LVV-H7 attenuates hyperactivity and depressive-like behaviors in spontaneously hypertensive rats
Background
The spontaneously hypertensive rat (SHR) model is widely used to study attention-deficit/hyperactivity disorder (ADHD)-like behaviors and associated comorbidities. Current treatments often have side effects or limited efficacy for complex behavioral profiles. LVV-H7, a decapeptide derived from β-hemoglobin, is known to inhibit insulin-regulated aminopeptidase (IRAP), an enzyme that degrades oxytocin (OT). While LVV-H7 shows oxytocin receptor (OTR)-dependent behavioral effects in control rats, its impact on hyperactive behavioral disorders, particularly in the SHR model, remained unexplored, representing a significant knowledge gap.
Study Design
Researchers investigated LVV-H7's effects on behavior in male SHR and Wistar (WT) rats. Animals were injected intraperitoneally (i.p.) with vehicle (NaCl 0.9%) or LVV-H7 at doses of 0.1 mg/kg or 10 mg/kg 30 minutes before behavioral assessments. Locomotion, exploration, anxiety- and depressive-like behaviors were evaluated using the open field (OF), elevated plus maze (EPM), and forced swim (FS) tests. Plasma OT levels were measured, and hypothalamic OTR protein expression was compared between strains. An in silico analysis also compared the primary structures of OT, OTR, and IRAP across WT, SHR, and humans.
Results
Baseline analysis showed SHR exhibited greater hyperactivity, spending more time in EPM open arms and displaying augmented grooming, crossing, and rearing episodes in the OF compared to WT rats. Crucially, LVV-H7 produced behavior-specific effects exclusively in SHR, with no significant changes observed in WT rats. > LVV-H7 significantly reduced the time SHR spent in the EPM closed arms, decreased rearing episodes during both EPM and OF tests, and attenuated immobility time during the FS test. While LVV-H7 increased plasma OT levels in WT rats, the same treatment paradoxically decreased circulating OT in SHR. Hypothalamic OTR protein levels were similar between strains. In silico analysis suggested that although OT and OTR structures are identical between WT and SHR, the IRAP of SHR might display alterations in its trafficking region, potentially explaining the differential OT response and behavioral effects.
Key Findings
- LVV-H7 reduced time in EPM closed arms in SHR, indicating decreased anxiety-like behavior.
- LVV-H7 attenuated rearing episodes in both EPM and OF tests in SHR, suggesting reduced hyperactivity.
- LVV-H7 decreased immobility time during the forced swim test in SHR, indicating antidepressant-like effects.
- LVV-H7 increased plasma oxytocin in WT rats but decreased it in SHR, highlighting strain-specific responses.
- In silico analysis suggests potential alterations in SHR IRAP trafficking region, despite identical OT/OTR structures.
Why It Matters
This study highlights LVV-H7 as a potential therapeutic agent for managing specific behavioral alterations, such as hyperactivity and depressive-like states, particularly relevant for conditions like ADHD or anxiety disorders. The finding that LVV-H7's effects in SHR are independent of an increase in OT, and even occur with a decrease in circulating OT, suggests a novel mechanism of action, possibly through direct or indirect modulation of IRAP function or other pathways. This opens new avenues for drug development beyond direct oxytocin agonism, which can have complex systemic effects. Further research into LVV-H7's precise mechanism, especially its interaction with IRAP trafficking and downstream signaling, could lead to more targeted interventions for neurobehavioral disorders. While preclinical, these results warrant investigation into human translational potential.
lvv-h7
shrs
hyperactivity
anxiety
depression
oxytocin