Petros N. Karamanakos

CYP2E1 and risk of chemically mediated cancers

Importance of the field: Among various human CYPs, CYP2E1 is of particular interest because of its involvement in the metabolic activation of many low molecular mass procarcinogens. CYP2E1 induction, which may be a consequence of genetic polymorphism or/and gene induction by xenobiotics, is the first step leading to the development of certain chemically-mediated cancers. The aim of this review is to outline the current knowledge on chemically-induced cancers through activation by CYP2E1, with emphasis on the association between polymorphisms of the CYP2E1 gene and incidence of different neoplasias. Areas covered in this review: Literature searches of MEDLINE (1966 to July 2009) for English articles in CYP2E1-induced carcinogenesis were conducted. What the reader will gain: CYP2E1 genetic polymorphisms leading to enhanced CYP2E1 gene transcription have been associated with increased risk of development of malignant tumours, through increased biotransformation of procarcinogens. Likewise, long-term intake of CYP2E1 inducers, such as ethanol, isoniazid, various solvents and chemicals, also increase the probability of developing malignancy, especially for carriers of certain CYP2E1 alleles. Take home message: Genetic screening for CYP2E1 ‘carcinogenic’ polymorphisms and CYP2E1 phenotype determination of susceptible subjects, as well as the development of effective CYP2E1 inhibitors, could be a future perspective towards prevention of CYP2E1-mediated cancers.

Pharmaceutical agents known to produce disulfiram-like reaction: effects on hepatic ethanol metabolism and brain monoamines.

Several pharmaceutical agents produce ethanol intolerance, which is often depicted as disulfiram-like reaction. As in the case with disulfiram, the underlying mechanism is believed to be the accumulation of acetaldehyde in the blood, due to inhibition of the hepatic aldehyde dehydrogenases. In the present study, chloramphenicol, furazolidone, metronidazole, and quinacrine, which are reported to produce a disulfiram-like reaction, as well as disulfiram, were administered to Wistar rats and the hepatic activities of alcohol and aldehyde dehydrogenases (1A1 and 2) were determined. The expression of aldehyde dehydrogenase 2 was further assessed by Western blot analysis, while the levels of brain monoamines were also analyzed. Finally, blood acetaldehyde was evaluated after ethanol administration in rats pretreated with disulfiram, chloramphenicol, or quinacrine. The activity of aldehyde dehydrogenase 2 was inhibited by disulfiram, chloramphenicol, and furazolidone, but not by metronidazole or quinacrine. In addition, although well known for metronidazole, quinacrine also did not increase blood acetaldehyde after ethanol administration. The protein expression of aldehyde dehydrogenase 2 was not affected at all. Interestingly, all substances used, except disulfiram, increased the levels of brain serotonin. According to our findings, metronidazole and quinacrine do not produce a typical disulfiram-like reaction, because they do not inhibit hepatic aldehyde dehydrogenase nor increase blood acetaldehyde. Moreover, all tested agents share the common property to enhance brain serotonin, whereas a respective effect of ethanol is well established. Therefore, the ethanol intolerance produced by these agents, either aldehyde dehydrogenase is inhibited or not, could be the result of a “toxic serotonin syndrome,” as in the case of the concomitant use of serotonin-active medications.

Involvement of the brain serotonergic system in the locomotor stimulant effects of chlorpheniramine in Wistar rats: implication of postsynaptic 5-HT1A receptors.

Antihistamines, such as chlorpheniramine (CPA), are lipophilic agents which readily cross the blood-brain barrier, producing sedation in 10-25% of users. However, with excessive doses instead of sedation a stimulating action has been reported. The aim of the present study was to investigate the influence of CPA on the locomotor activity of the rat in relation to its effects on brain biogenic monoamines. Wistar rats were given CPA (40 mg/kg, i.p.) and locomotor activity was measured in a photocell cage. Body temperature was also monitored. In addition, in three brain subregions (striatum, hypothalamus, and midbrain), the levels of 5-HT, NA, DA, as well as their metabolites, were determined by HPLC. Soon after injection, CPA produced a significant increase in locomotor activity, while a hypothermic response was also induced. In striatum and hypothalamus, which are known to be rich in postsynaptic 5-HT1A receptors, we found a significant time-dependent increase of 5-HT, correlated with the clearly enhanced locomotor activity of the animals. On the contrary, in midbrain, where presynaptic 5-HT1A receptors are dominating, no changes could be detected in 5-HT. In all three brain regions measured, 5-HIAA levels were decreased. The levels of the other brain monoamines were only marginally affected. In support of a role in receptor specificity, pretreatment with the 5-HT1A receptor agonist 8-OH-DPAT (1.25 mg/kg, i.p., two times) or with the 5-HT(1A/B) receptor antagonist pindolol (30 mg/kg, i.p., two times), enhanced or blocked, respectively, the hyperlocomotion induced by CPA. These findings suggest that the central serotonergic system may play a key role in the locomotor stimulant effects of CPA in the rat. Moreover, this behavioral component of CPA seems to be primarily mediated via the postsynaptic 5-HT1A receptors.

Mutagenicity, developmental toxicity and carcinogenicity of cannabis

Data on the mutagenicity, developmental toxicity and carcinogenicity of cannabis are reviewed in this article. The available evidence on the possible mutagenic effects of cannabinoids is still inconclusive. There is no consensus on the induction of point mutations, while some experimental results suggest that cannabinoids may cause chromosomal damage. Concerning the developmental effects of cannabis, an increased embryolethality and somatic growth retardation have been observed in animals, as well as changes in motor behaviour, after perinatal exposure to cannabinoids. An elevated risk for infertility has been suggested for women smoking marijuana. On the other hand, intrauterine exposure to cannabinoids may be followed by changes of behaviour later in childhood. Finally, the experimental work concerning the possible carcinogenic action of cannabinoids has shown that cannabis acts as a tumour promotor in animals. Epidemiological studies have incriminated cannabis smoking for the development of head and neck carcinomas and for carcinomas of the respiratory tract in humans, but several confounding factors have rendered this evidence inconclusive. At least part of the great popularity of cannabis smoking is due to the widespread belief that it is harmless. However, the studies presented in this review show that, despite their low acute toxicity profile, cannabinoids represent several risks in terms of chronic toxicity.

Ontogenesis and Expression of ALDH Activity in the Skin and the Eye of the Rat

As the body’s first line of defense against external insult, both the eye and the skin are exposed routinely to chemical agents, serving as a portal of entry for topical contactants. In addition, global atmospheric changes like ozone depletion in the stratosphere contribute to enhanced chronic exposure of the skin and the eye of human tissue to UV light (Hendee, 1989). The hazardous effects of UV light on the eye were already recognized in 1920 by van der Hoeve. By the 1920s, basal cell carcinomas of the skin were also noted.

Acute-phase response to benzo[a]pyrene and induction of rat ALDH3A1

The aldehyde dehydrogenase-3A1 (ALDH3A1) enzyme, encoded by a member of the [Ah]-gene family, is dramatically increased (more than 100-fold) by benzo[a]pyrene (BaP) and other polycyclic hydrocarbons. Although much is known regarding the mechanism for the drug-metabolizing enzymes up-regulated by the Ah receptor, the physiological role of that tremendously increased ALDH3A1 enzyme activity is not yet fully clarified. The aim of this study was to identify a possible acute-phase response to different classes of xenobiotics affecting the metabolic capacity of the hepatocyte, by studying possible changes of serum acute-phase proteins (APPs) of hepatic origin, before and after BaP administration. Male Wistar rats were used in different series of experiments. The effects of BaP were estimated in terms of dose-response and time-response, with regard to the serum level of several APPs such as alpha-1-acid-glycoprotein (AAG), alpha-1-antitrypsin (AAT), C-reactive protein (CRP), and haptoglobin (HPT). In parallel experiments, levels of the same proteins have been determined after a time-dependent treatment with lipopolysaccharide (LPS). The changes in serum proteins were compared with the results of BaP or LPS administration on both hepatic ALDH3A1 and total ALDH enzyme activities. The results showed that BaP induced CRP and HPT in a time-dependent way, proportional to that caused by LPS. Additionally, ALDH3A1, CRP, and HPT were induced by BaP subacute treatment, whereas another type of ALDH inducer, phenobarbital, did not affect the levels of APPs or ALDH3A1, but did increase ALDH1A3 activity. Former studies of our group have shown that the inhibitory effects of different non-steroidal anti-inflammatory drugs (NSAIDs) on the ALDH3A1 induction were most possibly due to a decreased formation of arachidonic products like prostaglandins. Considering the changes of APPs caused by BaP, this study further supports the suggestion that the induction of ALDH3A1 is related to an atypical hepatocyte inflammation produced by xenobiotics.

Phenobarbital inducibility and differences in protein expression of an animal model.

Aldehyde dehydrogenases (ALDHs) are a group of enzymes which catalyze the conversion of aldehydes to the corresponding carboxylic acids in a NAD(P)(+)-dependent reaction. In mammals, different ALDHs are constitutively expressed in liver, stomach, eye and skin. In addition, inducible ALDH-isoenzymes are detectable in many tissues; apart from other physico- and immuno-chemical differences, two cytosolic ALDHs (ALDH1A3 and ALDH3A1) are known to be activated in rat liver, by different types of inducers of drug metabolism. Phenobarbital-type inducers increase the ALDH1A3, while polycyclic hydrocarbons (such as BaP and TCDD) increase the expression of the two members of ALDH3A subfamily (3A1 and 3A2). In this study, we used two Wistar rat substrains which have been well-characterized for different inducibility of ALDH1A3 enzyme activity after treatment with phenobarbital. Animals that respond (RR) or do not respond (rr) to treatment have been inbred for almost 25 years, offering a useful experimental model. Apart from the level of ALDH1A3 induced enzyme expression after phenobarbital treatment, no other differences between the two substrains have been noticed, as far as drug metabolizing enzyme activities (like the pentoxy- and ethoxy-O-dealkylation rate) are concerned. According to the present results, the ALDH1A3 expression is still the only difference between the two substrains. Immunoblotting experiments with polyclonal antibodies raised against CYP2B1 or/and CYP1A1/1A2 showed no differences between the two substrains. Additionally, data concerning time- and dose-response induction of ALDH1A3 after phenobarbital and griseofulvin treatment are presented. It is concluded that these two Wistar rat substrains represent a unique animal model for studying what seems to be the only difference between these substrains - the genetic basis of the phenobarbital induction.

Comment on "Dextromethorphan-induced serotonin syndrome".

A 9-year-old boy presented with a 2-day history of severe headache associated with recurrent vomiting and high-grade fever following a single wasp sting on the left side of his neck. The sting was associated with marked local swelling and cervical lymphadenopathy. He had no history of recent illness, head trauma, or intake of other medications. He was being treated with ibuprofen and oral amoxicillin-clavulanate. The pupils were bilaterally symmetrical with normal reaction to light and accommodation. The examination of the optic fundi revealed papilledema stage 2 (early papilledema as per Frisen scale). The other cranial nerves and the remainder of the neurological examination were normal. Review of the other major systems was non-contributory. Serum glucose, electrolytes, renal function tests, and complete blood cell count were normal. The cranial magnetic resonance (MR) and MR venography revealed no abnormalities. The lumbar puncture revealed an opening pressure of 412 mm of water and clear cerebro-spinal fluid (CSF) with normal cell count, protein, and glucose content. He was treated with oral furosemide and acetazolamide, to which he responded favorably. The culture of the CSF was sterile. A diagnosis of PC secondary to Hymenoptera sting was made. He was discharged on the 10th post-admission day, having made full neurological recovery. Clinical and CSF examination results at 6 weeks were normal. Neurological complications following Hymenoptera sting are rare. Cerebral infarction, the most commonly described, may lead to seizure, hemiparesis, aphasia, apraxia, dysarthria, ataxia, visual and speech deficits, cranial neuropathies, cerebellar symptoms, and coma (2). Other reported CNS complications include optic neuritis, myasthenia gravis, acute inflammatory polyradiculopathy, encephalomyeloradiculoneuritis (3), parkinsonian syndrome (4), encephalopathy, limb numbness, and trigeminal neuralgia (5). An instance of combined cerebral infarction leading to stroke and ischemic optic neuropathy following multiple bee stings is also reported (2). To our knowledge, there is a single report of PC occurring as an isolated complication of wasp sting. Sorabjee et al. (6) described a 42-year-old woman who developed fever, severe headache, and toxemia following a single wasp sting over her right eyelid. The diagnosis was made on the basis of normal lumbar puncture study, papilledema, and normal MR study of the brain with unremarkable cranial MR venography. The boy had no history of previous wasp or bee stings. Furthermore, other risk factors for the development of PC, especially infections and drugs, were excluded. The temporal course of events implicates the wasp sting for the symptoms in the boy. Sorabjee et al. (6) hypothesized that the proximity of the sting to the brain might have been a factor in causing the elevated CSF pressures as a result of intracranial inflammation due to the potentially neurotoxic wasp venom. The boy had the sting on his neck, which may support the explanation put forward. In conclusion, whereas severe neurological manifestations remain well documented, milder neurological manifestations like PC may be seen in children following wasp stings on the head or neck. Monitoring of such children, especially with minor neurological symptoms, is indicated.

Disulfiram neuropathy: two cases of distal axonopathy

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Comment on: Disulfiram Induced Psychosis (Mohapatra and Rath, Clin Psychopharmacol Neurosci 2017;15:68-69)

Comment on: Disulfiram Induced Psychosis (Mohapatra and Rath, Clin Psychopharmacol Neurosci 2017;15:68-69)