Enzyme replacement therapy in ENU2 phenylketonuric mice using oral microencapsulated phenylalanine ammonia-lyase: a preliminary report

The presence of an extensive enterorecirculation of amino acids between the intestine and the body allows the removal of systemic phenylalanine in PKU rats by oral microencapsulated phenylalanine ammonia lyase. The work presented in this article has the main goal of assessing the feasibility of yeast phenylalanine ammonia-lyase (PAL) loaded collodion microcapsules in reducing elevated plasma phenylalanine concentrations to standard levels in genetically mutated PKU mice, within a 30 day time frame. The distinguishing aspect from previous studies lies in the available animal model. Rather than artificial induction of elevated phenylalanine plasma levels, the mice representing the human phenylketonuric condition, are mutated strains which are deficient in the enzyme phenylalanine hydroxylase. The first in vivo study established a method for orally feeding microcapsules, both control and enzyme loaded, over 30 consecutive days, by mixing with soft, unripened cheese. Under this unique regime a decrease of 51.3% +/- 9.02% in phenylalanine plasma levels was observed after 23 days. Reduction in the phenylalanine plasma levels to within the desired maintenance range of 250-1000 umol/L was observed in 2 out of 4 PAL treated mice, with only 50% of the PAL dose used in previous rat studies by Chang's group. The second animal study confirmed the finding in the first in vivo study that there is no significant decrease in the plasma phenylalanine levels within the first seven days. This may be due to the severely deteriorated physical condition of the ENU mice used, the PAL enzyme preparations available or the fact that normal mice contain 10 times the amount of phenylalanine hydroxylase as compared with humans, thus requiring larger doses of PAL in order to be effective in a shorter time span.

A new theory of enterorecirculation of amino acids and its use for depleting unwanted amino acids using oral enzyme-artificial cells, as in removing phenylalanine in phenylketonuria

Oral binders remove intestinal bile acid and prevent its reabsorption and recycling thereby lowering systemic cholesterol levels. The results in this paper demonstrate the presence of another extensive enterorecirculation for amino acids. Pancreatic and other glandular secretions into the intestine contain large amounts of proteins, enzymes and polypeptides. Tryptic digestion converts these into amino acids which are then reabsorbed back into the body as they pass down the intestine. This paper shows that this forms a large enterorecirculation of amino acids between the body and intestine. The dietary protein source of amino acids is negligible when compared to the endogenous source, since this paper shows that protein-free diet did not alter the intestinal amino acid concentration. This raises the possibility of using this for the selective depletion of specific body amino acids. In this paper we use a phenylketonuria (PKU) model in rats to test the use of this hypothesis. In PKU rats, artificial cells microencapsulated phenylalanine ammonia lyase (PAL) given orally is more effective than a phenylalanine-free diet. The enzyme artificial cells are more efficient in lowering PHE in the intestine, plasma and cerebrospinal fluid. Compared to PKU on PHE-free diet, this has resulted in better weight gain and general physical condition. Preliminary studies also show that artificial cells microencapsulated asparaginase, glutaminase and tyrosinase given orally can deplete the corresponding amino acid from the intestine.

Superoxide dismutase and catalase cross-linked to polyhemoglobin reduces methemoglobin formation in vitro

Superoxide dismutase (SOD) and catalase (CAT) were evaluated for their ability to reduce methemoglobin formation in chemically cross-linked hemoglobin that was incubated in Tris-HCl buffer. Two parallel studies were carried out using identical experimental conditions with one exception only. This involved the physical state of SOD and CAT in solution such that the enzymes were either cross-linked directly to hemoglobin (hemoglobin-SOD-CAT) or simply incubated with polyhemoglobin. The concentration of SOD and CAT was subsequently varied to examine and compare the effect on the rate of methemoglobin formation between the two experiments. Overall, a comparison between the results clearly indicated that cross-linking SOD and CAT to hemoglobin was more effective at reducing methemoglobin levels than incubating polyhemoglobin with SOD and CAT. More specifically, the incubation experiment would require an enzyme concentration exceeding twice that cross-linked to hemoglobin in order to achieve a similar beneficial effect. However, it was more striking to observe that the presence of SOD and CAT during the cross-linking reaction had markedly reduced the initial formation of methemoglobin. When SOD and CAT were included during the chemical process of generating polyhemoglobin, about 7% methemoglobin was formed in the cross-linked hemoglobin-SOD-CAT product. By comparison, methemoglobin had increased about 20% after the cross-linking reaction when generating polyhemoglobin.

Roles of gut hormones in negative-feedback regulation of pancreatic exocrine secretion in humans

BACKGROUND/AIMS

Secretin has been shown to mediate feedback control of pancreatic secretion of fluid and bicarbonate in rats, guinea pigs, and dogs. However, little is known about secretin in the feedback regulation in humans. We investigated the roles of secretin, cholecystokinin, neurotensin, and pancreatic polypeptide on feedback regulation of pancreatic secretion in 10 human volunteers.

METHODS

A 5-lumen tube was positioned in the proximal jejunum of fasting subjects under fluoroscopy so that gastric juice via lumen 1 and duodenal contents via lumen 3 were collected separately in 15-minute samples while polyethylene glycol solution was infused into duodenum via lumen 2. An acidified (pH 2.0) 4.25% amino acid mixed with phenol red was infused into proximal jejunum via lumen 4, which was alternated with NaHCO3 (control solution) or trypsin (test solution) via lumen 5 intermittently every 15 minutes during separate test periods.

RESULTS

Infusion of control solution significantly increased both bicarbonate (total change [delta], 7799 +/- 1400 mumol/h) and chymotrypsin (delta 5500 +/- 762 mumol/h) outputs and levels of all four plasma hormones. The test solution significantly inhibited both bicarbonate (delta 2999 +/- 700 mumol/h; P < 0.01) and chymotrypsin output (delta 1000 +/- 120 U/h, P < 0.01), which coincided with a significant suppression of plasma concentration of secretin and cholecystokinin but not pancreatic peptide and neurotensin.

CONCLUSIONS

A negative-feedback regulation of pancreatic secretion of bicarbonate and enzyme occurs in humans and is mediated via both secretin and cholecystokinin.

Physiological role of cholecystokinin on gastric emptying and acid output in dogs

We investigated the physiological role of cholecystokinin (CCK) on gastric emptying and acid secretion in seven conscious dogs with gastric cannulae. Two hundred milliliters of a 4% amino acid meal was given via the cannula, and both gastric emptying and acid output were measured concurrently using a dye-dilution technique. Gastric emptying of the liquid amino acid meal was exponential, and the acid output and plasma concentrations of CCK, gastrin, and somatostatin peaked within 30 min after the meal. Intravenous infusion of CCK-8 at 28 and 56 pmol/kg/hr but not 14 pmol/kg/hr increased plasma levels of the peptide and inhibited gastric emptying as well as acid output. Plasma gastrin was not affected significantly by the CCK infusion, whereas plasma somatostatin increased significantly in response to 56 pmol/kg/hr of CCK-8. Loxiglumide, 22 mumol/kg/hr, significantly enhanced gastric emptying and augmented acid output, as well as plasma gastrin response, whereas it abolished the postprandial rise in plasma somatostatin. We concluded that in dogs, CCK plays an important role in the physiologic regulation of postprandial gastric emptying of a liquid caloric meal and acid output. Its inhibitory effect on gastric acid secretion appears to be mediated, at least in part, by somatostatin.

Effect of rate of intracellular transport and diacytosis on cytotoxicity of hybrid toxins. Study with hybrids using hepatic asialoglycoprotein receptor-mediated endocytosis

The effects of diacytosis and intracellular transport rate on cytotoxicity of hybrid toxins were studied with conjugates of diphtheria toxin fragment A (DTA) to asialoorosomucoid (ASOR) and its reduced and carboxymethylated cyanogen bromide fragment I (RC-ASCNBr-I) in cultured rat hepatocytes. In the hepatocytes the kinetics of uptake of the conjugate of asialoorosomucoid (DTA-ASOR) and that of the conjugate of the cyanogen bromide fragment (DTA-RC-ASCNBr-I) were quite similar, but the rate of accumulation of DTA moiety into the lysosomes, as determined by Percoll density gradient centrifugation, was found to be greater for the latter than the former. However, after internalization, DTA-RC-ASCNBr-I was diacytosed to a lesser extent than that of DTA-ASOR, particularly when colchicine was present during internalization. Analysis of the subunits of DTA-ASOR internalized by the hepatocytes indicated that they were accumulated disproportionately in a time-dependent manner so that the glycoprotein moiety was accumulated progressively more than the toxin moiety. Cytotoxicity of DTA-ASOR toward the hepatocytes was 2-times as much as that of DTA-RC-ASCNBr-I. Colchicine enhanced the toxicity of DTA-RC-ASCNBr-I (33-fold) to a greater extent than that of DTA-ASOR (12-fold). The difference in enhancement by colchicine was also observed in the rate of cell intoxication by the conjugates. Both conjugates were more toxic to the hepatocytes after incubation with the cells at 18 degrees C than at 37 degrees C. In the presence of vanadate (0.2 mM), which enhanced diacytosis, toxicity of DTA-ASOR decreased by 5-fold. After incubation with the hepatocytes, a partial dissociation of DTA-ASOR was found to occur independently of the receptor-mediated endocytosis. Taken together, these results indicate that diacytosis, subunit dissociation and rapid transport of conjugate toward lysosomes affect kinetically the rate of accumulation of the conjugate into a yet unidentified compartment of toxin translocation.

Effect of protein derivatives on pancreatic secretion and release of secretin and CCK in rats

We investigated the effect of intraduodenal administration of oligopeptide and a mixed amino acid solution, which contains the same amino acid composition as oligopeptide, on pancreatic exocrine secretion and the release of secretin and cholecystokinin (CCK). Anesthetized rats were prepared with pyloric ligation and cannulation of pancreatic duct and bile duct. Protein derivatives in three different doses (oligopeptide: 25, 100, and 400 mg/h; and mixed amino acid solution: 70, 140, and 280 mg/h, pH 7.0) were infused into the duodenum for 1 h. Pancreatic juice was collected, and plasma concentrations of secretin and CCK were measured by radioimmunoassay. In addition, the effect of intravenous injection of an antisecretin serum or a CCK antagonist, loxiglumide, on pancreatic secretion stimulated by oligopeptide or mixed amino acid solution was also studied. Oligopeptide produced a significant dose-related increase in pancreatic secretion including volume, HCO3-, amylase, and trypsin output, plasma secretin (r = 0.792, P < 0.001), and plasma CCK (r = 0.421, P < 0.01). Similarly, mixed amino acid solution produced a dose-related increase in pancreatic juice volume, HCO3-, amylase, and trypsin output. Compared with CCK, the percentage increase in plasma secretin was 7.3x and 2.8x higher in response to oligopeptide (400 mg/h) and mixed amino acid solution (280 mg/h), respectively. An antisecretin serum almost completely inhibited volume flow and HCO3- output stimulated by oligopeptide as well as mixed amino acid solution, but not amylase and trypsin output. In contrast, loxiglumide significantly suppressed amylase and trypsin output stimulated by protein derivatives, but did not affect volume flow or HCO3- output.(ABSTRACT TRUNCATED AT 250 WORDS)

Secretin: a physiological regulator of gastric emptying and acid output in dogs

Secretin has been known to inhibit gastric acid secretion in several species. However, the physiological role of secretin on the postprandial acid output and gastric emptying in an intact stomach remains controversial. In the present study, we reinvestigated the role of secretin in physiological dose range and endogenous secretin on gastric acid secretion and emptying in the stomach without influencing intragastric luminal pH in dogs. In seven conscious dogs with gastric cannulas, a 4% amino acid meal was administered intragastrically, and three different doses of secretin and an antisecretin serum were infused intravenously in each dog on separate days. Gastric emptying and net acid output were measured using a dye dilution technique, and plasma secretin and gastrin were determined by specific radioimmunoassays. After the meal, gastric emptying was exponential: acid output peaked at 25 min, and plasma concentrations of gastrin and secretin peaked at 15 and 60 min, respectively. Intravenous infusion of secretin at 1.25, 2.5, and 5.0 pmol.kg-1.h-1 dose dependently increased plasma levels of the peptide and suppressed postprandial plasma gastrin response and gastric acid output and emptying of the meal. Immunoneutralization of circulating secretin with a rabbit antisecretin serum abolished the postprandial rise of plasma secretin and significantly increased plasma gastrin, and augmented gastric emptying as well as acid output. It is concluded that, in dogs, secretin plays a physiological role in the regulation of gastric emptying and acid output after a liquid amino acid meal and that these effects may be mediated in part by suppression of the release of gastrin.

Mechanism of action of insulin on pancreatic exocrine secretion in perfused rat pancreas

In conscious rats, we have previously shown that immunoneutralization of circulating insulin with a rabbit anti-insulin serum abolished the pancreatic exocrine secretion stimulated by a meal or a combination of exogenous secretin and cholecystokinin octapeptide (CCK-8). To investigate the mechanism of endogenous insulin action on the exocrine pancreas, isolated rat pancreata were perfused with intra-arterial infusion of Krebs-Henseleit solution (37 degrees C) at 1.2 ml/min, whereas both pancreatic juice and portal venous effluent were collected separately in 15-min samples. Simultaneous intra-arterial infusion of secretin and CCK-8 in doses of 0.75 and 4.2 pmol/h; respectively, significantly increased volume, bicarbonate, and protein output in 7 rat pancreata (P < 0.01). When a rabbit anti-insulin serum was administered intra-arterially (0.1-ml bolus followed by 0.1 ml for 10 min), pancreatic secretion of volume, bicarbonate, and protein output was profoundly suppressed (n = 7, P < 0.01), whereas a normal rabbit serum failed to influence pancreatic secretion. The decrease in pancreatic secretion by the antiserum coincided with a significant increase in somatostatin in portal venous effluent from 1.4 +/- 0.2 to 4.1 +/- 0.8 pM (n = 6, P < 0.05). The combined administration of a rabbit antisomatostatin serum (0.4 ml) and the anti-insulin serum partially reversed the effect of the anti-insulin serum alone. Thus the pancreatic secretion was significantly greater than that achieved by the anti-insulin serum alone (P < 0.05). These observations strongly suggest that the action of insulin on exocrine pancreas is mediated by its local or paracrine action.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of the release of cholecystokinin from a murine neuroendocrine tumor cell line, STC-1

The murine neuroendocrine cell line, STC-1, was found to contain 296.8 +/- 1.8 fmol of cholecystokinin-like immunoreactivity (CCK-LI) per mg cell protein. Immunocytochemical stain of STC-1 cells maintained in monolayer culture indicated that CCK-LI activity was present in 93% of the cells. Analysis by reverse-phase high-performance liquid chromatography indicated that STC-1 cells contained CCK-8 and an unidentified form as the predominant storage form. form. However, only CCK-8 was released into the culture medium upon stimulation by various secretagogues. The release of CCK-LI from STC-1 cells was stimulated by dibutyryl cAMP, forskolin, KCl, A23187, 4 beta-phorbol 12-myristate 13-acetate and luminal stimulants, e.g., sodium oleate, L-tryptophan, camostat and plaunotol. The release of CCK-LI from STC-1 cells was also stimulated by a neuropeptide, bombesin. The stimulatory effects of most of these agents were dose dependent. The stimulatory effects of dibutyryl cAMP, forskolin, and plaunotol were potentiated by 3-isobutyl-1-methyl xanthine, while that of camostat was not. The results obtained in this study indicate that the release of CCK from STC-1 cells shares the same characteristics of CCK release as from the CCK-secreting cells of the intestinal mucosa observed both in the dog and the rat in vitro and in vivo. Thus, the cellular mechanism of CCK release which appears to be cAMP- and Ca(2+)-dependent may be modulated by cellular protein kinase C activity. The STC-1 cell appears to be a suitable model for studying the mechanism of CCK release.

Xenotransplantation of microencapsulated canine islets into diabetic rats

Islets of Langerhans were isolated in high yields from canine pancreata. In the procedure, the pancreata were perfused and digested with collagenase, and the islets were then purified on histopaque density gradients. As many as 60,000 islets were isolated from a single pancreas. Islets were encapsulated in alginate-polylysine-alginate membranes with the aid of an air-jet droplet generator. In vitro studies demonstrated that the isolated and encapsulated islets secreted insulin in response to glucose and IBMX challenge for at least 9 weeks. In in vivo studies 6 diabetic Wistar rats were transplanted with 5,000 to 8,000 encapsulated islets each. The diabetic condition was reversed in all recipients for up to 112 days. In control animals, which received free, unencapsulated islets, the xenografts remained functional for fewer than 21 days. Microcapsules retrieved from normoglycemic transplant recipients 1 and 2 months posttransplantation were shown to contain viable islet tissue, and no cellular overgrowth was observed on capsular surfaces. The results of the study indicate a considerable clinical potential of microencapsulated canine islet xenografts.

Submicron biodegradable polymer membrane hemoglobin nanocapsules as potential blood substitutes: a preliminary report

We used biodegradable polymers like polylactic acid, poly-isobutylcyanoacrylate and others to prepare nanocapsules containing hemoglobin. We prepared the optimal mean diameters of between 0.08 to 0.12 micron (80-120 nm). They are spherical and homogeneous. The membrane thickness is 0.005-0.015 micron (5-15nm). With different formulation, the hemoglobin contents in the particles may be varied from 30-45%. Phospholipid is not required in bovine hemoglobin. It is required for human hemoglobin in order to retain cofactors required for optimal P50. The P50 of the biodegradable polymer membrane containing bovine hemoglobin was between 27-29 mmHg. This is the same P50 as bovine hemoglobin used in the preparation. Thus the procedure of preparation did not damage hemoglobin.

Assessment of blood substitutes: II. In-vitro complement activation of human plasma and blood for safety studies in research, development, industrial production and preclinical analysis

Animal safety study cannot predict the effects of blood substitutes in human response. Response of human, especially in immunology and complement activation, need not be the same as those in animals. We have earlier reported an in-vitro preclinical screening test based on testing the effects of modified hemoglobin on complement activation of human plasma or blood in vitro. In this test, modified hemoglobin is added to human plasma in a test tube. Complement activation is followed by the C3a levels. Since this directly measures the effect of modified hemoglobin on human plasma, it would be the closest response in human next to injecting this into human. Thus, this could be an important bridge before clinical use in patients. However, why wait for the completion of research, industrial production and preclinical animal studies? Why don't we do this test right at the beginning during the research stage? If a new system is found to cause complement activation at this stage, one can avoid tremendous waste of time and money in further development, industrial production and preclinical animal study. This paper analyzes this approach in research, development, industrial production and preclinical analysis.

Human hemoglobin anaerobically reacted with divinyl sulfone: a source for oxygen carriers

Human hemoglobin (HbA) was reacted in anaerobic conditions with divinyl sulfone (DVS). The structural and oxygenation properties of the resulting chemically-modified product were studied in order to assess its potential as a physiological oxygen carrier. The reaction was carried out anaerobically at 25 degrees C and pH 7.4 for 3 h. Quenching was performed with lysine-HCl solution and the resulting solution dialysed to remove unbound DVS and excess lysine. The product, designated Poly HbA-DVS, was characterized structurally using gel-permeation HPLC and SDS-PAGE and functionally employing a Hemox-analyzer at 37 degrees C and pH 7.4. From gel-permeation HPLC it was estimated that about 60% of the starting material was polymerized, with a molecular mass range from 130 to about 500 kDa, and about 40% remained monomeric with a molecular mass of 64 kDa. The virtual absence of a 32 kDa band from the SDS-PAGE pattern of the last eluting HPLC peak and the oxygenation properties of this peak material (P50 = 33 mm Hg, n = 2.2; P50 very different from the approximately 1.5 mm Hg associated with native HbA solution) indicated that the monomeric (64 kDa) component was modified, but virtually noncrosslinked, within the tetramer. The product solution, Poly HbA-DVS, had a P50 of 35 mm Hg, a Hill coefficient n of 1.8 and a methemoglobin content of 5-7%. This material has characteristics appropriate for an oxygen carrier, and can probably be used as such in perfusional and transfusional fluids.

Assessment of blood substitutes: I. Efficacy studies in anesthetized and conscious rats with loss of 1/3, 1/2 and 2/3 blood volume

Acute and long-term recovery (14 days) studies were conducted in conscious rats bled 1/3, 1/2, and 2/3 blood volume, and in anesthetized rats bled 1/3 volume. Study I: bled 1/3 blood volume. Study Ia: Anesthetized rats bled 1/3 blood volume were in shock and most died within 1 hour; the group which received infusion of 3x volume Ringer's lactate regained blood pressure with 100% long-term recovery. Study Ib: In conscious rats bled 1/3 blood volume, blood pressure did not fall to shock levels, and the long-term recovery in both the control group and the group which received 3x volume Ringer's lactate was 100%. Study II: Bled 1/2 blood volume. In conscious rats bled 1/2 volume, the blood pressure of the control group was slightly above 70 mmHg. Infusion of 3x volume Ringer's lactate or 7 gm% human albumin in Ringer's lactate increased blood pressure to above 90 mmHg in the acute study. Long-term recovery and survival rate was 80% in both the controls and the Ringer's lactate group, and 100% in the albumin group. Study III: bled 2/3 blood volume. In conscious animals, loss of 2/3 blood volume resulted in fall of blood pressure to shock levels and death of the animal within 1 hour. Infusion of 3x volume Ringer's lactate did not increase blood pressure to above shock level. Stroma-free hemoglobin and polyhemoglobin increased blood pressure, and whole blood returned blood pressure to normal. In long-term recovery, poly-hemoglobin, but not SFHb, was as effective as whole blood with 100% long term recovery. Animal models in Study I and II are suitable only for studies of volume replacement. Animal models in Study III, especially using long-term recovery studies, are more suitable for studying both volume and red blood cells replacements.

Effect of digested protein on pancreatic exocrine secretion and gut hormone release in the dog

The hormonal mechanisms mediating protein-stimulated pancreatic exocrine secretion were investigated in four conscious dogs with gastric cannulas and Thomas duodenal cannulas. Pancreatic juice was collected by direct cannulation of the main pancreatic duct in response to intraduodenal infusates prepared with cooked beef liver. When the homogenized liver was administered intraduodenally, cholecystokinin (CCK) in plasma significantly increased. This increase was accompanied by a significant increase in pancreatic exocrine secretion, including volume, bicarbonate, and protein output. The liver homogenate incubated with pancreatic enzymes further increased both plasma CCK and exocrine pancreatic secretion. However, plasma secretin was not affected by the protein digests. Intravenous administration of loxiglumide at the rate of 5.0 and 10.0 mg/kg/h resulted in a significant decrease in the stimulated pancreatic secretion of fluid, bicarbonate, and protein. The study indicates that endogenous CCK released by protein digests exerts not only enzyme secretion but also bicarbonate secretion in dogs.

Toxicity of liposomes containing low mol% of dienoyl phosphocholine to blood: use of carboxymethyl chitin to reduce toxicity

Toxic effects of liposomes composed of the synthetic lipid, 1,2-bis(octadeca-2,4-dienoyl)-sn-glycero-3-phosphocholine (C18DENPC) and cholesterol (Cho) were studied. In the present work, we have explored, 1) fusion between C18DENPC/Cho-liposomes and erythrocyte ghost (EG) membranes with resonance energy transfer assay, 2) hemolysis induced by C18DENPC/Cho-liposomes and 3) turbidity changes in native plasma on contact with C18DENPC/Cho-liposomes, in the presence or absence of carboxymethyl chitin (CM-chitin). In the absence of CM-chitin, extents of fusion, hemolysis and turbidity changes in native plasma increased with the decrease in C18DENPC content. In the presence of CM-chitin at a concentration of 10(-3) or 10(-2)% (w/v), fusion of C18DENPC/Cho-liposome with EG was inhibited. Extents of hemolysis and turbidity changes in native plasma induced by C18DENPC/Cho-liposomes were reduced depending upon CM chitin concentration.

Mass isolation of highly purified canine islets using an automated method and Histopaque Ficoll gradients

Eighteen pancreata from adult mongrel dogs were used for the study of islet isolation. The pancreas was distended with collagenase in Hanks' solution. The automated screen method and Histopaque Ficoll gradients were used to isolate and purify the canine islets. In vitro, the viability of isolated islets was assessed by both histology and perifusion studies. In vivo, the islet function was evaluated by using a nude mice xenograft model. Fair to good isolation and purification was found in 12 experiments. Before and after purification, the isolated islet count was 4767.1 +/- 560.1 and 3637.7 +/- 333.4 islet equivalence (I.E.)/gm pancreatic tissue. The purity was above 90%. Aldehyde Fuchsin stain disclosed islets with copious beta granules. The stimulation index of islets responding to 16.7 mM glucose plus 1 mM 3-isobutyl-1-methylxanthine (IBMX) versus 1.67 mM glucose was 12.93 +/- 4.75. Normoglycemia was restored and maintained for up to 2 weeks in 7 of 10 and up to 3 weeks in 5 of 10 diabetic nude mice transplanted with canine islets. In conclusion, the automated screen method and Histopaque Ficoll gradients afford a good yield of highly purified canine islets, and functional viability was verified both in vitro and in vivo. This will be an ideal model for isolation of human islets.

Role of secretin in negative feedback regulation of postprandial pancreatic secretion in dogs

BACKGROUND

A negative feedback regulation of pancreatic exocrine secretion has been observed in fasting rats, pigs, and humans, but this phenomenon could not be found in fasting dogs. The aims of the present study were to investigate whether or not postprandial pancreatic secretion is regulated by a negative feedback mechanism and to determine if the mechanism is mediated by secretion and/or cholecystokinin (CCK) in dogs.

METHODS

In eight dogs prepared with gastric and Herrera's pancreatic cannulas, pancreatic juice was collected for 3 hours after feeding a mixed meal to measure volume, bicarbonate, and trypsin output. Peripheral venous blood was obtained to determine plasma immunoreactive secretin and CCK levels. Four groups of experiments were performed while pancreatic juice was diverted from the duodenum: (1) diversion of pancreatic juice alone, (2) intraduodenal infusion of fresh pancreatic juice while pancreatic juice was diverted, (3) intraduodenal infusion of 150 mg/h of trypsin and 300 mg/h of chymotrypsin, and (4) intraduodenal infusion of 0.1 mol/L NaHCO3.

RESULTS

Pancreatic secretion during diversion of pancreatic juice was significantly greater than that obtained while pancreatic juice was returned. Diversion-induced pancreatic hypersecretion was significantly suppressed by intraduodenal administration of pancreatic proteases, but it was not influenced significantly by 0.1 mol/L NaHCO3. The suppression by either pancreatic juice or proteases paralleled the decrease in plasma secretin response, whereas the CCK response remained unchanged. The inhibitory effect of pancreatic proteases on pancreatic secretion was blocked by a physiological dose of exogenous secretin, 0.06 clinical U.kg-1.h-1.

CONCLUSIONS

In dogs, postprandial pancreatic secretion is controlled by a negative feedback mechanism mediated mainly by the release of secretin, but not by CCK.

A physiological role of peptide YY on exocrine pancreatic secretion in rats

BACKGROUND

Peptide YY (PYY) given intravenously was shown to inhibit pancreatic exocrine secretion both in the dog and the rat. However, a possible physiological role of PYY on the pancreatic secretion has not been clarified. The present study was undertaken to investigate its physiological role on the exocrine pancreas.

METHODS

In conscious rats, plasma PYY was determined in response to oral ingestion of a 6-mL meal and intravenous infusion of PYY; small intestinal transit time was measured by phenol red as a nonabsorbable marker, and pancreatic secretory studies were performed in rats with pancreatic fistulas and jugular vein catheters.

RESULTS

Oral ingestion of the meal (containing phenol red, 1.6 mg/100 mL) significantly increased plasma PYY within 30 minutes. During this period, most (97%) of the phenol red was detected in the proximal two-thirds of the small intestine. Intravenous infusion of PYY in 25, 50, and 100 pmol.kg-1 x h-1 produced a dose-dependent increase in plasma PYY. The dose of PYY that simulated the peak postprandial level was 50 pmol.kg-1 x h-1, and this dose of PYY significantly inhibited the pancreatic secretion stimulated by physiological doses of secretin and cholecystokinin-8 (CCK-8). After the meal, pancreatic secretion of bicarbonate and protein significantly increased in rats pretreated with normal rabbit serum, whereas this increase was significantly augmented in rats pretreated with an anti-PYY serum because the postprandial increase in plasma PYY was abolished.

CONCLUSIONS

PYY plays a regulatory role in the postprandial pancreatic exocrine secretion in rats.

Secretion of erythropoietin from microencapsulated rat kidney cells: preliminary results

Rat kidney epithelial cells were microencapsulated within alginate-poly(L)lysine-alginate membrane. The microencapsulated cells were incubated using a culture media containing cobalt and another without cobalt. The viability was measured by trypan blue exclusion test. Secretion of erythropoietin (EPO) was measured by radioimmunoassay (RIA). Viability of free cells was 53%. The viability of microencapsulated cells increased to 72% after 12 days of incubation and remained at this level. Samples of the culture media were collected every 2 days for RIA. Samples within the microcapsules were collected by breaking the microcapsules open. RIA of these samples showed the following for the media containing cobalt. Between day 16 and day 32 the concentrations of EPO were 5.3 mU/ml inside and 18.3 mU/ml outside the microcapsule. The medium from the same number of free cells contained 21.2 mU/ml of EPO. Culture media without cobalt collected during the same period contained 1.8 mU/ml inside and 9.9 mU/ml outside the microcapsules. The free cell culture with this media during the same period contained 8.3 mU/ml.

The anaerobic reaction of bovine hemoglobin with divinyl sulfone: structural changes and functional consequences

The anaerobic reaction of bovine hemoglobin with divinyl sulfone results in a non-cross-linked intramolecularly-modified new derivative. This chemically-modified hemoglobin is homogeneous with respect to its molecular mass (64 kDa) and electrophoretic properties. The absence of any 32 kDa band from its SDS-PAGE pattern proves the lack of intramolecular cross-linkage, while a single-peak high-performance gel-permeation chromatogram demonstrates the absence of intermolecular cross-linkage. The oxygen binding properties determined at 37 degrees C, 0.15 M Cl- and pH 7.4 display a P50 of 52 mmHg and a Hill coefficient n of 1.9. Under the same experimental conditions the oxygen affinity is not sensitive to chloride anions, suggesting that the covelant modification is in the beta-cleft. The maximum number of Bohr protons released is 0.8/tetramer, which is half that of normal bovine hemoglobin. The retention time in circulation, measured in rats, is similar to that of native bovine hemoglobin. Using a high molar ratio of divinyl sulfone to modified hemoglobin, it is feasible to effect anaerobic intermolecular cross-linkage. The polymerized material, isolated from a 24 h reaction, is a mixture of modified intermolecularly-crosslinked hemoglobins with a molecular mass range from 130 to approx. 500 kDa. The oxygen-transport characteristics of the polymerized material are similar to those of the modified non-cross-linked derivative, whereas its retention time in rats is increased three-fold with respect to native bovine hemoglobin.

Characterization of secretin release in secretin cell-enriched preparation isolated from canine duodenal mucosa

The release of secretin was studied in secretin cell-enriched preparations isolated from canine duodenal mucosa. The crude enterocytes were isolated by treating the duodenal mucosa sequentially with collagenase and ethylenediaminetetraacetic acid. Secretin cell-enriched fraction was prepared by centrifugation of the crude enterocytes in a counterflow elutriation rotor to obtain a final preparation containing 3.2 +/- 0.3 pmol/10(6) cell of immunoreactive secretin, which was 13-fold greater than the crude cell preparation (N = 5). The cells were incubated in Hanks' balanced salt solution for 20 min at 37 degrees C under 95% O2/5% CO2 before adding various agents and further incubated for various periods of time. The amounts of secretin released into the medium and retained by the cells were then determined by a specific radioimmunoassay. The release of immunoreactive secretin was increased dose-dependently over the control by dibutyryl cyclic-3',5'-adenosine monophosphate, forskolin, 4 beta-12-O-tetradecanoylphorbol-13-acetate, the synthetic serine protease inhibitor, camostat, and the calcium ionophore, A23187. The effects of forskolin, the phorbol ester, and A23187 were time-dependent and not observed at 4 degrees C. The release of immunoreactive secretin was also stimulated by KCl in high concentration and by sodium oleate. The effect of A23187 was abolished in a Ca(2+)-free medium, while those of dibutyryl cyclic-3',5'-adenosine monophosphate and forskolin were potentiated by 3-isobutyl-1-methylxanthine, which did not have a significant effect when added alone. These results indicate that the release of secretin is regulated by both Ca(2+)- and cyclic-3',5'-adenosine monophosphate-dependent mechanisms.2+ release.

Cross-linked hemoglobin-superoxide dismutase-catalase scavenges oxygen-derived free radicals and prevents methemoglobin formation and iron release

In this study, we prepared PolyHb-SOD-catalase (intermolecularly cross-linked hemoglobin, superoxide dismutase (SOD), and catalase). We found that PolyHb-SOD-catalase is effective in scavenging oxygen-derived free radicals. In the xanthine/xanthine oxidase system, the initial rate of cytochrome c reduction was 2.13 +/- 0.26 nmoles cyt. c/min for PolyHb alone. PolyHb- SOD-catalase reduced this to 0.56 +/- 0.08 nmoles cyt. c/min because of its ability to eliminate superoxide (O2-). Addition of PolyHb to 200 microM of hydrogen peroxide (H2O2), changed the H2O2 level slightly to 192 +/- 0.4 microM. Addition of PolyHb-SOD-catalase, on the other hand, lower the level to 41 +/- 0.3 microM. Results also show that both effects were dependent on the concentration of SOD-catalase cross-linked with hemoglobin. Oxidative challenge with H2O2 resulted in minimal changes in the absorbance spectra of PolyHb-SOD-catalase. With PolyHb, there were spectral changes reflecting the formation of methemoglobin and heme degradation. Furthermore, the amount of iron released, after incubation with 250 microM H2O2, was 6.8 +/- 1.8 micrograms/dl for PolyHb-SOD-catalase and 76.6 +/- 1.0 micrograms/dl for PolyHb. These results show that cross-linked SOD-catalase prevents oxidative reactions involving the hemoglobin component of PolyHb-SOD-catalase.