Crucial role of aldose reductase activity and plasma glucose level in sorbitol accumulation in erythrocytes from diabetic patients

Neutrophil (dys)function due to altered immuno-metabolic axis in type 2 diabetes: implications in combating infections

Metabolic and inflammatory pathways are highly interdependent, and both systems are dysregulated in Type 2 diabetes (T2D). T2D is associated with pre-activated inflammatory signaling networks, aberrant cytokine production and increased acute phase reactants which leads to a pro-inflammatory 'feed forward loop'. Nutrient 'excess' conditions in T2D with hyperglycemia, elevated lipids and branched-chain amino acids significantly alter the functions of immune cells including neutrophils. Neutrophils are metabolically active cells and utilizes energy from glycolysis, stored glycogen and β-oxidation while depending on the pentose phosphate pathway for NADPH for performing effector functions such as chemotaxis, phagocytosis and forming extracellular traps. Metabolic changes in T2D result in constitutive activation and impeded acquisition of effector or regulatory activities of neutrophils and render T2D subjects for recurrent infections. Increased flux through the polyol and hexosamine pathways, elevated production of advanced glycation end products (AGEs), and activation of protein kinase C isoforms lead to (a) an enhancement in superoxide generation; (b) the stimulation of inflammatory pathways and subsequently to (c) abnormal host responses. Neutrophil dysfunction diminishes the effectiveness of wound healing, successful tissue regeneration and immune surveillance against offending pathogens. Hence, Metabolic reprogramming in neutrophils determines frequency, severity and duration of infections in T2D. The present review discusses the influence of the altered immuno-metabolic axis on neutrophil dysfunction along with challenges and therapeutic opportunities for clinical management of T2D-associated infections.

A novel method of producing the key intermediate ASI-2 of ranirestat using a porcine liver esterase (PLE) substitute enzyme

(R)-2-amino-2-ethoxycarbonylsuccinimide (ASI-2) is a key intermediate used in the pharmaceutical industry and is valuable for the industrial synthesis of ranirestat, which is a potent aldose reductase inhibitor. ASI-2 was synthesized in a process combining chemical synthesis and bioconversion. Bioconversion in this study is a key reaction, since optically active carboxylic acid derivative ((R)-1-ethyl hydrogen 3-benzyloxycarbonylamino-3-ethoxycarbonylsuccinate, Z-MME-AE) is synthesized from a prochiral ester, diethyl 2-benzyloxycarbonylamino-2-ethoxycarbonylsuccinate, Z-MDE-AE, at a theoretical yield of 100%. Upon screening for microorganisms that asymmetrically hydrolyze Z-MDE-AE, Bacillus thuringiensis NBRC13866 was found. A novel esterase EstBT that produces Z-MME-AE was purified from Bacillus thuringiensis NBRC13866 and was stably produced in Escherichia coli JM109 cells. Using EstBT rather than porcine liver esterase (PLE), ASI-2 was synthesized with a 17% higher total yield by a novel method, suggesting that the esterase EstBT is a PLE substitute enzyme and therefore, may be of interest for future industrial applications.

Involvement of hyperglycemia in the development of platelet procoagulant response: the role of aldose reductase and platelet swelling

: Rise in mean platelet volume (MPV) has been demonstrated to be associated with increased platelet reactivity. In diabetes patients, augmented MPV was proposed to contribute to increased risk of thrombotic complications. Therefore, the aim of this study was to investigate whether under hyperglycemic conditions, aldose reductase (AR)-mediated sorbitol formation and associated rise in cell volume, which subsequently results in platelet hyperactivation. Platelets were obtained from 30 healthy volunteers and 13 patients with diabetes. We evaluated changes in platelet size, their reactivity (measured as aggregation and secretion), and sorbitol content evoked by glucose. Measurement of procoagulant activity and thromboelastography were performed to assess how hyperglycemia affects coagulation. We have found that incubation of platelets with glucose (>10 mmol/l) leads to increased MPV, potentiation of collagen-evoked platelet aggregation, secretion, and procoagulant response (measured as platelet-dependent thrombin generation and phosphatidylserine expression). Glucose-treated platelets had higher sorbitol content and demonstrated enhanced tubulin polymerization. All the above-mentioned phenomena were reduced following the blocking of AR or by vincristine (microtubule destabilizing agent). Thromboelastography measurements demonstrated that hyperglycemia is associated with reduction of clotting time (R) and increase in the alpha angle (reflects platelet activation). Addition of sorbinil (AR inhibitor) or vincristine normalized R variable and alpha angle. The hyperglycemic conditions may accelerate platelet-related thrombin generation through the activation of polyol pathway, enhanced tubulin polymerization and associated with it rise in platelet volume.

The interactions of cephalosporins on polyol pathway enzymes from sheep kidney

CONTEXT

Cephalosporins are derived from the fungus Acremonium. Due to their strong bactericidal ability, these drugs have to a wide usage in medicine.

OBJECTIVE

An investigation of the effects on sheep renal aldose reductase (AR) and sorbitol dehydrogenase (SDH) of cefoperazone, cefazolin, cefuroxime, ceftazidime and ceftriaxone as cephalosporin drugs was carried out in the present study.

METHODS

AR and SDH were purified from sheep kidney by ion exchange, gel filtration and affinity methods with approximately 219- and 484-fold, respectively. Some kinetic properties of the enzymes were determined such as optimal pH, optimal ionic strength, optimal temperature, stable pH, K_m and V_max. IC₅₀ values of the drugs were found for each enzyme.

RESULTS

While the AR was inhibited by all drugs, SDH enzyme was inhibited by only CXM (IC₅₀ 8.10 mM). Interestingly, CZO activated SDH enzyme. This result was evaluated as important for the flow of the polyol reactions. K_i values and inhibition types were determined for AR. However, these values could not have determined for SDH, due to insufficient inhibition.

CONCLUSIONS

From these results, it was concluded that cephalosporins may have an important effect on flow of the polyol metabolism.

Aldose reductase (AKR1B) deficiency promotes phagocytosis in bone marrow derived mouse macrophages

Macrophages are critical drivers of the immune response during infection and inflammation. The pathogenesis of several inflammatory conditions, such as diabetes, cancer and sepsis has been linked with aldose reductase (AR), a member of the aldo-keto reductase (AKR) superfamily. However, the role of AR in the early stages of innate immunity such as phagocytosis remains unclear. In this study, we examined the role of AR in regulating the growth and the phagocytic activity of bone marrow-derived mouse macrophages (BMMs) from AR-null and wild-type (WT) mice. We found that macrophages derived from AR-null mice were larger in size and had a slower growth rate than those derived from WT mice. The AR-null macrophages also displayed higher basal, and lipopolysaccharide (LPS) stimulated phagocytic activity than WT macrophages. Moreover, absence of AR led to a marked increase in cellular levels of both ATP and NADPH. These data suggest that metabolic pathways involving AR suppress macrophage energy production, and that inhibition of AR could induce a favorable metabolic state that promotes macrophage phagocytosis. Hence, modulation of macrophage metabolism by inhibition of AR might represent a novel strategy to modulate host defense responses and to modify metabolism to promote macrophage hypertrophy and phagocytosis under inflammatory conditions.

Identification of Novel Aldose Reductase Inhibitors from Spices: A Molecular Docking and Simulation Study

Hyperglycemia in diabetic patients results in a diverse range of complications such as diabetic retinopathy, neuropathy, nephropathy and cardiovascular diseases. The role of aldose reductase (AR), the key enzyme in the polyol pathway, in these complications is well established. Due to notable side-effects of several drugs, phytochemicals as an alternative has gained considerable importance for the treatment of several ailments. In order to evaluate the inhibitory effects of dietary spices on AR, a collection of phytochemicals were identified from Zingiber officinale (ginger), Curcuma longa (turmeric) Allium sativum (garlic) and Trigonella foenum graecum (fenugreek). Molecular docking was performed for lead identification and molecular dynamics simulations were performed to study the dynamic behaviour of these protein-ligand interactions. Gingerenones A, B and C, lariciresinol, quercetin and calebin A from these spices exhibited high docking score, binding affinity and sustained protein-ligand interactions. Rescoring of protein ligand interactions at the end of MD simulations produced binding scores that were better than the initially docked conformations. Docking results, ligand interactions and ADMET properties of these molecules were significantly better than commercially available AR inhibitors like epalrestat, sorbinil and ranirestat. Thus, these natural molecules could be potent AR inhibitors.

PARASITOID VENOM INDUCES METABOLIC CASCADES IN FLY HOSTS

Parasitoid wasps inject insect hosts with a cocktail of venoms to manipulate the physiology, development, and immunity of the hosts and to promote development of the parasitoid offspring. The jewel wasp Nasonia vitripennis is a model parasitoid with at least 79 venom proteins. We conducted a high-throughput analysis of Nasonia venom effects on temporal changes of 249 metabolites in pupae of the flesh fly host (Sarcophaga bullata), over a five-day time course. Our results show that venom does not simply arrest the metabolism of the fly host. Rather, it targets specific metabolic processes while keeping hosts alive for at least five days post venom injection by the wasp. We found that venom: (a) Activates the sorbitol biosynthetic pathway while maintaining stable glucose levels, (b) Causes a shift in intermediary metabolism by switching to anaerobic metabolism and blocking the tricarboxylic acid cycle, (c) Arrests chitin biosynthesis that likely reflects developmental arrest of adult fly structures, (d) Elevates the majority of free amino acids, and (e) May be increasing phospholipid degradation. Despite sharing some metabolic effects with cold treatment, diapause, and hypoxia, the venom response is distinct from these conditions. Because Nasonia venom dramatically increases sorbitol levels without changing glucose levels, it could be a useful model for studying the regulation of the sorbitol pathway, which is relevant to diabetes research. Our findings generally support the view that parasitoid venoms are a rich source of bioactive molecules with potential biomedical applications.

Polyol pathway and diabetic nephropathy revisited: Early tubular cell changes and glomerulopathy in diabetic mice overexpressing human aldose reductase

Aims/Introduction:  The polyol pathway has long been involved in the pathogenesis of diabetic nephropathy. It remains still unclear, however, how the polyol pathway is implicated in this process. We explored the effects of the enhanced polyol pathway on renocortical tubular cells and glomeruli in experimentally-induced diabetes.

MATERIALS AND METHODS

  Transgenic mice (Tg) overexpressing human aldose reductase were made diabetic by streptozotocin and followed for 8 weeks. Renocortical pathology, expressions of tonicity-responsive enhancer binding protein (TonEBP) and carboxymethyllysine of advanced glycation end-products, were examined. Wild-type non-transgenic mice (Wt) were also made diabetic and served as controls.

RESULTS

  Diabetic Tg showed augmented expression of TonEBP in renocortical tubular cells with vacuolated degenerative changes. These structural changes were associated with pronounced deposition of carboxymethyllysine. There was a significant increase in kidney weight, glomerular size, and mesangial area in diabetic animals and there was a trend for more severe changes in these measures in diabetic transgenic mice compared with those in control diabetic mice. Treatment with aldose reductase inhibitor significantly prevented polyol accumulation, mesangial expansion and expressions of TonEBP and carboxymethyllysine in diabetic Tg, but its effects on the renal structure were equivocal in control diabetic Wt.

CONCLUSIONS

  Our findings suggest that tubuloglomerular change might contribute to early diabetic nephropathy under the influence of the enhanced polyol pathway. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2010.00071.x, 2010).

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.

Protective effects of dietary chamomile tea on diabetic complications

Matricaria chamomilla L., known as "chamomile", has been used as an herbal tea or supplementary food all over the world. We investigated the effects of chamomile hot water extract and its major components on the prevention of hyperglycemia and the protection or improvement of diabetic complications in diabetes mellitus. Hot water extract, esculetin (3) and quercetin (7) have been found to show moderate inhibition of sucrase with IC50 values of 0.9 mg/mL and 72 and 71 microM, respectively. In a sucrose-loading test, the administration of esculetin (50 mg/kg body weight) fully suppressed hyperglycemia after 15 and 30 min, but the extract (500 mg/kg body weight) and quercetin (50 mg/kg body weight) were less effective. On the other hand, a long-term feed test (21 days) using a streptozotocin-induced rat diabetes model revealed that the same doses of extract and quercetin showed significant suppression of blood glucose levels. It was also found that these samples increased the liver glycogen levels. Moreover, chamomile extract showed potent inhibition against aldose reductase (ALR2), with an IC50 value of 16.9 microg/mL, and its components, umbelliferone (1), esculetin (3), luteolin (6), and quercetin (7), could significantly inhibit the accumulation of sorbitol in human erythrocytes. These results clearly suggested that daily consumption of chamomile tea with meals could contribute to the prevention of the progress of hyperglycemia and diabetic complications.

Inhibitory effects of Zingiber officinale Roscoe derived components on aldose reductase activity in vitro and in vivo

Ginger (Zingiber officinale Roscoe) continues to be used as an important cooking spice and herbal medicine around the world. Scientific research has gradually verified the antidiabetic effects of ginger. Especially gingerols, which are the major components of ginger, are known to improve diabetes including the effect of enhancement against insulin-sensitivity. Aldose reductase inhibitors have considerable potential for the treatment of diabetes, without increased risk of hypoglycemia. The assay for aldose reductase inhibitors in ginger led to the isolation of five active compounds including 2-(4-hydroxy-3-methoxyphenyl)ethanol (2) and 2-(4-hydroxy-3-methoxyphenyl)ethanoic acid (3). Compounds 2 and 3 were good inhibitors of recombinant human aldose reductase, with IC50 values of 19.2 +/- 1.9 and 18.5 +/- 1.1 microM, respectively. Furthermore, these compounds significantly suppressed not only sorbitol accumulation in human erythrocytes but also lens galactitol accumulation in 30% of galactose-fed cataract rat model. A structure-activity relationship study revealed that the applicable side alkyl chain length and the presence of a C3 OCH3 group in the aromatic ring are essential features for enzyme recognition and binding. These results suggested that it would contribute to the protection against or improvement of diabetic complications for a dietary supplement of ginger or its extract containing aldose reductase inhibitors.

The association of aldose reductase gene (AKR1B1) polymorphisms with diabetic neuropathy in adolescents

AIMS

Variants in the aldose reductase gene (AKR1B1) have been implicated in the development of diabetic retinopathy and nephropathy, with the most convincing data identifying a (CA)(n) repeat microsatellite allele (Z-2), which has a functional role in gene expression. In this study the association between polymorphisms in the AKR1B1 gene and diabetic neuropathy was investigated.

METHODS

The pupillary response to light was used as the major outcome in this study along with abnormal hot thermal threshold. Three hundred and sixty-three adolescents underwent genotyping of the AKR1B1 gene. The microsatellite (CA)(n) repeat was sequenced and two single nucleotide polymorphisms, -106C-->T and -12C-->G, were investigated by restriction fragment length polymorphism.

RESULTS

Seventy-six percent of participants had pupillary abnormalities (45% with two, 15% with three abnormalities). Presence of the Z-2/Z-2 genotype increased the risk nearly three-fold for pupillary abnormalities [odds ratio (OR) 3.02, 95% confidence interval (CI) 1.14, 7.98). The susceptibility genotypes (Z-2/Z-2 with -106C/-106C, Z-2/Z with -106C/-106C or Z/Z with -106C/-106C) were associated with resting pupil diameter abnormalities when compared with the protective genotypes (Z+2/Z+2 or -106T/-106T) (OR 2.83, 95% CI 1.25, 6.41). The combination of Z+2/-106T reduced the risk of abnormal heat discrimination (OR 0.48, 95% CI 0.23, 0.99).

CONCLUSIONS

In this study we have shown that Z-2/Z-2 genotype is significantly associated with the development of pupillary abnormality, an early indicator of diabetic autonomic neuropathy, in adolescent Australian patients with Type 1 diabetes.

Aldose reductase inhibition in the treatment of diabetic neuropathy: where are we in 2004?

Diabetic neuropathy is a major complication of poorly controlled diabetes mellitus. Aldose reductase, the first enzyme of the polyol pathway, is thought to play a role in initiating the metabolic damage to peripheral nerves during hyperglycemia. Aldose reductase inhibitors (ARIs) have been proposed to dampen the flux of glucose through the pathway during hyperglycemia; however, clinical trials in diabetic patients to demonstrate efficacy in the prevention or amelioration of diabetic neuropathy have failed thus far. Recent improved understanding of the pitfalls of past trials and some improved ARIs and clinical evaluation instruments show promise that success in the 20-plus year search for efficacious ARIs may soon be at hand.

Association of aldose reductase gene Z+2 polymorphism with reduced susceptibility to diabetic nephropathy in Caucasian Type 1 diabetic patients

AIMS

The Z-2 allele of the (AC)n polymorphism in the aldose reductase gene (ALR2) confers increased risk of microvascular diabetic complications, whereas the Z+2 allele has been proposed to be a marker of protection. However data are conflicting. Therefore, we investigated whether this polymorphism is associated with diabetic nephropathy and retinopathy in Type 1 diabetes mellitus in a large case-control study and a family-based analysis.

METHODS

A total of 431 Type 1 diabetic patients with diabetic nephropathy and 468 patients with longstanding Type 1 diabetes and persistent normoalbuminuria were genotyped for the case-control study. In addition, 102 case trios and 98 control trios were genotyped for a family-based study.

RESULTS

Thirteen different alleles were identified. In the case-control study, the Z+2 allele frequency was significantly higher in the normoalbuminuric diabetic than in patients with diabetic nephropathy (0.17 vs. 0.11, P = 0.008), suggesting a protective function of the Z+2 allele. No significant increase in the frequency of the putative risk allele Z-2 was found in patients with diabetic nephropathy vs. controls (0.39 vs. 0.36). No association with diabetic retinopathy was found. Although the results of the transmission of the Z-2 and Z+2 alleles in the independent family-based study were consistent with the association study, the number of informative families was limited and thus differences were not statistically significant.

CONCLUSIONS

The Z+2 allele of the ALR2 promoter polymorphism is associated with a reduced susceptibility to diabetic nephropathy in Danish Type 1 diabetic patients, suggesting a minor role for the polyol pathway in the pathogenesis of diabetic kidney disease. No association of the ALR2 polymorphism with diabetic retinopathy was found.

Clinical Potential of Aldose Reductase Inhibitors in Diabetic Neuropathy

A number of aldose reductase inhibitors (ARIs) have been developed over the past few decades with the expectation of therapeutic effects for diabetic complications. Neuropathy is the complication that has been most intensively studied as a potential target for ARIs. Most ARIs have shown satisfactory effects in animal models. However, the clinical potential of ARIs in diabetic patients has been controversial due to the lack of conclusive evidence. The safety of this category of drugs is also uncertain. This article summarizes the results of clinical trials of ARIs for patients with diabetic neuropathy that have been performed to date. The efficacy and toxicity of each ARI will be briefly assessed by the clinical data. The theoretical background along with major issues in the evaluation of drug efficacy will also be discussed. Overall the observed efficacy varied among the compounds. A few ARIs showed favorable effects in multiple endpoints in the majority of trials, while the results from many ARIs seemed ambivalent. One drug barely exhibited positive effects on any endpoint. This discrepancy may be attributable at least in part to the different degree of inhibition of the polyol pathway in nerve tissues, which is determined not only by the pharmacokinetic properties of the drug but also by its penetration into nerve tissues. In addition to the uncertain potential of each ARI, the issues of design and analytical methods used for clinical trials may underlie the ambivalent outcomes. The power of analysis and the duration of trials were apparently inadequate in a large number of the studies. Various indices selected as endpoints are not necessarily sensitive or reproducible. Studies of longer duration, large-scale trials, better methods to assess neuropathy, and the selection of patients with a homogenous background would provide more conclusive evidence. The risk of serious adverse reactions, for example, hypersensitivity reactions and hepatic damage, has led to some ARIs being withdrawn from the market or from further development. These adverse effects, however, do not appear to result from the inhibition of aldose reductase activity per se but from specific reactions to each compound. In conclusion, sufficient inhibition of the nerve aldose reductase activity seems likely to prevent or ameliorate diabetic neuropathy, and further development of more potent and safe ARIs is necessary before extensive clinical application.

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.

Susceptibility to diabetic neuropathy in patients with insulin dependent diabetes mellitus is associated with a polymorphism at the 5' end of the aldose reductase gene

OBJECTIVES

There is evidence that the polyol pathway is involved in the pathogenesis of diabetic neuropathy. Aldose reductase (ALR2) is the first and rate limiting enzyme of this pathway and recent studies have suggested that polymorphisms in and around the gene are associated with the development of diabetic microvascular disease. The aim was to examine the role of ALR2 in the susceptibility to diabetic neuropathy in patients with insulin dependent diabetes mellitus (IDDM).

METHODS

One hundred and fifty nine British white patients with IDDM and 102 normal healthy controls were studied using the polymerase chain reaction to test for a highly polymorphic microsatellite marker 2.1 kilobase (kb) upstream of the initiation site of the ALR2 gene.

RESULTS

Seven alleles were detected (Z-6, Z-4, Z-2, Z, Z+2, Z+4, and Z+6). There was a highly significant decrease in the frequency of the Z+2 allele in those patients with overt neuropathy compared with those with no neuropathy after 20 years duration of diabetes (14.1% v 38.2%, chi2 =17.3, p<0.00001). A similar difference was also found between the neuropathy group and those patients who have had diabetes for < five years with no overt neuropathy (14.1% v 30.2%, chi2=9.0, p<0.0025). The neuropathy group also had a significant decrease in the frequency of the Z/Z+2 genotype compared with those patients who have no neuropathy after 20 years duration of diabetes (14.0% v 44.7%, chi2=13.0, p<0.0005).

CONCLUSION

These results suggest that the aldose reductase gene is intimately involved in the pathogenesis of diabetic neuropathy.

Urinary pyrraline as a biochemical marker of non-oxidative Maillard reactions in vivo

The presence of pyrraline, a non-oxidative glucose-derived Maillard reaction product in plasma proteins has been established previously. In this study we have investigated the presence of pyrraline in human urine to determine whether pyrraline-containing proteins are metabolized or selectively retained. Pyrraline was detected by means of HPLC, and its presence was confirmed by UV and electrospray-mass spectrometry. The quantification of pyrraline in urine from healthy individuals showed 1.21 +/- 0.4 micrograms/mg creatinine. In urine from diabetic patients, pyrraline levels varied considerably, although the mean level was higher than in healthy subjects (1.37 +/- 0.6 micrograms/mg creatinine). These data further support the presence of a catabolic pathway for advanced non-oxidative Maillard reaction products in vivo and suggest their role in the pathogenesis of diabetes.

Tolrestat pharmacokinetic and pharmacodynamic effects on red blood cell sorbitol levels in normal volunteers and in patients with insulin-dependent diabetes

OBJECTIVES

To examine the effect of diabetes mellitus on the pharmacokinetics of tolrestat and to investigate its effect on red blood cell sorbitol levels according to a new pharmacodynamic model for this class of drugs.

METHODS

Single and multiple doses of tolrestat (200 mg/twice a day) were administered to 12 patients with insulin-dependent (type I) diabetes and 12 healthy volunteers in an open parallel trial.

RESULTS

Tolrestat disposition was characterized by first-order absorption and biexponential disposition: In normal subjects the terminal disposition half-life (t1/2) was 13 +/- 3 hours (mean +/- SD) and the apparent oral clearance (CL/F) was 48 +/- 9 ml/hr/kg, similar to the values in patients with type I diabetes mellitus (t1/2 = 14 +/- 4 hours; CL/F = 55 +/- 10 ml/hr/kg). Red blood cell sorbitol concentrations, which declined because of tolrestat's inhibition of aldose reductase, were characterized by an indirect-response model including a 50% inhibition constant (IC50) for production of sorbitol by aldose reductase. The removal of sorbitol (kout) was slower in patients with diabetes. The plasma IC50 averaged 2.0 +/- 1.3 micrograms/ml in normal subjects and 2.5 +/- 1.9 micrograms/ml in patients with diabetes. IC50 values expressed in free (unbound) concentrations (fu = 0.64%), which ranged from 12 to 16 ng/ml, were similar to the in vitro IC50 for inhibition of sorbitol accumulation in human red blood cells.

CONCLUSIONS

Tolrestat pharmacokinetics were similar in normal subjects and in patients with diabetes; however, the patients with diabetes had higher baseline sorbitol levels (11 versus 5 nmol/ml for normal subjects) and slower sorbitol efflux rates. The proposed biochemically realistic, dynamic model characterized well the red blood cell sorbitol response patterns after administration of single and multiple doses of tolrestat.

Thermal stress and diabetic complications

Activities of erythrocyte aldose reductase were compared in 34 normal subjects, 45 diabetic patients, and nine young men following immersion in water at 25, 39, and 42 degrees C. Mean basal enzyme activity was 1.11 (SEM 0.12) U/g Hb and 2.07 (SEM 0.14) U/g Hb in normal controls and diabetic patients, respectively (P < 0.0001). Activities of the enzyme showed a good correlation with hemaglobin A1 (HbA1) concentrations (P < 0.01) but not with fasting plasma glucose concentrations. After immersion at 42 degrees C for 10 min, enzyme activity was increased by 37.6% (P < 0.01); however, the activity decreased by 52.2% (P < 0.005) after immersion for 10 min at 39 degrees C and by 47.0% (P < 0.05) at 25 degrees C. These changes suggest that heat stress might aggravate diabetic complications, and body exposure to hot environmental conditions is not recommended for diabetic patients.

Altered aldose reductase gene regulation in cultured human retinal pigment epithelial cells

Aldose reductase (AR2), a putative "hypertonicity stress protein" whose gene is induced by hyperosmolarity, protects renal medullary cells against the interstitial hyperosmolarity of antidiuresis by catalyzing the synthesis of millimolar concentrations of intracellular sorbitol from glucose. Although AR2 gene induction has been noted in a variety of renal and nonrenal cells subjected to hypertonic stress in vitro, the functional significance of AR2 gene expression in cells not normally exposed to a hyperosmolar milieu is not fully understood. The physiological impact of basal AR2 expression in such cells may be limited to hyperglycemic states in which AR2 promotes pathological polyol accumulation, a mechanism invoked in the pathogenesis of diabetic complications. Since AR2 overexpression in the retinal pigment epithelium has been associated with diabetic retinopathy, the regulation of AR2 gene expression and associated changes in sorbitol and myo-inositol were studied in human retinal pigment epithelial cells in culture. The relative abundance of aldehyde reductase (AR1) and AR2 mRNA was quantitated by filter hybridization of RNA from several human retinal pigment epithelial cell lines exposed to hyperglycemic and hyperosmolar conditions in vitro. AR2 but not AR1 mRNA was significantly increased some 11- to 18-fold by hyperosmolarity in several retinal pigment epithelial cell lines. A single cell line with a 15-fold higher basal level of AR2 mRNA than other cell lines tested demonstrated no significant increase in AR2 mRNA in response to hypertonic stress. This cell line demonstrated accelerated and exaggerated production of sorbitol and depletion of myo-inositol upon exposure to 20 mM glucose. Therefore, abnormal AR2 expression may enhance the sensitivity of cells to the biochemical consequences of hyperglycemia potentiating the development of diabetic complications.

Quantitative determination of human aldose reductase by enzyme-linked immunosorbent assay. Immunoassay of human aldose reductase

An antibody-sandwich enzyme-linked immunosorbent assay (ELISA) for evaluating tissue levels of aldose reductase was developed using a polyclonal antibody prepared against the recombinant enzyme expressed in a baculovirus system. The specificity of this antibody to aldose reductase was verified by immunoprecipitation, immunoblotting and ELISA. The polyclonal antibody did not crossreact with human aldehyde reductase, an enzyme in the same aldo-keto reductase family structurally and functionally related to aldose reductase. The sensitivity and specificity of this assay method enabled direct determination of aldose reductase level in various human tissues including the erythrocyte. The highest level of aldose reductase was detected in the kidney medulla among tissues investigated. More than a 2-fold variability in the erythrocyte aldose reductase was demonstrated among healthy individuals, indicating the heterogeneity of this enzyme expression in a human population. This assay system may be useful for direct measurement of the level of tissue aldose reductase in conjunction with the evaluation of the efficacy of aldose reductase inhibitors prescribed for the treatment of diabetic complications.

Association of erythrocyte aldose reductase activity with diabetic complications in type 1 diabetes mellitus

Erythrocyte aldose reductase was isolated and its activity measured in 72 Type 1 (insulin dependent) diabetic patients and 21 age and sex matched non-diabetic subjects. The diabetic patients were categorized into two groups in terms of presence (n = 29) or absence (n = 43) of severe diabetic complications. Age, sex, duration of diabetes and HbA1c levels were matched between the diabetic groups. Erythrocyte aldose reductase (mean +/- SEM) was increased in patients with Type 1 diabetes compared to the non-diabetic subjects (7.22 +/- 0.24 vs 5.66 +/- 0.19 Ul-erythrocytes-1, < 0.0001). There was a four-fold variation in its activity among the diabetic patients (3.38-12.23 Ul-erythrocytes-1). The enzyme activity was significantly higher in patients with complications than those without (8.17 +/- 0.39 vs 6.58 +/- 0.26 Ul-erythrocytes-1, p < 0.002). When the patients were stratified by duration of the disease, the enzyme activity was highest in patients who had developed complications with a duration of less than 20 years and lowest in those without complications for 20 years or longer (8.54 +/- 0.48 vs 6.46 +/- p +/- 0.33 Ul-erythrocytes-1, p < 0.002). Patients who had an aldose reductase activity greater than the mean +/- 2SD of that seen in non-diabetic controls were four times more likely to have diabetic complications than those whose enzyme activity fell within 2SD of non-diabetic individuals (p < 0.0005).(ABSTRACT TRUNCATED AT 250 WORDS)