Animal models and their limitations: On the problem of high-to-low dose extrapolations following inhalation exposures

Controlled pulmonary drug and gene delivery using polymeric nano-carriers

Pulmonary drug and gene delivery to the lung represents a non-invasive avenue for local and systemic therapies. However, the respiratory tract provides substantial barriers that need to be overcome for successful pulmonary application. In this regard, micro- and nano-sized particles offer novel concepts for the development of optimized therapeutic tools in pulmonary research. Polymeric nano-carriers are generally preferred as controlled pulmonary delivery systems due to prolonged retention in the lung. Specific manipulation of nano-carrier characteristics enables the design of "intelligent" carriers specific for modulation of the duration and intensity of pharmacological effects. New formulations should be tested for pulmonary absorption and distribution using more advanced ex vivo and in vivo models. The delivery of nano-carriers to the air-space enables a detailed characterization of the interaction between the carrier vehicle and the natural pulmonary environment. In summary, polymeric nanoparticles seem to be especially promising as controlled delivery systems and represent a solid basis for future advancement for pulmonary delivery applications.

Alternatives for Lung Research: Stuck between a Rat and a Hard Place

The respiratory system acts as a portal into the human body for airborne materials, which may gain access via the administration of medicines or inadvertently during inhalation of ambient air (e.g. air pollution). The burden of lung disease has been continuously increasing, to the point where it now represents a major cause of human morbidity and mortality worldwide. In the UK, more people die from respiratory disease than from coronary heart disease or non-respiratory cancer. For this reason alone, gaining an understanding of mechanisms of human lung biology, especially in injury and repair events, is now a principal focus within the field of respiratory medicine. Animal models are routinely used to investigate such events in the lung, but they do not truly reproduce the responses that occur in humans. Scientists committed to the more robust Three Rs principles of animal experimentation ( Reduction, Refinement and Replacement) have been developing viable alternatives, derived from human medical waste tissues from patient donors, to generate in vitro models that resemble the in vivo human lung environment. In the specific case of inhalation toxicology, human-oriented models are especially warranted, given the new REACH regulations for the handling of chemicals, the rising air pollution problems and the availability of pharmaceutically valuable drugs. Advances in tissue-engineering have made it feasible and cost-effective to construct human tissue equivalents of the respiratory epithelia. The conducting airways of the lower respiratory system are a critical zone to recapitulate for use in inhalation toxicology. Three-dimensional (3D) tissue designs which make use of primary cells, provide more in vivo-like responses, based on the targeted interactions of multiple cell types supported on artificial scaffolds. These scaffolds emulate the native extracellular matrix, in which cells differentiate into a functional pulmonary tissue. When 3-D cell cultures are employed for testing aerosolised chemicals, drugs and xenobiotics, responses are captured that mirror the events in the in situ human lung and provide human endpoint data.

Intentional exposure studies of environmental agents on human subjects: assessing benefits and risks

In this article, I assess the benefits and risks of studies that intentionally expose research subjects to environmental agents. I describe these types of studies, identify their benefits and risks, compare them to other research methods that can be used to investigate the relationship between environmental exposures and disease, and discuss some issues related to research design and risk minimization. I argue that the benefits of intentional environmental exposure studies outweigh the risks when 1) the knowledge gained is likely to improve our understanding of the relationship between environmental exposure and disease, 2) this knowledge cannot be obtained by other methods, 3) the experiments are well designed, 4) the subjects will receive some benefits, such as medical evaluations, 5) risks are minimized, and 6) the risks to human subjects are less than those encountered in a typical Phase I drug study. Only in rare circumstances (i.e., when an intentional environmental exposure study is needed to implement an important environmental or public health intervention or regulation) may such studies expose research subjects to risks as high as those encountered in a typical Phase I drug trail.

Ethical issues in clinical trials involving nanomedicine

Nanomedicine shows tremendous promise for improving medical diagnosis, treatment, and prevention, but it also raises a variety of ethical concerns. Because of the paucity of data on the physicochemical properties of nanoscale materials in biological systems, clinical trials of nanomedicine products present some unique challenges related to risk minimization, management and communication involving human subjects. Although these clinical trials do not raise any truly novel ethical issues, the rapid development of nanotechnology and its potentially profound social and environmental impacts, add a sense of urgency to the problems that arise.