Among a vast number of chemical
mediators of inflammation such as
histamine,
5-hydroxytryptamine,
bradykinin,
SRS-A the metabolites of
arachidonic acid (AA) attracted vivid attention in the last ten years.
Aspirin-like drugs are inhibitors of AA cyclo-oxygenation, while anti-inflammatory
steroids inhibit the liberation of AA from
phospholipids. These biochemical effects of steroidal and non-steroidal anti-inflammatory drugs lead to a suppression of generation of primary
prostaglandins (e.g.
PGE2) and therefore the curative action of these drugs has been explained in terms of depletion of pro-inflammatory
prostaglandins. Recently, Samuelsson et al. described a new class of AA metabolites--leukotriens. Leukotrien C, which derives from 5-hydroperoxyeicosatetranoic
acid and
cysteine, is supposed to be
SRS-A. The discovery of Samuelsson revived a known idea, that any biochemical transformation of AA (including the
cyclo-oxygenase pathway) is initiated by its lipoxydation. Thus formed highly active hydroperoxy
fatty acids and deriving
oxygen-centred
free radicals are important not only for a further biochemical transformation of AA, but also because of their
biological action per se. In this respect Kuehl et al. proposed the most interesting idea that a true mediator of
inflammation is
PGG2 owing to the presence of 15-hydroperoxy group in its molecule, and its capability to generate either TXA2 or free hydroxy radical. It may well be that primary
prostaglandins play a secondary role in
inflammation, whereas unstable metabolites of AA are the real
mediators of inflammation, owing to generation of either destructive
free radicals or non-
prostaglandin pro-inflammatory mediators (e.g.
thromboxane A2, leukotrien C,
prostacyclin).