Cyclooxygenase expression is not required for release of arachidonic acid from cells by some nonsteroidal anti-inflammatory drugs and cancer preventive agents

Abstract

Background: Nonsteroidal anti-inflammatory drugs (NSAIDs) have been shown to be effective in inhibiting colorectal cancer. Cyclooxygenase activity is thought to mediate, in part, this cancer preventive effect. From observations made when cells that express cyclooxygenase activity were treated with NSAIDs and known cancer preventive agents, I have postulated that arachidonic acid (AA) release is associated with cancer prevention. In this study, the effects of NSAIDs on two cells that do not express cycloxygenase activity are detailed.

Results: NSAIDs and several cancer preventive agents release AA from human colon cancer cells (the HCT-15 cell line). The concentrations of NSAIDs required to release significant amounts of AA from the HCT-15 cells are greater than those required to inhibit the lactacystin plus 12-0-tetradecanoyl-13-acetate stimulated cyclooxygenase activity of rat liver cells. NSAIDs, tamoxifen and simvastatin were found to hemolyze erythrocyte cells which also do not express cyclooxygenase activity

Conclusion: The data demonstrate that AA release is independent of cyclooxygenase activity and together with hemolysis suggest that intercalation of the plasma membrane by some NSAIDs and cancer preventive agents, e.g. tamoxifen, mediates this release. A mechanism by which many of these drugs affect several diverse biologic properties including deesterification of membrane phospholipids by phospholipases to release AA is presented.

Figure 1

Release of AA from HCT-15 cells by increasing quantities of celecoxib (O), sulindac sulfide (◇), indomethacin (□) or ibuprofen (△). The HCT-15 cells were incubated with the NSAIDs for 19 h. Centrifuged culture fluids (200 μl) were counted for radioactivity.

Figure 2

Release of AA from HCT-15 cells by various concentrations of thapsigargin (□), tamoxifen (△), simvastatin (○) and tetrandrine (◇). The experiment was done with triplicate dishes. Incubation conditions were similar to those described in Fig. 1.

Figure 3

Hemolysis of 6.5 × 10⁷ SRBC (2.6 × 10⁷/ml) by various concentrations of celecoxib (□), sulindac sulfide (◇), indomethacin (○) and ibuprofen (△). Experimental conditions were similar to those described in Table 4.

Figure 4

Hemolysis of 6.5 × 10⁷ SRBC (2.6 × 10⁷/ml) by various concentrations of tamoxifen (□) and simvastatin (◇). Experimental and controls are described in Table 4.

Figure 5

Schematic representation of the mechanism of action of high doses of NSAIDs on cell membranes.