**5. New delivery applications for essential oils**

Till date, NDs are incurable despite many scientific efforts in drug discovery and development in NDs. Most drugs discovered successfully treat the symptoms without curing the pathogenesis or root cause of the NDs with their attendant toxicities or side effects. Hence, in NDs, most molecules are for managing the conditions and are not curative. Antioxidants are adjudged safe that serve as very potent and effective molecules to many diseases by abrogating oxidative stress implicated in most disorders.

NDs most especially affect neurons of the CNS and the brain. The nature of the architecture of the CNS accounts for the innumerable hindrances to drug delivery for effective actions. The blood-brain barrier (BBB) limits the permeability and solubility of antioxidant molecules [48]; hence the antioxidant cannot reach the target CNS. In addition, antioxidants are sometimes unstable and prone to gastrointestinal degradation [14, 49]. The BBB of the brain function as the structure that controls the movement of substances (regulatory role) in the neural microenvironment. This is the interface between the blood and neural tissue, bringing about regulation [48]. Different lines of evidence suggest that BBB breakdown contributes to the pathogenesis of NDs such as ALS, MS, PD, AD, etc. This is because BBB is highly sensitive to

### *Essential Oils and Their Antioxidant Importance: The* In Vitro *and* In Vivo *Treatment... DOI: http://dx.doi.org/10.5772/intechopen.113031*

OS-induced damage and distortion evident in physiological factors like neural aging, vascular disorder, molecular irregularities and anatomical pathologies [13].

The important aspect or standard for drugs or molecules is ensuring a delivery system that will circumvent the mentioned hindrances and hence promote potency, stability, specificity and safety. However, the BB is the main obstacle of CNS targeted therapies in NDs, which is addressed primarily through technology. Nanotechnology is an emerging and highly innovative field with tremendous potential in different areas, such as pharmaceuticals and medicine, thanks to distinctive physical and chemical features, such as minimal size and functionalized surface characteristics of materials [50, 51]. Nanomaterials are used in nanotechnology, which have unique physical, chemical, and biological properties due to their nanoscale dimensions (typically between 1 and 100 nm). These materials come in different sizes, shapes, compositions, surface chemical features, and hollow or solid structures, which can be adjusted to produce optical, electronic, magnetic, and biological characteristics suitable for their applications. The advantage of this nanotechnology is that it made possible the interaction of specific molecules or cellular targets by creating an excellent drug delivery system and hence targeted treatments, especially in ND conditions. This drug delivery system permits concerted multifunctional qualities such as bioactivity, targeting, imaging capabilities and gene delivery. Based on these characteristics, nanotechnology in drug delivery systems is now widely accepted.

The neuroprotective properties of EOs are attributed to their unique anti-free radical and antioxidant properties, as revealed in past research or studies. The improvement of cholinergic neuron deterioration that is eminent in most NDs conditions using EOs containing antioxidants improves cognitive function and prevents brain damage. Thus, these improved mental functions are evident in memory, attention span, planning, decision-making, judgments, speech and overall coordination [52]. EOs quickly find their way across the BBB, reaching the CNS after systemic absorption and could bring some neurological intoxications. Some molecules though lipophilic (solubility) in nature, show very poor permeability across the BBB, resulting from the active efflux mechanism in the membranes of BBB. There could be instances of improved drug accumulation that are non-target sites specific, although there is improved or increased lipid solubility in the BBB [53, 54]. Additionally, the exposure of molecules bound across the cerebral endothelial membrane to degrading enzymes [54], recognition of neuropeptide and their quick degradation by BBB itself and the reinforcement of high amount concentrations of P-glycoproteins (Pgp) that remove or prevent a range of molecules from passing across brain parenchyma [55, 56] are recognized barriers to CNS drug delivery.

Over the years, many enhanced strategies for enhanced CNS drug delivery have been developed. These strategies involve pharmaceutical manipulation, BBB disruption and other methods using nanocarriers, which would help transport molecules to target sites in the brain. Some strategies are viral vectors, polymeric nanoparticles, liposomes, dendrimers, micelles, carbon nanotubes, carbon dots and carbon nanoonions, which have been exhaustively reviewed [56]. These approaches increase therapeutic responses of natural products, including EOs, with overall effectiveness in the treatment and management by increasing bioavailability and ensuring effectiveness. For example, circumventing or overcoming BBB in NDs treatments is achievable through a nanoparticles-mediated brain drug delivery approach, as revealed in AD and HD [57–59].

Over the years, increasingly published works suggest the importance of EOs and drug delivery systems in medicine, food and pharmaceuticals. Although different

applications could be adopted, this chapter focuses on the strategy of encapsulating EOs. The encapsulation is advantageous, which helps to overcome the fragility and volatility, enzymatic reactions, and preserve the biological activity that confers increased activity and decreased toxicity. The overall effect of the encapsulation EOs in drug delivery systems would be the avenue for controlled drug release, increased bioavailability and efficiency [60]. The vesicular and nanoparticles lipid–based delivery formulations vis a vis micro- and nanoemulsion, liposomes, solid lipid nanoparticles (SLN), and nanostructured lipid carriers approaches have unique characteristics.
