Methylamine metabolism to formaldehyde by vascular semicarbazide-sensitive amine oxidase

Formaldehyde initiates memory and motor impairments under weightlessness condition

During space flight, prolonged weightlessness stress exerts a range of detrimental impacts on the physiology and psychology of astronauts. These manifestations encompass depressive symptoms, anxiety, and impairments in both short-term memory and motor functions, albeit the precise underlying mechanisms remain elusive. Recent studies have revealed that hindlimb unloading (HU) animal models, which simulate space weightlessness, exhibited a disorder in memory and motor function associated with endogenous formaldehyde (FA) accumulation in the hippocampus and cerebellum, disruption of brain extracellular space (ECS), and blockage of interstitial fluid (ISF) drainage. Notably, the impairment of the blood-brain barrier (BBB) caused by space weightlessness elicits the infiltration of albumin and hemoglobin from the blood vessels into the brain ECS. However, excessive FA has the potential to form cross-links between these two proteins and amyloid-beta (Aβ), thereby obstructing ECS and inducing neuron death. Moreover, FA can inhibit N-methyl-D-aspartate (NMDA) currents by crosslinking NR1 and NR2B subunits, thus impairing memory. Additionally, FA has the ability to modulate the levels of certain microRNAs (miRNAs) such as miRNA-29b, which can affect the expression of aquaporin-4 (AQP4) so as to regulate ECS structure and ISF drainage. Especially, the accumulation of FA may inactivate the ataxia telangiectasia-mutated (ATM) protein kinase by forming cross-linking, a process that is associated with ataxia. Hence, this review presents that weightlessness stress-derived FA may potentially serve as a crucial catalyst in the deterioration of memory and motor abilities in the context of microgravity.

Organelle-resolved imaging of formaldehyde reveals its spatiotemporal dynamics

Understanding the spatiotemporal dynamics of formaldehyde (FA) is crucial for elucidating its pathophysiology. In this study, we designed a series of organelle-resolved probes to investigate FA dynamics. By incorporating various organelle anchors into a coumarin hydrazonate, we developed a series of probes with excellent organelle selectivity and FA specificity, enabling rapid and precise sensing of FA in an organelle-resolved way. Leveraging these probes, we captured the spatiotemporal dynamics of native FA in response to exogenous FA or oxidative stress challenges. In particular, we unveiled the distinct responses of various organelles to identical cellular stressors. Moreover, we observed the dynamic response within individual organelles when cells were exposed to stressors for varying durations. We envision these probes will serve as versatile tools for probing FA pathophysiology.

Replication-Independent ICL Repair: From Chemotherapy to Cell Homeostasis

Interstrand crosslinks (ICLs) are a type of covalent lesion that can prevent transcription and replication by inhibiting DNA strand separation and instead trigger cell death. ICL inducing compounds are commonly used as chemotherapies due to their effectiveness in inhibiting cell proliferation. Naturally occurring crosslinking agents formed from metabolic processes can also pose a challenge to genome stability especially in slowly or non-dividing cells. Cells maintain a variety of ICL repair mechanisms to cope with this stressor within and outside the S phase of the cell cycle. Here, we discuss the mechanisms of various replication-independent ICL repair pathways and how crosslink repair efficiency is tied to aging and disease.

New Insights into Alzheimer’s Disease: Novel Pathogenesis, Drug Target and Delivery

Alzheimer’s disease (AD), the most common type of dementia, is characterized by senile plaques composed of amyloid β protein (Aβ) and neurofilament tangles derived from the hyperphosphorylation of tau protein. However, the developed medicines targeting Aβ and tau have not obtained ideal clinical efficacy, which raises a challenge to the hypothesis that AD is Aβ cascade-induced. A critical problem of AD pathogenesis is which endogenous factor induces Aβ aggregation and tau phosphorylation. Recently, age-associated endogenous formaldehyde has been suggested to be a direct trigger for Aβ- and tau-related pathology. Another key issue is whether or not AD drugs are successfully delivered to the damaged neurons. Both the blood–brain barrier (BBB) and extracellular space (ECS) are the barriers for drug delivery. Unexpectedly, Aβ-related SP deposition in ECS slows down or stops interstitial fluid drainage in AD, which is the direct reason for drug delivery failure. Here, we propose a new pathogenesis and perspectives on the direction of AD drug development and drug delivery: (1) aging-related formaldehyde is a direct trigger for Aβ assembly and tau hyperphosphorylation, and the new target for AD therapy is formaldehyde; (2) nano-packaging and physical therapy may be the promising strategy for increasing BBB permeability and accelerating interstitial fluid drainage.

Acute high-altitude hypoxia exposure causes neurological deficits via formaldehyde accumulation

INTRODUCTION

Acute high-altitude hypoxia exposure causes multiple adverse neurological consequences. However, the exact mechanisms are still unclear, and there is no targeted treatment with few side effects. Excessive cerebral formaldehyde (FA) impairs numerous functions, and can be eliminated by nano-packed coenzyme Q10 (CoQ10).

AIMS

In this study, we aimed to investigate whether cerebral FA was accumulated after hypobaric hypoxia exposure, and further explored the preventative effect of CoQ10 through FA elimination.

RESULTS

Accumulated cerebral FA was found in C57BL/6 mice after acute high-altitude hypoxia exposure, which resulted in FA metabolic disturbance with the elevation of semicarbazide-sensitive amine oxidase, and declination of aldehyde dehydrogenase-2. Excessive FA was also found to induce neuronal ferroptosis in vivo. Excitingly, administration with CoQ10 for 3 days before acute hypobaric hypoxia reduced cerebral FA accumulation, alleviated subsequent neuronal ferroptosis, and preserved neurological functions.

CONCLUSION

Cerebral FA accumulation mediates neurological deficits under acute hypobaric hypoxia, and CoQ10 supplementation may be a promising preventative strategy for visitors and sojourners at plateau.

Identification of the Antithrombotic Mechanism of Leonurine in Adrenalin Hydrochloride-Induced Thrombosis in Zebrafish via Regulating Oxidative Stress and Coagulation Cascade

Thrombosis is a general pathological phenomenon during severe disturbances to homeostasis, which plays an essential role in cardiovascular and cerebrovascular diseases. Leonurine (LEO), isolated from Leonurus japonicus Houtt, showes a crucial role in anticoagulation and vasodilatation. However, the properties and therapeutic mechanisms of this effect have not yet been systematically elucidated. Therefore, the antithrombotic effect of LEO was investigated in this study. Hematoxylin-Eosin staining was used to detect the thrombosis of zebrafish tail. Fluorescence probe was used to detect the reactive oxygen species. The biochemical indexes related to oxidative stress (lactate dehydrogenase, malondialdehyde, superoxide dismutase and glutathione) and vasodilator factor (endothelin-1 and nitric oxide) were analyzed by specific commercial assay kits. Besides, we detected the expression of related genes (fga, fgb, fgg, pkcα, pkcβ, vwf, f2) and proteins (PI3K, phospho-PI3K, Akt, phospho-Akt, ERK, phospho-ERK FIB) related to the anticoagulation and fibrinolytic system by quantitative reverse transcription and western blot. Beyond that, metabolomic analyses were carried out to identify the expressions of metabolites associated with the anti-thrombosis mechanism of LEO. Our in vivo experimental results showed that LEO could improve the oxidative stress injury, abnormal platelet aggregation and coagulation dysfunction induced by adrenalin hydrochloride. Moreover, LEO restored the modulation of amino acids and inositol metabolites which are reported to alleviate the thrombus formation. Collectively, LEO attenuates adrenalin hydrochloride-induced thrombosis partly via modulating oxidative stress, coagulation cascade and platelet activation and amino acid and inositol metabolites.

Inhibition of vascular adhesion protein 1 protects dopamine neurons from the effects of acute inflammation and restores habit learning in the striatum

Background

Changes in dopaminergic neural function can be induced by an acute inflammatory state that, by altering the integrity of the neurovasculature, induces neuronal stress, cell death and causes functional deficits. Effectively blocking these effects of inflammation could, therefore, reduce both neuronal and functional decline. To test this hypothesis, we inhibited vascular adhesion protein 1 (VAP-1), a membrane-bound protein expressed on the endothelial cell surface, that mediates leukocyte extravasation and induces oxidative stress.

Method

We induced dopaminergic neuronal loss by infusing lipopolysaccharide (LPS) directly into the substantia nigra (SN) in rats and administered the VAP-1 inhibitor, PXS-4681A, daily.

Results

LPS produced: an acute inflammatory response, the loss of dopaminergic neurons in the SN, reduced the dopaminergic projection to SN target regions, particularly the dorsolateral striatum (DLS), and a deficit in habit learning, a key function of the DLS. In an attempt to protect SN neurons from this inflammatory response we found that VAP-1 inhibition not only reduced neutrophil infiltration in the SN and striatum, but also reduced the associated striatal microglia and astrocyte response. We found VAP-1 inhibition protected dopamine neurons in the SN, their projections to the striatum and promoted the functional recovery of habit learning. Thus, we reversed the loss of habitual actions, a function usually dependent on dopamine release in DLS and sensitive to striatal dysfunction.

Conclusions

We establish, therefore, that VAP-1 inhibition has an anti-inflammatory profile that may be beneficial in the treatment of dopamine neuron dysfunction caused by an acute inflammatory state in the brain.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02288-8.

Perspectives on formaldehyde dysregulation: Mitochondrial DNA damage and repair in mammalian cells

Maintaining genome stability involves coordination between different subcellular compartments providing cells with DNA repair systems that safeguard against environmental and endogenous stresses. Organisms produce the chemically reactive molecule formaldehyde as a component of one-carbon metabolism, and cells maintain systems to regulate endogenous levels of formaldehyde under physiological conditions, preventing genotoxicity, among other adverse effects. Dysregulation of formaldehyde is associated with several diseases, including cancer and neurodegenerative disorders. In the present review, we discuss the complex topic of endogenous formaldehyde metabolism and summarize advances in research on fo dysregulation, along with future research perspectives.

Accumulation of formaldehyde causes motor deficits in an in vivo model of hindlimb unloading

During duration spaceflight, or after their return to earth, astronauts have often suffered from gait instability and cerebellar ataxia. Here, we use a mouse model of hindlimb unloading (HU) to explore a mechanism of how reduced hindlimb burden may contribute to motor deficits. The results showed that these mice which have experienced HU for 2 weeks exhibit a rapid accumulation of formaldehyde in the gastrocnemius muscle and fastigial nucleus of cerebellum. The activation of semicarbazide-sensitive amine oxidase and sarcosine dehydrogenase induced by HU-stress contributed to formaldehyde generation and loss of the abilities to maintain balance and coordinate motor activities. Further, knockout of formaldehyde dehydrogenase (FDH^-/-) in mice caused formaldehyde accumulation in the muscle and cerebellum that was associated with motor deficits. Remarkably, formaldehyde injection into the gastrocnemius muscle led to gait instability; especially, microinfusion of formaldehyde into the fastigial nucleus directly induced the same symptoms as HU-induced acute ataxia. Hence, excessive formaldehyde damages motor functions of the muscle and cerebellum.

The cellular function and molecular mechanism of formaldehyde in cardiovascular disease and heart development

As a common air pollutant, formaldehyde is widely present in nature, industrial production and consumer products. Endogenous formaldehyde is mainly produced through the oxidative deamination of methylamine catalysed by semicarbazide-sensitive amine oxidase (SSAO) and is ubiquitous in human body fluids, tissues and cells. Vascular endothelial cells and smooth muscle cells are rich in this formaldehyde-producing enzyme and are easily damaged owing to consequent cytotoxicity. Consistent with this, increasing evidence suggests that the cardiovascular system and stages of heart development are also susceptible to the harmful effects of formaldehyde. Exposure to formaldehyde from different sources can induce heart disease such as arrhythmia, myocardial infarction (MI), heart failure (HF) and atherosclerosis (AS). In particular, long-term exposure to high concentrations of formaldehyde in pregnant women is more likely to affect embryonic development and cause heart malformations than long-term exposure to low concentrations of formaldehyde. Specifically, the ability of mouse embryos to effect formaldehyde clearance is far lower than that of the rat embryos, more readily allowing its accumulation. Formaldehyde may also exert toxic effects on heart development by inducing oxidative stress and cardiomyocyte apoptosis. This review focuses on the current progress in understanding the influence and underlying mechanisms of formaldehyde on cardiovascular disease and heart development.

SSAO/VAP-1 in Cerebrovascular Disorders: A Potential Therapeutic Target for Stroke and Alzheimer's Disease

The semicarbazide-sensitive amine oxidase (SSAO), also known as vascular adhesion protein-1 (VAP-1) or primary amine oxidase (PrAO), is a deaminating enzyme highly expressed in vessels that generates harmful products as a result of its enzymatic activity. As a multifunctional enzyme, it is also involved in inflammation through its ability to bind and promote the transmigration of circulating leukocytes into inflamed tissues. Inflammation is present in different systemic and cerebral diseases, including stroke and Alzheimer’s disease (AD). These pathologies show important affectations on cerebral vessels, together with increased SSAO levels. This review summarizes the main roles of SSAO/VAP-1 in human physiology and pathophysiology and discusses the mechanisms by which it can affect the onset and progression of both stroke and AD. As there is an evident interrelationship between stroke and AD, basically through the vascular system dysfunction, the possibility that SSAO/VAP-1 could be involved in the transition between these two pathologies is suggested. Hence, its inhibition is proposed to be an interesting therapeutical approach to the brain damage induced in these both cerebral pathologies.

An inexpensive and sensitive turn-on luminescence protocol for sensing formaldehyde

Formaldehyde (FA), the simplest and most widely-used aldehyde, can pose serious health issues when present at elevated concentrations. Here, we report a "turn-on" terbium photoluminescence method for the efficient detection of FA. A pro-sensitizer molecule was designed and synthesised, which releases the sensitizer in the presence of FA inside the terbium cholate hydrogel matrix, resulting in a "turn-on" luminescence response. The introduction of a paper-based sensing approach makes the protocol simpler and cost-effective, and has a detection limit as low as 100 nM.

Interplay between Cellular Metabolism and the DNA Damage Response in Cancer

Metabolism is a fundamental cellular process that can become harmful for cells by leading to DNA damage, for instance by an increase in oxidative stress or through the generation of toxic byproducts. To deal with such insults, cells have evolved sophisticated DNA damage response (DDR) pathways that allow for the maintenance of genome integrity. Recent years have seen remarkable progress in our understanding of the diverse DDR mechanisms, and, through such work, it has emerged that cellular metabolic regulation not only generates DNA damage but also impacts on DNA repair. Cancer cells show an alteration of the DDR coupled with modifications in cellular metabolism, further emphasizing links between these two fundamental processes. Taken together, these compelling findings indicate that metabolic enzymes and metabolites represent a key group of factors within the DDR. Here, we will compile the current knowledge on the dynamic interplay between metabolic factors and the DDR, with a specific focus on cancer. We will also discuss how recently developed high-throughput technologies allow for the identification of novel crosstalk between the DDR and metabolism, which is of crucial importance to better design efficient cancer treatments.

Amino acid dependent formaldehyde metabolism in mammals

Aldehyde dehydrogenase class 3, encoded by ADH5 in humans, catalyzes the glutathione dependent detoxification of formaldehyde. Here we show that ADH5 deficient cells turn over formaldehyde using alternative pathways starting from the reaction of formaldehyde with free amino acids. When mammalian cells are exposed to formaldehyde, the levels of the reaction products of formaldehyde with the amino acids cysteine and histidine - timonacic and spinacine - are increased. These reactions take place spontaneously and the formation of timonacic is reversible. The levels of timonacic are higher in the plasma of Adh5-/- mice relative to controls and they are further increased upon administration of methanol. We conclude that mammals possess pathways of cysteine and histidine dependent formaldehyde metabolism and that timonacic is a formaldehyde reservoir.

Beneficial Impact of Semicarbazide-Sensitive Amine Oxidase Inhibition on the Potential Cytotoxicity of Creatine Supplementation in Type 2 Diabetes Mellitus

Creatine supplementation of the population with type 2 diabetes mellitus (T2DM) combined with an exercise program is known to be a possible therapy adjuvant with hypoglycemic effects. However, excessive administration of creatine leads to the production of methylamine which is deaminated by the enzyme semicarbazide-sensitive amine oxidase (SSAO) and as a result, cytotoxic compounds are produced. SSAO activity and reaction products are increased in the serum of T2DM patients. Creatine supplementation by diabetics will further augment the activity of SSAO. The current review aims to find a feasible way to ameliorate T2DM for patients who exercise and desire to consume creatine. Several natural agents present in food which are involved in the regulation of SSAO activity directly or indirectly are reviewed. Particularly, zinc-α2-glycoprotein (ZAG), zinc (Zn), copper (Cu), histamine/histidine, caffeine, iron (Fe), and vitamin D are discussed. Inhibiting SSAO activity by natural agents might reduce the potential adverse effects of creatine metabolism in population of T2DM.

Formate metabolism in health and disease

BACKGROUND

Formate is a one-carbon molecule at the crossroad between cellular and whole body metabolism, between host and microbiome metabolism, and between nutrition and toxicology. This centrality confers formate with a key role in human physiology and disease that is currently unappreciated.

SCOPE OF REVIEW

Here we review the scientific literature on formate metabolism, highlighting cellular pathways, whole body metabolism, and interactions with the diet and the gut microbiome. We will discuss the relevance of formate metabolism in the context of embryonic development, cancer, obesity, immunometabolism, and neurodegeneration.

MAJOR CONCLUSIONS

We will conclude with an outlook of some open questions bringing formate metabolism into the spotlight.

How formaldehyde reacts with amino acids

Formaldehyde is a biological electrophile produced via processes including enzymatic demethylation. Despite its apparent simplicity, the reactions of formaldehyde with even basic biological components are incompletely defined. Here we report NMR-based studies on the reactions of formaldehyde with common proteinogenic and other nucleophilic amino acids. The results reveal formaldehyde reacts at different rates, forming hydroxymethylated, cyclised, cross-linked, or disproportionated products of varying stabilities. Of the tested common amino acids, cysteine reacts most efficiently, forming a stable thiazolidine. The reaction with lysine is less efficient; low levels of an Nε-methylated product are observed, raising the possibility of non-enzymatic lysine methylation by formaldehyde. Reactions with formaldehyde are faster than reactions with other tested biological carbonyl compounds, and the adducts are also more stable. The results reveal reactions of formaldehyde with amino acids, and by extension peptides and proteins, have potential roles in healthy and diseased biology, as well as in evolution.

Chemoenzymatic Hydrogen Production from Methanol through the Interplay of Metal Complexes and Biocatalysts

Microbial methylotrophic organisms can serve as great inspiration in the development of biomimetic strategies for the dehydrogenative conversion of C₁ molecules under ambient conditions. In this Concept article, a concise personal perspective on the recent advancements in the field of biomimetic catalytic models for methanol and formaldehyde conversion, in the presence and absence of enzymes and co-factors, towards the formation of hydrogen under ambient conditions is given. In particular, formaldehyde dehydrogenase mimics have been introduced in stand-alone C₁ -interconversion networks. Recently, coupled systems with alcohol oxidase and dehydrogenase enzymes have been also developed for in situ formation and decomposition of formaldehyde and/or reduced/oxidized nicotinamide adenine dinucleotide (NADH/ NAD⁺ ). Although C₁ molecules are already used in many industries for hydrogen production, these conceptual bioinspired low-temperature energy conversion processes may lead one day to more efficient energy storage systems enabling renewable and sustainable hydrogen generation for hydrogen fuel cells under ambient conditions using C₁ molecules as fuels for mobile and miniaturized energy storage solutions in which harsh conditions like those in industrial plants are not applicable.

Attenuation of the effects of oxidative stress by the MAO-inhibiting antidepressant and carbonyl scavenger phenelzine

Phenelzine (β-phenylethylhydrazine) is a monoamine oxidase (MAO)-inhibiting antidepressant with anxiolytic properties. It possesses a number of important pharmacological properties which may alter the effects of oxidative stress. After conducting a comprehensive literature search, the authors of this review paper aim to provide an overview and discussion of the mechanisms by which phenelzine may attenuate oxidative stress. It inhibits γ-aminobutyric acid (GABA) transaminase, resulting in elevated brain GABA levels, inhibits both MAO and primary amine oxidase and, due to its hydrazine-containing structure, reacts chemically to sequester a number of reactive aldehydes (e.g. acrolein and 4-hydroxy-2-nonenal) proposed to be implicated in oxidative stress in a number of neurodegenerative disorders. Phenelzine is unusual in that it is both an inhibitor of and a substrate for MAO, the latter action producing at least one active metabolite, β-phenylethylidenehydrazine (PEH). This metabolite inhibits GABA transaminase, is a very weak inhibitor of MAO but a strong inhibitor of primary amine oxidase, and sequesters aldehydes. Phenelzine may ameliorate the effects of oxidative stress by reducing formation of reactive metabolites (aldehydes, hydrogen peroxide, ammonia/ammonia derivatives) produced by the interaction of MAO with biogenic amines, by sequestering various other reactive aldehydes and by inhibiting primary amine oxidase. In PC12 cells treated with the neurotoxin MPP⁺, phenelzine has been reported to reduce several adverse effects of MPP⁺. It has also been reported to reduce lipid peroxidative damage induced in plasma and platelet proteins by peroxynitrite. In animal models, phenelzine has a neuroprotective effect in global ischemia and in cortical impact traumatic brain injury. Recent studies reported in the literature on the possible involvement of acrolein in spinal cord injury and multiple sclerosis indicate that phenelzine can attenuate adverse effects of acrolein in these models. Results from studies in our laboratories on effects of phenelzine and PEH on primary amine oxidase (which catalyzes formation of toxic aldehydes and is overexpressed in Alzheimer's disease), on sequestration of the toxic aldehyde acrolein, and on reduction of acrolein-induced toxicity in mouse cortical neurons are also reported.

NMR analyses on N-hydroxymethylated nucleobases - implications for formaldehyde toxicity and nucleic acid demethylases

Formaldehyde is produced in cells by enzyme-catalysed demethylation reactions, including those occurring on N-methylated nucleic acids. Formaldehyde reacts with nucleobases to form N-hydroxymethylated adducts that may contribute to its toxicity/carcinogenicity when added exogenously, but the chemistry of these reactions has been incompletely defined. We report NMR studies on the reactions of formaldehyde with canonical/modified nucleobases. The results reveal that hydroxymethyl hemiaminals on endocyclic nitrogens, as observed with thymidine and uridine monophosphates, are faster to form than equivalent hemiaminals on exocyclic nitrogens; however, the exocyclic adducts, as formed with adenine, guanine and cytosine, are more stable in solution. Nucleic acid demethylase (FTO)-catalysed hydroxylation of (6-methyl)adenosine results in (6-hydroxymethyl)adenosine as the major observed product; by contrast no evidence for a stable 3-hydroxymethyl adduct was accrued with FTO-catalysed oxidation of (3-methyl)thymidine. Collectively, our results imply N-hydroxymethyled adducts of nucleic acid bases, formed either by reactions with formaldehyde or via demethylase catalysis, have substantially different stabilities, with some being sufficiently stable to have functional roles in disease or the regulation of nucleic acid/nucleobase activity.

Protective Effects of Total Flavones of Elaeagnus rhamnoides (L.) A. Nelson against Vascular Endothelial Injury in Blood Stasis Model Rats

The aim was to evaluate the protective effects of total flavones of Elaeagnus rhamnoides (L.) A. Nelson (TFE) against vascular endothelial injury in blood stasis model rats and explore the potential mechanisms preliminarily. The model of blood stasis rat model with vascular endothelial injury was induced by subcutaneous injection of adrenaline combined with ice-water bath. Whole blood viscosity (WBV), histological examination, and prothrombin time (PT), activated partial thromboplastin time (APTT), and fibrinogen (FIB) were measured. Meanwhile, the levels of Thromboxane B2 (TXB2), 6-keto-PGF1α , von Willebrand factor (vWF), and thrombomodulin (TM) were detected. In addition, Quantitative Real-Time PCR (qPCR) was performed to identify PI3K, Erk2, Bcl-2, and caspase-3 gene expression. The results showed that TFE can relieve WBV, increase PT and APTT, and decrease FIB content obviously. Moreover, TFE might significantly downregulate the levels of TXB2, vWF, and TM in plasma and upregulate the level of 6-keto-PGF1α in plasma. Expressions of PI3K and Bcl-2 were increased and the expression of caspase-3 was decreased by TFE pretreatment in the rat model. Consequently, the study suggested that TFE may have the potential against vascular endothelial injury in blood stasis model rats induced by a high dose of adrenaline with ice-water bath.

The inhibitor of semicarbazide-sensitive amine oxidase, PXS-4728A, ameliorates key features of chronic obstructive pulmonary disease in a mouse model

BACKGROUND AND PURPOSE

Chronic obstructive pulmonary disease (COPD) is a major cause of illness and death, often induced by cigarette smoking (CS). It is characterized by pulmonary inflammation and fibrosis that impairs lung function. Existing treatments aim to control symptoms but have low efficacy, and there are no broadly effective treatments. A new potential target is the ectoenzyme, semicarbazide-sensitive mono-amine oxidase (SSAO; also known as vascular adhesion protein-1). SSAO is elevated in smokers' serum and is a pro-inflammatory enzyme facilitating adhesion and transmigration of leukocytes from the vasculature to sites of inflammation.

EXPERIMENTAL APPROACH

PXS-4728A was developed as a low MW inhibitor of SSAO. A model of COPD induced by CS in mice reproduces key aspects of human COPD, including chronic airway inflammation, fibrosis and impaired lung function. This model was used to assess suppression of SSAO activity and amelioration of inflammation and other characteristic features of COPD.

KEY RESULTS

Treatment with PXS-4728A completely inhibited lung and systemic SSAO activity induced by acute and chronic CS-exposure. Daily oral treatment inhibited airway inflammation (immune cell influx and inflammatory factors) induced by acute CS-exposure. Therapeutic treatment during chronic CS-exposure, when the key features of experimental COPD develop and progress, substantially suppressed inflammatory cell influx and fibrosis in the airways and improved lung function.

CONCLUSIONS AND IMPLICATIONS

Treatment with a low MW inhibitor of SSAO, PXS-4728A, suppressed airway inflammation and fibrosis and improved lung function in experimental COPD, demonstrating the therapeutic potential of PXS-4728A for this debilitating disease.

Elevation of rat brain tyrosine levels by phenelzine is mediated by its active metabolite β-phenylethylidenehydrazine

Phenelzine, a non-selective irreversible inhibitor of monoamine oxidase (MAO), has been used in the treatment of depression and anxiety disorders for several decades. It is a unique inhibitor of MAO as it is also a substrate for MAO, with one of the metabolites being β-phenylethylidenehydrazine (PEH), and it also inhibits several transaminases (e.g. GABA transaminase) in the brain when administered i.p. to rats. Administration of either phenelzine or PEH to rats has been reported to produce dramatic increases in rat brain levels of GABA and alanine while reducing levels of glutamine; these effects are abolished for phenelzine, but not for PEH, when the animals are pre-treated with another MAO inhibitor, suggesting that they are mediated by the MAO-catalyzed formation of PEH from phenelzine. In the present report, we have found that phenelzine and E- and Z-geometric isomers of PEH significantly increased rat whole brain concentrations of L-tyrosine. In a time-response study, acute administration of phenelzine, E-PEH and Z-PEH (30 mg/kg i.p.) elevated rat whole brain L-tyrosine levels at 3 and 6h following injection, reaching approximately 265-305% of vehicle-treated controls at 3h. To determine whether the effect on L-tyrosine is MAO-dependent, animals were pre-treated with the non-selective MAO inhibitor tranylcypromine (1mg/kg i.p.) prior to administration of phenelzine, racemic PEH or vehicle controls. This pre-treatment reversed the effects of phenelzine, but not of PEH, on brain L-tyrosine levels, suggesting that the tyrosine-elevating property of phenelzine is largely the result of its active metabolite PEH. These results are discussed in relation to possible therapeutic applications of these drugs.

A glutathione-dependent detoxification system is required for formaldehyde resistance and optimal survival of Neisseria meningitidis in biofilms

AIM

The glutathione-dependent AdhC-EstD formaldehyde detoxification system is found in eukaryotes and prokaryotes. It is established that it confers protection against formaldehyde that is produced from environmental sources or methanol metabolism. Thus, its presence in the human host-adapted bacterial pathogen Neisseria meningitidis is intriguing. This work defined the biological function of this system in the meningococcus using phenotypic analyses of mutants linked to biochemical and structural characterization of purified enzymes.

RESULTS

We demonstrated that mutants in the adhC and/or estD were sensitive to killing by formaldehyde. Inactivation of adhC and/or estD also led to a loss of viability in biofilm communities, even in the absence of exogenous formaldehyde. Detailed biochemical and structural analyses of the esterase component demonstrated that S-formylglutathione was the only biologically relevant substrate for EstD. We further showed that an absolutely conserved cysteine residue was covalently modified by S-glutathionylation. This leads to inactivation of EstD.

INNOVATION

The results provide several conceptual innovations. They provide a new insight into formaldehyde detoxification in bacteria that do not generate formaldehyde during the catabolism of methanol. Our results also indicate that the conserved cysteine, found in all EstD enzymes from humans to microbes, is a site of enzyme regulation, probably via S-glutathionylation.

CONCLUSION

The adhc-estD system protects against formaldehyde produced during endogenous metabolism.

Comparison of phenelzine and geometric isomers of its active metabolite, β-phenylethylidenehydrazine, on rat brain levels of amino acids, biogenic amine neurotransmitters and methylamine

Phenelzine is a monoamine oxidase (MAO) inhibitor used in treatment of depression and anxiety disorders. It also elevates brain levels of γ-aminobutyric acid (GABA) and inhibits primary amine oxidase (PrAO), an enzyme whose activity and/or expression has been reported to be increased in diabetes mellitus, Alzheimer's disease and cardiovascular disorders. Phenelzine is not only an inhibitor of, but also a substrate for, MAO and it has been suggested that an active metabolite, namely β-phenylethylidenehydrazine (PEH), is responsible for phenelzine's effects on amino acids. PEH is also a strong inhibitor of PrAO but has weak effects on MAO. PEH has a double bond and can thus exist as (E)- and (Z)-geometric isomers, but to date the two isomers have not been compared with regard to their neurochemical effects. We have investigated the effects of phenelzine, (E)- and (Z)-PEH on rat whole brain levels of amino acids, biogenic amine neurotransmitters and methylamine (an endogenous substrate of PrAO). Under the conditions used in the study, (E)- and (Z)-PEH appear to be equivalent in their neurochemical properties. Both PEH isomers and phenelzine produced marked increases in rat brain levels of GABA and alanine while decreasing brain levels of glutamine. Phenelzine increased brain levels of biogenic amine neurotransmitters (noradrenaline, dopamine and serotonin), whereas neither PEH isomer altered levels of these neurotransmitters to a considerable extent. All three drugs significantly increased rat brain levels of methylamine, with (E)- and (Z)-PEH causing a greater increase than phenelzine. These results are discussed in relation to the possible therapeutic applications of these drugs.

Cellular mechanism underlying formaldehyde-stimulated Cl- secretion in rat airway epithelium

BACKGROUND

Recent studies suggest that formaldehyde (FA) could be synthesized endogeneously and transient receptor potential (TRP) channel might be the sensor of FA. However, the physiological significance is still unclear.

METHODOLOGY/PRINCIPAL FINDINGS

The present study investigated the FA induced epithelial Cl(-) secretion by activation of TRPV-1 channel located in the nerve ending fiber. Exogenously applied FA induced an increase of I(SC) in intact rat trachea tissue but not in the primary cultured epithelial cells. Western blot and immunofluorescence analysis identified TRPV-1 expression in rat tracheal nerve ending. Capsazepine (CAZ), a TRPV-1 specific antagonist significantly blocked the I(SC) induced by FA. The TRPV-1 agonist capsaicin (Cap) induced an increase of I(SC), which was similar to the I(SC) induced by FA. L-703606, an NK-1 specific inhibitor and propranolol, an adrenalin β receptor inhibitor significantly abolished the I(SC) induced by FA or Cap. In the ion substitute analysis, FA could not induce I(SC) in the absence of extracelluar Cl(-). The I(SC) induced by FA could be blocked by the non-specific Cl(-) channel inhibitor DPC and the CFTR specific inhibitor CFTR(i-172), but not by the Ca(2+)-activated Cl(-) channel inhibitor DIDS. Furthermore, both forskolin, an agonist of adenylate cyclase (AC) and MDL-12330A, an antagonist of AC could block FA-induced I(SC).

CONCLUSION

Our results suggest that FA-induced epithelial I(SC) response is mediated by nerve, involving the activation of TRPV-1 and release of adrenalin as well as substance P.

Synthetic liver X receptor agonist T0901317 inhibits semicarbazide-sensitive amine oxidase gene expression and activity in apolipoprotein E knockout mice

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes oxidative deamination of primary aromatic and aliphatic amines. Increased SSAO activity has been found in atherosclerosis and diabetes mellitus. We hypothesize that the anti-atherogenic effect of liver X receptors (LXRs) might be related to the inhibition of SSAO gene expression and its activity. In this study, we investigated the effect of LXR agonist T0901317 on SSAO gene expression and its activity in apolipoprotein E knockout (apoE(-/-)) mice. Male apoE(-/-) mice (8 weeks old) were randomly divided into four groups: basal control group; vehicle group; prevention group; and treatment group. SSAO gene expression was analyzed by real-time quantitative polymerase chain reaction and its activity was determined. The activity of superoxide dismutase and content of malondialdehyde in the aorta and liver were also determined. In T0901317-treated mice, SSAO gene expression was significantly decreased in the aorta, liver, small intestine, and brain. SSAO activities in serum and in these tissues were also inhibited. The amount of superoxide dismutase in the aorta and liver of the prevention group and treatment group was significantly higher compared with the vehicle group (P<0.05). Malondialdehyde in the tissues of these two groups was significantly lower compared with the vehicle group (P<0.05). Our results showed that T0901317 inhibits SSAO gene expression and its activity in atherogenic apoE(-/-) mice. The atheroprotective effect of LXR agonist T0901317 is related to the inhibition of SSAO gene expression and its activity.

The dual face of endogenous alpha-aminoketones: pro-oxidizing metabolic weapons

Amino metabolites with potential prooxidant properties, particularly alpha-aminocarbonyls, are the focus of this review. Among them we emphasize 5-aminolevulinic acid (a heme precursor formed from succinyl-CoA and glycine), aminoacetone (a threonine and glycine metabolite), and hexosamines and hexosimines, formed by Schiff condensation of hexoses with basic amino acid residues of proteins. All these metabolites were shown, in vitro, to undergo enolization and subsequent aerobic oxidation, yielding oxyradicals and highly cyto- and genotoxic alpha-oxoaldehydes. Their metabolic roles in health and disease are examined here and compared in humans and experimental animals, including rats, quail, and octopus. In the past two decades, we have concentrated on two endogenous alpha-aminoketones: (i) 5-aminolevulinic acid (ALA), accumulated in acquired (e.g., lead poisoning) and inborn (e.g., intermittent acute porphyria) porphyric disorders, and (ii) aminoacetone (AA), putatively overproduced in diabetes mellitus and cri-du-chat syndrome. ALA and AA have been implicated as contributing sources of oxyradicals and oxidative stress in these diseases. The end product of ALA oxidation, 4,5-dioxovaleric acid (DOVA), is able to alkylate DNA guanine moieties, promote protein cross-linking, and damage GABAergic receptors of rat brain synaptosome preparations. In turn, methylglyoxal (MG), the end product of AA oxidation, is also highly cytotoxic and able to release iron from ferritin and copper from ceruloplasmin, and to aggregate proteins. This review covers chemical and biochemical aspects of these alpha-aminoketones and their putative roles in the oxidative stress associated with porphyrias, tyrosinosis, diabetes, and cri-du-chat. In addition, we comment briefly on a side prooxidant behaviour of hexosamines, that are known to constitute building blocks of several glycoproteins and to be involved in Schiff base-mediated enzymatic reactions.

Soluble semicarbazide-sensitive amine oxidase (SSAO) activity is related to oxidative stress and subchronic inflammation in streptozotocin-induced diabetic rats

Diabetes is known to increase the risk of Alzheimer's disease (AD) and vascular dementia via oxidative stress and inflammation. There are speculations that SSAO activity might be related to the development of AD. Our aim was to investigate whether changes of soluble SSAO activity, oxidative stress and inflammation markers are related to each other in diabetes. Soluble and tissue-bound SSAO activities (from serum and aorta, respectively) were determined in streptozotocin (STZ)-induced diabetic rats without insulin treatment, receiving insulin once, or twice daily compared to control animals. After three weeks of treatment soluble and tissue-bound SSAO activities (seSSAO and aoSSAO, respectively), serum total antioxidant status (TAS), high sensitivity C-reactive protein (hsCRP), fructose amine levels and routine laboratory parameters were determined. SeSSAO activity significantly increased in the diabetic groups without treatment and receiving insulin once daily, and a marked decrease in aoSSAO activity was seen in all diabetic groups. Increased oxidative stress was correlated with hsCRP elevation, while hsCRP and seSSAO activity were also significantly correlated. In all groups seSSAO and aoSSAO activities were in negative correlation with each other. Our results support the view that poor metabolic control leads to increased oxidative stress, which in turn may cause the elevation of hsCRP levels. Soluble SSAO on the one hand acts as an adhesion molecule--thus possibly being a factor responsible for the late complications of diabetes--and on the other hand, it may contribute to oxidative stress. Our parsimonious conclusion is that there is a relation between the risk factors of AD and vascular dementia (diabetes, oxidative stress and chronic inflammation) and SSAO activity, which may originate from the vessel wall.

Diabetes and semicarbazide-sensitive amine oxidase (SSAO) activity: A review

The enzyme of semicarbazide-sensitive amine oxidase (SSAO) activity has been reported to be elevated in blood from diabetic patients. SSAO are widely distributed in plasma membranes of various tissues and blood plasma. SSAO-mediated production of toxic aldehydes has been proposed to be related to pathophysiological conditions. Cytotoxic metabolites by SSAO may cause endothelial injury and subsequently induce atherosclerosis. The precise physiological functions of SSAO could play an important role in the control of energy balance in adipose tissue. It is possible that the increased SSAO activity in diabetes may be a result of up-regulation due to increase of SSAO substrates, such as methylamine or aminoacetone. SSAO could play an important role in the regulation of adipocyte homeostasis. Inhibition of SSAO could be of therapeutic value for treatment of diabetic patient.

Proteomic and transcriptomic analyses of macrophages with an increased resistance to oxidized low density lipoprotein (oxLDL)-induced cytotoxicity generated by chronic exposure to oxLDL

The uptake of oxidized low density lipoprotein (oxLDL) by macrophages leads to foam cell formation and fatty streaks, which represent early sites of potential atheroma development. We developed a cell culture model of chronic oxLDL exposure to determine whether hallmark parameters of oxLDL uptake and cytotoxicity are altered during foam cell formation and to determine changes in protein and mRNA expression that distinguish acute and chronic oxLDL exposure. Although the extent of oxLDL uptake did not change, a resistance to oxLDL-induced cytotoxicity was observed in the chronically exposed cells. Macrophages that have been chronically exposed to oxLDL required a 40% higher concentration of oxLDL to achieve 50% survival in a 48-h treatment relative to macrophages subjected to a single oxLDL exposure. A main feature of the differentially expressed proteome was a series of significantly overexpressed antioxidant and antioxidant-related proteins in the oxLDL-exposed cells. A large proportion of these proteins (45%) was overexpressed in the chronically exposed cells prior to the oxLDL treatment, indicative of the unique phenotype produced by the chronic treatment. Analysis of the transcriptome also revealed a broad increase in the expression of antioxidant and antioxidant-related proteins. In addition, the transcriptome experiments found an increased inflammatory response under conditions of both acute and chronic oxLDL exposure. Overall the combined functional, proteomic, and transcriptomic experiments show that macrophages respond to oxLDL by developing an oxidative stress resistance that increases and stabilizes with chronic exposure. Furthermore this protective response and the increased foam cell survival that it supports amplifies their proatherogenic role by promoting a continued inflammatory state.

Involvement of SSAO-mediated deamination in adipose glucose transport and weight gain in obese diabetic KKAy mice

Semicarbazide-sensitive amine oxidase (SSAO) is located on outer surfaces of adipocytes and endothelial and vascular smooth muscle cells. This enzyme catalyzes deamination of methylamine and aminoacetone, leading to production of toxic formaldehyde and methylglyoxal, respectively, as well as hydrogen peroxide and ammonium. Several lines of evidence suggest that increased SSAO activity is related to chronic inflammation and vascular disorders related to diabetic complications. We found that a highly potent and selective SSAO inhibitor, (E)-2-(4-fluorophenethyl)-3-fluoroallylamine (FPFA), was capable of reducing numbers of atherosclerotic lesions as well as weight gain in obese KKAy mice fed an atherogenic diet. SSAO inhibitors cause a moderate and long-lasting hyperglycemia. Such an increase in serum glucose is a result of reduction of glucose uptake by adipocytes. SSAO-mediated deamination of endogenous methylamine substrates induces adipocyte glucose uptake and lipogenesis. Highly selective SSAO inhibitors can effectively block induced glucose uptake. The results suggest that increased SSAO-mediated deamination may be concomitantly related to obesity and vascular disorders associated with type 2 diabetes.

Vasoactive effects of methylamine in isolated human blood vessels: role of semicarbazide-sensitive amine oxidase, formaldehyde, and hydrogen peroxide

It is hypothesized that methylamine (MA) and semicarbazide-sensitive amine oxidase (SSAO) activity are involved in the cardiovascular complications in human diabetics. To test this, we 1) determined the acute vasoactive effects of MA (1-1,000 micromol/l) in uncontracted and norepinephrine (NE; 1 micromol/l)-precontracted human blood vessels used for coronary artery bypass grafts [left internal mammary artery (LIMA), radial artery (RA), and right saphenous vein (RSV)]; 2) tested whether MA effects in LIMA and RSV were dependent on SSAO activity using the SSAO inhibitor semicarbazide (1 mmol/l, 15 min); 3) determined the effects of MA metabolites formaldehyde and hydrogen peroxide in LIMA and RSV; 4) tested whether the MA response was nitric oxide, prostaglandin, or hyperpolarization dependent; 5) measured the LIMA and RSV cGMP levels after MA exposure; and 6) quantified SSAO activity in LIMA, RA, and RSV. In NE-precontracted vessels, MA stimulated a biphasic response in RA and RSV (rapid contraction followed by prolonged relaxation) and dominant relaxation in LIMA (mean +/- SE, %relaxation: 55.4 +/- 3.9, n = 30). The MA-induced relaxation in LIMA was repeatable, nontoxic, and age independent. Semicarbazide significantly blocked MA-induced relaxation (%inhibition: 82.5 +/- 4.8, n = 7) and SSAO activity (%inhibition: 98.1 +/- 1.3, n = 26) in LIMA. Formaldehyde (%relaxation: 37.3 +/- 18.6, n = 3) and H(2)O(2) (%relaxation: 55.6 +/- 9.0, n = 9) at 1 mmol/l relaxed NE-precontracted LIMA comparable with MA. MA-induced relaxation in LIMA was nitric oxide, prostaglandin, and possibly cGMP independent and blocked by hyperpolarization. We conclude that vascular SSAO activity may convert endogenous amines, like MA, to vasoactive metabolites.

Semicarbazide sensitive amine oxidase overexpression has dual consequences: insulin mimicry and diabetes-like complications

Semicarbazide-sensitive amine oxidases (SSAO) are copper-containing enzymes that oxidatively deaminate primary amines to produce hydrogen peroxide, ammonium, and specific aldehydes. Vascular adhesion protein-1 (VAP-1) is a cell surface and soluble molecule that possesses SSAO activity. VAP-1 protein, SSAO activity, and SSAO reaction products are elevated in the serum of patients with diabetes, congestive heart failure, and specific inflammatory liver diseases. By expressing human VAP-1/SSAO on mouse endothelial cells and subsequently in the serum, and by chronically treating the transgenic mice for 15 months with a high-fat diet and a physiological substrate for SSAO, methylamine, the in vivo roles of SSAO were assessed. The VAP-1 transgene increased the mouse body mass index and subcutaneous abdominal fat pad weights in a manner independent of food consumption. The transgene together with increased SSAO substrate availability enhanced glucose uptake in an SSAO-dependent manner. The increased SSAO activity also led to diabetes-like complications, including advanced glycation end product formation, elevated blood pressure, altered atherosclerosis progression, and nephropathy. These findings suggest that, although manipulation of VAP-1/SSAO has potential to serve as a therapeutic treatment in insulin-resistant conditions, care must be taken to fully understand its impact on obesity and vascular damage.

A novel sensitive high-performance liquid chromatography/electrochemical procedure for measuring formaldehyde produced from oxidative deamination of methylamine and in biological samples

Formaldehyde is a well-known environmental toxic hazard. It is also a product of oxidative deamination of methylamine catalyzed by semicarbazide-sensitive amine oxidase (SSAO). Increased SSAO-mediated deamination has been implicated in some pathophysiological conditions, such as diabetic complications. The measurement of formaldehyde in the enzymatic reactions and in vivo production using conventional methods was not straightforward due to limitations of selectivity and sensitivity. A novel high-performance liquid chromatography (HPLC)/electrochemical procedure for the measurement of formaldehyde has been developed. The measurement is based on the formation of adducts between formaldehyde and dopamine. These adducts can be selectively purified and concentrated using a batch method of alumina absorption, separated by HPLC, and electrochemically quantified. The method is highly selective and substantially more sensitive, i.e., detection of picomole levels of formaldehyde, than the conventional methods. The procedure not only facilitates the assessment of SSAO activity in vitro but also is useful for assessing formaldehyde in tissues and biological fluids.

Physiological and pathological implications of semicarbazide-sensitive amine oxidase

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes the deamination of primary amines. Such deamination has been shown capable of regulating glucose transport in adipose cells. It has been independently discovered that the primary structure of vascular adhesion protein-1 (VAP-1) is identical to SSAO. VAP-1 regulates leukocyte migration and is related to inflammation. Increased serum SSAO activities have been found in patients with diabetic mellitus, vascular disorders and Alzheimer's disease. The SSAO-catalyzed deamination of endogenous substrates, that is, methylamine and aminoacetone, led to production of toxic formaldehyde and methylglyoxal, hydrogen peroxide and ammonia, respectively. These highly reactive aldehydes have been shown to initiate protein cross-linkage, exacerbate advanced glycation of proteins and cause endothelial injury. Hydrogen peroxide contributes to oxidative stress. 14C-methylamine is converted to 14C-formaldehyde, which then forms labeled long-lasting protein adduct in rodents. Chronic methylamine treatment increased the excretion of malondialdehyde and microalbuminuria, and enhanced the formation of fatty streaks in C57BL/6 mice fed with an atherogenic diet. Treatment with selective SSAO inhibitor reduces atherogenesis in KKAy diabetic mice fed with high-cholesterol diet. Aminoguanidine, which blocks advanced glycation and reduces nephropathy in animals, is in fact more potent at inhibiting SSAO than its effect on glycation. It suggests that SSAO is involved in vascular disorders under certain pathological conditions. Although SSAO has been known for several decades, its physiological and pathological implications are just beginning to be recognized.

Semicarbazide-sensitive amine oxidase in aortic smooth muscle cells mediates synthesis of a methylglyoxal-AGE: implications for vascular complications in diabetes

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes formation of methylglyoxal (MG) from aminoacetone; MG then reacts with proteins to form advanced glycation end products or AGEs. Because of its potential to generate MG, SSAO may contribute to AGE-associated vascular complications of aging and diabetes. We developed a method to measure SSAO activity in bovine aortic smooth muscle cells (BASMC) based on the oxidation of 2',7'-dichlorofluorescin by hydrogen peroxide and horseradish peroxidase. The SSAO activity was completely inhibited by 10 mM semicarbazide. Argpyrimidine is a readily detectable fluorescent product of the reaction between MG and arginine. Cell lysates incubated with aminoacetone formed argpyrimidine in a reaction that was inhibited by 20 mM semicarbazide. Immunostaining of tissue sections showed that aminoacetone-treated rats (normal as well as diabetic) formed more argpyrimidine in aortic smooth muscle than untreated controls. We believe that SSAO can enhance AGE synthesis in the macrovasculature of diabetic individuals by production of MG.

Culture medium enhances semicarbazide-sensitive amine oxidase activity

Components of fetal calf serum (FCS) are known to contribute to growth and maintenance of cultured cells. Fetal calf serum supplementation of media also may contribute to the cytotoxicity of other substances to cells grown in vitro. Semicarbazide-sensitive amine oxidase (SSAO) enzyme, present in FCS, metabolizes primary amines and contributes to amine cytotoxicity in vascular smooth muscle cells (VSMC). In cell culture experiments, the media used may greatly affect enzymic activities such as SSAO. In these studies, the SSAO activity in FCS, cultured rat aortic VSMC, and rat plasma was determined in the presence and absence of various culture media. Semicarbazide-sensitive amine oxidase activity in FCS (5-20 microl) was significantly enhanced (approximately 1.5- to 2-fold) in the presence of various culture media, with Dulbecco modified Eagle medium (DMEM), causing the greatest enhancement. Dulbecco modified Eagle medium enhanced the SSAO activity of cultured VSMC in two of the four passages but reduced activity in two passages. Activity in rat plasma was reduced by approximately 25% in the presence of DMEM. The concentrations of various media components, such as glucose, sodium pyruvate, pyridoxine.HCl, and L-glutamine, were not correlated with enhancement. This study identifies an important enhancement effect of culture media on the FCS enzyme, SSAO, although the media components responsible for the enhancement are yet to be identified.

Semicarbazide-sensitive amine oxidase (SSAO) in the brain

Semicarbazide-sensitive amine oxidase (SSAO) is widely distributed in almost tissues. However, its presence in brain microvessels is still controversial. The affinity of SSAO towards benzylamine (Bz) is considerably higher than that of monoamine oxidase (MAO). SSAO plays a role in the toxicity of several environmental and endogenous amines. SSAO-mediated production of toxic aldehydes has been proposed to be related to pathophysiological conditions. The most potent of inhibition of SSAO in monkey brain was observed by tricyclic antidepressant drug imipramine, as compared to tetracyclic drug maprotiline or non-cyclic drug nomifensine. An endogenous SSAO modulator in rat brain cytosol after immobilization stress (IMMO) was found and that this inhibitor could be induced by IMMO. SSAO activity in rat brain might be regulated by the level of this inhibitor. Semicarbazide, a SSAO inhibitor, enhances the formation of .OH products of efflux/oxidation due to 1-methyl-4-phenylpyridinium ion (MPP+). The precise physiological functions of SSAO could play an important role in the control of energy balance in adipose tissue. SSAO could play an important role in the regulation of adipocyte homeostasis.

Methylamine and benzylamine induced hypophagia in mice: modulation by semicarbazide-sensitive benzylamine oxidase inhibitors and aODN towards Kv1.1 channels

1. In starved mice, the anorectic activity of methylamine (MET) and benzylamine (BZ), both substrates of semicarbazide-sensitive benzylamine oxidases (Bz-SSAO), was compared with that of the potassium channel blocking agents charybdotoxin (ChTX), tetraethylammonium (TEA), gliquidone (GLI), ammonium chloride (NH(4)(+)) and of the anoressants amphetamine (AMPH) and nicotine (NIC). After i.c.v. administration, an approximate ranking order of potency was: ChTX> or =AMPH>NIC=TEA> or =GLI> or =MET>BZ>NH(4)(+). 2. Clorgyline (2.5 mg kg(-1) i.p.) or deprenyl (10 mg kg(-1) i.p.) potentiated the anorectic effect of i.c.v.-administered BZ, NIC and AMPH. The effect of TEA was increased only by deprenyl, while MET, NH(4)(+), ChTX and GLI were not affected by either of the inhibitors. 3. The Bz-SSAO inhibitors alpha-aminoguanidine (50 mg kg(-1) i.p.), B24 (100 mg kg(-1) i.p.) and MDL 72274 (2.5 mg kg(-1) i.p.) potentiated the effect of i.p., but not of i.c.v.-administered MET. 4. Antisense oligodeoxyribonucleotides (aODN) to Kv1.1 potassium channels abolished the effect of BZ and TEA, but was ineffective in reducing the activity of MET and other compounds. 5. These results suggest that MET is endowed with peculiar hypophagic effects at dosage levels that are not able to affect gross behaviour in mice. The effect of MET, differently from BZ, seems unrelated to an increase in the central release of monoaminergic mediators, as well as to a Kv1.1 blocking activity. Through a reduction of the endogenous breakdown of MET, Bz-SSAO inhibitors enhance the central pharmacological activity of this amine.

Amine metabolism: a novel path to coronary artery vasospasm

We hypothesized that allylamine (AA) induces subendocardial necrosis in mammals via coronary artery (CA) vasospasm. Additionally, AA toxicity is likely dependent on the enzyme semicarbazide-sensitive amine oxidase (SSAO), which is highly expressed in the aorta of rats and humans. We tested whether AA or acrolein (1, 10, 100, and 1000 microM), a highly reactive product of AA metabolism by SSAO, could contract CA or thoracic aorta (TA) in vitro and if the AA effects involved SSAO. AA or acrolein produced a similar pattern of responses in both CA and TA rings at 100 and 1000 microM, including (1) increased basal tension, (2) enhanced agonist-induced contraction (hypercontractility or vasospasm), (3) remarkable, agonist-induced slow wave vasomotion (vasospasm), and (4) irreversible reduction in vessel contractility after 1 mM exposure. Endothelium-dependent acetylcholine-induced relaxation was not altered during vasospasm in either vessel. Pretreatment with the SSAO inhibitor semicarbazide (1 mM; 10 min) prevented or significantly reduced the majority of AA's effects in both CA and TA rings and inhibited 100% of the SSAO activity present in rat TA and human CA and TA. We propose a two-step model for AA induction of CA vasospasm and resultant myocardial necrosis: (1) metabolism of AA to acrolein by coronary arterial SSAO activity and (2) acrolein induction of CA vasospasm independent of endothelial injury-a novel path.

Formaldehyde promotes and inhibits the proliferation of cultured tumour and endothelial cells

Formaldehyde was applied in various doses (0.1-10.0 mM) to HT-29 human colon carcinoma and HUV-EC-C human endothelial cell cultures. Cell number, apoptotic and mitotic index as well as proportion of cells in S-phase was investigated by morphological methods and flow cytometry. Ten mM of formaldehyde caused high degree of cell damage and practically eradicated the cell cultures. One mM of formaldehyde enhanced apoptosis and reduced mitosis in both types of cell cultures, in a moderate manner. The low dose (0.1 mM) enhanced cell proliferation and decreased apoptotic activity of the cultured cells, the tumour cells appeared to be more sensitive. The possible role of this dose-dependent effect of formaldehyde in various pathological conditions, such as carcinogenesis and atherogenesis is discussed with emphasis on the eventual interaction between formaldehyde and hydrogen peroxide.