What are adenosine and thymidine?
Adenosine and thymidine are both nucleosides found in DNA. Adenosine occurs also in RNA [1].
Adenosine consists of a ribose sugar and a purine—adenine. In addition to its crucial function as a storage and transmitter of genetic information, adenosine has other functions. It works as a vasodilator, cardioprotective, and anti-inflammatory molecule [2].
One of the characteristics of adenosine is its short metabolism of it via cell absorption and deaminase degradation [2].
Thymidine, on the other hand, is made of ribose sugar and pyrimidine. It plays a crucial role in cell division and growth and is also vital in the biosynthesis of DNA [3].
How does adenosine function?
Adenosine is crucial for energy storage and use. It is part of the adenosine triphosphate (ATP) molecule, which stores energy on bonds between the phosphorus atoms. ATP is the most common energy giver for the most energy-demanding reaction in the body [4]. It makes adenosine essential for life, as it is used by all cells.
The cells release adenosine during low blood or oxygen delivery [5]. It connects to four types of receptors that can be found in many systems, including the circulatory, respiratory, nervous, and urinary [6].
The activation of these receptors triggers many processes, such as vasodilation, cell proliferation, vessel remodeling, and inflammation [5].
It influences the heart rhythm [7]. Many of the adenosine receptors in the heart are focused on the atrioventricular node, a key structure in heart rhythm regulation [6]. Additionally, adenosine plays a crucial role in the heart's response to heart failure and pulmonary hypertension [8].
Adenosine also plays a significant role in regulating glucose homeostasis [9] and kidney processes like sodium reabsorption and tubuloglomerular feedback [10].
In the brain, adenosis inhibits neuronal activities and regulates blood flow [4].
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What does thymidine do?
Thymidine has no direct functions like adenosine. Its main function is to encode genetic information [12].
However, thymidine is an important substrate for many crucial biochemical processes. The active molecule that thymidine is turned into is called thymidine monophosphate (dTMP). This compound is essential for the biosynthesis and repair of DNA [12, 13]
The enzyme thymidine phosphorylase converts thymidine into another active molecule, the 2-deoxy-α-D-ribose-1-phosphate (dRib-1-P) [14].
This converted version of thymidine can enter the glycolytic pathway, allowing the survival of nutrient-deprived cells [15].
However, dRib-1-P and its metabolites also participate in many tumor-related processes, such as metastasis, invasion, autoimmune system evasion, tumor angiogenesis, and apoptosis resistance [14].
Interestingly, the same enzyme that converts thymidine into dRib-1-P plays a role in cancer treatment. It allows for a target oriented activation of a commonly used in oncology drug fluoropyrimidine capecitabine [14, 16].