Md. Nurul Islam

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.

Protective Effects of Hyperoside against Carbon Tetrachloride-Induced Liver Damage in Mice

In this study, the hepatoprotective effects of hyperoside (1), a flavonoid glycoside isolated from Artemisia capillaris, have been examined against carbon tetrachloride (CCl4)-induced liver injury. Mice were treated intraperitoneally with vehicle or 1 (50, 100, and 200 mg·kg(-1)) 30 min before and 2 h after CCl4 (20 μL·kg(-1)) injection. Levels of serum aminotransferases were increased 24 h after CCl4 injection, and these increases were attenuated by 1. Histological analysis showed that 1 prevented portal inflammation, centrizonal necrosis, and Kupffer cell hyperplasia. Lipid peroxidation was increased and hepatic glutathione content was decreased significantly after CCl4 treatment, and these changes were reduced by administration of 1. Protein and mRNA expression of tumor necrosis factor-α (TNF-α), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and heme oxygenase-1 (HO-1) and nuclear protein expression of nuclear factor erythroid 2-related factor 2 (Nrf2) significantly increased after CCl4 injection. Compound 1 suppressed TNF-α, iNOS, and COX-2 protein and mRNA expression and augmented HO-1 protein and mRNA expression and Nrf2 nuclear protein expression. These results suggest that 1 has protective effects against CCl4-induced acute liver injury, and this protection is likely due to enhancement of the antioxidative defense system and suppression of the inflammatory response.

Protein Tyrosine Phosphatase 1B and α-Glucosidase Inhibitory Phlorotannins from Edible Brown Algae, Ecklonia stolonifera and Eisenia bicyclis

The present work investigates protein tyrosine phosphatase 1B (PTP1B) and the α-glucosidase inhibitory activities of two edible brown algae, Ecklonia stolonifera and Eisenia bicyclis, as well as in their isolated phlorotannins. Since the individual extracts and fractions showed significant inhibitory activities, column chromatography was performed to isolate six phlorotannins, phloroglucinol (1), dioxinodehydroeckol (2), eckol (3), phlorofurofucoeckol-A (4), dieckol (5), and 7-phloroeckol (6). Phlorotannins 3–6 were potent and noncompetitive PTP1B inhibitors with IC50 values ranging from 0.56 to 2.64 μM; 4–6 exhibited the most potent α-glucosidase inhibition with IC50 values ranging from 1.37 to 6.13 μM. Interestingly, 4 and 6 were noncompetitive, while 5 exhibited competitive inhibition in an α-glucosidase assay. E. stolonifera and E. bicyclis as well as their isolated phlorotannins therefore possessed marked PTP1B and α-glucosidase inhibitory activities; this could lead to opportunities in the development of therapeutic agents to control the postprandial blood glucose level and thereby prevent diabetic complications.

Inhibition of 5-lipoxygenase and skin inflammation by the aerial parts of Artemisia capillaris and its constituents

The aerial parts of Artemisia capillaris Thunberg (Compositae) have been used in Chinese medicine as a liver protective agent, diuretic, and for amelioration of skin inflammatory conditions. This study was conducted to establish the scientific rationale for treating skin inflammation and to find active principles from A. capillaris. To accomplish these goals, the 70% ethanol extract of the aerial parts of A. capillaris (AR) was prepared and its 5-lipoxygenase (5-LOX) inhibitory action was studied since 5-LOX products are known to be involved in several allergic and skin inflammatory disorders. AR showed potent inhibitory activity against 5-LOX-catalyzed leukotriene production by ionophore-induced rat basophilic leukemia-1 cells, with an IC50 of < 1.0 μg/mL. Nine major compounds, scopoletin, scopolin, scoparone, esculetin, quercetin, capillarisin, isorhamnetin, 3-O-robinobioside, isorhamnetin 3-O-galactoside and chlorogenic acid, were isolated from A. capillaris, and their effects were examined to identify the active principle(s). Several coumarin and flavonoid derivatives were found to be 5-LOX inhibitors. In particular, esculetin and quercetin were potent inhibitors, with IC50 values of 6.6 and 0.7 μM, respectively. Against arachidonic acid-induced ear edema in mice, AR, and esculetin strongly inhibited edematic response. AR and esculetin also inhibited delayed-type hypersensitivity response in mice. In conclusion, AR and some of their major constituents are 5-LOX inhibitors, and these in vitro and in vivo activities may contribute to the therapeutic potential of AR in skin inflammatory disorders in traditional medicine.

Potent α-glucosidase and protein tyrosine phosphatase 1B inhibitors from Artemisia capillaris

As a part of our ongoing effort to identify anti-diabetic constituents from natural sources, we examined the inhibitory activity of the methanol extracts of 12 species of the genus Artemisia, against α-glucosidase and protein tyrosine phosphatase 1B (PTP1B). The methanol extracts of different species exhibited promising α-glucosidase and PTP1B inhibitory activities. Since the methanol extract of Artemisia capillaris exhibited the highest α-glucosidase inhibitory activity together with significant PTP1B inhibitory activity, it was selected for further investigation. Repeated column chromatography based on bioactivity guided fractionation yielded 10 coumarins (esculetin, esculin, scopolin, isoscopolin, daphnetin, umbelliferone, 7-methoxy coumarin, scoparone, scopoletin, 6-methoxy artemicapin C), 8 flavonoids (hyperoside, quercetin, isorhamnetin, cirsilineol, arcapillin, isorhamnetin 3-robinobioside, linarin, isorhamnetin 3-glucoiside), 6 phenolic compounds (1,5-dicaffeoylquinic acid, 3,4-dicaffeoylquinic acid, 3,5-dicaffeoylquinic acid, 3,5-dicaffeoylquinic acid methyl ester, 4,5-dicaffeoylquinic acid, 3-caffeoylquinic acid), and one chromone (capillarisin). Among these compounds, esculetin, scopoletin, quercetin, hyperoside, isorhamnetin, 3,5-dicaffeoylquinic acid methyl ester, 3,4-dicaffeoylquinic acid, and 1,5-dicaffeoylquinic acid exhibited potent α-glucosidase inhibitory activity when compared to the positive control acarbose. In addition, esculetin and 6-methoxy artemicapin C displayed PTP1B inhibitory activity. Interestingly, all isolated dicaffeoylquinic acids showed significant PTP1B inhibitory activity. Therefore, the results of the present study clearly demonstrate the potential of the A. capillaris extract to inhibit α-glucosidase and PTP1B. These inhibitory properties can be largely attributed to a combination of different chemical structures, including coumarins, flavonoids, and dicaffeoylquinic acids, which could be further explored to develop therapeutic or preventive agents for the treatment of diabetes.

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.

Molecular mechanism of capillarisin-mediated inhibition of MyD88/TIRAP inflammatory signaling in in vitro and in vivo experimental models

ETHNOPHARMACOLOGICAL RELEVANCE Artemisia capillaris Thunberg (Compositae) have been used as traditional medicine as a diuretic, liver protective agent, and for amelioration of inflammatory and analgesic disorders. The present study was carried out to establish the scientific rationale for treating inflammation and to find active principles from A. capillaris. The aim of the present study is to investigate the possible anti-inflammatory mechanism of the major component (capillarisin) isolated from A. capillaris via inhibition of MyD88/TIRAP inflammatory signaling both in vitro and in vivo models. MATERIALS AND METHODS The nitrite, PGE(2), and TNF-α productions were evaluated by Griess reagent and ELISA kits. The protein and mRNA expression levels were investigated by Western blot and RT-PCR. The NF-κB and AP-1 DNA-binding was performed by electrophoretic mobility shift assay. The CFA- and carrageenan-induced paw edema was performed in ICR mice in which 20 and 80 mg/kg body weight of capillarisin was administered intraperitoneally (i.p.). RESULTS The results demonstrated that pretreatment with capillarisin effectively inhibited the LPS-induced activation of NF-κB, Akt, and MAP kinase-activated inflammatory genes, which is mediated by MyD88 and TIRAP. Treatment with capillarisin reduced the mRNA and protein levels of iNOS and COX-2 in RAW 264.7 cells as assessed by RT-PCR and Western blot. Capillarisin suppressed LPS-induced inhibitory kappa kinase (IKK) phosphorylation and the degradation of inhibitory kappa B (IκBα) and prevented the nuclear translocation of p65 and p50. Capillarisin also exhibited a promising inhibitory effect on the LPS-induced NF-κB and AP-1 DNA binding activity based on an electrophoretic mobility shift assay. The LPS-induced activation of p-JNK, p-p38, p-ERK, and p-Akt was significantly inhibited. In addition, the TNF-α level in the media was effectively reduced by capillarisin. In vivo experimental analysis revealed that capillarisin (20 and 80 mg/kg, i.p.) inhibited complete Freunds adjuvant (CFA)-and carrageenan-induced paw edema, nitrite production in plasma, and TNF-α, a pro-inflammatory cytokine production. CONCLUSION The results presented here demonstrate that capillarisin has consistent anti-inflammatory properties and acts by inhibiting inflammatory mediators in in vitro and in vivo experimental models, and suggest its potential utility in the control of inflammatory disorders.

In vitro antioxidant and anti-inflammatory activities of Angelica decursiva

Mounting evidences continue to support the involvement of oxidative/nitrosative stress and inflammation in the pathogenesis of many diseases. Plant constituents having antioxidant activities together with anti-inflammatory activities may provide better opportunities to develop anti-inflammatory agents. In view of this, we evaluated the antioxidant and antiinflammatory activities of methanolic extract of whole plants of Angelica decursiva, and its solvent soluble fractions via in vitro activities against lipopolysaccharide-induced nitric oxide (NO) production in RAW 264.7 cells, as well as in vitro scavenging activities against 1,1-diphenyl-2-picrylhydrazyl, 2,2′-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid, NO, and peroxynitrite. Among the tested fractions, the ethyl acetate fraction was found as the most active antioxidant fraction together with significant anti-inflammatory effect. From the active ethyl acetate fraction, four coumarin derivatives consisting of nodakenin, nodakenetin, umbelliferone, and umbelliferone-6-carboxylic acid, along with a phenolic compound, vanillic acid, were isolated. Among them, umbelliferone 6-carboxylic acid and vanillic acid were isolated for the first time from this plant. In all antioxidant assays, vanillic acid showed the highest antioxidant potential followed by umbelliferone 6-carboxylic acid among the isolated compounds. In the anti-inflammatory assay, umbelliferone 6-carboxylic acid exhibited the highest inhibitory activity against lipopolysaccharide-induced NO production in RAW 264.7 cells with an IC50 value of 72.98 μg/mL. Therefore, the present study reveals the potential antioxidant and antiinflammatory activities of whole plants of A. decursiva and its constituents, mainly umbelliferone 6-carboxylic acid, which could be used in the development of therapeutic and preventive agents for oxidative stress-related inflammatory diseases.

Inhibitory activity of coumarins from Artemisia capillaris against advanced glycation endproduct formation

Since glycation can lead to the onset of diabetic complications due to chronic hyperglycemia, several indigenous Artemisia species were evaluated as potential inhibitors of advanced glycation endproducts (AGE). Among them, the Artemisia capillaris plant demonstrated the highest AGE inhibitory activity. Repeated column chromatography was performed to isolate a new acylated flavonoid glycoside, acacetin-7-O-(6″-O-acetyl)-β-d-glucopyranosyl-(1→2)[α-l-rhamnopyranosyl]-(1→6)-β-d-glucopyranoside, along with 11 known flavonoids (acacetin-7-O-β-d-glucopyranosyl-(1→2)[α-l-rhamnopyranosyl]-(1→6)-β-d-glucopyranoside, linarin, quercetin, hyperoside, isorhamnetin, isorhamnetin 3-galactoside, isorhamnetin 3-glucoside, isorhamnetin 3-arabinoside, isorhamnetin 3-robinobioside, arcapillin, and cirsilineol), six coumarins (umbelliferone, esculetin, scopoletin, scopolin, isoscopolin, and scoparone), and two phenolic derivatives (4,5-di-O-caffeoylquinic acid and chlorogenic acid). In determining the structure-activity relationship (SAR), it was found that the presence and position of hydroxyl group of test coumarins (coumarin, esculin, isoscopoletin, daphnetin, 4-methylcoumarin, and six isolated coumarins) may play a crucial role in AGE inhibition. A free hydroxyl group at C-7 and a glucosyl group instead of a methoxyl group at C-6 are two important parameters for the inhibitory potential of coumarins on AGE formation. A. capillaris and five key AGE inhibitors, including 4,5-di-Ocaffeoylquinic acid, umbelliferone, esculetin, esculin, and scopoletin, were identified as potential candidates for use as therapeutic or preventive agents for diabetic complications and oxidative stress-related diseases. We understand this to be the first detailed study on the SAR of coumarins in AGE inhibition.

Vicenin 2 isolated from Artemisia capillaris exhibited potent anti-glycation properties.

Vicenin 2, isolated from a traditionally used medicinal plant Artemisia capillaris, is a 6,8-di-C-glucoside of apigenin which has been previously reported to possess a wide variety of pharmacological activities including antioxidant, anti-inflammatory, anti-cancer, and hepatoprotective. However, there have not been any reports concerning its anti-diabetic potential until now. Therefore, in the present study, we evaluated the anti-diabetic potential of vicenin 2 via α-glucosidase, protein tyrosine phosphatase 1B (PTP1B), rat lens aldose reductase (RLAR), and advanced glycation end products (AGE) formation inhibitory assays. Vicenin 2 strongly inhibited α-glucosidase, PTP1B, and RLAR in the corresponding assays. In addition, vicenin 2 inhibited the formation of both fluorescent AGE and nonfluorescent AGE, e.g., CML, as well as the level of fructosamine in glucose-fructose-induced bovine serum albumin (BSA) glycation. In the test system, vicenin 2 suppressed glycation-induced protein oxidation by attenuating the formation of protein carbonyl groups as well as by inhibiting the modification of protein thiol groups. Moreover, vicenin 2 was found to be a potent inhibitor of glycation-induced formation of amyloid cross-β structures in BSA. Taken together, vicenin 2 might be a useful lead for the development of multiple target-oriented therapeutic modalities for the treatment of diabetes and diabetes-associated complications.