Pathogenesis of A⁻β⁺ ketosis-prone diabetes

Abstract

A⁻β⁺ ketosis-prone diabetes (KPD) is an emerging syndrome of obesity, unprovoked ketoacidosis, reversible β-cell dysfunction, and near-normoglycemic remission. We combined metabolomics with targeted kinetic measurements to investigate its pathophysiology. Fasting plasma fatty acids, acylcarnitines, and amino acids were quantified in 20 KPD patients compared with 19 nondiabetic control subjects. Unique signatures in KPD--higher glutamate but lower glutamine and citrulline concentrations, increased β-hydroxybutyryl-carnitine, decreased isovaleryl-carnitine (a leucine catabolite), and decreased tricarboxylic acid (TCA) cycle intermediates--generated hypotheses that were tested through stable isotope/mass spectrometry protocols in nine new-onset, stable KPD patients compared with seven nondiabetic control subjects. Free fatty acid flux and acetyl CoA flux and oxidation were similar, but KPD had slower acetyl CoA conversion to β-hydroxybutyrate; higher fasting β-hydroxybutyrate concentration; slower β-hydroxybutyrate oxidation; faster leucine oxidative decarboxylation; accelerated glutamine conversion to glutamate without increase in glutamate carbon oxidation; and slower citrulline flux, with diminished glutamine amide-nitrogen transfer to citrulline. The confluence of metabolomic and kinetic data indicate a distinctive pathogenic sequence: impaired ketone oxidation and fatty acid utilization for energy, leading to accelerated leucine catabolism and transamination of α-ketoglutarate to glutamate, with impaired TCA anaplerosis of glutamate carbon. They highlight a novel process of defective energy production and ketosis in A⁻β⁺ KPD.

FIG. 1.

Lipid kinetics (mean ± SE) in A⁻β⁺ KPD patients and control subjects. *P ≤ 0.05; †P < 0.1 (N = 9 for KPD, N = 7 for control subjects).

FIG. 2.

BOHB concentration, rate of conversion of acetate to BOHB, BOHB flux, and BOHB oxidation (mean ± SE) in A⁻β⁺ KPD patients and control subjects (for BOHB concentration: N = 9 for KPD, N = 7 for control subjects; for all other measurements N = 7 for KPD, N = 3 for control subjects). *P < 0.05; †P = 0.09.

FIG. 3.

Leucine flux, oxidative decarboxylation, and nonoxidative disposal and valine flux (mean ± SE) in A⁻β⁺ KPD patients and control subjects. †P = 0.06 (N = 9 for KPD, N = 7 for control subjects).

FIG. 4.

A: Glutamine flux, glutamine plasma concentration, and absolute conversion rate of glutamine to glutamate (mean ± SE) in A⁻β⁺ KPD patients and control subjects (N = 9 for KPD, N = 7 for control subjects). B: Fractional synthesis rate of glutamate from glutamine, oxidation of glutamate carbon (derived from glutamine), and glutamate plasma concentration (mean ± SE) in A⁻β⁺ KPD patients and control subjects. *P < 0.05; †P = 0.06 (N = 9 for KPD, N = 7 for control subjects).

FIG. 5.

Citrulline flux and rate of transfer of glutamine amide-N to citrulline (mean ± SE) in A⁻β⁺ KPD patients and control subjects. *P < 0.05; †P = 0.10 (N = 9 for KPD, N = 7 for control subjects).

FIG. 6.

Schematic representation of metabolic defects in KPD as revealed by a combination of metabolomics and kinetics. Short black arrows represent increase or decrease in a metabolite measured in the metabolomics survey, whereas short white arrows represent increase, decrease, or no change in a metabolite measured in the kinetic studies. Lipid bilayer indicates the boundary of a liver cell. Dashed long arrows indicate decreased flux, and solid long arrows indicate increased flux. See text for details. alpha-KG, alpha-ketoglutarate; CPS, carbamoyl phosphate synthetase; GDH, glutamate dehydrogenase.