R. Pirisino

Semicarbazide-sensitive amine oxidase activity (SSAO) of rat epididymal white adipose tissue

An amine oxidase activity distinguishable from MAO, which is inhibited by carbonyl reagents is present in rat epididymal WAT. This enzyme, referred to as semicarbazide-sensitive amine oxidase (SSAO), appears concentrated in adipose cells. Close homologies between WAT SSAO and the circulating plasma BAO are discussed.

Sulfhydryl groups and peroxidase-like activity of albumin as scavenger of organic peroxides

The concentration, the reactivity of sulfhydryl (SH) groups and the peroxidase-like activity (PLA) of bovine serum albumin (BSA) have been determined in vitro after treatment with peroxides. Tert-butylhydroperoxide (tBOOH), cumene hydroperoxide (CuOOH), benzoyl hydroperoxide (BOOH) and hydrogen peroxide reacted with BSA, decreasing the titratable SH group concentration and increasing the value of the ratio between the reaction rate and the concentration of albumin SH groups in the sulfhydryl-disulfide exchange reaction. This value was defined as reaction constant (Kr). PLA of albumin was independent of the presence of the SH group, as SH depleted BSA maintained the same activity as the control. From our findings it derives that albumin may have two possibilities of scavenging peroxides: PLA and the SH group. The plasma SH concentration, Kr and PLA of albumin were also determined in carrageenan paw edema and in experimental adjuvant-arthritis in rats. A decrease in SH concentration, an increase in Kr and PLA of rat plasma albumin were observed in both inflammatory processes.

Skin Wound Healing: Some Biochemical Parameters in Guinea‐pig

Abstract— Hairs were removed from the dorsal skin of guinea‐pigs and 5–6 wounds (7 × 7 mm) were surgically induced by totally removing the epidermal and part of the dermal surface. They were then allowed to heal. The newly formed wound tissues were dissected at different times during the process and analysed by biochemical and histological methods. Hydroxyproline, proteins, DNA and semicarbazide‐sensitive amine oxidase (SSAO) were measured, as were [14C]leucine and [3H]thymidine incorporation in some samples. The peroxidase‐like activity of plasma albumin and the histology of wounds stained with haematoxylin‐eosin were also studied. It was shown that SSAO enzymes, which are present in normal guinea‐pig skin and have a high affinity for benzylamine are localized in fibroblasts. During skin healing in the newly formed tissue there was an increase in protein content which reached a maximum after 4–6 days; DNA content also increased. The rate of incorporation of [3H]thymidine and [14C]leucine paralleled DNA and protein content, respectively. The content of hydroxyproline had greatly decreased with respect to that in normal skin after 2–10 days. SSAO activity increased much less than DNA after 4 days whereas after 10–11 days it increased more than DNA, thus indicating that at this time it was probably produced by fibroblasts. No significant increase in the peroxidase‐like activity of albumin was observed 4, 8 or 11 days after surgery. Treatment of the animals with methylprednisolone acetate (20 mg kg−1, i.m.) two days before surgery decreased the rate of skin healing but did not alter the level of albumin peroxidase activity of the plasma. Histology showed that in the animals treated with this drug the re‐epithelialization was slower and after 11 days the wound appeared similar in appearance to the 8‐day control wounds. In the methylprednisolone‐treated animals a positive correlation was observed between the DNA content of regenerating tissue and the hydroxyproline content, whereas a negative correlation was observed in the control wounds. This correlation was in full agreement with the histological observation which showed an increased amount of cytogen collagen in the wounds of the treated animals. The simultaneous study of the biochemical parameters (DNA, proteins, SSAO, hydroxyproline) appears to be a good method for differentiating the pharmacological effects on the different cells which are responsible for wound healing.

Isolation and pharmacological activities of the Tecoma stans alkaloids

Tecoma stans is a plant traditionally used in Mexico for the control of diabetes. Amongst the alkaloids isolated from the plant harvested in Egypt, Tecomine was shown to be one of the compounds responsible for the hypoglycemic action. Given the interest in substances able to treat type II diabetes, we isolated the main alkaloids present in the plant growing in Egypt and Brazil and tested them in vivo on db/db mice. Contrary to previous literature reports on different animal models, Tecomine was unable to modify glycemia; the only effect seen being a decrease in plasma cholesterol levels. On the contrary, when tested in vitro on glucose uptake in white adipocytes, the compound showed a marked effect. The two other alkaloids isolated, namely 5beta-Hydroxyskitanthine, early called Base C, and Boschniakine were inactive both in vivo and in vitro assays.

Histamine lipolytic activity and semicarbazide-sensitive amine oxidase (SSAO) of rat white adipose tissue (WAT)

Histamine has previously been described as a possible substrate for the semicarbazide-sensitive amine oxidase activity (SSAO) of rat white adipose tissue (WAT). We report here on a histamine function in this tissue which concerns the activity of this deaminating system distinct from the classical diamine oxidase. Our results show that: (1) histamine plays a role in controlling rat adipose tissue lipolysis with the contribution of H1 and H2 receptors that participate in histamine lipolysis in an opposite way. Both H1 and H2 roles can be differentiated using selective agonists (2- and 4-methyl histamine) and antagonists (pyrilamine and cimetidine); (2) histamine might also control rat lipolysis induced by noradrenergic agonists; (3) the SSAO present in rat WAT controls histamine levels at the receptor sites as shown by the modification of histamine lipolytic potency obtained when inhibitors of this enzyme are used.

Further studies on semicarbazide-sensitive amine oxidase activities (SSAO) of white adipose tissue

1. White adipose tissue (WAT) from mice, rabbits, pigs and human subjects was investigated for the characterization of the tissue-bound semicarbazide-sensitive benzylamine oxidase activities (SSAO) present in each species. 2. Enzymes from mice, rabbits and pigs shared similar biochemical characteristics: they exerted histaminase activity, oxidized methylamine and acetylputrescine and were completely blocked by carbonyl reagents and by 3,5-ethoxy-4-aminomethylpyridyne (B24), in a dose-dependent fashion. 3. SSAO activity from human WAT had a lower affinity for benzylamine compared with enzymes in the other species and did not show any histaminase activity. 4. These results show that SSAO from human tissues might have different properties from SSAO of other species.

Cultured preadipocytes produce a semicarbazide-sensitive amine oxidase (SSAO) activity*

The presence of an amine oxidase activity which is resistant to pargyline, an acetylenic MAO inhibitor, but sensitive to semicarbazide, is described in rat white and brown preadipocytes.

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

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 (NH4+) and of the anoressants amphetamine (AMPH) and nicotine (NIC). After i.c.v. administration, an approximate ranking order of potency was: ChTXAMPH>NIC=TEAGLIMET>BZ>NH4+. 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, NH4+, ChTX and GLI were not affected by either of the inhibitors. The Bz‐SSAO inhibitors α‐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. 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. 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.

Hydrogen peroxide generation by monoamine oxidases in rat white adipocytes: role on cAMP production.

In rat, white adipocytes monoamine oxidases (EC 1.4.3.4.) generate hydrogen peroxide (H(2)O(2)). Recent studies suggested that, in addition to its toxic features, H(2)O(2) may behave as a cell second messenger. In the present study, using fluorimetric and chemiluminescence (CL) assays, we showed that tyramine degradation by monoamine oxidases in intact adipocytes resulted in the concentration-dependent generation of H(2)O(2). In addition, we found that, in the presence of low tyramine concentrations, forskolin-dependent cAMP production was significantly increased as compared to that of the control and this increase was prevented by the monoamine oxidase inhibitor pargyline or by the H(2)O(2) trapping system homovanillic acid-peroxidase. Finally, we demonstrated that tyramine degradation by monoamine oxidases increased the ability of isoproterenol to induce cell lipolysis. Taken together, these data suggest that H(2)O(2) produced during substrate degradation by monoamine oxidases may participate in the regulation of adipocyte metabolism.

Histaminase activity in rat lung and its comparison with intestinal mucosal diamine oxidase

In rat lung microsomes, an enzyme showing high histaminase activity is present. The oxidation of histamine is dependent on the presence of two enzymic activities, both inhibited by alpha-aminoguanidine and by B24, an inhibitor of semicarbazide-sensitive amine oxidases (SSAO) which have benzylamine as preferential substrate. These enzymic activities differ in substrate specificity: one appears to be a classical tissue bound SSAO enzyme with high affinity for benzylamine, the other a diamine oxidase (DAO) with properties that are very different from the classical DAO. This latter enzyme is not inhibition by high histamine concentrations and is more active at pH 8.5 than at pH 7.4.