Adjustment of the myelin sheath to axonal atrophy in the rat spinal root by the formation of infolded myelin loops

Atrophy of the L4 dorsal and ventral spinal roots was experimentally induced by unilateral sciatic neurectomy in groups of young (2 and 4 months) and older (12 months) albino rats. During the 4 months following neurectomy, the occurrence of infolded myelin loops (IMLs) was quantitatively examined in transverse sections prepared using perfusion fixation with glutaraldehyde and embedding in epoxy resin. The number of IMLs was higher on the operated side and increased with the time of survival and the age of the animals. The formation of IMLs is a characteristic early response of a large-caliber myelin sheath to axonal atrophy, probably reflecting the presence of redundant myelin.     

Introns and reading frames: correlation between splicing sites and their codon positions

Computer analyses of the entire GenBank database were conducted to examine correlation between splicing sites and codon positions in reading frames. Intron insertion patterns (i.e., splicing site locations with respect to codon positions) have been analyzed for all of the 74 codons of all the eukaryote taxonomic groups: primates, rodents mammals, vertebrates, invertebrates, and plants. We found that reading frames are interrupted by an intron at a codon boundary (as opposed to the middle of a codon) significantly more often than expected. This observation is consistent with the exon shuffling hypothesis, because exons that end at codon boundaries can be concatenated without causing a frame shift and thus are evolutionarily advantageous. On the other hand, when introns interrupt at the middles of codons, they exist in between the first and second bases much more frequently than between the second and third bases, despite the fact that boundaries between the first and second bases of codons are generally far more important than those between the second and third bases. The reason for this is not clear and yet to be explained. We also show that the length of an exon is a multiple of 3 more frequently than expected. Furthermore, the total length of two consecutive exons is also more frequently a multiple of 3. All the observations above are consistent with results recently published by Long, Rosenberg, and Gilbert (1995).      

A Metabolomic Analysis of Omega-3 Fatty Acid-Mediated Attenuation of Western Diet-Induced Nonalcoholic Steatohepatitis in LDLR -/- Mice

Background

Nonalcoholic steatohepatitis (NASH) is a progressive form of nonalcoholic fatty liver disease and a risk factor for cirrhosis, hepatocellular carcinoma and liver failure. Previously, we reported that dietary docosahexaenoic acid (DHA, 22:6,n-3) was more effective than eicosapentaenoic acid (EPA, 20:5,n-3) at reversing western diet (WD) induced NASH in LDLR^-/- mice.

Methods

Using livers from our previous study, we carried out a global non-targeted metabolomic approach to quantify diet-induced changes in hepatic metabolism.

Results

Livers from WD + olive oil (WD + O)-fed mice displayed histological and gene expression features consistent with NASH. The metabolomic analysis of 320 metabolites established that the WD and n-3 polyunsaturated fatty acid (PUFA) supplementation had broad effects on all major metabolic pathways. Livers from WD + O-fed mice were enriched in saturated (SFA) and monounsaturated fatty acids (MUFA), palmitoyl-sphingomyelin, cholesterol, n-6 PUFA, n-6 PUFA-containing phosphoglycerolipids, n-6 PUFA-derived oxidized lipids (12-HETE) and depleted of C_20-22 n-3 PUFA-containing phosphoglycerolipids, C_20-22 n-3 PUFA-derived oxidized lipids (18-HEPE, 17,18-DiHETE) and S-lactoylglutathione, a methylglyoxal detoxification product. WD + DHA was more effective than WD + EPA at attenuating WD + O-induced changes in NASH gene expression markers, n-6 PUFA and oxidized lipids, citrate and S-lactosyl glutathione. Diet-induced changes in hepatic MUFA and sphingolipid content were associated with changes in expression of enzymes involved in MUFA and sphingolipid synthesis. Changes in hepatic oxidized fatty acids and S-lactoylglutathione, however, correlated with hepatic n-3 and n-6 C_20-22 PUFA content. Hepatic C_20-22 n-3 PUFA content was inversely associated with hepatic α-tocopherol and ascorbate content and positively associated with urinary F2- and F3-isoprostanes, revealing diet effects on whole body oxidative stress.

Conclusion

DHA regulation of hepatic SFA, MUFA, PUFA, sphingomyelin, PUFA-derived oxidized lipids and S-lactoylglutathione may explain the protective effects of DHA against WD-induced NASH in LDLR^-/- mice.     

Metabolome and metaboproteome remodeling in nuclear reprogramming

Nuclear reprogramming resets differentiated tissue to generate induced pluripotent stem (iPS) cells. While genomic attributes underlying reacquisition of the embryonic-like state have been delineated, less is known regarding the metabolic dynamics underscoring induction of pluripotency. Metabolomic profiling of fibroblasts vs. iPS cells demonstrated nuclear reprogramming-associated induction of glycolysis, realized through augmented utilization of glucose and accumulation of lactate. Real-time assessment unmasked downregulated mitochondrial reserve capacity and ATP turnover correlating with pluripotent induction. Reduction in oxygen consumption and acceleration of extracellular acidification rates represent high-throughput markers of the transition from oxidative to glycolytic metabolism, characterizing stemness acquisition. The bioenergetic transition was supported by proteome remodeling, whereby 441 proteins were altered between fibroblasts and derived iPS cells. Systems analysis revealed overrepresented canonical pathways and interactome-associated biological processes predicting differential metabolic behavior in response to reprogramming stimuli, including upregulation of glycolysis, purine, arginine, proline, ribonucleoside and ribonucleotide metabolism, and biopolymer and macromolecular catabolism, with concomitant downregulation of oxidative phosphorylation, phosphate metabolism regulation, and precursor biosynthesis processes, prioritizing the impact of energy metabolism within the hierarchy of nuclear reprogramming. Thus, metabolome and metaboproteome remodeling is integral for induction of pluripotency, expanding on the genetic and epigenetic requirements for cell fate manipulation.     

Mechanisms for the prevention of vitamin E excess

The liver is at the nexus of the regulation of lipoprotein uptake, synthesis, and secretion, and it is the site of xenobiotic detoxification by cytochrome P450 oxidation systems (phase I), conjugation systems (phase II), and transporters (phase III). These two major liver systems control vitamin E status. The mechanisms for the preference for α-tocopherol relative to the eight naturally occurring vitamin E forms largely depend upon the liver and include both a preferential secretion of α-tocopherol from the liver into the plasma for its transport in circulating lipoproteins for subsequent uptake by tissues, as well as the preferential hepatic metabolism of non-α-tocopherol forms. These mechanisms are the focus of this review.     

Greater γ-tocopherol status during acute smoking abstinence with nicotine replacement therapy improved vascular endothelial function by decreasing 8-iso-15(S)-prostaglandin F2α

Nicotine replacement therapy (NRT) improves the long-term success rate of smoking cessation, but induces oxidative stress and inflammatory responses that may delay the restoration of vascular endothelial function (VEF). No studies have examined co-therapy of NRT-assisted smoking abstinence with γ-tocopherol (γ-T), a vitamin E form with antioxidant and anti-inflammatory activities, on improvements in VEF. In a randomized, double-blind, placebo-controlled study, healthy smokers (25 ± 1 y old; mean ± SEM) received NRT and abstained from smoking for 24 h with placebo (n = 12) or oral administration of γ-T-rich mixture of tocopherols (γ-TmT; n = 11) that provided 500 mg γ-T. Brachial artery flow-mediated dilation (FMD), and biomarkers of nitric oxide metabolism, antioxidant status, inflammation, and lipid peroxidation [8-iso-prostaglandin F_2α stereoisomers (8-iso-15(R)-PGF_2α and 8-iso-15(S)-PGF_2α)] were measured prior to and after 24 h of smoking abstinence. Smoking abstinence with NRT regardless of γ-TmT similarly decreased urinary naphthol (P < 0.05) without affecting plasma cotinine. γ-TmT increased plasma γ-T by 4-times and the urinary metabolite of γ-T, γ-carboxyethyl-chromanol, by three times. Smoking abstinence with γ-TmT, but not smoking abstinence alone, increased FMD without affecting plasma nitrate/nitrite or the ratio of asymmetric dimethylarginine/arginine. Urinary 8-iso-15(S)-PGF_2α decreased only in those receiving γ-TmT and was inversely correlated to FMD (R = −0.43, P < 0.05). Circulating markers of inflammation were unaffected by smoking abstinence or γ-TmT. Short-term NRT-assisted smoking abstinence with γ-TmT, but not NRT-assisted smoking abstinence alone, improved VEF by decreasing 8-iso-15(S)-PGF_2α, a vasoconstrictor that was otherwise unaffected by NRT-assisted smoking abstinence.