Table 3.

Neurologic effects of catechins on Down syndrome.

Author (Year)	Objective	Type of Study and Sample Size	Interventions	Methodology	Main Outcomes	Conclusions	Quality of Evidence
Gu et al., 2020 [50]	To evaluate the effect of EGCG on DYRK1A kinase activity	C57Bl/6J mice overexpressing Dyrk1A (TgBACDyrk1A) model (n = 30) (n = 30)	FontUp administration by oral gavage (25 mg/kg, 50 mg/kg or 75 mg/kg).	Three experimental groups (FontUp administration of 25 mg/kg, 50 mg/kg, or 75 mg/kg) Protein extraction and analysis. Truncated DYRK1A (DYRK1A-ΔC) purification. DYRK1A inhibition analysis HPLC analysis for FontUp polyphenols quantification. Computational molecular docking (ECG) and epicatechin (EC) on DYRK1A kinase activity.	EGCG and ECG ↓ DYRK1A activity EGC and EC = DYRK1A activity. FontUp = liver and cardiac function EGCG crosses blood-brain barrier	Oral FontUp® normalized brain and plasma biomarkers altered in TgBACDyrk1A, without damaging liver and cardiac performances	++
Catuara-Solarz et al., 2016 [96]	To explore the effects of a combined therapy with EE and EGCG on neurological disorders of DS at young age	Experimental Ts65Dn 1–2-month-female mouse models of DS. (WT = 8; TS = 7; WT-EE-EGCG = 7; TS-EE-EGCG = 7)	Green tea extract containing 45% EGCG administrations by oral feeding (EGCG dosage: 0.326 mg/mL, 0.65 mg per day; 30 mg/kg per day during 30 days)	Four experimental groups (WT, TS, WT-EE-EGCG, TS-EE-EGCG). Morris Water Maze Novel object recognition test Quantification of dendritic spine density. Immunohistochemistry for synaptic studies Immunohistochemistry for synaptic modifications studies	EE-EGCG treatment ↑ corticohippocampal-dependent learning and memory. ↑ cornu ammonis 1 (CA1) dendritic spine density. Improvement of excitatory and inhibitory synaptic markers in CA1 and dentate gyrus	EE-EGCG treatment derived cognitive improvements are linked to modulation of neural synapsis at the hippocampus and normalization in dendritic spine density	++
Goodlett et al., 2020 [97]	To test the effects of EGCG on neurobehavioral and skeletal phenotypes in a mouse model	Experimental Ts65Dn mouse models of DS (Euploid PB = 13 Euploid EGCG = 11 Ts65Dn PB = 12 Ts65Dn EGCG = 8	Three-week EGCG oral gavage therapy (200 mg/kg/day)	Multivariate concentric square field maze. BB and MWM. Morris water maze CT imaging HPLC kinase activity assay WB for DYIRK1A protein quantification	↓ growth in both euploid and trisomic mice =results in on conductual assessment of Ts65Dn mice. Ts65Dn mice. ↓ cortical bone formation and potency in Ts65Dn mice	EGCG has no effects on behavior. High-dose EGCG caused deleterious effects on growth and skeletal phenotypes	++
Stringer et al., 2015 [98]	To evaluate the therapeutic effects of EGCG on locomotor activity and learning and memory on a mice model of DS	Experimental Ts65Dn mouse models of DS and euploid treatments: Ts65Dn—EGCG n = 8, water n = 9; Euploid—EGCG n = 12, water n = 13	Ts65Dn or euploid mouse models were randomized to receive EGCG + H3PO4 (n = 10/n = 8), EGCG (n = 14/n = 8), water + H3PO4 (n = 9/n = 13) or water (n = 9/n = 17) for three months	20 mg/kg/day EGCG HPLC/MS degradation analysis Locomotor activity assessment, NOR, DNMP, BB and MWM. Dyrk1A kinase activity assay	Ts65Dn ↑ locomotive performance Ts65Dn↓ novel object detection, balance beam and spatial learning and memory. EGCG did not ameliorate performance of the Ts65Dn mice on these tasks	Oral EGCG treatment up to 20 mg/kg/day did not improve learning and memory performance in adolescent Ts65Dn mice	++
Souchet et al., 2015 [95]	To investigate the consequences of one-month therapy with EGCG-containing products on excitation/inhibition balance in DS adults.	Experimental adult mBACtgDyrk1a mice Transgenic (TG) = 10 Wild-type (WT) = 10 Treated transgenic (TG*) = 10	Administration of 225 mg/kg/day of Polyphenon 60 for four months in adult mice mBACtgDyrk1a or for six weeks before and during behavioral analysis in Ts65Dn	Indicators of GABAergic and glutaminergic synaptic routes were evaluated by immunoblot Y-maze paradigm to assess working memory	↓ GABA in cortex, hippocampus and cerebellum ↑ GLUR1, NR1, NR2a, VGLUT1 in cortex ↑ Ratio of PCAMKII/CAMKII in the hippocampus ↑ Short term memory	EGCG therapy restores excitation/inhibition balance disorders in DS adults	++
Stringer et al., 2017 [99]	To investigate if an EGCG would yield improvements in either cognitive or skeletal deficits.	Experimental Ts65Dn mouse models of DS Eup + water = 19 Eup + EGCG = 18 Tsg + water = 13 Tsg + EGCG = 15	Oral administration of EGCG from PD24 to PD68	MCSF, NOR, BB, and MWM. CT, HPLC kinase activity assay and WB for Dyrk1A quantification	=growth ↓ Kinase activity (cerebellum) =cognitive deficits ↑ Adverse changes in skeleton	No beneficial therapeutic effects were seen with EGCG intake on behavior. Caused detrimental skeletal effects in Ts65Dn mice.	++
Catuara et al., 2015 [100]	To investigate the effect of coadjuvant treatment with EGCG and EE on the cognitive decline in DS.	Experimental Ts65Dn mouse models of DS 5–6 months old female mice WT = 10; TS = 11; WT-EE = 14; TS-EE = 11; WT-EGCG = 11; TS-EGCG = 9; WT-EE-EGCG = 12; TS-EE-EGCG = 8.	Administration of green tea extract including 45% EGCG (0.326 mg/mL, 0.9 mg per day; 30 mg/kg per day) during 30 days	MWM for hippocampal-dependent learning and memory evaluation.	EGCG or EE = spatial learning EGCG + EE ↓ learning alterations of middle age Ts65Dn mice and this stratification continued upon treatments	Combining EE and EGCG ameliorates age-related cognitive degeneration in DS	++
Valenti 2013 Italy [101]	To test the capability of EGCG to reestablish the energy in mitochondria and reduce oxidative stress in DS cells	Experimental Cultured lymphoblasts and fibroblasts from DS patients	Lymphoblastoid and fibroblast cells were treated with 20 μM EGCG joined to the cell culture for 24 h	Assessment of mitochondrial ATP production rate, cellular ATP and ROS detection	↑ mitochondrial complex I and ATP synthase catalytic action ↓ oxidative stress. ↑ mitochondrial biogenesis ↑ Sirt1-dependent PGC-1α deacetylation, NRF-1 and T-FAM protein levels	EGCG antioxidant effects rescues mitochondrial energy and ROS production impairment, prevents overproduction of reactive oxygen species (ROS) and peroxidation of lipid membranes and increases mitochondrial biogenesis	++
Valenti et al., 2016 [102]	To establish possible function of mitochondria in DS cognitive disability	Experimental Ts65Dn mouse models of DS Ts65Dn = 12 WT = 12	NPCs, cultured for 48 h were complemented with EGCG and RSV, at a concentration of 20 μM and 10 μM, respectively	Measurements of oxygen consumption, mitochondrial ATP production and L-lactate, mitochondrial chain complex activities, ROS production. Immunoblot analysis, quantitative analysis of mtDNA content.	↑ Oxidative phosphorylation ↑ Mitochondrial biogenesis ↑ Proliferation of NCPs ↑ PGC-1α/Sirt1/AMK axis mitochondrial energy, and improved growth of NPCs	EGCG and RSV reactivates mitochondria bioenergetics and biogenesis and promotes NPCs in DS	++
Stagni et al., 2016 [103]	To study the effect of EGCG in hippocampal development and memory performance	Experimental Ts65Dn mouse models of DS EGCG: Euploid n = 40 and Ts65Dn n = 25 NT:Age-matched euploid (n = 53) and Ts65Dn (n = 25)	EGCG daily subcutaneous injection from PN3 to PN15 (25 mg/kg).	Nissl staining Immunohistochemistry (ki67, cleaved caspase-3, BrdU, NeuN, GFAP, Ayn, PSD-95) Western Blot (GSK3β) MWM and Y-maze	=brain and body weight =locomotor activity and learning and memory Short term effects: ↑ Ki67, BrdU, granular cells in hippocampus, SYN, PSD-95 ↓ GSK3β Long term effects: ↓ BrdU/NeuN, BrdU/GFAP, GSK3β =Ki67, SYN, PSD-95	EGCG rescues hippocampal neurogenesis and synaptic processes but these effects do not persist for a long time.	++
de La Torre et al., 2014 [104]	To explore if EGCG rescues the intellectual disabilities in adult DS	-Experimental Ts65Dn or TgDyrk1A mouse models of DS: WT untreated n = 13/n = 19; TG/Ts65Dn–untreated n = 16/n = 14; WT-EGCG n = 16/n = 22; TG-EGCG/Ts65Dn n = 14/n = 14.14. -A randomized, double blind, placebo-controlled study in DS humans: 13 EGCG group 16 placebo group	Mice were administered EGCG in drinking water for one month (90 mg/mL for a dose of 2–3 mg per day) Pilot study: groups were randomized to receive oral EGCG at dosage of 9 mg/kg/day or placebo over six months	Mouse model: -Water maze for hippocampal-dependent spatial recognition -NOR for learning and memory assessment deficits. -Dyrk1A kinase activity and homocysteine evaluation Pilot study: -Neurophysiological testing -Blood test and ALT, AST, glucose, cholesterol, TG, GSH-Px analysis -HPLC/MS for EGCG determinations	Mouse model: ↓ DYRK1A ↑ homocysteine ↑ Learning and memory Pilot study: =ALT, AST, TG, glucose, GSH-Px ↓ cholesterol ↑ Episodic and learning memory, visual memory recognition	EGCG improved learning and memory disorders in DS, blocking Dyrk1A expression Plasmatic homocysteine are a biomarker of hippocampal DYRK1A activity in human study	++++
de La Torre et al., 2016 [85]	To test if the administration of EGCG would enhance the outcomes of intellectual rehabilitation in young adults with DS	Double blind, placebo-controlled, phase 2, single center trial (TESDAD) in DS humans 43: EGCG and intellectual treatment group 41: placebo and intellectual treatment group Aged 16–34 years	Randomization and EGCG (9 mg/kg per day) or placebo and cognitive rehabilitation for 12 months. Follow- up of 6 months after intervention discontinuation	Intellectual assessment for working memory, executive performance. Homocysteine, Dyrk1A kinase activity, ALT, AST, cholesterol, TG measurements. fMRI and TMS for functional connectivity patterns studies.	↓ Cholesterol ↑ Homocysteine ↑ Inhibitory control, recognition memory, adaptive behavior =BMI ↑ Brain connectivity	EGCG joined to intellectual rehabilitation for 12 months had greater results than placebo and intellectual rehabilitation at improving visual memorial perception conduct control, and compliant behavior	++++
De Toma et al., 2019 [105]	To compare proteomic changes in DS EE or GTE treated DS individuals	Experimental Ts65Dn male mouse models of DS at thee months 144 animals: 38 NT mice (18 TG, 20 WT); 38 EGCG (18 TG, 21 WT); 36 EE (16 TG, 18 WT); 33 EGCG + EE (16 TG, 17 WT)	EGCG 326.25 mg per capsule mixed with drinking water at 0.33 mg/mL at medium dose of 42 mg/kg per day for one month.	Western Blot for Dyrk1A quantification Mass-spectrometry-based proteomics Liquid chromatography tandem-mass spectrometry NOR	-Dyrk1A overexpression impacted the phosphoproteome in TG hippocampus (mainly proteins plasticity and cognitive-related proteins) -These (phospho-) proteomic changes were rescued by green tea and/or EE	-t Dyrk1A overexpression causes changes in the proteome and phosphoproteome of the hippocampus of transgenic mice -The cognitive enhancer treatments rescued these alterations	++
De Toma et al., 2020 [106]	To study the effects of EGCG, EE and their mixture using proteome, and phosphoproteome analysis in the hippocampi of DS	Experimental Ts65Dn mouse models of DS Five mice per group, randomly chosen (40 total mice)	EGCG: 326.25 mg per capsule. mixed with water at 0.33 mg/mL equivalent to a medium dose of 42 mg/kg per day for one month.	Mass-spectrometry-based proteomics Liquid chromatography tandem-mass spectrometry Western blot.	-Neurocognitive-related GTPase/kinase activity and chromatin proteins were impaired. -EGCG, EE, and their mixture rescued higher than 70% of the phosphoprotein impairment in Ts65Dn, and induced probable beneficial effects	Green tea extracts may restore an appropriate epigenetic profile and reverse the kinome deregulation promoting the cognitive rescue	++
Starbuck et al., 2021 [107]	To investigate the effect of GTE-EGCG for ameliorating facial dysmorphologies associated with DS	Experimental mouse models 55 Ts65Dn Cross sectional study in children 0–18 years old with DS 63 DS 4 mosaics 13 treated with EGCG 207 euploids	High (100 mg/kg/day) or low doses (30 mg/kg/day) of GTE-EGCG, were administered from embryonic Day 9 to Day 29 post-delivery, in mouse models. Children with DS received low doses of EGCG	Morphometric facial analysis evaluation by CT 3D quantitative morphometric measures of the face in mice and photogrammetry in humans	-The smallest GTE-EGCG dose ameliorated facial skeleton characteristics in a mouse model of DS. -In humans, GTE-EGCG administration restored facial dysmorphic features in children with DS if therapy was given over the first 3 years of life. -Greater GTE-EGCG dosing disrupted normal growth and augmented facial dysmorphic features in trisomy and euploid mice	GTE-EGCG modulates facial development with dose-dependent effects, but high doses have potentially detrimental effects observed in mice	+++

Abbreviations: EGCG: Epigallocatechin-gallate; DS: Down syndrome; HPLC: high performance liquid chromatography; GTE: green tea extract; EE: environmental enrichment; MWM: Morris water maze spatial learning task; NOR: novel object recognition; BB: balance beam task; WT: wild type mouse; NT: no treatment; CT: computerized tomography; NOR: novel object recognition; DNMP: T-maze delayed non-matching to place; MCSF: multivariate concentric square field; NPCs: neural precursor cells; NRF-1: nuclear respiratory factor; T-FAM: mitochondrial transcription factor; RSV: resveratrol; PN: postnatal; BrdU: bromodeoxyuridine; SYN: synaptophisin; PSD-95: post-synaptic density protein; GSK3β: glycogen synthase kinase 3β; NeuN: neuronal nuclei; GFAP: glial fibrillary acidic protein; ALT: alanine transaminase; AST aspartate transaminase; TG: triglycerides; GSH-Px: glutathione peroxidase; BMI: body mass index; fMRI: functional magnetic resonance imaging; TMS: Transcranial magnetic stimulation. ↑: increment; ↓: reduction. Quality of evidence grades: High (++++), moderate (+++), low (++), very low (+).