[Immunological effect of systemically administered allopurinol in experimental autoimmune uveitis]

Cannabinoids, loratadine and allopurinol as novel additions to the antipsoriatic ammunition

As the current antipsoriatic medications are commonly associated with deleterious side-effects, a determined search for safer agents, which could be used alone or in combination with current antipsoriatic drugs, would be very imperative. Psoriasis is believed to be characterized by a type 1 cytokine pattern; interferon-gamma, interleukin (IL)-2 and tumour necrosis factor (TNF)-alpha are predominantly expressed in this disorder. Nitric oxide, reactive oxygen species, histamine, leukotriene B4, and decreased [corrected] keratinocyte cyclic adenosine monophosphate/cyclic guanosine monophosphate (cAMP/cGMP) ratio are supposed to play roles in the pathogenesis of this disorder. Based on the immunopathogenesis of psoriasis, this paper introduces three novel, potential treatments for this clinical conundrum: (i) cannabinoids, which exert inhibitory effects on antigen processing and macrophage/T-cell interaction and also on the release of IL-2, TNF-alpha and nitric oxide from immune cells; (ii) loratadine, which is an antihistamine capable of increasing [corrected] the cAMP/cGMP ratio and the production of leukotriene B4; and (iii) allopurinol, which scavenges free radicals, inhibits the production of TNF-alpha, and downregulates the expression of intercellular adhesion molecule-1 and P2X7 receptors on monocytes/macrophages, which are involved in antigen presentation and production of the inflammatory response, respectively. Importantly, allopurinol, especially in combination with cyclosporin, has been shown to be effective against experimental autoimmune uveitis, which, like psoriasis, is a cell-mediated autoimmune disorder.

Cetirizine and allopurinol as novel weapons against cellular autoimmune disorders

Type 1, or cellular, immune response is characterized by overproduction of TNF-alpha, IFN-gamma, IL-1, IL-2 and IL-8 and is the underlying immune mechanism of psoriasis, alopecia areata, rheumatoid arthritis, Crohn's disease, multiple sclerosis, insulin-dependent diabetes mellitus and experimental autoimmune uveitis (EAU). Type 2 immune response is seen in antibody-mediated autoimmune diseases. Based on the pharmacokinetic effects of cetirizine and allopurinol, this paper introduces these two safe and inexpensive drugs as novel potential agents against cell-mediated autoimmune disorders. Cetirizine, supposed to inhibit DNA binding activity of NF-kappa B, inhibits the expression of adhesion molecules on immunocytes and endothelial cells and the production of IL-8 and LTB4, two potent chemoattractants, by immune cells. It induces the release of PGE2, a suppressor of antigen presentation and MHC class II expression, from monocyte/macrophages and reduces the number of tryptase positive mast cells in inflammation sites. Tryptase is a chemoattractant, generates kinins from kininogen, activates mast cells, triggers maturation of dendritic cells and stimulates the release of IL-8 from endothelial cells and the production of Th1 lymphokines by mononuclear immunocytes. Allopurinol is a free radical scavenger, suppresses the production of TNF-alpha and downregulates the expression of ICAM-1 and P2X(7) receptors on monocyte/macrophages. ICAM-1 serves as a ligand for LFA-1 (on T lymphocytes), allowing proper antigen presentation. P2X(7) receptors are thought to be involved in IL-1beta release, mitogenic stimulation of T lymphocytes and the probable cytoplasmic communication between macrophages and lymphocytes at inflammation sites. Allopurinol was markedly more effective than prednisolone in treating experimental autoimmune uveitis and in combination with cyclosporine suppressed the inflammatory reaction of this condition more effectively than either agent alone. As allopurinol is a competitive inhibitor of xanthine oxidase and decreases serum levels of uric acid, which is protective against multiple sclerosis, it should preferably be coadministered with uric acid precursors in the treatment of this condition. Cetirizine and allopurinol may prove of benefit in the treatment of various cellular autoimmune disorders.

Immunological effects of allopurinol in the treatment of experimental autoimmune uveitis (EAU) after onset of the disease

PURPOSE

Allopurinol reduces oxidative tissue damage and exerts immunomodulating effects in the treatment of experimental autoimmune uveitis (EAU). However, the mechanism of the immunologic pathway remains unclear. In previous studies, treatment was started at the time of immunization. Therefore, whether allopurinol prevents the onset of the disease (i.e., acts in a protective manner) is not known.

METHODS

Sixteen male Lewis rats were used: 6 EAU without therapy [control]; 4 EAU with allopurinol treatment starting 7 days after immunization [AL7]; and 6 EAU with allopurinol treatment starting 11 days after immunization [AL11]. Their sera were tested against Western blots of sodium dodecyl sulfate-polyacrylamide gel electrophoresis of retinal proteins. Based on digital image analysis, analysis of discriminance was done.

RESULTS

There were significant immunomodulating effects in both therapy groups (Wilks' lambda 0.001, P < 0.008) compared to controls. However, the effects were more pronounced in the AL7 group, where peak intensities and the number of peaks were markedly more reduced.

CONCLUSIONS

Immunomodulating effects of allopurinol can be detected even if the therapy starts after the onset of the disease. Thus allopurinol strongly influences the immunologic mechanism in this model of autoimmune disease. In view of its minimal side effects, the drug could be a promising alternative for the therapy and prophylaxis of uveitis and other autoimmune diseases.

Topical allopurinol or corticosteroids and acetylcysteine in the early treatment of experimental corneal alkali burns: a pilot study

PURPOSE

To investigate the effect of topical allopurinol on experimental corneal burns and to compare this to established treatment modalities such as topical prednisolone and acetylcysteine.

METHODS

Twenty Wistar rats were randomly assigned to four groups (n=5 each). The groups were controls (normal saline), allopurinol 0.4% eye drops, prednisolone acetate 1% eye drops and acetylcysteine 8% eyedrops. Corneal burn was induced using a 3 mm paper disc soaked in 1N NaOH for 60 seconds. Drops were instilled 6 times per day. In addition, one drop/day ofloxacine was given to prevent secondary infections. Eyes were enucleated 50 hours later and fixed in 4.5% formaldehyde. Three histological levels of each globe were stained with hematoxylin-eosin and examined by two independent masked investigators using a 0 to 4+ inflammatory score. All pair-wise multiple comparison procedures (Student-Newman-Keuls method) were applied for statistical work-up.

RESULTS

All three substances significantly reduced the number of histologically visible inflammatory cells compared to the control group (p<0.05).

CONCLUSIONS

In the present study, topical allopurinol was as effective as established drugs, namely steroids and acetylcysteine, in the early treatment of experimental alkali corneal burns.

Allopurinol has immunomodulating activity following topical and systemic application in experimental autoimmune uveitis

PURPOSE

Allopurinol has beneficial effects in the systemic treatment of lens-induced uveitis and experimental autoimmune uveitis (EAU). This is believed to be due to a reduction of oxidative tissue damage through its dose-dependent free radical scavenging ability, and to an immunomodulating effect. The purpose of this study was to demonstrate the immunological effects on the IgG-antibody repertoire in EAU after topical and systemic allopurinol and steroids.

METHODS

We assigned 43 male Lewis rats to 6 different groups: healthy rats (BASE, n=3)