Comparison of permitted daily exposure (PDE) values for active pharmaceutical ingredients (APIs) - Evidence of a robust approach.

Permitted Daily Exposure Limits (PDEs) are set for Active Pharmaceutical Ingredients (APIs) to control cross-contamination when manufacturing medicinal products in shared facilities. With the lack of official PDE lists for pharmaceuticals, PDEs have to be set by each company separately. Although general rules and guidelines for the setting of PDEs exist, inter-company variations in the setting of PDEs occur and are considered acceptable within a certain range. To evaluate the robustness of the PDE approach between different pharmaceutical companies, data on PDE setting of five marketed APIs (amlodipine, hydrochlorothiazide, metformin, morphine, and omeprazole) were collected and compared. Findings show that the variability between PDE values is within acceptable ranges (below 10-fold) for all compounds, with the highest difference for morphine due to different Point of Departures (PODs) and Adjustment Factors (AFs). Factors of PDE variability identified and further discussed are: (1) availability of data, (2) selection of POD, (3) assignment of AFs, (4) route-to-route extrapolation, and (5) expert judgement and differences in company policies. We conclude that the investigated PDE methods and calculations are robust and scientifically defensible. Additionally, we provide further recommendations to harmonize PDE calculation approaches across the pharmaceutical industry.

Acceptable intakes (AIs) for 11 small molecule N-nitrosamines (NAs).

Low levels of N-nitrosamines (NAs) were detected in pharmaceuticals and, as a result, health authorities (HAs) have published acceptable intakes (AIs) in pharmaceuticals to limit potential carcinogenic risk. The rationales behind the AIs have not been provided to understand the process for selecting a TD50 or read-across analog. In this manuscript we evaluated the toxicity data for eleven common NAs in a comprehensive and transparent process consistent with ICH M7. This evaluation included substances which had datasets that were robust, limited but sufficient, and substances with insufficient experimental animal carcinogenicity data. In the case of robust or limited but sufficient carcinogenicity information, AIs were calculated based on published or derived TD50s from the most sensitive organ site. In the case of insufficient carcinogenicity information, available carcinogenicity data and structure activity relationships (SARs) were applied to categorical-based AIs of 1500 ng/day, 150 ng/day or 18 ng/day; however additional data (such as biological or additional computational modelling) could inform an alternative AI. This approach advances the methodology used to derive AIs for NAs.

Deriving harmonised permitted daily exposures (PDEs) for paracetamol (acetaminophen) CAS #: 103-90-2.

In the pharmaceutical industry, cleaning criteria are required for multipurpose manufacturing facilities. These Health Based Exposure Limits (HBELs), also called permitted daily exposures (PDEs) values, are derived from toxicological and pharmacological evaluation of the active pharmaceutical ingredients (APIs). The purpose of this publication is to show an example of how authors from different companies evaluate a generic drug, paracetamol, and discuss different approaches and relevance of the nonclinical studies for deriving PDEs. PDE limits of 25 mg/day for the oral route, and 20 mg/day for the intravenous (i.v.) and inhalation (inhal.) routes, respectively, were established herein. However, it has been already recognised that there are acceptable differences in the PDE calculations, which may be based on data accessibility, company-specific science-policy decisions or expert judgments. These differences can cause up to a 3-fold lower or higher values. If unnecessarily high factors are applied, this would result in a very conservative PDE value and unneeded additional cleaning and higher manufacturing costs. The PDE values presented are considered to be protective against adverse and pharmacological effects observed in clinical trials and in this case, a very long postmarketing period of paracetamol.

What to consider for a good quality PDE document?

For the handling of active pharmaceutical ingredients (APIs) and production of medicinal products in shared facilities, the European Medicines Agency (EMA) has introduced the determination of permitted daily exposure (PDE) values to provide limits for cross-contamination. APIs have a desired pharmacological effect in the patient who intendedly uses a certain medicinal product. However, this effect is undesired in a patient that receives this API unintendedly as a cross-contamination of another medicinal product. In particular, for approved APIs for human use, a multitude of data is available on the pharmacological activity as well as adverse effects, which have to be taken into account in PDE setting. Thus, the setting of PDEs for APIs needs a structured scientific evaluation of all properties and identification of the most critical effect, which is the basis for PDE calculation. In this publication, we provide guidance on points for consideration when setting PDEs for APIs, or when evaluating the quality of documents describing the derivation of PDEs received, e.g. by third parties.

Species-specific activation of nuclear receptors correlates with the response of liver drug metabolizing enzymes to EMD 392949 in vitro.

We previously reported on the species-specific effects on drug metabolizing enzymes (DME), in particular cytochrome P450-dependent monooxygenases (P450s), by the drug development candidate EMD 392949 (EMD) in vitro and in vivo. Induction of P450s occurs via activation of specific transcription factors such as the arylhydrocarbon receptor (AhR) and the nuclear xenobiotic receptors (NXRs). We analyzed whether the reported species-specific P450 induction by EMD could be related to a specific activation of the CYP1A regulator AhR and the CYP3A regulator pregnane X receptor (PXR) in human and rat cell lines. The human HepG2 and rat H4IIE cell lines exhibited inducibility of CYP1A and 3A and expressed functional AhR as well as PXR. CYP3A was induced by EMD in human HepG2 cells exceeding the level induced by rifampicin, but was not induced in rat H4IIE cells. Regulation of P450s was not related to expression levels of their respective transcription factor, but EMD treatment resulted in a significant reporter gene activation in xenobiotic response enhancer module (XREM)-transfected HepG2 but not H4IIE cells indicating activation of human but not rat PXR. In summary, we showed that the P450 inducing properties of EMD were perfectly reflected by its ability to activate AhR or PXR in a species-specific manner. These findings support the tight correlation of species-specific nuclear receptor activation with P450 induction and foster the use of nuclear receptor activation as a complementary screen to identify cytochrome P450 inducers.

Serum-free collagen sandwich cultures of adult rat hepatocytes maintain liver-like properties long term: a valuable model for in vitro toxicity and drug-drug interaction studies.

Cultures of primary hepatocytes from various species, including human, are used in several applications during pre-clinical drug development. Their use is however limited by cell survival and conservation of liver-specific functions in vitro. The differentiation status of hepatocytes in culture strongly depends on medium formulation and the extracellular matrix environment. We incubated primary rat hepatocytes for 10 days on collagen monolayer and in collagen sandwich cultures with or without serum. Restoration of polygonal cell shape and formation of functional bile canaliculi-like structures was stable only in serum-free sandwich cultures. Variations in general cell viability, as judged by the cellular ATP content, LDH release or apoptosis, were less pronounced between alternative cultures. The intracellular glutathione content was preserved close to in vivo levels especially in serum-free sandwich cultures. Basal activities of cytochrome P450 enzymes (P450) varied strongly between cultures. There was a minor effect on CYP1A but CYP2B activity was only detectable in the serum-free sandwich culture after 3 days and beyond. CYP2C activity was slightly elevated in both sandwich cultures, whereas CYP3A showed increased levels in both serum-free cultures. Inducibility of these P450s was fully maintained over time in serum-free collagen sandwich only. Gene expression was largely constant over time in serum-free sandwich cultures that was closest to liver. This liver-like property was supported by protein profiling results. Taken together, the serum-free collagen sandwich culture of primary rat hepatocytes maintained liver-like features over 10 days and is therefore a suitable model for long-term toxicity and drug-drug interaction studies.

Extracellular matrix modulates sensitivity of hepatocytes to fibroblastoid dedifferentiation and transforming growth factor beta-induced apoptosis.

UNLABELLED: Hepatocytes in culture are a valuable tool to investigate mechanisms involved in the response of the liver to cytokines. However, it is well established that hepatocytes cultured on monolayers of dried stiff collagen dedifferentiate, losing specialized liver functions. In this study, we show that hepatocyte dedifferentiation is a reversible consequence of a specific signaling network constellation triggered by the extracellular matrix. A dried stiff collagen activates focal adhesion kinase (FAK) via Src, leading to activation of the Akt and extracellular signal-regulated kinase (ERK) 1/2 pathways. Akt causes resistance to transforming growth factor beta (TGF-beta)-induced apoptosis by antagonizing p38, whereas ERK1/2 signaling opens the route to epithelial-mesenchymal transition (EMT). Apoptosis resistance is reversible by inhibiting Akt or Src, and EMT can be abrogated by blocking the ERK1/2 pathway. In contrast to stiff collagen, a softer collagen gel does not activate FAK, keeping the hepatocytes in a state where they remain sensitive to TGF-beta-induced apoptosis and do not undergo EMT. In this culture system, inhibition of p38 as well as overexpression of constitutively active Akt causes apoptosis resistance, whereas constitutively active Ras induces EMT. Finally, we show that matrix-induced EMT is reversible by replating cells from dried stiff to soft gel collagen. Our results demonstrate that hepatocyte dedifferentiation in vitro is an active process driven by FAK-mediated Akt and ERK1/2 signaling. This leads to similar functional and morphological alterations as observed for regenerating hepatocytes in vivo and is reversible when Akt and/or ERK1/2 signaling pathways are antagonized. CONCLUSION: Hepatocytes can exist in a differentiated and a dedifferentiated state that are reversible and can be switched by manipulating the responsible key factors of the signaling network.

Species-specific toxicity of diclofenac and troglitazone in primary human and rat hepatocytes.

Troglitazone was withdrawn from the market shortly after approval for diabetes type II therapy because of strong hepatotoxic effects in man that could not be predicted from regulatory animal or in vitro studies. Another pharmaceutical that is regularly associated with adverse effects on the liver, sometimes leading to acute liver failure, is the widely used non-steroidal anti-inflammatory drug (NSAID) diclofenac. Since the underlying molecular mechanisms are not yet fully known, we treated primary rat and human hepatocyte monolayer cultures for 24h with different doses of troglitazone and diclofenac to analyze species differences related to toxicity in vitro. Metformin an antidiabetic drug which does not cause severe adverse reactions served as negative control. Human hepatocytes showed a higher sensitivity to troglitazone than rat hepatocytes, while diclofenac-induced cytotoxicity at fairly similar concentrations. By co-treatment with specific inhibitors for cytochrome P450 (CYP) 2C and CYP3A - the major phase I enzymes involved in liver xenobiotic metabolism - we could confirm the prominent role of CYP3A in the bioactivation of troglitazone as well as the role of CYP3A and CYP2C in the activation of diclofenac. Inhibition of these enzymes increased the viability of treated cells in both species. Furthermore, we were able to demonstrate marked species differences in gene expression patterns of troglitazone treated rat and human hepatocytes. In contrast to rat hepatocytes, human cells showed distinct upregulation of various CYPs, regulators of xenobiotic metabolism and marker genes for oxidative stress. In contrast, gene expression alterations in rat and human hepatocytes treated with Diclofenac were rather similar. Altogether our study showed that species-specific effects as well as indications for the mode of action of compounds can be addressed by the use of primary hepatocyte cultures from various species in combination with gene expression profiling.

Primary hepatocytes as a model to analyze species-specific toxicity and drug metabolism.

BACKGROUND: Compound failures have been emerging in later stages of pharmaceutical drug development and are in many cases not detected until the administration to humans in clinical trials or even after approval. Among the most frequent adverse effects are drug-induced liver injury generated by species-specific susceptibilities (e.g., in xenobiotic metabolism and/or the occurrence of idiosyncratic drug hepatotoxicity). OBJECTIVES: Detecting or predicting unfavorable drug effects on the liver as early as possible in drug development is crucial in making the drug development process more efficient and the application of new drugs to humans in clinical studies and medical use safer. METHODS: To achieve this goal, primary hepatocyte cultures from various species, including humans, are analyzed for morphological, functional and gene expression alterations after compound treatment. RESULTS/CONCLUSION: Primary hepatocyte cultures appear to be a promising tool for the detection of general or liver toxicity and the evaluation of species-specific drug effects.

Species differences in the response of liver drug-metabolizing enzymes to (S)-4-O-tolylsulfanyl-2-(4-trifluormethyl-phenoxy)-butyric acid (EMD 392949) in vivo and in vitro.

Induction of drug-metabolizing enzymes (DMEs) is highly species-specific and can lead to drug-drug interaction and toxicities. In this series of studies we tested the species specificity of the antidiabetic drug development candidate and mixed peroxisome proliferator-activated receptor (PPAR) alpha/gamma agonist (S)-4-O-tolylsulfanyl-2-(4-trifluormethyl-phenoxy)-butyric acid (EMD 392949, EMD) with regard to the induction of gene expression and activities of DMEs, their regulators, and typical PPAR target genes. EMD clearly induced PPARalpha target genes in rats in vivo and in rat hepatocytes but lacked significant induction of DMEs, except for cytochrome P450 (P450) 4A. CYP2C and CYP3A were consistently induced in livers of EMD-treated monkeys. Interestingly, classic rodent peroxisomal proliferation markers were induced in monkeys after 17 weeks but not after a 4-week treatment, a fact also observed in human hepatocytes after 72 h but not 24 h of EMD treatment. In human hepatocyte cultures, EMD showed similar gene expression profiles and induction of P450 activities as in monkeys, indicating that the monkey is predictive for human P450 induction by EMD. In addition, EMD induced a similar gene expression pattern as the PPARalpha agonist fenofibrate in primary rat and human hepatocyte cultures. In conclusion, these data showed an excellent correlation of in vivo data on DME gene expression and activity levels with results generated in hepatocyte monolayer cultures, enabling a solid estimation of human P450 induction. This study also clearly highlighted major differences between primates and rodents in the regulation of major inducible P450s, with evidence of CYP3A and CYP2C inducibility by PPARalpha agonists in monkeys and humans.

Alternatives in pharmaceutical toxicology: global and focussed approaches--two case studies.

Safety testing of potential drugs has been and will continue to be a challenging task for the toxicologist in the pharmaceutical industry. We present two examples for the use of target-specific cell models to detect and assess species-specific toxicity. In the first example, adrenal models based on primary cells as well as a permanent human adrenal cell line were used. Both cell systems enabled a good prediction of adrenal effects in rodents, non-rodents and humans. The second example made use of primary hepatocytes. In this project, a potential drug candidate showed unexpected toxicity in vitro as well as species-specific cytochrome P450 (CYP) induction in vivo. We therefore analysed CYP induction and gene expression signatures in rat and human hepatocytes as well as in samples from in vivo animal toxicity studies. By this approach, the rat hepatocyte model correctly predicted the effects observed in rats and the in vitro/in vivo comparison enabled a solid extrapolation of consequences in humans. These examples demonstrate that an intelligent testing strategy, using alternative methods, can enable a meaningful safety assessment for humans by adding a ''tailor-made'' range of technologies to ''classic'' toxicological methods.

Primary hepatocytes: current understanding of the regulation of metabolic enzymes and transporter proteins, and pharmaceutical practice for the use of hepatocytes in metabolism, enzyme induction, transporter, clearance, and hepatotoxicity studies.

This review brings you up-to-date with the hepatocyte research on: 1) in vitro-in vivo correlations of metabolism and clearance; 2) CYP enzyme induction, regulation, and cross-talk using human hepatocytes and hepatocyte-like cell lines; 3) the function and regulation of hepatic transporters and models used to elucidate their role in drug clearance; 4) mechanisms and examples of idiosyncratic and intrinsic hepatotoxicity; and 5) alternative cell systems to primary human hepatocytes. We also report pharmaceutical perspectives of these topics and compare methods and interpretations for the drug development process.

Effects of cell culture conditions on primary rat hepatocytes-cell morphology and differential gene expression.

We incubated primary rat hepatocytes on collagen monolayer as well as in collagen sandwich cultures with serum-containing or serum-free medium formulations. Morphological monitoring of hepatocytes revealed that hepatocytes cultured on collagen monolayer adopted their polygonal shape and started to create aggregates earlier than sandwich-cultured cells. Bile canaliculi-like structures were observed in every cell culture system but were more prominent in serum-free cultures. Hepatocytes in collagen-sandwich configuration and serum-free medium were the most viable after 72 h of culture, still displaying polygonal shape, clear cytoplasm and stable canaliculi-like structures. Differential gene expression patterns were determined for each cell culture condition using quantitative TaqMan Low Density Arrays (LDA). Gene expression analysis revealed distinct profiles in monolayer versus sandwich cultures and in particular in serum-free versus serum-containing culture medium. The hepatocytes cultured in the collagen-sandwich with serum-free medium showed the least variation in expression values over time. Importantly, stress markers were not induced in the serum-free sandwich culture, in contrast to the monolayer and the serum-containing sandwich cultures. Additionally, expression of the investigated cytochrome P450 genes was maintained in the serum-free monolayer and the sandwich cultures. In conclusion, culturing primary rat hepatocytes in a sandwich between two layers of gelled collagen and in a serum-free medium formulation, appears to be most suitable for long-term in vitro hepatotoxicity screening.