Methionine, an essential amino acid for humans, is an important amino acid in proteins, as well as the key component of S-adenosyl methionine (SAM), the main donor of methyl groups in the biosynthesis of biomolecules like choline, creatine, and adrenaline, as well as in DNA methylation. Following SAM demethylation, homocysteine (HCys) is formed. HCys accumulates when its recycling pathways become impaired, leading to hyperhomocysteinemia, that is typical in cardiovascular diseases, neurological/psychiatric disorders and cancer. Whether excessive HCys is causing the pathological conditions or only a biomarker remains to be established.
In the present project we will evaluate the biological properties of HCys-derived molecules.
Last year we synthesized HCSA and established that it can be converted into homohypotaurine via a bio-based route. Both compounds are not available commercially. As part of this project, we will find the best conditions for the bio-based synthesis and purification of homohypotaurine. We will test its biological effects both in bacteria and eukaryotic cells. Very little is known on the biological role of homohypotaurine respect to homotaurine, its oxidation product, in widespread pharmaceutical and laboratory use.
Furthermore, we plan to investigate the metabolic role of biomolecules related to taurine. Particular emphasis will be on thiotaurine, a biomolecule releasing hydrogen sulfide (H2S), and on the role of these molecules in controlling inflammation. The specific signaling pathways involved will be dissected and proteomic profiling of human neutrophils carried out. The aim of this study is to identify the proteins that change their expression level or undergo post-translational modifications, including nitrosylation/nitration, persulfidation. Finally, the effect of H2S will be assessed in pathologies characterized by an increase of oxidative stress, as it occurs in some respiratory diseases such as Chronic Obstructive Pulmonary Disease.
While a great deal of work is carried out on taurine and homotaurine (the latter, free or derivatized, is in widespread pharmaceutical and laboratory use), an extensive search of the literature retrieved more limited information on the properties of homohypotaurine, the decarboxylation product of HCSA. The properties of this latter molecule and of HCSA, structurally the closest homologues of GABA and L-Glutamate, the major inhibitory and excitatory neurotransmitters in the CNS, respectively, need a more in-depth investigation. To date it is known that HCSA acts as an agonist of the metabotropic glutamate receptors (mGluR) [20], and that it increases glucose uptake in skeletal muscle via stimulation of AMP-activated protein kinase [21]. These findings point to a role of HCSA in diabetes.
With this work De Biase's group will also set out the basis for a deeper investigation of the possible biological activity of homohypotaurine as compared to homotaurine. Depending on the outcome of the work planned in this project, we will seek for collaborations to assay the biological activity of homohypotaurine on eukaryotic cells and laboratory animals. In fact, even though this work will begin with testing bacterial GAD (with HCSA and HCA) and GABA transaminase (with homohypotaurine and homotaurine), human GAD (available in De Biase¿s group) will eventually be considered for activity on both HCSA and HCA.
Non-steroidal anti-inflammatory drugs are among the most commonly used drugs. Despite efforts to produce non-steroidal anti-inflammatory drugs that do not cause gastrointestinal ulceration and bleeding, these adverse effects remain major limitations to their use. On the contrary it has been reported that H2S donors can increase the resistance of the gastric mucosa to injury and accelerate damaged tissue repair [22]. These observations suggest that anti-inflammatory molecules that are chemically modified to release H2S will exhibit improved efficacy and reduced toxicity. In this context thiotaurine biomolecule structurally related to taurine and to hypotaurine, particularly abundant in neutrophil granulocytes, has a thiosulfonate (RSO2SH) group which can potentially release H2S. This biocompound could mimic the role of H2S in inflammation, but also play a protective role on the gastric mucosa when administered with an anti-inflammatory drug. The study of anti-inflammatory effect of thiotaurine and its derivatives will also lead to new therapeutic applications for the treatment of inflammatory lung diseases.
The mechanisms involved in the interaction of the reactive oxygen (ROS) and nitrogen species (RNS) with sulfinates have only recently been investigated [23]. Interestingly, the oxidation of sulfinates by radicals is accompanied by the generation of highly reactive sulfonyl radicals which can promote oxidative reactions. In light of this, establishing the pathophysiological role of sulfonyl radicals will be an outcome of this work.
References
20. Shi Q. et al. (2003) J. Pharmacol. Exp. Ther. 305, 131
21. Kim J.H. et al. (2011) J. Biol. Chem. 286, 7567
22. Wallace JL (2007) Trends Pharmacol Sci, 28, 501
23. Baseggio Conrado A. et al. (2014) Free Radic. Res. 48, 1300.