The inhibition of hepatic S-3-hydroxy-3-methylglutaryl-CoA reductase by 3,3,5-trimethylcyclohexanol and its mandelic acid ester, cyclandelate

Chemical synthesis of dual-radiolabelled cyclandelate and its metabolism in rat hepatocytes and mouse J774 cells

1. The chemical synthesis of 3,3,5-trimethyl[1-3H]cyclohexanol, 3,3,5-trimethyl[2,3-3H]cyclohexanol and 3,3,5-trimethyl[2,3-3H]cyclohexanyl[1-14C]mandelate (cyclandelate) are described. The ratio of 3H/14C radioactivity in the ester was 27:1. 2. Cultured rat hepatocytes accumulated trimethylcyclohexanol rapidly and excreted its glucuronide into the culture medium. Rat hepatocytes also accumulated cyclandelate rapidly, hydrolysing the ester and excreting trimethylcyclohexanol into the medium. This trimethylcyclohexanol then re-entered the cells and was converted to its glucuronide prior to excretion. 3. In contrast, no hydrolysis of cyclandelate was seen on incubation with J774 cells, a transformed mouse macrophage. 4. Similar differences in hydrolytic activity were seen with microsomal fractions prepared from rat liver and J774 cells. Hepatic microsomes caused a rapid hydrolysis of cyclandelate while no hydrolysis was detectable after incubations of over an hour with J774 microsomes. 5. This difference in hydrolytic activity may have important implications for the action of cyclandelate on cholesterol metabolism in extrahepatic tissues.

Microbial metabolism of mandelate: a microcosm of diversity

This review highlights the diversity of prokaryotic and eukaryotic microorganisms that can metabolise mandelate and it describes how a wide range of compounds related to mandelate is formed in many environments. The chief aspects that are summarised include the various pathways whereby mandelate and its structural analogues are converted into catechol or protocatechuate, the properties of the enzymes that are involved in the pathways, and the regulation and genetics of the pathways. The review incorporates the idea that the study of peripheral metabolic pathways is particularly useful for illuminating evolutionary speculations and it concludes with a list of questions that need to be answered.

Inhibition of cellular cholesterol esterification can decrease low density lipoprotein receptor number in human fibroblasts

In fibroblasts deprived of exogenous cholesterol to induce low density lipoprotein receptors there is a continuing flux of cholesterol esterification. The structurally unrelated inhibitors of acyl-CoA; cholesterol acyl-transferase, progesterone, trimethylcyclohexanyl mandelate and 3-[decyldimethylsilyl]-N-[2-(4-methylphenyl)-1-phenylethyl] propanamide, (58035), could all inhibit this basal rate of esterification within 1h of addition. Exposure of cholesterol-deprived fibroblasts for 17h to progesterone or trimethylcyclohexanyl mandelate caused decreased specific binding and metabolism of low density lipoprotein. The effect was not a direct inhibition of lipoprotein binding; it was time dependent and followed from the reversible inhibition of cholesterol esterification by these two compounds. The irreversible inhibition of esterification by 58035 left the receptor number unaffected. The results indicate that down regulation of low density lipoprotein receptors is initiated by accumulation of cholesterol in a specific intracellular pool. Inhibition of cholesterol esterification by progesterone and trimethylcyclohexanyl mandelate causes accumulation of cholesterol in this pool but 58035 does not.

Cyclandelate versus flunarizine. A double-blind study in a selected group of patients with dementia

A double-blind, double-dummy clinical trial was conducted in which the efficacy of cyclandelate 1600 mg daily was compared with that of flunarizine 10mg daily in 40 patients (25 men and 15 women) with dementia of cerebrovascular origin. Parameters were assessed before treatment, and after 45 and 90 days of therapy. At 90 days, significant improvements were observed in patients given cyclandelate in measurements of P100 latency in the left eye, neurological impairment, dementia scores, ischaemia scores, Gottfries mental deterioration scale, Hamilton depression scores, short term visual memory, long term memory, Bender-Gestalt test and Koh's blocks test. In flunarizine recipients, improvements were observed in neurological impairment, ischaemia scores, Gottfries scale and Hamilton depression scores. Patients treated with cyclandelate showed significantly greater ameliorations in symptoms as assessed by the ischaemia scale, evoked visual potential, visual memory and Koh's block test compared with those given flunarizine. However, in none of the parameters was flunarizine superior to cyclandelate.

Cyclandelate. An inhibitor of cholesterol esterification

In an in vitro study the action of cyclandelate on cholesterol metabolism was investigated. The addition of cyclandelate (100 mumol/L) inhibited the incorporation of acetate into sterol but not into fatty acid in human fibroblasts incubated with the drug for 3 hours. Further exposure of fibroblasts to cyclandelate for 17 hours resulted in a similar inhibition in the uptake and hydrolysis of LDL. Moreover, in the presence of cyclandelate (100 mumol/L), cholesterol esterification was inhibited by 90% in fibroblasts cultured with LDL and in human monocyte derived macrophages cultured with acetyl-LDL. It is likely that the inhibition by cyclandelate of cholesterol esterification in whole cells is due to a direct inhibition of the hepatic microsomal enzyme acyl coenzyme A: cholesterol acyl transferase (ACAT), since addition of the drug in a concentration of 100 mumol/L inhibited by 74% the activity of ACAT derived from rat liver. Furthermore, the intact drug molecule was required for maximal inhibition of microsomal ACAT.

Cyclohexanol and methylcyclohexanols. A family of inhibitors of hepatic HMGCoA reductase in vivo

Oral dosing of rats with cyclohexanol and methylcyclohexanols resulted in the inhibition of hepatic HMGCoA reductase. Neither cyclohexane or cyclohexane diols exerted any effects. Inhibition was not due to alcohol dehydrogenase mediated changes in redox state since 3,3',5-trimethylcyclohexanol (TMC), a non substrate for alcohol dehydrogenase, was a potent inhibitor of HMGCoA reductase. Following a single dose of TMC there was no alteration in total hepatic HMGCoA reductase activity for more than 6 hr after which the enzyme activity was depressed in a dose-dependent manner. The normal diurnal rhythm of HMGCoA reductase was reduced in amplitude following TMC administration but the phase was unaltered and the t 1/2 for activity decay following the peak of activity was unaffected. Prior to the inhibitory effect of a TMC dose becoming apparent in total HMGCoA reductase activity we found that the expressed activity of the enzyme (after isolation in F- medium to suppress endogenous protein phosphatase) was depressed by 43%. The inhibitory effect of TMC on total HMGCoA reductase activity seen 8 hr or more after dosing was reflected by inhibition of sterol synthesis in liver measured in vivo after [3H]-H2O administration.

In vivo inhibition of hepatic lipogenesis in the rat by cyclandelate (3,3',5-trimethylcyclohexanylmandelate)

Rates of hepatic lipogenesis were measured in vivo in rats by incorporation into lipids of [3H] from injected [3H]H2O 17 hr after a single oral dose of cyclandelate (3,3',5-trimethylcyclohexanylmandelate, a vasoactive substance). Cyclandelate administration resulted in a significant inhibition (40-60%) of both sterol and fatty acid synthesis in the livers which was independent of the 3.2-fold diurnal variation in the rates of hepatic sterol and fatty acid synthesis. The inhibition of accumulation of newly synthesized fatty acid in intestine also reached statistical significance. The accumulation of newly synthesized sterol was significantly depressed in serum but did not result in any change in the concentration of serum total cholesterol. These results are interpreted in terms of the inhibitory effect of cyclandelate on hepatic 3-hydroxy-3-methylglutaryl-CoA reductase previously reported by us (Biochem. Pharmac. 32, 649, 1983).