Endotoxin-induced uveitis in the rat. A study of the role of inflammation mediators

Hypotony in uveitis: an overview of medical and surgical management

Hypotony is a well-recognised, sight-threatening complication of uveitis. It can also be the final common endpoint for a multitude of disease entities. Multiple mechanisms underlie hypotony, and meticulous clinical history alongside ocular phenotyping is necessary for choosing the best intervention and therapeutic management. In this narrative review, a comprehensive overview of medical and surgical treatment options for the management of non-surgically induced hypotony is provided. Management of ocular hypotony relies on the knowledge of the aetiology and mechanisms involved. An understanding of disease trajectory is vital to properly educate patients. Both anatomical and functional outcomes depend on the underlying pathophysiology and choice of treatment.

Targeting TBK1 attenuates ocular inflammation in uveitis by antagonizing NF-κB signaling

Uveitis with complex pathogenesis is a kind of eye emergency involving refractory and blinding inflammation. Dysregulation of TANK binding kinase 1 (TBK1), which plays an important role in innate immunity, often leads to inflammatory diseases in various organs. However, the role of TBK1 in uveitis remains elusive. In this study, we identified that the mRNA expression level of TBK1 and its phosphorylation level were significantly increased in peripheral blood mononuclear cells (PBMCs) of patients with uveitis. Consistent with this, the expression of Tbk1 was elevated in the ocular tissues of uveitis rats and primary peritoneal macrophages while its phosphorylation levels, which present activation forms, were upregulated as well, accompanied by an increase in the level of nuclear factor-κB (NF-κB) and proinflammatory cytokines. In addition, inhibition of TBK1 may effectively reduce the inflammatory response of uveitis rats by blocking NF-κB entry into the nucleus and impeding the initiation of NLRP3 inflammasome- and caspase-1-mediated pyroptosis pathways.

Blocking the inflammasome: A novel approach to treat uveitis

Uveitis is a complex ocular inflammatory disease often accompanied by bacterial or viral infections (infectious uveitis) or underlying autoimmune diseases (non-infectious uveitis). Treatment of the underlying infection along with corticosteroid-mediated suppression of acute inflammation usually resolves infectious uveitis. However, to develop more effective therapies for non-infectious uveitis and to better address acute inflammation in infectious disease, an improved understanding of the underlying inflammatory pathways is needed. In this review, we discuss the disease aetiology, preclinical in vitro and in vivo uveitis models, the role of inflammatory pathways, as well as current and future therapies. In particular, we highlight the involvement of the inflammasome in the development of non-infectious uveitis and how it could be a future target for effective treatment of the disease.

Leukotriene B4 receptors as therapeutic targets for ophthalmic diseases

Leukotriene B₄ (LTB₄) is an inflammatory lipid mediator produced from arachidonic acid by multiple reactions catalyzed by two enzymes 5-lipoxygenase (5-LOX) and LTA₄ hydrolase (LTA₄H). The two receptors for LTB₄ have been identified: a high-affinity receptor, BLT1, and a low-affinity receptor, BLT2. Our group identified 12(S)-hydroxy-5Z,8E,10E-heptadecatrienoic acid (12-HHT) as a high-affinity BLT2 ligand. Numerous studies have revealed critical roles for LTB₄ and its receptors in various systemic diseases. Recently, we also reported the roles of LTB₄, BLT1 and BLT2 in the murine ophthalmic disease models of mice including cornea wound, allergic conjunctivitis, and age-related macular degeneration. Moreover, other groups revealed the evidence of the ocular function of LTB₄. In the present review, we introduce the roles of LTB₄ and its receptors both in ophthalmic diseases and systemic inflammatory diseases. LTB₄ and its receptors are putative novel therapeutic targets for systemic and ophthalmic diseases.

Effects of Post-Treatment Hydrogen Gas Inhalation on Uveitis Induced by Endotoxin in Rats

Background

Molecular hydrogen (H₂) has been widely reported to have benefiicial effects in diverse animal models and human disease through reduction of oxidative stress and inflammation. The aim of this study was to investigate whether hydrogen gas could ameliorate endotoxin-induced uveitis (EIU) in rats.

Material/Methods

Male Sprague-Dawley rats were divided into a normal group, a model group, a nitrogen-oxygen (N-O) group, and a hydrogen-oxygen (H-O) group. EIU was induced in rats of the latter 3 groups by injection of lipopolysaccharide (LPS). After that, rats in the N-O group inhaled a gas mixture of 67% N₂ and 33% O₂, while those in the H-O group inhaled a gas mixture of 67% H₂ and 33% O₂. All rats were graded according to the signs of uveitis after electroretinography (ERG) examination. Protein concentration in the aqueous humor (AqH) was measured. Furthermore, hematoxylin-eosin staining and immunostaining of anti-ionized calcium-binding adapter molecule 1 (Iba1) in the iris and ciliary body (ICB) were carried out.

Results

No statistically significant differences existed in the graded score of uveitis and the b-wave peak time in the Dark-adapted 3.0 ERG among the model, N-O, and H-O groups (P>0.05), while rats of the H-O group showed a lower concentration of AqH protein than that of the model or N-O group (P<0.05). The number of the infiltrating cells in the ICB of rats from the H-O group was not significantly different from that of the model or N-O group (P>0.05), while the activation of microglia cells in the H-O group was somewhat reduced (P<0.05).

Conclusions

Post-treatment hydrogen gas inhalation did not ameliorate the clinical signs, or reduce the infiltrating cells of EIU. However, it inhibited the elevation of protein in the AqH and reduced the microglia activation.

Effects of hydrogen-rich saline on endotoxin-induced uveitis

The therapeutic effects of hydrogen-rich saline (HRS) have been reported for a wide range of diseases mainly via selectively reducing the amount of reactive oxygen species. Oxidative stress plays an important role in the pathogenesis of uveitis and endotoxin-induced uveitis (EIU). In this study, we investigated whether HRS can mitigate EIU in rats. Sprague-Dawley rats were randomly divided into Norm group, Model group, HRS group, dexamethasone (DEX) group, and rats in the latter three groups were injected with equal amount of lipopolysaccharide (LPS) to induce EIU of different severities (by 1 mg/kg of LPS, or 1/8 mg/kg of LPS). Rats in HRS group were injected with HRS intraperitoneally at three different modes to purse an ameliorating effect of EIU (10 mL/kg of HRS immediately after injection of 1 mg/kg of LPS, 20 mL/kg of HRS once a day for 1 week before injection of 1 mg/kg of LPS and at 0, 0.5, 1, 2, 6, 8, 12 hours after LPS administration, or 20 mL/kg of HRS once a day for 1 week before injection of 1/8 mg/kg of LPS, and at 0, 0.5, 1, 2, 6, 8, 12, 24 hours and once a day for 3 weeks after LPS administration). Rats of DEX group were injected with 1 mL/kg of DEX solution intraperitoneally immediately after LPS administration. Rats in Norm and Model groups did not receive any treatment. All rats were examined under slit lamp microscope and graded according to the clinical signs of uveitis. Electroretinogram, quantitative analysis of protein in aqueous humor (AqH) and histological examination of iris and ciliary body were also carried out. Our results showed that HRS did not obviously ameliorate the signs of uveitis under slit lamp examination and the inflammatory cells infiltration around iris and cilliary body of EIU induced by 1 mg/kg or 1/8 mg/kg of LPS (P > 0.05), while DEX significantly reduced the inflammation reflected by the above two indicators (P < 0.05). The impaired retinal function of mild EIU induced by 1/8 mg/kg of LPS, showed by delay of peak time of b-wave of Dark adapted 3.0 electroretinogram, was not significantly restored by HRS (P > 0.05), while DEX had an obvious therapeutic effect (P < 0.05). However, HRS exerted an inhibition trend on elevation of protein in AqH of EIU induced by 1 mg/kg of LPS, and significantly reduced the increasing amount of protein in AqH of mild EIU induced by 1/8 mg/kg of LPS (P < 0.05). In conclusion, HRS could not obviously mitigate EIU in rats, while it could inhibit the elevation of AqH protein.

An anti-interleukin-2 receptor drug attenuates T- helper 1 lymphocytes-mediated inflammation in an acute model of endotoxin-induced uveitis

The aim of the present study was to evaluate the anti-inflammatory efficacy of Daclizumab, an anti-interleukin-2 receptor drug, in an experimental uveitis model upon a subcutaneous injection of lipopolysaccharide into Lewis rats, a valuable model for ocular acute inflammatory processes. The integrity of the blood-aqueous barrier was assessed 24 h after endotoxin-induced uveitis by evaluating two parameters: cell count and protein concentration in aqueous humors. The histopathology of all the ocular structures (cornea, lens, sclera, choroid, retina, uvea, and anterior and posterior chambers) was also considered. Enzyme-linked immunosorbent assays of the aqueous humor samples were performed to quantify the levels of the different chemokine and cytokine proteins. Similarly, a biochemical analysis of oxidative stress-related markers was also assessed. The inflammation observed in the anterior chamber of the eyes when Daclizumab was administered with endotoxin was largely prevented since the aqueous humor protein concentration substantially lowered concomitantly with a significant reduction in the uveal and vitreous histopathological grading. Th1 lymphocytes-related cytokines, such as Interleukin-2 and Interferon-γ, also significantly reduced with related anti-oxidant systems recovery. Daclizumab treatment in endotoxin-induced uveitis reduced Th1 lymphocytes-related cytokines, such as Interleukin-2 and Interferon gamma, by about 60–70% and presented a preventive role in endotoxin-induced oxidative stress. This antioxidant protective effect of Daclizumab may be related to several of the observed Daclizumab effects in our study, including IL-6 cytokine regulatory properties and a substantial concomitant drop in INFγ. Concurrently, Daclizumab treatment triggered a significant reduction in both the uveal histopathological grading and protein concentration in aqueous humors, but not in cellular infiltration.

Lipoic acid lessens Th1-mediated inflammation in lipopolysaccharide-induced uveitis reducing selectively Th1 lymphocytes-related cytokines release

Inflammation results in the production of free radicals. We evaluated the anti-inflammatory and antioxidant capacity of lipoic acid in an experimental uveitis model upon a subcutaneous injection of endotoxin into Lewis rats. The role of oxidative stress in the endotoxin-induced uveitis model is well-known. Besides, the Th1 response classically performs a central part in the immunopathological process of experimental autoimmune uveitis. Exogenous sources of lipoic acid have been shown to exhibit antioxidant and anti-inflammatory properties. Our results show that lipoic acid treatment plays a preventive role in endotoxin-induced oxidative stress at 24 h post-administration and reduced Th1 lymphocytes-related cytokines by approximately 50-60%. Simultaneously, lipoic acid treatment caused a significant reduction in uveal histopathological grading and in the protein concentration in aqueous humors, but not in cellular infiltration.

Calprotectin is raised in endogenous posterior uveitis

Calprotectin, the L1 leucocyte protein, is found in large quantities in the cytosol of granulocytes and monocytes. Plasma calprotectin levels are increased in infections, malignant tumours, vascular insults and various other pathogenic conditions. The authors have investigated plasma calprotectin and ANCA levels in 27 patients with endogenous posterior uveitis (EPU) and six healthy volunteers. Compared to the control values, the mean levels of plasma calprotectin were raised in patients with active uveitis (p<0.005 (ANOVA)). Raised serum ANCA titres, which are also associated with neutrophil activation, were also detected in some patients with EPU but the level of ANCA did not correlate with that of calprotectin. The authors suggest that measurement of plasma calprotectin may be a sensitive indicator of disease activity in patients with endogenous posterior uveitis.

Therapeutic benefit of melatonin in experimental feline uveitis

Uveitis is a frequent ophthalmic disorder which constitutes one of the main causes of blindness in domestic cats. The aim of this report was to analyze the effect of melatonin on experimentally induced uveitis in cats. Bacterial lipopolysaccharide (LPS) was injected intravitreally into one eye from intact cats, while the contralateral eye was injected with vehicle. Melatonin was orally administered every 24 hr to a group of ten cats, from 24 hr before until 45 days after intravitreal injections. Eyes were evaluated by means of clinical evaluation, intraocular pressure (IOP), blood-ocular barrier integrity (via measurement of protein concentration and cell content in samples of aqueous humor [AH]), electroretinogram (ERG), and histological examination of the retinas. In LPS-treated eyes, several clinical signs were observed until day 45 postinjection. The treatment with melatonin significantly decreased clinical signs and prevented the reduction in IOP induced by LPS. In LPS-injected eyes, melatonin significantly preserved the blood-ocular barrier integrity, as shown by a decrease in the number of infiltrating cells and protein concentration in the AH. Mean amplitudes of scotopic ERG a- and b-waves were significantly reduced in eyes injected with LPS, whereas melatonin significantly prevented the effect of LPS. At 45 days after injection, LPS induced alterations in photoreceptors and at the middle portion of the retina, whereas melatonin preserved the retinal structure. These results indicate that melatonin prevented clinical, biochemical, functional, and histological alterations induced by LPS injection. Thus, melatonin might constitute a useful tool for the treatment of feline uveitis.

Elevated levels of anti-endotoxin antibodies in patients with bilateral idiopathic acute anterior uveitis

PURPOSE

Endotoxins have been proved to be responsible for acute anterior uveitis (AAU) in animals in a well-established experimental model of endotoxin-induced uveitis (EIU). The purpose of our study was the detection of antibodies against endotoxins of selected enterobacteria in the serum of patients with idiopathic AAU and searching for correlations between the levels of these antibodies and the presence of HLA-B27 antigen as well as characteristic signs of EIU such as bilaterality and the absence of spontaneous recurrences of the disease.

METHODS

Reactions of serum IgG antibodies with lipopolysaccharides (LPSs) of Escherichia coli O1, E. coli O10, E. coli O111, E. coli J5, and Klebsiella pneumoniae O3 were determined for 60 patients with idiopathic AAU and 40 healthy volunteers. The presence of HLA-B27 antigen in patients was determined. Documentation of the frequency of recurrences of AAU during a follow-up period of 8 years was collected.

RESULTS

We have observed that the sera of patients with a first attack of AAU reacted stronger with the LPS of K. pneumoniae O3 than the sera of patients with relapse of the disease. Patients with bilateral AAU had markedly higher levels of antibodies against four of the five used LPSs than patients with one eye involved. A multiply comparison showed higher levels of IgG reacting with LPS of E. coli O111 in patients with bilateral eye inflammation admitted with the first attack of AAU comparing to controls. The incidence of recurrent form of AAU was significantly increased in HLA-B27-positive patients compared to HLA-B27-negative patients. However, we found in HLA-B27 carriers that those with the bilateral form of AAU had over three times smaller risk of recurrence and showed stronger immunization by endotoxins than patients with unilateral inflammation.

CONCLUSION

Our results suggest a potential role of endotoxins in the aetiology of the nonrecurrent bilateral form of AAU. We suggest that not only HLA-B27 status but also determination of number of involved eyes may be useful to assess the risk of recurrence of the idiopathic AAU.

Effects of Caffeic Acid Phenethyl Ester on Endotoxin-Induced Uveitis in Rats

PURPOSE

Caffeic acid phenethyl ester (CAPE) has antimicrobial, anti-inflammatory, antioxidant, immunomodulatory, and carcinostatic properties. In this study, the efficacy of CAPE in endotoxin-induced uveitis (EIU) in rats is investigated.

METHODS

EIU was induced by a footpad injection of lipopolysaccharide (LPS). In the treatment group, 10 micromol/kg CAPE was injected intraperitoneally immediately after LPS injection. At 24 hr after LPS injection, the number of infiltrating cells, protein concentration, and levels of myeloperoxidase (MPO) in aqueous humor; malondialdehyde (MDA), MPO, and total antioxidant levels in serum were determined. Eyes were enucleated for histopathologic evaluation, and, counting inflammatory cells in iris-ciliary body (ICB), the efficacy of treatment was determined.

RESULTS

CAPE significantly suppressed LPS-induced increase in the number of inflammatory cells (p = 0.0001), protein concentration (p = 0.0001), and MPO levels (p = 0.0001) in aqueous humor as well as MDA (p = 0.001) and MPO (p = 0.0001) levels in serum. Histopathologic evaluation of ICB showed significant reduction in the inflammatory cell counts in the treatment group (p = 0.0001).

CONCLUSIONS

CAPE was found efficient in suppressing inflammation and ocular tissue damage induced by LPS in rats.

Downregulation of endotoxin-induced uveitis by intravitreal injection of polylactic-glycolic acid (PLGA) microspheres loaded with dexamethasone

We tested the short- and long-term ability of polylactic-glycolic acid (PLGA) microspheres loaded with dexamethasone to reduce ocular inflammation in rabbits elicited by intravitreal lipopolysaccharide (LPS) injection. PLGA microspheres loaded with dexamethasone were prepared by the solvent evaporation technique from an oil/water emulsion and sterilized by gamma irradiation (25 kGy). The microsphere fraction selected was 2:10 (dexamethasone:PLGA) and contained 141 +/- 0.38 microg dexamethasone/mg PLGA. Microsphere diameters were 20-53 microm, and the mean encapsulation efficiency was 92.97 +/- 0.75%. Seven days prior to the induction of panuveitis, 10 mg of dexamethasone-free or dexamethasone-loaded microspheres were injected into the vitreous. Control animals received no injection. Panuveitis was induced in male New Zealand rabbits (2.5-3.0 kg) by intravitreal injection of Escherichia coli LPS. Clinical evaluation, electroretinography and histopathologic studies were performed in short-term studies of 15 days and in long-term studies of 33 days. Efficacy in reducing inflammation was also studied in vitrectomized eyes. In short-term studies eyes injected with dexamethasone-loaded microspheres had less inflammation than control eyes and eyes injected with blank microspheres. Inflammation reverted in all groups by 15 days after LPS injection. A second LPS dose given on Day 30 provoked a high peak of inflammation in control eyes and in those injected with blank microspheres. In contrast, only slight inflammation occurred in eyes injected with dexamethasone-loaded microspheres. Histopathology and electroretinography supported these results. Dexamethasone-loaded microspheres effectively reduced intraocular inflammation caused by LPS in both short- and long-term studies.

Ocular surface-evoked Fos-like immunoreactivity is enhanced in trigeminal subnucleus caudalis by prior exposure to endotoxin

Endotoxin-induced uveitis (EIU) is a common animal model for anterior uveitis in humans that causes long-term changes in trigeminal brain stem neurons. This study used c-fos immunohistochemistry to assess the effects of different routes of administration of endotoxin on activation of trigeminal brain stem neurons produced by ocular surface stimulation. A single dose of endotoxin (lipopolysaccharide (LPS)) given to male rats by systemic (i.p., 1 mg/kg) or intraocular (ivt, 20 microg) routes increased the number of Fos-positive neurons in rostral (trigeminal subnucleus interpolaris/subnucleus transition (Vi/Vc)) and caudal portions of trigeminal subnucleus caudalis (trigeminal subnucleus caudalis/upper cervical spinal cord transition (Vc/C(1-2))) by 20% mustard oil (MO) applied to the ocular surface 7 days, but not at 2 days, after LPS compared with naïve rats. I.c.v. (20 microg) LPS did not affect MO-evoked Fos. To determine if the pattern of enhanced Fos expression after systemic LPS also depended on the nature of the ocular surface stimulus, additional groups received ocular stimulation by 10% histamine or dry eye conditions. Seven days, but not 2 days, after i.p. LPS both histamine- and dry eye-evoked Fos was increased at the Vi/Vc transition, while smaller effects were seen at other regions. These results suggested that EIU modulation of trigeminal brain stem neuron activity was mediated mainly by peripheral actions of LPS. Enhancement of Fos at the Vi/Vc region after MO, histamine and dry eye conditions supports the hypothesis that this region integrates innocuous as well as noxious sensory information, while more caudal portions of Vc process mainly nociceptive signals from the eye.

In vivo pharmacokinetics and in vitro pharmacodynamics of nepafenac, amfenac, ketorolac, and bromfenac

PURPOSE

To evaluate the aqueous humor concentrations and cyclooxygenase (COX) inhibitory activities of nepafenac, amfenac, ketorolac, and bromfenac after topical ocular administration of Nevanac (nepafenac 0.1%), Acular LS (ketorolac 0.4%), or Xibrom (bromfenac 0.09%).

SETTING

Five private ophthalmology practices throughout the United States.

METHODS

Patients requiring cataract extraction were randomized to 1 of 3 treatment groups: Nevanac, Acular LS, or Xibrom. Patients were administered 1 drop of the test drug 30, 60, 120, 180, or 240 minutes before cataract surgery. At the time of paracentesis, an aqueous humor sample was collected and later analyzed for drug concentration. In addition, COX-1 (homeostatic) and COX-2 (inducible) inhibitory activities of nepafenac, amfenac, ketorolac, and bromfenac were determined via the in vitro measurement of prostaglandin E(2) (PGE(2)) inhibition.

RESULTS

Seventy-five patients participated in the study. The prodrug nepafenac had the shortest time to peak concentration and the greatest peak aqueous humor concentration (C(max)). The C(max) of nepafenac was significantly higher than that of the other drugs (P<.05), including the higher-concentration ketorolac (0.4%). The area under the curve (AUC) of nepafenac was significantly higher (P<.05) than the AUCs of amfenac, ketorolac, and bromfenac. The combined AUCs of nepafenac and amfenac were the highest of all drugs tested (P<.05). Ketorolac showed the most potent COX-1 inhibition, whereas amfenac was the most potent COX-2 inhibitor. The PGE(2) aqueous humor levels of each study medication were highly variable; as a result, meaningful interpretation of the data was not possible.

CONCLUSION

Nepafenac showed significantly greater ocular bioavailability and amfenac demonstrated greater potency at COX-2 inhibition than ketorolac or bromfenac.

Endotoxin-Induced Uveitis Causes Long-Term Changes in Trigeminal Subnucleus Caudalis Neurons

Endotoxin-induced uveitis (EIU) is commonly used in animals to mimic ocular inflammation in humans. Although the peripheral aspects of EIU have been well studied, little is known of the central neural effects of anterior eye inflammation. EIU was induced in male rats by endotoxin or lipopolysaccharide (LPS, 1 mg/kg ip) given 2 or 7 days earlier. Neurons responsive to mechanical stimulation of the ocular surface were recorded under barbiturate anesthesia at the trigeminal subnucleus interpolaris/caudalis (Vi/Vc) transition and subnucleus caudalis/cervical cord (Vc/C1) junction, the main terminal regions for corneal nociceptors. Two days after LPS, Vc/C1 units had reduced responses to histamine, nicotine, and CO2 gas applied to the ocular surface, whereas unit responses were increased 7 days after LPS. Those units with convergent cutaneous receptive fields at Vc/C1 were enlarged 7 days after LPS. Units at the Vi/Vc transition also had reduced responses to histamine and CO2 2 days after LPS but no enhancement was seen at 7 days. Tear volume evoked by CO2 was reduced 2 days after LPS and returned toward control values by 7 days, whereas CO2-evoked eye blinks were normal at 2 days and increased 7 days after LPS. These results indicate that a single exposure to endotoxin causes long-term changes in the excitability of second-order neurons responsive to noxious ocular stimulation. The differential effects of EIU on tear volume and eye blink lend further support for the hypothesis that ocular-sensitive neurons at the Vi/Vc transition and Vc/C1 junction regions mediate different aspects of pain during intraocular inflammation.

Effects of anti-glaucoma drugs timolol and GLC756, a novel mixed dopamine D2 receptor agonist and D1 receptor antagonist, on endotoxin-induced-uveitis and -arthritis in rats

Anti-glaucoma drugs exhibiting anti-inflammatory properties are desirable for the long-term treatment of glaucoma since they may reduce the risk for treatment-related inflammatory processes in outer compartments of the eye. The purpose of this study was to evaluate potential anti-inflammatory effects of two topically and systemically applied anti-glaucoma drugs i.e. GLC 756, a novel mixed dopamine D2 receptor agonist and D1 receptor antagonist, and timolol a beta-adrenoceptor antagonist using endotoxin-induced uveitis (EIU) and arthritis in rats as an in vivo model. For EIU, 8-week-old Lewis rats were intravenously injected at 160 microg lipopolysaccharide (LPS) from Salmonella typhimurium. GLC756, timolol, or betamethasone, as a positive control, were either topically (0.4%, 0.5%, and 0.1%, respectively, 16-times 20 microL eye drops during 48 h) or systemically (1mg/kg subcutaneous for 5 days) administered. Cell infiltration in tissue of the eye and knee joint were assessed histopathologically and in special compartments of the eye by confocal microscopy 48 h after LPS-induction. Numerous infiltrating cells were detected in the eyes after LPS-induction and half of the animals showed arthritis. Topical and systemic pre-treatment with GLC756 and timolol resulted in reduced cell infiltration in the eye. In addition, GLC756 reduced, whereas timolol increased the incidence of arthritis. Betamethasone suppressed almost completely the cell infiltration in the eye and the incidence of arthritis. In conclusion, the observations that GLC756 reduced cell infiltration in the eye and the incidence of arthritis after LPS-induction is compatible with anti-inflammatory properties of this drug. By contrast, timolol produced no consistent anti-inflammatory effect since both inhibitory as well as stimulatory effects on inflammatory processes were seen.

The surgical management of chronic hypotony due to uveitis

PURPOSE

Evaluate surgery in chronic hypotony secondary to uveitis.

METHOD

Retrospective analysis of six patients operated for chronic hypotony (< or =5 mmHg) of at least 1 month's duration. Surgery involved removal of all traction and membranes on the ciliary processes. Use of oil was limited to patients with atrophic ciliary processes.

RESULTS

The average postoperative follow-up was 24 months (12-43). The average pressure increase was 7 mmHg at 6 months. Four of six uveitis patients had significantly increased vision.

CONCLUSION

Improved vision, and a sustained pressure rise are possible in hypotonous uveitis. The presence of ciliary processes is necessary. However, they do not need to be intact.

Secretoneurin in the human aqueous humor and the absence of an effect of frequently used eye drops on the levels

Secretoneurin (SN) was detected in the aqueous humor (AH) of patients treated topically with tobramycine eye drops alone or tobramycine and cyclosporine A, tobramycine and diclofenac or tobramycine and rimexolone. The levels of the peptide were found to be higher in the uninflamed human than in the rabbit aqueous humor which may be the result of species differences and/or age-related circumstances. Furthermore, they are approximately one hundred times higher than those of classical neuropeptides indicating release from nerve fibers and/or secretion from non-pigmented ciliary epithelium cells. Despite a slight tendency by rimexolone to decrease the levels, there was no significant effect seen for either of the drops. It must be considered that aminoglycosides are known to have toxic side effects and that they can influence the levels of SN which may be not diminished by low topical doses of corticosteroids or nonsteroidal antiinflammatory drugs. The high levels of the peptide are of relevance and may indicate a significant role of secretoneurin in the anterior segment of the eye. This should encourage performing functional studies.

Susceptibility to endotoxin induced uveitis is not reduced in mice deficient in BLT1, the high affinity leukotriene B4 receptor

AIM

To investigate the role of arachidonic acid derived chemotactic factor, LTB(4), in the development of endotoxin induced uveitis (EIU), using mice deficient in the BLT1 gene which encodes the high affinity LTB(4) receptor.

METHODS

BLT1 gene deficient and wild type BALB/c mice were injected intravitreally with Escherichia coli 055:B5 lipopolysaccharide (250 ng/2 microl). Number of leukocytes invading the anterior chamber 24 hours later were counted on tissue cross sections.

RESULTS

In all mice, EIU was characterised by a polymorphonuclear and mononuclear cell infiltrate. Numbers of infiltrating cells did not differ significantly between control and BLT1 gene knockout mice.

CONCLUSION

Chemotactic factors other than LTB(4) are primarily responsible for leukocyte migration into the eye during murine EIU.

A novel inflammatory eye disease induced by lymphocytes from knockout mice sensitized against the deleted ocular antigen

Lens-associated uveitis (LAU), a severe inflammatory eye disease, is thought to be mediated by autoimmunity against lens crystallins. Previously described animal models for this disease are antibody-mediated, since no cellular response to self crystallins could be induced in experimental animals. Here, we describe a new model for LAU, in which lymphocytes from knockout mice deficient in alphaB-crystallin are sensitized against the deleted protein and induce severe ocular inflammation when adoptively transferred into wild type recipients. Similar to LAU, the experimental disease developed only following rupture of the lens capsule, produced in this study by capsulotomy; no disease was detected in recipient eyes with no capsulotomy, or in those treated with cautery, or in eyes affected by systemic treatment with sodium iodate, lipopolysaccharide or X-irradiation. The ocular changes in affected eyes included heavy cellular infiltration and proteinaceous exudate in both the anterior and posterior segments of the eye, that reached their peak on day 4 following cell transfer and subsided quite rapidly thereafter.

Role of oxygen and nitrogen species in experimental uveitis: anti-inflammatory activity of the synthetic antioxidant ebselen

This study was aimed at examining the role of oxygen and nitrogen reactive species in a model of experimental uveitis upon intravitreal injection of bacterial endotoxin to albino New Zealand rabbits. The inflammatory response was evaluated in terms of: (i) the integrity of the blood aqueous barrier (protein and cell content in samples of aqueous humor), (ii) histopathological changes of the eyes, (iii) clinical evaluation (with a score index based on clinical symptoms), and (iv) the concentration of malondialdehyde (MDA), in aqueous humor, as a marker of oxidative stress. Betamethasone was used as reference treatment, superoxide dismutase as quencher of superoxide anion, L-N(G)-nitro-L-arginine-methyl-esther (L-NAME) and chlorpromazine as nitric oxide synthase inhibitors, and ebselen, a glutathione peroxidase mimic, as peroxynitrite reductant. All the substances were injected subconjunctivally to the rabbits immediately after the intravitreal endotoxin injection. Ebselen was the only treatment able to decrease MDA concentration to control values, exerting an effect similar to that elicited by L-NAME on the rest of the parameters tested. The data presented render ebselen a notable choice for the treatment of uveitis, with implications for clinical trials.

Suppressive effects of histamine H1 receptor antagonist diphenhydramine on the leukocyte infiltration during endotoxin-induced uveitis

Histamine has been shown to play an important role in the step of leukocyte rolling, the initial step to leukocyte infiltration into an inflamed region. We investigated the roles of histamine in the leukocyte recruitment during endotoxin-induced uveitis (EIU) in vivo using acridine orange digital fluorography. An injection of histamine into the vitreous cavity of a Lewis rat induced leukocyte rolling along the major retinal veins. In other experiments, EIU was induced in Lewis rats by footpad injection of lipopolysaccharide (LPS). Leukocyte rolling was also observed in the retinal veins of EIU rats. To block the histamine H1 receptor, diphenhydramine (DPH) was administered intraperitoneally 15 min before the LPS injection. DPH significantly inhibited leukocyte rolling along the major retinal veins of EIU rats, suppressing leukocyte infiltration into the vitreous cavity. The vasodilation in EIU was also significantly suppressed with DPH. Moreover, leukocyte infiltration into aqueous humor was significantly suppressed in DPH-treated rats. Although the inhibitory effects of DPH was less obvious at later time points, addition of DPH every 12 hr showed prolonged anti-inflammatory effects up to 48 hr after LPS injection. In contrast, protein leakage into the aqueous humor was not suppressed as much as leukocyte infiltration with DPH. These results suggest that histamine would play a pivotal role in leukocyte recruitment during EIU in rats. Blocking the histamine H1 receptor might help to prevent or minimize leukocyte infiltration in uveitis.

Therapeutic applications of antiflammin peptides in experimental ocular inflammation

Antiflammins are synthetic peptides derived from the region of highest local similarity between uteroglobulin and lipocortin. These peptides have shown anti-inflammatory activity on carrageenan-induced rat footpad edema. They are potent inhibitors for phospholipase A2 activation both in vitro and in vivo. Previously, we have demonstrated the effectiveness of topical antiflammins in suppressing acute ocular inflammation and allergic response in rodent endotoxin-induced uveitis and murine allergic conjunctivitis. The mechanisms by which antiflammins protect against inflammation and allergy in these ocular models may involve inhibition of phospholipase A2 and inducible nitric oxide synthase (iNOS) as well as the production of proinflammatory cytokine, interleukin-6.

Basic pathogenic mechanisms operating in experimental models of acute anterior uveitis

Acute anterior uveitis is a recurrent inflammatory disease of the eye that occurs commonly, is distressing for the patient, and may have potentially blinding sequelae. The pathogenesis of the disease is poorly understood, and anti-inflammatory treatment is consequently non-specific and may be associated with significant complications. Animal models are a possible key to a better understanding of this disease. In one model, rats and mice develop a relatively short-lived anterior uveal inflammation almost immediately after systemic injection of bacterial endotoxin. Accumulating evidence suggests that cytokine production by resident uveal macrophages initiates endotoxin-induced uveitis which is characterized by an infiltration of neutrophils and mononuclear cells. A second model displays features in keeping with a delayed-type hypersensitivity immune response. Experimental melanin-induced uveitis is an acute recurrent uveitis with delayed onset but extended duration, observed when rats are immunized with bovine ocular melanin. Both animal models have clinical features in common with acute anterior uveitis, although experimental melanin-induced uveitis appears to mimic the human disease more closely. Novel treatment options to target implicated inflammatory cells and molecules are currently under consideration.

Effect of macrophage depletion by liposomes containing dichloromethylene-diphosphonate on endotoxin-induced uveitis

Footpad injection of lipopolysaccharide (LPS) from Salmonella typhimurium in Lewis rats induces an acute anterior and posterior endotoxin-induced uveitis (EIU). To investigate the role of macrophages in the pathogenesis of EIU, we eliminated macrophages by means of liposomes containing dichloromethylene-diphosphonate (Cl2MDP), a drug which depletes macrophages but not other immunocompetent cells. Intravenous injection of CL2MDP-liposomes clearly inhibited clinical and histological manifestations of uveitis in the anterior segment of the eye (iris/ciliary body) and reduced TNF level in aqueous humor. Specific immunostaining showed that CL2MDP-liposome injections decreased the number of ED2 + resident macrophages in the iris/ciliary body and the choroid. After LPS injection, CL2MDP-liposome treatment reduced the density of infiltrating ED1 + cells (mainly monocytes/macrophages) in the iris/ciliary body but not in the choroid; little or no effect was detected on the OX42 + cellular infiltration (mainly polymorphonuclear leukocytes). The inflammatory cellular infiltration of the retina was not modified by the treatment. These findings suggest that macrophages play a key role in the pathogenesis of ocular inflammation.

Interferon gamma immunoreactivity in iris nerve fibres during endotoxin induced uveitis in the rat

AIMS

Previous studies have implied that interferon gamma (IFN-gamma) is involved in the pathogenesis of endotoxin induced uveitis (EIU) in the rat. This study investigated the source of IFN-gamma in the iris during EIU.

METHODS

Whole mounts of iris were isolated from Lewis rats before and at different times (from 4 hours to 14 days) after foot pad injection of 200 micrograms Salmonella typhimurium lipopolysaccharide (LPS). Immunohistological analysis was performed using monoclonal antibodies (mAbs) specific to rat IFN-gamma (DB12 and DB13). mAbs specific to monocytes, macrophages, and dendritic cells and MHC class II were used to asses the inflammatory response in the eye (ED-1, ED-2, and OX-6). An antibody specific to neurofilaments (2H3) was used to stain nerve fibres in the normal iris.

RESULTS

LPS administration induced acute intraocular inflammation, characterised by a massive infiltration of monocytes/macrophages and increased numbers of MHC class II positive cells in the iris. IFN-gamma immunoreactive cells were not detected in iris whole mounts of control rats. Strikingly, IFN-gamma immunoreactivity was found in fibres from 4 hours until 10 days after LPS injection, with the most intense staining at 48-72 hours. Other DB12 or DB13 positive cells were not detected in the iris. The pattern of DB12 and DB13 staining in the inflamed iris was similar to the 2H3 staining of neurons in the iris of control rats.

CONCLUSION

These results show that systemic LPS administration induces IFN-gamma immunoreactivity in iris fibres and suggest that iris nerve fibres may be a source of IFN-gamma during EIU. The IFN-gamma immunoreactive material in the iris nerve fibres may be identical to neuronal IFN-gamma.

Involvement of TNF alpha, IL-1 beta and IL-1 receptor antagonist in LPS-induced rabbit uveitis

The objective of the study was to investigate involvement of TNF alpha, IL-1 beta and IL-1 receptor antagonist (IL-1Ra) in lipopolysaccharide (LPS)-induced uveitis. Intravitreal injection of LPS (100 ng) to rabbits induced a massive leukocyte infiltration and protein leakage into the aqueous humor. Aqueous leukocyte counts and protein levels reached a peak 24 hr after this injection. The peak concentrations of aqueous TNF alpha (230 +/- 37 pg ml-1, at 9 hr) and IL-1 beta (185 +/- 80 pg ml-1, at 18 hr) preceded peak levels of aqueous leukocyte counts and protein levels. In contrast, the levels of aqueous IL-1Ra peaked at 48 hr (12,239 +/- 1964 pg ml-1) and a fairly high concentration of IL-1Ra remained when the inflammatory reactions subsided. Immunohistochemistry and leukocyte-depletion studies showed that infiltrating leukocytes were the major cellular sources of aqueous TNF alpha, IL-1 beta and IL-1Ra. Intravitreal injection of homologous TNF alpha (0.1-1.5 micrograms) or IL-1 beta (0.5-5 ng) reproduced a rapid leukocyte infiltration and protein leakage. Administration of anti-TNF alpha mAb (10 micrograms) suppressed the number of LPS-induced infiltrating neutrophils by 50%, mononuclear cells by 58%, and protein leakage by 42%. Administration of rabbit IL-1Ra (10 micrograms) also suppressed neutrophil influx by 78%, however, neither mononuclear cell influx nor protein leakage was inhibited by rabbit IL-1Ra. Co-administration of the two inhibitors enhanced inhibition of neutrophil infiltration to 88%, and protein leakage to 64%. We conclude that TNF alpha and IL-1 beta are the principal mediators of LPS-induced uveitis. Our observations also suggest that endogenous IL-1Ra may down-regulate inflammatory reactions.

Intraocular production of a cytokine (CINC) responsible for neutrophil infiltration in endotoxin induced uveitis

AIMS/BACKGROUND

The subcutaneous injection of bacterial endotoxin in Lewis rats produces an acute intraocular inflammation evolving over a 24 hour period. This endotoxin induced uveitis (EIU) is characterised by a biphasic protein exudation and a cellular infiltrate composed of macrophages and polymorphonuclear neutrophils (PMNs). This model was used to study the mechanism of cellular infiltration in ocular inflammation.

METHODS

EIU was induced by a subcutaneous injection of lipopolysaccharide (LPS) (S typhimurium) at 350 micrograms/kg. The levels of cytokine induced neutrophil chemoattractant (CINC) were measured every 2 hours in the serum and in the aqueous humour by ELISA. The intraocular inflammation was quantified by protein measurement and leucocyte counting.

RESULTS

The kinetics of CINC production in the systemic circulation showed a rapid rise, peaking 2 hours after LPS injection, followed by a progressive decline over the next 8 hours. In the eye, the CINC levels increased above the serum levels 10 hours after EIU induction corresponding to the time of cellular infiltration. When leucocyte entry in the eye was inhibited by 56% and 64% with an antiadhesion molecule antibody, there was only a slight reduction in the aqueous humour CINC levels of 9% and 16%, respectively, indicating that CINC was produced by ocular tissue cells. The specific effect of CINC in the eye was confirmed when a direct intraocular injection of 250 ng of purified CINC was followed by significant PMN infiltration, in the absence of protein exudation.

CONCLUSION

The data indicate that the production of the CINC chemotactic factor by ocular tissue participates in the inflammatory reaction in EIU.

IL-12 inhibits endotoxin-induced inflammation in the eye

Interleukin-12 (IL-12) is a heterodimeric cytokine that induces interferon (IFN)-gamma production and an increased generation of Th1 cells. Both IL-12 and IL-12 antagonists are being studied for the treatment of allergic reactions, autoimmune disease and malignancy. The goal of the present experiments was to examine the importance of IL-12 in endotoxin-induced ocular inflammation. The number of inflammatory cells infiltrating eyes with endotoxin-induced uveitis (EIU) was significantly increased in animals treated with intraperitoneal anti-IL-12 antibody when compared to control animals, but there was no difference in infiltrating inflammatory cells in the eyes of animals treated with IL-12 when compared to controls. In contrast, intraocular injection of IL-12 significantly inhibited the development of endotoxin-induced intraocular inflammation. The infiltrating inflammatory cells were reduced in the eyes of animals receiving intraocular IL-12 when compared to controls. Cytokine analysis of the aqueous humor obtained from eyes with EIU showed increased levels of IFN-gamma and decreased levels of IL-6 in eyes receiving intraocular IL-12. These data show that IL-12 has an inhibitory effect on endotoxin-induced inflammation in the eye and suggest that IL-12 can have an immunoregulatory function in some forms of inflammatory disease.

Monoclonal antibodies against CD54 (ICAM-1) and CD11a (LFA-1) prevent and inhibit endotoxin-induced uveitis

We studied the effect of monoclonal antibodies (mAbs) against CD54 (intercellular adhesion molecule-1; ICAM-1) and CD11a (lymphocyte function-associated antigen-1; LFA-1) on the prevention and treatment of endotoxin-induced uveitis (EIU). When treated at the time of endotoxin injection the mean number of inflammatory cells infiltrating the eye +/- S.E.M. on histologic sections was 469.2 +/- 51.9 for controls, 13.8 +/- 2.6 for rats receiving anti-ICAM-1 mAb (P < 0.0001), and 195.8 +/- 48.8 for rats receiving anti-LFA-1 mAb (P = 0.0003). When treated after the start of inflammatory disease, the mean number of infiltrating inflammatory cells +/- S.E.M. was 273.0 +/- 30.7 for controls, 6.4 +/- 1.7 for rats receiving anti-ICAM-1 mAb (P < 0.0001), and 54.2 +/- 7.6 for rats receiving anti-LFA-1 mAb (P < 0.0001). The mean number of cells per milliliter of aqueous humor +/- S.E.M. was 1867.6 +/- 321.8 for controls, 21.7 +/- 5.3 for rats receiving anti-ICAM-1 mAb (P < 0.0001), and 295.1 +/- 71.2 for rats receiving anti-LFA-1 mAb (P < 0.0001). MAbs against ICAM-1 and LFA-1 significantly inhibited the development of EIU and were effective in treating clinically evident ocular inflammatory disease.

Distribution of intercellular adhesion molecule-1 on leukocytes and corneal endothelium after endotoxin stimulation in rats

After stimulation with Salmonella typhimurium endotoxin, the intercellular adhesion molecule-1 (ICAM-1) was studied on the corneal endothelium and associated leukocytes in rats using immunoscanning electron microscopy. Two hundred micrograms of the endotoxin was injected in Lewis rats. The corneae were excised at 0-h and 16-h-postinjection time (n = 5, respectively). The corneae were prepared in hypothermic University of Wisconsin (UW) solution for immunoscanning electron microscopy. Histotopographical examination visualized ICAM-1 antigen on cytoplasmic processes of the corneal endothelium, arranged along microfolds, especially at the peaks. In the leukocytes, ICAM-1 was located primarily in morphologically non-specialized domains of the cell body surface, and only rarely scattered on the surface of microvillar projections. We concluded that the endotoxin stimulation can increase ICAM-1 in both corneal endothelium and associated leukocytes. Increased ICAM-1 may be an important factor for the leukocytes to form clustering and adhering to the corneal endothelium.

The effect of intraperitoneal and topic sodium diclofenac on the arachidonic acid metabolism in endotoxin-induced uveitis in the rabbit

Endotoxin-induced uveitis (EIU) was produced in albino rabbits by intravitreal injection in the right eye of 10 ng of salmonella endotoxin in 5 ± l of saline solution by a Hamilton syringe. PGE2 and LTB4 were measured in the aqueous humor by the R.I.A. method 24 hours after endotoxin injection in order to examine the activity of the arachidonic acid metabolism. The authors have used seven groups of 12 animals each. The control group was injected with saline (5 ± l) and the endotoxin group (ET) with 10 ng of endotoxin. One experimental group was injected with the same amount of ET and treated with three intraperitoneal injections (-2h, 0h, 12h) of DFNa (32 mg/kg). Another group (ET+S) was injected with ET and treated with saline intraperitoneally (-2h, 0h, 12h). The topically treated groups received ET and topic DFNa (0.1%) every 6h, 4h and 2h respectively. Mean aqueous PGE2 concentration of the negative control group (0.03 ± 0.02 ng/ml) was significantly lower (p < 0.01) than in the ET group (7.26 ± 4.16). All the treated groups showed a statistical difference as compared to the ET group (p < 0.01, Student test). Mean LTB4 concentration of the negative control group (4.44 ± 0.33 ng/ml) was also significantly lower (p<0.01) than in the ET group (5.10 ± 0.61). Treatment with DFNa did not result in a decrease of the aqueous LTB4 levels. It is concluded that topical DFNa results in a decrease of aqueous PGE(2), without affecting LTB levels. To the best of our knowledge, such an effect of topical DFNa has not been reported previously.

The antiinflammatory effect of nordihydroguaiaretic acid in endotoxin induced uveitis in rabbits

The authors evaluated the anti-inflammatory effect of nordihydroguaiaretic acid (NDGA) and dexamethasone on an endotoxin induced uveitis (EIU) model, in rabbits. Six groups of 12 rabbits were formed. In groups II to V a uveitis was induced by an intravitreal injection of 5 ul of saline, containing 10 ng of endotoxin of Salmonella typhi. In group I, which is considered as the control, an intravitreal injection of 5 ul of saline was given. Each group received a different treatment and the inflammatory reaction was evaluated after 24 hours, quantifying the following parameters: clinical scoring, cells, proteins, PGE2, LTB4 in the aqueous and histopathological scoring. Compared to group II (non treated), group VI (treated with intraperitoneal 2 mg/kg dexamethasone) showed a decrease of 61% of proteins and LTB4, and a decrease of more than 90% of the other parameters studied. All these differences are statistically significant (p < 0.001). In groups III (intraperitoneal NDGA 10 mg/kg), IV and V (NDGA 1% topically every two and four hours respectively), the proteins showed a change of less than 5.5% and the PGE2 was reduced to around 50% compared to group II; these changes are not statistically significant (p > 0.05). The authors observed an important and significant decrease of the other parameters when compared to group II (p < 0.001). It can be concluded that at the doses given here, NDGA shows an effective action on the lipoxygenase pathway without an increase of the production of PGE2.

The effect of chlorpromazine on endotoxin-induced uveitis in the Lewis rat

Chlorpromazine (CPZ) has been used extensively in the treatment of psychiatric disorders, and has recently been shown to possess systemic anti-inflammatory properties as well. To investigate the potential effects of CPZ on ocular inflammation, we evaluated its action on endotoxin-induced uveitis (EIU) in Lewis rats. At three different dosage levels, CPZ produced highly significant reductions in the mean aqueous aspirate inflammatory cell counts and histological inflammatory scores as compared to controls treated with vehicle only. Analysis of aqueous fluid demonstrated a similar decrease in protein concentration and phospholipase A2 (PLA-2) activity in the treated animals. The ability of CPZ to inhibit the development of EIU may be related to its properties as a calcium channel blocker and inhibitor of the enzyme phospholipase A2.

Experimental autoimmune anterior uveitis (EAAU), a new form of experimental uveitis. I. Induction by a detergent-insoluble, intrinsic protein fraction of the retinal pigment epithelium

The uveitogenicity of several protein fractions of the bovine retinal pigment epithelium (RPE) was studied in Lewis rats, and a major pathogenic fraction was selected. Fresh RPE cells were carefully isolated and purified in order to minimize the presence of rod outer segments (ROS). The buffer-insoluble part of the cells was extracted by Triton X-100. Most uveitogenicity was found in the Triton-insoluble pigment and cytoskeleton-containing fraction of RPE (RPE-TI). The S-antigen and opsin contents of RPE-TI were too low to induce an inflammatory response, while transducin, IRBP and cGMP-phosphodiesterase were absent. Hence, a hitherto unknown uveitogenic RPE protein, called PEP-X, evoked the pathogenic response. A typical dose-dependent experimental autoimmune anterior uveitis (EAAU) developed when the rats were immunized with RPE-TI. Initially, mononuclear cells infiltrated the anterior segment. In subsequent severe stages polymorphonuclear cells predominated in the anterior chamber. EAAU differed in particular from the known forms of EAU induced by photoreceptor proteins in that the inflammation remained exclusively anterior and the photoreceptor cells and the pineal gland were not affected. In immunized rats the immune responses to ROS proteins were very low. In contrast, there were consistently high cellular and humoral immune responses to RPE-TI. As in experimental autoimmune (uveo)retinitis (EAU), the development of EAAU could be inhibited by cyclosporin treatment indicating T-cell-dependency. A combination of histopathological, immunological and biochemical results indicates that PEP-X is an intrinsic RPE protein that is highly pathogenic. In view of its characteristics, EAAU may be a valuable model for human acute anterior uveitis, the most prevalent form of uveitis.

Ocular permeability after systemic administration of endotoxin in humans

Acute anterior uveitis in response to the administration of systemic gram-negative endotoxin was studied in humans. The blood-aqueous barrier was evaluated in eight normal human subjects at 8 or 24 hours after systemic administration of purified gram-negative endotoxin. No significant changes in the blood-aqueous barrier were found, as evaluated by permeability to fluorescein, number of aqueous cells, flare, or intraocular pressure, despite profound endotoxin-induced cardiac, pulmonary, and circulatory effects. Gram-negative endotoxin does not appear to affect the human blood-aqueous barrier in doses that can safely be given to humans.

Role of bacterial debris in inflammatory diseases of the joint and eye

Several distinct rheumatic conditions (including Lyme arthritis, Reiter's syndrome and rheumatic fever) as well as certain forms of the blinding disease, uveitis, may share a common etiology. In each instance specific bacterial pathogens may infect a distant site, which on interaction with the immune system, leads to a sterile inflammation in the joint or eye. These "reactive" conditions may result, in some cases, from prior localization of non-viable bacterial remnants (including the cell wall or peptidoglycan) or alternatively "dormant" fastidious bacteria in the affected joint or eye where they act as persisting antigens. Classical culture techniques, would not detect the presence of these putative microbial antigens. Alternative approaches for detection of ubiquitous components of bacteria in the host (using appropriate chemical, molecular and immunological techniques) are discussed.

Endotoxin-induced production of inflammatory mediators by cultured ciliary epithelial cells

Systemic injection of bacterial endotoxin (Lipopolysaccharide, LPS) in experimental animals induces anterior uveitis without major pathological changes in other organs. The present study investigates the effect of LPS on production of inflammatory mediators in cultured bovine pigmented ciliary epithelial cells (CB-cells) by means of radioimmunoassays and bioassays. LPS was found to stimulate CB-cells to secrete prostaglandin E2 and prostacyclin (assayed as its stable metabolite 6-keto-prostaglandin F1a), but not leukotriene B4 or thromboxane A2 (assayed as its stable metabolite thromboxane B2). CB-cells produced membrane-associated interleukin 1-activity in response to LPS, but no tumor necrosis factor-activity was found after challenge of CB-cells with LPS. The direct effect of LPS on production of inflammatory mediators by cells from the anterior uvea could play a role in the pathophysiology of endotoxin-induced uveitis.

Induction of MHC class II antigen in cultured bovine ciliary epithelial cells

The expression of major histocompatibility complex (MHC) class II antigens in cultured bovine ciliary epithelial cells was investigated by means of indirect immunohistochemistry and immunocytofluorometry. Ciliary epithelial cells grown in control tissue-culture medium did not express MHC class II. However, after incubation with bovine gamma-interferon (IFN-G) in concentrations as low as 0.3 units/ml, nearly all cells stained for MHC class II. Tumor necrosis factor increased IFN-G-induced MHC class II expression. A reduction in IFN-G-induced MHC class II expression was observed with dexamethasone, prostaglandin E2 and alpha-interferon. To test whether MHC class II expression in response to IFN-G was specific for the ciliary epithelium, several intraocular tissues were grown in culture and incubated with IFN-G. MHC class II expression was observed in all tissues tested for response to IFN-G, but at different sensitivities. Retinal pigment epithelium and ciliary epithelium exhibited the highest sensitivity, followed by corneal endothelium and lens epithelium; the lowest sensitivity was observed for retinal vascular pericytes. The results are discussed in the context of MHC class II expression on the ciliary epithelium in anterior uveitis.

Endotoxin-induced uveitis in the rat: a hypothesis for preferential involvement of the anterior uvea

Endotoxin-induced Uveitis (EIU) was produced in Lewis rats by footpad injection of Salmonella endotoxin. Protein and cells were measured both in the aqueous humor and in the cerebrospinal fluid (CSF) in order to examine if the inflammation was strictly limited to the anterior uvea. EIU was also induced in Fischer and Brown Norway rats and the inflammation was compared among the three strains. Although the function and structure of the choroid plexus is very similar to the ciliary body, no signs of inflammation were seen in the choroid plexus and the CSF. Among the 3 tested strains of rats, EIU was maximal in Lewis rats, less severe in Fischer rats and least pronounced in Brown Norway rats. It is thought that because of its specific microvascular structure, the ciliary body is specially prone to endotoxin induced inflammation. The amount of inflammation however depends on the genetic background of the animal.

Endotoxin-induced uveitis (EIU) in the rat: a study of inflammatory and immunological mechanisms

Endotoxin-induced uveitis (EIU) can be produced by systemic injection of endotoxin (ET). It is not clear yet why exclusive ocular involvement occurs in this model. To clarify this question and to establish the sequence of inflammatory events, EIU was induced in Lewis rats by footpad injection of Salmonella ET. Ocular inflammatory response (anterior chamber cells and proteins), aqueous inflammation mediators (thromboxane B2, prostaglandin E2, leukotriene B4 and substance P) and MHC class 2 (Ia) antigen expression in the ciliary body were monitored for 72 hours. Thromboxane B2 was detected early in the aqueous humor, peaking already 1 hour after ET injection. Prostaglandin E2 & leukotriene B4 peaks and a second peak of thromboxane B2 were recorded 18 hours after ET-injection, at the time of maximal ocular inflammation. MHC-class 2 expression was first detected in the ciliary body stroma at the vascular level 6 hours after ET injection and was massively expressed in the ciliary body epithelium at 18 and 72 hours. It is hypothesized that ciliary body endothelium is particularly sensitive to the effect of ET and is the site of thrombocyte adherence. Vascular damage leads in succession to cellular infiltration, release of inflammation mediators and disruption of blood-ocular barrier. MHC-class 2 expression is a secondary phenomenon and is probably at the origin of additional tissue damage from immune effector mechanisms.

Immunopharmacological analysis of endotoxin-induced uveitis in the rat

Footpad injection of endotoxin causes exclusive ocular inflammation in the rat. In order to clarify its physiopathologic mechanism, we studied the effect of different treatments on endotoxin-induced uveitis (EIU). Salmonella endotoxin was injected into the footpads of Lewis rats. 18 hr later, inflammation was assessed by evaluating proteins and cells in the anterior chamber; arachidonic acid (AA) metabolites, prostaglandin E2 and leukotriene B4, as well as substance P were measured by radioimmunoassay, and Ia-(MHC class II)-antigen expression in ciliary body was assessed by immunohistochemistry. The effect of inhibitors of phospholipase A2 (EPC), of lipoxygenase (azelastine) and of cyclo-oxygenase (diclofenac), as well as dexamethasone, cyclosporine (CsA) and anti-Ia antibody, were evaluated on these parameters. Phospholipase A2 inhibitor EPC and dexamethasone were most effective on inflammation: they also reduced AA metabolites very effectively and prevented Ia-expression. Lipoxygenase and cyclo-oxygenase inhibitors were partially effective on inflammation and on AA metabolites but failed to prevent Ia-expression. Immunosuppressive treatments (CsA and anti-Ia-antibody) also reduced inflammation. Our findings suggest that inflammation mediators initiate inflammation in EIU. Ia-Ag-expression is secondarily produced by mediators leading to additional inflammation due to immune mediated mechanisms.