Establishment of mouse as an animal model for study of diabetic cataracts: biochemical studies

A model of type 2 diabetes in the guinea pig using sequential diet-induced glucose intolerance and streptozotocin treatment

Type 2 diabetes is a leading cause of morbidity and mortality among noncommunicable diseases, and additional animal models that more closely replicate the pathogenesis of human type 2 diabetes are needed. The goal of this study was to develop a model of type 2 diabetes in guinea pigs, in which diet-induced glucose intolerance precedes β-cell cytotoxicity, two processes that are crucial to the development of human type 2 diabetes. Guinea pigs developed impaired glucose tolerance after 8 weeks of feeding on a high-fat, high-carbohydrate diet, as determined by oral glucose challenge. Diet-induced glucose intolerance was accompanied by β-cell hyperplasia, compensatory hyperinsulinemia, and dyslipidemia with hepatocellular steatosis. Streptozotocin (STZ) treatment alone was ineffective at inducing diabetic hyperglycemia in guinea pigs, which failed to develop sustained glucose intolerance or fasting hyperglycemia and returned to euglycemia within 21 days after treatment. However, when high-fat, high-carbohydrate diet-fed guinea pigs were treated with STZ, glucose intolerance and fasting hyperglycemia persisted beyond 21 days post-STZ treatment. Guinea pigs with diet-induced glucose intolerance subsequently treated with STZ demonstrated an insulin-secretory capacity consistent with insulin-independent diabetes. This insulin-independent state was confirmed by response to oral antihyperglycemic drugs, metformin and glipizide, which resolved glucose intolerance and extended survival compared with guinea pigs with uncontrolled diabetes. In this study, we have developed a model of sequential glucose intolerance and β-cell loss, through high-fat, high-carbohydrate diet and extensive optimization of STZ treatment in the guinea pig, which closely resembles human type 2 diabetes. This model will prove useful in the study of insulin-independent diabetes pathogenesis with or without comorbidities, where the guinea pig serves as a relevant model species.

Anthocyanin-rich extract from Hibiscus sabdariffa calyx counteracts UVC-caused impairments in rats

CONTEXT

Ultraviolet radiation (UV) was reported to cause oxidative stress. Hibiscus sabdariffa L. (Malvaceae) calyx is commonly used in traditional Asian and African medicines and possesses strong antioxidant capacity due to its anthocyanin (ANTH) content.

OBJECTIVE

This study researched the possible protective role of Hibiscus sabdariffa calyx extract (HSCE) in UVC exposure of rats.

MATERIAL AND METHODS

Levels of serum enzymes, renal function tests, and some oxidant/antioxidant biomarkers of skin, lens, and retina tissues were monitored. Rats were exposed to UVC 4 h daily for 40 d and simultaneously received HSCE containing 2.5, 5, and 10 mg doses of ANTH in drinking water.

RESULTS

Significant (p < 0.05) increases in the levels of serum aminotransferases, lactate dehydrogenase, urea, creatinine, and uric acid were noted after UVC exposure. In skin, lens, and retina tissues, total oxidant status, oxidative stress index, lipid peroxidation, and protein oxidation escalated markedly (p < 0.05) whereas total antioxidant status, reduced glutathione, and superoxide dismutase decreased dramatically (p < 0.05) related to UVC. Co-administration of HSCE with each ANTH dose significantly (p < 0.05) reversed aforementioned parameters (except total oxidant status) almost in all tissues. The LD50 of HSCE in rats was determined to be above 5000 mg/kg.

DISCUSSION AND CONCLUSION

Our data revealed that HSCE has a remarkable potential to counteract UVC-caused impairments, probably through its antioxidant and free radical-defusing effects. Therefore, HSCE could be useful against some cutaneous and ocular diseases in which UV and oxidative stress have a role in the etiopathogenesis.

Protective effects of recombinant human brain natriuretic peptide against LPS-Induced acute lung injury in dogs

BACKGROUND

Acute lung injury (ALI) is a common component of systemic inflammatory disease without more effective treatments. However, recent studies have demonstrated that the recombinant human brain natriuretic peptide (rhBNP) has anti-inflammatory effects. Therefore, we found that rhBNP could prevent lipopolysaccharide (LPS)-induced acute lung injury in a dog model.

METHODS

Dogs were injected with LPS and subjected to continuous intravenous infusion (CIV) of saline solution or rhBNP. We detected the protective effects of rhBNP by histological examination and determination of serum cytokine levels and lung myeloperoxidase (MPO) activity and malondialdehyde (MDA) activity. Histological examination indicated marked inflammation, edema and hemorrhage in lung tissue taken 12h after rhBNP treatment compared with tissue from dogs which received saline treatment after LPS injection. LPS injection induced cytokine (IL-6 and TNF-α) secretion and lung MPO and MDA activities, which were also attenuated by rhBNP treatment.

RESULTS

Inductions of IL-6 and TNF-α were significantly attenuated in the L-rhBNP and the H-rhBNP groups. The ratios of the L-rhBNP group and H-rhBNP group were lower than that in the lung injury group. Furthermore, MPO and MDA activities were significantly lower in the H-rhBNP group compared to those in the LI group.

CONCLUSION

Our data indicate that rhBNP treatment may exert protective effects and may be associated with adjusting endogenous antioxidant enzymes. Thus, rhBNP may be considered as a therapeutic agent for various clinical conditions involving lung injury by sepsis.

Beneficial influence of topical extra virgin olive oil application on an experimental model of penile fracture in rats

Penile fracture (PF) is known as a traumatic rupture of the tunica albuginea of corpus cavernosum. In this study, we aimed to investigate the healing influence of topical extra virgin olive oil (EVOO) on PF through evaluating levels of some oxidative stress biomarkers for the first time. Histopathological evaluation was also realized. A total of 18 male Sprague-Dawley albino rats were divided into three groups of six rats each as control group, in PF (alone) group, and PF + EVOO group. Experimental PF was formed via incising from the proximal dorsal side of the penis in the rats of all groups except control. While in PF (alone) group, fracture was formed and the incision was primarily closed, in PF + EVOO group in addition to foregoing processes, EVOO was also administrated topically twice a day for 3 weeks. At the end of the experiment, all rats were killed and penectomy was carried out. While malondialdehyde, myeloperoxidase, lipid hyroperoxide, and total oxidant status significantly (p < 0.05) increased, reduced glutathione and total free sulfhydryl groups markedly (p < 0.05) decreased in PF (alone) group when compared with PF + EVOO group. Levels of these parameters were reversed to nearly normal values by topical EVOO application. Protection by EVOO is further substantiated via the improved histological findings in PF + EVOO group as against degenerative changes in the rats of PF (alone) group. Our data revealed that EVOO has protective effect in penile cavernosal tissue through probably its antioxidant, free radical defusing, anti-inflammatory, and antimicrobial effects.

Therapeutic potential of some plant extracts used in Turkish traditional medicine on streptozocin-induced type 1 diabetes mellitus in rats

Diabetes mellitus (DM) is known to impair many physiological functions. Some reports claim that medicinal plants can reduce these alterations caused by DM. The aim of this study was to investigate the therapeutic potential of aqueous-methanol extracts of Urtica dioica, Thymus vulgaris (TV), Myrtus communis (MC), Scolymus hispanicus (SH) and Cinnamomun zeylanicum (CZ) on streptozotocin (STZ)-induced type 1 DM in rats. Diabetes was induced via a single i.p. injection of STZ (65 mg/kg body weight). After 1 week to allow for development of diabetes, each plant extract was administered to diabetic rats separately at a dose of 100 mg/kg body weight daily for 28 days. The results showed that only SH extract significantly (P < 0.05) amended fasting blood glucose level. The lipid profile was ameliorated especially by supplementations of TV, MC and CZ extracts. Almost all plant extract treatments markedly (P < 0.05) increased reduced glutathione content and decreased lipid peroxidation levels of erythrocyte, plasma, retina and lens tissues. They also significantly (P < 0.05) amended erythrocyte catalase activity, levels of marker serum enzymes (except amylase), urea and blood urea nitrogen when compared to diabetic rats treated with nothing. Furthermore, none of the plant extracts counteracted body weight loss of diabetic rats. Our data revealed that the aforementioned plant extracts have remarkable potential to counteract DM-caused alterations, probably through their antioxidant and free radical-defusing effects.

Oxidative status and its relation with insulin resistance in young non-obese women with polycystic ovary syndrome

BACKGROUND

Oxidative stress may play a role in the pathophysiology of polycystic ovary syndrome (PCOS). Insulin resistance (IR) also can be found in young non-obese women with PCOS. Hyperglycemia may increase reactive oxygen species production and decrease antioxidant levels.

AIM

To investigate oxidative status and its relation with IR in young non-obese patients with PCOS.

MATERIAL/SUBJECTS AND METHODS

Thirty-one patients with hyperinsulinemic (no.=13) and normoinsulinemic (no.=18) PCOS and 29 healthy controls were included in this study. Serum levels of glucose, insulin, gonadotropins, total testosterone, DHEAS, SHBG, 2-h plasma glucose on oral glucose tolerance test, malondialdehyde (MDA), protein carbonyl (PC), reduced glutathione (GSH), β carotene, vitamin A, C, E and the enzyme activities of catalase and glutathione S-transferase (GST), IR [by homeostasis model assessment (HOMA)-IR], and β cell function [by HOMA-B] were assessed.

RESULTS

Serum glucose, insulin, total testosterone, DHEAS, HOMA-IR levels, and LH/FSH ratios were higher in young non-obese women with PCOS. Serum MDA and PC levels were also higher but GSH, vitamin C and E levels, and GST enzyme activity were lower in these women than in healthy controls, independently of the status of IR (p<0.05).

CONCLUSIONS

Oxidative stress characterized by increased oxidants and decreased antioxidant levels which are independent of IR may be involved in the pathogenesis of PCOS in young non-obese women.

Increased oxidative stress in patients with familial Mediterranean fever during attack period

OBJECTIVES

We aimed to investigate the status of oxidant and antioxidants during attack period (AP) and attack free periods (AFP) in Familial Mediterranean fever (FMF) patients.

METHODS

Measured the levels of malondialdehyde (MDA), protein carbonyl (PC), glutathione (GSH) and antioxidant vitamins (A,C and E) as well as the activities of catalase (CAT) and glutathione peroxidase (GSH-Px) in serum and whole blood of FMF patients in FMF-AP and FMF-AFP.

RESULTS

Levels of MDA and PC were found significantly higher (p <0.05) both in serum and whole blood of FMF-AP group compared with other groups. The CAT and GSH-Px activities in FMF-AP group were found markedly lower (p <0.05) comparing to HC group. However, there were no statistically significant differences between the groups in terms of antioxidant vitamin levels.

CONCLUSIONS

Our study demonstrated increased oxidative stress in patients with FMF during AP. Investigations are needed to establish the effect of antioxidant supplementation on FMF attack frequency and severity. We also suggest that these increased MDA and PC levels and decreased antioxidants may be used as supportive markers to differentiate AP from AFP. These conclusions need to be validated in further multicenter studies with high number of FMF patients.

Photoprotective effect of flax seed oil (Linum usitatissimum L.) against ultraviolet C-induced apoptosis and oxidative stress in rats

The aim of this study is to determine antioxidant and antiapoptotic effects of flax seed oil (FSO) on rats exposed to ultraviolet C (UVC). Malondialdehyde (MDA), protein carbonyl (PC) and reduced glutathione (GSH) levels as well as glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities were measured in lens, skin and serum. In addition, β-carotene, vitamin A, C and E contents were measured in serum, while apoptosis was determined in retina. Rats were divided into three groups as control, UVC and UVC + FSO. UVC and UVC + FSO groups were exposed to UVC light for 1 h twice a day for 4 weeks. FSO (4 ml/kg bw) was given by gavage before each irradiation period to the UV + FSO group. While MDA and PC levels of the UVC group increased compared to the control group, their levels decreased in the UVC + FSO group compared with the UVC group in skin, lens and serum. Skin GSH level decreased significantly in the UVC and UVC + FSO groups. As GPx and SOD activities of the UVC group were lower, their activities were higher in the UVC + FSO group in skin, lens and serum. There was only marked elevation of vitamin A level in the UVC group compared to the control group. Apoptosis increased in the UVC group and the UVC + FSO groups in retina. However, retinal apoptosis were lower in the UVC + FSO group compared with the UVC group. This investigation demonstrated that UVC exposure led to oxidative stress and apoptosis in rats as reflected by increased MDA, PC contents and decreased enzymatic and nonenzymatic antioxidant levels, FSO may be useful for preventing photoreactive damage.

Subacute effect of cigarette smoke exposure in rats: protection by pot marigold (Calendula officinalis L.) extract

This study was carried out to determine the preventive effect of Calendula officinalis L. (pot marigold) on rats exposed to cigarette smoke (CS). Rats were divided into three groups as control, CS and CS + pot marigold (PM). The rats in the CS and CS + PM groups were subjected to CS for 1 h twice a day for 23 days. PM (100 mg/kg body weight) was given to rats in the CS + PM group by gavage, 1 h before each administration period. While malondialdehyde, protein carbonyl contents and reduced glutathione level of the CS group increased, their levels diminished by PM administration. In addition, glutathione peroxidase (GPx), superoxide dismutase activities and β-carotene, vitamins A and C levels decreased in the CS group compared to control, however activities of these enzymes and concentration of vitamins were elevated by PM supplementation. This investigation showed that administration of PM supplied relative protection against subacute CS-induced cell injury.

Gastroprotective effect of small centaury (Centaurium erythraea L) on aspirin-induced gastric damage in rats

The aim of this study was to determine the antiulcer and antioxidant activities of Centaurium erythraea L (small centaury) in aspirin (ASA) induced acute gastric ulcer model. The gastroprotective effect of the 50% aqueous-ethanolic small centaury (SC) extract was investigated in rats at a dose of ASA 200 mg/kg body weight. Twenty-one Sprague-Dawley albino rats were divided into three groups of seven rats each as follows: (1) control group; (2) acute ASA-treated group and (3) ASA plus SC group. At the end of the 4-h drug administration, ulcer index, oxidant and antioxidant levels were measured and compared between the groups. The percentage of lesion area to total gastric surface area (ulcer index) was significantly reduced (77%) in ASA plus SC group as compared with acute ASA-treated group. The oral administration of ASA decreased catalase (CAT), reduced glutathione (GSH), and increased lipid peroxidation (LPO) levels. Although myeloperoxidase (MPO) activity was increased by ASA, it was found to be lower in the ASA plus SC group. GSH and Vitamin A levels were determined higher in the ASA plus SC group compared with ASA group. These results suggest that SC extract protects against ASA-induced damage due to its antioxidizing activity.

Both isoforms of ketohexokinase are dispensable for normal growth and development

Dietary fructose intake has dramatically increased over recent decades and is implicated in the high rates of obesity, hypertension, and type 2 diabetes (metabolic syndrome) in Western societies. The molecular determinants of this epidemiologic correlation are incompletely defined, but high-flux fructose catabolism initiated by ketohexokinase (Khk, fructokinase) is believed to be important. The Khk gene encodes two enzyme isoforms with distinctive substrate preferences, the independent physiological roles of which are unclear. To investigate this question, and for testing the importance of Khk in metabolic syndrome, isoform-selective genetic lesions would be valuable. Two deficiency alleles of the mouse Khk gene were designed. The first, Khk3a, uses targeted “knock-in” of a premature termination codon to induce a selective deficiency of the minor Khk-A isoform, preserving the major Khk-C isoform. The second, the KhkΔ allele, ablates both isoforms. Mice carrying each of these Khk-deficiency alleles were generated and validated at the DNA, RNA, and protein levels. Comparison between normal and knockout animals confirmed the specificity of the genetic lesions and allowed accurate analysis of the cellular distribution of Khk within tissues such as gut and liver. Both Khk3a/3a and KhkΔ/Δ homozygous mice were healthy and fertile and displayed minimal biochemical abnormalities under basal dietary conditions. These studies are the first demonstration that neither Khk isoform is required for normal growth and development. The new mouse models will allow direct testing of various hypotheses concerning the role of this enzyme in metabolic syndrome in humans and the value of Khk as a pharmacological target.

Increased occupational coal dust toxicity in blood of central heating system workers

Coal dust causes lung diseases in occupational exposure. Reactive oxygen species have been implicated in the pathogenesis of its toxicity. In this study, serum enzymes, lipid profile and other biochemical values with oxidant/antioxidant status in whole blood and serum of central heating system workers (CHSW; the persons responsible for heating the apartment with coal) were determined to reflect the cell injury. Blood samples were obtained from CHSW (n = 25) and healthy individuals (n = 25). All values were measured in whole blood and serum. ANOVA was used for the estimation of statistical data. In the group of CHSW, creatinine, ferritin, alanin aminotransferase, aspartate aminotransferase, creatine phosphokinase, gamma glutamyl transferase, lactate dehydrogenase and glutathione reductase activities as well as triglyceride, very low density lipoprotein, protein carbonyl and malondialdehide were significantly higher, while transferrin, high density lipoprotein and catalase (CAT) activities were lower than the group of healthy individuals. This result is consistent with hypothesis that respirable coal dust generates lipid and protein oxidation and induces leakage of serum enzymes by cell damage. It also leads to imbalance in antioxidant defense system, lipid profile and other biochemical parameters.

Comparative toxicity of 4 commonly used intravitreal corticosteroids on rat retina

OBJECTIVE

To investigate the effects of 4 commonly used steroids (dexamethasone, triamcinolone, betamethasone, and methylprednisolone) on 50 retinas of 25 adult pigmented rats.

STUDY DESIGN

Experimental animal study.

PARTICIPANTS

Twenty-five pigmented Long-Evans male rats.

METHODS

Each steroid drug with 2 different doses (0.025 mL and 0.050 mL) was injected into the vitreous of each eye of 5 rats. The low drug dose was injected into the right eye and the high dose was injected into the left eye. Ten eyes of 5 randomly selected rats were used as a control group and intravitreal saline was injected into these eyes. Oxidative damage and intrinsic antioxidative capacity were determined by measuring retinal malondialdehyde (MDA) and glutathione (GSH) levels, respectively.

RESULTS

No statistically meaningful difference was observed in retinal GSH and MDA measurements in the low- and high-dose triamcinolone (1 and 2 mg), low-dose betamethasone (0.075 mg), and low-dose dexamethasone (0.1 mg) groups, compared with the control group. Both doses of methylprednisolone (1.6 mg and 3.2 mg), high-dose betamethasone (0.15 mg), and high-dose dexamethasone (0.2 mg) markedly altered retinal GSH and MDA levels.

CONCLUSIONS

The results of our study show that the toxicity of triamcinolone is not evident even in high doses. It may be used safely. We also suggest that intravitreal use of low doses of betamethasone and dexamethasone is safer than higher doses of these drugs and both doses of methylprednisolone.

Electron impact mass spectroscopic studies on mouse retinal fatty acids: effect of diabetes

AIM

The primary objective of these investigations was to determine the fatty acid composition of the mouse retina as affected by diabetes. Additionally, in order to ascertain if there is any accumulation of lipids in the diabetic retina as occurs in many diabetic tissues, its total fatty acid content was also determined.

METHODS

Lipids in the retina of normal and diabetic mice were trans-methylated with methanolic HCl. The esters so prepared were analyzed for fatty acids by gas chromatography-mass spectrometry, qualitatively as well as quantitatively.

RESULTS

The major fatty acids in the retina were palmitic (PA), oleic (OA), stearic (SA), arachidonic (AA) and docosahexaenoic (DHA) acids. The content of all these fatty acids increased significantly in the diabetic retina, reflecting lipidosis. The major increases (approximately 3 times the normal) were found in PA, OA, SA and AA. The increase in DHA, however, was much less (approximately 1.4 times). The relative percentages of fatty acids were also affected. While the relative percentages of PA and OA increased in the diabetic retina, there were insignificant changes in the percentages of SA and AA. Interestingly, the relative percentage of DHA underwent a significant decrease, about 50% of the normal.

CONCLUSIONS

The results show that there is excessive accumulation of lipids in the diabetic retina. This is consistent with the known increased mobilization of lipids from the adipose tissue and their accumulation in other tissues under diabetic conditions. On a percentage profile basis, while the relative percentage of most of the fatty acids increased, the DHA percentage significantly decreased. This could be explained by its dilution by the fatty acids coming from the fat depots which lack DHA. Physiologically, the excessive accumulation of fatty acids in the diabetic retina correlates with the lipofuscinosis and neural dysfunction associated with this disease.

Dietary soy isoflavones increase insulin secretion and prevent the development of diabetic cataracts in streptozotocin-induced diabetic rats

Soy isoflavone-containing diets have been reported to be beneficial in diabetes. This present study investigated the hypoglycemic effects of isoflavones in streptozotocin (STZ)-induced diabetes. Diabetes was induced in male Sprague-Dawley rats by intraperitoneal injection of 100 mg/kg STZ. Diabetic rats were then randomly divided into 3 groups and received a special diet supplemented with casein (control), low-isoflavone soy (LIS) protein, and high-isoflavone soy protein (HIS) for 8 weeks. Compared with the control or LIS groups, those rats on the HIS diet had significantly increased body weight and serum insulin levels and reduced serum glucose and methylglyoxal levels. Serum glutathione levels were also increased in rats given the HIS diet compared with those in the control or LIS (P < .01). Serum high-density lipoprotein cholesterol level was significantly higher in HIS-fed rats than that of the control or LIS rats (P < .05). More importantly, the death rate and incidence of cataracts in the diabetic rats were markedly decreased in the HIS group. In conclusion, ingestion of high-isoflavone soy protein not only lowers glucose levels but also reduces the incidence of cataracts in diabetic rats. The beneficial effects of soy isoflavones are attributed to increased insulin secretion, a better glycemic control, and antioxidant protection.

Upregulation of glyoxalase I fails to normalize methylglyoxal levels: a possible mechanism for biochemical changes in diabetic mouse lenses

Glyoxalase I is the first enzyme in a two-enzyme glyoxalase system that metabolizes physiological methylglyoxal (MGO). MGO reacts with proteins to form irreversible adducts that may lead to crosslinking and aggregation of lens proteins in diabetes. This study examined the effect of hyperglycemia on glyoxalase I activity and its mRNA content in mouse lens epithelial cells (mLE cells) and in diabetic mouse lenses and investigated the relationship between GSH and MGO in organ cultured lenses. mLE cells cultured with 25 mM D-glucose (high glucose) showed an upregulation of glyoxalase I activity and a higher content of glyoxalase I mRNA when compared with either cells cultured with 5 mM glucose (control) or with 20 mM L-glucose + 5 mM D-glucose. MGO concentration was significantly elevated in cells cultured with high D-glucose, but not in L-glucose. GSH levels were lower in cells incubated with high glucose compared to control cells. Glyoxalase I activity and mRNA levels were elevated in diabetic lenses compared to non-diabetic control mouse lenses. MGO levels in diabetic lenses were higher than in control lenses. Incubation of lenses with buthionine sulfoximine (BSO) resulted in a dramatic decline in GSH but the MGO levels were similar to lenses incubated without BSO. Our data suggest that in mouse lenses MGO accumulation may occur independent of GSH concentration and in diabetes there is an upregulation of glyoxalase I, but this upregulation is inadequate to normalize MGO levels, which could lead to MGO retention and chemical modification of proteins.

Influence of glutathione fructosylation on its properties

Incubation of fructose and glutathione leads to the formation of N-2-deoxy-glucos-2-yl glutathione as the major glycation product, with characteristic positive ion at 470 Th in LC-MS spectra. Glutathione disulfide and fructose generate two compounds: N-2-deoxy-glucos-2-yl glutathione disulfide (m/z=775 Th) and bis di-N,N'-2-deoxy-glucos-2-yl glutathione disulfide (m/z=937 Th). N-2-deoxy-glucos-2-yl glutathione is 2.5-fold less effective than glutathione in reducing dehydroascorbic acid. Glutathione peroxidase and glutahione-S-transferase exhibit marginal activity toward N-2-deoxy-glucos-2-yl glutathione, while glyoxalase I shows 44.9% of the enzyme's specific activity. Glutathione reductase demonstrates 6.9% of the enzyme's specific activity with bis di-N,N'-2-deoxy-glucos-2-yl glutathione, while with mono-N-glucosyl glutathione disulfide retained 5 6.1% of the original activity. Glutathione reductase could not reduce N-2-deoxy-glucos-2-yl glutathione in mixed disulfide with gammaS-crystallin, but reduced glutathione in mixed disulfide with gammaS-crystallin by 90%. The presence of N-2-deoxy-glucos-2-yl glutathione in mixed disulfide with gammaS-crystallin makes this molecule more susceptible to unfolding than native gammaS-crystallin.

Protective effects of various antioxidants during ischemia-reperfusion in the rat retina

BACKGROUND

Oxidative stress during ischemia-reperfusion (I/R) is thought to be a major cause of retinal injury after I/R. The present study was aimed at investigating the protective role of antioxidant application.

METHODS

Four commonly used antioxidants (vitamin E=alpha tocopherol, lutein, fenugreek=Trigonella foenum-graecum and germander=Teucrium multicaule) were applied in ischemia-reperfusion (I/R) injury of the right retinae of 51 adult pigmented rats. Each of the antioxidants was administered every 6 h, beginning 6 h before the ischemia. After 60 min ischemia and 24 h reperfusion, we assayed (1) oxidative damage by measuring malondialdehyde (MDA), (2) apoptosis by measuring activated caspase-3 (using immunoblots), and (3) intrinsic antioxidative capacity by measuring glutathione (GSH) levels in the retinae.

RESULTS

In the order of lutein>Trigonella>vitamin E>Teucrium, all four compounds were effective in preventing retinal damage by I/R, as (1) they significantly decreased the formation of MDA (8.83, 16.48, 17.24, 18.5 nmol/100 mg tissue wet weight, respectively) compared with I/R without protection (23.29 nmol/100 mg tissue wet weight; controls: 8.0 nmol/100 mg tissue wet weight); (2) they significantly inhibited the activation of caspase-3 [0.01, 0.02, 0,02, and 0.04 arbitrary units (AU), respectively, versus control, 0.0, and I/R, 0.08 AU]; and (3) they significantly decelerated the loss of GSH (from control levels of 36.04 nmol/100 mg tissue wet weight) to 30.4, 15.98, 18.1, 15.02 nmol/100 mg tissue wet weight, respectively (lutein, Trigonella, vitamin E, Teucrium), compared with unprotected I/R (12.84 nmol/100 mg tissue wet weight).

CONCLUSIONS

Our study shows that lutein, Trigonella, Teucrium and vitamin E exert protection against in vivo retinal I/R injury in rats; this may recommend these compounds (in particular, lutein) for clinical use in patients with different types of ocular I/R injuries.

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.

In vitro glucose-induced cataract in copper-zinc superoxide dismutase null mice

The purpose of this study was to evaluate the involvement of the superoxide radical in glucose-induced cataract using lenses from mice lacking the cytosolic copper-zinc superoxide dismutase (SOD1). Lenses from wild-type mice and SOD1 null mice were kept in organ culture with either 5.6 or 55.6 mM glucose for 6 days. The cataract formation was followed with digital image analysis and ocular staging. The lens damage was further quantified by analysis of the leakage of lactate dehydrogenase into the medium by the uptake of 86Rb and by determining the water content of the lenses. The formation of superoxide radicals in the lenses was assessed with lucigenin-derived chemiluminescence. Immunohistochemical staining for SOD1 was also performed on murine lenses. The SOD1 null lenses exposed to high glucose developed more cataract showed an increased leakage of lactate dehydrogenase and developed more oedema compared to the control lenses. At 5.6 mM glucose there was no difference between the SOD1 null and wild-type lenses. Staining for SOD1 was seen primarily in the cortex of the wild-type lens. This in vitro model suggests an involvement of the superoxide radical and a protective effect of SOD1 in glucose-induced cataract formation.

Glucose-derived Amadori compounds of glutathione

Under the chromatographic conditions used in these studies we observed time- and concentration-dependent formation of N-1-Deoxy-fructos-1-yl glutathione as the major glycation product formed in the mixtures of GSH with glucose. N-1-Deoxy-fructos-1-yl glutathione had a characteristic positively charged ion with m/z=470 Th in its LC-MS spectra. Mixtures of glutathione disulfide and glucose generated two compounds: N-1-Deoxy-fructos-1-yl GSSG (m/z=775 Th) as major adduct and bis di-N, N'-1-Deoxy-fructos-1-yl GSSG (m/z=937 Th) as the minor one. All three compounds showed a resonance signal at 55.2 ppm in the 13C-NMR spectra as C1 methylene group of deoxyfructosyl, which represents direct evidence that they are Amadori compounds. All three compounds purified from GSSG/Glc or GSH/Glc mixtures also showed LC-MS/MS fragmentation patterns identical to those of the synthetically synthesized N-1-Deoxy-fructos-1-yl glutathione, N-1-Deoxy-fructos-1-yl GSSG and bis di-N, N'-1-Deoxy-fructos-1-yl GSSG. N-1-Deoxy-fructos-1-yl glutathione was shown to be a poor substrate for glutathione peroxidase (6.7% of the enzyme's original specific activity) and glutathione-S-transferase (25.7% of the original enzyme's specific activity). Glutathione reductase failed to recycle the disulfide bond within the structure of di-substituted bis di-N, N'-1-Deoxy-fructos-1-yl GSSG. It showed only 1% of the original enzyme's specific activity, but retained its ability to reduce the disulfide bond within the structure of N-1-Deoxy-fructos-1-yl GSSG by 57% of its original specific activity. Since the GSH concentration in diabetic lens is significantly decreased and the glucose concentration can increase 10-fold and higher, the formation of Amadori products of the different forms of glutathione with this monosaccharide may be favored under these conditions and could contribute to a lowering of glutathione levels and an increase of oxidative stress observed in diabetic lens.

Morphogenetic and apoptotic changes in diabetic cataract: prevention by pyruvate

Studies have been conducted to ascertain the preventive effect of pyruvate against diabetes induced damage to DNA and associated morphogenetic changes in the mouse lens. Such changes were characterized by DNA nicks as well as by gross morphological changes in the nuclei, evident respectively by TUNEL and Hoechst staining procedures. Morphogenetic changes were also apparent by abnormal diferentiation of the germinal epithelial cells and errors in their migratory pathway. These changes were prevented by simultaneous administration of pyruvate to the diabetic animals. The preventive effect of this agent is attributable to its property of scavenging oxy-radicals generated by high levels of the sugars.

Cataracts in experimentally diabetic mouse: morphological and apoptotic changes

AIM

The objective of these investigations was to extend our earlier study on the induction of cataracts in diabetic mice, a low aldose reductase (AR) animal model at morphological level. Previous studies were done primarily at biochemical level.

METHODS

Diabetes was induced by intraperitoneal administration of streptozotocin. The lenses isolated after the establishment of diabetes were then subjected to histologic and electron microscopic studies.

RESULTS

Morphological alterations were characterized by shrinkage, elongation and lobulization of the nuclei of the epithelial cells. This was associated with chromatin condensation and its margination. Similar structural aberrations were also observed in a significant number of the subepithelial fibre cells representing defect in fibre maturation. More interestingly, unlike that in other common animal models of diabetic cataract, such abnormally nucleated cells were also found to be prevalent in the posterior subcapsular region, a finding common in human diabetics also.

CONCLUSION

The present studies further affirm the suitability of the mouse model for a study of cataractogenesis induced by diabetes. Because of the findings reported herein, as well as the known biochemical similarity between the lenses of the mice and humans in respect of AR deficiency, contrary to the rat model where it is very high, use of this species is considered more useful towards understanding the basic aetiology as well as for evaluating the efficacy of various referred nutritional and metabolic antioxidants against such cataracts.

Expression, regulation and function of Na,K-ATPase in the lens

Na,K-ATPase is responsible for maintaining the correct concentrations of sodium and potassium in lens cells. Na,K-ATPase activity is different in the two cell types that make up the lens, epithelial cells and fibers; specific activity in the epithelium is higher than in fibers. In some parts of the fiber mass Na,K-ATPase activity is barely detectable. There is a large body of evidence that suggests Na,K-ATPase-mediated ion transport by the epithelium contributes significantly to the regulation of ionic composition in the entire lens. In some species different Na,K-ATPase isoforms are present in epithelium and fibers but in general, fibers and epithelium express a similar amount of Na,K-ATPase protein. Turnover of Na,K-ATPase by protein synthesis may contribute to preservation of high Na,K-ATPase activity in the epithelium. In ageing lens fibers, oxidation, and glycation may decrease Na,K-ATPase activity. Na,K-ATPase activity in lens fibers and epithelium also may be subject to regulation as the result of protein tyrosine phosphorylation. Moreover, activation of G protein-coupled receptors by agonists such as endothelin-1 elicits changes of Na,K-ATPase activity. The asymmetrical distribution of Na,K-ATPase activity in the epithelium and fibers may contribute to ionic currents that flow in and around the lens. Studies on human cataract and experimental cataract in animals reveal changes of Na,K-ATPase activity but no clear pattern is evident. However, there is a convincing link between abnormal elevation of lens sodium and the opacification of the lens cortex that occurs in age-related human cataract.