Prenatal Exposure to Cadmium During Organogenesis Impairs Memory in Young Rats

Effect of cadmium administration on the antioxidant system and neuronal death in the hippocampus of rats

Cadmium (Cd) is a heavy metal classified as a carcinogen whose exposure could affect the function of the central nervous system. Studies suggest that Cd modifies neuronal morphology in the hippocampus and affects cognitive tasks. The oxidative stress pathway is proposed as a mechanism of toxicity. However, this mechanism is not precise yet. This study aimed to evaluate the effect of Cd administration on oxidative stress markers in the male rat's hippocampus. Male Wistar rats were divided into (1) control (drinking water) and (2) treatment with Cd (32.5 ppm of cadmium chloride (CdCl₂ ) in water). The Cd was administered for 2, 3, and 4 months. The results show that the oral administration of CdCl₂ increased the concentration of Cd in plasma and hippocampus, and this response is time-dependent on its administration. Likewise, it caused an increase in lipid peroxidation and nitrosative stress markers. Moreover, it increased reactive astrogliosis and antioxidant enzyme activity. Consequently, the progression of the oxidative response exacerbated neurodegeneration in hippocampal cells. Our results suggest that Cd exposure induces a severe oxidative response that contributes critically to hippocampal neurodegeneration. It is suggested that exposure to Cd increases the risk of developing neurological diseases, which contributes to a decrease in the quality of life of the human and the environment in which it lives.

The Effect of Short-Term Exposure to Cadmium on the Expression of Vascular Endothelial Barrier Antigen in the Developing Rat Forebrain and Cerebellum: A Computerized Quantitative Immunofluorescent Study

Clinical and laboratory studies have shown that environmental exposure to cadmium produces damage to several organs, including bones, lungs, and kidneys. The involvement of cadmium in central nervous system (CNS) disorders has also been widely reported, but the precise pathophysiological mechanism is not yet fully understood. Children who were exposed to cadmium during pregnancy are known to suffer from developmental delays, learning difficulties, attention deficit hyperactivity disorder (ADHD), and other cognitive and neurobehavioral deficits. Results from numerous studies suggest that dysfunction of the blood-brain barrier (BBB) structures is an important step in the neurotoxicity of cadmium. A rat-specific BBB marker protein, the endothelial barrier antigen (EBA), has been previously isolated and classified by Sternberger and others. The mouse IgG1 clone, anti-endothelial barrier antigen (anti-EBA), detects a protein triplet (23.5kDa, 25 kDa, and 30kDa) localized to the luminal surface of central and peripheral nervous system (CNS and PNS) vascular endothelial cells with selective permeability barrier functions. This marker has been widely used for characterizing BBB alterations under demyelinating, inflammatory, and other CNS pathologies. Many studies have been published using the rat model system for studying the neurotoxic effect of acute and chronic exposure to cadmium. We applied the indirect immunofluorescent techniques using the anti-EBA antibody in conjunction with the Olympus cellSens computerized image analysis to detect and quantify the surface areas of BBB-competent microvessel profiles in paraformaldehyde-fixed, paraffin-embedded brains of term-delivered young rats after intraperitoneal injection of a single dose of cadmium chloride. We detected a statistically significant reduction in EBA-positive microvessel surface areas in the forebrain (t = 5.86, df = 1789, p-value < 0.001) and cerebellum (t=73.40, df=1337, p < 0.001) of cadmium-treated rats compared to the normal controls. Thus, this study supports the hypothesis that the EBA is a sensitive and measurable indicator for quantitative assessment of the impact of cadmium exposure in the developing rat brain.

Effects of Cadmium Exposure on Gut Villi in Danio rerio

In aquatic organisms, cadmium exposure occurs from ovum to death and the route of absorption is particularly wide, being represented by skin, gills and gastrointestinal tract, through which contaminated water and/or preys are ingested. It is known that cadmium interferes with the gut; however, less information is available on cadmium effects on an important component of the gut, namely goblet cells, specialized in mucus synthesis. In the present work, we studied the effects of two sublethal cadmium concentrations on the gut mucosa of Danio rerio. Particular attention was paid to changes in the distribution of glycan residues, and in metallothionein expression in intestinal cells. The results show that cadmium interferes with gut mucosa and goblet cells features. The effects are dose- and site-dependent, the anterior gut being more markedly affected than the midgut. Cadmium modifies the presence and/or distribution of glycans in the brush border and cytoplasm of enterocytes and in the goblet cells’ cytoplasm and alters the metallothionein expression and localization. The results suggest a significant interference of cadmium with mucosal efficiency, representing a health risk for the organism in direct contact with contamination and indirectly for the trophic chain.

Resolvin D1 protects against cadmium chloride-induced memory loss and hippocampal damage in rats: A comparison with docosahexaenoic acid

BACKGROUND

Intoxication with cadmium (Cd) ions leads to hippocampal damage and cognitive impairment. However, omega-3 polyunsaturated fatty acids (n-3 PUFAs) exert neuroprotective effects in different animal models of neurodegeneration.

PURPOSE

This study compared the neuroprotective effect of the n-3 PUFA, docosahexaenoic acid (DHA), and its downstream metabolite, resolvin D1 (RVD1), on hippocampal damage and memory deficits in cadmium chloride (CdCl₂)-treated rats.

RESEARCH DESIGN

Control or CdCl₂ (0.5 mg/kg)-treated rats were subdivided into three groups (n = 18/each) and treated for 6 weeks as follows: (1) fed control diet, (2) fed DHA-rich diets (0.7 g/100 g), or (3) treated with RVD1 (0.2 μg/kg, i.p).

RESULTS

Treatment with a DHA-rich diet or RVD1 significantly increased the levels of docosahexaenoic acid and RVD1, respectively, in the hippocampal of CdCl₂-treated rats without affecting the reduction in the expression of the 15-lipooxygenase-1 (ALOX15). These effects were associated with improvements in rats' memory function and hippocampal structure, as well as a redction in the hippocampal levels of reactive oxygen species (ROS), malondialdehyde (MDA), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), nuclear localization of the nuclear factor-kappa beta p65 (NF-κB p65), and expression of cleaved caspase-3. Concomitantly, hippocampi of both groups of rats showed significantly higher levels of Bcl-2, superoxide dismutase (SOD), and glutathione (GSH), as well as enhanced nuclear levels of the nuclear factor erythroid 2-related factor 2 (Nrf-2). The effects of RVD1 on all these markers in the CdCl₂-induced rats were more profound than those of DHA. Also, the increase in the nuclear protein levels of Nrf-2 and the decrease in the levels of Bax and nuclear protein levels of NF-κB p65 were only seen in the hippocampal of CdCl₂ + RVD1-treated rats.

CONCLUSION

RVD1 is more powerful than DHA in preventing CdCl₂-induced memory loss and hippocampal damage in rats.

Kaempferol protects against cadmium chloride-induced hippocampal damage and memory deficits by activation of silent information regulator 1 and inhibition of poly (ADP-Ribose) polymerase-1

The neuroprotective effect of Kaempferol against cadmium chloride (CdCl₂) -induced neurotoxicity is well reported. The silent information regulator 1 (SIRT1) and poly (ADP-Ribose) polymerase-1 (PARP1) are two related cellular molecules that can negatively affect the activity of each other to promote or inhibit cell survival, respectively. It is still largely unknown if the neurotoxicity of CdCl₂ or the neuroprotection of Kaempferol are mediated by modulating SIRT1 and/or PAPR1 activities. In this study, we tested the hypothesis that CdCl₂-induced memory deficit and hippocampal damage are associated with downregulation/inhibition of SIRT1 and activation of PAPR1, an effect that can be reversed by co-treatment with Kaempferol. Rats (n = 12/group) were divided into 4 groups as control, control + Kaempferol (50 mg//kg), CdCl₂ (0.5 mg/kg), and CdCl₂ + Kaempferol. All treatments were administered orally for 30 days daily. As compared to control rats, CdCl2 reduced rat's final body weights (21.8%) and their food intake (30%), induced oxidative stress and apoptosis in their hippocampi, and impaired their short and long-term recognition memory functions. Besides, the hippocampi of CdCl₂-treated rats had higher levels of TNF-α (197%), and IL-6 (190%) with a concomitant increase in nuclear activity and levels of NF-κB p65 (721% & 554%). Besides, they showed reduced nuclear activity (53%) and levels (74%) of SIRT1, higher nuclear activity and levels of PARP1 (292% & 138%), increased nuclear levels of p53 (870%), and higher acetylated levels of NF-κB p65 (513%), p53 (644%), PARP1 (696%), and FOXO-2 (149%). All these events were significantly reversed in the CdCl₂ + Kaempferol-treated rats. Of note, Kaempferol also increased levels of MnSOD (73.5%), and GSH (40%), protein levels of Bcl-2 (350%), and nuclear activity (67%) and levels (46%) of SIRT1 in the hippocampi of the control rats. In conclusion, Kaempferol ameliorates CdCl₂-induced memory deficits and hippocampal oxidative stress, inflammation, and apoptosis by increasing SIRT1 activity and inhibiting PARP1 activity.