Aqueous extract of Phyllanthus amarus inhibits chromium(VI)-induced toxicity in MDA-MB-435S cells

Abstract

Cr(VI) (hexavalent) is a very strong oxidant which causes high cytotoxicity through oxidative stress in tissue systems. Its abundance in groundwater and drinking water in several parts of the world has been noted to cause severe toxicity to both flora and fauna. This study evaluated the effects of aqueous extract of Phyllanthus amarus Schum. & Thon. against Cr(VI)-induced oxidative toxicity in vitro in MDA-MB-435S human breast carcinoma cells, along with an estimation of its antioxidant potential, inhibition of lipid peroxidation and determination of its polyphenolic composition. The extract showed significant (P < 0.05) potential in scavenging free radicals (DPPH and ABTS⁺) and Fe⁺³, and in inhibiting lipid peroxidation. A distinct decline in Cr(VI)-induced cytotoxicity was noticed in MDA-MB-435S cells with an increase in extract dosage. Furthermore, the extract proved to contain a high content of phenolic compounds which were found to have strong and significant (P < 0.05) positive correlations to free-radical scavenging potential, lipid peroxidation inhibition capacity and cyto-protective efficiency against Cr(VI)-induced oxidative cellular damage. HPLC analysis identified some of the major phenolic compounds in it. It was concluded that P. amarus aqueous extract has high antioxidant potential (by virtue of its phenolic constituents) which simultaneously inhibits Cr(VI)-induced oxidative toxicity to MDA-MB-435S cells.

Introduction

Chromium(VI) (hexavalent) is the most toxic and mutagenic heavy metal in biological systems (Mortuza et al., 2005). It exists as oxo-species such as CrO₃ and ${\text{CrO}}_4^{2-}$ that are robustly oxidizing (Cotton and Wilkinson, 1980), and result in excessive cytotoxicity which might lead to dermal damage, gastrointestinal bleeding, renal failure, intravascular hemolysis, liver damage, coma and even death (Lin et al., 2009). Cr(VI) is transported into cells through the sulfate transporter (Arslan et al., 1987), and leads to alteration of signal transduction pathways (Kim and Yurkow, 1996), cell transformation (Biedermann and Landolph, 1990), and increases the risk for developing cancer (International Agency for Research on Cancer, 1990). Simultaneously, it is also known to inhibit cell proliferation/cell cycle (Xu et al., 1996), thereby inducing growth arrest, accompanied by the generation of reactive oxygen species (ROS) that presumably trigger oxidative damage to DNA (Zhang et al., 2001) and consequent apoptosis (D’Agostini et al., 2002). Oxidative damage is associated with the generation of free radicals in cells exposed to Cr(VI) ion, and the propensity of cells to develop mutations in response to Cr(VI)-induced oxidative damage has been reported (Singh et al., 1998, Benzie and Strain, 1996).

A range of compounds with differential antioxidant properties are found in floral assets, and are considered to hold lofty prospects in perspective of therapeutic approaches to encounter and prevent free-radical-induced damage as that caused by Cr(VI) toxicity. Phyllanthus amarus Schum. & Thon. (Euphorbiaceae), also known as ‘carry me seed’, ‘black catnip’ and ‘hurricane weed’, has been traditionally used as a cure for dropsy, jaundice, diarrhea, dysentery, intermittent fevers, diseases of urino-genital system, scabies ulcers and wounds (Kuber et al., 1997). It has been evaluated for its various pharmacological activities, and has been proved to have potent hepatoprotective effect (Sane et al., 1995) and antiviral activity against hepatitis B virus (Ott et al., 1997, Lee et al., 1996, Mehrotra et al., 1991). It has also been reported to have diuretic, hypotensive and hypoglycaemic effects (Srividya and Periwal, 1995, Moshi et al., 1997). In vivo (rat) models demonstrated that the plant has protective activity towards liver cells against ethanol-induced oxidative stress (Faremi et al., 2008) and alloxan-induced diabetes mellitus (Raphael et al., 2002). It has also been reported that P. amarus has anti-mutagenic and anticarcinogenic effects on hamster liver cells (Sripanidkulchai et al., 2002). However, till date, there has been no report of the plant’s protective potential in cells against Cr(VI)-administered damage. This study was aimed at evaluating the effects of aqueous extract of P. amarus against Cr(VI)-induced (CrO₃-induced) oxidative toxicity in MDA-MB-435S human breast carcinoma cells, along with an estimation of its antioxidant potential and capacity for inhibition of lipid peroxidation, which were analyzed to hold strong correlation with its phenolic constituents that were characterized by HPLC study.