M. J. Parnham

Immunomodulatory-antiinflammatory functions of E-type prostaglandins. Minireview with emphasis on macrophage-mediated effects.

The biological transformation of arachidonic acid (AA) leads to a wide array of physiologically active products which are involved in several aspects of the inflammatory process. Depending upon various factors, including its anatomical location, arachidonic acid undergoes biotransformation by the membrane-bound enzyme cyclo-oxygenase and by cytoplasmic lipoxygenase enzymes. The capacities of the prostaglandins PGE2 and PGD2 and of prosta- cyclin (PGI2)--all derived via the cyclo-oxygenase pathway--to enhance the vascular-exudative com- ponent of inflammation have been most extensively studied. Furthermore, substances such as the hydroxy acid 12-HETE and particularly the recently discovered leukotrienes--all generated via the lipoxygenase pathways--are markedly chemotactic and contribute to cellular infiltration during inflam- mation. Thus, the majority of established concepts of inflammation emphasize these and other metabolites of AA as proinflammatory substances. The fact that inhibitors of cyclo-oxygenase are powerful anti- inflammatory agents is also telling evidence in favour of the above view, which has gained additional momentum from more recent observations, suggest- ing that similar anti-inflammatory drugs may also counteract the formation of at least some lipoxy- genase products (Atkinson & Collier, 1980). Never- theless, the view that the inflammatory process is exclusively promoted by metabolites of AA is over- simplified. Evidence is accumulating that, depending on the experimental situation that is studied, PGE2 displays either pro- or anti-inflammatory effects (Morley, 1979; Bonta & Parnham, 1978, 1980). While such a dual function has not been convincingly shown for other products of AA-bioconversion, the bis-homo-gamma-linoleic acid derived PGEI does share this property with PGE2 (Kunkel, Thrall, Kunkel, McCormick, Ward & Zurier, 1979; Bonta & Parnham, 1978, 1980). AA and bis-homo-gamma- linoleic acid are essential fatty acids (EFA) and EFAs

Reduced exudation and increased tissue proliferation during chronic inflammation in rats deprived of endogenous prostaglandin precursors

Two models of chronic inflammation were studied in rats deprived of endogenous precursors of prostaglandins by feeding the animals on essential fatty acid deficient (EFAD) food. During kaolin-induced pouch-granuloma, exudate production was markedly reduced in EFAD rats, when compared with normal animals. The exudates from normal rats contained large amounts of PGE, but in the exudates from EFAD rats the amount of PGE was very markedly reduced. Similarly, with carrageenan-impregnated polyether sponges, the exudative component of inflammation was reduced in EFAD rats. However, the proliferative component was significantly increased, particularly in relation to the stunted growth of EFAD rats. Sponge exudates from EFAD rats contained fewer leucocytes than those from normal animals but the fall in leucocyte count was much smaller than the very marked reduction in PGE activity. EFAD rats also exhibited a significant increase in adrenal weights. The results are discussed in the light of the ambivalent (pro- or anti-inflammatory) role of endogenous PGS. It appears that, in the proliferative phase of inflammation, the anti-inflammatory role of PGs is more dominant.

5 Anti-Rheumatic Drugs: Present Deadlock and New Vistas

Publisher Summary This chapter discusses anti-rheumatic drugs. The broadly accepted views on anti-rheumatic drugs in present clinical use have been discussed mainly as background information. The side effects of clinically used anti-rheumatic drugs or rather, biopharmaceutical and structural modifications required to abolish side effects, have also been discussed in this chapter. It discusses several drugs that are not anti-inflammatory but do benefit rheumatoid arthritis patients, influence events that are either not involved in conventional inflammatory animal models or their possible involvement has not been sufficiently explored. Besides rheumatoid arthritis, there are two other joint conditions in which inflammation dominates: gouty arthritis induced by monosodium urate crystal deposits and pseudo-gout. The chapter discusses physiological mechanisms, as they seem to operate (as defective autoregulatory processes) during rheumatoid arthritis to cause the unpredictably fluctuating spontaneous remissions.

Prostaglandin E2 elevation of cyclic-AMP in granuloma macrophages at various stages of inflammation: Relevance to anti-inflammatory and immunomodulatory functions

In the carrageenin-induced granuloma of rats the inflammatory tissue growth and macrophage invasion on the one hand and the cyclic-AMP content of the macrophages on the other, display opposite directional changes. Macrophages, isolated from this tissue at different stages of inflammation, were used to examine the effect of prostaglandin E2 on intracellular levels of c-AMP. It appears that during infiltration of the macrophages into the inflammatory tissue, the sensitivity of adenylate cyclase to activation by PGE2 increases. Arguments are presented that these observations made in vitro, are in direct relevance to the previous described anti-inflammatory effect of PGE on granuloma tissue in vivo.

The use of essential fatty acid deficient rats to study pathophysiological roles of prostaglandins. Comparison of prostaglandin production with some parameters of deficiency

In a retrospective study on essential fatty acid deficient, (EFAD) rats used to study pathophysiological roles of prostaglandins (PGs) slight increases in the linoleic acid content of the diet were found to gradually restore the depressed growth rate and to increase the reduced endogenous PG production. These apparently poorly deficient animals had a serum triene tetraene (ω9:ω6) ratio much higher than the value of 0.4 used as a criterion for EFA deficiency by nutritionists. Changes in body weight, serum ω9∶ω6 and platelet PG production were not correlated with each other. Feeding rats on a diet containing <0.1 mg/g/linoleic acid led to decreasing platelet PG production as the degree of EFA deficiency increased. At this high level of deficiency, a serum ω9∶ω6 ratio of 6 or over was achieved. This high ratio may be taken as anindicator of the degree of EFA deficiency required for studies of PG deprivation, but PG production by the tissue investigated or by plalets should preferentially be measured.

Cannulated sponge implants in rats for the study of time-dependent pharmacological influences on inflammatory granulomata

Abstract An experimental granuloma method is described which consists essentially of implanting carrageenin-impregnated polyether sponges, provided with a polythene cannula, into dorsal subdermal tissue of rats. The cannula is exteriorized at the back of the neck and allows the administration of drugs into the sponge implant at any chosen time during the different phases of granuloma development. The value of the method is illustrated by brief reference to the effects of PGEs and the phenolic antioxidant, MK-447, on exudative and proliferative components of 8-day inflammatory granulomata. With each of the substances, the effects were either facilitary or inhibitory depending on the time at which the administration into the inflamed site took place.

Distinction between prostaglandin E2 and prostacyclin as inhibitors of granulomatous inflammation

Prostaglandins (PGs) of the E series, are detectable at inflamed sites and exert pro-inflammatory actions, such as vasodilatation and potentiation of plasma exudation induced by other mediators (see Flower 1977). However, with animal models of chronic inflammation, high doses of PGEs exert anti-inflammatory actions in vivo (see Bonta & Parnham 1978). Recently, we observed that local administration of PGE,, at 1000-fold lower doses than those used by other authors, during the early phase of spongeinduced granulomatous inflammation, enhances subsequent granuloma formation, whereas administration during the later phase inhibits granuloma formation (Bonta & Parnham 1979). In fact, in rats which were deficient in the fatty acid precursors of endogenous PGs, exogenous PGEl inhibited granuloma formation when given at the low daily dose of 50ng. We now report similar proand anti-granuloma effects with low doses of PGE, (the most commonly detected PG at inflamed sites) and additionally show that the later inhibitory effects of PGE, on granuloma formation are capable of counteracting the early stimulatory effects. We have also compared the inhibitory action of PGE, with other PGs including prostacyclin (PGIJ, a novel PG (Moncada et al 1976) which has been found to exert similar actions to PGE,, including vasodilatation and increased vascular permeability (Peck & Williams 1978; Higgs et al 1978b; Murota et al 1978). Granulomatous inflammation was induced in rats, using subcutaneously implanted, carrageenan-soaked, polyether sponges (2 per rat) with indwelling cannulae (Bonta et a1 1979), and the PGs were injected either with the 1 ml 2% Na carrageenan on implantation (day 1) and/or through the cannulae (in 0.51111) at different times, as described earlier (Bonta & Parnham (Moncada et a1 1976). All rats were killed on day 8, sponges removed and granuloma formation expressed as the dry weight of tissue surrounding the sponges (Bonta et a1 1979). In some experiments, both adrenals from each rat were removed and weighed together, their weights being expressed in terms of 1OOg body weight. Table 1 shows that, while injection of PGE, (2 pg) into sponges on implantation (day 1) had no effect on granuloma formation, measured after 8 days, the same daily dose administered on days 1-3 enhanced granuloma formation after 8 days. This action is similar to the granuloma stimulation produced by PGE, (1 pg), which was thought to be secondary to an initial vasodilating action, following injection on day 1 (Bonta & Parnham 1979). Furthermore, the inhibition of 8 day granuloma formation caused by administration of PGEa on days 4-7 (Table 1) was identical to the effect of PGE, administered over the same period (Bonta & Parnham 1979). It should be noted that the increase in control (saline-treated) granuloma weights with progressively later treatment periods, is coinci dental, since, in a large number of control experiments, granuloma weight was unrelated to timing of saline treatment, despite considerable variation in granuloma weights (Bonta et al 1979). Furthermore, it was previously found that this variation in granuloma weights did not alter the effects of added PGEl (Bonta & Parnham 1979). Thus, PGE, injected on day 1 enhanced granuloma weight when control values ranged from 0.32 to 0.78 g and when injected on days 4-7, PGE, inhibited granuloma weight in experiments in which control values ranged from 0.35 to 1.03 g. In the present study PGE,, administered on days 4-7, inhibited granuloma weight in two experiments in which

Bioassay by cascade superfusion using a highly sensitive laminar flow technique

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Comparison of the effects of inhibitors of cytochrome P-450-mediated reations on human platelet aggregation and arachidonic acid metabolism

Metyrapone and SKF-525A, together with amphenone B, a structural analogue of metyrapone, which are all inhibitors of cytochrome P-450-mediated reactions, were shown to inhibit the arachidonic acid-induced aggregation of human platelets. Amphenone B, like metyrapone, exhibited a type II (ligand) binding spectrum with rat liver microsomal cytochrome P-450, in contrast to SKF 525A which is a type I (substrate) binding agent. Independently of their type of binding spectra and of their maximum spectral change, however, the affinity of the three compounds for rat liver cytochrome P-450 showed a close proportional correlation with their platelet aggregation inhibitory potency. All three compounds inhibited the formation of [1-14C]thromboxane B2 from [1-14C]arachidonic acid by human platelets aggregated with collagen. The effect of metyrapone on the remaining labelled products suggested that it is a selective thromboxane synthesis inhibitor, while amphenone B exhibited activity reminiscent of cyclo-oxygenase inhibitors. SKF 525A produced complex effects possibly attributable to cyclo-oxygenase inhibition and enhanced lipid peroxidation, since it also enhanced platelet malonaldehyde formation, which the other two compounds inhibited. These data provide further support for a role of cytochrome P-450 in thromboxane synthesis and platelet aggregation.

Enhancement by prostaglandin E1 and essential fatty acid deficiency of the passive transfer of delayed hypersensitivity to PPD in rats. Comparison with effects on delayed hypersensitivity to SRBC in mice.

Abstract Treatment of Freunds complete adjuvant sensitised rats with PGE1 (1.5 mg/kg/day), on days 6–13 after sensitization, or feeding them an essential fatty acid deficient (EFAD) diet, both enhanced the delayed hypersensitivity (DH) response to purified protein derivative of tuberculin (PPD), measured following transfer of donor lymph node cells into syngeneic recipients. The effect of EFA deficiency was more marked than that of PGE1. In vitro preincubation of lymph node cells obtained from sensitised rats with PGE1 (1 μg/ml) for 10 min, 2 h or 19 h also enhanced the subsequent transfer of DH to PPD. Lower doses of PGE1 were without effect after 10 min incubation. A single 100 μg dose of PGE1, given 24 h before transfer of spleen cells from mice sensitised with sheep red blood cells (SRBC), diminished the subsequent development of the DH response to SRBC in recipient mice. The primary DH response was inhibited more markedly than the secondary response. The results with PGE1 in rats confirm earlier results of other authors on the effects of PGE1 given directly to rats and guinea pigs in which a state of DH to PPD was established. It is suggested that PGE1 may act either through a cyclic AMP-mediated stimulation of a subpopulation of T-lymphocytes or via inhibition of T-suppressor cells activated by PPD. The results with EFAD rats are most likely attributable to removal of an inhibitory effect of EFAs per se on T-lymphocyte activation. The effects of PGE1 on DH to SRBC in mice confirm other data on the inhibitory effects of this PG on lymphocyte function and clearly indicate a difference in the effect of PGE1 on different models of DH.