Long-term retention of neurotoxic beta-carbolines in brain neuromelanin

beta-Carbolines show structural resemblance to the neurotoxic N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and are metabolized to mitochondrial toxicants. Humans are continuously exposed to low levels of beta-carbolines through cooked food, coffee, alcoholic beverages and tobacco smoke. beta-Carbolines have previously been detected in higher levels in the pigmented substantia nigra than in the cortex of humans. The distribution of H-3-labelled harman and norharman in the brain of pigmented and albino mice and in frogs (a species having neuromelanin) was studied by tape-section and light-microscopic autoradiography. Furthermore, the binding of these beta-carbolines to dopamine-melanin and melanin granules from Sepia officinalis was examined. The results revealed a high affinity binding to melanin and a long-term retention (up to 30 days) in pigmented tissues, including neuromelanin-containing neurons of frogs after a single injection. The role of long-term exposure to food-related beta-carbolines and a retention of these compounds in pigment-containing neurons in the induction of idiopathic Parkinson's disease should be further considered

Binding of the potent allergen hexahydrophthalic anhydride in the mucosa of the upper respiratory and alimentary tract following single inhalation exposures in guinea pigs and rats

Hexahydrophthalic anhydride (HHPA; CAS No. 13149-00-3) is a highly allergenic compound commonly used in the chemical industry. Guinea pigs and rats were exposed to [3H2]HHPA by inhalation for 3-8 h and were killed at various intervals during 7 days. The tissue distribution of non-volatile and covalently bound radioactivity was studied by autoradiography. Tissue bound radioactivity was mainly found in the mucosa of the upper respiratory airways, whereas negligible levels were observed in the lungs. In addition, tissue bound radioactivity was present in the gastrointestinal tract and conjunctiva. Moreover, in the cortex of the kidneys in rats, but not in guinea pigs, a low level of tissue bound radioactivity was found. The radioactivity in the tissues persisted for at least 7 days after the end of exposure. Plasma proteins and soluble proteins from trachea, lung, and kidney from [3H2]HHPA-exposed animals were separated by gel filtration. The radioactivity in dialysed plasma was mainly found in the same fractions as albumin. The soluble proteins from trachea, lung, and kidney in both rats and guinea pigs showed a similar pattern as found in blood. The radioactivity in dialysed plasma from both guinea pigs and rats seemed to decay according to a two-compartment model. The non-extractable binding of [3H2]HHPA in the upper respiratory airways and conjunctiva may be of relevance for symptoms in workers with allergy, since they mainly develop symptoms and signs from the nose and eyes

Cell-specific expression of CYP2A5 in the mouse respiratory tract: Effects of olfactory toxicants

We performed a detailed analysis of mouse cytochrome P450 2A5 (CYP2A5) expression by in situ hybridization (ISH) and immunohistochemistry (IHC) in the respiratory tissues of mice. The CYP2A5 mRNA and the corresponding protein co-localized at most sites and were predominantly detected in the olfactory region, with an expression in sustentacular cells, Bowman’s gland, and duct cells. In the respiratory and transitional epithelium there was no or only weak expression. The nasolacrimal duct and the excretory ducts of nasal and salivary glands displayed expression, whereas no expression occurred in the acini. There was decreasing expression along the epithelial linings of the trachea and lower respiratory tract, whereas no expression occurred in the alveoli. The hepatic CYP2A5 inducers pyrazole and phenobarbital neither changed the CYP2A5 expression pattern nor damaged the olfactory mucosa. In contrast, the olfactory toxicants dichlobenil and methimazole induced characteristic changes. The damaged Bowman’s glands displayed no expression, whereas the damaged epithelium expressed the enzyme. The CYP2A5 expression pattern is in accordance with previously reported localization of protein and DNA adducts and the toxicity of some CYP2A5 substrates. This suggests that CYP2A5 is an important determinant for the susceptibility of the nasal and respiratory epithelia to protoxicants and procarcinogens

Neurotoxin-Induced Neuropeptide Perturbations in Striatum of Neonatal Rats

The cyanobacterial toxin β-<i>N</i>-methylamino-l-alanine (BMAA) is suggested to play a role in neurodegenerative disease. We have previously shown that although the selective uptake of BMAA in the rodent neonatal striatum does not cause neuronal cell death, exposure during the neonatal development leads to cognitive impairments in adult rats. The aim of the present study was to characterize the changes in the striatal neuropeptide systems of male and female rat pups treated neonatally (postnatal days 9–10) with BMAA (40–460 mg/kg). The label-free quantification of the relative levels of endogenous neuropeptides using mass spectrometry revealed that 25 peptides from 13 neuropeptide precursors were significantly changed in the rat neonatal striatum. The exposure to noncytotoxic doses of BMAA induced a dose-dependent increase of neurosecretory protein VGF-derived peptides, and changes in the relative levels of cholecystokinin, chromogranin, secretogranin, MCH, somatostatin and cortistatin-derived peptides were observed at the highest dose. In addition, the results revealed a sex-dependent increase in the relative level of peptides derived from the proenkephalin-A and protachykinin-1 precursors, including substance P and neurokinin A, in female pups. Because several of these peptides play a critical role in the development and survival of neurons, the observed neuropeptide changes might be possible mediators of BMAA-induced behavioral changes. Moreover, some neuropeptide changes suggest potential sex-related differences in susceptibility toward this neurotoxin. The present study also suggests that neuropeptide profiling might provide a sensitive characterization of the BMAA-induced noncytotoxic effects on the developing brain

Neurotoxin-Induced Neuropeptide Perturbations in Striatum of Neonatal Rats

The cyanobacterial toxin β-<i>N</i>-methylamino-l-alanine (BMAA) is suggested to play a role in neurodegenerative disease. We have previously shown that although the selective uptake of BMAA in the rodent neonatal striatum does not cause neuronal cell death, exposure during the neonatal development leads to cognitive impairments in adult rats. The aim of the present study was to characterize the changes in the striatal neuropeptide systems of male and female rat pups treated neonatally (postnatal days 9–10) with BMAA (40–460 mg/kg). The label-free quantification of the relative levels of endogenous neuropeptides using mass spectrometry revealed that 25 peptides from 13 neuropeptide precursors were significantly changed in the rat neonatal striatum. The exposure to noncytotoxic doses of BMAA induced a dose-dependent increase of neurosecretory protein VGF-derived peptides, and changes in the relative levels of cholecystokinin, chromogranin, secretogranin, MCH, somatostatin and cortistatin-derived peptides were observed at the highest dose. In addition, the results revealed a sex-dependent increase in the relative level of peptides derived from the proenkephalin-A and protachykinin-1 precursors, including substance P and neurokinin A, in female pups. Because several of these peptides play a critical role in the development and survival of neurons, the observed neuropeptide changes might be possible mediators of BMAA-induced behavioral changes. Moreover, some neuropeptide changes suggest potential sex-related differences in susceptibility toward this neurotoxin. The present study also suggests that neuropeptide profiling might provide a sensitive characterization of the BMAA-induced noncytotoxic effects on the developing brain