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Biomedical subjects

L G Cleland

Publications and source records attributed to L G Cleland.

At least 19 recordsLinked to original sources

Applying a research ethics committee approach to a medical practice controversy: the case of the selective COX-2 inhibitor rofecoxib.

The new class of anti-inflammatory drugs, the COX-2 inhibitors, have been commercially successful to the point of market dominance within a short time of their launch. They attract a price premium on the basis that they are associated with fewer adverse gastric events than traditional anti-inflammatory drugs. This marketing continues even though a pivotal safety study with one of the COX-2 inhibitors, rofecoxib, showed a significant increase in myocardial infarction with rofecoxib use compared with a traditional anti-inflammatory drug. This finding has led to a series of publications containing pooled analyses of existing data that both support and refute the possibility of increased cardiovascular risk with COX-2 inhibitors. These medical journal publications have served to obfuscate rather than provide guidance for medical practitioners. Consideration of a research ethics committee approach to this issue suggests that it would deal with the controversy in a straightforward manner-namely, it would simply inform research participants of the trial results with rofecoxib. The certainty of this research ethics committee approach raises the issue of whether it should be applied in normal medical practice outside of the research environment. A consideration of the legal tests for disclosure of information suggests that therapeutic medical practice should mirror that within the research environment, in this case.

Cardiovascular Diseases↗

Dietary n-3 fats as adjunctive therapy in a prototypic inflammatory disease: issues and obstacles for use in rheumatoid arthritis.

Eicosanoids derived from the n-6 fatty acid, arachidonic acid, and the cytokines interleukin-1beta and tumour necrosis factor-alpha are involved in the signs and symptoms of inflammatory joint disease, as well as the cartilage degradation seen in established rheumatoid arthritis (RA). Then n-3 fatty acids in fish and fish oil can inhibit production of both eicosanoid and cytokine inflammatory mediators and therefore, have the potential to modify RA pathology. Epidemiological studies suggest that fish intake may be preventive for RA and double-blind placebo-controlled studies demonstrate that dietary fish oil can alleviate the signs and symptoms of RA. The implementation of these findings will require among other things, a range of n-3 fat enriched foods, as well as physician awareness of the possibilities for dietary n-3 fat increases to be used as adjunctive therapy in RA.

Arthritis, Rheumatoid↗

A practical approach to increasing intakes of n-3 polyunsaturated fatty acids: use of novel foods enriched with n-3 fats.

OBJECTIVES: To assess the effects of providing a wide range of foodstuffs containing n-3 polyunsaturated fatty acids (PUFA), occurring naturally or from fortification, on intake and blood and tissue proportions of n-3 PUFA. DESIGN: Before/after dietary intervention study. SETTING: Adelaide, Australia. SUBJECTS: 16 healthy males recruited from the community. INTERVENTIONS: Subjects were provided with a range of foodstuffs naturally containing n-3 PUFA (fresh fish, canned fish, flaxseed meal, canola oil) and items fortified with fish oil (margarine spread, milk, sausages, luncheon meat, french onion dip). Food choices were left to the discretion of each subject. Intake was estimated by diet diary. Blood was collected at-2, 0, 2, and 4 weeks for fatty acid analysis. MAIN OUTCOME MEASURES: Dietary intakes; plasma, platelet, and mononuclear cell phospholipid fatty acids. RESULTS: Consumption of n-3 PUFA increased significantly: alpha-linolenic acid (ALA) from 1.4 to 4.1 g/day (P<0.001), eicosapentaenoic acid (EPA) from 0.03 to 0.51 g/day (P<0.001), and docosahexaenoic acid (DHA) from 0.09 to 1.01 g/day (P<0.001). Linoleic acid (LA) intake decreased from 13.1 to 9.2 g/day (P<0.001). The proportions of EPA and DHA increased significantly in all phospholipid pools examined; plasma EPA from 1.13% of total fatty acids to 3.38% (P<0.001) and DHA from 3.76 to 7.23% (P<0.001); mononuclear cell EPA from 0.40 to 1.25% (P<0.001) and DHA from 2.33 to 4.08% (P<0.001); platelet EPA from 0.41 to 1.2% (P<0.001) and DHA from 1.64 to 3.07% (P<0.001). CONCLUSION: Incorporating fish oil into a range of novel commercial foods provides the opportunity for wider public consumption of n-3 PUFA with their associated health benefits. SPONSORSHIP: Dawes Scholarship, Royal Adelaide Hospital.

Adult↗

Roles of cyclooxygenase (COX)-1 and COX-2 in prostanoid production by human endothelial cells: selective up-regulation of prostacyclin synthesis by COX-2.

The two cyclooxygenase (COX) isoforms, COX-1 and COX-2, both metabolize arachidonic acid to PGH(2), the common substrate for thromboxane A(2) (TXA(2)), prostacyclin (PGI(2)), and PGE(2) synthesis. We characterized the synthesis of these prostanoids in HUVECs in relation to COX-1 and COX-2 activity. Untreated HUVEC expressed only COX-1, whereas addition of IL-1beta caused induction of COX-2. TXA(2) was the predominant COX-1-derived product, and TXA(2) synthesis changed little with up-regulation of COX-2 by IL-1beta (2-fold increase). By contrast, COX-2 up-regulation was associated with large increases in the synthesis of PGI(2) and PGE(2) (54- and 84-fold increases, respectively). Addition of the selective COX-2 inhibitor, NS-398, almost completely abolished PGI(2) and PGE(2) synthesis, but had little effect on TXA(2) synthesis. The up-regulation of COX-2 by IL-1beta was accompanied by specific up-regulation of PGI synthase and PGE synthase, but not TX synthase. An examination of the substrate concentration dependencies showed that the pathway of TXA(2) synthesis was saturated at a 20-fold lower arachidonic acid concentration than that for PGI(2) and PGE(2) synthesis. In conclusion, endothelial prostanoid synthesis appears to be differentially regulated by the induction of COX-2. The apparent PGI(2) and PGE(2) linkage with COX-2 activity may be explained by a temporal increase in total COX activity, together with selective up-regulation of PGI synthase and PGE synthase, and different kinetic characteristics of the terminal synthases. These findings have particular importance with regard to the potential for cardiovascular consequences of COX-2 inhibition.

Aspirin↗

COX-2 inhibition and thrombotic tendency: a need for surveillance.

Cyclooxygenase-2 (COX-2) inhibitors belong to a new class of drugs which have anti-inflammatory efficacy similar to that of traditional non-steroidal anti-inflammatory drugs (NSAIDs), but are associated with a reduced incidence of adverse upper gastrointestinal events. Biochemical evidence that COX-2 inhibitors could promote or exacerbate a tendency to thrombosis is supported by recent results from clinical trials and case reports. Two agents in this class, celecoxib and rofecoxib, have been listed on the Pharmaceutical Benefits Scheme (PBS) for very broad indications in chronic arthropathies, suggesting that they will move into widespread community use. It is important to canvass the possibility that use of these agents could be associated with thrombotic events.

Anti-Inflammatory Agents, Non-Steroidal↗

Up-regulation of endothelial cyclooxygenase-2 and prostanoid synthesis by platelets. Role of thromboxane A2.

Platelet-vascular endothelial cell interactions are central to the maintenance of vascular homeostasis. Thromboxane A2 (TXA2) and prostacyclin (prostaglandin (PG)I2) are the major products of cyclooxygenase (COX) metabolism by platelets and the vascular endothelium, respectively. Here we report the effects of platelet-endothelial interactions on human umbilical vein endothelial cells (HUVECs) COX-2 expression and prostanoid synthesis. Co-incubation of platelets with HUVECs resulted in a dose-dependent induction in COX-2 expression. This was accompanied by a relatively small increase in thromboxane B2 synthesis (2 ng) by comparison to the production of 6-keto-PGF1alpha and PGE2, which increased by approximately 14 and 12 ng, respectively. Abrogation of platelet-HUVEC interactions excluded direct cell-cell contact as a required event. Preincubation of HUVECs with SQ29548, a TXA2 receptor antagonist, dose-dependently inhibited platelet-induced COX-2 expression and prostanoid synthesis. Similarly, if platelet TXA2 synthesis was inhibited no induction of COX-2 was observed. Furthermore, a TXA2 analog, carbocyclic TXA2, induced HUVEC COX-2 expression and the synthesis of 6-keto-PGF1alpha and PGE2. This was also associated with an increase in the expression and activity of PGI synthase and PGE synthase but not TX synthase. Platelet co-incubation (or TXA2) also selectively activated the p44/42 mitogen-activated protein kinase pathway to regulate HUVEC COX-2 expression. Thus it seems that platelet-derived TXA2 can act in a paracrine manner to up-regulate endothelial COX-2 expression and PGI2 synthesis. These observations are of particular importance given the recent observations regarding selective COX-2 inhibitors and the suppression of PGI2 synthesis.

Blood Platelets↗

Eicosanoid production by human monocytes: does COX-2 contribute to a self-limiting inflammatory response?

The eicosanoids, prostaglandin E2 (PGE2) and thromboxane A2 (TXA2), are involved in inflammatory events. TXA2 has potentially pro-inflammatory actions and PGE2 has actions which can be considered both pro- and antiinflammatory. Therefore, it is potentially significant that production of TXA2 and PGE2 by stimulated monocytes have very different time courses. TXA2 synthesis is immediate and dependent on cyclooxygenase Type 1 (COX-1) activity whereas PGE2 synthesis is delayed and dependent on COX-2 activity. These apparent COX-isotype dependencies of TXA2 and PGE2 synthesis can be explained by differences in the affinities of TXA synthase and PGE synthase for the common substrate, PGH2. The findings have implications for the use of NSAIDs and selective COX-2 inhibitors whose actions can increase the monocyte TXA2/PGE2 ratio.

Cyclooxygenase 2↗

Characterization of thoracic duct cells that transfer polyarthritis.

Polyarthritis may result from the haematogenous distribution of arthritogenic effector lymphocytes that emerge in the efferent lymph and pass through the thoracic duct (TD) to the circulation. We therefore examined whether TD cells collected from rats in the late prodrome of adjuvant-induced arthritis (AA) could transfer polyarthritis adoptively and whether these cells included a subpopulation of arthritogenic cells that could be identified phenotypically. Unfractionated TD cells collected from donor rats 9 days after adjuvant inoculation were injected intravenously into normal syngeneic recipients in numbers equivalent to the overnight harvest from a single donor. TD cell subpopulations, equivalent in number to proportions in the same inoculum, were prepared by negative selection. Unfractionated TD cells transferred polyarthritis without in vitro stimulation or conditioning of recipient animals. Abrogation of arthritogenicity by depletion of alpha/beta TCR(+) cells showed that the polyarthritis was transferred by T cells. Negatively selected CD4(+) but not CD8(+) TD cells transferred AA. An arthritogenic subpopulation of CD4(+) T cells, enriched by either negative or positive selection, expressed the activation markers CD25 (IL-2 receptor alpha), CD71 (transferrin receptor), CD134 (OX40 antigen) and MHC class II. Cells expressing these markers were more numerous in TD lymph from arthritic rats than in lymph from normal rats and they included the majority of large CD4(+) T cells. Thus, arthritogenic effector T cells bearing activation markers are released into the central efferent lymph in the late prodrome of AA. Recruitment of these arthritogenic cells to synovium probably determines the polyarticular pattern of AA.

Adoptive Transfer↗

Recruitment of mononuclear leucocytes to osteoarthritic human synovial xenografts in the ears of SCID mice.

A system has been established to assess the recruitment of 99mTc-hexamethylpropylene amine oxamine (99mTc-HMPAO)-labelled PBMC and [125I]iododeoxyuridine-labelled Con A stimulated lymphoblasts to allogeneic human synovial xenografts in the ears of SCID mice. Successful engraftment of osteoarthritic synovium was achieved in approximately 90% of cases and a connection between the human microvasculature of the xenograft and the circulation of the mouse was shown. Cells were delivered to the xenograft by a system of regional vascular perfusion, thus avoiding the major murine vascular beds. The accumulation of 99mTc-HMPAO-labelled PBMC in mouse ears was monitored in real time. Direct injection of xenograft-bearing ears with recombinant human TNF-alpha, 7 h prior to perfusion, increased the accumulation of both PBMC and lymphoblasts in cytokine-injected ears compared to contralateral control-injected ears. Autoradiography revealed the presence of [125I]iododeoxyuridine-labelled lymphoblasts associated with human microvasculature within the xenograft. However, the increased accumulation of lymphoblasts in cytokine-injected ears occurred in the tissues surrounding the xenograft, where lymphoblasts were associated more often with murine than human vessels. Although the system described offers advantages over similar models, the propensity for mouse endothelium to interact with human leucocytes is likely to be a generic disadvantage for models of human leucocyte recruitment to xenografts in immunodeficient mice.

Animals↗

Differential regulation of prostaglandin E2 and thromboxane A2 production in human monocytes: implications for the use of cyclooxygenase inhibitors.

There is an autocrine relationship between eicosanoid and cytokine synthesis, with the ratio of prostaglandin E2 (PGE2)/thromboxane A2 (TXA2) being one of the determinants of the level of cytokine synthesis. In monocytes, cyclooxygenase type 1 (COX-1) activity appears to favor TXA2 production and COX-2 activity appears to favor PGE2 production. This has led to speculation regarding possible linkage of COX isozymes with PGE and TXA synthase. We have studied the kinetics of PGE2 and TXA2 synthesis under conditions that rely on COX-1 or -2 activity. With small amounts of endogenously generated prostaglandin H2 (PGH2), TXA2 synthesis was greater than PGE2. With greater amounts of endogenously generated PGH2, PGE2 synthesis was greater than TXA2. Also, TXA synthase was saturated at lower substrate concentrations than PGE synthase. This pattern was observed irrespective of whether PGH2 was produced by COX-1 or COX-2 or whether it was added directly. Furthermore, the inhibition of eicosanoid production by the action of nonsteroidal anti-inflammatory drugs or by the prevention of COX-2 induction with the p38 mitogen-activated protein kinase inhibitor SKF86002 was greater for PGE2 than for TXA2. It is proposed that different kinetics of PGE synthase and TXA synthase account for the patterns of production of these eicosanoids in monocytes under a variety of experimental conditions. These properties provide an alternative explanation to notional linkage or compartmentalization of COX-1 or -2 with the respective terminal synthases and that therapeutically induced changes in eicosanoid ratios toward predominance of TXA2 may have unwanted effects in long-term anti-inflammatory and anti-arthritic therapy.

Arachidonic Acid↗

Assay of cyclooxygenase-1 and 2 in human monocytes.

OBJECTIVE AND DESIGN: There is frequently poor correlation between in vitro methods for calculated cyclooxygenase (COX)-1/COX-2 selectivities of inflammatory agents. Therefore, we have examined the use of a single stimulus in a single cell type containing both COX isoforms, for determining the selectivities of COX-inhibitory agents. METHODS: Fresh human monocytes were stimulated with arachidonic acid (AA; 10 microM) for 15 min and prostaglandin E2 (PGE2) and thromboxane B2 (TXB2) production were used as a measure of COX-1 activity. To measure COX-2 activity, cells were transiently pre-treated with aspirin to irreversibly inhibit constitutive COX-1, treated with lipopolysaccharide (LPS) to induce COX-2 and then stimulated with AA. RESULTS: Eicosanoid production in resting monocytes was predominantly COX-1 derived since it was not inhibited by NS-398 and also, COX-2 was not detectable. In LPS treated monocytes pre-treated transiently with aspirin, neither the level of induced COX-2 nor the activity was affected. Using the mean of the results for PGE2 and TXB2 inhibition, the COX-1/COX-2 ratios of the IC50 values for aspirin and NS-398 are < 0.1 and > 130, respectively. CONCLUSIONS: This study has provided a system for investigating inhibition of COX isotypes without the potentially confounding effects of using different cell types with different stimuli for each isotype as seen in other published systems. Dose responses to aspirin and NS-398 which are COX- and COX-2 selective inhibitors respectively, confirmed the utility of this system.

Aspirin↗

Genetic susceptibility and the link between cat exposure and rheumatoid arthritis.

OBJECTIVES: Rheumatoid arthritis (RA) is a chronic inflammatory disease for which immunogenetic susceptibility factors have been defined. In a recent case control study, it was shown that a prior intimate relationship with pet cats or budgerigars confers risk for subsequent development of RA after a period of latency. Pets are a potential reservoir for putative microbial agents that could be a stimulus for chronic inflammation subject to the influence of immunogenetic factors. Therefore, a study was undertaken to determine whether the presence of HLA-DRB1 alleles bearing the RA susceptibility motif influenced risk for RA associated with prior exposure to pets. METHODS: Blood samples were obtained from available RA patients and their case controls who had participated in the prior epidemiologic study. DR and DQ genotypes were determined by sequence analysis of oligonucleotides amplified from the DRB1 and DQB1 genes by polymerase chain reactions (PCR). Subjects were segregated according to pet exposure (as determined previously) and genotype for statistical analyses. RESULTS: The odds ratio (OR) for prepubertal exposure to cats and RA in available subjects irrespective of DRB1 genotype was 4.2 (CI, 2.1 to 8.5; P<.00002). The OR between prior exposure to cats and RA in subjects with the RA susceptibility genotype DRB1 *0401 and *0404 was 5.8 (CI, 1.4 to 26; P<.02) and >24 (CI, 1.6 to 813; P<.01), respectively. In subjects with the genotype DRB1 *1501, the association between RA and prior cat exposure was OR 8.4 (CI, 1.7 to 45; P<.01). No significant association between RA and pet exposure was found in patients selected according to other genotypes. The association between RA and the recognized HLA-DR susceptibility motif was slightly stronger in subjects with a history of intimate cat exposure (OR 4.7 [CI, 1.5 to 14.8], P<.005) than subjects without prior intimate exposure (OR 3.3 [CI; 1.2 to 9.3], P<.02). In the small number of subjects who had reported an intimate association with pet birds, no influence of DR genotype on risk for RA was discerned. CONCLUSIONS: Risk for RA associated with prior intimate exposure to cats is concentrated in subjects with the RA-susceptibility conferring genotypes DRB1 *0401 and *0404. The findings suggest an interaction between an environmen-tal agent associated with pet cats and certain RA susceptibility-conferring DR genotypes. The risk for RA associated with intimate cat exposure also was significant in subjects with DRB1*1501, a genotype not otherwise associated with RA, but which shares with known RA susceptibility-bearing alleles the presence of an electropositive pocket (Pocket 4) in the DR peptide binding groove.

Adult↗

Dietary polyunsaturated fatty acids and inflammatory mediator production.

Many antiinflammatory pharmaceutical products inhibit the production of certain eicosanoids and cytokines and it is here that possibilities exist for therapies that incorporate n-3 and n-9 dietary fatty acids. The proinflammatory eicosanoids prostaglandin E(2) (PGE(2)) and leukotriene B(4) (LTB(4)) are derived from the n-6 fatty acid arachidonic acid (AA), which is maintained at high cellular concentrations by the high n-6 and low n-3 polyunsaturated fatty acid content of the modern Western diet. Flaxseed oil contains the 18-carbon n-3 fatty acid alpha-linolenic acid, which can be converted after ingestion to the 20-carbon n-3 fatty acid eicosapentaenoic acid (EPA). Fish oils contain both 20- and 22-carbon n-3 fatty acids, EPA and docosahexaenoic acid. EPA can act as a competitive inhibitor of AA conversion to PGE(2) and LTB(4), and decreased synthesis of one or both of these eicosanoids has been observed after inclusion of flaxseed oil or fish oil in the diet. Analogous to the effect of n-3 fatty acids, inclusion of the 20-carbon n-9 fatty acid eicosatrienoic acid in the diet also results in decreased synthesis of LTB(4). Regarding the proinflammatory ctyokines, tumor necrosis factor alpha and interleukin 1beta, studies of healthy volunteers and rheumatoid arthritis patients have shown < or = 90% inhibition of cytokine production after dietary supplementation with fish oil. Use of flaxseed oil in domestic food preparation also reduced production of these cytokines. Novel antiinflammatory therapies can be developed that take advantage of positive interactions between the dietary fats and existing or newly developed pharmaceutical products.

Arachidonic Acid↗

Biochemical effects of a diet containing foods enriched with n-3 fatty acids.

BACKGROUND: Results of many studies indicate that consumption of n-3 fatty acids can benefit persons with cardiovascular disease and rheumatoid arthritis. However, encapsulated fish oil is unlikely to be suited to lifetime daily use and recommendations to increase fish intake have not been effective. OBJECTIVE: The objective was to examine the effectiveness of a diet that incorporates foods rich in n-3 fatty acids in elevating tissue concentrations of eicosapentaenoic acid and in suppressing the production of inflammatory mediators. DESIGN: Healthy male volunteers were provided with foods that were enriched in alpha-linolenic acid (cooking oil, margarine, salad dressing, and mayonnaise) and eicosapentaenoic and docosahexaenoic acids (sausages and savory dip) and with foods naturally rich in n-3 fatty acids, such as flaxseed meal and fish. Subjects incorporated these products into their food at home for 4 wk. Fatty acid intakes, cellular and plasma fatty acid concentrations, and monocyte-derived eicosanoid and cytokine production were measured. RESULTS: Analyses of dietary records indicated that intake of eicosapentaenoic acid plus docosahexaenoic acid averaged 1.8 g/d and intake of alpha-linolenic acid averaged 9. 0 g/d. These intakes led to an average 3-fold increase in eicosapentaenoic acid in plasma, platelet, and mononuclear cell phospholipids. Thromboxane B(2), prostaglandin E(2), and interleukin 1beta synthesis decreased by 36%, 26%, and 20% (P < 0.05), respectively. CONCLUSIONS: Foods that are strategically or naturally enriched in n-3 fatty acids can be used to achieve desired biochemical effects without the ingestion of supplements or a change in dietary habits. A wide range of n-3-enriched foods could be developed to support large-scale programs on the basis of the therapeutic and disease-preventive effects of n-3 fatty acids.

Adult↗

Accessible xenografts of human synovium in the subcutaneous tissues of the ears of SCID mice.

This work was undertaken to examine whether human synovium could be engrafted into subcutaneous pouches in the ears of severe combined immunodeficient (SCID) mice. Synovium was transplanted into surgically constructed ear pouches. The grafts were examined by histological and immunohistochemical methods after varying periods after engraftment, or after percutaneous injection of TNF-alpha. Normal, osteo-arthritic and rheumatoid synovium was engrafted successfully in subcutaneous ear pouches. The general morphology and cellular compositions of xenografts were retained including human endothelial cells. In rheumatoid xenografts, macrophages, fibroblasts and lymphocytes persisted for at least 4 weeks. Vascular expression of intercellular adhesion molecule-1 (ICAM-1) was maintained but expression of vascular adhesion molecule-1 (VCAM-1), E-selectin and MHC class II diminished with time. Percutaneous injection of TNF-alpha induced up-regulation of VCAM-1. Human synovium can be engrafted into subcutaneous ear pouches in SCID mice. The xenografts are accessible and respond to injection of a pro-inflammatory cytokine.

Adult↗

Effects of tumor necrosis factor-alpha, interleukin 1beta, and activated peripheral blood mononuclear cells on the expression of adhesion molecules and recruitment of leukocytes in rheumatoid synovial xenografts in SCID mice.

OBJECTIVE: To examine expression of adhesion molecules within human synovial xenografts in vivo after injection of human cytokines or peripheral blood mononuclear cells (PBMC). METHODS: Rheumatoid synovium was transplanted into subcutaneous pouches in the ears of severe combined immunodeficient (SCID) mice. Tumor necrosis factor-alpha (TNF-alpha), interleukin 1beta (IL-1beta), or PBMC were injected into the xenografts. The grafts were assessed by immunohistochemistry and quantitative video image analysis. RESULTS: TNF-alpha, IL-1beta, and concanavalin A activated PBMC increased the expression of vascular cellular adhesion molecule 1 and intercellular adhesion molecule 1 significantly on vessels and nonvascular synovial cells compared with injection of medium only. Vascular expression of E-selectin, but not of MHC Class II, was also increased. These stimuli also induced the migration of murine leukocytes into the xenografts. CONCLUSION: Rheumatoid synovial xenografts in SCID mice respond by upregulation of adhesion molecule expression when challenged in vivo with proinflammatory cytokines or activated PBMC.

Animals↗