Disease relevance of Squalestatin

• RESULTS: Continuous squalestatin infusion (15 micrograms/h) decreased C7 alpha H specific activities to 4% and 12% of paired biliary fistula controls at 24 and 48 hours, respectively (P < 0.05) without any changes in S27H specific activities (82% and 95% of controls) [1].
• They inhibited cholesterol synthesis in Hep G2 cells, and zaragozic acid A was an inhibitor of acute hepatic cholesterol synthesis in the mouse (50% inhibitory dose of 200 micrograms/kg of body weight) [2].
• To verify whether cholesterol synthesis was required for the induction of hsp70 by OxLDL, squalestatin I (25 nM to 100 nM), an inhibitor of squalene synthase, another key enzyme of the cholesterol pathway, was used: OxLDL toxicity and hsp70 expression were not affected by this compound [3].

High impact information on Squalestatin

• METHODS: Rats with biliary fistulas were infused with squalestatin for 24 and 48 hours; specific activities of cholesterol 7 alpha-hydroxylase (C7 alpha H) and sterol 27-hydroxylase (S27H) and rates of bile acid synthesis were determined [1].
• Similar changes in C7 alpha H, S27H, and bile acid synthesis were observed in primary rat hepatocytes after addition of squalestatin (1.0 mumol/L) [1].
• 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 [4].
• Squalestatin cures prion-infected neurons and protects against prion neurotoxicity [5].
• Inhibition of mammalian squalene synthetase activity by zaragozic acid A is a result of competitive inhibition followed by mechanism-based irreversible inactivation [6].

Biological context of Squalestatin

• Cotransfection of female Wistar-Kyoto rat hepatocyte cultures with plasmid expressing either mouse or rat CAR restored squalestatin 1-inducible CYP2B1-reporter expression [7].
• Cell death was also induced by treatment with squalestatin, which specifically inhibits cholesterol biosynthesis at a site downstream from the generation of nonsterol metabolites [8].
• No significant change was observed in the levels of sterol response element binding protein 2, the form that mediates induced transcription, in response to zaragozic acid A treatment, indicating that this protein might not be involved in mediating the observed transcriptional changes [9].
• In gene reporter assays in COS-7 cells, the basal activity of the LXR responsive reporter gene (LXRE-luc) was suppressed by 10 microM lovastatin and zaragozic acid A, suggesting that this activity was attributed to the activation of native LXRs, by endogenously produced mevalonate products [10].
• The increase in HMG-CoA reductase gene expression was closely related to the degree of inhibition of cholesterol synthesis caused by zaragozic acid A [11].

Anatomical context of Squalestatin

• In the present study, the squalene synthase inhibitor squalestatin reduced the cholesterol content of cells and prevented the accumulation of PrP(Sc) in three prion-infected cell lines (ScN2a, SMB, and ScGT1 cells) [5].

Associations of Squalestatin with other chemical compounds

• In marmosets, a species with a lipoprotein profile similar to that of man, squalestatin 1 lowers serum cholesterol by up to 75% [12].
• Incubation of cultured hepatocytes with squalestatin 1 caused marked accumulations (maximal elevations that were approximately 25-100% of phenobarbital-elicited increases) of CYP2B mRNA and immunoreactive protein but not of CYP1A, CYP3A, or CYP4A [13].
• 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 [7].
• Lovastatin, a hepatic hydroxymenthyl coenzyme A reductase inhibitor that reduced the cellular FPP pool, increased the activity of J-104,871, whereas 3 microM zaragozic acid A, an SS inhibitor that raised the FPP level, completely abrogated the activity of J-104,871 even at 100 microM [14].
• Mevalonolactone (2 mM) failed to restore cholesterol 7 alpha-hydroxylase specific activity or steady-state mRNA levels in squalestatin-treated cells [15].

Gene context of Squalestatin

• In hepatocytes pre-treated with squalestatin or 25-hydroxycholesterol before infection, viral RNA accumulation increased or decreased in parallel with LDLR mRNA expression and LDL entry [16].
• 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) [17].
• 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 [7].
• Squalestatin 1-inducible expression of rat CYP2B: evidence that an endogenous isoprenoid is an activator of the constitutive androstane receptor [7].
• 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 [7].

Analytical, diagnostic and therapeutic context of Squalestatin

• METHODS: Expression and activity of LDLR were assessed by RT-PCR and LDL entry, in the absence or presence of squalestatin or 25-hydroxycholesterol that up- or down-regulates LDLR expression, respectively [16].
• PCR primers designed to selectively amplify the unique C-methyltransferase domain of fungal polyketide synthases were used to selectively clone a polyketide synthase gene involved in the biosynthesis of the squalene synthase inhibitor squalestatin S1 , heterologous expression of which led to the biosynthesis of the squalestatin side-chain [18].
• 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 [17].
• Immunoblots were used to determine the effects of simvastatin or squalestatin on the distribution of the PAF receptor and an enzyme linked immunoassay was used to quantify the amounts of PAF receptor [19].

References