Experimental germanium dioxide-induced neuropathy in rats

Essential References for Structural Analysis of the Peripheral Nervous System for Pathologists and Toxicologists

Toxicologic neuropathology for the peripheral nervous system (PNS) is a vital but often underappreciated element of basic translational research and safety assessment. Evaluation of the PNS may be complicated by unfamiliarity with normal nerve and ganglion biology, which differs to some degree among species; the presence of confounding artifacts related to suboptimal sampling and processing; and limited experience with differentiating such artifacts from genuine disease manifestations and incidental background changes. This compilation of key PNS neurobiology, neuropathology, and neurotoxicology references is designed to allow pathologists and toxicologists to readily access essential information that is needed to enhance their proficiency in evaluating and interpreting toxic changes in PNS tissues from many species.

Functional changes on ascending auditory pathway in rats caused by germanium dioxide exposure: an electrophysiological study

The semiconductor element, germanium (Ge), is essential for the manufacture of modern integrated circuits. Because of its anti-tumor and immunomodulative effects, Ge-containing compounds are also used as health-promoting ingredients in food. However, some histological studies have shown the toxic effects of Ge-containing compounds on various organs, including the central nervous system. Even now, the effect of germanium on auditory system function is not completely clear. To clarify this question, brainstem auditory evoked potentials (BAEPs) were applied to examine the effect of germanium dioxide (GeO(2)) on the ascending auditory pathway. Since the voltage-gated sodium channel is important to neuron activation and nerve conduction, the effect of GeO(2) on voltage-gated sodium channels was also examined. The result revealed GeO(2) elevated the BAEPs threshold dose-dependently. GeO(2) also prolonged latencies and interpeak latencies (IPLs) of BAEPs, but the amplitudes of suprathreshold intensities (90dB) did not show any obvious change. In addition, the results of whole cell patch clamp studies indicated GeO(2) reduced inward sodium current. These results suggest the toxic effect of GeO(2) on the conduction of the auditory system, and that inhibitory effect of GeO(2) on the voltage-gated sodium channels might play a role in GeO(2)-induced abnormal hearing loss.

Germanium dioxide induces mitochondria-mediated apoptosis in Neuro-2A cells

Germanium (Ge) is commonly used in the semiconductor industry as well as health-promoting and medical field. Biologically, germanium possesses erythropoietic, anti-microbial, anti-tumor, anti-amyloidosis, and immunomodulative effects. However, toxic effects of Ge-containing compounds on kidney, muscle, neuronal cells, and nerves have been reported. Mitochondrial dysfunction was found to be involved in the pathogenesis of GeO(2)-induced nephropathy and myopathy. Since it is well known that mitochondria play a major role in apoptosis triggered by many stimuli, an effort was made to examine whether the Ge-induced neurotoxicity occurs through mitochondria-mediated apoptosis. A mouse neuroblastoma cell line, Neuro-2A, was used in the present study. After incubating with 0.1-800microM of GeO(2) for 0-72h, the cell viability of Neuro-2A cells was inhibited in a dose- and time-dependent manner. Further analysis showed that aside from the changes in the nuclear morphology responsible for apoptosis, the release of cytochrome c, the loss of mitochondrial membrane potential, the translocation of Bax, and the reduction of Bcl-2 expression were also observed in Neuro-2A cells after GeO(2) treatment. These results indicate that the mitochondria-mediated apoptosis is involved in this in vitro model of GeO(2)-induced neurotoxicity.

ORAL SINGLE- AND REPEATED-DOSE TOXICITY STUDIES ON GERANTI BIO-GE YEAST, ORGANIC GERMANIUM FORTIFIED YEASTS, IN DOGS

Single- and 13-week repeated-dose toxicities of Geranti Bio-Ge Yeast, organic germanium fortified yeasts, were investigated in dogs. Both sexes of Beagle dogs were orally administered once at a dose of 2,000 mg/kg in single-dose toxicity or daily for 13 weeks at doses of 500, 1,000 or 2,000 mg/kg in repeated-dose toxicity tests. In single-dose toxicity test, no animal dead, moribund, or showing clinical signs or changes in body weight gain was found. In repeated-dose toxicity study, there were no considerable changes in ophthalmoscopy and urinalysis. Several alterations were observed in electrocardiography, hematology and blood biochemistry, including heart rate, R-R interval, QT correcting, reticulocytes, activated partial thromboplastin time and albumin/globulin ratio in only male dogs, but not in females, administered with Geranti Bio-Ge Yeast in a dose-independent manner. In gross findings, several cases of abnormal findings were observed in both control and treatment groups, showing diffuse dark brown to black discoloration of liver, in a dose-independent manner. In microscopic examination, mild lesions, including cholestasis and inflammatory cell foci in liver, kidneys and prostate, were found sporadically in both control and treatment groups. In spite of some alterations in electrocardiography, hematology, blood biochemistry, gross and microscopic findings, such effects were not considered to include toxicopathological significance, based on the marginal changes within normal ranges and lack of dose-dependency, consistent time-course and gender relationship. Taken together, it is suggested that no observed adverse effect level (NOAEL) of Geranti Bio-Ge Yeast is considered to be 2,000 mg/kg in dogs, and that long-term treatment in clinical trials might not exert adverse effects.

ORAL SINGLE- AND REPEATED-DOSE TOXICITY STUDIES ON GERANTI BIO-GE YEAST, ORGANIC GERMANIUM FORTIFIED YEASTS, IN RATS

Single- and 13-week repeated-dose toxicities of Geranti Bio-Ge Yeast, organic germanium fortified yeasts, were investigated in rats. Both sexes of Sprague-Dawley rats were orally administered once at a dose of 2,000 mg/kg in single-dose toxicity or daily for 13 weeks at doses of 500, 1,000 or 2,000 mg/kg in repeated-dose toxicity tests. In single-dose toxicity test to determine dose levels in repeated-dose toxicity study, the body weight gain was suppressed at 2,000 mg/kg, although no death, clinical signs and pathological findings related to the treatment were observed. In repeated-dose toxicity test, there were no clinical signs in animals administered up to 2,000 mg/kg, except one rat died due to a gavage error. In addition, no significant changes in feed consumption and body weight gain were obtained during the treatment period, in spite of week-to-week fluctuation of water consumption. There were no considerable changes in ophthalmoscopy, urinalysis, hematology and serum biochemistry, except a significant decrease in albumin/globulin ratio in males treated with 1,000 mg/kg. In contrast, a significant increase in relative heart weight was observed in both male and female rats treated with a high dose (2,000 mg/kg) of Geranti Bio-Ge Yeast. In microscopic examination, mild lesions were found sporadically in both control and treatment groups in a dose-independent manner. In spite of some alterations in water consumption, serum biochemistry and organ weights, such effects were not considered to include toxicopathological significance, based on the lack of dose-dependency, consistent time-course and gender relationship. Taken together, it is suggested that no observed adverse effect level (NOAEL) of Geranti Bio-Ge Yeast is considered to be over 2,000 mg/kg in rats, and that long-term oral intake in humans might not exert adverse effects.

Germanium oxide enhances the radiosensitivity of cells

We investigated here the combined effect of GeO(2) and radiation on cell viability. Cells were treated with 0 to 22 mM GeO(2) for 12 h followed by 1 Gy X irradiation. A synergistic cytotoxic effect was observed for the combined treatment with a dose-dependent reduction of cell viability. Complete survival curves showed a 2.3- and 2.75-fold increase in radiosensitivity for 50% cell death in the presence of 5 and 15 mM GeO(2), respectively. The increased radiosensitivity also occurred when GeO(2) was given either 4 h prior to irradiation or immediately after radiation exposure. GeO(2) did not affect the total soluble thiol content or the activities of catalase and glutathione S-transferase. Analysis of the production of reactive oxygen species (ROS) revealed that the combined treatment dramatically increased the synthesis of ROS. Addition of N-acetyl cysteine (NAC, 20 mM) decreased the production of ROS in cells. NAC, however, increased cell viability only slightly after treatment with GeO(2) and radiation. Thus increased production of ROS makes little or no contribution to the observed death. The combination of GeO(2) and X radiation, however, significantly increased the frequency of DNA double-strand breaks (DSBs). Notably, the presence of GeO(2) also reduced the efficiency of DNA repair. We conclude that treatment with GeO(2) followed by X irradiation increases DNA DSBs and cell death.

Germanium oxide inhibits the transition from G2 to M phase of CHO cells

We report here for the first time that germanium oxide (GeO(2)) blocks cell progression. GeO(2) is not genotoxic to Chinese hamster ovary (CHO) cells and has limited cytotoxicity. However, GeO(2) arrests cells at G2/M phase. The proportion of cells stopped at G2/M phase increased dose-dependently up to 5 mM GeO(2) when treated for 12 h, but decreased at GeO(2) concentration was greater than 5 mM. Analysis of 5-bromodeoxyuridine-labeled cells indicated that GeO(2) delayed S phase progression in a dose-dependent manner, and blocked cells at G2/M phase. Microscopic examination confirmed that GeO(2) treatment arrested cells at G2 phase. Similar to several other events that cause G2 block, the GeO(2)-induced G2 block can also be ameliorated by caffeine in a dose- and time-dependent manner. To explore the mechanism of G2 arrest by GeO(2), cyclin content and cyclin-dependent kinase activity were examined. Cyclin B1 level was not affected after GeO(2) treatment in CHO cells. However, GeO(2) decreased p34(cdc2) kinase (Cdk1) activity. The kinase activity recovered within 9 h after GeO(2) removal and correlated with the transition of G2/M-G1 phase of the cells. This result suggests that GeO(2) treatment reduces Cdk1 activity and causing the G2 arrest in CHO cells.

Kinetics of germanium dioxide in rats

The kinetics of germanium dioxide (GeO2) in single dose and repeated exposures were investigated in male Wistar rats. In the single dose GeO2 (100 mg/kg BW, p.o.) exposure study, values of several kinetic parameters were shown as follows, a maximum concentration in serum of 15.5+/-0.7 microg/ml (mean +/- S.E.M.), an absorption half-life of 0.7+/-0.1 h (mean +/- S.E.M.), an elimination half-life of 2.3+/-0.5 h (mean +/- S.E.M.), a distribution of the central compartment Vp (3.1+/-0.3 1, mean +/- S.E.M.), and the apparent volume of distribution of the tissue compartment Vt (8.5+/-2.9 1, mean +/- S.E.M.). In the repeated exposure study, 730+/-92 mg GeO2 in 1 1 double-distilled H2O ( = 100 mg/kg/day) was given daily to rats for 4 weeks (p.o.). After sacrificing the rats, the analysis of tissue distribution showed that GeO2 was accumulated in some important organs or tissues in the body, especially the peripheral nerves and kidney. These results indicate that GeO2 could be absorbed rapidly but had a longer elimination half-life in rats. In addition, GeO2 was accumulated especially in the nerves and kidney following long-term exposure.

Polyneuropathy due to cobalamin deficiency in the rat

In the present study, we investigated the peripheral nervous system (PNS) (both in terms of its ultrastructure and in terms of its function) of rats made cobalamin (Cbl)-deficient either through total gastrectomy or through prolonged feeding on a Cbl-deficient diet. In both these types of Cbl-deficient neuropathies we found: (a) ultrastructurally, intramyelin and endoneural edema, with no or minimal axonal damage in the PNS, in dorsal root ganglia, and the ventral and dorsal rootlets of the spinal cord; (b) electrophysiologically, a significant reduction in the nerve conduction velocity, consistent with that reported in (a); (c) morphometrically, a significant reduction in the density of myelinated fibers both in the sciatic nerve and in the peroneal nerve. All these pathological changes were reversed by chronic postoperative administration of Cbl into totally gastrectomized (TGX)-rats, hinting at the specificity of the damage itself in relation to the permanent Cbl-deficient status of the TGX-rats. No signs of segmental demyelination or remyelination were found. We also observed a turning of type I fibers into type II fibers in the soleus muscle of all our Cbl-deficient rats, however the Cbl deficiency had been induced. This muscular change was still present in TGX- and Cbl-treated rats, and it cannot be related to a malnutrition status, since it has been observed also in rats fed a Cbl-deficient diet. All these results demonstrate that Cbl deficiency strongly affects rat PNS within different parameters.

Hazard assessment of germanium supplements

Germanium-containing dietary supplements became popular in the 1970s in Japan and later in other countries, as elixirs for certain diseases (e.g., cancer and AIDS). Germanium is not an essential element. Its acute toxicity is low. However, at least 31 reported human cases linked prolonged intake of germanium products with renal failure and even death. Signs of kidney dysfunction, kidney tubular degeneration, and germanium accumulation were observed. Other adverse effects were anemia, muscle weakness, and peripheral neuropathy. Recovery of renal function is slow and incomplete even long after germanium intake was stopped. The total dose of ingested germanium (as dioxide, carboxyethyl germanium sesquioxide, germanium-lactate-citrate, or unspecified forms) varied from 15 to over 300 g; the exposure duration varied from 2 to 36 months. In laboratory animals, elevated germanium in tissues and impaired kidney and liver function were observed in a life-time drinking water (5 ppm germanium) study. Other toxicities associated with ingested germanium products in human cases were also demonstrated in animal studies with germanium dioxide and sometimes other germanium compounds. Based on the evidence of persistent renal toxicity associated with germanium dioxide, the lack of conclusive findings of differential nephrotoxicity of organic germanium compounds, and the possibility of contamination of the organic germanium products with inorganic germanium, it is clear that germanium products present a potential human health hazard.