Jeffrey J. Lochhead

Intranasal delivery of biologics to the central nervous system.

Treatment of central nervous system (CNS) diseases is very difficult due to the blood-brain barriers (BBB) ability to severely restrict entry of all but small, non-polar compounds. Intranasal administration is a non-invasive method of drug delivery which may bypass the BBB to allow therapeutic substances direct access to the CNS. Intranasal delivery of large molecular weight biologics such as proteins, gene vectors, and stem cells is a potentially useful strategy to treat a variety of diseases/disorders of the CNS including stroke, Parkinsons disease, multiple sclerosis, Alzheimers disease, epilepsy, and psychiatric disorders. Here we give an overview of relevant nasal anatomy and physiology and discuss the pathways and mechanisms likely involved in drug transport from the nasal epithelium to the CNS. Finally we review both pre-clinical and clinical studies involving intranasal delivery of biologics to the CNS.

Oxidative Stress Increases Blood–Brain Barrier Permeability and Induces Alterations in Occludin during Hypoxia–Reoxygenation

The blood–brain barrier (BBB) has a critical role in central nervous system homeostasis. Intercellular tight junction (TJ) protein complexes of the brain microvasculature limit paracellular diffusion of substances from the blood into the brain. Hypoxia and reoxygenation (HR) is a central component to numerous disease states and pathologic conditions. We have previously shown that HR can influence the permeability of the BBB as well as the critical TJ protein occludin. During HR, free radicals are produced, which may lead to oxidative stress. Using the free radical scavenger tempol (200 mg/kg, intraperitoneal), we show that oxidative stress produced during HR (6% O2 for 1 h, followed by room air for 20 min) mediates an increase in BBB permeability in vivo using in situ brain perfusion. We also show that these changes are associated with alterations in the structure and localization of occludin. Our data indicate that oxidative stress is associated with movement of occludin away from the TJ. Furthermore, subcellular fractionation of cerebral microvessels reveals alterations in occludin oligomeric assemblies in TJ associated with plasma membrane lipid rafts. Our data suggest that pharmacological inhibition of disease states with an HR component may help preserve BBB functional integrity.

Rapid Transport within Cerebral Perivascular Spaces Underlies Widespread Tracer Distribution in the Brain after Intranasal Administration

The intranasal administration route is increasingly being used as a noninvasive method to bypass the blood—brain barrier because evidence suggests small fractions of nasally applied macromolecules may reach the brain directly via olfactory and trigeminal nerve components present in the nasal mucosa. Upon reaching the olfactory bulb (olfactory pathway) or brainstem (trigeminal pathway), intranasally delivered macromolecules appear to rapidly distribute within the brains of rodents and primates. The mechanisms responsible for this distribution have yet to be fully characterized. Here, we have used ex vivo fluorescence imaging to show that bulk flow within the perivascular space (PVS) of cerebral blood vessels contributes to the rapid central distribution of fluorescently labeled 3 and 10 kDa dextran tracers after intranasal administration in anesthetized adult rats. Comparison of tracer plasma levels and fluorescent signal distribution associated with the PVS of surface arteries and internal cerebral vessels showed that the intranasal route results in unique central access to the PVS not observed after matched intravascular dosing in separate animals. Intranasal targeting to the PVS was tracer size dependent and could be regulated by modifying nasal epithelial permeability. These results suggest cerebral perivascular convection likely has a key role in intranasal drug delivery to the brain.

Occludin oligomeric assemblies at tight junctions of the blood–brain barrier are altered by hypoxia and reoxygenation stress

Hypoxic (low oxygen) and reperfusion (post‐hypoxic reoxygenation) phases of stroke promote an increase in microvascular permeability at tight junctions (TJs) of the blood–brain barrier (BBB) that may lead to cerebral edema. To investigate the effect of hypoxia (Hx) and reoxygenation on oligomeric assemblies of the transmembrane TJ protein occludin, rats were subjected to either normoxia (Nx, 21% O2, 60 min), Hx (6% O2, 60 min), or hypoxia/reoxygenation (H/R, 6% O2, 60 min followed by 21% O2, 10 min). After treatment, cerebral microvessels were isolated, fractionated by detergent‐free density gradient centrifugation, and occludin oligomeric assemblies associated with plasma membrane lipid rafts were solubilized by perfluoro‐octanoic acid (PFO) exclusively as high molecular weight protein complexes. Analysis by non‐reducing and reducing sodium dodecyl sulfate (SDS)–polyacrylamide gel electrophoresis/western blot of PFO‐solubilized occludin revealed that occludin oligomeric assemblies co‐localizing with ‘TJ‐associated’ raft domains contained a high molecular weight ‘structural core’ that was resistant to disassembly by either SDS or a hydrophilic reducing agent ex vivo, and by Hx and H/R conditions in vivo. However, exposure of PFO‐solubilized occludin oligomeric assemblies to SDS ex vivo revealed the non‐covalent association of a significant amount of dimeric and monomeric occludin isoforms to the disulfide‐bonded inner core, and dispersal of these non‐covalently attached occludin subunits to lipid rafts of higher density in vivo was differentially promoted by Hx and H/R. Our data suggest a model of isoform interaction within occludin oligomeric assemblies at the BBB that enables occludin to simultaneously perform a structural role in inhibiting paracellular diffusion, and a signaling role involving interactions of dimeric and monomeric occludin isoforms with a variety of regulatory molecules within different plasma membrane lipid raft domains.

Atorvastatin therapy lowers circulating cholesterol but not free radical activity in advance of identifiable clinical benefit in the treatment of mild-to-moderate AD.

Cholesterol-induced production of amyloid beta (Abeta) as a putative neurotoxin in Alzheimers disease (AD), along with epidemiological evidence, suggests that statin drugs may provide benefit in treatment of the disorder. We tested the effect of once daily atorvastatin calcium (80 mg; two 40 mg tablets) on cognitive and/or behavioral decline in patients with mild-to-moderate AD. The study was designed as a pilot intention-to-treat, proof-of-concept, double-blind, placebo-controlled, randomized (1:1) trial with a 1-year exposure to study medication employing last-observation-carried-forward (LOCF) ANCOVA as the primary statistical method of assessment. Alternate statistical methods were employed to further explore the effect of atorvastatin treatment on progression of deterioration. Of the 98 individuals with mild-to-moderate AD (Mini-Mental State Examination score of 12-28) providing Informed Consent, 71 were eligible for randomization, 67 were randomized and 63 completed the 3-month visit and were statistically evaluable. The primary outcome measures were change in the Alzheimer Disease Assessment Scale-Cognitive (ADAS-cog) performance and the Clinical Global Impression of Change (CGIC). Secondary outcome measures included the MMSE, Geriatric Depression Scale (GDS), the Neuropsychiatric Inventory (NPI) and the ADCS Activities of Daily Living inventory (ADCS-ADL). Tertiary outcome measures included levels of total circulating cholesterol, LDL and VLDL, and circulating activity of the free radical scavenger enzymes superoxide dismutase (SOD) and glutathione peroxidase (GpX). Atorvastatin reduced circulating cholesterol levels and produced a positive signal on each of the clinical outcome measures compared to placebo, but did not elicit a difference in circulating SOD or GpX activities. The observed beneficial clinical effect reached significance for the GDS (p = 0.040) and the ADAS-cog at 6 months (p = 0.003), was all but significant for the ADAS-cog (p = 0.055) at 12 months, and was of marginal significance for the CGIC (p = 0.073) and NPI (p = 0.071) at 12 months when employing the primary statistical approach (ANCOVA with LOCF). Application of repeated measures ANCOVA statistics revealed the difference was significant for the CGIC and marginally significant for the ADAS-cog, but not significant for the other clinical indices. This evaluation indicated significant time-by-treatment interactions (altered progression) for the ADAS-cog and MMSE, but not the CGIC. Application of random intercept regression analysis revealed a significant difference for the CGIC, ADAS-cog and MMSE. Regression analysis also indicated that atorvastatin produced change in the slope of deterioration on the MMSE. Accordingly, atorvastatin therapy may be an effective treatment and may slow the progression of AD among mild-to-moderately affected patients.

Tempol modulates changes in xenobiotic permeability and occludin oligomeric assemblies at the blood-brain barrier during inflammatory pain.

Our laboratory has shown that λ-carrageenan-induced peripheral inflammatory pain (CIP) can alter tight junction (TJ) protein expression and/or assembly leading to changes in blood-brain barrier xenobiotic permeability. However, the role of reactive oxygen species (ROS) and subsequent oxidative stress during CIP is unknown. ROS (i.e., superoxide) are known to cause cellular damage in response to pain/inflammation. Therefore, we examined oxidative stress-associated effects at the blood-brain barrier (BBB) in CIP rats. During CIP, increased staining of nitrosylated proteins was detected in hind paw tissue and enhanced presence of protein adducts containing 3-nitrotyrosine occurred at two molecular weights (i.e., 85 and 44 kDa) in brain microvessels. Tempol, a pharmacological ROS scavenger, attenuated formation of 3-nitrotyrosine-containing proteins in both the hind paw and in brain microvessels when administered 10 min before footpad injection of λ-carrageenan. Similarly, CIP increased 4-hydroxynoneal staining in brain microvessels and this effect was reduced by tempol. Brain permeability to [(14)C]sucrose and [(3)H]codeine was increased, and oligomeric assemblies of occludin, a critical TJ protein, were altered after 3 h CIP. Tempol attenuated both [(14)C]sucrose and [(3)H]codeine brain uptake as well as protected occludin oligomers from disruption in CIP animals, suggesting that ROS production/oxidative stress is involved in modulating BBB functional integrity during pain/inflammation. Interestingly, tempol administration reduced codeine analgesia in CIP animals, indicating that oxidative stress during pain/inflammation may affect opioid delivery to the brain and subsequent efficacy. Taken together, our data show for the first time that ROS pharmacological scavenging is a viable approach for maintaining BBB integrity and controlling central nervous system drug delivery during acute inflammatory pain.

Water quality has a pronounced effect on cholesterol-induced accumulation of Alzheimer amyloid β (Aβ) in rabbit brain

Increased circulating cholesterol is known to promote risk of coronary artery disease. It is now emerging that cholesterol promotes production and accumulation of amyloid beta (Abeta) deposited in the hallmark pathologic lesion of Alzheimers disease (AD), the senile plaque, perhaps by shifting away from normal metabolism of amyloid beta protein precursor (AbetaPP) to beta. Previous studies employing the cholesterol-fed rabbit model of AD demonstrated that induction of AD-like Abeta accumulation in brain could be reversed by co-administration of cholesterol lowering drugs or removing cholesterol, prompted initiation of an AD Cholesterol-Lowering (Statin) Treatment Trial. We now present data that identify a previously unrecognized role for dietary water quality on the severity of neuropathology induced by elevated cholesterol. Neuronal accumulation of Abeta induced by increased circulating concentrations of cholesterol in the New Zealand white rabbit is attenuated when distilled drinking water is administered compared to use of tap water. The numbers of neurons in cholesterol-fed rabbits that exhibited Abeta immunoreactivity, relative to normal chow-fed controls, increased approximately 2.5 fold among animals on tap water but only approximately 1.9 fold among animals on distilled water. This yielded a statistically significant approximately 28% reduction due to the use of distilled water. In addition, the subjectively assessed intensity of neuronal Abeta immunoreactivity was consistently reduced among cholesterol-fed rabbits allowed distilled drinking water compared to cholesterol-fed rabbits on tap water. As intensity of antibody immunoreactivity is likely related to concentration of antigen, the identified difference among cholesterol-fed rabbits allowed distilled drinking water may hold greater importance than a significant reduction in numbers of affected neurons. The effect on neuronal Abeta immunoreactivity intensity was observable among cholesterol-fed rabbits reared and allowed tap water when performing studies in three distinct locales. Pilot data suggest the possibility of increased clearance of Abeta from the brain, identified as increased blood levels, among cholesterol-fed rabbits administered distilled water compared to animals on tap water. The agent(s) occurring in tap water, excluded by distillation, promoting accumulation of neuronal Abeta immunoreactivity is(are) yet undisclosed, but arsenic, manganese, aluminum, zinc, mercury, iron and nitrate have tentatively been excluded because they were not identifiable (below detection limits) in the tap water of the three locales where the cholesterol-induced neuropathologic difference was observable. These findings suggest that water quality may impact on human health in the setting of increased circulating cholesterol levels, and could illustrate a truly simple life-style change that could be of benefit in AD.

Cholesterol modifies classical conditioning of the rabbit (Oryctolagus cuniculus) nictitating membrane response.

Cholesterol plays an important role in synapse formation, receptor function, and synaptic plasticity, and animal studies show that modifying cholesterol may improve learning and memory. Other data show that feeding animals cholesterol can induce beta amyloid accumulation. Rabbits (Oryctolagus cuniculus) fed 2% cholesterol for 8 weeks were given trace conditioning of the nictitating membrane response using a 100-ms tone, a 700-ms trace, and periorbital electrical stimulation or airpuff. Rabbits fed cholesterol showed significant facilitation of trace conditioning to airpuff and conditioning-specific reflex modification to periorbital electrical stimulation and airpuff. The cholesterol-fed rabbits had beta amyloid accumulation in the cortex, but little in the hippocampus. The data suggest cholesterol had facilitative effects that outweighed potential amnesic effects of cortical beta amyloid.

Relative vascular permeability and vascularity across different regions of the rat nasal mucosa: implications for nasal physiology and drug delivery.

Intranasal administration provides a non-invasive drug delivery route that has been proposed to target macromolecules either to the brain via direct extracellular cranial nerve-associated pathways or to the periphery via absorption into the systemic circulation. Delivering drugs to nasal regions that have lower vascular density and/or permeability may allow more drug to access the extracellular cranial nerve-associated pathways and therefore favor delivery to the brain. However, relative vascular permeabilities of the different nasal mucosal sites have not yet been reported. Here, we determined that the relative capillary permeability to hydrophilic macromolecule tracers is significantly greater in nasal respiratory regions than in olfactory regions. Mean capillary density in the nasal mucosa was also approximately 5-fold higher in nasal respiratory regions than in olfactory regions. Applying capillary pore theory and normalization to our permeability data yielded mean pore diameter estimates ranging from 13–17 nm for the nasal respiratory vasculature compared to <10 nm for the vasculature in olfactory regions. The results suggest lymphatic drainage for CNS immune responses may be favored in olfactory regions due to relatively lower clearance to the bloodstream. Lower blood clearance may also provide a reason to target the olfactory area for drug delivery to the brain.

Hypoxic Stress and Inflammatory Pain Disrupt Blood-Brain Barrier Tight Junctions: Implications for Drug Delivery to the Central Nervous System

A functional blood-brain barrier (BBB) is necessary to maintain central nervous system (CNS) homeostasis. Many diseases affecting the CNS, however, alter the functional integrity of the BBB. It has been shown that various diseases and physiological stressors can impact the BBB’s ability to selectively restrict passage of substances from the blood to the brain. Modifications of the BBB’s permeability properties can potentially contribute to the pathophysiology of CNS diseases and result in altered brain delivery of therapeutic agents. Hypoxia and/or inflammation are central components of a number of diseases affecting the CNS. A number of studies indicate hypoxia or inflammatory pain increase BBB paracellular permeability, induce changes in the expression and/or localization of tight junction proteins, and affect CNS drug uptake. In this review, we look at what is currently known with regard to BBB disruption following a hypoxic or inflammatory insult in vivo. Potential mechanisms involved in altering tight junction components at the BBB are also discussed. A more detailed understanding of the mediators involved in changing BBB functional integrity in response to hypoxia or inflammatory pain could potentially lead to new treatments for CNS diseases with hypoxic or inflammatory components. Additionally, greater insight into the mechanisms involved in TJ rearrangement at the BBB may lead to novel strategies to pharmacologically increase delivery of drugs to the CNS.