Genetic deficiency of aldose reductase counteracts the development of diabetic nephropathy in C57BL/6 mice

Aldo-keto reductase (AKR) superfamily website and database: An update

The aldo-keto reductase (AKR) superfamily is a large family of proteins found across the kingdoms of life. Shared features of the family include 1) structural similarities such as an (α/β)8-barrel structure, disordered loop structure, cofactor binding site, and a catalytic tetrad, and 2) the ability to catalyze the nicotinamide adenine dinucleotide (phosphate) reduced (NAD(P)H)-dependent reduction of a carbonyl group. A criteria of family membership is that the protein must have a measured function, and thus, genomic sequences suggesting the transcription of potential AKR proteins are considered pseudo-members until evidence of a functionally expressed protein is available. Currently, over 200 confirmed AKR superfamily members are reported to exist. A systematic nomenclature for the AKR superfamily exists to facilitate family and subfamily designations of the member to be communicated easily. Specifically, protein names include the root "AKR", followed by the family represented by an Arabic number, the subfamily-if one exists-represented by a letter, and finally, the individual member represented by an Arabic number. The AKR superfamily database has been dedicated to tracking and reporting the current knowledge of the AKRs since 1997, and the website was last updated in 2003. Here, we present an updated version of the website and database that were released in 2023. The database contains genetic, functional, and structural data drawn from various sources, while the website provides alignment information and family tree structure derived from bioinformatics analyses.

Pathomechanisms of Diabetic Kidney Disease

The worldwide occurrence of diabetic kidney disease (DKD) is swiftly rising, primarily attributed to the growing population of individuals affected by type 2 diabetes. This surge has been transformed into a substantial global concern, placing additional strain on healthcare systems already grappling with significant demands. The pathogenesis of DKD is intricate, originating with hyperglycemia, which triggers various mechanisms and pathways: metabolic, hemodynamic, inflammatory, and fibrotic which ultimately lead to renal damage. Within each pathway, several mediators contribute to the development of renal structural and functional changes. Some of these mediators, such as inflammatory cytokines, reactive oxygen species, and transforming growth factor β are shared among the different pathways, leading to significant overlap and interaction between them. While current treatment options for DKD have shown advancement over previous strategies, their effectiveness remains somewhat constrained as patients still experience residual risk of disease progression. Therefore, a comprehensive grasp of the molecular mechanisms underlying the onset and progression of DKD is imperative for the continued creation of novel and groundbreaking therapies for this condition. In this review, we discuss the current achievements in fundamental research, with a particular emphasis on individual factors and recent developments in DKD treatment.

Response of a Human Lens Epithelial Cell Line to Hyperglycemic and Oxidative Stress: The Role of Aldose Reductase

A common feature of different types of diabetes is the high blood glucose levels, which are known to induce a series of metabolic alterations, leading to damaging events in different tissues. Among these alterations, both increased polyol pathway flux and oxidative stress are considered to play relevant roles in the response of different cells. In this work, the effect on a human lens epithelial cell line of stress conditions, consisting of exposure to either high glucose levels or to the lipid peroxidation product 4-hydroxy-2-nonenal, is reported. The occurrence of osmotic imbalance, alterations of glutathione levels, and expression of inflammatory markers was monitored. A common feature of the two stress conditions was the expression of COX-2, which, only in the case of hyperglycemic stress, occurred through NF-κB activation. In our cell model, aldose reductase activity, which is confirmed as the only activity responsible for the osmotic imbalance occurring in hyperglycemic conditions, seemed to have no role in controlling the onset of the inflammatory phenomena. However, it played a relevant role in cellular detoxification against lipid peroxidation products. These results, in confirming the multifactorial nature of the inflammatory phenomena, highlight the dual role of aldose reductase as having both damaging but also protecting activity, depending on stress conditions.

The role of protein kinase C in diabetic microvascular complications

Protein kinase C (PKC) is a family of serine/threonine protein kinases, the activation of which plays an important role in the development of diabetic microvascular complications. The activation of PKC under high-glucose conditions stimulates redox reactions and leads to an accumulation of redox stress. As a result, various types of cells in the microvasculature are influenced, leading to changes in blood flow, microvascular permeability, extracellular matrix accumulation, basement thickening and angiogenesis. Structural and functional disorders further exacerbate diabetic microvascular complications. Here, we review the roles of PKC in the development of diabetic microvascular complications, presenting evidence from experiments and clinical trials.

Aldose Reductase: a cause and a potential target for the treatment of diabetic complications

Diabetes mellitus, a disorder of metabolism, results in the elevation of glucose level in the blood. In this hyperglycaemic condition, aldose reductase overexpresses and leads to further complications of diabetes through the polyol pathway. Glucose metabolism-related disorders are the accumulation of sorbitol, overproduction of NADH and fructose, reduction in NAD⁺, and excessive NADPH usage, leading to diabetic pathogenesis and its complications such as retinopathy, neuropathy, and nephropathy. Accumulation of sorbitol results in the alteration of osmotic pressure and leads to osmotic stress. The overproduction of NADH causes an increase in reactive oxygen species production which leads to oxidative stress. The overproduction of fructose causes cell death and non-alcoholic fatty liver disease. Apart from these disorders, many other complications have also been discussed in the literature. Therefore, the article overviews the aldose reductase as the causative agent and a potential target for the treatment of diabetic complications. So, aldose reductase inhibitors have gained much importance worldwide right now. Several inhibitors, like derivatives of carboxylic acid, spirohydantoin, phenolic derivatives, etc. could prevent diabetic complications are discussed in this article.

Stabilized-chitosan selenium nanoparticles efficiently reduce renal tissue injury and regulate the expression pattern of aldose reductase in the diabetic-nephropathy rat model

One of the global alarming prevalent metabolic diseases is Type 2 diabetes mellitus (T2DM) than other diabetes and sustains a substantial burden on public and healthcare systems. This study attempts to endeavor the beneficial effect of chitosan stabilized nanoparticles Ch-SeNPs on combating diabetic nephropathy (DN) after induction of T2DM in rats (DN.STZ-induced T2D). High-fat diet (HFD) and STZ were used for the induction of T2DM in rats, and then they were treated with either metformin alone (MEF) (500 mg/kg b.wt.) or combined with (Ch-SeNPs) (2 mg Se/kg b.wt.) for eight weeks. The microvascular complications in renal tissue of diabetic rats were pronounced by the prevalence of microalbuminuria and elevated levels of urea, creatinine, and BUN. Pronounced oxidative stress with enhanced inflammatory response. In the urine of diabetic rats, a marked increase in Kim 1, β2-microglobulin, and urinary albumin. Renal morphological alterations were observed in all groups upon induction of T2DM, except for the Ch-SeNPs/MEF group showed noticeable improvements. The expression levels of Aldo-keto reductase AKr1B1, profibrotic protein transforming growth factor-β1 (TGF-β1), nestin, desmin, and vimentin, were up-regulated in the diabetic group. Significant down-regulation of their expression and restored antioxidant capacity was observed in the combined-treated group than single treated ones. Ch-SeNPs helped limit the prevalence of TNF-α, IL-6, and IL-1β while used after T2DM induction by STZ and HFD. Ch-SeNPs/MEF co-therapy could effectively guard the kidneys and reduce the renal tissue injury via inhibiting oxidative stress and restoring glucose hemostasis, which indicates a promising line for treating T2DM nephropathy.

Targeting Redox Imbalance as an Approach for Diabetic Kidney Disease

Diabetic kidney disease (DKD) is a worldwide public health problem. It is the leading cause of end-stage renal disease and is associated with increased mortality from cardiovascular complications. The tight interactions between redox imbalance and the development of DKD are becoming increasingly evident. Numerous cascades, including the polyol and hexosamine pathways have been implicated in the oxidative stress of diabetes patients. However, the precise molecular mechanism by which oxidative stress affects the progression of DKD remains to be elucidated. Given the limited therapeutic options for DKD, it is essential to understand how oxidants and antioxidants are controlled in diabetes and how oxidative stress impacts the progression of renal damage. This review aims to provide an overview of the current status of knowledge regarding the pathological roles of oxidative stress in DKD. Finally, we summarize recent therapeutic approaches to preventing DKD with a focus on the anti-oxidative effects of newly developed anti-hyperglycemic agents.

Tolrestat acts atypically as a competitive inhibitor of the thermostable aldo-keto reductase Tm1743 from Thermotoga maritima

Tolrestat and epalrestat have been characterized as noncompetitive inhibitors of aldo-ketone reductase 1B1 (AKR1B1), a leading drug target for the treatment of type 2 diabetes complications. However, clinical applications are limited for most AKR1B1 inhibitors due to adverse effects of cross-inhibition with other AKRs. Here, we report an atypical competitive binding and inhibitory effect of tolrestat on the thermostable AKR Tm1743 from Thermotoga maritima. Analysis of the Tm1743 crystal structure in complex with tolrestat alone and epalrestat-NADP⁺ shows that tolrestat, but not epalrestat, binding triggers dramatic conformational changes in the anionic site and cofactor binding pocket that prevents accommodation of NADP⁺ . Enzymatic and molecular dynamics simulation analyses further confirm tolrestat as a competitive inhibitor of Tm1743.

Redox imbalance stress in diabetes mellitus: Role of the polyol pathway

In diabetes mellitus, the polyol pathway is highly active and consumes approximately 30% glucose in the body. This pathway contains 2 reactions catalyzed by aldose reductase (AR) and sorbitol dehydrogenase, respectively. AR reduces glucose to sorbitol at the expense of NADPH, while sorbitol dehydrogenase converts sorbitol to fructose at the expense of NAD⁺, leading to NADH production. Consumption of NADPH, accumulation of sorbitol, and generation of fructose and NADH have all been implicated in the pathogenesis of diabetes and its complications. In this review, the roles of this pathway in NADH/NAD⁺ redox imbalance stress and oxidative stress in diabetes are highlighted. A potential intervention using nicotinamide riboside to restore redox balance as an approach to fighting diabetes is also discussed.

Aldose reductase interacts with AKT1 to augment hepatic AKT/mTOR signaling and promote hepatocarcinogenesis

Marked up-regulation of aldose reductase (AR) is reportedly associated with the development of hepatocellular carcinoma (HCC). We investigated how aberrantly overexpressed AR might promote oncogenic transformation in liver cells and tissues. We found that overexpressed AR interacted with the kinase domain of AKT1 to increase AKT/mTOR signaling. In both cultured liver cancer cells and liver tissues in DEN-induced transgenic HCC model mice, we observed that AR overexpression-induced AKT/mTOR signaling tended to enhance lactate formation and hepatic inflammation to enhance hepatocarcinogenesis. Conversely, AR knockdown suppressed lactate formation and inflammation. Using cultured liver cancer cells, we also demonstrated that AKT1 was essential for AR-induced dysregulation of AKT/mTOR signaling, metabolic reprogramming, antioxidant defense, and inflammatory responses. These findings suggest that aberrantly overexpressed/over-activated hepatic AR promotes HCC development at least in part by interacting with oncogenic AKT1 to augment AKT/mTOR signaling. Inhibition of AR and/or AKT1 might serve as an effective strategy for the prevention and therapy of liver cancer.

Aldose reductase mediates endothelial cell dysfunction induced by high uric acid concentrations

BACKGROUND

Uric acid (UA) is an antioxidant found in human serum. However, high UA levels may also have pro-oxidant functions. According to previous research, aldose reductase (AR) plays a vital role in the oxidative stress-related complications of diabetes. We sought to determine the mechanism by which UA becomes deleterious at high concentrations as well as the effect of AR in this process.

METHOD

and vWF levels were measured in vivo.

RESULTS

production in hyperuricemic mice and protected endothelial cell function.

CONCLUSIONS

could protect endothelial function and maintain the antioxidant activities of UA. These findings provide new insight into the role of UA in chronic kidney disease.

The aldo-keto reductases (AKRs): Overview

The aldo-keto reductase (AKR) protein superfamily contains >190 members that fall into 16 families and are found in all phyla. These enzymes reduce carbonyl substrates such as: sugar aldehydes; keto-steroids, keto-prostaglandins, retinals, quinones, and lipid peroxidation by-products. Exceptions include the reduction of steroid double bonds catalyzed by AKR1D enzymes (5β-reductases); and the oxidation of proximate carcinogen trans-dihydrodiol polycyclic aromatic hydrocarbons; while the β-subunits of potassium gated ion channels (AKR6 family) control Kv channel opening. AKRs are usually 37kDa monomers, have an (α/β)8-barrel motif, display large loops at the back of the barrel which govern substrate specificity, and have a conserved cofactor binding domain. AKRs catalyze an ordered bi bi kinetic mechanism in which NAD(P)H cofactor binds first and leaves last. In enzymes that favor NADPH, the rate of release of NADP(+) is governed by a slow isomerization step which places an upper limit on kcat. AKRs retain a conserved catalytic tetrad consisting of Tyr55, Asp50, Lys84, and His117 (AKR1C9 numbering). There is conservation of the catalytic mechanism with short-chain dehydrogenases/reductases (SDRs) even though they show different protein folds. There are 15 human AKRs of these AKR1B1, AKR1C1-1C3, AKR1D1, and AKR1B10 have been implicated in diabetic complications, steroid hormone dependent malignancies, bile acid deficiency and defects in retinoic acid signaling, respectively. Inhibitor programs exist world-wide to target each of these enzymes to treat the aforementioned disorders. Inherited mutations in AKR1C and AKR1D1 enzymes are implicated in defects in the development of male genitalia and bile acid deficiency, respectively, and occur in evolutionarily conserved amino acids. The human AKRs have a large number of nsSNPs and splice variants, but in many instances functional genomics is lacking. AKRs and their variants are now poised to be interrogated using modern genomic and informatics approaches to determine their association with human health and disease.

Therapeutic strategies of diabetic nephropathy: recent progress and future perspectives

Diabetic nephropathy (DN) is one of the most common complications of diabetes with high mortality rates worldwide. The treatment of DN has posed a formidable challenge to the scientific community. Simple control of risk factors has been insufficient to cope with the progression of DN. During the process of anti-DN drug discovery, multiple pathogeneses such as oxidative stress, inflammation and fibrosis should all be considered. In this review, the pathogenesis of DN is summarized. The major context focuses on a few small molecules toward the pathogenesis available in animal models and clinical trials for the treatment of DN. The perspectives of novel anti-DN agents and the future directions for the prevention of DN are discussed.

Aldose reductase regulates miR-200a-3p/141-3p to coordinate Keap1-Nrf2, Tgfβ1/2, and Zeb1/2 signaling in renal mesangial cells and the renal cortex of diabetic mice

Aberrant regulation in oxidative stress, fibrogenesis, and the epithelial-mesenchymal transition (EMT) in renal cells under hyperglycemic conditions contributes significantly to the onset and progression of diabetic nephropathy. The mechanisms underlying these hyperglycemia-induced dysregulations, however, have not been clearly elucidated. Herein, we report that aldose reductase is capable of regulating the expression of miR-200a-3p/141-3p negatively in renal mesangial cells. MiR-200a-3p/141-3p, in turn, act to target Keap1, Tgfβ2, fibronectin, and Zeb2 directly and regulate Tgfβ1 and Nrf2 indirectly under high-glucose conditions, resulting in profound dysregulations in Keap1-Nrf2, Tgfβ1/2, and Zeb1/2 signaling. In vivo in streptozotocin-induced diabetic mice, we found that aldose reductase deficiency caused significant elevations in miR-200a-3p/141-3p in the renal cortex, which were accompanied by a significant downregulation of Keap1, Tgfβ1/2, and fibronectin but significant upregulation of Nrf2. Moreover, in vivo administration of inhibitors of miR-200a-3p in diabetic animals significantly exacerbated cortical and glomerular fibrogenesis and increased urinary albumin excretion, tightly linking dysregulated miR-200a-3p with the development of diabetic nephropathy. Collectively, our results reveal a novel mechanism whereby hyperglycemia induces aldose reductase to regulate renal expression of miR-200a-3p/141-3p to coordinately control hyperglycemia-induced renal oxidative stress, fibrogenesis, and the EMT. Our novel findings also suggest that inhibition of aldose reductase and in vivo renal cortical restoration of miR-200a-3p/141-3p or their combination are very promising avenues for the development of therapeutic strategies or drugs against diabetic nephropathy.

VEGF and podocytes in diabetic nephropathy

Vascular endothelial growth factor-A (VEGF-A) is a protein secreted by podocytes that is necessary for survival of endothelial cells, podocytes, and mesangial cells. VEGF-A regulates slit-diaphragm signaling and podocyte shape via VEGF-receptor 2-nephrin-nck-actin interactions. Chronic hyperglycemia-induced excess podocyte VEGF-A and low endothelial nitric oxide drive the development and the progression of diabetic nephropathy. The abnormal cross-talk between VEGF-A and nitric oxide pathways is fueled by the diabetic milieu, resulting in increased oxidative stress. Recent findings on these pathogenic molecular mechanisms provide new potential targets for therapy for diabetic renal disease.

Aldose reductase, oxidative stress, and diabetic mellitus

Diabetes mellitus (DM) is a complex metabolic disorder arising from lack of insulin production or insulin resistance (Diagnosis and classification of diabetes mellitus, 2007). DM is a leading cause of morbidity and mortality in the developed world, particularly from vascular complications such as atherothrombosis in the coronary vessels. Aldose reductase (AR; ALR2; EC 1.1.1.21), a key enzyme in the polyol pathway, catalyzes nicotinamide adenosine dinucleotide phosphate-dependent reduction of glucose to sorbitol, leading to excessive accumulation of intracellular reactive oxygen species (ROS) in various tissues of DM including the heart, vasculature, neurons, eyes, and kidneys. As an example, hyperglycemia through such polyol pathway induced oxidative stress, may have dual heart actions, on coronary blood vessel (atherothrombosis) and myocardium (heart failure) leading to severe morbidity and mortality (reviewed in Heather and Clarke, 2011). In cells cultured under high glucose conditions, many studies have demonstrated similar AR-dependent increases in ROS production, confirming AR as an important factor for the pathogenesis of many diabetic complications. Moreover, recent studies have shown that AR inhibitors may be able to prevent or delay the onset of cardiovascular complications such as ischemia/reperfusion injury, atherosclerosis, and atherothrombosis. In this review, we will focus on describing pivotal roles of AR in the pathogenesis of cardiovascular diseases as well as other diabetic complications, and the potential use of AR inhibitors as an emerging therapeutic strategy in preventing DM complications.

Prediabetic nephropathy as an early consequence of the high-calorie/high-fat diet: relation to oxidative stress

This study evaluated early renal functional, structural, and biochemical changes in high-calorie/high-fat diet fed mice, a model of prediabetes and alimentary obesity. Male C57BL6/J mice were fed normal (11 kcal% fat) or high-fat (58 kcal% fat) diets for 16 wk. Renal changes were evaluated by histochemistry and immunohistochemistry, Western blot analysis, ELISA, enzymatic assays, and chemiluminometry. High-fat diet consumption led to increased body and kidney weights, impaired glucose tolerance, hyperinsulinemia, polyuria, a 2.7-fold increase in 24-h urinary albumin excretion, 20% increase in renal glomerular volume, 18% increase in renal collagen deposition, and 8% drop of glomerular podocytes. It also resulted in a 5.3-fold increase in urinary 8-isoprostane excretion and a 38% increase in renal cortex 4-hydroxynonenal adduct accumulation. 4-hydroxynonenal adduct level and immunoreactivity or Sirtuin 1 expression in renal medulla were not affected. Studies of potential mechanisms of the high-fat diet induced renal cortex oxidative injury revealed that whereas nicotinamide adenine dinucleotide phosphate reduced form oxidase activity only tended to increase, 12/15-lipoxygenase was significantly up-regulated, with approximately 12% increase in the enzyme protein expression and approximately 2-fold accumulation of 12(S)-hydroxyeicosatetraenoic acid, a marker of 12/15-lipoxygenase activity. Accumulation of periodic acid-Schiff -positive material, concentrations of TGF-β, sorbitol pathway intermediates, and expression of nephrin, CAAT/enhancer-binding protein homologous protein, phosphoeukaryotic initiation factor-α, and total eukaryotic initiation factor-α in the renal cortex were indistinguishable between experimental groups. Vascular endothelial growth factor concentrations were reduced in high-fat diet fed mice. In conclusion, systemic and renal cortex oxidative stress associated with 12/15-lipoxygenase overexpression and activation is an early phenomenon caused by high-calorie/high-fat diet consumption and a likely contributor to kidney disease associated with prediabetes and alimentary obesity.