Dietary cholesterol induces changes in molecular species of hepatic microsomal phosphatidylcholine

Alteration of the Fatty Acid Metabolism in the Rat Kidney Caused by the Injection of Serum from Patients with Collapsing Glomerulopathy

Patients with collapsing glomerulopathy (CG) have marked proteinuria that rapidly progresses to chronic renal failure. In this study, we investigated if the nephropathy produced in a rat model by the injection of serum from CG patients induced alterations in fatty acid (FA) metabolism. Twenty-four female Sprague-Dawley rats were divided into four groups of six rats each: Group I, control rats (C); Group II, rats that received injections of 1 mL of 0.9% NaCl saline solution (SS); Group III, rats injected with 25 mg/mL of serum from healthy subjects (HS); and Group IV, rats injected with 25 mg/mL of serum from CG patients. In all groups, the systolic blood pressure (SBP), proteinuria, creatinine clearance (CC), cholesterol and total FA composition in the kidney and serum were evaluated. The administration of serum from CG patients to rats induced glomerular collapse, proteinuria, reduced CC and elevated SBP (p ≤ 0.01) in comparison with the C, SS and HS rats. The FA composition of the serum of rats that received the CG serum showed an increase in palmitic acid (PA) and a decrease in arachidonic acid (AA) when compared to serum from HS (p ≤ 0.02). In rats receiving the CG serum, there was also a decrease in the AA in the kidney but there was an increase in the PA in the serum and kidney (p ≤ 0.01). These results suggest that the administration of serum from CG patients to rats induces alterations in FA metabolism including changes in PA and in AA, which are precursors for the biosynthesis of the prostaglandins that are involved in the elevation of SBP and in renal injury. These changes may contribute to collapsing glomerulopathy disease.

Expression of Delta(12) fatty acid desaturase during the induced accumulation of the antifungal diene in avocado fruits

SUMMARY The preformed (Z,Z)-1-acetoxy-2-hydroxy-4-oxo-heneicosa-12,15-diene (AFD) is the most active antifungal compound in avocado; it affects the quiescence of Colletotrichum gloeosporioides in unripe fruit. One of the genes encoding Delta(12) fatty acid desaturase (avfad12) was hypothesized to take part in the biosynthesis of AFD, and its expression pattern and enzymatic activity were determined in relation to the content of AFD. Using avfad12-3 as a probe, high levels of expression were detected in young fruits and leaves, where the level of AFD was highest. In contrast, Northern analysis of RNA from mature leaves and fruits showed no transcripts from the avfad12 gene family and lower AFD content. The transcripts from the avfad12 gene family, the enzymatic activity of Delta(12) fatty acid desaturase, and the level of AFD in unripe-resistant fruits increased transiently when the fruits were inoculated with C. gloeosporioides or exposed to ethylene (40 microL/L), low temperature (4 degrees C) or 1 mm H(2)O(2), but ripe fruits were not affected. The effect of H(2)O(2) on the transcripts from the avfad12 gene family is of specific importance, because reactive oxygen species were produced by unripe-resistant host fruit soon after inoculation of C. gloeosporioides. In addition, the fungus itself produced H(2)O(2) in culture medium at pH 5.0, which is similar to the pH of unripe-resistant fruit, but not at pH 7.0. Treatments that enhanced Delta(12) fatty acid desaturase activity increased the concentration of the AFD precursor, linoleic acid, and its incorporation into AFD; these treatments also caused a delay in decay development. The present results demonstrate temporal relationships among the transcripts from the avfad12 gene family, the synthesis of the precursor of AFD (linoleic acid), the AFD content and quiescence of C. gloeosporioides in unripe fruits.

High-cholesterol diets induce changes in lipid composition of rat erythrocyte membrane including decrease in cholesterol, increase in alpha-tocopherol and changes in fatty acids of phospholipids

Effects of high dietary cholesterol on erythrocyte membrane lipids were studied. Feeding rats with a diet containing 0.5% cholesterol and 0.15% sodium cholate for two weeks induced changes in erythrocyte membrane lipids including a decrease in cholesterol, an increase in alpha-tocopherol (alpha-Toc) and changes in the fatty acid composition of phospholipids. Oleic acid and linoleic acid increased, while arachidonic acid decreased in phosphatidylcholine. Saturated fatty acids decreased and unsaturated fatty acids increased in phosphatidylethanolamine. Almost the same changes in membrane lipids were also noted after six weeks of feeding rats with the diet. A diet containing 0.5% cholesterol but without sodium cholate caused a decrease in erythrocyte cholesterol and an increase in erythrocyte alpha-Toc after two weeks of feeding, as compared to the basal diet, indicating that high dietary cholesterol, but not sodium cholate, was responsible for these changes in the erythrocyte membrane.

Dietary cholesterol modulates delta6 and delta9 desaturase mRNAs and enzymatic activity in rats fed a low-eFA diet

The effects of a 1% addition of cholesterol to a diet low in EFA on FA desaturases were examined. The administration of cholesterol markedly increased the esterified cholesterol content in microsomes and total liver lipids from the first day, whereas the proportion of free cholesterol remained unaltered throughout the treatment. An excellent homeostasis in the free cholesterol content was apparently evoked by the acyl-CoA cholesterol acyltransferase. The cholesterol esters were mainly oleate, palmitate, and stearate, and the addition of cholesterol increased the relative proportions of cholesterol palmitoleate and oleate. The addition of cholesterol to a low-EFA diet induced, as in animals fed a high-EFA diet, a marked increase in liver stearoyl-CoA desaturase-1 mRNA and enzyme activity. This increased activity apparently evoked a similar enhancement of palmitoleic and oleic acids in total and microsomal liver lipids. The cholesterol-rich diet depressed the liver A6 and delta5 desaturase activity. However, the abundance of delta6 desaturase mRNA was not modified throughout the treatment. This indicates that the depressive effect is evoked at a step beyond that controlled by the mRNA level. The depression of both enzymatic activities was consistent with the decrease in the percentages of arachidonic acid and DHA in total and microsomal liver lipids. Taken together, these results indicate that through its modulating effect on the desaturases, dietary cholesterol may lead an animal or human fed low-EFA diet to a true deficiency by the decreased synthesis of the highly polyunsaturated acids derived from linoleic and alpha-linolenic acids.

Dietary alpha-linolenic acid lowers postprandial lipid levels with increase of eicosapentaenoic and docosahexaenoic acid contents in rat hepatic membrane

This study was designed to examine the effects of dietary n-3 and n-6 polyunsaturated fatty acids (PUFA) on postprandial lipid levels and fatty acid composition of hepatic membranes. Male Sprague-Dawley rats were trained for a 3-h feeding protocol and fed one of five semipurified diets: one fat-free diet or one of four diets supplemented with 10% (by weight) each of corn oil, beef tallow, perilla oil, and fish oil. Two separate experiments were performed, 4-wk long-term and 4-d short-term feeding models, to compare the effects of feeding periods. Postprandial plasma lipid was affected by dietary fats. Triacylglycerol (TG) and total cholesterol levels were decreased in rats fed perilla oil and fish oil diets compared with corn oil and beef tallow diets. Hepatic TG and total cholesterol levels were also reduced by fish oil and perilla oil diets. Fatty acid composition of hepatic microsomal fraction reflected dietary fatty acids and their metabolic conversion. The major fatty acids of rats fed the beef tallow diet were palmitic, stearic, and oleic. Similarly, linoleic acid (LA) and arachidonic acid in the corn oil group, alpha-linolenic acid (ALA) and eicosapentaenoic acid (EPA) in the perilla oil group, and palmitic acid and docosahexaenoic acid (DHA) in the fish oil group were detected in high proportions. Both long- and short-term feeding experiments showed similar results. In addition, microsomal DHA content was negatively correlated with plasma lipid levels. Hepatic lipid levels were also negatively correlated with EPA and DHA contents. These results suggest that n-3 ALA has more of a hypolipidemic effect than n-6 LA and that the hypolipidemic effect of n-3 PUFA may be partly related to the increase of EPA and DHA in hepatic membrane.

Effect of dexamethasone on the fatty acid composition of total liver microsomal lipids and phosphatidylcholine molecular species

Dexamethasone depresses delta6 and delta5 and increases delta9 desaturase and synthase activities. Therefore, we investigated the effect on the fatty acid composition of microsomal liver lipids and phosphatidylcholine (PtdCho) molecular species. After 15 d of treatment we found a notable decrease in arachidonic acid, a small decrease in stearic acid, and increases of linoleic, oleic, palmitoleic, and palmitic acids in liver microsomal total lipids and PtdCho. The study of the distribution of the PtdCho molecular species indicated that 18:0/20:4n-6, 16:0/20:4n-6, and 16:0/18:2n-6 predominated in the control animals. Dexamethasone, as expected because of its depressing effect on arachidonic acid synthesis and activation of oleic and palmitic acid synthesis, evoked a very significant decrease in 18:0/20:4n-6 PtdCho (P<0.001) and an important increase in 16:0/18:2n-6. The invariability of 16:0/20:4n-6 PtdCho could be related to the antagonistic effect of arachidonic and palmitic acid synthesis. PtdCho species containing oleic acid were not significant. The bulk fluidity and dynamic properties of the microsomal lipid bilayer measured by fluorometry using the probes 1,6-diphenyl-1,3,5-hexatriene and 4-trimethylammonium-phenyl-6-phenyl-1,3,5-hexatriene showed no significant modification, probably owing to a compensatory effect of the different molecular species, but changes of particular domains not detected by this technique are possible. However, the extremely sensitive Laurdan detected increased lipid packing in the less-fluid domains of the polar-nonpolar interphase of the bilayer, possibly evoked by the change of molecular species and cholesterol/phospholipid ratio. The most important effect found is the decrease of arachidonic acid pools in liver phospholipids as one of the corresponding causes of dexamethasone-dependent pharmacological effects.