Early Neurodevelopmental Exposure to Low Lead Levels Induces Fronto-executive Dysfunctions That Are Recovered by Taurine Co-treatment in the Rat Attention Set-Shift Test: Implications for Taurine as a Psychopharmacotherapy Against Neurotoxicants

Individual and combined effects of cadmium and lead exposure in rats

The exposure of humans and animals to environmental compounds is rarely restricted to a single chemical. Cadmium (Cd) and lead (Pb) are two heavy metals known to be the most toxic. Deleterious effects of each metal alone are well documented. Unfortunately, very few studies were conducted to determine their combined effect. Four groups of Wistar rats were treated intravenously for 15 days. The control group received physiological saline solution; groups 2 and 3 were treated with Cd chloride and lead acetate, respectively ; and the treatment group 4 received a combined treatment of Cd and Pb . A significant decrease was recorded for hematological parameters , with an increase in white blood cells and an inhibition in δ-ALAD level. Cell injury in the livers and kidneys was clearly shown by the significant elevation of the biochemical markers. Cd and Pb induced oxidative stress and had adverse health effects at lower exposure levels than previously thought.

The Protective Effects of Taurine, a Non-essential Amino Acid, Against Metals Toxicities: A Review Article

Taurine is a non-proteinogenic amino acid derived from cysteine. It is involved in several phenomena such as the regulation of growth and differentiation, osmoregulation, neurohormonal modulation, and lipid metabolism. Taurine is important because of its high levels in several tissues such as the central nervous system (CNS), heart, skeletal muscles, retinal membranes, and platelets. In this report, we present the functional properties of taurine indicating that it has potential effects on various metal toxicities. Therefore, a comprehensive literature review was performed using the Scopus, PubMed, and Web of Science databases. According to the search keywords, 61 articles were included in the study. The results indicate that taurine protects tissues against metal toxicity through enhancement of enzymatic and non-enzymatic antioxidant capacity, modulation of oxidative stress, anti-inflammatory and anti-apoptotic effects, involvement in different molecular pathways, and interference with the activity of various enzymes. Taken together, taurine is a natural supplement that presents antitoxic effects against many types of compounds, especially metals, suggesting public consumption of this amino acid as a prophylactic agent against the incidence of metal toxicity.

Taurine Supplementation for 48-Months Improved Glucose Tolerance and Changed ATP-Related Enzymes in Avians

Avians differ from mammals, especially in brain architecture and metabolism. Taurine, an amino acid basic to metabolism and bioenergetics, has been shown to have remarkable effects on metabolic syndrome and ameliorating oxidative stress reactions across species. However, less is known regarding these metabolic relationships in the avian model. The present study serves as a preliminary report that examined how taurine might affect avian metabolism in an aged model system. Two groups of pigeons (Columba livia) of mixed sex, a control group and a group that received 48 months of taurine supplementation (0.05% w/v) in their drinking water, were compared by using blood panels drawn from their basilic vein by a licensed veterinarian. From the blood panel data, taurine treatment generated higher levels of three ATP-related enzymes: glutamate dehydrogenase (GLDH), lactate dehydrogenase (LDH), and creatine kinase (CK). In this preliminary study, the role that taurine treatment might play in the adult aged pigeon's metabolism on conserved traits such as augmenting insulin production as well as non-conserved traits maintaining high levels of ATP-related enzymes was examined. It was found that taurine treatment influenced the avian glucose metabolism similar to mammals but differentially effected avian ATP-related enzymes in a unique way (i.e., ∼×2 increase in CK and LDH with a nearly ×4 increase in GLDH). Notably, long-term supplementation with taurine had no negative effect on parameters of lipid and protein metabolism nor liver enzymes. The preliminary study suggests that avians may serve as a unique model system for investigating taurine metabolism across aging with long-term health implications (e.g., hyperinsulinemia). However, the suitability of using the model would require researchers to tightly control for age, sex, dietary intake, and exercise conditions as laboratory-housed avian present with very different metabolic panels than free-flight avians, and their metabolic profile may not correlate one-to-one with mammalian data.

Taurine-Derived Compounds Produce Anxiolytic Effects in Rats Following Developmental Lead Exposure

Lead (Pb2+) is a developmental neurotoxicant that disrupts the GABA-shift and subsequently causes alterations in the brain's excitation-to-inhibition (E/I) balance. Taurine is a well-established neuroprotective and inhibitory compound for regulating brain excitability. Since mechanistically taurine can facilitate neuronal inhibition through the GABA-AR, the present study examined the anxiolytic potential of taurine derivatives. Treatment groups consisted of the following developmental Pb2+-exposures: Control (0 ppm) and Perinatal (150 ppm or 1,000 ppm lead acetate in the drinking water). Rats were scheduled for behavioral tests between postnatal days (PND) 36-45 with random drug assignments to either saline, taurine, or taurine-derived compound (TD-101, TD-102, or TD-103) to assess the rats' responsivity to each drug in mitigating the developmental Pb2+-exposure and anxiety-like behaviors through the GABAergic system. Long-Evans hooded rats were assessed using an open field (OF) test for preliminary locomotor assessment. Twenty-four hours later, the same rats were exposed to the elevated plus maze (EPM) and were given an i.p. injection of 43 mg/Kg of the saline, taurine, or TD drugs 15 min prior to testing. Each rat was tested using the triple-blind random assignment method for each drug condition. The OF data revealed that Control female rats had increased locomotor activity over Control male rats, and the Pb2+-exposed males and females had increased locomotor activity when compared to the Control male and female rats. However, in the EPM, the Control female rats exhibited more anxiety-like behaviors over Control male rats, and the Pb2+-exposed male and female rats showed selective responsivity to TD drugs when compared to taurine. For Pb2+-exposed males, TD-101 showed consistent recovery of anxiety-like behaviors similar to that of taurine regardless of Pb2+ dose, whereas in Pb2+-exposed females TD-101 and TD-103 showed greater anxiolytic responses in the EPM. The results from the present psychopharmacological study suggests that taurine and its derivatives are interesting drug candidates to explore sex-specific mechanisms and actions of taurine and the associated GABAergic receptor properties by which these compounds alleviate anxiety as a potential behavioral pharmacotherapy for neurodevelopmental Pb2+ exposure.

A combined therapeutic regimen of citalopram and environmental enrichment ameliorates attentional set-shifting performance after brain trauma

Traumatic brain injuries (TBI) have led to lasting deficits for an estimated 5.3 million American patients. Effective therapies for these patients remain scarce and each of the clinical trials stemming from success in experimental models has failed. We believe that the failures may be, in part, due to the lack of preclinical assessment of cognitive domains that widely affect clinical TBI. Specifically, the behavioral tasks in the TBI literature often do not focus on common executive impairments related to the frontal lobe such as cognitive flexibility. In previous work, we have demonstrated that the attentional set-shifting test (AST), a task analogous to the clinically-employed Wisconsin Card Sorting Test (WCST), could be used to identify cognitive flexibility impairments following controlled cortical impact (CCI) injury. In this study, we hypothesized that both the administration of the antidepressant drug citalopram (CIT) and exposure to a preclinical model of neurorehabilitation, environmental enrichment (EE), would attenuate cognitive performance deficits on AST when provided alone and lead to greater benefits when administered in combination. Adult male rats were subjected to a moderate-severe CCI or sham injury. Rats were randomly divided into experimental groups that included surgical injury, drug therapy, and housing condition. We observed that both CIT and EE provided significant cognitive recovery when administered alone and reversal learning performance recovery increased the most when the therapies were combined (p < 0.05). Ongoing studies continue to evaluate novel ways of assessing more clinically relevant measurements of high order cognitive TBI-related impairments in the rat model.

Evaluation of Analytes Characterized with Potential Protective Action after Rat Exposure to Lead

Lead (Pb) was revealed for its role as a neurodevelopmental toxin. The determination of neurotransmitters (NTs) in particular brain regions could ameliorate the precise description and optimization of therapeutic protocols able to restore the harmony of signaling pathways in nervous and immune systems. The determination of selected analytes from the group of NTs based on the liquid chromatography (LC)-based method was carried out to illustrate the changes of amino acid (AA) and biogenic amine (BA) profiles observed in chosen immune and nervous systems rat tissues after Pb intoxication. Also, a protective combination of AA was proposed to correct the changes caused by Pb intoxication. After the administration of Pb, changes were observed in all organs studied and were characterized by a fluctuation of NT concentrations in immune and nervous systems (hypothalamus samples). Using a protective mixture of bioactive compounds prevented numerous changes in the balance of NT. The combined analysis of the immune and nervous system while the normalizing effect of curative agents on the level of differentially secreted NTs and AA is studied could present a new approach to the harmonization of those two essential systems after Pb intoxication.

Combined exposure of lead and cadmium leads to the aggravated neurotoxicity through regulating the expression of histone deacetylase 2

Lead (Pb) and cadmium (Cd) are common heavy metals in the environment, exerting detrimental effects on central nervous system. Although increasing evidence demonstrated the Pb and Cd-induced neurotoxicity, the exact epigenetic mechanisms induced by combined exposure (co-exposure) of Pb and Cd are still unclear. In this study, the neurotoxicity of individual exposure and co-exposure to Pb and Cd in vivo (150 ppm and 5 ppm respectively) and in vitro (10 μM and 0.1 μM respectively) was investigated. The results showed that neurite outgrowth was inhibited by either individual or combined exposure to Pb/Cd, whereas the co-exposure aggravated the inhibitory effect in PC12 cells. The results of Morris Water Maze (MWM), Y maze and Golgi-Cox staining showed that either Pb or Cd alone exposure damaged the ability of learning and memory and decreased the dendritic spine density in both the hippocampal CA1 and DG area of Sprague---Dawley (SD) rats, and that the co-exposure aggravated the damages. Subsequently, histone deacetylase (HDAC) 2 was significantly increased in both hippocampal tissues and PC12 cells co-exposed to Pb and Cd, and the treatment of trichostatin A (TSA) and HDAC2-knocking down construct (shHDAC2) could markedly prevent neurite outgrowth impairment in PC12 cells. In summary, HDAC2 plays essential regulatory roles in neurotoxicity induced by the co-exposure to Pb and Cd, providing a potential molecular target for neurological intervention.