Aldose reductase does catalyse the reduction of glyceraldehyde through a stoichiometric oxidation of NADPH

How Reversible Are the Effects of Fumed Silica on Macrophages? A Proteomics-Informed View

Synthetic amorphous silica is one of the most used nanomaterials, and numerous toxicological studies have studied its effects. Most of these studies have used an acute exposure mode to investigate the effects immediately after exposure. However, this exposure modality does not allow the investigation of the persistence of the effects, which is a crucial aspect of silica toxicology, as exemplified by crystalline silica. In this paper, we extended the investigations by studying not only the responses immediately after exposure but also after a 72 h post-exposure recovery phase. We used a pyrolytic silica as the test nanomaterial, as this variant of synthetic amorphous silica has been shown to induce a more persistent inflammation in vivo than precipitated silica. To investigate macrophage responses to pyrolytic silica, we used a combination of proteomics and targeted experiments, which allowed us to show that most of the cellular functions that were altered immediately after exposure to pyrolytic silica at a subtoxic dose, such as energy metabolism and cell morphology, returned to normal at the end of the recovery period. However, some alterations, such as the inflammatory responses and some aldehyde detoxification proteins, were persistent. At the proteomic level, other alterations, such as proteins implicated in the endosomal/lysosomal pathway, were also persistent but resulted in normal function, thus suggesting cellular adaptation.

Glucose induces metabolic reprogramming in neutrophils during type 2 diabetes to form constitutive extracellular traps and decreased responsiveness to lipopolysaccharides

Recurrent infections are one of the common morbidities in Type 2 Diabetes (T2D) subjects. Bidirectional activation of innate immune cells such as neutrophils and glucose metabolism in T2D conditions leads to a pro-inflammatory milieu and reduced neutrophil function, which can be a potential cause for recurrent infections. In pathological conditions of sterile inflammation associated T2D, neutrophils form constitutive extracellular traps (NETs) due to hyperglycemia and respond poorly to infections. The present study was aimed at understanding the cellular and metabolic consequences, and NETs formation in T2D. We show that glucose induces NADPH oxidase derived reactive oxygen species and further citrullinates the histones to form weaker NETs leading to reduced response to lipopolysaccharide (LPS). Untargeted metabolomics analysis in neutrophils cultured under high glucose and from T2D subjects revealed enrichment of polyol pathway intermediates (1-anhydrosorbitol) and reduced glutathione metabolism products (cysteinylglycine). NADPH is an absolute requirement for three independent pathways of formation of 1-anhydrosorbitol via aldose reductase under excess glucose, induction of glutathione synthesis and glucose induced NETs formation. During T2D and in presence of high glucose, there is a competition for NADPH between these processive reactions, which leads to its insufficiency to produce NETs in response to LPS. Interestingly, supplementation of NADPH and pharmacological inhibitor of aldose reductase, ranirestat, restored NETs formation in presence of LPS. Our study provides novel insights on the metabolic reprogramming of neutrophils, which may lead to susceptibility of T2D subjects to infections.

Addressing selectivity issues of aldose reductase 2 inhibitors for the management of diabetic complications

Aldose Reductase 2 (ALR2), the rate-limiting enzyme of the polyol pathway, plays an important role in detoxification of some toxic aldehydes. Under hyperglycemia, this enzyme overactivates and causes diabetic complications (DC). Therefore, ALR2 inhibition has been established as a potential approach to manage these complications. Several ALR2 inhibitors have been reported, but none of them could reach US FDA approval. One of the main reasons is their poor selectivity over ALR1, which leads to the toxicity. The current review underlines the molecular connectivity of ALR2 with DC and comparative analysis of the catalytic domains of ALR2 and ALR1, to better understand the selectivity issues. This report also discusses the key features required for ALR2 inhibition and to limit toxicity due to off-target activity.

Construction of an alternative glycerol-utilization pathway for improved β-carotene production in Escherichia coli

Glycerol, which is an inevitable by-product of biodiesel production, is an ideal carbon source for the production of carotenoids due to its low price, good availability and chemically reduced status, which results in a low requirement for additional reducing equivalents. In this study, an alternative carbon-utilization pathway was constructed in Escherichia coli to enable more efficient β-carotene production from glycerol. An aldehyde reductase gene (alrd) and an aldehyde dehydrogenase gene (aldH) from Ralstonia eutropha H16 were integrated into the E. coli chromosome to form a novel glycerol-utilization pathway. The β-carotene specific production value was increased by 50% after the introduction of alrd and aldH. It was found that the glycerol kinase gene (garK), alrd and aldH were the bottleneck of the alternative glycerol metabolic pathway, and modulation of garK gene with an mRS library further increased the β-carotene specific production value by 13%. Finally, co-modulation of genes in the introduced aldH–alrd operon led to 86% more of β-carotene specific production value than that of the strain without the alternative glycerol-utilization pathway and the glycerol-utilization rate was also increased. In this work, β-carotene production of E. coli was significantly improved by constructing and optimizing an alternative glycerol-utilization pathway. This strategy can potentially be used to improve the production of other isoprenoids using glycerol as a cheap and abundant substrate, and therefore has industrial relevance.

Synthesis and biological evaluation of 4-hydroxy-5-oxo-2,5-dihydro-1H-pyrrole-3-carboxamides and their zinc(ii) complexes as candidate antidiabetic agents

Five new zinc(ii) complexes with 4-hydroxy-5-oxo-2,5-dihydro-1H-pyrrole-3-carboxamides were synthesized, and four of them exhibited insulin-mimetic activity in vitro.

Synthesis of optically pure (S)-2-amino-5-arylpent-4-ynoic acids by Sonogashira reactions and their potential use as highly selective potent inhibitors of aldose reductase

A new and convenient synthesis of optically pure (S)-2-amino-5-[aryl]pent-4-ynoic acids (alkynylated amino acids) is reported.

Aldehyde reductase activity in the antennae of Helicoverpa armigera

In the present study, we identified two aldehyde reductase activities in the antennae of Helicoverpa species, NADH and NADPH-dependent activity. We expressed one of these proteins of H. armigera, aldo-keto reductase (AKR), which bears 56% identity to bovine aldose reductase, displays a NADPH-dependent activity and is mainly expressed in the antennae of adults. Whole-mount immunostaining showed that the enzyme is concentrated in the cells at the base of chemosensilla and in the nerves. The enzyme activity of H. armigera AKR is markedly different from those of mammalian enzymes. The best substrates are linear aliphatic aldehydes of 8-10 carbon atoms, but not hydroxyaldehydes. Both pheromone components of H. armigera, which are unsaturated aldehydes of 16 carbons, are very poor substrates. Unlike mammalian AKRs, the H. armigera enzyme is weakly affected by common inhibitors and exhibits a different behaviour from the action of thiols. A model of the enzyme suggests that the four cysteines are in their reduced form, as are the seven cysteines of mammalian enzymes. The occurrence of orthologous proteins in other insect species, that do not use aldehydes as pheromones, excludes the possibility of classifying this enzyme among the pheromone-degrading enzymes, as has been previously described in other insect species.

Benzothiazolyl substituted iminothiazolidinones and benzamido-oxothiazolidines as potent and partly selective aldose reductase inhibitors

Two new series of oxothiazolidine benzoate and acetate derivatives were synthesized and evaluated as aldehyde reductase (ALR1) and aldose reductase (ALR2) inhibitors.

Aerobic utilization of crude glycerol by recombinant Escherichia coli for simultaneous production of poly 3-hydroxybutyrate and bioethanol

Crude glycerol, an inevitable byproduct during biodiesel production, is emerging as a potential feedstock for fermentation, due to its availability and a reasonable price. Biological utilization of abundant crude glycerol to several value added products is contemporary research area with beneficial features. Solving the problem of proper disposal and raising economic viability of biodiesel industries. Several researches have been directed toward the production of numerous products by using Escherichia coli, an ideal organism for heterologous expression of various foreign proteins. In this fashion, recombinant E. coli strains were constructed for the simultaneous production of poly 3-hydroxybutyrate (P3HB) and bioethanol from crude glycerol. The incorporation of aldehyde reductase (Alrd) and aldehyde dehydrogenase (AldH) in recombinant strain showed 2-fold increment in crude glycerol utilization under aerobic condition. Moreover, these two enzymes introduced an alternative pathway leading toward the potential production of bioethanol which was more than redox-balancing steps. Acetate was accumulated as an intermediate product. Subsequently, acetate was utilized as substrate in the second pathway, which directly converted acetyl-CoA to P3HB. This strategy demonstrated a potential production manner of bioethanol as an extracellular product and P3HB as water insoluble inclusion bodies inside E. coli. The maximum production of bioethanol and P3HB in the recombinant strain was 0.8 g L(-1) (17.4 mmol L(-1)) and 30.2% (w/w dry cell weight), respectively, which were higher than the parental strain.

A new approach to control the enigmatic activity of aldose reductase

Aldose reductase (AR) is an NADPH-dependent reductase, which acts on a variety of hydrophilic as well as hydrophobic aldehydes. It is currently defined as the first enzyme in the so-called polyol pathway, in which glucose is transformed into sorbitol by AR and then to fructose by an NAD(+)-dependent dehydrogenase. An exaggerated flux of glucose through the polyol pathway (as can occur in diabetes) with the subsequent accumulation of sorbitol, was originally proposed as the basic event in the aethiology of secondary diabetic complications. For decades this has meant targeting the enzyme for a specific and strong inhibition. However, the ability of AR to reduce toxic alkenals and alkanals, which are products of oxidative stress, poses the question of whether AR might be better classified as a detoxifying enzyme, thus raising doubts as to the unequivocal advantages of inhibiting the enzyme. This paper provides evidence of the possibility for an effective intervention on AR activity through an intra-site differential inhibition. Examples of a new generation of aldose reductase "differential" inhibitors (ARDIs) are presented, which can preferentially inhibit the reduction of either hydrophilic or hydrophobic substrates. Some selected inhibitors are shown to preferentially inhibit enzyme activity on glucose or glyceraldehyde and 3-glutathionyl-4-hydroxy-nonanal, but are less effective in reducing 4-hydroxy-2-nonenal. We question the efficacy of D, L-glyceraldehyde, the substrate commonly used in in vitro inhibition AR studies, as an in vitro reference AR substrate when the aim of the investigation is to impair glucose reduction.

Curcumin analogues as possible anti-proliferative & anti-inflammatory agents

A series of novel curcumin analogues has been designed, synthesized and tested in vitro/in vivo as potential multi-target agents. Their anti-proliferative and anti-inflammatory activities were studied. Compounds 1b and 2b were stronger inhibitors of soybean lipoxygenase (LOX) than curcumin. Analogue 1b was also the most potent aldose reductase (ALR2) inhibitor. Two compounds, (1a and 1f) exhibited in vivo anti-inflammatory activity comparable to that of indomethacin, whereas derivative 1i exhibited even higher activity. The derivatives were also tested for their anti-proliferative activity using three different human cancer cell lines. Compounds 1a, 1b, 1d and 2b exhibited significant growth inhibitory activity as compared to curcumin, against all three cancer cell lines. Lipophilicity was determined as R(M) values using RPTLC and theoretically. The results are discussed in terms of the structural characteristics of the compounds. Docking simulations were performed on LOX and ALR2 inhibitor 1b and curcumin. Compound 1b is well fitted in the active site of ALR2, binding to the ALR2 enzyme in a similar way to curcumin. Allosteric interactions may govern the LOX-inhibitor binding.

Regulation of intracellular glucose and polyol pathway by thiamine and benfotiamine in vascular cells cultured in high glucose

Hyperglycemia is a causal factor in the development of the vascular complications of diabetes. One of the biochemical mechanisms activated by excess glucose is the polyol pathway, the key enzyme of which, aldose reductase, transforms d-glucose into d-sorbitol, leading to imbalances of intracellular homeostasis. We aimed at verifying the effects of thiamine and benfotiamine on the polyol pathway, transketolase activity, and intracellular glucose in endothelial cells and pericytes under high ambient glucose. Human umbilical vein endothelial cells and bovine retinal pericytes were cultured in normal (5.6 mmol/liter) or high (28 mmol/liter) glucose, with or without thiamine or benfotiamine 50 or 100 mumol/liter. Transketolase and aldose reductase mRNA expression was determined by reverse transcription-PCR, and their activity was measured spectrophotometrically; sorbitol concentrations were quantified by gas chromatography-mass spectrometry and intracellular glucose concentrations by fluorescent enzyme-linked immunosorbent assay method. Thiamine and benfotiamine reduce aldose reductase mRNA expression, activity, sorbitol concentrations, and intracellular glucose while increasing the expression and activity of transketolase, for which it is a coenzyme, in human endothelial cells and bovine retinal pericytes cultured in high glucose. Thiamine and benfotiamine correct polyol pathway activation induced by high glucose in vascular cells. Activation of transketolase may shift excess glycolytic metabolites into the pentose phosphate cycle, accelerate the glycolytic flux, and reduce intracellular free glucose, thereby preventing its conversion to sorbitol. This effect on the polyol pathway, together with other beneficial effects reported for thiamine in high glucose, could justify testing thiamine as a potential approach to the prevention and/or treatment of diabetic complications.

[1-(3,5-Difluoro-4-hydroxyphenyl)-1H-pyrrol-3-yl]phenylmethanone as a Bioisostere of a Carboxylic Acid Aldose Reductase Inhibitor

[1-(3,5-Difluoro-4-hydroxyphenyl)-1H-pyrrol-3-yl]phenylmethanone (6) was synthesized as a putative bioisostere of the known aldose reductase (AR) inhibitor (3-benzoylpyrrol-1-yl)acetic acid (I). It was found that 6 is approximately 5 times more potent as an in vitro inhibitor of AR than I, with an IC(50) value in the submicromolar range. Furthermore, 6 showed considerable activity in an in vitro experimental glycation model of diabetes mellitus. Our results support the notion that 6 might become a useful lead structure.

Substituted pyrrol-1-ylacetic acids that combine aldose reductase enzyme inhibitory activity and ability to prevent the nonenzymatic irreversible modification of proteins from monosaccharides

Starting from the known inhibitory activity of (3-benzoylpyrrol-1-yl)acetic acid (I) and (2-benzoylpyrrol-1-yl)acetic acid (II), a series of 3-aroyl and 2,4-bis-aroyl derivatives (54-75) were synthesized and tested for inhibition of aldose reductase, an enzyme involved in the appearance of diabetic complications. It was found that a number of the tested compounds exhibited considerable activity in the micromolar range. Important structural features for the potent compounds is the presence of substituents with relatively low Hammett sigma values and/or moieties which increase their overall aromatic area. The most active derivative was the [2,4-bis(4-methoxybenzoyl)pyrrol-1-yl]acetic acid (75), with potency favorably compared to known ARIs such as tolrestat, epalrestat, zopolrestat, and fidarestat. Four selected derivatives were also evaluated for their ability to interfere with the oxidative modification of serum albumin in an in vitro experimental glycation model of diabetes mellitus. All of them showed considerable activity, comparable to the known inhibitor trolox. Our results, taken together, indicate that compound 75 combines favorably two biological activities directly connected to a number of pathological conditions related to the chronic diabetes mellitus.

A facile preparation of 1-(6-hydroxyindol-1-yl)-2,2-dimethylpropan-1-one

An effective synthesis of 1-(6-hydroxyindol-1-yl)-2,2-dimethylpropan-1-one (4) was developed starting from 1H-indole (2). The key step involved suitable utilization of 4-(1-pyrrolidino)pyridine for the removal of the chloroacetyl moiety from chloroacetic acid 1-(2,2-dimethylpropionyl)-1H-indol-6-yl ester (3); a possible mechanism is, also, presented. Compound 4 might lead to selectively substituted derivatives, either on the phenolic-OH or the indolyl-NH, with putative biological interest. In this respect, we found that the core structure of 1H-indol-6-ol (1) possesses a degree of aldose reductase inhibitory potential, at a concentration of 100 microM.