Current Drug Metabolism - Volume 13, Issue 9, 2012

Quantitative bioanalysis is urgently required for the evaluation of pharmacokinetic properties of a drug and to demonstrate the body exposure to the parent drug and/or metabolite for interpretation of the efficacy and toxicity. New trends in drug discovery and development will be always posing challenges on LC–MS-based quantitative bioanalysis. The focus of this minireview is to highlight the commonly used strategies for improving the quantitative bioanalytical performance including overcoming matrix effects and improving MS detectability. “LC-electrolyte effects” and “pulse gradient chromatography” proposed by our group are new approaches that have also showed potential efficiencies on improving overall bioassay performance, including lowering lower limit of quantification (LLOQ), enlarging upper limit of quantification (ULOQ), decreasing matrix effects, and overcoming elutropic effects, etc.. They should also work well in metabolic profiling studies and other important analytical fields, such as food pesticide residue analysis, environmental analysis, clinical and forensic toxicology, doping control, and so on.

Understanding the metabolic and pharmacokinetic fate of a drug in humans is a key factor in its development and registration, as well as in the elaboration of new therapeutic agents. To carry out these studies, stable isotope labeling techniques have been effectively used by drug metabolism scientists and toxicologists in order to gain better understanding of the drugs’ disposition, bioavailability and toxicity in in vivo studies. Among the different analytical techniques used, mass spectrometry (MS) coupled to separation techniques has become the detection method of choice due to its high sensitivity and selectivity. In vitro quantification of metabolite levels in biofluids by MS is often difficult if a proper internal standard is not available due to the inherent problems associated with the technique (e.g. chromatographic coelutions, ion suppression, low reproducibility etc.). Stable isotope coding approaches alleviate these drawbacks and allow comparative drug metabolomics studies similarly to the differential proteomic techniques developed in the last decade. This review describes a selection of methodological improvements in the use of stable isotopes labeling in combination with MS to detect drug metabolites. In the first part of the paper, the application of labeled compounds to study the absorption, distribution, metabolism, excretion and toxicology of drugs (ADMET) in addition to the elucidation of metabolic pathways is presented. In the second part, recent developments of stable isotope coded tags for the in vitro relative metabolite quantification in biofluids are presented.

Recent advances in analytical methodologies have made it possible to bring metabolomic profiling into quantitative metabolomics that permits precise measurements of comprehensive small-molecule profiles. Modern liquid chromatography-tandem mass spectrometry (LC-MS/MS) with multiple reaction monitoring (MRM) mode serves as the foundation for accurate simultaneous multi-analyte quantitation across large sample sets to provide high-quality information on target molecular profiles in complex systems. Despite the intrinsic multiplexing potential of the LC-MRM-MS technique, the key bottleneck in current LC-MRM-based assays is generally the limited analyte coverage and throughput capacity. Nowadays, the MRM-based approach has emerged as an attractive strategy for quantitative proteomic analysis and high-throughput biomarker discovery. So far, the full potential of the contemporary LCMRM methodology unleashed for quantitative metabolite profiling and metabolomic measurements of non-peptidic small molecules is rarely discussed. In this review we attempt to provide an overview on the major recent developments in LC-MRM-based strategies for quantitative profiling of multi- and non-target small molecules in biological samples. This article highlights the utility and power of the LC-MRM-based targeted approaches as valuable bioanalytical tools for low-cost, multiplexed quantitation on a large scale, with special emphasis on the promise of combining various strategies for expanding coverage and throughput of the LC-MRM-based assays to cover the gap between a widely targeted profiling and large-scale unknown screening towards comparative or quantitative metabolomics. General issues raised in metabolite profiling, such as basic aspects of bioanalysis, methodological dilemmas and challenges in quantitative metabolomics are addressed, and different strategies to circumvent the existing bottleneck and potential pitfalls of the current LC-MRM-MS techniques are outlined. In addition, the rudiments of LC-MRM-MS and its recent applications in combination with such strategies for biomarker quantitation and verification is also described.

In the recent years the way of thinking about human health necessarily passes by human food. Recent discoveries are not only concerned about valuable biomolecules but also contaminants. Thus, the screening of substances in animal and vegetable matrices by analytical techniques is focused on the presence and absence of target substance. In both cases, the majority of these substances are present as traces or in very low levels. Contaminants could be naturally present in the food, inserted on it or even developed on it as a consequence of food processing or cooking. Pesticides, mycotoxins, dioxins, acrylamide, Sudan red, melamine and now 4(5)-methylimidazole can be, at present, be listed as some of the world big problems related to food contaminants and adulterants. With the development of liquid chromatography coupled to mass spectrometry (LC-MS-MS), in the last few decades, analysis of some food contaminants in trace levels trace become less laborious, more accurate and precise. The multiple approach of those techniques make possible to obtain many results in one single run. On the other hand, European Union (2002/657/EC) established regulations for analytical methods regarding mass spectrometry as detection tool, showing the importance of this technique in food quality control. The EU criteria uses identification points (IPs) that could be achieved basically with four product ions (including molecular ion) or reduced with the use of high resolution equipments. This kind of mass spectrometers made the IPs criteria more accessible, as the exact mass information is a differential tool. In view of this the aim of this review is to present the actual scenario for mass spectrometry analysis in a complex vegetable food matrix such as roasted coffee, with emphasis on needs and challenges regarding the LC-MS technique in order to meet and contribute to food safety standards in this complex matrix.

Accompanying with hot discussions on developing multi-target drugs for the therapy of multi-gene diseases, herbal medicines are receiving more and more attention worldwide in both academic and industrial fields. Pharmacokinetic and metabolic research is one of the important issues for intensive understanding of therapeutic benefits/risks of herbal medicines. The qualitative and quantitative analysis of herbal medicines, which is a prerequisite for pharmacokinetic and metabolic evaluations, remains a great challenge because of the intrinsic complexity of herbal medicines. This paper provides a review on the recent development of qualitative and quantitative methodologies on herbal medicines analysis. Powerful hybrid mass spectrometric tools such as Q-TOF and IT-TOF are highly useful for both the qualitative and quantitative analysis of complicated components. In the past decade, some universal useful strategies to the qualitative and quantitative analysis and pharmacokinetic assessment of complicated herbal components have been also proposed. Nonetheless, it is urgent to develop additional strategies to resolve the critical challenges underlying herbal analyses, such as the lack of authentic compounds, the difficulties in information processing, and the elimination of complex matrixes interferences.

Thiopurines (azathioprine, 6-mercaptopurine and 6-thioguanine), are drugs useful in the treatment of leukemia, autoimmune diseases, as well as in organ transplantation. After many years of use is still not well understood their mode of action. Recently, several groups have found that thiopurines can activate autophagy by different mechanisms. Autophagy is a process of auto-digestion. After an infection, radiation, injury, oxidative stress, or after drug treatment, the cellular organelles may be damaged. In those cases the damaged structures are recognized by the cell, isolated in a double-membrane vacuole and finally degraded in autolysosomes. The digestion gives rise to biosynthetic precursors needed to regenerate partially destroyed structures, so as to produce the energy essential in the anabolic process. During fasting, the protein aggregates, lipid droplets and glycogen deposits are degraded by this pathway for releasing nutrients to the blood. Therefore this process is of vital importance in the maintaining of cellular functions and in the systemic homeostasis of whole organism. The therapy with thiopurines leads to adverse effects such as myelosuppression and hepatotoxicity whose mechanism is not well understood today. Autophagy is also involved in liver degeneration induced by drugs, alcohol or viruses. Therefore, seems to be very attractive know whether the autophagy induced by thiopurines is the cause of the hepatotoxicity associated with these drugs, or rather, autophagy is a compensatory response that protects the liver against the deleterious effects of the thiopurines. Our results and previous data suggest that autophagy is beneficial for the liver because protects it against the deleterious effects of thiopurines.

Thiopurine S-methyltransferase (TPMT) catalyzes the methylation of thiopurine drugs, such as azathioprine and mercaptopurine, which are used in a variety of diseases. Several mutations in the TPMT gene correlate with low enzyme activity and subsequent adverse effects, mainly myelotoxicity. Hence, genotyping TPMT makes it possible to identify patients at high risk of drug toxicity and adjust dosage accordingly. However, further research about the availability of a reliable and universal screening method and more costeffectiveness studies are necessary.

Inflammatory bowel disease (IBD) encompasses 2 independent but related entities: ulcerative colitis (UC) and Crohn’s disease. Crohn’s disease is characterised by transmural patchy inflammation which can involve any portion of the gastrointestinal tract. UC is characterised by superficial inflammation that begins in the rectum and extends proximally along the colon. In Europe, approximately 2.2 million people have a diagnosis of IBD. The aetiology of IBD is unknown, however, immune, environmental and genetic factors are thought to be involved. Individuals with IBD are at risk of developing osteoporosis. In line with this, there are clear guidelines that recommend vitamin D supplementation for IBD patients to prevent bone disease, especially when undergoing steroid treatment. Despite an established role for vitamin D in IBD, deficiency is common. More novel effects of vitamin D beyond bone are emerging. It is now well established that vitamin D is an important regulator of the immune system which may have implications for the development, severity and management of immune related disorders such as IBD. The efficacy of vitamin D as an immune modulator in IBD remains to be proven. This review aims to evaluate the evidence implicating vitamin D deficiency in IBD pathogenesis, to examine vitamin D’s anti-inflammatory mechanisms and to explore its therapeutic potential, optimal serum levels and dietary intakes which may support immune function in this disease.

Proton pump inhibitors (PPIs) are the most potent acid suppressants available. PPIs undergo hepatic metabolism via the CYP2C system for the isoforms CYP2C19 and CYP3A4 in particular. Genetic polymorphisms in CYP2C19 may affect the metabolism of individual PPIs to different extents. Although PPIs are highly effective as a class, differences in their pharmacokinetics, such as bioavailability and metabolism, may translate into differences in clinical outcomes. In Helicobacter pylori infection, a significantly lower eradication rate was seen in extensive metabolizers with omeprazole but no with rabeprazole.

Colorectal cancer (CRC) is one of the leading causes of mortality in the western world. It is widely accepted that neoplasms such as colonic polyps are precursors to CRC formation; with the polyp-adenoma-carcinoma sequences well described in medical literature [1, 2]. It has been shown that Aspirin and other non-steroid anti-inflammatory drugs (NSAID) have a negative effect on polyp and cancer formation. This review aims to describe some of the mechanism behind the chemoprotective properties of aspirin; COX 2 inhibition, regulation of proliferation and apoptosis and effects on the immune system and also the current evidence that supports its use as a chemoprevention agent against CRC. We will also aim to explore the side effects with the use of aspirin and the pitfalls of using aspirin routinely for primary prophylaxis against CRC.

Eosinophilic oesophagitis is a clinicopathological disease characterized by oesophageal eosinophilia and gastrointestinal symptoms. Currently, the optimal treatment regimens remain unclear. The pathogenesis of eosinophilic oesophagitis appears to involve immune dysregulation, while acid reflux may have a secondary role; the mainstays in treatment are aimed principally at these dual processes. While a trial of a PPI is worthwhile it is likely that PPI therapy is treating concurrent acid reflux rather than true eosinophilic oesophagitis. Dietary elimination with elemental feed is safe but poorly tolerated. Swallowed topical steroids are the mainstay of commercially available therapies. Both fluticasone and budesonide have been proven to be beneficial both symptomatically and in reducing oesophageal eosinophil counts in the short and medium term. Basic studies have determined a role for IL-5 in oesophageal remodelling in eosinophilic esophagitis. Initial clinical studies have shown single or multiple infusions of monoclonal antibody to IL-5 to be well tolerated and to cause a long-term decrease in both peripheral and sputum eosinophil count in these eosinophil driven conditions. At present, swallowed corticosteroids are the mainstay of treatment for patients with eosinophilic oesophagitis in patients failing PPI therapy. Studies have been heterogenous in their diagnostic criteria for eosinophilic oesophagitis and in the definition of response to therapy, making comparison of results difficult.

Expression and activity of several key drug metabolizing enzymes (DMEs) and transporters are altered in various pathophysiological conditions, leading to altered drug metabolism and disposition. This can have profound impact on the pharmacotherapy of widely used clinically relevant medications in terms of safety and efficacy by causing inter-individual variabilities in drug responses. This review article highlights altered drug disposition in inflammation and infectious diseases, and commonly encountered disorders such as cancer, obesity/diabetes, fatty liver diseases, cardiovascular diseases and rheumatoid arthritis. Many of the clinically relevant drugs have a narrow therapeutic index. Thus any changes in the disposition of these drugs may lead to reduced efficacy and increased toxicity. The implications of changes in DMEs and transporters on the pharmacokinetics/pharmacodynamics of clinically-relevant medications are also discussed. Inflammation-mediated release of pro-inflammatory cytokines and activation of toll-like receptors (TLRs) are known to play a major role in down-regulation of DMEs and transporters. Although the mechanism by which this occurs is unclear, several studies have shown that inflammation-associated cell-signaling pathway and its interaction with basal transcription factors and nuclear receptors in regulation of DMEs and transporters play a significant role in altered drug metabolism. Altered regulation of DMEs and transporters in a multitude of disease states will contribute towards future development of powerful in vitro and in vivo tools in predicting the drug response and opt for better drug design and development. The goal is to facilitate a better understanding of the mechanistic details underlying the regulation of DMEs and transporters in pathophysiological conditions.

The prevalence of obesity continues to rise throughout the world. Increasingly, bariatric surgery is used for those with morbid obesity as a pivotal approach to achieve weight loss. Along with substantial weight loss, malabsorption of essential vitamins, minerals, and drugs also occurs. Therefore, more than ever, a better understanding of the physiology and mechanisms by which these deficiencies occur is essential. We review the normal physiology of vitamin, mineral, and drug absorption. This is followed by a description of currently performed bariatric surgeries in the United States. A detailed review of specific nutrient and mineral deficiency states is presented, based on the most significant studies published in the last two decades. Of note, screening and supplementation recommendations have been included. Drug absorption data after these procedures is presented and discussed. Studies were identified by searching the Cochrane Registry and MEDLINE using relevant search terms, as well as through review of the reference section of included manuscripts. Conclusions: Bariatric surgery can be effectively used to achieve sustainable weight-loss in morbidly obese patients. It simultaneously brings forth important functional consequences on nutrient deficiencies and drug absorption that clinician’s must be aware of. Further prospective, randomized research on specific procedures and deficiencies is required.