Kupffer Cells Sense Free Fatty Acids and Regulate Hepatic Lipid Metabolism in High-Fat Diet and Inflammation.

A high fat Western-style diet leads to hepatic steatosis that can progress to steatohepatitis and ultimately cirrhosis or liver cancer. The mechanism that leads to the development of steatosis upon nutritional overload is complex and only partially understood. Using click chemistry-based metabolic tracing and microscopy, we study the interaction between Kupffer cells and hepatocytes ex vivo. In the early phase of steatosis, hepatocytes alone do not display significant deviations in fatty acid metabolism. However, in co-cultures or supernatant transfer experiments, we show that tumor necrosis factor (TNF) secretion by Kupffer cells is necessary and sufficient to induce steatosis in hepatocytes, independent of the challenge of hepatocytes with elevated fatty acid levels. We further show that free fatty acid (FFA) or lipopolysaccharide are both able to trigger release of TNF from Kupffer cells. We conclude that Kupffer cells act as the primary sensor for both FFA overload and bacterial lipopolysaccharide, integrate these signals and transmit the information to the hepatocyte via TNF secretion. Hepatocytes react by alteration in lipid metabolism prominently leading to the accumulation of triacylglycerols (TAGs) in lipid droplets, a hallmark of steatosis.

Ceramide synthase inhibition by fumonisins: a perfect storm of perturbed sphingolipid metabolism, signaling, and disease.

Fumonisins are mycotoxins that cause diseases of plants and, when consumed by animals, can damage liver, kidney, lung, brain, and other organs, alter immune function, and cause developmental defects and cancer. They structurally resemble sphingolipids (SLs), and studies nearly 30 years ago discovered that the most prevalent fumonisin [fumonisin B1 (FB1)] potently inhibits ceramide synthases (CerSs), enzymes that use fatty acyl-CoAs to N-acylate sphinganine (Sa), sphingosine (So), and other sphingoid bases. CerS inhibition by FB1 triggers a "perfect storm" of perturbations in structural and signaling SLs that include: reduced formation of dihydroceramides, ceramides, and complex SLs; elevated Sa and So and their 1-phosphates, novel 1-deoxy-sphingoid bases; and alteration of additional lipid metabolites from interrelated pathways. Moreover, because the initial enzyme of sphingoid base biosynthesis remains active (sometimes with increased activity), the impact is multiplied by the continued production of damaging metabolites. Evidence from many studies, including characterization of knockout mice for specific CerSs and analyses of human blood (which found that FB1 intake is associated with elevated Sa 1-phosphate), has consistently pointed to CerS as the proximate target of FB1 It is also apparent that the changes in multiple bioactive lipids and related biologic processes account for the ensuing spectrum of animal and plant disease. Thus, the diseases caused by fumonisins can be categorized as "sphingolipidoses" (in these cases, due to defective SL biosynthesis), and the lessons learned about the consequences of CerS inhibition should be borne in mind when contemplating other naturally occurring and synthetic compounds (and genetic manipulations) that interfere with SL metabolism.

Uptake and metabolism of ß-apo-8'-carotenal, ß-apo-10'-carotenal, and ß-apo-13-carotenone in Caco-2 cells.

ß-Apocarotenoids are eccentric cleavage products of carotenoids formed by chemical and enzymatic oxidations. They occur in foods containing carotenoids and thus might be directly absorbed from the diet. However, there is limited information about their intestinal absorption. The present research examined the kinetics of uptake and metabolism of ß-apocarotenoids. Caco-2 cells were grown on 6-well plastic plates until a differentiated cell monolayer was achieved. ß-Apocarotenoids were prepared in Tween 40 micelles, delivered to differentiated cells in serum-free medium, and incubated at 37°C for up to 8 h. There was rapid uptake of ß-apo-8'-carotenal into cells, and ß-apo-8'-carotenal was largely converted to ß-apo-8'-carotenoic acid and a minor metabolite that we identified as 5,6-epoxy-ß-apo-8'-carotenol. There was also rapid uptake of ß-apo-10'-carotenal into cells, and ß-apo-10'-carotenal was converted into a major metabolite identified as 5,6-epoxy-ß-apo-10'-carotenol and a minor metabolite that is likely a dihydro-ß-apo-10'-carotenol. Finally, there was rapid cellular uptake of ß-apo-13-carotenone, and this compound was extensively degraded. These results suggest that dietary ß-apocarotenals are extensively metabolized in intestinal cells via pathways similar to the metabolism of retinal. Thus, they are likely not absorbed directly from the diet.

Dietary lysophosphatidylcholine-EPA enriches both EPA and DHA in the brain: potential treatment for depression.

EPA and DHA protect against multiple metabolic and neurologic disorders. Although DHA appears more effective for neuroinflammatory conditions, EPA is more beneficial for depression. However, the brain contains negligible amounts of EPA, and dietary supplements fail to increase it appreciably. We tested the hypothesis that this failure is due to absorption of EPA as triacylglycerol, whereas the transporter at the blood-brain barrier requires EPA as lysophosphatidylcholine (LPC). We compared tissue uptake in normal mice gavaged with equal amounts (3.3 µmol/day) of either LPC-EPA or free EPA (surrogate for current supplements) for 15 days and also measured target gene expression. Compared with the no-EPA control, LPC-EPA increased brain EPA >100-fold (from 0.03 to 4 µmol/g); free EPA had little effect. Furthermore, LPC-EPA, but not free EPA, increased brain DHA 2-fold. Free EPA increased EPA in adipose tissue, and both supplements increased EPA and DHA in the liver and heart. Only LPC-EPA increased EPA and DHA in the retina, and expression of brain-derived neurotrophic factor, cyclic AMP response element binding protein, and 5-hydroxy tryptamine (serotonin) receptor 1A in the brain. These novel results show that brain EPA can be increased through diet. Because LPC-EPA increased both EPA and DHA in the brain, it may help in the treatment of depression as well as neuroinflammatory diseases, such as Alzheimer's disease.

PEMT, Δ6 desaturase, and palmitoyldocosahexaenoyl phosphatidylcholine are increased in rats during pregnancy.

DHA is important for fetal neurodevelopment. During pregnancy, maternal plasma DHA increases, but the mechanism is not fully understood. Using rats fed a fixed-formula diet (DHA as 0.07% total energy), plasma and liver were collected for fatty acid profiling before pregnancy, at 15 and 20 days of pregnancy, and 7 days postpartum. Phosphatidylethanolamine methyltransferase (PEMT) and enzymes involved in PUFA synthesis were examined in liver. Ad hoc transcriptomic and lipidomic analyses were also performed. With pregnancy, DHA increased in liver and plasma lipids, with a large increase in plasma DHA between day 15 and day 20 that was mainly attributed to an increase in 16:0/DHA phosphatidylcholine (PC) in liver (2.6-fold) and plasma (3.9-fold). Increased protein levels of Δ6 desaturase (FADS2) and PEMT at day 20 and increased Pemt expression and PEMT activity at day 15 suggest that during pregnancy, both DHA synthesis and 16:0/DHA PC synthesis are upregulated. Transcriptomic analysis revealed minor changes in the expression of genes related to phospholipid synthesis, but little insight on DHA metabolism. Hepatic PEMT appears to be the mechanism for increased plasma 16:0/DHA PC, which is supported by increased DHA biosynthesis based on increased FADS2 protein levels.

Weekday variation in triglyceride concentrations in 1.8 million blood samples.

Triglyceride (TG) concentration is used as a marker of cardiometabolic risk. However, diurnal and possibly weekday variation exists in TG concentrations. The objective of this work was to investigate weekday variation in TG concentrations among 1.8 million blood samples drawn between 2008 and 2015 from patients in the Capital region of Denmark. Plasma TG was extracted from a central clinical laboratory information system. Weekday variation was investigated by means of linear mixed models. In addition to the profound diurnal variation, the TG concentration was 4.5% lower on Fridays compared with Mondays (P < 0.0001). The variation persisted after multiple adjustments for confounders and was consistent across all sensitivity analyses. Out-patients and in-patients, respectively, had 5.0% and 1.9% lower TG concentrations on Fridays compared with Mondays (both P < 0.0001). The highest weekday variations in TG concentrations were recorded for out-patients between the ages of 9 and 26 years, with up to 20% higher values on Mondays compared with Fridays (all P < 0.05). In conclusion, TG concentrations were highest after the weekend and gradually declined during the week. We suggest that unhealthy food intake and reduced physical activity during the weekend increase TG concentrations which track into the week. This weekday variation may carry implications for public health and future research practice.

Genetic and hormonal control of hepatic steatosis in female and male mice.

The etiology of nonalcoholic fatty liver disease is complex and influenced by factors such as obesity, insulin resistance, hyperlipidemia, and sex. We now report a study on sex difference in hepatic steatosis in the context of genetic variation using a population of inbred strains of mice. While male mice generally exhibited higher concentration of hepatic TG levels on a high-fat high-sucrose diet, sex differences showed extensive interaction with genetic variation. Differences in percentage body fat were the best predictor of hepatic steatosis among the strains and explained about 30% of the variation in both sexes. The difference in percent gonadal fat and HDL explained 9.6% and 6.7% of the difference in hepatic TGs between the sexes, respectively. Genome-wide association mapping of hepatic TG revealed some striking differences in genetic control of hepatic steatosis between females and males. Gonadectomy increased the hepatic TG to body fat percentage ratio among male, but not female, mice. Our data suggest that the difference between the sexes in hepatic TG can be partly explained by differences in body fat distribution, plasma HDL, and genetic regulation. Future studies are required to understand the molecular interactions between sex, genetics, and the environment.

Lipid Emulsion Formulation of Parenteral Nutrition Affects Intestinal Microbiota and Host Responses in Neonatal Piglets.

BACKGROUND: Total parenteral nutrition (TPN) is a cause of intestinal microbial dysbiosis and impaired gut barrier function. This may contribute to life-threatening parenteral nutrition-associated liver disease and sepsis in infants. We compared the effects of a lipid emulsion containing long-chain ω-3 polyunsaturated fatty acids (PUFAs; SMOFlipid) and a predominantly ω-6 PUFA emulsion (Intralipid) on microbial composition and host response at the mucosal surface. MATERIALS AND METHODS: Neonatal piglets were provided isocaloric, isonitrogenous TPN for 14 days versus sow-fed (SF) controls. Equivalent lipid doses (10 g/kg/d) were given of either SMOFlipid (ML; n = 10) or Intralipid (SO; n = 9). Ileal segments and mucosal scrapings were used to characterize microbial composition by 16S rRNA gene sequencing and quantitative gene expression of tight junction proteins, mucins, antimicrobial peptides, and inflammatory cytokines. RESULTS: The microbial composition of TPN piglets differed from SF, while ML and SO differed from each other (analysis of molecular variance; P < .05); ML piglets were more similar to SF, as indicated by UniFrac distance ( P < .05). SO piglets showed a specific and dramatic increase in Parabacteroides ( P < .05), while ML showed an increase in Enterobacteriaceae ( P < .05). Gene expression of mucin, claudin 1, ß-defensin 2, and interleukin 8 were higher in TPN; overall increases were significantly less in ML versus SO ( P < .05). CONCLUSION: The formulation of parenteral lipid is associated with differences in the gut microbiota and host response of TPN-fed neonatal piglets. Inclusion of ω-3 long-chain PUFAs appears to improve host-microbial interactions at the mucosal surface, although mechanisms are yet to be defined.