Serum lipids in spontaneously hypertensive rats and Sprague-Dawley rats fed menhaden oil

Butyrate regulates inflammatory cytokine expression without affecting oxidative respiration in primary astrocytes from spontaneously hypertensive rats

Neurons and glia exhibit metabolic imbalances in hypertensive animal models, and loss of metabolic homeostasis can lead to neuroinflammation and oxidative stress. The objective of this study was to determine the effects of the microbial metabolite butyrate on mitochondrial bioenergetics and inflammatory markers in mixed brainstem and hypothalamic primary cultures of astrocytes between normotensive (Sprague-Dawley, S-D) and spontaneously hypertensive (SHR) rats. Bioenergetics of mitochondria in astrocytes from normotensive S-D rats were modified with butyrate, but this was not the case in astrocytes derived from SHR, suggesting aberrant mitochondrial function. Transcripts related to oxidative stress, butyrate transporters, butyrate metabolism, and neuroinflammation were quantified in astrocyte cultures treated with butyrate at 0, 200, 600, and 1000 μmol/L. Butyrate decreased catalase and monocarboxylate transporter 1 mRNA in astrocytes of S-D rats but not in the SHR. Moreover, while butyrate did not directly regulate the expression of 3-hydroxybutyrate dehydrogenase 1 and 2 in astrocytes of either strain, the expression levels for these transcripts in untreated cultures were lower in the SHR compared to S-D. We observed higher levels of specific inflammatory cytokines in astrocytes of SHR, and treatment with butyrate decreased expression of Ccl2 and Tlr4 in SHR astrocytes only. Conversely, butyrate treatment increased expression of tumor necrosis factor in astrocytes from SHR but not from the S-D rats. This study improves our understanding of the role of microbial metabolites in regulating astrocyte function, and provides support that butyrate differentially regulates both the bioenergetics and transcripts related to neuroinflammation in astrocytes from SHR versus S-D rats.

Beneficial effects of simulated gastro-intestinal digests of fried egg and its fractions on blood pressure, plasma lipids and oxidative stress in spontaneously hypertensive rats

Background

We have previously characterized several antihypertensive peptides in simulated digests of cooked eggs and showed blood pressure lowering property of fried whole egg digest. However, the long-term effects of this hydrolysate and its fractions on blood pressure are not known. Therefore, the objectives of the study were to determine the effects of long term administration of fried whole egg hydrolysate and its fractions (i.e. egg white and egg yolk) on regulation of blood pressure and associated factors in cardiovascular disease such as plasma lipid profile and tissue oxidative stress.

Methods and Results

We used spontaneously hypertensive rats (SHR), an animal model of essential hypertension. Hydrolysates of fried egg and its fractions were prepared by simulated gastro-intestinal digestion with pepsin and pancreatin. 16–17 week old male SHRs were orally administered fried whole egg hydrolysate, non-hydrolyzed fried whole egg, egg white hydrolysate or egg yolk hydrolysates (either defatted, or not) daily for 18 days. Blood pressure (BP) and heart rate were monitored by telemetry. Animals were sacrificed at the end of the treatment for vascular function studies and evaluating plasma lipid profile and tissue oxidative stress. BP was reduced by feeding fried whole egg hydrolysate but not by the non-hydrolyzed product suggesting a critical role for in vitro digestion in releasing anti-hypertensive peptides. Egg white hydrolysate and defatted egg yolk hydrolysate (but not egg yolk hydrolysate) also had similar effects. Reduction in BP was accompanied by the restoration of nitric oxide (NO) dependent vasorelaxation and reduction of plasma angiotensin II. Fried whole egg hydrolysate also reduced plasma levels of triglyceride although it was increased by the non-hydrolyzed sample. Additionally the hydrolyzed preparations attenuated tissue oxidative stress.

Conclusion

Our results demonstrate that fried egg hydrolysates exert anti-hypertensive effects, improve plasma lipid profile and attenuate tissue oxidative stress in vivo.

Desaturation and esterification of fatty acids in kidney cells from spontaneously hypertensive rats

In previous studies, several alterations in lipid metabolism have been related to hypertension, but the mechanisms explaining this relationship have not been elucidated. None of the previous works has focused on the lipid metabolism in kidney, which is a key organ in the overall regulation of blood pressure. The aim of the present work was to study the metabolism of polyunsaturated fatty acids, and the possible compositional changes in kidney from hypertensive rats. Radiolabelled linoleic acid (18:2,n-6) and dihomogammalinolenic acid (20:3, n-6) were incubated with isolated kidney cells from spontaneously hypertensive rats (SHR) or the parent normotensive strain (Wistar Kyoto, WKY). The rats were divided into groups of age 9 (young) and 17 (adult) weeks. Cellular uptake, desaturation, chain-elongation, oxidation and distribution into phospholipids and triacylglycerols were measured. Additionally, the lipid composition of kidney was characterized. With each of the labelled fatty acid substrates the uptake in cells from the SHR rats, compared to the WKY rats, was numerically lower in the young group and higher in the adult group. The incorporation of labelled fatty acids into phospholipids was increased and concomitantly decreased in triacylglycerols in cells from adult SHR rats. The delta6-desaturation, measured as the conversion of labelled 18:2(n-6) to 18:3(n-6) was between two and three times increased in cells from the adult rats compared to the young ones, while no difference was found in hypertensives compared to normotensives. Concomitantly, no difference in conversion of labelled 20:3(n-6) to 20:4(n-6) was observed in relation to blood pressure, but, different from delta6-desaturation, the delta5-desaturation was significantly decreased by age. Taken together, this study demonstrates for the first time desaturation of long-chain polyunsaturated fatty acids in isolated kidney cells in suspension and that, contrary to what has been observed in liver, the desaturase activity is unaffected by hypertension. Also different from what has been observed in liver, no blood-pressure-related changes in lipid composition of kidney were found.

Blood pressure-lowering effect of fish oil is independent of thromboxane A2 level in spontaneously hypertensive rats

Whether the alterations in the synthesis of thromboxane A2 (TXA2) is the direct mechanism underlying the blood pressure-lowering effect of fish oil was investigated in this study. Six groups of 11 male spontaneously hypertensive rats were fed semipurified diets containing corn or fish oils and graded levels (50, 5000 or 15,000 ppm) of dietary vitamin E for 8 weeks. Plasma TXA2, assayed by RIA, was significantly greater in the corn oil group than in the fish oil group (P < 0.05). Compared to 50 ppm dietary vitamin E, 5000 and 15 000 ppm dietary vitamin E, respectively, significantly decreased plasma TXA2 (P < 0.05). Systolic, mean or diastolic blood pressure, evaluated by the tail cuff method, were significantly higher in the corn oil group than in the fish oil group (P < 0.05). However, vitamin E had no effect on blood pressure. No relationship between TXA2 and blood pressure was found. Experimental results indicated that the alterations in the synthesis of TXA2 were not the direct antihypertensive effect of fish oil.

Fish oils modulate blood pressure and vascular contractility in the rat and vascular contractility in the primate

The effect of dietary fish oils on development of hypertension and vascular response in vitro were studied in rats and a primate. Dietary fish oils (MaxEPA and an n-3 ethyl ester concentrate of higher EPA and DHA content) were administered to spontaneously hypertensive (SHR), stroke-prone spontaneously hypertensive (SHR-SP) and a backcross of SHR and Wistar Kyoto (SHR/WKY) rats from 4-16 weeks of age. Blood pressure was monitored during the feeding period and vascular responses measured in the aorta and mesenteric vascular bed in vitro. Depending on the strain of rat used and the composition of the fish oil the attenuation in blood pressure was 10-26 mmHg. Fish oils attenuated the response mediated by sympathetic nerve stimulation or intralumenal norepinephrine in the perfused mesenteric vascular bed preparation from the SHR. This attenuation was more pronounced for fish oils enriched with eicosapentaenoic acid and docosahexaenoic acid and was more prominent in the SHR and SHR/WKY backcross than it was in the SHR-SP. Prostanoid synthesis or nitric oxide modulation of alpha-adrenoceptor responses were shown not to be involved in the attenuation of vascular responses produced by fish oil. The maximum contraction of aortic ring preparations in response to norepinephrine (NE) was significantly smaller in SHR than WKY rats fed olive oil and for SHR rats maintained on fish oils the contraction was close to WKY olive oil values. Evidence was obtained also for a modulation of vasoconstrictor responses by dietary fish oils in the perfused mesenteric bed of the marmoset monkey.

High fish oil diet increases oxidative stress potential in mammary gland of spontaneously hypertensive rats

1. The purpose of this study was to determine whether high omega-3 (19% menhaden oil, 1% corn oil) or high omega-6 (20% corn oil) fatty acid diets would decrease expression of hypertension in the female spontaneously hypertensive rat (SHR), promote tumourigenesis in the rat 7,12-dimethylbenz[a]anthracene (DMBA) model of mammary cancer or increase the susceptibility of the mammary gland to lipid peroxidation. A group of rats on a 5% corn oil diet served as the low fat control group. 2. We found that the high omega-3 and high omega-6 fatty acid diets did not significantly decrease mean arterial pressure. Marked differences occurred between the effects of omega-3 and omega-6 high fatty acid diets on baseline oxidation, auto-oxidation and iron-ascorbate catalyzed oxidation. The omega-3 diet showed 675% increase in basal oxidation, a 2624% increase in auto-oxidation and a 4244% increase in iron-ascorbate catalyzed oxidation compared to the omega-6 diet in mammary tissue homogenates. Although all rats were given 5 mg DMBA (i.g.), no mammary tumours were observed in any of the dietary groups. 3. We conclude that: (i) high polyunsaturated fatty acid diets do not decrease blood pressure in the female SHR; (ii) high fish oil diet markedly increases oxidative potential in the mammary gland; and (iii) the female SHR is resistant to DMBA-induced tumourigenesis.

Dietary fish oil administration retards blood pressure development and influences vascular properties in the spontaneously hypertensive rat (SHR) but not in the stroke prone-spontaneously hypertensive rat (SHR-SP)

In the present study, we compared the blood pressure in the SHR-SP and in the spontaneously hypertensive rat (SHR) after dietary administration of fish oil from 4 to 17 weeks of age. The retarding influence of dietary fish oils on the development of hypertension was prominent in the SHR (26 mmHg) and not evident in the SHR-SP (8 mmHg). The enhanced development of blood pressure in both the SHR and the SHR-SP is characterised by an elevated maximum contraction in the mesenteric vascular bed to sympathetic nerve stimulation and to injected noradrenaline. In SHR, but not SHR-SP, this maximum contraction was significantly attenuated by dietary fish oil. Likewise, acetylcholine mediated relaxation of the isolated aorta was enhanced in preparations from the SHR but not the SHR-SP. These physiological changes were also associated with a change in the total n-3 polyunsaturated fatty acids (PUFAs) content in vascular tissue, which were inversely proportional to the prevailing blood pressure values seen in all three strains of rat receiving dietary fish oils. Platelet activated thromboxane production was equally depressed in WKY (Wistar Kyoto), SHR and SHR-SP rats. The results indicate that the blood pressure lowering effect of fish oil when administered during the period of development of hypertension is much greater in the SHR than it is in the SHR-SP. Furthermore the lowering of blood pressure by fish oil administration is related to a restoration of normal vascular contraction and normal vascular relaxation, but not related to a suppression of serum thromboxane production.

The effects of tannic acid on serum and liver lipids of RAIF and RICO rats fed on high fat diet

1. Male genetically hypercholesterolemic (RICO) and normocholesterolemic (RAIF) rats were divided into four groups and each group was fed one of the following diets for 10 weeks: a standard diet (STD); STD supplemented with tannic acid (STD + T); a high fat diet (HFD) and a high fat diet with tannic acid (HFD + T). 2. The RAIF and RICO rats when fed on HFD + T showed beneficial changes in serum lipids compared to the rats fed HFD. The lipid parameters between the groups fed STD and STD + T in both strains were unchanged. 3. The possible modes of hypocholesterolemic action of tannic acid in these rats is discussed.

Influence of dietary fatty acid composition on cholesterol synthesis and esterification in hamsters

To investigate the effects of dietary fat quality on synthesis and esterification of cholesterol, Syrian hamsters were fed diets containing corn, olive, coconut or menhaden oils (10% w/w) with added cholesterol (0.1% w/w). After 3 weeks, animals were sacrificed 90 min following IP injection of 3H2O. Synthesis of free cholesterol and movement of free cholesterol into ester pools were measured from 3H-uptake rate in liver and duodenum. Plasma total cholesterol and triglycerides levels were highest in coconut oil-fed animals, whereas hepatic total cholesterol and ester levels were elevated in olive oil-fed animals, as compared with all other groups. No diet-related differences were seen in duodenal cholesterol or total fatty acid content. In duodenum, uptake of 3H per g tissue into cholesterol was greater compared with liver; however, within each tissue, 3H-uptake into cholesterol was similar across groups. Notably, 3H-uptake into cholesterol ester in liver was highest in menhaden oil-fed animals. These data suggest that menhaden fish oil consumption results in enhanced movement of newly synthesized cholesterol into ester as compared with other fat types.

Effect of metoprolol on plasma lipids and arterial intimal lipid deposition in spontaneously hypertensive rats

The purpose of the present study was to characterize possible effects of dietary-induced plasma lipid elevations on the development of arterial lesions in spontaneously hypertensive rats (SHR) and to reveal any influence of treatment with metoprolol on these parameters. Metoprolol treatment caused an 8% decrease in heart rate and a 13% decrease in blood pressure and led to a rise in plasma triglycerides, 24%, 17% and 34% after 1, 3 and 6 months of metoprolol treatment, respectively. However, no effect on plasma triglycerides was observed after 9 months of metoprolol treatment while a reduced cholesterolemic response was observed. Intimal proliferations containing accumulations of lipids were observed in small intramural branches of coronary arteries (greater than 100 microns) in 11 of 31 control rats fed the atherogenic diet for 9 months. In contrast, similar changes were observed in only 1 of 34 metoprolol-treated rats fed an otherwise identical diet. The corresponding figures for the frequency of lipid containing intimal plaques in aorta were 6/19 in controls and 2/24 in the metoprolol-treated group.