Neuroprotein Targets of γ-Diketone Metabolites of Aliphatic and Aromatic Solvents That Induce Central-Peripheral Axonopathy

An introduction to environmental neurotoxicology: Lessons from a clinical perspective

In 1992, the Committee on Neurotoxicology and Models for Assessing Risk of the National Academy of Sciences in Washington DC focused with a scientific perspective on the identification of substances with neurotoxic potential, studies of exposed populations, risk assessment, and biologic markers of disease. This Committee recommended: "all physicians should be trained to take a thorough occupational-exposure history and to be aware of other possible sources of toxic exposure". Although convened after several outbreaks of neurotoxic syndromes, clinical neurological considerations were lacking. After defining keys words, namely Environment, Neurotoxicology and Neurotoxicants, we present some demonstrative cases; e.g., the Epidemic Neuropathy in Cuba, Minamata disease, ALS/PDC on Guam, and the ALS hot spot in the French Alps. Always with a clinical and practical approach, we will then review the milieux that contain and convey potential neurotoxicants, the different exposure routes and the clinical presentations. Drawing lessons from clinical cases, we offer some thoughts concerning the future of Environmental Neurotoxicology (ENT). Pointing notably to the diffuse chemical contamination of ecosystems and living beings, including Homo sapiens, we question the real impact of agents with neurotoxic potential on the human brain, considering the effects, for example, of air pollution, endocrine disruptors and nanoparticles. Concern is expressed over the lack of knowledge of the non-monotonic kinetics of many of these chemicals, the major concern being related to mixtures and low-dose exposures, as well as the delayed appearance in clinical expression of prevalent neurodegenerative diseases.

[Neuropathy in n-hexane poisoning]

N-Hexane is a solvent widely used in manufacturing as a cleaner, degreaser and component of rubber cement. Chronic exposure to n-hexane either through contact with unprotected skin or inhalation can lead to the development of clinical symptoms and electrophysiological changes similar to those of inflammatory demyelinating polyneuropathy which requires careful differential diagnosis. This article presents three cases of severe predominantly motor polyneuropathy with demyelinating features in 15- and 16-year-old adolescents. The results of laboratory tests were within normal limits; electroneuromyography revealed symmetrical involvement of sensory and motor fibers of the nerves of the legs and arms with a decrease in the speed of propagation of excitation and conduction blocks. Sural nerve biopsy revealed intraneural and perineural swelling without any signs of inflammation or fibrosis confirming the genesis of the neuropathy. Despite a relatively favorable prognosis there is no specific therapy for hexane poisoning and the recovery period can last up to several years.

Towards Substitution of Hexane as Extraction Solvent of Food Products and Ingredients with No Regrets

Hexane is a solvent used extensively in the food industry for the extraction of various products such as vegetable oils, fats, flavours, fragrances, colour additives or other bioactive ingredients. As it is classified as a "processing aid", it does not have to be declared on the label under current legislation. Therefore, although traces of hexane may be found in final products, especially in processed products, its presence is not known to consumers. However, hexane, and in particular the n-hexane isomer, has been shown to be neurotoxic to humans and has even been listed as a cause of occupational diseases in several European countries since the 1970s. In order to support the European strategy for a toxic-free environment (and toxic-free food), it seemed important to collect scientific information on this substance by reviewing the available literature. This review contains valuable information on the nature and origin of the solvent hexane, its applications in the food industry, its toxicological evaluation and possible alternatives for the extraction of natural products. Numerous publications have investigated the toxicity of hexane, and several studies have demonstrated the presence of its toxic metabolite 2,5-hexanedione (2,5-HD) in the urine of the general, non-occupationally exposed population. Surprisingly, a tolerable daily intake (TDI) has apparently never been established by any food safety authority. Since hexane residues are undoubtedly found in various foods, it seems more than necessary to clearly assess the risks associated with this hidden exposure. A clear indication on food packaging and better information on the toxicity of hexane could encourage the industry to switch towards one of the numerous other alternative extraction methods already developed.

Protein pyrrole adducts are associated with elevated glucose indices and clinical features of diabetic diffuse neuropathies

INTRODUCTION

Diabetic neuropathy is the most prevalent complication of diabetes mellitus. Although the precise etiology of this neurological disorder has yet to be defined, elevated blood glucose promotes anerobic glycolysis; this produces excess advanced glycation end-products, many of which have a pyrrole structure. Here, we test the hypothesis that protein pyrrole adducts are associated with elevated glucose indices and some clinical features of diabetic diffuse neuropathies.

METHOD

We investigated the levels of plasma pyrrole adducts and adjusted urinary pyrrole adducts in a group of elderly persons (n = 516, age 60-79) residing in the District of Luohu, Shenzhen, China between 2017 and 2018. Symptoms of distal symmetric polyneuropathy (DSPN) and resting heart rate, a measure of autonomic nervous system function, were collected from participants (n = 258) with elevated glucose indices.

RESULT

Protein pyrrole adducts showed a strong correlation with glucose indices before and after adjustment for age and estimated glomerular filtration rates. Stratified analysis showed that the medians and interquartile values of pyrrole adducts grew as glucose indices of the subgroups increased. Participants with symptoms of DSPN and sinus tachycardia presented elevated levels of plasma pyrrole adducts.

CONCLUSION

This study provides a novel link between glucose indices and the etiology of diabetic diffuse neuropathies.

The Role of Protein Adduction in Toxic Neuropathies of Exogenous and Endogenous Origin

The peripheral (axonal) neuropathy associated with repeated exposure to aliphatic and aromatic solvents that form protein-reactive γ-diketones shares some clinical and neuropathological features with certain metabolic neuropathies, including type-II diabetic neuropathy and uremic neuropathy, and with the largely sub-clinical nerve damage associated with old age. These conditions may be linked by metabolites that adduct and cross-link neuroproteins required for the maintenance of axonal transport and nerve fiber integrity in the peripheral and central nervous system.