Antimicrobial pomegranate rind extracts: enhancement by Cu(II) and vitamin C combinations against clinical isolates of Pseudomonas aeruginosa.

Recently, natural products have been further evaluated as sources of antimicrobial agents with efficacies against a variety of microorganisms. This study reports the antimicrobial activities of pomegranate rind extract (PRE) in combination with Fe(II) and Cu(II) salts against extended-spectrum multidrug-resistant Pseudomonas aeruginosa. Antimicrobial suspension assays were carried out using aqueous extract of pomegranate alone or in combination with metals salts against P. aeruginosa. The extract:metal salt combination was also enhanced with the addition of vitamin C. Marked activities were observed for the aqueous PRE/Cu(II) preparations, which were greatly enhanced by the addition of the reductant vitamin C. In contrast, the aqueous PRE/Fe(II) preparations were inactive, regardless of addition of vitamin C. The combination of PRE and Cu(II) salts and vitamin C showed the greatest activity against clinical isolates of P. aeruginosa. These results warrant further investigation of PRE as a potential source of new antimicrobial agents.

Receptor-dependent transcriptional activation of cytochrome P4503A genes: induction mechanisms, species differences and interindividual variation in man.

1. The importance of CYP3A enzymes in drug metabolism and toxicology has yielded a wealth of information on the structure, function and regulation of this subfamily and recent research emphasis has been placed on the human forms, namely CYP3A4, CYP3A5, CYP3A7 and CYP3A43. 2. The current review will focus on the receptor-dependency of CYP3A regulation and includes consideration of the regulatory roles of the glucocorticoid (GR), pregnane X (PXR) and constitutive androstane (CAR) receptors. 3. Emphasis has been placed on the topics of expression and substrate specificity, assessment of induction, species differences in induction, CYP3A promoter sequences and regulation of gene expression, structural and functional aspects of receptor-mediated, CYP3A gene activation, receptor variants and interindividual variation in human CYP3A expression, the latter encompassing environmental, physiological and genetic aspects. 4. An outline of future research needs will be discussed in the context of receptor-mediated molecular mechanisms of CYP3A gene regulation and the impact on interindividual variations in CYP3A expression. 5. Taken collectively, this review highlights the importance of understanding the molecular mechanisms of CYP3A induction as a means of rationalizing human responses to many clinically used drugs, in addition to providing a mechanistically coherent platform to understand and predict interindividual variations in response and drug-drug interactions.

Use of a reporter gene assay to predict and rank the potency and efficacy of CYP3A4 inducers.

Regulation of the CYP3A4 gene has been studied using an in vitro reporter gene assay. The effect of 17 xenobiotics on approximately 1 kilobase of the CYP3A4 proximal promoter, upstream of a secretory placental alkaline phosphatase reporter gene was investigated following transfection into the HepG2 cell line. Transfections were carried out either in the basal system or with cotransfection of expression plasmids for the human pregnane X receptor (hPXR) and the human glucocorticoid receptor (hGR), two important receptors in the regulation of CYP3A4 gene expression. Compounds were tested at four concentrations, and the resulting data were used to calculate maximal induction (I(max)) and EC(50) values. An "overall inductive ability" (IA) was derived by dividing I(max) by EC(50). Of the compounds tested seven were established transcriptional inducers, all of which were positive in the in vitro assay. The remaining 10 compounds represented a group with preliminary evidence for CYP3A transcriptional activation. Nine of these compounds produced statistically significant inductions in vitro, with only pravastatin failing to activate the reporter gene. This is of potential interest in light of the high IA values observed with the other structurally and functionally similar statins tested. We conclude that a four-concentration-point, in vitro model is capable of identifying CYP3A4 transcriptional inducers and yields an IA value allowing the ranking of compounds for their overall ability to induce CYP3A4 transcription. In addition, the majority of the compounds tested showed increased IA values in the hPXR/hGR cotransfected system, underpinning the importance of these receptors in CYP3A4 gene transcriptional regulation.

Regulation of the CYP3A4 gene by hydrocortisone and xenobiotics: role of the glucocorticoid and pregnane X receptors.

The molecular mechanisms of regulation of the CYP3A4 gene have been examined in an in vitro reporter gene system, containing -1 kb of the CYP3A4 promoter, in a HepG2 cell line. This system allows for the separate and combined transfection of expression plasmids encoding the human glucocorticoid receptor (hGR) and the human pregnane X receptor (hPXR), and, therefore, the opportunity to assess the role of these receptors in the induction process. Hydrocortisone produces a dose-dependent increase in CYP3A4 activation, a response that is increased in the presence of either receptor. Moreover, transfection of the hPXR decreased the EC(50) for hydrocortisone-dependent induction by a factor of 3.3, a response that was not changed by simultaneous cotransfection of the hGR. In addition, the hydrocortisone dose-response curve falls within the physiological blood level concentration of this steroid, implicating a regulatory role for hydrocortisone in the basal level of CYP3A4 expression. Although the responses to dexamethasone and rifampicin were both increased by both receptors, dexamethasone activation of CYP3A4 was similar for both the hGR and the hPXR, whereas rifampicin-dependent activation favored the hPXR. We conclude that regulation of the CYP3A4 gene is receptor-dependent and that hydrocortisone may function as a regulator of basal expression via the hPXR and the hGR. The implications of this latter conclusion for possible regulatory interactions between hydrocortisone and xenobiotic inducers remain to be clarified.