Chemically modified tetracyclines selectively inhibit IL-6 expression in osteoblasts by decreasing mRNA stability

Network pharmacology integrated with experimental verification reveals the antipyretic characteristics and mechanism of Zi Xue powder

CONTEXT

Zi Xue Powder (ZXP) is a traditional formula for the treatment of fever. However, the potential mechanism of action of ZXP remains unknown.

OBJECTIVE

This study elucidates the antipyretic characteristics of ZXP and the mechanism by which ZXP alleviates fever.

MATERIALS AND METHODS

The key targets and underlying fever-reducing mechanisms of ZXP were predicted using network pharmacology and molecular docking. The targets of ZXP anti-fever active ingredient were obtained by searching TCMSP, STITCH and HERB. Moreover, male Sprague-Dawley rats were randomly divided into four groups: control, lipopolysaccharide (LPS), ZXP (0.54, 1.08, 2.16 g/kg), and positive control (acetaminophen, 0.045 g/kg); the fever model was established by intraperitoneal LPS injection. After the fever model was established at 0.5 h, the rats were administered treatment by gavage, and the anal temperature changes of each group were observed over 10 h after treatment. After 10 h, ELISA and Western blot analysis were used to further investigate the mechanism of ZXP.

RESULTS

Network pharmacology analysis showed that MAPK was a crucial pathway through which ZXP suppresses fever. The results showed that ZXP (2.16 g/kg) decreased PGE2, CRH, TNF-a, IL-6, and IL-1β levels while increasing AVP level compared to the LPS group. Furthermore, the intervention of ZXP inhibited the activation of MAPK pathway in LPS-induced fever rats.

CONCLUSIONS

This study provides new insights into the mechanism by which ZXP reduces fever and provides important information and new research ideas for the discovery of antipyretic compounds from traditional Chinese medicine.

Changes in Gut Microbiota Induced by Doxycycline Influence in Vascular Function and Development of Hypertension in DOCA-Salt Rats

Previous experiments in animals and humans show that shifts in microbiota and its metabolites are linked to hypertension. The present study investigates whether doxycycline (DOX, a broad-spectrum tetracycline antibiotic) improves dysbiosis, prevent cardiovascular pathology and attenuate hypertension in deoxycorticosterone acetate (DOCA)-salt rats, a renin-independent model of hypertension. Male Wistar rats were randomly assigned to three groups: control, DOCA-salt hypertensive rats, DOCA-salt treated with DOX for 4 weeks. DOX decreased systolic blood pressure, improving endothelial dysfunction and reducing aortic oxidative stress and inflammation. DOX decreased lactate-producing bacterial population and plasma lactate levels, improved gut barrier integrity, normalized endotoxemia, plasma noradrenaline levels and restored the Treg content in aorta. These data demonstrate that DOX through direct effects on gut microbiota and its non-microbial effects (anti-inflammatory and immunomodulatory) reduces endothelial dysfunction and the increase in blood pressure in this low-renin form of hypertension.

Effects of doxycycline on intestinal ischemia reperfusion injury induced by abdominal compartment syndrome in a rat model

BACKGROUND

Abdominal compartment syndrome (ACS) refers to organ dysfunction and ischemia resulting from intra-abdominal hypertension (IAH). Ischemia of the gut results in the triggering of a systemic inflammatory response by releasing cytokines which, in turn, causes capillary leakage leading to bowel edema, further increasing intra-abdominal pressure and resulting in a morbid cycle of ischemia and edema.

OBJECTIVE

The aim of this study was to determine the effects of doxycycline on intestinal ischemia reperfusion (I/R) injury in a rat model of ACS.

METHODS

Sprague-Dawley rats were divided into 5 equal groups. In groups 1 and 2, saline (1 cc IP) was administered during induction of ACS and intestinal samples were removed at 1 and 24 hours, respectively, after decompression. In groups 3 and 4, doxycycline (10 mg/kg IP) was injected during induction of ACS and, similarly, intestinal samples were removed at 1 and 24 hours after decompression. In the control group (group 5), intestinal samples were collected without induction of ACS. Malon-dialdehyde (MDA), interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, matrix metalloproteinase-2 (MMP-2), and tissue inhibitor of metalloproteinase-1 were studied and the apoptotic cells were enumerated histopathologically. Apoptosis and β-cell lymphoma 2 (βcl-2) expression were assessed immunohistochemically.

RESULTS

Thirty-five rats were evenly divided into 5 groups of 7 rats each. MDA, IL-1β, IL-6, TNF-α, and MMP-2 levels were significantly higher in group 1 one hour after the reperfusion period compared with the control group (P < 0.001, P < 0.001, P < 0.05, P < 0.001, and P < 0.01, respectively). The same parameters were significantly lower in group 3, in which doxycycline was administered, than in group 1 (P < 0.001, P < 0.05, P < 0.05, P < 0.001, and P < 0.01, respectively). However, there was no significant difference between groups 2 and 4 in the 24th hour (all, P > 0.05). The mean (SD) number of apoptotic cells and the expression of βcl-2 was highest in group 2 at 24 hours after the reperfusion period (92.5 [11.4] and 35.9 [5.0], respectively) and significantly greater than that in group 4 (P < 0.001 and P < 0.05, respectively).

CONCLUSION

Doxycycline was associated with protective effects against I/R injury through decreasing apoptosis via attenuating the response of proinflammatory cytokines and inhibiting the activity of MMP-2 in this rat model.

Immunoexpression of p38 Mitogen-Activated Proteinkinase in Patients with Aggressive and Chronic Periodontitis

The influence of p38 mitogen-activated proteinkinase (MAPK) expression in the development and progression of periodontal disease is currently under investigation. The aim of the present study is to investigate whether the p38 MAPK expression in gingival tissues correlates with IL-1β levels in gingival crevicular fluid (GCF). Twenty patients with generalized aggressive periodontitis (GAgP), 15 patients with generalized chronic periodontitis (GCP) and 10 healthy subjects (H) were enrolled in the study. Clinical data, gingival tissue biopsies and GCF samples were collected. The expression of p38 was investigated by immunohistochemistry. The levels of IL-1β in GCF were measured using ELISA. Mean clinical parameters and GCF volumes were statistically higher in patients with GAgP and GCP compared to H subjects. Higher levels of IL-1β were found in both periodontitis groups. The p38 expression was significantly increased in inflamed gingival tissues. There were no statistically significant differences in levels of IL-1β and p38 expression between subjects with GAgP and GCP. Our data support the hypothesis that MAPK signaling pathway is an additional player in the pathogenesis of periodontitis. This is the first report to evaluate the involvement of p38 MAPK in patients with GAgP and GCP which might be, in part, considered of value in understanding disease mechanisms.

Therapeutic strategies in the treatment of periodontitis

Periodontitis is a chronic inflammatory process which affects the tooth - supporting structures of the teeth. The disease is initiated by subgingival periopathogenic bacteria in susceptible periodontal sites. The host immune response towards periodontal pathogens helps to sustain periodontal disease and eventual alveolar bone loss. Although scaling and root planing is the standard treatment modality for periodontitis, it suffers from several drawbacks such as the inability to reach the base of deep pockets and doesn’t arrest migration of periodontal pathogens from other sites in the oral cavity. In order to overcome the limitations of scaling and root planning, adjunctive chemotherapeutics and host modulatory agents to the treatment are used. These therapeutic agents show substantial beneficial effects when compared to scaling and root planning alone. This review will cover an update on chemotherapeutic and past and future host immune modulatory agents used adjunctively to treat and manage periodontal diseases.

Jack of all trades: pleiotropy and the application of chemically modified tetracycline-3 in sepsis and the acute respiratory distress syndrome (ARDS)

Sepsis is a disease process that has humbled the medical profession for centuries with its resistance to therapy, relentless mortality, and pathophysiologic complexity. Despite 30 years of aggressive, concerted, well-resourced efforts the biomedical community has been unable to reduce the mortality of sepsis from 30%, nor the mortality of septic shock from greater than 50%. In the last decade only one new drug for sepsis has been brought to the market, drotrecogin alfa-activated (Xigris™), and the success of this drug has been limited by patient safety issues. Clearly a new agent is desperately needed. The advent of recombinant human immune modulators held promise but the outcomes of clinical trials using biologics that target single immune mediators have been disappointing. The complex pathophysiology of the systemic inflammatory response syndrome (SIRS) is self-amplifying and redundant at multiple levels. In this review we argue that perhaps pharmacologic therapy for sepsis will only be successful if it addresses this pathophysiologic complexity; the drug would have to be pleiotropic, working on many components of the inflammatory cascade at once. In this context, therapy that targets any single inflammatory mediator will not adequately address the complexity of SIRS. We propose that chemically modified tetracycline-3, CMT-3 (or COL-3), a non-antimicrobial modified tetracycline with pleiotropic anti-inflammatory properties, is an excellent agent for the management of sepsis and its associated complication of the acute respiratory distress syndrome (ARDS). The purpose of this review is threefold: (1) to examine the shortcomings of current approaches to treatment of sepsis and ARDS in light of their pathophysiology, (2) to explore the application of COL-3 in ARDS and sepsis, and finally (3) to elucidate the mechanisms of COL-3 that may have potential therapeutic benefit in ARDS and sepsis.

Role of mitogen-activated protein kinase in osteoblast differentiation

Local control of osteoblast differentiation and bone formation is not well understood. We have previously seen biphasic effects on cell differentiation in response to the short- and long-term exposure to IL-1β in rat calvarial osteoblasts. To characterize the signaling pathway mechanisms regulating IL-1β biphasic effects, we examined the contribution of mitogen-activated protein kinase (MAPK) family. Cells were pretreated with specific inhibitors to extracellular signal-regulated kinase (ERK, PD98059), p38 (SB203580), and c-JUN N-terminal kinase (JNK, SP600125), then co-cultured with IL-1β for 2, 4, and 6 days. Cell differentiation was determined by measuring bone nodules after 10 days of culture. These inhibitors did not alter biphasic effects of IL-1β on cell differentiation. However, PD98059 and U2016, another inhibitor of ERK activation robustly increased osteoblast differentiation compared to vehicle-treated control in a time- and dose-dependent manner. PD98059 appears to stimulate alkaline phosphatase (ALP) activity to promote cell differentiation, where IL-1β appears to suppress it. Interestingly, continuous ERK inhibition with PD98059, after 2 and 4 days of IL-1β treatment, enhanced the IL-1β anabolic effect by increasing bone nodules formed. These observations provide a potential mechanism involving ERK pathway in osteoblasts differentiation and suggest that MAPK family may not directly regulate IL-1β biphasic effects.

Using tetracyclines to treat osteoporotic/osteopenic bone loss: from the basic science laboratory to the clinic

Periodontitis (progressive inflammatory disease characterized by alveolar bone loss, a major cause of tooth loss worldwide) is associated with both systemic osteoporosis and its milder form, osteopenia. Tetracyclines, by virtue of their non-antimicrobial pro-anabolic and anti-catabolic properties, are excellent candidate pharmaceuticals to simultaneously treat these local and systemic disorders. This paper reviews the foundational basic science and translational research which lead to a pivotal multicenter randomized clinical trial in postmenopausal women with both periodontitis and systemic (skeletal) osteopenia. This trial was designed primarily to examine whether subantimicrobial dose doxycycline (SDD) could reduce progressive alveolar (oral) bone loss associated with periodontitis and, secondarily, whether SDD could reduce systemic bone loss in the same subjects. This paper describes the efficacy and safety findings from this clinical trial and also outlines future directions using this promising and novel approach to manage both oral and systemic bone loss.

Rapid non-genomic effects of glucocorticoids on oxidative stress in a guinea pig model of asthma

BACKGROUND AND OBJECTIVE

Glucocorticoids (GC) may exert therapeutic effects in asthma by a rapid non-genomic mechanism. The lungs of asthmatic patients are exposed to oxidative stress, which is believed to be critical in the pathogenesis of asthma. The aim of this study was to investigate whether GC exert a rapid non-genomic effect on oxidative stress in asthmatic guinea pigs.

METHODS

The guinea pig asthma model was used to assess inhibitory effects of budesonide (BUD) on oxidative stress. BAL fluid (BALF), trolox equivalent antioxidant capacity and lung manganese superoxide dismutase (MnSOD) activity were measured by spectrophotometry. Superoxide anion production was measured by cytochrome c reduction assay.

RESULTS

Oxidative stress occurred within minutes following antigen challenge and BUD reduced the severity of oxidative stress in asthmatic guinea pigs within 15 min. BUD significantly decreased BALF trolox equivalent antioxidant capacity and lung MnSOD activity, as compared with those of vehicle-treated asthmatic guinea pigs (P < 0.05). Additionally, BUD rapidly inhibited in vitro superoxide anion production by BALF cells and bronchi harvested from sensitized animals. These rapid effects were not blocked by the GC receptor antagonist RU486 and/or the protein synthesis inhibitor cycloheximide.

CONCLUSIONS

BUD reduced oxidative stress in a guinea pig model of asthma by a rapid non-genomic mechanism. These data suggest new mechanisms whereby GC treatments may benefit asthma.

Tetracycline suppresses ATP gamma S-induced CXCL8 and CXCL1 production by the human dermal microvascular endothelial cell-1 (HMEC-1) cell line and primary human dermal microvascular endothelial cells

Tetracyclines (TCN) have powerful anti-inflammatory properties in addition to their anti-microbial effects. These anti-inflammatory effects are thought to play a role in inhibiting cutaneous inflammation in patients with rosacea and acne; however, the mechanism(s) of this action remains poorly understood. We have previously shown that adenosine-5'-triphosphate (ATP)gamma S, a hydrolysis-resistant ATP analogue, augments secretion of pro-inflammatory messengers by a human dermal microvascular endothelial cell line (HMEC-1). ATP released by the sympathetic nerves during stress may stimulate release of pro-inflammatory chemokines by dermal vessel endothelial cells, resulting in recruitment of inflammatory cells and exacerbation of inflammatory skin disease. Here we demonstrate that TCN inhibits ATP gamma S-induced release of pro-inflammatory mediators by HMEC-1 cells and primary human dermal microvascular endothelial cells. TCN dose-dependently inhibited ATP gamma S-induced augmentation of CXCL8 (interleukin-8) and CXCL1 (growth-regulated oncogene-alpha) production by HMEC-1 cells and primary human dermal endothelial cells in vitro. TCN and ATP gamma S did not affect HMEC-1 cell viability as determined by trypan-blue exclusion and cell counts. Inhibition of production of inflammatory mediators by endothelial cells may be one mechanism by which TCN improves inflammatory skin diseases. The ability to inhibit release of inflammatory mediators induced in HMEC-1 cells by purinergic agonists may be a useful way to screen for potential therapeutic agents for cutaneous inflammation.

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.

A p38 mitogen-activated protein kinase inhibitor arrests active alveolar bone loss in a rat periodontitis model

BACKGROUND

Gram-negative bacterial species, such as Actinobacillus actinomycetemcomitans, contain lipopolysaccharide (LPS) that initiates the innate immune system, resulting in inflammatory alveolar bone loss. LPS activates Toll-like receptors on membrane surfaces, stimulating many intracellular signaling cascades, including the p38 mitogen-activated protein kinase (MAPK). Activation of p38 signaling mediates inflammatory cytokine expression, contributing toward osteoclastogenesis and bone loss. The aim of this study was to determine whether the novel, orally active p38 MAPK inhibitor SD282 could arrest progression of LPS-induced alveolar bone destruction in rats.

METHODS

Three groups of female Sprague-Dawley rats received LPS injections to the palatal molar gingiva three times per week for 4 weeks to establish periodontitis. From weeks 5 through 8, two groups received the drug SD282 (N = 14) or 1% polyethylene glycol drug vehicle (N = 14) via oral gavage in addition to LPS injections. The third group continued to receive only LPS injections (N = 8). Microcomputed tomography was used to measure volumetric alveolar bone loss, expressed as bone volume fraction (BVF). Expression of interleukin (IL)-1 and -6 and tumor necrosis factor-alpha (TNF-alpha) was assessed by immunohistochemistry, and osteoclasts were enumerated by tartrate-resistant acid phosphatase staining.

RESULTS

By 4 weeks, severe alveolar bone resorption was seen in LPS-injected animals. Administration of SD282 significantly blocked additional volumetric bone loss in the LPS-only versus LPS + SD282 groups (0.37 +/- 0.01 BVF versus 0.43 +/- 0.01 BVF; P < 0.01). Significant reductions in IL-1beta (P < 0.01 ), TNF-alpha (P < 0.05), and osteoclast formation (P < 0.01) occurred in the presence of SD282.

CONCLUSIONS

An orally active p38 MAPK inhibitor reduced LPS-induced inflammatory cytokine expression, osteoclastogenesis, and alveolar bone loss in rats. Within the limits of the current study, SD282 arrested periodontal disease progression, thus highlighting the therapeutic potential of this novel class of inhibitors.

Efficacy of sub-antimicrobial dose doxycycline in post-menopausal women: clinical outcomes

AIMS

To determine the clinical efficacy of a 2-year continuous sub-antimicrobial dose doxycycline (SDD; 20 mg bid) in post-menopausal, osteopenic, oestrogen-deficient women on periodontal maintenance.

MATERIALS AND METHODS

One-hundred and twenty-eight subjects were randomized to SDD (n=64) or placebo (n=64). Clinical measurements were performed at posterior interproximal sites at baseline and every 6 months during this 2-year randomized, double-blind, placebo-controlled clinical trial with adjunctive, no-cost 3-4-month periodontal maintenance. Statistical analyses of secondary outcomes from this clinical trial used Generalized Estimating Equations in primarily intent-to-treat analyses.

RESULTS

For the placebo group, 3.4% of the sites showed improvement in clinical attachment levels (CAL) and 2.7% had progressive loss in CAL; for the SDD group, 5.0% of the sites showed an improvement in CAL and 2.2% had progressive loss in CAL. This difference (2.1% of sites) was more favourable in the SDD group than in the placebo [odds ratio (OR)=0.81 [corrected] 95% confidence interval (CI): 0.67-0.97, p=0.03] in these well-maintained patients, whereas probing depths, bleeding on probing and supragingival plaque did not differ significantly between groups (p>0.2). However, in exploratory subgroup analysis of non-smokers, SDD showed reduced bleeding versus placebo (27%versus 33%; p=0.05). In protocol-adherent subjects, the odds of bleeding were 34% lower for SDD (p=0.05).

CONCLUSIONS

Analyses of secondary outcomes of this clinical trial indicated that SDD may be of benefit in reducing progressive attachment loss in post-menopausal females; additional research is needed to confirm these findings. Protocol registered at (ClinicalTrials.gov). Identifier:NCT00066027.

Actinobacillus actinomycetemcomitans lipopolysaccharide induces interleukin-6 expression through multiple mitogen-activated protein kinase pathways in periodontal ligament fibroblasts

Actinobacillus actinomycetemcomitans plays a major role in the pathogenesis of aggressive periodontitis. Lipopolysaccharide (LPS) derived from A. actinomycetemcomitans is a key factor in inflammatory cytokine generation within periodontal tissues. In this study, we identify major mitogen-activated protein kinase (MAPK) signaling pathways induced by A. actinomycetemcomitans LPS, Escherichia coli LPS and interleukin-1beta (IL-1beta) in a murine periodontal ligament (mPDL) fibroblast cell line. Immunoblot analysis was used to assess the phosphorylated forms of p38, extracellular-regulated kinase (ERK) and c-jun N-terminal kinase (JNK) MAPK following stimulation with A. actinomycetemcomitans LPS, E. coli LPS and IL-1beta. IL-6 mRNA induction was detected via reverse transcription-polymerase chain reaction, while protein levels were quantified via enzyme-linked immunosorbent assays (ELISA). We utilized biochemical inhibitors of p38, ERK and JNK MAPK to identify the MAPK signaling pathways needed for IL-6 expression. Additional use of stable mPDL cell lines containing dominant negative mutant constructs of MAPK kinase-3 and -6 (MKK-3/6) and p38 null mutant mouse embryonic fibroblast (MEF) cells were used to substantiate the biochemical inhibitor data. Blocking p38 MAPK with SB203580 reduced the induction of IL-6 mRNA by A. actinomycetemcomitans LPS, E. coli LPS and IL-1beta by >70%, >95% and approximately 60%, respectively. IL-6 ELISA indicated that blocking p38 MAPK reduced the IL-6 protein levels induced by A. actinomycetemcomitans LPS, E. coli LPS and IL-1beta by approximately 60%, approximately 50% and approximately 70%, respectively. All MAPK inhibitors significantly reduced the IL-6 protein levels induced by A. actinomycetemcomitans LPS, E. coli LPS and IL-1beta whereas only p38 inhibitors consistently reduced the A. actinomycetemcomitans LPS, E. coli LPS and IL-1beta induction of IL-6 mRNA steady-state levels. The contribution of p38 MAPK LPS-induced IL-6 expression was confirmed using MKK-3/6 dominant negative stable mPDL cell lines. Wild-type and p38alpha(-/-) MEF cells provided additional evidence to support the role of p38alpha MAPK in A. actinomycetemcomitans LPS-stimulated IL-6. Our results indicate that induction of IL-6 by E. coli LPS, IL-1beta and A. actinomycetemcomitans LPS requires signaling through MKK-3-p38alpha ERK, JNK and p38 MAPK in mPDL cells.

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.

MKK3/6-p38 MAPK signaling is required for IL-1beta and TNF-alpha-induced RANKL expression in bone marrow stromal cells

Coupled bone turnover is directed by the expression of receptor-activated NF-kappaB ligand (RANKL) and its decoy receptor, osteoprotegerin (OPG). Proinflammatory cytokines, such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) induce RANKL expression in bone marrow stromal cells. Here, we report that IL-1beta and TNF-alpha-induced RANKL requires p38 mitogen-activating protein kinase (MAPK) pathway activation for maximal expression. Real-time PCR was used to assess the p38 contribution toward IL-1beta and TNF-alpha-induced RANKL mRNA expression. Steady-state RANKL RNA levels were increased approximately 17-fold by IL-1beta treatment and subsequently reduced approximately 70%-90% when p38 MAPK was inhibited with SB203580. RANKL mRNA stability data indicated that p38 MAPK did not alter the rate of mRNA decay in IL-1beta-induced cells. Using a RANKL-luciferase cell line receptor containing a 120-kB segment of the 5' flanking region of the RANKL gene, reporter expression was stimulated 4-5-fold by IL-1beta or TNF-alpha treatment. IL-1beta-induced RANKL reporter expression was completely blocked with specific p38 inhibitors as well as dominant negative mutant constructs of MAPK kinase-3 and -6. In addition, blocking p38 signaling in bone marrow stromal cells partially inhibited IL-1beta and TNF-alpha-induced osteoclastogenesis in vitro. Results from these studies indicate that p38 MAPK is a major signaling pathway involved in IL-1beta and TNF-alpha-induced RANKL expression in bone marrow stromal cells.

A p38alpha selective mitogen-activated protein kinase inhibitor prevents periodontal bone loss

In the oral microbial environment, Gram-negative bacterial derived lipopolysaccharide (LPS) can initiate inflammatory bone loss as seen in periodontal diseases. p38 Mitogen-activated protein kinase (MAPK) signaling is critical to inflammatory cytokine and LPS-induced cytokine expression, which may contribute toward periodontal bone loss. The purpose of this proof-of-principle study was to evaluate the ability of an orally active p38alpha MAPK inhibitor (SD-282) to reduce periopathogenic LPS-induced alveolar bone loss in an experimental rat model. Five groups of Sprague-Dawley rats received one of the following treatments: LPS injected to the palatal gingiva adjacent to the maxillary molars three times per week for 8 weeks, LPS plus two doses of SD-282 (15 or 45 mg/kg) twice daily by oral gavage, or control groups given drug vehicle (1% polyethylene glycol) or SD-282 (45 mg/kg) only. Baseline and 8-week alveolar bone loss was assessed by microcomputed tomography (microCT) and histological examination. LPS induced severe bone loss over this time period, whereas control groups were unchanged from baseline measurements. Both doses of SD-282 showed significant protection from LPS-induced bone loss. Bone area and volumetric analysis of maxillas by microCT indicated significant loss of bone volume with LPS treatment, which was blocked with the p38 inhibitor. Histological examination indicated significantly fewer tartate-resistant acid phosphatase-positive osteoclasts and a significant decrease in interleukin (IL)-6, IL-1beta, and tumor necrosis factor alpha expression in p38 inhibitor-treated groups compared with LPS groups by immunostaining. Results from this in vivo study suggest that orally active p38 MAPK inhibitors can reduce LPS-induced inflammatory cytokine production and osteoclast formation and protect against LPS-stimulated alveolar bone loss.

Posttranscriptional mechanisms regulating the inflammatory response

The inflammatory response is a complex physiologic process that requires the coordinate induction of cytokines, chemokines, angiogenic factors, effector-enzymes, and proteases. Although transcriptional activation is required to turn on the inflammatory response, recent studies have revealed that posttranscriptional mechanisms play an important role by determining the rate at which mRNAs encoding inflammatory effector proteins are translated and degraded. Most posttranscriptional control mechanisms function to dampen the expression of pro-inflammatory proteins to ensure that potentially injurious proteins are not overexpressed during an inflammatory response. Here we discuss the factors that regulate the stability and translation of mRNAs encoding pro-inflammatory proteins.

p38 MAPK regulates IL-1beta induced IL-6 expression through mRNA stability in osteoblasts

Osteoblast-derived IL-6 functions in coupled bone turnover by supporting osteoclastogenesis favoring bone resorption instead of bone deposition. Gene regulation of IL-6 is complex occurring both at transcription and post-transcription levels. The focus of this paper is at the level of mRNA stability, which is important in IL-6 gene regulation. Using the MC3T3-E1 as an osteoblastic model, IL-6 secretion was dose dependently decreased by SB203580, a p38 MAPK inhibitor. Steady state IL-6 mRNA was decreased with SB203580 (2 microM) ca. 85% when stimulated by IL-1beta (1-5 ng/ml). These effects require de novo protein synthesis as they were inhibited by cycloheximide. p38 MAPK had minor effects on proximal IL-6 promoter activity in reporter gene assays. A more significant effect on IL-6 mRNA stability was observed in the presence of SB203580. Western blot analysis confirmed that SB203580 inhibited p38 MAP kinase, in response to IL-1beta in a dose dependent manner in MC3T3-E1 cells. Stably transfected MC3T3-E1 reporter cell lines (MC6) containing green fluorescent protein (GFP) with the 3'untranslated region of IL-6 were constructed. Results indicated that IL-1beta, TNFalpha, LPS but not parathyroid hormone (PTH) could increase GFP expression of these reporter cell lines. Endogenous IL-6 and reporter gene eGFP-IL-6 3'UTR mRNA was regulated by p38 in MC6 cells. In addition, transient transfection of IL-6 3'UTR reporter cells with immediate upstream MAP kinase kinase-3 and -6 increased GFP expression compared to mock transfected controls. These results indicate that p38 MAPK regulates IL-1beta-stimulated IL-6 at a post transcriptional mechanism and one of the primary targets of IL-6 gene regulation is the 3'UTR of IL-6.

The healing of confined critical size cancellous defects in the presence of silk fibroin hydrogel

In vitro and in vivo behaviour of an injectable silk fibroin (SF) hydrogel was studied through osteoblast cultures and after implantation in critical-size defects of rabbit distal femurs. A commercial synthetic poly(D,L lactide-glycolide) copolymer was used as control material. In vitro biocompatibility was evaluated by measuring LDH release, cell proliferation (WST1), differentiation (ALP, OC), and synthetic activity (collagen I, TGF ss1, IL-6). Bone defect healing rate and quality of the newly formed bone inside the defects were determined in vivo by measuring trabecular bone volume (BV/TV), trabecular thickness (Tb.Th), trabecular number (Tb.N), trabecular separation (Tb.Sp), mineral apposition rate (MAR) and bone formation rate (BFR/B.Pm). In vitro tests indicated that both materials significantly increased cell proliferation in comparison with the negative control. A significant increase in the TGF-beta1 level was found for SF hydrogel in comparison with the control material and negative control. Both materials promoted bone healing when used to fill critical size defects in rabbit femurs. The new-formed bone of the SF hydrogel treated defects showed significantly higher BV/TV, Tb.Th, MAR and BFR/B.Pm and lower Tb.Sp values in comparison with the control gel. At 12 weeks the re-grown bone of the SF hydrogel-treated defects appeared more similar to normal bone than that of the control synthetic polymeric material-treated defects, except for the Tb.N value that differed significantly from that of normal bone (p<0.05). MAR and BFR/B.Pm presented significantly (p<0.05) higher values for SF hydrogel-treated defects in comparison with controls treated with a synthetic polymeric material, confirming that SF hydrogel accelerated remodelling processes.

Tetracycline Impregnation Delays Collagen Membrane Degradation In Vivo

BACKGROUND

Guided tissue and bone regeneration using bioabsorbable collagen membranes is a common practice. Collagen promotes progenitor cell adhesion, chemotaxis, homeostasis, and physiologic degradation with low immunogenicity, which makes it an ideal material for barrier preparation. Collagen membranes have to maintain integrity for a proper time, thus ensuring successful cell exclusion. Early collagen membrane degradation is detrimental for the success of regenerative procedures. This in vivo study was conducted to evaluate the effect of soaking collagen membranes in different tetracycline hydrochloride (TCN) concentration solutions on its degradation.

METHODS

Five mm disks of collagen membrane were soaked in either 100 mg/ml TCN (group 100) or 50 mg/ml TCN (group 50); a group of non-treated disks served as controls. All disks were labeled with aminohexanoyl-biotin-N-hydroxy-succinimide ester (biotin) and implanted in rat calvaria bone. Block sections were taken after 3 weeks and histological slides stained with horseradish peroxidase (HRP) to detect remnants of biotinylated collagen. Staining intensity was analyzed by image-analysis software taking quadruplicate measurements of a 500 microm2 area each. Data were analyzed using analysis of variance (ANOVA) with repeated measures and paired t test with Bonferroni correction.

RESULTS

Staining intensity of membranes in group 100 was > 5-fold higher than the control while group 50 exhibited > 11-fold higher intensity than the control and > 2.5-fold higher than the 100. All of these differences were statistically significant (P < 0.001).

CONCLUSION

Soaking collagen membranes in 50 mg/ml TCN solution is a useful, practical, and simple tool to slow membrane degradation.