Cyanide Detoxification in Rats Exposed to Acetonitrile and Fed a Low Protein Diet

doi:10.1006/faat.1996.0107

Fundamental and Applied Toxicology

Volume 32, Issue 1, July 1996, Pages 66-71

Fundamental and Appl...

https://doi.org/10.1006/faat.1996.0107 Get rights and content

Abstract

Different neurological syndromes have been associated with exposure to cyanide. Dietary cyanide exposure from cassava roots combined with a low intake of the sulfur amino acids necessary for cyanide detoxification has been implicated in the causation of konzo, an upper motoneuron disease identified in Africa. We have investigated the effect of a low protein diet on the capacity for cyanide detoxification. Rats were fed normal chow containing 18% protein or a low protein diet with 5% protein. To expose rats to cyanide the drinking water was supplemented with 40 or 80 mMacetonitrile (CH₃CN) for up to 4 weeks. Weight gain was monitored and 24-hr urines were collected for analyses of total sulfur, inorganic sulfate, thiocyanate, and 2-aminothiolazine-4-carboxylic acid (ATC). Blood was collected for analyses of cyanide and cyanate. Rats on a normal diet grew throughout the experiment, while those on a low protein diet initially lost weight and then stabilized at a constant weight. Rats exposed to acetonitrile all progressively lost weight, those on a low protein diet at the highest rate. Signs of neurological damage were not observed. Rats not exposed to acetonitrile excreted <0.2% of sulfur as thiocyanate and those on a low protein diet reduced their total sulfur excretion to one-third that of rats on the normal diet. Rats on the normal diet did not change total sulfur excretion during exposure to acetonitrile, although thiocyanate now contributed more than two-thirds of excreted sulfur. Rats on a low protein diet exposed to acetonitrile increased both total sulfur and thiocyanate excretion to the levels of rats on a normal diet. Rats exposed to acetonitrile had manyfold increases of circulating concentrations of cyanide and cyanate and of urinary excretion of ATC. There was a positive correlation between blood cyanide concentrations and the plasma concentration of cyanate. It is concluded that the rat has a high capacity for detoxification of cyanide. During adaptation to a low protein intake, sulfur is conserved but cyanide detoxification is still possible at the cost of extensive protein catabolism. It is thus possible that subclinical cyanide exposure could interfere with normal growth and development. The observation of a relationship between circulating cyanide on the one hand and circulating cyanate and urinary excretion of ATC on the other highlights the possibility that cyanide metabolites may mediate neurotoxic effects of cyanide.

References (0)

Cited by (23)

On the biomarkers and mechanisms of konzo, a distinct upper motor neuron disease associated with food (cassava) cyanogenic exposure
2011, Food and Chemical Toxicology
Citation Excerpt :
CN is also converted into trace amounts of cyanate (OCN) and 2-aminothiazoline-4-carboxylic acid (ATCA). Under conditions of SAA-deficiency, oxidative detoxification pathways are favored and there is increased production of OCN (Swenne et al., 1996; Tor-Agbidye et al., 1999). The identities of the neurotoxic agent(s) that trigger motor-system degeneration are not known.
Konzo is a self-limiting central motor-system disease associated with food dependency on cassava and low dietary intake of sulfur amino acids (SAA). Under conditions of SAA-deficiency, ingested cassava cyanogens yield metabolites that include thiocyanate and cyanate, a protein-carbamoylating agent. We studied the physical and biochemical modifications of rat serum and spinal cord proteins arising from intoxication of young adult rats with 50–200 mg/kg linamarin, or 200 mg/kg sodium cyanate (NaOCN), or vehicle (saline) and fed either a normal amino acid- or SAA-deficient diet for up to 2 weeks. Animals under SAA-deficient diet and treatment with linamarin or NaOCN developed hind limb tremors or motor weakness, respectively. LC/MS–MS analysis revealed differential albumin carbamoylation in animals treated with NaOCN, vs. linamarin/SAA-deficient diet, or vehicle. 2D-DIGE and MALDI-TOF/MS–MS analysis of the spinal cord proteome showed differential expression of proteins involved in oxidative mechanisms (e.g. peroxiredoxin 6), endocytic vesicular trafficking (e.g. dynamin 1), protein folding (e.g. protein disulfide isomerase), and maintenance of the cytoskeleton integrity (e.g. α-spectrin). Studies are needed to elucidate the role of the aformentioned modifications in the pathogenesis of cassava-associated motor-system disease.
A new unifying hypothesis for lathyrism, konzo and tropical ataxic neuropathy: Nitriles are the causative agents
2011, Food and Chemical Toxicology
Citation Excerpt :
Recently, the low sulfur amino acid content of grass pea has also been reported, leading to the hypothesis that this deficiency may also play a role in lathyrism (Getahun et al., 2005) in addition to konzo. The cyanide-metabolite hypothesis for konzo and the ODAP hypothesis for lathyrism have been addressed in a number of animal studies (Swenne et al., 1996; Tor-Agbidye et al., 1999a,b; Spencer et al., 1986; Kusama-Eguchi et al., 2005), but the data obtained are not conclusive. In the case of TAN, a causative role for cassava cyanogens has been proposed (see, for instance, Onabolu et al., 2002), but no precise hypothesis has been posited regarding the mechanisms involved in its pathogenesis.
Konzo and lathyrism are associated with consumption of cassava and grass pea, respectively. Cassava consumption has also been associated with a third disease, tropical ataxic neuropathy (TAN). This review presents a new unifying hypothesis on the causative agents for these diseases: namely, that they are nitriles, compounds containing cyano groups. The diseases may be caused by different but similar nitriles through direct neurotoxic actions not mediated by systemic cyanide release. Both cassava and Lathyrus contain nitriles, and other unidentified nitriles can be generated during food processing or in the human body. Available data indicate that several small nitriles cause a variety of neurotoxic effects. In experimental animals, 3,3′-iminodipropionitrile (IDPN), allylnitrile and cis-crotononitrile cause sensory toxicity, whereas hexadienenitrile and trans-crotononitrile induce selective neuronal degeneration in discrete brain regions. IDPN also induces a neurofilamentous axonopathy, and dimethylaminopropionitrile is known to cause autonomic (genito-urinary) neurotoxicity in both humans and rodents. Some of these actions depend on metabolic bioactivation of the parental nitriles, and sex- and species-dependent differences in susceptibility have been recorded. Recently, neuronal degeneration has been found in rats exposed to acetone cyanohydrin. Taken together, the neurotoxic properties of nitriles make them excellent candidates as causative agents for konzo, lathyrism and TAN.
The targets of acetone cyanohydrin neurotoxicity in the rat are not the ones expected in an animal model of konzo
2010, Neurotoxicology and Teratology
Citation Excerpt :
The second is that deficient intake of sulphur aminoacids may compromise cyanide metabolism to thiocyanate by rhodanese [14]. The attempts to explore these hypotheses [40–42] have not provided an animal model of konzo. The aim of this study was to explore an alternative hypothesis, namely that acetone cyanohydrin is the causative agent for konzo.
Konzo is a neurotoxic motor disease caused by excess consumption of insufficiently processed cassava. Cassava contains the cyanogenic glucoside linamarin, but konzo does not present the known pathological effects of cyanide. We hypothesized that the aglycone of linamarin, acetone cyanohydrin, may be the cause of konzo. This nitrile rapidly decomposes into cyanide and acetone, but the particular exposure and nutrition conditions involved in the emergence of konzo may favor its stabilization and subsequent acute neurotoxicity. A number of preliminary observations were used to design an experiment to test this hypothesis. In the experiment, young female Long–Evans rats were given 10 mM acetone cyanohydrin in drinking water for 2 weeks, and then 20 mM for 6 weeks. Nutrition deficits associated with konzo were modeled by providing tapioca (cassava starch) as food for the last 3 of these weeks. After this period, rats were fasted for 24 h in order to increase endogenous acetone synthesis, and then exposed to 0 (control group) or 50 μmol/kg-h of acetone cyanohydrin for 24 h (treated group) through subcutaneous osmotic minipump infusion (n = 6/group). Motor activity and gait were evaluated before exposure (pre-test), and 1 and 6 days after exposure. Brains (n = 4) were stained for neuronal degeneration by fluoro-jade B. Rats exposed to 50 μmol/kg-h of acetone cyanohydrin showed acute signs of toxicity, but no persistent motor deficits. Two animals showed fluoro-jade staining in discrete thalamic nuclei, including the paraventricular and the ventral reuniens nuclei; one also exhibited labeling of the dorsal endopiriform nucleus. Similar effects were not elicited by equimolar KCN exposure. Therefore, acetone cyanohydrin may cause selective neuronal degeneration in the rat, but the affected areas are not those expected in an animal model of konzo.
Neurological diseases associated with intake of cassava varieties with high gluconitrile content
2004, Endocrinologia y Nutricion
Food plants often contain toxic compounds. Food processing is normally adapted to ensure safe consumption. However, in some circumstances, these toxic compounds cause diseases, especially neurological disorders. An important example is that of cassava, the main source of starch in many tropical regions. Cassava contains two gluconitrile, linamarin and lotaustralin, which can break down to cyanide. Epidemiological data associate cassava consumption with hypothyroidism and with two very different neurological diseases. These are tropical ataxic neuropathy (TAN), a polyneuropathy with sensorineural hearing loss and optic atrophy, and konzo, a spastic paraparesis. TAN and konzo are associated with two distinct patterns of cassava consumption. TAN is a chronic disease, appearing in people over 40 years old is areas of Nigeria in which a monotonous diet with cassava as the main component is common. Konzo affects mainly women and children; it appears abruptly during periods of alimentary in which cassava is almost the only food available. The pathogenic mechanisms of both TAN and konzo are unknown. The dietary origin of TAN has not yet been fully demonstrated. There is no doubt that konzo is a toxic-nutritional disease associated with cassava; however, the simplest hypothesis attributing a causal role to cyanide does not seem valid.
Los alimentos vegetales contienen, con frecuencia, compuestos tóxicos. En condiciones normales, el procesamiento de dichos alimentos está adaptado para permitir su consumo seguro. Sin embargo, en determinadas circunstancias, estos tóxicos provocan la aparición de enfermedades, entre las que destacan las de tipo neurológico. Un caso importante es el de la mandioca o yuca, la principal fuente de fécula en múltiples regiones tropicales. La mandioca contiene los gluconitrilos linamarina y lotaustralina, cuya degradación genera cianuro. Datos epidemiológicos asocian el consumo de mandioca a hipotiroidismo y a 2 enfermedades neurológicas muy diferentes entre sí: la neuropatía atáxica tropical, una polineuropatía periférica que cursa con sordera sensitivoneural y atrofia óptica, y el konzo, una paraparesia espástica. La neuropatía atáxica tropical y el konzo se asocian a 2 patrones diferentes de consumo de mandioca. La neuropatía atáxica tropical es una enfermedad crónica, que se presenta en personas de más de 40 años en determinadas regiones de Nigeria en las que se da una dieta monótona predominada por la mandioca. El konzo es una enfermedad que afecta preferentemente a niños y mujeres y que aparece de forma abrupta en períodos de crisis alimentaria, en los que la mandioca se mantiene prácticamente como el único alimento disponible. La patogenia de ambas enfermedades sigue sin esclarecerse. Para la neuropatía atáxica tropical, su origen alimentario no está suficientemente demostrado. En el caso del konzo, el origen tóxico-nutricional y la vinculación con la mandioca parecen indudables; sin embargo, la hipótesis más simple, la que supone un papel causal del cianuro, no parece cierta.
Konzo
2004, Handbook of Clinical Neurophysiology
Citation Excerpt :
Cyanide has been suggested as a causal factor because of its potential inhibitor effect on the mitochondrial energy transformation secondarily inducing neuronal dysfunction (Pettersen and Cohen, 1993), and thiocyanate, because of its potential action on the AMP (alpha-amino-3hydroxy- 5methyl-isoxazole-4-propionic acid) receptors (Arai et al., 1995; Hawkinson and Espitia, 1997), leading to excitotoxic effects and hence neuronal dysfunction or cell death. Cyanate is a potential causal factor of konzo because it may carbamoylate neural proteins and lead to functional or structural neuronal changes (Shaw et al., 1974; Kuckel et al., 1993; Swenne et al., 1996; Kraus and Krauss, 1998). 2-Iminothiazolidine-4-carboxylic acid is among the candidates responsible for konzo because it shows neurological effects (seizures and hippocampal damage) in experimental studies (Bitner et al., 1997; Spencer, 1999).
Konzo is a permanent spastic paraparesis or tetraparesis of abrupt onset. Konzo occurs among the undernourished populations of poor rural areas. The severity of konzo is graded as mild when the subject is able to walk without support, moderate when the subject has to use one or two sticks, and severe when the subject is unable to walk. The onset of konzo is sudden, without prodromata. The initial symptoms of konzo are trembling or cramping in the legs, heaviness or weakness of the legs, and a tendency to fall or an inability to stand. Investigations of konzo support two conflicting etiological hypotheses. The first relates to infectious agents and the second to toxico-nutritional factors. While an infectious etiology is highly improbable, a toxico-nutritional etiology is strongly supported by both clinical and epidemiological studies. Somatosensory evoked potential (SEP) abnormalities do not correlate with the severity of konzo, the duration of the disease, or the occurrence of sensory symptoms at the onset of the disease. Not all the clinical or electrophysiological abnormalities of konzo are explicable on the basis of a cortical motor disorder.
Induction by nitriles of sex chromosome aneuploidy: Tests of mechanism
1998, Mutation Research - Fundamental and Molecular Mechanisms of Mutagenesis
Genetic and biochemical assays were conducted to determine if nitrile induced adult paralysis and germline aneuploidy in female Drosophila melanogaster requires a biochemical activation mechanism which results in the release of free cyanide. Two nitriles predicted to differ substantially in their susceptibility to enzymatic cyanide release were found to be equally effective inducers of aneuploidy. Regardless of differences in chemical structure, nitriles seem to be affecting a common cellular target as judged by the lack of synergistic effects when two nitriles are presented simultaneously. Mitochondrial respiration was not inhibited by acetonitrile under conditions in which sodium cyanide completely blocked respiration. A sensitive luciferase enzyme inhibition assay suggests that some, but not all, nitriles may affect hydrophobic protein interactions. These results suggest that there is no single biochemical mechanism by which all nitriles induced aneuploidy, although the cellular target disrupted is probably the same for each chemical. The implications of these findings for structural alert based pre-screening of mutagens are discussed.

View all citing articles on Scopus

View full text

Regular ArticleCyanide Detoxification in Rats Exposed to Acetonitrile and Fed a Low Protein Diet

Abstract

Regular Article
Cyanide Detoxification in Rats Exposed to Acetonitrile and Fed a Low Protein Diet