Intrathecal Autologous Thrombin-Activated Condensed Platelet Cytokines in Chronic Neurodegenerative Disease: Anti-inflammatory and Regenerative Responses, Phase I

1. Introduction

The need to provide a cure for chronic neurodegenerative diseases has never been more acute. Despite decades of uninterrupted international scientific efforts, clinical trials for Alzheimer’s disease (AD) have scored the lowest yield of almost any medical research endeavor [1]. Forecasts for breakthroughs in Parkinson’s disease (PD) are similarly bleak [2]. And as global incidence of neurodegenerative diseases is expected to increase three-fold by 2050 [3,4] the socioeconomic importance of this public health concern is outpacing the medical research meant to check them.

While the poor return on AD and PD research has been discussed by others [2,5], against this busy background one path to cure still remains largely untraveled: Intrathecal platelet-rich plasma (PRP). Considering novel recombinants synthesized to alter production of specified brain proteins, autologous PRP risks being discounted as simplistic by comparison. However, in addition to platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor (VEGF) and other better-known PRP constituents, activated platelet (PLT) releasate also includes nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT3), plus other potent neurotrophic signals [6,7]. Notwithstanding animal data on inflammatory myelin damage in multiple sclerosis showing recovery after intrathecal PRP [8], a literature search intersecting ‘intrathecal’ and ‘platelet-rich plasma’ identifies only seven publications—and none specifically address AD or PD. While the paucity of published data on intrathecal PRP for neurodegenerative conditions is notable, more worrisome is a survey of registered clinical trials on this topic, where no investigations are currently underway or planned [9]. This means that not only is scant knowledge available on this point now, the research pipeline is extremely unlikely to deliver anything of relevance going forward. Accordingly, this account puts intrathecal PRP under fresh scrutiny as an alternative anti-inflammatory, regenerative, disease-modifying option in AD and PD.

2. Cerebrospinal fluid and neurodegenerative pathology

Substantial neuronal loss occurs in both AD and PD. For both conditions, diagnosis depends on clinical tests where detection of early-stage disease is far from ideal. Indeed, at initial presentation the stage of neurodegeneration may already be quite advanced [10]. A recent study of noradrenaline, 3-methoxy-4-hydroxyphenylglycol, and noradrenaline transport availability for both conditions found that PD shows markedly lower levels of noradrenaline and 3-methoxy-4-hydroxyphenylglycol in cerebrospinal fluid (CSF), as well as poor hypothalamic noradrenaline transport availability [11]. In AD, profoundly reduced amyloid-β clearance is observed compared to healthy controls yet production quantity is unchanged [12]. While there is disagreement on how much time must pass before these changes will manifest, the relation highlights the role of disordered brain clearance systems [13,14] where resident microglia and peripheral mononuclear phagocytes somehow exhaust their governance over cerebral deposition of amyloid-β [15,16].

Cellular water handling is also relevant to CSF dynamics, and the aquaporin (AQP) family has been extensively studied with at least 12 different AQPs operating in specific cell types. While function of transmembrane channels is subject to resting voltage potentials [17], how PLT cytokines influence cell portal operation is only now being investigated. Loss of membrane integrity from inflammation is often reversible, and ongoing work should extend recent discoveries concerning how gap junctions are targets for selected PLT cytokines [18]. If this also applies to the main aquaporin in neural tissue (AQP4), then PLT cytokines may actuate this transmembrane gate to mediate amyloid-β clearance [19] and manage extracellular volume during synaptic action [20]. Moreover, this proposal incorporates PLT activation by thrombin [21] rather than calcium chloride or calcium gluconate [22], to minimize risk of electrolyte upset.

When CSF cytokines in AD patients were referenced against healthy controls, eotaxin, IL-1ra, IL-4, IL-7, IL-8, IL-9, IL-10, IL-15, GCSF, monocyte chemotactic protein 1, PDGF, and TNF-alpha were all elevated [16]. Of note, a negative correlation was observed between disease progression and IL-1β, IL-4, IL-6, IL-9, IL-17A, FGF, GCSF, GMCSF, interferon gamma, and macrophage inflammatory protein-1β [16]. By contrast, CSF features in PD include α-synuclein (αSyn) levels which are often much lower than expected in normal health [23]. This diminished αSyn could be explained by passage of this protein from CSF into adjacent tissues [24,25], precipitates which could be worsened by slower circulation secondary to local inflammation. Oxidative stress is central to both cause and course of PD pathology, typified by mitochondrial dysfunction, excitotoxicity, and loss of dopaminergic action [26,27]. Since CSF biomarkers have discriminatory value for these neurogenerative conditions [11] this becomes a plausible route for cytokine normalization, enabling a directed therapeutic purpose, as proposed here.

3. Neural targets, intrathecal access

Effective therapy for neurodegenerative conditions, mass lesions, infections, or refractory pain relies on direct drug delivery to bypass the blood-brain barrier [28], explaining why many systemically administered agents never achieve therapeutic levels in brain tissue [29]. The current design extends prior work where drug delivery was via transdermal adhesive patch placed dorsally on the neck [30], by intranasal insufflation [31], or similar techniques [32,33]. Access to cerebrospinal and intraventricular space by intrathecal dosing [34] has the benefit of placing PLT cytokines in close proximity to glymphatic control sites most likely affected by oxidative stress, inflammation, or fibrosis [35,36,37].

The glymphatic system is a perivascular network for CSF transport connecting distally to the dural/meningeal lymphatic system. As the chief efflux channel for brain tissue [38], the glymphatic network clears metabolic products to prevent pathologic accretion in brain parenchyma and interstitial fluid [39]. Produced at a rate of 500-700 mL/d, total average CSF volume is ~140mL in healthy adults [40,41]. While there is broad consensus that CSF originates from choroid plexus in humans, anatomical exit routes beyond arachnoid granulations are less well characterized [42].

A standard intrathecal/lumbar catheter inserted at L3-L5 permits safe injection of volumes ranging from 0.5 to 5mL. While the concept of intrathecal therapy for neurodegenerative disease is underdeveloped, placement of blood products here is not: For spinal headache, needle access near a lumbar puncture site is often used to inject an autologous ‘blood patch’ to reduce symptoms and promote dural healing [43,44].

The 2009 priority paper outlining intrathecal dosing of conventional PRP in the management of AD and PD may be attributed to Shen et al [7]. Their insight was predicated not necessarily on anti-inflammatory properties (see Figure 1), but on the observed neurotrophic capacity of PLT growth factors which, individually or in concert, could ameliorate neurodegenerative diseases. Interventions to remove biochemical residue to assuage neurodegenerative loss gained momentum from animal research, where glymphatic dysfunction was noted after traumatic brain injury or stroke as well as animal models for normal aging and AD [45,46,47,48]. These findings helped frame workable ways to assure proper physiologic elimination of waste solutes [48,49]. Downshifting tau production would be another logical process to address AD pathology, and favorable results from a first-in-human Phase Ib clinical trial described a tau-targeting antisense oligonucleotide given intrathecally for this purpose [50]. While devices adapted to alleviate neurodegenerative symptoms are in preclinical development [51], using fresh autologous condensed PLT cytokines in this context represents an application not previously considered. Indeed, recent laboratory and clinical gains in PLT processing include better preparations of plasma cytokine samples and their delivery—including cell-free substrates following PLT subtraction. But might intrathecal use of an autologous PLT product have efficacy in AD or PD?

5. Conclusions

As with all early investigations, it is impossible to predict if intrathecal autologous condensed plasma cytokines/PRP can become a disease-modifying agent for AD or PD. Given the long history of prior interventions aspiring to manage these conditions, the odds are not especially favorable. Most PRP applications tend to support tissue regeneration, although some authors are more reserved [79,80]. Notwithstanding the growing interest in PRP and its derivatives in new domains [81], nonuniform sample preparations [82,83] have made randomized controlled trials difficult to standardize and almost impossible to interpret. While any diffuse hyperinflammation corrected by PLT cytokine use is welcome, numerous CNS signal pathways are impacted upon PLT activation to facilitate tissue repair, angiogenesis and neurogenesis [84]. This work therefore expands prior descriptions of PRP treatment for CNS disorders [7] given its recuperative effects in SCI and peripheral nerve damage documented elsewhere [68,85]. This approach also extends earlier PRP use in kidney disease, which balanced difficulties of treating an encapsulated solid organ with the need to dose PRP locally [86]. Because a generic PRP-based clinical trial entails no FDA new drug clearance and requires few resources to establish the study program, the project joins the AD/PD research discourse as an outlier. Under assessment by an institutional review board, repurposing PLT-derived cytokines represents a readily available, relatively inexpensive, low risk, and underutilized therapy for intrathecal use in AD/PD. This concept should contribute to AD/PD treatment options by opening renewed appreciation for this therapeutic paradigm.