Enterostatin (VPDPR) Has Anti-analgesic and Anti-amnesic Activites

Enterostatin (VPDPR), an anorexigenic peptide derived from the amino terminus of procolipase, significantly inhibited analgesia induced by the mu-opioid agonist morphine (5 mg/kg, s.c.) after i.c.v. administration to mice at a dose of 100 nmol. On the other hand, VPDPR (approximately 200 nmol, i.c.v.) did not attenuate analgesia induced by the kappa-opioid agonist D-Phe-D-Phe-D-Nle-D-Arg-NH2 (100 microg/mouse, i.c.v.) or delta-opioid agonist DTLET (4 nmol/mouse, i.c.v.). VPDPR (100 nmol, i.c.v.) significantly improved amnesia induced by scopolamine (0.2 mg/kg, i.p.) in mice. However, VPDPR did not enhance memory in normal mice at the same dose.

Vagal-Central Nervous System Interactions Modulate the Feeding Response to Peripheral Enterostatin

Enterostatin selectively inhibits the intake of dietary fat after both peripheral and central administration. We have investigated the role of the hepatic vagus nerve in modulating the peripheral response to enterostatin in Sprague-Dawley rats adapted to a high fat (HF) diet. Intraperitoneal (ip) enterostatin reduced intake of HF diet after overnight starvation. This response was abolished by selective vagal hepatic branch transection. Immunohistochemical techniques were used to identify the location of Fos protein in brain nuclei after ip enterostatin. Fos protein was evident in the nucleus tractus solitarius (NTS), parabrachial, paraventricular and supraoptic nuclei. The pattern of expression of Fos-like immunoreactivity differed from that induced by the lipoprivic agent beta-mercaptoacetate. Transection of the hepatic vagus blocked the central Fos responses to ip enterostatin. We conclude that afferent hepatic vagal nerve activity is required for the feeding response to peripheral enterostatin.

Enterostatin affects cyclic AMP and ERK signaling pathways to regulate Agouti-related protein (AgRP) expression

Enterostatin, a gut-brain peptide, inhibits dietary fat intake in rats. The purpose of this study was to identify the intracellular signaling pathways that are responsive to enterostatin and that modulate the effects of enterostatin on the expression of Agouti-related protein (AgRP). We used the hypothalamic GT1-7 neuronal cell line to identify the effects of enterostatin on cyclic AMP and ERK signaling using conventional immunoassays or Western blots to assay the activity of these pathways. Enterostatin enhanced the level of cyclic AMP, PKA(RIIbeta) and phospho-CREB and increased pERK levels in GT 1-7 cells. The effects on pERK were rapid (7.5 min) and dose-dependent. These signaling responses were blocked by an antibody to the enterostatin receptor (beta subunit of F1-ATPase), by the pERK inhibitor U0126 and by the P2Y receptor antagonist Suramin. Enterostatin showed a biphasic effect on AgRP mRNA, initially increasing but subsequently decreasing the levels. The cyclic AMP activator Sp-cAMP increased AgRP mRNA expression. Transfection of a wild type ERK construct reduced AgRP mRNA levels. Enterostatin inhibited expression of Krüppel-like factor 4 (KLF4), a transcriptional regulator of AgRP. KLF4 gene expression was increased by Sp-cAMP but decreased by wild-type ERK expression. U0126 blocked the effect of enterostatin on KLF4 expression. We conclude that enterostatin binding to its receptor activates the pERK pathway to inhibit AgRP gene expression but may enhance AgRP expression through activation of the cyclic AMP pathway. These pathways probably mediate the enterostatin inhibition of dietary fat intake.

Enterostatin reduces serum cholesterol levels by way of a CCK(1) receptor-dependent mechanism

Enterostatin (APGPR), an anorectic pentapeptide derived from the amino terminus of procolipase, significantly reduced serum cholesterol levels after oral administration at a dose of 100 mg/kg for 3 days in mice fed a high-cholesterol-cholic acid diet. The hypocholesterolemic effect of APGPR was inhibited by pretreatment with lorglumide, an antagonist for cholecystokinin 1 (CCK(1)) receptor, even though APGPR does not have any affinity for CCK(1) receptors. Similarly, the hypocholesterolemic activity of VPDPR, an APGPR analogue, was blocked by lorglumide. These results suggest that the hypocholesterolemic effects of APGPR and VPDPR are mediated by a CCK(1) receptor-dependent mechanism.

Enterostatin (APGPR) suppresses the analgesic activity of morphine by a CCK-dependent mechanism

Enterostatin (APGPR) found in the gastrointestinal tract and brain is an anorectic pentapeptide. We found that APGPR inhibited morphine-induced analgesia after intracerebroventricular administration in mice at a dose of 10nmol/mouse. The anti-analgesic effect of APGPR was inhibited by pretreatment with lorglumide and LY225910, antagonists for cholecystokinin 1 (CCK1) and cholecystokinin 2 (CCK2) receptors, respectively. The anti-analgesic effect of APGPR may be mediated by CCK release, since APGPR does not have affinity for CCK receptors.

Proteolytic cleavage of ostrich and turkey pancreatic lipases: production of an active N-terminal domain

OBJECTIVES

The aim of this study was to check some biochemical and structural properties of ostrich and turkey pancreatic lipases (OPL and TPL, respectively).

METHODS

Limited proteolysis of OPL and TPL was performed in conditions similar to those reported for porcine pancreatic lipase.

RESULTS

In the absence of bile salts and colipase, OPL failed to catalyze the hydrolysis of pure tributyrin or efficiently hydrolyze olive oil emulsion. When bile salts and colipase were preincubated with the substrate, the OPL kinetic behavior remained linear for more than 30 minutes. The enzyme presented a penetration power value into an egg phosphatidylcholine monomolecular film that was comparable to that of HPL and lower than that of TPL. Chymotrypsin, trypsin, and thermolysin were able to hydrolyze OPL and TPL in different ways. In both cases, only N-terminal fragments accumulated during the hydrolysis, whereas no C-terminal fragment was obtained in either case. Tryptic cleavage of OPL and TPL completely degraded the enzymes. Nevertheless, chymotryptic attack generated 35-kd and 43-kd forms for TPL and OPL, respectively. Interestingly, the OPL 43-kd form was inactive, whereas the TPL 35-kd protein conserved its lipolytic activity.

CONCLUSIONS

OPL, TPL, and mammal pancreatic lipases share a high amino acid sequence homology. Further investigations are, however, needed to identify key residues involved in substrate recognition responsible for biochemical differences between the 2 classes of lipases.

Further biochemical characterization of human pancreatic lipase-related protein 2 expressed in yeast cells

Recombinant human pancreatic lipase-related protein 2 (rHPLRP2) was produced in the protease A-deficient yeast Pichia pastoris. A major protein with a molecular mass of 50 kDa was purified from the culture medium using SP-Sepharose and Mono Q chromatography. The protein was found to be highly sensitive to the proteolytic cleavage of a peptide bond in the lid domain. The proteolytic cleavage process occurring in the lid affected both the lipase and phospholipase activities of rHPLRP2. The substrate specificity of the nonproteolyzed rHPLRP2 was investigated using pH-stat and monomolecular film techniques and various substrates (glycerides, phospholipids, and galactolipids). All of the enzyme activities were maximum at alkaline pH values and decreased in the pH 5-7 range corresponding to the physiological conditions occurring in the duodenum. rHPLRP2 was found to act preferentially on substrates forming small aggregates in solution (monoglycerides, egg phosphatidylcholine, and galactolipids) rather than on emulsified substrates such as triolein and diolein. The activity of rHPLRP2 on monogalactosyldiglyceride and digalactosyldiglyceride monomolecular films was determined and compared with that of guinea pig pancreatic lipase-related protein 2, which shows a large deletion in the lid domain. The presence of a full-length lid domain in rHPLRP2 makes it possible for enzyme activity to occur at higher surface pressures. The finding that the inhibition of nonproteolyzed rHPLRP2 by tetrahydrolipstatin and diethyl-p-nitrophenyl phosphate does not involve any bile salt requirements suggests that the rHPLRP2 lid adopts an open conformation in aqueous media.

Enterostatin (APGPR) enhances memory consolidation in mice

Enterostatin (APGPR) is a pentapeptide released from its precursor protein, procolipase. We found for the first time that enterostatin has memory-enhancing activity. Enterostatin enhanced memory consolidation after central or oral administration at a dose of 10 nmol/mouse or 300 mg/kg, respectively, in a step-through type passive avoidance test in mice. The memory-enhancing activity of enterostatin was inhibited by pretreatment with lorglumide, an antagonist for cholecystokinin 1 (CCK1) receptor. However, enterostatin had no affinity for CCK receptors. These results suggest that enterostatin improves memory retention through CCK release.

Enterostatin inhibition of dietary fat intake is modulated through the melanocortin system

Enterostatin injected into the amygdala selectively reduces dietary fat intake by an action that involves a serotonergic component in the paraventricular nucleus. We have investigated the role of melanocortin signaling in the response to enterostatin by studies in melanocortin 4 receptor (MC4R) knock out mice and by the use of the MC4R and MC3R antagonist SHU9119, and by neurochemical phenotyping of enterostatin activated cells. We also determined the effect of enterostatin in vivo on the expression of AgRP in the hypothalamus and amygdala of rats and in culture on a GT1-7 neuronal cell line. Enterostatin had no effect on food intake in MC4R knock out mice. SHU9119 i.c.v. blocked the feeding response to amygdala enterostatin in rats. Amygdala enterostatin induced fos activation in alpha-melanocyte stimulating hormone (alpha-MSH) neurons in the arcuate nucleus. Enterostatin also reduced the expression of AgRP in the hypothalamus and amygdala and in GT1-7 cells. These data suggest enterostatin inhibits dietary fat intake through a melanocortin signaling pathway.

Biochemical characterization, cloning, and molecular modelling of chicken pancreatic lipase

Chicken pancreatic lipase (CPL) was purified from delipidated pancreas. Pure CPL was obtained after ammonium sulphate fractionation, then DEAE-cellulose, Sephacryl S-200 gel filtration, and FPLC Mono-Q Sepharose columns. The pure lipase is a glycosylated monomer having a molecular mass of about 50kDa. The 23 N-terminal amino acid residues of CPL were sequenced. The sequence is similar to those of avian and mammalian pancreatic lipases. CPL presents the interfacial activation phenomenon tested with tripropionin or vinyl ester. When CPL was inhibited by synthetic detergent (TX-100) or amphipathic protein (BSA), simultaneous addition of bile salts and colipase was required to restore the full CPL activity. In the absence of colipase and bile salts, CPL was unable to hydrolyse tributyrin emulsion. This enzyme can tolerate, more efficiently than HPL, the accumulation of long-chain free fatty acids at the interface when olive oil emulsion was used as substrate in the absence of bile salts and colipase. The CPL activity, under these conditions, was linear whereas that of HPL decreased rapidly. Anti-TPL polyclonal antibodies cross-reacted specifically with CPL. The gene encoding the mature CPL was cloned and sequenced. The deduced amino acid sequence of the mature lipase shows a high degree of homology with the mammalian pancreatic lipases. A 3D structure model of CPL was built using the HPL structure as template. We have concluded that a slight increase in the exposed hydrophobic residues on the surface of CPL, as compared to HPL, could be responsible for a higher tolerance to the presence of long-chain free fatty acids at the lipid/water interface.

Different metabolic responses to central and peripheral injection of enterostatin

Enterostatin, a pentapeptide cleaved from procolipase, suppresses fat intake after peripheral and central administration. Chronic treatment of rats with enterostatin decreases body weight and body fat. The effect was greater than could be accounted by the reduction in food intake alone. Hence, we have investigated the effect of enterostatin on energy metabolism. Male Sprague-Dawley rats adapted to a high-fat diet were implanted with lateral cerebral ventricular or amygdala cannulas. The metabolic effects were determined by indirect calorimetry. After habituation to the test cages, fasted rats were injected with either saline vehicle or enterostatin given either intraperitoneally (100 nmol) or intracerebroventricularly (1 nmol) or into specific brain regions [amygdala (0.01 nmol) or paraventricular nucleus (PVN) (0.1 nmol)]. Respiratory quotient (RQ) and energy expenditure were monitored over 2 h. Intraperitoneal enterostatin reduced RQ (saline: 0.81 +/- 0.02 vs. enterostatin: 0.76 +/- 0.01) and increased energy expenditure by 44%. Intracerebroventricular enterostatin increased the energy expenditure without any effects on RQ, whereas PVN enterostatin increased metabolic rate, while preventing the increase in RQ observed in the control animals. In contrast, neither RQ nor energy expenditure was altered after enterostatin was injected into the amygdala. Enterostatin activated AMP-activated protein kinase in primary cultures of human myocytes in a dose- and time-dependent manner and increased the rate of fatty acid beta-oxidation. These findings suggest that enterostatin regulates energy expenditure and substrate partitioning through both peripheral and central effects.

Effect of enterostatin on the feeding responses to galanin and NPY

We have investigated the possibility that enterostatin may inhibit the intake of dietary fat by inhibiting either galanin or NPY-induced feeding pathways. Rats, adapted to either high fat (HF) or low fat-high carbohydrate (HC) diets and fitted with third ventricular cannulas were used to study the effects of intracerebroventricular (i.c.v.) enterostatin on i.c.v. NPY and galanin induced feeding responses in satiated rats. An equimolar dose of enterostatin (0.1 nmoles) inhibited, while a tenfold excess of enterostatin abolished the feeding response to galanin in rats adapted to a HF diet. The galanin stimulation of food intake was reduced in rats adapted to the HC diet and this response was less sensitive to inhibition by enterostatin. Enterostatin had no inhibitory effects on NPY-induced feeding in rats adapted to the HC diet and only a small inhibitory effect, at tenfold molar excess, in rats adapted to the HF diet. The ability of enterostatin to bind to galanin or NPY Y-1 receptors was investigated in ligand binding studies. Enterostatin failed to displace 125I-galanin or 125I-PYY from specific binding sites in rat forebrain homogenates or SK-N-MC cells respectively. The data provide support for the hypothesis that enterostatin specifically inhibits a galanin-responsive fat intake system, but indicate that this effect is not modulated by direct interaction with either galanin or NPY-Y1 receptors.

Enterostatin decreases postprandial pancreatic UCP2 mRNA levels and increases plasma insulin and amylin

This study investigated the chronic effect of enterostatin on body weight and some of the associated changes in postprandial metabolism. Rats were adapted to 6 h of food access/day and a choice of low-fat and high-fat (HF) food and then given enterostatin or vehicle by an intraperitoneally implanted minipump delivering 160 nmol enterostatin/h continuously over a 5-day infusion period. Enterostatin resulted in a slight but significant reduction of HF intake and body weight. After the last 6-h food access period, enterostatin-treated animals had lower plasma triglyceride and free fatty acid but higher plasma glucose and lactate levels than control animals. Enterostatin infusion resulted in increased uncoupling protein-2 (UCP2) expression in various tissues, including epididymal fat and liver. UCP2 was reduced in the pancreas of enterostatin-treated animals, and this was associated with increased plasma levels of insulin and amylin. Whether these two hormones are involved in the observed decreased food intake due to enterostatin remains to be determined. As lipid metabolism appeared to be altered by enterostatin, we measured peroxisome proliferator-activated receptor (PPAR) expression in tissues and observed that PPARalpha, -beta, -gamma1, and -gamma2 expression were modified by enterostatin in epididymal fat, pancreas, and liver. This further links altered lipid metabolism with body weight loss. Our data suggest that alterations in UCP2 and PPARgamma2 play a role in the control of insulin and amylin release from the pancreas. This implies that enterostatin changes lipid and carbohydrate metabolic pathways in addition to its effects on food intake and energy expenditure.

The F1-ATPase beta-subunit is the putative enterostatin receptor

It has been suggested that the F1-ATPase beta-subunit is the enterostatin receptor. We investigated the binding activity of the purified protein with a labeled antagonist, beta-casomorphin1-7, in the absence and presence of cold enterostatin. 125I-beta-casomorphin1-7 weakly binds to the rat F1-ATPase beta-subunit. Binding was promoted by low concentrations of cold enterostatin but displaced by higher concentrations. To study the relationship between binding activity and feeding behavior, we examined the ability of a number of enterostatin analogs to affect beta-casomorphin1-7 binding to the F1-ATPase beta-subunit. Peptides that suppressed food intake promoted beta-casomorphin1-7 binding whereas peptides that stimulated food intake or did not affect the food intake displaced beta-casomorphin1-7 binding. Surface plasmon resonance measurements show that the beta-subunit of F1-ATPase binds immobilized enterostatin with a dissociation constant of 150 nM, where no binding could be detected for the assembled F1-ATPase complex. Western blot analysis showed the F1-ATPase beta-subunit was present on plasma and mitochondrial membranes of rat liver and amygdala. The data provides evidence that the F1-ATPase beta-subunit is the enterostatin receptor and suggests that enterostatin and beta-casomorphin1-7 bind to distinct sites on the protein.

Pancreatic lipase-related protein 2 is the major colipase-dependent pancreatic lipase in suckling mice

Suckling mice express colipase before the expression of pancreatic triglyceride lipase. Yet, efficient fat digestion in newborns requires colipase, suggesting that colipase may act as a cofactor for another lipase such as pancreatic lipase-related protein 2 (PLRP2). We determined whether PLRP2 or another lipase depends on colipase for maximal activity in newborn mice by analyzing extracts from the pancreas of 4-d-old colipase-deficient and PLRP2-deficient mice. Pancreatic extracts from colipase-deficient pups had lipase activity that was stimulated onefold by the addition of exogenous colipase (P<0.001). The activity was completely inhibited by an antibody against pancreatic triglyceride lipase that also recognizes PLRP2. In contrast, pancreatic extracts from PLRP2-deficient pups had significantly lower baseline activity and no colipase-dependent activity. The baseline activity was not inhibited by the anti-pancreatic triglyceride lipase antibody or an antibody against carboxyl ester lipase. We next separated the extracts into two fractions, one containing PLRP2 and the other devoid of PLRP2. All of the colipase-dependent activity segregated with the PLRP2-containing fraction, consistent with the conclusion that PLRP2 is the major colipase-dependent lipase in the pancreas of newborns.

Enterostatin inhibition of dietary fat intake is dependent on CCK-A receptors

Enterostatin, a pentapeptide released from the exocrine pancreas and gastrointestinal tract, selectively inhibits fat intake through activation of an afferent vagal signaling pathway. This study investigated if the effects of enterostatin were mediated through a CCK-dependent pathway. The series of in vivo and in vitro experiments included studies of 1) the feeding effect of peripheral enterostatin on Otsuka Long Evans Tokushima Fatty (OLETF) rats lacking CCK-A receptors, 2) the effect of CCK-8S on the intake of a two-choice high-fat (HF)/low-fat (LF) diet, 3) the effects of peripheral or central injection of the CCK-A receptor antagonist lorglumide on the feeding inhibition induced by either central or peripheral enterostatin, and 4) the ability of enterostatin to displace CCK binding in a 3T3 cell line expressing CCK-A receptor gene and in rat brain sections. The results showed that OLTEF rats did not respond to enterostatin (300 microg/kg ip) in contrast to the 23% reduction in intake of HF diet in Long Evans Tokushima Otsuka (LETO) control rats. CCK (1 microg/kg ip) decreased the intake of the HF diet in a two-choice diet regime with a compensatory increase in intake of the LF diet. Peripheral injection of lorglumide (300 microg/kg) blocked the feeding inhibition induced by either near-celiac arterial or intracerebroventricular enterostatin, whereas intracerebroventricular lorglumide (5 nmol icv) only blocked the response to intracerebroventricular enterostatin but not to arterial enterostatin. Enterostatin did not bind on CCK-A receptors because neither enterostatin nor its analogs VPDPR and beta-casomorphin displaced [3H]L-364,718 from CCK-A receptors expressed in 3T3 cells or the binding of 125I-CCK-8S from rat brain sections. The data suggest that both the peripheral and central responses to enterostatin are mediated through or dependent on peripheral and central CCK-A receptors.

The effects of enterostatin intake on food intake and energy expenditure

Enterostatin (ENT) has been found to inhibit food intake and selectively inhibit fat intake in rats. Both peripheral and central mechanisms have been proposed. It also has been suggested that ENT may increase thermogenesis. The present study investigated the effects of oral ENT administration on food intake, energy expenditure and body weight in subjects with a preference for a high-fat diet. In a double-blind, placebo-controlled, randomized and crossover design, nine female and three male healthy subjects (age 34 (sd 11) years, BMI 24.5 (sd 2.5) kg/m(2)) with a preference for a high-fat diet ingested ENT (3 x 15 mg/d) or placebo (PLA) while consuming a high-fat diet ad libitum for 4 d. Eight subjects ended each intervention with a 36 h stay in the respiration chamber, continuing the diet and treatment. Body-weight loss was significant (ENT 0.8 (se 0.3) kg, P<0.05; PLA 1.3 (se 0.3) kg, P<0.001), but not different between treatments. There was no difference between treatments in total energy intake (ENT 37.1 (se 2.6), PLA 35.9 (se 3.2) MJ), macronutrient composition, hunger, satiety and hedonic scores during the 4 d high-fat diet. Energy expenditure (24 h) (ENT 9.6 (se 0.4), PLA 9.5 (se 0.4) MJ), sleeping and resting metabolic rate, diet-induced thermogenesis, activity-induced energy expenditure and 24 h RQ (ENT 0.77 (se 0.01), PLA 0.77 (se 0.01)) were similar for both treatments. We conclude that oral ENT administration did not affect food intake, energy expenditure or body weight in subjects with a preference for a high-fat diet experiencing a negative energy and fat balance.

In vitro lipolysis by human pancreatic lipase is specifically abolished by its inactive forms

In human adults, the enzymatic hydrolysis of dietary fat along the digestive tract is sequentially catalyzed by two main enzymes, human gastric lipase (HGL) and human pancreatic lipase (HPL). Both a chemically inhibited form of HPL as well as an inactive HPL mutant with a glycine residue substituted for its catalytic serine were found to be strong inactivators of HPL activity. In the presence of bile salts, this inhibition was clearly due to competition for colipase. We established that the chemically inhibited HPL, probably in its open conformation, had a much greater affinity for colipase than the closed native form of HPL. These inhibitory effects are quite substantial, because a 0.2-M excess of the chemically inhibited HPL form relative to HPL reduced the catalytic lipolytic activity by 50% in the presence of an equimolar amount of colipase.

The beta 5' loop of the pancreatic lipase C2-like domain plays a critical role in the lipase-lipid interactions

The structural similarities between the C-terminal domain of human pancreatic lipase (C-HPL) and C2 domains suggested a similar function, the interaction with lipids. The catalytic N-terminal domain (N-HPL) and C-HPL were produced as individual proteins, and their partitioning between the water phase and the triglyceride-water interface was assessed using trioctanoin emulsions (TC8). N-HPL did not bind efficiently to TC8 and was inactive. C-HPL did bind to TC8 and to a phospholipid monolayer with a critical surface pressure of penetration similar to that of HPL (15 mN m(-1)). These experiments, performed in the absence of colipase and bile salts, support an absolute requirement of C-HPL for interfacial binding of HPL. To refine our analysis, we determined the contribution to lipid interactions of a hydrophobic loop (beta 5') in C-HPL by investigating a HPL mutant in which beta 5' loop hydrophobicity was increased by introducing the homologous lipoprotein lipase (LPL) beta 5' loop. This mutant (HPL-beta 5'LPL) penetrated into phospholipid monolayers at higher surface pressures than HPL, and its level of binding to TC8 was higher than that of HPL in the presence of serum albumin (BSA), an inhibitory protein that competes with HPL for interfacial adsorption. The beta 5' loop of LPL is therefore tailored for an optimal interaction with the surface of triglyceride-rich lipoproteins (VLDL and chylomicrons) containing phospholipids and apoproteins. These observations support a major contribution of the beta 5' loop in the interaction of LPL and HPL with their respective substrates.

Regulation of feeding behavior, gastric emptying, and sympathetic nerve activity to interscapular brown adipose tissue by galanin and enterostatin: the involvement of vagal-central nervous system interactions

Galanin and enterostatin, which are distributed in both the central nervous system and the gastrointestinal tract, regulate the feeding behavior. In the first set of experiments, we investigated the effects of galanin and enterostatin, injected into the third ventricle, on food intake, gastric emptying, and the sympathetic activity of nerves innervating interscapular brown adipose tissue in rats. Galanin dose-dependently increased the intake of a high-fat diet after overnight starvation, but it did not affect low-fat diet intake. In contrast, enterostatin suppressed the intake of the high-fat diet, while intake of the low-fat diet was not affected. Galanin significantly and dose-dependently suppressed gastric emptying rate. However, gastric emptying showed no response to enterostatin. Galanin produced a dose-dependent suppression of sympathetic firing rate. In rats fed a high-fat diet, the injection of enterostatin showed a dose-dependent increase in firing rate. In contrast, animals fed a chow diet showed almost no response. In the second set of experiments, we investigated the role of the hepatic vagus nerve in modulating the peripheral response to enterostatin in rats. Intraperitoneal (i.p.) enterostatin reduced the intake of a high-fat diet. Immunohistochemical identification indicated that the Fos protein was present in the nucleus tractus solitarius, and parabrachial, paraventricular, and supraoptic nuclei after IP enterostatin. These responses to i.p. enterostatin were blocked by hepatic vagotomy. These results suggest that galanin and enterostatin coordinate to regulate feeding behavior, gastric emptying, and sympathetic activity to interscapular brown adipose tissue via central and peripheral sites of action, one of which was the interaction which was found to exist through the vagal system.

Mitochondrial ATP synthase--a possible target protein in the regulation of energy metabolism in vitro and in vivo

The increasing prevalence of obesity in the Western world has stimulated an intense search for mechanisms regulating food intake and energy balance. A number of appetite-regulating peptides have been identified, their receptors cloned and the intracellular events characterized. One possible energy-dissipating mechanism is the mitochondrial uncoupling of ATP-synthesis from respiratory chain oxidation through uncoupling proteins, whereby energy derived from food could be dissipated as heat, instead of stored as ATP. The exact role of the uncoupling proteins in energy balance is, however, uncertain. We show here that mitochondrial F1F0-ATP synthase itself is a target protein for an anorectic peptide, enterostatin, demonstrated both after affinity purification of rat brain membranes and through a direct physical interaction between enterostatin and purified F1-ATP synthase. In insulinoma cells (INS-1) enterostatin was found to target F1F0-ATP synthase, causing an inhibition of ATP production, an increased thermogenesis and increased oxygen consumption. The experiments suggest a role of mitochondrial F1F0-ATP synthase in the suppressed insulin secretion induced by enterostatin. It could be speculated that this targeting mechanism is involved in the decreased energy efficiency following enterostatin treatment in rat.

Effects of enterostatin (Val-Pro-Asp-Pro-Arg) on fat intake and blood levels of glucose and insulin in rats

Enterostatin may be involved in the preference for fat and the control of fat intake. Using two different feeding patterns, we observed a change in food intake after injection of enterostatin (VPDPR) into the third ventricle. When rats were adapted to free selection choice between low fat (LF) and high fat (HF) diets, VPDPR inhibited intake of the LF diet at 100, 200 and 800 ng and inhibited intake of the HF diet at 200 ng. The dose-response of HF diet intake to VPDPR was U-shaped. However, even the optimal dose (200 ng), which reduced the intake of both LF and HF diets when both diets were given together, was not effective when the LF diet was given alone. In the present study, VPDPR has also shown to not affect plasma glucose or insulin levels. These results suggest that exogenous VPDPR may inhibit appetite when endogenous enterostatin secretion is increased by ingestion of dietary fat, and that VPDPR has a limited range of effects on feeding behavior. We support the hypothesis that the early satiety sense of VPDPR as an anorectic agent in a central site is directly related to endogenous enterostatin or procolipase levels after fat intake, but not glucose or insulin levels.

Intragastric beta-casomorphin(1-7) attenuates the suppression of fat intake by enterostatin

The current experiments were designed to compare the feeding response to enterostatin and beta-casomorphin(1-7) injected intragastrically. Sprague-Dawley rats with a gastric cannula were allowed to chose from high-fat diet (HF) or low-fat diet (LF) in separate jars. Enterostatin injected intragastrically into overnight fasted rats caused a U-shaped dose-dependent reduction in the intake of the HF diet for the first two hours after infusion but had no effect on the LF intake. beta-Casomorphin(1-7) stimulated the intake of the HF diet but had no effect on the LF diet. Finally, beta-casomorphin(1-7) blocked the inhibitory effect of enterostatin on HF intake in fasted rats.

Effect of high-fat diet, surrounding temperature, and enterostatin on uncoupling protein gene expression

Nonshivering thermogenesis induced in brown adipose tissue (BAT) during high-fat feeding is mediated through uncoupling protein 1 (UCP1). UCP2 is a recently identified homologue found in many tissues. To determine the role of UCP1 and UCP2 in thermoregulation and energy balance, we investigated the long-term effect of high-fat feeding on mRNA levels in mice at two different ambient temperatures. We also treated mice with the anorectic peptide enterostatin and compared mRNA levels in BAT, white adipose tissue (WAT), stomach, and duodenum. Here, we report that high-fat feeding at 23 degrees C increased UCP1 and UCP2 levels in BAT four- and threefold, respectively, and increased UCP2 levels fourfold in WAT. However, at 29 degrees C, UCP1 decreased, whereas UCP2 remained unchanged in BAT and increased twofold in WAT. Enterostatin increased UCP1 and decreased UCP2 mRNA in BAT. In stomach and duodenum, high-fat feeding decreased UCP2 mRNA, whereas enterostatin increased it. Our results suggest that the regulation of uncoupling protein mRNA levels by high-fat feeding is dependent on ambient temperature and that enterostatin is able to modulate it.

Enterostatin suppresses food intake in rats after near-celiac and intracarotid arterial injection

Enterostatin (Ent) selectively suppresses the intake of dietary fat after peripheral and central administration. To further investigate the site of action of Ent, we compared the feeding responses to Ent injected intra-arterially near the celiac artery, into the carotid artery, or intravenously in rats adapted to a high-fat diet. After near-celiac arterial injection there was an immediate dose-dependent (0.05-13.5 nmol) inhibition of food intake occurring within 5 min in overnight-fasted rats that lasted up to 20 min. Carotid arterial Ent had a similar, immediate dose-related response, and the inhibitory effect was long lasting. The response to intravenous Ent was only evident at the highest dose (13.5 nmol) and was delayed for at least 120 min. Pretreatment with capsaicin, which causes degeneration of vagal sensory neurons, abolished the inhibitory responses to near-celiac Ent but not to intravenous or intracarotid Ent. These results provide further evidence for both a gastrointestinal site of action for peripheral Ent and a central site of action for intracarotid Ent and suggest that the delayed response to intravenous Ent may reflect either binding or slow uptake of this peptide into the central nervous system.

The role of enterostatin and apolipoprotein AIV on the control of food intake

Procolipase is secreted as a protein consisting of 101 amino acids. In the intestinal lumen, procolipase is activated by trypsin and cleaves to form the active colipase and the pentapeptide from the amino terminus. This pentapeptide is called enterostatin. Pancreatic procolipase synthesis is stimulated by a high-fat diet. A large body of evidence has been gathered in the past decade demonstrating the role of enterostatin in the inhibition of food intake; in particular, fat intake. This aspect of enterostatin will be discussed in this review. Other functions of enterostatin such as the inhibition of insulin secretion, will not. Apolipoprotein AIV is a protein synthesized by the human intestine. Similar to procolipase, the synthesis and secretion of apo AIV are also stimulated by fat absorption. In 1992, Fujimoto et al. first demonstrated that apo AIV is a satiety signal secreted by the small intestine following the ingestion of a lipid meal. Subsequently, this initial observation was followed by a number of studies supporting apo AIV's role in the inhibition of food intake. This review will discuss the role of apo AIV in inhibiting food intake.

Human pancreatic lipase: colipase dependence and interfacial binding of lid domain mutants

Five key amino acid residues from human pancreatic lipase (HPL) are mutated in some pancreatic lipase-related proteins 2 (PLRP2) that are not reactivated by colipase in the presence of bile salts. One of these residues (Y403) is involved in a direct interaction between the HPL C-terminal domain and colipase. The other four residues (R256, D257, Y267, and K268) are involved in the interactions stabilizing the open conformation of the lid domain, which also interacts with colipase. Here we produced and characterized three HPL mutants: HPL Y403N, an HPL four-site mutant (R256G, D257G, Y267F, and K268E), and an HPL five-site mutant (R256G, D257G, Y267F, K268E, and Y403N), in which the HPL amino acids were replaced by those present in human PLRP2. Colipase reactivated both the HPL Y403N mutant and HPL, and Y403 is therefore not essential for lipase-colipase interactions. Both the HPL four-site and five-site mutants showed low activity on trioctanoin, were inhibited by bile salts (sodium taurodeoxycholate, NaTDC) and were not reactivated by colipase. The interfacial binding of the HPL four-site mutant to a trioctanoin emulsion was suppressed in the presence of 4 mM NaTDC and was not restored by addition of colipase. Protein blotting/protein overlay immunoassay revealed that the HPL four-site mutant-colipase interactions are not abolished, and therefore, the absence of reactivation of the HPL four-site mutant is probably due to a lid domain conformation that prevents the interfacial binding of the lipase-colipase complex. The effects of colipase were also studied with HPL(-lid), an HPL mutant showing an 18-residue deletion within the lid domain, which therefore has only one colipase interaction site. HPL(-lid) showed a low activity on trioctanoin, was inhibited by bile salts, and recovered its lipase activity in the presence of colipase. Reactivation of HPL(-lid) by colipase was associated with a strong interfacial binding of the mutant to a trioctanoin emulsion. The lid domain is therefore not essential for either the interfacial binding of HPL or the lipase-colipase interactions.

Stability of porcine and microbial lipases to conditions that approximate the small intestine of young birds

In vitro experiments were conducted to study the stability of lipase activities from bacterial, fungal, and animal sources under conditions that approximate the small intestine. In the first experiment, the effects of preincubation with trypsin (500, 1,000, and 2,000 U/mL), chymotrypsin (200, 400, and 800 U/mL), and trypsin plus chymotrypsin (TC; 2,000 U/mL trypsin + 800 U/inL chymotrypsin) for 30 min at 40 C, on lipase activities from sources of Pseudomonas spp. (PL1, PL2), Chromobacterium viscosum (CVL), and Aspergillus niger (ANL) were determined. None of the enzymes were inhibited by trypsin. The chymotrypsin decreased the activity of all of the lipases. The TC had no additional negative effect on the activities of PL1 and PL2; however, ANL and CVL activities were further decreased relative to the chymotrypsin only treatment. In the second study, the effects of Na taurodeoxycholate (0.1 to 16 mM) on the activities of PL1, PL2, CVL, ANL, and crude porcine lipase (CPL) at 23 and 40 C were evaluated. At 23 C, in order of potency, Na taurodeoxycholate inhibited the activities of ANL, CPL, and CVL. At this temperature, Na taurodeoxycholate did not inhibit PL1 and PL2. An increase in the temperature to 40 C increased the activity of all of the enzymes tested. At 40 C, Na taurodeoxycholate had similar effects on lipase activities; however, higher Na taurodeoxycholate levels were required to inhibit ANL activity, and only a partial inhibition of CPL occurred. At 23 C, porcine colipase restored the activity of CPL but had no effect on ANL and CVL in the presence of inhibitory levels of Na taurodeoxycholate. At 40 C, porcine colipase had no effect on Na taurodeoxycholate inhibition of lipase activity. The results of this study indicate that PL is more stable than CVL and ANL, and that colipase addition has no beneficial effects on microbial lipase activities under conditions that approximate the avian small intestine.

Effects of enterostatin in non-food-deprived rats with limited or continuous access to oil or sucrose

The peptide enterostatin has been proposed to function as a selective signal for fat-induced satiety. In the majority of enterostatin studies, however, rats were food-deprived, and the test food was also the maintenance diet. The present study sought to determine if enterostatin would selectively reduce consumption of oil that was provided in addition to a standard diet in non-food-deprived rats. Rats had either continuous (24-h/day) or limited access (120-min/day) to either a 32% sucrose solution or 100% corn oil. In addition to the sucrose and the oil, rats also had 22-h access to a standard pelleted rodent diet. Control rats had unlimited access to the standard diet but no access to oil or sucrose. Rats were maintained on their respective diets for 3 weeks before enterostatin testing. Food intake and body weight were monitored. Rats with continuous access to oil or sucrose consumed more calories and gained more weight than control rats. Caloric intake and body weight of the rats with limited access to oil or sucrose did not differ significantly from controls. Enterostatin, administered intraperitoneally (i.p.) at doses of 0 (vehicle), 89, 178, and 356 microg/kg, had no effect on consumption of oil, sucrose, or standard diet in these non-food-deprivation paradigms; however, 356 microg/kg reduced standard-diet intake when rats were overnight food-deprived, thus verifying peptide activity. These results do not support a role for enterostatin in the regulation of fat intake when optional high-fat foods are provided in addition to a readily available standard diet.

Inhibition of insulin release by enterostatin

OBJECTIVE

These studies were designed to investigate the mechanism through which enterostatin inhibits insulin secretion from pancreatic islets.

DESIGN

A static islet incubation method was used to study the effects of enterostatin on insulin secretion induced by various secretagogues and to investigate the effect of calcium ions and 8-Br-cyclic AMP on the response to enterostatin. Measurements of islet cAMP concentrations in response to enterostatin were also made.

RESULTS

Enterostatin (10(-9) to 10(-5) M) inhibited insulin secretion from islets incubated in the presence of 16.7 mM glucose in a dose-dependent manner. Enterostatin also inhibited insulin secretion stimulated by glybenclamide (5.0 and 10 microM), phorbol 12-myristate-13-acetate (TPA) (50 and 100 nM), and the kappa-opioid agonist U50,488 (100 nM). The inhibitory effect of enterostatin on TPA-induced insulin secretion was attenuated but still remained in the absence of extracellular Ca2+. The enterostatin inhibition of insulin secretion was blocked by 8-Br-cAMP (1 mM) independent of extracellular Ca2+. Enterostatin reduced the increase in intracellular cyclic AMP (cAMP) content produced by U50,488 (100 nM) and the changes in cAMP content were parallel with changes in insulin release.

CONCLUSION

Enterostatin may suppress insulin secretion through the reduction of cAMP, but other mechanisms may also be possible.

Chronic ingestion of dietary fat is a prerequisite for inhibition of feeding by enterostatin

Enterostatin (Ent), the activation pentapeptide from procolipase, inhibits the intake of dietary fat. The selectivity of the response to fat suggests that the rat must recognize a permissive signal related to dietary fat for the Ent biological response. To investigate the nature of this signal, we studied the effects of Ent in rats that were adapted to either a high-fat (HF) or high-carbohydrate/low-fat (HC) diet and then naively exposed to either HF or HC diets. Ent (1 nmol) was injected into the lateral ventricle of overnight-fasted rats, and food intake was measured. Rats adapted to HF diet and tested with HC diet responded to Ent, but rats adapted to HC diet and tested with HF did not respond to Ent. The groups were maintained on their new test diets for up to 21 days and tested again for their response to Ent at 3, 7, 14, and 21 days. Ent response did not appear in HC-adapted rats switched to HF diet before 21 days. Conversely, the HF-adapted rats, which responded to Ent when tested with HC diet for the first time, did not respond at any subsequent testing time. The data suggest that chronic ingestion of dietary fat is required for Ent action and that chronic consumption of fat initiates a postingestion metabolic, endocrine, or neurochemical change that is required for the biological response to Ent.

Beta-casomorphins stimulate and enterostatin inhibits the intake of dietary fat in rats

The effects of beta-casomorphins 1-7, 1-5 and 1-4 on food intake of rats adapted to either a high fat (HF) or high carbohydrate (HC) diet have been studied and compared to the effects of enterostatin. Intracerebroventricular (icv) beta-casomorphin1-7 (beta-CM1-7) stimulated intake of HF diet in overnight fasted rats, but beta-CM1-5 and beta-CM1-4 were ineffective. Peripheral injection of beta-CM1-7 also increased the intake of a high fat diet, but reduced the intake of HC diet in satiated rats. Intracerebroventricular (ICV) beta-CM1-7 caused a dose-dependent increase in the intake of HF diet, but a dose-dependent inhibition of HC ingestion in satiated rats. Enterostatin (ICV) inhibited the beta-CM1-7 stimulation of HF intake, as did the general opioid antagonist naloxone. Ligand binding studies with [3H-pro] enterostatin identified on low affinity binding site (Kd 100nM) on a crude brain membrane preparation. This binding was displaced by beta-CM1-7, beta-CM1-5 and beta-CM1-4. These data suggest that at high doses enterostatin and beta-CM1-7 may interact with the same low affinity receptor to modulate intake of dietary fat.

Effects of enterostatin on consumption of optional foods in non-food-deprived rats

Enterostatin, the activation peptide of procolipase, has been reported to reduce high-fat food consumption in rats. This reduction has been reliably demonstrated using procedures in which the test diet was also the maintenance diet of the animals. Other reports, though, have shown that peripherally administered enterostatin had no effect on the consumption of oil provided as an option to the diet, and that centrally administered enterostatin had no effect on the consumption of an optional high-fat mixed food. However, the effects of peripherally administered enterostatin on the consumption of an optional high-fat mixed food have not been examined. This experiment, then, examined the effects of peripherally administered enterostatin on the consumption of optional, mixed foods (no-fat and high-fat cookies) provided in addition to a standard diet under choice and nonchoice conditions. Four experiments were conducted. In experiment I, the effect of enterostatin in a two-choice feeding paradigm was assessed. In experiment II, the effect of enterostatin in a nonchoice feeding paradigm was assessed. In experiment III, the effect of enterostatin administered at five different pretreatment times in a non-choice feeding paradigm was assessed. Enterostatin had no effect on cookie intake in any of these experiments. Finally, experiment IV was undertaken to verify the activity of the peptide. Enterostatin significantly reduced the consumption of a standard diet in overnight food-deprived rats, thus confirming the activity of the peptide used in experiments I to III. Enterostatin may not play a major role in the regulation of food intake that is stimulated by optional foods that are periodically provided in addition to a standard well-balanced diet.

Enterostatin--a peptide regulating fat intake

A high fat intake, together with an inability to match lipid oxidation to fat intake, has been found to be correlated with obesity in humans. This review describes our current understanding of enterostatin, a peptide that selectively reduces fat intake. Enterostatin is formed in the intestine by the cleavage of secreted pancreatic procolipase, the remaining colipase serving as an obligatory cofactor for pancreatic lipase during fat digestion. Enterostatin is also produced in the gastric mucosa and the mucosal epithelia of the small intestine. Procolipase gene transcription and enterostatin release into the gastrointestinal lumen are increased by high-fat diets. After feeding, enterostatin appears in the lymph and circulation. Enterostatin will selectively inhibit fat intake during normal feeding and in experimental paradigms that involve dietary choice. Its anorectic effect has been demonstrated in a number of species. Both peripheral and central sites of action have been proposed. The peripheral mechanism involves an afferent vagal signaling pathway to hypothalamic centers. The central responses are mediated through a pathway that includes both serotonergic and opioidergic components. Chronically, enterostatin reduces fat intake, bodyweight, and body fat. This response may involve multiple metabolic effects of enterostatin, which include a reduction of insulin secretion, an increase in sympathetic drive to brown adipose tissue, and the stimulation of adrenal corticosteroid secretion. A possible pathophysiological role is suggested by studies that have linked low enterostatin production and/or responsiveness to strains of rat that become obese and prefer dietary fat. Humans with obesity also exhibit a lower secretion of pancreatic procolipase after a test meal, compared with persons of normal weight.

Comparisons of the effects of enterostatin on food intake and gastric emptying in rats

The effects of central and peripheral administration of enterostatin (ENT) on food intake and gastric emptying of a non-nutrient liquid meal have been studied in rats. Intraperitoneal and intragastric administration of ENT at a dose of 120 nmol suppressed the intake of a high-fat diet but failed to inhibit gastric emptying in Sprague-Dawley (SD) rats. Intracerebroventricular (i.c.v.) ENT (1 nmol) reduced intake of a high-fate diet in Osborne-Mendel (OM) and SD rats but not in S5B/Pl rats, whereas it decreased gastric emptying in S5B/P1 and SD rats but not in OM rats. The data suggest that although central ENT may reduce gastric emptying rate, this effect is not related to the inhibitory effect of ENT on food intake.

Pancreatic lipase structure-function relationships by domain exchange

We designed chimeric mutants by exchanging the lid domains of the classical human pancreatic lipase (HPL) and the guinea pig pancreatic lipase related protein 2 (GPLRP2). This latter enzyme possesses naturally a large deletion within the lid domain and is not activated by lipid/water interfaces. Furthermore, GPLRP2 exhibits phospholipase A1 and lipase activities in the same order of magnitude, whereas HPL has no significant phospholipase activity and displays a clear interfacial activation. An HPL mutant [HPL(-lid)] with GPLRP2 mini-lid domain does not display interfacial activation. Its specific activity toward triglycerides is, however, dramatically reduced. A GPLRP2 mutant [GPLRP2(+lid)] with HPL full-length lid domain is not interfacially activated, and its lid domain probably exists under a permanent open conformation. Therefore, the phenomenon of interfacial activation in HPL is not only due to the presence of a full-length lid domain but also to other structural elements which probably allow the existence of stabilized closed and open conformations of the lid. GPLRP2(+lid) phospholipase activity is significantly reduced as compared to GPLRP2, whereas its lipase activity remains at the same level. Therefore, the lid domain plays a major role in substrate selectivity and can be considered as part of the active site. However, the presence of a full-length lid domain is not sufficient to explain the absence of phospholipase activity in HPL since HPL(-lid) does not display any phospholipase activity. We also produced a chimeric GPLRP2 mutant in which the C-terminal domain was substituted by the HPL C-terminal domain. The colipase effects, i.e., anchoring and stabilization of the lipase at the interface, are clearly observed with the chimera, whereas GPLRP2 is insensitive to colipase. The kinetic characterization of this chimera reveals for the first time that the interfacial stability of pancreatic lipases depends on the structure of the C-terminal domain.

Enterostatin actions in the amygdala and PVN to suppress feeding in the rat

The pentapeptide enterostatin (ENT) inhibits feeding after injection into the cerebral ventricles. To localize the central sites of action of ENT, the peptide (0.01 to 3.3 nM) was microinjected into several brain regions and the intake of a high fat diet was measured. The results show that ENT injection in the paraventricular nucleus (PVN) or the amygdala (AMYG) produced a bi-phasic dose related feeding response, low doses of ENT inhibited feeding while higher dose had no effect. The effective dose to inhibit feeding in the AMYG was 10 fold lower than that in the PVN. No changes in food intake were observed after ENT injection into the ventromedial hypothalamus and nucleus tractus solitarius. The data provide further support that there are targets in the CNS for ENT and suggest that central ENT function is site specific.

Effect of enterostatin and kappa-opioids on macronutrient selection and consumption

Enterostatin, the activation peptide of pancreatic procolipase, suppresses consumption of high-fat diets and selectively suppresses fat consumption over carbohydrate consumption. Kappa-opioid subtype agonists stimulate feeding whereas antagonists suppress feeding. We investigated the effects of enterostatin, the kappa-opioid agonist U50488, and the kappa-opioid antagonist nor-binaltorphimine (nor-BNI) on macronutrient selection and food consumption in rats adapted to choose between a high-fat (HF) diet or a low-fat-high-carbohydrate (LF) diet. In fasted rats, lateral cerebro-ventricular injection (LV) of enterostatin selectively suppressed consumption of the HF diet, with no effect on LF diet consumption. Nor-BNI also selectively suppressed consumption of the HF diet without affecting LF diet consumption. Additionally, U50488 prevented the suppression of consumption of the HF diet in response to enterostatin. In food-sated rates, U50488 preferentially increased consumption of the HF diet and had no effect on consumption of the LF diet. Combined infusions of subthreshold doses of enterostatin and nor-BNI also inhibited consumption of the HF but not the LF diet, whereas combined infusions of maximal doses of enterostatin and nor-BNI had no additive effects. Collectively, these data suggest that a kappa-opioid pathway modulates selection and consumption of diets high in fat and that enterostatin modulates consumption of dietary fat by interacting with this pathway.

Inhibition of insulin release by intraduodenally infused enterostatin-VPDPR in rats

Enterostatin, an amino-terminal pentapeptide produced in the intestinal lumen after cleavage of pancreatic procolipase, has been shown to suppress fat intake in rats after intraduodenal infusion. In this study, female Sprague-Dawley rats fitted with a duodenal catheter were intestinally infused with enterostatin (Val-Pro-Asp-Pro-Arg, 11.3 and 22.6 nmol/kg/min) plus 20% Intralipid for 30 min. Plasma insulin levels were significantly reduced, whereas plasma glucose concentrations were not altered by enterostatin-VPDPR. The tripeptide Asp-Pro-Arg was also found to decrease the levels of plasma insulin. However, the pentapeptide with the sequence Val-Pro-Gly-Pro-Arg, des-Arg-enterostatin Val-Pro-Asp-Pro and the tripeptide Pro-Asp-Pro failed to cause the reduction of plasma insulin levels in rats following intestinal infusion of these peptides. Radiolabeled enterostatin ([3H]VPDPR) was identified in plasma by HPLC following intraduodenal infusion of the peptide, indicating that the appearance of an intact enterostatin-VPDPR in blood. It is concluded that intestinally administered enterostatin-VPDPR and its metabolites reduce plasma levels of insulin stimulated by Intralipid.

Chronic ICV enterostatin preferentially reduced fat intake and lowered body weight

The pancreatic peptide enterostatin will acutely reduce fat intake in rats provided a choice of diets. Chronic ICV infusions of enterostatin suppress the intake of high fat diet. However, the effects of chronic ICV enterostatin on diet choice has not previously been studied. To investigate this, enterostatin (0.5 microgram/h) or artificial cerebrospinal fluid (CSF) was infused for 9 days into the lateral ventricle of rats adapted to a two-choice high-fat (HF) and low-fat (LF) diet regime. Enterostatin reduced intake of HF diet with the maximum depression at day 4, but there was no compensatory increase in LF intake. The body weight of enterostatin-infused rats declined. This was associated with a reduction in fat pad and liver weights compared to the CSF-infused control rats. Serum triglycerides and insulin were decreased and corticosterone was elevated in enterostatin-infused rats. The data show that enterostatin will chronically reduce fat intake and body weight and suggest that enterostatin may attenuate the appetite for fat.

The affinities of procolipase and colipase for interfaces are regulated by lipids

It has been suggested that at physiological pH, the trypsin-catalyzed activation of the lipase cofactor, procolipase, to colipase has no consequence for intestinal lipolysis and serves primarily to release the N-terminal pentapeptide, enterostatin, a satiety factor (Larsson, A., and C. Erlanson-Albertsson 1991. The effect of pancreatic procolipase and colipase on pancreatic lipase activation. Biochim. Biophys. Acta 1083:283-288). This hypothesis was tested by measuring the adsorption of [14C]colipase to monolayers of 1-stearoyl-2-oleoyl-sn-3-glycerophosphocholine and 13, 16-cis, cis-docosadienoic acid in the presence and absence of procolipase. With saturating [14C]colipase in the subphase, the surface excess of [14C]colipase is 29% higher than that of procolipase, indicating that colipase packs more tightly in the interface. With [14C]colipase-procolipase mixtures, the proteins compete equally for occupancy of the argon-buffer interface. However, if a monolayer of either or both lipids is present, [14C]colipase dominates the adsorption process, even if bile salt is present in the subphase. If [14C]colipase and procolipase are premixed for > 12 h at pH approximately 8, this dominance is partial. If they are not premixed, procolipase is essentially excluded from the interface, even if procolipase is added before [14C]colipase. These results suggest that the tryptic cleavage of the N-terminal pentapeptide of procolipase may be of physiological consequence in the intestine.

Importance of standardization of lipase assays by using appropriate calibrators

Comparability of lipase catalytic activities was poor when lipase was determined in 50 patients' specimens by a turbidimetric (Boehringer) and a colorimetric (Sigma) assay. Mean values of results differed by a ratio of 2.39. Optimal common conditions were defined for the titration of lipase activity in two commercial calibrators and in a home-purified preparation of human pancreatic lipase (HPL). When using these titers for each calibrator, comparability was greatly improved (ratio = 1.25). This result indicates that a significant part of between-method discrepancy is due to the lack of a reference method for the titration of lipase calibrators. Intermethod behavior of each material was compared with that of patients' specimens. By using HPL as calibrator, comparability was still dramatically improved (ratio = 1.01). This study shows the importance of the validation of a material for defined routine measurement procedures, before its use as calibrator.

Enterostatin efflux in cat intestinal lymph: relation to lymph flow, hyaluronan, and fat absorption

The question addressed in this study was whether enterostatin, the pancreatic procolipase activation peptide, modulates intestinal hyaluronan turnover via lymph. In anesthetized cats, segments of ileum were surgically isolated from the proximal and distal gut, the draining lymphatic was cannulated, and the segment was autoperfused in situ. In several groups, concentrations of immunoreactive enterostatin in lymph were compared with that in plasma at baseline and elevated lymph flow and in the absence and presence of fat absorption. The baseline ratio of lymph enterostatin to that in plasma (L/P) in the absence of fat absorption was 1.44 +/- 0.29 compared with 4.93 +/- 0.42 after cream feeding (P < 0.05). In a separate group, when the intestinal lumen was perfused for 2 h with a mixture of oleic acid and taurocholate, enterostatin L/P doubled compared with baseline. At high lymph flows, enterostatin concentrations fell in all groups, resulting in an L/P of 0.47 +/- 0.09 (P < 0.05) in the absence of fat absorption, 0.77 +/- 0.35 after oleic acid, and 1.26 +/- 0.13 in the cream-fed group. These changes correlate with the pattern of hyaluronan efflux from the ileum into lymph after fat absorption [R.K. Reed, M.I Townsley, V.H. Pitts, T.C. Laurent, and A.E. Taylor. Am. J. Physiol, 263 (Gastrointest. Liver Physiol. 26): G6-G11, 1992] However, in separate groups when enterostatin was introduced into ileum, either as a close intra-arterial bolus or via the intestinal lumen, there were no resultant changes in efflux of hyaluronan from the intestine into lymph. In conclusion, despite the fact that delivery of pancreatic exocrine secretions to the ileal lumen was blocked in this model, enterostatin concentration in lymph increased after fat absorption. Nonetheless, it seems clear that enterostatin does not modify intestinal hyaluronan turnover.

Effect of enterostatin on insulin, glucagon, and somatostatin secretion in the perfused rat pancreas

Enterostatin is a pentapeptide generated by trypic digestion of procolipase in the small intestine. Both peripheral and central administration of this peptide to rats has been shown to reduce food intake, this reduction being due to specific suppression of fat intake. In perifused pancreatic rat islets, enterostatin has been shown to inhibit the insulin response to a high glucose concentration. In the present study, we have investigated the effect of exogenous enterostatin on insulin, glucagon, and somatostatin secretion by the isolated perfused rat pancreas. Enterostatin, at 100 mmol/l, inhibited the insulin response to 9 mmol/l glucose (by 70%), 0.1 mmol/l tolbutamide (by 40%), and 5 mmol/l arginine (by 70%). Enterostatin had no effect on glucagon and somatostatin release at a maintained glucose level (5.5 mmol/l) or in response to 5 mmol/l arginine. Finally, preinfusion of the rat pancreas with a high enterostatin concentration (500 nmol/l) did not alter the insulin response to glucose, an observation that would rule out a toxic effect of this peptide on the beta-cell. In summary, in the perfused rat pancreas, enterostatin, at putatively physiological concentrations, inhibits insulin secretion without affecting glucagon or somatostatin output, thus pointing to a direct effect of enterostatin on the beta-cell and not through an alpha-cell or delta-cell paracrine effect. Because enterostatin is generated in the small intestine after feeding, it might play a role in the enteroinsular axis as an anti-incretin agent.

Procolipase is produced in the rat stomach--a novel source of enterostatin

Procolipase was identified in the stomach by in situ hybridisation. A strong autoradiographic labelling of chief cells was seen in the fundus region, declining more distally and being almost absent in antrum. There was no labelling seen in the intestine. Colipase activity was estimated in rat gastric juice following pentagastrin stimulation and was found to average 2 microM. Furthermore, enterostatin, the N-terminal pentapeptide of procolipase, has been identified in the rat gut and pancreas. Extracts from gastric mucosa, intestinal mucosa and pancreas were purified by gel filtration (Sephadex G25), ion-exchange chromatography (CM-Sepharose) and HPLC (C18 reverse phase). Using an ELISA assay with antibodies directed against enterostatin, two forms of the peptide were identified both in the gut and in the pancreas, with the amino-acid sequences APGPR and VPGPR, respectively. APGPR was found to be the predominant form of enterostatin, whereas only a small amount had the structure VPGPR. Enterostatin in the form of APGPR, when injected intracerebroventricularly in female Sprague-Dawley rats, significantly reduced high-fat food intake in a two-choice situation of low-fat (14% fat by energy) and high-fat (38% fat) food. It is concluded that procolipase is produced in the stomach and secreted into the gastric juice. This is also a novel source of enterostatin.

Role of intraduodenally administered enterostatin in rats: inhibition of food

Central and peripheral administration of enterostatin have been reported to reduce fat or high-fat food intake in rats. Enterostatin is formed in the intestinal lumen by tryptic cleavage of pancreatic procolipase during intraluminal fat digestion. The present experiments were designed to test if enterostatin following intraintestinal infusion would affect food intake in a similar way as intracerebraventricularly or intravenously administered enterostatin. Female Sprague-Dawley rats were fitted with a duodenal catheter and adapted to feeding schedule for 6 hours each day. After 10 days enterostatin (5.65 and 11.3 nmol/kg/min) or saline were infused into the duodenum and food intake measured. Enterostatin significantly reduced high-fat food intake during the 6 hours of feeding, but had no inhibitory effect on low-fat food intake. Addition of tetracaine to the enterostatin infusates blocked the satiating potency of intestinal enterostatin. These results support the hypothesis of a preabsorptive site of action for enterostatin.

Effect of galanin and enterostatin on sympathetic nerve activity to interscapular brown adipose tissue

The effects of galanin and enterostatin on sympathetic activity have been examined in rats using electrophysiological techniques. Galanin, in doses of 25-300 pmol, and enterostatin, in doses of 0.5-10 nmol, were injected into the third ventricle of anesthetized male Sprague-Dawley rats in 1-microliter volumes. Galanin produced a dose-dependent suppression (ranging between 20 and 80%) of sympathetic firing rate of nerves innervating interscapular brown adipose tissue. In rats fed a chow diet, injection of enterostatin produced only a transient 10% rise in firing rate which returned to baseline within 10-15 min. In contrast, animals fed a high-fat diet showed a dose-dependent increase in firing rate lasting for 60 min. The results of this experiment are consistent with the hypothesis that food intake and sympathetic nervous system activity have a reciprocal relationship. The implications of this relationship are discussed.

Intracerebroventricular enterostatin stimulates food intake in non-food-deprived rats

Previous studies reported that ICV enterostatin reduced high-fat food intake in food-deprived rats. The present study sought to determine if ICV enterostatin would decrease intake of a high-fat food in non-food-deprived rats. Eight doses (0-32 micrograms) were tested. Enterostatin (32 micrograms) significantly stimulated cookie intake at 30 min. Enterostatin did not reduce food intake at any dose. These results conflict with previous reports and suggest that central enterostatin does not play a role in suppressing, but may play a role in stimulating, high-fat food consumption in non-food-deprived rats.