In respect to organic chemistry, a thiol is a compound - an organosulfur which consists of carbon-bonded sulfhydryl group. Thiols are very important and interesting, judging from their very many uses. These uses take the involvement of thiols in different forms or rather in different components as will be discussed below.
A recent study shows that protective antioxidants containing thiol, namely NAC and NBMI, attenuates the loss of the endothelial barrier function of bleomycin. This same study goes ahead and shows that “the effectiveness of the lipid-soluble thiol-protectant, NBMI, at µM concentrations, is comparable to mM concentrations of the water-soluble thiol-protectant, NAC” (Patel, et al., 2012).
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To secondly mention, thiol groups together with disulfides are key to improving the solubility and stability of proteins (Patel, et al., 2012). This is because thiols and disulfides are very reactive components. They majorly occur in a group of cysteine, which is lightly acidic and has pKa values with a 4 to 9 range depending on the protein structure and environment. In general, this makes thiols a very important component in such activities of living organisms such as catalysis, metal binding, and being a molecular switch (Gethin, Aslan, Helen, & Rita, 2015). However, research is still being done to find out the role of thiols and disulfides in problems relating to protein molecules.
Thiols can exist as a component called thiol redox whose imbalance is a significant factor contributing to neurodegenerative disease. It is significant in determining the likelihood of an oxidative damage, neurodegeneration, and excitotoxicity (Gethin, Aslan, Helen, & Rita, 2015). Therefore, restoration of redox balance may be a way of minimizing neuronal loss when neurodegeneration takes place.
When it comes to thiol antioxidants, there is a component known as GSH which is to actually state, a major thiol antioxidant. GSH works with a system of redox couples containing “NADþ/NADH, NADPþ/NADPH and GSH/GSSG that work in concert with GSH/ glutathione reductase (GSR), Grx/GSH, Trx/oxidised Trx and thioredoxin reductase (TrxR) and Prx to maintain redox homeostasis” (Gethin, Aslan, Helen, & Rita, 2015). For neurons, the pentose phosphate or phosphogluconate pathway for the GSR to regenerate GSH from GSSG provides the NADPH. Moreover, neurons normally oxidize glucose for antioxidant defense instead of the production of energy, because of the key activator’s low activity of “glycolysis, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase-3” (Gethin, Aslan, Helen, & Rita, 2015).
Cysteine is also a thiol component that must be supplied in the brain either in situ synthesis or from extra cellular medium. Astrocytes and microglial cells are what produces GSH in the brain. Cystine is then imported and taken to the cytosol where it is immediately reduced to cysteine. (Gethin, Aslan, Helen, & Rita, 2015)
Thiol redox homeostasis is an important thiol process in glaucoma as well. Glaucoma is a condition that leads to irreversible blindness worldwide, whereby it is the caused by continued damage of the optic nerve. What happens is that the retina has many vascular body tissues, hence become affected by oxidation because of high oxygen consumption and light exposure (Gethin, Aslan, Helen, & Rita, 2015). Metabolic rates per tissue, therefore, become very high, hence the need for maintaining normal GSH levels.
There has been an argument and evidence for neurodegeneration redox disturbance. This is where autopsy tissue expression or circulating cells and plasma is altered. Research has it that there is a limited analysis of Grx1 when it comes to human neurodegenerative disease. However, recent post-mortem studies of PD patients’ midbrain show that Grx1 content is decreased in PD (Gethin, Aslan, Helen, & Rita, 2015).
All the above components and functions of thiols show how a thiol is a very important component. Little is told about thiols and their importance is hardly recognized hence underestimated. However, it should be noted that thiols have the power to exist in many forms, hence function in different important ways, such as being an antioxidant and activities like catalysis among others.
References
Gethin, M. J., Aslan, M., Helen, G. R., & Rita, T. C. (2015). Thiol redox homeostasis in neurodegenerative disease. ELSEVIER , 1-9.
Patel, R. B., Sainath, K. R., A, L. S., Smitha, M., Travis, G. O., Niladri, G. N., . . . Narasimham, P. L. (2012). Thiol-redox antioxidants protect against lung vascular endothelial cytoskeletal alterations caused by pulmonary fibrosis inducer, bleomycin: comparison between classical thiol protectant, N-acetyl-L-cysteine, and novel thiol antioxidant, N,N′- bis-2-merca. Columbus: NIH Public Access.
