Taurine is an essential amino acid derivative with many functions in the body. It plays a key role in antioxidation, managing fluid balance, protecting nerves, and controlling metabolism. However, studying exactly how it works is difficult. This is because taurine's levels change quickly, it is found in specific tissues, and it interacts complexly with the body's microbes. Using multiple "omics" technologies together, like metabolomics, microbiomics, and transcriptomics, provides new ways to research taurine. This combined approach helps reveal how taurine functions in diseases, which offers vital support for medical treatments.
Physiological Functions of Taurine
Antioxidant Effect
Taurine is a strong antioxidant. It effectively clears out harmful free radicals and reactive oxygen species (ROS). This helps reduce cell damage from oxidative stress. Studies show higher taurine levels in organs with more oxidative stress, like the brain, liver, and heart, proving its important protective role there. Additionally, taurine can boost cells' own antioxidant defenses by adjusting how certain antioxidant enzymes are expressed.
Osmoregulation
Taurine plays an important role in maintaining the osmotic pressure balance inside and outside the cell. It regulates the intracellular taurine level through active absorption of Na⁺/Cl⁻-dependent TAUT transporters and passive release of volume-regulated anion channels (VRACs), thereby maintaining cell volume stability. In a hypotonic or hypertonic environment, the absorption and release mechanisms of taurine change to adapt to different osmotic pressure conditions.
Neuroprotective effect
Taurine is very important for protecting the central nervous system. It helps neurons grow and survive. Also, by controlling how neurotransmitters are released and how receptors work, taurine affects our thinking, feelings, behavior, memory, and learning. It also reduces neuron death (apoptosis) and swelling (inflammation). This suggests it could help treat brain diseases like Alzheimer's and Parkinson's. When the brain has an ischemic injury (lack of blood flow), taurine is released from specific cells (Bergmann glial cells) to protect it. Taurine can also calm down brain activity by working with the GABAA receptor complex.
Metabolic regulation
Taurine also plays an important role in metabolic regulation. It participates in the regulation of fatty acid metabolism, bile acid synthesis and energy metabolism, helps maintain the balance of fat and sugar, and thus has a preventive and therapeutic effect on metabolic diseases such as metabolic syndrome and diabetes. In addition, taurine can also affect the stability of cell membranes and signal transduction by regulating calcium ion levels.
Other Features
Taurine also has multiple functions such as anti-inflammatory, antiviral, and anti-tumor. For example, it can reduce inflammatory responses by regulating the activity of immune cells; in some cases, taurine can also inhibit the proliferation of tumor cells and has potential anti-cancer effects. In addition, the application of taurine in livestock and poultry feed has also shown its positive effects in promoting animal growth, improving feed utilization, and enhancing immunity.
Molecular Mechanism of Taurine Metabolism
Mammals (such as humans and mice) can synthesize taurine through three different pathways, including: ① cysteine sulfinic acid pathway, ② cysteamine pathway and ③ sulfoalanine pathway. Among them, the cysteine sulfinic acid pathway (①) is the main biosynthetic pathway, and the latter two belong to auxiliary synthesis pathways. In the main synthesis pathway, the key enzymes that limit the synthesis rate of taurine are cysteine dioxygenase (CDO) and cysteine sulfinic acid decarboxylase (CSAD), and their enzyme activities directly affect the efficiency of taurine synthesis in the body. There are significant differences in this synthesis ability among different species: rodents have a higher synthesis level, followed by humans, and cats have almost no ability to synthesize taurine by themselves. In addition, individuals have different potential for taurine synthesis at different physiological stages. Compared with adults, the activity of the enzymes responsible for converting methionine to cysteine in the liver of newborns is weaker, resulting in insufficient ability to synthesize taurine by themselves, so they are more dependent on obtaining sufficient taurine from food.
Figure 1. The metabolic pathways of taurine.
The transport and metabolism of taurine in the body
Taurine transporters are found on cell membranes throughout the body. Their main job is to move taurine from outside to inside cells. There are two primary types: the Na⁺/Cl⁻-dependent taurine transporter (TauT) and the proton-coupled amino acid transporter (PAT1). TauT binds strongly to taurine, especially when outside taurine levels are low, making it the main transporter then. PAT1, however, binds more weakly but can transport a lot of taurine, typically working when taurine levels are high. In mice lacking TauT, taurine transport significantly drops. This leads to about a 98% decrease in taurine in muscle and heart tissue, and a 70-90% drop in the brain, kidneys, and liver. These findings show that TauT is vital for regulating taurine transport in living organisms. A lack of TauT also causes severe problems like heart muscle damage, kidney development issues, and liver problems such as fibrosis, inflammation, and even tumors. These studies emphasize taurine's crucial role in maintaining the body's balance and normal development.
After entering the small intestine, taurine from food is taken up into intestinal cells through the transporter proteins TauT and PAT1 on the intestinal epithelial cell membrane, and then transported to the liver through the portal vein system and further distributed to tissues throughout the body. Among them, taurine concentrations are particularly abundant in tissues such as the heart, brain, and skeletal muscle. In the human liver, the main bile acids synthesized by hepatocytes include cholic acid (CA) and chenodeoxycholic acid (CDCA). Under the coordinated catalysis of bile acid-CoA ligase (BAL) and bile acid acyl CoA: amino acid N-acyltransferase (BAT), these primary bile acids can undergo conjugation reaction with taurine to generate taurine-conjugated bile acids (Tau-BAs), mainly including taurocholic acid (TCA) and taurochenodeoxycholic acid (TCDCA), which become important components of primary bile acids. Conjugated bile acids constitute the vast majority of the bile acid pool, accounting for about 90%. In adults, bile acids mostly exist in the form of glycine conjugation, and Tau-BAs account for about 30% of the entire bile acid pool; in mice, taurine-conjugated bile acids account for about 95%.
The Relationship between Taurine and Disease
Metabolic syndrome
Taurine plays an important role in the prevention and treatment of metabolic syndrome. Studies have shown that taurine can improve insulin sensitivity, lower blood sugar levels, and reduce the risk of dyslipidemia and obesity. In addition, taurine can also improve multiple pathological features of metabolic syndrome by regulating lipid metabolism and energy metabolism.
Cardiovascular disease
Taurine plays an important protective role in the cardiovascular system. It supports heart health by regulating heart contraction, stabilizing cell membranes, and regulating calcium levels. In addition, taurine can lower blood pressure, prevent atherosclerosis and myocardial damage, and has potential therapeutic value for cardiovascular disease.
Neurodegenerative diseases
Taurine also shows a positive effect in the prevention and treatment of neurodegenerative diseases. It can protect neurons from damage by reducing neuronal apoptosis and inflammation. In addition, taurine can improve cognitive function and emotional state by regulating the release of neurotransmitters and receptor function.
Intestinal diseases
Taurine also plays an important role in intestinal health. Studies have shown that taurine can affect the immune function and barrier function of the intestine by regulating the composition of intestinal microbial communities and metabolites. In addition, taurine can also affect the absorption and utilization of nutrients by regulating the metabolic pathways of intestinal flora.
Tumor metabolism
Taurine and hypotaurine metabolism is significantly altered in a variety of tumors. For example, in gliomas, hypotaurine can promote tumor cell invasion while inhibiting demethylase activity. In endometrial cancer, tumors of different grades show unique metabolic phenotypes, and low-grade tumors are more dependent on the antioxidant function of taurine and hypotaurine. In addition, taurine and hypotaurine metabolism also show significant changes in diseases such as breast cancer and drug-induced osteonecrosis of the jaw.
Research Methods and Strategies
Metabolomics analysis
Metabolomics technology is widely used to study the metabolic network of taurine and hypotaurine. Through highly sensitive detection methods, such as ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS/MS), multiple amino metabolites can be quantified simultaneously to comprehensively analyze the metabolic network of taurine and hypotaurine.
Gene Editing Technology
The use of gene editing technology to construct tissue-specific knockout models is helpful to study the precise functions of taurine and hypotaurine in specific physiological processes. For example, by knocking out the ezrin gene, the study found that impaired placental uptake of hypotaurine can lead to fetal growth restriction, revealing the importance of hypotaurine in fetal development.
Conclusion
Taurine is a versatile amino acid derivative with many important jobs in the body. It helps with antioxidation, managing fluid balance, protecting nerves, and controlling metabolism. Problems with taurine metabolism are linked to various diseases, including metabolic syndrome, heart disease, neurodegenerative disorders, gut problems, and even cancer, suggesting it could have preventive and therapeutic benefits. Right now, research on taurine is advancing with tools like multi-omics strategies, including metabolomics, gene editing, and microbiome studies. Its interaction with gut microbes is a particularly hot research area. Using precise models and high-throughput technologies, scientists are uncovering how taurine works in disease development, which provides essential knowledge and practical support for using taurine in medical treatments.
References
- Edgar, S. E., Kirk, C. A., Rogers, Q. R., & Morris, J. G. (1998). Taurine status in cats is not maintained by dietary cysteinesulfinic acid. The Journal of nutrition, 128(4), 751–757. https://doi.org/10.1093/jn/128.4.751
- Baliou, S., Kyriakopoulos, A. M., Goulielmaki, M., Panayiotidis, M. I., Spandidos, D. A., & Zoumpourlis, V. (2020). Significance of taurine transporter (TauT) in homeostasis and its layers of regulation (Review). Molecular medicine reports, 22(3), 2163–2173. https://doi.org/10.3892/mmr.2020.11321
