Effects of stigmastanyl-phosphocholine (Ro 16-6532) and lovastatin on lipid and lipoprotein levels and lipoprotein metabolism in the hamster on different diets

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.

Anacetrapib promotes reverse cholesterol transport and bulk cholesterol excretion in Syrian golden hamsters

Cholesteryl ester transfer protein (CETP) transfers cholesteryl ester (CE) and triglyceride between HDL and apoB-containing lipoproteins. Anacetrapib (ANA), a reversible inhibitor of CETP, raises HDL cholesterol (HDL-C) and lowers LDL cholesterol in dyslipidemic patients; however, the effects of ANA on cholesterol/lipoprotein metabolism in a dyslipidemic hamster model have not been demonstrated. To test whether ANA (60 mg/kg/day, 2 weeks) promoted reverse cholesterol transport (RCT), ³H-cholesterol-loaded macrophages were injected and (3)H-tracer levels were measured in HDL, liver, and feces. Compared to controls, ANA inhibited CETP (94%) and increased HDL-C (47%). ³H-tracer in HDL increased by 69% in hamsters treated with ANA, suggesting increased cholesterol efflux from macrophages to HDL. ³H-tracer in fecal cholesterol and bile acids increased by 90% and 57%, respectively, indicating increased macrophage-to-feces RCT. Mass spectrometry analysis of HDL from ANA-treated hamsters revealed an increase in free unlabeled cholesterol and CE. Furthermore, bulk cholesterol and cholic acid were increased in feces from ANA-treated hamsters. Using two independent approaches to assess cholesterol metabolism, the current study demonstrates that CETP inhibition with ANA promotes macrophage-to-feces RCT and results in increased fecal cholesterol/bile acid excretion, further supporting its development as a novel lipid therapy for the treatment of dyslipidemia and atherosclerotic vascular disease.

Synthesis and structure-activity studies of novel orally active non-terpenoic 2,3-oxidosqualene cyclase inhibitors

New orally active non-terpenoic inhibitors of human 2,3-oxidosqualene cyclase (hOSC) are reported. The starting point for the optimization process was a set of compounds derived from a fungicide project, which in addition to showing high affinity for OSC from Candida albicans showed also high affinity for human OSC. Common structural elements of these inhibitors are an amine residue and an electrophilic carbonyl C atom embedded in a benzophenone system, which are at a distance of about 10.7 A. Considering that the keto moiety is in a potentially labile position, modifications of the substitution pattern at the benzophenone as well as annelated heteroaryl systems were explored. Our approach combined testing of the compounds first for increased binding affinity and for increased stability in vitro. Most promising compounds were then evaluated for their efficacy in lowering plasma total cholesterol (TC) and plasma low-density lipoprotein cholesterol (LDL-C) in hyperlipidemic hamsters. In this respect, the most promising compounds are the benzophenone derivative 1.fumarate and the benzo[d]isothiazol 24.fumarate, which lowered TC by 40% and 33%, respectively.

Regulation of cholesterol metabolism by dietary plant sterols

Renewal has occurred in the use of plant sterols for the treatment of hypercholesterolemias. A novel development was to convert plant sterols to corresponding stanols and esterify them to fat soluble form. In contrast to the crystalline plant sterols or stanols, plant stanol esters can be easily consumed during normal food intake in soluble form in different fat-containing food constituents when they have a potent cholesterol-lowering effect, shown in normo- and hypercholesterolemic men and women without or with coronary heart disease, children and diabetes. Cholesterol lowering is approximately 10% for total and 15% for LDL cholesterol, with the respective values for stanol ester margarine (2-3 g/day stanols) being 15% and 20%. Stanol esters reduce cholesterol absorption efficiency by up to 65%, increase cholesterol elimination in feces as cholesterol itself, usually not as bile acids, and stimulate cholesterol synthesis. Serum beta-carotene level is lowered, but no fat malabsorption or lowering of serum fat soluble vitamins have been observed. In contrast to plant sterols, stanols and their esters are minimally absorbed and they reduce serum plant sterol concentrations, also preventing statin-induced increase of plant sterols. Stanol ester margarine has been included in dietary treatment of hypercholesterolemia followed by the addition of drug treatment in resistant cases.

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.

Regulation of very low density lipoprotein apo B metabolism by dietary fat saturation and chain length in the guinea pig

Studies investigated the effects of dietary fatty acid composition and saturation on the regulation of very low density lipoprotein (VLDL) apo B flux, clearance, and conversion to low density lipoprotein (LDL) in guinea pigs fed semipurified diets containing 15% (w/w) corn oil (CO), lard (LA), or palm kernel oil (PK). Plasma cholesterol levels were highest with dietary PK (3.1 +/- 1.0 mmol/L) followed by LA (2.4 +/- 0.4 mmol/L) and CO (1.6 +/- 0.4 mmol/L) intake. VLDL particles were larger (P < 0.05) in the LA (78 +/- 7 nm) and PK (69 +/- 10 nm) groups compared to animals fed CO (49 +/- 5 nm). VLDL-apo B fractional catabolic rates (FCR) were highest in guinea pigs fed the LA diet (P < 0.05) and VLDL apo B flux, estimated from VLDL 125I-apo B turnover kinetics, were higher in LA compared to PK or CO fed guinea pigs. In the case of PK consumption, the kinetic estimates of VLDL apo B flux significantly underestimated rates compared to direct VLDL apo B secretion measurements and LDL turnover analyses. These data demonstrate that differences in the composition and amount of saturated fatty acids have differential effects on VLDL apo B flux, catabolism, and conversion to LDL which, together with changes in LDL receptor-mediated catabolism, determine plasma LDL cholesterol levels in guinea pigs. The data also indicate that kinetic analysis of VLDL metabolism in PK fed animals is inaccurate possibly due to the presence of a small, nonequilibrating pool of newly synthesized VLDL which is rapidly converted to LDL.

Steroidal glycoside cholesterol absorption inhibitors

We have explored the use of steroidal glycosides as cholesterol absorption inhibitors which act through an unknown mechanism. The lead for this program was tigogenin cellobioside (1, tiqueside) which is a weak inhibitor (ED50 = 60 mg/kg) as measured in an acute hamster cholesterol absorption assay. Modification of the steroid portion of the molecule led to the discovery of 11-ketotigogenin cellobioside (5, pamaqueside) which has an ED50 of 2 mg/kg. Replacement of the cellobiose with other sugars failed to provide more potent analogs. However, large improvements in potency were realized through modification of the hydroxyl groups on the cellobiose. This strategy ultimately led to the 4", 6"-bis[(2-fluorophenyl)carbamoyl]-beta-D-cellobiosyl derivative of 11-ketotigogenin (51) with an ED50 of 0.025 mg/kg in the hamster assay, as well as the corresponding hecogenin analog 64 (ED50 = 0.07 mg/kg).

Cholesterol metabolism and non-cholesterol sterols in patients with ileal pouch anastomosis

BACKGROUND

Previous studies suggest only minor changes in bile acid metabolism after panproctocolectomy with ileal pouch construction.

AIMS/METHODS

To investigate these changes further, we studied cholesterol absorption and serum, biliary and fecal non-cholesterol sterols and lipids in 12 ileal pouch patients and 10 controls.

RESULTS

In patients, cholesterol absorption was markedly reduced and was associated with low serum total and LDL cholesterol and LDL triglyceride levels, but surprisingly, cholesterol synthesis, as indicated by sterol-balance data or serum cholesterol precursor levels, was within low normal limits. The high proportions of serum plant sterol to cholesterol, particularly that of campesterol, were not related to cholesterol absorption, but were attributable to a markedly reduced biliary cholesterol secretion. Interestingly, in these patients the fractional absorption of campesterol was normal, whereas that of sitosterol, like cholesterol, was reduced and was positively related to the intestinal influx of cholesterol. The patients' serum cholestanol proportion was normal, but the proportion of the cholestanol formed during intestinal passage was significantly reduced (17.9% vs 65.2% in controls).

CONCLUSIONS

Thus ileal pouch patients are characterized by sterol malabsorption, lowered serum total and LDL-cholesterol levels, but unexpectedly without any increase in cholesterol synthesis. The lack of high serum cholestanol, shown earlier frequently in unoperated patients with ulcerative colitis, may indicate reversible cholestasis, a finding deserving further exploration.

Inhibition of cholesterol absorption with CP-148,623 lowers serum cholesterol in humans

OBJECTIVE

To determine the effects of the reduction of intestinal cholesterol absorption with CP-148,623 on serum cholesterol levels in men with mild hyperlipidemia.

METHODS

In an outpatient study in a university medical center, healthy male volunteers (n = 25) with borderline-high serum cholesterol levels participated in a double-blind, placebo-controlled parallel-group study. A 3-week dietary run-in period was followed by 2 weeks of treatment with either CP-148,623 (300 mg twice a day; n = 12) or placebo (n = 13).

RESULTS

Fractional cholesterol absorption (by the dual-isotope, continuous-feeding technique), fecal neutral sterol excretion, and serum lipids were measured after the diet run-in and after the treatment periods. CP-148,623 caused a marked inhibition (by 38%) of fractional cholesterol absorption (50% +/- 2% [baseline] to 31% +/- 1%) and a 71% increase in fecal neutral sterol excretion (481 +/- 39 mg/day [baseline] to 804 +/- 55 mg/day), compared with negligible changes in the placebo group (p < 0.0001 for both). Mean percent reductions from baseline in serum low-density lipoprotein (LDL) cholesterol levels were 11.6% with CP-148,623 (119 +/- 17 mg/dl to 104 +/- 13 mg/dl) versus a nonsignificant 1.8% reduction with placebo (change with CP-148,623 versus placebo, p < 0.0002).

CONCLUSIONS

In healthy male volunteers with mild hypercholesterolemia, treatment for 2 weeks with 600 mg/day CP-148,623 inhibited fractional cholesterol absorption by 35% to 40%, increased fecal neutral sterol excretion by 60% to 70%, and reduced serum LDL cholesterol by 10% to 12%.

Effects of simvastatin on plasma lipids and apolipoproteins in familial hypercholesterolemic swine

Familial hypercholesterolemia (FHC) in swine, which resembles human familial combined hyperlipidemia, is a complex lipid and lipoprotein disorder associated with the development of severe coronary lesions similar to those occurring in advanced human coronary disease. The disorder is characterized by elevated plasma total cholesterol (TC), triglycerides (TG), LDL-cholesterol (LDL-C), apolipoproteins (apo) B, C-III, and E, and by decreased levels of HDL-cholesterol (HDL-C), apoA-I, and lecithin:cholesterol acyltransferase (LCAT) activity. A dose-response study with simvastatin, a specific inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, was conducted in four treatment groups of FHC animals, exhibiting TC > or = 250 mg/dL. The animals were fed 0, 80, 200, or 400 mg simvastatin daily for 3 weeks. The measured serum parameters included the levels of TC, VLDL-C, LDL-C, HDL-C, TG, lathosterol, apoA-I, B, C-III, and E, as well as LCAT activity. Simvastatin at 200 mg/d significantly decreased the levels of TC (-25%), LDL-C (-27%), lathosterol (-40%), apoB (-22%), apoC-III (-37%), and apoE (-24%) and modestly decreased the levels of HDL-C (-12%) and apoA-I (-11%) (percent relative to the average pretreatment and posttreatment baseline values) but did not affect the levels of TG, VLDL-C, the lathosterol/TC ratio, or LCAT activity. The levels of TC, LDL-C, apoB, and E were also lowered by simvastatin at 80 or 400 mg/d, but to a lesser extent than at 200 mg/d, while the other parameters were not influenced at these doses. The simvastatin-induced decreases of LDL-C, HDL-C, and apoA-I, B, C-III, and E were significantly correlated among each other. These results show that the trend of responses in TC, LDL-C, apoB, apoC-III, and apoE to simvastatin in the FHC swine is similar to that observed in humans, although the drugs is less potent and efficacious in swine, while the results are different from those in humans with regard to the remaining parameters.