Activities of thiamine-dependent enzymes in two experimental models of thiamine deficiency encephalopathy: 3. Transketolase

Thiamine ameliorates metabolic disorders induced by a long-term high-concentrate diet and promotes rumen epithelial development in goats

Data indicate that dietary thiamine supplementation can partly alleviate rumen epithelium inflammation and barrier function in goats fed a high-concentrate diet. The current work aimed to explore whether thiamine promotes rumen epithelium development by regulating carbohydrate metabolism during a long period of feeding high levels of concentrate. For the experiment, 24 female Boer goats (35.62 ± 2.4 kg of body weight) in parity 1 or 2 were allocated to 3 groups (8 goats per replicate) receiving a low-concentrate diet (concentrate:forage 30:70), a high-concentrate diet (HC; concentrate:forage 70:30), or a high-concentrate diet (concentrate:forage 70:30) supplemented with 200 mg of thiamine/kg of dry matter intake (HCT; concentrate:forage 70:30). On the last day of 12 wk, rumen fluid and blood samples were collected to measure ruminal parameters, endotoxin lipopolysaccharide, and blood inflammatory cytokines. Goats were slaughtered to collect ruminal tissue to determine differential metabolites, enzyme activities, and gene expression. Liquid chromatography-tandem mass spectrometry analysis revealed that the HCT group had significantly increased concentrations of d-glucose 6-phosphate, d-fructose 6-phosphate, glyceraldehyde 3-phosphate, thiamine pyrophosphate, oxaloacetate, acetyl-CoA, succinyl-CoA, sedoheptulose 7-phosphate, ribose 5-phosphate, and NADPH compared with the HC group. The pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, and transketolase enzyme activities in the rumen epithelium of the HCT group were higher than those in the HC group. The plasma total antioxidant capacity values for the HCT group were greater than those for the HC group. The rumen epithelium ATP content in the HCT group was higher than that in the HC group. Compared with the HCT group, the HC group had a lower mRNA abundance of CCND1, CCNA2, CDK2, CDK4, CDK6, BCL2, PI3K, and AKT1. Taken together, the results suggest that dietary thiamine supplementation could ameliorate disorders in the tricarboxylic acid cycle and the pentose phosphate pathway induced by a long-term high-concentrate diet and could promote rumen epithelial growth.

Thiamine Alleviates High-Concentrate-Diet-Induced Oxidative Stress, Apoptosis, and Protects the Rumen Epithelial Barrier Function in Goats

High-concentrate diets are continually used in ruminants to meet the needs of milk yield, which can lead to the occurrence of subacute rumen acidosis in ruminants. This study investigated the protective effects of dietary thiamine supplementation on the damage of the ruminal epithelium barrier function in goats fed a high-concentrate diet. Twenty-four healthy Boer goats (live weight of 35.62 ± 2.4 kg; age, 1 year) were randomly assigned into three treatments, with eight goats in each treatment, consuming one of three diets: a low-concentrate diet (CON; concentrate/forage, 30:70), a high-concentrate diet (HC; concentrate/forage, 70:30), or a high-concentrate diet with 200 mg of thiamine/kg of dry matter intake (HCT; concentrate/forage, 70:30) for 12 weeks. The additional dose of thiamine was based on our previous study wherein thiamine ameliorates inflammation. Compared with HC treatment, the HCT treatment had markedly higher concentrations of glutathione, superoxide dismutase, and glutathione peroxidase and total antioxidant capacity (P < 0.05) in plasma and rumen epithelium. The results showed that the apoptosis index was lower (P < 0.05) in the HCT treatment than in that of the HC treatment. Compared with the HC treatment, permeability and the electrophysiology parameter short circuit current for ruminal epithelial tissue were significantly decreased (P < 0.05) in the HCT treatment. The immunohistochemical results showed that the expression distribution of tight junctions including claudin-1, claudin-4, occludin, and zonula occludin-1 (ZO-1) was greater (P < 0.05) in the HCT treatments than in the HC treatment. The mRNA expression in the rumen epithelium of ZO-1, occludin, claudin-1, B-cell lymphoma/leukemia 2, nuclear factor erythroid-2 related factor 2 (Nrf2), superoxide dismutase 2 (SOD2), glutathione peroxidase 1, and the phase II metabolizing enzymes quinone oxidoreductase and heme oxygenase in the HCT group was significantly increased in comparison with the HC diet treatment (P < 0.05), whereas the mRNA expression of caspase 3, caspase 8, caspase 9, bcl-2 associated X protein, lipopolysaccharide binding protein, toll-like receptor 4, nuclear factor kappa-B (NFκB), tumor necrosis factor alpha, interleukin-1β, interleukin, and tumor necrosis factor receptor-associated factor 6 decreased significantly in the HCT treatment (P < 0.05). Compared with the HC treatment, the HCT diet significantly increased the protein expression of ZO-1, occludin, claudin-1, NQO1, HO-1, SOD2, serine/threonine kinase, p-Akt, Nrf2, and p-Nrf2; conversely, the expression of NFκB-related proteins p65 and pp65 was significantly decreased (P < 0.05). In addition, thiamine relieved the damage on the ruminal epithelium caused by the HC diet. The results show that dietary thiamine supplementation improves the rumen epithelial barrier function by regulating Nrf2-NFκB signaling pathways during high-concentrate-diet feeding.

Thiamine deficiency impairs common eider (Somateria mollissima) reproduction in the field

The Baltic Sea population of the common eider (Somateria mollissima) has declined dramatically during the last two decades. Recently, widespread episodic thiamine (vitamin B₁) deficiency has been demonstrated in feral birds and suggested to contribute significantly to declining populations. Here we show that the decline of the common eider population in the Baltic Sea is paralleled by high mortality of the pulli a few days after hatch, owing to thiamine deficiency and probably also thereby associated abnormal behaviour resulting in high gull predation. An experiment with artificially incubated common eider eggs collected in the field revealed that thiamine treatment of pulli had a therapeutic effect on the thiamine status of the brain and prevented death. The mortality was 53% in untreated specimens, whereas it was only 7% in thiamine treated specimens. Inability to dive was also linked to brain damage typical for thiamine deficiency. Our results demonstrate how thiamine deficiency causes a range of symptoms in the common eider pulli, as well as massive die-offs a few days after hatch, which probably are the major explanation of the recent dramatic population declines.

Widespread episodic thiamine deficiency in Northern Hemisphere wildlife

Many wildlife populations are declining at rates higher than can be explained by known threats to biodiversity. Recently, thiamine (vitamin B1) deficiency has emerged as a possible contributing cause. Here, thiamine status was systematically investigated in three animal classes: bivalves, ray-finned fishes, and birds. Thiamine diphosphate is required as a cofactor in at least five life-sustaining enzymes that are required for basic cellular metabolism. Analysis of different phosphorylated forms of thiamine, as well as of activities and amount of holoenzyme and apoenzyme forms of thiamine-dependent enzymes, revealed episodically occurring thiamine deficiency in all three animal classes. These biochemical effects were also linked to secondary effects on growth, condition, liver size, blood chemistry and composition, histopathology, swimming behaviour and endurance, parasite infestation, and reproduction. It is unlikely that the thiamine deficiency is caused by impaired phosphorylation within the cells. Rather, the results point towards insufficient amounts of thiamine in the food. By investigating a large geographic area, by extending the focus from lethal to sublethal thiamine deficiency, and by linking biochemical alterations to secondary effects, we demonstrate that the problem of thiamine deficiency is considerably more widespread and severe than previously reported.

Thiamine Deficiency in Tropical Pediatrics: New Insights into a Neglected but Vital Metabolic Challenge

In humans, thiamine is a micronutrient prone to depletion that may result in severe clinical abnormalities. This narrative review summarizes current knowledge on thiamine deficiency (TD) and bridges the gap between pathophysiology and clinical presentation by integrating thiamine metabolism at subcellular level with its function to vital organs. The broad clinical spectrum of TD is outlined, with emphasis on conditions encountered in tropical pediatric practice. In particular, TD is associated with type B lactic acidosis and classic forms of beriberi in children, but it is often unrecognized. Other severe acute conditions are associated with hypermetabolism, inducing a functional TD. The crucial role of thiamine in infant cognitive development is also highlighted in this review, along with analysis of the potential impact of TD in refeeding syndrome during severe acute malnutrition (SAM). This review aims to increase clinical awareness of TD in tropical settings where access to diagnostic tests is poor, and advocates for an early therapeutic thiamine challenge in resource-limited settings. Moreover, it provides evidence for thiamine as treatment in critical conditions requiring metabolic resuscitation, and gives rationale to the consideration of increased thiamine supplementation in therapeutic foods for malnourished children.

Thiamin diphosphate-dependent enzymes: from enzymology to metabolic regulation, drug design and disease models

Bringing a knowledge of enzymology into research in vivo and in situ is of great importance in understanding systems biology and metabolic regulation. The central metabolic significance of thiamin (vitamin B1 ) and its diphosphorylated derivative (thiamin diphosphate; ThDP), and the fundamental differences in the ThDP-dependent enzymes of metabolic networks in mammals versus plants, fungi and bacteria, or in health versus disease, suggest that these enzymes are promising targets for biotechnological and medical applications. Here, the in vivo action of known regulators of ThDP-dependent enzymes, such as synthetic structural analogs of the enzyme substrates and thiamin, is analyzed in light of the enzymological data accumulated during half a century of research. Mimicking the enzyme-specific catalytic intermediates, the phosphonate analogs of 2-oxo acids selectively inhibit particular ThDP-dependent enzymes. Because of their selectivity, use of these compounds in cellular and animal models of ThDP-dependent enzyme malfunctions improves the validity of the model and its predictive power when compared with the nonselective and enzymatically less characterized oxythiamin and pyrithiamin. In vitro studies of the interaction of thiamin analogs and their biological derivatives with potential in vivo targets are necessary to identify and attenuate the analog selectivity. For both the substrate and thiamin synthetic analogs, in vitro reactivities with potential targets are highly relevant in vivo. However, effective concentrations in vivo are often higher than in vitro studies would suggest. The significance of specific inihibition of the ThDP-dependent enzymes for the development of herbicides, antibiotics, anticancer and neuroprotective strategies is discussed.

Decoding Alzheimer's disease from perturbed cerebral glucose metabolism: implications for diagnostic and therapeutic strategies

Alzheimer's disease (AD) is an age-related devastating neurodegenerative disorder, which severely impacts on the global economic development and healthcare system. Though AD has been studied for more than 100 years since 1906, the exact cause(s) and pathogenic mechanism(s) remain to be clarified. Also, the efficient disease-modifying treatment and ideal diagnostic method for AD are unavailable. Perturbed cerebral glucose metabolism, an invariant pathophysiological feature of AD, may be a critical contributor to the pathogenesis of this disease. In this review, we firstly discussed the features of cerebral glucose metabolism in physiological and pathological conditions. Then, we further reviewed the contribution of glucose transportation abnormality and intracellular glucose catabolism dysfunction in AD pathophysiology, and proposed a hypothesis that multiple pathogenic cascades induced by impaired cerebral glucose metabolism could result in neuronal degeneration and consequently cognitive deficits in AD patients. Among these pathogenic processes, altered functional status of thiamine metabolism and brain insulin resistance are highly emphasized and characterized as major pathogenic mechanisms. Finally, considering the fact that AD patients exhibit cerebral glucose hypometabolism possibly due to impairments of insulin signaling and altered thiamine metabolism, we also discuss some potential possibilities to uncover diagnostic biomarkers for AD from abnormal glucose metabolism and to develop drugs targeting at repairing insulin signaling impairment and correcting thiamine metabolism abnormality. We conclude that glucose metabolism abnormality plays a critical role in AD pathophysiological alterations through the induction of multiple pathogenic factors such as oxidative stress, mitochondrial dysfunction, and so forth. To clarify the causes, pathogeneses and consequences of cerebral hypometabolism in AD will help break the bottleneck of current AD study in finding ideal diagnostic biomarker and disease-modifying therapy.

Are brain and heart tissue prone to the development of thiamine deficiency?

Thiamine deficiency is a continuing problem leading to beriberi and Wernicke's encephalopathy. The symptoms of thiamine deficiency develop in the heart, brain and neuronal tissue. Yet, it is unclear how rapid thiamine deficiency develops and which organs are prone to development of thiamine deficiency. We investigated these issues in a thiamine deficient animal model. Twenty-four male Lewis rats were fed a thiamine deficient diet, which contained 0.04% of normal thiamine intake. Six control rats were fed 200 μg of thiamine per day. Every week a group of six rats on the thiamine-deficient diet was sacrificed and blood, urine and tissue were stored. Blood and tissue transketolase activity, thiamine and thiamine metabolites were measured and PCR of thiamine transporter-1 (ThTr-1) was performed. Transketolase activity was significantly reduced in red blood cells, liver, lung, kidney and spleen tissue after two weeks of thiamine deficient diet. In brain tissue, transketolase activity was not reduced after up to four weeks of thiamine deficient diet. The amount of thiamine pyrophosphate was also significantly conserved in brain and heart tissue (decrease of 31% and 28% respectively), compared to other tissues (decrease of ~70%) after four weeks of thiamine deficient diet. There was no difference between tissues in ThTr-1 expression after four weeks of thiamine deficient diet. Despite the fact that the heart and the brain are predilection sites for complications from thiamine deficiency, these tissues are protected against thiamine deficiency. Other organs could be suffering from thiamine deficiency without resulting in clinical signs of classic thiamine deficiency in beriberi and Wernicke's encephalopathy.

Pathophysiologic mechanisms responsible for the reversible (thiamine-responsive) and irreversible (thiamine non-responsive) neurological symptoms of Wernicke's encephalopathy

Chronic alcoholism results in thiamine deficiency as a result of poor nutrition and impaired gastrointestinal absorption of the vitamin. Pyrithiamine-induced thiamine deficiency in the rat reproduces a neurological syndrome and ultimately neuropathological damage of a nature and distribution that is similar to that encountered in Wernicke's encephalopathy in humans. Pyrithiamine-induced thiamine deficiency results in selective reversible decreases in activity of the thiamine-dependent enzyme alpha-ketoglutarate dehydrogenase and concomitant reversible changes in brain amino acids. It is proposed that these changes constitute "the biochemical lesion" in thiamine deficiency encephalopathy. If sufficiently severe and prolonged, decreased activities of alpha-ketoglutarate dehydrogenase may result in compromised brain energy metabolism and in lactate accumulation in brain, both of which could be responsible for neuronal cell death in this condition. In addition, it has been suggested that cell death results from NMDA-receptor mediated excitotoxic damage. Similar pathophysiologic mechanisms could be responsible for brain cell death in Wernicke's encephalopathy in humans.

Cortical cholinergic abnormalities contribute to the amnesic state induced by pyrithiamine-induced thiamine deficiency in the rat

Although the key neuropathology associated with diencephalic amnesia is lesions to the thalamus and/or mammillary bodies, functional deactivation of the hippocampus and associated cortical regions also appear to contribute to the memory dysfunction. For example, there is loss of forebrain cholinergic neurons and alterations in stimulated acetylcholine (ACh) levels in the hippocampus and cortex in animal models of diencephalic amnesia associated with thiamine deficiency. In the present study, the pyrithiamine-induced thiamine deficiency rat model was used to assess the functional relationships between thalamic pathology, behavioral impairment, ACh efflux and cholinergic innervation of the hippocampus and cortex. In pyrithiamine-induced thiamine deficiency-treated rats, ACh efflux during behavioral testing was blunted to differing degrees in the hippocampus, medial frontal cortex and retrosplenial cortex. In addition, significant reductions in cholinergic fiber densities were observed in each of these regions. However, only hippocampal cholinergic fiber density correlated significantly with ACh efflux in the same region, suggesting that the reduction in cortical ACh efflux in cases of diencephalic amnesia cannot be fully explained by a loss of cholinergic fiber innervation. This notion supports the emerging theory that the functional consequences of the distal effects of lesions go beyond simple deafferentation. Specifically, some frontal cortical regions exhibit hypersensitivity to deafferentation that is only detected during behavioral and/or physiological demand.

Thiamine deficiency results in downregulation of the GLAST glutamate transporter in cultured astrocytes

Pyrithiamine-induced thiamine deficiency (TD) is a well-established model of Wernicke's encephalopathy in which a glutamate-mediated excitotoxic mechanism may play an important role in determining selective vulnerability. In order to examine this possibility, cultured astrocytes were exposed to TD and effects on glutamate transport and metabolic function were studied. TD led to decreases in cellular levels of thiamine and thiamine diphosphate (TDP) after 24 h of treatment and decreased activities of the TDP-dependent enzymes alpha-ketoglutarate dehydrogenase and transketolase after 4 and 7 days, respectively. TD treatment for 10 days led to a reversible decrease in the uptake of [(3)H]-D-aspartate, a nonmetabolizable analogue of glutamate. Kinetic analysis revealed that the uptake inhibition was caused by a 47% decrease in the V(max) for uptake of [(3)H]-D-aspartate, with no change in the K(m) value. Immunoblotting showed that this decrease in uptake was due to an 81% downregulation of the astrocyte-specific GLAST glutamate transporter. Loss of uptake activity and GLAST protein were blocked by treatment with the protein kinase C inhibitor H7, while exposure to DCG IV, a group II metabotropic glutamate receptor (mGluR) agonist, resulted in improvement of [(3)H]-D-aspartate uptake and a partial reversal of transporter downregulation. These results are consistent with our recent in vivo findings of a loss of astrocytic glutamate transporters in TD and provide evidence that TD conditions may increase phosphorylation of GLAST, contributing to its downregulation. In addition, manipulation of group II mGluR activity may provide an important strategy in the treatment of this disorder.

Effects of furazolidone, PCB77, PCB126, Aroclor 1248, paraquat and p,p'-DDE on transketolase activity in embryonal chicken brain

The effect of in ovo exposure to PCBs, DDE and paraquat on transketolase activity was measured in 19-day-old chicken embryos. Furazolidone was used as a positive control for decreased activity of the enzyme. The potency of contaminants to interact with transketolase was also tested in an in vitro system, using control brain 7000xg supernatants containing the enzyme. No effects were found on transketolase activity after in ovo or in vitro exposure to PCB126, Aroclor, DDE or paraquat. PCB77 decreased transketolase activity in vitro, but only at concentrations that, extrapolated to in ovo exposure, would be lethal to the embryo. Furazolidone decreased transketolase activity both in ovo and in vitro. For this contaminant, thiamine residues were analysed in the yolk sacs, but no differences were found between exposed and non-exposed eggs. Transketolase is dependent on thiamine pyrophosphate as a cofactor, and therefore, the decreased enzyme activity could be the result of an interaction between furazolidone and thiamine metabolism. Since thiamine residues were not affected by furazolidone and transketolase inhibition in vitro was similar to the inhibition after in ovo exposure, it was concluded that furazolidone interacted with transketolase on the enzymatic level rather than by a depletion of thiamine.

Selective down-regulation of the astrocyte glutamate transporters GLT-1 and GLAST within the medial thalamus in experimental Wernicke's encephalopathy

Although earlier studies on thiamine deficiency have reported increases in extracellular glutamate concentration in the thalamus, a vulnerable region of the brain in this disorder, the mechanism by which this occurs has remained unresolved. Treatment with pyrithiamine, a central thiamine antagonist, resulted in a 71 and 55% decrease in protein levels of the astrocyte glutamate transporters GLT-1 and GLAST, respectively, by immunoblotting in the medial thalamus of day 14 symptomatic rats at loss of righting reflexes. These changes occurred prior to the onset of convulsions and pannecrosis. Loss of both GLT-1 and GLAST transporter sites was also confirmed in this region of the thalamus at the symptomatic stage using immunohistochemical methods. In contrast, no change in either transporter protein was detected in the non-vulnerable frontal parietal cortex. These effects are selective; protein levels of the astrocyte GABA transporter GAT-3 were unaffected in the medial thalamus. In addition, astrocyte-specific glial fibrillary acidic protein (GFAP) content was unchanged in this brain region, suggesting that astrocytes are spared in this disorder. Loss of GLT-1 or GLAST protein was not observed on day 12 of treatment, indicating that down-regulation of these transporters occurs within 48 h prior to loss of righting reflexes. Finally, GLT-1 content was positively correlated with levels of the neurofilament protein alpha-internexin, suggesting that early neuronal drop-out may contribute to the down-regulation of this glutamate transporter and subsequent pannecrosis. A selective, focal loss of GLT-1 and GLAST transporter proteins provides a rational explanation for the increase in interstitial glutamate levels, and may play a major role in the selective vulnerability of thalamic structures to thiamine deficiency-induced cell death.

Glucose induced IEG expression in the thiamin-deficient rat brain

Glucose loading of rats made thiamin deficient by dietary deprivation of thiamin and the administration of pyrithiamin (40 microg/100 g, i.p.) precipitates an acute neuropathy, a model of Wernicke's encephalopathy in man (Zimitat and Nixon, Metab. Brain Dis. 1999;14:1-20). Immunohistochemical detection of Fos proteins was used as a marker to identify neuronal populations in the thiamin-deficient rat brain affected by glucose loading. As thiamin deficiency progressed, the extent and intensity of Fos-like immunoreactivity (FLI) in brain structures typically affected by thiamin deficiency (the thalamus, mammillary bodies, inferior colliculus, vestibular nucleus and inferior olives) were markedly increased when compared to thiamin-replete controls. Glucose loading for 1-3 days further increased the intensity of FLI in these same regions, consistent with a dependence of Fos expression on carbohydrate metabolism as well as on thiamin deficiency. The timed acute changes that follow a bolus glucose load administered to thiamin-deficient animals may provide a sequential account of events in the pathogenesis of brain damage in this model of Wernicke's encephalopathy.

Thiamine deficiency results in metabolic acidosis and energy failure in cerebellar granule cells: an in vitro model for the study of cell death mechanisms in Wernicke's encephalopathy

Thiamine deficiency (TD) in both humans and experimental animals results in severe compromise of mitochondrial function and leads to selective neuronal cell death in diencephalic and cerebellar structures. To examine further the influence of TD on neuronal survival in relation to metabolic changes, primary cultures of rat cerebellar granule cells were exposed to thiamine-deficient medium for up to 7 days in the absence or presence of the central thiamine antagonist pyrithiamine (Py). Exposure of cells for 7 days to thiamine-deficient medium alone resulted in no detectable cell death. On the other hand, 50 microM Py treatment led to reductions of thiamine phosphate esters, decreased activities of the thiamine-dependent enzymes alpha-ketoglutarate dehydrogenase and transketolase, a twofold increase in lactate release (P < 0.001), a lowering of pH, and significant (58%, P < 0.001) cell death. DNA fragmentation studies did not reveal evidence of apoptotic cell death. Addition of 50 microM alpha-tocopherol (vitamin E) or 100 microM of butylated hydroxyanisole (BHA) to Py-treated cells resulted in significant neuroprotection. On the other hand, addition of 10 microM MK-801, an NMDA receptor antagonist, was not neuroprotective. These results suggest that reactive oxygen species (ROS) play a major role in thiamine deficiency-induced neuronal cell death. Insofar as this experimental model recapitulates the metabolic and mitochondrial changes characteristic of thiamine deficiency in the intact animal, it might be useful in the elucidation of mechanisms involved in the neuronal cell death cascade resulting from thiamine deficiency.

Alcohol-thiamine interactions: an update on the pathogenesis of Wernicke encephalopathy

Wernicke encephalopathy is a neurological disorder commonly observed in chronic alcohol abuse, in patients with AIDS, and in other conditions of compromised nutritional status. The underlying cause of the disorder is thiamine deficiency. The present review highlights data focusing on alcohol-thiamine interactions and their relationship to the pathogenesis of Wernicke encephalopathy. Recent findings on the effects of alcohol on thiamine absorption and storage and on thiamine phosphorylation to the enzyme co-factor form (thiamine diphosphate) are discussed with regard to the postulated "biochemical lesion" of Wernicke encephalopathy. Also discussed are new findings on the molecular genetics of the thiamine-dependent enzyme transketolase in patients with Wernicke encephalopathy. A discussion of the hypotheses regarding the mechanisms underlying the phenomenon of selective neuronal cell death observed in this disorder including cerebral energy deficit, focal lactic acidosis, glutamate excitotoxicity, increased expression of immediate-early genes, free radicals and perturbations of the blood-brain barrier are presented. Finally, the possible role of thiamine deficiency in alcoholic peripheral neuropathy is reviewed.

Glucose loading precipitates acute encephalopathy in thiamin-deficient rats

A rat model of glucose-precipitated Wernicke's encephalopathy (WE) has been developed in which glucose loading (10 g/kg, i.p.) of ataxic thiamin-deficient (TD) rats induced episodes of gross neurological dysfunction and sometimes death. The acute effects of a glucose load on the neurological state of thiamin-replete control and TD rats were assessed by scoring of clinical observations and performance measured on a moving belt (MB) apparatus at 30 min intervals for 2 hr after the challenge. Glucose loading or saline treatment (2.5 mL, i.p.) had no significant behavioural or clinical consequences when administered to controls or rats fed TD diet for <21 days. Glucose loading of ataxic rats fed TD diet for 28-35 days precipitated episodes of gross ataxia and signs of advanced neurological dysfunction (e.g. loss of righting reflex and hyperexcitability) leading to significant increases in the Ataxia (p<0.05) and Advanced Sign (p<0.05) scores within 2 hr after the challenge. Simultaneously, the performance of these animals on the MB decreased 10-fold. Regular glucose challenges significantly increased the rate of progression of disease in TD rats when compared with untreated TD rats. This model may be useful for the further investigation of the pathogenesis of WE at the molecular level.

Early microglial response in experimental thiamine deficiency: an immunohistochemical analysis

Early glial changes have consistently been reported in experimental thiamine deficiency (TD) (Tellez and Terry, Am. J. Pathol. 52:777-794, 1968.) and in Wernicke Encephalopathy in humans (Victor et al., F.A. Davis Co., Philadelphia, 1989.). However, the precise nature of these changes and their relationship to the phenomenon of selective neuronal cell loss in TD has not been elucidated. In the present studies, antibodies against GFAP and ED1 were used to evaluate astrocytic and microglial/macrophagic changes respectively in adjacent sections of the brains of thiamine-deficient rats at various stages (n = 6 per stage) during the progression of encephalopathy. Additionally, the integrity of the blood-brain barrier at the same stages was assessed using IgG immunohistochemistry. Counts of immuno-positive cells revealed significant increases of ED1-immunostaining in the inferior olive, medial geniculate nucleus, and medial thalamic nuclei on day 8 of the treatment paradigm, prior to any evidence of increased IgG immunostaining or significant neuronal cell loss. ED1 immunostaining increased over time, resulting in intense staining by the loss of righting reflex stage (day 13-15). Focal increases of IgG-immunoreactivity in inferior olive, medial dorsal thalamus, and medial geniculate nucleus were observed on day 10, followed by increased GFAP-immunostaining consistent with reactive gliosis. Early microglial activation leading to the release of cytotoxic substances including reactive oxygen species, glutamate and cytokines appears to be the initial cellular response to TD and could be responsible for the focal neuronal loss characteristic of this disorder.

Properties and functions of the thiamin diphosphate dependent enzyme transketolase

This review highlights recent research on the properties and functions of the enzyme transketolase, which requires thiamin diphosphate and a divalent metal ion for its activity. The transketolase-catalysed reaction is part of the pentose phosphate pathway, where transketolase appears to control the non-oxidative branch of this pathway, although the overall flux of labelled substrates remains controversial. Yeast transketolase is one of several thiamin diphosphate dependent enzymes whose three-dimensional structures have been determined. Together with mutational analysis these structural data have led to detailed understanding of thiamin diphosphate catalysed reactions. In the homodimer transketolase the two catalytic sites, where dihydroxyethyl groups are transferred from ketose donors to aldose acceptors, are formed at the interface between the two subunits, where the thiazole and pyrimidine rings of thiamin diphosphate are bound. Transketolase is ubiquitous and more than 30 full-length sequences are known. The encoded protein sequences contain two motifs of high homology; one common to all thiamin diphosphate-dependent enzymes and the other a unique transketolase motif. All characterised transketolases have similar kinetic and physical properties, but the mammalian enzymes are more selective in substrate utilisation than the nonmammalian representatives. Since products of the transketolase-catalysed reaction serve as precursors for a number of synthetic compounds this enzyme has been exploited for industrial applications. Putative mutant forms of transketolase, once believed to predispose to disease, have not stood up to scrutiny. However, a modification of transketolase is a marker for Alzheimer's disease, and transketolase activity in erythrocytes is a measure of thiamin nutrition. The cornea contains a particularly high transketolase concentration, consistent with the proposal that pentose phosphate pathway activity has a role in the removal of light-generated radicals.

Mechanisms of neuronal cell death in Wernicke's encephalopathy

Wernicke's Encephalopathy (WE) is a serious neurological disorder resulting from thiamine deficiency, encountered in chronic alcoholics and in patients with grossly impaired nutritional status. Neuropathologic studies as well as Magnetic Resonance Imaging reveal selective diencephalic and brainstem lesions in patients with WE. The last decade has witnessed major advances in the understanding of pathophysiologic mechanisms linking thiamine deficiency to the selective brain lesions characteristic of WE. Activities of the thiamine-dependent enzyme alpha-ketoglutarate dehydrogenase, a rate-limiting tricarboxylic acid cycle enzyme are significantly reduced in autopsied brain tissue from patients with WE and from rats treated with the central thiamine antagonist, pyrithiamine. In the animal studies, evidence suggests that such enzyme deficits result in focal lactic acidosis, cerebral energy impairment and depolarization resulting from increased release of glutamate in vulnerable brain structures. It has been proposed that this depolarization may result in N-Methyl-D-Aspartate receptor-mediated excitotoxicity as well as increased expression of immediate early genes such as c-fos and c-jun resulting in apoptotic cell death. Other mechanisms involved in thiamine deficiency-induced cell loss may involve free radicals and alterations of the blood-brain barrier. Additional studies are still required to identify the site of the initial cellular insult and to explain the predilection of diencephalic and brainstem structures due to thiamine deficiency.

Cortical and subcortical white matter damage without Wernicke's encephalopathy after recovery from thiamine deficiency in the rat

The relative etiologic roles of ethanol and thiamine deficiency in the cortical atrophy and loss of cerebral white matter in chronic alcoholics are uncertain. The present study examined the distribution of degenerating axons within cortical and subcortical tracts 1 week after recovery from early to late symptomatic stages of thiamine deficiency in the absence of ethanol in Sprague-Dawley rats. The brains of rats exposed to an early symptomatic stage of pyrithiamine-induced thiamine deficiency, 12-13 days of treatment, contained degenerating axons in corpus callosum, anterior commissure, external and internal capsules, optic and olfactory tracts, and fornix and mammillothalamic tracts. A dense pattern of degenerating axons was evident in layers III-IV of frontal and parietal cortex. Less intense and more evenly distributed degenerating axons were present in layers IV-VI of frontal, parietal, cingulate, temporal, retrosplenial, occipital, and granular insular cortex. Neuronal counts in mammillary body nuclei and areal measurements of the mammillary body were unchanged from controls and the thalamus was relatively undamaged. In animals reversed at later and more advanced symptomatic stages of thiamine deficiency, 14-15 days of treatment, degenerating axons were found in other cortical regions and hippocampus and there was extensive neuronal loss and gliosis within mammillary body and medial thalamus. These results demonstrate that a single episode of thiamine deficiency can selectively damage cortical white matter tracts while sparing the thalamus and mammillary body and may be a critical factor responsible for the pathological and behavioral changes observed in alcoholics without Wernicke's encephalopathy.

Neuronal cell death in Wernicke's encephalopathy: pathophysiologic mechanisms and implications for PET imaging

Thiamine deficiency in humans is associated with Wernicke's encephalopathy (WE) which is characterized neuropathologically by neuronal loss in selective brain regions. Pyrithiamine-induced thiamine-deficiency in the rat results in lesions which are similar in nature and distribution to those seen in human WE. Several mechanisms have been implicated in the pathogenesis of neuronal loss in thiamine deficiency including, (i) impaired cerebral energy metabolism, (ii) focal lactic acidosis, (iii) NMDA-receptor mediated excitotoxicity and (iv) blood-brain barrier breakdown. WE is difficult to diagnose during life and a large number of cases are missed by routine clinical neurological evaluation. Recently, non-invasive diagnostic procedures such as CT and MRI have been used for the evaluation of acute and chronic WE. Autoradiographic studies reveal that increased densities of binding sites for the astrocytic ligand 3H-PK11195 closely parallel the topographic distribution of reactive gliosis and neuronal loss in selective brain regions of pyrithiamine-induced thiamine-deficient rats. In contrast, binding sites for the neuronal ligand 3H-Ro15-1788 show poor regional correlation with neuronal loss in thiamine deficiency. Both of these ligands are available, and have been used in PET assessment of various disorders in humans. The results of autoradiographic studies suggest that 11C-PK11195 may offer a useful PET ligand for the assessment of brain damage in WE in humans.

Alterations of thiamine phosphorylation and of thiamine-dependent enzymes in Alzheimer's disease

There is a growing body of evidence to suggest that thiamine neurochemistry is disrupted in Alzheimer's Disease (AD). Studies in autopsied brain tissue from neuropathologically proven AD patients reveal significantly reduced activities of the thiamine phosphate dephosphorylating enzymes thiamine diphosphatase (TDPase) and thiamine monophosphatase (TMPase) as well as the thiamine diphosphate-dependent enzymes, pyruvate dehydrogenase complex, alpha-ketoglutarate dehydrogenase (alpha KGDH) and transketolase. Reductions in enzyme activities are present both in affected areas of AD brain as well as in relatively well conserved tissue. Decreased TDP concentrations and concomitantly increased TMP in autopsied brain tissue from AD patients and in CSF from patients with Dementia of the Alzheimer Type suggests that CNS thiamine phosphorylation-dephosphorylation mechanisms are disrupted in AD. alpha KGDH is a rate-limiting enzyme for cerebral glucose utilization and decreases in its activity are associated with lactic acidosis, cerebral energy failure and neuronal cell loss. Deficiencies of TDP-related metabolic processes could therefore participate in neuronal cell death mechanisms in AD.

Reduced activities of thiamine-dependent enzymes in brains of alcoholics in the absence of Wernicke's encephalopathy

The relative roles of alcohol per se, thiamine deficiency, and liver disease in the pathogenesis of alcohol-related brain damage have not been fully elucidated. In particular, the extent to which alterations of brain thiamine metabolism contribute to cognitive dysfunction in alcoholism in the absence of Wernicke's encephalopathy has not been established. In the present study, thiamine diphosphate-dependent enzymes were measured using standard spectrophotometric techniques in homogenates of brain tissue obtained at autopsy from eight alcoholic patients, all of whom died in hepatic coma without clinical or neuropathological evidence of Wernicke's encephalopathy and six nonalcoholic, age-matched controls, matched for autopsy delay time and free, at the time of death, from gross malnutrition or other neurological or psychiatric disorders. Transketolase activities were reduced in cerebellum (by 35%, p < 0.01), thalamus (by 35%, p < 0.01), frontal cortex (by 22%, p < 0.01), temporal cortex (by 20%, p < 0.01), and prefrontal cortex (by 19%, p < 0.01). Activities of the pyruvate dehydrogenase complex were selectively reduced in prefrontal cortex by 25% (p < 0.01). Activities of alpha-ketoglutarate dehydrogenase were within normal limits in all brain regions of alcoholic patients. The generalized reductions of transketolase activity undoubtedly result from thiamine deficiency. Previous studies suggest that the presence of liver disease may exacerbate thiamine deficiency in alcoholics. A sustained loss of transketolase activity in brain could result in disruption of pentose shunt activity and concomitant reductions in reducing equivalents and lipid metabolism within the cell. The selective loss of pyruvate dehydrogenase activity in prefrontal cortex of alcoholic cirrhotics could relate to the phenomenon of hepatic coma.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for early blood-brain barrier breakdown in experimental thiamine deficiency in the mouse

In order to assess the involvement of blood-brain barrier (BBB) breakdown in the pathogenesis of thiamine deficiency encephalopathy, autologous albumin immunohistochemistry was performed in mice which were rendered thiamine-deficient by pyrithiamine, a BBB-permeant antagonist of thiamine. In the presymptomatic animals until day 8 of the treatment, histological lesions were not detected by H&E staining. However, localized straining of albumin was evident, suggesting an extravascular leakage of the endogenous intravascular protein. On day 10 of thiamine deficiency, when neurological signs appeared, both histological lesions and massive albumin extravasation were demonstrated in all the animals. The BBB breakdown was only occasionally observed in the brains of mice treated with oxythiamine, a BBB-impermeant antagonist or in control animals. These results suggest that BBB breakdown is not only a phenomenon secondary to tissue destruction, but it is more directly involved in the pathogenesis of thiamine deficiency encephalopathy.

Regional alterations of thiamine phosphate esters and of thiamine diphosphate-dependent enzymes in relation to function in experimental Wernicke's encephalopathy

Thiamine phosphate esters (thiamine monophosphate-TMP; thiamine diphosphate-TDP and thiamine triphosphate-TTP) were measured as their thiochrome derivatives by High Performance Liquid Chromatography in the brains of pyrithiamine-treated rats at various stages during the development of thiamine deficiency encephalopathy. Severe encephalopathy was accompanied by significant reductions of all three thiamine phosphate esters in brain. Neurological symptoms of thiamine deficiency appeared when brain levels of TMP and TDP fell below 15% of normal values. Activities of the TDP-dependent enzyme alpha-ketoglutarate dehydrogenase were more severely reduced in thalamus compared to cerebral cortex, a less vulnerable brain structure. On the other hand, reductions of TTP, the non-cofactor form of thiamine, occurred to a greater extent in cerebral cortex than thalamus. Early reductions of TDP-dependent enzymes and the ensuing metabolic pertubations such as lactic acidosis impaired brain energy metabolism, and NMDA-receptor mediated excitotoxicity offer rational explanations for the selective vulnerability of brain structures such as thalamus to the deleterious effects of thiamine deficiency.

Nutritional and metabolic characterization of a thiamine-deficient rat model

The effects of a thiamine-deficient diet on plasma and tissue vitamin concentrations and on whole-body glucose metabolism were assessed. Male Sprague-Dawley rats (175 to 200 g body weight) fed a thiamine-deficient (TD) or nutritionally complete purified diet were used for plasma thiamine mononitrate and monophosphate and for red blood cell and tissue thiamine pyrophosphate (TPP) determinations weekly for up to 5 weeks. Additional rats were used for assessment of basal glucose kinetics by using a primed constant infusion of [3-3H]glucose. Plasma thiamine mononitrate levels decreased 60% at 1 week and were undetectable after 5 weeks on the diet. Plasma thiamine monophosphate decreased 80% after 1 week on the TD diet, and levels were undetectable after 4 weeks on the diet. Red blood cell TPP in the TD group decreased progressively with time: 54% at 1 week, 86% at 3 weeks, and 92% at 5 weeks. At 1 and 4 weeks, the decrease in tissue TPP was significant in the liver (65% and 89%, respectively), gut (52% and 94%, respectively), spleen (40% and 60%, respectively), and skeletal muscle (37% and 76%, respectively), with the brain (7% and 84%, respectively) showing the slowest initial rate of depletion. The TD diet did not alter plasma glucose concentrations, but it increased plasma lactate by 75% and plasma pyruvate by 50% to 75%. Rates of hepatic glucose production and peripheral glucose utilization were not different between the control and TD rats at 2 weeks, but they were 25% higher in the TD rats after 6 weeks on the diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Application of high field localised in vivo 1H MRS to study biochemical changes in the thiamin deficient rat brain under glucose load

In vivo, volume-selected 1H NMR spectroscopy employing the SPACE technique was used to monitor biochemical changes in the thiamin deficient rat brain in response to glucose loading. The concentrations of brain N-acetylaspartate, glutamate/glutamine/gamma-aminobutyric acid, lactate and glucose differed significantly from those of control animals. The results are consistent with a metabolic block at the reaction catalyzed by the thiamin dependent enzyme alpha-keto glutarate dehydrogenase soon after the onset of neurological symptoms of thiamin deficiency, and a further block at pyruvate dehydrogenase arising late in the course of thiamin deficiency.

Enhanced proteolytic activities in cultured fibroblasts of Alzheimer patients are revealed by peculiar transketolase alterations

Characteristic alterations of transketolase (TK) in extracts from cultured Alzheimer fibroblasts have previously been reported (Paoletti et al. (1990) Biochem. Biophys. Res. Commun., 172: 396-401). These abnormalities, encountered in 9 out of 13 Alzheimer patients, were revealed following isoelectric focusing and consisted of enzyme forms having unusually high alkaline pI values (alkaline bands). The present work has shown that immunologically detected alkaline bands were progressively expressed when Alzheimer fibroblasts were incubated for three weeks without medium changes. Full expression of the altered enzyme pattern was not linked to relative cell density in the petri dish; rather, it appeared to be dependent directly on the time elapsed since cell confluence was reached. Alkaline bands could artificially be induced also in both crude and pure TK preparations from normal cells by a treatment with commercial proteases, particularly chymotrypsin. Moreover, specific inhibitors of endogenous cysteine-proteases were capable of abolishing TK alkaline bands in Alzheimer fibroblasts thus turning a pathological into a normal enzyme pattern. Results obtained suggest that Alzheimer fibroblasts contain enhanced Ca(2+)-independent cysteine-proteolytic activities as compared to normal and other pathological cells. These enzymes, exhibiting chymotrypsin-like activity, might exert their degradative effects at the time of cell extraction using TK and probably other cell components as potential substrates. However, peculiar TK abnormalities represent so far an useful biochemical marker detectable in fibroblasts of living Alzheimer patients and closely associated to this neurological disorder.

Application of high-performance liquid chromatography to the study of thiamine metabolism and in particular thiamine triphosphatase

Thiamine triphosphate can be found in most tissues at very low levels, but its role is unknown. Organs and muscles that generate electrical impulses are particularly rich in this compound. This paper describes a thiamine triphosphatase from the electrical organ of Electrophorus electricus. The activity of this enzyme, as measured by a high-performance liquid chromatographic method, is closely anion-regulated. Furthermore, thiamine triphosphate increases chloride uptake in membrane vesicles prepared from rat brain. Our results suggest that this compound could play an important role in the regulation of chloride permeability.

Thiamine-dependent enzyme changes in temporal cortex of patients with Alzheimer's disease

Activities of thiamine-dependent enzymes [pyruvate dehydrogenase (PDHC), alpha-ketoglutarate dehydrogenase (alpha KGDH), and transketolase (TK)] were measured in autopsied samples of temporal cortex from six patients with Alzheimer's disease and from eight age-matched control subjects who were free from neurological or psychiatric diseases. Times from death to freezing of dissected material at -70 degrees C were matched. Significant decreases in PDHC (decreased by 70%; P less than 0.01), alpha KGDH (decreased by 70%; p less than 0.01), and TK (decreased by 52%; P less than 0.01) were observed in brain tissue from patients with Alzheimer's disease. In contrast, activities of glutamate dehydrogenase were within normal limits. These findings suggest a possible role for alterations of brain thiamine metabolism or utilization in Alzheimer's disease.

Effects of thiamine deficiency on thiamine-dependent enzymes in regions of the brain of pregnant rats and their offspring

Thiamine needs in pregnancy and lactation are known to be increased. Previous studies suggest that developing rat brain is more susceptible to a lack of thiamine intake than is adult brain. In order to study the basis of this susceptibility, activities of the three thiamine-dependent enzymes [pyruvate dehydrogenase complex (PDHC), alpha-ketoglutarate dehydrogenase (alpha KGDH), and transketolase (TK)] were measured in homogenates of brain tissue from thiamine-deficient female rats and their offspring. The study revealed a more rapid progression of thiamine deficiency in pregnant thiamine-deficient rats compared to nonpregnant rats as seen by significantly increased "TPP effect" values. No differences in activities of the three thiamine-dependent enzymes in brain were observed between pregnant and nonpregnant animals. However, activities of all three thiamine-dependent enzymes were significantly reduced in cerebral cortex of the offspring of thiamine-deficient mothers 13 days postnatally. TK activities were also reduced in cerebellum and brain stem of these animals. Since thiamine-dependent enzymes are important for the establishment of adult patterns of cerebral energy metabolism and also in myelin synthesis, maternal thiamine deficiency resulting in reductions of activities of these enzymes at a vulnerable period in brain development could have serious metabolic consequences leading to permanent neurological sequellae in the offspring.

Regionally selective alterations in enzymatic activities and metabolic fluxes during thiamin deficiency

To further elucidate the molecular basis of the selective damage to various brain regions by thiamin deficiency, changes in enzymatic activities were compared to carbohydrate flux through various pathways from vulnerable (mammillary bodies and inferior colliculi) and nonvulnerable (cochlear nuclei) regions after 11 or 14 days of pyrithiamin-induced thiamin deficiency. After 11 days, large decreases (-43 to -59%) in transketolase (TK) occurred in all 3 regions; 2-ketoglutarate dehydrogenase (KGDHC) declined (-45%), but only in mammillary bodies; pyruvate dehydrogenase (PDHC) was unaffected. By day 14, TK remained reduced by 58%-66%; KGDHC was now reduced in all regions (-48 to -55%); PDHC was also reduced (-32%), but only in the mammillary bodies. Thus, the enzyme changes did not parallel the pathological vulnerability of these regions to thiamin deficiency. 14CO2 production from 14C-glucose labeled in various positions was utilized to assess metabolic flux. After 14 days, CO2 production in the vulnerable regions declined severely (-46 to 70%) and approximately twice as much as those in the cochlear nucleus. Also by day 14, the ratio of enzymatic activity to metabolic flux increased as much as 56% in the vulnerable regions, but decreased 18 to 30% in the cochlear nuclei. These differences reflect a greater decrease in flux than enzyme activities in the two vulnerable regions. Thus, selective cellular responses to thiamin deficiency can be demonstrated ex vivo, and these changes can be directly related to alterations in metabolic flux. Since they cannot be related to enzymatic alterations in the three regions, factors other than decreases in the activity of these TPP-dependent enzymes must underlie selective vulnerability in this model of thiamin deficiency.

Reversible alterations of cerebral gamma-aminobutyric acid in pyrithiamine-treated rats: implications for the pathogenesis of Wernicke's encephalopathy

Treatment of rats with the central thiamine antagonist, pyrithiamine, results in severe neurological symptoms such as loss of righting reflex. Measurement of gamma-aminobutyric acid (GABA) content of brain tissue from symptomatic pyrithiamine-treated (PT) rats revealed significant reductions in thalamus, cerebellum, and pons. GABA content of cerebral cortex, however, was unaltered. Activities of the thiamine-dependent enzyme alpha-ketoglutarate dehydrogenase (alpha KGDH) were reduced in parallel with the GABA changes. On the other hand, activities of the GABA-synthetic enzyme glutamic acid decarboxylase (GAD) remained within normal limits, with the exception of a small but significant decrease in thalamus of symptomatic PT rats. Affinities and densities of high-affinity [3H]muscimol binding sites on crude cerebral membrane preparations from symptomatic PT rats were unchanged. Thiamine administration to symptomatic animals resulted in correction of abnormal righting reflexes and in normalization of decreased GABA levels and reduced alpha KGDH activities in cerebellum and pons. Thalamic GABA levels and alpha KGDH activities, on the other hand, remained significantly lower than normal. These results suggest that the reversible symptoms of pyrithiamine treatment may result from imparied GABA synthesis in cerebellum and pons of these animals. Similar mechanisms may play a role in the pathogenesis of the reversible symptoms of Wernicke's encephalopathy in man.

The effect of thiamine deficiency on the structure and physiology of the rat forebrain

Dietary thiamine deficiency, enhanced by pyrithiamine administration in adult rats, produces overt lesions in the brain that are especially prominent in the thalamus. The present study was undertaken to determine whether the thalamic lesions could be correlated with alterations in the physiological properties of neurons in the thalamus and somatosensory cortex. The regimen for experimentally inducing thiamine deficiency produced large lesions in the thalamus of every case; the lesions included most, if not all, of the neurons in the intralaminar thalamic nuclei. The extent of the lesion in the intralaminar thalamus was highly correlated with the loss of bilaterally synchronous spontaneous activity in the cerebral cortex. This correlation was seen in animals analyzed as early as 1-18 hr after the appearance of opisthotonus, the crisis state of thiamine deficiency, and as late as 2-9 weeks of recovery following thiamine replacement therapy. The loss of bilateral synchronous bursting neuronal activity following intralaminar thalamic lesions is consistent with the proposed role of the intralaminar thalamus as a pacemaker for rhythmic cortical activity (Armstrong-James et al., Exp. Brain Res., 1985; Fox and Armstrong-James, Exp. Brain Res. 63: 505-518, 1986). The location and size of the central lesions within the thalamus suggest that the observed neuronal loss could result from a nonhemorrhagic infarction in the ventromedial branches of the superior cerebellar arteries. Experimental thiamine deficiency also produced alterations in the receptive field properties of the somatosensory cortex neurons in all animals examined. Changes in cortical receptive field properties were correlated with the destruction of sensory relay neurons in the thalamic ventrobasal complex. The loss of the central lateral thalamic input to the cortex and the loss of somatosensory relay neurons in the ventrobasal thalamus in experimental thiamine deficiency produce alterations in cortical function which may contribute to deficits in memory and cognition analogous to those which characterize Korsakoff's psychosis in humans.