Polyamine Oxidase Is Involved in Spermidine Reduction of Transglutaminase Type 2-Catalyzed βH-Crystallins Polymerization in Calcium-Induced Experimental Cataract

In an in vitro Ca2+-induced cataract model, the progression of opacification is paralleled by a rapid decrease of the endogenous levels of spermidine (SPD) and an increase of transglutaminase type 2 (TG2, EC 2.3.2.13)-catalyzed lens crystallins cross-linking by protein-bound N1-N8-bis(γ-glutamyl) SPD. This pattern was reversed adding exogenous SPD to the incubation resulting in a delayed loss of transparency of the rabbit lens. The present report shows evidence on the main incorporation of SPD by the catalytic activity of TG2, toward βH-crystallins and in particular to the βB2- and mostly in βB3-crystallins. The increase of endogenous SPD in the cultured rabbit lens showed the activation of a flavin adenine dinucleotide (FAD)-dependent polyamine oxidases (PAO EC 1.5.3.11). As it is known that FAD-PAO degrades the N8-terminal reactive portion of N1-mono(γ-glutamyl) SPD, the protein-bound N8-mono(γ-glutamyl) SPD was found the mainly available derivative for the potential formation of βB3-crystallins cross-links by protein-bound N1-N8-bis(γ-glutamyl)SPD. In conclusion, FAD-PAO degradation of the N8-terminal reactive residue of the crystallins bound N1-mono(γ-glutamyl)SPD together with the increased concentration of exogenous SPD, leading to saturation of glutamine residues on the substrate proteins, drastically reduces N1-N8-bis(γ-glutamyl)SPD crosslinks formation, preventing crystallins polymerization and avoiding rabbit lens opacification. The ability of SPD and MDL 72527 to modulate the activities of TG2 and FAD-PAO involved in the mechanism of lens opacification suggests a potential strategy for the prevention of senile cataract.

Metabolic and pathologic profiles of human LSS deficiency recapitulated in mice

Skin lesions, cataracts, and congenital anomalies have been frequently associated with inherited deficiencies in enzymes that synthesize cholesterol. Lanosterol synthase (LSS) converts (S)-2,3-epoxysqualene to lanosterol in the cholesterol biosynthesis pathway. Biallelic mutations in LSS have been reported in families with congenital cataracts and, very recently, have been reported in cases of hypotrichosis. However, it remains to be clarified whether these phenotypes are caused by LSS enzymatic deficiencies in each tissue, and disruption of LSS enzymatic activity in vivo has not yet been validated. We identified two patients with novel biallelic LSS mutations who exhibited congenital hypotrichosis and midline anomalies but did not have cataracts. We showed that the blockade of the LSS enzyme reaction occurred in the patients by measuring the (S)-2,3-epoxysqualene/lanosterol ratio in the forehead sebum, which would be a good biomarker for the diagnosis of LSS deficiency. Epidermis-specific Lss knockout mice showed neonatal lethality due to dehydration, indicating that LSS could be involved in skin barrier integrity. Tamoxifen-induced knockout of Lss in the epidermis caused hypotrichosis in adult mice. Lens-specific Lss knockout mice had cataracts. These results confirmed that LSS deficiency causes hypotrichosis and cataracts due to loss-of-function mutations in LSS in each tissue. These mouse models will lead to the elucidation of the pathophysiological mechanisms associated with disrupted LSS and to the development of therapeutic treatments for LSS deficiency.

Prevention of Diabetic Complications by Walnut Leaf Extract via Changing Aldose Reductase Activity: An Experiment in Diabetic Rat Tissue

BACKGROUND

Increased activity of aldose reductase (AR) is one of the mechanisms involved in the development of diabetic complications. Inhibiting AR can be a target to prevent diabetes complications. This study is aimed at evaluating the effect of cyclohexane (CH) and ethanol extracts (ET) of walnut leaves on AR activity in the lens and testis of diabetic rats.

METHODS

Fifty-six male rats classified into seven groups as control and treatment groups and treated for 30 days. The treatment groups were treated with different concentrations of ET and CH. The diabetic control (DC) group was exposed to streptozotocin. AR activity was measured in the lens and testis. The expression of AR in the testis was evaluated by the immunohistochemistry method.

RESULTS

Both extracts significantly reduced the AR activity (ng/mg of tissue protein) in the testis (0.034 ± 0.004, 0.038 ± 0.010, and 0.040 ± 0.007 in the treatment groups vs. 0.075 ± 0.007 in the DC group) and lens (1.66 ± 0.09, 2.70 ± 0.47, and 1.77 ± 0.20 in the treatment groups vs. 6.29 ± 0.48 in the DC group) of the treatment group compared to those of the DC group (P < 0.05). AR expression in the testes of the treatment groups was decreased compared with that of the DC group (P < 0.0001).

CONCLUSION

Walnut leaf extracts can reduce the activity and localization of AR in the testes and its activity in the lens of diabetic rats.

Screening and Isolating Major Aldose Reductase Inhibitors from the Seeds of Evening Primrose (Oenothera biennis)

Aldose reductase (AR) is a drug target for therapies to treat complications caused by diabetes mellitus, and the development of effective AR inhibitors (ARIs) of natural origin is considered to be an attractive option for reducing these complications. In this research, the rat lens AR (RLAR) inhibitory activity of evening primrose (Oenothera biennis) seeds was investigated for the first time. In our results, the 50% (v/v) methanol extract of evening primrose seeds exhibits excellent RLAR inhibitory activity (IC₅₀ value of 7.53 μg/mL). Moreover, after enrichment of its bioactive components, the ARIs are more likely to be present in the ethyl acetate fraction of 50% (v/v) methanol extract (EME) of evening primrose seeds, which exhibits superior RLAR inhibitory activity (IC₅₀ value of 3.08 µg/mL). Finally, gallic acid (1), procyanidin B3 (2), catechin (3), and methyl gallate (4) were identified as the major ARIs from the EME by affinity-based ultrafiltration-high-performance liquid chromatography and were isolated by high speed countercurrent chromatography, with gallic acid (11.46 µmol/L) and catechin (14.78 µmol/L) being the more potent inhibitors of the four ARIs identified. The results demonstrated that evening primrose seeds may be a potent ingredient of ARIs.

3-Hydroxykynurenine Transamination Leads to the Formation of the Fluorescent Substances in Human Lenses

The levels of alanine, aspartate and glutamine transaminase increase considerably in some diseases. We measured the activity of these enzymes and of the transaminase of 3-hydroxykynurenine, an aminoacid, which acts as a UV lens filter. Alanine and glutamine transaminases (carboxypeptidase) were not detected in normal and cataractous human lenses, and aspartate transaminase was found only in the cortex of normal lenses. 3-hydroxykynurenine transaminase was not found in lenses from persons below thirty years of age, but was found in lenses at about fifty years of age, and in cataractous lenses. Transamination of 3-hydroxykynurenine leads to the formation of xanthurenic acid and its derivatives. These substances appear to be responsible for the increase of lens fluorescence during cataract development.

Simultaneous separation of taxon-specific crystallins from Mule duck and characterization of their enzymatic activities and structures

Methods to obtain pure proteins in large amounts are indispensible in protein research. We report here a large-scale/simultaneous isolation of taxon-specific crystallins (ɛ- and δ-crystallin) from the eye lenses of Mule duck. We also investigate the compositions, enzymatic activities, and structures of these purified taxon-specific proteins. A relatively mild method of ion-exchange chromatography was developed to fractionate ɛ-crystallin and δ-crystallin in large amount, ca. ∼6.60mg/g-lens and ∼41.0mg/g-lens, respectively. Both crystallins were identified by electrophoresis, HPLC, and MALDI-TOF-MS. ɛ-Crystallin, with native composition of M_r 142kDa, consisted of two subunits of 35kDa and 36kDa, while δ-Crystallin, with native molecular mass of 200kDa, comprised single subunit of M_r ∼50kDa. Both ɛ- and δ-crystallin were tetramers. The former showed lactate dehydrogenase (LDH) activity, while the latter appeared slightly active in an argininosuccinate lyase (ASL) assay. Raman spectroscopic results indicated that the secondary structures of ɛ- and δ-crystallin were predominantly α-helix as evidenced by the vibrational stretching of amide III over 1260cm^-1 and amide I at 1255cm^-1, in greatly contrast to the anti-parallel β-sheet of α- and β-crystallin as demonstrated by amide III at 1238cm^-1 and amide I at 1672cm^-1. The microenvironments of aromatic amino acids and the status of thiol groups also vary in different crystallins. The compositions, enzyme activities, and structures of the ɛ- and δ-crystalline of Mule duck are different from those of Muscovy duck (Cairina moschata) or Kaiya duck (Anas Platyrhynchos var. domestica), which reflect faithfully species specificity.

Chemical Constituents of Smilax china L. Stems and Their Inhibitory Activities against Glycation, Aldose Reductase, α-Glucosidase, and Lipase

The search for natural inhibitors with anti-diabetes properties has gained increasing attention. Among four selected Smilacaceae family plants, Smilax china L. stems (SCS) showed significant in vitro anti-glycation and rat lens aldose reductase inhibitory activities. Bioactivity-guided isolation was performed with SCS and four solvent fractions were obtained, which in turn yielded 10 compounds, including one phenolic acid, three chlorogenic acids, four flavonoids, one stilbene, and one phenylpropanoid glycoside; their structures were elucidated using nuclear magnetic resonance and mass spectrometry. All solvent fractions, isolated compounds, and stem extracts from plants sourced from six different provinces of South Korea were next tested for their inhibitory effects against advanced glycation end products, as well as aldose reductase. α-Glucosidase, and lipase assays were also performed on the fractions and compounds. Since compounds 3, 4, 6, and 8 appeared to be the superior inhibitors among the tested compounds, a comparative study was performed via high-performance liquid chromatography with photodiode array detection using a self-developed analysis method to confirm the relationship between the quantity and bioactivity of the compounds in each extract. The findings of this study demonstrate the potent therapeutic efficacy of SCS and its potential use as a cost-effective natural alternative medicine against type 2 diabetes and its complications.

Gigantol from Dendrobium chrysotoxum Lindl. binds and inhibits aldose reductase gene to exert its anti-cataract activity: An in vitro mechanistic study

ETHNOPHARMACOLOGICAL RELEVANCE

Dendrobium. chrysotoxum Lindl is a commonly used species of medicinal Dendrobium which belongs to the family of Orchidaceae, locally known as "Shihu" or "Huangcao". D. chrysotoxum Lindl is widely known for medicinal values in traditional Chinese medicine as it possesses anti-inflammatory, anti-hyperglycemic induction, antitumor and antioxidant properties.

STUDY AIM

To characterize the interaction between gigantol extracted from D. chrysotoxum Lindl and the AR gene, and determine gigantol's efficacy against cataractogenesis.

MATERIALS AND METHODS

Human lens epithelial cells (HLECs) were induced by glucose as the model group. Reverse transcription polymerase chain reaction (RT-PCR) was used to assess AR gene expression. Then, the mode of interaction of gigantol with the AR gene was evaluated by UV-visible spectroscopy, atomic force microscope (AFM) and surface-enhanced Raman spectroscopy (SERS). The binding constant was determined by UV-visible.

RESULTS

Gigantol depressed AR gene expression in HLECs. UV-visible spectra preliminarily indicated that interaction between the AR gene and gigantol may follow the groove mode, with a binding constant of 1.85×10³L/mol. Atomic force microscope (AFM) data indicated that gigantol possibly bound to insert AR gene base pairs of the double helix. Surface-enhanced Raman spectroscopy (SERS) studies further supported these observations.

CONCLUSION

Gigantol extracted from D. chrysotoxum Lindl not only has inhibitory effects on aldose reductase, but also inhibits AR gene expression. These findings provide a more comprehensive theoretical basis for the use of Dendrobium for the treatment of diabetic cataract.

Flavonoids from Litsea japonica Inhibit AGEs Formation and Rat Lense Aldose Reductase In Vitro and Vessel Dilation in Zebrafish

In our ongoing efforts to identify effective naturally sourced agents for the treating of diabetic complications, two new (1 and 2) and 11 known phenolic compounds (3-13) were isolated from an 80 % ethanol extract of Litsea japonica leaves. The structures of the new compounds were established by spectroscopic and chemical studies. These isolates (1-13) were subjected to an in vitro bioassay evaluating their inhibitory activity on advanced glycation end products formation and rat lens aldose reductase activity. Of the compounds evaluated, the flavonoids (3, 4, 6-8, 11, and 12) markedly inhibited advanced glycation end products formation, with IC₅₀ values of 7.4-72.0 µM, compared with the positive control, aminoguanidine (IC₅₀ = 975.9 µM). In the rat lens aldose reductase assay, consistent with the inhibition of advanced glycation end products formation, the flavonoids (3, 4, 6-8, 11, and 12) exhibited considerable inhibition of rat lens aldose reductase activity, with IC₅₀ values of 1.1-12.5 µM. In addition, the effects of kaempferol (4) and tiliroside (7) on the dilation of hyaloid-retinal vessels induced by high glucose in larval zebrafish were investigated. Only kaempferol significantly reduced the diameters of high glucose-induced hyaloid-retinal vessels, by 52.2 % at 10 µM, compared with those in the high glucose-treated control group.

Characterization of Emodin as a Therapeutic Agent for Diabetic Cataract

Aldose reductase (AR) in the lens plays an important role in the pathogenesis of diabetic cataract (DC) by contributing to osmotic and oxidative stress associated with accelerated glucose metabolism through the polyol pathway. Therefore, inhibition of AR in the lens may hold the key to prevent DC formation. Emodin, a bioactive compound isolated from plants, has been implicated as a therapy for diabetes. However, its inhibitory activity against AR remains unclear. Our results showed that emodin has good selectively inhibitory activity against AR (IC50 = 2.69 ± 0.90 μM) but not other aldo-keto reductases and is stable at 37 °C for at least 7 days. Enzyme kinetic studies demonstrated an uncompetitive inhibition against AR with a corresponding inhibition constant of 2.113 ± 0.095 μM. In in vivo studies, oral administration of emodin reduced the incidence and severity of morphological markers of cataract in lenses of AR transgenic mice. Computational modeling of the AR-NADP(+)-emodin ternary complex indicated that the 3-hydroxy group of emodin plays an essential role by interacting with Ser302 through hydrogen bonding in the specificity pocket of AR. All the findings above provide encouraging evidence for emodin as a potential therapeutic agent to prevent cataract in diabetic patients.

Phenolic Compounds from the Leaves and Twigs of Osteomeles schwerinae That Inhibit Rat Lens Aldose Reductase and Vessel Dilation in Zebrafish Larvae

Three new phenolic biphenyl derivatives (1-3) and one new lignan glycoside (4) were isolated from the leaves and twigs of Osteomeles schwerinae. The structures of the new compounds were established by spectroscopic data interpretation. The inhibitory effects of 1-4 on rat lens aldose reductase in vitro were examined, and compounds 1-3 markedly inhibited the enzyme with IC50 values of 3.8 to 13.8 μM. In addition, the effects of these isolates on the dilation of hyaloid-retinal vessels induced by high glucose (HG) in zebrafish larvae were investigated. Compound 1 was the most effective in reducing HG-induced dilation of hyaloid-retinal vessels.

RAC1 overexpression promotes the proliferation, migration and epithelial-mesenchymal transition of lens epithelial cells

Cataract is a main cause of blindness worldwide. RAC1 has been reported to have a close relationship with the proliferation and migration of cells. However, the relationship between RAC1 and cataract is not yet clear. The proliferation and migration of lens epithelial cells are key factors in the formation of cataract as well as in the complication of cataract surgery. In this study, the effect of RAC1 overexpression on the proliferation and migration of lens epithelial cells was explored. Results showed that RAC1 overexpression promoted the proliferation of lens epithelial cells and increased the protein level of proliferating cell nuclear antigen. RAC1 overexpression also promoted migration and invasion of lens epithelial cells and had an influence on the epithelial-mesenchymal transition process. These results indicate that RAC1 may become a therapeutic target of cataract and inhibition of RAC1 may become a promising way for the therapy of cataract.

Inhibition of p38 mitogen-activated protein kinase phosphorylation decreases H₂O₂-induced apoptosis in human lens epithelial cells

BACKGROUND

Oxidative damage resulting from ROS is a known causal factor for cataractogenesis. The mitogen-activated protein kinases (MAPK) pathway plays an important role in the apoptosis of HLE cells. The purpose of this study was to investigate the role of phosphorylated p38 mitogen-activated protein kinase in H2O2-induced apoptosis in cultured human lens epithelial (HLE) cells.

METHODS

The effect of SB203580 on HLE cells treated with H2O2 was determined by various assays. Cell viability was monitored by the MTT assay. The rates of apoptosis and ROS generation were determined by flow cytometric analysis. The numbers of mitotic and apoptotic cell nuclei were determined after staining with Hoechst 33342. The protein level of phospho-p38 was measured using western blot analysis.

RESULTS

SB203580 reduced H2O2-induced cellular apoptosis and inhibited the generation of reactive oxygen species (ROS); it also delayed the progression of H2O2-induced opacification of lenses. The level of p-p38 was increased when cells were exposed to H2O2 and significantly SB203580-inhibited phosphorylation of p38. The p38MAPK pathway plays an important role in H2O2-induced apoptosis of HLE cells.

CONCLUSIONS

The study demonstrates that activation of p38MAPK plays an important role in H2O2-induced apoptosis of HLE cells. SB203580 may potentially be exploited as a useful tool for cataract prevention.

Evaluation of in vitro aldose reductase inhibitory potential of alkaloidal fractions of Piper nigrum, Murraya koenigii, Argemone mexicana, and Nelumbo nucifera

BACKGROUND

Aldose reductase is primarily involved in development of long-term diabetic complications due to increased polyol pathway activity. The synthetic aldose reductase inhibitors are not very successful clinically. Therefore, the natural sources may be exploited for safer and effective aldose reductase inhibitors.

METHODS

In the present study, the aldose reductase inhibitory potential of hydroalcoholic and alkaloidal extracts of Piper nigrum, Murraya koenigii, Argemone mexicana, and Nelumbo nucifera was evaluated. The hydroalcoholic and alkaloidal extracts of the selected plants were prepared. The different concentrations of hydroalcoholic and alkaloidal extracts of these plants were evaluated for their goat lens aldose reductase inhibitory activity using dl-glyceraldehyde as substrate. The aldose reductase inhibitory potential of extracts was assessed in terms of their IC50 value.

RESULTS

Amongst the hydroalcoholic extracts, the highest aldose reductase inhibitory activity was shown by P. nigrum (IC50 value 35.64±2.7 μg/mL) followed by M. koenigii (IC50 value 45.67±2.57 μg/mL), A. mexicana (IC50 value 56.66±1.30 μg/mL), and N. nucifera (IC50 value 59.78±1.32 μg/mL). Among the alkaloidal extracts, highest inhibitory activity was shown by A. mexicana (IC50 value 25.67±1.25 μg/mL), followed by N. nucifera (IC50 value 28.82±1.85 μg/mL), P. nigrum (IC50 value 30.21±1.63 μg/mL), and M. koenigii (IC50 value 35.66±1.64 μg/mL).

CONCLUSIONS

It may be concluded that the alkaloidal extracts of these plants possess potent aldose reductase inhibitory activity and may be therapeutically exploited in diabetes-related complications associated with increased activity of aldose reductase.

Grape seed extract and zinc containing nutritional food supplement prevents onset and progression of age-related cataract in wistar rats

OBJECTIVE

To study possible inhibition of oxidative stress and cataract formation by single combined formulation of grape seed extract and Zincovit tablets against sodium selenite-induced age-related cataract in Wistar rat pups.

METHODS

Oxidative stress and consequent cataract formation was induced by subcutaneous administration of a single dose of sodium selenite (10 µmoles/kg) to Wistar rat pups on day 7 post-natally. In experiments designed to inhibit such cataract formation, the pups were pretreated subcutaneously with combined formulation of grape seed extract and Zincovit tablets (40, 80 and 160 mg/kg), one day prior to the administration of selenite and continuing such treatment till day 20, when the experiments were terminated. The extent of tissue damage caused by the selenite was assessed biochemically by measurements of the levels of reduced glutathione, glutathione peroxidase, glucose-6-phosphate dehydrogenase, protein thiol, catalase, superoxide dismutase, malondialdehyde, aldose reductase, sorbitol dehydrogenase and adenosine triphosphate in the isolated lenses. Cataract formation and its prevention were monitored by examining the eye with pen light illumination and subsequent photography of the isolated lenses.

RESULTS

Injection of selenite led to a significant loss of lens clarity due to cataract formation. In the group treated with combined formulation of grape seed extract and Zincovit tablets, the formation of cataract was significantly prevented. In the normal and selenite induced senile cataract control group, the levels of lens oxidative stress markers, G6PD and ATP were substantially lower than in the grape seed extract with Zincovit tablets treated group (p < 0.05).

CONCLUSION

Over all, the results suggest that single combined formulation of grape seed extract and Zincovit tablets may offer a prophylactic measure against onset and progression of age- related cataract of human subjects as nutritional food supplement.

Presence and distribution of L-kynurenine aminotransferases immunoreactivity in human cataractous lenses

PURPOSE

To investigate the presence and distribution of l-kynurenine aminotransferases immunoreactivity in human and animal lenses during cataract formation.

METHODS

Immunohistochemistry was conducted using polyclonal antibodies against KAT I, KAT II and KAT III on sections of 26 anterior capsules from patients undergoing surgical treatment of anterior subcapsular cataract (ASC) and 22 cataractous lenses from human eyes enucleated because of choroidal malignant melanoma. Additionally, the eyes of 11-month-old DBA/2J mice (6 eyes) were investigated (with KAT I and II). Ten clear human lenses and four BL6 mice lenses were used as controls. Spatial immunoreactivity patterns of enzymes were compared with Periodic Acid - Schiff (PAS)-stained sections.

RESULTS

Immunohistochemical analysis revealed presence of KAT I, KAT II and KAT III in extracellular structures of all studied types of cataract in human eyes showing specific pattern of the stain. In cortical cataract, immunoreactivity was observed on cortical lens fibres. In nuclear cataract, KAT II revealed stronger and diffused staining than KAT I. Additionally, both KAT showed more pronounced staining at the edge of small clefts. In normal human lenses, KAT I, II and III, immunoreactivity was not observed. Presence of KAT I and KAT II in the intercellular substance of DBA/2J mice cataract was observed. In BL6 mice lenses without cataract, only weak KAT I and KAT II staining was observed.

CONCLUSIONS

Presence of l-kynurenine aminotransferases in extracellular matrix (ECM) during human cataract formation suggests that products of l-kynurenine pathway might be involved in mechanisms of cataractogenesis.

Kinetics and molecular docking studies of an anti-diabetic complication inhibitor fucosterol from edible brown algae Eisenia bicyclis and Ecklonia stolonifera

In the present study, we investigated the anti-diabetic potential of fucosterol by evaluating the ability of this compound to inhibit rat lens aldose reductase (RLAR), human recombinant aldose reductase (HRAR), protein tyrosine phosphatase 1B (PTP1B), and α-glucosidase. Fucosterol displayed moderate inhibitory activity against RLAR, HRAR, and PTP1B. However, it showed weak or no activity against AGE formation and α-glucosidase. In addition, our kinetic study revealed that fucosterol showed a mixed type inhibition against RLAR and HRAR, while it noncompetitively inhibited PTP1B. Since fucosterol inhibited aldose reductase (AR), it holds great promise for use in the treatment of diabetic complications. Therefore, we predicted the 3D structure of AR in rat and human using the Autodock program to simulate binding between AR and fucosterol and evaluate the binding site-directed inhibition of AR by fucosterol. Results of the docking simulations of fucosterol demonstrated negative binding energies (-8.2 kcal/mol for RLAR and -8.5 kcal/mol for HRAR), which indicated a higher affinity and tighter binding capacity of fucosterol for the active site of the enzyme. In particular, the hydrophobic ring system and the aliphatic side chain of fucosterol were found to be tightly bound in a specificity pocket through apolar amino acid residues on AR, while the anion binding site on AR interacts with the 3-hydroxyl group and the double bond on the side chain of fucosterol. The results of the present study clearly demonstrated the potential of using fucosterol for the management and treatment of diabetes and diabetes-associated complications.

Inhibition of aldose reductase by Aegle marmelos and its protective role in diabetic cataract

ETHNOPHARMACOLOGICAL RELEVANCE

Aegle marmelos (L.) Corr. Serr. (Aegle marmelos) leaves were extensively used in the Ayurvedic, Unani and Siddha systems of Indian medicine as an anti-diabetic agent, which serves as hypoglycemic agent. However, the significance of this plant on secondary complications of diabetes such as cataract remained unknown. The aim of the study was to investigate the possible anti-cataractous activity of Aegle marmelos against streptozotocin (STZ) induced diabetic cataract in rats.

MATERIALS AND METHODS

Aegle marmelos leaf extract was prepared using three different solvents (petroleum ether, ethyl acetate and methanol) and tested for inhibition against rat lens aldose reductase (AR), a key enzyme of polyol pathway. Furthermore, the pharmacological potential of Aegle marmelos extract was investigated against osmotic stress induced opacification of lens in ex vivo organ culture and streptozotocin (STZ) induced diabetic cataract in rats.

RESULTS

Ethyl acetate extract of Aegle marmelos inhibited rat lens AR in vitro with an IC50 value of ≈ 15 µg/ml. This extract also prevented the hyperglycemia induced increase in AR activity, sorbitol accumulation and opacification of rat lens in ex vivo lens organ culture. Supplementation of ethyl acetate extract of Aegle marmelos to STZ-induced diabetic rats decreased the blood glucose levels due to hyperglycemia and inhibited the AR activity and delayed cataract progression in dose dependent manner. α-crystallin isolated from diabetic rats fed with Aegle marmelos showed improved chaperone activity than that of isolated from rats naïve to Aegle marmelos.

CONCLUSION

This study indicates that ethyl acetate extract of Aegle marmelos has pharmacologically active components with a potential to inhibit rat lens AR and consequential decrease in osmotic stress. Besides this, the present study also demonstrates that the extract prevented loss of antioxidants contributing to the integrity of α-crystallin's chaperone activity and thereby delaying cataract.

In vitro and in vivo inhibitory activities of four Indian medicinal plant extracts and their major components on rat aldose reductase and generation of advanced glycation endproducts

The polyol enzyme aldose reductase (AR) and advanced glycation endproducts (AGEs) play an important role in diabetic complications such as cataracts. The purpose of this study was to investigate four standardized plant extracts used for the treatment of diabetes and related diseases, and their principal components for AR inhibitory activity and to find out their influence in diabetic complications. Thus, Boswellia serrata Triana & Planch. (Burseraceae), Lagerstroemia speciosa (L.) Pers. (Lythraceae), Ocimum gratissimum (L.) (Lamiaceae) and Syzygium cumin (L.) Skeels. (Myrthaceae) and their respective major constituents, boswellic acid, corosolic acid, ursolic acid and ellagic acid, were studied for their inhibitory activity against rat lens AR, rat kidney AR, human recombinant AR and generation of AGEs. In addition, in vivo inhibition of lens galactitol accumulation by the major constituents of the plants in galactose-fed rat has been studied. The results revealed that all the tested extracts and their active ingredients possess significant AR inhibitory actions in both in vitro and in vivo assays with urosolic acid showing the most potent effect. Furthermore, the study indicates the potential of the studied plants and their major constituents as possible protective agents against long-term diabetic complications.

Xanthine oxidase and lens oxidative stress markers in diabetic and senile cataract patients

Xanthine oxidase (XOD) is a prooxidant enzyme possibly implicated in diabetic lens injury and genesis of senile cataract (SC). We evaluated the impact of diabetes on XOD activity and its relationships with lens oxidative stress markers in patients operated on for SC. Serum and lens XOD activities, lens malondialdehyde (MDA), conjugated dienes, superoxide dismutase (SOD), glutathione peroxidase (GPx) and reduced glutathione (GSH) levels were measured in 62 non-diabetic and 29 diabetic patients operated on for SC. Lens XOD, SOD, GPx and GSH levels were gradually declining, while MDA and serum XOD were increasing with patient's age. Lens XOD activity was positively correlated with conjugated dienes concentration (rho=0.316; p=0.003) while being inversely correlated with age (rho=-0.371; p<0.001), indicating that low ocular expression of XOD could be related to lower intensity of oxidative stress and delayed occurrence of SC. When samples were adjusted for confounding factors, serum XOD (p<0.001), lens XOD (p=0.003) and conjugated dienes (p=0.002) were significantly higher in diabetic than in non-diabetic group. Lens SOD and GPx were moderately increased while MDA and GSH were unchanged in diabetic, compared with non-diabetic SC group. Blood HbA1C concentration was positively correlated with lens XOD (rho=0.346; p<0.001) as well as serum XOD activity (rho=0.485; p<0.001). These results suggest that poor glycemic control may upregulate systemic and ocular XOD activities contributing to lens oxidative stress and possibly to earlier onset of cataract.

Effect of methionine sulfoxide reductase B1 silencing on high-glucose-induced apoptosis of human lens epithelial cells

AIMS

To determine roles of methionine sulfoxide reductase B1 (MsrB1) in protecting lens mitochondria against oxidative damage, the influences of MsrB1 gene silencing on high-glucose-induced apoptosis in human lens epithelial (HLE) cells were studied.

MAIN METHODS

Our study used four groups of cells: normal control, MsrB1 gene silenced, high glucose (30mM) exposed and MsrB1 gene silenced cells followed with high glucose exposure. In all cases we detected cell viability, cell apoptosis rate, intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) levels, alteration of mitochondrial membrane potential, release of mitochondrial cytochrome c as well as an increase in activity of caspase-3.

KEY FINDINGS

The results showed that MsrB1 gene silencing by short interfering RNA (siRNA) in HLE cells clearly resulted in oxidative stress, decrease in mitochondrial membrane potential and release of mitochondrial cytochrome c as well as an increase in activity of caspase-3 and the percentage of apoptotic cells. When MsrB1-silenced HLE cells were exposed to high glucose, characteristic of high-glucose-induced mitochondrial dysfunctions were further exacerbated.

SIGNIFICANCE

MsrB1 plays important roles in protecting HLE cell mitochondria against oxidative damage and inhibits oxidative stress-induced apoptosis in diabetic cataracts by scavenging ROS.

[Study on anti-cataract effect of gigantol combined with syringic acid and their mechanism]

OBJECTIVE

To study the anti-cataract effect of gigantol combined with syringic acid and their action mechanism.

METHOD

H202-induced lens oxidative injury in vitro rat model was establish to observe the impact of gigantol combined with syringic acid on lens transparency under a dissecting microscope. D-galactose-induced cataract rat model was established to observe the impact of gigantol combined with syringic acid on lens transparency under a slit-lamp. UV spectrophotometry was adopted to detect the inhibitory activity of gigantol combined with syringic acid against AR. Molecular docking method was used to detect binding sites, binding types and pharmacophores of gigantol combined with syringic acid in prohibiting aldose reductase.

RESULT

Both in vitro and in vivo experiments showed a good anti-sugar cataract activity in the combination of gigantol and syringic acid and a better collaborative effect than single component-gigantol and syringic acid and positive control drug Catalin. Molecular docking and dynamic simulation showed their collaborative AR-inhibiting amino acid residue was Asn160 and the major acting force was Van der Waals' force, which formed common pharmacophores.

CONCLUSION

Gigantol combined with syringic acid shows good anti-cataract, their action mechanism is reflected in their good collaborative inhibitory effect on AR.

The isolation and characterization of β-glucogallin as a novel aldose reductase inhibitor from Emblica officinalis

Diabetes mellitus is recognized as a leading cause of new cases of blindness. The prevalence of diabetic eye disease is expected to continue to increase worldwide as a result of the dramatic increase in the number of people with diabetes. At present, there is no medical treatment to delay or prevent the onset and progression of cataract or retinopathy, the most common causes of vision loss in diabetics. The plant Emblica officinalis (gooseberry) has been used for thousands of years as a traditional Indian Ayurvedic preparation for the treatment of diabetes in humans. Extracts from this plant have been shown to be efficacious against the progression of cataract in a diabetic rat model. Aldose reductase (ALR2) is implicated in the development of secondary complications of diabetes including cataract and, therefore, has been a major drug target for the development of therapies to treat diabetic disease. Herein, we present the bioassay-guided isolation and structure elucidation of 1-O-galloyl-β-D-glucose (β-glucogallin), a major component from the fruit of the gooseberry that displays selective as well as relatively potent inhibition (IC₅₀ = 17 µM) of AKR1B1 in vitro. Molecular modeling demonstrates that this inhibitor is able to favorably bind in the active site. Further, we show that β-glucogallin effectively inhibits sorbitol accumulation by 73% at 30 µM under hyperglycemic conditions in an ex-vivo organ culture model of lenses excised from transgenic mice overexpressing human ALR2 in the lens. This study supports the continued development of natural products such as β-glucogallin as therapeutic leads in the development of novel therapies to treat diabetic complications such as cataract.

Evaluation of in vitro aldose reductase inhibitory potential of different fraction of Hybanthus enneaspermus Linn F. Muell

OBJECTIVE

To evaluate the aldose reductase inhibitory (ARI) activity of different fractions of Hybanthus enneaspermus for potential use in diabetic cataract.

METHODS

Total phenol and flavonoid content of different fractions was determined. ARI activity of different fractions in rat lens was investigated in vitro.

RESULTS

The results showed significant level of phenolic and flavonoid content in ethyl acetate fraction [total phenol (212.15±0.79 mg/g), total flavonoid (39.11±2.27 mg/g)] and aqueous fraction [total phenol (140.62±0.57 mg/g), total flavonoid (26.07±1.49 mg/g)] as compared with the chloroform fraction [total phenol (68.56±0.51 mg/g), total flavonoid (13.41±0.82 mg/g)] and petrolium ether fraction [total phenol (36.68±0.43 mg/g), total flavonoid (11.55±1.06 mg/g)]. There was a significant difference in the ARI activity of each fraction, and it was found to be the highest in ethyl acetate fraction [IC50 (49.26±1.76 µg/mL)] followed by aqueous extract [IC50 (70.83±2.82 µg/mL)] and it was least in the petroleum ether fraction [IC50 (118.89±0.71 µg/mL)]. Chloroform fraction showed moderate activity [IC50 (98.52±1.80 µg/mL)].

CONCLUSIONS

Different fractions showed significanct amount of ARI activity, where in ethyl acetate fraction it was found to be maximum which may be due to its high phenolic and flavonoid content. The extract after further evaluation may be used in the treatment of diabetic cataract.

Inhibitory effect of two Indian medicinal plants on aldose reductase of rat lens in vitro

OBJECTIVE

To assesse the inhibitory effect of alcoholic extract of two Indian medicinal plants namely Ceasalpinia digyna Rottler and, Alangium lamarckii Thwaits on aldose reductase (AR) of rat lens.

METHODS

Rats lens were enucleated through posterior approach and their homogenate was prepared and centrifuged to obtain a clear supernatant for the determination of AR activity and protein content.

RESULTS

The alcoholic extract of Ceasalpinia digyna and Alangium lamarckii had a potent inhibitory effect on the lens AR enzyme. The IC(50) values of alcoholic extract of the selected plants were calculated and were (46.29±11.17) and (106.00±5.11) μg/mL, respectively. Quercetin was used as a positive control and its IC(50) value was (2.95±1.53) μg/mL.

CONCLUSIONS

Thus, it is concluded that alcoholic extracts of the selected plant exhibit significant inhibitory effects on AR in the rat lens in vitro.

Oxidative stress defense and repair systems of the ocular lens

It is well accepted that reactive oxygen species (ROS) play a critical role in many biological processes including disease and longevity. Oxidation of proteins has been linked to many disease states and even the aging process itself. This was first proposed as "The free radical theory of aging" in 1956 by Denham Harman which suggests that free radicals causes cumulative and irreversible damage to macromolecules, loss of cellular function and cell death over time directly impacting health and lifespan. Cellular damage from ROS exposure has been termed oxidative stress, which is an imbalance between cellular ROS production and the ability of the cell to regulate ROS levels and repair damage caused by ROS. This review focuses on the role of oxidative stress in the eye lens as a model for understanding the role of oxidative stress systems in age-related human disease.

Regulation of cytosolic phospholipase A2 (cPLA2alpha) and its association with cell proliferation in human lens epithelial cells

PURPOSE

To investigate the molecular mechanism for cytosolic phospholipase A2 (cPLA(2)α) regulation and its association to platelet-derived growth factor (PDGF)-induced cell proliferation.

METHODS

cPLA(2)α was examined using human lens epithelial (HLE) B3 cells. Reactive oxygen species (ROS) generation induced by PDGF was analyzed by luminescence assay. Cell proliferation was measured by cell counting and by BrdU assay. Human cPLA(2)α gene was cloned via RT-PCR followed by site-directed mutagenesis to construct HLE B3 cells expressing either inactive cPLA(2)α enzyme with S228A mutation (S228A), or cPLA(2)α truncated at the calcium-binding C2 domain (C2D). Activity of cPLA(2)α was measured by arachidonic acid (AA) release from cell membranes using [(3)H]-arachidonic acid prelabeled cells. The effect of intracellular calcium level on cPLA(2)α function was examined by treating cells with ionomycin (calcium influx), thapsgargin (endoplasmic reticulum [ER] calcium store release) or 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis (BAPTA; calcium chelator). Activation of extracellular signal-regulated kinases (ERK), JNK, p38, or Akt was detected by Western blot analysis using specific antibodies.

RESULTS

S228A mutant showed suppressed PDGF-induced reactive oxygen species generation, ERK and JNK activation (no effect on p38 or Akt), and cell proliferation in comparison with the vector alone (Vec) control. Calcium-binding C2 domain cells lost the ability of membrane translocation and activation of cPLA(2)α. PDGF cell signaling was calcium-dependent, and the calcium was supplied either from the external flux or endoplasmic reticulum store. However, enrichment of cellular calcium not only augmented PDGF function, but also demonstrated a cPLA(2)α-dependent calcium-signaling cascade that led to cell proliferation.

CONCLUSIONS

cPLA(2)α is regulated by calcium mobilization and mitogen-activated protein kinases (MAPK) activation. Both PDGF mitogenic action and calcium signaling are cPLA(2)α-dependent.

Insulin resistance mediated biochemical alterations in eye lens of neonatal streptozotocin-induced diabetic rat

Cataract, the leading cause of blindness worldwide, is associated with many risk factors including diabetes. Impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) states are associated with pre-diabetes and insulin resistance. This condition subsequently leads to the development of type-2 diabetes. Epidemiological studies indicated that not only diabetes but IGT/IFG will also lead to the development of microvascular disorders and cataract. However, there are no studies on the mechanism of insulin resistance induced changes in the eye lens. In the present study, IGT/IFG-induced changes in lens using neonatal-streptozotocin (nSTZ) rat model have been investigated. Though, nSTZ rats showed the signs of IGT and insulin resistance starting from two months old, they did not develop cataract even at the age of 8-months. However, biochemical analysis indicates a three-fold increase in sorbitol levels in nSTZ lens upon prolonged (6-months) IGT and insulin resistance. Also there was an increase in lipid peroxidation and alterations in antioxidant enzymes. Results of this study showed that activation of polyol pathway and increased oxidative stress, commonly associated with long-term complications of diabetes, have been observed in eye lens due to prolonged IGT and insulin resistance which may lead to cataract.

Spermidine delays eye lens opacification in vitro by suppressing transglutaminase-catalyzed crystallin cross-linking

A Ca(2+)-dependent TG activity, identified in the eye lens of several mammalian species, has long been implicated in cataract formation. The precise mechanism of the involvement of this enzyme in this process remains unclear. The purpose of this work was to investigate the modulatory effect of polyamines on TG activity during rabbit eye lens in vitro opacification. We observed, in an in vitro Ca(2+)-induced cataract model, a rapid decrease of the endogenous levels of SPD with the progression of opacification, paralleled by an increase of crystallin cross-linking by bis(γ-glutamyl)SPD. This pattern was reversed adding exogenous SPD to the incubation medium. Indeed, endogenous SPD levels were restored and cross-linking by bis(γ-glutamyl)SPD were drastically reduced. Surprisingly, under this experimental condition, the loss of transparency of lens was delayed. We found that exogenous SPD incubation led to a remarkable increase of mono(γ-glutamyl)SPD, likely responsible of the inhibition of cross-linking of lens crystallins and of the transparency persistence.

Aldose reductase-mediated induction of epithelium-to-mesenchymal transition (EMT) in lens

Cataract is a key factor in the morbidity associated with diabetes. While the pathogenesis of diabetic cataract formation is poorly understood, previous research has identified aldose reductase (ALR2) as a key player. To elucidate a potential role for this enzyme in diabetic cataract formation, we created a series of transgenic mice designed for expression of human ALR2 (AKR1B1) in epithelial and outer cortical fiber cells of the lens. One of the founder lines, designated PAR39, developed an early onset cataract that involved formation of a plaque of cells at the anterior aspect of the lens. These cells appear to separate from the anterior epithelium and undergo a dramatic change that is reminiscent of the epithelial to mesenchymal transition (EMT). We characterized this phenotype in the PAR39 strain by examining rates of cell proliferation and by immunostaining for markers of EMT. Incorporation of the thymidine analog bromodeoxyuridine (BrdU) was used to estimate cell proliferation in two functional areas of the lens epithelium: the mitotically active germinative zone (GZ) and the less proliferative center zone (CZ). Staining cell nuclei with diamido 4',6-diamidino-2-phenylindole (DAPI) was used to establish a total cell count in the demarcated areas. Lens epithelium in PAR39 transgenic mice demonstrated a decrease in the percentage of BrdU/DAPI staining within the GZ as compared to nontransgenic littermate controls (8.1% vs. 10.9%). A similar decrease in BrdU/DAPI was observed in the CZ (0.6% compared to 3.3%). However, cell density was greater within the GZ of PAR39 mice as compared with nontransgenic controls, while it was not significantly different in the CZ among the two groups. Furthermore, cells associated with the epithelial plaque did not stain positive for BrdU, but were strongly positive for alpha-smooth muscle actin, a classical marker for EMT. These findings suggest that ALR2 over-expression is associated with an alteration in the balance between proliferation and apoptosis of epithelial cells in the mouse lens, and that cells associated with epithelial plaques in the PAR39 lens have features in common with cells undergoing EMT.

Antiglycating potential of Zingiber officinalis and delay of diabetic cataract in rats

PURPOSE

Advanced glycation end products (AGE) are associated in the development of several pathophysiologies including diabetic cataract. Earlier we have reported that some common dietary agents have antiglycating activity and ginger (Zingiber officinalis) was one of the few prominent agents that effectively prevented AGE formation in vitro. In this study we investigated the potential of ginger to prevent diabetic cataract in rats.

METHODS

Diabetes was induced in Wistar-NIN rats by intraperitoneal injection of streptozotocin (35 mg/kg bodyweight) and the control rats received vehicle alone. While a set of diabetic animals received AIN-93 diet, another set received either 0.5 or 3% ginger in their diet for a period of two months. Cataract progression was monitored by slit-lamp biomicroscope. At the end of two months, the animals were sacrificed to evaluate non-enzymatic glycation and osmotic stress in the eye lens.

RESULTS

Slit-lamp examination revealed that feeding of ginger not only delayed the onset but also the progression of cataract in rats. Molecular analyses indicated that feeding of ginger significantly inhibited the formation of various AGE products including carboxymethyl lysine in the eye lens. In addition, ginger also countered hyperglycemia-induced osmotic stress in the lens.

CONCLUSIONS

The results indicated that ginger was effective against the development of diabetic cataract in rats mainly through its antiglycating potential and to a lesser extent by inhibition of the polyol pathway. Thus, ingredients of dietary sources, such as ginger, may be explored for the prevention or delay of diabetic complications.

Inhibitory effect of pyridyloxy- or phenoxylphenoxyalkanate derivatives on rat lens aldose reductase and rat platelet aggregation

The therapeutic potential of aldose reductase inhibitors for the prevention of the secondary complications of diabetes has been extensively reported. On the other hand, the hyperaggregability of platelets in diabetic patients has also been reported as a cause of chronic diabetic complications. The purpose of this study was to develop new compounds with these dual effects from pyridyloxy- or phenoxylphenoxyalkanate synthesized derivatives and examine the effect of their structure-activity relationships on the inhibition of rat lens aldose reductase (RLAR) as well as on platelet aggregation. 2-[4-(2,6-dichloro-3-methyl-phenoxy)-3-nitro-phenoxy]-propionic acid (3) exhibited the most potent inhibitory effect (IC50 = 3.0 ± 0.21 μM), comparable to tetramethylene glutaric acid (IC50 = 6.1 ±0.2 μM), which is used as a positive control on RLAR, and showed potent inhibitory activities on rat platelet aggregation induced by ADP and collagen (IC50 = 0.093 ± 0.01 and 0.032 ± 0.01 μM, respectively) comparable with aspirin (IC50 = 0.15 ± 0.05 and 0.047 ± 0.01 μM, respectively), used as a positive control.

Synthesis of flavonoids and their effects on aldose reductase and sorbitol accumulation in streptozotocin-induced diabetic rat tissues

Aldose reductase, the key enzyme of the polyol pathway, and oxidative stress are known to play important roles in the complications of diabetes. A drug with potent inhibition of aldose reductase and oxidative stress, therefore, would be a most promising drug for the prevention of diabetic complications. The purpose of this study was to develop new compounds with these dual-effects through synthesis of chalcone derivatives and by examining the structure-activity relationships on the inhibition of rat lens aldose reductase as well as on antioxidant effects. A series of 35 flavonoid derivatives were synthesized by Winget's condensation, oxidation, and reduction of appropriate acetophenones with appropriate benzaldehydes. The inhibitory activity of these derivatives on rat lens aldose reductase and their antioxidant effects, measured using Cu2+ chelation and radical scavenging activities on 1,1-diphenyl-picrylhydrazyl in-vitro, were evaluated. Their effect on sorbitol accumulation in the red blood cells, lenses and sciatic nerves of streptozotocin-induced diabetic rats was also estimated. Among the new flavonoid derivatives synthesized, those with the 2′,4′-dihydroxyl groups in the A ring such as 2,4,2′,4′-tetrahydroxychalcone (22), 2,2′,4′-trihydroxychalcone (11), 2′,4′-dihydroxy-2,4-dimethylchalcone (21) and 3,4,2′,4′-tetrahydroxychalcone (18) were found to possess the highest rat lens aldose reductase inhibitory activity in-vitro, their IC50 values (concentration of inhibitors giving 50% inhibition of enzyme activity) being 1.6 times 10−7, 3.8 times 10−7, 4.0 times 10−7 and 4.6 times 10−7 M, respectively. All of the chalcones tested except 3, 18, 23 with o-dihydroxy or hydroquinone moiety showed a weak free radical scavenging activity. In the in-vivo experiments, however, compound 18 with o-dihydroxy moiety in the B ring showed the strongest inhibitory activity in the accumulation of sorbitol in the tissues. It also showed the strongest activity in transition metal chelation and free radical scavenging activity. Of the 35 4,2′-dihydroxyl and 2′,4′-dihydroxyl derivatives of flavonoid synthesized, including chalcone, flavone, flavanone, flavonol and dihydrochalcone, some chalcone derivatives synthesized were found to possess aldose reductase inhibition and antioxidant activities in-vitro as well as inhibition in the accumulation of sorbitol in the tissues in-vivo. 3,4,2′,4′-Tetrahydroxychalcone (18, butein) was the most promising compound for the prevention or treatment of diabetic complications.

Glutathione synthetase of bovine lens: Anomalies of the enzyme-catalyzed formation of ophthalmic acid

The activity of glutathione synthetase from bovine lens was examined as a functions of the concentration of L-gamma-glutamyl-L-alpha-aminobutyrate, the dipeptide substrate required in the formation of ophthalmic acid. Several significant anomalies of the glutathione synthetase-catalyzed formation of ophthalmic acid were found. Curvilinearity of double reciprocal plots occurred with this substrate; this curvilinearity shows substrate activation of the reaction which is likely a result of negative cooperativity. Both ATP4- and, to a lesser extent Mg2+ inhibited the reaction, whereas MgATP2- is the substrate; maximum activity occurred with 2 mM Mg2+ in excess of the concentration of added ATP. This investigation shows that it is necessary to establish a defined set of conditions for reporting enzyme activity and that the usual practice of using very large concentrations of Mg2+ relative to ATP, and 5- to 20-fold excess of the dipeptide will give less than optimum activity. The unit of enzyme activity is suggested to be that activity in ml using 2 mM ATP, 4 mM Mg2+, 30 mM glycine and 15 mM L-gamma-glutamyl-alpha-aminobutyrate, which results in the formation of 1 nmole/minute of ADP or P(i). In this study, 5'-AMP was for the first time, shown to be an inhibitor of the reaction with a K(i) of 0.9 mM.

Inhibitors of aldose reductase and formation of advanced glycation end-products in moutan cortex (Paeonia suffruticosa)

The methanol extract of Moutan cortex (Paeonia suffruticosa) afforded two new compounds, 8-O-benzoylpaeonidanin (1) and 5-hydroxy-3S-hydroxymethyl-6-methyl-2,3-dihydrobenzofuran (2), in addition to 4-O-butylpaeoniflorin (3) as an artifact of the separation, seven monoterpene glycosides (4-10), two monoterpenes (11, 12), four acetophenones (13-16), and two triterpenes (17, 18). The structures of the compounds were determined by spectroscopic methods, and the compounds were evaluated for inhibitory effects against rat lens aldose reductase (RLAR) and advanced glycation end-product (AGEs) formation. Compounds 17 and 18 showed the most potent inhibitory activity against RLAR, with IC(50) values of 11.4 and 28.8 microM, respectively. Compounds 3 and 6 also inhibited RLAR with IC(50) values of 36.2 and 44.6 microM, respectively. The positive control, 3,3-tetramethyleneglutamic acid, had an IC(50) value of 31.8 microM. Compounds 3 and 6 inhibited AGE formation with IC(50) values of 10.8 and 11.3 microM, respectively. Compound 2 had an IC(50) value of 177.0 microM, whereas the positive control, aminoguanidine, had an IC(50) value of 1026.8 microM.

Revival of Glutathione Reductase in Human Cataractous and Clear Lens Extracts by Thioredoxin and Thioredoxin Reductase, in Conjunction with α -Crystallin or Thioltransferase

Glutathione reductase (GR) plays a key role in maintaining thiol groups in the lens, and its activity decreases with aging and cataract formation. Mammalian thioredoxin (Trx) and thioredoxin reductase (TrxR), or the Trx/TrxR system, participates in the repair of oxidatively damaged lens proteins and enzymes. Alpha-crystallin, a molecular chaperone, prevents the aggregation of partially denatured proteins under various stress conditions. Thioltransferase (TTase, or glutaredoxin) can maintain the homeostasis of lens protein thiols thus protecting against oxidative stress. We investigated whether the Trx/TrxR system can revive GR activity in both the cortex and nucleus of human cataract and clear aged lenses and whether alpha-crystallin and TTase can help this effect. The GR activity in the cortex and nucleus of the cataractous lenses was significantly lower than that of the aged clear lenses. The highest activity in the cortex was observed in the clear aged lenses. The combination of Trx and TrxR revived the activity of GR from both the cortex and nucleus of aged clear lenses. However, in cataract lenses (grade II and grade IV), there was a statistically significant recovery of GR activity in the cortex, but not in the nucleus. No recovery was observed when Trx or TrxR were used separately. Alpha-crystallin successfully revived GR activity in the cortex of cataract grade II lenses, but not in the nucleus. The combination of alpha-crystallin and Trx/TrxR gave a further increase of activity. TTase alone revived some of the GR activity but together with the Trx/TrxR system gave no statistically significant enhancement of GR activity. These results indicate that both disulfide bond formation and protein unfolding are responsible for GR inactivation.

Protein Kinase C-γ Activation in the Early Streptozotocin Diabetic Rat Lens

PURPOSE

The purpose of this study is to demonstrate the early activation of the protein kinase C-gamma (PKC-gamma) pathway in the streptozotocin (STZ)-induced diabetic rat lens.

METHODS

Twelve-week-old male and female Sprague-Dawley rats were injected with 80 mg/kg (body weight) of STZ (N-[methylnitrosocarbamoyl]-D-glucosamine) intraperitoneally. Very high glucose (VHG) diabetes was defined as a nonfasting blood glucose level of at least 450 mg/dl, confirmed by daily monitoring with Accu-Check Advantage test strips, and occurred about 2 weeks after STZ administration. All assayed lenses were from VHG or age-matched control rats, harvested within 24 hr of VHG detection. PKC-gamma activation was measured by enzyme activity assay and by Western blotting to show autophosphorylation on Thr514. Cellular insulin-like growth factor-1 (IGF-1), PKC-gamma phosphorylation of Cx43 on Ser368, and activation of phospholipase C-gamma 1 (PLC-gamma 1), extracellular signal-regulated kinase (ERK1/2), and caspase-3 were determined by Western blotting. Endogenous diacylglycerol (DAG) levels were measured with a DAG assay kit. Lens gap junction activity was determined by the microinjection/Lucifer yellow dye transfer assay. Electron microscopy was applied to affirm fiber cell damage in the VHG diabetic lenses.

RESULTS

In the lenses of VHG diabetic rats, PKC-gamma enzyme was activated. PKC-gamma could be further activated by 400 nM phorbol-12-myristate-13-acetate (PMA), but the PKC-gamma protein levels remained constant. No elevation of IGF-1 level was observed. Western blots showed that activation of PKC-gamma may be due to activation of PLC-gamma 1, which synthesized endogenous DAG, a native PKC activator. The level of PKC-gamma -catalyzed phosphorylation of Cx43 on Ser368 and resulting inhibition of lens gap junction dye transfer activity was increased in the VHG diabetic lenses. At this early time period, the diabetic lens showed no activation of either caspase-3 or ERK1/2. Only a single fiber cell layer deep within the cortex (approximately 90 cell layers from capsule surface) showed vacuoles and damaged cell connections.

CONCLUSIONS

Early activation of PLC-gamma 1 and elevated DAG were observed within VHG diabetic lenses. These were correlated with activation of PKC-gamma, phosphorylation of Cx43 on Ser368, and inhibition of dye transfer. Abnormal signaling from PKC-gamma to Cx43 in the epithelial cells/early fiber cells, observed within VHG diabetic lenses, may be responsible for fiber cell damage deeper in the lens cortex.

The effects of age on glutathione synthesis enzymes in lenses of Old World simians and prosimians

The activities of gamma-glutamylcysteine synthetase and glutathione synthetase, the two enzymes required for glutathione synthesis, were determined as a function of age in lenses of three species of Old World higher primates: orangutan, pigtail monkey and olive baboon. These were compared to enzyme activities in lenses of two prosimians: mouse lemur and galago. gamma-Glutamylcysteine synthetase activity decreased as a function of age in all three Old World simians. The rate of decrease was greatest in the juvenile lenses. In contrast, the enzyme activity increased continuously with age in the galago lens. In the mouse lemur the enzyme activity increased per lens, but was constant when expressed as specific activity or as units per gram of lens. The loss of enzyme activity with age was limited to Old World higher primates apparently representing genetic change. Glutathione synthetase activity decreased logarithmically with age in the lenses of all five species.

Expression of calpain small subunit 2 in mammalian tissues

PURPOSE

The purpose of the current experiments was to more closely define the distribution and the function of calpain small subunit 2 (css2). Css2 is a newly discovered regulatory protein for the calcium activated proteases, mu- and m-calpains.

METHODS

Tissues from rat, monkey, and man of various ages were used to determine expression patterns of css2 by relative quantitative RT-PCR using 18S rRNA as an endogenous standard. Recombinant css2 and the 80 kDa catalytic subunit of m-calpain (80 kDa/css2) were co-expressed in Escherichia coli. Casein zymography was used to measure the enzymatic activity of 80 kDa/css2 proteins. Lens alpha-crystallin and beta B1-crystallin were used as substrates to determine proteolysis by 80 kDa/css2. Computer-based homology modeling was used to predict interactions between the traditional small subunit (css1) or css2 with the 80 kDa catalytic subunit.

RESULTS

Css2 appears to be a functional equivalent of css1 in vitro in that the calcium-dependent proteolytic activity of 80 kDa/css2 was similar to recombinant m-calpain (80 kDa/css1). In rat and human lens, css2 transcripts increased with age, whereas css1 transcripts decreased with age. Human beta B1-crystallin and rat alpha A-crystallin were cleaved similarly by 80 kDa/css2 and 80 kDa/css1. Interestingly, alpha A-insert crystallin was not hydrolyzed when css2 was substituted for css1 in the calpain dimer, suggesting that css2 may perform different functions from css1 in terms of proteolysis of lens crystallins during maturational growth of the lens. Css2 may also assist in the proper folding of the 80 kDa subunit and regulate protease activity in the absence of calcium.

CONCLUSIONS

The wide distribution of css2 transcripts in rat and monkey suggested that css2 is a second, widely distributed (rather than tissue-specific) calpain small subunit, in addition to the long-recognized css1. Further studies at the protein level will indicate if css2 has unique functions apart from css1.

Glutathione-Related Enzymes and the Eye

Glutathione and the related enzymes belong to the defence system protecting the eye against chemical and oxidative stress. This review focuses on GSH and two key enzymes, glutathione reductase and glucose-6-phosphate dehydrogenase in lens, cornea, and retina. Lens contains a high concentration of reduced glutathione, which maintains the thiol groups in the reduced form. These contribute to lens complete transparency as well as to the transparent and refractive properties of the mammalian cornea, which are essential for proper image formation on the retina. In cornea, gluthatione also plays an important role in maintaining normal hydration level, and in protecting cellular membrane integrity. In retina, glutathione is distributed in the different types of retinal cells. Intracellular enzyme, glutathione reductase, involved in reducing the oxidized glutathione has been found at highest activity in human and primate lenses, as compared to other species. Besides the enzymes directly involved in maintaining the normal redox status of the cell, glucose-6-phosphate dehydrogenase which catalyzes the first reaction of the pentose phosphate pathway, plays a key role in protection of the eye against reactive oxygen species. Cornea has a high activity of the pentose phosphate pathway and glucose-6-phosphate dehydrogenase activity. Glycation, the non-enzymic reaction between a free amino group in proteins and a reducing sugar, slowly inactivates gluthathione-related and other enzymes. In addition, glutathione can be also glycated. The presence of glutathione, and of the related enzymes has been also reported in other parts of the eye, such as ciliary body and trabecular meshwork, suggesting that the same enzyme systems are present in all tissues of the eye to generate NADPH and to maintain gluthatione in the reduced form. Changes of glutathione and related enzymes activity in lens, cornea, retina and other eye tissues, occur with ageing, cataract, diabetes, irradiation and administration of some drugs.

Ocimum sanctumModulates Selenite-Induced Cataractogenic Changes and Prevents Rat Lens Opacification

PURPOSE

To study the effect of Ocimum sanctum (OS) on selenite-induced morphological and biochemical changes in isolated rat lenses as well as on cataract incidence in rat pups.

METHODS

Transparent rat lenses were divided into normal, selenite-only, and four treated groups. Selenite-only and treated group lenses were subjected to oxidative stress in vitro by incorporating sodium selenite (100 microM) in the culture medium. The effect of OS (70, 140, 280, and 560 microg/ml) was studied on the levels of reduced glutathione (GSH) and thiobarbituric acid reacting substances (TBARS) in selenite-challenged lenses. The lowest concentration of OS offering significant modulation on these two parameters was determined. Subsequently, the effect of prior and cotreatment with the lowest effective concentration of OS was studied on TBARS, GSH, and on lens antioxidant enzymes such as superoxide dismutase (SOD), glutathione peroxidase (GSHPx), catalase (CAT), and glutathione-S-transferase (GST). Changes in lens protein profiles under different incubation conditions were analyzed by SDS gel-electrophoresis. In vivo, cataract was induced by a single subcutaneous injection of sodium selenite (25 micromole/kg b.w.) to 9-day-old rat pups. The anticataract effect of OS (5 and 10 mg/kg b.w.) injected intraperitoneally 4 hr prior to selenite challenge was evaluated by the presence of lens nuclear opacity in rat pups on the 16th postnatal day. Insolubilization of lens proteins post-selenite injection was monitored for 4 days.

RESULTS

The lenses in the selenite-only group developed cortical opacities in 24 hr. OS showed different degrees of positive modulation in selenite-induced morphological as well as biochemical changes. The lowest effective dose of OS that significantly modulated glutathione and thiobarbituric acid reacting substances was found to be 140 microg/ml. At this dose, a significant increase in antioxidant enzyme levels and preservation of normal lens protein profile was observed. OS at the dose of 70 microg/ml did not show any significant protection with respect to either morphology or biochemistry of lenses. In vivo, 5 and 10 mg/kg of OS reduced the incidence of selenite cataract by 20% and 60%, respectively, and prevented protein insolubilization as well.

CONCLUSIONS

Aqueous extract of OS possesses potential anticataract activity against selenite-induced experimental cataractogenesis. The protective effect was supported by restoration of the antioxidant defense system and inhibition of protein insolubilization of rat lenses as well.

Effects of Mobile Phones on Oxidant/Antioxidant Balance in Cornea and Lens of Rats

PURPOSE

To investigate the effects of mobile-phone-emitted radiation on the oxidant/antioxidant balance in corneal and lens tissues and to observe any protective effects of vitamin C in this setting.

METHODS

Forty female albino Wistar rats were assigned to one of four groups containing 10 rats each. One group received a standardized daily dose of mobile phone radiation for 4 weeks. The second group received this same treatment along with a daily oral dose of vitamin C (250 mg/kg). The third group received this dose of vitamin C alone, while the fourth group received standard laboratory care and served as a control. In corneal and lens tissues, malondialdehyde (MDA) levels and activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) were measured with spectrophotometric methods.

RESULTS

In corneal tissue, MDA level and CAT activity significantly increased in the mobile phone group compared with the mobile phone plus vitamin C group and the control group (p < 0.05), whereas SOD activity was significantly decreased (p < 0.05). In the lens tissues, only the MDA level significantly increased in the mobile phone group relative to mobile phone plus vitamin C group and the control groups (p < 0.05). In lens tissue, significant differences were not found between the groups in terms of SOD, GSH-Px, or CAT (p > 0.05).

CONCLUSIONS

The results of this study suggest that mobile telephone radiation leads to oxidative stress in corneal and lens tissues and that antioxidants such as vitamin C can help to prevent these effects.

In vitro production of steroid cataract in bovine lens. Part II: measurement of sodium-potassium adenosine triphosphatase activity

Fresh calf lesnses incubated in nutritive media containing dexamethasone phosphate or ouabain in concentrations ranging from 1 X 10(-4) M to 1 X 10(-8) M developed cortical opacification and showed significant inhibition of Na(+)-K(+) ATP'ase activity. Over a 3-day incubation period the decrease in Na+-K+ ATP'ase activity correlated well with the observed decrease in light transmission. The degree of enzyme inhibition and decrease in light transmission varied directly with the concentration of dexamethasone phosphate and ouabain, with significant changes observed at 'physiologic' and 'pharmacologic' concentrations of these agents. Lenses incubated for 4 days in dexamethasone phosphate or ouabain showed substantial increases in water content as well as an increase in Na+ and a decrease in K+ concentration. These data suggest that inhibition of the cation pump may play a significant role in the formation of steroid cataract in vitro.

Interaction between Connexin50 and mitogen-activated protein kinase signaling in lens homeostasis

Both connexins and signal transduction pathways have been independently shown to play critical roles in lens homeostasis, but little is known about potential cooperation between these two intercellular communication systems. To investigate whether growth factor signaling and gap junctional communication interact during the development of lens homeostasis, we examined the effect of mitogen-activated protein kinase (MAPK) signaling on coupling mediated by specific lens connexins by using a combination of in vitro and in vivo assays. Activation of MAPK signaling pathways significantly increased coupling provided by Cx50, but not Cx46, in paired Xenopus laevis oocytes in vitro, as well as between freshly isolated lens cells in vivo. Constitutively active MAPK signaling caused macrophthalmia, cataract, glucose accumulation, vacuole formation in differentiating fibers, and lens rupture in vivo. The specific removal or replacement of Cx50, but not Cx46, ameliorated all five pathological conditions in transgenic mice. These results indicate that MAPK signaling specifically modulates coupling mediated by Cx50 and that gap junctional communication and signal transduction pathways may interact in osmotic regulation during postnatal fiber development.

Genetic variation in the purine nucleoside phosphorylase activity of sheep red cells

The purine nucleoside phosphorylase (NP) activity of sheep red cells was determined by starch gel electrophoresis and by a spectrophotometric assay technique. Some sheep had high activity (NP-high type) and some had low or zero activity (NP-low type). The enzyme deficiency is apparently confined to the red cell since other tissues from NP-low type animals had activities similar to those from NP-high type individuals. Family data indicated that NP activity is controlled by a pair of autosomal allelic genes, designated NPH and NPL. Sheep heterozygous for the NP genes had lower enzymic activities than homozygous high-type individuals. The frequency of NP types in different breeds of sheep was determined. Barbary and Mouflon sheep had activities similar to NP-high type domestic sheep; goats had high enzyme activities but their NP had a slower electrophoretic mobility than that of sheep.

Expression and activity of paraoxonase 1 in human cataractous lens tissue

Paraoxonase 1 (PON1) is a high-density lipoprotein-associated enzyme that is believed to be involved in the protection against oxidative stress. There is evidence that paraoxonase activity is reduced in patients with diabetes and cataract. In the current study, we analyzed mRNA expression of PON1 as well as other members of the paraoxonase family, PON2 and PON3, in human cataractous lens samples. Our results indicate that only PON1 is expressed at the gene and protein levels in human lens tissues. We quantified MDA levels and measured PON1 (paraoxonase/arylesterase) enzymatic activities in subjects suffering from cataract due to aging and diabetes. Decreased PON1 activity was more pronounced in diabetic patients (p< 0.001) compared to senile subjects, which may be due to glycation and increased oxidative insult. To examine the structural alterations that occur in response to glycation, we constructed a three-dimensional model of PON1 and its glycated variant. Glycation at Lys70 and Lys75 is predicted to cause hindrance in binding of substrate to the active site of the enzyme.

Molecular cloning and oxidative modification of human lens ALDH1A1: implication in impaired detoxification of lipid aldehydes

Earlier studies showed that human lens ALDH1A1 plays a critical role in protection against oxidative stress-induced cytotoxicity in human lens epithelial cells (HLEC), and opacification of rat and mouse lens. The complete coding sequence of ALDH1A1 was cloned from human lens cDNA library by using PCR methods and expressed it in Escherichia coli. The cloned human lens ALDH1A1 cDNA encodes a 501-amino-acid protein (molecular mass = 54.8 kD) that is 100% identical to human liver ALDH1A1 and shares significant identity with the same isozyme from other tissues and species. The purified recombinant human lens ALDH1A1 exhibited optimal catalytic activity at pH 8 and preferred NAD(+) as cofactor and specifically catalyzed the oxidation of toxic lipid aldehydes such as 4-hydroxynonenal (HNE; K(m) = 4.8 microM) and malonaldehyde (K(m) MDA = 3.5 microM). Citral, disulfiram, and cyanamide were found to inhibit human lens ALDH1A1 at IC50 values of 55, 101, and 22610 microM, respectively, whereas diethylstilbestrol (DES) was found to be an activator (EC(50), 1.3 microM). Further, modification of recombinant human lens ALDH1A1 with nitric oxide donors such as S-nitroso-N-acetylpenicillamine (SNAP) and S-nitrosoglutathione (GSNO) significantly inhibited the enzyme activity. It therefore appears that activation of ALDH1A1, which efficiently catalyzes the detoxification of lipid-derived toxic aldehydes, and/or prevention of its oxidative modification may be novel therapeutic interventions against oxidative stress-induced lens pathologies.

Changes in erythrocyte glucose-6-phosphate dehydrogenase (G6PD) and reduced glutathione (GSH) activities in the development of senile and diabetic cataracts

Oxidative and osmotic stress have been implicated in the pathogenesis of cataracts. Reactive oxygen intermediates (ROI) mediate peroxidation of membrane lipids and cause irreversible damage to lens proteins. The purpose of this study was to assess the changes in erythrocyte glucose- 6-phosphate dehydrogenase enzyme (G6PD) and reduced glutathione (GSH) levels in the development of senile and diabetic cataracts. The activity of erythrocyte G6PD and the concentration of GSH were measured to assess changes in oxidation-reduction status. The oxidation-reduction status of 26 non-diabetic non-cataract (control) subjects were compared with 24 diabetic non-cataract, 30 diabetic cataract and 28 non-diabetic cataract subjects. The results revealed that the GSH and G6PD levels of the subjects with senile cataracts were significantly lower than the subjects without cataracts. The present study reveals the risk of developing senile cataracts is associated with decreased levels of erythrocyte G6PD and GSH. In the formation of diabetic cataracts an adequate supply of NADPH (G6PD activity) is essential to produce osmotically active sorbitol in the lens.

Erigeroflavanone, a flavanone derivative from the flowers of Erigeron annuus with protein glycation and aldose reductase inhibitory activity

A novel 2,3-dioxygenated flavanone, erigeroflavanone ( 1), as well as eight known flavonoids and two known gamma-pyranone derivatives, were isolated from an ethyl acetate-soluble extract of the flowers of Erigeron annuus. The structure of compound 1 was elucidated by interpretation of spectroscopic data. All of the isolates were subjected to in vitro bioassays to evaluate their inhibitory activity against advanced glycation end products formation and rat lens aldose reductase.