Essential fatty acid deficiency, prostaglandin synthesis and humoral immunity in Lewis rats

Plasma essential fatty acid on hospital admission is a marker of COVID-19 disease severity

It is important for allocation of resources to predict those COVID patients at high risk of dying or organ failure. Early signals to initiate cellular events of host immunity can be derived from essential fatty acid metabolites preceding the cascade of proinflammatory signals. Much research has focused on understanding later proinflammatory responses. We assessed if remodelling of plasma phospholipid content of essential fatty acids by the COVID-19 virus provides early markers for potential death and disease severity. Here we show that, at hospital admission, COVID-19 infected subjects who survive exhibit higher proportions of C20:4n-6 in plasma phospholipids concurrent with marked proinflammatory cytokine elevation in plasma compared to healthy subjects. In contrast, more than half of subjects who die of this virus exhibit very low C18:2n-6 and C20:4n-6 content in plasma phospholipids on hospital admission compared with healthy control subjects. Moreover, in these subjects who die, the low level of primary inflammatory signals indicates limited or aberrant stimulation of host immunity. We conclude that COVID-19 infection results in early fundamental remodelling of essential fatty acid metabolism. In subjects with high mortality, it appears that plasma n-6 fatty acid content is too low to stimulate cellular events of host immunity.

Delayed-type hypersensitivity and humoral immunity modulation by dietary lipids in a murine model of pulmonary tumorigenesis induced by urethan

Mice fed on semisynthetic formulas containing 15% of corn oil (CO), cod fish liver oil (FO), oleic acid (O) or a mixture of 46% of palmitic and 50% of stearic acids (PS) were treated with urethan during 18 weeks for lung tumor induction. Delayed-type hypersensitivity (DTH) assay, hemagglutination assay and the amount of lung nodes (alveolar adenocarcinomas) were recorded. Results showed significantly greater DTH in CO and FO with respect to O and PS feeding mice; the two last ones induced an essential fatty acid (EFA) deficiency (EFAD). In the O lot there was a non-significant diminution of the humoral response. EFAD animals exhibited a tendency to increase number of lung nodes in relation to CO and FO lots. Splenomegalia was recorded in FO lot. Confront between spleen weight and DTH showed a 72% correlation, suggesting an increase in cellular immunity as increasing unsaturation. It may be concluded that in this suitable model of tumorigenesis the manipulation of dietary lipids may be a strategy to modify the immune system response.

Effects of dietary essential fatty acid deficiency on the development of the rat thymus and immune system

The paper describes an effect of essential fatty acid (EFA) deficiency on the development of the rat thymus and pups' immune system. From birth until being weaned (22nd day), the pups were hand-fed artificial milk diets containing a low (EFA-D) or high (EFA-R) proportion of EFA in the lipid fraction. The weight parameters of the body, thymus and spleen, the fatty acid composition of the individual thymus phospholipid subclasses, and mitogen-induced proliferation of thymus and spleen lymphocytes were studied. The results show that the total body weight of the EFA-deficient (EFA-D) fed animals was significantly decreased in comparison with the EFA-rich (EFA-R) and rat milk hand-fed animals. For the EFA-D group of young rats a high level of the (n-9) and (n-7) series fatty acids [mainly oleic 18:1(n-9) and eicosatrienoic 20:3(n-9) acids] was characteristic of the fatty acids in phosphatidylcholine and phosphatidylethanolamine in the thymus, compensating for the reduction of the content of arachidonic acid 20:4(n-6). The biochemical index of the EFA nutritional deficit in the thymus tissue was observable as early as on day 7. The mitogen-induced (Con A) proliferation of the thymus and spleen lymphocytes was decreased both on the 30th and 40th day of life. The results show that the EFA nutritional deficit in the early postnatal period caused damage to the structure of thymus in the young rats, most probably as a result of the change in the composition of the lipid fraction. These changes also affected the development of the immune system of the whole organism.

Effects of dietary lipids on recovery from mucosal injury

The present studies were conducted to determine if diets containing a large amount of fat stimulate the regeneration of damaged intestinal mucosa in the presence or absence of essential fatty acid deficiency. To simulate injury, male Sprague-Dawley rats were given methotrexate, 2.5 mg/kg body wt, subcutaneously for 3 consecutive days. Twenty-four hours after the last methotrexate injection, rats were placed on diets containing either 0%, 1%, or 10% safflower oil. Mucosal weight, protein, deoxyribonucleic acid, maltase, sucrase, lactase, alkaline phosphatase, leucine aminopeptidase, and fatty acids were all determined 3 and 12 days after methotrexate. Crypt-cell production rates were also determined. Essential fatty acid deficiency was confirmed in the 0% safflower oil group, in which triene-tetraene ratios were greater than 0.4. Mucosal weight, deoxyribonucleic acid, protein content, and villus height were all greater in the 1% safflower oil group than in the 0% group at 12 days. In the ileum, 1-h thymidine incorporation was greater in the 0% safflower oil group than in the other two groups. No differences in any of the parameters studied were observed between the 1% and 10% groups. These results suggest that diets deficient in essential fatty acids may impair the recovery of intestinal mucosa from injury.

Essential fatty acid deficiency depletes rat glomeruli of resident macrophages and inhibits angiotensin II-induced eicosanoid synthesis

Essential fatty acid (EFA) deficiency exerts a beneficial effect on immune-mediated glomerulonephritis, preventing both the tissue injury and consequent mortality. Because both macrophages and eicosanoids are thought to play pathogenic roles in glomerulonephritis, and because macrophages play an important role in modulating arachidonate metabolism at sites of renal injury, the effects of EFA deficiency on the population of resident glomerular macrophages and on glomerular eicosanoid generation were examined. EFA deficiency led to a striking reduction in the number of resident glomerular macrophages and a corresponding reduction in the number of resident glomerular Ia+ cells. This phenomenon was not strain-specific, was not due to a decrease in circulating monocytes, was not a function of changes in cell surface labeling characteristics, and was not restricted to a specific subset of glomeruli. In addition, EFA deficiency affected other areas of the renal cortex: a comparable depletion of interstitial macrophages and Ia+ cells was also observed. In conjunction with the decrease in glomerular macrophages seen with the deficiency state, a marked decrease in both basal and angiotensin II-stimulated glomerular eicosanoid production was noted. In contrast to angiotensin II, platelet-activating factor-induced eicosanoid production was not significantly affected by the deficiency state. These changes in glomerular eicosanoid production could not be attributed to changes in glomerular cyclooxygenase or reacylation capacity. Dietary (n-6) fatty acid supplementation, but not (n-3) fatty acid supplementation, reversed both the decrease in glomerular macrophages and the diminished eicosanoid metabolism seen with the deficiency state. Understanding the mechanisms behind the changes in the glomerular microenvironment induced by EFA deficiency may provide a basis for elucidating the protective effect of dietary fatty acid manipulation on immune-mediated glomerulonephritis.

Dietary fat and neoplasia--the role of net energy in enhancement of carcinogenesis: effects of fat and calories on the immune system

The mechanism by which carcinogenesis is enhanced by dietary fat is not understood. We know that a minimum level of essential fatty acids (EFA) is necessary for mammary tumor development and that this level probably exceeds the normal requirements of rats. Once the minimum level of EFA has been supplied, the calorie contribution of dietary fat may account for its enhancement of carcinogenesis. In this regard, we must recognize that the efficiency with which dietary energy is utilized is known to increase as the fat content of the diet is raised. Hence even when fed isocalorically to low fat diets, high fat diets will provide more net energy. Modulation of host immunity has been proposed as a mechanism of action of both fat and calorie intake on neoplasia. We review the literature examining the effects of fat and calories on the cell-mediated immune system, that arm of the immune system most directly responsible for the killing of neoplastic cells.