he generation of reactive oxygen
species (free radicals) is an important factor in
the development and maintenance of
rheumatoid arthritis in humans and animal
models. One source of free radicals is nitric
oxide produced within the synoviocytes and
chondrocytes and giving rise to the highly toxic
radical peroxynitrite. Several cytokines,
including tumour necrosis factor-alpha (TNFalpha)
are involved in the formation of free
radicals, partly by increasing the activity of
nitric oxide synthase. Indeed, nitric oxide may
mediate some of the deleterious effects of
cytokines on bone resorption. Aspirin,
tetracyclines, steroids and methotrexate can
suppress nitric oxide synthase. Dietary
antioxidants include ascorbate, and the
tocopherols and beneficial effects of high
doses have reported especially in
osteoarthritis. There is also evidence for
beneficial effects of beta-carotene and
selenium, the latter being a component of the
antioxidant enzyme glutathione peroxidase.
The polyunsaturated fatty acids (PUFA)
include the n-3 compounds, some of which are
precursors of eicosanoid synthesis, and the n-
6 group, which can increase formation of the
pro-inflammatory cytokines TNFalpha, and
interleukin-6, and a reactive oxygen species.
Some prostaglandins, however, suppress
cytokine formation, so that n-3 PUFA often
oppose the inflammatory effects of some n-6-
PUFA. Gamma-linelenic acid (GLA) is a
precursor of prostaglandin E1, a fact that may
account for its reported ability to ameliorate
arthritic symptoms. Fish oil supplements, rich
in n-3 PUFA such as eicosapentaenoic acid
have been claimed as beneficial in rheumatoid
arthritis, possibly by suppression of the
immune system and its cytokine repertoire.
Some other oils of marine origin (e.g. from
green-lipped mussel) and a range of vegetable
oils (e.g. olive oil and evening primrose oil)
have indirect anti-inflammatory actions,
probably mediated via prostaglandin E1.
Overall, there is a growing scientific rationale
for the use of dietary supplements as adjuncts
in the treatment of inflammatory disorders such
as rheumatoid arthritis and osteoarthritis.
Darlington LG, Stone TW, Brit J Nutr 2001;85:251-
269
Copyright © 2003 Anamol Laboratories Ltd.
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