Thiamine and benfotiamine protect neuroblastoma cells against paraquat and ß-amyloid toxicity by a coenzyme-independent mechanism.

BACKGROUND: Benfotiamine (BFT) is a synthetic thiamine precursor with high bioavailability. It is efficient in treating complications of type 2 diabetes and has beneficial effects in mouse models of neurodegenerative diseases. The mechanism of action of BFT remains unknown, though it is sometimes suggested that it may be linked to increased thiamine diphosphate (ThDP) coenzyme function. METHODS: We used a mouse neuroblastoma cell line (Neuro2a) grown in thiamine-restricted medium. The cells were stressed by exposure to paraquat (PQ) or amyloid ß1-42 peptide in the presence or absence of BFT and the cell survival was measured using the MTT method. In each case, BFT was compared with sulbutiamine (SuBT), an unrelated thiamine precursor, and thiamine. Metabolites of BFT were determined by HPLC and mass spectrometry. RESULTS: At 50 µM, BFT protects the cells against PQ and amyloid ß1-42 peptide-induced toxicity with the same efficacy. Protective effects were also observed with SuBT and with higher concentrations of thiamine. The main metabolites of BFT were thiamine and S-benzoylthiamine (S-BT). Treatment with both precursors induces a strong increase in intracellular content of thiamine. Protective effects of BFT and SuBT are directly related to thiamine (but not ThDP) levels in Neuro2a cells. CONCLUSIONS: BFT, SuBT and thiamine all protect the cells against oxidative stress, suggesting an antioxidant effect of thiamine. Our results are not in favor of a direct ROS scavenging effect of thiamine but rather an indirect effect possibly mediated by some antioxidant signaling pathway. It is however not clear whether this effect is due to thiamine itself, its thiol form or an unknown metabolite. GENERAL SIGNIFICANCE: Our results suggest a role of thiamine in protection against oxidative stress, independent of the coenzyme function of thiamine diphosphate.

Benfotiamine treatment activates the Nrf2/ARE pathway and is neuroprotective in a transgenic mouse model of tauopathy.

Impaired glucose metabolism, decreased levels of thiamine and its phosphate esters, and reduced activity of thiamine-dependent enzymes, such as pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase and transketolase occur in Alzheimer's disease (AD). Thiamine deficiency exacerbates amyloid beta (Aß) deposition, tau hyperphosphorylation and oxidative stress. Benfotiamine (BFT) rescued cognitive deficits and reduced Aß burden in amyloid precursor protein (APP)/PS1 mice. In this study, we examined whether BFT confers neuroprotection against tau phosphorylation and the generation of neurofibrillary tangles (NFTs) in the P301S mouse model of tauopathy. Chronic dietary treatment with BFT increased lifespan, improved behavior, reduced glycated tau, decreased NFTs and prevented death of motor neurons. BFT administration significantly ameliorated mitochondrial dysfunction and attenuated oxidative damage and inflammation. We found that BFT and its metabolites (but not thiamine) trigger the expression of Nrf2/antioxidant response element (ARE)-dependent genes in mouse brain as well as in wild-type but not Nrf2-deficient fibroblasts. Active metabolites were more potent in activating the Nrf2 target genes than the parent molecule BFT. Docking studies showed that BFT and its metabolites (but not thiamine) bind to Keap1 with high affinity. These findings demonstrate that BFT activates the Nrf2/ARE pathway and is a promising therapeutic agent for the treatment of diseases with tau pathology, such as AD, frontotemporal dementia and progressive supranuclear palsy.

Thiamine and benfotiamine prevent stress-induced suppression of hippocampal neurogenesis in mice exposed to predation without affecting brain thiamine diphosphate levels.

Thiamine is essential for normal brain function and its deficiency causes metabolic impairment, specific lesions, oxidative damage and reduced adult hippocampal neurogenesis (AHN). Thiamine precursors with increased bioavailability, especially benfotiamine, exert neuroprotective effects not only for thiamine deficiency (TD), but also in mouse models of neurodegeneration. As it is known that AHN is impaired by stress in rodents, we exposed C57BL6/J mice to predator stress for 5 consecutive nights and studied the proliferation (number of Ki67-positive cells) and survival (number of BrdU-positive cells) of newborn immature neurons in the subgranular zone of the dentate gyrus. In stressed mice, the number of Ki67- and BrdU-positive cells was reduced compared to non-stressed animals. This reduction was prevented when the mice were treated (200mg/kg/day in drinking water for 20days) with thiamine or benfotiamine, that were recently found to prevent stress-induced behavioral changes and glycogen synthase kinase-3ß (GSK-3ß) upregulation in the CNS. Moreover, we show that thiamine and benfotiamine counteract stress-induced bodyweight loss and suppress stress-induced anxiety-like behavior. Both treatments induced a modest increase in the brain content of free thiamine while the level of thiamine diphosphate (ThDP) remained unchanged, suggesting that the beneficial effects observed are not linked to the role of this coenzyme in energy metabolism. Predator stress increased hippocampal protein carbonylation, an indicator of oxidative stress. This effect was antagonized by both thiamine and benfotiamine. Moreover, using cultured mouse neuroblastoma cells, we show that in particular benfotiamine protects against paraquat-induced oxidative stress. We therefore hypothesize that thiamine compounds may act by boosting anti-oxidant cellular defenses, by a mechanism that still remains to be unveiled. Our study demonstrates, for the first time, that thiamine and benfotiamine prevent stress-induced inhibition of hippocampal neurogenesis and accompanying physiological changes. The present data suggest that thiamine precursors with high bioavailability might be useful as a complementary therapy in several neuropsychiatric disorders.

Thiamine and benfotiamine improve cognition and ameliorate GSK-3ß-associated stress-induced behaviours in mice.

Thiamine (vitamin B1) deficiency in the brain has been implicated in the development of dementia and symptoms of depression. Indirect evidence suggests that thiamine may contribute to these pathologies by controlling the activities of glycogen synthase kinase (GSK)-3ß. While decreased GSK-3ß activity appears to impair memory, increased GSK-3ß activity is associated with the distressed/depressed state. However, hitherto direct evidence for the effects of thiamine on GSK-3ß function has not been reported. Here, we administered thiamine or, the more bioavailable precursor, benfotiamine at 200mg/kg/day for 2weeks to C57BL/6J mice, to determine whether treatment might affect behaviours that are known to be sensitive to GSK-3ß activity and whether such administration impacts on GSK-3ß expression within the brain. The mice were tested in models of contextual conditioning and extinction, a 5-day rat exposure stress test, and a modified swim test with repeated testing. The tricyclic antidepressant imipramine (7.5mg/kg/day), was administered as a positive control for the effects of thiamine or benfotiamine. As for imipramine, both compounds inhibited the upregulation of GSK-3ß induced by predator stress or repeated swimming, and reduced floating scores and the predator stress-induced behavioural changes in anxiety and exploration. Coincident, thiamine and benfotiamine improved learning and extinction of contextual fear, and the acquisition of the step-down avoidance task. Our data indicate that thiamine and benfotiamine have antidepressant/anti-stress effects in naïve animals that are associated with reduced GSK-3ß expression and conditioning of adverse memories. Thus thiamine and benfotiamine may modulate GSK-3ß functions in a manner that is dependent on whether the contextual conditioning is adaptive or maladaptive.

Deuterium content of water increases depression susceptibility: the potential role of a serotonin-related mechanism.

Environmental factors can significantly affect disease prevalence, including neuropsychiatric disorders such as depression. The ratio of deuterium to protium in water shows substantial geographical variation, which could affect disease susceptibility. Thus the link between deuterium content of water and depression was investigated, both epidemiologically, and in a mouse model of chronic mild stress. We performed a correlation analysis between deuterium content of tap water and rates of depression in regions of the USA. Next, we used a 10-day chronic stress paradigm to test whether 2-week deuterium-depleted water treatment (91 ppm) affects depressive-like behavior and hippocampal SERT. The effect of deuterium-depletion on sleep electrophysiology was also evaluated in naïve mice. There was a geographic correlation between a content of deuterium and the prevalence of depression across the USA. In the chronic stress model, depressive-like features were reduced in mice fed with deuterium-depleted water, and SERT expression was decreased in mice treated with deuterium-treated water compared with regular water. Five days of predator stress also suppressed proliferation in the dentate gyrus; this effect was attenuated in mice fed with deuterium-depleted water. Finally, in naïve mice, deuterium-depleted water treatment increased EEG indices of wakefulness, and decreased duration of REM sleep, phenomena that have been shown to result from the administration of selective serotonin reuptake inhibitors (SSRI). Our data suggest that the deuterium content of water may influence the incidence of affective disorder-related pathophysiology and major depression, which might be mediated by the serotoninergic mechanisms.

Concomitant manipulation of murine NMDA- and AMPA-receptors to produce pro-cognitive drug effects in mice.

Bifunctional drug therapy targeting distinct receptor signalling systems can generate increased efficacy at lower concentrations compared to monofunctional therapy. Non-competitive blockade of the NMDA receptors or the potentiation of AMPA receptors is well documented to result in memory enhancement. Here, we compared the efficacy of the low-affinity NMDA receptor blocker memantine or the positive modulator of AMPA receptor QXX (in C57BL/6J at 1 or 5mg/kg, ip) with new derivatives of isothiourea (0.5-1 mg/kg, ip) that have bifunctional efficacy. Low-affinity NMDA blockade by these derivatives was achieved by introducing greater flexibility into the molecule, and AMPA receptor stimulation was produced by a sulfamide-containing derivative of isothiourea. Contextual learning was examined in a step-down avoidance task and extinction of contextual memory was studied in a fear-conditioning paradigm. Memantine enhanced contextual learning while QXX facilitated memory extinction; both drugs were effective at 5 mg/kg. The new derivative IPAC-5 elevated memory scores in both tasks at the dose 0.5 mg/kg and exhibited the lowest IC50 values of NMDA receptor blockade and highest potency of AMPA receptor stimulation. Thus, among the new drugs tested, IPAC-5 replicated the properties of memantine and QXX in one administration with increased potency. Our data suggest that a concomitant manipulation of NMDA- and AMPA-receptors results in pro-cognitive effects and supports the concept bifunctional drug therapy as a promising strategy to replace monofunctional therapies with greater efficacy and improved compliance.

Altered emotionality, hippocampus-dependent performance and expression of NMDA receptor subunit mRNAs in chronically stressed mice.

N-Methyl-D-aspartate receptor (NMDAR)-mediated neurotransmission in the hippocampus is implicated in cognitive and emotional disturbances during stress-related disorders. Here, using quantitative RT-PCR, we investigated the hippocampal expression of NR2A, NR2B and NR1 subunit mRNAs in a mouse stress paradigm that mimics clinically relevant conditions of simultaneously affected emotionality and hippocampus-dependent functions. A 2-week stress procedure, which comprised ethologically valid stressors, exposure to a rat and social defeat, was applied to male C57BL/6J mice. For predation stress, mice were introduced into transparent containers that were placed in a rat home cage during the night; social defeat was applied during the daytime using aggressive CD1 mice. This treatment impaired hippocampus-dependent performance during contextual fear conditioning. A correlation between this behavior and food displacement performance was demonstrated, suggesting that burrowing behavior is affected by the stress procedure and is hippocampus-dependent. Stressed mice (n = 22) showed behavioral invigoration and anomalous anxiolytic-like profiles in the O-maze and brightly illuminated open field, unaltered short-term memory in the step-down avoidance task and enhanced aggressive traits, as compared to non-stressed mice (n = 10). Stressed mice showed increased basal serum corticosterone concentrations, hippocampal mRNA expression for the NR2A subunit of the NMDAR and in the NR2A/NR2B ratio; mRNA expression of NR2B and NR1 was unchanged. Thus, stress-induced aberrations in both hippocampal-dependent performance and emotional abnormalities are associated with alterations in hippocampal mRNA NR2A levels and the NR2A/NR2B ratio and not with mRNA expression of NR2B or NR1.

Anhedonic-like traits and lack of affective deficits in 18-month-old C57BL/6 mice: Implications for modeling elderly depression.

The prevalence of depression increases with aging. We hypothesized that like humans, old animals exhibit anhedonic-like behavior, along with signs of behavioral despair. In rodents, anhedonia, a reduced sensitivity to reward, which is listed as a core feature of major depression in the DSM-IVR, can be measured by a decrease in intake of and preference for sweet solutions. Here, sucrose intake, forced swimming, immobility in the modified tail suspension test, novelty exploration, grooming, anxiety and locomotor activity were compared in naïve 3- and 18-month-old male C57BL/6 mice. The absolute amounts and the ratio of consumed 1% sucrose solution to water intake was significantly smaller in 18-month-old mice than in 3-month-old mice. The consumption of 5%-sucrose solution requiring high levels of drinking effort, novelty exploration in two setups and grooming behavior in the splash test were reduced in older animals. Analysis of other behaviors suggested that the above-mentioned signs of anhedonic-like traits were unlikely to be attributable to the potential effect of aging on metabolic needs for water, taste perception, motor capabilities or the induction of essential anxiety and neophobia. A 4-week treatment with the antidepressant imipramine (7mg/kg/day) or dimebon, a compound with suggested neuroprotective proneurogenic properties (1mg/kg/day) restored sucrose intake and preference in 18-month-old mice. Meanwhile, young and old mice showed no differences in the parameters of behavioral despair evaluated in the forced swim and modified tail suspension tests. Thus, the behavioral profile of aged mice parallels that of humans with elderly depression, in whom the symptoms of hedonic deficits typically outweigh affective disturbances. The assessment of anhedonic-like traits with the sucrose preference test in 18-month-old mice will be useful in preclinical studies of elderly depression.

Dimebon enhances hippocampus-dependent learning in both appetitive and inhibitory memory tasks in mice.

Pre-clinical and clinical studies on dimebon (dimebolin or latrepirdine) have demonstrated its use as a cognitive enhancer. Here, we show that dimebon administered to 3-month-old C57BL6N mice 15 min prior to training in both appetitive and inhibitory learning tasks via repeated (0.1 mg/kg) and acute (0.5 mg/kg) i.p. injections, respectively, increases memory scores. Acute treatment with dimebon was found to enhance inhibitory learning, as also shown in the step-down avoidance paradigm in 7-month-old mice. Bolus administration of dimebon did not affect the animals' locomotion, exploration or anxiety-like behaviour, with the exception of exploratory behaviour in older mice in the novel cage test. In a model of appetitive learning, a spatial version of the Y-maze, dimebon increased the rate of correct choices and decreased the latency of accessing a water reward after water deprivation, and increased the duration of drinking behaviour during training/testing procedures. Repeated treatment with dimebon did not alter the behaviours in other tests or water consumption. Acute treatment of water-deprived and non-water-deprived mice with dimebon also did not affect their water intake. Our data suggest that dimebon enhances hippocampus-dependent learning in both appetitive and inhibitory tasks in mice.