Effects of higenamine on regulation of ion transport in guinea pig distal colon

Pharmacological effects of higenamine based on signalling pathways and mechanism of action

Higenamine (HG) is a chemical compound found in various plants, such as aconite. Recent pharmacological studies have demonstrated its effectiveness in the management of many diseases. Several mechanisms of action of HG have been proposed; however, they have not yet been classified. This review summarises the signalling pathways and pharmacological targets of HG, focusing on its potential as a naturally extracted drug. Articles related to the pharmacological effects, signalling pathways and pharmacological targets of HG were selected by searching the keyword "Higenamine" in the PubMed, Web of Science and Google Scholar databases without limiting the search by publication years. HG possesses anti-oxidant, anti-apoptotic, anti-inflammatory, electrophysiology regulatory, anti-fibrotic and lipid-lowering activities. It is a structural analogue of catecholamines and possesses characteristics similar to those of adrenergic receptor ligands. It can modulate multiple targets, including anti-inflammation- and anti-apoptosis-related targets and some transcription factors, which directly or indirectly influence the disease course. Other naturally occurring compounds, such as cucurbitacin B (Cu B) and 6-gingerol (6-GR), can be combined with HG to enhance its anti-apoptotic activity. Although significant research progress has been made, follow-up pharmacological studies are required to determine the exact mechanism of action, new signalling pathways and targets of HG and the effects of using it in combination with other drugs.

β2 -Adrenoceptor agonist activity of higenamine

Higenamine was included in the World Anti-Doping Agency (WADA) Prohibited Substances and Methods List as a β2 -adrenoceptor agonist in 2017, thereby resulting in its prohibition both in and out of competition. The present mini review describes the physiology and pharmacology of adrenoceptors, summarizes the literature addressing the mechanism of action of higenamine and extends these findings with previously unpublished in silico and in vitro work. Studies conducted in isolated in vitro systems, whole-animal preparations and a small number of clinical studies suggest that higenamine acts in part as a β2 -adrenoceptor agonist. In silico predictive tools indicated that higenamine and possibly a metabolite have a high probability of interacting with the β2 -receptor as an agonist. Stable expression of human β2 -receptors in Chinese hamster ovary (CHO) cells to measure agonist activity not only confirmed the activity of higenamine at β2 but also closely agreed with the in silico prediction of potency for this compound. These data confirm and extend literature findings supporting the inclusion of higenamine in the Prohibited List.

cAMP-stimulated Cl- secretion is increased by glucocorticoids and inhibited by bumetanide in semicircular canal duct epithelium

Background

The vestibular system controls the ion composition of its luminal fluid through several epithelial cell transport mechanisms under hormonal regulation. The semicircular canal duct (SCCD) epithelium has been shown to secrete Cl^- under β₂-adrenergic stimulation. In the current study, we sought to determine the ion transporters involved in Cl^- secretion and whether secretion is regulated by PKA and glucocorticoids.

Results

Short circuit current (I_sc) from rat SCCD epithelia demonstrated stimulation by forskolin (EC₅₀: 0.8 μM), 8-Br-cAMP (EC₅₀: 180 μM), 8-pCPT-cAMP (100 μM), IBMX (250 μM), and RO-20-1724 (100 μM). The PKA activator N6-BNZ-cAMP (0.1, 0.3 & 1 mM) also stimulated I_sc. Partial inhibition of stimulated I_sc individually by bumetanide (10 & 50 μM), and [(dihydroindenyl)oxy]alkanoic acid (DIOA, 100 μM) were additive and complete. Stimulated I_sc was also partially inhibited by CFTR_inh-172 (5 & 30 μM), flufenamic acid (5 μM) and diphenylamine-2,2^′-dicarboxylic acid (DPC; 1 mM). Native canals of CFTR^+/− mice showed a stimulation of I_sc from isoproterenol and forskolin+IBMX but not in the presence of both bumetanide and DIOA, while canals from CFTR^−/− mice had no responses. Nonetheless, CFTR^−/− mice showed no difference from CFTR^+/− mice in their ability to balance (rota-rod). Stimulated I_sc was greater after chronic incubation (24 hr) with the glucocorticoids dexamethasone (0.1 & 0.3 μM), prednisolone (0.3, 1 & 3 μM), hydrocortisone (0.01, 0.1 & 1 μM), and corticosterone (0.1 & 1 μM) and mineralocorticoid aldosterone (1 μM). Steroid action was blocked by mifepristone but not by spironolactone, indicating all the steroids activated the glucocorticoid, but not mineralocorticoid, receptor. Expression of transcripts for CFTR; for KCC1, KCC3a, KCC3b and KCC4, but not KCC2; for NKCC1 but not NKCC2 and for WNK1 but only very low WNK4 was determined.

Conclusions

These results are consistent with a model of Cl^- secretion whereby Cl^- is taken up across the basolateral membrane by a Na⁺-K⁺-2Cl^- cotransporter (NKCC) and potentially another transporter, is secreted across the apical membrane via a Cl^- channel, likely CFTR, and demonstrate the regulation of Cl^- secretion by protein kinase A and glucocorticoids.

Influence of racemic higenamine on the sinus node

The aim of this study was to explore the mechanism of racemic higenamine in the treatment of sick sinus syndrome (SSS). A total of 40 New Zealand rabbits were randomly divided into normal sinus node and damaged sinus node (SND) groups, and each group was randomly divided into treatment and control groups (n=10). The SND model was established by formaldehyde wet dressing of the sinus node area. The treatment groups were administered an intravenous infusion of 0.04 mg/kg racemic higenamine via the marginal ear vein within 5 min. The electrophysiological indicators of sinoatrial function, including the sinus node recovery time (SNRT), corrected sinus node recovery time (CSNRT), total sinoatrial conduction time (TSACT) and sinus cycle length (SCL), were determined before and 20 min after medication and the changes in these indicators were evaluated. The two control groups were administered 10 ml physiological saline. Following the administration of racemic higenamine, the SNRT, CSNRT, TSACT and SCL in the normal sinus node and SND groups were significantly shortened compared with those in the control groups (P<0.01). The electrophysiological influence of racemic higenamine on sinoatrial function in the SND group was significantly greater than that in the normal sinus node group (P<0.01), and its effect in the treatment of arrhythmia caused by a damaged sinus node was statistically significant (P<0.05). The main electrophysiological mechanism of racemic higenamine in the treatment of SSS was the enhancement of sinus node self-discipline and improvement of sinoatrial and atrioventricular conduction function.

Chloride secretion by semicircular canal duct epithelium is stimulated via beta 2-adrenergic receptors

The ductal epithelium of the semicircular canal forms much of the boundary between the K+-rich luminal fluid and the Na+-rich abluminal fluid. We sought to determine whether the net ion flux producing the apical-to-basal short-circuit current (I(sc)) in primary cultures was due to anion secretion and/or cation absorption and under control of receptor agonists. Net fluxes of 22Na, 86Rb, and 36Cl demonstrated a basal-to-apical Cl- secretion that was stimulated by isoproterenol. Isoproterenol and norepinephrine increased I(sc) with an EC50 of 3 and 15 nM, respectively, and isoproterenol increased tissue cAMP of native canals with an EC50 of 5 nM. Agonists for adenosine, histamine, and vasopressin receptors had no effect on I(sc). Isoproterenol stimulation of I(sc) and cAMP was inhibited by ICI-118551 (IC50 = 6 microM for I(sc)) but not by CGP-20712A (1 microM) in primary cultures, and similar results were found in native epithelium. I(sc) was partially inhibited by basolateral Ba2+ (IC50 = 0.27 mM) and ouabain, whereas responses to genistein, glibenclamide, and DIDS did not fully fit the profile for CFTR. Our findings show that the canal epithelium contributes to endolymph homeostasis by secretion of Cl- under beta 2 adrenergic control with cAMP as second messenger, a process that parallels the adrenergic control of K+ secretion by vestibular dark cells. The current work points to one possible etiology of endolymphatic hydrops in Meniere's disease and may provide a basis for intervention.