The good and the bad: alkaloid screening and brineshrimp bioassays of aqueous extracts of 31 medicinal plants of eastern Nicaragua.

CONTEXT

Presence/absence tests for alkaloids of 31 medicinal vascular plant species from 31 genera and 26 families of eastern Nicaragua provided a baseline for bioactivity tests.

OBJECTIVE

To determine the bioactivity and cytoxicity of aqueous extracts of widely used medicinal species in eastern Nicaragua.

MATERIALS AND METHODS

Ethnomedicinal applications were obtained from interviews of traditional healers. We used Dragendorff's reagent to test alkaloids and brine shrimp for cytotoxicity of aqueous extracts.

RESULTS

Twenty-nine of the 31 species tested positive for alkaloids. The median lethal concentration that kills 50% of the larvae within 24 h of contact with the extract (LC(50) was less than 1000 µg/mL for 4 (13%) species (the usual cytotoxic category), 1001-5000 µg/mL for 23 (74%) species, and between 5001-7500 µg/mL for the remaining 4 (13%) species.

DISCUSSION AND CONCLUSION

Twenty-five of the ethnomedicines contain alkaloids but are not cytotoxic. In contrast to first suppositions, we suggest that this is a good and desirable, and perhaps expected, outcome. Medicinal plants that are cytotoxic may obviously control or kill bacteria or other pathogens, but may also negatively affect the patient; some high alkaloid levels have been associated with carcinogens. Thus, perhaps the majority of effective medicinals should be expected to be noncytotoxic. We suggest that this is a new paradigm for consideration of the overall value and effectiveness of medicinals. Of course, medicinals also can be effective in numerous ways (e.g., organ stimulation or other physiological functions) other than simply as antimicrobials or antipathogens.