Acylcarnitine Profiles Research Articles

Assessment of plasma acylcarnitines before and after weight loss in obese subjects

Acylcarnitines, fatty acid oxidation (FAO) intermediates, have been implicated in diet-induced insulin resistance and type 2 diabetes mellitus, as increased levels are found in obese insulin resistant humans. Moreover plasma acylcarnitines have been associated with clinical parameters related to glucose metabolism, such as fasting glucose levels and HbA1c. We hypothesized that plasma acylcarnitines would correlate with energy expenditure, insulin sensitivity and other clinical parameters before and during a weight loss intervention. We measured plasma acylcarnitines in 60 obese subjects before and after a 12 week weight loss intervention. These samples originated from three different interventions (diet alone (n = 20); diet and exercise (n = 21); diet and drug treatment (n = 19)). Acylcarnitine profiles were analysed in relation to clinical parameters of glucose metabolism, insulin sensitivity and energy expenditure. Conclusions were drawn from all 60 subjects together. Despite amelioration of HOMA-IR, plasma acylcarnitines levels increased during weight loss. HOMA-IR, energy expenditure and respiratory exchange ratio were not related to plasma acylcarnitines. However non-esterified fatty acids correlated strongly with several acylcarnitines at baseline and during the weight loss intervention (p < 0.001). Acylcarnitines did not correlate with clinical parameters of glucose metabolism during weight loss, questioning their role in insulin resistance and type 2 diabetes mellitus.

Alterations of the Lipid Metabolome in Dairy Cows Experiencing Excessive Lipolysis Early Postpartum.

A decrease in insulin sensitivity enhances adipose tissue lipolysis helping early lactation cows counteracting their energy deficit. However, excessive lipolysis poses serious health risks for cows, and its underlying mechanisms are not clearly understood. The present study used targeted ESI-LC-MS/MS-based metabolomics and indirect insulin sensitivity measurements to evaluate metabolic alterations in the serum of dairy cows of various parities experiencing variable lipolysis early postpartum. Thirty (12 primiparous and 18 multiparous) cows of Holstein Friesian and Simmental breeds, fed the same diet and kept under the same management conditions, were sampled at d 21 postpartum and classified as low (n = 10), medium (n = 8), and high (n = 12) lipolysis groups, based on serum concentration of nonesterified fatty acids. Overall, excessive lipolysis in the high group came along with impaired estimated insulin sensitivity and characteristic shifts in acylcarnitine, sphingomyelin, phosphatidylcholine and lysophospholipid metabolome profiles compared to the low group. From the detected phosphatidylcholines mainly those with diacyl-residues showed differences among lipolysis groups. Furthermore, more than half of the detected sphingomyelins were increased in cows experiencing high lipomobilization. Additionally, strong differences in serum acylcarnitines were noticed among lipolysis groups. The study suggests an altered serum phospholipidome in dairy cows associated with an increase in certain long-chain sphingomyelins and the progression of disturbed insulin function. In conclusion, the present study revealed 37 key metabolites as part of alterations in the synthesis or breakdown of sphingolipids and phospholipids associated with lowered estimated insulin sensitivity and excessive lipolysis in early-lactating cows.

Secondary Carnitine Deficiency in Dialysis Patients: Shall We Supplement It?

Carnitine, essential for fatty acid β-oxidation, is obtained from diet and through de novo biosynthesis. The organic cation/carnitine transporter 2 (OCTN2) facilitates carnitine cellular transport and kidney resorption. Carnitine depletion occurs in OCTN2-deficient patients, with serious clinical complications including cardiomyopathy, myopathy, and hypoketotic hypoglycaemia. Neonatal screening can detect OCTN2 deficiency. OCTN2-deficiency is also known as primary carnitine deficiency. Carnitine deficiency may result from fatty acid β-oxidation disorders, which are diagnosed via plasma acylcarnitine profiling, but also under other conditions including haemodialysis. Given the importance of the kidney in maintaining carnitine homeostasis, it is not unexpected that longterm haemodialysis treatment is associated with the development of secondary carnitine deficiency, characterised by low endogenous L-carnitine levels and accumulation of deleterious medium and long- chain acylcarnitines. These alterations in carnitine pool composition have been implicated in a number of dialysis-related disorders, including erythropoietin-resistant renal anaemia. The association between erythropoietin resistance and carnitine levels has been demonstrated, with the proportion of medium and long-chain acylcarnitines within the total plasma carnitine pool positively correlated with erythropoietin resistance. Recent research has demonstrated that carnitine supplementation results in a significant reduction in erythropoietin dose requirements in patients with erythropoietin-resistant anaemia. Few studies have been conducted assessing the treatment of carnitine deficiency and haemodialysisrelated cardiac complications, particularly in children. Thus, a study was recently conducted which showed that intravenous carnitine in children receiving haemodialysis significantly increased plasma carnitine.

Fermentable soluble fibres spare amino acids in healthy dogs fed a low-protein diet.

BackgroundResearch in cats has shown that increased fermentation-derived propionic acid and its metabolites can be used as alternative substrates for gluconeogenesis, thus sparing amino acids for other purposes. This amino acid sparing effect could be of particular interest in patients with kidney or liver disease, where this could reduce the kidneys’/liver’s burden of N-waste removal. Since dogs are known to have a different metabolism than the obligatory carnivorous cat, the main objective of this study was to assess the possibility of altering amino acid metabolism through intestinal fermentation in healthy dogs. This was studied by supplementing a low-protein diet with fermentable fibres, hereby providing an initial model for future studies in dogs suffering from renal/liver disease.ResultsEight healthy dogs were randomly assigned to one of two treatment groups: sugar beet pulp and guar gum mix (SF: soluble fibre, estimated to mainly stimulate propionic acid production) or cellulose (IF: insoluble fibre). Treatments were incorporated into a low-protein (17 %) extruded dry diet in amounts to obtain similar total dietary fibre (TDF) contents for both diets (9.4 % and 8.2 % for the SF and IF diet, respectively) and were tested in a 4-week crossover feeding trial. Apparent faecal nitrogen digestibility and post-prandial fermentation metabolites in faeces and plasma were evaluated. Dogs fed the SF diet showed significantly higher faecal excretion of acetic and propionic acid, resulting in a higher total SCFA excretion compared to IF. SF affected the three to six-hour postprandial plasma acylcarnitine profile by significantly increasing AUC of acetyl-, propionyl-, butyryl- + isobutyryl-, 3-OH-butyryl-, 3-OH-isovaleryl- and malonyl-L-carnitine. Moreover, the amino acid plasma profile at that time was modified as leucine + isoleucine concentrations were significantly increased by SF, and a similar trend for phenylalanine and tyrosine’s AUC was found.ConclusionThese results indicate that guar gum and sugar beet pulp supplementation diminishes postprandial use of amino acids favoring instead the use of short-chain fatty acids as substrate for the tricarboxylic acid (TCA) cycle. Further research is warranted to investigate the amino acid sparing effect of fermentable fibres in dogs with kidney/liver disease.

Two Siblings with Beta-Ketothiolase Deficiency: One Genetic Defect Two Different Pictures

Deficiency of mitochondrial acetoacetyl-coenzyme A thiolase T2 (methylacetoacetyl-coenzyme A thiolase, MAT) or β-ketothiolase is a rareautosomal recessive disorder that is characterized by ketoacidosis episodes. Outcomes vary from normal development to severe cognitive impairment or even death after an acute episode of ketoacidosis. The classical biochemical profile of T2 deficiency is a result of mutations in both alleles of the ACAT1 gene and comprises characteristic abnormalities in urinary organic acids and blood or plasma acylcarnitine profiles. In this study, we present two sibling cases with quite different clinical properties.

Two Siblings with Beta-Ketothiolase Deficiency: One Genetic Defect Two Different Pictures

Deficiency of mitochondrial acetoacetyl-coenzyme A thiolase T2 (methylacetoacetyl-coenzyme A thiolase, MAT) or β-ketothiolase is a rareautosomal recessive disorder that is characterized by ketoacidosis episodes. Outcomes vary from normal development to severe cognitive impairment or even death after an acute episode of ketoacidosis. The classical biochemical profile of T2 deficiency is a result of mutations in both alleles of the ACAT1 gene and comprises characteristic abnormalities in urinary organic acids and blood or plasma acylcarnitine profiles. In this study, we present two sibling cases with quite different clinical properties.

Plasma acylcarnitines and risk of cardiovascular disease: effect of Mediterranean diet interventions1–3

Previous studies have suggested that metabolite profiles of elevated acylcarnitines were associated with increased risk of cardiovascular disease (CVD) in populations with established coronary disease. However, to our knowledge, this association has not been evaluated in the context of primary cardiovascular prevention. We evaluated the association between 28 plasma acylcarnitine species and risk of incident CVD and the potential modifying effect of Mediterranean diet (MedDiet) interventions. We measured plasma acylcarnitines with the use of high-throughput liquid chromatography-tandem mass spectrometry at baseline and after 1 y of follow-up, both individually and classified into short-, medium-, or long-chain scores, in a case-cohort study within the Prevención con Dieta Mediterránea (PREDIMED) study, which is a randomized Mediterranean dietary intervention for primary cardiovascular prevention. A randomly selected subcohort (n = 751) and all available incident CVD cases (n = 229) after 4.8 y of follow-up were included in the current study. After adjustment for age, sex, body mass index, and other CVD risk factors, participants in the highest quartile of baseline short- and medium-chain acylcarnitines had a higher risk of CVD than did participants in the lowest quartile [HRs: 1.80 (95% CI: 1.11, 2.91; P-trend 0.01) and 1.55 (95% CI: 1.01, 2.48; P-trend = 0.04), respectively]. Increased short-chain acylcarnitines after 1 y were associated with higher risks of total CVD and stroke. Participants with higher baseline concentrations of short-, medium-, and long-chain acylcarnitines who were randomly assigned to the control group had a higher risk of CVD than did subjects with lower concentrations of acylcarnitines who were assigned to the MedDiet group. Our data support the conclusion that metabolite profiles characterized by elevated concentrations of acylcarnitines are independently associated with risks of total CVD and stroke alone in participants at high risk of CVD. MedDiet interventions may mitigate the adverse associations shown between higher concentrations of acylcarnitines and CVD. This trial was registered at www.controlled-trials.com as ISRCTN35739639.

Altered plasma acylcarnitine and amino acid profiles in type 2 diabetic kidney disease

Dysregulation of acylcarnitines (AcylCNs) and amino acids metabolism have implicated in abnormality of fatty acid oxidation in type 2 diabetes (T2D). However, it is not well known whether altered plasma AcylCN, and amino acid profiles are associated with albuminuria or diabetic nephropathy (DN) in T2D. The aim of this study was to elucidate alterations in plasma levels of AcylCNs and amino acids with respect to the T2D patients with various stages of albuminuria. We recruited 52 healthy subjects as control, and 156 T2D patients which were divided into 52 normoalbuminuria, 52 microalbuminuria, and 52 macroalbuminuria. Plasma 37 AcylCNs and 12 amino acids were analyzed by tandem mass spectrometry. We found that T2D with normoalbuminuria and microalbuminuria had lower shot-, medium-, and long-chain AcylCNs, whereas T2D with macroalbuminuria had higher short-and medium-chain AcylCNs and lower long-chain AcylCNs than healthy subjects. Moreover, estimated glomerular filtration rate (eGFR) was a negative, independent and significant predictor of albumin to creatinine ratio (ACR) levels (β = −0.376, P < 0.001), whereas plasma Low-density lipoprotein cholesterol (LDL-C) was significantly and positively associated with ACR levels (β = 0.169, P = 0.049). Furthermore, multivariate ordinal logistic regression analysis revealed that isobutyrylcarnitine (C4) was a positive, independent, and significant predictor of ACR levels with higher odds of having T2D patients with progression normoalbuminuria to microalbuminuria [OR = 9.93, 95 % CI (3.51–28.05), P < 0.001]. The findings suggest that plasma C4 may serve as a potential biomarker for the early stages of DN.

Outcomes and genotype-phenotype correlations in 52 individuals with VLCAD deficiency diagnosed by NBS and enrolled in the IBEM-IS database.

Very long chain acyl-CoA dehydrogenase (VLCAD) deficiency can present at various ages from the neonatal period to adulthood, and poses the greatest risk of complications during intercurrent illness or after prolonged fasting. Early diagnosis, treatment, and surveillance can reduce mortality; hence, the disorder is included in the newborn Recommended Uniform Screening Panel (RUSP) in the United States. The Inborn Errors of Metabolism Information System (IBEM-IS) was established in 2007 to collect longitudinal information on individuals with inborn errors of metabolism included in newborn screening (NBS) programs, including VLCAD deficiency. We retrospectively analyzed early outcomes for individuals who were diagnosed with VLCAD deficiency by NBS and describe initial presentations, diagnosis, clinical outcomes and treatment in a cohort of 52 individuals ages 1-18years. Maternal prenatal symptoms were not reported, and most newborns remained asymptomatic. Cardiomyopathy was uncommon in the cohort, diagnosed in 2/52 cases. Elevations in creatine kinase were a common finding, and usually first occurred during the toddler period (1-3years of age). Diagnostic evaluations required several testing modalities, most commonly plasma acylcarnitine profiles and molecular testing. Functional testing, including fibroblast acylcarnitine profiling and white blood cell or fibroblast enzyme assay, is a useful diagnostic adjunct if uncharacterized mutations are identified.

Metabolomic profiles of lipid metabolism, arterial stiffness and hemodynamics in male coronary artery disease patients

Background/objectivesMetabolomic profiling allows to take a detailed look at lipid metabolism and to study the levels and roles of its numerous intermediates and products in the pathogenesis of cardiovascular disease (CVD). This study aimed to investigate the relationship between the metabolic profiles of lipid metabolism, arterial stiffness and hemodynamics in patients with coronary artery disease (CAD) and for healthy controls. MethodsSerum levels of 186 metabolites were determined with the AbsoluteIDQ™ p180 kit (BIOCRATES Life Sciences AG, Innsbruck, Austria). The technique of applanation tonometry was used for non-invasive pulse wave analysis and carotid-femoral pulse wave velocity (cf-PWV) assessments. Principal component analysis (PCA) was carried out in order to reduce the large number of correlated metabolites to fewer uncorrelated factors. ResultsElevated levels of C16:1, C18:1, C3-DC(C4-OH), PC aa C40:6, Met-SO/Met, and reduced levels of lysoPC a C18:2 were observed in the CAD group compared to the healthy controls. The cf-PWV showed positive correlations with C14, C16:1, (C2+C3)/C0, C2/C0 and the CPT-1 ratio for the CAD group. Moreover, PCA-derived factor 3 (medium- and long-chain acylcarnitines) proved to be an independent determinant of cf-PWV for these patients. ConclusionsWe demonstrated an independent association between the serum medium- and long-chain acylcarnitine profile and aortic stiffness for the CAD patients. In addition to the lipid-related classical CVD risk markers, the intermediates of lipid metabolism may serve as novel indicators for altered vascular function.

Renal Fanconi Syndrome Is Caused by a Mistargeting-Based Mitochondriopathy.

We recently reported an autosomal dominant form of renal Fanconi syndrome caused by a missense mutation in the third codon of the peroxisomal protein EHHADH. The mutation mistargets EHHADH to mitochondria, thereby impairing mitochondrial energy production and, consequently, reabsorption of electrolytes and low-molecular-weight nutrients in the proximal tubule. Here, we further elucidate the molecular mechanism underlying this pathology. We find that mutated EHHADH is incorporated into mitochondrial trifunctional protein (MTP), thereby disturbing β-oxidation of long-chain fatty acids. The resulting MTP deficiency leads to a characteristic accumulation of hydroxyacyl- and acylcarnitines. Mutated EHHADH also limits respiratory complex I and corresponding supercomplex formation, leading to decreases in oxidative phosphorylation capacity,mitochondrial membrane potential maintenance, and ATP generation. Activity of the Na(+)/K(+)-ATPase is thereby diminished, ultimately decreasing the transport activity of the proximal tubule cells.

The impact of altered carnitine availability on acylcarnitine metabolism, energy expenditure and glucose tolerance in diet-induced obese mice

AimAcylcarnitines are fatty acid oxidation (FAO) intermediates, which have been implicated in diet-induced insulin resistance. Elevated acylcarnitine levels are found in obese, insulin resistant humans and rodents, and coincide with lower free carnitine. We hypothesized that increasing free carnitine levels by administration of the carnitine precursor γ-butyrobetaine (γBB) could facilitate FAO, thereby improving insulin sensitivity. MethodsC57BL/6N mice were fed with a high fat or chow diet with or without γBB supplementation (n=10 per group). After 8weeks of diet, indirect calorimetry, glucose tolerance and insulin sensitivity tests were performed. AC profiles and carnitine biosynthesis intermediates were analyzed in plasma and tissues by tandem mass spectrometry (MS) and liquid chromatography tandem MS. ResultsγBB supplementation did not facilitate FAO, was unable to curb bodyweight and did not prevent impaired glucose homeostasis in the HFD fed mice in spite of marked alterations in the acylcarnitine profiles in plasma and liver. Remarkably, γBB did not affect the acylcarnitine profile in other tissues, most notably muscle. Administration of a bolus acetylcarnitine also caused significant changes in plasma and liver, but not in muscle acylcarnitine profiles, again without effect on glucose tolerance. ConclusionAltogether, increasing carnitine availability affects acylcarnitine profiles in plasma and liver but does not modulate glucose tolerance or insulin sensitivity. This may be due to the lack of an effect on muscle acylcarnitine profiles, as muscle tissue is an important contributor to whole body insulin sensitivity. These results warrant caution on making associations between plasma acylcarnitine levels and insulin resistance.

Signatures of acylcarnitine and acyl‐CoA species suggest specific alterations of mitochondrial oxidation in mouse models of obesity and diabetes

Obesity, insulin resistance and diabetes are characterized by changes in circulating plasma metabolite markers derived from amino acid and fatty acid metabolism including acylcarnitines (AC). In identifying organs and pathways as origins of the changes in plasma metabolites, we determined AC profiles in plasma and tissues from mouse models representing different stages of obesity and diabetes development. The leptin‐deficient ob/ob mouse served as a model for obesity associated with insulin resistance but pancreas hypertrophy whereas the db/db mouse is obese, insulin resistant with severe hyperglycemia and eventually pancreatic failure. A streptozotocin‐induced insulin‐deficient mouse was employed as a model for type I diabetes or end‐point stage type II diabetes with extreme hyperglycemia and ketosis. We used a sensitive LC‐MS/MS method to quantify around 45 AC derived from fatty acid and amino acid oxidation pathways. We furthermore determined concentrations of odd‐numbered fatty acids for which the metabolic origin is largely unknown. Since AC are derived from the conversion of acyl‐CoA we additionally determined a number of corresponding acyl‐CoA species in liver and assessed how they correlate with AC levels. Results displayed strong increases in AC derived from branched‐chain amino acid degradation in plasma and tissues of all mouse models, but most pronounced in streptozotocin‐treated animals. All mice also displayed increased levels of odd‐numbered AC in liver while dicarboxylic‐acylcarnitines derived from omega‐oxidation were strongly decreased in ob/ob and db/db mice. Correlations between AC and acyl‐CoA concentrations in liver were strongest for monocarboxylic metabolites, while dicarboxylic acylcarnitines like malonylcarnitine and succinylcarnitine showed no or negative correlations with their respective acyl‐CoA species. In summary, our analysis revealed major alterations in specific pathways of mitochondrial fatty acid and amino acid oxidation in the different mouse models during diabetes progression.

Screening of Free Carnitine and Acylcarnitine Status in Children With Familial Mediterranean Fever.

This study aims to demonstrate the patterns of free carnitine (FC) and acylcarnitine (AC) esters in familial Mediterranean fever (FMF) patients. A total of 205 patients (106 males, 99 females; mean age 131.3±52.1 months; range 24 to 254 months) with FMF and 50 healthy controls (27 males, 23 females; mean age 125.7±49.6 months; range 32 to 217 months) were enrolled. Fasting dried blood samples were taken for showing FC and AC ester levels with tandem mass spectrometry from both patients and controls. Screening of AC profile revealed increased FC, 3-hydroxypalmitoylcarnitine (C16-OH), and 3-Hydroxy octadecanoylcarnitine (C18:2-OH) carnitine levels, while decreased acetyl-carnitine (C2), propionyl-carnitine (C3), butyryl-carnitine (C4), tiglyl-carnitine (C5:1), hexanoyl-carnitine (C6), octanoyl-carnitine (C8), decenoylcarnitine (C10:1), decadienoylcarnitine (C10:2), malonylcarnitine (C3DC), methylmalonylcarnitine (C4DC), glutarylcarnitine (C5DC), hexadecenoylcarnitine (C16:1), 3-Hydroxy butyrylcarnitine (C4-OH), and 3-Hydroxy oleylcarnitine (C18:1-OH) carnitine levels in FMF patients compared to controls. Total AC levels (p<0.001) and AC to FC ratio (p<0.001) were also lower in FMF patients than the controls. In this study, we were able to detect some of the AC profile variations in FMF patients; however, usage of carnitine in all patients with FMF is not recommended since we were not able to demonstrate secondary carnitine deficiency in FMF patients of this study.

Multiple acyl-CoA dehydrogenase deficiency (MADD) as a cause of late-onset treatable metabolic disease

IntroductionLate-onset multiple acyl-CoA dehydrogenase deficiency (MADD) is a rare, treatable, beta-oxidation disorder responsible for neuromuscular symptoms in adults. This case series describes the clinical and biochemical features of 13 French patients with late-onset MADD. Methods and resultsThirteen ambulant patients (eight women, five men), with a median age at onset of 27 years, initially experienced exercise intolerance (n=9), isolated muscle weakness (n=1) and a multisystemic pattern with either central nervous system or hepatic dysfunction (n=3). During the worsening period, moderate rhabdomyolysis (n=5), a pseudomyasthenic pattern (n=5) and acute respiratory failure (n=1) have been observed. Weakness typically affected the proximal limbs and axial muscles, and there was sometimes facial asymmetry (n=3). Moderate respiratory insufficiency was noted in one case. Median baseline creatine kinase was 190IU/L. Lactacidemia was sometimes moderately increased at rest (3/10) and after exercise (1/3). The acylcarnitine profile was characteristic, with increases in all chain-length acylcarnitine species. Electromyography revealed a myogenic pattern, while muscle biopsy showed lipidosis, sometimes with COX-negative fibers (n=2). The mitochondrial respiratory chain was impaired in five cases, with coenzyme Q10 decreased in two cases. All patients harbored mutations in the ETFDH gene (four homozygous, seven compound heterozygous, two single heterozygous), with nine previously unidentified mutations. All patients were good responders to medical treatment, but exercise intolerance and/or muscular weakness persisted in 11 of them. ConclusionLate-onset forms of MADD may present as atypical beta-oxidation disorders. Acylcarnitine profiling and muscle biopsy remain the most decisive investigations for assessing the diagnosis. These tests should thus probably be performed more widely, particularly in unexplained cases of neuromuscular and multisystemic disorders.

Unique plasma metabolomic signatures of individuals with inherited disorders of long-chain fatty acid oxidation.

Blood and urine acylcarnitine profiles are commonly used to diagnose long-chain fatty acid oxidation disorders (FAOD: i.e., long-chain hydroxy-acyl-CoA dehydrogenase [LCHAD] and carnitine palmitoyltransferase 2 [CPT2] deficiency), but the global metabolic impact of long-chain FAOD has not been reported. We utilized untargeted metabolomics to characterize plasma metabolites in 12 overnight-fasted individuals with FAOD (10 LCHAD, two CPT2) and 11 healthy age-, sex-, and body mass index (BMI)-matched controls, with the caveat that individuals with FAOD consume a low-fat diet supplemented with medium-chain triglycerides (MCT) while matched controls consume a typical American diet. In plasma 832 metabolites were identified, and partial least squared-discriminant analysis (PLS-DA) identified 114 non-acylcarnitine variables that discriminated FAOD subjects and controls. FAOD individuals had significantly higher triglycerides and lower specific phosphatidylethanolamines, ceramides, and sphingomyelins. Differences in phosphatidylcholines were also found but the directionality differed by metabolite species. Further, there were few differences in non-lipid metabolites, indicating the metabolic impact of FAOD specifically on lipid pathways. This analysis provides evidence that LCHAD/CPT2 deficiency significantly alters complex lipid pathway flux. This metabolic signature may provide new clinical tools capable of confirming or diagnosing FAOD, even in subjects with a mild phenotype, and may provide clues regarding the biochemical and metabolic impact of FAOD that is relevant to the etiology of FAOD symptoms.

Acylcarnitine Profiles in HIV-Exposed, Uninfected Neonates in the United States.

We sought to determine the prevalence of abnormal acylcarnitine profiles (ACP) in HIV-exposed uninfected (HEU) newborns and to explore the association of abnormal ACP with clinical laboratory outcomes and antiretroviral drug exposures. Clinically, ACP are used to assess for fatty acid oxidation (FAO) dysfunction and normal FAO is necessary for optimal fetal/neonatal growth and development. We analyzed serum ACP in 522 HEU neonates enrolled in the Surveillance Monitoring for ART Toxicities (SMARTT) study of the Pediatric HIV/AIDS Cohort Study (PHACS) and evaluated the associations of abnormal ACP with in utero exposure to combination antiretroviral therapy (cART) in logistic regression models, adjusting for maternal demographic, disease, and behavioral characteristics. We evaluated the associations of abnormal ACP with laboratory parameters and measures of neurodevelopment and growth. Of 522 neonates, 89 (17%) had abnormal ACP. In adjusted analyses, in utero exposure to a protease inhibitor (PI) was associated with higher odds of having an abnormal ACP [adjusted odds ratio (aOR) = 2.35, 95% CI: 0.96, 5.76, p = 0.06] with marginal significance while exposure to a nonnucleoside reverse transcriptase inhibitor (NNRTI) was associated with lower odds (aOR = 0.23, 95% CI: 0.07, 0.80, p = 0.02). Mean ALT levels were slightly higher in those with abnormal ACP, but no differences in lactate, glucose, or CPK were observed. ACP status was not associated with neurodevelopment at 1 year or growth at 2 and 3 years of age. Abnormal ACP in HEU neonates are associated with exposure to PI-containing as opposed to NNRTI-containing antiretroviral (ARV) regimens but are not associated with serious postnatal clinical problems. Further studies are needed to determine the long-term health implications of abnormal acylcarnitine metabolism at birth in HEU children.

Inborn Errors of Metabolism (Metabolic Disorders).

By their very nature, rare inborn errors of metabolism challenge the generation and application of evidence-based medicine. • On the basis of limited research evidence as well as consensus, newborn screening for select metabolic disorders, including phenylketonuria, medium-chain acyl CoA dehydrogenase deficiency, and glutaric acidemia type I, may improve long-term outcomes for affected children. • On the basis of primarily consensus, due to lack of relevant clinical studies, inborn errors due to defects in the metabolism of energy sources (protein, fatty acids, and carbohydrates) may present in infancy with overwhelming metabolic decompensation, and initial laboratory evaluations may reveal hyperammonemia, nonketotic hypoglycemia, or a metabolic acidosis with an elevated anion gap, depending on the disorder. • On the basis of primarily consensus, due to lack of relevant clinical studies, specific laboratory testing for inborn errors of metabolism should include plasma amino acids, urine organic acids, plasma carnitine, and plasma acylcarnitine profile. • On the basis of primarily consensus, due to lack of relevant clinical studies, disorders of cellular organelles, such as lysosomal and peroxisomal disorders, may present with progressive organomegaly, developmental regression, dysmorphic facial characteristics. or sensory loss.

Reliable Diagnosis of Carnitine Palmitoyltransferase Type IA Deficiency by Analysis of Plasma Acylcarnitine Profiles.

Carnitine palmitoyltransferase IA (CPT-IA) deficiency is an inherited disorder of the carnitine cycle (MIM #255120). Patients affected by this deficiency might be missed easily because of lack of specific and sensitive biochemical markers. In this study, sensitivity and specificity of plasma free carnitine (C0) and long-chain acylcarnitines (lc-ac: C16:0-, C16:1-, C18:0-, C18:1- and C18:2-ac) was evaluated, including the sum of lc-ac (∑lc-ac) and the molar ratios C0/(C16:0-ac+C18:0-ac) and C0/∑lc-ac. Nine plasma acylcarnitine profiles of 4 CPT-IA deficient patients were compared with profiles of 2,190 subjects suspected of or diagnosed with an inherited disorder of metabolism. Age-dependent reference values were calculated based on the patient population without a definite diagnosis of an inborn error of metabolism (n = 1,600). Sensitivity, specificity, and Receiver Operating Characteristic (ROC) curves were calculated based on samples of the whole patient population. Concentrations of C0 in plasma were normal in all CPT-IA deficient patient samples. ROC analyses showed highest diagnostic values for C18:0-ac, C18:1-ac, and ∑lc-ac (AUC 1.000) and lowest for C0 (AUC 0.738). Combining two markers, i.e., a plasma C18:1-ac concentration <0.05μmol/L and a molar ratio of C0/(C16:0-ac+C18:0-ac) >587, specificity to diagnose CPT-IA deficiency increased to 99.3% compared with either C18:1-ac (97.4%) or C0/(C16:0-ac+C18:0-ac) (96.9%) alone, all at a sensitivity of 100%. Combination of a low concentration of C18:1-ac with a high molar ratio of C0/(C16:0-ac+C18:0-ac) ratio in plasma has high diagnostic value for CPT-IA deficiency. Patients with a clinical suspicion of CPT-IA deficiency can be diagnosed with this test combination.

Development of a Tandem Mass Spectrometry Method for Rapid Measurement of Medium- and Very-Long-Chain Acyl-CoA Dehydrogenase Activity in Fibroblasts.

Mitochondrial fatty acid oxidation is a vital biochemical process for energy metabolism. Among the known fatty-acid metabolism disorders, very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency and medium-chain acyl-CoA dehydrogenase (MCAD) deficiency count among the most frequent. Both are potentially very serious diseases as they carry a risk of severe neurological post-crisis sequelae, and even sudden death. Diagnosis relies on plasma acylcarnitine profile analysis and urine organic acid analysis, followed by genetic testing to confirm diagnosis. However, in some cases, it is crucial to run a specific diagnostic assay for enzyme activity, which is generally performed in leukocytes or fibroblasts. The aim of this study was to address this need, first by developing a MCAD and VLCAD enzyme activity-specific diagnostic assay in fibroblasts (by measuring the reaction products, i.e. enoyl-CoA) via a rapid LC-MS/MS-based technique, and then by testing MCAD-deficient patients (n=6), VLCAD-deficient patients (n=10), and control patients (n=12). MCAD activity was significantly different in the MCAD-deficiency (MCADD) group (mean=0.07nmol C8:1 formed/min/mg protein) compared to the control group (mean=0.36nmol C8:1 formed/min/mg protein). All MCADD patients showed less than 35% residual MCAD activity. VLCAD activity was significantly decreased in the VLCADD group (mean=0.06nmol C16:1 formed/min/mg protein) compared to the control group (mean=0.86nmol C16:1 formed/min/mg protein, respectively). All VLCADD patients showed less than 35% residual VLCAD activity. This technique allowed also to confirm that a novel ACADVL gene mutation (c.1400T>C) is responsible for a defective VLCAD activity (residual activity at 10%).