The response of intact Strongyloides ratti infective (L3) larvae to substrates and inhibitors of respiratory electron transport

Murine strongyloidiasis: the effects of cyclosporin A and thiabendazole administered singly and in combination

A single Cyclosporin A (CsA) dose of 30 mg kg-1 given orally at day 4 post-infection (p.i.) to Sprague-Dawley rats infected with Strongyloides ratti, reduced the faecal larval count by 46.8 +/- 1.2%. CsA was equally effective when the same dose rate was administered subcutaneously at day 4 p.i., reducing the faecal larval count by 41.6 +/- 8.6%. Thiabendazole (TBZ) given orally at 5 or 10 mg kg-1 (single dose at day 4 p.i.) reduced the faecal larval counts by 57.1 +/- 4.1% and 69.0 +/- 9.6%, respectively. Orally administered CsA was less effective than 5 mg TBZ kg-1 (at day 4 p.i.) Co-administration of 5 mg TBZ kg-1 and CsA did not elicit synergy or additive efficacy, indicating that CsA did not antagonise the anti-strongyloides activity of TBZ. The data suggests that for patients with current, historical or serological evidence of strongyloidiasis, CsA may be used where immunosuppressive therapy is required for other concurrent reasons or when TBZ is contraindicated.

Enumeration of viable Candida albicans blastospores using tetrabromofluorescein (eosin Y) and flow cytometry

A rapid assay was developed for determination of the viability of blastospores of Candida albicans utilizing flow cytometry to detect the accumulation of tetrabromofluorescein in non-viable yeast cells. Eosin Y was shown to stain non-viable C. albicans blastospores selectively without affecting the cellular viability of competent yeast cells or resulting in non-specific staining of viable cells. Results of these studies show that this flow cytometric method of determining cell viability of C. albicans is more accurate and more precise than the more common method of enumerating colony forming units.

Steady-state content of glycolytic/tricarboxylic acid-cycle intermediates, adenine nucleotide pools and the cellular redox-status in the infective (L3) larvae of (homogonic) Strongyloides ratti

Infective (L3) larvae of Strongyloides ratti (homogonic strain) were freeze-clamped (-196 degrees C) and the steady-state content of the glycolytic, Krebs tricarboxylic acid (KTA)-cycle intermediates and adenine nucleotides analysed. Comparison of the mass-action ratios (MARs) of the glycolytic enzymes with their apparent equilibrium constants (K9eq) indicate that phosphoglucomutase, glucosephosphate isomerase, triosephosphate isomerase, phosphoglyceromutase and phosphopyruvate hydratase reactions were all at or near equilibrium, whilst hexokinase, phosphofructokinase and pyruvate kinase were displaced from equilibrium. The S. ratti aldolase and myokinase appear to be somewhat displaced from equilibrium and thus may have pseudoregulatory roles. The adenylate energy charge (AEC), ATP/ADP ratio and the available adenylate energy (AAE) indices were 0.9 +/- 0.04, 8.76 +/- 1.5 and 397 +/- 43, respectively. The free [NAD+]/[NADH+H+] ratio of the cytoplasmic compartment of S. ratti L3 larvae calculated employing the steady-state content of the oxidised and reduced substrates of lactate dehydrogenase (E.C. 1.1.1.27) and the combined glyceraldehyde 3-phosphate dehydrogenase (E.C. 1.2.1.12)/3-phosphoglycerate kinase (E.C. 2.7.2.3) system were ca. 523 and 1200, respectively. The free[NAD+]/[NADH+H+] ratio in the mitochondrial compartment of S. ratti L3 larvae calculated using the malate dehydrogenase (E.C. 1.1.1.37) equilibrium was found to be 1962:1. The data is discussed with respect to the predominantly aerobic nature of the energy metabolism of the L3 larvae.

The effect of electron transport (ET) inhibitors and thiabendazole on the fumarate reductase (FR) and succinate dehydrogenase (SDH) of Strongyloides ratti infective (L3) larvae

The fumarate reductase (FR) and succinate dehydrogenase (SDH) activities of isolated submitochondrial particles (SMPs) prepared from axenised L3 larvae of S. ratti were characterised with respect to their response to a selected range of inhibitors. Rotenone (a specific inhibitor of electron transport Complex I) inhibited the S. ratti FR (EC50 = 3.0 x 10(-7) M) but not SDH. This strongly suggests that the S. ratti FR is functionally linked with the S. ratti ET-Complex I. 2-Thenoyltrifluoroacetone (TTFA, an inhibitor of ET-Complex II) inhibited FR (EC50 = 2.6 x 10(-5) M) and SDH (EC50 = 2.8 x 10(-5) M) with similar effectiveness. Sodium malonate (substrate analogue of succinate) had a greater affinity for SDH (EC50 = 6.8 x 10(-4) M), than FR (EC50 = 1.9 x 10(-2) M). Sodium fumarate was ca. 8-fold more effective in inhibiting the S. ratti FR (EC50 = 6.0 x 10(-4) M) than SDH (EC50 = 4.8 x 10(-3) M). The S. ratti FR was more sensitive to inhibition by thiabendazole (TBZ; EC50 = 4.6 x 10(-4) M) than SDH (EC50 > 1.0 x 10(-3) M), suggesting that one of the sites-of-action of TBZ to be the FR of S. ratti mitochondria. More potent inhibitors of S. ratti FR, if developed, may prove to be effective chemotherapeutic agents in the management of human strongloidiasis.

Strongyloides ratti: mitochondrial enzyme activities of the classical electron transport pathway in the infective (L3) larvae

Submitochondrial particles prepared from S. ratti L3 larvae exhibited NADH-oxidase (NOX), NADH-ferricyanide reductase (NFR), NADH-cytochrome-c-reductase (NCR), succinate-cytochrome-c-reductase (SCR), and cytochrome-aa3-oxidase activities of 2.1 +/- 0.3, 8.9 +/- 1.3, 0.6 +/- 0.1., 1.0 +/- 0.2 and 1.2 +/- 0.3 nm min-1 mg protein-1 respectively, at 37 degrees C. The NCR and NOX activities were 39.3% and 23.5% of the NFR activity, suggesting the occurrence of a rate-limiting step or bifurcation of the respiratory electron transport (RET) pathway on the oxygen-side of RET-Complex I. The NCR activity was 50% that of cytochrome-aa3-oxidase activity which suggests partitioning of electron flow at the level of RET-Complex III and/or the quinone-function. Antimycin A and rotenone but not 2-thenoyl trifluoroacetone (TTFA) inhibited NCR activity, the EC50 values were 3.6 x 10(-6) M, 3.7 x 10(-7) M, respectively. SCR activity was inhibited by antimycin A (EC50 = 3.8 x 10(-6) M) and TTFA (EC50 = 2.8 x 10(-5) M) but not by rotenone. The results suggest that presence of classical and alternate RET-pathways in S. ratti L3 larvae.

Strongyloides ratti: fumarate reductase and succinate dehydrogenase activities of infective larvae

Submitochondrial particles prepared from axenised infective (L3) larvae of S. ratti (homogonic-strain) were assayed spectrophotometrically for fumarate reductase (FR) and succinate dehydrogenase (SDH) and their kinetic properties characterised. The S. ratti FR (pH 8.2; 37 degrees C) exhibited a maximum specific activity of 3.45 nmol (min)-1 (mg protein)-1 at a sodium fumarate concentration of 0.3 mM. Interestingly, the FR activity declined at fumarate concentrations greater than 0.3 mM. The mechanism of this unusual inhibitory effect requires further study. The S. ratti SDH (pH 8.2; 37 degrees C) showed a Vmax of 17.4 nmol (min)-1 (mg protein)-1; the Kmsucc was 0.5 mM. Although the SDH:FR ratio cannot predicate vectorial electron flow as would occur in vivo, an in vitro ratio of 5.04:1 was observed for SMPs derived from S. ratti L3 larvae.

An alternative protocol for the serial passage and maintenance of a homogonic strain of Strongyloides ratti in female Sprague-Dawley rats

A method which does not involve the tedious use of watch glass coprocultures for obtaining filariform infective (L3) larvae of Strongyloides ratti from faecal pellets of infected Sprague-Dawley rats is described. The alternative method utilises Baermannization (18 h) of faecal pellets to yield rhabditiform (L1) larvae of S. ratti and their subsequent culture for 72 h at 19 degrees C in tissue-culture-flasks containing only dechlorinated tap water to yield infective filariform (L3) larvae. The yields and infectivity of the L3 larvae obtained from the two methods were essentially similar.

The efficacy of two electron transport inhibitors (720C80 and 993C76) on murine strongyloidiasis: a comparison with albendazole

The clinical efficacy of albendazole (ABZ) in the treatment of chronic uncomplicated strongyloidiasis has been reported to be highly variable. In our murine model of strongyloidiasis a single oral dose of 5 and 10 mg kg-1 ABZ reduced (at day 4 post infection) the faecal larval count (FLC) by 54.2 +/- 12.5% and 81.5 +/- 10.2%, respectively. 100 mg kg-1 ABZ reduced the FLC by 100%. Two inhibitors of protozoan and filarial electron transport (720C80 and 993C76) inhibited the endogenous O2 consumption of intact infective (L3) larvae of S. ratti by > 50% at 2 x 10(-5) M in vitro, and reduced the FLC by 72 +/- 9.3% and 62.0 +/- 10.3% respectively in vivo, at a dose of 70 mg kg-1. These results suggest that compounds designed as selective inhibitors of protozoan electron transport have significant efficacy against murine strongyloidiasis and may prove useful in the management of human strongyloidiasis.