Hurel -- an in vivo-surrogate assay platform for cell-based studies

Naturally-Derived Biomaterials for Tissue Engineering Applications

Naturally-derived biomaterials have been used for decades in multiple regenerative medicine applications. From the simplest cell microcarriers made of collagen or alginate, to highly complex decellularized whole-organ scaffolds, these biomaterials represent a class of substances that is usually first in choice at the time of electing a functional and useful biomaterial. Hence, in this chapter we describe the several naturally-derived biomaterials used in tissue engineering applications and their classification, based on composition. We will also describe some of the present uses of the generated tissues like drug discovery, developmental biology, bioprinting and transplantation.

Modelling foetal exposure to maternal smoking using hepatoblasts from pluripotent stem cells

The liver is a dynamic organ which is both multifunctional and highly regenerative. A major role of the liver is to process both endo and xenobiotics. Cigarettes are an example of a legal and widely used drug which can cause major health problems for adults and constitute a particular risk to the foetus, if the mother smokes during pregnancy. Cigarette smoke contains a complex mixture of thousands of different xenobiotics, including nicotine and polycyclic aromatic hydrocarbons. These affect foetal development in a sex-specific manner, inducing sex-dependant molecular responses in different organs. To date, the effect of maternal smoking on the foetal liver has been studied in vitro using cell lines, primary tissue and animal models. While these models have proven to be useful, poor cell phenotype, tissue scarcity, batch-to-batch variation and species differences have led to difficulties in data extrapolation toward human development. Therefore, in this study we have employed hepatoblasts, derived from pluripotent stem cells, to model the effects of xenobiotics from cigarette smoke on human hepatocyte development. Highly pure hepatocyte populations (>90%) were produced in vitro and exposed to factors present in cigarette smoke. Analysis of ATP levels revealed that, independent of the sex, the majority of smoking derivatives tested individually did not deplete ATP levels below 50%. However, following exposure to a cocktail of smoking derivatives, ATP production fell below 50% in a sex-dependent manner. This was paralleled by a loss metabolic activity and secretory ability in both female and male hepatocytes. Interestingly, cell depletion was less pronounced in female hepatocytes, whereas caspase activation was ~twofold greater, indicating sex differences in cell death upon exposure to the smoking derivatives tested.

In vitro models for liver toxicity testing

Over the years, various liver-derived in vitro model systems have been developed to enable investigation of the potential adverse effects of chemicals and drugs. Liver tissue slices, isolated microsomes, perfused liver, immortalized cell lines, and primary hepatocytes have been used extensively. Immortalized cell lines and primary isolated liver cells are currently most widely used in vitro models for liver toxicity testing. Limited throughput, loss of viability, and decreases in liver-specific functionality and gene expression are common shortcomings of these models. Recent developments in the field of in vitro hepatotoxicity include three-dimensional tissue constructs and bioartificial livers, co-cultures of various cell types with hepatocytes, and differentiation of stem cells into hepatic lineage-like cells. In an attempt to provide a more physiological environment for cultured liver cells, some of the novel cell culture systems incorporate fluid flow, micro-circulation, and other forms of organotypic microenvironments. Co-cultures aim to preserve liver-specific morphology and functionality beyond those provided by cultures of pure parenchymal cells. Stem cells, both embryonic- and adult tissue-derived, may provide a limitless supply of hepatocytes from multiple individuals to improve reproducibility and enable testing of the individual-specific toxicity. This review describes various traditional and novel in vitro liver models and provides a perspective on the challenges and opportunities afforded by each individual test system.

Microfluidic device to investigate factors affecting performance in biosensors designed for transdermal applications

In this work we demonstrate a novel microfluidic based platform to investigate the performance of 3D out-of-plane microspike array based glucose and lactate biosensors. The microspike array was bonded with a glass slide and modified with glucose oxidase or lactate oxidase using covalent coupling chemistry. An epoxy-polyurethane based membrane was used to extend the linear working range (from 0 to 25 mM of substrate) of these biosensors. Both lactate and glucose sensors performed well in the clinically relevant substrate concentration range. Glucose microspikes were further investigated with respect to the effects of substrate transfer by incorporation into a microfluidic system. Data from the microfluidic system revealed that the sensor response is mainly dependent on enzyme kinetics rather than membrane permeability to glucose. The robustness of the sensors was demonstrated by its consistency in performance extending over 48 h.

Human tissue in the evaluation of safety and efficacy of new medicines: a viable alternative to animal models?

The pharma Industry's ability to develop safe and effective new drugs to market is in serious decline. Arguably, a major contributor to this is the Industry's extensive reliance on nonhuman biology-based test methods to determine potential safety and efficacy, objective analysis of which reveals poor predictive value. An obvious alternative approach is to use human-based tests, but only if they are available, practical, and effective. While in vivo (phase 0 microdosing with high sensitivity mass spectroscopy) and in silico (using established human biological data), technologies are increasingly being used, in vitro human approaches are more rarely employed. However, not only are increasingly sophisticated in vitro test methods now available or under development, but the basic ethically approved infrastructure through which human cells and tissues may be acquired is established. Along with clinical microdosing and in silico approaches, more effective access to and use of human cells and tissues in vitro provide exciting and potentially more effective opportunities for the assessment of safety and efficacy of new medicines.

Integrated Testing Strategies and the Prediction of Toxic Hazard

Over the past 20-30 years there has been a move towards reducing the use of animals in toxicity testing for industrial chemicals, pharmaceuticals, personal care and household products, for economic, scientific and animal welfare reasons. The need for alternatives has been emphasised by the EU REACH regulation, which requires the evaluation of tens of thousands of new and existing chemicals, and also within the pharmaceutical industry owing to the increasing rate at which drugs are being withdrawn from the market due to adverse effects not detected during preclinical testing. Significant effort is being placed into the development of non-animal test procedures using existing data, bioinformatics, in chemico, in silico and in vitro approaches and ethical human studies. Information from these diverse sources needs to be used intelligently and selectively leading to the development of what have become known as Integrated Testing Strategies (ITS). In this chapter factors that need to be considered in the development, evaluation, acceptance and use of ITS will be discussed.