Effects of serial cervical or tail blood sampling on toxicity and toxicokinetic evaluation in rats

Impact of microsampling on toxicological evaluation in rodent safety studies

Recently, animal welfare has been attracting worldwide attention, and implementation of 3Rs (replacement, reduction, and refinement) is prioritized in every way possible in the drug development. Microsampling, in which small amounts of blood are collected, is attracting attention in this context. ICH S3A Q&A focused on microsampling was published in November 2017 to help accelerate the application of microsampling for toxicokinetic assessment. The increased sensitivity of drug measurement apparatuses such as mass spectrometers has made it possible to measure drug concentrations with small amounts of blood samples. In this review, we summarized the reports on toxicological influence of microsampling in rodents (rats and mice) with or without drug administration or recovery period after blood collection and influences that may arise from differences in the blood sampling site or blood sampling volume. We also summarized some perspectives on further implementation of microsampling in toxicology studies. The use of microsampling in regulatory toxicology studies has gradually increased, although at a lower rate than in discovery studies. Since more animals are used in GLP toxicology studies than in discovery studies, the effect of reducing the number of animals by microsampling is expected to be greater in the toxicology studies. This report aims to promote the application of microsampling to nonclinical studies, as it is beneficial for improving animal welfare and can contribute to the 3Rs.

Blood microsampling in cynomolgus monkey and evaluation of plasma PK parameters in comparison to conventional sampling

Microsampling, a reduced volume sampling method, has successfully gained attention at the International Conference on Harmonization (ICH) level and established benefits support its use in Toxicokinetic (TK) studies. These improved sampling techniques are less invasive and in large animal species improve animal welfare (refinement). To evaluate if the plasma concentrations of drugs were influenced by the blood sampling method, the traditional method from femoral vein and microsampling from tail vein in Cynomolgus monkeys were compared. The pharmacokinetic parameters (Cmax, Tmax and AUC) of four drugs (selected based on acid-base and volume of distribution properties) in non-human primate were correlated. The plasma samples were quantified using standard LC-MS/MS methods, qualified to evaluate the precision and accuracy before the analysis of real samples. The results reported in this work demonstrated the suitability of microsampling in supporting PK/TK studies in non-human primates. The data show that the exposure of drugs tested after blood collection using standard procedure from femoral vein and microsampling from tail vein is correlated and is not influenced by acid-base characteristics and volume of distribution.

Impact of repeated micro and macro blood sampling on clinical chemistry and haematology in rats for toxicokinetic studies

Non-clinical rodent safety studies are essential in the development of new medicines to assess for potential adverse effects. Typically, toxicokinetic samples are collected from a satellite group. AstraZeneca implemented repeated microsampling of main study animals as standard in the one-month small molecule regulatory toxicology studies. A retrospective analysis of the clinical chemistry and haematology data collected in 52 independent studies from the adult rat controls explored the impact of micro and macro sampling of main study animals. For the majority of variables, the blood sampling technique had no significant impact on the mean or range. For microsampling, a few variables had statistically significant effects on the mean signal but these were considered to have limited biological relevance and would therefore not introduce a meaningful bias to any toxicological evaluation. The macrosampling had the expected effects on the red cell parameters of haemoglobin, haematocrit and red blood count due to the larger blood volume draw. In contrast, microsampling showed no such changes. In conclusion, this large-scale retrospective analysis supports the use of microsampling, for toxicokinetics, of main study animals and enables us to conduct rodent toxicology studies without satellite animals and further reduce the number of animals used in toxicological assessments.

The influence of serial 50 μL microsampling on rats administered azathioprine, the immunosuppressive drug

According to the ICH S3A Q&A, microsampling is applicable to pharmaceutical drugs and toxicological analysis. Few studies have reported the effect of microsampling on the toxicity of immunotoxicological drugs. The aim of this multicenter study was to evaluate the toxicological effects of serial microsampling on rats treated with azathioprine as a model drug with immunotoxic effects. Fifty microliters of blood were collected from the jugular vein of Sprague-Dawley rats at six time points from day 1 to 2 and 7 time points from day 27 to 28. The study was performed at three organizations independently. The microsampling effect on clinical signs, body weights, food consumption, hematological parameters, biochemical parameters, urinary parameters, organ weights, and tissue pathology was evaluated. Azathioprine-induced changes were observed in certain hematological and biochemical parameters and thymus weight and pathology. Microsampling produced minimal or no effects on almost all parameters; however, at 2 organizations, azathioprine-induced changes were apparently masked for two leukocytic, one coagulation, and two biochemical parameters. In conclusion, azathioprine toxicity could be assessed appropriately as overall profiles even with blood microsampling. However, microsampling may influence azathioprine-induced changes in certain parameters, especially leukocytic parameters, and its usage should be carefully considered.

Effects of microsampling on toxicity assessment of hematotoxic compounds in a general toxicity study in rats

Microsampling (MS) has been increasingly used in toxicity studies reducing animal use for toxicokinetic analysis. However, especially for drugs with hematotoxic properties, the potential effects of MS on hematological parameters and subsequent toxicity assessment should be considered, while such properties are frequently unknown at the discovery stage. Here, we conducted a rat 2-week study of hematotoxic compounds and evaluated the effects of MS on toxicity assessment. Six-week-old female SD rats were orally dosed with vehicle, methylene blue trihydrate (MB: 300 mg/kg/day), or azathioprine (AZP: 12 and 24 mg/kg/day) for 2 weeks. Each treatment group was divided into non-MS and MS subgroups, and in the MS subgroups, 50 μL/time point of blood was collected from the jugular vein at 7 time points each on Days 1 and 13 of dosing. The test items included clinical signs, body weight, urinalysis, hematology, blood chemistry, necropsy, organ weight, and histopathology. In the MB non-MS subgroup, there were low values in red blood cell parameters, high values in reticulocytes and bilirubin, and increased extramedullary hematopoiesis, reflecting hemolytic anemia. In the AZP non-MS subgroup, there were low values of red and white blood cell parameters and decreased cellularity in the bone marrow, reflecting myelosuppression. The effects of MB and AZP were similarly observed in the MS subgroups, and the effects of MS on the toxicological endpoints were generally small. Based on these results, the effects of MS on toxicity assessment were considered to be small in rat toxicity studies even for hematotoxic compounds.