Polygonum tinctorium extract suppresses nitric oxide production by activated macrophages through inhibiting inducible nitric oxide synthase expression

Indigo plant leaf extract inhibits the binding of SARS‑CoV‑2 spike protein to angiotensin‑converting enzyme 2

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) uses its S1 spike protein to bind to angiotensin-converting enzyme 2 (ACE2) on human cells in the first step of cell entry. Tryptanthrin, extracted from leaves of the indigo plant, Polygonum tinctorium, using d-limonene (17.3 µg/ml), is considered to inhibit ACE2-mediated cell entry of another type of coronavirus, HCoV-NL63. The current study examined whether this extract could inhibit the binding of the SARS-CoV-2 spike protein to ACE2. Binding was quantified as cell-bound fluorescence intensity in live cell cultures in which canine kidney MDCK cells overexpressing ACE2 were incubated with fluorescein-labeled S1 spike protein. When indigo extract, together with S1 protein, was added at 8,650x and 17,300x dilutions, fluorescence intensity decreased in a dose- and S1 extract-dependent manner, without affecting cell viability. When 4.0-nM tryptanthrin was added instead of the indigo extract, fluorescence intensity also decreased, but to a lesser degree than with indigo extract. Docking simulation analyses revealed that tryptanthrin readily bound to the receptor-binding domain of the S1 protein, and identified 2- and 7-amino acid sequences as the preferred binding sites. The indigo extract appeared to inhibit S1-ACE2 binding at high dilutions, and evidently contained other inhibitory elements as well as tryptanthrin. This extract may be useful for the prevention or treatment of SARS-CoV-2 infection.

Anti-inflammatory and bioavailability studies on dietary 3,5,4'-trihydroxy-6,7-methylenedioxyflavone-O-glycosides and their aglycone from indigo leaves in a murine model of inflammatory bowel disease

Persicaria tinctoria (Aiton) Spach, also called Polygonum tinctorium Lour., (family Polygonaceae) for indigo plant has been traditionally useful as a medicinal or edible plant with a variety of biological activities. Of these, much attention has been paid to their anti-inflammatory activities. We have recently demonstrated that indigo leaves contain high levels of flavonol O-glycosides with 3,5,4'-trihydroxy-6,7-methylenedioxyflavone (TMF) as an aglycone. In this study, we attempted to evaluate anti-inflammatory activities of TMF-O-glycosides and free TMF prepared from indigo leaves after extraction with hot water. Free TMF was found to appreciably down-regulate the gene expression of pro-inflammatory cytokines including interleukin (IL)-1β, IL-6, inducible nitric oxide, and tumor necrosis factor-α in cultured macrophage cells stimulated with lipopolysaccharide while up-regulating the expression of anti-inflammatory IL-10. However, no study has been conducted regarding in vivo anti-inflammatory activities of TMF-O-glycosides and free TMF until now. Here, we assessed in vivo anti-inflammatory effects of these dietary compounds on ulcerative colitis in a murine model of inflammatory bowel disease by the induction with dextran sulfate sodium (DSS). Histological evaluation revealed that both TMF-O-glycosides and free TMF effectively protected against DSS-induced ulcerative colitis. The analysis of digested products by liquid chromatography and mass spectrometry led us to detect free TMF as a predominant metabolite in the feces of mice fed with TMF-O-glycosides. Moreover, free TMF was later detected as glucuronyl conjugates of TMF in the liver of mice fed with both fractions. These results indicate the effective digestion of TMF-O-glycosides and the subsequent absorption of free TMF in the gut of mice for exerting anti-inflammatory effects. Taken together, our findings suggest that dietary TMF-O-glycosides could be promising natural sources for the utilization as herbal medicine and nutraceuticals to expect in vivo anti-inflammatory activities.

Immunomodulatory effect of Parsley (Petroselinum crispum) essential oil on immune cells: mitogen-activated splenocytes and peritoneal macrophages

INTRODUCTION

Parsley (Petroselinum crispum) has been traditionally used for the treatment of allergy, autoimmune and chronic inflammatory disorders. The present study aims to investigate the suppressive effects of parsley essential oil on mouse splenocytes and macrophages cells.

METHODS AND MATERIALS

Parsley essential oil was harvested. It was treated on splenocytes and phytohemagglutinin (PHA) (5 μg/mL) and lipopolysaccharide (LPS) (10 μg/mL) activated splenocytes in different concentrations (0.01-100 μg/mL); then, proliferation was assayed by methyl tetrazolium (MTT) method. Treatment was also performed on the macrophages and LPS-stimulated macrophages (10 μg/ml) and the nitrite levels were measured using the diazotization method based on the Griess reaction and MTT assay for evaluation of the viability of the macrophages.

RESULTS

Proliferation of splenocytes in all the treated groups was suppressed. In PHA-stimulated splenocytes, the suppression was seen in all the examined concentrations (0.01-100 μg/mL), while in the unstimulated and LPS-stimulated groups suppression was relatively dose dependent and in high concentration (10 and100 μg/mL).The viability of the macrophages in all groups was the same and in the unstimulated groups; NO suppression was significant in all the concentrations but in LPS-stimulated groups, it was significant in the three higher concentrations (1, 10, and100 μg/mL).

CONCLUSION

The results of this study indicate that parsley essential oil may be able to suppress the cellular and humoral immune response. It can also suppress both NO production and the functions of macrophages as the main innate immune cells. These results may suggest that parsley essential oil is a proper suppressant for different applications.

Pro-inflammatory cytokine gene expression and nitric oxide regulation of aqueous extracted Astragali radix in RAW 264.7 macrophage cells

Astragali radix, which has tonifying and circulatory effect as well as immune response, is one of the oldest and most frequently used crude drug for oriental medicine in many Asian countries. The present study was conducted to evaluate the effect of aqueous extract of Astragali radix (ARE) on the functions of murine macrophage cell line, RAW 264.7 macrophage cells. In the cell proliferation assay, methotrexate (MTX), an agent of immune suppression, decreased the cell proliferation of RAW 264.7 macrophage cells (IC(50): 100 microg/ml), but the suppression of cell proliferation was significantly protected by ARE treatment in RAW 264.7 macrophage cells. The expressions of cytokine gene by ARE were investigated using reverse transcription polymerase chain reaction (RT-PCR). In RT-PCR, IL-1alpha, IL-1beta and IL-6 mRNA expressions was induced in ARE-treated RAW 264.7 macrophage cells. We also investigated the effect of the nitric oxide (NO) synthesis and inducible nitric oxide synthase (iNOS) mRNA expression by ARE. ARE alone had no effect on NO synthesis and iNOS mRNA expression in RAW 264.7 cells. In the case of lipopolysaccharide (LPS) stimulation, NO production and iNOS mRNA expression were detected in RAW 264.7 cells. However, NO production and iNOS mRNA expression which is induced by LPS decreased after treatment of ARE. These data demonstrate that ARE can reduce the suppression of macrophage cell proliferation induced by MTX, and induce IL-1alpha, IL-1beta and IL-6 mRNA expressions in RAW 264.7 macrophage cells. Also, ARE inhibit NO production in LPS-stimulated RAW 264.7 macrophage cells, and the inhibition of NO production may be associated with the inhibition of iNOS mRNA expression.

The natural plant product tryptanthrin ameliorates dextran sodium sulfate-induced colitis in mice

The therapeutic effects of tryptanthrin (TRYP), a natural product from the medicinal plant Polygonum tinctorium, were examined in a murine model of inflammatory bowel disease (IBD). Colitis was induced by 5% dextran sodium sulfate (DSS) in drinking water for 7 days from day 0. TRYP (100 mg/kg) was administered orally suspended in 5% arabia gum everyday from day 3 for 5 days. Histopathological analysis showed reduced colon damage in TRYP-treated mice on day 6; however, colon injury resumed after treatment was stopped. The production of prostaglandin E2 (PGE2), tumor necrosis factor-alpha (TNF-alpha) and nitric oxide (NO) by untreated and treated mouse colon tissues cultured in vitro were mostly unchanged by TRYP treatment. However, mitogen-stimulated spleen cells from TRYP-treated colitic mice produced less interleukin 2 (IL-2) and less interferon-gamma (IFN-gamma) than untreated colitic mouse spleen cells, early after induction of colitis. When colitis was induced with 5% DSS for 7 days and TRYP was given to the mice for 8 days from day 3, TRYP enhanced the survival of the mice but results were not significant. A significant reduction of weight loss was observed in TRYP-treated mice with colitis induced by 5% DSS for 4 days as compared to control mice. Remarkably, whereas 90% of the vehicle-treated mice died from wasting disease, all the TRYP-treated mice survived, suggesting that TRYP may have a therapeutic effect on colitis.

Carbofuran suppresses T-cell-mediated immune responses by the suppression of T-cell responsiveness, the differential inhibition of cytokine production, and NO production in macrophages

The effects of carbofuran (2,3-dihydro-2,2-dimethyl-7-benzo-furanol N-methylcarbamate) on the functions of T cells in splenocytes and peritoneal macrophages were examined in view of T-cell-mediated immune response (CMIR) in male C57BL/6 mice. Intraperitoneal administration of carbofuran (0.075, 0.15 and 0.3 mg/kg body weight) resulted in significant suppression of delayed type hypersensitivity (DTH), indicating that it caused the suppression of CMIR. Carbofuran decreased Concanavalin A (Con A)- and alloantigen-induced proliferation, and interleukin (IL)-2 production of splenocytes. In vitro addition of rIL-2 could not completely restore the suppressed T-cell proliferation, and IL-2-induced proliferation of Con A-activated splenocytes was also suppressed, which implied that carbofuran caused defects in IL-2 production and responsiveness of splenocytes to IL-2, leading to the suppression of T-cell proliferation. Con A-induced production of interferon-gamma (IFN-gamma) was significantly suppressed by carbofuran, while that of IL-4 was not affected. The production of transforming growth factor-beta from splenocytes was also significantly inhibited by carbofuran. Judging from these results, carbofuran might directly suppress the cytokine production in T helper 1 (Th1) cells. In addition, IFN-gamma-induced production of nitric oxide (NO) in macrophages was also inhibited by carbofuran, which might be one of the important mechanisms of carbofuran-induced CMIR suppression in mice. Collectively, the present study suggests that carbofuran might suppress CMIR through the suppression of T-cell responsiveness, IFN-gamma production in Th1 cells, and NO generation in macrophages.

Tryptanthrin inhibits nitric oxide and prostaglandin E(2) synthesis by murine macrophages

Nitric oxide (NO) and prostaglandins have been implicated in the pathogenesis of several inflammatory diseases. In this study, we investigated the effect of tryptanthrin (6,12-dihydro-6, 12-dioxoindolo-(2,1-b)-quinazoline), an antimicrobial and antitumoral plant compound isolated from Porigonum tinctorium, on NO and prostaglandin E(2) production by interferon-gamma and lipopolysaccharide-stimulated murine macrophage-like RAW 264.7 cells. Tryptanthrin markedly inhibited both NO and prostaglandin E(2) production in a dose-dependent manner. Tryptanthrin at 20 microM fully inhibited expression of inducible NO synthase, suggesting that the inhibitory effect on NO synthesis was mediated by inhibited expression of the enzyme. On the other hand, tryptanthrin had no effect on the levels of cyclooxygenase-2 protein, but inhibited cyclooxygenase enzyme activity with a ICM(50) value of 1.5 microM. Thus, tryptanthrin has the dual functions of inhibiting both NO and prostaglandin E(2) production by activated macrophages, suggesting that tryptanthrin exhibits anti-inflammatory properties.