Intake of Heated Leaf Extract of Coriandrum sativum Contributes to Resistance to Oxidative Stress via Decreases in Heavy Metal Concentrations in the Kidney

Coriandrum sativum (coriander) is an annual herb of the Apiaceae family and has been used as a traditional remedy. Here we examined whether heated leaf extract of coriander decreases the concentrations of heavy metals in tissues. Male ddY mice were given a drinking water containing 0.25% of heated leaf extract of coriander for 8 weeks. Eight weeks after the intake, the concentrations of zinc, iron, copper, arsenic, and cadmium were measured in the liver and kidney. The intake of coriander did not modify the concentrations of all heavy metals tested in the liver, but decreased the concentrations of iron, arsenic, and cadmium in the kidney. Because heavy metals can induce oxidative stress, the effect of coriander intake on hydrogen peroxide-induced oxidative stress was compared between slices from the kidney and liver. The slices were immersed in Ringer solution containing 100 μM hydrogen peroxide and aminophenyl fluorescein (APF), a probe for detecting reactive oxygen species (ROS). APF fluorescence was markedly increased in the control kidney slices, while the increase was completely blocked in kidney slices from coriander intake group. In contrast, APF fluorescence was also markedly increased in the control liver slices, while the increase was not blocked by coriander intake. The present study indicates that intake of coriander leaf extract contributes to powerful resistance to oxidative stress in the kidney, probably via decreased concentrations in heavy metals. It is likely that decrease in arsenic concentration to the detection limit is a major factor for the resistance.

The Impact of Synaptic Zn2+ Dynamics on Cognition and Its Decline

The basal levels of extracellular Zn²⁺ are in the range of low nanomolar concentrations and less attention has been paid to Zn²⁺, compared to Ca²⁺, for synaptic activity. However, extracellular Zn²⁺ is necessary for synaptic activity. The basal levels of extracellular zinc are age-dependently increased in the rat hippocampus, implying that the basal levels of extracellular Zn²⁺ are also increased age-dependently and that extracellular Zn²⁺ dynamics are linked with age-related cognitive function and dysfunction. In the hippocampus, the influx of extracellular Zn²⁺ into postsynaptic neurons, which is often linked with Zn²⁺ release from neuron terminals, is critical for cognitive activity via long-term potentiation (LTP). In contrast, the excess influx of extracellular Zn²⁺ into postsynaptic neurons induces cognitive decline. Interestingly, the excess influx of extracellular Zn²⁺ more readily occurs in aged dentate granule cells and intracellular Zn²⁺-buffering, which is assessed with ZnAF-2DA, is weakened in the aged dentate granule cells. Characteristics (easiness) of extracellular Zn²⁺ influx seem to be linked with the weakened intracellular Zn²⁺-buffering in the aged dentate gyrus. This paper deals with the impact of synaptic Zn²⁺ signaling on cognition and its decline in comparison with synaptic Ca²⁺ signaling.

Innervation from the entorhinal cortex to the dentate gyrus and the vulnerability to Zn2

Hippocampal Zn²⁺ homeostasis is critical for cognitive activity and hippocampus-dependent memory. Extracellular Zn²⁺ signaling is linked to extracellular glutamate signaling and leads to intracellular Zn²⁺ signaling, which is involved in cognitive activity. On the other hand, excess intracellular Zn²⁺ signaling that is induced by excess glutamate signaling is involved in cognitive decline. In the hippocampal formation, the dentate gyrus is the most vulnerable to aging and is thought to contribute to age-related cognitive decline. The layer II of the entorhinal cortex is the most vulnerable to neuronal death in Alzheimer's disease. The perforant pathway provides input from the layer II to the dentate gyrus and is one of the earliest affected pathways in Alzheimer's disease. Medial perforant pathway-dentate granule cell synapses are vulnerable to either excess intracellular Zn²⁺ or β-amyloid (Aβ)-bound zinc, which induce transient cognitive decline via attenuation of medial perforant pathway LTP. However, it is unknown whether the vulnerability to excess intracellular Zn²⁺ is involved in region-specific vulnerability to aging and Alzheimer's disease. To discover a strategy to prevent short-term cognitive decline in normal aging process and the pre-dementia stage of Alzheimer's disease, the present paper deals with vulnerability of medial perforant pathway-dentate granule cell synapses to intracellular Zn²⁺ dyshomeostasis and its possible involvement in differential vulnerability to aging and Alzheimer's disease in the hippocampal formation.

Significance of synaptic Zn2+ signaling in zincergic and non-zincergic synapses in the hippocampus in cognition

A portion of zinc concentrates in the synaptic vesicles in the brain and is released from glutamatergic (zincergic) neuron terminals. It serves as a signaling factor (in a form of free Zn²⁺). Both extracellular Zn²⁺ signaling, which predominantly originates in Zn²⁺ release from zincergic neuron terminals, and intracellular Zn²⁺ signaling, which is often linked to extracellular Zn²⁺ signaling, are involved in hippocampus-dependent memory. At mossy fiber-CA3 pyramidal cell synapses and Schaffer collateral-CA1 pyramidal cell synapses, which are zincergic, extracellular Zn²⁺ signaling leads to intracellular Zn²⁺ signaling and is involved in learning and memory. At medial perforant pathway-dentate granule cell synapses, which are non-zincergic, intracellular Zn²⁺ signaling, which originates in the internal stores containing Zn²⁺, is involved in learning and memory. The blockade of Zn²⁺ signaling with Zn²⁺ chelators induces memory deficit, while the optimal amount range of Zn²⁺ signaling is unknown. It is possible that the degree and frequency of Zn²⁺ signaling, which determine the increased Zn²⁺ levels, modulates learning and memory as well as intracellular Ca²⁺ signaling. To understand the precise role of synaptic Zn²⁺ signaling in the hippocampus, the present paper summarizes the current knowledge on Zn²⁺ signaling at zincergic and non-zincergic synapses in the hippocampus in cognition and involvement of zinc transporters and zinc-binding proteins in synaptic Zn²⁺ signaling.

Influx of extracellular Zn(2+) into the hippocampal CA1 neurons is required for cognitive performance via long-term potentiation

Physiological significance of synaptic Zn(2+) signaling was examined in the CA1 of young rats. In vivo CA1 long-term potentiation (LTP) was induced using a recording electrode attached to a microdialysis probe and the recording region was locally perfused with artificial cerebrospinal fluid (ACSF) via the microdialysis probe. In vivo CA1 LTP was inhibited under perfusion with CaEDTA and ZnAF-2DA, extracellular and intracellular Zn(2+) chelators, respectively, suggesting that the influx of extracellular Zn(2+) is required for in vivo CA1 LTP induction. The increase in intracellular Zn(2+) was chelated with intracellular ZnAF-2 in the CA1 1h after local injection of ZnAF-2DA into the CA1, suggesting that intracellular Zn(2+) signaling induced during learning is blocked with intracellular ZnAF-2 when the learning was performed 1h after ZnAF-2DA injection. Object recognition was affected when training of object recognition test was performed 1h after ZnAF-2DA injection. These data suggest that intracellular Zn(2+) signaling in the CA1 is required for object recognition memory via LTP. Surprisingly, in vivo CA1 LTP was affected under perfusion with 0.1-1μM ZnCl2, unlike the previous data that in vitro CA1 LTP was enhanced in the presence of 1-5μM ZnCl2. The influx of extracellular Zn(2+) into CA1 pyramidal cells has bidirectional action in CA1 LTP. The present study indicates that the degree of extracellular Zn(2+) influx into CA1 neurons is critical for LTP and cognitive performance.

Zinc-65 imaging of rat brain tumors

The uptake of zinc, an essential nutrient, is critical for cell proliferation. On the basis of the idea that zinc uptake can be an index of viability in proliferating cells, tumor imaging with (65)Zn was performed using autoradiography. After s.c. implantation of ascites hepatoma (AH7974F) cells into the dorsum, 1 h after i.v. injection of (65)ZnCl(2), (65)Zn uptake in the tumor was higher than in the brain tissue but lower than in the liver, which suggests that brain tumors can be positively imaged with (65)Zn. After implantation of AH7974F cells into the periaqueductal gray, 1 h after i.v. injection of (65)ZnCl(2), (65)Zn uptake in the tumor was approximately 10 times higher than in other brain regions. After implantation of C6 glioma cells into the hippocampus, (65)Zn uptake in the tumor was also much higher than in other brain regions. The present findings demonstrate that brain tumors can be imaged with radioactive zinc. To compare brain tumor imaging with (65)Zn with that of [(18)F]fluorodeoxyglucose (FDG), which is widely used for the diagnosis of brain tumors, (14)C-FDG imaging of the C6 glioma was performed in the same manner. (14)C-FDG uptake in the tumor was approximately 1.5 times higher than in the contralateral region in which (14)C-FDG uptake was relatively high. It is likely that zinc uptake is more specific for brain tumors than is FDG uptake, which suggests that there is great potential for the use of (69m)Zn, a short half-life gamma emitter, in the diagnosis of brain tumors.

Hepatic zinc response via metallothionein induction after tumor transplantation

Based on previous findings that liver zinc and metallothionein (MT) levels increase after tumor transplantation, zinc metabolism in tumor-bearing mice was studied to clarify the role of zinc-MT in host defense systems. Zinc in the hepatic cytosolic MT fraction did not increase in tumor-bearing mice fed a zinc-deficient diet, suggesting that dietary zinc is necessary for apo-MT induction in the liver after tumor transplantation and is then incorporated into the apo-MT. When (65)ZnCl(2) was intravenously injected, liver (65)Zn levels in the tumor-bearing mice were higher than those in control mice for 72 h after the injection. Pancreatic and blood (65)Zn levels in tumor-bearing mice were lower than those in controls for 24 h (pancreas) and 6 h (blood) after the injection. These findings indicate that the hepatic zinc response via MT induction influences zinc metabolism in the body after tumor transplantation. Moreover, (65)Zn uptake in the liver of MT-deficient tumor-bearing mice was lower than that in control tumor-bearing mice 1 h after injection. (65)Zn uptake in the tumor and blood (65)Zn levels in the MT-deficient tumor-bearing mice were higher than those in the control tumor-bearing mice. Tumor weight increased more in MT-deficient mice than in control mice. The formation of zinc-MT in the liver of tumor-bearing mice might decrease blood zinc availability for tumors and other tissues, such as the pancreas.

Characteristic induction of hepatic metallothionein in mice by tumor transplantation

Based on the previous finding that hepatic metallothionein (MT) level was tumor-growth dependently elevated in tumor-transplanted mice, the mode of induction of hepatic MT in tumor-bearing mice was comparatively studied with inflammation-induced and stress-subjected mice. The prefeeding with zinc (Zn)-deficient diet for 1 wk suppressed both the growth of tumor and the increase of hepatic MT and Zn in tumor-bearing mice. The postfeeding with Zn-deficient diet also suppressed hepatic MT induction in the course of tumor growth. On the other hand, in the other two experimental model mice, the prefeeding with Zn-deficient diet did not suppress the increase of hepatic MT and Zn. Further, the dexamethasone treatment stimulated hepatic MT induction in tumor-bearing mice, but rather reduced that in inflammation-induced mice. These results suggest that hepatic MT was induced uniquely in tumor-bearing mice and that Zn may play a key role for the induction of hepatic MT by tumor transplantation.

65Zn uptake by liver of rats fed 3'-methyl-dimethylaminoazobenzene

The uptake of 65Zn, determined by gamma-counting and also by autoradiography, significantly increased with the increasing level of metallothionein in liver 4 weeks after the start of feeding a diet containing 3'-methyl-dimethylaminoazobenzene (3'-Me-DAB), at which time the serum gamma-glutamyl transpeptidase activity was not yet significantly elevated. At this time, furthermore, hepatic uptake of 67Ga-citrate did not increase and that of 99mTc-Sn-colloid decreased in 3'-Me-DAB-fed rats. These results suggest that a short-life gamma-emitting isotope such as 69mZn may be useful for the detection at the early stage of hepatic carcinogenesis.

Differential hepatic response of 65Zn distribution between mice bearing experimental tumor and inflammation

Discriminative detection of tumor and inflammation was tried by radio-imaging of hepatic uptake of 65Zn. This closely related to the level of metallothionein (MT) and reflected the extent of tumor growth in mice and rats transplanted with experimental tumor. The elevation of 65Zn distribution in liver of experimental tumor-bearing mice was inhibited by treatment with Zn-deficient diet, while stimulated by dexamethasone. This stimulation occurred 2 days after tumor transplantation, at which time 67Ga-citrate could not image the tumor. On the other hand, hepatic distribution of 65Zn was also elevated in mice by inducing experimental abscess, although the effect of both treatments on this elevation was different from the case of tumor; the elevation was inhibited by treatment with dexamethasone. These results suggest that radio-imaging of hepatic Zn uptake with a short-life gamma emitting isotope such as 69mZn with use of dexamethasone, if required, may be useful for a preliminary test to detect early-stage malignant disease.

Elevation of hepatic levels of metallothionein during experimental carcinogenesis

From the early stage of pancreatic adenocarcinoma in hamsters and also of hepatocellular carcinoma in rats, induced by treatment with N-nitrosobis (2-oxopropyl)amine and 3'-methyl-dimethylaminoazobenzene, respectively, hepatic levels of metallothionein (MT) were found to be continuously elevated. In the hepatoma-induced rats, this elevation preceded that of serum gamma-glutamyl transpeptidase activity, a marker enzyme for hepatocellular carcinoma. These results indicate that, in the course of chemical carcinogenesis, the elevation of hepatic MT level occurred and continued from the early stage of carcinogenesis. This type of elevation of hepatic MT level was also observed in lung metastasis-induced mice. On the other hand, in rats with pancreatitis caused by the administration of deoxycholate, the hepatic level of MT rose only transiently.

Elevation of hepatic levels of metallothionein and zinc in mice bearing experimental tumors

A tumor growth-dependent elevation in the hepatic levels of Zn and metallothionein (MT), without a change in the level of Cu, was found in mice and rats bearing solid tumors in the inguinal region. The levels of Zn and MT thus elevated gave a significant correlation (r = 0.95) between them. Nevertheless, when tumor-bearing mice and rats were fed a Zn-deficient diet, the hepatic levels of Zn and MT did not increase. In mice in which inflammation was induced at the same region, on the other hand, hepatic levels of Zn and MT increased transiently after the injection of turpentine or carrageenan even when they were fed the Zn-deficient diet. These results suggest that the elevation of MT and Zn levels can be a helpful marker for detecting malignancy.