Description

Pyrogallol [C₆H₃ (OH)₃] is an organic white water-soluble solid compound that finds several uses. It is used as an ingredient in the hair cosmetic industry (Mazzei et al., 2007), photography (Upadhyay et al., 2010), and as an antipsoriatic drug (Khan et al., 2002). Besides its beneficiary roles in industries and as a consumer product, some previous studies report the toxicity caused by pyrogallol due to its tendency to produce free radicals and trigger apoptosis (Han and Park, 2002). Oxidative stress is mainly the cause of its toxicity and was reported to be carcinogenic and tumorigenic in female and male mice respectively (Mercado et al., 2013). Humans are often exposed to pyrogallol through hair dyes and ingestion of beverages like tea, coffee, and cause deleterious effects if consumed beyond the permissible amount. However, some previous studies also suggest its therapeutic role in inhibiting tumor growth in certain animal models as well as induces G2-M arrest in human lung cancer cells (Yang et al., 2009). Additionally, the protective effect of pyrogallol along with other phenols against the oxidative stress caused due to hydrogen peroxide has been reported in Saccharomyces cerevisiae (Mendes et al., 2015).

By considering these facts and background information, we examine the effects of pyrogallol treatment in fission yeast. We tested the dose-dependent consequences of pyrogallol on cell viability, sporulation efficacy, and intracellular ROS generation. The toxicity and cell viability parameters were checked in S. pombe at various concentrations by spot assay. We observed that the wild type cells were unable to grow on plates containing pyrogallol in a dose-dependent manner (Fig.1A). Previously, we have shown that the fission yeast wat1/pop3 is required for the oxidative stress response and exhibits sensitivity towards hydrogen peroxide (Ahamad et al. 2016). To further ascertain the role of pyrogallol in oxidative stress response, we checked the pyrogallol sensitivity of wat1/pop3 delete cells. The spotting assay revealed the enhanced pyrogallol sensitivity of wat1/pop3 delete cells as compared to wild type cells (Fig. 1A) suggesting that the pyrogallol induces oxidative stress. Next, we examined the level of reactive oxygen species (ROS) in untreated control and pyrogallol treated wild type cells by staining with H₂DCFDA dye which produces green fluorescence in the presence of ROS. We noticed a significant enhancement in green fluorescence under the confocal microscope displayed by pyrogallol treated cells in comparison with control (Fig. 1B) suggesting that the exposure to pyrogallol leads to increased production of ROS. Moreover, it has been reported from the previous studies that at hoisted concentrations, ROS deploys diverse detrimental effects on normal cellular pathways (Azad et al., 2014). Previously we have shown that the increase in ROS due to the inactivation of Wat1/pop3 protein leads to defects in sporulation in fission yeast (Ahamad et al., 2016; Ahamad et al., 2018). To examine the effect of pyrogallol on the sporulation in S. pombe we mixed the wild type cells of opposite mating type on the minimal media plates containing various concentrations of pyrogallol. On control plates, nearly 57.5% asci with four spores were observed indicating the normal sporulation. In contrast, we observed a decrease in the number of asci on the plate containing pyrogallol in a dose-dependent manner. At 1mM and 2mM pyrogallol concentration, the sporulation was reduced to 30% and 2.7% respectively (Fig. 1C & D). Thus, our study demonstrates that oxidative stress is implicated in pyrogallol-mediated toxicity that leads to affect the sporulation in fission yeast Schizosaccharomyces pombe.

Taken together, the present study highlighted the role of pyrogallol inducing oxidative stress response in S. pombe. Alterations in the level of ROS caused by pyrogallol are one of its inherent pro-oxidant properties which cause cell death and sporulation defects. Our results emphasize that it is essential to verify the effects of pyrogallol through various modes to fully understand its mechanism. Hence, further studies are needed to identify the cellular and intracellular targets of this compound.