Intranasal delivery to the central nervous system: Mechanisms and experimental considerations

Intranasal delivery of biologics to the central nervous system

Anatomical and physiological parameters affecting gastrointestinal absorption in humans and rats

Neurotrophic factors are proteins with considerable potential in the treatment of central nervous system (CNS) diseases and traumatic injuries. However, a significant challenge to their clinical use is the difficulty associated with delivering these proteins to the CNS. Neurotrophic factors are hydrophilic, typically basic, monomeric or dimeric proteins, mostly in the size range of 5 to 30 kDa. Neurotrophic factors potently support the development, growth and survival of neurons, eliciting biological effects at concentrations in the nanomolar to femtomolar range. They are not orally bioavailable and the blood-brain and blood-cerebrospinal fluid barriers severely limit their ability to enter into and act on sites in the CNS following parenteral systemic routes of administration. Most neurotrophic factors have short in vivo half-lives and poor pharmacokinetic profiles. Their access to the CNS is restricted by rapid enzymatic inactivation, multiple clearance processes, potential immunogenicity and sequestration by binding proteins and other components of the blood and peripheral tissues. The development of targeted drug delivery strategies for neurotrophic factors will probably determine their clinical effectiveness for CNS conditions. Achieving significant CNS target site concentrations while limiting systemic exposure and distribution to peripheral sites of action will lessen unwanted pleiotropic effects and toxicity. Local introduction of neurotrophic factors into the CNS intraparenchymally by direct injection/infusion or by implantation of delivery vectors such as polymer matrices or genetically modified cells yields the highest degree of targeting, but is limited by diffusion restrictions and invasiveness. Delivery of neurotrophic factors into the cerebrospinal fluid (CSF) following intracerebroventricular or intrathecal administration is less invasive and allows access to a much wider area of the CNS through CSF circulation pathways. However, diffusional and cellular barriers to penetration into surrounding CNS tissue and significant clearance of CSF into the venous and lymphatic circulation are also limiting. Unconventional delivery strategies such as intranasal administration may offer some degree of CNS targeting with minimal invasiveness. This review presents a summary of the neurotrophic factors and their indications for CNS disorders, their physicochemical characteristics and the different approaches that have been attempted or suggested for their delivery to the CNS. Future directions for further research such as the potential for CNS disease treatment utilising combinations of neurotrophic factors, displacement strategies, small molecule mimetics, chimaeric molecules and gene therapy are also discussed.

Delivery of neurotrophic factors to the central nervous system: pharmacokinetic considerations.

Recommendations for the standardisation of oxytocin nasal administration and guidelines for its reporting in human research.

While nasal cancer is relatively rare among the general population, workers in the nickel refining, leather manufacturing, and furniture building industries exhibit increased incidences of nasal cancer. To investigate the causes of nasal cancer and to design ameliorative strategies, an appropriate animal model for the human upper respiratory regions is required. The present report describes, compares, and assesses the anatomy and physiology of the nasal passages and upper airways of humans, rats, and monkeys for the purpose of determining a relevant animal model in which to investigate potential causes of nasal cancer. Based on the mode of breathing, overall geometry of the nasal passages, relative nasal surface areas, proportions of nasal surfaces lined by various epithelia, mucociliary clearance patterns, and inspiratory airflow routes, the rat, which is very different from humans, is a poor model. In contrast, the monkey exhibits many similarities to humans. Although the monkey does differ from humans in that it exhibits a more rapid respiratory rate, smaller minute and tidal volumes, larger medial turbinate, and a vestibular wing that creates an anterior vortex during inspiration, it offers a more appropriate model for studying the toxic effects of inhaled substances on the nasal passages and extrapolating the findings to humans.

DeSesso Jm

Papers

The relevance to humans of animal models for inhalation studies of cancer in the nose and upper airways