2026 ECNP Congress

PS02-2202

The formation of dopamine and serotonin in a CYP2D6-humanized rat brain

Renata Pukło — E. Bromek, A. Haduch, W. Kuban, N. Alenina, M. Bader, W.A. Daniel · Maj Institute of Pharmacology Polish Academy of Sciences, Department of Pharmacokinetics and Drug Metabolism, Kraków, Poland

2026 ECNP Congress

Background

The brain dopaminergic and serotonergic systems are involved in different psychiatric and neurological diseases. Our previous studies have shown that, apart from the classical pathways of neurotransmitter synthesis (from tyrosine or tryptophan, respectively), an additional pathway of their formation exists in the brain, mediated by cytochrome P450 enzymes belonging to the CYP2D subfamily [1-5]. These enzymes catalyze the hydroxylation of tyramine to dopamine and the 5-methoxytryptamine O-demethylation to serotonin, as demonstrated in vitro in rat brain microsomes and human neuronal cells, and in vivo in rat brain microdialysis model (by measuring extracellular neurotransmitter level). In the present study, we investigated the role of the human CYP2D6 enzyme in dopamine and serotonin synthesis in CYP2D6-humanized rat brain (by measuring total tissue neurotransmitter level).

Methods

To assess the importance of human CYP2D6-mediated dopamine and serotonin formation for total brain neurotransmitter synthesis, we developed an in vivo model overexpressing human CYP2D6 in the rat brain. The AAV5-CYP2D6 construct was introduced into the striatum or prefrontal cortex on one side; on the other side, AAV5 was given. After seven days, the expression and activity of brain CYP2D6 was tested. Subsequently, tyramine or 5-methoxytryptamine was injected into the striatum or prefrontal cortex (bilaterally). Dopamine formation from tyramine was measured in male Wistar Han WT rats, whereas serotonin formation from 5-methoxytryptamine was measured in male Dark Agouti WT or TPH2-KO (brain tryptophan hydroxylase knockout) rats. In addition, serotonin levels were assessed in male Sprague Dawley rats: WT or TPH1-KO (peripheral tryptophan hydroxylase knockout). Neurotransmitter levels (dopamine, serotonin, and their metabolites) were measured by HPLC with coulometric detection. Results were statistically analyzed using Student’s t-test for dependent data (AAV5-CYP2D6 vs. AAV5).

Results

Administration of AAV5-CYP2D6 alone did not affect the level of neurotransmitters in the examined brain structures, but increased their level when the substrate (tyramine or 5-MT) was administered. Intrastructural administration of tyramine to Wistar Han rats overexpressing human CYP2D6, significantly increased dopamine levels in the striatum but not in the frontal cortex. The metabolite DOPAC remained unchanged. Intrastructural administration of 5-methoxytryptamine to Dark Agouti WT rats overexpressing human CYP2D6 significantly increased serotonin levels in the striatum but not in the frontal cortex. Injection of 5-methoxytryptamine to TPH2-KO rats overexpressing human CYP2D6 significantly increased serotonin levels in both the striatum and the frontal cortex. 5-HIAA levels increased only in the frontal cortex. In Sprague Dawley TPH1-KO rats, no changes in serotonin levels were observed after introducing the human CYP2D6 gene into the frontal cortex.

Conclusions

These results indicate that human CYP2D6 may play a role in modulating brain dopamine and serotonin levels when the substrate is present in sufficient concentration in the enzyme environment, particularly under conditions of disruption of the classical neurotransmitter synthesis pathway. Further studies are advisable to determine whether similar effects on neurotransmitter levels occur after introducing the CYP2D6 gene into other brain areas, particularly when the CYP2D6 overexpression occurs in structures containing neuronal cell bodies.

References

  1. Bromek, E., Haduch, A., Daniel, W.A., 2010. The ability of cytochrome P450 2D isoforms to synthesize dopamine in the brain: An in vitro study. Eur. J. Pharmacol. 626, 171-8.
  2. Bromek, E., Haduch. A., Gołembiowska, K., Daniel, W.A., 2011. Cytochrome P450 mediates dopamine formation in the brain in vivo. J. Neurochem. 118, 806-15.
  3. Haduch, A., Bromek, E., Sadakierska-Chudy, A., Wójcikowski, J., Daniel, W.A., 2013. The catalytic competence of cytochrome P450 in the synthesis of serotonin from 5-methoxytryptamine in the brain: an in vitro study. Pharmacol. Res. 67, 53-9.
  4. Haduch, A., Bromek, E., Kot, M., Kamińska, K., Gołembiowska, K., Daniel, W.A., 2015. The cytochrome P450 2D-mediated formation of serotonin from 5-methoxytryptamine in the brain in vivo: a microdialysis study. J. Neurochem. 133, 83-92.
  5. Haduch, A., Daniel, W.A., 2018. The engagement of brain cytochrome P450 in the metabolism of endogenous neuroactive substrates: a possible role in mental disorders. Drug Metab. Rev. 50, 415-429.