n-3 fatty acids in human fat tissue aspirates are stable for up to 6 y.

OBJECTIVES: The content of n-3 (omega-3) polyunsaturated fatty acids in fat tissue is a valid indicator of their long-term consumption. We studied the stability of n-3 fatty acids in human subcutaneous fat microbiopsies after 6 and 11 y of storage. DESIGN: Microbiopsies were taken from a lump of human adipose tissue and stored at +20 and -80 degrees C. SETTING: Laboratory study. RESULTS: After 5.6 y at -80 degrees C the proportion of six out of seven highly polyunsaturated fatty acids varied between 91 and 102% (mean 97%) of their baseline values. Storage at +20 degrees C yielded recoveries between 82 and 105%. After 11 y at -80 degrees C the proportions in the original lump of tissue ranged from 88 to 101% (mean 94%). CONCLUSION: n-3 fatty acids in stored fat tissue aspirates are stable for 6-11 y, and are suitable markers of baseline diet in long-term epidemiological studies. SPONSORSHIP: Wageningen Centre for Food Sciences.

Determination of trans-beta-carotene and other carotenoids in blood plasma using high-performance liquid chromatography and thermal lens detection.

Thermal lens spectrometry (TLS) was applied for the detection of beta-cryptoxanthin, alpha-carotene, trans-beta-carotene, and lycopen in blood plasma. This combined high-performance liquid chromatography-TLS (HPLC-TLS) method was validated by comparison with HPLC-UV-Vis analysis of blood plasma under identical chromatographic conditions and by comparing the results obtained from an independent, standard HPLC procedure for determination of carotenoids in blood plasma samples. The results demonstrated good agreement with the target values for carotenoids in an in-laboratory control sample and confirmed the accuracy of the HPLC-TLS technique. Limits of detection for blood plasma samples were 70 pg/ml for beta-cryptoxanthin, 85 pg/ml for alpha-carotene, 100 pg/ml for trans-beta-carotene, and 120 pg/ml for lycopen. This represents a 100-fold improvement compared to the HPLC analysis with UV-Vis detection.

Plasma oxysterols and angiographically determined coronary atherosclerosis: a case control study.

Several in vitro and in vivo experiments have implicated oxysterols in the aetiology and progression of atherosclerosis. Oxysterols may be formed endogenously by oxidation of cholesterol and thus may form a marker of LDL oxidation. They may also be obtained exogenously through dietary intake. We investigated the association of oxysterols with the degree of coronary stenosis in patients undergoing coronary angiography. Cases with severe coronary atherosclerosis 80 stenosis in one of the major coronary vessels, n =80 were compared with controls with no or minor stenosis 50 stenosis in all three major coronary vessels, n =79 . Cases and controls were prestratified on age, gender and smoking habits. Evaluated were plasma levels of unesterified 7 hydroxycholesterol, 7 hydroxycholesterol, 25 hydroxycholesterol, 7 ketocholesterol, cholestane triol and 5,6 epoxycholestanol. 7 Hydroxycholesterol made up 67 of the total amount of plasma oxysterol concentration and was the only one significantly higher in cases 1.53 mu g per 100 ml vs 1.27 mu g per 100 ml, p 0.05 . Further, cases had somewhat higher LDL cholesterol levels and significantly lower HDL cholesterol levels than controls. After multivariate adjustment to account for this difference in lipid levels and for the prestratification factors the mean difference between cases and controls for 7 hydroxycholesterol 0.14 mu g per 100 ml was no longer significant. Also the other oxysterols showed no significant association with the degree of coronary stenosis. Multiple logistic regression analyses showed an adjusted odds ratio of 1.07 95 CI, 0.45-2.59 in the highest tertile of total plasma oxysterol level. We conclude, that this study does not support the hypothesis that plasma oxysterols form an additional risk factor for coronary atherosclerosis.

Detection of Total Trans Fatty Acids Content in Margarine: An Intercomparison Study of GLC, GLC + TLC, FT-IR, and Optothermal Window (Open Photoacoustic Cell).

Four techniques, i.e., gas-liquid chromatography, gas-liquid chromatography + thin-layer chromatography, and two spectroscopic methods, Fourier transform infrared spectroscopy and optothermal window, a variant of the open photoacoustic cell, were intercompared to determine their potential to detect the total trans fatty acid content in margarine. At the same time, this study represents a first application of the optothermal window technique at long wavelengths (10 µm). The total trans fatty acid data obtained by different methods show good mutual agreement. Besides offering several attractive advantages above conventional methods, the optothermal window also proved suitable for measuring total trans fatty acid content as low as 2%.

Stability of n-3 fatty acids in human fat tissue aspirates during storage.

The content of n-3 (omega 3) polyunsaturated fatty acids in fat tissue is an indicator of their long-term consumption. Therefore, a method for determining n-3 fatty acids in human fat tissue microbiopsies was validated and the stability of n-3 fatty acids in biopsies was checked under various conditions of storage. Methyl esters were prepared from 25 to 35 mg adipose tissue and separated by capillary gas chromatography. Recovery of added eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) was 98-105%. The change after storage of fat samples at room temperature or at 4, -20, or -80 degrees C for 3 mo averaged +3.3% for EPA and +2.1% for DHA, with no effect of temperature. Storage at +20 or -80 degrees C for 7 mo yielded no perceptible change in EPA, DHA, or five other n-3 polyunsaturated fatty acids. EPA and DHA concentrations in adipose tissue aspirates are remarkably stable and deserve attention as biomarkers in epidemiological studies.

Quantification of oxysterols in Dutch foods: egg products and mixed diets.

A sensitive and specific method is described for quantifying various cholesterol oxidation products in foodstuffs, including 7 beta-hydroxycholesterol, cholesterol-alpha-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 degrees C. The detection limit was about 0.5 microgram/g dry weight for egg yolk powder. Fresh egg yolk contained only 1.2 micrograms/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 micrograms/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 micrograms/g dry weight were found. In duplicates of mixed Dutch diets, total amounts ranged from 3.6 to 6.2 micrograms/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.