Endosulfine, an endogenous peptidic ligand for the sulfonylurea receptor: purification and partial characterization from ovine brain

Antidiabetic sulfonylureas act through receptors coupled to ATP-dependent potassium channels. Using the binding of [3H]glibenclamide, a highly potent sulfonylurea, to rat brain membranes to follow the purification procedure, we extracted from ovine brain, purified, and partially characterized two peptides that are endogenous ligands for the central nervous system sulfonylurea receptors. These peptides, referred to as alpha and beta endosulfine, differ by their isoelectric points, the beta form being more basic. Each form of endosulfine is recognized equally by the sulfonylurea receptors from the central nervous system and from insulin-secreting beta cells. In the same concentration range that is active on the receptors, beta endosulfine releases insulin from a beta-cell line. Endosulfine is a good candidate for being implicated in the physiology of beta cells and their disorders (e.g., type II diabetes) and in certain pathologies related to modifications of ion fluxes.

[Acute non-obstructive necrotizing enterocolitis in adults]

Acute non-obstructive necrotizing enterocolitis in adults is characterized by pathological features: it is an intestinal necrosis beginning in the mucosa, without obstruction of the mesenteric vessels. The disease occurs in a variety of circumstances which may be roughly divided into infections and fall in proximal or distal mesenteric flow rate, the infectious and circulatory mechanisms often coexisting. Little information on the diagnosis is provided by clinical and paraclinical data. Management is medical and/or surgical; it includes alleviation of the symptoms in intensive care unit, attempts at producing local vasodilation whenever possible and resection of the intestinal segment affected. In many cases the diagnosis is made at exploratory laparotomy. The prognosis is poor; it depends on the patient's age, on the extent of the lesions which sometimes require wide intestinal resections, and on the time to diagnosis.

Oxyntomodulin-like immunoreactivity: diurnal profile of a new potential enterogastrone

The biological specificity of oxyntomodulin toward the gastric mucosa results from its C-terminal octapeptide. A RIA using a specific antibody raised against this region permitted quantification of the whole set of proglucagon-derived peptides that interact with the oxyntomodulin recognition systems, corresponding to the new concept of oxyntomodulin-like-immunoreactivity (OLI). The present report describes the physiological 24-h OLI profile in human plasma (eight men and eight women; mean age, 45 yr; range, 20-77 yr). Blood was withdrawn every hour from 0700-1900 h and every 2 h from 2100-0500 h. A meal-dependent profile was found for circulating OLI, with basal values (60 +/- 7 ng/L) at 0500 h and rises elicited by each food intake. The highest value (136 +/- 21 ng/L) was obtained at 2100 h. Plasma concentrations and diurnal variations of OLI were similar to those of the other intestinal peptides known to exert an endocrine function. The mean circulating OLI values increased with age, whereas no change was noticed according to sex. The inhibitory effect exerted by the peptides of the OLI family on gastric acid secretion, the meal dependence of their plasma concentrations, and the observed synchronism of their diurnal profile with that previously described for somatostatin make them candidates for an enterogastrone action.

[Double heart valve replacement disclosing antiphospholipid syndrome]

In patients with systemic lupus erythematosus (SLE) heart valve lesions are usually discovered at echocardiography; their haemodynamic repercussions are uncommon, and valve replacement is exceptional. We report the case of a woman who had undergone aortic and mitral valve replacement before antiphospholipid antibodies were found associated with 4 ARA criteria of SLE. Histopathological examination confirmed the diagnosis of Libman-Sachs specific endocarditis. The presence of antiphospholipid antibodies leads to a discussion of their role in the physiopathology of the heart valve lesions and vascular accidents that occurred in this patient. The overlap observed between the diagnostic criteria of SLE and those of primary antiphospholipid syndrome is discussed. Heart valve lesions may be one of the modes of access to the antiphospholipid syndrome.

Characterization of binding sites for oxyntomodulin on a somatostatin-secreting cell line (RIN T3)

Oxyntomodulin (OXM), a glucagon-containing peptide extended at its C-terminal end by an octapeptide, is a potent inhibitor of gastric acid secretion in rat and man. OXM appears to act on gastric mucosa at least partially through a stimulation of gastric somatostatin release. We have investigated the effects of OXM on a somatostatin-secreting cell line (RIN T3) derived from a radiation-induced rat insulinoma and characterized specific binding sites for this peptide. OXM increased somatostatin release with an ED50 of 2.3 nM. OXM also stimulated the cAMP accumulation in intact RIN T3 cells and adenylate cyclase activity in RIN T3 cell membranes with ED50 values of 0.5 and 11 nM, respectively. On these parameters, glucagon was 10-30 times less potent than OXM. Forskolin, isobutylmethylxanthine, and 8-bromo-cAMP mimicked the effect of OXM on somatostatin release. Specific binding for mono-[125I]OXM was dependent upon time and membrane concentration. Binding of mono-[125I]OXM was inhibited by OXM and glucagon in a concentration-dependent manner, with dissociation constants (Kd) of 4.5 and 43 nM, respectively. The nonhydrolyzable analogs of GTP (guanosine 5',3-O-(thio)triphosphate and guanosine 5' (beta,gamma-imino)triphosphate decreased the binding of mono-[125I]OXM to its binding sites. Covalent cross-linking of mono-[125I]OXM or mono-[125I]glucagon to RIN T3 cell membranes followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated a single radiolabeled band at 63,000 mol wt, which differed from that observed after cross-linking with liver plasma membranes (55,000 mol wt). These results demonstrate the presence of specific high affinity binding sites for OXM in a somatostatin-secreting cell line (RIN T3) and their coupling to adenylate cyclase via guanine nucleotide-binding proteins.

Role of G protein beta gamma subunits in the regulation of the plasma membrane Ca2+ pump

In Zajdela hepatoma cells (ZHC) the plasma membrane Ca2+ pump displayed no sensitivity to glucagon (19-29) (mini-glucagon), whereas in hepatocyte this metabolite of glucagon evoked a biphasic regulation of the Ca2+ pump system via a cholera toxin-sensitive G protein. Analysis of G protein subunits in ZHC membranes indicated the presence of cholera toxin-sensitive Gs alpha and G beta gamma proteins, whose functionality was manifested by GTP and NaF stimulation of adenylylcyclase activity, and pertussis toxin-catalyzed ADP-ribosylation of Gi alpha, respectively. However, immunoblotting experiments suggested a lower content in beta gamma subunits in ZHC as compared with hepatocyte plasma membranes. Complementation of ZHC or hepatocyte plasma membranes with purified beta gamma subunits from transducin (T beta gamma) caused inhibition of the basal activity of the Ca2+ pump at 10 and 300 ng/ml, respectively, and revealed (in ZHC) or increased (in hepatocytes) sensitivity of the system to mini-glucagon. After cholera toxin treatment of ZHC, T beta gamma no longer reconstituted the response of the Ca2+ pump to mini-glucagon, suggesting that the mechanism of beta gamma action is dependent on an association with the alpha subunit of a cholera toxin-sensitive G protein. It is concluded that G beta gamma subunits control both the basal activity of the plasma membrane Ca2+ pump and its inhibition by mini-glucagon.

N-acetyl oxyntomodulin30-37: pharmacokinetics and activity on gastric acid secretion

Oxyntomodulin, an intestinal hormone which inhibits gastric acid secretion, is composed of glucagon and a C-terminal octapeptide. This octapeptide mimics the biological activity of the hormone. We have studied the activity of the N-acetyl octapeptide, partially protected against enzymatic degradation, on pentagastrin-, histamine- and milk meal-stimulated secretion in conscious rats and compared it to that of oxyntomodulin and its derivatives. The N-acetylated octapeptide had a 3-fold higher potency than the octapeptide on pentagastrin-stimulated secretion. On histamine-stimulated secretion, the differences between the acetylated and the free octapeptides were that the former displayed a dose-response curve parallel to that of oxyntomodulin and a 4-fold higher potency. The increase in potency appears to be related in part to a decrease in the metabolic clearance rate in vivo (6-fold) and, in vitro, to an increase in half-life (3-fold) when incubated with rat liver plasma membranes. Similarly to the free octapeptide, the acetylated form decreased acid secretion stimulated by a milk meal, when infused before the meal. Acetylation of the Lysine side chains resulted in a totally inactive molecule. The results indicate that acetylating the N-terminus of the octapeptide of oxyntomodulin increases the similarities with the natural hormone.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxyntomodulin and related peptides control somatostatin secretion in RIN T3 cells

We studied the effects of oxyntomodulin (OXM), of its C-terminal (19-37) fragment (OXM (19-37)) and of glucagon (GLU) on somatostatin release, cyclic AMP accumulation and inositol phosphate turnover in somatostatin-secreting RIN T3 cells in culture. Rapid changes in cellular free Ca2+ were also measured using fura-2. Carbachol was used as a control test agent for the parameters involving the inositol phosphate/Ca2+ cascade. OXM, GLU and OXM (19-37) were all able to stimulate somatostatin release with relative ED50 of approx. 1, 22 and 45, respectively. OXM and GLU stimulated cyclic AMP levels with relative ED50 of approx. 1 and 30, respectively, whereas OXM (19-37) was totally ineffective on this parameter. In contrast to carbachol, none of the peptides significantly modified the inositol phosphate turnover or induced rapid changes in cellular free Ca2+. We conclude that the RIN T3 cells contain a receptor-cyclic AMP system similar to that found in gastric mucosa and that this system is linked to somatostatin release. Another receptor-second messenger mechanism linked to somatostatin release is triggered by the (19-37) fragment. This mechanism is not the inositol phosphate/Ca2+ cascade triggered in the same cells by cholinergic agents.

Oxyntomodulin and its (19-37) and (30-37) fragments inhibit histamine-stimulated gastric acid secretion in the conscious rat

Oxyntomodulin, a hormone released from jejuno-ileum and composed of the glucagon sequence extended by a C-terminal octapeptide displays original tissue specificity for the gastric mucosa. The aim of this study was to compare the effect of oxyntomodulin on histamine (0.4 mg/kg per h)-stimulated gastric acid secretion in the conscious rat to that of three of its fragments: oxyntomodulin-(19-37) produced from oxyntomodulin by enzymatic cleavage, oxyntomodulin-(30-37) corresponding to the molecular difference between oxyntomodulin and glucagon and oxyntomodulin-(32-37) produced during proglucagon processing to glucagon. The metabolic clearance rate (MCR) in the anesthetized rat was evaluated for each peptide. Oxyntomodulin, oxyntomodulin-(19-37) and oxyntomodulin-(30-37) inhibited the histamine-stimulated gastric acid secretion dose dependently. The dose-response curves for oxyntomodulin and oxyntomodulin-(19-37) were parallel. The potency of oxyntomodulin (19-37) (ED50 approximately 70 pmol/kg) was the same as that of oxyntomodulin (ED50 approximately 35 nmol/kg) after correction of the curve for the MCR (two-fold higher for the fragment). Although the dose-response curve for oxyntomodulin-(30-37) was not entirely parallel to that of the two other peptides, its maximal inhibition (at 15 nmol/kg) was the same as that of oxyntomodulin-(19-37). Thus, oxyntomodulin-(30-37) was an efficient as the longer molecules but approximately 150-fold less potent than oxyntomodulin. The MCR for oxyntomodulin-(30-37) was approximately 250 fold higher than that of oxyntomodulin, partly explaining the difference in potency. The (32-37) fragment, which is naturally released from the endocrine pancreas, was devoid of activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Miniglucagon [glucagon-(19-29)] is a component of the positive inotropic effect of glucagon

Glucagon is well known for its cardiotonic effect, but its mechanism of action remains undetermined. In the present study, we showed that glucagon, under minimal degradation conditions, had no effect on the amplitude of contractility of beating chick embryo ventricular cells. This raised the question of the contribution of the active metabolite of glucagon, glucagon-(19-29), referred to as miniglucagon, to the positive inotropic effect of glucagon. Incubation of glucagon with heart cells led to its rapid conversion into miniglucagon, as measured by radioimmunoassay. Accumulation of the metabolite was maximal after 8 min and remained stable until 15 min. reaching 6% of the initial glucagon concentration. Bacitracin inhibited this processing of glucagon into miniglucagon. Miniglucagon, from 0.1 pM to 1 nM, exerted a potent negative inotropic action. The most striking observation was a 45% increase in the amplitude of cell contractility elicited by the combination of 30 nM glucagon with 1 nM miniglucagon. A similar effect was obtained when glucagon was replaced by a low concentration (75 microM) of 8-bromoadenosine 3',5'-cyclic monophosphate. We conclude that glucagon processing into miniglucagon may be essential for the positive inotropic effect of glucagon on heart contraction.

Glucagon-(19-29), a Ca2+ pump inhibitory peptide, is processed from glucagon in the rat liver plasma membrane by a thiol endopeptidase

Glucagon-(19-29) is 1000-fold more potent that glucagon as an inhibitor of the liver plasma membrane calcium pump, which suggests that this peptide fragment is naturally occurring. Since glucagon-(19-29) is undetectable in plasma, the processing of glucagon into its (19-29) fragment may occur upon interaction of glucagon with its target tissues. The use of a specific radioimmunoassay for glucagon-(19-29) in association with the separation and identification of peptides by high performance liquid chromatography revealed that, upon incubation at 37 degrees C with hepatic plasma membranes, glucagon is processed into its (19-29) C-terminal fragment. The identity of the fragment was confirmed by amino acid sequencing. The processing activity was inhibited by reagents of the thiol group and by 1,10-phenanthroline, suggesting that a thiol endopeptidase containing a catalytically active metal is involved in this processing. Following its production, glucagon-(19-29) was degraded with a half-life of less than 10 s. This degradation was inhibited by bacitracin and by the aminopeptidase inhibitors bestatin and amastatin. When glucagon was incubated with liver plasma membranes in the absence of inhibitors, the accumulation of glucagon-(19-29) reached a maximum at 2 min (1% of initial glucagon), followed by a slow decline. In the presence of bacitracin and bestatin, the amounts of glucagon-(19-29) obtained from glucagon increased continuously, 1 and 2% of glucagon being transformed after 10 and 30 min, respectively. The production of glucagon-(19-29) did not appear to be associated with the binding of glucagon to its receptors, since (i) guanosine 5'-(3-O-thio)triphosphate, a compound which decreases the glucagon-receptor interaction, could not decrease the conversion of glucagon into glucagon-(19-29); (ii) a glucagon analogue which displays a strongly decreased affinity for the hepatic glucagon receptors was processed similarly to glucagon. The conversion also occurs upon incubation with intact hepatoma cells in monolayer culture. These observations suggest that, under physiological conditions, glucagon is processed in liver by cleavage of the Arg17-Arg18 basic doublet, leading to the production of a fragment which is known to display an original biological specificity, namely the modulation of the hepatocyte plasma membrane calcium pump.

Metabolic clearance rates of oxyntomodulin and glucagon in the rat: contribution of the kidney

The half-life (t1/2) and metabolic clearance rate (MCR) of exogenous natural porcine oxyntomodulin (porcine OXM) and the synthetic analog of rat oxyntomodulin, [Nle27]-OXM (rat OXM), were compared with that of glucagon in control, sham-operated and acutely nephrectomized rats using the primed-continuous infusion technique. The half-disappearance times for porcine OXM (8.2 +/- 0.5 min) and rat OXM (6.4 +/- 0.5 min) were 3-fold slower than that of glucagon (1.9 +/- 0.1 min). Acute bilateral nephrectomy significantly prolonged the half-disappearance time of rat OXM (8.2 +/- 0.7 min) and glucagon (3.6 +/- 0.4 min) compared with that of sham-operated animals (6.5 +/- 0.8 min and 2.5 +/- 0.2 min, respectively). The mean MCRs were similar for porcine and rat OXM (11.3 +/- 0.7 and 11.9 +/- 0.5 ml.kg-1.min-1) but were 3 times lower than that measured with glucagon (36 +/- 5 ml.kg-1.min-1). Bilateral nephrectomy reduced the MCR of OXM and glucagon by 38% and 34%, respectively. No significant increase in C-terminal glucagon immunoreactivity was noticed during infusion of either porcine or rat OXM, measured directly in plasma, with a specific C-terminal glucagon antiserum or after HPLC. In the course of the glucagon infusion, blood glucose was increased 2-fold, while the same dose of porcine OXM or of rat OXM induced only a small increase over the values in phosphate buffer-infused rats. 10 times higher doses of rat OXM were necessary to obtain a similar hyperglycemic effect. These results indicate that: (1) the metabolism of OXM is 3-fold slower than that of glucagon, (2) renal clearance contributed close to 35% of the overall metabolic plasma extraction for OXM and glucagon and (3) OXM, although effective at a higher dose, when compared with glucagon, displays a hyperglycemic effect probably through the glucagon receptors.

[Value of biopsy of accessory salivary glands for the diagnosis of amyloidosis]

There are few reports of amyloidosis diagnosed by deliberate biopsy of accessory salivary glands. Usually, a biopsy performed for dry mouth syndrome reveals an unsuspected amyloidosis. We report the case of 2 patients with lambda-type light chain monoclonal gammapathy complicated by generalized amyloidosis and in whom biopsy of the accessory salivary glands showed signs of amyloidosis. In the first patient accessory salivary gland biopsy was performed because these glands were enlarged, and the monoclonal dysglobulinaemia was subsequently diagnosed by serum immunoelectrophoresis. In the second patient with nephrotic syndrome, renal biopsy could not be carried out owing to the presence of a renal malformation; amyloidosis was confirmed by periumbilical fat aspiration, and a systematic biopsy of accessory salivary glands also showed evidence of amyloidosis. Biopsy of accessory salivary glands seems to be a particularly simple and safe method to detect generalized amyloidosis in patients with chronic inflammatory disease or monoclonal dysglobulinaemia.

Glucagon-(19-29) exerts a biphasic action on the liver plasma membrane Ca2+ pump which is mediated by G proteins

We have recently shown that nanomolar concentrations of glucagon-(19-29), which can derive from native glucagon by proteolytic cleavage of the dibasic doublet Arg17-Arg18, inhibit the Ca2+ pump in liver plasma membrane vesicles independently of adenylyl cyclase activation (Mallat, A., Pavoine, C., Dufour, M., Lotersztajn, S., Bataille, D., and Pecker, F. (1987) Nature 325, 620-622). We report here that the regulation of the Ca2+ pump by glucagon-(19-29) is dependent on guanine nucleotides. In the presence of 10 microM guanosine 5'-3-O-(thio) triphosphate (GTP gamma S) or 75 microM GTP, glucagon-(19-29) caused a biphasic regulation of the Ca2+ pump. ATP-dependent Ca2+ transport was inhibited in the presence of 10 pM to 1 nM glucagon-(19-29), while higher concentrations of the peptide (1-100 nM) reversed the inhibition caused by lower ones. GTP gamma S alone, at high concentrations (100 microM), reproduced the inhibitory effect of glucagon-(19-29) and induced a 40% inhibition of the basal activity of the Ca2+ pump which was reversed by low concentrations of glucagon-(19-29) (10 pM to 1 nM). Treatment of rats with cholera toxin resulted in a 70% increase in the basal activity of the Ca2+ pump, a loss of sensitivity to GTP gamma S and to the biphasic regulation by glucagon-(19-29). Treatment with pertussis toxin did not affect the response of the Ca2+ pump to GTP gamma S and glucagon-(19-29). We conclude that glucagon-(19-29) can exert a biphasic effect on the Ca2+ pump which is mediated by G protein(s) sensitive to cholera toxin.