A review of pomegranate supplementation: A promising remedial avenue for Alzheimer's disease

Abstract

Neurodegenerative complications, like Alzheimer's disease (AD) exert adverse effects i.e. psychological and physiological in the central nervous system. The synthetic drugs used for these complications have negative effects on body health and therefore natural remedies are a good and targeted approach to counter such complications. Alternatively, fruits and a variety of biochemicals which are an important source of diet, can be used for remedial purposes. Due to the antioxidant properties of polyphenolic compounds, several companies utilize this property to advertise polyphenol-rich beverages. Pomegranate (Punica granatum L.), is one such fruit that is well known for its medical usage due to its antioxidant properties. In the cuurent study a literature search survey was performed on traditional uses, phytochemicals on pomegranate and their medical applications especaily in neurodegenerative deasese using electronic data bases like PubMed, Google Scholar, Scopus, Science Direct Wikipedia and Springer Nature. Based on previous preclinical and clinical studies, pomegranate juice, extracts, and its bioactive constituents have shown many mitigating properties, including suppression of inflammatory cell signaling, reduction in expression of genes associated with oxidative stress as well as pro-inflammatory cytokines in neurons, decreased production of inflammatory and oxidative stress biomarkers and increased expression of endothelial nitric oxide synthase. It also decreases the expression of soluble amyloid protein procurer β (sAPPβ), β-secretase and carboxyl terminal fragment β (CTFβ). Similarly, during an in-vivo study on APP/PS1 mice, pomegranate supplementation has been shown to impart cognitive aid by the protection of neurons and triggering neurogenesis through anti-inflammatory signaling pathway. In conclusion, pomegranate supplementation can be a promising source of protection against Alzheimer's disease.

1. Introduction

Neurodegenerative diseases, such as Alzheimer's disease (AD) impart negative psychological and physiological effects due to alterations in central nervous system [1]. AD is a progressive neurodegenerative disorder characterized by clinical cognitive and memory impairments [2]. According to the recent estimate, there are at least 36.5 million patients of AD worldwide, and a new case of AD is reported every 7 s [3]. The prevalence of AD is increasing exponentially with age, which is its main risk factor [[4], [5], [6]]. The neuropathogenesis or exact etiology of AD is still unclear, however it is considered be a complex multi-factorial disease, and no medication is currently available to prevent or slow down disease progression [7,8]. Food and Drug Administration (FDA) approved therapeutic agents for AD are limited and lack efficacy and researchers from all over the world are trying to discover new possible prevention and treatment options for AD [9]. There is an ever increasing evidence that brain health can be improved with good diet [10], and the guidelines suggests sufficient consumption of fruits, vegetables, nuts, whole grains, legumes and seeds for AD and healthy brain aging [11].

Extracellular deposition of Amyloid-Beta (Aβ) called senile plaques and formation of intracellular, twisted neurofibrillary tangles having hyperphosphorylated tau proteins are the main pathological hallmarks of AD [12]. Aβ plaques can cause neuronal damage by inducing synaptic loss in the regions of neocortex and limbic system. Moreover, they can induce neuronal injury by activating microglia, the brain cells responsible for immunoregulation, causing release of neurotoxic and proinflammatory cytokines, including Interleukin (IL)-1β, Tumor Necrosis Factor (TNF)-α and extremely reactive free radicals [13]. The activation of microglia is the critical step in clearing Aβ from brain through endocytosis [14,15].

Recent research has generated an important evidence of the role of oxidative processes of AD pathogenesis [16]. Changes in the brain cells show that oxidative stress is the process that leads to the appearance of major pathological features of the disease, such as senile plaques and neurofibrillary tangles [17]. The abnormal production of reactive free radicals from pathological mechanisms, including aberrant accumulation of transition metals and mitochondrial dysfunction [18]. Moreover, abnormal accumulation of Aβ and tau proteins appear to increase the redox imbalance. This results in oxidative stress, which has been implicated in Aβ- or tau-induced neurotoxicity [19]. Moreover, evidence suggests that this oxidative stress augments the aggregation of Aβ and promotes the polymerization and phosphorylation of tau proteins, thus initiating a vicious cycle that leads to initiation and progression of AD [20]. Thus, therapeutic agents targeting neuroinflammation and activation of microglia are hugely desirable [21].

The synaptic dysfunction is another pathological feature of AD as synaptic plasticity is important for maintaining learning and optimal memory [[22], [23], [24]]. Since, problems with synaptic plasticity leads to synaptic loss, changes in synaptic regulatory proteins is a crucial biomarker for AD progression and cognitive impairment [25,26].

2. Research scientific methods

In the digital age, electronic databases have become indispensable tools for conducting comprehensive literature surveys and synthesizing knowledge from a vast array of sources. The study was based on literature search survey by using various key words like, pomegranate, pomegranate, punica, Alzheimer's disease, clinical trils, preclinical trils, pomegranate's antioxidant potential, pomegranate's phytochemicals, pomegranate traditional uses, pomegranate's polyphenolic and terpenoids etc. terms were used as search terms and medical terms in electronic data bases like PubMed, Google Scholar, Scopus, Science Direct, Wikipedia and Springer Nature.

3. Importance and uses of pomegranate

Punica grantum L. have been noted to be one of the most important part of various societies for their medicinal properties and their significances has a rich cultural histories, around the globe (Table 1). A number of studies have shown different pharmacological evidences of pomegranates [[27], [28], [29]]. Accumulating of such evidences are associated to pharmacological reports of pomegranate. On the same way various ethnopharmacological features of the whole plant as well as its various parts like, flowers, peel, root, seeds, fruits etc. are the reasons for its ultimate demands and popularity [30]. It was noted that root and bark demonstrate healing potential against anthelmintic and vermifuge effects [31]. Additionally, the flower buds are mainly utilized to improve the symptoms of dysentery, brachiates and diarrhea, in order to reduce inflammation of the gums and other alignments of ulcer, eyes and throats (Table 1).

Table 1.

Dfferent uses of pomegranate.

Plant Part	Administration	Consumption	Medicinal Uses	Reference
Root and bark	Oral	Plants tissues i.e. leaves, root, peel and flowers are powdered and take it orally with milk/water, while juice are drinking	Vermifuge and anthelmintic	[32]
Peel			Diarrhea	[33]
Juice			Blood tonic	[34]
Root			Beneficial in fevers and chronic debility due to malaria	[35]
Flowers			Antidiabetic properties	[36]
Peel, bark, and leaves			Stomach disorders	[37]
Peel			Treat vaginal white discharges
Juice			Weight loss
Seeds	Ophthalmic	From the dry powder extract are made in milk and drops are taken in eyes	To slow the development of cataracts and anemia
	Oral	Powdered and take it orally with milk/water	Fatigue and hear loss
			Cure sore throat, dental plaque, dysentery, cholera
			Cure hemorrhoid flare ups
Juice	Oral and or nasal	Powdered and take it orally with milk/water or few drops are taken in nose	Stop nosebleeds	[35]
Peel and Bark	Oral	Powdered and take it orally with milk/water	Against diarrhea, dysentery, and intestinal parasites	[36]
Flower juice, peel, and bark	Oral and nasal	Powdered and take it orally with milk/water or few drops are taken in nose	Nose bleeds	[38]
	Oral	Powdered and take it orally with milk/water	Gum diseases
	Tropical	Traditional usage specific to particular places	Treat hemorrhoids Wounds healing
Leaves and bark	Oral	Powdered and take it orally with milk/water	Tonic for the heart and throat	[39]

Among other tissues, the fruits of pomegranate is thought to be the most valuable part as compared to others [31]. Pomegranate fruit's parts like, arils, seeds and peel contains a number of valuable compounds that have shown different biological bioassays [40,41]. In general, the fruit is the rich source of diverse phytochemicals like, flavonoids and polyphenols that have potential antioxidant properties which indicates the diminishing risk of diseases in human beings. In the last few decades, a number of studies have highlighted different biological activities like, antiobesity, anticancer [42,43], ROS [44], antidiabetic [45] and cardioprotective properties [46].

4. Phytochemical profile of Punica granatum L

Several studies have confirm the traditional usage of pomegranate recipes, however, more recently those recipes were confirmed by the presence of several classes of different secondary metabolites (Fig. 1A-P) [47]. A number of phytochemicals have been isolated and identified previously from different parts of the P. grantum; via; different approaches, like, DAD (diode array detection), ESR (electron spin response), FD (fluorescence detection) MS (mass spectrometry) GC-MS (gas/mass chromatography) IR (infrared spectroscopy) and NMR (nuclear magnetic resonance) [48]. However, it should be taken under consideration that disparities concerning the absence/presence of certain phytochemicals in one tissue have been confirmed in different pomegranate cultivars [49].

Fig. 1.

Reported secondary metabolite from the pomegranate. These phytochemicals includes, chalcones (A), flavanones (B), flavones (C), luteolin (D), tricetin (E), quercetin (F), estriol (G), pelletierine (H), resveratrol (I), curcumin (J), Punicalin (K), 1,6 digalloil-glucol (L) cyanidin 3,5-diglucoside (M), catechin flavanones (N), delphinidin-3,5-diglucoside (O), punicic acid (P).

4.1. Flavonoids

Pomegranate fruit's parts for example, peel, aril, bark and derived juice and extracts are rich in flavonoids of miscellaneous structures, occurrence and functions [50]. Among such compounds, aglycones and glycosides of chalcones (Fig. 1A), flavanones (Fig. 1B), flavanols, flavones (Fig. 1C), procyanidins, ATs and flavn-3-ols [50]. On the same way, two other flavones namely, luteolin (Fig. 1D) and tricetin (Fig. 1E) were found in the methanolic extract of pomegranate flowers [51].

Additionally, like other plants, the leaves of pomegranate also accumulates high level of falvones-glycosides like, apigenin and luteolin [52]. Interestingly, two other flavanone-di-glycosides and one flavanol di-glycoside were also isolated from the pomegranate stem and barks. On the same way, other parts also showed various form flavonoids like, eriodictyol-7-O-α-l-arabinofuranosyl-(1–6)-β-D-glucoside, followed by quecetin-3,4′-di-methyl ether 7-O- α-l-arabinofuranosyl-(1–6)-β-d-glucose and naringenin-4′-methyl ether 7-O-α-l-arabinofuranosyl-(1–6)-β-D-glucoside through NMR analysis/approach [53]. Furthermore, two iso-flavones (daidzein and genistein) and other flavonol (quercetin) (Fig. 1F) were also detected in the seeds of pomegranate through High-Performance Liquid Chromatography with Diode-Array Detection (HPLC-DAD) [54].

4.2. Triterpenes and phytosterols

The triterpenes (C30) are the main biosynthetic precursors of steroids in plants clade i.e. phytosterols. In animals it's known as animal-hormones or simply hormones [55]. Triterpenes and phytosterols have widely been found in the pomegranate tissues, like, fruits, stem, seeds, flower, leaves, and bark [56]. While the presence of human steroid hormones including, estradiol estrone, testosterones and estriol (Fig. 1G) are interestingly being found in the pomegranate seeds were reported recently through TLC separations and colorimetric approaches [57,58]. On the other hand, GC-Ms and HPLC-DAD based analysis revealed that such steroidal hormones could not be identified in the pomegranate seeds using such reliable and sensitive analytical approaches [59].

4.3. Alkaloids and indolamines

It has been taken under consideration that several alkaloids like, N-methylpelleterine, pseudopelletierine and pelletierine (Fig. 1H) were found in the pomegranate tissues e.g. root, bark and stem [60]. On the same way, sedridine, 2-(2′-hydroxypropyl) - Δ1 piperideine, norpseudopelletierine, 2-(2′-propenyl)- Δ1piperodeone and other pyrrolidines alkaloids with a membered N-containing ring, hygrine and norhygrine were also seems in the root bark at very low concentrations [61]. Moreover, the alkaloids that mostly accumulated in the root and stem bark are N-(2′, 5′-dihydroxyphenyl)-pyridinium chloride was also predicted in the pomegranate leaves. Similarly, pyrrolidine-types of alkaloid punigratane (2, 5-diheptyl-N-methylpyrrolidine) was newly being characterized in the fruit peel of pomegranate [62]. Although, low level of other alkaloids like, indolamines (amines derivatives of indole) containing tryptamine, serotonin and melatonin etc were also taken under consideration in the fruit extract of pomegranate [63].

4.4. Phenolic and other organic acids

Phenolic acids like, aromatic acid, cinnamic and, benzoic acid, resveratrol (Fig. 1I), curcumin (Fig. 1J) Punicalin (Fig. 1K),6 digalloil-glucol (Fig. 1L), Cyanidin 3,5-diglucoside (Fig. 1M), Catechin (Fig. 1N), Delphinidin-3,5-diglucoside (Fig. 1O) and their derivatives are normally found in the pomegranate tissues like, juice, leaf, fruit peel, seeds and flowers [64]. On the same way, the commonly occurred phenolic contents are, substituted-coumarin, 7, 8-dihydroxy-methyl-coumarin-5-carboxylic acid was recently being identified in the pomegranates flowers through NMR approach [65]. Several organic acids for example malic acid and citric acid are the main components of pomegranate juice. On the same way, the juice of pomegranate also contain other organic acid like, fumaric acid, succinic acid, ascorbic acid, oxalic acid, tartaric acid, guinic acid and some other which have been isolated and identified in the fruit peel, leaf and seeds tissues [44,66,67].

4.5. Lipids and fatty acid

It has been taken under consideration that medium (C6, C8, C10 and C12), longer chain (C14, C16, C18 and C20) and extremely longer chain like, C22 and C24) fatty acids (FAs) have been reported in the juice, seeds and fruit peel through, GC-MS, LC-MS, HPLC, NMR and IR [68]. On the same way, other polyunsaturated FAs punicic acid (Fig. 1P) namely, 9Z followed by 11E and 13Z-octadecatrienoic acid characterizes the most abundant FAs in the pomegranate seeds that considered to have more than 60 % of seeds oil. Additionally, triacylglycerols (TAGs) containing 9E, 11Z and 13E-octadecatrienoic acid are mainly produced in the pomegranate seeds and their structures were being characterized through NMR [[68], [69], [70]]. Interestingly, a new representative glycosphingolipid N-palmitoyl cerebroside was isolated and identified from the pomegranate seeds oils through GC-FID and TLC approaches [71].

5. Food and Drug Administration (FDA) approved drugs for AD; importance of pomegranate

Despite major advancements in Alzheimer's disease (AD) treatment, a solution for this progressive neurological illness remains elusive [72]. Currently, available therapeutics, such as AChEI, memantine, and the drugs in clinical trials are intended to improve the quality of life, alleviate the symptoms and slow down the progression of the disease. Some medications are now no longer in use due to their adverse effects, such as Tacrine that has been discontinued due to hepatotoxicity [73]. Furthermore, CNS defects are reported with some agents such as memantine, which can cause confusion, agitation, and restlessness. Even though AD is a different disorder in its pathophysiology, all neurodegenerative disorders are usually quite complex, where multiple disease pathways tend to transpire simultaneously [74].

Unless a therapeutic agent and strategy that simultaneously targets multiple ailments co-exists, permanent treatment of neurodegenerative disorders is the need of the hour [75]. Despite the above-mentioned factors, the cost of drugs is also a problem in the developing world [76]. These medications must be taken for the rest of one's life because they are only beneficial as a symptomatic treatment. As a result, a huge financial burden lies on the patient and the family. In addition to these associated pre-concerns, AD will remain a debilitating disorder that will continue to affect millions of people throughout the globe [77].

As AD-associated dementia is the most common issue raised among elderly people in the western world, it relates to the syndrome of disturbances in cortical functions, such as memory, thinking, learning capacity and judgment [78]. N-methyl-d-aspartate (NMDA) receptor antagonists and cholinesterase inhibitors are the two classes of medications approved by FDA, however these medications only offer symptomatic relief in some patients with early stage AD [79]. Additionally, caprylic triglyceride was approved by FDA as a medical food in 2009, for the management of mild-to-moderate AD. It is thought to provide an alternative source of energy to brain cells, which lost their ability to utilize glucose [80].

Inflammation is a substantial contributor to the development and progression of AD and serves as a major process target for the prevention and cure of the disease [81]. An upregulation of numerous inflammatory cytokines, including TNF-α, IL-1β and IL-6 is seen in the brain cells of AD patients, which is likely to result in an accumulation of Aβ plaques and hyperphosphorylation of tau proteins, leading to neuronal loss [[82], [83], [84]]. It is now established that the inflammatory pathology of AD can be curbed by antioxidant mechanisms and phytonutrients [85,86]. Antioxidants are produced both endogenously and exogenously, and they prevent or slow down the injury to cells caused by reactive free radical species [87]. The antioxidant compounds can be obtained from both natural and synthetic sources and some plant-based foods are believed to be rich in antioxidants [88].

Fruits are an important source of a variety of biochemicals. Due to the antioxidant properties of polyphenolic compounds, several companies utilize this property to advertise polyphenol-rich beverages [89]. Pomegranate (Punica granatum L.), is a widely consumed fruit obtained from the tree of Punica L. genus, Punicaceae family [90]. The fruit derives its name from the Latin words ‘Pomus’ and ‘granum’ (apple with grains), which is referred to the consumable part of the pomegranate tree [91]. Pomegranate and its derivatives are widely known for its medical use having a variety of pharmacological and therapeutic properties as shown in Fig. 2 [92]. Urolithin A (UA) is a compound produced endogenously by human gut microbiota from dietary polyphenolic precursors that include ellagic acid (EA) and ellagitannins (ET), such as punicalagin, collectively known as urolithins [[93], [94], [95]]. Pomegranate extract has demonstrated important bioactive properties, such as anti-inflammatory and antioxidant effects [[96], [97], [98]]. Based on previous preclinical and clinical studies, pomegranate juice, extracts, and its bioactive constituents have shown many remedial properties, including suppression of inflammatory cell signaling, reduction in expression of genes associated with oxidative stress as well as pro-inflammatory cytokines in neurons, decreased production of inflammatory and oxidative stress biomarkers and increased expression of endothelial nitric oxide synthase [[99], [100], [101]].

Fig. 2.

Representation of pomegranate application in treatment of different Alzheimar disease.

6. Pomegranate and its metabolites as a promising supplement for AD

6.1. Preclinical studies

Recently, various animal studies have shown memory and other cognitive benefits of polyphenolic compounds, which are found abundantly in pomegranate juice (Table 1). Pomegranate juice was found to reduce the Aβ levels and amyloid plaques in animal models, when given to transgenic mice of amyloid precursor protein (APP). Moreover, it improved cognitive performance and spatial learning. In another study, extracellular amyloid plaques and Ab-42 levels were significantly reduced in hippocampus. Moreover, their cognitive performance and spatial learning were improved during behavioral assessment tests [102]. Pomegranate extract (4 %) was found to activate phosphatidylinositol-3 kinase (PI3K)/protein kinase B mammalian target of rapamycin (mTOR) signaling pathway, and thus ameliorating the synaptic function. It also caused a reduction in amyloid protein precursor β (sAPPβ), β-secretase and carboxyl terminal fragment β (CTFβ) expression [103]. In another study, animals at 4 months of age received a diet having pomegranate extract (4 %) inserted directly into the food pellets until they were 19 months old. The results demonstrated decreased progression of cognitive and behavioral changes in AD with pomegranate dietary supplement [104].

Moreover, pomegranate have shown to have antioxidant effects and provide protection against oxidative stress in Tg2576 AD mice, which may be related to the antioxidant activity of their phenolic constituents. According to this study, the onset and progression of neurodegenerative diseases may be delayed or mitigated by using dietary agents protective against AD by decreasing the oxidative stress [105]. Another study showed that pomegranate juice successfully enhanced learning capacity, spatial memory and reduced cognitive impairment in female mice treated with AlCl3 [106].

In an APP/PS1 mice study, pomegranate extract attenuated Aβ plaque deposition and microgliosis [107]. Furthermore, pomegranate inhibited PC12 neuronal death caused by Aβ-induced oxidative stress, learning and memory deficiency in mice [108]. Similarly, another study reported that UA imparted cognitive protection by protecting neurons from death and triggering neurogenesis through anti-inflammatory signaling in APP/PS1 mice (Table 1) [109].

Morzelle et al. [110], detected and quantify the phenolics compounds in pulp and peel of pomegranate using HPLC approach and reported their antioxidant and acetylcholinesterase (Alzheimer target) poteitnal. It was found that among the extracts, peel showed highiest phonolic contents and significant antioxidant and acetylcholinesterase potential, as compared to pulp. These phenolic compounds in the peel extracts need advanced/authenticate method for the isolation and identification to used on industrial level.

Subash et al. [104], investigated the effect of dietary food supplementation from Omani's pomegranate extracts on different aspects like learning skills, memory loss and anxiety in Alzheimer's disease mouse model with double Swedish APP mutations namely, APPsw/Tg2576, respectively. Mice groups APP-Tg were fed a normal diet with 4 % pomegranate and different aspects like, psychomotor coordination, anxiety, special memory loss, and learning capabilities were taken under consideration in Tg and wild type, respectively. Readings were taken after 4–5 and 18–19 months for different tests. Mice with APPsw/Tg2576 were fed a standard normal chow diet showed significant anxiety, memory deficits and sever impairment in spatial learning capabilities like, motor coordination's and position discrimination, as compared to wild-type at age of 18–19 months. In contrasting case, mice with APPsw/Tg2576 were fed containing 4 % pomegranate showed significant improvements in the memory loss, learning and locomotion traits, and clear-cut reduction in anxiety, as compared to APPsw/Tg2576 mice fed standard diet (chow). This study suggests the dietary supplementation continuing pomegranates dose (4 %) showed slow progression of different cognitive and other behavioral traits in Alzheimer diseases mice.

Braidy et al. [111], used different group of mice i.e. Appsw/Tg2576 and wild-type were treated with standard and pomegranate extract (4 %) and after 15 months different behavioral traits were taken under consideration via; in vivo approach. It was found that diet containing 4 % pomegranate extracts showed significant loss of synaptic structure of protein i.e. munc18-1, followed by PSD-95 and SNAP25, synaptophysin and the phosphorylation of Ca2+/Calmodulin dependent proteins containing kinases II α [p-CaMKIIα/CaMKIIα] and phosphorylation of other cyclic AMP-response elements binding proteins namely, pCREB/CREB. On the same way, the inhibition of neuroinflamation capabilities and significantly enhances the autophagy and activate the phosphoinositide-3-kinase-AKt-mammalian rapamycin signal transduction pathway. Similarly, the neuroprotective effects were linked with reduced beta-site cleavage of Amyloid precursor protein in APPsw/Tg2576 containing mice. The long term supplementation with pomegranate extract can actively attenuate AD pathology by reducing inflammation and changing APP-dependent progressions.

Essa et al. [112], investigated effects of dietary supplementations with pomegranate, figs and dates on the inhibition of cytokines in APPsw/Tg3576 mice. Using different groups of mice with changes in plasma cytokines and Aβ and inflammatory cytokines in the brain of transgenic model mice Via; in vivo approach. It was found that different inflammatory cytokines IL-1β, IL-2, followed by IL-3, IL-4, IL-6, IL-9, IL-10, TNF- α and Eotaxin bioassays were significantly decreased by the administration of diet containing pomegranate, figs and dates. Similarly, the putative delays in the formation of senile plaques, as shown by the lowering tendency of brain Aβ1-40 and other Aβ1-42 contents were also taken under consideration. It was predicted from the current study the reduction of inflammatory cytokine during aging process may represent a mechanism through which such supplements exert a beneficial effect against neurodegenerative complication, like Alzheimer disease.

Khokar et al. [113], carried out an attempt to quantify the phenolic contents profile being isolated from pomegranate peel extract and monitored their anti-cholinesterase and antioxidant potential via; in vitro and in silico approaches for the development of Alzheimer disease. Pomegranate peel's extraction was carried out in different solvents and preliminary phytochemical were screened and its antioxidant potential were carried out by in vivo approach. The study was also extended to check its in silico conformation. Phytochemical analysis showed various tannins, alkaloids, terpenoids, flavonoids and carbohydrates contents. The total flavonoids and phenolic contents from the butanol extract showed highly significant antioxidant potential, while showed less inhibition of AChE activity than chloroform extract. On the same way, catechin, a polyohenolic compound isolated have lower binding energy for the AChE as compared to Beta-secretase-1. It forms consecutive three and two hydrogen bonds with AChE and BACE-1, respectively, via; in silico studies. It was taken under consideration that peel-buthanolic extracts from the pomegranate was rich in phenolic compounds and showed excellent antioxidant potential via; in vitro and in silico, approaches.

Hartman et al. [102], used Transgenic mice-APPsw/Tg2576 treated with pomegranate, water-control from 6 to 12 months of their age, via; in vivo approach. It was taken under consideration that pomegranate's juice treated mice acknowledge/learned water maze task much faster and hence swam faster as compared to control. On the same way, as compared to control, mice treated with PJ has found to contain approximately 50 % accumulation of soluble Aβ42 and other amyloid deposition in hippocampus. It was also found that pomegranate juice contains precious compounds responsible for Alzheimer complication in especially, transgenic mice.

Rojanathammanee et al. [107], reported that as compare to control, after three month of pomegranate treated feeding mice showed significant decrease in path length to escape mice. Further it was also found that the brain cells of mice treated with PE showed lower tumor necrosis factor α (TNF- α) and lower nuclear factor of activated t-cell (NFAT) transcriptional bioassay, as compared to control at P < 0.05. It was also taken under consideration that immunocytochemistry analysis revealed that pomegranate fed mice had attenuated microgliosis and Aβ plaque deposition in 12 months old mice, as compared to control at P < 0.05. On the same way, cell culture experiment also confirm 2 polyphenol components of pomegranate extract punicalagin and ellagic acid, significantly lessened NFAT bioassay in a reported cell line and also decreases Aβ-stimulated TNF- α secretion through murine microgalia at P < 0.05. It was taken under consideration that died containing pomegranate extract produces brain inti-inflammatory effects that directly and indirectly decrease the Alzheimer disease.

Morzelle et al. [114], supposed to check the effect of pomegranate peel extract on spatial memory, biomarkers of neuroplasticity, inflammation and oxidative stress status in mouse model of neurodegeneration. A male mice with C57Bl/6 were chronically infused for 35 days amyloid-β peptide ranging from 1 to 42 (Aβ) or control wit mini-osmotic pumps. On the same fashion, another group was also imparted with Aβ ad was treated with pomegranate peel extract i.e. P.O = βA + PPE (800 mg/kg/day) and spatial memory potential was taken consideration in the Barmes Maze. Mice treated with pomegranate peel extract (PPE) and control group showed a decline in failure to escape box, a result was not indicated in the Aβ group. On the same way PPE significantly reduced the amyloid plaque density, enhanced the expression of neurotrophin BDNF and significantly reduced the potential of acetylcholinesterase enzyme activity. Additionally, reduction in the lipids peroxidation and in the concentration of pro-inflammatory cytokine TNF- α was also taken under consideration in PPE group. Interestingly, hepatic lesions were not seen in the mouse treated with PPE. The administration of PPE has potential neuroprotective effects through different mechanisms to prevent the establishment as well as the progression of neurodegenerative process persuaded by the infusion with amyloid-β peptide in mice. Different possible mechanism of Alzheimer disease (AD by some phytochemicals reported in pomegranate (Fig. 3).

Fig. 3.

Diagrammatic representation of different mechanisms related to Alzheimer's disease (AD) and the potential impact of certain phytochemicals found in pomegranate. AD is characterized by key hallmarks such as amyloid plaques and neurofibrillary tangles (NFT), which can be inhibited by important precursors, namely, luteolin, curcumin, apigenin and genistein, through the GSK3β signal transduction pathway [115].

6.2. Clinical studies

In a randomized controlled trial on pomegranate extract, memory testing was performed and functional brain activation (fMRI) outcomes were measured in older subjects with age-associated memory complaints. Thirty-two participants were randomly assigned to 2 groups who were either given eight ounces of pomegranate juice or a flavored placebo drink for 4 weeks. After 4 weeks, the group of individuals taking pomegranate juice demonstrated a significant increase in plasma Trolox-equivalent antioxidant capacity (TEAC) and a substantial improvement in the Buschke selective reminding test of verbal memory. The pomegranate group showed enhanced fMRI activity during visual and verbal memory assignments as compared to the placebo group. These results suggest a role of pomegranate juice in augmenting memory function through task-related increase in functional brain activity [116] (Table 2).

Table 2.

Clinical studies highlighting the potential usage of pomegranate role in AD.

Pomegranate	Effects on Alzhemar disease	Reference
Juice	The juice of pmegranate showed an interesting improvement in the Buschke Selective Reminding test (BSRT) of verbal memory and also significantly increases the plasma trolox-equivalent antioxident potentital (TEAP), respectively.	[116]
Extract	The placebo group revleaed a clear cut reduction in the post surgery memory retention with the pomegranate treatment. It was also found that pomegranate treatement also improve the memory rentention capibilities via; in vivo	[117]
Juice	It has been found that the daily use of promegranate juice actively stabilizes the capibilities to learn visual informations over 12 months of peroids, accordinly.	[118]

On the same way, another study also confirmed that a patient undertaking elective coronary artery bypass grafting (ECABG) and agree upon surgery. Interestingly, 2 g of pomegranate extract in the 2 POMxpills were taken per day from one week before and after six weeks of surgery. The patients were also administered a battery of neuropsychological tests to assess memory function one week before surgery (baseline), two weeks after surgery, and six weeks after surgery. The placebo group had significant deficits in post-surgery memory retention, and the pomegranate treatment not only protected against this effect but also improved memory retention performance for up to 6 weeks after surgery compared to pre-surgery baseline performance [117].

Similarly, in a study for 12 months with the randomized, double-blind, placebo-controlled trial of pomegranate juice in middle-aged and older adults, two hundred and sixty-one subjects (aged 50–75 y) consumed pomegranate juice [8 oz (236.5 mL) per day] or a placebo drink (8 oz, matched constituents of pomegranate juice except for pomegranate polyphenols). The Memory measures [Brief Visuospatial Memory Test-Revised (BVMT-R) and Buschke Selective Reminding Test (SRT)] were assessed at six and 12 months and analyzed using a mixed-effects general linear model. This study investigated the long-term effect of pomegranate juice on memory in non-demented middle-aged and older adults. Results suggest that daily consumption of pomegranate juice may stabilize the ability to learn visual information over a 12-months period [118] (Table 2).

7. Newly approved drugs for AD

Currently, the following FDA approved medications are currently used to treat AD. The five medications are: (1) an anti-amyloid antibody (Aducanumab); (2) acetylcholinesterase inhibitors (Rivastigmine, Donepezil, Galantamine, and Tacrine); (3) glutamate inhibitors (Memantine); (4) chelating agents (Clioquinol and deferiprone); and (5) natural substances (berberine, curcumin, epigallocatechin-3-gallate, ginsenoside Rg1, genistein etc [119].

8. Conclusion and future prospectives

Pomegranate different tissues like seeds, fruit, fruit-peel and leaves have been extensively utilized traditionally as a herbal medicines for the treatment of different diseases. Interestingly, studies have confirmed the presence of precious phytochemicals in the fruits peel and juice and recently, it received greater attention than the other tissues. Different biological activities taken under consideration via; in vitro, in vivo and in silico approaches have also confirmed significant effects as a anti-inflammatory, antioxidants, Alzheimer and other important complications, respectively. Pomegranate Extract Gummies (Natural Cardio protect syrup) and Melograno punica granum GranaGard by Granalix BioTechnologies are being marketed as nutraceuticals. It is concluded from the preclinical and clinical studies that pomegranate supplementation can be a promising remedial source for Alzheimer disease through underlying mechanisms via reduction in the β-secretase, soluble amyloid protein procurer β (sAPPβ), and cognitive protection by protecting neurons from death through anti-inflammatory signaling. Different studies have been carried out which demonstrated significant health benefits on alzheimer dieases (AD) through various animal models. The presence of diverse phytochemicals make pomegranate tissues a wonderful source with the least side effects. However, the biological activities of such phytochemicals should be taken under consideration in the future as well. Similarly, comprehensive metabolites profiling, its characterization, identification and isolation from various cultivars, which are growing under diverse conditions i.e. abiotic and biotic stresses, can also be beneficial to explore their phytochemicals diversity and biologicals activities via; in silico, in vitro and in vivo approaches, respectively.

Funding

The project was supported by grant from The Oman Research Council (TRC) through the funded project (BFP/RGP/EBR/22/021).

CRediT authorship contribution statement

Aman Ullah: Conceptualization, Methodology. Asif Khan: Data curation, Formal analysis, Investigation. Sagheer Ahmed: Investigation, Methodology. Hafiz Muhammad Irfan: Data curation, Software. Amin A. Hafiz: Funding acquisition, Resources, Software. Kainat Jabeen: Formal analysis, Investigation. Mubarak Alruwaili: Data curation, Formal analysis. Muteb Alotaibi: Formal analysis, Software, Visualization. Waiel Al Naeem: Data curation, Funding acquisition. Ajmal Khan: Conceptualization, Data curation, Writing – original draft. Ahmed Al-Harrasi: Supervision, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.