Human CYP2D6 Is Functional in Brain In Vivo: Evidence from Humanized CYP2D6 Transgenic Mice

Abstract

CYP2D metabolizes many drugs that act within the brain, and variable expression of CYP2D in the brain may alter local drug and metabolite levels sufficiently to affect behavioral responses. Transgenic mice that express human CYP2D6 (TG) were compared to wild type mice (WT). Following selective inhibition of human CYP2D6 in TG brain, we demonstrated in vivo that human CYP2D6 in the brain was sufficient to alter a drug-induced behavioral response. After a 4-h pre-treatment with intracerebroventricular (i.c.v.) propranolol, CYP2D activity in vivo and in vitro was reduced in TG brain, whereas CYP2D activity in vivo, but not in vitro, was reduced in WT brain. After a 24-h pre-treatment with i.c.v. propranolol, CYP2D activity in vivo and in vitro was reduced in TG brain, whereas CYP2D activity in vivo and in vitro was not changed in WT brain. These results indicate that i.c.v. propranolol irreversibly inhibited human CYP2D6 in TG brain but not mouse CYP2D in TG and WT brain. Pre-treatments with propranolol did not change liver CYP2D activity in vivo or in vitro. Furthermore, 24-h pre-treatment with i.c.v. propranolol resulted in a significant decrease of the haloperidol-induced catalepsy response in TG, but not in WT, without changing serum haloperidol levels in either mouse line. These studies reveal a new tool to selectively and irreversibly inhibit human CYP2D6 in TG brain and indicate that human CYP2D6 has a functional role within the brain sufficient to impact the central nervous system response from peripherally administered drugs.

Keywords: CYP2D6; Drug metabolism; Haloperidol; Neurotoxicology; Propranolol.

Fig. 1

TG had higher brain DOR/DEX ratio in vivo and faster brain DOR formation rate in vitro in brain membranes compared to WT. a Brain DOR/DEX ratio and b brain DOR formation rate are shown for TG and WT. P values are calculated using a two-tailed, unpaired t test

Fig. 2

The 4-h pre-treatment with i.c.v. propranolol decreased the brain DOR/DEX ratio in vivo in TG and WT, and decreased the DOR formation rate in vitro in brain membranes in TG, but not in WT. a Experimental design. b Brain DOR/DEX ratio, c brain DOR formation rate, d serum DOR/DEX ratio, and e liver DOR formation rate are shown for TG (left side) and WT (right side). The data is illustrated as the mean, relative to the vehicle pre-treatment group within mouse line, plus standard deviation. The brain DOR/DEX data from one TG animal was excluded due to DEX levels being 9-fold above the mean brain DEX level. Data analysis was run on all remaining animals. However, the brain DOR/DEX data from one WT animal was excluded from this figure (value 3.09). P values are calculated using a two-tailed, unpaired t test

Fig. 3

The 24-h pre-treatment with i.c.v. propranolol decreased the brain DOR/DEX ratio in vivo and the DOR formation rate in vitro in brain membranes in TG, but not in WT. a Experimental design. b Brain DOR/DEX ratio, c brain DOR formation rate, d serum DOR/DEX ratio, and e liver DOR formation rate are shown for TG (left side) and WT (right side). The data is illustrated as the mean, relative to the vehicle pre-treatment group within mouse line, plus standard deviation. P values are calculated using a two-tailed, unpaired t test

Fig. 4

TG experienced longer catalepsy, compared to WT. a Haloperidol-induced catalepsy is assessed. b Catalepsy at 120 min post-haloperidol (shaded in a) is in the linear portion of the dose response curve for each line. The data (b) is illustrated as the mean catalepsy plus (for TG) or minus (for WT) standard deviation. Effect of dose (two-way ANOVA, F_2.21 = 10.50, p < 0.001) and mouse line (two-way ANOVA, F_1.21 = 15.35, p < 0.001)

Fig. 5

The 24-h pre-treatment with i.c.v. propranolol decreased the haloperidol-induced catalepsy in TG, but not in WT. a Experimental design. b Mean catalepsy and c serum haloperidol AUC_60–180 are shown for TG (left side) and WT (right side). Lines represent data from individual mice crossed by pre-treatment. The data is illustrated as the mean, relative to the vehicle pre-treatment group within mouse line, plus standard deviation. P value is calculated using a two-tailed, paired t test