Clinical, biochemical and molecular characterization of 12 patients with pyruvate carboxylase deficiency treated with triheptanoin

Pyruvate carboxylase (PC) deficiency is a rare autosomal recessive mitochondrial neurometabolic disorder of energy deficit resulting in high morbidity and mortality, with limited therapeutic options. The PC homotetramer has a critical role in gluconeogenesis, anaplerosis, neurotransmitter synthesis, and lipogenesis. The main biochemical and clinical findings in PC deficiency (PCD) include lactic acidosis, ketonuria, failure to thrive, and neurological dysfunction. Use of the anaplerotic agent triheptanoin on a limited number of individuals with PCD has had mixed results. We expand on the potential utility of triheptanoin in PCD by examining the clinical, biochemical, molecular, and health-related quality-of-life (HRQoL) findings in a cohort of 12 individuals with PCD (eight with Type A and two each with Types B and C) treated with triheptanoin ranging for 6 days to about 7 years. The main endpoints were changes in blood lactate and HRQoL scores, but collection of useful data was limited to about half of subjects. An overall trend of lactate reduction with time on triheptanoin was noted, but with significant variability among subjects and only one subject reaching close to statistical significance for this endpoint. Parent reported HRQoL assessments with treatment showed mixed results, with some subjects showing no change, some improvement, and some worsening of overall scores. Subjects with buried amino acids in the pyruvate carboxyltransferase domain of PC that undergo destabilizing replacements may be more likely to respond (with lactate reduction or HRQoL improvement) to triheptanoin compared to those with replacements that disrupt tetramerization or subunit-subunit interface contacts. The reason for this difference is unclear and requires further validation. We observed significant variability but an overall trend of lactate reduction with time on triheptanoin and mixed parent reported outcome changes by HRQoL assessments for subjects with PCD on long-term triheptanoin. The mixed results noted with triheptanoin therapy in this study could be due to endpoint data limitation, variability of disease severity between subjects, limitation of the parent reported HRQoL tool, or subject genotype variability. Alternative designed trials and more study subjects with PCD will be needed to validate important observations from this work.

Solvent accessibility of E1α and E1β residues with known missense mutations causing pyruvate dehydrogenase complex (PDC) deficiency: Impact on PDC-E1 structure and function

Pyruvate dehydrogenase complex deficiency is a major cause of primary lactic acidemia resulting in high morbidity and mortality, with limited therapeutic options. PDHA1 mutations are responsible for >82% of cases. The E1 component of PDC is a symmetric dimer of heterodimers (αβ/α'β') encoded by PDHA1 and PDHB. We measured solvent accessibility surface area (SASA), utilized nearest-neighbor analysis, incorporated sequence changes using mutagenesis tool in PyMOL, and performed molecular modeling with SWISS-MODEL, to investigate the impact of residues with disease-causing missense variants (DMVs) on E1 structure and function. We reviewed 166 and 13 genetically resolved cases due to PDHA1 and PDHB, respectively, from variant databases. We expanded on 102 E1α and 13 E1β nonduplicate DMVs. DMVs of E1α Arg112-Arg224 stretch (exons 5-7) and of E1α Arg residues constituted 40% and 39% of cases, respectively, with invariant Arg349 accounting for 22% of arginine replacements. SASA analysis showed that 86% and 84% of residues with nonduplicate DMVs of E1α and E1β, respectively, are solvent inaccessible ("buried"). Furthermore, 30% of E1α buried residues with DMVs are deleterious through perturbation of subunit-subunit interface contact (SSIC), with 73% located in the Arg112-Arg224 stretch. E1α Arg349 represented 74% of buried E1α Arg residues involved in SSIC. Structural perturbations resulting from residue replacements in some matched neighboring pairs of amino acids on different subunits involved in SSIC at 2.9-4.0 Å interatomic distance apart, exhibit similar clinical phenotype. Collectively, this work provides insight for future target-based advanced molecular modeling studies, with implications for development of novel therapeutics for specific recurrent DMVs of E1α.

Acute sleep disruption- and high-fat diet-induced hypothalamic inflammation are not related to glucose tolerance in mice

Chronic insufficient sleep is a major societal problem and is associated with increased risk of metabolic disease. Hypothalamic inflammation contributes to hyperphagia and weight gain in diet-induced obesity, but insufficient sleep-induced neuroinflammation has yet to be examined in relation to metabolic function. We therefore fragmented sleep of adult male C57BL/6J mice for 18 h daily for 9 days to determine whether sleep disruption elicits inflammatory responses in brain regions that regulate energy balance and whether this relates to glycemic control. To additionally test the hypothesis that exposure to multiple inflammatory factors exacerbates metabolic outcomes, responses were compared in mice exposed to sleep fragmentation (SF), high-fat diet (HFD), both SF and HFD, or control conditions. Three or 9 days of high-fat feeding reduced glucose tolerance but SF alone did not. Transient loss of body mass in SF mice may have affected outcomes. Comparisons of pro-inflammatory cytokine concentrations among central and peripheral metabolic tissues indicate that patterns of liver interleukin-1β concentrations best reflects observed changes in glucose tolerance. However, we demonstrate that SF rapidly and potently increases Iba1 immunoreactivity (-ir), a marker of microglia. After 9 days of manipulations, Iba1-ir remains elevated only in mice exposed to both SF and HFD, indicating a novel interaction between sleep and diet on microglial activation that warrants further investigation.