Cholesterol metabolism in serum and aorta of inbred mice fed a high-cholesterol diet

Biochemical evidence of atherosclerosis progression mediated by increased oxidative stress in apolipoprotein E-deficient spontaneously hyperlipidemic mice exposed to chronic cigarette smoke

Cigarette smoking is a major risk factor for cardiovascular disease. The induction of oxidative stress by smoking plays a key role in the progression of atherosclerosis. However, the underlying mechanisms are not fully understood. In the present study, we investigated whether long-term smoking can accelerate the progression of atherosclerosis and whether oxidative stress is implicated in its pathogenesis. Apolipoprotein E-deficient spontaneously hyperlipidemic mice, a model of atherosclerosis, were exposed to the gas-phase of smoke, from which tar and nicotine had been removed, for 15 min a day, 6 days a week, for 16 weeks. Exposure to cigarette smoke significantly increased the serum levels of oxidative stress markers such as thiobarbituric acid-reactive substances, oxidatively modified low-density lipoproteins, and 3-nitrotyrosine, but it did not affect serum cholesterol and triglyceride levels. Exposure to smoke also accelerated the accumulation of total cholesterol levels in the aorta that was accompanied by an increase in 3-nitrotyrosine levels of the atherosclerotic mice. These changes in the serum and aorta that progressed with exposure to smoke were prevented by vitamin E administration. Our data suggest that chronic cigarette smoking promotes and aggravates atherosclerosis and that the antioxidant vitamin E exerts an anti-atherogenic effect via reduction of oxidative stress.

Beneficial effect of coenzyme Q10 on increased oxidative and nitrative stress and inflammation and individual metabolic components developing in a rat model of metabolic syndrome

Metabolic syndrome (MetS) is a group of cardiovascular risk factors, including visceral obesity, glucose intolerance, hypertension, and dyslipidemia. Increased oxidative and nitrative stress and inflammation and decreased endothelial function occur in an animal model of metabolic syndrome, SHR/NDmcr-cp (SHR/cp) rats. The present study investigated the effects of coenzyme Q10 (CoQ10), one of the important antioxidants, on the abnormal oxidative condition and characteristic components of metabolic syndrome in SHR/cp rats by maintaining them on a diet supplemented with 0.07% - 0.7% CoQ10 for 26 weeks. We determined serum levels of oxidatively modified low-density lipoprotein (Ox-LDL) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) as oxidative stress markers, 3-nitrotyrosine as a nitrative stress marker, 3-chlorotyrosine as a marker of myeloperoxidase (MPO)-catalyzed oxidation and high-sensitivity C-reactive protein (hsCRP) as an inflammatory marker. The administration of CoQ10 significantly attenuated the increase of oxidative and nitrative stress markers and inflammatory markers in a dose-dependent manner. CoQ10 prevented the elevated serum insulin levels, although it did not affect the elevated glucose level and dyslipidemia. CoQ10 also reduced elevated blood pressure, but did not affect body weight gain. In addition, CoQ10 improved endothelial dysfunction in the mesenteric arteries. These findings suggest that the antioxidant properties of CoQ10 can be effective for ameliorating cardiovascular risk in MetS.

Elevated circulating levels of markers of oxidative-nitrative stress and inflammation in a genetic rat model of metabolic syndrome

Metabolic syndrome is a cluster of metabolic diseases that in essence greatly promotes progression of atherosclerosis. We used a genetic model of the metabolic syndrome, the SHR/NDmcr-cp (SHR/cp) rat, from 6 to 40 weeks of age to investigate whether systemic oxidative stress, a major cause of atherosclerosis, increases in this syndrome. Nine-week-old male rats already showed manifestations of metabolic syndrome, including heavier body weight, higher blood pressure and higher levels of serum glucose, insulin and various lipids compared to the age-matched Wistar Kyoto (WKY) rats used as a genetic control. These metabolic parameters gradually progressed with age. Likewise, the serum levels of oxidative stress markers, including lipid peroxides, which oxidatively modify low-density lipoprotein (LDL) and 8-hydroxydeoxyguanosine (8-OHdG), gradually increased in SHR/cp rats. The serum levels of 3-nitrotyrosine and 3-chlorotyrosine also persistently increased, indicating the involvement of peroxynitrite or myeloperoxidase-catalyzed oxidation. In addition, high-sensitivity C-reactive protein (hsCRP), an early marker of inflammation, temporarily increased in SHR/cp rats compared to WKY rats. These findings suggest that oxidative stress, as well as nitrative stress and inflammation, increases in the metabolic syndrome, which may contribute to the development of atherosclerosis.

Facilitated nitration and oxidation of LDL in cigarette smokers

BACKGROUND

Cigarette smoking increases the risk of developing atherosclerosis and ischaemic heart disease. Smoking-induced oxidative stress is considered to favour oxidation of low-density lipoprotein (LDL) and subsequently promotes the atherogenic process. We investigated whether peroxynitrite, a reaction product of cigarette smoke, is involved in facilitated oxidation of LDL in smokers.

MATERIALS AND METHODS

Plasma LDL was obtained from 10 healthy asymptomatic cigarette smokers and 10 healthy nonsmokers. The state of enhanced oxidative stress in the plasma was assessed by LDL subfraction assay using anion-exchange high-performance liquid chromatography (AE-HPLC) and measurements of thiobarbituric acid-reactive substances (TBARS), 8-hydroxydeoxyguanosine (8-OHdG), vitamin E, 3-nitrotyrosine and 3-chlorotyrosine.

RESULTS

Smokers showed a significantly higher level of TBARS and 8-OHdG as well as a significantly lower level of vitamin E than nonsmokers, even after stopping smoking for 10 h or more. The LDL subfraction assay demonstrated an increase in oxidatively modified LDL, as expressed by lower levels of LDL1 and higher levels of LDL2. The 3-nitrotyrosine levels in apolipoprotein B in LDL were significantly higher in smokers than nonsmokers, while the 3-chlorotyrosine levels remained unchanged. In addition, these changes observed in the smokers were further accelerated within 30 min after resumption of cigarette smoking when compared with the levels before smoking resumption.

CONCLUSION

The present study suggests that peroxynitrite plays a significant role in oxidative modification of plasma LDL induced by cigarette smoking.

Fluvastatin reduces modification of low-density lipoprotein in hyperlipidemic rabbit loaded with oxidative stress

The in vivo antioxidant effect of fluvastain, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, was investigated using Watanabe heritable hyperlipidemic (WHHL) rabbits subjected to nicotine-free cigarette smoke extracts as oxidative stress. Fluvastatin was given orally at doses of 10 and 30 mg/kg per day for 5 months. The cigarette smoke extracts were prepared by bubbling the gas phase of smoke into phosphate-buffered saline and was injected daily into the rabbit ear vein. The rabbits chronically treated with the cigarette smoke extracts showed an increase in plasma lipid peroxide levels, estimated as thiobarbituric acid-reactive substances. Oxidative modification of plasma low-density lipoprotein (LDL) was assessed by anion-exchange high-performance liquid chromatographic analysis, LDL susceptibility to oxidation, LDL incorporation into macrophages and thiobarbituric acid-reactive substances levels in LDL. Treatment with fluvastatin significantly reduced these effects induced by the cigarette smoke extracts in a dose-related manner and exerted a cholesterol-lowering effect. At the end of the experiment, the cigarette smoke extracts caused accumulation of cholesteryl ester in the thoracic aorta, while fluvastatin significantly prevented this accumulation. These results indicate that fluvastatin can exert an antioxidant effect in vivo, with a strong effect on oxidative stress such as smoking, a major risk factor of atherosclerosis.

Oxidants in cigarette smoke extract modify low-density lipoprotein in the plasma and facilitate atherogenesis in the aorta of Watanabe heritable hyperlipidemic rabbits

Epidemiological studies have shown that cigarette smoking is a major cause of atherosclerosis. Oxidants as well as nicotine in cigarette smoke have been implicated in atherogenesis. To clarify the mechanism involved, we examined the chronic effects of nicotine and nicotine-free cigarette smoke extracts (CSE) on oxidative modification of low-density lipoprotein (LDL) in the plasma of Watanabe heritable hyperlipidemic rabbits and atherogenesis in the aorta. CSE was prepared by bubbling the gas phase of smoke (1 ml/three cigarettes) into phosphate buffer saline, and 3 ml of this CSE was injected daily into the ear vein of the rabbit for five months. The rabbits treated with CSE showed an increase in lipid peroxide levels, estimated as thiobarbituric acid reactive substances (TBARS), with a corresponding decrease in vitamin E levels in the plasma. They also showed enhanced oxidative modification of LDL, assessed by anion-exchange HPLC, incorporation into macrophages and measurement of TBARS. These events could be efficiently prevented by administering vitamin E (150 mg/kg/day, p.o.). Nicotine alone (0.5 mg/kg/day, s.c.) led to a temporary increase in the plasma triglyceride level. At the end of the experiment, CSE but not nicotine had caused progression of atherosclerotic lesions together with accumulation of cholesteryl ester in the thoracic aorta, while vitamin E had significantly prevented such atheromatous formation. These results indicate that oxidants in CSE can promote the development of atherosclerosis through oxidative modification of plasma LDL, particularly in hypercholesterolemia, and offer evidence for increased vitamin E utilization in smokers.

Antioxidant activity of the extracts from fruiting bodies of cultured Cordyceps sinensis

Cordyceps sinensis is one of the most valued herbs in traditional Chinese medicine. We investigated the antioxidant activities of the cultured fruiting bodies of Cordyceps sinesis. The water and ethanol extracts of Cordyceps sinensis were found to possess a potent antioxidant activity. The scavenging effects of the extracts on superoxide were very weak, but the extracts moderately inhibited malondialdehyde formation via hydroxyl radical induced by SIN-1, a peroxynitrite generator. Of the extracts examined, the hot water extract (70 degrees C for 5 min) showed the greatest oxygen free radical scavenging activity. Also, when low-density lipoprotein (LDL) was incubated with macrophages in the presence of CuCl2 (1 microM), the hot water extract showed a strong inhibitory effect against lipid peroxidation in the medium and consequent accumulation of cholesteryl ester in macrophages. Their activities were comparable to that of authentic Cu/Zn SOD. These results suggest that the extracts of cultured Cordyceps sinensis possess potent antioxidant and anti-lipid peroxidation activities and inhibit accumulation of cholesteryl ester in macrophages via suppression of LDL oxidation.

Evidence of modified LDL in the plasma of hypercholesterolemic WHHL rabbits injected with aqueous extracts of cigarette smoke

Cigarette smoking is a major risk factor for atherosclerosis, and oxidative modification of low density lipoprotein (LDL) is a key event in the development of atherosclerosis. The aim of the present study was to determine whether modified LDL would be formed in the plasma of Watanabe heritable hyperlipidemic (WHHL) rabbits injected with nicotine-free cigarette smoke extracts (CSE). In order to assess this, cigarette smoke-modified LDL (CS-LDL) was prepared by incubation of rabbit native LDL (N-LDL) with CSE for 24 h. The oxidative modification in CS-LDL was well established by the reduced ratio between two LDL subfractions (LDL2/LDL3) separated by anion-exchange HPLC, together with the fast migration in the anodic direction in agarose gel electrophoresis and the increased lipid peroxide levels. Very similar modification was noted with mildly oxidatively modified LDL prepared by incubation of N-LDL with 5 µM CuCl(2) for 1 h. When WHHL rabbits (n=4) intravenously received a single injection of CSE, the ratio of LDL2/LDL3 was markedly reduced compared with the control rabbits (n=4) while total cholesterol levels in the plasma gradually decreased until 24 h after the injection. These results suggest that oxidatively modified LDL, probably like CS-LDL, is produced in the plasma of WHHL rabbits injected with CSE.

Altered endothelium-dependent responsiveness in the aortas and renal arteries of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of non-insulin-dependent diabetes mellitus

We examined endothelium-dependent relaxation in the aortas and renal arteries of Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of non-insulin-dependent diabetes mellitus, in comparison with non-diabetic Long-Evans Tokushima Otsuka rats as controls. Acetylcholine-induced relaxation in both arteries was attenuated, and the attenuation was restored to the control level by indomethacin. The relaxation was inhibited completely in the aortas, but only partially in renal arteries by N(G)-nitro-L-arginine methyl ester, and the degree of the latter inhibition was greater in OLETF rats than in the controls. The relaxation was inhibited by aminoguanidine in both arteries of OLETF rats but not in the controls. Serum NO(2) plus NO(3) levels significantly increased in OLETF rats. These results suggest that impairment of relaxation in OLETF rat arteries is due to increased release of contractile factors but not decreased release of nitric oxide.

Excessive salt or cholesterol intake alters the balance among endothelium-derived factors released from renal arteries in spontaneously hypertensive rats

We investigated the vasorelaxation in renal arteries isolated from spontaneously hypertensive rats (SHRs) fed a basal, a high-salt, or a high-cholesterol diet for 8 weeks. In renal arterial rings from the control group, acetylcholine (ACh)-induced endothelium-dependent relaxations were markedly increased by indomethacin (IND) and ONO-3708, a prostaglandin H2/thromboxane A2-receptor antagonist, but not affected by OKY-046, a thromboxane A2 synthetase inhibitor. These increased relaxations were partially inhibited by either NG-nitro-L-arginine methyl ester (L-NAME) or charybdotoxin (CTX), and almost completely abolished by the combination of L-NAME plus CTX. The ACh-induced endothelium-dependent relaxations in the absence of IND were significantly attenuated by the high-salt intake but not affected by the high-cholesterol intake. The degrees of relaxations in the presence of IND were approximately equal among the three diet groups. On the other hand, the relaxations in the presence of IND plus L-NAME were significantly augmented by a high-cholesterol intake and abolished by a high-salt intake, and the relaxations in the presence of IND plus CTX were slightly reduced by a high-cholesterol intake and significantly augmented by a high-salt intake. The production of cyclic guanosine monophosphate (cGMP) in response to ACh was significantly decreased by a high-cholesterol intake and tended to be increased by a high-salt intake. These findings indicate that in the renal artery of SHRs, ACh causes production of a sufficient amount of nitric oxide (NO), together with a relaxing factor resembling endothelium-derived hyperpolarizing factors (EDHFs) and also endothelium-derived contracting factors (EDCFs), probably prostaglandin H2. Our results also suggest that excessive salt intake increases the release of EDCF and NO and decreases that of an EDHF-like factor, whereas excessive cholesterol intake increases release of an EDHF-like factor and decreases that of NO.

High-performance liquid chromatographic assay of hydroperoxide levels in oxidatively modified lipoproteins

An anion-exchange HPLC method has been developed for the chemiluminescence (CL) assay of hydroperoxide (HPO) levels in native and oxidized low density lipoproteins (N- and Ox-LDLs, respectively) of Watanabe heritable hyperlipidemic (WHHL) rabbits. The method involves anion-exchange HPLC separation in N- and Ox-LDLs using a DEAE-glucomannan gel, and direct CL detection of HPOs in them without extraction of the lipids following postcolumn reaction with isoluminol, microperoxidase and Triton X-100. Addition of Triton X-100, which could solubilize lipids, were essential for the detection of HPOs in N- and Ox-LDLs. With an increase in the degree of oxidation, Ox-LDL was more retained on the DEAE-glucomannan gel with a concomitant increase in the CL intensity. The proposed method could analyze the HPO levels in N- and Ox-LDLs of WHHL rabbits without extraction of the lipids.

Anion-exchange high-performance liquid chromatographic assay of plasma lipoproteins of rabbits, rats and mice

A fast, accurate and precise high-performance liquid chromatographic assay method has been developed for plasma lipoproteins of experimental animals, rabbits, rats and mice. The method includes complete separation of high, low and very low density lipoproteins from one another within 20 min by a DEAE-glucomannan gel using stepwise elution, and determination by postcolumn reaction with an enzymatic cholesterol reagent as the total cholesterol level. The relative standard deviation of each lipoprotein assay was highly reproducible, being less than 2.0 and 2.4% for repeatability and intermediate precision, respectively. The method was successfully applied to the assays of plasma lipoproteins in three species of normolipidemic and hyperlipidemic animals.

Evidence of modified lipoprotein in the plasma of Watanabe heritable hyperlipidemic rabbits by anion-exchange high-performance liquid chromatographic assay

We searched for evidence for the presence of oxidatively modified low density lipoproteins (Ox-LDL) in the plasma of Watanabe heritable hyperlipidemic (WHHL) rabbits using an anion-exchange high-performance liquid chromatographic (HPLC) method newly developed for the assay of artificially modified lipoproteins. Various Ox-LDLs were prepared by incubation of native LDL (N-LDL) from rabbit plasma with 5 microM CuCl2 for 0, 1, 3 and 24 h, and separated by anion-exchange HPLC method using a DEAE-glucomannan gel column. With an increase in the incubation time, LDL was further oxidized and retained on the DEAE-glucomannan gel. This oxidized LDL migrated faster in the anodic direction in agarose gel electrophoresis, accompanied by an increase in lipid peroxide levels, estimated as thiobarbituric acid reactive substances (TBARS). There was a good agreement in the chromatographic and electrophoretic behaviors of the various Ox-LDLs. LDL from WHHL rabbits showed increases in TBARS levels, electrophoretic mobility on agarose gel electrophoresis and cholesteryl ester accumulation in mouse peritoneal macrophages compared to that from normolipidemic Japanese white (JW) rabbits. When LDLs from both animals were compared by the anion-exchange HPLC method using linear gradient or stepwise elution, LDL from WHHL rabbits had a longer retention time and was eluted by a higher concentration of sodium chloride. These results suggest that LDL in WHHL rabbit plasma may undergo mild oxidative modification.

Mechanisms of impairment of endothelium-dependent relaxation to acetylcholine in Watanabe heritable hyperlipidaemic rabbit aortas

1. The mechanism of impairment of the endothelium-dependent relaxation in response to acetylcholine (ACh) in aortas from Watanabe heritable hyperlipidaemic (WHHL) rabbits was investigated using a modified sandwich (layered) technique. Intact aortas from WHHL rabbits or Japanese white (JW) rabbits as the control were used as donor strips of endothelium-derived relaxing factor (EDRF) and endothelium-denuded aortas from JW rabbits were used as detector strips. The EDRF released from a donor strip could be directly detected as the relaxation response in a detector strip. 2. The endothelium-dependent relaxations in all rabbit arteries were almost abolished by treatment with N(G)-nitro-L-arginine methyl ester (an inhibitor of nitric oxide synthase). 3. The ACh-induced endothelium-dependent relaxations in the donor strips were impaired in WHHL rabbits in comparison with relaxations in JW and heterozygous WHHL rabbits. Similarly, the relaxation in the detector strips induced by EDRF released from donor strips was reduced in WHHL rabbits. There was a good negative correlation between the aortic total cholesterol content in the donor strips and the degree of relaxation in the detector strips from WHHL rabbits. 4. The reduced relaxation in the detector strips when using donor strips with high cholesterol accumulation or atheromatous plaque was not affected by superoxide dismutase plus catalase (scavengers of superoxide anions), indomethacin (an inhibitor of cyclo-oxygenase), ONO-3708 (an antagonist of endoperoxide/thromboxane receptor) and 97-139 (an antagonist of endothelin ET(A) receptor). 5. These results suggest that the mechanism of impaired endothelium-dependent relaxations in atherosclerotic WHHL rabbit aortas may be due to the reduced amount of EDRF, probably nitric oxide, from the endothelium and not due to its inactivation by oxygen-derived free radicals or masking by increased production of endothelium-derived contracting factors.

Possible mechanism for the anti-atherosclerotic action of the calcium channel blocker AE0047 in cholesterol-fed rabbits

1. The present study was designed to investigate the anti-atherosclerotic effect of AE0047, a calcium channel blocker, and to compare it with that of nilvadipine in cholesterol-fed rabbits. Furthermore, the effects of AE0047 on low-density lipoprotein (LDL) oxidation were studied in vitro. 2. A 7 week treatment period with AE0047 (3 and 10 mg/kg, p.o.) led to a dose-dependent reduction in the lipid deposition area by Oil Red-O staining (surface index) without affecting serum lipid levels. There was no reduction in the surface index following treatment with the same dose of nilvadipine (10 mg/kg). 3. In a vehicle-administered high-fat diet group of rabbits, levels of total cholesterol (TC) and esterified cholesterol (EC) and calcium content in the aorta were increased approximately two- to three-fold over those of the normal diet group. Increased levels of TC and EC and calcium content were reduced to the same levels as the normal diet group by AE0047 treatment, whereas nilvadipine did not affect TC and EC levels. 4. In an in vitro study, AE0047 (10 micromol/L) inhibited LDL oxidation and the aggregation of apolipoprotein (Apo) B-100 induced by Cu2+. Furthermore, AE0047 inhibited the degradation of oxidized LDL by macrophages. In contrast, the same dose of nilvadipine (10 micromol/L) did not inhibit either LDL oxidation or the aggregation of ApoB-100. 5. In summary, AE0047 inhibited LDL oxidation, resulting in a decrease of its uptake into macrophages and an inhibition of cholesterol esterification. This leads to an anti-atherosclerotic effect of AE0047. Thus, AE0047 may have therapeutic potential in preventing cardiovascular disease in hypertensive patients.

Dietary cholesterol enhances impaired endothelium-dependent relaxations in aortas of salt-induced hypertensive Dahl rats

We investigated the effect of hypercholesterolemia on the vascular reactivity of thoracic aortas isolated from hypertensive Dahl salt-sensitive (DS) rats. DS rats were fed on a low-sodium diet (control group), a low-sodium plus high-cholesterol diet (CHOL group), a high-sodium diet (NaCl group) or a high-sodium plus high-cholesterol diet (NaCl + CHOL group) for 8 weeks. Hypercholesterolemia developed in the CHOL and NaCl + CHOL groups, while hypertension developed in the NaCl and NaCl + CHOL groups, with these changes being greatest in the NaCl + CHOL group. Aortic cholesteryl ester accumulation was attenuated in the aortic rings from the NaCl and NaCl + CHOL groups, compared to the control group. The degree of attenuation in the NaCl + CHOL group was significantly greater than that in the NaCl group. Endothelium-dependent relaxations induced by the calcium ionophore A23187 were attenuated only in the NaCl + CHOL group. Endothelium-independent relaxations in response to sodium nitroprusside were slightly but significantly attenuated in the NaCl + CHOL group. The relaxations in the CHOL group were comparable to those in the control group. These findings indicate that cholesterol feeding strikingly enhances the impaired endothelium-dependent relaxations and the slightly impaired endothelium-independent relaxations in the aorta of DS rats with salt-induced hypertension, parallel to the development of hypertension, hypercholesterolemia and cholesterol deposition.

Different cholesterol deposition in aorta of Dahl salt-sensitive rats and spontaneously hypertensive rats fed a high-cholesterol diet

1. We compared the serum and aortic lipid levels in spontaneously hypertensive rats (SHR) and Dahl salt-sensitive rats (DSR) fed a high-cholesterol (HC) diet. 2. In SHR fed the HC diet, the serum cholesterol level significantly increased, but no aortic cholesterol deposition was observed. 3. The serum cholesterol level in DSR fed the HC diet markedly increased compared to that in DSR fed the basal diet, and this change was greater with the diet containing 8% NaCl than 0.4% NaCl. A significant increase in the content of aortic cholesterol, notably cholesteryl ester, was observed in only DSR fed the HC diet containing 8% NaCl. 4. These results suggest that the combination of hypercholesterolaemia with salt-induced hypertension acts as a greater risk factor for atherosclerosis than that with genetic hypertension.

Comparison of the effects of hypercholesterolaemia on relaxation responses in aortas of spontaneously hypertensive rats and Dahl salt-sensitive rats

1. We investigated the effects of hypercholesterolaemia on relaxation responses in thoracic aortas isolated from two different types of hypertensive rats; spontaneously hypertensive rats (SHR) and Dahl salt-sensitive rats (DSR). 2. All rats fed the high cholesterol diet for 8 weeks showed a significant increase in the serum cholesterol level. The high cholesterol diet did not change the blood pressure of SHR, but increased that of hypertensive DSR fed a high-salt diet. 3. In aortas of SHR, the high-cholesterol diet did not change the endothelium-dependent and -independent relaxation induced by acetylcholine (ACh) and sodium nitroprusside (SNP), respectively. 4. In aortas of hypertensive DSR, the high-cholesterol diet notably reduced the ACh-induced relaxations and slightly reduced SNP-induced relaxation. 5. These results suggest that hypercholesterolaemia causes greater impairment of endothelium-dependent relaxation in rat aorta with salt-induced hypertension than genetic hypertension.

Differences in endothelium-dependent relaxation in various arteries from Watanabe heritable hyperlipidaemic rabbits with increasing age

1. Endothelium-dependent relaxation in response to acetylcholine (ACh) and the calcium ionophore A23187 was examined in aorta, coronary, basilar and renal arteries isolated from Watanabe heritable hyperlipidaemic (WHHL) rabbits of 2, 6 and 12 months of age, with normolipidaemic heterozygous WHHL rabbits as controls. 2. In the rings of WHHL rabbit aortae and coronary arteries preconstricted with vasoconstrictors, endothelium-dependent relaxation in response to ACh was attenuated with age compared to the heterozygous WHHL rabbits. A significant negative correlation was found between the total cholesterol content and the relaxation response to ACh in the aortae or coronary arteries from 6 and 12 month old WHHL rabbits. 3. In the rings of basilar arteries, endothelium-dependent relaxations to ACh were not modified with age. Similarly, in the rings of renal arteries, the relaxation response to ACh was not changed with age, but in the 6 and 12 month preparations, after the age of 6 months, a contraction following the relaxation appeared at higher concentrations of ACh (10(-7) to 10(-6) mol/L). The contraction was endothelium-dependent and inhibited by indomethacin. 4. A23187-induced endothelium-dependent relaxations were also markedly attenuated in the aorta and significantly in the coronary artery with age. 5. Endothelium-independent relaxation to sodium nitroprusside was not changed in all arteries from WHHL rabbits of different ages. 6. These findings indicate that in the aorta and coronary artery of the WHHL rabbit, the endothelium-dependent relaxation to ACh and A23187 becomes impaired with increasing age (i.e., with the progression of cholesterol deposition in the arterial wall) but is preserved in the basilar and renal artery.

Enhancement of aortic cholesterol deposition by dietary linoleic acid in cholesterol-fed mice: an animal model for primary screening of antiatherosclerotic agents

We tried to develop an experimental model using mice for the primary screening of antiatherosclerotic agents. Male ICR strain mice were given a high-cholesterol diet supplemented with 10% linoleic acid for 14 weeks. Throughout the experimental period, weight gain of these mice was significantly inhibited as compared to that of control mice given a basal diet, but displayed a steady increase comparable to that of the high-cholesterol diet without linoleic acid. The cholesterol and linoleic acid-fed mice showed increased serum cholesterol and phospholipid levels, and decreased serum triglyceride and high-density lipoprotein-(HDL) cholesterol levels and lecithin/cholesterol acyltransferase (LCAT) activity, as well as a markedly increased lipid peroxide level which was a characteristic appearance in the serum of this mouse model. At the end of the experiment, uniform and significant increases in cholesterol, notably cholesteryl ester, were observed in the aorta. Also found were marked decreases in the aorta contents of desmosine and isodesmosine, which are cross-linking amino acids present only in the elastin. Histological observations showed accumulations of fatty droplets in the intima. These changes were much less in mice receiving a high-cholesterol diet without linoleic acid. In this mouse model, probucol prevented elevation of serum cholesterol, phospholipid, and cholesterol accumulation in the aorta. Increases in lipid peroxide level and decreases in LCAT activity were also prevented. These findings indicate that this mouse model is useful for primary screening of antiatherosclerotic agents with antioxidative activity.

Effects of the new anti-ulcer drug ecabet sodium (TA-2711) on pepsin activity. II. Interaction with substrate protein

To define the mechanism of the protection by ecabet (TA-2711) of the gastric mucosa from peptic attack, the characteristics of protein binding of this drug and its effect on peptic hydrolysis of substrate proteins were investigated in vitro. Both the binding to proteins and the hydrophobicity of ecabet were dependent on the pH; the lower the pH, the higher both parameters. The percentage of ecabet bound to proteins was nearly constant, being independent of the drug concentration at pH's below 2, indicating that this drug is bound to proteins in a non-specific manner. The activity of peptic hydrolysis of bovine serum albumin (BSA) decreased in the presence of ecabet, and this was not due to the interaction between pepsin and ecabet judging from the kinetic studies. The apparent Km values of peptic hydrolysis of BSA increased depending on the quantity of ecabet bound to BSA. These results suggest that ecabet is bound to substrate proteins by a non-specific hydrophobic interaction to form a complex that is less vulnerable to peptic hydrolysis.

Effects of the new anti-ulcer drug ecabet sodium (TA-2711) on pepsin activity. I. Inactivation of enzyme protein

To investigate the mechanism of the anti-peptic action of ecabet sodium (TA-2711) observed in pylorous-ligated rats, effects of this drug on the peptic activity of rat gastric juice, purified hog pepsin and pepsinogen were studied in vitro. After incubation with or without ecabet at acidic pH, the reaction mixture was centrifuged, and the peptic activity of the supernatant was measured. Ecabet depressed the peptic activity of pepsin and pepsinogen in parallel with a decrease in the protein concentration of the respective supernatant. Depression was greatest with pepsinogen (97% at 2.5 mg/ml of the drug) followed by gastric juice (about 60% at 10 mg/ml), and inhibition of the peptic activity of pepsin was weakest (about 10% at 10 mg/ml). When a fraction of the rat gastric juice containing substances with molecular weights below 10,000 was added to the pepsin solution, the anti-peptic activity of ecabet was potentiated. These results suggest that oral dosing of ecabet reduces the peptic activity of gastric juice by precipitating pepsin, which is facilitated by an unknown component(s) of gastric juice, and that the inactivation of pepsinogen may also contribute to the anti-peptic activity of ecabet.

Atherosclerosis mouse model induced by a high-cholesterol diet supplemented with beta-aminopropionitrile: effects of various anti-atherosclerotic agents on the biochemical parameters

A mouse model of atherosclerosis was produced by feeding a 1.5% cholesterol diet with 0.4% beta-aminopropionitrile (BAPN) fumarate, a chemical lathyrogen, for 10 weeks, and the pharmacological sensitivity and specificity of this model were evaluated biochemically with various hypolipidemic drugs and calcium antagonists. Histological findings on this model showed typical angiolathyrism with foam cells in the media of the thoracic aorta. Uniform and marked accumulation of cholesterol, notably esterified cholesterol, in the aorta was observed, although it was much less in mice receiving a high-cholesterol diet or BAPN alone. The reduction in elastin contents in the aorta was a characteristic feature of this model. Clofibrate, cetaben and elastase tended to prevent the increase of cholesterol contents in the aorta, together with their significant hypocholesterolemic effects. Nifedipine, diltiazem and verapamil showed a slight preventive effect on the cholesterol accumulation and on the reduction of elastin content in the aorta without a cholesterol lowering effect in the serum. MgCl2 was more effective than other calcium antagonists and even had a hypocholesterolemic effect. The results indicate that this mouse atherosclerosis model may be usable for primary drug evaluation.

High-performance liquid chromatographic determination of desmosine and isodesmosine in tissues and its application to studies of alteration of elastin induced by atherosclerosis

A rapid, sensitive high-performance liquid chromatographic method has been developed for the determination of desmosine (DES) and isodesmosine (IDE), the specific cross-linking amino acids of elastin, in the tissue hydrolysates of rats. DES and IDE in the hydrolysate samples were separated on a C18 column using 0.1 M phosphate buffer-acetonitrile (2.8:1) containing 20 mM sodium dodecyl sulphate (final pH 4.5) followed by detection at 270 nm. The recoveries of the added standards of DES and IDE from the aorta hydrolysate samples were 99.6 +/- 2.7% and 98.4 +/- 1.8%, respectively (n = 10). At DES and IDE concentrations of 2 micrograms/ml, within- and between-run precisions were 1.11-1.85% and 0.55-1.24%, respectively. The detection limits of DES and IDE were 0.1 microgram/ml with a 50-microliter injection at a signal-to-noise ratio of 3. The method was successfully applied to a study of the alteration of DES and IDE contents (i.e. elstin contents) in the tissues of rats treated with beta-aminopropionitrile and an atherogenic diet. A negative correlation between the contents of these amino acids and of cholesterol was noted in the atherosclerotic aorta.

Suppression of adjuvant arthritis in rats by cholesterol

Dietary cholesterol suppressed adjuvant arthritis, a chronic inflammatory disease, in rats, but did not significantly affect carrageenin edema, an acute inflammation. When rats were fed a high-cholesterol diet beginning 10 days before injection of adjuvant, the development of the adjuvant-induced arthritis was greatly suppressed. Cholesterol feeding prevented hypertrophy of the adrenal gland in arthritic rats, but had little influence on the serum corticosterone level. A significant positive correlation was observed between the adrenal weight and the severity of the arthritis. These findings suggest that the effect of cholesterol feeding is not due to increased adrenal sterol synthesis. Dietary cholesterol also prevented hypertrophy of the spleen, but had no effect on atrophy of the thymus in adjuvant-treated rats. Cholesterol-fed rats showed a significant decrease in the serum lipid peroxide level and a significant increase in the serum copper level. Adjuvant treatment not only enhanced hypercholesterolemia produced by cholesterol feeding, but also the level of free cholesterol in serum. These results suggest that dietary cholesterol may exert some effect on the immune response through changes in spleen and liver functions.

Lipid deposition in the aorta of adjuvant arthritic rats with hypercholesterolemia

This study offers findings which should aid in the development of a convenient animal model of atherosclerosis. Inbred Fisher strain rats were fed an atherogenic diet containing 1.5% cholesterol and 0.5% cholic acid and given a single subcutaneous injection of adjuvant (Mycobacterium butyricum) into the base of the tail. The animals were maintained for 8 weeks. Rats given the atherogenic diet showed markedly increased serum cholesterol levels, and all of those given the adjuvant injection developed severe polyarthritis. Cholesterol feeding tended to delay the onset of arthritis and remarkably suppressed the inflammatory response, particularly in the early stage of development. This may have been due to the lowered lipid peroxide levels in the serum of rats fed the atherogenic diet. Adjuvant arthritis together with cholesterol feeding markedly increased the cholesterol content of the aorta, whereas either treatment alone had little effect. The amounts of the connective tissue components and minerals in the aorta were not changed by both treatments. These results show that early atherosclerosis could be produced under the conditions used and that chronic inflammation and hypercholesterolemia are principal factors in the pathogenesis.

Hyperlipidemic effects of adriamycin in rats

Adriamycin, an anticancer drug, caused dramatic increases in the serum lipid levels of rats fed a high-cholesterol diet. Male Lewis inbred rats were fed a basal or 1.5% cholesterol diet containing 0.5% cholic acid for 8 weeks. The rats were injected with adriamycin in doses of 1.5 mg/kg body weight, twice a week, and 6.0 mg/kg body weight, every other week. The serum lipid peroxide level gradually rose in adriamycin-treated rats, reaching a four-fold level at the end of the experiment. Cholesterol feeding, however, had a lowering effect on the lipid peroxide level. Adriamycin treatment or cholesterol feeding moderately elevated serum lipid levels, but their combination exerted a synergistic effect. In rats injected with a large dose of adriamycin and fed a high-cholesterol diet, the serum cholesterol, triglyceride and phospholipid levels strikingly increased by approx. 2000, 1500 and 1300 mg/100 ml, respectively. However, the ester ratio of cholesterol remained almost constant. Furthermore, serum GOT, GPT and ALP activities were only slightly different from the control values. Adriamycin treatment produced severe hypoalbuminemia. Ascites was also observed in rats given a large dose of adriamycin. The present findings indicate that the hyperlipidemia we observed may basically result from adriamycin-induced nephrosis and can be markedly enhanced when rats are fed a high-cholesterol diet. In spite of remarkably high levels of serum lipids and lipid peroxides, the aortic cholesterol level increased only slightly.