Quantifying Beta-Galactosylceramide Kinetics in Cerebrospinal Fluid of Healthy Subjects Using Deuterium Labeling

Therapeutics promoting myelin synthesis may enhance recovery in demyelinating diseases, such as multiple sclerosis. However, no suitable method exists to quantify myelination. The turnover of galactosylceramide (myelin component) is indicative of myelination in mice, but its turnover has not been determined in humans. Here, six healthy subjects consumed 120 mL 70% D₂O daily for 70 days to label galactosylceramide. We then used mass spectrometry and compartmental modeling to quantify the turnover rate of galactosylceramide in cerebrospinal fluid. Maximum deuterium enrichment of body water ranged from 1.5–3.9%, whereas that of galactosylceramide was much lower: 0.05–0.14%. This suggests a slow turnover rate, which was confirmed by the model‐estimated galactosylceramide turnover rate of 0.00168 day⁻¹, which corresponds to a half‐life of 413 days. Additional studies in patients with multiple sclerosis are needed to investigate whether galactosylceramide turnover could be used as an outcome measure in clinical trials with remyelination therapies.

Hypoxia-induced apoptotic cell death is prevented by oestradiol via oestrogen receptors in the developing central nervous system

The neuroprotective effects of oestrogens have been demonstrated against a variety of insults, including excitotoxicity, oxidative stress and cerebral ischemia under certain conditions. However, the molecular mechanisms underlying oestrogen neuroprotection are still unclear. We aimed to determine whether 17beta-oestradiol (E(2)) administration post-hypoxia (p-hx) was neuroprotective and whether these actions were mediated through oestrogen receptors (ER). For this purpose, 12-embyonic day-old chickens were subjected to acute hypoxia [8% (O(2)), 60 min], followed by different reoxygenation periods. To test the neuroprotective effect of E(2) and its mechanism, embryos were injected 30 min after the end of hypoxia with E(2) alone or with ICI 182 780, a competitive antagonist of ER. Cytochrome c (cyt c) release, an indicator of mitochondrial apoptotic pathway, was measured by western blot in optic lobe cytosolic extracts. DNA fragmentation by TUNEL fluorescence and caspase-3 fragmentation by immunofluorescence were detected on optic lobe sections. Acute hypoxia produces a significant increase in cyt c release from mitochondria at 4 h p-hx, followed by an increase in TUNEL positive cells 2 h later (6 h p-hx). Administration of E(2) (0.5 mg/egg) produced a significant decrease in cytosolic cyt c levels at 4 h p-hx, in caspase-3 activation and in TUNEL positive cells at 6 h p-hx compared to vehicle treated embryos. In the E(2)-ICI 182 780 treated embryos, cyt c release, caspase-3 fragmentation and TUNEL positive cells were similar to the hypoxic embryos, thus suggesting the requirement of an E(2)-ER interaction for E(2) mediated neuroprotective effects. In conclusion, E(2) prevents hypoxia-induced cyt c release and posterior cell death and these effects are mediated by oestrogen receptors.

Acute hypoxia and programmed cell death in developing CNS: Differential vulnerability of chick optic tectum layers

The chick optic tectum displays an alternating pattern of cellular and plexiform layers and at embryonic day (ED) 12 there are mainly four cellular layers: transient cell compartment 3 (TCC3), compartment "h-i-j"(C"h-i-j"), stratum griseum centrale (SGC) and subventricular zone (SvZ). In the present work we characterized the programmed cell death (PCD) of these layers and their vulnerability to acute hypoxia at ED12, and also identified the main cellular type involved in hypoxic cell death. The colocalization of three independent markers of cell degeneration: pyknotic nuclei by Hoechst staining, fragmented DNA by TdT-mediated dUTP nick-end labeling (TUNEL), and presence of active caspase-3 by immunofluorescence, was analyzed in embryos that developed in normoxic conditions (control embryos) and embryos that were subjected to hypoxia (8% O(2)/92% N(2)) for 60 min (hypoxic embryos), followed by 0-12 h of normoxic recovery. In control embryos cell death rate within each layer was constant through time, but there were significant differences (P<0.01) in cell death rates among the different layers. In contrast, in hypoxic embryos, a significant increase (P<0.01) in cell death rate was observed in layers TCC3, C"h-i-j" and SGC. This change was evident only at 6 h post-hypoxia, and at later time points cell death rate was similar to control values. Each of these layers had a different vulnerability to the hypoxic event while the SvZ layer was not affected. In addition, the significant colocalization between the neuron specific nuclear protein (NeuN) and TUNEL signal showed that hypoxia affected primarily neurons. In conclusion, our findings demonstrate that in the chick optic tectum at ED12, PCD is layer dependent and that acute hypoxia causes a transient increase in neuronal death in a delayed fashion, which is also layer dependent. The morphological features of the neuronal death process at the light microscope level resembled apoptosis.

The role of mitochondria in the regulation of hypoxia-inducible factor 1 expression during hypoxia

Hypoxia-inducible factor 1 (HIF-1) is a heterodimeric transcription factor that regulates transcriptional activation of several genes responsive to the lack of oxygen, including erythropoietin, vascular endothelial growth factor, glycolytic enzymes, and glucose transporters. Because the involvement of mitochondria in the regulation of HIF-1 has been postulated, we tested the effects of mitochondrial electron transport chain deficiency on HIF-1 protein expression and DNA binding in hypoxic cells. The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) inhibits electron transport chain at the level of complex I. MPTP is first converted to a pharmacologically active metabolite 1-methyl-4-phenylpyridinum (MPP+). MPP+ effectively inhibited both complex I activity and hypoxic accumulation of HIF-1alpha protein in dopaminergic cell lines PC12 and CATH.a. In C57BL/6 mice, a single dose of MPTP (15 mg/kg, intraperitoneal) inhibited complex I activity and HIF-1alpha protein accumulation in the striatum in response to a subsequent hypoxic challenge (8% O(2), 4 h). In a genetic model system, 40% complex I-inhibited human-ape xenomitochondrial cybrids, hypoxic induction of HIF-1alpha was severely reduced, and HIF-1 DNA binding was diminished. However, succinate, the mitochondrial complex II substrate, restored the hypoxic response in cybrid cells, suggesting that electron transport chain activity is required for activation of HIF-1. A partial complex I deficiency and a mild reduction in intact cell oxygen consumption effectively prevented hypoxic induction of HIF-1alpha protein.

The excitatory amino acid glutamate mediates reflexly increased tracheal blood flow and airway submucosal gland secretion

In six decerebrated and in eight alpha-chloralose anesthetized, paralyzed and mechanically ventilated beagle dogs, we have studied involvement of glutamate and glutamate receptors in transmission of excitatory inputs from the airway sensory receptors to the nucleus tractus solitarius and from this site to airway-related vagal preganglionic cells that regulate the tracheal circulation and the submucosal gland secretion. Stimulation of airway sensory fibers by lung deflation-induced reflex increase in tracheal blood flow and submucosal gland secretion. These responses were diminished by prior administration of AMPA/kainate receptor antagonist CNQX into the fourth ventricle (n=6). Furthermore, topical application or microinjection of AMPA/kainate receptor blockers, into the region of the ventrolateral medulla, where airway-related vagal preganglionic neurons are located, abolished the reflex changes in tracheal submucosal gland secretion (n=8); in these dogs mucosal blood flow was not measured). These findings indicate that reflex increase in tracheal blood flow and submucosal gland secretions are mediated mainly via release of glutamate and activation of the AMPA/kainate subtype of glutamate receptors.

Inter and intra-species-related differences in the regulation of the cardiac autonomic system

The heart rate response to isoproterenol (HR-Iso), density and affinity (kd) of beta-adrenergic (beta-AR) and muscarinic (M2) receptors were compared among three rodents with different generation-life histories of confinement and of high altitude exposure. The European guinea pig (Cavia porcellus) (EGp), a laboratory animal that arrived in Europe after the Spanish Conquest of South America and the Peruvian guinea pig (C. porcellus) (PGp), a semi-wild animal that came from the altiplano to sea level at least 25 generations ago, were used for intra-species comparison. Wistar rats (WR) were used for inter-species comparison as representative of a typical sea level laboratory animal. The HR-Iso was lower in EGp than in the PGp. The PGp showed the highest beta-AR density (P < 0.0005) and the highest beta-AR kd values (P < 0.0005) when compared to both EGp and WR groups (beta-AR Bmax (fmol mg-1 prot), WR, 19 +/- 4; Egp, 34 +/- 10; PGp, 74 +/- 15. beta-AR kd (pM), WR, 24 +/- 10; Egp, 17 +/- 7; PGp, 39 +/- 14). In contrast, PGp showed lower M2 receptor density values than the EGp (P < 0.0005). The WR had the highest M2 receptor densities (M2 Bmax (fmol mg-1 prot), WR, 188 +/- 15; Egp, 147 +/- 9; PGp, 118 +/- 6 and M2 kd (pM), WR, 65 +/- 12; Egp, 67 +/- 6; PGp, 92 +/- 2). The inter and intra-species differences found may be related to their respective history of confinement rather than to their history of exposure to high altitude.

Hypoxia- and normoxia-induced reversibility of autonomic control in Andean guinea pig heart

We herein describe the regulation of cardiac receptors in a typical high-altitude native animal. Heart rate response to isoproterenol (HRIso) (beats.min-1.mg Iso.kg-1) and atropine, the density of beta-adrenergic (beta AR) and muscarinic (M2) receptors, and the ventricular content of norepinephrine (NE) and dopamine (DA) were studied in guinea pigs (Cavia porcellus). Animals native to Lima, Peru (150 m) were studied at sea level (SL) and after 5 wk at 4,300-m altitude (SL-HA). Animals native to Rancas [Pasco, Peru (4,300 m)] were studied at high altitude (HA) and after 5 wk at SL (HA-SL). HA animals had a lower HRIso, maximum number of beta AR binding sites (Bmax), beta AR dissociation constant (Kd), NE, and DA (P < 0.05) and a higher M2 Bmax (P < 0.001) when compared with the SL group. HA-SL showed an increase of the HRIso, beta Ar Kd, and NE (P < 0.05) and a decrease of the M2 Bmax and Kd (P < 0.0001) when compared with the HA group. The present study demonstrates the differential regulation and reversibility of the autonomic control in the guinea pig heart.