Bioactivation of cyanide to cyanate in sulfur amino acid deficiency: relevance to neurological disease in humans subsisting on cassava

Protein content and amino acid composition in the diet of Danish vegans: a cross-sectional study

BACKGROUND

A growing proportion of the population are replacing their dietary animal protein with plant protein. A particular example of this trend is the vegan diet, which excludes all food items of animal origin. However, the DIAAS score for individual plant proteins is generally lower than that of animal proteins due to an unbalanced amino acid composition and lower bioavailability. Care must therefore be taken to meet the nutritional recommendations in the daily food intake.

METHODS

A three-day dietary food record was carried out by 40 Danish vegans in a cross-sectional study. The data were analysed, with particular emphasis on protein requirements and the essential amino acid composition of the diet.

RESULTS

The protein recommendations were met on all three days by 60% of the participants. In contrast, 18% did not meet the protein recommendations on any of the three days and 7% met the recommendations on only one of the days. Lysine was the most limiting amino acid (only 50% met the recommendations every day) followed by the sulphur-containing amino acids (recommendations met by 67.5%), leucine and valine (recommendations met by 70%). Combining both the amount of protein and the intake of the essential amino acids showed that less than half of the participants met the recommendations on all three days (47.5%) and 35% did not meet the recommendations on any days or on one day only.

CONCLUSION

In conclusion, our study showed that many of the participants in the present study failed to meet the daily protein intake requirements, both on single days and on all three days. Furthermore, the food intake was found to have an inadequate amino acid composition and was particularly limited by the essential amino acids lysine, the sulphur-containing amino acids, and leucine and valine. This could be ascribed to the fact that only a limited number of protein sources were consumed during a day.

11C-Labeled Radiotracer for Noninvasive and Quantitative Assessment of the Thiocyanate Efflux System in the Brain

Thiocyanate (SCN^-) alters the potency of certain agonists for the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor, and dysfunctions in AMPA receptor signaling are considered to underlie a number of neurological diseases. While humans may be exposed to SCN^- from the environment, including food sources, a carrier-mediated system transports SCN^- from the brain into the blood and is an important regulator of SCN^- distribution in the central nervous system. The assessment of this SCN^- efflux system in the brain would thus be useful for understanding the mechanisms underlying the neurotoxicity of SCN^- and for elucidating the relationship between the efflux system and brain diseases. However, the currently available technique for studying SCN^- efflux is severely limited by its invasiveness. Here, we describe the development of a SCN^- protracer, 9-pentyl-6-[¹¹C]thiocyanatopurine ([¹¹C]1), to overcome this limitation. [¹¹C]1 was synthesized by the reaction of the iodo-precursor and [¹¹C]SCN^- or the reaction of the disulfide precursor with [¹¹C]NH₄CN. The protracer [¹¹C]1 entered the brain after intravenous injection into mice and was rapidly metabolized to [¹¹C]SCN^-, which was then eliminated from the brain. The efflux of [¹¹C]SCN^- was dose-dependently inhibited by perchlorate, a monovalent anion, and the highest dose caused an 82% reduction in the efflux rate. Our findings demonstrate that [¹¹C]1 can be used for the noninvasive and quantitative assessment of the SCN^- efflux system in the brain.

Dietary intake of sulfur amino acids and risk of kwashiorkor malnutrition in eastern Democratic Republic of the Congo

BACKGROUND

Kwashiorkor is an often-fatal type of severe acute malnutrition affecting hundreds of thousands of children annually, but whose etiology is still unknown. Evidence suggests inadequate sulfur amino acid (SAA) status may explain many signs of the condition but studies evaluating dietary protein intake in relation to the genesis of kwashiorkor have been conflicting. We know of no studies of kwashiorkor that have measured dietary SAAs.

OBJECTIVES

We aimed to determine whether children in a population previously determined to have high prevalence of kwashiorkor [high-prevalence population (HPP)] have lower dietary intakes of SAAs than children in a low-prevalence population (LPP).

METHODS

A cross-sectional census survey design of 358 children compared 2 previously identified adjacent populations of children 36-59 mo old in North Kivu Province of the Democratic Republic of the Congo. Data collected included urinary thiocyanate (SCN), cyanogens in cassava-based food products, recent history of illness, and a 24-h quantitative diet recall for the child.

RESULTS

The HPP and LPP had kwashiorkor prevalence of 4.5% and 1.7%, respectively. A total of 170 children from 141 households in the LPP and 169 children from 138 households in the HPP completed the study. A higher proportion of HPP children had measurable urinary SCN (44.8% compared with 29.4%, P < 0.01). LPP children were less likely to have been ill recently (26.8% compared with 13.6%, P < 0.01). Median [IQR] intake of SAAs was 32.4 [22.9-49.3] mg/kg for the LPP and 29.6 [18.1-44.3] mg/kg for the HPP (P < 0.05). Methionine was the first limiting amino acid in both populations, with the highest risk of inadequate intake found among HPP children (35.1% compared with 23.6%, P < 0.05).

CONCLUSIONS

Children in a population with a higher prevalence of kwashiorkor have lower dietary intake of SAAs than children in a population with a lower prevalence. Trial interventions to reduce incidence of kwashiorkor should consider increasing SAA intake, paying particular attention to methionine.

Konzo risk factors, determinants and etiopathogenesis: What is new? A systematic review

Konzo is a toxico-nutritional upper motor neuron disease causing a spastic paraparesis in schoolchildren and childbearing women in some African countries. Almost a century since the first description of konzo, its underlying etiopathogenic mechanisms and causative agent remain unknown. This paper aims at refreshing the current knowledge of konzo determinants and pathogenesis in order to enlighten potential new research and management perspectives. Literature research was performed in PubMed and Web of Science databases according to the PRISMA methodology. Available data show that cassava-derived cyanide poisoning and protein malnutrition constitute two well-documented risk factors of konzo. However, observational studies have failed to demonstrate the causal relationship between konzo and cyanide poisoning. Thiocyanate, the current marker of choice of cyanide exposure, may underestimate the actual level of cyanide poisoning in konzo patients as a larger amount of cyanide is detoxified via other unusual pathways in the context of protein malnutrition characterizing these patients. Furthermore, the appearance of konzo may be the consequence of the interplay of several factors including cyanide metabolites, nutritional deficiencies, psycho-emotional and geo-environmental factors, resulting in pathophysiologic phenomena such as excitotoxicity or oxidative stress, responsible for neuronal damage that takes place at sparse cellular and/or subcellular levels.

Motor control and cognition deficits associated with protein carbamoylation in food (cassava) cyanogenic poisoning: Neurodegeneration and genomic perspectives

A case-control design determined whether konzo, an upper motoneuron disease linked to food (cassava) toxicity was associated with protein carbamoylation and genetic variations. Exon sequences of thiosulfate sulfurtransferase (TST) or mercaptopyruvate sulfurtransferase (MPST), plasma cyanide detoxification rates, and 2D-LC-MS/MS albumin carbamoylation were assessed in 40 children [21 konzo-affected and 19 putatively healthy controls, mean (SD) age: 9.2 (3.0) years] subjected to cognition and motor testing using the Kaufman Assessment Battery and the Bruininks/Oseretsky Test, respectively. Konzo was significantly associated with higher levels of carbamoylated peptides 206-219 (LDELRDEGKASSAK, pep1) after adjusting for age, gender, albumin concentrations and BUN [regression coefficient: 0.03 (95%CI:0.02-0.05), p = 0.01]. Levels of pep1 negatively correlated with performance scores at all modalities of motor proficiency (r = 0.38 to 0.61; all p < 0.01) or sequential processing (memory)(r = - 0.59, p = 0.00) and overall cognitive performance (r = - 0.48, p = 0.00) but positively with time needed for cyanide detoxification in plasma (r = 0.33, p = 0.04). Rare potentially damaging TST p.Arg206Cys (rs61742280) and MPST p.His317Tyr (rs1038542246) heterozygous variants were identified but with no impact on subject phenotypes. Protein carbamoylation appears to be a reliable marker for cassava related neurodegeneration.

Review of canine dilated cardiomyopathy in the wake of diet-associated concerns

Dilated cardiomyopathy (DCM) has been in the literature and news because of the recent opinion-based journal articles and public releases by regulatory agencies. DCM is commonly associated with a genetic predisposition in certain dog breeds and can also occur secondary to other diseases and nutritional deficiencies. Recent communications in veterinary journals have discussed a potential relationship between grain-free and/or novel protein diets to DCM, citing a subjective increase in DCM in dog breeds that are not known to have a genetic predisposition for the disease. This literature review describes clinical presentations of DCM, common sequelae, treatment and preventative measures, histopathologic features, and a discussion of the varied etiological origins of the disease. In addition, current literature limitations are addressed, in order to ascertain multiple variables leading to the development of DCM. Future studies are needed to evaluate one variable at a time and to minimize confounding variables and speculation. Furthermore, to prevent sampling bias with the current FDA reports, the veterinary community should be asked to provide information for all cases of DCM in dogs. This should include cases during the same time period, regardless of the practitioner's proposed etiology, due to no definitive association between diets with specific characteristics, such as, but not limited to, grain-free diets and those containing legumes, novel protein diets, and those produced by small manufacturers to DCM in dogs. In summary, in order to determine if certain ingredients, categories of diets, or manufacturing processes are related to an increased risk of DCM, further studies investigating these variables are necessary.

Chronic consumption of cassava juice induces cellular stress in rat substantia nigra

OBJECTIVES

Cassava (Manihot esculenta Crantz) contains cyanogenic glycosides (linamarin and lotaustralin) that have been associated with neurological disorders in humans and rats. In basal ganglia, the dopaminergic neurons of substantia nigra pars compacta (SNpc) show high cytotoxic susceptibility; therefore, the chronic consumption of cassava (CCC) could induce neurodegeneration in SNpc. In this study we examine the impact of CCC on the integrity of the nigrostriatal system, including apoptosis and microgliosis.

MATERIALS AND METHODS

Male Wistar rats were administered cassava juice daily (3.57 g/kg and 28.56 g/kg, per os) or linamarin (0.15 mg/ml, IP), and its effects were evaluated in rota-rod and swim tests at days 7, 14, 21, 28, and 35 of administration. In SNpc, oxidative/nitrosative stress was determined by malondialdehyde/4-hydroxyalkenals (MDA-4-HAD) and nitrite contents. Tyrosine hydroxylase immunoreactivity (TH-IR) was evaluated in SNpc, neostriatum (NE), and nucleus accumbens (NA). Apoptosis and microgliosis were determined by active-caspase-3 (C3) and CD11b/c (OX42) expression in the medial region of SNpc.

RESULTS

Chronic administration of cassava juice, or linamarin, increased motor impairment. The rats that received 28.56 g/kg cassava showed increased MDA-4-HAD content in SNpc and nitrite levels in NE with respect to controls. Significant loss of TH-IR in SNpc, NE, and NA was not found. The 28.56 g/kg cassava administration produced dopaminergic atrophy and microgliosis, whereas linamarin induced hypertrophy and C3-related apoptosis in SNpc.

CONCLUSION

CCC induces cellular stress on dopaminergic neurons, which could contribute to motor impairment in the rat.

Preclinical and clinical research on the toxic and neurological effects of cassava (Manihot esculenta Crantz) consumption

Cassava (Manihot esculenta Crantz) is a tropical plant that is used as fresh food, processed food, or raw material for the preparation of flours with high nutritional value. However, cassava contains cyanogenic glycosides, such as linamarin and lotaustralin, that can trigger severe toxic effects and some neurological disorders, including motor impairment, cognitive deterioration, and symptoms that characterize tropical ataxic neuropathy and spastic epidemic paraparesis (Konzo). These alterations that are associated with the consumption of cassava or its derivatives have been reported in both humans and experimental animals. The present review discusses and integrates preclinical and clinical evidence that indicates the toxic and neurological effects of cassava and its derivatives by affecting metabolic processes and the central nervous system. An exhaustive review of the literature was performed using specialized databases that focused on the toxic and neurological effects of the consumption of cassava and its derivatives. We sought to provide structured information that will contribute to understanding the undesirable effects of some foods and preventing health problems in vulnerable populations who consume these vegetables. Cassava contains cyanogenic glycosides that contribute to the development of neurological disorders when they are ingested inappropriately or for prolonged periods of time. Such high consumption can affect neurochemical and neurophysiological processes in particular brain structures and affect peripheral metabolic processes that impact wellness. Although some vegetables have high nutritional value and ameliorate food deficits in vulnerable populations, they can also predispose individuals to the development of neurological diseases.

Tropical ataxic neuropathy: Findings of a neuroepidemiological survey of Odeda, southwest Nigeria

BACKGROUND

Tropical ataxic neuropathy seems to have dwindled in public health importance in Nigeria despite the high consumption of cassava-based meals by a huge proportion of people in local Nigerian communities. Yet a recent report suggest its persistence in the same ethnogeographic setting where it was first reported in Nigeria. Our objective was to investigate the prevalence of tropical ataxic neuropathy in Odeda, Ogun state, southwest Nigeria inhabited by a different ethnic group compared to Epe where the disease was first described.

METHODS

A two-stage, cross-sectional survey of Odeda local government area for the prevalence and profile of toxiconutritional neurological disorders was carried out between May and June 2015. A screening instrument was applied by trained non - medical interviewers with positive responders further evaluated by a neurologist.

RESULTS

2392 individuals aged 18 years or older were screened and had a mean age of 37.2 ± 16.1 years, were predominantly of Egba Yoruba ethnicity. Thirty nine cases of tropical ataxic neuropathy were diagnosed and crude prevalence rate was 16.3/1000 (95% CI 11.2-21.4/1000). Older age and rural residence were associated with higher prevalence. Distal sensory polyneuropathy was the most common feature whereas sensorineural deafness was the least common finding.

CONCLUSION

This report provides evidence that tropical ataxic neuropathy persists and in a wider geographic spread. Thus tropical ataxic neuropathy still remains a significant public health importance and concerted efforts are required to mitigate or eradicate tropical ataxic neuropathy in southwest Nigeria and other regions of Africa affected by cassava- related toxiconutritional disorders.

Selective and sensitive detection of cyanate using 3-amino-2-naphthoic acid-based turn-on fluorescence probe

The cyanate anion (CNO^-), formed spontaneously within cells from urea and carbamoyl phosphate, usually functions as a biomarker of some diseases such as chronic kidney disease. Therefore, accurate determination of CNO^- is highly demanded. Herein, a 3-amino-2-naphthoic acid-based "turn-on" fluorescence probe was developed for specific detection of CNO^-. Upon the addition of sodium cyanate, the weak-fluorescent 3-amino-2-naphthoic acid could react with CNO^-, which triggered intense emission of green fluorescence. And up to 9-fold fluorescence enhancement was observed. The fluorescence enhancement ratios displayed a good linear relationship with the concentrations of CNO^- in the range of 0.5-200 μM. The high selectivity and sensitivity for CNO^- detection were investigated with the detection limit as low as 260 nM. The probe was further successfully applied to determine CNO^- in real samples such as tap water, human urine and serum samples, which offered a promising approach in practical applications. Graphical abstract.

Evaluation of the health risks related to the presence of cyanogenic glycosides in foods other than raw apricot kernels

In 2016, the EFSA Panel on Contaminants in the Food Chain (CONTAM) published a scientific opinion on the acute health risks related to the presence of cyanogenic glycosides (CNGs) in raw apricot kernels in which an acute reference dose (ARfD) of 20 μg/kg body weight (bw) was established for cyanide (CN). In the present opinion, the CONTAM Panel concluded that this ARfD is applicable for acute effects of CN regardless the dietary source. To account for differences in cyanide bioavailability after ingestion of certain food items, specific factors were used. Estimated mean acute dietary exposures to cyanide from foods containing CNGs did not exceed the ARfD in any age group. At the 95th percentile, the ARfD was exceeded up to about 2.5-fold in some surveys for children and adolescent age groups. The main contributors to exposures were biscuits, juice or nectar and pastries and cakes that could potentially contain CNGs. Taking into account the conservatism in the exposure assessment and in derivation of the ARfD, it is unlikely that this estimated exceedance would result in adverse effects. The limited data from animal and human studies do not allow the derivation of a chronic health-based guidance value (HBGV) for cyanide, and thus, chronic risks could not be assessed.

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.

Homocysteine and the pathogenesis of atherosclerosis

The homocysteine theory of arteriosclerosis was discovered by study of arteriosclerotic plaques occurring in homocystinuria, a disease caused by deficiencies of cystathionine synthase, methionine synthase or methylenetetrahydrofolate reductase. According to the homocysteine theory, metabolic and nutritional abnormalities leading to elevation of plasma homocysteine cause atherosclerosis in the general population without these rare enzymatic abnormalities. Through studies of metabolism of homocysteine thiolactone, the anhydride of homocysteine, in cell cultures from homocystinuric children, the pathway for synthesis of sulfate was found to be dependent upon thioretinamide, the amide formed from retinoic acid and homocysteine thiolactone. Two molecules of thioretinamide form the complex thioretinaco with cobalamin, and oxidative phosphorylation is catalyzed by reduction of oxygen, which is bound to thioretinaco ozonide, by electrons from electron transport particles. Atherogenesis is attributed to formation of aggregates of homocysteinylated lipoproteins with microorganisms, which obstruct the vasa vasorum during formation of arterial vulnerable plaques.

Protein carbamylation in kidney disease: pathogenesis and clinical implications

Carbamylation describes a nonenzymatic posttranslational protein modification mediated by cyanate, a dissociation product of urea. When kidney function declines and urea accumulates, the burden of carbamylation naturally increases. Free amino acids may protect proteins from carbamylation, and protein carbamylation has been shown to increase in uremic patients with amino acid deficiencies. Carbamylation reactions are capable of altering the structure and functional properties of certain proteins and have been implicated directly in the underlying mechanisms of various disease conditions. A broad range of studies has demonstrated how the irreversible binding of urea-derived cyanate to proteins in the human body causes inappropriate cellular responses leading to adverse outcomes such as accelerated atherosclerosis and inflammation. Given carbamylation's relationship to urea and the evidence that it contributes to disease pathogenesis, measurements of carbamylated proteins may serve as useful quantitative biomarkers of time-averaged urea concentrations while also offering risk assessment in patients with kidney disease. Moreover, the link between carbamylated proteins and disease pathophysiology creates an enticing therapeutic target for reducing the rate of carbamylation. This article reviews the biochemistry of the carbamylation reaction, its role in specific diseases, and the potential diagnostic and therapeutic implications of these findings based on recent advances.

Reduced foodborne toxin exposure is a benefit of improving dietary diversity

Naturally occurring foodborne toxins are common in subsistence diets of low-income human populations worldwide. Often, these populations rely on one or two staple foods for the bulk of their calories, making them more susceptible to chronic intake of certain toxins. Exposure to common foodborne toxins is associated with diverse conditions such as cancer, immunotoxicity, growth impairment, and neurological deficits. Interventions focused solely on reducing toxin levels have proven difficult to sustain. Using case studies of two foodborne toxins, aflatoxin and cassava cyanide, this article addresses the heightened risk of particular diseases from eating monotonous diets based in maize, groundnuts, and cassava: common in sub-Saharan Africa and parts of Asia. We also discuss the potential role of increased dietary diversity in counteracting these diseases. Increased dietary diversity can reduce consumption of toxins and increase intake of nutrients that could counteract the toxicity of such chemicals. In Qidong, China, a population that previously consumed a monotonous maize-based diet and increased dietary diversity since the 1980s has experienced a dramatic reduction in liver cancer mortalities. That liver cancer decreased as dietary diversity increased is the catalyst for the hypothesis that dietary diversity could have a direct impact on reducing health effects of foodborne toxins. Future research, agricultural development, and food policy reforms should take into consideration the multifaceted benefits associated with improved dietary diversity. Collaborations between toxicologists, nutritionists, and policymakers are important to development of sustainable interventions to reduce foodborne toxin exposure and promote health through increased dietary diversity.

Determinants of cognitive performance in children relying on cyanogenic cassava as staple food

While risk factors for konzo are known, determinants of cognitive impairment in konzo-affected children remain unknown. We anchored cognitive performance (KABC-II scores) to serum levels of free-thyroxine (free-T4), thyroid-stimulating hormone (TSH), albumin, and motor proficiency (BOT-2 scores) in 40 children including 21 with konzo (median age: 9 years) and 19 without konzo (median age: 8 years). A multiple regression model was used to determine variables associated with changes in KABC-II scores. Age (β: -0.818, 95% CI: -1.48, -0.152) (p = 0.018), gender (β: -5.72; 95% CI: -9.87, -1.57 for females) (p = 0.009), BOT-2 score (β: 0.390; 95% CI: 0.113, 0.667) (p = 0.008), and free-T4 (β: 1.88; 95% CI: 0.009, 3.74) (p = 0.049) explained 61.1 % of variation in KABC-II scores. Subclinical hypothyroidism was not associated with poor cognition. A crude association was found between serum albumin and KABC-II scores (β: 1.26; 95 % CI: 0.136, 2.39) (p = 0.029). On spot urinary thiocyanate reached 688 μmol/l in children without konzo and 1,032 μmol/L in those with konzo. Female gender and low serum albumin are risk factors common to cognitive and proportionally associated motor deficits in children exposed to cassava cyanogens. The two types of deficits may share common mechanisms.

Memory deficits associated with sublethal cyanide poisoning relative to cyanate toxicity in rodents

Food (cassava) linamarin is metabolized into neurotoxicants cyanide and cyanate, metabolites of which we sought to elucidate the differential toxicity effects on memory. Young 6-8 weeks old male rats were treated intraperitoneally with either 2.5 mg/kg body weight (bw) cyanide (NaCN), or 50 mg/kg bw cyanate (NaOCN), or 1 μl/g bw saline, daily for 6 weeks. Short-term and long-term memories were assessed using a radial arm maze (RAM) testing paradigm. Toxic exposures had an influence on short-term working memory with fewer correct arm entries (F(2, 19) = 4.57 p < 0.05), higher working memory errors (WME) (F(2, 19) = 5.09, p < 0.05) and longer RAM navigation time (F(2, 19) = 3.91, p < 0.05) for NaOCN relative to NaCN and saline treatments. The long-term working memory was significantly impaired by cyanide with fewer correct arm entries (F(2, 19) = 7.45, p < 0.01) and increased working memory errors (F(2, 19) = 9.35 p < 0.05) in NaCN relative to NaOCN or vehicle treated animals. Reference memory was not affected by either cyanide or cyanate. Our study findings provide an experimental evidence for the biological plausibility that cassava cyanogens may induce cognition deficits. Differential patterns of memory deficits may reflect the differences in toxicity mechanisms of NaOCN relative to NaCN. Cognition deficits associated with cassava cyanogenesis may reflect a dual toxicity effect of cyanide and cyanate.

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.

Carbamoylation correlates of cyanate neuropathy and cyanide poisoning: relevance to the biomarkers of cassava cyanogenesis and motor system toxicity

We sought to elucidate the protein carbamoylation patterns associated with cyanate neuropathy relative to cyanide poisoning. We hypothesized that under a diet deficient in sulfur amino acids (SAA), the carbamoylation pattern associated with cyanide poisoning is similar to that of cyanate neuropathy. Male rats (6–8 weeks old) were fed a diet with all amino acids (AAA) or 75%-deficiency in SAA and treated with 2.5 mg/kg/body weight (bw) NaCN, or 50 mg/kg/bw NaOCN, or 1 μl/g/bw saline, for up to 6 weeks. Albumin and spinal cord proteins were analyzed using liquid chromatography mass spectrometry (LC-MS/MS). Only NaOCN induced motor deficits with significant levels of carbamoylation. At Day 14, we found a diet-treatment interaction effect on albumin carbamoylation (p = 0.07). At Day 28, no effect was attributed to diet (p = 0.71). Mean number of NaCN-carbamoylated sites on albumin was 47.4% higher relative to vehicle (95% CI:16.7-86.4%). Only NaOCN carbamoylated spinal cord proteins, prominently, under SAA-restricted diet. Proteins targets included myelin basic and proteolipid proteins, neurofilament light and glial fibrillary acidic proteins, and 2', 3' cyclic-nucleotide 3'-phosphodiesterase. Under SAA deficiency, chronic but not acute cyanide toxicity may share biomarkers and pathogenetic similarities with cyanate neuropathy. Prevention of carbamoylation may protect against the neuropathic effects of cyanate.

The use of microorganisms in increasing the protein yield of cassava (Manihot esculenta Crantz) peel wastes

Growth and microbial protein production on hydrolyzed cassava peel waste by Trichoderma viride and Lactobacillus delbrueckii NRRL B-763 were investigated. Trichoderma viride was selected based on its high cellulase activity on filter paper (2.91 mg glucose/mL), cotton wool (3.08 mg glucose/mL) and carboxymethylcellulose (3.46 mg glucose/ mL) while Lactobacillus delbrueckii NRRL B-763 produced 5.84 mg protein/g in cassava peel after 72 h. Samples of cassava peel were hydrolyzed with the solutions of HCl, H2SO4 and NaOH at 0.5% concentration. The hydrolysate was neutralized to pH 6.5 and supplemented with KH2PO4 (5% w/v), urea (2.7% w/v) and (NH4)2SO4 (9% w/v). The hydrolysates produced by the solutions of HCl contained higher reducing sugar and soluble sugar content than H2SO4 and NaOH hydrolysates. The culture of Trichoderma viride was used in single culture fermentation of hydrolyzed cassava peels or in mixed culture fermentation with Lactobacillus delbrueckii NRRL B-763. Protein yield produced in 0.5% HCl hydrolysates was significantly (p ≤ 0.01) higher than that in H2SO4. The unhydrolyzed control samples produced the lowest protein. This study demonstrated the potential of cassava peel waste as a substrate for a recycling process and by- product recovery.

Study of the effects of hydrogen cyanide exposure in Cassava workers

BACKGROUND

Hydrogen cyanide is the chemical responsible for tissue hypoxia. Chronic exposure to HCN may cause neurological, respiratory, cardiovascular and thyroid defects. Onset of symptoms depends on dose and duration of exposure. Large scale of Cassava processing could be disastrous due to discharge of hydrocyanic acid into the air. Cassava processing is the major industrial work in and around Salem. Hence the present study is taken to assess the effects of HCN exposure in Cassava workers.

MATERIALS AND METHODS

Thirty-nine workers from a Cassava processing unit at Salem and age-matched controls of the same economic status were taken up for this study. Clinical history was obtained with a questionnaire and their Blood sugar, lipid profile, serum total protein, urea, creatinine, AST, ALT and T(3), T(4), TSH were estimated using a fasting blood sample and AIP was calculated. Statistical analysis was done by student t test.

RESULTS

Our study reveals a significant increase in triglyceride in Cassava workers when compared to the control. Atherogenic index of plasma (AIP) is statistically highly significant. A significant decrease was seen in T(4.)

CONCLUSION

An increase in TGL and AIP shows a higher degree of cardiovascular risk. A decrease in T4 suggests an insufficient iodine uptake by thyroid gland. Hence a periodic medical evaluation should be done on such workers for their safety and to prevent the health hazard.

Interrelationships of undernutrition and neurotoxicity: food for thought and research attention

The neurotoxic actions of chemical agents on humans and animals are usually studied with little consideration of the subject's nutritional status. States of protein-calorie, vitamin and/or mineral undernutrition are associated with a range of neurodevelopmental, neurological and psychiatric disorders, commonly with involvement of both the central and the peripheral nervous system. Undernutrition can modify risk for certain chemical-induced neurologic diseases, and in some cases undernutrition may be a prerequisite for neurotoxicity to surface. In addition, neurologic disease associated with undernutrition or neurotoxicity may show similarities in clinical and neuropathological expression, especially in the peripheral nervous system. The combined effects of undernutrition and chemical neurotoxicity are most relevant to people with low incomes who experience chronic hunger, parasitism and infectious disease, monotonous diets of plants with neurotoxic potential (notably cassava), environmental pollution from rapid industrial development, chronic alcohol abuse, or prolonged treatment with certain therapeutic drugs. Undernutrition alone or in combination with chemical exposure is also important in high-income societies in the setting of drug and alcohol abuse, old age, food faddism, post-bariatric surgery, and drug treatment for certain medical conditions, including cancer and tuberculosis. The nutritional demands of pregnancy and lactation increase the risk of fetal and infant undernutrition and chemical interactions therewith.

Control of konzo in DRC using the wetting method on cassava flour

Fifty konzo cases were identified in four villages in Popokabaka Health Zone, DRC. One third of people had only one meal per day, mainly of cassava flour consumed as a thick porridge (fufu) and pounded, boiled cassava leaves. Retention of cyanogens in flour resulted from short soaking of cassava roots. A 1.5 years intervention was made in the largest village Kay Kalenge, where the wetting method was taught to all women of the village, who accepted it willingly. The total cyanide content of cassava flour was reduced to below 10 ppm. Fufu from treated flour tasted and stored better than fufu from untreated flour. The mean urinary thiocyanate content of 100 school children reduced from 332 to 130 μmole/L and the number of samples exceeding 350 μmole/L decreased from 26 to 0 during the intervention. No new konzo cases occurred, which included two dry seasons when konzo peaks. Konzo was first identified by Dr. Trolli in 1938 in Popokabaka Health Zone and it has now been prevented for the first time in the same area. The methodology is now in use in Boko Health Zone and we believe it is the most effective way to control konzo in tropical Africa.

Konzo: from poverty, cassava, and cyanogen intake to toxico-nutritional neurological disease

Konzo is a distinct neurological entity with selective upper motor neuron damage, characterized by an abrupt onset of an irreversible, non-progressive, and symmetrical spastic para/tetraparesis. Despite its severity, konzo remains a neglected disease. The disease is associated with high dietary cyanogen consumption from insufficiently processed roots of bitter cassava combined with a protein-deficient diet. Epidemics occur when these conditions coincide at times of severe food shortage. Up to 1993, outbreaks in poor rural areas in Africa contributed to more than 3,700 cases of konzo. The number of affected people is underestimated. From unofficial reports, the number of cases was estimated to be at least 100,000 in 2000, in contrast to the 6,788 cases reported up to 2009 from published papers.

Neurological disorders associated with cassava diet: a review of putative etiological mechanisms

Tropical ataxic neuropathy (TAN) and epidemic spastic paraparesis (konzo) are two neurological disorders associated with the consumption of cassava (Manihot esculenta) in several African countries. TAN is characterized by sensory polyneuropathy, sensory ataxia, bilateral optic atrophy and bilateral sensori-neural deafness. It occurs in elderly individuals subsisting on a monotonous cassava diet with minimal protein supplementation. Konzo is a syndrome of symmetrical spastic paraparesis with a predilection for children and young women and invariably associated with consumption of inadequately processed bitter cassava roots with minimal protein supplementation. Despite numerous epidemiological, clinical and biochemical studies aimed at elucidating the etiological mechanisms of these disorders, their etiologies remain unknown, and there is no known treatment. The diseases continue to be prevalent in endemic areas, causing significant disability and increased mortality. A fresh appraisal of the putative etiologic mechanisms proposed for these intriguing and enigmatic syndromes is presented in this paper. Evidences against a causal role for cyanide intoxication are discussed, and evidences implicating thiamine deficiency as a unifying etiological mechanism for these neurological syndromes are presented. It is concluded that urgent research is needed to evaluate thiamine status and implement a therapeutic trial of thiamine in these debilitating neurological disorders.

Cassava: an appraisal of its phytochemistry and its biotechnological prospects

The present state of knowledge of the phytochemistry of small molecules isolated from the roots and leaves of cassava, Manihot esculenta Crantz (Euphorbiaceae), is reviewed. Cassava roots are an important source of dietary and industrial carbohydrates, mainly eaten as a source of starch, forming the staple food to over 500 million; additionally, the roots have value as a raw material for industrial starch production and for animal feed giving the crop high economic value, but it suffers markedly from post-harvest physiological deterioration (PPD). The hydroxycoumarins scopoletin and its glucoside scopolin as well as trace quantities of esculetin and its glucoside esculin are identified from cassava roots during PPD. The biotechnological prospects for cassava are also reviewed including a critical appraisal of transgenic approaches for crop improvement, together with its use for bioethanol production, due to cassava's efficient ability to fix carbon dioxide into carbohydrate.

Brain glutathione as a target for aetiological factors in neurolathyrism and konzo

Both neurolathyrism and konzo are associated with the nutritional dependence of human populations on a single plant food. These diseases express themselves as chronic disorders of upper motor neurones, leading to signs and symptoms that characterise amyotrophic lateral sclerosis (motor neurone disease). The plant food associated with neurolathyrism is grass pea, which contains the neurotoxic β-N-oxalyl-α,β-diaminopropionic acid (β-ODAP). The plant food associated with konzo is cassava, which may contain significant concentrations of cyanogenic glycosides and their degradation products. A monotonous diet of grass pea is likely to generate nutritional deficiencies; it is proposed that one of these, plasma methionine deficiency, may predispose neurones to the neurotoxic effects of β-ODAP. Subjects suffering from konzo also have low concentrations of plasma methionine as a result of a dietary deficiency of this amino acid. However, the plasma cystine concentration is also compromised because cyanide released from cyanogenic glycosides in cassava probably reacts with plasma cystine non-enzymatically. The product of this reaction is 2-imino-4-thiazolidine carboxylic acid. Since both plasma methionine and cystine are used for glutathione synthesis it seems likely that one common feature that leads to motor neurone death in neurolathyrism and konzo is the depletion of glutathione in the central nervous system.

On the biomarkers and mechanisms of konzo, a distinct upper motor neuron disease associated with food (cassava) cyanogenic exposure

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 50-200mg/kg linamarin, or 200mg/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

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.

Unraveling the mechanism of β-N-oxalyl-α,β-diaminopropionic acid (β-ODAP) induced excitotoxicity and oxidative stress, relevance for neurolathyrism prevention

β-N-Oxalyl-α,β-diaminopropionic acid (β-ODAP) is a plant metabolite present in Lathyrus sativus (L. Sativus) seeds that is proposed to be responsible for the neurodegenerative disease neurolathyrism. This excitatory amino acid binds to α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors and several lines of evidence indicate that β-ODAP triggers motor neuron degeneration by inducing excitotoxic cell death and increasing oxidative stress. In addition, this toxin is known to disturb the mitochondrial respiration chain and recent data indicate that β-ODAP may inhibit the uptake of cystine thereby compromising the cells' abilities to cope with oxidative stress. Recent work from our group furthermore suggests that β-ODAP disturbs the cellular Ca(2+) homeostasis machinery with increased Ca(2+) loading in the endoplasmic reticulum (ER)-mitochondrial axis. In this review, we aim to integrate the various mechanistic levels of β-ODAP toxicity into a consistent pathophysiological picture. Interestingly, the proposed cascade contains several aspects that are common with other neurodegenerative diseases, for example amyotrophic lateral sclerosis (ALS). Based on these mechanistic insights, we conclude that dietary supplementation with methionine (Met) and cysteine (Cys) may significantly lower the risk for neurolathyrism and can thus be considered, in line with epidemiological data, as a preventive measure for neurolathyrism.

The targets of acetone cyanohydrin neurotoxicity in the rat are not the ones expected in an animal model of 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 10mM acetone cyanohydrin in drinking water for 2 weeks, and then 20mM 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 24h in order to increase endogenous acetone synthesis, and then exposed to 0 (control group) or 50 micromol/kg-h of acetone cyanohydrin for 24h (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 micromol/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.

Poisonous plants of veterinary and human importance in southern Africa

Southern Africa is inherently rich in flora, where the habitat and climatic conditions range from arid environments to lush, sub-tropical greenery. Needless to say, with such diversity in plant life there are numerous indigenous poisonous plants, and when naturalised exotic species and toxic garden varieties are added the list of potential poisonous plants increases. The economically important poisonous plants affecting livestock and other plant poisonings of veterinary significance are briefly reviewed. In addition, a synopsis of the more common plant poisonings in humans is presented. Many of the plants mentioned in this review are also used ethnobotanically for treatment of disease in humans and animals and it is essential to be mindful of their toxic potential.

Seed storage protein deficiency improves sulfur amino acid content in common bean (Phaseolus vulgaris L.): redirection of sulfur from gamma-glutamyl-S-methyl-cysteine

The contents of sulfur amino acids in seeds of common bean ( Phaseolus vulgaris L.) are suboptimal for nutrition. They accumulate large amounts of a gamma-glutamyl dipeptide of S-methyl-cysteine, a nonprotein amino acid that cannot substitute for methionine or cysteine in the diet. Protein accumulation and amino acid composition were characterized in three genetically related lines integrating a progressive deficiency in major seed storage proteins, phaseolin, phytohemagglutinin, and arcelin. Nitrogen, carbon, and sulfur contents were comparable among the three lines. The contents of S-methyl-cysteine and gamma-glutamyl-S-methyl-cysteine were progressively reduced in the mutants. Sulfur was shifted predominantly to the protein cysteine pool, while total methionine was only slightly elevated. Methionine and cystine contents (mg per g protein) were increased by up to ca. 40%, to levels slightly above FAO guidelines on amino acid requirements for human nutrition. These findings may be useful to improve the nutritional quality of common bean.

Evidence for a functional genetic polymorphism of the human mercaptopyruvate sulfurtransferase (MPST), a cyanide detoxification enzyme

Mercaptopyruvate sulfurtransferase (MPST) plays a central role in both cysteine degradation and cyanide detoxification. Moreover, deficiency in MPST activity has been suggested to be responsible for a rare inheritable disorder known as mercaptolactate-cysteine disulfiduria (MCDU). To date, no mutation of the human MPST gene has been reported. We developed a screening strategy to search for mutations in the MPST gene of 50 unrelated French individuals. Two intronic polymorphisms (IVS1-110C>G and IVS2+39C>T) and a nonsense mutation (Tyr(85)Stop) were identified and their functional consequences were assessed in vivo by measurement of erythrocyte MPST activity and/or in vitro using heterologous expression or transient transfection assay. The nonsense mutation likely leads to the synthesis of a severely truncated protein without enzymatic activity, as supported by our in vitro data. This work constitutes the first report of the existence of a functional genetic polymorphism affecting MPST and should be of great help to investigate certain disorders such as MCDU.

Developmental neurotoxicology

The developing brain has a distinctive set of characteristics that make it unusually sensitive to damage by toxic agents. Mechanistic understanding of the vulnerability of the immature nervous system to various chemicals is important from a preventive perspective but has also frequently given us new insights into maturation of neural circuitry. This review examines some of the developmental consequences of contact with various exogenous agents, including metals, solvents, pharmaceuticals, and natural products. This review emphasizes how subtle suboptimal brain function rather than acute toxicity can be a consequence of chemical exposures occurring during ontogenesis. The rate of brain aging may be influenced by events taking place in embryogenesis, following a prolonged asymptomatic period. The potential for appearance of adverse effects after prolonged latent periods is underscored.

Fish consumption (hair mercury) and nutritional status of Amazonian Amer-Indian children

Fish are abundant and important dietary items for the Amer-Indians, and total hair-Hg (HHg) concentration is a reliable marker of fish consumption. We studied the impact of fish consumption (HHg) on the nutritional status of Indian children of Eastern Amazonia. Weight-for-height Z score (WHZ) was measured, and HHg was determined in 203 children younger than 10 years of age in three villages. There was significantly higher fish consumption in Kayabi children (16.55 microg Hg/g; SD, 11.44) than in children of the Munduruku villages of Missão-Cururu (4.76 microg Hg/g; SD, 2.09) and Kaburua (2.87 microg Hg/g; SD, 2.13). Anthropometric indices showed WHZ means of -0.27, -0.22, and 0.40, respectively, for Kayabi, Missão-Cururu and Kaburua villages. Despite a different pattern of fish-protein consumption between tribes, there was no significant correlation between WHZ and HHg concentrations (r2 = 0.0079; P < 0.2021). Dietary differences among Amazonian tribes can be traced and used in measuring health outcomes. Higher fish consumption, although important for Kayabis, was compensated by other protein sources by the Kaburua villagers.

Sodium cyanate-induced opening of calcium-activated potassium currents in hippocampal neuron-derived H19-7 cells

We investigated the chemical toxic agent sodium cyanate (NaOCN) on the large conductance calcium-activated potassium channels (BK(Ca)) on hippocampal neuron-derived H19-7 cells. The whole-cell and cell-attach configuration of patch-clamp technique were applied to investigate the BK(Ca) currents in H19-7 cells in the presence of NaOCN (0.3 mM). NaOCN activated BK(Ca) channels on H19-7 cells. The single-channel conductance of BK(Ca) channels was 138+/-7pS. The presence of NaOCN (0.3 mM) caused an obvious increase in open probability of BK(Ca) channels. NaOCN did not exert effect on the slope of the activation curve and stimulated the activity of BK(Ca) channels in a voltage-dependent fashion in H19-7 cells. The presence of paxilline or EGTA significantly reduced the BK(Ca) amplitude, in comparison with the presence of NaOCN. These findings suggest that during NaOCN exposure, the activation of BK(Ca) channels in neurons could be one of the ionic mechanisms underlying the decreased neuronal excitability and neurological disorders.