Site-specific differences in the responses of guinea-pig adipose tissue to changes in the fatty acid composition of the diet

Different fatty acid composition in central and peripheral adipose tissues of the American mink (Mustela vison)

Fatty acid (FA) composition in the intraabdominal (IAB), subcutaneous (SC) and peripheral adipose tissues of the semiaquatic American mink (Mustela vison) was examined in comparison to the diet by gas-liquid chromatography. There was a clear compositional gradient from the IAB via SC to peripheral adipose tissues and the anatomically different adipose tissues accumulated or metabolized FA selectively. The total lipids of the body appendages had smaller proportions of saturated (SFA) and larger proportions of monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA) than the lipids of the trunk adipose tissues. Especially n-3 PUFA were enriched in the periphery. The appendages were also characterized with a high ratio of unsaturated FA to SFA, an increased Delta9-desaturation index and increased mean numbers of double bonds and carbon atoms in a FA molecule. The proportions of SFA and MUFA of the diet resembled the trunk adipose tissues while the dietary percentage of n-3 PUFA surpassed those of the trunk fat depots but was lower than those of the peripheral fats. These data confirm that the FA signatures of mammals reflect not only their dietary history but also metabolic modifications of ingested FA.

The effects of dietary lipids on adrenergically-stimulated lipolysis in perinodal adipose tissue following prolonged activation of a single lymph node

The effects of feeding beef suet (mostly saturated and monoenoic fatty acids), sunflower oil (rich inn-6 fatty acids) and fish oil (rich inn-3 fatty acids) on the response of mesenteric, omental, popliteal and perirenal adipocytes to experimentally-induced local inflammation were studied in adult guinea pigs. After 6 weeks on the experimental diets, the animals were fed standard chow, and lipopolysaccharide was injected unilaterally daily for 4 d to induce swelling of one popliteal lymph node. Basal lipolysis in the perinodal adipocytes of all depots studied was higher in the sunflower oil-fed animals than in the controls fed on standard chow, and lower in those fed on suet or fish oil. Dietary lipids altered rates of lipolysis during incubation with 10-5M noradrenaline in all samples studied from the locally-activated popliteal depot, but only in adipocytes within 5 mm of a large lymph node in the other depots. The fish-oil diet attenuated the spread of increased lipolysis within the locally-activated popliteal adipose tissue, and from this depot to other node-containing depots. These experiments show thatn-6 polyunsaturated fatty acids promote andn-3 fatty acids suppress the spread of immune activation to adipocytes within and between depots, and alter the sensitivity of perinodal adipocytes to noradrenaline. Dietary effects are reduced or absent in adipocytes in sites remote from lymph nodes, and thus such samples do not adequately represent processes in perinodal adipose tissue. These results are consistent with the hypothesis that perinodal adipocytes interact with adjacent lymphoid cells during immune responses.

Dietary fatty acids influence the appearance of tumour necrosis factor-α receptors on adipocytes following an immune challenge

Rats were fed from weaning on chow supplemented with suet or sunflower oil (10 % (w/w) each). The appearance of receptors for tumour necrosis factor-α on perinodal adipocytes from the popliteal depot following a subcutaneous injection of bacterial lipopolysaccharide was examined. In rats fed on sunflower oil-supplemented chow receptors appeared at a time similar to that described in rats fed unsupplemented chow, but in rats fed on chow supplemented with suet receptor appearance was significantly delayed. The popliteal adipocytes were found to contain different proportions of fatty acids as assessed by GLC. These preliminary results suggest that the fatty acid component of the diet can, by influencing the triacylglycerol-fatty acids within adipocytes, directly alter the time course of an early inflammatory immune response.

The effects of dietary lipids on dendritic cells in perinodal adipose tissue during chronic mild inflammation

The effects of dietary lipids on the abundance of dendritic cells in adipose tissue in anatomically defined relationships to chronically inflamed lymph nodes were investigated in mature male rats fed plain chow or chow plus 20 % sunflower-seed or fish oil. The popliteal lymph nodes were stimulated by local subcutaneous injection of 20 μg lipopolysaccharide to both hindlegs three times/week for 2 weeks. The masses of the major adipose depots and the numbers of dendritic cells emerging from perinodal adipose tissue and samples 5 and 10 mm from the popliteal lymph nodes were measured, and those from omental and mesenteric adipose tissue around and remote from lymphoid tissue, and mesenteric and popliteal lymph nodes. Dendritic cells were most numerous in the perinodal adipose tissue, with the corresponding ‘remote’ samples containing 25–50 % fewer such cells under all conditions studied. Dietary sunflower-seed oil increased the numbers of dendritic cells by about 17 % in all adipose samples and fish oil reduced the numbers in perinodal tissue by about 5 %. The fish-oil diet diminished responses of the intra-abdominal adipose depots to local stimulation of the popliteal node. Correlations in dendritic cell numbers were stronger between perinodal samples from different depots than between remote and perinodal samples from the same depot and after the sunflower-seed-oil diet compared with fish oil. These data show that dietary lipids modulate the number of dendritic cells in lymphoid tissue-containing adipose depots and support the hypothesis that perinodal adipose tissue interacts locally with lymphoid cells.

The effects of feeding suet-enriched chow on site-specific differences in the composition of triacylglycerol fatty acids in adipose tissue and its interactions in vitro with lymphoid cells

The effects of diet on the composition and properties of adipose tissue in relation to lymph nodes were studied in adult guinea-pigs. The proportions of monoenoic triacylglycerol fatty acids were constant in all sites in adipose tissue of similarly fed guinea-pigs, but were substantially greater in samples from guinea-pigs fed on suet-enriched chow. Triacylglycerols in adipose tissue from near nodes contained significantly fewer saturated fatty acids, and significantly more 18:2n-6 and 18:3n-3 than those in samples from sites remote from nodes within the same depot. Depots that interact most strongly with lymphoid cells in vitro had the largest and most consistent within-depot differences. The gradients of triacylglycerol fatty acid composition with distance from lymph nodes in two small intermuscular depots were similar in guinea-pigs fed on plain or suet-enriched chow. These findings are consistent with the hypothesis that adipose tissue around lymph nodes is specialized for local interactions with the lymphoid cells therein, and help to explain the variability of serial or duplicate measurements of adipose tissue composition. When cultured alone, lipopolysaccharide-stimulated lymph node lymphoid cells from suet-fed guinea-pigs incorporated as much labelled thymidine as the controls. Adipose tissue explants from suet-fed guinea-pigs inhibited lymphocyte proliferation much less than those of the controls, although the site-specific differences were similar. The pattern of site-specific differences in glycerol released from explants incubated alone was generally similar for both dietary groups, but except in the popliteal depot, the increases following co-culturing with lymphoid cells were smaller for samples from suet-fed guinea-pigs. These experiments show that minor changes in the fatty acid composition of the diet can substantially alter the interactions between adipose tissue and lymphoid cells.