Chemically modified tetracyclines act through multiple mechanisms directly on osteoclast precursors

Role of various pharmacologic agents in alveolar bone regeneration: A review

Alveolar bone and gingiva are components of the periodontium that house the tooth. It constantly adapts itself to the masticatory forces and position of the tooth. However, localized diseases like chronic periodontitis and certain systemic diseases destroy periodontal tissues, which include the alveolar bone. Various pharmacological agents are being explored for their pleiotropic properties to combat the destruction of alveolar bone. This review focuses on the role of pharmacological agents in alveolar bone regeneration.

Effects of Minocycline Hydrochloride as an Adjuvant Therapy for a Guided Bone Augmentation Procedure in The Rat Calvarium

This in vivo study reports the influence of minocycline-HCl administration on extra-skeletal bone generation in a Guided Bone Augmentation model, utilizing titanium caps placed on the intact as well as perforated calvaria of rats. The test group was administered 0.5 mg/mL minocycline-HCl with the drinking water, and the amount of bone tissue in the caps was quantified at three time points (4, 8 and 16 weeks). A continuously increased tissue fill was observed in all groups over time. The administration of minocycline-HCl as well as perforation of the calvaria increased this effect, especially with regard to mineralization. The strongest tissue augmentation, with 1.8 times that of the untreated control group, and, at the same time, the most mineralized tissue (2.3× over untreated control), was produced in the combination of both treatments, indicating that systemic administration of minocycline-HCl has an accelerating and enhancing effect on vertical bone augmentation.

Tetracyclines and bone: Unclear actions with potentially lasting effects

Tetracyclines are a broad-spectrum class of antibiotics that have unclear actions with potentially lasting effects on bone metabolism. Initially isolated from Streptomyces, tetracycline proved to be an effective treatment for Gram +/- infections. The emergence of resistant bacterial strains commanded the development of later generation agents, including minocycline, doxycycline, tigecycline, sarecycline, omadacycline, and eravacycline. In 1957, it was realized that tetracyclines act as bone fluorochrome labels due to their high affinity for the bone mineral matrix. Over the course of the next decade, researchers discerned that these compounds are retained in the bone matrix at high levels after the termination of antibiotic therapy. Studies during this period provided evidence that tetracyclines could disrupt prenatal and early postnatal skeletal development. Currently, tetracyclines are most commonly prescribed as a long-term systemic therapy for the treatment of acne in healthy adolescents and young adults. Surprisingly, the impact of tetracyclines on physiologic bone modeling/remodeling is largely unknown. This article provides an overview of the pharmacology of tetracycline drugs, summarizes current knowledge about the impact of these agents on skeletal development and homeostasis, and reviews prior work targeting tetracyclines' effects on bone cell physiology. The need for future research to elucidate unclear effects of tetracyclines on the skeleton is addressed, including drug retention/release mechanisms from the bone matrix, signaling mechanisms at bone cells, the impact of newer third generation tetracycline antibiotics, and the role of the gut-bone axis.

Regenerative Medicine Technologies to Treat Dental, Oral, and Craniofacial Defects

Additive manufacturing (AM) is the automated production of three-dimensional (3D) structures through successive layer-by-layer deposition of materials directed by computer-aided-design (CAD) software. While current clinical procedures that aim to reconstruct hard and soft tissue defects resulting from periodontal disease, congenital or acquired pathology, and maxillofacial trauma often utilize mass-produced biomaterials created for a variety of surgical indications, AM represents a paradigm shift in manufacturing at the individual patient level. Computer-aided systems employ algorithms to design customized, image-based scaffolds with high external shape complexity and spatial patterning of internal architecture guided by topology optimization. 3D bioprinting and surface modification techniques further enhance scaffold functionalization and osteogenic potential through the incorporation of viable cells, bioactive molecules, biomimetic materials and vectors for transgene expression within the layered architecture. These computational design features enable fabrication of tissue engineering constructs with highly tailored mechanical, structural, and biochemical properties for bone. This review examines key properties of scaffold design, bioresorbable bone scaffolds produced by AM processes, and clinical applications of these regenerative technologies. AM is transforming the field of personalized dental medicine and has great potential to improve regenerative outcomes in patient care.

Biomaterial-Based Nanocomposite for Osteogenic Repurposing of Doxycycline

Background

Besides its antimicrobial action, doxycycline (DX) has lately been repurposed as a small-molecule drug for osteogenic purposes. However, osteogenic DX application is impeded by its dose-dependent cytotoxicity. Further, high-dose DX impairs cell differentiation and mineralization.

Purpose

Integrating DX into a biomaterial-based delivery system that can control its release would not only ameliorate its cytotoxic actions but also augment its osteogenic activity. In this work, we managed to engineer novel composite DX–hydroxyapatite–polycaprolactone nanoparticles (DX/HAp/PCL) to modify DX osteogenic potential.

Methods

Employing a 2³-factorial design, we first optimized HApN for surface-area attributes to maximize DX loading. Composite DX/HAp/PCL were then realized using a simple emulsification technique, characterized using various in vitro methods, and evaluated for in vitro osteogenesis.

Results

The developed HApN exhibited a favorable crystalline structure, Ca:P elemental ratio (1.67), mesoporous nature, and large surface area. DX/HAp/PCL achieved the highest reported entrapment efficiency (94.77%±1.23%) of DX in PCL-based particles. The developed composite system achieved controlled release of the water-soluble DX over 24 days. Moreover, the novel composite nanosystem managed to significantly ameliorate DX cytotoxicity on bone-marrow stem cells, as well as enhance its overall proliferation potential. Alkaline phosphatase and mineralization assays revealed superior osteodifferentiation potential of the composite system. Quantification of gene expression demonstrated that while DX solution was able to drive bone-marrow stem cells down the osteogenic lineage into immature osteoblasts after 10-day culture, the innovative composite system allowed maturation of osteodifferentiated cells. To the best of our knowledge, this is the first work to elaborate the impact of DX on the expression of osteogenic genes: RUNX2, OSP, and BSP. Further, the osteogenicity of a DX-loaded particulate-delivery system has not been previously investigated.

Conclusion

Our findings indicate that repurposing low-dose DX in complementary biomaterial-based nanosystems can offer a prominent osteogenic candidate for bone-regeneration purposes.

Doxycycline encapsulated in β-cyclodextrin for periodontitis: a clinical trial

This clinical trial compared the efficacy of doxycycline (DOX) in β-cyclodextrin (DOX)/βCD) with DOX- alone in gel on thirty-three subjects with periodontitis. Patients were randomized to group 1 GI; 10% DOX + scaling and root planning (SRP); group 2 (GII (10% DOX /β-CD + SRP), and group 3 (GIII; SRP). Gels were applied in GI and GII at baseline (T0) and 30 days later (T1). Periodontal Probing Depth (PPD), Clinical Attachment Level (CAL), Bleeding on Probing (BOP) and Visible Plaque Index (VPI) were evaluated at (T0), 30 days (T1) and 60 days after T0 (T2). Bone density was analyzed after 18 months (T3). GII showed the most significant reduction of PPD (2.62 mm; p <0.003), and greatest gain in CAL (2.54 mm p <0.003) at T2. BOP and the VPI had a strong reduction in all groups at T2 (p <0.05), both decreased by ≥5 times and 2 times, respectively, in all groups at T1. Bone density increased in all groups in radiographs (T3). The use of DOX encapsulated in β-CD gel with SRP resulted in significant improvements in clinical periodontal parameters; such molecular inclusion of doxycycline into β-CD in gel for local application is relatively simple and useful in dentistry.

A Novel Analysis via Micro-CT Imaging Indicates That Chemically Modified Tetracycline-3 (CMT-3) Inhibits Tooth Relapse after Orthodontic Movement: A Pilot Experimental Study

Objective

To evaluate the effect of chemically modified tetracycline-3 (CMT-3) and simvastatin on tooth relapse after orthodontic movement in rats using a novel analysis method employing high-resolution micro-CT (Micro-CT) images. In addition, the correlation between bone density and orthodontic relapse was also evaluated for each experimental group.

Methods

Forty adult male Wistar rats had stainless steel springs installed on their left upper first molars in order to generate tooth movement for 18 days. After this initial period, the animals were divided into three groups: (1) 30 mg/kg of CMT-3; (2) 5 mg/kg of simvastatin; and (3) 0.5% carboxymethylcellulose, and each group was treated for 20 days. Micro-CT images were analyzed (conventional method and 3D reconstruction) on the 7th and 18th days following spring fixation and finally, 20 days after treatment either with CMT-3 or simvastatin (38th day). Bone mineral density (BMD) of the mesial and distal roots of the upper first molar was also analyzed.

Results

The difference was statistically significant between the groups as to recurrence (p=0.048), and the post hoc test identified the value of p=0.007 between the control group and the CMT-3 group. Simvastatin was not able to inhibit tooth relapse. The bone mineral densities of both the mesial and distal roots were different between the three groups, after the 20th day of drug use (p=0001 and p < 0001).

Conclusion

Our findings support the initial evidence that CMT-3 is able to prevent relapse after tooth movement. Future trials in humans should evaluate such treatment as a promising approach to preventing this common phenomenon.

Clinical Relevance

Considering the results obtained, CMT-3 can be used to avoid relapse after tooth movement.

Doxycycline induces bone repair and changes in Wnt signalling

Doxycycline (DOX) exhibits anti-inflammatory and MMP inhibitory properties. The objectives of this study were to evaluate the effects of DOX on alveolar bone repair. Controls (CTL) and DOX-treated (10 and 25 mg·kg^-1) molars were extracted, and rats were killed 7 or 14 days later. The maxillae were processed and subjected to histological and immunohistochemical assays. Hematoxylin-eosin staining (7th day) revealed inflammation in the CTL group that was partly reversed after DOX treatment. On the 14th day, the CTL group exhibited bone neoformation, conjunctive tissue, re-epithelization and the absence of inflammatory infiltrate. DOX-treated groups exhibited complete re-epithelization, tissue remodelling and almost no inflammation. Picrosirius red staining in the DOX10 group (7th and 14th days) revealed an increased percentage of type I and III collagen fibres compared with the CTL and DOX25 groups. The DOX10 and DOX25 groups exhibited increases in osteoblasts on the 7th and 14th days. However, there were fewer osteoclasts in the DOX10 and DOX25 groups on the 7th and 14th days. Wnt-10b-immunopositive cells increased by 130% and 150% on the 7th and 14th days, respectively, in DOX-treated groups compared with the CTL group. On the 7th day, Dickkopf (Dkk)-1 immunostaining was decreased by 63% and 46% in the DOX10 and DOX25 groups, respectively. On the 14th day, 69% and 42% decreases in immunopositive cells were observed in the DOX10 and DOX25 groups, respectively, compared with the CTL group. By increasing osteoblasts, decreasing osteoclasts, activating Wnt 10b and neutralising Dkk, DOX is a potential candidate for bone repair in periodontal diseases.

Matrix Metalloproteinases in Bone Resorption, Remodeling, and Repair

Matrix metalloproteinases (MMPs) are the major protease family responsible for the cleavage of the matrisome (global composition of the extracellular matrix (ECM) proteome) and proteins unrelated to the ECM, generating bioactive molecules. These proteins drive ECM remodeling, in association with tissue-specific and cell-anchored inhibitors (TIMPs and RECK, respectively). In the bone, the ECM mediates cell adhesion, mechanotransduction, nucleation of mineralization, and the immobilization of growth factors to protect them from damage or degradation. Since the first description of an MMP in bone tissue, many other MMPs have been identified, as well as their inhibitors. Numerous functions have been assigned to these proteins, including osteoblast/osteocyte differentiation, bone formation, solubilization of the osteoid during bone resorption, osteoclast recruitment and migration, and as a coupling factor in bone remodeling under physiological conditions. In turn, a number of pathologies, associated with imbalanced bone remodeling, arise mainly from MMP overexpression and abnormalities of the ECM, leading to bone osteolysis or bone formation. In this review, we will discuss the functions of MMPs and their inhibitors in bone cells, during bone remodeling, pathological bone resorption (osteoporosis and bone metastasis), bone repair/regeneration, and emergent roles in bone bioengineering.

Benign Tumors of the Spine: Has New Chemotherapy and Interventional Radiology Changed the Treatment Paradigm?

STUDY DESIGN

Clinically based systematic review.

OBJECTIVE

To determine the role of (A) medical treatment and (B) interventional radiology as either adjuvant or stand-alone treatment in primary benign bone tumors of the spine.

METHODS

A multidisciplinary panel of spine surgeons, radiation oncologists, and medical oncologists elaborated specific focused questions regarding aneurysmal bone cyst, giant cell tumor, and osteoid osteoma. Denosumab, bisphosphonate, interferon, bone marrow aspirate, doxycycline, thermal ablation, and selective arterial embolization were identified as areas of interest for the article. A systematic review was performed through MEDLINE and EMBASE. Recommendations based on the literature review and clinical expertise were issued using the GRADE system.

RESULTS

The overall quality of the literature is very low with few multicenter prospective studies. For giant cell tumor, combination with Denosumab identified 14 pertinent articles with four multicenter prospective studies. Nine studies were found on bisphosphonates and six for selective arterial embolization. The search on aneurysmal bone cyst and selective arterial embolization revealed 12 articles. Combination with Denosumab, Doxycycline, and bone marrow aspirate identified four, two, and three relevant articles respectively. Eleven focused articles were selected on the role of thermal ablation in osteoid osteoma.

CONCLUSION

Alternative and adjuvant therapy for primary benign bone tumors have emerged. Their ability to complement or replace surgery is now being scrutinized and they may impact significantly the algorithm of treatment of these tumors. Most of the data are still emerging and further research is desirable. Close collaboration between the different specialists managing these pathologies is crucial.

LEVEL OF EVIDENCE

N/A.

Functional osteoclastogenesis: the baseline variability in blood donor precursors is not associated with age and gender

Mononuclear osteoclast precursors circulate in the monocyte fraction of peripheral blood and form multinuclear cells with all osteoclastic phenotypic characteristics when cultured in the presence of macrophage colony stimulating factor (M-CSF) and receptor activator of nuclear factor kB ligand (RANKL). The method to obtain osteoclast precursors from peripheral blood is simple but the number of recovered osteoclasts is often largely insufficient for functional analyses. The original aim of this study was to develop a rapid and efficient method that could overcome the donor variability and enrich the osteoclast precursors from a small volume of peripheral blood as a basis for future clinical studies to correlate the differentiation potential of circulating osteoclast precursors with bone lesions in cancer patients. We improved the efficiency of osteoclastogenesis by reducing isolation and purification times and overcame the use of flow cytometry and immunomagnetic purification procedures. In our culture system the osteoclast number was increased several-fold and the precursors were able to reach a full differentiation within seven days of culture. Both age as well as gender differences in osteoclastogenesis efficiency were no longer evident by processing limited volume blood samples with this simple and rapid method.

The Effect of Local Delivery Doxycycline and Alendronate on Bone Repair

The aim of the present study was to investigate the local effect of 10% doxycycline and 1% alendronate combined with poly(lactic-co-glycolic acid) (PLGA) on bone repair. Thirty rats were divided into three groups, as follows: control group (CG), drug group (DG), and vehicle-PLGA group (VG). Bone defect was created in the right femur and filled with the following: blood clot (CG); PLGA gel, 10% doxycycline and 1% alendronate (DG); or vehicle-PLGA (VG). The animals were euthanized 7 or 15 days after surgery. Bone density, bone matrix and number of osteoclasts were quantified. At 7 days, the findings showed increased density in DG (177.75 ± 76.5) compared with CG (80.37 ± 27.4), but no difference compared with VG (147.1 ± 41.5); no statistical difference in bone neoformation CG (25.6 ± 4.8), VG (27.8 ± 4), and DG (18.9 ± 7.8); and decrease osteoclasts in DG (4.6 ± 1.9) compared with CG (26.7 ± 7.4) and VG (17.3 ± 2.7). At 15 days, DG (405.1 ± 63.1) presented higher density than CG (213.2 ± 60.9) and VG (283.4 ± 85.8); there was a significant increase in percentage of bone neoformation in DG (31.5 ± 4.2) compared with CG (23 ± 4), but no difference compared with VG (25.1 ± 2.9). There was a decreased number of osteoclasts in DG (20.7 ± 4.7) and VG (29.5 ± 5.4) compared with CG (40 ± 9.4). The results suggest that the association of 10% doxycycline and 1% alendronate with PLGA-accelerated bone repair.

Percutaneous Doxycycline Treatment of Juxtaphyseal Aneurysmal Bone Cysts

BACKGROUND

A recurrence rate of 19% to 23% has been reported in juxtaphyseal aneurysmal bone cysts (ABC) without en bloc resection or amputation. No percutaneous surgical techniques or drug treatments have demonstrated consistent bone healing with normal physeal growth and a recurrence rate of <19%. Doxycycline has properties that may make it an appropriate agent for percutaneous treatment of juxtaphyseal ABC in skeletally immature patients.

METHODS

We retrospectively reviewed 16 patients who underwent percutaneous treatment of ABCs with doxycycline from 2006 to 2011. The mean age was 7.1 years (range, 2 to 15 y). There were 16 treatment locations: humerus (9), tibia (3), fibula (2), femur (1), and ulna (1). Sixteen patients completed treatment involving 102 treatment sessions (2 to 14 sessions per patient). Treatment response was evaluated radiographically by measuring the lytic component, thickness of involved cortex, and signs of bony remodeling, and evidence of physeal growth arrest. Recurrence was indicated by new areas of lytic destruction after completion of treatment. The minimum follow-up was 18 months (mean, 39 mo).

RESULTS

All 16 patients demonstrated reduction in lytic destruction, bony healing, and bony remodeling. One patient demonstrated recurrent minimal lytic destruction after 20 months of observation. Seven patients (7/16, 44%) demonstrated physeal ABC involvement; 5 of 7 patients healed with a physeal bone bridge, all ≤15% of the physeal surface area, 1 with mild central physeal deformity. All patients with focal transphyseal ABC involvement (4/4, 100%) demonstrated focal bone bridge after treatment. No patient had diffuse physeal growth arrest; only patients with intraphyseal or transphyseal ABC involvement had focal physeal growth arrest.

CONCLUSIONS

In this series, patients undergoing percutaneous doxycycline treatment of juxtaphyseal ABCs demonstrated ABC healing and a recurrence rate of 6% at >18 months. Patients without physeal ABC involvement demonstrated no evidence of physeal growth arrest.

Black bone disease in a healing fracture

Black bone disease refers to the hyperpigmentation of bone secondary to prolonged usage of minocycline. We present a report of a 34-year-old man who underwent femoral shaft fracture fixation complicated by deep infection requiring debridement. The implants were removed 10 months later after long-term treatment with minocycline and fracture union. A refracture of the femoral shaft occurred 2 days after implant removal and repeat fixation was required. Intraoperatively, abundant heavily pigmented and dark brown bone callus was noted over the old fracture site. There was no evidence of other bony pathology and the appearance was consistent with minocycline-associated pigmentation. As far as we are aware, this is the first case of black bone disease affecting callus within the interval period of bone healing. We also discuss the relevant literature on black bone disease to bring light on this rare entity that is an unwelcomed surprise to operating orthopaedic surgeons.

Chemically modified tetracyclines: The novel host modulating agents

Periodontal pathogens and destructive host responses are involved in the initiation and progression of periodontitis. The emergence of host response modulation as a treatment concept has resulted from our improved understanding of the pathogenesis of periodontal disease. A variety of drugs have been evaluated as host modulation agents (HMA), including Non Steroidal Anti Inflammatory Drugs (NSAIDS), bisphosphonates, tetracyclines, enamel matrix proteins and bone morphogenetic proteins. Chemically modified tetracyclines (CMTs) are one such group of drugs which have been viewed as potential host modulating agents by their anticollagenolytic property. The CMTs are designed to be more potent inhibitors of pro inflammatory mediators and can increase the levels of anti inflammatory mediators.

A histomorphometric study of the effect of doxycycline and erythromycin on bone formation in dental alveolar socket of rat

Background:

The aim of the present study was to evaluate whether subantimicrobial doses of doxycycline (DOX) and erythromycin (EM) used for the treatment of peri-implant osteolysis due to their anti-osteoclastogenesis can interfere with the osseous wound healing process in rat alveolar socket.

Materials and Methods:

Forty-five male Wistar rats had their first maxillary right molar extracted and were divided into three groups. DOX and EM at the doses of 5 mg/kg/day orally (p.o.) and 2 mg/kg/day intraperitoneally (i.p.) were administered respectively to two separate groups for 7 days after operation. In the control group the animals received normal saline (5 ml/kg). Five rats were sacrificed at 7, 14 and 21 days post-extraction in each study group. A histomorphometric analysis was used to evaluate new bone formation inside the alveolar socket. Significant level was set at 0.05.

Results:

The findings showed that the percentage of new bone formation (NBF) enhanced significantly on days 7 and 14. There was no significant difference in the NBF between DOX and EM groups.

Conclusion:

Short-term treatment with both DOX and EM enhanced new bone formation without any advances in favor of each drug.

Dramatic osteonecrosis of the jaw associated with oral bisphosphonates, periodontitis, and dental implant removal

INTRODUCTION

Osteoporosis affects millions of elderly patients, and anti-resorptive drugs (ARD) such as bisphosphonates (BP) represent the first-line therapy. Despite the benefits related to the use of these medications, osteonecrosis of the jaw is a significant complication in a subset of patients receiving these drugs.

CASE PRESENTATION

This report documents a case of dramatic bisphosphonate-related osteonecrosis associated with periodontitis and dental implant removal in an osteoporotic patient treated with per os bisphosphonates for an uninterrupted period of 15 years.

CONCLUSION

The aim of this report was to discuss the administration period of BP in the treatment of osteoporosis, the decision-making and clinical management of severe MRONJ and the indications for dental implant placement in these specific patients.

Anti-inflammatory Actions of Adjunctive Tetracyclines and Other Agents in Periodontitis and Associated Comorbidities

The non-antimicrobial properties of tetracyclines such as anti-inflammatory, proanabolic and anti-catabolic actions make them effective pharmaceuticals for the adjunctive management of chronic inflammatory diseases. An over-exuberant inflammatory response to an antigenic trigger in periodontitis and other chronic inflammatory diseases could contribute to an autoimmune element in disease progression. Their adjunctive use in managing periodontitis could have beneficial effects in curbing excessive inflammatory loading from commonly associated comorbidities such as CHD, DM and arthritis. Actions of tetracyclines and their derivatives include interactions with MMPs, tissue inhibitors of MMPs, growth factors and cytokines. They affect the sequence of inflammation with implications on immunomodulation, cell proliferation and angiogenesis; these actions enhance their scope, in treating a range of disease entities. Non-antimicrobial chemically modified tetracyclines (CMTs) sustain their diverse actions in organ systems which include anti-inflammatory, anti-apoptotic, anti-proteolytic actions, inhibition of angiogenesis and tumor metastasis. A spectrum of biological actions in dermatitis, periodontitis, atherosclerosis, diabetes, arthritis, inflammatory bowel disease, malignancy and prevention of bone resorption is particularly relevant to minocycline. Experimental models of ischemia indicate their specific beneficial effects. Parallel molecules with similar functions, improved Zn binding and solubility have been developed for reducing excessive MMP activity. Curbing excessive MMP activity is particularly relevant to periodontitis, and comorbidities addressed here, where specificity is paramount. Unique actions of tetracyclines in a milieu of excessive inflammatory stimuli make them effective therapeutic adjuncts in the management of chronic inflammatory disorders. These beneficial actions of tetracyclines are relevant to the adjunctive management of periodontitis subjects presenting with commonly prevalent comorbidities addressed here.

Bioactive implant surface with electrochemically bound doxycycline promotes bone formation markers in vitro and in vivo

OBJECTIVES

The objective of this study was to demonstrate a successful binding of Doxy hyclate onto a titanium zirconium alloy surface.

METHODS

The coating was done on titanium zirconium coins in a cathodic polarization setup. The surface binding was analyzed by SEM, SIMS, UV-vis, FTIR and XPS. The in vitro biological response was tested with MC3T3-E1 murine pre-osteoblast cells after 14 days of cultivation and analyzed in RT-PCR. A rabbit tibial model was also used to confirm its bioactivity in vivo after 4 and 8 weeks healing by means of microCT.

RESULTS

A mean of 141 μg/cm(2) of Doxy was found firmly attached and undamaged on the coin. Inclusion of Doxy was documented up to a depth of approximately 0.44 μm by tracing the (12)C carbon isotope. The bioactivity of the coating was documented by an in vitro study with murine osteoblasts, which showed significantly increased alkaline phosphatase and osteocalcin gene expression levels after 14 days of cell culture along with low cytotoxicity. Doxy coated surfaces showed increased bone formation markers at 8 weeks of healing in a rabbit tibial model.

SIGNIFICANCE

The present work demonstrates a method of binding the broad spectrum antibiotic doxycycline (Doxy) to an implant surface to improve bone formation and reduce the risk of infection around the implant. We have demonstrated that TiZr implants with electrochemically bound Doxy promote bone formation markers in vitro and in vivo.

Percutaneous doxycycline treatment of aneurysmal bone cysts with low recurrence rate: a preliminary report

BACKGROUND

Aneurysmal bone cyst (ABC) has a recurrence rate of between 12% and 71% without en bloc resection or amputation. There is no percutaneous ABC treatment drug regimen demonstrating consistent evidence of bone healing with recurrence of < 12%. Doxycycline has properties that may make it appropriate for percutaneous treatment.

QUESTIONS/PURPOSES

We therefore asked: (1) Is there reduction in ABC lytic cyst volume with injectable doxycycline? (2) Is it associated with thickening of involved bony cortex? (3) Is the recurrence rate after percutaneous treatment < 12%?

METHODS

We retrospectively reviewed 20 patients who underwent percutaneous treatment of ABCs with doxycycline from 2006 to 2010. The mean age was 10 years (range, 3-18 years). There were 21 treatment locations: humerus (six), spine (five), clavicle (two), fibula (one), femur (two), ulna (two), tibia (two), and scapula (one). Twenty patients completed treatment involving 118 treatment sessions (two to 14 sessions per patient). Treatment response was evaluated radiographically by measuring the lytic component and thickness of involved cortex. Recurrence was indicated by new areas of lytic destruction after completion of treatment. The minimum followup was 24 months (mean, 38 months).

RESULTS

Twenty of 20 patients demonstrated reduction in lytic destruction and bony healing. All patients demonstrated cortical thickening. One patient demonstrated recurrent minimal lytic destruction after 20 months of observation.

CONCLUSIONS

In this series, patients undergoing percutaneous doxycycline treatment of ABCs demonstrated a healing response and a recurrence rate of 5% at more than 24 months.

Chemically modified tetracyclines: Novel therapeutic agents in the management of chronic periodontitis

Chronic periodontitis is a complex infection initiated by gram-negative bacteria which destroy the supporting structures of the tooth. Recently, it has been recognized that it is the host response to bacterial infection which causes greater destruction of the connective tissue elements, periodontal ligament and alveolar bone in periodontitis. This has led to the development of various host modulating approaches to target cells and their destructive mediators involved in tissue degradation. Chemically modified tetracyclines (CMTs) are derivatives of tetracycline group of drugs which lack antimicrobial action but have potent host modulating affects. They inhibit pathologically elevated matrix metal loproteinases, pro-inflammtory cytokines and other destructive mediators. Bone resorption is also suppressed due to their combined anti-proteinase and apoptotic affects on osteoblasts and osteoclasts, respectively. Development of resistant bacteria and gastrointestinal toxicity seen with parent tetracyclines is not produced by CMTs. Hence, CMTs are viewed as potential therapeutic agents in the management of chronic diseases like periodontitis that involve destruction of connective tissue and bone.

Minocycline-induced black bone disease encountered during total knee arthroplasty

Finding discolored bone intraoperatively can be confusing and concerning to orthopedic surgeons. Multiple causes of pigmented bone exist, including ochronosis, metabolic bone diseases, metal deposits, sequestrum, metastatic disease, and minocycline use. Bone quality is an important consideration in intraoperative decision making with respect to components and fixation options in total joint arthroplasty. Abnormal bone encountered in routine arthroplasty can raise concerns over the integrity and healing potential of the bone when the etiology is uncertain.Minocycline is a drug routinely used for the treatment of acne, rosacea, and rheumatoid arthritis. Pigmentation is a commonly recognized adverse reaction associated with most of the drugs in the tetracycline family, affecting the skin, nails, teeth, oral mucosa, bones in the oral cavity, ocular structures, cartilage, thyroid, and other visceral structures.This article describes a case of pigmented bone secondary to minocycline use in a 55-year-old woman undergoing total knee arthroplasty. This entity has rarely been documented in the orthopedic literature; however, orthopedic surgeons should be aware of this side effect secondary to the widespread use of minocycline. Questions concerning the effect of minocycline on bone metabolism and structural integrity have yet to be fully answered, but an understanding and recognition of the entity will help guide surgeons with intraoperative decision making.

Tetracyclines convert the osteoclastic-differentiation pathway of progenitor cells to produce dendritic cell-like cells

Tetracyclines, such as doxycycline and minocycline, are used to suppress the growth of bacteria in patients with inflammatory diseases. Tetracyclines have been shown to prevent bone loss, but the mechanism involved is unknown. Osteoclasts and dendritic cells (DCs) are derived from common progenitors, such as bone marrow-derived macrophages (BMMs). In this article, we show that tetracyclines convert the differentiation pathway, resulting in DC-like cells not osteoclasts. Doxycycline and minocycline inhibited the receptor activator of NF-κB ligand (RANKL)-induced osteoclastogenesis of BMMs, but they had no effects on cell growth and phagocytic activity. They influenced neither the proliferation nor the differentiation of bone-forming osteoblasts. Surprisingly, doxycycline and minocycline induced the expression of DC markers, CD11c and CD86, in BMMs in the presence of RANKL. STAT5 is involved in DC differentiation induced by GM-CSF. Midostaurin, a STAT5-signaling inhibitor, and an anti-GM-CSF-neutralizing Ab suppressed the differentiation induced by GM-CSF but not by tetracyclines. In vivo, the injection of tetracyclines into RANKL-injected mice and RANKL-transgenic mice suppressed RANKL-induced osteoclastogenesis and promoted the concomitant appearance of CD11c(+) cells. These results suggested that tetracyclines prevent bone loss induced by local inflammation, including rheumatoid arthritis and periodontitis, through osteoclast-DC-like cell conversion.

The aqueous extract of Angelica sinensis, a popular Chinese herb, inhibits wear debris-induced inflammatory osteolysis in mice

BACKGROUND

More and more studies have shown Angelica sinensis' (AS) therapeutic action on chronic inflammatory diseases in recent years. We investigated effects of aqueous extract of AS on inflammatory cytokines release and wear debris particles-induced osteolysis.

MATERIALS AND METHODS

Ultra high molecular weight polyethylene (UHMWPE) particles were used to induce inflammation in RAW264.7 cell and C57BL/J6 mice. AS extract was obtained through a series of purification steps, and divided into high dose group and low dose group during the research of cell culture, tissue culture, and animal treatment. After 72 h culture with optimal particles, supernatants were collected for cytokine analysis. Calvaria were harvested from the mice model after 10 d treatment with the AS extract. Six calvaria of each group were cultured into medium for 72 h for analyzing cytokine generated in vivo. Histologic analyses and micro-computed tomography (micro-CT) scan were used to determine osteoclastogenesis and inflammatory bone resorption.

RESULTS

Concentration of tumor necrosis-alpha (TNF-α) and interleukin-1beta (IL-1β) was significantly attenuated by AS extract both in vitro and in vivo. The osteolysis area and the osteoclast numbers were decreased from 0.406 ± 0.0799 to 0.117 ± 0.0103 mm(2), and from 22.7 ± 5.0 to 11.3 ± 1.8, respectively (P < 0.01). Compared with the control group, the protection effects of AS extract was further confirmed with data of the more accurate 3-dimension micro-CT reconstruction.

CONCLUSIONS

This study suggests a potential resolution of inhibiting wear debris particles-induced inflammatory bone resorption, as well as a possible way of inhibiting aseptic loosening after joint replacement surgery.

Bone regeneration using porous titanium particles versus bovine hydroxyapatite: a sinus lift study in rabbits

AIM

The first objective of this study was to qualitatively and quantitatively assess the bone formation process, particularly the long-term behavior and three-dimensional volume stability of subsinusal bone regeneration, using titanium (Ti) or bovine hydroxyapatite (BHA) granules, in a rabbit model. The second objective was to evaluate the effect of the hydration of the BHA particles with a therapeutic concentration of doxycycline solution on the osteogenesis and biomaterial resorption.

MATERIALS AND METHODS

Rabbits underwent a double sinus lift procedure using one of three materials: grade 1 porous Ti particles, BHA, or BHA hydrated with doxycycline solution (0.1mg/ml) (BHATTC). Animals were sacrificed after 1 week, 5 weeks, or 6 months. Samples were analyzed using µCT and nondecalcified histology.

RESULTS

The materials used in each of the three groups allowed an optimal bone formation; bone quantities and densities were not statistically different between the three groups. At 6 months, more stable three-dimensional volume stability was found with Ti and BHATTC (p=.0033). At 5 weeks and 6 months, bone to material contact corroborating osteoconduction was significantly higher with BHA and BHATTC than with Ti (p<.0001).

CONCLUSIONS AND CLINICAL IMPLICATIONS

Even though the studied biomaterials displayed different architectures, they are relevant candidates for sinus lift bone augmentation prior to dental implants because they allow adequate three-dimensional stability and osteogenesis. However, to recommend the clinical use of Ti, both an observation on the drilling effects of Ti particles and clinical trials are needed.

M-CSF potently augments RANKL-induced resorption activation in mature human osteoclasts

Macrophage-CSF (M-CSF) is critical for osteoclast (OC) differentiation and is reported to enhance mature OC survival and motility. However, its role in the regulation of bone resorption, the main function of OCs, has not been well characterised. To address this we analysed short-term cultures of fully differentiated OCs derived from human colony forming unit-granulocyte macrophages (CFU-GM). When cultured on dentine, OC survival was enhanced by M-CSF but more effectively by receptor activator of NFκB ligand (RANKL). Resorption was entirely dependent on the presence of RANKL. Co-treatment with M-CSF augmented RANKL-induced resorption in a concentration-dependent manner with a (200-300%) stimulation at 25 ng/mL, an effect observed within 4-6 h. M-CSF co-treatment also increased number of resorption pits and F-actin sealing zones, but not the number of OCs or pit size, indicating stimulation of the proportion of OCs activated. M-CSF facilitated RANKL-induced activation of c-fos and extracellular signal-regulated kinase (ERK) 1/2 phosphorylation, but not NFκB nor nuclear factor of activated T-cells, cytoplasmic-1 (NFATc1). The mitogen-activated protein kinase kinase (MEK) 1 inhibitor PD98059 partially blocked augmentation of resorption by M-CSF. Our results reveal a previously unidentified role of M-CSF as a potent stimulator of mature OC resorbing activity, possibly mediated via ERK upstream of c-fos.

Inhibition of matrix metalloproteinase-9 activity by doxycycline ameliorates RANK ligand-induced osteoclast differentiation in vitro and in vivo

Tetracycline antibiotics, including doxycycli\e (DOX), have been used to treat bone resorptive diseases, partially because of their activity to suppress osteoclastogenesis induced by receptor activator of nuclear factor kappa B ligand (RANKL). However, their precise inhibitory mechanism remains unclear. Therefore, the present study examined the effect of Dox on osteoclastogenesis signaling induced by RANKL, both in vitro and in vivo. Although Dox inhibited RANKL-induced osteoclastogenesis and down-modulated the mRNA expression of functional osteoclast markers, including tartrate-resistant acid phosphatase (TRAP) and cathepsin K, Dox neither affected RANKL-induced MAPKs phosphorylation nor NFATc1 gene expression in RAW264.7 murine monocytic cells. Gelatin zymography and Western blot analyses showed that Dox down-regulated the enzyme activity of RANKL-induced MMP-9, but without affecting its protein expression. Furthermore, MMP-9 enzyme inhibitor also attenuated both RANKL-induced osteoclastogenesis and up-regulation of TRAP and cathepsin K mRNA expression, indicating that MMP-9 enzyme action is engaged in the promotion of RANKL-induced osteoclastogenesis. Finally, Dox treatment abrogated RANKL-induced osteoclastogenesis and TRAP activity in mouse calvaria along with the suppression of MMP9 enzyme activity, again without affecting the expression of MMP9 protein. These findings suggested that Dox inhibits RANKL-induced osteoclastogenesis by its inhibitory effect on MMP-9 enzyme activity independent of the MAPK-NFATc1 signaling cascade.

In growing pigs, chlortetracycline induces a reversible green bone discoloration and a persistent increase of bone mineral density dependent of dosing regimen

We studied in growing pigs the effects of exposure to dietary chlortetracycline on bone mineral density (BMD) and bone color. Pigs were randomly allocated to a drug-free diet (n=48) or a diet fortified with 800 ppm of chlortetracycline, starting either at 28- or 84-d of age, and for either a 28- or 56-d duration (n=16 pigs/group). The lumbar vertebral discoloration and BMD of randomly chosen pigs were evaluated at 28-d intervals up to 168-d of age. The odds of bone discoloration increased with dosing duration and age at treatment onset, and decreased with the withdrawal time and age at treatment onset interaction (p < or = 0.001). The measured trabecular BMD linearly increased with age and squared treatment duration (p < or = 0.005). Therefore, TC-induced bone discoloration is reversible, and may be prevented with proper dosing regimen design. Moreover, TC induces a persistent increase on BMD that could be detected with quantitative computed tomography.

Tetracyclines inhibit rat osteoclast formation and activity in vitro and affect bone turnover in young rats in vivo

An experiment was designed to investigate whether systemic administration of tetracyclines (TCs) as bone fluorochrome labels could interfere with bone modeling in vivo and inhibit osteoclast formation and activity in vitro. Cell cultures of rat bone marrow macrophages revealed that TC and oxytetracycline inhibited osteoclastogenesis and bone resorption and stimulated apoptosis. Forty rats in five groups were treated with saline, calcein green, alizarin red S, TC, or oxytetracycline. Their tibias were used for histomorphometric analysis, including bone static, dynamic, and resorption parameters in the tibial proximal metaphysis. No significant differences in bone volume per tissue volume, trabecular number, trabecular thickness, trabecular separation, bone formation rate per bone surface, mineralizing surface, or mineral apposition rate were observed. TC or oxytetracycline decreased eroded surface, number of osteoclasts per bone perimeter, and osteoclast surface per bone surface by about 50%. The results demonstrated that TC and oxytetracycline inhibit rat osteoclast formation and activity in vitro, and histomorphometric parameters involved in bone turnover may be affected by the use of oxytetracycline and TC as fluorescent bone labels in vivo.

Comparison of osteoclast precursors in peripheral blood mononuclear cells from rheumatoid arthritis and osteoporosis patients

Osteolytic disorders cause serious problems for quality of life with aging. Osteolysis is performed by osteoclasts of the hematopoietic lineage that share some characteristics with monocytes and macrophages. As osteoclast precursors (pOCs) are present in peripheral blood, their characterization in osteolytic diseases may help us to understand risk factors. Although essential factors for osteoclastogenesis have been reported, the effective induction from pOCs in human peripheral blood mononuclear cells (PBMCs) to mature osteoclasts in culture requires further improvement. The aim of this study was development of an efficient culture system for human osteoclastogenesis and providing a simple system for the enrichment of pOCs from PBMCs. We employed coculturing of human PBMCs with a mouse stromal cell line. Significant numbers of tartrate-resistant acid phosphatase-positive (TRAP(+)) multinucleated osteoclasts (MNCs), which could resorb dentine slices, were efficiently induced in this culture condition. pOCs were enriched in an anti-CD16 antibody column-passed anti-CD14 antibody-bound cell population isolated by magnetic cell sorting. We compared the percentage of the CD14(high) CD16(dull) cell population, which mainly contained pOCs in PBMCs, from age-matched patients with rheumatoid arthritis (RA) and osteoporosis (OP), but it was comparable. However, the mean number of TRAP(+) MNCs generated in cultures from PBMCs of RA was higher. In contrast, the frequency of pOCs in PBMCs from OP was relatively higher. These results suggest the characteristics of pOCs from RA and OP may be different, because single pOCs from OP gave rise to lower numbers of osteoclasts than those from RA.

Cell-induced response by tetracyclines on human bone marrow colonized hydroxyapatite and Bonelike

Semi-synthetic tetracyclines are commonly used antibiotics that also seem to play an important role in the modulation of the immuno-inflammatory imbalance, verified in several bone diseases. The association of a therapeutic agent (that prevents bacterial infection and induces tissue formation) to a biomaterial aiming to repair/regenerate bone defects could contribute to a more predictable clinical outcome. The present study intends to evaluate the proliferation and functional activity of osteoblast-induced human bone marrow cells, cultured on the surface of hydroxyapatite (HA) and Bonelike, in the presence of therapeutic concentrations of doxycycline and minocycline. First passage bone marrow cells were cultured for 35 days on the surface of HA and Bonelike discs, in the absence or presence of 1 microg ml(-1) doxycycline and minocycline. Cultures performed in standard tissue culture plates were used as control. Doxycycline or minocycline induced cell proliferation and increased the extent of matrix mineralization in osteoblastic cell cultures established in the three substrates. Also, an improved biological behavior was verified in seeded Bonelike compared with HA. The results suggest that the local delivery of tetracyclines might associate the antimicrobial activity in implant-related bone infection with an eventual induction of osteoblastic proliferation and maintenance of the characteristic biological activity of these cells.

A role for non-antimicrobial actions of tetracyclines in combating oxidative stress in periodontal and metabolic diseases: a literature review

This review addresses the role of adjunctive tetracycline therapy in the management of periodontal diseases and its efficacy in reducing inflammatory burden, oxidative stress and its sequelae in patients with coexisting features of metabolic syndrome. Removal of the dimethylamine group at C4 of the tetracycline molecule reduces its antibiotic properties, enhancing its non-antimicrobial actions; this strategy has aided the development of several chemically modified tetracyclines such as minocycline and doxycycline, by altering different regions of the molecule for focused action on biological targets. Tetracyclines are effective in reducing inflammation by inhibiting matrix metalloproteinases, preventing excessive angiogenesis, inhibiting apoptosis and stimulating bone formation. There are important applications for tetracyclines in the management of diabetic, dyslipidaemic periodontal patients who smoke. The diverse mechanisms of action of tetracyclines in overcoming oxidative stress and enhancing matrix synthesis are discussed in this review.

Inhibition of smooth muscle cell proliferation by a chemically modified tetracycline

INTRODUCTION

Chemically modified tetracyclines (CMTs) are a group of nonantimicrobial derivatives of tetracycline, which exert antiproliferative and anticollagenolytic properties. The molecular mechanisms, however, are poorly understood.

MATERIALS AND METHODS

The effect of CMT-3 on cultured, subconfluent rat aortic smooth muscle cells (SMCs) was analyzed by [(3)H]-thymidine incorporation, counting cell numbers, and flow cytometry analysis.

RESULTS

CMT-3 inhibited the incorporation of [(3)H]-thymidine and reduced the cell number dose-dependently, with approximately 60% inhibition at the maximal CMT-3 concentration used (20 mumol/l). CMT-3 decreased the SMC proportion in S-phase and gradually increased the proportion at G2/M. Initially, the proportion of cells in G1-phase increased and then gradually decreased back to baseline as the CMT-3 concentration increased. CMT-3 treatment of confluent SMCs for 24 h did not induce apoptosis.

CONCLUSIONS

CMT-3 inhibited SMC proliferation by inducing cell cycle arrest at the G2/M restriction point. Nonetheless, CMT-3 did not induce SMC apoptosis.

Inhibiting wear particles-induced osteolysis with doxycycline

AIM

To study the effect of doxycycline (DOX) on osteoclastogenesis, mature osteoclast fate and function, wear particles-induced osteoeolysis, and to provide some foundation for treating aseptic loosening and osteolysis after joint arthroplasty.

METHODS

Osteoclasts were generated from mouse bone marrow monocytes with the receptor activator of NF-kappaB ligand and the macrophage colony stimulating factor. DOX at a concentration of 5, 10, 15, and 20 microg/mL was respectively added to the medium. Seven days later, the osteoclasts were determined through tartrate-resistant acid phosphatase (TRAP) staining. Mature osteoclasts were isolated from newborn rabbits and cultured for 3 d in 24-well plates or on bone slices. DOX at a concentration of 5, 10, 15, and 20 microg/mL was respectively added to the medium. After TRAP staining, the osteoclasts were counted, resorption on bone slices was quantified, and the area was calculated after toluidine blue and Mayer-hematoxylin staining. Polymethyl methacrylate (PMMA) or ultra-high molecular weight polyethylene (UHMWPE) particles were implanted on the calvariae of C57BL/J6 mice. DOX, at a dose of 2 and 10 mg x kg(-1) x d(-1), was respectively given intraperitoneally for 7 d. Seven days later, the calvariae were removed and processed for pathological analysis.

RESULTS

DOX treatment effectively inhibited in vitro osteoclastogenesis, affected the fate of mature osteoclasts, and inhibited mature osteoclasts, causing bone resorption. In vivo data indicated that DOX strongly inhibited PMMA or UHMWPE-induced osteolysis and osteoclastogenesis.

CONCLUSION

DOX can effectively inhibit osteoclastogenesis and affect mature osteoclast fate and suppress wear particles induced by osteolysis and osteoclastogenesis. DOX might be useful in the treatment or prevention of wear particles-induced osteolysis and aseptic loosening for its effect on osteoclast generation and mature osteoclast fate and function.

CMT-3 inhibits orthodontic tooth displacement in the rat

OBJECTIVE

Orthodontic tooth movement requires extensive remodeling of the periodontal ligament (PDL) and the alveolar bone. Osteoclasts resorb bone, allowing teeth to migrate in the direction of the force. Matrix metalloproteinases (MMPs) are able to degrade the extracellular matrix of the periodontal tissues. Chemically modified tetracyclines (CMTs) can inhibit MMPs, but lack antimicrobial activity. We hypothesize that CMT-3 will decrease the rate of orthodontic tooth movement in the rat.

DESIGN

Eighteen Wistar rats received a standardized orthodontic appliance at one side of the maxilla. During 14 days, three groups of six rats received a daily dose of 0, 6 or 30mg/kg CMT-3, and tooth displacement was measured. Thereafter, osteoclasts were counted on histological sections using an ED-1 staining. Multi- and mononuclear ED-1-positive cells in the PDL were also counted. In addition, sections were stained for MMP-9.

RESULTS

CMT-3 significantly inhibited tooth movement (p=0.03) and also decreased the number of osteoclasts at the compression sides in the 30mg/kg group (p<0.05). Significantly more mono- than multinuclear ED-1-positive cells were present in the PDL, but no significant differences were found between the dosage groups. Osteoclasts in the 30mg/kg group seemed to contain less MMP-9 than in the control.

CONCLUSIONS

CMT-3 inhibits tooth movement in the rat, probably by reducing the number of osteoclasts at the compression side. This might be due to induction of apoptosis in activated osteoclasts or reduced osteoclast migration. Reduced MMP activity by CMT-3 might also directly inhibit degradation of the organic bone matrix.

Effect of therapeutic levels of doxycycline and minocycline in the proliferation and differentiation of human bone marrow osteoblastic cells

Semi-synthetic tetracyclines (TCs) have been reported to reduce pathological bone resorption through several mechanisms, although their effect over bone physiological metabolism is not yet fully understood. The present study aims at evaluate the behaviour of osteoblastic-induced human bone marrow cells regarding proliferation and functional activity, in the presence of representative therapeutic concentrations of doxycycline and minocycline. First passage human osteoblastic bone marrow cells were cultured for 35 days in conditions known to favor osteoblastic differentiation. Doxycycline (1-25 micro g/ml) or minocycline (1-50 micro g/ml) were added continuously, with the culture medium, twice a week with every medium change. Cultures were characterised at several time points for cell proliferation and function. Present data showed that 1 micro g/ml of both tetracyclines, level representative of that attained in plasma and crevicular fluid with the standard therapeutic dosage, increased significantly the proliferation of human bone marrow osteoblastic cells without altering their specific phenotype and functional activity. Long-term exposure to these TCs induced a significant increase in the number of active osteoblastic cells that yielded a proportional amount of a normal mineralised matrix, suggesting a potential application in therapeutic approaches aiming to increase bone formation. The presence of higher levels of these agents led to a dose-dependent deleterious effect over cell culture, delaying cell proliferation and differentiation.

Tetracycline analogues (doxycycline and COL-3) induce caspase-dependent and -independent apoptosis in human colon cancer cells

Tetracycline analogues (TCNAs) possess cytotoxic activities as well as matrix metalloproteinase (MMP) inhibitory properties. Previously, we demonstrated that doxycycline (DOXY) could induce apoptosis in human HT29 colon cancer cells. In present study, the molecular apoptotic mechanisms induced by two kinds of TCNAs, designated as DOXY and COL-3 (chemically modified tetracycline-3; 6-demethyl, 6-deoxy, 4-dedimethylamino tetracycline), were evaluated in cultured HT29 cells. Both TCNAs inhibited the proliferation of 6 different colorectal cancer cell lines in a dose-dependent manner. Especially, COL-3 had a stronger effect on cancer cells than DOXY. Apoptotic changes were actually observed by 10 mug/ml COL-3 and 20 mug/ml DOXY in a time-dependent manner. COL-3 produced the increase in cytosolic cytochrome c and the loss of mitochondrial membrane potential after 3 hr treatment, and thereafter activated caspases. In case of DOXY, these changes were observed after 24 hr. Bax translocation was not a prerequisite for cytochrome c releasing in COL-3 treatment. Pretreated pancaspase inhibitor (Z-VAD-FMK) reduced COL-3 and DOXY mediated apoptosis up to 81.3 and 35.3%, as compared with nontreated cells, respectively. These data indicated that TCNAs could induce mitochondria-mediated apoptosis through both caspase-dependent and -independent pathway. In fact, endonuclease G and apoptosis-inducing factor were released into cytosol after the treatment of TCNAs, which indicated that caspase-independent apoptotic pathway is also one of the key mechanisms for the treatment of TCNAs. Taken together, we believe that TCNAs could have strong potentials for clinical application in treating colorectal cancers and improve cancer chemotherapy.

Chemically modified tetracyclines induce apoptosis in cultured mast cells

Chemically modified tetracyclines are a group of non-antimicrobial tetracycline derivatives, which possess antiinflammatory, anticollagenolytic and antiproliferative properties. Here we studied the effects of four different chemically modified tetracyclines (CMT-1, CMT-3, CMT-8 and CMT-308) on proliferation and viability of cultured mouse and human mast cells. All studied CMTs (25 microM) effectively inhibited the viability and proliferation of human mast cell line (HMC-1) cells and mouse bone marrow derived mast cells (mBMMCs), as judged by trypan blue exclusion and by incorporation of [(3)H]thymidine. The antiproliferative effect of CMTs was not dependent on the stimulating growth factor, i.e. CMTs inhibited both IL-3 and c-kit ligand-induced proliferation of mBMMCs. The reduced viability of mast cells was due to induction of apoptosis, as indicated by the increased amount of apoptotic nucleosomes and the appearance of TUNEL positive cells in the presence of CMTs. The induction of apoptosis was further confirmed by showing that CMT-3 induces activation of caspase-3 and caspase-9 in HMC-1 cells. Additionally, CMT-3 induced downregulation of the expression of antiapoptotic Bcl-2 protein in HMC-1 cells. Compared to doxycycline, the antiproliferative and proapoptotic effects of different CMTs were clearly more pronounced. Of the studied CMTs, CMT-3 and CMT-8 appeared to be the most potent inhibitors of mast cell proliferation and survival. The present results show that CMTs have an antiproliferative and proapoptotic effect on both malignant and non-malignant mast cells. In conclusion, CMTs could offer a novel means to treat disorders with inappropriate expansion of mast cells, such as rheumatoid arthritis and systemic mast cell diseases.

Role and function of matrix metalloproteinases in the differentiation and biological characterization of mesenchymal stem cells

Matrix metalloproteinases (MMPs), known as matrixins, are Ca- and Zn-dependent endoproteinases involved in a wide variety of developmental and disease-associated processes, proving to be crucial protagonists in many physiological and pathological mechanisms. The ability of MMPs to alter, by limited proteolysis and through the fine control of tissue inhibitors of metalloproteinases, the activity or function of numerous proteins, enzymes, and receptors suggests that they are also involved in various important cellular functions during development. In this review, we focus on the differentiation of mesenchymal stem cells (including those of the myoblastic, osteoblastic, chondroblastic, neural, and apidoblastic lineages) and the possible, if unexpected, biological significance of MMPs in its regulation. The MMP system has been implicated in several differentiation events that suggests that it mediates the proliferative and prodifferentiating effect of the matrixin proteolytic cascade. We summarize these regulatory effects of MMPs on the differentiation of mesenchymal stem cells and hypothesize on the function of MMPs in the stem cell differentiation processes.