Shortcomings in methodology complicate measurements of serum retinol binding protein (RBP4) in insulin-resistant human subjects.

AIMS/HYPOTHESIS: Levels of retinol binding protein (RBP4) are increased in the serum of insulin-resistant human subjects even before overt diabetes develops. RBP4 levels correlate with insulin resistance, BMI, WHR, dyslipidaemia and hypertension. Improvement of insulin sensitivity with exercise training is associated with reduction in serum RBP4 levels. Therefore serum RBP4 may be useful for early diagnosis of insulin resistance and for monitoring improvements in insulin sensitivity. We sought to determine the performance of assays for this application. SUBJECTS AND METHODS: We compared quantitative western blotting and three commercially available multiwell immunoassays in parallel measurements of RBP4 concentrations in serum from insulin-sensitive subjects and from insulin-resistant subjects with impaired glucose tolerance or type 2 diabetes. RESULTS: The assays yielded different absolute values and magnitudes of elevation of serum RBP4. Western blotting and a sandwich ELISA reported RBP4 concentrations that highly inversely correlated with insulin sensitivity measured by euglycaemic-hyperinsulinaemic clamp. However, western blotting yielded concentrations with a greater dynamic range and less overlap between control and insulin-resistant subjects. Two competitive enzyme-linked immunoassays undervalued serum RBP4 concentrations in insulin-resistant subjects, possibly due to assay saturation. Poor linearity of dilution also limited assay utility. All assays tested exhibited greater immunoreactivity with urinary (C-terminal proteolysed) RBP4 than with full-length RBP4, the predominant form in serum. CONCLUSIONS/INTERPRETATIONS: These findings support the use of quantitative western blotting standardised to full-length RBP4 protein as a 'gold standard' method for measuring serum RBP4 in insulin-resistant states. Other assays should use full-length RBP4 and be extensively cross-validated using other methods.

Increased risk for gestational diabetes mellitus associated with insulin receptor and insulin-like growth factor II restriction fragment length polymorphisms.

Gestational diabetes mellitus (GDM) is defined as glucose intolerance with onset or first recognition during pregnancy. We have examined restriction fragment length polymorphisms (RFLPs) near "candidate diabetogenic genes" as one approach to identify molecular markers for GDM genes. Genotypes for insulin hypervariable region (HVR), insulin-like growth factor II (IGF2), insulin receptor (INSR), and glucose transporter (GLUT1) RFLPs were studied in 96 GDM and 164 control subjects, matched to GDM for race, age, and gravidity. Logistic regression analysis was used to explore the relationship between genotypes at these candidate gene loci and GDM, while adjusting for the effects of potential confounding variables. Among black subjects, the INSR allele 1 (P = 0.001) and interactions between INSR allele 1 with body mass index (BMI) (P = 0.002) and history of DM in subject's mother (P = 0.004) contributed significantly to GDM risk. Among Caucasian subjects, a similar relationship between the INSR allele 1 (P = 0.007) and INSR allele 1-BMI interactions (P = 0.011) on GDM risk were observed. In Caucasians, an additional significant risk factor was determined by an INSR allele 1-IGF2 allele 2 interaction (P = 0.018). No risk factors were identified in Hispanic subjects. These data continue to support the hypothesis that GDM is a heterogeneous disorder with respect to phenotypic and genotypic features. Furthermore, our data suggest that risk for GDM in black and Caucasian subjects is not due to obesity perse but to interactions between obesity and INSR alleles. In Caucasian women, INSR and IGF2 alleles interact to confer additional risk for GDM. Thus genes underlying susceptibility to GDM in some women may be similar to genes conferring risk to NIDDM, while in others novel genes may contribute to GDM risk.

Restriction fragment length polymorphisms of the insulin gene hypervariable region in gestational onset diabetes mellitus.

Restriction fragment length polymorphisms in the insulin gene hypervariable region are compared among 93 women with gestational onset diabetes mellitus and 146 women with normal glucose tolerance during pregnancy. No significant differences in gene or genotype frequencies were observed in the overall sample (p greater than 0.50). However, an increased frequency of one allele (class 1) was observed among nonoverweight patients with gestational onset diabetes mellitus with elevated fasting plasma glucose levels compared with age-, race-, and parity-matched control subjects (p = 0.061). These data suggest that gestational onset diabetes mellitus is a heterogeneous disorder with respect to both genotypic and phenotypic characteristics, and that restriction fragment length polymorphisms near the insulin gene may serve as a molecular marker for susceptibility to gestational onset diabetes mellitus only in some women.

Reagent strip glucose monitoring methods in chronic hemodialysis.

Reagent strip blood glucose testing methods have not been extensively validated in dialysis patients, a serious omission as thousands of diabetic patients are now entering dialysis. Severe anemia and uremia are potentially confounding variables that might impair those testing methods. Various methods were tested pre- and postdialysis, and compared with standard laboratory results. In general, strip methods (SM) underestimated laboratory results by approximately 15%. Extremes of blood urea nitrogen, hematocrit, or blood glucose levels did not affect this reliability. Such methods appear to be suitable for use in chronic hemodialysis patients.