The effects of thioctic acid on motor nerve terminals in acrylamide-poisoned rats

Review on Acrylamide: A Hidden Hazard in Fried Carbohydrate-Rich Food

Abstract:

Acrylamide is classified as a hazard whose formation in carbohydrate-rich food cooked at a high temperature has created much interest in the scientific community. The review attempts to comprehend the chemistry and mechanisms of formation of acrylamide and its levels in popular foods. A detailed study of the toxicokinetic and biochemistry, carcinogenicity, neurotoxicity, genotoxicity, interaction with biomolecules, and its effects on reproductive health has been presented. The review outlines the various novel and low-cost conventional as well as newer analytical techniques for the detection of acrylamide in foods with the maximum permissible limits. Various effective approaches that can be undertaken in industries and households for the mitigation of levels of acrylamide in foods have also been discussed. This review will assist to provide in depth understanding about acrylamide that will make it simpler to assess the risk to human health from the consumption of foods containing low amounts of acrylamide.

Neurotoxicity of acrylamide in exposed workers

Acrylamide (ACR) is a water-soluble chemical used in different industrial and laboratory processes. ACR monomer is neurotoxic in humans and laboratory animals. Subchronic exposure to this chemical causes neuropathies, hands and feet numbness, gait abnormalities, muscle weakness, ataxia, skin and in some cases, cerebellar alterations. ACR neurotoxicity involves mostly the peripheral but also the central nervous system, because of damage to the nerve terminal through membrane fusion mechanisms and tubulovescicular alterations. Nevertheless, the exact action mechanism is not completely elucidated. In this paper we have reviewed the current literature on its neurotoxicity connected to work-related ACR exposure. We have analyzed not only the different pathogenetic hypotheses focusing on possible neuropathological targets, but also the critical behavior of ACR poisoning. In addition we have evaluated the ACR-exposed workers case studies. Despite all the amount of work which have being carried out on this topic more studies are necessary to fully understand the pathogenetic mechanisms, in order to propose suitable therapies.

Lipoic Acid as a Potential First Agent for Protection from Mycotoxins and Treatment of Mycotoxicosis

Mycotoxins--toxic substances produced by fungi or molds--are ubiquitous in the environment and are capable of damaging multiple biochemical mechanisms, resulting in a variety of human symptoms referred to collectively as "mycotoxicosis." In fact, mycotoxins mimic multiple xenobiotics, not only with respect to their ultimate damage, but also in their routes of detoxification. This suggests potential therapeutic options for the challenging treatment of mycotoxicosis. In this brief review, the author examines the use of lipoic acid as an example of an inexpensive and available nutrient that has been shown to protect against, or reverse, the adverse health effects of mycotoxins.

Neurochemical changes related to ageing in the rat brain and the effect of DL-alpha-lipoic acid

Age-related impairments of cognitive and motor function have been linked to a number of deleterious morphological and functional changes involving different areas of the brain. Loss of neurotransmitters, their receptors and responsiveness to neurotransmitters are key manifestations of neurological ageing and age-related disorders. In the present investigation we have evaluated the effect of DL-alpha-lipoic acid on neurotransmitters in discrete brain regions of young and aged rats. The levels of neurotransmitters were found to be lowered in aged rats. Moreover, DL-alpha-lipoic acid treated aged rats showed a increase in the status of dopamine, serotonin and norepinephrine. The results of this study provide evidence that DL-alpha-lipoic acid (a potent antioxidant) treatment can improve neurotransmitters during ageing. Hence, it can be concluded that DL-alpha-lipoic acid act as a potent neuromodulator in the brain of aged rats.

Nerve terminals as the primary site of acrylamide action: a hypothesis

Acrylamide (ACR) is considered to be prototypical among chemicals that cause a central-peripheral distal axonopathy. Multifocal neurofilamentous swellings and eventual degeneration of distal axon regions in the CNS and PNS have been traditionally considered the hallmark morphological features of this axonopathy. However, ACR has also been shown to produce early nerve terminal degeneration of somatosensory, somatomotor and autonomic nerve fibers under a variety of dosing conditions. Recent research from our laboratory has demonstrated that terminal degeneration precedes axonopathy during low-dose subchronic induction of neurotoxicity and occurs in the absence of axonopathy during higher-dose subacute intoxication. This relationship suggests that nerve terminal degeneration, and not axonopathy, is the primary or most important pathophysiologic lesion produced by ACR. In this hypothesis paper, we review evidence suggesting that nerve terminal degeneration is the hallmark lesion of ACR neurotoxicity, and we propose that this effect is mediated by the direct actions of ACR at nerve terminal sites. ACR is an electrophile and, therefore, sulfhydryl groups on presynaptic proteins represent rational molecular targets. Several presynaptic thiol-containing proteins (e.g. SNAP-25, NSF) are critically involved in formation of SNARE (soluble N-ethylmaleimide (NEM)-sensitive fusion protein receptor) complexes that mediate membrane fusion processes such as exocytosis and turnover of plasmalemmal proteins and other constituents. We hypothesize that ACR adduction of SNARE proteins disrupts assembly of fusion core complexes and thereby interferes with neurotransmission and presynaptic membrane turnover. General retardation of membrane turnover and accumulation of unincorporated materials could result in nerve terminal swelling and degeneration. A similar mechanism involving the long-term consequences of defective SNARE-based turnover of Na+/K(+)-ATPase and other axolemmal constituents might explain subchronic induction of axon degeneration. The ACR literature occupies a prominent position in neurotoxicology and has significantly influenced development of mechanistic hypotheses and classification schemes for neurotoxicants. Our proposal suggests a reevaluation of current classification schemes and mechanistic hypotheses that regard ACR axonopathy as a primary lesion.

Activities of glucose-metabolizing enzymes in experimental neurotoxic models with lipoate as an alleviator

Acrylamide (35 mg kg(-1) body wt, i.p.) and mercuric chloride (1 mg kg(-1)body wt, i.m.) were administered as specific and non-specific toxins, respectively, to induce neurotoxicity in rats for a period of 10 days. Two different concentrations (35 and 70 mg kg(-1) body wt, i.p.) of lipoic acid were given as prophylactic therapy to mitigate the toxic neuropathies. Homogenates of cerebrum, cerebellum and sciatic nerves were used for the determination of the activities of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), neuron-specific enolase (NSE), hexokinase, phosphoglucoisomerase, aldolase and glucose-6-phosphatase. Inhibition of the activities of these glucose-metabolizing enzymes by the neurotoxins emphasizes the reduction in glucose utilization by the neural tissues to impart its normal function. The degree of inhibition of the enzymes varies with both of the toxins. Acrylamide seems to be a specific inhibitor of GAPDH and NSE, whereas the inhibition caused by HgCl(2) on the enzymes was more general. Enhanced activities of the enzymes indicate increased glucose utility on lipoate administration. This result may be due to the detoxifying potency and possibly due to the cofactor vitality of lipoate.

alpha-Lipoic acid corrects neuropeptide deficits in diabetic rats via induction of trophic support

This study compared the effects of treatment of diabetic rats with either alpha-lipoic acid (100 mg/kg/day i.p. 5 days/week) or with recombinant human nerve growth factor (rhNGF; 0.2 mg/kg s.c. 3 days/week) on NGF-like immunoreactivity (NGFLI) and neuropeptide Y-like immunoreactivity (NPYLI) levels in the sciatic nerve and on the release of substance P-like immunoreactivity (SPLI) from the spinal cord in response to electrical stimulation of the dorsal roots in vitro. Diabetic rats showed depletion of NGFLI and NPYLI, together with reduced release of SPLI. Treatment with NGF increased the sciatic nerve NGFLI (to four times that seen in untreated diabetic rats) and normalised stimulus-evoked release of SPLI, but did not affect the sciatic nerve NPYLI. Treatment with alpha-lipoic acid caused a small non-significant increase in sciatic nerve NGFLI, but normalised both NPYLI levels and stimulus-evoked release of SPLI. These findings indicate that alpha-lipoic acid can boost neurotrophic support in diabetic rats, with effects beyond those related to NGF.

Alpha-lipoic acid: antioxidant potency against lipid peroxidation of neural tissues in vitro and implications for diabetic neuropathy

Nerve lipid peroxidation is increased in experimental diabetic neuropathy, and alpha-lipoic acid will prevent the deficits in nerve blood flow, oxidative stress, and distal sensory conduction. Because these alterations can occur by mechanisms other than augmenting lipid peroxidation in vivo, and because both pro-oxidant and antioxidant effects of the agent have been reported, we undertook studies of in vitro lipid peroxidation of brain and sciatic nerve using an in vitro lipid peroxidation model with an ascorbate-iron-EDTA system. We evaluated the effectiveness of the R(+)-, S(-)-enantiomers, and racemate of alpha-lipoic acid in reducing thiobarbituric acid reactive substances (TBARS) generation in rat brain and sciatic nerve. Studies were also done in an incubation medium containing 20 mM glucose, which increased lipid peroxidation up to fourfold. A dose-dependent and statistically significant reduction in lipid peroxidation was seen with both tissues with similar potencies for both enantiomers. This effect was unassociated with any reduction in the loss of alpha-tocopherol.

Treatment of symptomatic diabetic peripheral neuropathy with the anti-oxidant alpha-lipoic acid. A 3-week multicentre randomized controlled trial (ALADIN Study)

Anti-oxidant treatment has been shown to prevent nerve dysfunction in experimental diabetes mellitus, thus providing a rationale of potential therapeutic value for diabetic patients. The effects of the anti-oxidant alpha-lipoic acid (thioctic acid) were studied in a 3-week multicentre, randomized, double-blind placebo-controlled trial (Alpha-Lipoic Acid in Diabetic Neuropathy; ALADIN) in 328 non-insulin-dependent diabetic patients with symptomatic peripheral neuropathy who were randomly assigned to treatment with intravenous infusion of alpha-lipoic acid using three doses (1200, 600, or 100 mg ALA) or placebo (PLAC). Neuropathic symptoms (pain, burning, paraesthesiae, and numbness) were scored at baseline and at each visit (days 2-5, 8-12, and 15-19) prior to infusion. In addition, the Hamburg Pain Adjective List, a multidimensional specific pain questionnaire, and the Neuropathy Symptom and Disability Scores were assessed at baseline and day 19. According to the protocol 260 (65/63/66/66) patients completed the study. The total symptom score in the feet decreased from baseline to day 19 by -4.5 +/- 3.7 (-58.6%) points (mean +/- SD) in ALA 1200, -5.0 +/- 4.1 (-63.5%) points in ALA 600, -3.3 +/- 2.8 (-43.2%) points in ALA 100, and -2.6 +/- 3.2 (-38.4%) points in PLAC (ALA 1200 vs PLAC: p = 0.003; ALA 600 vs PLAC: p < 0.001). The response rates after 19 days, defined as an improvement in the total symptom score of at least 30%, were 70.8% in ALA 1200, 82.5% in ALA 600, 65.2% in ALA 100, and 57.6% in PLAC (ALA 600 vs PLAC; p = 0.002). The total scale of the Pain Adjective List was significantly reduced in ALA 1200 and ALA 600 as compared with PLAC after 19 days (both p < 0.01). The rates of adverse events were 32.6% in ALA 1200, 18.2% in ALA 600, 13.6% in ALA 100, and 20.7% in PLAC. These findings substantiate that intravenous treatment with alpha-lipoic acid using a dose of 600 mg/day over 3 weeks is superior to placebo in reducing symptoms of diabetic peripheral neuropathy, without causing significant adverse reactions.

Effects of lipoic acid in hexacarbon-induced neuropathy

The effects of lipoic acid on hexacarbon neurotoxicity in rats were investigated. Rats were exposed by inhalation to n-hexane for 24 hours/day, 7 days/week, up to a total period of 9 weeks. Eight animals were exposed to 700 ppm n-hexane only, and eight animals were exposed to 700 ppm n-hexane and additionally received 100 mumol/kg lipoic acid PO daily. Clinical status of the animals was evaluated by examination of general condition, motor performance tests and neurophysiological measurements of caudal nerve motor conduction velocity. Results showed that animals exposed to 700 ppm n-hexane developed severe motor neuropathy leading to paralysis by the 6th week. Motor distal latencies of these animals were severely prolonged. In contrast, in animals treated with lipoic acid the onset of motor neuropathy was delayed for approximately 3 weeks as could be demonstrated by motor performance tests and measurements of motor distal latencies.