Clinical analysis of aldose reductase for differential diagnosis of the pathogenesis of diabetic complication

The challenging inhibition of Aldose Reductase for the treatment of diabetic complications: a 2019-2023 update of the patent literature

INTRODUCTION

Aldose reductase (AKR1B1, EC: 1.1.1.21) is a recognized target for the treatment of long-term diabetic complications since its activation in hyperglycemia and role in the polyol pathway. In particular, the tissue-specificity of AKR1B1 expression makes the design of the traditional Aldose Reductase Inhibitors (ARIs) and the more recent Aldose Reductase Differential Inhibitors (ARDIs) exploitable strategies to treat pathologies resulting from diabetic conditions.

AREAS COVERED

A brief overview of the roles and functions of AKR1B1 along with known ARIs and ARDIs was provided. Then, the design of the latest inhibitors in the scientific scenario was discussed, aiming at introducing the research achievement in the field of intellectual properties. Patents dealing with AKR1B1 and diabetes filed in the 2019-2023 period were collected and analyzed. Reaxys, Espacenet, SciFindern, and Google Patents were surveyed, using 'aldose reductase' and 'inhibitor' as the reference keywords. The search results were then filtered by PRISMA protocol, thus obtaining 16 records to review.

EXPERT OPINION

Although fewer in number than in the early 2000s, patent applications are still being filed in the field of ARIs, with a large number of Chinese inventors reporting new synthetic ARIs in favor of the repositioning approach.

The Role of Aldose Reductase in Polyol Pathway: An Emerging Pharmacological Target in Diabetic Complications and Associated Morbidities

The expression of aldose reductase leads to a variety of biological and pathological effects. It is a multifunctional enzyme which has a tendency to reduce aldehydes to the corresponding sugar.alcohol. In diabetic conditions, the aldose reductase enzyme converts glucose into sorbitol using nicotinamide adenine dinucleotide phosphate as a cofactor. It is a key enzyme in polyol pathway which is a surrogate course of glucose metabolism. The polyol pathway has a significant impact on the aetiology of complications in individuals with end-stage diabetes. The exorbitant level of sorbitol leads to the accumulation of intracellular reactive oxygen species in diabetic heart, neurons, kidneys, eyes and other vasculatures, leading to many complications and pathogenesis. Recently, the pathophysiological role of aldose reductase has been explored with multifarious perspectives. Research on aldose reductase suggest that besides implying in diabetic complications, the enzyme also turns down the lipid-derived aldehydes as well as their glutathione conjugates. Although aldose reductase has certain lucrative role in detoxification of toxic lipid aldehydes, its overexpression leads to intracellular accumulation of sorbitol which is involved in secondary diabetic complications, such as neuropathy, cataractogenesis, nephropathy, retinopathy and cardiovascular pathogenesis. Osmotic upset and oxidative stress are produced by aldose reductase via the polyol pathway. The inhibition of aldose reductase alters the activation of transcription factors like NF-ƙB. Moreover, in many preclinical studies, aldose reductase inhibitors have been observed to reduce inflammation-related impediments, such as asthma, sepsis and colon cancer, in diabetic subjects. Targeting aldose reductase can bestow a novel cognizance for this primordial enzyme as an ingenious strategy to prevent diabetic complications and associated morbidities. In this review article, the significance of aldose reductase is briefly discussed along with their prospective applications in other afflictions.

Insight into the Molecular Mechanism of Diabetic Kidney Disease and the Role of Metformin in Its Pathogenesis

Diabetic kidney disease (DKD) is one of the leading causes of death among patients diagnosed with diabetes mellitus. Despite the growing knowledge about the pathogenesis of DKD, we still do not have effective direct pharmacotherapy. Accurate blood sugar control is essential in slowing down DKD. It seems that metformin has a positive impact on kidneys and this effect is not only mediated by its hypoglycemic action, but also by direct molecular regulation of pathways involved in DKD. The molecular mechanism of DKD is complex and we can distinguish polyol, hexosamine, PKC, and AGE pathways which play key roles in the development and progression of this disease. Each of these pathways is overactivated in a hyperglycemic environment and it seems that most of them may be regulated by metformin. In this article, we summarize the knowledge about DKD pathogenesis and the potential mechanism of the nephroprotective effect of metformin. Additionally, we describe the impact of metformin on glomerular endothelial cells and podocytes, which are harmed in DKD.

Rationale and design of the Aldose Reductase Inhibition for Stabilization of Exercise Capacity in Heart Failure Trial (ARISE-HF) in patients with high-risk diabetic cardiomyopathy

BACKGROUND

Diabetic cardiomyopathy (DbCM) is a specific form of heart muscle disease that may result in substantial morbidity and mortality in individuals with type 2 diabetes mellitus (T2DM). Hyperactivation of the polyol pathway is one of the primary mechanisms in the pathogenesis of diabetic complications, including development of DbCM. There is an unmet need for therapies targeting the underlying metabolic abnormalities that drive this form of Stage B heart failure (HF).

METHODS

Aldose reductase (AR) catalyzes the first and rate-limiting step in the polyol pathway, and AR inhibition has been shown to reduce diabetic complications, including DbCM in animal models and in patients with DbCM. Previous AR inhibitors (ARIs) were limited by poor specificity resulting in unacceptable tolerability and safety profile. AT-001 is a novel investigational highly specific ARI with higher binding affinity and greater selectivity than previously studied ARIs. ARISE-HF (NCT04083339) is an ongoing Phase 3 randomized, placebo-controlled, double blind, global clinical study to investigate the efficacy of AT-001 (1000 mg twice daily [BID] and 1500 mg BID) in 675 T2DM patients with DbCM at high risk of progression to overt HF. ARISE-HF assesses the ability of AT-001 to improve or prevent decline in exercise capacity as measured by functional capacity (changes in peak oxygen uptake [peak VO₂]) over 15 (and possibly 27) months of treatment. Additional endpoints include percentage of patients progressing to overt HF, health status metrics, echocardiographic measurements, and changes in cardiacbiomarkers.

RESULTS

The ARISE-HF Trial is fully enrolled.

CONCLUSIONS

This report describes the rationale and study design of ARISE-HF.

In Search of Differential Inhibitors of Aldose Reductase

Aldose reductase, classified within the aldo-keto reductase family as AKR1B1, is an NADPH dependent enzyme that catalyzes the reduction of hydrophilic as well as hydrophobic aldehydes. AKR1B1 is the first enzyme of the so-called polyol pathway that allows the conversion of glucose into sorbitol, which in turn is oxidized to fructose by sorbitol dehydrogenase. The activation of the polyol pathway in hyperglycemic conditions is generally accepted as the event that is responsible for a series of long-term complications of diabetes such as retinopathy, cataract, nephropathy and neuropathy. The role of AKR1B1 in the onset of diabetic complications has made this enzyme the target for the development of molecules capable of inhibiting its activity. Virtually all synthesized compounds have so far failed as drugs for the treatment of diabetic complications. This failure may be partly due to the ability of AKR1B1 to reduce alkenals and alkanals, produced in oxidative stress conditions, thus acting as a detoxifying agent. In recent years we have proposed an alternative approach to the inhibition of AKR1B1, suggesting the possibility of a differential inhibition of the enzyme through molecules able to preferentially inhibit the reduction of either hydrophilic or hydrophobic substrates. The rationale and examples of this new generation of aldose reductase differential inhibitors (ARDIs) are presented.

Aldose Reductase: An Emerging Target for Development of Interventions for Diabetic Cardiovascular Complications

Diabetes is a leading cause of cardiovascular morbidity and mortality. Despite numerous treatments for cardiovascular disease (CVD), for patients with diabetes, these therapies provide less benefit for protection from CVD. These considerations spur the concept that diabetes-specific, disease-modifying therapies are essential to identify especially as the diabetes epidemic continues to expand. In this context, high levels of blood glucose stimulate the flux via aldose reductase (AR) pathway leading to metabolic and signaling changes in cells of the cardiovascular system. In animal models flux via AR in hearts is increased by diabetes and ischemia and its inhibition protects diabetic and non-diabetic hearts from ischemia-reperfusion injury. In mouse models of diabetic atherosclerosis, human AR expression accelerates progression and impairs regression of atherosclerotic plaques. Genetic studies have revealed that single nucleotide polymorphisms (SNPs) of the ALD2 (human AR gene) is associated with diabetic complications, including cardiorenal complications. This Review presents current knowledge regarding the roles for AR in the causes and consequences of diabetic cardiovascular disease and the status of AR inhibitors in clinical trials. Studies from both human subjects and animal models are presented to highlight the breadth of evidence linking AR to the cardiovascular consequences of diabetes.

[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.

Aldose reductase and cardiovascular diseases, creating human-like diabetic complications in an experimental model

Hyperglycemia and reduced insulin actions affect many biological processes. One theory is that aberrant metabolism of glucose via several pathways including the polyol pathway causes cellular toxicity. Aldose reductase (AR) is a multifunctional enzyme that reduces aldehydes. Under diabetic conditions AR converts glucose into sorbitol, which is then converted to fructose. This article reviews the biology and pathobiology of AR actions. AR expression varies considerably among species. In humans and rats, the higher level of AR expression is associated with toxicity. Flux via AR is increased by ischemia and its inhibition during ischemia reperfusion reduces injury. However, similar pharmacological effects are not observed in mice unless they express a human AR transgene. This is because mice have much lower levels of AR expression, probably insufficient to generate toxic byproducts. Human AR expression in LDL receptor knockout mice exacerbates vascular disease, but only under diabetic conditions. In contrast, a recent report suggests that genetic ablation of AR increased atherosclerosis and increased hydroxynonenal in arteries. It was hypothesized that AR knockout prevented reduction of toxic aldehydes. Like many in vivo effects found in genetically manipulated animals, interpretation requires the reproduction of human-like physiology. For AR, this will require tissue specific expression of AR in sites and at levels that approximate those in humans.

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.

Central role for aldose reductase pathway in myocardial ischemic injury

Aldose reductase (AR), a member of the aldo-keto reductase family, has been implicated in the development of vascular and neurological complications of diabetes. Recently, we demonstrated that aldose reductase is a component of myocardial ischemic injury and that inhibitors of this enzyme protect rat hearts from ischemia-reperfusion injury. To rigorously test the effect of aldose reductase on myocardial ischemia-reperfusion injury, we used transgenic mice broadly overexpressing human aldose reductase (ARTg) driven by the major histocompatibility complex I promoter. Hearts from these ARTg or littermate mice (WT) (n=6 in each group) were isolated, perfused under normoxic conditions, then subjected to 50 min of severe low flow ischemia followed by 60 min of reperfusion. Creatine kinase (CK) release (a marker of ischemic injury) was measured during reperfusion; left ventricular developed pressure (LVDP), end diastolic pressure (EDP), and ATP were measured throughout the protocol. CK release was significantly greater in ARTg mice compared with the WT mice. LVDP recovery was significantly reduced in ARTg mice compared with the WT mice. Furthermore, ATP content was higher in WT mice compared with ARTg mice during ischemia and reperfusion. Infarct size measured by staining techniques and myocardial damage evaluated histologically were also significantly worse in ARTg mice hearts than in controls. Pharmacological inhibition of aldose reductase significantly reduced ischemic injury and improved functional recovery in ARTg mice. These data strongly support key roles for AR in ischemic injury and impairment of functional and metabolic recovery after ischemia. We propose that interventions targeting AR may provide a novel adjunctive approach to protect ischemic myocardium.

RAGE and its ligands: a lasting memory in diabetic complications?

The complications of diabetes are myriad and represent a rising cause of morbidity and mortality, particularly in the Western world. The update of the Diabetes Control and Clinical Trials Group/Epidemiology of Diabetes Interventions and Complications Research Group (DCCT/EDIC) suggested that previous strict control of hyperglycaemia was associated with reduced carotid atherosclerosis compared to conventional treatment, even after levels of glycosylated haemoglobin between the two treatment groups became indistinguishable. These intriguing findings prompt the key question, why does the blood vessel 'remember'? This review focuses on the hypothesis that the ligand/RAGE axis contributes importantly to glycaemic 'memory'. Studies in rodent models of diabetes suggest that blockade or genetic modification of RAGE suppress diabetes-associated progression of atherosclerosis, exaggerated neointimal expansion consequent to acute arterial injury, and cardiac dysfunction. We propose that therapeutic RAGE blockade will intercept maladaptive diabetes-associated memory in the vessel wall and provide cardiovascular protection in diabetes.

Glycation, inflammation, and RAGE: a scaffold for the macrovascular complications of diabetes and beyond

The cardiovascular complications of diabetes represent the leading cause of morbidity and mortality in affected subjects. The impact of hyperglycemia may be both direct and indirect: indirect consequences of elevated blood glucose lead to generation of advanced glycation endproducts, the products of nonenzymatic glycation/oxidation of proteins/lipids that accumulate in the vessel wall, and are signal transduction ligands for Receptor for AGE (RAGE). Although enhanced in diabetes, AGE accumulation also occurs in euglycemia and aging, albeit to lower degrees, driven by oxidant stress and inflammation. In hyperglycemia, production of 3-deoxyglucosone, at least in part via the polyol pathway, provides an amplification loop to sustain AGE generation, oxidant stress, and vascular activation. Furthermore, recruitment of inflammatory cells bearing S100/calgranulins, also ligands for RAGE, augments vascular dysfunction. We hypothesize that activation of RAGE is a final common pathway that transduces signals from these diverse biochemical and molecular species, leading to cardiovascular perturbation. Ultimately, these pathways synergize to construct a scaffold on which the complications of diabetes in the vasculature and heart may be built. We propose that antagonism of RAGE will provide a unique means to dismantle this scaffold and, thereby, suppress initiation/progression of vascular disease and cardiac dysfunction that accompany diabetes and aging.

Polyol pathway and diabetic peripheral neuropathy

This chapter critically examines the concept of the polyol pathway and how it relates to the pathogenesis of diabetic peripheral neuropathy. The two enzymes of the polyol pathway, aldose reductase and sorbitol dehydrogenase, are reviewed. The structure, biochemistry, physiological role, tissue distribution, and localization in peripheral nerve of each enzyme are summarized, along with current informaiton about the location and structure of their genes, their alleles, and the possible links of each enzyme and its alleles to diabetic neuropathy. Inhibitors of pathway enzyme and results obtained to date with pathway inhibitors in experimental models and human neuropathy trials are updated and discussed. Experimental and clinical data are analyzed in the context of a newly developed metabolic odel of the in vivo relationship between nerve sorbitol concentration and metabolic flux through aldose reuctase. Overall, the data will be interpreted as supporting the hypothesis that metabolic flux through the polyol pathway, rather than nerve concentration of sorbitol, is the predominant polyol pathway-linked pathogeneic factor in diabetic preipheral nerve. Finally, key questions and future directions for bsic and clinical research in this area are considered. It is concluded that robust inhibition of metabolic flux through the polyol pathway in peripheral nerve will likely result in substantial clinical benefit in treating and preventing the currently intractable condition of diabetic peripheral neuropathy. To accomplish this, it is imperative to develop and test a new generation of "super-potent" polyol pathway inhibitors.

Plasma 3-deoxyglucosone elevation in chronic renal failure is associated with increased aldose reductase in erythrocytes

BACKGROUND

Serum concentrations of 3-deoxyglucosone (3DG), a highly reactive dicarbonyl compound, are elevated in uremic patients. Aldose reductase (AR) is an enzyme involved in both the detoxification of 3DG and producing precursors of 3DG.

METHODS

We examined the relationship between plasma 3DG and erythrocyte AR content in uremic patients. Patients were divided into three groups: (1) progressive renal disease without hemodialysis (HD; chronic renal failure [CRF] group), (2) patients without diabetes mellitus (DM) treated with maintenance HD (HD group), and (3) patients with DM treated with maintenance HD (DM-HD group). High-performance liquid chromatography was used to measure 3DG, and erythrocyte AR was measured by means of enzyme-linked immunosorbent assay.

RESULTS

Both 3DG and erythrocyte AR levels were significantly greater in the CRF, HD, and DM-HD groups than in healthy controls. These results did not change after HD sessions in the HD or DM-HD groups. Serum creatinine levels correlated with 3DG and erythrocyte AR levels in the control and CRF groups (3DG: r = 0.67; P < 0.001; erythrocyte AR: r = 0.71; P < 0.001). Both erythrocyte AR and 3DG levels then increased as renal function declined. A positive correlation was seen between 3DG and erythrocyte AR levels in all groups (r = 0.65; P < 0.001), and also between plasma osmolality and erythrocyte AR level (r = 0.46; P < 0.001).

CONCLUSION

Both erythrocyte AR and 3DG levels are increased in uremic patients, and these increases could possibly contribute to the development of uremic symptoms.

Aldose reductase inhibitors: therapeutic implications for diabetic complications

The 'late complications' of diabetes mellitus, i.e., nephropathy, neuropathy and retinopathy are firmly rooted in inadequate control of blood glucose: hyperglycaemia. Hyperglycaemia causes elevated cytosolic glucose and/or rates of glucose metabolism, i.e., 'hyperglysolia,' within cells of vulnerable tissues. Although the molecular basis for the pathogenic effects of hyperglysolia remains to be proven, substantial evidence points to a key role for increased glucose metabolism through a cytosolic enzyme, aldose reductase (AR). Recent human genetic and biochemical data link polymorphisms of the AR gene (technically called the AR2 gene) and elevated tissue levels of AR with strongly altered risks for diabetic complications. Despite several genetic reports failing to confirm such an association, there are now ten concordant reports from five continents that certain polymorphisms of the AR gene are associated with an ~ 3- to 20-fold higher risk for diabetic complications. Moreover, in US and European diabetic study populations the principle allele of the AR gene associated with elevated disease risk, the Z-2 allele, correlates with an ~ 2- to 3-fold increase in AR expression. These results, together with recent clinical, experimental and pharmacological data, provide powerful new support for the rationale for research and development of aldose reductase inhibitors (ARIs) targeted at slowing the progression of diabetic complications. Although past clinical trials of ARIs have been disappointing, this has stemmed from overly optimistic expectations, inadequate trial designs and lack of pharmacological robustness and/or acceptable systemic toleration of the agents tested. However, a more realistic and encouraging perspective for therapeutic expectations for ARIs has arisen from recent data revealing that the seemingly modest short-term effects of intensified glycaemic control and of pancreatic transplantation are followed by substantial long-term benefits on diabetic complications. In addition, robust inhibition of AR in human nerve has recently yielded dose-dependent efficacy on nerve structure and function. Thus, the quest for well-tolerated, potent ARIs continues to be a worthy and more urgent objective than ever before.