Farnesol-derived dicarboxylic acids in the urine of animals treated with zaragozic acid A or with farnesol

Discovery of Novel 11-Membered Templates as Squalene Synthase Inhibitors

Squalene synthase is one of the most promising pharmaceutical targets to treat hyperlipidemia. Inhibition of the squalene synthase causes a decrease in the hepatic cholesterol concentration. We have already reported the design and synthesis of highly potent benzhydrol-type squalene inhibitors. Although these templates showed unique and potent cyclic active conformations via intramolecular hydrogen bonds, the in vivo cholesterol-lowering efficacy was insufficient. We attempted to improve their potential as an orally active medicine. In our medicinal chemistry effort, cyclized 11-membered ring templates were acquired. The novel series of compounds exhibited potent squalene synthase inhibitory activity, and one of the derivatives, isomer A-(1S, 3R)-14i, showed plasma lipid-lowering efficacy in hamster and marmoset repeated-dose studies. Our findings provide valuable insights into the design and development of novel and unique 11-membered ring-type highly potent squalene synthase inhibitors.

Identification of non-conventional small molecule degraders and stabilizers of squalene synthase

Squalene synthase (SQS) is an essential enzyme in the mevalonate pathway, which controls cholesterol biosynthesis and homeostasis. Although catalytic inhibitors of SQS have been developed, none have been approved for therapeutic use so far. Herein we sought to develop SQS degraders using targeted protein degradation (TPD) to lower overall cellular cholesterol content. We found that KY02111, a small molecule ligand of SQS, selectively causes SQS to degrade in a proteasome-dependent manner. Unexpectedly, compounds based on the same scaffold linked to E3 ligase recruiting ligands led to SQS stabilization. Proteomic analysis found KY02111 to reduce only the levels of SQS, while lipidomic analysis determined that KY02111-induced degradation lowered cellular cholesteryl ester content. Stabilizers shielded SQS from its natural turnover without recruiting their matching E3 ligase or affecting enzymatic target activity. Our work shows that degradation of SQS is possible despite a challenging biological setting and provides the first chemical tools to degrade and stabilize SQS.

UHPLC-DAD Method Development and Validation: Degradation Kinetic, Stress Studies of Farnesol and Characterization of Degradation Products Using LC-QTOF-ESI-MS with in silico Pharmacokinetics and Toxicity Predictions

Farnesol (FAR) is a sesquiterpene molecule with high lipophilicity that has antibacterial and other pharmacological properties along with broad nutritional values with high commercial values. Although having potential, FAR stability behavior and degradation kinetics are not available in the literature. Hence, it is very essential to develop a simple, rapid, accurate, precise, robust, cheap UHPLC-DAD method for FAR. It was also proposed to study mechanistic insights into FAR under different degradation conditions. Therefore, we hypothesized to do systematic stability studies along with degradation kinetic and accelerated stability studies. The developed method was validated. FAR was studied for stress studies, degradation kinetics and ADMET prediction of degradants. Degradation products were characterized using LC-QTOF-ESI-MS. Developed method consists of an isocratic mobile phase with a wavelength of 215 nm. The percent recoveries for FAR were observed within the acceptance limit of 98-102%. The eight major degradation products were formed during stress studies. FAR follows first-order degradation kinetics. FAR and all degradants were found to have more than 75% good human oral absorption, and are non-toxic. FAR UHPLC-DAD method was developed, validated and performed stability studies to know the possible degradation pattern along with degradation kinetic studies.

Roles of Farnesyl-Diphosphate Farnesyltransferase 1 in Tumour and Tumour Microenvironments

Farnesyl-diphosphate farnesyltransferase 1 (FDFT1, squalene synthase), a membrane-associated enzyme, synthesizes squalene via condensation of two molecules of farnesyl pyrophosphate. Accumulating evidence has noted that FDFT1 plays a critical role in cancer, particularly in metabolic reprogramming, cell proliferation, and invasion. Based on these advances in our knowledge, FDFT1 could be a potential target for cancer treatment. This review focuses on the contribution of FDFT1 to the hallmarks of cancer, and further, we discuss the applicability of FDFT1 as a cancer prognostic marker and target for anticancer therapy.

Squalene Synthase Deficiency: Clinical, Biochemical, and Molecular Characterization of a Defect in Cholesterol Biosynthesis

Mendelian disorders of cholesterol biosynthesis typically result in multi-system clinical phenotypes, underlining the importance of cholesterol in embryogenesis and development. FDFT1 encodes for an evolutionarily conserved enzyme, squalene synthase (SS, farnesyl-pyrophosphate farnesyl-transferase 1), which catalyzes the first committed step in cholesterol biosynthesis. We report three individuals with profound developmental delay, brain abnormalities, 2-3 syndactyly of the toes, and facial dysmorphisms, resembling Smith-Lemli-Opitz syndrome, the most common cholesterol biogenesis defect. The metabolite profile in plasma and urine suggested that their defect was at the level of squalene synthase. Whole-exome sequencing was used to identify recessive disease-causing variants in FDFT1. Functional characterization of one variant demonstrated a partial splicing defect and altered promoter and/or enhancer activity, reflecting essential mechanisms for regulating cholesterol biosynthesis/uptake in steady state.

Differential Regulation of Gene Expression by Cholesterol Biosynthesis Inhibitors That Reduce (Pravastatin) or Enhance (Squalestatin 1) Nonsterol Isoprenoid Levels in Primary Cultured Mouse and Rat Hepatocytes

Squalene synthase inhibitors (SSIs), such as squalestatin 1 (SQ1), reduce cholesterol biosynthesis but cause the accumulation of isoprenoids derived from farnesyl pyrophosphate (FPP), which can modulate the activity of nuclear receptors, including the constitutive androstane receptor (CAR), farnesoid X receptor, and peroxisome proliferator-activated receptors (PPARs). In comparison, 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (e.g., pravastatin) inhibit production of both cholesterol and nonsterol isoprenoids. To characterize the effects of isoprenoids on hepatocellular physiology, microarrays were used to compare orthologous gene expression from primary cultured mouse and rat hepatocytes that were treated with either SQ1 or pravastatin. Compared with controls, 47 orthologs were affected by both inhibitors, 90 were affected only by SQ1, and 51 were unique to pravastatin treatment (P < 0.05, ≥1.5-fold change). When the effects of SQ1 and pravastatin were compared directly, 162 orthologs were found to be differentially coregulated between the two treatments. Genes involved in cholesterol and unsaturated fatty acid biosynthesis were up-regulated by both inhibitors, consistent with cholesterol depletion; however, the extent of induction was greater in rat than in mouse hepatocytes. SQ1 induced several orthologs associated with microsomal, peroxisomal, and mitochondrial fatty acid oxidation and repressed orthologs involved in cell cycle regulation. By comparison, pravastatin repressed the expression of orthologs involved in retinol and xenobiotic metabolism. Several of the metabolic genes altered by isoprenoids were inducible by a PPARα agonist, whereas cytochrome P450 isoform 2B was inducible by activators of CAR. Our findings indicate that SSIs uniquely influence cellular lipid metabolism and cell cycle regulation, probably due to FPP catabolism through the farnesol pathway.

Nonsterol Isoprenoids Activate Human Constitutive Androstane Receptor in an Isoform-Selective Manner in Primary Cultured Mouse Hepatocytes

Our laboratory previously reported that accumulation of nonsterol isoprenoids following treatment with the squalene synthase inhibitor, squalestatin 1 (SQ1) markedly induced cytochrome P450 (CYP)2B1 mRNA and reporter activity in primary cultured rat hepatocytes, which was dependent on activation of the constitutive androstane receptor (CAR). The objective of the current study was to evaluate whether isoprenoids likewise activate murine CAR (mCAR) or one or more isoforms of human CAR (hCAR) produced by alternative splicing (SPTV, hCAR2; APYLT, hCAR3). We found that SQ1 significantly induced Cyp2b10 mRNA (∼3.5-fold) in primary hepatocytes isolated from both CAR-wild-type and humanized CAR transgenic mice, whereas the 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor pravastatin had no effect. In the absence of CAR, basal Cyp2b10 mRNA levels were reduced by 28-fold and the effect of SQ1 on Cyp2b10 induction was attenuated. Cotransfection with an expression plasmid for hCAR1, but not hCAR2 or hCAR3, mediated SQ1-induced CYP2B1 and CYP2B6 reporter activation in hepatocytes isolated from CAR-knockout mice. This effect was also observed following treatment with the isoprenoid trans,trans-farnesol. The direct agonist CITCO increased interaction of hCAR1, hCAR2, and hCAR3 with steroid receptor coactivator-1. However, no significant effect on coactivator recruitment was observed with SQ1, suggesting an indirect activation mechanism. Further results from an in vitro ligand binding assay demonstrated that neither farnesol nor other isoprenoids are direct ligands for hCAR1. Collectively, our findings demonstrate that SQ1 activates CYP2B transcriptional responses through farnesol metabolism in an hCAR1-dependent manner. Further, this effect probably occurs through an indirect mechanism.

Role of Phosphatidic Acid Phosphatase Domain Containing 2 in Squalestatin 1-Mediated Activation of the Constitutive Androstane Receptor in Primary Cultured Rat Hepatocytes

Farnesyl pyrophosphate (FPP) is a branch-point intermediate in the mevalonate pathway that is normally converted mainly to squalene by squalene synthase in the first committed step of sterol biosynthesis. Treatment with the squalene synthase inhibitor squalestatin 1 (SQ1) causes accumulation of FPP, its dephosphorylated metabolite farnesol, and several oxidized farnesol-derived metabolites. In addition, SQ1 treatment of primary cultured rat hepatocytes increases CYP2B expression through a mechanism that requires FPP synthesis and activation of the constitutive androstane receptor (CAR). Because direct farnesol treatment also increases CYP2B expression, it seems likely that SQ1-mediated CAR activation requires FPP dephosphorylation to farnesol. The lipid phosphatase, phosphatidic acid phosphatase domain containing 2 (PPAPDC2), was recently reported to catalyze FPP dephosphorylation. We therefore determined the effect of overexpressing or knocking down PPAPDC2 on SQ1-mediated CAR activation in primary cultured rat hepatocytes. Cotransfection of rat hepatocytes with a plasmid expressing rat or human PPAPDC2 enhanced SQ1-mediated activation of a CAR-responsive reporter by 1.7- or 2.4-fold over the SQ1-mediated activation that was produced when hepatocytes were cotransfected with empty expression plasmid. Similarly, transduction of rat hepatocytes with a recombinant adenovirus expressing PPAPDC2 enhanced SQ1-mediated CYP2B1 mRNA induction by 1.4-fold over the induction that was seen in hepatocytes transduced with control adenovirus. Cotransfection with a short hairpin RNA targeting PPAPDC2 reduced SQ1-mediated CAR activation by approximately 80% relative to the activation that occurred in hepatocytes transfected with nontargeting short hairpin RNA. These results indicate that PPAPDC2 plays an important role in SQ1-mediated CAR activation, most likely by catalyzing the conversion of FPP to farnesol.

Statins inhibit blastocyst formation by preventing geranylgeranylation

STUDY HYPOTHESIS

Statins, inhibitors of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase of the mevalonate pathway and prescription drugs that treat hypercholesterolemia, compromise preimplantation mouse development via modulation of HIPPO signaling.

STUDY FINDING

HMG-CoA reductase activity is required for trophectoderm specification, namely blastocyst cavity formation and Yes-associated protein (YAP) nuclear localization, through the production of isoprenoid geranylgeranyl pyrophosphate (GGPP) and the action of geranylgeranyl transferase.

WHAT IS KNOWN ALREADY

Previous studies have shown that treatment of mouse embryos with mevastatin prevents blastocyst formation, but how HMG-CoA reductase is involved in preimplantation development is unknown. HIPPO signaling regulates specification of the trophectoderm lineage of the mouse blastocyst by controlling the nuclear localization of YAP. In human cell lines, the mevalonate pathway regulates YAP to mediate self-renewal and survival through geranylgeranylation of RHO proteins. These studies suggest that in preimplantation development, statins may act through HIPPO pathway to interfere with trophectoderm specification and thereby inhibit blastocyst formation.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Eight-cell stage (E2.5) mouse embryos were treated in hanging drop culture with chemical agents, namely statins (lovastatin, atorvastatin, cerivastatin and pravastatin), mevalonic acid (MVA), cholesterol, squalene, farnesyl pyrophosphate (FPP), geranylgeranyl pyrophosphate (GGPP), geranylgeranyltransferase inhibitor GGTI-298, RHO inhibitor I, and squalene synthase inhibitor YM-53601, up to the late blastocyst stage (E4.5). Efficiency of blastocyst formation was assessed based on gross morphology and the measurement of the cavity size using an image analysis software. Effects on cell lineages and HIPPO signaling were analyzed using immunohistochemistry with confocal microscopy based on the expression patterns of the lineage-specific markers and the nuclear accumulation of YAP. Effects on cell lineages were also examined by quantitative RT-PCR based on the transcript levels of the lineage-specific marker genes. Data were analyzed using one-way ANOVA and two-sample t-test.

MAIN RESULTS AND THE ROLE OF CHANCE

All four statins examined inhibited blastocyst formation. The adverse impact of statins was rescued by supplementation of MVA (P < 0.01) or GGPP (P < 0.01) but not squalene nor cholesterol. Blastocyst formation was also prevented by GGTI-298 (P < 0.01). These results indicate that HMG-CoA reductase activity is required for blastocyst formation mainly through the production of GGPP but not cholesterol. Inhibition of RHO proteins, known targets of geranylgeranylation, impaired blastocyst formation, which was not reversed by GGPP supplementation. Nuclear localization of YAP was diminished by statin treatment but fully restored by supplementation of MVA (P < 0.01) or GGPP (P < 0.01). This suggests that HIPPO signaling is regulated by GGPP-dependent mechanisms, possibly geranylgeranylation of RHO, to enable trophectoderm formation. YM-53601 prevented blastocyst formation (P < 0.01), but its adverse impact was not rescued by supplementation of squalene or cholesterol, suggesting that squalene synthesis inhibition was not the cause of blastocyst defects.

LIMITATIONS, REASONS FOR CAUTION

Analyses were conducted on embryos cultured ex vivo, but they enable the determination of specific concentrations that impair embryo development which can be compared with drug concentrations in the reproductive tract when testing in vivo impact of statins through animal experimentations. Also, analyses were conducted in only one species, the mouse. Epidemiological studies on the effects of various types of statins on the fertility of women are necessary.

WIDER IMPLICATIONS OF THE FINDINGS

Our study reveals how the mevalonate pathway is required for blastocyst formation and intersects with HIPPO pathway to provide a mechanistic basis for the embryotoxic effect of statins. This bears relevance for women who are taking statins while trying to conceive, since statins have potential to prevent the conceptus from reaching the blastocyst stage and to cause early conceptus demise.

LARGE SCALE DATA

Not applicable.

STUDY FUNDING AND COMPETING INTERESTS

This study was supported by grants from the George F. Straub Trust of the Hawaii Community Foundation (13ADVC-60315 to V.B.A.) and the National Institutes of Health, USA (P20GM103457 to V.B.A.). The authors have no conflict of interest to declare.

Transcriptional Regulation of Cytosolic Sulfotransferase 1C2 by Intermediates of the Cholesterol Biosynthetic Pathway in Primary Cultured Rat Hepatocytes

Cytosolic sulfotransferase 1C2 (SULT1C2) is expressed in the kidney, stomach, and liver of rats; however, the mechanisms regulating expression of this enzyme are not known. We evaluated transcriptional regulation of SULT1C2 by mevalonate (MVA)-derived intermediates in primary cultured rat hepatocytes using several cholesterol synthesis inhibitors. Blocking production of mevalonate with the 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor pravastatin (30 μM), reduced SULT1C2 mRNA content by ∼40% whereas the squalene synthase inhibitor squalestatin (SQ1, 0.1 μM), which causes accumulation of nonsterol isoprenoids, increased mRNA content by 4-fold. Treatment with MVA (10 mM) strongly induced SULT1C2 mRNA by 12-fold, and this effect was blocked by inhibiting squalene epoxidase but not by more distal cholesterol inhibitors, indicating the effects of MVA are mediated by postsqualene metabolites. Using rapid amplification of cDNA ends (RACE), we characterized the 5' end of SULT1C2 mRNA and used this information to generate constructs for promoter analysis. SQ1 and MVA increased reporter activity by ∼1.6- and 3-fold, respectively, from a construct beginning 49 base pairs (bp) upstream from the longest 5'-RACE product (-3140:-49). Sequence deletions from this construct revealed a hepatocyte nuclear factor 1 (HNF1) element (-2558), and mutation of this element reduced basal (75%) and MVA-induced (30%) reporter activity and attenuated promoter activation following overexpression of HNF1α or 1β. However, the effects of SQ1 were localized to a more proximal promoter region (-281:-49). Collectively, our findings demonstrate that cholesterol biosynthetic intermediates influence SULT1C2 expression in rat primary hepatocytes. Further, HNF1 appears to play an important role in mediating basal and MVA-induced SULT1C2 transcription.

Discovery of DF-461, a Potent Squalene Synthase Inhibitor

We report the development of a new trifluoromethyltriazolobenzoxazepine series of squalene synthase inhibitors. Structure-activity studies and pharmacokinetics optimization on this series led to the identification of compound 23 (DF-461), which exhibited potent squalene synthase inhibitory activity, high hepatic selectivity, excellent rat hepatic cholesterol synthesis inhibitory activity, and plasma lipid lowering efficacy in nonrodent repeated dose studies.

A novel bisphosphonate inhibitor of squalene synthase combined with a statin or a nitrogenous bisphosphonate in vitro

Statins and nitrogenous bisphosphonates (NBP) inhibit 3-hydroxy-3-methylglutaryl-coenzyme-A reductase (HMGCR) and farnesyl diphosphate synthase (FDPS), respectively, leading to depletion of farnesyl diphosphate (FPP) and disruption of protein prenylation. Squalene synthase (SQS) utilizes FPP in the first committed step from the mevalonate pathway toward cholesterol biosynthesis. Herein, we have identified novel bisphosphonates as potent and specific inhibitors of SQS, including the tetrasodium salt of 9-biphenyl-4,8-dimethyl-nona-3,7-dienyl-1,1-bisphosphonic acid (compound 5). Compound 5 reduced cholesterol biosynthesis and lead to a substantial intracellular accumulation of FPP without reducing cell viability in HepG2 cells. At high concentrations, lovastatin and zoledronate impaired protein prenylation and decreased cell viability, which limits their potential use for cholesterol depletion. When combined with lovastatin, compound 5 prevented lovastatin-induced FPP depletion and impairment of protein farnesylation. Compound 5 in combination with the NBP zoledronate completely prevented zoledronate-induced impairment of both protein farnesylation and geranylgeranylation. Cotreatment of cells with compound 5 and either lovastatin or zoledronate was able to significantly prevent the reduction of cell viability caused by lovastatin or zoledronate alone. The combination of an SQS inhibitor with an HMGCR or FDPS inhibitor provides a rational approach for reducing cholesterol synthesis while preventing nonsterol isoprenoid depletion.

Molecular pathways and agents for lowering LDL-cholesterol in addition to statins

Recent guidelines in North America and Europe recommend lowering low density lipoprotein associated cholesterol (LDLC) to achieve optimal coronary heart disease risk reduction. Statins have been the therapy of choice and proven successful and relatively safe. However, we are now facing new challenges and it appears that additional or alternative drugs are urgently needed. This boosts research in the field, reopening old cases like other inhibitors of cholesterol synthesis or making attractive tools from the latest technologies like gene silencing by anti-sense oligonucleotides. LDLs are cholesterol-enriched lipoproteins stabilized by the hepatic apolipoprotein B100, and derived from TG rich very low density lipoprotein. This review focuses on the molecular pathways involved in plasma LDLC production and elimination, in particular cholesterol absorption and the hepatobiliary route, apoB100 and VLDL production, and LDL clearance via the LDL receptor. We will identify important or rate-limiting proteins (including Niemann-Pick C1-like 1 (NPC1L1), microsomal TG transfer protein (MTP), acyl-coenzyme A/cholesterol acyltransferase (ACAT), Acyl-CoA:diacylglycerol acyltransferases 2 (DGAT2), proprotein convertase subtilisin kexin type 9 (PCSK9)), and nuclear receptors (farnesoid X receptor (FXR), thyroid hormone receptor (TR)) that constitute interesting therapeutic targets. Numerous compounds already in use modulate these pathways, such as phytosterols, ezetimibe, bile acids sequestrants, niacin, and fibrates. Many pathways can be considered to lower LDLC, but the road has been paved with disappointments and difficulties. With new targets identified and diversification of the drugs, a new era for better LDLC management is plausible.

Farnesylcysteine lyase is involved in negative regulation of abscisic acid signaling in Arabidopsis

The Arabidopsis FCLY gene encodes a specific farnesylcysteine (FC) lyase, which is responsible for the oxidative metabolism of FC to farnesal and cysteine. In addition, fcly mutants with quantitative decreases in FC lyase activity exhibit an enhanced response to ABA. However, the enzymological properties of the FCLY-encoded enzyme and its precise role in ABA signaling remain unclear. Here, we show that recombinant Arabidopsis FC lyase expressed in insect cells exhibits high selectivity for FC as a substrate and requires FAD and molecular oxygen for activity. Arabidopsis FC lyase is also shown to undergo post-translational N-glycosylation. FC, which is a competitive inhibitor of isoprenylcysteine methyltransferase (ICMT), accumulates in fcly mutants. Moreover, the enhanced response of fcly mutants to ABA is reversed by ICMT overexpression. These observations support the hypothesis that the ABA hypersensitive phenotype of fcly plants is the result of FC accumulation and inhibition of ICMT.

Pharmacologic inhibition of squalene synthase and other downstream enzymes of the cholesterol synthesis pathway: a new therapeutic approach to treatment of hypercholesterolemia

Hypercholesterolemia is a major risk factor for the development of atherosclerotic vascular diseases. The most popular agents for cholesterol reduction are the statin drugs, which are competitive inhibitors of hydroxymethylglutaryl-coenzyme A (HMG-CoA) reductase, the primary rate-limiting enzyme in the hepatic biosynthesis of cholesterol. Although relatively safe and effective, the available statins can cause elevations in liver enzymes and myopathy. Squalene synthase is another enzyme that is downstream to HMG-CoA reductase in the cholesterol synthesis pathway and modulates the first committed step of hepatic cholesterol biosynthesis at the final branch point of the cholesterol biosynthetic pathway. Squalene epoxidase and oxidosqualene cyclase are other enzymes that act distally to squalene synthase. Pharmacologic inhibitors of these downstream enzymes have been developed, which may reduce low-density lipoprotein cholesterol and reduce the myopathy side effect seen with upstream inhibition of HMG-CoA. At this juncture, one squalene synthase inhibitor, lapaquistat (TAK-475) is in active clinical trials as a monotherapy, but there have been suggestions of increased hepatotoxicity with the drug.

Other therapies for reducing low-density lipoprotein cholesterol: medications in development

Although the past 30 years have been fruitful and productive in lipid research, from basic science to drug development to demonstration of clinical benefit, cardiovascular disease remains the major cause of mortality and morbidity in industrialized societies. With the rapid industrialization of countries, such as India and China, cardiovascular disease rapidly is becoming the leading cause of global death and disability. Although most of the effective lipid-lowering drugs, the statins, have become generic and inexpensive, there remains a need for effective and safe agents. Hopefully, some of those discussed in this article will fill that need.

Suppression of CYP2B induction by alendronate-mediated farnesyl diphosphate synthase inhibition in primary cultured rat hepatocytes

We previously reported that squalestatin 1-mediated induction of CYP2B expression is attributable to squalene synthase inhibition and accumulation of an endogenous isoprenoid(s) that is capable of activating the constitutive androstane receptor. To determine whether squalestatin 1-mediated CYP2B induction is strictly dependent on the biosynthesis of farnesyl pyrophosphate (FPP), the substrate for squalene synthase, the effects of alendronate, a nitrogen-containing bisphosphonate inhibitor of farnesyl diphosphate synthase, on basal, squalestatin 1-inducible, and phenobarbital-inducible CYP2B expression in primary cultured rat hepatocytes were assessed. Alendronate treatment alone had no effect on CYP2B or CYP3A mRNA expression in the hepatocyte cultures, but alendronate cotreatment completely suppressed squalestatin 1-mediated CYP2B mRNA induction at concentrations (60 and 100 microM) that effectively inhibited cellular farnesyl diphosphate synthase activity, as assessed by reductions of squalestatin 1-mediated FPP accumulation, and that were not toxic to the cells, as indicated by a lack of effect on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide activity. Alendronate cotreatment also partially suppressed phenobarbital-inducible CYP2B expression, and this suppressive effect was attenuated by additional cotreatment with the upstream pathway inhibitor, pravastatin. These findings not only demonstrate that squalestatin 1-mediated CYP2B induction cannot occur in the absence of FPP biosynthesis but also indicate that one or more upstream isoprenoids, possibly isopentenyl pyrophosphate and/or dimethylallyl pyrophosphate, function to antagonize the CYP2B induction process.

Accumulation of prenyl alcohols by terpenoid biosynthesis inhibitors in various microorganisms

Squalene synthase inhibitors significantly accelerate the production of farnesol by various microorganisms. However, farnesol production by Saccharomyces cerevisiae ATCC 64031, in which the squalene synthase gene is deleted, was not affected by the inhibitors, indicating that farnesol accumulation is enhanced in the absence of squalene synthase activity. The combination of diphenylamine as an inhibitor of carotenoid biosynthesis and a squalene synthase inhibitor increases geranylgeraniol production by a yeast, Rhodotorula rubra NBRC 0870. An ent-kauren synthase inhibitor also enhances the production of farnesol and geranylgeraniol by a filamentous fungus, Gibberella fujikuroi NBRC 30336. These results indicate that the inhibition of downstream enzymes from prenyl diphosphate synthase leads to the production of farnesol and geranylgeraniol.

Quinuclidine derivatives as potential antiparasitics

There is an urgent need for the development of new drugs for the treatment of tropical parasitic diseases such as Chagas' disease and leishmaniasis. One potential drug target in the organisms that cause these diseases is sterol biosynthesis. This paper describes the design and synthesis of quinuclidine derivatives as potential inhibitors of a key enzyme in sterol biosynthesis, squalene synthase (SQS). A number of compounds that were inhibitors of the recombinant Leishmania major SQS at submicromolar concentrations were discovered. Some of these compounds were also selective for the parasite enzyme rather than the homologous human enzyme. The compounds inhibited the growth of and sterol biosynthesis in Leishmania parasites. In addition, we identified other quinuclidine derivatives that inhibit the growth of Trypanosoma brucei (the causative organism of human African trypanosomiasis) and Plasmodium falciparum (a causative agent of malaria), but through an unknown mode(s) of action.

Arabidopsis thaliana plants possess a specific farnesylcysteine lyase that is involved in detoxification and recycling of farnesylcysteine

In plants, prenylated proteins are involved in actin organization, calcium-mediated signal transduction, and many other biological processes. Arabidopsis thaliana mutants lacking functional protein prenyltransferase genes have also revealed roles for prenylated proteins in phytohormone signaling and meristem development. However, to date, the turnover of prenylated plant proteins and the fate of the prenylcysteine (PC) residue have not been described. We have detected an enzyme activity in Arabidopsis plants that metabolizes farnesylcysteine (FC) to farnesal, which is subsequently reduced to farnesol. Unlike its mammalian ortholog, Arabidopsis FC lyase exhibits specificity for FC over geranylgeranylcysteine (GGC), and recognizes N-acetyl-FC (AFC). FC lyase is encoded by a gene on chromosome 5 of the Arabidopsis genome (FCLY, At5g63910) and is ubiquitously expressed in Arabidopsis tissues and organs. Furthermore, T-DNA insertions into the FCLY gene cause significant decreases in FC lyase activity and an enhanced response to abscisic acid (ABA) in seed germination assays. The effects of FCLY mutations on ABA sensitivity are even greater in the presence of exogenous FC. These data suggest that plants possess a specific FC detoxification and recycling pathway.

Effect of farnesol on a mouse model of systemic candidiasis, determined by use of a DPP3 knockout mutant of Candida albicans

This work extends our previous observation that the fungus Candida albicans secretes micromolar levels of farnesol and that accumulation of farnesol in vitro prevents the yeast-to-mycelium conversion in a quorum-sensing manner. What does farnesol do in vivo? The purpose of this study was to determine the role of farnesol during infection with a well-established mouse model of systemic candidiasis with C. albicans A72 administered by tail vein injection. This question was addressed by altering both endogenous and exogenous farnesol. For endogenous farnesol, we created a knockout mutation in DPP3, the gene encoding a phosphatase which converts farnesyl pyrophosphate to farnesol. This mutant (KWN2) produced six times less farnesol and was ca. 4.2 times less pathogenic than its SN152 parent. The strain with DPP3 reconstituted (KWN4) regained both its farnesol production levels and pathogenicity. These mutants (KWN1 to KWN4) retained their full dimorphic capability. With regard to exogenous farnesol, farnesol was administered either intraperitoneally (i.p.) or orally in the drinking water. Mice receiving C. albicans intravenously and farnesol (20 mM) orally had enhanced mortality (P < 0.03). Similarly, mice (n = 40) injected with 1.0 ml of 20 mM farnesol i.p. had enhanced mortality (P < 0.03), and the onset of mortality was 30 h sooner than for mice which received a control injection without farnesol. The effect of i.p. farnesol was more pronounced (P < 0.04) when mice were inoculated with a sublethal dose of C. albicans. These mice started to die 4 days earlier, and the percent survival on day 6 postinoculation (p.i.) was five times lower than for mice receiving C. albicans with control i.p. injections. In all experiments, mice administered farnesol alone or Tween 80 alone remained normal throughout a 14-day observation period. Finally, beginning at 12 h p.i., higher numbers of C. albicans cells were detected in kidneys from mice receiving i.p. farnesol than in those from mice receiving control i.p. injections. Thus, reduced endogenous farnesol decreased virulence, while providing exogenous farnesol increased virulence. Taken together, these data suggest that farnesol may play a role in disease pathogenesis, either directly or indirectly, and thus may represent a newly identified virulence factor.

Manipulation of isoprenoid biosynthesis as a possible therapeutic option in mevalonate kinase deficiency

OBJECTIVE

In cells from patients with the autoinflammatory disorder mevalonate kinase (MK) deficiency, which includes the hyperimmunoglobulin D with periodic fever syndrome, MK becomes the rate-limiting enzyme in the isoprenoid biosynthesis pathway. This suggests that up-regulation of residual MK activity in these patients could be a way in which to prevent or alleviate the associated symptoms. We studied the effect of 2 specific inhibitors of isoprenoid biosynthetic enzymes on the residual activity of MK in cells from patients with MK deficiency.

METHODS

Skin fibroblasts from MK-deficient patients and from controls were cultured for 7 days with either simvastatin, an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, or zaragozic acid A, an inhibitor of squalene synthase. Following culture, MK activity, MK protein levels, MVK messenger RNA levels, and the effect on the pathway flux toward non-sterol isoprenoid biosynthesis were determined.

RESULTS

Treatment of the fibroblasts with either of the inhibitors led to a marked increase in residual MK enzyme activity, which was largely attributable to increased MVK gene transcription. This effect was even more pronounced when the cells were cultured in lipoprotein-depleted medium. The flux toward nonsterol isoprenoid end-product synthesis was reduced when cells were treated with simvastatin but was partly restored by concomitant treatment with zaragozic acid A.

CONCLUSION

Our results indicate that manipulations of the isoprenoid biosynthesis pathway that promote the synthesis of nonsterol isoprenoids may provide an interesting therapeutic option for the treatment of MK deficiency.

The chemistry of exploding ants, Camponotus spp. (cylindricus complex)

A detailed comparative analysis of the exocrine chemistry of nine Bruneian Camponotus species in the cylindricus complex is reported. Workers of these species are known to have hypertrophied mandibular glands and release their glandular contents suicidally from the head by rupturing the intersegmental membrane of the gaster. All of the species produce mixtures of polyacetate-derived aromatics, including hydroxyacetophenones, which display pH-dependent color changes, and aliphatic hydrocarbons and alcohols. In addition, three species contained (6R)-2,6-dimethyl-(2E)-octen-1,8-dioic acid (9) or (3S)-8-hydroxycitro-nellic acid (10a), previously unreported from insects. These compounds were characterized from their spectral data, and confirmed by comparison with synthetic samples. The allomonal role of these compounds is based on numerous field observations, and their chemotaxonomic value is presented.

ω-Hydroxylation of farnesol by mammalian cytochromes P450

Studies have shown that mammalian cytochromes p450 participate in the metabolism of terpenes, yet their role in the biotransformation of farnesol, an endogenous 15-carbon isoprenol, is unknown. In this report, [(14)C]-farnesol was transformed to more polar metabolites by NADPH-supplemented mammalian microsomes. In experiments with microsomes isolated from acetone-treated animals, the production of one polar metabolite was induced, suggesting catalysis by CYP2E1. The metabolite was identified as (2E, 6E, 10E)-12-hydroxyfarnesol. In studies with purified CYP2E1, 12-hydroxyfarnesol was obtained as the major product of farnesol metabolism. Among a series of available human p450 enzymes, only CYP2C19 also produced 12-hydroxyfarnesol. However, in individual human microsomes, CYP2E1 was calculated to contribute up to 62% toward total 12-hydroxyfarnesol production, suggesting CYP2E1 as the major catalyst. Mammalian cells expressing CYP2E1 demonstrated further farnesol metabolism to alpha,omega-prenyl dicarboxylic acids. Since such acids were identified in animal urine, the data suggest that CYP2E1 could be an important regulator of farnesol homeostasis in vivo. In addition, CYP2E1-dependent 12-hydroxyfarnesol formation was inhibited by pharmacological alcohol levels. Given that farnesol is a signaling molecule implicated in the regulation of tissue and cell processes, the biological activity of ethanol may be mediated in part by interaction with CYP2E1-dependent farnesol metabolism.

Isoprenoids: Remarkable diversity of form and function

The isoprenoid biosynthetic pathway is the source of a wide array of products. The pathway has been highly conserved throughout evolution, and isoprenoids are some of the most ancient biomolecules ever identified, playing key roles in many life forms. In this review we focus on C-10 mono-, C-15 sesqui-, and C-20 diterpenes. Evidence for interconversion between the pathway intermediates farnesyl pyrophosphate and geranylgeranyl pyrophosphate and their respective metabolites is examined. The diverse functions of these molecules are discussed in detail, including their ability to regulate expression of the beta-HMG-CoA reductase and Ras-related proteins. Additional topics include the mechanisms underlying the apoptotic effects of select isoprenoids, antiulcer activities, and the disposition and degradation of isoprenoids in the environment. Finally, the significance of pharmacological manipulation of the isoprenoid pathway and clinical correlations are discussed.

Farnesyl-O-acetylhydroquinone and geranyl-O-acetylhydroquinone suppress the proliferation of murine B16 melanoma cells, human prostate and colon adenocarcinoma cells, human lung carcinoma cells, and human leukemia cells

Farnesyl-O-acetylhydroquinone (IC(50)=2.5 microM/l) suppressed the proliferation of murine B16F10 melanoma cells with a potency much greater than those of farnesol (IC(50)=45 microM/l) and farnesyl anthranilate (IC(50)=46 microM/l), its alcohol, and ester counterparts with proven anti-tumor activities in vivo. Geranyl-O-acetylhydroquinone (IC(50)=5.1 microM/l) also had a much-improved activity compared to geraniol (IC(50)=160 microM/l) and geranyl anthranilate (IC(50)=30 microM/l). The suppression by farnesyl-O-acetylhydroquinone was concentration- and time-dependent and was accompanied by arrest of cell cycle at G1 and G2/M phases as shown by flow cytometry. Farnesyl-O-acetylhydroquinone and lovastatin had additive impact on B16 cell proliferation. Farnesyl-O-acetylhydroquinone also suppressed the proliferations of human cancer cells HL-60, DU145, PC-3, LNCaP, Caco-2, and A549. Our results suggested that farnesyl derivatives, suppressors of tumor 3-hydroxy-3-methylglutaryl coenzyme A reductase activities, have potential as chemopreventive or chemotherapeutic agents.

Lipid-lowering properties of TAK-475, a squalene synthase inhibitor, in vivo and in vitro

1. Squalene synthase is the enzyme that converts farnesyl pyrophosphate to squalene in the cholesterol biosynthesis pathway. We examined the lipid-lowering properties of 1-[[(3R,5S)-1-(3-acetoxy-2,2-dimethylpropyl)-7-chloro-5-(2,3-dimethoxyphenyl)-2-oxo-1,2,3,5-tetrahydro-4,1-benzoxazepin-3-yl]acetyl]piperidine-4-acetic acid (TAK-475), a novel squalene synthase inhibitor. 2. TAK-475 inhibited hepatic cholesterol biosynthesis in rats (ED(50), 2.9 mg kg(-1)) and showed lipid-lowering effects in beagle dogs, marmosets, cynomolgus monkeys and Wistar fatty rats. 3. In marmosets, TAK-475 (30, 100 mg kg(-1), p.o., for 4 days) lowered both plasma non-high-density lipoprotein (HDL) cholesterol and triglyceride, but did not affect plasma HDL cholesterol. On the other hand, atorvastatin (10, 30 mg kg(-1), p.o., for 4 days) lowered the levels of all these lipids. A correlation between decrease in triglyceride and increase in HDL cholesterol was observed, and TAK-475 increased HDL cholesterol with a smaller decrease in triglyceride than did atorvastatin. 4. TAK-475 (60 mg kg(-1), p.o., for 15 days) suppressed the rate of triglyceride secretion from the liver in hypertriglyceridemic Wistar fatty rats, which show an enhanced triglyceride secretion rate from the liver compared with their lean littermates. 5. In HepG2 cells, TAK-475 and its pharmacologically active metabolite, T-91485, increased the binding of (125)I-low-density lipoprotein (LDL) to LDL receptors. 6. These results suggest that TAK-475 has clear hypolipidemic effects in animals via inhibition of hepatic triglyceride secretion and upregulation of LDL receptors, and that TAK-475 might increase HDL cholesterol by decreasing triglyceride. Thus, TAK-475 is expected to be useful for the treatment of dyslipidemia.

Farnesol biosynthesis in Candida albicans: cellular response to sterol inhibition by zaragozic acid B

The dimorphic fungus Candida albicans produces farnesol as a quorum-sensing molecule that regulates cellular morphology. The biosynthetic origin of farnesol has been resolved by treating these cells with zaragozic acid B, a potent inhibitor of squalene synthase in the sterol biosynthetic pathway. Treatment with zaragozic acid B leads to an eightfold increase in the amount of farnesol produced by C. albicans. Furthermore, C. albicans cell extracts contain enzymatic activity to convert [(3)H]farnesyl pyrophosphate to [(3)H]farnesol. Many common antifungal antibiotics (e.g., zaragozic acids, azoles, and allylamines) target steps in sterol biosynthesis. We suggest that the fungicidal activity of zaragozic acid derives in large part from the accumulation of farnesol that accompanies the inhibition of sterol biosynthesis.

Squalene synthase inhibitors suppress triglyceride biosynthesis through the farnesol pathway in rat hepatocytes

We recently demonstrated that squalene synthase (SQS) inhibitors reduce plasma triglyceride through an LDL receptor-independent mechanism in Watanabe heritable hyperlipidemic rabbits (Hiyoshi et al. 2001. Eur. J. Pharmacol. 431: 345-352). The present study deals with the mechanism of the inhibition of triglyceride biosynthesis by the SQS inhibitors ER-27856 and RPR-107393 in rat primary cultured hepatocytes. Atorvastatin, an HMG-CoA reductase inhibitor, had no effect on triglyceride biosynthesis, but reversed the inhibitory effect of the SQS inhibitors. A squalene epoxidase inhibitor, NB-598, affected neither triglyceride biosynthesis nor its inhibition by ER-27856 and RPR-107393. The reduction of triglyceride biosynthesis by ER-27856 and RPR-107393 was potentiated by mevalonolactone supplementation. Treatment of hepatocytes with farnesol and its derivatives reduced triglyceride biosynthesis. In addition, we found that ER-27856 and RPR-107393 significantly reduced the incorporation of [1-(14)C]acetic acid into oleic acid, but not the incorporation of [1-(14)C]oleic acid into triglyceride. Though ER-27856 and RPR-107393 increased mitochondrial fatty acid beta-oxidation, the inhibition of beta-oxidation by RS-etomoxir had little effect on their inhibition of triglyceride biosynthesis. These results suggest that SQS inhibitors reduce triglyceride biosynthesis by suppressing fatty acid biosynthesis via an increase in intracellular farnesol and its derivatives.

Squalestatin 1-inducible expression of rat CYP2B: evidence that an endogenous isoprenoid is an activator of the constitutive androstane receptor

Because our previous studies indicated that squalestatin 1 treatment induces CYP2B expression in primary cultures of rat hepatocytes as a direct consequence of squalene synthase inhibition, we investigated possible underlying mechanisms. Cotransfection of cultured Sprague-Dawley male rat hepatocytes with each of the three sterol regulatory element binding protein (SREBP) transcription factors failed to induce luciferase expression from a squalestatin 1-responsive CYP2B1 reporter plasmid. Squalestatin 1 treatment of primary hepatocyte cultures from male Wistar-Kyoto rats produced a greater induction of CYP2B mRNA than occurred in cultures from female rats, consistent with the previously demonstrated response dimorphism that has been attributed to differences in constitutive androstane receptor (CAR) levels. Cotransfection of female Wistar-Kyoto rat hepatocyte cultures with plasmid expressing either mouse or rat CAR restored squalestatin 1-inducible CYP2B1-reporter expression. Cotransfection of Sprague-Dawley rat hepatocyte cultures with plasmid expressing rat CAR lacking the C-terminal AF-2 subdomain inhibited squalestatin 1-inducible CYP2B1-reporter expression. Squalestatin 1-mediated CYP2B mRNA induction in rat hepatocyte cultures was completely abolished by pretreatment with the 3-hydroxymethyl-3-glutaryl CoA reductase inhibitor pravastatin and was rescued by mevalonate supplementation, whereas phenobarbital-mediated induction was unaffected by these treatments. Finally, direct addition of trans,trans-farnesol to the culture medium caused the rapid induction of CYP2B mRNA. These results indicate that squalestatin 1 treatment induces CYP2B expression, not by inhibiting sterol synthesis and activating SREBPs, but by evoking the accumulation of an endogenous isoprenoid and activating CAR.

Volatile isoprenoid constituents of fruits, vegetables and herbs cumulatively suppress the proliferation of murine B16 melanoma and human HL-60 leukemia cells

Substantial evidence from epidemiological studies supports the inverse association between the intake of fruits, vegetables and other plant products and cancer incidence. Cancer-preventive constituents of fruits and vegetables may inhibit carcinogen activation, enhance carcinogen detoxification, prevent carcinogens from interacting with critical target sites, or impede tumor progression. These activities, however, are achievable only when levels of individual bioactive constituents reach beyond those attainable from a normal balanced diet. Isoprenoids, a broad class of mevalonate-derived phytochemicals ubiquitous in the plant kingdom, suppress the proliferation of tumor cells and the growth of implanted tumors. A search for volatile isoprenoid constituents of food products spanning seven plant families identified 179 isoprenoids. Of these, 41 purchased from commercial sources were screened for efficacy in suppressing the proliferation of murine B16 melanoma cells. Individual isoprenoids suppressed the proliferation of B16 and HL-60 promyelocytic leukemia cells with varying degrees of potency. Cell cycle arrest at the G(0)-G(1) phase and apoptosis account, at least in part, for the suppression. Blends of isoprenoids suppressed B16 and HL-60 cell proliferation with efficacies equal to the sum of the individual impacts. These findings suggest that the cancer-protective property of fruits, vegetables, and related products is partly conferred by the cumulative impact of volatile isoprenoid constituents.

Genetic disorders of cholesterol biosynthesis in mice and humans

Over the past few years, the number of identified inborn errors of cholesterol biosynthesis has increased significantly. The first inborn error of cholesterol biosynthesis to be characterized, in the mid 1980s, was mevalonic aciduria. In 1993, Irons et al. ( 1 ) (M. Irons, E. R. Elias, G. Salen, G. S. Tint, and A. K. Batta, Lancet 341:1414, 1993) reported that Smith-Lemli-Opitz syndrome, a classic autosomal recessive malformation syndrome, was due to an inborn error of cholesterol biosynthesis. This was the first inborn error of postsqualene cholesterol biosynthesis to be identified, and subsequently additional inborn errors of postsqualene cholesterol biosynthesis have been characterized to various extent. To date, eight inborn errors of cholesterol metabolism have been described in human patients or in mutant mice. The enzymatic steps impaired in these inborn errors of metabolism include mevolonate kinase (mevalonic aciduria as well as hyperimmunoglobulinemia D and periodic fever syndrome), squalene synthase (Ss-/- mouse), 3beta-hydroxysteroid Delta14-reductase (hydrops-ectopic calcification-moth-eaten skeletal dysplasia), 3beta-hydroxysteroid dehydrogenase (CHILD syndrome, bare patches mouse, and striated mouse), 3beta-hydroxysteroid Delta8,Delta7-isomerase (X-linked dominant chondrodysplasia punctata type 2, CHILD syndrome, and tattered mouse), 3beta-hydroxysteroid Delta24-reductase (desmosterolosis) and 3beta-hydroxysteroid Delta7-reductase (RSH/Smith-Lemli-Opitz syndrome and Dhcr7-/- mouse). Identification of the genetic and biochemical defects which give rise to these syndromes has provided the first step in understanding the pathophysiological processes which underlie these malformation syndromes.

Farnesol oxidation in insects: evidence that the biosynthesis of insect juvenile hormone is mediated by a specific alcohol oxidase

The oxidation of farnesol to farnesoic acid is a key step in insect juvenile hormone biosynthesis. We herein present preliminary characterization of the enzyme-catalyzed oxidation of farnesol to farnesal in larval corpora allata homogenates of the tobacco hornworm, Manduca sexta. This conversion, which is highly substrate specific, has a K(m) apparent of 1 microM and a pH optimum between 6 and 7. Results from chemical modification experiments indicate that the enzyme possesses an active site tyrosine residue. Although farnesol oxidation in adult M. sexta corpora allata homogenates was previously identified as being catalyzed by a dehydrogenase, the corresponding conversion in larvae is not effected by the addition of nicotinamide cofactors. Instead, enzymatic activity is slightly enhanced by the addition of FAD, decreases when incubations are performed anaerobically, and is completely inhibited when either sodium dithionite or glucose oxidase is added. Although the effect of various additives suggests that the oxidation of farnesol to farnesal does not require a metal redox center, 1,10-phenanthroline (but not 4,7-phenanthroline) is a weak irreversible inhibitor of farnesol oxidation (IC(50)=11 mM). The addition of exogenous metals (Fe2+, Cu2+, Ni2+, and Co2+) caused differential effects on farnesol metabolism, with Cu2+ being highly inhibitory. Taken together, this data suggests that the oxidation of farnesol to farnesal in larval corpora allata is mediated by a specific oxygen-dependent enzyme, perhaps a flavin and/or iron-dependent oxidase.

Farnesyl anthranilate suppresses the growth, in vitro and in vivo, of murine B16 melanomas

The numbers of isoprene residues and unsaturated bonds, cis/trans configuration, and head group polarity influence the tumor-suppressive potency of acyclic isoprenoid hydrocarbons and alcohols; within the series tested, trans, trans farnesol had the greatest potency. Geraniol esters had increased potency relative to that of the free alcohol. Farnesyl anthranilate induced a concentration-dependent decrease in the B16 melanoma cell population, in part due to an increased proportion of cells in the G1 phase of the cell cycle and in part by the increased the proportion of apoptotic cells. Farnesyl anthranilate (1.5 mmol/kg diet) significantly suppressed the growth of implanted B16 melanomas and lowered the plasma cholesterol levels of tumor-free mice.

Cloning and characterization of the Yarrowia lipolytica squalene synthase (SQS1) gene and functional complementation of the Saccharomyces cerevisiae erg9 mutation

The squalene synthase (SQS) gene encodes a key regulatory enzyme, farnesyl-diphosphate farnesyltransferase (EC 2.5.1.21), in sterol biosynthesis. The SQS1 gene was isolated from a subgenomic library of the industrially important yeast Yarrowia lipolytica, using PCR-generated probes. Probes were based on conserved regions of homologues from different organisms. The complete nucleotide sequence of the coding region and the corresponding amino acid sequence were determined. The sequences showed extensive homologies with squalene synthase genes and enzymes from a number of other organisms and extreme amino acid conservation within the binding and catalytic domains. Direct cloning of a 4.3 kb genomic Y. lipolytica fragment, also comprising its own promoter and terminator sequences, into autonomously replicating plasmid YEp352 and subsequent transformation of a Saccharomyces cerevisiae mutant strain with relevant erg9: ura3-1 markers, resulted in functional complementation of these deficiencies, although Northern blot analyses did not reveal a unique full-length messenger. The availability of the Y. lipolytica SQS1 gene (GenBank Accession No. AF092497) offers prospects for metabolic engineering of the isoprenoid and sterol biosynthetic pathways.

Oxysterols: modulators of cholesterol metabolism and other processes

Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.

Farnesol-induced generation of reactive oxygen species dependent on mitochondrial transmembrane potential hyperpolarization mediated by F(0)F(1)-ATPase in yeast

An isoprenoid farnesol (FOH) inhibited cellular oxygen consumption and induced mitochondrial generation of reactive oxygen species (ROS) in cells of Saccharomyces cerevisiae in correlation with hyperpolarization of the mitochondrial transmembrane potential (mtDeltaPsi). The FOH-induced events were coordinately abolished with the F(1)-ATPase inhibitor sodium azide as well as the F(0)F(1)-ATPase inhibitor oligomycin, suggesting the dependence of ROS generation on mtDeltaPsi hyperpolarization mediated by the proton pumping function of F(0)F(1)-ATPase as a result of ATP hydrolysis. The role of F(1)-ATPase activity in mtDeltaPsi hyperpolarization was supported by the intracellular depletion of ATP in FOH-treated cells and its protection with sodium azide. An indirect mechanism was suggested to exist in the regulation of F(0)F(1)-ATPase by FOH to accelerate its ATP-hydrolyzing activity.

Embryonic lethality and defective neural tube closure in mice lacking squalene synthase

Squalene synthase (SS) catalyzes the reductive head-to-head condensation of two molecules of farnesyl diphosphate to form squalene, the first specific intermediate in the cholesterol biosynthetic pathway. We used gene targeting to knock out the mouse SS gene. The mice heterozygous for the mutation (SS+/-) were apparently normal. SS+/- mice showed 60% reduction in the hepatic mRNA levels of SS compared with SS+/+ mice. Consistently, the SS enzymatic activities were reduced by 50% in the liver and testis. Nevertheless, the hepatic cholesterol synthesis was not different between SS+/- and SS+/+ mice, and plasma lipoprotein profiles were not different irrespective of the presence of the low density lipoprotein receptor, indicating that SS is not a rate-limiting enzyme in the cholesterol biosynthetic pathway. The mice homozygous for the disrupted SS gene (SS-/-) were embryonic lethal around midgestation. E9.5-10.5 SS-/- embryos exhibited severe growth retardation and defective neural tube closure. The lethal phenotype was not rescued by supplementing the dams either with dietary squalene or cholesterol. We speculate that cholesterol is required for the development, particularly of the nervous system, and that the chorioallantoic circulatory system is not mature enough to supply the rapidly growing embryos with maternal cholesterol at this developmental stage.

Modulation of neuronal voltage-gated calcium channels by farnesol

The modulation of presynaptic voltage-dependent calcium channels by classical second messenger molecules such as protein kinase C and G protein betagamma subunits is well established and considered a key factor for the regulation of neurotransmitter release. However, little is known of other endogenous mechanisms that control the activity of these channels. Here, we demonstrate a unique modulation of N-type calcium channels by farnesol, a dephosphorylated intermediate of the mammalian mevalonate pathway. At micromolar concentrations, farnesol acts as a relatively non-discriminatory rapid open channel blocker of all types of high voltage-activated calcium channels, with a mild specificity for L-type channels. However, at 250 nM, farnesol induces an N-type channel-specific hyperpolarizing shift in channel availability that results in approximately 50% inhibition at a typical neuronal resting potential. Additional experiments demonstrated the presence of farnesol in the brain (rodents and humans) at physiologically relevant concentrations (100-800 pmol/g (wet weight)). Altogether, our results indicate that farnesol is a selective, high affinity inhibitor of N-type Ca(2+) channels and raise the possibility that endogenous farnesol and the mevalonate pathway are implicated in neurotransmitter release through regulation of presynaptic voltage-gated Ca(2+) channels.

A cytochrome P450 terpenoid hydroxylase linked to the suppression of insect juvenile hormone synthesis

A cDNA encoding a cytochrome P450 enzyme was isolated from a cDNA library of the corpora allata (CA) from reproductively active Diploptera punctata cockroaches. This P450 from the endocrine glands that produce the insect juvenile hormone (JH) is most closely related to P450 proteins of family 4 and was named CYP4C7. The CYP4C7 gene is expressed selectively in the CA; its message could not be detected in the fat body, corpora cardiaca, or brain, but trace levels of expression were found in the midgut and caeca. The levels of CYP4C7 mRNA in the CA, measured by ribonuclease protection assays, were linked to the activity cycle of the glands. In adult females, CYP4C7 expression increased immediately after the peak of JH synthesis, reaching a maximum on day 7, just before oviposition. mRNA levels then declined after oviposition and during pregnancy. The CYP4C7 protein was produced in Escherichia coli as a C-terminal His-tagged recombinant protein. In a reconstituted system with insect NADPH cytochrome P450 reductase, cytochrome b5, and NADPH, the purified CYP4C7 metabolized (2E,6E)-farnesol to a more polar product that was identified by GC-MS and by NMR as (10E)-12-hydroxyfarnesol. CYP4C7 converted JH III to 12-trans-hydroxy JH III and metabolized other JH-like sesquiterpenoids as well. This omega-hydroxylation of sesquiterpenoids appears to be a metabolic pathway in the corpora allata that may play a role in the suppression of JH biosynthesis at the end of the gonotrophic cycle.

Massive production of farnesol-derived dicarboxylic acids in mice treated with the squalene synthase inhibitor zaragozic acid A

The zaragozic acids are potent inhibitors of squalene synthase. In vivo studies in mice confirmed our earlier observations that inhibition of squalene synthase by zaragozic acid A was accompanied by an increase in the incorporation of label from [3H]mevalonate into farnesyl-diphosphate (FPP)-derived isoprenoic acids (J. D. Bergstrom et al., 1993, Proc. Natl. Acad. Sci. USA 90, 80-84). Farnesyl-diphosphate-derived metabolites appear transiently in the liver. We were unable to detect any farnesol formation in the zaragozic acid-treated animals which indicates that FPP is readily converted to farnesoic acid and dicarboxylic acids in the liver. These metabolites were found to be produced only in the liver and not in the kidney. trans-3,7-Dimethyl-2-octaen-1,8-dioic acid and 3, 7-dimethyloctan-1,8-dioic acid were identified as the major end products of farnesyl-diphosphate metabolism in the urine of mice treated with zaragozic acid A. Quantitative analysis of these FPP-derived dicarboxylic acids by gas-liquid chromatography revealed that approximately 11 mg of total dicarboxylic acids is excreted per day into the urine of a mouse after 3 days of treatment with zaragozic acid A.