Retinol-binding protein 4 and insulin resistance in polycystic ovary syndrome.
OBJECTIVE
Polycystic ovary syndrome (PCOS) is an insulin-resistant state with insulin resistance being an established therapeutic target; however, measurement of insulin resistance remains challenging. We aimed to 1) determine serum retinol-binding protein 4 (RBP4) levels (purported to reflect insulin resistance) in women with PCOS and control subjects, 2) examine the relationship of RBP4 to conventional markers of insulin resistance, and 3) examine RBP4 changes with interventions modulating insulin resistance in overweight women with PCOS.


METHODS
At baseline, 38 overweight women (BMI >27 kg/m(2)) with PCOS and 17 weight-matched control subjects were compared. Women with PCOS were then randomly assigned to 6 months of a higher-dose oral contraceptive pill (OCP) (35 microg ethinyl estradiol/2 mg cyproterone acetate) or metformin (1 g b.i.d.). Outcome measures were insulin resistance (total insulin area under the curve) on an oral glucose tolerance test, RBP4, and metabolic/inflammatory markers.


RESULTS
Overweight women with PCOS were more insulin resistant than control subjects, yet RBP4 levels were not different in women with PCOS versus those in control subjects (35.4 +/- 4.3 vs. 28.9 +/- 3.1 microg/ml, P = 0.36). RBP4 correlated with cholesterol and triglycerides but not with insulin resistance. Metformin improved insulin resistance by 35%, whereas the OCP worsened insulin resistance by 33%. However, RBP4 increased nonsignificantly in both groups (43.7 +/- 6.3 vs. 42.6 +/- 5.5 microg/ml, P = 0.92).


CONCLUSIONS
Overweight women with PCOS were more insulin resistant than control subjects, but this finding was not reflected by RBP4 levels. RBP4 correlated with lipid levels but not with insulin resistance markers. RBP4 levels did not change when insulin resistance was reduced by metformin or increased by the OCP. These data suggest that RBP4 is not a useful marker of insulin resistance in PCOS but may reflect other metabolic features of this condition.
Hutchison
Samantha K
SK
Jean Hailes Foundation Research Group, Monash University Institute of Health Services Research, Melbourne, Australia.
Harrison
Cheryce
C
Stepto
Nigel
N
Meyer
Caroline
C
Teede
Helena J
HJ
D000328:Adult; D015992:Body Mass Index; D003276:Contraceptives, Oral / Q000627:therapeutic use; D003534:Cyproterone / Q000627:therapeutic use; D004997:Ethinyl Estradiol / Q000627:therapeutic use; D005260:Female; D005951:Glucose Tolerance Test; D006801:Humans; D007004:Hypoglycemic Agents / Q000627:therapeutic use; D007333:Insulin Resistance; D008687:Metformin / Q000627:therapeutic use; D050177:Overweight / Q000097:blood; D011085:Polycystic Ovary Syndrome / Q000097:blood*; D054839:Retinol-Binding Proteins, Plasma / Q000378:metabolism*; D049629:Waist-Hip Ratio
D003276:Contraceptives, Oral; D007004:Hypoglycemic Agents; C101326:RBP4 protein, human; D054839:Retinol-Binding Proteins, Plasma; D004997:Ethinyl Estradiol; D008687:Metformin; D003534:Cyproterone