Comparative evaluation of the human whole blood and human peripheral blood monocyte tests for pyrogens

Standardized pyrogen testing of medical products with the bacterial endotoxin test (BET) as a substitute for rabbit Pyrogen testing (RPT): A scoping review

The Bacterial Endotoxin Test (BET) is a method for exclusion of endotoxin-related pyrogen contamination in pharmaceutical products, as an alternative to the Rabbit Pyrogen Test (RPT). However, BET does not detect a broad range of biologically relevant pyrogens, and interferences can limit its practical use for different medical products. This work aimed to scope the evidence in the scientific literature for case-by-case validity assessments of BET in different uses for medical products. A search strategy was conducted in PubMed, Scopus, and Web of Science in April 2020, according to the PRISMA-ScR statement. Twenty-two references were included, evaluating medical products for endotoxin contamination through both BET and RPT according to standardized protocols. A critical appraisal was performed through ToxRTool, followed by data extraction and qualitative synthesis of outcomes and methodological issues. Four classes of products assessed by BET were identified, including nanoparticles, drugs, blood and biological products. A considerable variation was observed on the BET methods used. Collectively, the evidence indicates different factors influencing the outcome of BET, including the chemical nature of samples that may cause interference depending on the selected method. While some applications to medical products appear adequate, others, such as nanoparticles, may require the use of different in vitro pyrogen testing methods, reinforcing the need for case-by-case validation for each BET method and type of medical product.

Enhanced antitumor efficacy of biocompatible magnetosomes for the magnetic hyperthermia treatment of glioblastoma

In this study, biologically synthesized iron oxide nanoparticles, called magnetosomes, are made fully biocompatible by removing potentially toxic organic bacterial residues such as endotoxins at magnetosome mineral core surfaces and by coating such surface with poly-L-lysine, leading to magnetosomes-poly-L-lysine (M-PLL). M-PLL antitumor efficacy is compared with that of chemically synthesized iron oxide nanoparticles (IONPs) currently used for magnetic hyperthermia. M-PLL and IONPs are tested for the treatment of glioblastoma, a dreadful cancer, in which intratumor nanoparticle administration is clinically relevant, using a mouse allograft model of murine glioma (GL-261 cell line). A magnetic hyperthermia treatment protocol is proposed, in which 25 µg in iron of nanoparticles per mm3 of tumor are administered and exposed to 11 to 15 magnetic sessions during which an alternating magnetic field of 198 kHz and 11 to 31 mT is applied for 30 minutes to attempt reaching temperatures of 43-46 °C. M-PLL are characterized by a larger specific absorption rate (SAR of 40 W/gFe compared to 26 W/gFe for IONPs as measured during the first magnetic session), a lower strength of the applied magnetic field required for reaching a target temperature of 43-46 °C (11 to 27 mT compared with 22 to 31 mT for IONPs), a lower number of mice re-administered (4 compared to 6 for IONPs), a longer residence time within tumours (5 days compared to 1 day for IONPs), and a less scattered distribution in the tumour. M-PLL lead to higher antitumor efficacy with full tumor disappearances achieved in 50% of mice compared to 20% for IONPs. This is ascribed to better ability of M-PLL, at equal iron concentrations, to maintain tumor temperatures at 43-46°C over a longer period of times.

In vitro drug metabolism testing using blood-monocyte derivatives

INTRODUCTION

Monocytes and their cell derivatives can participate in drug metabolism. These cells express different Phase-I or -II drug metabolizing enzymes and can be differentiated into neo-hepatocytes (NeoHep) and represent a promising alternative strategy to test drug metabolism. This is particularly useful as primary human hepatocytes (PHH), are difficult to obtain and maintain in culture.

AREAS COVERED

The authors analyze the use of blood monocytes and their derivatives for the study of drug metabolism. They also compare them to the in vitro ability of cells from different sources including: PHH, immortalized hepatocytes, tumor cell lines and NeoHep.

EXPERT OPINION

The use of monocytes, macrophages, dendritic or Kupffer cells, to test drug metabolism, has serious limitations because these cells express lower levels of cytochrome P450 enzymes than PHH. The best available option, to replace PHH, have been tumor cell lines such as HepaRG, as well as immortalized hepatocytes from adult or fetal sources. Monocyte-derived NeoHep cells are novel and easily accessible cells, which express many drug metabolizing enzymes at levels comparable to PHH. These cells allow drug evaluation under a diverse genetic background. While these cells are in the early stages of evaluation and do need to be examined more thoroughly, they constitute a promising new tool for in vitro drug testing.

A new cell-based innate immune receptor assay for the examination of receptor activity, ligand specificity, signalling pathways and the detection of pyrogens

The pattern recognition receptors (PRRs) of the innate immune system are the first defence line of the immune system. Toll-like receptors (TLRs) are the most well known and the best examined of the PR receptors. In the last years TLRs had been studied in different ways resulting in a lot of new insights in the function and signalling pathways of these receptors. However, it was not possible to investigate individual combinations of the TLRs and their specific ligands, because of the complex network in immune signalling resulting in interference with each other. This work shows a new cell-based assay, established for the analysis of single PRRs or heterodimers. For this purpose NIH3T3 (mouse fibroblasts) were stably transfected with the NF-kappaB-inducible reporter gene secreted alkaline phosphatase (SEAP) together with the corresponding combinations of human TLRs and their co-receptors (e.g. TLR1/2, TLR2/6 and TLR4/CD14). The specificity of the respective cell lines was shown by induction with variations of specific and unspecific ligands (immune-stimulating components of microorganisms or synthetic ligands). Analysis via the NF-kappaB-dependent reporter gene SEAP allows a direct way to detect the human TLR-activity. Our results showed that this assay is highly sensitive and specific for the respective ligands. For the synthetic ligands Pam(2)CysSK(4) the assay demonstrates a detection limit of 1 pg/ml for TLR2/6. In summary, this test system allows the investigation of individual human PRR-receptors in a highly specific way, without interference with other immune components opening new avenues for novel insights in the innate immune system and its applications.

TNFα Measurement in Rat and Human Whole Blood as an in vitro Method to Assay Pyrogens and its Inhibition by Dexamethasone and Erythromycin

To ensure the safety of potential drugs, pyrogen tests are traditionally performed in rabbits. New methods have been developed as alternatives to the test to reduce the use of experimental animals. Among these methods there are the Limulus amoebocyte lysate test and the determination of cytokine production by human leukocytes and whole blood. When exposed to a range of concentrations of endotoxins, human and rat whole blood release TNFalpha at amounts that are detectable by a commercially available enzyme-linked immunosorbent assay (ELISA). Our results show that the sensitivity of human and rat blood to endotoxins from Salmonella abortus equi and Escherichia coli is similar. In rat blood, TNFalpha was detected after contact with the pyrogens only in fresh blood, collected on the same day of incubation with the pyrogenic substances. The measurement of TNFalpha production would be a reliable alternative to the rabbit pyrogen test. However, given that the addition of erythromycin and dexamethasone inhibited the production of this cytokine, this method is limited when parenteral formulations contain these two drugs. Similar inhibition has been observed in the rabbit test. Additional experiments will be necessary to demonstrate that the rat whole blood test system is useful and reliable for the pyrogens evaluation.