EFFECT OF COBALT AND CHROMIUM IONS ON CASPASE ACTIVITY IN HUMAN MACROPHAGES

Abstract

The aim of this study was to analyze in human macrophages the effects of Co²⁺ and Cr³⁺ ions on the activity of caspase-8 and caspase-3, initiator and executioner of apoptosis, respectively. Caspase-3 and -8 activities were measured by colorimetric assays. Results show that Co²⁺ ions induced caspase-3 activity in a time-dependent manner. Co²⁺ had no effect on caspase-8 activity. The activation of caspase-3 by Cr³⁺ was time-dependent while caspase-8 activity reached a maximum after eight hours and decreased thereafter. Since caspase-8 is primarily activated by membrane-associated events, our results suggest that Cr³⁺ interacts with cell membrane components to induce macrophage apoptosis, whereas Co²⁺ seems to stimulate apoptosis most likely through intracellularly located mechanisms.

Because of their potential for improved wear performance, there has been a revived interest in metal-metal bearings, made of cobalt-chromium-molybdenum alloys, as an alternative to the use of conventional metal-polyethylene bearings. However, metal ion toxicity remains a major cause for concern. Previous studies suggested that both cobalt (Co²⁺) and chromium (Cr³⁺) ions induce macrophage apoptosis. The interest in apoptosis lies in the fact that it offers specific targets for therapeutic intervention.

The aim of this study was to analyze the effects in human macrophages of Co²⁺ and Cr³⁺ ions on the activity of caspase-8 and caspase-3, initiator and executioner of apoptosis, respectively.

U937 human macrophages were exposed to 0–10 ppm Co²⁺ (CoCl₂) and 0–500 ppm Cr³⁺ (CrCl₃). Caspase-3 and caspase-8 activities were measured by colorimetric assays based on the recognition of specific amino acid sequences (DEVD and IETD, respectively).

Results show that Co²⁺ ions induced caspase-3 activity with a significant increase after four hour incubation and a maximal 2.65-fold increase reached after twenty-four hour with 10 ppm. Co²⁺ had no effect on caspase-8 activity.

Cr³⁺ ions significantly stimulated caspase-3 activity after four hours with a maximal 1.75-fold stimulation reached after twenty-four hours, reaching only 50% of that observed with Co²⁺. Caspase-8 activity was significantly increased after two hours incubation, peaking at eight hours with a 2.2-fold increase, and decreasing thereafter.

Since caspase-8 is primarily activated by membrane-associated events, our results suggest that Cr³⁺ interacts with cell membrane components to induce macrophage apoptosis. On the other hand, Co²⁺ seems to stimulate caspase-3 activity and apoptosis most likely through intracellularly located mechanisms.