Inhibition of the carbohydrate-hydrolyzing enzymes α-amylase and α-glucosidase by hydroxylated xanthones

Xanthones are oxygen-containing heterocyclic compounds that exhibit a wide range of biological and pharmacological properties. Some natural and synthetic derivatives have been identified for their antidiabetic profile, mainly as α-glucosidase inhibitors. However, studies concerning the inhibition of both carbohydrate-hydrolyzing enzymes α-amylase and α-glucosidase are scarce. Thus, in order to identify some of these dual-target antidiabetic agents, a series of new synthetic xanthones were evaluated together with their commercial parents mangiferin (4), α-mangostin (5) and γ-mangostin (6). The results showed that xanthones exhibited a systematic stronger inhibition against α-glucosidase rather than for α-amylase. Derivatives 2c, 3a and 3b, bearing one catechol moiety, were the most active inhibitors of α-amylase, while xanthones 2c, 3b and 3c were the most active against α-glucosidase activity, with IC50 values lower than 10 μM. These findings suggest that the substitution pattern of the xanthone scaffold modulated the inhibitory activity of these compounds, and some structure–activity relationships could be established for both assays. In addition, the type of inhibition was also studied, and the results indicate a competitive type of inhibition for α-amylase activity by xanthones 2c, 3b, 3c and γ-mangostin (6). On the other hand, non-competitive inhibition mechanisms can be ascribed for all xanthones 1–6 against α-glucosidase. The present work can open a promising area of research based on the design of novel xanthone derivatives, based on natural ones, for targeting key enzymes involved in glucose metabolism and therefore in the management of type 2 diabetes mellitus.The work was supported by UIBD/00690/2020 and UIDB/50006/2020 with funding from FCT/MCTES through national funds, and by EXPL/MED-QUI/0815/2021, with funding from FCT. Carina Proença acknowledges funding from FCT and MCTES through national funds and COMPETE, grant number PTDC/MED-QUI/29243/2017 -POCI-01-0145-FEDER-029243. Marisa Freitas acknowledges her contract under the Scientific Employment Stimulus - Individual Call (CEEC Individual) 2020.04126.CEECIND/CP1596/CT0006.info:eu-repo/semantics/publishedVersio

Synthesis and in vitro α-glucosidase inhibitory activity of polyhydroxylated 2-styrylchromones

2-Styrylchromones (2-SC) are a small class of naturally-occurring oxygen-containing heterocycles. Although they are scarce in nature, a large number of 2-SC derivatives has been synthesized and their biological activ ity evaluated, namely as antiallergic, anti-inflammatory, antimicrobial, antioxidant and antitumor agents [l]. As far as we know, the antidiabetic activity of 2-SC is still unexplored. With this rational in mind, a series of 12 polyhydroxylated derivatives of 2-SC (1) were synthethized and used as inhibitors of the carbohydrate hydrolyzing enzyme a-glucosidase. This enzyme catalyzes the final step of the digestive process of starch and break down oligosaccharides to monosaccharides being one of the most currently used therapeutic approaches to decrease postprandial hyperglycemia and consequently to control type 2 diabetes mellitus [2]. The synthesis of polyhydroxylated 2-SC involves a multi-step strategy starting with the condensation of the appropriate 2'-hydroxyacetophenones with cinnamic acid derivatives, base-promoted Baker- Yenkataraman rearrangement of the esters formed, cyclodehydration and finnaly cleavage of the protecting groups to afford the desired polyhydroxylated 2-SC (3]. The in vitro assay to evaluate the inhibitory activity of the compounds under study and the positive control, acarbose, against a-glucosidase was performed by monitoring the hydrolysis of the substrate p-nitrophenyl glucopyranoside into the product p-nitrophenol at 405 nm. In addition, the study of the inhibition type was carried out through nonlinear regression Michaelis-Menton enzymatic kinetics and the corresponding Lineweaver-Burk plot [4].This work received financial support from the European Union (FEDER funds POCI/01 /0145/FEDER/007265) and National Funds (FCT/MEC, Fundayiio para a Ciencia e Tecnologia and Ministerio da Educação e Ciência) under the Partnership Agreement PT2020 UID/ AGR/00690/2013; UID/QUI/50006/2013; UID/QUI/00062/2019, and "Programa Operacional Competitividade e Intemacionalizayiio" (COMPETE) (POCI-01-0145-FEDER-029241), and under the framework of QREN (NORTE-01-0145-FEDER-000024).info:eu-repo/semantics/publishedVersio

A study towards drug discovery for the management of type 2 diabetes: Mellitus through inhibition of the carbohydrate-hydrolyzing enzymes α-amylase and α-glucosidase by chalcone derivatives

The inhibition of carbohydrate-hydrolyzing enzymes, α-amylase and α-glucosidase, is one of the major therapeutic strategies for the treatment of type 2 diabetes mellitus. Chalcones have been recognized for their multiple biological activities, including antidiabetic properties, through unclear mechanisms. In the present work, a panel of chalcones bearing hydroxy, methoxy, methyl, nitro, chloro, fluoro and bromo substituents were evaluated against α-amylase and α-glucosidase activities, most of them for the first time. The results showed that the substitution patterns and the type of substituents of chalcones influence their inhibitory activity. The presence of hydroxy groups at C-2’- and C-4’ of the A ring and at C-3 and C-4 of the B ring favors the intended effect. Chalcones holding nitro groups and chloro substituents, together with a hydroxy group in the chalcone scaffold, showed strong inhibition of the α-glucosidase activity. The present study provides related scaffolds that may serve as the basis for the design and synthesis of new structures in order to obtain the ideal antidiabetic chalcone.This work received financial support from the European Union (FEDER funds POCI/01/0145/FEDER/007265) and National Funds (FCT/MEC, Fundação para a Ciência e Tecnologia and Ministério da Educação e Ciência) under the Partnership Agreement PT2020 UID/QUI/50006/2013, and “Programa Operacional Competitividade e Internacionalização” (COMPETE) (POCI-01-0145-FEDER-029241). Thanks are due to University of Aveiro, Instituto Politécnico de Bragança, FCT/ MEC for the financial support to the QOPNA (FCT UID/QUI/ 00062/2013) and CIMO (UID/AGR/00690/2013) research Units through national funds and where applicable co-financed by the FEDER, within the PT2020 Partnership Agreement, and also to the Portuguese NMR Network. Sónia Rocha acknowledges FCT the financial support for the PhD grant (PD/BD/ 145169/2019), in the ambit of “QREN – POPH – Tipologia 4.1 – Formação Avançada”, co-sponsored by Fundo Social Europeu (FSE) and by national funds of Ministério da Ciência, Tecnologia e Ensino Superior (MCTES).info:eu-repo/semantics/publishedVersio

Generalized St\"ackel Transform and Reciprocal Transformations for Finite-Dimensional Integrable Systems

We present a multiparameter generalization of the St\"ackel transform (the latter is also known as the coupling-constant metamorphosis) and show that under certain conditions this generalized St\"ackel transform preserves the Liouville integrability, noncommutative integrability and superintegrability. The corresponding transformation for the equations of motion proves to be nothing but a reciprocal transformation of a special form, and we investigate the properties of this reciprocal transformation. Finally, we show that the Hamiltonians of the systems possessing separation curves of apparently very different form can be related through a suitably chosen generalized St\"ackel transform.Comment: 21 pages, LaTeX 2e, no figures; major revision; Propositions 2 and 7 and several new references adde

Bamboo fibre processing: insights into hemicellulase and cellulase substrate accessibility

A biological approach for degumming bamboo substrates has been assessed. The ability of various commercially available enzymes, including cellulase, xylanase, pectinase and mannanase, to hydrolyze bamboo powders was investigated. In addition, a commercial cellulase preparation was applied onto bamboo fibre bundles obtained by natural retting. It was found that almost all enzymes applied can use bamboo material as a substrate. Mild autoclave pre-treatment can enhance reducing sugar yield from different enzyme treatments. A most pronounced effect was observed with cellulase treatment in which the hydrolysis degree increased 1.7 fold as measured by reducing sugars for autoclave pre-treated bamboo powders versus non-treated powders after only a short period of incubation. The combined treatment of hemicellulase preparations showed no effect on the hydrolysis of bamboo substrates. The effect of autoclave pre-treatment on cellulase-treated samples was confirmed by the increase of sugar yield, protein absorption as well as by the enhancement of surface modification and enzyme penetration observed by CLSM (confocal laser scanning microscopy). This work establishes a base for future studies to develop enzymatic hydrolysis of bamboo materials, making them suitable for textile processing.This work was made possible by support from the earmarked fund for Modern Agro-industry Technology Research System (nycytx-19-E23), the European Union Biorenew Project [Sixth Framework Programme (FP6-2004-NMP-NI-4)] and the Fundamental Research Funds for the Central Universities (JUSRP211A02)

Tailoring cutinase activity towards polyethylene terephthalate and polyamide 6,6 fibers

Cutinase from Fusarium solani pisi was genetically modified near the active site, by site-directed mutagenesis, to enhance its activity towards polyethylene terephthalate (PET) and polyamide 6,6 (PA 6,6) fibers. The mutations L81A, N84A, L182A, V184A and L189A were done to enlarge the active site in order to better fit a larger polymer chain. Modeling studies have shown enhanced free energy stabilization of model substrate tetrahedral intermediate (TI) bound at the enzyme active site for all mutants, for both model polymers. L81A and L182A showed an activity increase of four- and five-fold, respectively, when compared with the wild type, for PET fibers. L182A showed the one- and two-fold higher ability to biodegrade aliphatic polyamide substrates. Further studies in aliphatic polyesters seem to indicate that cutinase has higher ability to recognize aliphatic substrates.Fundação para a Ciência e a Tecnologia (FCT) - SFRH/BD/22490/2005, SFRH/BD/22149/2005European Community - Biosyntex Project, no. G5RD-CT-2000-30110 “Competitive and Sustainable Growth

Solute transport across plant cell membranes

CanaBQ is a Journal of the Portuguese Biochemical Society (http://canalbq.spb.pt/index.html)The transport of solutes across cell membranes, including organic nutrients, such as sugar, osmolytes, ions or metabolic waste products, is of extreme importance in all living systems. Up to 14% of the genome of all organisms represents information for transport proteins, which reflects the importance of such process. Transporters are also involved in the transduction of environmental and endogenous signals. Several transport systems have been identified and fully characterised at both molecular and biophysical levels in a wide variety of living organisms, from bacteria to humans, with the bacterial lactose permease (LacY) being a good example of such successful studies. The majority of transporter proteins are very well conserved throughout living systems, and some of them, such as sugar transporters, belong to a large family (SP, Sugar Porter). In higher plants, the photoassimilated carbon is transported from mature leaves throughout the phloem, mainly in the form of sucrose, as in the grapevine, or mannitol, as in the olive tree, to heterotrophic organs such as developing leaves, flowers, fruits and roots, which rely on its supply for their growth and development. Thus, the unlocking of the mechanisms of photoassimilate transport into plant sink tissues, as well as their regulation, has an important basic and applied relevance. Moreover, as most living organisms, plants also face a continuous battle against adverse environmental factors like increasing soil salinity, heat and drought. In this context, solute transport also has a relevant role in plant defence. For instance, the efficient exclusion of Na+ excess from the cytoplasm and vacuolar Na+ accumulation are the most important steps towards the maintenance of ion homeostasis under salt stress. The production, transport and accumulation of compatible solutes like mannitol are also important plant responses to salinity and drought. Like animals, where important diseases such as depression and hypertension are commonly treated with drugs targeted to specific transporters, plants have also benefited from the extensive and ongoing study of membrane transport. The present review provides an overview on the investigation that has been conducted in our laboratory under the scope of this fascinating topic.This work was supported by the Portuguese Foundation for Science and Technology (FCT) (research project ref. PTDC/AGR-ALI/100636/2008; to A. Conde, grant ref. SFRH/BD/47699/2008; to V. Martins, grant ref. SFRH/BD/64587/2009; to H. Noronha, grant ref. SFRH/BD/75257/2010, to N. Fontes, grant ref. SFRH/ BD/23169/2005, and to C. Conde, grant ref. SFRH/ BPD/34998/2007). We are also grateful to BabeliUM, the Language Centre of the University of Minho, namely Ana Teresa Correia, for revising the English version of the manuscript

Antimicrobial and antioxidant linen via laccase-assisted grafting

A laccase from Ascomycetemyceliophthora thermophila was used to assist the binding of chitosan and catechin onto a previous enzymatically oxidized linen surface. The process consists of the pre-treatment of the linen with laccase followed by the application of chitosan in a first step and catechin plus laccase in a second step. The results presented here support the conclusion that laccase is able to oxidize phenols naturally existing in flax fibres, and that the o-quinones formed promote the attachment of chitosan or/and catechin. The pre-treatment of linen with laccase is therefore the key factor for the success of catechin and chitosan grafting. A multifunctional linen product with both antioxidant and antibacterial properties was obtained with an acceptable level of durability in terms of end user requirements.Carla Silva would like to acknowledge the Portuguese Fundacao para a Ciencia e a Tecnologia (FCT) for funding under the scholarship SFRH/BPD/46515/2008

Regulation of CD1 Antigen-presenting Complex Stability

For major histocompatibility complex class I and II molecules, the binding of specific peptide antigens is essential for assembly and trafficking and is at the center of their quality control mechanism. However, the role of lipid antigen binding in stabilization and quality control of CD1 heavy chain (HC).beta(2)-microglobulin (beta(2)m) complexes is unclear. Furthermore, the distinct trafficking and loading routes of CD1 proteins take them from mildly acidic pH in early endososmal compartments (pH 6.0) to markedly acidic pH in lysosomes (pH 5.0) and back to neutral pH of the cell surface (pH 7.4). Here, we present evidence that the stability of each CD1 HC.beta(2)m complex is determined by the distinct pH optima identical to that of the intracellular compartments in which each CD1 isoform resides. Although stable at acidic endosomal pH, complexes are only stable at cell surface pH 7.4 when bound to specific lipid antigens. The proposed model outlines a quality control program that allows lipid exchange at low endosomal pH without dissociation of the CD1 HC.beta(2)m complex and then stabilizes the antigen-loaded complex at neutral pH at the cell surface