Hasidah Mohd Sidek

The Antimalarial Effect of Curcumin Is Mediated by the Inhibition of Glycogen Synthase Kinase-3β

Curcumin, a bioactive compound in Curcuma longa, exhibits various pharmacological activities, including antimalarial effects. In silico docking simulation studies suggest that curcumin possesses glycogen synthase kinase-3β (GSK3β)-inhibitory properties. The involvement of GSK3 in the antimalarial effects in vivo is yet to be demonstrated. In this study, we aimed to evaluate whether the antimalarial effects of curcumin involve phosphorylation of host GSK3β. Intraperitoneal administration of curcumin into Plasmodium berghei NK65-infected mice resulted in dose-dependent chemosuppression of parasitemia development. At the highest dose tested (30 mg/kg body weight), both therapeutic and prophylactic administrations of curcumin resulted in suppression exceeding 50% and improved median survival time of infected mice compared to control. Western analysis revealed a 5.5-fold (therapeutic group) and 1.8-fold (prophylactic group) increase in phosphorylation of Ser 9 GSK3β and 1.6-fold (therapeutic group) and 1.7-fold (prophylactic group) increase in Ser 473 Akt in liver of curcumin-treated infected animals. Following P. berghei infection, levels of pro- and anti-inflammatory cytokines, tumor necrosis factor (TNF)-α, interferon (IFN)-γ, interleukin (IL)-10, and IL-4 were elevated by 7.5-, 35.0-, 33.0-, and 2.2-fold, respectively. Curcumin treatment (therapeutic) caused a significant decrease (by 6.0- and 2.0-fold, respectively) in serum TNF-α and IFN-γ level, while IL-10 and IL-4 were elevated (by 1.4- and 1.8-fold). Findings from the present study demonstrate for the first time that the antimalarial action of curcumin involved inhibition of GSK3β.

Anti-malarial activities of two soil actinomycete isolates from sabah via inhibition of glycogen synthase kinase 3β

Exploiting natural resources for bioactive compounds is an attractive drug discovery strategy in search for new anti-malarial drugs with novel modes of action. Initial screening efforts in our laboratory revealed two preparations of soil-derived actinomycetes (H11809 and FH025) with potent anti-malarial activities. Both crude extracts showed glycogen synthase kinase 3β (GSK3β)-inhibitory activities in a yeast-based kinase assay. We have previously shown that the GSK3 inhibitor, lithium chloride (LiCl), was able to suppress parasitaemia development in a rodent model of malarial infection. The present study aims to evaluate whether anti-malarial activities of H11809 and FH025 involve the inhibition of GSK3β. The acetone crude extracts of H11809 and FH025 each exerted strong inhibition on the growth of Plasmodium falciparum 3D7 in vitro with 50% inhibitory concentration (IC50) values of 0.57 ± 0.09 and 1.28 ± 0.11 µg/mL, respectively. The tested extracts exhibited Selectivity Index (SI) values exceeding 10 for the 3D7 strain. Both H11809 and FH025 showed dosage-dependent chemo-suppressive activities in vivo and improved animal survivability compared to non-treated infected mice. Western analysis revealed increased phosphorylation of serine (Ser 9) GSK3β (by 6.79 to 6.83-fold) in liver samples from infected mice treated with H11809 or FH025 compared to samples from non-infected or non-treated infected mice. A compound already identified in H11809 (data not shown), dibutyl phthalate (DBP) showed active anti-plasmodial activity against 3D7 (IC50 4.87 ± 1.26 µg/mL which is equivalent to 17.50 µM) and good chemo-suppressive activity in vivo (60.80% chemo-suppression at 300 mg/kg body weight [bw] dosage). DBP administration also resulted in increased phosphorylation of Ser 9 GSK3β compared to controls. Findings from the present study demonstrate that the potent anti-malarial activities of H11809 and FH025 were mediated via inhibition of host GSK3β. In addition, our study suggests that DBP is in part the bioactive component contributing to the anti-malarial activity displayed by H11809 acting through the inhibition of GSK3β.

Pencirian molekul glikogen sintase kinase-3 dari Eimeria tenella

Penemuan sasaran dadah antikoksidia baharu merupakan antara usaha yang diperlukan untuk mengawal penyakit koksidiosis ayam yang disebabkan oleh spesies Eimeria. Dalam kajian ini, serpihan yang mengekodkan glikogen sintase kinase-3 (GSK-3) Eimeria tenella putatif telah diamplifikasi daripada cDNA E. tenella. Hasil pemadanan homologi menunjukkan jujukan GSK-3 E. tenella yang terjana mempunyai padanan yang tinggi dengan jujukan GSK-3 organisma lain. Domain terpulihara GSK-3 dan residu yang penting untuk aktiviti GSK-3 juga diramalkan hadir dalam jujukan GSK-3 E. tenella. Analisis struktur sekunder serta pemodelan homologi menunjukkan pembahagian struktur protein kepada domain bebenang beta pada hujung N dan domain heliks alfa pada hujung C, yang merupakan ciri enzim GSK-3. Kesemua hasil analisis ini menyokong bahawa jujukan yang dikaji mengekodkan protein GSK-3 dalam E. tenella. Walaupun darjah keterpuliharaan adalah tinggi, namun terdapat perbezaan yang bermakna diperhatikan antara GSK-3 E. tenella dan perumahnya. Residu Ser 9 yang dilaporkan penting untuk perencatan aktiviti GSK-3 didapati tidak terpulihara dalam GSK-3 E. tenella. Memandangkan Ser 9 merupakan tapak pemfosfatan bagi GSK-3β dalam haiwan vertebrata, ketiadaan residu ini dalam jujukan GSK-3 E. tenella mencadangkan bahawa pengawalaturan GSK-3 E. tenella melibatkan tapak pemfosfatan dan mekanisme yang berbeza. Tambahan pula, hasil analisis filogenetik menunjukkan bahawa GSK-3 E. tenella mempunyai pertalian yang rapat dengan protein GSK-3 tumbuh-tumbuhan. Analisis superposisi GSK-3 E. tenella dengan GSK-3β Homo sapiens pula menunjukkan bahawa perencat GSK-3 mampu berinteraksi dengan protein GSK-3 E. tenella. Keputusan kajian ini mencadangkan bahawa GSK-3 E. tenella mempunyai potensi untuk diperkembangkan sebagai sasaran dadah antikoksidia.