Mercury induces the externalization of phosphatidyl-serine in human renal proximal tubule (HK-2) cells.

Dwayne Sutton,Paul Tchounwou

doi:10.3390/ijerph2007040008

Abstract

The underlying mechanism for the biological activity of inorganic mercury is believed to be the high affinity binding of divalent mercuric cations to thiols of sulfhydryl groups of proteins. A comprehensive analysis of published data indicates that inorganic mercury is one of the most environmentally abundant toxic metals, is a potent and selective nephrotoxicant that preferentially accumulates in the kidneys, and is known to produce cellular injury in the kidneys. Binding sites are present in the proximal tubules, and it is in the epithelial cells of these tubules that toxicants such as inorganic mercury are reabsorbed. This can affect the enzymatic activity and the structure of various proteins. Mercury may alter protein and membrane structure and function in the epithelial cells and this alteration may result in long term residual effects. This research was therefore designed to evaluate the dose-response relationship in human renal proximal tubule (HK-2) cells following exposure to inorganic mercury. Cytotoxicity was evaluated using the MTT assay for cell viability. The Annexin-V assay was performed by flow cytometry to determine the extent of phosphatidylserine externalization. Cells were exposed to mercury for 24 hours at doses of 0, 1, 2, 3, 4, 5, and 6 microg/mL. Cytotoxicity experiments yielded a LD50 value of 4.65 +/- 0.6 microg/mL indicating that mercury is highly toxic. The percentages of cells undergoing early apoptosis were 0.70 +/- 0.03%, 10.0 +/- 0.02%, 11.70 +/- 0.03%, 15.20 +/- 0.02%, 16.70 +/- 0.03%, 24.20 +/-0.02%, and 25.60 +/- 0.04% at treatments of 0, 1, 2, 3, 4, 5, and 6 microg/mL of mercury respectively. This indicates a dose-response relationship with regard to mercury-induced cytotoxicity and the externalization of phosphatidylserine in HK-2 cells.

Highlights

Inorganic mercury is toxic and exerts its effects in a number of organs, tissues, and cell systems, but the kidneys constitute the primary target organ for inorganic mercury toxicity and mercuric ion accumulation in humans and mammals [1 - 4]
The MTT cell viability assay was carried out to establish cell viability in human renal proximal tubule HK-2 cells treated with concomitant doses of mercury
The effects of inorganic mercury on the viability of human renal proximal tubule (HK-2) cells are shown in figure 1

Summary

Introduction

Inorganic mercury is toxic and exerts its effects in a number of organs, tissues, and cell systems, but the kidneys constitute the primary target organ for inorganic mercury toxicity and mercuric ion accumulation in humans and mammals [1 - 4]. A variety of renal systems have shown an extremely steep dose response relationship for inorganic mercury [10 - 14]. In some of these systems, a threshold. Above the dose where an effect is observed, cell death progresses rapidly, and in some but not all of these systems, an all or none response is observed [15 - 19]. Above a certain dose or concentration of mercury, the ligands are depleted, and the mercuric ions can bind readily to critical nucleophilic groups in the cell causing functional impairment. Knowledge of the molecular and cellular mechanisms of mercury induced toxicity in the target organ (kidney) and the target cells (the epithelial cells lining the proximal tubule) is essential for early diagnosis and treatment regimens

Materials and Methods

Discussion

Findings

Conclusions