Role of intrapartum hypoxia in carnitine nutritional status during the early neonatal period

Effect of Acetyl-L-carnitine Used for Protection of Neonatal Hypoxic-Ischemic Brain Injury on Acute Kidney Changes in Male and Female Rats

Neonatal hypoxia-ischemia (HI) is a common cause of brain injury in infants. Acute kidney injury frequently occurs after birth asphyxia and is associated with adverse outcome. Treatment with acetyl-L-carnitine (ALCAR) after HI protects brain and improves outcome. Rat pups underwent carotid ligation and 75 min hypoxia on postnatal day 7 to determine effects of HI on kidney which is understudied in this model. HI + ALCAR pups were treated at 0, 4 and 24 h after HI. The organic cation/carnitine transporter 2 (OCTN2), transports ALCAR and functions to reabsorb carnitine and acylcarnitines from urine. At 24 h after injury OCTN2 levels were significantly decreased in kidney from HI pups, 0.80 ± 0.04 (mean ± SEM, p < 0.01), compared to sham controls 1.03 ± 0.04, and HI + ALCAR pups 1.11 ± 0.06. The effect of HI on the level of pyruvate dehydrogenase (PDH) was determined since kidney has high energy requirements. At 24 h after HI, kidney PDH/β-actin ratios were significantly lower in HI pups, 0.98 ± 0.05 (mean ± SEM, p < 0.05), compared to sham controls 1.16 ± 0.06, and HI + ALCAR pups 1.24 ± 0.03, p < 0.01. Treatment of pups with ALCAR after HI prevented the decrease in renal OCTN2 and PDH levels at 24 h after injury. Protection of PDH and OCTN2 after HI would improve energy metabolism in kidney, maintain tissue carnitine levels and overall carnitine homeostasis which is essential for neonatal health.

The metabolomic profile of umbilical cord blood in neonatal hypoxic ischaemic encephalopathy

Background

Hypoxic ischaemic encephalopathy (HIE) in newborns can cause significant long-term neurological disability. The insult is a complex injury characterised by energy failure and disruption of cellular homeostasis, leading to mitochondrial damage. The importance of individual metabolic pathways, and their interaction in the disease process is not fully understood. The aim of this study was to describe and quantify the metabolomic profile of umbilical cord blood samples in a carefully defined population of full-term infants with HIE.

Methods and Findings

The injury severity was defined using both the modified Sarnat score and continuous multichannel electroencephalogram. Using these classification systems, our population was divided into those with confirmed HIE (n = 31), asphyxiated infants without encephalopathy (n = 40) and matched controls (n = 71). All had umbilical cord blood drawn and biobanked at −80°C within 3 hours of delivery. A combined direct injection and LC-MS/MS assay (AbsolutIDQ p180 kit, Biocrates Life Sciences AG, Innsbruck, Austria) was used for the metabolomic analyses of the samples. Targeted metabolomic analysis showed a significant alteration between study groups in 29 metabolites from 3 distinct classes (Amino Acids, Acylcarnitines, and Glycerophospholipids). 9 of these metabolites were only significantly altered between neonates with Hypoxic ischaemic encephalopathy and matched controls, while 14 were significantly altered in both study groups. Multivariate Discriminant Analysis models developed showed clear multifactorial metabolite associations with both asphyxia and HIE. A logistic regression model using 5 metabolites clearly delineates severity of asphyxia and classifies HIE infants with AUC = 0.92. These data describe wide-spread disruption to not only energy pathways, but also nitrogen and lipid metabolism in both asphyxia and HIE.

Conclusion

This study shows that a multi-platform targeted approach to metabolomic analyses using accurately phenotyped and meticulously biobanked samples provides insight into the pathogenesis of perinatal asphyxia. It highlights the potential for metabolomic technology to develop a diagnostic test for HIE.

Oxygen glucose deprivation in rat hippocampal slice cultures results in alterations in carnitine homeostasis and mitochondrial dysfunction

Mitochondrial dysfunction characterized by depolarization of mitochondrial membranes and the initiation of mitochondrial-mediated apoptosis are pathological responses to hypoxia-ischemia (HI) in the neonatal brain. Carnitine metabolism directly supports mitochondrial metabolism by shuttling long chain fatty acids across the inner mitochondrial membrane for beta-oxidation. Our previous studies have shown that HI disrupts carnitine homeostasis in neonatal rats and that L-carnitine can be neuroprotective. Thus, this study was undertaken to elucidate the molecular mechanisms by which HI alters carnitine metabolism and to begin to elucidate the mechanism underlying the neuroprotective effect of L-carnitine (LCAR) supplementation. Utilizing neonatal rat hippocampal slice cultures we found that oxygen glucose deprivation (OGD) decreased the levels of free carnitines (FC) and increased the acylcarnitine (AC): FC ratio. These changes in carnitine homeostasis correlated with decreases in the protein levels of carnitine palmitoyl transferase (CPT) 1 and 2. LCAR supplementation prevented the decrease in CPT1 and CPT2, enhanced both FC and the AC∶FC ratio and increased slice culture metabolic viability, the mitochondrial membrane potential prior to OGD and prevented the subsequent loss of neurons during later stages of reperfusion through a reduction in apoptotic cell death. Finally, we found that LCAR supplementation preserved the structural integrity and synaptic transmission within the hippocampus after OGD. Thus, we conclude that LCAR supplementation preserves the key enzymes responsible for maintaining carnitine homeostasis and preserves both cell viability and synaptic transmission after OGD.

Metabolomic analyses of plasma reveals new insights into asphyxia and resuscitation in pigs

Background

Currently, a limited range of biochemical tests for hypoxia are in clinical use. Early diagnostic and functional biomarkers that mirror cellular metabolism and recovery during resuscitation are lacking. We hypothesized that the quantification of metabolites after hypoxia and resuscitation would enable the detection of markers of hypoxia as well as markers enabling the monitoring and evaluation of resuscitation strategies.

Methods and Findings

Hypoxemia of different durations was induced in newborn piglets before randomization for resuscitation with 21% or 100% oxygen for 15 min or prolonged hyperoxia. Metabolites were measured in plasma taken before and after hypoxia as well as after resuscitation. Lactate, pH and base deficit did not correlate with the duration of hypoxia. In contrast to these, we detected the ratios of alanine to branched chained amino acids (Ala/BCAA; R².adj = 0.58, q-value<0.001) and of glycine to BCAA (Gly/BCAA; R².adj = 0.45, q-value<0.005), which were highly correlated with the duration of hypoxia. Combinations of metabolites and ratios increased the correlation to R²adjust = 0.92. Reoxygenation with 100% oxygen delayed cellular metabolic recovery. Reoxygenation with different concentrations of oxygen reduced lactate levels to a similar extent. In contrast, metabolites of the Krebs cycle (which is directly linked to mitochondrial function) including alpha keto-glutarate, succinate and fumarate were significantly reduced at different rates depending on the resuscitation, showing a delay in recovery in the 100% reoxygenation groups. Additional metabolites showing different responses to reoxygenation include oxysterols and acylcarnitines (n = 8–11, q<0.001).

Conclusions

This study provides a novel strategy and set of biomarkers. It provides biochemical in vivo data that resuscitation with 100% oxygen delays cellular recovery. In addition, the oxysterol increase raises concerns about the safety of 100% O₂ resuscitation. Our biomarkers can be used in a broad clinical setting for evaluation or the prediction of damage in conditions associated with low tissue oxygenation in both infancy and adulthood. These findings have to be validated in human trials.

Serum carnitine levels in newborns with perinatal asphyxia and relation to neurologic prognosis

Neonatal hypoxic encephalopathy is one of the major causes of permanent neurological sequel. This study was conducted to investigate serum total, free and acylcarnitine levels in asphyxiated newborns with or without encephalopathy. Serum total, free and acylcarnitine levels were investigated in 21 newborns with and seven asphyxiated newborns without signs of encephalopathy. The newborns with encephalopathy were further divided into grade 1, 2 and 3 encephalopathy groups. Serum total and acylcarnitine concentrations of the whole encephalopathy group were significantly lower than the non-encephalopathy group (p = 0.042 for both). Serum total and acylcarnitine concentrations of grade 3 encephalopathy group were significantly lower than the non-encephalopathy group (p = 0.014 and p = 0.040, respectively). No significant differences were noticed for free carnitine levels. Total carnitine levels were positively correlated with birth weight and 10th minute apgar score, whereas acylcarnitine levels were found to correlate with cord blood pH and free carnitine levels with birth weight. Cord blood pH, and total carnitine levels were found to be the most significant determinants of the neurological outcome at one year of age. It was emphasized that carnitine deficiency could occur in severely affected asphyxiated newborns and it is related to the outcome at one year of age.

Carnitine content and expression of mitochondrial beta-oxidation enzymes in placentas of wild-type (OCTN2(+/+)) and OCTN2 Null (OCTN2(-/-)) Mice

Placenta requires energy to support its rapid growth, maturation, and transport function. Fatty acids are used as energy substrates in placenta, but little is known about the role played by carnitine in this process. We have investigated the role of carnitine in the expression of the enzymes involved in fatty acid beta-oxidation in placenta of OCTN2(-/-) mice with defective carnitine transporter (OCTN2). Heterozygous (OCTN2(+/-)) female mice were mated with heterozygous (OCTN2(+/-)) male mice. Pregnant mice were killed and fetuses and placentas were collected. Carnitine was measured using HPLC and tandem mass spectrometry. Immunohistochemistry was used to detect enzyme expression. Enzyme activities were measured spectrophotometrically. The fetal and placental weights were similar among the three genotypes (OCTN2(+/+), OCTN2(+/-), and OCTN2(-/-)). The levels of carnitine were markedly reduced (<20%) in homozygous OCTN2(-/-) null fetuses and placentas compared with wild-type OCTN2(+/+) controls. However, carnitine concentration in placenta was 2- to 7-fold higher than in the fetus in all three genotypes. Immunohistochemistry revealed that beta-oxidation enzymes are expressed in trophoblast cells. Catalytic activities of these enzymes were present at comparable levels in wild-type (OCTN2(+/+)) and homozygous (OCTN2(-/-)) mouse placentas, with the exception of SCHAD, for which activity was significantly higher in OCTN2(-/-) placentas than in OCTN2(+/+) placentas. These data show that placental OCTN2 is obligatory for accumulation of carnitine in placenta and fetus, that fatty acid beta-oxidation enzymes are expressed in placenta, and that reduced carnitine levels up-regulate the expression of SCHAD in placenta.

Intracranial venous thrombosis after hypoxic-ischemic brain insult in two newborns: could low serum carnitine levels have contributed?

Sinovenous thrombosis is a definite cause of mortality or morbidity in newborns. Perinatal hypoxia is one of the well known risk factors. Two term newborns were diagnosed to have cerebral venous thrombosis after a hypoxic-ischemic insult. They were later found to have carnitine deficiency. Both of the patients died. Carnitine was previously shown to have inhibitory effects on thrombogenesis in experimental studies. The possible contribution of carnitine in thrombogenesis was discussed.