Plasma lipoproteins in the golden Syrian hamster (Mesocricetus auratus): heterogeneity of apoB- and apoA-I-containing particles

ApoF knockdown increases cholesteryl ester transfer to LDL and impairs cholesterol clearance in fat-fed hamsters

Cholesteryl ester transfer protein (CETP) regulates intravascular lipoprotein metabolism. In vitro studies indicate that ApoF alters CETP function by inhibiting its activity with LDL. To explore in vivo the complexities driving ApoF's effects on CETP, we developed a siRNA-based hamster model of ApoF knockdown. In both male and female hamsters on chow- or fat-fed diets, we measured lipoprotein levels and composition, determined CETP-mediated transfer of cholesteryl esters (CEs) between lipoproteins, and quantified reverse cholesterol transport (RCT). We found that apoF knockdown in chow-fed hamsters had no effect on lipoprotein levels or composition, but these ApoF-deficient lipoproteins supported 50-100% higher LDL CETP activity in vitro. ApoF knockdown in fat-fed male hamsters created a phenotype in which endogenous CETP-mediated CE transfer from HDL to LDL increased up to 2-fold, LDL cholesterol increased 40%, HDL declined 25%, LDL and HDL lipid compositions were altered, and hepatic LDLR gene expression was decreased. Diet-induced hypercholesterolemia obscured this phenotype on occasion. In fat-fed female hamsters, ApoF knockdown caused similar but smaller changes in plasma CETP activity and LDL cholesterol. Notably, ApoF knockdown impaired HDL RCT in fat-fed hamsters but increased sterol excretion in chow-fed animals. These in vivo data validate in vitro findings that ApoF regulates lipid transfer to LDL. The consequences of ApoF knockdown on lipoproteins and sterol excretion depend on the underlying lipid status. By minimizing the transfer of HDL-derived CE to LDL, ApoF helps control LDL cholesterol levels when LDL clearance mechanisms are limiting.

Saccharomyces boulardii CNCM I-745 changes lipidemic profile and gut microbiota in a hamster hypercholesterolemic model

Hypercholesterolemia is a main risk factor of cardiovascular disease. Probiotics are a safe approach to reduce elevated cholesterol without any deleterious effect to human health. Saccharomyces boulardii CNCM I-745 probiotic properties are well documented in a context of intestinal dysbiosis. Recent in vitro and preclinical studies have suggested its potential effects on dyslipidemia. This is the first controlled study investigating the effects of S. boulardii CNCM I-745 on lipidemic profile and gut microbiota in a hamster hypercholesterolemic model. Daily administration (3 g/kg) of S. boulardii for 21 or 39 days in hamsters fed a 0.3% cholesterol-diet significantly reduced total plasma cholesterol (P<0.001) and increased faecal total cholesterol (P<0.05) compared to vehicle-treated animals. S. boulardii significantly modified the gut microbiota composition of the hamster fed a 0.3% cholesterol-diet. These microbial abundancy modifications of the microbiota were correlated to variations of lipidemic values or liver genes expressions. In particularly we found that abundance of g_Allobaculum, the most modified taxon after S. boulardii treatment (+236%; P<0.05), was correlated to variations in plasmatic lipoproteins level and ABCG5 hepatic gene expression. We also observed a not previously described correlation between the levels of g_Oxalobacter in the gut microbiota and total cholesterol plasma concentration. In conclusion, we confirmed the cholesterol-lowering effects of S. boulardii intake and we demonstrated for the first time the S. boulardii effect on gut microbiota in the context of hypercholesterolemia in hamsters. Our results provide new insights for a beneficial and safe approach of hypercholesterolemia treatment and could be considered for clinical development, alone or in addition to conventional treatment.

Cholesterol-Lowering and Liver-Protective Effects of Cooked and Germinated Mung Beans (Vigna radiata L.)

We investigated the hypocholesterolemic and liver-protective effects of cooked and germinated whole mung beans. Hamsters were fed for 28 days on diets rich in saturated fatty acids and cholesterol, differing only in protein source (20%): casein, cooked whole mung bean, and germinated mung bean. After 28 days, we found reduced plasma concentrations of total cholesterol and non-HDL cholesterol, increased faecal cholesterol excretion, and reduced levels of asparagine aminotransferase and alanine aminotransferase enzymes in the liver. Reduction in hepatic lipid deposition was observed between each of the mung bean groups relative to the casein group. In addition, the animals of the geminated mung bean group showed a lack of inflammatory infiltrate and better vascularisation of the hepatic tissue. Results from this study show significant hypocholesterolemic and liver-protective properties of the mung bean, which are further enhanced after germination.

Comparative studies of three cholesteryl ester transfer proteins and their interactions with known inhibitors

Cholesteryl ester transfer protein (CETP) is a plasma protein that mediates bidirectional transfers of cholesteryl esters and triglycerides between low-density lipoproteins and high-density lipoproteins (HDL). Because low levels of plasma CETP are associated with increased plasma HDL-cholesterol, therapeutic inhibition of CETP activity is considered an attractive strategy for elevating plasma HDL-cholesterol, thereby hoping to reduce the risk of cardiovascular disease. Interestingly, only a few laboratory animals, such as rabbits, guinea pigs, and hamsters, have plasma CETP activity, whereas mice and rats do not. It is not known whether all CETPs in these laboratory animals are functionally similar to human CETP. In the current study, we compared plasma CETP activity and characterized the plasma lipoprotein profiles of these animals. Furthermore, we studied the three CETP molecular structures, physicochemical characteristics, and binding properties with known CETP inhibitors in silico. Our results showed that rabbits exhibited higher CETP activity than guinea pigs and hamsters, while these animals had different lipoprotein profiles. CETP inhibitors can inhibit rabbit and hamster CETP activity in a similar manner to human CETP. Analysis of CETP molecules in silico revealed that rabbit and hamster CETP showed many features that are similar to human CETP. These results provide novel insights into understanding CETP functions and molecular properties.

Serum perfluorooctanoic acid (PFOA) concentrations in normal and hyperlipidemic female hamsters dosed orally with ammonium perfluorooctanoate (APFO) for up to 30 days

In epidemiology studies, the presence of perfluorooctanoate (PFOA) in human blood has been associated with higher serum cholesterol concentrations. A possible explanation for these results is that elevated serum cholesterol might reduce clearance of PFOA. In this study, female hamsters, which transport and regulate cholesterol in a manner similar to humans, were fed normal diet or diet supplemented with 0.05% cholesterol and 10% coconut oil (high-fat diet) resulting in hyperlipidemia throughout the study in supplemented animals. Hamsters on either a normal and high-fat diet were given oral doses of 0.1, 1.0, or 10 mg APFO/kg for 30 days. Serum PFOA concentrations evaluated 24 h after 1, 10, 20, and 30 doses of APFO were not altered in hyperlipidemic hamsters compared to those fed normal diet. For a given dose group, serum concentrations of PFOA were highest following the 10 doses (except for the 10 mg/kg group where concentrations were the highest after the first dose) and were lowest after 20 and 30 doses. Under the condition of this study, higher serum lipids did not affect the absorption and clearance of serum PFOA. Serum PFOA concentrations declined over the course of the study despite continued daily dosing with APFO. This does not support the hypothesis that higher serum lipids might increase the retention of PFOA in the body.

Dietary carbohydrate dictates development of Type 2 diabetes in the Nile rat

Amount and type of dietary carbohydrate (CHO), as well as the CHO:fat ratio, are thought to be critical for both the rate of development and severity of Type 2 diabetes mellitus. Thus, these nutritional considerations were examined in the previously described "spontaneous" model of diabetes and metabolic syndrome, the Nile rat. Weanling male Nile rats (n=92) were fed semipurified diets, modifying glycemic index and load by changing the amount of fiber or altering the CHO:fat ratio. Random and fasting blood glucose and body weight were assessed, and diabetes was characterized in terms of blood glucose, relevant plasma and liver parameters, food and water intake and terminal organ weights. Nile rats fed with hiCHO became more hyperglycemic than rats fed with modCHO (P<.05), while loCHO and hiCHO+hiFiber rats remained essentially normoglycemic. Liver lipid and glycogen accumulation was associated with severe hyperlipemia in diabetic rats, analogous to metabolic syndrome in humans. Advanced diabetes was linked to liver and kidney damage and elevated blood urea nitrogen with weight loss. Dispersing dietary CHO by fiber or replacing it by moderate fat (reducing the glycemic index and load) delayed the onset of diabetes but did not prevent signs of insulin resistance. A very low content of dietary CHO (high fat) seemed to prevent even these early indicators of insulin resistance. Thus, the Nile rat represents a novel CHO-sensitive model for study of Type 2 diabetes that reliably follows the course of disease in humans.

Brain regional correlation of amyloid-β with synapses and apolipoprotein E in non-demented individuals: potential mechanisms underlying regional vulnerability to amyloid-β accumulation

To reveal the underlying mechanisms responsible for the regional vulnerability to amyloid-β (Aβ) accumulation prior to the development of Alzheimer's disease, we studied distribution of Aβ, apolipoprotein E (apoE), synaptic markers, and other molecules involved in Aβ metabolism in multiple brain areas of non-demented individuals. Twelve brain regions including neocortical, limbic, and subcortical areas were dissected from brains of non-demented individuals and extracted according to increasing insolubility by a sequential three-step method. The levels of Aβ40, Aβ42, apoE, APP, APP-CTFβ, BACE1, presenilin-1, neprilysin, insulysin, LRP1, LDLR, synaptophysin, PSD95, GFAP, and lactate were determined by ELISAs or enzymatic assays. The regional distribution of apoE showed moderate-to-strong inverse correlation with levels of Aβ, especially insoluble Aβ40. On the other hand, the regional distributions of synaptic markers, particularly PSD95, showed moderate-to-strong positive correlation with levels of Aβ, especially soluble Aβ40. The regional correlations between Aβ and LRP1, GFAP, or lactate were mild-to-moderate. Moderate-to-strong positive regional correlations were observed between apoE and GFAP or lactate and between PSD95 and LRP1. No significant regional correlations were detected between Aβ and APP, APP-CTFβ, BACE1, or presenilin-1, those involved in Aβ production. There were no significant negative regional correlations between Aβ and two major Aβ degrading enzymes, neprilysin and insulysin. These regional correlations remained consistent regardless of the degree of Aβ accumulation. The regional vulnerability to Aβ accumulation may be due to a net balance between two competing processes: (1) synapses involved in promoting the initial Aβ accumulation and (2) astrocyte-derived apoE involved in preventing Aβ accumulation.

Elevation of tumor necrosis factor-alpha induces the overproduction of postprandial intestinal apolipoprotein B48-containing very low-density lipoprotein particles: evidence for related gene expression of inflammatory, insulin and lipoprotein signaling in enterocytes

The aim of this study was to determine whether systemic elevation of tumor necrosis factor (TNF)-alpha induces intestinal-derived apolipoprotein B (apoB)48-containing very low-density lipoprotein (VLDL) production in hamsters after fat loading and whether TNF-alpha disturbs the related mRNA expression in inflammatory, insulin and lipoprotein signaling pathways in primary enterocytes. In vivo TNF-alpha and Triton-WR1339 infusion, Western blotting and reverse transcriptase-polymerase chain reaction were combined to explore the mechanisms underlying intestinal overproduction of apoB48-containing chylomicrons and VLDL(1) particles by TNF-alpha. TNF-alpha infusion increased intestinal production of chylomicron and VLDL(1)-apoB48 in postprandial (fat load) states. Following TNF-alpha-treatment in enterocytes, there was enhanced gene expression of Il1alpha and beta, Il6 and Tnf and decreased mRNA levels of components of the insulin signaling pathway including the insulin receptor (Ir), Ir substrate-1 and 2, PI3 k, and Akt, but increased phosphatase and tensin homolog deleted on chromosome ten (Pten) protein and mRNA expression. TNF-alpha also induced Cd36 and peroxisome proliferators-activated receptor (Ppar)gamma expression, as well as microsomal triglyceride transfer protein (Mtp) protein and mRNA, but suppressed the sterol regulatory element binding protein (Srebp)1c protein and mRNA level. Systemic elevation of TNF-alpha stimulates the postprandial overproduction of apoB48-containing chylomicrons and VLDL(1) particles by disturbing intestinal gene expression of the inflammatory, insulin and lipoprotein pathways. These findings provide mechanistic links among the inflammatory factor, TNF-alpha, intestinal inflammatory/insulin insensitivity and the overproduction of intestinal apoB48-containing lipoproteins.

Cholesterol-lowering properties of whole cowpea seed and its protein isolate in hamsters

Hypercholesterolemic hamsters were fed for 4 wk on diets rich in saturated fatty acids and cholesterol, differing only in protein source (20 %): casein (control group, HC), whole cowpea seed (HWS), and cowpea protein isolate (HPI). Hamsters fed on HWS and HPI presented significant reductions in plasma total cholesterol and non-HDL cholesterol. HPI and HC presented similar protein digestibility, which were significantly higher than that of HWS. Animals fed on HWS presented significantly higher levels of bile acids and cholesterol in feces than did the animals fed on casein or HPI diets. Histological analyses of the liver showed that HC diet resulted in steatosis widely distributed throughout the hepatic lobule, while HWS and HPI diets promoted reductions in liver steatosis. The effectiveness of HWS for modulating lipid metabolism was greater than that of HPI, as measured by plasma cholesterol reduction and liver steatosis.

Effect of esterified 4-desmethylsterols and -stanols or 4,4′-dimethylsterols on cholesterol and bile acid metabolism in hamsters

4-Desmethylsterols and -stanols reduce plasma total cholesterol (TC) and LDL cholesterol by inhibition of intestinal cholesterol absorption, while the cholesterol-lowering potential of 4,4′-dimethylsterols is less well defined. The present study aimed to compare the effects of 4-desmethylsterols, -stanols, and 4,4′-dimethylsterols on plasma and hepatic cholesterol, sterol excretion and bile acid metabolism. Male golden Syrian hamsters were fed diets containing 13 g/100 g fat, 0·08 g/100 g cholesterol and 0 (control), 0·24 or 0·48 % (w/w) esterified 4-desmethylsterols (sterols) and esterified hydrogenated 4-desmethylsterols (stanols) from common vegetable oils or esterified 4,4′-dimethylsterols from rice bran oil for 5 weeks. Sterol and stanol esters at the dose of 0·24 % were equally effective and significantly (P<0·05) lowered TC by 15 %, while 0·24 % 4,4-dimethylsterols reduced TC by 10 %. Liver total and esterified cholesterol concentrations were significantly (P<0·05) lowered by 40, 22, 43 and 31 % in hamsters fed 0·48 % sterols, 0·24 % stanols, 0·48 % stanols or 0·48 % dimethylsterols, respectively. Daily faecal bile acid excretion and hepatic cholesterol 7α-hydroxylase activity were not altered, indicating that sterols, stanols and dimethylsterols had no effect on the intestinal re-absorption of bile acids or on hepatic bile acid synthesis. Daily excretion of cholesterol was significantly higher in hamsters fed esterified sterols and stanols, but was only slightly increased in those fed dimethylsterols. The results indicate that esterified sterols and stanols were equally effective in lowering plasma TC and LDL cholesterol, while dimethylsterol esters caused a weaker cholesterol-lowering effect. Sterols and stanols achieve their cholesterol-lowering effect by stimulating faecal cholesterol excretion through inhibiting intestinal cholesterol absorption, but do not affect bile acid excretion. Other mechanisms need to be considered to explain the effect on plasma and hepatic cholesterol of dimethylsterols.

Gender-related response of lipid metabolism to dietary fatty acids in the hamster

Gender and dietary fatty acids are involved in the regulation of lipid metabolism, disturbances of which can lead to pathologies such as metabolic syndrome or CVD. Possible interactions between these factors were investigated in male and female hamsters fed diets rich in either saturated fatty acids (‘butter’ diet) or in α-linolenic acid (‘linseed oil’ diet). Gender effect predominated over the diet effect on cholesterol (CH) metabolism; compared to males, females exhibited lower concentrations of plasma total CH (−20%,P<0·001), LDL-CH (−40%,P<0·001) and HDL-CH (−16%,P<0·001), together with higher LDL receptor (+40%) and lower HDL receptor (−60%) hepatic content. Triacylglycerol (TG) metabolism was affected by diet above all: compared to animals fed the ‘butter’ diet, those fed the ‘linseed oil’ diet exhibited lower plasma (−23%,P=0·046) and liver TG (−20%,P=0·026) concentration which may result from both an increased β-oxidation (P<0·001), without any change in PPARα mRNA, and a decreased hepatic lipogenesis (P=0·023), without increased sterol response element binding protein 1c (SREBP1c) mRNA. The response to diet was much more pronounced in males than in females, without gender effect on the transcription level of PPARα and SREBP1c. Finally, the ‘linseed oil’ diet decreased the insulin resistance index (−80%,P<0·001) with a more marked effect in males, in relation to their higher hepatic PPARγ expression (+90%,P=0·012). In conclusion, in our model, the response of either TG or CH to dietary fatty acids is modulated differently by gender. The possible relevance of these interactions to dietary practice should be taken into account in man.

Rumenic Acid Significantly Reduces Plasma Levels of LDL and Small Dense LDL Cholesterol in Hamsters Fed a Cholesterol- and Lipid-Enriched Semi-Purified Diet

Conjugated linoleic acids (CLAs) consist of a series of positional and geometrical isomers of linoleic acid. CLA have been reported to beneficially affect cardiovascular risk factors in animal models. In order to assess the role of individual CLA isomers on lipoprotein cholesterol concentration, 30 hamsters were fed for 12 weeks an hyperlipidic diet containing pure cis-9,trans-11 CLA (c9,t11) or pure trans-10, cis-12 CLA (t10,c12) isomers given alone or as a mixture. Plasma total cholesterol, LDL and HDL cholesterol concentrations were significantly lower in the c9,t11 CLA isomer fed hamsters relative to the Control group, with the most substantially effect on LDL cholesterol (-56%; P < 0.05). Plasma triacylglycerol concentrations did not differ significantly regarding those two groups. Plasma cholesterol parameters showed a tendency to decrease in the t10,c12 CLA isomer and CLA mixture fed hamsters compared with the Control group, but differences were not significant. For the first time, the atherogenic fraction of small dense LDL was investigated. Plasma small dense LDL cholesterol concentration was lower in the c9,t11 CLA relative to Control, while the t10,c12 and CLA mixture groups showed only a non significant tendency to decrease. Taken together, these data indicate that feeding rumenic acid (c9,t11 CLA) may beneficially affect lipoprotein profile in hamster fed a cholesterol- and lipid-enriched semi-purified diet, when t10,c12 CLA isomer or CLA mixture would be less active.

Fish oil fatty acid esters of phytosterols alter plasma lipids but not red blood cell fragility in hamsters

In an attempt to combine the hypocholesterolemic properties of plant sterols with the hypotriglyceridemic action of fish oil FA, plant sterols have recently been esterified to fish oil n-3 PUFA. The objective of this study was to determine the effects of plant sterols esterified to n-3 PUFA on plasma lipid levels and erythrocyte fragility. For 5 wk, male Golden Syrian hamsters were fed diets varying in cholesterol and plant sterol content: (i) Non-cholesterol (semipurified diet with no added cholesterol or plant sterols) (ii), Cholesterol (0.25% cholesterol) (iii), Sterols (0.25% cholesterol plus 1% nonesterified plant sterols), or (iv) Fish oil esters of plant sterols (0.25% cholesterol plus 1.76% EPA and DHA sterol esters, providing 1% plant sterols). The addition of fish oil esters of plant sterols to the cholesterol diet decreased (P = 0.001) plasma total cholesterol levels by 20%, but nonesterified plant sterols did not have such a beneficial impact. In addition, non-HDL cholesterol concentrations were 29% lower in hamsters fed fish oil esters of plant sterols than in hamsters fed nonesterified plant sterols (P < 0.0001). Despite higher (P < 0.0001) plant sterol levels in whole erythrocytes of hamsters fed nonesterified plant sterols and fish oil esters of plant sterols compared with hamsters fed no plant sterols, no difference was observed in erythrocyte fragility. The present results show that EPA and DHA esters of plant sterols have a hypocholesterolemic effect in hamsters, and that these new esters of plant sterols exert no detrimental effect on erythrocyte fragility.

Metabolic effects of voluntary wheel running in young and old Syrian golden hamsters

To explore the metabolic effects of high volume wheel running in the Syrian golden hamster, 6-week old (YOUNG) and 6-month old (OLD) male animals were randomly divided into sedentary (i.e., YOUNG-S or OLD-S) or running wheel (i.e., YOUNG-RW or OLD-RW) groups (n = 8/group). RW groups had 24-h access to activity wheels while S were housed in standard rodent cages. At the start of wheel exposure, the number of revolutions were similar in both groups, but by day 15 were nearly two-fold higher in the YOUNG vs. OLD. OLD ate more than YOUNG and wheel running increased food intake by approximately 50%. YOUNG-RW maintained the same total body mass as YOUNG-S, while OLD-RW had a transient weight loss of approximately 10 g. Perirenal fat mass was smaller in YOUNG- and OLD-RW groups compared with S groups (45% and 66%, respectively. Plantaris muscle cytochrome c oxidase activity was also approximately 2-fold higher in YOUNG-RW than in YOUNG-S hamsters but was similar between OLD-RW and OLD-S groups. Plasma leptin levels were approximately 60% lower in YOUNG-RW compared with YOUNG-S and correlated significantly with visceral fat pad mass (r2 = 0.58, p = 0.001). Corticosterone levels were lower in YOUNG-RW (13.0 +/- 0.36 ng/ml) than in YOUNG-S (16.4 +/- 0.83 ng/ml) hamsters and higher in OLD-RW (22.62 +/- 0.47 ng/ml) than in OLD-S (15.54 +/- 0.13 ng/ml) hamsters. These observations reveal that the hamster is a suitable model for accelerating the effects of exercise on body composition and metabolic alterations associated with training and that the training adaptations are more pronounced in younger compared with older hamsters, possibly as a result of the higher voluntary wheel activity in the former group.

Dose effect of alpha-linolenic acid on lipid metabolism in the hamster

In order to meet dietary requirements, the consumption of alpha-linolenic acid (ALA, 18:3 n-3) must be promoted. However, its effects on triglyceride (TG) and cholesterol metabolism are still controversial, and may be dose-dependent. The effects of increasing dietary ALA intakes (1%, 10%, 20% and 40% of total FA) were investigated in male hamsters. ALA replaced oleic acid while linoleic and saturated FA were kept constant. Triglyceridemia decreased by 45% in response to 10% dietary ALA and was not affected by higher intakes. It was associated with lower hepatic total activities of acetyl-CoA-carboxylase (up to -29%) and malic enzyme (up to -42%), which were negatively correlated to ALA intake (r(2) = 0.33 and r(2) = 0.38, respectively). Adipose tissue lipogenesis was 2-6 fold lower than in the liver and was not affected by dietary treatment. Substitution of 10% ALA for oleic acid increased cholesterolemia by 15% but, as in TG, higher ALA intakes did not amplify the response. The highest ALA intake (40%) dramatically modified the hepatobiliary metabolism of sterols: cholesterol content fell by 45% in the liver and increased by 28% in the faeces. Besides, faecal bile acids decreased by 61%, and contained more hydrophobic and less secondary bile acids. Thus, replacing 10% oleic acid by ALA is sufficient to exert a beneficial hypotriglyceridemic effect, which may be counteracted by the slight increase in cholesterolemia. Higher intakes did not modify these parameters, but a very high dose resulted in adverse effects on sterol metabolism.

Free phytosterols facilitate excretion of endogenous cholesterol in gerbils

To determine whether phytosterols (PST) facilitate excretion of whole body cholesterol and whether dietary fat or enhancing gallbladder contraction with curcumin might influence this process, four experiments were conducted in gerbils. In Experiment 1, naive gerbils received cholesterol-free purified diets with 30% energy from fat and 0% or 0.75% free PST from tall oil for 4 weeks. In Experiment 2, body cholesterol pools were expanded by feeding a diet containing 0.3% cholesterol for 3 weeks. Subsequently, PST was provided in either fat-free or normal-fat diets without cholesterol for only 2 h each morning, followed by a low-fat diet for the rest of the day and food restriction overnight. In Experiment 3, gerbils were preloaded with cholesterol, followed by either PST alone or PST+curcumin to enhance gallbladder contraction. In Experiment 4, curcumin or curcumin+PST were fed with 30% as fat and 0.15% cholesterol throughout the study. Because of the small whole body cholesterol pool in Experiment 1, the impact of PST was limited. When whole body cholesterol was expanded in Experiments 2 and 3, subsequent reductions of liver esterified cholesterol by PST were significant. In the presence of dietary fat, PST caused a greater reduction (23%) than in a fat-free diet (8%) compared to respective controls. Curcumin (Experiments 3 and 4) proved ineffective in reducing liver or plasma cholesterol pools, and the 3:1 ratio between PST/diet cholesterol was less effective at blocking cholesterol absorption than a 5:1 ratio previously employed. Thus, free PST removed whole body cholesterol, which was enhanced by concomitant fat intake, but was unaffected by a gallbladder contracting agent.

Intestinal assembly and secretion of highly dense/lipid-poor apolipoprotein B48-containing lipoprotein particles in the fasting state: evidence for induction by insulin resistance and exogenous fatty acids

Emerging evidence suggests that overproduction of intestinally derived apolipoprotein (apo) B48-containing lipoprotein particles may be an important contributor to both fasting and postprandial dyslipidemia in insulin-resistant states. Mechanisms regulating the assembly and secretion of apoB48-containing lipoproteins are not fully understood particularly in the diabetic/insulin-resistant intestine. In the present study, we have investigated the density profile of apoB48 lipoproteins assembled in primary hamster enterocytes. Both intracellular and secreted apoB48 particles were examined in intestinal enterocytes isolated from normal or insulin-resistant fructose-fed hamsters, as well as in enterocytes treated with exogenous oleic acid. Microsomal luminal contents and culture media were analyzed by discontinuous and sequential ultracentrifugation on sucrose and KBr gradients, respectively. ApoB48 was mostly secreted on VLDL-, LDL-, and denser HDL-sized particles in the fasting state. In pulse-chase labeling experiments, nascent apoB48-containing particles initially accumulated in the microsomal lumen as HDL-sized particles, with subsequent formation of apoB48-VLDL particles, with only a minute amount of chylomicrons observed. Treatment with 720 mu mol/L of oleic acid, increased microsomal apoB48 HDL synthesis, and induced a marked shift toward lighter more buoyant particles. A marked enhancement in assembly of apoB48-containing lipoproteins was also observed in the microsomal lumen of fructose-fed hamster enterocytes, suggesting facilitated assembly and secretion of dense intestinal lipoprotein particles in insulin-resistant states. Overall, these observations suggest that a major proportion of apoB48-containing lipoprotein particles is assembled and secreted as highly dense, HDL-sized particles. The production of these small, dense, and potentially atherogenic apoB48 particles can be stimulated by increased free fatty acid flux as well as in insulin-resistant diabetes.

Novel short-term effects of adenovirus Ad-36 on hamster lipoproteins

OBJECTIVE

Human adenovirus Ad-36 induces adiposity and lowers total serum cholesterol in chickens, mice and marmosets and Ad-36 antibodies are associated with human obesity. We examined the early effects of Ad-36 inoculation on plasma cholesterol levels in hamsters fed a hyperlipidemic diet.

DESIGN

A total of 32 male Golden Syrian hamsters were divided into two equal weight-matched groups and intranasally inoculated with Ad-36 (INF: infected) or media (CON: control). In each group, the animals were fed either a purified diet (PF, n=8) 40%en fat +/-194 mg cholesterol/1000 kcal or chow (C, n=8) ad libitum. Animals were killed 5 weeks postinoculation.

RESULTS

Nested PCR assay detected Ad-36 DNA in the lung, liver, visceral adipose tissue and skeletal muscle of the INF group, but not in the CON animals. Ad-36 antibodies were detected in the INF group only. For all animals, total plasma cholesterol (TC) was not significantly affected by Ad-36 treatment (203+/-92 vs 193+/-75 mg/dl, P=NS; INF vs CON, respectively). In 5 weeks, Ad-36 infection had no effect on TC concentration in hamsters fed chow (128+/-39 vs 130+/-27 mg/dl, INF-C vs CON-C, respectively) or those fed PF (269+/-70 vs 256+/-47 mg/dl, INF-P vs CON-P, respectively). However, lipoproteins isolated by density gradient ultracentrifugation showed a greater proportion of LDL cholesterol in INF animals, as compared to CON (28.4+/-1.6% vs 16.4+/-1.2%, P=0.02), regardless of dietary treatment (INF-P vs CON-P: 27.3+/-2.1 vs 15.7+/-1.5%, P=0.07; and INF-C vs CON-C: 29.4+/-1.2 vs 17.0+/-1.1%, P=0.009). This shift appears to be from HDL cholesterol to the LDL fractions.

CONCLUSION

These data suggest that in the hamster (a model resembling several aspects of human lipoprotein metabolism), Ad-36 infection may acutely affect the intravascular processing of lipoproteins resulting in a more atherogenic lipoprotein profile.

Effects of dietary alpha linolenic acid on cholesterol metabolism in male and female hamsters of the LPN strain

N-3 polyunsaturated fatty acids and estrogens are recognized as protective factors of atherosclerosis, however their interactions on cholesterol metabolism remain unclear. Male and female hamsters were fed for 9 weeks diets containing 12.5% lipids and rich in either alpha-linolenic acid ("linseed" diet) or saturated fatty acids ("butter" diet). Hamsters fed the "linseed" diet exhibited lower plasma concentrations of cholesterol (-29%), total LDL (-35%) and HDL (-17%), glucose (-20%), insulin (-40%) and of the LDL-cholesterol/HDL-cholesterol ratio (-27%) than those fed the "butter" diet. In the liver, cholesterol content was 2.7-fold lower in response to the "linseed" diet, whereas the concentration of HDL receptor (SR-BI) and the activities of HMGCoA reductase and cholesterol 7alpha-hydroxylase were 30 to 50% higher than with the "butter" diet. By contrast, the LDL receptor concentration did not vary with the diet. Females exhibited higher concentration of LDL (+24%), lower concentration of plasma triglycerides (-34%), total VLDL (-46%) and VLDL-cholesterol (-37%) and of biliary phospholipids (-19%). Besides, there was also an interaction between gender and diet: in males fed the "butter" diet, plasma triglycerides and VLDL concentration, were 2 to 4 fold higher than in the other groups. These data suggest that gene and/or metabolic regulations by fatty acids could interact with that of sex hormones and explain why males are more sensitive to dietary fatty acids.

Effect of structure and form on the ability of plant sterols to inhibit cholesterol absorption in hamsters

We investigated the effect of three types of plant sterols (4-desmethylsterols, 4,4'-dimethylsterols, and pentacyclic triterpene alcohols) in three forms (free, esterified with FA, or with phenolic acids) on cholesterol absorption. Plant sterol fractions derived from soybean (99% 4-desmethylsterols), rice bran (70% 4,4'-dimethylsterols), or shea nut (89% pentacyclic triterpene alcohols) were fed to male hamsters (n = 20/group) as free sterols or esterified with FA or phenolic acids (cinnamic or ferulic). Cholesterol absorption was measured after 5-8.5 (mean, 7) wk by a dual-isotope technique. Soybean sterol intake significantly reduced cholesterol absorption efficiency (23%) and plasma total cholesterol (11%). Rice bran sterols tended to lower cholesterol absorption efficiency by 7% and plasma total cholesterol by 5%, whereas shea nut sterols had no effect. In hamsters, dietary 4-desmethylsterols were more effective than 4,4'-dimethylsterols in lowering cholesterol absorption and levels of cholesterol in blood. Pentacyclic triterpene alcohols had no effect on the absorption of cholesterol or on its level in blood. Esterification with FA did not impair the ability of 4-desmethylsterols and 4,4'-dimethylsterols to inhibit cholesterol absorption, whereas esterification with phenolic acids reduced this ability. This study supports the use of 4-desmethylsterols, esterified with FA to increase solubility, as the most effective cholesterol-lowering plant sterols in the diet.

Species differences in the physiological activity of dietary lignan (sesamin and episesamin) in affecting hepatic fatty acid metabolism

The effect of sesame (Sesamum orientale) lignan preparation containing equivalent amounts of sesamin and episesamin on hepatic fatty acid metabolism was compared in rats, mice and hamsters. Animals were fed on either a diet free of lignan or a diet containing 2 g lignan/kg for 15 d. The lignan preparation greatly increased hepatic activity and the mRNA levels of enzymes involved in fatty acid oxidation, while it strongly down-regulated those of enzymes involved in lipogenesis in rats. In contrast, lignan did not modify these variables in mice and hamsters. Changes observed, if any, were more attenuated in these mice and hamsters than in rats. Sesamin and episesamin concentrations in serum and liver of animals fed on lignan-containing diets were significantly greater (P<0.05) in rats than in mice and hamsters. Moreover, sesamin:episesamin values in tissues were far from that expected from the value in the lignan preparation given to the animals and were dependent on the animal species. Liver microsomes from each animal species degraded sesamin and episesamin in the presence of NADPH. The combined value of sesamin and episesamin degradation rates was lower in rats than in mice and hamsters. In addition, there was considerable diversity in the specificity of the enzyme reaction toward sesamin and episesamin among animal species. The differences in the amounts of lignan remaining in the tissues may account for the species dependence of the physiological activity of sesame lignan in affecting hepatic fatty acid oxidation and synthesis.

Replacing 40% of dietary animal fat with vegetable oil is associated with lower HDL cholesterol and higher cholesterol ester transfer protein in cynomolgus monkeys fed sufficient linoleic acid

This study was designed to evaluate whether replacing approximately 40 g/100 g dietary animal fat with vegetable oil would improve plasma lipids and lipoproteins when diets contained prudent levels of total saturated acid (SFA), monounsaturated acid (MUFA) and PUFA. Using a cross-over design, male Cynomolgus monkeys (n = 10) were fed purified diets containing a mixture of fats. For the diet based on animal fat (AF-diet), approximately 85 g/100 g of the total fat was derived from pork fat, and approximately 40 g/100 g of this was replaced with olive oil for the vegetable oil-based diet (VO-diet). Thus, the fat content of the VO diet comprised 50% pork fat and 35% olive oil. The remaining 15% of the total fat (for both diets) was safflower oil. Both diets provided approximately 30% of total energy (%en) from fat, <10%en SFA and approximately 6-7%en from PUFA. Monkeys were rotated through two 7-wk feeding periods, during which time plasma lipids and lipoproteins were evaluated. Compared with the AF diet, plasma total cholesterol (TC) concentrations tended to be lower ( approximately 10%) after monkeys consumed the VO diet (3.18 +/- 0.83 vs. 3.52 +/- 0.93 mmol/L, P = 0.099), and this was due entirely to a significant 12% reduction in HDL cholesterol (1.53 +/- 0.41 vs. 1.73 +/- 0.47, mmol/L, P = 0.0009). Although plasma lipoprotein compositional analyses revealed no significant differences in either lipoprotein composition or the estimated particle diameters, the measurement of cholesterol ester transfer protein (CETP) using (3)H-cholesterol ester-labeled HDL revealed that the lower HDL cholesterol (HDL-C) when monkeys consumed the VO diet was associated with a 31% increase in transfer (P = 0.04). However, despite the changes in HDL-C, the TC/HDL-C ratio did not differ between monkeys after the two diet treatments. Regression analyses of data from these monkeys revealed a significant correlation between the dietary 16:0/18:2 ratio and plasma HDL-C. These data suggest that within the context of currently recommended prudent diets, it may be possible to manipulate HDL-C beneficially. Whether a similar effect would occur in humans warrants investigation.

Photodynamic therapy effect of m-THPC (Foscan) in vivo: correlation with pharmacokinetics

m-Tetra(hydroxyphenyl)chlorin (m-THPC, Foscan, Temoporfin) has an unusually high photodynamic efficacy which cannot be explained by its photochemical properties alone. In vivo interactions are therefore of critical importance in determining this high potency. The pharmacokinetics of m-THPC in a rat tumour model was determined using (14)C m-THPC in an LSBD(1) fibrosarcoma implanted into BDIX rats. The photodynamic therapy (PDT) efficacy was determined at different drug administrations to light intervals and correlated with the tumour and plasma pharmacokinetic data. The plasma pharmacokinetics of m-THPC can be interpreted by compartmental analysis as having three half-lives of 0.46, 6.91 and 82.5 h, with a small initial volume of distribution, suggesting retention in the vascular compartment. Tissues of the reticuloendothelial system showed high accumulation of m-THPC, particularly the liver. PDT efficacy of m-THPC over the same time course seemed to exhibit two peaks of activity (2 and 24 h), in terms of tumour growth delay with the peak at 24 h postinjection correlating to the maximum tumour concentration. Investigation on tumour cells isolated from m-THPC-treated tumours suggested that the peak PDT activity at 2 h represents an effect on the vasculature while the peak at 24 h shows a more direct response. These results indicate that the in vivo PDT effect of m-THPC occurs via several mechanisms.

VLDL-induced triglyceride accumulation in human macrophages is mediated by modulation of LPL lipolytic activity in the absence of change in LPL mass

Mixed dyslipidemia of phenotype IIB is characterized by elevated levels of very low density lipoprotein (VLDL)-1 and VLDL-2 subfractions and of low density lipoprotein (LDL), which are associated with premature formation of atherosclerotic plaques, characterized by the presence of lipid-rich macrophage foam cells. Lipoprotein lipase (LPL) is a key factor in mediating macrophage lipid accumulation and foam-cell formation from native VLDL particles. The action of macrophage-derived LPL in the induction of intracellular lipid accumulation from triglyceride-rich lipoprotein (TRL) subfractions (VLDL-1, VLDL-2) is, however, indeterminate, as is the potential role of VLDL-1 and VLDL-2 in modulating macrophage LPL expression. We evaluated the role of LPL in the interaction of type IIB VLDL-1 and VLDL-2 with human macrophages. Both VLDL-1 and VLDL-2 subfractions induced significant accumulation of triglyceride (9.8-fold, P<0.0001, and 4.8-fold, P<0.0001, respectively) and of free cholesterol content (1.4-fold, P<0.001, and 1.2-fold, P=0.02, respectively). Specific inhibition (90%) of the lipolytic activity of endogenous LPL by tetrahydrolipstatin (THL) in the presence of VLDL-1 or VLDL-2 resulted in marked reduction in cellular loading of both triglycerides (-89%, P=0.008, and -89%, P=0.015, respectively) and free cholesterol (-76%, P=0.02, and -55%, P=0.06 respectively). Furthermore, VLDL-1 and VLDL-2 induced marked increase in macrophage-derived LPL enzyme activity (+81%, P=0.002, and +45%, P=0.02), but did not modulate macrophage-derived LPL mRNA and protein expression; consequently, LPL specific activity was significantly increased from 1.6 mU/microg at baseline to 4.1 mU/microg (P=0.01) and 3.1 mU/microg (P=0.05), in the presence of VLDL-1 and VLDL-2, respectively. We conclude that type IIB VLDL-1 and VLDL-2 induce triglyceride accumulation in human monocyte-macrophages primarily via the lipolytic action of LPL, which may involve stabilization and activation of the macrophage-secreted enzyme, rather than via modulation of enzyme production.

Dietary conjugated linoleic acid lowers plasma cholesterol during cholesterol supplementation, but accentuates the atherogenic lipid profile during the acute phase response in hamsters

Conjugated linoleic acid (CLA) reportedly exerts anticarcinogenic and antiatherosclerotic effects in animals. To test the hypothesis that the putative antiatherosclerotic effect of CLA might derive from an anti-inflammatory or antioxidant action on lipoprotein metabolism, an acute phase response (APR) was elicited in hamsters while varying dietary cholesterol and vitamin E intakes in two experiments. The effect of CLA intake (to 1%) was examined with 0% (Experiment 1, 7 wk) and 0 or 0.3% (Experiment 2, 12 wk) cholesterol, at which point APR was induced. In hamsters not fed dietary cholesterol (Experiment 1), CLA exaggerated the rise in plasma and LDL cholesterol observed during the APR. When CLA was fed concurrently with cholesterol (Experiment 2), plasma and liver cholesterol were reduced up to 40% independent of the APR. In addition, CLA decreased body weight gain and adipose reserves in Experiment 1, but not in Experiment 2. Because CLA failed to attenuate APR and was not influenced by vitamin E status, an antioxidant/anti-inflammatory role was not apparent. However, the reduced burden on liver and lipoprotein cholesterol induced by CLA during cholesterol feeding, suggests that CLA curtailed cholesterol absorption, whereas the rise during APR suggests that CLA exaggerated the impaired clearance of plasma cholesterol associated with acute inflammation.

Fasting and postprandial overproduction of intestinally derived lipoproteins in an animal model of insulin resistance. Evidence that chronic fructose feeding in the hamster is accompanied by enhanced intestinal de novo lipogenesis and ApoB48-containing lipoprotein overproduction

Insulin-resistant states are characterized by hypertriglyceridemia, predominantly because of overproduction of hepatic very low density lipoprotein particles. The additional contribution of intestinal lipoprotein overproduction to the dyslipidemia of insulin-resistant states has not been previously appreciated. Here, we have investigated intestinal lipoprotein production in a fructose-fed hamster model of insulin resistance previously documented to have whole body and hepatic insulin resistance, and hepatic very low density lipoprotein overproduction. Chronic fructose feeding for 3 weeks induced significant oversecretion of apolipoprotein B48 (apoB48)-containing lipoproteins in the fasting state and during steady state fat feeding, based on (a) in vivo Triton WR1339 studies of apoB48 production as well as (b) ex vivo pulse-chase labeling of intestinal enterocytes from fasted and fed hamsters. ApoB48 particle overproduction was accompanied by increased intracellular apoB48 stability, enhanced lipid synthesis, higher abundance of microsomal triglyceride transfer protein mass, and a significant shift toward the secretion of larger chylomicron-like particles. ApoB48 particle overproduction was not observed with short-term fructose feeding or in vitro incubation of enterocytes with fructose. Secretion of intestinal apoB48 and triglyceride was closely linked to intestinal enterocyte de novo lipogenesis, which was up-regulated in fructose-fed hamsters. Inhibition of fatty acid synthesis by cerulenin, a fatty acid synthase inhibitor, resulted in a dose-dependent decrease in intestinal apoB48 secretion. Overall, these findings further suggest that intestinal overproduction of apoB48 lipoproteins should also be considered as a major contributor to the fasting and postprandial dyslipidemia observed in response to chronic fructose feeding and development of an insulin-resistant state.

Palmitic and stearic acids similarly affect plasma lipoprotein metabolism in cynomolgus monkeys fed diets with adequate levels of linoleic acid

This study was designed to evaluate whether the exchange of specific saturated fatty acids [SFA; palmitic acid (16:0) for stearic acid (18:0)] would differentially affect plasma lipids and lipoproteins, when diets contained the currently recommended levels of total SFA, monounsaturated fatty acids and polyunsaturated fatty acids (PUFA). Ten male cynomolgus monkeys were fed one of two purified diets (using a cross-over design) enriched either in 16:0 (palmitic acid diet) or 18:0 (stearic acid diet). Both diets provided 30% of energy as fat (SFA/monounsaturated fatty acid/PUFA: 1/1/1). The palmitic acid and stearic acid diets were based on palm oil or cocoa butter (59% and 50% of the total fat, respectively). By adding different amounts of sunflower, safflower and olive oils, an effective exchange of 16:0 for 18:0 of approximately 5% of energy was achieved with all other fatty acids being held constant. Monkeys were rotated through two 10-wk feeding periods, during which time plasma lipids and in vivo lipoprotein metabolism (following the simultaneous injection of (131)I-LDL and (125)I- HDL were evaluated). Plasma triacyglycerol (0.40 +/- 0.03 vs. 0.37 +/- 0.03 mmol/L), plasma total cholesterol (3.59 +/- 0.18 vs. 3.39 +/- 0.23 mmol/L), HDL cholesterol (1.60 +/- 0.16 vs 1.53 +/- 0.16 mmol/L) and non-HDL cholesterol (2.02 +/- 0.26 vs. 1.86 +/- 0.23 mmol/L) concentrations did not differ when monkeys consumed the palmitic acid and stearic acid diets, respectively. Plasma lipoprotein compositional analyses revealed a higher cholesteryl ester content in the VLDL fraction isolated after consumption of the stearic acid diet (P < 0.10), as well as a larger VLDL particle diameter (16.3 +/- 1.7 nm vs. 13.8 +/- 3.6 nm; P < 0.05). Kinetic analyses revealed no significant differences in LDL or HDL transport parameters. These data suggest that when incorporated into diets following current guidelines, containing adequate PUFA, an exchange of 16:0 for 18:0, representing approximately 11 g/(d.10.46 mJ) [ approximately 11 g/(d.2500 kcal)] does not affect the plasma lipid profile and has minor effects on lipoprotein composition. Whether a similar effect would occur in humans under comparable dietary conditions remains to be established.

Pork fat and chicken fat similarly affect plasma lipoprotein metabolism in cynomolgus monkeys fed diets with adequate levels of linoleic acid

The effects on plasma lipoprotein metabolism of replacing pork fat (PF) with chicken fat (CF) (formulated as part of currently recommended prudent diets) was evaluated in 10 male cynomolgus monkeys. Monkeys were rotated through three dietary periods, (each of 10-wk duration), during which total cholesterol (TC), triacylglycerol (TG) and HDL-cholesterol (HDL-C) were measured (7, 8 and 9 wk) and in vivo lipoprotein metabolism evaluated (after 9 wk). Initially, all monkeys were fed a high-fat, high-cholesterol reference diet [38% of energy (en) from fat, 18%en saturated fatty acids (SFA), 10%en monounsaturated fatty acids (MUFA), 10%en polyunsaturated fatty acids (PUFA), 0.045 mg cholesterol/kJ diet]. Subsequently, monkeys were rotated through two test diets (30%en fat, SFA/MUFA/PUFA 1:1:1, 0.004-0.005 mg cholesterol/kJ diet), in which 80% of the fat was either PF or CF, with the remaining 20% derived from high-linoleic safflower oil. There was no significant difference between the two test diets for TG, TC, nonHDL-C, HDL-C or the ratio of TC/HDL-C. Lipoprotein composition, LDL apolipoprotein B pool size, fractional catabolic rate and transport rate were also not significantly different when monkeys consumed the two test diets. These data suggest that when incorporated into diets following current guidelines and containing adequate PUFA ( approximately 7-9%en), PF and CF similarly affect plasma lipids.

Muscle-specific overexpression of FAT/CD36 enhances fatty acid oxidation by contracting muscle, reduces plasma triglycerides and fatty acids, and increases plasma glucose and insulin

Increasing evidence has implicated the membrane protein CD36 (FAT) in binding and transport of long chain fatty acids (FA). To determine the physiological role of CD36, we examined effects of its overexpression in muscle, a tissue that depends on FA for its energy needs and is responsible for clearing a major fraction of circulating FA. Mice with CD36 overexpression in muscle were generated using the promoter of the muscle creatine kinase gene (MCK). Transgenic (MCK-CD36) mice had a slightly lower body weight than control litter mates. This reflected a leaner body mass with less overall adipose tissue, as evidenced by magnetic resonance spectroscopy. Soleus muscles from transgenic animals exhibited a greatly enhanced ability to oxidize fatty acids in response to stimulation/contraction. This increased oxidative ability was not associated with significant alterations in histological appearance of muscle fibers. Transgenic mice had lower blood levels of triglycerides and fatty acids and a reduced triglyceride content of very low density lipoproteins. Blood cholesterol levels were slightly lower, but no significant decrease in the cholesterol content of major lipoprotein fractions was measured. Blood glucose was significantly increased, while insulin levels were similar in the fed state and higher in the fasted state. However, glucose tolerance curves, determined at 20 weeks of age, were similar in control and transgenic mice. In summary, the study documented, in vivo, the role of CD36 to facilitate cellular FA uptake. It also illustrated importance of the uptake process in muscle to overall FA metabolism and glucose utilization.

The acute phase response in apolipoprotein A-1 knockout mice: apolipoprotein serum amyloid A and lipid distribution in plasma high density lipoproteins

In plasma, the bulk of apoSAA, a positive acute phase reactant protein, is transported in high density lipoproteins (HDL), especially HDLH (apoA1-rich HDL). In this study we tested whether apoA1 deficiency would adversely affect apoSAA concentration and lipid distribution in mouse plasma lipoproteins. Acute phase response (APR) was induced in C57BL/6J (apoA1+/+) and apoA1-knockout mice (apoA1-/-) by a subcutaneous injection of silver nitrate. The APR increased cholesterol concentrations in LDL of apoA1-/- mice and apoA1+/+ mice in a like manner. In contrast to apoA1+/+ mice, concentrations of cholesterol, phospholipids and proteins in both HDLL (1.063<d<1.103 g/ml) and HDLH (1.103<d<1.21 g/ml) were significantly increased by the APR in apoA1-/- mice. Total concentration of plasma apoSAA and its distribution in lipoprotein fractions was similar in both APR groups. The bulk of plasma apoSAA was contained in HDL and not in VLDL or LDL even when the HDL concentration was low. In apoA1-/- mice, HDLL and HDLH contained more apoSAA than in apoA1+/+ mice. These results indicate that apoA1-/- mice are not deterred from mounting an apoSAA response similar to apoA1+/+ mice and that apoA1-rich HDL particles are not necessary for apoSAA transport in the plasma.

The effects of diet and lovastatin on regression of fatty streak lesions and on hepatic and intestinal mRNA levels for the LDL receptor and HMG CoA reductase in F1B hamsters

This study examined the effects of lovastatin supplementation (25 mg/kg per day) in conjunction with an atherogenic diet (10% coconut oil (w/w), 0.05% cholesterol) on regression of pre-existing foam cells and on hepatic and intestinal LDL receptor and HMG CoA reductase mRNA levels. F1B hamsters fed the atherogenic diet had significantly greater (p < 0.0002) foam cell accumulation (10078 +/- 1452 (S.E.M.) micron2) compared to those fed a low fat, no cholesterol chow diet (64 +/- 10 micron2) or the atherogenic diet supplemented with lovastatin (1621 +/- 132 micron2). Regression of fatty streak lesions was achieved by feeding either a chow diet or supplementing the atherogenic diet with lovastatin as evidenced by the significant (p < 0.0002) reduction in foam cell accumulation in the chow regression (94 +/- 55 micron2) and lovastatin regression (48 +/- 18 micron2) groups compared to the atherogenic diet group (10078 +/- 1452 micron2). Lovastatin supplementation of the atherogenic diet induced significant upregulation of both LDL receptor and HMG CoA reductase message levels in liver and intestine compared to the chow and atherogenic diet fed groups. These data demonstrate that lovastatin supplementation of an atherogenic diet decreases foam cell accumulation and induces upregulation of hepatic and intestinal LDL receptor and HMG CoA reductase mRNA levels. Furthermore, regression of pre-existing, diet-induced fatty streak lesions can be achieved by lovastatin supplementation of an atherogenic diet or by feeding a low fat, low cholesterol chow diet. The specific effects of lovastatin on foam cell accumulation and regression and messenger RNA levels are secondary to reductions in plasma total cholesterol concentrations and do not demonstrate a direct effect of lovastatin on atherosclerotic lesions.

Divergent responses of the liver to increased delivery of glucose or fatty acids: implications for the pathogenesis of type IV hyperlipoproteinemia

This study examines the patterns of response of primary cultures of hamster hepatocytes to increased delivery of glucose or oleate. Increased glucose in the medium produced: (1) increased triglyceride in the cells and the medium; (2) no change in cholesterol ester in the cells or the medium; (3) no change in apo B100 secreted into the medium; (4) more apo B100 particles within the VLDL range with an increase in the VLDL triglyceride to apo B100 ratio. By contrast, increased oleate in the medium resulted in: (1) increased triglyceride in the cells and the medium; (2) increased cholesterol ester in the cells and the medium; and (3) increased apo B100 secreted into the medium. Important differences in the intracellular metabolism of triglyceride and cholesterol ester were also documented. Under all circumstances, there was substantially more radiolabelled triglyceride (overall eight times more) in the cell than in the medium, indicating that up to 90% of the newly synthesized triglyceride enters the cellular pool rather than being secreted with apo B100. By contrast, almost half of the newly synthesized cholesterol ester molecules were secreted with apo B100, pointing to an equal probability of entering the cell storage pool as opposed to being secreted. The data establish therefore two patterns of response of the liver to increased triglyceride synthesis depending on whether the substrate drive is glucose or oleate.

Myristic acid-rich fat raises plasma LDL by stimulating LDL production without affecting fractional clearance in gerbils fed a cholesterol-free diet

The imbalance that develops between low-density lipoprotein (LDL) production and clearance during saturated fat consumption is responsible for expanding the circulating LDL pool. To assess the imbalance attributable to fatty acids alone, i.e., without the interaction of dietary cholesterol, the most fat-sensitive species available (the gerbil) was challenged with either a 12:0+14:0 rich-fat (high coconut, low safflower) or high 18:2 (high safflower, low coconut) fat for 4-5 wks. The plasma lipoprotein cholesterol profile, including lipoprotein composition, particle size and 125I-LDL turnover were measured. Although total plasma cholesterol (TC) was threefold higher with saturated fatty acid (SFA) feeding (230 vs. 70 mg/100 mL; 5.9 +/- 0.1 vs. 1.8 +/- 0.05 mmol/L, P < 0. 0001) and LDL cholesterol (LDL-C) was fivefold greater (10 vs. 54 mg/100 mL; 0.26 +/- 0.02 vs. 1.4 +/- 0.02 mmol/L, P < 0.001), the high-density lipoprotein (HDL2) fraction increased the most (27 vs. 79 mg/100 mL; 0.7 +/- 0.02 vs. 2.0 +/- 0.1 mmol/L, P < 0.05) with minimal HDL3 (NS) difference (16 vs. 26 mg/100 mL; 0.43 +/- 0.08 vs. 0. 7 +/- 0.05 mmol/L). Particle composition and size did not differ between groups. LDL kinetic analyses revealed that the fractional catabolic rate did not differ between gerbils with these extreme fat intakes, implicating overproduction and not reduced clearance as the primary consideration in LDL expansion. Thus SFA-induced cholesterolemia can be severe in the absence of dietary cholesterol with a greater impact on high-density lipoprotein than LDL and without an appreciable role attributed to LDL clearance (receptors).

Plasma LDL and HDL subspecies are heterogenous in particle content of tocopherols and oxygenated and hydrocarbon carotenoids. Relevance to oxidative resistance and atherogenesis

Epidemiological data indicate that dietary tocopherols and carotenoids can exert cardioprotective effects, which may be mediated by their antioxidant actions. The oxidative modification of LDL underlies the atherogenicity of these cholesterol-rich particles. The resistance of LDL to oxidation is influenced by several endogenous factors, among which the content of tocopherols and carotenoids is prominent. Of the exogenous factors, HDL inhibits oxidation of LDL via several mechanisms. In view of the paucity of data on the distribution of diverse tocopherol and carotenoid components among the apoB- and apoA-I-containing lipoproteins of human plasma, we evaluated the quantitative and qualitative features of the LDL and HDL particle subspecies in normolipidemic subjects. The bulk of tocopherols and hydrocarbon carotenoids (lycopene, alpha- and beta-carotene) was transported in LDL (45% and 76%, respectively), in contrast to the oxygenated carotenoids (lutein/zeaxanthin, canthaxanthin, and beta-cryptoxanthin), which were equally distributed between LDL and HDL. alpha-Tocopherol content was independently associated with lipid core size (cholesteryl ester and triglyceride) in VLDL, LDL, and HDL (P < .005); by contrast, the particle content of the oxygenated carotenoids lutein/zeaxanthin and canthaxanthin was strongly related to that of phospholipids. A significant and progressive decrease in the molar content of alpha- and gamma-tocopherols was found with increase in density from light to dense LDL subspecies (LDL1 to LDL5); a similar trend was observed in HDL subspecies. Furthermore, particle contents of lutein/zeaxanthin, beta-cryptoxanthin, beta-carotene, and lycopene were markedly reduced in small, dense LDL (LDL5, d = 1.050 to 1.065 g/mL). We conclude that diminished contents in such carotenoids as well as in tocopherols could underlie not only the diminished oxidative resistance of small, dense LDL but also reduced tissue targeting of antioxidants in subjects with a dense LDL phenotype.

Reduced cholesterol absorption in hamsters by crilvastatin, a new 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor

Crilvastatin, a new drug from the pyrrolidone family, has been previously shown to inhibit the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase, in vitro and in vivo, to reduce the absorption of dietary cholesterol and to stimulate the activity of cholesterol 7 alpha-hydroxylase in the rat. The aim of this study was to evaluate the effects of crilvastatin on cholesterol and bile acid metabolism in the hamster. In hamsters fed on a lithogenic diet for 8 weeks, crilvastatin treatment (200 mg/day per kg body weight) did not change plasma lipid levels, failed to improve bile parameters and did not prevent gallstone formation. In hamsters fed on a basal cholesterol-rich (0.2%) diet for 8 weeks, crilvastatin at the same dose reduced the cholesterol level in the plasma by 20%, with a decrease of both low-density and high-density lipoprotein cholesterol. The drug did not significantly stimulate the biliary secretion of bile acids but significantly decreased the activity of acyl coenzyme A:cholesterol acyltransferase in the small intestine by 64%. This effect was enhanced when cholestyramine, a bile acid-sequestering resin, was given in combination with crilvastatin. Crilvastatin alone did not change the activity of cholesterol 7 alpha-hydroxylase in the liver, despite the marked reduction in both hepatic cholesterogenesis and intestinal absorption of dietary cholesterol (the absorption coefficient was 44 +/- 2% in treated hamsters vs. 61 +/- 7% in controls).