The activation peptide of pancreatic procolipase decreases food intake in rats

Preclinical Toxicology of Vaccines1

Immunity to targeted infectious diseases may be conferred or enhanced by vaccines, which are manufactured from recombinant forms as well as inactivated or attenuated organisms. These vaccines have to meet requirements for safety, quality, and efficacy. In addition to antigenic components, various adjuvants may be included in vaccines to evoke an effective immune response. To ensure the safety of new vaccines, preclinical toxicology studies are conducted prior to the initiation of, and concurrently with, clinical studies. There are five different types of preclinical toxicology study in the evaluation of vaccine safety: single and/or repeat dose, reproductive and developmental, mutagenicity, carcinogenicity, and safety pharmacology. If any adverse effects are observed in the course of these studies, they should be fully evaluated and a final safety decision made accordingly. Successful preclinical toxicology studies depend on multiple factors including using the appropriate study designs, using the right animal model, and evoking an effective immune response. Additional in vivo and in vitro assays that establish the identity, purity, safety, and potency of the vaccine play a significant role in assessing critical characteristics of vaccine safety.

Identification of Enterostatin and the Relation between Lipase and Colipase in Various Species

Enterostatin, the N-terminal activation peptide of pancreatic procolipase, has been identified in three different forms in rat: VPDPR (Val-Pro-Asp-Pro-Arg), APGPR (Ala-Pro-Gly-Pro-Arg) and VPGPR (Val-Pro-Gly-Pro-Arg). We investigated the possibility for a species to have several isoforms of enterostatin. Pancreas was purified from four different species (rat, mouse, cat and pig) and the enterostatin sequences were identified. At the same time, the activities of pancreatic lipase and colipase were measured. In rat and mouse pancreas APGPR was the only form of enterostatin identified. The colipase activity was 188 ± 25 U/mg protein in rat and 189 ± 16 U/mg in mouse and the lipase activity 354 ± 33 U/mg and 292 ± 19 U/mg respectively. Rat and mouse had a colipase/lipase ratio close to 0.5. In pancreas from cat and pig we only detected the form VPDPR (Val-Pro-Asp-Pro-Arg). We found the colipase activity in cat to be 493 ± 92 U/mg, while the lipase activity was three times lower, 167 ± 18 U/mg. Pig pancreas concentrations of colipase was 110 ± 8 U/mg and of lipase 38 ± 5 U/mg. In both cat and pig the colipase/lipase ratio was close to 3. This suggests that colipase might have an additional role than to restore the activity of lipase. Our hypothesis is that an overproduction of colipase and hence also enterostatin is involved in the regulation of fat metabolism.

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.

Enterostatin deficiency increases serum cholesterol but does not influence growth and food intake in mice

A pentapeptide released from procolipase, enterostatin, selectively attenuates dietary fat intake when administered peripherally or centrally. Enterostatin may act through the afferent vagus nerve and in the hypothalamus and amygdala, primarily in the central nucleus of the amygdala. To investigate the physiological role of endogenous enterostatin, we created an enterostatin-deficient, colipase-sufficient (Ent(-/-)) mouse. Ent(-/-) mice are viable, normally active, and fertile. They exhibit normal growth on low-fat and high-fat diets. Furthermore, Ent(-/-) mice develop diet-induced obesity, as do Ent(+/+) mice, and have normal responses to a two-macronutrient choice diet and to a switch from a high-fat to a low-fat diet. Levels of total serum (P = 0.004) and non-HDL (P Collapse

Key Words

• appetite regulation
• fat intake
• procolipase
• satiety

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MESH Headings

• Animals
• Animals, Newborn
• Antisense Elements (Genetics)
• Body Temperature/physiology
• Cholesterol/blood
• Colipases/deficiency
• Colipases/genetics
• DNA/genetics
• Diet
• Dietary Fats/metabolism
• Eating/genetics
• Eating/physiology
• Enzyme Precursors/deficiency
• Enzyme Precursors/genetics
• Growth/physiology
• Hormones/blood
• Intestinal Absorption/genetics
• Metabolism/genetics
• Mice
• Mice, Knockout
• Mice, Transgenic
• Phenotype
• Reverse Transcriptase Polymerase Chain Reaction
• Weight Gain/genetics

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Grants

• DK-53100 NIDDK NIH HHS

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Affiliation(s)

Rita Miller Department of Pediatrics, Children's Hospital of Pittsburgh of University of Pittsburgh Medical Center, Pittsburgh, PA 15213, USA
Dymphna D'Agostino
Charlotte Erlanson-Albertsson
Mark E Lowe

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Procolipase gene: no association with early-onset obesity or fat intake

BACKGROUND

Several lines of evidence in volvement of procolipase (CLPS) or its derivative enterostatin in dietary fat absorption, regulation of fat intake, and body weight in rodents. We explored the relationship between genetic variation in CLPS, early-onset obesity and fat intake in humans.

METHODS

We screened the CLPS in 93 extremely obese children and adolescents and 96 underweight young adults for sequence variations and genotyped single nucleotide polymorphisms (SNPs) in extremely obese children and adolescents, healthy normal-and underweight young adults and obesity trios. Case-control and family-based association analyses were performed.

RESULTS

Five sequence variations were identified: two non-synonymous SNPs: rs2766597 (Leu8Pro), rs41270082 (Arg109Cys); one SNP in the 5'UTR: rs3748050; one intronic SNP: rs3748051; and one infrequent novel non-synonymous variant: Arg55His. For rs2766597, rs3748050, and rs3748051 we obtained no evidence for an association with obesity in the case-control comparison. For rs41270082 there was a trend for association which could not be substantiated in the family-based association analysis. Additionally, we found no association in subgroup analyses pertaining to the extremely obese children and adolescents in the lowest and highest quartile of the percentage of energy consumed as fat.

CONCLUSIONS

We found no evidence for an association of CLPS SNPs rs2766597, rs41270082, rs3748050, and rs3748051 with obesity or percentage of dietary fat intake.

Constant darkness is a mammalian biological signal

Environmental light is a potent modulator of mammalian circadian rhythm and expression of clock genes. Constant darkness (DD) is regarded as a "free-running" circadian state. In nature, hibernating mammals encounter constant darkness (DD) seasonally. Circadian expression of enzymes involved in fat catabolism, procolipase (CLP) and pancreatic-lipase-related protein 2 (PLRP2), were identified in many peripheral organs of mice during DD but not during regular light/dark (LD) cycles. Circulating 5'-adenosine monophosphate (5'-AMP) was associated with DD-activated gene expression. Synthetic 5'-AMP, when injected into LD mice, activated procolipase expression in their peripheral organs and the animals become severely hypothermic, both key features of hibernating mammals. These findings identified a circadian-regulated metabolic cycle in mammals that may be associated with hypometabolic behaviors such as hibernation and torpor.

Constant darkness is a circadian metabolic signal in mammals

Environmental light is the 'zeitgeber' (time-giver) of circadian behaviour. Constant darkness is considered a 'free-running' circadian state. Mammals encounter constant darkness during hibernation. Ablation of the master clock synchronizer, the suprachiasmatic nucleus, abolishes torpor, a hibernation-like state, implicating the circadian clock in this phenomenon. Here we report a mechanism by which constant darkness regulates the gene expression of fat catabolic enzymes in mice. Genes for murine procolipase (mClps) and pancreatic lipase-related protein 2 (mPlrp2) are activated in a circadian manner in peripheral organs during 12 h dark:12 h dark (DD) but not light-dark (LD) cycles. This mechanism is deregulated in circadian-deficient mPer1-/-/mPer2m/m mice. We identified circadian-regulated 5'-AMP, which is elevated in the blood of DD mice, as a key mediator of this response. Synthetic 5'-AMP induced torpor and mClps expression in LD animals. Torpor induced by metabolic stress was associated with elevated 5'-AMP levels in DD mice. Levels of glucose and non-esterified fatty acid in the blood are reversed in DD and LD mice. Induction of mClps expression by 5'-AMP in LD mice was reciprocally linked to blood glucose levels. Our findings uncover a circadian metabolic rhythm in mammals.

Enterostatin (VPDPR) and its peptide fragment DPR reduce serum cholesterol levels after oral administration in mice

We found that enterostatin (VPDPR), an anorexigenic peptide for a high-fat diet, significantly reduces serum cholesterol levels after oral administration of 100 mg/kg for 3 days in mice fed a high cholesterol-cholic acid diet. DPR, a peptide fragment of VPDPR, also had hypocholesterolemic activity at a dose of 50 mg/kg. Food intake was not suppressed under these dietary conditions. Fecal excretion of cholesterol and bile acids was increased significantly by both VPDPR and DPR. Interestingly, DPR induced hypocholesterolemic effects just two hours after a single oral administration at a dose of 100 mg/kg.

Anti-analgesic activity of enterostatin (VPDPR) is mediated by corticosterone

Although enterostatin (VPDPR) inhibited morphine-induced analgesia, it had no affinity for mu-opioid receptors. VPDPR administration was reported to elevate serum corticosterone levels. We found that corticosterone exhibited a similar anti-analgesic effect selective for mu-opioid. Furthermore, the anti-analgesic effect of VPDPR was inhibited by RU486, an antagonist for the glucocorticoid receptor. The anti-analgesic effect of VPDPR was not observed in adrenalectomized mice. These results suggest that the anti-analgesic activity of VPDPR is mediated by corticosterone released from the adrenal cortex.

Uptake across the blood-brain barrier and tissue distribution of enterostatin after peripheral administration in rats

Enterostatin, the N-terminal activation pentapeptide of procolipase that is produced by the pancreas, reduces food intake from high-fat diet when injected either peripherally or centrally to rats. We investigated uptake across the blood-brain barrier (BBB) and tissue distribution of enterostatin by giving radioactive-labeled enterostatin (3H-VPDPR) intravenously. Low levels of 3H-VPDPR were detected in many areas of the brain, with greatest radioactivity in the frontal cortex, hippocampus and cerebellum. Radioactivity was found in the plasma and all tissues, with the highest amount detected in the pancreas.

Pharmacological approaches for the treatment of obesity

The high incidence of obesity, its multifactorial nature, the complexity and lack of knowledge of the bodyweight control system, and the scarcity of adequate therapeutics have fuelled anti-obesity drug development during a considerable number of years. Irrespective of the efforts invested by researchers and companies, few products have reached a minimum level of effectiveness, and even fewer are available in medical practice. As a consequence of anti-obesity research, our knowledge of the bodyweight control system increased but, despite this, the pharmacological approaches to the treatment of obesity have not resulted yet in effective drugs. This review provides a panoramic of the multiple different approaches developed to obtain workable drugs. These approaches, however, rely in only four main lines of action: control of energy intake, mainly through modification of appetite;control of energy expenditure, essentially through the increase of thermogenesis;control of the availability of substrates to cells and tissues through hormonal and other metabolic factors controlling the fate of the available energy substrates; andcontrol of fat reserves through modulation of lipogenesis and lipolysis in white adipose tissue. A large proportion of current research is centred on neuropeptidic control of appetite, followed by the development of drugs controlling thermogenic mechanisms and analysis of the factors controlling adipocyte growth and fat storage. The adipocyte is also a fundamental source of metabolic signals, signals that can be intercepted, modulated and used to force the brain to adjust the mass of fat with the physiological means available. The large variety of different approaches used in the search for effective anti-obesity drugs show both the deep involvement of researchers on this field and the large amount of resources devoted to this problem by pharmaceutical companies. Future trends in anti-obesity drug research follow closely the approaches outlined; however, the increasing mass of information on the molecular basis of bodyweight control and obesity will in the end prevail in our search for effective and harmless anti-obesity drugs.

Comparative study of enterostatin sequence in five rat strains and enterostatin binding proteins in rat and chicken serum

Enterostatin, a pentapeptide derived from the precursor protein procolipase has been shown to inhibit dietary fat intake and to reduce body fat after chronic administration in rats. We repeat that the enterostatin amino acid sequence from the genomic DNA of 5 different rat strains is APGPR. 125I-APGPR bound to three proteins (300, 205 and 60 kDa) in rat serum and one 60 kDa protein in chicken serum. These serum binding proteins were also eluted by APGPR affinity chromatography. Western blot analysis of serum protein identified enterostatin-like immunoreactivity associated with the same molecular weight bands. Our results demonstrate the enterostatin sequence in rat is APGPR and suggest the presence of enterostatin binding proteins in rat and chicken serum.

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.

Pharmacology of appetite suppression

Despite a rising worldwide epidemic of obesity there is currently only a very small number of anti-obesity drugs available to manage the problem. Large numbers of differing pharmacological agents reliably produce a reduction in food intake when administered acutely to animals, and when administered chronically they result in a significant decrease in body mass. Behavioural analysis of drug-induced anorexia in animals demonstrates that various compounds profoundly effect feeding behaviour in differing ways. This indicates the variety of mechanisms by which pharmacological agents can induce changes in food intake, body weight and eventually body composition. Some of the same drugs produce decreases in food intake and weight loss in humans. Some of these drugs do so by modifying the functioning of the appetite system as measured by subjective changes in feelings of hunger and fullness (indices of satiety). Such drugs can be considered as "appetite suppressants" with clinical potential as anti-obesity agents. Other drugs induce changes in food intake and body weight through various physiological mechanisms inducing feelings of nausea or even by side effect related malaise. Of the drugs considered suitable candidates for appetite suppressants are agents which act via peripherally satiety peptide systems (such as CCK, Bombesin/GRP, Enterostatin and GLP-1), or alter the CNS levels of various hypothalamic neuropeptides (NPY, Galanin, Orexin and Melanocortins) or levels of the key CNS appetite monoamine neurotransmitters such as serotonin (5-HT) and noradrenaline (NA). Recently, the hormone leptin has been regarded as a hormonal signal linking adipose tissue status with a number of key central nervous system circuits. The peptide itself stimulates leptin receptors and it links with POMC and MC-4 receptors. These receptors may also provide drug targets for the control of appetite. Any changes induced by a potential appetite suppressant should be considered in terms of the (i) psychological experience and behavioural expression of appetite, (ii) metabolism and peripheral physiology, and (iii) functioning of CNS neural pathways. In humans, modulation of appetite may involve changes in total caloric consumption, subjective changes in feelings of hunger and fullness, preferences for specific food items, and general macronutrient preferences. These may be expressed behaviourally as changes in meal patterns, snacking behaviour and food choice. Within the next 20 years it is certain that clinicians will have a new range of anti-obesity compounds available to choose from. Such novel compounds may act on a single component of the appetite system or target a combination of these components detailed in this review. Such compounds used in combination with lifestyle changes and dietary intervention may be useful in dealing with the rising world epidemic of obesity.

Enterostatin (Val-Pro-Asp-Pro-Arg)-like immunoreactivity in rat urine: relationship to corticosterone output

Numerous studies have documented a role for enterostatins in appetitive behavior. However, due to the lack of knowledge about the distribution of enterostatins in tissues and body fluids, it has not been possible to examine the role of endogenous enterostatin in this process. To this end, using a polyclonal antibody raised against enterostatin -- Val-Pro-Asp-Pro-Arg (VPDPR), we examined the nature and distribution of enterostatin-like immunoreactivity in the rat urine by ELISA and chromatography. The results reported here show for the first time the presence of VPDPR-like immunoreactivity (VPDPR-LI) in rat urine. Further characterization of rat urine VPDPR-LI revealed that it is not due to VPDPR but to another peptide similar to VPDPR. Furthermore, as urinary excretion of corticosterone increases, the level of VPDPR-LI in urine decreases.

Hormones in Foods: Presence of Enterostatin-Like Immunoreactivities in Bovine Milk

Enterostatins, pentapeptides (Val-Pro-Asp-Pro-Arg [VPDPR], Val-Pro-Gly-Pro-Arg, Ala-Pro-Gly-Pro- Arg [APGPR], and others) derived from the amino terminus of procolipase, are endogenous to a variety of tissues and body fluids including brain, gut, blood, cerebrospinal fluid, and urine. The administration of exogenous peptides has been shown to elicit a variety of biologic activities, including a decrease in dietary fat preference and pancreatic insulin secretion. Since milk is a rich source of a variety of bioactive substances, especially peptides, we investigated the presence of enterostatin-like immunoreactivity in bovine milk. We measured enterostatins-APGPR and VPDPR-in milk from a herd of 19 cows randomly selected from the Louisiana State University Department of Dairy Science Research Herd in Baton Rouge; the results of this study show a mean peptide concentration in raw milk of 33.7 ± 2.9 ng/ml for APGPR and of 104.5 ± 16.3 ng/ml for VPDPR. A further chromatographic characterization of the nature of APGPR- and VPDPR-like immunoreactivities suggested the endogenous peptides share a common epitope with APGPR or VPDPR but are not APGPR or VPDPR. Unlike APGPR or VPDPR, the endogenous peptides were heat-labile and therefore their values were much lower in pasteurized milk.

On the nature and distribution of enterostatin (Val-Asp-Pro-Asp-Arg)-like immunoreactivity in rat plasma

Enterostatins, pentapeptides represented at the amino-terminus of the procolipase molecule, are derived following tryptic cleavage of the procolipase molecule in the lumen of the gut. Val-Pro-Asp-Pro-Arg or VPDPR is one such enterostatin. Despite pharmacologic studies suggesting a role for VPDPR in appetite regulation and insulin secretion, the function of this endogenous peptide has been impossible to discern due to the lack of a suitable assay. Using polyclonal antibodies raised against VPDPR and different chromatographic methods, we examined the nature and distribution of enterostatin-like immunoreactivity in rat plasma. The results reported here show for the first time the presence of VPDPR-like immunoreactivity in rat plasma. Further characterization of the plasma VPDPR-like immunoreactivity revealed that a) it is not due to APGPR, VPGPR, or VPDPR but to another peptide similar to VPDPR, and b) plasma VPDPR-like immunoreactivity may circulate bound to large carrier proteins.

Capillary diffusion capacity and tissue distribution of pancreatic procolipase in rat

The permeability-surface area product of procolipase and its apparent distribution volume in rat tissues were assessed using a tissue uptake technique. Procolipase was investigated together with 51Cr-EDTA, used as an inert extracellular marker, and 131I-albumin, used as a plasma volume marker. The tissue uptake of procolipase seemed to occur by passive transport in most of the organs studied, such as in muscle, liver, lung, adipose tissue, adrenal glands, colon, and skin. However, throughout the gastrointestinal tract, except in the colon, there was a high uptake of procolipase, greatly exceeding that of 51Cr-EDTA. This was especially evident in the stomach, in which the procolipase uptake was nonsaturable within the experimental period. Also, in the central nervous system (CNS), there was evidence of specific, possibly carrier-mediated, transport. These results suggest that procolipase may have specific, conceivably receptor-mediated, transport pathways across the microvascular endothelium in the stomach, pancreas, duodenum, ileum, and the CNS.

Endogenous Enterostatin, Proteases, and Dietary Fat Preference in Rats

Many studies clearly demonstrate inhibition of dietary fat preference by exogenous enterostatins in rodents. However, what role endogenous enterostatin, if any, may play in the regulation of fat intake is not clear. To this end, we examined whether there is a relationship between plasma enterostatin (VPDPR)-like immunoreactivity and fat preference. Additionally, since enterostatin is a product of tryptic cleavage of procolipase, we examined the effect of camostat, a protease inhibitor known to inhibit trypsin and other proteases, on dietary fat preference and plasma enterostatin concentration. The results of these studies show that while there was a significant inverse relationship between plasma enterostatin and fat preference, the effect of camostat on fat preference or plasma enterostatin concentration was not clear.

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.

The pharmacologic approach to the treatment of obesity

Obesity is a major risk factor for morbidity and mortality, and a series of pharmacologic approaches are available for helping to manage the problem. Obesity is caused by an imbalance between caloric intake and energy expenditure, which is influenced by both environmental and genetic factors. Pharmacologic treatments include anorexigenic agents, which fall into two broad categories: those that act via brain catecholamine pathways and those that act via serotonin pathways. The most recent oral agents approved are dexfenfluramine, which is currently being marketed, and sibutramine. Both agents inhibit the control reuptake of serotonin but in addition may have effects on thermogenesis. Under investigation are agents that increase energy expenditure: the beta 3-adrenergic receptor agonists and drugs that prevent the intestinal absorption of free fatty acids and cholesterol. In development are innovative approaches to influence leptin and its receptors, various obesity genes, and biologic substances thought to influence satiety (neuropeptide Y, enterostatin, cholecystokinin, bombesin, and amylin). Obesity has now become a major target for drug development not only for affecting obesity per se but also for managing and preventing comorbid conditions such as diabetes and cardiovascular disease.

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.

The inhibition of intestinal dipeptidylaminopeptidase-IV promotes the absorption of enterostatin and des-arginine-enterostatin across rat jejunum in vitro

Transport of enterostatin (VPDPR) across rat jejunum was investigated using Grass-Sweetana diffusion chambers. The rate of absorption of enterostatin and its metabolites were studied in absence and in presence of diisopropylfluorophosphate (DFP), a serine protease inhibitor. An extensive hydrolysis of enterostatin was observed during incubation with brush border membranes and when exposed to the mucosal side of the jejunal epithelium. No accumulation of enterostatin occurred in serosal tissue. Addition of DFP delayed enterostatin disappearance and abolished des-arg-enterostatin degradation. Under these conditions, a low amount of enterostatin was able to cross the epithelium intact. Moreover, a substantial amount of des-arg-enterostatin is absorbed across the jejunal epithelium, probably through passive diffusion. Thus, a decreased metabolic activity increased the absorption of a tetrapeptide (VPDP). Dipeptidylaminopeptidase IV, remains a limiting step in transfer of intact enterostatin and its metabolite des-arg-enterostatin across intestinal wall.

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.

Enterostatin in gut endocrine cells--immunocytochemical evidence

The presence of enterostatin, a pentapeptide acting as a potential satiety signal in rats, was investigated in rat intestine by immunocytochemical methods. Using antibodies directed against the C-terminal part of enterostatin, the peptide was identified in endocrine cells in the antral part of the stomach and in the small intestine of rat. The immunoreactive cells were more frequent in the antrum and duodenum and became gradually fewer towards the distal small intestine. In some of the labeled endocrine cells, a coexistence of enterostatin with serotonin was revealed by immunocytochemical double staining, implying that the cells were enterochromaffin cells. In the pancreas, no enterostatin-immunoreactive cells were detected, indicating enterostatin to be included in its parent molecule, procolipase. In addition, the existence of procolipase in the gastrointestinal tract, including the pancreas, was investigated. Procolipase immunoreactivity was also identified, except in the pancreas, in chief cells in the fundus region of the stomach. The number of labeled cells declined distally in the stomach, finally being absent in the intestine. Immunoreactive enterostatin was measured with a specific ELISA method. Intestinal content and serum were found to average 540 +/- 70 and 50 +/- 4 nM, respectively. Pancreatic duct ligation strongly reduced the levels of enterostatin in intestinal content to 5.4 +/- 1.5 nM (p < 0.001), and also reduced the serum enterostatin level to 35 +/- 5 nM (p < 0.05). It is concluded that the peptide enterostatin in the rat is produced both in the exocrine pancreas, as part of pancreatic procolipase, and in gut endocrine cells, both sources of peptide being important for the circulating enterostatin.

Serotonin, eating behavior, and fat intake

There is an intimate relationship between nutritional intake (eating) and serotonin activity. Experimental manipulations (mainly neuropharmacological) of serotonin influence the pattern of eating behavior, subjective feelings of appetite motivation, and the response to nutritional challenges. Similarly, nutritional manipulations (food restriction, dieting, or altered nutrient supply) change the sensitivity of the serotonin network. Traditionally, serotonin has been linked to the macronutrient carbohydrate via the intermediary step of plasma amino acid ratios. However, it has also been demonstrated that 5-HT drugs will reduce energy intake and reverse body weight gain in rats exposed to weight increasing high fat diets. 5-HT drugs can also reduce food intake and block weight gain of rats on a high fat cafeteria diet. Some diet selection studies in rats indicate that the most prominent reduction of macronutrient intake is for fat. These data indicate that 5-HT activity can bring about a reduction in fat consumption. In turn, different types of dietary fat can alter brain 5-HT activity. In human studies the methodology of food choice experiments has often precluded the detection of an effect of 5-HT manipulation on fat intake. However, there is evidence that in obese and lean subjects some 5-HT drugs can readily reduce the intake of high fat foods. Data also suggest that 5-HT activation can lead to a selective avoidance of fat in the diet. These effects of 5-HT on the intake of dietary fat may involve a pre-absorptive mechanism and there is evidence that 5-HT is linked to cholecystokinin and enterostatin. These proposals have theoretical and practical implications and suggest possible strategies to intensify or advance fat-induced satiety signals.

A step towards developing the expertise to control hunger and satiety: regulatory role of satiomem--a membrane proteoglycan

Regulation of hunger and satiety is a complex process thought to be controlled by a complex interplay of neurotransmitters in the hypothalamic region of the brain. Reduced food intake or anorexia has also been observed under various disease or disorder conditions including AIDS and cancer. On the other hand, increased appetite because of some impairment of central mechanisms regulating the food intake could also cause/obesity. A large number of substances including neuropeptides, hormones, drugs, and synthetic peptides have been implicated in the regulation of appetite and food intake behavior in normal as well as disease or disorder conditions. Most of these substances are not directly involved in the regulation of normal hunger and satiety but exert their effect indirectly via other media. Some of them are involved under certain pathologic conditions and during the course they become involved directly or indirectly in the triggering of hunger and satiety regulatory mechanism. Recently, we have been able to isolate and purify an endogenous proteoglycan from membranes of animal and plant sources. This membrane anchored proteoglycan termed as 'Satiomem' reduces food intake without any rebound effects and has no apparent toxicity. It also fulfils all the criteria of a true satiety or anorexigenic substance. The release of satiomem from the cell surface could be mediated by a specific phospholipase-C. Satiomem seems to be involved in transducing activating signals and may also act as a source of second messenger for the regulatory mechanism of appetite. This article summarizes the regulatory aspects of hunger and satiety mechanisms controlled by endogenous substances with the emphasis on our present knowledge about satiomem.

Augmentation of dietary fat preference by chronic, but not acute, hypercorticosteronemia

Numerous studies have documented a role for corticosterone in appetitive behavior, including caloric intake and dietary fat preference. In the present study, we have examined the mechanism(s) underlying modulation of dietary fat preference by corticosterone. The results of these studies show a) an increased fat preference with increased basal urinary output, or decreased stimulation of corticosterone output on fasting, b) elevation of fat preference following chronic, but not acute, hypercorticosteronemia produced by exogenous corticosterone administration, and c) emergence of hypercorticosteronemia prior to the development of increased fat preference in developing rats. These observations have led us to suggest that increased fat preference after chronic hypercorticosteronemia may be secondary to changes in the levels or actions of agents known to affect fat intake.

Intravenous enterostatin does not affect single meal food intake in man

Enterostatin, a pentapeptide released with colipase from pancreatic procolipase in man, affects eating behaviour in animals. We report the first phase II study of intravenous (i.v.) enterostatin (D3800) in obese but otherwise healthy men. Eighteen men (mean age 37 years, mean body mass index 34.9 kg/m2) completed a double-blind, randomized, crossover placebo controlled trial. After in initial session, each man received i.v. 4 mg D3800, 16 mg D3800 or placebo in random order over three sessions, immediately before a test meal served on a universal eating monitor. No statistically significant effect of i.v. enterostatin on any uptake or rating variable was observed. Several factors may explain the lack of effect, e.g. the inability of i.v. enterostatin to reach a site of action, the time between i.v. administration and eating, and the possibility that the only human responders are those who express particular fat preferences.

Metabolism of enterostatin in rat intestine, brain membranes, and serum: differential involvement of proline-specific peptidases

The degradation of enterostatin (VPDPR), a potent inhibitor of food intake, by intestinal brush-border membranes, brain membranes, and rat serum has been investigated in the presence of specific inhibitors. Hydrolysis by intestinal membranes was found to be 10 and 100 times faster than in serum and brain membranes, respectively. Enterostatin hydrolysis by intestinal and brain membranes involves the removal of C-terminal arginine by carboxypeptidase P, leading to the production of des-Arg-enterostatin, and the splitting of the Pro2-Asp3 bond by dipeptidyl aminopeptidase IV (DPP IV). A small amount of the potent anorectic peptide Pro2-Asp3-Pro4 was released during hydrolysis of des-Arg-enterostatin by brain membranes and rat serum. In rat serum, enterostatin degradation was mainly due to DPP IV.

Bioactive cyclic dipeptides

Cyclic dipeptides are among the simplest peptide derivatives commonly found in nature. Most cyclic dipeptides found to date appear to have emerged as by-products of fermentation and food processing. However, many are endogenous to members of animal and plant kingdoms; these include cyclo(Pro-Leu), cyclo(Pro-Val), cyclo(Pro-Phe), cyclo(Ala-Leu), cyclo(Pro-Tyr), cyclo(Pro-Trp), and cyclo(His-Pro). Although the five cyclic dipeptides--cyclo(His-Pro), cyclo(Leu-Gly), cyclo(Tyr-Arg), cyclo(Asp-Pro), and cyclo(Pro-Phe)--exhibit interesting physiological and/or pharmacological activities in mammals, only one of these, cyclo(His-Pro), has been conclusively shown to be endogenous to mammals. On the other hand, cyclo(Leu-Gly), cyclo(Tyr-Arg), and cyclo(Asp-Pro) are structurally related to endogenous peptides Pro-Leu-Gly-NH2 (melanocyte-stimulating hormone release inhibiting factor), Tyr-Arg (kyotorphin), and Val-Pro-Asp-Pro-Arg (enterostatin), respectively, which may serve as precursor peptides. It needs to be determined, however, whether these peptides can indeed result from the processing of their respective precursors. In conclusion, it appears that cyclic dipeptides are a relatively unexplored class of bioactive peptides that may hold great promise for the future.

The in vitro intestinal absorption of enterostatin is limited by brush-border membrane peptidases

The intestinal metabolism and absorption of enterostatin was studied using brush-border membrane vesicles and an in vitro model of intestinal segments from rabbit ileum mounted in Sweetana-Grass diffusion chamber. Hydrolysis of enterostatin was observed with both epithelial sheets and brush-border membranes. The main metabolite was found to be des-arginine-enterostatin. Dipeptidylpeptidase IV was found to play a minor role in enterostatin degradation, whereas carboxypeptidase P activity accounted for the initial step of peptide hydrolysis. More than 50% of the amount of enterostatin added to the mucosal compartment of the Sweetana-Grass diffusion chamber was degraded after 30 min. Enterostatin was mainly absorbed as degradation products but a small transepithelial passage of des-arginine-enterostatin and immunoreactive enterostatin was also detected. Although immunoreactive enterostatin exhibits a low apparent permeability coefficient in rabbit ileum, the luminal production of this peptide may be of physiological importance in the control of appetite.

Enterostatin inhibits insulin secretion from isolated perifused rat islets

The effect of enterostatin on glucose-induced insulin secretion was examined in isolated, perifused rat islets. In the presence of 16.67 mM glucose, there was significant inhibition of insulin secretion at concentrations of 200 nM, 2, 20 and 40 microM enterostatin. In particular, the second phase of insulin secretion was inhibited. With a low concentration of glucose (2.78 mM), there was no significant effect on insulin secretion by enterostatin. The inhibition of insulin secretion exerted by enterostatin may be an important effect in the prevention of insulin resistance.

Structural requirements for the biological activity of enterostatin

A series of enterostatin analogues were tested to investigate the minimal structure required for activity to suppress the intake of high-fat (HF) diets. The dose-response curve to intracerebroventricular (ICV) enterostatin was U-shaped (maximal inhibition at 1 nmol). Removal or modification of the N-terminal valine from enterostatin (Val-Pro-Asp-Pro-Arg) abolished activity, as did C-terminal amidation. The tripeptide (Pro-Asp-Pro) and the cyclo-diketopiperazine cyclo-Asp-Pro retained activity whereas the linear Asp-Pro dipeptide was inactive. In rats adapted to a three-choice macronutrient diet, cyclo-Asp-Pro specifically inhibited fat intake and had near maximal inhibition (50%) at the 0.03 nmol dose. The enterostatin inhibitory effect on fat intake may reside in the cyclo-diketopiperazine molecule, cyclo-Asp-Pro.

Corticosterone facilitation of inhibition of fat intake by enterostatin (Val-Pro-Asp-Pro-Arg)

Enterostatin or Val-Pro-Asp-Pro-Arg (VPDPR) is the amino-terminal pentapeptide of procolipase; VPDPR is generated during tryptic activation of procolipase to lipase. In rodents, exogenous VPDPR has been shown to cause a selective decrement in fat appetite. To understand the mechanism(s) underlying the action of this peptide, we have studied the effects of corticosterone, an adrenal hormone known to modulate caloric intake, on VPDPR-mediated inhibition of appetite. The results of this study show a significant increase in the inhibition of total caloric intake by 250 micrograms/kg VPDPR following corticosterone treatment (control, 2.3%; corticosterone treated, 22.7%). Furthermore, the decrement in the caloric intake in corticosterone-treated rats was exclusively due to the loss of fat intake.

Pharmacological aspects of appetite: implications for the treatment of obesity

The properties of an ideal weight-reducing drug would be to produce a sustained decrease in body fat, to oppose the recidivism in obese patients and to improve compliance to dietary requirements. More specifically the drug would have to decrease hunger, be active in the long term, preferably produce no tolerance or rebound effects, and prevent any decrease in basal metabolic rate. Moreover, the drug should reduce the intake of dietary fat which is now regarded as a major cause of weight gain (and regain) [14]. Can this be achieved? Can drug-induced appetite control be used to combat obesity? Some drugs have already demonstrated a capacity to adjust appetite so as to produce significant improvements in the pattern of eating and the control of body weight. What mechanisms are responsible for such an action and how can new drugs be developed so as to advance the pharmacological control of appetite?

Effect of a satiating meal on the concentrations of procolipase propeptide in the serum and urine of normal and morbidly obese subjects

The effect of a satiating meal on the serum and urinary concentrations of procolipase propeptide (Ala-Pro-Gly-Pro-Arg, APGPR) immunoreactivity, as measured by enzyme linked immunosorbent assay (ELISA) specific for free APGPR, has been studied in normal and morbidly obese human subjects. The normal subjects displayed a biphasic response with coordinate increases in both serum and urine APGPR immunoreactivity both occurring within the first two hours after the meal. In two of three of the morbidly obese subjects, this early rise in APGPR concentration in urine was not seen but was followed by a slow rise in urinary APGPR immunoreactivity at four to six hours. In both the normal and obese groups, the urinary immunoreactive signal was found to coelute with synthetic APGPR on gel chromatography. In rats, procolipase propeptide (Val-Pro-Asp-Pro-Arg, VPDPR) specifically inhibits fat intake early in the postprandial period when given peripherally or centrally. This study suggests that in humans APGPR reaches the circulation shortly after feeding and is excreted in the urine. These findings are consistent with the hypothesis that human procolipase propeptide may also act as a satiety signal. In addition the late appearance of the peptide in some of the morbidly obese patients could be associated with perturbation of appetite control in these subjects.

Chronic effects of intracerebral ventricular enterostatin in Osborne-Mendel rats fed a high-fat diet

Enterostatin, a pentapeptide found in the procolipase molecule of the pancreas, has been infused chronically into the lateral ventricle of Osborne-Mendel rats for 11 days. Treatment with enterostatin acutely lowered food intake more in the treated animals than in the vehicle-treated controls. Weight gain and serum insulin were significantly reduced by enterostatin. Corticosterone was significantly increased in rats receiving chronic infusions of enterostatin into the lateral ventricle and was also increased following an acute ICV injection of enterostatin. CRH antagonist did not block the acute feeding response to enterostatin in Sprague-Dawley rats. The elevation of corticosterone during chronic infusion of enterostatin reduced the level of hepatic glucocorticoid receptor as measured by Western blot. We conclude that body weight gain of OM rats is reduced by centrally administered enterostatin, and that the acute effects of enterostatin on food intake are not mediated through stimulation of CRH secretion.

The peptide enterostatin may produce early satiety

The time course of feeding, grooming, exploration, and sleeping behaviors has been measured following treatment with enterostatin, the signal pentapeptide from procolipase. The peptide was injected intraperitoneally prior to presenting food, and the frequency of feeding and grooming activity, drinking, and rest or sleeping were observed at 10-s intervals for 60 min. Enterostatin did not delay the onset of feeding but shortened the time spent eating compared to saline injected controls. Conversely, grooming activity appeared earlier following enterostatin, activity was reduced, and resting behavior occurred earlier with this peptide. There were no changes in the drinking behavior. For the first hour following enterostatin, eating represented 20.8% of the time, grooming 9.2%, activity 18.3%, and rest or sleep 47.2%, with drinking making up the other 4.4%. In contrast, saline-injected animals ate for 27.1% of the time, groomed for 12.4%, were active 28.5% of the time, had sleep or rest time equal to 27.9%, and drank for 4.1% of the time. In fasted animals, the onset of grooming, the decrease in activity, and the increase in time sleeping occurred earlier than with saline. These studies support the concept that enterostatin decreases food intake by producing early satiety.

The nutrient balance hypothesis: peptides, sympathetic activity, and food intake

Food intake can be increased or decreased after either central or peripheral administration of peptides. Galanin, neuropeptide Y, opioid peptides, growth hormone releasing hormone and desacetyl-MSH increase food intake whereas insulin, glucagon, cholecystokinin, anorectin, corticotropin releasing hormone, neurotensin, bombesin, enterostatin, cyclo-his-pro and thyrotropin-releasing hormone reduce food intake. A number of these peptides also affect the activity of the sympathetic nervous system. The peptides which have been tested have a reciprocal effect on food intake and sympathetic activity. Opioids, NPY and GHRH, which increase food intake, decrease sympathetic activity. Conversely, peptides which reduce food intake, increase sympathetic activity, with glucagon, cholecystokinin, corticotropin releasing hormone, calcitonin, neurotensin and bombesin being examples, Several of these peptides also affect the intake of specific nutrients. Insulin reduces food intake in animals fed a high carbohydrate diet, but not when fed a high fat diet. Neuropeptide Y increases carbohydrate intake. Galanin and opioid peptides increase fat intake. Enterostatin and cyclo-His-Pro, on the other hand reduce fat intake. Glucagon decreases protein intake. The effect of peptides on the intake of specific nutrients suggests that peptides may work in part by modulating basic feeding mechanisms to lead to the selection of specific nutrients from the diet. This hypothesis might be called a nutrient specific model of peptide-induced food intake.

Food intake, sympathetic activity, and adrenal steroids

Food Intake is reciprocally related to the activity of sympathetic nerves to brown adipose tissue. This reciprocal or feedback relation is shown for hypothalamic lesions, drugs, and many peptides. These peptides also modulate intake of specific nutrients. Galanin and opioids increase fat intake, whereas enterostatin decreases fat intake. NPY increases carbohydrate intake and growth hormone releasing hormone decreases protein intake. The activity of the sympathetic nervous system is low in obesity and adrenalectomy reverses this decrease in sympathetic activity and reverses or stops the progression of obesity. One mechanism for this effect of adrenal steroids is through a transacting substance which is involved in steroid actions and the production of obesity.

Effect of enterostatin given intravenously and intracerebroventricularly on high-fat feeding in rats

The effect of enterostatin, the amino-terminal pentapeptide of pancreatic procolipase, on high-fat food intake has been investigated after intracerebroventricular as well as after intravenous injection. After an overnight fast enterostatin given i.c.v. at doses of 167 pmol and 333 pmol produced a significant and dose-dependent reduction in high-fat food intake, while a higher dose of 667 pmol had no effect. Following intravenous injection of enterostatin the intake of high-fat food was suppressed at doses of 8.3 nmol and 16.7 nmol, while no effect was observed at higher doses. The inhibition of feeding started 3 h after the initiation of feeding and persisted to the end of the test period (6 h). Enterostatin at a dose of 16.7 nmol gave no sign of aversion in an aversion test comparing the effect of enterostatin, lithium chloride and saline on liquid intake. The data suggest that enterostatin may exert its satiety effect on high-fat feeding by being absorbed into the bloodstream.