The inhibitory effects of levo-tetrahydropalmatine on rat Kv1.5 channels expressed in HEK293 cells

A Comprehensive Review on the Chemical Properties, Plant Sources, Pharmacological Activities, Pharmacokinetic and Toxicological Characteristics of Tetrahydropalmatine

Tetrahydropalmatine (THP), a tetrahydroproberine isoquinoline alkaloid, is widely present in some botanical drugs, such as Stephania epigaea H.S. Lo (Menispermaceae; Radix stephaniae epigaeae), Corydalis yanhusuo (Y.H.Chou & Chun C.Hsu) W.T. Wang ex Z.Y. Su and C.Y. Wu (Papaveraceae; Corydalis rhizoma), and Phellodendron chinense C.K.Schneid (Berberidaceae; Phellodendri chinensis cortex). THP has attracted considerable attention because of its diverse pharmacological activities. In this review, the chemical properties, plant sources, pharmacological activities, pharmacokinetic and toxicological characteristics of THP were systematically summarized for the first time. The results indicated that THP mainly existed in Papaveraceae and Menispermaceae families. Its pharmacological activities include anti-addiction, anti-inflammatory, analgesic, neuroprotective, and antitumor effects. Pharmacokinetic studies showed that THP was inadequately absorbed in the intestine and had rapid clearance and low bioavailability in vivo, as well as self-microemulsifying drug delivery systems, which could increase the absorption level and absorption rate of THP and improve its bioavailability. In addition, THP may have potential cardiac and neurological toxicity, but toxicity studies of THP are limited, especially its long-duration and acute toxicity tests. In summary, THP, as a natural alkaloid, has application prospects and potential development value, which is promising to be a novel drug for the treatment of pain, inflammation, and other related diseases. Further research on its potential target, molecular mechanism, toxicity, and oral utilization should need to be strengthened in the future.

Challenges Faced with Small Molecular Modulators of Potassium Current Channel Isoform Kv1.5

The voltage-gated potassium channel Kv1.5, which mediates the cardiac ultra-rapid delayed-rectifier (IKur) current in human cells, has a crucial role in atrial fibrillation. Therefore, the design of selective Kv1.5 modulators is essential for the treatment of pathophysiological conditions involving Kv1.5 activity. This review summarizes the progress of molecular structures and the functionality of different types of Kv1.5 modulators, with a focus on clinical cardiovascular drugs and a number of active natural products, through a summarization of 96 compounds currently widely used. Furthermore, we also discuss the contributions of Kv1.5 and the regulation of the structure-activity relationship (SAR) of synthetic Kv1.5 inhibitors in human pathophysiology. SAR analysis is regarded as a useful strategy in structural elucidation, as it relates to the characteristics that improve compounds targeting Kv1.5. Herein, we present previous studies regarding the structural, pharmacological, and SAR information of the Kv1.5 modulator, through which we can assist in identifying and designing potent and specific Kv1.5 inhibitors in the treatment of diseases involving Kv1.5 activity.

Endothelial-Dependent and Independent Vascular Relaxation Effect of Tetrahydropalmatine on Rat Aorta

Tetrahydropalmatine (THP) is an active natural alkaloid isolated from Corydalis yanhusuo W.T. Wang which has been widely used for treating pain and cardiovascular disease in traditional Chinese medicine. Previous studies suggested THP have various pharmacological effects in neural and cardio tissue while the vascular reactivity of THP was not fully established. The present study found that THP relaxed rat aorta which contracted by phenylephrine (Phe), KCl, and U46619. The vascular relaxation effect of THP was partially attenuated by PI3K inhibitor wortmannin, Akt inhibitor IV, endothelial nitric oxide synthetase (eNOS) inhibitor L-NAME, guanylate cyclase inhibitors and the mechanical removal of endothelium. Also, the eNOS substrate L-arginine reversed the inhibition effect of L-NAME on THP-induced vascular relaxation. THP also induced intracellular NO production in human umbilical vein endothelial cells. However, Pre-incubation with β-adrenergic receptor blocker propranolol, angiotensin II receptor 1 (AT1) inhibitor losartan, angiotensin II receptor 2 (AT1) inhibitor PD123319 or angiotensin converting enzyme inhibitor enalapril enhanced the vascular relaxation effect of THP. THP did not affect the angiotensin II induced vascular contraction. Cyclooxygenase-2 (COX2) inhibitor indomethacin did not affect the vascular relaxation effect of THP. Furthermore, pre-treatment THP attenuated KCl and Phe induced rat aorta contraction in standard Krebs solution. In Ca²⁺ free Krebs solution, THP inhibited the Ca²⁺ induced vascular contraction under KCl or Phe stress and reduced KCl stressed Ca²⁺ influx in rat vascular smooth muscle cells. THP also inhibited intracellular Ca²⁺ release induced vascular contraction by blocking Ryr or IP3 receptors. In addition, the voltage-dependent K⁺ channel (Kv) blocker 4-aminopyridine, ATP-sensitive K⁺ channel (KATP) blocker glibenclamide and inward rectifying K⁺ channel blocker BaCl₂ attenuated THP induced vascular relaxation regardless of the Ca²⁺-activated K⁺ channel (KCa) blocker tetraethylammonium. Thus, we could conclude that THP relaxed rat aorta in an endothelium-dependent and independent manner. The underlying mechanism of THP relaxing rat aorta involved PI3K/Akt/eNOS/NO/cGMP signaling path-way, Ca²⁺ channels and K⁺ channels rather than COX2, β-adrenergic receptor and renin-angiotensin system (RAS). These findings indicated that THP might be a potent treatment of diseases with vascular dysfunction like hypertension.