Uptake, metabolism, accumulation and toxicity of cyanide in Willow trees

Chemicals taken up into plants may be accumulated so leading to toxic effects. Uptake and phytotoxicity of free cyanide was determined with the willow-tree transpiration test. Willow sets were grown in sand and irrigated with varying levels of cyanide (CN). Toxicity was determined by measuring transpiration. At CN concentrations below 10 mg/L, no toxic effects were observed. At 20 mg/L, transpiration was reduced to approximately 50% after 96 h. With 30, 40 and 50 mg/L, the transpiration decreased with a similar rate to < 20% of the initial transpiration within 96 h. Accumulation of cyanide in plant tissue was observed at 40 and 50 mg/L. The kinetics of metabolism of cyanide by roots, stems and leaves of willows was determined by the closed-bottle metabolism test. The Michaelis-Menten parameters v(max) and K(M)(maximal metabolic velocity and half-saturation constant, respectively) were determined by nonlinear regression. Estimates of uptake and metabolism were balanced using a nonlinear mathematical model. The model predicted that at low doses (<10 mg/L), the cyanide would be rapidly metabolized. At higher doses, uptake would be faster than metabolism and consequently cyanide would accumulate in the plant tissue. This relation between external dose and internal accumulation is nonlinear and explains the toxic effects observed.

In vivo monitoring of amino acids by microdialysis sampling with on-line derivatization by naphthalene-2,3-dicarboxyaldehyde and rapid micellar electrokinetic capillary chromatography

An analytical method was developed to monitor amino acids collected by in vivo microdialysis. Microdialysate was continuously derivatized on-line by mixing 6 mM naphthalene-2,3-dicarboxyaldehyde (NDA) and 10 mM potassium cyanide with the dialysate stream in a fused silica capillary to form fluorescent products. Reaction time, determined by the flow rate and volume of reaction capillary, was 3 min. Derivatized amino acids were continuously delivered into a flow-gated interface and periodically injected onto a capillary electrophoresis unit equipped with a laser-induced fluorescence detection based on a commercial microscope. Separation was performed in the micellar electrokinetic chromatography mode using 30 mM sodium dodecyl sulfate in 15 mM phosphate buffer at pH 8.0 as the separation media. An electric field of 1.3 kV/cm was applied across a 10 cm long, 10 microm internal diameter separation capillary. These conditions allowed 17 amino acid derivatives to be resolved in less than 30 s. On-line injections could be performed at 30 s intervals for in vivo samples. Detection limits were from 10 to 30 nM for the amino acids. The method was applied to monitor the acute ethanol-induced amino acid level changes in freely moving rats. The results demonstrate the utility of the method to reveal dynamics of amino acid concentration in vivo.

Removal of cyanide by woody plants

Hydrogen cyanide is a high volume production chemical that causes severe environmental problems. The toxicity of potassium cyanide (KCN) to basket willow trees (Salix viminalis) was tested. In aqueous solution, 2 mg CN l(-1) as KCN depressed the transpiration after 72 h about 50%. Trees exposed to 0.4 mg CN l(-1) in aqueous solution showed initially a depression of transpiration, but recovered. Doses of 8 and 20 mg CN l(-1) in aqueous solution were quickly mortal to the trees. At the end of the test, almost all cyanide had disappeared from the solutions. Levels of cyanide in plants were related to the toxicity, with no elevated levels of cyanide in plants exposed to 0.4 mg CN l(-1). Willows grown in sand survived 423.5 h irrigation with 20 mg CN l(-1). Willows grown in sand irrigated with 50 mg CN l(-1) died within a few days. The roots of the surviving willows were able to consume about 10 mg CN kg fresh weight(-1)h(-1). Vascular plants possess the enzymes beta-cyanoalanine synthase and beta-cyanoalanine hydrolase, which convert free cyanide to the amino acid asparagine. The in vivo capacity of woody plants (willow, poplar, elder, rose, birch) to remove cyanide was evaluated. Tests were performed with detached leaves and roots in KCN solutions of different concentrations. The highest removal capacity was obtained for basket willow hybrids (Salix viminalis x schwerinii). The Michaelis-Menten kinetics was determined. Realistic values of the half-saturation constant, K(M), were between 0.6 and 1.7 mg CN l(-1); the maximum metabolic capacity, v(max), was around 9.3 mg CN kg fresh weight(-1)h(-1). The removal of cyanide by plants might be useful in phytoremediation and treatment of wastewater from gold mining.

Toxicokinetics of cyanide in rats, pigs and goats after oral dosing with potassium cyanide

The aim of the present study was to determine the effect of the species on the toxicokinetics of cyanide and its main metabolite, thiocyanate. Forty-two rats, six pigs and six goats were dosed orally with 3.0 mg KCN/kg body weight, and cyanide and thiocyanate concentrations in blood were measured within 24 h. After the single oral dose, KCN was rapidly absorbed by rats and goats, with a time of peak concentration ( T(max)) of 15 min. The maximum plasma concentration ( C(max)) of cyanide was observed in goats (93.5 micro mol/l), whereas the C(max) of thiocyanate was higher in rats (58.1 micro mol/l). The elimination half-life ( t(1/2)) and volume of distribution ( Vd(area)) of both cyanide and thiocyanate were higher in goats (1.28 and 13.9 h, and 0.41 and 1.76 l/kg, respectively). Whereas the area under the curve (AUC) of cyanide was significantly higher in goats (234.6 micro mol.l/h), the AUC of thiocyanate was higher in rats (846.5 micro mol.l/h). In conclusion, the results of the present study support the hypothesis that the metabolism of cyanide and its main metabolite, thiocyanate, is species-linked, with the goat being more sensitive to the toxic effects of cyanide/thiocyanate.

Milk transfer of cyanide and thiocyanate: Cyanide exposure by lactation in goats

The present work was aimed at evaluating the effects of maternal exposure to potassium cyanide (KCN) during lactation in goats. Twenty-seven lactating female goats were orally dosed with 0 (control), 1.0, 2.0, or 3.0 mg KCN/kg body weight/day from lactation days 0 to 90. After this period, all male kids and one mother from each group were killed for a pathological study. Cyanide treatment promoted the clinical signs of maternal toxicity in the highest KCN group but did not affect body weight. Both cyanide and thiocyanate presented increased levels in both dams and kids from the treated groups. Microscopic lesions, but without alterations on the biochemical panel, were found in the brain, thyroid, liver, and kidneys of both dams and kids from the treated groups. These findings suggest that lactating offspring can be indirectly intoxicated by maternal exposure to cyanide.

Relative role of heme nitrosylation and beta-cysteine 93 nitrosation in the transport and metabolism of nitric oxide by hemoglobin in the human circulation

To quantify the reactions of nitric oxide (NO) with hemoglobin under physiological conditions and to test models of NO transport on hemoglobin, we have developed an assay to measure NO-hemoglobin reaction products in normal volunteers, under basal conditions and during NO inhalation. NO inhalation markedly raised total nitrosylated hemoglobin levels, with a significant arterial-venous gradient, supporting a role for hemoglobin in the transport and delivery of NO. The predominant species accounting for this arterial-venous gradient is nitrosyl(heme)hemoglobin. NO breathing increases S-nitrosation of hemoglobin beta-chain cysteine 93, however only to a fraction of the level of nitrosyl(heme)hemoglobin and without a detectable arterial-venous gradient. A strong correlation between methemoglobin and plasma nitrate formation was observed, suggesting that NO metabolism is a primary physiological cause of hemoglobin oxidation. Our results demonstrate that NO-heme reaction pathways predominate in vivo, NO binding to heme groups is a rapidly reversible process, and S-nitrosohemoglobin formation is probably not a primary transport mechanism for NO but may facilitate NO release from heme.

Acute cyanide poisoning: a case report with toxicokinetic study

Cyanide poisoning is a life threatening condition. But specific antidotes exist and can be easily prepared from available substances in hospital. Administration of antidotes will produce methemoglobin, which itself causes hypoxia. Nitrite induced methemoglobin can be extremely dangerous and even lethal. Before administering the antidotes, the diagnosis should be confirmed. Nitrite should not be given if the poisoning is mild or diagnosis is uncertain, to avoid excessive methemoglobin, dosage of sodium nitrite must be adjusted according to hemoglobin level (Table 1). Usage of sodium nitrite and sodium thiosulfate in the recommended doses are safe and effective for cyanide poisoning.

Toxicokinetic aspects of chronic cyanide exposure in the rat

Rats received 40, 80 and 160 mg KCN/kg body wt./24 h in the drinking water for 13 weeks. Fairly constant dose-related cyanide and thiocyanate levels were measured in blood, plasma and urine during the exposure. Blood cyanide concentrations were in the range of 16.0-25.5 nmol CN-/ml blood, thiocyanate concentrations in the range of 341-877 nmol SCN-/ml plasma following continuous administration of the maximum tolerated dose-level of 160 mg/kg body wt/24 h. The results suggest that continuous 13-week maximum tolerated cyanide exposure does not lead to saturation of cyanide detoxification pathways.

Pattern of enzyme changes in rabbits administered linamarin or potassium cyanide

Diseases like tropical ataxic neuropathy and endemic goitre have been reported to have definite correlation with a chronic ingestion of cassava (Manihot esculenta Crantz). The toxicity of cassava has been attributed to its two cyanogenic glycosides, linamarin and lotaustralin. In this study, an attempt has been made to understand the pattern of changes in certain clinically significant enzymes brought about by the chronic administration of sublethal doses of linamarin to rabbits. The profound elevation in rhodanese activity observed in the linamarin and cyanide treated rabbits indicated the attempt of the tissues to detoxify cyanide. That intact linamarin could be hydrolysed in vivo was a significant finding from the study. The mode of toxicity of linamarin was similar to that of cyanide by producing a gradual shift from aerobic to anaerobic metabolism.

Pharmacokinetics of intravenous potassium cyanide

The pharmacokinetics of intravenously injected potassium cyanide have been studied in Beagle bitches. In the period up to about 80 min after dosing, blood levels fell in a manner consistent with first-order elimination kinetics. Thereafter blood cyanide concentrations fell at a slower rate, indicating that a second phase of slower elimination had been entered.