Triacylglycerol Release Research Articles

MLDSR, the transcriptional regulator of the major lipid droplets protein MLDS, is controlled by long-chain fatty acids and contributes to the lipid-accumulating phenotype in oleaginous Rhodococcus strains.

Microorganism lipid droplet small regulator (MLDSR) is a transcriptional regulator of the major lipid droplet (LD)-associated protein MLDS in Rhodococcus jostii RHA1 and Rhodococcus opacus PD630. In this study, we investigated the role of MLDSR on lipid metabolism and triacylglycerol (TAG) accumulation in R. jostii RHA1 at physiological and molecular levels. MLDSR gene deletion promoted a significant decrease of TAG accumulation, whereas inhibition of de novo fatty acid biosynthesis by the addition of cerulenin significantly repressed the expression of the mldsr-mlds cluster under nitrogen-limiting conditions. In vitro and in vivo approaches revealed that MLDSR-DNA binding is inhibited by fatty acids and acyl-CoA residues through changes in the oligomeric or conformational state of the protein. RNAseq analysis indicated that MLDSR not only controls the expression of its own gene cluster but also of several genes involved in central, lipid, and redox metabolism, among others. We also identified putative MLDSR-binding sites on the upstream regions of genes coding for lipid catabolic enzymes and validated them by EMSA assays. Overexpression of mldsr gene under nitrogen-rich conditions promoted an increase of TAG accumulation, and further cell lysis with TAG release to the culture medium. Our results suggested that MLDSR is a fatty acid-responsive regulator that plays a dual role in cells by repression or activation of several metabolic genes in R. jostii RHA1. MLDSR seems to play an important role in the fine-tuning regulation of TAG accumulation, LD formation, and cellular lipid homeostasis, contributing to the oleaginous phenotype of R. jostii RHA1 and R. opacus PD630.

Coadministration of olanzapine causes minor impacts on the diabetogenic outcomes induced by dexamethasone treatment in rats

AimsInvestigate whether the coadministration of olanzapine exacerbates the diabetogenic effects of dexamethasone, two agents used in the antiemetic cocktails indicated to mitigate the adverse effects of chemotherapy. Main methodsAdult Wistar rats (both sexes) were treated daily with dexamethasone (1 mg/kg, body mass (b.m.), intraperitoneal (i.p.)) with or without olanzapine (10 mg/kg, b.m., orogastric (o.g.)) for 5 consecutive days. During and at the end of the treatment, we evaluated biometric data and parameters involving glucose and lipid metabolism. Key findingsDexamethasone treatment resulted in glucose and lipid intolerance, higher plasma insulin and triacylglycerol levels, higher content of hepatic glycogen and fat, and higher islet mass in both sexes. These changes were not exacerbated by concomitant treatment with olanzapine. However, coadministration of olanzapine worsened the weight loss and plasma total cholesterol in males, while in females resulted in lethargy, higher plasma total cholesterol, and higher hepatic triacylglycerol release. SignificanceCoadministration of olanzapine does not exacerbate any diabetogenic dexamethasone effect on glucose metabolism and exerts a minor impact on the lipid homeostasis of rats. Our data favor the addition of olanzapine in the antiemetic cocktail considering the low incidence of metabolic adverse effects for the period and dosage analyzed in male and female rats.

Competition of rapeseed proteins and oleosomes for the air-water interface and its effect on the foaming properties of protein-oleosome mixtures

There is an increasing interest to apply oleosomes (plant oil storage organelles) as natural oil droplets in food systems. Lipids are usually known to be detrimental for protein-stabilised foams due to the weakening of interactions between adsorbed proteins, or by forming oil bridges between two protein surfaces. Both mechanisms can lead to film rupture, and thereby destabilise protein-stabilised foams. Little is known about the influence of oleosomes on protein-stabilised interfaces and foams. Therefore, these properties were studied for rapeseed protein–oleosome mixtures at various protein concentrations and ratios. At 0.1 and 0.2% (w/w) protein content, oleosomes were found to co-adsorb with proteins at the interface, followed by rupture of oleosomes and release of triacylglycerols and phospholipids. This led to weaker in-plane interactions between adsorbed proteins. As a result, the foamability and foam stability of protein-oleosome systems were substantially lower compared to systems made with pure proteins. At 0.5 and 1.0% (w/w) protein content, the rapeseed proteins were found to dominate the interfacial properties. The proteins formed a dense solid-like layer at such high concentrations, which prevented the oleosomes from co-adsorbing at the interface. Also, in foam systems at high protein concentrations, the proteins seemed to outcompete the oleosomes for the interface, leading to higher foam stability. Here, we have demonstrated that the detrimental influence of oleosomes on protein-stabilised interfaces and foams can be controlled by varying the amount of oleosomes and rapeseed proteins in the mixture, which is a promising outcome to further utilise oleosomes in aerated food systems.

The Hypotriglyceridemic Effect of Sciadonic Acid is Mediated by the Inhibition of Δ9-Desaturase Expression and Activity.

Sciadonic acid (Scia; 20:3Δ5,11,14) is a distinctive fatty acid (FA) with a polymethylene-interrupted double bond at C5. It is specifically found in seeds from gymnosperms such as pine nuts. Published papers describe a decrease in liver and plasma triacylglycerols in rats fed with this nutriment. The present study seeks to identify the action mechanism of Scia on triacylglycerol synthesis. In this way, its nutritional effect on FA metabolism involving the Stearoyl-CoA Desaturase 1 (SCD1) is investigated. Scia is discerned in trace amount in various tissues of rats and in human serum. It is produced by Δ5-desaturation of 20:2n-6 in human transfected SH-SY5Y cell lines and also in rat hepatocytes. When Scia is incubated with cultured hepatocytes as a nutrient, the cellular FA profile is modified. In particular, the proportion of the monoenes (18:1n-9, 18:1n-7, 16:1n-7) are all decreased, correlating to the reduction of triacylglycerol amounts. This effect is mediated by the inhibition of SCD1 expression. Furthermore, Scia, as well as 20:3n-6 and 20:3n-9 but not 20:3n-3, strongly inhibit the SCD1 activity measured on liver microsomes. Overall, this study shows that Scia, despite its unusual structure, contributes to the FA metabolism and reduced triacylglycerol release by inhibiting SCD1 activity.

The brown adipocyte protein CIDEA promotes lipid droplet fusion via a phosphatidic acid-binding amphipathic helix.

Maintenance of energy homeostasis depends on the highly regulated storage and release of triacylglycerol primarily in adipose tissue, and excessive storage is a feature of common metabolic disorders. CIDEA is a lipid droplet (LD)-protein enriched in brown adipocytes promoting the enlargement of LDs, which are dynamic, ubiquitous organelles specialized for storing neutral lipids. We demonstrate an essential role in this process for an amphipathic helix in CIDEA, which facilitates embedding in the LD phospholipid monolayer and binds phosphatidic acid (PA). LD pairs are docked by CIDEA trans-complexes through contributions of the N-terminal domain and a C-terminal dimerization region. These complexes, enriched at the LD-LD contact site, interact with the cone-shaped phospholipid PA and likely increase phospholipid barrier permeability, promoting LD fusion by transference of lipids. This physiological process is essential in adipocyte differentiation as well as serving to facilitate the tight coupling of lipolysis and lipogenesis in activated brown fat.

Mechanistic insights revealed by lipid profiling in monogenic insulin resistance syndromes.

BackgroundEvidence from several recent metabolomic studies suggests that increased concentrations of triacylglycerols with shorter (14–16 carbon atoms), saturated fatty acids are associated with insulin resistance and the risk of type 2 diabetes. Although causality cannot be inferred from association studies, patients in whom the primary cause of insulin resistance can be genetically defined offer unique opportunities to address this challenge.MethodsWe compared metabolite profiles in patients with congenital lipodystrophy or loss-of-function insulin resistance (INSR gene) mutations with healthy controls.ResultsThe absence of significant differences in triacylglycerol species in the INSR group suggest that changes previously observed in epidemiological studies are not purely a consequence of insulin resistance. The presence of triacylglycerols with lower carbon numbers and high saturation in patients with lipodystrophy suggests that these metabolite changes may be associated with primary adipose tissue dysfunction. The observed pattern of triacylglycerol species is indicative of increased de novo lipogenesis in the liver. To test this we investigated the distribution of these triacylglycerols in lipoprotein fractions using size exclusion chromatography prior to mass spectrometry. This associated these triacylglycerols with very low-density lipoprotein particles, and hence release of triacylglycerols into the blood from the liver. To test further the hepatic origin of these triacylglycerols we induced de novo lipogenesis in the mouse, comparing ob/ob and wild-type mice on a chow or high fat diet, confirming that de novo lipogenesis induced an increase in relatively shorter, more saturated fatty acids.ConclusionsOverall, these studies highlight hepatic de novo lipogenesis in the pathogenesis of metabolic dyslipidaemia in states where energy intake exceeds the capacity of adipose tissue.Electronic supplementary materialThe online version of this article (doi:10.1186/s13073-015-0179-6) contains supplementary material, which is available to authorized users.

Dietary Diacylglycerol Induces the Regression of Atherosclerosis in Rabbits ,2

Recent studies of the relation between serum triacylglycerol concentration and the risk for coronary artery disease suggest that inefficient clearance of postprandial triacylglycerols promotes atherogenesis. We recently demonstrated that dietary diacylglycerol (DAG), rich in the 1,3-species, suppresses the postprandial increase in serum triacylglycerol levels compared with dietary triacylglycerol (TAG). Here, we investigated the effects of dietary DAG on atherosclerosis in rabbits with cholesterol-induced atherosclerosis. New Zealand White rabbits (n = 20) were fed a diet containing 3% lard and 1.3% cholesterol for 50 d to induce atherosclerotic lesions. Thereafter, the rabbits were assigned to 2 groups and fed 90 g/d nonpurified diet and orally administered 5 g DAG or TAG for an additional 34 d. Reference rabbits (n = 5) were fed only the nonpurified diet throughout the 84-d study. The area of atherosclerotic lesions and aortic lipid concentrations were significantly lower in DAG-fed rabbits compared with TAG-fed rabbits. The VLDL receptor and macrophage antigen-1 mRNA expression levels were significantly lower in DAG-fed rabbits than in TAG-fed rabbits. In the liver of DAG-fed rabbits, the triacylglycerol concentration was lower and the carnitine palmitoyltransferase activity higher than in TAG-fed rabbits. Stimulation of hepatic lipid catabolism might be related to the reduced lipid accumulation in the liver and aorta by reducing the release of triacylglycerol into the circulation. Thus, long-term consumption of DAG, which reduces postprandial lipemia, might be useful for the regression of atherosclerosis by stimulating hepatic lipid catabolism and thereby modulating monocyte/macrophage migration and aortic lipid accumulation.

Net flux of nonesterified fatty acids, cholesterol, triacylglycerol, and glycerol across the portal-drained viscera and liver of pregnant ewes.

The objective of this study was to determine the pattern of nutrient flux across portal-drained viscera (PDV) and liver in ewes with varying numbers of fetuses. Catheters were placed in the hepatic portal vein, a branch of the hepatic vein, a mesenteric vein, and the abdominal aorta of each ewe. Plasma flow and net cholesterol, nonesterified fatty acids (NEFA), and glycerol release across the PDV and liver were determined prior to exposure to rams. Ewes were subsequently mated. Two ewes were not pregnant, six ewes gave birth to singles, and 11 ewes gave birth to twins. Additional measurements were taken 103, 82, 61, 39, 19, and 6 d before parturition. There was a net PDV uptake of nonesterified cholesterol in the nonpregnant ewes and a net release in the ewes with singles and twins. Net nonesterified cholesterol hepatic release did not differ with days from parturition (P = .77). There was a net hepatic release of nonesterified cholesterol in the ewes with twins and a net hepatic uptake in the ewes with singles and in nonpregnant ewes (P = .03). There was a net PDV release of NEFA; however, it did not differ with litter size (P = .59) or days from parturition (P = .63). Hepatic NEFA uptake increased with litter size (P = .03) and increased as gestation progressed (P = .006). There was an interaction (P = .04) between litter size and days from parturition for net PDV glycerol release. Net PDV glycerol release in the nonpregnant ewes decreased over time, but release in pregnant ewes tended to increase over time. Hepatic glycerol uptake increased with litter size and increased as gestation progressed. There was a net PDV uptake of triacylglycerol, but it did not differ with litter size (P = .11) or with days from parturition (P = .06). There was a net hepatic release of triacylglycerol, but it did not differ with litter size (P = .59) or with days from parturition (P = .67). Liver utilization of glycerol and NEFA as substrates for metabolism increases as pregnancy progresses. In the nonpregnant ewe, the combined contribution of glycerol and NEFA carbon accounted for 10% of the carbon taken up by the liver, and in ewes pregnant with twins, the combined contribution accounted for 42% of the carbon uptake 19 d before parturition. In conclusion, these data demonstrate NEFA are an important metabolite when determining carbon balance across the liver and their relative contribution to carbon balance increases as pregnancy progresses.

Release of Lipids during Yeast Autolysis in a Model Wine System

The release of lipids during the aging of sparkling wines in contact with yeast can influence wine sensory attributes and, especially, foam characteristics. Model systems allow study of the autolysis process in a reasonable period of time compared to natural conditions, at which it can last several months. In this paper, the release of the different classes of lipids during the autolysis of three commercial yeast strains in a model wine medium has been monitored. Due to the absence of accurate quantitative methods, an HPLC method for separating and quantifying the different neutral and polar yeast lipid classes was developed. Lipids were eluted through a YMC PVA-Sil column with a complex solvent mixture. Detection was carried out with a light-scattering detector. The yeasts were suspended in the model wine buffer and incubated at 30 degrees C for up to 12 days. A release of triacylglycerols, 1,3-diacylglycerols, 2-monoacylglycerols, free fatty acids, sterol esters, and sterols was observed over the first 2 days, a period that corresponded to the maximum loss of yeast viability. A decrease in most of these lipids was observed from day 2, possibly indicative of the release of yeast hydrolytic enzymes due to the breakdown of the cell wall. Phospholipids were not detected in any of the autolysates. The mean lipid content in the autolysates as a percentage of the total lipid content in the yeasts was 8.6% for sterol esters, 3.8% for sterols, 2% for triacylglycerols, and <2% for 1,3-diacylglycerols and free fatty acids.

Regulation of milk lipid secretion: effects of oxytocin, prolactin and ionomycin on triacylglycerol release from rat mammary gland slices

A system for the study of the regulation of the release of triacylglycerols by mammary gland slices was developed. By prelabelling the triacylglycerol pool with [3H]oleate measurements of release of both mass of triacylglycerol and of newly synthesized triacylglycerol have been made. Oxytocin and ovine prolactin stimulated release of triacylglycerol and protein, but the former was 40-fold more effective. Recombinant bovine prolactin was even less active than ovine prolactin, suggesting that contamination of the latter with oxytocin and/or vasopressin was partly responsible for its stimulatory effect on release. The findings support the view that the major effect of oxytocin is to stimulate contraction of myoepithelial cells and thus release secreted lipid stored in the lumen of the mammary gland alveoli. Ionomycin, a Ca2+ ionophore, also stimulated lipid release, but probably not by the usual apocrine route. Parathyroid hormone-related protein, a peptide produced by the mammary gland, did not stimulate release or antagonize the effects of oxytocin. Release of lipid was also measured in mammary gland slices from late-pregnant, early- and mid-lactating rats and lactating rats made prolactin-deficient. Hormonal stimulation in vitro showed the maturation of response seen in vivo on transition from late pregnancy to peak lactation. Prolactin deficiency resulted in decreased release of newly synthesized lipid in response to oxytocin.

Inhibitory effect of gastrin and cholecystokinin fragments on the secretion of triacylglycerol in rat hepatocytes

In this investigation we studied the influence of two gastrin fragments, pentagastrin and nonsulfated heptadecagastrin, and two cholecystokinin fragments, sulfated and desulfated cholecystokinin 26-33, on intracellular and secreted triacylglycerol in isolated hepatocyte cultures. Both gastrin fragments inhibited triacylglycerol release in a biphasic manner, exhibiting maximal effect at 0.1 nmol/L (nonsulfated heptadecagastrin) and 0.3 nmol/L (pentagastrin). At these concentrations triacylglycerol secretion was 42% (nonsulfated heptadecagastrin, p < 0.001) and 62% (pentagastrin, p < 0.001) lower than in cells untreated with gastrin. Sulfated cholecystokinin 26-33 caused a 35% decrease in triacylglycerol secretion at 0.1 nmol/L (p < 0.01), and desulfated cholecystokinin 26-33 caused a 53% decrease at 0.2 nmol/L (p < 0.001). In all experiments, the hormone-induced decrease in triacylglycerol secretion was accompanied by an increase in intracellular triacylglycerol content. The cholecystokinin-A receptor antagonist L-364, 718 did not affect the decrease in triacylglycerol secretion induced by 0.3 nmol/L pentagastrin, whereas the cholecystokinin-B receptor antagonist L-365, 260 inhibited the pentagastrin effect at concentrations above 50 nmol/L. These results suggest that gastrin, cholecystokinin or some other gastrinlike hormone (or all three) may play a previously unrecognized regulatory role with respect to hepatic very low density lipoprotein secretion.

Inhibitory effect of gastrin and cholecystokinin fragments on the secretion of triacylglycerol in rat hepatocytes

In this investigation we studied the influence of two gastrin fragments, pentagastrin and nonsulfated heptadecagastrin, and two cholecystokinin fragments, sulfated and desulfated cholecystokinin 26–33, on intracellular and secreted triacylglycerol in isolated hepatocyte cultures. Both gastrin fragments inhibited triacylglycerol release in a biphasic manner, exhibiting maximal effect at 0.1 nmol/L (nonsulfated heptadecagastrin) and 0.3 nmol/L (pentagastrin). At these concentrations triacylglycerol secretion was 42% (non-sulfated heptadecagastrin, p < 0.001) and 62% (pentagastrin, p < 0.001) lower than in cells untreated with gastrin. Sulfated cholecystokinin 26–33 caused a 35% decrease in triacylglycerol secretion at 0.1 nmol/L (p < 0.01), and desulfated cholecystokinin 26–33 caused a 53% decrease at 0.2 nmol/L (p < 0.001). In all experiments, the hormone-induced decrease in triacylglycerol secretion was accompanied by an increase in intracellular triacylglycerol content. The cholecystokinin-A receptor antagonist L-364, 718 did not affect the decrease in triacylglycerol secretion induced by 0.3 nmol/L pentagastrin, whereas the cholecystokinin-B receptor antagonist L-365, 260 inhibited the pentagastrin effect at concentrations above 50 nmol/L. These results suggest that gastrin, cholecystokinin or some other gastrinlike hormone (or all three) may play a previously unrecognized regulatory role with respect to hepatic very low density lipoprotein secretion. (HEPATOLOGY 1993;18:1232-1237).

Induction of preadipocyte differentiation by mature fat cells in the rat.

In this study we investigated the influence of mature adipocytes, derived from rat adipose tissue, on the replication and differentiation of preadipocytes in primary culture. Mature fat did not inhibit preadipocyte replication within the 6-d period studied. Preadipocyte differentiation, as assessed by both cytoplasmic lipid accretion and an increase in glycerophosphate dehydrogenase (GPDH) activity, was significantly stimulated by the presence of mature fat tissue or isolated adipocytes. The proportion of cells containing visible lipid droplets by oil red O staining was 47 +/- 10 to 58 +/- 10% (depending on the site of origin of the preadipocytes) when cocultured with mature fat compared with less than 1 to 2 +/- 1% when cultured in medium alone, while GPDH activity was 344 +/- 9 compared with 43 +/- 3 nM NADH/min per mg protein, respectively. This effect was not due to release of triacylglycerols from damaged adipocytes. Fatty acids added to the medium promoted lipid accumulation but did not stimulate a rise in GPDH activity. We concluded that mature adipocytes may release factor(s) that promote preadipocyte differentiation (and maturation).

Evolution of the Lipid Contents of Champagne Wine During the Second Fermentation ofSaccharomyces cerevisiae

During the second fermentation by <i>Saccharomyces cerevisiae</i> in Champagne wine, the neutral lipid composition of the wine was greatly affected. The main characteristic of this process was the release of triacylglycerol from yeasts into the wine. Moreover, changes of the lipid contents resulted from multiple chemical reactions which occurred in wine, <i>i.e.</i>, the degradation of both free fatty acids and diacylglycerols. The oxidation of triacylglycerol fatty acids (specifically on C-2 position of glycerol) and their release into the wine was an additional reaction; these peculiar fatty acids were rapidly degraded into smaller molecules which could have important organoleptic properties and thus partly modify the flavor of Champagne wine.

Biochemical studies on fatty liver. Part XI. Triacylglycerol release by the perfusion in situ of fatty liver induced by an amino acid imbalance.

Biochemical studies on fatty liver. Part XI. Triacylglycerol release by the perfusion in situ of fatty liver induced by an amino acid imbalance.

Effects of adenosine on liver cell damage induced by carbon tetrachloride

Adenosine administration delayed the fatty liver and cell necrosis induced by carbon tetrachloride without affecting the action of the hepatotoxin on protein synthesis and liver triacylglycerol release. Adenosine produced a drastic antilipolytic effect accompanied by a decrease in the incorporation of [1- 14C]palmitic acid into triacylglycerols and free fatty acids of the liver. Furthermore, a decrease in the serum levels of ketone bodies was observed at early times. The nucleoside also avoided the release of intracellular enzymes and prevented the lipid peroxidation produced by carbon tetrachloride during the 4 hr of treatment. The protective action of adenosine was transient, lasting 3–4 hr, probably the time required to be metabolized. The results suggest that the antilipolytic effect of the nucleoside, the inhibition of hepatic fatty acid metabolism, and the decrease in carbon tetrachloride-induced lipoperoxidation that it produced are involved in the delayed acute hepatotoxicity induced by carbon tetrachloride.

The effects of insulin and glucagon on the release of triacylglycerols by isolated rat hepatocytes are mere reflections of the hormonal effects on the rate of triacylglycerol synthesis

1. Isolated hepatocytes from meal-fed donor rats secrete newly synthesized very-low-density lipoproteins (VLDL) when incubated in a simple bicarbonate buffer. When incubated with 3H 2O for 2 h, 72–81% of the 3H-labelled triacylglycerols secreted by the hepatocytes were recovered in VLDL. The secretion of newly synthesized triacylglycerols shows a lag phase of about 30 min. 2. Insulin stimulates the secretion of newly synthesized VLDL triacylglycerols, whereas glucagon has an inhibitory effect on this process. 3. When hepatocyte triacylglycerols were labelled by preincubating the cells with 3H 2O or [1- 14C]oleate and the cells were subsequently washed and further incubated in radioisotope-free buffer containing hormones, it was observed that the release of the prelabelled triacylglycerols is not hormone-sensitive. This suggests that insulin and glucagon do not affect the release of triacylglycerols per se. 4. It is concluded that the effects of insulin and glucagon on the overall process of triacylglycerol secretion are reflections of the hormone-determined rate of triacylglycerol synthesis.

Myo-Inositol action on gerbil intestine : Reversal of a diet-induced lipodystrophy and change in microsomal lipase activity

An intestinal lipodystrophy induced by dietary fat in female Mongolian gerbils ( Meriones unguiculatus) was reversed to normal by myo-inositol given in the diet or by injection within 1–4 days. An increase m plasma chylomicron and lipid concentrations was observed before the occurrence of rapid disappearance of accumulated lipids from the intestine. Dietary myo-inositol also caused an increase in triacylglycerol release from everted gut sacs. Thus, myo-inositol might act on the intestine to stimulate the production and secretion of chylomicrons, travelling via the lymphatic pathway into the bloodstream. The activity of pH 9.0 microsomal lipase (EC 3.1.1.3) of gerbil intestine was decreased due to myo-inositol deficiency. The lowered activity could be restored to high levels by feeding or injecting myo-inositol in vivo. A time-course study during intestinal recovery indicates that the increase in microsomal lipase activity correlated with the rapid lipid removal phase of the intestine, but not the initial increase in plasma chylomicron and triacylglycerol concentrations.

Effect of feeding amino acid mixtures on lipid transport from rat liver as measured by liver perfusion.

The present study examined lipid transport from the liver by application of a perfusion technique in situ in rats fed diets consisting of a low level Wheat- or Rice- or Miyazaki-pattern amino acid mixture. The net release of hepatic lipids was directly estimated from analysis of the perfusate continuously circulated through the liver. The net release of triacylglycerol from the liver into the perfusate was much more severely inhibited in the Wheat-pattern diet group, and more depressed in the Rice-pattern diet group than in the control group, and slightly reduced in the Miyazaki-pattern diet group compared with the control. For serum lipoproteins fractionated by the Quick-Disc electrophoresis method, there was a significant decrease in the serum pre-beta lipoprotein fraction in all the rats of the Wheat-, Rice- and Miyazaki-pattern diet groups compared with the control. These observations provide firm support for the hypothesis that in rats given diets consisting of a low level of the Wheat-, Rice- and Miyazaki-pattern amino acid mixture, fatty liver may be produced mainly by an impaired transport of triacylglycerols from the liver.

Studies of the formation and relase of glycerolipids by primary monolayer cultures of adult rat hepatocytes

Primary monolayer culture of adult rat hepatocytes represents a relatively novel and potentially useful in vitro technique for studying various hepatic processes for extended periods of time. This study evaluates the potential of hepatocyte monolayers for studying hepatic glycerolipid biosynthesis. Hepatocyte monolayers synthesize glycerolipids from [1,3- 14C]glycerol and fatty acids and release them into the culture medium. Glycerolipid synthesis and release by monolayers declines 40 to 50% during the first 24 h of culture and these lower rates are maintained for at least 72 h. Triacylglycerol formation and release is dependent upon fatty acid concentration in the incubation medium although phospholipid is not. The release of triacylglycerol is greater in the presence of unsaturated acids (16 : 1, 18 : 1 and 18 : 2) than saturated acids (16 : 0 and 18 : 0) although saturated acids produce equal or greater amounts of intracellular triacylglycerol. Phospholipid and triacylglycerol release is reduced in monolayers exposed to colchicine for 24 h but only triacylglycerol release is lowered by the presence of cycloheximide. These results suggest release of triacylglycerol-containing lipoprotein by hepatocyte monolayers. However, we were unable to detect known apolipoprotein in the culture medium by immunologie techniques. Exposure of hepatocyte monolayers to ethanol and estradiol causes alterations in glycerolipid production and release. These changes in glycerolipid formation correlate well with corresponding alterations in glycerol kinase activity measured in monolayer homogenates. These experiments demonstrate the potential usefulness of hepatocytes in monolayer to study various aspects of glycerolipid metabolism. Their longer viability, days rather than hours, is an advantage over other in vitro liver preparations (slices, homogenates, isolated hepatocytes and liver perfusion) for many types of experiments.