General Description

Creatine monohydrate, vital for muscle cell energy production, is synthesized from arginine and glycine, forming guanidinoacetate, then methylated in the liver. It can also be sourced from meat. Transported into skeletal muscle against its gradient by the CreaT transporter, its expression is dependent on creatine levels. Exercise enhances this process. Creatine monohydrate acts as a precursor for ATP synthesis, facilitated by creatine kinase. Mitochondrial CK synthesizes phosphocreatine, while cytosolic CK regenerates ATP. Creatine monohydrate serves as an energy buffer, regulating pH and metabolically influencing glucose metabolism and muscle glycogen synthesis. Overall, Creatine monohydrate's synthesis, transport, and metabolic roles are crucial for cellular energy production and function.

Figure 1. Creatine monohydrate

Synthesis and Transport

Creatine monohydrate, a vital compound for energy production in muscle cells, is synthesized and transported through a series of processes in the body. 1

Synthesis

The synthesis of Creatine monohydrate begins with arginine and glycine, which undergo enzymatic reactions to form guanidinoacetate in the kidney. This guanidinoacetate is then transported to the liver, where it is methylated to produce creatine. On average, the body synthesizes about 1 to 2 g of creatine daily. Additionally, Creatine monohydrate can be obtained through dietary sources, mainly from meat and poultry consumption, adding another 1 to 2 g per day from an omnivorous diet.

Transport

Once synthesized or ingested, Creatine monohydrate enters the bloodstream during digestion and is transported to skeletal muscle where it acts as a vital source of energy. The transportation of Creatine monohydrate into muscle cells occurs against its concentration gradient, facilitated by the CreaT transporter, which utilizes a Na?/Cl–dependent mechanism. The expression of CreaT is influenced by the levels of creatine and phosphocreatine in the body. Studies suggest that exercise can enhance the translocation of CreaT to muscle cell membranes, increasing cytoplasmic creatine stores. Ultimately, Creatine monohydrate is excreted in the form of creatinine through glomerular filtration in the kidneys, with most of the synthesized and dietary creatine exiting the body in this manner, totaling approximately 2 g per day. 

This synthesis and transport of Creatine monohydrate play a crucial role in maintaining energy levels within muscle cells and overall bodily functions. 

Role in Energy Metabolism

Precursor for ATP Synthesis

Creatine monohydrate plays a crucial role in energy metabolism by acting as a vital precursor in the synthesis of ATP, the energy currency of cells. When the body requires increased energy, phosphocreatine donates its phosphate group to ADP, converting it into ATP through the action of creatine kinase (CK) enzyme. This process ensures a quick and efficient energy supply during high-demand activities.

Mitochondrial and Cytosolic Creatine Kinase

Two forms of CK, mitochondrial CK, and cytosolic CK, have distinct functions in energy metabolism. Mitochondrial CK synthesizes phosphocreatine from ATP produced through oxidative phosphorylation, while cytosolic CK regenerates ATP from phosphocreatine at specific sites where energy consumption is high. Disruption of CK function, especially in muscle and brain tissues, can lead to various metabolic abnormalities affecting muscle function, weight regulation, fat metabolism, and behavioral patterns.

Metabolic Regulator and Anabolic Signal

Creatine monohydrate serves as a spatial, pH, and temporal-energy buffer in energy metabolism. It facilitates the transportation of ATP from mitochondria to the cytosol, buffering temporal energy fluctuations and regulating cellular pH levels. Studies have shown that creatine supplementation influences glucose metabolism independently of insulin, indicating its direct impact on glycolytic pathways. Moreover, creatine supplementation after resistance training has been linked to increased expression of glucose transporters like GLUT-4 and enhanced muscle glycogen content, potentially through the stimulation of AMP-activated protein kinase activity and anabolic signaling pathways. The mechanism underlying creatine's effects on glucose metabolism is still under investigation, with theories suggesting alterations in phosphocreatine levels and cellular osmolarity triggering signaling cascades that regulate muscle glycogen synthesis. Overall, creatine monohydrate's role in energy metabolism highlights its significance in supporting cellular energy production and metabolic functions. ²

Reference

1. Brudnak MA. Creatine: are the benefits worth the risk? Toxicol Lett. 2004; 150: 123–130.

2. Pearlman JP, Fielding RA. Creatine monohydrate as a therapeutic aid in muscular dystrophy. Nutr Rev. 2006;64(2 Pt 1):80-88.