Role Of The Advanced Glycation End Products (AGEs)-its Receptor(RAGE) Axis In Diabetic Cataract

Objective: Accumulating evidence has demonstrated thatAGEs-RAGE axis-induced signaling pathways are involved in the pathogenesisof diabetic cataract. In this study, we observed the progress of the lens opacity,the levels of oxidative damage and advanced glycation end products (AGEs)and the expression of receptor for advanced glycation end product (RAGE) andnuclear factor-κBp65(NF-κBp65) in the diabetic rats which were induced bystreptozotocin (STZ). Methods: Healthy SD rats without eyes diseases wererandomly divided into normal group (n=32) and diabetic group (n=36). Rats indiabetic group were subjected to intraperitoneal injection of1%STZ (65mg/kgbody weight) to induce diabete and those in the normal group were injectedwith the same volume of buffer solution. Diabetic model was affirmed upon afasting (12h) tail vein blood glucose>16.6mmol/L after3days. Then weobserve the general conditions everyday and detect blood glucose and weighttwice week and measured lens opacity weekly which through the slit lamp afterdilating the pupil by amide compound tropicamide eye drops under deepanesthesia. At end of4weeks,8weeks,12weeks after STZ injection, rats weresacrificed respectively and lenses were enucleated. In each group, three lensesfrom different rats were fixed, embedded and sectioned using for evaluatinghistopathology by HE staining and the expression of RAGE and NF-κBp65inthe normal and diabetic lens epithelial cells by immunohisochemistry. RNA wasisolated from five lenses from different group with Trizol to detect theexpression of RAGE mRNA and NF-κBp65mRNA by reversetransciption-poly-merase chain reaction (RT-PCR).And the rest lenses werehomogenated to evaluate the content of AGEs and malondialdehyde (MDA),the activity of total superoxide dismutase (T-SOD), glutanthione peroxidase (GSH-PX) and catalase (CAT). Results:1.Rats appeared typical diabetessymptoms after STZ injection, and blood glucose were significant higher thanthe normal rats(t4周=22.84，P=0.000；t8周=26.01，P=0.000；t12周=30.94，P=0.000).In the early time, diabetic rats with polyphagia were not getting fat,but then got weight loss clearly which compared with normal rats werestatistically different(t4周=6.54，P=0.000；t8周=20.39，P=0.000；t12周=46.91，P=0.000).2. Lenses of normal rats kept transparent throughout the wholeexperimental period. While lenses of diabetic subjects appeared small vacuolesin the surrounding cortex and under posterior capsule since4weeks.Vacuolesslowly extend to the center and there was cloudy-like mass of opacity in thepupil area. Diabetic lenses which showed patchy cortical opacity after8weekslater accelerated with muddy of cortex around nuclear and nucleus and becamecompletely opacity by12weeks.3. Diabetic LECs presented morphologicaldiversity with the cytoplasm light-dyed, vacuoles and narrow nucleus, Lensfibers arranged disorderly within polycystic foam and water splitting by HEstaining.4. There was no expression of RAGE and rare expression ofNF-κBp65in normal group, but both postive expression in diabeticlenses(RAGE：t4周=90.73，P=0.000；t8周=176.77，P=0.000；t12周=148.67，P=0.000；NF-κBp65：t4周=83.98，P=0.000；t8周=130.61，P=0.000；t12周=195.69，P=0.000). As the experiment progressed, expression of RAGE and NF-κB werepronouncedly enhanced. Accordingly, RAGE mRNA and NF-κBp65mRNA ofdiabetic group presented higher than the normal group(RAGE：t4周=20.36，P=0.000；t8周=29.90，P=0.000；t12周=57.19，P=0.000；NF-κBp65：t4周=11.34，P=0.000；t8周=32.21，P=0.000；t12周=41.03，P=0.000).5. At4weeks,8weeksand12weeks of experiment, AGEs in cataractous lenses were higher comparedwith normal rats were statistically different(t4周=9.01，P=0.000；t8周=6.45， P=0.000；t12周=9.38，P=0.000)which accumulated in cataractous lenses asduration of diabetes.6. T-SOD, GSH-PX and CAT activity of diabetic ratswere markedly lower than the normal rats,while the concentration of MDAincreased observably(P<0.05). Conclusion:1. AGEs high-accumulation inlenses of diabetic rats combining to its receptor (RAGE) would enhance NF-κBactivation. Then NF-κBp65increased RAGE gene transcription and proteinsynthesis. As result, more RAGE combined with AGEs.2. AGEs weregradually accumulated in cataractous lenses of diabetic rats as the extension ofthe course. In addition, the activity of antioxidant enzyme further reducedcausing LECs oxidative damage aggravation.3. AGEs-RAGE axis systemmight be a mechanism of occurrence and development of diabetic cataractthrough mediating oxidative stress and in various signal transduction pathwayswhich forming a cascade amplification reaction. In the process, NF-κB is thekey intermediate.