Terpyridyl oxovanadium(IV) complexes for DNA crosslinking and mito-targeted photocytotoxicity.

Oxovanadium(IV) complexes [VO(L1/L2)Cl2]n+ (1,2) of (anthracenyl)terpyridine (An-tpy as L1 in 1, n=0) and triphenylphosphonium-appended (anthracenyl)terpyridine (An-tpy-TPP+ as L2 in 2, n=1) were synthesized, characterized and their DNA crosslinking ability, photocytotoxicity in visible light and cellular localization in cancer cells studied. The bromide derivative of 2, viz. [VO(An-tpy-TPP)Br2]Br (3) is structurally characterized. The structure showed trans disposition of two halides in the coordination sphere and the TPP+ unit is a pendant to the terpyridyl ligand. The DNA melting and comet assay studies on the complexes suggest the formation of DNA crosslinks. Complexes 1 and 2 displayed ~10 fold increase in cytotoxicity on exposure to visible light (400-700nm) when compared to those in dark in HeLa and MCF-7 cells. FACScan (Fluorescence Associated Cell Sorter Scan) analysis showed cellular apoptosis when treated with the complex in visible light in comparison to their dark controls. Fluorescence microscopic studies using complex 2 revealed its mitochondrial localization within the cancer cells.

Role of areca nut induced JNK/ATF2/Jun axis in the activation of TGF-ß pathway in precancerous Oral Submucous Fibrosis.

Oral submucous fibrosis (OSF) is potentially premalignant with progressive and irreversible extracellular matrix deposition accompanied by epithelial atrophy and like other fibrotic disorders, is primarily a TGF-ß driven disease. OSF is caused by prolonged chewing of areca nut. Our previous studies reported a pivotal role for TGF-ß activation and its effects contributing to OSF. However, the mechanism for activation of TGF-ß signaling in OSF is still unknown. In this study we demonstrate activation of TGF-ß signaling with sub-cytotoxic dose of areca nut in epithelial cells and discovered a key role for pJNK in this process. In good correlation; pJNK was detected in OSF tissues but not in normal tissues. Moreover, activation of JNK was found to be dependent on muscarinic acid receptor induced Ca2+/CAMKII as well as ROS. JNK dependent phosphorylation of ATF2/c-Jun transcription factors resulted in TGF-ß transcription and its signaling. pATF2/p-c-Jun were enriched on TGF-ß promoter and co-localized in nuclei of epithelial cells upon areca nut treatment. In corroboration, OSF tissue sections also had nuclear pATF2 and p-c-Jun. Our results provide comprehensive mechanistic details of TGF-ß signaling induced by etiological agent areca nut in the manifestation of fibrosis which can lead to new therapeutic modalities for OSF.

Epithelial atrophy in oral submucous fibrosis is mediated by copper (II) and arecoline of areca nut.

Exposure of oral cavity to areca nut is associated with several pathological conditions including oral submucous fibrosis (OSF). Histopathologically OSF is characterized by epithelial atrophy, chronic inflammation, juxtaepithelial hyalinization, leading to fibrosis of submucosal tissue and affects 0.5% of the population in the Indian subcontinent. As the molecular mechanisms leading to atrophied epithelium and fibrosis are poorly understood, we studied areca nut actions on human keratinocyte and gingival fibroblast cells. Areca nut water extract (ANW) was cytotoxic to epithelial cells and had a pro-proliferative effect on fibroblasts. This opposite effect of ANW on epithelial and fibroblast cells was intriguing but reflects the OSF histopathology such as epithelial atrophy and proliferation of fibroblasts. We demonstrate that the pro-proliferative effects of ANW on fibroblasts are dependent on insulin-like growth factor signalling while the cytotoxic effects on keratinocytes are dependent on the generation of reactive oxygen species. Treatment of keratinocytes with arecoline which is a component of ANW along with copper resulted in enhanced cytotoxicity which becomes comparable to IC(50) of ANW. Furthermore, studies using cyclic voltammetry, mass spectrometry and plasmid cleavage assay suggested that the presence of arecoline increases oxidation reduction potential of copper leading to enhanced cleavage of DNA which could generate an apoptotic response. Terminal deoxynucleotidyl transferase dUTP Nick End Labeling assay and Ki-67 index of OSF tissue sections suggested epithelial apoptosis, which could be responsible for the atrophy of OSF epithelium.

Activation of TGF-ß pathway by areca nut constituents: a possible cause of oral submucous fibrosis.

Oral submucous fibrosis (OSF) is a chronic inflammatory disease characterized by the accumulation of excess collagen, and areca nut chewing has been proposed as an important etiological factor for disease manifestation. Activation of transforming growth factor-ß signaling has been postulated as the main causative event for increased collagen production in OSF. Oral epithelium plays important roles in OSF, and arecoline has been shown to induce TGF-ß in epithelial cells. In an attempt to understand the role of areca nut constituents in the manifestation of OSF, we studied the global gene expression profile in epithelial cells (HaCaT) following treatment with areca nut water extract or TGF-ß. Interestingly, 64% of the differentially regulated genes by areca nut water extract matches with the TGF-ß induced gene expression profile. Out of these, expression of 57% of genes was compromised in the presence of ALK5 (TßRI) inhibitor and 7% were independently induced by areca nut, highlighting the importance of TGF-ß in areca nut actions. Areca nut water extract treatment induced p-SMAD2 and TGF-ß downstream targets in HaCaT cells but not in human gingival fibroblast cells (hGF), suggesting epithelial cells could be the source of TGF-ß in promoting OSF. Water extract of areca nut consists of polyphenols and alkaloids. Both polyphenol and alkaloid fractions of areca nut were able to induce TGF-ß signaling and its downstream targets. Also, SMAD-2 was phosphorylated following treatment of HaCaT cells by Catechin, Tannin and alkaloids namely Arecoline, Arecaidine and Guvacine. Moreover, both polyphenols and alkaloids induced TGF-ß2 and THBS1 (activator of latent TGF-ß) in HaCaT cells suggesting areca nut mediated activation of p-SMAD2 involves up-regulation and activation of TGF-ß. These data suggest a major causative role for TGF-ß that is induced by areca nut in OSF progression.