Md. Yousof Ali

Effects of C-glycosylation on anti-diabetic, anti-Alzheimer’s disease and anti-inflammatory potential of apigenin

Apigenin has gained particular interests in recent years as a beneficial and health promoting agent because of its low intrinsic toxicity. Vitexin and isovitexin, naturally occurring C-glycosylated derivatives of apigenin, have been known to possess potent anti-diabetic, anti-Alzheimers disease (anti-AD), and anti-inflammatory activities. The present study was designed to investigate the anti-diabetic, anti-AD, and anti-inflammatory potential of apigenin and its two C-glycosylated derivatives, vitexin and isovitexin by in vitro assays including rat lens aldose reductase (RLAR), human recombinant aldose reductase (HRAR), advanced glycation endproducts (AGEs), protein tyrosine phosphatase 1B (PTP1B), acetylcholinesterase (AChE), butyrylcholinesterase (BChE), β-site amyloid precursor (APP) cleaving enzyme 1 (BACE1), and nitric oxide (NO), inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in lipopolysaccharide (LPS)-induced RAW 264.7 cells. Among them, isovitexin was found as the most potent inhibitor against RLAR, HRAR, AGE, AChE, and BChE while vitexin showed the most potent PTP1B inhibitory activity. Despite the relatively weak anti-diabetic and anti-AD potentials, apigenin showed powerful antiinflammatory activity by inhibiting NO production and iNOS and COX-2 expression while vitexin and isovitexin were inactive. Therefore, it could be speculated that C-glycosylation of apigenin at different positions might be closely linked to relative intensity of anti-diabetic, anti-AD, and anti-inflammatory potentials.

Phlorotannins isolated from the edible brown alga Ecklonia stolonifera exert anti-adipogenic activity on 3T3-L1 adipocytes by downregulating C/EBPα and PPARγ

The dramatic increase in obesity-related diseases emphasizes the need to elucidate the cellular and molecular mechanisms underlying fat metabolism. Inhibition of adipocyte differentiation has been suggested to be an important strategy for preventing or treating obesity. In our previous study, we characterized an Ecklonia stolonifera extract and non-polar fractions thereof, including dichloromethane and ethyl acetate fractions. We showed that these fractions inhibited adipocyte differentiation and lipid formation/accumulation in 3T3-L1 preadipocytes, as assessed by Oil Red O staining. As part of our ongoing search for anti-obesity agents derived from E. stolonifera, in this work, we characterized five known phlorotannins, including phloroglucinol, eckol, dieckol, dioxinodehydroeckol, and phlorofucofuroeckol A, all of which were isolated from the active ethyl acetate fraction of E. stolonifera. We determined the chemical structures of these phlorotannins through comparisons of published nuclear magnetic resonance (NMR) spectral data. Furthermore, we screened these phlorotannins for their abilities to inhibit adipogenesis over a range of concentrations (12.5-100 μM). Of these five phlorotannins, phloroglucinol, eckol, and phlorofucofuroeckol A significantly concentration-dependently inhibited lipid accumulation in 3T3-L1 cells without affecting cell viability. In addition, the five isolated phlorotannins also significantly reduced the expression levels of several adipocyte marker genes, including proliferator activated receptor γ (PPARγ) and CCAAT/enhancer-binding protein α (C/EBPα), although they did so to different extents. These results suggest that the molecular weight of a phlorotannin is an important factor affecting its ability to inhibit adipocyte differentiation and modulate the expression levels of adipocyte marker genes.

The effects of C-glycosylation of luteolin on its antioxidant, anti-Alzheimer's disease, anti-diabetic, and anti-inflammatory activities.

To investigate the effect of C-glycosylation at different positions of luteolin, the structure–activity relationships of luteolin and a pair of isomeric C-glycosylated derivatives orientin and isoorientin, were evaluated. We investigated the effects of C-glycosylation on the antioxidant, anti-Alzheimer’s disease (AD), anti-diabetic and anti-inflammatory effects of luteolin and its two C-glycosides via in vitro assays of peroxynitrite (ONOO−), total reactive oxygen species (ROS), nitric oxide (NO), 1,1-diphenyl-2-picrylhydraxyl (DPPH), aldose reductase, protein tyrosine phosphatase 1B (PTP1B), acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and β-site amyloid precursor cleaving enzyme 1 (BACE1), and cellular assays of NO production and inducible nitric oxide synthase (iNOS)/cyclooxygenase-2 expression in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. Of the three compounds, isoorientin showed the highest scavenging activity against DPPH, NO, and ONOO−, while luteolin was the most potent inhibitor of ROS generation. In addition, luteolin showed the most potent anti-AD activity as determined by its inhibition of AChE, BChE, and BACE1. With respect to anti-diabetic effects, luteolin exerted the strongest inhibitory activity against PTP1B and rat lens aldose reductase. Luteolin also inhibited NO production and iNOS protein expression in LPS-stimulated macrophages, while orientin and isoorientin were inactive at the same concentrations. The effects of C-glycosylation at different positions of luteolin may be closely linked to the intensity and modulation of antioxidant, anti-AD, anti-diabetic, and anti-inflammatory effects of luteolin and its C-glycosylated derivatives.

Coptis chinensis alkaloids exert anti-adipogenic activity on 3T3-L1 adipocytes by downregulating C/EBP-α and PPAR-γ.

Obesity is a complex, multifactorial, and chronic disease that increases the risk for type 2 diabetes, coronary heart disease and hypertension, and has become a major worldwide health problem. Developing novel anti-obesity drugs from natural products is a promising solution to the global health problem of obesity. While screening anti-obesity potentials of natural products, the methanol extract of the rhizome of Coptis chinensis (Coptidis Rhizoma) was found to significantly inhibit adipocyte differentiation and lipid contents in 3T3-L1 cells, as assessed by Oil-Red O staining. Five known alkaloids, berberine, epiberberine, coptisine, palmatine, and magnoflorine, were isolated from the n-BuOH fraction of the methanol extract of Coptidis Rhizoma. We determined the chemical structure of these alkaloids through comparisons of published nuclear magnetic resonance (NMR) spectral data. Furthermore, we screened these alkaloids for their ability to inhibit adipogenesis over a range of concentrations (12.5-50 μM). All five Coptidis Rhizoma alkaloids significantly inhibited lipid accumulation in 3T3-L1 cells without affecting cell viability in a concentration dependent manner. In addition, the five alkaloids significantly reduced the expression levels of several adipocyte marker genes including proliferator activated receptor-γ (PPAR-γ) and CCAAT/enhancer-binding protein-α (C/EBP-α). In the present study, we found that the isolated alkaloids inhibited adipogenesis in a dose-dependent manner in 3T3-L1 cells; this inhibition was attributed to their abilities to downregulate the protein levels of the adipocyte marker proteins PPAR-γ and C/EBP-α. Thus, these results suggest that Coptidis Rhizoma extract and its isolated alkaloids may be of therapeutic interest with respect to the treatment of obesity.

Protein tyrosine phosphatase 1B inhibitory activity of alkaloids from Rhizoma Coptidis and their molecular docking studies.

ETHNOPHARMACOLOGIC RELEVANCE Rhizoma Coptidis (the rhizome of Coptis chinensis Franch) has commonly been used for treatment of diabetes mellitus in traditional Chinese medicine due to its blood sugar-lowering properties and therapeutic benefits which highly related to the alkaloids therein. However, a limited number of studies focused on the Coptis alkaloids other than berberine. MATERIALS AND METHODS In the present study, we investigated the anti-diabetic potential of Coptis alkaloids, including berberine (1), epiberberine (2), magnoflorine (3), and coptisine (4), by evaluating the ability of these compounds to inhibit protein tyrosine phosphatase 1B (PTP1B), and ONOO(-)-mediated protein tyrosine nitration. We scrutinized the potentials of Coptis alkaloids as PTP1B inhibitors via enzyme kinetics and molecular docking simulation. RESULTS The Coptis alkaloids 1-4 exhibited remarkable inhibitory activities against PTP1B with the IC50 values of 16.43, 24.19, 28.14, and 51.04 μM, respectively, when compared to the positive control ursolic acid. These alkaloids also suppressed ONOO(-)-mediated tyrosine nitration effectively in a dose dependent manner. In addition, our kinetic study using the Lineweaver-Burk and Dixon plots revealed that 1 and 2 showed a mixed-type inhibition against PTP1B, while 3 and 4 noncompetitively inhibited PTP1B. Moreover, molecular docking simulation of these compounds demonstrated negative binding energies (Autodock 4.0=-6.7 to -7.8 kcal/mol; Fred 2.0=-59.4 to -68.2 kcal/mol) and a high proximity to PTP1B residues, including Phe182 and Asp181 in the WPD loop, Cys215 in the active sites and Tyr46, Arg47, Asp48, Val49, Ser216, Ala217, Gly218, Ile219, Gly220, Arg221 and Gln262 in the pocket site, indicating a higher affinity and tighter binding capacity of these alkaloids for the active site of the enzyme. CONCLUSION Our results clearly indicate the promising anti-diabetic potential of Coptis alkaloids as inhibitors on PTP1B as well as suppressors of ONOO(-)-mediated protein tyrosine nitration, and thus hold promise as therapeutic agents for the treatment of diabetes and related disease.

Inhibitory activities of major anthraquinones and other constituents from Cassia obtusifolia against β-secretase and cholinesterases.

ETHNOPHARMACOLOGICAL RELEVANCE Semen Cassiae has been traditionally used as an herbal remedy for liver, eye, and acute inflammatory diseases. Recent pharmacological reports have indicated that Cassiae semen has neuroprotective effects, attributable to its anti-inflammatory actions, in ischemic stroke and Alzheimers disease (AD) models. AIM OF THE STUDY The basic goal of this study was to evaluate the anti-AD activities of C. obtusifolia and its major constituents. Previously, the extract of C. obtusifolia seeds, was reported to have memory enhancing properties and anti-AD activity to ameliorate amyloid β-induced synaptic dysfunction. However, the responsible components of C. obtusifolia seeds in an AD are currently still unknown. In this study, we investigated the inhibitory effects of C. obtusifolia and its constituents against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and β-site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) enzyme activity. MATERIALS AND METHODS In vitro cholinesterase enzyme assays by using AChE, BChE, and BACE1 were performed. We also scrutinized the potentials of Cassiae semen active component as BACE1 inhibitors via enzyme kinetics and molecular docking simulation. RESULTS In vitro enzyme assays demonstrated that C. obtusifolia and its major constituents have promising inhibitory potential against AChE, BChE, and BACE1. All Cassiae semen constituents exhibited potent inhibitory activities against AChE and BACE1 with IC50 values of 6.29-109µg/mL and 0.94-190µg/mL, whereas alaternin, questin, and toralactone gentiobioside exhibited significant inhibitory activities against BChE with IC50 values of 113.10-137.74µg/mL. Kinetic study revealed that alaternin noncompetitively inhibited, whereas cassiaside and emodin showed mixed-type inhibition against BACE1. Furthermore, molecular docking simulation results demonstrated that hydroxyl group of alaternin and emodin tightly interacted with the active site residues of BACE1 and their relevant binding energies (-6.62 and -6.89kcal/mol), indicating a higher affinity and tighter binding capacity of these compounds for the active site of BACE1. CONCLUSION The findings of the present study suggest the potential of C. obtusifolia and its major constituents for use in the development of therapeutic or preventive agents for AD, especially through inhibition of AChE, BChE and BACE1 activities.

Anti-diabetic and anti-Alzheimer’s disease activities of Angelica decursiva

Diabetes mellitus (DM) and Alzheimer’s disease (AD) constitute two global health issues. DM is an ever-increasing epidemic affecting millions of elderly people worldwide, causing major repercussions on patients’ daily lives, mostly due to chronic complications. Complications from DM can affect the brain, thereby characterizing DM as a risk factor for AD. In the present study, we examined the inhibitory activity of methanol extracts of different parts of 12 Angelica species against α-glucosidase, protein tyrosine phosphatase 1B (PTP1B), acetylcholinesterase (AChE), and butyrylcholinesterase (BChE). The methanol extract of Angelicadecursiva exhibited the highest inhibitory activities against α-glucosidase, PTP1B, AChE, and BChE and so was selected for further investigation. Repeated column chromatography based on bioactivity-guided fractionation yielded seven compounds (1–7). Among these compounds, nodakenin (1), nodakenetin (2), umbelliferone (3), cis-3′-acetyl-4′-angeloylkhellactone (4), 3′(R)-O-acetyl-4′(S)-O-tigloylkhellactone (5), isorutarine (6), and para-hydroxybenzoic acid (7) exhibited potent inhibitory activities against α-glucosidase, PTP1B, rat lens aldose reductase (RLAR), AChE, BChE, and β-site amyloid precursor protein cleaving enzyme 1 (BACE1). Our results clearly indicate the potential inhibition of α-glucosidase, PTP1B, RLAR, AChE, BChE, and BACE1 by A. decursiva as well as its isolated constituents, which could be further explored to develop therapeutic modalities for the treatment of DM and AD.

BACE1 molecular docking and anti-Alzheimer's disease activities of ginsenosides

ETHNOPHARMACOLOGICAL RELEVANCE Ginsenosides are natural product steroid glycosides and triterpene saponins obtained from the Panax species. Panax ginseng has been widely used as a traditional Chinese medicine (TCM) for around a thousand years, especially in East Asian countries. Ginseng, the root and rhizome of the most popular species P. ginseng, used as tonic, prophylactic agent and restorative. In TCM, ginseng is highly valued herb and has been applied to a variety of pathological conditions and illnesses such as hypodynamia, anorexia, shortness of breath, palpitation, insomnia, impotence, hemorrhage and diabetes. AIM OF THE STUDY The basic aim of this study was to evaluate the anti-Alzheimers disease activities of selected ginsenosides (Rb1, Rb2, Rc, Re, Rg1, and Rg3) according to peroxynitrite (ONOO(‒)) scavenging activity and inhibitory activity of ONOO(-)-mediated nitrotyrosine formation as a measure of changes in oxidative stress. In addition, molecular docking simulation studies were performed to predict binding energies of the ginsenosides with β-site amyloid precursor protein cleaving enzyme 1 (BACE1, β-secretase) and identify the interacting residues. MATERIALS AND METHODS In vitro cholinesterase enzyme assays by using acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and BACE1 were performed. In vitro authentic peroxynitrite scavenging activity and inhibitory activity against ONOO(-)-mediated nitrotyrosine formation were also performed. Molecular docking simulation studies were performed with Autodock Vina software and Discovery studio 4.1. RESULTS In vitro enzyme assays demonstrated that ginsenosides have significant inhibitory potential against AChE, BChE, and BACE1, as well as ONOO(-) and nitrotyrosine formation. Most importantly, significant AChE inhibitory activities were observed for Re; BChE for Rg3; and BACE1 for Rc, with IC50 values of 29.86±3.20, 16.80±0.36, and 59.81±2.74μg/mL, respectively. Among the tested ginsenosides, Rb1 exhibited a higher scavenging activity against ONOO(-) with an IC50 value of 27.86±1.34μg/mL, while Rc and Rg3 exhibited impressive inhibitory activity against the formation of nitrotyrosine. In addition, molecular docking studies revealed potential BACE1 inhibitory activity of ginsenosides, especially Rb1 and Rb2, which exhibited good binding affinities towards BACE1, with docking scores of -10kcal/mol. CONCLUSION The findings of the present study suggest the potential of ginsenosides (Rb1, Rb2, Rc, Re, Rg1, and Rg3) for use in the development of therapeutic or preventive agents for Alzheimers disease, especially through inhibition of AChE, BChE and BACE1 activities, as well as scavenging of ONOO(-) and inhibition of nitrotyrosine formation.

α-Glucosidase and Protein Tyrosine Phosphatase 1B Inhibitory Activity of Plastoquinones from Marine Brown Alga Sargassum serratifolium

Sargassum serratifolium C. Agardh (Phaeophyceae, Fucales) is a marine brown alga that belongs to the family Sargassaceae. It is widely distributed throughout coastal areas of Korea and Japan. S. serratifolium has been found to contain high concentrations of plastoquinones, which have strong anti-cancer, anti-inflammatory, antioxidant, and neuroprotective activity. This study aims to investigate the anti-diabetic activity of S. serratifolium and its major constituents through inhibition of protein tyrosine phosphatase 1B (PTP1B), α-glucosidase, and ONOO−-mediated albumin nitration. S. serratifolium ethanolic extract and fractions exhibited broad PTP1B and α-glucosidase inhibitory activity (IC50, 1.83~7.04 and 3.16~24.16 µg/mL for PTP1B and α-glucosidase, respectively). In an attempt to identify bioactive compounds, three plastoquinones (sargahydroquinoic acid, sargachromenol and sargaquinoic acid) were isolated from the active n-hexane fraction of S. serratifolium. All three plastoquinones exhibited dose-dependent inhibitory activity against PTP1B in the IC50 range of 5.14–14.15 µM, while sargachromenol and sargaquinoic acid showed dose-dependent inhibitory activity against α-glucosidase (IC50 42.41 ± 3.09 and 96.17 ± 3.48 µM, respectively). In the kinetic study of PTP1B enzyme inhibition, sargahydroquinoic acid and sargaquinoic acid led to mixed-type inhibition, whereas sargachromenol displayed noncompetitive-type inhibition. Moreover, plastoquinones dose-dependently inhibited ONOO−-mediated albumin nitration. Docking simulations of these plastoquinones demonstrated negative binding energies and close proximity to residues in the binding pocket of PTP1B and α-glucosidase, indicating that these plastoquinones have high affinity and tight binding capacity towards the active site of the enzymes. These results demonstrate that S. serratifolium and its major plastoquinones may have the potential as functional food ingredients for the prevention and treatment of type 2 diabetes.

Anti-adipogenic effect of epiberberine is mediated by regulation of the Raf/MEK1/2/ERK1/2 and AMPKα/Akt pathways

It has been reported that alkaloids derived from Coptis chinensis exert anti-adipogenic activity on 3T3-L1 adipocytes by downregulating peroxisome proliferation-activity receptor-γ (PPAR-γ) and CCAAT/enhancer binding protein-α (C/EBP-α). However, the signaling-based mechanism of the inhibitory role of epiberberine in the early stages of 3T3-L1 adipocyte differentiation is uncharacterized. Here, we show that epiberberine had inhibitory effects on adipocyte differentiation and significantly decreased lipid accumulation by downregulating an adipocyte-specific transcription factor, sterol regulatory element-binding protein-1 (SREBP-1). Furthermore, we observed that epiberberine markedly suppressed the differentiation-mediated phosphorylation of components of both the Raf/mitogen-activated protein kinase 1 (MEK1)/extracellular signal-regulated protein kinase 1/2 (ERK1/2) and AMP-activated protein kinase-α1 (AMPKα)/Akt pathways. In addition, gene expression of fatty acid synthase (FAS) was significantly inhibited by treatment with epiberberine during adipogenesis. These results indicate that the anti-adipogenic mechanism of epiberberine is associated with inhibition of phosphorylation of Raf/MEK1/ERK1/2 and AMPKα/Akt, followed by downregulation of the major transcription factors of adipogenesis, such as PPAR-γ, C/EBP-α, and SREBP-1, and FAS. Taken together, this study suggests that the anti-adipogenic effect of epiberberine is mediated by downregulation of the Raf/MEK1/ERK1/2 and AMPKα/Akt pathways during 3T3-L1 adipocyte differentiation. Moreover, the anti-adipogenic effects of epiberberine were not accompanied by modulation of β-catenin.