[icon name=”user” class=”” unprefixed_class=””] Suchitra Chari, MS
Creatine (Cr) is an organic molecule that is produced endogenously in the body and is also obtained from meat and fish and to a lesser extent from dairy products. 95% of the Cr in our body is present in skeletal muscle, substantial amounts in cardiac muscle, spermatozoa, and photoreceptors of the retina, and intermediate levels in the brain. Apart from this, Cr (in the form of Creatine Monohydrate or CrM) is also consumed by athletes to augment their performance during rigorous training and to provide them extra strength and endurance1. Recently, it has been proved that oral CrM supplementation can also modify brain Cr levels2.
ATP, CR AND ENERGY:
Adenosine-tri-phosphate (ATP) is the compound that supplies all the energy needs to the cells in our body. This helps the cells to maintain a constant energy flux in order to stay alive. The energy in ATP is stored in its high energy phosphate bonds. When ATP is converted in some cell processes to either Adenosine-di-phosphate (ADP) or Adenosine-mono-phophate (AMP), the phosphate groups are released producing a lot of energy. This energy is used in ion pumping or contracting special proteins.
Cr is also a substance that can form high energy phosphate bonds. Phosphocreatine (PCr) is formed from Cr by the enzyme Creatine kinase (CK). PCr is a metabolically inert, high-energy molecule that provides the energy requirements of cells and tissues. Both Cr and PCr are a part of an intracellular high energy system. Muscle cells and neurons or nerve cells are two types of cells that contain these intracellular levels of Cr and PCr along with ADP and ATP. The reason being both these kinds of cells have sudden bursts of energy requirements like during a rigorous workout or an intense brain activity. So we can call the Cr-PCr system as a kind of a backup or a reserve system to ADP–ATP system.
How is the Cr-PCr system tied to the ATP–ADP cycle? PCr is used to phosphorylate adenine compounds, specifically converting ADP into ATP. This specific reaction is called the Lohmann reaction3 and is a reversible one, meaning it can go in both directions. The high-energy PCr transfers its phosphate group to ATP for instant energy requirement. Reversibly, energy from ATP can be reconverted and stored in PCr which again is used for synthesis of ATP in the absence of oxygen and glucose4. This can occur during the first 2 to 7 seconds following an intense muscle or neuronal effort. There are 2 forms of the enzyme CK that are used for this reaction, one for the forward reaction and another for the backward one.
There are two main reasons why muscles and the brain use the Cr-PCr system. One is for instant energy requirement. The second is that Cr is a much smaller molecule than adenosine (belonging to ATP) and hence can be transported easily to its target tissues. Now, why does the brain need Cr? Since the brain needs a constant supply of energy to send signals from one neuron to another, an interruption in this energy supply would lead to impairment of brain functions. Many neurodegenerative diseases arise due to interruption in these energy supplies. AS explained in the previous paragraph, this sudden requirement of energy is provided by Cr. Neurons need energy in the form of ATP to maintain the function of the sodium-potassium pump that aids in signaling, to transport neurotransmitters and to trap them back into their vesicles. Hypoxia or lack of oxygen in the brain cells can be experimentally created to induce this effect.
FIRST AND FOREMOST – HOW IS CR OBTAINED IN THE BODY?
Cr is synthesized in the body from two amino acids (building blocks of protein), arginine and glycine. In the process there is an intermediary compound that is formed called Guanidinoacetate which is then methylated (addition of a methyl group) to Cr. Two enzymes are required for this process. The first process is catalyzed by an enzyme called L-arginine:glycine amidinotransferase (AGAT) and the second by an enzyme called S-adenosyl-L-methionine:N-guanidinoacetate methyltransferase (GAMT) (the substance donating the methyl group is S-adenosyl methionine or SAM)5. Creatine then degrades to Creatinine and flows through the bloodstream to be excreted by the kidneys.
The main organs that produce Cr are the liver and the kidney. The synthesized or the consumed Cr is transported through the bloodstream to target tissues by trans-membrane spanning Cr transporter (CRT). This transporter is present only in tissues that have high-energy demands or good absorptive properties. Although Cr can be transported into the brain across the blood_brain barrier (BBB) via CRT in the microcapillary endothelial cells this is not a very efficient method and the brain must produce it endogenously to keep asufficient store of Cr in it6.
A defect in any of the enzymes, GAMT7, AGAT8 or CRT9 results in Cr deficiency in the brain. Conditions like mental retardation, expressive and cognitive speech delay and epilepsy are associated with this condition10. Studying these creatine deficiency syndromes will help in understating the role of Cr in the brain and help in optimising treatment. So, can supplementary Cr be used to treat cerebral creatine-deficiency syndromes and various neurological conditions?
Yes, to some extent. Restoration of neural Cr with Cr supplementation improves the clinical symptoms experienced in Cr deficient patients suffering from AGAT and GAMT mutations especially if given pre symptomatically. However, oral Cr supplementation is not effective in treating the clinical symptoms in patients suffering from CRT mutations simply because of the fact that Cr from the bloodstream (whether consumed or produced endogenously) cannot be taken into the brain due to lack of the transporter, CRT.
Thus, a study was designed to answer two main questions. Would oral Cr supplementation augment neural Cr stores? In this increased level, would Cr have any effect on the psychological and physiological processes in the brain? The study was performed as explained below.
MATERIAL AND METHODS:
Fifteen healthy volunteers (10 male and 5 female) with an average age of 31 years participated in this study. Prior to the study it was made sure that they did not have any adverse reaction to Magnetic Resonance Imaging (MRI), to hypoxia (oxygen deficiency) induction or CrM supplementation.
Severe hypoxia or lack of oxygen was created in healthy adults after dietary CrM supplementation. Techniques used were Magnetic resonance spectroscopy (MRS) to measure neural Cr availability, computer-based neuropsychological assessments and transcranial magnetic stimulation (TMS) of primary motor cortex for cognitive function and corticomotor excitability respectively. The hypothesis was that Cr supplementation would offset the impaired brain function caused by hypoxia.
First a trial round (where patients inhaled atmospheric air) was conducted in which baseline neuropsychological data was collected and participants were introduced to the hypoxia intervention. Then the Cr supplementation was given. This was followed the next day by two experimental sessions where neurophysiological, neuropsychological and neuroimaging data were collected at baseline (while inhaling atmospheric air) and/or during hypoxia.
Participants were given either 5 g of Creatine Monohydrate (CrM) or the equivalent amount of placebo (control) (PLA) in the form of a low-calorie flavoured powder which they consumed by dissolving in one glass of water. This procedure was followed four times a day (a total of 20g of CrM per day) for a period of 7 days.
A condition called hypoxia (a condition in which the body or a region of the body is deprived of adequate oxygen supply) was induced in the patients. The amount of oxygen was kept to a bare minimum for a period of 90 mins while monitoring respiration, blood pressure and heart rate. A gas mixture with a fraction of inspired oxygen (FiO2) of 0.1 was used to produce the hypoxia and delivered via a one-way valve face-mask system. This was followed the next day by neuropsychological, neurophysiological and neuroimaging tests with and without hypoxia.
NEUROPSYCHOLOGY, NEUROPHYSIOLOGICAL AND NEUROIMAGING PROCEDURES:
There were seven tests to assess the neuropsychology of patients. Verbal and visual memory, finger tapping, symbol digit coding (pairing specific numbers with given geometric figures), the Stroop test (demonstration of interference in the reaction time of a task), a test of shifting attention, and a continuous performance test. Nine cognitive functions that reflected basic mental functions were assessed from the primary scores. These were composite memory, verbal memory, visual memory, processing speed, executive function, psychomotor speed, reaction time, complex attention, and cognitive flexibility. An overall neurocognitive index score was also taken.
Neurophysiological tests were done using peripheral nerve stimulation (PNS) and transcranial magnetic stimulation (TMS). PNS consists of placing a wire-like electrode next to one of the nerves located in nerves beyond the brain or the spinal cord (peripheral nerves). A generator is used to provide the electrical stimulus to the electrode. This method is used to check if these nerves get excited or not. TMS consists of placing a magnetic field generator or a “coil” near the head (over the left motor cortex region of the brain in this experiment) of the person. This is used to stimulate small regions of the brain and to measure the connection between the brain and muscle to check for damage from brain disorders. These procedures were done to check the peripheral and corticomotor excitability levels respectively. Neuroimaging was done a day after supplementation at baseline while inhaling atmospheric air. Images were acquired using a scanner for each participant. A BOLD-contrast imaging (Blood-oxygen-level dependent contrast imaging) was also done. This is used in functional magnetic resonance imaging (fMRI) to observe active regions of the brain or other organs.
RESULTS AND DISCUSSION:
A simple dietary supplementation was used in this study to perform mainly 3 tasks. One to augment neural Cr stores, two to increase corticomotor excitability and three to prevent the decline of cognition (particularly attention capacity) that accompanies lack of oxygen. The results above suggest that dietary Cr may be neuroprotective. The CrM might have worked to maintain basic neuronal function and other cellular processes similar to the earlier findings in vitro.
DID THE DIETARY CRM SUPPLEMENTATION PRDUCE THE DESIRED INCREASE IN NEURAL CR CONCENTRATION?
Using Magnetic Resonance Stimulation or MRS, an increase in amplitude of the Cr plus PCr peak was detected in the sensorimotor cortex after 1 week of dietary Cr supplementation. This indicates that 7 days of consuming CrM is able to produce an increase in total neural Cr supplementation (7.03 + 1.62 mmol/L) compared to the intake of just PLA (6.44 + 0.90 mmol/L). The density of gray matter (associated with learning), white matter (associated with cognition) and cerebrospinal fluid (CSF – the fluid in the brain) were not different between the supplementation treatments.
The increase in Cr concentration in the brain after 7 days of CrM was 9.2%. Previous studies have examined the gray matter, white matter and the central cerebellum to name a few that have shown an increase in Cr concentration following CrM supplementation.
DID THE HYPOXIA PRODUCE THE DESIRED EFFECT?
To confirm whether the gas mixture produced the necessary oxygen deficit or hypoxia in the body, autonomic functions were monitored. Oxygen saturation in the arteries was reduced by 19% and a compensatory heart rate increase of 12% was seen. There was no change in the blood pressure. These results were all expected and identical between the nutritional treatments suggesting similar disruption to energy metabolism between the groups.
COGNITION, HYPOXIA AND DIETARY CRM SUPPLEMENTATION:
Cognition was affected (degraded) by induced hypoxia as seen in the following tests – complex attention, composite memory and psychomotor speed. The neurocognitive index that represents overall cognitive index was reduced by 12% with hypoxia. Hence an uninterrupted energy supply is needed to maintain basic neuronal function to sustain compex cognitive processes. When participants were subjected to cognitive tests that were repeated in normal conditions after hypoxia it was noticed that they could not re-learn the task. Cognitive functions that were not affected by hypoxia were verbal memory, processing speed, executive function and reaction time.
A number of cognitive scores improved after the Cr supplementation, notably tasks involving complex attention (21% increase as compared to PLA controls). Executive function, cognitive flexibility and neurocognitive index scores showed trends for improvement. We can conclude that cognitive functions that are affected by hypoxia can be corrected by CrM supplementation as these scores were higher in participants who consumed CrM as compared to PLA subjects.
Since Cr was consumed prior to hypoxia, the fall of ATP levels was slower than normal during oxidative deprivation due to the conversion of Cr to PCr and supplying high-energy phosphates to areas of the brain affected by hypoxia. The correction of the neurocognitive deficits did not correlate with the amount of Cr that was stored due to the supplementation revealing other roles of Cr that did not involve energy transfer.
CONNECTION BETWEEN CORTICOMOTOR EXCITABILITY (MOTOR FUNCTIONS CONTROLLED BY THE CEREBRAL CORTEX) AND COGNITION:
When corticomotor excitability was low due to hypoxia induction, there was also reduced cognition (indicated by the overall neurocognitive index) with PLA. This was abolished with CrM. Compared to normoxia, hypoxia led to an increase in corticomotor excitability by 70% (this was associated with increased cognition) only with CrM but not with PLA. Thus increased neural Cr has a neuromodulatory (where a neuron uses neurotransmitters to regulate other neurons) effect on cortical excitability. This neuromodulation might overcome neuronal deficiencies caused by hypoxia by maintaining membrane potentials which might be possible only in a high-energy state.
Thus, this first in vivo investigation shows that a 7 d supply of CrM augments neural Cr which in turn increases corticomotor excitability and prevents attention deficit occurring during hypoxia. It thus acts as a neuroprotective agent and an ergonomic aid when energy supplies are compromised showing the importance of the Cr-PCr systemin maintain a constant supply of energy. Since neurodegenerative diseases cn be caused due to inadequate membrane potential which in turn needs energy, studies have to be done keeping in mind CrM as a therapeutic supplement.
Summarized from the article:
CREATINE SUPPLEMENTATION ENHANCES CORTICOMOTOR EXCITABILITY AND COGNITIVE PERFORMANCE DURING OXYGEN DEPRIVATION
Clare E. Turner, Winston D. Byblow, and Nicholas Gant
The Journal of Neuroscience, January 28, 2015 • 35(4):1773–1780 • 1773