الفهرس 
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Abstract
Diabetes mellitus (DM) is a metabolic disorder characterized by hyperglycemia and insulin dysregulation, mostly accompanied by severe chronic complications. Currently, DM affects more than 425 million people worldwide and this number is progressively increasing. Diabetic retinopathy (DR) is the most common microvascular complication of DM that is the leading cause of blindness among working-aged adults and affects nearly all patients with T1DM and about 80% of T2DM patients. DR pathophysiology is multifactorial and the exact mechanism of this disease remains poorly understood, but it involves microvascular changes, oxidative stress, inflammation and neurodegeneration in early stages. It is clinically divided into two distinct stages: nonproliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR). The current treatment strategies of DR include intravitreal pharmacological agents e.g. anti-VEGF drugs and steroids, laser photocoagulation and vitreous surgery. Streptozotocin (STZ) is an antimicrobial agent and chemotherapeutic alkylating agent. It is used to induce diabetes mellitus & DR in experimental animals as it causes specific necrosis of the pancreatic beta cells leading to pathological changes that mimic human T1DM & DR. It became an attractive model for DM due to its low cost and needs only single injection. It causes β-cell damage through oxidative stress & liberation of nitric oxide (NO). Ranibizumab is a recombinant monoclonal antibody that binds all active forms of VEGF-A. It has been approved by FDA for treatment of diabetic macular edema (DME), some stages of DR, age-related macular degeneration (AMD). It has been also tried in endometriosis. Rebastinib (DCC-2036) is a selective Tie-2 inhibitor that inhibits neovascularization & metastasis of some types of cancer such as breast cancer, CML, glioblastoma. 4-methyl catechol (4-MC) is a potent stimulant of NGF and BDNF that showed beneficial effects in diabetic nephropathy and some neurological disorders e.g. parkinsonism. Also, it was documented to have antiplatelet properties. Therefore, the aim of the study is to evaluate and compare the possible protective role of ranibizumab, rebastinib and 4MC in the progression of DR. This study was carried out on 60 male albino rats weighing (150-200gm). The animals were housed in wire mesh cages and fed standard animal diet and water. Animals were divided into 6 groups (10 rats each) as following: ▪ group 1: normal control group received single i.p. injection of citrate buffer. ▪ group 2: DR group, received vehicle of DMSO monthly intravitreally after induction of T1DM for 3 months. ▪ group 3: DR rats treated with ranibizumab (RBZ) intravitreally in a dose of 125 μg/eye/month after induction of T1DM for 3 months. ▪ group 4: DR rats treated with rebastinib (Reba) intravitreally in a dose of 5 μg /eye/month after induction of T1DM for 3 months. ▪ group 5: DR rats treated with rebastinib (Reba) intravitreally in a dose of 10 μg /eye/month after induction of T1DM for 3 months. ▪ group 6: DR rats treated with 4-methyl catechol (4MC) intravitreally in a dose of 100 μg/eye/month after induction of T1DM for 3 months. Induction of diabetic retinopathy (DR): STZ was injected once i.p. in a dose of 60 mg/kg to induce T1DM. The fasting blood glucose level was checked 3 days later using a blood sample from the tail where rats with glucose levels ≥ 200 mg/dl were considered diabetic. At the end of experimental time (90th day): A. The rats were anesthetized using i.p. pentobarbital then blood samples were collected through cardiac puncture, centrifuged and serum was separated and stored to be used in assay of: • Fasting serum glucose (spectrophotometry). B. After that, the rats were sacrificed, and both eyes were excised. The right eye was processed for histopathological examination, TEM and immunohistochemical assay of Bcl-2 and Tie-2 while the left eye was homogenized and centrifuged, then the supernatant was stored and further processed for assay of: • Vascular endothelial growth factor (VEGF-A) (ELISA). • Nerve growth factor (NGF) (ELISA). Results of the present study revealed the following: ▪ group 2 (untreated DR) showed significant increase in fasting serum glucose level, eye tissue VEGF-A, histopathological score and IHC score of Tie-2, but showed significant decrease in eye tissue NGF and IHC score of Bcl-2 in comparison to group 1 (normal control). Also, it showed histopathological changes & TEM findings in the retina similar to DR. ▪ group 3 (DR, RBZ treated) showed a significant decrease of eye tissue VEGF-A and IHC score of Tie-2 levels, but it showed significant increase in IHC score of Bcl-2 in comparison to group 2 (untreated DR). Nevertheless, it showed non-significant difference in fasting serum glucose and eye tissue NGF in comparison to group 2 (untreated DR). Also, it showed mild histopathological changes & TEM findings in the retina that resemble DR. ▪ group 4 (DR, reba 5 μg treated) showed a significant decrease of IHC score of Tie-2 in comparison to group 2 (untreated DR) & group 3 (DR, RBZ treated) and significant decrease in IHC score of Bcl-2 in comparison to group 3 (DR, RBZ treated) , but it showed significant increase in eye tissue NGF in comparison to group 2 (untreated DR) and significant increase in eye tissue VEGF-A, NGF, histopathological score in comparison to group 3 (DR, RBZ treated). However, it showed non-significant difference in fasting serum glucose level, eye tissue VEGF-A, histopathological score, IHC score of Bcl-2 in comparison to group 2 (untreated DR). Also, it showed histopathological changes & TEM findings in the retina resemble DR and similar to group 2. ▪ group 5 (DR, reba 10 μg treated) showed a significant increase in eye tissue VEGF-A, NGF in comparison to group 2 (untreated DR), significant increase in histopathological score, eye tissue VEGF-A, NGF in comparison to group 3 (DR, RBZ treated). It also showed significant decrease in IHC score of Tie-2 in comparison to group 2 (untreated DR) and group 3 (DR, RBZ treated), significant decrease in IHC score of Bcl-2 in comparison to group 3 (DR, RBZ treated). Nevertheless, it showed nonsignificant difference in fasting serum glucose, histopathological score, IHC score of Bcl-2 in comparison to group 2 (untreated DR), non-significant difference in fasting serum glucose in comparison to group 3 (DR, RBZ treated). It showed nonsignificant difference in all parameters in comparison to group 4. Also, it showed histopathological & TEM findings in the retina similar to group 4. ▪ group 6 (DR, 4MC treated) showed significant increase in eye tissue NGF & IHC score of Bcl-2 in comparison to group 2 (untreated DR), significant increase in eye tissue VEGF-A, NGF in comparison to group 3 (DR, RBZ treated), significant increase in IHC score of Bcl-2, Tie-2 in comparison to group 4 (DR, 5 μg rebastinib treated) and group 5 (DR, 10 μg rebastinib treated). Also, it showed significant decrease in histopathological score, IHC score of Tie-2 in comparison to group 2 (untreated DR), significant decrease in eye tissue VEGF-A & histopathological score in comparison to group 4 (DR, 5 μg rebastinib treated) and group 5 (DR, 10 μg rebastinib treated). Nevertheless, it showed non-significant difference in eye tissue VEGF-A in comparison to group 2 (untreated DR), non-significant difference in histopathological score, IHC score of Bcl-2 & Tie-2 in comparison to group 3 (DR, RBZ treated), non-significant difference in eye tissue NGF in comparison to group 4 (DR, 5 μg rebastinib treated) and group 5 (DR, 10 μg rebastinib treated). It showed also, non-significant difference in fasting serum glucose in comparison to group 2 (untreated DR), group 3 (DR, RBZ treated), group 4 (DR, 5 μg rebastinib treated) and group 5 (DR, 10 μg rebastinib treated). Also, it showed histopathological & TEM findings milder than group 2 (untreated DR).