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PubMed2000

Non-mevalonate isoprenoid biosynthesis: enzymes, genes and inhibitors.

The essential steps of the novel non-mevalonate pathway of isopentenyl diphosphate and isoprenoid biosynthesis in plants are described. The first five enzymes and genes of this 1-deoxy-D-xylulose 5-phosphate/2-C-methyl-D-erythritol 4-phosphate (DOXP/MEP) pathway are known. The herbicide fosmidomycin specifically blocks the second enzyme, the DOXP reductoisomerase. The DOXP/MEP pathway is also present in several pathogenic bacteria and the malaria parasite. Hence, all herbicides and inhibitors blocking this novel isoprenoid pathway in plants are also potential drugs against malaria and diseases caused by pathogenic bacteria.

Aldose-Ketose Isomerases↗

PubMed2001

Identification of novel essential Escherichia coli genes conserved among pathogenic bacteria.

We deleted a subset of 27 open reading frames (ORFs) from Escherichia coli which encode previously uncharacterized, probably soluble gene products homologous to proteins from a broad spectrum of bacterial pathogens such as Haemophilus influenzae, Staphylococcus aureus, Streptococcus pneumoniae and Enterococcus faecalis and only distantly related to eukaryotic proteins. Six novel bacteria-specific genes essential for growth in complex medium could be identified through a combination of bioinformatics-based and experimental approaches. We also compared our data to published results of gene inactivation projects with Mycoplasma genitalium and Bacillus subtilis and looked for homologs in all known prokaryotic genomes. Such analyses highlight the enormous metabolic flexibility of prokaryotes. Six of 27 studied genes have been functionally characterized up to now, amongst these four of the essential genes. The gene products YgbP, YgbB and YchB are involved in the non-mevalonate pathway of isoprenoid biosynthesis. KdtB is characterized as the posphopantetheine adenylyltransferase CoaD. There are indications that the other two essential gene products YjeE and YqgF, which we have identified, also possess enzymatic functions. These findings demonstrate the potential of such proteins to be used in screening of large chemical libraries for inhibitors which could be further developed to novel broad-spectrum antibiotics.

Bacillus subtilis↗

PubMed1992

Plasma ubiquinone, alpha-tocopherol and cholesterol in man.

Plasma ubiquinone, coenzyme Q10 or CoQ10 has been analyzed in plasma together with alpha-tocopherol and free cholesterol in healthy sedentary male subjects (SS), endurance trained male athletes (ET) and male patients with severe ischemic heart disease (IHD). Higher means were found in SS compared to both IHD and ET. Moreover, the ratios CoQ10 and alpha-tocopherol over free cholesterol were higher. In all groups significant relationships were found between the two products of the mevalonate pathway: CoQ10 and cholesterol (r ranged 0.66-0.86, p less than 0.01). The two lipophilic antioxidants, CoQ10 and alpha-tocopherol, were interrelated only in IHD (r = 0.86, p less than 0.001), borderline in SS (r = 0.51, p less than 0.05) but not in ET. It is assumed that plasma free cholesterol reflects the capacity to transport lipids and lipophilic compounds in blood. With metabolic stress and an elevated radical formation as in IHD and ET, the lower CoQ10 and alpha-tocopherol to cholesterol ratios mirror a subsequent toll on the scavenging potential. The difference in LDL levels between IHD and ET and the different storage capacity of CoQ10 and alpha-tocopherol might explain the tight coupling in IHD but not in ET. It is possible that the toll reflects both an intra- and extracellular radical quenching activity. The joint effect of the two lipophilic, extracellular antioxidants CoQ10 and alpha-tocopherol role in protecting e.g. LDL particles from peroxidation is suggested.

Cholesterol↗

PubMedDate not supplied

Mevastatin-induced apoptosis and growth suppression in U266 myeloma cells.

Statins have been used successfully in the treatment of hypercholesterinaemia. Moreover, in vitro studies have shown that statins can trigger apoptosis in a variety of tumor cell lines. In the present study we analysed the effect of mevastatin--a novel inhibitor of HMG-COA reductase, the rate-limiting enzyme of the mevalonate pathway--on U266 human myeloma cells. Apoptosis induced by mevastatin was associated with increased caspase activity and depolarisation of the mitochondrial membrane. Expression of Bcl-2 mRNA and protein was down-regulated, with no change in Bax or Bcl-XL protein production. The mitochondrial program was supported by caspase-8 and cleaved-Bid activity. None of the antibodies neutralizing the death-ligand/death-receptor pathway--TRAIL-R2Fc, anti-TNF-alpha, anti-FASL(NOK-1)--influenced the mevastatin-induced apoptosis. Mevastatin also stimulated shedding of syndecan-1 from the surface of myeloma cells. The apoptosis inducing effect of mevastatin could be considered as a potential participant in a complex antitumor protocol.

Apoptosis↗

PubMed2005

Alendronate inhibits intraperitoneal dissemination in in vivo ovarian cancer model.

Ovarian cancer is characterized by diffuse peritoneal carcinomatosis and often by large volumes of ascites. We previously reported that alendronate, a nitrogen-containing bisphosphonate, inhibited ovarian cancer cell migration by attenuating the activation of Rho through inhibiting the mevalonate pathway. However, questions remain about the ability of alendronate to inhibit the invasiveness of cancer cells to the adherent tissues and the growth of disseminated ovarian cancer in vivo. We established an in vivo ovarian cancer model with i.p. carcinomatosis in athymic immunodeficient mice. In the prevention model, in which alendronate administration started from the day after tumor inoculation, alendronate prevented the stromal invasion, reduced the tumor burden, and inhibited ascites accumulation. Histologic observation revealed that alendronate treatment decreased the stromal invasion of the i.p. tumor while inhibiting the metalloproteinase-2 activity in ascites. This antitumor effect might result from the inhibition of cancer cell migration and proteolytic activity. In the treatment model, in which alendronate was given from 10 days after tumor inoculation when macroscopic tumors are already implanted in the peritoneum, the antitumor effect was weaker but still significant. Furthermore, alendronate administration decreased the serum CA-125 levels of mice bearing disseminated ovarian cancer compared with those of nontreated mice. The potent effects of alendronate in reducing stromal invasion, tumor burden, and ascites suggest that it will be of value in regimens for treatment of women with ovarian cancer.

Alendronate↗

PubMed2003

[Evidences and the taking measurements against G-I tract adverse events in amino bisphosphonate].

Amino bisphosphonate (A-BP) is a potent inhibitor of bone resorption through inhibition of mevalonate pathway resulting in increase apoptosis of osteoclast. It is expected that the same metabolic effects of this compound may contribute on the cell damage at G-I tract. Although the some endoscopical studies indicated that alendronate administration significantly associated gastric ulcer or erosion, the data were inconsistent between the studies. Furthermore, recent analysis revealed that A-BP did not increase in adverse events in G-I tract from the reviews of the mega-trials of alendronate and risedronate. Post-marketing surveillance also indicated that amino A-BP did not increase in G-I adverse event (AE) at G-I tract, but physicians have to pay attention about G-I AE after A-BP treatment in the individual patients.

English Abstract↗

PubMed2002

[Bisphosphonates and adhesion molecules].

Bisphosphonates are highly effective inhibitors of osteoclastic bone resorption. They can be divided into two groups with distinct mechanisms of action. The nitrogen-containing bisphosphonates (pamidronate, alendronate, risedronate, incadronate etc) can inhibit the mevalonate pathway in osteoclasts and inhibit protein prenylation of small G proteins including Rho, which might lead to alter cytoskeletal organization and cell motility. Others, like etidronate and clodronate, do not inhibit protein prenylation and can be incorporated into ATP-containing compounds that may be cytotoxic to osteoclasts. Further studies would be required to elucidate the molecular mechanism of bisphosphonate actions.

English Abstract↗

PubMed2001

[Recent topics on therapeutics for osteoporosis in patients complicated with vascular diseases].

The association of osteoporosis with atherosclerosis in elderly patients has been often recognized. Recent evidence suggests that etiologic factors of osteoporosis may modulate the development of atherosclerosis, and vice versa. Furthermore, bisphosphonates may prevent the development of atherosclerosis, while statins may increase bone mineral density and thereby decrease the risk of osteoporotic fractures. These two drugs may have the common target of action, the mevalonate pathway. Therefore, it is important to consider the effects of therapeutic agents on cardiovascular system, when the treatment of osteoporosis in elderly patients is initiated.

English Abstract↗

PubMed2005

[Bisphosphonates: the molecular targets and mechanisms of action].

Bisphosphonates directly act on osteoclasts to inhibit bone resorption and used most widely to treat osteoporosis. The compounds can be classified into two groups with different modes of action. Nitrogen containing bisphosphonates exert their effects by inhibiting a key enzyme in the mevalonate pathway. The specific target is the isoprenoid biosynthetic enzyme, farnesyl pyrophosphate synthase, which is indispensable for protein prenylation and activation of intracellular signalling proteins, including the small GTPases Rho, Rac, Cdc42 and Ras. The disruption of the function of these key enzymes may explain the loss of osteoclast activity and induction of apoptosis. Whereas the first generation of bisphosphonates such as etidronate and clodronate (nitrogen deficient bisphosphonates) can be incorporated into nonhydrolysable analogues of ATP that may inhibit ATP-dependent intracellular events. Bisphosphonates are highly effective to inhibit bone resorption and increase bone mineral density, although their precise mechanisms of molecular action are not completely understood.

Diphosphonates↗

PubMed2005

Comparison of the effects of D-003, a mixture of high-molecular-weight aliphatic acids from sugarcane wax, and pravastatin on bones and osteoclast apoptosis of ovariectomized rats.

The mevalonate pathway is relevant in bone cells. Statins inhibit 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the key enzyme of this route, stimulating osteoblast differentiation and activity. Pravastatin increases bone formation markers in postmenopausal women and bone density in diabetics. D-003 is a mixture of high-molecular-weight acids purified from sugarcane wax which inhibits cholesterol biosynthesis through HMG-CoA reductase regulation, preventing bone loss in osteoporosis induced with ovariectomy and prednisolone in rats. We investigated the effects of D-003 (50 mg/kg) and pravastatin (20 mg/kg) orally administered for 12 weeks to ovariectomized rats. Female rats were randomized in four groups (10 rats/group): two control groups treated with the vehicle, one false-operated (sham) and another ovariectomized (positive control), while two other groups received D-003 or pravastatin. Bone resorption and formation was studied through histomorphometry and apoptosis through immunohistochemistry. D-003 and pravastatin significantly (p < 0.001) prevented the changes of trabecular bone versus ovariectomized rats and (p < 0.001) the increase of the surface and number of osteoclasts versus ovariectomized controls. D-003 and pravastatin, however, did not modify osteoblast surfaces, a bone formation marker D-003 and pravastatin increased osteoclast apoptosis and reduced (p < 0.05) osteoblast and osteocyte apoptosis versus ovariectomized controls; D-003 was more effective (p < 0.05) than pravastatin. In conclusion, D-003 (50 mg/kg) orally administered for 12 weeks prevented bone loss and bone resorption in ovariectomized rats, increasing osteoclast apoptosis. The preventive effects of D-003 on bone loss and resorption in ovariectomized rats are comparable to those of pravastatin. Both drugs inhibited osteoblast apoptosis but failed to change osteoblast surface. The effects of D-003 on bone cell apoptosis were greater than those of pravastatin. Therefore, D-003 could be used to prevent or treat bone loss in postmenopausal women, but further animal studies and clinical trials are required to confirm the clinical relevance of this potential effect.

Animals↗

PubMed2005

Effects of D-003 (5-200 mg/kg), a mixture of high molecular weight aliphatic acids from sugarcane wax, on bones and bone cell apoptosis in ovariectomized rats.

The mevalonate pathway is crucial for osteoclast function. D-003 is a mixture of high molecular weight acids purified from sugarcane wax, which inhibits cholesterol biosynthesis through HMG-CoA reductase regulation. D-003 administered at 50 and 200 mg/kg for 12 weeks prevented bone loss in ovariectomized rats, increasing osteoclast apoptosis. The present study investigated whether the effects of D-003 on bone resorption and osteoclast apoptosis are dose-dependent. Rats were randomized into seven groups (10 rats/group): two control groups orally treated with the vehicle, one false-operated (sham) and another ovariectomized group (positive control), while another four groups received D-003 (5, 25, 50 and 200 mg/kg). The effects on bone resorption and formation were studied through histomorphometry and the effects on apoptosis through immunohistochemistry. D-003 (5-200 mg/kg) dose-dependently and significantly prevented (p < 0.001) changes in trabecular bone and increase in osteoclast surface and number versus ovariectomized controls, leaving osteoblast surfaces unchanged. Across the dose range, D-003 significantly increased (p < 0.05) osteoclast apoptosis in a dose-dependent manner and reduced (p < 0.05) osteoblast and osteocyte apoptosis versus ovariectomized controls, but these effects did not show dose dependence. In conclusion, D-003 (5-200 mg/kg) orally administered at for 12 weeks prevented bone loss and bone resorption and increased osteoclast apoptosis in ovariectomized rats in a dose-dependent manner. These results are consistent with previous data, showing that D-003 administered at relatively low doses prevents bone loss induced with ovariectomy, which could be useful to prevent or treat bone loss in postmenopausal women. Further experimental and clinical studies, however, are needed to confirm these findings.

Animals↗

PubMed1989

Polyisoprenoid, cholesterol and ubiquinone levels in human hepatocellular carcinomas.

The lipid composition of human hepatocellular carcinomas was examined. The level of dolichol in the tumours was decreased compared to control tissue, whereas the concentration of dolichyl phosphate did not exhibit any major change. A decrease in the amount of dolichyl ester was also observed. The pattern of individual polyisoprenoids in the free dolichol pool was changed in several carcinomas with a relative increase in the shorter dolichols. The isoprenol composition in the dolichyl ester and phosphate fractions of tumours were basically similar to those of controls. alpha-Unsaturated polyisoprenols are present in control livers at a level of 3% of the total free polyisoprenoid fraction, while this value was increased in the tumours. Similar to dolichol, the amount of ubiquinone was also decreased. The content of cholesterol was increased, while the fatty acid pattern of the dolichyl esters showed minor alterations. These modifications in lipid content indicate different mechanisms for the regulation of dolichol and dolichyl phosphate concentrations. The high levels of sterols in contrast to the low polyisoprenol content suggests interference with the regulation of the mevalonate pathway, which is the common biosynthetic route for cholesterol, ubiquinone and dolichol.

Adult↗

PubMed1988

The lipid composition of highly differentiated human hepatomas, with special reference to fatty acids.

The lipid compositions of homogenates and microsomal fractions derived from surgical samples of highly differentiated human hepatoma, morphologically normal regions outside the tumours and from normal livers were analysed. A few enzyme activities were also assayed. Hepatoma microsomes demonstrated considerably lowered levels of cytochromes P-450 and b5. Hepatoma homogenates exhibited increased levels of cholesterol, normal amounts of dolichyl-P and slightly lowered levels of total phospholipid. The levels of dolichol, dolichol ester and ubiquinone in hepatoma homogenates were prominently decreased. In tumour microsomes the levels of cholesterol and dolichyl phosphate were increased considerably while the levels of phospholipid and dolichol were lowered. The phospholipid composition of tumour homogenates was roughly similar to that of control tissue. In tumour microsomes the relative amounts of phosphatidylserine and phosphatidylinositol were about 30% decreased, whereas the major phospholipids showed minor increases in amount. The rate and pattern of incorporation of [3H]glycerol into individual phospholipids in liver slices from control and hepatoma tissue did not differ to any larger extent. The fatty acid composition of tumour homogenates exhibited minor differences in comparison to the control with the greatest changes in the sphingomyelin fraction. In hepatoma microsomes the fatty acid compositions of the major phospholipids were altered moderately, with evident decreases in the relative amounts of the long-chain polyunsaturated fatty acids. In hepatoma homogenates the fatty acid composition of dolichol esters differed only slightly from the control pattern. These results indicate that the major disturbance in the lipid metabolism of highly differentiated hepatomas is localized to the mevalonate pathway, thus affecting mainly the levels of cholesterol, dolichol and ubiquinone.

Carcinoma, Hepatocellular↗

PubMed1995

A novel assay for cytosolic 3-hydroxy-3-methylglutaryl-coenzyme A synthase activity using reversed-phase ion-pair chromatography: demonstration that Lifibrol (K12.148) modulates the enzyme activity.

Cytosolic HMG-CoA synthase and microsomal 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase catalyze two sequential steps in the mevalonate pathway. Both enzymes are negatively regulated by cholesterol. Cytosolic HMG-CoA synthase is responsible for the generation of HMG-CoA from acetyl-CoA and acetoacetyl-CoA). We have developed a new method to determine HMG-CoA synthase activity. In this assay, HMG-CoA is formed from acetoacetyl-CoA and labeled acetyl-CoA. The HMG-CoA product is isolated from the reaction mixture by means of reversed-phase ion-pair chromatography. The recovery of the product was always greater than 90%. The average within-batch coefficient of variation for HMG-CoA synthase activity was 5.1%. Using the new assay, we demonstrate that Lifibrol (K12.148), a new hypolipidemic compound, inhibits HMG-CoA synthase. Because our assay is accurate and precise it may become useful in future studies on the regulation and the pharmacological modulation of cytosolic HMG-CoA synthase.

Animals↗

PubMed1994

Isoprenoid biosynthesis in rat liver mitochondria. Studies on farnesyl pyrophosphate synthase and trans-prenyltransferase.

Mevalonate pathway enzyme activities in rat liver mitochondria were investigated, and it was found that isopentenyl pyrophosphate can be utilized for the synthesis of all-trans-polyprenyl pyrophosphates in vitro. In this reaction sequence intermediate formation of farnesyl pyrophosphate (FPP) predominates, and the FPP synthase activity was studied in more detail. The mitochondrial activity constitutes 13% of the total hepatic capacity for FPP synthesis, exceeding the corresponding microsomal, nuclear, and peroxisomal activities by 10-fold. Mitochondrial FPP synthase exhibits trypsin sensitivity only after sonication of intact mitochondria and upon subfractionation the activity is found localized in the matrix. FPP synthase activities at different locations responded distinctly when rats were treated with a diet enriched in cholesterol or containing mevinolin or cholestyramine. With the high cholesterol diet, mitochondrial FPP synthase activity increased 2-fold, while the cytosolic activity was slightly decreased. Both mevinolin and cholestyramine treatment resulted in 3-fold increases in cytosolic FPP synthase activities, without altering the mitochondrial activity. FPP was utilized as substrate for trans-prenyltransferase activity in the inner mitochondrial membrane. The products formed in this reaction were identified as nona- and decaprenyl-PP, and the reaction was influenced by changes in both substrate and Mg2+ concentration, giving more decaprenyl-PP when the concentrations of these substances were increased. These results demonstrate that mitochondria utilize endogenously produced FPP for isoprenoid biosynthesis and that the biosynthetic steps in mitochondria are regulated independently from those occurring in other subcellular compartments.

Animals↗

PubMed1996

The biology of HMG-CoA reductase: the pros of contra-regulation.

Hydroxymethylglutaryl-CoA reductase (HMG-R) is a key enzyme in the mevalonate pathway, from which thousands of molecules are derived including cholesterol and prenyl moieties. The regulation of HMG-R is complex and includes feedback control, cross-regulation by independent bio-chemical processes and contra-regulation of separate isozymes. From studies in yeast, these separate modes of regulation can be considered in an integrated fashion.

Feedback↗

PubMed1996

Influence of dolichol on microsomal membrane functions.

Microsomal membranes from rat liver were extracted with n-pentane in order to remove the lipid products of the mevalonate pathway, dolichol, ubiquinone and cholesterol. Dolichol and cholesterol were subsequently reincorporated into these extracted membranes. Electron microscopic examination demonstrated that extraction did not alter the vesicular membrane structure of the microsomes. The extracted vesicles were permeable to uncharged molecules in the same manner as control microsomes but had an increased permeability for charged molecules. Enzyme denaturation was not observed. The contraction of extracted vesicles was greatly increased when the incubation medium was supplemented with non-penetrating compounds such as polyethylene glycol and was much greater than that of control microsomes. When extracted membranes were reconstituted with dolichol or cholesterol, the original lower degree of contraction was reestablished. The effects of dolichol reincorporation on a number of microsomal enzyme activities were investigated and some limited changes were observed. These results demonstrate that extraction of microsomes with n-pentane and subsequent reincorporation of dolichol is an effective approach for investigating the functions of this lipid. Dolichol and cholesterol both affect microsomal membrane fluidity, but only cholesterol modifies the activities of certain integral microsomal membrane enzymes to a larger extent.

Animals↗

PubMed1997

Polyprenol formation in the yeast Saccharomyces cerevisiae: effect of farnesyl diphosphate synthase overexpression.

Biosynthesis of polyprenols was followed in the erg mutants of Saccharomyces cerevisiae impaired in various steps of the mevalonate pathway. The end products of the enzymatic reaction carried out in vitro, in the wild type yeast and all mutants tested, were identified as dehydrodolichols (alpha-unsaturated polyprenols) whereas in vivo, yeast synthesize dolichols (alpha-saturated polyprenols) (Biochimie, 1996.78:111-112.) The strain defective in the farnesyl diphosphate (FPP) synthase, (coded by the erg20-2 gene) required the presence of exogenous FPP for synthesis of dehydrodolichols to occur in vitro. Overexpression of the ERG20 gene restored synthesis of polyprenols in vitro indicating that FPP is the allylic "starter" for cis-prenyltransferase in yeast. Overexpression of the ERG20 gene in the erg 9 mutant, defective in squalene synthase activity, not only restored synthesis of dehydrodolichols in vitro, but also increased the synthesis of dolichols in vivo, almost 10-fold in comparison with wild type yeast. On the other hand overexpression of the mutated FPP synthase, coded by the gene erg20-2 in the same genetic background, resulted in a 100-fold increase of the amount of dehydrodolichols. Interestingly, in addition to the family of typical for yeast C60-C80 compounds, dehydrodolichols of chain length up to C135 were synthesized both in vitro and in vivo.

Alkyl and Aryl Transferases↗