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Advances in natural products in China
Trends in Pharmacological Sciences November 1985 Chinese medicine - a tradition as old as civilization. Two articles consider the old in relation to the new. This month Wang Zhen-gang and Liu Gan-zhong discuss the application of modern screening methods to the thousands of natural products used in traditional and folk remedies: many have been shown to have very specific and exploitable pharmacological properties. Next month, Deng Quan-sheng describes Chinese pharmacology over the last 5000 years, from Yin and Yang to the Chinese Pharmacological Society.
Advances in natural products in China
ism between mixtures of drugs have also been studied. The following are a few examples.
Neuropharmacology Tetrahydropalmatine (THP) is an active principle from the Chinese herb Corydalis ambigua which has been used in traditional medicine as an analgesic. Only L-THP shows biological activity. Like reserpine, THP has analgesic, sedative, tranquillizing, bradycardiac and hypotensive effects. It has been demonstrated electrophysiologically and biochemically to deplete the rat monoaminergic transmitters including dopamine, noradrenaline and 5-HT 1,2.
Natural products studied in China have been mostly traditional medicines, which are a vast resource for pharmacological study - there are nearly six thousand traditional medicines and folk drugs. This has been the main subject of research in pharmacology ever since the establishment of m o d e m pharmacology in the early years of twentieth century. During these years K. K. Chen extracted, and introduced to the West, ephedrine, the active principle of various plants used for at least two thousand years in China. U
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In the past 35 years, thousands of traditional and folk drugs have been screened pharmacologically; hundreds have been studied in detail and many active principles extracted and isolated. The pharmacological actions, pharmacokinetics and mechanisms of action of some have been elucidated and some, following clinical trial, are now used routinely in clinics. Pharmacological actions of some prescriptions and nostrums and the synergism and antagon1985, Elsevier Science Publishers B.V., A m s t e r d a m
0165 - 6147/851502.00
424 These effects can be blocked by pretreatment with pargyline 1. Tranquillizing action and catalepsy induced by high dose of THP seem to be correlated with the depletion of dopamine in the limbic area and striatum respectively. THP-induced reduction in heart noradrenaline may be responsible for the bradycardiac and mild hypotension caused by this drug. However, in contrast to reserpine, THP has been shown to cause marked tranquillizing effects at doses that do not significantly influence levels of noradrenaline, 5-HT and dopamine, and the stereotyped behaviour induced by apomorphine or by benserazide/dopa/deprenyl in rats, and rotational activity evoked by amphetamine in oxidopaminelesioned rats, that can be antagonized by the dopaminergic receptor antagonist haloperidol, could also be antagonized by THP. This suggests that THP is a dopamine receptor blocker 2,3. Tetrahydroberberin ( ~ H B ) an analogue of THP, produced marked catalepsy in rats and mice which was diminished by apomorphine or Ldopa and scopolamine, but was enhanced by physostigmine. In contrast, THP-induced catalepsy was diminished by physostigmine and enhanced by scopolamine. This problem is being investigated 4. Muscle relaxants: these are all quarternary alkaloids. Anabasine hydrochloride from Alangium chinensis, cissampelin methiodide from Cissampelos pareira L. and tetrandrin dimethiodide from Stephania tetrandra have been listed in the 1977 edition of Chinese Pharmacopoeia 5. They are all competitive antagonists in the neuromuscular joint.
Cardiovascular pharmacology Cardiovascular pharmacology has taken an important place in Chinese medicinal research, partly because of the fact that cardiovascular disease is the leading cause of death in China. Several cardiovascular research centres are pursuing studies on new herbal extracts that possess anti-ischaemic, anti-arrhythmic, or anti-coagulative effects. In this context, there are hundreds of medicinal herbs that have been used by Chinese traditional medi-
TIPS - November 1985 cal practitioners for thousands of years, most of which have not been studied with modem methods. Medicinal preparations now available on the market for clinical use, include: Higenamine (dimethylcol-claurine), first isolated from aconite root by Kosuge, was shown to be a partial ~-adrenoceptor agonist. Higenamine exhibits concentration-dependent stimulating effects
Astragatus membranaceus (fisch) Bunge Peng ]s'ao Kang Plu by Li Shih Chen(1590.AJ] )
~J~J~: Characters Taste sweet ~tightLy w a r m
~'~"
Nontoxic
~ j ~ ~ Actions J~.~ ~t
improvethe functionpower of the body ImproJe
the negative etements
Extract from Peng Tsao Kang Ma - an old Chinese pharmacopeia.
on adenylate cyclase activity in turkey erythrocyte membrane which are potentiated by GTP and blocked by propranolol. Low concentrations enchance, while high concentrations reduce, the effect of isoprenaline on adenylate cyclase. The displacement of [3H]dihydroalprenol binding in turkey erythrocyte membrane by higenamine and isoprenaline revealed Ki values of 3 ~M and 1.9 ~M, respectively. Crude extracts from aconite root, the parent plant of higenamine, showed both 0cand ~-adrenoceptor activating effects in conscious dogs 6. The hypertensive response of dogs to the aqueous-alcoholic extracts of processed aconite root (the preparation used in the clinic), was reversed in the presence of the c¢adrenoceptor antagonist phentolamine. In these conditions the drug exerted depressor effects 4. Tetrandrine, an alkaloid isolated from Stephania tetrandra, has been reported to possess analgesic, hypotensive, anti-inflammatory and antisilicosis effects. Both in-vitro and in-vivo evidence showed that
the effects of tetrandrine on heart rate and blood pressure were similar to verapamil, suggesting that tetrandrine may be a Ca 2+ channel blocker. Tetrandrine counteracted chloroform- and adrenaline-induced ventricular fibrillation in cats, aconitine-induced arrhythmias in rats and ouabain-induced arrhythmias in guinea-pigs 7. Anisodine and anisodamine are new tropine alkaloids isolated from Scopolia tangulatica. The molecular structures of anisodine are similar to scopolamine but it has a hydroxy group on the tropine acid moiety. Anisodamine is similar to atropine, but has a hydroxy group on the sixth position of tropine. Experimental studies revealed that anisodamine inhibits synthesis of thromboxane A2, a potent vasoconstrictor and platelet aggregator, leading to an improvement of microcirculation. Anisodamine has been demonstrated to improve pulmonary ventilation and prolong survival time of endotoxin-shocked dogs. Intravenous infusion of anisodamine improved myocardial contractility and renal perfusion states in dogs 4. Anisodamine has also been used clinically in the management of circulatory depression in endotoxic shock with encouraging results. Since very high doses of anisodamine are required, the mechanism by which anisodamine exerts its benefit effects against endotoxic shock merits further studies. Guan Sin II is an injection prepared according to a classical Chinese prescription. It has been shown to inhibit platelet aggregation and increase platelet content of cAMP as a result of inhibition of phosphodiesterase of platelets, demonstrating that it is possible to investigate the mechanisms of traditional prescriptions at a molecular level s . The main component of Guan Sin II is tanshen, the root of Salvia miltiorrhiza Bunge, which is a herb widely used for the treatment of coronary heart disease. Many principles have been isolated from tanshen. The principle responsible for the inhibition of platelet aggregation has a mol. wt of 300, and is resistant to heat, acid-alkali and trypsin. The principle tanshinone II-A has been reported to inhibit platelet adhesion and aggregation, and prolong thrombus formation time and
425
TIPS - November 1985 p r o t h r o m b i n time in rats and mice. The salutary effects of t a n s h i n o n e II-A on ischaemic heart m a y p o s s i b l y be related to its anticoagulation and the acceleration of the o p e n i n g of coronary collaterals 9. S o d i u m ferulate, a constituent in Angelica sinensis i n h i b i t e d coagulation of platelets and release of 5-HT in rats. Interestingly, s o d i u m ferulate also i n h i b i t e d the synthesis of t h r o m b o x a n e , a p o t e n t antiaggregatory agent of platelets w i t h o u t affecting the s y n t h e s i s of PGI2, a p o t e n t anti-aggregatory agent, in the aorta, in contrast w i t h aspirin w h i c h i n h i b i t s the synthesis of b o t h t h r o m b o x a n e A2 and PGI2. Low concentrations of s o d i u m ferulate w o u l d enhance the i n h i b i t o r y effects of a s p i r i n on platelet aggregation and decrease its i n h i b i t i o n of PGI2 synthesis. S o d i u m ferulate m i g h t offer an a p p r o a c h to the pharmacological m a n i p u l a t i o n of platelet aggregation that m a y have i m p o r tant pathophysiological consequences 1°. The in-vitro aggregability of platelets and release of serotonin from platelet granulars are p r o p e r ties w i d e l y u s e d to screen h e r b s w h i c h have b e e n claimed to be blood-activating and sludgee l i m i n a t i n g b y traditional doctors. A hypercoagulative state has b e e n noted in platelets from patients w i t h t h r o m b o s i s , acute ischaemia, stroke or a d v a n c e d diabetes. Several herbal extracts have been u s e d clinically for the treatment of the a b o v e - m e n t i o n e d diseases with e n c o u r a g i n g results.
Others Qinghao (Artemisia annua) is a m e d i c i n a l h e r b u s e d b y Chinese traditional doctors for antimalaria and anti-infective purposes. A lipophilic c o m p o n e n t of Artemisia annua, artemisinine, has b e e n isolated and chemical analysis has s h o w n it to be a n e w sesquiterpene. A n i m a l e x p e r i m e n t s and clinical trials have i n d i c a t e d that a r t e m i s i n i n e is h i g h l y effective against erythrocytic parasite with low toxicity, particularly against chloroquine-resistant malaria. Howver, in the usual dosage of 0 . 6 m g d a y 1 for three days, the average recurrence rate is more than 10%. Several a r t e m i s i n i n e analogues
have b e e n s y n t h e s i z e d for laboratory exploration of s t r u c t u r e activity relationship 4. A r t e m i s i n i n e and its derivatives have b e e n found to possess schistosomicidal actions in mice, r a b b i t s and dogs e x p o s e d to schistosoma Japonicum cercariae. Artemether (methyl dihydroartemisinine) and sodium artesunate ( s o d i u m d i h y d r o artem i s i n e hemisuccinate) i n h i b i t g r o w t h of the FCC-1/HN strain of the parasite. A m o n g the derivatives tested, sodium artesunate was the most effective. Following oral a d m i n i s t r a t i o n of artesunate (450-900 m g kg -1 for three days) to infected mice, the total w o r m reduction rates were 70% and the female w o r m reduction rates were 83--91%. It was less effective in infected rabbits a n d was more effective against the o n e - w e e k - o l d i m m a t u r e worm. No severe side effects were o b s e r v e d in treated animals. Artemether, an ether derivative of r e d u c e d artemisinine, was effective against schistosomiasis b u t caused toxic histopathological changes in the stomach, intestine and liver in normal mice a n d dogs 4. Huang-chi (Astragalus membranaceus var. mongholicus) is one of the Chinese traditional m e d i c i n e s u s e d frequently as tonic (Figs 1, 2). O u r previous investigations have s h o w n that p l a s m a cAMP levels are increased after oral a d m i n i s t r a tion in normal h u m a n b e i n g s and mice. Further studies were carried out on plasma, liver a n d spleen levels of cAMP, cGMP in mice. W e have f o u n d that while the average p l a s m a cAMP is increased, cGMP is decreased; in contrast liver cAMP is decreased b u t cGMP is increased 11. Gossypol. Scientists from 14 provinces of China have joined in a multi-center trial of gossypol (gossypol, gossypol acetic acid and gossypol formic acid) b e g i n n i n g in 1973. To date, the total n u m b e r of volunteers taking part in these centres has a m o u n t e d to 8806. The antifertility effect and side effect m a y be s u m m a r i z e d as follows: (1) Dosage. The loading dose was 20 mg d a y q, given for 85 days, followed by a maintenance dose 50 mg w e e k -1. (2) The antifertility effect was 99.07%. (3) Side effects. In loading phase, c o m m o n side effects include
fatigue (averaging 12.6%), gastro-intestinal symptoms (7.36%), decreased l i b i d o and potency (5.01%). In maintenance phase, hypokalaemic paralysis is the most important side effect. 0.75% of cases suffered side effects which were s t u d i e d w i t h other safety data in a r a n d o m i z e d controlled clinical trial in the Departm e n t of Urology; Union Hospital, Chinese A c a d e m y of Medical Sciences, Beijing. (4) The fertility recovery rate was (90.08%) after discontinuing gossypol, while 9.92% rem a i n e d azospermic. Thus, gossypol has been found to be a very effective male antifertility agent. However, further research is necessary to u n d e r s t a n d and avoid the side effects, particularly h y p o k a l a e m i a and irreversibility 12. []
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This is only a brief introduction recent advances in the study of natural products of China. A n u m b e r of i m p o r t a n t results have b e e n achieved in clinical practice a n d scientific research b u t while this type of study remains successful in finding n e w drugs, it is not the only way. China is one of the d e v e l o p i n g countries, and all studies are still in a preliminary stage. The future holds great promise.
Acknowledgements This article has been p r e p a r e d u n d e r the inspiration of our teacher, the ex-President of the Chinese Pharmacological Society, Professor Zhou Jing-huang. I thank Yang Chun for his assistance in the p r e p a r a t i o n of this manuscript. WANG ZHEN-GANG AND LIU GAN-ZHONG
Wang Zhen-gang is President and Liu Ganzhong is Secretary-general of The Chinese Pharmacological Society, Department of Pharmacology, Chinese Academy of Medical Sciences, 5 Dong Dan San Tiao, Beijing, China.
References 1 Liu, G.-Q. (1983) Acta Pharm. Sin. 18, 472-474 2 Liu, G.-Q., Alger'i, S. and Garattini, S. (1983) Acta Parm. Sin. 18, 641~47
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3 Wu, H.-Q., Liu, G.-Q., Xie, I. and Jiang, Y. (1984) Acta Pharm. Sin. 19, 495-498 4 Chin, Y.-C. and Wang, Z.-G. (1984) Chinese Yearbook of Medical Sciences,
216-222 5 Chinese Pharmacopoeia (1977) pp. 450,
599, 191, People's Health Press, Beijing, China
6 Zhou, Y.-P. (1983) Acta Pharm. Sin. 18, 394-400 7 Zhong, X.-G., Jin, M.-W., Xin, G.-J., Fang, D.-C. and Jiang, M.-X. (1983)Acta Pharm. Sin. 4, 258-261 8 Chen, X.-Y.,Zhu, G.-J.,Wang, L., Dang, Y. and Yan, Y.-Z. (1981)Acta Acad. Med. Sin. 3, 27130
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Innovative approaches in drug research The 3rd Noordwijkerhout Symposium, September 1985, Noordwijkerhout, The Netherlands.
The aim of the N o o r d w i j k e r h o u t s y m p o s i a is to b r i n g together and stimulate real interaction b e t w e e n medicinal chemists with synthetic backgrounds, pharmacologists a n d last, b u t not least, QSAR-ists. The t h e m e of the first m e e t i n g (1977), 'Biological activity and chemical structure', served to b r i n g these groups together. Joint strategies a n d tactics were the t h e m e of the 1981 meeting, whereas this year's m e e t i n g illustrated the m a n y fascinating approaches to d e v e l o p i n g novel drugs. To treat prostate cancer, for example, it is possible to follow a classical approach at the level of the h y p o p h y s i s b y d e v e l o p i n g an LHRH antagonist or, as J.P. R a y n a u d (Paris) described, to use a more m o d e r n approach via d o w n regulation of the LHRH receptor with a 'superagonist'. Alternatively, a more futuristic approach, d e s c r i b e d b y F. A u d i b e r t (Paris), can be a d o p t e d b y raising antib o d i e s against LHRH so that vaccination is possible. A n u m b e r of other possibilities exist at the p e r i p h e r a l level. Is it possible to select the most p r o m i s i n g m e t h o d for clinical d e v e l o p m e n t or should all approaches be explored? A possible theme for another meeting!
differences in affinity for that receptor. It has become routine in d r u g d e v e l o p m e n t to s t u d y the biological effects of both enantiomers separately. O n l y w h e n these data are available is it possible to select the racemate or one of the e n a n t i o m e r s for clinical development. To p r e p a r e p u r e enantiomers the m e d i c i n a l chemist h a d to master n e w synthetic m e t h o d s such as e n z y m a t i c resolutions and enantioselective syntheses. These m e t h o d s were carefully r e v i e w e d b y A.J. Beld (Nijmegen) in a satellite s y m p o s i u m . A poster b y W. ten Hoeve et al. (Groningen) d e s c r i b e d chiral p h o s p h o r i c acids w h i c h have b e e n p r o v e d to be interesting n e w resolving agents for a m i n e s a n d a m i n o acids. To confirm the optical p u r i t y of the c o m p o u n d s p r e p a r e d , n e w analytical techniques such as HPLC with the recently d e v e l o p e d chiral supports, or NMR in chiral solvents or with a chiral complexing agent, h a d to be introduced. Finally the absolute configuration of the e n a n t i o m e r s has to be determined before structureactivity studies can be performed. It is fascinating to see h o w fast all these techniques have become d a y - t o - d a y routine in medicinal chemistry. The preparation and biological characterization of some twenty enantiomeric pairs was described in p a p e r s and posters. The cis-5-hydroxy-l-methyl-2-(di-
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This m e e t i n g stressed the importance of t h i n k i n g about drug molecules in terms of their threed i m e n s i o n a l structures, particularly w h e n dealing with chiral molecules. Enantiomers differ in structural c o m p l e m e n t a r i t y to a receptor w h i c h m a y result in ~ ) 1985, Elsevier Science P u b l i s h e r s B.V., A m s t e r d a m
n-propylamino)tetralins, described b y A. M. Johansson et al. (Uppsala) in a poster, form an interesting example. The 1R,2S-isomer is a d o p a m i n e receptor agonist while the 1S,2S-isomer is an antagonist, both acting preferentially on autoreceptors. W i t h the large n u m b e r of enantiomers at hand, pharmacologists find these a powerful tool for
0165 - 6147/85/$02.00
9 Chen, W.-Z. (1984) Acta Pharm. Sin. 19, 876--879 10 Mei, Q.-B. and Tao, J.-Y. (1983) Herbal Drugs 14, 379-383 11 Wang, Z.-G., Liu, J.-S., Lu, C.-H., Li, Y.-M., Wu, T. and Sheng, R.-G. (1982) Acta Acad. Med. Sin. 4, 303-305 12 Lei,H.-P. (1982)Acta Pharm. Sin. 17, 1-4 subclassification of receptors a n d mechanism of action studies. Enan-. tiomers have identical physical and chemical properties so that no differences in tissue d i s t r i b u t i o n are expected, although they differ in a chiral e n v i r o n m e n t such as is found on receptors or in contact with m e t a b o l i z i n g enzymes. Interesting examples were p r e s e n t e d in reviews b y G. Lambrecht (Frankfurt) and K.P. Bogeso (Copenhagen) and on n u m e r o u s posters. There remain, however, m a n y examples where small or even no differences in activity of the enantiomers were found. In these cases the racemate is the drug of choice for clinical development. A poster b y A. L o m b a r d et at. (Turin) showed that for the anti-inflammatory drugs ketoprofen and i n d o p r o f e n the S ( + ) - e n a n t i o m e r is the more potent one. Biotransformation in the liver, however, converts the R ( - ) - e n a n t i o m e r into the S(+)e n a n t i o m e r so that use of the pure S ( + ) - e n a n t i o m e r has no advantage over using the racemate. []
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Computer-assisted molecular m o d e l l i n g and graphics systems have become extremely powerful tools to visualize threed i m e n s i o n a l structures and to assist in rational drug design. K. M/iller (Basel) described the Roche Interactive Molecular Graphics system and s h o w e d its use in identifying the more p r o m i s i n g structures from a series of comp o u n d s suggested for synthesis. W i t h these computer systems at h a n d in a n u m b e r of industrial and university laboratories, a revival of q u a n t u m pharmacology could be noted. It remains to be seen in the future w h e t h e r this will lead to a real breakthrough of this specialism. []
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A n exciting n e w d e v e l o p m e n t in the receptor field arises from the application of molecular biology. It is based u p o n the powerful tech-
Advances in natural products in China
ism between mixtures of drugs have also been studied. The following are a few examples.
Neuropharmacology Tetrahydropalmatine (THP) is an active principle from the Chinese herb Corydalis ambigua which has been used in traditional medicine as an analgesic. Only L-THP shows biological activity. Like reserpine, THP has analgesic, sedative, tranquillizing, bradycardiac and hypotensive effects. It has been demonstrated electrophysiologically and biochemically to deplete the rat monoaminergic transmitters including dopamine, noradrenaline and 5-HT 1,2.
Natural products studied in China have been mostly traditional medicines, which are a vast resource for pharmacological study - there are nearly six thousand traditional medicines and folk drugs. This has been the main subject of research in pharmacology ever since the establishment of m o d e m pharmacology in the early years of twentieth century. During these years K. K. Chen extracted, and introduced to the West, ephedrine, the active principle of various plants used for at least two thousand years in China. U
[]
[]
In the past 35 years, thousands of traditional and folk drugs have been screened pharmacologically; hundreds have been studied in detail and many active principles extracted and isolated. The pharmacological actions, pharmacokinetics and mechanisms of action of some have been elucidated and some, following clinical trial, are now used routinely in clinics. Pharmacological actions of some prescriptions and nostrums and the synergism and antagon1985, Elsevier Science Publishers B.V., A m s t e r d a m
0165 - 6147/851502.00
424 These effects can be blocked by pretreatment with pargyline 1. Tranquillizing action and catalepsy induced by high dose of THP seem to be correlated with the depletion of dopamine in the limbic area and striatum respectively. THP-induced reduction in heart noradrenaline may be responsible for the bradycardiac and mild hypotension caused by this drug. However, in contrast to reserpine, THP has been shown to cause marked tranquillizing effects at doses that do not significantly influence levels of noradrenaline, 5-HT and dopamine, and the stereotyped behaviour induced by apomorphine or by benserazide/dopa/deprenyl in rats, and rotational activity evoked by amphetamine in oxidopaminelesioned rats, that can be antagonized by the dopaminergic receptor antagonist haloperidol, could also be antagonized by THP. This suggests that THP is a dopamine receptor blocker 2,3. Tetrahydroberberin ( ~ H B ) an analogue of THP, produced marked catalepsy in rats and mice which was diminished by apomorphine or Ldopa and scopolamine, but was enhanced by physostigmine. In contrast, THP-induced catalepsy was diminished by physostigmine and enhanced by scopolamine. This problem is being investigated 4. Muscle relaxants: these are all quarternary alkaloids. Anabasine hydrochloride from Alangium chinensis, cissampelin methiodide from Cissampelos pareira L. and tetrandrin dimethiodide from Stephania tetrandra have been listed in the 1977 edition of Chinese Pharmacopoeia 5. They are all competitive antagonists in the neuromuscular joint.
Cardiovascular pharmacology Cardiovascular pharmacology has taken an important place in Chinese medicinal research, partly because of the fact that cardiovascular disease is the leading cause of death in China. Several cardiovascular research centres are pursuing studies on new herbal extracts that possess anti-ischaemic, anti-arrhythmic, or anti-coagulative effects. In this context, there are hundreds of medicinal herbs that have been used by Chinese traditional medi-
TIPS - November 1985 cal practitioners for thousands of years, most of which have not been studied with modem methods. Medicinal preparations now available on the market for clinical use, include: Higenamine (dimethylcol-claurine), first isolated from aconite root by Kosuge, was shown to be a partial ~-adrenoceptor agonist. Higenamine exhibits concentration-dependent stimulating effects
Astragatus membranaceus (fisch) Bunge Peng ]s'ao Kang Plu by Li Shih Chen(1590.AJ] )
~J~J~: Characters Taste sweet ~tightLy w a r m
~'~"
Nontoxic
~ j ~ ~ Actions J~.~ ~t
improvethe functionpower of the body ImproJe
the negative etements
Extract from Peng Tsao Kang Ma - an old Chinese pharmacopeia.
on adenylate cyclase activity in turkey erythrocyte membrane which are potentiated by GTP and blocked by propranolol. Low concentrations enchance, while high concentrations reduce, the effect of isoprenaline on adenylate cyclase. The displacement of [3H]dihydroalprenol binding in turkey erythrocyte membrane by higenamine and isoprenaline revealed Ki values of 3 ~M and 1.9 ~M, respectively. Crude extracts from aconite root, the parent plant of higenamine, showed both 0cand ~-adrenoceptor activating effects in conscious dogs 6. The hypertensive response of dogs to the aqueous-alcoholic extracts of processed aconite root (the preparation used in the clinic), was reversed in the presence of the c¢adrenoceptor antagonist phentolamine. In these conditions the drug exerted depressor effects 4. Tetrandrine, an alkaloid isolated from Stephania tetrandra, has been reported to possess analgesic, hypotensive, anti-inflammatory and antisilicosis effects. Both in-vitro and in-vivo evidence showed that
the effects of tetrandrine on heart rate and blood pressure were similar to verapamil, suggesting that tetrandrine may be a Ca 2+ channel blocker. Tetrandrine counteracted chloroform- and adrenaline-induced ventricular fibrillation in cats, aconitine-induced arrhythmias in rats and ouabain-induced arrhythmias in guinea-pigs 7. Anisodine and anisodamine are new tropine alkaloids isolated from Scopolia tangulatica. The molecular structures of anisodine are similar to scopolamine but it has a hydroxy group on the tropine acid moiety. Anisodamine is similar to atropine, but has a hydroxy group on the sixth position of tropine. Experimental studies revealed that anisodamine inhibits synthesis of thromboxane A2, a potent vasoconstrictor and platelet aggregator, leading to an improvement of microcirculation. Anisodamine has been demonstrated to improve pulmonary ventilation and prolong survival time of endotoxin-shocked dogs. Intravenous infusion of anisodamine improved myocardial contractility and renal perfusion states in dogs 4. Anisodamine has also been used clinically in the management of circulatory depression in endotoxic shock with encouraging results. Since very high doses of anisodamine are required, the mechanism by which anisodamine exerts its benefit effects against endotoxic shock merits further studies. Guan Sin II is an injection prepared according to a classical Chinese prescription. It has been shown to inhibit platelet aggregation and increase platelet content of cAMP as a result of inhibition of phosphodiesterase of platelets, demonstrating that it is possible to investigate the mechanisms of traditional prescriptions at a molecular level s . The main component of Guan Sin II is tanshen, the root of Salvia miltiorrhiza Bunge, which is a herb widely used for the treatment of coronary heart disease. Many principles have been isolated from tanshen. The principle responsible for the inhibition of platelet aggregation has a mol. wt of 300, and is resistant to heat, acid-alkali and trypsin. The principle tanshinone II-A has been reported to inhibit platelet adhesion and aggregation, and prolong thrombus formation time and
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TIPS - November 1985 p r o t h r o m b i n time in rats and mice. The salutary effects of t a n s h i n o n e II-A on ischaemic heart m a y p o s s i b l y be related to its anticoagulation and the acceleration of the o p e n i n g of coronary collaterals 9. S o d i u m ferulate, a constituent in Angelica sinensis i n h i b i t e d coagulation of platelets and release of 5-HT in rats. Interestingly, s o d i u m ferulate also i n h i b i t e d the synthesis of t h r o m b o x a n e , a p o t e n t antiaggregatory agent of platelets w i t h o u t affecting the s y n t h e s i s of PGI2, a p o t e n t anti-aggregatory agent, in the aorta, in contrast w i t h aspirin w h i c h i n h i b i t s the synthesis of b o t h t h r o m b o x a n e A2 and PGI2. Low concentrations of s o d i u m ferulate w o u l d enhance the i n h i b i t o r y effects of a s p i r i n on platelet aggregation and decrease its i n h i b i t i o n of PGI2 synthesis. S o d i u m ferulate m i g h t offer an a p p r o a c h to the pharmacological m a n i p u l a t i o n of platelet aggregation that m a y have i m p o r tant pathophysiological consequences 1°. The in-vitro aggregability of platelets and release of serotonin from platelet granulars are p r o p e r ties w i d e l y u s e d to screen h e r b s w h i c h have b e e n claimed to be blood-activating and sludgee l i m i n a t i n g b y traditional doctors. A hypercoagulative state has b e e n noted in platelets from patients w i t h t h r o m b o s i s , acute ischaemia, stroke or a d v a n c e d diabetes. Several herbal extracts have been u s e d clinically for the treatment of the a b o v e - m e n t i o n e d diseases with e n c o u r a g i n g results.
Others Qinghao (Artemisia annua) is a m e d i c i n a l h e r b u s e d b y Chinese traditional doctors for antimalaria and anti-infective purposes. A lipophilic c o m p o n e n t of Artemisia annua, artemisinine, has b e e n isolated and chemical analysis has s h o w n it to be a n e w sesquiterpene. A n i m a l e x p e r i m e n t s and clinical trials have i n d i c a t e d that a r t e m i s i n i n e is h i g h l y effective against erythrocytic parasite with low toxicity, particularly against chloroquine-resistant malaria. Howver, in the usual dosage of 0 . 6 m g d a y 1 for three days, the average recurrence rate is more than 10%. Several a r t e m i s i n i n e analogues
have b e e n s y n t h e s i z e d for laboratory exploration of s t r u c t u r e activity relationship 4. A r t e m i s i n i n e and its derivatives have b e e n found to possess schistosomicidal actions in mice, r a b b i t s and dogs e x p o s e d to schistosoma Japonicum cercariae. Artemether (methyl dihydroartemisinine) and sodium artesunate ( s o d i u m d i h y d r o artem i s i n e hemisuccinate) i n h i b i t g r o w t h of the FCC-1/HN strain of the parasite. A m o n g the derivatives tested, sodium artesunate was the most effective. Following oral a d m i n i s t r a t i o n of artesunate (450-900 m g kg -1 for three days) to infected mice, the total w o r m reduction rates were 70% and the female w o r m reduction rates were 83--91%. It was less effective in infected rabbits a n d was more effective against the o n e - w e e k - o l d i m m a t u r e worm. No severe side effects were o b s e r v e d in treated animals. Artemether, an ether derivative of r e d u c e d artemisinine, was effective against schistosomiasis b u t caused toxic histopathological changes in the stomach, intestine and liver in normal mice a n d dogs 4. Huang-chi (Astragalus membranaceus var. mongholicus) is one of the Chinese traditional m e d i c i n e s u s e d frequently as tonic (Figs 1, 2). O u r previous investigations have s h o w n that p l a s m a cAMP levels are increased after oral a d m i n i s t r a tion in normal h u m a n b e i n g s and mice. Further studies were carried out on plasma, liver a n d spleen levels of cAMP, cGMP in mice. W e have f o u n d that while the average p l a s m a cAMP is increased, cGMP is decreased; in contrast liver cAMP is decreased b u t cGMP is increased 11. Gossypol. Scientists from 14 provinces of China have joined in a multi-center trial of gossypol (gossypol, gossypol acetic acid and gossypol formic acid) b e g i n n i n g in 1973. To date, the total n u m b e r of volunteers taking part in these centres has a m o u n t e d to 8806. The antifertility effect and side effect m a y be s u m m a r i z e d as follows: (1) Dosage. The loading dose was 20 mg d a y q, given for 85 days, followed by a maintenance dose 50 mg w e e k -1. (2) The antifertility effect was 99.07%. (3) Side effects. In loading phase, c o m m o n side effects include
fatigue (averaging 12.6%), gastro-intestinal symptoms (7.36%), decreased l i b i d o and potency (5.01%). In maintenance phase, hypokalaemic paralysis is the most important side effect. 0.75% of cases suffered side effects which were s t u d i e d w i t h other safety data in a r a n d o m i z e d controlled clinical trial in the Departm e n t of Urology; Union Hospital, Chinese A c a d e m y of Medical Sciences, Beijing. (4) The fertility recovery rate was (90.08%) after discontinuing gossypol, while 9.92% rem a i n e d azospermic. Thus, gossypol has been found to be a very effective male antifertility agent. However, further research is necessary to u n d e r s t a n d and avoid the side effects, particularly h y p o k a l a e m i a and irreversibility 12. []
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This is only a brief introduction recent advances in the study of natural products of China. A n u m b e r of i m p o r t a n t results have b e e n achieved in clinical practice a n d scientific research b u t while this type of study remains successful in finding n e w drugs, it is not the only way. China is one of the d e v e l o p i n g countries, and all studies are still in a preliminary stage. The future holds great promise.
Acknowledgements This article has been p r e p a r e d u n d e r the inspiration of our teacher, the ex-President of the Chinese Pharmacological Society, Professor Zhou Jing-huang. I thank Yang Chun for his assistance in the p r e p a r a t i o n of this manuscript. WANG ZHEN-GANG AND LIU GAN-ZHONG
Wang Zhen-gang is President and Liu Ganzhong is Secretary-general of The Chinese Pharmacological Society, Department of Pharmacology, Chinese Academy of Medical Sciences, 5 Dong Dan San Tiao, Beijing, China.
References 1 Liu, G.-Q. (1983) Acta Pharm. Sin. 18, 472-474 2 Liu, G.-Q., Alger'i, S. and Garattini, S. (1983) Acta Parm. Sin. 18, 641~47
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3 Wu, H.-Q., Liu, G.-Q., Xie, I. and Jiang, Y. (1984) Acta Pharm. Sin. 19, 495-498 4 Chin, Y.-C. and Wang, Z.-G. (1984) Chinese Yearbook of Medical Sciences,
216-222 5 Chinese Pharmacopoeia (1977) pp. 450,
599, 191, People's Health Press, Beijing, China
6 Zhou, Y.-P. (1983) Acta Pharm. Sin. 18, 394-400 7 Zhong, X.-G., Jin, M.-W., Xin, G.-J., Fang, D.-C. and Jiang, M.-X. (1983)Acta Pharm. Sin. 4, 258-261 8 Chen, X.-Y.,Zhu, G.-J.,Wang, L., Dang, Y. and Yan, Y.-Z. (1981)Acta Acad. Med. Sin. 3, 27130
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Innovative approaches in drug research The 3rd Noordwijkerhout Symposium, September 1985, Noordwijkerhout, The Netherlands.
The aim of the N o o r d w i j k e r h o u t s y m p o s i a is to b r i n g together and stimulate real interaction b e t w e e n medicinal chemists with synthetic backgrounds, pharmacologists a n d last, b u t not least, QSAR-ists. The t h e m e of the first m e e t i n g (1977), 'Biological activity and chemical structure', served to b r i n g these groups together. Joint strategies a n d tactics were the t h e m e of the 1981 meeting, whereas this year's m e e t i n g illustrated the m a n y fascinating approaches to d e v e l o p i n g novel drugs. To treat prostate cancer, for example, it is possible to follow a classical approach at the level of the h y p o p h y s i s b y d e v e l o p i n g an LHRH antagonist or, as J.P. R a y n a u d (Paris) described, to use a more m o d e r n approach via d o w n regulation of the LHRH receptor with a 'superagonist'. Alternatively, a more futuristic approach, d e s c r i b e d b y F. A u d i b e r t (Paris), can be a d o p t e d b y raising antib o d i e s against LHRH so that vaccination is possible. A n u m b e r of other possibilities exist at the p e r i p h e r a l level. Is it possible to select the most p r o m i s i n g m e t h o d for clinical d e v e l o p m e n t or should all approaches be explored? A possible theme for another meeting!
differences in affinity for that receptor. It has become routine in d r u g d e v e l o p m e n t to s t u d y the biological effects of both enantiomers separately. O n l y w h e n these data are available is it possible to select the racemate or one of the e n a n t i o m e r s for clinical development. To p r e p a r e p u r e enantiomers the m e d i c i n a l chemist h a d to master n e w synthetic m e t h o d s such as e n z y m a t i c resolutions and enantioselective syntheses. These m e t h o d s were carefully r e v i e w e d b y A.J. Beld (Nijmegen) in a satellite s y m p o s i u m . A poster b y W. ten Hoeve et al. (Groningen) d e s c r i b e d chiral p h o s p h o r i c acids w h i c h have b e e n p r o v e d to be interesting n e w resolving agents for a m i n e s a n d a m i n o acids. To confirm the optical p u r i t y of the c o m p o u n d s p r e p a r e d , n e w analytical techniques such as HPLC with the recently d e v e l o p e d chiral supports, or NMR in chiral solvents or with a chiral complexing agent, h a d to be introduced. Finally the absolute configuration of the e n a n t i o m e r s has to be determined before structureactivity studies can be performed. It is fascinating to see h o w fast all these techniques have become d a y - t o - d a y routine in medicinal chemistry. The preparation and biological characterization of some twenty enantiomeric pairs was described in p a p e r s and posters. The cis-5-hydroxy-l-methyl-2-(di-
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This m e e t i n g stressed the importance of t h i n k i n g about drug molecules in terms of their threed i m e n s i o n a l structures, particularly w h e n dealing with chiral molecules. Enantiomers differ in structural c o m p l e m e n t a r i t y to a receptor w h i c h m a y result in ~ ) 1985, Elsevier Science P u b l i s h e r s B.V., A m s t e r d a m
n-propylamino)tetralins, described b y A. M. Johansson et al. (Uppsala) in a poster, form an interesting example. The 1R,2S-isomer is a d o p a m i n e receptor agonist while the 1S,2S-isomer is an antagonist, both acting preferentially on autoreceptors. W i t h the large n u m b e r of enantiomers at hand, pharmacologists find these a powerful tool for
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9 Chen, W.-Z. (1984) Acta Pharm. Sin. 19, 876--879 10 Mei, Q.-B. and Tao, J.-Y. (1983) Herbal Drugs 14, 379-383 11 Wang, Z.-G., Liu, J.-S., Lu, C.-H., Li, Y.-M., Wu, T. and Sheng, R.-G. (1982) Acta Acad. Med. Sin. 4, 303-305 12 Lei,H.-P. (1982)Acta Pharm. Sin. 17, 1-4 subclassification of receptors a n d mechanism of action studies. Enan-. tiomers have identical physical and chemical properties so that no differences in tissue d i s t r i b u t i o n are expected, although they differ in a chiral e n v i r o n m e n t such as is found on receptors or in contact with m e t a b o l i z i n g enzymes. Interesting examples were p r e s e n t e d in reviews b y G. Lambrecht (Frankfurt) and K.P. Bogeso (Copenhagen) and on n u m e r o u s posters. There remain, however, m a n y examples where small or even no differences in activity of the enantiomers were found. In these cases the racemate is the drug of choice for clinical development. A poster b y A. L o m b a r d et at. (Turin) showed that for the anti-inflammatory drugs ketoprofen and i n d o p r o f e n the S ( + ) - e n a n t i o m e r is the more potent one. Biotransformation in the liver, however, converts the R ( - ) - e n a n t i o m e r into the S(+)e n a n t i o m e r so that use of the pure S ( + ) - e n a n t i o m e r has no advantage over using the racemate. []
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Computer-assisted molecular m o d e l l i n g and graphics systems have become extremely powerful tools to visualize threed i m e n s i o n a l structures and to assist in rational drug design. K. M/iller (Basel) described the Roche Interactive Molecular Graphics system and s h o w e d its use in identifying the more p r o m i s i n g structures from a series of comp o u n d s suggested for synthesis. W i t h these computer systems at h a n d in a n u m b e r of industrial and university laboratories, a revival of q u a n t u m pharmacology could be noted. It remains to be seen in the future w h e t h e r this will lead to a real breakthrough of this specialism. []
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A n exciting n e w d e v e l o p m e n t in the receptor field arises from the application of molecular biology. It is based u p o n the powerful tech-