Urolithin A production drives the effects of pomegranate on the gut microbial metabolism of bile acids and cholesterol in mild dyslipidaemic overweight and obese individuals

The metabolism of (poly)phenols and some host metabolites, including bile acids (BAs) and cholesterol, varies among individuals depending on their gut microbiota. The gut microbial metabolism of ellagitannins (ETs) and ellagic acid (EA) produces urolithins (Uros), yielding three metabotypes with quantitative and qualitative differences based on dissimilar Uro-producing profiles (UM-A, UM-B, and UM-0, i.e., non-producers). Previous animal studies demonstrated that polyphenols impact BAs and cholesterol microbial metabolism, but data on their effects in humans and data regarding the inter-individual variability of these metabolic conversions are scant. We evaluated whether UMs, as distinctive functional gut-microbiome signatures, could determine the potential effect of a pomegranate extract (PE) rich in ET-EA on the metabolism of BAs and cholesterol in mild dyslipidaemic overweight-obese individuals, with possible consequences on host-lipid homeostasis and gut health. At the baseline, UM-B presented the highest levels of faecal total and secondary BAs and coprostanol, suggesting that the lipid absorption capacity and gut cytotoxic risk could be augmented in UM-B. PE intake significantly reduced faecal coprostanol and BA production, especially secondary BAs, and modulated the gut microbiome, reducing the gut cytotoxic risk, especially in UM-B individuals. The lowering of faecal microbial coprostanol and BAs and some BA-metabolising bacteria was quantitatively correlated with Uro concentrations, mainly faecal Uro-A. This suggests that PE consumption could exert cardiovascular and gut protection through Uro-A production as a direct driver of the effects and indirectly by reducing the Coriobacteriaceae family and BA pool, known factors involved in the gut absorption of lipids.

A case of cerebrotendinous xanthomatosis with massive xanthomas but without a considerable increase in serum cholestanol levels

Cerebrotendinous xanthomatosis (CTX) is a rare autosomal recessive disorder caused by mutations in the sterol 27-hydroxylase gene (CYP27A1). Due to the deficiency of 27-hydroxylase, the synthesis of bile acids from cholesterol is impaired and excessive cholestanol accumulates in various tissues, such as the central nervous system, tendons, and lenses. Patients with CTX typically manifest intellectual decline, pyramidal tract symptoms, cerebellar symptoms, tendon xanthomas, juvenile cataracts, neonatal jaundice, chronic diarrhea, osteoporosis, and premature cardiovascular disease. Here, we report the atypical case of a 35-year-old female with CTX having massive xanthomas but without a considerable increase in serum cholestanol levels (3.9 µg/mL). In the differential diagnosis of xanthoma, CTX should not be ruled out even if the serum levels of cholestanol are not high, and genetic testing is necessary to make the appropriate diagnosis.

Pregnancy Cholesterol Metabolism Markers and the Risk of Gestational Diabetes Mellitus: A Nested Case-Control Study

This study aims to determine the association of pregnancy cholesterol metabolism markers with gestational diabetes mellitus (GDM) risk. We performed a nested case-control study in the Tongji Birth Cohort. GDM was diagnosed according to the 75 g 2 h oral glucose tolerance test (OGTT) at 24-28 gestational weeks. Nine cholesterol metabolism markers were detected using gas chromatography-mass spectrometry. Conditional logistic regression models were conducted. A total of 444 pregnant women were matched in a 1:2 ratio. The cholestanolTC and β-sitosterolTC in cholesterol absorption markers presented negative associations with the risks of GDM (adjusted OR: 0.77, 95% CI: 0.61-0.96; adjusted OR: 0.80, 95% CI: 0.64-1.00). The desmosterolTC in cholesterol synthesis markers were positively associated with the risks of GDM (adjusted OR: 1.25, 95% CI: 1.00-1.56), similar in the ratios of cholesterol synthesis to absorption markers. After adjustment for insulin or HOMA-IR, these effects were reduced. In conclusion, higher cholesterol synthesis and lower cholesterol absorption marker levels in the first pregnancy are associated with a higher risk of GDM, and insulin resistance may play a vital role in this association.

Prevalence of cerebrotendinous xanthomatosis among patients diagnosed with early-onset idiopathic bilateral cataracts: final analysis

Cerebrotendinous xanthomatosis (CTX) is a rare, autosomal recessive bile acid synthesis disorder caused by pathologic variants in CYP27A1, a gene involved in bile acid synthesis. Impaired function in this gene leads to accumulation of plasma cholestanol (PC) in various tissues, often in early childhood, resulting in such clinical signs as infantile diarrhea, early-onset bilateral cataracts, and neurological deterioration. The current study aimed to identify cases of CTX in a population of patients with a greater CTX prevalence than the general population, to facilitate early diagnosis. Patients diagnosed with early-onset, apparently idiopathic, bilateral cataracts between the ages of 2 and 21 years were enrolled. Genetic testing of patients with elevated PC and urinary bile alcohol (UBA) levels was used to confirm CTX diagnosis and determine CTX prevalence. Of 426 patients who completed the study, 26 met genetic testing criteria (PC ≥ 0.4 mg/dL and positive UBA test), and 4 were confirmed to have CTX. Prevalence was found to be 0.9% in enrolled patients, and 15.4% in patients who met the criteria for genetic testing.

Serum Phytosterols Are Not Associated with Inflammatory Markers in Two Cross-Sectional, Swiss Population-Based Studies (The CoLaus|PsyCoLaus Study)

Background: The association between inflammation and dietary sterols remains poorly assessed at the population level. Aims: To assess the possible association between serum levels of various phytosterols (PS) and inflammatory markers. Methods: Serum levels of six PS (campesterol, campestanol, stigmasterol, sitosterol, sitostanol, brassicasterol), four cholesterol synthesis markers (lathosterol, lanosterol, desmosterol, dihydroxylanosterol) and one cholesterol absorption marker (cholestanol) were measured together with levels of CRP, IL-6 and TNF-α in two cross-sectional surveys of a population-based, prospective study. Results: CRP levels were negatively associated with levels of cholestanol and of sterols of plant origin, although some associations were not statistically significant. CRP levels were positively associated with cholesterol synthesis markers in the first but not in the second follow-up. IL-6 levels were negatively associated with cholestanol in both follow-ups. No associations between IL-6 levels and PS were found in the first follow-up, while significant negative associations with campesterol, sitosterol, brassicasterol, sitostanol and campesterol:TC ratio were found in the second follow-up. TNF-α levels were negatively associated with cholestanol in both follow-ups. These associations did not withstand adjusting for sex, age, BMI and statin administration. Conclusions: In a population-based study, PS serum levels were not significantly associated with inflammatory markers.

Effects of Diet-Induced Weight Loss on Plasma Markers for Cholesterol Absorption and Synthesis: Secondary Analysis of a Randomized Trial in Abdominally Obese Men

Cross-sectional studies have shown that obesity is associated with lower intestinal cholesterol absorption and higher endogenous cholesterol synthesis. These metabolic characteristics have also been observed in patients with type 2 diabetes, metabolic syndrome, steatosis or cholestasis. The number of intervention studies evaluating the effect of weight loss on these metabolic characteristics is, however, limited, while the role of the different fat compartments has not been studied into detail. In a randomized trial, abdominally obese men (N = 54) followed a 6-week very low caloric (VLCD) diet, followed by a 2 week weight-maintenance period. Non-cholesterol sterols were measured at baseline and after 8 weeks, and compared to levels in lean participants (N = 25). After weight loss, total cholesterol (TC)-standardized cholestanol levels increased by 0.18 µmol/mmol (p < 0.001), while those of campesterol and lathosterol decreased by 0.25 µmol/mmol (p < 0.05) and 0.39 µmol/mmol (p < 0.001), respectively. Moreover, after weight loss, TC-standardized lathosterol and cholestanol levels were comparable to those of lean men. Increases in TC-standardized cholestanol after weight loss were significantly associated with changes in waist circumference (p < 0.01), weight (p < 0.001), BMI (p < 0.001) and visceral fat (p < 0.01), but not with subcutaneous and intrahepatic lipids. In addition, cross-sectional analysis showed that visceral fat fully mediated the association between BMI and TC-standardized cholestanol levels. Intrahepatic lipid content was a partial mediator for the association between BMI and TC-standardized lathosterol levels. In conclusion, diet-induced weight loss decreased cholesterol synthesis and increased cholesterol absorption. The increase in TC-standardized cholestanol levels was not only related to weight loss, but also to a decrease in visceral fat volume. Whether these metabolic changes ameliorate other metabolic risk factors needs further study.

Cerebrotendinous xanthomatosis with radiological abnormalities of the chest

A 55-year-old man with mental retardation and calcaneal tendon thickening was referred for a suspected genetic disease. His serum cholestanol was elevated and genetic analysis of his blood cells for CYP27A1 revealed a homozygous missense mutation. We diagnosed him with cerebrotendinous xanthomatosis (CTX). Chest radiography revealed diffuse micronodular and reticular opacities. Histological findings obtained from the transbronchial lung biopsy revealed foamy macrophages and multinucleate giant cells with marked lipid crystal clefts. Although there are few reports of pulmonary lesions in CTX, we concluded from the radiological and histopathological findings that the pulmonary lesions were indeed caused by the CTX. The patient was treated with chenodeoxycholic acid. His neurological findings and calcaneal tendon thickening were unchanged; however, his serum cholestanol and radiological abnormalities of the chest decreased.

Update on cerebrotendinous xanthomatosis

PURPOSE OF REVIEW

Cerebrotendinous xanthomatosis (CTX) is a rare genetic lipid storage disorder with highly pleomorphic clinical phenotype. Complications of this disease can be devastating and may include severe cognitive impairment and dementia in later stages. Disease progression can be prevented or stabilized by bile acid replacement therapy, although a subset of patients with advanced disease continue to deteriorate despite therapy.

RECENT FINDINGS

Delayed diagnosis of CTX continues to impede effective treatment. A clinical diagnostic algorithm for CTX was developed that can decrease the age of diagnosis of CTX. The strategy of screening children with bilateral juvenile cataracts for CTX also improved diagnosis, as this group had a 500-fold higher-rate of CTX than the general population. Improved diagnosis of CTX is critical, as patients treated early in the course of the disease have significantly better outcomes compared with those treated later. More sensitive and specific biochemical testing for CTX has been developed that is potentially more informative than blood cholestanol to assess treatment efficacy and medication compliance in CTX.

SUMMARY

Because we are recognizing more severe presentations of CTX in infants and children, and delayed diagnosis and treatment worsens the prognosis, CTX is an excellent candidate disorder for newborn screening using recently reported methods for newborn dried bloodspot analysis.

The impact of anthropogenic activity at the tropical Sergipe-Poxim estuarine system, Northeast Brazil: Fecal indicators

The individual concentrations and sources of sterols in sediments samples collected in two periods 2017 (dry period /March and rainy period/August) were determined along with the Sergipe-Poxim estuarine system, Aracaju, Brazil. The individual sterols concentration ranged from 135 to 21,746 ng g^-1 (March) and 191 to 144,748 ng g^-1 (August) and the distribution was mainly dominated by β-sitosterol in both periods with 37.2% (March) and 70.8% (August) of the total sterols found. In all the sampling sites, the coprostanol levels were higher than 100 ng g¹ (March) and 500 ng g^-1 (August), indicating sewage contamination. Diagnostic ratios between sterols suggested the predominance of sewage sources. Pearson correlation assessed a correlation significant (March) and negligible (August) between coprostanol concentration levels and organic matter. The principal component analysis (PCA) showed that the sterols levels influenced strongly C1, as well as C2 distinguished between the plant sterols and from sewage.

Clinical and molecular genetic features of cerebrotendinous xanthomatosis patients in Chinese families

Cerebrotendinous xanthomatosis (CTX) is a lipid-storage disease caused by mutations in CYP27A1. Current publications of Chinese CTX were mainly based on case reports. Here we investigated the clinical manifestations, genetic features in Chinese CTX patients. The clinical materials of 4 Chinese CTX pedigrees were collected. The genetic testing was done by polymerase chain reaction plus Sanger sequencing. The features of Chinese CTX patients reported previously were also reviewed. Three novel mutations of p.Arg513Cys, c.1477-2A > C in family 1 and p.Arg188Stop in family 4 (NM 000784.3) in CYP27A1 were found. The probands in our study manifested cerebellar ataxia, tendon xanthoma and spastic paresis in family 1 and 4, tendon xanthoma plus spastic paraparesis in family 2, asymptomatic tendon xanthoma in family 3. Three known mutations of p.Arg137Gln, p.Arg127Trp and p.Arg405Gln were found respectively in Family 2, 3 and 4. For the Chinese patients reviewed, the most common findings were xanthomatosis (100%), pyramidal signs (100%), cerebellar ataxia (66.7%), cognitive impairment (66.7%), cataracts (50.0%), and peripheral neuropathy (33.3%). Chronic diarrhea was infrequently seen (5.6%). No mutation was found associated with any given clinical features. We identified 3 novel mutations in CYP27A1. In Chinese CTX patients, xanthomatosis was the most common symptom while cataracts and chronic diarrhea were less frequent. The special features in Chinese CTX patients might caused by the lack of serum cholestanol test and should be confirmed in larger number of patients in the future.

Cerebrotendinous xanthomatosis: a treatable cause of metabolic ataxia

Cerebrotendinous xanthomatosis is an exceptionally rare condition in Indian subcontinent, however, it is potentially treatable if diagnosed. We present and discuss the clinical presentation and investigations in a case of cerebrotendinous xanthomatosis (CTX).

Interaction of the Glycoalkaloid Tomatine with DMPC and Sterol Monolayers Studied by Surface Pressure Measurements and Brewster Angle Microscopy

The interaction of the glycoalkaloid tomatine with monolayers of dimyristoylphosphatidylcholine (DMPC) and cholesterol, as well as other selected sterols, has been investigated using surface pressure measurements at constant area and Brewster angle microscopy (BAM). The interaction of tomatine with sterol monolayers is found to vary with the structure of the sterol. The interaction of tomatine with cholesterol-containing monolayers results in a surface pressure increase accompanied by the appearance of a mottled texture. Morphological changes are observed that suggest the formation of tomatine-cholesterol complexes that aggregate at the water-air interface. No morphology change observable by BAM is observed for monolayers containing epicholesterol, suggesting that the stereochemistry of hydrogen bonding between the sterol and the sugar units on tomatine is of particular significance. Strong interactions are observed with cholestanol- and coprostanol-containing monolayers, and BAM reveals formation of spiked aggregates upon interaction with 7:3 mole ratio DMPC/coprostanol mixed monolayers. More modest surface pressure changes are observed for cholestenone- and epicoprostanol-containing monolayers. A much smaller surface pressure increase is observed when tomatine is injected beneath a pure DMPC monolayer.

Acid-catalyzed plasmenylcholine hydrolysis and its effect on bilayer permeability: a quantitative study

This laboratory has previously shown (Anderson, V.C. and Thompson, D.H. (1992) Biochim. Biophys. Acta 1109, 33-42; Thompson, D.H., Gerasimov, O.V., Wheeler, J.J., Rui, Y. and Anderson, V.C. (1996) Biochim. Biophys. Acta 1279, 25-34), that plasmenylcholine (1-alk-1'-enyl-2-palmitoyl-sn-glycero-3-phosphocholine; PlsPamCho) liposomes release hydrophilic contents upon photooxidation or acid-catalyzed hydrolysis. We now report the kinetics and chemical mechanism of the acid-catalyzed reaction and its effect on calcein leakage rates. Hydrolysis of the plasmenylcholine vinyl ether linkage generates fatty aldehydes and 1-hydroxy-2-palmitoyl-sn-glycero-3-phosphocholine (lysolipid); HPLC and 1H-NMR experiments establish that the former is readily air-oxidized to fatty acids, while the latter undergoes rapid acid-catalyzed rearrangement to 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine. Lysolipid formation obeys first order kinetics, yielding observed pseudo-first order rate constants that are pH-dependent. Bimolecular hydrolysis rate constants, k(bi), have also been determined. Calcein release rates from plasmenylcholine liposomes are strongly dependent on both the dihydrocholesterol (DHC) content and the extent of PlsPamCho hydrolysis within the bilayer. DHC-free plasmenylcholine liposomes (38 degrees C, pH 2.5) require < 5% PlsPamCho hydrolysis to effect > 50% calcein release within 10 min. The presence of > or = 25 mol% DHC, however, greatly reduces the observed calcein release rate; nearly 30% PlsPamCho hydrolysis is required to effect 50% calcein release over a 70-min period in 6:4 PlsPamCho/DHC liposomes. Bacteriochlorophyll a-sensitized photooxidation of plasmenylcholine liposomes also produces fatty aldehyde and another intermediate, tentatively described as 1-formyl-2-palmitoyl-sn-glycero-3-phosphocholine, that hydrolyzes to form the 1-hydroxy lysolipid. These results have important implications for the quantitative description of lysolipid effects on membrane permeability and on the design of triggerable liposomes for drug delivery.

DSC, X-ray and NMR properties of cholesterol-cholestanol-dihydrate crystals

The melting point, X-ray diffraction and longitudinal relaxation time (T1) of cholesterol-cholestanol-dihydrate crystals (CC2W) were studied in an effort to produce new experimental data related to atherosclerotic plaques. The crystals were precipitated from ethanolic solutions at several cholesterol: cholestanol (CS:CN) ratios. The melting point of CC2W crystals obtained at the CS:CN ratio 75:25, 50:50, 25:75 was 122-124 degrees C. The X-ray patterns recorded from these crystals of the same CN:CS ratios showed two additional diffraction peaks, as compared to those of CN and CS patterns. On the other hand, the values of T1 relaxation time measured by proton magnetic resonance were different for every CS:CN ratio for the various solution compositions. This latter method seems to be more precise for the detection of the presence of coprecipitated components in the CC2W mixed crystals than X-ray or thermal analysis. The results suggest that CN and CS do not have to be present in equimolar quantities in order for CC2W crystals to be formed. The presence of CC2W in the blood may have significance in the nucleation of cholesterol crystals in atherosclerotic plaques.

Effect of sterol incorporation on head group separation in liposomes

Electrophoretic mobilities of multilamellar liposomes of varying composition have been measured to determine the effect of incorporated sterols on surface charge density. Liposomes made from mixtures of zwitterionic egg phosphatidylcholine (PC) and anionic egg phosphatidylglycerol (PG) in varying proportions were shown to have electrophoretic mobilities consistent with the anticipated surface charge density. Incorporation of cholesterol up to 50 mole per cent in the bilayer produced no detectable change in surface charge density. Similar results were obtained for lanosterol and epicoprostanol. These results are interpreted to mean that incorporation of the sterols into the bilayers produced no detectable change (less than 3%) in the spacing of charged phospholipids. It is inferred that sterols are incorporated among the fatty acyl chains of these phospholipid bilayers with little or no displacement of the head groups at the surface.

Molecular packing in steroid-lecithin monolayers. IV. Mixed films of epicoprostanol with dipalmitoyl phosphatidylcholine

Studies of the two-component monomolecular film system, dipalmitoyl phosphatidylcholine (DPPC) - epicoprostanol have been carried out at 21 degrees C utilizing a wide compositional range of films. The results obtained indicate that on initial mixing of the two components, epicoprostanol condensed expanded DPPC films to a greatly reduced degree and expanded condensed DPPC films to a significantly greater degree compared with cholesterol. It is thought that, even on an initial compressional procedure, partial microscopic segregation of epicoprostanol takes place. The segregation is postulated to result from an epicoprostanol-epicoprostanol overlap, leading to row packing with an accompanying reduction in the number of adjacent acyl chains. Subsequent decompression and recompression of DPPC-epicoprostanol films leads to macroscopic segregation of pure or nearly pure epicoprostanol; however, partial miscibility below 20 mol% epicoprostanol may persist. The phase diagram of the initially compressed film may be of the eutectic type, but the mixed system is unstable. The inability of epicoprostanol to substitute for cholesterol appears to be due to a combination of two effects: the tilting of the sterol at the air-water interface, to satisfy the immersion requirements of the 3 alpha-OH group, and the bent alpha-face of the sterol. The alpha-OH group of epicoprostanol is postulated to play an indirect role in the weak condensation capabilities of this sterol by inducing a tilt in the molecule and reducing epicoprostanol - acyl chain hydrophobic interactions.

25-hydroxylation of C27-steroids and vitamin D3 by a constitutive cytochrome P-450 from rat liver microsomes

A constitutive cytochrome P-450 catalyzing 25-hydroxylation of C27-steroids and vitamin D3 was purified from rat liver microsomes. The enzyme fraction contained 16 nmol of cytochrome P-450/mg of protein and showed only one protein band with a minimum molecular weight of 51,000 upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified cytochrome P-450 catalyzed 25-hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha-diol, 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol, and 1 alpha-hydroxyvitamin D3 up to 50 times more efficiently, and 25-hydroxylation of vitamin D3 about 150 times more efficiently than the microsomes. The cytochrome P-450 showed no detectable 25-hydroxylase activity towards vitamin D2 and was inactive in cholesterol 7 alpha-hydroxylation as well as in 12 alpha- and 26-hydroxylations of C27-steroids. It catalyzed hydroxylations of testosterone and demethylation of ethylmorphine at the same rates as, or lower rates than, microsomes. The 25-hydroxylation of 5 beta-cholestane-3 alpha, 7 alpha, 12 alpha-triol and vitamin D3 with the purified cytochrome P-450 was not stimulated by addition of phospholipid or cytochrome b5 to the reconstituted system. Emulgen inhibited 25-hydroxylase activity towards both substrates. The possibility that 25-hydroxylation of C27-steroids and vitamin D3 is catalyzed by the same species of cytochrome P-450 is discussed.

Hypersecretion of mucus glycoprotein by the gallbladder epithelium in experimental cholelithiasis

In three models of cholelithiasis (dihydrocholesterol-fed rabbits, cholesterol-cholic acid-fed mice, and Lincomycin-treated guinea pigs), the quantity and chemical composition of gallbladder epithelial mucin have been studied using (1) a spectrum of histochemical glycoprotein stains, and (2) biochemical extraction, purification and analysis of the carbohydrate components of epithelial mucin. Despite the diverse mechanism of stone induction and difference in stone composition, a common pattern of response by the epithelial mucin was observed in all three models. There was a quantitative increase in epithelial mucus production at a time before stones were formed and this increase persisted till stones were formed. There was no difference, qualitatively, between mucus produced by normal and stone-forming gallbladders.

Enhanced fluid transport across gallbladder mucosa in experimental cholelithiasis

Fluid transport of the gallbladder has been studied in two models of experimental cholelithiasis: dihydrocholesterol-induced gallstones in the rabbit and lincomycin-induced gallstones in the guinea pig. Using the noneverted explained gallbladder of the rabbit and the guinea pig, the transport of luminal to serosal fluid has been quantitated before, during, and after stone formation. The everted gallbladder preparation of the rabbit has also been used to measure fluid transport before and during gallstone formation. In both models, an increased fluid transport was observed in the phase of gallstone induction and a return to normal after stones were formed. This abnormality preceded the appearance of conventional histological features of cholecystitis. There was also a coincidental increase in glycoprotein production from and cell proliferation of the gallbladder epithelium. This enhancement of fluid transfer may play a contributing role in the genesis of gallstones.

Cctionic selectivity of bimolecular membranes in the presence of nystatin and amphotericin B

Ergosterin or 7-dehydrocholesterin-containing artificial membranes are selectively permeable for cations of alkaline metals in aqueous solutions of nistatin and amphotericine B. Membrane permeability changes spontaneously within several tens of minutes from the cation to the anion one. A decrease of temperature, an increase of medium pH or introduction of dimethylsulphoxide into aqueous solution inhibit, while the addition of calcium accelerate this transition.

Molecular aspects of polyene- and sterol-dependent pore formation in thin lipid membranes

Amphotericin B modifies the permeability properties of thin lipid membranes formed from solutions containing sheep red cell phospholipids and cholesterol. At 10(-6)M amphotericin B, the DC membrane resistance fell from approximately 10(8) to approximately 10(2) ohm-cm(2), and the membranes became Cl(-)-, rather than Na(+)-selective; the permeability coefficients for hydrophilic nonelectrolytes increased in inverse relationship to solute size, and the rate of water flow during osmosis increased 30-fold. These changes may be rationalized by assuming that the interaction of amphotericin B with membrane-bound sterol resulted in the formation of aqueous pores. N-acetylamphotericin B and the methyl ester of N-acetylamphotericin B, but not the smaller ring compounds, filipin, rimocidin, and PA-166, produced comparable permeability changes in identical membranes, and amphotericin B and its derivatives produced similar changes in the properties of membranes formed from phospholipid-free sterol solutions. However, amphotericin B did not affect ionic selectivity or water and nonelectrolyte permeability in membranes formed from solutions containing phospholipids and no added cholesterol, or when cholesterol was replaced by either cholesterol palmitate, dihydrotachysterol, epicholesterol, or Delta5-cholesten-3-one. Phospholipid-free sterol membranes exposed to amphotericin B or its derivatives were anion-selective, but the degree of Cl(-) selectivity varied among the compounds, and with the aqueous pH. The data are discussed with regard to, first, the nature of the polyene-sterol interactions which result in pore formation, and second, the functional groups on amphotericin B responsible for membrane anion selectivity.

THE DIFFERENTIAL-PHOTOMETRIC ESTIMATION OF COPROSTANOL IN THE PRESENCE OF CHOLESTEROL, SITOSTEROL, AND OTHER 3β-HYDROXYSTEROLS

A method is described for the differential-photometric estimation of coprostanol in faeces, based upon the change in extinction coefficients of cholesterol and coprostanol with time in the Liebermann-Burchard reaction. Recoveries of coprostanol added to artificial sterol mixtures averaged 97.9 ± 6.4% (S.D.). Recoveries after its addition to crude alcoholic extracts of faecal lipids averaged 102.7 ± 4.5%.Corrections can be readily made for the presence of Δ7-stenols by application of the Rosenheim-Callow reaction and a modified Liebermann-Burchard reagent.A distinct advantage of this procedure for coprostanol is the fact that the presence of sitosterol (β- and (or) γ-isomer) does not interfere because its chromogenic behavior in the Liebermann-Burchard reaction enables one to treat it and cholesterol as a single entity despite the relatively large differences in the extinction coefficients.