Main Research Findings

1) Use of 7,8-dihydroxyflavone hydrate may have the potential to treat depressive disorders, as well as a variety of neurological impairments.

2) Treatment with 7,8-dihydroxyflavone hydrate is capable of improving spatial memory and increasing spine density in an animal model of neuronal loss similar to Alzheimer’s Disease.

 

Selected Data

1) The research team of Liu et al examined the effects of activating TrkB receptor, 7,8-dihydroxyflavone hydrate, and its ability to elicit anti-depressive effects in animal experimental models. Several different derivatives of the lead compound, 7,8-dihydroxy, were synthesized for the purpose of this study; they are labeled and defined as follows: 2) 4-Aminomethyl benzoate, 3) Methyl 4-Pyrrolidin-1-yl benzoate, 4) 4-(Pyrrolidin-1-yl)benzoic acid, 5) 4-(Pyrrolidin-1-yl)benzoyl chloride, 8) 3-acetamido-6-acetyl-2-nitrophenyl 4-(dimethylamino)benzoate, 9) 7-Amino-2-(4’-(dimethylamino)phenyl)-8-nitro-4H-chromen-4-one, 10) 7,8-Diamino-2-(4’-(dimethylamino)phenyl)-4H-chromen-4-one hydrochloride, 11) 8-(4’-(dimethylamino)phenyl)chromeno[7,8-d]imidazole-6(1H)-one, 12) and 13), 8-(4’-(Pyrrolidin-1-yl)phenyl)chromeno[7,8-d]imidazole-6(1H)-one, 15) Methyl 2-methoxy-4-methylbenzoate, 16) Methyl 2-methoxy-4,5-dimethylbenzoate, 17) Methyl 2-methoxy-4,5-dimethyl-3-nitrobenzoate, 18) (E)-Methyl 4-(2-(dimethylamino)vinyl)-2-methoxy-5-methyl-3-nitrobenzoate, 19) Methyl 7-methoxy-1H-indole-6-carboxylate, 20) 7-Methoxy-1H-indole-6-carboxylic acid, 21) 7-Methoxy-1H-indole-6-carbonyl chloride, and 23) 2-(4-(Pyrrolidin-1-yl)phenyl)pyrano[3,2-g]indol-4(9H)-one [1].

2 month old male, wild-type C57BL/6 mice were used in this experiment. The animals were randomly assigned to experimental groups and perorally administered 1 mg/kg of various derivatives of 7,8-dihydroxy or subcutaneously injected with saline to serve as a control. In order to assess the ability of the compound to treat various depressive and neurological disorders, the mice were subjected to the forced swim and tail suspension behavioral tests, and locomotor activity of the animals was recorded throughout.

The forced swim test took place first following 21 days of oral treatment with either saline or the TrkB agonist compounds. The mice were allowed to habituate to the test room for 2 days. This was followed by placing the animals in a clear glass cylinder half-filled with water, not allowing them to touch the bottom of the glass. The animals were in the cylinder for a total of 6 minutes while immobile activity during the final 4 minutes was recorded by an investigator blinded to the treatment groups [1].

The forced swim test was followed by the tail suspension test. All mice were individually suspended by their tail 30 cm above the floor for a total of 6 minutes. The researchers recorded the time it took for the transition from latency to immobility, as well as the amount of time each mouse spent immobile. Overall locomotor activity was observed using an automated system that utilizes photobeams to record ambulation. All mice treated with an experimental drug were placed in a locomotion chamber in order to record their activity levels over 2 hours in 30 minutes intervals [1].

Following the behavioral testing the mice were euthanized and the brains tissues were dissected and fixed in 4% paraformaldehyde overnight prior to paraffin embedding. After cutting into 6 um sections, the samples were deparaffinized in xylene and rehydrated while 3% hydrogen peroxide was used to block endogenous peroxidase activity for 5 minutes. The slides were then boiled for 10 minutes in a 10 mM sodium citrate buffer and specific antibodies were used to detect phosphorylated TrkB and TrkB 816. Additional brain sections were deparaffinized in xylene and rehydrated in a gradient ethanol solution followed by boiling for 20 minutes in a 10 mM sodium citrate buffer in order to retrieve antigens in the samples. Finally, remaining brain sections were incubated with anti-TrkB while secondary antibodies and anti-mouse-fluorescein isothiocyanate were applied for nuclear staining [1].

2) The research team of Castello et al analyzed GFP-labeled neurons in mice in order to assess how treatment with 7,8-dihydroxyflavone hydrate improves cognitive functioning in animal models of Alzheimer’s Disease. Female, homozygous Tet-DTa mice were crossed with homozygous Thy1-GFP-M male mice in order to produce a GFP-expressing CaM/Tet-DTa mouse. Once the desired homozygosity was reached the mice were maintained on a diet of 2000 parts per gram doxycycline to suppress induction of DTa. DTa expression was then induced by replacing 2000 ppg doxycycline with normal mouse chow for 25 days. To override DTa expression the chow was replaced and the mice were given 2 mg/ml doxycycline-supplemented drinking water for 2 days. After 2 days, the mice continued eating doxycycline chow but were given regular drinking water. Following the initiation of experimental protocol, the mice were subjected to several behavioral procedures in order for the researchers to examine changes in cognitive functioning [2].

At the beginning of the behavioral test all mice, 3.5-5 months-old were age and sex matched from 4 different independent litters in order to avoid litter effects. The elevated plus maze test was conducted first in order to assess anxious behavior in the animals. The maze apparatus was elevated 40 cm above the ground and consisted of 4 intersection arms, 2 of which were closed with dividing walls and 2 that were open with no dividing walls. The animals were placed into the apparatus at the junction of the arms and allowed to explore the maze for 5 minutes while being recorded in order for the researchers to determine the total number or arm entries and how much time was spent inside of the arms.

Next, to assess for motor deficits the animals were subjected to rotarod testing. The animals were tested on a rotarod apparatus that accelerated linearly from 4 to 40 rpm over 5 minutes. Once the animal fell off of the rotarod or were able to hold on to the apparatus for 2 revolutions without walking, the trial was considered over. Each animal underwent 3, 5 minute trials each separated by a 10 minutes resting period. The elevated plus maze test and the rotarod testing was followed by water maze testing that included a 1 meter diameter circular pool filled with opaque water. During the training period the mice were placed in the pool and allowed to find and climb onto a submerged platform. After the 4 day training period ended the escape platform was removed and the mice were tested on a recorded probe trial 24 hours later [2].

After behavioral testing was concluded the mice were anesthetized using sodium pentobarbital and transcardially perfused with PBS at a rate of 11 ml/minute. The brains of the animals were then dissected and fixed in 4% paraformaldehyde for 48 hours and cryoprotected in 30% sucrose. A subset of the collected tissues were randomly selected for further histological analysis. Free floating sections were washed and incubated in PBS for 1 hour, followed by overnight incubation in primary antibodies for MAP2, NeuN, or synaptophysin. After the overnight incubation Alexa Fluor 555 fluorescent secondary antibody was applied for an additional hour of incubation time. The sections were finally mounted on slides for confocal microscopic imaging [2].

 

Discussion

1) Several derivatives of the nootropic 7,8-dihydroxy were synthesized by the research team of Castello et al in order to examine how manipulating the active catechol group of lead compound changes the elicited benefits. The derivatives developed were labeled and defined as follows: 2) 4-Aminomethyl benzoate, 3) Methyl 4-Pyrrolidin-1-yl benzoate, 4) 4-(Pyrrolidin-1-yl)benzoic acid, 5) 4-(Pyrrolidin-1-yl)benzoyl chloride, 8) 3-acetamido-6-acetyl-2-nitrophenyl 4-(dimethylamino)benzoate, 9) 7-Amino-2-(4’-(dimethylamino)phenyl)-8-nitro-4H-chromen-4-one, 10) 7,8-Diamino-2-(4’-(dimethylamino)phenyl)-4H-chromen-4-one hydrochloride, 11) 8-(4’-(dimethylamino)phenyl)chromeno[7,8-d]imidazole-6(1H)-one, 12) and 13), 8-(4’-(Pyrrolidin-1-yl)phenyl)chromeno[7,8-d]imidazole-6(1H)-one, 15) Methyl 2-methoxy-4-methylbenzoate, 16) Methyl 2-methoxy-4,5-dimethylbenzoate, 17) Methyl 2-methoxy-4,5-dimethyl-3-nitrobenzoate, 18) (E)-Methyl 4-(2-(dimethylamino)vinyl)-2-methoxy-5-methyl-3-nitrobenzoate, 19) Methyl 7-methoxy-1H-indole-6-carboxylate, 20) 7-Methoxy-1H-indole-6-carboxylic acid, 21) 7-Methoxy-1H-indole-6-carbonyl chloride, and 23) 2-(4-(Pyrrolidin-1-yl)phenyl)pyrano[3,2-g]indol-4(9H)-one [1].

Compounds 11 (8-(4’-(dimethylamino)phenyl)chromeno[7,8-d]imidazole-6(1H)-one) and 32 in particular were administered to the mice via oral gavage as a dose of 1 mg/kg. Compound 11 was found to have time-dependently activated TrkB receptors, with activation peaking at 4 hours and fading by 16 hours, while compound 32 elicited less potent effects on TrkB receptor activation. When examining the p-Akt immunoblotting results, compound 11 was shown to gradually activate Akt with effects peaking at 8 hours with the signal elevated by approximately 250% above control levels. Compound 32 was also found to activate p-Akt signaling with its effects peaking at 1 hour, diminishing at hour 4, and returning to normal by hour 8.

Figure 1: Changes in P-Akt S473 activation patterns over 16 hours in the brains of mice treated with 1 mg/kg doses of compound 11 and compound 32.

In addition to observing TrkB receptor and Akt signaling activation, the researchers also guided the animals through the forced swim test in order to screen the potential antidepressant effects of 7,8-dihydroxy and its derivatives after 3 weeks of daily treatment with 5 mg/kg of the compounds. Both compound 11 and compound 32 were found to reduce immobility in the mice during the forced swim test with compound 11 eliciting a stronger effect than compound 32. Overall, treatment with compound 11 was found to significantly enhance locomotor activity in comparison to compound 32 and a vehicle compound. Additionally, once brain tissue was collected, immunoblotting performed on samples from the cortex and hippocampus revealed that both compounds 11 and 32 increased TrkB phosphorylation during the 3 week treatment period, in comparison to the mice included in the control group [1].

Figure 2: Changes in immobility during the forced swim test in mice that were orally administered 5 mg/kg of either a vehicle, compound 11, or compound 32.

Treatment with compound 11 had the potential to significantly increase the stimulatory effects of TrkB and reduce immobility during the forced swim test. After 3 weeks of administration it was found to have elevated locomotor activity, raising concerns for the research team. That being said, imidazole and indole-substituted compounds were synthesized and immunoblotting and p-Akt ELISA analysis was performed to reveal that compound 13 and compound 23 had higher efficacy than compound 11 in activating TrkB and Akt in primary neurons. The study proceeded with examining the antidepressant effects of compound 13 and compound 23 through the forced swim test and tail suspension assay [1].

Figure 3: Changes in locomotor activity over 120 minutes in mice treated with either a vehicle, compound 11, or compound 32.

Compound 13 and compound 23 were administered to the mice daily via oral gavage at a dose of 2.5 mg/kg for 3 weeks. Results of the forced swim test revealed that compound 13 reduced immobility by 45% in comparison to the control group, while compound 23 elicited no significant effects on immobility. The tail suspension test was performed next; the researchers were observing the animals for immobile posture and escape-related behavior in the subjects treated with the nootropic derivatives. In comparison to the control group of animals, treatment with compound 13 was shown to significantly reduce the occurrence of immobile postures, while treatment with compound 23 lacked efficacy [1].

Figure 4: Changes in immobility during the forced swim test in mice that were orally administered 2.5 mg/kg of either a vehicle, compound 13, or compound 23.

Figure 5: Changes in locomotor activity over 120 minutes in mice treated with either a vehicle, compound 13, or compound 23.

Additionally, analysis of the animals’ locomotor activity found that motion activity was not significantly altered by compound 13 or compound 23 in comparison to control animals. However, immunoblotting using anti-p-TrkB Y816 and anti-p-TrkB Y706 antibodies found that both experimental compounds activated TrkB receptors, which then correlated with p-Akt immunoblotting. After examining the results of immunohistochemistry staining with anti-p-TrkB, the researchers concluded that treatment with compound 13 promotes TrkB activation in the hippocampus and elicits strong anti-depressant effects [1].

2) The research team of Liu et al investigated the ability of 7,8-dihydroxyflavone hydrate to improve spatial memory and anxiety-like behavior in animal models. 5 mg/kg of the nootropic or a vehicle was intraperitoneally injected to CaM/Tet-DTa mice and Tet-DTa mice over the course of 2 weeks. During the 2nd week of treatment the animals were tested using an elevated plus maze. The researchers found that control mice spent 17% of the 5 minute trial in the open arms while the mice with induced synaptic loss were found to spend 61% of the 5 minute trial in the open arms of the maze. However, the groups spent an equal amount of time exploring the maze apparatus [2].

Figure 6: Changes in A) the amount of time spent and B) the number of entries in the open arms of the elevated plus maze apparatus by control and lesioned animals treated with a vehicle of 5 mg/kg of 7,8-dihydroxyflavone.

Overall, it was found that treatment with 7,8-dihydroxyflavone did not result in a significant change in spatial memory measured by the elevated plus maze test. Additionally, to determine if the DTa-induced lesion affects motor coordination the animals underwent an accelerated 3-trial protocol of rotarod testing. The lesion was not found to cause motor deficits as all groups were able to stay on the rotarod for equal amounts of time.

Figure 7: Changes in the time it took for the animals to fall off of the rotarod testing apparatus over 3 trials.

In addition to the elevated plus maze test and the rotarod testing, the animals underwent a water maze test in order for the research team to observe the impact of TrkB agonism on behavior dependent on hippocampal activity. The results of the water maze found that the DTa-induced lesioned mice treated with a vehicle were slowed to find the hidden platform on days 2-4 of the training period. Comparatively, by day 4 the lesioned mice treated with 7,8-dihydroxyflavone hydrate found the hidden platform significantly faster than the control group. As for the escape latencies of the mice, on days 2 and 4 there were no significant differences between the lesioned mice treated with a control versus those treated with the nootropic [2].

Figure 8: Changes in the amount of time it took to reach the hidden escape platform during the water maze test over 4 days of experimental trials.

24 hours after the final training day the mice were assessed on a 1-minute probe trial where the researchers removed the hidden platform in the water maze. The lesioned mice were slower than the control animals to reach the former location of the platform, and were typically much further from the previous location. That being said, probe latency for the lesion mice treated with 7,8-dihydroxyflavone hydrate was similar to control animals and significantly lower than the lesioned mice treated with a vehicle. The lesioned mice treated with the nootropic were also typically closer in proximity to the prior location of the platform in comparison to the lesioned mice treated with a vehicle. It was also noted by the researchers that video tracking software was used to record the swimming activity of the animals to ensure there were no differences in motivation or swimming ability that could potentially skew data [2].

Figure 9: Changes in E) latency, F) mean proximity, and G) swim speed of the control and lesioned animals treated with either a vehicle or 7,8-dihydroxyflavone hydrate, during the 24 hour probe trial.

As it was previously mentioned, the mice were euthanized after the behavioral testing was complete in order for the research team to measure the extent of neuronal loss in the lesioned animals by conducting immunohistochemistry for the neuronal nuclei marker, NeuN. In lesioned mice expressing GFP, the animals were shown to have 71% less immunoreactivity for NeuN in the CA1 pyramidal layer. These results were similar to those found in lesioned mice that did not express GFP that experienced a 74% reduction in CA1 pyramidal neurons. These findings indicate that introducing the Thyl-GFP transgene does not alter the functioning of the inducible lesion systems. The researchers also mentioned that there was a significant loss of NeuN immunoreactivity in the dentate gyrus and entorhinal cortex, while there were no changes in immunoreactivity in the CA3 pyramidal neurons [2].

Figure 10: Changes in optical density of the neurons in control animals compared to the lesioned animals.

 

 

Disclaimer

**LAB USE ONLY**
*This information is for educational purposes only and does not constitute medical advice. THE PRODUCTS DESCRIBED HEREIN ARE FOR RESEARCH USE ONLY. All clinical research must be conducted with oversight from the appropriate Institutional Review Board (IRB). All preclinical research must be conducted with oversight from the appropriate Institutional Animal Care and Use Committee (IACUC) following the guidelines of the Animal Welfare Act (AWA).

 

Citations

[1] Liu X, Chan CB, Qi Q, et al. Optimization of a small tropomyosin-related kinase B (TrkB) agonist 7,8-dihydroxyflavone active in mouse models of depression. J Med Chem. 2012;55(19):8524-8537. doi:10.1021/jm301099x.

[2] Castello NA, Nguyen MH, Tran JD, Cheng D, Green KN, LaFerla FM. 7,8-Dihydroxyflavone, a small molecule TrkB agonist, improves spatial memory and increases thin spine density in a mouse model of Alzheimer disease-like neuronal loss. PLoS One. 2014;9(3):e91453. Published 2014 Mar 10. doi:10.1371/journal.pone.0091453

Mechanisms of Action

7,8-dihydroxyflavone hydrate (7,8-DHF) is a newly discovered flavonoid compound identified during a screening study aiming to find molecules with neurotrophic factors similar to that of brain-derived neurotrophic factor (BDNF). The results of the study reported that 7,8-DHF is a crucial activator of the BDNF signaling pathway. This leads to the prevention of apoptosis, increased neurogenesis, and an improvement in neuroprotection.

This initial study also found that 7,8-DHF acts as a direct ligand to tropomyosin-related kinase B (TrkB) receptors. In order to promote neuron growth and survival, TrkB is typically activated by BDNF. This leads experts to believe that not only does 7,8-DHF play a role in the BDNF signaling pathway, but the compound may be able to mimic the actions of BDNF and elicit the same expected outcomes via TrkB activation.

There has been a multitude of animal-based studies examining how 7,8-DHF is absorbed in the body. Poor absorption is a trait typically seen in flavonoids. In the case of 7,8-DHF, the compound is capable of oral absorption, however, it is metabolized so quickly it doesn’t make it to the bloodstream. Researchers Liu et. Al have been modifying the structure of the compound in an attempt to optimize its effects. Liu et. Al determined that these modifications have led to 7,8-DHF becoming orally bioavailable in mice, however, the compound is still subject to rapid, first-pass metabolism. Further research should be conducted in order to determine whether manipulation of various oral pharmacokinetic properties could be deemed beneficial (https://pubmed.ncbi.nlm.nih.gov/22984948/).

On the other hand, researchers Andero et. Al examined how 7,8-DHF was absorbed when peripherally injected rather than orally administered. 5 mg/kg doses of the compound were administered to mice; results of the study reported that TrkB receptors were activated. This suggests that 7,8-DHF is capable of effectively passing the blood-brain-barrier (BBB), a task BDNF is not capable of.

 

Effects of 7,8-DHF on Neurogenesis

As it was previously mentioned, 7,8-DHF has been shown to potentially increase neurogenesis and prevent apoptosis. Researchers have theorized that this is due to the compound’s interaction with TrkB receptors and BDNF, however, data is still mixed in regards to the exact mechanism of action and how heavily the compounds are related. A notable study conducted by Zhang et. Al reported that administration of 500 nM of 7,8-DHF in vitro led to an increase in dendritic length and synaptic size. Researchers Castello et. Al supported this conclusion, and further determined that 7,8-DHF may not lead to an increase in axon terminals, but rather promote growth of the density dendrites. It is important to know that growth of the density dendrites is directly related to expression of BDNF via 7,8-DHF-induced TrkB activation (https://pubmed.ncbi.nlm.nih.gov/24614170/).

The work of Castello et. Al was solidified by additional studies examining the efficacy of 7,8-DHF in cases of Alzheimer’s Disease. Mice subjected to scopolamine-induced Alzheimer’s were injected with doses of 1 mg/kg of 7,8-DHF. Results reported that the subjects experienced restoration in field excitatory postsynaptic potential to the same level as the control subjects. These results indicate an overall improvement in synaptic transmission. Further research conducted by Lin et. Al examined the effects of 7,8-DHF on a transgenic model of Alzheimer’s in mice where hippocampal cells are destroyed. The researchers were able to conclude that 5 mg/kg doses of the compound led to restoration of synaptic density in damaged neurons.

 

Effects of 7,8-DHF on Metabolism and Performance

Current research has found that 7,8-DHF is able to positively affect aspects of metabolic rate and physical performance through its relationship to BDNF and TrkB receptors. As it was previously mentioned, 7,8-DHF is able to activate and mimic both these crucial variables. Researchers have concluded that BDNF tends to lower food intake in rats by binding to the TrkB receptors, however, BDNF has a short half-life and cannot permeate the BBB. This led to the hypothesis that 7,8-DHF may be a better option for improving metabolism due to its similarity to BDNF and ability to pass the BBB. This idea is supported by the work of Chan et. Al. The researchers examined how daily administration of 7,8-DHF for 20 weeks affected obese mice and found that overall the compound is capable of preventing obesity.

In terms of physical performance, neurotrophins such as BDNF are known to be involved in muscle contraction through the activation of TrkB receptors that promote the release of acetylcholine (ACh). Since 7,8-DHF is closely related to both BDNF and TrkB receptors, researchers Mantilla et. Al determined how neuromuscular transmission was changed when 7,8-DHF was administered. Results reported that when the mice test subjects were given 10µM of 7,8-DHF, there was a 32% improvement in neuromuscular transmission. While these conclusions are promising, further research should be conducted in order to determine additional benefits (https://pubmed.ncbi.nlm.nih.gov/22246885/).

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