Informed development of a multi-species biofilm in chronic obstructive pulmonary disease

Recent evidence indicates that microbial biofilm aggregates inhabit the lungs of COPD patients and actively contribute towards chronic colonization and repeat infections. However, there are no contextually relevant complex biofilm models for COPD research. In this study, a meta-analysis of the lung microbiome in COPD was used to inform development of an optimized biofilm model composed of genera highly associated with COPD. Bioinformatic analysis showed that although diversity matrices of COPD microbiomes were similar to healthy controls, and internal compositions made it possible to accurately differentiate between these cohorts (AUC = 0.939). Genera that best defined these patients included Haemophilus, Moraxella and Streptococcus. Many studies fail to account for fungi; therefore, Candida albicans was included in the creation of an interkingdom biofilm model. These organisms formed a biofilm capable of tolerating high concentrations of antimicrobial therapies with no significant reductions in viability. However, combined therapies of antibiotics and an antifungal resulted in significant reductions in viable cells throughout the biofilm (p < 0.05). This biofilm model is representative of the COPD lung microbiome and results from in vitro antimicrobial challenge experiments indicate that targeting both bacteria and fungi in these interkingdom communities will be required for more positive clinical outcomes.

Destabilization of the Medial Meniscus and Cartilage Scratch Murine Model of Accelerated Osteoarthritis

Osteoarthritis is the most prevalent musculoskeletal disease in people over 45, leading to an increasing economic and societal cost. Animal models are used to mimic many aspects of the disease. The present protocol describes the destabilization and cartilage scratch model (DCS) of post-traumatic osteoarthritis. Based on the widely used destabilization of the medial meniscus (DMM) model, DCS introduces three scratches on the cartilage surface. The current article highlights the steps to destabilize the knee by transecting the medial meniscotibial ligament followed by three intentional superficial scratches on the articular cartilage. The possible analysis methods by dynamic weight-bearing, microcomputed tomography, and histology are also demonstrated. While the DCS model is not recommended for studies that focus on the effect of osteoarthritis on the cartilage, it enables the study of osteoarthritis development in a shorter time window, with special focus on (1) osteophyte formation, (2) osteoarthritic and injury pain, and (3) the effect of cartilage damage in the whole joint.

Losartan protects endothelium-dependent relaxation in vivo in a murine model of rheumatoid arthritis

Angiotensin II-type 1 receptor stimulation is recognised to promote inflammation, a state central to the development and maintenance of rheumatoid arthritis. Herein we examined the use of losartan, an angiotensin II-type 1 receptor antagonist, on vascular reactivity, knee joint diameter and behavioural assessment of pain in a Freund's complete adjuvant (FCA) mouse model of joint inflammation. Monoarthritis was induced via FCA in the presence or absence of losartan with naive mice serving as controls. Knee joint swelling, joint pain (assessed by dynamic weight bearing of limb use), knee joint artery reactivity (assessed ex vivo) and blood perfusion of the knee joint (assessed in vivo) were determined. FCA mediated a significant increase in knee joint diameter and reduced weight-bearing (a surrogate for pain sensation) of the affected limb. Notably, these phenomena were substantially reduced when mice were prophylactically treated with losartan. Assessment of arterial relaxation and blood perfusion with acetylcholine stimulation revealed that FCA resulted in significant vascular dysfunction, which was resolved to naïve levels with losartan treatment. Through the actions of losartan, these findings indicate that the angiotensin II-type 1 receptor is a likely therapeutic target of importance in the development of the physical changes, pain sensation and vascular dysfunction found in inflammatory arthritis.

Trypsin-Like Proteases and Their Role in Muco-Obstructive Lung Diseases

Trypsin-like proteases (TLPs) belong to a family of serine enzymes with primary substrate specificities for the basic residues, lysine and arginine, in the P1 position. Whilst initially perceived as soluble enzymes that are extracellularly secreted, a number of novel TLPs that are anchored in the cell membrane have since been discovered. Muco-obstructive lung diseases (MucOLDs) are characterised by the accumulation of hyper-concentrated mucus in the small airways, leading to persistent inflammation, infection and dysregulated protease activity. Although neutrophilic serine proteases, particularly neutrophil elastase, have been implicated in the propagation of inflammation and local tissue destruction, it is likely that the serine TLPs also contribute to various disease-relevant processes given the roles that a number of these enzymes play in the activation of both the epithelial sodium channel (ENaC) and protease-activated receptor 2 (PAR2). More recently, significant attention has focused on the activation of viruses such as SARS-CoV-2 by host TLPs. The purpose of this review was to highlight key TLPs linked to the activation of ENaC and PAR2 and their association with airway dehydration and inflammatory signalling pathways, respectively. The role of TLPs in viral infectivity will also be discussed in the context of the inhibition of TLP activities and the potential of these proteases as therapeutic targets.

Protease activated receptor 2 and matriptase expression in the joints of cats with and without osteoarthritis

OBJECTIVES

The aim of this study was to determine the presence of protease-activated receptor 2 (PAR2) and matriptase proteins and quantify PAR2 and matriptase mRNA expression in the articular cartilage and synovial membrane of cats with and without osteoarthritis (OA).

METHODS

A total of 28 articular cartilage samples from adult cats (14 OA and 14 normal), 10 synovial membranes from adult cats (five OA and five normal) and three cartilage samples from 9-week-old fetal cats were used. The presence of PAR2 and matriptase in the cartilage and synovial membrane of the adult samples was detected by immunohistochemical (IHC) staining, while real-time PCR was used for mRNA expression analyses in all samples.

RESULTS

PAR2 was detected in all OA and normal articular cartilage and synovial membrane samples but confined to only a few superficial chondrocytes in the normal samples. Matriptase was only detected in OA articular cartilage and synovial membrane samples. PAR2 and matriptase mRNA expression were, however, detected in all cartilage and synovial membrane samples. PAR2 and matriptase mRNA expression levels in OA articular cartilage were five (P <0.001) and 3.3 (P <0.001) times higher than that of the healthy group, respectively. There was no significant difference (P = 0.05) in the OA synovial membrane PAR2 and matriptase mRNA expression compared with the normal samples.

CONCLUSIONS AND RELEVANCE

Detection of PAR2 and matriptase proteins and gene expression in feline articular tissues is a novel and important finding, and supports the hypothesis that serine proteases are involved in the pathogenesis of feline OA. The consistent presence of PAR2 and matriptase protein in the cytoplasm of OA chondrocytes suggests a possible involvement of proteases in cartilage degradation. Further investigations into the PAR2 and matriptase pathobiology could enhance our understanding of the proteolytic cascades in feline OA, which might lead to the development of novel therapeutic strategies.

Exosomes in intercellular communication and implications for osteoarthritis

Osteoarthritis (OA) is the most prevalent of the musculoskeletal conditions and represents a significant public health burden. While degeneration of articular cartilage is a key feature, it is now increasingly recognized as a complex condition affecting the whole joint, with synovial inflammation present in a significant proportion of patients. As a secretory tissue, the OA synovium is a rich source of both soluble inflammatory mediators and extracellular vesicles, including exosomes, which have been implicated in cell-cell communication. Exosome cargo has been found to include proteins, lipids and various RNA subtypes such as mRNA and miRNA, potentially capable of regulating gene expression in target cells and tissues. Profiling of exosome cargo and understanding effects on cartilage could elucidate novel regulatory mechanisms within the joint, providing insight for targeted treatment. The aim of this article is to review current literature on exosome biology, highlighting the relevance and application for OA pathogenesis.

Accelerated post traumatic osteoarthritis in a dual injury murine model

OBJECTIVE

Joint injury involving destabilisation of the joint and damage to the articular cartilage (e.g., sports-related injury) can result in accelerated post-traumatic osteoarthritis (PTOA). Destabilised medial meniscotibial ligament (DMM) surgery is one of the most commonly used murine models and whilst it recapitulates Osteoarthritis (OA) pathology, it does not necessarily result in multi-tissue injury, as occurs in PTOA. We hypothesised that simultaneous cartilage damage and joint destabilisation would accelerate the onset of OA pathology.

METHODS

OA was induced in C57BL/6 mice via (a) DMM, (b) microblade scratches of articular cartilage (CS) or (c) combined DMM and cartilage scratch (DCS). Mice were culled 7, 14 and 28 days post-surgery. Microcomputed tomography (μCT) and histology were used to monitor bone changes and inflammation. Dynamic weight bearing, an indirect measure of pain, was assessed on day 14.

RESULTS

Osteophytogenesis analysis via μCT revealed that osteophytes were present in all groups at days 7 and 14 post-surgery. However, in DCS, osteophytes were visually larger and more numerous when compared with DMM and cartilage scratch (CS). Histological assessment of cartilage at day 14 and 28, revealed significantly greater damage in DCS compared with DMM and CS. Furthermore, a significant increase in synovitis was observed in DCS. Finally, at day 14 osteophyte numbers correlated with changes in dynamic weight bearing.

CONCLUSION

Joint destabilisation when combined with simultaneous cartilage injury accelerates joint deterioration, as seen in PTOA. Thus, DCS provides a novel and robust model for investigating multiple pathological hallmarks, including osteophytogenesis, cartilage damage, synovitis and OA-related pain.

Rheumatic Disease: Protease-Activated Receptor-2 in Synovial Joint Pathobiology

Protease-activated receptor-2 (PAR2) is one member of a small family of transmembrane, G-protein-coupled receptors. These receptors are activated via cleavage of their N terminus by serine proteases (e.g., tryptase), unveiling an N terminus tethered ligand which binds to the second extracellular loop of the receptor. Increasing evidence has emerged identifying key pathophysiological roles for PAR2 in both rheumatoid arthritis (RA) and osteoarthritis (OA). Importantly, this includes both pro-inflammatory and destructive roles. For example, in murine models of RA, the associated synovitis, cartilage degradation, and subsequent bone erosion are all significantly reduced in the absence of PAR2. Similarly, in experimental models of OA, PAR2 disruption confers protection against cartilage degradation, subchondral bone osteosclerosis, and osteophyte formation. This review focuses on the role of PAR2 in rheumatic disease and its potential as an important therapeutic target for treating pain and joint degradation.

Proteinase-activated receptor 2 modulates OA-related pain, cartilage and bone pathology

OBJECTIVE

Proteinase-activated receptor 2 (PAR2) deficiency protects against cartilage degradation in experimental osteoarthritis (OA). The wider impact of this pathway upon OA-associated pathologies such as osteophyte formation and pain is unknown. Herein, we investigated early temporal bone and cartilage changes in experimental OA in order to further elucidate the role of PAR2 in OA pathogenesis.

METHODS

OA was induced in wild-type (WT) and PAR2-deficient (PAR2^-/-) mice by destabilisation of the medial meniscus (DMM). Inflammation, cartilage degradation and bone changes were monitored using histology and microCT. In gene rescue experiments, PAR2^-/- mice were intra-articularly injected with human PAR2 (hPAR2)-expressing adenovirus. Dynamic weight bearing was used as a surrogate of OA-related pain.

RESULTS

Osteophytes formed within 7 days post-DMM in WT mice but osteosclerosis was only evident from 14 days post induction. Importantly, PAR2 was expressed in the proliferative/hypertrophic chondrocytes present within osteophytes. In PAR2^-/- mice, osteophytes developed significantly less frequently but, when present, were smaller and of greater density; no osteosclerosis was observed in these mice up to day 28. The pattern of weight bearing was altered in PAR2^-/- mice, suggesting reduced pain perception. The expression of hPAR2 in PAR2^-/- mice recapitulated osteophyte formation and cartilage damage similar to that observed in WT mice. However, osteosclerosis was absent, consistent with lack of hPAR2 expression in subchondral bone.

CONCLUSIONS

This study clearly demonstrates PAR2 plays a critical role, via chondrocytes, in osteophyte development and subchondral bone changes, which occur prior to PAR2-mediated cartilage damage. The latter likely occurs independently of OA-related bone changes.

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.

Proteinase-activated receptor-2 modulates human macrophage differentiation and effector function

Proteinase-activated receptor-2 (PAR-2) was shown to influence immune regulation; however, its role in human macrophage subset development and function has not been addressed. Here, PAR-2 expression and activation was investigated on granulocyte macrophage (GM)-CSF(M1) and macrophage (M)-CSF(M2) macrophages. In both macrophages, the PAR-2-activating peptide, SLIGKV, increased PAR-2 expression and regulated TNF-α and IL-10 secretion in a manner similar to LPS. In addition, HLA-DR on M1 cells also increased. Monocytes matured to an M1 phenotype in the presence of SLIGKV had reduced cell area, and released less TNF-α after LPS challenge compared with vehicle ( P < 0.05, n = 3). Cells matured to an M2 phenotype with SLIGKV also had a reduced cell area and made significantly more TNF-α after LPS exposure compared to vehicle ( P < 0.05, n = 3) with reduced IL-10 secretion ( P < 0.05, n = 3). Thus, PAR-2 activation on macrophage subsets regulates HLA-DR and PAR-2 surface expression, and drives cytokine production. In contrast, PAR-2 activation during M1 or M2 maturation induces altered cell morphology and skewing of phenotype, as evidenced by cytokine secretion. These data suggest a complex role for PAR-2 in macrophage biology and may have implications for macrophage-driven disease in which proteinase-rich environments can influence the immune process directly.

Immunomodulatory role of proteinase-activated receptor-2

OBJECTIVE

Proteinase-activated receptor-2 (PAR(2)) has been implicated in inflammatory articular pathology. Using the collagen-induced arthritis model (CIA) the authors have explored the capacity of PAR(2) to regulate adaptive immune pathways that could promote autoimmune mediated articular damage.

METHODS

Using PAR(2) gene deletion and other approaches to inhibit or prevent PAR(2) activation, the development and progression of CIA were assessed via clinical and histological scores together with ex vivo immune analyses.

RESULTS

The progression of CIA, assessed by arthritic score and histological assessment of joint damage, was significantly (p<0.0001) abrogated in PAR(2) deficient mice or in wild-type mice administered either a PAR(2) antagonist (ENMD-1068) or a PAR(2) neutralising antibody (SAM11). Lymph node derived cell suspensions from PAR(2) deficient mice were found to produce significantly less interleukin (IL)-17 and IFNγ in ex vivo recall collagen stimulation assays compared with wild-type littermates. In addition, substantial inhibition of TNFα, IL-6, IL-1β and IL-12 along with GM-CSF and MIP-1α was observed. However, spleen and lymph node histology did not differ between groups nor was any difference detected in draining lymph node cell subsets. Anticollagen antibody titres were significantly lower in PAR(2) deficient mice.

CONCLUSION

These data support an important role for PAR(2) in the pathogenesis of CIA and suggest an immunomodulatory role for this receptor in an adaptive model of inflammatory arthritis. PAR(2) antagonism may offer future potential for the management of inflammatory arthritides in which a proteinase rich environment prevails.

PAR(2) expression in peripheral blood monocytes of patients with rheumatoid arthritis

OBJECTIVES

Proteinase-activated receptor 2 (PAR(2)) is a G protein-coupled receptor activated by serine proteinases with proinflammatory activity. A study was undertaken to investigate the presence and functional significance of PAR(2) expression on rheumatoid arthritis (RA)-derived leucocyte subsets.

METHODS

Venous blood was obtained from patients with RA and osteoarthritis (OA) as well as healthy control subjects. Surface expression of PAR(2) on peripheral blood mononuclear cells (PBMCs) was analysed by flow cytometry and interleukin 6 (IL-6) generation by ELISA.

RESULTS

Patients with RA had elevated but variable surface expression of PAR(2) on CD14+ monocytes compared with control subjects (median (1st to 3rd quartiles) 1.76% (0.86-4.10%) vs 0.06% (0.03-0.81%), p<0.0001). CD3+ T cells showed a similar pattern with significantly higher PAR(2) expression in patients with RA compared with controls (3.05% (0.36-11.82%) vs 0.08% (0.02-0.28%), p<0.0001). For both subsets, PAR(2) expression was significantly higher (p<0.00001) in patients with high levels of disease activity: PAR(2) expression for both CD14+ and CD3+ cells correlated to C reactive protein and erythrocyte sedimentation rate. Furthermore, in a cohort of patients with newly diagnosed RA, elevated PAR(2) expression in both CD14+ and CD3+ cells was significantly reduced 3 months after methotrexate or sulfasalazine treatment and this reduction correlated significantly with the reduction in the 28-joint Disease Activity Scale score (p<0.05). PAR(2) expression on cells from patients with OA was low, similar to levels seen in control subjects. Generation of IL-6 by monocytes in response to a selective PAR(2) agonist was significantly greater in patients with RA than in patients with OA and control subjects (p<0.05).

CONCLUSIONS

These findings are consistent with a pathogenic role for PAR(2) in RA.

Matriptase is a novel initiator of cartilage matrix degradation in osteoarthritis

OBJECTIVE

Increasing evidence implicates serine proteinases in pathologic tissue turnover. The aim of this study was to assess the role of the transmembrane serine proteinase matriptase in cartilage destruction in osteoarthritis (OA).

METHODS

Serine proteinase gene expression in femoral head cartilage obtained from either patients with hip OA or patients with fracture to the neck of the femur (NOF) was assessed using a low-density array. The effect of matriptase on collagen breakdown was determined in cartilage degradation models, while the effect on matrix metalloproteinase (MMP) expression was analyzed by real-time polymerase chain reaction. ProMMP processing was determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis/N-terminal sequencing, while its ability to activate proteinase-activated receptor 2 (PAR-2) was determined using a synovial perfusion assay in mice.

RESULTS

Matriptase gene expression was significantly elevated in OA cartilage compared with NOF cartilage, and matriptase was immunolocalized to OA chondrocytes. We showed that matriptase activated proMMP-1 and processed proMMP-3 to its fully active form. Exogenous matriptase significantly enhanced cytokine-stimulated cartilage collagenolysis, while matriptase alone caused significant collagenolysis from OA cartilage, which was metalloproteinase-dependent. Matriptase also induced MMP-1, MMP-3, and MMP-13 gene expression. Synovial perfusion data confirmed that matriptase activates PAR-2, and we demonstrated that matriptase-dependent enhancement of collagenolysis from OA cartilage is blocked by PAR-2 inhibition.

CONCLUSION

Elevated matriptase expression in OA and the ability of matriptase to activate selective proMMPs as well as induce collagenase expression make this serine proteinase a key initiator and inducer of cartilage destruction in OA. We propose that the indirect effects of matriptase are mediated by PAR-2, and a more detailed understanding of these mechanisms may highlight important new therapeutic targets for OA treatment.

Protease-activated receptor 2: a novel pathogenic pathway in a murine model of osteoarthritis

Objective

Osteoarthritis is a global clinical challenge for which no effective disease-modifying agents currently exist. This study identified protease-activated receptor 2 (PAR-2) as a novel pathogenic mechanism and potential therapeutic target in osteoarthritis.

Methods

Experimental osteoarthritis was induced in wild-type and PAR-2-deficient mice by sectioning the medial meniscotibial ligament (MMTL), leading to the development of a mild arthropathy. Cartilage degradation and increased subchondral bone formation were assessed as indicators of osteoarthritis pathology.

Results

Four weeks following MMTL section, cartilage erosion and increased subchondral bone formation was evident in wild-type mice but was substantially reduced in PAR-2-deficient mice. Crucially, the therapeutic inhibition of PAR-2 in wild-type mice, using either a PAR-2 antagonist or a monoclonal antibody targeting the protease cleavage site of PAR-2, was also equally effective at reducing osteoarthritis progression in vivo. PAR-2 was upregulated in chondrocytes of wild-type but not sham-operated mice. Wild-type mice showed further joint degradation 8 weeks after the induction of osteoarthritis, but PAR-2-deficient mice were still protected.

Conclusions

The substantial protection from pathology afforded by PAR-2 deficiency following the induction of osteoarthritis provides proof of concept that PAR-2 plays a key role in osteoarthritis and suggests this receptor as a potential therapeutic target.

Strain dependence in murine models of monoarthritis

OBJECTIVE AND DESIGN

This study explores the inflammatory response in various murine strains. Utilising several approaches, monoarthritis was induced in the knee, providing an inflammatory model relevant to arthritis.

METHODS

Acute (carrageenan/kaolin; C/K) or chronic inflammatory models (Freund's complete adjuvant; FCA) or antigen-induced arthritis (AIA), were induced by peri- and/or intra-articular injection.

RESULTS

C/K elicited an acute inflammatory response in various strains of mice, with significant (P < 0.005) phenotypic variation. FCA induction provided a chronic inflammatory response. The magnitude of the response in both acute and chronic models was strain dependent, with BalbC exhibiting the most resistance to swelling in all models. AIA produced only an acute response in three strains tested.

CONCLUSIONS

The data presented, demonstrating variation in the magnitude of acute and chronic inflammatory responses in different mice strains, allows informed selection of appropriate strains and models for future experimental studies.

Expression and proinflammatory role of proteinase-activated receptor 2 in rheumatoid synovium: ex vivo studies using a novel proteinase-activated receptor 2 antagonist

OBJECTIVE

Serine proteinases activate the G protein-coupled receptor, proteinase-activated receptor 2 (PAR-2), via cleavage and exposure of a tethered ligand. PAR-2 is known to exert proinflammatory actions in a murine model of arthritis, since PAR-2-deficient mice exhibit strikingly reduced articular inflammation. This study was undertaken to examine synovial PAR-2 expression and to determine the effect of a novel PAR-2 antagonist on synovial cytokine production, in order to investigate the hypothesis that PAR-2 plays a critical role in the pathogenesis of rheumatoid arthritis (RA).

METHODS

Using a monoclonal antibody to human PAR-2, expression in RA synovium and cultured synovial fibroblasts was characterized. The novel PAR-2 antagonist, ENMD-1068, was added to primary cultures of RA synovial tissue, from which spontaneous cytokine release was measured.

RESULTS

PAR-2 was substantially up-regulated in RA synovium compared with control synovial tissue from patients with osteoarthritis or seronegative inflammatory arthritis, neither of which exhibited significant PAR-2 expression. Importantly, spontaneous release of tumor necrosis factor alpha and interleukin-1beta from RA synovium was substantially inhibited by ENMD-1068, in a dose-dependent manner.

CONCLUSION

These findings identify PAR-2 as a novel upstream regulator of proinflammatory cytokine production in RA and indicate its potential as a novel therapeutic target in inflammatory arthritis.

The therapeutic potential of proteinase-activated receptors in arthritis

Proteinase-activated receptors are a family of seven-transmembrane G-protein-coupled receptors. Activation of PARs is initiated through cleavage of the N-terminus, unmasking a tethered ligand that can then interact with the receptor and lead to its activation. PARs exhibit both anti- and pro-inflammatory properties, although recent evidence has pointed towards a detrimental role for PARs, particularly PAR-2, in arthritis. Initial research using PAR-2 knockout mice identified PAR-2 as a key mediator of chronic joint inflammation. Further research examined the role of PAR-2 in human articular cell types, demonstrating upregulation of PAR-2 in cells from an inflammatory background compared with non-inflammatory cells, with PAR-2 levels being further upregulated by pro-inflammatory cytokines and growth factors. To date, there is no clinical evidence of a role for PAR-2 in vivo in humans, although recent studies utilizing human joint tissue and articular cells are emerging.

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.

Therapeutic promise of proteinase-activated receptor-2 antagonism in joint inflammation

Biological therapies such as tumor necrosis factor-alpha inhibitors have advanced the treatment of rheumatoid arthritis, but one-third of patients do not respond to such therapy. Furthermore, these inhibitors are now usually administered in combination with conventional disease-modifying antirheumatic drugs, suggesting they have not achieved their early promise. This study investigates a novel therapeutic target, proteinase-activated receptor (PAR)-2, in joint inflammation. Intra-articular carrageenan/kaolin (C/K) injection in mice resulted in joint swelling that was associated with synovial PAR2 up-regulation. Inhibiting receptor up-regulation using small interfering RNA technology, as confirmed by immunoblotting, substantially reduced the inflammatory response in the joint. Serine proteinase-induced joint swelling was mediated primarily via PAR2 activation, since the response to exogenous application of trypsin and tryptase was absent in PAR2 knockout mice. Furthermore, serine proteinase inhibitors were effective anti-inflammatory agents in this model. Disrupting proteolytic activation of PAR2 using antiserum (B5) directed to the receptor cleavage/activation site also attenuated C/K-induced inflammation, as did the similarly targeted PAR2 monoclonal antibody SAM-11. Finally, we report the activity of a novel small molecule PAR2 antagonist, N1-3-methylbutyryl-N4-6-aminohexanoyl-piperazine (ENMD-1068), that dose dependently attenuated joint inflammation. Our findings represent a major advance in collectively identifying PAR2 as a novel target for the future treatment of arthritis.

Divergent roles of nitrergic and prostanoid pathways in chronic joint inflammation

BACKGROUND

Nitrergic and prostanoid pathways have both been implicated in inflammatory processes.

OBJECTIVE

To investigate their respective contributions in a rat model of chronic arthritis.

METHODS

Male Wistar rats (n = 4-6/group) received either an intra-articular injection of 2% carrageenan/4% kaolin (C/K) or intra- and periarticular injections of Freund's complete adjuvant (FCA; 10 mg/ml M tuberculosis). Joint diameter, urinary nitric oxide metabolites (NO(x)), and prostaglandin E(2) (PGE(2)) levels were measured as indices of the inflammatory process. A prophylactic and therapeutic (day 5) dose ranging study of an inducible nitric oxide synthase inhibitor, L-N-(1-iminoethyl)-lysine (L-NIL), and a cyclo-oxygenase-2 (COX-2) inhibitor, SC-236, was performed with the drugs given subcutaneously. Submaximal doses were identified and used for combination studies. Appropriate vehicle controls were included.

RESULTS

L-NIL and SC-236 dose dependently inhibited C/K induced acute joint swelling, the magnitude being greatest when they were given in combination. Both prophylactic and therapeutic administration of SC-236 in the FCA induced model of chronic arthritis produced a dose dependent reduction in all the measures assessed. However, although L-NIL demonstrated similar dose dependent inhibition of urinary NO(x) and PGE(2) levels, joint swelling was significantly exacerbated in this model. Co-administration of the inhibitors nullified the benefits of SC-236.

CONCLUSION

Whereas COX-2 derived prostaglandins are proinflammatory in both acute and chronic joint inflammation, NO seems to have divergent roles, being anti-inflammatory in chronic and proinflammatory in acute joint inflammation.

Pathophysiology of vascular dysfunction in a rat model of chronic joint inflammation

The impact of chronic joint inflammation on articular vascular function in rats was investigated to address whether joint swelling and the associated vascular dysfunction are dependent upon a common prostanoid mechanism. Urinary nitrate/nitrite (NO(x)) and PGE(2) excretion, knee joint diameter and body weight were measured following induction of adjuvant-induced arthritis (AIA). Ten days postinduction of AIA, joint vascular reactivity was assessed by measuring the perfusion response using a laser Doppler imager (LDI) to topical application of acetylcholine (ACh) and sodium nitroprusside (SNP). Four groups were compared: a non-inflamed control group and three AIA groups treated i.p. with vehicle, indomethacin or SC-236 (at equimolar doses). The selective cyclooxygenase-2 (COX-2) inhibitor (SC-236) was used to differentiate between COX-1 and -2-derived prostaglandins. Urinary NO(x) and PGE(2) levels increased substantially during the early phase of AIA but decreased thereafter. Toxicity to indomethacin but not SC-236 was observed, as indicated by a marked decrease in body weight. Joint swelling was similarly attenuated by indomethacin and SC-236 (P= 0.0001 cf. vehicle-treated AIA; n= 5-6 per group), indicating that this is due to COX-2 and not COX-1 inhibition. The AIA-induced changes in urinary NO(x) and PGE(2) were corrected by both COX inhibitors. While vascular reactivity to ACh and SNP was significantly attenuated by AIA (P < 0.002; n= 5-10 per group), the perfusion responses to these vasodilating agents were similar in all three AIA groups, demonstrating that the vascular dysfunction was not corrected by inhibition of either COX-1 or COX-2 enzymes. Furthermore, the attenuation of both ACh and SNP-induced responses in AIA suggest that vascular dysfunction was not exclusively endothelial in nature. In conclusion, the joint swelling and vascular dysfunction associated with AIA appear to be mediated, at least in part, by independent mechanisms. While COX-1/COX-2 inhibition reduced joint swelling, vascular dysfunction in AIA is independent of constitutive or inducible prostanoid mechanisms, and appears not to be solely endothelial-derived, but to involve other components such as the vascular smooth muscle.

Protective effect of sensory denervation in inflammatory arthritis (evidence of regulatory neuroimmune pathways in the arthritic joint)

OBJECTIVE

To investigate the direct effect of joint innervation on immune mediated joint inflammation in a patient with psoriatic arthritis (PsA).

CASE REPORT

The patient developed arthritis mutilans in all digits of both hands with the exception of the left 4th finger, which had prior sensory denervation following traumatic nerve dissection. Plain radiography, ultrasonography and nerve conduction studies of the hands confirmed the absence of articular disease and sensory innervation in the left 4th digit.

METHODS

This relationship between joint innervation and joint inflammation was investigated experimentally by prior surgical sensory denervation of the medial aspect of the knee in six Wistar rats in which carrageenan induced arthritis was subsequently induced. Prior sensory denervation--with preservation of muscle function--prevented the development of inflammatory arthritis in the denervated knee.

DISCUSSION

Observations in human and animal inflammatory arthritis suggest that regulatory neuroimmune pathways in the joint are an important mechanism that modulates the clinical expression of inflammatory arthritis.

Gender differences in regional cutaneous microcirculatory responses to capsaicin

Vascular responsiveness between healthy male and female subjects to capsaicin, an agent promoting neuropeptide release, was compared. Changes in skin perfusion were measured non-invasively using laser Doppler imaging. Topical application of a 3% solution of capsaicin to the dorsum of the hand resulted in vasodilatation in nine of 10 male subjects, but in less than half of the female subjects. Responses to capsaicin at the shin were smaller but did not show gender differences. Fingertip temperature was significantly lower in females compared with males and this correlated (r = 0.54, P < 0.01) with the maximum response to capsaicin. These effects were specific to capsaicin as endothelium-dependent and -independent vasodilator mechanisms, assessed non-invasively by iontophoresis of acetylcholine and sodium nitroprusside, respectively, showed no gender differences. These findings suggest a specific anomaly in capsaicin-sensitive vasodilator mechanisms in some subjects, perhaps indicative of subclinical expression of Raynaud's phenomenon.

Combined inhibition of nitrergic and prostanoid pathways in J774 macrophages

OBJECTIVES

Nitric oxide and prostaglandins are both implicated in the pathogenesis of inflammatory conditions such as rheumatoid arthritis (RA). The hypothesis that simultaneous inhibition of nitric oxide synthase (NOS) and cyclooxygenase (COX) was more effective than inhibition of either enzyme alone was tested.

METHODS

J774 macrophages were pre-incubated with L-NAME and/or indomethacin, prior to activation with LPS (10 micrograms/ml).

RESULTS

LPS significantly increased NO2-; PGE2 and TNF-alpha levels by 24 h. Quantitative real-time PCR demonstrated a dose-dependent reduction in the expression of COX-2 in the presence of increasing doses of L-NAME. NO2- and PGE2 production were inhibited in a dose-dependent manner by either indomethacin or L-NAME. Combined administration of L-NAME and indomethacin produced a significantly greater inhibition of NO2- and PGE2 than either inhibitor alone.

CONCLUSION

The data supports the therapeutic potential of combined inhibition of the prostanoid and nitrergic systems as an anti-inflammatory treatment strategy and supports the progression of this work into models of arthritis.

Essential role for proteinase-activated receptor-2 in arthritis

Using physiological, pharmacological, and gene disruption approaches, we demonstrate that proteinase-activated receptor-2 (PAR-2) plays a pivotal role in mediating chronic inflammation. Using an adjuvant monoarthritis model of chronic inflammation, joint swelling was substantially inhibited in PAR-2-deficient mice, being reduced by more than fourfold compared with wild-type mice, with virtually no histological evidence of joint damage. Mice heterozygous for PAR-2 gene disruption showed an intermediate phenotype. PAR-2 expression, normally limited to endothelial cells in small arterioles, was substantially upregulated 2 weeks after induction of inflammation, both in synovium and in other periarticular tissues. PAR-2 agonists showed potent proinflammatory effects as intra-articular injection of ASKH95, a novel synthetic PAR-2 agonist, induced prolonged joint swelling and synovial hyperemia. Given the absence of the chronic inflammatory response in the PAR-2-deficient mice, our findings demonstrate a key role for PAR-2 in mediating chronic inflammation, thereby identifying a novel and important therapeutic target for the management of chronic inflammatory diseases such as rheumatoid arthritis.

Elimination of Electrically Induced Iontophoretic Artefacts: Implications for Non-Invasive Assessment of Peripheral Microvascular Function

Iontophoretic assessment of skin microvascular function is complicated by the occurrence of electrically induced hyperaemia, especially at the cathode. Studies were performed to identify means of reducing such effects. Skin vasodilator responses were measured using a laser Doppler imager that controlled iontophoretic current delivery. A novel feature involved monitoring voltage across the iontophoresis chambers. Comparison between responses to vehicle (distilled H(2)O), acetylcholine (ACh) and sodium nitroprusside (SNP) showed electrically induced hyperaemia at the cathode associated with the vehicle, whose time course overlapped with that of the SNP response. Voltage across the chambers containing drugs dissolved in H(2)O was significantly (p = 0.018, n = 7) lower than the voltage profile of H(2)O alone. H(2)O iontophoresis was associated with cathodal hyperaemic responses in most subjects, whereas a 0.5% NaCl vehicle produced lower voltages and eliminated this artefact. Voltage.time integral rather than charge was the prime determinant of electrically induced hyperaemic responses. No significant correlation was found between skin fold thickness and either calculated skin resistance (r(2) = 0.0002) or vascular response to ACh (r(2) = 0.13). Smaller chamber size led to higher voltages and greater electrically induced hyperaemic responses. These appear to be prostaglandin dependent as they were ablated by cyclooxygenase inhibition. Use of a low-resistance vehicle combined with larger chamber sizes and lower currents can prevent such artefacts, thereby increasing the robustness of this methodology for clinical assessment of endothelial function.

Pathophysiological basis of acute inflammatory hyperaemia in the rat knee: roles of cyclo-oxygenase-1 and -2

The role of different isoforms of cyclo-oxygenase (COX) in mediating the acute (0-6 h) and late (24 h) phases of inflammation was investigated in the rat knee joint following intra-articular injection of carrageenan. The hyperaemic response was assessed transcutaneously using laser Doppler imaging (LDI). Samples were taken at corresponding time points for detection of synovial COX-1, COX-2 and inducible nitric oxide synthase (iNOS) mRNA, and measurement of urinary prostaglandin (PG) and nitric oxide metabolites (NO(x)). A non-selective COX inhibitor (indomethacin, 15 mg kg(-1) I.P.), a selective COX-2 inhibitor (SC-236, 16.8 mg kg(-1) I.P.) or vehicle were administered 1 h prior to carrageenan in the acute phase study. LDI scans were taken hourly for 4 h post-induction. Inflammatory hyperaemia in the vehicle group was attenuated in the indomethacin- (P < 0.001, two-way ANOVA) and SC-236-treated groups (P < 0.0001), with no difference between these treatments. At 24 h, I.V. infusion of indomethacin (0.1 mg min(-1)), increased vascular resistance (24 +/- 7.1 %; P < 0.05) compared to vehicle infusion, whereas SC-236 (0.11 mg min(-1)) did not. Resistance changes to indomethacin also differed from SC-236 (P < 0.05). Knee joint diameter progressively increased over 24 h (P < 0.0001, one-way ANOVA). Urinary PG levels increased by 6 h (P < 0.05), but returned to baseline by 24 h. COX-1 mRNA was detectable at all time points; COX-2 mRNA only at 3 h. Urinary NO(x) levels increased progressively over 24 h (P < 0.05), paralleled by induction of iNOS in the 3 and 24 h samples. Prostaglandin production via COX-2 appears to mediate the development of acute inflammatory hyperaemia, but nitrergic mechanisms may supervene subsequently. COX-1 but not COX-2 contributes to the maintenance of basal blood flow in the hyperaemic joint at 24 h.

Metacarpophalangeal joints in rheumatoid arthritis: laser Doppler imaging--initial experience

Laser Doppler imaging is a noninvasive method yielding a spatial perfusion map. With use of a near-infrared laser, elevated perfusion associated with the metacarpophalangeal joints was detectable in patients with active rheumatoid arthritis. Findings at laser Doppler imaging correlated with pain scores and synovitis detected at ultrasonography, whereas the power Doppler sign (red pixels inside the active green box) did not. Laser Doppler imaging has the potential to help assess soft-tissue inflammation.

Expression of constitutive but not inducible cyclooxygenase maintains articular perfusion in the rat knee

Experiments were performed in the normal rat knee joint to investigate the role of different isoforms of cyclooxygenase (COX) in the regulation of basal joint blood flow. Laser Doppler imaging (LDI) was used to measure articular perfusion, and reverse transcriptase polymerase chain reaction (RT-PCR) for the detection of COX-1 and COX-2 mRNA in joint tissue. Intravenous infusion of indomethacin (a non-selective inhibitor of COX; 0.34 nmol min(-1)) over 40 min produced a time dependent increase in articular vascular resistance (maximum 22.5 % at 40 min; P < 0.0001, one-way ANOVA) whereas vehicle over a similar time period had no effect in a control group. An equimolar concentration of a highly selective inhibitor for COX-2, SC-236, was administered in a further group of rats but this did not increase articular vascular resistance. While there was no significant difference between the response to vehicle and SC-236 (two-way ANOVA; P = 0.686, n = 6) the response to indomethacin was significantly greater than vehicle or SC-236 (two-way Anova; P < 0.0001, n = 6). COX-1, but not COX-2, was detectable by RT-PCR in all joint tissue samples examined (n = 4). The results of this study indicate that prostaglandins (PGs) play an important role in the maintenance of basal perfusion in the rat knee joint, with COX-1 being the physiologically relevant isoform. Experimental Physiology (2001) 86.2, 191-197.

Modulation of synovial blood flow by the calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP(8-37)

1. The effect of the calcitonin gene-related peptide (CGRP) receptor antagonist, CGRP(8-37) on blood flow in the knee joint of the anaesthetized rat was investigated. 2. Synovial blood flow in both exposed and intact, skin-covered knees was measured by laser Doppler perfusion imaging. 3. Topical application of CGRP(8-37) caused a dose-dependent fall in synovial blood flow in the exposed knee joint of the rat. At low (1.5 nmol) doses of CGRP(8-37) there was no significant effect on synovial blood flow. In rats treated with 7.5 nmol CGRP(8-37) there was a fall in synovial blood flow (maximum effect at 10 min: -28.8 +/- 4.6%; n=7), which returned to resting levels within 30 min. The highest dose (15 nmol) of antagonist used in this study caused a marked (maximum at 10 min: -35.6 +/- 9.3%; n=8), and prolonged (up to 30 min) fall in blood flow. 4. Ten days after surgical denervation, CGRP(9-37) (15 nmol, topical) had no significant effect on blood flow in the rat exposed knee joint (change in flux at 10 min: -5.1+/-3.6%; n=4). This suggests that CGRP(8-37) acts selectively to antagonize the actions of a neurally derived product, probably CGRP, on the rat synovial vasculature. 5. In skin-covered knee joints, intra-articular injection of CGRP(8-37) (15 nmol; bolus) elicited a significant fall in synovial blood flow (maximum effect at 10 min: -15.5 +/- 5.8%; n=6). 6. CGRP (0.01, 0.1 or 1.0 nmol; topical) caused a dose-dependent increase in exposed knee joint blood flow, which was attenuated by co-administration of 1.5 nmol CGRP(8-37). For example, 1 nmol CGRP elicited a peak increase in flux at 10 min of 94.7 +/- 31.8% (n=8) and 28.8 +/- 8.9% (n=7) in the absence and presence of CGRP(8-37), respectively. The vasodilator responses induced by acetylcholine (ACh) (10 nmol, topical; n=4-5) or sodium nitroprusside (SNP) (10 nmol, topical; n=4-5) were unaltered in the presence of CGRP(8-37) (1.5 nmol, topical). 7. Thus, the CGRP receptor antagonist CGRP(8-37) elicits vasoconstriction in the rat synovium. This suggests that the endogenous, basal release of CGRP may play a physiological role in the regulation of blood flow in the rat knee joint.

Tachykinin regulation of basal synovial blood flow

1. Experiments were performed to investigate the role of endogenously released tachykinins in the regulation of blood flow to the rat knee joint. Synovial perfusion was assessed by laser Doppler perfusion imaging, which permitted spatial measurement of relative changes in perfusion from control (pre drug administration), expressed as the percentage change. Most experiments were performed on the exposed medial aspect of the knee joint capsule. 2. Neither the selective tachykinin NK1 receptor antagonist, FK888, nor the selective tachykinin NK2 receptor antagonist, SR48968, significantly influenced synovial blood flow at doses of 10(-12), 10(-10) and 10(-8) mol. However, topical co-administration of these agents produced significant dose-dependent reductions in basal synovial perfusion of 6.3 +/- 4.6 and 12.0 +/- 3.4 and 19.9 +/- 2.6%, respectively; n = 29. The non-selective tachykinin NK1/NK2 receptor antagonist, FK224, also produced significant (at 10(-10) and 10(-8) mol), but less potent, reductions in perfusion of 5.3 +/- 4.0, 8.4 +/- 2.2 and 5.9 +/- 2.8%, respectively; n = 25. 3. Topical administration of the alpha 1-, alpha 2-adrenoceptor antagonist phenoxybenzamine elicited a 31.3 +/- 6.2% increase in blood flow which was substantially reduced to 10.4 +/- 3.8% by co-administration of the FK888 and SR48968 (both at 10(-8) mol; n = 8-13), suggesting that normally there is sympathetic vasoconstrictor "tone' which is opposed by the vasodilator action of endogenous tachykinins. 4. One week after surgical interruption of the nerve supply to the knee joint, co-administration of FK888 and SR48968 (both at 10(-8) mol) now produced slight vasodilatation (6.7 +/- 4.6%; n = 9) which did not differ significantly from vehicle treatment. Depletion of tachykinins from sensory nerve fibres by systemic capsaicin administration also resulted in abolition of the vasoconstrictor effect of FK888 and SR48968 (both at 10(-8) mol), with these agents only producing a slight vasodilatation (2.5 +/- 5.3%; n = 6). 5. By use of a near infra-red laser source it was possible to image knee joint perfusion transcutaneously, the overlying skin being left intact. In this more physiological situation, close intra-arterial injection of the combination of FK888 and SR48968 (both at 10(-8) mol) again elicited vasoconstriction (48.8 +/- 16.2% reduction in blood flow; n = 4). 6. These results indicate that endogenous tachykinins may be continuously released from sensory fibers innervating the joint. Basal release of tachykinins could therefore be an important physiological influence opposing sympathetic vasoconstrictor tone.

Laser Doppler perfusion imaging of synovial tissues using red and near infra-red lasers

A new laser Doppler perfusion imaging (LDI) system was evaluated by comparing it with the well-established radiolabelled microsphere technique for measuring blood flow in the rabbit knee joint capsule. In this study two laser sources (635 and 835 nm) were compared at three scan speeds (50, 10 and 4 ms/pixel). With blood flow to the rabbit hindlimb controlled via a peristaltic pump, the comparison of LDI and microsphere measurement techniques yielded highly significant correlations for both laser sources (r = 0.9; p = 0.0001; 14 measurements in 7 animals). Comparison of the three scan speeds demonstrated acceptable agreement without significant bias between measurements, suggesting that the inevitable narrowing of the bandwidth at the fastest scan speed does not cause significant deterioration of the signal. The flux values obtained with 635 and 835 nm laser sources were linearly related (r = 0.93, p = 0.0001; 66 measurements in 12 animals), although there was a small but significant bias for higher values with the 635-nm laser (mean ratio of flux values 1.06, 95% confidence interval 1.01-1.12). These results validate the use of LDI with either wavelength laser for the assessment of joint capsule perfusion.

Laser Doppler perfusion imaging of skin blood flow using red and near-infrared sources

At present, scanning laser Doppler imaging uses a 633-nm helium-neon laser (RED) as the only light source, but this restricts its ability to measure blood flow (i) at darkly pigmented skin and (ii) from deeper or subdermal structures. Because near-infrared (NIR) light is known to penetrate deeper into tissue and to be less absorbed than RED, two imagers were adapted to include a NIR laser diode source (one of 830 nm for UK studies; one of 780 nm for leprosy field trials) in parallel with the existing RED source. In human hands representing a range of skin pigmentations, RED scans were unobtainable at the darkest areas of skin, but intact NIR scans could be collected in all cases. In experiments at the rat knee and the dorsal human hand, NIR and RED values were similar on normal skin. Over underlying vessels, however, NIR values greatly exceeded RED values, an effect abolished by occlusion. Similarly, in patients with leprosy and in healthy controls in Spain, fingerpulp NIR values exceeded RED values to the greatest degree when thermoregulatory flow was highest, i.e., when the deeper-lying arteriovenous anastomoses were open. Over areas of experimental inflammation, NIR gave higher values and also exhibited a greater degree of spatial heterogeneity than RED. We conclude that some current limitations of laser Doppler imaging technology can be overcome by the use of NIR laser diode sources.

Laser Doppler perfusion imaging of proximal interphalangeal joints in patients with rheumatoid arthritis

OBJECTIVE

A non-invasive imaging technique (laser Doppler perfusion imaging-LDI) based on measurement of backscattered Doppler-broadened near infra-red laser radiation was used to provide two-dimensional images of perfusion over the proximal interphalangeal (PIP) joints of a group of normal subjects compared to a group of patients with rheumatoid arthritis (RA).

RESULTS

Some PIP joints of the RA group showed areas of increased perfusion whereas normal subjects showed much less variation in perfusion between joints. These hyperaemic areas arose from the underlying joint, as scans taken with a less penetrating red laser did not show such areas.

CONCLUSION

Apart from its obvious dermatological uses, LDI could be employed to image hyperaemia associated with a variety of inflammatory conditions affecting subcutaneous structures.

Restoration of vasa recta hemodynamics and pressure natriuresis in SHR by L-arginine

An increase in medullary blood flow has been implicated as a mediator of the natriuresis following increases in renal perfusion pressure (RPP). We examined whether administration of L-arginine, the substrate for nitric oxide production, restores the impaired vasa recta hemodynamic response to increases in RPP and the blunted pressure natriuresis of the spontaneously hypertensive rat (SHR). The response of descending (QDVR) and ascending vasa recta blood flow (QAVR) and of urinary sodium excretion (UNaV) was examined as RPP was increased by means of an adjustable aortic clamp placed above the renal arteries in young SHR and Wistar-Kyoto (WKY) rats. When RPP was increased in SHR receiving infusion of L-arginine (n = 7), QDVR and QAVR increased significantly in association with increases in UNaV. In SHR receiving the inactive enantiomer, D-arginine (n = 7), similar increases in RPP failed to increase QAVR and QDVR and were associated with an attenuated increase in UNaV. WKY animals infused with either D-arginine or L-arginine had increases in QDVR, QAVR, and UNaV in response to increases in RPP that were of similar magnitude to SHR receiving L-arginine. Thus the administration of L-arginine to SHR restores the pressure-dependent increases in renal medullary hemodynamics in association with restoration of pressure natriuresis.

Perfusion pressure and volume status determine the microvascular response of the rat kidney to NG-monomethyl-L-arginine

This study investigated the role of volume status and perfusion pressure on the hemodynamic response of cortical and medullary renal capillaries to systemic inhibition of nitric oxide. NG-Monomethyl-L-arginine (L-NMMA) was infused intravenously (15-mg/kg bolus and 500-micrograms.min-1.kg-1 infusion), and blood flow in cortical capillaries (QCC) and in descending (QDVR) and ascending vasa recta (QAVR) was measured by fluorescence videomicroscopy in euvolemic and volume-expanded anesthetized Munich-Wistar rats. L-NMMA in euvolemic rats decreased vasa recta blood flow (delta QDVR, 3.97 +/- 0.80 nL/min [P < .01]; delta QAVR, 1.90 +/- 0.39 nL/min [P < .01]; n = 6) and QCC (delta QCC, 0.57 +/- 0.15 nL/min [P < .01]; n = 7) despite increases in renal perfusion pressure (RPP). Fractional excretion of sodium (FENa) remained unchanged. In volume-expanded rats, L-NMMA decreased vasa recta blood flow when RPP increased (delta QDVR, 1.42 +/- 0.79 nL/min [P = .05]; delta QAVR, 1.95 +/- 0.34 nL/min [P < .001]; n = 9) or was held constant by partial aortic occlusion (delta QDVR, 1.19 +/- 0.45 nL/min [P < .05]; delta QAVR, 1.44 +/- 0.40 nL/min [P < .01]; n = 8). QCC was unchanged by L-NMMA when RPP increased (delta QCC, 0.27 +/- 0.20 nL/min; n = 8) but decreased significantly by 0.61 +/- 0.11 nL/min (P < .01, n = 8) when increases in RPP were prevented. FENa increased when RPP increased (delta FENa, 2.47 +/- 0.51%; P < .001) and was held constant (delta FENa, 2.64 +/- 0.46%; P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)

Direct measurement of renal medullary blood flow in the dog

We studied the responses of total renal blood flow (RBF) and renal medullary blood flow (RMBF) to changes in renal perfusion pressure (RPP) within and below the range of renal autoregulation in the anesthetized dog (n = 7). To measure RMBF, we developed a technique in which the medulla is exposed by excising a section of infarcted cortex and a multiple optical fiber flow probe, connected to a laser-Doppler flowmeter, is placed on the medulla. At the baseline RPP of 120 +/- 1 mmHg, RBF was 2.58 +/- 0.33 ml.min-1.g perfused kidney wt-1, and RMBF was 222 +/- 45 perfusion units. RPP was then decreased in consecutive 20-mmHg steps to 39 +/- 1 mmHg. At 80 +/- 1 mmHg, RBF remained at 89 +/- 4% of the baseline value; however, RMBF had decreased significantly (P < 0.05) to 73 +/- 4% of its baseline value. The efficiency of autoregulation of RBF and of RMBF within the RPP range of 120 to 80 mmHg was determined by calculating an autoregulatory index (AI) for each parameter using the formula AI = (%delta blood flow)/(%delta RPP). An AI of 0 indicates perfect autoregulation, and an index of 1 indicates a system with a fixed resistance. The AI for RBF averaged 0.33 +/- 0.12 over this pressure range and showed a significantly greater (P < 0.05) autoregulatory ability than did the RMBF (0.82 +/- 0.13). Decreasing perfusion pressure < 80 mmHg produced significant decreases in both RBF and RMBF.(ABSTRACT TRUNCATED AT 250 WORDS)

Natriuretic response to renal interstitial hydrostatic pressure during angiotensin II blockade

Increases in renal interstitial hydrostatic pressure (RIHP) increase urinary sodium excretion (UNaV). Experimentally increasing RIHP by direct renal interstitial volume expansion (DRIVE) has been shown to decrease proximal tubule sodium reabsorption. The purpose of the present study was to investigate whether the renin-angiotensin system modulates the natriuretic response to DRIVE. Unilateral nephrectomy and implantation of two polyethylene matrices were performed 3 wk before the acute experiment. Fractional sodium excretion (FENa), RIHP, and glomerular filtration rate (GFR) were measured before and after DRIVE in control rats (n = 9) and in rats receiving the angiotensin II (ANG II) receptor antagonist, losartan potassium (10 mg/kg i.v.; n = 10). DRIVE was achieved by infusing 100 microliters of 2.5% albumin solution directly into the renal interstitium. GFR remained unchanged by DRIVE in both groups. In control animals, DRIVE significantly increased both RIHP (delta 3.8 +/- 0.5 mmHg) and FENa (delta 0.92 +/- 0.19%). In the losartan-treated group, RIHP (delta 2.8 +/- 0.4 mmHg) and FENa (delta 1.93 +/- 0.41%) also significantly increased. The natriuretic response to DRIVE was significantly enhanced during ANG II receptor blockade compared with control animals (delta UNaV/delta RIHP = 2.01 +/- 0.67 vs. 0.44 +/- 0.17 mu eq.min-1 x mmHg-1, respectively; P < 0.05). These results suggest that the blockade of angiotensin enhances the natriuretic response to increased RIHP during DRIVE.

Soil Quality and Financial Performance of Biodynamic and Conventional Farms in New Zealand

Biodynamic farming practices and systems show promise in mitigating some of the detrimental effects of chemical-dependent, conventional agriculture on the environment. The physical, biological, and chemical soil properties and economic profitability of adjacent, commercial biodynamic and conventional farms (16 total) in New Zealand were compared. The biodynamic farms in the study had better soil quality than the neighboring conventional farms and were just as financially viable on a per hectare basis.

Relation between vasa recta blood flow and renal interstitial hydrostatic pressure during pressure natriuresis

Pressure natriuresis may be mediated through increases in inner medullary vasa recta blood flow (QVR). By means of acute renal decapsulation to prevent increases in renal interstitial hydrostatic pressure (RIHP), the effect of increases in QVR in the presence and absence of changes in RIHP in the natriuretic and diuretic responses to increases in renal perfusion pressure (RPP) was evaluated. Blood flow in descending (QDVR) and ascending (QAVR) vasa recta was determined in the exposed papilla by fluorescence videomicroscopy in anesthetized euvolemic Munich Wistar rats. In rats with intact renal capsules (n = 12), increases in RPP from 101 +/- 0.5 to 132 +/- 2.9 mm Hg caused significant increases in QDVR (from 4.7 +/- 0.9 to 5.5 +/- 0.9 nl/min, p < 0.001) and QAVR (from 2.8 +/- 0.2 to 3.5 +/- 0.2 nl/min, p < 0.001) in association with increases in RIHP (from 4.6 +/- 1.3 to 7.6 +/- 1.3 mm Hg, p < 0.001), urine flow (from 16.2 +/- 2.6 to 20.2 +/- 3.2 microliters.min-1 x g kidney wt-1, p < 0.01), and urinary sodium excretion (from 2.10 +/- 0.38 to 3.36 +/- 0.62 mu eq.min-1 x g kidney wt-1, p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Do rheological variables play a role in diabetic peripheral neuropathy?

Whole blood viscosity and its determinants were measured in diabetic patients with and without peripheral neuropathy to assess whether these variables could have a role in the microvascular aetiology of diabetic peripheral neuropathy. Although corrected whole blood viscosity at high and low shear rates (5.29 +/- 0.51 and 21.10 +/- 3.03 mPa s), plasma viscosity (1.41 +/- 0.13 mPa s), and red cell filtration ratio (0.49 +/- 0.04) in diabetic patients were significantly different from non-diabetic control subjects (high shear rate 4.83 +/- 0.54, low shear rate 17.36 +/- 2.78, plasma 1.29 +/- 0.09 mPa s, all p less than 0.001, and red cell filtration ratio 0.55 +/- 0.03, p less than 0.001) there were no significant differences between diabetic patients with neuropathy and those without. Blood rheology is altered to a similar extent in diabetic patients with and without neuropathy.