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Z D Liu

Publications and source records attributed to Z D Liu.

At least 19 recordsLinked to original sources
PubMed2002

Characterization of two isomeric beta-d-glucosiduronic acids derived from 1,2-diethyl-3-hydroxypyridin-4-one (CP94) in rat liver homogenate incubates.

1,2-Diethyl-3-hydroxypyridin-4-one (CP94) is an orally active iron chelator with potential for use in photodynamictherapy. This investigation reports the formation and characterization of two isomeric glucuronides of CP94 in rat liver homogenate incubates. To assign the glucuronidation sites in the CP94 molecule, two O-methylated derivatives of CP94 have been synthesized. By comparing the spectral characteristics of the CP94 3-O- and 4-O-methyl derivatives with CP94 and the CP94 glucuronides formed during incubation, evidence was obtained which enabled the assignment of these two isomeric glucuronides to the 3-O-glucuronide and 4-O-glucuronide of CP94. It was found that the 3-O-glucuronide was the dominant CP94 metabolite under in-vitro conditions. In an attempt to understand the potential influence of structural variation on the glucuronidation of CP94 analogues, the 1-and 2-monoethyl derivatives of CP94 were investigated. The 2-monoethyl derivative of CP94 yielded only the 3-O-glucuronide in rat liver homogenate incubate, while no glucuronide was formed from the 1-monoethyl derivative. In addition, no glucuronide from the 3-O-methyl or 4-O-methyl derivatives of CP94 could be detected. The relevance of these findings to the development of new 3-hydroxypyridin-4-one iron chelators is discussed.

Animals↗
PubMed2001

Structure-function investigation of the interaction of 1- and 2-substituted 3-hydroxypyridin-4-ones with 5-lipoxygenase and ribonucleotide reductase.

The structural and physiochemical properties of 3-hydroxypyridin-4-one chelators (HPOs) which influence inhibition of the iron-containing metalloenzymes ribonucleotide reductase (RR) and 5-lipoxygenase (5-LO) have been investigated. HPOs with substituents at the 1- and 2-positions of the pyridinone ring have been synthesized, and their inhibitory properties compared with those of desferrioxamine (DFO). Varying the alkyl substituents does not affect the affinity constant of these ligands for iron(III), but permits a systematic investigation of the effect of hydrophobicity and molecular shape on inhibitory properties. The inhibition of RR was monitored, indirectly by measuring tritiated thymidine incorporation into DNA and directly by the quantification of the EPR signal of the enzyme tyrosyl radical. 5-LO inhibition was examined spectrophotometrically, measuring the rate of linoleic hydroperoxide formation by soybean lipoxygenase. The results indicate that the substituent size introduced at the 2-position of the HPO ring is critical for determining inhibition of both enzymes. Large substituents on the 2-position, introduce a steric factor which interferes with accessibility to the iron centers. These studies have identified chelators such as 1,6-dimethyl-2-(N-4',N-propylsuccinamido)methyl-3-hydroxypyridin-4-one (CP358), which causes only a 10% inhibition of 5-LO after 24 h of incubation at 110 microm IBE (iron-binding equivalents) in comparison to simple dialkyl HPOs such as Deferiprone (CP20) which cause up to 70% inhibition. Using EPR spectroscopy, CP358 inhibits RR at a slower rate than CP20, while chelating intracellular iron(III) at a similar rate, a finding consistent with an indirect inhibition of the tyrosyl radical. However, hepatocellular iron is mobilized at a faster rate by CP358 (P < 0.001). These findings demonstrate that it is possible to design bidentate HPOs which access intracellular iron pools rapidly while inhibiting non-heme iron-containing enzymes relatively slowly, at rates comparable to DFO. It is anticipated that such compounds will possess a superior therapeutic safety margin to currently available bidentate HPOs.

Arachidonate 5-Lipoxygenase↗
PubMed2001

Structure-activity investigation of the inhibition of 3-hydroxypyridin-4-ones on mammalian tyrosine hydroxylase.

3-Hydroxypyridin-4-ones are currently one of the main candidates for the development of orally active iron chelators. Small bidentate ligands tend to inhibit iron-containing metalloenzymes and therefore can cause undesirable side effects. A range of 3-hydroxypyridin-4-ones with different R2 substituents was selected for the investigation of the structure-activity relationship between the chemical nature of the ligand and the inhibition of mammalian tyrosine hydroxylase. Results indicated that lipophilicity was the dominant factor in controlling the ability of this class of chelator to inhibit mammalian tyrosine hydroxylase. Ligands with hydrophilic R2 substituents tended to be weak inhibitors. No significant correlation was found in this study between iron-binding affinity, extended R2 chain length, and enzyme inhibitory activity. In contrast, both the LogP values of the entire molecule and of the R2 segment correlated well with inhibitory activity.

Animals↗
PubMed2001

Synthesis of 2-amido-3-hydroxypyridin-4(1H)-ones: novel iron chelators with enhanced pFe3+ values.

The synthesis of a range of 2-amido-3-hydroxypyridin-4-ones as bidentate iron(III) chelators with potential for oral administration is described. The pKa values of the ligands together with the stability constants of their iron(III) complexes have been determined. Results indicate that the introduction of an amido substituent at the 2-position leads to an appreciable enhancement of the pFe3+ values. The ability of these novel 3-hydroxypyridin-4-ones to facilitate the iron excretion in bile was investigated using a 59Fe-ferritin loaded rat model. The optimal effect was observed with the N-methyl amido derivative 15b, which has an associated pFe3+ value of 21.7, more than two orders of magnitude higher than that of deferiprone (1,2-dimethyl-3-hydroxypyridin-4-one) 1a (pFe3+ = 19.4). Dose response studies suggest that chelators with high pFe3+ values scavenge iron more effectively at lower doses when compared with simple dialkyl substituted hydroxypyridinones.

Animals↗
PubMed2000

Hydrolytic and metabolic characteristics of the esters of 1-(3'-hydroxypropyl)-2-methyl-3-hydroxypyridin-4-one (CP41), potentially useful iron chelators.

1-(3'-Hydroxypropyl)-2-methyl-3-hydroxypyridin-4-one (CP41) has been extensively investigated as an orally effective iron chelator. In order to improve the pharmacokinetic and metabolic properties of CP41, eleven aromatic esters have been synthesised and tested as potential prodrugs. In the present study, the hydrolytic rates of these CP41 esters in phosphate buffer (pH2.0 and pH 7.4), rat blood and rat liver homogenate have been determined and found to cover a wide range. Generally, they possessed relatively slow hydrolytic rates in phosphate buffer (0-50 nmol/ml/hr at pH 2.0 and 0-140 nmol/ml/hr at pH 7.4). The hydrolytic rates in rat blood fell in the range of 9-5766 nmol/ml blood/hr and in rat liver homogenate 1-800 micromol/g liver tissue/hr. All esters possess a higher lipophilicity than that of the parent compound CP41. Although no apparent relationship was observed between the lipophilicities and hydrolytic rates, the esters with relatively higher hydrolytic rates in liver homogenate tend to possess higher iron scavenging efficacies. Further investigation of the metabolism of selected CP41 esters indicates that metabolism is a key factor influencing the efficacy of CP41 esters, as some esters can be metabolically inactivated in the liver in preference to undergoing ester hydrolysis. Ester design, combined with a knowledge of the prodrug metabolism, is a useful strategy for the production of 3-hydroxypyridin-4-ones with enhanced iron scavenging efficacy.

Animals↗
PubMed2000

Design, synthesis, and biological evaluation of aromatic ester prodrugs of 1-(3'-hydroxypropyl)-2-methyl-3-hydroxypyridin-4-one (CP41) as orally active iron chelators.

In order to improve chelation efficacy and to minimise toxicity, eleven aromatic ester prodrugs of 1-(3'-hydroxypropyl)-2-methyl-3-hydroxypyridin-4-one (CP41) have been synthesised. The distribution coefficients of these ester prodrugs between 1-octanol and MOPS buffer pH 7.4 were measured together with their rates of hydrolysis at pH 2 and pH 7.4, in rat blood and liver homogenate. The biliary metabolic profiles of selected ester prodrugs were investigated in rats. The in vivo iron mobilisation efficacy of these ester prodrugs has been compared with that of the parent drug using a 59Fe-ferritin loaded rat model. The hydrolytic rates of these esters vary appreciably, esters with heteroaromatic acid moieties being less stable than the corresponding benzoyl analogues. Many prodrugs were found to enhance the ability of the parent hydroxypyridinone to facilitate 59Fe excretion, the optimal effect being observed with the 4-methylbenzoyl ester derivative 8d. However, not all prodrugs provide an increased efficacy, indicating that lipophilicity is not the only factor which influences drug efficacy. Furthermore no clear correlation between lipophilicity, susceptibility towards hydrolysis and efficacy was detected.

Animals↗
PubMed2000

Design, synthesis and evaluation of N-basic substituted 3-hydroxypyridin-4-ones: orally active iron chelators with lysosomotrophic potential.

To investigate the possibility of targeting chelators into the lysosomal iron pool, nine bidentate 3-hydroxypyridin-4-ones with basic chains have been synthesized. As the turnover of ferritin iron is centred in the lysosome, such strategy is predicted to increase chelator efficacy of bidentate ligands. The pKa values of the ligands together with their distribution coefficients between 1-octanol and 4-morpholinepropane sulphonic acid (MOPS) buffer pH 7.4 have been determined. The in-vivo iron mobilization efficacy of these basic 3-hydroxypyridin-4-ones has been investigated in a 59Fe-ferritin-loaded rat model. No obvious correlation was observed between efficacy and the pKa value of the side chain, although those with pKa > 7.0 tended to be more efficient than those with pKa < 7.0. The imidazole-containing molecules are much less effective than the tertiary amine derivatives. A dose-response study suggested that basic pyridinones are relatively more effective at lower doses when compared with N-alkyl hydroxypyridinones. Optimal effects were observed with the piperidine derivatives 4h and 4i. The derivative 4i at a dose of 150 micromol kg(-1) was more effective than 450 micromol kg(-1) deferiprone, the widely adopted clinical dose.

Alkalies↗
PubMed2000

Biliary and urinary metabolic profiles of 1,2-diethyl-3-hydroxypyridin-4-one (CP94) in the rat.

This study compares the biliary and urinary metabolic profiles of 1,2-diethyl-3-hydroxypyridin-4-one (CP94), an orally active iron chelator, in the normal rat. Surprisingly, CP94 was found to form two phase II metabolites, the 3-O- and 4-O-glucuronides. These glucuronides accounted for 38 and 28% of the administered CP94 dose, in bile and urine, respectively. Unchanged CP94 accounted for 5% of the CP94 dose in both bile and urine. The 2-(1'-hydroxy) metabolite of CP94 was found to be the dominant metabolite in urine. In addition, an unstable metabolite was detected in the bile although its structure remains unknown at the present stage. The excretion of iron in bile, after administration of CP94, was found to parallel the biliary elimination of CP94 together with its hydroxylated derivatives, indicating the importance of metabolites in iron excretion.

Animals↗
PubMed2000

[The characteristics of Bacillus thuringiensis strain YBT833 and its transformants that containing different ICP genes].

Four different transformants were selected by transferring cry1C into Bacillus thuringiensis strain YBT833. Southern blot and Plasmid profiles results all proved that cry1C was transferred into strain YBT833. However, it was found by PCR analysis that transformant YBT833-1 kept all indigenous ICP(insecticidal crystal protein) genes of strain YBT833 while transformant YBT833-2 lost cry1Ab, and transformant YBT833-3 lost all ICP genes. SDS-PAGE showed that transformants of YBT833-1, YBT833-2 and YBT833 all had 130 kDa and 65 kDa peptide bands, but transformant YBT833-3 did not have 65 kDa peptide band. Bioassay results showed that the toxicities of all transformants to Spodoptera exigua, Heliothis armigera and Plutella xylostella were lower than that of strain YBT833, except the toxicity of transformant YBT833-2 to P. xylostella which was obviously higher than that of YBT833.

Bacillus thuringiensis↗
PubMed2000

[Transfer of cry1C gene into Bacillus thuringiensis by electroporation to construct strain with broader insecticidal activity].

Three Transformants were selected by transferring cry1C into Bacillus thuringiensis strain YBT1535. Plasmid profiles, PCR and Southern blot result all proved that cry1C had been transferred into strain YBT1535. Bioassay results showed that the transformants of strain YBT1535 displayed significantly higher toxicity against Spodoptera exigua than strain YBT1535, but the toxicities against Heliothis armigera and Plutella xylostella did not rise except transformant YBT1535-2.

Bacillus thuringiensis↗
PubMed2000

[Cloning of plasmid pBMB2062 in Bacillus thuringiensis strain YBT-1520 and construction of plasmid vector with genetic stability].

A small plasmid pBMB2062 in Bacillus thuringiensis strain YBT-1520 was cloned and sequenced. Its 2,062 bp sequence contains two potential open reading frames (orfs). The orf1 and orf2 encode a tentative replication initial protein consisting of 289 amino acid residues and a tentative replication protein consisting of 80 amino acid residues, respectively. Two homological plasmids were found by Blast searching. There are 23 nucleotides difference occurring among three of the plasmids. The difference occurred in the orf1 causes different encoding capability. Comparing with the orf1 in pBMB2062, the orf1 in the homological plasmids are truncated, one at the N-terminal and another at the C-terminal. cDNA synthesis and PCR detection showed that the mRNA corresponding to orf1 in pBMB2062 really occurs. Shuttle vectors were constructed based on pBMB2062 and showed the ability to express insecticidal crystal gene. Under nonselective condition, recombinant plasmids based on pBMB2062 were genetically stable.

Amino Acid Sequence↗
PubMed1999

Synthesis, physicochemical characterization, and biological evaluation of 2-(1'-hydroxyalkyl)-3-hydroxypyridin-4-ones: novel iron chelators with enhanced pFe(3+) values.

The synthesis of a range of 2-(1'-hydroxyalkyl)-3-hydroxypyridin-4-ones as bidentate iron(III) chelators with potential for oral administration is described. The pK(a) values of the ligands and the stability constants of their iron(III) complexes have been determined. Results indicate that the introduction of a 1'-hydroxyalkyl group at the 2-position leads to a significant improvement in the pFe(3+) values. Such an effect was found to be greater with the hydroxyethyl substituent than with the hydroxymethyl substituent, particularly in the cases of 1-ethyl-2-(1'-hydroxyethyl)-3-hydroxypyridin-4-one (pFe(3+) = 21.4) and 1,6-dimethyl-2-(1'-hydroxyethyl)-3-hydroxypyridin-4-one (pFe(3+) = 21.5) where an enhancement on pFe(3+) values in the region of two orders of magnitude is observed, as compared with Deferiprone (1, 2-dimethyl-3-hydroxypyridin-4-one) (pFe(3+) = 19.4). The ability of these novel 3-hydroxypyridin-4-ones to facilitate the iron excretion in bile was investigated using a [(59)Fe]ferritin-loaded rat model. Chelators and prodrug chelators possessing high pFe(3+) values show great promise in their ability to remove iron under in vivo conditions.

Animals↗
PubMed1999

Gradient ion-pair high-performance liquid chromatographic method for analysis of 3-hydroxypyridin-4-one iron chelators.

A gradient ion-pair HPLC separation of highly hydrophilic 3-hydroxypyridin-4-one (HPO) iron chelators is described. The separation of HPOs was performed using a reversed-phase polymer HPLC column (PLRP-S 100 A, 15x0.46 cm ID, 5 microm). The ion-pair buffer contained 1-heptanesulfonic acid (sodium salt) (5 mM) and the pH was adjusted to 2.0 using HCl. The gradient was 2%-35% CH3CN in 20 min and post-run was followed for 5 min using 2% CH3CN and 98% buffer. The flow-rate was 1 ml/min and the analytes were monitored at 280 nm. The retention times of 30 hydrophilic HPOs fell in the range of 10-18 min with sharp peak shapes, although these iron chelators possess various functional groups and distribution coefficients. The application of this HPLC method in the analysis of HPO chelators and their metabolites in rat bile and urine is described.

Animals↗
PubMed1999

Investigation into the correlation between the structure of hydroxypyridinones and blood-brain barrier permeability.

Bidentate hydroxypyridinones are under active development as orally active iron chelators. With applications for the treatment of general body iron overload, for instance with thalassaemia, the distribution of the chelators should be limited to peripheral tissue and they should not enter the central nervous system. This study compares the predictive abilities of LogPoctanol and LogPcyclohexane and reports the existence of good correlations between blood-brain barrier (BBB) permeability and both values for N-alkylpyridinones. 1,omega-Hydroxyalkyl hydroxypyridinones penetrate the BBB much more slowly than the simple 1-alkyl derivatives. This observation is likely to have important toxicological implications.

Animals↗
PubMed1999

In vivo iron mobilisation evaluation of hydroxypyridinones in 59Fe-ferritin-loaded rat model.

Although there are a number of well-characterised animal models available for testing and comparing the efficacy of iron chelators, most are expensive to operate and are not capable of providing rapid and reproducible results. The method described herein is based on the labelling of rat liver with 59Fe using rat 59Fe-ferritin. This method produces highly reproducible data of the type necessary for dose-response investigations, comparison of the efficacies of different administration routes, and structure activity studies.

Animals↗