Rat Plantar Fascia Stem/Progenitor Cells Showed Lower Expression of Ligament Markers and Higher Pro-Inflammatory Cytokines after Intensive Mechanical Loading or Interleukin-1ß Treatment In Vitro.

The pathogenesis of plantar fasciitis is unclear, which hampers the development of an effective treatment. The altered fate of plantar fascia stem/progenitor cells (PFSCs) under overuse-induced inflammation might contribute to the pathogenesis. This study aimed to isolate rat PFSCs and compared their stem cell-related properties with bone marrow stromal cells (BMSCs). The effects of inflammation and intensive mechanical loading on PFSCs' functions were also examined. We showed that plantar fascia-derived cells (PFCs) expressed common MSC surface markers and embryonic stemness markers. They expressed lower Nanog but higher Oct4 and Sox2, proliferated faster and formed more colonies compared to BMSCs. Although PFCs showed higher chondrogenic differentiation potential, they showed low osteogenic and adipogenic differentiation potential upon induction compared to BMSCs. The expression of ligament markers was higher in PFCs than in BMSCs. The isolated PFCs were hence PFSCs. Both IL-1ß and intensive mechanical loading suppressed the mRNA expression of ligament markers but increased the expression of inflammatory cytokines and matrix-degrading enzymes in PFSCs. In summary, rat PFSCs were successfully isolated. They had poor multi-lineage differentiation potential compared to BMSCs. Inflammation after overuse altered the fate and inflammatory status of PFSCs, which might lead to poor ligament differentiation of PFSCs and extracellular matrix degeneration. Rat PFSCs can be used as an in vitro model for studying the effects of intensive mechanical loading-induced inflammation on matrix degeneration and erroneous stem/progenitor cell differentiation in plantar fasciitis.

Mesenchymal stem cells alleviate dexamethasone-induced muscle atrophy in mice and the involvement of ERK1/2 signalling pathway.

BACKGROUND: High dosage of dexamethasone (Dex) is an effective treatment for multiple diseases; however, it is often associated with severe side effects including muscle atrophy, resulting in higher risk of falls and poorer life quality of patients. Cell therapy with mesenchymal stem cells (MSCs) holds promise for regenerative medicine. In this study, we aimed to investigate the therapeutic efficacy of systemic administration of adipose-derived mesenchymal stem cells (ADSCs) in mitigating the loss of muscle mass and strength in mouse model of DEX-induced muscle atrophy. METHODS: 3-month-old female C57BL/6 mice were treated with Dex (20 mg/kg body weight, i.p.) for 10 days to induce muscle atrophy, then subjected to intravenous injection of a single dose of ADSCs ([Formula: see text] cells/kg body weight) or vehicle control. The mice were killed 7 days after ADSCs treatment. Body compositions were measured by animal DXA, gastrocnemius muscle was isolated for ex vivo muscle functional test, histological assessment and Western blot, while tibialis anterior muscles were isolated for RNA-sequencing and qPCR. For in vitro study, C2C12 myoblast cells were cultured under myogenic differentiation medium for 5 days following 100 [Formula: see text]M Dex treatment with or without ADSC-conditioned medium for another 4 days. Samples were collected for qPCR analysis and Western blot analysis. Myotube morphology was measured by myosin heavy chain immunofluorescence staining. RESULTS: ADSC treatment significantly increased body lean mass (10-20%), muscle wet weight (15-30%) and cross-sectional area (CSA) (~ 33%) in DEX-induced muscle atrophy mice model and down-regulated muscle atrophy-associated genes expression (45-65%). Hindlimb grip strength (~ 37%) and forelimb ex vivo muscle contraction property were significantly improved (~ 57%) in the treatment group. Significant increase in type I fibres (~ 77%) was found after ADSC injection. RNA-sequencing results suggested that ERK1/2 signalling pathway might be playing important role underlying the beneficial effect of ADSC treatment, which was confirmed by ERK1/2 inhibitor both in vitro and in vivo. CONCLUSIONS: ADSCs restore the pathogenesis of Dex-induced muscle atrophy with an increased number of type I fibres, stronger muscle strength, faster recovery rate and more anti-fatigue ability via ERK1/2 signalling pathway. The inhibition of muscle atrophy-associated genes by ADSCs offered this treatment as an intervention option for muscle-associated diseases. Taken together, our findings suggested that adipose-derived mesenchymal stem cell therapy could be a new treatment option for patient with Dex-induced muscle atrophy.

Emerging role of lncRNAs in osteoarthritis: An updated review.

Osteoarthritis (OA) is a prevalent joint disease, which is associated with progressive articular cartilage loss, synovial inflammation, subchondral sclerosis and meniscus injury. The molecular mechanism underlying OA pathogenesis is multifactorial. Long non-coding RNAs (lncRNAs) are non-protein coding RNAs with length more than 200 nucleotides. They have various functions such as modulating transcription and protein activity, as well as forming endogenous small interfering RNAs (siRNAs) and microRNA (miRNA) sponges. Emerging evidence suggests that lncRNAs might be involved in the pathogenesis of OA which opens up a new avenue for the development of new biomarkers and therapeutic strategies. The purpose of this review is to summarize the current clinical and basic experiments related to lncRNAs and OA with a focus on the extensively studied H19, GAS5, MALAT1, XIST and HOTAIR. The potential translational value of these lncRNAs as therapeutic targets for OA is also discussed.

Green tea extract synergistically enhances the effectiveness of an antiresorptive drug on management of osteoporosis induced by ovariectomy in a rat model.

Antiresorptive drugs are effective for reducing bone loss in postmenopausal women, but their long-term application may be associated with adverse effects. The present study aimed to investigate the potential in vivo synergistic effects of green tea extract (GTE) and alendronate or raloxifene on the management of osteoporosis. Ovariectomized rats were fed orally with GTE, alendronate and raloxifene at different concentrations and various combinations for 4 weeks. Bone mineral density (BMD) at the lumbar spine, femur and tibia was monitored weekly using peripheral quantitative computed tomography. Bone microarchitecture in the left distal femur was analyzed using micro-CT, while serum biochemical levels were measured using ELISA kits at the end of the study. GTE alone effectively mitigated BMD loss and improved bone microarchitecture in rats. The co-administration of GTE and alendronate increased total BMD in the lumbar spine, femur and tibia. Particularly, GTE synergistically enhanced the effect of alendronate at a low dose on bone microarchitecture and decreased serum tartrate-resistant acid phosphatase. These findings imply that the dosage of certain antiresorptive agents could be reduced when they are administrated simultaneously with GTE, so that their adverse effects are minimized. The findings may be used to support the development of a new synergistic intervention between food therapy and pharmacotherapy on the management of osteoporosis in a long-term basis.

Topical application of Chinese herbal medicine DAEP relieves the osteoarthritic knee pain in rats.

BACKGROUND: The potential adverse effects of conventional oral pharmacotherapy of osteoarthritis (OA) restrict their long-term use. Topical application of a Chinese herbal paste for relieving OA knee pain can be effective and safe. However, evidence-based scientific research is insufficient to support its application worldwide. The aim of this study was to investigate the in vivo efficacy of a topical Chinese herbal paste on relieving OA knee pain and its underlying mechanism. METHODS: An OA rat model was developed by anterior cruciate ligament transection (ACLT) followed by treadmill running. A herbal paste including Dipsaci Radix, Achyranthis Bidentatae Radix, Eucommiae Cortex and Psoraleae Fructus, named as DAEP, was applied topically on the knee joint of the rats (DAEP). The rats without DAEP treatment served as Control. Rats with surgery but without ACLT, treadmill running and DAEP treatment acted as Sham. The morphologic change of the knee joint was observed radiographically. Nociception from the knee of the rats was assessed using Incapacitent test and CatWalk gait system. The therapeutic mechanism was investigated by analyzing the gene and protein expression of inflammatory markers via qPCR and Western blot, respectively. RESULTS: Radiographic images showed less destruction at the posterior tibial plateau of the DAEP group compared with the Control after 2 weeks of treatment. The static weight ratio and the gait parameters of the Control were reduced significantly via Incapacitance test and CatWalk gait analysis, respectively. DAEP treatment increased the Print Area and Maximum Intensity significantly compared with the Control. DAEP significantly suppressed the upregulation of gene expression of interleukin (IL)-6, tumor necrosis factor (TNF)-α, and inducible nitric oxide synthase (iNOS). CONCLUSIONS: DAEP exhibited its effect via the nuclear factor (NF)-κB pathway by suppressing the phosphorylation of IκB kinase αß (p-IKKαß) and cyclooxygenase-2 (COX-2) protein expression. This study provides scientific evidence to support the clinical application of the Chinese herbal paste on reliving OA pain.

Chinese topical herbal medicine gives additive effect on pharmaceutical agent on fracture healing.

OBJECTIVE: To investigate the efficacy on the combination of oral strontium ranelate (SrR) with a topical Chinese herbal paste on facilitation of fracture healing. METHODS: An open fracture was created at the mid-shaft of the right tibia of rat. A herbal paste called CDR containing Honghua (Flos Carthami), Chuanxuduan (Radix Dipsaci Asperoidis) and Dahuang (Radix Et Rhizoma Rhei Palmati) was prepared. The rats were treated with either CDR topically on the fracture site, or SrR orally, or their combinations. Bone turnover biochemical markers in serum were measured. Microarchitecture of the fracture was analyzed using micro-CT after 14 and 28 d, followed by histomorphometrical analysis. RESULTS: Micro-computed tomography analysis revealed that the combined treatment of CDR with 600 mg/g SrR significantly increased the total callus density, mineralized callus volume fraction, mineralized callus mineral content and mineralized callus density of the callus after 28 d of treatment. This result was consistent with the histomorphometrical analysis on the osteoid volume. Analysis of biochemical markers showed that the combined treatments reduced the bone resorption that occurs temporarily after fracture. CONCLUSION: This study demonstrated that the combined treatment of oral SrR and topical CDR is effective to promote fracture healing by their additive effect on promoting bone formation and retarding bone resorption.

Neuroprotective effect of Da Chuanxiong Formula against cognitive and motor deficits in a rat controlled cortical impact model of traumatic brain injury.

ETHNOPHARMACOLOGICAL RELEVANCE: Da Chuanxiong Formula (DCXF) is one of the famous herb pairs that contains dried rhizomes of Ligusticum chuanxiong Hort. and Gastrodia elata Bl. in the mass ratio of 4:1. This classic representative traditional Chinese medicine has been widely used to treat brain diseases like headache and migraine caused by blood stasis and wind pathogen. However, the therapeutic effect of DCXF on traumatic brain injury (TBI) has not been reported yet. AIM OF STUDY: The present study was performed to investigate the neuroprotective effects of DCXF and its underlying mechanisms in the controlled cortical impact (CCI)-induced TBI rat model. MATERIALS AND METHODS: Male Sprague-Dawley rats were divided into four groups: Sham, TBI control, 1X DCXF (520.6 mg/kg) and 5X DCXF (2603.0 mg/kg). Two treatment groups (1X and 5X DCXF) were intragastrically administered daily for 7 days before CCI-induced TBI and then DCXF treatments were continued post-TBI until the animal behavioral tests, including Morris water maze test, acceleration rotarod motor test and CatWalk quantitative gait analysis test, were done. The brain water content and blood brain barrier (BBB) integrity were measured by wet-dry weight method and Evans blue method, respectively. The number of neuron cells, neural stem cells (NSCs), GFAP positive cells (astrocyte) as well as Iba-1 positive cells (microglia) were determined by histology and immunohistochemistry. RESULTS: Treatment with DCXF significantly improved the learning ability and memory retention in Morris water maze test, and remarkably enhanced motor performances in acceleration rotarod motor test and catwalk quantitative gait analysis test after TBI. Moreover, DCXF treatment was able to reduce BBB permeability, brain edema, microglia and astrocyte activation, improve the proliferation of NSCs and decrease neurons loss in the brain with TBI. CONCLUSIONS: The present study demonstrated that DCXF treatment could decrease BBB leakage and brain edema, reduce neuron loss, microglia and astrocyte activation, and increase NSCs proliferation, which may contribute to the cognitive and motor protection of DCXF in the TBI rats. It is the first time to provide potentially underlying mechanisms of the neuroprotective effect of DCXF on TBI-induced brain damage and functional outcomes.

The roles of cellular and molecular components of a hematoma at early stage of bone healing.

Bone healing is a complex repair process that commences with the formation of a blood clot at the injured bone, termed hematoma. It has evidenced that a lack of a stable hematoma causes delayed bone healing or non-union. The hematoma at the injured bone constitutes the early healing microenvironment. It appears to dictate healing pathways that ends in a regenerative bone. However, the hematoma is often clinically removed from the damaged site. Conversely, blood-derived products have been used in bone tissue engineering for treating critical sized defects, including fibrin gels and platelet-rich plasma. A second generation of platelet concentrate that is based on leukocyte and fibrin content has also been developed and introduced in market. Conflicting effect of these products in bone repair are reported. We propose that the bone healing response becomes dysregulated if the blood response and subsequent formation and properties of a hematoma are altered. This review focuses on the central structural, cellular, and molecular components of a fracture hematoma, with a major emphasis on their roles in regulating bone healing mechanism, and their interactions with mesenchymal stem cells. New angles towards a better understanding of these factors and relevant mechanisms involved at the beginning of bone healing may help to clarify limited or adverse effects of blood-derived products on bone repair. We emphasize that the recreation of an early hematoma niche with critical compositions might emerge as a viable therapeutic strategy for enhanced skeletal tissue engineering.

Dihydrofisetin exerts its anti-inflammatory effects associated with suppressing ERK/p38 MAPK and Heme Oxygenase-1 activation in lipopolysaccharide-stimulated RAW 264.7 macrophages and carrageenan-induced mice paw edema.

Dihydrofisetin is a flavanonol derived from some edible wild herbs and traditional Chinese medicines. It has been found to possess many biological activities. However, the anti-inflammatory potential of Dihydrofisetin remains uncharacterized. The aim of the present study was to investigate the anti-inflammatory activity of Dihydrofisetin and its underlying mechanisms. We found that Dihydrofisetin dose-dependently inhibited lipopolysaccharide-induced productions of nitric oxide (NO) and prostaglandin E2 (PGE2) in RAW 264.7 macrophages, probably through suppressing the protein expressions of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). The expressions of pro-inflammatory cytokines, such as tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß), interleukin-6 (IL-6) and monocyte chemotactic protein (MCP-1) were also suppressed. We further demonstrated that Dihydrofisetin inhibited the activation of mitogen-activated protein kinases (MAPKs) pathway and phosphorylation of IκB-α whereas upregulated the expression of heme oxygenase-1 (HO-1). The in vivo carrageenan-induced mice paw edema study also indicated that treatment with 100 mg/kg of Dihydrofisetin could significantly inhibit carrageenan induced paw edema, decrease the levels of TNF-α, IL-6 and MDA, and increase the activity of GSH-Px in paw tissues. Taken together, Dihydrofisetin may act as a natural agent for treating inflammatory diseases by targeting MAPK, NF-κB and HO-1 pathways.

Evaluation of the combined use of metronomic zoledronic acid and Coriolus versicolor in intratibial breast cancer mouse model.

ETHNOPHARMACOLOGICAL RELEVANCE: Coriolus versicolor (CV) is a mushroom traditionally used for strengthening the immune system and nowadays used as immunomodulatory adjuvant in anticancer therapy. Breast cancer usually metastasizes to the skeleton, interrupts the normal bone remodeling process and causes osteolytic bone lesions. The aims of the present study were to evaluate its herb-drug interaction with metronomic zoledronate in preventing cancer propagation, metastasis and bone destruction. MATERIALS AND METHODS: Mice inoculated with human breast cancer cells tagged with a luciferase (MDA-MB-231-TXSA) in tibia were treated with CV aqueous extract, mZOL, or the combination of both for 4 weeks. Alteration of the luciferase signals in tibia, liver and lung were quantified using the IVIS imaging system. The skeletal response was evaluated using micro-computed tomography (micro-CT). In vitro experiments were carried out to confirm the in vivo findings. RESULTS: Results showed that combination of CV and mZOL diminished tumor growth without increasing the incidence of lung and liver metastasis in intratibial breast tumor model. The combination therapy also reserved the integrity of bones. In vitro studies demonstrated that combined use of CV and mZOL inhibited cancer cell proliferation and osteoclastogenesis. CONCLUSIONS: These findings suggested that combination treatment of CV and mZOL attenuated breast tumor propagation, protected against osteolytic bone lesion without significant metastases. This study provides scientific evidences on the beneficial outcome of using CV together with mZOL in the management of breast cancer and metastasis, which may lead to the development of CV as adjuvant health supplement for the control of breast cancer.

Integrative Approach to Facilitate Fracture Healing: Topical Chinese Herbal Paste with Oral Strontium Ranelate.

Strontium ranelate (SrR) is one of the pharmaceutical agents reported to be effective on the promotion of fracture healing. This study aimed to evaluate the integrative effect of the oral SrR with a topical Chinese herbal paste, namely, CDR, on facilitation of bone healing. The in vivo efficacy was evaluated using rats with tibial fracture. They were treated with either CDR topically, or SrR orally, or their combined treatments. The in vivo results illustrated a significant additive effect of CDR on SrR in increasing the yield load of the fractured tibia. The in vitro results showed that neither SrR nor CDR exhibited a cytotoxic effect on UMR106 and bone-marrow stem cell (BMSC), but both of them increased the proliferation of BMSC at low concentrations. The combination of CDR at 200 µg/mL with SrR at 200 or 400 µg/ml also showed an additive effect on increasing the ALP activity of BMSC. Both SrR and CDR alone reduced osteoclast formation, and the effective concentration of SrR to inhibit osteoclastogenesis was reduced in the presence of CDR. This integrative approach by combining oral SrR and topical CDR is effective in promoting fracture healing properly due to their additive effects on proosteogenic and antiosteoclastogenic properties.

A traditional Chinese formula composed of Chuanxiong Rhizoma and Gastrodiae Rhizoma (Da Chuanxiong Formula) suppresses inflammatory response in LPS -induced RAW 264.7 cells through inhibition of NF-κB pathway.

ETHNOPHARMACOLOGICAL RELEVANCE: Da Chuanxiong Formula (DCXF) which origins from Jin Dynasty is a famous classical 2-herb Chinese medicinal prescription. It is composed of dried rhizomes of Ligusticum chuanxiong (Chuanxiong Rhizoma, CR) and Gastrodia elata (Gastrodiae Rhizoma, GR) at the ratio of 4:1 (w/w). It has been used to treat headache which is caused by wind pathogen and blood stasis for thousands of years in China. AIM OF STUDY: The present study was performed to investigate the anti-inflammatory effect of DCXF and elucidate its underlying molecular mechanisms using LPS-stimulated RAW 264.7 cells. MATERIALS AND METHODS: The anti-inflammatory effect of DCXF was evaluated using LPS-stimulated RAW 264.7 cells. Generation of nitric oxide (NO) and prostaglandin E2 (PGE2) were measured by the Griess colorimetric method and enzyme-linked immunosorbent assay (ELISA), respectively. The gene expressions of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) were detected by reverse transcription-polymerase chain reaction (RT-PCR). Furthermore, the effect of DCXF on NF-κB activation was measured by western blot assay. RESULTS: Treatment with DCXF significantly suppressed the productions of NO and PGE2 through inhibitions of iNOS and COX-2 expressions in LPS-stimulated RAW 264.7 cells. DCXF significantly decreased IκBα phosphorylation, inhibited p65 expression and reduced p-p65 level. These results suggested the anti-inflammatory effect of DCXF was associated with the reduction of inflammatory mediators through inhibition of NF-κB pathway. CONCLUSIONS: These results indicated that DCXF inhibited inflammation in LPS-stimulated RAW 264.7 cells through inactivation of NF-κB pathway.

Cocoa tea (Camellia ptilophylla) water extract inhibits adipocyte differentiation in mouse 3T3-L1 preadipocytes.

Cocoa tea (Camellia ptilophylla) is a naturally decaffeinated tea plant. Previously we found that cocoa tea demonstrated a beneficial effect against high-fat diet induced obesity, hepatic steatosis, and hyperlipidemia in mice. The present study aimed to investigate the anti-adipogenic effect of cocoa tea in vitro using preadipocytes 3T3-L1. Adipogenic differentiation was confirmed by Oil Red O stain, qPCR and Western blot. Our results demonstrated that cocoa tea significantly inhibited triglyceride accumulation in mature adipocytes in a dose-dependent manner. Cocoa tea was shown to suppress the expressions of key adipogenic transcription factors, including peroxisome proliferator-activated receptor gamma (PPAR γ) and CCAAT/enhancer binding protein (C/EBP α). The tea extract was subsequently found to reduce the expressions of adipocyte-specific genes such as sterol regulatory element binding transcription factor 1c (SREBP-1c), fatty acid synthase (FAS), Acetyl-CoA carboxylase (ACC), fatty acid translocase (FAT) and stearoylcoenzyme A desaturase-1 (SCD-1). In addition, JNK, ERK and p38 phosphorylation were inhibited during cocoa tea inhibition of 3T3-L1 adipogenic differentiation. Taken together, this is the first study that demonstrates cocoa tea has the capacity to suppress adipogenesis in pre-adipocyte 3T3-L1 similar to traditional green tea.

Flavonoid Compound Icariin Activates Hypoxia Inducible Factor-1α in Chondrocytes and Promotes Articular Cartilage Repair.

Articular cartilage has poor capability for repair following trauma or degenerative pathology due to avascular property, low cell density and migratory ability. Discovery of novel therapeutic approaches for articular cartilage repair remains a significant clinical need. Hypoxia is a hallmark for cartilage development and pathology. Hypoxia inducible factor-1alpha (HIF-1α) has been identified as a key mediator for chondrocytes to response to fluctuations of oxygen availability during cartilage development or repair. This suggests that HIF-1α may serve as a target for modulating chondrocyte functions. In this study, using phenotypic cellular screen assays, we identify that Icariin, an active flavonoid component from Herba Epimedii, activates HIF-1α expression in chondrocytes. We performed systemic in vitro and in vivo analysis to determine the roles of Icariin in regulation of chondrogenesis. Our results show that Icariin significantly increases hypoxia responsive element luciferase reporter activity, which is accompanied by increased accumulation and nuclear translocation of HIF-1α in murine chondrocytes. The phenotype is associated with inhibiting PHD activity through interaction between Icariin and iron ions. The upregulation of HIF-1α mRNA levels in chondrocytes persists during chondrogenic differentiation for 7 and 14 days. Icariin (10-6 M) increases the proliferation of chondrocytes or chondroprogenitors examined by MTT, BrdU incorporation or colony formation assays. Icariin enhances chondrogenic marker expression in a micromass culture including Sox9, collagen type 2 (Col2α1) and aggrecan as determined by real-time PCR and promotes extracellular matrix (ECM) synthesis indicated by Alcian blue staining. ELISA assays show dramatically increased production of aggrecan and hydroxyproline in Icariin-treated cultures at day 14 of chondrogenic differentiation as compared with the controls. Meanwhile, the expression of chondrocyte catabolic marker genes including Mmp2, Mmp9, Mmp13, Adamts4 and Adamts5 was downregulated following Icariin treatment for 14 days. In a differentiation assay using bone marrow mesenchymal stem cells (MSCs) carrying HIF-1α floxed allele, the promotive effect of Icariin on chondrogenic differentiation is largely decreased following Cre recombinase-mediated deletion of HIF-1α in MSCs as indicated by Alcian blue staining for proteoglycan synthesis. In an alginate hydrogel 3D culture system, Icariin increases Safranin O positive (SO+) cartilage area. This phenotype is accompanied by upregulation of HIF-1α, increased proliferating cell nuclear antigen positive (PCNA+) cell numbers, SOX9+ chondrogenic cell numbers, and Col2 expression in the newly formed cartilage. Coincide with the micromass culture, Icariin treatment upregulates mRNA levels of Sox9, Col2α1, aggrecan and Col10α1 in the 3D cultures. We then generated alginate hydrogel 3D complexes incorporated with Icariin. The 3D complexes were transplanted in a mouse osteochondral defect model. ICRS II histological scoring at 6 and 12 weeks post-transplantation shows that 3D complexes incorporated with Icariin significantly enhance articular cartilage repair with higher scores particularly in selected parameters including SO+ cartilage area, subchondral bone and overall assessment than that of the controls. The results suggest that Icariin may inhibit PHD activity likely through competition for cellular iron ions and therefore it may serve as an HIF-1α activator to promote articular cartilage repair through regulating chondrocyte proliferation, differentiation and integration with subchondral bone formation.

Formation of blood clot on biomaterial implants influences bone healing.

The first step in bone healing is forming a blood clot at injured bones. During bone implantation, biomaterials unavoidably come into direct contact with blood, leading to a blood clot formation on its surface prior to bone regeneration. Despite both situations being similar in forming a blood clot at the defect site, most research in bone tissue engineering virtually ignores the important role of a blood clot in supporting healing. Dental implantology has long demonstrated that the fibrin structure and cellular content of a peri-implant clot can greatly affect osteoconduction and de novo bone formation on implant surfaces. This article reviews the formation of a blood clot during bone healing in relation to the use of platelet-rich plasma (PRP) gels. It is implicated that PRP gels are dramatically altered from a normal clot in healing, resulting in conflicting effect on bone regeneration. These results indicate that the effect of clots on bone regeneration depends on how the clots are formed. Factors that influence blood clot structure and properties in relation to bone healing are also highlighted. Such knowledge is essential for developing strategies to optimally control blood clot formation, which ultimately alter the healing microenvironment of bone. Of particular interest are modification of surface chemistry of biomaterials, which displays functional groups at varied composition for the purpose of tailoring blood coagulation activation, resultant clot fibrin architecture, rigidity, susceptibility to lysis, and growth factor release. This opens new scope of in situ blood clot modification as a promising approach in accelerating and controlling bone regeneration.

Controlling whole blood activation and resultant clot properties by carboxyl and alkyl functional groups on material surfaces: a possible therapeutic approach for enhancing bone healing.

Most research virtually ignores the important role of a blood clot in supporting bone healing. In this study, we investigated the effects of surface functional groups carboxyl and alkyl on whole blood coagulation, complement activation and blood clot formation. We synthesised and tested a series of materials with different ratios of carboxyl (-COOH) and alkyl (-CH3, -CH2CH3 and -(CH2)3CH3) groups. We found that surfaces with -COOH/-(CH2)3CH3 induced a faster coagulation activation than those with -COOH/-CH3 and -CH2CH3, regardless of the -COOH ratios. An increase in -COOH ratios on -COOH/-CH3 and -CH2CH3 surfaces decreased the rate of coagulation activation. The pattern of complement activation was entirely similar to that of surface-induced coagulation. All material coated surfaces resulted in clots with thicker fibrin in a denser network at the clot/material interface and a significantly slower initial fibrinolysis when compared to uncoated glass surfaces. The amounts of platelet-derived growth factor-AB (PDGF-AB) and transforming growth factor-ß (TGF-ß1) released from an intact clot were higher than a lysed clot. The release of PDGF-AB was found to be correlated with the fibrin density. This study demonstrated that surface chemistry can significantly influence the activation of blood coagulation and complement system, resultant clot structure, susceptibility to fibrinolysis as well as release of growth factors, which are important factors determining the bone healing process.