Frequency of the mutant MDR1 allele in dogs in the UK

The ATP-binding cassette proteins ABCB1 and ABCC1 as modulators of glucocorticoid action

Responses to hormones that act through nuclear receptors are controlled by modulating hormone concentrations not only in the circulation but also within target tissues. The role of enzymes that amplify or reduce local hormone concentrations is well established for glucocorticoid and other lipophilic hormones; moreover, transmembrane transporters have proven critical in determining tissue responses to thyroid hormones. However, there has been less consideration of the role of transmembrane transport for steroid hormones. ATP-binding cassette (ABC) proteins were first shown to influence the accumulation of glucocorticoids in cells almost three decades ago, but observations over the past 10 years suggest that differential transport propensities of both exogenous and endogenous glucocorticoids by ABCB1 and ABCC1 transporters provide a mechanism whereby different tissues are preferentially sensitive to different steroids. This Review summarizes this evidence and the new insights provided for the physiology and pharmacology of glucocorticoid action, including new approaches to glucocorticoid replacement.

Occurrence of MDR1 1-delta mutation in herding dog breeds in Portugal

The impact of drug transporters in veterinary medicine has been recognized in recent years. One of the most well-characterized is the product of the MDR1 gene, P-gp. A 4-bp deletion in the MDR1 gene known since 2001 has been described to affect herding dog breeds. Since many used drugs in veterinary medicine are substrates for P-gp, including the macrocyclic lactones, such as avermectins, this 4-bp deletion causes a pathological condition known as “ivermectin toxicosis.” For this reason, it is important to determine the animal status concerning this mutation. In Portugal, the information of the occurrence of this mutation in our breeds is limited. The aim of the present study was to determine the occurrence of this mutation and evaluate its association with Portuguese and non-Portuguese dog breeds in Portugal. To achieve this, a total of 105 animals were studied for the presence of the MDR1 4-bp deletion, 23 of which were from Barbado da Terceira, 10 from Cão da Serra d'Aires, 55 belonging to breeds known to carry the mutation (Australian Shepperd, Border Collie and others) and 17 to other breeds (Labrador Retriever, Jack Russel, and others). Despite the small sample size, we observed the presence of the MDR1 1—delta mutation in previously described breeds and identified this mutation in Barbado da Terceira breed for the first time.

Prevalence of the MDR1 gene mutation in herding dog breeds and Thai Ridgebacks in Thailand

Background and Aim:

A canine multi-drug resistance 1 (MDR1) nt230(del4) is a well-known inherited disorder that primarily affects collies and various herding breeds. The most recognized clinical implication for affected dogs is associated with an increased risk of multiple drug toxicity. To date, MDR1 gene mutations have been identified globally, especially in dogs from the USA and European countries. This study aimed to investigate the prevalence of MDR1 nt230(del4) in herding dog breeds and Thai Ridgebacks in Thailand.

Materials and Methods:

We clarified the prevalence of MDR1 nt230(del4) in 263 dogs of eight purebred dog breeds in Thailand using an allele-specific multiplex polymerase chain reaction method and direct DNA sequencing.

Results:

Rough Collies, Australian Shepherds, Shetland Sheepdogs, and Old English Sheepdogs were affected by the mutation with mutant allelic frequencies of 57.14%, 12.82%, 11.28%, and 8.33%, respectively. Among these populations, the prevalence of the MDR1 (+/–) genotype was 57.14% (12/21) for Rough Collies, 25.64% (10/39) for Australian Shepherds, 16.13% (15/93) for Shetland Sheepdogs, and 16.67% (2/12) for Old English Sheepdogs, whereas the MDR1 (–/–) mutation was only identified in Rough Collies and Shetland Sheepdogs, with prevalences of 28.57% (6/21) and 3.22% (3/93), respectively. However, the MDR1 nt230(del4) was not identified in Border Collies, German Shepherds, White Swiss Shepherds, or Thai Ridgebacks.

Conclusion:

This study provides the current situation regarding MDR1 nt230(del4) in herding dog breeds in Thailand. In this survey, we investigated for the first time the status of MDR1 genotype in Thai Ridgebacks. These results are helpful for veterinarians managing effective therapeutic plans for commonly affected dog breeds, and these results will encourage all breeders to improve their selective breeding programs based on the MDR1 nt230(del4) status.

Heartworm disease - Overview, intervention, and industry perspective

Dirofilaria immitis, also known as heartworm, is a major parasitic threat for dogs and cats around the world. Because of its impact on the health and welfare of companion animals, heartworm disease is of huge veterinary and economic importance especially in North America, Europe, Asia and Australia. Within the animal health market many different heartworm preventive products are available, all of which contain active components of the same drug class, the macrocyclic lactones. In addition to compliance issues, such as under-dosing or irregular treatment intervals, the occurrence of drug-resistant heartworms within the populations in the Mississippi River areas adds to the failure of preventive treatments. The objective of this review is to provide an overview of the disease, summarize the current disease control measures and highlight potential new avenues and best practices for treatment and prevention.

Molecular pathology in the cancer clinic - where are we now and where are we headed?

Molecular pathology is a developing sub-microscopic discipline of pathology that studies the effects of molecular variations and mutations on disease processes. The ultimate goal of molecular pathology in cancer is to predict risk, facilitate diagnosis and improve prognostication based on a complete understanding of the biological impact of specific molecular variations, mutations and dysregulations. This knowledge will provide the basis for customised cancer treatment, so-called precision medicine. Rapid developments in genomics have placed this field at the forefront of clinical molecular pathology and there are already a number of well-established genetic tests available for clinical use including PCR of antigen receptor rearrangement and KIT mutational analysis. Moving beyond tests assessing a single gene, there are significant research efforts utilising genomics to predict cancer risk, forecast aggressive behaviour and identify druggable mutations and therapeutic biomarkers. Researchers are also investigating the use of circulating cells and nucleic acid for clinically useful low morbidity genomic assessments. If we are to realise the full potential of molecular pathology and precision medicine there are a number of challenges to overcome. These include developing our understanding of the underlying biology (in particular intra-tumoural heterogeneity), methodological standardisation of assays, provision of adequate infrastructure and production of novel therapeutics backed by high-quality clinical data supporting the precision medicine approach. The era of molecular pathology holds the potential to revolutionise veterinary cancer care, but its impact on clinical practice will depend upon the extent to which the inherent challenges can be overcome.

Genotypic and allelic frequencies of MDR1 gene in dogs in Italy

Background

A mutation in the canine multidrug resistance MDR1 gene (also referred as ABCB1), encoding for the multidrug resistance (MDR) P-glycoprotein (P-gp) transponder, causes a pathological condition known as ‘ivermectin toxicosis’. The causative mutation, known since 2001, has been described to affects sheep herding breeds related to collie lineage. The present study is a retrospective investigation of the presence of MDR1 mutated allele in Italian dog populations in a 5 years’ time lapse. The aim of the research is to offer a deep knowledge in MDR1 allelic and genotypic frequencies in canine breeds and populations raised in Italy.

Methods

Genotype data for the 4-bp deletion (c296_299del4) in MDR1 gene from 811 dogs belonging to 32 breeds/populations were collected.

Results

The mutated allele has been found in 9 out of 31 breeds: Rough Collie, Smooth Collie, Border Collie, Bearded Collie, Shetland Sheepdog, Australian Shepherd, White Swiss Shepherd, Old English Sheepdog, Whippet and also in crossbreed. The breeds with the highest allelic mutation frequency are Smooth and Rough Collies with 75 per cent and 66 per cent of mutant MDR1 allele, respectively.

Conclusions

The results support the usefulness of this genetic analysis to optimise medical care in dogs at risk of multidrug resistance and to create an objective basis in breeding programme definition and in the risk evaluation in different breeds.

Evaluation of a 0.75 × 109 /L absolute neutrophil count cut-off for antimicrobial prophylaxis in canine cancer chemotherapy patients

Absolute neutrophil count (ANC) cut-offs for antimicrobial prophylaxis in veterinary cancer chemotherapy patients are empirical and vary between institutions. Evidence based cut-offs are vital for antimicrobial stewardship, particularly as global antimicrobial resistance rises. The primary objectives of this study were to evaluate the tolerability of a <0.75 × 10⁹ /l ANC cut-off for antimicrobial prophylaxis in dogs after receiving chemotherapy and its impact on antimicrobial prescription. Predicted nadir ANCs (pnANCs) were stratified into six groups (<0.75 × 10⁹ /l [receiving antimicrobial prophylaxis], 0.75-0.99 × 10⁹ /l, 1-1.49 × 10⁹ /l, 1.5-1.99 × 10⁹ /l, 2.0-3.59 × 10⁹ /l and 3.6-12 × 10⁹ /l [reference interval]). The incidences of post-nadir febrile neutropenia (FN) and non-haematological toxicity (NHT) were compared between groups. Five hundred and eighty-six pnANCs were recorded for 181 dogs. There were four episodes of post-nadir FN and 90 episodes of post-nadir NHT. There was no significant difference in incidence of post-nadir FN (P = .063) or post-nadir NHT (P = .084) between pnANC groups. Antimicrobial prophylaxis was prescribed following 8.8% of the chemotherapy administrations; had cut-off values of <1.0 × 10⁹ /l or <1.5 × 10⁹ /l been used it would have been prescribed in 15.3% and 25.8% of cases respectively. An ANC cut-off of <0.75 × 10⁹ /l for antimicrobial prophylaxis appears to be well tolerated and minimizes the prescription of antimicrobials.

Translating Pharmacogenetics and Pharmacogenomics to the Clinic: Progress in Human and Veterinary Medicine

As targeted personalized therapy becomes more widely used in human medicine, clients will expect the veterinary clinician to be able to implement an evidence-based strategy regarding both the prescribing of medicines and also recognition of the potential for adverse drug reactions (ADR) for their pet, at breed and individual level. This review aims to provide an overview of current developments and challenges in pharmacogenetics in medicine for a veterinary audience and to map these to developments in veterinary pharmacogenetics. Pharmacogenetics has been in development over the past 100 years but has been revolutionized following the publication of the human, and then veterinary species genomes. Genetic biomarkers called pharmacogenes have been identified as specific genetic loci on chromosomes which are associated with either positive or adverse drug responses. Pharmacogene variation may be classified according to the associated drug response, such as a change in (1) the pharmacokinetics; (2) the pharmacodynamics; (3) genes in the downstream pathway of the drug or (4) the effect of “off-target” genes resulting in a response that is unrelated to the intended target. There are many barriers to translation of pharmacogenetic information to the clinic, however, in human medicine, international initiatives are promising real change in the delivery of personalized medicine by 2025. We argue that for effective translation into the veterinary clinic, clinicians, international experts, and stakeholders must collaborate to ensure quality assurance and genetic test validation so that animals may also benefit from this genomics revolution.

A Remote Assay for Measuring Canine Platelet Activation and the Inhibitory Effects of Antiplatelet Agents

BACKGROUND

Antiplatelet medications are increasingly used in dogs. Remote analysis of platelet activity is challenging, limiting assessment of antiplatelet drug efficacy.

HYPOTHESIS/OBJECTIVES

To evaluate a method used in humans for stimulation and remote analysis of canine platelet activity.

ANIMALS

Forty-five dogs of various ages without a coagulopathy or thrombocytopenia. Six were receiving antiplatelet medication.

METHODS

Prospective observational study. Platelets were stimulated with combinations of arachidonic acid (AA) and epinephrine (Epi) or adenosine diphosphate (ADP) and the thromboxane A₂ -mimetic U46619 (U4). PAMFix was added to the blood samples to facilitate delayed analysis of platelet activity. Activity was assessed by flow cytometric measurement of surface P-selectin (CD62P) expression.

RESULTS

Canine platelets could be stimulated with both AA/Epi and ADP/U4. The levels of P-selectin were significantly greater than paired, unstimulated samples (P < 0.001). Inhibition of P-selectin expression occurred after this stimulation by adding antiplatelet drugs in vitro. The efficacy of antiplatelet drugs in samples from treated dogs was also measurable ex vivo using this method. Delayed analysis of platelet activity at time points up to 22 days demonstrated excellent correlation between respective mf values at each time point (r²  = 0.92, P < 0.0001).

CONCLUSIONS AND CLINICAL IMPORTANCE

This study evaluated a new method to remotely assess canine platelet activity. It shows that PAMFix can be used for this purpose. This provides opportunities to interrogate the inhibitory action of antiplatelet drugs in clinical settings.

Frequency of canine nt230(del4) MDR1 mutation in prone pure breeds, their crosses and mongrels in Israel - insights from a worldwide comparative perspective

Background

Sensitivity to macrocyclic lactones, which are commonly used in veterinary clinics, was first found in Rough Collies, and was attributed in 2001 to a 4 bp deletion in the MDR1 gene. The list of affected breeds currently includes 13 breeds. Researchers from different countries and continents examined the allelic frequencies of the nt230(del4) MDR1 mutation, emphasizing the clinical importance of this test not only to mutation-prone dogs, but also to their crosses and mongrels, since treatment of a deletion carrier with these compounds may lead to its death.

In this study, the allelic frequencies of nt230(del4) MDR1 mutation in affected breeds, their crosses, unrelated pure breeds and mongrels are reported for the state of Israel (n = 1416 dogs). The Israeli data were compared with reports from the US, Europe, UK, Australia and Japan.

Results

The allelic frequencies of nt230(del4) MDR1 mutation in Israel for Australian, Swiss and German Shepherds (31%, 17% and 2.4%, respectively) are similar to the corresponding frequencies worldwide, much higher for Border Collies (4.8%), twice lower for Rough Collies (28%, compared to 55% or more elsewhere), and ~1% for mongrels. The frequencies for crosses of Australian Shepherd and Border Collies in Israel are 4 and 1.6 times lower, respectively, compared to the frequencies for the respective pure breeds.

Conclusions

This work, that for the first time presents the frequency of nt230(del4) MDR1 mutation in Israel, along with a worldwide survey, has implications for clinicians, owners and breeders of sheepdogs and their crosses and supports the need for extra care in treatment and in future breeding. Of note, the relative proportion of affected breeds, in the overall tested dogs, might be higher than their actual proportion in Israel due to directed samples collection by veterinarians for clinical purposes, as these are mainly limited to certain affected breeds or dogs that resemble them.

Electronic supplementary material

The online version of this article (10.1186/s12917-017-1251-9) contains supplementary material, which is available to authorized users.

Fast and simple detection methods for the 4-base pair deletion of canine MDR1/ ABCB1 gene by PCR and isothermal amplification

Dogs with a 4-bp deletion in the MDR1 (or ABCB1) gene show intolerance to certain drugs routinely used in veterinary medicine, such as ivermectin, vincristine, and doxorubicin. The mutation leads to a dysfunctional P-glycoprotein drug transporter, which results in drug accumulation in the brain and severe neurotoxicity. A rapid and accurate in-house test to determine the genotype of patients in cases of acute neurotoxic signs or in tumor patients is desirable. We describe a cost-effective detection method with simple technical equipment for veterinary practice. Two allele-specific methods are presented, which allow discrimination of all genotypes, require little hands-on time, and show the results within ~1 h after DNA sampling. DNA from buccal swabs of 115 dogs with known genotype (no mutation, n = 54; heterozygous for the mutation, n = 37; homozygous for the mutation, n = 24) was extracted either by using a column-based extraction kit or by heating swabs in a simple NaOH-Tris buffer. Amplification was performed either by allele-specific fast polymerase chain reaction or by allele-specific loop-mediated isothermal amplification (LAMP). Analysis was done either on agarose gels, by simple endpoint visualization using ultraviolet light, or by measuring the increase of fluorescence and time to threshold crossing. Commercial master mixes reduced the preparation time and minimized sources of error in both methods. Both methods allowed the discrimination of all 3 genotypes, and the results of the new methods matched the results of the previous genotyping. The presented methods could be used for fast individual MDR1/ ABCB1 genotyping with less equipment than existing methods.

Use of 20% intravenous lipid emulsion for the treatment of loperamide toxicosis in a Collie homozygous for the ABCB1-1∆ mutation

OBJECTIVE

To describe the successful treatment of loperamide toxicosis in a dog using intravenous lipid emulsion (ILE).

CASE SUMMARY

An 8-month-old male neutered Rough Collie weighing 20.0 kg was given a total dose of 0.75 mg/kg loperamide over 3 days as treatment for diarrhea. The dog was subsequently evaluated for signs of dull mentation, anxiety, ptyalism and ataxia, thought to be a result of loperamide intoxication. The dog was treated with a 1.5 mL/kg IV bolus of 20% ILE solution followed by 0.25 mL/kg/min of the same solution for 2 hours. The dog's mentation improved rapidly following ILE infusion, and he was neurologically normal 3 hours after initiation of ILE treatment. The dog was subsequently found to be homozygous for the ATP-binding cassette (ABC) transporter gene (ABCB1-1∆) mutation. There were no adverse effects noted during or following ILE infusion.

NEW OR UNIQUE INFORMATION PROVIDED

ILE was successful in the treatment of loperamide toxicosis in a Collie with the ABCB1-1∆ mutation. ILE may be of benefit for treatment of other intoxications in dogs with ABCB1-1Δ mutations.

P-glycoprotein mediated drug interactions in animals and humans with cancer

Drug–drug interactions can cause unanticipated patient morbidity and mortality. The consequences of drug–drug interactions can be especially severe when anticancer drugs are involved because of their narrow therapeutic index. Veterinary clinicians have traditionally been taught that drug–drug interactions result from alterations in drug metabolism, renal excretion or protein binding. More recently, drug–drug interactions resulting from inhibition of P‐glycoprotein‐mediated drug transport have been identified in both human and veterinary patients. Many drugs commonly used in veterinary patients are capable of inhibiting P‐glycoprotein function and thereby causing an interaction that results in severe chemotherapeutic drug toxicity. The intent of this review is to describe the mechanism and clinical implications of drug–drug interactions involving P‐glycoprotein and anticancer drugs. Equipped with this information, veterinarians can prevent serious drug–drug interactions by selecting alternate drugs or adjusting the dose of interacting drugs.

Frequency of the MDR1 mutant allele associated with multidrug sensitivity in dogs from Brazil

To date, a 4-bp deletion in the MDR1 gene has been detected in more than ten dog breeds, as well as in mixed breed dogs, in several countries, however information regarding this mutation in dogs from Brazil is lacking. For this reason, 103 Collies, 77 Border Collies, 76 Shetland Sheepdogs, 20 Old English Sheepdogs, 55 German Shepherds, 16 Australian Shepherds, and 53 Whippets from Brazil were screened for the presence of the mutation. The heterozygous mutated genotype, MDR1 (+/−), frequency found for Collies, Australian Shepherd, and Shetland Sheepdog was 50.5% (95% CI =41.1%–59.9%), 31.3% (95% CI =8.6%–53.2%), and 15.8% (95% CI =7.7%–23.9%), respectively. Homozygous mutated genotype, MDR1 (−/−), was detected only in Collies 35.9%. The MDR1 allele mutant frequency found for Collies, Australian Shepherd, and Shetland Sheepdog was 61.2% (95% CI =54.8%–67.5%), 15.6% (95% CI =3.1%–28.2%), and 7.9% (95% CI =3.7%–12.1%), respectively. Additionally, even free of the mutant allele, the maximum mutant prevalence (MMP) in that population, with 95% CI, was 3.8%, 5.2%, 5.4%, and 13.8% for Border Collies, German Shepherds, Whippets, and Old English Sheepdogs, respectively. In this way, this information is important, not only for MDR1 genotype-based breeding programs and international exchange of breeding animals of predisposed breeds, but also for modification of drug therapy for breeds at risk.