Altered cytochrome P450 and P-glycoprotein levels in rats during simulated weightlessness.

Background: In order to investigate the effects of simulated weightlessness on drug metabolism, liver, kidney, and small intestine, microsomal proteins from tail-suspended rats were analyzed to determine cytochrome P450 (CYP) and P-glycoprotein levels following varying durations of tail-suspension.

Hypothesis: P-glycoprotein and CYP levels would both decrease similar to previous findings from actual spaceflight data.

Methods: Six groups of four Sprague-Dawley rats each were tail-suspended for up to 21 d; CYP and P-glycoprotein levels in the liver, kidney and small intestine were then measured by Western blotting. The results were compared with a control group of unsuspended rats.

Results: Our data showed there were significant changes in the levels of hepatic CYP2C11, 2E1, 4A1, and P-glycoprotein and significant changes in the levels of P-glycoprotein and CYP4A1 in the kidney. However, there were no significant changes detected in the levels of CYP3A2 in the liver or small intestine.

Conclusions: We conclude that simulated weightlessness, using the tail-suspended rat model, showed significant suppressive effects on levels of CYP2C11, 2E1, and P-glycoprotein in the liver and CYP4A1 in the kidney, while demonstrating no significant effect on the levels of CYP3A2 in the liver or small intestine. Thus, generalized predictions on the effect of simulated microgravity on drug metabolism cannot be made and the overall effect of spaceflight on individual enzymes should be investigated.