Anti-α-Glucosidase and Antiglycation Activities of α-Mangostin and New Xanthenone Derivatives: Enzymatic Kinetics and Mechanistic Insights through In Vitro Studies.

Diabetes mellitus is characterized by chronic hyperglycemia that promotes ROS formation, causing severe oxidative stress. Furthermore, prolonged hyperglycemia leads to glycation reactions with formation of AGEs that contribute to a chronic inflammatory state. This research aims to evaluate the inhibitory activity of α-mangostin and four synthetic xanthenone derivatives against glycation and oxidative processes and on α-glucosidase, an intestinal hydrolase that catalyzes the cleavage of oligosaccharides into glucose molecules, promoting the postprandial glycemic peak. Antiglycation activity was evaluated using the BSA assay, while antioxidant capacity was detected with the ORAC assay. The inhibition of α-glucosidase activity was studied with multispectroscopic methods along with inhibitory kinetic analysis. α-Mangostin and synthetic compounds at 25 µM reduced the production of AGEs, whereas the α-glucosidase activity was inhibited only by the natural compound. α-Mangostin decreased enzymatic activity in a concentration-dependent manner in the micromolar range by a reversible mixed-type antagonism. Circular dichroism revealed a rearrangement of the secondary structure of α-glucosidase with an increase in the contents of α-helix and random coils and a decrease in ß-sheet and ß-turn components. The data highlighted the anti-α-glucosidase activity of α-mangostin together with its protective effects on protein glycation and oxidation damage.

Treatment with the tumor necrosis factor-alpha-inducing drug 5,6-dimethylxanthenone-4-acetic acid enhances the antitumor activity of the photodynamic therapy of RIF-1 mouse tumors.

DMXAA (5,6-dimethylxanthenone-4-acetic acid) is an antivascular agent that exerts its antitumor effect at least partly through the induction of tumor necrosis factor (TNF)-alpha. Photodynamic therapy (PDT), the activation of a photoreactive drug in tumor tissue with visible light, is used clinically to control solid malignancies. PDT has been shown previously to be potentiated, in mice, by the i.p. administration of recombinant human TNF-alpha. Here, we investigated the activity of DMXAA as a modifier of Photofrin-based PDT of implanted murine RIF-1 tumors. The DMXAA dose (20 mg.kg(-1)) used throughout this study had little effect on tumor growth. The combination of DMXAA and PDT led to a reduction in tumor volume and significant delays in regrowth, giving a PDT-dose modification factor of 2.81. This enhancement was found to be strongly schedule dependent. The most pronounced responses were achieved when DMXAA was administered 1-3 h before the local illumination of the tumors; less activity was observed at other intervals within +/-24 h of PDT-light delivery. Using a 2-h DMXAA-light interval, histological examination showed significantly reduced blood vessel counts (CD31 immunostaining) and marked necrosis (H&E) in the tumors given combination therapy compared with the tumors given either agent alone. Conversely, peritumoral tissue was still intact 24 h after the combined therapy. DMXAA did not augment the damage to normal mouse feet after low-dose PDT (1.5 mg.kg(-1) Photofrin); however, there was some enhancement of normal tissue phototoxicity when DMXAA was combined with high-dose PDT. The antitumor effect after DMXAA plus low-dose PDT (1.5 mg.kg(-1) Photofrin) appeared to be dependent on TNF-alpha because neutralizing antibodies to this cytokine reduced the tumor response to control levels. DMXAA by itself induced TNF-alpha in RIF-1 tumors whereas PDT did not. However, the addition of PDT after DMXAA resulted in decreases in TNF-alpha, suggesting that the enhanced antitumor activity of the combination therapy was not attributable simply to an increased induction of the cytokine by PDT over that from DMXAA alone. These observations suggest a promising new combination therapy with considerable therapeutic advantage.

Estrogen modulation properties of mangiferin and quercetin and the mangiferin metabolite norathyriol.

Mango fruit contain many bioactive compounds, some of which are transcription factor regulators. Estrogen receptor alpha (ERα) and beta (ERß) are two regulators of gene transcription that are important in a variety of physiological processes and also in diseases including breast cancer. We examined the ability of the mango constituents quercetin, mangiferin, and the aglycone form of mangiferin, norathyriol, to activate both isoforms of the estrogen receptor. Quercetin and norathyriol decreased the viability of MCF-7 breast cancer cells whereas mangiferin had no effect on MCF-7 cells. We also determined that quercetin and mangiferin selectively activated ERα whereas norathyriol activated both ERα and ERß. Despite quercetin, mangiferin and norathyriol having similar polyphenolic structural motifs, only norathyriol activated ERß, showing that bioactive agents in mangoes have very specific biological effects. Such specificity may be important given the often-opposing roles of ERα and ERß in breast cancer proliferation and other cellular processes.

Relevance of the palatal protein kinase A pathway to the pathogenesis of cleft palate by secalonic acid D in mice.

Secalonic acid-D (SAD) is a teratogenic mycotoxin inducing cleft palate (CP) in the offspring of the exposed mice by reducing palatal shelf size secondary to reduced proliferation of the palatal mesenchymal (PM) cells. Co-administration of dimethylsulfoxide (DMSO) reversed the CP-inducing effect of SAD. Although SAD has been shown to affect both protein kinases A (PKA) and C (PKC) pathways, the relevance of each of these pathways to its CP induction is unknown. The present studies were designed to test the hypothesis that the protective effect of DMSO is mediated by its specific reversal of the effect(s) of SAD on one of these two pathways using ELISA-based activity assays, Western blot analysis, electrophoretic mobility shift assays (EMSA), and murine embryonic PM (MEPM) cell growth in culture. Within the PKA pathway, SAD inhibited the activity of the catalytic subunit of PKA and its migration into the nucleus, elevated phosphorylated cyclic AMP (cAMP) response element (CRE)-binding protein (pCREB) level, and reduced the binding of CREB to CRE. In the PKC pathway, SAD reduced the activity of PKC and the binding of transcription factors (TF) to 12-O-tetradecanoate-13 phorbol acetate-response element (TRE). SAD also inhibited MEPM cell growth and the expression of the CRE- and TRE-containing gene, proliferating cell nuclear antigen (PCNA). Reversal, by DMSO, of the effects of SAD on MEPM cell growth, on PCNA expression and on all components of the PKA, but not of PKC, pathway suggests that the perturbation of the PKA pathway by SAD is relevant to its induction of CP in mice.