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B P Yu

Publications and source records attributed to B P Yu.

At least 37 records · Page 2Linked to original sources
PubMed1998

Norepinephrine transmitter metabolite generates free radicals and activates mitochondrial permeability transition: a mechanism for DOPEGAL-induced apoptosis.

3,4-Dihydroxyphenylglycolaldehyde (DOPEGAL) is the monoamine oxidase A metabolite of norepinephrine (NE) and epinephrine. DOPEGAL, but neither NE nor its other metabolites induces apoptosis in differentiated PC-12 cells by an unknown mechanism. To study the mechanism of DOPEGAL-induced apoptosis, we tested DOPEGAL and NE for their capacity to generate free radicals and to induce mitochondrial permeability transition (PT). Results show that DOPEGAL but not NE forms reactive free radical intermediates under oxidative stress and enhances Ca2+-mediated induction of the mitochondrial PT. Linkage of these events to apoptosis is described. Implications for degenerative diseases are discussed.

Aldehydes↗
PubMed1998

Melatonin enhances tamoxifen's ability to prevent the reduction in microsomal membrane fluidity induced by lipid peroxidation.

The indoleamine melatonin and the synthetic antiestrogenic drug tamoxifen seem to have similar mechanisms in inhibiting the growth of estrogen receptor positive breast cancer cells. In this study, we compared the ability of these molecules, alone and in combination, in stabilizing microsomal membranes against free radical attack. Hepatic microsomes were obtained from male rats and incubated with or without tamoxifen (50-200 microM), melatonin (1 mM) or both; lipid peroxidation was induced by addition of FeCl3, NADPH and ADP. After oxidative damage, membrane fluidity, measured by fluorescence polarization techniques, decreased whereas malonaldehyde (MDA) and 4-hydroxyalkenals (4-HDA) concentrations increased. Incubation of the microsomes with tamoxifen prior to exposure to free radical generating processes inhibited, in a dose-dependent manner, the increase in membrane rigidity and the rise in MDA + 4-HDA levels. When melatonin was added, the efficacy of tamoxifen in preventing membrane rigidity was enhanced. Thus, the IC50s for preventing membrane rigidity and for inhibiting lipid peroxidation obtained for tamoxifen in the presence of melatonin were lower than those obtained with tamoxifen alone. Moreover, tamoxifen (50-200 microM) in the presence of melatonin reduced basal membrane fluidity and MDA + 4-HDA levels in microsomes. These synergistic effects of tamoxifen and melatonin in stabilizing biological membranes may be important in protecting membranes from free radical damage.

Animals↗
PubMed1998

Age-related mitochondrial DNA deletions: effect of dietary restriction.

Results from quantitative PCR analysis of the frequency of deleted mitochondrial genomes in male Fischer 344 rats reveal an age-related rise in this molecular abnormality. We used this model to examine the ability of dietary restriction (DR) to prevent this potentially pathogenic change. DR prevented age-related increase in frequency of mitochondrial deletions in the liver. In contrast, however, DR had no effect on the age-related increase in deletion frequency in the brain. These data suggest that the effects of DR on age-related accumulation of mitochondrial DNA deletions may be tissue specific.

Aging↗
PubMed1998

Can antioxidant supplementation slow the aging process?

The oxidative stress theory of aging is well supported by accumulated evidence from various aging intervention studies. Early antioxidant supplementation studies indicate life span extensions by antioxidant feeding in various experimental organisms. Data collected under tightly controlled conditions show that the feeding of 2-mercaptoethanol (0.25%) effectively prolonged both the median and maximum life spans of mice. Evidence has been obtained showing dietary vitamin E to protect against oxidative damage to DNA in human lymphocytes and white blood cells. Other clear evidence of vitamin E's protective effect has been seen in its suppressive action of LDL oxidation both in vitro and in vivo. New evidence on the physiological roles of antioxidants, in addition to their well-known role as free radical scavengers, is emerging from recent research. For instance, the beneficial effect of vitamin E in improving glucose transport and the insulin sensitivity and its putative role as a regulator of cell proliferation should open new research dimensions. This presentation will review some of the anti-aging aspects of dietary antioxidant supplementation, as well as the potential problems of its long-term administration that stem from our lack of knowledge about free radical metabolism and the regulation of endogenous defense mechanisms.

Aging↗
PubMed1998

Dietary restriction augments protection against induction of the mitochondrial permeability transition.

Exposure to oxidants or phosphate, especially in the presence of calcium, has been long known to lead to mitochondrial structural alteration and damage. In the past 15 years, it has become increasingly appreciated that this damage is often the result of a cyclosporin A-sensitive event, the "permeability transition" (PT). Using liver mitochondria isolated from male Fischer 344 rats of 6-24 months of age, we now present evidence that long-term, life-prolonging, dietary restriction regimens greatly delay induction of a PT following challenge. Dietary restriction slowed induction by 25 microM calcium, or by calcium in conjunction with the strong oxidant t-butyl hydroperoxide, by approximately 50%. The increased resistance to PT induction was maintained through 24 months of age. Dietary restriction also protected against t-butyl hydroperoxide in the presence of high calcium challenges (250 microM), although the extent of this protection was age-dependent. Induction by 2.5 mM phosphate alone was blocked in most 6-month-old dietary restricted animals and was slowed by 50-100% in animals 12-24 months of age. Susceptibility to 25 microM calcium in conjunction with phosphate varied in an age-dependent manner, ranging from 4-12 times slower in the dietary restricted animals than in their ad lib fed counterparts. Together, these data provide evidence that the factors regulating PT induction are affected by long-term physiological and environmental conditions such as age and diet. The observed effects represent one of the largest recognized dietary restriction-mediated increases in a parameter related to antioxidant defenses. These data also suggest that the endogenous defense systems that protect mitochondria from calcium in conjunction with inorganic phosphate differ from those that protect against calcium in conjunction with an oxidant.

Aging↗
PubMed1998

Melatonin reduces the increase in 8-hydroxy-deoxyguanosine levels in the brain and liver of kainic acid-treated rats.

In the present study, the effect of melatonin on oxidative DNA damage induced by kainic acid (KA) treatment was investigated. 8-hydroxy-deoxyguanosine (8-OH-dG) is a main product of oxidatively damaged DNA and was used as the endpoint in these studies. The levels of 8-OH-dG were found to be elevated in the hippocampus and frontal cortex of rats treated with KA. These elevated levels were significantly reduced in animals that were co-treated with melatonin. Thus, there was no difference in 8-OH-dG levels in the brain of control rats compared to those treated with KA (10 mg/kg) plus melatonin (10 mg/kg). The levels of 8-OH-dG also increased in the liver of rats treated with KA. This rise in oxidatively damaged DNA was also prevented by melatonin administration. Melatonin's ability to reduce KA-induced increases in neural and hepatic 8-OH-dG levels presumably relates to its direct free radical scavenging ability and possibly to other antioxidative actions of melatonin.

8-Hydroxy-2'-Deoxyguanosine↗
PubMed1998

Neonatal treatment with 192 IgG-saporin produces long-term forebrain cholinergic deficits and reduces dendritic branching and spine density of neocortical pyramidal neurons.

The role of basal forebrain-derived cholinergic afferents in the development of neocortex was studied in postnatal rats. Newborn rat pups received intraventricular injections of 192 IgG-saporin. Following survival periods ranging from 2 days to 6 months, the brains were processed to document the cholinergic lesion and to examine morphological consequences. Immunocytochemistry for choline acetyltransferase (ChAT) and in situ hybridization for ChAT mRNA demonstrate a loss of approximately 75% of the cholinergic neurons in the medial septum and nucleus of the diagonal band of Broca in the basal forebrain. In situ hybridization for glutamic acid decarboxylase mRNA reveals no loss of basal forebrain GABAergic neurons. Acetylcholinesterase histochemistry demonstrates a marked reduction of the cholinergic axons in neocortex. Cholinergic axons are reduced throughout the cortical layers; this reduction is more marked in medial than in lateral cortical areas. The thickness of neocortex is reduced by approximately 10%. Retrograde labeling of layer V cortico-collicular pyramidal cells reveals a reduction in cell body size and also a reduction in numbers of branches of apical dendrites. Spine densities on apical dendrites are reduced by approximately 20-25% in 192 IgG-saporin-treated cases; no change was detected in number of spines on basal dendrites. These results indicate a developmental or maintenance role for cholinergic afferents to cerebral cortical neurons.

Acetylcholinesterase↗
PubMed1998

The effects of dietary restriction on age-related changes in rat serum prostaglandins.

This study investigated whether or not dietary restriction (DR), consisting of 60% of the daily caloric allowance of ad libitum fed (AL) rats, has a modulating effect on prostaglandins (PGs), thromboxane (TXA), and lipids in the serum of rats. Results showed that DR rats had consistently, 30-40% lower overall lipid peroxide levels than AL rats. On the other hand, the age-related increases in arachidonic acid contents observed in AL rats were significantly suppressed by DR during aging; while unsaturated/saturated fatty acid ratios remained consistently higher (15-50%) in DR rats than in AL rats. Serum PGE2 and PGF2 levels in DR rats were maintained at consistently higher levels (30-65% and 40-90%, respectively) than in AL rat serum. PGI2 levels (as measured by 6-keto PGF2) in serum of DR rats were also consistently higher (40-50%) than those of AL rats, while TXA2 levels sustained lower levels (15-20%) than those of AL rats, showing a significantly higher (27-38%) PGI2/TXA2 ratios in DR than in AL rats. Thus, our study clearly indicated that DR effectively modulates prostaglandin levels by preventing age-related decreases in PGI2 levels and increases in TXA2 levels. These findings, with the other known beneficial actions of DR, strongly suggest vascular activity to be well-regulated in DR animals.

Age Factors↗
PubMed1998

Microsomal cytochrome P-450 degradation by in vitro lipid peroxidation.

In this study, the influence of in vivo lipid peroxidation (LPO) on cytochrome P-450 (P-450) degradation was investigated using rat liver microsomes. To identify the nature of P-450 degradation, three different perturbant LPO-initiation systems were employed: NADPH/ADP-Fe, cumene hydroperoxide (CHP), and 2,2'-azobis (2-amidino- propane) hydrochloride (AAPH). The results show that each of these systems readily induced P-450 degradation during in vitro LPO and that the progression and extent of the degradation increased with incubation time. However, attempts to elicit P-450 degradation by the use of hydrogen peroxide, superoxide, or hexanal failed to induce damage. Interestingly, the addition of several well-known radical scavengers and radical scavenging enzymes, including superoxide dismutase and catalase, into the incubation media provided little protection against P-450 degradation or malondialdehyde (MDA) formation. It was found, however, that sulfhydryl compounds, including GSH and substrates of P-450-dependent monooxygenases, provided varying degrees of protection. Based on the specificity of protective action, it was concluded that the structural stability of P-450 to defend against LPO requires reduced thiols and/or substrate binding. This suggests that P-450 degradation by LPO is closely related to the oxidation of certain essential thiol groups located at the substrate binding site of the P-450 molecule during LPO reaction.

Animals↗
PubMed1998

Dietary restriction as a modulator of age-related changes in rat kidney prostaglandin production.

Prostaglandin (PG) levels in kidney glomeruli isolated from rats under the dietary restriction (DR) regimen were investigated beginning at 6 weeks of age. The modulation of age and DR on PGs, thromboxane (TXA), and their precursor fatty acids were documented for PGE2, PGF2, 6 keto-PGF1, and TXA2 status in aged kidney. The results show that PGE2 and PGF2 production by the glomeruli of DR rats were consistently higher (10-17% and 11-25%, respectively) than in those of AL rats. Although levels of the potent vasodilator, PGI2 (as determined by 6 keto-PGF1,) were shown to decrease after 12 months of age in AL rats, steady levels were shown throughout life in DR rats. In contrast, levels of the typical vasoconstrictor, TXA2, were markedly elevated in AL rats compared to DR rats. As a consequence, PGI2/TXA2 ratios were shown to be decreased in AL rats, while remaining well-maintained in DR rats throughout lifespan. These results indicate that the life-prolonging action of DR attenuates age-related prostaglandin imbalances to preserve and maintain the autoregulation of the glomerular filtration rate (GFR) and other related kidney functions.

Age Factors↗
PubMed1997

Melatonin prevents changes in microsomal membrane fluidity during induced lipid peroxidation.

We tested the effect of melatonin on membrane fluidity in microsomes of a rat liver model in which lipid peroxidation was induced by the addition of FeCl3, ADP and NADPH. Membrane fluidity was monitored using fluorescence spectroscopy and lipid peroxidation was estimated by quantifying malonaldehyde (MDA)+4-hydroxyalkenals (4-HDA) concentrations following the induction of lipid peroxidation with and without pre-incubation with melatonin (1 microM-3 mM). Membrane rigidity increased during induced lipid peroxidation while melatonin reduced in a concentration-dependent manner both membrane rigidity and MDA+4-HDA generation. Melatonin's protective effect may relate to its known ability to scavenge free radicals and function as an antioxidant.

Adenosine Diphosphate↗
PubMed1997

Defects at center P underlie diabetes-associated mitochondrial dysfunction.

Detailed respiration studies on isolated liver mitochondria from streptozotocin-induced diabetic Sprague-Dawley rats revealed a disease-associated decrease in the ADP/O ratio, a marker for mitochondrial ability to couple the consumption of oxygen to the phosphorylation of ADP. This decrease was observed following induction of respiration with glutamate/malate, succinate, or duroquinol, which enter the electron transport chain selectively at complexes I (NADH dehydrogenase), II (succinate dehydrogenase), or III (cytochrome bc1 complex), respectively. These data, coupled with studies using respiratory inhibitors (most importantly antimycin A and myxothiazol), localize at least a portion of this defect to a single site within the electron transport chain (center P in the Q-cycle portion of complex III). These results suggest that liver mitochondria from diabetic animals may generate increased levels of reactive oxygen species at the portion of the electron transport chain already established as the major site of mitochondrial free radical generation. The reduction in the ADP/O ratio occurred in mitochondria that do not have overt defects in the respiratory control ratio or in State 3 and State 4 respiration. The data in this paper suggest that defects in center P of the electron transport chain likely increase mitochondrial exposure to oxidants in the diabetic. This data may partially explain the evidence of altered exposure and/or response to reactive species in mitochondria from diabetics. This work thus provides further clues to the interaction between oxidative stress and diabetes-associated mitochondrial dysfunction.

Adenosine Diphosphate↗
PubMed1997

Oxidant-mediated repression of mitochondrial transcription in diabetic rats.

Diabetes-associated mitochondrial dysfunction is recognized, but the underlying mechanisms are unknown. Using isolated liver mitochondria from streptozotocin-induced diabetic Sprague-Dawley rats, we showed that diabetes can result in a > 95% loss in mitochondrial transcriptional capacity. Decreased transcription correlated well with both disease status, as indicated by serum lipemia and ketone levels, and with increased resistance of the mitochondrial transcription system to oxidative stress imposed by the hydrophilic AAPH [2,2'-azobis-(2-amidino-propane) hydrochloride] or the hydrophobic AMVN [2,2'-azobis-(2,4,-dimethyl-valeronitrile)]. The onset of AAPH- or AMVN-induced lipid peroxidation was also delayed; this suggests that liver mitochondrial membranes from diabetics have increased resistance to peroxyl radical-mediated lipid peroxidation. Lipid peroxidation induced endogenously was increased, however, suggesting a state of increased oxidative stress likely exists in vivo. Furthermore, changes in the rate of lipid peroxidation occurring during the propagation phase were also affected by diabetes. This implies possible changes in lipid composition or structure. Analysis indicated that the factors protecting mitochondria from lipid peroxidation differ from those involved in protecting the transcription system, and that both are independent of free radical scavenger levels. These results suggested that diabetes alters mitochondrial exposure and/or response to reactive species and provided clues to the role of oxidant stress in the development of diabetes-associated mitochondrial dysfunction.

Amidines↗
PubMed1996

Abnormalities in the mitochondrial permeability transition in diabetic rats.

Evidence of mitochondrial dysfunction in diabetes led us to examine whether diabetes altered the nature of the mitochondrial permeability transition. Our data reveal three diabetes-associated abnormalities in PT function: consistently delayed induction with calcium-phosphate, a variable delay with calcium-t-butyl-hydroperoxide (t-BuOOH), and an enhanced magnitude of response. The consistently delayed induction in calcium and phosphate is correlated with serum glucose levels, and is consistent with known changes in calcium uniporter function in diabetics. These data expand our knowledge of diabetes-associated abnormalities in mitochondrial function, represent the first evidence that the PT is altered by chronic disease, and provide potential partial mechanistic explanations for the previously observed resistance of diabetic tissues to ischemia-reperfusion injury and the altered Ca2+ homeostasis in diabetics.

Animals↗
PubMed1996

4-Hydroxyhexenal is a potent inducer of the mitochondrial permeability transition.

Mitochondria undergo at least two types of structural alteration in response to various physiological and pathophysiological stimuli. One type is nonreversible and is associated with mitochondrial lysis. The second is reversible and appears to be associated with calcium-mediated activation of a specific inner mitochondrial membrane channel. The mechanisms underlying the induction of this second alteration, termed a mitochondrial permeability transition (PT), have been the subject of a great deal of recent research. Using rat liver mitochondria, our data demonstrate that calcium-mediated PT induction can be affected by the lipid peroxidation byproducts 4-hydroxynonenal and 4-hydroxyhexenal (HHE). 4-Hydroxynonenal appears inactive at concentrations <1 micromole but displays both stimulatory and inhibitory effects as part of a biphasic dose response between approximately 1 and 200 micromole. In contrast, HHE consistently enhances calcium-mediated induction of the PT, even at femtomolar concentrations. The exquisite specificity and sensitivity of HHE led to further studies to examine the nature of this induction. Studies showing that HHE-mediated induction could be prevented by cyclosporin A confirmed PT involvement. Further studies showed that induction was dependent on both calcium and electron transport chain function. Pretreatment of the HHE with glutathione also prevented PT induction, but simultaneous addition of the thiol reagents dithiothreitol or glutathione, which often prevents PT induction, was ineffective, attesting to the effectiveness of HHE as an inducer. Together, these data provide a possible mechanistic explanation for the previously observed effects of lipid peroxidation on PT induction.

Aldehydes↗