Synthesis and evaluation of inhaled [11C]butane and intravenously injected [11C]acetone as potential radiotracers for studying inhalant abuse

Radiosynthesis, Preclinical, and Clinical Positron Emission Tomography Studies of Carbon-11 Labeled Endogenous and Natural Exogenous Compounds

The presence of positron emission tomography (PET) centers at most major hospitals worldwide, along with the improvement of PET scanner sensitivity and the introduction of total body PET systems, has increased the interest in the PET tracer development using the short-lived radionuclides carbon-11. In the last few decades, methodological improvements and fully automated modules have allowed the development of carbon-11 tracers for clinical use. Radiolabeling natural compounds with carbon-11 by substituting one of the backbone carbons with the radionuclide has provided important information on the biochemistry of the authentic compounds and increased the understanding of their in vivo behavior in healthy and diseased states. The number of endogenous and natural compounds essential for human life is staggering, ranging from simple alcohols to vitamins and peptides. This review collates all the carbon-11 radiolabeled endogenous and natural exogenous compounds synthesised to date, including essential information on their radiochemistry methodologies and preclinical and clinical studies in healthy subjects.

The last two decades on preclinical and clinical research on inhalant effects

This paper reviews the scientific evidence generated in the last two decades on the effects and mechanisms of action of most commonly misused inhalants. In the first section, we define what inhalants are, how they are used, and their prevalence worldwide. The second section presents specific characteristics that define the main groups of inhalants: (a) organic solvents; (b) aerosols, gases, and volatile anesthetics; and (c) alkyl nitrites. We include a table with the molecular formula, structure, synonyms, uses, physicochemical properties and exposure limits of representative compounds within each group. The third and fourth sections review the direct acute and chronic effects of common inhalants on health and behavior with a summary of mechanisms of action, respectively. In the fifth section, we address inhalant intoxication signs and available treatment. The sixth section examines the health effects, intoxication, and treatment of nitrites. The seventh section reviews current intervention strategies. Finally, we propose a research agenda to promote the study of (a) solvents other than toluene; (b) inhalant mixtures; (c) effects in combination with other drugs of abuse; (d) age and (e) sex differences in inhalant effects; (f) the long-lasting behavioral effects of animals exposed in utero to inhalants; (g) abstinence signs and neurochemical changes after interrupting inhalant exposure; (h) brain networks involved in inhalant effects; and finally (i) strategies to promote recovery of inhalant users.

Butane detection after long-term treatment of burns in two autopsy cases

A man and a woman were rescued from a room that had exploded. Many empty cassette gas cylinders were found in the room. The man and woman were hospitalized immediately for the treatment of burns. The woman died 6 days later, and the man died 31 days later without regaining consciousness. Carbonization and hardening of the frontal facial skin and parts of the left and right fingers were observed on the man's body. In both cases, systemic burns had led to progressive systemic edema and markedly suppressed circulation. Analytical samples for butanes obtained from their bodies at autopsy were stored at -20 °C for 14 and 25 days, respectively, before analysis. Normal butane and isobutane were quantified in the brain and subcutaneous adipose tissue of the woman. Only the isobutane was quantified in the adipose tissue of the man. The evidence suggests that the man lit a cigarette while breathing gas and the entire room exploded. Our results also suggest that butane can be detected in the adipose tissue of autopsy cases long after inhalation even under the present storage conditions, and isobutane may remain in adipose tissue longer than n-butane.

Is it worth carrying out determination of N-butane in postmortem samples? A case report and a comprehensive review of the literature

The aim of this article is to illustrate the importance of N-butane determination in postmortem samples through a case report and to propose actions and precautions to be taken into consideration when butane is suspected to be involved in cases of death. The case concerns a 15-year-old boy found dead after sniffing a cigarette lighter refill. Toxicological investigation revealed the presence of butane in the heart and femoral blood (1280 and 1170 μg/L, respectively), in the gastric contents (326 μg/L), and in the liver (1010 μg/kg) and lung tissues (210 μg/kg). Propane was present only in the blood samples at concentrations tenfolds lower.Butane can be involved in three kinds of fatalities: deliberate inhalations including volatile substance abuse (VSA), involuntary exposure, and homicides. A fatal outcome of butane inhalation can be caused by asphyxia and/or cardiac arrhythmia. In the context where butane exposure is evidenced by non-toxicological investigations, the usefulness of the determination of butane in postmortem samples is often questionable. However, it is admitted that butane-related deaths are generally underreported. Several difficulties including sample handling and storage, substantial variation in tissue concentrations, and lack of a lethal threshold make the interpretation of butane results challenging. In our opinion, systematic toxicological methods should be developed in order to analyze butane, at least when it concerns a typical VSA victim, even when butane is not actually suspected to be the cause of death.

Volatile substance misuse : clinical considerations, neuropsychopharmacology and potential role of pharmacotherapy in management

Volatile substance misuse is among the most prevalent and toxic forms of psychoactive drug use, and often results in highly deleterious social, psychological and medical consequences. The prevalence of this pernicious form of substance misuse owes in part to the fact that volatile substances of misuse are ubiquitous in the natural environment. Commonly misused commercial products include glue, shoe polish, nail polish remover, butane lighter fluid, gasoline and computer duster spray. National samples of volatile substance misusers tend to exhibit high rates of psychiatric problems and antisocial behaviour. In addition, cognitive impairments and affective dysregulation are often observed among these individuals. Volatile substances exert their complex neuropharmacological effects on dopaminergic, glutamatergic, GABAergic and serotoninergic receptor systems, as well as on cell membranes and ion channels. Concomitantly, pharmacotherapies for volatile substance abuse might profitably target a number of mechanisms, including reward circuitry in the brain, symptoms of craving and withdrawal, neuropsychiatric and emotional impairments that promote volatile substance abuse, and cognitive enhancement to rectify deficits in executive function. This review details the modes of use, subjective effects, epidemiology, adverse consequences, neuropsychopharmacology and drug treatment of volatile substance misuse, and discusses the potential role of novel forms of pharmacological intervention for this oft-overlooked public health threat of epidemic proportions.

Methyl ethyl ketone blocks status epilepticus induced by lithium-pilocarpine in rats

BACKGROUND AND PURPOSE

A ketogenic diet has been used successfully to treat patients with intractable epilepsy, although the mechanism is unknown. Acetone has been shown to have an anticonvulsive effect in various animal models. The main purpose of this study was to determine whether other ketones, 2-butanone (methyl ethyl ketone: MEK) and 3-pentanone (diethyl ketone: DEK), also show anticonvulsive effects in lithium-pilocarpine (Li-pilocarpine)-induced status epilepticus (SE) in rats.

EXPERIMENTAL APPROACH

Anticonvulsive effects of MEK and DEK in Li-pilocarpine SE rats were measured by behavioural scoring. Anti-seizure effects of MEK were also evaluated using electroencephalography (EEG). Neuroprotective effect of MEK was investigated by haematoxylin and eosin staining 4 weeks after the treatment with pilocarpine.

KEY RESULTS

Acetone, MEK and DEK showed anticonvulsant effects in Li-pilocarpine-induced SE rats. Treatment with MEK twice (8 mmol.kg(-1) and 5 mmol.kg(-1)) almost completely blocked spontaneous recurrent cortical seizure EEG up to 4 weeks after the administration of pilocarpine. MEK also showed strong neuroprotective effects in Li-pilocarpine-treated rats 4 weeks following the administration of pilocarpine. Significant neural cell death occurred in the hippocampus of Li-pilocarpine SE rats, especially in the CA1 and CA3 subfields. In contrast, normal histological characteristics were observed in these regions in the MEK-pretreated rats.

CONCLUSIONS AND IMPLICATIONS

Both MEK and DEK showed strong anticonvulsive effects in Li-pilocarpine-induced SE rats. They also inhibited continuous recurrent seizure and neural damage in hippocampal region for 4 weeks after the treatment with pilocarpine. These findings appear to be of value in the investigation of epilepsy.

Methylglyoxal and glucose metabolism: a historical perspective and future avenues for research

Methylglyoxal, an alpha-oxoaldehyde discovered in the 1880s, has had a hectic scientific career, at times being considered of fundamental importance and at other times viewed as playing a very subordinate role. Much has been learned about methylglyoxal, but the function of its production in the metabolic machinery is still unknown. This paper gives an overview of the changing role of methylglyoxal from a historical aspect and arrives at the conclusion that methylglyoxal is tightly bound to glycolysis from an evolutionary perspective, its production therefore being inevitable. It is not situated in the main stream of the glycolytic sequence, but a role can be assigned to its production in the phosphate supply of operating glycolysis in some prokaryotes and yeast under conditions of phosphate deficiency. This function is presumed to be performed by the enzyme methylglyoxal synthase, which is specialized for the conversion of dihydroxyacetone-phosphate to methylglyoxal. However, it is still unknown whether this enzyme and this kind of regulation also exist in animals.

Inhalant abuse among adolescents: neurobiological considerations

Experimentation with volatile substances (inhalants) is common during early adolescence, yet limited work has been conducted examining the neurobiological impact of regular binge use during this key stage of development. Human studies consistently demonstrate that chronic use is associated with significant toxic effects, including neurological and neuropsychological impairment, as well as diffuse and subtle changes in white matter. However, most preclinical research has tended to focus on acute exposure, with limited work examining the neuropharmacological or toxicological mechanisms underpinning these changes or their potential reversibility with abstinence. Nevertheless, there is growing evidence that commonly abused inhalants share common cellular mechanisms, and have similar actions to other drugs of abuse. Indeed, the majority of acute behavioural effects appear to be underpinned by changes in receptor and/or ion channel activity (for example, GABA(A), glycine and 5HT(3) receptor activation, NMDA receptor inhibition), although nonspecific interactions can also arise at high concentrations. Recent studies examining the effects of toluene exposure during the early postnatal period are suggestive of long-term alterations in the function of NMDA and GABA(A) receptors, although limited work has been conducted investigating exposure during adolescence. Given the critical role of neurotransmitter systems in cognitive, emotional and brain development, future studies will need to take account of the substantial neuromaturational changes that are known to occur in the brain during childhood and adolescence, and to specifically investigate the neuropharmacological and toxicological profile of inhalant exposure during this period of development.

The ketogenic diet and brain metabolism of amino acids: relationship to the anticonvulsant effect

In many epileptic patients, anticonvulsant drugs either fail adequately to control seizures or they cause serious side effects. An important adjunct to pharmacologic therapy is the ketogenic diet, which often improves seizure control, even in patients who respond poorly to medications. The mechanisms that explain the therapeutic effect are incompletely understood. Evidence points to an effect on brain handling of amino acids, especially glutamic acid, the major excitatory neurotransmitter of the central nervous system. The diet may limit the availability of oxaloacetate to the aspartate aminotransferase reaction, an important route of brain glutamate handling. As a result, more glutamate becomes accessible to the glutamate decarboxylase reaction to yield gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter and an important antiseizure agent. In addition, the ketogenic diet appears to favor the synthesis of glutamine, an essential precursor to GABA. This occurs both because ketone body carbon is metabolized to glutamine and because in ketosis there is increased consumption of acetate, which astrocytes in the brain quickly convert to glutamine. The ketogenic diet also may facilitate mechanisms by which the brain exports to blood compounds such as glutamine and alanine, in the process favoring the removal of glutamate carbon and nitrogen.

Possible mechanism for the effect of ketogenic diet in cases of uncontrolled seizures

High fat and low carbohydrate diet, designated ketogenic diet, has been successfully used for the treatment of intractable epilepsy in a portion of patients, particularly in children. Several hypotheses have been worked out for the explanation of its beneficial effects, among others acetone has been raised as a causative factor. However, despite the endeavours the mode of action of the diet is still an enigma. And it is also not known why the diet is effective in some patients, while in others it is without any effect. Here a possible way for the effect of ketogenic diet is proposed in which the central point of seizure preventing effect of the diet is the metabolism of acetone. The proposal nominates S-D-lactoylglutathione, an intermediate of acetone metabolism, as a factor being responsible for seizure controlling effect of ketogenic diet and on the other hand, a sequence of evidence is given for the support of suggestion. S-D-lactoylglutathione would exert its effect by the influence of K(+) channels. The proposal also gives an explanation of why only a portion of patients benefit while on the diet. A proposition is also made for the future directions of research involving the measurement of intermediates of S-D-glutathione breakdown in the cerebrospinal fluid and clinical trials with selected groups of patients. The establishment of this specific mechanism for the ketogenic diet may lead to novel strategies for the investigation and the treatment of intractable epilepsies.