Siobhán E. McQuaid

Downregulation of Adipose Tissue Fatty Acid Trafficking in Obesity A Driver for Ectopic Fat Deposition

OBJECTIVE Lipotoxicity and ectopic fat deposition reduce insulin signaling. It is not clear whether excess fat deposition in nonadipose tissue arises from excessive fatty acid delivery from adipose tissue or from impaired adipose tissue storage of ingested fat. RESEARCH DESIGN AND METHODS To investigate this we used a whole-body integrative physiological approach with multiple and simultaneous stable-isotope fatty acid tracers to assess delivery and transport of endogenous and exogenous fatty acid in adipose tissue over a diurnal cycle in lean (n = 9) and abdominally obese men (n = 10). RESULTS Abdominally obese men had substantially (2.5-fold) greater adipose tissue mass than lean control subjects, but the rates of delivery of nonesterified fatty acids (NEFA) were downregulated, resulting in normal systemic NEFA concentrations over a 24-h period. However, adipose tissue fat storage after meals was substantially depressed in the obese men. This was especially so for chylomicron-derived fatty acids, representing the direct storage pathway for dietary fat. Adipose tissue from the obese men showed a transcriptional signature consistent with this impaired fat storage function. CONCLUSIONS Enlargement of adipose tissue mass leads to an appropriate downregulation of systemic NEFA delivery with maintained plasma NEFA concentrations. However the implicit reduction in adipose tissue fatty acid uptake goes beyond this and shows a maladaptive response with a severely impaired pathway for direct dietary fat storage. This adipose tissue response to obesity may provide the pathophysiological basis for ectopic fat deposition and lipotoxicity.

Elevated Expression of Osteopontin May Be Related to Adipose Tissue Macrophage Accumulation and Liver Steatosis in Morbid Obesity

OBJECTIVE—Osteopontin (OPN) plays an important role in the development of insulin resistance and liver complications in dietary murine models. We aimed to determine the expression pattern of OPN and its receptor CD44 in obese patients and mice according to insulin resistance and liver steatosis. RESEARCH DESIGN AND METHODS—OPN and CD44 expressions were studied in 52 morbidly obese patients and in mice. Cellular studies were performed in HepG2 cells. RESULTS—Hepatic OPN and CD44 expressions were strongly correlated with liver steatosis and insulin resistance in obese patients and mice. This increased OPN expression could be due to the accumulation of triglycerides, since fat loading in HepG2 promotes OPN expression. In contrast, OPN expression in adipose tissue (AT) was enhanced independently of insulin resistance and hepatic steatosis in obese patients. The elevated OPN expression in AT was paralleled with the AT macrophage infiltration, and both phenomena were reversed after weight loss. The circulating OPN level was slightly elevated in obese patients and was not related to liver steatosis. Further, AT did not appear to secrete OPN. In contrast, bariatric surgery–induced weight loss induced a strong increase in circulating OPN. CONCLUSIONS—The modestly elevated circulating OPN levels in morbidly obese patients were not related to liver steatosis and did not appear to result from adipose tissue secretion. In subcutaneous AT, expression of OPN was directly related to macrophage accumulation independently from liver complications. In contrast, hepatic OPN and CD44 expressions were related to insulin resistance and steatosis, suggesting their local implication in the progression of liver injury.

The Contribution of Splanchnic Fat to VLDL Triglyceride Is Greater in Insulin-Resistant Than Insulin-Sensitive Men and Women: Studies in the Postprandial State

OBJECTIVE—We aimed to determine differences in the postprandial contributions of different fatty acid sources to VLDL triglycerides (TGs) in healthy men and women with varying degrees of insulin resistance. RESEARCH DESIGN AND METHODS—Insulin-resistant (n = 11) and insulin-sensitive (n = 11) men and women (n = 6) were given an intravenous infusion of [2H2]palmitic acid to investigate systemic nonesterified fatty acid (NEFA) incorporation into VLDL TGs. Participants were also fed a mixed meal containing [U-13C]palmitic acid to investigate the contribution of dietary fatty acids to VLDL TG production. Blood samples were taken over the following 6 h. Separation of VLDL was performed by density gradient ultracentrifugation and immunoaffinity techniques specific to apolipoprotein B-100. RESULTS—Insulin-resistant and insulin-sensitive men had similar postprandial chylomicron and chylomicron remnant TG concentrations, but insulin-resistant men had higher postprandial VLDL TG concentrations (median [range]; area under the curve 485 μmol/l [123–992] vs. 287 μmol/l [162–510]; P < 0.05). At 360 min, most of the difference in VLDL TGs was accounted for by an additional contribution from splanchnic fat (means ± SE; 331 ± 76 μmol/l vs. 89 ± 25 μmol/l; P < 0.01). The contribution of fatty acids from endogenous systemic NEFAs was similar across the groups, as were dietary fatty acids. There was no difference in the VLDL TG concentration or the contribution of different fatty acid sources between insulin-sensitive men and women. CONCLUSIONS—In the postprandial period, the only sources of fatty acids for VLDL TG production to differ in the insulin-resistant compared with the insulin-sensitive men are those derived from splanchnic sources.

Distinct Developmental Profile of Lower-Body Adipose Tissue Defines Resistance Against Obesity-Associated Metabolic Complications

Upper- and lower-body fat depots exhibit opposing associations with obesity-related metabolic disease. We defined the relationship between DEXA-quantified fat depots and diabetes/cardiovascular risk factors in a healthy population-based cohort (n = 3,399). Gynoid fat mass correlated negatively with insulin resistance after total fat mass adjustment, whereas the opposite was seen for abdominal fat. Paired transcriptomic analysis of gluteal subcutaneous adipose tissue (GSAT) and abdominal subcutaneous adipose tissue (ASAT) was performed across the BMI spectrum (n = 49; 21.4–45.5 kg/m2). In both depots, energy-generating metabolic genes were negatively associated and inflammatory genes were positively associated with obesity. However, associations were significantly weaker in GSAT. At the systemic level, arteriovenous release of the proinflammatory cytokine interleukin-6 (n = 34) was lower from GSAT than ASAT. Isolated preadipocytes retained a depot-specific transcriptional “memory” of embryonic developmental genes and exhibited differential promoter DNA methylation of selected genes (HOTAIR, TBX5) between GSAT and ASAT. Short hairpin RNA–mediated silencing identified TBX5 as a regulator of preadipocyte proliferation and adipogenic differentiation in ASAT. In conclusion, intrinsic differences in the expression of developmental genes in regional adipocytes provide a mechanistic basis for diversity in adipose tissue (AT) function. The less inflammatory nature of lower-body AT offers insight into the opposing metabolic disease risk associations between upper- and lower-body obesity.

Femoral Adipose Tissue May Accumulate the Fat That Has Been Recycled as VLDL and Nonesterified Fatty Acids

OBJECTIVE Gluteo-femoral, in contrast to abdominal, fat accumulation appears protective against diabetes and cardiovascular disease. Our objective was to test the hypothesis that this reflects differences in the ability of the two depots to sequester fatty acids, with gluteo-femoral fat acting as a longer-term “sink.” RESEARCH DESIGN AND METHODS A total of 12 healthy volunteers were studied after an overnight fast and after ingestion of a mixed meal. Blood samples were taken from veins draining subcutaneous femoral and abdominal fat and compared with arterialized blood samples. Stable isotope-labeled fatty acids were used to trace specific lipid fractions. In 36 subjects, adipose tissue blood flow in the two depots was monitored with 133Xe. RESULTS Blood flow increased in response to the meal in both depots, and these responses were correlated (rs = 0.44, P < 0.01). Nonesterified fatty acid (NEFA) release was suppressed after the meal in both depots; it was lower in femoral fat than in abdominal fat (P < 0.01). Plasma triacylglycerol (TG) extraction by femoral fat was also lower than that by abdominal fat (P = 0.05). Isotopic tracers showed that the difference was in chylomicron-TG extraction. VLDL-TG extraction and direct NEFA uptake were similar in the two depots. CONCLUSIONS Femoral fat shows lower metabolic fluxes than subcutaneous abdominal fat, but differs in its relative preference for extracting fatty acids directly from the plasma NEFA and VLDL-TG pools compared with chylomicron-TG.

Differences in partitioning of meal fatty acids into blood lipid fractions: a comparison of linoleate, oleate, and palmitate

There has been much interest in the health effects of dietary fat, but few studies have comprehensively compared the acute metabolic fate of specific fatty acids in vivo. We hypothesized that different classes of fatty acids would be variably partitioned in metabolic pathways and that this would become evident over 24 h. We traced the fate of fatty acids using equal amounts of [U-13C]linoleate, [U-13C]oleate, and [U-13C]palmitate given in a test breakfast meal in 12 healthy subjects. There was a tendency for differences in the concentrations of the tracers in plasma chylomicron-triacylglycerol (TG) (oleate > palmitate > linoleate). This pattern remained in plasma nonesterified fatty acid (NEFA) and very low-density lipoprotein (VLDL)-TG (P ≤ 0.01 and P ≤ 0.02 for [U-13C]oleate vs. both [U-13C]palmitate and [U-13C]linoleate for NEFA and VLDL-TG, respectively). There was significantly more [U-13C]linoleate than the other two tracers in plasma cholesteryl ester and phospholipid (PL). Using the values for isotopic enrichment in the different lipid fractions compared with the test meal, we calculated the contribution of meal fatty acids to the respective fractions. At 24 h, 10% of plasma PL-linoleate originated from the breakfast test meal. This was significantly greater than for oleate and palmitate (both 3 ± 0.3%; P < 0.05). This pattern was also true for erythrocyte PL fatty acids. The marked rapid incorporation of linoleate from a single meal into blood PL fractions may have functional consequences such as maintenance of membrane fluidity and may explain why linoleate is a useful biomarker of dietary intake.

Effect of anaesthetic technique on the natural killer cell anti-tumour activity of serum from women undergoing breast cancer surgery: a pilot study.

BACKGROUND Animal models and retrospective clinical data suggest that certain anaesthetic techniques can attenuate immunosuppression and minimize metastasis after cancer surgery. Natural killer (NK) T cells are a critical component of the anti-tumour immune response. We investigated the effect of serum from women undergoing primary breast cancer surgery, randomized to propofol-paravertebral block (PPA) or sevoflurane-opioid (GA) anaesthetic techniques, on healthy human donor NK cell function and cytotoxicity against oestrogen and progesterone receptor-positive breast cancer cells (HCC1500). METHODS Ten subjects who donated serum before operation and 24 h after operation in an ongoing randomized prospective trial (NCT 00418457) were randomly selected. Serum from PPA (n=5) and GA (n=5) subjects was co-cultured with HCC1500 and healthy primary NK cells. NK cell activating receptors (NKp30, NKp44, NKp46, 2b4, CD16, NKG2D), cytokine production, NK CD107a expression, and cytotoxicity towards HCC1500 were examined. RESULTS Serum from PPA subjects did not alter normal NK marker expression or secretion of cytokines. Serum from GA subjects reduced NK cell activating receptor CD16 [from mean (sem), 82 (2)% to 50 (4)%, P=0.001], IL-10 [from 1700 (80) to 1200 (92) pg ml(-1), P=0.001], and IL-1β [from 68 (12) to 19 (4) pg ml(-1), P=0.01]. An increase in NK cell CD107a [23 (2)% to 37(3)%, P=0.007] and apoptosis of HCC1500 [11 (1)% to 21 (2)%, P=0.0001] was observed with PPA serum, but not GA serum, treated NK cells. CONCLUSION Serum from women with breast cancer undergoing surgical excision who were randomized to receive a PPA anaesthetic technique led to greater human donor NK cell cytotoxicity in vitro compared with serum from women who received GA. CLINICAL TRIAL REGISTRATION NCT 041857.

Greater dietary fat oxidation in obese compared with lean men: an adaptive mechanism to prevent liver fat accumulation?

Liver fat represents a balance between input, secretion, and oxidation of fatty acids. As humans spend the majority of a 24-h period in a postprandial state, dietary fatty acids make an important contribution to liver fat metabolism. We compared hepatic fatty acid partitioning in healthy lean (n = 9) and abdominally obese (n = 10) males over 24 h. Volunteers received three mixed meals adjusted for basal metabolic rate. U-13C-labeled fatty acids were incorporated into the meals, and [2H2]palmitate was infused intravenously to distinguish between sources of fatty acids incorporated into VLDL-TG. Immunoaffinity chromatography was used to isolate VLDL-TG of hepatic origin. Liver and whole body fatty acid oxidation was assessed by isotopic enrichment of 3-hydoxybutyrate and breath CO2. We found a similar contribution of dietary fatty acids to VLDL-TG in the two groups over 24 h. The contribution of fatty acids from splanchnic sources was higher (P < 0.05) in the abdominally obese group. Ketogenesis occurred to a significantly greater extent in abdominally obese compared with lean males, largely due to lessened downregulation of postprandial ketogenesis (P < 0.001). The appearance of 13C in breath CO2 was also greater (P < 0.001) in abdominally obese compared with lean men. Hepatic elongation and desaturation of palmitic acid were higher (P < 0.05) in abdominally obese than in lean males. Oxidation of dietary fatty acids and hepatic desaturation and elongation of palmitic acid occurred to a greater extent in abdominally obese men. These alterations may represent further pathways for redirection of fatty acids into export from the liver or oxidation to prevent liver fat accumulation.

Development of an Arterio-venous Difference Method to Study the Metabolic Physiology of the Femoral Adipose Tissue Depot

Gluteofemoral adipose tissue (AT) has interesting positive associations with metabolic health, yet little is known of its metabolic physiology. Here, we describe a technique for cannulation of a vein draining the femoral fat depot. Using ultrasound guidance, a cannula was introduced into a superficial branch of the great saphenous vein. We also obtained arterialized blood and, for comparison, blood representing drainage from forearm muscle and from subcutaneous abdominal AT. We measured appropriate biomarkers of skeletal muscle (creatinine) and AT (nonesterified fatty acids (NEFAs), glycerol, leptin) drainage. Blood obtained in this way from the saphenous vein did not show creatinine release (creatinine concentration 100.5 ± 0.4%, mean ± s.e.m., of that in arterialized blood), whereas creatinine concentrations in blood draining forearm muscle averaged 121 ± 1% of those in arterialized blood. Fatty acid release from the tissue drained was suppressed after feeding and increased during β‐adrenergic stimulation. We also demonstrated leptin secretion. These findings suggest that blood so obtained is representative of AT drainage with little apparent contribution of skeletal muscle. We believe this technique will facilitate physiological studies of a lower‐body fat depot in humans.