Action of Certain Tetrapyrrole Derivatives in Experimental Trypanosoma congolense Infections

SummaryA number of tetrapyrrole derivatives of both plant and animal origin were tested for ability to influence the course of Trypanosoma congolense infections in mice. Of these, chlorophyllins, containing either magnesium or copper, and hematoporphyrin were effective in delaying deaths from trypanosomiasis and with prolonged administration cures could be effected. The non-metallic phaeophorbide relatives of chlorophyllin were ineffective as were deuteroporphyrin, mesoporphyrin, phylloporphyrin, pyrroporphyrin, rhodoporphyrin and uroporphyrin, as well as certain bile pigments. The antitrypanosomal effect of chlorophyllin and hematoporphyrin could be reversed, either completely or partially, by hemin, but not by protoporphyrin. The hypothesis that the mechanism of action of these tetrapyrrole derivatives in suppressing trypanosome infection involves competitive inhibition of a growth factor essential for the parasite (apparently hemin, rather than protoporphyrin) seems to be supported by our experiments. Other species of hemoflagellates and certain other parasites were uninfluenced by compounds active in T. congolense infections. It is conjectured that sensitivity of this particular parasite may be attributable to a certain combination of physiological attributes which is not possessed by its relatives.