Isoprenoid geranylgeraniol: the influence on cell characteristics of endothelial progenitor cells after bisphosphonate therapy in vitro

Significance of bisphosphonates on angiogenesis in vivo and their effect under geranyl-geraniol addition - could it alter the treatment of bisphosphonate-associated necrosis of the jaw?

PURPOSE

The aim of this study was to contribute to the understanding of the inhibitory effects of bisphosphonates on tissues, with a special focus on angiogenesis. Referring to bisphosphonate-associated osteonecrosis of the jaw (BP-ONJ), it should be shown that the local addition of the isoprenoid geranyl-geraniol (GGOH) prevents vascularization processes.

METHODS

A mouse model with n = 24 animals which received an injection of a collagen matrix was used. In 4 subgroups (n = 6), we examined the effect of zoledronate on the sprouting of capillary-like structures into the matrix, with and without the presence of geranyl-geraniol, as well as testing against control groups with PBS injections or collagen matrix containing PBS instead of GGOH. This was followed by a histological evaluation of the capillary-like structures.

RESULTS

Zoledronate inhibits the sprouting of blood vessels into a collagen matrix in vivo; in the presence of GGOH this effect is significantly weakened by a factor of 3.9 (p = 0.00068).

CONCLUSION

This work commits to the investigation of the pathophysiology of BP-ONJ and shows a possible causal therapeutic path via the topical application of GGOH.

Mechanism, prevention, and treatment for medication-related osteonecrosis of the jaws

The morbidity rate of medication-related osteonecrosis of the jaws (MRONJ) increased rapidly in recent years. Thusfar, the mechanism of MRONJ has no consensus. The possible mechanisms may include bone remodeling inhibition theory, angiogenesis inhibition theory, oral microorganism infection theory, immunosuppression theory, cytotoxicity-targeted oral epithelial cells, microcrack formation of maxillary or mandibular bone, and single nucleotide polymorphism. However, the efficacy of prevention and treatment based on a single mechanism is not ideal. Routine oral examination before MRONJ-related drug treatment, treatment of related dental diseases, and regular oral follow-up during drug treatment are of great significance for the prevention of MRONJ. During the treatment of MRONJ, the stage of MRONJ must be determined accurately, treatment must be standardized in accordance with the guidelines, and personalized adjustments must be made considering the specific conditions of patients. This review aimed to combine the latest research and guidelines for MRONJ and the experiences on the treatment of MRONJ in the Maxillofacial Surgery Department of West China Hospital of Stomatology, Sichuan University, and discuss the strategies to improve the clinical process.

Key Enzymes for the Mevalonate Pathway in the Cardiovascular System

ABSTRACT

Isoprenylation is an important post-transcriptional modification of small GTPases required for their activation and function. Isoprenoids, including farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate, are indispensable for isoprenylation by serving as donors of a prenyl moiety to small G proteins. In the human body, isoprenoids are mainly generated by the mevalonate pathway (also known as the cholesterol-synthesis pathway). The hydroxymethylglutaryl coenzyme A reductase catalyzes the first rate-limiting steps of the mevalonate pathway, and its inhibitor (statins) are widely used as lipid-lowering agents. In addition, the FPP synthase is also of critical importance for the regulation of the isoprenoids production, for which the inhibitor is mainly used in the treatment of osteoporosis. Synthetic FPP can be further used to generate geranylgeranyl pyrophosphate and cholesterol. Recent studies suggest a role for isoprenoids in the genesis and development of cardiovascular disorders, such as pathological cardiac hypertrophy, fibrosis, endothelial dysfunction, and fibrotic responses of smooth-muscle cells. Furthermore, statins and FPP synthase inhibitors have also been applied for the management of heart failure and other cardiovascular diseases rather than their clinical use for hyperlipidemia or bone diseases. In this review, we focus on the function of several critical enzymes, including hydroxymethylglutaryl coenzyme A reductase, FPP synthase, farnesyltransferase, and geranylgeranyltransferase in the mevalonate pathway which are involved in regulating the generation of isoprenoids and isoprenylation of small GTPases, and their pathophysiological role in the cardiovascular system. Moreover, we summarize recent research into applications of statins and the FPP synthase inhibitors to treat cardiovascular diseases, rather than for their traditional indications respectively.

Bisphosphonates hinder osteoblastic/osteoclastic differentiation in the maxillary sinus mucosa-derived stem cells

OBJECTIVES

Although bisphosphonates (BPs) are known to be associated with osteonecrosis of the maxilla, the precise effects of BPs on bone metabolism in human maxillary sinus mucosal cells (HMSMCs) are not yet known. The purposes of this study were to examine the effects of the BPs zoledronate (ZOL) and alendronate (ALN) on osteoblastic and osteoclastic differentiation in HMSMCs and to investigate the signaling pathways involved.

MATERIALS AND METHODS

The effects of ZOL and ALN were assessed for osteoblast differentiation by alkaline phosphatase (ALP) activity, alizarin red staining, and RT-PCR for genes encoding Runx2 and osterix. Receptor activator of nuclear factor-κB ligand (RANKL)-mediated osteoclast differentiation in bone marrow macrophages (BMMs) was also examined.

RESULTS

ZOL and ALN both suppressed osteoblastic differentiation, as evidenced by their effects on ALP activity, mineralization nodule formation, and the mRNA expression levels of osteoblastic transcript factors. The RANKL/osteoprotegerin ratio in HMSMCs was increased by ALN, whereas ZOL had the opposite effect. Conditioned medium obtained from ALN-treated HMSMCs stimulated osteoclast formation and upregulated NFATc1 expression, whereas conditioned medium from ZOL-treated cells did not. ALN was more cytotoxic and stimulated apoptosis more strongly than ZOL. BPs decreased the protein levels of the non-canonical Wnt signaling protein Wnt5a and calmodulin-dependent kinase II. Moreover, recombinant human Wnt5a reversed the effects of BPs on osteoblastic and osteoclastic differentiation.

CONCLUSION

This study is the first demonstration that BPs exert negative effects on osteoblastic and osteoclastic processes via the non-canonical Wnt pathway in HMSMSCs.

CLINICAL RELEVANCE

It suggests that patients taking BPs during the period of maxillary sinus lifting and amentation should be given special attention.

A novel function of geranylgeraniol in regulating testosterone production

Isoprenoids play widely differing roles in various physiological processes in animals and plants. Geranylgeraniol (GGOH) is an isoprenoid found in plants, and is an important metabolic derivative in the isoprenoid/cholesterol synthesis pathway. Earlier studies focused on GGOH's ability to improve the side effects of bisphosphonate therapy by regulating the mevalonate pathway. More recently, the mevalonate pathway-independent effects of GGOH have been described, including anti-inflammatory, anti-tumorigenic, and neuroprotective activities. It is noteworthy that GGOH regulates the steroidogenesis pathway in testis-derived I-10 tumor cells. Testosterone is a hormone produced via steroidogenesis in testicles and plays a role in fetal development and the male reproductive system. GGOH enhanced testosterone and progesterone (its precursor) levels in I-10 cells by activating adenylate cyclase via cAMP/PKA signaling, without altering phosphodiesterase activity. These findings highlight the potential benefits of GGOH as a therapeutic agent for low testosterone levels, such as late-onset hypogonadism in men.

Angiogenesis in the Development of Medication-Related Osteonecrosis of the Jaws: An Overview

Medication-related osteonecrosis of the jaws (MR-ONJ) is one of the most relevant side effects of bisphosphonate therapy; it is clinically defined as a non-healing wound in combination with an avascular and necrotic jaw within ongoing bisphosphonate therapy or after completed bisphosphonate therapy. Different theories concerning the development of MR-ONJ have been reported, while the exact pathophysiology is still unknown. Recent studies have increasingly focused on angiogenesis and revascularization concerning MR-ONJ pathophysiology, which seems to be a relevant factor in the development of MR-ONJ and a possible and promising point of action for MR-ONJ prevention and therapy. Therefore, and with respect to the different aspects and specific forms of angiogenesis, the enclosed review summarizes the possible role of angiogenesis and revascularization in the pathophysiology of MR-ONJ. Special focus is given to the strong negative influence of bisphosphonates on progenitor and mature endothelial cells in vitro as well as on microvessel sprouting in vitro and in vivo, which might result in overall reduced wound healing of oral soft and hard tissues, and therefore in an exposed and avascular jaw from a clinical viewpoint. Further, it will be summarized whether and in what way the aspect of angiogenesis might be used for possible MR-ONJ prevention and therapy.

The influence of geranylgeraniol on microvessel sprouting after bisphosphonate substitution in an in vitro 3D-angiogenesis assay

OBJECTIVES

Recent studies focused on angiogenesis in the pathophysiology of bisphosphonate-associated osteonecrosis of the jaws (BP-ONJ) and identified geranylgeraniol (GGOH) as a feasible option for BP-ONJ therapy. This study investigated the influence of GGOH on microvessel sprouting after BP-incubation in vitro.

MATERIALS AND METHODS

Ten experimental set-ups were randomly designed in an in vitro 3D-angiogenesis assay. Two groups included HUVEC cell spheroids with and without (±) GGOH substitution as controls and eight groups pairwise contained either clodronate or the nitrogen-containing bisphosphonates (N-BP) ibandronate, pamidronate, and zoledronate ± GGOH. The size of the cell spheroids including the outbranching sprouts (SpS) as well as the density (SpD) and length of the sprouts (SpL) were analyzed by a grid system after 0, 24, 48, and 72 h.

RESULTS

For controls and NN-BP clodronate, no significant differences at any tested parameter and any point of measurement could be detected within the experimental set-ups ± GGOH (p each ≥0.05). For N-BP ibandronate, the experimental set-ups +GGOH showed a significantly increased SpS, SpD, and SpL after 48 and 72 h (p each ≤0.002) compared to the experimental set-ups -GGOH. For N-BPs pamidronate and zoledronate, the experimental set-ups + GGOH demonstrated a significantly increased SpS, SpD, and SpL after 24, 48, and 72 h (p each ≤0.001) compared to the experimental set-ups -GGOH.

CONCLUSIONS

The strong negative influence of N-BPs on microvessel sprouting could be significantly reversed by GGOH.

CLINICAL RELEVANCE

Since supportive therapeutic options for BP-ONJ are lacking, GGOH might be a promising substitute for BP-ONJ prevention and therapy.

Significance of endothelial progenitor cells (EPC) for tumorigenesis of head and neck squamous cell carcinoma (HNSCC): possible marker of tumor progression and neovascularization?

OBJECTIVES

Angiogenesis and neovascularisation plays a crucial role for tumorigenesis and tumor progression in head and neck squamous cell carcinoma (HNSCC). The aim of our study was to investigate the neovascularization capacity by endothelial progenitor cells (EPC) in tumor patient as a possible predictor for tumor progression and tumor stage.

MATERIALS AND METHODS

Therefore, we investigated the cell number and biologic activity by cell migration and colony-forming ability of EPC. Cells were isolated from the peripheral venous blood of 79 patients who suffer HNSCC in different stages of disease. Thirty-three healthy individuals served as the control group.

RESULTS

Significantly increased biological activities were reflected by expression of the migration rate (1027 ± 1510) in comparison to the control group (632 ± 269) and the clonal potency measured by colony-forming unit (CFU) (tumor patients (19.7 ± 12.3) vs. control group (10.84 ± 4.8)). To determine whether or not EPC number can be used as a valid prognostic marker for clinical outcome of tumor patients, we furthermore compared a "high EPC-number-subgroup" (HI) with a "low EPC-number-subgroup" (LO) in a Kaplan-Meier survival curve. The HI-subgroup shows herein clearly a worse outcome.

CONCLUSIONS

Our findings indicate a possible pathway for EPC to play a critical role in the vasculogenesis and consequently in the progression of HNSCC.

CLINICAL RELEVANCE

Our findings could serve as possible predictors for the neovascularisation potential in HNSCC tumor patients.

Geranylgeraniol and Neurological Impairment: Involvement of Apoptosis and Mitochondrial Morphology

Deregulation of the cholesterol pathway is an anomaly observed in human diseases, many of which have in common neurological involvement and unknown pathogenesis. In this study we have used Mevalonate Kinase Deficiency (MKD) as a disease-model in order to investigate the link between the deregulation of the mevalonate pathway and the consequent neurodegeneration. The blocking of the mevalonate pathway in a neuronal cell line (Daoy), using statins or mevalonate, induced an increase in the expression of the inflammasome gene (NLRP3) and programmed cell death related to mitochondrial dysfunction. The morphology of the mitochondria changed, clearly showing the damage induced by oxidative stress and the decreased membrane potential associated with the alterations of the mitochondrial function. The co-administration of geranylgeraniol (GGOH) reduced the inflammatory marker and the damage of the mitochondria, maintaining its shape and components. Our data allow us to speculate about the mechanism by which isoprenoids are able to rescue the inflammatory marker in neuronal cells, independently from the block of the mevalonate pathway, and about the fact that cell death is mitochondria-related.

PRGF exerts a cytoprotective role in zoledronic acid-treated oral cells

OBJECTIVES

Bisphosphonates-related osteonecrosis of the jaw (BRONJ) is a common problem in patients undergoing long-term administration of highly potent nitrogen-containing bisphosphonates (N-BPs). This pathology occurs via bone and soft tissue mechanism. Zoledronic acid (ZA) is the most potent intravenous N-BP used to prevent bone loss in patients with bone dysfunction. The objective of this in vitro study was to evaluate the role of different ZA concentrations on the cells from human oral cavity, as well as the potential of plasma rich in growth factors (PRGF) to overcome the negative effects of this BP.

MATERIAL AND METHODS

Primary human gingival fibroblasts and primary human alveolar osteoblasts were used. Cell proliferation was evaluated by means of a fluorescence-based method. A colorimetric assay to detect DNA fragmentation undergoing apoptosis was used to determine cell death, and the expression of both NF-κB and pNF-κB were quantified by Western blot analysis.

RESULTS

ZA had a cytotoxic effect on both human gingival fibroblasts and human alveolar osteoblasts. This BP inhibits cell proliferation, stimulates apoptosis, and induces inflammation. However, the addition of PRGF suppresses all these negative effects of the ZA.

CONCLUSIONS

PRGF shows a cytoprotective role against the negative effects of ZA on primary oral cells.

CLINICAL RELEVANCE

At present, there is no definitive treatment for bisphosphonates-related osteonecrosis of the jaw (BRONJ), being mainly palliatives. Our results revealed that PRGF has a cytoprotective role in cells exposed to zoledronic acid, thus providing a reliable adjunctive therapy for the treatment of BRONJ pathology.