R e v i s t a d a S o c i e d a d e B r a s i le i r a d e M e d i c i n a T r o p i c a l 2 2 ( 4 ) : 1 8 3 - 1 8 6 , O u t- D e z , 1 9 8 9 .
R A T E O F A C T I O N O F S C H I S T O S O M I C I D E S I N M I C E I N F E C T E D W I T H S C H I S T O S O M A M A N S O N I
N a fta le K a tz 1, E m m a n u e l Pin to D ia s t, C e c ilia P e re ira d e S o u z a 1, J o h n I. B ru c e 2, G e ra ld C. C o le s 3
M i c e i n f e c t e d w i t h a d u l t Schistosoma mansoni w e r e d o s e d w i t h a s i n g l e o r a l d o s e o f 1 2 5 o r 2 5 0 m g / k g o l t i p r a z , 5 0 o r 1 0 0 m g / k g o x a m n i q u i n e , o r 2 0 0 o r 4 0 0 m g / k g
p r a z i q u a n t e l . T h e m o r t a l i t y r a t e o f w o r m s a n d o o g r a m c h a n g e s w e r e d e t e r m i n e d b e t w e e n 1 a n d 1 6 w e e k s a f t e r d o s i n g . T h e t i m e r e q u i r e d b e t w e e n d o s i n g a n d p o s t m o r t e m t o o b t a i n m a x i m u m e f f e c t i v e n e s s w a s 1 w e e k f o r p r a z i q u a n t e l , 2 w e e k s f o r o x a m n i q u i n e a n d 8 w e e k s f o r o l t i p r a z . C h a n g e s i n o o g r a m s p e r s i s t e d t h r o u g h o u t m o s t o f t h e
e x p e r i m e n t , a l t h o u g h r e l a p s e h a s b e e n o b s e r v e d a t t h e 4 t h w e e k o n .
K e y - w o r d s : Schistosoma mansoni. S c h i s t o s o m i c i d e s . W o r m m o r t a l i t y .
The speed at which drugs affect parasitic hel minths varies widely. Nematodes such as H a e m o n -c h u s -c o n t o r t u s which live in the intestinal tract can be removed within 1 hour, as paralysis causes the worms to lose their hold and they are swept away2. By contrast, schistosomes which live in the blood vessels die more slowly, and Bueding e t a l have reported that oltipraz did not exert its maximum effect on adult S c h i s t o s o m a m a n s o n i until 8 weeks after dosing^.
To determine whether drug resistance has deve loped in isolates from treated uncured patients, expe riments on mice were chosen^. This is a time consu ming as snails must be infected and worms allowed to mature in mice. If the period between dosing and postmortem could be reduced the total time for the experiment would be shorter. On the other hand, examination of mice must be performed when the full activity of the schistosomicides on the worms can be demonstrated. In the present work we report the mortality rates of S . m a n s o n i worms and oogram changes found in mice between one and sixteen weeks after dosing with three different schistosomicides.
M A T E R IA L A N D M ETH O D S
The LE strain of S . m a n s o n i which has been laboratory maintained for about 2 0 years, was used to infect B i o m p h a l a r i a g l a b r a t a . Cercariae collected
1. Centro de Pesquisa “ René Rachou’VFIOCRUZ. 2. Center for Tropical Diseases, University of Lowell. 3. Departm ent of Zoology, University of Massachusetts.
Correspondence to: Dr. Naftale Katz. Centro de Pesqui sas “René Rachou”/F IO C R U Z . CP: 1743. 30190 Belo Horizonte, M G , Brasil.
t Deceased on 10/23/89
Recebido para publicação em 11/11/89.
within 50 days after exposure of snails were used to infect Swiss outbred strain male mice by subcutaneous injection on the back with 100 cercariae each. Forty five days after infection mice were left untreated or treated with a single oral dose of 125 or 250 mg/kg oltipraz, 50 or 100 mg/kg oxamniquine or 200 or 400 mg/kg praziquantel suspended in 1% agar solution. At 1,2, 4, 8 and 16 weeks after treatment mice were killed by cervical dislocation, and after perfusion of the mesenteric and portal veins the numbers o f living and dead worms were counted and alterations in the oogram from intestinal fragments of the mice deter mined6.
R ESULTS
The percentage of dead worms present are shown in Figures 1 and 2. Changes in oograms are shown in Tables 1, 2 and 3. The results indicate that praziquantel and oxamniquine act relatively quickly but worms continue to die for at least 8 weeks after treatment with oltipraz. Changes in oograms persisted throughout most of the experiment, but relapse can be detected at the 4th week on, with the drugs used.
D ISC U SSIO N
From a knowledge of the mechanism of action of praziquantel1 it would be expected that death of worms after treatment would be rapid. The data confirm this conclusion and indicate that killing of mice within one week of dosing is satisfactory to determine the activity of praziquantel. Oxamniquine acts quite differently to praziquantel, probably by being activated, binding to D N A and preventing synthesis of RN A 4. This drug also acts relatively rapidly and post mortem of mice 2 weeks after dosing is sufficient to show full efficacy of the drug. Two weeks
K a t z N , D i a s E P , S o u z a C P , B r u c e J I , C o l e s G C . R a t e o f a c t i o n o f s c h i s t o s o m i c i d e s i n m i c e i n f e c t e d w i t h Schistosom a m ansoni. R e v i s t a d a S o c i e d a d e B r a s i l e i r a d e M e d i c i n a T r o p i c a l 2 2 : 1 8 3 - 1 8 6 , O u t - D e z , 1 9 8 9 .
between dosing and postmortem and counting num bers of live -worms is thus the optimal period for detection of strains of drug resistant schistosomes.
By contrast the full efficacy of oltipraz is slow to appear, in agreement with the observations of Bueding and coworkers^, and mice must be left for 8 weeks to
observe the maximum effect. Although oltipraz has been reported to affect glutathione levels in the worms^ and the maximum drug concentrations are present within worms at 18 hours of dosing^ it is not clear why it should take so long for oltipraz to take its full effect.
K a t z N , D i a s E P , S o u z a C P , B r u c e J I , C o l e s G C . R a t e o f a c t i o n o f s c h i s t o s o m i c i d e s i n m i c e i n f e c t e d w i t h Schistosom a m ansoni. R e v i s t a d a S o c i e d a d e B r a s i l e i r a d e M e d i c i n a T r o p i c a l 2 2 : 1 8 3 - 1 8 >, O u t - D e z , 1 9 8 9 .
K a t z N , D i a s E P , S o u z a C P , B r u c e J I , C o le s G C . R a t e o f a c t i o n o f s c h i s t o s o m i c i d e s in m i c e i n f e c t e d w ith Schistosoma mansoni. R e v i s t a d a S o c i e d a d e B r a s i le i r a d e M e d i c i n a T r o p i c a l 2 2 : 1 8 3 - 1 8 6 , O u t - D e z , 1 9 8 9 .
RESUM O
Camundongos infectados experimentalmente com
S c h i s t o s o m a m a n s o n i foram tratados por via oral com dose única de 125 ou 250 mg/kg de oltipraz, 50 ou 100 mg/kg de oxamniquine, e 200 ou 400 mg/kg de praziquantel. O número de vermes e alteração do oograma foram determinados entre a l.a e 16? semanas após o tratamento. O tempo necessário para observar o máximo de atividade da droga foi de 1 semana para o praziquantel, 2 semanas para o oxamniquine e 8 semanas para o oltipraz. Alterações do oograma persis tiram durante o período de observação, embora recidiva tenha sido detectada, já na 4? semana, com as drogas utilizadas.
P a l a v r a s - c h a v e s : Schistosoma mansoni. E s
-q u i s s o m i c i d a s . M o r t a l i d a d e d e v e r m e s .
R E FE R E N C E S
1. Andrews P. Praziquantel: mechanisms of anti-schisto somal activity. Pharmacology and Therapeutics 29:129- 156, 1985.
2. Briscoe M G, Coles GC. The speed o f action of anthel mintics. Veterinary Record 106:58, 1980.
3. Bueding E, D olan P, Leroy JP. The antischistosomal activity of oltipraz. Research Communications in Che mical Pathology and Pharmacology 37: 293-303, 1982. 4. Cioli D, Pica-M attoccia L, Rosenberg S, Archer S.
Evidence for the mode of antischistosomal action of hycanthone. Life Sciences 37:161-167, 1985. 5. Katz N, Dias EP, Araujo N, Souza CP. Estudo de uma
cepa humana de S c h i s t o s o m a m a n s o n i resistente a agentes esquistossomicidas. Revista da Sociedade Bra sileira de Medicina Tropical 7:381-387, 1973. 6. Pellegrino J, K atz N. Chemotherapy of S c h i s t o s o m a
