Side-chain oxidation of lipoprotein-bound [24,25-3H]cholesterol in the rat: comparison of HDL and LDL and implications for bile acid synthesis

Metabolic Profiling Reveals Aggravated Non-Alcoholic Steatohepatitis in High-Fat High-Cholesterol Diet-Fed Apolipoprotein E-Deficient Mice Lacking Ron Receptor Signaling

Non-alcoholic steatohepatitis (NASH) represents the progressive sub-disease of non-alcoholic fatty liver disease that causes chronic liver injury initiated and sustained by steatosis and necroinflammation. The Ron receptor is a tyrosine kinase of the Met proto-oncogene family that potentially has a beneficial role in adipose and liver-specific inflammatory responses, as well as glucose and lipid metabolism. Since its discovery two decades ago, the Ron receptor has been extensively investigated for its differential roles on inflammation and cancer. Previously, we showed that Ron expression on tissue-resident macrophages limits inflammatory macrophage activation and promotes a repair phenotype, which can retard the progression of NASH in a diet-induced mouse model. However, the metabolic consequences of Ron activation have not previously been investigated. Here, we explored the effects of Ron receptor activation on major metabolic pathways that underlie the development and progression of NASH. Mice lacking apolipoprotein E (ApoE KO) and double knockout (DKO) mice that lack ApoE and Ron were maintained on a high-fat high-cholesterol diet for 18 weeks. We observed that, in DKO mice, the loss of ligand-dependent Ron signaling aggravated key pathological features in steatohepatitis, including steatosis, inflammation, oxidation stress, and hepatocyte damage. Transcriptional programs positively regulating fatty acid (FA) synthesis and uptake were upregulated in the absence of Ron receptor signaling, whereas lipid disposal pathways were downregulated. Consistent with the deregulation of lipid metabolism pathways, the DKO animals exhibited increased accumulation of FAs in the liver and decreased level of bile acids. Altogether, ligand-dependent Ron receptor activation provides protection from the deregulation of major metabolic pathways that initiate and aggravate non-alcoholic steatohepatitis.

Large versus small unilamellar vesicles mediate reverse cholesterol transport in vivo into two distinct hepatic metabolic pools. Implications for the treatment of atherosclerosis

Phospholipid liposomes are synthetic mediators of "reverse" cholesterol transport from peripheral tissue to liver in vivo and can shrink atherosclerotic lesions in animals. Hepatic disposal of this cholesterol, however, has not been examined. We compared hepatic effects of large (approximately equal to 120-nm) and small (approximately equal to 35-nm) unilamellar vesicles (LUVs and SUVs), both of which mediate reverse cholesterol transport in vivo but were previously shown to be targeted to different cell types within the liver. On days 1, 3, and 5, rabbits were intravenously injected with 300 mg phosphatidylcholine (LUVs or SUVs) per kilogram body weight or with the equivalent volume of saline. After each injection, LUV- and SUV-injected animals showed large increases in plasma concentrations of unesterified cholesterol, indicating mobilization of tissue stores. After hepatic uptake of this cholesterol, however, SUV-treated animals developed persistently elevated plasma LDL concentrations, which by day 6 had increased to more than four times the values in saline-treated controls. In contrast, LUV-treated animals showed normal LDL levels. By RNase protection assay, SUVs suppressed hepatic LDL receptor mRNA at day 6 (to 61 +/- 4% of control, mean +/- SEM), whereas LUVs caused a statistically insignificant stimulation. Hepatic HMG-CoA reductase message was also significantly suppressed with SUV, but not LUV treatment, and hepatic 7 alpha-hydroxylase message showed a similar trend. These data on hepatic mRNA levels indicate that SUVs, but not LUVs, substantially perturbed liver cholesterol homeostasis. We conclude that LUVs and SUVs mobilize peripheral tissue cholesterol and deliver it to the liver, but to distinct metabolic pools that exert different regulatory effects. The effects of one of these artificial particles, SUVs, suggest that reverse cholesterol transport may not always be benign. In contrast, LUVs may be a suitable therapeutic agent, because they mobilize peripheral cholesterol to the liver without suppressing hepatic LDL receptor mRNA and without provoking a subsequent rise in plasma LDL levels.

Remodeling and shuttling. Mechanisms for the synergistic effects between different acceptor particles in the mobilization of cellular cholesterol

In normal physiology, cells are exposed to cholesterol acceptors of different sizes simultaneously. The current study examined the possible interactions between two different classes of acceptors, one large (large unilamellar phospholipid vesicles, LUVs) and one small (HDL or other small acceptors), added separately or in combination to Fu5AH rat hepatoma cells. During a 24-hour incubation, LUVs of palmitoyl-oleoyl phosphatidylcholine at 1 mg phospholipid (PL) per milliliter extracted approximately 20% of cellular unesterified cholesterol (UC) label and mass in a slow, continuous fashion (half-time [t1/2] for UC efflux was approximately 50 hours) and human HDL3 at 25 micrograms PL per milliliter extracted approximately 15% cellular UC label with no change in cellular cholesterol mass (t1/2 of approximately 8 hours). In contrast, the combination of LUVs and HDL3 extracted over 90% of UC label (t1/2 of approximately 4 hours) and approximately 50% of the UC mass, indicating synergy. To explain this synergy, specific particle interactions were examined, namely, remodeling, in which the two acceptors alter each other's composition and thus the ability to mobilize cellular cholesterol, and shuttling, in which the small acceptor ferries cholesterol from cells to the large acceptor. To examine remodeling, LUVs and HDL were coincubated and reisolated before application to cells. This HDL became UC depleted, PL enriched, and lost a small amount of apolipoprotein A-I. Compared with equivalent numbers of control HDL particles; remodeled HDL caused faster efflux (t1/2 approximately 4 hours) and exhibited a greater capacity to sequester cellular cholesterol over 24 hours (approximately 38% versus approximately 15% for control HDL), consistent with their enrichment in PL. Remodeled LUVs still extracted approximately 20% of cellular UC. Thus, remodeling accounted for some but not all of the synergy between LUVs and HDL. To examine shuttling, several approaches were used. First, reisolation of particles after an 8-hour exposure to cells revealed that HDL contained very little of the cellular UC label. The label was found almost entirely with the LUVs, suggesting that LUVs continuously stripped the HDL of cellular UC. Second, bidirectional flux studies demonstrated that LUVs blocked the influx of HDL UC label into cells, while the rate of efflux of cellular UC was maintained. These kinetic effects explained the massive net loss of cellular UC to LUVs with HDL. Third, cyclodextrin, an artificial small acceptor that does not acquire PL and hence does not become remodeled, exhibited substantial synergy with LUVs, supporting shuttling. Thus, the presence of large and small acceptors together can overcome intrinsic deficiencies in each. Small acceptors are efficient at extracting cellular cholesterol because they approach cell surfaces easily but have a low capacity, whereas large acceptors are inefficient but have a high capacity. When present simultaneously, where the small acceptor can transfer cholesterol quickly to the large acceptor, high efficiency and high capacity are achieved. The processes responsible for this synergy, namely, remodeling and shuttling, may be general phenomena allowing cooperation both during normal physiology and after therapeutic administration of acceptors to accelerate tissue cholesterol efflux in vivo.

Nutrient intake and psychological and physiological assessment in eumenorrheic and amenorrheic female athletes: a preliminary study

The present study showed that amenorrheic athletes (AAs) scored higher on the Eating Attitudes Test (EAT) (p < .05) than eumenorrheic athletes (EAs), indicating more aberrant eating patterns in the first group. Scores on the EAT were inversely correlated with fat intake (p < .05), simple carbohydrate intake (p < .01), and percentage saturation of iron (p < .05) and were positively correlated with total iron binding capacity (p < .01) for the total sample. Physiological assessment of athletes revealed that there were no significant differences between groups in serum lipoproteins, with both EAs and AAs having serum lipid profiles indicative of low cardiovascular risk. Furthermore, low-density lipoprotein cholesterol was the only lipoprotein significantly and positively correlated with serum estradiol levels for the entire sample (p = .01). The present study was in agreement with previous work showing that scores of the EAT represent a primary difference between EAs and AAs; the present study was somewhat different than previous work in that serum lipoproteins were not significantly related to menstrual status.

Rapid transformation of [3H]cholesteryl ester in rat high-density lipoprotein: in vivo and in vitro studies

[24,25-3H]Cholesteryl ester-labeled rat high-density and low-density lipoproteins were administered to recipient rats. Following death of the rats, a major portion of the radioactivity in administered [3H]cholesteryl ester-high-density lipoprotein rapidly appeared in less dense [3H]cholesteryl ester-lipoproteins and was isolated with the low-density lipoprotein fraction. The specific activity of the esterified cholesterol in the product lipoproteins found with the low-density lipoproteins exceeded that of the precursor high-density lipoproteins. In vitro, the addition of [3H]cholesteryl ester-high-density lipoprotein to plasma resulted in a five- to six-fold increase in radioactivity recovered in the low-density lipoprotein. These results demonstrate that, under a variety of experimental conditions, isolated high-density lipoprotein particles (both in vitro and in vivo) tend to become larger and less dense. Rapid changes in the density of lipoproteins labeled with [3H]cholesteryl ester must be considered when interpreting physiologic studies using this label.

Generation of plasma free cholesterol from circulating lipoprotein-associated cholesteryl ester

Studies were performed to investigate the contribution of lipoprotein-associated cholesteryl ester (CE) in the monkey to circulating free cholesterol (FC). Monkey plasma was incubated with [14C]- or [3H]cholesteryl ester, and radiolabeled low-density lipoproteins (LDL) and high-density lipoproteins (HDL) were isolated by ultracentrifugation. Animals received labeled LDL or HDL. A rapid transfer of CE between lipoproteins was observed, consistent with an active CE transfer protein activity in the monkey. Within 4 h the percent of plasma radioactivity in FC after injection of CE-labeled LDL or HDL was, respectively, 30 and 7% of that of the ester. To determine whether the generation of FC was due to a circulating plasma cholesteryl ester hydrolase, monkey plasma was incubated with CE-labeled lipoproteins with and without 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB). A small amount of FC (less than 3% of the radioactivity) was generated during this incubation but most of the FC production was inhibited by DTNB. Although a small amount of FC can be produced by a plasma cholesteryl esterase (perhaps via reverse action of lecithin-cholesterol acyltransferase), most of the FC in plasma derived from lipoprotein-associated CE is probably due to tissue uptake of lipoproteins and subsequent intracellular hydrolysis of the CE to produce FC.

Casein-induced hypercholesterolaemia in rabbits is calcium-dependent

Young male rabbits were fed semi-purified diets containing either casein or soy protein, both at a normal (0.84%, w/w) and a high (1.44%, w/w) level of dietary calcium. At the normal calcium level, casein, as compared with soy protein, increased the concentration in serum of total and free cholesterol and the ratio of free cholesterol to phospholipid. Also, casein increased the intestinal phosphate absorption and decreased the faecal fat excretion. The hypercholesterolaemic response of the rabbits on the casein diet was significantly correlated with both phosphate absorption (r = +0.744) and fat excretion (r = -0.701). The increased amount of dietary calcium inhibited the casein-specific effects on both the intestinal and the serum lipid parameters. In contrast, calcium did not change these parameters in rabbits fed the soy protein diet. These results support the hypothesis that the degree of phosphorylation of casein is involved in the mechanism of the casein-induced hypercholesterolaemia by means of its effect on the enterohepatic cycle of bile acids.