Treatment of experimental lens-induced uveitis by dimethyl thiourea

The chemopreventive effect of dimethylthiourea against carmustine-induced myelotoxicity in rats

The possible chemopreventive role of dimethylthiourea (DMTU) against carmustine (1,3-bis(2-chloroethyl)-1-nitrosourea, BCNU)-induced myelotoxicity was assessed through evaluation of apoptosis, lipid peroxidation, glutathione (GSH) content and some antioxidant enzymes activities in bone marrow cells of rats. Thirty-six rats were randomly classified into four groups. The first group was injected i.p. with ethanol and served as a control. The second group was treated with BCNU. The third group was given DMTU, while the fourth group was co-administered with DMTU prior to BCNU administration. BCNU treatment in a single dose of 30 mg/kg significantly decreased the normal counts of RBCs, WBCs and platelets as well as hemoglobin level. In addition, BCNU exhibited marked apoptotic effect associated with significant alterations in the oxidative cascade parameters. Treatment of animals with DMTU in a single dose of 500 mg/kg 1h before BCNU injection, followed by 125 mg/kg twice daily for 5 consecutive days significantly mitigated the induced changes in the hematological parameters. The induced alterations in the oxidant and antioxidant parameters as well as apoptosis were also improved. Conclusively, DMTU treatment exhibited marked chemopreventive effect against BCNU-induced myelotoxicity; an effect which may be partially attributed to its inherently antioxidant potential.

Differences in the composition of inflammatory cell infiltrate in lens-induced uveitis under therapy with allopurinol or steroids

PURPOSE

The aim of this study was to compare the qualitative changes in the composition of inflammatory cell infiltrate in lens-induced uveitis (LIU) under treatment with allopurinol (Allo), methylprednisolone (Pred) or the two drugs combined (Allo/Pred).

METHODS

Twenty male Wistar rats were sensitized with lens proteins for eight weeks. Intravenous (IV) therapy was started after anterior capsule disruption in one eye of each animal. Five rats were randomly assigned to each of the four groups: controls, Allo (50 mg/kg bw), Pred (7.5 mg/kg bw) and Allo/Pred (50 mg/7.5 mg per kg bw). Eyes were enucleated 24 hours later and fixed in paraformaldehyde/glutaraldehyde. Sections at three levels were stained with Giemsa and examined using a 0 to 4+ score for each type of inflammatory cell. Granulocytes were seen as neutrophils and eosinophils. Neutrophils were divided into polymorphs and "others", and graded with lymphocytes.

RESULTS

In all therapy groups there was a significant reduction of polymorphs (p<0.05) in comparison to the control group. There was also a significant reduction in lymphocytes (p<0.05) in the Pred and Allo/Pred groups as compared to the control group and the Allo group.

CONCLUSIONS

Single-dose IV allopurinol significantly reduced the overall number of polymorphonuclear leucocytes in LIU. Unlike methylprednisolone, allopurinol did not have any significant impact on lymphocytes.

Lens-induced uveitis

has been described in humans and many animal species. Traumatic rupture of the lens capsule may result in vision-threatening intraocular inflammation that is poorly responsive to medical management. Phthisis bulbi, persistent uveitis or glaucoma often occurs in these eyes. Surgical removal of the lens material is generally indicated shortly after the injury in an effort to preserve vision. Leaking of lens proteins through an intact lens capsule may result in a lympho-plasmacytic anterior uveitis. This is most commonly associated with the presence of a hypermature cataract. The presence of lens-induced uveitis prior to cataract surgery significantly reduces the success rate of cataract surgery. Small amounts of circulating lens proteins maintain a normal T-cell tolerance for lens proteins. Lens-induced uveitis develops when a breakdown occurs of this normal T-cell tolerance. Immune complexes play an important role in the tissue damage associated with the ensuing inflammation. Other factors associated with the tissue damage include hydroxyl radicals, nitroxide radicals, and hydrogen peroxide and arachidonic acid metabolites. Treatment consists of topical and systemic anti-inflammatory medications, mydriatic agents, and glaucoma medications when indicated. Experimental pharmacological agents include dual cyclooxygenase/lipoxygenase inhibitors, interleukin-1 blockers, antioxidants and hydroxyl radical scavengers.

Free radical mediated photoreceptor damage in uveitis

Uveitis is a major cause of blindness, with the visual loss that occurs being due primarily to retinal tissue damage. The tissue damage is mediated mainly by phagocytic inflammatory cells, such as macrophages, by the release of various proteolytic enzymes, arachidonic acid metabolites, cytokines and free radicals. The latter are found to be potent cytotoxic agents that readily cause tissue damage by peroxidation of lipid cell membranes. Recent studies of experimental uveitis indicate that other potent oxidants are generated in uveitis by macrophages. One of these is ONOO-, which is formed from *NO and O(-)2. The macrophages generate *NO preferentially in the outer retina following iNOS expression. In these phagocytes, outer retinal proteins, especially arrestin, are found to be potent iNOS inducers. Current studies of RPE show that these cells protect the retina from ONOO- mediated damage in uveitis by releasing a novel protein called retinal pigment epithelial protective protein. This protein is found to suppress O(-)2 and *NO generation by the phagocytes, in both in vitro and in vivo uveitis models. The protective protein expression is restricted to RPE, its suppressive effect is a result of the inhibition of the phosphorylation of cytosolic proteins, p47-phox, required for the assembly of NADPH and activation of NFkappaB, which are required for generation of 0(-)2 and expression of iNOS respectively. Either pharmacologically or chemically, up-regulation of RPP generation could help in preventing retinal degeneration in uveitis or other degenerative dis

Thiourea and dimethylthiourea inhibit peroxynitrite-dependent damage: nonspecificity as hydroxyl radical scavengers

Thiourea and, more recently, dimethylthiourea, have been used as hydroxyl radical (OH.) scavengers in experiments both in vitro and in vivo. We show that both compounds can inhibit nitration of the amino acid tyrosine on addition of peroxynitrite, and also the inactivation of alpha1-antiproteinase by peroxynitrite. Hence, protective effects of (dimethyl) thiourea could be due to inhibition of peroxynitrite-dependent damage as well as to OH. scavenging, and these compounds must not be regarded as specific OH. scavengers.

Phacoanaphylactic endophthalmitis

Phacoanaphylactic endophthalmitis is a rare disease that develops infrequently after lens injury. The recent popularity of extracapsular cataract extraction with intraocular lens implants and the recently described possible association of low-grade infections have stimulated renewed interest in phacoanaphylactic endophthalmitis. It was formerly believed that this disease was due to the rejection of a lens protein that had been sequestered prior to lens injury. Recent observations indicate that this concept is incorrect and that phacoanaphylactic endophthalmitis represents altered tolerance to lens proteins. Clinical and histopathologic features as well as controversies in clinical management are discussed. Recent evidence concerning mechanisms of pathogenesis is reviewed [corrected].

Free radicals and antioxidants in the pathogenesis of eye diseases

There is fairly convincing evidence that free radical mechanisms are involved in the pathogenesis of cataracts and uveitis and that antioxidants may be protective. Studies on retinal degeneration are almost entirely limited to dietary manipulation of vitamins C and D. Unfortunately, antioxidant properties are not easily isolated from other metabolic effects of vitamins. Cataracts, uveitis, and retinal degeneration cause nearly one-third of all blindness. The evidence that free radical mechanisms are important in the pathogenesis of these diseases is compelling incentive to encourage more extensive and detailed investigation.