Remodeling of mouse kidney phospholipid classes and subclasses by diet

Human and great ape red blood cells differ in plasmalogen levels and composition

Background

Plasmalogens are ether phospholipids required for normal mammalian developmental, physiological, and cognitive functions. They have been proposed to act as membrane antioxidants and reservoirs of polyunsaturated fatty acids as well as influence intracellular signaling and membrane dynamics. Plasmalogens are particularly enriched in cells and tissues of the human nervous, immune, and cardiovascular systems. Humans with severely reduced plasmalogen levels have reduced life spans, abnormal neurological development, skeletal dysplasia, impaired respiration, and cataracts. Plasmalogen deficiency is also found in the brain tissue of individuals with Alzheimer disease.

Results

In a human and great ape cohort, we measured the red blood cell (RBC) levels of the most abundant types of plasmalogens. Total RBC plasmalogen levels were lower in humans than bonobos, chimpanzees, and gorillas, but higher than orangutans. There were especially pronounced cross-species differences in the levels of plasmalogens with a C16:0 moiety at the sn-1 position. Humans on Western or vegan diets had comparable total RBC plasmalogen levels, but the latter group showed moderately higher levels of plasmalogens with a C18:1 moiety at the sn-1 position. We did not find robust sex-specific differences in human or chimpanzee RBC plasmalogen levels or composition. Furthermore, human and great ape skin fibroblasts showed only modest differences in peroxisomal plasmalogen biosynthetic activity. Human and chimpanzee microarray data indicated that genes involved in plasmalogen biosynthesis show cross-species differential expression in multiple tissues.

Conclusion

We propose that the observed differences in human and great ape RBC plasmalogens are primarily caused by their rates of biosynthesis and/or turnover. Gene expression data raise the possibility that other human and great ape cells and tissues differ in plasmalogen levels. Based on the phenotypes of humans and rodents with plasmalogen disorders, we propose that cross-species differences in tissue plasmalogen levels could influence organ functions and processes ranging from cognition to reproduction to aging.

Dietary (n-3) polyunsaturated fatty acids remodel mouse T-cell lipid rafts

In vitro evidence indicates that (n-3) polyunsaturated fatty acids (PUFA) suppress T-cell activation in part by displacing proteins from lipid rafts, specialized regions within the plasma membrane that play an important role in T-cell signal transduction. However, the ability of (n-3) PUFA to influence membrane microdomains in vivo has not been examined to date. Therefore, we compared the effect of dietary (n-3) PUFA on raft (liquid ordered) vs. soluble (liquid disordered) microdomain phospholipid composition in mouse T cells. Mice were fed diets containing either 5 g/100 g corn oil (control) or 4 g/100 g fish oil [contains (n-3) PUFA] + 1 g/100 g corn oil for 14 d. Splenic T-cell lipid rafts were isolated by density gradient centrifugation. Raft sphingomyelin content (mol/100 mol) was decreased (P < 0.05) in T cells isolated from (n-3) PUFA-fed mice. Dietary (n-3) PUFA were selectively incorporated into T-cell raft and soluble membrane phospholipids. Phosphatidylserine and glycerophosphoethanolamine, which are highly localized to the inner cytoplasmic leaflet, were enriched to a greater extent with unsaturated fatty acids compared with sphingomyelin, phosphatidylinositol and glycerophosphocholine. These data indicate for the first time that dietary (n-3) PUFA differentially modulate T-cell raft and soluble membrane phospholipid and fatty acyl composition.

Dietary gamma-linolenic acid suppresses aortic smooth muscle cell proliferation and modifies atherosclerotic lesions in apolipoprotein E knockout mice

The present study was conducted to evaluate the antiatherogenic effects of dietary gamma-linolenic acid (GLA) (primrose oil) in apolipoprotein E (apoE) genetic knockout mice. Five-wk-old male mice were fed cholesterol-free diets containing 10 g/100 g lipid as corn oil (CO) [control diet, 0 mol/100 mol GLA and (n-3) polyunsaturated fatty acids (PUFA)], primrose oil (PO, 10 mol/100 mol GLA), fish oil-CO mix [FC; 9:1 wt/wt, 0 mol/100 mol GLA and 17 mol/100 mol (n-3) PUFA] or fish oil-PO mix [FP, 1:3 wt/wt, 8 mol/100 mol GLA and 5 mol/100 mol (n-3) PUFA] for 15 wk. Subsequently, diets were supplemented with cholesterol (1.25 g/100 g) and sodium cholate (0.5 g/100 g) and fed for an additional 10 and 16 wk. Plasma cholesterol and triglyceride levels generally did not differ among groups at 20, 30 and 36 wk of age. Mice fed GLA-containing diets (PO and FP) had significantly (P < 0.05) higher liver phospholipid levels of dihomo-gamma-linolenic acid, the elongated product of GLA, relative to CO and FC groups. Consumption of GLA (PO and FP diets) significantly reduced (P < 0.05) aortic vessel wall medial layer thickness at 20 and 30 wk. A parallel GLA-dependent suppression in the number of proliferating (proliferating cell nuclear antigen positive) aortic smooth muscle cells was also observed. Diets containing either GLA or (n-3) PUFA reduced (P < 0.05) atherosclerotic lesion size in 30-wk-old mice. These results indicate that dietary GLA can suppress smooth muscle cell proliferation in vivo and retard the development of diet-induced atherosclerosis in apoE knockout mice.

Docosahexaenoic acid suppresses function of the CD28 costimulatory membrane receptor in primary murine and Jurkat T cells

(n-3) polyunsaturated fatty acids (PUFA) have been widely documented to reduce inflammation in diseases such as rheumatoid arthritis. This study sought to elucidate the mechanism whereby (n-3) PUFA downregulate T-cell proliferation. We hypothesized that membrane incorporation of dietary PUFA would alter membrane structure and consequently membrane receptor function. Female C57BL/6 mice were fed for 14 d one of three diets containing arachidonic acid (AA), fish oil or docosahexaenoic acid (DHA) that varied in lipid composition only. Spleens were harvested and T cells ( approximately 90% purity) were activated with agonists that stimulated proliferation at the receptor level [anti-CD3 (alphaCD3)/anti-CD28 (alphaCD28)], intracellularly [phorbol-12-myristate-13-acetate (PMA)/ionomycin] or with a combined receptor/intracellular agonist (alphaCD3/PMA). Although there was no significant difference (P > 0.05) in proliferative response across dietary groups within each agonist set, interleukin (IL)-2 secretion was significantly reduced (P = 0.05) in cells from DHA-fed mice stimulated with alphaCD3/alphaCD28. In parallel in vitro experiments, Jurkat T cells were incubated with 50 micromol/L linoleic acid, AA, or DHA. Similar agonists sets were employed, and cells incubated with DHA and AA had a significantly reduced (P < 0.05) IL-2 secretion in three of the agonist sets. However, only when the CD28 receptor was stimulated was there a significant difference (P < 0.05) between DHA and AA. The results of this study suggest the involvement of the CD28 receptor in reducing IL-2 secretion in DHA-fed mice and DHA-incubated Jurkat cells and that purified T cells from DHA-fed mice require accessory cells to modulate proliferative suppression.

Dietary very long chain fatty acids directly influence the ratio of tetracosenoic (24:1) to tetracosanoic (24:0) acids of sphingomyelin in rat liver

Twenty-one groups of weanling male Wistar rats were fed semipurified diets containing 5% (w/w) of different dietary fats. After 2 wk, liver sphingomyelin (SM) fatty acid composition was determined. The ratio of 24:1 to 24:0 in liver SM varied over a tenfold range in response to dietary fat type. Step-wise multiple regression analysis indicated that dietary 24:1, 24:0, and 22:1 were the most significant factors in predicting the 24:1/24:0 ratio of liver SM. The mathematical relation between the dietary fatty acid composition and liver SM 24:1/24:0 was y = 1.88 (24:1) -1.49 (24:0) +0.21 (22:1) +0.01 (18:1) +0.26, r2 = 0.95, P < 0.0001. These results were confirmed by a second experiment in which the rats were fed olive oil-based diets supplemented with various fatty acid ethyl esters.

Changes in ether-linked phospholipids in rat kidney by dietary alpha-linolenic acid in vivo

We investigated the effects of perilla oil containing a high level of alpha-linolenic acid on in vivo phospholipid metabolism, particularly three subclasses of choline glycerophospholipids (CGP) and ethanolamine glycerophospholipids (EGP), in rat kidney. After three weeks of feeding, a significantly lower proportion (by 35%) of the alkylacyl subclass of CGP was found in the perilla oil, as compared to corn oil-fed animals. The alkylacyl species of EGP was also higher in the perilla oil than in the corn oil-fed animals. These alterations were accompanied by a remarkably lower proportion of arachidonic acid and a higher level of eicosapentaenoic acid (EPA) in all six subclasses of CGP and EGP in the perilla oil-fed animals. The levels of linoleic acid were even higher in the diacyl subclasses of CGP and EGP in the perilla oil group, suggesting that desaturase and elongase enzymes prefer n-3 to n-6 fatty acids as substrates for diacyl species. These data are useful in defining the effects of alpha-linolenic acid on the biosynthesis of renal phospholipids and on the replacement of n-6 with n-3 fatty acids in the six CGP and EGP subclasses.

Borage or primrose oil added to standardized diets are equivalent sources for gamma-linolenic acid in rats

The aim of this study was to evaluate the effect of different doses and sources of dietary gamma-linolenic acid (GLA) on the tissue phospholipid fatty acid composition. Rats fed four different levels of GLA (2.3, 4.6, 6.4 and 16.2 g of GLA/kg diet) in the form of either borage oil or evening primrose oil during 6 wk were compared with animals fed corn oil. The levels of dihomo-gamma-linolenic acid (DHLA) and GLA showed a significant dose-related increase in liver, erythrocyte and aorta phospholipids. Moreover, the arachidonic acid/DHLA ratios in tissues decreased with increasing intake of dietary GLA. There was no significant difference in tissue GLA and DHLA levels within groups given equal amounts of dietary GLA either as borage oil or evening primrose oil. The amount of dietary GLA administered did not significantly influence prostaglandin E2 production in stimulated aortic rings and thromboxane B2 levels in serum; however, an increase in prostaglandin E1 derived from DHLA was observed in the supernatants of stimulated aorta.

Abnormal lipid and fatty acid compositions of kidneys from mice with polycystic kidney disease

Renal cyst development in polycystic kidney disease (PKD) involves hyperplastic growth and extensive membrane alterations, suggesting abnormal membrane composition and function. Using thin-layer and gas-liquid chromatography, we analyzed the lipid components of the kidneys from 120-day-old DBA/2FG-pcy (pcy) having PKD as compared to normal DBA/2J (DBA) mice. At sacrifice, kidneys from pcy mice were four times larger than DBA controls, indicating that extensive renal cyst growth had occurred. The ratios of cholesterol/phospholipid, choline glycerophospholipid (GPC)/ethanolamine glycerophospholipid (GPE) and alkenylacyl GPE/diacyl GPE were higher (by 25%, 41% and 72%, respectively) in the cystic kidneys, while total phosphatidylinositol (PI), GPE and cardiolipin (DPG) were lower (by 13%, 23% and 27%, respectively). With respect to fatty acid compositions, there were significantly lower levels of docosahexaenoic acid (DHA, 22:6n-3) and higher levels of adrenic acid (AdA, 22:4n-6) in the phospholipids of pcy mouse kidneys. These changes were not present in serum, indicating that they were not generalized differences. Interestingly, the lower level of DHA in GPE was found to be associated with the alkenylacyl, but not the diacyl species. The fatty acids comprising the product/substrate ratio for the delta 4 desaturase activity were lower across all phospholipids, indicating a possible abnormality in polyunsaturated fatty acid metabolism in this model of PKD. These lipid abnormalities may influence membrane-mediated events such as receptor activation, signal transduction, ion transport and enzyme activities. The renal pathophysiologies associated with PKD may be related to the tissue lipid abnormalities described herein.

Alteration in mouse splenic phospholipid fatty acid composition and lymphoid cell populations by dietary fat

The fatty acid composition of diacyl- and alkylacylglycerophosphocholine (PC), phosphatidylinositol (PI), phosphatidylserine (PS), alkenylacyl-glycerophosphoethanolamine (aPE), and diacyl- and alkylacyl-glycerophosphoethanolamine (dPE) was assessed in isolated splenocytes from C3H/Hen mice fed one of four purified isocaloric diets for six weeks. Diets contained 20% by weight of either a high-linoleate sunflower oil (Hi 18:2), a high-oleate sunflower oil (Hi 18:1), a mixture of 17% menhaden fish oil and 3% high-linoleate sunflower oil (Hi n-3), or a mixture of 17% coconut oil and 3% high-linoleate sunflower oil (Hi SFA). Spleen weight and immune cell yield were significantly higher (P less than 0.05) in mice fed the Hi 18:1 or the Hi n-3 diets compared with those fed the Hi 18:2 and Hi SFA diets. Distinctive patterns of fatty acids were observed for each phospholipid in response to dietary fatty acids. Dietary fat significantly affected (P less than 0.05) total polyunsaturated fatty acids (PUFA) in PC and dPE, total saturated fatty acids (SFA) in PC, total monounsaturated fatty acids (MUFA), and n-3 PUFA in all phospholipid classes examined. In mice fed the Hi n-3 diet, n-3 PUFA were significantly elevated, whereas n-6 PUFA decreased in all of the phospholipids. In these mice, eicosapentaenoic acid (EPA) was the predominant n-3 PUFA in PC and PI, whereas docosahexaenoic acid (DHA) was the major n-3 PUFA in aPE and PS.(ABSTRACT TRUNCATED AT 250 WORDS)