Metabolomics Profiling of Patients With A-β+ Ketosis-Prone Diabetes During Diabetic Ketoacidosis

Abstract

When stable and near-normoglycemic, patients with "A-β+" ketosis-prone diabetes (KPD) manifest accelerated leucine catabolism and blunted ketone oxidation, which may underlie their proclivity to develop diabetic ketoacidosis (DKA). To understand metabolic derangements in A-β+ KPD patients during DKA, we compared serum metabolomics profiles of adults during acute hyperglycemic crises, without (n = 21) or with (n = 74) DKA, and healthy control subjects (n = 17). Based on 65 kDa GAD islet autoantibody status, C-peptide, and clinical features, 53 DKA patients were categorized as having KPD and 21 type 1 diabetes (T1D); 21 nonketotic patients were categorized as having type 2 diabetes (T2D). Patients with KPD and patients with T1D had higher counterregulatory hormones and lower insulin-to-glucagon ratio than patients with T2D and control subjects. Compared with patients withT2D and control subjects, patients with KPD and patients with T1D had lower free carnitine and higher long-chain acylcarnitines and acetylcarnitine (C2) but lower palmitoylcarnitine (C16)-to-C2 ratio; a positive relationship between C16 and C2 but negative relationship between carnitine and β-hydroxybutyrate (BOHB); higher branched-chain amino acids (BCAAs) and their ketoacids but lower ketoisocaproate (KIC)-to-Leu, ketomethylvalerate (KMV)-to-Ile, ketoisovalerate (KIV)-to-Val, isovalerylcarnitine-to-KIC+KMV, propionylcarnitine-to-KIV+KMV, KIC+KMV-to-C2, and KIC-to-BOHB ratios; and lower glutamate and 3-methylhistidine. These data suggest that during DKA, patients with KPD resemble patients with T1D in having impaired BCAA catabolism and accelerated fatty acid flux to ketones-a reversal of their distinctive BCAA metabolic defect when stable. The natural history of A-β+ KPD is marked by chronic but varying dysregulation of BCAA metabolism.

Figure 1

Individual serum I/G ratios of nondiabetic control subjects (Control), T2D patients in hyperglycemic crisis, KPD patients with DKA, and T1D patients with DKA. None of these patients received insulin therapy prior to blood collection. Median value is expressed as a line for each group. Data were analyzed by nonparametric one-way ANOVA (Kruskal-Wallis test) with post hoc Dunn multiple comparisons (*P < 0.05; **P < 0.01).

Figure 2

Individual serum glutamate (A) and 3-MH (B) concentrations of healthy control subjects (Control), T2D patients in hyperglycemic crisis, KPD patients with DKA, and T1D patients with DKA. Median value is expressed as a line for each group. Data were analyzed by nonparametric one-way ANOVA (Kruskal-Wallis test) with post hoc Dunn multiple comparisons (*P < 0.05; **P < 0.01; ***P < 0.001; ****P < 0.0001).

Figure 3

Schema of key findings in fatty acid and BCAA catabolic pathways in liver, skeletal muscle, adipose tissue, and blood of KPD and T1D patients during DKA. Blue and yellow backgrounds indicate cytosol and mitochondrion, respectively. Dashed arrows/lines indicate decreased substrate or metabolite flow through a pathway, and green and red arrows indicate increased and decreased concentrations, respectively. Markedly increased lipolysis in adipose tissues results in higher blood levels of fatty acids despite increased uptake and β-oxidation by liver and muscle. Increased β-oxidation depletes whole body carnitine availability, compromising mitochondrial BCKA (hence BCAA) catabolism, especially in muscle, which has lower BCKD activity and does not synthesize carnitine. Consequently, net muscle uptake of BCAA is decreased and BCKA release into blood is greater than its uptake and catabolism by liver and other tissues, leading to higher blood levels of these metabolites. See text for additional details. AAs, other amino acids; AcAc, acetoacetate; α-KG, α-ketoglutarate; Acetylcarn, acetylcarnitine; Acylcarn, acylcarnitine; β-Oxd, β-oxidation; Carn, carnitine; CoASH, coenzyme A; FA, fatty acids; Glu, glutamic acid; Gly, glycerol; im, intramyocellular; TG, triglyceride.