How to Measure Adipose Tissue Insulin Sensitivity.

Area of Science:

• Metabolic Physiology
• Endocrinology
• Insulin Resistance Research

Background:

• Adipose tissue insulin resistance can drive hepatic and skeletal muscle insulin resistance via elevated free fatty acids (FFAs).
• A lack of consensus exists regarding standardized methods for quantifying adipose tissue insulin sensitivity.

Purpose of the Study:

• To compare three methods for measuring adipose tissue insulin sensitivity: the single-step insulin clamp, the multistep pancreatic clamp, and the adipose tissue insulin resistance index (Adipo-IR).

Main Methods:

• Insulin sensitivity was assessed in 25 adults using multistep and one-step hyperinsulinemic-euglycemic clamps to determine the insulin concentration (IC50) for 50% palmitate flux suppression.
• Palmitate kinetics were analyzed via continuous [U-13C]palmitate infusion.
• Adipo-IR was calculated using fasting insulin and FFA levels.

Main Results:

• Adipo-IR demonstrated reproducibility (CV 10.0%) and strong correlation with the multistep clamp IC50 (r=0.86, P<0.001).
• Age and physical fitness (VO2 peak) significantly predicted residual variation between Adipo-IR and IC50 (P=0.02 for both).
• Both clamp methods showed good correlation (r=0.73, P<0.001).

Conclusions:

• Adipo-IR and the one-step clamp are viable predictors of adipose tissue insulin sensitivity, comparable to gold standards.
• Age and physical fitness introduce systematic variability, impacting predictive accuracy.
• Adipo-IR is suitable for large studies, while the multistep clamp is preferred for mechanistic investigations.