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Biomedical subjects

A F Hofmann

Publications and source records attributed to A F Hofmann.

At least 271 records · Page 15Linked to original sources
PubMed1977

Radioimmunoassay of sulfated lithocholates.

A sensitive, rapid radioimmunoassay for sulfated species of lithocholic acid (sulfolithocholyglycine, sulfolithocholyltaurine, and sulfolithocholic acid) was developed and used to measure the total concentration of sulfated lithocholates in serum from healthy human subjects. Sulfolithocholylglycine was conjugated to bovine serum albumin by a carbodiimide procedure, and the reaction product, emulsified in Freund's adjuvant, was injected into rabbits. The antiserum obtained was capable to binding 40% of [3H]sulfolithocholylglycine at 1:1000 dilution. The assay featured a 2-hr binding step at 42 degrees C followed by precipitation of bound tracer with polyethylene glycol at 4 degrees C. The assay can be used with 0.1 ml of serum and was reproducible. The antibody had little affinity for the 3-sulfate of cholic or chenodeoxycholic acid, a number of steroid sulfates, or unsulfated bile acids. In 50 healthy subjects, mean (+/-SE) fasting-state serum levels of immunoreactive sulfated lithocholyl conjugates (+sulfated lithocholate) was 1.6 +/- 0.1 micrometer; based on results with a separate radioimmunoassay for unsulfated lithocholyl conjugates, most of the lithocholate in serum in healthy man is present in sulfated form.

Antibody Specificity↗
PubMed1977

Suitability of [11, 12-3H2]chenodeoxycholic acid and [11, 12-3H2]lithocholic acid for isotope dilution studies of bile acid metabolism in man.

Studies were carried out to assess the stability of the label in [11,12-(3)H(2)]chenodeoxycholic acid and [11,12-(3)H(2)]lithocholic acid during enterohepatic cycling and thus define the suitability of these tracers for isotope dilution studies of bile acids in man. To do this, [11,12-(3)H(2)]-chenodeoxycholic acid and [24-(14)C]chenodeoxycholic acid were administered simultaneously to six healthy adults. The (3)H/(14)C ratio of biliary chenodeoxycholic acid and the specific activity of biliary chenodeoxycholic acid were determined to permit calculation of pool size and turnover rate by the conventional isotope dilution procedure of Lindstedt (1957. Acta Physiol. Scand. 40: 1). Excretion of label in urine was measured as well as the (3)H/(14)C ratio of fecal bile acids. Similar studies were carried out with [11,12-(3)H(2)]lithocholic acid and [24-(14)C]lithocholic acid. With [11,12-(3)H(2)]chenodeoxycholic acid, 10-15% of the label was lost during the first 24 hours, after which the (3)H/(14)C ratio of biliary chenodeoxycholic acid remained constant. The loss of (3)H caused a consistent overestimate of pool size by 10-15%, but since the fractional turnover rate of the two isotopes was identical, the calculated rate of synthesis was 10-15% greater when determined using (3)H. The loss of (3)H was attributed to the presence of (3)H in positions other than 11 and 12 occurring during the labeling procedure when the unsaturated precursor was exposed to carrier-free tritium gas. The (3)H/(14)C ratio of feces was consistently below that of bile, suggesting bacterial removal of additional (3)H during distal intestinal passage. In contrast, [11,12-(3)H(2)]lithocholic acid lost (3)H continuously, so that by 2 days after administration, the (3)H/(14)C ratio had fallen to nearly half of that of the administered mixture. It is concluded that isotope dilution studies may be carried out with one preparation of [11,12-(3)H(2)]chenodeoxycholic acid with an error of 10-15%; possibly a more stable preparation can be prepared with a gentler tritiation procedure. One preparation of [11,12-(3)H(2)]lithocholic acid was unsatisfactory for isotope dilution studies in man.

Adult↗
PubMed1976

Chemical synthesis of bilirubin glucuronide conjugates.

In dimethylformamide, the two carboxyl groups of bilirubin react with the bifunctional coupling agent, carbonyldimidazole, to form bilirubin diimidazole, which was isolated and crystallised. The bilirubin diimidazole, termed "activated bilirubin", was shown to react spontaneously with primary alcohols to form diesters of bilirubin. After addition of the tetrabutyl ammonium salt of glucuronic acid, compounds with chromatographic mobilities similar to those of bilirubin mono- and diglucuronides from bile were formed. Bilirubin diglucuronides were isolated by barium precipitation followed by solvent extraction. The bilirubin diglucuronides were considered to be a mixture of alpha and beta glucuronides esterified at positions 1,2,3, or 4 of glucuronic acid because the compound(s) was resistant to hydrolysis with glucuronidase and gave multiple sponts by chromatography after diazotization with ethyl anthranilate. The model compounds lauryl glucuronides were synthesized similarly; the most polar product by chromatography and had identical chromatographic mobility to synthetic lauryl 1-D-glucuronide prepared by reductive debenzylation of lauryl (benzyl (2,3,4-tri-O-benzyl))-D-glucuronide. It is concluded that bilirubin-1-di-beta-D-glucuronide can be synthesized when suitable protecting groups for the 2, 3, and 4 hydroxyl groups of glucuronic acid become available.

Bilirubin↗
PubMed1976

Lithocholate metabolism during chenotherapy for gallstone dissolution. 1. Serum levels of sulphated and unsulphated lithocholates.

Serum levels of total sulphated and total unsulphated lithocholates were each measured by a specific radioimmunoassay in 66 patients ingesting chenodeoxycholic (chenic) acid for gallstone dissoultion and in 35 gallstone patients ingesting either cholic acid or placebo. No changes occurred in serum lithocholate levels in the control groups. In patients ingesting chenic acid, there was a twofold increase in serum levels of total lithocholate, but the percent sulphation (greater than 75%) remained unchanged during chenotherapy. There was no correlation in the chenic acid treated group between serum lithocholate levels and the proportion of lithocholate in biliary bile acids or changes in serum SGOT. The data suggest that there is effective sulphation of lithocholate in such patients; this may explain the lack of hepatotoxicity observed during ingestion of chenic acid.

Aspartate Aminotransferases↗
PubMed1976

Lithocholate metabolism during chemotherapy for gallstone dissolution. 2. Absorption and sulphation.

The amount of lithocholate input and the size of the total lithocholate exchangeable pool were measured using isotope dilution in three patients ingesting chenodeoxycholic acid for gallstone dissolution and two healthy control subjects. Because the specific activity decay curve was biexponential in appearance, input was calculated using a stochastic analysis employing the Stewart-Hamilton equation. By this method, the lithocholate input and the size of the exchangeable pool in gallstone patients during chenic acid ingestion was four to five times that observed in the healthy control subjects. It was calculated that about one-fifth of the newly formed lithocholate was absorbed in both gallstone patients and healthy control subjects. The extent of sulphation of absorbed lithocholate was then measured in seven gallstone patients whto had been ingesting chenodeoxycholic acid for gallstone dissolution by defining the chemical form of radioactivity in bile after intravenous administration of labelled lithocholate. Similar studies were carried out in eight healthy control subjects, but, in addition the extent of sulphation of injected lithocholylglycine and lithocholyltaurine was also defined. When lithocholate was injected, the majority of radioactivity in bile (50-60%) was present as sulphated conjugates, both in gallstone patients and healthy control subjects. The degree of sulphation was greater for glycine than taurine conjugates, and these findings, which suggested preferential sulphation of the glycine conjugates of lithocholate, were confirmed by showing that injected lithocholylglycine was sulphated to a much greater extent than injected lithocholyltaurine. These findings indicate that in patients receiving chenic acid there is effective sulphation of lithocholate, especially its glycine conjugates, despite a considerable increase in lithocholate absorption; they may provide an explanation for the lack of hepatotoxicity of chenic acid in man.

Adult↗
PubMed1976

Role of fat maldigestion in pathogenesis of steatorrhea in ileal resection. Fat digestion after two sequential test meals with and without cholestyramine.

To clarify the role of fat maldigestion in the pathogenesis of steatorrhea in patients with ileal resection the total and aqueous phase concentrations of bile acid and fatty acid were characterized in 8 such patients (5 patients with small ileal resection, bile acid diarrhea, and steatorrhea less than 20 g per day; 3 patients with large ileal resection, fatty acid diarrhea, and steatorrhea greater than 20 g per day) as well as 4 healthy control subjects after a morning and an afternoon liquid test meal. The study was then repeated with cholestyramine, 4 g being administered before each meal to induce fat maldigestion. After a conventional test meal, patients with large resections and severe steatorrhea had significantly lower aqueous phase concentrations of bile acids (and fatty acids) than patients with smaller resections or control subjects, explained in part by intraluminal precipitation of about one-half of the bile acids during digestion. When cholestyramine was administered before the meal, aqueous phase bile acid concentrations decreased in all patients, including the normal control subjects; the degree of fat maldigestion induced in the patients with small resections (and the control subjects) became similar to that present after the conventional test meal in the patients with large resections. Because steatorrhea increased little in the patients with small resections when cholestyramine was administered continuously, the data suggest that fat maldigestion per se does not induce severe fat malabsorption in patients with sufficient anatomical reserve, because such patients can absorb fat efficiently by utilizing the distal small intestine. In patients with large ileal resections, severe steatorrhea is explained in part by the combination of fat maldigestion and decreased surface area. It is also speculated that the steatorrhea occurring in patients with small resections and relatively normal fat digestion during two test meals may be explained by impaired fat digestion which occurs during the final meal of the day, which is often the largest meal.

Adult↗
PubMed1976

The enterohepatic circulation of bile acids in man.

It is clear that a truly spectacular increase in our understanding of the biliary circulation has occurred during the past 5 years. A steady-state situation has now become dynamic. In a sense, we have clarified the anatomy and physiology of the biliary circulation, and the challenge now is to describe its biochemistry. Specifically, we remain totally ignorant of the mechanism of cell transport of bile acids, the regulation of their synthesis and the action of bile acids in bile formation. When we understand the biliary circulation, we can then clarify its diseases. That, in turn, should lead to the development of a new specialty of biliary therapy.

Amino Acids↗
PubMed1976

Sampling intestinal content with a sequestering capsule. A noninvasive technique for determining bile acid kinetics in man.

A noninvasive technique for determining bile acid kinetics by isotope dilution in man features the intravenous injection of a radiolabeled bile acid, together with daily oral administration, for several days, of capsules of dialysis membrane containing cholestyramine and colored beads for dating. The cholestyramine traps conjugated bile acids during transit of the small intestine. Capsules are recovered from stool by sieving, sequestered bile acid is eluted, conjugated bile acids are isolated chromatographically, and their specific activity is determined. The precision and validity of this sequestering capsule technique were assessed by comparing the specific activity decay curve of chenodeoxycholyl conjugates obtained from capsule samples with that obtained from duodenal samples in seven healthy volunteers in whom the bile acid pool had been labeled with [14C]chenodeoxycholic acid. Estimates of pool size by the two methods correlated well (r = 0.98), as did the daily fractional turnover rate (r = 0.96). The mean (+/-SD) percentage differences for the kinetic parameters of pool size (8.3 +/- 13.6), fractional turnover rate (-15.2 +/- 11.5), and synthesis rate (-4.3 +/- 11.4) were fairly small, indicating that the noninvasive method has validity. However, agreement between simultaneously administered capsules was only fair, especially when the amount of bile acid trapped was small, suggesting that the precision of the capsule technique may be less than that of the conventional duodenal sampling technique; the latter probably obtains a more valid sample of the bile acid pool.

Administration, Oral↗
PubMed1976

Impaired lithocholate sulfation in the rhesus monkey: a possible mechanism for chenodeoxycholate toxicity.

Radioactive lithocholate was administered intravenously to female rhesus monkeys with an exteriorized enterohepatic circulation, and the chemical form of biliary radioactivity was defined by thin layer chromatography. Most radioactivity was excreted in bile in the form of unsulfated conjugates (77%), indicating impaired sulfation relative to published data for man. Defective sulfation of lithocholate, the major bacterial biotransformation product of chenodeoxycholic acid, can explain accumulation of lithocholate in the enterohepatic circulation and provide a possible mechanism for the hepatotoxicity observed during chenodeoxycholic acid administration to the nonhuman primate.

Animals↗
PubMed1976

Synthesis of 11, 12-2H2- and 11, 12-3H2-labeled chenodeoxycholic and lithocholic acids.

Deuterium- and tritium-labeled chenodeoxycholic acid and lithocholic were prepared by catalytic reduction of their respective delta11 derivatives. Structures of the intermediates and their isotopic purity were verified by chemical ionization and electron impact mass spectrometry and by nuclear magnetic resonance spectroscopy. Experimental conditions for reductive deuteration were defined which gave complete reduction of the olefin and a product of high isotopic purity. Conditions for optimal tritiation were developed with which little exchange of protons with the solvent occurred; the product had high specific activity. To test biological stability of the label, the 3H-labeled chenodeoxycholic acid was administered simultaneously with 14C-labeled chenodeoxycholic acid to two healthy subjects and the 3H/14C ratio in bile was determined daily for several days. The ratio remained identical to that administered, suggesting that the 11,12-3Hlabel in chenodeoxycholic acid is stable during enterohepatic cycling and can be used for valid estimates fo bile acid kinetics in many by the isotope dilution technique.

Chenodeoxycholic Acid↗
PubMed1975

Prospective comparison of indirect methods for detecting lactase deficiency.

To compare sensitivity, specificity and convenience, four indirect methods of detecting lactase deficiency were tested prospectively in 25 subjects with biopsy-proved lactase deficiency and in 25 with normal lactase activity. After ingestion of 50 g of lactose, containing 1-14Clactose, breath hydrogen was abnormally elevated in all 25 lactase-deficient subjects (greater than 0.30 ml per minute at two hours); breath 14CO2 was below the normal range in 23, and in 19 the plasma glucose increased by less than 20 mg per deciliter. When lactose and ethanol were given together, the rise in plasma galactose remained less than 5 mg per deciliter in 24 of the lactase-deficient subjects. The specificity of the four tests was excellent, with only one false-positive plasma glucose test. Measurement of breath hydrogen is sensitive and specific, and does not require ethanol or isotopes. It is noninvasive, and is not influenced by gastric emptying or metabolic factors. We believe it to be the most suitable test for population screening for lactase deficiency.

Adult↗
PubMed1975

Development of an intravenous bile acid tolerance test. Plasma disappearance of cholylglycine in health.

To develop an intravenous bile acid tolerance test that might be useful for detecting impaired liver function or liver injury, the plasma disappearance of intravenously injected cholyglycine was characterized in healthy man by a radiommunoassay, specific for conjugates of cholic acid, on serial samples of venous blood. Cholylglycine disappearance was rapid (mean half-life plus or minus S.E. equals 2.6 plus or minus 0.1 minutes) and of first-order kinetics; the rate of disappearance was independent of dose between 2 and 15 mumoles per kilogram of body weight. A dose of 5 mumoles per kilogram was selected as an optimal dose, and its clearance was defined in 45 healthy subjects. After intravenous injection of this dose, conjugates of cholic acid increased 10-fold, but in all subjects the concentration of these bile acids had returned to 1 muM (the upper limit of normal, fasting state) by 10 minutes. No side effects were observed.

Adult↗
PubMed1975

Validity and sensitivity of an intravenous bile acid tolerance test in patients with liver disease.

A bile acid tolerance test, which measures the plasma disappearance rate of injected cholyglycine by radioimmunoassay, was studied in 36 patients with biopsy-proved chronic liver disease and compared to fasting-state levels of conjugated cholic acid and other conventional liver tests. In 25 patients in whom one or more of the conventional tests for liver disease showed abnormal results, fasting-state levels of conjugated cholic acid were increased in 20, but plasma disappearance of cholyglycine was delayed in all. Of the 11 other patients in whom conventional tests were within normal limits, fasting-state levels of conjugated cholic acid were increased in three of 10, but cholyglycine disappearance was dealyed in nine of 11. The bile acid tolerance test indicated liver disease more sensitively than the fasting-state level of conjugated cholic acid, which, in turn, was more sensitive than other conventional liver tests.

Cholic Acids↗