Temperature, humidity, and ionisation effect of iodine oxoacid nucleation

Iodine oxoacids are recognised for their significant contribution to the formation of new particles in marine and polar atmospheres. Nevertheless, to incorporate the iodine oxoacid nucleation mechanism into global simulations, it is essential to comprehend how this mechanism varies under various atmospheric conditions. In this study, we combined measurements from the CLOUD (Cosmic Leaving OUtdoor Droplets) chamber at CERN and simulations with a kinetic model to investigate the impact of temperature, ionisation, and humidity on iodine oxoacid nucleation. Our findings reveal that ion-induced particle formation rates remain largely unaffected by changes in temperature. However, neutral particle formation rates experience a significant increase when the temperature drops from +10 °C to -10 °C. Running the kinetic model with varying ionisation rates demonstrates that the particle formation rate only increases with a higher ionisation rate when the iodic acid concentration exceeds 1.5 × 107 cm-3, a concentration rarely reached in pristine marine atmospheres. Consequently, our simulations suggest that, despite higher ionisation rates, the charged cluster nucleation pathway of iodic acid is unlikely to be enhanced in the upper troposphere by higher ionisation rates. Instead, the neutral nucleation channel is likely to be the dominant channel in that region. Notably, the iodine oxoacid nucleation mechanism remains unaffected by changes in relative humidity from 2% to 80%. However, under unrealistically dry conditions (below 0.008% RH at +10 °C), iodine oxides (I2O4 and I2O5) significantly enhance formation rates. Therefore, we conclude that iodine oxoacid nucleation is the dominant nucleation mechanism for iodine nucleation in the marine and polar boundary layer atmosphere.

Assessing the importance of nitric acid and ammonia for particle growth in the polluted boundary layer

Aerosols formed and grown by gas-to-particle processes are a major contributor to smog and haze in megacities, despite the competition between growth and loss rates. Rapid growth rates from ammonium nitrate formation have the potential to sustain particle number in typical urban polluted conditions. This process requires supersaturation of gas-phase ammonia and nitric acid with respect to ammonium nitrate saturation ratios. Urban environments are inhomogeneous. In the troposphere, vertical mixing is fast, and aerosols may experience rapidly changing temperatures. In areas close to sources of pollution, gas-phase concentrations can also be highly variable. In this work we present results from nucleation experiments at -10 °C and 5 °C in the CLOUD chamber at CERN. We verify, using a kinetic model, how long supersaturation is likely to be sustained under urban conditions with temperature and concentration inhomogeneities, and the impact it may have on the particle size distribution. We show that rapid and strong temperature changes of 1 °C min-1 are needed to cause rapid growth of nanoparticles through ammonium nitrate formation. Furthermore, inhomogeneous emissions of ammonia in cities may also cause rapid growth of particles.

Role of sesquiterpenes in biogenic new particle formation

Biogenic vapors form new particles in the atmosphere, affecting global climate. The contributions of monoterpenes and isoprene to new particle formation (NPF) have been extensively studied. However, sesquiterpenes have received little attention despite a potentially important role due to their high molecular weight. Via chamber experiments performed under atmospheric conditions, we report biogenic NPF resulting from the oxidation of pure mixtures of β-caryophyllene, α-pinene, and isoprene, which produces oxygenated compounds over a wide range of volatilities. We find that a class of vapors termed ultralow-volatility organic compounds (ULVOCs) are highly efficient nucleators and quantitatively determine NPF efficiency. When compared with a mixture of isoprene and monoterpene alone, adding only 2% sesquiterpene increases the ULVOC yield and doubles the formation rate. Thus, sesquiterpene emissions need to be included in assessments of global aerosol concentrations in pristine climates where biogenic NPF is expected to be a major source of cloud condensation nuclei.

NO at low concentration can enhance the formation of highly oxygenated biogenic molecules in the atmosphere

The interaction between nitrogen monoxide (NO) and organic peroxy radicals (RO₂) greatly impacts the formation of highly oxygenated organic molecules (HOM), the key precursors of secondary organic aerosols. It has been thought that HOM production can be significantly suppressed by NO even at low concentrations. Here, we perform dedicated experiments focusing on HOM formation from monoterpenes at low NO concentrations (0 - 82 pptv). We demonstrate that such low NO can enhance HOM production by modulating the RO₂ loss and favoring the formation of alkoxy radicals that can continue to autoxidize through isomerization. These insights suggest that HOM yields from typical boreal forest emissions can vary between 2.5%-6.5%, and HOM formation will not be completely inhibited even at high NO concentrations. Our findings challenge the notion that NO monotonically reduces HOM yields by extending the knowledge of RO₂-NO interactions to the low-NO regime. This represents a major advance towards an accurate assessment of HOM budgets, especially in low-NO environments, which prevails in the pre-industrial atmosphere, pristine areas, and the upper boundary layer.

Survival of newly formed particles in haze conditions

Intense new particle formation events are regularly observed under highly polluted conditions, despite the high loss rates of nucleated clusters. Higher than expected cluster survival probability implies either ineffective scavenging by pre-existing particles or missing growth mechanisms. Here we present experiments performed in the CLOUD chamber at CERN showing particle formation from a mixture of anthropogenic vapours, under condensation sinks typical of haze conditions, up to 0.1 s⁻¹. We find that new particle formation rates substantially decrease at higher concentrations of pre-existing particles, demonstrating experimentally for the first time that molecular clusters are efficiently scavenged by larger sized particles. Additionally, we demonstrate that in the presence of supersaturated gas-phase nitric acid (HNO₃) and ammonia (NH₃), freshly nucleated particles can grow extremely rapidly, maintaining a high particle number concentration, even in the presence of a high condensation sink. Such high growth rates may explain the high survival probability of freshly formed particles under haze conditions. We identify under what typical urban conditions HNO₃ and NH₃ can be expected to contribute to particle survival during haze.

Illustration of how ammonium nitrate formation can cause rapid growth of nucleating particles, increasing survival of particles in polluted conditions.

Role of iodine oxoacids in atmospheric aerosol nucleation

Iodic acid (HIO3) is known to form aerosol particles in coastal marine regions, but predicted nucleation and growth rates are lacking. Using the CERN CLOUD (Cosmics Leaving Outdoor Droplets) chamber, we find that the nucleation rates of HIO3 particles are rapid, even exceeding sulfuric acid-ammonia rates under similar conditions. We also find that ion-induced nucleation involves IO3 - and the sequential addition of HIO3 and that it proceeds at the kinetic limit below +10°C. In contrast, neutral nucleation involves the repeated sequential addition of iodous acid (HIO2) followed by HIO3, showing that HIO2 plays a key stabilizing role. Freshly formed particles are composed almost entirely of HIO3, which drives rapid particle growth at the kinetic limit. Our measurements indicate that iodine oxoacid particle formation can compete with sulfuric acid in pristine regions of the atmosphere.

Photo-oxidation of Aromatic Hydrocarbons Produces Low-Volatility Organic Compounds

To better understand the role of aromatic hydrocarbons in new-particle formation, we measured the particle-phase abundance and volatility of oxidation products following the reaction of aromatic hydrocarbons with OH radicals. For this we used thermal desorption in an iodide-adduct Time-of-Flight Chemical-Ionization Mass Spectrometer equipped with a Filter Inlet for Gases and AEROsols (FIGAERO-ToF-CIMS). The particle-phase volatility measurements confirm that oxidation products of toluene and naphthalene can contribute to the initial growth of newly formed particles. Toluene-derived (C₇) oxidation products have a similar volatility distribution to that of α-pinene-derived (C₁₀) oxidation products, while naphthalene-derived (C₁₀) oxidation products are much less volatile than those from toluene or α-pinene; they are thus stronger contributors to growth. Rapid progression through multiple generations of oxidation is more pronounced in toluene and naphthalene than in α-pinene, resulting in more oxidation but also favoring functional groups with much lower volatility per added oxygen atom, such as hydroxyl and carboxylic groups instead of hydroperoxide groups. Under conditions typical of polluted urban settings, naphthalene may well contribute to nucleation and the growth of the smallest particles, whereas the more abundant alkyl benzenes may overtake naphthalene once the particles have grown beyond the point where the Kelvin effect strongly influences the condensation driving force.

Rapid growth of new atmospheric particles by nitric acid and ammonia condensation

A list of authors and their affiliations appears at the end of the paper New-particle formation is a major contributor to urban smog1,2, but how it occurs in cities is often puzzling3. If the growth rates of urban particles are similar to those found in cleaner environments (1-10 nanometres per hour), then existing understanding suggests that new urban particles should be rapidly scavenged by the high concentration of pre-existing particles. Here we show, through experiments performed under atmospheric conditions in the CLOUD chamber at CERN, that below about +5 degrees Celsius, nitric acid and ammonia vapours can condense onto freshly nucleated particles as small as a few nanometres in diameter. Moreover, when it is cold enough (below -15 degrees Celsius), nitric acid and ammonia can nucleate directly through an acid-base stabilization mechanism to form ammonium nitrate particles. Given that these vapours are often one thousand times more abundant than sulfuric acid, the resulting particle growth rates can be extremely high, reaching well above 100 nanometres per hour. However, these high growth rates require the gas-particle ammonium nitrate system to be out of equilibrium in order to sustain gas-phase supersaturations. In view of the strong temperature dependence that we measure for the gas-phase supersaturations, we expect such transient conditions to occur in inhomogeneous urban settings, especially in wintertime, driven by vertical mixing and by strong local sources such as traffic. Even though rapid growth from nitric acid and ammonia condensation may last for only a few minutes, it is nonetheless fast enough to shepherd freshly nucleated particles through the smallest size range where they are most vulnerable to scavenging loss, thus greatly increasing their survival probability. We also expect nitric acid and ammonia nucleation and rapid growth to be important in the relatively clean and cold upper free troposphere, where ammonia can be convected from the continental boundary layer and nitric acid is abundant from electrical storms4,5.

Molecular Composition and Volatility of Nucleated Particles from α-Pinene Oxidation between -50 °C and +25 °C

We use a real-time temperature-programmed desorption chemical-ionization mass spectrometer (FIGAERO-CIMS) to measure particle-phase composition and volatility of nucleated particles, studying pure α-pinene oxidation over a wide temperature range (-50 °C to +25 °C) in the CLOUD chamber at CERN. Highly oxygenated organic molecules are much more abundant in particles formed at higher temperatures, shifting the compounds toward higher O/C and lower intrinsic (300 K) volatility. We find that pure biogenic nucleation and growth depends only weakly on temperature. This is because the positive temperature dependence of degree of oxidation (and polarity) and the negative temperature dependence of volatility counteract each other. Unlike prior work that relied on estimated volatility, we directly measure volatility via calibrated temperature-programmed desorption. Our particle-phase measurements are consistent with gas-phase results and indicate that during new-particle formation from α-pinene oxidation, gas-phase chemistry directly determines the properties of materials in the condensed phase. We now have consistency between measured gas-phase product concentrations, product volatility, measured and modeled growth rates, and the particle composition over most temperatures found in the troposphere.

Multicomponent new particle formation from sulfuric acid, ammonia, and biogenic vapors

A major fraction of atmospheric aerosol particles, which affect both air quality and climate, form from gaseous precursors in the atmosphere. Highly oxygenated organic molecules (HOMs), formed by oxidation of biogenic volatile organic compounds, are known to participate in particle formation and growth. However, it is not well understood how they interact with atmospheric pollutants, such as nitrogen oxides (NO _x ) and sulfur oxides (SO _x ) from fossil fuel combustion, as well as ammonia (NH₃) from livestock and fertilizers. Here, we show how NO _x suppresses particle formation, while HOMs, sulfuric acid, and NH₃ have a synergistic enhancing effect on particle formation. We postulate a novel mechanism, involving HOMs, sulfuric acid, and ammonia, which is able to closely reproduce observations of particle formation and growth in daytime boreal forest and similar environments. The findings elucidate the complex interactions between biogenic and anthropogenic vapors in the atmospheric aerosol system.

The role of low-volatility organic compounds in initial particle growth in the atmosphere

About half of present-day cloud condensation nuclei originate from atmospheric nucleation, frequently appearing as a burst of new particles near midday. Atmospheric observations show that the growth rate of new particles often accelerates when the diameter of the particles is between one and ten nanometres. In this critical size range, new particles are most likely to be lost by coagulation with pre-existing particles, thereby failing to form new cloud condensation nuclei that are typically 50 to 100 nanometres across. Sulfuric acid vapour is often involved in nucleation but is too scarce to explain most subsequent growth, leaving organic vapours as the most plausible alternative, at least in the planetary boundary layer. Although recent studies predict that low-volatility organic vapours contribute during initial growth, direct evidence has been lacking. The accelerating growth may result from increased photolytic production of condensable organic species in the afternoon, and the presence of a possible Kelvin (curvature) effect, which inhibits organic vapour condensation on the smallest particles (the nano-Köhler theory), has so far remained ambiguous. Here we present experiments performed in a large chamber under atmospheric conditions that investigate the role of organic vapours in the initial growth of nucleated organic particles in the absence of inorganic acids and bases such as sulfuric acid or ammonia and amines, respectively. Using data from the same set of experiments, it has been shown that organic vapours alone can drive nucleation. We focus on the growth of nucleated particles and find that the organic vapours that drive initial growth have extremely low volatilities (saturation concentration less than 10(-4.5) micrograms per cubic metre). As the particles increase in size and the Kelvin barrier falls, subsequent growth is primarily due to more abundant organic vapours of slightly higher volatility (saturation concentrations of 10(-4.5) to 10(-0.5) micrograms per cubic metre). We present a particle growth model that quantitatively reproduces our measurements. Furthermore, we implement a parameterization of the first steps of growth in a global aerosol model and find that concentrations of atmospheric cloud concentration nuclei can change substantially in response, that is, by up to 50 per cent in comparison with previously assumed growth rate parameterizations.

Ion-induced nucleation of pure biogenic particles

Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood. Globally, around half of cloud condensation nuclei originate from nucleation of atmospheric vapours. It is thought that sulfuric acid is essential to initiate most particle formation in the atmosphere, and that ions have a relatively minor role. Some laboratory studies, however, have reported organic particle formation without the intentional addition of sulfuric acid, although contamination could not be excluded. Here we present evidence for the formation of aerosol particles from highly oxidized biogenic vapours in the absence of sulfuric acid in a large chamber under atmospheric conditions. The highly oxygenated molecules (HOMs) are produced by ozonolysis of α-pinene. We find that ions from Galactic cosmic rays increase the nucleation rate by one to two orders of magnitude compared with neutral nucleation. Our experimental findings are supported by quantum chemical calculations of the cluster binding energies of representative HOMs. Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution.

HDL lipid composition is profoundly altered in patients with type 2 diabetes and atherosclerotic vascular disease

BACKGROUND AND AIMS

We have previously shown that the anti-inflammatory and anti-oxidant functions of HDL are impaired in T2D patients. In this study, we examined whether HDL from T2D patients contains elevated levels of oxidized fatty acids and whether those levels correlate with cardiovascular disease (CVD).

METHODS AND RESULTS

HETEs and HODEs on HDL were determined by LC-MS/MS in 40 non-diabetic controls (ND), 40 T2D without CVD (D⁺CVD⁻) and 38 T2D with known history of CVD (D⁺CVD⁺). HDL oxidant index was evaluated by a cell-free assay using dichlorofluorescein. Twenty-six randomly selected subjects from the three groups underwent coronary calcium score evaluation (CAC). Major cardiovascular risk factors were similar among the groups. HETEs and HODEs content were significantly increased in HDL from D⁺CVD⁺ when compared to D⁺CVD⁻ and ND patients. HDL oxidant index was not different among the three groups; however, it was significantly higher in patients with CAC score >100 when compared to patients with CAC score <100.

CONCLUSION

Patients with D⁺CVD⁻ and D⁺CVD⁺ are characterized by a severe, graded enrichment of oxidized fatty acids on HDL. In the present study, a loss of HDL function (as estimated by the HDL oxidant index) is observed only in patients with more advanced atherosclerosis.

Comparison of CT colonography, colonoscopy, sigmoidoscopy and faecal occult blood tests for the detection of advanced adenoma in an average risk population

BACKGROUND AND AIMS

This prospective trial was designed to compare the performance characteristics of five different screening tests in parallel for the detection of advanced colonic neoplasia: CT colonography (CTC), colonoscopy (OC), flexible sigmoidoscopy (FS), faecal immunochemical stool testing (FIT) and faecal occult blood testing (FOBT).

METHODS

Average risk adults provided stool specimens for FOBT and FIT, and underwent same-day low-dose 64-multidetector row CTC and OC using segmentally unblinded OC as the standard of reference. Sensitivities and specificities were calculated for each single test, and for combinations of FS and stool tests. CTC radiation exposure was measured, and patient comfort levels and preferences were assessed by questionnaire.

RESULTS

221 adenomas were detected in 307 subjects who completed CTC (mean radiation dose, 4.5 mSv) and OC; 269 patients provided stool samples for both FOBT and FIT. Sensitivities of OC, CTC, FS, FIT and FOBT for advanced colonic neoplasia were 100% (95% CI 88.4% to 100%), 96.7% (82.8% to 99.9%), 83.3% (95% CI 65.3% to 94.4%), 32% (95% CI 14.9% to 53.5) and 20% (95% CI 6.8% to 40.7%), respectively. Combination of FS with FOBT or FIT led to no relevant increase in sensitivity. 12 of 45 advanced adenomas were smaller than 10 mm. 46% of patients preferred CTC and 37% preferred OC (p<0.001).

CONCLUSIONS

High-resolution and low-dose CTC is feasible for colorectal cancer screening and reaches sensitivities comparable with OC for polyps >5 mm. For patients who refuse full bowel preparation and OC or CTC, FS should be preferred over stool tests. However, in cases where stool tests are performed, FIT should be recommended rather than FOBT.

Hyperthermia-induced HSP expression correlates with improved rat renal isograft viability and survival in kidneys harvested from non-heart-beating donors

Transient sublethal hyperthermia followed by recovery from heat stress, referred to as heat shock preconditioning, exerts a protective effect on ischemia/reperfusion-induced injury in many systems. This effect is considered to be correlated to heat shock proteins (HSPs) and might be a critical factor in kidney graft function and survival. This study was designed to examine the impact of heat shock preconditioning on kidney isograft function and survival in a model utilizing non-heart-beating (NHB) donors. Four groups of male Lewis rats (n = 10/group) subjected either to whole body hyperthermia (groups A and C) or to sham anesthesia (groups B and D) were allowed 24 h recovery. Thereafter, 20 min of warm ischemia (A/B), and in a separate set of experiments 40 min of warm ischemia (C/D), were induced by suprarenal aortic cross clamping before renal procurement. After 24-h preservation with University of Wisconsin solution at 4 degrees C, orthotopic kidney transplantations were performed to syngeneic bilaterally nephrectomized recipients. Tissue specimens were taken to determine HO-1/HSP32, 72, and 90 induction by Western blot analysis. Renal function was measured by means of serum creatinine and creatinine clearance on days 0, 3, and 7 as well as urine volume, protein content, and creatinine levels daily. HO-1/HSP32 and HSP72 were found to be expressed constitutively. Moreover, heat shock strongly induced renal HSP72 and HSP32/HO-1, and to a lesser extent HSP90, expression. For recipients of group A grafts, the graft survival rate was 10/10, whereas it was 7/10 (70 %) in recipients of group B grafts (log rank p < 0.05). Following 40 min of warm ischemia, 6/10 (60 %) recipients survived, whereas all sham treated animals died with anuria within 6 days (log rank p = 0.01). Heat shock preconditioning strongly improved graft viability and reduced functional impairment. Creatinine clearance (CRC) on day 3 post Tx was 0.43 +/- 0.24 ml/min in preconditioned animals (group A) and 0.07 +/- 0.09 ml/min (p < 0.001) in sham preconditioned (group B), whereas it was 0.91 +/- 0.33 ml/min and 0.03 +/- 0.02 ml/min (p < 0.00 001) on day 7 post Tx. Following 40 min NHB time, CRC in survivors of preconditioned graft recipients (group C) was 0.32 +/- 0.2 ml/min (day 3 post Tx) and 0.23 +/- 0.08 ml/min (day 7 post Tx) and was significantly better than CRC of group B (p < 0.01 and p < 0.00001, respectively). CRCs prior to NHB procedures were comparable in all animals ranging between 1.31 and 1.72 ml/min. Serum creatinine as well as proteinuria were significantly increased after transplantation in both groups but recovered within 5 days in recipients of preconditioned grafts, whereas kidneys from donors without HP did not recover function. Histological alterations were also diminished following HP. Hyperthermic preconditioning induces strong and long lasting HO-1/HSP32, HSP72, and HSP90 expression in rat kidneys. HP increases survival following transplantation and improves renal graft function including proteinuria, volume output, and creatinine clearance. HSP induction might be used to develop novel approaches in clinical transplantation.

Treatment of hepatic hydrothorax and reduction of chest tube output with octreotide

Hepatic hydrothorax is a dreaded complication in patients with liver cirrhosis. Placement of chest tubes can alleviate respiratory distress, but patients often succumb due to excessive fluid and protein loss via the open drain. Our case illustrates that high-dose octreotide can strongly reduce hepatic hydrothorax drainage volume. This allows removal of the chest tube, which would otherwise not have been possible.

High-density lipoprotein loses its anti-inflammatory properties during acute influenza a infection

BACKGROUND

Viruses have been identified as one of a variety of potential agents that are implicated in atherogenesis.

METHODS AND RESULTS

C57BL/6J mice were killed before or 2, 3, 5, 7, or 9 days after intranasal infection with 10(5) plaque-forming units (pfu) of Influenza A strain WSN/33. Peak infectivity in lungs was reached by 72 hours, and it returned to baseline by 9 days. No viremia was observed at any time. The activities of paraoxonase and platelet-activating factor acetylhydrolase in HDL decreased after infection and reached their lowest levels 7 days after inoculation. The ability of HDL from infected mice to inhibit LDL oxidation and LDL-induced monocyte chemotactic activity in human artery wall cell cocultures decreased with time after inoculation. Moreover, as the infection progressed, LDL more readily induced monocyte chemotaxis. Peak interleukin-6 and serum amyloid A plasma levels were observed at 2 and 7 days after inoculation. HDL apoA-I levels did not change. ApoJ and ceruloplasmin levels in HDL peaked 3 days after infection. Ceruloplasmin remained elevated throughout the time course, whereas apoJ levels decreased toward baseline after the third day.

CONCLUSIONS

We conclude that alterations in the relative levels of paraoxonase, platelet-activating factor acetylhydrolase, ceruloplasmin, and apoJ in HDL occur during acute influenza infection, causing HDL to lose its anti-inflammatory properties.

Stress kinase inhibition modulates acute experimental pancreatitis

AIM: To examine the role of p38 during acute experimental cerulein pancreatitis.

METHODS: Rats were treated with cerulein with or without a specific JNK inhibitor (CEP1347) and/or a specific p38 inhbitor (SB203580) and pancreatic stress kinase activity was determined. Parameters to assess pancreatitis included trypsin, amylase, lipase, pancreatic weight and histology.

RESULTS: JNK inhibition with CEP1347 ameliorated pancreatitis, reducing pancreatic edema. In contrast, p38 inhibition with SB203580 aggravated pancreatitis with higher trypsin levels and, with induction of acinar necrosis not normally found after cerulein hyperstimulation. Simultaneous treatment with both CEP1347 and SB203580 mutually abolished the effects of either compound on cerulein pancreatitis.

CONCLUSION: Stress kinases modulate pancreatitis differentially. JNK seems to promote pancreatitis development, possibly by supporting inflammatory reactions such as edema formation while its inhibition ameliorates pancreatitis. In contrast, p38 may help reduce organ destruction while inhibition of p38 during induction of cerulein pancreatitis leads to the occurrence of acinar necrosis.

[Barrett's esophagus: screening and prognosis]

The diagnostic criteria for Barrett's disease have changed very considerably during the last 10 years. Classically, the definition asked for columnar epithelium in the lower esophagus extending for at least 3 cm proximally. Now, the diagnosis rests on the finding of specialised intestinal metaplasia, i.e. columnar epithelium with goblet cells, in the esophagus, regardless of the extension. This is important because it is this type of metaplasia that is associated with an increased risk for the development of esophageal adenocarcinoma and esophageal adenocarcinoma is the tumor with the fastest rising incidence in the western world in recent years. The criteria of the current definition of Barrett's esophagus are described in detail and the implications this change in definition carries for screening and surveillance of patients is discussed.

Oxidized phospholipids induce changes in hepatic paraoxonase and ApoJ but not monocyte chemoattractant protein-1 via interleukin-6

In this study, we tested if interleukin-6 (IL-6) plays a role in mediating the effects of oxidized phospholipids (OXPL). Treatment of HepG2 cells with oxidized 1-palmitoyl-2-arachidonyl-sn-glycero-3-phosphoryl choline (OX-PAPC), or biologically active lipids present in mildly oxidized low density lipoprotein, increased apolipoprotein J (apoJ), and decreased paraoxonase (PON) mRNA levels. Antibodies to IL-6 blocked these changes. IL-6 treatment in the absence of OXPL produced the same pattern of mRNA changes observed with OXPL treatment alone. In vivo, OX-PAPC injected into C57BL/6J mice resulted in a marked reduction in PON activity and an increase in apoJ levels in plasma after 16 h. Injection of OX-PAPC into IL-6-deficient C57BL/6J mice (IL-6 -/-) did not alter either PON activity or apoJ levels. We then tested if other mechanisms involved in fatty streak formation depended upon IL-6. Antibody to IL-6 had no effect on OX-PAPC-induced secretion of MCP-1 by endothelial cells nor on MCP-1 mRNA expression in HepG2 cells. C57BL/6J and IL-6 -/- mice fed an atherogenic diet both demonstrated markedly reduced plasma PON activities and the IL-6 -/- mice developed fatty streaks to a greater degree than wild-type mice. We conclude that IL-6 is critical to short term but not long term regulation of PON and that IL-6 is not required for OXPL regulation of MCP-1.

Heat shock response is associated with protection against acute interstitial pancreatitis in rats

We recently reported that hyperthermia induces pancreatic expression of heat shock proteins (HSPs), particularly HSP70 isoforms, and protects against cerulein pancreatitis. We have now studied whether a double hyperthermia amplifies these effects and whether hyperthermia also protects against dibutyltin dichloride (DBTC)-induced pancreatitis. A further aim was to examine whether hyperthermia induces changes in transforming growth factor-beta1 (TGF-beta1). Following pretreatment without or with a single or double hyperthermia, pancreatitis was induced by application of cerulein or DBTC. Pancreatic HSP and TGF-beta1 expression were studied by immunoblotting. Pancreas injury was assessed by light microscopy and serum pancreatic enzyme activity. Hyperthermia as well as DBTC induced HSP72, whereas cerulein did not. A double hyperthermia led to a further increase in HSP72 compared to a single heat stress. In both models, hyperthermia significantly reduced pancreatic injury. Although a double hyperthermia slightly decreased the severity of cerulein pancreatitis compared to a single heat treatment, an improved pancreas protection against DBTC cytotoxicity was not achieved. We also found that hyperthermia induces the expression of TGF-beta1. In conclusion, hyperthermia preconditioning exerts protective effects against two pathophysiologically different types of pancreatitis by a mechanism that involves the up-regulation of HSP70 isoforms as well as TGF-beta1.

Map kinase phosphatases (MKP's) are early responsive genes during induction of cerulein hyperstimulation pancreatitis

Mitogen-activated protein kinase (MAPK) family members such as c-jun N-terminal kinase (JNK) may act as signal transducers early during pancreatitis development and evidence indicates that MAPK phosphatases (MKP) downregulate MAPK. We therefore investigated expression and regulation of pancreatic MKP in vivo. Pancreatic MKP mRNA levels were near or below the detection threshold in unstimulated animals. Cerulein hyperstimulation strongly induced MKP-1, MKP-3, and MKP-5 expression, peaking 30 to 60 min after treatment. Thus, MKP's clearly are early responsive genes during pancreatitis induction. Interestingly, inhibition of MKP-1 expression by Ro-31-8220 maximally induced activation of JNK but not of p38 and ERK in acutely isolated acini. These effects indicate that JNK may indeed be a preferred MKP-1 substrate in vivo.

[Drug treatment of chronic inflammatory bowel diseases: current status and prospects]

The medical treatment of inflammatory bowel disease is dependent on disease activity and bowel involvement. Severe Crohn's disease and ulcerative colitis are primarily treated with corticosteroids. Alternatively, if inflammation is localised in the right colon and ileum, budesonide may be used in view of its low systemic side effects. In distal colitis and perianal disease, topical therapy with steroids is very effective. In moderate disease preparations containing 5-aminosalicylate (5-ASA) may be used. The latter are highly effective applied locally in distal disease. Steroids should be tapered down and whenever possible not used to maintain remission. In patients with ulcerative colitis, 5-ASA is effective in maintaining remission, whereas this medication plays only a limited role in Crohn's disease. Refractory disease or patients with multiple flare-ups should be treated with azathioprine. Infliximab, an anti-TNF-alpha antibody, is a potent therapy for fistulising Crohn's disease or steroid-refractory disease. Other approved and experimental treatments are discussed.

CEP-1347 inhibits caerulein-induced rat pancreatic JNK activation and ameliorates caerulein pancreatitis

Pancreatic caerulein-induced activation of c-Jun NH(2)-terminal kinase (JNK) has been reported, and JNK has been proposed as a mediator during induction of hyperstimulated pancreatitis. CEP-1347 has recently been described as a specific JNK inhibitor. We tested whether CEP-1347 inhibits caerulein-induced pancreatic JNK activation in isolated acini and in vivo. CEP-1347 dose dependently inhibited acinar caerulein-induced JNK activation with nearly complete inhibition at 2 microM but had no effect on digestive enzyme release. For in vivo studies, rats were pretreated with CEP-1347 before caerulein hyperstimulation. For assessment of JNK activation and histological alterations, animals were killed 30 min or 2 and 4 h after caerulein hyperstimulation, respectively. Pancreatic wet weight, serum enzyme levels, and pancreatic activity of p38 and extracellular signal-regulated kinase (ERK) were also determined. Caerulein hyperstimulation strongly activated JNK, p38, and ERK. CEP-1347 pretreatment dose dependently reduced caerulein-induced pancreatic JNK activation without p38 or ERK inhibition. JNK inhibition also reduced pancreatic edema formation and reduced histological severity of pancreatitis. Thus we show that CEP-1347 inhibits JNK activation in vivo and ameliorates caerulein-induced pancreatitis.

Hyperthermia, inducing pancreatic heat-shock proteins, fails to prevent cerulein-induced stress kinase activation

The dually phosphorylated c-jun kinase and p38 mitogen-activated protein (MAP) kinase, also termed stress kinases, are members of the MAP kinase family. They are activated early during cerulein pancreatitis induction and have been proposed as regulators during pancreatitis development by us and others. We recently showed that hyperthermia preconditioning induces expression of pancreatic heat-shock proteins (HSP) and protects against cerulein pancreatitis. Because it was further reported that HSP70 can prevent activation of stress kinases in lymphoid tumor cells, we investigated whether hyperthermia preconditioning might reduce hyperstimulation-mediated activation of pancreatic stress kinases. Pancreatic HSP expression was induced by whole-body hyperthermia preconditioning. Without prior HSP induction, cerulein led to a rapid and dose-dependent increase in serum lipase and amylase levels, pancreatic wet weight through edema formation, and activation of pancreatic MAP kinases. Hyperthermia preconditioning, although strongly inducing HSP70 and almost completely preventing edema formation, as well as the increase of serum amylase and lipase, did not reduce cerulein-mediated stress kinase activation. This indicates that in the pancreas, cerulein can strongly activate MAP kinases even when pancreatitis development is greatly inhibited, and that pancreatic HSPs do not inhibit activation of pancreatic stress kinases in vivo.

p38 map kinase is expressed in the pancreas and is immediately activated following cerulein hyperstimulation

BACKGROUND

The pathophysiology of pancreatitis and the pancreatic stress response are not well understood. In the pancreas, mitogen-activated protein kinase (MAPK) and stress-activated protein kinase (SAPK) are reportedly regulated by secretagogue stimulation and hyperstimulation. However, no data exist on the expression and regulation of pancreatic p38 Map kinase.

AIMS

Pancreatic expression of p38 Map kinase and MAPK, SAPK and p38 regulation during pancreatic stress were investigated.

METHODS

For hyperstimulation and secretory stress, cerulein was given intravenously, while hyperthermia preconditioning stress was induced by whole body hyperthermia (42 degreesC).

RESULTS

In addition to MAPK and SAPK, p38 Map kinase was found to be expressed in the rat pancreas. Cerulein regulated all kinases time- and dose-dependently. MAPK and p38 Map kinase showed basal activity and were further activated at low cerulein doses. SAPK had no basal activity and its activation required maximal secretory to supramaximal amounts of cerulein. Cerulein hyperstimulation, inducing pancreatitis, activated p38 more rapidly than SAPK and more strongly than MAPK. In contrast to cerulein hyperstimulation stress, hyperthermia stress only activated p38 Map kinase.

CONCLUSIONS

p38 Map kinase is expressed in the pancreas and is most rapidly activated following cerulein hyperstimulation. Both SAPK and p38 Map kinase are possibly important regulators during the onset of cerulein pancreatitis.

Membrane dipeptidase and glutathione are major components of pig pancreatic zymogen granules

Membrane proteins of highly purified porcine zymogen granules were separated by two-dimensional gel electrophoresis in order to isolate proteins which are involved in intracellular trafficking of digestive enzymes in the exocrine pancreas. A 48-kDa glycoprotein was a major component in membrane preparations washed with 0.1 M Na2CO3 and 0.5 M NaCl. By N-terminal amino acid sequencing this protein was identified as membrane dipeptidase (MDP; EC 3.4.13.19). MDP mRNA levels in rat pancreas were increased threefold by feeding rats with FOY-305, which is a known stimulus of endogenous cholecystokinin release from the gut. Cholecystokinin then stimulates secretion in pancreatic acinar cells. In another set of experiments treatment of the rat pancreatic acinar tumor cell line AR42J with dexamethasone led to an eightfold increase in the expression of MDP. Thus, the expression pattern of the MDP gene in response to hormonal stimulation in vivo and in vitro resembles those found for most of the enzymes and proteins which are involved in secretion. Since MDP has been thought to have a role in glutathione (GSH) metabolism, we also measured GSH concentration in zymogen granules and found high levels of GSH. Based on our data we propose a working model for the function of MDP. According to this model, MDP might play a pivotal role in maintaining the oxidizing conditions in the ER, which are required for the correct folding of secretory proteins.

Caerulein pancreatitis increases mRNA but reduces protein levels of rat pancreatic heat shock proteins

We have recently reported that preconditioning through hyperthermia induces expression of pancreatic heat shock proteins (HSPs) and protects against caerulein pancreatitis. Here, we investigate caerulein-mediated effects on pancreatic HSPs without prior hyperthermia. Caerulein time and dose dependently increased pancreatic mRNA levels of the constitutive isoform of HSP70 (HSC70). However, pancreatic HSC70 protein levels were decreased, as were HSP60 protein levels. Also, in contrast to hyperthermia preconditioning, caerulein did not induce measurable levels of mRNA or protein of the inducible isoform of HSP70. Thus the pancreas reacts to different kinds of stress (hyperthermia vs. hyperstimulation) with differential induction of HSP mRNAs. Clearly, hyperthermia leads to induction of HSP protein expression, whereas caerulein treatment does not. Therefore, our current study further supports the idea that hyperthermia-induced protection against caerulein pancreatitis may be mediated through increased protein levels of pancreatic HSPs. It is further tempting to hypothesize that failure to appropriately increase HSP protein levels in response to high doses of caerulein might be a factor in the development of pancreatitis.

Small bowel lengthening by mechanical distraction

To evaluate whether the small bowel can be distracted by mechanical stress in analogy to limb lengthening by osteodistraction, a gut-lengthening apparatus was designed. This distractor was placed at the antimesenterical side of a defined jejunum segment in rabbits. Distraction was performed by 1 mm lengthening of the distractor once daily using extracorporal screws. An effective gut lengthening was achieved of 9.9 +/- 0.5 mm (approximately 100%) within 3 weeks. Treated animals gained weight and remained in good general condition. Fasting plasma levels of cholecystokinin, neurotensin, glucagon-like peptide-1, gastric inhibitory polypeptide, and insulin remained unaffected. Postoperative factor XIII levels were significantly diminished and gastrin was elevated during gut distraction. DNA and protein concentrations in the mucosa of the distracted gut segments corresponded to controls. Mucosal lactase and saccharase activities were reduced. In the distracted bowel segments total tunica muscularis thickness was more than doubled due to muscle cell hypertrophy. In distracted segments villous width was increased. Detection of proliferating mucosal crypt cells utilizing BrdUrd labeling revealed no effects. In conclusion, small gut lengthening by mechanical distraction is possible without major changes in gut morphology. This technique may hint a novel experimental approach for the treatment of short bowel syndrome.

Hyperthermia induces heat shock protein expression and protection against cerulein-induced pancreatitis in rats

BACKGROUND & AIMS

Heat shock proteins (HSPs) are part of the cellular stress response machinery. HSPs are expressed in the pancreas, but their protective potential has not been thoroughly investigated. The aim of this study was to characterize the pancreatic heat shock response both in vitro and in vivo and to study whether this response has protective effects.

METHODS

For in vitro experiments, rat pancreatic acini were exposed to heat and protein expression was analyzed through 35S-methionine labeling or Western blots. In vivo, cerulein pancreatitis was induced after whole body hyperthermia (42 degrees C).

RESULTS

After thermal stress (42 degrees C), acini increasingly expressed five proteins of 92, 72, 59, 58, and 30 kilodaltons, with HSP. 70 the most strongly induced 72-kilodalton protein. In vivo, increased expression of four isoforms of pancreatic HSP-70 was found. Isoform-specific antibodies identified the inducible and constitutively expressed (HSC-70) isoform of HSP-70. HSP-60 was also weakly induced after hyperthermia. Concomitantly, cerulein-induced pancreatic organ damage was greatly reduced after whole-body hyperthermia. The time course and strength of HSP induction correlated well with the time course and degree of protection against cerulein-induced pancreatitis.

CONCLUSIONS

A causal relation between hyperthermia-induced HSP expression and organ protection seems possible.

Calcium induces rapid changes in protein phosphorylation in permeabilized pancreatic acini

Calcium is an important mediator of pancreatic stimulus-secretion coupling, and in streptolysin O-permeabilized acini maximal amylase release can be induced by 1 microMCa2+. Two-dimensional analysis of acinar phosphoproteins using 32P-labeled acini showed that 1-min stimulation of permeabilized acini with 1 microMCa2+ induced a number of rapid protein phosphorylation and dephosphorylation events similar to previously observed effects of secretagogues acting on intact acini. The rapid Ca2+ effects on protein phosphorylation correlated well with the earliest detectable onset of amylase release after 1 min of incubation with Ca2+. Our findings indicate that some of the agonist-induced changes in protein phosphorylation are mediated by Ca2+ and also provide evidence for the possible involvement of Ca(2+)-mediated dephosphorylation in acinar stimulus-secretion coupling.

Molecular cloning of a new member of the Rab protein family, Rab 26, from rat pancreas

Members of the Rab family of low molecular weight GTP-binding (LMWG) proteins regulate vesicular transport; distinct Rab proteins are located in specific vesicular compartments within the exocytotic and endocytotic pathway. Pancreatic zymogen granules possess multiple LMWG. Rab 3A, however, which has been suggested to regulate exocytosis of synaptic vesicles, is not present in rat pancreatic acinar cells or on zymogen granules (BBRC 1994,269:542-548). To look for homologues of Rab 3A we have screened a rat pancreatic cDNA library using Rab 3A as a probe. We now report the cDNA and deduced amino acid sequence of a new member of the Rab protein family. Rab 26 is a 190 AA protein with a predicted molecular mass of 21,459 Dalton. It is expressed in pancreas, kidney, brain, submandibular gland, and lung. It is most closely related to Rab 8. There is also close homology to Rab 15, Sec4 and Rab 3.

Secretagogue regulation of pancreatic acinar cell protein phosphorylation shown by large-scale 2D-PAGE

High-resolution large-scale two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) combined with computer-assisted image analysis was used to construct a database of secretagogue/second messenger-induced phosphoprotein modifications in intact rat pancreatic acinar cells. Isolated acini were labeled with 32Pi, exposed to hormones and other test agents, and subjected to large-scale 2D-PAGE and autoradiography. This procedure resolved 500 phosphoproteins in pancreatic acinar whole cell lysates, approximately 90% of which were localized in the soluble fraction of centrifuged samples. Soluble proteins were further characterized as to heat and acid stability. Cholecystokinin (CCK), carbachol, and bombesin altered the phosphorylation state of about 27 proteins with both increases and decreases observed. Subsets of proteins were phosphorylated in response to phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA), calcium ionophore A-23187, and adenosine 3',5'-cyclic monophosphate (cAMP) analogue 8-bromo-cAMP. One of these proteins was identified as the myristoylated, alanine-rich, C-kinase substrate (MARCKS) protein by immunoprecipitation. The time course and dose response of phosphorylation changes due to CCK showed considerable variation between proteins, although a temporal hierarchy of phosphorylation events was clearly exhibited. Particularly striking was the rapid dephosphorylation within 30 s of a 19-kDa soluble protein to a minimum of 20 +/- 1% of control. Increased phosphorylation of the MARCKS and other TPA-regulated proteins suggests that CCK, carbachol, bombesin, and the CCK partial agonist, JMV-180, all activate protein kinase C in intact acini.

Anemia with LDH-elevation in a patient with aortic valve replacement

In a 63-year old patient with a history of aortic valve replacement in 1986, a reduced hemoglobin of 91 g/l was found by a family physician. Since serum LDH was also increased, the patient was diagnosed to suffer from mechanically induced, hemolytic anemia and presented at our hospital for further diagnosis and evaluation of the aortic valve prosthesis.

Cyclosporin A inhibits Ca2+/calmodulin-dependent protein phosphatase and secretion in pancreatic acinar cells

The immunosuppressant cyclosporin A (CsA) was utilized as a highly specific inhibitor of the Ca2+/calmodulin-dependent protein phosphatase, PP2B in rat pancreatic acinar cells. Treatment of cells with CsA for 20 min resulted in a concentration-dependent inhibition of PP2B that was maximal (> 90%) at 1 microM and exhibited an IC50 of 65 nM. CsA also inhibited cholecystokinin-, 100 pM, or carbamylcholine-, 10 microM, induced amylase release in a concentration-dependent manner. A maximal inhibition to 55% of stimulated control cells occurred at 1 microM CsA with half-maximal inhibition occurring at approximately 200 nM. Secretion in response to 1 microM 12-O-tetradecanoylphorbol-13-acetate (TPA) was uneffected by CsA treatment. Conversely, amylase release stimulated by the Ca2+ mobilizing agent, thapsigargin, when added alone at 2 microM or in combination with TPA, was inhibited by CsA to 66 and 61% of control cells, respectively. These data indicate that CsA-mediated inhibition occurs only when stimulation involves an increase in intracellular Ca2+. In addition, analogues of CsA, 6-methyl-alanine-CsA, and 11-methyl-leucine-CsA had no effect on PP2B activity or amylase secretion. The chemically distinct immunosuppressant, FK506, produced only partial inhibition of PP2B activity and did not significantly inhibit amylase secretion at concentrations up to 1 microM. Two-dimensional gel electrophoresis of proteins from 32P-labeled acinar cells revealed that CsA specifically blocked the cholecystokinin-stimulated dephosphorylation of a 24-kDa protein in a concentration range similar to that seen for inhibition of secretion. Using 32P-labeled cytosol and purified calcineurin, a Ca(2+)- and calmodulin-dependent dephosphorylation of the 24-kDa protein was also demonstrated in vitro. Collectively, these data indicate that the Ca2+/calmodulin-dependent protein phosphatase, PP2B, plays a significant role in stimulus-secretion coupling in pancreatic acinar cells.

Identification of Rab 5 but not Rab 3A in rat pancreatic zymogen granule membranes

Low molecular weight GTP-binding (LMWG) proteins are known to be present on secretory organelles and a role for Rab 3A in exocytosis of synaptic vesicles has been postulated. Pancreatic zymogen granules possess multiple LMWG proteins which were shown to be on the outside of the granules by pronase susceptibility. Rab 3A, however, could not be identified in rat pancreatic acinar cells or on zymogen granules by immunoblots or by northern blots or PCR amplification although all three techniques demonstrated its presence in rat brain, RINm5F and AR42J cells. Immunoblots revealed expression of Rab 5, Rab 7, Rab 11 and ARF in acini. Of these, Rab 5 was identified in purified zymogen granule membranes where it may be involved in the endocytotic retrieval of granule membrane following exocytosis.

GP-3, a newly characterized glycoprotein on the inner surface of the zymogen granule membrane, undergoes regulated secretion

We have recently reported the cloning of the rat zymogen granule membrane glycoprotein GP-3 and the related pancreatic secretory lipase (Wishart, M. J., Andrews, P. C., Nichols, R., Blevins, G. T., Logsdon, C.D., and Williams, J. A. (1993) J. Biol. Chem. 268, 10303-10311). Specific antipeptide antibodies were generated against both GP-3 and secretory lipase and used for the biochemical and physiological characterization of GP-3. Western blotting confirmed that GP-3 was found exclusively in zymogen granule membranes and was absent from zymogen granule content which contains the majority of secretory lipase. Extraction of zymogen granule membranes with Triton X-114 showed GP-3 to be significantly more hydrophobic than lipase. The GP-3 amino acid sequence contains one potential N-linked glycosylation site at Asn-336. The loss of concanavalin A labeling after both chemical deglycosylation with trifluoromethanesulfonic acid and enzymatic deglycosylation with N-glycanase showed GP-3 to possess a small N-linked oligosaccharide side chain. Digestion of intact and permeabilized zymogen granules with the nonspecific protease Pronase localized GP-3 to the inner surface of zymogen granule membranes. Since GP-3 is resident on the inner surface of the zymogen granule membrane, it should appear on the outer cellular surface after exocytosis. Although membrane attachment of GP-3 was resistant to treatment with phosphatidylinositol-specific phospholipase C, we observed that GP-3 is released into the pancreatic juice and that secretion of GP-3 was greatly enhanced by cholecystokinin.

Multiple inhibitory effects of genistein on stimulus-secretion coupling in rat pancreatic acini

Genistein, a tyrosine kinase inhibitor, inhibited cholecystokinin (CCK)-induced maximal amylase release from rat pancreatic acini by 18, 31, and 46% at concentrations of 100, 300, and 750 microM, respectively, after 30 min preincubation. Genistein similarly decreased amylase release stimulated by bombesin but not that stimulated by secretin or vasoactive intestinal peptide. The steps of stimulus-secretion coupling affected by genistein were further evaluated. We found genistein dose dependently suppressed CCK-as well as NaF-induced polyphosphoinositide hydrolysis with a 50% inhibitory concentration of 380 and 400 microM, respectively, but only slightly suppressed the increase of intracellular Ca2+ concentration in response to either low or high concentrations of CCK. Genistein at 300 microM also decreased incorporation of [3H]inositol into phosphatidylinositol 4,5-bisphosphate. Most strikingly, 300 microM genistein inhibited Ca(2+)-stimulated amylase release by 85% in streptolysin O-permeabilized acini and thapsigargin-stimulated amylase release by 69% in intact acini. Daidzein, the inactive analogue of genistein, had no effect on any of the above parameters. Genistein, up to 750 microM, did not affect amylase release in response to phorbol ester. To relate these inhibitory effects of genistein to its inhibition of tyrosine phosphorylation, Western blotting was performed with an anti-phosphotyrosine monoclonal antibody. Genistein at 100 microM partly and at 300 microM completely inhibited CCK-induced tyrosine phosphorylation. In conclusion, genistein inhibits amylase release at multiple stages of stimulus-secretion coupling. These effects most likely involve both tyrosine kinase-dependent and -independent mechanisms.

Low molecular weight GTP-binding proteins: molecular switches regulating diverse cellular functions

Low molecular weight GTP-binding proteins (LMWG proteins) form a family of proteins that shows homology with Ras, are 18-30 kDa in mass, and bind and hydrolyze GTP. They act as molecular switches, being active when binding GTP. Their activity is regulated by other proteins that influence the dissociation of GDP and the rate of GTP hydrolysis. Roles are emerging for these proteins in regulation of membrane fusion and cytoskeletal organization and growth. In the gastrointestinal tract, the best studied physiological processes that may be regulated by LMWG proteins are digestive enzyme and gastric acid secretion.

Pancreatic zymogen granule membrane proteins: molecular details begin to emerge

Regulated secretion and exocytosis require the controlled docking and fusion of secretory storage organelles with the plasma membrane. Proteins resident in secretory organelle membranes are, therefore, likely to have critical functions as a part of these processes. The exocrine pancreas with its secretory storage organelle, the zymogen granule, represents a classical model of regulated secretion and exocytosis. Until recently, however, little has been known of zymogen granule membrane protein structure and function. With the recent cloning of two zymogen granule membrane proteins, GP-2 and GP-3, and with the identification of the presence of low molecular weight guanosine triphosphate binding proteins, it is now possible to approach the role of the zymogen granule membrane proteins at the molecular level.

Effects of calyculin A on amylase release in streptolysin-O permeabilized acinar cells

The effects of the phosphatase inhibitors calyculin A and okadaic acid on amylase release from streptolysin-O permeabilized rat pancreatic acini were investigated. Both agents induced similar biphasic effects with moderate potentiation of calcium-stimulated amylase release at medium and strong inhibition at higher concentrations. Calyculin A was thirty times more potent than okadaic acid and at 100 nM totally inhibited calcium-induced amylase release while 3 microM okadaic acid reduced amylase release by 78%. 100nM calyculin A also completely inhibited GTP gamma S-potentiated amylase release and partially inhibited phorbol ester potentiated secretion. The data indicate that inhibition of a serine/threonine phosphatase, probably a type 1 phosphatase, leads to inhibition of calcium-induced amylase release in permeabilized pancreatic acini.

Effects of okadaic acid indicate a role for dephosphorylation in pancreatic stimulus-secretion coupling

Okadaic acid completely inhibits phosphatase 2A at nanomolar concentrations, while complete inhibition of type 1 phosphatases occurs at 1 microM. Phosphatase 2B is significantly inhibited only at concentrations > 1 microM. In rat pancreatic acini, 1 microM okadaic acid shifted the cholecystokinin (CCK) dose-response curve for stimulating amylase release to the right without reducing maximal secretion. At 3 microM, okadaic acid inhibited maximal CCK-induced amylase release to 78 +/- 7% of control, whereas the inactive analogue 1-Nor-okadaone had no effect. Three lines of evidence indicate that this inhibition by okadaic acid occurs at a late step in stimulus-secretion coupling: 1) intracellular Ca2+ signaling in response to agonist stimulation was not appreciably altered by okadaic acid; 2) stimulation with phorbol ester plus thapsigargin (thus by-passing receptor activation), which gave 85 +/- 4% of maximal CCK-induced amylase release, was inhibited 66 +/- 4% by 3 microM okadaic acid; and 3) Ca(2+)-induced amylase secretion in streptolysin O-permeabilized cells was also reduced by 85 +/- 7%. Two-dimensional polyacrylamide gel electrophoresis of 32P-labeled acini and autoradiography demonstrated that okadaic acid dose dependently increased overall protein phosphorylation. Correspondingly, okadaic acid also led to an inhibition of CCK-induced dephosphorylation. These results show that okadaic acid inhibits pancreatic acinar secretion at a step after generation of intracellular messengers and indicate a role for protein dephosphorylation in stimulus-secretion coupling.

Endothelin increases [Ca2+]i in rat pancreatic acinar cells by intracellular release but fails to increase amylase secretion

In individual fura-2 loaded cells of rat pancreatic acini endothelin-1 (ET-1) (10-50 nM) induced sustained oscillations in [Ca2+]i. At higher concentrations a larger, but transient increase in [Ca2+]i was observed, which was largely unaffected by removal of extracellular Ca2+. ET-1 induced the release of Ca2+i from the same store as cholecystokinin (CCK), but with less potency. At concentrations of endothelin which transiently increased Ca2+, ET-1 increased the accumulation of inositol phosphates. Specific binding sites for 125I-endothelin were demonstrated on rat pancreatic acini. A single class of binding sites was identified with an apparent Kd 108 +/- 12 pM and Bmax of 171 +/- 17 fmol/mg for ET-1. The relative potency order for displacing [125I]ET was ET-1 greater than ET-2 greater than ET-3. In contrast to CCK and the non-phorbol ester tumour promoter Thapsigargin (TG) which induce both transient and sustained components of [Ca2+]i elevation, ET-1 failed to increase amylase release over the range 100 pM-1 microM.