Characterization of the interaction of the novel antihypertensive etamicastat with human dopamine-β-hydroxylase: Comparison with nepicastat

Molecular pathways underlying sympathetic autonomic overshooting leading to fear and traumatic memories: looking for alternative therapeutic options for post-traumatic stress disorder

The sympathoadrenal medullary system and the hypothalamic-pituitary-adrenal axis are both activated upon stressful events. The release of catecholamines, such as dopamine, norepinephrine (NE), and epinephrine (EPI), from sympathetic autonomic nerves participate in the adaptive responses to acute stress. Most theories suggest that activation of peripheral β-adrenoceptors (β-ARs) mediates catecholamines-induced memory enhancement. These include direct activation of β-ARs in the vagus nerve, as well as indirect responses to catecholamine-induced glucose changes in the brain. Excessive sympathetic activity is deeply associated with memories experienced during strong emotional stressful conditions, with catecholamines playing relevant roles in fear and traumatic memories consolidation. Recent findings suggest that EPI is implicated in fear and traumatic contextual memories associated with post-traumatic stress disorder (PTSD) by increasing hippocampal gene transcription (e.g., Nr4a) downstream to cAMP response-element protein activation (CREB). Herein, we reviewed the literature focusing on the molecular mechanisms underlying the pathophysiology of memories associated with fear and traumatic experiences to pave new avenues for the treatment of stress and anxiety conditions, such as PTSD.

Treatment With Nepicastat Decreases Contextual Traumatic Memories Persistence in Post-traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a common anxiety mental disorder and can be manifested after exposure to a real or perceived life-threatening event. Increased noradrenaline and adrenaline in plasma and urine have been documented in PTSD. Dopamine-β-hydroxylase (DBH) catalyzes the conversion of dopamine to noradrenaline and consequently, DBH inhibition reduces catecholamines. Our aim was to evaluate if nepicastat treatment decreases PTSD signs in an animal model. Wild-type (129x1/SvJ) female mice were submitted to PTSD induction protocol. DBH-inhibitor nepicastat (30 mg/kg) or vehicle (0.2% HPMC) were administered once daily since day 0 until day 7 or 12. The percentage of freezing was calculated on days 0, 1, 2, and 7, and behavioral tests were performed. Quantification of nepicastat in plasma and DBH activity in the adrenal gland was evaluated. Catecholamines were quantified by HPLC with electrochemical detection. mRNA expression of Npas4 and Bdnf in hippocampus was evaluated by qPCR.Mice in the PTSD-group and treated with nepicastat showed a decrease in freezing, and an increase in the time spent and entries in open arms in elevated plus maze test. In mice treated with nepicastat, adrenal gland DBH activity was decreased, and catecholamines were also decreased in plasma and tissues. On day 7, in mice treated with nepicastat, there was an increase of Npas4 and Bdnf mRNA expression in the hippocampus.In conclusion, DBH inhibitor nepicastat has an effect consistent with a decrease in the persistence of traumatic memories and anxiety-like behavior in this PTSD mice model. The disruption of traumatic memories through interference with the formation, consolidation, retrieval, and/or expression processes may be important to decrease PTSD symptoms and signs. The increase in Npas4 and Bdnf mRNA expression in the hippocampus may be important to develop a weaker traumatic contextual memory after nepicastat treatment.

Effects of nepicastat upon dopamine-β-hydroxylase activity and dopamine and norepinephrine levels in the rat left ventricle, kidney, and adrenal gland

Background and Objective: Evaluate the activity of dopamine-β-hydroxylase (DβH) as well as the effect of the DβH inhibitor nepicastat upon enzyme activity and levels of dopamine (DA) and norepinephrine (NE) in the rat left ventricle, kidney, and adrenal glands.Methods: DβH assay consisted of the enzymatic hydroxylation of tyramine into octopamine, and DA and NE tissues levels were quantified by HPLC-ED.Results: Nepicastat (30 mg/kg, p.o.) reduced DβH activity by 93% and 80% in the adrenals at 4 h and 8 h postdrug administration, accompanied by significant reductions in NE and epinephrine tissue levels and an increase in DA levels and of DA/NE tissue ratios, with similar findings for NE, DA and of DA/NE tissue ratios in left ventricle and kidney. DβH activity in the left ventricle and kidney showed a high degree of variability, which does not allow corroboration of the effects of nepicastat upon catecholamine tissue levels.Conclusion: The assay of DβH activity in heart and kidney lacks the necessary robustness, but DβH activity in the adrenals appears to be an appropriate marker. However, the effect size upon DA/NE tissue ratios (an indirect measure of DβH activity) as induced by nepicastat was very similar in sympathetically innervated tissues, left ventricle and kidney, and the adrenal medulla.

Effects of zamicastat treatment in a genetic model of salt-sensitive hypertension and heart failure

Hyperactivity of sympathetic nervous system plays an important role in the development and progression of cardiovascular diseases. An approach to mitigate the enhanced sympathetic nervous system drive is restricting the biosynthesis of noradrenaline via inhibition of the enzyme dopamine β-hydroxylase (DβH), that catalyzes the hydroxylation of dopamine to noradrenaline in sympathetic nerves. The aim of the present study was to evaluate the effects of zamicastat, a novel DβH inhibitor that decreases noradrenaline and increases dopamine levels in peripheral sympathetically innervated tissues, on the hemodynamic and cardiometabolic parameters in salt-induced hypertension and heart failure in the Dahl salt-sensitive (SS) rat. Zamicastat (10, 30 and 100 mg/kg body weight) was tested acutely against salt-induced hypertension in the Dahl SS rat. Chronic zamicastat treatment (30 mg/kg/day) was evaluated against salt-induced cardiac hypertrophy and biomarkers of cardiometabolic risk and inflammation in Dahl SS rats and upon the survival rate in aged Dahl SS rats fed a high-salt diet. The reduction in the sympathetic tone attained with zamicastat shaped a dose- and time-dependent effect on blood pressure. Prolonged treatment with zamicastat ameliorated end-organ damage, metabolic syndrome and inflammation hallmarks in hypertensive Dahl SS rats. Survival rate of Dahl SS rats fed a high-salt diet demonstrated that zamicastat increased median survival of Dahl SS rats fed a high-salt diet. The use of DβH inhibitors, like zamicastat, is a promising approach to treat hypertension, heart failure and cardiovascular diseases where a reduction in the sympathetic tone has beneficial effects.

In vitro assessment of the interactions of dopamine β-hydroxylase inhibitors with human P-glycoprotein and Breast Cancer Resistance Protein

Inhibition of the biosynthesis of noradrenaline is a currently explored strategy for the treatment of hypertension, congestive heart failure and pulmonary arterial hypertension. While some dopamine β-hydroxylase (DBH) inhibitors cross the blood-brain barrier (BBB) and cause central as well as peripheral effects (nepicastat), others have limited access to the brain (etamicastat, zamicastat). In this context, peripheral selectivity is clinically advantageous, in order to prevent alterations of noradrenaline levels in the CNS and the occurrence of adverse central effects. A limited brain exposure results from the combination of several factors, such as a reduced passive permeability or affinity for efflux transporters, but efflux liabilities may also lead to unwanted drug-drug interactions (DDIs) in the presence of co-administered substrates or inhibitors. Thus, the purpose of the study herein presented was to explore the interaction of P-glycoprotein (P-gp) and Breast Cancer Resistance Protein (BCRP), the two major efflux transporters of the BBB that hamper the entry of several drugs to the brain, with the DBH inhibitors, etamicastat, nepicastat and zamicastat. Madin-Darby canine kidney cells (MDCK II) and transfected lines with human MDR1 (MDCK-MDR1) and ABCG2 (MDCK-BCRP) genes were used as a BBB surrogate model. P-gp and BCRP substrates and/or inhibitors were identified through intracellular accumulation and bidirectional permeability assays. The obtained data revealed that zamicastat is a concentration-dependent dual P-gp and BCRP inhibitor with IC₅₀ values of 73.8 ± 7.2 μM and 17.0 ± 2.7 μM, while etamicastat and nepicastat inhibited BCRP to greater extent than P-gp, with IC₅₀ values of 47.7 ± 1.8 μM and 59.2 ± 9.4 μM, respectively. Additionally, etamicastat was identified as P-gp and BCRP dual substrate, as demonstrated by net flux ratios of 5.84 and 3.87 and decreased >50% by verapamil and Ko143. Conversely, nepicastat revealed to be a P-gp-only substrate, with a net flux ratio of 2.01, reduced to 0.92 in the presence of verapamil. Furthermore, nepicastat displayed a consistently higher apparent permeability (>8.49 × 10^-6 cm s^-1) than etamicastat (<0.58 × 10^-6 cm s^-1). The identification of etamicastat as a dual efflux substrate suggests that P-gp and BCRP may be partially responsible for the limited central exposure of this compound, in association with its low passive permeability. Moreover, the weak efflux inhibitory potencies of etamicastat and nepicastat revealed a low DDI risk, while the dual P-gp/BCRP inhibition of zamicastat could be studied in the future with synergically effluxed compounds, for which BBB penetration is severely impaired.