Isoprenoids control germ cell migration downstream of HMGCoA reductase

3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCoAr) provides attractive cues to Drosophila germ cells, guiding them toward the embryonic gonad. However, it remains unclear how HMGCoAr mediates this attraction. In a genomic analysis of the HMGCoAr pathway, we found that the fly genome lacks several enzymes required for cholesterol biosynthesis, ruling out cholesterol and cholesterol-derived proteins as mediators of PGC migration. Genetic analysis of the pathway revealed that two enzymes, farnesyl-diphosphate synthase and geranylgeranyl-diphosphate synthase, required for the production of isoprenoids, act downstream of HMGCoAr in germ cell migration. Consistent with a role in geranylgeranylation, embryos deficient in geranylgeranyl transferase type I show germ cell migration defects. Our data, together with similar findings in zebrafish, implicate an isoprenylated protein in germ cell attraction. The specificity and evolutionary conservation of the HMGCoAr pathway for germ cells suggest that an attractant common to invertebrates and vertebrates guides germ cells in early embryos.

Evolution of a pathway to novel long-chain carotenoids

Using methods of laboratory evolution to force the C(30) carotenoid synthase CrtM to function as a C(40) synthase, followed by further mutagenesis at functionally important amino acid residues, we have discovered that synthase specificity is controlled at the second (rearrangement) step of the two-step reaction. We used this information to engineer CrtM variants that can synthesize previously unknown C(45) and C(50) carotenoid backbones (mono- and diisopentenylphytoenes) from the appropriate isoprenyldiphosphate precursors. With this ability to produce new backbones in Escherichia coli comes the potential to generate whole series of novel carotenoids by using carotenoid-modifying enzymes, including desaturases, cyclases, hydroxylases, and dioxygenases, from naturally occurring pathways.

Characterization of botryococcene synthase enzyme activity, a squalene synthase-like activity from the green microalga Botryococcus braunii, Race B

The extracellular matrix of the alga Botryococcus braunii, Race B, consists mainly of botryococcenes, which have potential as a hydrocarbon fuel. Botryococcenes are structurally similar to squalene raising the possibility of a common enzyme for the biosynthesis of both. While B. braunii squalene synthase (SS) enzyme activity has been documented, botryococcene synthase (BS) enzyme activity has not been. In the current study, an assay for BS activity has been developed and used to show that many of the assay conditions for BS enzyme activity are similar to those of SS. However, SS enzyme activity is stimulated by Tween 80 while BS enzyme activity is inhibited. Moreover, BS enzyme activity was correlated with the accumulation of botryococcenes during a B. braunii culture growth cycle, which was distinctly different from the profile of SS enzyme activity. While the current results indicate a conservation of enzymological features amongst the BS and SS enzymes, raising the possibility of one enzyme capable of catalyzing both activities, they are also consistent with these two activities arising from separate and distinct enzymes.

Comparing myotoxic effects of squalene synthase inhibitor, T-91485, and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors in human myocytes

TAK-475 is a squalene synthase inhibitor, rapidly metabolized to T-91485 in vivo. We investigated the myotoxicities of T-91485 and 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors in a human rhabdomyosarcoma cell line, RD, and in human skeletal myocytes. In differentiated RD cells, T-91485, atorvastatin (ATV) and simvastatin acid (SIM) inhibited cholesterol biosynthesis, with IC(50) values of 36, 2.8 and 3.8 nM, respectively. ATV and SIM decreased the intracellular ATP content, with IC(25) values (concentrations giving a 25% decrease in intracellular ATP content) of 0.61 and 0.44 microM, respectively. Although T-91485 potently inhibited cholesterol synthesis in RD cells, the IC(25) value exceeded 100 microM. In human skeletal myocytes, T-91485, ATV and SIM concentration-dependently inhibited cholesterol biosynthesis, with IC(50) values of 45, 8.6 and 8.4 nM, respectively. ATV and SIM decreased intracellular ATP content, with IC(25) values of 2.1 and 0.72 microM, respectively. Although T-91485 potently inhibited cholesterol synthesis, the IC(25) value exceeded 100 microM. Myotoxicity induced by ATV was prevented by mevalonate or geranylgeranyl-PP, but not by squalene in skeletal cells. Furthermore, T-91485 attenuated the myotoxicity of ATV. These findings suggest that TAK-475 and T-91485 may not only be far from myotoxic, they may also decrease statin-induced myotoxicity in lipid-lowering therapy.

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.

Detection of farnesyl diphosphate accumulation in yeast ERG9 mutants

A sensitive method was developed for measuring farnesyl diphosphate (FPP) accumulation in a mutant strain of Saccharomyces cerevisiae. The strain was blocked at squalene synthase (ERG9 gene) in the isoprenoid pathway and had the catalytic domain of the 3-hydroxy-3-methylglutaryl coenzyme A reductase gene integrated into the chromosome. It required ergosterol for growth and produced E,E-farnesol. The method was based on the isolation of FPP using the anion exchanger Macro Prep High Q and conversion of FPP to E,E-farnesol with alkaline phosphatase. Farnesol was measured using gas chromatography-mass spectrometry. Background farnesol in the cell-free extract was also retained by the anion exchanger, but was removed with repeated washing with methanol. Both 1M NaCl and 40% (v/v) methanol were required in the elution buffer to effectively elute FPP. The preparation of cell-free extract in Bis-Tris propane/HCl, pH 7, buffer containing 0.025% (w/v) Triton X-100 and 15 mM MgCl(2) provided optimum conditions for the stabilization of FPP.

A C35 carotenoid biosynthetic pathway

Upon coexpression with Erwinia geranylgeranyldiphosphate (GGDP) synthase in Escherichia coli, C(30) carotenoid synthase CrtM from Staphylococcus aureus produces novel carotenoids with the asymmetrical C(35) backbone. The products of condensation of farnesyldiphosphate and GDP, C(35) structures comprise 40 to 60% of total carotenoid accumulated. Carotene desaturases and carotene cyclases from C(40) or C(30) pathways accepted and converted the C(35) substrate, thus creating a C(35) carotenoid biosynthetic pathway in E. coli. Directed evolution to modulate desaturase step number, together with combinatorial expression of the desaturase variants with lycopene cyclases, allowed us to produce at least 10 compounds not previously described. This result highlights the plastic and expansible nature of carotenoid pathways and illustrates how combinatorial biosynthesis coupled with directed evolution can rapidly access diverse chemical structures.

Mechanism of action of 4-phenoxyphenoxyethyl thiocyanate (WC-9) against Trypanosoma cruzi, the causative agent of Chagas' disease

We investigated the molecular basis of the activity of 4-phenoxyphenoxyethyl thiocyanate (WC-9) against Trypanosoma cruzi, the etiological agent of Chagas' disease. We found that growth inhibition of T. cruzi epimastigotes induced by this compound was associated with a reduction in the content of the parasite's endogenous sterols due to a specific blockade of their de novo synthesis at the level of squalene synthase.

Syntheses and biological evaluation of novel quinuclidine derivatives as squalene synthase inhibitors

Squalene synthase (E.C. 2.5.1.21) catalyses the reductive dimerization of two molecules of farnesyl diphosphate to form squalene and is involved in the first committed step in cholesterol biosynthesis. Inhibition of this enzyme is therefore an attractive target for hypocholesterolemic strategies. A series of quinuclidine derivatives incorporating a tricyclic system was synthesized and evaluated for their ability to inhibit squalene synthase in vitro. A 9H-fluorene moiety was found to be optimal as the tricyclic system for potent inhibitory activity. Improved activity can be achieved with a conformationally constrained three-atom linkage connecting the tricyclic system with the quinuclidine nucleus. Among these compounds, (Z)-3-[2-(9H-fluoren-2-yloxy)ethylidene]-quinuclidine hydrochloride 31 was found to be a potent inhibitor of squalene synthase derived from hamster liver and human hepatoma cells with IC(50) values of 76 and 48 nM, respectively. Oral dosing of compound 31 demonstrated effective reduction of plasma non-HDL cholesterol levels in hamsters.

Biosynthesis of structurally novel carotenoids in Escherichia coli

Previously, we utilized in vitro evolution to alter the catalytic functions of several carotenoid enzymes and produce the novel carotenoids tetradehydrolycopene and torulene in Escherichia coli. Here we report on the successful extension of these pathways and the C(30) carotenoid diaponeurosporene pathway with additional carotenoid genes. Extension of the known acyclic C(30) pathway with C(40) carotenoid enzymes-spheroidene monooxygenase and lycopene cyclase-yielded new oxygenated acylic products and the unnatural cyclic C(30) diapotorulene, respectively. Extension of acyclic C(40) pathways with spheroidene monooxygenase generated novel oxygenated carotenoids including the violet phillipsiaxanthin. Extension of the torulene biosynthetic pathway with carotene hydroxylase, desaturase, glucosylase, and ketolase yielded new torulene derivatives. These results demonstrate the utility of extending an in vitro evolved central metabolic pathway with catalytically promiscuous downstream enzymes in order to generate structurally novel compounds.

cDNA cloning, mRNA expression, and mutational analysis of the squalene synthase gene of Lotus japonicus

A full-length cDNA for squalene synthase was isolated from Lotus japonicus, a model leguminous plant. The transcript was abundant in roots, symbiotic root nodules, and shoots, in that order. In situ hybridization revealed that the mRNA level is high in expanding root cells but low in dividing root tip ones. The transcript is also abundant in vascular bundles and the basal portions of mature nodules. L. japonicus squalene synthase has an unusual Asp residue near the active site, where mammalian enzymes have Gln, and replacement of the Gln by Glu has been reported to cause severe inactivation. Site-directed mutagenesis of the L. japonicus enzyme and assaying in vitro showed that this Asp residue can be substituted by not only Gln but also Glu, suggesting that the local structure of plant squalene synthases is different from that of mammalian enzymes.

Up-regulation of soyasaponin biosynthesis by methyl jasmonate in cultured cells of Glycyrrhiza glabra

Exogenously applied methyl jasmonate (MeJA) stimulated soyasaponin biosynthesis in cultured cells of Glycyrrhiza glabra (common licorice). mRNA level and enzyme activity of beta-amyrin synthase (bAS), an oxidosqualene cyclase (OSC) situated at the branching point for oleanane-type triterpene saponin biosynthesis, were up-regulated by MeJA, whereas those of cycloartenol synthase, an OSC involved in sterol biosynthesis, were relatively constant. Two mRNAs of squalene synthase (SQS), an enzyme common to both triterpene and sterol biosyntheses, were also up-regulated by MeJA. In addition, enzyme activity of UDP-glucuronic acid: soyasapogenol B glucuronosyltransferase, an enzyme situated at a later step of soyasaponin biosynthesis, was also up-regulated by MeJA. Accumulations of bAS and two SQS mRNAs were not transient but lasted for 7 d after exposure to MeJA, resulting in the high-level accumulation (more than 2% of dry weight cells) of soyasaponins in cultured licorice cells. In contrast, bAS and SQS mRNAs were coordinately down-regulated by yeast extract, and mRNA accumulation of polyketide reductase, an enzyme involved in 5-deoxyflavonoid biosynthesis in cultured licorice cells, was induced transiently by yeast extract and MeJA, respectively.

Biosynthesis of sterols and triterpenes in cell suspension cultures of Uncaria tomentosa

Pectin administered to Uncaria tomentosa cell suspension cultures, was found to increase the production of triterpene acids (ursolic and oleanolic acid), however, neither growth nor sterol accumulation were affected. Cell cultures showed that pectin treatment caused a rapid threefold increase in the activities of enzymes involved in the biosynthesis of C(5) and C(30 )isoprenoid, such as isopentenyl diphosphate isomerase and squalene synthase. The activity of a farnesyl diphosphatase, which could divert the flux of farnesyl diphosphate to farnesol, was two times lower in elicited than in control cells. Elicited cells also transformed more rapidly a higher percentage of [5-(3)H]mevalonic acid into triterpene acids. Interestingly, addition of terbinafine, an inhibitor of squalene epoxidase, to elicited cell cultures inhibited sterol accumulation while triterpene production was not inhibited. These results suggest that in U. tomentosa cells, both the previously mentioned enzymes and those involved in squalene 2,3-oxide formation play an important regulatory role in the biosynthesis of sterols and triterpenes.

A genomics approach to the early stages of triterpene saponin biosynthesis in Medicago truncatula

The saponins of the model legume Medicago truncatula are glycosides of at least five different triterpene aglycones: soyasapogenol B, soyasapogenol E, medicagenic acid, hederagenin and bayogenin. These aglycones are most likely derived from beta-amyrin, a product of the cyclization of 2,3-oxidosqualene. Mining M. truncatula EST data sets led to the identification of sequences putatively encoding three early enzymes of triterpene aglycone formation: squalene synthase (SS), squalene epoxidase (SE), and beta-amyrin synthase (beta-AS). SS was functionally characterized by expression in Escherichia coli, two forms of SE by complementation of the yeast erg1 mutant, and beta-AS by expression in yeast. Beta-amyrin was the sole product of the cyclization of squalene epoxide by the recombinant M. truncatulabeta-AS, as judged by GC-MS and NMR. Transcripts encoding beta-AS, SS and one form of SE were strongly and co-ordinately induced, associated with accumulation of triterpenes, upon exposure of M. truncatula cell suspension cultures to methyl jasmonate. Sterol composition remained unaffected by jasmonate treatment. Molecular verification of induction of the triterpene pathway in a cell culture system provides a new tool for saponin pathway gene discovery by DNA array-based approaches.

Evolution of the C30 carotenoid synthase CrtM for function in a C40 pathway

The C30 carotene synthase CrtM from Staphylococcus aureus and the C40 carotene synthase CrtB from Erwinia uredovora were swapped into their respective foreign C40 and C30 biosynthetic pathways (heterologously expressed in Escherichia coli) and evaluated for function. Each displayed negligible ability to synthesize the natural carotenoid product of the other. After one round of mutagenesis and screening, we isolated 116 variants of CrtM able to synthesize C40 carotenoids. In contrast, we failed to find a single variant of CrtB with detectable C30 activity. Subsequent analysis revealed that the best CrtM mutants performed comparably to CrtB in an in vivo C40 pathway. These mutants showed significant variation in performance in their original C30 pathway, indicating the emergence of enzymes with broadened substrate specificity as well as those with shifted specificity. We discovered that Phe 26 alone determines the specificity of CrtM. The plasticity of CrtM with respect to its substrate and product range highlights the potential for creating further new carotenoid backbone structures.

Effect of YM-53601, a novel squalene synthase inhibitor, on the clearance rate of plasma LDL and VLDL in hamsters

1. To better understand how it decreases plasma cholesterol and triglyceride, we evaluated the effect of YM-53601 ((E-2-[2-fluoro-2-(quinuclidin-3-ylidene) ethoxy]-9H-carbozole monohydrochloride) on the clearance rate of low density lipoprotein (LDL) and very low density lipoprotein (VLDL) in hamsters. 2. Treatment with YM-53601 at 50 mg kg(-1) for 5 days in hamsters fed a normal diet enhanced the disappearance of 1,1'-Dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI)-VLDL and DiI-LDL. This effect on DiI-LDL was lost in the early phase after DiI-methyl(met)-LDL, chemically modified to block LDL receptor binding, was injected in hamsters, but was retained in the late phase. Pre-treatment with protamine sulphate, which inhibits the activity of LPL, also failed to enhance DiI-VLDL clearance rate by YM-53601. 3. Even on single oral administration at 30 mg kg(-1), YM-53601 enhanced the disappearance of the high concentration of plasma triglyceride after injection of intrafat, an emulsion of fat. Plasma triglyceride was significantly decreased as soon as 1 h after single administration of YM-53601 in hamsters fed a normal diet. 4. These results indicate that the decrease in plasma total cholesterol and triglyceride after the treatment with YM-53601 is due to its enhancement of the clearance rate of LDL and VLDL, respectively. Moreover, YM-53601 may be effective in decreasing plasma triglyceride levels early in the course of treatment of hypertriglyceridaemia in humans.

Inhibition of squalene synthase and squalene epoxidase in tobacco cells triggers an up-regulation of 3-hydroxy-3-methylglutaryl coenzyme a reductase

To get some insight into the regulatory mechanisms controlling the sterol branch of the mevalonate pathway, tobacco (Nicotiana tabacum cv Bright Yellow-2) cell suspensions were treated with squalestatin-1 and terbinafine, two specific inhibitors of squalene synthase (SQS) and squalene epoxidase, respectively. These two enzymes catalyze the first two steps involved in sterol biosynthesis. In highly dividing cells, SQS was actively expressed concomitantly with 3-hydroxy-3-methylglutaryl coenzyme A reductase and both sterol methyltransferases. At nanomolar concentrations, squalestatin was found to inhibit efficiently sterol biosynthesis as attested by the rapid decrease in SQS activity and [(14)C]radioactivity from acetate incorporated into sterols. A parallel dose-dependent accumulation of farnesol, the dephosphorylated form of the SQS substrate, was observed without affecting farnesyl diphosphate synthase steady-state mRNA levels. Treatment of tobacco cells with terbinafine is also shown to inhibit sterol synthesis. In addition, this inhibitor induced an impressive accumulation of squalene and a dose-dependent stimulation of the triacylglycerol content and synthesis, suggesting the occurrence of regulatory relationships between sterol and triacylglycerol biosynthetic pathways. We demonstrate that squalene was stored in cytosolic lipid particles, but could be redirected toward sterol synthesis if required. Inhibition of either SQS or squalene epoxidase was found to trigger a severalfold increase in enzyme activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase, giving first evidence for a positive feedback regulation of this key enzyme in response to a selective depletion of endogenous sterols. At the same time, no compensatory responses mediated by SQS were observed, in sharp contrast to the situation in mammalian cells.

Recombinant squalene synthase. Synthesis of non-head-to-tail isoprenoids in the absence of NADPH

Squalene synthase (SQase) catalyzes two consecutive reactions in sterol biosynthesis. The first is the condensation of two molecules of farnesyl diphosphate (FPP) to form a cyclopropylcarbinyl intermediate, presqualene diphosphate (PSPP). The subsequent conversion of PSPP to squalene (SQ) involves an extensive rearrangement of the carbon skeleton and a NADPH-dependent reduction. Incubation of a truncated soluble form of recombinant yeast SQase with FPP in buffer lacking NADPH gave (1R,2R,3R)-PSPP. As the incubation continued, SQase catalyzed the subsequent conversion of PSPP to a mixture of triterpenes. Two of the major products, (Z)-dehydrosqualene (DSQ) and (R)-12-hydroxysqualene (HSQ), have the same 1'-1 linkage between the farnesyl units from FPP that is found in squalene. The other major product, (10S,13S)-10-hydroxybotryococcene (HBO), has a 1'-3 linkage between the farnesyl units. Small quantities of (S)-HSQ and (10R,13S)-HBO were also formed. Three additional triterpenes, the allylic isomers of HSQ and HBO, and an unidentified alcohol were produced in minor amounts. A methyl ether corresponding to HSQ was detected when methanol was present in the incubation buffer. These compounds are the expected "solvolysis" products from PSPP. They provide strong support for mechanisms that propose cyclopropylcarbinyl cations as intermediates in the SQase-catalyzed rearrangement of PSPP to SQ and unambiguously demonstrate that the catalytic machinery of SQase is capable of synthesizing a variety of irregular isoprenoids.

Recombinant squalene synthase. A mechanism for the rearrangement of presqualene diphosphate to squalene

Squalene synthase (SQase) catalyzes the condensation of two molecules of farnesyl diphosphate (FPP) to form presqualene diphosphate (PSPP) and the subsequent rearrangement and NADPH-dependent reduction of PSPP to squalene (SQ). These reactions are the first committed steps in cholesterol biosynthesis. When recombinant SQase was incubated with FPP in the presence of dihydroNADPH (NADPH3, an unreactive analogue lacking the 5,6-double bond in the nicotinamide ring), three products were formed: dehydrosqualene (DSQ), a C30 analogue of phytoene; 10(S)-hydroxysqualene (HSQ), a hydroxy analogue of squalene; and rillingol (ROH), a cyclopropylcarbinyl alcohol formed by addition of water to the tertiary cyclopropylcarbinyl cation previously proposed as an intermediate in the rearrangement of PSPP to SQ (Poulter, C. D. Acc. Chem. Res. 1990, 23, 70-77). The structure and absolute stereochemistry of the tertiary cyclopropylcarbinyl alcohol were established by synthesis using two independent routes. Isolation of ROH from the enzyme-catalyzed reaction provides strong evidence for a cyclopropylcarbinyl-cyclopropylcarbinyl rearrangement in the biosynthesis of squalene. By comparing the SQase-catalyzed solvolysis of PSPP in the absence of NADPH3 to the reaction in the presence of NADPH3, it is apparent that the binding of the cofactor analogue substantially enhances the ability of SQase to control the regio- and stereochemistry of the rearrangements of PSPP.

Regulation of squalene synthase, a key enzyme of sterol biosynthesis, in tobacco

Squalene synthase (SS) represents a putative branch point in the isoprenoid biosynthetic pathway capable of diverting carbon flow specifically to the biosynthesis of sterols and, hence, is considered a potential regulatory point for sterol metabolism. For example, when plant cells grown in suspension culture are challenged with fungal elicitors, suppression of sterol biosynthesis has been correlated with a reduction in SS enzyme activity. The current study sought to correlate changes in SS enzyme activity with changes in the level of the corresponding protein and mRNA. Using an SS-specific antibody, the initial suppression of SS enzyme activity in elicitor-challenged cells was not reflected by changes in the absolute level of the corresponding polypeptide, implicating a post-translational control mechanism for this enzyme activity. In comparison, the absolute level of the SS mRNA did decrease approximately 5-fold in the elicitor-treated cells, which is suggestive of decreased transcription of the SS gene. Study of SS in intact plants was also initiated by measuring the level of SS enzyme activity, the level of the corresponding protein, and the expression of SS gene promoter-reporter gene constructs in transgenic plants. SS enzyme activity, polypeptide level, and gene expression were all localized predominately to the shoot apical meristem, with much lower levels observed in leaves and roots. These later results suggest that sterol biosynthesis is localized to the apical meristems and that apical meristems may be a source of sterols for other plant tissues.

Cloning and expression of squalene synthase cDNA from hot pepper (Capsicum annuum L.)

We isolated and artificially expressed a cDNA clone of the Capsicum annuum squalene synthase (CASS) gene to elucidate the pattern of alternatively regulated two-branch point enzymes. The 1,674-bp CASS cDNA contained an open reading frame of 411 amino acids, yielding a predicted molecular mass of about 45 kDa. A deduced amino acid sequence comparison to other squalene syntheses showed identities with Nicotiana tabacum (91%), Nicotiana benthamiana (90%), Arabidopsis thaliana (79%), and rats (40%). The artificially expressed soluble form of the CASS enzyme was identified by the enzyme activity that converted FPP to squalene and by SDS-PAGE. A Southern blot analysis indicated that at least two copies of the squalene synthase gene exist in the hot pepper genome. In hot pepper, the regulation of the branch point enzymes, squalene synthase and sesquiterpene cyclase was investigated in the UV-challenged leaves of Capsicum annuum. The transcript level and enzyme activity of the CASS were slightly reduced by UV. However, those of the CASC were rapidly induced within 24 h and slowly decreased thereafter.

Experimental model of escape phenomenon in hamsters and the effectiveness of YM-53601 in the model

1. The aim of this study was to establish an experimental model of the escape phenomenon, in which plasma cholesterol, initially reduced by a 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase inhibitor such as pravastatin, increases again on long-term administration. We also evaluated the efficacy of YM-53601 ((E)-2-[2-fluoro-2- (quinuclidin-3-ylidene) ethoxy]-9H-carbazole monohydrochloride), a squalene synthase inhibitor, in this model. 2. Pravastatin inhibited cholesterol biosynthesis in hamster primary hepatocytes (IC(50), 14 nM). After pre-treatment with pravastatin, in contrast, almost no effect on cholesterol biosynthesis was seen. 3. In hamsters fed a high fat diet, 3 mg kg(-1) pravastatin for 9 days decreased plasma non-HDL cholesterol (total cholesterol - high density lipoprotein cholesterol) (P<0.01), but this effect was lost between 17 and 27 days of treatment, accompanied by an increase in HMG-CoA reductase activity. No such increase in plasma non-HDL cholesterol was seen with YM-53601 at 30 mg kg(-1) after 9 (P<0.001), 17 (P<0.01) or 27 (P<0.001) days of treatment. Replacement of pravastatin with YM-53601 caused a decrease in plasma non-HDL cholesterol by 53% (P<0.001) and in HMG-CoA reductase activity. 4. This animal model thus satisfactorily replicates the escape phenomenon observed in humans and may therefore be useful in evaluation of lipid-lowering agents, specifically comparison of HMG-CoA reductase inhibitors. Further, YM-53601 may be useful in the treatment of hypercholesterolemia without induction of the escape phenomenon.