Morpho-Physiological and Biochemical Criteria of Acanthamoeba spp. Isolated from the Egyptian Aquatic Environment

BACKGROUND

The free-living amoebae Acanthamoeba spp., have been recognized as etiologic agents of amoebic encephalitis, keratitis, otitis, lung lesions and other skin infections mainly in immuno-compromised individuals. In this study, morpho-physiological and biochemical characterization of Acanthamoeba strains isolated from the Egyptian aquatic environment were surveyed.

METHODS

Some Acanthamoeba species were cultivated on non-nutrient agar. Isolated strains of Acanthamoeba were identification based on the morphology of trophic and cyst forms in addition to temperature and osmo-tolerance assays. Biochemical characterization of the isolated amoeba strains was performed using quantitative assay as well as qualitative determination of proteolytic activity in zymograph analysis.

RESULTS

Potentially pathogenic Acanthamoeba species were isolated from all of the examined water sources. Colorimetric assays showed protease activity in the heat-tolerant isolates of Acanthamoeba. All pathogenic isolates of Acanthamoeba exhibited higher protease activity than did the non-pathogenic ones. The zymographic protease assays showed various banding patterns for different strains of Acanthamoeba.

CONCLUSION

The incidence and prevalence of the pathogenic Acanthamoeba species in the aquatic environment using parasitological and biochemical diagnostic tools will provide baseline data against which the risk factors associated with waterborne transmission can be identified.

Setaria equina: in vivo effect of diethylcarbamazine citrate on microfilariae in albino rats

Although diethylcarbamazine citrate (DEC) is successful drug in eliminating human filariasis, yet, its mode of action is still debatable. Herein, the effect of DEC to treat albino rats infected with the animal filarial parasite Setaria equina was tested. Microfilarial (mf) counts and sections from liver, lung, kidney as well as spleen were investigated at different time points after treatment by light microscopy. After 45 and 300min of treatment, a significant decrease in blood mf was observed accompanied by adherence of degenerated mf to both kupffer cells and leukocyte in liver sections. In lung sections, loss of sheath was observed at 45min, while degeneration was observed at later time points. In kidney sections, more mf counts and less matrix were observed in the glomeruli at all time points after treatment. Degenerated mf were observed in spleen sections only at, late time point, 480min after treatment. In conclusion, one of the possible mechanisms by which DEC reduces blood microfilarial count is trapping larvae in organs and killing them through cellular adherence.

Enzyme-linked immunosorbent assay with worm vomit and cercarial secretions of Schistosoma mansoni to detect infections in an endemic focus of Burkina Faso

Cercariae and adult Schistosoma mansoni were used to prepare, respectively, cercarial secretions (CS) and worm vomit (WoV). These were used as antigens in an enzyme-linked immunosorbent assay (ELISA) to test the IgG-reactivity of sera obtained in an S. mansoni-endemic area of Burkina Faso. Among the egg-excreting individuals (n=240), 94.6% reacted positively with WoV, but only 62.9% with CS, thus suggesting a high diagnostic sensitivity of WoV, but not of CS. Among those individuals without detectable eggs in two Kato-Katz thick smears from different stool specimens (n=215), the respective percentages of positive IgG reactivity were 78.1% and 63.3%. These positive reactions in the absence of detectable eggs are interpreted in terms of limited sensitivity of parasitological stool examinations. Optical density values in ELISA with CS, but not with WoV, correlated negatively with age, which may reflect decreasing exposure to cercariae in older individuals.

Novel growth of aluminium nitride nanowires

This work describes novel growth of aluminium nitride (AIN) nanowires by nitridation of a mixture consists of aluminium and ammonium chloride powders (Al:NH4Cl = 1.5:1 weight ratio) at 1000 degrees C for 1 h in flowing nitrogen gas (1 l/min). XRD analysis of the product showed the formation of pure hexagonal AIN. SEM micrographs of as-synthesized product revealed the growth of homogeneous AIN nanowires (phi 40-150 nm). No droplets were observed at the tips of obtained nanowires which suggests that they were grown mainly by a vapor-phase reactions mechanism. Thermodynamic analysis of possible intermediate reactions in the operating temperatures range illustrates that these nanowires could be grown via spontaneous vapor-phase chlorination-nitridation sequences.

Detection of inducible nitric oxide synthase in Schistosoma japonicum and S. mansoni

Schistosoma japonicum and S. mansoni were tested for reactivity with an anti-inducible nitric oxide (iNOS) antibody and the distribution of iNOS was studied by immunofluorescent tests in different stages of the parasites. Reactivity was associated with the tegument in both larval schistosomes (sporocysts and cercariae) and eggs. With adult worms, the majority of the immunofluorescence was predominantly subtegumental in S. japonicum and parenchymal in S. mansoni. Fluorescence was also observed in host tissues (snails and mouse liver). In Western blots, the enzyme of S. japonicum had an apparent molecular weight of about 210 kDa. The possible role of worm and host iNOS in the parasite-host interrelation remains to be clarified.

Serine protease and phenoloxidase activities in hemocytes of Biomphalaria glabrata snails with varying susceptibility to infection with the parasite Schistosoma mansoni

The snail Biomphalaria glabrata possesses hemocytes, which are supposed to interact with the larval stages of the human parasite Schistosoma mansoni. We describe trypsin-like serine protease(s) and phenoloxidase activities in lysates from these hemocytes. Both enzymes have activity optima around pH 9.5. The serine protease was inhibited by EDTA, PMSF, antipain and aprotinin, and the phenoloxidase activity by diethydithiocarbamate. By comparison, the serine protease activity in secretions of S. mansoni cercariae also had an alkaline pH optimum around 10.5 and was sensitive to the same inhibitors. In addition, serine protease activities from snails and cercariae had the same molecular mass of 28 kDa. However, the K(m) value of the serine protease(s) and the K(i) values of different inhibitors were generally lower for the snail enzyme than for the cercarial enzyme. The serine protease activity varied among individual snails but activity in hemocyte lysates and hemolymph correlated strongly. There was no detectable difference in the levels of activity between snails which are susceptible or resistant to schistosome infection.

Biochemical comparison of the serine protease (elastase) activities in cercarial secretions from Trichobilharzia ocellata and Schistosoma mansoni

We report on serine protease activity in cercarial secretions (CSs) from the bird parasite Trichobilharzia ocellata. Using a colorigenic substrate, the biochemical properties of this enzyme were studied and its activity was compared to the homologous one in CSs from the human parasite Schistosoma mansoni. The specific serine protease activity was always 2- to 3-fold higher in CSs from T. ocellatacompared to S. mansoni. The enzyme has its optimal activity at pH 10.5, is Ca2+-dependent (inhibition with EDTA) and has a trypsin-like (inhibition with anti-pain) serine proteinase activity (inhibition with PMSF and aprotinin). The K(m) value of the serine protease from T. ocellatawas higher than that of S. mansoni, and the K(i) values for several inhibitors were generally lower for the enzyme of T. ocellatathan that of S. mansoni except for EDTA. The enzyme activities from both parasites had a molecular weight of 30 kDa in gelatin-SDS-polyacrylamide gels. The intensity of the gelatin digestion bands was stronger with the T. ocellata than with the S. mansoni enzyme.

Species-restricted antibody response against a DNA-construct coding for aspartic proteinase from Schistosoma japonicum

DNA-based vaccine technology was used to immunize against the schistosome digestive enzyme, cathepsin D aspartic proteinase. The cDNA coding for Schistosomajaponicum aspartic proteinase was cloned in a mammalian expression vector under control of the CMV promoter/enhancer and expressed for the first time in transfected mammalian cells as well as in mice immunized--by means of intra-ear pinna injection--with the aspartic proteinase-encoding DNA construct. Mice developed antibodies which recognized the native protein in homogenates of S. japonicum worms and reacted with the gut and, to a much lesser degree, with the parenchyma of the parasites in cryostat sections. It was noteworthy that the vaccinated mouse sera did not detectably cross-react with S. mansoni antigens either in homogenates or on cryostat sections. By contrast, infection sera of mice or humans strongly cross-reacted with both schistosome species. We conclude that DNA vaccination can induce species-restricted antibody responses against schistosome proteins. The implications of this previously unrecognized specificity are discussed.

Antibodies induced in mice by a DNA-construct coding for the elastase of Schistosoma mansoni recognize the enzyme in secretions and preacetabular glands of cercariae

A DNA-construct coding for the elastase of the parasite Schistosoma mansoni was prepared from adult S. mansoni worm RNA which was reverse transcribed into cDNA. The gene coding for the elastase was amplified using primers specific for the sequence of cercarial elastase and was cloned into a mammalian expression vector. Expression of the elastase gene at the transcriptional level was achieved for the first time in transfected mammalian cells (COS-7) and was also successful in muscle tissue of mice injected with the DNA-construct. These mice developed antibodies recognizing in Western blots the elastase from cercarial secretions. Also, these antibodies reacted in immunofluorescence tests with the preacetabular glands of cercariae, i.e. the site of origin for elastase. Thus, the DNA-construct induced the expression of elastase in mice and formation of antibodies that recognized the native antigen.

DNA vaccination with asparaginyl endopeptidase (Sm32) from the parasite Schistosoma mansoni: anti-fecundity effect induced in mice

DNA-based vaccine technology was used to induce an immune response in mice against a schistosome cysteine proteinase, asparaginyl endopeptidase (Sm32). The cDNA coding for Sm32 was cloned in a mammalian expression vector under control of the CMV promoter/enhancer and expressed for the first time in transfected mammalian cells as well as in mice immunized with the Sm32-encoding DNA construct. These mice developed antibodies which recognized the native protein not only in homogenates of Schistosoma mansoni worms but also in the gut on cryostat sections of the parasites. This DNA vaccine led to an anti-fecundity effect: female worms of a challenge infection produced 37% less eggs than those growing in naïve mice. The results suggest that Sm32 may be a candidate antigen for the generation of an anti-pathology vaccine against schistosomes.

Infection induces antibodies against the cercarial secretions, but not against the cercarial elastases of Schistosoma mansoni, Schistosoma haematobium, Schistosoma japonicum and Trichobilharzia ocellata

Cercarial secretions from different species of the parasite Schistosoma and from Trichobilharzia ocellata contain a proteolytic activity, cercarial elastase, which was demonstrated by a 30 kDa band in gelatin gels. Sera of patients infected with Schistosoma mansoni, Schistosoma haematobium or Schistosoma japonicum contain immunoglobulin G which react in ELISA with cercarial secretions from all schistosomes and cross-react among the different parasite species. In Western blots, however, infection sera from patients, as well as heavily infected mice or rabbits, did not react with a 30-kDa protein. Moreover, when sections from infected snails (Biomphalaria, Bulinus and Lymnaea) were analysed by immunofluorescence using the same infection sera, only the tegument of the developing cercariae was recognized, but not the acetabular glands. In contrast, when antisera against purified cercarial elastase from either S. mansoni or S. haematobium were tested with sections of infected Biomphalaria or Bulinus, fluorescence was strong in the preacetabular glands of the cercariae of either species, but undetectable with the tegument. Cross-reactivity of both antisera extended to T. ocellata-infected Lymnaea, but not to S. japonicum-infected Oncomelania. In conclusion, although immunization with purified cercarial elastase results in antibody production, the enzyme does not induce an apparent antibody response following natural infection.

Blockage of skin invasion by schistosome cercariae by serine protease inhibitors

Invasion of skin by schistosome cercariae is facilitated by a serine protease secreted from the acetabular cells of cercariae in response to skin lipid. Specific inhibitors of the protease, when applied to human skin in formulations designed to retain the inhibitor on and in the upper stratum corneum layers, block cercarial invasion of human skin. Both peptide-based, irreversible inhibitors and non-peptide, reversible inhibitors block cercarial invasion when applied in a propylene glycol:isopropyl alcohol (3:1) formulation in vitro. Arrest of cercarial invasion could be achieved even after immersion of treated skin in water for 2 hr. Peptide-based irreversible inhibitors in the presence of three different Topicare Delivery Compounds optimized arrest of cercarial invasion. The three Topicare Delivery Compounds applied alone prevented 80-100% of cercarial invasion. With inclusion of the inhibitor, there was 97-100% inhibition in vitro. The optimal formulation with inhibitor was then applied to the tails of BALB/c mice, and the mice were exposed to 120 cercariae by tail immersion. With the carrier lotion alone, there was a 50% reduction in worm burden and a 70% reduction in egg burden. When inhibitor was included, an 80% reduction in worm burden and a 92% reduction in egg burden was observed.

Evaluation of a stage-specific proteolytic enzyme of Schistosoma mansoni as a marker of exposure

Cercarial elastase (CE) is one of the first proteins released in the host by invading schistosome cercariae. An enzyme-linked immunosorbent assay (ELISA)-formatted immunoassay has been developed to detect antibodies to the stage-specific CE antigen of Schistosoma mansoni as marker of exposure. We have evaluated this test system as an epidemiologic tool, using well-characterized sera collected from S. mansoni- and S. haematobium-infected subjects residing in endemic areas and from control subjects living in nonendemic areas in Egypt. Urine, stool specimens, and blood samples were collected from a sample of 272 endemic subjects randomly selected to represent different age groups in the range of 2-20 years of age. Of 47 S. mansoni-infected subjects, 41 (87.2%) had anti-CE IgG antibodies. Of 52 S. haematobium-infected cases, 38 (73.0%) had IgM antibodies to CE and 43 (82.7%) had IgG antibodies to CE. Of 173 egg-negative people in the endemic area, 84 (48.6%) were IgM positive and 99 (57.2%) were IgG positive. The mean IgM and IgG antibody levels were similar in the infected groups but were significantly lower in the egg-negative group (P = 0.001). All sera from young children (2-3 years of age) were uniformly ELISA negative. The prevalence of IgM and IgG antibodies to CE in children less than six years of age were significantly lower than in other age groups. There was no significant difference in prevalence rates of IgM and IgG anti-CE antibodies between subjects having other parasites present in the endemic area (Ascaris lumbricoides, Entrobius vermicularis, Hymenolepis nana, H. diminuta, Trichostrongylus spp., and Entamoeba histolytica) and those without any parasitic infection. All nonendemic sera (58), including those with other helminth infections, were uniformly ELISA negative for antibodies to CE. These findings suggest that antibodies to elastase indicate exposure, but not necessarily active schistosome infection.

Effect of pyridoxine on the blood-retina barrier in experimentally induced hyperglycemia in rats

We studied the effects on the blood-retina barrier of pyridoxal S phosphate, the biologically active form of vitamin B6 (pyridoxine), in 23 male Long-Evans rats in which hyperglycemia had been induced by means of intraperitoneal injection of streptozocin. Twelve rats were treated with pyridoxine, and 11 rats served as the control group. Vitreous fluorophotometry was used to quantitatively evaluate the effect of pyridoxine. The procedure was done before and 2 weeks after the induction of hyperglycemia, readings being taken 5 and 60 minutes after injection of the dye. In both groups the mean vitreous fluorescein levels after hyperglycemia was induced were significantly higher than those before hyperglycemia was induced (p less than 0.05). The mean levels before hyperglycemia was induced were not significantly different between the two groups. The mean level 60 minutes after injection of the dye after hyperglycemia was induced was lower in the treated group than in the untreated group, although not significantly so. The incidence of lens opacities at 5 weeks was higher in the untreated group than in the treated group (p less than 0.01). We conclude that administration of pyridoxine to hyperglycemic rats for 5 weeks has no significant effect on the permeability of the blood-retina barrier.

Effect of piroxicam on the blood-retina barrier in experimentally induced diabetes in rats

The effect of piroxicam on the blood-retina barrier was evaluated in rats with experimentally induced diabetes. Diabetes was induced in rats by intraperitoneal injection of streptozocin (STZ). Diabetic rats were divided into two equal groups: those treated with piroxicam, a long-acting platelet inhibitor, and an untreated control group. Vitreous fluorophotometry (VFP) was performed both before and two weeks after induction of diabetes and piroxicam intake. Streptozocin-induced diabetes caused an alteration in the blood-retinal barrier evidenced by an increase in vitreous fluorescein concentration in diabetic rats compared with normal rats. Piroxicam intake did not lead to significant change in vitreous fluorescein concentrations. However, the examination had to be terminated at two weeks because of cataract formation. The piroxicam treated group showed less incidence of lens opacity formation (59.1% compared to 81.8% in the untreated group, p = 0.0006). Piroxicam administration appears to protect the diabetic rat eye against lens opacification.