Low cost polymer intramedullary nails for fracture fixation: a biomechanical study in a porcine femur model.

INTRODUCTION: Whilst intramedullary nailing is a commonly accepted technique for lower limb fracture fixation, the cost of nails can be prohibitive in hospitals in developing nations. In these institutions bone cement has found many off label applications, that whilst are effective do not meet manufacturers guidelines. The aim of this study was to examine the biomechanics of one such application, fracture fixation using a bone cement intramedullary nail. MATERIALS AND METHODS: Five porcine femurs underwent a mid-shaft osteotomy and were fixed using a nail made from antibiotic simplex bone cement. The torsional and flexural stiffness and shear modulus of these constructs were compared to five intact porcine femurs. RESULTS: The bone cement intramedullary nail was able to achieve relative stability in both torsion, with a mean shear modulus of 0.17 GPa and in flexion with a mean flexural stiffness of 358 N/mm. This corresponds to 47 and 22% of the respective measurements in the intact femurs. The mean ultimate flexural strength of fracture/nail constructs was 936 +/- 350 N, which is 20% of the ultimate flexural strength of an intact porcine femur (4,820 +/- 698 N). CONCLUSION: Intramedullary nails made from bone cement were able to provide sufficient promise in this situation to warrant further investigation for their applicability as a low cost alternative for use in developing countries.

Plasma lipids, lipoprotein composition and profile during induction and treatment of hepatic lipidosis in cats and the metabolic effect of one daily meal in healthy cats.

Anorexia in obese cats may result in feline hepatic lipidosis (FHL). This study was designed to determine plasma lipids and lipoprotein profiles in queens at different stages during experimental induction of FHL (lean, obese, FHL), and after 10 weeks of treatment. Results were compared with those obtained from lean queens of same age fed the same diet but at a maintenance level, once a day. Hepatic lipidosis led to an increase in plasma triacylglycerol (TG), very low density lipoprotein (VLDL) and low density lipoprotein (LDL), and an enrichment of LDL with TG and of high density lipoprotein (HDL) with cholesterol, suggesting that VLDL secretion is enhanced, VLDL and LDL catabolism is lowered, and lipoprotein exchanges are impaired in FHL. This study also showed that cholesterolaemia is increased in cats fed at a dietary rhythm of one meal per day compared to ad libitum feeding.

Postprandial variations in the cholesteryl ester transfer protein activity, phospholipid transfer protein activity and plasma cholesterol efflux capacity in normolipidemic men.

BACKGROUND AND AIM: Plasma cholesterol efflux capacity is stimulated during postprandial (PP) hypertriglycerdemia. Plasma cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP) are the key proteins in lipoprotein metabolism and remodelling, but their role during the PP cholesterol efflux process remains indeterminate. The aim of this study was to determine the effect of a fatty meal intake on plasma CETP and PLTP activities, and the capacity of plasma to promote cholesterol efflux, as well as to evaluate the relationship between these three key mechanisms of the reverse cholesterol transport process. METHODS AND RESULTS: CETP and PLTP activities and the cholesterol efflux capacity of plasma were measured over eight hours following a fatty meal (1000 kcal, 62% fat) in 13 normolipidemic men. CETP activity and the cholesterol efflux capacity of plasma from Fu5AH cells increased after the meal, reaching a maximum after eight hours (respectively 32%, p = 0.06, and 6.5%, p = 0.045), whereas PLTP activity remained unchanged. CETP and PLTP activities did not correlate with plasma cholesterol efflux capacity in the fasting or PP state. Plasma CETP activity in the fasting state positively correlated with the plasma non-esterified fatty acid (NEFA) levels, but no correlation was found with any lipid or apolipoprotein postprandially. The cholesterol efflux capacity of plasma correlated positively with high-density lipoprotein (HDL) components, the best correlation being with the HDL phospholipid fraction in both the fasting and PP states. CONCLUSIONS: These findings suggest that plasma CETP and PLTP activities in healthy normolipidemic subjects are differently regulated in the PP state, and are not correlated with the increased cholesterol efflux capacity of PP plasma. HDL-phospholipid remains the key factor in the regulation of the capacity of plasma to promote Fu5AH cell cholesterol efflux.

Diet-dependent effects of insulin infusion on the hepatic lipoprotein receptors and the key enzymes of bile acid synthesis in the hamster.

The effects of an induced hyperinsulinemia on both the cholesterol and bile acid metabolisms were analyzed in the hamster. The role of dietary sucrose as modulator of these effects was evaluated by feeding the animals with two semi-synthetic diets containing a low (SD, 20%) and a high (LD, 62.5%) sucrose proportion. Hamsters fed under basal nutritional conditions (chow diet, CD) were also used. LD enabled the consequences of an insulin infusion on cholesterol gallstone formation to be evaluated. Subcutaneous osmotic pumps were implanted in all the animals and delivered either 3 IU/day of insulin (insulin groups: CDI, SDI, LDI) or saline (control groups: CDC, SDC, LDC). Several parameters bound to lipid metabolism were measured. The plasma cholesterol concentration remained constant in all the insulin treated groups compared to the controls. Phospholipid and triglyceride concentrations decreased in both the plasma and liver in the CDI and SDI groups. A lower SR-BI mass (around 50%) was found in the liver of CDI and SDI hamsters with concomitant higher hydroxy-methyl-glutaryl coenzyme A reductase activity. The LDL-receptor mass and cholesterol 7alpha-hydroxylase activity in the LDI group were both decreased (-47%, -71% respectively). No variations in the cholesterol gallstone incidence were observed. In conclusion, chronic insulin infusion in growing hamsters induced similar effects on cholesterol metabolism in the CD and SD groups but different ones, between diets containing a low (SD) and a high (LD) sucrose proportion. The distribution of triglycerides and phospholipids in the plasma, liver and bile was also affected by the insulin infusion.

Insulin injections enhance cholesterol gallstone incidence by changing the biliary cholesterol saturation index and apo A-I concentration in hamsters fed a lithogenic diet.

BACKGROUND/AIMS: A link between insulin and cholesterol gallstone disease has often been suspected but never demonstrated. The aim was to evaluate the direct implication of insulin in the gallbladder cholesterol gallstone formation process. METHODS: Hamsters fed with a soft-inducing lithogenic diet, enriched with sucrose, were injected daily, for 1 week, either with long-acting insulin or saline (controls). RESULTS: Insulin injections doubled the cholesterol gallstone incidence. The cholesterol saturation index (CSI) of bile significantly increased (+19%) and biliary apolipoprotein A-I (apo A-I) decreased, both in concentration (-71%) and the proportion relative to the total biliary proteins (-25%). No modifications in the biliary bile acid composition were noticed. Hepatic HMGCoA reductase activity was higher (+341%), CYP7A1 activity was lower (-52%), whereas CYP27A1 and CYP7B1 were not affected. The hepatic low-density liprotein (LDL)-receptor and SR-BI masses did not vary. The hepatic total cholesterol content increased (+42%). Fasting plasma phospholipid and triglyceride concentrations significantly decreased (-15 and -60%, respectively), but the cholesterol concentration remained constant. CONCLUSIONS: These results suggest that insulin injections enhance cholesterol gallstone incidence by increasing the CSI of bile and decreasing the concentration and proportion of a biliary anti-nucleating protein, apo A-I. Insulin modulates the major enzymes of cholesterol and bile acid metabolisms in vivo.

Hamsters predisposed to sucrose-induced cholesterol gallstones (LPN strain) are more resistant to excess dietary cholesterol than hamsters that are not sensitive to cholelithiasis induction.

We compared the effects of cholesterol feeding in male hamsters from two strains with different propensities to sucrose-induced cholelithiasis; Laboratoire de Physiologie de la Nutrition (LPN) hamsters are predisposed to developing biliary cholesterol gallstones, whereas Janvier (JAN) hamsters are not. When fed a basal control diet, LPN hamsters had a lower cholesterolemia (-21%, P = 0.01) than JAN hamsters, and a higher activity of 3-hydroxy-3-methyl glutaryl coenzyme A reductase in liver (+148%, P = 0.018) and intestine (+281%, P < 0.0001). After feeding the same diet enriched with 0.3% cholesterol for 5 wk, cholesterolemia increased more dramatically in JAN hamsters (+235%, P < 0.001) than in LPN hamsters (+108%, P < 0.001), as did the liver concentration of cholesterol, which reached 152.30 +/- 13.00 and 44.41 +/- 9.06 micromol/g, respectively. Only JAN hamsters displayed hepatomegaly, with an increased cholesterol saturation index of the gallbladder bile (+100%, P < 0.01), due to the cholesterol challenge. In liver, cholesterol feeding reduced cholesterol 7alpha-hydroxylase activity and mRNA level, and stimulated sterol 27-hydroxylase and oxysterol 7alpha-hydroxylase activities. Hepatic levels of LDL receptor decreased by approximately 60% in both strains, whereas HDL receptor scavenger class B type 1 (SR-BI) levels were unaffected by dietary cholesterol. The greater resistance of LPN hamsters to the hypercholesterolemic diet can be explained by a lower capacity to store cholesterol in the liver and greater efficiency in reducing the activity of 3-hydroxy-3-methyl glutaryl coenzyme A reductase in response to cholesterol feeding [from 11263 to 261 pmol/(min x organ) in LPN hamsters and from 4530 to 694 pmol/(min x organ) in JAN hamsters]. These results highlight the usefulness of this two-strain model, which offers some analogy with the inverse association between the predisposition to cholelithiasis and the risk of atherosclerosis in humans.

Overexpression of SR-BI in hamsters treated with a novel ACAT inhibitor (F12511).

The effect of a novel acyl-coenzyme A: cholesterol acyltransferase (ACAT) inhibitor on cholesterol metabolism was studied in hamsters. Oral administration of F12511 (10 mg/kg/d) for 4 weeks produced a decrease in dietary cholesterol absorption (-18%) and in the liver concentration of esterified cholesterol (-75%), as compared with control values in untreated hamsters. While the hepatic expression of LDLr was unchanged by the treatment, that of SR-BI was increased (+142%), which suggests that the hepatic expression of SR-BI could be upregulated by a depletion of the cholesterol stores, due to ACAT inhibition. This SR-BI overexpression, however, did not induce a fall in plasma HDL-cholesterol concentration, in contrast with previous reports in transgenic mice overexpressing SR-BI at a higher extent.

Effects of F2833 on cholesterol metabolism in the genetically hyperlipidemic rat.

The effects of the new hypolipidemic agent, F2833 or (chloro 2' (1-1') biphenyl-4)-2 propanol-2, on cholesterol metabolism were studied in genetically hyperlipidemic rats (RICO). Cholesterolemia decreased after 2 days of treatment to 60% of its initial value (1.20+/-0.10 g/l vs. 1.99+/-0.08, P < 0.001) and then stabilised within 10 days. This hypocholesterolemic action was effective for as long as 3 months. Concerning the different classes of lipoproteins, a significant drop was observed in HDL (high density lipoproteins) (25%, 0.49 +/- 0.02 g/l vs. 0.66 +/- 0.007, P < 0.01) and particularly in LDL (low density lipoproteins) (70%, 0.30 +/- 0.04 g/l vs. 0.92 +/- 0.05, P < 0.001). Whole body cholesterol showed a higher fractional catabolic rate (0.25 +/- 0.02 vs. 0.17 +/- 0.005 day(-1), P < 0.01) together with an increased cholesterol synthesis (60 +/- 5 vs. 36 +/- 4 mg/day, P < 0.01). LDL kinetics showed that the decrease in these lipoproteins is essentially caused by an increase in the fractional catabolic rate (10.6 +/-0.1%/h vs. 5.2 +/- 0.1%/h, P < 0.001) and by a lesser decrease in the LDL production rate. This cholesterol metabolic profile created by treatment suggests an effect through stimulation of cholesterol output (biliary cholesterol elimination or cholesterol transformation into bile acids).

Cholesterol, bile acid, and lipoprotein metabolism in two strains of hamster, one resistant, the other sensitive (LPN) to sucrose-induced cholelithiasis.

A comprehensive study of cholesterol, bile acid, and lipoprotein metabolism was undertaken in two strains of hamster that differed markedly in their response to a sucrose-rich/low fat diet. Under basal conditions, hamsters from the LPN strain differed from Janvier hamsters by a lower cholesterolemia, a higher postprandial insulinemia, a more active cholesterogenesis in both liver [3- to 4-fold higher 3-hydroxy 3-methylglutaryl coenzyme A reductase (HMG-CoAR) activity and mRNA] and small intestine, and a lower hepatic acyl-coenzyme A:cholesterol acyltransferase activity. Cholesterol saturation indices in the gallbladder bile were similar for both strains, but the lipid concentration was 2-fold higher in LPN than in Janvier hamsters. LPN hamsters had a lower capacity to transform cholesterol into bile acids, shown by the smaller fraction of endogenous cholesterol converted into bile acids prior to fecal excretion (0.34 vs. 0.77). In LPN hamsters, the activities of cholesterol 7alpha-hydroxylase (C7OHase) and sterol 27-hydroxylase (S27OHase), the two rate-limiting enzymes of bile acid synthesis, were disproportionably lower (by 2-fold) to that of HMG-CoAR. When fed a sucrose-rich diet, plasma lipids increased, dietary cholesterol absorption improved, hepatic activities of HMG-CoA reductase, C7Ohase, and S27OHase were reduced, and intestinal S27OHase was inhibited in both strains. Despite a similar increase in the biliary hydrophobicity index due to the bile acid enrichment in chenodeoxycholic acid and derivatives, only LPN hamsters had an increased lithogenic index and developed cholesterol gallstones (75% incidence), whereas Janvier hamsters formed pigment gallstones (79% incidence). These studies indicate that LPN hamsters have a genetic predisposition to sucrose-induced cholesterol gallstone formation related to differences in cholesterol and bile acid metabolism.

Short and long-term effects of streptozotocin on dietary cholesterol absorption, plasma lipoproteins and liver lipoprotein receptors in RICO rats.

Adult male genetically hypercholesterolemic RICO rats were studied 6 and 28 days after streptozotocin (STZ) administration together with untreated RICO controls. The absorption coefficient of dietary cholesterol was determined using dual-isotope blood ratio method. Plasma lipoproteins as well as fecal neutral sterols and bile acids were analysed at both experimental times. Liver lipid parameters were measured and lipoprotein receptors (LDLr, SR-BI and HB2) were assayed by immunodetection. Six days after STZ administration, dietary cholesterol absorption was more efficient (+49%) in treated rats than in controls, and stayed higher (+68%) in the diabetic rats sacrificed at day 28. Fecal neutral sterol elimination decreased soon after STZ administration (by 35% at day 6), due to a higher cholesterol absorption coefficient, then increased to control level at day 28, due to installed diabetes-induced hyperphagia. Comparison of the lipoprotein profiles indicated that the concentration of HDL1. which is typically high in control Rico rats, fell significantly in diabetic rats at both experimental times, whereas that of HDL2 increased only at day 28. In diabetic rats, an early and strong enhancement of the hepatic expression of SR-BI appeared at day 6 (+415%) and persisted at day 28, but at a lesser extent (+85%). The expression of LDLr and HB2 was unchanged at day 6, but was significantly modified at day 28 (+140% for LDLr and -50% for HB2). These data show that streptozotocin-induced diabetes in Rico rats results in modifications of the expression of liver lipoprotein receptors which can contribute to alterations of the lipoprotein profile.

Assay of microsomal oxysterol 7alpha-hydroxylase activity in the hamster liver by a sensitive method: in vitro modulation by oxysterols.

A method of assaying hepatic cytochrome P-450, oxysterol 7alpha-hydroxylase (CYP7B), was developed by combining the use of 25-[26,27-(3)H]hydroxycholesterol as a substrate and hydroxypropyl-beta-cyclodextrin as a substrate vehicle. When these assay conditions were tested, an undesirable transformation was observed of the reaction product, 7alpha,25-dihydroxycholesterol, into 3-oxo-7alpha,25-dihydroxy-4-cholesten by the activity of 3beta-hydroxy-Delta(5)-C(27) steroid oxydoreductase, a microsomal NAD(+) and NADP(+) dependent enzyme of bile acid metabolism. A great improvement was reached by using a continuous NADPH generating system which constantly re-transforms NADP(+) into NADPH, thus inhibiting this activity. This improved CYP7B assay, comparable to our previously described assay for cholesterol 7alpha-hydroxylase (CYP7A), allowed a 3-fold increase of the apparent enzyme activity. The possibility to simultaneously measure CYP7A and CYP7B activities on the same microsomal preparation was investigated. A marked decrease (-33%) in the CYP7B activity was noticed, while that of CYP7A remained unchanged. The CYP7B activity was observed to be inhibited by cholesterol (-30%) and also by the oxysterols 7alpha-hydroxycholesterol (-21%), 7beta-hydroxycholesterol (-25%) and epicoprostanol (-20%), and by cyclosporin A (-26%). It can be concluded that this sensible and easy to perform CYP7B assay allows to observe, at least in vitro, a modulation of the enzyme activity by oxysterols.

Cholesterol crystallization in gall-bladder bile of pigs given cholesterol-beta-cyclodextrin-enriched diets with either casein or soyabean concentrate as protein sources.

Cholesterol precipitation from supersaturated bile is the earliest and determinant step in the formation of cholesterol gallstones, which is thought to be diet-dependent. Bile composition, appearance and growth of cholesterol crystals were studied in fresh gall-bladder biles from pigs adapted to four different protein-containing diets over 3 weeks: 160 g dietary protein/kg as casein (C16; n 6), or as soyabean-protein concentrate (S16; n 6), or a mixture of both protein sources (casein-soyabean protein, 70:30, w/w) (CS16; n 6), or 320 g of the mixed protein/kg (CS32; n 6). Moreover, all four diets contained 3 g cholesterol/kg and 50 g beta-cyclodextrin/kg as modifiers of bile composition towards cholesterol pro-crystallization. Cholesterol precipitation was most active after the high-protein diet, CS32, and the casein diet, C16, and lowest after the soyabean-protein diet, S16. It was intermediate after the mixed diet, CS16, but still much lower than in the former two groups. These diet-induced variations were suggested to be mediated through modifications in the biliary profile of bile acids, whereas all other biliary constituents studied were essentially unchanged. The fasting level of plasma cholesterol was lowest in both 160 g protein/kg diets containing soyabean protein (S16 and CS16), highest for the high-protein diet CS32, and intermediate for the C16 diet. These results should encourage clinical studies on the effect of soyabean protein, or other vegetable proteins, for primary or recurrence prevention of cholelithiasis at its earliest stage.

In vivo gallbladder bile diffusion coefficient measurement by diffusion-weighted echo planar imaging in hamster fed normal and lithogenic diets.

It is shown that in vivo measurement of bile water apparent diffusion coefficient (ADC) by diffusion-weighted echo-planar imaging (EPI) in hamster gallbladder is possible providing motion artifact-free ADC values. These ADC values are used to estimate bile viscosity variation induced by normal diets, cholesterol gallstone-inducing diets, and an antilithiasic drug, and to determine if a link exists between bile viscosity and cholesterol gallstone formation. Measurements were performed at 4.7 T with respiratory triggering in five groups of hamsters fed a commercial (RC) or a semisynthetic (SSD) diet, a SSD containing 0.2% hyodeoxycholic acid (SSD+HDC) and two lithogenic diets (LD5, LD10). ADC decreased significantly in LD10 (2.15+/-0.07x 10(-3) mm(2)s(-1)) and SSD+HDC (2.03+/-0.04) compared to RC (2.40+/-0.05) but not in the most lithogenic LD5 diet (2.33+/-0.06). No direct relationship was found between bile viscosity and gallstone incidence; however, viscosity seems to be related to lipid contents of diets. Magn Reson Med 43:854-859, 2000.

Catabolism of HDL1 cholesteryl ester in the rat. Effect of ethinyl estradiol treatment.

The present study was performed in control and ethinyl estradiol-treated rats in order to determine the mechanisms involved in the catabolism of HDL1 cholesteryl ester. Ligand blottings on liver membranes showed that purified HDL1, containing about 70% apolipoprotein E and 10% apolipoprotein AI, bind to the LDL receptor (130 kDa) and not to HB2 (100 kDa) or SR-BI (82 kDa), candidate HDL receptors. Immunoblots showed that the treatment increased the hepatic level of the LDL receptor five- to ten-fold, strongly decreased that of SRBI and did not change that of HB2. An in vivo kinetic study showed that the turnover of HDL1 cholesteryl ester is more rapid in treated than control rats. The liver participation (60%) in this clearance was not modified by the treatment. Therefore, it can be concluded that the catabolism of HDL1 cholesteryl ester, in control as in treated rats, is essentially ensured by the uptake of entire particles in the hepatocytes via LDL receptors.

[The RICO rat (genetically hypercholesteremic): a good model for testing a food substance or a drug specific for a key enzyme of cholesterol metabolism]. / Le rat RICO (génétiquement hypercholestérolémique): un bon modèle pour tester un composé alimentaire ou une drogue spécifique d'une enzyme-clé du métabolisme du cholestérol?

The genetically hypercholesterolemic RICO rat: a good model for testing a food substance or a drug specific for a key enzyme involved in cholesterol metabolism? The genetically hypercholesterolemic RICO rat, whose cholesterolemia is situated between 1.3 and 1.5 mg x mL(-1), possibly reaching 2 mg x mL(-1), after the addition of cholesterol to its food, possesses a different lipoprotein spectrum than man, because approximatively 70% of the plasma cholesterol is carried by HDL (28% of which are carried by the light HDL1 subfraction, rich in apolipoproteinE (apoE). The effects of certain substances in food (carbohydrates, cholesterol, allyldisulfide, etc.) or drugs (ethinylestradiol, streptozotocin, statins, inhibitors of ACAT, etc.) on the cholesterolemia of the rat were studied, in relation to certain important parameters of cholesterol metabolism (LDLr, VLDL liver secretion, activities of lipolytic enzymes: LPL, HL, etc.). The increase in a number of LDL receptors (LDLr) in the RICO rat, induced by ethinylestradiol, streptozotocin, etc., provokes an important decrease in the apoE-rich HDL concentration, filtered out by its receptors. This decrease is observed in man for LDL. Simvastatin, which stimulates LDLr in man and not in rat, lowers the level of LDL in man and has no effect on the cholesterolemia of the RICO rat. In rat and man, the concentration of plasma cholesterol is inversely proportional to the rate of cholesterol synthesis in the organism and to its plasma turnover rate. The concentration of cholesterol in the plasma carried by the HDL1 of the rat, is however, proportional to hepatic cholesterogenesis. This fraction is positively correlated to the activity of hepatic lipase (HL) and negatively to the activity of lipoprotein lipase (LPL), released by heparin. These data demonstrate the importance of the liver and lipolytic enzymes in the intraplasmatic hydrolysis of HDL3 (precursors of HDL1), murine particles that can be considered similar to human LDL.

Modulation of cholesterol 7alpha-hydroxylase and sterol 27-hydroxylase activities by steroids and physiological conditions in hamster.

Our purpose was to examine the in vitro modulation of liver mitochondrial sterol 27-hydroxylase (S27OHase) and microsomal cholesterol 7alpha-hydroxylase (CH7alphaOHase) activities by certain drugs, sterols, oxysterols and bile acids, and to compare the influence of sex, age, diet and cholestyramine on these activities, in the hamster. In vitro, 7beta-hydroxycholesterol and 5alpha-cholestan-3beta-ol (cholestanol) were strong inhibitors (at 2 microM) of both enzyme activities, while 5beta-cholestan-3alpha-ol (epicoprostanol, 2 microM) and cyclosporin A (20 microM) inhibited S27OHase, but not CH7alphaOHase. These data suggest that a hydroxyl group at the 7alpha position is not required to inhibit CH7alphaOHase and that the presence of an aliphatic CH2-CH-(CH3)2 chain appears to be structurally important for S27OHase activity. Both enzyme activities remained unchanged by hyodeoxycholic acid (40 or 80 microM) while epicoprostanol inhibited only S27OHase and chenodeoxycholic acid only CH7alphaOHase. Adult (9-week old) male or female hamsters displayed similar S27OHase activity but the CH7alphaOHase activity was lower in females than in males, suggesting that the neutral bile acid pathway has a less important role in females. In male hamsters, S27OHase activity did not change with age, while CH7alphaOHase activity significantly increased (one-year vs 9-week old). A semi-purified sucrose-rich (lithogenic) diet significantly lowered both enzyme activities compared to the commercial diet. Cholestyramine induced a stimulation of both enzymes, slightly more vigorously however for the key enzyme involved in the neutral pathway. Taken together, these data indicate that the two enzymes are separately regulated and that certain drugs or steroid compounds can be useful for specifically inhibiting or stimulating the neutral or acidic bile acid pathway.

Antilithiasic effect of beta-cyclodextrin in LPN hamster: comparison with cholestyramine.

Beta-Cyclodextrin (BCD), a cyclic oligosaccharide that binds cholesterol and bile acids in vitro, has been previously shown to be an effective plasma cholesterol lowering agent in hamsters and domestic pigs. This study examined the effects of BCD as compared with cholestyramine on cholesterol and bile acid metabolism in the LPN hamster model model for cholesterol gallstones. The incidence of cholesterol gallstones was 65% in LPN hamsters fed the lithogenic diet, but decreased linearly with increasing amounts of BCD in the diet to be nil at a dose of 10% BCD. In gallbladder bile, cholesterol, phospholipid and chenodeoxycholate concentrations, hydrophobic and lithogenic indices were all significantly decreased by 10% BCD. Increases in bile acid synthesis (+110%), sterol 27-hydroxylase activity (+106%), and biliary cholate secretion (+140%) were also observed, whereas the biliary secretion of chenodeoxycholate decreased (-43%). The fecal output of chenodeoxycholate and cholate (plus derivatives) was increased by +147 and +64%, respectively, suggesting that BCD reduced the chenodeoxycholate intestinal absorption preferentially. Dietary cholestyramine decreased biliary bile acid concentration and secretion, but dramatically increased the fecal excretion of chenodeoxycholate and cholate plus their derivatives (+328 and +1940%, respectively). In contrast to BCD, the resin increased the lithogenic index in bile, induced black gallstones in 34% of hamsters, and stimulated markedly the activities of HMG-CoA reductase (+670%), sterol 27-hydroxylase (+310%), and cholesterol 7alpha-hydroxylase (+390%). Thus, beta-cyclodextrin (BCD) prevented cholesterol gallstone formation by decreasing specifically the reabsorption of chenodeoxycholate, stimulating its biosynthesis and favoring its fecal elimination. BCD had a milder effect on lipid metabolism than cholestyramine and does not predispose animals to black gallstones as cholestyramine does in this animal model.

Regional cholesterol synthesis in the intestinal mucosa of the genetically hypercholesterolaemic RICO rat: kinetic study following whole-body gamma-irradiation.

PURPOSE: To investigate regional cholesterol synthesis and kinetics following whole-body gamma-irradiation in the genetically hypercholesterolaemic RICO rat. MATERIALS AND METHODS: Male RICO rats were fed a semi-purified diet for 1 month. At 10 weeks old they were exposed to gamma-irradiation (4 Gy, 1.5 Gy/min) together with controls. At intervals from 1-8 days after irradiation an intraperitoneal administration of [1-14C] acetate was given in order to estimate cholesterogenesis in mucosal cells located at different sites in the small intestine. The protein and DNA contents of the different enterocytes isolated along the crypt/villus axis in four equal parts of the intestine were also determined. RESULTS: A marked decrease of the mean quantities of cholesterol, DNA or protein in mucosa was seen 1 and 2 days after irradiation, showing the loss of 30-40% of the intestinal epithelium. An overshoot of the cell amount was observed after 4 days with a return to basal values by 8 days after irradiation. The kinetic and topological evolution of cholesterol radioactivity, which reflects in situ cholesterol synthesis, showed a typical gradient in controls and at 8 days after irradiation. Cholesterogenesis decreased from the first to the third quarter of the small intestine (duodenum to proximal ileum), and then increased in the fourth quarter (distal ileum). In all segments of the small intestine, cholesterogenesis decreased from crypt cells to villus tip. At days 1 and 2 the gradient of cholesterogenesis on the villus was abolished. A slow recovery was seen from day 4 with a strong overshoot of cholesterol synthesis in crypt cells in every part of the small intestine. CONCLUSIONS: The RICO rat is a useful model for studying the effect of irradiation on regional cholesterogenesis in intestinal mucosa. Cholesterol synthesis in crypt cells was lowered 1 and 2 days after irradiation, over-expressed after 4 days and subsequently returned to its normal level.

Ionizing radiation alters hepatic cholesterol metabolism and plasma lipoproteins in Syrian hamster.

PURPOSE: The investigation of the effects of ionizing radiation on hepatic cholesterol metabolism and the concentration and composition of plasma lipoproteins in the male Syrian hamster. MATERIALS AND METHODS: After sublethal whole-body 60Co gamma-irradiation (8 Gy, 1 Gy/min), plasma lipoproteins were separated by density-gradient ultracentrifugation. Activities of hydroxymethylglutarylCoA (HMGCoA) reductase and of cholesterol 7alpha-hydroxylase were measured in hepatic microsomes and the low-density lipoprotein (LDL) receptor mass was determined in hepatic total membranes. Lipid peroxidation in LDL was assessed in vitro as the formation of conjugated dienes at 234 nm. A group of pair-fed animals served as controls as the food intake was markedly decreased with exposure to radiation. RESULTS: Plasma lipid concentrations decreased 2 days post-irradiation and then markedly increased by day 6 post-irradiation; plasma cholesterol was increased by 77% and triglycerides by +207%. LDL accumulated in plasma while high-density lipoprotein (HDL) levels decreased. HDL contained significant amounts of apo SAA, the acute phase apolipoprotein. The activities of hepatic HMGCoA reductase, the rate-limiting enzyme for cholesterol synthesis, increased (+125%, p=0.06); hepatic cholesterol 7alpha-hydroxylase, the rate-limiting enzyme for bile acid synthesis, decreased (-85%); and the hepatic LDL receptor mass also decreased (-44%). The susceptibility of LDL to oxidation was also increased when animals were exposed to radiation. CONCLUSIONS: Lipoprotein modifications that appeared following radiation exposure may result from an induced inflammatory state and may further contribute to vascular damage.