Cryptolepis Root

The root of the plant cryptolepis (Cryptolepis sanguinolenta (Lindl.) Schlecter, Asclepiadaceae or Periplocaceae) is used in traditional African medicine to treat a variety of diseases, including malaria.1-6 Scientific investigations have indicated a number of biological/pharmacological effects of compounds isolated from the plant material, including anti-bacterial, anti-hyperglycemic, anti-inflammatory, anti-plasmodial/anti-malarial, and anti-viral effects.7-19 Some of these effects have been demonstrated in the crude extract as well as its fractions, including a dose-dependent inhibitory effect on the classical pathway of complement fixation.*11 During the past few years, cryptolepis has received additional attention by the phytomedicine division of a pharmaceutical company in Ghana, which developed an herbal tea based on this traditional medicinal herb and recently demonstrated the clinical efficacy of a tea-bag formulation in the treatment of malaria.20 A preliminary clinical study in 1989 conducted with an aqueous extract of cryptolepis, prepared by boiling powdered cryptolepis roots in water, also suggested the efficacy of the plant material against malaria.21

Unlike most other plant-derived malaria medications on the market (i.e., the drug quinine, a pure compound extracted from the bark of Cinchona spp. of the family Rubiaceae, and the recently developed pure compound artemisinin and semi-synthetic derivatives from the Chinese herb quin hao or sweet wormwood, Artemisia annua L., Asteraceae), the herbal tea based on cryptolepis is a true herbal remedy containing the naturally occurring complex mixture of phytochemicals in a traditional dosage form, with a long-established history of use, just like the old remedies from which the two aforementioned malaria drugs were derived
The major alkaloid, cryptolepine, was first isolated from C. sanguinolenta in Nigeria29 and later in Ghana by Dwuma-Badu and his co-workers.22 According to Ablordeppey et al.,30 and Tackie et al.,31 this indoloquinoline alkaloid was isolated from the roots of C. triangularis, a plant native to the Belgian Congo and synonymous with C. sanguinolenta. Curiously, cryptolepine was first artificially synthesized in 1906 by Fichter et al., but naturally-occurring cryptolepine from C. triangularis isolated by Clinquart was reported 23 years later in 1929.7

In addition to cryptolepine, several related minor alkaloids and their salts have been isolated from C. sanguinolenta. These include the hydrochloride (although the hydrochloride salt of a chemical compound is usually not considered a distinct compound) and the 11-hydroxy derivatives of cryptolepine, cryptoheptine, iso- and neo-cryptolepine, quindoline, and the dimers biscryptolepine, cryptoquindoline, and cryptospirolepine.23,31,32 The dimers have been found to be less active than the monomers, and they include cryptosanguinolentine, cryptotakienine, and cryptomisrine.33,34

Cryptolepine, the major alkaloid in cryptolepis, is not the only alkaloid with biological/pharmacological activity. Almost all the minor alkaloids also have anti-plasmodial activity. However, the activities of these, based on the inhibition of the chloroquine-sensitive strain of the malaria parasite Plasmodium falciparum, are less than the activity of cryptolepine.35 Samples of cryptolepis contain cryptolepine at varying concentrations, and since the minor alkaloids also have biological activity, using the content of cryptolepine alone for standardization is questionable. Total alkaloidal content or high performance thin-layer chromatography (HPTLC) with densitometry would be the preferred analytical methods for standardization.

Biology and Pharmacology

Numerous biological/pharmacological activities have been demonstrated in extracts from the roots of C. sanguinolenta, as well as for the alkaloids isolated from these extracts. They include anti-plasmodial (both chloroquine-sensitive and chloroquine-resistant strains of the malaria parasite), anti-bacterial, anti-viral, anti-inflammatory, anti-diabetic and hypotensive effects, as discussed below and in the accompanying sidebar on Pharmacology. Aqueous extracts, which are normally used by traditional medical practitioners, have been shown to be less effective compared to ethanolic extracts in some of the studies showing activity against the malaria parasite35 and bacteria.26,36
In vitro anti-plasmodial activities, which are indicative of anti-malarial activity, have been carried out using inhibition of the incorporation of the malaria parasite into red blood cells.12,13,15,19,35,37 In one study in which both the chloroquine-sensitive D6 strain and the chloroquine-resistant K-1 and W-2 strains of the malaria parasite were used, the anti-plasmodial activity was measured using the incorporation of 3H-hypoxanthine into red blood cells infected with P. falciparum, the standard anti-plasmodial assay. Aqueous, alcoholic, and total alkaloidal extracts, and compounds isolated from the plant material were found to be effective against all three strains of parasite to varying degrees. Of the extracts, the total alkaloid was the most active with mean IC50 values of 47, 42, and 54 micromolar for the three strains, respectively, compared to values of 2.3, 72, and 68 micromolar, for chloroquine. The aqueous extract was the least active. Of the isolated compounds, cryptolepine was the most effective, with mean IC50 values of 27, 33 and 41 micromolar for the D6 chloroquine-sensitive and K-1 and W-2 chloroquine-resistant strains, respectively. Hydroxy-cryptolepine was the next best compound with IC50 values of 31, 45, and 59 micromolar, respectively, followed by neocryptolepine. Quindoline, or nor-cryptolepine, without the methyl group, was the least active anti-plasmodial of the isolated compounds.35 This is an indication that the methyl group contributes to anti-malarial activity, at least in part. The result of this study with respect to the K-1 strain is in agreement with the work of Noamesi and coworkers,15 as well as Kirby and coworkers,13 who reported the anti-plasmodial activity of cryptolepine against the multi-drug resistant K-1 strain of P. falciparum.

In another study, Wright et al., using multi-drug resistant K1 strain of P. falciparum and a method of assessing inhibition of parasite growth based on measurement of lactate dehydrogenase activity, showed that among a number of anhydronium bases, only cryptolepine, the major alkaloid in cryptolepis, had anti-plasmodial activity similar to that of chloroquine.19 The mean IC50 value, determined from linear regression analysis of dose-response curves, was 0.114 micromolar for cryptolepine, compared to a mean value of 0.2 micromolar for chloroquine diphosphate.

Inhibition of beta-hematin formation in a cell-free system is another in vitro test for anti-plasmodial activity. Reduction or elimination of the characteristic peaks of beta-hematin at 1663 and 1210 cm-1 in an infrared spectrum indicates efficacy. Cryptolepine has been shown to be effective in this model, the peaks disappearing when the reaction mixture was pre-incubated with the alkaloid,37 suggesting that cryptolepine’s anti-plasmodial effect depended, at least in part, on a quinine-like mode of action. A relatively simple method of measuring beta-hematin, using absorbance in a simple spectrophotometer, is currently being used in the Department of Biochemistry of the University of Ghana, and could be adopted for assessing the efficacy of extracts of cryptolepis and compounds isolated from them in a research and development effort to develop this particular phytomedicine.

Studies have been carried out to evaluate the anti-microbial properties of cryptolepis extracts and compounds isolated from them. In a program of biological evaluation to justify traditional uses of herbal remedies, cryptolepis was studied because of its successful use in treating diarrhea caused by intestinal amoebiasis, and found to be effective in vitro against Entamoeba histolytica.5 Diarrheal diseases are very common in West Africa and therefore, any anti-diarrheal remedy is of great interest. Over 100 strains of Campylobacter species, which are causative agents for gastroenteritis, have been used to study the effect of cryptolepis and compounds isolated from it on diarrheal bacteria.17 The finding that cryptolepine was more effective than co-trimoxazole and sulfamethoxazole, just as effective as ampicillin and less effective than erythromycin and streptomycin, the antibiotics usually used against diarrheal diseases, indicates that cryptolepis may be a potential remedy for diarrhea. The ethanolic extract, not the aqueous one, had activity but not as good as that of the isolated alkaloid. The effect of the plant material was not so dramatic when Vibrio cholerae, the causative agent for enteric infections, was used as the test organism. Obviously, cryptolepis could be used as therapy for gastroenteritis although it is not known as such in the region where it is used to manage a number of infections.

Out of 12 plants used in Guinea-Bissau traditional remedies to treat infectious diseases, only cryptolepis was found effective against Escherichia coli and nine out of 10 microbial test organisms used; only Pseudomonas aeruginosa was not susceptible.1 Ineffectiveness against P. aeruginosa was also reported in another anti-microbial screening study in vitro, using extracts as well as five alkaloids isolated from cryptolepis.26

Of all the isolated alkaloids, cryptolepine is the most active anti-bacterial agent, and it is more active against Gram-positive bacteria than the Gram-negative ones.28,38 Some of the minor alkaloids are also effective as anti-bacterial agents, including the hydrochloride,9 cryptoheptine, neocryptolepine, and biscryptolepine; cryptoquindoline was not active.38 The anti-bacterial actions of neocryptolepine appear to mirror those of the major alkaloid, cryptolepine.39 Cryptolepine also has some anti-fungal activity against Saccharomyces cerevisiae but not the Candida species.18 Its anti-fungal activity seems to be limited compared to its anti-bacterial activities.

Some pharmacological effects of cryptolepis, quite unrelated to the use of the plant in folkloric medicine, are its anti-inflammatory and anti-hyperglycemic properties. It has been more than two decades since the anti-inflammatory properties were established, as indicated by inhibition of carageenan-induced edema and that of platelet aggregation.8,16 (Carageenan-induced edema is a typical pharmacological test for antiinflammatory drugs; carageenan, a gelatinous preparation made from seaweed, is injected into parts, often the paw, of test animals to produce a localized inflammation – usually, the type characterized by accumulated fluids, i.e., edema. The tested agent is then measured for its ability to inhibit the resulting inflammation.) The anti-hyperglycemic property has been shown as enhanced insulin-mediated glucose disposal in a mouse model of diabetes and in an in vitro system using the 3T3-L1 glucose transport assay, indicating an effect on Type 2 diabetes.7,25 Hypotensive properties have also been reported, including effects on cholinergic nerve transmission, alpha-adrenoceptors, and muscarinic receptors.40,41 Malaria and other infectious diseases are more prevalent in the West African sub-region and therefore the anti-plasmodial and anti-bacterial properties of cryptolepis are more exciting. However, one should not underestimate the potential of cryptolepis in treating some of these other diseases.