Study On P-glycoprotein Mediated Blood-brain Penetration And Central Nervous System Toxicity Of Fentanyl Drugs

Fentanyl and sufentanil are synthetic?-opioid receptor agonists with a potent analgesic effect.They are the most commonly used opioid analgesics to treat acute and perioperative pain as well as chronic pain in cancer patient.Because of minimal cardiovascular side effects and rapid onset and withdraw of actionthey are used in various types of surgical anesthesia and postoperative analgesia.In recent years,increased prescription and illicit use of fentanyl drugs have led to a growing death toll,which causes major safety concerns world-wide.The most serious adverse reaction of fentanyl and sufentanil is respiratory depression.However,to date,the toxicological mechanism of fentanyl and sufentanil induced overdose death has not been thoroughly investigated.In the present studiy,the role of P-gp at BBB on fentanyl's exposure and CNS effects was examined.Sedative effect and respiratory funsction of fentanyl drugs were measured and analyze to determine whether P-gp modulated brain exposure was associated with CNS toxicity of fentanyl.The study enhances understanding of the toxicological mechanisms of the drugs,and also provides scientific basis for evaluating fentanyl induced drug-drug interaction risks and also for safe use of the drugs in clinic.In this study,two rapid and sensitive LC-MS/MS methods were developed and validated to quantitatively determine fentanyl and sufentanil in rat plasma and brain tissues.The induction model of P-gp at blood-brain barrier was established by pretreating rats with oral dexamethasone for three consecutive days.The model was validated by measuring P-gp protein expression level in rat brain and the steady-state brain-to-blood ratio of the positive substrate loperamide.The results showed that the model was suitable for use in the study.The distribution and elimination of fentanyl or sufentanyl in brain and plasma were determined after a single i.v.dose at 40?g/kg or 20?g/kg.Fentanyl could enter the brain rapidly.The peak level was measured at 5min and higher than that in plasma.To diminish the influence of non-specific protein binding on fentanyl exposures between the plasma and brain,all the concentrations were corrected by measuredf_u,_plasmaorf_u,_brain.The results showed that the ratios of brain/plasma free concentration of fentanyl and sufentanil were1.6 and 1.5,respectively,indicating that fentanyl could penetrate BBB easily.The CNS effects of these two drugs,including the durations of LORR and respiratory depression,showed a pattern of fast on and fast off.With the dose increase?80?g/kg for fentanyl,40?g/kg for sufentanil?,the durations of LORR were increased and the respiratory depression were aggravated,illustrating the dose dependent CNS inhibition induced by both fentanyl and sufentanil.When the efflux function of P-gp was inhibited by tariquidar,the brain exposure of unbounded fentanyl or sufentanil was remarkably elevated to about 2.8-fold or 3-fold of the fentanyl or sufentanil alone group.Meanwhile,the durations of LORR were significantly extended and the respiratory depression were further aggravated,which illustrated the key role of P-gp in limiting fentanyl's entry into the CNS.In contrast,the durations of LORR induced by fentanyl and sufentanilwere remarkably shorten,and the respiratory functions were significantly improved in the rats of DEX induction group.This was due to the increased P-gp expression at BBB by DEX.P-gp induction resulted in a notable CNS protect effect against respiratory toxicity of fentanyl drugs.The results above demonstrated that the sedative effect?duration of LORR?and respiratory toxicity of fentanyl drugs were associated with their brain exposure levels.To assess the role of CYP enzymes in the brain exposure and CNS effects of fentanyl and sufentanil,rats were pretreated with CYP inhibitor ABT.When compared to the fentanyl or sufentanil alone group,no significant changes were observed for brain drug concentrations?15 min?of ABT treated groups,similarly,the LORR duration and respiratory functions were also not significantly affected.In summary,the current mechanistic study revealed the role of P-gp in the modulation of brain penetration of fentanyl and sufentaniland the association between their brain exposure and CNS toxicity.In vivo evaluations provided convincing evidence that CNS accumulation of fentanyl drugs and resulting respiratory depression are P-gp-dependent.Despite the fact that the high lipophilic property of fentanyl drugs allows easy BBB passage,P-gp acts as a“switch”and modulate the brain entry and CNS effects of the drugs.Due to the relatively narrow therapeutic windows of the fentanyl drugs,the pharmacokinetic drug-drug interaction between fentanyl drugs and potent P-gp inhibitors may lead to severe or even deadly consequences.A close monitoring is required in clinic when fentanyl drugs is used in combination with P-gp inhibitors.