Current Drug Metabolism - Volume 11, Issue 10, 2010

Cytochrome P450 enzymes (CYPs) are a superfamily of monooxygenases found in almost all living organisms. CYPs are predominantly localized in the endoplasmic reticulum membranes as integral membrane proteins, where they metabolize a variety of endogenous and xenobiotic compounds. CYPs also reside in other subcellular compartments, including the plasma membranes and mitochondria. CYP localization in mitochondria is regulated in one of two ways: (1) direct targeting of inherent CYPs with canonical mitochondrial signals in their protein sequence after synthesis in the cytosol or (2) mitochondrial localization of microsomal CYPs after processing of the NH2-terminal region. Microsomal CYPs targeted to mitochondria demonstrate conventional or altered catalytic activities using electrons provided by the mitochondrial electron transport system. Mechanisms of microsomal CYP targeting to mitochondria, regulation of localization, and the implications of these in drug metabolism are described in the present review.

The vaginal route of drug administration provides women with a valid alternative to more conventional methods of contraception. Drugs absorbed in the upper part of the vagina can bypass the liver and, if metabolized, are subject to a reduced hepatic first-pass effect. Current vaginally-administered contraceptive formulations deliver similar doses of gestagens to those provided by oral methods but release lower amounts of oestrogens. This results in a systemic exposure to gestagens similar to that achieved via other routes, thereby maintaining contraceptive efficacy while limiting systemic, but not uterine, exposure to oestrogen. In this way, the probability of systemic oestrogen-related adverse effects are theoretically reduced without compromising cycle control. In addition, the fact that the effects of a contraceptive ring last a complete cycle makes it more user-friendly than other methods and results in better patient compliance. The present review will explain in detail the specificities of this route of delivery of hormonal contraception and will compare it to more classic forms of contraception received via the oral (pill), intramuscular (injected), transdermic (patch) and subcutaneous (implants) routes of administration.

Cells undergo phenotypic changes after exposure to a wide range of exogenous stimuli that include growth factors, proinflammatory cytokines and environmental chemicals. Such stimuli may arise as components of disease pathogenesis and cellular injury, or as a result of exposure to environmental chemicals and radiation. These stimuli modulate the proliferation and differentiation of cells by altering the regulation of genes that control homeostasis. A generalized response appears to be a decline in the expression and function of many cytochrome P450 (CYP) genes in liver and other tissues. Thus, individuals who have been exposed to such exogenous stimuli often exhibit a decreased capacity for drug clearance, which has important consequences for concurrent drug therapy. Several signaling pathways transduce exogenous stimuli within cells, with the mitogen-activated protein kinases (MAPKs) being one of the most important. Evidence is increasing that MAPKs may impair the expression of multiple CYP genes by modulating the activity of transcription factors, including nuclear receptors, the aryl hydrocarbon receptor, and the activator protein-1 complex. MAPKs catalyze the phosphorylation of transcription complexes that incorporate these factors, which modulates their capacity to transactivate target genes, including CYPs. An understanding of the mechanisms that account for the regulatory impact of MAPKs on the transcriptional factors that regulate CYP genes will provide critical insight into the consequences from exposure to injurious stresses that impact cellular function.

Poly(lactic-co-glycolic acid) (PLGA) nanoparticles (PLGANPs) have been widely investigated for sustained and targeted delivery of various drugs including small molecular drugs (hydrophobic/ hydrophilic drugs) and macromolecule drugs (such as proteins, peptides, genes, vaccines, antigens, human growth factors, etc.). The in vivo pharmacokinetics and disposition profile of these encapsulated drugs and PLGANPs themselves is a key factor that determines their therapeutic index and potential for clinical use. Therefore, this review attempts to outline the in vivo behaviors of diverse drugs loaded PLGANPs administrated via different routes such as oral route, intravenous injection, nasal path, etc. . Also, the associated analytical techniques used to investigate the in vivo disposition of PLGANPs loaded with drugs are focused on.

The method of predicting CYP induction drug-drug interactions (DDIs) from a relative induction score (RIS) calibration has been developed to provide a novel model facilitating predictions for any CYP-inducer substrate combination by inclusion of parameters such as the fraction of hepatic clearance mediated by a specific CYP and fraction of the dose escaping intestinal extraction. In vitro HepaRG CYP3A4 induction data were used as a basis for the approach and a large number of DDIs were well predicted. Primary human hepatocyte data were also used to make predictions, using the HepaRG calibration as a foundation. Similar predictive accuracy suggests that HepaRG and primary hepatocyte data can be used inter-changeably within the same laboratory. A comparison of this ‘indirect’ calibration method with a direct in vitro-in vivo scaling approach was made and investigations undertaken to define the most appropriate in vivo inducer concentration to use. Additionally, a reasonably effective prediction model based on F2 (the concentration of inducer taken to increase the CYP mRNA 2-fold above background) was established. An accurate prediction for the CYP1A2-dependent omeprazolecaffeine interaction was also made, demonstrating that the methods are useful for the evaluation of DDIs from induction involving mechanisms other than PXR activation. Finally, a dynamic mechanistic model accounting for the simultaneous influence of CYP induction and reversible and irreversible CYP inhibition in both the liver and intestine was written to provide a prediction of the overall DDI when several interactions occur concurrently. The rationale for using the various models described, alongside commercially available prediction tools, at various stages of the drug discovery process is described.

The inner ear is difficult to access by conventional systemic drug delivery due to formidable physiological and anatomic barriers. There is an increasing interest in the treatment of inner ear disorders by topical application of drugs to the inner ear. One of the most important issues to overcome before full clinical application is the development of smart delivery systems for drugs to the target sites and controlled release in the inner ear. This is an area where nanoparticles will play an extremely important role. These submicron particles have exhibited improved biocompatibility, in vivo stability, target specificity, and cell/tissue uptake and internalization of the encapsulated therapeutic agents, leading to a decrease in the dose required and a decrease in side effects. This unique combination of properties makes nanoparticles a novel delivery device, which fulfils the requirements for inner ear application. This review will summarize recent findings and applications of various nanoparticle-based systems like poly (D, L-lactic/glycolic acid) nanoparticles, magnetic nanoparticles, lipid nanoparticles, liposomes, polymersomes, hydroxyapatite nanoparticles, and silica nanoparticles in the field of inner ear drug delivery. Moreover, the review will provide an insight into the future strategies of nanoparticle-based cochlear drug delivery. In conjunction, physiological considerations related to inner ear administration will be highlighted. The routes and applications for local inner- ear drug delivery will also be mentioned. In closing, this review will give an overview of the potential future development in inner ear administration with nanoparticles.