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LAT is essential for the mast cell stabilising effect of tHGA in IgE-mediated mast cell activation

Tan JW, Israf DA, Md Hashim NF, Cheah YK, Harith HH, Shaari K, et al.

Biochem Pharmacol, 2017 Nov 15;144:132-148.
PMID: 28813645 DOI: 10.1016/j.bcp.2017.08.010

Mast cells play a central role in the pathogenesis of allergic reaction. Activation of mast cells by antigens is strictly dependent on the influx of extracellular calcium that involves a complex interaction between signalling molecules located within the cells. We have previously reported that tHGA, an active compound originally isolated from a local shrub known as Melicope ptelefolia, prevented IgE-mediated mast cell activation and passive systemic anaphylaxis by suppressing the release of interleukin-4 (IL-4) and tumour necrosis factor (TNF)-α from activated rat basophilic leukaemia (RBL)-2H3 cells. However, the mechanism of action (MOA) as well as the molecular target underlying the mast cell stabilising effect of tHGA has not been previously investigated. In this study, DNP-IgE-sensitised RBL-2H3 cells were pre-treated with tHGA before challenged with DNP-BSA. To dissect the MOA of tHGA in IgE-mediated mast cell activation, the effect of tHGA on the transcription of IL-4 and TNF-α mRNA was determined using Real Time-Polymerase Chain Reaction (qPCR) followed by Calcium Influx Assay to confirm the involvement of calcium in the activation of mast cells. The protein lysates were analysed by using Western Blot to determine the effect of tHGA on various important signalling molecules in the LAT-PLCγ-MAPK and PI3K-NFκB pathways. In order to identify the molecular target of tHGA in IgE-mediated mast cell activation, the LAT and LAT2 genes in RBL-2H3 cells were knocked-down by using RNA interference to establish a LAT/LAT2 competition model. The results showed that tHGA inhibited the transcription of IL-4 and TNF-α as a result of the suppression of calcium influx in activated RBL-2H3 cells. The results from Western Blot revealed that tHGA primarily inhibited the LAT-PLCγ-MAPK pathway with partial inhibition on the PI3K-p65 pathway without affecting Syk. The results from RNAi further demonstrated that tHGA failed to inhibit the release of mediators associated with mast cell degranulation under the LAT/LAT2 competition model in the absence of LAT. Collectively, this study concluded that the molecular target of tHGA could be LAT and may provide a basis for the development of a mast cell stabiliser which targets LAT.

Matched MeSH terms: Mast Cells/drug effects*
Fulltext In vitro anti-allergic activity of Moringa oleifera Lam. extracts and their isolated compounds

Abd Rani NZ, Kumolosasi E, Jasamai M, Jamal JA, Lam KW, Husain K

BMC Complement Altern Med, 2019 Dec 11;19(1):361.
PMID: 31829185 DOI: 10.1186/s12906-019-2776-1

BACKGROUND: Moringa oleifera Lam. is a commonly used plant in herbal medicine and has various reported bioactivities such as antioxidant, antimicrobial, anticancer and antidiabetes. It is rich in nutrients and polyphenols. The plant also has been traditionally used for alleviating allergic conditions. This study was aimed to examine the anti-allergic activity of M. oleifera extracts and its isolated compounds.
METHOD: M. oleifera leaves, seeds and pods were extracted with 80% of ethanol. Individual compounds were isolated using a column chromatographic technique and elucidated based on the nuclear magnetic resonance (NMR) and electrospray ionisation mass spectrometry (ESIMS) spectral data. The anti-allergic activity of the extracts, isolated compounds and ketotifen fumarate as a positive control was evaluated using rat basophilic leukaemia (RBL-2H3) cells for early and late phases of allergic reactions. The early phase was determined based on the inhibition of beta-hexosaminidase and histamine release; while the late phase was based on the inhibition of interleukin (IL-4) and tumour necrosis factor (TNF-α) release.
RESULTS: Two new compounds; ethyl-(E)-undec-6-enoate (1) and 3,5,6-trihydroxy-2-(2,3,4,5,6-pentahydroxyphenyl)-4H-chromen-4-one (2) together with six known compounds; quercetin (3), kaempferol (4), β-sitosterol-3-O-glucoside (5), oleic acid (6), glucomoringin (7), 2,3,4-trihydroxybenzaldehyde (8) and stigmasterol (9) were isolated from M. oleifera extracts. All extracts and the isolated compounds inhibited mast cell degranulation by inhibiting beta-hexosaminidase and histamine release, as well as the release of IL-4 and TNF-α at varying levels compared with ketotifen fumarate.
CONCLUSION: The study suggested that M. oleifera and its isolated compounds potentially have an anti-allergic activity by inhibiting both early and late phases of allergic reactions.

Matched MeSH terms: Mast Cells/drug effects*
Anti-allergic activity of 2,4,6-trihydroxy-3-geranylacetophenone (tHGA) via attenuation of IgE-mediated mast cell activation and inhibition of passive systemic anaphylaxis

Tan JW, Israf DA, Harith HH, Md Hashim NF, Ng CH, Shaari K, et al.

Toxicol Appl Pharmacol, 2017 03 15;319:47-58.
PMID: 28167223 DOI: 10.1016/j.taap.2017.02.002

tHGA, a geranyl acetophenone compound originally isolated from a local shrub called Melicope ptelefolia, has been previously reported to prevent ovalbumin-induced allergic airway inflammation in a murine model of allergic asthma by targeting cysteinyl leukotriene synthesis. Mast cells are immune effector cells involved in the pathogenesis of allergic diseases including asthma by releasing cysteinyl leukotrienes. The anti-asthmatic properties of tHGA could be attributed to its inhibitory effect on mast cell degranulation. As mast cell degranulation is an important event in allergic responses, this study aimed to investigate the anti-allergic effects of tHGA in cellular and animal models of IgE-mediated mast cell degranulation. For in vitro model of IgE-mediated mast cell degranulation, DNP-IgE-sensitized RBL-2H3 cells were pre-treated with tHGA before challenged with DNP-BSA to induce degranulation. For IgE-mediated passive systemic anaphylaxis, Sprague Dawley rats were sensitized by intraperitoneal injection of DNP-IgE before challenged with DNP-BSA. Both in vitro and in vivo models showed that tHGA significantly inhibited the release of preformed mediators (β-hexosaminidase and histamine) as well as de novo mediators (interleukin-4, tumour necrosis factor-α, prostaglandin D2 and leukotriene C4). Pre-treatment of tHGA also prevented IgE-challenged RBL-2H3 cells and peritoneal mast cells from undergoing morphological changes associated with mast cell degranulation. These findings indicate that tHGA possesses potent anti-allergic activity via attenuation of IgE-mediated mast cell degranulation and inhibition of IgE-mediated passive systemic anaphylaxis. Thus, tHGA may have the potential to be developed as a mast cell stabilizer for the treatment of allergic diseases in the future.

Matched MeSH terms: Mast Cells/drug effects*
Fulltext Mechanistic Studies of the Antiallergic Activity of Phyllanthus amarus Schum. & Thonn. and Its Compounds

Abd Rani NZ, Lam KW, Jalil J, Mohamad HF, Mat Ali MS, Husain K

Molecules, 2021 Jan 28;26(3).
PMID: 33525733 DOI: 10.3390/molecules26030695

Phyllanthus amarus Schum. & Thonn. (Phyllanthaceae) is a medicinal plant that is commonly used to treat diseases such as asthma, diabetes, and anemia. This study aimed to examine the antiallergic activity of P. amarus extract and its compounds. The antiallergic activity was determined by measuring the concentration of allergy markers release from rat basophilic leukemia (RBL-2H3) cells with ketotifen fumarate as the positive control. As a result, P. amarus did not stabilize mast cell degranulation but exhibited antihistamine activity. The antihistamine activity was evaluated by conducting a competition radioligand binding assay on the histamine 1 receptor (H1R). Four compounds were identified from the high performance liquid chromatography (HPLC) analysis which were phyllanthin (1), hypophyllanthin (2), niranthin (3), and corilagin (4). To gain insights into the binding interactions of the most active compound hypophyllanthin (2), molecular docking was conducted and found that hypophyllanthin (2) exhibited favorable binding in the H1R binding site. In conclusion, P. amarus and hypophyllanthin (2) could potentially exhibit antiallergic activity by preventing the activation of the H1 receptor.

Matched MeSH terms: Mast Cells/drug effects
Fulltext Mast cell stabilizing effect of a geranyl acetophenone in dengue virus infection using in vitro model of DENV3-induced RBL-2H3 cells

Tan JW, Wan Zahidi NF, Kow ASF, Soo KM, Shaari K, Israf DA, et al.

Biosci Rep, 2019 06 28;39(6).
PMID: 31110077 DOI: 10.1042/BSR20181273

Mast cells (MCs), a type of immune effector cell, have recently become recognized for their ability to cause vascular leakage during dengue virus (DENV) infection. Although MC stabilizers have been reported to attenuate DENV induced infection in animal studies, there are limited in vitro studies on the use of MC stabilizers against DENV induced MC degranulation. 2,4,6-trihydroxy-3-geranyl acetophenone (tHGA) has been reported to be a potential MC stabilizer by inhibiting IgE-mediated MC activation in both cellular and animal models. The present study aims to establish an in vitro model of DENV3-induced RBL-2H3 cells using ketotifen fumarate as a control drug, as well as to determine the effect of tHGA on the release of MC mediators upon DENV infection. Our results demonstrated that the optimal multiplicities of infection (MOI) were 0.4 × 10-2 and 0.8 × 10-2 focus forming units (FFU)/cell. Ketotifen fumarate was proven to attenuate DENV3-induced RBL-2H3 cells degranulation in this in vitro model. In contrast, tHGA was unable to attenuate the release of both β-hexosaminidase and tumor necrosis factor (TNF)-α. Nonetheless, our study has successfully established an in vitro model of DENV3-induced RBL-2H3 cells, which might be useful for the screening of potential MC stabilizers for anti-dengue therapies.

Matched MeSH terms: Mast Cells/drug effects*