A Review on Ingested Cyanide: Risks, Clinical Presentation, Diagnostics, and Treatment Challenges.

Cyanide, a metabolic poison, is a rising chemial threat and ingestion is the most common route of exposure. Terrorist organizations have threatened to attack the USA and international food and water supplies. The toxicokinetics and toxicodynamics of oral cyanide are unique, resulting in high-dose exposures, severe symptoms, and slower onset of symptoms. There are no FDA-approved therapies tested for oral cyanide ingestions and no approved intramuscular or oral therapies, which would be valuable in mass casualty settings. The aim of this review is to evaluate the risks of oral cyanide and its unique toxicokinetics, as well as address the lack of available rapid diagnostics and treatments for mass casualty events. We will also review current strategies for developing new therapies. A review of the literature using the PRISMA checklist detected 7284 articles, screened 1091, and included 59 articles or other reports. Articles referenced in this review were specific to risk, clinical presentation, diagnostics, current treatments, and developing therapies. Current diagnostics of cyanide exposure can take hours or days, which can delay treatment. Moreover, current therapies for cyanide poisoning are administered intravenously and are not specifically tested for oral exposures, which can result in higher cyanide doses and unique toxicodynamics. New therapies developed for oral cyanide exposures that are easily delivered, safe, and can be administered quickly by first responders in a mass casualty event are needed. Current research is aimed at identifying an antidote that is safe, effective, easy to administer, and has a rapid onset of action.

The potential use of 2-aminothiazoline-4-carboxylic acid (ATCA) as a forensic marker for cyanide exposure in medicolegal death investigation: A review.

Cyanide (CN) is one of the most toxic of all substances and can be found in various natural and anthropogenic sources. Sensitive and effective methods for the confirmation of CN exposure are crucial in medical, military, and forensic settings. Due to its high volatility and reactivity, direct detection of CN from postmortem samples could raise inconclusive interpretation issues that may hinder accurate determination of the cause of death. The detection of the alternative CN metabolites as markers to test CN exposure may offer a solution to reduce the potential for false-negative and false-positive results. 2-Aminothiazoline-4-carboxylic acid (ATCA) is a minor metabolite of CN and has been proposed to be a potential alternative forensic marker for the confirmation of CN exposure. According to the current state of knowledge, ATCA has not yet been associated with other metabolic pathways except for CN detoxification. Moreover, ATCA is stable under various conditions over time. This article reviews analytical methods developed for the analysis of ATCA as well as studies related to potential use of ATCA as a marker for the diagnosis of CN exposure. The need for research related to the use of ATCA as a reliable forensic marker for CN exposure in medicolegal death investigations is also discussed.

Biomonitoring Equivalents for cyanide.

Exposure to cyanide is widespread in human populations due to a variety of natural and anthropogenic sources. The potential health risks of excess cyanide exposure are dose-dependent and include effects on the thyroid, the male reproductive system, developmental effects, neuropathies and death. Many organizations have derived exposure guideline values for cyanide, which represent maximum recommended exposure levels for inhalation and oral routes of exposure. Biomonitoring Equivalents (BEs) are estimates of the average biomarker concentrations that correspond to these reference doses. Here, we determine BE values for cyanide. The literature on the pharmacokinetics of cyanide was reviewed to identify a biomarker of exposure. Despite issues with biomarker specificity, thiocyanate (SCN-) in the urine or plasma was identified as the most practical biomarker. BE values were produced that correspond to previously published critical effect levels. These BE values range from 0.0008 to 0.8 mg/L and 0.0005-2.5 mg/L for SCN- in urine and plasma, respectively. Confidence in these BE values varies, depending on route of exposure, biomarker, and health endpoint of interest. We anticipate that these BE values will be useful for lower tier (screening level) chemical risk assessment; however due to issues with biomarker specificity and uncertainty in background levels of SCN-, this approach requires refinement to be useful at higher tiers.

Bioavailability of cyanide after consumption of a single meal of foods containing high levels of cyanogenic glycosides: a crossover study in humans.

The acute toxicity of cyanide is determined by its peak levels reached in the body. Compared to the ingestion of free cyanide, lower peak levels may be expected after consumption of foods containing cyanogenic glycosides with the same equivalent dose of cyanide. This is due to possible delayed and/or incomplete release of cyanide from the cyanogenic glycosides depending on many factors. Data on bioavailability of cyanide after consumption of foods containing high levels of cyanogenic glycosides as presented herein were necessary to allow a meaningful risk assessment for these foods. A crossover study was carried out in 12 healthy adults who consumed persipan paste (equivalent total cyanide: 68 mg/kg), linseed (220 mg/kg), bitter apricot kernels (about 3250 mg/kg), and fresh cassava roots (76-150 mg/kg), with each "meal" containing equivalents of 6.8 mg cyanide. Cyanide levels were determined in whole blood using a GC-MS method with K(13)C(15)N as internal standard. Mean levels of cyanide at the different time points were highest after consumption of cassava (15.4 µM, after 37.5 min) and bitter apricot kernels (14.3 µM, after 20 min), followed by linseed (5.7 µM, after 40 min) and 100 g persipan (1.3 µM, after 105 min). The double dose of 13.6 mg cyanide eaten with 200 g persipan paste resulted in a mean peak level of 2.9 µM (after 150 min). An acute reference dose of 0.075 mg/kg body weight was derived being valid for a single application/meal of cyanides or hydrocyanic acid as well as of unprocessed foods with cyanogenic glycosides also containing the accompanying intact ß-glucosidase. For some of these foods, this approach may be overly conservative due to delayed release of cyanide, as demonstrated for linseed. In case of missing or inactivated ß-glucosidase, the hazard potential is much lower.

Roles of Sulfur Metabolism and Rhodanese in Detoxification and Anti-Oxidative Stress Functions in the Liver: Responses to Radiation Exposure.

Organisms must confront various environmental stresses. The liver is central to protecting against such stresses in mammals, and it has many detoxification and anti-oxidative stress functions. Radiation is a source of oxidative stress and is known to affect the liver and induce anti-oxidative responses. The detoxification enzyme rhodanese, which is also called thiosulfate sulfurtransferase (TST), has been demonstrated to be induced in the liver in response to radiation. Cyanide detoxification is a function of the liver, and rhodanese is a key enzyme involved in sulfur metabolism in that detoxification. Though the anti-oxidative stress system in which sulfur molecules such as thiol compounds are involved has attracted attention as a defense against radiation, detoxification enzymes may have other roles in this defense. Understanding how these functions are affected by alterations of sulfur metabolism (including thiol compounds) after irradiation would help uncover their roles in defense against cancer and other deleterious health effects, as well as environmental stress responses. This article reviews the roles of sulfur-related metabolism in oxidative stress regulation and detoxification for recovery from liver damage after radiation exposure, with particular attention to recent findings of sulfur-related enzymes such as rhodanese, which is unique in sulfur metabolism.

Cyanide toxicokinetics: the behavior of cyanide, thiocyanate and 2-amino-2-thiazoline-4-carboxylic acid in multiple animal models.

Cyanide causes toxic effects by inhibiting cytochrome c oxidase, resulting in cellular hypoxia and cytotoxic anoxia, and can eventually lead to death. Cyanide exposure can be verified by direct analysis of cyanide concentrations or analyzing its metabolites, including thiocyanate (SCN(-)) and 2-amino-2-thiazoline-4-carboxylic acid (ATCA) in blood. To determine the behavior of these markers following cyanide exposure, a toxicokinetics study was performed in three animal models: (i) rats (250-300 g), (ii) rabbits (3.5-4.2 kg) and (iii) swine (47-54 kg). Cyanide reached a maximum in blood and declined rapidly in each animal model as it was absorbed, distributed, metabolized and eliminated. Thiocyanate concentrations rose more slowly as cyanide was enzymatically converted to SCN(-). Concentrations of ATCA did not rise significantly above the baseline in the rat model, but rose quickly in rabbits (up to a 40-fold increase) and swine (up to a 3-fold increase) and then fell rapidly, generally following the relative behavior of cyanide. Rats were administered cyanide subcutaneously and the apparent half-life (t1/2) was determined to be 1,510 min. Rabbits were administered cyanide intravenously and the t1/2 was determined to be 177 min. Swine were administered cyanide intravenously and the t1/2 was determined to be 26.9 min. The SCN(-) t1/2 in rats was 3,010 min, but was not calculated in rabbits and swine because SCN(-) concentrations did not reach a maximum. The t1/2 of ATCA was 40.7 and 13.9 min in rabbits and swine, respectively, while it could not be determined in rats with confidence. The current study suggests that cyanide exposure may be verified shortly after exposure by determining significantly elevated cyanide and SCN(-) in each animal model and ATCA may be used when the ATCA detoxification pathway is significant.

Cross-species and tissue variations in cyanide detoxification rates in rodents and non-human primates on protein-restricted diet.

We sought to elucidate the impact of diet, cyanide or cyanate exposure on mammalian cyanide detoxification capabilities (CDC). Male rats (~8 weeks old) (N=52) on 75% sulfur amino acid (SAA)-deficient diet were treated with NaCN (2.5mg/kg bw) or NaOCN (50mg/kg bw) for 6 weeks. Macaca fascicularis monkeys (~12 years old) (N=12) were exclusively fed cassava for 5 weeks. CDC was assessed in plasma, or spinal cord, or brain. In rats, NaCN induced seizures under SAA-restricted diet whereas NaOCN induced motor deficits. No deficits were observed in non-human primates. Under normal diet, the CDC were up to ~80× faster in the nervous system (14 ms to produce one µmol of thiocyanate from the detoxification of cyanide) relative to plasma. Spinal cord CDC was impaired by NaCN, NaOCN, or SAA deficiency. In M. fascicularis, plasma CDC changed proportionally to total proteins (r=0.43; p<0.001). The plasma CDC was ~2× relative to that of rodents. The nervous system susceptibility to cyanide may result from a "multiple hit" by the toxicity of cyanide or its cyanate metabolite, the influences of dietary deficiencies, and the tissue variations in CDC. Chronic dietary reliance on cassava may cause metabolic derangement including poor CDC.

Toxicological analysis of formalin-fixed or embalmed tissues: a review.

During the autopsy of forensic cases, when there is no suspicion of drug use or chemical exposure, biological fluids may not be obtained for toxicological analysis, while specimens of tissues may be collected and preserved in a formalin solution for histological examination. When specific questions arise after the burial, the only possible options are the exhumation of an embalmed body or the toxicological analysis of the formalin-fixed specimens. The drug concentrations in these specimens can be altered due to the extraction efficiency and/or the chemical activity of the formalin solutions used during chemical fixation or embalming process. The aim of this paper is to review the published studies about the determination of specific groups of drugs in formalin-fixed or embalmed specimens and their stability after chemical fixation or embalming process. The analytical aspects of this determination are also discussed. The stability of drugs in formalin environment and the possible reaction of the drugs with formaldehyde, which is a highly reactive chemical substance, should always be considered during post-mortem/post-embalming forensic analysis. The additional analysis of the formalin solution in which the tissue was preserved is considered necessary. The identification and the evaluation of the possible degradation products or chemical derivatives are extremely useful during the interpretation of the results.

Comparison of cyanide exposure markers in the biofluids of smokers and non-smokers.

Cyanide is highly toxic and is present in many foods, combustion products (e.g. cigarette smoke), industrial processes, and has been used as a terrorist weapon. In this study, cyanide and its major metabolites, thiocyanate and 2-amino-2-thiazoline-4-carboxylic acid (ATCA), were analyzed from various human biofluids of smokers (low-level chronic cyanide exposure group) and non-smokers to gain insight into the relationship of these biomarkers to cyanide exposure. The concentrations of each biomarker tested were elevated for smokers in each biofluid. Significant differences (p < 0.05) were found for thiocyanate in plasma and urine, and ATCA showed significant differences in plasma and saliva. Additionally, biomarker concentration ratios, correlations between markers of cyanide exposure, and other statistical methods were performed to better understand the relationship between cyanide and its metabolites. Of the markers studied, the results indicate plasma ATCA, in particular, showed excellent promise as a biomarker for chronic low-level cyanide exposure.

Structure of soybean ß-cyanoalanine synthase and the molecular basis for cyanide detoxification in plants.

Plants produce cyanide (CN-) during ethylene biosynthesis in the mitochondria and require ß-cyanoalanine synthase (CAS) for CN- detoxification. Recent studies show that CAS is a member of the ß-substituted alanine synthase (BSAS) family, which also includes the Cys biosynthesis enzyme O-acetylserine sulfhydrylase (OASS), but how the BSAS evolved distinct metabolic functions is not understood. Here we show that soybean (Glycine max) CAS and OASS form α-aminoacrylate reaction intermediates from Cys and O-acetylserine, respectively. To understand the molecular evolution of CAS and OASS in the BSAS enzyme family, the crystal structures of Gm-CAS and the Gm-CAS K95A mutant with a linked pyridoxal phosphate (PLP)-Cys molecule in the active site were determined. These structures establish a common fold for the plant BSAS family and reveal a substrate-induced conformational change that encloses the active site for catalysis. Comparison of CAS and OASS identified residues that covary in the PLP binding site. The Gm-OASS T81M, S181M, and T185S mutants altered the ratio of OASS:CAS activity but did not convert substrate preference to that of a CAS. Generation of a triple mutant Gm-OASS successfully switched reaction chemistry to that of a CAS. This study provides new molecular insight into the evolution of diverse enzyme functions across the BSAS family in plants.

Bioavailability of cyanide and metal-cyanide mixtures to aquatic life.

Cyanide can be toxic to aquatic organisms, and the U.S. Environmental Protection Agency has developed ambient water-quality criteria to protect aquatic life. Recent work suggests that considering free, rather than total, cyanide provides a more accurate measure of the biological effects of cyanides and provides a basis for water-quality criteria. Aquatic organisms are sensitive to free cyanide, although certain metals can form stable complexes and reduce the amount of free cyanide. As a result, total cyanide is less toxic when complexing metals are present. Cyanide is often present in complex effluents, which requires understanding how other components within these complex effluents can affect cyanide speciation and bioavailability. The authors have developed a model to predict the aqueous speciation of cyanide and have shown that this model can predict the toxicity of metal-cyanide complexes in terms of free cyanide in solutions with varying water chemistry. Toxicity endpoints based on total cyanide ranged over several orders of magnitude for various metal-cyanide mixtures. However, predicted free cyanide concentrations among these same tests described the observed toxicity data to within a factor of 2. Aquatic toxicity can be well-described using free cyanide, and under certain conditions the toxicity was jointly described by free cyanide and elevated levels of bioavailable metals.

Excreted thiocyanate detects live reef fishes illegally collected using cyanide--a non-invasive and non-destructive testing approach.

Cyanide fishing is a method employed to capture marine fish alive on coral reefs. They are shipped to markets for human consumption in Southeast Asia, as well as to supply the marine aquarium trade worldwide. Although several techniques can be used to detect cyanide in reef fish, there is still no testing method that can be used to survey the whole supply chain. Most methods for cyanide detection are time-consuming and require the sacrifice of the sampled fish. Thiocyanate anion (SCN(-)) is a metabolite produced by the main metabolic pathway for cyanide anion (CN(-)) detoxification. Our study employed an optical fiber (OF) methodology (analytical time <6 min) to detect SCN(-) in a non-invasive and non-destructive manner. Our OF methodology is able to detect trace levels (>3.16 µg L(-1)) of SCN(-) in seawater. Given that marine fish exposed to cyanide excrete SCN(-) in the urine, elevated levels of SCN(-) present in the seawater holding live reef fish indicate that the surveyed specimens were likely exposed to cyanide. In our study, captive-bred clownfish (Amphiprion clarkii) pulse exposed for 60 s to either 12.5 or 25 mg L(-1) of CN(-) excreted up to 6.96±0.03 and 9.84±0.03 µg L(-1) of SCN(-), respectively, during the 28 days following exposure. No detectable levels of SCN(-) were recorded in the water holding control organisms not exposed to CN(-), or in synthetic seawater lacking fish. While further research is necessary, our methodology can allow a rapid detection of SCN(-) in the holding water and can be used as a screening tool to indicate if live reef fish were collected with cyanide.

Heated indoor swimming pools, infants, and the pathogenesis of adolescent idiopathic scoliosis: a neurogenic hypothesis.

BACKGROUND: In a case-control study a statistically significant association was recorded between the introduction of infants to heated indoor swimming pools and the development of adolescent idiopathic scoliosis (AIS). In this paper, a neurogenic hypothesis is formulated to explain how toxins produced by chlorine in such pools may act deleteriously on the infant's immature central nervous system, comprising brain and spinal cord, to produce the deformity of AIS. PRESENTATION OF THE HYPOTHESIS: Through vulnerability of the developing central nervous system to circulating toxins, and because of delayed epigenetic effects, the trunk deformity of AIS does not become evident until adolescence. In mature healthy swimmers using such pools, the circulating neurotoxins detected are chloroform, bromodichloromethane, dibromochloromethane, and bromoform. Cyanogen chloride and dichloroacetonitrile have also been detected. TESTING THE HYPOTHESIS: In infants, the putative portals of entry to the blood could be dermal, oral, or respiratory; and entry of such circulating small molecules to the brain are via the blood-brain barrier, blood-cerebrospinal fluid barrier, and circumventricular organs. Barrier mechanisms of the developing brain differ from those of adult brain and have been linked to brain development. During the first 6 months of life cerebrospinal fluid contains higher concentrations of specific proteins relative to plasma, attributed to mechanisms continued from fetal brain development rather than immaturity. IMPLICATIONS OF THE HYPOTHESIS: The hypothesis can be tested. If confirmed, there is potential to prevent some children from developing AIS.

Impact of functionalized coligands on the pharmacokinetics of 99mTcIII '4+1' mixed-ligand complexes conjugated to bombesin.

Bombesins (BN) containing (99m)Tc '4+1' complexes may be useful to detect tumors expressing the gastrin-releasing peptide receptor (GRPR). Derivatives of the formula [(99m)Tc(NS(3)R)(L2-BN(st))] were synthesized, in which Tc(III) is coordinated by an isocyanide L2-BN(st) bearing the peptide (BN(st)=ßAla-ßAla-Gln-Trp-Ala-Val-Gly-His-Cha-Nle-NH(2)) and a tetradentate chelator NS(3)R. NS(3)R consists of 2,2',2″-nitrilotriethanethiol (NS(3)) bearing a crown ether (NS(3)crown), an aliphatic amine (NS(3)en) and a tricarboxylic acid (NS(3)(COOH)(3)). Non-radioactive Re compounds were prepared and analysed by electrospray ionization mass spectrometry. The structural similarity to the (99m)Tc conjugates was demonstrated by their identical HPLC elution profiles. The lipophilicity of [(99m)Tc(NS(3)R)(L2-BN(st))] decreased depending on the coligands NS(3)crown (log D(O/W), pH=7.4, 0.98 ± 0.11), NS(3)en (-0.49 ± 0.07) and NS(3)(COOH)(3) (-2.01 ± 0.09). Biodistribution in normal rats was characterized by an increasing kidney uptake and a decreasing uptake into the liver corresponding to the reduced lipophilicity of the conjugates. The pancreatic uptake expressed by the organ/blood ratio of standardized uptake values at 60 min p.i. in rats was 8.6 ± 1.2 for [(99m)Tc(NS(3)en)(L2-BN(st))] and higher compared to the other conjugates. The pancreas/liver ratio of the SUV at 60 min p.i. in rats was highest for [(99m)Tc(NS(3)(COOH)(3))(L2-BN(st))] at 8.4 ± 1.3. [(99m)Tc(NS(3)en)(L2-BN(st))] was further studied in tumor-bearing mice and its pancreas/blood and pancreas/liver ratios were lower, however the pancreas/kidney ratios were higher in mice compared to rats. The activity uptake of [(99m)Tc(NS(3)en)(L2-BN(st))] into the PC-3 tumor xenografts was low (%ID/g: 0.83 ± 0.18 at 60 min; SUV: 0.21 ± 0.05 at 60 min) but specific.

Cobinamide is superior to other treatments in a mouse model of cyanide poisoning.

CONTEXT: Cyanide is a rapidly acting cellular poison, primarily targeting cytochrome c oxidase, and is a common occupational and residential toxin, mostly via smoke inhalation. Cyanide is also a potential weapon of mass destruction, with recent credible threats of attacks focusing the need for better treatments, as current cyanide antidotes are limited and impractical for rapid deployment in mass casualty settings. OBJECTIVE: We have used mouse models of cyanide poisoning to compare the efficacy of cobinamide (Cbi), the precursor to cobalamin (vitamin B(12)), to currently approved cyanide antidotes. Cbi has extremely high affinity for cyanide and substantial solubility in water. MATERIALS AND METHODS: We studied Cbi in both an inhaled and intraperitoneal model of cyanide poisoning in mice. RESULTS: We found Cbi more effective than hydroxocobalamin, sodium thiosulfate, sodium nitrite, and the combination of sodium thiosulfate-sodium nitrite in treating cyanide poisoning. Compared to hydroxocobalamin, Cbi was 3 and 11 times more potent in the intraperitoneal and inhalation models, respectively. Cobinamide sulfite (Cbi-SO(3)) was rapidly absorbed after intramuscular injection, and mice recovered from a lethal dose of cyanide even when given at a time when they had been apneic for over 2 min. In range-finding studies, Cbi-SO(3) at doses up to 2000 mg/kg exhibited no clinical toxicity. DISCUSSION AND CONCLUSION: These studies demonstrate that Cbi is a highly effective cyanide antidote in mouse models, and suggest it could be used in a mass casualty setting, because it can be given rapidly as an intramuscular injection when administered as Cbi-SO(3). Based on these animal data Cbi-SO(3) appears to be an antidote worthy of further testing as a therapy for mass casualties.

Differential role of CYP2E1-mediated metabolism in the lethal and vestibulotoxic effects of cis-crotononitrile in the mouse.

Several alkylnitriles are toxic to sensory systems, including the vestibular system, through yet undefined mechanisms. This study addressed the hypothesis that the vestibular toxicity of cis-crotononitrile depends on CYP2E1-mediated bioactivation. Wild-type (129S1) and CYP2E1-null female mice were exposed to cis-crotononitrile at 0, 2, 2.25 or 2.5 mmol/kg (p.o.) in either a baseline condition or following exposure to 1% acetone in drinking water to induce CYP2E1 expression. The exposed animals were assessed for vestibular toxicity using a behavioral test battery and through surface observation of the vestibular sensory epithelia by scanning electron microscopy. In parallel groups, concentrations of cis-crotononitrile and cyanide were assessed in whole blood. Contrary to our hypothesis, CYP2E1-null mice were slightly more susceptible to the vestibular toxicity of cis-crotononitrile than were control 129S1 mice. Similarly, rather than enhance vestibular toxicity, acetone pretreatment actually reduced it slightly in 129S1 controls, although not in CYP2E1-null mice. In addition, significant differences in mortality were recorded, with the greatest mortality occurring in 129S1 mice after acetone pretreatment. The highest mortality recorded in the 129S1+acetone mice was associated with the lowest blood concentrations of cis-crotononitrile and the highest concentrations of cyanide at 6 h after nitrile exposure, the time when deaths were initially recorded. We conclude that cis-crotononitrile is a CYP2E1 substrate as hypothesized, but that CYP2E1-mediated metabolism of this nitrile is not necessary for vestibular toxicity; rather, this metabolism constitutes a major pathway for cyanide release and subsequent lethality.

Spectrum of cyanide toxicity and allocation in Heliconius erato and Passiflora host plants.

The larvae of three races of Heliconius erato were fed various species of Passiflora containing varying levels of cyanoglucosides. The mortality rate of larvae and pupae rose when larvae were fed species of Passiflora capable of releasing larger quantities of cyanide. When larvae were fed species of Passiflora with these properties, the resulting adult butterflies also released higher levels of cyanide. This may serve as a defense mechanism. The compounds responsible for the release of cyanide were not evenly distributed throughout the adult butterfly's body. The thorax contained the highest concentration of cyanogenic substances, followed by the head, wings, and abdomen. The younger tissues of Passiflora plants had higher levels of cyanide-releasing compounds than stems and mature leaves. Cyanogenic glycoside distribution within the plants is consistent with optimal allocation theory. The levels of cyanide-releasing substances in plants varied depending on the season.

Development of a plant uptake model for cyanide.

A model for cyanide species uptake by willow (Salix eriocephala L. var. Michaux) was developed to interpret data from hydroponic experiments quantitatively. While the potential for cyanide phytoremediation has been demonstrated modeling will aid in determining plant processes that contribute to cyanide transport and metabolism in willow and will target specific physiological parameters for field-scale phytoremediation design and optimization. The objective of the model development was to gain insight into the relative role of different processes with respect to dissolved free and iron-complexed cyanide transport and assimilation in plants and to determine rates at which these processes occur within the willow plant under the experimental conditions. A physiologically-based model describing plant uptake, transport, and metabolism of cyanide species was developed to reflect the processes that influence the movement of cyanide into and throughout the plant. Plant compartmentalization (root, stem, and leaf) corresponded to the level of detail in the data collected via hydroponic experiments. Inclusion of more detailed intra- and intercellular processes would create a model inconsistent with the macroscale nature of the data. Mass balances around each compartment were developed via kinetic representations for the mass transfer processes and were combined to form a model describing the fate of cyanide species within plant-water systems.

Parameter estimation of a plant uptake model for cyanide: application to hydroponic data.

A plant uptake model is applied to describe free cyanide and ferrocyanide transport and fate in willow (Salix eriocephala var. Michaux) grown in hydroponics. The model is applied to experimental data to determine best-fit parameter values, their associated uncertainty, and their relative importance to field-scale phytoremediation applications. The fitted model results, using least-squares optimization of the observed log concentrations, indicate that free cyanide volatilization from leaf tissue and free cyanide cell wall adsorption were negligible. The free cyanide maximum uptake rate and assimilate (noncyanide 15N) first-order leaf loss rate were the only coefficients that significantly affected the model goodness of fit and were concurrently sensitive to data uncertainty in the parameter optimization. Saturation kinetics may be applicable for free cyanide uptake into plants, but not for ferrocyanide uptake, which may occur via preferential protein-mediated or inefficient transpiration stream uptake. Within the free cyanide system, the relative magnitudes of the saturation uptake parameters and the demonstration of an active role for plants in uptake relative to transpiration suggest the potential importance of preferential diffusion through the cell membranes as reported in the literature, rather than protein-mediated uptake. The fitted 13-parameter model matched the observed data well except for the predicted stem and leaf tissue assimilate concentrations, which were significantly underestimated, particularly in the free cyanide system. These low predicted values, combined with the slightly underestimated solution free cyanide removal, suggest that noncyanide 15N redistribution in phloem should be considered.

Pharmacokinetic-pharmacodynamic modelling of the schedule-dependent effect of the anti-cancer agent CHS 828 in a rat hollow fibre model.

N-(6-Chlorophenoxyhexyl)-N'-cyano-N''-4-pyridylguanidine (CHS 828) is a novel anticancer agent that shows schedule-dependent effects in vitro and in vivo, as well as in Phase I clinical trials. A rat hollow fibre model was used to investigate whether this dependency is due to pharmacokinetic and/or pharmacodynamic factors. The effect on two cell lines, MDA-MB-231 (breast cancer) and CCRF-CEM (leukaemia) were studied after CHS 828 was administered orally as a single dose or in a 5-day schedule, at different total dose levels. The 5-day schedules were associated with greater effects on both cell lines compared with single doses. A one-compartment pharmacokinetic model, with a half-life of 2.3h and a consecutive zero- and first-order process to describe dissolution and absorption, fit the concentration data. Pharmacokinetics were dose-dependent, as the fraction absorbed decreased with increasing dose. Clearance increased with accumulative exposure. Twenty hours after administration, concentrations started to increase again, probably due to coprophagy. Pharmacokinetic-pharmacodynamic models characterized the cell growth and cell kill over time and showed that schedule-dependent antitumour effects were present also when the dose-dependent pharmacokinetics were accounted for. The prolonged schedules of CHS 828 were therefore associated with greater antitumour effects than single doses of the same total exposure.