Divergent roles of nitrergic and prostanoid pathways in chronic joint inflammation

Electroporation-enhanced transdermal diclofenac sodium delivery into the knee joint in a rat model of acute arthritis

Purpose

Since electroporation (EP) can increase the permeability of biological membranes, we hypothesized that it offers an opportunity to enhance the transdermal delivery of drugs for intra-articular indications. Our aim was to compare the anti-inflammatory and analgesic efficacy of EP-combined topical administration of diclofenac sodium hydrogel (50 mg mL^-1 in 230 µL volume) with that of an equivalent dose of oral (75 mg kg^-1) and simple topical administration.

Methods

Arthritis was induced with the injection of 2% λ-carrageenan and 4% kaolin into the right knee joints of male Sprague Dawley rats. EP was applied for 8 min with 900 V high-voltage pulses for 5 ms followed by a 20 ms break. Drug penetration into the synovial fluid and plasma was detected by high-performance liquid chromatography. Leukocyte-endothelial interactions were visualized by intravital videomicroscopy on the internal surface of the synovium. Inflammation-induced thermal and mechanical hyperalgesia reactions, knee joint edema, and inflammatory enzyme activities were assessed at 24 and 48 h after arthritis induction.

Results

EP significantly increased the plasma level of diclofenac as compared with the topical controls 10 min after the 2% λ-carrageenan and 4% kaolin injection. Increased leukocyte-endothelial interactions were accompanied by joint inflammation, which was significantly reduced by oral and EP diclofenac (by 45% and by 30%, respectively) and only slightly ameliorated by simple topical diclofenac treatment (by 18%). The arthritis-related secondary hyperalgesic reactions were significantly ameliorated by oral and EP-enhanced topical diclofenac treatments. The knee cross-section area (which increased by 35%) was also reduced with both approaches. However, simple topical application did not influence the development of joint edema and secondary hyperalgesia.

Conclusion

The study provides evidence for the first time of the potent anti-inflammatory and analgesic effects of EP-enhanced topical diclofenac during arthritis. The therapeutic benefit provided by EP is comparable with that of oral diclofenac; EP is a useful alternative to conventional routes of administration.

Effect of fucoxanthin alone and in combination with D-glucosamine hydrochloride on carrageenan/kaolin-induced experimental arthritis in rats

The objective of the present study was to investigate the effect of the fucoxanthin (FUCO) alone and in combination with glucosamine hydrochloride (GAH) on carrageenan/kaolin-induced inflammatory arthritis model in rats and to explore its underlying mechanisms. Joint swelling, muscle weight ratio (%), histopathological examination and scoring, and proteoglycan degradation were examined. Pro-inflammatory interleukin (IL-1β) and tumor necrosis (TNF-α) levels, cyclooxygenase-2 (COX-2), and inducible nitric oxide synthase(iNOS) protein expression and nitric oxide (NO) level in knee synovial tissue extract were analyzed using enzyme-linked immunosorbent assay, western blotting analysis, and Griess reagent assay, respectively. FUCO and FUCO + GAH not only may significantly reduce degrees of knee joint swelling and prevent against muscle atrophy, but also may significantly attenuate inflammation in synovial tissue, cartilage erosion, and proteoglycan loss. The efficacies of FUCO + GAH were stronger than that of GAH or FUCO. FUCO alone and FUCO + GAH can significantly inhibit upregulation of COX-2 and iNOS protein expressions, decrease of IL-1β and TNF-α levels, and reduce NO production in knee synovial tissue extract. These results indicated that FUCO is an effective anti-arthritis agent through an antiinflammation mechanism. FUCO may enhance therapeutic effect of GAH on rat arthritis through mechanism of antiinflammation.

Angiotensin II Type 1 receptor blockade protects endothelium-derived hyperpolarising factor-mediated relaxation in a rat model of monoarthritis

AIMS

Rheumatoid arthritis (RA) is associated with high cardiovascular mortality. Impaired endothelial cell (EC) function and elevated angiotensin II levels may be central to the link between vascular dysfunction and RA. Here we investigated the action of angiotensin type 1 receptor (AT1R) blockade on endothelium-dependent relaxation of the isolated saphenous artery in a rat model of monoarthritis.

MAIN METHODS

Adjuvant arthritis was induced in rats with and without prophylactic losartan (AT1R antagonist) treatment. Vehicle-treated rats were used as controls. Wire myography was employed to investigate EC function of isolated rings of saphenous artery.

KEY FINDINGS

EC-dependent relaxation in arteries from non-inflamed control rats was mediated by both nitric oxide (NO) and endothelium-derived hyperpolarising factor (EDHF) with the EDHF response dependent principally on functional myoendothelial gap junctions. While NO-dependent relaxation remained unaffected, the EDHF-mediated response was abolished in arteries from arthritic rats (P<0.001), however, substantial protection (approximately 50%) of the EDHF-relaxation was found in arthritic rats treated with losartan (P<0.01). Thus, the attenuated EDHF response found in the saphenous artery of arthritic rats was significantly reversed by AT1R blockade.

SIGNIFICANCE

These results suggest a key role for the angiotensin system in the EC dysfunction found in chronic joint inflammation and highlights AT1R as a potential therapeutic target to redress the vascular impairment and mortality associated with RA.

Interdicting protease-activated receptor-2-driven inflammation with cell-penetrating pepducins

Protease-activated receptor-2 (PAR2), a cell surface receptor for trypsin-like proteases, plays a key role in a number of acute and chronic inflammatory diseases of the joints, lungs, brain, gastrointestinal tract, and vascular systems. Despite considerable effort by the pharmaceutical industry, PAR2 has proven recalcitrant to targeting by small molecule inhibitors, which have been unable to effectively prevent the interaction of the protease-generated tethered ligand with the body of the receptor. Here, we report the development of first-in-class cell-penetrating lipopeptide "pepducin" antagonists of PAR2. The design of the third intracellular (i3) loop pepducins were based on a structural model of a PAR2 dimer and by mutating key pharmacophores in the receptor intracellular loops and analogous pepducins. Individual pharmacophores were identified, which controlled constitutive, agonist, and antagonist activities. This approach culminated in the identification of the P2pal-18S pepducin which completely suppressed trypsin and mast cell tryptase signaling through PAR2 in neutrophils and colon cancer cells. The PAR2 pepducin was highly efficacious in blocking PAR2-dependent inflammatory responses in mouse models. These effects were lost in PAR2-deficient and mast-cell-deficient mice, thereby validating the specificity of the pepducin in vivo. These data provide proof of concept that PAR2 pepducin antagonists may afford effective treatments of potentially debilitating inflammatory diseases and serve as a blueprint for developing highly potent and specific i3-loop-based pepducins for other G protein-coupled receptors (GPCRs).

Can L(+)-lactate be used as a marker of experimentally induced inflammation in rats?

OBJECTIVE

The purpose of this study was to investigate if L(+)-lactate (lactate) can be used as a marker of progression of joint inflammation in comparison with a reference marker, prostaglandin E2 (PGE(2)), and to analyse implications for drug treatments.

MATERIALS AND METHODS

The assessment of the inflammation time course and the treatment efficacy studies were performed on two occasions. At specific time points, synovial fluid was extracted from Sprague-Dawley rats (n = 87) challenged with either carrageenan (Cg) or Freund's complete adjuvant (FCA) or from six non-inflamed rats. Naproxen (7.5 or 30 micromol/kg) or rofecoxib (30 micromol/kg) was administered per os 2 h post Cg or at 48 h post FCA. Levels of PGE(2) and lactate were assessed either by immuno-assay or by colorimetric assay.

RESULTS

Increased levels of both markers were detected following Cg or FCA injection. Pharmacological treatments resulted in lower concentrations of PGE(2) whereas levels of lactate remained unaffected compared to the vehicle-treated group.

CONCLUSION

Our results suggest that lactate may be useful as an additional biomarker of inflammatory processes, especially for monitoring the non-cox-inhibitor sensitive cascade.

Oral phosphatidylcholine pretreatment alleviates the signs of experimental rheumatoid arthritis

INTRODUCTION

Phosphatidylcholine and phosphatidylcholine-derived metabolites exhibit anti-inflammatory properties in various stress conditions. We hypothesized that dietary phosphatidylcholine may potentially function as an anti-inflammatory substance and may decrease inflammatory activation in a chronic murine model of rheumatoid arthritis (collagen-induced arthritis).

METHODS

The experiments were performed on male DBA1/J mice. In groups 1 to 3 (n = 10 each), collagen-induced arthritis was induced by administration of bovine collagen II. In group 2 the animals were fed ad libitum with phosphatidylcholine-enriched diet as a pretreatment, while the animals of group 3 received this nourishment as a therapy, after the onset of the disease. The severity of the disease and inflammation-linked hyperalgesia were evaluated with semiquantitative scoring systems, while the venular leukocyte-endothelial cell interactions and functional capillary density were assessed by means of in vivo fluorescence microscopy of the synovial tissue. Additionally, the mRNA expressions of cannabinoid receptors 1 and 2, TNFalpha and endothelial and inducible nitric oxide synthase were determined, and classical histological analysis was performed.

RESULTS

Phosphatidylcholine pretreatment reduced the collagen-induced arthritis-induced hypersensitivity, and decreased the number of leukocyte-endothelial cell interactions and the extent of functional capillary density as compared with those of group 1. It also ameliorated the tissue damage and decreased inducible nitric oxide synthase expression. The expressions of the cannabinoid receptors and TNFalpha were not influenced by the phosphatidylcholine intake. Phosphatidylcholine-enriched food administrated as therapy failed to evoke the aforementioned changes, apart from the reduction of the inducible nitric oxide synthase expression.

CONCLUSIONS

Phosphatidylcholine-enriched food as pretreatment, but not as therapy, appears to exert beneficial effects on the morphological, functional and microcirculatory characteristics of chronic arthritis. We propose that oral phosphatidylcholine may be a preventive approach in ameliorating experimental rheumatoid arthritis-induced joint damage.

Quantitative assessment of synovial vascularity using contrast-enhanced power Doppler ultrasonography: correlation with histologic findings and mr imaging findings in arthritic rabbit knee model

Objective

To validate contrast-enhanced power Doppler ultrasonography (PD US) for the evaluation of synovial vascularity in an arthritic rabbit knee model in correlation with MR and histological findings.

Materials and Methods

Power Doppler ultrasonography was performed for carrageenin-induced arthritic left knee and control right knee of 13 rabbits, first without and then with sonic contrast agent enhancement (Levovist, Schering, Berlin Germany), followed by gadolinium-enhanced MR imaging. Synovial vascularity was quantitatively assessed by calculating the color pixel area in power Doppler sonography using a computer-aided image analysis program and by grading the enhancement on MR images: grade 1, enhancement of knee joint is less than one-third of the area; grade 2, one-third to two-thirds enhancement; and grade 3, more than two-thirds enhancement. Microvessel density (MVD) was measured on slides stained immunohistochemically for CD31 antigen for histological assessment.

Results

The mean area of color pixels in PD US changed from 4.37 to 16.42 mm² in the arthritic knee after enhancement (p < 0.05), whereas it changed from 0.77 to 2.31 mm² in the control knee (p < 0.05). Arthritic knees had greater power Doppler signal than control knees both before and after contrast administration (p < 0.05). The average MVD was 88 in arthritic knees and 46 in control knees. MVDs correlated with color pixel areas of contrast-enhanced power Doppler imaging in arthritic knees. In MR grading of arthritic knees, five were grade 2 and eight were grade 3. MVD and PD US revealed no significant difference between grade 2 and 3 arthritic knees (p > 0.05).

Conclusion

Sonic contrast-enhanced PD US improves the visualization of synovial vascularity and allows quantitative measurement in experimentally induced rabbit arthritic knees.

The arthritis severity quantitative trait loci Cia4 and Cia6 regulate neutrophil migration into inflammatory sites and levels of TNF-alpha and nitric oxide

Neutrophils are required for the development of arthritis, and their migration into the synovial tissue coincides with the onset of clinical disease. Synovial neutrophil numbers also correlate with rheumatoid arthritis disease activity and severity. We hypothesized that certain arthritis severity genes regulate disease via the regulation of neutrophil migration into the joint. This hypothesis was tested in the synovial-like air pouch model injected with carrageenan using arthritis-susceptible DA and arthritis-resistant F344 rats. DA had nearly 3-fold higher numbers of exudate neutrophils compared with F344 (p < 0.001). Five DA.F344(QTL) strains congenic for severity loci and protected from autoimmune arthritis were studied. Only DA.F344(Cia4) (chromosome 7) and DA.F344(Cia6) (chromosome 8) congenics had significantly lower exudate neutrophil counts compared with DA. TNF-alpha levels were 2.5-fold higher in DA exudates as compared with F344 exudates, and that difference was accounted for by the Cia4 locus. Exudate levels of NO, a known inhibitor of neutrophil chemotaxis, were higher in F344, compared with DA, and that difference was accounted for by Cia6. This is the first time that non-MHC autoimmune arthritis loci are found to regulate three central components of the innate immune response implicated in disease pathogenesis, namely neutrophil migration into an inflammatory site, as well as exudate levels of TNF-alpha and NO. These observations underscore the importance of identifying the Cia4 and Cia6 genes, and suggest that they should generate useful novel targets for development of new therapies.

Angiotensin II type 1 receptor as a novel therapeutic target in rheumatoid arthritis: in vivo analyses in rodent models of arthritis and ex vivo analyses in human inflammatory synovitis

OBJECTIVE

Angiotensin II (Ang II) is known to have proinflammatory actions, and Ang II type 1 (AT(1)) receptors are up-regulated in the rheumatoid synovium, suggesting that this receptor could be a therapeutic target. The purpose of this study was to investigate the antiinflammatory potential of the selective AT(1) receptor antagonist losartan, which is currently used for the treatment of cardiovascular disease.

METHODS

Dose-ranging studies of losartan (1-50 mg/kg) were initially conducted in a rat model of acute (carrageenan/kaolin) arthritis, with subsequent evaluation in a rat model of adjuvant-induced arthritis (Freund's complete adjuvant). Losartan (10(-10) to 10(-6)M) was further tested ex vivo in human inflammatory synovitis, using collagenase-digested synovium.

RESULTS

Western blot and immunohistochemical analyses both revealed a substantial increase in AT(1) receptor protein content in synovium from acutely and chronically inflamed rat knee joints. Similarly, synovial Ang I/II protein content was elevated during inflammation. Losartan inhibited acute joint inflammation in a dose-dependent manner, with 15 mg/kg being the optimal dose (and used in subsequent studies). Both prophylactic and therapeutic administration of 15 mg/kg of losartan substantially reduced knee joint swelling in rats with adjuvant monarthritis (> or =50%; P < 0.0001). Losartan also suppressed tumor necrosis factor alpha generation from inflamed human synovium in a dose-dependent manner (P < 0.05).

CONCLUSION

Targeting the angiotensin pathway, particularly AT(1) receptors, could have significant therapeutic potential. Randomized placebo-controlled trials are now warranted to establish the extent to which angiotensin receptor blockers may provide antiinflammatory benefits.