The Cerebral Plasticity Prospect of Stingless Bee Honey-Polyphenols Supplementation in Rehabilitation of Post-Stroke Vascular Cognitive Impairment

Abstract

The neuroprotective potential of stingless bee honey (SBH) is still to be documented from numerous studies including that of its effect on cerebrovascular event. This review should guide stroke rehabilitation specialties to a high understanding of the overall circuit changes post-stroke, the clinical relevance of this change in stroke to cognitive impairment and dementia, and SBH as a supplementation in modern stroke rehabilitation in progresses. However, the potential of SBH as a supplementation therapy and highlights treatment to induced plasticity for post-stroke vascular cognitive impairment (PSVCI) remains largely unexplored. This Chapter attempts to deliberate on recent evidence that highlight the therapeutic properties of honey and SBH, the features of PSVCI, and proposing the plausible mechanism of action for SBH as a supplementation during stroke rehabilitation that could halt the progression of PSVCI. It is hoped that such an approach could complement the existing evidence-based stroke care, and which will help in the development of future direction of brain plasticity to delay the progression of cognitive impairment post-stroke.

1. Introduction

Stroke, whether ischemic or hemorrhage is the phenomena of brain infarction resulted from the alteration of blood supply to the brain tissue leading to cause of death and disabilities. American Heart Association [1] reported that stroke is third leading cause of death and disabilities worldwide, which the global prevalence of stroke in 2019 was 101.5 million people, whereas that ischemic stroke was 77.2 million, that of intracerebral hemorrhage was 20.7 million and that of subarachnoid hemorrhage was 8.4 million [1]. Specific to post-stroke vascular cognitive impairment (PSVCI), it is a syndrome that includes all neurological disorders from mild cognitive impairment to dementia caused by cerebral vascular disease that occurred within three months after stroke onset [2, 3]. PSVCI prevalence is reported between 36 to 67% of survivors and the studies demonstrated that stroke increase risk of persistent and cognitive decline in particular in executive functioning [4, 5, 6]. The knowledge pertaining the PSVCI remain in active research, given that a stroke may induce VCI through multiple mechanisms that are often cumulative or synergistic. Thus, a better understanding from the molecular to cellular processes involved in the neuro-gliovascular unit dysfunction may also help to improved prevention and treatments for PSVCI.

Increasing body of evidence had shown that honey exert several medicinal beneficial effects such as gastroprotective [7] reproductive [8, 9] hepatoprotective [10], antihyperglycemic [11] antioxidant [11] and anti-inflammatory [12, 13] properties. SBH or Trigona Honey which is rich in polyphenols is an antioxidant has been shown to prevent neuroinflammation, promote learning, memory, and cognitive function, and protect against neurotoxin-induced neuronal injury in the brain [14, 15, 16, 17]. Therefore, this Chapter attempts to describe the cerebral plasticity prospect of SBH -polyphenols supplementation in rehabilitation of PSVCI.

2. Stroke

Stroke is a disease affecting the blood vessel (i.e., arteries) leading to and within the brain. Stroke occurs when a blood vessel that carries oxygen and nutrients to the brain is either blocked by a clot or bursts (or ruptures). When that happens, part of the brain becomes deprived of the blood (and oxygen) it needs, resulting in rapid brain cells death leading to stroke [5]. Stroke is defined as a disruption of blood supply to a part of the brain characteristic by rapid developing of clinical signs of focal (or global) disturbance of cerebral function, resulting in ischemic and tissue death with no apparent cause other than that of vascular origin [18].

2.1 Classification of stroke and location

Stroke has been classified into two major types; firstly, hemorrhagic stroke and secondly is ischemic stroke [1]. The classification of hemorrhagic stroke i.e., due to blood vessel ruptured and bleeding in the brain includes subarachnoid (SAH) and intracerebral hemorrhage (ICH) [1], and for ischemic stroke largely based on the vascular occlusion [19]. The most widely used TOAST classification includes large vessel atherothrombosis (i.e., atherosclerotic disease), cardiogenic embolic or cardio embolism, small artery thrombosis or small vessel disease (i.e., lacunar stroke), other determined causes, and cryptogenic (undetermined causes—include cases involving more than one primary mechanism) [19, 20].

Moreover, stroke is divided into two broad categories according to the lesion location in the brain and vascular territory. Firstly, is anterior (carotid) artery circulation that include middle cerebral artery (MCA) territory, approximately 85% of these are ischemic stroke that mostly led to aphasia (dominant hemisphere), hemiparesis or hemiplegia, hemisensory loss or disturbance, homonymous hemianopia, parietal lobe dysfunction (e.g., astereognosis, agrapha-esthesia, impaired two-point discrimination, sensory and visual inattention, left–right dissociation, and acalculia) [21]. Whilst stroke in anterior cerebral artery (ACA) will lead to weakness of lower limbs more than the upper limbs [22]. Secondly, stroke occur in posterior (or vertebrobasilar) artery circulation, responsible for 20% of all strokes and it feeds the posterior region of the brain, including brainstem, the thalamus, the cerebellum and areas of the occipital and temporal lobes, clinically patient can present with homonymous hemianopia, cortical blindness, ataxia, dizziness or vertigo, dysarthria, diplopia, dysphagia, Horner’s syndrome, hemiparesis or hemisensory loss contralateral to the cranial nerves palsy, and cerebellar sign [23].

2.2 Risk factors of stroke

The risk factors for stroke can be classified as modifiable or non-modifiable [17, 24, 25]. Modifiable risk factors that are less specific and more prevalent for example for ischemic stroke the modifiable risk factors includes cardiac disease, diabetes, history of hypertension, hypercholesterolemia, transient ischemic attacks (TIAs), cigarette smoking, hyperhomocysteinemia, obesity, and low physical activity. Meanwhile the modifiable risk factors for hemorrhagic stroke includes the use of anticoagulant, hypertension, heavy drinking, illegal drug use (especially cocaine and crystal meth) and thrombolytic therapy. All this affect health in several ways and provide opportunities to modify risk in large numbers of people [26]. On the other hand, non-modifiable risk factors such as age (stroke risk doubling with each decade of life after the age of 55 years), and race or ethnicity are similar for both ischemic and hemorrhagic stroke. Meanwhile gender (more men have strokes than women; however, more women die of strokes), geographic location, and genetic factors such Fabry’s disease may increase risk for ischemic stroke [27].

2.3 Pathophysiology of a stroke

A stroke is a sudden loss of brain function resulting from an interference with the blood supply to the central nervous system (CNS). Normal cerebral blood flow (CBF) is approximately 50–60 ml/100 g/min. The reduction in CBF below 20 ml/100 g/min results in an electrical silence and less than 10 ml/100 g/min causes irreversible neuronal injury [28]. The pathophysiology of stroke is complicated, and associated with excitotoxicity mechanisms, inflammatory pathways, oxidative damage, ionic imbalances, apoptosis, angiogenesis, and neuroprotection. The ultimate result of ischemic cascade initiated by acute stroke is neuronal death along with an irreversible loss of neuronal function [28]. Beside, neuronal cell loss, damage to and loss of astrocytes as well as injury to white matter contributes also to cerebral injury. The core problems in stroke are loss of neuronal cells which makes recovery difficult or even not possible in the late states [29, 30].

Stroke frequently resulting in cerebral edema or secondary ischemia due to mass lesion and subarachnoid hemorrhage, with involvement of hippocampal and frontotemporal regions, causes VCI with visuospatial memory and language deficits [31, 32]. In this case, it is reported that VCI is attributed to the impact of the subdural membrane on dural lymphatic drainage [33]. Therefore, both ischemic and hemorrhagic strokes may lead to a high risk of VCI.

Stroke elicits profound white matter injury, a risk factor for higher stroke incidence and poor neurological outcomes. Depending on the duration and the severity of the ischemic stroke, the effects that are evident in the white matter include activated microglia, clasmatodendritic astrocytosis, and myelin breakdown, presence of axonal bulbs and degeneration and reactivation and loss of oligodendroglia [6]. The majority of damage caused by stroke is located in subcortical regions and, remarkably, white matter occupies nearly half of the average infarct volume [32]. Indeed, white matter is exquisitely vulnerable to ischemia and is often injured more severely than gray matter [32]. The sign and symptoms related to white matter injury include cognitive dysfunction and thus impaired the executive function and verbal fluency, emotional disorders, sensorimotor impairments, as well urinary incontinence and pain, all of this are related to destruction and remodeling of white matter connectivity [32]. A study found that post-stroke survivors who exhibited greater frontal white matter hyperintensities volumes are predicted to have shorter time to dementia onset, with the exhibited disruption of gliovascular interactions and blood brain barrier damage [34]. They also found that, clasmatodendrosis which is linked to white matter hyperintensities, and frontal white matter changes is the substrate that contributed to delayed post- stroke dementia [34].

3. Post stroke vascular cognitive impairment (PSCVI)

Post-stroke cognitive impairment is a new cognitive deficit that begin in first three months following stroke and continue for minimal of six months, which is not explained by any other condition or disease [35]. This deficits occur in 30–40% of individuals in one or more cognitive domains, including language, executive function, visuospatial cognition, episodic and working memory. Moreover, cognitive, affective and behavioral outcome of stroke are more frequently associated with bad quality of life (QoL) than measures of physical disability [35]. While European Stroke Organization (ESO) and European Academy of Neurology (EAN) guideline define post-stroke cognitive impairment as all problems in cognitive function that occur following a stroke, irrespective of the etiology. There is distinction between the broad construct of cognitive impairment and dementia (or major neurocognitive disorder) [36]. However, the risk of dementia after stroke is high, with a post-event incidence of 34% one year after severe stroke (NIHSS>10), with lower rate after TIA and minor stroke [35]. The lesions, such as focal stroke, may disrupt networks either directly, or indirectly, through secondary mechanisms of injury. Specific to neurocognitive impairment post-stroke. Figure 1 showed a proper account of the consequences of damage to specific areas of brain therefore requires an understanding of the distributed neural networks that underpin these neurocognitive domains and their interaction [35].

Figure 1.

Neural networks that underpin the neurocognitive domains. Each figure sketches the major regions recognized as part of the network supporting each domain. Key points are that all networks are widely distributed across the brain frequently intersecting and overlapping so that multiple networks may be injured by a single stroke. Copyright from McDonald MW, et al. 2019.

3.1 Pathomechanism of PSVCI

Multiple studies had discussed the probable causes of VCI, particularly vascular origin such as reduced blood supply to the brain i.e., cBF [37]. The affected brain areas undergo a neuronal tissue loss which compromises its structure and function and manifests as a VCI. The onset of ischemic cascade showed the initiation of many steps including inflammation, excitotoxicity, nitric oxide production, free radical damage, and apoptosis, all of these play a role in tissue injury. The molecular consequences of brain ischemia following a stroke includes temporal change in cell signaling, signal transduction, metabolism, and gene regulation/expression [28, 38].

In the case of stroke, pro-inflammatory mediators, and amyloid deposition (i.e., cerebral amyloid angiopathy [CAA]) in the vessel walls play a crucial role in the development and progression of PSVCI [5, 39]. However, PSVCI generally occurs in a shorter time frame (i.e., less than 1 year) compared to other forms of VCI [40, 41]. The damage caused by CSVD is late onset due to the cortical and subcortical microinfarcts [42]. The brain region is affected by a state of cerebral hypoperfusion which, in the long term, is responsible for the damage of white matter and for the emergence of cognitive dysfunction [43, 44]. These types of multiple infarctions and diffuse white matter lesions often appear in the lateral ventricle and subcortical structures, resulting in multiple cognitive domain impairments [42, 43, 44]. It is also known that VCI can also occur after a cerebral hemorrhage [43, 44], such as CAA-related intracranial hemorrhage [36, 37, 45, 46] that resulting in cerebral edema or secondary ischemia due to mass lesion and subarachnoid hemorrhage, with involvement of hippocampal and frontotemporal regions, resulting VCI with visuospatial memory and language deficits [38, 39, 47, 48]. In this case, it is reported that VCI is attributed to the impact of the subdural membrane on dural lymphatic drainage [49]. Therefore, both ischemic and hemorrhagic strokes may lead to a high risk of PSVCI.

Figure 2 illustrate the description multiple mechanisms of the PSVCI that include, (1) cerebral vascular lesions (i.e., ischemic or hemorrhages) in a strategic area in terms of cognitive functioning; (2) previous silent CSVD (i.e., leukoaraiosis, cortical microinfarct, silent brain infarcts, cerebral microbleeds, Binswanger leukoencephalopathy, and brain atrophy) that contribute to the burden responsible for VCI through a cumulative effect or dysconnectivity; (3) accelerated evolution of pre-existing degenerative lesions through hypoxia mechanism; (4) direct effect of vascular or metabolic risk factors associated with stroke occurrence on cognitive functioning; (5) direct induction of neurodegeneration responsible for global or regional brain atrophy; (6) endothelial cells dysfunction and blood brain barrier (BBB) damage; and (7) neuro-thrombo-inflammation [6]. A better understanding from the molecular to cellular processes involved in the neuro-gliovascular unit dysfunction may also help to improved prevention and treatments for PSVCI.

Figure 2.

Proposed general mechanisms on post-stroke vascular cognitive impairment (PSVCI). Crosstalk between the reduced cerebral blood flow (cBF), aberrant neuro-gliovascular unit and blood brain barrier (BBB) damage initiated by ischemic/hypoxic related cerebral vascular lesion and/or occlusion leading to cascade of catastrophic event such as increase reactive oxygen species (ROS), thrombo-inflammation and subsequent endothelial cells dysfunction and/or vasoconstriction. These lead to neuro-glial cells death and synaptic dysfunction, hence cause brain ischemia or hemorrhage and subsequent PSVCI. CAA, cerebral amyloid angiopathy; CSVD, cerebral small vessel disease; ICH, intracerebral hemorrhage; No, nitric oxide; VCI, vascular cognitive impairment.

Moreover, inflammation and oxidative stress remains an important pathway involved in both neuronal and vascular endothelial dysfunctions [50]. Besides, neurovascular uncoupling is also responsible for disturbance of brain oxygenation and vascular reactivity necessary to supply sufficient cBF in response to neuronal metabolism [51]. In neurohormonal pathways, changes in brain plasticity or neurotrophic factors, ion channels and mitochondrial dysfunction [3, 52, 53] and cognitive dysfunction have all been observed in PSVCI [54]. Interestingly, impairment of neurotransmission pathways, i.e., glutamate or cholinergic transmission has also been associated with cognitive deterioration (Figure 1) [55].

Therefore, more clinical, and pre-clinical studies are needed to better characterize all the molecular mechanisms contributing to cellular (i.e., neuronal damage) in PSVCI in order to design for potential pharmacological targets with disease-modifying therapy with pleiotropic compounds or multimodal combinations targeting such as endothelial function and BBB, neuronal death, cerebral plasticity and compensatory mechanism, and degenerative disease-related protein misfolding.

4. Honey and its classification

Honey is the natural sweet substance produced by bees from plants nectar, plant secretions or excretions of plant-sucking insects on the living parts of plants. The bees collect, transform by combining with specific substances of their own, deposit, dehydrate, store, and leave in the honeycomb to ripen and mature [54]. Honey can be classified or categorized according to several properties. Firstly, is bee species, whereby based on the main species of bees, the commercial honey is further categorized as honeybee honey (i.e., produced by all honeybees such as Apis spp.) and stingless bee honey (SBH) (i.e., produced by all stingless bees such as Melipona spp. and Trigona spp.) [55]. Secondly, based on floral or botanical origin or source, whereby honey is also further categorized as unifloral, multifloral, blossom, and) honeydew. The unifloral honey is produced mainly from a single plant species, with identifiable organoleptic characteristics including appearance, color, flavor, and taste, and contains more than 45% of the total pollen from the same plant species as analyzed using visual pollen identification analysis (melissopalynology). The multifloral, also known as polyfloral or blend honey, contains pollen from more than one plant species with no domination by any single plant species [56]. In contrast, the blossom or nectar honey originates from nectars of plants, while honeydew honey comes mainly from excretions of plant sucking insects (Hemiptera) on the living parts of plants or secretions of living parts of plants [54].

Thirdly, it is based on geographical or topographical region of origin, whereby geo- or topographical region is used when honey is exclusively collected and produced within the specific area [57]. Next, is based on the method of beekeeping, where honey is categorized as organic honey which is produced by apiaries with certified organic beekeeping which does not contain toxic residues of pesticides used in agriculture and beekeeping [58]. Besides, honey is also categorized based on the mode of processing, such as squeezed honey when it is obtained by traditionally squeezing the honeycombs, drained honey when it is obtained by draining decapped broodless comb and extracted honey when it is obtained by centrifuging decapped honeycombs which is mainly produced by beekeepers who manage bees in moveable comb hives [58]. The consistency and appearance of honey is also crucial in categorizing the honey for example liquid honey when it is either thinner or thicker in consistency and free of visible crystals, and crystallized honey when it is completely granular or solidified [49].

Moreover, honey can also be classified based on their color, whereby honey color varies from nearly colorless to dark brown [57]. Hence, honey has been categorized as white honey, dark brown or amber and golden honey [49]. However, Department of Agriculture from the United States of America categorizes honey color into seven categories including water white, extra white, white, extra light amber, light amber, amber and dark amber with Pfund color scale of 0 to more than 114 mm [58]. Finally, is based on the style of marketing, honey can be categorized as chunk honey when honey is sold in a piece of a sealed and undamaged honeycomb, comb honey when honey is sold in sealed whole honeycombs, and comb honey in fluid honey when it is sold as a cut honeycomb inserted in fluid honey [56].

5. Stingless bee honey (SBH)

Stingless bee species belonged to the same family as the sting bee, Hymenoptera, but classified in a different subfamily level. The stingless bee belongs to the Meliponinae subfamily. Like the sting bee, the stingless bee produces honey and other by-products such as bee bread, propolis and royal jelly [59]. Unlike the sting bees, stingless bees store their honey in vertical pots made of cerumen [60]. This part is exclusively known and different to the propolis of the Apis mellifera. Propolis, is a natural resinous and waxy product which is produced by mixing beeswax and resins collected from various plant parts. Meanwhile, cerumen is a mixture that similar to propolis but with addition of mandibular secretion of the stingless bee during its construction [61].

Additionally, the stingless bees can be differentiated by the size of their body, which is smaller compared to the sting bees. Apart from being small, the stingless bees have a pot-like structure of honey pot instead of vertical honeycomb produced by the sting bees. There are about 500 species of stingless bees reported with 64 genera distributed in Latin America (Melipona spp., Tetragonisca spp., Scaptotrigona spp., and Plebeia spp.), Australia (Tetragonula spp.), Africa (Meliponula spp.), and Asia (Lepidotrigona spp., Tetrigona spp., Homotrigona spp., Lisotrigona spp.) [62, 63]. In Asia, particularly in Malaysia, more than 30 species of stingless bees from the genus Trigona spp. were reported. The most popular species for rearing and having commercial values include Geniotrigona thoracica (Smith), Heterotrigona itama (Cockerell), Lepidotrigona terminata (Smith), Tetragonula fuscobalteata (Cameron), and Tetraponera laeviceps [64].

SBH, in Malaysia also known as Kelulut honey (produced by Trigona spp. And Melipona spp.) was reported to have distinct features compared to sting bees honey in terms of the taste and the aroma. Kelulut honey is stored in clusters of small resin pots that are different from the hexagonal-shaped combs that most are familiar with. It has amber brown appearance and is more diluted as it has high water content compared to the other types of honey. The taste of SBH (i.e., Kelulut honey) was reported to be sourer like as well as the aroma, waterier in texture and undergoes a slow crystallization [62].

5.1 Physicochemical composition of SBH

In general, honey contains about 200 distinct compounds [65]. Each honey’s composition and properties are uniquely different which depend on the several factors as discussed in Section 3 [55, 56, 57, 58]. However, there are many techniques that have been employed to determine the floral and geographical origin of honey produced which include pollen identification, gas chromatography spectrometry, and identification of selected chemical parameters [66].

A good quality honey should have a moisture content that is no more than 20 g/100 g, and a sum of both fructose and glucose that is not less than 60 g/100 g, sucrose content less than 5 g/100 g, free acidity of less than 50 milliequivalents acid per 1 kg (meq/kg), ash content of less than 0.5 g/100 g, diastase activity that is not less than 8 diastase number (DN), hydroxymethylfurfural (HMF) content about less than 40 mg/kg, and electrical conductivity of less than 0.8mS/cm [54, 57]. However, this standard is unfavorable to SBH because it has higher moisture content, invertase activity, and free acidity as well as lower pH and lack of diastase [62, 67]. Therefore, Malaysia Honey production released a standard specifically for Malaysian SBH (MS 2683: 2017) which stated that the quality of raw SBH should follow these requirements: moisture content should be less than 35 g/100 g; sucrose content is less than 7.5 g/100 g, ash content is less than 1.0 g/100 g, HMF content is less than 30 mg/kg, pH between 2.5 to 3.8 and presence of plant phenolics [68].

Apart from geographical origin, the physicochemical properties of honey can also vary depending on the variation of bee species. Although varying, the measured parameters remain common in the SBH compositions, which are the moisture content, followed by free acidity, sugar profile, pH, HMF, ash content, and electrical conductivity. Other frequently studied parameters include enzyme activity, nitrogen, soluble solids, color, minerals, and phenolic compound [69]. Table 1 summarized the different in physiochemical composition between honey and SBH (based on Malaysia standard) [63, 70, 71, 72, 73, 74, 75].

Composition	Honey	SBH
Moisture	≤ 20 g/100 g	≤ 35 g/100 g
Sugar (i.e., Fructose + Glucose)	≥ 60 g/100 g	≥ 40 g/100 g
Sucrose	< 5 g/100 g	< 7.5 g/100 g
Free Acid	< 50 mg/kg	≤ 50 mg/kg
Ash content	< 0.5 g/100 g	< 1.0 g/100 g
Diastase number (DN)	≥ 8 DN	≥ 5 DN
Hydroxymethylfurfural (HMF) content	< 40 mg/kg	< 30 mg/kg
Electrical conductivity (EC)	0.8 mS/cm	0.1 mS/cm
pH	3.2–4.5	3.15–6.64
Nitrogen content	5–200 mg/kg	107–816 mg/kg

Table 1.

Different in physiochemical composition between honey and SBH (based on Malaysia standard).

DN, diastase number; EC, electrical conductivity; HMF, Hydroxymethylfurfura; SBH, stingless bee honey; g, gram; mg, milligram, cm; centimeter.

5.2 Minerals and phenolic compound of SBH

Generally, the mineral content of honey is often related to the nutritional benefit of honey [73]. In SBH, a total of 14 minerals are studied and four major minerals are detected in SBH, which are potassium (K⁺), Sodium (Na⁺), Calcium (Ca²⁺) and Magnesium (Mg²⁺). The most abundant mineral detected in SBH is K⁺, followed by Na⁺, Ca²⁺, and lastly, Mg²⁺ [62, 76].

Moreover, SBH has been reported to have a higher content of polyphenol than any other kind of honey [62]. Therefore, the best indicator for SBH quality is the presence of the plant phenolic compounds. These includes benzoic acid, phenylpropanoic acid, 4-hydroxybenzoic acid, 4-hydroxyphenylacetic acid, vanilic acid, protocatechuic acid and p-coumaric acid [68]. Other phenolic compound reported to be present in SBH are luteolin, gallic acid, salicylic acid, syringic acid, cinnamic acid, naringenin, quercetin, isorhamnetin, apigenin, kaempferol, methyl quercetin, taxifolin, isorhamnetin deoxyhexosyl hexoside, quercetin deoxyhexosyl hexoside, and kaempferol deoxyhexosyl hexoside [75, 76].

5.3 SBH: Health benefits and mechanistic profiles

Modern science has found that most traditional practice of using SBH as a great potential as an added value in modern medicine and considered to have a higher medicinal value than other bee species. As discussed, SBH mays serve as anti-inflammatory, anti-cancer [72] anti-bacterial [77], antioxidant, and anti-tumor [63]. According to several physicochemical criteria, the composition of stingless bee honey differs from that of other species [78].

Moreover, SBH was generously studied and reported to possess varieties health-beneficial effect. A study reported that administration of SBH on male diabetic rats showed an ameliorative effect on the testicular structure and function [79]. Furthermore, SBH also showed a potential as antihyperglycemic agent after being administered for 14 days in diabetic rats [9]. Another study on SBH also reported that SBH showed an antimicrobial activity through an in vitro study [80, 81]. Administration of this honey also reported to increase sperm production and elevate testosterone level in diabetic rats [9]. Traditionally, SBH is used for anti-aging, enhancing libido, treatment for bronchial phlegm, relieving sore throat cough and cold, and improving immune system [82]. Interestingly, Kelulut honey has been found to have multitude pharmacological properties, which include anti-inflammatory [83, 84] antibacterial [85, 86], anticancer [86, 87, 88] and antioxidant [89, 90].

However, antioxidants (i.e., molecules that slow or stop other molecules from oxidizing) preventing diseases like neurological disorders. Antioxidants protect cell structure by neutralizing ROS and thereby terminating the harmful chain reaction in the body [22]. As discussed, the principal beneficial compounds found in SBH are polyphenols. Polyphenols and phenolic acids are thought to be richer in SBH than in any other type of honey [62, 76]. SBH samples have a much higher antioxidant capacity than Tualang honey samples, with statistically significant relationships between antioxidant outcomes and polyphenols concentration (p < 0.0.05) interestingly, SBH composition with strong antioxidant and anti-inflammatory factors had been shown to improve cognitive deficits [8, 9], namely from high flavonoids and polyphenols that protect against neurodegenerative disorders through modulating neuronal and glial signaling pathways (10).

High polyphenols content in SBH (i.e., Kelulut honey) can help to ameliorate PSVCI due to the oxidative damage thus providing an inexpensive neuroprotective therapeutic role. Not only dietary polyphenols can help in protecting brain from oxidative-stress injury, it also can mitigate neuroinflammation [91] protecting against neurodegeneration and promoting learning and memory and cognitive function [71, 92, 93]. Additionally, polyphenols are the significant bioactive molecules which act as the antioxidant that present in honey that may contribute relatively to the proven pharmacological properties of the SBH (i.e., Kelulut honey) [94]. Kelulut honey has been proven to have higher content of polyphenol than other honey [76, 84]. There is significant correlation between high polyphenol content to the antioxidant properties [76]. The common groups of polyphenols that have been detected are flavonoids and phenolic acid. There are several most reported phenolic and flavonoid compounds that can be found in Kelulut honey which may help in alleviating or reversing the cognitive decline in post-stroke patients, namely gallic acid, caffeic acid, catechin, apigenin, chrysin, cinnamic acid, kaempferol, p-coumaric acid and quercetin [78, 95]. Several important polyphenols components that can be found in Kelulut honey and act as neuroprotective (i.e., antioxidants and anti-inflammatory) and aided in cerebral plasticity following PSVCI is summarized in Table 2.

Phenolic compounds	Neuroprotective potentials		Cerebral plasticity prospect
	Antioxidants	Anti-Inflammatory
Chrysin	Reduced neuronal damage by decreasing oxidative injury [96].	Against neuronal damage by inhibiting inflammatory response [96].	Protect against memory impairment due to neurodegeneration and ameliorate cognitive deficit [96, 97].
Gallic acid	Promotes cerebral antioxidant defense and excellent free radical scavenger [98].; Reduce oxidative stress cause by 6-OHDA and protect against cognitive impairment [99].	Potent anti-inflammatory agent against vascular disease [100].	Reinstated the spatial memory in animal models of vascular dementia due to the ischemic brain injury [101].; Against the acute and chronic oxidative stress that is the basis of neurodegeneration [102]
Cinnamic acid	Potent oxidative stress reduction capacity and antigenotoxic capacity of p-coumaric acid [103].	p-Coumaric acid exhibited neuroprotective effects against 5-S-cysteinyl-dopamine-induced neurotoxicity [104].	p-Coumaric acid had the potential to be the main element for the prevention or treatment of AD and the development of novel monoamine oxidase inhibitors [105].
Quercetin	Protect against oxidative damage caused by induced cerebral stroke in young and old rats [106].; Attenuated oxidative stress induced by high fat diet in mice and improving spatial learning and memory [107].	Helps in ICH by deterring inflammatory response and apoptosis and reducing lesion volume hence stimulating restoration of neural function [4].	Ameliorate the ischemic injury by regulating acid-sensing ion channel led calcium and lipid peroxidation in neural cell [108].; Enhancing the neuronal count in the hippocampus area, which is the worst affected region post-stroke [109].; Delaying the development of AD and cognitive function deficit [110, 111].
Catechins	Ameliorate oxidative stress-caused by neurodegeneration diseases [112].; Mitigate oxidative stress following the insult caused by the cerebral ischemia [113].; Able to indirectly enhance the body’s endogenous antioxidants to fight against the oxidative damage cause by various reasons [113].	Mitigate the inflammatory reaction following the insult caused by the cerebral ischemia [113].	Significant neuroprotective effect against neuronal insult caused by transient global ischemia [114].; High dose may help in attenuating the formation of post-ischemic brain oedema and reduced the volume infarction following the unilateral cerebral ischemia [115].; Improve learning and memory function in aged mice [116].
Apigenin	Protects neurons against oxygen–glucose deprivation/reperfusion-induced injury in cultured primary hippocampal neurons by improving sodium/potassium-ATPase (Na^+/K^+-ATPase) activities [117].	Inhibits the kainic acid-induced excitotoxicity of hippocampal cells in a dose-dependent manner by quenching ROS and by inhibiting the depletion of reduced glutathione levels [118].	Neuroprotective effect against ischemia/reperfusion injury by promoting cell proliferation, reduced cerebral infarct areas, alleviated apoptosis, and improved neurological function [119, 120]; Stimulates the adult neurogenesis that underlies learning and memory [93].
Caffeic Acid	Potent antioxidant against ischemic/reperfusion injury [121].	Reduce infarct volume and neuroinflammation activity [122].	Neuroprotective effect against ischemic/reperfusion injury and adverse drug reactions [121].
Kaempferol	Ameliorated antioxidant defenses and antiapoptotic effects involve the enhancement of mitochondrial turnover, which is mediated by autophagy [123].	Attenuate ischemic brain damage and inflammation by preventing the activation of STAT3 and NF-κB pathway and ameliorate neurological deficit caused by the ischemic stroke [124].	Administration of kaempferol to ischemic stroke rats’ model for 7 days post cerebral ischemia/reperfusion was able to significantly reduce cerebral infarct volume, decreased inflammation and help promoting intact BBB [125].; Optimal treatment for improving cognitive function due to its positive effects on depression, mood, and cognitive functions [126].

Table 2.

List of important polyphenols components found in SBH and its neuroprotective potentials (i.e., antioxidants, anti-inflammatory) and their cerebral plasticity prospect.

6-OHDA, 6-hydroxy dopamine; AD, Alzheimer’s disease; ATPase, adenosine triphosphatase; BBB, blood brain barriers; GSH, glutathione; ICH, intracerebral hemorrhages; NF-κB, nuclear factor kappa B; ROS, reactive oxygen species; STAT3, signal transducer and activator of transcription 3.

6. Cerebral plasticity prospect of SBH supplementation in rehabilitation of PSVCI

Cerebral plasticity of SBH supplementation in rehabilitation for PSVCI have been developed with two main aims: restoration of cerebral flow and the minimization of the deleterious effects of ischemia on neurons, [28] and the mechanism of polyphenols in SBH as neuroprotective in brain reported able to prevent neuro-inflammation, promote memory, learning and cognitive function and protect against neurotoxin-induced neuronal injury, hence improved the defend mechanism against oxidative stress, neuro-inflammation and attenuated free radical-mediated molecular destruction [14, 92]. There are ongoing studies to investigate the potential positive effect of flavonoids from honey as cerebral plasticity prospect to delay the progression of cognitive impairment [17].

6.1 Prevent neuro-inflammation

Inflammation has been identified as important factor in the pathogenic mechanisms of cerebrovascular disease and neurodegenerative disease such as dementia [127]. There are evidence that chronic inflammation involved in the pathogenesis of several condition post-stroke and dementia. Human and animal studies indicates that inflammation mediated by inflammatory cells, cytokines, cell adhesion molecules, and eicosanoids occurs after ischemic injury and may exacerbate ischemic injury [28]. The mechanism in vascular damage seen in brain is encourage and maintain by cytokines, acute phase proteins, endothelial cell adhesive molecular and other immune-related protein. Microvascular inflammation is a hypo-perfusion model with markers of chronic inflammation and endothelial activation, can lead to increase BBB permeability and to infiltration of inflammatory factors like interleukins, MMPs, Tumor necrosis factors (TNFα), toll like receptor 4 (TLR4) and C-reaction protein (CRP). This product upon enter into brain, these inflammatory factors can exacerbate white matter damage [127], in early in the pathology process of Alzheimer disease in patients with mild cognitive impairment (MCI) [128].

Human and animal studies indicates that inflammation mediated by inflammatory cells, cytokines, the cell adhesion molecules, and eicosanoids occurs after ischemic injury and may exacerbate ischemic injury [28]. The common studies biomarkers in VCI and dementia are interleukin-6 (IL-6), MMPs, Tumor necrosis factors (TNFα), toll like receptor 4 (TLR4) and C-reactive protein (CRP) [17].

Potential therapeutic targets to minimize tissue loss and neurologic deficit by lessening the proportion of penumbral tissue recruited into the infection area. Inflammation occurs by molecular and cellular components at blood-microvacular endothelial cell interface [28]. SBH with phenolic acid consumption is an antioxidant that act as neuroprotective effect to prevent neuro-inflammation, promote memory, learning, cognitive function and protect against neurotoxin-induced neuronal injury in brain [14, 16, 129]. Flavonoid or myricetin modulates an interleukin −1 beta –mediated inflammatory response in human astrocytes in alleviation of neuroinflammation [15].

In this perspective, the role of honey as one of the natural supplements worth to be explored for its potential in halting the progression of cognitive impairment and dementia [15, 16, 95]. Nevertheless, to our best knowledge, limited such study exists on stroke patients whether with cognitive or physical impairment with the used of honey in promoting recovery in functional and to delay the progression of impairments.

6.2 Against oxidative stress

As mentioned earlier in this chapter, oxidative stress in brain tissue had been proven to contribute to reducing cognitive function in aging brain [130]. Oxidative stress defines the inadequate balance between free radicals and antioxidant protective activity [129]. Oxidate stress is a common manifestation of all type of biochemical insults to the structural and functional integrity of neural cells, such as aging, neuroinflammation, development of neurological disease (Alzheimer disease and Parkinson’s disease) and neurotoxins [14, 16]. In addition, increased oxidative stress may impair learning [78] and memory [131] thus overall cognitive function. It has been proven also that oxidative stress is part of the pathology of traumatic brain injury (TBI) and impairs the neuronal function [129]. Oxidative stress biomarkers had been found to be increased within 24-hour post onset of acute ischemic stroke and reduced within 3 months due to the activated antioxidant system [132]. Taking all together, this prove that oxidative stress plays a part in reducing cognitive function post-stroke that impair learning and memory.

Honey with an antioxidant property such as phenolic acid can decrease oxidative stress by improved the defend mechanism against oxidative stress and attenuated free radical-mediated molecular destruction [14, 15, 16, 129]. One of SBH most essential characteristics is their antioxidant ability, which helps to prevent certain diseases by protecting cells from oxidative agents like free radicals.

6.3 Increase learning and memory

The progression of cognitive impairment or dementia post stroke can be delayed or prevented by introducing honey as supplementary therapy in early stage of stroke patient with mild cognitive impairment in animal study [9, 92, 93, 133]. Honey was reported can against chronic cerebral hypoperfusion such as in Alzheimer’s disease and effect on memory and learning process such as in prevent dementia. Studied the use of honey as a natural preventive therapy of cognitive decline and dementia in 2893 subjects in Iraq. Only 95 from 1495 subject who received honey were found to develop dementia (6.35%) as compared to placebo group (n = 1400) whereby 394 subjects developed dementia (28.1%) (p < 0.05) [15]. This study suggested that honey and its properties act as natural preventive therapies for both cognitive impairment and dementia but still less evidence to support the association between honey and the progression of dementia. Concerning neurodegenerative disorder, honey (Tualang) was found to have significant activity against chronic cerebral hypoperfusion that have protective effects in learning and memory, which is one of several factors contributing to dementia and Alzheimer’s disease (AD) [76].

Honey also showed able to enhance memory by effect to increase proliferation of neuron in hippocampal region [16, 93]. Study reported that reported that both short and long term and supplementations with honey at a dose of 230 mg/kg of body weight significantly decreased the number of degenerated neuronal cells in hippocampus region, which acts as defense mechanism against stress [93].

The study finding stated that SBH supplementation effect and increase learning and memory performance of brain and it is because content of high antioxidant that enhance synaptic plasticity through synaptogenesis in brain [92]. It is because quercetin is another flavonoid with antioxidant activity found in honey improves memory and hippocampal synaptic plasticity in models of memory impairment that cause by chronic lead exposure. Quercetin also has neuroprotective effect against colchicine-induced cognitive impairment [95]. While Cafeic acid present in honey give an effect as neuroprotective on neuronal cell in brain in prevention learning and memory deficit and catechin contribute as antioxidant that give effect as neuroprotection on neuronal cell that delay memory impairment. Finding of studies reported that honey is significantly reduced molecular destruction and improvement in the memory performance that delay the progression of cognitive impairment or dementia [133].

Recent study showed that one of the components of SBH from Trigona spp. (i.e., phenylalanine) may be able to trigger the upregulation of brain-derived neurotrophic factor (BDNF) and inositol 1, 4, 5-triphosphate receptor type 1 (ITPR1) [95, 134] which are genes involved in synaptic function [135]. Therefore, trigona displayed capabilities in improving cerebral plasticity (especially after PSVCI) including spatial working memory, spatial reference memory and memory consolidations. Another study also suggested that SBH improves memory and reduces anxiety, in addition to its potential to reduce triglyceride, LDL, and normalize blood glucose in rats with metabolic syndrome [94].

6.4 Attenuated free radical-mediated molecular destruction

Free radical lead to protein dysfunction, DNA damage, and lipid peroxidation, resulting in cell death due to the disruption of the blood–brain barrier in stroke. Free radicals are highly unstable, and therefore very reactive atoms, molecules, or compounds due to their atomic or molecular structure, which has one or more unpaired electrons. They attempt to pair up with other molecules, atoms, or even individual’s electrons to create a stable compound, receiving electrons from other atoms [131]. This generates reactive oxygen species (ROS) and free radicals that can bring about molecular transformation and gene mutations in many types of organisms. This is called oxidative stress and is deemed to contribute to the development of chronic and neurodegenerative diseases such as Alzheimer disease that could lead to dementia [12]. ROS are produced naturally by metabolism such as due to the inflammation or result from poor living conditions and environmental pollution. The radical theory in human physiology claims that active free radicals are involved in almost all cellular degradation processes and lead to cell death.

In order to better clinical prognosis, more studies focus on pharmaceutical and non-pharmaceutical neuroprotective therapies against free radical damage [136]. Honey with high phenolic acid can improved the defend mechanism against attenuated free radical-mediated molecular destruction [14, 15]. As reported, apigenin in honey provide as radical scavenging activity where it is protects neuron against oxygen–glucose deprivation/reperfusion-induced injury in cultured primary hippocampal neuross by improving sodium/potassium ATPase (Na+/K + -ATPase) activities [15].

6.5 Polyphenols as anti-acetylcholinesterase activity

Loss of cholinergic activity, atrophy of the nucleus basalts of Meynert as the major source of acetylcholine (Ach), and loss of cortically projecting cholinergic neurons, as well as increased cognitive deficits, are some of the notable findings in various neurodegenerative diseases such as AD, Parkinson disease, and dementia and including PSVCI. Diminished Ach synthesis owing to reduced choline acetyltransferase, choline absorption, cholinergic neuronal and axonal abnormalities, and cholinergic neuron death can all cause cholinergic dysfunction in neurodegenerative disorders [137].

As a result, utilizing acetylcholinesterase inhibitors, which work by stimulating both the muscarinic and nicotinic acetylcholine receptors, has proven to be an effective treatment for the cognitive symptoms of neurodegenerative disease [138]. In the brain, there are two different types of Ach receptors: ligand gated nicotinic Ach receptors (nAChRs) and metabotropic muscarinic Ach receptors (mAChRs). mAChRs are divided into five subtypes (M1-M5). The most prevalent subtype of M1 mAChR is found in the cerebral cortex and hippocampus, which are the most vulnerable brain areas to the formation of amyloid plaques and neurofibrillary tangles [139]. Some polyphenols found in SBH have been proven to inhibit cholinesterase. The anti-cholinergic effect of polyphenol was accompanied by improvements in cognitive function, such as learning and memory, in most in vivo investigations [140]. In a study, resveratrol was found to inhibit acetylcholine release from adrenal chromaffin cells. Huperzine A, Quercetin, Kuwanon U, E, and C, kaempferol, tri- and tetrahydroxyflavone, and other polyphenols found in SBH have an anti-butyrylcholinesterase activity in addition to anti-cholinesterase activity [140].

Huperzine A of polyphenols has the highest acetylcholinesterase (AChE) inhibitory activity after donepezil, while tacrine, physostigmine, galantamine, and rivastigmine were less potent. Huperzine A has also shown better penetration through the.

BBB, higher oral bioavailability, and longer duration of Ache-l activity [140]. Clinical trials with Huperzine A, for treatment of cognitive and functional impairments of AD and schizophrenia and the increase in memory performance of normal individuals, have been promising [141, 142]. In China, Huperzine A has been studied in phase IV clinical trials and revealed a significant improvement of memory of elderly people, patients with AD and patients with vascular dementia [138]. Several meta-analyses have shown that administration of Huperzine A for at least 8 weeks might lead to a significant improvement in cognitive function, mood, behavior, and daily activity of patients with AD [142, 143].

Taking all together, polyphenol compounds that can be found in SBH have the neuroprotective effect to ameliorate many neurological deficits and any improve cerebral plasticity during neurorehabilitation after PSVCI. This shows the huge potential of SBH (i.e., Kelulut honey) to become a therapeutic treatment and neurorehabilitation in stroke and PSVCI. The proposed mechanism of action of SBH derived polyphenols is described in Figure 3.

Figure 3.

The proposed mechanism of action of SBH derived polyphenols. Catechins (Ct) enhance the body’s endogenous antioxidants to fight against the oxidative stress. Chrysin (Chy), gallic acid (GA), and cinnamic acid (CA) are potent antioxidants, and radical scavengers, hence protect against oxidative damage. GA also potent anti-thrombo-inflammatory agent. Apigenin (APG), kaempferol (KF), GA, and Chy ameliorated antioxidant defenses and reduced thrombo-inflammatory reaction, hence attenuate neuro-glial cells death, atrophy and reduced synaptic dysfunction. Quercetin (Qc) and KF also serve as anti-cholinesterase activity and improve cholinergic transmission. Caffeic acid (CfA) is a potent antioxidant against ischemia and help reduce neuroinflammation and infarct volume. Optimal treatment of SBH-derived polyphenols may improve cerebral plasticity following post-stroke vascular cognitive impairment (PSVCI) – in term of neurogenesis, memory, learning and cognition.

7. Conclusions

In this chapter, we highlighted the neuroprotective potential and cerebral plasticity prospect of SBH as a dietary supplementation, specifically for PSVCI. Further translational and clinical research can consider the putative mechanisms of action as deliberated here to demonstrate its beneficial impact it may have on cerebral plasticity as part of stroke rehabilitation. It is hoped that such an approach could complement the existing evidence-based stroke care and contribute to halt the progression of vascular cognitive impairment among stroke survivors.

Acknowledgments

The authors express their gratitude to the Universiti Sains Malaysia, especially the Research University Individual (RUI)-Special Grant Scheme with project No: 1001/PPSP/8012384, Project Code: UO2026 (Reference No: 2021/0310) and Universiti Sains Malaysia, Short Term Grant (STG) 2020 with project No:304/PPSP/6315445, that have been granted for Stingless Bee Honey RCT project and, more specifically in exploring the prospect of stingless bee honey (SBH) as the neuroprotective intervention in stroke rehabilitation against vascular cognitive impairment (VCI).

Conflict of interest

The authors declare no conflict of interest.

Notes/thanks/other declarations

Thanks for all.