Acylcarnitine profile in Alaskan sled dogs during submaximal multiday exercise points out metabolic flexibility and liver role in energy metabolism

Alaskan sled dogs develop a particular metabolic strategy during multiday submaximal exercise, allowing them to switch from intra-muscular to extra-muscular energy substrates thus postponing fatigue. Specifically, a progressively increasing stimulus for hepatic glycogenolysis and gluconeogenesis provides glucose for both fueling exercise and replenishing the depleted muscle glycogen. Moreover, recent studies have shown that with continuation of exercise sled dogs increase their insulin-sensitivity and their capacity to transport and oxidize glucose and carbohydrates rather than oxidizing fatty acids. Carnitine and acylcarnitines (AC) play an essential role as metabolic regulators in both fat and glucose metabolism; they serve as biomarkers in different species in both physiologic and pathologic conditions. We assessed the effect of multiday exercise in conditioned sled dogs on plasma short (SC), medium (MC) and long (LC) chain AC by tandem mass spectrometry (MS/MS). Our results show chain-specific modification of AC profiles during the exercise challenge: LCACs maintained a steady increase throughout exercise, some SCACs increased during the last phase of exercise and acetylcarnitine (C2) initially increased before decreasing during the later phase of exercise. We speculated that SCACs kinetics could reflect an increased protein catabolism and C2 pattern could reflect its hepatic uptake for energy-generating purposes to sustain gluconeogenesis. LCACs may be exported by muscle to avoid their accumulation to preserve glucose oxidation and insulin-sensitivity or they could be distributed by liver as energy substrates. These findings, although representing a “snapshot” of blood as a crossing point between different organs, shed further light on sled dogs metabolism that is liver-centric and more carbohydrate-dependent than fat-dependent and during prolonged submaximal exercise.

Glutaric Acidemia type 1 with Atypical Acylcarnitine Profile During Newborn Screening

Background and aims Glutaric acidemia type 1 (GA1) is a treatable disorder of cerebral organic acid metabolism caused by a defective glutaryl-CoA dehydrogenase (GCDH) gene. There is scarcity of reports of GA1 diagnoses following newborn screening (NBS) in the Chinese population. We assessed the acylcarnitine profiles and genetic characteristics of patients with GA1 identified via NBS.Materials and methods From January 2014 to September 2020, a total of 517,484 newborns screened by tandem mass spectrometry were recruited for this study. Newborns with elevated isovalerylcarnitine (C5DC) levels were recalled, those who tested positive on second screen were referred for confirmatory tests.Results Of 517,484 screened newborns, thirteen patients were diagnosed with GA1, including eleven neonatal GA1 and two maternal GA1 patients. The incidence of GA1 in the Quanzhou region was estimated to be 1 in 47,044 newborns. The initial NBS results showed that all but one of the patients had moderately or markedly increased C5DC levels. The neonatal GA1 patient with low free carnitine (C0) level suggestive of primary carnitine deficiency (PCD) while just the contrary to a typical GA1. Nine neonatal GA1 patients underwent urinary organic acid analyses: eight had elevated GA levels and one was reported in the normal range. Ten distinct GCDH variants were identified, eight were previously reported and two were newly identified. In silico prediction tools and protein modelling analysis suggested that the newly identified variants were potentially pathogenic. The most common variant was c.1244-2A > C, which had an allelic frequency of 54.55% (12/22), followed by c.1261G > A (p.Ala421Thr) (9.09%, 2/22). Conclusions GA1 patients may show only with low C0 levels at the initial screening and recall stages that may be overlooked. Maternal GA1 patients can also be detected during NBS duo to the low C0 levels in their infants. Therefore, PCD should be included in the differential diagnosis for GA1, and multigene panel testing should be performed in newborns with low C0 levels.

The outcome of 41 Late-Diagnosed Turkish GA-1 Patients: A Candidate for the Turkish NBS

Background Glutaric aciduria type 1(GA-1) is an inherited cerebral organic aciduria. Untreated patients with GA-1 have a risk of acute encephalopathic crises during the first 6 years of life. In so far as GA-1 desperately does not exist in Turkish newborn screening (NBS) program, most patients in our study were late-diagnosed. Method This study included 41 patients diagnosed with acylcarnitine profile, urinary organic acids, mutation analyses in the symptomatic period. We presented with clinical, neuroradiological, and molecular data of our 41 patients. Results The mean age at diagnosis was 14.8 ± 13.9 (15 days to 72 months) and, high blood glutaconic acid, glutarylcarnitine and urinary glutaric acid (GA) levels in 41 patients were revealed. Seventeen different mutations in the glutaryl-CoA dehydrogenase gene were identified, five of which were novel. The patients, most of whom were late-diagnosed, had a poor neurological outcome. Treatment strategies made a little improvement in dystonia and the frequency of encephalopathic attacks. Conclusion All GA-1 patients in our study were severely affected since they were late-diagnosed, while others show that GA-1 is a treatable metabolic disorder if it is diagnosed with NBS. This study provides an essential perspective of the severe impact on GA-1 patients unless it is diagnosed with NBS. We immediately advocate GA-1 to be included in the Turkish NBS.

The Acylcarnitine Profile in Dried Blood Spots is Affected by Hematocrit: A Study of Newborn Screening Samples in Very-Low-Birth-Weight Infants

Objective The acylcarnitine profile is analyzed in dried blood spots (DBS) to screen for inborn errors of metabolism. Hematocrit (Ht) is known to affect the result of quantitative analyses of DBS samples; however, the effects of Ht on the acylcarnitine profiles in DBS have not been studied in actual samples from newborns. Study Design The acylcarnitine profiles in DBS for newborn screening tests and Ht levels of very-low-birth-weight infants were obtained from medical records. We investigated the relationship between Ht and each acylcarnitine using Pearson's correlation coefficient (r). Results We examined 77 newborns in this study. There was a significantly positive correlation between Ht and C0, C2, C12, C16, C18, C18:1, and C18:1-OH, respectively (p < 0.0025). The correlation was the greatest on C2 (r = 0.59). Conclusion This study clarifies that Ht and C0, C2, C12, C16, C18, C18:1, and C18:1-OH are significantly correlated in DBS, which is consistent with previous studies. Hence, the effect of Ht should be considered when interpreting the results of acylcarnitine profiles in DBS. Key Points

Late-onset multiple acyl-CoA dehydrogenase deficiency mimicking myositis in an elderly patient: a case report

Background Late-onset multiple acyl-CoA dehydrogenase deficiency (MADD) is a rare and treatable inherited lipid storage myopathy. Here, we report an elderly patient with MADD mimicking myositis. Case presentation An 80-year-old woman had progressive weakness in her limbs, exercise intolerance, and no muscle pain for 3 months. The patient’s serum creatine kinase level was slightly elevated. The initial diagnosis was myositis. However, muscle biopsy showed many cytoplasmic vacuoles stained with oil red O, indicating the presence of lipid storage myopathy. The plasma acylcarnitine profile showed increased medium-chain and long-chain acylcarnitine species, consistent with the diagnosis of MADD. Riboflavin treatment dramatically improved muscle weakness. Conclusions MADD should be considered when evaluating elderly patients with subacute muscle weakness.

Microbiome-derived metabolites reproduce the mitochondrial dysfunction and decreased insulin sensitivity observed in type 2 diabetes

Diabetes is a global health problem that was estimated to be the 7th leading cause of death worldwide in 2016. Type 2 diabetes mellitus (T2DM) is classically associated with genetic and environmental factors, however recent studies have demonstrated that the gut microbiome, which is altered in T2DM patients, is also likely to play a significant role in disease development. Despite this, the identity of microbiome-derived metabolites that influence T2DM onset and/or progression remain elusive. Here we demonstrate that a serum biomarker for T2DM, previously of unknown structure and origin, is actually two microbiome-derived metabolites, 3-methyl-4-(trimethylammonio)butanoate (3M-4-TMAB) and 4-(trimethylammonio)pentanoate (4-TMAP). These metabolites are produced by the Lachnospiraceae family of bacteria, which are highly prevalent in the gut microbiome of T2DM patients and are associated with high dietary fat intake. Treatment of human liver cells with 3M-4-TMAB and 4-TMAP results in a distinct change in the acylcarnitine profile in these cells and significantly reduced their insulin sensitivity; both indicators of T2DM. These results provide evidence of a mechanistic link between gut microbiome derived metabolites and T2DM.