A comparison of the kinetics of low-density lipoprotein oxidation initiated by copper or by azobis (2-amidinopropane)

Efficacy of Saudi propolis and bee pollen in the reduction of oxidative stress induced with CCl4 in a testis mice model

Low testosterone levels are caused by alcoholism, cigarette smoking, and exposure to toxic chemicals. This work focused on investigating the activities of propolis (PE) and bee pollen (BPE) extracts in reducing the oxidative stress of carbon tetrachloride (CCl4) in male mice models. The 48 male Swiss Albino mice weighed 27.5 ± 2.5 g and were divided into: Group1: Control (-) received distilled water only through oral intubation; Group 2: Control (- -) received corn oil by intraperitoneal (i.p.) injection once a day; Group 3: Control (+) received a sublethal dose of CCL4 intraperitoneally the end of the experiment. Group 4: Stander treated with silymarin at a daily dose of 200 mg/kg orally. Group 5: The mice were given 8.4 mg/ kg bw of (PE) orally. Group 6: The mice were given (BPE) extract (140 mg/kg bw) orally. After five consecutive days of treatment, all mice had testis injury in all groups except G1& G2, by a single i.p injection of CCL4 at a dose of 0.5 mL/kg (bw; 20% v/v in corn oil). The result showed a significant increase in luteinizing, follicle-stimulating, and testosterone hormone levels in the serum and semen parameters in the groups treated with PE and BPE. The histological results showed the greatest improvements in testis structures in the BPE group, which was confirmed using (Bcl-2; immunohistochemistry). These results suggest an important role of the antioxidative effects of PE and BPE in the attenuation of CCl4 oxidative stress.

Jujuboside B Inhibited High Mobility Group Box Protein 1-Mediated Severe Inflammatory Responses in Human Endothelial Cells and Mice

High mobility group box protein 1 (HMGB1) is a biomolecule that acts as an alerting signal of late sepsis by accelerating the production of proinflammatory cytokines, and eventually leads to various inflammation-related symptoms. When released into plasma at high concentration, it disrupts precise diagnosis and prognosis and worsens the survival of patients with systemic inflammatory conditions. Jujuboside B (JB) is a natural compound pressed from the seed of Zizyphi Spinosi Semen, which is known for its medical efficacies in treating various conditions such as hyperlipidemia, hypoxia, and platelet aggregation. Nevertheless, the medicinal activity of JB on HMGB1-involved inflammatory response in vascular cells in the human body is still ambiguous. Therefore, we hypothesized that JB could regulate the lipopolysaccharide (LPS)-induced dynamics of HMGB1 and its mediated cascade in inflammatory responses in human umbilical vein endothelial cells (HUVECs). In this experiment, JB and HMGB1 were administered in that order. In vitro and in vivo permeability, and cell viability, adhesion, and excavation of leukocytes, development of cell adhesion molecules, and lastly production of proinflammatory substances were investigated on human endothelial cells and mouse disease models to investigate the efficacy of JB in inflammatory condition. JB substantially blocked the translocation of HMGB1 from HUVECs and controlled HMGB1-induced adhesion and extravasation of the neutrophils through LPS-treated HUVECs. Moreover, JB decreased the formation of HMGB1 receptors and continually prevented HMGB1-induced proinflammatory mechanisms by blocking transcription of nuclear factor-κB and synthesis of tumor necrosis factor-α. In conclusion, JB demonstrated preventive effects against inflammatory pathologies and showed the potential to be a candidate substance for various inflammatory diseases by regulating HMGB1-mediated cellular signaling.

Milk thistle (Silybum Marianum) as an antidote or a protective agent against natural or chemical toxicities: a review

Biological and chemical agents cause dangerous effects on human health via different exposing ways. Recently, herbal medicine is considered as a biological and safe treatment for toxicities. Silybum marianum (milk thistle), belongs to the Asteraceae family, possesses different effects such as hepatoprotective, cardioprotective, neuroprotective, anti-inflammatory and anti-carcinogenic activities. Several studies have demonstrated that this plant has protective properties against toxic agents. Herein, the protective effects of S. marianum and its main component, silymarin, which is the mixture of flavonolignans including silibinin, silydianin and silychristin acts against different biological (mycotoxins, snake venoms, and bacterial toxins) and chemical (metals, fluoride, pesticides, cardiotoxic, neurotoxic, hepatotoxic, and nephrotoxic agents) poisons have been summarized. This review reveals that main protective effects of milk thistle and its components are attributed to radical scavenging, anti-oxidative, chelating, anti-apoptotic properties, and regulating the inflammatory responses.

Anti-inflammatory effects of Baicalin, Baicalein, and Wogonin in vitro and in vivo

Here, three structurally related polyphenols found in the Chinese herb Huang Qui, namely baicalin, baicalein, and wogonin, were examined for its effects on inflammatory responses by monitoring the effects of baicalin, baicalein, and wogonin on lipopolysaccharide (LPS)-mediated vascular inflammatory responses. We found that each compound inhibited LPS-induced barrier disruption, expression of cell adhesion molecules (CAMs), and adhesion/transendothelial migration of monocytes to human endothelial cells. Each compound induced potent inhibition of phorbol-12-myristate 13-acetate and LPS-induced endothelial cell protein C receptor shedding. It also suppressed LPS-induced hyperpermeability and leukocytes migration in vivo. Furthermore, each compound suppressed the production of tumor necrosis factor-α or interleukin-6 and the activation of nuclear factor-κB or extracellular regulated kinases 1/2 by LPS. Moreover, treatment with each compound resulted in reduced LPS-induced lethal endotoxemia. These results suggest that baicalin, baicalein, and wogonin posses anti-inflammatory functions by inhibiting hyperpermeability, expression of CAMs, and adhesion and migration of leukocytes, thereby endorsing its usefulness as a therapy for vascular inflammatory diseases.

Mathematical modeling of area under the curve assessment criteria to quantify the antioxidant and pro-oxidant capacity: Coffee extracts as a case study

The development of a convenient mathematical application for testing the antioxidant and pro-oxidant capacity is essential in order to investigate potential sources of new agents and processes. In this regard, authors use the standardized values of the area under the curve of a kinetic profile of a dose-response agent, as a way to bypass the complex process of analyzing the kinetic variations of agents. In general, linear approaches are used, but such patterns frequently lead to unreliable results and misinterpretations, making it extremely difficult to compare the results from different assays. In this work, we have demonstrated the non-linearity of the dose-response area under the curve assessment criteria by means of simulations. A simple non-linear dose-response model was developed to describe the accurate response. As a case study, experimental data of extracts of unroasted coffee beans from five different country-climate locations for the two most common coffee varieties (Robusta and Arabica) were obtained using the β-carotene and crocin bleaching in vitro assays. Their antioxidant capacity was analyzed in detail and compared with commercial standards. The results show that the antioxidant capacity was greater than some of the commercial standards in terms of its maximum capacity, while when the analyses are based on rate parameters, the coffee extracts show between 6 and 40 times lower values than the standard antioxidants. In addition, to illustrate the advantages of using the standardized area units and the mathematical model developed, other more complex scenarios were recreated. We believe that the model application developed provides a simple alternative to summarize meaningful parameters that characterize the response, facilitates rigorous comparisons among the effects of different compounds and experimental approaches and helps to comprehend multi-variable scenarios.

3,5,4'-Trihydroxy-6,7,3'-trimethoxyflavone protects astrocytes against oxidative stress via interference with cell signaling and by reducing the levels of intracellular reactive oxygen species

Oxidative stress is tightly involved in various neurodegenerative diseases such as Parkinson's and Alzheimer's diseases, and conditions such as ischemia. Astrocytes, the most abundant glial cells in the brain, protect neurons from reactive oxygen species (ROS) and provide them with trophic support. Therefore, any damage to astrocytes will affect neuronal survival. In a previous study we have demonstrated that an extract prepared from the plant Achillea fragrantissima (Af) prevented the oxidative stress-induced death of astrocytes and attenuated the intracellular accumulation of ROS in astrocytes under oxidative stress. In the present study, using activity guided fractionation, we have purified from this plant the active compound, determined to be a flavonoid named 3,5,4'-trihydroxy-6,7,3'-trimethoxyflavone (TTF). The effects of TTF in any biological system have not been studied previously, and this is the first study to characterize the anti-oxidant and protective effects of this compound in the context of neurodegenerative diseases. Using primary cultures of astrocytes we have found that TTF prevented the hydrogen peroxide (H2O2)-induced death of astrocytes, and attenuated the intracellular accumulation of ROS following treatment of these cells with H2O2 or the peroxyl radicals generating molecule 2,2'-Azobis(amidinopropane) (ABAP). TTF also interfered with cell signaling events and inhibited the phosphorylation of the signaling proteins stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), extracellular signal regulated kinase (ERK 1/2) and mitogen activated protein kinase kinase (MEK1) and the phosphorylation of the transcription factor cyclic AMP response element-binding protein (CREB). The mechanism of the protective effect of TTF against H2O2-cytotoxicity could not be attributed to a direct H2O2 scavenging but rather to the scavenging of free radicals as was shown in cell free systems. Thus, TTF might be a therapeutic candidate for the prevention/treatment of neurodegenerative diseases where oxidative stress is part of the pathophysiology.

Vascular barrier protective effects of pellitorine in LPS-induced inflammation in vitro and in vivo

Pellitorine (PT), an active amide compound, is well known to possess insecticidal, antibacterial and anticancer properties. In this study, we first investigated the possible barrier protective effects of pellitorine against pro-inflammatory responses induced by lipopolysaccharide (LPS) and the associated signaling pathways in vitro and in vivo. The barrier protective activities of PT were determined by measuring permeability, monocyte adhesion and migration, and activation of pro-inflammatory proteins in LPS-activated human umbilical vein endothelial cells (HUVECs) and in mice. We found that PT inhibited LPS-induced barrier disruption, expression of cell adhesion molecules (CAMs) and adhesion/transendothelial migration of monocytes to human endothelial cells. PT also suppressed LPS-induced hyperpermeability and leukocyte migration in vivo. Further studies revealed that PT suppressed the production of tumor necrosis factor-α (TNF-α) or Interleukin (IL)-6 and activation of nuclear factor-κB (NF-κB) or extracellular regulated kinases (ERK) 1/2 by LPS. Moreover, treatment with PT resulted in reduced LPS-induced lethal endotoxemia. These results suggest that PT protects vascular barrier integrity by inhibiting hyperpermeability, expression of CAMs, and adhesion and migration of leukocytes, thereby endorsing its usefulness as a therapy for vascular inflammatory diseases.

Protective and antioxidant effects of a chalconoid from Pulicaria incisa on brain astrocytes

Oxidative stress is involved in the pathogenesis of neurodegenerative diseases such as Parkinson's and Alzheimer's diseases. Astrocytes, the most abundant glial cells in the brain, protect neurons from reactive oxygen species (ROS) and provide them with trophic support, such as glial-derived neurotrophic factor (GDNF). Thus, any damage to astrocytes will affect neuronal survival. In the present study, by activity-guided fractionation, we have purified from the desert plant Pulicaria incisa two protective compounds and determined their structures by spectroscopic methods. The compounds were found to be new chalcones—pulichalconoid B and pulichalconoid C. This is the first study to characterize the antioxidant and protective effects of these compounds in any biological system. Using primary cultures of astrocytes, we have found that pulichalconoid B attenuated the accumulation of ROS following treatment of these cells with hydrogen peroxide by 89% and prevented 89% of the H₂O₂-induced death of astrocytes. Pulichalconoid B exhibited an antioxidant effect both in vitro and in the cellular antioxidant assay in astrocytes and microglial cells. Pulichalconoid B also caused a fourfold increase in GDNF transcription in these cells. Thus, this chalcone deserves further studies in order to evaluate if beneficial therapeutic effect exists.

Antioxidant and astroprotective effects of a Pulicaria incisa infusion

Oxidative stress is involved in the pathogenesis of neurodegenerative diseases such as Parkinson's and Alzheimer's diseases. Astrocytes, the most abundant glial cells in the brain, protect neurons from reactive oxygen species (ROS) and provide them with trophic support, such as glial-derived neurotrophic factor (GDNF). Thus, any damage to astrocytes will affect neuronal survival. In the present study, an infusion prepared from the desert plant Pulicaria incisa (Pi) was tested for its protective and antioxidant effects on astrocytes subjected to oxidative stress. The Pi infusion attenuated the intracellular accumulation of ROS following treatment with hydrogen peroxide and zinc and prevented the H(2)O(2)-induced death of astrocytes. The Pi infusion also exhibited an antioxidant effect in vitro and induced GDNF transcription in astrocytes. It is proposed that this Pi infusion be further evaluated for use as a functional beverage for the prevention and/or treatment of brain injuries and neurodegenerative diseases in which oxidative stress plays a role.

Anti-neuroinflammatory effects of the extract of Achillea fragrantissima

BACKGROUND

The neuroinflammatory process plays a central role in the initiation and progression of neurodegenerative diseases such as Parkinson's and Alzheimer's diseases, and involves the activation of brain microglial cells. During the neuroinflammatory process, microglial cells release proinflammatory mediators such as cytokines, matrix metalloproteinases (MMP), Reactive oxygen species (ROS) and nitric oxide (NO). In the present study, extracts from 66 different desert plants were tested for their effect on lipopolysaccharide (LPS) - induced production of NO by primary microglial cells. The extract of Achillea fragrantissima (Af), which is a desert plant that has been used for many years in traditional medicine for the treatment of various diseases, was the most efficient extract, and was further studied for additional anti-neuroinflammatory effects in these cells.

METHODS

In the present study, the ethanolic extract prepared from Af was tested for its anti-inflammatory effects on lipopolysaccharide (LPS)-activated primary cultures of brain microglial cells. The levels of the proinflammatory cytokines interleukin1β (IL-1β) and tumor necrosis factor-α (TNFα) secreted by the cells were determined by reverse transcriptase-PCR and Enzyme-linked immunosorbent assay (ELISA), respectively. NO levels secreted by the activate cells were measured using Griess reagent, ROS levels were measured by 2'7'-dichlorofluorescein diacetate (DCF-DA), MMP-9 activity was measured using gel zymography, and the protein levels of the proinflammatory enzymes cyclooxygenase-2 (COX-2) and induced nitric oxide synthase (iNOS) were measured by Western blot analysis. Cell viability was assessed using Lactate dehydrogenase (LDH) activity in the media conditioned by the cells or by the crystal violet cell staining.

RESULTS

We have found that out of the 66 desert plants tested, the extract of Af was the most efficient extract and inhibited ~70% of the NO produced by the LPS-activated microglial cells, without affecting cell viability. In addition, this extract inhibited the LPS - elicited expression of the proinflammatory mediators IL-1β, TNFα, MMP-9, COX-2 and iNOS in these cells.

CONCLUSIONS

Thus, phytochemicals present in the Af extract could be beneficial in preventing/treating neurodegenerative diseases in which neuroinflammation is part of the pathophysiology.

Utilizing hydroglycolic extract from myrobalan fruits to counteract reactive oxygen species

The hydroglycolic (HG) extract from 70% propylene glycol (PG) extraction of myrobalan fruits showed the most appreciable antioxidant efficiency towards 1,1-diphenyl-2-picrylhydrazyl (DPPH) in comparison to the extracts from 30, 50, 70 and 100% ethyl alcohol (EA), and 30, 50 and 100% PG . Its total polyphenols were also higher than others. The additional analysis of antioxidant power revealed that this HG extract was able to counteract the induced oxidation caused by hydrogen peroxide (H(2) O(2) ) and 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH). The quantification for the antioxidant capacity of the extract showed it was equivalent to 93.78 mg of 6-hydroxy-2,5,7,8-tetramethychroman-2-carboxylic acid (Trolox) g(-1) by 2,2'-azino-bis(3-ethylbenzthiazoline-6-suphonic acid) diammonium (ABTS) assay, and was 140.17 mg ascorbic acid (AA) equivalent g(-1) and 107.50 mg Trolox equivalent g(-1) by photochemiluminescence (PCL) assay. The incorporation of the HG myrobalan extract into lotion and sunscreen lotion rendered these products to provide the similar antioxidant power as the extract alone.

Protective activity of plicatin B against human LDL oxidation induced in metal ion-dependent and -independent processes. Experimental and theoretical studies

Oxidation of low-density lipoproteins (LDL) is thought to be a major factor in the pathophysiology of atherosclerosis. Natural antioxidants have been shown to protect LDL from oxidation and to inhibit atherogenic developments in animals. Structurally related prenylated pterocarpans, erybraedin C and bitucarpin A, and the prenylchalcone plicatin B were examined for their ability to inhibit LDL oxidation in vitro. The kinetic profile of peroxidation is characterized by the lag time of oxidation (t(lag)), the maximal rate of oxidation (V(max)) and the maximal accumulation of oxidation products (OD(max)). Specific variation of the set of kinetic parameters by antioxidants may provide important information about the mechanism of inhibitory action of a given compound. At equimolar concentrations (1 microM) the prenylated derivatives tested were found to inhibit 1 microM copper sulphate-induced oxidation of LDL (50 microg protein/ml) in accordance with the following order of activity: plicatin B>erybraedin Cbitucarpin A. Structural aspects, such as hydrogen-donating substituents, their number and arrangement in the aromatic ring moieties, and the prenyl and methoxy substituents, were investigated in order to explain the findings obtained. It is well known that the antioxidant activity of flavonoids is believed to be caused by a combination of transition metal chelation and free-radical-scavenging activities. To investigate these differences we comparatively studied the protective mechanism of plicatin B in copper-dependent or -independent LDL oxidation. The latter was mediated by 2,2'-azo-bis-(2-amidinopropane) dihydrochloride (ABAP). We measured the formation of conjugated dienes (OD(234 nm)). Plicatin B (0.2-1.5 microM) delayed the Cu(2+) (1 microM) promoted oxidation as conjugate diene formation (t(lag)) of the LDL by 45.2-123.5 min and reduced V(max) by 0.46-0.29 microM/min. In the ABAP (0.2mM) promoted LDL oxidation t(lag) increased by 67.2-110.2 min through plicatin B (0.5-2.5 microM). In experiments in which Cu(2+) concentrations increased (0.5 - 3 microM) and the amount of plicatin B (1 microM) was maintained constant, a significant decrease in t(lag) and an increase in V(max) was observed. In this study plicatin B appeared to exhibit a mixed mechanism, interfering with the formation of the radicals by chelating copper involved in the initiation/propagation reaction, but also by scavenging free hydroperoxyl radicals resulting from ABAP thermolysis. In addition, theoretical analysis indicated that plicatin B preferentially established the chelating complex with Cu(2+), because its affinity value is notably higher (by a factor of 5) than that for Cu(+).

Antioxidant and pro-oxidant effects of red wine and its fractions on Cu(II) induced LDL oxidation evaluated by absorbance and chemiluminescence measurements

Cu(II) mediated low density lipoprotein (LDL) oxidation has been followed by the changes in absorbance at 234 nm and the emitted low level chemiluminescence (CL). The similarity of the time profiles allows us to conclude that the emitted CL is due to the decomposition of a transient product, most likely a hydroperoxide. Red wine, as well as its fractions, afford a noticeable protection when added prior to the start of the LDL oxidation process. On the other hand, when they are added after the onset of the autocatalytic oxidation phase, red wine and its fractions behave as pro-oxidants. This is particularly evidenced by a strong burst of CL (enhancement of the light by a factor approximately 20). This burst is reduced by metal chelators (EDTA and DFO) and can be associated to a sequence of reactions such as XOH + Cu(II) --> X* + H(+) + Cu(I), Cu(I) + LOOH --> chemiluminescence where XOH is a phenolic compound and LOOH is a peroxide-like compound produced in the LDL oxidation.

Selenoprotein P Protects Low-density Lipoprotein Against Oxidation

Selenoprotein P (SeP) is an extracellular glycoprotein with 8-10 selenocysteines per molecule, containing approximately 50% of total selenium in human serum. An antioxidant function of SeP has been postulated. In the present study, we show that SeP protects low-density lipoproteins (LDL) against oxidation in a cell-free in-vitro system. LDL were isolated from human blood plasma and oxidized with CuCl2, 2,2'-azobis(2-amidinopropane) (AAPH) or peroxynitrite in the presence or absence of SeP, using the formation of conjugated dienes as parameter for lipid peroxidation. SeP delayed the CuCl2- and AAPH-induced LDL oxidation significantly and more efficiently than bovine serum albumin used as control. In contrast, SeP was not capable of inhibiting peroxynitrite-induced LDL oxidation. The protection of LDL against CuCl2- and AAPH-induced oxidation provides evidence for the antioxidant capacity of SeP. Because SeP associates with endothelial membranes, it may act in vivo as a protective factor inhibiting the oxidation of LDL by reactive oxygen species.

Paraoxonase-1 (PON-1) genotype and activity and in vivo oxidized plasma low-density lipoprotein in Type II diabetes

The HDL (high-density lipoprotein)-associated enzyme PON (paraoxonase)-1 protects LDL (low-density lipoprotein) from oxidative modification in vitro, although it is unknown if this anti-atherogenic action occurs in vivo. In a cross-sectional study of 58 Type II diabetic subjects and 50 controls, we examined the fasting plasma LDL basal conjugated diene concentration [a direct measurement of circulating oxLDL (oxidatively modified LDL)], lipoprotein particle size by NMR spectroscopy, PON-1 polymorphisms (coding region polymorphisms Q192R and L55M, and gene promoter polymorphisms −108C/T and −162G/A), PON activity (with paraoxon or phenyl acetate as the substrates) and dietary antioxidant intake. Plasma oxLDL concentrations were higher in Type II diabetic patients (males, P=0.048; females, P=0.009) and unrelated to NMR lipoprotein size, PON-1 polymorphisms or PON activity (with paraoxon as the substrate) in any group. In men with Type II diabetes, however, there was a direct relationship between oxLDL concentrations and PON activity (with phenyl acetate as the substrate; r=0.611, P=0.0001) and an atherogenic NMR lipid profile in those who were PON-1 55LL homozygotes. Circulating oxLDL concentrations in vivo were unrelated to PON-1 genotypes or activity, except in male Type II diabetics where there was a direct association between PON activity (with phenyl acetate as the substrate) and oxLDL levels. These in vivo data contrast with in vitro data, and may be due to confounding by dietary fat intake. Male Type II diabetic subjects with PON-1 55LL homozygosity have an atherogenic NMR lipid profile independent of LDL oxidation. These data do not support an in vivo action of PON on LDL oxidation.

Cell culture media are potent antioxidants that interfere during LDL oxidation experiments

In vitro cell-induced low-density lipoprotein (LDL) oxidation is a model frequently used for studies on antioxidant compounds which may be potentially antiatherogens. Using Cu2+ or the free radical generator 2,2'-azobis-[2-amidinopropane] dihydrochloride (AAPH) to oxidize human LDL, we showed that the cell culture media Ham's F10 and RPMI are potent antioxidants which reduce LDL-protective effect of various thyroid compounds. The culture media interfered with the compounds depending on their mechanism of action, and RPMI had the greatest antioxidant effect, completely hiding antioxidant efficiency of the compounds whatever the prooxidant agent was. We suggest some recommendations for study of antioxidant compounds using cell-induced LDL oxidation models.

Differences in LDL oxidizability by glycemic status: the insulin resistance atherosclerosis study

OBJECTIVE

To investigate differences in LDL oxidizability by glycemic status within the Insulin Resistance Atherosclerosis Study cohort.

RESEARCH DESIGN AND METHODS

LDL oxidizability (lag time and oxidation rate) after exposure to copper was compared among 352 subjects with normal glucose tolerance (NGT), impaired glucose tolerance (IGT), newly diagnosed type 2 diabetes, and known type 2 diabetes.

RESULTS

After adjustment for age, clinic, ethnicity, sex, and smoking status, LDL oxidation rates differed by glycemic status (P = 0.001), with a strong trend (P = 0.0001) for reduced LDL oxidation rate with increasing extent and duration of glucose intolerance (2,378 +/- 54, 2,208 +/- 65, 2,145 +/- 71, and 2,115 +/- 48 arbitrary units [mean +/- SE] for NGT, IGT, newly diagnosed type 2 diabetes, and known type 2 diabetes, respectively). Differences in LDL oxidation rate among groups were relatively unaltered by adjustment for lipids and lipoproteins, hypertension, BMI, and waist-to-hip ratio (WHR) and remained significant even after further adjustment for dietary antioxidants and fatty acids, as well as medications. LDL lag times differed marginally by glycemic status (P = 0.058), with similar values for NGT, IGT, and newly diagnosed type 2 diabetes (57-60 min) but higher values for known type 2 diabetes (65 +/- 2). These differences were eliminated by further adjustment for lipids and lipoproteins, hypertension, BMI, and WHR.

CONCLUSIONS

We found that glycemic status influenced LDL oxidizability, with a paradoxical reduction in LDL oxidizability, as indicated by a lower LDL oxidation rate with increased extent and duration of glucose intolerance. This difference was only slightly attenuated by adjustment for relevant demographic, metabolic, dietary, and pharmacological factors that potentially influence LDL oxidation.

Alpha-tocopherol protects against diet induced atherosclerosis in New Zealand white rabbits

In this study, we asked the question "does alpha-tocopherol supplementation prevent an increase in total plasma cholesterol (TPC) concentration and reduce the deposition of cholesterol in arterial plaques of rabbits fed atherogenic diets?" Isocaloric diets containing 0.1% cholesterol to induce atherosclerosis were enriched in one of three fats: saturated fats (SAT), monounsaturated fats (MONO), or n-6 polyunsaturated fats (POLY). Half of each of the three diets were supplemented with 2,500 IU alpha-tocopherol/kg-diet. Unsupplemented diets contained 25 IU alpha-tocopherol/kg-diet. Rabbits supplemented with alpha-tocopherol had plasma alpha-tocopherol concentrations 10-fold higher and an average TPC concentration 31% lower, P = 0.017, than rabbits fed unsupplemented diets. Among the three fat-fed groups, the difference was greatest for the POLY fat fed group (54%, P = 0.041). POLY fat-fed rabbits without alpha-tocopherol supplementation had plasma HDL cholesterol concentrations that were less than half that of rabbits fed other fats, P < or = 0.0001. In general, differences in mean esterified artery cholesterol concentrations among the three fat-fed groups, with and without alpha-tocopherol supplementation, paralleled differences in TPC concentration among the groups. This study suggests that for rabbits fed high pharmacological doses of alpha-tocopherol, atherosclerosis can be diminished in situations where the plasma cholesterol concentrations are also significantly lower.

Simple and rapid assessment of lipoprotein susceptibility to oxidation in the macromolecule fraction of plasma

BACKGROUND

Susceptibility of lipoprotein to oxidation is usually studied using purified lipoproteins. However, for large clinical studies or routine clinical assessment, a rapid, less time-consuming method that minimizes hydroperoxide accumulation in lipoprotein during preparation is desirable. Methods using whole plasma are complicated by the presence of an anticoagulant that may affect oxidation and the presence of antioxidants in the plasma aqueous phase. Lipoproteins in serum are relatively unprotected from initiation of oxidation.

METHODS

We studied copper-mediated oxidation of a macromolecule fraction of plasma prepared by simple molecular sieve chromatography.

RESULTS

LDL was more susceptible to oxidation than plasma macromolecules. The lag times approached zero as the copper concentration increased. The propagation rate was linear for PM vs. the copper concentration while LDL became saturated at 10-20 micromol/l. The interassay CVs for the lag phase rate, lag time, PR and maximal DeltaA(max) were 23%, 7.7%, 4.9%, and 3.3%, respectively.

CONCLUSIONS

This procedure should be applicable to large numbers of individuals in investigations regarding the effects of drugs and diets on lipid composition and oxidative susceptibility.

Inhibition of rat lipoprotein lipid peroxidation by the oral administration of D003, a mixture of very long-chain saturated fatty acids

Previous results have demonstrated that policosanol, a mixture of aliphatic primary alcohols isolated and purified from sugar cane wax, whose main component is octacosanol, inhibited lipid peroxidation in experimental models and human beings. D003 is a defined mixture of very long-chain saturated fatty acids, also isolated and purified from sugar cane wax, whose main component is octacosanoic acid followed by traicontanoic, dotriacontanoic, and tetracontanoic acids. Since very long-chain fatty acids are structurally related to their corresponding alcohols, we investigated the effect of oral treatment with D003 (0.5, 5, 50, and 100 mg/kg) over 4 weeks in reducing the susceptibility of rat lipoprotein to oxidative modification. The combined rat lipoprotein fraction VLDL + LDL was subjected to several oxidation systems, including those containing metal ions (CuSO4), those having the capacity to generate free radicals 2,2-azobis-2-amidinopropane hydrochloride (AAPH), and a more physiological system (resident macrophages). D003 (5, 50, and 100 mg/kg) significantly inhibited copper-mediated conjugated-diene generation in a concentration-dependent manner. D003 increased lag phase by 53.1, 115.3, and 119.3%, respectively, and decreased the rate of conjugate-diene generation by 16.6, 21.5, and 19.6%, respectively. D003 also inhibited azo-compound initiated and macrophage-mediated lipid peroxidation as judged by the significant decrease in thiobarbituric acid reactive substance (TBARS) generation. In all the systems the maximum effect was attained at 50 mg/kg. There was also a parallel attenuation in the reduction of lysine amino groups and a significant reduction of carbonyl content after oxidation of lipoprotein samples. Taken together, the present results indicate that oral administration of D003 protects lipoprotein fractions against lipid peroxidation in the lipid as well in the protein moiety.

Isoprostane levels in lipids extracted from atherosclerotic arteries of nonhuman primates

Nonhuman primates used in these studies had been fed for 5 years diets enriched with cholesterol and one of three classes of fatty acids: saturated, monounsaturated, or polyunsaturated fatty acids. Atherosclerotic iliac artery lipid extracts were quantitatively analyzed for cholesterol, cholesteryl esters, fatty acid composition, and a marker of lipid oxidation, the F(2)-isoprostanes. There was no significant difference in the mean accumulation of F(2)-isoprostanes among the different diet groups. To account for the small, individual variation in the arachidonate concentration the F(2)-isoprostane mass from each sample was normalized by dividing by arachidonate mass: F(2)-isoprostane mass/(mass arachidonate). At lower levels of cholesterol accumulation, the F(2)-isoprostane mass/(mass arachidonate) ratio was greater in lipids from POLY arteries compared to SAT arteries, but the reverse was true at high levels of cholesterol. F(2)-isoprostane/(mass arachidonate) increased with mole fraction linoleate for the SAT group, but decreased for the POLY group. In summary, these studies demonstrated that there is no simple explanation of how F(2)-isoprostane accumulation did not depend on the concentration of oxidizable lipids that promote free-radical lipid oxidation.

Cu2+ -induced low density lipoprotein peroxidation is dependent on the initial O2 concentration: an O2 consumption study

Atherosclerotic plaques form in the arterial intima, where low density lipoprotein (LDL) is thought to be oxidatively modified at sites which may contain catalytic amounts of copper in the presence of low O2 tension. We have investigated O2 consumption during LDL peroxidation induced by Cu2+ ions in vitro and found two phases: a lag phase followed by a phase of rapid O2 consumption. The length of the lag phase was dependent on Cu2+ and on initial O2 concentrations; increasing either decreased the lag time; however, LDL. concentration had no effect. LDL-induced Cu2+ reduction, however, was not affected by low initial O2 concentrations, suggesting that O2 is not required for LDL-mediated reduction of Cu2+. Following the lag phase, O2 consumption was dependent upon LDL or initial O2 concentrations; Cu2+ concentrations had little effect, suggesting that the propagation phase is more dependent on the presence of LDL lipids and O2 as substrates for the reaction. In summary, LDL peroxidation takes place in the presence of Cu2+ at low O2 tension; however, the reaction is dependent upon initial O2 concentrations; increases shorten the lag phase and accelerate O2 consumption.

Potential role of oxidized lipids and lipoproteins in antioxidant defense

The atherogenic oxidative modification of low-density lipoprotein is suggested to occur in the aortic intima. There is reasonable evidence to suggest that antioxidants might be beneficial in preventing or retarding the progression of atherosclerosis. Exercise, estrogens, and substitution of polyunsaturated fat for saturated fat are beneficial in the prevention of atherosclerosis. Yet, paradoxically, they are capable of inducing an oxidative stress. To reconcile with this paradox, we postulate that under certain conditions an oxidative stress might be beneficial by inducing antioxidant enzymes in arterial cells. However, those with genetic deficiency in antioxidant enzymes or those who poorly respond to oxidative stress or those with overwhelming plasma oxidative stress might need additional antioxidant protection.

Role of the cyclic AMP-dependent pathway in free radical-induced cholesterol accumulation in vascular smooth muscle cells

We have previously reported that free radical-treated vascular smooth muscle cells (SMC) lead to cholesterol accumulation in vitro. In the current study, we investigated the effects of oxidative stress on cyclic AMP concentration and cAMP-dependent enzymes involved in cholesterol homeostasis in A7r5 cells. Under our conditions of a mild oxidative stress, namely with no change in cell viability, we found that free radicals, initiated using azobis-amidinopropane dihydrochloride (AAPH), resulted in a dose-dependent decrease in cellular cAMP which was opposed by vitamin E preincubation. Although the addition of adenylate cyclase activators (carbacyclin and forskolin) increased cAMP levels it did not succeed in restoring the AAPH-induced decrease. The oxidative stress-induced increase in activities of 3-hydroxy-3-methylglutaryl coenzyme A reductase and of acyl coenzyme A: cholesterol acyltransferase and the decrease in neutral cholesteryl ester hydrolase activity were suppressed by addition of dibutyryl cAMP. Taken together, these results strongly suggest that free radicals reduce cAMP concentrations by altering cell membrane adenylate cyclase activity. The changes of cAMP-dependent enzymes induced by oxidative stress resulting in cholesterol accumulation might be one of the processes leading to SMC-derived foam cells depicted in atheroma plaque. Moreover, if extrapolated to in vivo, these data may explain in part the beneficial effects of antioxidants in the reduction of cardiovascular diseases.

In vitro oxidation of low-density lipoprotein in two species of nonhuman primates subjected to caloric restriction

Caloric restriction (CR), which increases longevity and retards age-associated diseases in laboratory rodents, is being evaluated in nonhuman primate trials. CR reduces oxidative stress in rodents and appears to improve risk factors for cardiovascular disease in nonhuman primates. We tested the hypothesis that low-density lipoprotein (LDL) oxidizability is reduced in two monkey species (rhesus and cynomolgus) subjected to chronic CR. In both species, no significant differences occurred between CR and control animals on total, LDL, or high-density lipoprotein (HDL) cholesterol. In rhesus monkeys, triglycerides were higher in controls than CR (139 +/- 23 vs 66 +/- 8 mg/dl,p < .01, respectively). LDL from CR rhesus monkeys was reduced in triglyceride content and molecular weight compared to controls, whereas LDL composition in cynomolgus monkeys was similar in CR and control animals. In keeping with minor deviations in lipids, antioxidants, and LDL composition, no consistent differences in in vitro LDL oxidizability were apparent between CR and controls in either species.

Physiological aspects of low-density lipoprotein oxidation

The oxidation of LDL is thought to be a major contributor to the development of atherosclerosis. Considerable descriptive evidence has been accumulated showing that oxidized LDL promotes pro-atherogenic events. However, direct evidence that oxidized LDL causes atherosclerosis is lacking. This article summarizes the results of recent studies that demonstrate how oxidized LDL affects cellular function, and highlights key issues that should be addressed to link LDL oxidation with atherosclerosis.

HDL composition and HDL antioxidant capacity in patients on regular haemodialysis

Recent evidence suggests that HDL can directly inhibit LDL oxidation, a key early stage in atherogenesis. Patients with chronic renal failure are at increased cardiovascular risk, have reduced HDL levels and altered HDL composition. We have therefore investigated whether compositional changes in HDL lead to decreased HDL antioxidant capacity in these patients. In comparison to control subject HDL, patient HDL contained less total cholesterol, cholesterol esters, phospholipids and alpha-tocopherol. LDL, HDL and LDL + HDL were standardised for protein and oxidised in the presence of Cu2+. The rate of propagation during HDL oxidation was reduced in the patient group (3.28+/-0.65 x 10(-5) vs. 4.60+/-0.97 x 10(-5) abs. U/min, P < 0.01). Lipid peroxide generation in patient HDL was decreased: 6.56+4.4 versus 13.42+/-7.0 nmol malondialdehyde (MDA)/mg HDL protein after 90 min and 14.45+/-3.8 versus 20.11+/-7.8 nmol MDA/mg HDL protein after 180 min. This is attributable to reduced HDL polyunsaturated fatty acid content in patients (0.53+/-0.12 vs. 0.72+/-0.16 mmol/g HDL, P < 0.01). The inhibitory effect of HDL on LDL oxidation was similar: 71 and 33% for patient HDL compared to 68 and 31% for control HDL, after 90 and 180 min, respectively. Compositional changes of HDL in patients on haemodialysis did not affect the antioxidant capacity of HDL after standardisation for HDL protein. However, reduced HDL levels in vivo may result in reduced HDL antioxidant capacity in these patients.