Endogenous Leptin Concentrations Poorly Predict Metreleptin Response in Patients With Partial Lipodystrophy

Abstract

Context: Leptin replacement with metreleptin improves glycemia and hypertriglyceridemia in severely hypoleptinemic patients with generalized lipodystrophy (GLD), but its effects are variable in partially leptin-deficient patients with partial lipodystrophy (PLD).

Objective: Compare 3 leptin assays (Study I); identify diagnostic performance of leptin assays to detect responders to metreleptin for each assay (Study II).

Design: Study I: cross-sectional analysis of average bias between leptin assays. Study II: retrospective analysis of diagnostic accuracy of potential leptin cut points to detect clinical responders to metreleptin.

Setting: National Institutes of Health; University of Michigan.

Participants and interventions: Study I: Metreleptin-naïve patients with lipodystrophy (GLD, n = 33, PLD, n = 67) and healthy volunteers (n = 239). Study II: GLD (n = 66) and PLD (n = 84) patients treated with metreleptin for 12 months.

Outcome measures: Leptin concentrations by Millipore radioimmunoassay (RIA), Millipore enzyme-linked immunosorbent assay (MELISA), and R&D Systems enzyme-linked immunosorbent assay (RDELISA). Response to metreleptin therapy was defined as either reduction ≥1.0% in A1c or ≥30% in serum triglycerides.

Results: RDELISA measured 3.0 ± 9.5 ng/mL higher than RIA; MELISA measured 11.0 ± 17.8 and 14.0 ±19.2 less than RIA and RDELISA, respectively. Leptin by RIA, MELISA, and RDELISA modestly predicted metreleptin response in GLD + PLD [receiver operating characteristic (ROC) area under the curve (AUC) 0.74, 0.69, and 0.71, respectively; P < 0.01 for all] with lower predictive power in PLD (ROC AUC 0.63, 0.61 and 0.65, respectively; P > 0.05 for all). The only reproducible cut point identified on sensitivity analyses was RIA leptin 7.2 ng/mL (sensitivity 56%; specificity 78%).

Conclusions: Three common leptin assays are not interchangeable, and a reliable cut point to select responders to metreleptin was not identified.

Trial registration: ClinicalTrials.gov NCT00001987 NCT00025883 NCT01778556 NCT00428987 NCT00677313 NCT01679197.

Keywords: ELISA; RIA; assay; cut point; leptin; lipodystrophy; metreleptin.

Published by Oxford University Press on behalf of the Endocrine Society 2021.

Figures

Figure 1.

Effect of sample storage duration on the measured leptin levels. Abbreviations: RIA, Millipore radioimmunoassay; MELISA, Millipore enzyme-linked immunosorbent assay; RDELISA, R&D Systems enzyme-linked immunosorbent assay.

Figure 2.

Study I: Agreement between commercial leptin assays. (A) Serum leptin measured by Millipore radioimmunoassay, Millipore enzyme-linked immunosorbent assay, and R&D Systems enzyme-linked immunosorbent assay in patients with lipodystrophy (red circles, generalized lipodystrophy; blue circles, partial lipodystrophy) and controls without lipodystrophy (gray circles) and (B) their correlation with tissue %fat measured by dual energy X-ray absorptiometry. (C-E) Scatterplots comparing the 3 assays of interest (insets show the subset of data in subjects with leptin levels

Figure 3.

Study II: Performance of baseline serum leptin levels as predictors of treatment response in patients with lipodystrophy treated with metreleptin. Baseline serum leptin differed between responders and nonresponders in the entire lipodystrophy population [generalized lipodystrophy (GLD) + partial lipodystrophy population (PLD)], measured by (A) Millipore radioimmunoassay (RIA), (B) Millipore enzyme-linked immunosorbent assay (MELISA), and (C) R&D Systems enzyme-linked immunosorbent assay (RDELISA). Red circles: GLD; blue circles: PLD. Baseline serum leptin did not differ between responders and nonresponders in the PLD only, measured by (D) RIA, (E) MELISA, and (F) RDELISA. Receiver operating characteristic (ROC) curves for baseline leptin measured by (G) RIA (H) MELISA, and (I) RDELISA. (J) Body mass index and (K) total tissue fat mass% ROC curves were comparable to baseline serum leptin. (L) Baseline leptin by RIA correlated with absolute reduction in hemoglobin A1c in the entire lipodystrophy population (GLD + PLD, black line), but this association was not present for either GLD or PLD alone (red and blue lines, respectively). Dashed black line in panels (A) and (D) show the RIA cut point of 7.2 ng/mL, which had the highest sensitivity and specificity. Abbreviations: AUC, area under the curve; BMI, body mass index; FM%, total body tissue %fat measured by dual-energy X-ray absorptiometry; LD, lipodystrophy; MELISA, Millipore enzyme-linked immunosorbent assay; NR, nonresponder; RDELISA, R&D Systems enzyme-linked immunosorbent assay; R, responder; RIA, Millipore radioimmunoassay; ROC, receiving operator characteristic.