Nasal Spray to the Rescue of Neurons in Stroke
Authors: Christian Alzheimer
Journal: Molecular Therapy (2018)

Stroke is a medical emergency requiring immediate therapeutic intervention. It has been estimated that, in patients suffering from a typical large vessel acute ischemic stroke, 120 million neurons, 830 billion synapses, and 714 km of myelinated fibers are lost each hour.1Saver J.L. Time is brain--quantified.Stroke. 2006; 37: 263-266Crossref PubMed Scopus (1205) Google Scholar Thus, stroke therapy is governed by the principle that "time is brain." A new paper from Buchthal et al.2Buchthal B. Weiss U. Bading H. Post-injury Nose-to-Brain Delivery of Activin A and SerpinB2 Reduces Brain Damage in a Mouse Stroke Model.Mol Ther. 2018; 26 (this issue, 2357–2365)Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar in this issue of Molecular Therapy shows an intriguing way to confine the evolution of ischemic tissue damage through the intranasal administration of neuroprotective substances after stroke onset. While performed in a mouse model of acute vessel occlusion, the means of drug delivery from nose to brain is so stunningly simple and, at the same time, efficient, that the paper has substantial translational value and holds therapeutic promise for stroke patients. To meet the need of urgent medical care in acute ischemic stroke, many larger hospitals worldwide have established specialized stroke units where, after expeditious diagnostic selection of eligible patients, intravenous thrombolysis or intra-arterial device-based interventions are used as recanalization therapies. However, these interventions will work only within the initial 4.5 and 6 hours, respectively, after stroke onset.3Catanese L. Tarsia J. Fisher M. Acute Ischemic Stroke Therapy Overview.Circ. Res. 2017; 120: 541-558Crossref PubMed Scopus (200) Google Scholar Unfortunately, many acute stroke patients will not reach specialized centers within this short time window. A recent review on acute stroke therapy suggested, therefore, that the initiation of neuroprotection already in the ambulance could be an exciting possibility to slow the development of the ischemic core, thereby extending the period in which patients remain candidates for interventional therapies.3Catanese L. Tarsia J. Fisher M. Acute Ischemic Stroke Therapy Overview.Circ. Res. 2017; 120: 541-558Crossref PubMed Scopus (200) Google Scholar This is exactly where the paper by Buchthal et al.2Buchthal B. Weiss U. Bading H. Post-injury Nose-to-Brain Delivery of Activin A and SerpinB2 Reduces Brain Damage in a Mouse Stroke Model.Mol Ther. 2018; 26 (this issue, 2357–2365)Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar comes in. Over many years, Bading and co-workers have developed an elaborate concept on how opposing neuroprotective and death-promoting pathways, mainly involving an antagonism between synaptic versus extrasynaptic NMDA receptors, determine the plastic properties of CNS neurons under physiological conditions as well as their fate in the diseased brain.4Hardingham G.E. Bading H. Synaptic versus extrasynaptic NMDA receptor signalling: implications for neurodegenerative disorders.Nat. Rev. Neurosci. 2010; 11: 682-696Crossref PubMed Scopus (1128) Google Scholar, 5Bading H. Nuclear calcium signalling in the regulation of brain function.Nat. Rev. Neurosci. 2013; 14: 593-608Crossref PubMed Scopus (244) Google Scholar In particular, they identified an intrinsic neuroprotective mechanism that is effected by "activity-regulated inhibitors of death." Among them are the secreted proteins activin A and serpinB2. Here, they have exploited their accumulated knowledge on the fundamentals of neuronal loss and survival to demonstrate the therapeutic potential of these two proteins in a realistic, i.e., clinically relevant, scenario. The authors first show that intracerebroventricular (icv) injection of activin A or serpinB2 reduces infarct size in a widely used stroke model (middle cerebral artery occlusion [MCAO]). While activin A, a member of the large transforming growth factor β (TGF-β) family, is an established factor that affords neuroprotection in excitotoxic and ischemic lesion models,6Link A.S. Zheng F. Alzheimer C. Activin Signaling in the Pathogenesis and Therapy of Neuropsychiatric Diseases.Front. Mol. Neurosci. 2016; 9: 32Crossref PubMed Scopus (14) Google Scholar serpinB2 is a newer player in this field. With few exceptions, animal studies exploring novel neuroprotective mechanisms in stroke and other lesion models would end here, leaving the reader wondering how to translate the findings into a clinical setting, because icv application or viral overexpression of recombinant proteins are not feasible strategies. The authors of the present study show that both factors are equally protective when applied transnasally in the same stroke model. The nose-to-brain delivery was achieved by intermittent application of drops of 2 μL in the left naris while the animal was placed in a supine position. The transnasal treatment had to meet two requirements to be efficient: (1) the first delivery of the substances had to start 10 min after MCAO, whereas a delay of 1 hr proved detrimental to their protective action; and (2) both proteins had to be applied in the presence of an absorption enhancer. Transnasal drug administration offers a safe and non-invasive pathway to target therapeutic agents to the brain. It bypasses the blood-brain barrier, avoids hepatic first-pass elimination, and reduces systemic exposure and unwarranted side effects. Thanks to its rapid absorption, drugs also exhibit a rapid onset of action—a distinct asset in acute stroke treatment. The idea to harness the advantages of the nose-to-brain pathway in the pharmacological treatment of neurological disorders is not new. In fact, William H. Frey II, who is credited with the introduction and development of this method, published the first proof-of-principle paper in 19957Thorne R.G. Emory C.R. Ala T.A. Frey 2nd, W.H. Quantitative analysis of the olfactory pathway for drug delivery to the brain.Brain Res. 1995; 692: 278-282Crossref PubMed Scopus (291) Google Scholar followed by a paper in 2001,8Liu X.F. Fawcett J.R. Thorne R.G. DeFor T.A. Frey 2nd, W.H. Intranasal administration of insulin-like growth factor-I bypasses the blood-brain barrier and protects against focal cerebral ischemic damage.J. Neurol. Sci. 2001; 187: 91-97Abstract Full Text Full Text PDF PubMed Scopus (213) Google Scholar demonstrating that transnasally administered insulin-like growth factor 1 (IGF-1) protects against ischemic damage in the MCAO stroke model. Since then, a number of preclinical stroke studies using transnasal delivery of different proteins, including IGF-1 (alone or together with erythropoietin), vascular endothelial growth factor (VEGF), TGF-β1, and basic fibroblast growth factor (bFGF, FGF2), have underscored the strength of this approach in reducing infarct volume (reviewed in Lochead and Thorne9Lochhead J.J. Thorne R.G. Intranasal delivery of biologics to the central nervous system.Adv. Drug Deliv. Rev. 2012; 64: 614-628Crossref PubMed Scopus (724) Google Scholar). Although the precise mechanisms remain to be elucidated, intranasally administered drugs are thought to travel to the brain along extracellular compartments of the olfactory and trigeminal nerve bundles. While Buchthal et al.2Buchthal B. Weiss U. Bading H. Post-injury Nose-to-Brain Delivery of Activin A and SerpinB2 Reduces Brain Damage in a Mouse Stroke Model.Mol Ther. 2018; 26 (this issue, 2357–2365)Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar did not detect measurable levels of transnasally applied recombinant activin A in the mouse brain, another member of the same family of growth and differentiation factors, namely TGF-β1, was found significantly enriched in the olfactory bulb, striatum, thalamus, cortex, and trigeminal nerve within 30 min of intranasal delivery and remained enhanced in the olfactory tubercle, striatum, thalamus, hippocampus, and cortex 6 hours after administration in rats.9Lochhead J.J. Thorne R.G. Intranasal delivery of biologics to the central nervous system.Adv. Drug Deliv. Rev. 2012; 64: 614-628Crossref PubMed Scopus (724) Google Scholar The reason for this discrepancy is not immediately obvious but might be related to the much higher diffusibility of activin when compared to TGF-β1, species differences (rat versus mouse), and/or different drug concentrations and application regimens. Extrapolating their experimental findings from the stroke model, Buchthal et al.2Buchthal B. Weiss U. Bading H. Post-injury Nose-to-Brain Delivery of Activin A and SerpinB2 Reduces Brain Damage in a Mouse Stroke Model.Mol Ther. 2018; 26 (this issue, 2357–2365)Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar advance intranasal activin A as a viable treatment option in chronic neurodegenerative diseases in which cell death is thought to be brought about by over-activation of extrasynaptic NMDA receptors, such as Alzheimer's disease, Huntington's disease, or amyotrophic lateral sclerosis. However, when considering a sustained elevation of activin levels in the brain along the transnasal route, some caveats must be expressed. First, activin A levels are normally very low in the mature brain. They display significant but brief rises in an activity-dependent fashion, e.g. following the exploration of a new enriched environment or the electrical induction of synaptic long-term potentiation (LTP), the presumed substrate of newly formed memory traces.6Link A.S. Zheng F. Alzheimer C. Activin Signaling in the Pathogenesis and Therapy of Neuropsychiatric Diseases.Front. Mol. Neurosci. 2016; 9: 32Crossref PubMed Scopus (14) Google Scholar It remains to be determined how an exogenously raised activin concentration might possibly interfere with its many neuromodulatory functions in the brain.10Krieglstein K. Zheng F. Unsicker K. Alzheimer C. More than being protective: functional roles for TGF-β/activin signaling pathways at central synapses.Trends Neurosci. 2011; 34: 421-429Abstract Full Text Full Text PDF PubMed Scopus (96) Google Scholar Second, in addition to its positive activity as a neurotrophic and protective factor in the brain, activin signaling has several potentially negative effects in other organs and tissue systems, where it has been implicated in fibrotic and inflammatory diseases, cancer progression, and sarcopenia in the elderly population.11Werner S. Alzheimer C. Roles of activin in tissue repair, fibrosis, and inflammatory disease.Cytokine Growth Factor Rev. 2006; 17: 157-171Crossref PubMed Scopus (187) Google Scholar, 12Antsiferova M. Werner S. The bright and the dark sides of activin in wound healing and cancer.J. Cell Sci. 2012; 125: 3929-3937Crossref PubMed Scopus (83) Google Scholar Consequently, inhibitors of activin signaling have been devised or are under way as treatments for these diseases and conditions. For example, activin A had been identified as an important driver of pathological tissue remodeling in a mouse asthma model.13Hardy C.L. Nguyen H.A. Mohamud R. Yao J. Oh D.Y. Plebanski M. Loveland K.L. Harrison C.A. Rolland J.M. O'Hehir R.E. The activin A antagonist follistatin inhibits asthmatic airway remodelling.Thorax. 2013; 68: 9-18Crossref PubMed Scopus (37) Google Scholar Notably, intranasal administration of follistatin, an activin antagonist, was reported to inhibit effective asthmatic airway remodeling.13Hardy C.L. Nguyen H.A. Mohamud R. Yao J. Oh D.Y. Plebanski M. Loveland K.L. Harrison C.A. Rolland J.M. O'Hehir R.E. The activin A antagonist follistatin inhibits asthmatic airway remodelling.Thorax. 2013; 68: 9-18Crossref PubMed Scopus (37) Google Scholar This finding demonstrated that, after intranasal delivery, appreciable amounts of a drug, depending on its physicochemical properties, might escape the cranial transport pathways, as noted earlier, based on anatomical considerations.9Lochhead J.J. Thorne R.G. Intranasal delivery of biologics to the central nervous system.Adv. Drug Deliv. Rev. 2012; 64: 614-628Crossref PubMed Scopus (724) Google Scholar Thus, for long-term intranasal activin A to be safe in chronic neurodegenerative disorders, it will be essential to demonstrate that even small amounts of the protein do not enter the systemic circulation. Does the transnasal route of drug delivery work in humans? Several lines of evidence permit a cautious "yes." The neuropeptide oxytocin was presumably the first drug ever to be applied intranasally (in a study with lactating women in the 1950s), and, half a century later, intranasally self-applied puffs of oxytocin in healthy volunteers have been reported to modulate amygdala-associated neural circuitry implicated in social phobias and autism.14Jiang Y. Li Y. Liu X. Intranasal delivery: circumventing the iron curtain to treat neurological disorders.Expert Opin. Drug Deliv. 2015; 12: 1717-1725Crossref PubMed Scopus (31) Google Scholar Over the last decade, intranasal insulin in Alzheimer's disease patients has arguably drawn the most attention, giving rise to a surge of clinical studies. The reason is 2-fold. Conceptually, central insulin resistance has been posited as a major causative factor in Alzheimer's disease, and, pharmacologically, intranasal application has been shown to raise insulin concentration in cerebrospinal fluid (CSF), but not, or only marginally, in serum, thereby avoiding systemic side effects.15Chapman C.D. Schiöth H.B. Grillo C.A. Benedict C. Intranasal insulin in Alzheimer's disease: Food for thought.Neuropharmacology. 2018; 136: 196-201Crossref PubMed Scopus (62) Google Scholar Although based on small sample numbers and restricted to treatment periods of ≤4 months, the clinical trials with intranasal insulin reported beneficial effects for both cognitive deficits and brain volumetric measures (reviewed in Chapman et al.15Chapman C.D. Schiöth H.B. Grillo C.A. Benedict C. Intranasal insulin in Alzheimer's disease: Food for thought.Neuropharmacology. 2018; 136: 196-201Crossref PubMed Scopus (62) Google Scholar). In May 2018, Johnson & Johnson published a news release on the results of a phase 3 study in patients with treatment-resistant depression, in which esketamine nasal spray yielded rapid improvement (https://clinicaltrials.gov/ct2/show/NCT02418585?term=NCT02418585&rank=1). This (incomplete) overview on clinical trials with intranasal drug administration underscores the potential impact of this unorthodox shortcut from the periphery to the brain as a valuable pharmacological approach for a number of different neuropsychiatric disorders. It also raises hope that, as posited by Buchthal et al.,2Buchthal B. Weiss U. Bading H. Post-injury Nose-to-Brain Delivery of Activin A and SerpinB2 Reduces Brain Damage in a Mouse Stroke Model.Mol Ther. 2018; 26 (this issue, 2357–2365)Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar a nasal spray containing activin A or another preclinically proven neuroprotective factor might emerge eventually as an easy-to-handle treatment procedure to mitigate neuronal loss in acute stroke patients. The author declares no conflict of interest. Post-injury Nose-to-Brain Delivery of Activin A and SerpinB2 Reduces Brain Damage in a Mouse Stroke ModelBuchthal et al.Molecular TherapyJuly 23, 2018In BriefA novel non-invasive neuroprotective treatment has been developed that uses intranasal application of Activin A and SerpinB2. This therapeutic approach reduces brain damage in a mouse stroke model, and it may also be beneficial in chronic neurodegenerative diseases. Full-Text PDF Open Archive