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Candesartan attenuates diabetic retinal vascular pathology by restoring glyoxalase-I function.

Miller AG, Tan G, Binger KJ, Pickering RJ, Thomas MC, Nagaraj RH, Cooper ME, Wilkinson-Berka JL - Diabetes (2010)

Bottom Line: In BREC and BRP, Ang II induced apoptosis and reduced GLO-I activity and mRNA, with a concomitant increase in nitric oxide (NO(•)), the latter being a known negative regulator of GLO-I in BRP.In BREC and BRP, candesartan restored GLO-I and reduced NO(•).Similar events occurred in vivo, with the elevated RAS of the diabetic Ren-2 rat, but not the diabetic Sprague-Dawley rat, reducing retinal GLO-I.

View Article: PubMed Central - PubMed

Affiliation: Oxidative Stress Laboratory, Diabetes Division, Baker IDI Heart and Diabetes Institute, Melbourne, Australia. antonia.miller@monash.edu

ABSTRACT

Objective: Advanced glycation end products (AGEs) and the renin-angiotensin system (RAS) are both implicated in the development of diabetic retinopathy. How these pathways interact to promote retinal vasculopathy is not fully understood. Glyoxalase-I (GLO-I) is an enzyme critical for the detoxification of AGEs and retinal vascular cell survival. We hypothesized that, in retina, angiotensin II (Ang II) downregulates GLO-I, which leads to an increase in methylglyoxal-AGE formation. The angiotensin type 1 receptor blocker, candesartan, rectifies this imbalance and protects against retinal vasculopathy.

Research design and methods: Cultured bovine retinal endothelial cells (BREC) and bovine retinal pericytes (BRP) were incubated with Ang II (100 nmol/l) or Ang II+candesartan (1 μmol/l). Transgenic Ren-2 rats that overexpress the RAS were randomized to be nondiabetic, diabetic, or diabetic+candesartan (5 mg/kg/day) and studied over 20 weeks. Comparisons were made with diabetic Sprague-Dawley rats.

Results: In BREC and BRP, Ang II induced apoptosis and reduced GLO-I activity and mRNA, with a concomitant increase in nitric oxide (NO(•)), the latter being a known negative regulator of GLO-I in BRP. In BREC and BRP, candesartan restored GLO-I and reduced NO(•). Similar events occurred in vivo, with the elevated RAS of the diabetic Ren-2 rat, but not the diabetic Sprague-Dawley rat, reducing retinal GLO-I. In diabetic Ren-2 rats, candesartan reduced retinal acellular capillaries, inflammation, and inducible nitric oxide synthase and NO(•), and restored GLO-I.

Conclusions: We have identified a novel mechanism by which candesartan improves diabetic retinopathy through the restoration of GLO-I.

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Related in: MedlinePlus

GLO-I activity and mRNA, and MGO-AGE levels in diabetic Ren-2 rats. In Ren-2 rats after 4 weeks of diabetes, retinal GLO-I activity (A) is reduced compared with nondiabetic control and tends to be restored with Cand, although this is not significant (*P < 0.03 vs. nondiabetic Ren-2 control). In Ren-2 rats after 20 weeks of diabetes, retinal GLO-I mRNA (B) is clearly reduced compared with nondiabetic control and is restored to control levels with Cand (*P < 0.005 vs. nondiabetic Ren-2 control, †P < 0.05 vs. diabetic Ren-2 control). In comparison, in Sprague-Dawley (SD) rats (B), no changes in retinal GLO-I mRNA are observed with 20 weeks of diabetes. In Ren-2 rats after 4 weeks of diabetes, the reduction in retinal GLO-I activity (A) is accompanied by an increase in the levels of retinal MGO-AGE (C), (*P < 0.01 vs. nondiabetic Ren-2 control). In diabetic Ren-2 rats, Cand tends to decrease the levels of retinal MGO-AGE, but this is not significant. In diabetic Ren-2 rats at 4 weeks, the levels in retina of the specific MGO-AGE, argpyrimidine (D), and NO• levels (E) are unchanged compared with nondiabetic controls; however, Cand reduced retinal argpyrimidine (*P < 0.05 vs. nondiabetic Ren-2 control, †P < 0.01 vs. diabetic Ren-2 control) and NO• levels (*P < 0.05 vs. nondiabetic Ren-2 control. †P < 0.01 vs. diabetic Ren-2 control). F: Plasma MGO-AGEs (black bars) are increased in Ren-2 rats after 20 weeks of diabetes compared with nondiabetic controls and are reduced with Cand to nondiabetic levels (*P < 0.05 vs. nondiabetic Ren-2 control; †P < 0.05 vs. diabetic Ren-2 control). Other AGEs (non-MGO AGEs, white bars) and total AGEs (MGO-AGE + other AGEs, black + white bars) were increased in Ren-2 rats after 20 weeks of diabetes and reduced with Cand to nondiabetic control levels (‡P < 0.005 versus “other AGE” nondiabetic Ren-2 control; §P < 0.04 versus “other AGE” diabetic Ren-2 control; #P < 0.02 versus “total AGE” nondiabetic Ren-2 control; **P < 0.02 versus “total AGE” diabetic Ren-2 control). N = 5–8 animals/group. Values are mean ± SEM. Data in panels C and D were analyzed by one-way ANOVA, followed by Bonferroni post hoc tests. All other datasets in this figure were analyzed by Kruskal-Wallis tests, followed by Mann-Whitney U tests.
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Figure 7: GLO-I activity and mRNA, and MGO-AGE levels in diabetic Ren-2 rats. In Ren-2 rats after 4 weeks of diabetes, retinal GLO-I activity (A) is reduced compared with nondiabetic control and tends to be restored with Cand, although this is not significant (*P < 0.03 vs. nondiabetic Ren-2 control). In Ren-2 rats after 20 weeks of diabetes, retinal GLO-I mRNA (B) is clearly reduced compared with nondiabetic control and is restored to control levels with Cand (*P < 0.005 vs. nondiabetic Ren-2 control, †P < 0.05 vs. diabetic Ren-2 control). In comparison, in Sprague-Dawley (SD) rats (B), no changes in retinal GLO-I mRNA are observed with 20 weeks of diabetes. In Ren-2 rats after 4 weeks of diabetes, the reduction in retinal GLO-I activity (A) is accompanied by an increase in the levels of retinal MGO-AGE (C), (*P < 0.01 vs. nondiabetic Ren-2 control). In diabetic Ren-2 rats, Cand tends to decrease the levels of retinal MGO-AGE, but this is not significant. In diabetic Ren-2 rats at 4 weeks, the levels in retina of the specific MGO-AGE, argpyrimidine (D), and NO• levels (E) are unchanged compared with nondiabetic controls; however, Cand reduced retinal argpyrimidine (*P < 0.05 vs. nondiabetic Ren-2 control, †P < 0.01 vs. diabetic Ren-2 control) and NO• levels (*P < 0.05 vs. nondiabetic Ren-2 control. †P < 0.01 vs. diabetic Ren-2 control). F: Plasma MGO-AGEs (black bars) are increased in Ren-2 rats after 20 weeks of diabetes compared with nondiabetic controls and are reduced with Cand to nondiabetic levels (*P < 0.05 vs. nondiabetic Ren-2 control; †P < 0.05 vs. diabetic Ren-2 control). Other AGEs (non-MGO AGEs, white bars) and total AGEs (MGO-AGE + other AGEs, black + white bars) were increased in Ren-2 rats after 20 weeks of diabetes and reduced with Cand to nondiabetic control levels (‡P < 0.005 versus “other AGE” nondiabetic Ren-2 control; §P < 0.04 versus “other AGE” diabetic Ren-2 control; #P < 0.02 versus “total AGE” nondiabetic Ren-2 control; **P < 0.02 versus “total AGE” diabetic Ren-2 control). N = 5–8 animals/group. Values are mean ± SEM. Data in panels C and D were analyzed by one-way ANOVA, followed by Bonferroni post hoc tests. All other datasets in this figure were analyzed by Kruskal-Wallis tests, followed by Mann-Whitney U tests.

Mentions: In Ren-2 rats, the retinal pathology that occurred at 4 and 20 weeks of diabetes was accompanied by modulations in GLO-I function. A decrease in retinal GLO-I activity was observed at 4 weeks of diabetes, although changes in mRNA levels were not detected (Fig. 7 and supplementary Fig. 2, available in the online appendix, respectively). However, after 20 weeks of diabetes, retinal GLO-I mRNA was decreased (Fig. 7). Candesartan increased GLO-I expression in the retina of diabetic Ren-2 rats, which is consistent with our findings in BREC and BRP. To determine whether the reduction in retinal GLO-I in diabetic Ren-2 rats is related to the overexpression of the RAS in these animals, comparisons were made to nondiabetic and diabetic Sprague-Dawley rats with a suppressed RAS (Fig. 7). The expression of GLO-I in retina from nondiabetic Sprague-Dawley rats was unchanged with diabetes. We then investigated whether GLO-I dysregulation by the RAS increased MGO-derived AGEs. After 4 weeks of diabetes in Ren-2 rats, MGO-AGE levels in retina were increased. In diabetic Ren-2 rats, candesartan tended to reduce the increase in retinal MGO-AGE, but this was not significant (Fig. 7). The specific MGO-AGE, argpyrimidine, was also measured in retina and was unchanged with diabetes in the Ren-2 rat; however, candesartan did reduce the levels of retinal argpyrimidine compared with controls (Fig. 7). After 20 weeks of diabetes, both plasma MGO-AGEs and total AGEs were elevated in diabetes and significantly reduced with candesartan (Fig. 7). Retinal NO• was significantly suppressed in the diabetic Ren-2 rats treated with candesartan compared with both diabetic and nondiabetic controls (Fig. 7).


Candesartan attenuates diabetic retinal vascular pathology by restoring glyoxalase-I function.

Miller AG, Tan G, Binger KJ, Pickering RJ, Thomas MC, Nagaraj RH, Cooper ME, Wilkinson-Berka JL - Diabetes (2010)

GLO-I activity and mRNA, and MGO-AGE levels in diabetic Ren-2 rats. In Ren-2 rats after 4 weeks of diabetes, retinal GLO-I activity (A) is reduced compared with nondiabetic control and tends to be restored with Cand, although this is not significant (*P < 0.03 vs. nondiabetic Ren-2 control). In Ren-2 rats after 20 weeks of diabetes, retinal GLO-I mRNA (B) is clearly reduced compared with nondiabetic control and is restored to control levels with Cand (*P < 0.005 vs. nondiabetic Ren-2 control, †P < 0.05 vs. diabetic Ren-2 control). In comparison, in Sprague-Dawley (SD) rats (B), no changes in retinal GLO-I mRNA are observed with 20 weeks of diabetes. In Ren-2 rats after 4 weeks of diabetes, the reduction in retinal GLO-I activity (A) is accompanied by an increase in the levels of retinal MGO-AGE (C), (*P < 0.01 vs. nondiabetic Ren-2 control). In diabetic Ren-2 rats, Cand tends to decrease the levels of retinal MGO-AGE, but this is not significant. In diabetic Ren-2 rats at 4 weeks, the levels in retina of the specific MGO-AGE, argpyrimidine (D), and NO• levels (E) are unchanged compared with nondiabetic controls; however, Cand reduced retinal argpyrimidine (*P < 0.05 vs. nondiabetic Ren-2 control, †P < 0.01 vs. diabetic Ren-2 control) and NO• levels (*P < 0.05 vs. nondiabetic Ren-2 control. †P < 0.01 vs. diabetic Ren-2 control). F: Plasma MGO-AGEs (black bars) are increased in Ren-2 rats after 20 weeks of diabetes compared with nondiabetic controls and are reduced with Cand to nondiabetic levels (*P < 0.05 vs. nondiabetic Ren-2 control; †P < 0.05 vs. diabetic Ren-2 control). Other AGEs (non-MGO AGEs, white bars) and total AGEs (MGO-AGE + other AGEs, black + white bars) were increased in Ren-2 rats after 20 weeks of diabetes and reduced with Cand to nondiabetic control levels (‡P < 0.005 versus “other AGE” nondiabetic Ren-2 control; §P < 0.04 versus “other AGE” diabetic Ren-2 control; #P < 0.02 versus “total AGE” nondiabetic Ren-2 control; **P < 0.02 versus “total AGE” diabetic Ren-2 control). N = 5–8 animals/group. Values are mean ± SEM. Data in panels C and D were analyzed by one-way ANOVA, followed by Bonferroni post hoc tests. All other datasets in this figure were analyzed by Kruskal-Wallis tests, followed by Mann-Whitney U tests.
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Figure 7: GLO-I activity and mRNA, and MGO-AGE levels in diabetic Ren-2 rats. In Ren-2 rats after 4 weeks of diabetes, retinal GLO-I activity (A) is reduced compared with nondiabetic control and tends to be restored with Cand, although this is not significant (*P < 0.03 vs. nondiabetic Ren-2 control). In Ren-2 rats after 20 weeks of diabetes, retinal GLO-I mRNA (B) is clearly reduced compared with nondiabetic control and is restored to control levels with Cand (*P < 0.005 vs. nondiabetic Ren-2 control, †P < 0.05 vs. diabetic Ren-2 control). In comparison, in Sprague-Dawley (SD) rats (B), no changes in retinal GLO-I mRNA are observed with 20 weeks of diabetes. In Ren-2 rats after 4 weeks of diabetes, the reduction in retinal GLO-I activity (A) is accompanied by an increase in the levels of retinal MGO-AGE (C), (*P < 0.01 vs. nondiabetic Ren-2 control). In diabetic Ren-2 rats, Cand tends to decrease the levels of retinal MGO-AGE, but this is not significant. In diabetic Ren-2 rats at 4 weeks, the levels in retina of the specific MGO-AGE, argpyrimidine (D), and NO• levels (E) are unchanged compared with nondiabetic controls; however, Cand reduced retinal argpyrimidine (*P < 0.05 vs. nondiabetic Ren-2 control, †P < 0.01 vs. diabetic Ren-2 control) and NO• levels (*P < 0.05 vs. nondiabetic Ren-2 control. †P < 0.01 vs. diabetic Ren-2 control). F: Plasma MGO-AGEs (black bars) are increased in Ren-2 rats after 20 weeks of diabetes compared with nondiabetic controls and are reduced with Cand to nondiabetic levels (*P < 0.05 vs. nondiabetic Ren-2 control; †P < 0.05 vs. diabetic Ren-2 control). Other AGEs (non-MGO AGEs, white bars) and total AGEs (MGO-AGE + other AGEs, black + white bars) were increased in Ren-2 rats after 20 weeks of diabetes and reduced with Cand to nondiabetic control levels (‡P < 0.005 versus “other AGE” nondiabetic Ren-2 control; §P < 0.04 versus “other AGE” diabetic Ren-2 control; #P < 0.02 versus “total AGE” nondiabetic Ren-2 control; **P < 0.02 versus “total AGE” diabetic Ren-2 control). N = 5–8 animals/group. Values are mean ± SEM. Data in panels C and D were analyzed by one-way ANOVA, followed by Bonferroni post hoc tests. All other datasets in this figure were analyzed by Kruskal-Wallis tests, followed by Mann-Whitney U tests.
Mentions: In Ren-2 rats, the retinal pathology that occurred at 4 and 20 weeks of diabetes was accompanied by modulations in GLO-I function. A decrease in retinal GLO-I activity was observed at 4 weeks of diabetes, although changes in mRNA levels were not detected (Fig. 7 and supplementary Fig. 2, available in the online appendix, respectively). However, after 20 weeks of diabetes, retinal GLO-I mRNA was decreased (Fig. 7). Candesartan increased GLO-I expression in the retina of diabetic Ren-2 rats, which is consistent with our findings in BREC and BRP. To determine whether the reduction in retinal GLO-I in diabetic Ren-2 rats is related to the overexpression of the RAS in these animals, comparisons were made to nondiabetic and diabetic Sprague-Dawley rats with a suppressed RAS (Fig. 7). The expression of GLO-I in retina from nondiabetic Sprague-Dawley rats was unchanged with diabetes. We then investigated whether GLO-I dysregulation by the RAS increased MGO-derived AGEs. After 4 weeks of diabetes in Ren-2 rats, MGO-AGE levels in retina were increased. In diabetic Ren-2 rats, candesartan tended to reduce the increase in retinal MGO-AGE, but this was not significant (Fig. 7). The specific MGO-AGE, argpyrimidine, was also measured in retina and was unchanged with diabetes in the Ren-2 rat; however, candesartan did reduce the levels of retinal argpyrimidine compared with controls (Fig. 7). After 20 weeks of diabetes, both plasma MGO-AGEs and total AGEs were elevated in diabetes and significantly reduced with candesartan (Fig. 7). Retinal NO• was significantly suppressed in the diabetic Ren-2 rats treated with candesartan compared with both diabetic and nondiabetic controls (Fig. 7).

Bottom Line: In BREC and BRP, Ang II induced apoptosis and reduced GLO-I activity and mRNA, with a concomitant increase in nitric oxide (NO(•)), the latter being a known negative regulator of GLO-I in BRP.In BREC and BRP, candesartan restored GLO-I and reduced NO(•).Similar events occurred in vivo, with the elevated RAS of the diabetic Ren-2 rat, but not the diabetic Sprague-Dawley rat, reducing retinal GLO-I.

View Article: PubMed Central - PubMed

Affiliation: Oxidative Stress Laboratory, Diabetes Division, Baker IDI Heart and Diabetes Institute, Melbourne, Australia. antonia.miller@monash.edu

ABSTRACT

Objective: Advanced glycation end products (AGEs) and the renin-angiotensin system (RAS) are both implicated in the development of diabetic retinopathy. How these pathways interact to promote retinal vasculopathy is not fully understood. Glyoxalase-I (GLO-I) is an enzyme critical for the detoxification of AGEs and retinal vascular cell survival. We hypothesized that, in retina, angiotensin II (Ang II) downregulates GLO-I, which leads to an increase in methylglyoxal-AGE formation. The angiotensin type 1 receptor blocker, candesartan, rectifies this imbalance and protects against retinal vasculopathy.

Research design and methods: Cultured bovine retinal endothelial cells (BREC) and bovine retinal pericytes (BRP) were incubated with Ang II (100 nmol/l) or Ang II+candesartan (1 μmol/l). Transgenic Ren-2 rats that overexpress the RAS were randomized to be nondiabetic, diabetic, or diabetic+candesartan (5 mg/kg/day) and studied over 20 weeks. Comparisons were made with diabetic Sprague-Dawley rats.

Results: In BREC and BRP, Ang II induced apoptosis and reduced GLO-I activity and mRNA, with a concomitant increase in nitric oxide (NO(•)), the latter being a known negative regulator of GLO-I in BRP. In BREC and BRP, candesartan restored GLO-I and reduced NO(•). Similar events occurred in vivo, with the elevated RAS of the diabetic Ren-2 rat, but not the diabetic Sprague-Dawley rat, reducing retinal GLO-I. In diabetic Ren-2 rats, candesartan reduced retinal acellular capillaries, inflammation, and inducible nitric oxide synthase and NO(•), and restored GLO-I.

Conclusions: We have identified a novel mechanism by which candesartan improves diabetic retinopathy through the restoration of GLO-I.

Show MeSH
Related in: MedlinePlus