Analysis of nematode motion using an improved light-scatter based system

Background

The detailed assessment of nematode activity and viability still remains a relatively undeveloped area of biological and medical research. Computer-based approaches to assessing the motility of larger nematode stages have been developed, yet these lack the capability to detect and analyze the more subtle and important characteristics of the motion of nematodes. There is currently a need to improved methods of assessing the viability and health of parasitic worms.

Methods

We describe here a system that converts the motion of nematodes through a light-scattering system into an electrical waveform, and allows for reproducible, and wholly non-subjective, assessment of alterations in motion, as well as estimation of the number of nematode worms of different forms and sizes. Here we have used Brugia sp. microfilariae (L1), infective larvae (L3) and adults, together with the free-living nematode Caenorhabditis elegans.

Results

The motion of worms in a small (200ul) volume can be detected, with the presence of immotile worms not interfering with the readings at practical levels (up to at least 500 L1 /200ul). Alterations in the frequency of parasite movement following the application of the anti-parasitic drugs, (chloroquine and imatinib); the anti-filarial effect of the latter agent is the first demonstrated here for the first time. This system can also be used to estimate the number of parasites, and shortens the time required to estimate parasites numbers, and eliminates the need for microscopes and trained technicians to provide an estimate of microfilarial sample sizes up to 1000 parasites/ml. Alterations in the form of motion of the worms can also be depicted.

Conclusions

This new instrument, named a "WiggleTron", offers exciting opportunities to further study nematode biology and to aid drug discovery, as well as contributing to a rapid estimate of parasite numbers in various biological samples.

Assessment of the health and number of nematodes still relies heavily on subjective monitoring of their motion. Although less-subjective techniques exist that utilize the motility as the primary indicator, the current approaches tend to be designed for use with larger worms and not for early developmental stages. We have describe here a sensitive technique that converts the motion of nematodes into electrical waveforms, which then be used for an estimation of the number parasites present, and for detailed analysis of alterations in their movements. Using parasites of different sizes, including different stages of Brugia sp. and Caenorhabditis elegans, we have shown that the system can analyse samples containing up to 1000 microfilariae/ml, and can be used to used to detect the decrease in motility as a worm loses viability. We have also demonstrated its use in assessing the effects of chloroquine and imatinib on filariae. This sensitive technique is likely to be value to research and field laboratories where there is a need to rapidly estimate the number of parasites present in liquid samples, and can be used in drug screening programs to assess the effects of different anthelminthics.

Awareness of health personnel about lymphatic filariasis and mass drug administration in Kerala State

The mass drug administration programme to eliminate lymphatic filariasis with DEC in Kerala was started in 1997, extended to all the 11 endemic districts by 2005. Since the beginning of Mass drug Administration, the drug consumption rate was found to be not satisfactory. The reasons for noncompliance indicated that the community is not fully convinced about the programme. The knowledge of the medical and para medical workers is certainly a factor in the success of implementation of the programme and is vital. To ascertain the knowledge, a study was undertaken and found not satisfactory. Hence intensive training on all aspects of lymphatic filariasis and the Mass drug Administration programme to achieve the requisite drug consumption rate to meet the goal is needed.

Treatment of Brugia timori and Wuchereria bancrofti infections in Indonesia using DEC or a combination of DEC and albendazole: adverse reactions and short-term effects on microfilariae

Filariasis caused by Brugia timori and Wuchereria bancrofti is an important public health problem on Alor island, East Nusa Tenggara, Indonesia. To implement a control programme, adverse reactions and short-term effects on the microfilaria (mf) density were studied following a divided dose of diethylcarbamazine (DEC, 6 mg/kg body weight - 100 mg on day 1 and the rest on day 3) or a single dose of DEC (6 mg/kg body weight on day 3) and albendazole (Alb, 400 mg). In order to define the most appropriate regimen, 30 persons infected with B. timori were treated in the hospital and results were compared with those obtained from the treatment of 27 persons infected with W. bancrofti. Adverse reactions consisted of systemic reactions such as fever, headache, myalgia, itching and local reactions such as adenolymphangitis. Fever experienced by a number of patients in both treatment groups generally occurred 12-24 h after drug administration and lasted up to 2 days. Adenolymphangitis tended to occur later and was resolved within 4 days. The number of W. bancrofti patients suffering from adverse reactions was lower and the reactions were milder than those of the B. timori patients. There was no difference in adverse reactions between DEC alone and DEC-Alb treatment for either infection. The geometric mean mf count decreased on day 7 in the B. timori infected patients from 234 mf/ml in the DEC group and from 257 mf/ml in the DEC-Alb group to 7 and 8 mf/ml, respectively. The mf densities of the W. bancrofti infected patients decreased on day 7 from 214 mf/ml in the DEC group and from 559 mf/ml in the DEC-Alb group to 15 and 14 mf/ml, respectively. Our data indicate that the microfilaricidal effect of the drugs is achieved more rapidly for B. timori, which is associated with more adverse reactions than W. bancrofti. In addition, 111 B. timori infected persons were treated in the community with DEC-Alb in one selected village. The adverse reactions and the reduction of mf density was similar to the findings of the hospital-based study. In this group, there was a strong correlation of mf density with the frequency and severity of adverse reactions. The addition of Alb resulted in no additional adverse reactions compared with DEC treatment alone and can also be used for the treatment of B. timori infection. In Indonesia, where the prevalence of intestinal helminths is high, the use of a combination of DEC and Alb to control lymphatic filariasis may also have impact on the control of intestinal helminths.

Interleukin-4 influences the production of microfilariae in a mouse model of Brugia infection

Sub-cutaneous infection of interleukin (IL)-4-/- mice on the BALB/c background with third stage larva (L3) of Brugia pahangi revealed an altered cytokine profile consistent with the absence of the Th2 promoting cytokine IL-4. Splenocytes from IL-4-/- mice secreted significantly more antigen (Ag)-specific IL-2 and interferon-gamma and significantly less Ag-specific IL-5, compared to those from L3-infected wild-type mice. However, levels of Ag-specific IL-13 were similar between groups. Despite the alteration in immune responses, there was no significant difference in recovery of developing worms from the peritoneal cavity of the two strains of mice at any time postinfection. However, at later time points of infection, the IL-4-/- mice contained large numbers of microfilariae (Mf) in the peritoneal cavity while the wild-type mice contained comparatively few Mf. The differences in Mf levels appear to relate to differences in worm fecundity in the two strains of mice, with adult female worms from the wild-type mice containing few developing Mf. Moreover, implantation of sexually mature adult female worms into the peritoneal cavity of both strains of mice resulted in equal levels of Mf, confirming that the primary role of IL-4 is to limit fecundity during the maturation phase of infection.

Effects of tetracycline on the filarial worms Brugia pahangi and Dirofilaria immitis and their bacterial endosymbionts Wolbachia

Wolbachia endosymbiotic bacteria have been shown to be widespread among filarial worms and could thus play some role in the biology of these nematodes. Indeed, tetracycline has been shown to inhibit both the development of adult worms from third-stage larvae and the development of the microfilaraemia in jirds infected with Brugia pahangi. The possibility that these effects are related to the bacteriostatic activity of tetracycline on Wolbachia symbionts should be considered. Here we show that tetracycline treatment is very effective in blocking embryo development in two filarial nematodes, B. pahangi and Dirofilaria immitis. Embryo degeneration was documented by TEM, while the inhibition of the transovarial transmission of Wolbachia was documented by PCR. Phylogenetic analysis on the ssrDNA sequence of the Wolbachia of B. pahangi confirms that the phylogeny of the bacterial endosymbionts is consistent with that of the host worms. The possibility that tetracycline inhibition of embryo development in B. pahangi and D. immitis is determined by cytoplasmic incompatibility is discussed.

Antifilarial activity of macrocyclic lactones: comparative studies with ivermectin, doramectin, milbemycin A4 oxime, and moxidectin in Litomosoides carinii, Acanthocheilonema viteae, Brugia malayi, and B. pahangi infection of Mastomys coucha

The avermectins ivermectin and doramectin and the milbemycins milbemycin A4 oxime and moxidectin were tested for filaricidal activity in Mastomys coucha infected with Litomosoides carinii, Acanthocheilonema viteae, Brugia malayi, and B. pahangi. Single subcutaneous doses of 0.005-5 mg/kg (L. carinii), 0.0005-0.5 mg/kg (A. viteae), 0.5 and 5 mg/kg (B. malayi), and 5 mg/kg (B. pahangi) were injected. Necropsies were performed 42 days after treatment. The avermectins caused a strong and rapid reduction of microfilaraemia in L. carinii and A. viteae infections within a few hours after treatment but showed only moderate efficacies on microfilariae of Brugia spp. The effects of the milbemycin derivatives on L. carinii and A. viteae microfilariae were generally weaker than those of the avermectins. However, moxidectin was comparatively active against microfilariae of Brugia spp. Subsequently the parasitaemia levels of L. carinii and A. viteae infected animals remained either almost completely depressed or tended to reincrease in a dose dependent manner whereas there was generally a continuous decrease of microfilaraemia levels in Brugia spp. infected animals. Adulticidal effects were limited to A. viteae although with neither dose of neither drug > 95% reductions of adult worm counts were reached. However, pathogenic influences of the drugs were observed on intrauterine embryonic stages of the parasites.

External stimuli and intracellular signalling in the modification of the nematode surface during transition to the mammalian host environment

Previous work has shown that the surface of infective larvae of parasitic nematodes will not bind the fluorescent lipid analogue 5-N-(octadecanoyl)aminofluorescein (AF18) until after exposure of the parasite to mammalian tissue-culture conditions. In this study, culture media which are permissive or non-permissive for the acquisition of lipophilicity for AF18 were altered in order to examine possible stimuli involved. This showed that external alkaline pH and high sodium ion concentration were highly stimulatory. The internal signalling pathways which may be involved in the surface alteration were then examined using agents which are known to affect intracellular signalling in mammalian cells. The results indicated that elevation of cGMP levels was stimulatory whereas inhibition of a putative Na+/H+ antiporter or calcium mobilization was inhibitory, and it is argued that high intracellular levels of cAMP may be inhibitory. Whilst the precise effects of the agents used on nematode cells remain to be established, these results provide a framework for the examination of the processes involved in the modification of the nematode surface which takes place immediately after the infection event.

Experimental chemotherapy of filariasis: comparative evaluation of the efficacy of filaricidal compounds in Mastomys coucha infected with Litomosoides carinii, Acanthocheilonema viteae, Brugia malayi and B. pahangi

Eleven types/classes of compound with antifilarial activity were comparatively evaluated in Mastomys coucha infected with Litomosoides carinii, Acanthocheilonema viteae, Brugia malayi or B. pahangi. The paper deals with the efficacy of (i) predominantly microfilaricidal compounds [diethylcarbamazine, levamisole, avermectins (ivermectin, milbemycin), nitrofurans (nitrofurantoin, hydroxymethylnitrofurantoin, nifurtimox, furazolidone, furapyrimidone), organophosphorals (metrifonate, haloxon), and aminophenyl-amidines], (ii) predominantly macrofilaricidal compounds [suramin, benzimidazoles (flubendazole, mebendazole, oxfendazole, ciclobendazole, albendazole, cambendazole, fenbendazole), and arsenicals (thiacetarsamide, Mel PH, R7/45)], and (iii) micro- and macrofilaricidal compounds [benzazole derivatives (CGP 20376 and other benzothiazoles) and nitrophenylamines (amoscanate, CGP 6140)]. Minimum effective doses against microfilariae and minimum curative doses against adult filariae as well as detailed data on dose-efficacy relationships are reported for the various drugs. The results obtained in M. coucha are compared with those published for other experimental in vivo filarial systems, thus attempting to describe a general status of in vivo antifilarial activity of the compounds.

Identification of a novel transglutaminase from the filarial parasite Brugia malayi andits role in growth and development

Recently, we reported the presence of a putative transglutaminase in adult female worms of Brugia malayi [1]. The enzyme activity was shown to be essential for in utero growth and development of microfilariae. Here, we demonstrate that adult worms of B. malayi have a large amount of epsilon-(gamma-glutamyl)lysine isopeptide bonds, a product of physiologically active transglutaminase. A 25-kDa immunoreactive band detected in female worm extracts by a monospecific monoclonal antibody (CUB 7401) against guinea pig liver transglutaminase was associated with the enzymatic activity. Unlike the mammalian enzyme, the parasite enzyme did not require Ca2+ for its catalytic activity. Furthermore, in utero developing embryos, especially during early stages of development, contained very high amounts of this enzyme. Adult female worms contained several proteins that could serve as suitable substrates for the enzyme. Inhibition of the enzyme activity by an enzyme-specific pseudosubstrate, monodansylcadaverine, led to a time- and dose-dependent inhibition of microfilariae production and release by gravid female worms. The inhibition of microfilariae production was due to the inhibition of transglutaminase-catalyzed crosslinking of parasite proteins that in turn seemed to be essential for in utero growth and development of the embryos. The results suggest that transglutaminase-catalyzed reactions may play an important role during early development of embryos to mature microfilariae inside the adult female worms of filarial parasites.

Induction of protective immunity to Brugia pahangi in jirds by drug-abbreviated infection

Protective immunity of homologous challenge infection was examined in jirds after drug-abbreviated infection with Brugia pahangi. Mebendazole (MBZ) treatment at the early prepatent (5-7 weeks of post infection) or the late prepatent (7-9 weeks of post infection) period was highly effective in causing almost complete eradication of the primary infection. After challenge infection, the worm burden was significantly reduced 19% (31.1 in average) and 77% (9.5) to that of the controls (38.8 and 41.7), respectively. The magnitude of eosinophil response paralleled the degree of protection. No or only a few microfilariae were seen after challenge infection in jirds treated during the prepatent periods. They were also resistant to intravenous challenge with the microfilariae of B. pahangi. MBZ treatment at the patent period was, on the contrary, incomplete against primarily infected adult worms, and was not able to induce either significant protection (30.1 vs 33.1 in control) or eosinophil response to the challenge infection.

Brugia malayi: ivermectin inhibits the exsheathment of microfilariae

Brugia malayi-infected microfilaremic jirds (Meriones unguiculatus) were treated with ivermectin at a single dose of 200 micrograms/kg of body weight injected subcutaneously. Susceptible Aedes aegypti mosquitoes were fed on treated jirds 24 hours later. Mosquitoes fed on untreated jirds served as controls. Infected mosquitoes were dissected at 1, 3, 24, 48, 72, and 96 hr after the blood meal, and differential counts of sheathed microfilariae, exsheathed microfilariae, and cast sheaths were performed using fluoresceinated wheat germ agglutinin. Microfilariae failed to exsheath in mosquitoes fed on ivermectin-treated jirds. Microfilariae from ivermectin-treated jirds also did not exsheath in vitro in the presence of 10 mM CaCl2, whereas 85-90% of sheathed microfilariae from untreated jirds exsheathed in vitro. In addition, sheathed microfilariae from untreated jirds, when pretreated in vitro with ivermectin at 0.25, 0.5, or 1 microgram/ml, lost their ability to exsheath in vitro in the presence of 10 mM CaCl2. However, ivermectin treatment had no effect on exsheathing of microfilariae when incubated with papaya protease. Thus, ivermectin appears to inhibit the intrinsic exsheathing process of microfilariae in the mosquito host, thereby blocking their development and further transmission of infection.

Tropical pulmonary eosinophilia

Tropical pulmonary eosinophilia is one of the many PIE syndromes [pulmonary infiltrates with eosinophilia (of the peripheral blood)]. It is caused by immunologic hyperresponsiveness to the filarial parasites Wuchereria bancrofti or Brugia malayi. Its clinical presentation includes nocturnal cough, dyspnea, wheezing, fever, weight loss, fatigue, interstitial mottling on chest radiograph, predominantly restrictive but also obstructive lung function abnormalities, and peripheral blood eosinophilia of more than 3000 per microliter. It can be distinguished from other PIE syndromes by the patient's history of residence in the tropics, by the presence of extraordinarily high levels of both serum IgE and antifilarial antibodies, and by the dramatic clinical improvement after treatment with the antifilarial drug diethylcarbamazine. Recent studies indicate that the compromised lung diffusion capacity of patients with acute tropical pulmonary eosinophilia is a function of the degree of the eosinophilic alveolitis present and that, despite a 3-week course of diethylcarbamazine, low-grade alveolitis persists in almost half of such patients; this persistent alveolitis is likely to be the cause of the progressive interstitial fibrosis seen in many untreated or inadequately treated patients with tropical pulmonary eosinophilia.

Effect of carrageenan on the resistance of congenitally athymic nude and normal BALB/c mice to infective larvae of Brugia malayi

Resistance of BALB/c mice to infective third-stage larvae (L3) of the human filarial parasite Brugia malayi is thymus-dependent, although the actual effector mechanisms that mediate larval killing are unknown. The present study examined the effect of carrageenan (CGN) on the mechanisms of resistance to B. malayi infection in heterozygous (nu/+) and nude (nu/nu) mice. Mice were treated with CGN at a single dose of 20 or 200 mg/kg and were inoculated intraperitoneally 1 day later with 100 L3. The results showed a dose-dependent increase in the numbers of L4 and L5 that were recovered from nu/+ and nu/nu mice. CGN treatment also enhanced the recovery of mature adult worms from nu/nu mice and appeared to abolish partially the dichotomy of resistance between the usually more susceptible male and the more resistant female nu/nu mouse. Microfilariae were found in the peripheral blood and the peritoneal cavity of CGN-treated male and female nu/nu mice and in the peritoneal cavity of male but not female nu/+ mice. Fewer larval granulomas were recovered from the peritoneal cavity of treated mice. CGN-treated, parasitized nu/+ and nu/nu mice showed high titers of IgM and IgG antibodies. An experimental compound, CGP 20376, showed 100% larvicidal activity following the administration of a single dose of 20 mg/kg to CGN-treated mice. From this study, we conclude that macrophages alone or in conjunction with other cells are actively involved in the resistance of mice to B. malayi L3.

Diethylcarbamazine inhibits endothelial and microfilarial prostanoid metabolism in vitro

Diethylcarbamazine (DEC) rapidly lowers the number of microfilariae in the peripheral circulation. The mechanism of action is unknown, but may involve alterations of arachidonic acid metabolism in vascular tissues. We studied the effects of DEC on arachidonic acid metabolism by bovine pulmonary arterial endothelium monolayers, human platelets and Brugia malayi microfilariae. DEC at a concentration of 2.5 microM, a level achieved in vivo, rapidly decreased prostacyclin, prostaglandin E2 and thromboxane B2 release from endothelial monolayers by 78% (P less than 0.001), 57% (P = 0.05), and 75% (P less than 0.05), respectively. High-pressure liquid chromatography of extracts of endothelial monolayers incubated with DEC showed similar inhibition of these cyclooxygenase pathway products, but exposure to the drug did not result in formation of new eicosanoids. DEC did not inhibit endothelial phospholipase A2-dependent release of arachidonate from membrane stores, whereas prostaglandin H2 synthase activity (cyclooxygenae, EC 1.14.99.1) was reduced to a degree similar to that effected by acetylsalicylic acid. Microfilarial but not platelet synthesis of cyclooxygenase products was also reduced by DEC. These data suggest that the mechanism by which DEC lowers the level of microfilariae in the circulation may in part involve its effects on host endothelial and parasite eicosanoid production.

Brugia malayi and Acanthocheilonema viteae: antifilarial activity of transglutaminase inhibitors in vitro

The possible involvement of transglutaminase-catalyzed reactions in survival of adult worms, microfilariae (mf), and infective larvae of the filarial parasite Brugia malayi was studied in vitro by using the specific pseudosubstrate monodansylcadaverine (MDC) and the active-site inhibitors cystamine or iodoacetamide. These inhibitors significantly inhibited parasite mobility in a dose-dependent manner. This inhibition was associated with irreversible biochemical lesions followed by filarial death. A structurally related, inactive analog of MDC, dimethyldansylcadaverine, did not affect the mobility or survival of the parasites. Adult worms failed to release mf when they were incubated in the presence of MDC or cystamine, and this inhibitory effect on mf release was concentration dependent. Similar embryostatic and macrofilaricidal effects of MDC were observed in Acanthocheilonema viteae adult worms. These studies suggest that transglutaminase-catalyzed reactions may play an important role in the growth, development, and survival of filarial parasites.

In vitro effects of 2-tert-butyl-benzothiazole derivatives on microfilariae of Litomosoides carinii, Brugia malayi and Acanthocheilonema viteae

Six 2-tert-butyl-benzothiazole derivatives (2-tert-butyl-6-iso-thiocyanato-5-methyl-benzothiazole CGP 21306); 3-[(2-tert-butyl-5-methyl-benzothiazole-6-yl) aminothiocarbonylthiol] propionic acid (CGP 21835); 2-tert-butyl-5-methyl-6-(N-methyl-piperazinyl-thiocarbonylamino)-b enzothiazole (CGP 21833); 2-tert-butyl-5-methyl-6-(4-dimethylamino-piperid-1-yl-thiocarbo nylamino)- benzothiazole (CGP 26702); CGP 20376, the 5-methoxy analogue to CGP 21835 and CGP 20309, the 5-methoxy analogue to CGP 21833) with known, high filaricidal activity in vivo were tested for in vitro efficacy against microfilariae of L. carinii (Lc), B. malayi (Bm) and A. viteae (Av) in order to study intrinsic antifilarial activities. All drugs affected the motility of the microfilariae of the three species in a species, dose and time dependent fashion. Lc was the most sensitive, Av the most resistant species. CGP 20376 and 21835 were the most effective compounds followed by CGP 21306. Complete immobilization of microfilariae was observed after 20 h in protein-free medium RPMI 1640 at drug concentrations of 0.1 to 10 nmol/ml. Effects were still marked 2 when graded on a 4 (full motility) to 0 (immobile) scale at concentrations of 0.01-0.1 nmol/ml. In the case of the thiourea derivatives CGP 21833, 26702 and 20309 concentrations had to be increased 10-100 fold to obtain similar effects. When proteins were present in the incubation medium (10% foetal calf serum, 100% normal serum) the efficacy of the compounds was reduced, i.e. drug concentrations had to be increased up to 100 fold to produce similar effects as in protein-free medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of diethylcarbamazine on the patent period of infection in periodic Brugia malayi

The patent period of infection which reflects the fecundic life span of the adult female worm was estimated for periodic B. malayi in south India by using immigration death model. Longitudinal data on natural loss of infection or that due to different degrees of DEC pressure in a cohort population of microfilaria carriers after a three years period, were used for the estimations. The patent period of infection was estimated to be 3.45 yr under natural conditions (without DEC therapy), which was reduced to 1.67 yr following one full course of selective therapy (6 mg/kg body wt/day for 12 days). When selective therapy was supplemented with four rounds of biannual single-dose mass DEC therapy (6 mg/kg body wt) the patent period was further reduced to 1.34 yr. The proportion loss of infection was relatively higher in microfilaria carriers who discontinued DEC selective therapy, when compared to natural loss. The percentage reduction in the mean microfilaria count was observed to decrease with increasing DEC pressure. Neither sex nor the age of the host was found to influence the fecundic life span or the survival of female adult worm.

Efficacy of diethylcarbamazine and pirimiphos-methyl residual spraying in controlling brugian filariasis

A control programme against subperiodic brugian filariasis was implemented in three villages, (Kg. Ampungan, Kg. Sebangkoi and Kg. Sebamban) in Sarawak, Malaysia. In Kampong Ampungan, the mass administration of diethylcarbamazine (DEC-citrate) combined with residual house spraying of pirimiphos-methyl reduced microfilarial rate to 8% of the pre-treatment level and microfilarial density (MfD50) to 44% of the pre-treatment level over a period of four years. In Kampong Sebangkoi and Kampong Sebamban, where only mass DEC therapy was applied, the microfilarial rate and MfD50 declined distinctly in the second blood survey but increased gradually in two subsequent follow-up blood surveys. In Kg, Ampungan, we observed a significant reduction of infective biting rate (88.3%), infection rate (62.5%) and transmission potential (88.1%) of Mansonia bonneae at the fourth spray round. The corresponding reduction rates in Kg. Sebangkoi and Kg. Sebamban were 35.3%, 26.7%, 42.2% and 24%, 30.8% and 15.4% respectively. The biting density of the vector was reduced by 79.8% indoors and 31.8% outdoors at the sprayed village, while only a slight decrease in densities (17.9% indoors and 12.4% outdoors) was observed at the unsprayed village. Bioassay tests revealed that pirimiphos-methyl had a substantial fumigant effect on the vector. The integrated control measure in controlling subperiodic brugian filariasis is discussed.

Effect of CGP 20376 on Brugia malayi and parasite antigenemia in jirds

This study was designed to investigate the activity of CGP 20376, a benzothiazole derivative, against Brugia malayi in jirds and to illustrate the utility of parasite antigen detection as a means of monitoring drug efficacy in filariasis. Drug treatment was 100% effective in jirds treated 3 or 24 days after infection. Microfilaria and adult worm counts were reduced (relative to counts in sham-treated control animals) by 96% and 95%, respectively, in animals treated 153 days after infection. Four of 6 animals in this treatment group cleared their microfilaremias and were free of adult worms 5 mo after treatment. Thus, CGP 20376 was effective against all life cycle stages of B. malayi in jirds. Parasite antigen levels in jird sera were consistent with parasitological results in all treatment groups, but antigen clearance was incomplete in some cases after apparently successful treatment of mature and immature infections.

Effect of bis(benzyl)polyamine derivatives on polyamine transport and survival of Brugia pahangi

A potent filaricidal effect of bis(benzyl)polyamine derivatives is reported; the addition of 1 microM MDL 27695 to Brugia pahangi maintained in vitro killed the worms within 1 week. Using the labelled derivative, MDL 27391 uptake was demonstrated and evidence was provided for an uptake system that is independent of and clearly distinguishable from those for polyamines. The Km value for the uptake of MDL 27391 was determined to be 2 microM, and that for putrescine, spermidine, and spermine was 4.9, 1.7, and 4.8 microM, respectively. The uptake of MDL 27391 was not affected by polyamines. In contrast, bis(benzyl)polyamines were shown to be strong inhibitors of both the putrescine and the spermidine/spermine uptake system. As shown for MDL 27391, bis(benzyl)polyamines are not metabolized after uptake by Brugia worms; therefore, it is expected that the filaricidal effect of the drug depends on its interaction with potential polyamine-binding sites.

Antifilarial activities of benzazole derivatives. 3. Effects of benzothiazoles on third stage larvae and preadult worms of Acanthocheilonema viteae, Brugia malayi and B. pahangi in Mastomys natalensis

Ten structurally defined benzothiazoles (5-methyl and the analogous 5-methoxy derivatives) with known macrofilaricidal and microfilaricidal activities were tested for efficacy against third stage larvae and preadult worms in Acanthocheilonema viteae, Brugia malayi, and B. pahangi infected Mastomys natalensis. Drugs were administered in single oral doses of maximally 100 mg/kg. The benzothiazoles were active against the two stages of the three species. Generally the 5-methoxy derivatives displayed slightly higher activity than the 5-methyl compounds. 6-Isothiocyanates (CGP 21306, CGP 20308) and 6-dithiocarbamic-S-(2-carboxyethyl)esters (CGP 21835, CGP 20376) were more active than thiocarbonylamides (CGP 21833, CGP 20309, CGP 26702, CGP 24589). 6-Dithiocarbamic-S-(sulfomethylsodium)esters (CGP 26701, CGP 24588) showed intermediate efficacy. A. viteae was usually slightly more resistant than the Brugia spp. Minimum curative doses (greater than 95% reduction of worms) against the two stages of the various species were either identical or preadult worms were slightly more resistant than third stage larvae. When these curative doses were compared with curative adulticidal doses or effective doses against microfilariae the various doses were very similar and never differed from each other by more than the factor 2.

Possible direct effect of diethylcarbamazine on the infective larvae of Brugia pahangi

The direct action of diethylcarbamazine (DEC) on the infective larvae of Brugia pahangi was studied. The larvae were cultured in RPMI 1640 supplemented with foetal bovine serum and antibiotics for 22 days. Most of the larvae remained alive for 8 days, but survival rate of larvae decreased rapidly from day 10 onwards. The larvae did not grow in the culture system. The addition of DEC did not affect the morbidity of the larvae and no difference was observed in the morphological characteristics between the larvae cultured in the presence or absence of DEC. The infective larvae were cultured in vitro for 5 days in the presence or absence of DEC, and inoculated into jirds. The animals were necropsied at intervals, and developing larvae and adult worms were recovered. When the larvae were cultured without DEC and then inoculated subcutaneously into jirds, 29.8% of the inoculum was recovered 3-15 days, and 25% 19-22 weeks, post-inoculation. However, when the larvae were exposed to DEC in vitro and inoculated into jirds, the rate of recovery was reduced to 25% 3-15 days post-inoculation and 2% after 19-22 weeks. When the control larvae cultured in vitro were inoculated intraperitoneally into jirds, 41.3% of inoculum was recovered 3-15 days, and 42.8% 19-22 weeks, post-inoculation. Again the corresponding value for larvae exposed to DEC in vitro was reduced to 19.8% 3-15 days, and 8% 19-22 weeks, post-inoculation. It was observed that the larvae exposed to DEC in vitro were retarded in their development in jirds.(ABSTRACT TRUNCATED AT 250 WORDS)

Brugia malayi and Brugia pahangi: transmission blocking activity of ivermectin and brugian filarial infections in Aedes aegypti

Brugia malayi- or Brugia pahangi-infected, microfilaremic jirds (Meriones unguiculatus) were treated with ivermectin at a single dose of 200 micrograms/kg body weight, administered subcutaneously. After different time intervals, Aedes aegypti mosquitoes were fed on treated or untreated jirds. Sausage stage, L2, and L3 larvae failed to develop in mosquitoes that fed on jirds from 15 to 30 days post-treatment. After 1 month, the numbers of L3 larvae recovered from mosquitoes fed on treated B. pahangi jirds were comparable to controls. However, the number of L3's recovered from mosquitoes fed on B. malayi jirds remained significantly lower than controls, 2 and 3 months after treatment. This reduction suggests that ivermectin may be more effective in blocking transmission of B. malayi than B. pahangi. Ivermectin treatment had no effect on the mean number of circulating microfilariae in treated jirds. Therefore, mosquitoes ingested comparable numbers of microfilariae when compared to those mosquitoes fed on untreated controls. Only in the case of jirds infected with B. malayi did the circulating microfilarial counts fall 30 days after treatment. The failure of microfilariae to develop to the L3 stage in mosquitoes fed on jirds within 30 days of treatment was not due to failure of mosquitoes to ingest microfilariae. Brugia malayi microfilariae also failed to develop to L3 in mosquitoes that were allowed to feed on microfilaremic jird blood treated with ivermectin (50 ng/ml) in vitro, indicating its efficacy at low concentrations. In addition to N-acetyl glucosamine, microfilariae obtained for a period of 15 days from ivermectin-treated but not control jirds showed D-mannose, N-acetyl galactosamine, and L-fucose moieties on the surface of the sheath.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative susceptibility to anthelmintics of Brugia pahangi in jirds infected by different methods

It is possible to infect jirds with Brugia pahangi by three methods. Infective larvae (L3) can be injected either intraperitoneally (ip), when adults develop in the peritoneal cavity, or sub-cutaneously (sc), when they develop in the lymphatics or the heart and blood vessels associated with the lungs. Alternatively adult worms which have been grown in the peritoneal cavities of jirds can be implanted into the peritoneal cavities of other jirds. This latter system has been widely used for screening for new filaricides. We have compared the activity of 9 macrofilaricidal compounds against these 3 types of infection. Mebendazole and albendazole were more active against implanted adults than against L3 induced adults in the peritoneal cavity. Oxibendazole, flubendazole, CGP24588A and oxfendazole were equally active against both types of worm. CGP20376, Mel Ga and Mel Ni were more active against adult worms derived from inoculated L3 than implanted worms. When comparing intra-lymphatic and ip adults (both derived from L3 infections and in the same jirds) albendazole and CGP20376 were active at the same levels against both types of infection. Mebendazole, flubendazole, oxfendazole, CGP24588A, Mel Ga and Mel Ni were more active against ip adults than intra-lymphatic adults. No drug was more active against intra-lymphatic adults than against adults.

The anthelmintic activity of a novel organic arsenical, R7/45, upon Brugia pahangi in Meriones unguiculatus

The new organic arsenical R7/45 is a rapidly acting and very potent anthelmintic against adult Brugia pahangi in jirds. Against adult worms implanted into the peritoneal cavity 5 subcutaneous (SC) injections at 2.5 mg/kg of R7/45 killed 100% of adult worms. A single dose SC of 20 mg/kg was 100% effective and 10 mg/kg 76% effective against adult worms. When jirds were autopsied at different times after treatment at 20 mg/kg SC 89% of worms were dead within three days. R7/45 was not active when given by stomach intubation. Pretreatment of jirds with R7/45 had no effect on adult worms subsequently implanted into jirds. R7/45 was highly active against third and fourth stage larvae of B. pahangi in jirds.

Antifilarial activity of intravenous suramin and oral diethylcarbamazine citrate on subperiodic Brugia malayi in the leaf-monkey, Presbytis cristata

The known filaricides, suramin and diethylcarbamazine citrate, were tested against subperiodic Brugia malayi infection in the leaf-monkey, Presbytis cristata. As expected, intravenous suramin at 10 mg/kg daily x 5 days or 17 mg/kg weekly x 5 weeks, did not show any microfilaricidal activity, but substantially reduced the recovery of live adult worms to 50.6% and 13.6% of controls respectively. Oral diethylcarbamazine citrate at 6 mg/kg daily x 6 or 10 days reduced final microfilarial counts to 30% of initial counts four weeks post-treatment and adult worm recovery was reduced to 4.5% and 0% of controls respectively. Although the antifilarial activity of these drugs against the infection in this non-human primate model appears to be similar to that seen in man, these results have to be confirmed using larger groups of animals.

Brugia pahangi adults implanted into mice: a possible screen for filaricidal activity

Brugia pahangi adults grown in the peritoneal cavities of jirds (Meriones unguiculatus) were implanted into the peritoneal cavities of six inbred mouse strains to investigate this system as a screen for detecting filaricidal activity. The mice were given 15 adult B. pahangi and autopsied 35 days later. The recoveries of adult worms were 25%, 35%, 49%, 33%, 26% and 27% of the number implanted respectively for the MF1, TO, NIH, CBA, BALB/c and C3H/HE strains. There was great variation in the number of worms recovered from each strain of mouse. It is concluded that the variation in recoveries was so high that this system is not useful in detecting low level filaricidal activity.

Antifilarial activity of CGP 20376 against subperiodic Brugia malayi in the leaf-monkey Presbytis cristata

CGP 20376, a 5-methoxyl-6-dithiocarbamic-S- (2-carboxy-ethyl) ester derivative of benzothiazole was evaluated for its antifilarial properties and shown to be extremely effective against subperiodic Brugia malayi in the leaf-monkey, Presbytis cristata at oral doses of 20-100 mg/kg. The compound and/or its metabolites had complete micro- and microfilaricidal activities even when given at a single dose of 20 mg/kg. Lower doses had incomplete filaricidal action.

The effect of two novel analogues of antimycin A on oxygen consumption and survival of filarial nematodes in vitro

The effects of two novel analogues of antimycin A (BWA466C and BWA728C) on filarial oxygen consumption, energy generation and survival were investigated in vitro. For comparison, incubations were performed with a range of mitochondrial respiration inhibitors. All compounds tested (rotenone, antimycin A, KCN, oligomycin, CCCP, rafoxanide, BWA466C and BWA728C) inhibited oxygen uptake. The two analogues were less potent than antimycin A at impairing respiration of either filariae or beef heart submitochondrial particles. However, the two compounds affected motility and were lethal in vitro. Although the analogues affected oxygen uptake similarly to antimycin A itself, the levels of ATP were significantly lower than those noted in the presence of antimycin A. Glucose consumption and lactate output were markedly reduced by BWA466C and BWA728C. Glucose transport (measured as 2-deoxy-[2,6-3H]glucose) was reduced after treatment with BWA728C. It is likely that a combination of the effects on glucose transport and inhibition of oxidative pathways of carbohydrate metabolism may lead to worm death in vitro.

Fine-structure alterations in female Brugia malayi and Litomosoides carinii after in vivo treatment with flubendazole

Female filariae of the species Brugia malayi and Litomosoides carinii were investigated by means of electron microscopy after in vivo treatment with flubendazole. The earliest fine-structure alteration in both species was the disappearance of microtubuli from the intestinal cells as soon as 6 h after treatment. There was no further disintegration of intestinal cells for several days. Microtubuli disappeared from the outer zone of the hypodermal cytoplasm 24 h after treatment. At this time, marked alterations were also observed in the oogonia and in the embryonic cells. Many of these were swollen; their nuclear envelope was partly resolved and the chromatin was condensed, but no spindle apparatus was formed. The early fine-structure alterations observed after in vivo treatment with flubendazole consisted of the disappearance of microtubuli from various tissues. This led to the interruption of cell division in oogonia and embryonic cells and, and subsequently, to the disintegration of most other filarial tissues. These morphological alterations differed considerably from those observed after treatment with benzothiazole derivatives, which do not affect the microtubuli of the filariae.

Effect of ivermectin on filariae of Mastomys natalensis

The efficacy of ivermectin (Iv) was evaluated against four species of filariae, Litomosoides carinii, Acanthocheilonema viteae, Brugia pahangi and Brugia malayi in Mastomys natalensis. Animals with patent infections, induced with L3 larvae, by intravenous (iv) infusion of the respective microfilariae (Mf) (5 x 10(4) Mf per animal) or by intraperitoneal (ip) route (2 x 10(4) Mf per animal) were used in this study. A single dose of Iv (100 micrograms.kg-1) given subcutaneously (sc) to Mastomys infected with L. carinii or A. viteae resulted in the disappearance of microfilaremia within 2 h of treatment. Iv treatment of sc-infected animals with Brugia spp. had no immediate effect on the circulating Mf 60 days post-treatment. In contrast, such treatment of animals infected with Mf by intravenous infusion completely eliminated the larvae of all four species from the circulation. Iv treatment had no significant effect on the Mf of L. carinii, B. pahangi and B. malayi in animals infected by the ip route. However, the drug had dramatic effect in killing the Mf of A. viteae in the peritoneal cavity. Sera from Iv-treated normal or from L. carinii- or A. viteae-infected Mastomys were effective in clearing the circulating Mf of the species when administered to animals with the respective infections. Similar rapid clearance of Mf was seen when the sera were administered to animals infected iv with these larvae. Furthermore, adult females of L. carinii and A. viteae recovered from Mastomys on different days after Iv treatment released smaller numbers of Mf in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo effect of benzothiazole and amoscanate derivatives on the fine structure of adult Brugia spp. and Litomosoides carinii

Alterations in the fine structures of female Brugia spp. and Litomosoides carinii were investigated after in vivo treatment with curative doses of 4 compounds: CGP 20376 [2-tert-butyl-benzothiazole-5-methoxy-6-dithiocarbamic-S-(2- carboxyethyl)-ester], CGP 21833 (2-tert-butyl-benzothiazole-5-methyl-6- N-methylamino-piperazinylthiocarbonylamide), CGP 6140 [4-Nitro-4'-(N-methyl-piperazinylthiocarbonylamido)-diphenylamine] and amoscanate (4-isothiocyanato-4'-nitrodiphenylamine). All compounds caused early alterations in the somatic muscle cells. These alterations usually appeared within 24 h after treatment; they occurred later only after treatment of L. carinii with amoscanate. In Brugia spp., swelling of the muscle cells occurred in which the glycogen deposits considerably increased in size. The electron density of the cytoplasm surrounding the myofilaments in the fibrillar portion of the muscle cells increased, and light zones appeared between the fibrils. The muscle cell mitochondria swelled, particularly their inner matrix, which became more electron-lucent, with some dense spots. In L. carinii the muscle cells were not increased in size, but their mitochondria were considerably swollen before disintegration; this was followed by disintegration of the myofilaments and vacuolization of the cytoplasm. Vacuolization before mitochondrial swelling was observed only after treatment with CGP 6140. Other tissues of this species were not altered before the 2nd day after treatment. In Brugia spp., electron-lucent appeared in the hypodermis either simultaneously with the alterations in the muscle cells or a few hours later. At 24 h after treatment with amoscanate, blebs were formed on the luminal side of the intestinal membrane.

Effects of intermediary metabolites and electron transport inhibitors on action of chloroquine on Brugia pahangi and Onchocerca volvulus

We examined the possibility that chloroquine is interfering with aerobic energy-generating processes in the adult filarial parasites, Brugia pahangi and Onchocerca volvulus. Using motility of these parasites as an assay of drug effect, we found that micromolar concentrations of chloroquine caused significant paralysis, but only in alkaline medium (pH 8.4). The addition of 12 mM glutamine or 10 mM albizziin to the medium completely antagonized drug-induced paralysis. In addition, in B. pahangi, all of the tricarboxylic acid cycle intermediates (10 mM) except citrate and pyruvate antagonized the effect of chloroquine on motility; in O. volvulus, oxaloacetate as well as glutamine inhibited the effect of the drug. The effect of chloroquine on both parasites was enhanced when it was used in combination with 10 microM acivicin, a glutamine antimetabolite. Here motility of B. pahangi was reduced significantly within 24-48 hr at acidic (6.8) neutral (7.4) and alkaline (8.4) pH. This effect was partially reversible by glutamine (12 mM). Motility of O. volvulus was reduced to near zero within 4 hr with this drug combination. Antimycin A and rotenone, both electron transport inhibitors, also synergized with chloroquine at any pH to produce paralysis in B. pahangi. The effects of the rotenone and chloroquine combination were reversed in the presence of 10 mM succinate. However, glutamine (12 mM) was unable to antagonize the effects of chloroquine plus antimycin A on the motility of B. pahangi. These findings suggest that chloroquine may be inhibiting aerobic energy metabolism in the filariae, possibly at the level of electron transport. Furthermore, since chloroquine is well-tolerated but only weakly filaricidal in vivo, the data indicate that use of this drug in combination with other inhibitors of aerobic energy metabolism may be a chemotherapeutically useful approach to the treatment of filariases.

Effects of potential inhibitors on Brugia pahangi in vitro: macrofilaricidal action and inhibition of microfilarial production

A series of compounds that apparently disrupt hormonally regulated processes in insects have been examined for effects on the viability and microfilarial production of adult Brugia pahangi cultured in vitro. The azasteroids, 25-azacoprostane and 25-azacholestane, inhibited the production of microfilariae at 5 ppm, the former also exhibiting macrofilaricidal activity at this concentration. The brassinosteroids examined inhibited microfilarial production at 5 ppm but did not affect worm viability. Azadirachtin also proved to be a significant inhibitor of microfilarial release without effect on worm motility or viability. Of all the compounds tested, the non-steroidal amines appeared to be the most promising as potential filaricides, several of them proving to be macrofilaricidal at 1 ppm and affecting microfilarial production at even lower concentrations.

Antifilarial activities of synthetic and natural retinoids in vitro

Fourteen synthetic retinoids with known and different binding affinities to retinol binding proteins of Dirofilaria immitis, retinol, and retinoic acid were tested in vitro against female Litomosoides carinii (drug levels 20, 10, 1 nM/ml) and against microfilariae of L. carinii, Brugia malayi, B. pahangi and Acanthocheilonema viteae (drug levels 100, 20, 10, 1 nM/ml). All compounds including retinol and retinoic acid had at least some effects on the filarial parasites. Except for 3 synthetic retinoids, continuous exposure of adult L. carinii to the drugs reduced the motility of the worms completely or remarkably by day 7 of incubation in a dose and time dependent fashion. Also, the release of microfilariae was completely or remarkably suppressed in a dose and time dependent manner by 20 and 10 nM/ml of all except 4 of the retinoids. Short term exposure to the drugs (up to 20 nM/ml) for 4 h followed by subsequent incubation in drug-free medium was ineffective except for one synthetic retinoid (13-cis-N-(2-hydroxyethyl)retinamide:13-cis-Her). Effects on microfilariae were also dose and time dependent. All compounds affected markedly the motility of L. carinii microfilariae within 20 h at dose levels of 1 nM/ml and above. Microfilariae of B. malayi, B. pahangi and especially of A. viteae were generally less sensitive. Eight of the synthetic retinoids, but not retinol and retinoic acid, were effective (10 nM/ml). There were generally no correlations between the various effects of individual compounds; i.e., activities varied within one species depending on the parameters used and depending on the parasite species.(ABSTRACT TRUNCATED AT 250 WORDS)

The further application of MTT-formazan colorimetry to studies on filarial worm viability

Experiments have confirmed that MTT-formazan colorimetry in its simplest form (incubation of intact worms with MTT and direct visualisation of any formazan formed) can be readily applied to several species of filariae including Onchocerca volvulus. Data is presented which will assist the development of quantitative MTT reduction viability tests for a selection of the smaller filarial species. Assays of pieces of Onchocerca gutturosa and O. volvulus females have led us to tentatively conclude that the tips of filariae, particularly the anterior ends, may well be metabolically the most active part of the worm. Selective sampling of these regions for Onchocerca might therefore be a useful indicator for the viability of the parasite. An example of how MTT-formazan colorimetry has been applied to yield additional data to support motility observations on the in vitro survival of male O. gutturosa is also given. The in vitro timecourse of worm death caused by 10 microM CGP 20376 on Acanthocheilonema viteae females has been examined by MTT reduction and compared with 6 other non-subjective parameters. The results suggests that the parameters examined could be divided into two groups according to the time taken for CGP 20376 to cause 50% inhibition (t50) of the parameter. Fast response parameters had t50's between 1 and 6 h (motility indices, 14CO2 evolution, adenine uptake and leucine uptake), they are more sensitive measures of viability and indicate possible worm damage which may or may not be reversible. Slow response parameters had t50's between 34 and 48.5 h (lactate output, MTT reduction and adenine leakage), and are probably linked with severe degenerative changes and are indicative of worm death.(ABSTRACT TRUNCATED AT 250 WORDS)

The efficacy of 22,23-dihydroavermectin B1 (Ivermectin) acting singly or in combination with a benzodiazepine on microfilariae of Onchocerca species and Brugia pahangi (an in vitro study)

An in vitro study of the antinematodal action of two groups of compounds which act on the receptor complex of the inhibitory neurotransmitter, Gamma-aminobutyric acid (GABA) in mammalian systems is described. The compounds, Ivermectin and two benzodiazepines, Diazepam and a water soluble Midazolam were tested singly or in combination against two microfilarial parasites Onchocerca lienalis (closely related to Onchocerca volvulus) and Brugia pahangi. The combination of ivermectin and diazepam at a concentration of 0.1 microgram/ml and 33 micrograms/ml respectively achieved the same effect on microfilarial motility as when ivermectin was given at 1 microgram/ml alone or diazepam at 66 micrograms/ml alone. Similarly when the combination of ivermectin at 0.1 microgram/ml and midazolam at 10 micrograms/ml was used it achieved the same effect as ivermectin at 1 microgram/ml alone or midazolam at 33 micrograms/ml alone. This showed that both benzodiazepines had a synergistic effect on the activity of ivermectin. The microfilariae of B. pahangi were insensitive to both groups of compounds at all concentrations used.

Anti-filarial effects of nine quinoline-containing drugs on adult filariae in vitro

The potencies and efficacies of 9 quinoline-containing anti-malarials including chloroquine, (bis)desethylchloroquine, SN6911, SN12108, amodiaquine, CN-2999-2K, primaquine, quinacrine, and quinine were examined in vitro against adult female Brugia pahangi. Parasite motility and lactate excretion were measured as indicators of drug effects. All of the agents tested showed time-dependent increases in potency over a 24-72-hr incubation period. SN12108 was the most potent at 72 hr, reducing motility by greater than or equal to 50% (IC50) at 1.0 x 10(-7) M. Chloroquine (IC50 2.3 x 10(-6) M), desethylchloroquine (IC50 7.0 x 10(-6) M), quinacrine (IC50 1.9 x 10(-6) M), and quinine (IC50 1.5 x 10(-5) M) were the least potent. All of the drugs caused time-dependent decreases in lactate excretion, except quinine; decreases were found to be dose dependent. A high correlation (r greater than 0.85) was seen between time-dependent effects on motility and lactate excretion. The effects of chloroquine (10 microM) on motility were also examined in female Acanthocheilonema viteae, Dirofilaria immitis, Onchocerca volvulus, and male Onchocerca gutturosa. Dirofilaria immitis was less sensitive to chloroquine than B. pahangi; A. viteae was equally sensitive. Species of Onchocerca were the most sensitive parasites studied. Adult O. gutturosa and O. volvulus were affected by 10 microM chloroquine within 4-6 hr; motility was reduced by 80% within 24 hr. Although the mechanism of anti-filarial activity of the quinoline-containing drugs is not known, their in vitro activity against a variety of adult filariae at clinically relevant concentrations, as well as differential sensitivity seen between the different filariae examined, warrants further study of these compounds.

Respiration in the filarial nematode Brugia pahangi

Glucose-supported O2 uptake in the filarial nematode Brugia pahangi was partially inhibited by antimycin A (30-40%), with the remaining activity being sensitive to o-hydroxydiphenyl or salicylhydroxamic acid (SHAM). The production of CO2 by B. pahangi in the presence of D-glucose was stimulated by O2; the stimulation of CO2; the stimulation of CO2 production was sensitive to antimycin A. The O2 dependencies of respiration showed that the apparent O2 affinity for B. pahangi was diminished in the presence of antimycin A; O2 thresholds for inhibition of respiration were observed which showed that the alternative electron transport pathway was less sensitive to inhibition at elevated O2 concentrations. H2O2 production and its excretion could be detected in whole B. pahangi; higher rates were observed in the presence of the uncoupler carbonyl cyanide m-chlorophenylhydrazone. The effects of inhibitors on H2O2 production suggest two sites of H2O2 production, one associated with the classical antimycin A-sensitive pathway, the other with the alternative respiratory pathway. The similarity in the O2 dependencies of H2O2 production and respiration may indicate that H2O2 production is involved in O2-mediated toxicity. Succinate and malate respiring sub-mitochondrial particles of B. pahangi produced O2.- radicals at a site on the antimycin A-sensitive respiratory pathway. Inhibition of the alternative electron pathway by SHAM was unusual; sub-millimolar concentrations markedly stimulated respiration, H2O2 production and O2.- production by 30, 20 and 25%, respectively, whereas higher concentrations (greater than 2.5 mM) inhibited respiration by 75% and H2O2 and O2.- production by up to 85%.

pH-dependent uptake and macrofilaricidal effects of chloroquine on adult filarial parasites in vitro

Uptake and macrofilaricidal effects of chloroquine (CQ) and other aminoquinolines were found to be highly pH dependent in Brugia pahangi, Acanthocheilonema viteae, Onchocerca volvulus, and Dirofilaria immitis. Using [3H]CQ, it was found that all of the parasites took up more drug under alkaline conditions (RPMI 1640 at pH 8.4) than in neutral (pH 7.4) or acidic (pH 6.8) media. Differences were seen in the amount of drug taken up among the filariae studied. B. pahangi and A. viteae took up 7 times more chloroquine per milligram of tissue than did O. volvulus, and 30 times more than D. immitis during a 60-min incubation period at pH 8.4. Sensitivity to the aminoquinolines also increased with increasing media pH, and was measured using parasite motility as an indicator of drug efficacy. Potency of chloroquine against B. pahangi increased 100-fold at pH 8.4 compared to pH 7.4. A. viteae and O. volvulus showed similar sensitivity to chloroquine compared to B. pahangi; D. immitis was less sensitive. While uptake of chloroquine was linear from pH 6.8 to 8.4, B. pahangi was unaffected by 32 microM of the drug below pH 7.6; at any pH above this, motility of this parasite was completely inhibited. Calculations of the internal pH of this parasite indicated that it shifted upwards significantly with changes in media pH. It was concluded that these shifts in internal pH may render parasites more sensitive to the effects of chloroquine.

Antifilarial activities of benzazole derivatives. 2. Microfilaricidal effects against Litomosoides carinii, Acanthocheilonema. vitae, Brugia malayi and B. pahangi in Mastomys natalensis

The spectrum of antimicrofilarial activities of eighteen 2-tertbutylbenzazole derivatives was evaluated comparatively in Mastomys natalensis infected with Litomosoides carinii, Acanthocheilonema viteae, Brugia malayi or B. pahangi. The minimal effective dose (DEM) against microfilariae (greater than 95% reduction of microfilariae counts in the peripheral blood) was determined on day 3 (DEM-3), on day 7, 14, 21, 28 and 42 (DEM-7, DEM-14, DEM-21, DEM-28 and DEM-42) after the first treatment. All compounds were effective against the microfilariae of all 4 species. The benzoxazole derivatives were invariably less potent than the corresponding benzothiazole analogues. Upon repeated oral treatment (once daily [o.d.] for five days) the DEM-7 of the benzoxazoles varied depending on the species and on the chemical structure between 25 mg/kg o.d. x 5 and greater than 100mg/kg o.d. x 5 days. Within the benzothiazole series the DEM-7 varied between 6.25 mg/kg o.d. x 5 and 100 mg/kg x 5. In all but 5 of the 40 parasite-compound combinations of the benzothiazoles the 5-methoxy-derivates were more effective than the 5-methyl analogues. Similar differences were found with the eight benz-oxazoles tested. The lowest DEM-7 was observed with compound CGP 20308 which is 2-tert-butyl-5-methoxy-6-isothio-cyanatobenzothiazole and with compound CGP 20376 which is 3-(2-tert-butyl-5-methoxy-benzothiazol-6-yl] amino-thiocabo-nylthio) propionic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of diethylcarbamazine on the in vitro serum-mediated adherence of feline granulocytes to microfilariae of Brugia pahangi

The effect of the antifilarial drug diethylcarbamazine (DEC) on immunologically mediated destruction of the microfilariae (mf) of Brugia pahangi in vitro is addressed by studying the drug's influence on the granulocyte adherence to the surface of mf and the subsequent death of these parasites. DEC enhanced the adherence of cat blood-derived granulocytes to the surface of mf through the meditation of cuticle direct antibodies but not that mediated by complement alone; the parasites became immobilized and degenerated subsequent to cell adherence. The rate of cell adherence in the antibody-containing cultures was enhanced by DEC. As previously reported, this drug had no direct effect on the viability of the parasites. Preincubation of the cells in DEC had a greater effect on cell adherence than did preincubating the parasites in the drug, thus supporting the contention that this antifilarial compound may act on host components. Further investigation of this possibility may contribute significantly to a more complete understanding of why DEC can cause severe side reactions in filariae infected patients.

In vitro motility of isolated adults and segments of Onchocerca volvulus, Brugia pahangi and Acanthocheilonema viteae

Observations were made on the spontaneous motility in vitro of entire adult worms and segments of Onchocerca volvulus, Brugia pahangi and Acanthocheilonema viteae. Segment motility was recorded in a mechano-transducer apparatus and responses of worm tissues to anthelmintics and other pharmacological agents were compared. Entire adult female O. volvulus showed varied patterns of motor activity, ranging from continuous low level whole body motion to periodic spasmodic contractions interspersed between intervals of quiescence lasting from a few to 30 seconds. The same range characterized movements of 1.5-4 cm segments cut from worms liberated from collagenase digested nodules. However, fresh segments dissected directly from surgical specimens were completely inactive due to the paralyzing effect of xylocaine, used as local anesthetic. This effect wore off in 2-5 hours in vitro, and recovered segments behaved in the same way as those from enzymatically liberated worms. Segments of B. pahangi and A. viteae also showed motor activity patterns which reflected those of whole adults. Segments of O. volvulus behaved reproducibly, whether examined in the field in endemic areas, or after transport of nodules or freed worms to Michigan from Guatemala or Sudan. Segments of all worms were unresponsive to most anthelmintics, but O. volvulus was susceptible to paralysis by CGP 6140, levamisole, pyrantel and carbachol at concentrations of ten to a thousand times lower than those required to produce any influence on B. pahangi. Segments of A. viteae more closely resembled O. volvulus in their dose responses to these drugs, although CGP 6140 was without effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative effects of anthelmintics on motility in vitro of Onchocerca gutturosa, Brugia pahangi and Acanthocheilonema viteae

The effects of standard anthelmintics on the motor activity in vitro of adult Onchocerca gutturosa, Brugia pahangi and Acanthocheilonema viteae were determined using a micromotility meter. Fresh adult males dissected from bovine tissues were the best source for observations on O. gutturosa. Parasites liber-ated by collagenase digestion showed poor viability and motility. Only segments of O. gutturosa females were obtainable by dissection and these were not able to sustain motility in vitro. Adult males and females of O. volvulus were active after collagenase digestion of human nodular tissue, but behaved so irregularly that satisfactory monitoring of their movements with the meter was not possible on a regular enough basis to permit quantitation of drug-induced changes. Inhibitory effects on motility of O. gutturosa, B. pahangi and A. viteae were produced by anthelmintics which showed macrofilaricidal effects in vivo in a laboratory rodent model, with the exception of the benzimidazoles. O. gutturosa was, however, much more sensitive than B. pahangi or A. viteae to the temporary paralyzing effects of levamisole and pyrantel. The utility of in vitro screening against O. gutturosa and B. pahangi was evaluated by determining the discriminatory capacity of the tests in detecting novel compounds with reproducible in vivo activity in the jird-B. pahangi/A. viteae model. The results suggested that this would be a valuable selective screening procedure. Although false positives were detected at the rate of 15-17% of the novel anthelmintic chemical series tested, no false negatives were allowed through the screen provided both O. gutturosa and B. pahangi were included.2=

Leakage of incorporated radiolabelled adenine--a marker for drug-induced damage of macrofilariae in vitro

An objective in vitro assay has been developed for quantifying drug-induced damage in Dipetalonema viteae macrofilariae. The method involves radiolabelling the worms ATP pool by incubating macrofilariae with [U-14C]-adenine. As determined by HPLC 72% of the incorporated label was in ATP, 15% in ADP and about 4% in each of NAD and AMP. Macrofilariae labelled with [U-14C]-adenine show a linear efflux of [14C]-label amounting to 21.3% of the total incorporation (mainly as uncharged catabolites) over a time course of 120 h in vitro incubation. When prelabelled worms were exposed to compounds exerting macrofilaricidal effects in vitro a marked stimulation in the leakage of [14C]-label from the worms was noted. The [14C]-label leakage appears to be linked with membrane (or cuticle) damage and the reduction of macrofilarial ATP levels. Determination of the amount of [14C]-label remaining in drug-treated worms relative to appropriate control provides a simple, sensitive and quantitative measure of drug-induced damage in macrofilariae (including Onchocerca). The method has been used to describe the macrofilaricidal activity of a wide range of antifilarial standards, membrane disruptive agents, respiratory inhibitors, fasciolicides and anti-cestode compounds.

The potential of mice as animal models for antifilarial screening

Transplanted infections of Brugia pahangi and Dipetalonema viteae in male BALB/c and CDI mice were investigated as models for evaluating potential antifilarial compounds. The physiology and genetics of the above mouse strains are better defined than any of the rodent species currently used for primary in vivo screening, facilitating a more reproducible means for predicting the filaricidal activity of compounds. The recoveries of B. pahangi macrofilariae, implanted intraperitoneally were greater than or equal to 50% up to six weeks after implant in both CDI and BALB/c mice. The recoveries of D. viteae macrofilariae, implanted subcutaneously, were greater than 50% up to four weeks post implant but had fallen to less than 30% by six weeks. The survival of B. pahangi and D. viteae macrofilariae simultaneously implanted into mice mimicked that seen with the mono-infections, but significantly better recoveries were obtained from dual implanted CDI mice compared to the BALB/c mice when the numbers of macrofilariae implanted were varied. Standard antifilarials were evaluated against D. viteae and B. pahangi dual implanted into either CDI mice or gerbils. The mouse dual implant detected significant worm reductions against D. viteae, B. pahangi or both with all antifilarials tested except CGP 6140. Similarly under the test conditions CGP 6140 was not detected in the gerbil assay, but there were marked differences in the results obtained with the mice and gerbil models. The reasons for these differences are discussed.

Antifilarial activities of benzazole derivatives. 1. Macrofilaricidal effects against Litomosoides carinii, Dipetalonema viteae, Brugia malayi, and B. pahangi in Mastomys natalensis

Eighteen 2-tert-butyl-benzazole derivatives were evaluated comparatively as macrofilaricidal agents against L. carinii (L.c.), D. viteae (D.v.), B. malayi (B.m.) and B. pahangi (B.p.). Upon repeated treatment (once daily) for five consecutive days the eight benzoxazole derivatives were invariably less potent than the corresponding benzothiazole derivatives. The minimal curative dose (DCM) of the benzoxazoles varied depending on the species and on the chemical structure between 25 and 100 mg/kg p.o. once daily for five days. In the benzothiazole series the lowest DCMs were observed with compound CGP 20376 which is the 5-methoxy-6-dithiocarbamic-S-(2-carboxy-ethyl)ester derivative. This compound eliminated all macrofilariae of L.c., B.m. and Bp. at 6.25 mg/kg p.o. once a day for five days, whereas 12.5 mg/kg x 5 days were needed against D.v. For all other benzothiazole derivatives the DCMs varied between 6.25 mg/kg p.o. x 5 to 100 mg/kg x 5. Six of the most potent benzothiazoles were tested by single oral treatment. In general doses had to be increased 2-4 times to reach minimum curative effects. CGP 20376 was fully effective against B.m. and B.p. at 12.5 mg/kg p.o., against L.c. at 25 mg/kg p.o. and against D.v. at 50 mg/kg p.o.. This compound has been selected from this series of novel benzazoles as a first candidate for trials against human bancroftian filariasis.

DEC-inhibited development of third-stage Brugia pahangi in vitro

The effect of diethylcarbamazine (DEC) on infective larvae and immature worms of Brugia pahangi was studied in vitro. The in vitro culture of larvae was done using the technique of Mak et al. (1983). In control cultures, most larvae remained alive for 14 days; over 50% survived until day 22 of cultivation. The addition of DEC did not affect the life span of the larvae. Among those which survived for 22 days in control cultures, 77.8% reached the fourth stage, their length being 2908.2 +/- 453.2 microns. When DEC was added to a final concentration of 0.1 mg/ml, the percentage of larvae attaining the fourth stage was reduced (42.9%) and their growth retarded; the length of the fourth-stage larvae was 2548.4 +/- 414.0 microns. The addition of 1.0 mg/ml DEC completely arrested the growth and development of the larvae.