Metallothionein induction by bismuth in neonatal rat primary astrocyte cultures

Expression and functional role of metallothioneins I and II in the spinal cord in inflammatory and neuropathic pain models

In this study, the expression and functional role of metallothioneins I and II (MT-I/II) were evaluated in the spinal cord in rat models of inflammatory and neuropathic pain. Complete Freund's adjuvant (CFA) injection into the hindpaw induced an increase in MT-I/II protein expression in bilateral dorsal and ventral horns throughout the spinal cord, while chronic constriction injury (CCI) of the sciatic nerve induced an increase in MT-I/II expression in the ipsilateral dorsal and ventral horns of the lower lumbar spinal cord. Increased MT-I/II immunoreactivity was predominantly localized to vascular endothelial cells. CFA injection- and CCI-induced MT-I/II expression was inhibited by intrathecal administration of MT-I siRNA. Treatment with MT-I siRNA before CFA injection or at early time points after CCI resulted in a significant attenuation of mechanical allodynia and thermal hyperalgesia, while treatment at later time points had no effect on established pain behaviors. Our results suggest that endogenous MT-I/II might play an important role in the pathogenesis of pain behaviors, participating in the initiation of inflammatory and neuropathic pain rather than in their maintenance.

In vivo distribution of bismuth in the mouse brain: influence of long-term survival and intracranial placement on the uptake and transport of bismuth in neuronal tissue

Bismuth is used for a multitude of industrial purposes and has partly replaced toxic heavy metals such as lead and mercury in e.g. lubricants and shotgun pellets. In medicine, bismuth-compounds have long been used to remedy gastrointestinal disorders; lately in combination with antibiotics to treat Helicobacter pylori associated peptic ulcers. An epidemic episode of bismuth-induced encephalopathy in France in the 1970s revealed the neurotoxic potential of bismuth. This incidence, involving almost 1000 patients, remains unexplained and the contribution of other factors besides bismuth has been postulated. Recently an autometallographic technique made it possible to detect bismuth in morphologically intact tissue. In the present study, autometallographicly detectable bismuth was seen throughout the brain following intraperitoneal and intracranial exposure. The neuronal staining pattern seems highly organized with some areas heavily stained and others with low or no staining. Long-term (8 months) intraperitoneal exposure led to higher bismuth uptake than short-term (2 weeks) exposure. Following both intraperitoneal and intracranial exposure, high amounts of bismuth were found in the reticular and hypothalamic nuclei, in the oculomotor and hypoglossal nuclei and in Purkinje cells. Within the central nervous system (CNS) retrograde axonal transport was seen after intracranial bismuth exposure. Axonal transport seems to influence the distribution of bismuth as the highest uptake of bismuth after intraperitoneal exposure was seen in the facial and the trigeminal motor nuclei, i.e. neurones with processes outside the blood-brain barrier, whereas these nuclei contained no bismuth following ic exposure. Ultrastructurally, accumulation of bismuth was seen in lysosomes.

Gene expression changes induced by bismuth in a macrophage cell line

We have investigated the effect of bismuth by autometallography, cell viability, TUNEL assay and microarray analysis of a macrophage cell line. The cells accumulate bismuth in their lysosomes in a time- and dose-dependent manner. Cell viability assays show a significant decrease in the number of viable cells related to both bismuth concentrations and exposure time. TUNEL assays after 12 h and 24 h at a bismuth-citrate concentration of 50 microM revealed the presence of 30% and 70% TUNEL-positive cells, respectively, compared with 8% in the controls. We have analysed gene expression profiles for cells exposed to 50 microM bismuth-citrate and for untreated controls at 12 h and 24 h by microarray analysis, which confirmed that bismuth is a powerful metallothionein inducer. A number of glycolytic enzymes are induced by bismuth, suggesting that bismuth is able to induce "hypoxia-like" stress. BCL2/adenovirus E1B 19-kDa-interacting protein 3 (Bnip3) has been suggested as a regulator of hypoxia-induced cell death independent of caspase-3 activation and cytochrome c release. Bnip3 is up-regulated indicating the involvement of Bnip3 as a possible mechanism for bismuth-induced cell death. Differences have been noticed in cell viability and in the modification of the mRNA expression levels at 12 and 24 h. Only 13 genes are modified at both these times, suggesting a time-dependent molecular cascade in which bismuth-exposed cells enter a dormant stage with mRNA down-regulation being followed by cell death of susceptible cells.

Influence of bismuth on the number of neurons in cerebellum and hippocampus of normal and hypoxia-exposed mouse brain: a stereological study

The industrial use of bismuth is increasing. In medicine, bismuth compounds have long been used in the treatment of gastrointestinal disorders, recently in combination with antibiotics for the treatment of Helicobacter pylori-associated peptic ulcers. Bismuth-induced encephalopathy is a known side-effect. One of the symptoms of bismuth encephalopathy is ataxia, suggesting possible cerebellar involvement. The introduction of autometallography (AMG) for tracing BiS/BiSe nanocrystals has provided histochemical evidence supporting the cerebellum being involved in bismuth encephalopathy, but the effect of bismuth on the neuron number in the cerebellum has never been evaluated. In vitro studies have indicated that CA1 neurons may be targets for bismuth intoxication, but results have been conflicting. Recently, the loss of dorsal root ganglion cells was reported after moderate bismuth exposure. This raises the question whether the use of another neurotoxic stimulus, such as hypoxia, amplifies the toxic effects of bismuth. Despite AMG-detectable bismuth accumulations, stereological examinations revealed no statistically significant decrease in the number of Purkinje, CA1 or CA3 neurons or in the volume of the cerebellar granule layer. Surprisingly, intermittent hypoxia led to a statistically significant loss of Purkinje cells without affecting the hippocampus. Bismuth neither ameliorated nor exacerbated the hypoxic effects on the cerebellum.

Foreign metallothionein-I expression by transient transfection in MT-I and MT-II null astrocytes confers increased protection against acute methylmercury cytotoxicity

The mechanisms associated with metallothionein (MT) gene regulation are complex and poorly understood. Only a modest increase in brain MT expression levels is attained by exposure to metals, MT gene transfection, and MT gene knock-in techniques. Accordingly, in the present study, MT null astrocytes isolated from transgenic mice deficient in MT-I and MT-II genes were introduced as a zero background model of MT expression. MT protein levels were determined by western blot analysis. MT proteins in MT-I and MT-II null astrocytes were undetectable. Transient MT-I gene transfection increased the levels of foreign MT expression in MT-I and MT-II null astrocytes by 2.3-fold above basal levels in wild-type astrocytes. Intracellular Na(2)51CrO(4) efflux and D-[2,3-3H]aspartate uptake were studied as indices of acute methylmercury (MeHg) (5 microM) cytotoxicity. In MT-I and MT-II knockout astrocytes MeHg led to significant (p<0.01) increase in Na(2)51CrO(4) efflux and a significant (p<0.05) decrease in the initial rate (1 min) of D-[2, 3-3H]aspartate uptake compared to MT-I and MT-II knockout controls. Transfection of the MT-I gene in MT-I and MT-II null mice significantly (p<0.01) decreased the effect of MeHg on Na(2)51CrO(4) efflux in MT null, as well as wild-type astrocytes. MT-I gene transfection in MT-I and MT-II null astrocytes reversed the inhibitory effect of MeHg on D-[2,3-3H]aspartate uptake, such that initial rates of uptake in MT-I transfected cells in the presence and absence of MeHg (5 microM) were indistinguishable. These results demonstrate that: (1) astrocytes lacking MTs are more sensitive to MeHg than those with basal MT protein levels, (2) the MT-I gene can be overexpressed in MT-I and MT-II null astrocytes by transient MT-I gene transfection, and (3) that foreign MT expression endows astrocytes with increased resistance to MeHg.

Primary cortical glial reaction versus secondary thalamic glial response in the excitotoxically injured young brain: astroglial response and metallothionein expression

In this study we have evaluated the primary astroglial reactivity to an injection of N-methyl-D-aspartate into the right sensorimotor cortex, as well as the secondary astroglial response in the thalamic ventrobasal complex, caused by the anterograde degeneration of descending corticothalamic fibres and/or target deprivation of the developing thalamic neurons. The astroglial response was evaluated from 4 h to 30 days post-lesion, by the immunocytochemical detection of the cytoskeletal proteins glial fibrillary acidic protein and vimentin, and the antioxidant and metal binding protein metallothionein I-II. In the lesioned cortex, hypertrophied reactive astrocytes showed increased glial fibrillary acidic protein labelling that correlated with a strong expression of vimentin and metallothionein I-II. Maximal astrocytic response was seen at one week post-lesion. The glial scar that formed later on remained positive for all astroglial markers until the last survival time examined. In contrast, in the anterogradely/retrogradely affected thalamus, the induced astroglial secondary response was not as prominent as in the cortex and was characteristically transitory, being undetectable by 14 days post-lesion. Interestingly, thalamic reactive astrocytes showed increased glial fibrillary acidic protein expression but no induction of vimentin and metallothionein I-II. In conclusion, in the young brain, the pattern of astroglial reactivity is not homogeneous and is strongly dependent on the grade of tissue damage: both in response to primary neuronal death and in response to retrograde/anterograde secondary damage, reactive astrocytes show hypertrophy and increased glial fibrillary acidic protein expression. However, astroglial vimentin and metallothionein I-II expression are only observed in areas undergoing massive neuronal death, where glial scar is formed.

Transfection and overexpression of metallothionein-I in neonatal rat primary astrocyte cultures and in astrocytoma cells increases their resistance to methylmercury-induced cytotoxicity

Metallothionein-I (MT-I) was expressed in neonatal rat primary astrocyte cultures and an astrocytoma cell line by pGFAP-MT-I plasmid transfection under the control of the astrocyte-specific glial fibrillary acidic protein (GFAP) promoter. Following transient transfection of the pGFAP-MT-I plasmid, MT-I mRNA and MT-I protein levels were determined by northern blot and immunoprecipitation analyses, respectively. The ability of cells over-expressing MT-I to withstand acute methylmercury (MeHg) treatment was measured by the release of preloaded Na251CrO4, an indicator of membrane integrity. Transfection with the pGFAP-MT-I plasmid led to increased mRNA (2. 5-fold in astrocytes and 7.4-fold in astrocytomas) and MT-I protein (2.4-fold in astrocytes and 4.0-fold in astrocytomas) levels compared with their respective controls. Increased expression of MT-I was associated with attenuated release of Na251CrO4 upon MeHg (5 microM) treatment. These results demonstrate that MT-I can be highly expressed both in primary astrocyte cultures and astrocytomas by pGFAP-MT-I plasmid transfection, and lend credence to the hypothesis that increased expression of MT-I affords protection against the cytotoxic effects of MeHg. Taken together, the data suggest that MT offer effective cellular adaptation to MeHg cytotoxicity.