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1.
Absorption of dietary cholesterol oxidation products and incorporation into rat lymph chylomicrons 总被引:1,自引:0,他引:1
Cholesterol oxidation products (oxysterols) induce macrophage lipid loading and accumulate in early arterial fatty streaks.
The origin of lesion oxysterols has not been elucidated. The absorption of oxysterols from the diet and transport to the arterial
wall by postprandial lipoprotein remnants may be a significant source. This study aimed to investigated the extent of oxysterol
absorption and the effect on chylomicron composition. Cholesterol was heat-treated, causing 30% oxidation; the major oxidation
products were 7β-hydroxycholesterol, 7-ketocholesterol, 5α,6α-epoxycholesterol, and 5β,6β-epoxycholesterol. Conscious lymph-cannulated
rats were given a bolus gastric infusion of 50 mg oxidized cholesterol or 50 mg purified cholesterol in a vehicle of triglyceride.
In the rats given the oxidized cholesterol, 6% of the oxysterol load was absorbed and incorporated into lymph chylomicrons.
Rats given pure cholesterol had no increase in oxysterols above baseline levels. The incorporation of oxysterols into lymph
chylomicrons differed over time with 7β-hydroxycholesterol, having peak absorption at 3 h, followed by 7-ketocholesterol at
4 h and 5α,6α-epoxycholesterol at 5 h. The absorption of oxysterols in animals given the oxidized cholesterol gastric infusate
was associated with lymph chylomicron compositional changes at 2–4 h. The oxidized cholesterol-treated group has a twofold
increase in the cholesterol (890±84 μg vs. 440±83 μg at 3 h) and triglyceride content (19.76±3.4 μg vs. 8.49±3.8 μg at 3 h).
This led to a doubling of chylomicron size over this postprandial period, with particles having a mean diameter of 294 nm
in the oxidized cholesterol-treated animals, compared to 179 nm in the purified cholesterol group. In conclusion, dietary
oxysterols appear to influence postprandial lipoprotein particle size and composition. These changes may have effects on the
clearance of chylomicrons from plasma, arterial delivery of oxysterols, and possible deposition in arterial lesions. 相似文献
2.
Kyoichi Osada Amir Ravandi Arnis Kuksis 《Journal of the American Oil Chemists' Society》1999,76(7):863-871
Extensive evidence of the deleterious biological effects of oxidized 5-cholesten-3β-ol (cholesterol) derivatives has led to
great interest in their detection. We observed that known oxidized cholesterol derivatives can be rapidly quantitated by combining
reversed-phase high-performance liquid chromatography (HPLC) with ultraviolet (UV) absorption and evaporative laser light-scattering
(ELSD) detection. Using a 20 × 0.46 cm C18 HPLC column and methanol/acetonitrile (60:40, vol/vol) as the mobile phase at 1.0
mL/min, 10 species of oxidized cholesterol derivative were measured by UV (205, 234, and 280 nm) while 5-cholestan-5α,6α-epoxy-3β-ol
(5α-epoxycholesterol), 5-cholestan-5β,6β-epoxy-3β-ol (5β-epoxycholesterol), and 5-cholestan-3β,5α,6β-triol (cholestanetriol)
were detected by only ELSD. The minimal limits of detection ranged from 100 to 500 ng depending on sterol and detector. The
response was linear in the range 0–1000 or 0–2000 ng depending on detector. These oxidized cholesterol derivatives were also
identified by HPLC/mass spectrometry analysis combined with UV detector. Heated tallow contained cholestanetriol, 5-cholesten-3β,7α-diol
(7α-hydroxycholesterol), 5-cholesten-3β,7β-diol (7β-hydroxycholesterol), 5-cholesten-3β-ol-7-one (7-ketocholesterol), 5α-
and 5β-epoxycholesterols under the developed analysis condition. Photooxidized cholesterol had cholestanetriol, 7α- and 7β-hydroxycholesterols
and 3,5-cholestadien-7-one. On the other hand, 7α- and 7β-hydroxycholesterols, 7-ketocholesterol, 5α- and 5β-epoxycholesterols
and 3,5-cholestadien-7-one were observed in copper-oxidized low-density lipoprotein. Thus, this developed HPLC analysis method
could be applied to identification of oxidized cholesterol derivatives in food and biological specimen. 相似文献
3.
Cholesterol oxidation in lard containing two levels of added cholesterol was monitored using capillary gaschromatography.
Loss of cholesterol and formation of cholesterol oxidation products (COPs) were measured. Lard samples with 10 times (Test
I) and 2 times (Test II) the amount of cholesterol originally found in each batch of lard were heated at 180°C for 10 hr a
day for 240 and 160 hr, respectively. Cholesterol steadily decreased throughout the heating period in both tests. Cholesterol
loss followed a first-order reaction rate, with a rate constant (k) of −1.18×10−3 h−1 for Test I and −9.45×10−3 h−1 for Test II. The COPs accumulated during both heating tests. But the amount of COPs formed did not total the amount of cholesterol
lost. During heating, thermal degradation of cholesterol likely occurred, and those products were not detected. During cooling,
hydroperoxides formed, which further oxidized into the COPs that were detected. The 7-ketocholesterol and 5α,6α-epoxycholesterol
were the predominant COPs formed. The isomeric 7α-and 7β-hydroxycholesterols also accumulated in the heating tests. The 3β,5α,6β-cholestantriol
was found in very small amounts and the 25-hydroxycholesterol was not detected.
Presented in part at the 80th AOCS Annual Meeting, Cincinnati, OH, in May, 1989. 相似文献
4.
Parameters influencing cholesterol oxidation 总被引:3,自引:3,他引:0
The purpose of this study was to investigate the effects of temperature, oxidation time, presence of water, pH, type of buffer
and form of substrate used on cholesterol oxidation. Microcrystalline cholesterol films, both solid and melted, and aqueous
suspensions of film fragments were used as substrates. Use of dispersing agents was avoided. Quantitative analysis of the
unaltered substrate and the products of its autoxidation was carried out by gas chromatography over the course of oxidation.
Solid cholesterol films were found to be resistant to autoxidation in the dry state. However, when heated at 125°C, a sudden
increase in oxidation rate occurred at a point coinciding with the visible melting followed by a plateau of the oxidation
rate. All of the autoxidation products formed underwent further decomposition. Film fragments of cholesterol oxidized at a
faster rate in aqueous suspensions than when oxidized in the dry state. In aqueous suspensions, the differences in the resistance
of cholesterol to oxidation were not significant within the pH range 6.0–7.4, except for the early stages of oxidation. The
7-ketocholesterol/7-hydroxycholesterol ratio dropped significantly with increasing pH. However, at all pH levels tested, this
ratio remained relatively constant during the 6 h of heating. While the 7β-hydroxycholesterol/7α-hydroxycholesterol ratio
was not affected by pH in the range of 6.0–7.4, at pH 7.4 a high preference was observed for the cholesterol β-epoxide over
its α-isomer. The β/α-epoxide ratio decreased with time of heating and with decreasing pH. The data show that the physical
state of the substrate exerts a major influence on the oxidative behavior of cholesterol. 相似文献
5.
A fast, sensitive, high performance liquid chromatographic method was developed for the quantitation of cholesterol and four
of its major oxidation products: 3β-hydroxycholest-5-en-7-one (7-ketocholesterol), cholest-5-ene-3β, 7α-diol (7α-hydroxycholesterol),
cholest-5-ene-3β,7β-diol (7β-hydroxycholesterol), and cholest-5-ene-3β,25-diol (25-hydroxycholesterol). In this procedure
2∶1 chloroform:methanol (v/v) extracts of tissue homogenate were combined, dried over anhydrous Na2SO4, filtered, evaporated to dryness under N2 and dissolved with a mobile phase of either 97∶3 or 93∶7 hexane:isopropanol (v/v). After membrane filtration and without
further purification, aliquots were directly injected onto a 10-μm pore size, 30×0.39 cm μ-Porasil normal phase column. The
separation of cholesterol and its oxidation products was monitored by a UV detector at 206 and 233 nm. This method was successfully
applied to pork muscle as well as mouse liver tissues and was able to detect cholesterol oxidation products (COP) in the ppm
range. The identity of the COP was confirmed by mass spectroscopy. 相似文献
6.
Oxysterols in cultured bovine aortic smooth muscle cells and in the monocyte-like cell line U937 were analyzed by gas-liquid
chromatography. The following products were detected: 7α- and 7β-hydroxycholesterol, 7-ketocholesterol, cholesterol-α-epoxide,
cholesterol-β-epoxide, cholestanetriol, and 20- and 25-hydroxycholesterol. The proportions of oxidized cholesterol varied
from 1 to 3% of total cholesterol. The concentrations of oxysterols were lower when the smooth muscle cells were maintained
in a vitamin E-enriched medium, and were higher in U937 cells when the cells were activated with phorbol myristate acetate.
The cell oxysterol content appears to be regulated by factors that inhibit or enhanced free radical generation. The concentrations
of oxysterols found in cells may serve as an indicator of the extent of lipid peroxidation. 相似文献
7.
The preparation of cholesterol and radiocholesterol oxidation products on a microscale is difficult. Cholesterol generally
resists oxidation unless it is well dispersed under controlled conditions. A method was developed to reliably produce 7α-
and 7β-hydroxycholesterol and 7-ketocholesterol. Small changes in pH, metal ions present, or in the colloidal dispersion,
resulted in production of completely different oxysterols. Attempts to oxidize aged radiocholesterol were not successful even
after purification by several thin-layer chromatographic steps, and this appeared to be due to a time-related change in the
radioactive material. Fresh radiocholesterol oxidized readily. 相似文献
8.
The plasma levels of free oxysterols (7-ketocholesterol: 7α-hydroxy-, 7β-hydroxy-, 25-hydroxy-, and 27-hydroxycholesterol;
and 5α,6α-epoxycholestanol) in patients with diabetes mellitus and hypercholesterolemia were determined using gas chromatography-mass
spectrometry with selective ion monitoring. We studied 39 patients with diabetes mellitus, 20 nondiabetic patients with hypercholesterolemia,
and 37 normal controls. Plasma cholesterol levels in diabetic and hypercholesterolemic patients showed no statistical difference.
Plasma 7-ketocholesterol was significantly higher in patients with diabetes (31.6±2.8 ng/mL) or hypercholesterolemia (52.3±5.9)
than in the control group (22.4±1.2). The increased plasma cholesterol can be regarded as an oxidation substrate for the oxidant
stress and the higher absolute levels of oxysterols in hypercholesterolemic plasma compared with the control plasma. This
difference disappeared when 7-ketocholesterol was expressed in proportion to total cholesterol. The oxidizability of plasma
cholesterol was evaluated by comparing the increased ratio of 7-ketocholesterol after CuSO4 oxidation to the ratio before. We demonstrated that the patients with diabetes showed increased oxidizability (77.5%) compared
with the control (36.6%) or hyperlipemic group (45.3%), which is likely due to the lower amounts of α-tocopherol in the diabetics.
Measurement of oxysterols may serve as a marker for in vivo oxidized lipoproteins in diabetes and hyperlipemia. 相似文献
9.
Cholesterol and seven of its oxidation products in aqueous suspensions of multilamellar vesicles or sonicated aqueous suspensions
were subjected individually to γ-radiation (10 KGy) at 0–4°C in air, N2 or N2O. All compounds underwent some changes under the influence of radiation. β-Epoxide (cholesterol 5β,6β-epoxide) and, to a
much lesser extent, α-epoxide (cholesterol 5α,6α-epoxide) were converted in low yield to 6-ketocholestanol (5α-cholestan-3β-ol-6-one).
7β-Hydroxycholesterol (cholest-5-ene-3β,7β-diol) and, to a lesser extent, 7α-hydroxycholesterol (cholest-5-ene-3β,7α-diol)
gave low yields of 7-ketocholestanol (5α-cholestan-3β-ol-7-one). The latter compound also was obtained by irradiation of 7-ketocholesterol
(cholest-5-ene-3β-ol-7-one). 6-Ketocholestanol and 7-ketocholestanol are potential biomarkers for irradiated meat and poultry. 相似文献
10.
Naoyuki Matoba Syoji Kuroki Bertram I. Cohen Erwin H. Mosbach Charles K. McSherry 《Lipids》1988,23(5):465-468
The effect of 7-methyl substituted bile acid and bile alcohol analogues on cholesterol metabolism was studied in the hamster.
Animals were fed chow plus 0.1% cholesterol supplemented with 0.1% of one of the following steroids: chenodeoxycholic acid,
7-methyl-chenodeoxy-cholic acid, 7β-methyl-24-nor-5β-cholestane-3α,7α,25-triol, cholic acid, 7-methyl-cholic acid, or 7β-methyl-24-nor-5β-cholestane-3α,7α,12α,25-tetrol.
Cholesterol absorption was determined from fecal analysis after feeding of radiolabeled cholesterol and β-sitosterol.
Of the six compounds studied, chenodeoxycholic acid and 7-methyl-chenodeoxycholic acid decreased intestinal cholesterol absorption
(17% and 31% decrease, respectively). Only 7-methyl-chenodeoxycholic acid decreased serum cholesterol concentration (29% decrease),
but there were no analogous changes of liver and biliary cholesterol concentration and cholesterol saturation of bile. Total
fecal neutral sterol excretion was increased in the groups fed chenodeoxycholic acid and 7-methyl-chenodeoxycholic acid. In
addition, the production of coprostanol was increased in both groups. These data suggest that 7-methyl-chenodeoxycholic acid
resembles chenodeoxycholic acid in its effect on cholesterol metabolism and may be a potential candidate for further studies
of its gallstone-dissolving properties. 相似文献
11.
Cholestyramine increases activities of hepatic cholesterol 7α-hydroxylase and serum levels of 7α-hydroxycholesterol. To examine
if serum 7α-hydroxycholesterol levels parallel with enzyme activity, 0, 0.5, 1, 2, 4, and 10% of cholestyramine was administered
to female golden Syrian hamsters for 28 d in the dose-dependent study, and 2% cholestyramine for 0, 1, 3, 7, 14, 21, and 28
d in the time-dependent study. In the dose-dependent study, hepatic and serum cholesterol levels were significantly decreased
dose-dependently when more than 0.5% of cholestyramine was fed for 28 d. Cholestyramine increased the cholesterol 7α-hydroxylase
activity in a dose-dependent manner, while the serum 7α-hydroxycholesterol level was essentially unchanged. No correlation
was found between the serum level and the hepatic enzyme activity. In the time-dependent study, hepatic and serum cholesterol
levels markedly decreased when 2% cholestyramine was fed for longer than 3 d. The serum triglyceride level increased significantly
for the first 7 d and then decreased. Cholesterol 7α-hydroxylase activity increased significantly as early as day 1, reached
maximum activity level on day 7, and then kept the significantly high values until day 28. The serum 7α-hydroxycholesterol
level significantly increased for the first 7 d and decreased to the pretreatment level thereafter. 7α-Hydroxycholesterol
levels significantly correlated with serum cholesterol and triglyceride levels. We conclude that the serum 7α-hydroxycholesterol
level does not always reflect the activity of hepatic cholesterol 7α-hydroxylase, when cholesterol metabolism is severely
disturbed by cholestyramine. 相似文献
12.
The effects of 5 μg/ml of 25-hydroxycholesterol; cholestane-3β, 5α,6β-triol; and cholesterol on acyl CoA cholesterol acyltransferase,
acid cholesteryl ester hydrolase and neutral cholesteryl ester hydrolase was studied in cultured rabbit aortic smooth muscle
cells. After 1 hour incubation, 25-hydroxycholesterol resulted in a fourfold stimulation of acyl CoA cholesterol acyltrans-ferase
activity. No stimulation by 25-hydroxycholesterol was noted before 15 minutes or after 5 hours of incubation. Neither cholestane-3β,5α,6β-triol
nor cholesterol influenced acyl CoA cholesterol acyltransferase activity at any time interval. No significant effects of any
of the sterols were noted on acid cholesteryl ester hydrolase or neutral cholesteryl ester hydrolase activity. The imbalance
between acyl CoA cholesterol acyl trans-ferase and hydrolase activities induced by 25-hydroxycholesterol could result in cholesteryl
ester accumulation by arterial smooth muscle cells, which may be associated with atherosclerosis. 相似文献
13.
A method to detect 7-ketocholesterol, cholesterol-5β,6β-epoxide, cholesterol-5α,6α-epoxide, 4-cholesten-3-one, 4,6-cholestadien-3-one
and 4-cholestene-3,6-dione in unirradiated and irradiated beef, pork and veal was developed by use of chloroform-methanol-water
extraction, solid-phase extraction, column separation, thin-layer chromatography and gas chromatography. This method recovered
78–88% of the cholesterol oxidation products and detected the cholesterol oxidation products at 10 ppb or higher. Irradiation
of the meats to a dose of 10 kGy increased these compounds, except 4,6-cholestadien-3-one for all three types of meat, over
unirradiated, and except cholesterol-5α,6α-epoxide and 4-cholesten-3-one for the pork. All the cholesterol oxidation products
in the unirradiated meats increased during storage at 0–4°C for 2 wk with some exceptions for the pork. The increases of cholesterol
oxidation products in stored irradiated meats were greater than those in the unirradiated. 相似文献
14.
Cholesterol and α-tocopherol oxidations were studied in brain subcellular fractions isolated from cerebral hemispheres of
4-month-old, male Fischer 344 rats. The fractions were suspended in buffered media (pH 7.4, 37°C) and oxidized by adding (i)
ferrous iron (Fe2+) with or without ascorbate or (ii) peroxynitrite (an endogenous oxidant produced by the reaction of superoxide and nitric
oxide). Treatment of subcellular fractions with Fe2+ in the presence or absence of ascorbate produced primarily 7-keto- and 7-hydroxy-cholesterols and small amounts of 5α,6α-epoxycholesterol.
Since brain contains high levels of ascorbate, any release of iron could result in oxysterol formation. Peroxynitrite oxidized
α-tocopherol but not cholesterol. Hence, the toxicity of peroxynitrite or nitric oxide could not be due to cytotoxic oxysterols.
When synaptosomes were incubated for 5 min in the presence of 0.5 to 2 μM Fe2+ and ascorbate, α-tocopherol was oxidized while cholesterol remained unchanged. Thus, α-tocopherol is functioning as an antioxidant,
protecting cholesterol. Diethylenetriaminepentaacetic acid blocked production of oxysterols, whereas citrate, ADP and EDTA
dit not. A significant percentage of mitochondrial cholesterol was oxidized by treatment with Fe2+ and ascorbate. Hence, mitochondrial membrane properties dependent on cholesterol could be particularly susceptible to oxidation.
The oxysterols formed were retained within the membranes of synaptosomes and mitochondria. The 7-oxysterols produced are known
to be inhibitors of membrane enzymes and also can modify membrane permeability. Hence, oxysterols may play an important role
in brain tissue damage during oxidative stress. 相似文献
15.
Lipid peroxidation has gained renewed attention with increasing evidence showing its biological role in producing toxic compounds
and cellular signaling mediators. The assessment of lipid peroxidation levels in vivo is difficult partly because lipids are
oxidized by different oxidants by different mechanisms to give versatile types of products, which may undergo metabolism and
secondary reactions. In the present study, total hydroxyoctadecadienoic acids (tHODE) and 7α- and 7β-hydroxycholesterol (t7-OHCh)
from 44 healthy human subjects were assessed as biomarkers after reduction with sodium borohydride followed by saponification
with potassium hydroxide comparing with the prevailing standard 8-isoprostaglandin F2α (t8-iso-PGF2α). The average concentrations of tHODE, total 8-isoprostaglandin F2α (t8-iso-PGF2α), t7α-OHCh, and t7β-OHCh were 203, 0.727, 87.1, and 156 nmol/l plasma and 1,917, 12.8, 1,372, and 3,854 nmol/l packed erythrocytes,
respectively. The ratios of tHODE and t7-OHCh to the parent substrates were 194 and 3,519 μmol tHODE/mol linoleates and 40.9
and 686 μmol t7-OHCh/mol cholesterol in plasma and erythrocytes, respectively. It was found that (1) t7-OHCh in blood was
unexpectedly high, as high as or even higher than tHODE, (2) the amounts of tHODE was more than 100 fold higher than t8-iso-PGF2α (3) the level of lipid oxidation products in erythrocytes was higher than that in plasma, and (4) lipid peroxidation products
level tended to increase while antioxidant level decrease with age. These products may be used as potential biomarker for
assessment of lipid peroxidation and oxidative stress in vivo. 相似文献
16.
A sensitive and specific method is described for quantifying various cholesterol oxidation products in foodstuffs, including
7β-hydroxycholesterol, cholesterol-α-epoxide, cholestane-triol, 7-ketocholesterol and 25-hydroxycholesterol. A chloroform-methanol
extract of the food was fractionated over two successive silica columns. Two fractions containing different classes of oxysterols
were then analyzed as trimethylsilyl derivatives by capillary gas liquid chromatography, using on-column injection and a temperature
gradient from 70 to 200°C. The detection limit was about 0.5 μg/g dry weight for egg yolk powder. Fresh egg yolk contained
only 1.2 μg/g of total oxides per g dry weight, showing that artifactual oxidation during the procedure was minimal. Recovery
of 5 pure oxysterols added to egg yolk at levels of 6.5 and 10 μg/g was between 93 and 102%. In commercial egg yolk and whole
egg powder stored for one year, total amounts of oxysterols ranging from 21 to 137 μg/g dry weight were found. In duplicates
of mixed Dutch diets, total amounts ranged from 3.6 to 6.2 μg/g dry weight. Duplicates containing mostly fried and baked foods
did not have higher levels than duplicates in which foods had been prepared by boiling or left raw. We conclude that a normal
mixed diet provides only minor amounts of cholesterol oxidation products. 相似文献
17.
Jaffar Nourooz-Zadeh Lars-Åke Appelqvist 《Journal of the American Oil Chemists' Society》1989,66(4):586-592
Lard samples, manufactured from adipose tissue, were found to contain traces and/or quantifiable concentrations of certain
cholesterol oxides, viz., 5α-, 6α-epoxycholestanol, 7-ketocholesterol, 7α-hydroxycholesterol, 20α-hydroxycholesterol and 25-hydroxycholesterol at the detection limit 0.1 ppm. The influence of steam refining and chemical
refining on the cholesterol oxide levels in a few of the crude lard samples was investigated. The analyses showed that these
processes had no appreciable effect on the concentrations of cholesterol oxides, compared with the controls. Analysis of cold-stored
consumer packages of lard (2-mo old up to 18-mo old samples) indicated that there were no differences in the pattern of cholesterol
oxides. On the other hand, storage of refined superior and regular grade lard samples at 50°C for up to 18 days caused only
a slight increase in the levels of the isomeric 5,6-epoxycholestanols. Raw bacon, bacon fried at 170°C for 10 and 20 min and
bacon dripping were analyzed. The analyses showed that quantifiable levels of 5α-,6α-epoxycholestanol, C-7 oxidation derivatives of cholesterol and 25-hydroxycholesterol could be detected only in the fried
rind. A substantial amount (about 0.5 ppm) of a cholesterol metabolite was detected in the lard samples. Its identification
as 7α-hydroxycholest-4-en-3-one was based on the comparison of RRT value and mass spectral information, as TMS-ether, to that of
synthetic 7α-hydroxycholest-4-en-3-one. 相似文献
18.
Leif Aringer 《Lipids》1980,15(8):563-571
The formation of dioxygenated metabolites of cholesterol, epicholesterol (5-cholesten-3α-ol) 4-cholesten-3β-ol, 4-cholesten-3α-ol,
4-cholesten-3-one and 4-stigmasten-3-one was studied after incubations with soybean lipoxygenase and linoleic acid. From cholesterol
and epicholesterol were formed the 7α-hydroxy-, 7α-hydroperoxy-, 7β-hydroxy-, 7β-hydroperoxy-, 7-oxo and 5,6-epoxyderivatives
as well as 6β-hydroxy-4-cholesten-3-one. All Δ4-steroids were hydroxylated in the 6α- and 6β-positions. The ratios between the yields of 6β- and 6α-hydroxylated metabolites
varied between 3∶1 and 2∶1. Incubations with 4-cholesten-3α-ol and 4-cholesten-3β-ol also afforded the 4,5-epoxides of these
steroids. The ratios between the yields of the 4β,5β- and 4α,5α-epoxides were ca. 4∶1 for 4-cholesten 3β-ol and ca. 3∶2 for
4-cholesten-3α-ol. With iron-supplemented microsomes from rat liver, the compounds formed were qualitatively and quantitatively
the same as with soybean lipoxygenase, whereas with 18,000 × g rat liver supernatant fractions the yields of all products
formed—except 7α-hydroxycholesterol and 6β-hydroxy-4-cholesten-3-one—were markedly decreased. The results indicate the presence
of a rat liver microsomal 6β-hydroxylase which can use 4-cholesten-3-one as a substrate and extend previous findings of similarities
between soybean lipoxygenase and a nonspecific lipoxygenase in rat liver microsomes. 相似文献
19.
B. Larkeson P. C. Dutta I. Hansson 《Journal of the American Oil Chemists' Society》2000,77(6):675-680
The presence of cholesterol oxidation products (COP) in the diet is a health concern for their various known adverse effects.
It is important that the generation of COP be assessed during different stages of production, handling, and storage of meats
and meat products so that relevant measures can be taken to minimize the production of COP. In a preliminary study, we investigated
the content of COP in the lipids of raw meatballs (50% prok+50% beef), prefried meatballs (50% pork +50% beef), raw hamburger
(100% beef), and prefried burger (50% pork+50% beef). Six of the common COP, viz 7α- and 7β-hydroxycholesterol, 7-ketocholesterol, 5α,6α-epoxycholestanol, 5β,6β-epoxycholestanol, and cholestanetriol, were
analyzed by gas chromatography (GC) and GC-mass spectroscopy. The total content of these COP was in the range of 7 to 10 μg/g
lipids in raw meatballs, prefried meat balls, and raw hamburger, after frying these samples for consumption. The prefried
hamburger had ca. 8μg/g lipids of the total COP before frying, and this amount increased to 29 μg/g lipids after frying. During the storage
of this fried sample, the total COP increased to 42 and 50 μg/g lipids, after 1 and 2 wk of storage, respectively. The results
of this study show that freshly prepared meat products are a minor source of COP in the diet. However, if semiprepared frozen
meat products are fried once and then stored for future consumption, the levels of COP can increase considerably, and this
may be of concern for certain groups of consumers.
Presented in part as a poster at the 88th AOCS Annual Meeting and Exposeattle, WA, May 11–14, 1997. 相似文献
20.
Various methods were assessed for the synthesis of 7-ketocholesterol and epimeric 7-hydroxycholesterols. Upon the oxidation
of cholesteryl acetate with t-butyl chromate, the resulting ketosterol acetate crystallized from methanol consisted of about
25% unoxidized cholesteryl acetate. After the sterol acetates were hydrolyzed in an aqueous K2CO3 medium, preparative TLC was used to fractionate the ketone from cholesterol.
Of all the reducing agents employed, only LiAlH4 reduced completely the purified 7-ketocholesterol to 7-hydroxycholesterols without side reaction products and ketone contamination.
Yields of 21.3 mg of 7α-hydroxycholesterol and 72.6 mg of 7β-hydroxycholesterol were obtained by preparative TLC of a diol
mixture prepared by the LiAlH4-reduction of 100 mg of 7-ketocholesterol. To accomplish the preparative TLC separation of diol bands without overlapping,
a double development of a chromatoplate with ethyl ether-cyclohexane (90∶10, v/v) and ethyl ether was essential.
Data on the melting point, optical rotation and infrared spectra, as well as TLC and GLC characteristics, were obtained for
purified 7-ketocholesterol and epimeric 7-hydroxycholesterols. 相似文献