STI571 (Glivec) affects histamine release and intracellular pH after alkalinisation in HMC-1560, 816

The human mast cell line (HMC-1(560, 816)) was used to study the effect of the tyrosine kinase inhibitor STI571 (Glivec) on exocytosis, intracellular Ca(2+) and pH changes, because STI571 inhibits the proliferation of HMC-1(560) and induces its apoptosis. This drug does not have these effects on HMC-1(560, 816). Exocytosis in HMC-1(560, 816) cells can be stimulated by alkalinisation with NH(4)Cl as well as with ionomycin. Surprisingly 24-h pre-incubation with STI571 decreases spontaneous histamine release of HMC-1(560, 816) cells, but increases the histamine response after alkalinisation and not after ionomycin-stimulation. After addition of NH(4)Cl, pH(i) has a higher increase in STI571 pre-incubated cells, without changing intracellular Ca(2+) concentration. Activation of PKC in combination with tyrosine kinase inhibition increases also histamine release in HMC-1(560, 816) cells. Strangely, STI571 pre-incubated cells with PKC inhibited by rottlerin show the same effects. In these cells, cytosolic pH increases more than in control cells. This is the first report of STI571 effect in HMC-1(560, 816) cells. It seems that different pathways modulate signals for proliferation and exocytosis. STI571 does not only inhibit KIT TyrK, but may also influence cytosolic pH after alkalinisation in both cell lines, HMC-1(560) and HMC-1(560, 816), and this ends in induced histamine release. This work is important since HMC-1(560, 816) cells are reported in 80% of aggressive systemic mastocytosis cases and the understanding of some signalling pathways involved in mast cell response could facilitate drug targeting.

Sodium Bicarbonate Enhances Membrane-bound and Soluble Human Semicarbazide-sensitive Amine Oxidase Activity In Vitro

Semicarbazide-sensitive amine oxidase (SSAO) is a multifunctional enzyme with different biological roles that depend on the tissue where it is expressed. Because SSAO activity is altered in several pathological conditions, we were interested in studying the possible regulation of the human enzyme activity. It has been previously reported that SSAO activity is increased in the presence of Dulbecco's modified Eagle medium (DMEM) in vitro. The aim of the present work was to investigate the effects of the different constituents of DMEM on human SSAO activity. We found that sodium bicarbonate was the only component able to mimic the enhancement of both human aorta and plasma SSAO activity in vitro, suggesting a possible physiological role of bicarbonate as an intrinsic modulator of the human enzyme. Failure to take this activating effect into account could also result in inaccuracies in the reported tissue activities of this enzyme.

Studies on the insulinomimetic effects of benzylamine, exogenous substrate of semicarbazide-sensitive amine oxidase enzyme in streptozotocin induced diabetic rats

Semicarbazide-sensitive amine oxidase/vascular adhesion protein-1 (SSAO) is believed to be a bifunctional membrane protein. It is localized extracellularly and preferentially oxidizes short chain primary amines to aldehydes, hydrogen peroxide and ammonia, but also functions as an adhesion molecule, which is involved in leukocyte migration. Serum SSAO activity is increased in diabetic patients and animals and the aldehydes formed in the enzyme reaction may contribute to vascular damage. However, administration of exogenous substrates has been shown to improve glucose tolerance and reduce hyperglycaemia in diabetic animals. Hydrogen peroxide and/or its vanadate complexes have been suggested responsible for these effects. Streptozotocin induced diabetic rats were treated with benzylamine (BZA) +/- vanadate (V) or insulin. In contrast to insulin, BZA + V treatment did not reduce HbA(1C) levels. However, it reduced the elevated serum SSAO activity, decreased the accumulation of advanced-glycation end products and increased the bioavailability of nitric oxide in diabetic animals, similarly to insulin. BZA alone did not affect any of these parameters.

Hydrazine and amphetamine binding to amine oxidases: old drugs with new prospects

Tranylcypromine (TCP), an amphetamine, is a reversible inhibitor of copper-containing amine oxidases. We have solved the structure of the complex of TCP with the amine oxidase from E. coli (ECAO) and shown that only the (+)-enantiomer of TCP binds. Kinetic studies on 2-phenylethylamine and TCP binding to wild-type ECAO and mutational variants fully support the model in which binding of the protonated amine is the first step in the catalytic cycle. Hydrazines are irreversible inhibitors of copper-containing amine oxidases. Binding of hydrazines leads to an adduct ("Adduct 1") with a chromophore at 430 nm which converts at higher pH to another adduct ("Adduct 2") with a chromophore at 520 nm. We have determined the structures of Adduct 1 and 2 for 2-hydrazinopyridine reacted with ECAO. It has been found that Adduct 1 corresponds to the hydrazone and azo tautomers whilst Adduct 2 corresponds to the azo tautomer coordinated to the active site copper. The implications of these results in developing more specific drugs are discussed.

Hydrogen peroxide derived from amine oxidation mediates the interaction between aminosugars and semicarbazide-sensitive amine oxidase

Semicarbazide-sensitive amine oxidase (SSAO) also functions as a vascular-adhesion protein (VAP-1). The nature of the target site on lymphocytes to which endothelial-cell SSAO/VAP-1 binds is unknown. We have shown that amino sugars (galactosamine, glucosamine and mannosamine), which are not SSAO substrates, can bind to the enzyme as reversible inhibitors. Thus, they serve as a model system in which to study the interaction process. Binding occurred during substrate (benzylamine) oxidation but not when the amino sugar was incubated, for extended periods, with SSAO alone. These results suggest that one, or more of the products of the SSAO-catalysed amine oxidation might be necessary for the inhibitory process to occur. Two of the reaction products of benzylamine oxidation, benzaldehyde and ammonia were found to have no effect on the inhibition of SSAO by galactosamine. Preincubation of the enzyme with galactosamine plus H(2)O(2) was, however, found to result in time-dependent inhibition. This is not a result of the non-enzymic reaction between H(2)O(2) and the amino sugar, since preincubation of galactosamine with H(2)O(2) alone, for extended periods, did not give rise to an inhibitory species. The amount of exogenously added H(2)O(2) necessary for inhibition was very much greater than that formed during substrate oxidation. These results suggest that the H(2)O(2) formed as a product of the SSAO-catalysed oxidation reaction is more efective in promoting the binding of amino sugars.

The effects of buffer cations on interactions between mammalian copper-containing amine oxidases and their substrates

We and others have observed that substrates for copper-containing amine oxidases cause substrate inhibition at high concentrations. Through use of a novel "pseudoquantitative" rapid equilibrium approach, kinetic analyses with human and bovine enzymes indicate that these effects are consistent with substrates binding to oxidised and reduced enzyme forms. Small cations compete with binding of substrates to oxidised and reduced enzyme, influencing both substrate turnover and substrate inhibition patterns. Cations reduce affinity of the resting bovine enzyme for spermidine, but not benzylamine, indicating that the predominant effect of cations on substrate oxidation results from binding to an anionic site outside the active site. However, binding of cations to the active site of the reduced form of both enzymes attenuates substrate inhibition with both spermidine and benzylamine. Our observations have significant practical implications for researchers assaying kinetic behaviour of these enzymes, and particularly those developing novel inhibitors of human copper-containing amine oxidases.

L-lysine as a recognition molecule for the VAP-1 function of SSAO

Semicarbazide-sensitive amine oxidase (EC 1.4.3.6) acts as a vascular-adhesion protein (VAP-1), mediating the adhesion of lymphocytes to vascular endothelial cells under inflammatory conditions. The relationship between the adhesive and the enzymatic functions of SSAO have not yet been fully defined. Previous studies from this laboratory showed aminohexoses, which were neither substrates nor direct inhibitors of SSAO, bound to the enzyme as reversible inhibitors in the presence of H(2)O(2) generated during substrate oxidation. The possibility that surface L-lysine could act similarly has been investigated in the present study. The presence of L-lysine during the oxidation of benzylamine resulted in time- and dose-dependent inhibition of SSAO activity, in a process that was dependent on the H(2)O(2) formed during benzylamine oxidation. The possible implications of this in terms of the therapeutic uses of lysine are discussed.

Decreased serum activity of semicarbazide-sensitive amine oxidase (SSAO) in patients treated with second generation antipsychotics: a link to impaired glucose metabolism?

OBJECTIVE

Although the treatment of schizophrenia with many second generation antipsychotics is known to be associated with metabolic changes, such as hyperglycemia or hypercholesterolemia, the underlying mechanisms of these adverse reactions remain unclear. In light of the recent focus on the involvement of semicarbazide-sensitive amine oxidase (SSAO) in glucose metabolism, we investigated SSAO serum activity in schizophrenic patients treated with antipsychotics with the objective of determining a possible link between SSAO and impaired glucose metabolism.

METHODS

Blood samples were drawn from 44 schizophrenic patients (24 receiving second generation antipsychotics known to disturb glucose metabolism) on day 1 and day 5 of inpatient treatment. Forty-one healthy adults with no medical condition known to influence SSAO served as controls.

RESULTS

Of the 44 schizophrenic patients, the 24 treated with second generation antipsychotics known to disturb glucose metabolism showed significantly lower SSAO serum activity [day 1 (mean +/- SD): 477 +/- 105 mU/L; day 5: 438 +/- 86 mU/L] than the 20 patients treated with other antipsychotics not known to influence glucose metabolism (day 1: 513 +/- 124 mU/L, p = 0.359; day 5: 542 +/- 204 mU/L, p = 0.021) only after 5 days of treatment and compared to healthy controls (526 +/- 142 mU/L, p = 0.021). No differences were observed between schizophrenic patients treated with first generation antipsychotics and the controls.

CONCLUSION

We found decreased SSAO serum activity exclusively in schizophrenic patients treated with second generation antipsychotics known to disturb glucose metabolism. In terms of the role of SSAO in glucose metabolism, the observed decrease in SSAO serum activity may be linked to metabolic changes that are known to occur in schizophrenic patients being treated with many second generation antipsychotics.

Polyamines promote root elongation and growth by increasing root cell division in regenerated Virginia pine (Pinus virginiana Mill.) plantlets

Polyamines have been demonstrated to play an important role in adventitious root formation and development in plants. Here, we present a detailed analysis of influence of exogenously added polyamines on adventitious root development and its relationship to cold tolerance in Virginia pine (Pinus virginia Mill.). Our results demonstrated that polyamines putrescine (Put), spermidine (Spd), and spermine (Spm) at 0.001 mM improve rooting frequency and promote root elongation. Put, Spd, and Spm at 0.01-1 mM decrease rooting frequency and reduce root elongation root elongation. Measurements of diamine oxidase (DAO, EC 1.4.3.6) and polyamine oxidase (PAO, EC 1.4.3.4) activities showed that higher DAO and PAO enzyme activities were obtained when high concentrations of polyamines were applied and when plantlets were treated for 5-7 week at 4 degrees C and 16 degrees C. Survival rate of plantlets increased with the treatment of polyamines at low temperature. Polyamines increased mitotic index of cells in root tips of regenerated plantlet cultured on medium containing 0.001 microM Put, Spd, or Spm, but did not increase mitotic index in tissues of needle tips of the same plantlets. These results demonstrated that polyamines promote root elongation and growth by increasing root cell division in regenerated Virginia pine plantlets.

A copper chelating agent suppresses carbonyl stress in diabetic rat lenses

To clarify whether transition metals are involved in carbonyl stress in diabetic tissues, we observed the effects of a metal chelating agent, trientine (TE) hydrochloride on the levels of methylglyoxal (MG), 3-deoxyglucosone (3-DG), advanced glycation end products, 8-hydroxy-2'-deoxyguanosine (8-OHdG), and polyol pathway metabolites along with semicarbazide-sensitive amine oxidase (SSAO) enzyme activity in lenses from streptozotocin-induced diabetic rats. Lens MG and 3-DG levels were significantly higher in diabetic rats than nondiabetic controls, and TE significantly restored the increase of these compounds. Lens argpyrimidine was also increased in diabetic rats as compared with controls and was significantly reduced by TE. Lens SSAO activity and 8-OHdG were also significantly elevated in diabetic rats, and TE suppressed both of them, whereas TE showed no effect on the polyol pathway metabolites. The results indicate that transition metals play a significant role in the formation of MG and 3-DG via oxidative stress and SSAO activity.

Exploring the binding mode of semicarbazide-sensitive amine oxidase/VAP-1: identification of novel substrates with insulin-like activity

We previously reported that substrates of semicarbazide-sensitive amine oxidase in combination with low concentrations of vanadate exert potent insulin-like effects. Here we performed homology modeling of the catalytic domain of mouse SSAO/VAP-1 and searched through chemical databases to identify novel SSAO substrates. The modeling of the catalytic domain revealed that aromatic residues Tyr384, Phe389, and Tyr394 define a pocket of stable size that may participate in the binding of apolar substrates. We identified a number of amines as substrates of human, rat, and mouse SSAO. The compounds PD0119035, 2,3-dimethoxy-benzylamine, and C-naphthalen-1-yl-methylamine showed high affinity as substrates of rat SSAO. C-Naphthalen-1-yl-methylamine was the only substrate that showed high affinity for human SSAO. C-Naphthalen-1-yl-methylamine and 4-aminomethyl-benzenesulfonamide showed the highest capacity to stimulate glucose transport in isolated rat adipocytes. The impact of these findings on the development of new treatments for diabetes is discussed.

Semicarbazide-sensitive amine oxidase and extracellular matrix deposition by smooth-muscle cells

We have recently reported in vivo disruption of collagen and elastin architecture within blood vessel walls resulting from the selective inhibition of the enzyme semicarbazide-sensitive amine oxidase (SSAO). This study further investigates the effects of SSAO inhibition on extracellular matrix deposition by smooth-muscle cells (SMCs) cultured from neonatal rat hearts. SMCs were characterized, SSAO activity was measured, and soluble and insoluble collagen and elastin in the extracellular matrix (ECM) were quantified. Cultured neonatal rat heart SMC exhibited a monotypic synthetic phenotype that likely represents a myofibroblast. Detectable levels of SSAO activity present throughout 30-d culture peaked at 7-14 d, coinciding with the production of ECM. The addition of enzyme inhibitors and alternate SSAO substrates (benzylamine) produced varied and, in some cases, marked changes in SSAO activity as well as in the composition of mature and soluble matrix components. Similar to our previous in vivo findings, in vitro SSAO inhibition produced aberrations in collagen and elastin deposition by heart SMC. Because changes in SSAO activity are associated with cardiovascular pathologic states, this enzyme may play a protective or modulating role by regulating ECM production during pathologic insult.

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.

Inhibition of monoamine oxidase modulates the behaviour of semicarbazide-sensitive amine oxidase (SSAO)

The specific activity and kinetic behaviour of semicarbazide-sensitive amine oxidase (EC 1.4.3.6; SSAO) towards benzylamine, in the rat heart, is affected by in vivo treatment with the non-selective monoamine oxidase (MAO) inhibitor tranylcypromine, but not by the selective MAO-A and -B inhibitors, clorgyline and lazabemide. SSAO activity was increased to 178% of control activity after 7 days of treatment with tranylcypromine. This increase appears to represent an increase in the limiting velocity (V(max)) for benzylamine oxidation with no significant change in the K(m) at that time-point. However, the K(m) for benzylamine oxidation was found to decrease in both controls and treated groups, in a time-dependent manner, during the treatment regime. These findings suggest a link between SSAO and cellular stress and may have importance in the context of the recent finding that tissue-SSAO is identical to a vascular adhesion protein (VAP1), involved in the process of inflammation.

Inhibition of monkey brain semicarbazide-sensitive amine oxidase by various antidepressants

We examined whether the antidepressant drugs, such as the dicyclic drug zimeldine, the tricyclic drug imipramine, tetracyclic drug maprotiline, and the non-cyclic drug nomifensine, inhibit in vitro semicarbazide-sensitive amine oxidase (SSAO) activity in monkey brain. The deamination of 1 microM benzylamine was not inhibited at high concentrations of clorgyline or deprenyl, while it was highly sensitive for semicarbazide. When corresponding experiments were performed with 100 microM benzylamine, the opposite results were obtained. The most potent of inhibition of SSAO was observed by imipramine, followed by maprotiline, zimeldine and nomifensine. Inhibition of SSAO was not enhanced by varying the time of preincubation of the enzyme and various antidepressant drugs, indicating direct action on and reversible inhibition of SSAO. We found the tricyclic antidepressant drug to be the most selective inhibitors of SSAO activity in monkey brain, as compared with other type of antidepressant drugs.

Effects of acute ethanol exposure on polyamine and gamma-aminobutyric acid metabolism in the regenerating liver

Recently, it has been suggested that ethanol-induced inhibition of liver regeneration results from decreases in hepatic putrescine levels and/or increases in hepatic gamma-aminobutyric acid (GABA)ergic activity. Because putrescine can be metabolized by diamine (DAO) and monoamine (MAO) oxidases to GABA, we documented the effects of acute ethanol exposure on hepatic MAO or DAO activity following partial hepatectomy (PHx) in rats. We also documented the effects of ethanol on GABA transaminase (GABA-T), the enzyme responsible for GABA metabolism in the liver, and tissue putrescine and GABA levels. Adult, male Sprague-Dawley rats (200-250 g) were treated with either ethanol (3 g/kg) or equal volumes of saline by gastric gavage 1 h prior to a 70% PHx or sham surgery. Rats were then sacrificed (n = 5-7/group) at various times (0-72 h) post-PHx. Enzymatic activity and putrescine/GABA levels were determined by standard isotopic techniques and high-performance liquid chromatography respectively. Hepatic DAO activities in ethanol-treated rats were transiently higher than in saline-treated controls (30% increases at 6 h, p < 0.05). Hepatic MAO and GABA-T activities in acute ethanol-treated rats were essentially identical to saline-treated controls. Although hepatic putrescine levels were similar in ethanol- and saline-treated rats, hepatic GABA levels were approximately three times higher in ethanol-treated rats at 12 and 24 h post-PHx (p < 0.0001). In conclusion, the results of this study indicate that acute ethanol exposure has a limited effect on the enzymatic conversion of putrescine to GABA following partial hepatectomy in the liver. The results also indicate that increased GABAergic inhibition rather than decreased putrescine stimulation is more likely to play a role in ethanol-induced inhibition of hepatic regeneration.

Probing the "active site" of diamine oxidase: structure-activity relations for histamine potentiation by O-alkylhydroxylamines on colonic epithelium

The responses of the canine colonic epithelium to histamine are potentiated by O-alkylhydroxylamines. A study of a series of such compounds suggested that active compounds had the structure R-O-NH2, substitution of a nitrogen led to total loss of activity. The locus of the potentiation effect was traced to the inhibition of diamine oxidase. A new series of aliphatic and aromatic O-alkylhydroxylamines were synthesized to explore further the structure-activity relations of this effect. The potentiating effects of these compounds were determined by examining the changes in short circuit current (Isc) produced by histamine and from the activity of a soluble preparation of diamine oxidase. We found that 1) branched compounds are less active than their straight chain counterparts, 2) greater steric bulk of the aliphatic substituent decreased activity, 3) the presence of a double bond had no significant effect though a triple bond reduced activity, 4) longer straight chain compounds were less active than the shorter chain derivatives and 5) all benzylic compounds were less active than the straight chain aliphatics. O-1-benzyl was inactive however the meta or para oxygen substituted compounds as well as the O-(1-E-Cinnamyl) derivative were active. A current model for the action of diamine oxidase proposes a crucial role for a trihydroxyphenylalanine quinone cofactor as part of the active site together with a copper atom. Using molecular modeling based on our inhibition data we are able to define the region of space that is just beyond the reactive carbonyl of the trihydroxyphenylalanine residue at the active site of diamine oxidase. We suggest that a negatively charged species, such as an aspartate or a glutamate, resides in a trough about 7 to 8 A from the trihydroxyphenylalanine carbonyl carbon and this species aids in the strong selective binding of substrates such as putrescine and histamine.

Studies on the behaviour of semicarbazide-sensitive amine oxidase in Sprague-Dawley rats treated with the monoamine oxidase inhibitor tranylcypromine

The possibility that increased levels of the activity of the semicarbazide-sensitive amine oxidase (SSAO) might, to some extent, compensate for the loss of monoamine oxidase (MAO) activity in the atypical form of Norrie Disease, was examined using the rat as a model. Long-term treatment with the MAO inhibitor tranylcypromine (1 mg/kg/day) resulted in sustained inhibition of MAO-A and MAO-B activities in liver and brain. After one week, the SSAO activity in heart had increased by 79% above the control levels. This increase was maintained for 3 weeks. Since such alterations might result from enzyme induction, the turnover of the enzyme was studied in cultured cells from rat aortic smooth muscle. The time-course of recovery of enzyme activity following irreversible inhibition by MDL 72145 corresponded to a half-life of approximately 6 days for this process.

Involvement of polyamines in the contragestational effect of hyperthermia

Although hyperthermia produces teratogenic effects in a great variety of animal species, the molecular mechanisms by which hyperthermia exerts its action remain unknown. We have studied the implications of polyamines in contragestational hyperthermia in rats. Our results show that the contragestational action of hyperthermia when applied in consecutive periods during days 8, 9 and 10 of rat pregnancy could be completely prevented by the previous administration of polyamines (putrescine and spermidine, 0.6 mmoles/kg and 0.03 mmoles/kg respectively) in combination with the diamine oxidase inhibitor aminoguanidine or by this inhibitor alone (0.12 mmoles/kg). The administration of polyamines alone partially prevented the fetotoxic effect of hyperthermia but produced a marked mortality (50%) in the pregnant rats. These findings support a major and complex role of polyamines in the mechanisms of hyperthermia-mediated teratogenesis, and suggest that the oxidative catabolism of polyamines could be in part responsible of the deleterious effect produced by hyperthermia in rat pregnancy.

Epidermal growth factor enhances repair of rat intestinal mucosa damaged by oral administration of methotrexate

To examine the trophic effect of epidermal growth factor on the rat small intestine, we measured diamine oxidase and ornithine decarboxylase activities in intestinal mucosa injured by methotrexate. Methotrexate was infused orally via a gastric tube at a dose of 10 mg/kg per day on 3 successive days (days 1-3). Epidermal growth factor was injected intraperitoneally at a dose of 40 micrograms/kg per day on 4 successive days following methotrexate infusion (days 4-7). Methotrexate caused a marked decrease in diamine oxidase activity; this decrease returned to a normal level on day 13 in controls. In rats injected with epidermal growth factor, diamine oxidase activity began to recover earlier than in the controls, and returned to a normal level on day 11. Epidermal growth factor enhanced the increase of ornithine decarboxylase activity in mucosa injured by methotrexate. When the increase of ornithine decarboxylase activity was suppressed by alpha-difluoromethylornithine, epidermal growth factor failed to facilitate the repair of intestinal mucosa. These results indicate that epidermal growth factor enhances intestinal repair following methotrexate infusion, and that this effect is mediated, at least in part, by ornithine decarboxylase. It is proposed that epidermal growth factor can be used clinically as a means to enhance mucosal repair of the intestine after chemotherapy with methotrexate.

[Plasma activity of diamine oxidase after heparin in patients with diabetic enteropathy]

Diamine oxidase (DAO) is an enzyme found almost exclusively in the enterocyte of the villous tips. In the basal state plasma DAO activity is low but increases significantly after i.v. injection of heparin. It is well recognised that postheparin plasma activity of DAO reflects clearly the integrity of the small bowel mucosa. The aim of this study was to investigate postheparin plasma DAO activity in diabetics with enteropathy. The study was carried out in a group of 72 individuals subdivided into five groups. Group I consisting of 16 patients with type 1 diabetes, group II--20 patients with type 2 diabetes, group III--8 patients with newly diagnosed type 1 diabetes, group IV--8 diabetics with enteropathy and group V--the control group. Blood samples were taken at the time 0' and at 60' and 120' intervals following i.v. injection of heparin. DAO activity was assessed by RIA methods. Basal values of DAO were nearly the same in all of the subjects (< 50 pmol/min/ml). After injection of heparin a very high DAO activity was observed in all groups (> 400 pmol/min/ml) except group IV (< 270 pmol/min/ml) (p < 0.001). There were no significant differences between the groups according to the type of diabetes, its duration and the methods of treatment. In conclusion, the postheparin plasma DAO activity in diabetics with enteropathy was very low, but of itself, diabetes and its treatments had no effect on the results under investigation.

Diamine oxidase in relation to diamine and polyamine metabolism

Diamine oxidase catalyzes the oxidative deamination of short chain aliphatic diamines, like putrescine, and histamine. The enzyme is rate-limiting in the terminal catabolism of polyamines, which are endogenous polycations important for cell growth and differentiation. This review examines the behavior of diamine oxidase in mammalian tissues in relation to diamine and polyamine metabolism under physiological and pathological conditions. The role of diamine oxidase in the control of putrescine levels in growing tissues and the known mechanisms responsible for the enzyme expression are also described.

Gentamicin nephrotoxicity in rat: some biochemical correlates

The present work examines the effect of treatment of rats with graded doses of the aminoglycoside antibiotic gentamicin on the concentration of reduced glutathione (GSH) and diamine oxidase (DAO) activity in the kidney, and DAO activity, creatinine and magnesium (Mg) in the plasma. The animals were given the antibiotic intramuscularly in doses of 20, 40, and 80 mg/kg/day for 6 days, and were killed 24 hr after the last injection. In another experiment rats were injected intramuscularly with gentamicin at a dose of 80 mg/kg/day for 6 days and were killed 1, 7 or 14 days after the last injection, and the above parameters were measured. Gentamicin reduced the body weights of rats in a dose-dependent manner. The weight reductions were most marked on days 4, 5 and 6 of the treatment. The body weights gradually recovered on withdrawing of the drug, and by day 14, they were not significantly different from those of the controls. Gentamicin produced significant and dose-dependent decreases in the renal concentration of GSH. Seven and 14 days after withdrawing the drug, the GSH concentrations were still significantly below that of the controls. Plasma Mg concentrations were significantly decreased, and plasma creatinine concentrations significantly increased by gentamicin. These effects persisted 7 and 14 days after cessation of treatment. Plasma DAO activity was not detectable in the control or gentamicin-treated rats. In the renal cortex, the activity of the enzyme, measured 1, 7 and 14 days after the treatment, was not significantly different from that of the control. Histopathologically, the drug produced dose-dependent proximal renal tubular necrosis.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparative study of the effects of the diamine oxidase inhibitor aminoguanidine, with or without dietary restriction, on the nucleic acid and protein composition of cardiac and type I and type II skeletal muscles of the rat

It has been proposed that the diamine oxidase inhibitor aminoguanidine may be a potential therapeutically important anabolic agent. An investigation was therefore made into the effects of aminoguanidine treatment with or without nutritional restriction, on cardiac and skeletal muscles containing mainly of either Type I (i.e. soleus) or Type II fibres (i.e. plantaris) or a mixture of Type I and II fibres (i.e. gastrocnemius). After 3 weeks, dietary restrictions reduced cardiac weight, protein, RNA and DNA contents by between 31 per cent and 36 per cent. Similar, but smaller, reductions were observed in the soleus (18-31 per cent), plantaris (22-34 per cent) and gastrocnemius (22-34 per cent). Aminoguanidine had no effect on the heart of the rats fed ad libitum, nor did it alter the response to dietary restriction. Treatment with aminoguanidine had no overt anabolic effect on skeletal muscle, but a reduction in DNA content was observed. It was concluded that cardiac protein and nucleic acid contents are more sensitive to dietary deprivation than either anaerobic or aerobic skeletal muscles. Furthermore, aminoguanidine does not appear to promote growth or reduce catabolism as previous studies have suggested.