Table 3.
Preclinical studies attesting the antioxidant, anti-inflammatory, and neuroprotective effects of ellagitannins, ellagic acid, or their metabolites in the brain.
| Substances Tested (ST)—Doses | Preclinical Model | Main Results | Reference |
|---|---|---|---|
| EA—p.o. administered in 3 doses: high (H), medium (M), and low (L) doses | Aging model obtained with D-gal (100 mg/kg/day, s.c., 8 weeks) in male Sprague–Dawley (SD) rats divided into 6 groups: (1) control, (2) D-gal, (3) positive control (vitamin E, 150 mg/kg, by gavage), (4) H-EA (D-gal + 150 mg EA/kg/day), (5) M-EA (D-gal + 100 mg EA/kg/day), (6) L-EA (D-gal + 50 mg EA/kg/day). | EA restored the antioxidant defense system (evaluated by SOD, CAT, GSH-Px, and T-AOC activities, and MDA levels, respectively) in the liver and brain of D-gal-induced aging rats, especially in H-dose. The treatment with M and H doses of EA for 8 weeks has significantly mitigated the D-gal-induced inflammation (TNF-α, IL-6, and IL-1β levels in serum) and the liver function decline (ALT and AST levels). Histopathological analysis showed that the H-dose of EA was more protective and kept the morphological structure in both the liver and brain. EA treatment significantly downregulated the expression of Bcl-2 and Bax proteins and showed anti-apoptotic effects in a concentration-dependent manner. | [175] |
| UA—p.o. administered in 3 doses: high (H), medium (M), and low (L) doses | I. Aging model obtained with D-gal (150 mg/kg/day, s.c., 8 weeks) in male Institute of Cancer Research (ICR) mice were divided into 5 groups: (1) control (Ctrl), (2) D-gal, (3) H-UA (D-gal + 150 mg UA/kg/day), (4) M-UA (D-gal + 100 mg UA/kg/day), (5) L-UA (D-gal + 50 mg UA/kg/day). II. Additional experiment with 4 groups:
|
UA treatment significantly ameliorated D-gal-induced behavioral impairments (in Open field, Morris Water Maze, and Object–Place Recognition tests). UA significantly lowered the AChE and MAO levels and the oxidative stress (the activities of SOD, CAT, GSH-Px, T-AOC, and MDA levels, respectively) in the brain of D-gal-induced aging mice. UA showed neuroprotection against D-gal-induced aging downregulating miR-34a in the hippocampal tissue and activated autophagy by upregulating SIRT1 and downregulating the protein expression of p53/p21 and the mTOR signaling pathway. | [176] |
| Urolithin B (UB)—i.g. administered in 3 doses: high (H), medium (M), and low (L) doses | I. Aging model obtained with D-gal (150 mg/kg/day, s.c., 8 weeks) in male C57BL/6 mice were divided into 5 groups: (1) control, (2) D-gal, (3) H-UB (D-gal + 150 mg UB/kg/day), (4) M-UB (D-gal + 100 mg UB/kg/day), (5) L-UB (D-gal + 50 mg UB/kg/day). II. Additional experiment with 4 groups:
|
Long-term UB treatment significantly ameliorated the behavioral features, learning, and memory function (in Open field, Morris Water Maze, and Y-maze tests) in D-gal-induced aging in mice. These outcomes were correlated with a significant reduction of AGE levels and elevation of Cu, Zn-SOD, and CAT expressions and activities in the brain. UB inhibited the apoptosis of hippocampal neurons induced by D-gal, downregulated the JNK signaling pathway, prevented the cytochrome c release from isolated mitochondria, increased the activation of Akt and p44/42 MAPK, and promoted the neuronal survival via the PI3K/Akt pathways. | [145] |
| EA—50 mg/kg/day, intragastric (i.g.) | Mouse model of AD: Male APP/PS1 double-transgenic and wild-type (WT) C57BL/6 mice were divided into 4 groups: (1) WT, (2) WT+EA, (3) APP/PS1, (4) APP/PS1 + EA, received EA or the same volume of 10% DMSO for 60 days. | EA treatment improved learning and memory abilities and ameliorated cognitive deficits in APP/PS1 mice, reduced neuronal cell apoptosis, the expression of caspase-3 level and the amyloid aggregates in hippocampus. EA also significantly inhibited tau hyperphosphorylation and decreased the expression of pSer199-tau and pSer396-tau in the hippocampus of APP/PS1 mice. Moreover, EA treatment significantly increased the expression of pSer473-AKT and decreased the pTyr216-GSK3β levels in APP/PS1 mice. | [177] |
| EA—50 mg/kg, p.o. | AD animal model induced with AlCl3 in male Wistar rats divided into 4 groups: (1) control, (2) EA (50 mg/kg, p.o., for 4 weeks), (3) AD model (50 mg AlCl3/kg, p.o., for 4 weeks), (4) AD + EA (50 mg AlCl3/kg, p.o., for 4 weeks, followed by 50 mg EA/kg/day, p.o., for 2 weeks). | The discrimination index for the novel object recognition test (NORT) was significantly increased by EA therapy in AD rats. EA treatment significantly increased SOD, GSH, and TAC levels and decreased MDA levels in the serum of AD rats. The neurofibrillary tangles and neuritic plaques in the entorhinal cortex (ERC) sections were reduced in the AD+EA group. Antioxidant activity of EA treatment (increased SOD mRNA expression and modulated the amyloid precursor protein toxicity and caspase-3-mediated apoptosis) was correlated with the restoration of ERC thickness in AD+EA rats vs. AD rats. | [178] |
| EA—50 mg/kg bw/day (EA50) and 100 mg/kg bw/day (EA100), i.p., for 21 days | Animal model of memory impairment and anxiety induced by sleep deprivation (SD). C57BL/6J mice were divided into 4 groups: (1) control, (2) SD, (3) SD + EA50, (4) SD + EA100. | EA ameliorated learning and memory deficits and alleviated anxiety-like behaviors in SD mice. EA treatment improved neuron survival, reversed dendritic spine density, and reduced shrinkage and loss of neurons in the hippocampus of SD mice. EA restored the SOD and GPx activities, decreased MDA levels, and activated the Nrf2/HO-1 pathway in the hippocampus of SD mice. EA also reduced the IL-1β, IL-6, and TNF-α hippocampal levels, normalized the expression levels of TLR4, MyD88, NF-κB p65, and p-IκBα, and inhibited the TLR4-mediated innate immune responses. Moreover, EA showed neuroprotective effects on glutamate-induced toxicity via both the Nrf2 and TLR4 signaling pathways. | [179] |
| EA—50, 75, and 100 EA mg/kg, by gavages, 3 times daily for one week | Animal model of brain inflammation induced by cerebral ischemia/reperfusion (I/R). Male Wistar rats were divided into 6 groups: (1) control (surgery without any I/R) + vehicle (Veh); (2) I/R + Veh; (3–5) I/R + EA; (6) positive control (intact rats received 100 mg EA/kg). | Only the higher dose of EA (100 mg/kg) improved post-ischemic complications: it significantly increased the neurological signs scores, significantly reversed all tested behaviors, restored the BBB permeability, and decreased brain edema and the brain tissue cytokine levels (TNF-α and IL-1β) vs. I/R + Veh rats. | [180] |
| UA—300 mg, p.o. | Mouse model of Alzheimer’s disease (AD): APPswe/PS1ΔE9 (APP/PS1) mice received 300 mg of UA dissolved in 0.5% carboxymethylcellulose each day for 14 days vs. 2 control groups: APP/PS1 transgenic mice and wild-type mice that received only the vehicle (0.5% carboxymethylcellulose). | UA ameliorated spatial learning and memory impairment, prevented neuronal apoptosis in the cortex and hippocampus, and enhanced hippocampal neurogenesis in APP/PS1 mice. UA also decreased Aβ plaque deposit levels in the cortex and hippocampus, attenuated reactive gliosis, and significantly reduced microglia and astrocyte activation in APP/PS1 mice. UA treatment increased the expression of p-AMPK and decreased the activation of P65NF-κB and P38MAPK. | [181] |
| UA—2.5 mg/kg/day, i.p., for 8 weeks | A streptozotocin (STZ)- induced diabetic mouse model. Male CrljOri:CD1(ICR) mice were divided into 2 groups: (1) STZ-control and (2) STZ-UA. | UA treatment improved cognitive impairment, APP and BACE1 expressions, Tau phosphorylation, and Aβ deposition in STZ-induced diabetic mice. UA decreased blood glucose levels, but only in control mice and not in the STZ-injected mice. | [143] |
| UA—2.5 mg/kg bw; egpigallocatechin gallate (EGCG)—25 mg/kg bw | Animal model of late-onset AD using humanized homozygous amyloid beta knockin (hAbKI) mice were divided into 3 groups: (1) control, (2) UA (i.p., 3×/week for 4 months), (3) UA+EGCG (i.p., 3×/week for 4 months). | Both UA and UA + EGCG have been effective in counteracting the onset of pathological features of AD in hAbKI mice: enhanced phenotypic behavior, significantly increased mitochondrial biogenesis proteins (Nrf2, TFAM), both mitophagy (PINK1, Parkin) and synaptic proteins (synaptophysin, PSD95), as well as autophagy proteins (Beclin, ATG5, LC3B1, LC3B2, BCL2). Neuroinflammatory biomarkers (microglial marker Iba1 and astrocytic marker GFAP) were reduced, and the neuronal marker NeuN was significantly increased by both UA and UA + EGCG treatments. Dendritic spines and lengths, mitochondrial length, and mitophagosomal formations were also increased by both treatments. However, combined treatment UA+EGCG was stronger and more effective than only UA for most of the determinations performed. | [182] |
| Juglans regia (Gimcheon 1ho cultivar, GC)—lyophilized ethanolic extracts (obtained with 80% ethanol at 40 °C for 2 h), containing EA and ellagitannins (pedunculagin/casuariin isomer, strictinin, tellimagrandin I, EA-O-pentoside, and EA)—20 mg/kg bw (GC20) and 50 mg/kg bw (GC50), p.o. | A diabetic animal model with cognitive dysfunction in mice induced by a high-fat diet (HFD) for 12 weeks. Male C57BL/6 mice were divided into 4 groups: (1) control, (2) HFD, (3) HFD+GC20, (4) HFD + GC50. The lyophilized extracts were administered for 4 weeks. |
GC significantly restored the behavioral and memory dysfunction in HFD-induced diabetic mice for both doses (GC 20 and GC50). GC also improved serum lipid profile and reduced white adipose tissue (WAT) and liver fat mass and showed antioxidant effects (reduced levels of MDA—in hepatic and cerebral tissues—and serum AGEs, and increased serum level of FRAP). GC inhibited AChE activity in cerebral tissue, suppressed AChE expression, and upregulated choline acetyltransferase expression vs. HFD group. GC restored mitochondrial membrane potential, regulated the mitochondrial ROS production and the protein expressions associated with synaptic disorders and neuronal apoptosis: decreased p-JNK, p-tau, and Aβ levels, upregulated p-Akt (Ser 473) and insulin-degrading enzyme (IDE), and downregulated BAX and caspase-3 expression levels vs. HFD group. Moreover, GC ameliorated TNF-α, IL-1β, p-NFκB, and caspase-1 expression levels and upregulated heme oxygenase-1 (HO-1) expression levels vs. HFD group. | [183] |
| Pomegranate juice (PJ) rich in ellagitannins (galloyl-hexoside, EA-hexoside, pedunculagin, casuarinin) and EA, containing 18.90 ± 0.96 g/L (EA equivalents per L of juice) | Rat model of Parkinson’s disease (PD) induced with rotenone (1.3 mg/kg bw/day, s.c., for 35 days). Male albino Wistar rats were divided into 4 groups: (1) control (vehicle only), (2) PJ (500 mg/kg bw/day, i.g.), (3) rotenone only (1.3 mg/kg bw/day, s.c.) from the 11th day (ROT), (4) PJ (500 mg/kg bw/day, i.g.) + rotenone from the 11th day (PJ + ROT). Experiment included 10 days pretreatment with PJ and 35 days with PJ + ROT combined treatment. | PJ improved postural stability in rats affected by rotenone, enhanced neuronal survival, protected against oxidative damage (reduced MDA levels and increased CAT, GPx, GST activities in midbrain) and α-synuclein aggregation, increased the activity of mitochondrial aldehyde dehydrogenase, and normalized the expression of anti-apoptotic Bcl-xL protein. | [184] |
| PJ | Rat model of Parkinson’s disease (PD) induced with rotenone (1.3 mg/kg bw/day, s.c., for 35 days). Male albino Wistar rats were divided into 4 groups: (1) control (vehicle only), (2) PJ (500 mg/kg bw/day, i.g.), (3) rotenone only (1.3 mg/kg bw/day, s.c.) from the 11th day (ROT), (4) PJ (500 mg/kg bw/day, i.g.) + rotenone from the 11th day (PJ + ROT). Experiment included 10 days pretreatment with PJ and 35 days with PJ + ROT combined treatment. | PJ treatment proved neuroprotection against PD: improved vertical activity in rotenone-injected rats mitigated the reduction of the olfactory discrimination index to the level observed in control animals, attenuated the depletion of the dopamine (DA) and 3,4-dihydroxy-phenylacetic acid (DOPAC) in the midbrain. | [185] |
| EA, α-lipoic acid (LA), myrtenal (Myrt)—50 mg/kg (i.p.) | Rat model of Parkinson’s disease (PD) induced with 6-hydroxydopamine (6-OHDA) (intrastriatal injection). Male Wistar rats divided into 5 groups: (1) control, (2) striatal 6-OHDA-lesioned control, (3–5) striatal 6-OHDA-lesioned rats pre-treated for 5 days with EA, LA, and Myrt. | All three compounds (EA, LA, and Myrt) improved learning and memory performance as well as neuromuscular coordination in rats with 6-OHDA-induced PD. Moreover, all these compounds significantly decreased lipid peroxidation (LPO) levels and restored catalase (CAT) activity and DA levels that were impaired by the challenge with 6-OHDA. | [186] |
| EA—10 mg/kg and 50 mg/kg, p.o. | Animal model of dopamine (DA) neuronal damage induced by lipopolysaccharides (LPS). Male Wistar rats were divided into 5 groups: (1) control, (2) EA (50 mg/kg), (3) LPS, (4) LPS+EA (10 mg/kg), and (5) LPS +EA (50 mg/kg). | EA (50 mg/kg) attenuated LPS-induced DA neuronal loss and ameliorated the decrease in tyrosine hydroxylase expression in the substantia nigra neurons. EA also attenuated the activation of the NLRP3 inflammasome in microglia and inhibited the NLRP3 inflammasome signaling pathway activated by LPS. The protein expressions of Iba-1 and proinflammatory cytokines IL-1β, TNF-α, and IL-18 were significantly suppressed by EA treatment. | [187] |
| EA—100 mg/kg and 200 mg/kg, i.p. and p.o. | Male albino Swiss mice—i.v. pentylenetetrazole (PTZ) seizure threshold test, maximal electroshock seizure test (MEST), grip-strength test, and chimney test, vs. valproic acid as reference drug. |
EA (100 mg/kg) significantly increased the threshold of mice injected with PTZ for the first myoclonic twitch and generalized clonic seizures associated with the loss of the righting reflex, but not the threshold for forelimb tonus. In the MEST test, EA affected the threshold for the tonic hindlimb extension only at the high dose (200 mg/kg). EA did not have any effects on neuromuscular strength and motor coordination in mice at any of the doses tested. | [188] |
| Corilagin—10 mg/kg and 20 mg/kg, i.p. | Male Wistar rats—i.v. PTZ seizure threshold test. | Corilagin significantly reduced the epileptic events and improved cognitive function (in the Morris water maze (MWM) navigation test), reduced TNF-α and increased IL-10 levels, reduced ROS production, mitochondrial swelling, and carbonic anhydrase activity in the brain tissues in a dose-dependent manner. Corilagin treatment prevented structural damage of neurons and maintained the number of surviving cells vs. control group. | [189] |
| UA—10, 25, or 50 mg/kg/day, p.o. | Animal model of an experimental autoimmune encephalomyelitis (EAE) in C57BL/6 female mice immunized with MOG35–55. | The dose of 25 mg/kg significantly suppressed the progress of EAE. UA treatment decreased demyelination, significantly inhibited inflammatory cell infiltration, reduced neuroinflammation (lowered numbers of M1-type microglia and inhibited the activation of dendritic cells). | [190] |
| Pomegranate peel extract (PEm) rich in EA and punicalagin, vs. EA—50 mg/kg/day of EA | Animal model of EAE in C57BL/6 female mice immunized with MOG35–55. | Both EA and PEm showed comparable efficiencies to reduce the progression of the EAE and to ameliorate the clinical symptoms in mice. Spinal microgliosis and astrocytosis were significantly reduced by the PEm treatment as well as a clear reduction of the CD45 staining in the spinal cord was observed. | [191] |
| UA—2.5 mg/kg, i.p. | Mouse model of traumatic brain injury (TBI). Male C57BL/6J mice were divided into 3 groups: (1) control, (2) TBI + vehicle, (3) TBI + UA. | UA attenuated neuronal apoptosis following TBI (significantly reduced the cleaved caspase-3 expression and increased the Bcl-2 expression vs. TBI+vehicle), reinforced neuronal autophagy (increased the immunopositivity of LC3 and p62, two neuronal autophagy markers), and downregulated (PI3K)/Akt/mTOR (decreased Akt and mTOR expression levels) and Akt/IKK/NFκB signaling pathways (decreased the phosphorylation levels of IκB, IKKα, and NFκB). | [192] |
| Oenothein B—100 or 500 mg/kg/day, p.o. | Male ddY mice received oenothein B once a day for 3 days (from days 1 to 3) or 7 days (from days 1 to 7). | Oenothein B (only 100 mg/kg/day) activated extracellular signal-regulated kinase 2 (ERK2) in the hippocampal region of healthy mice, the ratio pERK2/ERK2 being significantly increased after 7 days of daily treatment. The activation of cAMP response element-binding protein (CREB), reflected by pCREB/CREB ratio, was slightly increased, but without statistical significance (p = 0.0866). | [193] |
| UA (30 μg UA/100 μL PBS, i.p.) | BALB/cJInv female mice were chronically infected with Toxoplasma gondii (T. gondii). UA treatment started 2 days post-infection and continued daily for 5 weeks vs. a control group (injected with vehicle). | All UA-injected mice survived throughout the entire experiment vs. 60% in the control group (40% of the infected control mice died 10-days post-infection). UA treatment inhibited cyst formation in the brain and altered the response of infected mice toward cat odor. | [194] |
AChE—acetylcholinesterase; AD—Alzheimer’s disease; D-gal—D-galactose; EA—ellagic acid; EAE—experimental autoimmune encephalomyelitis; EGCG—egpigallocatechin gallate; GC—Juglans regia, Gimcheon 1ho cultivar; HFD—high-fat diet; Iba-1—ionized calcium-binding adapter molecule-1; i.g.—intragastric; IL—interleukin; i.p.—intraperiotoneal; i.v.—intravenous; MEST—maximal electroshock seizure test; MOG35–55—myelin oligodendrocyte protein 35–55 peptide; NLRP3—Nod-like receptor protein 3; 6-OHDA—6-hydroxydopamine; PBS—phosphate-buffered saline; PD—Parkinson’s disease; PEm—pomegranate peel extract; PJ—pomegranate juice; p.o.—per os; PTZ—pentylenetetrazole; ROT—rotenone; SD—sleep deprivation; TNF-α—tumor necrosis factor-α; UA—urolithin A; UB—urolithin B; WT—wild-type.