Construction of a coarse-grain quasi-classical trajectory method. I. Theory and application to N2-N2 system.

This work aims to construct a reduced order model for energy transfer and dissociation in non-equilibrium nitrogen mixtures. The objective is twofold: to present the Coarse-Grain Quasi-Classical Trajectory (CG-QCT) method, a novel framework for constructing a reduced order model for diatom-diatom systems; and to analyze the physics of non-equilibrium relaxation of the nitrogen molecules undergoing dissociation in an ideal chemical reactor. The CG-QCT method couples the construction of the reduced order model under the coarse-grain model framework with the quasi-classical trajectory calculations to directly construct the reduced model without the need for computing the individual rovibrational specific kinetic data. In the coarse-grain model, the energy states are lumped together into groups containing states with similar properties, and the distribution of states within each of these groups is prescribed by a Boltzmann distribution at the local translational temperature. The required grouped kinetic properties are obtained directly by the QCT calculations. Two grouping strategies are considered: energy-based grouping, in which states of similar internal energy are lumped together, and vibrational grouping, in which states with the same vibrational quantum number are grouped together. A zero-dimensional chemical reactor simulation, in which the molecules are instantaneously heated, forcing the system into strong non-equilibrium, is used to study the differences between the two grouping strategies. The comparison of the numerical results against available experimental data demonstrates that the energy-based grouping is more suitable to capture dissociation, while the energy transfer process is better described with a vibrational grouping scheme. The dissociation process is found to be strongly dependent on the behavior of the high energy states, which contribute up to 50% of the dissociating molecules. Furthermore, up to 40% of the energy required to dissociate the molecules comes from the rotational mode, underscoring the importance of accounting for this mode when constructing non-equilibrium kinetic models. In contrast, the relaxation process is governed primarily by low energy states, which exhibit significantly slower transitions in the vibrational binning model due to the prevalence of mode separation in these states.

Sympathetic hyper-excitation in obesity and pulmonary hypertension: physiological relevance to the 'obesity paradox'.

BACKGROUND: Within the lung, sympathetic nerve activity (SNA) has an important role in facilitating pulmonary vasodilation. As SNA is elevated in obesity, we aimed to assess the impact of sympathetic hyper-excitation on pulmonary vascular homeostasis in obesity, and its potential role in ameliorating the severity of pulmonary hypertension (PH); the well-documented 'obesity paradox' phenomenon. METHODS: Zucker obese and lean rats were exposed to normoxia or chronic hypoxia (CH-10% O2) for 2 weeks. Subsequently, pulmonary SNA (pSNA) was recorded (electrophysiology), or the pulmonary microcirculation was visualized using Synchrotron microangiography. Acute hypoxic pulmonary vasoconstriction (HPV) was assessed before and after blockade of ß1-adrenergic receptors (ARs) (atenolol, 3 mg kg(-1)) and ß1+ß2-adrenergic (propranolol, 2 mg kg(-1)). RESULTS: pSNA of normoxic obese rats was higher than lean counterparts (2.4 and 0.5 µV s, respectively). SNA was enhanced following the development of PH in lean rats, but more so in obese rats (1.7 and 6.8 µV s, respectively). The magnitude of HPV was similar for all groups (for example, ~20% constriction of the 200-300 µm vessels). Although ß-blockade did not modify HPV in lean rats, it significantly augmented the HPV in normoxic obese rats (ß1 and ß2 blockade), and more so in obese rats with PH (ß2-blockade alone). Western blots showed, while the expression of pulmonary ß1-ARs was similar for all rats, the expression of ß2-ARs was downregulated in obesity and PH. CONCLUSIONS: This study suggests that sympathetic hyper-excitation in obesity may have an important role in constraining the severity of PH and, thus, contribute in part to the 'obesity paradox' in PH.

Hyperventilation in normoxia following myocardial infarction in rats: a shift in the set point of the hypoxic ventilatory response.

AIM: The peripheral chemoreflex is augmented in heart failure, and it may contribute to sympathoexcitation. This study aimed to investigate both the chemoreflex and the cardiac sympathetic nerve activity in the acute-stage post-myocardial infarction. METHODS: Myocardial infarction was induced in male adult Sprague-Dawley rats by permanent ligation of the left anterior descending coronary artery. Within-animal repeated measure assessment of normoxic and hypoxic ventilation patterns was determined with whole-body plethysmography and compared to sham-operated controls. Cardiac function, morphology and cardiac sympathetic nerve activity were determined 14 days later. RESULTS: Infarction induced increases in normoxic ventilation through increases in tidal volume within 3 days. At the same time points, the hypoxic ventilatory response to short durations (10 min) of hypoxia (8, 10 and 12% inspired O2 ) was blunted. At the end of the experiment (D14), increases in nerve activity, specifically through increased firing rate, and significant cardiac dysfunction (ejection fraction 43%) were observed in myocardial infarction (MI) group. CONCLUSIONS: An augmentation of normoxic ventilation caused by myocardial infarction occurs before the amplification of the hypoxic ventilatory response. It occurs much earlier following myocardial injury than previously demonstrated and may have a role in initiating cardiac sympathoexcitation. The difference in the augmentation of hypoxic response between early and late stages post-myocardial infarction suggest that the initial change in the chemoreflex is an alteration to the operating point of chemoreflex.

Effect of pioglitazone on body composition and bone density in subjects with prediabetes in the ACT NOW trial.

AIMS: This study examined the effects of pioglitazone on body weight and bone mineral density (BMD) prospectively in patients with impaired glucose tolerance as pioglitazone (TZD) increases body weight and body fat in diabetic patients and increases the risk of bone fractures. METHODS: A total of 71 men and 163 women aged 49.3 (10.7) years [mean (s.d.)]; body mass index (BMI), 34.5 (5.9) kg/m(2) were recruited at five sites for measurements of body composition by dual energy X-ray absorptiometry at baseline and at conversion to diabetes or study end, if they had not converted. RESULTS: Mean follow-up was 33.6 months in the pioglitazone group and 32.1 months in the placebo group. Body weight increased 4.63 ± 0.60 (m ± s.e.) kg in the pioglitazone group compared to 0.98 ± 0.62 kg in the PIO group (p < 0.0001). Body fat rose 4.89 ± 0.42 kg in the pioglitazone group compared to 1.41 ± 0.44 kg, (p < 0.0001) in placebo-treated subjects. The increase in fat was greater in legs and trunk than in the arms. BMD was higher in all regions in men and significantly so in most. PIO decreased BMD significantly in the pelvis in men and women, decreased BMD in the thoracic spine and ribs of women and the lumbar spine and legs of men. Bone mineral content also decreased significantly in arms, legs, trunk and in the total body. CONCLUSIONS: Pioglitazone increased peripheral fat more than truncal fat and decreased BMD in several regions of the body.

A randomised trial of salsalate for insulin resistance and cardiovascular risk factors in persons with abnormal glucose tolerance.

AIMS/HYPOTHESIS: Chronic sub-acute inflammation contributes to the pathogenesis of type 2 diabetes mellitus and cardiovascular disease. High doses of salicylate reduce inflammation, glucose and triacylglycerols, and may improve insulin sensitivity, suggesting therapeutic potential in impaired fasting glucose and/or impaired glucose tolerance. This trial aimed to evaluate the effect of salsalate vs placebo on insulin resistance and glycaemia in impaired fasting glucose and/or impaired glucose tolerance. METHODS: We conducted a 12 week, two-centre, randomised, placebo-controlled study to evaluate the effect of salsalate (up to 4 g/day) vs placebo on systemic glucose disposal. Secondary objectives included treatment effects on glycaemia, inflammation and cardiovascular risk factors. Seventy-eight participants with impaired fasting glucose and/or impaired glucose tolerance from two VA healthcare systems were enrolled. Randomisation assignment was provided by the coordinating center directly to site pharmacists, and participants and research staff were blinded to treatment assignment. RESULTS: Seventy-one individuals were randomised to placebo (n = 36) or salsalate (n = 35). Glucose disposal did not change in either group (salsalate 1% [95% CI -39%, 56%]; placebo 6% [95% CI -20%, 61%], p = 0.3 for placebo vs salsalate). Fasting glucose was reduced by 6% during the study by salsalate (p = 0.006) but did not change with placebo. Declines in glucose were accompanied by declines in fasting C-peptide with salsalate. Insulin clearance was reduced with salsalate. In the salsalate group, triacylglycerol levels were lower by 25% (p = 0.01) and adiponectin increased by 53% (p = 0.02) at the end of the study. Blood pressure, endothelial function and other inflammation markers did not differ between groups. Adipose tissue nuclear factor κB (NF-κB) activity declined in the salsalate group compared with placebo (-16% vs 42%, p = 0.005), but was not correlated with metabolic improvements. The frequency of tinnitus was low but tended to be higher with salsalate therapy (n = 4 vs n = 2). CONCLUSIONS/INTERPRETATION: In summary, salsalate therapy was well tolerated, lowered fasting glucose, increased adiponectin and reduced adipose tissue NF-κB activity. These changes were not related to changes in peripheral insulin sensitivity, suggesting additional mechanisms for metabolic improvement. TRIAL REGISTRATION: ClinicalTrials.gov NCT00330733. FUNDING: Office of Research and Development, Medical Research Service, Department of Veterans Affairs and NIH K24 DK63214.

Exogenous ghrelin accentuates the acute hypoxic ventilatory response after two weeks of chronic hypoxia in conscious rats.

AIM: Ghrelin has been implicated as a modulator of numerous physiological pathways. To date, there have not been any studies describing the role of ghrelin in modulating the chemoreflex control of pulmonary ventilation. Yet the respiratory system impacts, at least to some degree, on virtually all homeostatic control systems. Chronic hypoxia (CH) can cause fundamental changes in ventilatory control, evident by alterations in the acute hypoxia ventilatory response (HVR). As ghrelin plays an important role in metabolic homeostasis, which is tightly linked to ventilatory control, we hypothesized that ghrelin may modulate HVR, especially following CH. METHODS: Whole body plethysmography was used to measure the HVR (8% O(2) for 10 min) in male Sprague-Dawley rats (body wt ∼180-220 g) before and after 14 days of CH (CH=10% O(2)). During CH, rats received daily subcutaneous injections of either saline (control; n=5) or ghrelin (150 µg kg(-1) day(-1); n=5). The HVR was measured in another four rats that had received daily injections of ghrelin during normoxia for 7 days. RESULTS: Ghrelin did not significantly alter basal ventilatory drive or acute HVR in normoxic rats. However, the acute HVR was accentuated following CH in ghrelin-treated rats compared with saline-treated rats. CONCLUSIONS: These results describe the impact that ghrelin has in altering ventilatory control following CH and, although the mechanisms remain to be fully elucidated, provide guidance for future ghrelin-based studies interpreting physiological data indirectly related to the chemoreflex control of pulmonary ventilation.

Determinants of glucose tolerance in impaired glucose tolerance at baseline in the Actos Now for Prevention of Diabetes (ACT NOW) study.

AIMS/HYPOTHESIS: The aim of the study was to examine the determinants of oral glucose tolerance in 602 persons with impaired glucose tolerance (IGT) who participated in the Actos Now for Prevention of Diabetes (ACT NOW) study. METHODS: In addition to the 602 IGT participants, 115 persons with normal glucose tolerance (NGT) and 50 with impaired fasting glucose (IFG) were identified during screening and included in this analysis. Insulin secretion and insulin sensitivity indices were derived from plasma glucose and insulin during an OGTT. The acute insulin response (AIR) (0-10 min) and insulin sensitivity (S(I)) were measured with the frequently sampled intravenous glucose tolerance test (FSIVGTT) in a subset of participants. RESULTS: At baseline, fasting plasma glucose, 2 h postprandial glucose (OGTT) and HbA(1c) were 5.8 +/- 0.02 mmol/l, 10.5 +/- 0.05 mmol/l and 5.5 +/- 0.04%, respectively, in participants with IGT. Participants with IGT were characterised by defects in early (DeltaI (0-30)/DeltaG (0-30) x Matsuda index, where DeltaI is change in insulin in the first 30 min and DeltaG is change in glucose in the first 30 min) and total (DeltaI(0-120)/DeltaG(0-120) x Matsuda index) insulin secretion and in insulin sensitivity (Matsuda index and S(I)). Participants with IGT in whom 2 h plasma glucose was 7.8-8.3 mmol/l had a 63% decrease in the insulin secretion/insulin resistance (disposition) index vs participants with NGT and this defect worsened progressively as 2 h plasma glucose rose to 8.9-9.94 mmol/l (by 73%) and 10.0-11.05 mmol/l (by 80%). The Matsuda insulin sensitivity index was reduced by 40% in IGT compared with NGT (p < 0.005). In multivariate analysis, beta cell function was the primary determinant of glucose AUC during OGTT, explaining 62% of the variance. CONCLUSION: Our results strongly suggest that progressive beta cell failure is the main determinant of progression of NGT to IGT.

Does central nitric oxide chronically modulate the acute hypoxic ventilatory response in conscious rats?

AIM: Hypoxia initiates an increase in ventilation (VE) through a cascade of events of which central nitric oxide (NO) has been implicated as an important neuromodulator. There have not been any reports describing the consequences of long-term imbalances in the central NO pathways on the modulation of the acute hypoxic ventilatory response (HVR). Chronic hypoxia (CH) can potentially modify the HVR, and so we hypothesized that central NO may be involved. In this study we describe the long-term role of central NO in the modulation of HVR before and after CH. METHODS: Male Sprague-Dawley rats (BW c. 200-320 g; n = 21) were implanted with an osmotic pump for continuous intracerebroventricular administration of either artificial cerebrospinal fluid (control), Nomega-nitro-L-arginine methyl ester (L-NAME) (150 microg kg(-1) day(-1)) or the NO-donor, 3-[4-morpholinyl]-sydnonimine-hydrochloride (SIN-1) (100 microg kg(-1) day(-1)). The VE response to acute poikilocapnic hypoxia (8% O2 for 20 min) was measured by plethysmography seven days after surgery, in normoxia, and again after 14 days of exposure to CH (CH = 12% O2). RESULTS: The magnitude of the HVR (c. 230% increase in VE) was unaltered by centrally infusing either L-NAME or SIN-1 for 1 week. CH did not modify the HVR, although baseline VE and HVR were shifted downward by L-NAME during CH - because of a reduction in the frequency component. CONCLUSIONS: These results suggest that long-term alterations in central NO levels may not alter the HVR under moderate CH, presumably because of the onset/development of compensatory mechanisms. However, NO appears to be an important component of the HVR following CH.

International variation in pancreatic cancer mortality for the period 1955-1998.

BACKGROUND: Pancreatic cancer is an important cause of cancer mortality in developed countries. This article examines time trends for pancreatic cancer mortality rates in 38 countries on five continents between 1955 and 1998. METHODS: We used the World Health Organization database on Age-Standardized World Population pancreatic cancer mortality rates by gender and fitted these data with linear regression models. This allowed us to (1) investigate the statistical significance of temporal trends; and (2) consider differences in trends among countries; and (3) predict future pancreatic cancer mortality rates. RESULTS: Over 44 years, pancreatic cancer mortality rates increased for females worldwide. Pancreatic cancer mortality rates for men increased in Southern Europe. In contrast, pancreatic cancer mortality rates for men in North America and Oceania increased until about 1975 and then decreased or remained stable. Our predictive models suggest that by 2005 the relative burden of pancreatic cancer mortality will have shifted away from Northern Europe and North America toward Southern Europe and Asia. CONCLUSIONS: Future research on pancreatic cancer should concentrate separately on the assessment of risk attributable to exposure to environmental factors, lifestyle factors, genetic determinates of pancreatic cancer, and the interactive influences of these factors on pancreatic cancer.

Degradation of hydroxyapatite coating on a well-functioning femoral component.

We carried out a histological study of a proximally hydroxyapatite (HA)-coated femoral component, retrieved after 9.5 years of good function. The HA coating had completely degraded. Bone was in direct contact with the titanium surface in all the areas which had been coated, with no interposing fibrous tissue. There were no signs of particles, third-body wear, adverse tissue reactions or osteolysis. Bone remodelling was evident by the presence of resorption lacunae; tetracycline labelling showed bone laid down six years after implantation. The loss of the HA-coating had no negative effect on the osseo-integration of the stem. We conclude that the HA coating contributes to the fixation of the implant and that its degradation does not adversely affect the long-term fixation.

Alpha-tocopherol and probucol reduce autoantibody titer to MDA-LDL in hypercholesterolemic rabbits.

We considered the hypothesis that antioxidant supplementation that increases aortic antioxidant concentrations would reduce autoantibody titer to MDA-LDL, a measure that may indicate in vivo oxidation. We assessed autoantibody titer to MDA-LDL in rabbits before and after 5 months of treatment with a nutritionally adequate hypercholesterolemic diet alone (control) or supplemented with synthetic alpha-tocopherol or probucol. Aortic cholesterol and antioxidants were assessed at the end of treatment. alpha-Tocopherol supplementation increased the ratio of aortic alpha-tocopherol to cholesterol by 20-30-fold, while probucol supplementation increased the ratio of aortic probucol to cholesterol to 4-13 micromol/mol. Before treatment, MDA-LDL autoantibody titer averaged 5.09 +/- 0.24 with no difference among groups (p =.53 by ANOVA). However, after treatment, autoantibody titers differed among groups (p <.03 by ANOVA). Autoantibody titers were similar in rabbits supplemented with alpha-tocopherol and probucol (3.69 +/- 0.21 and 3.73 +/- 0.48, respectively, p = 0.81), and 26% (p <.009) lower in antioxidant supplemented rabbits than unsupplemented hypercholesterolemic rabbits (5.03 +/- 0.47). There was an inverse J relationship between autoantibody titer after treatment and aortic alpha-tocopherol/cholesterol and probucol/cholesterol, with minimum values for autoantibody titers above 8-10 micromol antioxidant/mmol cholesterol. The results of this study are consistent with inhibition of in vivo intra-aortic oxidation when aortic alpha-tocopherol or probucol exceed 8-10 micro;mol/mmol cholesterol.

Vibrational energy levels for CH4 from an ab initio potential.

Many areas of astronomy and astrophysics require an accurate high temperature spectrum of methane (CH4). The goal of the present research is to determine an accurate ab initio potential energy surface (PES) for CH4. As a first step towards this goal, we have determined a PES including up to octic terms. We compare our results with experiment and to a PES based on a quartic expansion. Our octic PES gives good agreement with experiment for all levels, while the quartic PES only for the lower levels.

Soy protein reduces the arterial low-density lipoprotein (LDL) concentration and delivery of LDL cholesterol to the arteries of diabetic and nondiabetic male cynomolgus monkeys.

We have previously shown that soy protein consumption improves lipoprotein concentrations and reduces the progression of atherosclerosis in cynomolgus monkeys. The mechanism for these beneficial effects is unclear. The purpose of this study was to determine potential mechanisms for the atheroprotective effects of soy and to determine if these effects extend to diabetic monkeys. We designed an experiment with a 2 x 2 factorial design in which adult male monkeys (N = 23) were fed an atherogenic diet with a protein source of either soy isolate or casein and lactalbumin, and the monkeys were either control or streptozotocin-induced diabetic. Diabetics had significantly increased fasting glucose and glycated hemoglobin (GHb) levels; this relationship was not affected by the type of dietary protein. Diabetics also had increased total (TC) and low-density lipoprotein cholesterol (LDLC) concentrations. However, soy consumption significantly reduced TC and LDLC concentrations in both control and diabetic monkeys. Plasma and arterial LDL metabolism was determined by injecting 125I-LDL at 48 hours and 131I-tyramine cellobiose LDL at 1 hour prior to necropsy. This allowed a determination of the arterial LDL concentration, permeability, and arterial LDL delivery. An increase in the whole-body plasma LDL fractional catabolic rate (FCR) was found with soy. Soy significantly reduced the arterial LDL concentration across all arterial sites by an average of 50%. Soy also significantly reduced the delivery of LDLC to all arterial sites by an average of 40%. While this was primarily due to the lower plasma LDLC concentration, LDL permeability in the carotid bifurcation and internal carotid arteries was also reduced. There was no additional effect of diabetes. These beneficial effects on plasma and arterial LDL metabolism would be expected to reduce atherosclerosis and were found in both control and diabetic monkeys.

Determinants of bioactivity of oxidized phospholipids. Specific oxidized fatty acyl groups at the sn-2 position.

We previously described 3 bioactive oxidation products of 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (PAPC) containing oxovaleroyl (POVPC), glutaroyl (PGPC), and epoxyisoprostane (PEIPC) groups at the sn-2 position that were increased in minimally modified/oxidized low density lipoprotein (MM-LDL) and rabbit atherosclerotic lesions. We demonstrated specific and contrasting effects of POVPC and PGPC on leukocyte-endothelial interactions and described an effect of PEIPC on monocyte binding. The major purpose of the present study was to determine the effects of structural changes on the bioactivities of these 3 lipids. We demonstrate herein that the group at the sn-2 position determines the specific bioactivity and that the substitution of stearoyl for palmitoyl at the sn-1 position or ethanolamine for choline at the sn-3 position of the phospholipid did not alter bioactivity. Oxidized PAPC, oxidized 1-stearoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine, and oxidized 1-stearoyl-2-arachidonoyl-sn-glycero-3-phosphorylethanolamine stimulated monocyte binding and inhibited lipopolysaccharide-induced expression of the neutrophil-binding molecule E-selectin. Furthermore, all oxovaleroyl phospholipids but not the glutaroyl phospholipids induced monocyte binding without an increase in vascular cell adhesion molecule-1 (VCAM-1) expression and inhibited lipopolysaccharide-induced E-selectin expression. In contrast, glutaroyl phospholipids but not oxovaleroyl phospholipids stimulated E-selectin and VCAM-1 expression. We further demonstrate that all parts of the phospholipid molecules are required for these bioactivities. Hydrolysis with phospholipase (PL) A(1), PLA(2), and PLC strongly reduced the bioactivities of POVPC, PGPC, and mixed isomers of PEIPC. PLD had a smaller but still significant effect. The effects of POVPC and PEIPC could be abolished by sodium borohydride treatment, indicating the importance of the reducible groups (carbonyl and epoxide) in these molecules. In summary, these studies identify 6 new bioactive, oxidized phospholipids that are increased in MM-LDL and, where measured, in atherosclerotic lesions. They thus suggest that a family of phospholipid oxidation products containing oxovaleroyl, glutaroyl, and epoxyisoprostane at the sn-2 position play an important role in the regulation of leukocyte-endothelial interactions, bioactivity being in part controlled by several types of phospholipid hydrolases.

Metabolic evidence for sequestration of low-density lipoprotein in abdominal aorta of normal rabbits.

In rabbits, atherosclerosis develops preferentially at branch sites compared with the adjacent uniform aorta. This study investigated the hypothesis that low-density lipoprotein (LDL) is "sequestered" (present in a form that exchanges slowly with plasma LDL) in the aortas of normal rabbits and that more LDL is sequestered at branch sites. Thus 33 normal rabbits were injected with LDL labeled with (125)I-labeled tyramine cellobiose ((125)I-TC) to trace both undegraded LDL and aortic LDL degradation products. For 25 rabbits, LDL was also labeled with (131)I to trace undegraded LDL alone. The time-dependent aortic (125)I-TC and (131)I accumulation was determined from 0.6 to 120 h after injection. Compartmental modeling provided metabolic evidence for sequestration of LDL at the branch (P < 0.01) and uniform (P < 0.005) abdominal aorta. Concentrations of sequestered LDL were 109 +/- 28% higher (P < 0.0005) for branch sites. LDL mean residence time was 23.5 +/- 3.1 h for branch sites, 7.6 +/- 3.5 h longer (P < 0.05) than for the uniform abdominal aorta. Enhanced retention of higher concentrations of sequestered LDL at branch sites could account for the increased susceptibility of these aortic sites to atherosclerosis.

In vitro lipid peroxidation of LDL from postmenopausal cynomolgus macaques treated with female hormones.

Premenopausal women and postmenopausal women given estrogen are protected from cardiovascular diseases compared with men. Previous studies investigated whether estrogen treatment protects low density lipoprotein (LDL) from in vitro oxidation as a potential mechanistic explanation for the beneficial effect of estrogen. Results of these studies are mixed, and very few studies considered aspects of LDL that influence LDL oxidation. This study investigated whether treating postmenopausal female cynomolgus macaques with conjugated equine estrogens (CEE), medroxyprogesterone acetate (MPA), CEE + MPA, or tamoxifen, a mixed estrogen receptor agonist/antagonist, would protect LDL from in vitro oxidation. LDL was isolated from monkeys fed an atherogenic diet for 12 weeks or the same diet with CEE, MPA, CEE + MPA, or tamoxifen added at levels equivalent (on a caloric basis) to those given to women. LDL was subjected to Cu(2+) (3 micromol/L) or 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH, 1 mmol/L) and LDL oxidation was determined by the lag time before rapid formation of conjugated dienes and by the maximal rate of conjugated diene formation (propagation rate). Lag times and propagation rates were not affected by treatment. Lag times for Cu(2+) oxidation were related to LDL tocopherol while lag times for AAPH oxidation were related to high density lipoprotein (HDL) cholesterol and to LDL molecular weight. Multivariate analysis showed that LDL alpha- and gamma-tocopherol together could explain 27% of the variation in Cu(2+) mediated lag time (P < 0.005) among animals while HDL cholesterol, LDL gamma-tocopherol, and LDL molecular weight combined could explain 40% of the variation in AAPH- mediated lag time (P = 0.0006) among animals. After adjustment for these predictors, LDL lag times were not affected by treatment. In conclusion, in monkeys treated with female hormones, multiple factors influence in vitro low density lipoprotein (LDL) oxidation; future work will be needed to determine whether estrogen alters oxidation of LDL in the artery.-Schwenke, D. C., J. D. Wagner, and M. R. Adams. In vitro lipid peroxidation of LDL from postmenopausal cynomolgus macaques treated with female hormones.

Vitamin E combined with selenium inhibits atherosclerosis in hypercholesterolemic rabbits independently of effects on plasma cholesterol concentrations.

Several antioxidants inhibit atherosclerosis. This study investigated the hypothesis that combining vitamin E, a lipophilic antioxidant, with vitamin C, a hydrophilic antioxidant, and/or selenium, a cofactor of peroxidases that detoxify lipid peroxides, would inhibit atherosclerosis more effectively than vitamin E alone. We also considered whether regional variation in inhibition of atherosclerosis by antioxidants would be associated with regional variation in aortic lipophilic antioxidants. Rabbits were fed an atherogenic diet (control) or an atherogenic diet supplemented with vitamin E, vitamins E and C, vitamin E+selenium, vitamins E and C+selenium, or probucol (positive control). Supplements were as follows: vitamin E, 146 IU/d; vitamin C, 791 mg/d; selenium, 22 microg/d; or probucol, 406 mg/d. Vitamin C did not influence atherosclerosis. After 22 weeks of treatment, rank order of aortic atherosclerosis was control>vitamin E (with or without vitamin C)>vitamin E+selenium (with or without vitamin C)>probucol. Antioxidant treatment reduced aortic cholesterol concentrations 21% to 56%, 29% to 86%, and 19% to 75% for the aortic arch, descending thoracic aorta, and abdominal aorta, respectively (P<0.025 to P<0.0003 by ANOVA), with slightly greatly reductions for areas of atherosclerotic lesions. Some treatments reduced plasma cholesterol concentrations, but none altered the distribution of cholesterol among lipoproteins. Corrected for differences in plasma cholesterol concentrations, aortic cholesterol concentrations were reduced up to 72% (P<0.02) by the antioxidant treatments, with equal reductions by vitamin E+selenium and by probucol. Aortic alpha-tocopherol standardized by aortic cholesterol as a measure of aortic lipids was lower in the abdominal aorta than in the aortic arch of rabbits not given alpha-tocopherol and increased relatively more in the abdominal aorta than in the aortic arch with alpha-tocopherol supplementation. The results of this study suggest that vitamin E+ selenium inhibited atherosclerosis as effectively as an equally hypocholesterolemic dose of probucol by a mechanism(s) that is in part independent of effects on plasma and lipoprotein cholesterol concentrations. The tendency for greater efficacy of antioxidant treatments in the abdominal aorta than aortic arch may relate to the lower concentrations of alpha-tocopherol in the abdominal aorta of unsupplemented rabbits.

Aging, menopause, and free radicals.

As women undergo menopause, circulating concentrations of estrogen decrease. The relative estrogen deprivation in postmenopausal women is associated with physiological changes and increased risk of several diseases, including cardiovascular disease. Studies in animals have shown that exogenous estrogen inhibits atherosclerosis, the underlying cause of cardiovascular disease. Ongoing clinical trials will soon provide data for the effect of exogenous estrogen on cardiovascular disease in postmenopausal women. Estrogen has a number of effects that could influence atherogenesis and cardiovascular disease. Estrogens have favorable effects on lipoproteins, but such effects can only account for part of the protection from cardiovascular disease that appears to be conferred by estrogen. Evidence suggests that estrogens can have both prooxidant and antioxidant effects. However, the available evidence suggests that in vivo physiological concentrations of estrogen may have a modest antioxidant activity, and prooxidant activity is unlikely. The antioxidant activity of estrogens and inhibition by estrogens of cellular processes that are thought to promote atherosclerosis are likely to be additional mechanism(s) by which estrogen inhibits atherosclerosis and cardiovascular disease, but more work is needed. Studies of some effects of estrogens on atherogenic processes in isolated cells need to be extended to the whole animal. The influence of estrogen receptors on inhibition of atherosclerosis by estrogen needs to be clarified. Future studies should be designed to investigate separately the estrogenic and antioxidant activities of estrogens and estrogen analogs. Investigations of the antioxidant activities of estrogens should include careful consideration of the interaction of estrogens with endogenous antioxidants and fatty acid saturation, and more attention should be paid to the potential for estrogens to inhibit intraarterial oxidation.

Gender differences in intima-media permeability to low-density lipoprotein at atherosclerosis-prone aortic sites in rabbits. Lack of effect of 17 beta-estradiol.

Premenopausal women are protected from coronary heart disease, and premenopausal nonhuman primates are protected from atherosclerosis, the underlying cause of coronary heart disease. Estrogen is thought to account for this protection in females, and part of this protection is independent of the effects on risk factors, including lipoprotein levels. This study considered the hypothesis that reduced intima-media permeability to low-density lipoproteins (LDL) may account for the protection from atherosclerosis and coronary heart disease in premenopausal females and that this effect might be mediated by estrogen. Intima-media permeability to LDL was determined in male and female rabbits made hypercholesterolemic by feeding them 0.5% cholesterol for 8 days. The diet of half of the female rabbits was supplemented with 17 beta-estradiol (4 mg/d) during cholesterol feeding and the preceding 4 weeks. Estrogen treatment in the female rabbits did not influence the intima-media permeability to LDL. However, intima-media permeability to LDL for branch sites of the abdominal aorta and aortic arch (regions highly susceptible to atherosclerosis) was 43% and 38% lower, respectively, in male rabbits than in female rabbits: (2.93 +/- 0.39 microL/h/g, (n = 8), vs 6.28 +/- 0.86 microL/h/g, (n = 16), P < .001, and 4.69 +/- 0.28 microL/h/g, (n = 8) vs 7.57 +/- 0.75 microL/h/g, (n = 16), P < .02). In contrast, intima-media permeability to LDL in 7 of 8 aortic sites relatively resistant to atherosclerosis did not differ between male and female rabbits. These data suggest that the protection from atherosclerosis associated with female sex and estrogen is mediated by mechanism(s) other than reduction in intima-media permeability to LDL.