Research PaperThe integrated pharmacokinetics of major rhodojaponins correlates with the cardiotoxicity after oral administration of Rhododendri Mollis Flos extract in rats
Graphical abstract
Introduction
The use of toxic and potent drugs for therapeutic purpose is widespread in clinical practice of traditional Chinese herbal medicine (TCHM). For instance, the tubers and roots of Aconitum carmichaeli Debx. (Ranunculaceae), the seeds of Strychnos nux-vomica L. (Loganiaceae), and the flowers of Datura metel L. (Solanaceae), are still playing irreplaceable roles in dealing with hard-to-cure diseases. Rhododendron molle G. Don (Ericaceae), a well-known poisonous deciduous shrub, is widely distributed in Southern China. Both the roots and fruits of this plant have been applied against a broad spectrum of diseases including hypertension, migraine, stubborn tinea, swelling and pain in Chinese folk medicines (State Administration of Traditional Chinese Medicine, in Editorial Committee of Zhonghua Bencao (Ed.), 1999). Moreover, the dried flower of Rhododendron molle (Rhododendri Mollis Flos, RMF), termed as “Naoyanghua” in Chinese, is officially monographed in Chinese pharmacopoeia as an analgesic for the treatment of rheumatoid arthritis and bruises (Chinese Pharmacopoeia Committee, 2010). The treatment with RMF however is not without complication. The cardiotoxicity and neurotoxicity of this herb is potentially lethal, and the poisoning incidents due to improper usage have occasionally occurred in clinical practice (Zhong and Hu, 2000, Yang, 2010).
Previous chemical and pharmacological investigations demonstrated that grayanane diterpenoids were the main active components in RMF. The isolated diterpenoids were structurally divided into rhodojaponin-, grayanotoxin- and rhodomollein-types ( Ohta and Hikino, 1979, Miao et al., 1987, Liu and Pan, 1990, Chen et al., 2004, Patel et al., 2010), of which rhodojaponins were the predominant ones. A wealth of bioactivities, such as insecticidal, sedative, anti-hypertensive, anti-nociceptive, and anti-feedant effects (Feng and Chiu, 1990, Cheng et al., 2000, Hu et al., 2000, Zhong et al., 2005, Cheng et al., 2011, Qiang et al., 2011) were ascribed to grayanane diterpenoids in RMF. On the other hand, toxicities caused by rhodojaponins and RMF were occasionally reported (Zhong and Hu, 2000, Yang, 2010). Taking rhodojaponin III as an example, it was officially recorded in 1977 edition of Chinese pharmacopoeia as a commercial anti-hypertensive drug. Unfortunately, rhodojaponin III was withdrawn from the market due to safety concern, as its i.p. LD50 value was as little as 0.40 mg/kg in mice (Hikino et al., 1976). The narrow therapeutic window of rhodojaponins necessitates monitoring the pharmacokinetics and pharmacodynamics in practical applications of RMF.
Pharmacokinetics is an implementation approach of drug actions, which can guide the rational use of drugs (Walker, 2004). Although phytochemical and pharmacological investigations into RMF have been extensively conducted, little is known about in vivo pharmacokinetics, which becomes one of the limiting factors for the prediction and understanding of their efficacy and toxicity. Since herbal medicines have been widely claimed to act in a holistic mode of multiple constituents and multiple targets, how to describe the overall pharmacokinetics of a highly complicated herb becomes an important issue. Recently, an integrated pharmacokinetic strategy has been proposed (Li et al., 2008) and successfully applied to describe the holistic pharmacokinetic properties of some herbal medicines (Hao et al., 2009, Xie et al., 2010, Li et al., 2008, Zhu et al., 2012).
In the present study, the cardiotoxicity of RMF in rats was first evaluated in terms of cardiac function and various biochemical indices including lactate dehydrogenase (LDH), creatine kinase MB (CK-MB) and aspartate aminotransferase (AST). Then, a sensitive liquid chromatography–electrospray ionization–mass spectrometry (LC–ESI–MS) method was developed and validated for the quantification of major rhodojaponins including rhodojaponin I, II and III (R-I, II and III) in RMF-treated rat plasma. Furthermore, based on an AUC-weighting approach, the integrated pharmacokinetics of rhodojaponins was determined, so as to fill the pharmacokinetic research gap of RMF and to preliminarily explore the correlation between pharmacokinetics and cardiotoxicity.
Section snippets
Materials and reagents
The RMF was purchased from Bozhou traditional Chinese medicine market (Anhui province, China), and authenticated by Prof. Hui-Jun Li, China Pharmaceutical University. An authenticated voucher specimen (No. RMF201206GX) was deposited in State Key Laboratory of Natural Medicines. Three rhodojaponin standards (R-I, II and III) were isolated from RMF extract, and their structures were identified by comparison of their high-resolution mass spectroscopy and 1H and 13C NMR data with those reported
Effect of RMF on ventricular function
It has been reported that RMF could result in gastrointestinal, cardiac and neural toxicities at toxic dosage, excessive drooling, twisting, vomitting, ataxia, respiratory depression and convulsion were common adverse effects (Zhong and Hu, 2000). In the present study, no obvious poisoning symptoms were observed in the low-dose group. However, rats in the high-dose group displayed typical poisoning symptoms such as vomiting, muscle rigidity, convulsion and even death. These symptoms of acute
Conclusion
In conclusion, it was reported that myocardial damage was elicited by RMF extract in a dose-dependent manner and the biochemical indices of LDH and CK-MB in plasma could serve as potential markers of RMF-induced cardiotoxicity. A rapid and sensitive LC–MS method was developed and validated for the pharmacokinetic study of major rhodojaponins in RMF extract. Based on an AUC-weighting approach, the integrated pharmacokinetics was converted to describe the holistic pharmacokinetic profiles of R-I,
Acknowledgments
This work was financially supported by the National Natural Science Foundation of China (No. 81322051).
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