Preface

The purinergic system is a set of components capable of generating a cellular intercommunication network. Composed of signaling molecules, regulatory enzymes, and specific receptors, this organization can modulate several basal pathways of the organism. However, its understanding is relatively recent for researchers. In 1929, Drury and Szent-Gyorgyi described the extracellular functions associated with purines. In 1972, Burnstock defined the concept of purinergic neurotransmission, given that nucleotides and nucleosides were studied only in energy activities. In 1978, the extracellular receptors of the P1 and P2 groups were described in the literature by Burnstock when empirically demonstrating the role of adenosine triphosphate (ATP) as a transmitter and other functions in some processes.

Characterized as a common signaling pathway between cells, the purinergic system is capable of modulating physiological and biochemical processes. It has been widely studied for its therapeutic potential and modulation of physiological processes, such as performance in the process of apoptosis, thromboregulation, cell proliferation, platelet aggregation, endothelial vasodilation, and pain mechanism as well as neurotransmission and neuroprotection. In addition, several studies report an association of the purinergic system with inflammatory processes and immune responses.

In an initial approach, it is necessary to define the executing components of this system, given that its signaling is dependent on the biochemical interactions of these structures and conducted by purines. As for neurotransmitters, ATP, adenosine diphosphate (ADP), and adenosine monophosphate (AMP) constitute the nucleotides, while there is the adenosine nucleoside. Specific enzymes regulate these ectoenzymes, divided into adenosine deaminase (ADA) responsible for deaminating adenosine to inosine and ectonucleotidases E-NPP, E-NTPDases, ecto-5'-nucleotidase, and alkaline phosphates that hold nucleotides.

Nucleosides and nucleotides are signaling biomolecules that have functional diversity in the extracellular environment and modulate several biological effects. Its differences are noticeable initially by the number of phosphate groups and may have three groups (ATP) or be absent (adenosine). However, its regulation and reception also change. In this view, the receivers are from different organizations and initially differ in groups P1 and P2. The first is closely related to the nucleoside adenosine and are channels coupled to the G protein subdivided into A1, A2a, A2b, and A3. The second group has a preference for mono-, di-, and triphosphate nucleotides, such as AMP, ADP, and ATP, being subdivided into P2X, linked to ion channels that, when activated, result in the opening of pores in the cell membrane and the passage of Na+, K+, and cations Ca2+.

All cells have components of the purinergic system and could release nucleotides in a controlled manner. The mechanisms related to the release of nucleotides have been an intense focus of research activities. Studies have extensively investigated the physiology, pharmacology, and biochemistry of purinergic signaling. More recently, the focus has been on the pathophysiology and therapeutic potential of components of the purinergic system, especially concerning P1 and P2 receptors. It is currently established that changes in purinergic signaling are involved in the pathophysiology and therapy of many diseases, possibly in addition to being related to the effects of nutraceutical molecules.

This book describes the purinergic system and the correlation between the system and the health and disease process. It is divided into three sections and eight chapters describing purinergic and immune signaling, the purinergic system and diseases, and future perspectives.

We hope that academic researchers and students can learn and share the knowledge presented here. This book is the result of several collaborating parties. We gratefully acknowledge all the authors and reviewers for their contributions and the valuable assistance of Ms. Dolores Kuzelj and Mia Vulovic at IntechOpen for their support throughout the publication process.

> **Margarete Dulce Bagatini** Federal University of Fronteira Sul, Chapecó, SC, Brazil

Section 1
