Contrasting effects of oral versus transdermal estrogen on serum amyloid A (SAA) and high-density lipoprotein-SAA in postmenopausal women

Objectives - Previous studies indicated that oral estrogen increased C-reactive protein by a first-pass hepatic effect. In this study, we determine whether the route of estrogen administration influences serum amyloid A (SAA), another acute-phase protein produced by the liver, and the SAA content of the high-density lipoprotein (HDL-SAA) in postmenopausal women. Methods and Results - In 29 postmenopausal women without coronary heart disease, we conducted a randomized crossover placebo-controlled study to compare effects of transdermal versus oral estrogen on SAA and HDL-SAA. SAA, apolipoprotein A-I, HDL, and HDL-SAA were measured before and after 8 weeks of transdermal estradiol (100 mug per day), oral-conjugated estrogens (0.625 mg per day), or placebo. We found that oral estrogen significantly increased levels of SAA, HDL, and HDL-SAA, whereas transdermal estrogen reduced both SAA and HDL-SAA but had no effect on HDL in the same women. Conclusions - Oral estrogen increased SAA and altered HDL composition to contain a higher level of SAA by a first-pass hepatic mechanism. Because elevated SAA levels predict adverse prognosis in healthy postmenopausal women, and elevated HDL-SAA levels have been shown to interfere with HDL function, the route of administration may be an important consideration in minimizing side effects of estrogen replacement therapy on cardiovascular outcomes.