Over the years, scientific researches have validated the healing benefits of many psychopharmacotherapeutic plant-based drugs to ameliorate psychiatric disorders. In contrast, the use of chemical procedures to isolate and purify specific compounds from plants that have been used to treat autism spectrum disorders (ASDs) and its clinical features may contribute to improve the quality of life of many patients. Also, herbal pharmacological treatments could improve the core symptoms of autism with fewer side effects. This review will focus on the uses and actions of phytopharmaceuticals in the behavioral conditions of ASDs. A large number of natural compound-based plant drugs have been tested in murine models of autism and in clinical trials with remarkable success in reversing the core and associated behaviors with autism such as flavonoids, cannabinoids, curcuminoids, piperine, resveratrol, and bacosides. This plant-based drug alternative is safer given that many psychiatric disorders and neurodegenerative pathologies do not often respond well to currently prescribed medications or have significant side effects. However, it is noteworthy to consider the need for large clinical trials to determine safety and efficacy. Many results are based on case reports or small size samples, and often the studies are open label. Standardization of procedures (i.e., purity and concentrations) and quality controls are strictly required to ensure the absence of side effects.
Phytopharmaceuticals in the Modulation of Human Behavior
The seeking of natural compound plant based drugs (phytopharmaceuticals) increased significantly in recent years.1 Phytopharmaceutical drugs are also known as herbal medicinal products.2 According to U.S. Food and Drug Administration Botanical Drug Development Guidance, a botanical product could be classified as a food (including a dietary supplement), drug (including a biological drug), medical device, or cosmetic under the Federal Food, Drug, and Cosmetic Act.3 According to European Union legislation, the term “herbal medicinal products” are any medicine that contains a herbal base, one or more herbal preparations, or one or more of these herbal substances in combination with one or more such herbal preparations (DIRECTIVE 2004/24/EC).
Among the different diseases in which research on phytopharmaceuticals has been focused, special emphasis is given to the herbal extracts able to modulate the human behaviors. For example, Salvia sp. oil extracts have proven to be efficacy on cognitive ability, memory, and cognition.4–6 Salvinorin A is the major component of Salvia divinorum,7 and it has antinociceptive and antidepressant activities8; however, it also has intense hallucinogenic and dissociative effects.9 It has demonstrated the efficacy of three herbal extracts (lavender oil, Hypericum extract, and Ginkgo biloba extract) in treating anxiety, depression, and dementia, in elderly patients.10 Among the plant-derived phytochemicals, Sage (Salvia lavandulaefolia/officinalis), Lemon balm (Melissa officinalis), and Rosemary (Rosmarinus officinalis) show the most cognition-enhancing properties.11 Ginseng extract in more than 4% ginsenosides per oral dose also improves attention deficit, information processing, cognition, auditory reaction time, social skills, and mental health.12 Lemon balm shows mood modulation ability, as it is also able to ameliorate the negative induced mood effects.13
In dementia patients, essential oils have effects on agitation and aggression.12 It is very interesting that the essential oil of M. officinalis (Lemon balm), as aromatherapy, is able to reduce the agitation in people affected by severe dementia.14Hypericum perforatum (or St. John’s wort, from its popular name) has shown some efficacy in treating depression; in terms of efficacy and adverse effects, it has the same molecular target of selective serotonin reuptake inhibitors in patients with chronic depressive disorder.15Piper methysticum (kava) has been effectively used in treating generalized anxiety disorders.16 Kava also shows efficacy against obsessive-compulsive, phobic, and panic disorders, whereas Passiflora incarnata (Passionflower), Scutellaria lateriflora (Skullcap), and Zizyphus jujuba (Jujube) have been used for anxiety disorders.17 The green tea extracted polyphenol catechin is able to protect against reduced cognitive functions related to aging.18 Likely, resveratrol (RSV) and curcumin are the best known phytochemicals used in cognitive decline.19
Yokukansan, a traditional herbal medicine in Japan, is effective in treating behavioral and psychological symptoms associated to dementia.20 Fufangdanshen (Radix Salviae miltiorrhizae) tablets, a traditional Chinese medicine used to improve memory, have been positively investigated in treating cognitive symptoms in vascular dementia patients.21 In a research of mild cognitive impairments, 95 patients were treated with Dangguijagyag-san and showed improvements in cognitive skills without adverse events.22 Several phytopharmaceuticals have been proposed to treat brain inflammation. This process is common and highly prevalent in psychiatric disorders, such as depression and autism.23 The anxiolytic activity of Matricaria recutita, G. biloba, Passiflora incarnata, and S. lateriflora and antidepressant effects of Echium amoenum, Crocus sativus, and Rhodiola rosea have been investigated in several clinical trials, showing preliminary ameliorating effects, without the risk of harmful side effects.24,25 A new branch or research area is establishing: the herbomics,24 the complex, genetic, and epigenetic modes of action of the herbal compounds.
Valerian (Valeriana officinalis) has been proposed for the treatment of anxiety.26 Moreover, valerian root in association with Lemon balm is effective in treating attention deficit disorders, hyperactivity, and impulsiveness in children.27 This mixed compound is able to improve concentration, hyperactivity, and impulsiveness in primary school children.28 It has been proposed that the main constituents of valerian, the valerenic acid and valerenol, are able to bind a specific site on gamma-aminobutyric acid receptors with agonist activity.29 It has also been demonstrated that valerian was most effective in reducing sleep problems in children with hyperactivity.30
Sleep problems, anxiety, and hyperactivity are linked to autism spectrum disorders (ASDs), a neurodevelopmental disorder characterized by stereotyped behaviors, language deficits, and difficulties in communication and social interaction.31Considering that several neurodegenerative diseases and psychiatric disorders are usually poorly responsive to the current prescribed drugs or have important side effects,32 the herbal therapies/supplementations could enhance the therapeutic effect of drug treatments with less adverse events.33 Therefore, this review will focus on uses of the phytopharmaceuticals and actions in behavioral conditions of ASDs.
Phytopharmaceuticals and ASDs
Some individuals with ASDs have been exposed to environmental pro-oxidant factors such as heavy metals, pharmaceutical compounds (thalidomide, valproic acid, and retinoic acid), air pollutants, chemical and toxins, and bacterial and viral infections; those might be the triggering of oxidative stress in autism.34 To decrease levels of oxidative stress, green tea therapy using Camellia sinensis extract has been proposed. This plant is an important dietary source of polyphenols, specifically flavonoids. The main flavonoids present in C. sinensis extract include catechins (flavan-3-ols) such as epigallocatechin-3-gallate, epigallocatechin, epicatechin-3-gallate, and epicatechin; it also contains gallic acid, chlorogenic acid, caffeic acid, and flavonol derivatives such as kaempferol, myricetin, and quercetin, which are other constituents of green tea.35,36
The chemical structure of the polyphenols allows them to cross through the blood–brain barrier,37–47 and its intake has been associated with neuronal protection against toxicant agents’ impact. Green tea research shows an amelioration of behavioral aberrations by a daily intake dose of the extract; doses range from 75 to 300 mg/kg after postnatal day 14 up to day 40 in animals with valproate induced autism.37 Green tea effects have been well documented; due to upregulation mechanism of inhibitory neurotransmitters, it shows anxiolytic and sedative effects; this might be possible by neuromodulation of dopamine and serotonin in specific brain areas, increase in N-Methyl-D-aspartate (NMDA)-independent CA1-LTP (cornu Ammo 1 Pyramidal Neuro- long-term potentiation), and decrease in NMDA-dependent CA1-LPT. Besides, green tea extract decreases tumor necrosis factor-alpha (TNF-α) and C-reactive protein, both active cytokines in the acute-phase inflammatory process; this strongly suggests an anti-inflammatory mechanism of action.48
A green tea study using mice pups performed behavioral tests to assess nociception activity, motor coordination, exploratory activity, anxiety disorders, and cognitive skills, in which human doses are based in body surface area calculation,49 with doses from 6.08 mg to 24.32 mg/kg. Green tea doses might be used as dietary supplement due to its clinical recommendation as preventive. This study shows significant results in the improvement of behavioral assessments especially with 300 mg/kg of green tea extract; histological findings reveal the presence of a distinct Purkinje layer and cells after treatment with green tea, and this confirms that green tea at that dose has neuroprotective effects.
The cytoprotective action that green tea exerts in neuronal cells can be asserted and could be efficacious in the treatment of autism through early intervention with dietary substances.50 Among the adverse effects of green tea, it has been found that higher doses should not be taken with other drugs metabolized by CYP1A2, CYP2C9, CYP3A4, CYP1A1, CYP2B6, CYP2C8, and CYP2D6.51,52 The mechanism that explains the hepatotoxicity of catechins of green tea remains unclear, but factors related to the patient are becoming predominant.53
In recent years, ASD cases have been increasing from 1/20 live births in 200654 up to 1/68 live births in 201455; nonetiological causes have been determined yet, which hampered the development of treatments that contributes to alleviate ASD symptoms. Nowadays, phytopharmaceutical treatments have been tried out in clinical trials; one of the flavones that shows anti-inflammatory, antioxidant, antiallergy, and neuroprotective effects is Luteolin (NeuroProtek®) with a mixture of the flavonoids Quercetin and Rutin, which are structurally related in a liposomal formulation,56 these compounds have potent inhibition of histamine, interleukin (IL)-6 from microglia,44 IL-8, TNF, and tryptase release from human mast cells,57 and they also block mercury-induced cytokine release from human mast cells.58,59
Luteolin formulation (NeuroProtek) research in children with ASD states the improvement of ASD symptoms in those who used the formula for at least 4 months; 75% (28/37) of patients reported significant improvement in features such as their stool shape, smell, form, color, and habits within a period of 2 to 3 weeks. In most of the children (19/37) “Allergic-like” skin symptoms were also significantly reduced. Patients also improved in about 50% eye contact (15/37) and attention (12/37). Besides, 30%–50% of patients showed learned tasks (15/37) and social interactions (14/37) as significant improvement results. Remarkably, children started speaking words or short sentences in 10% of patients (4/37). No improvements in hyperactivity or aggressiveness were registered. Indeed, hyperactivity increased in 2/37 children and decreased after 2 weeks with lower doses.56 Based on this evidence researchers hypothesize if autism is kind of a brain allergy?60
Anti-inflammatory flavonoid open-label pilot study assessed a formulation that contains Luteolin, Quercetin, and Rutin, which is a form of quercetin glycoside in concentrations of 100/70/30 mg/capsule, respectively, extracted from Chamomile and Sophora japonica leaf. This formula shows its behavioral effects in children with autism (n = 50) enrolled for 26 weeks, assessing the effectiveness and tolerability. Significant improvements were registered in adaptive functioning such as communication, daily living, and social skills (p < 0.005). In addition to the reduction (26.6%–34.8%) in Aberrant Behavior Checklist subscale scores in overall behavior, there was also a transitory increased irritability from 1 to 8 weeks in 27/50 participants.61
Another anti-inflammatory lipid molecule with activity in acute is N-Palmitoylethanolamide (PEA), which behaves as a signaling molecule.62 There are a few studies dealing with phytopharmaceuticals in ASDs; another experimental research asserts the association of this ultramicronized lipid with Luteolin (co-ultraPEA-LUT®) in a murine model of autism, which is efficient in ameliorating nonsocial autistic symptoms. It also reduces pro-inflammatory molecules such as GFAP, Nitrotyrosine, and nuclear factor kappa B [NF-κB], increases neuroplasticity and neurogenesis, and modulates the apoptosis mechanism in several brain regions (cerebellum and hippocampus).63 The results of the assess co-ultraPEA-LUT assert this lipid combination as a potential biomedical therapy in the treatment of autism.
It has been reported that luteolin, to exert a hepatotoxic role, needs a connection with the cytochrome CYP3A-mediated reactive metabolite formation, and the direct glutathione depletion is an initiating event in luteolin mediated cytotoxicity in hepatocytes in murine models.64 In addition, previous studies have reported that luteolin can trigger the mitochondrial pathway of apoptosis by increasing the activity of caspases.65
Recently, the endocannabinoid (EC) system has gained great interest in ASD research.66 This endogenous system of signaling molecules consists of arachidonic acid compounds derived, associated enzymes, and receptors.67 The main compounds are 2-AG and AEA, which are able to bind and activate the G-protein-coupled cannabinoid receptors type-1 and type-2 (CB1 and CB2). Once activated, these receptors block the adenylate cyclase enzyme68 and the following decrease of the second messenger molecule cAMP concentrations inside the cell. The EC system shows a key role in ASDs.69 It has been demonstrated that CB2 is overexpressed on autistic-derived peripheral blood mononuclear cells.70 This upregulation occurs both at RNA and protein levels, and the fact that monocytes orchestrate immune responses could indicate that the EC system leads to immunological changes in ASDs.69 In addition, EC system also plays an important role in regulating other metabolic pathways involved in ASDs, such as energy metabolism, neuroinflammation, and food intake.71,72 Indirect CB2 stimulation with the use of palmitoylethanolamide has been proven to reduce autistic behaviors in an animal model and in two case reports.63,73
These data also open the way for a phytopharmaceutical control of the EC system in ASDs. However, as this system shows a role in the central nervous system (CNS) development, its activation might trigger long-lasting functional alterations.74 The famous phytocannabinoid tetrahydrocannabinol (THC), the principal psychoactive extract constituent from Cannabis sativaand Cannabis indica, could trigger persistent alterations in the still-maturing brain.75 Moreover, the nonpsychoactive phytocannabinoid Cannabidiol (CBD) could promise therapeutic options as immunomodulation, antioxidant defense, neuroprotection, and with no side effects.69 CBD has low affinity for CB1 and CB2, but at different concentrations it is able to activate a plethora of cellular processes.76 Some autism specialized physicians report CBD oil use to decrease ASD symptoms.
The use of cannabis-derived compounds for ASD treatment has been hypothesized some years ago77 and gave much attention also in general media.78 Indeed, the study to assess efficacy and safety of cannabinoids with a 20:1 ratio of CBD and THC in amelioration of behavioral alterations in children and youth with ASD has been approved; other trials aim to study the safety and efficacy of cannabidivarin (CBDV) (weight-based dosing of 10 mg/(kg·d) of CBDV for 12 weeks) in children with autism. CBDV, homolog to CBD, is another nonpsychoactive compound found in Cannabis; it differs from this by the side-chain shortened by two methylene bridges (Clinicaltrials.gov). Before recommending the use of EC drugs for the amelioration of core ASD symptoms, clinical trials need to be performed to establish safety, tolerability, and beneficial effects.69
The World Health Organization reported that medicinal plants are the best source of drugs (WHO, 2010).79 The major alkaloid commonly used for seizure disorders present in Piper longum and black pepper Piper nigrum is piperine. It has been shown to own antioxidant,80 neuroprotective,81 anxiolytic, and cognition enhancing effects.82 A study reports amelioration effects of piperine on behavioral alterations and oxidative stress markers in autism induced murine model, revealing that piperine treatment restored the motor deficits and decreased the reorientation time, due to its capability to struggle with the induced cerebellar damage by sodium valproate.
Piperine also has neuroprotective effects on glutamate at concentration of 20 mg/kg, which induced cell viability restoration.83 Oxidative stress alterations might be meaningfully reversed by treatment with piperine83; besides, a neurobiological finding in ASD is the restoration of the integrity of the cerebellum by a decrease in number of Purkinje cells, which are connected with cerebral cortex and limbic system. Therefore, autism could be a pharmacological condition for biomedical treatment with piperine.82
Recently, studies assert that RSV has a neuroprotective role such as anti-inflammatory and antioxidant effects in many diseases. RSV (3,5,4-trihydroxy-trans-stilbene) is a naturally occurring polyphenolic compound present in grapes, pines, peanuts, and red wine,84 such as all compounds described before these biological activities could be interesting in the treatment of ASDs.85 Some factors such as xenobiotics and valproic acid might trigger or play an important role in the development of ASD core features.86 Hence, molecular pathway research about RSV and autism treatment could result as relevant for ameliorating core symptoms of autism.87 In humans, the RSV metabolites half-life in serum is 9.72 h88 at concentrations of 20 and 40 mg/kg89 or 5, 10, 15 mg/kg per oral.90
A study reveals in experimental murine model that RSV improves social skills using a rate of 10:270 of RSV:VPA, the interaction of these molecules enhanced by its physicochemical features might have an indirect effect at cellular levels87; RSV regulates and activates sirtuins that are members of the class-III histone deacetylases.91 It is also known that RSV exerts neuroimmunomodulatory effects by regulating Th1/Th2/Th17/Treg transcription factor signaling,89 decreasing pro-inflammatory molecules (IL-6 and TNF-α) on dopaminergic neurons,92 inhibition of the NF-κB activation,93 suppression of T cells such as Treg,94,95 and inhibition of IL-17A.89 Another study supports that RSV suppresses neuroinflammation in ASDs, finding that RSV suppresses mitochondrial dysfunction, oxidative-nitrosative stress, and TNF-α expression in induced rats with ASDs. Hence, the efficacy of RSV could be as a potential therapeutic agent for ameliorating neurobehavioral and biochemical alterations related with ASDs.89
Indian spice turmeric (Curcuma longa) is well known for its protective effects against neurodegenerative diseases and neuropsychiatric disorders,96 in which the major curcuminoid is curcumin (diferuloyl methane), a nontoxic molecule, able to cross blood–brain barrier.97 Also, it is reported to have positive effects on the treatment of autism as curcumin targets several cell signaling pathways, and its effects are as follows: increasing intracellular levels of glutathione, reducing inflammatory components, mitochondrial dysfunction, oxidative/nitrosative stress, and protein aggregation, counteracting the damage caused by heavy metals, and supporting liver detoxification.98–99
Signs of brain toxicity and delayed maturation of brain have been studied in induced autism animal models; curcumin can ameliorate these alterations and is able to improve abnormal brain weight and delayed maturation.100 Pharmacokinetic assessments have showed that curcumin bioavailability is high and plasma levels of it increased to their highest levels (184 ng/mL) 80 min after oral administration; amorphous solid dispersion of curcumin has demonstrated enhanced bioefficiency in 10-fold lower dose.101 Daily doses of 50/100/200 mg/kg of curcumin regularly given over a period of 4 weeks were discovered to restore neurological, behavioral, biochemical, and molecular changes related to the ASD phenotype in murine in a dose-dependent manner. As such, curcumin can be developed as a neuro-psychopharmacotherapeutical drug due to its characteristics and potential effects for ASD treatment.99 Curcumin shows ambivalent effects of both genotoxicity and antigenotoxicity, endothelial growth, and development in tissue alterations. Concentration-dependent effects, as low as 0.1 μM of curcumin, lead to disproportionate DNA segregation, karyorrhexis, and micronucleation in proliferating endothelial cells.102–104
Bacosides are medicinal substances widely used by Indian tribes and are the main bioactive compounds extracted from Bacopa monnieri (L.) Wettst.105 This perennial creeping herb belongs to the family Scrophulariaceae and is extensively cultivated in Asia, including China and India. B. monnieri has numerous synonyms such as brahmi (derived from the word “Brahma”), Herpestis monniera, and Gratiola monniera.106 It has been used for ∼3,000 years in the Ayurvedic system of traditional Indian medicine and is classified as a medhyarasayana, a drug used to improve cognition and intellect107 and used as a nerve tonic.108
Two triterpenoid glycosides denoted as bacoside A109 and bacoside B110 are the major bioactive constituents found in B. monnieri; both of them are able to improve cognition.109,110 Pharmacological effects are attributed to the number of alkaloids, saponins, and sterols, which compose the extract.111 It has been reported that these bacosides modulate cholinergic densities93 along with acetylcholine levels,112 and in presence of these compounds, the central nervous system shows β-amyloid scavenging properties113 and anxiolytic reliving processes.114–116 Although its biological molecular mechanisms have not been proven, it is well known that bacoside-A interferes with aggregation and membrane activity in fragments of the prion protein 38; induction of fibril formation corresponding to inhibition of membrane interactions is likely the main factor that reduces amyloid protein toxicity by bacoside-A.117,118
Even though there are trials based on attention-deficit hyperactivity disorder (ADHD),119 which is a comorbidity of ASDs, little research has focused on the efficacy of bacosides in this population. There is only one report made up to date in murine models with induced ASDs120 where they evaluate the effect of B. monnieri extract (300 mg/kg/p.o.) by powdering the whole plant for rat consumption. Behavioral tests such as nociception, locomotor activity, exploratory activity, anxiety, and social behavior were performed. Treatment with B. monnieri significantly improved behavioral alterations and decreased oxidative stress markers; it significantly reduced pain threshold and normalized the locomotor activity and anxiety. Authors inferred that protective effect of B. monnieri on locomotor activity may be due to its antianxiety activity and that it decreases accumulated glutamate. Their rats with ASDs also showed neuronal degeneration and chromatolysis, and after treatment they observed its neuroprotective effect with histopathological changes in cerebellum. A single oral administration of B. monnieri extract at doses of 30, 60, 300, 1,500, and 5,000 mg/kg given for large time (270 days) did not produce any toxicity in murine models.121
Other Compounds with Phytopharmaceutical Relevance
Different types of phytopharmaceuticals and extracts have been studied briefly on the fields of ASD and ADHD (Table 1). A study with three ASD patients evaluated a standardized extract from the ground-up leaves of G. biloba denominated EGb 761, which was administered daily for 4 weeks (2 × 100 mg). Weekly ratings were performed using Aberrant Behavior and Symptom Checklist (ABC)122 with clinician ratings consisting of the Global Assessment Scale,123 Comprehensive Psychiatric Rating Scale (CPRS),124 and Clinical Global Improvement,125 which were assessed at the beginning and then weekly up to the end of the treatment period. This treatment improved slightly ABC factors such as irritability, hyperactivity, inadequate eye contact, and inappropriate speech. Although they showed a moderately therapeutic effect of G. biloba in treatment of core autism symptoms, their results showed no significant improvement on the clinician ratings.
Future Perspectives in the Design of Phytopharmaceuticals in ASds
The three main ways of obtaining drugs are currently nature, chemical synthesis, and biotechnology, which allows the discovery of new compounds by genetic engineering techniques. Currently, a high percentage of medicines used in the allopathic medicine are extracted from the vegetable kingdom, and there is a remarkable tendency to raise this figure, due to the discovery of new active principles of botanical origin. The synthesis and accumulation of the majority of the compounds with the medical science present in the plants vary according to the ecological and environmental factors. To increase the quality and efficacy of herbal medicines and adjustments, it is important to establish quality control protocols and standardization of their active ingredients that can produce many more drugs aimed at reestablishing minimal or no side effects. The design process helped by bioinformatics might help to understand combinations and specific parameters much more directly linked to ameliorate core autistic symptoms through its physiological, biochemical, and genetic base. In this way, when treating the “symptoms” we will treat the “causes” with potential recovery of the disorder.
Before claiming enthusiastic results, it is noteworthy to consider the need for large clinical trials to determine safety and efficacy. Many results are based on case reports or small size samples, and often the studies are open label. Two recent review articles on effectiveness of herbal remedies showed that data availability on controlled clinical studies is very limited and the use of different methodologies increases concerns about effectiveness of herbal medicines.143,144 However, the efficacy of herbal-based drugs for the treatment of ASD symptoms appears to be encouraging. There is also need for more trials using ASD animal models. This is an important research variable given that trials are often performed with small size sample; heterogeneity of ASD symptoms and the complex etiology of the condition are potential limitations and obstacles to develop new drugs.145
This review considers that of all plant-based drugs for neuromodulation of core ASD features. The flavonoid luteolin exhibits promising effects, as well as RSV due to its low toxicity reported, interaction with other drugs, and results with statistical significance. However, luteolin is the only molecule that has been directly tested in children with ASD in whom the core ASD behaviors have had clinical improvement. In contrast to RSV that has not been tested in humans but murine model, studies reported amelioration of autistic clinical features, in addition to its immunomodulatory effect. Regarding piperine, improvement of behavioral alterations, lowered oxidative stress markers, and restored histoarchitecture of cerebellum were reported. No toxicity studies have been carried out to date, limiting the authors to their clinical usage due to the high doses needed to achieve these effects.
To view Table 1, the list of abbreviations, and references click here.
ASSAY & Drug Development Technologies, published by Mary Ann Liebert, Inc., offers a unique combination of original research and reports on the techniques and tools being used in cutting-edge drug development. The above article was published in ASSAY & Drug Development Technologies with the title “Autism Spectrum Disorders: Potential Neuro-Psychopharmacotherapeutic Plant-Based Drugs“. The views expressed here are those of the authors and are not necessarily those of DNA and Cell Biology, Mary Ann Liebert, Inc., publishers, or their affiliates. No endorsement of any entity or technology is implied.