1. History of Sulforaphane Research in Brain Health
Sulforaphane (1-isothiocyanato-4-methylsulfonylbutane) is a potent dietary bioactive agent obtainable from cruciferous vegetables, such as broccoli, watercress, kale, cabbage, collard greens, brussels sprouts, bok choy, mustard greens, and cauliflower [1]. In cruciferous vegetables, sulforaphane is present as its precursor glucosinolate glucoraphanine [2]. When the tissues of cruciferous plants are processed by cutting, cooking, freezing, or mastication, glucoraphanine and an enzyme called myrosinase in the cruciferous vegetables are exposed to each other, which removes the glucose moiety on glucoraphanine and hydrolyzes glucoraphanine to sulforaphane [3]. β-Thioglucosidases occurring in the human gastrointestinal microbiome also convert precursor glucoraphanine into bioactive sulforaphane [4].
The study of the pharmacological effects of sulforaphane and cruciferous plants was started in 1992 by Zhang, Y. et al. [5]. They confirmed in rodent tissues that sulforaphane induces the expression of phase II detoxification enzymes, such as NAD(P)H:(quinone-acceptor) oxidoreductase 1 (NQO1) and glutathione S-transferases, indicating the possibility contributing to the detoxification mechanism of carcinogens and showing the possibility of chemoprevention [5]. Thereafter, the pharmacological potential of sulforaphane and cruciferous vegetables has been studied and published not only in cancer, but also in metabolic diseases, Helicobacter pylori infection, the nervous system, the cardiovascular system, liver, lungs, skin and even mortality. According to clinicaltrials.gov, clinical trials of 159 conditions to study the effects of sulforaphane on human health and diseases have been conducted or are in progress. In 1994, structural analogues of sulforaphane were synthesized, but none showed superior activity compared to sulforaphane [6], and no cases were applied to clinical studies.
The study on the neuroprotective effects of sulforaphane began in 2004 with studies showing the protective effects on neurons [7] and microglia [8] against oxidative stress via the activation of nuclear factor erythroid 2-related factor 2 (Nrf2), the transcription factor to induce the expression of detoxification, anti-oxidation, and immune system-modulating enzymes. Sulforaphane-induced hormetic activation of Nrf2 provides the possibility of reducing the wide range of human-related neurological pathologies in the experimental disease models on Alzheimer’s disease (AD) [9], Parkinson’s disease [10], Huntington’s disease [11], amyotrophic lateral sclerosis [12], multiple sclerosis [13], autism spectrum disorder (ASD) [14], and schizophrenia [15]. Now, sulforaphane studies are extended to various mechanisms via or not via Nrf2 and suggest the possibility of preventing or treating neurological diseases. Small-scale human clinical trials were conducted in patients with ASD and schizophrenia, and sulforaphane treatment reversed cognitive and behavior abnormalities that have been associated with ASD and schizophrenia [16,17,18,19,20]. In addition, the safety and efficacy of sulforaphane as an adjuvant to risperidone, an atypical antipsychotic agent, has recently been studied and no severe adverse events but improved irritability and hyperactivity symptoms in children with ASD were observed [21]. These findings suggest the possibility that sulforaphane reverses cognitive and behavior abnormalities in AD without severe adverse events. According to clinicaltrials.gov, there is a clinical trial underway in China using sulforaphane in patients with prodromal to mild AD (NCT04213391).
2. Evidence of Anti-AD Activity of Sulforaphane in Animals and Cells
Alzheimer’s disease is a slowly progressive neurodegenerative disease that currently has no effective treatment. The most discernible pathology that can identify AD is the extracellular formation of plaques produced by the accumulation of amyloid-β (Aβ) protein [22], and the formation of intraneuronal neurofibrillary tangles made of hyperphosphorylated and truncated tau proteins in cortical neurons [23]. These pathologies are known to occur decades before symptoms of AD appear [24]. Accumulation of Aβ and hyperphosphorylated and truncated tau proteins causes oxidative and inflammatory damage to brain tissue, which harms the function of neuronal synapses and induces neuronal degeneration, ultimately leading to symptoms of memory loss seen in AD [24].
Since there is no suitable treatment for AD, the overall goal of AD management is to reduce the incidence of disease in the target population and to ensure pre-symptomatic disease does not proceed to a later stage [25]. Several biomarkers are being studied to diagnose the likelihood of developing a disease early in the disease process, where prevention or treatment will be most effective, and to monitor a patient’s response to prevention and treatment [26]. Based on the biomarkers currently being studied for clinical practice [27,28,29,30], pre-clinical biomarkers (1) Aβ, (2) tau, (3) inflammation, (4) oxidative stress, (5) neurodegeneration, as well as (6) cognitive impairment were selected to investigate the pre-clinical anti-AD evidence of sulforaphane, and its effectiveness and plausible mechanisms. The characteristics of the AD-like cells and animal models cited in this review are described in detail in Table 1. Studies on transgenic mice [31,32,33,34,35] or cells carrying the gene mutations associated with AD [9,34], and animal models [36,37] or cells treated with Aβ [32,35,38,39,40,41,42,43] were reviewed (Table 2, Table 3, Table 4, Table 5 and Table 6).
i.c.v., intracerebroventricular; i.p., intraperitoneal; s.c., subcutaneously.
2.1. Sulforaphane and Aβ
Sulforaphane has been found to prevent Aβ production in the brains of AD-like animal models (Table 2). In the brains of PS1V97L mice, single-mutant transgenic model harboring PS1V97L, as described in Table 1, sulforaphane treatment decreased the expression of β-secretase (BACE1) and presenilin-1 (PS-1), which are involved in the sequential proteolytic cleavage of amyloid-β protein precursor (AβPP) to Aβ peptides [32]. In the study with these mice, sulforaphane inhibited the generation of all types (monomer, trimer, tetramer, hexamer, nonamer, and dodecamer) of Aβ oligomers [32], which may be associated with the inhibition of BACE1 and PS-1 expression. In another study, depletion of Nrf2 increases BACE1 and a BACE1 mRNA-stabilizing antisense RNA (BACE1-AS) expression and Aβ production and worsens cognitive deficits, and suggesting that sulforaphane-mediated Nrf2 activation decreases BACE1 and BACE1-AS expression and Aβ production and ameliorates cognitive deficits in 5×FAD and 3×Tg-AD mice [31]. On the other hand, kinetics and computational studies on direct sulforaphane effect on BACE1 showed that sulforaphane has selective and non-competitive BACE1 inhibitory activity [48].
i.p., intraperitoneally; p.o., per os (by mouth); Ace-H3K9, acetylated histone 3 lysine 9; Ace-H4K12, acetylated histone 4 lysine 12.
In the brains of APP/PS1 mice, sulforaphane decreased the increment of Aβ plaques and the mechanism underlying these effects was suggested to be associated with increased expression of p75 neurotrophin receptor (p75 NTR) via reducing the expression of histone deacetylase (HDAC) 1 and 3 [35]. p75 NTR has been reported to be significantly reduced in the brains of AD patients [50,51] and p75 NTR-ectodomain has been reported to reduce local Aβ plaques in APP/PS1 mice [52].
In the hippocampus of 3×Tg-AD mice, oral gavage of sulforaphane reduced the monomeric and polymeric forms of Aβ [34]. In this animal model, it was found that sulforaphane treatment increased the levels of heat shock protein 70 (HSP70) and the C-terminus of HSP70-interacting protein (CHIP), previously reported to influence Aβ metabolism [53], and the sulforaphane-mediated reduction in Aβ was dependent on CHIP expression, suggesting that sulforaphane clears the monomeric and polymeric forms of Aβ by upregulating CHIP [34]. Even in primary cortical neurons derived from 3×Tg-AD mice, sulforaphane increased CHIP and decreased Aβ [34]. In addition to that, sulforaphane treatment in mouse neuroblastoma N2a cells expressing APPswe decreased the levels of Aβs in both the cells and the culture medium [9].
Aβ aggregation studies with sulforaphane showed that Aβ is less prone to aggregate when sulforaphane is present [49]. Mass spectrometry experiments suggested a possible mechanism for sulforaphane’s effects, by showing that sulforaphane binds to free NH2 groups (N-terminal amino acid and lysines) in Aβ and forms three different 1:1 complexes of Aβ+sulforaphane [49].
Together, the above observations suggest that sulforaphane not only inhibits Aβ production by decreasing the expression of BACE1 and PS1 [32] but also clears Aβ molecules by inducing the expression of the HSP co-chaperone CHIP [34]. Sulforaphane-mediated activation of the Nrf2/ARE pathway negatively regulates BACE1 expression [31]. Sulforaphane-mediated upregulation of the p75 NTR at least in part through decreased expression of HDAC 1 and 3 may also contribute to reduce the increase in Aβ plaque [35]. Although further investigations are required, sulforaphane has the potential to inhibit Aβ aggregation by binding directly to Aβ in the brains of AD patients [49].
2.2. Sulforaphane and Tau
Tau is the main component of neurofibrillary tangles in AD and is a causative factor for AD [54,55]. Sulforaphane showed the ability of reducing protein levels of tau [34] and p-tau [31,32,34] in 3×Tg-AD and PS1V97L mice. In the study using 3×Tg-AD mice, sulforaphane treatment reduced tau and p-tau at the protein level, but not mRNA, suggesting post-translational modifications in tau expression [34]. Sulforaphane treatment has been observed to increase the level of HSP70 and CHIP, which has a unique binding affinity for tau and is known to play a role in tau ubiquitination and proteasome targeting for tau degradation [34,56]. In murine cortical neurons treated with Aβ oligomers, sulforaphane also decreased the Aβ-induced hyperphosphorylation of tau [32].
Although further studies are required to understand how sulforaphane affects tau biology, Aβ, Nrf2 lack, oxidative stress, and inflammation are known factors to promote tau phosphorylation [57,58,59,60], thus sulforaphane’s effect on inhibiting the production of Aβ [9,31,32,34,35,61], activating Nrf2 [9,10,31,38], and alleviating oxidative stress [9,32,37,40,43] and inflammation [9,32,37,38,39,42] may inhibit tau phosphorylation. The effects of sulforaphane on tau were overviewed in Table 2.
2.3. Sulforaphane and AD-Associated Inflammatory Biomarkers
Sulforaphane also affects inflammatory biomarkers associated with AD, as below in AD-like cell and animal models (Table 3). For example, sulforaphane treatment of PS1V97L mice resulted in decreased levels of interleukin (IL)-1β in brain tissue and tumor necrosis factor alpha (TNF-α) in the plasma [32]. Sulforaphane treatment of AD-like rat induced by Aβ reduced neuroinflammation measured through the reduction of TNF-α and IL-1β [37]. In mouse neuroblastoma N2a cells expressing APPswe, sulforaphane decreased the levels of IL-1β, IL-6, cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), and nuclear factor (NF)-κB p-p65 [9]. In human microglia-like THP-1 cells treated with Aβ, sulforaphane suppressed the activation of NLRP3 (NLRP3: NOD-like receptor, leucine-rich repeat (LRR), and pyrin domain-containing 3) inflammasome [38]. Aβ activation of the NLRP3 inflammasome in microglia has been reported to contribute to IL-1β maturation and subsequent inflammatory responses [62]. Mice that are deficient in NLRP3 are mostly protected from amyloid pathology, suppression of synaptic plasticity, and abnormal cognitive functions [62,63]. Thus, sulforaphane might play a role in reducing Aβ-induced neuroinflammation, amyloid pathology, and synaptic and cognitive dysfunction via inhibition of NLRP3. In human microglia-like THP-1 cells treated with Aβ, sulforaphane also suppressed subsequent IL-1β secretion via the dephosphorylation of signal transducers and activators of transcription-1 (STAT-1), and the activation of the Nrf2-regulated heme oxygenase-1 (HO-1) pathway [38]. microRNA (miRNA)-146a is a potential AD biomarker that appears to be selectively upregulated in the temporal cortex and hippocampus in AD [64,65] and sulforaphane treatment in THP-1 cells decreased the Aβ-induced expression of miRNA-146a [38].
i.p., intraperitoneally.
Meanwhile, it has been published that sulforaphane stimulates phagocytosis of immune cells [66,67]. According to recent research results, sulforaphane treatment was able to significantly induce the expression of formyl peptide receptor (Fpr2), which is known to regulate microglial phagocytosis and recovers the phagocytic activity of murine EOC-20 microglial cells decreased by Aβ oligomers [42]. In THP-1 cells, sulforaphane treatment attenuated the effects of Aβ induction, by reducing excessive intracellular Ca2+ levels and blocking NF-κB to rescue the decrease in Mer tyrosine kinase (MerTK) activity that is necessary for amyloid-stimulated phagocytosis [39]. Thus, sulforaphane inhibited NF-κB-mediated IL-1β and TNF-α secretion in THP-1 cells treated with Aβ [39]. As activation of Nrf2, an important sulforaphane target protein, suppresses the hyperactivation of microglia and protects against inflammatory disorders [68,69], sulforaphane-mediated activation of Nrf2 might also contribute to reducing the levels of AD-associated inflammatory biomarkers.
2.4. Sulforaphane and AD-Associated Oxidative Stress Biomarkers
Oxidative damage to brain tissue caused by accumulation of Aβ and tau proteins impairs the function of neuronal synapses, induces neuronal degeneration, and eventually causes the symptoms of memory loss seen in AD [24]. Sulforaphane inhibits the levels of AD-associated oxidative stress biomarkers in AD-like models (Table 4). Sulforaphane augmented the cell’s capacity for antioxidant defense by activating Nrf2 in N2a cells expressing APPswe [9] and in SH-SY5Y cells treated with Aβ [40,43]. In N2a cells expressing APPswe, this occurs by promotion of Nrf2 nuclear translocation by decreasing DNA methylation levels of the Nrf2 promoter [9]. In these cells, sulforaphane also caused decreased levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and increased superoxide dismutase (SOD) activity [9]. Even in PS1V97L mice and AD-like rat induced by Aβ, sulforaphane increased GSH levels and decreased MDA levels [32,37]. Crude juices of broccoli sprouts containing sulforaphane in SH-SY5Y cells treated with Aβ reduced oxidative stress by intracellular increase of glutathione (GSH), HO-1, thioredoxin (Trx), and thioredoxin reductase (TrxR) as well as NQO-1 activity, likely through the Nrf2 signaling pathway [43]. Together, these studies indicate that sulforaphane treatment attenuates biomarkers of oxidative stress that are associated with AD.
i.p., intraperitoneally; p.o., per os (by mouth); γ-GCS, γ -glutamylcysteine synthetase.
2.5. Sulforaphane and AD-Associated Biomarkers of Synaptic Damage and Neurodegeneration
Sulforaphane inhibits the levels of AD-associated biomarkers of synaptic damage and neurodegeneration in AD-like models, as well as inhibiting Aβ-induced neuronal cell death (Table 5). For example, the brain of 3×Tg-AD has low levels of brain-derived neurotrophic factor (BDNF), a neurotrophin that supports the survival of existing neurons and encourages the growth and differentiation of new neurons and synapses, but sulforaphane has been found to restore normal levels of BDNF of 3×Tg-AD mice [33]. In the frontal cortex of 3×Tg-AD mice, sulforaphane increased levels of neuronal and synaptic biomarkers, including: microtubule-associated protein 2 (MAP2), a dendritic marker and structural protein present in neurons; synaptophysin, a pre-synaptic protein; and postsynaptic density protein-95 (PSD-95), a membrane-associated protein located in neural postsynaptic densities [33]. It was reported that sulforaphane inhibits HDAC activity and increases histone-tail acetylation in 3×Tg-AD mice, thereby increasing BDNF levels and enhancing activation of the BDNF-TrkB signaling pathways, which might further facilitate neuronal differentiation and growth, promote survival of neurons, and induce synaptic plasticity and long-term potentiation [33]. Thus, sulforaphane might improve neuronal and cognitive functions, at least in part, by increasing BDNF levels epigenetically in BDNF-deficient neuronal disorders such as AD [33].
p.o., per os (by mouth).
Several studies have reported that sulforaphane prevented Aβ-induced cell death in neuron-like cells (Table 5) [32,35,40,41,43]. Treatment with broccoli sprouts juices containing sulforaphane overexpressed HSP70 and exerted a protective action against the cytotoxicity and cell death Aβ induced [43]. Sulforaphane rescued the dendritic length of the cortical neurons, which was reduced following Aβ incubation [32]. These studies indicate that sulforaphane treatment might attenuate AD pathology, as evidenced by its effect on pre-clinical biomarkers associated with synaptic damage and neurodegeneration.
2.6. Sulforaphane and Cognitive Impairment in AD-Like Animal Models
Sulforaphane ameliorated cognitive impairment in several transgenic AD-like animal models, including 5×FAD mice [31], 3×Tg-AD mice [31,34], APP/PS1 mice [35], and PS1V97L mice [32]. Additionally, sulforaphane treatment improved cognitive function in AD-like mouse and rat model induced by the administration of Aβ [36,37]. Although it is difficult to explain the exact mechanism, it is highly likely that the pharmacological effects of sulforaphane on the previously described pre-clinical AD biomarkers, Aβ, tau, inflammation, oxidative stress, and neurodegeneration have led to improvements in cognitive impairment. The types of AD-like models, the dose of sulforaphane, and cognitive recovery findings for sulforaphane are summarized in Table 6. These observations suggest that sulforaphane might be able to ameliorate cognitive impairment in AD patients.
i.p., intraperitoneally; p.o., per os (by mouth).
3. Conclusions and Future Perspectives
The anti-AD-like activity of sulforaphan has been identified in six different animal models and eight different cell models (Table 1, Table 2, Table 3, Table 4, Table 5 and Table 6). In animal models, four animal models produced by modifying AD-related genes in an animal model to create the pathology of human AD, and a mouse and a rat model made by direct intracerebroventricular (i.c.v.) injections of Aβ into the brain, which is known to induce AD-like pathology in the brain, were used to study the anti-AD-like activity of sulforaphan. In animal models, sulforaphane was administered daily or every other day, for oral administration (per os, p.o.) for 2 to 5 months, and for intraperitoneal injection (i.p.) for 7 days to 4 months. In the case of oral administration, a dose of 10–50 mg/kg, in the case of i.p. injection, 5–10 mg/kg was tried to show the anti-AD-like activity of sulforaphane. In cell models, sulforaphane showed anti-AD-like effectiveness under the conditions of 0.01 μM–10 μM, 0.5–48 h treatment.
It has been reported that AD already has pre-symptomatic pathologies in the brain 10–15 years before cognitive decline [26]. In order to apply food-derived physiologically active compounds such as sulforaphane to control AD, interventions that prevent or delay the initial onset of symptoms are necessary. For this, research to find and develop early diagnostic biomarkers capable of actively diagnosing patients with AD is essential. In 2018, the National Institute on Aging (NIA) and Alzheimer’s Association (AA) proposed a new framework to define AD diagnosis criteria based on pre-symptomatic biomarkers [70]. The research framework focuses on the diagnosis of AD with biomarkers grouped into those of Aβ deposition, pathologic tau, and neurodegeneration [70]. In this review, pre-clinical biomarkers (1) Aβ, (2) tau, (3) inflammation, (4) oxidative stress, and (5) neurodegeneration were selected based on the pre-symptomatic biomarkers currently being studied and suggested for clinical practices [27,28,29,30], and the effects and the mechanisms of sulforaphane on them were overviewed (Figure 1 and Table 2, Table 3, Table 4, Table 5 and Table 6). Most importantly, sulforaphane can prevent the production of Aβ and tau [9,31,32,34,35,48], which are the main causative factors for AD. Sulforaphane can inhibit AD-associated inflammation [9,32,37,38,39,42], oxidative stress [9,32,37,40,43], and neurodegeneration [32,33,35,40,41,43]. Thus far, multi-target effects of sulforaphane in many different cells and animal models suggest that sulforaphane consumption may reduce AD risk, raising the possibility of effective preventive strategies.
In one recent clinical trial, in which schizophrenic patients were administered sulforaphane-rich broccoli sprout extract (Kagome Co., Ltd., Nagoya, Japan), three tablets of sulforaphane per day (consisting of 30 mg of sulforaphane-glucosinolate per tablet) for 8 weeks resulted in improved cognitive function in schizophrenic patients [17]. In another clinical trial, administration of sulforaphane derived from broccoli sprouts (Johns Hopkins University, MD, USA) consisting of 50–150 μmol or 8.86–26.59 mg per day for 18 weeks improved behavior in young men with ASD [18]. Many sulforaphane supplements on the market are prepared in various ways from cruciferous plants, and the dosage, safety, and efficacy have not been verified. Among them, Avmavol® (a sulforaphane-producing dietary supplement) was studied to investigate (1) the dose-response evaluation of sulforaphane, (2) the bioavailability and mucosal bioactivity in healthy subjects, (3) the treatment effects for youth with ASDs, (4) the effects on autistic people living in New Jersey, USA, and (5) the effects on schizophrenia [71].
In-depth human studies are needed on the medical benefits of a sulforaphane-rich broccoli sprout diet. The association between the Keap1 and Nrf2 genes and cognitive function in patients with schizophrenial was studied, with an epistatic interaction between Nrf2 and Keap1 gene variants on cognitive impairment (e.g., working memory and processing speed) [72]. Since sulforaphane modifies Keap1 structure and activates Nrf2 [68], these findings suggest that the Keap1-Nrf2 system, which regulates oxidative stress and inflammation, may play a role in the cognitive impairment observed in schizophrenia. In order to study the medical benefits of a sulforaphane-rich broccoli sprout diet on cognitive impairment in AD, further studies on the intake of sulforaphane-rich broccoli sprout diet or sulforaphane in subjects at high risk of AD are needed. Besides cognitive impairment, a sulforaphane-rich broccoli sprout diet reduced colonization and attenuates gastritis in people infected with Helicobacter pylori [73] and sulforaphane-rich broccoli sprout beverages modulated the detoxification metabolism of airborne-pollutants in the body, thereby reducing their associated health risks [74]. It has also been reported that daily intake of a sulforaphane-rich broccoli sprout for 4 weeks improved defecation bowel habits in human subjects [75].
In 2003, the World Health Organization (WHO) International Agency for Research on Cancer (IARC) published a chapter on cruciferous vegetables as recommendations for cancer prevention. Whether in the form of a sulforaphane supplement or in large amounts of cruciferous vegetables, WHO recommended not to consume large amounts. It is generally not advisable for individuals to consume a diet that focuses on only one food type and should be encouraged to consistently consume a variety of cruciferous vegetables as part of their diet. On the other hand, several clinical trials showed little to no side effects when reasonable amounts of cruciferous vegetables containing sulforaphane were consumed [1].
Evidences from several animal- and cell-based studies indicate the need to pursue sulforaphane research in pre-symptomatic AD patients, which is challenging. The discovery and development of practical and inexpensive biomarkers that can diagnose pre-symptomatic AD patients is essential. Genetic polymorphism, intestinal microbiome, and body mass index (BMI) may affect the bioavailability of sulforaphane from cruciferous vegetable consumption [76,77,78,79,80,81,82,83], and through detailed follow-up studies, predictable response groups of sulforaphane might be selected for randomized controlled trial. The increase in pre-clinical evidence consistently suggests that sulforaphane has a multi-faceted neuroprotective effect on AD pathophysiology and prevents the progression of the disease.
Enlarge this image.Figure 1. Multi-faceted anti-AD-like activity of sulforaphane. Sulforaphane ameliorates cognitive impairment and decreases the level of AD biomarkers for amyloid-β, tau, inflammation, oxidative stress and neurodegeneration in AD-like animal and cell models. These anti-AD-like evidences of sulforaphane indicate the need to pursue sulforaphane research in pre-symptomatic AD patients.
Funding
This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2020R1I1A1A01054684).
Institutional Review Board Statement
Not applicable
Informed Consent Statement
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Data Availability Statement
Not applicable
Acknowledgments
I would like to thank Seungeun Kook for drawing the cruciferous plants in the Graphical Abstract.
Conflicts of Interest
The author has no conflict of interest to report.
1. Palliyaguru, D.L.; Yuan, J.M.; Kensler, T.W.; Fahey, J.W. Isothiocyanates: Translating the power of plants to people. Mol. Nutr. Food Res. 2018, 62, e1700965.
2. Thangstad, O.P.; Winge, P.; Husebye, H.; Bones, A. The myrosinase (thioglucoside glucohydrolase) gene family in Brassicaceae. Plant Mol. Biol. 1993, 23, 511-524.
3. Bones, A.M.; Rossiter, J.T. The enzymic and chemically induced decomposition of glucosinolates. Phytochemistry 2006, 67, 1053-1067.
4. Fahey, J.W.; Wehage, S.L.; Holtzclaw, W.D.; Kensler, T.W.; Egner, P.A.; Shapiro, T.A.; Talalay, P. Protection of humans by plant glucosinolates: efficiency of conversion of glucosinolates to isothiocyanates by the gastrointestinal microflora. Cancer Prev. Res. 2012, 5, 603-611.
5. Zhang, Y.; Talalay, P.; Cho, C.G.; Posner, G.H. A major inducer of anticarcinogenic protective enzymes from broccoli: isolation and elucidation of structure. Proc. Natl. Acad. Sci. USA 1992, 89, 2399-2403.
6. Posner, G.H.; Cho, C.G.; Green, J.V.; Zhang, Y.; Talalay, P. Design and synthesis of bifunctional isothiocyanate analogs of sulforaphane: correlation between structure and potency as inducers of anticarcinogenic detoxication enzymes. J. Med. Chem. 1994, 37, 170-176.
7. Kraft, A.D.; Johnson, D.A.; Johnson, J.A. Nuclear factor E2-related factor 2-dependent antioxidant response element activation by tert-butylhydroquinone and sulforaphane occurring preferentially in astrocytes conditions neurons against oxidative insult. J. Neurosci. 2004, 24, 1101-1112.
8. Konwinski, R.R.; Haddad, R.; Chun, J.A.; Klenow, S.; Larson, S.C.; Haab, B.B.; Furge, L.L. Oltipraz, 3H-1,2-dithiole-3-thione, and sulforaphane induce overlapping and protective antioxidant responses in murine microglial cells. Toxicol. Lett. 2004, 153, 343-355.
9. Zhao, F.; Zhang, J.; Chang, N. Epigenetic modification of Nrf2 by sulforaphane increases the antioxidative and anti-inflammatory capacity in a cellular model of Alzheimer's disease. Eur. J. Pharmacol. 2018, 824, 1-10.
10. Zhou, Q.; Chen, B.; Wang, X.; Wu, L.; Yang, Y.; Cheng, X.; Hu, Z.; Cai, X.; Yang, J.; Sun, X.; et al. Sulforaphane protects against rotenone-induced neurotoxicity in vivo: Involvement of the mTOR, Nrf2 and autophagy pathways. Sci. Rep. 2016, 6, 32206.
11. Liu, Y.; Hettinger, C.L.; Zhang, D.; Rezvani, K.; Wang, X.; Wang, H. Sulforaphane enhances proteasomal and autophagic activities in mice and is a potential therapeutic reagent for Huntington's disease. J. Neurochem. 2014, 129, 539-547.
12. Vargas, M.R.; Johnson, D.A.; Sirkis, D.W.; Messing, A.; Johnson, J.A. Nrf2 activation in astrocytes protects against neurodegeneration in mouse models of familial amyotrophic lateral sclerosis. J. Neurosci. 2008, 28, 13574-13581.
13. Li, B.; Cui, W.; Liu, J.; Li, R.; Liu, Q.; Xie, X.H.; Ge, X.L.; Zhang, J.; Song, X.J.; Wang, Y.; et al. Sulforaphane ameliorates the development of experimental autoimmune encephalomyelitis by antagonizing oxidative stress and Th17-related inflammation in mice. Exp. Neurol. 2013, 250, 239-249.
14. Nadeem, A.; Ahmad, S.F.; Al-Ayadhi, L.Y.; Attia, S.M.; Al-Harbi, N.O.; Alzahrani, K.S.; Bakheet, S.A. Differential regulation of Nrf2 is linked to elevated inflammation and nitrative stress in monocytes of children with autism. Psychoneuroendocrinology 2020, 113, 104554.
15. Shirai, Y.; Fujita, Y.; Hashimoto, K. Effects of the antioxidant sulforaphane on hyperlocomotion and prepulse inhibition deficits in mice after phencyclidine administration. Clin. Psychopharmacol. Neurosci. 2012, 10, 94-98.
16. Lynch, R.; Diggins, E.L.; Connors, S.L.; Zimmerman, A.W.; Singh, K.; Liu, H.; Talalay, P.; Fahey, J.W. Sulforaphane from broccoli reduces symptoms of autism: A follow-up case series from a randomized double-blind Study. Glob. Adv. Health Med. 2017, 6, 2164957x17735826.
17. Shiina, A.; Kanahara, N.; Sasaki, T.; Oda, Y.; Hashimoto, T.; Hasegawa, T.; Yoshida, T.; Iyo, M.; Hashimoto, K. An open study of sulforaphane-rich broccoli sprout extract in patients with schizophrenia. Clin. Psychopharmacol Neurosci. 2015, 13, 62-67.
18. Singh, K.; Connors, S.L.; Macklin, E.A.; Smith, K.D.; Fahey, J.W.; Talalay, P.; Zimmerman, A.W. Sulforaphane treatment of autism spectrum disorder (ASD). Proc. Natl. Acad. Sci. USA 2014, 111, 15550-15555.
19. Bent, S.; Lawton, B.; Warren, T.; Widjaja, F.; Dang, K.; Fahey, J.W.; Cornblatt, B.; Kinchen, J.M.; Delucchi, K.; Hendren, R.L. Identification of urinary metabolites that correlate with clinical improvements in children with autism treated with sulforaphane from broccoli. Mol. Autism. 2018, 9, 35.
20. Singh, K.; Zimmerman, A.W. Sulforaphane treatment of young men with autism spectrum disorder. CNS Neurol. Disord. Drug Targets 2016, 15, 597-601.
21. Momtazmanesh, S.; Amirimoghaddam-Yazdi, Z.; Moghaddam, H.S.; Mohammadi, M.R.; Akhondzadeh, S. Sulforaphane as an adjunctive treatment for irritability in children with autism spectrum disorder: A randomized, double-blind, placebo-controlled clinical trial. Psychiatry Clin. Neurosci. 2020, 74, 398-405.
22. DeTure, M.A.; Dickson, D.W. The neuropathological diagnosis of Alzheimer's disease. Mol. Neurodegener 2019, 14, 32.
23. Palmqvist, S.; Insel, P.S.; Stomrud, E.; Janelidze, S.; Zetterberg, H.; Brix, B.; Eichenlaub, U.; Dage, J.L.; Chai, X.; Blennow, K.; et al. Cerebrospinal fluid and plasma biomarker trajectories with increasing amyloid deposition in Alzheimer's disease. EMBO Mol. Med. 2019, 11, e11170.
24. Villemagne, V.L.; Burnham, S.; Bourgeat, P.; Brown, B.; Ellis, K.A.; Salvado, O.; Szoeke, C.; Macaulay, S.L.; Martins, R.; Maruff, P.; et al. Amyloid-β deposition, neurodegeneration, and cognitive decline in sporadic Alzheimer's disease: a prospective cohort study. Lancet Neurol. 2013, 12, 357-367.
25. Barcikowska, M. Guideline on the Clinical Investigation of Medicines for the Treatment of Alzheimer's Disease; CPMP/EWP/553/95 Rev.2; European Medicines Agency: London, UK, 2018.
26. Shaw, L.M.; Korecka, M.; Clark, C.M.; Lee, V.M.; Trojanowski, J.Q. Biomarkers of neurodegeneration for diagnosis and monitoring therapeutics. Nat. Rev. Drug Discov. 2007, 6, 295-303.
27. Zetterberg, H.; Bendlin, B.B. Biomarkers for Alzheimer's disease-preparing for a new era of disease-modifying therapies. Mol. Psychiatry 2021, 26, 296-308.
28. Collin, F.; Cheignon, C.; Hureau, C. Oxidative stress as a biomarker for Alzheimer's disease. Biomark. Med. 2018, 12, 201-203.
29. Khoury, R.; Ghossoub, E. Diagnostic biomarkers of Alzheimer's disease: A state-of-the-art review. Biomark. Neuropsychiatry 2019, 1, 100005.
30. Marcourakis, T.; Camarini, R.; Kawamoto, E.M.; Scorsi, L.R.; Scavone, C. Peripheral biomarkers of oxidative stress in aging and Alzheimer's disease. Dement. Neuropsychol. 2008, 2, 2-8.
31. Bahn, G.; Park, J.-S.; Yun, U.J.; Lee, Y.J.; Choi, Y.; Park, J.S.; Baek, S.H.; Choi, B.Y.; Cho, Y.S.; Kim, H.K.; et al. NRF2/ARE pathway negatively regulates BACE1 expression and ameliorates cognitive deficits in mouse Alzheimer's models. Proc. Natl. Acad. Sci. USA 2019, 116, 12516-12523.
32. Hou, T.T.; Yang, H.Y.; Wang, W.; Wu, Q.Q.; Tian, Y.R.; Jia, J.P. Sulforaphane inhibits the generation of amyloid-β oligomer and promotes spatial learning and memory in Alzheimer's disease (PS1V97L) transgenic mice. J. Alzheimers Dis. 2018, 62, 1803-1813.
33. Kim, J.; Lee, S.; Choi, B.R.; Yang, H.; Hwang, Y.; Park, J.H.; LaFerla, F.M.; Han, J.S.; Lee, K.W.; Kim, J. Sulforaphane epigenetically enhances neuronal BDNF expression and TrkB signaling pathways. Mol. Nutr. Food Res. 2017, 61, 2.
34. Lee, S.; Choi, B.R.; Kim, J.; LaFerla, F.M.; Park, J.H.Y.; Han, J.S.; Lee, K.W.; Kim, J. Sulforaphane upregulates the heat shock protein co-chaperone CHIP and clears amyloid-β and tau in a mouse model of Alzheimer's disease. Mol. Nutr. Food Res. 2018, 62, e1800240.
35. Zhang, J.; Zhang, R.; Zhan, Z.; Li, X.; Zhou, F.; Xing, A.; Jiang, C.; Chen, Y.; An, L. Beneficial effects of sulforaphane treatment in Alzheimer's disease may be mediated through reduced HDAC1/3 and increased P75NTR expression. Front Aging Neurosci. 2017, 9, 121.
36. Kim, H.V.; Kim, H.Y.; Ehrlich, H.Y.; Choi, S.Y.; Kim, D.J.; Kim, Y. Amelioration of Alzheimer's disease by neuroprotective effect of sulforaphane in animal model. Amyloid 2013, 20, 7-12.
37. Wang, W.; Wei, C.; Quan, M.; Li, T.; Jia, J. Sulforaphane reverses the amyloid-β oligomers induced depressive-like behavior. J Alzheimers Dis. 2020, 78, 127-137.
38. An, Y.W.; Jhang, K.A.; Woo, S.Y.; Kang, J.L.; Chong, Y.H. Sulforaphane exerts its anti-inflammatory effect against amyloid-β peptide via STAT-1 dephosphorylation and activation of Nrf2/HO-1 cascade in human THP-1 macrophages. Neurobiol. Aging 2016, 38, 1-10.
39. Jhang, K.A.; Park, J.S.; Kim, H.S.; Chong, Y.H. Sulforaphane rescues amyloid-β peptide-mediated decrease in MerTK expression through its anti-inflammatory effect in human THP-1 macrophages. J. Neuroinflammation 2018, 15, 75.
40. Lee, C.; Park, G.H.; Lee, S.R.; Jang, J.H. Attenuation of β-amyloid-induced oxidative cell death by sulforaphane via activation of NF-E2-related factor 2. Oxid. Med. Cell Longev. 2013, 2013, 313510.
41. Park, H.M.; Kim, J.A.; Kwak, M.K. Protection against amyloid-β cytotoxicity by sulforaphane: role of the proteasome. Arch Pharm. Res. 2009, 32, 109-115.
42. Chilakala, R.R.; Manchikalapudi, A.L.; Kumar, A.; Sunkaria, A. Sulforaphane attenuates Aβ oligomers mediated decrease in phagocytic activity of microglial cells. Neuroscience 2020, 429, 225-234.
43. Masci, A.; Mattioli, R.; Costantino, P.; Baima, S.; Morelli, G.; Punzi, P.; Giordano, C.; Pinto, A.; Donini, L.M.; d'Erme, M.; et al. Neuroprotective effect of Brassica oleracea sprouts crude juice in a cellular model of Alzheimer's disease. Oxid. Med. Cell Longev. 2015, 2015, 781938.
44. Oakley, H.; Cole, S.L.; Logan, S.; Maus, E.; Shao, P.; Craft, J.; Guillozet-Bongaarts, A.; Ohno, M.; Disterhoft, J.; Van Eldik, L.; et al. Intraneuronal β-amyloid aggregates, neurodegeneration, and neuron loss in transgenic mice with five familial Alzheimer's disease mutations: potential factors in amyloid plaque formation. J. Neurosci. 2006, 26, 10129-10140.
45. Oddo, S.; Caccamo, A.; Shepherd, J.D.; Murphy, M.P.; Golde, T.E.; Kayed, R.; Metherate, R.; Mattson, M.P.; Akbari, Y.; LaFerla, F.M. Triple-transgenic model of Alzheimer's disease with plaques and tangles: intracellular Abeta and synaptic dysfunction. Neuron 2003, 39, 409-421.
46. Jankowsky, J.L.; Slunt, H.H.; Gonzales, V.; Jenkins, N.A.; Copeland, N.G.; Borchelt, D.R. APP processing and amyloid deposition in mice haplo-insufficient for presenilin 1. Neurobiol Aging 2004, 25, 885-892.
47. Wang, Y.; Cheng, Z.; Qin, W.; Jia, J. Val97Leu mutant presenilin-1 induces tau hyperphosphorylation and spatial memory deficit in mice and the underlying mechanisms. J. Neurochem. 2012, 121, 135-145.
48. Youn, K.; Yoon, J.H.; Lee, N.; Lim, G.; Lee, J.; Sang, S.; Ho, C.T.; Jun, M. Discovery of sulforaphane as a potent BACE1 inhibitor based on kinetics and computational studies. Nutrients 2020, 12, 10.
49. Nagaveni, V.; Lakshmi, V.V.; Prabhakar, S. Sulforaphane interaction with amyloid-β 1-40 peptide studied by electrospray ionization mass spectrometry. Rapid. Commun. Mass Spectrom. 2014, 28, 2171-2180.
50. Kordower, J.H.; Gash, D.M.; Bothwell, M.; Hersh, L.; Mufson, E.J. Nerve growth factor receptor and choline acetyltransferase remain colocalized in the nucleus basalis (Ch4) of Alzheimer's patients. Neurobiol Aging 1989, 10, 67-74.
51. Salehi, A.; Ocampo, M.; Verhaagen, J.; Swaab, D.F. P75 neurotrophin receptor in the nucleus basalis of meynert in relation to age, sex, and Alzheimer's disease. Exp. Neurol. 2000, 161, 245-258.
52. Wang, Y.J.; Wang, X.; Lu, J.J.; Li, Q.X.; Gao, C.Y.; Liu, X.H.; Sun, Y.; Yang, M.; Lim, Y.; Evin, G.; et al. p75NTR regulates Aβ deposition by increasing Aβ production but inhibiting Aβ aggregation with its extracellular domain. J. Neurosci. 2011, 31, 2292-2304.
53. Kumar, P.; Ambasta, R.K.; Veereshwarayya, V.; Rosen, K.M.; Kosik, K.S.; Band, H.; Mestril, R.; Patterson, C.; Querfurth, H.W. CHIP and HSPs interact with β-APP in a proteasome-dependent manner and influence Aβ metabolism. Hum. Mol. Genet. 2007, 16, 848-864.
54. Du, X.; Wang, X.; Geng, M. Alzheimer's disease hypothesis and related therapies. Transl Neurodegener 2018, 7, 2.
55. Schelke, M.W.; Attia, P.; Palenchar, D.J.; Kaplan, B.; Mureb, M.; Ganzer, C.A.; Scheyer, O.; Rahman, A.; Kachko, R.; Krikorian, R.; et al. Mechanisms of risk reduction in the clinical practice of Alzheimer's disease prevention. Front Aging Neurosci. 2018, 10, 96.
56. Petrucelli, L.; Dickson, D.; Kehoe, K.; Taylor, J.; Snyder, H.; Grover, A.; De Lucia, M.; McGowan, E.; Lewis, J.; Prihar, G.; et al. CHIP and Hsp70 regulate tau ubiquitination, degradation and aggregation. Hum. Mol. Genet. 2004, 13, 703-714.
57. Escudero-Lourdes, C. Toxicity mechanisms of arsenic that are shared with neurodegenerative diseases and cognitive impairment: Role of oxidative stress and inflammatory responses. Neurotoxicology 2016, 53, 223-235.
58. Viola, K.L.; Klein, W.L. Amyloid-β oligomers in Alzheimer's disease pathogenesis, treatment, and diagnosis. Acta Neuropathol. 2015, 129, 183-206.
59. Jo, C.; Gundemir, S.; Pritchard, S.; Jin, Y.N.; Rahman, I.; Johnson, G.V.W. Nrf2 reduces levels of phosphorylated tau protein by inducing autophagy adaptor protein NDP52. Nat. Commun. 2014, 5, 3496.
60. Rojo, A.I.; Pajares, M.; Rada, P.; Nuñez, A.; Nevado-Holgado, A.J.; Killik, R.; Van Leuven, F.; Ribe, E.; Lovestone, S.; Yamamoto, M.; et al. NRF2 deficiency replicates transcriptomic changes in Alzheimer's patients and worsens APP and TAU pathology. Redox Biol. 2017, 13, 444-451.
61. Zhang, R.; Miao, Q.W.; Zhu, C.X.; Zhao, Y.; Liu, L.; Yang, J.; An, L. Sulforaphane ameliorates neurobehavioral deficits and protects the brain from amyloid-β deposits and peroxidation in mice with Alzheimer-like lesions. Am. J. Alzheimers Dis. Other Demen 2015, 30, 183-191.
62. Halle, A.; Hornung, V.; Petzold, G.C.; Stewart, C.R.; Monks, B.G.; Reinheckel, T.; Fitzgerald, K.A.; Latz, E.; Moore, K.J.; Golenbock, D.T. The NALP3 inflammasome is involved in the innate immune response to amyloid-β. Nat. Immunol. 2008, 9, 857-865.
63. Heneka, M.T.; Kummer, M.P.; Stutz, A.; Delekate, A.; Schwartz, S.; Vieira-Saecker, A.; Griep, A.; Axt, D.; Remus, A.; Tzeng, T.C.; et al. NLRP3 is activated in Alzheimer's disease and contributes to pathology in APP/PS1 mice. Nature 2013, 493, 674-678.
64. Muller, M.; Kuiperij, H.B.; Claassen, J.A.; Kusters, B.; Verbeek, M.M. MicroRNAs in Alzheimer's disease: differential expression in hippocampus and cell-free cerebrospinal fluid. Neurobiol. Aging 2014, 35, 152-158.
65. Sethi, P.; Lukiw, W.J. Micro-RNA abundance and stability in human brain: specific alterations in Alzheimer's disease temporal lobe neocortex. Neurosci. Lett. 2009, 459, 100-104.
66. Suganuma, H.; Fahey, J.W.; Bryan, K.E.; Healy, Z.R.; Talalay, P. Stimulation of phagocytosis by sulforaphane. Biochem. Biophys. Res. Commun. 2011, 405, 146-151.
67. Bewley, M.A.; Budd, R.C.; Ryan, E.; Cole, J.; Collini, P.; Marshall, J.; Kolsum, U.; Beech, G.; Emes, R.D.; Tcherniaeva, I.; et al. Opsonic phagocytosis in chronic obstructive pulmonary disease is enhanced by Nrf2 agonists. Am. J. Respir. Crit. Care Med. 2018, 198, 739-750.
68. Kim, J.; Cha, Y.N.; Surh, Y.J. A protective role of nuclear factor-erythroid 2-related factor-2 (Nrf2) in inflammatory disorders. Mutat. Res. 2010, 690, 12-23.
69. Koh, K.; Kim, J.; Jang, Y.J.; Yoon, K.; Cha, Y.; Lee, H.J.; Kim, J. Transcription factor Nrf2 suppresses LPS-induced hyperactivation of BV-2 microglial cells. J. Neuroimmunol. 2011, 233, 160-167.
70. Jack, C.R., Jr.; Bennett, D.A.; Blennow, K.; Carrillo, M.C.; Dunn, B.; Haeberlein, S.B.; Holtzman, D.M.; Jagust, W.; Jessen, F.; Karlawish, J.; et al. NIA-AA research framework: Toward a biological definition of Alzheimer's disease. Alzheimers Dement 2018, 14, 535-562.
71. ClinicalTrials.gov. clinicaltrials.gov. Available online: https://www.clinicaltrials.gov/ (accessed on 13 March 2021).
72. Shirai, Y.; Fujita, Y.; Hashimoto, R.; Ohi, K.; Yamamori, H.; Yasuda, Y.; Ishima, T.; Suganuma, H.; Ushida, Y.; Takeda, M.; et al. Dietary intake of sulforaphane-rich broccoli sprout extracts during juvenile and adolescence can prevent phencyclidine-induced cognitive deficits at adulthood. PLoS ONE 2015, 10, e0127244.
73. Yanaka, A.; Fahey, J.W.; Fukumoto, A.; Nakayama, M.; Inoue, S.; Zhang, S.; Tauchi, M.; Suzuki, H.; Hyodo, I.; Yamamoto, M. Dietary sulforaphane-rich broccoli sprouts reduce colonization and attenuate gastritis in Helicobacter pylori-infected mice and humans. Cancer Prev. Res. 2009, 2, 353-360.
74. Kensler, T.W.; Ng, D.; Carmella, S.G.; Chen, M.; Jacobson, L.P.; Muñoz, A.; Egner, P.A.; Chen, J.G.; Qian, G.S.; Chen, T.Y.; et al. Modulation of the metabolism of airborne pollutants by glucoraphanin-rich and sulforaphane-rich broccoli sprout beverages in Qidong, China. Carcinogenesis 2012, 33, 101-107.
75. Yanaka, A. Daily intake of broccoli sprouts normalizes bowel habits in human healthy subjects. J. Clin. Biochem. Nutr. 2018, 62, 75-82.
76. Gigliotti, J.C.; Tin, A.; Pourafshar, S.; Cechova, S.; Wang, Y.T.; Sung, S.J.; Bodonyi-Kovacs, G.; Cross, J.V.; Yang, G.; Nguyen, N.; et al. GSTM1 deletion exaggerates kidney injury in experimental mouse models and confers the protective effect of cruciferous vegetables in mice and humans. J. Am. Soc. Nephrol. 2020, 31, 102-116.
77. Tian, S.; Liu, X.; Lei, P.; Zhang, X.; Shan, Y. Microbiota: a mediator to transform glucosinolate precursors in cruciferous vegetables to the active isothiocyanates. J. Sci. Food Agric. 2018, 98, 1255-1260.
78. Nugon-Baudon, L.; Rabot, S.; Wal, J.M.; Szylit, O. Interactions of the intestinal microflora with glucosinolates in rapeseed meal toxicity: First evidence of an intestinal lactobacillus possessing a myrosinase-like activity in vivo. J. Sci. Food Agric. 1990, 52, 547-559.
79. Elfoul, L.; Rabot, S.; Khelifa, N.; Quinsac, A.; Duguay, A.; Rimbault, A. Formation of allyl isothiocyanate from sinigrin in the digestive tract of rats monoassociated with a human colonic strain of Bacteroides thetaiotaomicron. FEMS Microbiol. Lett. 2001, 197, 99-103.
80. Cheng, D.L.; Hashimoto, K.; Uda, Y. In vitro digestion of sinigrin and glucotropaeolin by single strains of Bifidobacterium and identification of the digestive products. Food Chem Toxicol. 2004, 42, 351-357.
81. Luang-In, V.; Narbad, A.; Nueno-Palop, C.; Mithen, R.; Bennett, M.; Rossiter, J.T. The metabolism of methylsulfinylalkyl- and methylthioalkyl-glucosinolates by a selection of human gut bacteria. Mol. Nutr. Food Res. 2014, 58, 875-883.
82. Tani, N.; Ohtsuru, M.; Hata, T. Purification and general characteristics of bacterial myrosinase produced by enterobacter cloacae. Agr. Biol. Chem. 1974, 38, 1623-1630.
83. Charron, C.S.; Vinyard, B.T.; Ross, S.A.; Seifried, H.E.; Jeffery, E.H.; Novotny, J.A. Absorption and metabolism of isothiocyanates formed from broccoli glucosinolates: effects of BMI and daily consumption in a randomised clinical trial. Br. J. Nutr. 2018, 120, 1370-1379.
Jiyoung Kim
Center for Food and Bioconvergence, College of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea
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