A novel inhibitory mechanism of nitrogen-containing bisphosphonate on the activity of Cl− extrusion in osteoclasts

The Role of Geranylgeraniol in Managing Bisphosphonate-Related Osteonecrosis of the Jaw

Medication-related osteonecrosis of the jaw (ONJ) is a rare but significant adverse side effect of antiresorptive drugs. Bisphosphonate-related ONJ (BRONJ) is the most prevalent condition due to the extensive use of the drug in cancer and osteoporosis treatment. Nitrogen-containing bisphosphonates suppress osteoclastic resorption by inhibiting farnesyl pyrophosphate synthase in the mevalonate pathway, leading to deficiency of the substrate for GTPase prenylation. The bone remodelling process is uncoupled, subsequently impairing bone healing and causing ONJ. Targeted administration of geranylgeraniol (GGOH) represents a promising approach to mitigate BRONJ because GGOH is a substrate for GTPase prenylation. In the current review, the in vitro effects of GGOH on osteoclasts, osteoblasts and other related cells of the jaw are summarised. We also present and appraise the current in vivo evidence of GGOH in managing BRONJ in animal models. Lastly, several considerations of using GGOH in the clinical management of BRONJ are highlighted. As a conclusion, GGOH is a promising topical agent to manage BRONJ, pending more research on an effective delivery system and validation from a clinical trial.

Pharmacogenomics of osteonecrosis of the jaw

Osteonecrosis of the jaw (ONJ) is a rare but serious drug induced adverse event, mainly associated with the use of antiresorptive medications, such as intravenous (IV) bisphosphonates (BPs) in cancer patients. In this review, we evaluated all the pharmacogenomic association studies for ONJ published up to December 2018. To date, two SNPs (CYP2C8 rs1934951 and RBMS3 rs17024608) were identified to be associated with ONJ by two genome-wide association studies (GWAS). However, all six subsequent candidate gene studies failed to replicate these results. In addition, six discovery candidate gene studies tried to identify the genetic markers in several genes associated with bone remodeling, bone mineral density, or osteoporosis. After evaluating the results of these 6 studies, none of the SNPs was significantly associated with ONJ. Recently, two whole-exome sequencing (WES) analysis (including one from our group) were performed to identify variants associated with ONJ. So far, only our study successfully replicated discovery result indicating SIRT1 SNP rs7896005 to be associated with ONJ. However, this SNP also did not reach genome-wide significance. The major limitations of these studies include lack of replication phases and limited sample sizes. Even though some studies had larger sample sizes, they recruited healthy individuals as controls, not subjects treated with BPs. We conclude that a GWAS with a larger sample size followed by replication phase will be needed to fully investigate the pharmacogenomic markers of ONJ.

ClC-7 Deficiency Impairs Tooth Development and Eruption

CLCN7 gene encodes the voltage gated chloride channel 7 (ClC-7) in humans. The mutations in CLCN7 have been associated with osteopetrosis in connection to the abnormal osteoclasts functions. Previously, we found that some osteopetrosis patients with CLCN7 mutations suffered from impacted teeth and root dysplasia. Here we set up two in vivo models under a normal or an osteoclast-poor environment to investigate how ClC-7 affects tooth development and tooth eruption. Firstly, chitosan-Clcn7-siRNA nanoparticles were injected around the first maxillary molar germ of newborn mice and caused the delay of tooth eruption and deformed tooth with root dysplasia. Secondly, E13.5 molar germs infected with Clcn7 shRNA lentivirus were transplanted under the kidney capsule and presented the abnormal changes in dentin structure, periodontal tissue and cementum. All these teeth changes have been reported in the patients with CLCN7 mutation. In vitro studies of ameloblasts, odontoblasts and dental follicle cells (DFCs) were conducted to explore the involved mechanism. We found that Clcn7 deficiency affect the differentiation of these cells, as well as the interaction between DFCs and osteoclasts through RANKL/OPG pathway. We conclude that ClC-7 may affect tooth development by directly targeting tooth cells, and regulate tooth eruption through DFC mediated osteoclast pathway.

The association of antidepressant medications and diabetic retinopathy among people with diabetes

OBJECTIVE

To determine if the use of antidepressants was associated with lower odds of diabetic retinopathy and if so, to determine if this association was mediated by decreased inflammation as measured by C-reactive protein (CRP).

DESIGN

This was a cross sectional study of 1,041 participants with type 2 diabetes 40-85years old from the 2005-2008 National Health and Nutrition Examination Survey (NHANES). Multiple logistic regression was used to examine the association between the outcome of diabetic retinopathy and the primary exposure of antidepressant medication usage. We also determined whether CRP meets standard criteria as a mediator between antidepressant use and diabetic retinopathy.

RESULTS

Participants using antidepressants were less likely to have diabetic retinopathy (OR 0.50, 95% CI: 0.31-0.82). CRP did not meet one of the criteria for mediation. However, CRP was an effect modifier such that the association of antidepressant use and diabetic retinopathy was only present among participants with CRP ≥0.3mg/dl. Among the antidepressant drug classes, selective serotonin reuptake inhibitor (SSRI) users had significantly lower odds of developing diabetic retinopathy compared to non-users of antidepressants.

CONCLUSIONS

Using representative survey data of US adults with type-2 diabetes, this study found that antidepressant use was associated with lower odds of diabetic retinopathy. Further longitudinal and experimental studies are necessary to confirm this finding and to determine if there is a role for antidepressants in preventing diabetic retinopathy in select patient populations.

Antidepressant-like effect of nitric oxide synthase inhibitors and sildenafil against lipopolysaccharide-induced depressive-like behavior in mice

Inflammation, oxidative and nitrosative stress underlie depression being assessed in rodents by the systemic administration of lipopolysacharide (LPS). There is an increasing body of evidence of an involvement of nitric oxide (NO) pathway in depression, but this issue was not investigated in LPS-induced model. Thus, herein we evaluated the effects of NO-pathway-modulating drugs, named aminoguanidine, l-NAME, sildenafil and l-arginine, on the behavioral (forced swimming test [FST], sucrose preference [SPT] and prepulse inhibition [PPI] of the startle) and neurochemical (glutathione [GSH], lipid peroxidation, IL-1β) alterations in the prefrontal cortex, hippocampus and striatum as well as in BDNF levels in the hippocampus 24h after LPS (0.5mg/kg, i.p.) administration, a time-point related to depressive-like behavior. Twenty-four hours post LPS there was an increase in immobility time in the FST, decrease in sucrose preference and PPI levels accompanied by a decrease in GSH levels and an increase in lipid peroxidation, IL-1β and hippocampal BDNF levels suggestive of a depressive-like state. The pretreatment with the NOS inhibitors, l-NAME and aminoguanidine as well as sildenafil prevented the behavioral and neurochemical alterations induced by LPS, although sildenafil and l-NAME were not able to prevent the increase in hippocampal BDNF levels induced by LPS. The iNOS inhibitor, aminoguanidine, and imipramine prevented all behavioral and neurochemical alterations induced by LPS. l-arginine did not prevent the alterations in immobility time, sucrose preference and GSH induced by LPS. Taken together our results show that the NO-cGMP pathway is important in the modulation of the depressive-like alterations induced by LPS.

Does an alkaline environment prevent the development of bisphosphonate-related osteonecrosis of the jaw? An experimental study in rats

OBJECTIVE

To investigate the preventive effect of locally applied sodium bicarbonate on bisphosphonate-related osteonecrosis of the jaw (BRONJ).

STUDY DESIGN

Thirty-six Sprague-Dawley rats were divided into 4 groups. Animals in group I received 0.1 mg/kg sterile saline 3 times per week for 8 weeks. Groups II, III, and IV received intraperitoneal zoledronate injection in the same manner with the same frequency and duration. The right first molar tooth was extracted in groups III and IV. One mL 8.4% sodium bicarbonate (SB) was applied to the extraction socket at the time of extraction in group IV. The effect of locally applied SB as an alkalizing agent was evaluated by histomorphometric analysis.

RESULTS

BRONJ was observed in none of the animals in the control groups, 67% of the animals in the tooth extraction group, and none of the animals in the local SB application group (P < .01).

CONCLUSIONS

Administration of locally applied SB had positive effects on the prevention of BRONJ in animals, but further studies are required to verify the effectiveness of this form of treatment before its use in humans.