Enzymatic and biochemical properties of lens in age-related cataract versus diabetic cataract: A narrative review

Lacidipine, thiamine pyrophosphate and their combination on the ocular ischemic syndrome induced by bilateral common carotid artery ligation

AIM

To investigate the effect of lacidipine, thiamine pyrophosphate (TPP) and the combination of lacidipine and TPP against oxidative and inflammatory eye damage induced by bilateral common carotid artery ligation in rats.

METHODS

Male albino Wistar rats were categorized as those who underwent sham surgery (SG), right and left common carotid cross-clamping and unclamping procedure (CCU), lacidipine+CCU (LCCU), TPP+CCU (TCCU), and combination of lacidipine and TPP (LTC)+CCU (LTCCU). One hour before anesthesia, the LCCU (n=6) received lacidipine (4 mg/kg, orally) and the TCCU (n=6) received TPP (20 mg/kg, intraperitoneally). The SG (n=6) and CCU (n=6) received the same volume of distilled water from the same route. After anesthesia (60 mg/kg ketamine, intraperitoneally), the necks of the rats were opened in the midline. Ischemia was created for 10min by placing clips on the right and left common carotid arteries. Rats in the SG only underwent subcutaneous incision. After 10min, the clips were removed and reperfusion was achieved for six days. Then, the animals were euthanized (120 mg/kg ketamine, intraperitoneally) and the levels of oxidant, antioxidant and proinflammatory cytokines in the eye tissues were determined. The retinal tissue of the eye was also examined histopathologically.

RESULTS

Lacidipine, TPP, and LTC significantly prevent the increase in malondialdehyde, tumor necrosis factor-alpha, interleukin-1β (IL-1β), and IL-6 levels, decrease in total glutathione levels, superoxide dismutase and catalase activities and histopathological retinal damage in eye tissue induced by bilateral common carotid artery ligation in rats. The impact of these drugs on protection is determined to be LTC>lacidipine>TPP.

CONCLUSION

As a result of the study, it is concluded that LTC may be more effective than lacidipine and TPP alone in treating ocular ischemic syndrome.

Molecular Insights into the Inhibitory Role of α-Crystallin against γD-Crystallin Aggregation

Cataracts, a major cause of global blindness, contribute significantly to the overall prevalence of blindness. The opacification of the lens, resulting in cataract formation, primarily occurs due to the aggregation of crystallin proteins within the eye lens. Despite the high concentration of these crystallins, they remarkably maintain the lens transparency and refractive index. α-Crystallins (α-crys), acting as chaperones, play a crucial role in preventing crystallin aggregation, although the exact molecular mechanism remains uncertain. In this study, we employed a combination of molecular docking, all-atom molecular dynamics simulations, and advanced free energy calculations to investigate the interaction between γD-crystallin (γD-crys), a major structural protein of the eye lens, and α-crystallin proteins. Our findings demonstrate that α-crys exhibits an enhanced affinity for the NTD2 and CTD4 regions of γD-crys. The NTD2 and CTD4 regions form the interface between the N-terminal domain (NTD) and the C-terminal domain (CTD) of the γD-crys protein. By binding to the interface region between the NTD and CTD of the protein, α-crys effectively inhibits the formation of domain-swapped aggregates and mitigates protein aggregation. Analysis of the Markov state models using molecular dynamics trajectories confirms that minimum free energy conformations correspond to the binding of the α-crystallin domain (ACD) of α-crys to NTD2 and CTD4 that form the interdomain interface.

Oxidative stress and antioxidants in cataract development

PURPOSE OF REVIEW

Oxidative stress plays a central role in cataract pathogenesis, a leading cause of global blindness. This review delves into the role of oxidative stress in cataract development and key biomarkers - glutathione (GSH), superoxide dismutase (SOD), malondialdehyde (MDA), and 4-hydroxynonenal (4-HNE) - to clarify their functions and potential applications in predictive diagnostics and therapies.

RECENT FINDINGS

Antioxidants serve as pivotal markers in cataract pathogenesis. GSH affects the central lens due to factors such as enzyme depletion and altered connexin expression, impairing GSH diffusion. Age-related oxidative stress may hinder GSH transport via connexin channels or an internal microcirculation system. N-acetylcysteine, a GSH precursor, shows promise in mitigating lens opacity when applied topically. Additionally, SOD, particularly SOD1, correlates with increased cataract development and gel formulations have exhibited protective effects against posterior subscapular cataracts. Lastly, markers of lipid peroxidation, MDA and 4-HNE, have been shown to reflect disease severity. Studies suggest a potential link between 4-HNE and connexin channel modification, possibly contributing to reduced GSH levels.

SUMMARY

Oxidative stress is a significant contributor to cataract development, underscoring the importance of antioxidants in diagnosis and treatment. Notably, GSH depletion, SOD decline, and lipid peroxidation markers are pivotal factors in cataract pathogenesis, offering promising avenues for both diagnosis and therapeutic intervention.

Effects of Angiotensin Receptor Blockers on Streptozotocin-Induced Diabetic Cataracts

This study aimed to determine the role of oxidative stress produced by the renin-angiotensin system (RAS) in cataract formation in streptozotocin-induced diabetic rats (STZ) using angiotensin II receptor blockers (ARBs). Rats were treated with streptozotocin and orally administered candesartan (2.5 mg/kg/day) or a normal diet for 10 weeks until sacrifice. Cataract progression was assessed through a slit-lamp examination. Animals were euthanized at 18 weeks, and the degree of cataract progression was evaluated. Oxidative stress was also assessed. In STZ-treated rats, lens opacity occurred at 12 weeks. Cataract progression was inhibited in the ARB-treated group compared with the placebo group (p < 0.05). STZ-treated rats exhibited upregulated angiotensin-converting enzyme (ACE) gene expression than control rats. Oxidative stress-related factors were upregulated in the placebo-treated group but suppressed in the ARB-treated group. A correlation coefficient test revealed a positive correlation between ACE gene expression and oxidative stress-related factors and a negative correlation between ACE and superoxide dismutase. Immunostaining revealed oxidative stress-related factors and advanced glycation end products in the lens cortex of the placebo-treated group. The mechanism of diabetic cataracts may be related to RAS, and the increase in focal ACE and angiotensin II in the lens promotes oxidative stress-related factor production.