Antiarrhythmic effects of ginsenoside Rg2 on calcium chloride-induced arrhythmias without oral toxicity

Abstract

Background: Malignant arrhythmias require drug therapy. However, most of the currently available antiarrhythmic drugs have significant side effects. Ginsenoside Rg2 exhibits excellent cardioprotective effects and appears to be a promising candidate for cardiovascular drug development. So far, the oral toxicity and antiarrhythmic effects of Rg2 have not been evaluated.

Methods: Acute oral toxicity of Rg2 was assessed by the Limit Test method in mice. Subchronic oral toxicity was determined by repeated dose 28-day toxicity study in rats. Antiarrhythmic activities of Rg2 were evaluated in calcium chloride-induced arrhythmic rats. Antiarrhythmic mechanism of Rg2 was investigated in arrhythmic rats and H9c2 cardiomyocytes.

Results: The results of toxicity studies indicated that Rg2 exhibited no single-dose (10 g/kg) acute oral toxicity. And 28-day repeated dose treatment with Rg2 (1.75, 3.5 and 5 g/kg/d) demonstrated minimal, if any, subchronic toxicity. Serum biochemical examination showed that total cholesterol in the high-dose cohort was dramatically decreased, whereas prothrombin time was increased at Day 28, suggesting that Rg2 might regulate lipid metabolism and have a potential anticoagulant effect. Moreover, pretreatment with Rg2 showed antiarrhythmic effects on the rat model of calcium chloride induced arrhythmia, in terms of the reduced duration time, mortality, and incidence of malignant arrhythmias. The antiarrhythmic mechanism of Rg2 might be the inhibition of calcium influx through L-type calcium channels by suppressing the phosphorylation of Ca²⁺/calmodulin-dependent protein kinase II.

Conclusion: Our findings support the development of Rg2 as a promising antiarrhythmic drug with fewer side effects for clinical use.

Keywords: Acute oral toxicity; Antiarrhythmia; Ginsenoside Rg2; Oral sub-chronic toxicity.

Fig. 1

Structrue and purity analysis of ginsenoside Rg2. (A) Chemical structure and (B) HPLC analysis of ginsenoside Rg2 prepared by a biotransformation method in comparison with reference standard Rg2.

Fig. 2

The changes of serum biochemistry of rats orally administrated with 0.5% CMC-Na (control) and low-, mid-, and high-dose ginsenoside Rg2 (1.75, 3.5, and 5 g/kg/d, respectively) for 28 days. (A) triglyceride (TG) and total cholesterol (TC). (B)total protein (TP) and albumin (ALB). (C) alanine aminotransferase (ALT), aspartate aminotransferase (AST), and alkaline phosphatase (ALP). (D) blood urea nitrogen (BUN) and creatinine (CREA). (E) potassium (K⁺), sodium (Na⁺), and chloride (Cl⁻). * represents significant difference to the control group (p < 0.05).

Fig. 3

Necropsy findings of male and female rats after oral administration with 0.5% CMC-Na solution (control) and high-dose Rg2 (5 g/kg/d) for 28 days. After sacrifice, the (A) liver, (B) pancreas, (C) lung, (D) spleen, (E) adrenal gland, (F) kidney, (G) thymus, (H) heart, (I) brain, (J) ovary of female rats, and (K) testis of male rats were isolated from the control and high-dose groups.

Fig. 4

Hematoxylin and eosin–stained tissue sections of the main organs from the control and high-dose Rg2 treatment group (5 g/kg/d).

Fig. 5

The changes of electrophysiological parameters and representative ECGs of rats in different groups after the induction of arrhythmia by CaCl₂. (A) PR interval, (B) QRS interval, (C) QT interval, and (D) HR. (E) representative ECGs in the control, verapamil, and high-dose Rg2 groups (each graph shows a 0.6-second ECG sample). ECG, electrocardiogram; HR, heart rate.

Fig. 6

Effects of Rg2 on Ca²⁺ influx through L-type Ca²⁺ channels. (A) and (B) The representative protein expression of p-CaMKII-δ, CaMKII-δ, and GAPDH and quantitative analysis of p-CaMKII-δ in hearts (A) and H9c2 cells (B). (C) Fluorescent images of Fluo-4AM in verapamil and Rg2 pretreated H9c2 cells and untreated cells before and after triggering Ca²⁺ influx by Bay-K8644. (D) Changes of fluorescence intensity of Fluo-4AM in verapamil and Rg2 pretreated H9c2 cells and untreated cells before and after triggering Ca²⁺ influx by Bay-K8644 (* represents for p < 0.05 compared with the model group, ** represents for p < 0.01 compared with the model group, ## represents for p < 0.05 compared with the normal control group).