Five oximes (K-27, K-33, K-48, BI-6 and methoxime) in comparison with pralidoxime: survival in rats exposed to the organophosphate paraoxon

Oximes are cholinesterase reactivators used in organophosphorus poisoning. Clinical experience with pralidoxime (PRX) and other oximes is disappointing and their routine use has been questioned. In addition it is known that not all oximes are equally effective against all existing organophosphorus compounds. There is a demand for broad-spectrum reactivators with a higher efficacy than PRX. Based on our previous in vitro work the protection conferred by the various new oximes against inhibition by paraoxon as quantified by the IC(50) shift (nM increase in the IC(50) of the inhibitor per microM oxime present) is: 0.3 (PRX), 0.4 (methoxime; MMC-4), 1 (K-33), 1.2 (BI-6), 1.5 (K-48) and 3.7 (K-27). The purpose of the study was to quantify in vivo the extent of oxime-conferred protection, using paraoxon (POX) as a cholinesterase inhibitor and to test whether in vitro efficacy translates to protection from mortality. There were seven groups of six rats in each cycle of the experiment. Group 1 (G1) received 1 micromol POX (approximately LD(75)), the other groups (G2-G7) received 1 micromol POX + of one the six reactivators. The animals were monitored for 48 h and the time of mortality was recorded. The procedure was repeated five times (cycles). All substances were applied i.p. The experiments were repeated using 2, 3, 5 and 10 micromol POX. Mortality data were compared and hazards ratios (relative risks) ranked using the Cox proportional hazards model using POX dose and group (reactivator) as time-independent covariables. The relative risk of death estimated by Cox analysis (95% CI) in oxime treated animals when compared with untreated animals, adjusted for POX dose (high/low) was K-27: 0.26 (0.19-0.35); K-48: 0.34 (0.25-0.45); methoxime: 0.38 (0.29-0.50); BI-6: 0.53 (0.41-0.69); PRX: 0.70 (0.54-0.91); K-33: 0.82 (0.63-1.07). It is concluded that K-27 and K-48 are the most promising new oximes. The compounds with the best results in vitro also confer the best protection in vivo. Further testing using methyl- and propyl-organophosphates are needed.     

Human intestinal schistosomiasis in communities living near three rivers of jimma town, South Western ethiopia

Background

Schistosoma mansoni is one of the parasites with high public and medical importance in Ethiopia. However, information is scarce about S. mansoni epidemiology in people living with higher risk of infection in Jimma town. This study was designed to determine point prevalence, intensity and risk factors of S. mansoni infection among residents nearby three rivers of Jimma town and assess the rate of Biomphalaria species shading cercariae from January to April, 2007.

Methods

A cross-sectional study was conducted in communities residing nearby three rivers of Jimma town. Structured questionnaires were used to collect data on socio- demographic and behavioral risk factors. After physical examination, stool samples were collected from 517 study participants and processed with Kato-Katz technique for microscopic examination and quantification of egg load. Snails were collected for identification of Biomphalaria species and then checked for cercarial shading.

Results

The prevalence of S. mansoni was 26.3 % with intensity ranging 24 to 936 eggs per gram of stool. Participants in the age group 10–19 years, OR = 2.19 (95% CI; 1.10 – 4.34), and those living near the Awetu River, OR = 2.67 (95% CI; 1.06 – 6.75), had higher risk of S. mansoni infection. Moreover, water contact while crossing a river, OR = 3.77 (95% CI; 1.79 – 7.95), and swimming, OR = 2.59 (95% CI; 1.37 – 4.91, was significantly associated with infection. Biomphalaria snails collected from Chore and Awetu Rivers shaded higher rate of cercariae compared with Kito River.

Conclusion

A moderate prevalence of S. mansoni infection was shown in the study population. Infection rate among the residents correlated with rate of cercarial shading Biomphalaria snails. Treatment of targeted groups, appropriate health education and environmental measures (e.g. snail control) are needed to improve the situation.     

A Comparison of the Efficacy of Acetylcholinesterase Reactivators against Cyclohexyl Methylphosphonofluoridate (GF Agent) by in vitro and in vivo Methods

Abstract: The purpose of this study was to compare the therapeutic efficacy of a new acetylcholinesterase reactivator, designated BI-6 (1-(2-hydroxyiminomethylpyridinium)-4-(4-carbamoylpyridinium)-2-butene dibromide), with presently used oximes (pralidoxime, obidoxime, methoxime) and H-oximes (HI-6, HLü-7) by in vitro and in vivo methods. In vitro, methoxime seems to be the most efficacious reactivator of GF agent-inhibited acetylcholinesterase because the phosphonylation of acetylcholinesterase by GF agent markedly increases its affinity for the enzyme. The oxime BI-6 is more efficacious than other presently used oximes (pralidoxime, obidoxime) but its reactivating efficacy does not reach the efficacy of H-oximes tested. On the other hand, obidoxime and pralidoxime appear to be very poor reactivators of GF agent-inhibited acetylcholinesterase because the phosphonylation of acetylcholinesterase by GF agent markedly decreases their affinity to the enzyme. In vivo, H oximes (HI-6, HLü-7) are the most efficacious antidotes for the treatment of acute poisoning with GF agent in rats while the presently used oximes such as pralidoxime and obidoxime are practically ineffective. BI-6 and methoxime are more efficacious than pralidoxime and obidoxime, nevertheless their therapeutic efficacy does not reach the efficacy of H oximes. Our results show that the ability of oximes to reactivate GF agent-inhibited acetylcholinesterase in vitro usually corresponds to their therapeutic effects against GF agent in vivo.     

Five oximes (K-27, K-48, obidoxime, HI-6 and trimedoxime) in comparison with pralidoxime: survival in rats exposed to methyl-paraoxon

There is a clear need for broad-spectrum cholinesterase reactivators (active against a multitude of organophosphorus ester enzyme inhibitors) with a higher efficacy than pralidoxime. The purpose of the study was to quantify in vivo the extent of oxime-conferred protection, using methyl-paraoxon [dimethyl p-nitrophenyl phosphate; (methyl-POX)] as a cholinesterase inhibitor. There were seven groups of six rats in each cycle of the experiment. Group 1 (G1) received 2 micromol methyl-POX ( approximately LD(50)), the other groups (G2-7) received 2 micromol methyl-POX + one of the six reactivators. The animals were monitored for 48 h and the time of mortality was recorded. The procedure was repeated six times. All substances were applied i.p. The experiments were repeated using 3 and 5 micromol methyl-POX. Mortality data were compared and hazards ratios (relative risks) ranked using the Cox proportional hazards model with methyl-POX dose and group (reactivator) as time-independent covariables. The relative risk of death estimated by Cox analysis (95% CI) in oxime-treated animals when compared with untreated animals, adjusted for methyl-POX dose (high/low) was K-27, 0.58 (0.42-0.80); K-48, 0.60 (0.43-0.83); trimedoxime, 0.76 (0.55-1.04); pralidoxime, 0.88 (0.65-1.20); obidoxime, 0.93 (0.68-1.26); HI-6, 0.96 (0.71-1.31). Only K-27 and K-48 provided statistically significant protection in rats exposed to methyl-POX. Despite the lower inhibitory potency (higher IC(50)) of methyl-POX compared with POX (ratio 4:1), the ability of oxime reactivators to protect from methyl-POX induced mortality was reduced compared with protection from POX (ethyl-analog).     

In vitro oxime reactivation of red blood cell acetylcholinesterase inhibited by methyl-paraoxon

Oximes are cholinesterase reactivators of use in poisoning with organophosphorus ester enzyme inhibitors. Pralidoxime (PRX) is the oxime used in the United States. Clinical experience with pralidoxime (and other oximes) is disappointing and the routine use has been questioned. Furthermore oximes are not equally effective against all existent enzyme inhibitors. There is a clear demand for 'broad spectrum' cholinesterase reactivators with a higher efficacy than those clinically available. To meet this need over the years new reactivators of cholinesterase of potential clinical utility have been developed.The purpose of the study was to quantify 'in vitro' the extent of protection conferred by available (pralidoxime and methoxime) and experimental (K-27, K-33 and K-48) oximes, using methyl-paraoxon (methyl-POX) as an esterase inhibitor and to compare the results with those previously obtained using paraoxon (POX) as an inhibitor.Red blood cell (RBC) acetylcholinesterase (AChE) activities in whole blood were measured photometrically in the presence of different methyl-POX concentrations and IC(50) values calculated. Determinations were repeated in the presence of increasing oxime concentrations. The IC(50) of methyl-POX (59 nm) increased with the oxime concentration in a linear manner. The calculated IC(50) values were plotted against the oxime concentrations to obtain an IC(50) shift curve. The slope of the shift curve (tg alpha) was used to quantify the magnitude of the protective effect (nm IC(50) increase per microm reactivator).Based on our determinations the new K-series of reactivators is superior to pralidoxime (tg alpha = 1.9) and methoxime (tg alpha = 0.7), K-27 and K-48 being the outstanding compounds with a tg alpha value of 10 (nm IC(50) increase per microm reactivator), which is approximately five times the reactivator ability of PRX. The tg alpha value determined for K-33 was 6.3.The ranking of reactivator potencies of the examined oximes determined with methyl-POX as an inhibitor (K-27 = K-48 > K-33 > pralidoxime > methoxime) is similar to the ranking previously reported by us using POX as an inhibitor (K-27 > or = K-48 > K-33 > methoxime = pralidoxime). There is an (expected) inverse relationship between the binding constant K and the slope of the IC(50) shift curve (tg alpha) for all oximes examined. K-27 and K-48 (the most protective substances judging by the tg alpha) having the lowest K value (highest affinity).In vivo testing of the new oximes as methyl-paraoxon protective agents is necessary.     

Evaluation of the Neuroprotective Efficacy of Newly Developed Oximes (K206, K269) and Currently Available Oximes (Obidoxime,HI‐6) in Cyclosarin‐Poisoned Rats

Abstract: The neuroprotective effects of newly developed oximes (K206, K269) and currently available oximes (obidoxime, HI‐6) in combination with atropine in rats poisoned with cyclosarin were studied. The cyclosarin‐induced neurotoxicity was monitored using a functional observational battery at 24 hr following cyclosarin challenge. The results indicate that a newly developed oxime K206 is able to counteract cyclosarin‐induced neurotoxicity while the neuroprotective potency of another newly developed oxime (K269) is negligible. The neuroprotective efficacy of K206 is markedly higher than commonly used obidoxime; nevertheless, its potency to eliminate cyclosarin‐induced neurotoxicity is slightly lower compared to the oxime HI‐6. Thus, a newly developed oxime K206 seems to be a better oxime for the antidotal treatment of cyclosarin poisonings than obidoxime due to higher neuroprotective potency although the oxime HI‐6 is still the most suitable oxime for the antidotal treatment of acute poisonings with cyclosarin.     

Comparison of Paracheck Pf® test with conventional light microscopy for the diagnosis of malaria in Ethiopia

ObjectiveTo assess the accuracy of Paracheck Pf® in reference to the conventional light microscopy.MethodsA total of 400 patients visiting Awash, Methara and Ziway malaria centers were simultaneously screened with both light microscopy and Paracheck Pf® for the presence of Plasmodium falciparum (P. falciparum) malaria.ResultsOf the 190 samples that were negative by light microscope, the Paracheck Pf® showed 11 false positive and 179 true negative results, and from a total of 210 samples positive by light microscope, Paracheck Pf® accurately diagnosed 200 true malaria cases. Taking the light microscopy as a standard test for malaria, the sensitivity, specificity, positive predictive value and negative predictive value of Paracheck Pf® is 95.2% [cofidence interval (CI)=92.4–97.1], 94.2% (CI=91.1–96.3), 94.8% (CI=92.0–96.7) and 94.7% (CI=91.6–96.8), respectively.ConclusionsParacheck Pf® showed good sensitivity and specificity for the diagnosis of P. falciparum malaria, and fulfill the world health organization (WHO) recommendation that requires the sensitivity of rapid diagnostic tests (RDTs) to be greater than 95%. Therefore, Paracheck Pf® can be used as an alternative to the Giemsa stain light microscopy in resource poor set ups.     

Outcome of tuberculosis retreatment in routine conditions in Cotonou, Benin.

SETTING: National Tuberculosis Programme (NTP), Cotonou, Benin. OBJECTIVE: To study the patient characteristics and outcome of tuberculosis retreatment cases in a well-functioning NTP. METHODS: A retrospective, register-based study of all smear-positive pulmonary tuberculosis cases put on retreatment (2SERHZ/1ERHZ/5R3H3E3) between 1992 and 2001 in Cotonou. For comparison, information on new smear-positive cases in Cotonou in 1999 was entered and analysed. RESULTS: Of 8103 tuberculosis patients registered, 642 were put on retreatment. The analysis is mainly based on the 236 patients whose initial treatment regimen records were available (113 relapses, 84 failures, 39 returns after default). Most of the relapse (57%) and return after default (72%) cases were put on retreatment within 12 months after stopping their initial treatment. Overall, the retreatment results were satisfactory (78% success) and comparable with those of new cases (82%); the failure rates were low (3%), as were those for initial treatment (1%). There were more defaulters from retreatment among those who had already defaulted from initial treatment (21%). Treatment success rates were better among women than men. CONCLUSION: The standardised retreatment regimen is effective in Cotonou, probably because the NTP is functioning well, there are no drug shortages, drug taking is strictly supervised, and a good treatment plan is followed.     

Case–control analysis of the health and nutrition of orphan schoolchildren in Ethiopia

Objectives To undertake a case–control analysis of the health, nutrition and caring practices of orphans enrolled in primary schools in Ethiopia. Methods Pupils of both sexes aged 7–17 who were randomly selected from Grades 3 and 4 of primary school during a national survey of schoolchildren in Ethiopia and who were classified as an orphan were matched by age, sex and school with non‐orphans. Logistic regression was used to compare children in terms of indicators of anthropometric and nutritional status, chronic infections, personal hygiene, diet, caring practices and self‐reported sensory disability. Results Of the 7752 children in the national survey, 1283 (16.9%) had lost either both parents or one parent. Of these orphans, 1048 were uniquely pair matched for the case–control analysis. About 60% of orphans had lost their father, and about 20% each had lost their mother or both parents. Orphans had better anthropometric measurements and indices than non‐orphans, although the differences were small, and they were less likely to have a goitre (OR = 0.68, P = 0.011). There were no differences in the odds of infections. Orphans were less likely than non‐orphans to have eaten breakfast or fruit and vegetables on the previous day and were more likely to report having trouble seeing and hearing. Conclusion Orphans were slight better nourished than non‐orphans, but this could have been a result of asystematic bias in underestimating the age of orphans. The indicators suggested that orphans were less well cared for than non‐orphans, but the differences were small.