Anandamide, known as AEA for short, plays a very important role in neuroprotection through CB1 receptor and CB2 receptor, or CB1/CB2-independent pathways.
There are three kinds of popular anandamide analogs on the market, namely methylfluorophosphonate, fatty acid ethanolamides and lipoamino acids.
Anandamide analogs have very similar bioactivity and chemical molecule framework as AEA, however their performing objective and process are not the same from anandamide. AEA analogs may not only show neuroprotective effects via CB1/CB2-independent pathway and inhibition of fatty acid amide hydrolase (FAAH), but in addition prevent some negative effects of AEA ingredient. For the far better understanding of anandamide and its analogs, this overview temporarily covers their bioactivities and mechanism of actions.
Cannabis has been used as a cultivated plant for centuries to treat a variety of diseases, such as arthritis and menstrual pain. There are about 60 kinds of natural active ingredients of cannabis, collectively known as cannabinoids. The main active ingredient is 9-tetrahydrocannabinol (9-THC), mainly by binding and activating the cell surface Cannabinoid receptors (CBI and CB2) function. A large number of experiments have proved that cannabinoids have various pharmacological effects such as analgesia, sedation, antispasmodic, anti-vomiting, anticonvulsant, anti-myocardial ischemia-reperfusion injury, and intraocular pressure reduction. Arachidonic acid ethanolamine (anandamide, AEA) and 2-arachidonic acid glycerol (2-AG) are the earliest endocannabinoids that have been isolated and identified, and are also important neurotransmitters in the brain. Protects various central nervous system injury models.
Anandamide and its analogs
AEA is a derivative of long-chain fatty acids, and its analogs mostly have fatty acyl groups. The earliest report shows that AEA analog methylfluorophosphonate compounds can inhibit the activity of AEA hydrolase-FAAH (fatty acid amide hydrolase). Studies found that when the number of saturated carbon chains is 12-18, it has a strong inhibitory effect on FAAH, but the introduction of unsaturated bonds does not affect its activity in inhibiting FAAH.
Another type of AEA analogues are fatty acylethanolamine compounds, which have inhibitory effect on FAAH and anti-inflammatory activity.
So far, the most systematically studied AEA analogues are fatty amino acids (lipoamino acids), which are composed of saturated or unsaturated fatty acids combined with different amino acids. Natural fatty acyl amino acids were first discovered in microorganisms such as Campylobacter.
In recent years, studies have confirmed that such compounds also exist in mammals, and their biological functions are found to be similar to anandamide. Foreign scholars call this kind of compound “elmiric acid” (EMA). At present, about 40 kinds of natural EMA have been found, and other types of EMAO can also be obtained through chemical synthesis methods. The biological activity of EMA on EMA is more reported. , And its structure-activity relationship study found that the compounds containing unsaturated fatty acyl groups in the EMA structure have strong anti-inflammatory activity, while members containing saturated fatty acyl groups have only partial anti-inflammatory activity, and the anti-inflammatory activities of these members vary with increase in the number of carbon.
AEA & its analogues and cannabinoid receptors
The classic cannabinoid receptors are divided into two types, CB1 and CB2, both of which are Gi / o type G protein coupled receptors. CBI receptors are mainly located in the brain, spinal cord, and peripheral nervous system. They can be activated by reducing the release of neurotransmitters (such as dopamine and aminobutyric acid) and participate in the regulation of memory, cognition, and motor control; CB2 receptors are mainly present in The immune system is mostly located in the periphery of the spleen, immune cells, tonsils, and thymus in the periphery. Its main role is to participate in immune regulation; in the central nervous system, it is mainly distributed in glial cells, and there is also a small distribution in neurons. When the nervous system is stimulated, the expression of CB2 receptors on glial cells will be greatly increased, which will increase the migration ability of the cells and reduce the secretion of the inflammatory factor interleukin (IL) 1 and the tumor necrosis factor a (TNF meter) , Play a neuroprotective role by regulating the immune response. In addition to the above two receptors, a 27-year study also confirmed a new type of cannabinoid receptor, an orphan receptor GPR55, which is also a Gi / o-type G protein-coupled receptor, and is endogenous cannabis. AEA has strong affinity, but the distribution of GPR55 and its mediated biological activity are still under further study.
Neuroprotective effect of AEA and its analogues
In the nervous system, endogenous cannabinoids play an important role in the survival of neurons. AEA not only participates in the protection of a variety of acute nerve injury models, but also protects a variety of neurodegenerative diseases.
First, AEA at the nanomolar level can reduce the death of neurons in the cortical neuron hypoxia-sugar damage model and improve neuronal vitality. A pmoL / L AEA can reduce the apoptosis of N18TG2 cells induced by low serum.
Secondly, using the Wisteria rat transient cerebral ischemia model, it was found that after 24 hours of intraperitoneal injection of 10 mg / kg AEA, the cerebral ischemia area was reduced by 25% compared with the model group, and the neurological score was not statistically different from the normal group, suggesting that AEA It has a protective effect on the damage caused by cerebral ischemia.
When acute neuronal damage such as brain trauma and cerebral hemorrhage occurs, the increase in AEA release is considered to be a compensatory protective function of the cannabinoid system. Multiple sclerosis is a neurodegenerative disease related to inflammation, and there are many reports of clinical and preclinical studies on the effects of endocannabinoids on the disease.
Using a mouse model of chronic allergic encephalomyelitis, it was found that 10 minutes after intraperitoneal injection of 10 my / kg AEA, the spasm of the lower limbs of the mouse can be effectively controlled.
Moreover, it was found in the viral multiple sclerosis cell model that AEA can promote the secretion of IL -10 by microglia, which can regulate the microglial immune response by reducing the release of inflammatory factors such as NO and TNF-a. In addition to the above-mentioned anti-inflammatory effects, AEA (1, 250 foot moI L) can dose-dependently reduce the neuronal death induced by amyloid cytoplasmic protein (A) fragment 140, and directly combat neuronal damage caused by Aß.
In addition to endogenous AEA, AEA analogs also have extensive neuroprotective effects. In vivo and in vitro studies have shown that EMA, such as N-stearoyl-L-tyrosine, N-stearoyl-L-serine and N-stearoyl-L-threonine, can affect rat cerebral ischemia models and in vitro Brain slice hypoxic injury has a protective effect; Palmitoylethanolamide can not only reduce the infarct size of the rat model of middle artery occlusion, but also improve the learning and memory function through peroxisome proliferator-activated receptor (PPARa); / CB2 pathway inhibits neuropathic pain; it can also inhibit lymphocyte proliferation through the CB2 pathway and exert immunomodulatory effects.
In the study of the anti-inflammatory activity of AEA analogs, it is found that NAGly, PEA and N-stearylethanolamine all have obvious anti-inflammatory effects, and the protective effect of PEA on the cerebral ischemia model through the anti-inflammatory mechanism has been confirmed.
Due to the obvious inflammatory response in the development of neurodegenerative diseases (such as multiple sclerosis, Alzheimer’s disease) and cerebral ischemia, AEA analogs can also exert nerves through the anti-inflammatory effects in the central nervous system Protective effects.
Neuroprotective mechanism of AEA and its analogues
Endocannabinoids can exert neuroprotective effects through various mechanisms. On the one hand, it can play a role through the CB1 / CB2 receptor pathway.
Activating the CB1 receptor can regulate synaptic growth and synapse generation; it can also reduce cellular Ca influx and inhibit the release of glutamatergic neurotransmitters; it can also up-regulate brain-derived nerve growth factor (BDNF) through antioxidant action ), activate cell protection signaling pathways, such as PI3K / Akt and PKA / ERK, to play a protective role.
At the same time, endogenous cannabinoids can also form a family of lipid signals responsible for the proliferation and differentiation of neural precursor cells. By acting on CB1 receptors, they produce beneficial proliferation signals, which have the potential to promote neural development and neuronal differentiation.
In addition, endogenous cannabinoids can also regulate immune responses by acting on CB1 / CB2 receptors on neurons, glial cells, mast cells, and lymphocytes, thereby indirectly exerting a protective effect.
On the other hand, although AEA is an endogenous ligand for CB1 and CB2, its biological activity can also be mediated through the non-CB1 / CB2 receptor pathway.
Studies have found that neither CB1 nor CB2 receptor antagonists can block the protective effect of AEA on neuronal ischemic injury, nor can it reverse the inhibitory effect of AEA on cellular Ca influx and glutamate neurotransmitter release.
One effect may be through the cation channel type receptor-capsaicin receptor 1 (TRPV-1). In the process of ischemic brain injury, the production of some inflammatory factors (such as TNF-alpha, etc.) can promote TRPV-1 activation, increase Ca2+ influx and glutamate release. AEA can inactivate TRPV-1, thereby inhibiting Ca2+ influx and glutamate release.
In addition, AEA can change the reactivity of TRPV-1 while activating cannabinoid receptors, and the activation of TRPV-1 can regulate the synthesis of AEA, which suggests that TRPV-1 acts as a receptor other than the classic CB1 and CB2 receptors. There is a close connection between cannabinoid systems.
At the same time, Melis et al also confirmed that AEA can directly act on the classical nuclear receptors PPARa and PPARy, participate in metabolism and immune inflammatory response, and exert regulation on the nervous system.
Regulating the activity of AEA synthesis / degradation enzyme system and increasing the level of endogenous AEA can also play a neuroprotective role.
AEA is synthesized from the phospholipid precursor N-acylphosphatidylethanolamine (NAPE) via N-acyltransferase and separated from NAPE after being catalyzed by phospholipase D. FAAH is a membrane protease of the serine hydrolase family. It is widely distributed in various parts of the body and has a high concentration in the brain and liver. It is the main hydrolase of AEA.
By inhibiting FAAH activity, the level of AEA in the body can be increased, and a series of biological activities can be produced. FAAH inhibitor URB597 can inhibit carrageenan-induced inflammatory pain in rats by acting on PPARa; FAAH irreversible inhibitor AM374 can also inhibit Hairen by activating extracellular kinase / mitogen-activated protein kinase (ERK / MAPK) pathway Alginic acid induced seizures and neuronal death.
On the other hand, inhibiting cellular AEA uptake can also increase AEA levels and exert a neuroprotective effect. The use of AMEA uptake inhibitor AM404 can not only reduce the cerebral ischemic injury of gerbils, but also inhibit the release of TNF-a and NO and apoptosis in the neuropathic pain model. Therefore, inhibiting the hydrolysis or reuptake of endocannabinoids has become a new target for the treatment of central nervous system diseases.
the research on the neuroprotective activity of AEA analogs and its mechanism of action started late, and it is now found that these compounds mainly function through anti-inflammatory mechanisms and inhibition of FAAH activity.
Compared with non-steroidal anti-inflammatory drugs, the anti-inflammatory activity of AEA analogs is not achieved by inhibiting COX-2, which provides new ideas for AEA analogs to participate in the protection of the nervous system through anti-inflammatory.
The study also found that some AEA analogs, such as NAGly, N-arachidonic acid-L-alanine, N-arachidonic acid-D-alanine and N-arachidonic acid isoleucine have inhibition FAAH activity, and there are species differences in this activity.
At the same time, palmitoylethanolamine (PEA) has also been shown to inhibit FAAH and exert neuroprotective effects by increasing AEA levels in the body.
In addition, some AEA analogs can also activate PPAR and TPRV-1 like AEA, NAGly and N-stearylethanolamine can inhibit T-type calcium channels through TPRV-1, and PEA can improve learning and memory functions by activating PPARa. Therefore, current research suggests that non-CB1 / CB2-mediated neuroprotective activity and the regulation of FAAH activity are important characteristics of this class of compounds.
Endocannabinoid AEA is an important signaling molecule in the body, and it can play a protective role in acute nerve injury models and various neurodegenerative disease models through the CB1 / CB2 pathway or the non-CB1 / CB2 pathway.
AEA analogs mainly include methyl fluorophosphates, fatty acyl
Alcohol amines and fatty acyl amino acid compounds, etc. The biological activity and chemical structure of these compounds are similar to AEA, but the target and mechanism of action are not completely the same.
Compared with AEA, not all AEA analogs can be active through the CB1 / CB2 receptor pathway. Non-CB1 / CB2-mediated neuroprotective activity and the regulation of FAAH activity are important features of this class of compounds, so activation can be avoided. The central nervous system side effects caused by CB1 / CB2.
In addition, AEA analogs have similar fat-soluble structural characteristics as AEA, making these small molecule compounds easily cross the blood-brain barrier and enter the central nervous system to play a role, thereby making the development of AEA analogs more potential application value. Although part of the neuroprotective effect of AEA and its analogues has been confirmed, more biological activity needs to be further discovered, and the target and mechanism of action of AEA analogues still require more in-depth research.