Preferential pharmacological inhibition of macrophage ACAT increases plaque formation in mouse and rabbit models of atherogenesis

The cholesteryl ester, foam cell-enriched vulnerable plaque is a principle pharmacological target for reducing athero-thrombosis. Acyl CoA:cholesterol Acyl Transferase (ACAT) catalyzes the esterification of free cholesterol in intestine, liver, adrenal and macrophages, leading in the latter cells to intracellular cholesteryl ester accumulation and foam cell formation in the arterial intima. Previous studies suggested the existence of several isoforms of ACAT with different tissue distribution and this has largely been confirmed by molecular cloning of ACAT-1 and ACAT-2. We developed a series of ACAT inhibitors that preferentially inhibited macrophage ACAT relative to hepatic or intestinal ACAT based on in vitro assays and ex vivo bioavailability studies. Four of these compounds were tested in three models of atherosclerosis at oral doses shown to give sufficient bioavailable monocyte/macrophage ACAT inhibitory activity. In fat-fed C57BL/6 mice, chow fed apo E-/- mice and KHC rabbits, the various ACAT inhibitors had either no effect or increased indices of atherosclerotic foam cell formation. Direct and indirect measurements suggest that the increase in plaque formation may have been related to inhibition of macrophage ACAT possibly leading to cytotoxic effects due to augmented free cholesterol. These results suggest that pharmacological inhibition of macrophage ACAT may not reduce, but actually aggravate, foam cell formation and progression.

Selection of cholesterol absorption inhibitors devoid of secondary intestinal effects

The digestive tolerance of cholesterol absorption inhibitors, which requires a constant improvement, was the main purpose of this study. Given the known hypocholesterolemic and antiatherosclerotic properties of some steroid glycosides, we synthesized a series of sterol derivatives by coupling some phytosterols known to interact with sterol absorption and also to be poorly absorbed to a cationic group. The first derivative was a potent inhibitor of cholesterol absorption and a potent hypocholesterolemic agent in different animal models, but was responsible for severe gastro-intestinal side-effects. In order to control the tolerance of the newly synthesized compounds, cholesterol and taurocholate absorption were measured in the jejunum and in the ileum, respectively. The intestinal water and ionic transport and the estimation of histological changes in the intestinal mucosae were determined simultaneously. The in-situ isolated loop technique, in anaesthetized rats, allowed the simultaneous control of these three parameters which were used to select the best derivative, inhibitor of cholesterol absorption devoid of any deleterious effect, as seen via a three-dimensional representation. The results showed that it was possible to obtain a specific cholesterol absorption inhibitor without secretory and deleterious effects and suggested that the amphiphilic characteristics of the molecules were responsible for their deleterious effects on digestive tract.

Inhibition of semicarbazide-sensitive amine oxidase by monoamine oxidase B inhibitors from the oxazolidinone series

The purpose of the present work was to study the semicarbazide-sensitive amine oxidase (SSAO) inhibitory properties of MD 240931 and MD 240928 (the two enantiomers of MD 780236) as well as those of the corresponding primary amines, MD220662 and MD220661, in rat heart and aorta. MD240928 and MD240931 are rather weak SSAO inhibitors, MD 240931 being more potent than MD 240928. Of the four compounds studied, the most potent inhibitor of SSAO is MD 220662, its IC50 value ranging from 2.10(-6) to 6.10(-6)M. The SSAO inhibitory potency of this compound does not change significantly with the time of preincubation in both the absence and presence of clorgyline (10(-4)M). MD 220661 is also an inhibitor of SSAO; however, its SSAO inhibitory potency, which without preincubation is comparable to that of MD 220662, does decrease with the time of preincubation to the same extent in both the absence and presence of clorgyline (10(-4)M). These results suggest that MD 220661 is not only an inhibitor of SSAO, but is also a substrate of the enzyme.

Monoamine oxidase and semicarbazide-sensitive amine oxidase in spontaneously hypertensive and in normotensive control rats

The aim of the present work was to compare monoamine oxidase (MAO) and semicarbazide sensitive amine oxidase (SSAO) activity in several tissues from spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto rats (WKY). Contribution of MAO-A, -B and SSAO to the metabolism of each substrate in each tissue was defined from experiments where the decrease of oxidative deamination of each substrate at a given concentration was measured as a function of increasing concentrations of a selective MAO-A, -B or SSAO inhibitor. In the heart, aorta and, to a lesser extent, the femoral arteries MAO-A activity was higher in SHR than in WKY. Similarly in the liver the enzyme activity was higher in SHR than in WKY but was due to the -B form of MAO. In all the other tissues studied (duodenum, brain, lungs, adrenals and kidneys) no difference in MAO-A, MAO-B or SSAO activity was found between SHR and WKY, except for the kidneys and brain, if the differences in the weights of these organs in SHR are taken into account.

The deamination of n-pentylamine by monoamine oxidase and a semicarbazide-sensitive amine oxidase of rat heart

n-Pentylamine is deaminated by homogenates of rat heart. Clorgyline inhibition curves at 10 and 100 microM n-pentylamine indicated that this substrate was deaminated by MAO-A, -B and a clorgyline-resistant amine oxidase sensitive to inhibition by semicarbazide. These results have been compared with two other commonly used monoamine substrates, beta-phenethylamine and benzylamine.

Different stereoselective inhibition of monoamine oxidase-B by the R- and S-enantiomers of MD 780236

MD 780236, a selective inhibitor of the B form of MAO behaves as an irreversible inhibitor in in-vitro conditions and mainly as a short-acting inhibitor in ex-vivo experiments. The enantiomer with the R absolute configuration (MD 240928) is fully reversible in ex-vivo conditions, whereas the S-enantiomer (MD 240931) has kept the irreversible component of the inhibition seen with MD 780236. The corresponding racemic alcohol derivative (MD 760548) is also a short-acting inhibitor of the B form of MAO; its S-enantiomer, which has an absolute configuration corresponding to that of MD 240928, has a selectivity towards the B form superior to that of the other enantiomer. The mechanism of the MAO inhibition by MD 780236 is discussed.