Thorax 2000;55 (Suppl 2):S3–S9 S3 Aspirin and other anti-inflammatory drugs Thorax: first published as 10.1136/thorax.55.suppl_2.S3 on 1 October 2000. Downloaded from Sir John Vane Historical introduction inhibiting COX, thereby reducing prosta- Salicylic acid, the active substance in plants glandin formation, providing a unifying expla- used for thousands of years as medicaments, nation for their therapeutic actions and their was synthesised by Kolbe in Germany in 1874. side eVects. This also firmly established certain MacLagan1 and Stricker2 showed that it was prostaglandins as important mediators of eVective in rheumatic fever. A few years later inflammatory disease (see reviews by Vane and sodium salicylate was also in use as a treatment Botting7 and Vane et al8). COX first cyclises for chronic rheumatoid arthritis and gout as arachidonic acid to form prostaglandin (PG) well as an antiseptic compound. G2 and the peroxidase part of the enzyme then Felix HoVman was a young chemist working reduces PGG2 to PGH2. at Bayer. Legend has it that his father, who was taking salicylic acid to treat his arthritis, Discovery of COX-2 complained to his son about its bitter taste. Over the next 20 years several groups postu- Felix responded by adding an acetyl group to lated the existence of isoforms of COX. Then salicylic acid to make acetylsalicylic acid. Rosen et al,9 studying COX in epithelial cells Heinrich Dreser, the Company’s head of phar- from the trachea, found an increase in activity macology, showed it to be analgesic, anti- of COX during prolonged cell culture. This 3 pyretic, and anti-inflammatory. Bayer intro- increase in activity was not accounted for by an duced the new drug as “aspirin” in 1899 and increase in the known mRNA of 2.8 kb. They sales have increased ever since. found a second mRNA of 4.0 kb and suggested In the latter part of the 20th century several that this was derived from a distinct COX- other non-steroidal anti-inflammatory drugs related gene which encoded for a protein with (NSAIDs) were discovered, including antipy- COX activity. Needleman and his group10–12 rine, phenacetin, phenylbutazone and, more reported that bacterial lipopolysaccharide recently, the fenamates, indomethacin and (LPS) increased the synthesis of prostaglandins naproxen. Despite the diversity of their chemi- in human monocytes in vitro and in mouse cal structures, these drugs all share the same peritoneal macrophages in vivo. This increase, therapeutic properties. They alleviate the but not the basal level of enzyme, was inhibited swelling, redness and pain of inflammation, by dexamethasone and associated with de novo reduce a general fever, and cure a headache. synthesis of new COX protein. This gave rise to They also share, but not equally, a number of the concept of “constitutive” and “inducible” side eVects including damage to the gastric forms of COX. http://thorax.bmj.com/ mucosa, delay in the birth process, and damage The breakthrough came from molecular to the kidney. A particularly interesting “side biologists outside the field of prostaglandins. eVect”, now used prophylactically, is the Simmons et al,13 studying neoplastic transfor- anti-thrombotic eVect. Many clinical trials mation, discovered a second form of COX have shown that aspirin given once a day in induced by v-src, serum, or phorbol esters in doses as low as 75 mg will help to prevent heart chicken embryo cells.13 14 It was encoded by a attacks or strokes. 4.1 kb mRNA similar in size to that reported When a chemically diverse group of drugs by Rosen et al.9 They cloned the gene, deduced on October 1, 2021 by guest. Protected copyright. shares not only the same therapeutic qualities the protein structure, and found it homologous (which in themselves have not much connec- to COX but to no other known protein. tion with each other), but also the same side Herschman and colleagues15 independently eVects, it is a fairly safe bet that their actions are found a similar gene in the mouse, as did Sim- based on a single biochemical intervention. For mons et al,16 O’Banion et al,17 and Sirois and many years pharmacologists and biochemists Richards.18 searched for such a common mode of action COX-1 and COX-2 have molecular weights without finding one that was satisfactory. of 71 kd and a 60% homology. Glucocorticoids It was against this background that, using a inhibit the expression of COX-2 and this is an crude preparation of prostaglandin synthase additional aspect of their anti-inflammatory (now known as cyclo-oxygenase or COX), action. The levels of COX-2, normally very low Vane4 found a dose dependent inhibition of in cells, are tightly controlled by a number of prostaglandin formation by aspirin, salicylate, factors including cytokines, intracellular mes- and indomethacin but not by morphine. Two sengers, and by the availability of substrate. other reports from the same laboratory lent 5 support to his findings. Smith and Willis COX-1 The William Harvey showed that aspirin prevented the release of COX-1 has three folding units: an epidermal Research Institute, prostaglandins from aggregating human plate- growth factor-like domain, a membrane bind- London EC1 6BQ, UK lets and Ferreira et al6 demonstrated that ing section, and an enzymatic domain. The JRVane aspirin-like drugs blocked prostaglandin re- sites for peroxidase and cyclo-oxygenase activ- Correspondence to: lease from the perfused, isolated spleen of the ity are adjacent but spatially distinct. The Sir John Vane dog. Vane4 proposed that all NSAIDs act by enzyme integrates into only a single leaflet of www.thoraxjnl.com S4 Vane the membrane lipid bilayer and thus the muscle cells, pulmonary endothelial cells, and Thorax: first published as 10.1136/thorax.55.suppl_2.S3 on 1 October 2000. Downloaded from position of the COX channel allows arachi- alveolar macrophages treated with LPS or donic acid to gain access to the active site from proinflammatory cytokines. In the carrageenin the interior of the bilayer.19 induced pleurisy model of inflammation, levels NSAIDs compete with arachidonic acid for of COX-2 protein increased maximally at two binding to the active site, thereby excluding hours in the cell pellets of pleural exudate.27 access for the substrate.20 Uniquely, aspirin However, lung tissue can also express COX-2 irreversibly inhibits COX-1 by acetylation of constitutively. COX-2 mRNA is weakly ex- serine 530. COX-1 has clear physiological pressed in unstimulated rat isolated perfused functions. Its activation leads, for instance, to lungs and is upregulated by nitric oxide (NO) the production of prostacyclin which, when donors.28 Human lungs obtained from accident released by the endothelium is victims29 and human cultured pulmonary anti-thrombogenic,21 and when released by the epithelial cells expressed more constitutive gastric mucosa is cytoprotective.22 COX-2 than constitutive COX-1.30 31 Interest- ingly, hypoxia induces COX-2 gene expression COX-2 in isolated perfused lungs of the rat without The structure of COX-223 closely resembles aVecting the mRNA for COX-1.28 This induc- that of COX-1 but, fortunately for the medici- tion of the COX-2 gene by hypoxia was inhib- nal chemist, the binding site for arachidonic ited by NO donors, which may represent one of acid (the COX channel) is slightly diVerent. the mechanisms of the beneficial eVect of The active site of COX-2 is a little larger and inhaled NO in pulmonary hypertension. can accommodate bigger structures than that Inflammatory stimuli cause diVerential re- of COX-1. A secondary internal pocket lease of prostaglandins from various regions of contributes significantly to the larger volume of the lungs. Human cultured pulmonary epithe- the active site of COX-2, although the central lial cells stimulated with LPS, interleukin (IL)- channel is also 17% bigger. 1á, tumour necrosis factor (TNF)á,ora Since COX-2 is induced by inflammatory mixture of cytokines synthesise mainly PGE2 stimuli and by cytokines in migratory and other together with smaller amounts of PGF2á, PGI2, cells, it is attractive to suggest that the and TXA2. This prostaglandin production can anti-inflammatory actions of NSAIDs result be suppressed by dexamethasone32 which indi- from the inhibition of COX-2, whereas the cates that it is caused by COX-2. unwanted side eVects such as damage to the Pollutants such as those in car exhausts can stomach lining are caused by inhibition of the also induce COX-2 in human cultured airway constitutive enzyme, COX-1. This general epithelial cells, resulting in an increased forma- 33 concept is now widely accepted. tion of PGE2 and PGF2á. PGE2 and TXB2,in addition to COX-2 protein, could be detected Functions of COX-1 and COX-2 in the inflammatory exudate produced by LUNGS injection of carrageenin into the rat pleural Prostacyclin is a potent vasodilator of the pul- cavity.34 Thus, it seems likely that COX-2 is monary circulation in humans and other upregulated in the inflamed lungs of asthmatic http://thorax.bmj.com/ species. This endothelium derived prostacyclin patients resulting in increased production of is well placed to function as a local vasodilator bronchoconstrictor prostaglandins which exert and to prevent the formation of micro- an exaggerated eVect on the bronchiolar thrombi.24 smooth muscle that has become hyperreactive Pulmonary blood vessels are constricted by to constrictor agents. PGF2á and thromboxane (TX) A2 but, in some species, they are dilated by PGE2. The ENDOTHELIUM vasoconstrictor responses to PGF2á are potenti- Endothelial cells generate prostacyclin which is on October 1, 2021 by guest. Protected copyright. ated by hypoxia. Mediators of inflammation anti-aggregatory and a vasodilator. They such as bradykinin, histamine, and clearly contain COX-1 but McAdam et al35 and 5-hydroxytryptamine all release prostaglandins Catella-Lawson et al,36 using the selective from lung tissue.