Novel aldose reductase inhibitors: a patent survey (2006--present).

INTRODUCTION: Initially studied for its central role in the pathogenesis of chronic diabetic complications, aldose reductase (ALR2) gains more attention over the years as its implication in inflammatory diseases is being established, along with the therapeutic potential of its inhibitors. AREAS COVERED: Reviewing the patents that were published since 2006, it is getting clear that the search for new chemical entities has subsided, giving rise to natural products and plant extracts with ALR2 inhibitory activity. Other aspects that were prominent were the search for proper forms of known inhibitors, in a way to improve their impaired physicochemical profile, as well as potential combination therapies with other compounds of pharmaceutical interest. On the spotlight were patents enhancing the therapeutic usage of aldose reductase inhibitors (ARIs) to various pathological conditions including cancer and inflammation-mediated diseases such as sepsis, asthma, and cancer. EXPERT OPINION: Although new chemical entities are scarcely registered and patented after many years of inconclusive clinical trials, the involvement of ALR2 to inflammatory pathologies might renew the interest in the field of ARIs.

Evaluation of aldose reductase inhibition and docking studies of 6'-nitro and 6',6''-dinitrorosmarinic acids.

Aldose reductase (ALR2) of the polyol metabolic pathway is a target enzyme for the treatment of diabetic complications. A variety of synthetic and natural compounds have been observed to inhibit aldose reductase. Among them, rosmarinic acid has been shown to be in vitro an aldose reductase inhibitor in a micromolar range. In this study, two nitro derivatives of rosmarinic acid synthesized previously, 6'-nitro and 6',6''-dinitrorosmarinic acids, are proposed as aldose reductase inhibitors. Docking studies of the nitro derivatives have been carried out in the active site of aldose reductase. The theoretical results have shown a higher estimated binding energy of both compounds in comparison to that of rosmarinic acid suggesting a higher ALR2 inhibitory activity. The in vitro biological assays confirmed that these compounds were more potent than the parent rosmarinic acid.

Carboxymethylated pyridoindole antioxidants as aldose reductase inhibitors: Synthesis, activity, partitioning, and molecular modeling.

Starting from the efficient hexahydropyridoindole antioxidant stobadine, a series of carboxymethylated tetrahydro- and hexahydropyridoindole derivatives was synthesized and tested for the inhibition of aldose reductase, an enzyme involved in the etiology of diabetic complications. In vitro inhibiton of rat lens aldose reductase was determined by a conventional method. Kinetic analysis of (2-benzyl-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole-8-yl)-acetic acid (5b) and (2-phenethyl-2,3,4,5-tetrahydro-1H-pyrido[4,3-b]indole-8-yl)-acetic acid (5c), the most potent compounds in this series with activities in micromolar range, showed uncompetitive inhibition. In addition to the importance of the acidic function, the inhibition efficacy was highly influenced by the steric conformation of the lipophilic aromatic backbone when comparing tetrahydro- and hexahydropyridoindole congeners. Selectivity with respect to the closely related aldehyde reductase was determined by measuring the corresponding inhibitory activities. Antioxidant action of the novel compounds was documented in a DPPH test and in a liposomal membrane model, oxidatively stressed by peroxyl radicals. The presence of a basicity center at the tertiary nitrogen, in addition to the acidic carboxylic function, predisposes these compounds to form double charged zwitterionic species, a characteristic which may remarkably affect their pH-lipophilicity profile. For compounds 5b and 5c, a maximal distribution ratio in a system comprised of 1-octanol/phosphate buffer was recorded near the neutral physiological pH, the region where the isoelectric point lies. Molecular docking simulations into the ALR2 active site performed for the zwitterionic species provided an explanation for the observed structure-activity relationships and the calculated parameters were in agreement with characteristic differences in the stereoelectronic profiles of the tetrahydro- versus hexahydropyridoindoles. 'Drug-likeness' of the novel aldose reductase inhibitors was assessed by applying the criteria of Lipinski's 'rule of five'.

Inhibitory effect of polar oregano extracts on aldose reductase and soybean lipoxygenase in vitro.

The effect of methanol and aqueous methanol extract of Origanum vulgare L. ssp. hirtum on aldose reductase and soybean lipoxygenase was investigated. The results revealed a promising potential of oregano for preventing diabetes complications in the long term and an antiinflammatory efficacy by inhibiting soybean lipoxygenase.