Caenorhabditis elegans mutants resistant to phosphine toxicity show increased longevity and cross-resistance to the synergistic action of oxygen

Phosphine (hydrogen phosphide, PH3) is the fumigant most widely used to protect stored products from pest infestation. Despite the importance of this chemical, little is known about its mode of action. We have created three phosphine-resistant lines (pre-1, pre-7, pre-33) in the model organism C. elegans, with LC50 values 2, 5, and 9 times greater than the fully susceptible parental strain. Molecular oxygen was shown to be an extremely effective synergist with phosphine as, under hyperoxic conditions, 100% mortality was observed in wild-type nematodes exposed to 0.1 mg/l phosphine, a nonlethal concentration in air. All three mutants were resistant to the synergistic effects of oxygen in proportion to their resistance to phosphine with one mutant, pre-33, showing complete resistance to this synergism. We take the proportionality of cross-resistance between phosphine and the synergistic effect of oxygen to imply that all three mutants circumvent a mechanism of phosphine toxicity that is directly coupled to oxygen metabolism. Compared with the wild-type strain, all three mutants have an extended average life expectancy of from 12.5 to 25.3%. This is consistent with the proposed involvement of oxidative stress in both phosphine toxicity and ageing. Because the wild-type and mutant nematodes develop at the same rate, the longevity is unlikely to be caused by a clk-type reduction in oxidative metabolism, a potential alternative mechanism of phosphine resistance.

Effect of Cu Toxicity on Growth of Cowpea (Vigna unguiculata)

Accurate determination of the rhizotoxicity of Cu in dilute nutrient solutions is hindered by the difficulty of maintaining constant, pre-determined concentrations of Cu (micromolar) in solution. The critical Cu2+ activity associated with a reduction in the growth of solution-grown cowpea (Vigna unguiculata (L.) Walp. cv Caloona) was determined in a system in which Cu was maintained constant through the use of a cation exchange resin. The growth of roots and shoots was found to be reduced at solution Cu2+ activities ≥ 1.7 µM (corresponding to 90 % maximum growth). Although root growth was most likely reduced due to a direct Cu2+ toxicity, it is considered that the shoot growth reduction is attributable to a decrease in tissue concentrations of K, Ca, Mg, and Fe and the formation of interveinal chlorosis. At high Cu2+ activities, roots were brown in color, short and thick, had bent root tips with cracking of the epidermis and outer cortex, and had local swellings behind the roots tips due to a reduction in cell elongation. Root hair growth was reduced at concentrations lower than that which caused a significant reduction in overall root fresh weight.

H-ras activation is an early event in the ptaquiloside-induced carcinogenesis: Comparison of acute and chronic toxicity in rats

Bracken fern (Pteridium spp.) produces cancer of the urinary bladder and oesophagus in grazing animals and is a suspected human carcinogen, The carcinogenic principle ptaquiloside (PT), when activated to a dienone (APT), forms DNA adducts which eventually leads to tumor. Two groups of female Sprague-Dawley rats were given a chronic dose of 3 mg APT weekly for 10 weeks either by intravenous (iv) tail vein or by intragastric (ig) route, A third group was given a weekly dose of 6 mg of APT for 3 weeks by the ig route corresponding to acute dosing. Both chronic iv and ig dosed animals showed ischemic tubular necrosis in the kidney but only iv dosed animals developed adenocarcinomas of the mammary glands. Acutely dosed ig animals produced apoptotic bodies in the liver, necrosis of blood cell precursors in the bone marrow and ischemic tubular necrosis in the kidney but they did not develop tumors, No mutations were found in the H-ras and p53 genes in the mammary glands of either the ig rats or the tumor-bearing iv rats. However, the mammary glands of a fourth group of rats, which received APT by iv and killed before tumor development, carried Pu to Pu and Pu to Py double mutations in codons 58 and 59 of H-ras. This study indicates that the route of administration plays a role in the nature of the disease expression from ptaquiloside exposure. In addition to confirming the role of APT in the PT-induced carcinogenesis our finding suggests that activation of H-ras is an early event in the PT-carcinogenesis model. (C) 1998 Academic Press.

Protein fold recognition score functions: Unusual construction strategies

We describe two ways of optimizing score functions for protein sequence to structure threading. The first method adjusts parameters to improve sequence to structure alignment. The second adjusts parameters so as to improve a score function's ability to rank alignments calculated in the first score function. Unlike those functions known as knowledge-based force fields, the resulting parameter sets do not rely on Boltzmann statistics, have no claim to representing free energies and are purely constructions for recognizing protein folds. The methods give a small improvement, but suggest that functions can be profitably optimized for very specific aspects of protein fold recognition, Proteins 1999;36:454-461. (C) 1999 Wiley-Liss, Inc.

A six-year longitudinal study of the relationship of physical activity to bone mineral accrual in growing children: The University of Saskatchewan bone mineral accrual study

To investigate the influence of physical activity on bone mineral accrual during the adolescent years, we analyzed 6 years of data from 53 girls and 60 boys. Physical activity, dietary intakes, and anthropometry were measured every 6 months and dual-energy X-ray absorptiometry scans of the total body (TB), lumbar spine (LS), and proximal femur (Hologic 2000, array mode) were collected annually. Distance and velocity curves for height and bone mineral content (BMC) were fitted for each child at several skeletal sites using a cubic spline procedure, from which ages at peak height velocity (PHV) and peak BMC velocity (PBMCV) were identified. A mean age- and gender-specific standardized activity (Z) score was calculated for each subject based on multiple yearly activity assessments collected up until age of PHV. This score was used to identify active (top quartile), average (middle 2 quartiles), or inactive (bottom quartile) groups. Two-way analysis of covariance, with height and weight at PHV controlled for, demonstrated significant physical activity and gender main effects (but no interaction) for PBMCV, for BMC accrued for 2 years around peak velocity, and for BMC at 1 year post-PBMCV for the TB and femoral neck and for physical activity but not gender at the LS (all p < 0.05). Controlling for maturational and size differences between groups, we noted a 9% and 17% greater TB BMC for active boys and girls, respectively, over their inactive peers 1 year after the age of PBMCV. We also estimated that, on average, 26% of adult TB bone mineral was accrued during the 2 years around PBMCV.

Toxicity of biorational insecticides to Helicoverpa spp. (Lepidoptera : Noctuidae) and predators in cotton field

Field trials on upland cotton (Gossypium hirstum L.) during its reproductive phase were used to assess the toxicity of several biorational pesticides and chemicals to Helicoverpa armigera (Hubner) and H. puntigera Wallengren, as well as major predators at Dalby, Queensland, Australia. Moderate rate-dependent control was obtained in plots treated with neem (Azadirachta indica A. Juss) seed extract-azadirachtin (Aza) at rates of 30, 60 and 90 g/ha. Plots treated with Talstar EC (bifenthrin) applications achieved the best results, followed by treatment with alternation of chemicals (methomyl, bifenthrin, thiodicarb and endosulfan) and biorational insecticides (neem oil, azadirachtin and Bacillus thuringiensis kurstaki var. Berliner). Predators, including lady beetles, lacewings, spiders and predatory bugs, were insensitive to Aza, tooseendanin (Tsdn) and BT applications. In contrast, chemicals were very destructive of predators. All treatments provided some protection from infestation of H. armigera and H. puntigera. The effect of Aza on Helicoverpa spp. was reflected in a relatively higher yield of seed cotton harvested from Aza-treated plots compared with the control, but chemical control achieved significantly higher yields than any other treatment.

Infiltration from surface and buried point sources: The average wetting water content

The assumption in analytical solutions for flow from surface and buried point sources of an average water content, (θ) over bar, behind the wetting front is examined. Some recent work has shown that this assumption fitted some field data well. Here we calculated (θ) over bar using a steady state solution based on the work by Raats [1971] and an exponential dependence of the diffusivity upon the water content. This is compared with a constant value of (θ) over bar calculated from an assumption of a hydraulic conductivity at the wetting front of 1 mm day(-1) and the water content at saturation. This comparison was made for a wide range of soils. The constant (θ) over bar generally underestimated (θ) over bar at small wetted radii and overestimated (θ) over bar at large radii. The crossover point between under and overestimation changed with both soil properties and flow rate. The largest variance occurred for coarser texture soils at low-flow rates. At high-flow rates in finer-textured soils the use of a constant (θ) over bar results in underestimation of the time for the wetting front to reach a particular radius. The value of (θ) over bar is related to the time at which the wetting front reaches a given radius. In coarse-textured soils the use of a constant value of (θ) over bar can result in an error of the time when the wetting front reaches a particular radius, as large as 80% at low-flow rates and large radii.

Copper-mediated amyloid-beta toxicity is associated with an intermolecular histidine bridge

Amyloid-beta peptide (A beta) is pivotal to the pathogenesis of Alzheimer disease. Here we report the formation of a toxic A beta-Cu2+ complex formed via a histidine-bridged dimer, as observed at Cu2+/ peptide ratios of > 0.6:1 by EPR spectroscopy. The toxicity of the A beta-Cu2+ complex to cultured primary cortical neurons was attenuated when either the pi- or tau-nitrogen of the imidazole side chains of His were methylated, thereby inhibiting formation of the His bridge. Toxicity did not correlate with the ability to form amyloid or perturb the acyl-chain region of a lipid membrane as measured by diphenyl- 1,3,5-hexatriene anisotropy, but did correlate with lipid peroxidation and dityrosine formation. P-31 magic angle spinning solid-state NMR showed that A beta and A beta-Cu2+ complexes interacted at the surface of a lipid membrane. These findings indicate that the generation of the A beta toxic species is modulated by the Cu2+ concentration and the ability to form an intermolecular His bridge.

The role of xenobiotic metabolizing enzymes in arylamine toxicity and carcinogenesis: Functional and localization studies

In both animal models and humans, the first and obligatory step in the activation of arylamines is N-hydroxylation. This pathway is primarily mediated by the phase-I enzymes CYP1A1, CYP1A2 and CYP4B1. In the presence of flavonoids such as alpha-naphthoflavone and flavone, both CYP3A4 and CYP3A5 have also been shown to play a minor role in the activation of food-derived heterocyclic amines. The further activation of N-hydroxyarylamines by phase-II metabolism can involve both N,O-acetylation and N,O-sulfonation catalyzed by N-acetyltransferases (NAT1 and NAT2) and sulfotransferases, respectively. Using an array of techniques, we have been unable to detect constitutive CYP1A expression in any segments of the human gastrointestinal tract. This is in contrast to the rabbit where CYP1A1 protein was readily detectable on immunoblots in microsomes prepared from the small intestine. In humans, CYP3A3/3A4 expression was detectable in the esophagus and all segments of the small intestine. Northern blot analysis of eleven human colons showed considerable heterogeneity in CYP3A mRNA between individuals, with the presence of two mRNA species in same subjects. Employing the technique of hybridization histochemistry (also known as in situ hybridization), CYP4B1 expression was observed in some human colons but not in the liver or the small intestine. Hybridization histochemistry studies have also demonstrated variable NAT1 and NAT2 expression in the human gastrointestinal tract. NAT1 and NAT2 mRNA expression was detected in the human liver, small intestine, colon, esophagus, bladder, ureter, stomach and lung. Using a general aryl sulfotransferase riboprobe (HAST1), we have demonstrated marked sulfotransferase expression in the human colon, small intestine, lung, stomach and liver. These studies demonstrate that considerable variability exists in the expression of enzymes involved in the activation of aromatic amines in human tissues. The significance of these results in relation to a role for heterocyclic amines in colon cancer is discussed.

Management of acute psychostimulant toxicity

Psychostimulants produce a broad range of effects. Adverse effects can exist on a spectrum of severity from minor symptoms to life threatening toxicity. Although regular use or use of high doses increases risk of adverse events, many adverse events requiring emergency intervention may occur even in the naïve user.