Development and resolution of brain lesions caused by pyrithiamine- and dietary-induced thiamine deficiency and alcohol exposure in the alcohol-preferring rat: a longitudinal magnetic resonance imaging and spectroscopy study.

Wernicke's encephalopathy (WE) is characterized by lesions in thalamus, hypothalamus (including mammillary nuclei), and inferior colliculi, results in serious disabilities, has an etiology of thiamine deficiency, is treatable with thiamine, and occurs most commonly with alcoholism. Despite decades of study, whether alcohol exposure exacerbates the neuropathology or retards its resolution remains controversial. To examine patterns of brain damage and recovery resulting from thiamine deprivation with and without alcohol exposure, we conducted in vivo magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) at 3 T in alcohol-preferring (P) rats, which had voluntarily consumed large amounts of alcohol before thiamine manipulation. A total of 18 adult male P rats (nine alcohol-exposed) received a thiamine-deficient diet for 2 weeks: 10 (five alcohol-exposed) received intraperitoneal (i.p.) pyrithiamine (PT) and eight (four alcohol-exposed) received i.p. thiamine supplementation. Neurological signs developed by day 14. Rats were scanned before thiamine depletion and 18 and 35 days after thiamine repletion. Two-dimensional J-resolved MRS single-voxel spectra with water reference were collected in a voxel subtending the thalamus; metabolite quantification was corrected for voxel tissue content. MRI identified significant enlargement of dorsal ventricles and increase in signal intensities in thalamus, inferior colliculi, and mammillary nuclei of PT compared with thiamine-treated (TT) groups from MRI 1-2, followed by significant normalization from MRI 2-3 in thalamus and colliculi, but not mammillary nuclei and lateral ventricles. Voxel-by-voxel analysis revealed additional hyperintense signal clusters in the dorsal and ventral hippocampus and enlargement of the fourth ventricle. MRS showed a significant decline and then partial recovery in thalamic N-acetylaspartate, a marker of neuronal integrity, in PT compared with TT rats, with no change detected in creatine, choline, or glutamate. PT rats with prior alcohol exposure exhibited attenuated recovery in the thalamus and arrested growth of the corpus callosum; further, two of the five alcohol-exposed PT rats died prematurely. Parenchymal and ventricular changes with thiamine manipulation concur with human radiological signs of WE. The enduring macrostructural and neurochemical abnormalities involving critical nodes of Papez circuit carry liabilities for development of amnesia and incomplete recovery from other cognitive and motor functions subserved by the affected neural systems.     

Changes in brain lipid composition in thiamine deficient rats

Brain lipid composition was studied in thiamine deficient rats treated with thiamine antimetabolites (oxythiamine: OT, and pyrithiamine: PT) and thiamine deficient diet (TDD). After intraperitoneal injection of OT (40 mg/kg/day) or TDD feeding for 6 days, body weight gain decreased. However, the PT (500 micrograms/kg/day) treated rats or the pair fed control (PFC: TDD + thiamine of 5 mg/kg, i.p.) showed no decrease in body weight gain compared with the regular diet control (C). Brain lipid levels (total lipid, total cholesterol, triglyceride, phospholipid, sphingomyelin and cerebroside) were examined in four brain regions (cerebral cortex, subcortical structure, brain stem and cerebellum). Total lipid level increased in four regions in OT or TDD treated rats, but total lipid level in the cerebellum in PT treated rats decreased. Total cholesterol level increased in all treated rats, while the triglyceride level in the brain stem decreased dramatically in OT or TDD treated rats. Cerebroside levels of four regions in the PT, OT or TDD group remarkably decreased, and PFC rats showed a significant improvement of the decrease in cerebroside level. It is conceivable that these changes in brain lipid composition provided some clues for the histological and morphological changes of the brain as manifested by the myelin degradation in acute thiamine deficiency.     

Thiamine deficiency in utero alters response to ethanol in adulthood

To determine whether prenatal thiamine deficiency, a frequent concomitant of alcoholism, reduces the response to ethanol during adulthood in the rat as does ethanol exposure in utero (Abel et al. 1981), pregnant Sprague-Dawley rats received either control or thiamine deficient diets together with daily injections of the thiamine antagonist pyrithiamine. At 7 months of age, male offspring were exposed to precisely regulated ethanol vapor concentrations in an inhalation chamber for 24 h and blood ethanol concentrations (BECs) and ethanol-induced intoxication were determined. Prenatally thiamine deficient rats and controls were indistinguishable in terms of appearance, body and liver weights, and the ratios of liver to body weight and brain to liver weight. However, total body water was significantly greater, and BECs and behavioral impairment were decreased, in the experimental rats. These findings indicate that prenatal thiamine deprivation is associated with reduced pharmacologic effect of ethanol as a result of increases in its volume of distribution and rate of metabolism.     

The string test: An early behavioral change in thiamine deficiency

Thiamine deficiency is a useful animal model of the interaction between biochemistry and behavior. Although numerous biochemical changes have been detected in thiamine deficiency, studies of behavioral changes are relatively scarce. We have modified and quantitated the string test, originally described by Miquel and Blasco, for application to thiamine-deficient rats. The string test is reproduciblt with time, and control rats have a narrow range of scores. 50% of rats treated with thiamine-deficient diet and pyrithiamine, a centrally-acting thiamine antagonist, have persistently decreased string test scores. This decrease is already present on day 5 of treatment, long before the onset of weight loss or neurological symptoms. Rats treated with oxythiamine, a peripherally acting thiamine antagonist, do not have decreased string test scores, even when anorectic and moribund. These findings suggest that impaired string test performance is a central nervous system effect of thiamine deficiency, and that it may also be a useful behavioral parameter to follow in other animal models of metabolic encephalopathies.     

Effects of thiamine deficiency on hepatic cytochromes P450 and drug-metabolizing enzyme activities

To elucidate the mechanisms by which thiamine deficiency affects hepatic microsomal monooxygenase activities, the effect of thiamine deficiency on two constitutive cytochrome P450 isozymes, P450IIE1 and P450IIC11, was investigated, using weanling male Sprague-Dawley rats. The clinical signs of thiamine deficiency were apparent after feeding a thiamine-deficient diet for 3 weeks. Thiamine deficiency caused an increase in P450IIE1, which was determined by N-nitrosodimethylamine demethylase assay and immunoquantitation of P450IIE1. This increase in the P450IIE1 level was mainly attributed to thiamine deficiency per se but not to dietary restriction. Ketone bodies were not elevated in thiamine-deficient rats, whereas ketone bodies were elevated and may have served as inducing factors in calorically restricted pair-fed animals. Injections of pyruvate or pyrithiamine in addition to thiamine deficiency did not potentiate the induction effect. On the other hand, thiamine deficiency did not affect the level of P450IIC11 during the 3 weeks of feeding the thiamine-deficient diet. In addition, thiamine deficiency increased cytosolic glutathione S-transferase activity but not steroid isomerase activity. The present study demonstrates the specificity of thiamine deficiency per se in the induction of P450IIE1 which does not involve an increase in the ketone body level.     

Neurotoxic effects of cadmium in young rats

This study examined the effects of cadmium on the brain of male, Sprague-Dawley rats of different ages. Cadmium was more toxic in 4-day-old than in adult rats, thus 2 and 4 mg/kg were given sc to the younger rats and 4 and 6 mg/kg to the older rats. The lower doses resulted in no mortality and the higher dose about 10% mortality in both groups. Four days after a sc injection of cadmium chloride (4 mg Cd/kg) to 4-day-old rats, lesions were evident in the corpus callosum, caudate-putamen, and cerebellum, while 2 mg/kg of cadmium produced only slight cerebellar damage. Nineteen days after injection of 4 mg Cd/kg to 4-day-old rats, a large cystic cavity was evident where the corpus callosum is normally located. In contrast, cadmium did not produce any observable brain damage in adult rats at 4 or 6 mg/kg, either 4 or 19 days after injection. Eighteen days after treatment, hyperactivity was evident in newborn rats exposed to 4 mg/kg of cadmium, but not in newborn rats exposed to 2 mg/kg of cadmium or in adult rats treated with 4 or 6 mg/kg of cadmium. Thus, cadmium at a dose that produces only a few deaths is toxic to the brain of newborn rats, as evident by hyperactivity and lesions.     

Comparative effects of developmental thiamine deficiencies and ethanol exposure on the morphometry of the CA3 pyramidal cells.

Maternal alcoholism and thiamine deficiency are frequently considered to be the causal agents of the central nervous system (CNS) damage associated with mental retardation in the offspring. For further understanding of pathological mechanisms underlying CNS damage in both disorders, histological studies were undertaken in developing rats to compare the hippocampus CA3 pyramidal cells measurements and density between three patterns of thiamine deficiency and chronic alcohol exposure. Female rats were given thiamine-deficient diet during different periods of gestation and lactation to obtain pre-, peri-, and postnatal thiamine-deficient pups. Twelve percent ethanol/water drinking fluid was given to mothers throughout gestation and lactation to obtain ethanol-exposed pups. Thiamine was administered during developmental ethanol exposure to assess the extent of interference between ethanol and thiamine metabolism. Nondrug-treated dams were allowed ad lib access to food and water during gestation and lactation to yield control pups. Hippocampus histology was performed in 45-day-old rats, and the CA3 pyramidal cells measurements and density assessed and compared between all treatment groups. It appears that the mean nuclear size of pyramidal cells in the field CA3 was significantly reduced in all the treatments compared to the control. While the mean nuclear size decreased more severely in development ethanol exposure than in the three patterns of thiamine deficiency, no significant difference was noted when pre-, peri-, and postnatal thiamine-deficient rats were compared. However, thiamine administration during developmental ethanol exposure partially restored the mean nuclear size. In contrast, comparisons between ethanol-exposed pups and the three patterns of thiamine-deficient pups, exhibited similar intensity in the deficit of CA3 pyramidal cells. Cell loss generated by ethanol treatment was not suppressed by thiamine administration. Common and separate mechanisms underlying the effects of alcohol intoxication and thiamine deficiency on cell death and cell atrophy were suggested.     

Physiological,biochemical and morphological studies of Baltic salmon yolk-sac fry with an experimental thiamine deficiency: relations to the M74 syndrome

Sea-run Baltic salmon (Salmo salar) populations are suffering from the M74 syndrome, a reproduction disorder affecting both broodfish and their progeny. The syndrome is usually manifested during the middle part of the yolk-sac fry stage and has been shown to be associated with a thiamine (vitamin B(1)) deficiency. Development of the disease is reversible by thiamine treatments of broodfish or progeny. This study aimed at investigating the ability of the thiamine antagonist pyrithiamine, administered by microinjections 3 days after hatch, to cause M74-like signs i.e. typical clinical symptoms, high mortality rates and histopathological changes. Furthermore, the effects of pyrithiamine on hepatic activities of the thiamine-dependent enzyme transketolase (TK), the glucose-6-phosphate dehydrogenase (G6PDH) and the cytochrome P4501A (CYP1A) were evaluated. Six family groups with differing thiamine status were sampled on three occasions during the yolk-sac fry stage. All pyrithiamine exposed groups, with the exception of the one with the highest thiamine concentration, showed M74-like symptoms and suffered from high mortality. Enzyme activities were not different in pyrithiamine groups as compared with controls. However, the TK-activities were strongly associated with the thiamine concentrations. The G6PDH-activity demonstrated small variations with the highest activities in the M74-groups. The [TK]/[G6PDH]-ratios were considerably lower in the M74-groups than in the healthy controls, indicating an imbalance between the oxidative and the non-oxidative part of the pentose-phosphate shunt due to a deficit in thiamine. The pyrithiamine-injections induced several M74-like symptoms including incoordination, lethargy, whitened liver and yolk-sac precipitates. They also caused high mortality rates, in addition to lowered glycogen levels and increased prevalence of necrotic brain cells. Moreover, the study demonstrates that the TK, G6PDH and CYP1A-activities are associated with the thiamine content.     

β-石竹烯对小鼠脑缺血/再灌注白质损伤的保护作用研究

目的研究β-石竹烯(β-caryophyllene,BCP)对小鼠脑缺血/再灌注(cerebral ischemia-reperfusion,CIR)白质损伤的保护作用。方法随机将C57BL/6小鼠分为正常对照组(Control)、模型组(CIR)、治疗组(36、72、144 mg·kg^-1)。线栓法建立小鼠大脑中动脉栓塞(middle cerebral artery oc-clusion,MCAO)模型。缺血1 h,再灌注24 h,TTC染色确定脑梗死体积,并进行神经行为学评分;干湿重法测脑含水量;HE染色及透射电镜观察胼胝体损伤情况;Luxol Fast Blue(LFB)染色标记脑神经髓鞘;Western blot测胼胝体髓鞘碱性蛋白(mbp)、神经丝蛋白(NF)、Bcl-2、Bax和caspase-3的表达。结果与模型组比较,BCP可降低神经行为学评分,减小脑梗死体积,减轻脑水肿和胼胝体髓鞘损伤,升高髓鞘染色光密度(optical density,OD),上调mbp、NF、Bcl-2表达,降低Bax和caspase-3表达。结论BCP对小鼠脑缺血/再灌注白质损伤有保护作用,可能与Bax/Bcl-2凋亡通路有关。     

Differential deficits in regional brain growth induced by postnatal alcohol

Neonatal rats were exposed to alcohol during a period of brain development equivalent to part of the human third trimester. Rat pups were fed a milk formula containing either alcohol (9.8 g/kg/day) or isocaloric maltose/dextrin using artificial rearing techniques from postnatal days 4-10. Blood alcohol concentrations reached 345.8 +/- 15.6 mg/dl on postnatal day 6. All animals, including a group of normally reared suckle controls, were sacrificed on postnatal day 10, and the brains were perfused and processed for the Timm histochemical technique. Significant microencephaly (30% reduction in brain growth) was found in the alcohol-exposed animals. Growth deficits also were found in specific brain regions of the alcohol-exposed rats. The overall area of the hippocampus proper at a midtemporal level was reduced by 26.1% compared to controls. Sublaminae within the hippocampus were stunted as much as 40.5%. An overall reduction of 14.5% was found in the midsagittal (vermal) cerebellum. In contrast, growth of the dentate gyrus appeared much less affected (6.8% deficit) by the alcohol exposure. These data indicate that not all regions of the brain are affected equally by alcohol exposure during the third trimester equivalent.     

Antioxidant effect of thiamine on acutely alcoholized rats and lack of efficacy using thiamine or glucose to reduce blood alcohol content

Although there is no consensus about the use of glucose and thiamine for the treatment of acute ethanol intoxication, this is a routine practice in many countries. Our objective was to determine the efficacy of this treatment and the changes it causes in the antioxidant status of the liver. Male Wistar rats were intoxicated with an ethanol dose of 5 g/kg and divided into three groups: ethanol (EtOH; untreated), EtOH+G (treated with glucose), and EtOH+B1 (treated with thiamine). Blood and urinary ethanol as well as hepatic malondialdehyde, reduced glutathione and vitamin E were determined in all animals. Blood alcohol levels did not differ between groups, although urinary excretion was about four times higher in the group treated with thiamine (EtOH+B1). The malondialdehyde, reduced glutathione and vitamin E values used here as parameters of the antioxidant system of the liver showed improvement for the thiamine-treated group (EtOH+B1). Treatment with glucose or thiamine was ineffective in reducing blood alcohol levels in rats with acute ethanol intoxication. However, the beneficial effect of thiamine as an antioxidant for ethanol metabolism was demonstrated. Further investigations are necessary to clarify the urinary excretion of ethanol reported here for the first time and the possibility of using thiamine as an antioxidant in situations of chronic alcohol use.     

Lead induced thiamine deficiency in the brain decreased the threshold of electroshock seizure in rat.

Many neurological disorders that occur frequently in lead intoxicated animals, have also been observed in thiamine deficient animals. To test whether lead intoxication could decrease the thiamine status and thresholds of electroshock seizure in rats, 3-week-old Wistar rats were treated with lead or lead plus thiamine. For comparison, a thiamine deficient group was included. Thiamine contents and transketolase activity, one of the thiamine dependent enzymes in the brain regions were significantly lowered by lead intoxication and thiamine deficiency. In both cases, thresholds of the electroshock seizure were significantly decreased. Thiamine supplementation reversed these signs and decreased the brain lead concentration in the lead treated group. The results from the present study suggest that the increased seizure susceptibility induced by lead intoxication in rats may be mediated at least in part through the changes of thiamine status.     

Alcohol consumption and premotor corpus callosum in older adults

Heavy alcohol consumption is toxic to the brain, especially to the frontal white matter (WM), but whether lesser amounts of alcohol negatively impact the brain WM is unclear. In this study, we examined the relationship between self-reported alcohol consumption and regional WM and grey matter (GM) volume in fifty-six men and thirty-seven women (70+- 7years) cognitively intact participants of the Baltimore Longitudinal Study of Aging (BLSA) with no history of alcohol abuse. We used regional analysis of volumes examined in normalized space (RAVENS) maps methodology for WM and GM segmentation and normalization followed by voxel based morphometry (VBM) implemented in SPM8 to examine the cross-sectional association between alcohol consumption and regional WM (and, separately, GM) volume controlling for age, sex, smoking, blood pressure and dietary thiamine intake. WM VBM revealed that in men, but not in women, higher alcohol consumption was associated with lower volume in premotor frontal corpus callosum. This finding suggests that even moderate amounts of alcohol may be detrimental to corpus callosum and white matter integrity.     

The effects of chronic postweaning amphetamine on rats exposed to alcohol in utero: Weight gain and behavior

Offspring of rats fed alcohol, pair-fed, or fed ad lib control diets during pregnancy were administered a dose of amphetamine (0, 2 or 10 mg/kg) daily from postnatal day 22 (PN22) to PN42. Body weight was measured regularly from PN22 to PN60, and behavior was measured on PN22, PN28, PN36 and PN42. Rats exposed to alcohol in utero weighed less than controls at birth and throughout most of the experiment, despite a significantly accelerated weight gain relative to controls. By PN60, prenatal alcohol-exposed rats weighed the same as pair-fed controls. There were dose-dependent reductions in the rate of weight gain during amphetamine administration. After the daily injections stopped, the high-dose (10-mg/kg) amphetamine groups showed a higher growth rate than the 0-mg/kg and 2-mg/kg groups. There were no interactions between prenatal treatment and dose of amphetamine on body weight gain. Rats exposed to alcohol in utero showed a greater locomotor activation than controls given 2 mg/kg amphetamine. The magnitude of the locomotor activation to this dose of amphetamine decreased equivalently over the four test days for all prenatal treatment groups. Male but not female rats exposed prenatally to alcohol showed an apparent sensitization to 10 mg/kg amphetamine not seen in control rats between PN28 and PN42. There were no group differences in amphetamine-induced stereotypy or SCH-23390-induced catalepsy. The results implied that children with Fetal Alcohol Syndrome who may be treated for attentional dysfunction would show different dose-responses for some behavioral effects of CNS stimulants, but not for growth-retarding “side effects.”     

Vanadium exposure through lactation produces behavioral alterations and CNS myelin deficit in neonatal rats

The current study was performed to assess the vanadium(V)-induced developmental toxicity in sucklings of Wistar rats. Dams of treated litters were intraperitoneally injected with 3 mg NaVO(3)/kg body weight/day during 12 days starting on postnatal day (PND) 10. Surface righting reflex, negative geotaxy and hindlimb support tests were performed on pups every 48 h, from 8th to 18th PND. Open field test was performed on the 21st PND. On 22nd PND, some animals were transcardially perfusion-fixed and their brains were removed and cut with a cryostat. Brain sections were processed for myelin histochemistry and for anti-myelin basic protein immunohistochemistry. Delay in eye opening and decreased muscular strength and locomotion were observed in V-exposed pups of both sexes. A decreased myelin staining in corpus callosum and cerebellum in these pups was also observed. Results suggest that vanadium exposure through lactation would induce neurotoxicity in rat developing CNS.     

The influence of thiamine deficiency and ethanol on rat brain catecholamines

In rats treated with a thiamine deficient diet for 30 days the brain content of total thiamine decreased by 27-50%. Thiamine deficiency decreased the dopamine (DA) concentration of the striatum indicating a reduced synthesis of DA. In the hypothalamus the levels of the catecholamine metabolites homovanillic acid (HVA) and 4-hydroxy-3-methoxyphenyl glycol (HMPG) were reduced indicating a reduced DA and noradrenaline (NA) turnover. Animals on a diet containing 5% ethanol had increased concentrations of HVA and HMPG in rest brain indicating an increased DA and NA turnover. The concentration of 1-carboxysalsolinol (1-CSAL) and salsolinol (SAL) in the brain stem was increased in animals receiving ethanol. Thus, both thiamine deficiency and ethanol treatment influenced the catecholamine system in a complex region-dependent way. In the brain regions most susceptible to brain damage in thiamine deficiency, i.e., hypothalamus and brain stem, 1-CSAL and SAL increased most following thiamine deficiency combined with ethanol intake.     

The use of thiamine and thiamine antagonists to investigate the etiology of early mortality syndrome in lake trout (Salvelinus namaycush)

Early mortality syndrome (EMS) is a non-infectious disease affecting lake trout and other salmonids in the Great Lakes and in inland lakes. It is characterised by loss of equilibrium, hyperexcitability, anorexia, and eventually death. EMS is associated with low thiamine and treatment of eggs or fry with thiamine-HCl eliminates symptoms and mortality. To verify the role of the active form of the vitamin as the prophylactic agent, we used thiamine pyrophosphate (TPP) to reverse EMS symptoms. We also investigated the ability of specific thiamine antagonists that either block TPP production or interfere with its function to induce EMS. When graded doses of TPP were administered to EMS-susceptible sac-fry, there was a dose-dependent reduction in EMS. The egg concentration of TPP that was associated with reduced EMS was similar to the threshold thiamine concentration found in feral lake trout stocks where EMS occurs. A thiamine deficient stock from Lake Ontario was very sensitive to the thiamine antagonist oxythiamine (OXY) with total mortality associated with developmental arrest occurring at an antagonist to thiamine molar ratio (ATR) above 7:1. The threshold ATR with OXY for development of EMS-like neurological signs in this stock was 1.6:1. In addition to EMS-like neurological signs, OXY caused dose-dependent increases in hydrocephalus, developmental arrest, and vitelline congestion in the Lake Ontario stock. These signs are consistent with those observed in feral fish exhibiting EMS. Much higher doses of antagonists were required (both pyrithiamine (PT) and OXY) to induce EMS-like clinical signs in the thiamine replete Lake Manitou stock. PT was a more potent inducer in this stock as the ATR associated with development of clinical signs was 111:1 for PT compared with 892:1 for OXY. These data provide experimental evidence supporting the hypothesis that a thiamine deficiency in the natural environment is the cause of EMS.     

Nipple attachment behavior in rat pups exposed to alcohol in utero

Two experiments were conducted to further characterize impaired nipple attachment behavior in 5-day-old rat pups exposed to alcohol prenatally. In Experiment 1, animals were given two different nipple attachment tests. In the pups-on-mother test, which required animals to first locate a nipple, alcohol-exposed pups displayed longer attachment latencies than controls. Furthermore, more than 50% of these pups failed to attach during testing. In the pups-on-nipple test, in which no search for the nipple was necessary, prenatal alcohol did not reliably affect attachment. To assess the extent to which alcohol-exposed pups utilize an olfactory cue for attachment, in Experiment 2, nipple attachment was observed using the pups-on-nipple test before and after olfactory cue removal. Similar to controls, the alcohol-exposed animals only attached to the normally scented nipples. Therefore, prenatal alcohol exposure impaired nipple search performance in young rats, but not attachment once at the nipple. Moreover, these pups performed like controls in response to olfactory cue manipulation. Possible mechanisms for the poor search behavior are discussed.     

The effect of thiamine pyrophosphate on ethambutol-induced ocular toxicity

Context: Ethambutol-induced retinal oxidative damage in patients with tuberculosis is still not being adequately treated. The protective effect of thiamine pyrophosphate against oxidative damage in some tissues has been reported, but no information on the protective effects of thiamine pyrophosphate against ethambutol-induced oxidative retinal damage has been found in the medical literature.

Objective: The objective is to investigate whether thiamine pyrophosphate has a protective effect against oxidative retinal damage in rats induced by ethambutol.

Materials and methods: Experimental animals divided into four groups (n?=?10): the healthy group (HG), the ethambutol control group (EMB), thiamine?+?ethambutol group (Thi–EMB) and thiamine pyrophosphate?+?ethambutol group (TPP–EMB). The rats in the TPP–EMB and Thi–EMB groups were administered thiamine pyrophosphate and thiamine, respectively, at doses of 20?mg/kg intraperitoneally. Distilled water was administered intraperitoneally to the HG and the EMB groups as a solvent in the same volumes. One hour after drug injection, 30?mg/kg ethambutol was administered via an oral gavage to the TPP–EMB, Thi–EMB and EMB groups. This procedure was repeated once a day for 90 days. At the end of this period, all rats were euthanized under high-dose thiopental sodium anesthesia, and biochemical and histopathological investigations of the retinal tissue were performed.

Results: Malondialdehyde (MDA) and DNA damage product 8-hydroxyguanine levels were significantly lower in the retinal tissue of TPP–EMB and HG groups compared to those of the Thi–EMB and EMB groups, and total glutathione (tGSH) was also found to be higher. In addition, severe retinal tissue vascularization, edema and loss of ganglion cells were observed in the Thi–EMB and EMB groups, whereas histopathological findings for the TPP–EMB group were observed to be close to normal.

Discussion and conclusion: These findings suggest that thiamine pyrophosphate protects retinal tissues from ethambutol-induced oxidative damage, and thiamine does not. This positive effect of thiamine pyrophosphate may be useful in the prevention of ocular toxicity that occurs during ethambutol use.