The nonapeptide hormone oxytocin (OT) has pivotal brain roles in social recognition and interaction and is thus a promising therapeutic drug for social deficits. Because of its peptide structure, however, OT is rapidly eliminated from the bloodstream, which decreases its potential therapeutic effects in the brain. We found that newly synthesized OT analogues in which the Pro7 of OT was replaced with N-(p-fluorobenzyl)­glycine (2) or N-(3-hydroxypropyl)­glycine (5) exhibited highly potent binding affinities for OT receptors and Ca2+ mobilization effects by selectively activating OT receptors over vasopressin receptors in HEK cells, where 2 was identified as a superagonist (E Max = 131%) for OT receptors. Furthermore, the two OT analogues had a remarkably long-acting effect, up to 16–24 h, on recovery from impaired social behaviors in two strains of CD38 knockout mice that exhibit autism spectrum disorder-like social behavioral deficits, whereas the effect of OT itself rapidly diminished.

Oxytocin (OT) is a nonapeptide that plays an important role in social behavior. Nasal administration of OT has been shown to improve trust in healthy humans and social interaction in autistic subjects. As is consistent with the nature of a peptide, OT has some unfavorable characteristics: it has a short half-life in plasma and shows poor permeability across the blood-brain barrier. Analogs with long-lasting effects may overcome these drawbacks. To this end, we have synthesized three analogs: lipo-oxytocin-1 (LOT-1), in which two palmitoyl groups are conjugated to the cysteine and tyrosine residues, lipo-oxytocin-2 (LOT-2) and lipo-oxytocin-3 (LOT-3), which include one palmitoyl group conjugated at the cysteine or tyrosine residue, respectively. The following behavioral deficits were observed in CD38 knockout (CD38−/−) mice: a lack of paternal nurturing in CD38−/− sires, decreased ability for social recognition, and decreased sucrose consumption. OT demonstrated the ability to recover these disturbances to the level of wild-type mice for 30 min after injection. LOT-2 and LOT-3 partially recovered the behaviors for a short period. Conversely, LOT-1 restored the behavioral parameters, not for 30 min, but for 24 h. These data suggest that the lipidation of OT has some therapeutic benefits, and LOT-1 would be most useful because of its long-last activity.

oxytocin (ot) is a critical molecule for social recognition and memory that mediates social and emotional behaviours. in addition, ot acts as an anxiolytic factor and is released during stress. Based on the activity of CD38 as an enzyme that produces the calcium-mobilizing second messenger cyclic ADP-ribose (cADPR), CD157, a sister protein of CD38, has been considered a candidate mediator for the production and release of OT and its social engagement and anti-anxiety functions. However, the limited expression of CD157 in the adult mouse brain undermined confidence that CD157 is an authentic and/or actionable molecular participant in OT-dependent social behaviour. Here, we show that CD157 knockout mice have low levels of circulating OT in cerebrospinal fluid, which can be corrected by the oral administration of nicotinamide riboside, a recently discovered vitamin precursor of nicotinamide adenine dinucleotide (NAD). NAD is the substrate for the CD157-and CD38-dependent production of cADPR. Nicotinamide riboside corrects social deficits and fearful and anxiety-like behaviours in CD157 knockout males. These results suggest that elevating NAD levels with nicotinamide riboside may allow animals with cADPR-and OT-forming deficits to overcome these deficits and function more normally. Oxytocin (OT) plays a role in social recognition, behaviour, and memory through a positive feedback system involving OT-induced OT release in the brain 1-3. OT is released in response to emotional, physical, and pharmacological stresses 1,2. It is known that OT counteracts stress-induced anxiety. Accordingly, OT in the brain is considered an anxiolytic factor 2,3. CD38 and CD157 are two related cell-surface molecules that form the calcium-mobilizing second messenger, cyclic ADP-ribose (cADPR) from nicotinamide adenine dinucleotide (NAD) 4-8 , the central coenzyme of metabolism 9. cADPR functions as a potential intracellular second messenger that triggers Ca 2+ mobilization from ryanodine receptor Ca 2+ pools to produce cellular responses 4,6. In the hypothalamus, cADPR triggers an increase in intracellular free Ca 2+ concentrations and, subsequently, Ca 2+-dependent OT release from oxytocinergic neurons 10. When this signalling cascade was blocked in CD38 knockout (CD38KO) mice, social memory and recognition and parental nurturing behaviours were disrupted, mainly due to reduced OT secretion 11,12. The treated mice increased levels of social behaviour, which was invoked by local re-expression of human CD38 in the

Recent studies provide evidence to support that cluster of differentiation 38 (CD38) and CD157 meaningfully act in the brain as neuroregulators. They primarily affect social behaviors. Social behaviors are impaired in Cd38 and Cd157 knockout mice. Single-nucleotide polymorphisms of the CD38 and CD157/BST1 genes are associated with multiple neurological and psychiatric conditions, including autism spectrum disorder, Parkinson’s disease, and schizophrenia. In addition, both antigens are related to infectious and immunoregulational processes. The most important clues to demonstrate how these molecules play a role in the brain are oxytocin (OT) and the OT system. OT is axo-dendritically secreted into the brain from OT-containing neurons and causes activation of OT receptors mainly on hypothalamic neurons. Here, we overview the CD38/CD157-dependent OT release mechanism as the initiation step for social behavior. The receptor for advanced glycation end-products (RAGE) is a newly identified molecule as an OT binding protein and serves as a transporter of OT to the brain, crossing over the blood–brain barrier, resulting in the regulation of brain OT levels. We point out new roles of CD38 and CD157 during neuronal development and aging in relation to nicotinamide adenine dinucleotide+ levels in embryonic and adult nervous systems. Finally, we discuss how CD38, CD157, and RAGE are crucial for social recognition and behavior in daily life.