Concomitant treatment with a 5-lipoxygenase inhibitor improves the anti-inflammatory effect of the inhibition of nitric oxide synthase during the early phase of endotoxin-induced uveitis in the rabbit

5-Lipoxagenase deficiency attenuates L-NAME-induced hypertension and vascular remodeling

BACKGROUND

Abnormalities of the L-arginine-nitric oxide pathway induce hypertension. 5-Lipoxygenase (5-LO) is the key enzyme involved in synthesis of leukotrienes (LTs). However, whether nitricoxide synthase dysfunction induces hypertensive vascular remodeling by regulating 5-LO activity and its downstream inflammatory metabolites remains unknown.

METHODS AND RESULTS

Six-week L-NAME treatment significantly induced hypertension and vascular remodeling in both wild-type (WT) and 5-LO-knockout (5-LO-KO) mice, and blood pressure in caudal and carotid arteries was lower in 5-LO-KO than WT mice with L-NAME exposure. On histology, L-NAME induced less media thickness, media-to-lumen ratio, and collagen deposition and fewer Ki-67-positive vascular smooth muscle cells (VSMCs) but more elastin expression in thoracic and mesenteric aortas of 5-LO-KO than L-NAME-treated WT mice. L-NAME significantly increased LT content, including LTB4 and cysteinyl LT (CysLTs), in plasma and neutrophil culture supernatants from WT mice. On immunohistochemistry, L-NAME promoted the colocalization of 5-LO and 5-LO-activating protein on the nuclear envelope of cultured neutrophils, which was accompanied by elevated LT content in culture supernatants. In addition, LTs significantly promoted BrdU incorporation, migration and phenotypic modulation in VSMCs.

CONCLUSION

L-NAME may activate the 5-LO/LT pathway in immune cells, such as neutrophils, and promote the products of 5-LO metabolites, including LTB4 and CysLTs, which aggravate vascular remodeling in hypertension. 5-LO deficiency may protect against hypertension and vascular remodeling by reducing levels of 5-LO downstream inflammatory metabolites.

Malondialdehyde and Antioxidant Enzyme Levels in the Aqueous Humor of Rabbits in Endotoxin-Induced Uveitis

PURPOSE

To investigate the role of oxidative stress in endotoxin-induced uveitis.

METHODS

Lipopolysaccharide was injected intravitreally into the right eyes of rabbits. Sterile saline was injected intravitreally into the left eyes as a control. Inflammation was assessed according to clinical score, aqueous humor cell count, and protein levels. Malondialdehyde, superoxide dismutase, glutathione peroxidase, catalase, and nitrite levels were measured in the aqueous humor.

RESULTS

The clinical grade (p < 0.01), inflammatory cell count (p < 0.001), and protein content (p < 0.001) were significantly higher in the aqueous humor of eyes with uveitis than in that of controls. Malondialdehyde (p < 0.01) and nitrite (p < 0.001) levels in the aqueous humor of eyes with uveitis were significantly higher than in the control group. Superoxide dismutase (p < 0.001), glutathione peroxidase (p < 0.001), and catalase (p < 0.001) levels were significantly lower in the aqueous humor of eyes with uveitis than in that of the controls.

CONCLUSIONS

Oxygen free radicals may be implicated as a mediator of inflammation in endotoxin-induced uveitis. The increase in free radicals in the aqueous humor may play a role in the pathogenesis of endotoxin-induced uveitis.

Anti-inflammatory effects of specific cyclooxygenase 2,5-lipoxygenase, and inducible nitric oxide synthase inhibitors on experimental autoimmune anterior uveitis (EAAU)

PURPOSE

Inflammation, in general, causes the release of a variety of inflammatory mediators that in turn induce cyclooxygenase (COX) 2, nitric oxide synthase (iNOS) and 5-lipoxygense (LP) synthesis, producing large amounts of inflammatory prostaglandins (PG), nitric oxide (NO), and leukotriene (LT) B4. Therefore, inhibition of these enzymes may abrogate intraocular inflammation in experimental autoimmune anterior uveitis (EAAU).

METHODS

Lewis rats were immunized with melanin-associated antigen (MAA) isolated from bovine iris and ciliary body. These animals were divided into three groups. The first group of rats received subcutaneous injection of COX 2 inhibitor CS 236 at different time points. The second and third groups of animals received subcutaneous aminoguanidine (AG), an iNOS inhibitor, and nordihydroguaiaretic acid (NDGA), a 5-LP inhibitor, respectively. Control animals received vehicle. Rat eyes were examined daily by slit-lamp biomicroscopy from Day 7 to 30 post injection for uveitis. Animals were also sacrificed at various time points for histologic analysis.

RESULTS

Control animals developed severe EAAU in both eyes. The disease started in these animals on Day 12 post immunization and lasted for ten days. Interestingly, CS 236, a potent COX 2 inhibitor, completely abrogated EAAU when the animals were treated daily from the Day 0 to 14 or Day 0 to 20 after MAA injection. Furthermore, daily CS 236 treatment after the onset of EAAU (Day 14-20) significantly reduced the severity (both clinical and histologic) of EAAU and shortened the duration of disease. iNOS inhibitor (AG) and 5-LP inhibitor (NDGA) partially attenuated EAAU.

CONCLUSIONS

Our results show that EAAU was partially attenuated by AG and NDGA. Interestingly, CS 236, a potent COX 2 inhibitor, completely inhibited EAAU in male Lewis rats most likely by inhibiting the initial phase and onset of the disease.

Effects of L-NAME and timolol on aqueous IL-1beta, IL-6, IL-8, TNF-alpha and NO levels after Nd:YAG laser iridotomy in rabbits

PURPOSE

Pro-inflammatory cytokines are produced by tissues and play a vital role in the host inflammatory response and uveitis. Nitric oxide (NO) can be produced in large amounts as a response to experimentally-induced uveitis or cytokines. In this study, we measured the levels of pro-inflammatory cytokines such as interleukin (IL)-1beta, IL-6, IL-8, tumor necrosis factor (TNF)-alpha and free-radical in aqueous humor after Nd:YAG laser iridotomy in rabbits, and investigated whether timolol maleate an anti-glaucoma drug, or a NO synthase inhibitor, NG-nitro-L-arginine methyl esther (L-NAME) had an inhibitory effect on these molecules, since L-NAME is a known anti-inflammatory agent in rabbits.

METHODS

Bilateral experimental Nd:YAG laser iridotomy (power 7.5 mJ, mode single burst, aiming beam 4) was performed on 18 rabbits under general plus topical anesthesia. Aqueous humor samples were taken by clear corneal paracentesis preoperatively, and 1 and 24 h postoperatively. Six rabbits (12 eyes) were given bilateral topical timolol maleate 0.5% (Timoptic) drop b.i.d. (group 1), six rabbits (12 eyes) received bilateral 0.1 ml subconjuntival injections of L-NAME (150 mg/kg) (group 2), and six rabbits (12 eyes) were treated with topical balanced salt solution (BSS) b.i.d. (control). RESULTS. Preoperative cytokine and NO levels were comparable in the three groups, with no significant differences. In addition, there was no significant difference in baseline cytokine levels between the right and left eyes. In all groups, pre- and postoperative mean IL-1beta levels were below the detection limit of the assay (<5.0 pg/ml). In the control group, postoperative mean IL-6, IL-8 and NO levels were significantly higher after Nd:YAG laser iridotomy than before (for each, p < 0.01). Timolol and L-NAME both inhibited the rise in IL-8 and TNF-alpha levels. Timolol also inhibited the rise in IL-6 but not NO. L-NAME had an inhibitory effect against NO, but not IL-6.

CONCLUSIONS

L-NAME has an inhibitory effect on IL-8, TNF-alpha and NO, but not on IL-6. Timolol had inhibitory effects on IL-6, IL-8 and TNF-alpha, but not on NO. These preliminary experimental results might help in assssing the effect of Nd:YAG laser iridotomy in aqueous humor, and to understand the inhibitory effects of timolol and L-NAME against these molecules.

Effects of Orengedoku-to and Senkanmeimoku-to, traditional herbal medicines, on the experimental elevation of aqueous flare in pigmented rabbits

We investigated the effects of Orengedoku-to (Huanglian-Jie-Du-Tang in Chinese) and Senkanmeimoku-to (Xygan-Ming-Mu-Tang in Chinese), traditional herbal medicines, on experimantal elevation of aqueous flare in pigmented rabbits. To produce the elevation of aqueous flare in rabbits, prostaglandin E2 (PGE2) was applied to the cornea with use of a glass cylinder, or lipopolysaccharides (LPS) were injected into the ear vein. Animals were pretreated by the oral administration of 150 g/day of food containing 0.7%, 0.2% or 0.07% (w/w) Orengedoku-to, or 2%, 0.6% or 0.2% (w/w) Senkanmeimoku-to for 5 days. Aqueous flare was measured with a laser flare-cell meter. Pretreatment with 0.7% or 0.2% Orengedoku-to and 2% Senkanmeimoku-to did suppress significantly (P < 0.05) elevation of aqueous flare induced by PGE2. Pretreatment with 0.7% or 0.2% Orengedoku-to and 2% or 0.6% Senkanmeimoku-to significantly suppressed (P < 0.001) elevation of aqueous flare induced by LPS. It is possible that Orengedoku-to and Senkanmeimoku-to may migrate some forms of uveitis.

The Nitrite/alpha crystallin reaction: a possible mechanism in lens matrix damage

Recent work has explored the potential deleterious role that nitric oxide (NO) and its derivatives may have in human disease. The many by-products of NO include nitrite ion, which accumulates in the anterior chamber during ocular inflammation and can be derived from cigarette smoking. Cigarette smoking has been strongly linked to nuclear cataract formation, although the mechanism remains unknown. We have previously observed that nitrite reactions with the matrix proteins elastin and collagen produce damaging effects that mimic those observed in age- and smoking-related illnesses. In the present study we report on the reaction of nitrite with alpha crystallin, the major lens matrix protein. Incubations at neutral pH and body temperature of nitrite with alpha crystallin resulted in protein modifications indicative of oxidative damage and similar to changes seen in the aging lens as well as cataracts. These include increased fluorescence, yellowing and protein cross-linking. L-kynurenine, a tryptophan derivative, was identified as a reaction product. L-kynurenine was also formed from the reaction of nitrite with free tryptophan. Thus, this non-enzymatic nitration of alpha crystallin provides a novel mechanism by which lens proteins may be damaged in vivo. Since human exposure to nitrite is increased by cigarette smoking, this reaction could provide an explanation for the association between nuclear cataracts and smoking.

Functional role of nitric oxide in regulation of ocular blood flow

Nitric oxide generated by three distinct enzyme systems appears to play a critical role in many diverse physiological processes. Using both conventional and immunohistochemical techniques, nitric oxide synthases have been identified throughout the body, including all regions of the eye. A large number of in vitro and in vivo preparations have been utilized showing nitric oxide to have an important role in regulation of regional ocular blood flow. Nitric oxide-mediated control of basal ocular blood flow is demonstrated by vasoconstriction seen in experiments where vascular endothelial cells are removed, or when nitric oxide synthase is inhibited. The endogenous source of nitric oxide in the eye appears to be both endothelial and neural. In addition, administration of drugs that can 'donate' nitric oxide produces vasodilation of the eye vasculature. Local vasodilation in response to illumination of the retina is controlled by generation and release of nitric oxide, whereas most other physiological adjustments of ocular blood flow (i.e., autoregulation and responses to altered blood gas levels) seem to be relatively independent of nitric oxide mechanisms. Nitric oxide is implicated in a variety of ocular pathophysiological states including uveitis, retinal ischemic disease, diabetes and glaucoma.