ONJ.