Effects of colesevelam HC1 on sterol and bile acid excretion in patients with type IIa hypercholesterolemia.

Colesevelam HC1 is a potent bile acid-binding polymer. This study's aim was to determine effects of colesevelam HCl on sterol and bile acid excretion in patients with type IIa hypercholesterolemia. Twenty-four patients (low-density lipoprotein cholesterol, 130 to 220 mg/dL) enrolled in an open-label, parallel-design study, entered an American Heart Association/National Cholesterol Education Program diet for 6 weeks and were randomized to colesevelam HCl, 2.3 or 3.8 g/day for 4 weeks. In an apparent dose-related manner, respective mean serum concentrations HCl of low-density lipoprotein cholesterol decreased by 10% (P < 0.01) and 13% (P = 0.05), mean total cholesterol levels decreased by 4.9% (P = 0.05) and 6.1% (P = 0.09), and total fecal bile acid excretion showed median changes of +324% (P < 0.05) and +316% (P < 0.05). Colesevelam HCl did not affect fecal neutral sterol or fecal fatty acid excretion; however, 24-hr urinary mevalonic acid levels significantly increased in both treatment groups (P < 0.05). The cholesterol-lowering action of colesevelam HCl appears to be mediated through increased bile acid excretion.

Effectiveness of colesevelam hydrochloride in decreasing LDL cholesterol in patients with primary hypercholesterolemia: a 24-week randomized controlled trial.

OBJECTIVE: To evaluate the efficacy, tolerability, and safety of colesevelam hydrochloride, a new nonsystemic lipid-lowering agent. PATIENTS AND METHODS: In this double-blind, placebo-controlled trial performed in 1998, 494 patients with primary hypercholesterolemia (low-density lipoprotein [LDL] cholesterol level > or = 130 mg/dL and < or = 220 mg/dL) were randomized to receive placebo or colesevelam (2.3 g/d, 3.0 g/d, 3.8 g/d, or 4.5 g/d) for 24 weeks. Fasting serum lipid profiles were measured to assess efficacy. Adverse events were monitored, and discontinuation rates and compliance rates were analyzed. The primary outcome measure was the mean absolute change of LDL cholesterol from baseline to the end of the 24-week treatment period. RESULTS: Colesevelam lowered mean LDL cholesterol levels 9% to 18% in a dose-dependent manner (P<.001), with a median LDL cholesterol reduction of 20% at 4.5 g/d. The reduction in LDL cholesterol levels was maximal after 2 weeks and sustained throughout the study. Mean total cholesterol levels decreased 4% to 10% (P<.001), while median high-density lipoprotein cholesterol levels increased 3% to 4% (P<.001). Median triglyceride levels increased by 5% to 10% in placebo and colesevelam treatment groups relative to baseline (P<.05), but none of these differences were significantly different from placebo. Mean apolipoprotein B levels decreased 6% to 12% in an apparent dose-dependent manner (P<.001). No significant differences occurred in adverse events or discontinuation rates between groups, and compliance rates were between 88% and 92% for all groups. CONCLUSIONS: Colesevelam was efficacious, decreasing mean LDL cholesterol levels by up to 18%, and well tolerated without serious adverse events.

Coadministration of colesevelam hydrochloride with atorvastatin lowers LDL cholesterol additively.

Colesevelam hydrochloride is a novel, potent, non-absorbed lipid-lowering agent previously shown to reduce low density lipoprotein (LDL) cholesterol. To examine the efficacy and safety of coadministration of colesevelam and atorvastatin, administration of these agents alone or in combination was examined in a double-blind study of 94 hypercholesterolemic men and women (baseline LDL cholesterol > or =160 mg/dl). After 4 weeks on the American Heart Association Step I diet, patients were randomized among five groups: placebo; colesevelam 3.8 g/day; atorvastatin 10 mg/day; coadminstered colesevelam 3.8 g/day plus atorvastatin 10 mg/day; or atorvastatin 80 mg/day. Fasting lipids were measured at screening, baseline and 2 and 4 weeks of treatment. LDL cholesterol decreased by 12-53% in all active treatment groups (P<0.01). LDL cholesterol reductions with combination therapy (48%) were statistically superior to colesevelam (12%) or low-dose atorvastatin (38%) alone (P<0.01), but similar to those achieved with atorvastatin 80 mg/day (53%). Total cholesterol decreased 6-39% in all active treatment groups (P<0.05). High density lipoprotein cholesterol increased significantly for all groups including placebo (P<0.05). Triglycerides decreased in patients taking atorvastatin alone (P<0.05), but were unaffected by colesevelam alone or in combination. The frequency of side effects did not differ among groups. At recommended starting doses of each agent, coadministration of colesevelam and atorvastatin was well tolerated, efficacious and produced additive LDL cholesterol reductions comparable to those observed with the maximum atorvastatin dose.

Low-dose combination therapy with colesevelam hydrochloride and lovastatin effectively decreases low-density lipoprotein cholesterol in patients with primary hypercholesterolemia.

BACKGROUND: Colesevelam hydrochloride is a novel, lipid-lowering agent that binds bile acids with high affinity. A multicenter, randomized, double-blind, placebo-controlled, parallel-design study was conducted to assess the efficacy and tolerability of combination low-dose colesevelam and lovastatin treatment in patients with primary hypercholesterolemia. HYPOTHESIS: Combination therapy with low doses of colesevelam and lovastatin decreases low density (LDL) cholesterol with minimal adverse events. METHODS: Following a 4- to 6-week dietary lead in, 135 patients were randomized into five groups for a 4-week treatment period: placebo, colesevelam 2.3 g at dinner, lovastatin 10 mg at dinner, the combination of colesevelam and lovastatin given at dinner (dosed together), and combination treatment with colesevelam given at dinner and lovastatin administered at bedtime (dosed apart). RESULTS: Combination colesevelam and lovastatin treatment decreased LDL cholesterol by 34% (60 mg/dl, p < 0.0001) and 32% (53 mg/dl, p < 0.0001) when colesevelam and lovastatin were dosed together or dosed apart, respectively. Both combination therapies were superior to either agent alone (p < 0.05). Decreases in LDL cholesterol exceeded the combined decreases observed for colesevelam alone (13 mg/dl, 7%) and lovastatin alone (39 mg/dl, 22%). Both combination treatments reduced total cholesterol by 21% (p < 0.0001) and apolipoprotein B by 24% (p < 0.0001). Neither combination treatment significantly altered high-density lipoprotein cholesterol or triglycerides. Adverse side effects were not significantly different among randomized groups. CONCLUSIONS: Combination colesevelam and lovastatin was efficacious and well tolerated, resulting in additive decreases in LDL cholesterol levels whether or not both agents were administered simultaneously.

Efficacy and safety of combination simvastatin and colesevelam in patients with primary hypercholesterolemia.

PURPOSE: To examine the efficacy and safety of colesevelam hydrochloride, a novel, nonsystemic, lipid-lowering agent, when coadministered with starting doses of simvastatin in a multicenter, randomized, double-blind, placebo-controlled trial. PATIENTS AND METHODS: Subjects with hypercholesterolemia (plasma low density lipoprotein [LDL] cholesterol level > 160 mg/dL and triglyceride level < or = 300 mg/dL) were randomly assigned to receive daily doses of placebo (n = 33), colesevelam 3.8 g (recommended dose, n = 37), simvastatin 10 mg (n = 35), colesevelam 3.8 g with simvastatin 10 mg (n = 34), colesevelam 2.3 g (low dose, n = 36), simvastatin 20 mg (n = 39), or colesevelam 2.3 g with simvastatin 20 mg (n = 37), for 6 weeks. RESULTS: Mean LDL cholesterol levels decreased relative to baseline in the placebo group (P < 0.05) and in all active treatment groups (P < 0.0001). For groups treated with combination therapy, the mean reduction in LDL cholesterol level was 42% (-80 mg/dL; P < 0.0001 compared with baseline), which exceeded the reductions for simvastatin 10 mg (-26%, -48 mg/dL) or 20 mg (-34%, -61 mg/dL) alone, or for colesevelam 2.3 g (-8%, -17 mg/dL) or 3.8 g (-16%, -31 mg/dL) alone (P < 0.001). The effects of combination therapy on serum HDL cholesterol and triglyceride levels were similar to those for simvastatin alone. Side effects were similar among treatment groups, and there were no clinically important changes in laboratory parameters. CONCLUSION: Coadministration of colesevelam and simvastatin was effective and well tolerated, providing additive reductions in LDL cholesterol levels compared with either agent alone.

Spread monomolecular films of monohydroxy bile acids and their salts: influence of hydroxyl position, bulk pH, and association with phosphatidylcholine.

Undissociated dihydroxy bile acids, alone or with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), lie with their long axes parallel to aqueous-lipid interfaces [Fahey, D. A., Carey, M. C., and Donovan, J. M. (1995) Biochemistry 34, 10886-10897]. To test the generality of this orientation, we used an automated Langmuir-Pockels surface balance to examine pressure-molecular area isotherms and dipole moments of insoluble monohydroxy bile acids and their salts, which are sparingly soluble because of their presumed high Krafft points. We studied lithocholic acid (LCA) (the natural 3alpha-OH isomer), glycolithocholic acid (GLCA) (its glycine conjugate), and the semisynthetic isomers, 7alpha-OH- and 12alpha-OH-cholanoic acids with and without POPC, at pH values ranging from 2 to 12. Monolayer collapse pressures increased sigmoidally with ionization, giving apparent pK values of 7.0-8.5 and implying a stronger affinity of the bile salt anions for the interface. At monolayer collapse, the molecular area of LCA was approximately 85 A(2) independent of pH, consistent with the steroid nucleus lying flat. In contrast, the interfacial area of 7-OH-cholanoic acid decreased from approximately 80 A(2) at pH 2 to approximately 40 A(2) above pH 9, consistent with a more vertical orientation and approximating 12-OH-cholanoic acid, which exhibited a molecular area of approximately 45 A(2) at all pH values. All monohydroxy bile acids condensed POPC monolayers more effectively at low than at high (ionized) pH. We conclude that the 3-OH group is crucial for anchoring bile acids and their salts to the aqueous interface, with all monohydroxy species condensing phospholipid membranes regardless of ionization state.

Drug interactions with colesevelam hydrochloride, a novel, potent lipid-lowering agent.

Colesevelam hydrochloride (colesevelam) is a novel, potent, bile acid-binding agent that has been shown to lower LDL cholesterol a mean of 19% at a dose of 3.8 g/d. We studied the pharmacokinetics of colesevelam coadministered with six drugs: digoxin and warfarin, agents with narrow therapeutic indices; sustained-release verapamil and metoprolol; quinidine, an antiarrhythmic with a narrow therapeutic index; and valproic acid, an antiseizure medication. Six individual studies were single-dose, crossover, with or without a 4.5-g dose of colesevelam. Plasma levels were determined using validated analytical methods. Values for the ratio of ln[AUC(0-t)] with and without colesevelam were 107% for quinidine, 102% for valproic acid, 89% for digoxin, 102% for warfarin, 82% for verapamil, and 112% for metoprolol. Values for the ratio of ln[Cmax] with and without colesevelam were 107% for quinidine, 92% for valproic acid, 96% for digoxin, 99% for warfarin, 69% for verapamil, and 112% for metoprolol. The 90% confidence intervals for these ratios and for values of ln[AUC(0-inf)] that could be determined were within the 80-125% range, with the exception of verapamil. In this study, verapamil had great interindividual variability, with a 28-fold range in Cmax and an 11-fold range in AUC(0-t). In summary, pharmacokinetic studies with colesevelam did not show clinically significant effects on absorption of six other coadministered drugs.

Self-assembly of helical ribbons.

The self-assembly of helical ribbons is examined in a variety of multicomponent enantiomerically pure systems that contain a bile salt or a nonionic detergent, a phosphatidylcholine or a fatty acid, and a steroid analog of cholesterol. In almost all systems, two different pitch types of helical ribbons are observed: high pitch, with a pitch angle of 54 +/- 2 degrees, and low pitch, with a pitch angle of 11 +/- 2 degrees. Although the majority of these helices are right-handed, a small proportion of left-handed helices is observed. Additionally, a third type of helical ribbon, with a pitch angle in the range 30-47 degrees, is occasionally found. These experimental findings suggest that the helical ribbons are crystalline rather than liquid crystal in nature and also suggest that molecular chirality may not be the determining factor in helix formation. The large yields of helices produced will permit a systematic investigation of their individual kinetic evolution and their elastic moduli.

Physical and metabolic factors in gallstone pathogenesis.

Gallstones form when the tenuous balance of solubility of biliary lipids tips in favor of precipitation of cholesterol, unconjugated bilirubin, or bacterial degradation products of biliary lipids. For cholesterol gallstones, metabolic alterations in hepatic cholesterol secretion combine with changes in gallbladder motility and intestinal bacterial degradation of bile salts to destabilize cholesterol carriers in bile and produce cholesterol crystals. For black pigment gallstones, changes in heme metabolism or bilirubin absorption lead to increased bilirubin concentrations and precipitation of calcium bilirubinate. In contrast, mechanical obstruction of the biliary tract is the major factor leading to bacterial degradation and precipitation of biliary lipids in brown pigment stones. Further understanding of the physical and metabolic factors of cholesterol and black pigment formation is likely to provide interventions to interrupt the earliest stages of gallstone formation.

Reinterpreting telepathy as unusual experiences of empathy and charisma.

Telepathy is often dismissed because it is judged to be contrary to the accepted facts of social psychology. This article argues that what is called telepathy may require nothing more than empathy and charisma and is reducible to these sociopsychological constructs. Two studies explore this hypothesis. In the first the proposed relationship is used to explain the sheep-goat effect. In the second study scores on charisma and empathy are used as direct predictors of telepathy scores. The results in combination support the interpretation of telepathy as phenomenologically impressive social psychological events which in less dramatic instances are termed empathy and charisma.

Is colonoscopy indicated for small adenomas found by screening flexible sigmoidoscopy?

BACKGROUND: There is controversy over whether patients who have a small tubular adenoma on screening flexible sigmoidoscopy should undergo colonoscopic examination of the proximal colon. OBJECTIVE: To prospectively determine the prevalence of advanced polyps in the proximal colon among patients who have small adenomas on screening sigmoidoscopy. DESIGN: Prospective cohort study. SETTING: A health maintenance organization and a Veterans Affairs medical center. PATIENTS: Asymptomatic patients older than 50 years of age who had no risk factors for colon cancer and underwent sigmoidoscopy. INTERVENTION: At the time of sigmoidoscopy, all polyps were biopsied and characterized. All patients with distal adenomas were offered colonoscopy. MEASUREMENTS: The size and histology of polyps identified by sigmoidoscopy and colonoscopy were noted. Polyps were considered advanced if they were larger than 10 mm or were tubulovillous, villous, or malignant. The prevalence of advanced proximal polyps was determined, and patients were stratified by the size and number of distal polyps found by sigmoidoscopy. RESULTS: Among 4490 patients who underwent sigmoidoscopy, a neoplastic lesion was detected in 401 (8.9%) and colonoscopy was done in 301 (75%). Of 90 patients with a single tubular adenoma 1 to 5 mm in diameter in the distal colon, 0% (95% CI, 0.0% to 4.0%) had an advanced proximal polyp compared with 5.4% (CI, 2.4% to 10.4%) of those who had multiple distal polyps 1 to 5 mm or 6 to 10 mm in diameter and 7.9% (CI, 2.6% to 17.6%) of those who had advanced distal polyps (P = 0.013 for trend). The low-risk group with a single tubular adenoma 1 to 5 mm in diameter represented 44% of all patients with distal adenomas or cancers found at flexible sigmoidoscopy. CONCLUSIONS: Among patients undergoing screening sigmoidoscopy, those with single tubular adenomas of 5 mm or less had a low prevalence of advanced proximal polyps. These patients may not benefit from colonoscopy.

Four addictions: the MMPI and discriminant function analysis.

Over the past twenty years many MMPI studies of substance abuse have investigated the complex relationship between personality profile and drug of choice. This work has repeatedly established that alcoholics, heroin, cocaine and polydrug addicts share 4-2/2-4 (Psychopathy and Depression) or 4-8/8-4 (Psychopathy and Thought Disorder) MMPI profiles, but that the substance abuse populations differ in the plane of severity in that general profile. The alcoholics occupy the least disturbed sector, the polydrug abusers the most disturbed level and the heroin and cocaine addicts positions of moderate disturbance. The vast majority of studies, however, cite only group means to buttress their conclusions. Our work probed more deeply into the data using Discriminant Function Analysis. With this methodology we discovered important differences between the groups, previously hidden, which may carry differential treatment implications.

Accurate separation of biliary lipid aggregates requires the correct intermixed micellar/intervesicular bile salt concentration.

The intermixed micellar/intervesicular bile salt (BS) concentration (IMC), composed of BS monomers and simple micelles, is in dynamic equilibrium with mixed micelles and vesicles. Accurate separation of biliary lipid aggregates is believed to depend on accurately measuring the IMC. Using centrifugal ultrafiltration, we measured the IMC of cholesterol-supersaturated model biles that were physiologically composed. Gel chromatography was performed using eluants containing the following: 1) the IMC; 2) the same BS composition as the IMC but higher or lower BS concentrations; 3) the same BS concentration as the IMC, but with more hydrophilic or hydrophobic BS; and 4) 10 mmol/L cholate. Compared with an eluant containing the same BS composition as the IMC, an eluant containing the same relative BS composition but 75% of the IMC increased the proportion of cholesterol in vesicles and decreased the vesicular cholesterol/egg yolk phosphatidylcholine (EYPC) ratio. In contrast, an eluant containing 150% of the IMC entirely transformed vesicles to micelles. Eluants containing slightly more hydrophobic or more hydrophilic BS eliminated or increased vesicular cholesterol content, respectively. An eluant of 10 mmol/L cholate overestimated vesicular cholesterol and in concentrated biles reproducibly produced an incompletely separated intermediate peak, possibly because of re-equilibration between mixed micelles and vesicles. Further, in concentrated biles, fractions eluting at volumes corresponding to mixed micelles were visibly turbid, irrespective of the eluant used. The correct IMC allows accurate separation of biliary lipid aggregates, but differences in BS concentration or composition substantially alter the vesicular percentage of cholesterol as well as the cholesterol/EYPC ratio. Elution with 10 mmol/L cholate may introduce artifactual gel-filtration peaks and inadequate separation of particles with widely differing molecular weights, both of which have confused previous analyses of biliary lipid aggregates.

Colorectal cancer in women: an underappreciated but preventable risk.

Colorectal cancer is the third most common non-skin malignancy in women, after breast and lung cancer. Although approximately 40% of the 65,000 women diagnosed each year eventually die of the disease, colon cancer is highly curable when diagnosed at an early stage. Moreover, because the majority of colon cancers arise in previously benign colonic polyps, there is a substantial period, up to several years, in which removal of polyps can reduce the risk of colon cancer. Recently, the United States Preventive Task Force recommended universal screening for colon cancer after age 50. Strong evidence from randomized controlled trials and case-control studies supports use of annual testing for occult blood in stool and flexible sigmoidoscopy every 5-7 years. Although the risk of colon cancer is similar in men and women, women frequently have the perception that colorectal cancer is a man's disease. Partially in consequence, women are less likely than men to undergo screening sigmoidoscopy. Further barriers include primary care providers' lack of awareness of updated guidelines and patients' lack of compliance with multiple screening tests and their fear of discomfort. Because the risk of colorectal cancer can be reduced by up to 75% in those who undergo screening and subsequent surveillance to remove further polyps, it is crucial that women be targeted to undergo screening tests for colorectal cancer.

Color Doppler ultrasound assessment of urethral artery location: potential implication for technique of visual internal urethrotomy.

PURPOSE: We assessed the location of urethral arteries in patients with urethral stricture using color Doppler ultrasound. MATERIALS AND METHODS: We performed 41 color ultrasound studies of the urethra in 33 patients 17 to 76 years old. The linear array transducer was placed on the ventral surface of the penis and perineum to image the urethra and periurethral structures. In addition to evaluating the extent of stricture disease, color Doppler ultrasound determined the location of the urethral arteries at the segment with stricture. RESULTS: The number and site of the urethral arteries vary among individuals. Contrary to the common belief that these arteries are located at the 3 and 9 o'clock positions, we have found that in the bulbous urethra the arteries are at the 1 to 2 o'clock positions in 14% of cases, 3 to 4 in 22%, 5 to 6 in 17%, 7 to 8 in 18%, 9 to 10 in 18% and 11 to 12 in 11%. The arteries may be close to the surface of the urethral lumen, especially in patients who have undergone previous urethral procedures. Preoperative evaluation of urethral artery location may be helpful for preventing arterial bleeding at visual internal urethrotomy. CONCLUSIONS: Color Doppler ultrasound can effectively assess the extent of stricture disease and urethral artery sites. Because the location of the urethral arteries varies among patients, individual preoperative assessment is advisable. Color Doppler ultrasound is currently our imaging method of choice for evaluating strictures of the pendulous and bulbous urethra.

Transbilayer movement of fully ionized taurine-conjugated bile salts depends upon bile salt concentration, hydrophobicity, and membrane cholesterol content.

Taurine-conjugated bile salts mediate rapid transmembrane flux of divalent cations, irrespective of whether bile salts and divalent cations are initially on the same or opposite side of the membrane. We therefore hypothesized that ionized bile salts can equilibrate between membrane hemileaflets. We quantitated bile salt binding to large unilamellar egg yolk phosphatidylcholine (EYPC) +/- cholesterol (Ch) vesicles under conditions in which one or both hemileaflets were initially exposed to bile salts. At unbound taurodeoxycholate (TDC) concentrations >0.2 mM, the dependence of binding on TDC concentration after 30 min was indistinguishable for vesicles prepared by either method and did not change from 30 minutes to 24 h. At unbound TDC concentrations <0.1 mM, the ratio of bound/free TDC to EYPC vesicles doubled over a single exponential time course. Equilibration times were greater for the more hydrophilic bile salts taurocholate and tauroursodeoxycholate, for EYPC/Ch vesicles, and at lower temperatures. For glycine-conjugated bile salts, time-dependent changes in binding did not occur, consistent with more rapid equilibration of the small fraction of the protonated form. We conclude that fully ionized conjugated bile salts translocate between lipid bilayer hemileaflets, in contrast to previous observations that equilibration of fully ionized unconjugated bile salts occurs at a negligible rate in small unilamellar vesicles. The rate of "flip-flop" increases with increases in intramembrane bile salt concentration and hydrophobicity but decreases with cholesterol content and lower temperature. We speculate that physiologically, even in the absence of a specific membrane transporter, bile salts can gain access to intracellular compartments and mediate increases in divalent cation flux that may underlie cytotoxicity.

Bladder stimulation therapy improves bladder compliance: results from a multi-institutional trial.

PURPOSE: We examined data from multiple institutions to determine whether intravesical bladder stimulation therapy is effective in improving bladder compliance by increasing bladder capacity and lowering bladder storage pressures. MATERIALS AND METHODS: The charts of 568 patients from 11 institutions were evaluated. Of the 568 patients 335 had adequate and accurate pretreatment and posttreatment urodynamic studies, and were included in this study. A total of 155 patients was from Children's Memorial Hospital, while the remaining 180 were from 10 other institutions. Bladder capacity and bladder capacity pressure were determined for each patient before and after therapy. RESULTS: Overall, 53% of patients had increased bladder capacity of 20% or greater after treatment (average increase 105 cc), which represents a 63% increase from pretreatment values. This increase occurred in an average of 1.9 years. Further analysis of this subset of patients revealed that in 90% intravesical storage pressures were decreased or maintained within a safe range (less than 40 cm. water). Evaluation of patients who did not respond to bladder stimulation with a 20% or greater increase in bladder capacity revealed that they had nearly normal bladder capacity before therapy. When the data on bladder capacity and bladder capacity pressure from Children's Memorial Hospital were compared to results from the 10 other institutions, there were no appreciable differences. CONCLUSIONS: Bladder stimulation is effective in increasing bladder capacity without significantly elevating storage pressure in a majority of patients. We conclude that this technique is safe and effective in improving bladder compliance, and that it is reproducible elsewhere.

Effects of submicellar bile salt concentrations on biological membrane permeability to low molecular weight non-ionic solutes.

Bile salts have been hypothesized to mediate cytotoxicity by increasing membrane permeability to aqueous solutes. We examined whether submicellar bile salt concentrations affect model and native membrane permeability to small uncharged molecules such as water, urea, and ammonia. Osmotic water permeability (Pf) and urea permeability were measured in large unilamellar vesicles composed with egg yolk phosphatidylcholine (EYPC) +/- cholesterol (Ch) or rat liver microsomal membranes by monitoring self-quenching of entrapped carboxyfluorescein (CF). Ammonia permeability was determined utilizing the pH dependence of CF fluorescence. Submicellar bile salt concentrations did not significantly alter Pf of EYPC +/- Ch or rat liver microsomal membranes. At taurodeoxycholate (TDC) or tauroursodeoxycholate concentrations approaching those that solubilized membrane lipids, CF leakage occurred from vesicles, but Pf remained unchanged. Higher bile salt concentrations (0.5-2 mM TDC) did not alter Pf of equimolar EYPC/Ch membranes. The activation energy for transmembrane water flux was unchanged (12.1 +/- 1.2 kcal/mol for EYPC) despite the presence of bile salts in one or both membrane hemileaflets, suggesting strongly that bile salts do not form transmembrane pores that facilitate water flux. Furthermore, submicellar bile salt concentrations did not increase membrane permeability to urea or ammonia. We conclude that at submicellar concentrations, bile salts do not form nonselective convective channels that facilitate transmembrane transport of small uncharged molecules. These results suggest that bile salt-mediated transport of specific substrates, rather than nonselective enhancement of membrane permeability, underlies bile salt cytotoxicity for enterocytes and hepatocytes.

Ultracentrifugation systematically overestimates vesicular cholesterol levels in bile.

To accurately determine the cholesterol (Ch) distribution between mixed micelles and vesicles in lithogenic bile, both ultracentrifugation and gel chromatography with the correct intermixed micellar/vesicular bile salt concentration (IMC) have been proposed. We have systematically compared both separation techniques with physiological model biles to ascertain their quantitative separation ability. After determination of optimal ultra-centrifugation conditions in systems containing only micelles or vesicles, Ch-supersaturated model biles [3-10 g/dL, 10 mol percent Ch, taurocholate (TC)]/([TC + egg yolk phosphatidylcholine (EYPC)] = 0.6 and 0.7) were adjusted to a density of 1.03 g/mL, and ultracentrifuged at 42,000 rpm and 37 degrees C for 13 hours. Identical model biles were subjected to gel chromatography with the correct IMC, either directly or after remixing and incubation at 37 degrees C after ultracentrifugation. By ultracentrifugation, 31 percent +/- 2 percent (TC/(TC + EYPC) = 0.6) and 40 percent +/- 5 percent (TC/(TC + EYPC) = 0.7) of total Ch were found in vesicles (Ch/EYPC molar ratios = 1.0 and 1.3, respectively). However, by gel chromatography, only 19 percent +/- 2 percent (Ch/EYPC = 1.0) and 22 percent +/- 2 percent (Ch/EYPC = 1.5) of total Ch were found in the corresponding biles. Gel chromatography of biles (TC/(TC + EYPC) = 0.7) ultracentrifuged for various durations showed a progressive increase in vesicular Ch to 41 percent after 13 hours. On incubation for 11.5 hours after ultracentrifugation, vesicular Ch decreased to 31 percent, thus approaching the initial (gel chromatography) value. Quasielastic light scattering also demonstrated formation of vesicles in ultracentrifuged Ch-unsaturated model bile (cholesterol saturation index (CSI) approximately 0.97). As compared with gel chromatography, ultracentrifugation systematically elevates vesicular Ch, possibly because of induced shifts in lipids between lipid aggregates caused by variation in local bile salt concentration. Because ultracentrifugation can alter the phases present in bile, gel chromatography with the correct IMC more accurately represents the distribution of Ch in biliary lipid aggregates.

Bone mineral disorders in children: evaluation with dual x-ray absorptiometry.

PURPOSE: To evaluate the utility of dual x-ray absorptiometry (DXA) in children with bone mineral disorders. MATERIALS AND METHODS: In phase 1, radial DXA was compared with single-energy photon absorptiometry (SPA) (n = 117). In phase 2, radial and lumbar bone mineral density (BMD) measured with DXA and second metacarpal cortical thickness were compared (254 examinations, 224 children). RESULTS: For radial BMD, DXA and SPA correlated well (r = .956) and SPA-equivalent values could be calculated from DXA measurements (mean residual error = 0.024 g/cm2). After controlling for age, sex, weight, and height, partial correlations were very small for lumbar BMD with radial BMD (r = .186) and lumbar BMD with cortical thickness (r = .158), and slightly better for radial BMD with cortical thickness (r = .544). Z scores also correlated poorly with no meaningful correlation for lumbar BMD with radial BMD (r = .07) CONCLUSION: In children with bone mineral disorders, radial DXA and SPA measurements correlate well. However, lumbar BMD, radial BMD, and cortical thickness correlate poorly and lumbar BMD frequently does not identify abnormality in patients with abnormal radial BMD. Lumbar BMD alone is not adequate for evaluation of bone mineral status in these patients.