Protection by iron salts against sporidesmin intoxication in sheep

Comparison of a novel form of zinc with zinc oxide bolus licensed for prevention of facial eczema, and interaction with copper oxide in sheep

To evaluate a novel elemental zinc bolus compared with a registered positive control zinc oxide bolus and assess serum zinc concentrations following concomitant treatment with a capsule containing copper oxide needles. Forty Romney-cross ewes were randomly allocated in a 2 × 2 factorial design study. On Day 0, 20 ewes received novel boluses containing elemental zinc (Investigational Veterinary Product, IVP) while 20 received a zinc oxide bolus (control; CP). Half the animals in each zinc treatment group (n = 10) were treated with a copper oxide needle capsule [Copasure® - Ewe]. Weekly, from Day -7 to 56, all ewes were assessed for signs of photosensitization, and for 10 ewes from each zinc treatment groups, samples were collected for analysis of serum GGT activity, serum zinc concentrations, faecal zinc concentrations and on Days -7 and 56, liver copper concentrations. Multivariable random-effects models assessed the effects of zinc treatment, copper treatment, treatment interactions and time on all analytes. Regression models examined associations between serum and faecal zinc concentrations and GGT activity. Low spore numbers indicated low Pithomyces chartarum challenge. Serum zinc levels were significantly higher in the IVP than in the CP group [p < 0.0001] and varied by time [p < 0.001] and positively associated with faecal zinc concentration [p < 0.001]. Copper treatment did not affect serum zinc [p = 0.82] or faecal zinc [p = 0.92] concentrations. Liver copper concentrations did not differ between zinc treatment groups on Day -7 [p = 0.6] or Day 56 [p = 0.95]. Only the CP/no copper group had no increase in liver copper concentrations.

Harmful and beneficial effects of organic monosulfides, disulfides, and polysulfides in animals and humans

Many organic sulfides (mono-, di-, and polysulfides) are present in our environment. Simple derivatives are produced by some plants and animals, while complex sulfides are secondary metabolites of several genera of bacteria and fungi. Sulfides play an important role in the smell and taste of food, and many such compounds are used as food flavorings. Some sulfides are toxic, and there is evidence that such toxicity is caused by the ability of these substances to generate reactive oxygen species. Some sulfides, however, have been shown to protect against toxicants and carcinogens. These beneficial effects are believed to involve, at least in part, the ability of sulfides to inhibit the enzymatic activation of pro-toxicants and to increase tissue activities of enzymes that protect against electrophiles. Some sulfides also have potential as cancer chemotherapeutics. In this review, the toxic and beneficial effects of sulfides in animals are described, and the possible value of sulfides in cancer chemoprotection and cancer chemotherapy is discussed.

A zinc-containing intraruminal device for prevention of the sporidesmin-induced cholangiopathy of facial eczema in calves

AIM

To develop and evaluate a zinc-containing intraruminal controlled-release bolus for protection of calves (175-250 kg bodyweight) against facial eczema (FE).

METHODS

Boluses releasing zinc, in the form of zinc oxide, at rates ranging from 1.67 to 4.25 g/day were administered to calves which were challenged 4 weeks later with the FE toxin, sporidesmin. The efficacy of the boluses in protecting against sporidesmin-induced cholangiopathy was determined by measuring serum activities of gamma-glutamyltransferase (GGT).

RESULTS

A bolus releasing zinc at approximately 4.25 g/day gave excellent protection against sporidesmin toxicity for periods of up to 5 weeks duration.

CONCLUSIONS

This zinc-containing intraruminal controlled-release bolus has the potential to markedly reduce the incidence and severity of FE in calves within a 175-250 kg bodyweight range.

Metal complexes of sporidesmin D and dimethylgliotoxin, investigated by electrospray ionisation mass spectrometry

Electrospray ionisation mass spectrometry (ES-MS) has been used to probe the coordination chemistry of metabolites such as sporidesmin D (spdD), found in the saprophytic fungus Pithomyces chartarum, and the related bisdethiobis(methylthio)gliotoxin (dimethylgliotoxin, Megtx). SpdD forms complexes of the type [spdD+M(MeCN)] and [2spdD+M]+ (M=Cu, Ag) and, at higher cone voltages, [spdD+M]+. The bis(ligand) ion [2spdD+M]+ was observed at very high cone voltages, indicating it has appreciable stability; the proposed structure of this species has a four-coordinate metal ion with two bidentate spdD ligands, coordinated through their SMe groups. 1H NMR titrations of spdD with K+, Ag+ and Cu+ provided additional evidence for complex formation with the soft metals. SpdD forms only relatively weak complexes with Zn2+, Cd2+, Co2+ and Mn2+, in keeping with the known reduced tendency of these metals to form stable thioether complexes. ES-MS studies of Megtx showed similar results to spdD, with stable adducts formed with Cu+ and Ag+ ions. The X-ray crystal structure of spdD is also reported.

Metal complexes of the mycotoxins sporidesmin A and gliotoxin, investigated by electrospray ionisation mass spectrometry

The mycotoxin sporidesmin A (spdA), responsible for the intoxication of animals, causing facial eczema, has been investigated by electrospray ionisation mass spectrometry. Protonated [spdA+H](+) and deprotonated [spdA-H](-) ions are observed in positive and negative ion modes respectively. Reduced spdA, formed by cleavage of the disulfide bond by Na[BH(4)] gives an ion [spdA+H](-), and forms ions of the type [2spdA+M](2-) with a range of divalent metal ions M(2+)=Zn(2+), Cd(2+), Hg(2+), Sn(2+) and Fe(2+). Sodium-containing analogues [2spdA+M+Na](-) are observed, particularly at high cone voltages, where they are stable towards cone voltage-induced fragmentation, indicating appreciable stability of the (spdA)(2)M system. A competition experiment between Cd(2+) and Zn(2+) demonstrates that reduced spdA has a higher affinity for Cd(2+) ions. The related gliotoxin (gtx) forms analogous [2gtx+M](2-) and [2gtx+M+Na](-) ions. The reduction and metal complexation of spdA can be monitored by (1)H NMR spectroscopy, and results in chemical shift changes for those protons adjacent to the sulfur atoms. The isolation of a polymeric cadmium-spdA complex is also reported.

Toxicity of thiols and disulphides: involvement of free-radical species

Sulphur is essential to life, and thiols and disulphides play essential roles in cellular biochemistry. Such compounds are also widely distributed in the food of man and his domestic animals, and they are extensively used in industry. However, many thiols and disulphides have been shown to be toxic. Aliphatic, aromatic, and heterocyclic compounds of this type are haemolytic agents in animals while aminothiols have been shown to induce many cytotoxic effects in vitro and the epidithiodioxopiperazine mycotoxin, sporidesmin, is a potent hepatotoxic agent. Structure-activity relationships among these compounds and factors which modulate their harmful effects are consistent with a toxic mechanism involving redox cycling between the thiol and the corresponding disulphide. Thiyl radicals and "active oxygen" species are formed in this process, and it is suggested that these substances are responsible for initiating the tissue damage provoked by thiols and disulphides.