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Biomedical subjects

W E Lands

Publications and source records attributed to W E Lands.

At least 19 recordsLinked to original sources
PubMed1992

Maintenance of lower proportions of (n - 6) eicosanoid precursors in phospholipids of human plasma in response to added dietary (n - 3) fatty acids.

Competition between the (n - 3) and (n - 6) types of highly unsaturated fatty acids can diminish the abundance of (n - 6) eicosanoid precursors in a tissue, which in turn can diminish the intensity of tissue responses that are mediated by (n - 6) eicosanoids. The mixture of 20- and 22-carbon highly unsaturated fatty acids maintained in the phospholipids of human plasma is related to the dietary intake of 18:2 (n - 6) and 18:3 (n - 3) by empirical hyperbolic equations in a manner very similar to the relationship reported for laboratory rats (Lands, W.E.M., Morris, A. and Libelt, B. (1990) Lipids 25, 505-516). Analytical results from volunteers ingesting self-selected diets showed an inter-individual variance for the proportion of (n - 6) eicosanoid precursors in the fatty acids of plasma phospholipids of about 5%, but the variance among multiple samples taken from the same individual throughout the day was less (about 3%), closer to the experimental variance of the analytical procedure (about 1%). The reproducibility of the results makes it likely that analysis of fatty-acid composition of plasma lipids from individuals will prove useful in estimating the diet-related tendency for severe thrombotic, arthritic or other disorders that are mediated by (n - 6) eicosanoids. Additional constants and terms were included in the equations to account for the effects of 20- and 22-carbon highly unsaturated (n - 3) fatty acids in the diet. A lower constant for the 20- and 22-carbon (n - 3) fatty acids compared to that for the 18-carbon (n - 3) fatty acid in decreasing the ability of dietary 18:2 (n - 6) to maintain 20:4 (n - 6) in tissue lipids confirmed the greater competitive effectiveness of the more highly unsaturated n - 3 fatty acids in the elongation/desaturation process. Also, a lower constant for direct incorporation of 20-carbon fatty acids of the n - 6 vs. the n - 3 type indicated a greater competitive effectiveness of 20:4 (n - 6) relative to 20:5 (n - 3) in reesterification after release from tissue lipids. The equations may be used in reverse to estimate the dietary intakes of the (n - 3) and (n - 6) fatty acids by using the composition of the fatty acids that had been maintained in plasma lipids.

Aged↗
PubMed1992

Biochemistry and physiology of n-3 fatty acids.

Considering the n-3 fatty acids to be partial agonists relative to n-6 fatty acids helps consolidate into a unified interpretation the many diverse reports and controversies on the actions of these two types of essential fatty acids. Some research reports illustrate the similarities between these two types and some emphasize the differences, leaving readers to evaluate the status of n-3 fatty acids from a viewpoint that is conceptually similar to regarding a glass of water as half empty or half full. Both n-3 and n-6 types of fatty acids must be obtained through the diet because they are not synthesized de novo by vertebrates. Both types can support important physiological and developmental processes, can form eicosanoids (prostaglandins, leukotrienes, lipoxins, etc.), can be esterified to and hydrolyzed from tissue glycerolipids, and can be metabolically elongated and desaturated to a variety of highly unsaturated fatty acids. However, some nonesterified n-6 acids are vigorously converted to potent n-6 eicosanoids that exert intense agonist actions at eicosanoid receptors, whereas the n-3 acids less vigorously form n-3 eicosanoids that often produce less intense (partial) actions. Because both types owe their presence in vertebrate tissues to dietary intake, important physiological consequences follow the inadvertent selection of different average daily dietary supplies of these two types of polyunsaturated fatty acids.

Animals↗
PubMed1991

Iodometric measurement of lipid hydroperoxides in human plasma.

Many assay techniques have been used to measure lipid hydroperoxides in plasma, including absorbance of conjugated dienes and reactivity with thiobarbituric acid. Because these measurements are not specific for lipid hydroperoxides, we modified an exisiting iodometric method to correct for interfering phenomena and to provide a more specific measurement of the lipid hydroperoxide content of plasma. To ensure reproducible extraction of hydroperoxides from the many possible forms in plasma, the plasma was treated to hydrolyze enzymatically cholesterol ester, triglycerides, and phospholipids, and the nonesterified fatty acid peroxides were then extracted with ethyl acetate. Extracted lipids were reacted with potassium iodide in acetic acid and methylene chloride, and the resulting triiodide ion (I3-) was measured spectrophotometrically. Correction for nonoxidizing chromophores was made after back-titration of the triiodide ion to iodide with sodium thiosulfate and other non-peroxide oxidants were estimated by their resistance to reduction with glutathione peroxidase. Recovery of added hydroperoxide standards provided routine validations of the procedure's efficiency. The method indicated that insignificant amounts of hydroperoxide may be in the less polar lipids, but the total amount of lipid hydroperoxide esterfied in the plasma lipids of apparently healthy humans may be as much as 4.0 +/- 1.7 microM.

Esterases↗
PubMed1991

Use of a voltage-responsive timer to quantitate hydroperoxides by the cyclooxygenase activation assay.

The importance of lipid hydroperoxides in the interpretations of physiological and pathological processes requires a valid and reliable microanalytical procedure. However, quantitation of the small amounts of lipid hydroperoxides in biological samples is often attempted with methods that have low sensitivity, low validity, and/or low reliability. The highly sensitive and specific enzymatic assay based upon cyclooxygenase activation has many complex kinetic features that have caused it to be cumbersome and unreliable. Analysis of the cyclooxygenase kinetics showed that a fixed percentage (20%) of full reaction accurately substituted for the measurements of the time required to reach optimal velocity. Consequently, a voltage-responsive timer can report endpoints that are dependent upon picomole amounts of lipid hydroperoxide. Additional features of the timer are described which make the hydroperoxide assay simpler, faster, more reliable, and easier to perform than the previous method while still retaining its sensitivity and specificity.

Animals↗
PubMed1991

Differential detection of plasma hydroperoxides in sepsis.

OBJECTIVE: To determine whether plasma lipid hydroperoxides may be a useful marker for sepsis. DESIGN: Exploratory, open-label study. SETTING: Critical care unit at a university medical center. PATIENTS: Twelve patients with sepsis syndrome requiring hemodynamic monitoring with pulmonary artery catheters. Seven patients were diagnosed with pulmonary infections and five patients had intra-abdominal infections. INTERVENTIONS: Fatty acid hydroperoxide was measured in the fresh arterial plasma (radial artery) and mixed venous plasma (pulmonary artery) from each patient. Hydroperoxide was determined using a sensitive assay based on activating the cyclooxygenase reaction of prostaglandin H synthase. MEASUREMENTS AND MAIN RESULTS: The mean difference between the amount of fatty acid hydroperoxide measured in the plasma draining involved regions (arterial plasma for pulmonary sepsis, mixed venous plasma for intra-abdominal sepsis) compared with the paired, uninvolved regions was 0.45 +/- 0.14 microM (mean +/- SEM; p less than .005). CONCLUSIONS: Increased lipid hydroperoxides in blood-draining septic foci are markers of oxyradical release associated with severe infection, although they are not specific for infectious conditions, being released also from nonseptic regions of surgical trauma. Assays for hydroperoxides may be useful when relatively free of other tissue trauma.

Adult↗
PubMed1990

Quantitative effects of dietary polyunsaturated fats on the composition of fatty acids in rat tissues.

A method combining data on fatty acid composition into subsets is used to illustrate general relative competitive selectivities in the metabolic and transport events that maintain fatty acid compositions in tissue lipids and to minimize differences among tissues or species in the amount of individual fatty acids. Fatty acid compositions of triglycerides and phospholipids in several tissues of the rat were maintained with simple relationships between the exogenous n-3 and n-6 dietary polyunsaturated fatty acids and the endogenous n-7 and n-9 types of fatty acid. The general pattern of fatty acids in triglycerides was similar for liver, plasma and adipose tissue, averaging about 30% as saturated acids, 67% as 16- and 18-carbon unsaturated acids and only about 2% as 20- and 22-carbon highly unsaturated acids. The tissues maintained a linear relationship between the amount of 18-carbon polyunsaturated fatty acids in the diet and in the tissue triglycerides, with the proportionality constant for 18:3n-3 being 60% of that for 18:2n-6. The total phospholipids of liver, plasma and red blood cells maintained about 45% of the fatty acids in the form of saturated fatty acids and 20-30% as 20- and 22-carbon highly unsaturated fatty acids irrespective of very different proportions of n-3, n-6 and n-9 types of fatty acids. In all three tissues, the 20-carbon highly unsaturated fatty acids of the n-3, n-6 and n-9 type were maintained in a competitive hyperbolic relationship with apparent EC50 values for dietary 18:2n-6 and 18:3n-3 near 0.1% of dietary calories. The consistent quantitative relationships described in this study illustrate an underlying principle of competition among fatty acids for a limited number of esterification sites. This approach may be useful in predicting the influence of diet upon tissue levels of the substrates and antagonists of eicosanoid biosynthesis.

Adipose Tissue↗
PubMed1990

Rapid analysis of fatty acids in plasma lipids.

A rapid and convenient procedure for the quantitative determination of the fatty acid composition of plasma lipids is described. Human plasma was applied directly to the preadsorbent zones of thin-layer silica gel plates with added antioxidant, internal standards and carriers. The thin-layer chromatography (TLC) plates were partially developed with methanol followed by chloroform/methanol (1:1, v/v), and then they were fully developed in hexane/diethyl ether/acetic acid (80:20:1, v/v/v) to separate the major classes of lipids. Silica gel from regions containing the separated lipids was scraped into screw-capped tubes and treated with boron trifluoride-methanol prior to gas chromatography. The method of direct application to TLC plates gave yields and compositions of fatty acids very similar to the method of applying extracted plasma lipids. This relatively simple method is suitable for analyzing the fatty acids in plasma lipids from a 50 microliter finger-tip blood samples from an individual, and it may be useful in wide-scale screening of different individuals to estimate the relative amounts of ingested polyunsaturated fatty acids.

Chromatography, Gas↗
PubMed1990

Differences between arterial and mixed venous levels of plasma hydroperoxides following major thoracic and abdominal operations.

Fatty acid hydroperoxides in the plasma of 18 patients who were undergoing normal postoperative periods following major thoracic or abdominal operations were measured by using a sensitive assay based upon the activation of the cyclooxygenase activity of prostaglandin H synthase. Following major thoracic operations of nine patients, the mean difference between the arterial (0.49 +/- 0.13 microM, mean +/- S.E.M.) and mixed venous (-0.09 +/- 0.12 microM) level of hydroperoxide was 0.58 +/- 0.13 microM (p less than 0.01). In marked contrast to this result, major abdominal operations of nine patients led to a mean difference between the arterial (-0.19 +/- 0.16 microM) and mixed venous (0.46 +/- 0.08 microM) hydroperoxide levels of -0.65 +/- 0.17 microM (p less than 0.01). Both pulmonary and intraabdominal tissues appear capable of generating significant amounts of fatty acid hydroperoxide in response to standard surgical procedures. The A-MV differences suggest that the blood-borne hydroperoxides were rapidly cleared from the circulation by tissue capillary beds.

Abdomen↗
PubMed1990

Changing dietary patterns.

Previously traditional dietary patterns in Japan are no longer typical. The current changing conditions provide an opportunity to examine more closely some important health conditions associated with the changed lifestyle and concentrations of dietary total fat and saturated fatty acid, and the ratio of n-3 to n-6 polyunsaturated fatty acids in the diet.

Diet↗
PubMed1989

n-3 fatty acids as precursors for active metabolic substances: dissonance between expected and observed events.

It may be hypothesized that many diseases are associated with an overproduction of eicosanoids from the n-6 acid, arachidonic acid (20:4n-6), and the formation and function of these n-6 eicosanoids can be antagonized by dietary n-3 fats. This hypothesis provides a basis for evaluating the benefits and risks of including various amounts of n-3 and n-6 fats in the diet. Understanding the impact of dietary polyunsaturated fats leads inevitably to a reappraisal of what is 'normal' in terms of what is typical and what is desirable for the fatty acid composition of tissue lipids, the magnitude of eicosanoid-mediated responses, and the frequency and severity of certain diseases.

Animals↗