OCULAR ANTI- INFLAMMATORY AGENTS Alison Clode, DVM, DACVO Port City Veterinary Referral Hospital Portsmouth, New Hampshire New England Equine Medical and Surgical Center Dover, New Hampshire Overview • Corticosteroids • NSAIDs Corticosteroids • Produced in the adrenal cortex from cholesterol • Glucocorticoids • Cortisol (endogenous) • Metabolic fxn • Immune fxn • Anti-inflammatory fxn • Mineralocorticoids • Electrolyte and H2O balance Glucocorticoids – MOA Glucocorticoids – Genomic MOA 1. Transactivation = activation of anti-inflammatory transcription factors 2. Transrepression = inhibition of transcription of pro- inflammatory genes (multiple mechanisms) Glucocorticoids – Genomic Effects Glucocorticoids – Transactivation Anti-inflammatory proteins 1. GC binds cytoplasmic receptor (cGCR) à 2. GC-cGCR complex translocates to nucleus à 3. Binds GRE in target gene à 4. Up-regulation of anti-inflammatory, immunomodulatory, and metabolic processes ** Numerous and cell-specific cofactors influence specific cellular response to GC Glucocorticoids – Transrepression Pro-inflammatory proteins 1. GC binds cytoplasmic receptor (cGCR) à 2. GC-cGCR complex translocates to nucleus à 3. Binds negative GRE à 4. Down-regulation of pro-inflammatory protein production Glucocorticoids – Transrepression Pro-inflammatory proteins 1. GC binds cytoplasmic receptor (cGCR) à 2. GC-cGCR complex interacts with specific transcription factors (TF) à 3. No binding of GC-cGCR complex or TFs to pro-inflammatory GREs à 4. Down-regulation of pro-inflammatory and immune stimulation factors Glucocorticoids – Transrepression Pro-inflammatory proteins 1. GC binds cytoplasmic receptor (cGCR) à 2. GC-cGCR complex translocates to nucleus à 3. GC-cGCR binds nuclear coactivators à 4. Inhibition of pro-inflammatory protein production GC – Transactivation and Transrepression Vandevyver S et al., Endocrinology 2013 Glucocorticoids – MOA Glucocorticoids – Non-Genomic Effects • Possibly explain more rapid clinical response than can be explained by genomic effects 1. Non-specific interactions between GC and cell membrane 2. Specific interactions between GC and membrane-bound GCR 3. Actions of cGCR that do not involve genome Glucocorticoids – Non-Genomic Effects 1. Non-specific interactions between GC and cell membrane: • High concentration of extracellular GC à intercalate with cell membrane à altered physicochemical properties of cell membrane à altered Na+ and Ca2+ transport across membranes of immune cells à rapid immunosuppression • Mitochondrial proton leak à impaired ATP production à altered cellular function Glucocorticoids – Non-Genomic Effects 2. Specific interactions between GC and membrane-bound GCR • mGCR is unique variant of cGCR • Upregulation with immunostimulation thought to be a protective mechanism • GC-induced mGCR-mediated apoptosis Glucocorticoids – Non-Genomic Effects 3. Actions of cGCR that do not involve genome: • cGCR exists in cytoplasm as multi-protein complex • Binding of GC to cGCR releases protein complex so GC-cGCR can translocate to nucleus • Released proteins mediate various rapid intracellular effects • HSPs, kinases, etc. • cGCR also inhibits release of AA from plasma membrane via a transcription-independent mechanism Glucocorticoids – ‘End’ Result • Anti-inflammatory actions: 1. Increase lipocortin-1 synthesis à • Suppression of phospholipase A2 à • Decreased production of pro-inflammatory prostaglandins and leukotrienes 2. Increase MAPK phosphatase 1 synthesis à • Suppression of c-Jun transcription à • Decreased transcription of pro-inflammatory genes 3. Inhibition of NF-κβ à • Decreased COX-2 synthesis à • Suppression of prostaglandin production Rhen T, et al., New Engl J Med 2008 Glucocorticoids – ‘End’ Result • Immunosuppressive actions: 1. Decrease B- and T-cell number and function • Via inhibition of NF-κβ 2. Inhibit cell-mediated immunity • Via inhibition of multiple interleukins 3. Inhibit humoral immunity • Via decreased synthesis of IL-2/IL-2 receptors Side Effects • Systemic: • Hyperglycemia • Skin fragility • Muscle breakdown • Osteoporosis • Etc… • Ocular: • Cataract • Ocular hypertension • Potentiate infection • Decrease wound healing • Corneal lipid deposition Glucocorticoid-Induced Cataract • Central posterior subcapsular • Initially clearly delineated • Vacuolated • Only associated with corticosteroids with GC activity • Overall prevalence of 22% (0% - 90%) • Dependent upon: • Dose • Duration • Route STEROID CATARACT 413 CONCLUSIONS tain, in particular because the data were gener- ated following short exposure times to glucocor- Despite the long-recognized association of glu- ticoid in vitro, and because in vivo steroid cataracts cocorticoids with PSCs, the mechanism(s) re- require many months of glucocorticoid adminis- sponsible for inducing steroid cataracts remains tration to develop. Hopefully, a clearer picture re- unknown. Glucocorticoids administered locally garding the altered expression of relevant genes (to the eye) or systemically (at a distance from in lens epithelial cells will emerge from extended the eye) are both effective in inducing steroid glucocorticoid treatment studies, preferably us- cataracts. It is possible, therefore, to present a case ing patient-derived PSC material. for steroid-induced cataracts as being the result Demonstration of an active glucocorticoid re- of the direct action of glucocorticoids on lens ep- ceptor in the lens has altered the perception of ithelial cells but also for an indirect action, as fa- what mechanism(s) may underlie the develop- vored by Jobling and Augusteyn13 through ment of steroid cataract. The data from DNA ar- changes to, for example, the levels of intraocular ray studies encourage the consideration of sev- growth factors. eral feasible hypotheses, but as yet, there are very Recent studies have demonstrated the defini- few supportive data. Defining and characterizing tive existence of a glucocorticoid receptor alpha the effects of glucocorticoid receptor activation on in lens epithelial cells, whose activation results in signal transduction mechanisms in lens epithelial changes in gene expression. Glucocorticoid re- cells will likely be one of the important next steps ceptor activation (in other cell types) is associ- in unraveling the mechanism of steroid cataract ated, in particular, with changes to gene expres- induction. Monitoring the intraocular environ- sion that are linked to alterations in: (i) cell ment of the lens following exposure to glucocor- proliferation and differentiation, (ii) apoptosis, ticoid for changes in the levels of growth factors (iii) gluconeogenesis, (iv) expression and activity also promises to yield additional useful data. The of growth factors, and (v) modifications to signal issues of ROS activity and lens cell membrane transduction pathways. Changes to the levels of permeability changes also require further resolu- transcription of genes involved in these processes tion in light of observed modifications to gene have been observed in the DNA array studies and transcription. Glucocorticoid-Inducedsupplementary investigations Cataractperformed with The etiology of steroid cataract induction will, cultured lens epithelial cells.25,43 However, the in all probability, turn out to be comprised of both relevance of these individual changes is uncer- direct effects of glucocorticoids on lens epithelial 1. Intralenticular glucocorticoid receptor activation à • Altered gene transcription • GC-induced lucine zipper protein • Nexin • Aberrant posterior LEC migration • Alterations in E-cadherin? • Alterations in ocular growth factors? • Alterations in enzyme pathways?FIG. 1. Steroid cataract formation: Pathways/factors potentially contributing to the formation of steroid-induced posterior subcapsular cataracts following glucocorticoid treatment. Likely prominent pathways are shown in black, with possible secondary contributing pathways in grey. GC, glucocorticoid; GSH, glutathione; ROS, reactive oxygen species; PSC, posterior subcapsular cataract; Na, sodium). 2. Alterations in oxidation and hydration GC-Induced Ocular Hypertension • ~30% of patients receiving dexamethasone eye drops topically for 4 weeks • Increased incidence in patients with glaucoma (46 – 92%) • “High responders” = 15 mmHg increase (4 – 6% of population) • “Moderate responders” = 6 – 15 mmHg increase (30% of population) www.ohsu.edu • All routes of administration • Generally reversible Armaly MF. Arch Ophthalmol 1963 Tripathi RC, et al., Drugs Aging 1999 McGhee CNJ, et al., Drug Safety 2002 Tawara A, et al., Graefe’s Arch Clin Exp Ophthalmol 2008 GC-Induced Ocular Hypertension • Alteration of drainage angle ECM • Activation of GC receptors in TM • Accumulation of basement membrane-like and fibrillar material in outer TM • Increased type IV collagen • Increased heparan sulfate proteoglycan • Increase fibronectin GC-Induced Ocular Hypertension in Animals • Cattle: • 1% or 0.5% prednisolone acetate TID x 49 days • Increase IOP from 16 mmHg to 30 – 35 mmHg • Within 3 – 4 weeks of treatment • Returns to normal within 4 – 5 weeks following discontinuation • Slight increase in contralateral eye GC-Induced Ocular Hypertension in Animals • TID topical prednisolone acetate IOVS 2011 • TM gene expression: • 258 upregulated • 187 downregulated • Cytoskeletal proteins • Enzymes • Growth factors • Transcription factors • ECM proteins • Immune response proteins GC-Induced Ocular Hypertension in Animals • Cats: • 1% dexamethasone or 1% prednisolone acetate BID • Significant increase