Neurodegeneration describes death of neurons in both central and peripheral nervous systems [1]. Neurodegenerative illness is characterized by progressive loss and dysfunction of neurons and neuron-supporting cells in the central nervous system (CNS). Herbal medicines and compounds extracted from plants, such as flavonoids, alkaloids, terpenes, celastrol, lycopene, and resveratrol, have attracted attention for their therapeutic potential [2].
Neurological disorders are characterized by progressive nature, weak responses to treatment and a wide range of side effects caused by conventional therapeutic strategies encourage the search for complementary and alternative medicine. Plant extracts are traditionally used for the treatment of several neurological disorders [3]. Availability, cost efficiency and lower incidence of side effects of plant extracts offers significant advantages.
Medicinal plants exert beneficial effects in neurological disorders through multiple cellular and molecular mechanisms, including suppression of apoptosis, alleviation of inflammatory responses, and improvement of the antioxidant performance. Modulation of intracellular signaling is an essential role for preventive and therapeutic potential of plant extracts for neurological disorders, such as Alzheimer’s, Parkinson’s, Autism Spectrum Disorders, Multiple Sclerosis [1, 4, 5].
Intracellular signaling that is repeatedly associated with neurological disorders, but is not given sufficient attention, is glutamate excitotoxicity. Overstimulation of glutamate receptors leading to neuronal damage. Exposure of neurons to excessive glutamate may cause deregulation of Ca2+ homeostasis, triggering oxidative stress, neuroinflammation, mitochondrial dysfunction and eventually neuron death. a consensus has developed that excitotoxicity is a common etiological mechanism in the pathogenesis of neurological and psychiatric disorders. Thus, targeting excitotoxic might be a useful therapeutic strategy [ 6].
Phytochemicals are promising candidates for treating glutamate-induced excitotoxicity, and novel therapeutic approaches might arise from constituents from plant sources [7]. Various medicinal plants and natural products are used to treat neurodegenerative disorders [8, 9]. Most recently, Afshari et al. [7] reviewed the protective influences of some phytochemicals used to treat glutamate-induced neurotoxicity.
Plicosepalus curviflorus (family Loranthaceae) is a medicinal plant grown in Saudi Arabia. Traditionally, stems were valued for cancer treatment in Yemen [10, 11] .Various phytochemical studies of crude leaf extracts of P. curviflorus showed the presence of flavonoids, flavane gallates, sterols, and terpenoids [12]. Al-Taweel et al. [13] and recently, Orfali, et al. [14] isolate quercetin (P1), catechin (P2), and a flavane gallate–2S, 3R-3, 3′, 4′, 5,7-pentahydroxyflavane-5-Ogallate (P3) (Fig. 1) from aerial portions of P. curviflorus.
The herb, lappa (Saussurea lappa) in the family Asteraceae, is used in traditional ethnic medicine [15]. The antioxidant properties of this herb are attributed to the presence of the polyphenols and flavonoids [16]. These constituents bolster antioxidant defenses in a variety of pathophysiologic conditions characterized by oxidant/antioxidant imbalance [17]. Anti-inflammatory and antiapoptotic effects of S. lappa are reported [18, 19].
Special attention has been given to green macroalgae as sources of medicinal products [20]. Cladophora glomerata is a filamentous freshwater green alga, in the Ulvophyceae, a common family many aquatic ecosystems [21]. Numerous investigations of Cladophora glomerata show the presence of bioactive compounds that establish the species as a source of pharmaceutical and natural nutritional products [22–24]. Additionally, previous studies report that C. glomerata extracts exhibit properties to treat gastric ulcer, inflammation, pain, hypotension, and oxidative stress in different in vitro and in vivo experimental models [25]. Further, C. glomerata, enriched in chromium ions, promoted cell proliferation and, viability, and reduced apoptosis [26].
Alterations in retinal function may imitate brain dysfunction in neurological and psychiatric disorders [27] and may be useful in filling the need for novel approaches to indirectly examine brain function. The retina is a developmental and structural extension of the central nervous system (CNS). This information motivated our interest in ameliorative effects of P. curviflorus, S. lappa, and C. glomerata extracts on glutamate-induced excitotoxicity in retinal ganglion primary cell lines RGCs.