Early lifetime zinc supplementation protects zinc-deficient diet-induced alterations

Zinc nutrition and dietary zinc supplements

As the second most abundant trace element in the human body, zinc nutrition is constantly a hot topic. More than one-third population is suffering zinc deficiency, which results in various types of diseases or nutritional deficiencies. Traditional ways of zinc supplementation seem with low absorption rates and significant side effects. Zinc supplements with dietary components are easily accessible and improve zinc utilization rate significantly. Also, mechanisms of maintaining zinc homeostasis are of broad interest. The present review focuses on zinc nutrition in human health in inductive methods. Mainly elaborate on different diseases relating to zinc disorder, highlighting the impact on the immune system and the recent COVID-19. Then raise food-derived zinc-binding compounds, including protein, peptide, polysaccharide, and polyphenol, and also analyze their possibilities to serve as zinc complementary. Finally, illustrate the way to maintain zinc homeostasis and the corresponding mechanisms. The review provides data information for maintaining zinc homeostasis with the food-derived matrix.

Alterations of Bio-elements, Oxidative, and Inflammatory Status in the Zinc Deficiency Model in Rats

Our previous study showed that dietary zinc restriction induces depression-like behavior with concomitant up-regulation of the N-methyl-D-aspartate receptor (NMDAR). Because metal ions, oxidative stress, and inflammation are involved in depression/NMDAR function, in the present study, bio-elements (zinc, copper, iron, magnesium, and calcium), oxidative (thiobarbituric acid-reactive substances; protein carbonyl content), and inflammatory (IL-1α, IL-1β) factors were measured in serum, hippocampus (Hp), and prefrontal cortex (PFC) of male Sprague-Dawley rats subjected to a zinc-adequate (ZnA) (50 mg Zn/kg) or a zinc-deficient (ZnD) (3 mg Zn/kg) diet for 4 or 6 weeks. Both periods of dietary zinc restriction reduced serum zinc and increased serum iron levels. At 4 weeks, lowered zinc level in the PFC and Hp as well as lowered iron level in the PFC of the ZnD rats was observed. At 6 weeks, however, iron level was increased in the PFC of these rats. Although at 6 weeks zinc level in the PFC did not differ between the ZnA and ZnD rats, extracellular zinc concentration after 100 mM KCl stimulation was reduced in the PFC of the ZnD rats and was accompanied by increased extracellular iron and glutamate levels (as measured by the in vivo microdialysis). The examined oxidative and inflammatory parameters were generally enhanced in the tissue of the ZnD animals. The obtained data suggest dynamic redistribution of bio-elements and enhancement of oxidative/inflammatory parameters after dietary zinc restriction, which may have a link with depression-like behavior/NMDAR function/neurodegeneration.

Antidepressant activity of fluoxetine in the zinc deficiency model in rats involves the NMDA receptor complex

The zinc deficiency animal model of depression has been proposed; however, it has not been validated in a detailed manner. We have recently shown that depression-like behavior induced by dietary zinc restriction is associated with up-regulation of hippocampal N-methyl-d-aspartate receptor (NMDAR). Here we examined the effects of chronic administration of a selective serotonin reuptake inhibitor, fluoxetine (FLX), on behavioral and biochemical alterations (within NMDAR signaling pathway) induced by zinc deficiency. Male Sprague Dawley rats were fed a zinc adequate diet (ZnA, 50mg Zn/kg) or a zinc deficient diet (ZnD, 3mg Zn/kg) for 4 weeks. Then, FLX treatment (10mg/kg, i.p.) begun. Following 2 weeks of FLX administration the behavior of the rats was examined in the forced swim test (FST) and the spontaneous locomotor activity test. Twenty four hours later tissue was harvested. The proteins of NMDAR (GluN1, GluN2A and GluN2B) or AMPAR (GluA1) subunits, p-CREB and BDNF in the hippocampus (Western blot) and serum zinc level (TXRF) were examined. Depression-like behavior induced by ZnD in the FST was sensitive to chronic treatment with FLX. ZnD increased levels of GluN1, GluN2A, GluN2B and decreased pS485-GluA1, p-CREB and BDNF proteins. Administration of FLX counteracted the zinc restriction-induced changes in serum zinc level and hippocampal GluN1, GluN2A, GluN2B and p-CREB but not BDNF or pS845-GluA1 protein levels. This finding adds new evidence to the predictive validity of the proposed zinc deficiency model of depression. Antidepressant-like activity of FLX in the zinc deficiency model is associated with NMDAR complex.

Zinc deficiency in rats is associated with up-regulation of hippocampal NMDA receptor

RATIONALE

Data indicated that zinc deficiency may contribute to the development of depression; however changes induced by zinc deficiency are not fully described.

OBJECTIVES

In the present paper we tested whether the dietary zinc restriction in rats causes alterations in N-methyl-D-aspartate receptor (NMDAR) subunits in brain regions that are relevant to depression.

METHODS

Male Sprague Dawley rats were fed a zinc adequate diet (ZnA, 50 mg Zn/kg) or a zinc deficient diet (ZnD, 3 mg Zn/kg) for 4 or 6weeks. Then, the behavior of the rats was examined in the forced swim test, sucrose intake test and social interaction test. Western blot assays were used to study the alterations in NMDAR subunits GluN2A and GluN2B and proteins associated with NMDAR signaling in the hippocampus (Hp) and prefrontal cortex (PFC).

RESULTS

Following 4 or 6 weeks of zinc restriction, behavioral despair, anhedonia and a reduction of social behavior occurred in rats with concomitant increased expression of GluN2A and GluN2B and decreased expression of the PSD-95, p-CREB and BDNF protein levels in the Hp. The up-regulation of GluN2A protein was also found in the PFC, but only after prolonged (6 weeks) zinc deprivation.

CONCLUSIONS

The procedure of zinc restriction in rats causes behavioral changes that share some similarities to the pathophysiology of depression. Obtained data indicated that depressive-like behavior induced by zinc deficiency is associated with the changes in NMDAR signaling pathway.

The involvement of the GPR39-Zn(2+)-sensing receptor in the pathophysiology of depression. Studies in rodent models and suicide victims

Zinc is one of the most important trace elements in our body. Patients suffering from depression show lower serum zinc levels compared to healthy controls. Zincs antagonism to the glutamatergic system seems to be responsible for mood recovery. Recent years have shown that zinc may regulate neurotransmission via the metabotropic GPR39 receptor. Activation of the GPR39-Zn(2+)-sensing receptor (GPR39) triggers diverse neuronal pathways leading to a cAMP-responsive element binding the protein (CREB) expression, which then induces synthesis of the brain-derived neurotrophic factor and, in turn, activation of the Tropomyosin receptor kinase B (TrkB) receptor. In the present study, we investigated the alteration of the GPR39 in different models of depression, such as zinc deficiency and olfactory bulbectomy and in suicide victims. Additionaly, we focused on CREB-BDNF/TrkB under zinc deficient conditions in mice. To demonstrate depressive-like behaviour, a standard and modified forced swim test (FST) was performed. To evaluate expression of GPR39, CREB, BDNF and TrkB, Western Blot analysis was used. Zinc deficient mice and rats showed decreased GPR39 expression in the hippocampus and frontal cortex. A decreased level of hippocampal and cortical GPR39 was also observed in suicide victims. In contrast, increased GPR39 in the hippocampus of olfactory bulbectomized rats was observed. Additionally, we found a decreased expression of CREB, BDNF and TrkB only in the hippocampus of zinc-deficient mice. Our present study demonstrates the associacion of the GPR39 Zn(2+)-sensing receptor in the pathomechanism of depression. Down-regulation of CREB, BDNF, TrkB and GPR39 receptor found under zinc-deficient conditions in the hippocampus, may play an important role in the pathophysiology of mood disorders, since most of patients suffering from depression show lower serum zinc.

Time course of zinc deprivation-induced alterations of mice behavior in the forced swim test

BACKGROUND

Zinc is an important trace element essential for numerous bodily functions. It is believed that a deficiency of zinc can lead to various conditions, including depression, on which this study is focused. It is still not known if hypozincemia leads to the development of depression or whether zinc deficiency is a result of depression. It is hypothesized that zinc may be a therapeutic agent or supplement that would help to reverse the symptoms of this disease.

METHODS

In the present study, the behavior of mice was assessed 2, 4, and 10 weeks following administration of a zinc deficient diet. To evaluate animal activity we used the forced swim test (FST).

RESULTS

After 2-week zinc deprivation we demonstrated a significant reduction in the immobility time. However, after 4 and 10 weeks of zinc deprivation the mice exhibited an increased immobility time. There were no changes in locomotor activity at each time period. After 2-, 4- and 10-week zinc deprivation and the subsequent FST, serum zinc concentration was decreased and determined to be 59, 61 and 20%, respectively, compared with appropriate controls. The serum corticosterone concentration in mice after 2-, 4- and 10-week zinc deprivation and subjected to the FST was also assessed, whereby the differences between the control and experimental animals were demonstrated (increased by: 11, 97 and 225%, respectively).

CONCLUSIONS

The obtained results indicate that zinc deprivation induced "pro-depressive" behavior (after the initial period of "antidepressive" behavior). This pro-depressive behavior correlates with enhanced serum corticosterone concentration.

Zinc in the central nervous system: From molecules to behavior

The trace metal zinc is a biofactor that plays essential roles in the central nervous system across the lifespan from early neonatal brain development through the maintenance of brain function in adults. At the molecular level, zinc regulates gene expression through transcription factor activity and is responsible for the activity of dozens of key enzymes in neuronal metabolism. At the cellular level, zinc is a modulator of synaptic activity and neuronal plasticity in both development and adulthood. Given these key roles, it is not surprising that alterations in brain zinc status have been implicated in a wide array of neurological disorders including impaired brain development, neurodegenerative disorders such as Alzheimer's disease, and mood disorders including depression. Zinc has also been implicated in neuronal damage associated with traumatic brain injury, stroke, and seizure. Understanding the mechanisms that control brain zinc homeostasis is thus critical to the development of preventive and treatment strategies for these and other neurological disorders.

Anxiolytic-like activity of zinc in rodent tests

Because zinc deficiency induces depression and anxiety-like behavior in rodents, we examined the effects of zinc administration in several tests by measuring anxiolytic activity in mice and rats. We now report that zinc significantly increased the number of entries into the open arms in the elevated plus maze in rats. Moreover, zinc treatment significantly increased the number of punished crossings in the four-plate test and attenuated stress-induced hyperthermia (SIH) in mice. However, no effect of zinc administration was observed in the elevated plus maze test in mice. This lack of effect in the latter case was probably due to the substantial zinc-induced reduction in locomotor activity by the doses used in mice. The present data demonstrate for the first time the anxiolytic-like activity of zinc in rodents and may indicate that zinc could be used as a novel therapeutic/adjunct agent in anxiolytic therapy.