Neurotoxic effects of methylcyclopentadienyl manganese tricarbonyl (MMT) in the mouse: basis of MMT-induced seizure activity

Toxic boost: Acute, reversible neurotoxicity after ingestion of methylcyclopentadienyl manganese tricarbonyl (MMT) mistaken for an energy drink

Methylcyclopentadienyl manganese tricarbonyl (MMT) is an organometallic compound used as a gasoline additive for its antiknock properties. Human ingestion of MMT has not previously been reported. We present the case of a 54-year-old man who developed seizures and altered mental status after drinking 12 oz. of MMT-containing NOS Octane Booster Racing Formula. Due to label similarities, he mistook this for the NOS High Performance energy drink. The patient was intubated due to persistent seizures despite benzodiazepine treatment and admitted to the intensive care unit. He had two further seizures while intubated, but he was successfully extubated on the 4th day post-ingestion. He was confused and ataxic following extubation, but one day later his symptoms resolved and he was discharged without further incident. This case highlights the importance of responsible labeling of consumables. It is important for clinicians and poison centers to report any such instances to the United States Food and Drug Administration.

Energy-Dispersive Total-Reflection Resonant Inelastic X-ray Scattering as a Tool for Elemental Speciation in Contaminated Water

This work presents a state-of the-art analytical methodology, by which chemical state information on metallic elements is obtained for liquid samples in a fast and simple manner. This method overcomes limitations of conventional X-ray techniques, such as X-ray absorption spectroscopy, by applying resonant inelastic X-ray scattering under total reflection geometry (TRIXS). TRIXS is particularly applicable for the analysis of small quantity of liquid samples deposited on polished reflectors. This feature is relevant for the chemical speciation of metallic trace elements contained in water samples, since the degree of their toxicity depends crucially on the concentration of specific chemical species included. The analytical merits of the proposed methodology were studied at Elettra Sincrotrone Trieste and at the Brazilian Synchrotron Light Laboratory. Contaminated water samples with low concentration of different chromium and manganese compounds were measured. Results prove the analytical potential of the TRIXS technique in characterizing different chemical species of metallic elements in water samples.

The divalent metal transporter homologues SMF-1/2 mediate dopamine neuron sensitivity in caenorhabditis elegans models of manganism and parkinson disease

Parkinson disease (PD) and manganism are characterized by motor deficits and a loss of dopamine (DA) neurons in the substantia nigra pars compacta. Epidemiological studies indicate significant correlations between manganese exposure and the propensity to develop PD. The vertebrate divalent metal transporter-1 (DMT-1) contributes to maintaining cellular Mn(2+) homeostasis and has recently been implicated in Fe(2+)-mediated neurodegeneration in PD. In this study we describe a novel model for manganism that incorporates the genetically tractable nematode Caenorhabditis elegans. We show that a brief exposure to Mn(2+) increases reactive oxygen species and glutathione production, decreases oxygen consumption and head mitochondria membrane potential, and confers DA neuronal death. DA neurodegeneration is partially dependent on a putative homologue to DMT-1, SMF-1, as genetic knockdown or deletion partially inhibits the neuronal death. Mn(2+) also amplifies the DA neurotoxicity of the PD-associated protein alpha-synuclein. Furthermore, both SMF-1 and SMF-2 are expressed in DA neurons and contribute to PD-associated neurotoxicant-induced DA neuron death. These studies describe a C. elegans model for manganism and show that DMT-1 homologues contribute to Mn(2+)- and PD-associated DA neuron vulnerability.

[Biology of the blood-brain barrier: Part I]

The blood-brain barrier provides the central nervous system with a unique protection against the toxic effects of many xenobiotics. This protection results from the unique anatomic and biological structure of the endothelium of blood vessels in the brain. The main features of the blood-brain barrier are the presence of tight intercellular junctions which strictly limit the diffusion of blood-borne solutes and cells into the brain and the polarized expression of transporters which specifically control the cerebral availability of nutrients, drugs or xenobiotics. Recent findings in molecular and cellular biology improved our knowledge of blood-brain barrier permeability and its regulation. The importance of these findings has been recently highlighted by the description of dysfunctions of the blood-brain barrier which could have an impact on the pathophysiology of several neurological diseases. This review focuses on recent advances in our understanding of blood-brain barrier biology and physiology, presenting the structural organization of the blood-brain barrier and the functional regulation of solute permeability and cellular transendothelial migration.

The effects of manganese on glutamate, dopamine and gamma-aminobutyric acid regulation

Exposure to high levels of manganese (Mn) results in a neurological disorder, termed manganism, which shares a similar phenotype to Parkinson's disease due to the involvement of the basal ganglia circuitry in both. The initial symptoms of manganism are likely due to the involvement of the globus pallidus, a region rich in gamma-aminobutyric acid (GABA) projections, while those of Parkinson's disease are related to the degeneration of the substantia nigra, a dopaminergic nucleus. Additionally, it is known that glutamate regulation is affected by increases in brain Mn levels. As Mn predominantly accumulates in the basal ganglia, it potentially could affect the regulation and interactions of all three neurotransmitters. This review will focus on the circuitry of these neurotransmitters within the basal ganglia and address potential sites for, as well as the temporal relationship, between Mn exposure and changes in the levels of these neurotransmitters. While most research has focused on perturbations in the dopaminergic system, there is evidence to support that early consequences of manganism also include disturbances in GABA regulation as well as glutamatergic-related excitotoxicity. Finally, we suggest that current research focus on the interdependence of these basal ganglial neurochemicals, with a greater emphasis on the GABAergic and glutamatergic systems.

The comparison of nail and serum trace elements in patients with epilepsy and healthy subjects

The objective of this prospective study was to determine the levels of manganese (Mn), copper (Cu), and zinc (Zn) levels in both nail and serum from patients with epilepsy. For this purpose, levels of these elements were measured in 31 patients with epilepsy and 19 healthy subjects. Element analyses were carried out by atomic absorption spectrophotometer (AAS). Increased Mn levels were detected in nail of patients with epilepsy compared to healthy controls (P<.008). The main nail Zn and Cu levels were found to be unchanged in epileptic patients compared to control subjects. There were no significant differences in serum Mn and Zn levels between epileptic patients and control subjects. However, there was a statistically significant increase in serum Cu levels in patients with epilepsy in comparison with control group (P<.009). Our results demonstrate that some trace element levels may vary in epileptic patients, and because of the more stable status, the analysis of these element levels in some tissues such as nail might be superior to serum analysis.

Manganese neurotoxicity: behavioral, pathological, and biochemical effects following various routes of exposure

The human central nervous system is an important target for manganese intoxication, which causes neurological symptoms similar to those of Parkinson's disease. With the increasing use of methylcyclopentadienyl manganese tricarbonyl (MMT) as an octane-improving additive to unleaded gasoline, the prospect of worldwide manganese exposure is once again attracting attention as increases in environmental manganese concentrations have been recorded relative to traffic density. One crucial question is whether a small increase of manganese contamination resulting from the widespread use of MMT could have neurotoxic effects. In this review we concentrate on central nervous system abnormalities and neurobehavioral disturbances. Most experimental animal studies on manganese neurotoxicity have been conducted in nonhuman primates and rodents. Most studies performed in rodents used oral manganese administration and did not assess bioaccumulation or central nervous system changes. The major effect found was transient modification of spontaneous motor activity. Very few inhalation toxicological studies were carried out. As manganese intoxication in humans usually occurs via inhalation, more studies are required using the respiratory route of administration. Given the proven neurotoxic effects of manganese and the prospect of worldwide MMT usage, this metal should be considered a new environmental pollutant having potentially widespread public health consequences.

Caspase-3-dependent proteolytic cleavage of protein kinase Cdelta is essential for oxidative stress-mediated dopaminergic cell death after exposure to methylcyclopentadienyl manganese tricarbonyl

In the present study, we characterized oxidative stress-dependent cellular events in dopaminergic cells after exposure to an organic form of manganese compound, methylcyclopentadienyl manganese tricarbonyl (MMT). In pheochromocytoma cells, MMT exposure resulted in rapid increase in generation of reactive oxygen species (ROS) within 5--15 min, followed by release of mitochondrial cytochrome C into cytoplasm and subsequent activation of cysteine proteases, caspase-9 (twofold to threefold) and caspase-3 (15- to 25-fold), but not caspase-8, in a time- and dose-dependent manner. Interestingly, we also found that MMT exposure induces a time- and dose-dependent proteolytic cleavage of native protein kinase Cdelta (PKCdelta, 72-74 kDa) to yield 41 kDa catalytically active and 38 kDa regulatory fragments. Pretreatment with caspase inhibitors (Z-DEVD-FMK or Z-VAD-FMK) blocked MMT-induced proteolytic cleavage of PKCdelta, indicating that cleavage is mediated by caspase-3. Furthermore, inhibition of PKCdelta activity with a specific inhibitor, rottlerin, significantly inhibited caspase-3 activation in a dose-dependent manner along with a reduction in PKCdelta cleavage products, indicating a possible positive feedback activation of caspase-3 activity by PKCdelta. The presence of such a positive feedback loop was also confirmed by delivering the catalytically active PKCdelta fragment. Attenuation of ROS generation, caspase-3 activation, and PKCdelta activity before MMT treatment almost completely suppressed DNA fragmentation. Additionally, overexpression of catalytically inactive PKCdelta(K376R) (dominant-negative mutant) prevented MMT-induced apoptosis in immortalized mesencephalic dopaminergic cells. For the first time, these data demonstrate that caspase-3-dependent proteolytic activation of PKCdelta plays a key role in oxidative stress-mediated apoptosis in dopaminergic cells after exposure to an environmental neurotoxic agent.

Comparative toxicokinetics of manganese chloride and methylcyclopentadienyl manganese tricarbonyl (MMT) in Sprague-Dawley rats

The toxicokinetics of manganese (Mn) was investigated in male and female rats either following a single intravenous (iv) or oral dose of MnCl2 (6.0 mg Mn/kg), or following a single oral dose of methylcyclopentadienyl manganese tricarbonyl (MMT) (20 mg MMT/kg or 5.6 mg Mn/kg). The plasma concentrations of manganese were quantified by atomic absorption spectrophotometry (AAS). Upon iv administration of MnCl2, manganese rapidly disappeared from blood with a terminal elimination t1/2 of 1.83 h and CL8 of 0.43 L/h/kg. The plasma concentration-time profiles of manganese could be described by C = 41.9e(-424t) + 2.1e(-0.44t). Following oral administration of MnCl2, manganese rapidly entered the systemic circulation (Tmax = 0.25 h). The absolute oral bioavailability was about 13%. Oral dose of MMT resulted in a delayed Tmax(7.6 h), elevated Cmax (0.93 microg/ml), and prolonged terminal t1/2 (55.1 h). The rats receiving MMT had an apparent clearance (CL/F = 0.09 L/h x kg) about 37-fold less than did those who were dosed with MnCl2. Accordingly, the area under the plasma concentration-time curves (AUC) of manganese in MMT-treated rats was about 37-fold greater than that in MnCl2-treated rats. A gender-dependent difference in toxicokinetic profiles of plasma manganese was also observed. Female rats displayed a greater AUC than that of male rats. Although the apparent volume of distribution of manganese was similar in both sexes, the apparent clearance in males was about twice that observed in females. The results indicated that after oral administration, the MMT-derived manganese displayed higher and more prolonged plasma concentration-time profiles than MnCl2-derived manganese. Thus, MMT-derived manganese appeared likely to accumulate in the body following repeated exposure.

Alterations in the properties and isoforms of sciatic nerve Na(+), K(+)-ATPase in methylcyclopentadienyl manganese tricarbonyl-treated mice

The in vivo effect of methylcyclopentadienyl manganese tricarbonyl (MMT), an organic manganese-containing compound, on the mouse motor nerve was studied. The motor nerve conduction velocity was markedly decreased in MMT-treated mice. The Na(+),K(+)-ATPase activity of sciatic nerve isolated from MMT-treated mice was decreased; however, the sciatic nerve Na(+),K(+)-ATPase activity was not affected by the in vitro treatment of MMT. Moreover, [(3)H]ouabain binding of sciatic nerve isolated from MMT-treated mice was decreased. Using Western blot analysis, the amount of Na(+),K(+)-ATPase catalytic alpha1 subunit polypeptide in sciatic nerve of MMT-treated mice was also decreased. These results indicate that a causal relationship may exist between reduced nerve Na(+),K(+)-ATPase activity and motor nerve conduction velocity in MMT-treated mice and that a measurable decrease in alpha1 catalytic subunit isoform of Na(+),K(+)-ATPase may be necessary for the development of peripheral neuropathy by MMT.