Antinociceptive effects of the endogenous cannabinoid peptide agonist VD-hemopressin(β) in mice

The Endogenous Cannabinoid and the Nitricoxidergic Systems Differently Influence Heat and Cold Stress-Induced Analgesia

Stress-induced analgesia (SIA) is a well-known phenomenon, in which mechanisms of development opioid and non-opioid components take part. The endogenous cannabinoid system (ECS) takes part in the non-opioid pathways and modulates nociception. Nitric oxide (NO) is also proverbial to interfere with pain perception. The present study was performed to investigate the effects from interaction between the ECS and NO after heat (heat stress) or cold (cold stress) exposure. Male Wistar rats subjected to one hour of heat or cold stress were injected with different combinations of cannabinoid receptor type 1 (CB1) agonist anandamide (AEA) or antagonist (AM251) along with NO-donor, NO-precursor or inhibitor of the NO-synthase (NOS). Nociception was evaluated using Paw pressure (Randall-Selitto) test. The results showed that AEA-administration immediately after the end of stress let to a tendency to increase cold-SIA, but decreased heat-SIA. AEA along with NO-donor increased both cold- and heat-SIA but to a different degree. AM251 and NOS-inhibitor decreased SIA. Our experiments confirmed that the endogenous cannabinoid and the nitricoxidergic systems interact between them in the modulation of SIA. The ECS exerts a more prominent influence on cold rather than heat SIA. Differences in modulation probably depend on the type of stress, due to the different participation of ECS in the mechanisms of SIA development.

Hemoglobin-derived peptides and mood regulation

Evidence accumulated over the past decades has revealed that red blood cells and hemoglobin (Hb) in the blood play important roles in modulating moods and emotions. The number of red blood cells affects the mood. Hb is the principal content in the red blood cells besides water. Denatured Hb is hydrolyzed to produce bioactive peptides. RVD-hemopressin α (RVD-Hpα), which is a fragment of α-chain (95-103) in Hb, functions as a negative allosteric modulator of cannabinoid receptor 1 and a positive allosteric modulator of cannabinoid receptor 2. Hemorphins, which are fragments of β-chain in Hb, exert their effects on opioid receptors. Two hemorphins, namely, LVV-hemorphin-6 and LVV-hemorphin-7, could induce anxiolytic-like effects. The use of Hb-derived bioactive peptides for the treatment of mood disorders is desirable due to cannabinoid-opioid cross modulation and the critical roles of the two systems in physiological processes, such as memory, mood and emotion.

Intracellular Peptides in Cell Biology and Pharmacology

Intracellular peptides are produced by proteasomes following degradation of nuclear, cytosolic, and mitochondrial proteins, and can be further processed by additional peptidases generating a larger pool of peptides within cells. Thousands of intracellular peptides have been sequenced in plants, yeast, zebrafish, rodents, and in human cells and tissues. Relative levels of intracellular peptides undergo changes in human diseases and also when cells are stimulated, corroborating their biological function. However, only a few intracellular peptides have been pharmacologically characterized and their biological significance and mechanism of action remains elusive. Here, some historical and general aspects on intracellular peptides' biology and pharmacology are presented. Hemopressin and Pep19 are examples of intracellular peptides pharmacologically characterized as inverse agonists to cannabinoid type 1 G-protein coupled receptors (CB1R), and hemopressin fragment NFKF is shown herein to attenuate the symptoms of pilocarpine-induced epileptic seizures. Intracellular peptides EL28 (derived from proteasome 26S protease regulatory subunit 4; Rpt2), PepH (derived from Histone H2B type 1-H), and Pep5 (derived from G1/S-specific cyclin D2) are examples of peptides that function intracellularly. Intracellular peptides are suggested as biological functional molecules, and are also promising prototypes for new drug development.