Low-level lead exposure triggers neuronal apoptosis in the developing mouse brain

While the toxic effects of lead have been recognized for millennia, it has remained a significant public health concern due to its continued use and toxicological potential. Of particular interest is the increased susceptibility of young children to the toxic effects of lead. Although the exact mechanism(s) for lead toxicity is currently not well understood, research has established that it can be a potent NMDA antagonist. Previous research has established that exposure to NMDA antagonists during the brain growth spurt period (first 2 weeks of life in mice) can produce apoptotic neurodegeneration throughout the brain. Based on this information, the ability of lead exposure (two injections of 350 mg/kg lead 4h apart) to produce apoptosis in the neonatal mouse brain was assessed histologically 8-24h after treatment using activated caspase-3 immunohistochemistry, De Olmos silver technique, Nissl staining, and electron microscopy. Lead exposure produced significant neurodegeneration in the caudate/putamen, hippocampus, subiculum, and superficial and deep cortical layers of the frontal cortical regions. Further ultrastructural examination revealed cellular profiles consistent with apoptotic cell death. Statistical results showed that lead exposure significantly increased apoptotic neurodegeneration above that seen in normal controls in animals treated at postnatal day 7, but not on day 14. The results of this study may provide a basis for further elucidation of mechanisms through which the immature nervous system may be particularly susceptible to lead exposure.

High dose magnesium sulfate exposure induces apoptotic cell death in the developing neonatal mouse brain

BACKGROUND

Magnesium sulfate (MgSO4) is often used as a treatment for pre-eclampsia/eclampsia and preterm labor, resulting in the exposure of a significant number of neonates to this drug despite a lack of evidence suggesting that it is safe, or effective as a tocolytic. While there is evidence that MgSO4 may be neuroprotective in perinatal brain injury, recent reviews have suggested that the effects are dependent upon dose, and that higher doses may actually increase neonatal morbidity and mortality. There is a lack of evidence investigating the neurotoxic effects of neonatal magnesium (Mg) exposure on the developing brain, specifically in terms of neurodevelopmental apoptosis, a cell-killing phenomenon known to be potentiated by other drugs with mechanisms of action at Mg-binding sites (i.e. NMDA receptor antagonists such as MK-801, ketamine, and PCP).

OBJECTIVE

To investigate the effects of Mg exposure on the neonatal mouse brain at different postnatal ages to determine whether MgSO4 treatment causes significant cell death in the developing mouse brain.

METHODS

C57Bl/6 mice were treated with four doses of MgSO4 (250 mg/kg) on postnatal days 3 (P3), 7 (P7) or 14 (P14). Caspase-3 immunohistochemistry, cupric silver staining, and electron microscopy techniques were used to examine Mg-treated brains for neurotoxic effects.

RESULTS

Qualitative evaluation using cupric silver staining revealed widespread damage throughout the brain in P7 animals. Results of electron microscopy confirmed that the cell death process was apoptotic in nature. Quantitative evaluation of damage to the cortex, caudate-putamen, hippocampus, thalamus, and cerebellum showed that Mg treatment caused significant brain damage in animals treated on P3 and P7, but not P14.

CONCLUSIONS

Administration of high doses of Mg may be detrimental to the fetal brain, particularly if exposure occurs during critical periods of neurodevelopment.

In the adult CNS, ethanol prevents rather than produces NMDA antagonist-induced neurotoxicity

Single doses of an NMDA antagonist cause an adult or a prepubertal form of neurodegeneration, depending on the age of the animal. Single doses of ethanol (EtOH) by blocking NMDA receptors produce apoptotic neurodegeneration in young animals. This capability could account, in part, for the ability of EtOH to produce the fetal alcohol syndrome. We investigated whether EtOH could produce NMDA antagonist-induced neurotoxicity (NAN), a different neurotoxicity that is seen only in adult animals. In spite of producing blood EtOH levels (30 to 600 mg/dl) known to block NMDA receptors, EtOH was unable to produce neurotoxicity in the adult central nervous system (CNS). Moreover, EtOH in a dose-dependent fashion (ED(50)=138 mg/dl) prevented the selective and powerful NMDA antagonist, MK-801, from producing NAN in adult animals, suggesting that activity at another site might be negating the neurotoxic effect of EtOH's inherent NMDA antagonistic activity. Because GABA(A) agonism and non-NMDA glutamate antagonism, properties which EtOH possesses, can prevent NAN, we proceeded to study whether GABA(A) antagonists (or agents capable of reversing EtOH's GABAergic effects) and non-NMDA agonists could reverse EtOH's protective effect. Bicuculline, Ro15-4513, finasteride, kainic acid or AMPA, alone or in combination, did not significantly reverse EtOH's protective effect. Given that EtOH has effects on a wide range of ion channels and receptors, determining the precise mechanism of EtOH's protective effect will take additional effort. The inability of EtOH to acutely produce NAN in the adult CNS indicates that, in contrast to fetuses, brief exposure of the adult CNS to EtOH is non-toxic for neurons.

Stability and microbiology of inhalant N-acetylcysteine used as an intravenous solution for the treatment of acetaminophen poisoning

STUDY OBJECTIVE

Intravenous N-acetylcysteine has been used as an antidote for acetaminophen poisoning for more than 25 years in Europe and Canada. In the United States, only the oral administration of N-acetylcysteine is approved by the US Food and Drug Administration. Many physicians routinely use the inhalant preparation as an intravenous formulation; however, no stability, microbiology, or pyrogen studies have been performed. In this study, we evaluate the stability and microbiology of inhalational N-acetylcysteine compounded as an intravenous formulation.

METHODS

A total of 8 N-acetylcysteine solutions (solution A through H) were prepared by injecting 150 mL of 20% solution through a 22-microm filter to 1 L of 5% dextrose (D(5)W; 2.6% solution). Solutions A through C were prepared at ambient conditions (25 degrees C [77 degrees F], 65% relative humidity), and solution D was prepared at accelerated conditions (40 degrees C [104 degrees F], 75% relative humidity) for stability testing. The assays were performed by means of high-performance liquid chromatography at 0, 4, 8, 12, 24, 36, 48, 60, and 72 hours according to US Pharmacopeia XXIV methodology. Solutions E through G were assessed for bacterial growth, and solution H underwent pyrogen testing by using a Limulus amebocyte lysate method.

RESULTS

Solutions A through C remained stable for at least 60 hours (<10% decomposition), but at 72 hours, there was a 10.3%, 14.9%, and 13.4% degradation, respectively. Under accelerated conditions (solution D), stability lasted for more than 72 hours. Solutions E through G remained free from bacterial growth at 72 hours, and solution H tested negative for endotoxins-pyrogens.

CONCLUSION

Inhalational N-acetylcysteine prepared as an intravenous solution meets US Pharmacopeia standards for stability up to 60 hours and is free from bacteria and their byproducts, offering a viable alternative to the traditional use of oral N-acetylcysteine.

Organ procurement and successful transplantation after malathion poisoning

BACKGROUND

One of the major limitations to organ procurement and donation is the lack of suitable donors. As the demand for suitable organs exceeds the supply, identification of potential donors continues to evolve. Due to perceived risks of transmittable toxins and insufficient understanding of toxicological fate, poisoned patients are often overlooked as organ donors.

CASE REPORT

A 17-year-old white male was found by his mother having a seizure in bed. A strong odor of pesticides was noted and an empty container of malathion was found. He was transported to an outlying hospital and underwent prolonged cardiopulmonary resuscitation. The patient exhibited symptoms consistent with cholinergic poisoning and received a total of 12 mg of atropine and a pralidoxime bolus of 1 g followed by an infusion at 500 mg/h. Initial plasma cholinesterase was 1433 IU/L (normal 7500-14,600). The patient developed aspiration pneumonia and remained comatose. No further treatment for cholinergic toxicity was needed 5 days after admission and a cerebral blood flow scan confirmed brain death. After review of the available literature on the disposition andfate of malathion in human tissues, the patient's liver and kidneys were harvested for transplantation. The recipients were all doing well 1 year posttransplantation.

CONCLUSIONS

This case of successful transplantation after organophosphate exposure underscores the fact that poisoned patients should not be overlooked as transplant candidates. Decisions should be based on the clinical presentation and knowledge of the properties of the toxin.

A pilot study to assess the safety of dobutamine stress echocardiography in the emergency department evaluation of cocaine-associated chest pain

STUDY OBJECTIVE

Chest pain in the setting of cocaine use poses a diagnostic dilemma. Dobutamine stress echocardiography (DSE) is a widely available and sensitive test for evaluating cardiac ischemia. Because of the theoretical concern regarding administration of dobutamine in the setting of cocaine use, we conducted a pilot study to assess the safety of DSE in emergency department patients with cocaine-associated chest pain.

METHODS

A prospective case series was conducted in the intensive diagnostic and treatment unit in the ED of an urban tertiary-care teaching hospital. Patients were eligible for DSE if they had used cocaine within 24 hours preceding the onset of chest pain and had a normal ECG and tropinin I level. Patients exhibiting signs of continuing cocaine toxicity were excluded from the study. All patients were admitted to the hospital for serial testing after the DSE testing in the intensive diagnostic and treatment unit.

RESULTS

Twenty-four patients were enrolled. Two patients had inadequate resting images, one DSE was terminated because of inferior hypokinesis, another DSE was terminated because of a rate-related atrial conduction deficit, and 1 patient did not reach the target heart rate. Thus, 19 patients completed a DSE and reached their target heart rates. None of the patients experienced signs of exaggerated adrenergic response, which was defined as a systolic blood pressure of greater than 200 mm Hg or the occurrence of tachydysrhythmias (excluding sinus tachycardia). Further suggesting lack of exaggerated adrenergic response, 13 (65%) of 20 patients required supplemental atropine to reach their target heart rates.

CONCLUSION

No exaggerated adrenergic response was detected when dobutamine was administered to patients with cocaine-related chest pain.