Morphogenetic and apoptotic changes in diabetic cataract: prevention by pyruvate

Pyruvate alleviates high glucose-induced endoplasmic reticulum stress and apoptosis in HK-2 cells

Endoplasmic reticulum (ER) stress plays a critical role in the development of diabetic nephropathy (DN). We previously demonstrated that pyruvate (Pyr)‐enriched oral rehydration solution improved glucometabolic disorders and ameliorated DN outcome in db/db mice. Here, we investigated the effects of Pyr on high glucose‐induced ER stress and apoptosis in HK‐2 cells. Our results suggest that high glucose can induce reactive oxygen species production, apoptosis and ER stress in HK‐2 cells, and that Pyr treatment can ameliorate these effects and restore the expression of key proteins involved in ER stress. Thus, Pyr may have potential for the development of novel strategies for the prevention and treatment of clinical DN.

Pyruvate-Enriched Oral Rehydration Solution Improves Glucometabolic Disorders in the Kidneys of Diabetic db/db Mice

Diabetes is prevalent worldwide, but ideally intensive therapeutic strategy in clinical diabetes and diabetic nephropathy (DN) is still lack. Pyruvate is protective from glucometabolic disturbances and kidney dysfunction in various pathogenic insults. Present studies focused on oral pyruvate effects on diabetes status and DN with 0.35% pyruvate in pyruvate-enriched oral rehydration solution (Pyr-ORS) and 1% pyruvate as drinking water for 8 weeks, using the model of diabetic db/db mice. Both Pyr-ORS and 1% pyruvate showed comparable therapeutic effectiveness with controls of body weight and blood sugar, increases of blood insulin levels, and improvement of renal function and pathological changes. Aberrant key enzyme activities in glucometabolic pathways, AR, PK, and PDK/PDH, were also restored; indexes of oxidative stress and inflammation, NAD⁺/NADH ratio, and AGEs in the kidneys were mostly significantly preserved after pyruvate treatments. We concluded that oral pyruvate delayed DN progression in db/db mice and the modified Pyr-ORS formula might be an ideal novel therapeutic drink in clinical prevention and treatment of type 2 diabetes and DN.

Ethyl pyruvate inhibits oxidation of LDL in vitro and attenuates oxLDL toxicity in EA.hy926 cells

Background

Ethyl pyruvate (EP) exerts anti-inflammatory and anti-oxidative properties. The aim of our study was to investigate whether EP is capable of inhibiting the oxidation of LDL, a crucial step in atherogenesis. Additionally, we examined whether EP attenuates the cytotoxic effects of highly oxidized LDL in the human vascular endothelial cell line EA.hy926.

Methods

Native LDL (nLDL) was oxidized using Cu²⁺ ions in the presence of increasing amounts of EP. The degree of LDL oxidation was quantified by measuring lipid hydroperoxide (LPO) and malondialdehyde (MDA) concentrations, relative electrophoretic mobilities (REMs), and oxidation-specific immune epitopes. The cytotoxicity of these oxLDLs on EA.hy926 cells was assessed by measuring cell viability and superoxide levels. Furthermore, the cytotoxicity of highly oxidized LDL on EA.hy926 cells under increasing concentrations of EP in the media was assessed including measurements of high energy phosphates (ATP).

Results

Oxidation of nLDL using Cu²⁺ ions was remarkably inhibited by EP in a concentration-dependent manner, reflected by decreased levels of LPO, MDA, REM, oxidation-specific epitopes, and diminished cytotoxicity of the obtained oxLDLs in EA.hy926 cells. Furthermore, the cytotoxicity of highly oxidized LDL on EA.hy926 cells was remarkably attenuated by EP added to the media in a concentration-dependent manner reflected by a decrease in superoxide and an increase in viability and ATP levels.

Conclusions

EP has the potential for an anti-atherosclerotic drug by attenuating both, the oxidation of LDL and the cytotoxic effect of (already formed) oxLDL in EA.hy926 cells. Chronic administration of EP might be beneficial to impede the development of atherosclerotic lesions.

Risk factors for incident cortical, nuclear, posterior subcapsular, and mixed lens opacities: the Los Angeles Latino eye study

PURPOSE

To identify sociodemographic and biological risk factors associated with the 4-year incidence of nuclear, cortical, posterior subcapsular (PSC), and mixed lens opacities.

DESIGN

Population-based, longitudinal study.

PARTICIPANTS

We included 4658 Latinos ≥40 years from 6 census tracts in Los Angeles, California.

METHODS

Participants underwent an interview and detailed eye examination, including best-corrected visual acuity and slit-lamp assessment of lens opacities using the Lens Opacities Classification System II (LOCS II) at baseline and again 4 years later. Each opacity type was defined in persons with a LOCS II score of ≥2. Univariate and forward stepwise logistic regression analyses were used to identify independent baseline risk factors associated with 4-year incidence of nuclear only, cortical only, PSC only, and mixed (when >1 opacity type developed in a person) lens opacities. These comprised 4 mutually exclusive groups, and were based on person rather than eye.

MAIN OUTCOME MEASURES

Odds ratios for independent risk factors associated with 4-year incidence of nuclear-only, cortical-only, PSC-only, and mixed lens opacities.

RESULTS

Of the 3471 participants with gradable lenses in the same eye at baseline and 4-year follow-up, 200 (5.8%) had incident nuclear-only opacities, 151 (4.1%) had incident cortical-only opacities, 16 (0.5%) had incident PSC-only lens opacities, and 88 (2.5%) had mixed lens opacities. Independent baseline risk factors for incident nuclear-only lens opacities included older age, current smoking, and presence of diabetes. Independent risk factors for incident cortical-only lens opacities included older age and having diabetes at baseline. Female gender was an independent risk factor for incident PSC-only lens opacities. Older age and presence of diabetes at baseline examination were independent risk factors for incident mixed lens opacities. Specifically, in diabetics, higher levels of hemoglobin A1c was associated with greater risk for 4-year incident nuclear-only, cortical-only and mixed lens opacities.

CONCLUSIONS

Improved diabetic control and smoking prevention may reduce the risk of developing lens opacities. Understanding both modifiable and nonmodifiable risk factors provides insight into the development of lens opacification.

Role of ultraviolet irradiation and oxidative stress in cataract formation-medical prevention by nutritional antioxidants and metabolic agonists

PURPOSE

Cataract is a significant cause of visual disability with relatively high incidence. It has been proposed that such high incidence is related to oxidative stress induced by continued intraocular penetration of light and consequent photochemical generation of reactive oxygen species, such as superoxide and singlet oxygen and their derivatization to other oxidants, such as hydrogen peroxide and hydroxyl radical. The latter two can also interact to generate singlet oxygen by Haber-Weiss reaction. It has been proposed that in addition to the endogenous enzymatic antioxidant enzymes, the process can be inhibited by many nutritional and metabolic oxyradical scavengers, such as ascorbate, vitamin E, pyruvate, and xanthine alkaloids, such as caffeine.

METHODS

Initial verification of the hypothesis has been done primarily by rat and mouse lens organ culture studies under ambient as well as ultraviolet (UV) light irradiation and determining the effect of such irradiation on its physiology in terms of its efficiency of active membrane transport activity and the levels of certain metabolites such as glutathione and adenosine triphosphate as well as in terms of apoptotic cell death. In vivo studies on the possible prevention of oxidative stress and cataract formation have been conducted by administering pyruvate and caffeine orally in drinking water and by their topical application using diabetic and galactosemic animal models.

RESULTS

Photosensitized damage to lens caused by exposure to visible light and UVA has been found to be significantly prevented by ascorbate and pyruvate. Caffeine has been found be effective against UVA and UVB. Oral or topical application of pyruvate has been found to inhibit the formation of cataracts induced by diabetes and galactosemia. Caffeine has also been found to inhibit cataract induced by sodium selenite and high levels of galactose. Studies with diabetes are in progress.

CONCLUSIONS

Various in vitro and in vivo studies summarized in this review strongly support the hypothesis that light penetration into the eye is a significant contributory factor in the genesis of cataracts. The major effect is through photochemical generation of reactive oxygen species and consequent oxidative stress to the tissue. The results demonstrate that this can be averted by the use of various antioxidants administered preferably by topical route. That they will be so effective is strongly suggested by the effectiveness of pyruvate and caffeine administered topically to diabetic and galactosemic animals.

Prevention of cataract in diabetic mice by topical pyruvate

Background:

It has been previously reported that oral administration of sodium pyruvate inhibits oxidative stress and cataract formation in diabetic animals. With a view to exploring the clinical usefulness of these findings, this study examined its preventive effect when administered topically as an eye drop.

Methods:

Diabetes was induced by intraperitoneal injections of streptozotocin. At the onset of diabetes, an eye drop preparation containing 2.5% sodium pyruvate was administered six times a day at 90-minute intervals. Treatment was continued for 6 weeks. Cataract formation was monitored ophthalmoscopically after mydriasis with 1% tropicamide eye drops. Subsequently, the treated and untreated diabetic animals and the age-matched normal controls were euthanized, their eyes enucleated, and the lenses isolated for biochemical assessment of protein glycation and glutathione levels.

Results:

Treatment with pyruvate eye drops was found to be significantly effective in inhibiting protein glycation. Glutathione levels were also better maintained. In addition, ophthalmoscopic examination revealed that the incidence of cataract in the pyruvate-treated group was only 12% as compared with the untreated diabetics in whom the incidence was 73%. Cataracts at this stage were largely equatorial.

Conclusion:

The results demonstrate that topical application of pyruvate can potentially be useful in attenuating or preventing cataract formation induced by diabetes and other conditions of oxidative stress.

Diabetic cataract-pathogenesis, epidemiology and treatment

Cataract in diabetic patients is a major cause of blindness in developed and developing countries. The pathogenesis of diabetic cataract development is still not fully understood. Recent basic research studies have emphasized the role of the polyol pathway in the initiation of the disease process. Population-based studies have greatly increased our knowledge concerning the association between diabetes and cataract formation and have defined risk factors for the development of cataract. Diabetic patients also have a higher risk of complications after phacoemulsification cataract surgery compared to nondiabetics. Aldose-reductase inhibitors and antioxidants have been proven beneficial in the prevention or treatment of this sightthreatening condition in in vitro and in vivo experimental studies. This paper provides an overview of the pathogenesis of diabetic cataract, clinical studies investigating the association between diabetes and cataract development, and current treatment of cataract in diabetics.

Prevention of oxidative damage to lens by caffeine

PURPOSE

The primary objective of this study was to examine the possibility of inhibiting oxidative damage to the lens in vitro by caffeine.

METHODS

Oxidative damage was inflicted by incubating mouse lenses in Tyrode medium containing 0.1 mM Fe(8)Br(8), an iron complex soluble in aqueous medium. Parallel incubations were conducted in the presence of caffeine (5 mM).

RESULTS

Lenses incubated in the medium containing Fe(8)Br(8) undergo oxidative stress, as evidenced by the inhibition of Na(+)-K(+) ATPase-driven rubidium transport and the loss of tissue glutathione and ATP. These effects were prevented in presence of caffeine. That the effects are due to the oxyradicals produced was ascertained further by parallel studies with Tempol (5 mM), a well-known scavenger of reactive oxygen species (ROS) with its activity being more pronounced with hydroxyl radicals as compared to other ROS.

CONCLUSIONS

Caffeine was found to be effective in preventing oxidative stress to the lens induced by iron under ambient conditions. The protective effect is attributable to its ability to scavenge ROS, particularly the hydroxyl radical.

Attenuation and delay of diabetic cataracts by antioxidants: effectiveness of pyruvate after onset of cataract

Cataract is one of the most significant vision-impairing complications of diabetes. The present study examined the feasibility of inhibiting cataract formation by treatment with pyruvate, a metabolite known to effectively scavenge reactive species of oxygen and inhibit protein glycation, both known to be involved in the genesis of diabetic cataracts. In addition, pyruvate stimulates tissue metabolism, which is depressed with the onset of cataract formation. The objective of our experiments was to determine if this compound could be effective in offsetting the progress of cataract, specifically if administered after the diabetes-induced lens changes have begun, as opposed to the previous reports wherein it has been reported to delay cataract formation if administered prophylactically with the immediate onset of diabetes. Diabetes was induced by intraperitoneal administration of streptozotocin to mice. Lens transparency was assessed by slit lamp examination and its photography. ATP was determined enzymatically by reacting it with luciferin-luciferase mixture and measuring the fluorescence intensity. The findings described herein are in accordance with this possibility. The incidence of cataract in the group of diabetic animals, where treatment with pyruvate was initiated after the initial lens changes set in, was significantly lower at all times of observation in comparison to the untreated diabetic group. In addition, the severity of opacities in the pyruvate-treated group, when present, was much minor, the transparency of these cases being close to that in the control animals. The ophthalmic findings are supported biochemically by ATP levels, which were significantly higher in the pyruvate group in comparison to the untreated group. The present findings emphasize the clinical usefulness of initiating treatment with anti-oxidants and metabolic agonists even when the lens changes are detected at the time of the diabetes diagnosis. The latter usually comes much later than the onset of visual aberrations. Prophylaxis is not an absolute requirement.

Prevention of cataract by pyruvate in experimentally diabetic mice

Previous studies have demonstrated that administration of pyruvate prevents cataract formation in diabetic rats. It is known that the induction of cataractous process in this case is initiated by aldose reductase (AR) catalyzed synthesis and accumulation of excessive sorbitol in the lens fibres and epithelium and their consequent osmotic hydration. Synthesis of this and other polyols is competitively inhibited by pyruvate. The objective of the present investigations was hence to determine whether pyruvate would have a similar protective effect in species where cataract formation is relatively independent of sorbitol synthesis such as in humans where the lens AR activity is extremely low, especially with glucose as a substrate. The Km of AR for glucose is known to be very high. The possible protective effect of pyruvate in the low AR models was conceived on the basis of our previous findings suggesting that it can also exert substantial antiglycating as well as antioxidant effects. The present studies have hence been conducted with mice, a species known to be low in lens AR, similar to that in humans. As stipulated, pyruvate administration has indeed been found to offer a significant protection against development of diabetic cataract in this model also. The effect correlated with the inhibition of protein glycation as well as of oxidative stress. The latter was apparent by the prevention of the loss of glutathione known to be associated with diabetes. Although there was a small but noticeable increment in the sorbitol content of the diabetic lenses, this was osmotically insignificant. Even this increase was prevented by pyruvate. The magnitude of the elevation in the contents of glycated proteins and the depression in the level of glutathione were, on the contrary, highly pronounced, suggesting a more prominent role of the latter factors. In addition, the possibility of a direct metabolic support it could offer to the tissue is also imminent by its effect on the maintenance of ATP, as shown earlier. The present studies are therefore considered more relevant to the pathogenesis of cataract in human diabetics and its possible prevention by endogenous compounds with antiglycating and antioxidant properties. Inhibition of cataract formation by pyruvate in an animal model with low lens AR, similar to that in humans, has been shown for the first time.