Inhibitory Mechanisms of Lekethromycin in Dog Liver Cytochrome P450 Enzymes Based on UPLC-MS/MS Cocktail Method

Lekethromycin (LKMS) is a synthetic macrolide compound derivative intended for use as a veterinary medicine. Since there have been no in vitro studies evaluating its potential for drug-drug interactions related to cytochrome P450 (CYP450) enzymes, the effect of the inhibitory mechanisms of LKMS on CYP450 enzymes is still unclear. Thus, this study aimed to evaluate the inhibitory effects of LKMS on dog CYP450 enzymes. A cocktail approach using ultra-performance liquid chromatography-tandem mass spectrometry was conducted to investigate the inhibitory effect of LKMS on canine CYP450 enzymes. Typical probe substrates of phenacetin, coumarin, bupropion, tolbutamide, dextromethorphan, chlorzoxazone, and testosterone were used for CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2D6, CYP2E1, and CYP3A4, respectively. This study showed that LKMS might not be a time-dependent inhibitor. LKMS inhibited CYP2A6, CYP2B6, and CYP2D6 via mixed inhibition. LKMS exhibited mixed-type inhibition against the activity of CYP2A6 with an inhibition constant (Ki) value of 135.6 μΜ. LKMS inhibited CYP2B6 in a mixed way, with Ki values of 59.44 μM. A phenotyping study based on an inhibition assay indicated that CYP2D6 contributes to the biotransformation of LKMS. A mixed inhibition of CYP2D6 with Ki values of 64.87 μM was also observed. Given that this study was performed in vitro, further in vivo studies should be conducted to identify the interaction between LKMS and canine CYP450 enzymes to provide data support for the clinical application of LKMS and the avoidance of adverse interactions between other drugs.

A Review: Effects of Macrolides on CYP450 Enzymes

As a kind of haemoglobin, cytochrome P450 enzymes (CYP450) participate in the metabolism of many substances, including endogenous substances, exogenous substances and drugs. It is estimated that 60% of common prescription drugs require bioconversion through CYP450. The influence of macrolides on CYP450 contributes to the metabolism and drug-drug interactions (DDIs) of macrolides. At present, most studies on the effects of macrolides on CYP450 are focused on CYP3A, but a few exist on other enzymes and drug combinations, such as telithromycin, which can decrease the activity of hepatic CYP1A2 and CYP3A2. This article summarizes some published applications of the influence of macrolides on CYP450 and the DDIs of macrolides caused by CYP450. And the article may subsequently guide the rational use of drugs in clinical trials. To a certain extent, poisoning caused by adverse drug interactions can be avoided. Unreasonable use of macrolide antibiotics may enable the presence of residue of macrolide antibiotics in animal-origin food. It is unhealthy for people to eat food with macrolide antibiotic residues. So it is of great significance to guarantee food safety and protect the health of consumers by the rational use of macrolides. This review gives a detailed description of the influence of macrolides on CYP450 and the DDIs of macrolides caused by CYP450. Moreover, it offers a perspective for researchers to further explore in this area.

Metabolism and pharmacokinetics of pharmaceuticals in cats (Felix sylvestris catus) and implications for the risk assessment of feed additives and contaminants

In animal health risk assessment, hazard characterisation of feed additives has been often using the default uncertainty factor (UF) of 100 to translate a no-observed-adverse-effect level in test species (rat, mouse, dog, rabbit) to a 'safe' level of chronic exposure in farm and companion animal species. Historically, both 10-fold factors have been further divided to include chemical-specific data in both dimensions when available. For cats (Felis Sylvestris catus), an extra default UF of 5 is applied due to the species' deficiency in particularly glucuronidation and glycine conjugation. This paper aims to assess the scientific basis and validity of the UF for inter-species differences in kinetics (4.0) and the extra UF applied for cats through a comparison of kinetic parameters between rats and cats for 30 substrates of phase I and phase II metabolism. When the parent compound undergoes glucuronidation the default factor of 4.0 is exceeded, with exceptions for zidovudine and S-carprofen. Compounds that were mainly renally excreted did not exceed the 4.0-fold default. Mixed results were obtained for chemicals which are metabolised by CYP3A in rats. When chemicals were administered intravenously the 4.0-fold default was not exceeded with the exception of clomipramine, lidocaine and alfentanil. The differences seen after oral administration might be due to differences in first-pass metabolism and bioavailability. Further work is needed to further characterise phase I, phase II enzymes and transporters in cats to support the development of databases and in silico models to support hazard characterisation of chemicals particularly for feed additives.

The critical role of porcine cytochrome P450 3A46 in the bioactivation of aflatoxin B1

Aflatoxin B₁ (AFB₁) is bioactivated by cytochrome P450 (CYP) 3A isoforms in humans to generate the highly reactive epoxide intermediate AFB₁-8,9-epoxide (AFBO), causing hepatotoxicity and hepatocarcinoma. Due to the unavoidable contamination in their feed, pigs are more likely to be exposed to AFB₁ and indirectly harm human health. Therefore, identifying the porcine CYP3A isoforms involved in AFB₁-8,9-epoxidation is critical. In this study, we used codon optimization and N-terminal coding sequence modification to modify a CYP3A46 recombinant protein that exhibits good structure and catalytic activities and revealed its strong AFB₁-8,9-epoxidase activity for the first time. Site-directed mutagenesis, kinetics and docking analyses were performed and demonstrated that residues Phe-108, Ser-119, Phe-215, Phe-304 and Thr-309 play important roles in AFB₁-8,9-epoxidation and its responsiveness to α-naphthoflavone. Interestingly, we uncovered the dual and reverse roles of Phe-304 in CYP3A46, CYP3A5 and CYP3A4 in AFB₁ oxidation. Unlike the π-π interaction between the Phe-304 phenyl of CYP3A4 and the AFB₁ aromatic ring, Phe-304 of CYP3A46 may function to provide steric hindrance to bind AFB₁. Phe-108 and Phe-215 could stabilize AFB₁ with a potentially productive orientation through van der Waals interactions with AFB₁. Ser-119 and Thr-309 are likely to function to form H-bonds with AFB₁. This study broadens our knowledge of AFB₁ bioactivation in pigs and may contribute to reduce the deleterious effects of AFB₁ in pigs and humans.

Possible drug-drug interaction in dogs and cats resulted from alteration in drug metabolism: A mini review

Pharmacokinetic drug-drug interactions (in particular at metabolism) may result in fatal adverse effects in some cases. This basic information, therefore, is needed for drug therapy even in veterinary medicine, as multidrug therapy is not rare in canines and felines. The aim of this review was focused on possible drug-drug interactions in dogs and cats. The interaction includes enzyme induction by phenobarbital, enzyme inhibition by ketoconazole and fluoroquinolones, and down-regulation of enzymes by dexamethasone. A final conclusion based upon the available literatures and author's experience is given at the end of the review.

Drug safety: The concept, inception and its importance in patients' health

BACKGROUND

Drug safety is one of the hottest topics in daily medical practice, particularly with regard to approving new medication or questioning the possibility of withdrawing a drug from the market.

AIM

The aim of this review is to highlight the importance of the drug safety concept and its impact on patients' health.

METHODS

A literature search was conducted using Pubmed®, EMBASE®, EBSCO and Medline in the period between 1980 and 2013. The terms used in the search included "Drug Safety", "Medication Safety", "Patient Safety", "Drug Interaction", "Drug Pharmacokinetic", and "Adverse Drug Reaction". All retrieved abstracts were evaluated within the context of the review objectives. The full texts of the selected articles were included in this review. Studies in non-English language were excluded in this review.

RESULTS

Since the early days of the past century, many acts, laws, or amendments have been created to make sure that approved drugs are first safe and then effective. Furthermore, these regulations are continuing to change to make sure that these drugs have a positive benefit-risk balance. Personalized medicine should be considered when medications are given to patients because the pharmacokinetic process inside the body varies from patient to patient and from one specific disease state to another. However, adverse drug reactions can be minimized if more precautions are taken by healthcare professionals, especially including the patient as one pillar of the therapeutic plan and providing more patient counseling, which will improve drug safety.

CONCLUSION

The drug safety concept has earned a lot of attention during the past decade due to the fact it plays a major role in patients' health. Recent laws stress this concept should be included in the process of new medications' approval and continued conduct of post-marketing drug evaluations. Benefit-risk assessment should be considered by all health care professionals when they need to give specific drugs to specific groups of patients. Therefore, more care should be given to some patients, such as pregnant women, children and the elderly, since they are considered vulnerable populations.