Purpose.: To investigate the protective effects of glucosamine (GlcN) using oxidative stress and rat models of ischemia-reperfusion (I/R) injury and to determine the antiapoptotic and anti-inflammatory mechanisms of GlcN treatment. Methods.: We determined the effects of GlcN and the levels of O-linked N-acetylglucosamine (O-GlcNAc) in in vitro retinal ganglion cells (RGCs) treated with or without H₂O₂. The survival and apoptosis rates of RGCs were compared after the addition of GlcN, glucose, or O-(2-acetamido-2-deoxy-Dglucopyranosylidene) amino-N-phenylcarbamate (PUGNAc). Retinal I/R injury was induced in Sprague-Dawley rats by elevating the IOP to 110 mm Hg for 60 minutes. An intraperitoneal injection of GlcN (1000 mg/kg) or normal saline was administered in the different groups, including a control group, a GlcN group, an I/R group, a GlcN+I/R group (1000 mg/kg GlcN 24 hours before I/R injury), and an I/R+GlcN group (7-day period of 1000 mg/kg GlcN 24 hours after I/R injury). The rats were killed 7 days after the I/R injury, and the retinas were collected from each rat for thickness measurements. Quantitative analysis of RGC survival was further determined using labeling with FluoroGold. Results.: The GlcN increased levels of O-GlcNAc in a dose-dependent manner in the RGCs treated with or without H₂O₂. The GlcN resulted in increased cell survival and reduced apoptosis in the RGCs under oxidative stress conditions. In the rat model of I/R injury, GlcN significantly protected against I/R-induced retinal thinning and suppressed the I/R-induced reductions in a- and b-wave amplitudes of the ERG. In terms of RGC survival, significant incremental density of RGCs was found in the I/R+GlcN group compared with the I/R group. Notably, the use of GlcN in the rat retina decreased apoptosis and the formation of reactive oxygen species (ROS) after I/R injury. We also found that mitogen-activated protein kinase signal pathways played a critical role in the GlcN-mediated attenuation of ROS-induced damage in vitro and I/R injury in vivo. Conclusions.: Glucosamine treatment provides multiple levels of retinal protection, including antiapoptotic, anti-inflammatory, and antioxidative benefits. More research on the role of GlcN as a potential agent for the prevention and treatment of glaucoma is warranted.

Background: Diabetic retinopathy (DR) is indicated as a major cause of blindness in the world. Emerging evidence supports the interaction of iron metabolism with diabetes. However, little research is available concerning the relationship between iron metabolism and DR. The intent of this paper is to describe the correlation between serum iron and the occurrence of DR. Methods: A total of 5321 participants who underwent related examinations as part of the National Health and Nutrition Examination Survey (2005–2008) were included. DR was defined by the criteria of the Early Treatment for Diabetic Retinopathy Study based on nonmydriatic fundus photography. The cutoff point of serum iron for DR was explored by the receiver operating characteristics curve. The relationship of serum iron with the occurrence of DR was explored by multivariate logistic regression models. Results: Participants with DR had significantly lower serum iron than the control group. Serum iron was negatively correlated with the occurrence of DR after the adjustment of pertinent variables (an odds ratio (OR) of 0.995 (95% CI: 0.992–0.999)). After dividing serum iron into quartiles, the third quartile was associated with DR with an OR of 0.601 (95% CI: 0.418–0.863). Furthermore, the cutoff point of serum iron had an inverse relationship for the occurrence of DR with an OR of 0.766 (95% CI: 0.597–0.984). Conclusion: Serum iron has an inverse association with the occurrence of DR in diabetic adults. The assessment of serum iron levels might be a part of follow-up visits with diabetic patients.

It has rarely been studied whether the presence and severity of diabetic retinopathy (DR) could influence the renal disease progression among all chronic kidney disease (CKD) diabetic patients. This study investigates the characteristics of diabetic patients, with different stages of chronic kidney disease (CKD), according to the occurrence of diabetic retinopathy and determines the influence of retinopathy in the deterioration of renal function. We conduct a multicenter, longitudinal cohort study based on the Epidemiology and Risk Factors Surveillance of the CKD project (2008–2013) and the National Health Insurance Research Database (NHIRD) (2001–2013). A total of 4050 diabetic patients with CKD, 20–85 years of age, from 14 hospitals and the community are included in this study. As compared to CKD patients without DR, CKD patients with DR have a lower baseline estimated glomerular filtration rate (eGFR) (39.17 ± 30.36 mL/min per 1.73 m² vs. 54.38 ± 33.67 mL/min per 1.73 m² ); poorer glycemic control (higher glycated hemoglobin (HbA1c) 7.85 ± 4.97 vs. 7.29 ± 4.02, p < 0.01); higher proteinuria (urine protein-to-creatinine ratio (UPCR )1.94 ± 2.96 g/dL vs. 0.91 ± 2.11 g/dL, p < 0.01); more anemia (Hb 11.22 ± 2.43 g/dL vs. 12.39 ± 3.85 g/dL, p < 0.01), and more hypoalbuminemia (3.88 ± 0.95 g/dL vs. 4.16 ± 1.74 g/dL, p < 0.01). Later stage (stage 3b–5) CKD patients with DR had significantly higher CKD progression compared with patients without DR (OR (odds ratio) 1.66 (1.36–2.02)). Patients with proliferative DR had significantly higher CKD progression events compared to patients with non-proliferative DR (OR 2.18 (1.71–2.78)). The presence and severity of DR is a risk factor for CKD progression among our Taiwanese CKD patients with diabetes. Prevention and early detection of DR are important and DR should be routinely screened as early as possible among diabetic CKD patients.

Age-related macular degeneration (AMD) is a vision-threatening age-associated disease. The retinal pigment epithelial (RPE) cells phagocytose and digest photoreceptor outer segment (POS). Incomplete digestion of POS leads to lipofuscin accumulation, which contributes to the pathology of the AMD. Autophagy could help reduce the amount of lipofuscin accumulation. In the present study, we evaluated the effects of glucosamine (GlcN), a natural supplement, on the induction of autophagy and POS-derived lipofuscin-like autofluorescence (LLAF) in ARPE-19 cells in vitro, and investigated the potential molecular pathway involved. Our results revealed that GlcN had no effect on phagocytosis of POS at the lower doses. GlcN treatment induced autophagy in cells. GlcN decreased the LLAF in native POS-treated cells, whereas malondialdehyde or 4-hydroxynonenal-modified POS attenuated this effect. 3-Methyladenine inhibited GlcN-induced autophagy and attenuated the effect of GlcN on the decrease of the native POS-derived LLAF. Furthermore, GlcN induced the phosphorylation of AMP-activated protein kinase (AMPK) and inhibited the phosphorylation of mammalian target of rapamycin (mTOR), whereas Compound C inhibited these effects of GlcN. Altogether, these results suggest that GlcN decreased the native POS-derived LLAF through induction of autophagy, at least in part, by the AMPK–mTOR pathway. This mechanism has potential for the preventive treatment of lipofuscin-related retinal degeneration such as AMD.

Background: Transforming growth factor (TGF) family members play important roles in the regulation of corneal integrity, and the pathogenesis of corneal fibrosis. Currently, there are no effective agents targeting TGF-β signaling to diminish corneal fibrosis. Glucosamine (GlcN), which is widely used in the treatment of osteoarthritis, abrogates the morphologic effects of TGF-β2 on retinal pigmented epithelial cells in a mouse disease model. Here, we sought to determine whether GlcN would exert beneficial effects against TGF-β1-induced corneal fibrosis.Methods: In human corneal fibroblasts (HCFs) treated with GlcN, the expression of Krüppel-like factor 4 (KLF4) and its downstream signaling effects were determined in the presence and absence of TGF-β1 using immunoblot analysis. We further explored GlcN inhibition of fibroblast-to-myofibroblast differentiation via KLF4 siRNA. The effect of cycloheximide on KLF4 protein levels with or without GlcN administration was assessed to determine whether GlcN affects the stability of the KLF4 protein.Results: In HCFs, GlcN induced the expression of KLF4, which regulated the maturation and maintenance of the ocular surface. GlcN partially suppressed the TGF-β1-induced expression of alpha-smooth muscle actin (α-SMA) and reduced the collagen contraction capacity in HCFs, suggesting a decrease in fibroblast-to-myofibroblast differentiation. This effect appeared to be mediated through suppression of Smad2 phosphorylation and ERK-dependent signaling. The levels of KLF4 mRNA were increased by GlcN and decreased by TGF-β1 and the TGF-β1-induced α-SMA mRNA expression was upregulated when the KLF4 gene was silenced. GlcN also appeared to stabilize the KLF4 protein, reducing its turnover in corneal fibroblasts.Conclusion: These findings shed light on a novel mechanism by which GlcN suppresses TGF-β1-induced fibroblast-to-myofibroblast differentiation through the upregulation of KLF4 expression. Current strategies for treating corneal fibrosis were not effective. Elevating KLF4 levels through the use of GlcN might provide an effective alternative to alleviate the development and progression of corneal fibrosis.