An appraisal of cholesterol feeding in experimental atherogenesis

Potential Pharmacological Applications of Nigella Seeds with a Focus on Nigella sativa and Its Constituents against Chronic Inflammatory Diseases: Progress and Future Opportunities

The leading cause of death worldwide has been identified as chronic illnesses, according to the World Health Organization (WHO). Chronic inflammatory conditions such as asthma, cancer, diabetes, heart disease, and obesity account for three out of every five deaths. Although many people benefit from using nonsteroidal anti-inflammatory medicines (NSAIDs) for pain and inflammation relief, there are significant adverse effects to using these medications. Medicinal plants possess anti-inflammatory properties with minimal or no side effects. Nigella sativa (NS), also known as black cumin, is one of the plants used in traditional medicine the most. Many studies on the NS have shown that their therapeutic properties are attributed to the seed, oil, and secondary metabolites. This plant has been studied extensively and has many medical uses, such as anti-inflammatory. NS or its phytochemical compounds, such as thymoquinone, can cause cell apoptosis via oxidative stress, block efflux pumps, enhance membrane permeability, and exert potent biocidal effects. Notwithstanding the extensively documented anti-inflammatory effectiveness observed in the experimental model, the precise mechanisms underlying its anti-inflammatory effects in diverse chronic inflammatory diseases and its multi-targeting characteristics remain largely unexplored. This review examines NS or its secondary metabolites, a valuable source for the therapeutic development of chronic inflammatory diseases. Most clinical studies were done for diabetes and cardiovascular disease; therefore, more studies are required to examine the NS extracts and phytoconstituents to treat cancer, obesity, diabetes, asthma, neurological disorders, and COVID-19. This study will be a significant resource for clinicians and biologists seeking a pharmaceutical solution for inflammatory diseases.

Therapeutic Carbohydrate Restriction as a Metabolic Modality for the Prevention and Treatment of Abnormal Uterine Bleeding

Therapeutic carbohydrate restriction diets have been becoming increasingly popular over the years, resulting in dramatic weight loss and an improvement in metabolic disorders. Obesity, insulin resistance, and diabetes are the risk factors for many gynecologic morbidities such as uterine leiomyoma, endometrial polyps, and polycystic ovarian syndrome. There is evidence suggesting that the pathogenesis of cardiovascular disease is similar to that seen in many causes of abnormal uterine bleeding. We aim to explain how cardiovascular disease risk factor reduction with the use of therapeutic carbohydrate restriction may prevent and potentially treat these gynecologic disorders.

Influence of Lavandula angustifolia, Melissa officinalis and Vitex angus-castus on the organism of rats fed with excessive fat-containing diet

Plant food additives are becoming more and more popular and broadly applied products, though the information on risks they poses to the organism is limited and contradictive. Obesity and overeating are some of the commonest health issues around the world, and people are increasingly consuming workability-enhancing preparations as a simple and fast method of weight control. The plant-based preparations are considered less harmful than the synthetic chemical ones. Lavandula angustifolia Mill., Melissa officinalis L. and Vitex angus-castus L. are broadly used as food additives and medicinal plants, despite the fact that their complex physiological assessment on model animals in the conditions of obesity has not yet been performed. We carried out a 30-day experiment on white male rats. All the animals were given high-fat diet, and the experimental animals, in addition to this diet, received 5% crumbled dry herbs of L. angustifolia, M. officinalis or V. angus-castus. Taking into account the overall amount of consumed food, the mean daily gain in body weight; at the end of the experiment, we determined the index of the weight of the internal organs, biochemical and morphological blood parameters. At the beginning and the end of the experiment, the rats were examined for motor and orienting activities, and emotional status. Rats on high-fat diet gained up to 112% body weight by the end of the experiment, while rats that had received V. angus-castus gained up to 119%, M. officinalis – 135%, L. angustifolia – 139%, compared with the initial body weight. Addition of medicinal plants to the diet led to increase in average daily weight increment, significantly and reliably after consuming lavender and lemon balm, less significantly and unreliably after eating Vitex. L. angustifolia and M. officinalis reduced the relative brain weight, and ingestion of L. angustifolia and M. officinalis caused notable decrease in the relative mass of the thymus (down to 58% and 47% of the relative weight of thymus in animals of the control group respectively). Also, these plants decreased the motor and orienting activities of the rats by the end of the experiment. As for the biochemical parameters of blood, the activity of alkaline phosphatase significantly increased to 406% following consumption of Melissa, to 350% after consuming lavender, and to 406% after Vitex, compared to the control group. Furthermore, all the groups were observed to have increased AST and ALT activities. Intake of lavender led to increases in cholesterol (to 125%) and LDL cholesterol (to 228%), whereas the groups that consumed lemon balm were observed to have decreases in urea nitrogen (to 79%), totalbilirubin (to 63%) and triglycerides (to 63%). Addition of Vitex led to increase in the index of aterogenecity against the background of notable fall in HDL cholesterol (to 52% of the control group). The medicinal plants also contributed to the normalization of the glucose level. Morphological analysis of blood revealed no significant changes, except heightened content of monocytes in blood, which is characteristic of all groups, including the control. Effects of L. angustifolia, M. officinalis and V. angus-castus on the organism of rats on excessive-fat diet require additional histological, histochemical and immunological surveys.

Effect of shear stress alteration on atherosclerotic plaque vulnerability in cholesterol-fed rabbits

Previously, we created an experimental murine model for the induction of vulnerable plaque (VP). Although this murine model offers the opportunity to study the different molecular biological pathways that regulate plaque destabilization, the size of the animals severely limits the use of the model for in vivo diagnostics and percutaneous interventions. This study aimed to create a VP model in the rabbit, based on the murine model, to aid the assessment and development of novel diagnostic and interventional tools. New Zealand white rabbits were fed on a 2% cholesterol diet. After 1 week, a shear stress-altering device was implanted around the right carotid artery. Twelve weeks after cast placement, the carotid artery was isolated and processed for (immuno-)histological analysis to evaluate the presence of a VP phenotype. Atherosclerotic plaques with high lipid and macrophage content, low vascular smooth muscle cell content and intimal neovascularization were located upstream and downstream of the cast. The plaques lacked a significant necrotic core. In conclusion, we were able to create atherosclerotic plaques with a phenotype beyond that of a fatty streak, with a high percentage of lipids and macrophages, a thick cap with some vascular smooth muscle cells and neovascularization. However, as there was only a small necrotic core, the overall phenotype seems less vulnerable as compared to the thin fibrous cap atheroma in patients.

Elucidation of mechanisms of actions of thymoquinone-enriched methanolic and volatile oil extracts from Nigella sativa against cardiovascular risk parameters in experimental hyperlipidemia

BACKGROUND

Nigella sativa belonging to the Ranunculaceae family has been reported to use for thousands of years as protective and curative traditional medicine against a number of diseases. GC-MS analysis of methanolic extract (ME) and volatile oil (VO) extracted from Nigella sativa seed oil was performed by two different mass spectrometry libraries, WIlEY8 and NIST05s. The cholesterol lowering and antioxidant actions of VO and ME fractions were investigated in atherogenic suspension fed rats.

METHODS

In this study, four groups of male Wistar rats were used: normolipidemic control (NLP-C), hyperlipidemic control (HLP-C), methanolic extract (HLP-ME) and volatile oil treated (HLP-VO) groups for 30 days of duration. P value < 0.05 was assumed as significant data in groups.

RESULTS

Administration of atherogenic suspension to male Wistar rats for 30 days resulted in a marked increase of plasma triglycerides and total cholesterol, and significant change in plasma lipoprotein levels along with a decrease in antioxidant arylesterase activity in hyperlipidemic control (HLP-C) group. The oral feeding of 100 mg ME or 20 mg VO per rat/day effectively reduced the plasma triglycerides to near normal level, while high density lipoprotein cholesterol and its subfraction along with arylesterase activity levels were significantly increased. The test fractions elicited a significant decrease in hepatic HMG-CoA reductase activity. The fractions significantly blocked the ex vivo basal and in vitro maximal formation of conjugated diene and malondialdehyde, and lengthened the lag times of low density lipoprotein, small dense low density lipoprotein and large buoyant low density lipoprotein. ME possessing ω-6 linoleic acid along with palmitic acid active compounds was more effective than VO extract containing thymol and isothymol phenolic antioxidant compounds, thymoquinone phenolic compound common to the both extracts, via reduction in hepatic HMG-CoA reductase activity as well as antioxidant mechanisms.

CONCLUSION

The both extracts especially, ME significantly improve cardiovascular risk parameters in treated rats, and can be used in reactive oxygen species disorders such as cardiovascular diseases.

Cerebral xanthomatosis in three green water dragons (Physignathus cocincinus)

Cerebral xanthomatosis was diagnosed in three female green water dragons (Physignathus cocincinus), all of which presented with progressive neurologic signs. No antemortem evidence for xanthomatosis was identified, but on postmortem examination cholesterol granulomas, composed of cholesterol clefts surrounded by macrophages and multinucleated giant cells, were found in the forebrain of each animal and were associated with significant displacement and pressure on the adjacent brain. Although the cause of xanthomatosis in these animals is unknown, nutrition and trauma may be involved in the pathogenesis of this condition. Cerebrum, cholesterol, green water dragon, Physignathus cocincinus, xanthoma.

Nigella sativa thymoquinone-rich fraction greatly improves plasma antioxidant capacity and expression of antioxidant genes in hypercholesterolemic rats

The antioxidant activities of the thymoquinone-rich fraction (TQRF) extracted from Nigella sativa and its bioactive compound, thymoquinone (TQ), in rats with induced hypercholesterolemia were investigated. Rats were fed a semipurified diet supplemented with 1% (w/w) cholesterol and were treated with TQRF and TQ at dosages ranging from 0.5 to 1.5 g/kg and 20 to 100 mg/kg body wt, respectively, for 8 weeks. The hydroxyl radical (OH(.))-scavenging activity of plasma samples collected from experimental rats was measured by electron spin resonance. The GenomeLab Genetic Analysis System was used to study the molecular mechanism that mediates the antioxidative properties of TQRF and TQ. Plasma total cholesterol and low-density-lipoprotein cholesterol levels were significantly decreased in the TQRF- and TQ-treated rats compared to untreated rats. Feeding rats a 1% cholesterol diet for 8 weeks resulted in a significant decrease in plasma antioxidant capacity, as measured by the capacity to scavenge hydroxyl radicals. However, rats treated with TQRF and TQ at various doses showed significant inhibitory activity toward the formation of OH(.) compared to untreated rats. Upon examination of liver RNA expression levels, treatment with TQRF and TQ caused the up-regulation of the superoxide dismutase 1 (SOD1), catalase, and glutathione peroxidase 2 (GPX) genes compared to untreated rats (P<0.05). In support of this, liver antioxidant enzyme levels, including SOD1 and GPX, were also apparently increased in the TQRF- and TQ-treated rats compared to untreated rats (P<0.05). In conclusion, TQRF and TQ effectively improved the plasma and liver antioxidant capacity and enhanced the expression of liver antioxidant genes of hypercholesterolemic rats.

Efficacy of piperine, an alkaloidal constituent from Piper nigrum on erythrocyte antioxidant status in high fat diet and antithyroid drug induced hyperlipidemic rats

The main aim of this study was to investigate the effect of piperine on erythrocyte antioxidant status in high fat diet (HFD) and antithyroid drug induced hyperlipidemic rats. Male Wistar rats were divided into eight groups. The first four groups were fed a control diet and in addition were given respectively 1% carboxymethyl cellulose (CMC); 10 mg/kg body weight carbimazole (CM); 10 mg CM + 40 mg/kg body weight piperine and 10 mg CM + 2 mg/kg body weight atorvastatin (ATV). A similar pattern was followed for the next four groups except that they were all fed HFD instead of the control diet. Erythrocyte osmotic fragility, total cholesterol, phospholipids, lipid peroxidation products, enzymic and non-enzymic antioxidant status were studied in all experimental groups. Significantly increased osmotic fragility, total cholesterol/phospholipid ratio, thiobarbituric acid reactive substances and lipid hydroperoxides were observed in the plasma and erythrocytes of HFD fed and CM treated rats compared to the control. Superoxide dismutase, catalase, glutathione peroxidase, vitamin E and reduced glutathione in erythrocytes and vitamin C in the plasma were also significantly lowered in HFD fed, antithyroid drug treated rats compared to control animals. Concurrent piperine supplementation along with HFD and antithyroid drug administration normalized erythrocyte osmotic fragility, reduced lipid peroxidation, and improved the enzymic and non-enzymic antioxidant status compared to those rats that did not receive piperine. Thus, our results indicate that piperine supplementation markedly protects erythrocytes from oxidative stress by improving the antioxidant status in HFD fed antithyroid drug treated rats.

Effect of lupeol and lupeol linoleate on lipemic – hepatocellular aberrations in rats fed a high cholesterol diet

Cholesterol feeding has been often used to study the etiology of hypercholesterolaemia-related metabolic disturbances. The aim of the present study is to investigate the effects of a pentacyclic triterpene, lupeol, and its ester derivative on hepatic abnormalities associated with hypercholesterolemic rats. Hypercholesterolaemia was induced in male Wistar rats by feeding them with a high cholesterol diet (HCD) containing normal rat chow supplemented with 4% cholesterol and 1% cholic acid, for 30 days. Lupeol and lupeol linoleate were supplemented (50 mg/kg body wt/day) during the last 15 days. Increased hepatic lipid profile along with abnormalities in lipid-metabolizing enzyme activities were seen in hypercholesterolemic rats. An apparent increase in the expression of Acyl-CoA cholesterol acyltransferase mRNA was seen in HCD fed rats. The activities of hepatic marker enzymes, which serve as indices of cellular injury, were altered in HCD fed rats. Treatment with triterpenes significantly modulated the abnormalities induced by hypercholesterolaemia. Also, an increased (P >0.001) faecal excretion of cholesterol and bile acids were observed in lupeol and lupeol linoleate group when compared with HCD fed group. Therefore, it can be concluded that triterpenes treatment afforded substantial protection against the anomalies, which are manifested during the early stage of hypercholesterolemic atherogenesis.

Effect of red wine on oxidative stress and hypercholesterolemia induced by feeding a high-cholesterol diet in rat

The effect of red wine on oxidative stress and hypercholesterolemia induced by feeding a high-cholesterol diet (supplemented with 1.65% of cholesterol (w/w) for 4 weeks) to female Wistar rats was examined. When red wine was simultaneously supplemented to high-cholesterol diet, total cholesterol, triglycerides, atherogenic index and lipid peroxidation products significantly decreased compared with the high-cholesterol diet alone, while GSH content and antioxidative enzymes activities were enhanced. In the hypercholesterolemic rat the excretion of fecal bile acids, as well as their plasma and hepatic concentrations were increased significantly. Administration of red wine enhanced these values, indicating an increase in the cholesterol degradation. These results suggest that red wine may have a protective effect against oxidative stress, hypercholesterolemia and atherogenic index induced by high-cholesterol diet.

Effect of hypercholesterolemia on transendothelial EBD-albumin permeability and lipid accumulation in porcine iliac arteries

Hypercholesterolemia is associated with increased cardiovascular mortality and is known to promote the advancement of atherosclerotic lesions in experimental animal models. Juvenile swine were fed a normal or high-cholesterol diet, and the transendothelial macromolecular permeability of the external iliac arteries of these animals was assessed by measuring the uptake rate of circulating Evans blue dye (EBD). The extent and patterns of lipid-containing lesions were also determined using en face staining with Oil Red O (ORO). Sites of ORO staining often excluded EBD, possibly via the fragmentation of the internal elastic lamina, to which EBD binds. By spatially averaging the EBD uptake in arterial segments relatively free of ORO-positive lesions, it was found that endothelial permeability to albumin was greater in hypercholesterolemic pigs than in those on a normal diet (p=0.056).

Hypothetical hypercholesterolaemia and atherosclerosis

Recent pathological advances in experimental and iatrogenic atherosclerosis and critical review of the epidemiology of coronary heart disease revealed fallacious data and methodological errors underlying the hypercholesterolaemia/lipid hypothesis. Misuse of risk factors, inappropriate use of surrogates and misinterpretation of data pertaining to cholesterol's role in atherogenesis necessitate greater precision in word usage and terminology, reinstitution of the statistical reference range for cholesterol and closer scientific surveillance of aetiological endeavours in medicine.

Melatonin reduces cholesterol accumulation and prooxidant state induced by high cholesterol diet in the plasma, the liver and probably in the aorta of C57BL/6J mice

We examined the hypolipidemic and antioxidative effects of melatonin in plasma, liver and aorta of C57BL/6J mice fed on a high cholesterol (HC) diet. Mice were fed normal mice chow containing 1.5% cholesterol and 0.5% cholic acid for 4 months with or without melatonin (10 mg/L in drinking water) treatment. HC diet was observed to increase cholesterol, triglyceride and diene conjugate (DC) levels in plasma and liver. There was a tendency towards an increase in cholesterol level in the aorta following HC diet. In addition, aortic DC levels were higher than those of control group. No fatty streaks or plaques developed in the aorta of mice following HC diet, but in some sections, derangement of the endothelial layer was detected. Melatonin treatment was found to reduce plasma, liver cholesterol and DC levels as well as liver triglyceride levels in hypercholesterolemic mice. Aortic cholesterol and DC levels were also reduced in hypercholesterolemic mice when given melatonin, although not statistically significant. There were no differences in aortic histopathological findings of mice fed on a HC diet with and without melatonin treatment. In conclusion, our results indicate that melatonin reduces HC diet-induced cholesterol accumulation and prooxidant state in the plasma, liver and probably in the aorta.

Advances in experimental dyslipidemia and atherosclerosis

Among the models of dyslipidemia and atherosclerosis, a number of wild-type, naturally defective, and genetically modified animals (rabbits, mice, pigeons, dogs, pigs, and monkeys) have been characterized. In particular, their similarities to and differences from humans in respect to relevant biochemical, physiologic, and pathologic conditions have been evaluated. Features of atherosclerotic lesions and their specific relationship to plasma lipoprotein particles have been critically reviewed and summarized. All animal models studied have limitations: the most significant advantages and disadvantages of using a specific animal species are outlined here. New insights in lipid metabolism and genetic background with regard to variations in pathogenesis of dyslipidemia-associated atherogenesis have also been reviewed. Evidence suggests that among wild-type species, strains of White Carneau pigeons and Watanabe Heritable Hyperlipidemic and St. Thomas's Hospital rabbits are preferable to the cholesterol-fed wild-type animal species in dyslipidemia and atherosclerosis research. Evidence for the usefulness of both wild-type and transgenic animals in studying the involvement of inflammatory pathways and Chlamydia pneumoniae infection in pathogenesis of atherosclerosis has also been summarized. Transgenic mice and rabbits are excellent tools for studying specific gene-related disorders. However, despite these significant achievements in animal experimentation, there are no suitable animal models for several rare types of fatal dyslipidemia-associated disorders such as phytosterolemia and cerebrotendinous xanthomatosis. An excellent model of diabetic atherosclerosis is unavailable. The question of reversibility of atherosclerosis still remains unanswered. Further work is needed to overcome these deficiencies.

Coronary heart disease, hypercholesterolemia, and atherosclerosis. I. False premises

Lipid-rich caseous debris of advanced lesions stimulated interest in the role of cholesterol and lipids in atherosclerosis. Lipid-containing arterial lesions in cholesterol-overfed animals (cholesterolosis) and xanthomatous vascular lesions in subjects with familial hypercholesterolemia were then misrepresented as being atherosclerotic and led to the development of the hypercholesterolemic/lipid hypothesis. It is untenable that cholesterol, an essential multifunctional metabolite, is pathogenic at all blood levels and hypercholesterolemia is not prerequisite for human or experimental atherosclerosis. Serum cholesterol levels display a poor correlation with atherosclerosis at autopsy and with unreliable national coronary heart disease (CHD) mortality in each sex. Atherosclerosis topography and its iatrogenic production in humans and experimentally in herbivores by hemodynamic means both support a biomechanical causation and preclude causality by any circulating humoral factor. CHD, not a specific disease, is a nonspecific complication of many diseases including atherosclerosis and cannot be equated with coronary atherosclerosis due to differences in pathology and pathogenesis. Thus, extrapolations from CHD risk factors or correlations with fallacious vital statistics to atherosclerosis are invalid. It follows that the hypercholesterolemic/lipid hypothesis evolving from false premises, misuse of CHD, scientific misrepresentation, and fallacious data has no legitimate basis.

The role of vitamin E on the anti-atherosclerotic effect of fish oil in diet-induced hypercholesterolemic rabbits

The role of vitamin E on the anti-atherosclerotic effect of fish oil in diet-induced hypercholesterolemic rabbits was studied in male New Zealand white rabbits. The animals were randomly divided into six groups of 14 each according to the chow given them. Group I, control, rabbits were fed regular laboratory rabbit chow. In addition to the regular chow, Group II rabbits were fed a high (1%) cholesterol-enriched diet. Group III had the same diet as Group II plus 450 mg vitamin E/1000 g chow. Group IV also had the same diet as Group II plus 10% fish oil, but without vitamin E. Group V's diet contained 1% cholesterol, 10% fish oil, and 450 mg vitamin E/1000 g chow. Group VI had the same diet as Group V, but with 150 mg vitamin E/1000 g chow. At the end of a 6-week feeding, the ascending aorta from seven rabbits from each group was harvested for the analysis of prostanoid production, thiobarbituric acid reactive substances (TBARS), superoxide dismutase activity, and cholesterol and vitamin E levels; the same tissue from the other seven rabbits from each group was obtained for the delineation of atherosclerotic lesions by planimetry after the Sudan IV stain. The high cholesterol diet-treated rabbits had worse prostanoid synthesis and higher TBARS levels, which paralleled the severity of the atherosclerosis. Vitamin E or fish oil supplementation in a high cholesterol diet had beneficial prostanoid production, reduced aortic TBARS levels, and attenuated atherosclerotic lesions; these effects were potentiated when vitamin E and fish oil were combined together. The atherosclerotic lesion reduction in rabbits treated with high cholesterol plus fish oil and 450 mg vitamin E/1000 g chow reached statistical significance (P < 0.05) compared to high cholesterol and the same dose of vitamin E-treated rabbits. The rabbits treated with high cholesterol plus fish oil, but without vitamin E or with 150 mg vitamin E/1000 g chow showed an increased plasma creatine kinase activity at 4 (P < 0.01 and 0.05, respectively) and 6 (P < 0.001 and 0.01, respectively) week of feeding. These results suggest that vitamin E and/or fish oil attenuate atherosclerosis in high cholesterol-fed rabbits; vitamin E and fish oil potentiated the effect of each other. Furthermore, without sufficient vitamin E supplementation, rabbits treated with high cholesterol plus fish oil will show an elevation of plasma creatine kinase activity.

The effects of L-arginine on neointimal formation and vascular function following balloon injury in heritable hyperlipidaemic rabbits

OBJECTIVE

The aims of this study were to determine the morphological and functional consequences of balloon angioplasty of the left subclavian artery of Froxfield heritable hyperlipidaemic (FHHL) rabbits and the influence of oral L-arginine therapy on these changes.

METHODS

Sixteen-week-old FHHL rabbits were subjected to balloon injury of the left subclavian artery under halothane anaesthesia. Control rabbits (n = 7) were given free access to food and normal tap water. L-Arginine-treated rabbits were given L-arginine (5 g.l-1 in the drinking water for 2 days prior to angioplasty and then for either 2 weeks (n = 7) or 4 weeks (n = 7) after surgery. All rabbits were euthanised 28-30 days after surgery and blood and tissue removed for quantification of neointimal size and determination of endothelial function using isolated vessel tension studies. The ability of the endothelium to prevent platelet aggregation was determined by challenging a vessel ring with carbachol when incorporated into a whole blood sample in which platelet aggregation was induced with collagen.

RESULTS

Balloon injury in non-treated rabbits resulted in the development of marked intimal hyperplasia (18.8[3.6]% of the area within the internal elastic lamina) while endothelial function remained intact. Maximum responses to carbachol and calcimycin were, respectively, a 66.6[14.7]% and 46.9[12.9]% relaxation of 5HT-induced tone, compared to 58.0[3.2]% and 39.8[9.4]% in non-injured vessels. Maximum contractile responses to 5HT and KCl were unaffected by injury. L-Arginine therapy alone had no effect on the vasodilator function of the endothelium, but reduced the endothelium-dependent inhibition of platelet aggregation (68.4[7.8] vs 109[10]% of the maximum extent of platelet aggregation in non-treated and 2-week L-arginine-treated non-injured vessels, respectively). L-Arginine significantly reduced the extent of neointimal formation (7.2[3.9]% of the area within the IEL; P < 0.05 vs. non-treated group). However, L-arginine significantly attenuated the relaxant responses to both carbachol (26.5[10.4]% and 31.4[9.4]% for 2- and 4-week L-arginine groups) and calcimycin (38.7[15.4]% and 16.4[10.7]%) in the injured artery (P < 0.05 compared to non-treated controls).

CONCLUSIONS

L-Arginine reduces neointimal formation following balloon catheter injury in heritable hypercholesterolaemic rabbits, which is consistent with previous findings in normocholesterolaemic models. However, in the presence of hypercholesterolaemia, L-arginine has a detrimental effect on endothelial function following injury. This may be a consequence of the presence of lipids in the vascular wall on nitric oxide synthase activity.

Chronic estrogen replacement inhibits aortic intimal hyperplasia independent of serum lipids

The role of estrogens in providing atheroprotection has been well documented in both epidemiologic and experimental studies. This phenomenon has traditionally been attributed to the beneficial lipid-modifying effects of estrogens. Yet lipid alterations may not be the sole mechanism of estrogen-mediated cardiovascular protection. Previous studies have utilized models of either diet- or injury-induced atherosclerosis. As such, the interrelationship between estrogens, lipids, and atherosclerosis remains unclear. The purpose of this study was to determine the effect of ovariectomy with or without estrogen replacement on the development of aortic intimal hyperplasia. Although we acknowledge the influence of estrogens on the lipid profile, we hypothesized that estrogens are atheroprotective independent of changes in serum lipids. Twelve Warhill ewes (7-11 years old) were randomized to sham (2 sheep) operation, ovariectomy (OVx-5 sheep), or ovariectomy with 17 beta-estradiol replacement (OVxE-5 sheep). Serum cholesterol and triglyceride levels were measured at 0, 6, and 12 months. Necropsy was performed at 6 and 12 months with histologic morphometric analysis of the aortoiliac bifurcation. Ovariectomy resulted in intimal thickening in comparison to the sham (p < 0.0001) and hormone replacement group (p < 0.0001). Serum cholesterol and triglyceride levels were similar and normal (40-60 mg/dl) among all groups. Estradiol abrogates aortic intimal hyperplasia following ovariectomy independent of the hormone's effects on lipid metabolism.

Hypercholesterolemia in the rabbit induced by feeding graded amounts of low-level cholesterol. Methodological considerations regarding individual variability in response to dietary cholesterol and development of lesion type

While a number of studies have presented detailed examinations of lesion development in the cholesterol-fed rabbit, individual variability in response to cholesterol feeding and type of lesion produced relative to the degree of cholesterol exposure is not well defined. This study analyzed such critical parameters in an attempt to further characterize the model and establish a baseline for future testing of treatments targeted at limiting atherosclerosis. For these experiments, male New Zealand White rabbits were fed atherogenic diets consisting of 0.05%, 0.10%, 0.15%, 0.20%, or 0.25% cholesterol dissolved in 6% peanut oil for 31 to 32 weeks. Raising dietary cholesterol from 0.05% to 0.15% resulted in a less than twofold stepwise increase in total plasma cholesterol (TPC) exposure (area under plasma cholesterol versus time curve), whereas further increases in cholesterol intake resulted in an exponential four- to fivefold increase in TPC exposure. Regression analysis of TPC exposure with aortic sudanophilia demonstrated a threshold of approximately 5000 cholesterol weeks; below this limit lesions were minimal, and above this value the degree of plaque correlated with TPC exposure. Furthermore, a wide biological variability occurred among rabbits with respect to individual responsiveness to dietary cholesterol. In the aorta, various types of plaques, from fatty streaks to atheromatous lesions, were observed, depending on the degree of cholesterol intake. Diets consisting of < 0.15% cholesterol resulted in the development of fatty streak lesions, while transitional lesions and atheromatous plaques were mostly found with higher cholesterol feeding. Coronary artery atherosclerosis was present in > 50% of animals fed diets > or = 0.15% cholesterol. Despite the level of TPC exposure, coronary lesions in epicardial vessels were generally the fibrous type, whereas intramyocardial arteries demonstrated predominantly intimal foam cells. In conclusion, by adjusting dietary cholesterol intake and selecting rabbits with a similar responsiveness to cholesterol, the overall cholesterol exposure can be more closely controlled to minimize the inherent individual variability among animals in this model. The nature of the target lesion must also be carefully considered, because the efficacy of some treatments may depend on the type of atherosclerotic plaque.

Interleukin-2 receptor-specific fusion toxin inhibits barotrauma-induced arterial atherosclerosis

Immunocytochemical analyses of human plaques and experimental arterial lesions have implicated activated lymphocytes and monocytes in the pathogenesis of atherosclerosis, as demonstrated by the expression of interleukin-2 (IL-2) membrane receptors and major histocompatibility complex class II epitopes. The objective is to determine if targeting these cells with an IL-2 receptor-specific chimeric toxin, DAB486-IL-2, can inhibit experimental post-angioplasty vascular neointimal thickening. Twenty-two atherogenically modeled rabbits were treated in vivo with DAB486-IL-2 (0.1 mg/kg per day i.v.; n = 11) or placebo (n = 11) for 10 days following aortic balloon angioplasty (4 atm x 30 s each x 2 dilatations). In vitro 3H-leucine incorporation studies of mononuclear leukocyte and vascular smooth muscle cell protein synthesis inhibition by DAB486-IL-2 were also performed. Angioplasty sites were examined for evidence of hyperproliferative atherosclerotic narrowing by quantitative angiography and histomorphometry of neointimal cross-sectional area at baseline and 6 weeks after injury. In vitro Concanavalin-A stimulated rabbit mononuclear leukocyte protein synthesis was 50% inhibited by DAB486-IL-2 at a concentration (IC50) of 6 x 10(-11) M. Rabbit vascular smooth muscle cells were approximately 150-fold less sensitive to DAB486-IL-2 (IC50 = 10(-8) M). In vivo studies showed no change in angioplasty site angiographic minimum luminal diameter at 6 weeks in DAB486-IL-2 treated animals (from 2.96 +/- 0.52 to 2.96 +/- 0.48 mm; percent cross-sectional area reduction = 1 +/- 10%; P = N.S.). In control animals, luminal diameter decreased from 2.79 +/- 0.4 to 2.32 +/- 0.52 mm at 6 weeks, and percent cross-sectional area was reduced by 34 +/- 14% (P < 0.01 vs. placebo). Quantitative histomorphometric angioplasty segmental intimal cross-sectional area reduction of treated and placebo vessels also differed significantly (19 +/- 16% vs. 31 +/- 21%; P < 0.05). DAB486-IL-2 caused no adverse effects on animal survival, weight or hepatic transaminase levels. We conclude that post-angioplasty administration of the chimeric toxin DAB486-IL-2 inhibits angiographic narrowing and neointimal thickening in the atherogenic rabbit model. Although this IL-2 receptor-specific molecule was cytotoxic in vitro for activated mononuclear leukocytes and vascular smooth muscle cells, systemic toxicity did not occur in vivo at a dose comparable to that evaluated in clinical trials of this agent. Potential anti-proliferative effects of this chimeric toxin may be mediated by direct local inhibition of leukocyte-mediated inflammation, or through the indirect modification of vascular cell mitogenesis and cytokine release.

Causal relationship between occlusive lesions of the coronary artery and myocardial fibrosis in arteriosclerotic rabbits--differences between cholesterol-fed and heritable hyperlipidemic rabbits

To investigate the causal relationship between lesions of either the proximal large or the distal small coronary arteries and myocardial fibrosis, the hearts and the aortas of 99 cholesterol-fed rabbits with either intermittent or continuous hyperlipidemia for 8 months or more, 44 Watanabe-heritable hyperlipidemic (WHHL) rabbits and 20 normal rabbits were studied histologically. The size and location of the myocardial fibrosis correlated closely with the almost completely occlusive distal small coronary artery which mainly consisted of macrophages, necrosis and calcification but did not correlate with the maximum % stenosis of the large proximal subepicardial coronary arteries in the cholesterol-fed-rabbits. Myocardial fibrosis and almost completely occlusive lesions of the distal small coronary arteries were very rare in the WHHL rabbits, and the maximum % stenosis of the proximal coronary artery and aortic lesions in the WHHL rabbits tended to be greater than those in the cholesterol-fed rabbits. Thus, we are still not certain as to whether or not, the organic stenosis of the subepicardial coronary artery is responsible for myocardial fibrosis in WHHL-rabbits. In conclusion, a causal relationship was observed between myocardial fibrosis and the occlusive lesions of the distal small coronary arteries in cholesterol-fed rabbits, while the arteriosclerotic lesions of the small coronary artery in cholesterol-fed rabbits completely differed from those observed in WHHL-rabbit.

The questionable wisdom of a low-fat diet and cholesterol reduction

The prevalent wisdom that a low-fat diet and cholesterol reduction are essential to good cardiovascular health is coming under increased scrutiny. An examination of the foundations of this view suggests that in many respects it was ill-conceived from the outset and, with the accumulation of new evidence, it is becoming progressively less tenable. Cross-sectional, longitudinal and cross-cultural investigations have variously suggested that the relationship between dietary fat intake and death from heart disease is positive, negative and random. These data are incompatible with the view that dietary fat intake has any causal role in cardiovascular health. Although hypercholesterolemia is associated with increased liability to death from heart disease, it is as frequently associated with increased overall life expectancy as with decreased life expectancy. These findings are incompatible with labelling hypercholesterolemia an overall health hazard. Moreover, it is questionable if the cardiovascular liability associated with hypercholesterolemia is either causal or reversible. The complex relationships between diet, serum cholesterol, atherosclerosis and mortality and their interactions with genetic and environmental factors suggest that the effects of simple dietary prescriptions are unlikely to be predictable, let alone beneficial. These cautions are borne out by numerous studies which have shown that multifactorial primary intervention to lower cholesterol levels is as likely to increase death from cardiovascular causes as to decrease it. Importantly, the only significant overall effect of cholesterol-lowering intervention that has ever been shown is increased mortality. The stress and helplessness associated with misapprehensions as to the dangers of dietary fat and the asceticism inherent in the war on cholesterol have considerable implications for health practices. Recent research in behavioral immunology suggests that stress and helplessness are likely to compromise immunity and promote ill-health.

Enhancement of thrombotic arterial occlusion following cholesterol feeding in the guinea-pig: a role for thromboxane A2

We have developed a photochemical model to induce thrombotic occlusion of the guinea-pig femoral artery. Using this model, we investigated the effect of cholesterol feeding on arterial occlusion time in the guinea-pig. Animals were divided into two groups, one on standard diet and the other on standard diet containing 0.5% cholesterol for 3 weeks. The time for femoral artery occlusion was significantly shorter (p < 0.05) in cholesterol fed animals as compared to the control group. In vitro collagen-, U-46619- (a thromboxane A2 adenosine diphosphate analogue) and (ADP)-induced platelet aggregation responses in whole blood in cholesterol-fed animals were increased 13-, 10- and 4-fold, respectively. U-46619- and collagen-induced washed platelet aggregation responses were also significantly enhanced by cholesterol feeding (p < 0.01). Further, TXA2 generation by collagen-stimulated washed platelets in cholesterol-fed animals increased similar to the platelet aggregation responses. However, platelet-activating factor (PAF)-induced platelet aggregation in whole blood was relatively unaffected by cholesterol feeding. 11-dehydro TXB2 levels in plasma were increased significantly by cholesterol feeding. Our observations suggest that increased plasma TXA2 level and platelet aggregation response to TXA2 and stimulated TXA2 synthesis in platelets play a role in enhanced arterial occlusion in cholesterol fed guinea-pigs.

Effect of cholesterol-supplemented diet in heritable hyperlipidemic Yoshida rats: functional and morphological characterization of thoracic aorta

In this study we have considered the possibility of inducing vascular damage in Yoshida Pittsburg (YOS) rat, an inbred strain which has endogenous hyperlipidemia without vascular atherosclerotic damage. Cholesterol-enriched diet (4% cholesterol plus 1% cholic acid and 0.5% thiouracil) was administered to YOS rats, in order to induce atherogenesis. The results indicate that, despite significant increase in serum (about 2-fold) and aortic tissue cholesterol (about 6-fold), no morphological damage occurred. A reduction in acetylcholine-mediated relaxation (of about 37%) was observed. No inhibition of ATP- or sodium nitrite-induced relaxation, or of contraction induced by norepinephrine was seen. Serum triglyceride concentration did not vary after administration of a cholesterol-enriched diet. Our results suggest that in heritable hyperlipidemic Yoshida rat, after 2 months of cholesterol-enriched diet, despite increased serum cholesterol levels, no atheromatous plaque developed on the aortic wall. Impaired vascular function and reductions in the response to acetylcholine were related to changed endothelial cell function. Administration of a high cholesterol diet to YOS rat may represent a new model of mixed endogenous and exogenous hyperlipidemia that can resemble many human dislipidemic diseases and therefore may become a useful tool for the study of isolated endothelial dysfunction.

The quality of epidemiological data in coronary heart disease and atherosclerosis

There are inherent difficulties in the use of indirect observations in the epidemiology of a chronic ubiquitous disease such as atherosclerosis. Such difficulties do not condone basic errors in epidemiological methodology, the use of low quality data, a lack of precision in measurements, invalid extrapolations and inappropriate use of terminology and coronary heart disease as a surrogate or synonym of coronary atherosclerosis and bias in the interpretation of data. These errors reveal a lack of rigorous and scientific standards in the epidemiology of coronary heart disease. Analysis cannot launder such data. Independent scientists must evaluate the data in respect of precision, logic and truth.

Science, atherosclerosis and the "age of unreason": a review

Research in atherosclerosis has been dominated by the lipid hypothesis. The pathology of both the cholesterol-fed animal and of familial hypercholesterolemia has been misrepresented. The vascular lesions of these disorders are not atherosclerotic but manifestations of fat storage. There has been undue faith in the epidemiology of coronary heart disease and atherosclerosis. Fundamental defects in the epidemiological approach to the cause of atherosclerosis include: (1) misuse of cause and risk factors; (2) misuse of coronary heart disease as an imprecise and inappropriate surrogate endpoint in clinical and mortality studies; (3) use of fallacious monocausal death certificates and mortality rates; (4) assumed causal role of risk factors; (5) use of fallacious dietary data; (6) ecological fallacies; (7) nonspecificity of statistical correlations and selection bias; (8) failure to take note of inconsistencies; (9) inappropriate use of the blood cholesterol level as a surrogate of atherosclerosis (substitution game) without demonstration of any such effect on arteries; and (10) misplaced faith in pathological and experimental corroborative evidence. The epidemiology of atherosclerosis is based on unscientific methodology and the lipid hypothesis as currently envisaged is invalid. There is need to review the cholesterol-lowering campaign especially for normolipidemic subjects.

Ovarian sex steroids and atherosclerosis

Estrogens have been found to protect against atherosclerosis in a variety of animal models, and these antiatherogenic properties have been confirmed by epidemiological and clinical studies in women as well. Since the estrogen-induced changes of plasma lipid and lipoprotein levels do not fully account for the prevention of atherosclerosis, additional effects must be assumed. Experimental studies suggest various direct vascular actions. Estrogens enhance the endothelial degradation of low-density lipoprotein cholesterol, and preliminary data indicate antioxidative actions on low-density lipoprotein particles in macrophages. They suppress intimal proliferation and extracellular matrix production in the arterial wall and induce marked vasodilatation in systemic and coronary arteries. Adverse effects on hemostatic factors described with high doses and synthetic compounds are not evident during hormonal replacement in postmenopausal women, in whom an estradiol-induced inhibition of platelet aggregation may even have beneficial clinical effects. The role of progesterone and other progestogens in the progression of atherosclerosis is controversial. Despite a partial antagonism to estrogen-induced changes of plasma lipids, their addition to estrogens does not alter the anti-atherosclerotic properties, at least in animal experiments. The direct vascular actions of progestogens-although not as well documented-seem to be less pronounced than those of estrogens. The experimental data indicate that direct vascular effects play an important role in the antiatherogenic properties of ovarian sex steroids. However, the underlying cellular and molecular mechanisms remain largely unknown.

Experimental induction of atherosclerosis associated with femoral arteriovenous fistulae in rabbits on a stock diet

Chronic femoral arteriovenous fistulae were surgically produced in stock-fed rabbits. The aortic bifurcation and branching sites of the ilio-femoral arteries from each side were examined histologically by the serial section technique in rabbits killed at varying times from 121 to 800 days postoperatively. Similar preparations were examined from old multiparous breeding does and rabbits with a control femoral arteriotomy. Tears of the internal elastic lamina were prominent in the abdominal aorta and homolateral ilio-femoral arteries of those with fistulae but were only occasional and sporadic in contralateral arteries and control animals. Intimal proliferation at branching sites proximal to the fistula exhibited varying degrees of enlargement, extension and progression to overt atherosclerosis with lipid accumulation, fibrin deposition and calcification. Such changes were minimal proximally in contralateral vessels of a few rabbits and non-existent in control material. These results (i) constitute the first experimental induction of the progression of intimal proliferation to overt atherosclerosis at branching sites in stock-fed animals and (ii) substantiate the importance of haemodynamics in atherogenesis.

Effects of dietary supplementation with fish oil on atherosclerosis and myocardial injury during acute coronary occlusion-reperfusion in diet-induced hypercholesterolemic rabbits

We studied myocardial injury during acute coronary occlusion-reperfusion and atherosclerosis in rabbits fed a high cholesterol diet with or without fish oil supplementation. New Zealand white male rabbits were divided into 3 groups. Eight control rabbits fed with laboratory standard rabbit chow were group I. In addition to the standard chow, 15 rabbits fed with a 1% cholesterol-enriched diet for 6 weeks were group II, and 10 rabbits fed with a 1% cholesterol-enriched and 10% fish oil supplemented diet for 6 weeks were group III. Acute coronary occlusion was induced by ligating the marginal branch of the left circumflex coronary artery for 1 h, followed by reperfusion for 4 h. Myocardial injury was assessed by tissue creatine kinase activities and amino-nitrogen concentrations from the ischemic (infarct) and nonischemic (normal) myocardium, and the infarct area/risk area ratios of the left ventricle. The surface area of the atherosclerotic lesions of the aorta and pulmonary artery was measured by planimeter. There was significantly more myocardial loss of creatine kinase and amino-nitrogen in the cholesterol-fed rabbits than the controls (p less than 0.01 and 0.02, respectively). The cholesterol and fish oil-treated rabbits had a nonsignificant reduction in myocardial loss of both agents as compared to their corresponding cholesterol-fed ones. The same trend was also found in the infarct area/risk area ratio. Fish oil treated rabbits had a good effect on the reduction of atherosclerotic lesions and tissue cholesterol levels in the aorta and pulmonary artery, but not in the left ventricle.(ABSTRACT TRUNCATED AT 250 WORDS)