Changes in lipid phase behaviour in human myelin during maturation and aging. Involvement of lipid peroxidation

Novel therapeutic approaches to target neurodegeneration

Ageing is the main risk factor common to most primary neurodegenerative disorders. Indeed, age-related brain alterations have been long considered to predispose to neurodegeneration. Although protein misfolding and the accumulation of toxic protein aggregates have been considered as causative events in neurodegeneration, several other biological pathways affected by brain ageing also contribute to pathogenesis. Here, we discuss the evidence showing the involvement of the mechanisms controlling neuronal structure, gene expression, autophagy, cell metabolism and neuroinflammation in the onset and progression of neurodegenerative disorders. Furthermore, we review the therapeutic strategies currently under development or as future approaches designed to normalize these pathways, which may then increase brain resilience to cope with toxic protein species. In addition to therapies targeting the insoluble protein aggregates specifically associated with each neurodegenerative disorder, these novel pharmacological approaches may be part of combined therapies designed to rescue brain function.

An accelerated degeneration of white matter microstructure and networks in the nondemented old-old

The nondemented old-old over the age of 80 comprise a rapidly increasing population group; they can be regarded as exemplars of successful aging. However, our current understanding of successful aging in advanced age and its neural underpinnings is limited. In this study, we measured the microstructural and network-based topological properties of brain white matter using diffusion-weighted imaging scans of 419 community-dwelling nondemented older participants. The participants were further divided into 230 young-old (between 72 and 79, mean = 76.25 ± 2.00) and 219 old-old (between 80 and 92, mean = 83.98 ± 2.97). Results showed that white matter connectivity in microstructure and brain networks significantly declined with increased age and that the declined rates were faster in the old-old compared with young-old. Mediation models indicated that cognitive decline was in part through the age effect on the white matter connectivity in the old-old but not in the young-old. Machine learning predictive models further supported the crucial role of declines in white matter connectivity as a neural substrate of cognitive aging in the nondemented older population. Our findings shed new light on white matter connectivity in the nondemented aging brains and may contribute to uncovering the neural substrates of successful brain aging.

Orientational changes of white matter fibers in Alzheimer's disease and amnestic mild cognitive impairment

White matter abnormalities represent early neuropathological events in neurodegenerative diseases such as Alzheimer's disease (AD), investigating these white matter alterations would likely provide valuable insights into pathological changes over the course of AD. Using a novel mathematical framework called "Director Field Analysis" (DFA), we investigated the geometric microstructural properties (i.e., splay, bend, twist, and total distortion) in the orientation of white matter fibers in AD, amnestic mild cognitive impairment (aMCI), and cognitively normal (CN) individuals from the Alzheimer's Disease Neuroimaging Initiative 2 database. Results revealed that AD patients had extensive orientational changes in the bilateral anterior thalamic radiation, corticospinal tract, inferior and superior longitudinal fasciculus, inferior fronto-occipital fasciculus, and uncinate fasciculus in comparison with CN. We postulate that these orientational changes of white matter fibers may be partially caused by the expansion of lateral ventricle, white matter atrophy, and gray matter atrophy in AD. In contrast, aMCI individuals showed subtle orientational changes in the left inferior longitudinal fasciculus and right uncinate fasciculus, which showed a significant association with the cognitive performance, suggesting that these regions may be preferential vulnerable to breakdown by neurodegenerative brain disorders, thereby resulting in the patients' cognitive impairment. To our knowledge, this article is the first to examine geometric microstructural changes in the orientation of white matter fibers in AD and aMCI. Our findings demonstrate that the orientational information of white matter fibers could provide novel insight into the underlying biological and pathological changes in AD and aMCI.

Aerobic exercise training decreases cognitive impairment caused by demyelination by regulating ROCK signaling pathway in aging mice

Recent studies have discovered a strong link between physical exercise and the prevention of neuro-degenerative symptoms, especially in elderly subjects, nonetheless, the exact underlying mechanism remains unclear. In this study, we hypothesized that aerobic exercise training may have a protective effect on myelin sheath in aged mice by regulating the ROCK signal pathway, which is considered as a crucial mechanism for decreasing apoptosis and promoting regeneration. Briefly, C57/BL aged mice underwent an exercise training (5 days/week, lasting 6 weeks). Memory and cognitive impairment were examined using Novel object recognition (NOR) test and Morris water maze test (MWM). Demyelination was explored using Luxol fast blue staining and transmission electron microscopy in the corpus callosum (CC), and the expression of ROCK and apoptotic protein were analyzed via western blot. We demonstrated the impairment of memory and cognitive and the decrease of myelin sheath thickness in aged mice. In addition, severe demyelination was observed in aged mice, accompanied with increased expression of RhoA, ROCK, ATF3, and Caspase 3, and reduced expression of MBP, Olig2, and NG2. Aerobic exercise training improved behavioral functions, increased the expression of MBP and myelin sheath thickness, reduced apoptosis and promoted myelination. To sum up, our data indicate that aerobic exercise training protects demyelination from aging-related white matter injury, which is associated with the up-regulation of ROCK signal pathway.

Retrieving neuronal orientations using 3D scanning SAXS and comparison with diffusion MRI

While diffusion MRI (dMRI) is currently the method of choice to non-invasively probe tissue microstructure and study structural connectivity in the brain, its spatial resolution is limited and its results need structural validation. Current ex vivo methods employed to provide 3D fiber orientations have limitations, including tissue-distorting sample preparation, small field of view or inability to quantify 3D fiber orientation distributions. 3D fiber orientation in tissue sections can be obtained from 3D scanning small-angle X-ray scattering (3D sSAXS) by analyzing the anisotropy of scattering signals. Here we adapt the 3D sSAXS method for use in brain tissue, exploiting the high sensitivity of the SAXS signal to the ordered molecular structure of myelin. We extend the characterization of anisotropy from vectors to tensors, employ the Funk-Radon-Transform for converting scattering information to real space fiber orientations, and demonstrate the feasibility of the method in thin sections of mouse brain with minimal sample preparation. We obtain a second rank tensor representing the fiber orientation distribution function (fODF) for every voxel, thereby generating fODF maps. Finally, we illustrate the potential of 3D sSAXS by comparing the result with diffusion MRI fiber orientations in the same mouse brain. We show a remarkably good correspondence, considering the orthogonality of the two methods, i.e. the different physical processes underlying the two signals. 3D sSAXS can serve as validation method for microstructural MRI, and can provide novel microstructural insights for the nervous system, given the method's orthogonality to dMRI, high sensitivity to myelin sheath's orientation and abundance, and the possibility to extract myelin-specific signal and to perform micrometer-resolution scanning.

Glycerophospholipid Supplementation as a Potential Intervention for Supporting Cerebral Structure in Older Adults

Modifying nutritional intake through supplementation may be efficacious for altering the trajectory of cerebral structural decline evident with increasing age. To date, there have been a number of clinical trials in older adults whereby chronic supplementation with B vitamins, omega-3 fatty acids, or resveratrol, has been observed to either slow the rate of decline or repair cerebral tissue. There is also some evidence from animal studies indicating that supplementation with glycerophospholipids (GPL) may benefit cerebral structure, though these effects have not yet been investigated in adult humans. Despite this paucity of research, there are a number of factors predicting poorer cerebral structure in older humans, which GPL supplementation appears to beneficially modify or protect against. These include elevated concentrations of homocysteine, unbalanced activity of reactive oxygen species both increasing the risk of oxidative stress, increased concentrations of pro-inflammatory messengers, as well as poorer cardio- and cerebrovascular function. As such, it is hypothesized that GPL supplementation will support cerebral structure in older adults. These cerebral effects may influence cognitive function. The current review aims to provide a theoretical basis for future clinical trials investigating the effects of GPL supplementation on cerebral structural integrity in older adults.

Proteasome and Organs Ischemia-Reperfusion Injury

The treatment of organ failure on patients requires the transplantation of functional organs, from donors. Over time, the methodology of transplantation was improved by the development of organ preservation solutions. The storage of organs in preservation solutions is followed by the ischemia of the organ, resulting in a shortage of oxygen and nutrients, which damage the tissues. When the organ is ready for the transplantation, the reperfusion of the organ induces an increase of the oxidative stress, endoplasmic reticulum stress, and inflammation which causes tissue damage, resulting in a decrease of the transplantation success. However, the addition of proteasome inhibitor in the preservation solution alleviated the injuries due to the ischemia-reperfusion process. The proteasome is a protein structure involved in the regulation the inflammation and the clearance of damaged proteins. The goal of this review is to summarize the role of the proteasome and pharmacological compounds that regulate the proteasome in protecting the organs from the ischemia-reperfusion injury.

Myelin changes at the early stage of 5XFAD mice

Previous studies have demonstrated myelin deficits in Alzheimer's disease (AD). However, it is still unclear whether myelin deficits occur at early stage of AD. Our study aimed to investigate myelin deficits in 5XFAD mice dynamically in different cognition-associated brain regions at early stage of AD. Transmission electron microscopy (TEM) was applied to detect myelin changes in late-myelinating regions such as prelimbic area (PrL), retrosplenial granular cortex (Rsg), field CA1 of hippocampus (CA1) and entorhinal cortex (ERC) respectively at different stages (1, 2, 3 and 5 months of age) in 5XFAD mouse model. In addition, we assessed spatial learning and memory with Morris water maze (MWM) in 5XFAD mice. Myelin deficits in 5XFAD mice started from 1 month of age and this deterioration continued during ageing, whereas the same myelin abnormality could only be observed in 5-month-old wild-type mice. Additionally, the g-ratio (an index associated with myelin thickness) was increased in 1-month-old 5XFAD mice in the regions including PrL, CA1 and ERC, compared to wild-type mice. As animals aged, the increased g-ratio in 5XFAD appeared in more regions of the brain. Moreover, 5XFAD mice showed spatial memory deficits from 1 month of age and spatial learning deficits from 2 months of age. In conclusion, myelin deficits occurred at an early stage and progressed with ageing in 5XFAD mouse model. Notably, a sequential myelin change was detected in cognition-associated brain regions. Combined with cognitive examinations, this study suggests that myelin changes might contribute to cognitive dysfunction.

Nano-antioxidants: An emerging strategy for intervention against neurodegenerative conditions

Oxidative stress has for long been linked to the neuronal cell death in many neurodegenerative conditions. Conventional antioxidant therapies have been less effective in preventing neuronal damage caused by oxidative stress due to their inability to cross the blood brain barrier. Nanoparticle antioxidants constitute a new wave of antioxidant therapies for prevention and treatment of diseases involving oxidative stress. It is believed that nanoparticle antioxidants have strong and persistent interactions with biomolecules and would be more effective against free radical induced damage. Nanoantioxidants include inorganic nanoparticles possessing intrinsic antioxidant properties, nanoparticles functionalized with antioxidants or antioxidant enzymes to function as an antioxidant delivery system. Nanoparticles containing antioxidants have shown promise as high-performance therapeutic nanomedicine in attenuating oxidative stress with potential applications in treating and preventing neurodegenerative conditions. However, to realize the full potential of nanoantioxidants, negative aspects associated with the use of nanoparticles need to be overcome to validate their long term applications.

Regional differences in white matter breakdown between frontotemporal dementia and early-onset Alzheimer's disease

BACKGROUND

White matter abnormalities have been associated with both behavioral variant frontotemporal dementia (bvFTD) and Alzheimer's disease (AD).

OBJECTIVE

Using MRI diffusion tensor imaging (DTI) measures, we compared white matter integrity between patients with bvFTD and those with early-onset AD and correlated these biomarkers with behavioral symptoms involving emotional blunting.

METHODS

We studied 8 bvFTD and 12 AD patients as well as 12 demographically-matched healthy controls (NCs). Using four DTI metrics (fractional anisotropy, axial diffusivity, radial diffusivity, and mean diffusivity), we assessed the frontal lobes (FWM) and genu of the corpus callosum (GWM), which are vulnerable late-myelinating regions, and a contrasting early-myelinating region (splenium of the corpus callosum). The Scale for Emotional Blunting Scale (SEB) was used to assess emotional functioning of the study participants.

RESULTS

Compared to AD patients and NCs, the bvFTD subjects exhibited significantly worse FWM and GWM integrity on all four DTI metrics sensitive to myelin and axonal integrity. In contrast, AD patients showed a numerical trend toward worse splenium of the corpus callosum integrity than bvFTD and NC groups. Significant associations between SEB ratings and GWM DTI measures were demonstrated in the combined bvFTD and AD sample. When examined separately, these relationships remained robust for the bvFTD group but not the AD group.

CONCLUSIONS

The regional DTI alterations suggest that FTD and AD are each associated with a characteristic distribution of white matter degradation. White matter breakdown in late-myelinating regions was associated with symptoms of emotional blunting, particularly within the bvFTD group.

Patterns of brain atrophy in clinical variants of frontotemporal lobar degeneration

BACKGROUND/AIMS

The clinical syndromes of frontotemporal lobar degeneration include behavioral variant frontotemporal dementia (bvFTD) and semantic (SV-PPA) and nonfluent variants (NF-PPA) of primary progressive aphasia. Using magnetic resonance imaging (MRI), tensor-based morphometry (TBM) was used to determine distinct patterns of atrophy between these three clinical groups.

METHODS

Twenty-seven participants diagnosed with bvFTD, 16 with SV-PPA, and 19 with NF-PPA received baseline and follow-up MRI scans approximately 1 year apart. TBM was used to create three-dimensional Jacobian maps of local brain atrophy rates for individual subjects.

RESULTS

Regional analyses were performed on the three-dimensional maps and direct comparisons between groups (corrected for multiple comparisons using permutation tests) revealed significantly greater frontal lobe and frontal white matter atrophy in the bvFTD relative to the SV-PPA group (p < 0.005). The SV-PPA subjects exhibited significantly greater atrophy than the bvFTD in the fusiform gyrus (p = 0.007). The NF-PPA group showed significantly more atrophy in the parietal lobes relative to both bvFTD and SV-PPA groups (p < 0.05). Percent volume change in ventromedial prefrontal cortex was significantly associated with baseline behavioral symptomatology.

CONCLUSION

The bvFTD, SV-PPA, and NF-PPA groups displayed distinct patterns of progressive atrophy over a 1-year period that correspond well to the behavioral disturbances characteristic of the clinical syndromes. More specifically, the bvFTD group showed significant white matter contraction and presence of behavioral symptoms at baseline predicted significant volume loss of the ventromedial prefrontal cortex.

Age-related slowing in cognitive processing speed is associated with myelin integrity in a very healthy elderly sample

Performance on measures of cognitive processing speed (CPS) slows with age, but the biological basis associated with this cognitive phenomenon remains incompletely understood. We assessed the hypothesis that the age-related slowing in CPS is associated with myelin breakdown in late-myelinating regions in a very healthy elderly population. An in vivo magnetic resonance imaging (MRI) biomarker of myelin integrity was obtained from the prefrontal lobe white matter and the genu of the corpus callosum for 152 healthy elderly adults. These regions myelinate later in brain development and are more vulnerable to breakdown due to the effects of normal aging. To evaluate regional specificity, we also assessed the splenium of the corpus callosum as a comparison region, which myelinates early in development and primarily contains axons involved in visual processing. The measure of myelin integrity was significantly correlated with CPS in highly vulnerable late-myelinating regions but not in the splenium. These results have implications for the neurobiology of the cognitive changes associated with brain aging.

Pathological aspects of lipid peroxidation

Lipid peroxidation (LPO) product accumulation in human tissues is a major cause of tissular and cellular dysfunction that plays a major role in ageing and most age-related and oxidative stress-related diseases. The current evidence for the implication of LPO in pathological processes is discussed in this review. New data and literature review are provided evaluating the role of LPO in the pathophysiology of ageing and classically oxidative stress-linked diseases, such as neurodegenerative diseases, diabetes and atherosclerosis (the main cause of cardiovascular complications). Striking evidences implicating LPO in foetal vascular dysfunction occurring in pre-eclampsia, in renal and liver diseases, as well as their role as cause and consequence to cancer development are addressed.

Cholesterol synthesis rate in human hippocampus declines with aging

During the last three to four decades, interest in the interaction of circulating and brain cholesterol has increased. As the CNS matures and cholesterol pools in the brain become constant, the rate of de novo synthesis of cholesterol in the brain is expected to decline. We measured cholesterol, its precursors and its brain specific metabolite 24S-hydroxycholesterol in hippocampus from 7 female and 13 male corpses by highly sensitive and specific gas chromatography-mass spectrometry. Two age groups (young, n=10; elderly, n=10) were formed with a cut-off at the median age of 38 years. The amount of cholesterol was comparable in young and elderly subjects. The concentrations of the cholesterol precursors lanosterol and lathosterol were significantly higher in young (P=0.036 and 0.005, respectively) than in elderly subjects. In accordance, there was a significantly negative correlation between age and lathosterol concentrations (r=-0.505; P=0.023). Absolute levels of 24S-hydroxycholesterol in the brain were slightly, but not significantly, lower in the hippocampal specimens from the elderly subjects. We conclude that during aging, cholesterol synthesis is decreased in the hippocampus, while absolute cholesterol content remains at a stable level.

Heterogeneous age-related breakdown of white matter structural integrity: implications for cortical "disconnection" in aging and Alzheimer's disease

Human and non-human primate data suggest that the structural integrity of myelin sheaths deteriorates during normal aging, especially in the late-myelinating association regions and may result in "disconnection" of widely distributed neural networks. Magnetic resonance imaging (MRI) was used to assess the heterogeneity of this process and its impact on brain aging and Alzheimer's disease (AD) by evaluating early- and later-myelinating regions of the corpus callosum, the splenium (Scc) and genu (Gcc), respectively. Calculated transverse relaxation rates (R2), an indirect measure of white matter structural integrity for the Gcc and Scc, were examined. The relationship between age and R2 differed in the two regions. A quadratic (inverted U) function with an accelerating rate of decline beginning at age 31 best represented the Gcc pattern while the Scc decline was three-fold smaller, gradual, and linear. These data suggest that the severity of age-related myelin breakdown is regionally heterogeneous, consistent with the hypothesis that differences in myelin properties make later-myelinating regions more susceptible to this process. In AD this process is globally exacerbated, consistent with an extracellular deleterious process such as amyloid beta-peptide toxicity. Non-invasive measures such as R2 may be useful in primary prevention studies of AD.

Age-related myelin breakdown: a developmental model of cognitive decline and Alzheimer's disease

A hypothetical model of Alzheimer's disease (AD) as a uniquely human brain disorder rooted in its exceptional process of myelination is presented. Cortical regions with the most protracted development are most vulnerable to AD pathology, and this protracted development is driven by oligodendrocytes, which continue to differentiate into myelin producing cells late into the fifth decade of life. The unique metabolic demands of producing and maintaining their vast myelin sheaths and synthesizing the brain's cholesterol supply make oligodendrocytes especially susceptible to a variety of insults. Their vulnerability increases with increasing age at differentiation as later-differentiating cells myelinate increasing numbers of axonal segments. These vulnerable late-differentiating cells drive the protracted process of intracortical myelination and by increasing local cholesterol and iron levels, progressively increase the toxicity of the intracortical environment forming the basis for the age risk factor for AD. At older ages, the roughly bilaterally symmetrical continuum of oligodendrocyte vulnerability manifests as a progressive pattern of myelin breakdown that recapitulates the developmental process of myelination in reverse. The ensuing homeostatic responses to myelin breakdown further increase intracortical toxicity and results in the relentless progression and non-random anatomical distribution of AD lesions that eventually cause neuronal dysfunction and degeneration. This process causes a slowly progressive disruption of neural impulse transmission that degrades the temporal synchrony of widely distributed neural networks underlying normal brain function. The resulting network "disconnections" first impact functions that are most dependent on large-scale synchronization including higher cognitive functions and formation of new memories. Multiple genetic and environmental risk factors (e.g. amyloid beta-peptide and free radical toxicity, head trauma, anoxia, cholesterol levels, etc.) can contribute to the cognitive deficits observed in aging and AD through their impact on the life-long trajectory of myelin development and breakdown. This development-to-degeneration model is testable through imaging and post mortem methods and highlights the vital role of myelin in impulse transmission and synchronous brain function. The model offers a framework that explains the anatomical distribution and progressive course of AD pathology, some of the failures of promising therapeutic interventions, and suggests further testable hypotheses as well as novel approaches for intervention efforts.

Effects of age on the thickness of myelin sheaths in monkey primary visual cortex

The effect of age on myelin sheath thickness was determined by an electron microscopic examination of cross sections of the vertical bundles of nerve fibers that pass through primary visual cortex of the rhesus monkey. The tissue was taken from the cortices of young (4-9 years of age) and old (over 24 years of age) monkeys, and the sections were taken at the level of layer 4Cbeta. From the electron photomicrographs, the diameters of axons and the numbers of lamellae in their myelin sheaths were determined. No change was found in the diameters of axons with age, although the mean numbers of myelin lamellae in the sheaths increased from 5.6 in the young monkeys to 7.0 in the old monkeys. Much of this increase in mean thickness was due to the fact that, in the old monkeys, thick myelin sheaths with more than ten lamellae are more common than in the young monkeys. While this increase in the thickness of myelin sheaths is occurring in old monkeys, there are also age-related changes in some of the sheaths. Consequently, it seems that, with age, there is some degeneration of myelin but, at the same time, a continued production of lamellae.

Walker-256 tumor growth causes oxidative stress in rat brain

The elevated rate of oxygen consumption and high amount of polyunsaturated fatty acids make the central nervous system vulnerable to oxidative stress. The effect of Walker-256 tumor growth on oxi-reduction indexes in the hypothalamus (HT), cortex (CT), hippocampus (HC) and cerebellum (CB) of male Wistar rats was investigated. The presence of the tumor caused an increase in thiobarbituric acid reactant substances (TBARs) in the HT, CB and HC. Due to tumor growth, the activity of glucose-6-phosphate dehydrogenase increased in the HT and CB, whereas citrate synthase activity was reduced in the HT, CT and CB. Therefore, the potential for generation of reducing power is increased in the cytosol and decreased in the mitochondria of various brain regions of Walker-256 tumor-bearing rats. These changes occurred concomitantly with an unbalance in the brain enzymatic antioxidant system. The tumor decreased the activities of catalase in the HT and CB and of glutathione peroxidase in the HT, CB and HC, and raised the CuZn-superoxide dismutase activity in the HT, CB and HC. These combined findings indicate that Walker-256 tumor growth causes oxidative stress in the brain.

Increased microglial activation and protein nitration in white matter of the aging monkey

Activated microglia are important pathological features of a variety of neurological diseases, including the normal aging process of the brain. Here, we quantified the level of microglial activation in the aging rhesus monkey using antibodies to HLA-DR and inducible nitric oxide synthase (iNOS). We observed that 3 out of 5 white matter areas but only 1 of 4 cortical gray matter regions examined showed significant increases in two measures of activated microglia with age, indicating that diffuse white matter microglial activation without significant gray matter involvement occurs with age. Substantial levels of iNOS and 3-nitrotyrosine, a marker for peroxynitrite, increased diffusely throughout subcortical white matter with age, suggesting a potential role of nitric oxide in age-related white matter injury. In addition, we found that the density of activated microglia in the subcortical white matter of the cingulate gyrus and the corpus callosum was significantly elevated with cognitive impairment in elderly monkeys. This study suggests that microglial activation increases in white matter with age and that these increases may reflect the role of activated microglia in the general pathogenesis of normal brain aging.

Oxidative inactivation of brain alkaline phosphatase responsible for hydrolysis of phosphocholine

Alkaline phosphatase, one of the enzymes responsible for the conversion of phosphocholine into choline, was purified from bovine brain membrane, where the phosphatase is bound as glycosylphosphatidylinositol-linked protein, and subjected to oxidative inactivation. The phosphatase activity, based on the hydrolysis of p-nitrophenyl phosphate and phosphocholine, decreased slightly after the exposure to H2O2. Inclusion of Cu2+ in the incubation with 1 mM H2O2 led to a rapid decrease of activity in a time- and concentration-dependent manner. In comparison, the H2O2/Cu2+ system was much more effective than the H2O2/Fe2+ system in inactivating brain phosphatase. In a further study, it was observed that the hydroxy radical scavengers mannitol, ethanol, or benzoate failed to prevent against H2O2/Cu2+-induced inactivation of the phosphatase, excluding the involvement of extraneous hydroxy radicals in metal-catalyzed oxidation. In addition, it was found that both substrates, p-nitrophenyl phosphate and phosphocholine, and an inhibitor, phosphate ion, at their saturating concentrations exhibited a remarkable, although incomplete, protection against the inactivating action of H2O2/Cu2+. A similar protection was also expressed by divalent metal ions such as Mg2+ or Mn2+. Separately, it was found that H2O2/Fe2+-induced inactivation was prevented by p-nitrophenyl phosphate or Mg2+ but not phosphate ions. Thus, it is implied that phosphocholine-hydrolyzing alkaline phosphatase in brain membrane might be one of enzymes susceptible to metal-catalyzed oxidation.

Aging and oxidative stress in neurodegeneration

The effect of oxidative stress on the function of brain synapse, the difference in susceptibility of synapse to hyperoxia with age, and the changes in vitamin E status by stress and aging were investigated. Synaptic membrane permeability to sucrose was increased with age. When rats were subjected to hyperoxia, the membrane permeability on each age increased significantly. The susceptibility of synapse of 25 month old rats exposed to stress was about 2.5 times higher than unexposed old rats. The synaptic plasma membrane fluidity decreased significantly either in response to hyperoxia or during aging. The thiobarbituric acid reactive substances (TBARS) in the synaptic plasma membranes increased with age, and those in the membranes of oxygen-exposed rats were higher than in the unexposed rats. The cholesterol/phospholipids (C/P) ratio of the membranes increased significantly with age, and the values in the membranes of oxygen-exposed rats increased more significantly than in unexposed rats of each age. In a measurement of fatty acid content in the membranes, the content of docosahexaenoic acid (DHA, C22:6) decreased significantly during aging and by hyperoxia. These results suggest that free radicals derived from oxygen may attack nerve terminals and peroxidize the membrane, resulting in the deterioration of function of brain synapse, and that susceptibility of synapse to oxidative stress was significantly increased with age. Vitamin E content in the synaptic plasma membranes decreased with age. When rats were subjected to oxidative stress, the content was lower in each age than in normal rat membranes. An intraperitoneal administration of vitamin E prior to stress reduced these abnormalities. It is obvious that vitamin E contributes to the protection against nerve terminal dysfunction caused by oxidative stress.

Oxidative injury of synapse and alteration of antioxidative defense systems in rats, and its prevention by vitamin E

In order to define whether active oxygen species actually induce oxidative damage to the nervous system, and how antioxidative defense systems are changed by oxidative stress, morphological and functional changes in the nervous system and antioxidant status were investigated. When rats were exposed to 100% oxygen in a chamber, many morphological changes, e.g. swollen astrocytes around vessels, deformed nuclei in nerve cells, pigmentation, swollen mitochondria, and abnormal accumulation of synaptic vesicles in swollen nerve terminals, were observed by electron microscopy. When synaptosomes isolated from oxygen-exposed rats were stimulated by KCl, acetylcholine release from the terminal was decreased more significantly than in synaptosomes from unexposed rats (P < 0.01). Synaptic plasma membrane fluidity decreased in response to oxygen exposure, and plasma membrane permeability to sucrose was increased significantly (P < 0.05). The cholesterol/phospholipid ratio of the plasma membranes was increased by oxidative stress and the content of unsaturated fatty acids, especially arachidonic acid and docosahexaenoic acid, decreased. The levels of thiobarbituric-acid-reactive substances in the plasma membranes of oxygen-exposed rats were significantly higher than in unexposed rats (P < 0.01). These results suggest that free radicals derived from oxygen may attack nerve terminals and peroxidize the plasma membrane. It was found that in response to the oxidative stress, the status of the defense system in synapse, i.e. the concentration of vitamin E, activities of superoxide dismutase and glutathione peroxidase changed, and that many of the changes observed were reduced remarkably by the intraperitoneal administration of vitamin E prior to stress. Data support the idea that vitamin E contributes to the protection against nerve dysfunction caused by oxidative stress.

Effects of AETT-induced neuronal ceroid lipofuscinosis on learning ability in rats

The behavioral effects of ceroid-lipofuscin accumulation, induced by intraperitoneal administration of acetyl-ethyl-tetramethyl-tetralin (AETT) in Wistar rats for 3 months, were examined in the present studies. A significant increase in neuronal ceroidlipofuscin was demonstrated neuropathologically as well as morphometrically. Although the AETT-intoxicated rats showed neither alteration of locomotor activity nor shock sensitivity, a significant impairment of learning ability, especially an acquisition trial in passive avoidance tests, was observed. Results of the present studies indicate the possibility that a diffuse lipofuscin accumulation causes a learning impairment in rats. The results also imply the possibility of a significant role of age-related lipofuscin accumulation in the dementing processes of human especially in the elderly.

Topology of CNS myelin proteolipid protein: evidence for the nonenzymatic glycosylation of extracytoplasmic domains in normal and diabetic animals

Myelin proteolipid protein (PLP), the main integral membrane protein in the central nervous system myelin, was labeled at the extracytoplasmic domains with the membrane impermeant reagents pyridoxal 5'-phosphate and tritiated borohydride. Lysine-217, located in the fourth hydrophilic domain of PLP, was found to be the major labeled residue, which defined this domain to be extracytoplasmic in agreement with our previously proposed topological model. The remarkably high reactivity in vitro of this residue as compared to all other lysines in PLP led us to investigate the possible modification of PLP in vivo by other carbonyl compounds. We demonstrate that PLP is the most highly nonenzymatically glycosylated membrane protein in murine and bovine brain. The degree of modification increases significantly under hyperglycemic conditions, as studied in diabetic mice. The majority of the glycosylation sites are also located at extracytoplasmic domains. The degree of nonenzymatic glycosylation of PLP may be related to late diabetic complications affecting the central nervous system.

Myelin in multiple sclerosis is developmentally immature

The etiology of multiple sclerosis (MS) is considered to involve genetic, environmental, infective, and immunological factors which affect the integrity of a normally assembled myelin sheath, either directly or indirectly resulting in demyelination. In a correlative study involving protein chemical, mass spectrometric, and electron microscopic techniques we have determined that myelin obtained from victims of MS is arrested at the level of the first growth spurt (within the first 6 yr of life) and is therefore developmentally immature. The data supporting this conclusion include (a) the pattern of microheterogeneity of myelin basic protein (MBP); (b) the NH2-terminal acylation of the least cationic component of MBP ("C-8"); (c) the phase transition temperature (Tc) of myelin isolated from victims of MS correlated with the increased proportion of the least cationic component of MBP; and (d) immunogold electron microscopy using an antibody specific for "C-8" showed that the distribution of gold particles in a 2-yr-old infant was similar to the distribution found in a victim of MS. We postulate that this developmentally immature myelin is more susceptible to degradation by one or a combination of factors mentioned above, providing the initial antigenic material to the immune system.

Lipid peroxidation inhibits oleoyl-CoA: 1-acyl-sn-glycero-3-phosphocholine O-acyltransferase in rat CNS axolemma-enriched fractions

The effect of phospholipid peroxidation on the acylation of lysoPtdCho (lysophosphatidylcholine) by axolemma-enriched fraction prepared from rat brain stem was investigated. After two types of peroxidative treatments, the in vitro induction of malondialdehyde and conjugated dienes formation in axolemmal membranes correlated to a shift in the ratio of saturated/unsaturated fatty acids. By using an Fe2+ (20 microM)-ascorbate (0.25 mM) peroxidation system, the residual acyltransferase activity was 55% of the initial one. No change in Km value for either oleoyl-CoA or lysoPtdCho was found, whereas a loss of 24% in Vmax was observed. After 5 min preincubation with 150 mM t-BuOOH, 70% inactivation of the acylation reaction was observed. A near suppression of enzyme activity was reached with 400 mM. The apparent Km for oleoyl-CoA decreased sharply (from 6.6 microM in control preparations to 4.1 microM in t-BuOOH-treated membranes), indicating a 2-fold increase in the enzymatic affinity for this substrate. The apparent Km for lysoPtdCho increased markedly (from 1.56 microM in the control preparations to 5.88 microM in t-BuOOH-treated membranes) whereas a decrease of Vmax (from 1.65 to 0.80 nmol/min/mg protein) for the same substrate was observed. Significant enzyme inactivation (loss of 60% of initial activity) was seen when 10 mumol of photooxidized phospholipids were preincubated with axolemmal membranes. Significant dose-dependent enzyme inactivation was brought about by addition of 10-60 mumol of peroxidized PtdEtn/100 micrograms axolemmal protein. The percent enzyme inhibition by peroxidized PtdCho at equivalent amounts was lower than that by PtdEtn.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related accumulation of phosphatidylcholine hydroperoxide in cultured human diploid cells and its prevention by alpha-tocopherol

The levels of phosphatidylcholine hydroperoxide in serially cultured human fetal diploid fibroblasts at various population doubling levels were determined by high-performance liquid chromatography combined with chemiluminescence detection. This methodology utilizes a mixture of cytochrome c and luminol as post-column hydroperoxide group specific luminescent reagents. The cellular hydroperoxide content increased with age from 0.34 to 27.72 pmol/10(6) cells. At the end of the cells' in vitro lifespan (51st population doubling level), the hydroperoxide content per 10(6) cells reached about 80 times the level found in cells of the 20th population doubling level. Supplementation of exogenous alpha-tocopherol to the culture medium prevented hydroperoxide accumulation, but did not extend the lifespan in vitro. The results indicate that substantial intracellular phospholipid hydroperoxide accumulation occurred in the course of aging of human fetal diploid fibroblasts.

Aging does not affect the susceptibility to lipid peroxidation and lysosomal enzyme release of rat visual system structures and sciatic nerve

The aim of the present study was to clarify the issue of lipid peroxidation operating in visual system structures and sciatic nerve of the rat as a contributing factor to senescence. In 4-, 14- and 28-month-old male rats, the amount of endogenous malondialdehyde, conjugated dienes and extractable phospholipids were all taken as indices of lipid peroxidation. In addition, the total free and released enzyme activities of four lysosomal hydrolases were evaluated. The susceptibility of all these parameters to in vitro iron-induced peroxidation was also taken as an age-related indicator of the endogenous peroxidative potential of the nervous tissues examined. Our data show that the content of malondialdehyde and phospholipids did not change in an age-related fashion. Furthermore, the susceptibility of rat visual system structures to lipid peroxidation, together with the release of lysosomal enzymes were unchanged as a function of aging. The results do not lend support to the hypothesis that an increase in overall lipid peroxidation is peculiar to the aging phenomenon of the central nervous system areas which delimit the rat visual pathway.

No relationship between the age-related decrease in prostacyclin production and the level of intracellular lipid peroxidation in human umbilical vein endothelial cells in culture

Some investigators have speculated that a decrease in prostacyclin production observed during ageing of endothelial cells is caused by an increase in intracellular lipid peroxide. We checked this speculation using an in vitro model to study the ageing of human vascular endothelial cells. For this purpose we determined the levels of intracellular lipid peroxide of endothelial cells at various culture ages, and found that the level of intracellular lipid peroxidation did not increase during in vitro ageing. Amounts of intracellular lipid peroxide also differed depending on the growth phase, the addition of heparin and the strain of endothelial cells, but the cells producing prostacyclin at a low level did not necessarily contain larger amounts of intracellular lipid peroxide. Therefore, we postulate that the age-related decrease in prostacyclin production is not due to an increase in the amount of intracellular lipid peroxide as a function of age.

High oxygen atmosphere for neuronal cell culture with nerve growth factor. II. Survival and growth of clonal rat pheochromocytoma PC12h cells

When clonal rat pheochromocytoma PC12h cells were cultured in a 50% O2 atmosphere, cells gradually died during the cultivation. On the other hand, the addition of NGF at the final concentration of 50 ng/ml could rescue the cells from death. The culture in a 40% O2 atmosphere had little effect on the growth of PC12h cells, as compared with the culture in a normal 20% O2 condition. A very high O2 concentration, as 60%, caused severe damage to PC12h cell growth, and the restoration of cell growth by NGF seemed to be insufficient. PC12h cells were fully differentiated and extended dense long neurites by NGF even in a 50% O2 atmosphere. However, the neurite extension in the culture in a 60% O2 atmosphere was suppressed. The cell-saving effect of NGF on cell death in culture under a 50% O2 atmosphere was dose-dependent, and the ED50 value of NGF was 5 ng/ml. Basic fibroblast growth factor and epidermal growth factor also had a potent effect to rescue the cell death in the high O2 culture, but insulin had no effect. Since the differentiation effects of NGF on PC12h cells are thought to offer a model system to investigate the effect of NGF on neurons, the present observations suggest that a protection machinery for high O2 toxicity to neurons may exist in the neuronal differentiated PC12h cells by NGF, but not in the undifferentiated cells.

Selective degeneration of oligodendrocytes mediated by reactive oxygen species

The mechanism underlying demyelination in inflammatory canine distemper encephalitis is uncertain. Macrophages and their secretory products are thought to play an important effector role in this lesion. Recently, we have shown that anti-canine distemper virus antibodies, known to occur in chronic inflammatory lesions, stimulate macrophages leading to the secretion of reactive oxygen species (ROS). To investigate whether ROS could be involved in demyelination, dog glial cell cultures were exposed to xanthine/xanthine oxidase (X/XO), a system capable of generating O2-. This treatment resulted in a specific time-dependent degeneration and loss of oligodendrocytes, the myelin producing cells of the central nervous system. Initial degeneration was not associated with a decrease in viability of oligodendrocytes as judged by trypan blue and propidium iodide exclusion. Astrocytes and brain macrophages were not affected morphologically by this treatment. Further, an evaluation of the effect of several ROS scavengers, transition metal chelators and inhibitors of poly (ADP-ribose) polymerase suggests that a metal dependent formation of .OH or a similar highly oxidizing species could be responsible for the observed selective damage to oligodendrocytes.

Brain chemiluminescence and oxidative stress in hyperthyroid rats

Newborn Wistar rats were made hyperthyroid by injection of tri-iodothyronine and assayed for survival, brain oxygen uptake, brain chemiluminescence and activity of antioxidant enzymes. Brain chemiluminescence was measured (1) by removing the parietal bones or (2) through the translucid parietal bones. Control animals showed a brain chemiluminescence of 130 +/- 12 c.p.s./cm2 and 99 +/- 10 c.p.s./cm2 for procedures (1) and (2) respectively. Hyperthyroid rats showed increases in the spontaneous brain photoemission of 46 and 70% compared with controls, measured by procedures 1 and 2 respectively. The hyperthyroid state did not modify the oxygen-dependent chemiluminescence of brain homogenates. The hyperthyroid animals showed a 30% increase in the oxygen uptake of brain slices and a dramatic shortening of life-span to about 16 weeks. Superoxide dismutase (the Cu-Zn enzyme), catalase and Se-dependent glutathione peroxidase activities of brain homogenates were increased by 18, 36 and 30% respectively in the hyperthyroid animals. Isolated brain mitochondria produced 0.18-0.20 nmol of H2O2/min per mg of protein in state 4 in the presence of succinate as substrate. No difference was observed between control and hyperthyroid animals. It is concluded that hyperthyroidism leads to hypermetabolism and oxidative stress in the brain. The increased levels of oxygen and peroxyl radicals may contribute to premature ageing in these animals.

Decreased peroxidative potential in rat brain microsomal fractions during ageing

Rough and smooth microsomes of brain in senescent rats showed less sensitivity to ascorbate-, NADPH- and cumene hydroperoxide-induced peroxidative damage compared with those of young adults. The observed decrease in peroxidative potential in senescent rats seemed to be due to decrease in the substrate for peroxidation in the form of phospholipids and increase in the level of antioxidants such as reduced glutathione and superoxide dismutase.

Buoyant density and lipid composition of purified myelin of aging human brain

Purified myelin of human brain from 15 young adult (below 50 years of age) and old (above 70 years of age) autopsy cases each was examined by isopycnic centrifugation in continuous sucrose gradients, and for lipid composition. The mean buoyant density of myelin was the same in both groups. Apparent features of old age were a wide range of density values, less compact myelin bands, and the dissociation of myelin into two bands in six of 15 old cases. Lipid analyses of randomly selected myelin samples of each group revealed an inverse relationship between the total lipid to protein ratio and density of myelin. In old age total lipids decreased by an average 10 mol lipid per mol protein. This decrease was accounted for by cholesterol, phosphatidylserine and cerebrosides. Changes in fatty acid moieties mainly affected sphingolipids. C20:0 and C24:0 of sphingomyelin increased, as did even more markedly the more hydrophilic OH-fatty acids of cerebrosides. Correlations with buoyant density existed for the ratios of cholesterol to protein in young adult cases, and those of galactolipids to protein in old cases. The results suggest that old age is associated with impaired stability and altered lipid composition of myelin.

Micromethods in single muscle fibers. 1. Determination of catalase and superoxide dismutase

Methods have been developed for the measurements of catalase and superoxide dismutase (SOD) in single, isolated muscle fibers. These fibers are also classified according to fiber type. Catalase is determined using a fluorescent method for the measurement of hydrogen peroxide consumed. SOD measurements are carried out using a modification of established techniques whereby the inhibition of oxidation of epinephrine by SOD is assayed fluorometrically. Both enzymes may be determined in submicrogram samples of dried muscle. This approach avoids the complication of the inclusion of nonmuscle tissue with varying enzymatic activities which is frequently experienced when using homogenates of muscle, particularly diseased muscle. In addition, these techniques can be used to determine the inherent variation in SOD and catalase activities within individual fibers of the same fiber type. The Km and Vmax for catalase, determined using homogenates of human muscle, were found to be 12 mM and 1.45 mumol/min/mg dry wt, respectively. Catalase of muscle was inhibited 50% by 2 microM sodium azide. Mn-SOD contributes less than one-fifth of the total SOD activity. Therefore the activity is largely due to the Cu-Zn form of SOD. These methods are applicable to a wide variety of tissues.

Effects of aging and alcohol on the biochemical composition of histologically normal human brain

Human brains were removed at autopsy and examined grossly and histologically for any abnormality or evidence of disease. Sixty-two brains appearing normal by these criteria were examined further. First, a detailed record of alcohol consumption was obtained. Second, frozen punches of gray and white matter were used to determine the compositional change associated with age and drinking patterns. Increased age was associated with an increase in the water content, particularly in the white matter, a decline in RNA content in gray matter, a decline in total protein in white matter, and a decline in both myelin and the myelin-like subfraction. The loss of myelin membrane in white matter corresponded to a similar increase in water content, although there was an additional loss of some nonmyelin protein. There was no significant shift in the density between the myelin and the myelin-like membranes, and the protein composition of myelin was not significantly altered by age. A history of heavy alcohol consumption was associated with a relative increase in total protein in white matter even though heavy drinking accelerated the age-related loss of myelin. Presumably, alcohol produced a lag in the rate at which nonmyelin proteins are lost or accelerated the accumulation of abnormal protein. Alcohol consumption did not influence the myelin composition or the ratio of myelin and myelin-like membranes. The interval between patient death and autopsy was shown to have little or no effect on the samples used in this study. These data show that normal aging, uncomplicated by other disease processes, can have a significant effect on the composition of brain tissue, particularly the white matter, and that heavy alcohol consumption accelerates degenerative change, even in tissue appearing normal by histology.

25-Hydroxycholesterol promotes myelin basic protein-induced leakage of phospholipid vesicles

Among several cholesterol oxidation products, 25-hydroxycholesterol is particularly potent in enhancing basic protein-induced carboxyfluorescence leakage from liposomes. Both myelin basic protein and poly(L-arginine) are effective at submicromolar concentrations in stimulating this vesicle rupture. Leakage is greatly augmented by the presence of only 1% of the 25-hydroxycholesterol. The possible relevance of these findings to myelin pathology is discussed.

Inhibition of lipid peroxidation by dihydroquinoline-type antioxidant (CH 402)

The in vitro effect of a non-toxic, water soluble, low molecular weight, stable dihydroquinoline-type antioxidant, CH 402 (Na (2,2-dimethyl-1,2-dihydroquinoline-4-yl)-methane sulphonic acid) was studied on free radical reactions in brain subcellular fractions. Experiments were performed using rat and mouse brain homogenate and microsomal fractions. Non-enzymatically induced lipid peroxidation by ascorbic acid was studied in correlation with ascorbic acid and CH 402 concentrations and incubation time. Malondialdehyde production during lipid peroxidation was measured by the thiobarbituric acid test. In a concentration range of 10(-2)-10(-5) M CH 402 dose-dependently inhibited the ascorbic acid induced in vitro lipid peroxidation in mouse and rat brain subcellular fractions.

D-aspartate in human brain

The presence of the biologically uncommon D-aspartic acid (D-aspartate) in human brain white matter has been previously reported. The earlier study has now been expanded to include D/L-aspartate ratios from 67 normal brains. The data show that the D-aspartate content increases rapidly from 1 year to approximately 35 years of age, levels off in middle age, and then appears to decrease somewhat. The D-aspartate content in gray matter remains at a consistently low level (half of that found in white matter) throughout the human life span. Within the limitations of current analytical methods, there was no detectable difference in D/L-aspartate ratios in white and gray matter of brains with Alzheimer's disease and several other pathologies when compared with brains of normal subjects. However, the presence of a significant D-aspartate level in white matter during the adult life span may lead to changes in protein configuration related to dysfunctions associated with the aging brain.

Modulation of myelin basic protein-induced aggregation and fusion of liposomes by cholesterol, aliphatic aldehydes and alkanes

The effect of cholesterol on myelin basic protein-induced aggregation of zwitterionic phospholipid vesicles was studied by turbidimetry, quasi-elastic light scattering and centrifugation techniques. Without cholesterol, the degree of vesicle aggregation caused by myelin basic protein is relatively low and is only slightly increased using cholesterol concentrations up to approx. 25-30 mol%. When the cholesterol content in the bilayer exceeds approx. 30 mol%, there is a dramatic increase in the susceptibility of the vesicles to aggregation in the presence of myelin basic protein. Palmitoyl aldehyde and eicosane, substances resembling products of lipid degradation, increase myelin basic protein promoted fusion of vesicles. The fusion is accompanied by increased leakage of entrapped carboxyfluorescein. In the presence of cholesterol, myelin basic protein-induced fusion of the liposomes becomes much more sensitive to the presence of aliphatic aldehydes or alkanes. The results suggest that cholesterol has an important role in promoting membrane adhesion in biological systems but these structures become unstable in the presence of small amounts of products of lipid degradation. The findings have important implications to the understanding of the stability of the myelin membrane.

Interface between membrane biology and clinical medicine

Many enzymes that are embedded within membranes of cells are sensitive to the chemical and physical properties of the lipid components of the membrane. Because of this, the functions of these integral membrane-bound enzymes can be regulated to some extent by changes within the lipid portions of biologic membranes. That the functions of membrane-bound proteins can be manipulated by modifications of their intimate environment is not surprising. It is well known, for example, that the properties of the surrounding aqueous phase can modulate the function of proteins that are soluble in the cytosol of cells. In contrast, whereas significant changes in the chemical composition and physical properties of the aqueous portion of the cell (e.g., ionic strength and pH) are not allowed, normally tolerable fluctuations of diet appear to influence significantly the composition and properties of the lipid portions of intracellular membranes to the extent of altering the function of some membrane-bound enzymes. In addition, it appears that changes of this type can be induced by diseases that alter dietary intake and/or intermediary metabolism. In other words, it is likely that the functions of at least some integral membrane proteins can be manipulated in patients. Such manipulations may prove to be efficacious. Alternatively, the importance of diet and processes of intermediary metabolism for altering the course of certain diseases may not be fully appreciated. It is worthwhile to review, therefore, current ideas of how the lipid portion of a membrane interacts with integral proteins. The property of the lipids that appears to be most important in this regard is their viscosity. The types of manipulations of function of membrane-bound enzymes that can be achieved are illustrated by in vitro effects secondary to varying the lipids used to reconstitute pure, delipidated forms of these enzymes. The functions of pure delipidated enzymes are discussed for the hepatic drug-metabolizing enzyme uridine diphosphoglucuronyltransferase. In addition, data are presented to indicate that the function of this enzyme can be modified extensively in intact animals by changing the diet.

Study of the expression of myelin proteolipid protein (lipophilin) using a cloned complementary DNA

We have prepared a lambda gt10 cDNA library with the mRNA isolated from fetal calf brains which were actively myelinating. Using two oligonucleotides made according to the known amino acid sequence of myelin proteolipid protein (PLP or lipophilin), we have isolated several cDNA clones for this major intrinsic membrane protein of myelin. One of these clones, designated as pLP1, is found to contain 444 bp of coding sequence for the C-terminal half of PLP and 486 bp of 3' untranslated sequence. Using pLP1 as a hybridization probe, we have studied the regulation of PLP at the mRNA level during rat brain development. Our results show that the relative amounts of mRNA for PLP and that for the major extrinsic protein of the myelin membrane, myelin basic protein, increase coordinately during the course of myelination in the brain.

The presence of aldehyde-reacted proteins in normal and multiple sclerosis white matter

The incorporation of tritium from NaB3H4 into the major protein components of myelin and the presence of weak fluorescence emission bands at wavelengths of approximately 440 and 500 nm from sodium dodecyl sulfate-solubilized, delipidated white matter are indicative of the presence of the products of aldehyde reactions with proteins. The incorporation of tritium from NaB3H4 into myelin proteins was confirmed by reaction with purified components of myelin basic protein or with lipophilin, a purified fraction of proteolipid protein. From the extent of tritium incorporation into the purified proteins, it is estimated that approximately 0.2 mol of tritium is incorporated/mol of myelin basic protein and approximately 0.4 mol of tritium/mol of proteolipid protein. There is approximately 50% greater incorporation of tritium into a more degraded, less positively charged form of the basic protein. The incorporation of tritium into normal and multiple sclerosis white matter was compared. There is a small but statistically significant difference in the percentage of the total counts incorporated into the major protein fractions for the two groups, with the multiple sclerosis samples showing a higher percentage of the counts in the Wolfgram protein and a lower percentage in the myelin basic protein compared with the normal samples.

Effect of reactive oxygen species on myelin membrane proteins

Fresh myelin, isolated from brainstems of adult rats, was incubated in the presence of Cu2+ and H2O2. Electrophoretic analysis of the reisolated myelin membrane revealed a gradual loss of the protein moiety from the characteristic pattern and an increase in aggregated material appearing at the origin of the gel. The aggregation of proteins was time-dependent and was concomitant with the accumulation of lipid peroxidation products reactive with thiobarbituric acid. Furthermore, during the course of incubation, there was a gradual decrease in the amount of recovered light myelin and a quantitatively similar increase in heavier myelin subfractions. The aggregation of proteins seems not to be directly related to the buoyant densities of myelin fragments. The peroxidative damage to the myelin proteins may be an important contributor to pathochemistry of myelin sheath, in particular, and in general it implies the susceptibility of the protein moiety of cell membranes to oxygen-induced deterioration.

Regional lipid peroxidation in rat brain in vitro: possible role of endogenous iron

Lipoperoxidative capacity of various brain areas of aging rats was examined in vitro using the thiobarbituric acid test. Significant regional differences in the generation of lipid peroxides were found in freshly prepared homogenates from different areas of brain incubated under air. Incubation under oxygen resulted in marked stimulation of lipid peroxidation, with highest increases in hypothalamus (144%). Addition of exogenous Fe2+ and ascorbic acid resulted in stimulation of lipid peroxidation ranging from 10-fold in cortex to 20-fold in hypothalamus homogenates during incubation in air. A linear relationship was found between endogenous iron content in brain regions and their ability to produce lipid peroxides in vitro under oxygen for all areas except striatum. Several iron chelating agents effectively inhibited lipid peroxidation under hyperbaric oxygen whereas oxygen-free radical scavengers, as well as catalase and superoxide dismutase were not effective. It is concluded that regional differences in lipoperoxidative capacity of brain areas in vitro are in part governed by local endogenous iron content and may indicate regional susceptibility to oxidative damage.