Biomedical subjects

W C Duane

Publications and source records attributed to W C Duane.

At least 19 recordsLinked to original sources

PubMed1995

Measurement of bile salt aggregation equilibria using kinetic dialysis and spreadsheet modeling.

Bile salts initially self-associate into small aggregates such as dimers and trimers before forming micelles at higher concentrations. The very size of these small aggregates hampers quantitation of their formation. We have devised a method using kinetic dialysis measurements to quantitatively examine aggregation of bile salt at concentrations below 10 mM. Data for rate of dialysis versus concentration were fitted to hypothetical models of aggregation using a personal computer spreadsheet. For sodium taurocholate these data best fit a model of initial dimer and trimer formation with stepwise association constants of 100 and 160, respectively. Addition of larger aggregates to the model did not improve the fit. For sodium taurodeoxycholate the data best fit a model which included not only dimers and trimers, but also tetramers or larger aggregates up to 10-mers with stepwise association constants of 40, 400, and 1700 for dimers, trimers, and tetramers, respectively. These data agree reasonably well with existing literature and suggest that kinetic dialysis with spreadsheet modeling is a useful technique for the study of bile salt aggregation at relatively low concentrations.

Bile Acids and Salts↗

PubMed1995

Abnormal bile acid absorption in familial hypertriglyceridemia.

To better define the abnormality of bile acid metabolism associated with hypertriglyceridemia, we measured bile acid kinetics and absorption as well as preferential use of newly synthesized cholesterol for bile acid synthesis in eleven controls and ten subjects with hypertriglyceridemia, six of whom could be classified as having familial hypertriglyceridemia (FHT). Fractional turnover rates of cholic acid and chenodeoxycholic acid were both significantly elevated in hypertriglyceridemic subjects to nearly twice the rates in controls. Bile acid synthesis was also significantly higher in hypertriglyceridemic subjects while bile acid pools were either unchanged or somewhat reduced. Consistent with these kinetics, bile acid absorption was significantly lower in hypertriglyceridemic subjects than in controls. Overall only 10-12% of bile acid was derived from newly synthesized cholesterol, and hypertriglyceridemic subjects did not differ from controls. Because hypertriglyceridemia should not alter bile acid absorption, these results are consistent with the previously suggested possibility (B. Angelin, K. S. Hershon, and J. D. Brunzell, 1987. Proc. Natl. Acad. Sci. USA. 84: 5434-5438) that impaired bile acid absorption may be a primary defect in some patients with hypertriglyceridemia.

Absorption↗

PubMed1995

Serum lathosterol levels in human subjects reflect changes in whole body cholesterol synthesis induced by lovastatin but not dietary cholesterol.

We measured serum lathosterol levels and whole body cholesterol synthesis by sterol balance in 12 human subjects on a metabolic ward in four randomly allocated, 6-7 week periods: 1) lovastatin (40 mg b.i.d.) + low cholesterol diet (mean 246 mg/day); 2) lovastatin + high cholesterol diet (mean 1071 mg/day); 3) low cholesterol diet alone; and 4) high cholesterol diet alone. Whole body cholesterol synthesis was significantly reduced both by lovastatin (P = 0.0004) and by high dietary cholesterol (P = 0.0005). Serum total lathosterol (micrograms/dl) was reduced by lovastatin (P < 0.0001), but was not significantly altered (and actually tended to increase) during consumption of the high cholesterol diet, presumably because eggs contained appreciable lathosterol as demonstrated by direct analysis. Results were similar for total versus free lathosterol and for lathosterol expressed as micrograms/dl serum versus micrograms/100 mg cholesterol. We conclude that serum lathosterol does not reflect changes in cholesterol synthesis induced by dietary cholesterol. Studies using serum lathosterol as an indicator of cholesterol synthesis must be carefully controlled for dietary cholesterol.

Biomarkers↗

PubMed1994

Effects of lovastatin in humans on biliary lipid composition and secretion as a function of dosage and treatment interval.

Biliary lipid composition and secretion were assessed in nine human subjects in four randomly ordered 3- to 4-week treatment periods during which they took 0 (base line), 20, 40 and 80 mg/day of lovastatin. The mean secretion of cholesterol was lower than base line for each of the three doses but the change reached statistical significance only for the 40- and 80-mg/day doses (P = .004 and .001, respectively). The mean secretion of bile acid and phospholipid was unchanged by any dose of lovastatin. The cholesterol saturation index and molar percent cholesterol in gallbladder bile were both significantly reduced by all doses of lovastatin (P = .001 to .008). For both cholesterol secretion and saturation index, increasing the dose from 20 to 40 mg/day caused an additional incremental reduction but increasing it from 40 to 80 mg/day had no additional effect. This finding suggests that any clinical trial of lovastatin for the treatment or prevention of gallstones would best be carried out with a dose of 40 mg/day. Studies performed in a subset of four subjects revealed that time-course changes in the saturation index and low-density lipoprotein cholesterol were similar and reached plateaus by 1 week after 80 mg/day of lovastatin was either started or stopped.

Adult↗

PubMed1994

Effects of lovastatin and chenodiol on bile acid synthesis, bile lipid composition, and biliary lipid secretion in healthy human subjects.

To assess the relationship between cholesterol synthesis and feedback inhibition of bile acid synthesis, we studied seven normal human subjects taking three different doses of chenodiol, 0, 5, and 15 mg/kg per day: once while taking no lovastatin and again while taking lovastatin 80 mg/day. Lovastatin and both doses of chenodiol significantly lowered bile acid synthesis measured by the 14CO2 method, but there was no significant interaction between the perturbations. Both also lowered cholesterol saturation index of gallbladder bile without appreciable interaction, and the combination was distinctly more effective than either medication alone. Lovastatin and low-dose chenodiol both lowered biliary cholesterol secretion without affecting bile acid secretion. Increasing the dose of chenodiol did not further lower cholesterol secretion, but did further reduce saturation index because of an increase in secretion of bile acid and phospholipid. These studies indicate that there is no interaction between cholesterol synthesis and feedback return of bile acid in the enterohepatic circulation with respect to either bile acid synthesis or biliary lipid secretion; that the combination of chenodiol and lovastatin is better than either alone for improving biliary cholesterol saturation; and that the mechanism by which chenodiol lowers cholesterol saturation is dose-dependent.

Aged↗

PubMed1994

Effects of lovastatin and dietary cholesterol on bile acid kinetics and bile lipid composition in healthy male subjects.

We measured bile acid kinetics and bile lipids in 12 human subjects on a metabolic ward in four randomly allocated, 6-7 week periods: 1) lovastatin (40 mg b.i.d) + low cholesterol diet (mean 246 mg/day); 2) lovastatin+high cholesterol diet (mean 1071 mg/day); 3) low cholesterol diet alone; and 4) high cholesterol diet alone. Lovastatin did not significantly alter fractional turnover, synthesis, absorption, enterohepatic cycling, or pool sizes of bile acid measured by the Lindstedt method. The high cholesterol diet increased fractional turnover and synthesis rate of cholic acid, but not chenodeoxycholic acid, without altering pool size of either bile acid. The high cholesterol diet decreased bile acid absorption, but only during lovastatin treatment, suggesting the possibility of a "cholestyramine-like" effect of dietary cholesterol, appreciable at least when biliary cholesterol secretion is reduced by lovastatin. As in previous studies, lovastatin markedly lowered saturation index of gallbladder bile. Increased cholesterol consumption did not significantly alter cholesterol saturation index, suggesting that dietary cholesterol may not be a major factor in cholesterol gallstone pathogenesis.

Absorption↗

PubMed1993

Effect of regulating cholesterol biosynthesis on breath isoprene excretion in men.

Isoprene is a normal constituent of human breath and may be derived from the cholesterol synthetic pathway. Acute and chronic lovastatin and a cholesterol-supplemented diet were used to determine whether a mechanistic link exists between isoprene and cholesterol biosynthesis in vivo in humans. The acute effects of lovastatin, a competitive inhibitor of the rate-limiting step of cholesterol biosynthesis, on breath isoprene excretion was determined by administering a single 20, 40 or 80 mg dose of this drug to five healthy male subjects at 8 p.m. and measuring their breath isoprene levels every 4 h for one 24 h cycle before and after treatment. When compared to the baseline cycle, all three doses of lovastatin significantly reduced breath isoprene levels at 6 and 10 h post-drug treatment. Chronic lovastatin therapy (40 mg b.i.d. for 6 wk) reduced 6 a.m. breath isoprene levels (time of maximum baseline value) by 27 +/- 9% (SEM) and cholesterol synthesis measured in freshly isolated mononuclear leukocytes (ML) by 12 +/- 6%. A cholesterol-supplemented diet (1070 mg, total) ingested for 6 wk reduced breath isoprene excretion and ML sterol synthesis by 16 +/- 5 and 19 +/- 4%, respectively. The parallel decreases in isoprene excretion and cholesterol synthesis caused by these pharmacologic and dietary means suggest that breath isoprene is derived from the cholesterol synthesis pathway.

Adolescent↗

PubMed1993

Effects of lovastatin and dietary cholesterol on sterol homeostasis in healthy human subjects.

We measured biliary and fecal sterol outputs in 12 human subjects on a metabolic ward in four randomly allocated, 6-7 wk periods: (a) lovastatin (40 mg b.i.d.) + low cholesterol diet (mean 246 mg/d), (b) lovastatin + high cholesterol diet (mean 1,071 mg/d), (c) low cholesterol diet alone, (d) high cholesterol diet alone. In addition to lowering serum LDL cholesterol, lovastatin significantly lowered biliary secretion of cholesterol, fecal output of endogenous neutral sterols, cholesterol balance, and systemic cholesterol input (the sum of cholesterol synthesis and absorbed dietary cholesterol). The high cholesterol diet significantly lowered cholesterol balance, but significantly increased systemic cholesterol input and fecal output of acidic sterols. There was no significant interaction between lovastatin and dietary cholesterol for any parameter measured. Judging from these data, the primary action of lovastatin is to lower cholesterol synthesis and systemic cholesterol input, the main compensatory response being reduced biliary cholesterol secretion. Conversely, increased dietary cholesterol appears to increase systemic cholesterol input, the major compensatory response being increased bile acid synthesis. There appears to be no interaction between these two perturbations of systemic cholesterol input.

Adult↗

PubMed1993

Facilitated method for measurement of biliary secretion rates in healthy humans.

We have developed a facilitated method for determining secretion of constituents into bile. The ratio of constituent/bilirubin was measured in gallbladder bile and multiplied by bilirubin secretion rate, estimated by measuring endogenous production of carbon monoxide (VCO) by breath sampling. Accuracy of this method was assessed by measuring secretion rate of 99mTechnetium-labeled disofenin during steady-state constant intravenous infusion. In nine subjects, mean (+/- SEM) secretion of disofenin by the CO method was 104.2 +/- 7.2% of expected and by standard marker perfusion was 97.8 +/- 13.1% of expected. In ten subjects, secretion rate of cholesterol by the CO method averaged 103 mumol/h by the CO method compared to 113 by marker perfusion (NS). Compared to marker perfusion (which is believed to reflect 24-h secretion rate), the CO method significantly underestimated secretion rate of bile acid (1110 vs. 1332 mumol/h, P = 0.076) and lecithin (295 vs. 413 mumol/h, P = 0.01), probably because gallbladder bile contained a disproportionate amount of fasting versus postprandial bile. Thus, this new method provides an accurate secretion rate for biliary constituents secreted at a relatively constant rate, including cholesterol, with less variability than marker perfusion. However, it can be used to estimate secretion of bile acid and lecithin only when a 20-30% underestimation of 24-h secretion is acceptable.

Adult↗

PubMed1992

Measurement of bile acid synthesis in man by release of 14CO2 from [26-14C]cholesterol: comparison to isotope dilution and assessment of optimum cholesterol specific activity.

Bile acid synthesis can be measured as release of 14CO2 from [26-14C]cholesterol divided by cholesterol specific activity, but this method has not been validated in human subjects. We made twelve comparisons of this CO2 method to standard isotope dilution in six normal subjects and found a mean discrepancy of 6%. Linear regression analysis of one value with respect to the other revealed a correlation coefficient of 0.83 (P less than 0.01), a Y-intercept close to zero (-4.98) and a slope close to 1 (1.06), suggesting good correspondence between the two methods. To assess the potential for error arising from use of serum cholesterol to estimate specific activity of cholesterol used for bile acid synthesis, we compared synthesis measured using serum free cholesterol specific activity to that measured using bile cholesterol specific activity, which is known to be near isotopic equilibrium with the precursor pool used for bile acid synthesis. Synthesis calculated in these two ways differed by less than 10%. The data indicate that the CO2 method using either serum or bile cholesterol specific activity provides a valid estimate of bile acid synthesis in man.

Bile Acids and Salts↗

PubMed1992

Lack of benefit of ursodeoxycholic acid in drug-induced cholestasis in the rat.

The administration of ursodeoxycholic acid (UDCA) has been reported to improve cholestasis in patients with primary biliary cirrhosis or sclerosing cholangitis. In the present study, we tested the hypothesis that UDCA similarly might reduce cholestasis induced by drugs. Rats were treated with three different drugs reported to induce cholestasis: 17 alpha-ethynylestradiol, alpha-napthylisothiocyanate, and cyclosporine A. UDCA administration (0.4.g/day-1.k-1 before and during administration of the cholestatic drug) did not improve survival, food intake, or serum indicators of cholestasis in any of these three animal models of cholestasis. To the extent that drug-induced cholestasis in rats mimics the human situation, we conclude that UDCA probably will not be beneficial in drug-induced cholestasis in humans.

1-Naphthylisothiocyanate↗

PubMed1992

Thyroid hormone differentially augments biliary sterol secretion in the rat. I. The isolated-perfused liver model.

Thyroid hormone lowers serum cholesterol and alters sterol metabolic processes. This laboratory has previously reported increased biliary lipid secretion as an early effect of triiodothyronine (T3) in the rat. To evaluate whether the bile lipid action of T3 is a primary or secondary effect, the isolated-perfused rat liver model was used. Red blood cells in lipid-free buffer were used to perfuse livers of euthyroid and methimazole-hypothyroid rats, as well as hypothyroid rats given T3 at intervals before perfusion. Bile flow was maintained by taurocholate perfusion. Hypothyroid rats had elevated pre-perfusion serum cholesterol compared to euthyroid (107 +/- 4 vs. 65 +/- 2 mg/dl) and decreased biliary cholesterol (0.016 +/- 0.001 vs. 0.031 +/- 0.004 mumol/g liver/h) secretion. Serum cholesterol decreased to euthyroid levels by 18 h after T3, an effect that was prevented by bile duct ligation. Bile cholesterol secretion doubled by 18 h, and reached levels twice euthyroid by 42 h, while phospholipid secretion doubled to levels just above euthyroid. The fourfold increase in biliary cholesterol secretion occurred with lipid-free perfusion and unchanging bile acid uptake or output. It occurred without a fall in hepatic lipoprotein cholesterol secretion. Blockade of cholesterol synthesis with lovastatin failed to alter T3-augmented bile cholesterol secretion. We conclude that T3 induces biliary cholesterol secretion concomitantly with the fall in serum cholesterol. This augmented biliary secretion did not appear to depend upon lipoprotein uptake, increased bile acid transport, or cholesterol synthesis. It did not occur at the expense of hepatic lipoprotein secretion. Facilitated biliary lipid secretion may be a primary effect of T3.

Animals↗

PubMed1992

Separation of bile vesicles and micelles by gel filtration chromatography: the importance of the intermicellar bile salt concentration.

Micelles and vesicles coexist in native bile. Mixed micelles are composed of bile salt, phospholipid, and cholesterol. Micellar bile salt is in equilibrium with the aqueous phase bile salt (intermicellar bile salt), and mixed micelles can be converted to cholesterol-phospholipid vesicles by depletion of bile salt. To determine the amount of cholesterol carried in vesicles and micelles, these two populations must be separated without altering the relative proportion of each. Based on the size difference between micelles and vesicles, gel filtration chromatography has been used to accomplish this separation. We reasoned that to maintain the proportion of micelles and vesicles in bile, the column must be equilibrated and eluted with buffer containing the intermicellar bile salt concentration (IMBC) and species. To test this hypothesis we created a model bile composed exclusively of micelles, a solution containing micelles and vesicles, and a model bile containing all vesicles, as demonstrated by quasielastic light scattering. Gel filtration on Sepharose 4B demonstrated that model vesicles and micelles could be separated on a column eluted with buffer containing bile salt at the IMBC. However, a modest decrease in the buffer bile salt concentration (less than 1 mmol/L) resulted in complete conversion of micelles to vesicles. A comparable increase in the buffer bile salt concentration converted vesicles to micelles. Using only taurocholate in the eluting buffer at the IMBC caused a complete shift of micelles to vesicles, whereas using only taurochenodeoxycholate resulted in conversion of vesicles to micelles. An initial collection of rat bile separated on a column equilibrated with the measured IMBC demonstrated that 94% of the cholesterol was in the micellar fractions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Serum lipid and fecal bile acid changes with cereal, vegetable, and sugar-beet fiber feeding.

Thirty-four subjects consumed six controlled formula diets for 3 wk each, supplemented with 0 g added fiber, 10 and 30 g dietary fiber as wheat bran (WB), 10 and 30 g dietary fiber as mixed vegetable fiber (VF), and 30 g dietary fiber as sugar-beet fiber (SBF). Serum cholesterol changes for fiber free, 10 g WB, 30 g WB, 10 g VF, 30 g VF, and 30 g SBF (-0.13, -0.18, -0.05, -0.17, -0.24, and -0.70 mmol/L, respectively) were significant for 30 g VF and 30 g SBF. Reduction in total cholesterol with SBF was largely due to significant lowering of low-density-lipoprotein cholesterol. Total fecal bile acid concentrations were significantly higher with the fiber-free diet than with 30 g WB, VF, and SBF (P less than 0.001) and were also higher with 30 g SBF than with 30 g WB and 30 g VF (P less than 0.005). Daily fecal bile acid excretion was not different on 30 g SBF compared with 30 g WB and 30 g VF. Differences in cholesterol reduction across the diets could not be explained by differences in fecal bile acid excretion.

Adult↗

PubMed1991

Liver denervation does not alter the circadian rhythm of bile acid synthesis in rats.

In both rats and humans there is a distinct circadian rhythm of bile acid synthesis that is independent of feedback regulation. To determine whether the circadian rhythm is directly mediated via hepatic nerves, bile acid synthesis was studied in selectively liver-denervated male Sprague-Dawley rats in a bile fistula model. Complete denervation was confirmed by histofluorescent staining for neural elements in frozen sections of livers. There was no significant difference in mean bile acid synthesis, amplitude of the circadian rhythm, or time of peak synthesis between the denervated rats and nondenervated controls. In one denervated rat studied four times at weekly intervals, there was no shift in acrophase, indicating that the rhythm had not become free running. We conclude that signals arriving via hepatic nerves neither directly cause nor entrain the circadian rhythm of bile acid synthesis in rats.

Animals↗

PubMed1991

Role of cholesterol synthesis in regulation of bile acid synthesis and biliary cholesterol secretion in humans.

We used lovastatin, a specific inhibitor of HMG-CoA reductase, to study the role of cholesterol synthesis in regulation of both bile acid synthesis, measured by release of 14CO2 from [26-14C]cholesterol, and biliary cholesterol secretion, measured by standard marked perfusion techniques, in humans. Six volunteers were studied in each of four periods: a) control; b) 6-10 hours after a single 40 mg oral dose of lovastatin to study acute effects; c) after 5-6 weeks of lovastatin 40 mg orally twice a day to study steady-state effects; and d) 24 h after cessation of chronic lovastatin. Mean bile acid synthesis fell to 69% of control (P less than 0.01) after single-dose lovastatin and remained at 83% of control after 5-6 weeks on lovastatin (P less than 0.05). After withdrawal of lovastatin, mean bile acid synthesis was 88% of control (NS). Mean biliary cholesterol secretion did not change after single-dose lovastatin (103% of control), but fell to 81% of control during chronic lovastatin treatment (P less than 0.05). After withdrawal of lovastatin, mean cholesterol secretion remained at 80% of control (P less than 0.05). These data suggest that in humans cholesterol synthesis is an immediate regulator of bile acid synthesis. Cholesterol synthesis also regulates biliary cholesterol secretion, but the effect is not immediate and therefore may be indirect.

Aged↗

PubMed1991

Effects of lovastatin on biliary lipid secretion and bile acid metabolism in humans.

Lovastatin, an inhibitor of HMG-CoA reductase, lowers cholesterol saturation of bile. To determine the mechanism of this effect and further define the role of cholesterol synthesis in regulation of biliary lipid metabolism, we studied ten human volunteers in a control period and again after 5-6 weeks on lovastatin, 40 mg b.i.d. Mean sterol production from acetate in mononuclear leukocytes fell from 1.18 to 0.84 pmol/min per 10(6) cells on lovastatin (P less than 0.02). Concomitantly there was reduction in mean biliary secretion of cholesterol from 143 to 96 mumol/h (P less than 0.02). On lovastatin, mean pool size of bile acids by the Lindstedt method fell from 3193 to 2917 mumol (one-sided P = 0.05) and mean pool size by the one-sample method fell from 5158 to 4091 mumol (P less than 0.002). Lovastatin had no effect on mean fractional turnover rate of either cholic acid (0.77 vs. 0.74 day-1) or chenodeoxycholic acid (0.51 vs. 0.54 day-1). Mean total bile acid synthesis was lower on lovastatin (1443 vs. 1240 mumol/day), but the difference did not quite achieve statistical significance. In humans, inhibition of cholesterol synthesis by lovastatin lowers biliary cholesterol saturation by reducing cholesterol secretion into bile. Bile acid pool size, and perhaps bile acid synthesis, are also reduced by this inhibition.

Adult↗

PubMed1990

Pathogenesis of gallstones: implications for management.

How do gallstones form, and what can be done to reverse or prevent the process? Bile acid physiology and pathophysiology are reviewed, especially with respect to cholesterol stones, and bile acid treatment to dissolve them is discussed. Although less well understood, the pathogenesis of pigment (black or brown) stones may involve bilirubin or carbonate salts, or infection.

Aging↗