3-Hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors: oxime ether analogs of pravastatin.

Pravastatin, a potent anti-hypercholesteremic drug, has been developed by Bristol-Myers Squibb for treatment of hypercholesterolemia and other related diseases. Several structurally related compounds (SQ 31,554, SQ 31,879, SQ 31,947, SQ 32,391, SQ 32,770, SQ 32,390 and SQ 32,469) modified at the 3-position of the hexahydronaphthalene ring system of pravastatin were prepared in the course of developing the basic reagents for a radioimmunoassay of the parent drug. The biological activity of these analogs was comparable to pravastatin itself. Indeed, one member of this series was found to be several times more potent than pravastatin.

Histamine receptor activation by unsaturated (allyl and propargyl) homologs of histamine.

The spectrum of agonist activity for three new homologs of histamine (cis- and trans-imidazolylallylamine and imidazolylpropargylamine) was evaluated in the isolated guinea pig ileum and right atrium. The homologs were about three log units less potent than histamine in stimulating contractions of the longitudinal muscles of the ileum, but they were histamine-like, pharmacologically, because they were sensitive to blockade by pyrilamine and resistant to blockade by atropine. In the right atrium, these weak agonists were partially sensitive to blockade by cimetidine. The agonist activity of the cis-isomer in particular was completely blocked by a combination of cimetidine and propranolol, but resistant to reserpine treatment (neuronal catecholamine depletion). Therefore, these homologs of histamine have the ability to stimulate H1- and H2-histamine receptors and beta-adrenoreceptors in vitro.

Influence of side-chain charge on hepatic transport of bile acids and bile acid analogues.

The importance of side-chain charge on hepatic uptake and biliary secretion of bile acids and analogues was studied using the isolated, perfused rat liver and the anesthetized rat with a bile fistula. Derivatives of cholic acid with negative, neutral, zwitterionic, or positive charges on the side chain were synthesized and studied. Hepatic uptake by the isolated perfused liver, determined by measuring the rate of disappearance of a single 20-mumol bolus added to the perfusate, was strongly influenced by side-chain charge. A fully positively charged bile acid derivative (cholylcholamine) and two fully zwitterionic bile acid derivatives (CHAPS and cholyllysine) showed no appreciable uptake (less than 1% of the uptake rate of cholyltaurine). Bile acid derivatives existing mostly in cationic form (cholylamine) at pH 7.4, in neutral form (cholylglycylhistamine), or in divalent anion form (cholylaspartate and cholylcysteate) had an uptake rate that was greater but only 7-19% that of cholyltaurine. Side-chain charge also appeared to influence the rate of secretion into bile. Bile acids existing in mono- or dianionic form were well secreted (greater than 95% of dose in 2 h) into the bile, but all other derivatives had much lower secretion rates (less than 20% of dose in 2 h). When the biliary secretion of each bile acid derivative was expressed in relation to the amount that had entered the liver, relative secretion rates (presumably from liver cell) into bile decreased in the following order: cholyltaurine greater than cholylaspartate and cholylcysteate greater than CHAPS greater than cholyllysine greater than cholylglycylhistamine approximately equal to cholylamine. In bile fistula rats, cholylaspartate was quantitatively secreted into bile when infused at rates below its secretory maximum, whereas only very low biliary secretion rates of CHAPS were observed even during relatively high infusion rates; cholylamine was cholestatic. The above data show that, although uncharged and anionic derivatives of cholic acid may be taken up by the liver at a moderate rate, only anionic derivatives (both monovalent and divalent) are well secreted from within the liver cell into bile. A single negative charge on the side chain appears to be required for optimal transport of a bile acid from sinusoidal blood to bile.

Biliary secretion and hepatic metabolism of taurine-conjugated 7 alpha-hydroxy and 7 beta-hydroxy bile acids in the dog. Defective hepatic transport and bile hyposecretion.

Experiments were carried out using chronic bile fistula dogs to define the physiologic properties and metabolism of two unnatural epimeric monohydroxy conjugated bile acids, 7 alpha-hydroxy cholanoyltaurine and 7 beta-hydroxy cholanoyltaurine. The compounds, labeled with 14C, were infused intravenously at a rate of 1 mumol/kg X min; effects on bile flow and biliary lipid secretion as well as hepatic biotransformation were defined. The 7-monohydroxy bile acids were secreted quite slowly in bile: recovery during the 90-min infusion interval averaged 16% for the 7 alpha compound and 23% for the 7 beta compound, and after 6 h was only about 60% for the 7 alpha compound and 80% for the 7 beta compound. Uptake by tissues, presumably the liver, appeared to be efficient, as the level of radioactivity in peripheral blood remained quite low. Both bile acids failed to induce the anticipated increase in bile flow; canalicular bile flow, which was assessed using erythritol clearance, was about half the value observed when cholyltaurine was infused at a similar rate. The "hyposecretion" of bile, which was thought likely to be caused by impaired canalicular transport of the monohydroxy conjugates, was fully reversible, as a subsequent cholyltaurine infusion at a rate of 1 mumol/min X kg immediately restored bile flow and the infused cholyltaurine was secreted normally. Each compound was partly 3-hydroxylated during hepatic passage: the 7 alpha compound, about 36% (to form chenodeoxycholyltaurine); the 7 beta compound, about 23% (to form ursodeoxycholyltaurine). No other biotransformation occurred. Each compound induced phospholipid and cholesterol secretion, but compared to the effects of cholyltaurine, the amount of phospholipid secretion induced (per micromole of secreted bile acid) was less, and that of cholesterol, greater. Thus, the two 7-monohydroxy taurine-conjugated bile acids caused a striking dissociation of induced phospholipid and cholesterol secretion. The results indicate that taurine-conjugated 7-monohydroxy bile acids are poorly secreted by the liver and that their impaired transport is associated with bile hyposecretion, possibly reflecting decreased bile acid-dependent flow; the configuration of their 7-hydroxy group influences their rate of secretion into bile. The results also establish a novel type of bile acid biotransformation (3-hydroxylation) in the dog.