Free radical scavenging and antioxidant activity of allopurinol and oxypurinol in experimental lens-induced uveitis

PURPOSE

In addition to the inhibition of xanthine oxidase, allopurinol is known to act, dependent on the dose, as a free radical scavenger, an antioxidant, and a "scavenger" of hypochlorous acid. This activity was investigated using a model of lens-induced uveitis.

METHODS

Lipid peroxides (LPO) were determined in aqueous humor and in retinal tissue. Reduced and oxidized glutathione (GSH and GSSG) of the aqueous humor and myeloperoxidase (MPO) activity in the iris-ciliary body complex were analyzed. Allopurinol and oxypurinol concentrations were determined by high-performance liquid chromatography in aqueous humor and retinal tissue of both control eyes and eyes with uveitis. These measurements were performed 6 hours after intravenous application of allopurinol.

RESULTS

In lens-induced uveitis, LPO are significantly elevated, GSH is reduced, and GSSG and MPO are increased. A xanthine oxidase inhibition dose (< 10 mg/kg body weight) of allopurinol showed no effects on oxidative tissue damage in the model used in this study. Higher doses, however, were able to reduce the oxidative damage. Allopurinol (20 mg/kg body weight) had slight effects on GSH and GSSG. All parameters improved using a dose of 50 mg/kg body weight; a dose of 100 mg/kg body weight only showed additional improvement in GSH and GSSG. There was no further change in the other parameters. Allopurinol and oxypurinol concentrations in aqueous humor and retinal tissue showed a dose dependency reaching scavenger concentrations after application of 50 mg/kg body weight of allopurinol.

CONCLUSIONS

These results suggest that the xanthine oxidase mechanism plays a minor role in the oxidative tissue damage due to lens-induced uveitis. Free radicals and oxidants are generated by activated leukocytes; therefore, the effect of higher doses of allopurinol is due to its free radical scavenging and antioxidative activity.

Ultrastructural and immunocytochemical studies of iris vessels in rats with experimental autoimmune uveoretinitis

In this study, we describe the ultrastructural and immunocytochemical changes that occur in the iris of rats with experimental autoimmune uveoretinitis (EAU). General changes include perivascular infiltration of inflammatory cells, followed by hemorrhage and extensive tissue destruction. Alterations in the iris epithelium were also noted. A breakdown in the blood-iris barrier was demonstrated in some vessels at the peak of inflammation; peroxidase reaction product was seen in the basement membrane and perivascular spaces. We found that, in inflamed iris vessels, endothelial cells and smooth muscle cells become hypertrophic and show increased amounts of synthetic organelles. This finding is similar to our previous observations on endothelial cells and smooth muscle cells in retinal vessels in EAU. In addition, as was reported in the retinal vascular basement membrane in EAU, there is an increase in immunoreactivity of several extracellular matrix molecules in the iris vascular basement membrane; during inflammation, there is a significant increase in immunoreactivity of collagen types I and III, entactin, fibronectin, and laminin. Activated endothelial cells and smooth muscle cells are likely to be involved in the synthesis of certain of these matrix molecules.

Animal model for uveitic glaucoma

BACKGROUND

This study was carried out in order to improve the understanding of the pathogenesis of uveitic glaucoma.

METHODS

Uveitis was induced in 48 Lewis rats by S-antigen injection. Intraocular pressure (IOP) was measured by Tono-Pen-2 daily for 24 days in 16 animals. Histopathology was performed sequentially in 14 rats on days 3, 5, 7, 9, 12, 15 and 18 after S-antigen injection. Aqueous dynamics studies were performed on days 0, 3, 7, 14 and 21. Aqueous humor production was measured using an FITC-albumin dilution technique; outflow facility was measured using anterior chamber infusion with constant pressure.

RESULTS

IOP decreased to a mean of 16.5 +/- 4.3 mmHg from days 2-5 after S-antigen injections from a mean pre-experimental value of 20.5 +/- 5.4 mmHg. IOP increased from days 6 to 20 (35.8 +/- 9.1 mmHg; P = 0.00001). Histopathologic study revealed inflammation of the anterior and posterior segments from days 9 to 21 after S-antigen injection. Aqueous humor production decreased and outflow facility increased at day 3 after S-antigen injection. At days 7 and 14 after S-antigen injection, acqueous humor production was increased while outflow facility remained normal or was decreased.

CONCLUSION

This model of uveitis glaucoma is characterized by three overlapping phases: (1) ocular hypertension, (2) ocular hypertension associated with clinical and histologic inflammation and (3) anatomic sequelae of uveitis and variable IOP. This model permits in vivo studies of mechanisms of IOP change associated with uveitis.

Experimental melanin-protein-induced uveitis in the Lewis rat. Immunopathologic processes

PURPOSE

To study the immunopathology of experimental melanin-protein-induced uveitis in the Lewis rat.

METHODS

Rats were immunized with bovine ocular melanin protein. The kinetics of experimental melanin-protein-induced uveitis was studied by clinical examination and immunopathology. Cellular and humoral responses were evaluated by lymphocyte proliferation, delayed-type hypersensitivity, and agglutination. After clinical disease subsided, recurrent experimental uveitis was induced with a low-dose footpad injection of lipopolysaccharide.

RESULTS

Experimental melanin-protein-induced uveitis was characterized by bilateral uveal infiltration mainly with lymphocytes and monocytes. Delayed-type hypersensitivity, lymphocyte proliferation, and agglutination to bovine ocular melanin protein were positive. Expressions of major histocompatibility complex class II and intercellular adhesion molecule-1 were observed before ocular infiltration. The predominantly infiltrating cells were CD4+ lymphocytes. Experimental melanin-protein-induced uveitis subsided within 1 month, spontaneously recurred within 1 week in approximately one quarter of the rats, and was inducible in most rats with 5 micrograms of lipopolysaccharide confirmed by histopathology.

CONCLUSIONS

Experimental melanin-protein-induced uveitis is a T-cell-mediated autoimmune uveitis, resembling noninfectious recurrent iridocyclitis and choroiditis in humans.

[Role of polymorphonuclear leukocytes in the activation of lipid peroxidation in uveitis (experimental study)]

Activation of polymorphonuclear leukocytes (PL) involving in the occurrence of inflammation results in inflammatory area accumulation of cytotoxic products, such as lipid peroxidation (LPO) initiators, which in turn may cause an increase and extent of inflammation. The regularities of changes in the functional activity of PL and plasma LPO parameters in the rabbit plasma and ocular tissue in the course of experimental toxic and allergic uveitis are studied. The level of the functional activity of PL, which was determined by luminol-dependent chemiluminescence was shown to correlate with the degree of uveitis. The peak was on days 3-7 and coincided with that of inflammatory changes in ocular tissues. Measurements of the plasma levels of PLO products, tocopherol (T), the activity of ceruloplasmin and total plasma antioxidative activity (AOA) led to the conclusion that there was a exhaustion of the antioxidative system and a drastic LPO activity on days 7 of uveitis. At the same time there were increased PLO products, decreased T levels and lower activity of superoxide dismutase in the ocular tissue. The use of antioxidants dibunol and pipolfen alleviated uveitis, reduced PL functional activity, normalized the ocular tissue and plasma levels of LPO products and enhanced the total plasma AOA. The fact that there is a close correlation between the level of the functional activity of PL, the degree of PLO activation in the plasma and ocular tissue has led to the conclusion that PL activation along with high functional activity is one of the main causes of enhanced PLO in uveitis.

[The effects of various doses of lipopolysaccharide on endotoxin-induced uveitis in rats]

We induced intraocular inflammation by foot pad injection of lipopolysaccharide (LPS) in rats to investigate the inflammatory effects of the various doses of the LPS and the anti-inflammatory effects of prostaglandin (PG) synthetase inhibitor. The aqueous protein concentration curve showed two peaks, an early one at 3 hours and another at 24 hours after the injection, at doses higher than 12.5 micrograms per rat. The PG synthetase inhibitor reduced the aqueous protein concentration by 30 to 60% at both of the two peaks. These results suggest the involvement of PG in the mechanism of the endotoxin-induced uveitis.

Prevention and treatment of ocular inflammation with a new class of non-steroidal anti-inflammatory agents

New non-steroidal anti-inflammatory agents (NSAIAs) were tested on lens protein-, endotoxin- and interleukin-1-induced ocular inflammation. It was found that most NSAIAs, including REV 5901, mefenamic acid, indomethacin, CK-17 and CK-102, inhibited lens protein-induced inflammation. Endotoxin induced inflammation indirectly through the release of IL-1 which was inhibited by fewer agents, including CK-17, CK-102 and prednisolone. However, the direct effect of IL-1 can only be suppressed by CK-17 and prednisolone. Therefore, CK-17 could become an important NSAIA which acts similarly to corticosteroids yet produces no steroidal side effects. CK-17 was different from most NSAIAs as it affected little, if any, arachidonate metabolism. Most importantly, CK-17 was found to be 2-fold more potent than prednisolone in inhibiting IL-1-induced uveitis, while no side effects were noted at doses tested to date.

Prevention of ocular inflammation induced by lens protein, endotoxin, and interleukin-1 with synthetic interleukin-1 blockers

It is well known that corticosteroids are potent anti-inflammatory agents, yet they produce serious side effects. Although arachidonate metabolite blockers have been developed for the treatment of inflammation, they are much less potent than corticosteroids. Furthermore, they still process serious side effects. In search of potent and safe non-steroidal anti-inflammatory agents (NSAIA), interleukin-1 (IL-1) blockers have been developed. Among 121 CK-analogs studied, CK-17, CK-101A and CK103A have been identified as promising anti-inflammatory agents as potent as prednisolone in inhibiting lens proteins-induced inflammation and twice as potent as prednisolone in inhibiting endotoxin-and IL-1-induced uveitis. No serious side effects could be noticed with the doses of these compounds tested to date. These results indicate that the development of potent NSAIAs is feasible. Moreover, these compounds are not related to arachidonate metabolites.

[Effects of interleukin-2 on experimental uveitis and pinealitis]

Interleukin-2 (IL-2) was injected intraperitoneally into Lewis rats immunized with interphotoreceptor retinoid-binding protein (IRBP) to study its effect on the development of experimental autoimmune uveoretinitis (EAU) and experimental autoimmune pinealitis (EAP) and on the immune response. It was found that the EAU and the EAP were significantly intensified by IL-2, and the peak of serum anti-IRBP antibody appeared on the 7th day after immunization while that in the controls on the 26th day. These results, together with those previously documented that the development, severity and subsidence of EAU depended on the level of IL-2, tend to support the authors' hypothesis that excessively elevated IL-2 enhances the development and recurrence of human uveoretinitis.

Studies on intraocular inflammation produced by intravitreal human interleukins in rabbits

Recombinant human interleukin-1 alpha, interleukin-1 beta (10, 80 or 200 units), interleukin-8 (10 or 40 units) or endotoxin was injected intravitreally into rabbit eyes. Twenty-four hours thereafter aqueous humor protein, leukocyte number, prostaglandin E2, leukotriene B4 and rabbit interleukin-1 beta were measured. In addition, synthesis of prostaglandin E2 and leukotriene B4 in iris-ciliary body and myeloperoxidase (MPO) activity were determined. Recombinant human interleukins 1 alpha and 1 beta, but not interleukin-8 induced signs of uveitis, i.e. protein and leukocytic infiltration into aqueous humor. At 200 unit activities, human interleukin-1 beta was significantly greater than interleukin-1 alpha in causing leukocyte infiltration response. Interleukin-1 alpha did not stimulate the release of prostaglandin E2 or leukotriene B4. In fact, interleukin-1 beta significantly inhibited the synthesis of prostaglandin E2 in iris-ciliary body. Both of these human interleukins caused a release of rabbit interleukin-1 beta in aqueous achieving a level significantly higher than observed after endotoxin injection. This study demonstrates that intravitreal injections of human IL-1 alpha and IL-1 beta induce uveitis by releasing rabbit interleukin-1 beta within the eye.

Inhibitory effects of tetrandrine on bovine serum albumin-induced uveitis in rabbits

Experimental uveitis was successfully induced in rabbits by bovine serum albumin (BSA). Tetrandrine (Tet), 50 mg/kg/d i.p., and dexamethasone (Dex), 5 mg/kg/d i.p., for 8 d showed marked inhibition of uveitis in rabbits. Eight d after drug administration, ocular inflammation was markedly inhibited. The maximum inhibitory rate of Tet and Dex was 48.9% and 56.0%, respectively. The protein content of the aqueous humor (PAH) was reduced significantly; phytohemagglutinin (PHA)-induced peripheral T lymphocyte transformation of 3H-thymidine (3H TdR) incorporation was suppressed markedly; and serum circulating immune complexes (CIC) also were reduced. Four d after Dex withdrawal, ocular inflammation, PHA and CIC rose again, but these parameters were not changed after Tet withdrawal. These results suggest that Tet is an effective inhibitory agent on BSA-induced uveitis in rabbits. The inhibiting action may be related to the suppression of cellular and humoral immune function and, unlike Dex, Tet did not produce withdrawal rebound.

Inhibition of interphotoreceptor retinoid-binding protein-induced uveitis by monoclonal antibodies

Immunization of Lewis rats with interphotoreceptor retinoid-binding protein (IRBP) resulted in development of uveoretinitis in 100% (12/12) of the animals so injected. In the present study, we attempted immunotherapy of this intraocular inflammation using the monoclonal antibodies anti-I-A and anti-I-E. The antibodies were injected 1 day before and on days 1 and 2 after IRBP sensitization, and the animals were killed 16 days later. Anti-I-A treatment inhibited the disease in 83% (10/12) of the animals, while anti-I-E antibodies resulted in inhibition of the disease in 67% (8/12) of the animals. All rats injected with preimmune IgG (control animals) developed uveoretinitis. The anti-I-A and anti-I-E antibodies exerted a specific suppressor effect on the immune response of these animals. Thus, anti-I-A and anti-I-E antibodies administered at the time of antigen priming abolished the immune function and inhibited the development of autoimmune uveitis.

Predominant usage of V beta 8.3 T cell receptor in a T cell line that induces experimental autoimmune uveoretinitis (EAU)

Experimental autoimmune uveoretinitis (EAU) is a T cell-mediated autoimmune disease induced in animals by immunization with retinal proteins (or synthetic fragments derived from them) in adjuvant, and it is considered a model of human autoimmune diseases of the eye. To study the T cell clonotypes that may be involved in EAU, we analyzed the T cell repertoire of three related T cell lines: the pathogenic line LR16, specific to the major uveitogenic epitope of IRBP; its pathogenic subline J; and its nonpathogenic subline A. We examined the expression of the genes coding for the variable regions of the 20 known Lewis rat T cell antigen receptor (TCR) V beta families. The nonpathogenic subline was found to contain mostly T cells expressing V beta 5, V beta 8.2, and V beta 19 while the pathogenic subline consisted mainly of cells expressing V beta 8.3 TCRs. Genomic Southern blot analysis of DNA from the pathogenic subline showed that V beta 8.3-expressing T cells were the dominant clonotype, and DNA sequence analyses of V beta 8.3 cDNAs revealed that two V beta 8.3 TCRs were expressed in the pathogenic subline. One of the V beta 8.3 cDNAs encoded a variable region gene segment identical to previously reported rat V beta 8.3 TCR while the other differed by two amino acids in the second complementarity determining region (CDR2). Taken together with previous data showing overrepresentation of V beta 8-expression in T cell lines that induce EAU, but not in nonuveitogenic T cell lines, our results suggest that V beta 8.3-expressing T cells represent a pathogenic clonotype in IRBP-induced EAU.

Does the lens serve as a 'sink' for iron during ocular inflammation?

Twenty-four hours after induction of ocular inflammation by intravitreal injection of endotoxin (10 ng), the intraocular fluid (IOF, aqueous and vitreous humors) concentration of iron (Fe) increased. This was presumably due to entry of the plasma Fe-binding protein, transferrin, into the IOFs through disrupted blood ocular barriers. After 1 day of inflammation the Fe concentration in lenses from the inflamed eye was 60% greater than that measured in contralateral control lenses. By day 15, lens Fe concentration had returned to levels of the contralateral control lenses. There was a distinct relationship between the dose of endotoxin used and the amount of Fe accumulated by the lens. The Fe concentration in lenses from eyes injected with 100 ng endotoxin was 0.376 +/- 0.027 micrograms g-1 wet weight compared to 0.214 +/- 0.014 micrograms g-1 in lenses from eyes injected with 0.25 ng endotoxin. In a previous study, copper (Cu) concentration in the IOFs was elevated to the same extent as Fe in response to intravitreal injection of endotoxin. However, in the present study, lenticular Cu concentration was unaltered at the highest (100 ng) dose of endotoxin. Since the increase in lens uptake was selective for Fe, there may be a specific Fe uptake mechanism in this ocular tissue. The physiological reasons for and possible pathological consequences of such a process are discussed.

Inhibition of experimental autoimmune uveitis by retinal photoreceptor antigens coupled to spleen cells

Experimental autoimmune uveitis (EAU) and experimental autoimmune pinealitis (EAP) are CD4+ T cell-mediated inflammatory diseases of the uveal tract and retina of the eye and of the pineal gland. EAU and EAP can be induced by several retinal autoantigens including S-antigen (S-Ag) and interphotoreceptor retinoid binding protein (IRBP). In this study we investigated the effect of intravenous administration of S-Ag and IRBP coupled to syngeneic spleen cells on the development of EAU and EAP. Injection of S-Ag or IRBP coupled to spleen cells 5 days prior to immunization with native S-Ag or IRBP, respectively, was effective in preventing the induction of EAU and EAP in LEW rats. Conversely, LEW rats receiving S-Ag-coupled spleen cells and challenged with IRBP or LEW rats receiving IRBP-coupled spleen cells and challenged with S-Ag developed a severe EAU within 10 days to 2 weeks following immunization, as did all control animals receiving sham-coupled spleen cells and challenged with the two retinal antigens. The results show that the administration of retinal autoantigens coupled to spleen cells effectively protects against the development of EAU when animals are subsequently challenged with the tolerizing antigen but not when challenged with another unrelated pathogenic retinal autoantigen.

Preclinical and clinical study of FK506 in uveitis

Efficacy of a new immunosuppressive agent, FK506, in refractory uveitis was studied in 8 patients: 5 with Behcet's disease and 3 with idiopathic retinal vasculitis. The agent was given by oral administration every 12 hours. The previous therapy with systemic corticosteroids or immunosuppressive agents including cyclosporine failed to subside uveitis in these cases. During the observation period of 21.6 +/- 7.8 weeks (mean +/- SD) under FK506 at doses with 0.05, 0.1, 0.15 or 0.2 mg/kg/day, the visual acuity was increased in 44% of treated eyes, unchanged in 44% and decreased in 12%. The inflammatory activity in the ocular fundus was improved in 69% and unchanged in 6% of treated eyes. The effects of FK506 on uveitis by the criteria of improvement of visual acuity and uveitis activity was dose-dependent: 0.05 and 0.1 mg/kg/day were ineffective but 0.15 and 0.2 mg/kg/day were effective in most cases. One patient with Behcet's disease converted from cyclosporine developed moderate renal impairment in 4 weeks under FK506 and the therapy was discontinued in 8 weeks, though the uveitis activity as well as visual acuity was markedly improved. Other 7 cases had no side effect of FK506. Although the number of cases was small and observation period was short, the present clinical data indicate that FK506 is effective to treat refractory uveitis.

[Participation of sodium iodate in the induction of experimental autoimmune uveoretinitis (EAU)]

It is known that Brown Norway (BN) rats show resistance to the development of experimental autoimmune uveoretinitis (EAU). Although BN rats don't develop EAU easily when they were immunized with S antigen containing emulsified complete Freund's adjuvant, this paper reports on the development of EAU at the rate of 40-60% in BN rats when immunization is preceded by an injection of more than 0.5 mg (1.79 mg/kg of body wt) of sodium iodate which leads to the destruction of retinal pigment epithelium (RPE). It was thought that the destruction of RPE participated in the induction of EAU. Therefore, it is considered that the existence of RPE may play an important role in the induction of EAU.

Glauline (metipranolol) induced uveitis and increase in intraocular pressure

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[Endogenous uveitis in disseminated intravascular coagulation induced by endotoxin]

A study was made of endogenous uveitis in experimental disseminated intravascular coagulation (DIC) in rabbits. Endotoxin was injected intravenously twice with a 24-hour interval. The time courses of the following were examined: 1) aqueous flare using a laser flare-cell meter 2) the number of leukocytes in the peripheral blood 3) the tumor necrosis factor (TNF) activity in the serum and 4) histopathological changes in the eye, lung, liver and kidney. Aqueous flare increased at 1 hour and was maximal at 6 hours, accompanied by a rapid increase in TNF activity at 1 hour following the first endotoxin administration. The number of leukocytes decreased to 963 +/- 266 cells/mm3 at 1.5 hours with subsequent leukocytosis within 12 hours. After the second injection of endotoxin, the aqueous flare peaked in 30 minutes and was twice as high as the first peak. Leukocyte number and TNF activity showed the same behavior. However, TNF activity was 20% that of the first peak. Histopathological examination indicated fibrin formation in the small vessels of systemic organs within 3 hours following the second administration of endotoxin. Endotoxin induced uveitis was induced in experimental DIC, and leukocytes and TNF activity may thus perform important roles.