POS0623 CYTOKINE PRODUCTION BY BLOOD LYMPHOCYTES DEFINES A PROFILE ASSOCIATED WITH NON-REMISSION IN PATIENTS WITH RHEUMATOID ARTHRITIS TREATED WITH TNF INHIBITORS

Background:

In clinical practice no more than 50% of the patients treated with TNF inhibitors (TNFi) achieve remission (REM). Previous investigations suggested that peripheral blood mononuclear cells (PBMC) may be markers associated with the TNFi treatment success1.

Objectives:

This study aims to analyse the intracellular cytokine production by PBMC and its association with REM achievement after 6 months (m) of TNFi treatment in patients with RA.

Methods:

This was a prospective study including 62 patients with RA starting the 1st TNFi. PBMC were isolated from patients at baseline and after 6m of treatment with TNFi and cryopreserved until studied. In vitro stimulation and intracellular cytokine production by PBMC was performed as follow: in the presence of 2µg/mL brefeldin and 2µmol/L monensin monocytes were stimulated with 20ng/mL LPS during 4h whereas lymphocytes were stimulated with 50ng/mL phorbol 12-myristate 13-acetate and 750ng/mL ionomycin for 4h at 37°C. To identify IL10-producing B cells, PBMC were pre-incubated with 3µg/mL of CpG oligonucleotide during 20h at 37°C prior to stimulation. Intracellular cytokine production (TNFα, IL6, GM-CSF, IL10) by the different cell subsets (monocytes, CD4+ and CD8+ T cells, naïve and memory B cells) was analysed by flow-cytometry. Clinical activity at baseline and after 6m was assessed by DAS28-ESR. REM was defined as DAS28≤2.6 at 6m. The association between cytokine production by each PBMC subset and REM was analysed through univariable and multivariable logistic regression models. Receiving operating curve (ROC) analysis was used to select the optimal ratio of cytokine production associated with REM status.

Results:

After 6m of TNFi treatment, 30 (48%) patients achieved REM. No significant differences between REM and non-REM groups were observed for patients’ characteristics at baseline except for DAS28, which was lower in the REM group (non-REM: 5.4±0.9; REM: 4.3±0.9; p<0.0001) (Table 1). Therefore, further analyses were adjusted by baseline DAS28. A lower ratio between calculated with the IL10 and TNFα production by B cells and by CD4+ T cells (IL10 B/TNF CD4) at 6m was found for non-REM patients (non-REM: 0.31 vs REM: 0.54; p=0.007). Based on a ROC analysis, we found that a (IL10 B/TNF CD4)<0.54 at 6 m was significantly associated with a higher probability of non-REM at 6 months (OR: 5.0; 95% CI: 1.1-21.7) (Figure 1).

Table 1.

Baseline predictors of reduction of disease activity at 12 months from start of abatacept. Linear regression.

Baseline patients’ characteristicsTotal patients (n=62)DAS28>2.6(n=32; 52%)DAS28≤2.6(n=30; 48%)p-valueAge (years)53±1253±1352±100.8Female55 (89)30 (94)25 (83)0.2Disease duration (years)8 (4-11)8 (4-12)7 (3-11)0.7RF positive49 (79)23 (72)26 (87)0.1ACPA positive54 (87)26 (81)28 (93)0.2Smoking habit (n=55)0.2Non-smokers26 (47)16 (55)10 (38) Smoker29 (53)13 (45)16 (51)Body mass index (kg/m2)25.9±5.625.8±5.726.0±5.60.9DAS284.9±1.05.4±0.94.3±0.9<0.0001Concomitant csDMARDs60 (97)32 (100)28 (93)0.3MTX [±OD]46 (74)26 (81)20 (67)0.3Only OD14 (23)6 (19)8 (26)0.3Prednisone36 (58)19 (59)17 (57)0.9

Conclusion:

Our results show that the proinflammatory IL10 B/TNF CD4 ratio is associated with non-REM status. It could be useful to analyse the success of TNFi treatment in patients with RA.

References:

[1]Rodríguez-Martín E, et al. Front Immunol. 2020; 11: 1913.

Acknowledgements:

ISCIII (PI16/00474; PI16/01092)

Disclosure of Interests:

Borja Hernández-Breijo: None declared, Eulalia Rodríguez-Martín: None declared, Carlota García-Hoz: None declared, Victoria Navarro-Compán Speakers bureau: Abbvie, Janssen, Lilly, MSD, Novartis, Pfizer and UCB, Grant/research support from: Abbvie, Janssen, Lilly, MSD, Novartis, Pfizer and UCB, Cristina Sobrino: None declared, ANA MARTÍNEZ-FEITO: None declared, Israel Nieto-Gañán: None declared, Javier Bachiller-Corral Speakers bureau: Abbvie, MSD, BMS and Roche, Grant/research support from: Pfizer, Paloma Lapuente-Suanzes: None declared, Gemma Bonilla: None declared, Cristina Pijoán-Moratalla: None declared, Mónica Vázquez: None declared, Alejandro Balsa Speakers bureau: Abbvie, BMS, Nordic, Novartis, Pfizer, Sandoz, Sanofi, Roche and UCB, DORA PASCUAL-SALCEDO: None declared, Luisa María Villar: None declared, Chamaida Plasencia Speakers bureau: AbbVie, Lilly, Novartis, Pfizer, Sanofi, Biogen and UCB

FRI0582 GM-CSF PRODUCED BY CD4+ T CELLS AS A MARKER OF CLINICAL REMISSION IN PATIENTS WITH RHEUMATOID ARTHRITIS TREATED WITH TNF INHIBITORS

Background:

According to the EULAR recommendations, the therapeutic target in patients with RA should be remission (REM). However, no more than 50% of the patients treated with TNF inhibitors (TNFi) attains this outcome. Previous investigations suggested the peripheral blood mononuclear cells (PBMC) as markers associated with the TNFi treatment success1,2. Granulocyte-monocyte colony-stimulating factor (GM-CSF) plays a relevant role in the pathogenesis of rheumatoid arthritis (RA) because it promotes the macrophage differentiation, survival and activation3.

Objectives:

To analyse the intracellular cytokine production by PBMC and its association with REM attainment after 6 months (m) of TNFi treatment in patients with RA.

Methods:

This was a prospective bi-center pilot study including 36 patients with RA. PBMC were isolated from patients at baseline and after 6m of treatment with TNFi and cryopreserved until studied. Intracellular cytokine production by PBMC was stimulated in the presence of 2µg/mL brefeldin as follow: monocytes were stimulated with 20ng/mL LPS during 4h; and simultaneously lymphocytes were stimulated with 50ng/mL phorbol 12-myristate 13-acetate (PMA) and 750ng/mL ionomycin during 4h at 37°C. To identify IL-10-producing B cells, PBMC were pre-incubated with 3µg/mL of CpG oligonucleotide during 20h at 37°C prior to stimulation in presence of 2µmol/L monensin. Intracellular cytokine production (TNFα, IL6, GM-CSF, IL10) by the different cell subsets (monocytes, CD4+and CD8+T cells, naïve and memory B cells) was analysed by flow-cytometry. Clinical activity at baseline and after 6m was assessed by DAS28. REM was defined as DAS28≤2.6 at 6m. The association between REM and the change in cytokine production (Δ, 6m-0m) by each PBMC subset was analysed through univariable and multivariable logistic regression models.

Results:

Seventy-eight percent of the patients were female. After 6m of TNFi treatment, 47% patients attained REM. Univariable analyses was performed to investigate the association between REM and the baseline variables. Male sex (OR: 12.6; 95% CI: 1.35-117.57; p=0.03) and having lower baseline DAS28 (OR: 0.4; 95% CI: 0.19-0.85; p=0.02) were independently associated with attaining REM after 6m of TNFi. In the multivariable analysis, only being male (OR: 19.7; 95% CI: 1.4-273.9; p=0.03) remained independently associated with REM after 6m of treatment. Therefore, further analyses were adjusted by sex. Decreased production of GM-CSF by CD4+T cells percentage was found after 6m of TNFi treatment in REM patients (0m: 6.07%; 6m: 3.87%; p=0.007) while no-REM patients did not show differences with the baseline (0m: 3.70%; 6m: 3.75%; p=0.9). The decrease was significantly associated with attaining REM (OR: 0.56; 95% CI: 0.33-0.95; p: 0.03). No significant association was found between any other analysed intracellular cytokine produced by the different PBMC subsets and REM.

Conclusion:

GM-CSF intracellular production by CD4+T cells was significantly decreased by TNFi treatment only in patients who attained REM. Therefore, our results suggest that GM-CSF production by CD4+T cells may be a useful marker of REM to TNFi in RA.

References:

[1] Sobrino C, et al. Ann Rheum Dis. 2019; 78 (S2): A1665.

[2] Hernández-Breijo B, et al. Ann Rheum Dis. 2019; 78 (S2): A711.

[3] Avci AB, et al. Clin Exp Rheumatol. 2016; 34 (S98), 39-44.

Figure. 1:

Association between the change in intracellular cytokine production (Δ, 6m-0m) by each PBMC subset and REM. Adjusted logistic regression analyses were performed for each cytokine.

Acknowledgments:

ISCIII (PI16/00474; PI16/01092)

Disclosure of Interests:

Borja Hernández-Breijo: None declared, Chamaida Plasencia: None declared, Carlota García-Hoz: None declared, Cristina Sobrino: None declared, Victoria Navarro-Compán Consultant of: Abbvie, Lilly, Novartis, Pfizer, UCB, Speakers bureau: AbbVie, MSD, Lilly, Novartis, Pfizer, UCB, ANA MARTÍNEZ-FEITO: None declared, Israel Nieto-Gañán: None declared, Paloma Lapuente-Suanzes: None declared, Javier Bachiller-Corral: None declared, Gemma Bonilla: None declared, Cristina Pijoan Moratalla: None declared, Garbiñe Roy: None declared, Mónica Vázquez Díaz: None declared, Alejandro Balsa Grant/research support from: BMS, Roche, Consultant of: AbbVie, Gilead, Lilly, Pfizer, UCB, Sanofi, Sandoz, Speakers bureau: AbbVie, Lilly, Sanofi, Novartis, Pfizer, UCB, Roche, Nordic, Sandoz, Luisa María Villar: None declared, DORA PASCUAL-SALCEDO Grant/research support from: Pfizer, Novartis & Progenika, Speakers bureau: Pfizer, Merck, Novartis, Takeda, Menarini & Grifols, Eulalia Rodríguez-Martín: None declared

Natural killer cell subsets in cerebrospinal fluid of patients with multiple sclerosis

Changes in blood natural killer (NK) cells, important players of the immune innate system, have been described in multiple sclerosis (MS). We studied percentages and total cell counts of different effector and regulatory NK cells in cerebrospinal fluid (CSF) of MS patients and other neurological diseases to gain clearer knowledge of the role of these cells in neuroinflammation. NK cell subsets were assessed by flow cytometry in CSF of 85 consecutive MS patients (33 with active disease and 52 with stable MS), 16 with other inflammatory diseases of the central nervous system (IND) and 17 with non-inflammatory neurological diseases (NIND). MS patients showed a decrease in percentages of different CSF NK subpopulations compared to the NIND group. However, absolute cell counts showed a significant increase of all NK subsets in MS and IND patients, revealing that the decrease in percentages does not reflect a real reduction of these immune cells. Remarkably, MS patients showed a significant increase of regulatory/effector (CD56(bright) /CD56(dim) ) NK ratio compared to IND and NIND groups. In addition, MS activity associated with an expansion of NK T cells. These data show that NK cell subsets do not increase uniformly in all inflammatory neurological disease and suggest strongly that regulatory CD56(bright) and NK T cells may arise in CSF of MS patients as an attempt to counteract the CNS immune activation characteristic of the disease.

Anti-myelin antibodies play an important role in the susceptibility to develop proteolipid protein-induced experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is the most common demyelinating disease of the central nervous system. It is an autoimmune disorder in which activated T cells cross the blood-brain barrier (BBB) to initiate an inflammatory response that leads to demyelination and axonal damage. The key mechanisms responsible for disease initiation are still unknown. We addressed this issue in experimental autoimmune encephalomyelitis (EAE), the animal model of MS. It is widely known that EAE manifests only in certain strains when immunized with myelin proteins or peptides. We studied the differential immune responses induced in two mouse strains that are susceptible or resistant to EAE induction when they are immunized with the 139-151 peptide of proteolipid protein, an encephalitogenic peptide capable of inducing EAE in the susceptible strain. The adequate combination of major histocompatibility complex alleles and myelin peptides triggered in susceptible mice a T helper type 17 (Th17) response capable of inducing the production of high-affinity anti-myelin immunoglobulin (Ig)G antibodies. These were not detected in resistant mice, despite immunization with the encephalitogenic peptide in junction with complete Freund's adjuvant and pertussis toxin, which mediate BBB disruption. These data show the pivotal role of Th17 responses and of high-affinity anti-myelin antibodies in EAE induction and that mechanisms that prevent their appearance can contribute to resistance to EAE.

Thiolic antioxidants protect from nitric oxide-induced toxicity in fetal midbrain cultures

Nitric oxide (NO) may act as a neuroprotector or neurotoxic agent in dopamine neurons, depending on cell redox status. We have investigated the effect of several thiolic antioxidants, glutathione (GSH), its cell permeable analog GSH ethyl ester (GSHEE), and the GSH synthesis precursor L-N-acetyl cysteine (L-NAC), as well as non-thiolic antioxidants like ascorbic acid (AA) and uric acid, on NO-induced toxicity in fetal midbrain cultures. The cultures were treated for 8-24 h with neurotoxic doses of the NO donor diethylamine/nitric oxide complex sodium DEA/NO (200-400 micro M) and/or antioxidants. Thiolic antioxidants, at equimolar concentrations, added at the same time or previous to DEA/NO, protected from cell death, from tyrosine hydroxylase (TH) positive cell number decrease and from intracellular GSH depletion, induced by DEA/NO, without increasing intracellular GSH content. In these conditions, S-nitrosothiol compound formation was detected in the culture media. Protection disappeared when antioxidants were supplied 30 min after NO treatment. Nevertheless, non-thiolic antioxidants, AA and uric acid, with similar peroxynitrite scavenging activity to thiolic antioxidants, and free radical-scavenging enzymes as catalase and Cu/Zn-superoxide dismutase, which prevent extracellular peroxynitrite ion formation, and 4,5-dihydroxy-1,3-benzene-disulfonic acid (Tiron), which prevents intracellular peroxynitrite ion formation, did not rescue cell cultures from neurotoxicity induced by NO. In addition, AA exacerbated DEA/NO-induced toxicity in a dose-dependent manner from 200 micro M AA. The present results suggest that only antioxidants with thiol group exert neuroprotection from NO-induced toxicity in fetal midbrain cultures, probably by direct interaction of NO and thiol groups, resulting in NO blocking. On the other hand, some classical antioxidants, like AA, exacerbate neurotoxicity due to NO.

Glutathione depletion switches nitric oxide neurotrophic effects to cell death in midbrain cultures: implications for Parkinson's disease

Nitric oxide (NO) exerts neurotrophic and neurotoxic effects on dopamine (DA) function in primary midbrain cultures. We investigate herein the role of glutathione (GSH) homeostasis in the neurotrophic effects of NO. Fetal midbrain cultures were pretreated with GSH synthesis inhibitor, L-buthionine-(S,R)-sulfoximine (BSO), 24 h before the addition of NO donors (diethylamine/nitric oxide-complexed sodium and S-nitroso-N-acetylpenicillamine) at doses tested previously as neurotrophic. Under these conditions, the neurotrophic effects of NO disappeared and turned on highly toxic. Reduction of GSH levels to 50% of baseline induced cell death in response to neurotrophic doses of NO. Soluble guanylate cyclase (sGC) and cyclic GMP-dependent protein kinase (PKG) inhibitors protected from cell death for up to 10 h after NO addition; the antioxidant ascorbic acid also protected from cell death but its efficacy decreased when it was added after NO treatment (40% protection 2 h after NO addition). The pattern of cell death was characterized by an increase in chromatin condensed cells with no DNA fragmentation and with breakdown of plasmatic membrane. The inhibition of RNA and protein synthesis and of caspase activity also protected from cell death. This study shows that alterations in GSH levels change the neurotrophic effects of NO in midbrain cultures into neurotoxic. Under these conditions, NO triggers a programmed cell death with markers of both apoptosis and necrosis characterized by an early step of free radicals production followed by a late requirement for signalling on the sGC/cGMP/PKG pathway.

L-DOPA and glia-conditioned medium have additive effects on tyrosine hydroxylase expression in human catecholamine-rich neuroblastoma NB69 cells

The aim of this study was to investigate the effect of L-DOPA and glia-conditioned medium (GCM) on cell viability, tyrosine hydroxylase (TH) expression, dopamine (DA) metabolism and glutathione (GSH) levels of NB69 cells. L-DOPA (200 microM) induced differentiation of NB69 cells of more than 4 weeks in vitro, as shown by phase-contrast microscopy and TH immunocytochemistry, and decreased replication, as shown by 5-bromodeoxyuridine immunostaining. L-DOPA did not increase the number of necrotic or apoptotic cells, as shown by morphological features, Trypan Blue, lactate dehydrogenase activity, bis-benzimide staining and TUNEL assay. Furthermore, L-DOPA (200 microM) increased Bcl-xL protein expression. Incubation of cells with L-DOPA (50, 100, 200 microM) for 24 h resulted in an increase in TH protein levels (174, 196 and 212% versus control). Neither carbidopa, an inhibitor of L-aromatic amino acid decarboxylase enzyme, nor L-buthionine sulfoximine, which inhibits GSH synthesis, or ascorbic acid, an antioxidant, blocked the L-DOPA-induced effect on TH protein expression. L-DOPA (0, 50, 100 and 200 microM) plus GCM further increased the amount of TH protein (346, 446, 472 and 424%). L-DOPA (200 microM) increased TH protein levels to 132, 191 and 245% of controls after incubation for 24, 48 and 72 h. DA metabolism in NB69 cells was increased in cultures treated with either L-DOPA (200-300 microM) or GCM and these two agents had a synergistic effect on DA metabolism. In addition, L-DOPA (200 microM) or/and GCM-treated cells increased their GSH extracellular levels (223, 257, 300% of controls) after 48 h of treatment. The L-DOPA-induced increase of TH protein expression in NB69 cells was independent of DA production, free radicals and GSH up-regulation.

Neurotrophic and neurotoxic effects of nitric oxide on fetal midbrain cultures

There is evidence suggesting that nitric oxide (NO) may play an important role in dopamine (DA) cell death. Thus, the aim of this study was to investigate the effects of NO on apoptosis and functionality of DA neurones and glial cells. The experiments were carried out in neuronal-enriched midbrain cultures treated with the NO donor diethylamine-nitric oxide complexed sodium (DEA-NO). DEA-NO, at doses of 25 and 50 microM, exerted neurotrophic effects on dopamine cells, increasing the number of tyrosine hydroxylase positive (TH(+)) cells, TH(+) neurite processes, DA levels and [(3)H]DA uptake. A dose of 25 microM DEA-NO protected DA cells from apoptosis. In addition, it induced de novo TH synthesis and increased intracellular reduced glutathione (GSH) levels, indicating a possible neuroprotective role for GSH. However, in doses ranging from 200 to 400 microM, DEA-NO decreased TH(+) cells, DA levels, [(3)H]DA uptake and the number of mature oligodendrocytes (O1(+) cells). No changes in either the amount or morphology of astrocytes and glial progenitors were detected. A dose- and time-dependent increase in apoptotic cells in the DEA-NO-treated culture was also observed, with a concomitant increase in the proapoptotic Bax protein levels and a reduction in the ratio between Bcl-xL and Bcl-xS proteins. In addition, DEA-NO induced a dose- and time-dependent increase in necrotic cells. 1H-[1,2,4]oxadiazolo[4, 3a]quinoxaline-1-one (ODQ, 0.5 microM), a selective guanylate cyclase inhibitor, did not revert the NO-induced effect on [(3)H]DA uptake. Glia-conditioned medium, obtained from fetal midbrain astrocyte cultures, totally protected neuronal-enriched midbrain cultures from NO-induced apoptosis and rescued [(3)H]DA uptake and TH(+) cell number. In conclusion, our results show that low NO concentrations have neurotrophic effects on DA cells via a cGMP-independent mechanism that may implicate up-regulation of GSH. On the other hand, higher levels of NO induce cell death in both dopamine neurones and mature oligodendrocytes that is totally reverted by soluble factors released from glia.

Nitric oxide induces differentiation in the NB69 human catecholamine-rich cell line

The nitric oxide (NO) donor, S-nitroso-N-acetyl-D,L-penicillamine (SNAP), induced differentiation of human neuroblastoma NB69 cells to a dopamine phenotype, as shown by phase-contrast microscopy and tyrosine hydroxylase (TH) immunocytochemistry. NB69 cells were treated with 50 to 750 microM SNAP in serum-free-defined medium for 24 h. SNAP treatment did not increase the number of necrotic or apoptotic cells. However, a decrease in the number of viable cells was observed at 750 microM SNAP. In addition, a decrease in (3)H-thymidine uptake was detected at the highest dose of SNAP. An increase in the antiapoptotic Bcl-2 and Bcl-xL protein levels and a decrease in the proapoptotic Bax and Bcl-xS protein levels were also detected by Western blot analysis after SNAP treatment. At low doses (50-125 microM), SNAP induced an increase in catecholamine levels, (3)H-dopamine uptake, TH activity and monoamine metabolism, while a decrease in all these parameters was observed at high doses (250-750 microM). The TH protein content, analyzed by Western blot, remained unchanged in SNAP-treated cells throughout the range of doses studied, when compared with the control group. SNAP produced a dose-dependent decrease in the glutathione (GSH) content of the culture medium, without altering intracellular GSH. In addition, cGMP levels and nitrite concentration, measured in the supernatant of SNAP-treated cells, increased in a dose-dependent manner, as compared to control levels. The guanylate cyclase inhibitor lH-[1,2, 4]oxadiazolo[4,3a]quinoxaline-l-one (ODQ) did not revert the SNAP-induced effect on (3)H-dopamine uptake to control values. These results suggest that NO, released from SNAP, induces differentiation of NB69 cells and regulates TH protein at the post-transcriptional level through a cGMP-independent mechanism.

Effect of nitric oxide on the somatostatinergic system in the rat exocrine pancreas

Nitric oxide (NO) and somatostatin (SS) are two important mediators of the exocrine and endocrine pancreas, exerting opposite effects on this organ. There is strong evidence suggesting an interaction between pancreatic NO and SS. The aim of this study was to determine whether L-arginine (L-Arg), the substrate for NO synthase (NOS), and Nomega-nitro-L-arginine methyl ester (L-NAME), a NOS inhibitor, regulate pancreatic somatostatin-like immunoreactivity (SSLI) content and the SS mechanism of action in pancreatic acinar cell membranes. L-Arg (150 mg/kg, intraperitoneally (i.p.)), L-NAME (50 mg/kg, i.p.) or L-NAME plus L-Arg were injected twice daily at 8 h intervals for 8 days. L-Arg decreased pancreatic SSLI content as well as the number of SS receptors in pancreatic acinar cell membranes whereas L-NAME increased both parameters. The stable SS analogue SMS 201-995 induced a significantly lower inhibition of forskolin-stimulated adenylyl cyclase activity in pancreatic acinar cell membranes from L-Arg-treated rats whereas an increased inhibition was observed in pancreatic acinar membranes from L-NAME-treated rats. These results indicate that the NO system may contribute to the regulation of the pancreatic somatostatinergic system.

Redistribution of protein kinase C isoforms in rat pancreatic acini during lactation and weaning

Freshly enzymatically isolated pancreatic acini from lactating and weaning Wistar rats were used to investigate the role of protein kinase C (PKC) isoforms during these physiologically relevant pancreatic secretory and growth processes. The combination of immunoblot and immunohistochemical analysis shows that the PKC isoforms alpha, delta, and epsilon are present in pancreatic acini from control, lactating and weaning rats. A vesicular distribution of PKC-alpha, -delta, and -epsilon was detected by immunohistochemical analysis in the pancreatic acini from all the experimental groups. PKC-delta showed the strongest PKC immunoreactivity (PKC-IR). In this vesicular distribution, PKC-IR was located at the apical region of the acinar cells. No differences were observed between control, lactating and weaning rats. However, the immunoblot analysis of pancreatic PKC isoforms during lactation and weaning showed a significant translocation of PKC-delta from the cytosol to the membrane fraction when compared with control animals. Translocation of PKC isoforms (alpha, delta and epsilon) in response to 12-O-tetradecanoyl phorbol 13-acetate (TPA) 1 microM (15 min, 37 degrees C) was comparable in pancreatic acini from control, lactating and weaning rats. In the control group, a significant translocation of all the isoforms (alpha, delta and epsilon) from the cytosol to the membrane was observed. The PKC isoform most translocated by TPA was PKC-delta. In contrast, no statistically significant increase in PKC-delta translocation was detected in pancreatic acini isolated from lactating or weaning rats. These results suggest that the PKC isoforms are already translocated to the surface of the acinar cells from lactating or weaning rats. In addition, they suggest that isoform specific spatial PKC distribution and translocation occur in association with the growth response previously described in the rat exocrine pancreas during lactation and weaning.

Bombesin induces a reduction of somatostatin inhibition of adenylyl cyclase activity, Gi function, and somatostatin receptors in rat exocrine pancreas

To analyze the effect of bombesin on the somatostatin (SS) mechanism of action in the exocrine pancreas, male Wistar rats (250-270 g) were injected intraperitoneally with bombesin (10 microg/kg) three times daily at 8-h intervals for 7 or 14 days. Bombesin attenuated the ability of SS to inhibit forskolin-stimulated adenylyl cyclase activity in pancreatic acinar membranes. However, it did not decrease the ability of forskolin to stimulate the adenylyl cyclase catalytic subunit. The ability of 5'-guanylylimidodiphosphate [Gpp(NH)p] (a nonhydrolyzable GTP analog) to inhibit forskolin-stimulated adenylyl cyclase activity was diminished in pancreatic acinar cell membranes from bombesin-treated rats. Bombesin administration did not affect the ADP-ribosylation of a 41-kDa G protein catalyzed by pertussis toxin. The maximal SS binding capacity of pancreatic acinar membranes from bombesin-treated rats was decreased when compared with controls at the two time periods studied. The bombesin/gastrin-releasing peptide antagonist [D-Tpi6,Leu13psi(CH2NH)Leu14]bombesin (6-14) (RC-3095) (10 microg/kg i.p.), injected three times daily at 8-h intervals for 7 or 14 days, had a similar effect to that of bombesin on the SS mechanism of action. The combined administration of bombesin and its antagonist RC-3095 had a greater effect on the SS receptor-effector system than when administered separately. The present study indicates that the pancreatic SS receptor-effector system may be regulated by bombesin in vivo.

The somatostatin receptor-adenylate cyclase system in rat pancreatic acinar membranes after temporary pancreaticobiliary duct ligation

The mechanism whereby somatostatin (SS) produces beneficial effects in established pancreatitis induced by pancreaticobiliary duct ligation (PBDL) is still not clear. The aim of the work was to evaluate the possibility of a direct action of SS on pancreatic acinar cells from rats with acute pancreatitis. For this purpose, we studied the SS-receptor-adenylate cyclase system in pancreatic acinar membranes from both, control rats and rats with experimentally induced acute pancreatitis. On the other hand, it has been reported that cholecystokinin (CCK) diminishes the number of SS receptors in pancreatic acinar cells. Proglumide, a CCK receptor antagonist reduces the severity of acute pancreatitis in the rat. Therefore, we have also examined the effect of proglumide on the somatostatinergic system in controls and rats with acute pancreatitis. Fourteen hours after PBDL, the SS receptors, the capacity of the SS analogue SMS 201-995 to inhibit forskolin-stimulated adenylate cyclase activity and PTX-catalyzed [32P] ADP-ribosylation of the alpha1 subunits of Gi proteins could not be detected in pancreatic acinar membranes. One month after reopening the closed pancreaticobiliary duct (PBD), the pancreas showed regeneration of acinar cells, and the above-mentioned parameters were significantly lower than in the control group. Two months after reopening the closed PBD, all these parameters had returned to control values. The administration of proglumide (20 mg/kg i.p.), a cholecystokinin receptor antagonist, accelerated pancreatic regeneration and approached all these parameters to control values one month after reopening the closed PBD. The present study suggests that the beneficial effects of SS on established pancreatitis induced by PBDL may not be due to a direct action of the peptide on pancreatic acinar cells at least at 14 hours after PBDL. In addition, these findings suggest that in established pancreatitis the effect of proglumide on the SS receptor-adenylate cyclase system could be due to its action on pancreatic regeneration.

Influence of fluoxetine and p-chloroamphetamine on the somatostatin receptor-adenylyl cyclase system in the rat frontoparietal cortex

There is evidence that suggests a reciprocal functional link between the serotonergic and the somatostatinergic system in the rat frontoparietal cortex. However, to date, the role of endogenous 5-hydroxytryptamine (serotonin) on the regulation of the somatostatin (SS) receptor-adenylyl cyclase (AC) system remains unclear. In the present study, the administration of fluoxetine (10 mg/kg i.p.), a 5-hydroxytryptamine uptake inhibitor in a single dose or administered daily for 14 days increased the number of specific [125I]Tyr11-SS receptors, with no change in the receptor affinity, in rat frontoparietal cortical membranes. However, the capacity of SS to inhibit forskolin (FK)-stimulated AC activity in these membranes was lower than in the control groups. The ability of the stable GTP analogue 5'-guanylylimidodiphosphate (Gpp(NH)p) to inhibit FK-stimulated AC activity in frontoparietal cortical membranes was also decreased in rats acutely and chronically treated with fluoxetine. p-Chloroamphetamine (5 mg/kg i.p.), which leads to a lasting reduction of 5-hydroxytryptamine innervation, administered on days 1, 3 and 5 and the rats sacrificed 1 or 3 weeks after the first injection, decreased the number of SS receptors without changing the receptor affinity. In this experimental group, SS also caused a significantly lower inhibition of FK-stimulated AC activity. p-Chloroamphetamine had no effect on the ability of Gpp(NH)p to inhibit FK-stimulated AC activity in frontoparietal cortical membranes at all the time periods studied. The present results suggest that under normal circumstances some SS receptors are under a tonic stimulatory control through the serotonergic system.

Dopamine enhances somatostatin receptor-mediated inhibition of adenylate cyclase in rat striatum and hippocampus

Although there is evidence that suggests that dopamine (DA) has stimulatory effects on somatostatinergic transmission, it is unknown to date if DA increases the activity of the somatostatin (SS) receptor-effector system in the rat brain. In this study, we evaluated the effects of the administration of DA and the DA D1-like (D1, D5) receptor antagonist SCH 23390 and the D2-like (D2, D3, D4) receptor antagonist spiperone on the SS receptor-adenylate cyclase (AC) system in the Sprague-Dawley rat striatum and hippocampus. An intracerebroventricular injection of DA (0.5 microgram/rat) increased the number of SS receptors and decreased their apparent affinity in the striatum and hippocampus 15 hr after its administration. The simultaneous administration of the DA receptor antagonists SCH 23390 (0.25 mg/kg, ip) and spiperone (0.1 mg/kg, ip) before DA injection partially prevented the DA-induced increase in SS binding. The administration of SCH 23390 plus spiperone alone produced a significant decrease in the number of SS receptors in both brain areas studied at 15 hr after injection, an effect that disappeared at 24 hr. The increased number of SS receptors in the DA-treated rats was associated with an increased capacity of SS to inhibit basal and forskolin (FK)-stimulated (AC) activity in the striatum and hippocampus at 15 hr after injection. This effect had disappeared at 24 hr. By contrast, basal and FK-stimulated enzyme activities were unaltered after DA injection. No significant changes in the levels of the alpha i (alpha i1 + alpha i2) subunits were found in DA-treated rats as compared with control rats. In addition, the immunodetection of the alpha i1 or alpha i2 subunits showed no significant changes in their levels in DA-treated rats when compared with controls. DA injection also induced an increase in SS-like immunoreactive content in the rat striatum but not hippocampus at 15 hr after administration and returned to control values at 24 hr. These results provide direct evidence of a functional linkage between the dopaminergic and somatostatinergic systems at the molecular level.

Lactational changes in the rat exocrine pancreas somatostatin receptors and modulation of guanylate cyclase

Hyperplasia of the pancreatic tissue during late lactation (third week) and lasting for at least the first two weeks after weaning has been observed by several authors. Since the tetradecapeptide somatostatin (SS) inhibits pancreatic growth and its plasma levels are elevated during these periods, the aim of the present study was to determine the possible implication of the somatostatinergic system in the pancreatic changes cited above. Thus, the present study investigated 125I-Tyr(11)-somatostatin (125I-Tyr(11)-SS) binding and the effects of SS on guanylate cyclase activity as well as pancreatic somatostatin-like immunoreactivity (SSLI) levels in pancreatic acinar membranes from control, lactating and weaning rats. SS receptors were identified using 125I-Tyr(11)-SS and isolated pancreatic acinar membranes in vitro. There was an increase in the number of SS receptors after the third week of lactation (244 +/- 6 vs. 155 +/- 12 fmol/mg protein, P < 0.01) and the first two weeks after weaning (327 +/- 8 vs. 164 +/-10 fmol/mg protein, P < 0.001). No change in the affinity of the receptor site was detected at either study time. In addition, SS-stimulated guanylate cyclase activity was markedly increased at the third week of lactation (119%) and at the second week after weaning (158%) when compared with the control group. In contrast, basal guanylate cyclase activity was not modified at either study period. Thus, SS-stimulated guanylate cyclase activity is increased in pancreatic acinar membranes at late lactation and at the second week after beginning weaning probably due to an increase in the number of SS receptors. Significant decreases in SSLI content were observed at the third week of lactation (69%) and the second week after weaning (37%) when compared with the respective controls. The present results suggest that pancreatic acinar cell growth observed at the third week of lactation and the second week after weaning is associated with up-regulation of SS receptors which would represent a mechanism promoted by the cell that would negatively regulate the mitogenic activity of the increased number of pancreatic growth factors observed during both periods.

Hippocampal somatostatin receptors and modulation of adenylyl cyclase activity in histamine-treated rats

In the present study, the effects of an intracerebroventricular (i.c.v.) dose of histamine (0.1, 1.0 or 10.0 micrograms) on the hippocampal somatostatin (SS) receptor/effector system in Wistar rats were investigated. In view of the rapid onset of histamine action, the effects of histamine on the somatostatinergic system were studied 2 h after its administration. Hippocampal SS-like immunoreactivity (SSLI) levels were not modified by any of the histamine doses studied. SS-mediated inhibition of basal and forskolin (FK)-stimulated adenylyl cyclase (AC) activity was markedly increased in hippocampal membranes from rats treated with 10 micrograms of histamine (23% +/- 1% vs. 17% +/- 1% and 37% +/- 2% vs. 23% +/- 1%, respectively). In contrast, neither the basal nor the FK-stimulated enzyme activities were affected by histamine administration. The functional activity of the hippocampal guanine-nucleotide binding inhibitory protein (Gi protein), as assessed by the capacity of the stable GTP analogue 5'-guanylylimidodiphosphate (Gpp[NH]p) to inhibit FK-stimulated AC activity, was not modified by histamine administration. These data suggest that the increased response of the enzyme to SS was not related to an increased functional activity of Gi proteins. In fact, the increased AC response to SS in hippocampal membranes from histamine (10 micrograms)-treated rats was associated with quantitative changes in the SS receptors. Equilibrium binding data obtained with [125I]Tyr11-SS indicate an increase in the number with specific SS receptors (541 +/- 24 vs. 365 +/- 16 fmol/mg protein, P < 0.001) together with a decrease in their apparent affinity (0.57 +/- 0.04 vs. 0.41 +/- 0.03 nM, P < 0.05) in rat hippocampal membranes from histamine (10 micrograms)-treated rats as compared to control animals. With the aim of determining if these changes were related to histamine binding to its specific receptor sites, the histaminergic H1 and H2 receptor antagonists mepyramine and cimetidine, respectively, were administered 1 h before histamine injection. The pretreatment with mepyramine or cimetidine induced an increase in the number and affinity constant of the SS receptors whereas the simultaneous pretreatment with both histamine antagonists prevented the histamine-induced changes in SS binding to its receptors. Since the hippocampal SS receptor/effector system is modulated by histamine, it is tempting to speculate that in the hippocampus, SS could be involved as a mediator of the histamine effects on behaviors such as learning and memory.

Somatostatin binding capacity, guanylate cyclase and tyrosine phosphatase activities during pancreatic proliferation in the rat induced by gastrectomy

Gastrectomy increased pancreatic growth and this effect was associated with an increase in the number of somatostatin-14 (SS) receptors (146% of control) without altering their affinity. SS increased guanylate cyclase activity twofold in pancreatic acinar membranes from gastrectomized rats. The gastrectomy decreased pancreatic SS-like immunoreactivity (SS-LI) content (55% of control levels) and tyrosine phosphatase activity (74% of control levels). Administration of proglumide (20 mg/kg, IP), a gastrin/cholecystokinin (CCK) receptor antagonist, suppressed the inhibitory effect of gastrectomy on basal tyrosine phosphatase activity and SS-LI content, which returned to control levels. Furthermore, proglumide suppressed the increase of the number of SS receptors and of SS-stimulated guanylate cyclase activity induced by gastrectomy. All this suggests that pancreatic acinar cell growth is associated with upregulation of SS receptors, which could represent a mechanism promoted by the cell to negatively regulate the mitogenic activity of pancreatic growth factors such as CCK. In addition, the results also suggest that the negative regulation of tyrosine phosphatase activity may be important in the events involved in the pancreatic hyperplasia observed after gastrectomy.

Effect of phenylephrine and prazosin on the somatostatinergic system in the rat frontoparietal cortex

Somatostatin (SS) and noradrenaline (NA) are distributed in the rat cerebral cortex, and seizure activity is one of the aspects of behavior affected by both neurotransmitters. Due to the possible interaction between both neurotransmitter systems, we studied whether phenylphrine, an alpha 1-adrenoceptor agonist, and prazosin, an alpha 1-adrenoceptor antagonist, can modulate SS-like immunoreactivity (SS-LI) levels, binding of [125I][Tyr11]SS to its specific receptors, the ability of SS to inhibit adenylate cyclase (AC) activity, and the guanine nucleotide binding regulatory protein G, and G., in the Sprague-Dawley rat frontoparietal cortex. An IP dose of 2 or 4 mg/kg of phenylephrine injected 7 h before decapitation decreased the number of SS receptors and increased the apparent affinity in frontoparietal cortex membranes. An IP dose of 20 or 25 mg/kg of prazosin administered 8 h before decapitation increased the number of SS receptors and decreased their apparent affinity. The administration of prazosin before the phenylephrine injection prevented the phenylephrine-induced changes in SS binding. The addition of phenylephrine and/or prazosin 10(-5) M to the incubation medium changed neither the number nor the affinity of the SS receptors in the frontoparietal cortex membranes. Phenylephrine or prazosin affected neither SS-LI content nor the basal or forskolin (FK)-stimulated AC activities in the frontoparietal cortex. In addition, SS caused an equal inhibition of AC activity in frontoparietal cortex membranes of phenylephrine-and prazosintreated rats compared with the respective control group. Finally, phenylephrine and prazosin did not vary the pertussis toxin (PTX)-catalyzed ADP ribosylation of Gi- and/or Go-proteins. These results suggest that the above-mentioned changes are related to the phenylephrine activation of alpha 1-adrenoceptors or to the blocking of these receptors by prazosin. In addition, these data provide further support for a functional interrelationship between the alpha 1-adrenergic and somatostatinergic systems in the rat frontoparietal cortex.