Potential role of autophagy in smokeless tobacco extract-induced cytotoxicity and in morin-induced protection in oral epithelial cells

Heavy water (D2O) induces autophagy-dependent apoptotic cell death in non-small cell lung cancer A549 cells by generating reactive oxygen species (ROS) upon microtubule disruption

OBJECTIVE

Deuterium oxide (D2O) or heavy water is known to have diverse biological activities and have a few therapeutic applications due to its limited toxicity to human subjects. In the present study, we investigated the mechanism of D2O-induced cytotoxicity in non-small cell lung cancer A549 cells.

RESULTS

We found that D2O-treatment resulted in cytotoxicity, cell cycle arrest, and apoptosis in A549 cells in a dose-dependent fashion. In contrast, limited cytotoxicity was observed in lung fibroblasts WI38 cells. Moreover, D2O-treatment resulted in the disruption of the cellular microtubule network, accompanied by the generation of ROS. On further investigation, we observed that the intracellular ROS triggered autophagic responses in D2O-treated cells, leading to apoptosis by inhibiting the oncogenic PI3K/ Akt/ mTOR signaling. D2O-treatment was also found to enhance the efficacy of paclitaxel in A549 cells.

SIGNIFICANCE

D2O induces autophagy-dependent apoptosis in A549 cells via ROS generation upon microtubule depolymerization and inhibition of PI3K/ Akt/ mTOR signaling. It augments the efficacy of other microtubule-targeting anticancer drug taxol, which indicates the potential therapeutic importance of D2O as an anticancer agent either alone or in combination with other chemotherapeutic drugs.

Natural flavonoid morin showed anti-bacterial activity against Vibrio cholera after binding with cell division protein FtsA near ATP binding site

BACKGROUND

Increasing antibiotic-resistance in bacterial strains has boosted the need to find new targets for drug delivery. FtsA, a major bacterial divisome protein can be a potent novel drug-target.

METHODS AND RESULTS

This study finds, morin (3,5,7,2',4'-pentahydroxyflavone), a bio-available flavonoid, had anti-bacterial activities against Vibrio cholerae, IC₅₀ (50 μM) and MIC (150 μM). Morin (2 mM) kills ~20% of human lung fibroblast (WI38) and human intestinal epithelial (HIEC-6) cells in 24 h in-vitro. Fluorescence studies showed morin binds to VcFtsA (FtsA of V. cholerae) with a K_d of 4.68 ± 0.4 μM, inhibiting the protein's polymerization by 72 ± 7% at 25 μM concentration. Morin also affected VcFtsA's ATPase activity, recording ~80% reduction at 20 μM concentration. The in-silico binding study indicated binding sites of morin and ATP on VcFtsA had overlapping amino acids. Mant-ATP, a fluorescent ATP-derivative, showed increased fluorescence on binding to VcFtsA in absence of morin, but in its presence, Mant-ATP fluorescence decreased. VcFtsA-S40A mutant protein did not bind to morin.

CONCLUSIONS

VcFtsA-morin interaction inhibits the polymerization of the protein by affecting its ATPase activity. The destabilized VcFtsA assembly in-turn affected the cell division in V. cholerae, yielding an elongated morphology.

GENERAL SIGNIFICANCE

Collectively, these findings explore the anti-bacterial effect of morin on V. cholerae cells targeting VcFtsA, encouraging it to become a potent anti-bacterial agent. Low cytotoxicity of morin against human cells (host) is therapeutically advantageous. This study will also help in synthesizing novel derivatives that can target VcFtsA more efficiently.

Effects of smokeless tobacco on cell viability, reactive oxygen species, apoptosis, and inflammatory cytokines in human umbilical vein endothelial cells

Smokeless tobacco products provide an alternative to cigarettes; however, smokeless tobacco is carcinogenic and harmful to human health. This study evaluated the toxicological effects of snus extracts and cigarette smoke total particulate matter (TPM) on human umbilical vein endothelial cells (HUVECs). Treated cells were examined for cell viability, reactive oxygen species (ROS), apoptosis, and inflammatory cytokines. Moreover, we explored the mechanism of programmed cell death induced by snus. The results showed that snus extracts significantly inhibited cell viability in a dose-dependent manner. ROS was significantly increased in treatment groups, and anti-oxidant treatment could not prevent snus extract-induced cell death. Snus extracts induced apoptosis, DNA damage, activation and cleavage of caspase-3 and caspase-8, pathway-related gene change, and interleukin (IL)-6 and IL-8 release in HUVECs. Snus extracts exposure may induce cytotoxicity, ROS generation, inflammatory cytokines release, and apoptosis or DNA damage through intrinsic and extrinsic pathways in HUVECs.

Isolation of cytotoxic monomeric protein and morin derivatives from Solena amplexicaulis (Lam.) Gandhi

Solena amplexicaulis (Lam.) Gandhi (family- Cucurbitaceae), is used both in the Indian traditional system and folk medicine to treat several pathophysiological conditions and complex diseases including cancer. The screening of the phytochemicals of this plant (aerial parts) was performed to evaluate their cytotoxic effect against an in vitro cancer model utilising acute promyelocytic leukaemia HL60 cell line. Phytoconstituents were isolated by column chromatography and characterised. The purified protein was extracted, isolated and purified by using standard techniques. The cytotoxicity was evaluated by MTT assay. Spectral analysis revealed the isolated phytochemicals to be Morin-3-O-xyloside (1) and Morin 3-O-glucoside (2). The purified protein (P1) was found to be monomeric having a molecular weight of 30.2 kDa. Watching over 24 h exposure, compound 1 (IC₅₀ 1.5 µmol/L), compound 2 (IC₅₀ 3.5 µmol/L), and P1 (2.67 µmol/L) exhibited significant cytotoxic activity.

A novel triazole, NMK-T-057, induces autophagic cell death in breast cancer cells by inhibiting γ-secretase-mediated activation of Notch signaling

Notch signaling is reported to be deregulated in several malignancies, including breast, and the enzyme γ-secretase plays an important role in the activation and nuclear translocation of Notch intracellular domain (NICD). Hence, pharmacological inhibition of γ-secretase might lead to the subsequent inhibition of Notch signaling in cancer cells. In search of novel γ-secretase inhibitors (GSIs), we screened a series of triazole-based compounds for their potential to bind γ-secretase and observed that 3-(3'4',5'-trimethoxyphenyl)-5-(N-methyl-3'-indolyl)-1,2,4-triazole compound (also known as NMK-T-057) can bind to γ-secretase complex. Very interestingly, NMK-T-057 was found to inhibit proliferation, colony-forming ability, and motility in various breast cancer (BC) cells such as MDA-MB-231, MDA-MB-468, 4T1 (triple-negative cells), and MCF-7 (estrogen receptor (ER)/progesterone receptor (PR)-positive cell line) with negligible cytotoxicity against noncancerous cells (MCF-10A and peripheral blood mononuclear cells). Furthermore, significant induction of apoptosis and inhibition of epithelial-to-mesenchymal transition (EMT) and stemness were also observed in NMK-T-057-treated BC cells. The in silico study revealing the affinity of NMK-T-057 toward γ-secretase was further validated by a fluorescence-based γ-secretase activity assay, which confirmed inhibition of γ-secretase activity in NMK-T-057-treated BC cells. Interestingly, it was observed that NMK-T-057 induced significant autophagic responses in BC cells, which led to apoptosis. Moreover, NMK-T-057 was found to inhibit tumor progression in a 4T1-BALB/c mouse model. Hence, it may be concluded that NMK-T-057 could be a potential drug candidate against BC that can trigger autophagy-mediated cell death by inhibiting γ-secretase-mediated activation of Notch signaling.

Greater Sensitivity of Oral Fibroblasts to Smoked Versus Smokeless Tobacco

BACKGROUND

Smokers have an increased incidence and severity of periodontal disease. Although cigarette smoke contains >4,000 chemical components that could affect periodontal tissues, less is understood about the effect of smokeless tobacco. Therefore, this study compares the effects of cigarette smoke extract (CSE) and smokeless tobacco extract (STE) on cell survival and motility of periodontal ligament (PDL) and gingival fibroblasts in vitro.

METHODS

PDL and gingival fibroblasts were exposed to various concentrations of CSE, STE, or nicotine alone. Viable cells were labeled with calcein acetoxymethyl, visualized using fluorescent microscopy, and quantified using a fluorescence multi-well plate reader. In vitro wounding and collagen gel contraction assays were used to assess cell motility.

RESULTS

Both gingival and PDL fibroblasts displayed reduced cell viability with increasing concentrations of CSE and STE. Based on relative nicotine content, CSE was significantly more cytotoxic than STE. PDL fibroblasts were also more sensitive to both CSE and STE compared with gingival fibroblasts. Finally, sublethal doses of CSE reduced cell motility and gel contraction, whereas STE had less effect. Nicotine alone ≤0.5 mM had little to no effect in any of these assays.

CONCLUSIONS

Many of the underlying effects of tobacco products on periodontal tissues may be due to direct inhibition of normal fibroblast function. CSE is found to be more deleterious to the function of both PDL and gingival fibroblasts than STE. PDL fibroblasts appear to be more sensitive to CSE and STE than gingival fibroblasts. Therefore, cigarette smoke may have more profound effects than smokeless tobacco.