Correlation between erythrocyte aldose reductase level and human diabetic retinopathy

Astaxanthin inhibits aldose reductase activity in Psammomys obesus, a model of type 2 diabetes and diabetic retinopathy

Astaxanthin (ATX) is a marine carotenoid known for its powerful antioxidant and neuroprotective properties. In this study, we investigated the in vitro and in vivo potential inhibitory effect of ATX on the aldose reductase (AR) activity, a key enzyme in the polyol pathway responsible for the pathogenesis of diabetic complications including diabetic retinopathy (DR). The gerbil Psammomys obesus (P. ob.), an animal model for type 2 diabetes and DR has been used. The erythrocyte and retinal AR activity of P. ob. individuals were, respectively, assessed monthly and at the 7th month during a 7-month hypercaloric diet (HD) using a NADPH oxidation method. Meanwhile, the body weight and blood glucose of the gerbils were monitored. After 7 months, P. ob. individuals were fed with ATX (4.8 mg/kg of body weight) once a day for 1 week. The results showed that the HD-fed animals developed significant obesity and hyperglycemia in comparison with controls. Erythrocyte AR activity showed a progressive and significant increase in the HD-fed group compared with controls. Retinal AR activity was higher in the 7-month HD-fed group compared with controls. Erythrocyte AR activity was markedly decreased after ATX-treatment in vitro and in vivo. These findings suggested that ATX inhibited the erythrocyte AR activity and could be used for DR prevention and/or early treatment.

[Enzymological Studies on the Mechanisms of Pathogenesis of Diabetic Complications]

　Aldose reductase (AR) is involved in the pathogenesis of complications in diabetes. In this study, the enzymatic properties of AR isolated from various sources and a recombinant human AR (rh-AR) were analyzed in detail. The sensitivity of different forms of AR to several AR inhibitors (ARIs) was compared. Our findings enabled us to propose that human AR should be used as the target enzyme in the development of ARIs. An enzyme-linked immunosorbent assay (ELISA) for human AR which employed monoclonal antibodies against rh-AR was created, and this method was used to demonstrate the distribution of AR in human tissues. AR was widely distributed in various organs and blood cell components. The levels of erythrocyte AR (e-AR) were 10.1±1.9 ng/mg Hb and 10.5±3.0 ng/mg Hb in healthy volunteers and diabetic patients, respectively, and thus there was no significant difference between them. The e-AR levels of diabetic patients were assayed using the ELISA developed to investigate the potential correlation between AR levels and the onset of diabetic complications. There were significant correlations between the incidence of diabetic neuropathy and e-AR levels in patients with disease duration of less than 10 years, and between the incidence of diabetic retinopathy and e-AR levels in patients with disease duration of 10-20 years. Our results suggest that measurement of e-AR levels in patients could help optimize drug therapy with ARIs and be a useful method to predict the onset of complications due to the upregulation of the polyol pathway.

The chlorite-based drug WF10 constantly reduces hemoglobin A1c values and improves glucose control in diabetes patients with severe foot syndrome

•

The chlorite-based drug WF10 improved healing of foot wounds in diabetic patients.

•

Infusion with WF10 markedly reduced HbA1c values in patients with diabetic foot syndrome.

•

After administration of WF10 HbA1c values remained low over at least 8 to 12 weeks.

•

The chlorite component of WF10 is known to inactivate efficiently cytotoxic hemoglobin forms.

•

This treatment prevented below knee amputation in patients with diabetic foot syndrome.

Aims

The intravenous application of the chlorite-based drug solution WF10 is known to improve wound healing in patients with diabetic foot syndrome. In this retrospective study, we addressed the question, which effects are caused by this drug in patients with diabetic foot ulcers on the hemoglobin A1c value.

Methods

Patients received five consecutive daily infusions of WF10. Three patients received a second cycle of WF10, and one patient a third cycle.

Results

On a group of twelve patients with diabetic foot syndrome, WF10 gradually reduced the HbA1c values from a high-risk range (9.1 ± 1.6% (76 ± 13 mmol/mol)) into a low-risk range in all patients but one. These values remain low over at least 8 to 12 weeks after the administration of WF10. This drug improved also considerably wound healing processes in eleven patients.

Conclusions

The chlorite component of WF10 is known to inactivate efficiently free cytotoxic hemoglobin forms that might accumulate in peripheral blood after hemolysis and induces the removal of pre-damaged red blood cells from circulation. By these mechanisms WF10 diminished toxic effects of hemolysis, improved microcirculation and glucose consumption in affected tissues, and prevented, thus, below knee amputation.

Bioactivity Focus of α-Cyano-4-hydroxycinnamic acid (CHCA) Leads to Effective Multifunctional Aldose Reductase Inhibitors

Bioactivity focus on α-cyano-4-hydroxycinnamic acid (CHCA) scaffold results in a small library of novel multifunctional aldose reductase (ALR2) inhibitors. All the entities displayed good to excellent inhibition with IC50 72-405 nM. (R,E)-N-(3-(2-acetamido-3-(benzyloxy)propanamido)propyl)-2-cyano-3-(4-hydroxy phenyl)acrylamide (5f) was confirmed as the most active inhibitor (IC50 72.7 ± 1.6 nM), and the best antioxidant. 5f bound to ALR2 with new mode without affecting the aldehyde reductase (ALR1) activity, implicating high selectivity to ALR2. 5f was demonstrated as both an effective ALR2 inhibitor (ARI) and antioxidant in a chick embryo model of hyperglycemia. It attenuated hyperglycemia-induced incidence of neural tube defects (NTD) and death rate, and significantly improved the body weight and morphology of the embryos. 5f restored the expression of paired box type 3 transcription factor (Pax3), and reduced the hyperglycemia-induced increase of ALR2 activity, sorbitol accumulation, and the generation of ROS and MDA to normal levels. All the evidences support that 5f may be a potential agent to treat diabetic complications.

A new gestational diabetes mellitus model: hyperglycemia-induced eye malformation via inhibition of Pax6 in the chick embryo

Gestational diabetes mellitus (GDM) is one of the leading causes of fetal malformations. However, few models have been developed to study the underlying mechanisms of GDM-induced fetal eye malformation. In this study, a high concentration of glucose (0.2 mmol per egg) was injected into the air sac of chick embryos on embryo development day (EDD) 1 to develop a hyperglycemia model. Results showed that 47.3% of embryonic eye malformation happened on EDD 5. In this model, the key genes regulating eye development, Pax6, Six3 and Otx2, were downregulated by hyperglycemia. Among these genes, the expression of Pax6 was the most vulnerable to hyperglycemia, being suppressed by 70%. A reduction in Pax6 gene expression induced eye malformation in chick embryos. However, increased expression of Pax6 in chick embryos could rescue hyperglycemia-induced eye malformation. Hyperglycemia stimulated O-linked N-acetylglucosaminylation, which caused oxidative stress in chick embryos. Pax6 was found to be vulnerable to free radicals, but the antioxidant edaravone could restore Pax6 expression and reverse eye malformation. These results illustrated a successful establishment of a new chick embryo model to study the molecular mechanism of hyperglycemia-induced eye malformation. The suppression of the Pax6 gene is probably mediated by oxidative stress and could be a crucial target for the therapy of GDM-induced embryonic eye malformation.

Summary: Hyperglycemia inhibited Pax6 via oxidative stress and impaired eye development in the chick embryo, a new gestational diabetes mellitus model.

Identifying Common Genetic Risk Factors of Diabetic Neuropathies

Type 2 diabetes mellitus (T2DM) is a global public health problem of epidemic proportions, with 60-70% of affected individuals suffering from associated neurovascular complications that act on multiple organ systems. The most common and clinically significant neuropathies of T2DM include uremic neuropathy, peripheral neuropathy, and cardiac autonomic neuropathy. These conditions seriously impact an individual's quality of life and significantly increase the risk of morbidity and mortality. Although advances in gene sequencing technologies have identified several genetic variants that may regulate the development and progression of T2DM, little is known about whether or not the variants are involved in disease progression and how these genetic variants are associated with diabetic neuropathy specifically. Significant missing heritability data and complex disease etiologies remain to be explained. This article is the first to provide a review of the genetic risk variants implicated in the diabetic neuropathies and to highlight potential commonalities. We thereby aim to contribute to the creation of a genetic-metabolic model that will help to elucidate the cause of diabetic neuropathies, evaluate a patient's risk profile, and ultimately facilitate preventative and targeted treatment for the individual.

Association of diabetic autonomic neuropathy with red blood cell aldose reductase activity

OBJECTIVE

Activation of polyol pathway based on increased activity of aldose reductase (AR) has been implicated in the development of diabetic complications including diabetic autonomic neuropathy (DAN). The relationship between DAN and hyperglycemia-induced activation of polyol pathway is still uncertain. In the present study, we investigate the association between aldose reductase activity and diabetic autonomic neuropathy by measuring AR level in red blood cells (RBC).

METHOD

In this study, 145 subjects with diabetes with or without DAN and 32 subjects without diabetes have been included. All subjects have been investigated for autonomic function tests and RBC aldose reductase activity. DAN was defined if results of any 2 of the tests of parasympathetic function were abnormal. RBC aldose reductase level was determined spectrophotometrically and expressed as unit/g of hemoglobin. The values were expressed as mean ± standard deviation, and ANOVA test has been applied for comparison between groups.

RESULTS

RBC aldose reductase activity was found to be significantly higher in people with diabetes with autonomic neuropathy in comparison to people with diabetes without autonomic neuropathy and healthy individuals without diabetes. Aldose reductase (AR) level ranges from 0.8 units/g Hb to 14.2 units/g Hb. The mean AR level was 8.6±2.95 units in subjects of DM with autonomic neuropathy, while mean AR level was 4.1±1.78 units and 2.0±0.89 units in people with diabetes without neuropathy and normal healthy individuals, respectively (p<0.001).

CONCLUSIONS

High aldose reductase activity is associated with the presence of autonomic neuropathy in subjects of type 2 DM.

Aldo-keto reductase and sorbitol dehydrogenase enzymes in Egyptian diabetic patients with and without proliferative diabetic retinopathy

BACKGROUND

Activation of the polyol pathway due to increased aldo-keto reductase (AKR) activity has been implicated in the development of diabetic complications, including proliferative diabetic retinopathy (PDR); however, the relationship between hyperglycaemia-induced activation of the polyol pathway in the retina and PDR is still uncertain.

METHODS

This study was conducted on 73 individuals, who were categorised into three groups: healthy individuals as normal control (15 age-matched subjects), diabetic patients treated with oral hypoglycaemic drugs (OHD, 34 patients), six of whom (17.7 per cent) were diagnosed with PDR and the rest were diagnosed with non-proliferative diabetic retinopathy (NPDR) and diabetic patients treated with insulin (INS, 24 patients), 12 of whom (50 per cent) were diagnosed with PDR and the rest had NPDR.

RESULTS

The AKR level in diabetic subjects showed a significant increase compared with the normal controls. Interestingly, AKR levels were significantly increased in the INS compared with the OHD group. Also the AKR level was significantly increased in the patients with proliferative compared with the non-proliferative retinopathy in both the insulin and oral diabetic groups. The sorbitol dehydrogenase (SDH) level in diabetic patients showed a significant decrease compared with the normal control level. Interestingly, the SDH level was significantly decreased in the INS compared with the OHD group. Also, the SDH level was significantly decreased in patients with proliferative compared with non-proliferative retinopathy in both INS and OHD groups. The HbA(1c) level in both INS and OHD subjects showed a significant increase compared with normal controls. In addition, the triglyceride level in insulin proliferative retinopathy showed a significant increase compared with other groups.

CONCLUSIONS

The AKR level was significantly increased in patients with proliferative compared with non-proliferative retinopathy in both insulin and oral diabetic groups. The SDH level was significantly decreased in patients with proliferative compared with non-proliferative retinopathy in both insulin and oral diabetic groups. Both AKR and SDH could be used as indicators for diabetic control.

Osmotic stress induced oxidative damage: possible mechanism of cataract formation in diabetes

Chronic hyperglycemia causes increased level of reactive oxygen species which is thought to be involved in the pathogenesis of diabetes associated complications including cataract. In diabetic cataractous lens, over production of free radicals and decreased capacity of antioxidant defense system are the major contributors to oxidative damage by polyol pathway and advanced glycation end products. The current study focused on analysis of factors associated with osmotic imbalance and oxidative stress in aging and diabetic human cataractous lenses. We examined activities of polyol pathway enzymes, G6PD and glutathione system in lenses from subjects suffering from cataract due to aging and diabetes. We observed elevated activities of aldose reductase and sorbitol dehydrogenase while G6PD and glutathione system enzyme activities were found to be lower in cataractous subjects suffering from diabetes. The findings from the current study support the premise that osmotic imbalance, AGEs formation and oxidative stress contribute synergistically to the development of lens opacity in hyperglycemia.

Attenuation of aldose reductase gene suppresses high-glucose-induced apoptosis and oxidative stress in rat lens epithelial cells

AIMS

A major contributory factor to diabetic cataract formation is increased aldose reductase (AR) activity in the polyol pathway. We investigated the effects of aldose reductase inhibition by RNA interference (RNAi) of the aldose reductase gene and administration of an aldose reductase inhibitor (ARI) on the changes induced by high glucose levels in rat lens epithelial cells (RLECs).

METHODS

Small interfering RNAs (siRNAs) were designed to target the coding sequence of rat AR-siRNA. RLECs were cultured in either normal or high d-glucose. Western analysis was performed to monitor AR expression. MTS (3-(4-5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium salt) and TUNEL assays were used to detect apoptotic cell death. Intracellular reactive oxygen species (ROS) were assessed by using DCFH-DA. Activation of nuclear factor-kappaB (NF-kappaB) was measured by an ELISA-based detection method.

RESULTS

Both siRNA and ARI suppressed increased levels of ROS, activation of NF-kappaB, and apoptotic cell death induced by high glucose levels. Inhibition of rAR expression by siRNA and inhibition of AR activity by ARI also suppressed sorbitol accumulation.

CONCLUSIONS

Both inhibition of rAR expression by rAR siRNA and inhibition of rAR activity by an ARI appeared effective in diminishing the changes of RLECs associated with high glucose levels.

Erythrocyte aldose reductase activity and sorbitol levels in diabetic retinopathy

PURPOSE

Activation of polyol pathway due to increased aldose reductase (ALR2) activity has been implicated in the development of diabetic complications including diabetic retinopathy (DR), a leading cause of blindness. However, the relationship between hyperglycemia-induced activation of polyol pathway in retina and DR is still uncertain. We investigated the relationship between ALR2 levels and human DR by measuring ALR2 activity and its product, sorbitol, in erythrocytes.

METHODS

We enrolled 362 type 2 diabetic subjects (T2D) with and without DR and 66 normal subjects in this clinical case-control study. Clinical evaluation of DR in T2D patients was done by fundus examination. ALR2 activity and sorbitol levels along with glucose and glycosylated hemoglobin (HbA1C) levels in erythrocytes were determined.

RESULTS

T2D patients with DR showed significantly higher specific activity of ALR2 as compared to T2D patients without DR. Elevated levels of sorbitol in T2D patients with DR, as compared to T2D patients without DR, corroborated the increased ALR2 activity in erythrocytes of DR patients. However, the increased ALR2 activity was not significantly associated with diabetes duration, age, and HbA1C in both the DR group and total T2D subjects.

CONCLUSIONS

Levels of ALR2 activity as well as sorbitol in erythrocytes may have value as a quantitative trait to be included among other markers to establish a risk profile for development of DR.

Epithelial cell density in cataractous lenses of patients with diabetes: association with erythrocyte aldose reductase

In the present study we evaluated the cell density of lens epithelium and its relation to the degree of erythrocyte aldose reductase (AR) in patients with type 2 diabetes. This prospective clinical study included 46 eyes of patients with type 2 diabetes and 48 eyes of patients without diabetes mellitus (DM). Flat preparations of lens epithelial cells (LECs) attached to the anterior capsule were studied. Multiple regression analysis was performed to evaluate the association between lens cell density and age, gender, type of cataract, duration of diabetes, diabetic retinopathy (DR), the levels of glycosylated hemoglobin (HbA1c) and erythrocyte AR. The mean density of LECs of patients with type 2 diabetes was 4,141+/-508cells/mm(2), which was significantly lower than that of patients without DM (4,560+/-458cells/mm(2); p<0.0001). Multiple regression analysis revealed that the level of erythrocyte AR was correlated with the reduction of LECs in the eyes of patients with type 2 diabetes. The correlation between the density of LECs and the amount of erythrocyte AR was significant in the diabetic group with a high value of HbA1c (>6.5%) or with DR. These results suggest that the polyol pathway via AR may be associated with the reduction of epithelial cell density in the eyes of patients with DM.

Bioinformatics analysis of diabetic retinopathy using functional protein sequences

Diabetic retinopathy is the leading cause of blindness among patients with diabetes mellitus. We evaluated the role of several proteins that are likely to be involved in diabetic retinopathy by employing multiple sequence alignment using ClustalW tool and constructed a phylogram tree using functional protein sequences extracted from NCBI. Phylogram was constructed using Neighbor-Joining Algorithm in bioinformatics approach. It was observed that aldose reductase and nitric oxide synthase are closely associated with diabetic retinopathy. It is likely that vascular endothelial growth factor, pro-inflammatory cytokines, advanced glycation end products, and adhesion molecules that also play a role in diabetic retinopathy may do so by modulating the activities of aldose reductase and nitric oxide synthase. These results imply that methods designed to normalize aldose reductase and nitric oxide synthase activities could be of significant benefit in the prevention and treatment of diabetic retinopathy.