Phase IIa study of the CD19 antibody MOR208 in patients with relapsed or refractory B-cell non-Hodgkin's lymphoma

Background

This two-stage, phase IIa study investigated the antitumor activity and safety of MOR208, an Fc-engineered, humanized, CD19 antibody, in patients with relapsed or refractory (R-R) B-cell non-Hodgkin’s lymphoma (NHL). CD19 is broadly expressed across the B-lymphocyte lineage, including in B-cell malignancies, but not by hematological stem cells.

Patients and methods

Patients aged ≥18 years, with R-R NHL progressing after ≥1 prior rituximab-containing regimen were enrolled into subtype-specific cohorts: diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), other indolent (i)NHL and mantle cell lymphoma (MCL). Treatment was MOR208, 12 mg/kg intravenously, weekly, for 8 weeks. Patients with at least stable disease could continue treatment for an additional 4 weeks. Those with a partial or complete response after 12 weeks could receive extended MOR208 treatment (12 mg/kg, either monthly or every second week) until progression. The primary end point was overall response rate.

Results

Ninety-two patients were enrolled: DLBCL (n = 35), FL (n = 34), other iNHL (n = 11) and MCL (n = 12). Responses were observed in DLBCL, FL and other iNHL cohorts (26%, 29% and 27%, respectively). They lasted ≥12 months in 5/9 responding patients with DLBCL, 4/9 with FL and 2/3 with other iNHL. Responses in nine patients are ongoing (>26 months in five instances). Patients with rituximab refractory disease showed a similar response rate and progression-free survival time to patients with non-refractory disease. The most common adverse events (any grade) were infusion-related reactions (12%) and neutropenia (12%). One patient experienced a grade 4 infusion-related reaction and eight patients (9%) experienced grade 3/4 neutropenia. No treatment-related deaths were reported.

Conclusions

MOR208 monotherapy demonstrated promising clinical activity in patients with R-R DLBCL and R-R FL, including in patients with rituximab refractory tumors. These efficacy data and the favorable safety profile support further investigation of MOR208 in phase II/III combination therapy trials in R-R DLBCL.

ClinicalTrials.gov number

NCT01685008.

Roles of enterobacteria, nitric oxide and neutrophil in pathogenesis of indomethacin-induced small intestinal lesions in rats

Roles of enterobacteria, nitric oxide (NO) and neutrophil in indomethacin-induced small intestinal lesions were examined in rats. Indomethacin (10 mg kg-1), administered s.c. as a single injection, caused haemorrhagic lesions in the small intestine, mostly in the jejunum and ileum. The lesions were first observed 6 h after administration of indomethacin, the severity increasing progressively with time up to 24 h later. Following indomethacin, the enterobacterial numbers, inducible NO synthase (iNOS) activity and NO production in the intestinal mucosa were also increased with time, and changes in the former preceded those in the latter two as well as the occurrence of intestinal damage. Treatment of the animals with both NG-nitro-L-arginine methyl ester (L-NAME) and aminoguanidine prevented intestinal lesions induced by indomethacin, with suppression of NO production. Both dexamethasone and FR167653 (an inhibitor of interleukin-1 beta/tumour necrosis factor-alpha production) also reduced the severity of intestinal lesions as well as the increase in iNOS activity following administration of indomethacin. Likewise, the occurrence of intestinal lesions was attenuated by pretreatment of the animals with anti-neutrophil serum (ANS). None of these treatments, however, affect the translocation of enterobacteria in the mucosa. By contrast, ampicillin (an anti-bacterial agent) suppressed the increase in mucosal iNOS activity as well as the enterobacterial numbers invaded in the mucosa and inhibited the occurrence of intestinal lesions after administration of indomethacin. These results strongly suggest that enterobacterial translocation in the mucosa is the first step required for activation of various factors such as iNOS/NO and neutrophils, all involved in the pathogenesis of indomethacin-induced intestinal lesions.

Increased susceptibility of diabetic rat gastric mucosa to food deprivation during cold stress

BACKGROUND

We investigated the mechanisms responsible for the increased susceptibility of diabetic rat gastric mucosa to damage inflicted by overnight food deprivation (18 h) and its worsening by the cold restraint stress (4 degrees C, 3 h).

METHODS

Gastric damage was measured in fasted animals, some of which were rendered diabetic by a single intraperitoneal injection of streptozotocin (STZ; 70 mg/kg) 5 weeks before experiments (STZ 5W).

RESULTS

STZ 5W rodents showed a number of hemorrhagic lesions in corpus mucosa (26. 8 +/- 5.2 mm(2)) which could be prevented by insulin or nitric oxide synthase (NOS) inhibitors: aminoguanidine or L-NAME (N(omega)-nitro-L-arginine methyl ester). Mucosal injury was further aggravated by low temperature (51.1 +/- 7.8 mm(2)), the damage ameliorated by insulin, aminoguanidine, or L-NAME. The salutary actions of L-NAME were L-arginine sensitive. Low temperature and L-NAME did not significantly influence the gastric secretory parameters in normal rats. On the other hand, L-NAME and aminoguanidine counteracted the attenuation of gastric juice acidity and acid output in STZ 5W rodents. Blood plasma nitrite and nitrate levels and outputs in gastric juice were augmented in STZ 5W animals in comparison to controls. The total activities of NOS including inducible NOS but not constitutive NOS were markedly enhanced by fasting and cold restraint in gastric mucosa of STZ 5W animals (2.2- and 3.7- or 2.4- and 17.9-fold respectively).

CONCLUSIONS

Stressful stimuli, such as food bereavement and cold challenge contribute to the elevated susceptibility of diabetic gastric mucosa to damage, even though the main aggressive factor, i.e., gastric acid secretion, is attenuated. The enhanced production of nitric oxide by inducible NOS during food deprivation and cold exposure seems to play an important role in gastric mucosal integrity disturbances during diabetes.

Increased susceptibility of gastric mucosa to ulcerogenic stimulation in diabetic rats--role of capsaicin-sensitive sensory neurons

1. We examined the gastric mucosal blood flow (GMBF) and ulcerogenic responses following barrier disruption induced by sodium taurocholate (TC) in diabetic rats and investigated the role of capsaicin-sensitive sensory neurons in these responses. 2. Animals were injected streptozotocin (STZ: 70 mg kg(-1), i.p.) and used after 5, 10 and 15 weeks of diabetes with blood glucose levels of > 350 mg dl(-1). The stomach was mounted on an ex-vivo chamber under urethane anaesthesia and exposed to 20 mM TC plus 50 mM HCl for 30 min in the presence of omeprazole. Gastric transmucosal potential difference (PD), GMBF, and luminal acid loss (H+ back-diffusion) were measured before and after exposure to 20 mM TC, and the mucosa was examined for lesions 90 min after TC treatment. 3. Mucosal application of TC caused PD reduction in all groups; the degree of PD reduction was similar between normal and diabetic rats, although basal PD values were lower in diabetic rats. In normal rats, TC treatment caused luminal acid loss, followed by an increase of GMBF, resulting in minimal damage in the mucosa. 4. The increased GMBF responses associated with H+ back-diffusion were mitigated in STZ-treated rats, depending on the duration of diabetes, and severe haemorrhagic lesions occurred in the stomach after 10 weeks of diabetes. 5. Intragastric application of capsaicin increased GMBF in normal rats, but such responses were mitigated in STZ diabetic rats. The amount of CGRP released in the isolated stomach in response to capsaicin was significantly lower in diabetic rats when compared to controls. 6. The deleterious influences on GMBF and mucosal ulcerogenic responses in STZ-diabetic rats were partially but significantly antagonized by daily insulin (4 units rat(-1)) treatment. 7. These results suggest that the gastric mucosa of diabetic rats is more vulnerable to acid injury following barrier disruption, and this change is insulin-sensitive and may be partly accounted for by the impairment of GMBF response associated with acid back-diffusion and mediated by capsaicin-sensitive sensory neurons.

Effects of diabetes mellitus on the contractile activity of carbachol and galanin in isolated gastric fundus strips of rats

The role of the cholinergic and peptidergic pathways in the impairment of gastric motility associated with diabetic gastroparesis was assessed at the postsynaptic level using isolated fundus smooth muscle strips. Maximal contractile responses to carbachol and galanin were significantly decreased in fundus strips isolated from rats rendered diabetic by a single intraperitoneal injection of streptozotocin (STZ, 70 mg/kg) 1, 4 and 8 weeks before experiments. We also observed notable decrements in the slopes and Hill's coefficients without conspicuous changes in the EC50 of the respective galanin concentration-response curves measured in strips obtained from STZ animals after 4 and 8 weeks. L-NAME reversed the above-mentioned alterations in an L-arginine-sensitive manner in STZ rats after 4 weeks but not in STZ rats after 8 weeks. The blood plasma nitrite/nitrate levels in STZ animals after 4 and 8 weeks were increased by 44.6 and 61.9%, respectively. Ca2+-independent nitric oxide synthase activity in gastric fundus strips and stomach corpus mucosa from STZ rats after 4 weeks was markedly enhanced by 37.4 and 31.9%, respectively, suggesting an enhanced nitric oxide production. In vivo insulin treatment prevented diabetes-induced alterations in smooth muscle contractility. We conclude that the smooth muscle dysfunction evoked by experimental diabetes causing diminished contractions of fundus strips to carbachol and galanin is at least partly due to the increased nitric oxide synthesis.

Influence of intracerebroventricular administration of tetanus toxin on experimental seizures and protection afforded by some antiepileptic drugs in mice

The dose to the intracerebroventricularly administered (i.c.v.) tetanus toxin (Tetx) evoking the death of 50% of experimental mice (LD50) was estimated to be 18.0 (11.5-28.2) times the minimal lethal dose (MLD). MLD is defined as the lowest does of Tetx necessary to kill a 20-g albino mouse within 96 h after intraperitoneal treatment. Tetx (0.25 and 0.5 LD50) increased the convulsive threshold of electric current from 24 to 96 and 120 h, respectively, following i.c.v. administration. Both doses of Tetx diminished convulsant potencies of pentylenetetrazole, bicuculline, aminophylline and pilocarpine 24 h after application. At the same time Tetx (0.5 LD50) increased the protection afforded by carbamazepine, valproate, phenobarbital and diazepam in maximal electroshock (MES) by approximately 36, 11, 21 and 26%, respectively, without affecting total blood plasma levels of antiepileptic drugs. No marked changes in gamma-aminobutyric acid (GABA) concentration and total activity of L-glutamic acid decarboxylase (GAD) assessed in the whole-brain homogenates resulted from Tetx treatment. Our results seem to indicate that low doses (< LD50) of i.c.v. administered Tetx may lead to a relative prevalence of inhibitory over excitatory processes in the central nervous system suggesting a complex action of Tetx at the neuronal level.

Inhibition of gastric acid secretion by galanin in rats. Relation to endogenous histamine release

Inhibitory effect of galanin on basal and secretagogs-stimulated gastric acid secretion was investigated in urethane-anesthetized rats. A rat stomach was mounted in an ex-vivo chamber, perfused with saline, and either gastric acid or alkaline secretion was determined by titrating the perfusate. Gastric mucosal blood flow (GMBF) was measured by a laser Doppler flowmeter. Intravenous infusion of galanin dose-dependently inhibited the increase of acid secretion induced by pentagastrin and carbachol but not by histamine, without any influence on the GMBF response. Galanin also reduced basal acid secretion while increasing GMBF, but did not evoke any change in basal gastric alkaline secretion. M15, which is a galanin receptor antagonist in the central nervous system but acts as a full agonist in the gastrointestinal smooth muscle, also suppressed pentagastrin-induced acid secretion, similar to galanin. In addition, pentagastrin increased the release of histamine into the gastric lumen, and this response was significantly inhibited by galanin. These results suggest that the inhibitory effect of galanin on acid secretion is mediated by suppression of endogenous histamine release from enterochromaffin-like cells and that the process may be related to the activation of the same subtype of galanin receptors as in the central nervous system and pancreatic beta-cells.

Pharmacological characterization of the contractile effects of galanin (1-29)-NH2, galantide and galanin (1-14)-(alpha-aminobutyric acid8)scyliorhinin-I in the rat gastric fundus

Porcine galanin (1-29)-NH2, galantide (M15) and galanin (1-14)-(alpha-aminobutyric acid8)-scyliorhinin-I used in concentrations of 300, 1,000 and 3,000 nM respectively caused contractions of rat fundus strips. The contractile responses to galanin(1-29)-NH2 were not modified by atropine (10 microM), guanethidine (10 microM), naloxone (1 microM), a mixture of propranolol (10 microM) and phentolamine (10 microM), indomethacin (10 microM), a mixture of mepyramine (10 microM) and cimetidine (10 microM), saralasin (10 microM), and spantide (100 microM). The effects of M15 and galanin(1-14)-(alpha-aminobutyric acid8)-scyliorhinin-I were significantly decreased by atropine for 36 and 18% and by spantide for 37 and 26% respectively. Indomethacin inhibited the muscle response to M15 without influence on the galanin (1-14)-(alpha-aminobutyric acid8)-scyliorhinin-I-induced action. These results support findings that galanin (1-29)-NH2 contracts rat gastric fundus strips by stimulating specific receptors localized on the surface of smooth muscle cells. M15 and galanin(1-14)-(alpha-aminobutyric acid8)-scyliorhinin-I seem to contract smooth muscles not only by acting at galanin receptors, but by interacting with muscarinic or tachykinin receptors or modulating the release of acetylcholine and substance P. Diltiazem (EC50 825 nM), dantrolene (EC50 30.2 microM) and the phospholipase C inhibitors U-73122 (EC50 549 microM) and U-73343 (EC50 751 microM) lowered the contraction to galanin(1-29)-NH2 in a concentration-dependent manner. These observations imply that though the extracellular Ca2+ influx plays a major role in the action of galanin(1-29)-NH2, the release of Ca2+ ions from the intracellular stores contributes to the response of smooth muscles of galanin(1-29) NH2. Norepinephrine (30, 60, 100 and 300 nM) concentration-dependently reduced the Emax to galanin (1-29)-NH2 and reduced the slopes of the concentration-contraction curves, without a notable change in EC50. Pertussis toxin pre-treatment (10 and 30 mg/kg intravenous [i.v.]), 120 h before the experiment, notably increased the maximal response of the rat gastric fundus to galanin(1-29)-NH2, without a significant change in the properties of the concentration-contraction curves (EC50, slopes). The observations may suggest that pertussis toxin-sensitive GTP-binding proteins are involved in the modulation of the excitatory effects of galanin(1-29)-NH2 in the rat gastric fundus.

Desensitisation of substance P decreases the contractile effect of M15 and Gal (1-14)-(Abu 8) SCY-I on the rat gastric fundus

Tachyphylaxis to SP decreased the effect of M15 and Gal(1-14)-[Abu8]SCY-I on gastric smooth muscles, without effect on the action of Gal. These findings support our initial hypothesis: the action of M15 and Gal(1-14)-[Abu8]SCY-I on the smooth muscles may not only be due to their agonist activity at Gal receptors, but may result from a subsequent stimulation of receptors for SP and perhaps for other tachykinins as well, however, a possibility that Gal analogues release endogenous SP can not be excluded. Further studies involving a tachykinin antagonist (spantide) are in progress at the moment. [1].

Lysine14galanin(1-15)-NH2: a partial agonist at galanin receptors in rat isolated gastric fundus

The study was undertaken to characterize the effects of the porcine galanin [pGal(1-29)-NH2] analogue [Lys14]pGal(1-15)-NH2 on rat gastric fundus. [Lys14]pGal(1-15)-NH2 is a less potent contractile agent than pGal(1-29)-NH2 (EC50 74.1 vs. 43.7 nmol/l, respectively) and shows a significantly lower maximal response than pGal(1-29)-NH2. Concentration-contraction curves were constructed for pGal(1-29)-NH2 alone (control) and pGal(1-29)-NH2 in the presence of 10, 100, and 1,000 nmol/l of [Lys14]pGal(1-15)-NH2. [Lys14]pGal(1-15)-NH2 shifted the concentration-contraction curves of pGal(1-29)-NH2 significantly to the right, whereas their linear portions remained parallel to that for the pGal(1-29)-NH2 control. [Lys14]pGal(1-15)-NH2 markedly increased the EC50 of the respective pGal(1-29)-NH2 concentration-contraction curves. It did not substantially change the maximal response of the muscles to pGal(1-29)-NH2 and the form of the respective concentration-contraction curves. Schild's plot gave a straight line with a slope of 0.84. The pA2 value for [Lys14]pGal(1-15)-NH2 was 8.23. [Lys14]pGal(1-15)-NH2 seems to be a partial Gal receptor agonist. Since the lack of specific Gal receptor antagonists in the gastrointestinal tract makes a precise characterization of its role as a motility modulator difficult, the position 14 in the pGal(1-29)-NH2 molecule looks as an attractive target in the search of a pure Gal receptor antagonist in the smooth muscles of the gut.

Contractile effects of porcine galanin(1-29)-NH2 on the rat isolated gastric fundus: mediation by potassium ions

Galanin (3-300 nM) evoked reproducible concentration-dependent contractions of rat isolated gastric fundus strips, EC50 of the peptide equalled 16.7 nM (6.2-39.2) and the slope of the concentration-response curve was 34.8 (24.0-45.7). The maximal response (Emax) to carbachol (30 nM) was not affected by the absence of the potassium ions in the bathing solution. On the contrary the Emax to galanin (300 nM) was decreased by almost 95% by the use of the potassium-free buffer. Re-exposure of the muscle strips to potassium containing bathing medium reversed the inhibition by about 35%, yet the value remained significantly lower than that of the control. Apamin (1 and 2 microM), glybenclamide (10 microM), clofilium tosylate (10 microM) did not significantly influence the Emax to carbachol. Apamin or glybenclamide did not affect the contractile action of galanin, while clofilium attenuated the Emax to the peptide in a concentration-dependent manner, the EC50 of the agent being 9.44 microM (164 nM-541 microM). It was concluded that the potassium ions play a modulatory role in gastric smooth muscle contraction following galanin receptor stimulation, probably by interacting with the extracellular calcium influx.

Impaired duodenal bicarbonate secretion in diabetic rats. Salutary effect of nitric oxide synthase inhibitor

We previously reported the impaired HCO3- secretion and the increased mucosal susceptibility to acid in the duodenum of streptozotocin (STZ)-induced diabetic rats. In this study, we investigated the salutary effect of the NO synthase inhibitor L-NAME (NG-nitro-L-arginine methyl ester) on these changes and compared it with those of insulin. Animals were injected streptozotocin (STZ: 70 mg/kg, ip) and used after 1, 3-4, and 5-6 weeks of diabetes with blood glucose levels of > 300 mg/dL. Under urethane anesthesia the HCO3- secretion was measured in the proximal duodenal loop using a pH-stat method and by adding 10 mM HCl. L-NAME (20 mg/kg x 2) or insulin (4 units/rat) was administered sc for 4-5 weeks, starting 1 week after STZ treatment. The duodenal HCO3- secretory responses to various stimuli such as mucosal acidification (10 mM HCl for 10 min), 16,16-dimethyl prostaglandin E2 (dmPGE2: 10 micrograms/kg, i.v.), and vagal stimulation (0.5 mA, 2 ms, 3 Hz) were significantly decreased in STZ-treated rats, depending on the duration of diabetes. Repeated administration of L-NAME, starting from 1 week after STZ treatment, significantly reduced blood glucose levels toward normal values and restored the HCO3- responses to various stimuli in STZ rats, the effects being similar to those observed after supplementation of insulin. Diabetic rats developed duodenal lesions after perfusion of the duodenum with 150 mM HCl for 4 h, but this ulcerogenic response was significantly inhibited by the repeated treatment with L-NAME as well as insulin. We conclude that L-NAME is effective in ameliorating hyperglycemic conditions in STZ-diabetic rats, similar to insulin, and restores the impaired HCO3- secretion and the increased mucosal susceptibility to acid in diabetic rat duodenums.

Galanin, galantide and galanin (1-14)-[alpha-aminobutyric acid8]-scyliorhinin-I: structure dependent effects on the rat isolated gastric fundus

The study was undertaken using selected pharmacodynamic parameters to describe the effects of porcine galanin(1-29)-NH2; porcine galanin fragments; galantide; porcine galanin(1-14)-[alpha-aminobutyric acid8]scyliorhinin-I and the analogues of the latter peptides on rat isolated gastric fundus muscle. All tested peptides, apart from galanin(16-29)-NH2 evoked reproducible concentration-dependent contractions with significantly decreased activities in comparison to the potency of the native galanin(1-29)-NH2 molecule. The order of the contractile ability in the group of galanin(1-29)-NH2 short fragments was as follows: [lysine14]galanin(1-15)-NH2 > galanin(1-15)-OH > galanin(1-15)-NH2 > [glycine5] galanin(1-15)-NH2 > galanin(2-15)-NH2 > [glycine5,lysine14]galanin(1-15)-NH2. Aside from [lysine14]galanin(1-15)-NH2 which had a lower efficacy, none of the peptides showed significant changes in this respect in comparison to the intact galanin(1-29)-NH2 molecule. The concentration-response curves of the tested peptides were to the right and their slopes besides from: galanin(1-15)-OH; galanin(2-15)-NH2; [glycine5]galanin(1-15)-NH2 remained not significantly different from galanin(1-29)-NH2. Hill's coefficient for galanin(1-29)-NH2 is 1.03 indicating an interaction of one galanin(1-29)-NH2 molecule with one receptor, fulfilling criteria of classical receptor theory. For galanin fragments Hill's coefficients are < 1 implying that the rules of classical theory may not apply. Galantide and analogues exhibited a subsequent decrease in potency: [cycloleucine4] galantide > galantide > [homoserine6]galantide > [phenylalnine(4fluor)17] galantide. Galanin(1-14)-[alpha-aminobutyric acid8]-scyliorhinin-I and its analogues contracted the gastric fundus with a decline in strength: galanin(1-13)-[norleucine10]-scyliorhinin-I(3-10) > galanin(1-13)-[phenylalanine(4fluor)7]-scyliorhinin-I > galanin(1-14)-[alpha-aminobutyric acid8]-scyliorhinin-I > galanin(1-13)-[alpha-aminobutyric acid8, norleucine10]-scyliorhinin-I(3-10). They all displayed a greater efficacy than galanin(1-29)-NH2, and the concentration-response curves were slightly to the right, almost parallel to that of galanin(1-29)-NH2. Slopes of the curves were not significantly different from galanin(1-29)-NH2. Hill's coefficient for the galantide, [cycloleucine4]galantide; [homoserine6]galantide; [phenylalanine(4fluor)17]galantide and galanin(1-13)-[phenylalanine(4fluor)7]-scyliorhinin-I are < 1. Hill's coefficients for galanin(1-13)-[norleucine10]-scyliorhinin-I(3-10); galanin(1-14)-[alpha-aminobutyric acid8]-scyliorhinin-I; galanin(1-14)-[alpha-aminobutyric acid8, norleucine10]-scyliorhinin-I(3-10) are > 1. A Hill's coefficient markedly different from 1 might indicate that an activation of more than one type of receptors, negative or positive receptor cooperativity or multiple-step agonist-receptor reaction.

Actions of galanin and some of its analogues on rat isolated gastric fundus

The study was undertaken to characterize the effects of porcine galanin (pGal) and some of its analogues on rat gastric fundus muscle strips. pGal, galantide (M15) and pGal(1-14)-[Abu8]SCY-I evoked reproducible concentration-dependent contractions in concentrations of 1-300, 3-1,000 and 100-3,000 nM, respectively, with EC50 values of 13, 70 and 187 nM. Hill's coefficient for pGal is 1.03, indicating an interaction of one pGal molecule with one receptor, fulfilling criteria of classical receptor theory. For M15 and pGal(1-14)-[Abu8]SCY-I, Hill's coefficients are significantly different from 1, namely 0.73 and 1.56, so that one drug molecule may not interact with one receptor. The stimulatory effects of pGal were not modified by dibenamine 10 microM or glybenclamide 1 or 10 microM. Diltiazem 0.1, 1 and 10 microM, papaverine 0.1, 10 microM or dibutyryl cAMP (dib cAMP) 100 and 300 microM, blocked the contraction to pGal in a concentration-dependent manner, indicating an important role for the influx of extracellular calcium ions and regulation by cAMP the pGal-evoked contraction. Diltiazem, dibutyryl cAMP and papaverine were not competitive antagonists of pGal in the stomach smooth muscle.

Contractile action of galanin analogues on rat isolated gastric fundus strips is modified by tachyphylaxis to substance P

This study was undertaken to characterize the interaction of porcine galanin (Gal) and some of its analogues with their receptors on rat gastric fundus muscle strips. Gal, galantide (M15) and Gal(1-14)-[Abu8]SCY-I evoked concentration-dependent contractions of gastric smooth muscle strips. Reproducible effects were observed in concentrations of 1-300, 3-1000 and 100-3000 nM, respectively. Specific EC50 for the contractile effect equalled 13.70 and 187 nM. Hill's coefficient for Gal is 1.03 indicating an interaction of one Gal molecule with one receptor, fulfilling the criteria of classical receptor theory. For M15 and Gal(1-14)-[Abu8]SCY-I Hill's coefficients are different from 1, namely 0.73 and 1.56, pointing out that the principle of interaction of one drug molecule with one receptor may not apply. The contraction induced by 300 nM of Gal was not significantly modified by tachyphylaxis to substance P (SP). On the contrary the introduction of tachyphylaxis to SP decreased the contractile effects of M15 and Gal(1-14)-[Abu8]SCY-I by about 57.7 +/- 3% and 39.6 +/- 5%, respectively. The findings suggest that contractile actions of M15 and Gal(1-14)-[Abu8]SCY-I are probably not only due to their agonist activities at Gal receptors but may result from a subsequent stimulation of receptors for SP or release of endogenous SP.

Intracerebroventricular pertussis toxin enhances sensitivity to chemical convulsants and decreases the protective efficacy of carbamazepine in mice

The effects of pretreatment with pertussis toxin on pentylenetetrazole-, bicuculline-, aminophylline- and pilocarpine-induced seizures were investigated in mice. In animals treated intracerebroventricularly with pertussis toxin (0.5 microgram animal-1 120 h prior to testing), the CD50 (convulsive dose in 50%) values were considerably decreased in comparison with the CD50 in sham-treated animals. CD50 values of pentylenetetrazole, bicuculline, pilocarpine and aminophylline were calculated to be 39.9, 2.0, 262 and 141 mg kg-1, whereas they were calculated to be 57.7, 2.7, 324 and 230 mg kg-1 in sham-treated animals. The observations suggest that the enhanced sensitivity to a number of chemical convulsants irrespective of their mode of action possibly results from a functional suppression of inhibitory transmission at receptors coupled to pertussis toxin sensitive G proteins, rather than a direct action on G protein linked excitatory neurotransmission. Pertussis toxin significantly decreased the protective action of carbamazepine, increasing its ED50 (effective dose in 50%) from 14.8 to 20.1 mg kg-1 in a maximal electroshock convulsive test. It influenced the ED50 of neither diphenylhydantoin nor diazepam. The diminution of carbamazepine's efficacy might result from a summation effect of adenosine receptor antagonist properties of the drug and a suppression of transmission at adenosine receptors coupled to G proteins sensitive to pertussis toxin. Pertussis toxin pretreatment remained without any significant influence on the total plasma levels of carbamazepine, diphenylhydantoin and diazepam. This may lead to the conclusion that the interaction between pertussis toxin and carbamazepine does not seem to be of a pharmacokinetic nature and occurs probably at neuronal level.

Nitric oxide synthase activity, viability and cyclic GMP levels in rat colonic epithelial cells: effect of endotoxin challenge

The present study has examined whether epithelial cells could be a source of the inducible form of nitric oxide synthase (iNOS) in the colon of rats challenged with E. coli lipopolysaccharide and whether such excessive endogenous nitric oxide (NO) or exogenous NO released from NO donors could affect their viability. Epithelial cells were isolated from rat colon, and cell viability was determined by trypan blue exclusion. The appearance of a calcium-independent iNOS determined by the conversion of radiolabeled L-arginine to citrulline was observed in cells harvested from lipoplysaccharide (3 mg/kg for 4 hr)-treated rats, with a 10-fold increase in total NOS activity compared with control. This was accompanied by a 3-fold decrease in epithelial cell viability. Levels of iNOS and of cellular injury were not significantly affected in rats made neutropenic by the administration of antineutrophil serum. Induction of NOS was also associated with an increase in epithelial cyclic guanylate monophosphate levels. Both iNOS activity and cell injury were inhibited by in vivo pretreatment with dexamethasone (1 mg/kg i.v., for 4 hr) or the NOS inhibitor NG-nitro-L-arginine methyl ester (10 mg/kg s.c.) in a dose that itself reduced viability. The incubation of epithelial cells with the NO donors, nitroprusside, S-nitroso-N-acetyl penicillamine or S-nitroso-N-glutathione (0.1-1 mM) produced concentration-dependent cytotoxicity. These findings indicate that the induction of NOS in colonic epithelial cells is not dependent upon infiltration of neutrophils and is accompanied by a reduction in cellular viability, an effect mimicked in vitro by NO donors.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of eicosanoids, nitric oxide, and afferent neurons in antacid induced protection in the rat stomach

The mechanism underlying the mucosal protective effect of antacids is still unclear. This study shows that in rats the aluminum containing antacid, hydrotalcit, induces dose dependent protection against gastric mucosal damage caused by ethanol or indomethacin which is considerably enhanced by acidification. Hydrotalcit did not increase gastric mucosal formation or the intraluminal release of prostaglandins, and did not prevent the increase in mucosal leukotriene C4 formation in response to ethanol. Pretreatment with indomethacin did not attenuate the protective effect of unmodified or acidified hydrotalcit. Furthermore, hydrotalcit significantly reduced the gastric damage caused by indomethacin even when it was administered up to 2 hours after the ulcerogen. In indomethacin treated rats, simultaneous administration of hydrotalcit did not affect the concentrations of indomethacin in serum or inflammatory exudates nor did it attenuate the inhibition of prostaglandin release into the exudates. In hydrotalcit treated rats there was no attenuation of the increase in sulphidopeptide leukotriene release or decrease in leukocyte influx into inflammatory exudates elicited by indomethacin administration. Functional ablation of afferent neurons and inhibition of endogenous nitric oxide partially antagonised the protective effect of unmodified, but not of acidified, hydrotalcit. It is concluded that (i) the protective effect of unmodified and acidified hydrotalcit is independent of the eicosanoid system; (ii) protection against indomethacin induced gastric lesions does not require treatment before dosing of the ulcerogen and does not interfere with absorption and anti-inflammatory actions of indomethacin; (iii) endogenous nitric oxide and afferent neurons contribute partly to the effect of unmodified, but not of acidified, hydrotalcit suggesting that different mechanisms mediate their mucosal protective activity.