A QUANTITATIVE ASSESSMENT OF THE TOPICAL ANTI-PHLOGISTIC POTENCIES OF CORTICOSTEROIDS AND NON-STEROIDS

Thesis Overview

INTRODUCTIONInjury to the body is inevitable. This could be consequent upon physical, chemical, biological or any other stimuli of sufficient intensity.Attempts by the body to limit the spread of the injury and/or the injurious agent as well as to resolve any consequent damage is referred to as inflammation. Inflammatory reactions are necessary for the maintenance of life and therefore for the continuity of the species (i). the diversity of the causative factors, makes inflammation one of the commonest and most important conditions in the clinics. Observational interests on inflammation is probably as old as man, but the earliest known descriptions by Edwin Smith’s Egyptian – papyrus dates from about 1550 B.C. (2). More documents from Egypt and other early civilizations leave no doubt that inflammation was recognized from very early times. However, the under-standing of the process took a long time. Calcium (BC 30 – AD 38) and Galen (AD 130 – 200) were among the first to appreciate the cardinal signs of inflammation=redness, heat, selling and pain (23)Thereafter, several investigations over the centuries have equipped us with a greater and appreciable under=standing of the inflammatory process.MAIN EVENTS OF THE INFLAMMATORY PROCESSSubsequent to injury, the inflammatory response results from the summation of small distinct local reactions in the injured tissue. Some of these events are illustrated in the Lewis’ ‘’Tripple response’’ as flush, flare and wheal (4). These being descriptions based on macroscopic observation. Macroscopic investigations have revealed that the responses of the vessels and other local components of the damaged tissue are far more complex than might be thought of from macroscopic observation.Although the inflammatory process in its entirety has been extensively studied over the past years, its complexity has prevented full elucidation of the various mediators and mechanism of mediation.However, auto pharmacological methods and the use of specific pharmacological antagonists have elaborated a serious of putative mediators of inflammation. Many of these agents share several common properties and may produce distinct and rele4vant signs and symptoms of the process. Some have been extensively studied, several are still not completely characterised.Inflammation therefore is a multi-mediated process and its signs and symptoms can be regarded as the expression of the pharmacological effects of endogenously mobilized materials acting locally (5).Immediately upon impact (as in physical stimuli), there is transient Ischaemia from vasoconstriction. Then follows a progressive dilatation of the blood vessels due to release of histamine and other vasoactive substances from resident cells (6). By anti-dromic stimulation of sensory nerve endings supplying the blood vessels, histamine produces a secondary vasodilatation there is evidence that ATP or ‘substance p’ may be the release vasodilator at this stage (7). These events lead to an increased local blood flow resulting in local heat and redness. Increased vasocular permeability with exudation of plasma proteins and fluid from the circulation into the adjacent extravascular tissue, is responsible for the local oedema seen during the process. Release of chemo-tactic factors (8,9,10,11.) enhance the emigration of blood leukocytes into the injured tissue, where they display increased pseudopodia movements, phagocytising foreign materials and cellular debris and releasing enzymes that are potentially tissue damaging (12). The pain of inflammation may be due to stimulation of sensory nerve endings by substance such as histamine, 5 – hydroxyl tryptamine (5HT), Kinins, low PH and ions from damaged cells (13, 14). Tissue damage and pain are largely responsible for the loss of function that may accompany the inflammatory process.THE ROLE OF ARACHIDONIC ACID METABOLITES IN INFLAMMATIONAlthough many mediators take part in the complex process of inflammation, some of the most important precursor (arachidonic acid), stored predominantly as an esterified component of cell membranes in most tissues (15). Archidonic acid is cleaved from its ester linkage and released by the enzymatic action of phospholipase A2 in response to the inflammatory stimuli. Since PG’s are not stored intracellular, they must be synthesized locally immediately following the release of arachidonic acid. This synthesis is achieved by multi enzyme complexes located in the microsomal fraction of the cell.Arachidomic acid metabolites are obtained via two different pathway (Fig. I).

1. The cyclo-oxygenase enzymatic pathway, which results in the synthesis of the leukotrienies (LTS).

The association between PG’s with inflammation has been demonstrated by a number of investigators (16, 17, 18). In addition to producing the classical signs of inflammation, PG’s also induce fever (1920) and potentiate the effects of histamine and brady kinin (21, 22).Another cyclo-oxygenase product thromboxane A2 has also been implicated in inflammation (23).Leukotrienes, as shown in fig. 1 are the most recently discovered compounds associated with inflammation that are derived via the lipoxygenase pathway. This pathway has been shown to be highly active in human skin. LPB4 is the most potent chemotactic agent known. LTC4 and LTD4 are inducers of increased vasoular permeability in the skin (27).Co-production of cytotoxic oxygen radicals, also cause damage to surrounding tissue.ANTI-INFLAMMATORY AGENTSFundamentally, inflammation is a protective and often life-saving process serving, to remove or neutralize exogenous and endogenous noxious agents; to dispose of cells and other constituents of the host tissue which have been killed or damaged in the defence reaction; and to repair the damage sustained either by complete restoration (regeneration) of the affected tissue or by scar formation. Although of great importance for survival, it may occasionally cause harmful effects. The inflammatory responses intended to destropy hostile elements may damage the body itself and excessive and prolonged inflammation is likely to occur when the offending agent cannot be eradicated. In often useful.NON-STEROIDAL ANTI-INFALMMATORY DRUGS (NSAID’S)Many pharmacological agents that produce anti-inflammatory activity, do so by inhibiting the synthesis of PG’S. There is a strong correlation between anti-inflammatory activity and inhibition of PG synthesis as indicated by the action of the NSAID’S.The NSAID’S cause a blockade of only the cyclooxygenase pathway of arachidonic acid metabolism by inactivating the enzyme – cyclo-oxygenase. Other anti-inflammatory effects of NSAIDS, some of which are associated with PG inhibition include the inhibition of: hyaluranidase enzymes activity, migration and phagocytic activity of polymorphs, the complement system, plasmin, kinin formation and platelet aggregation. NSAID’S may antagonize Algeria by depressing pain stimuli at a sub-cortical site. Their anti-pyretic potency is of benefit in reducing the pyrexia that may accompany the inflammatory response (24, 25, 26, 27). The side effects of the use of NSAIDS in inflammation ironically results from the mechanism by which they achieve their therapeutic effect, that is, by PG inhibition and include gastro intestinal irritation, ulceration dyspepsia, nephrotoxicity, prolonged bleeding, prolonged gestation heache, dizziness, tinnitus and blurred vision (28, 29).CORTICOSTEROIDSThe corticosteroids are steroid hormones produced by the cortex of the adrenal gland. Those with anti-inflammatory activity are the glucocorticoids (30, 31, 32), while those with significant inneralocorticoid activity have no effective anti-inflammatory actions (33).Modifications of the natural glucocorticoid structure yields derivative whose anti-inflammatory actions are more pronounced. However the means whereby anti-inflammatory potency is enhanced by these structural modifications are not yet understood.The glucocorticoids act by protein synthesis. They have been shown to block the production of arachidonic acid metabolites by inhibiting the enzyme phospholipase A2 (34, 35, 36). By this action both pathways (Cyclo-oxygenase and lipoxygenase) are automatically and simultaneously blocked.Other actions of the corticosteroids include the stimulation of adeny cyclase enzyme, stabilization of cellular and lysosornal membranes, inhibition of collagenase activity, depression of vascular reactivity modification of immune responses and blockade of pyragenic reactions.However, the use of steroids as anti-inflammatory drugs predispose patients to various types of adverse effects which include adrenal suppression, peptic ulceration, increased susceptibility to infection, rogenic Cushing syndrome, hypo kalaernia, alkalosis, oedema, myopathy, nervousness, insomnia and growth retardation (especially in children)The glucocorticoids show an increased activity over the non steroidal agents. This could be partly explained by the fact that steroids block both the cyclo and lipoxygenase pathways.Having examined the therapeutic basis of these agents, their potential toxicity following systemic administration as well as well as the greater anti-inflammatory activity of the cortico-steroids over the non-steroids, it became necessary to synthesize new glucorcorticoid preparations that possess different and variable degrees of such pharmacological properties as potency, duration of action, lipid solubility, plasma porotein binding and gastro intestinal tract stability.This study therefore compares the topical antiplogistic efficacy of some glucocorticoid derivatives (dexamethasnone, betamethasone, fluocortolone moneacetate, hydrocortisone and cortisone) relative to that of the non steroidal agents (acetyl salicyclic acid and indomethacin).