Appetitive operant behavior and free-feeding in rats exposed to acute stress

This study investigated whether appetitive operant food reinforcement or free-feeding behavior in rats, food-restricted to 85% of body weight, was disrupted by exposures to 3 h of restraint stress or by 3 h of restraint plus water immersion stress (RWI). Rats were trained under a 3-cycle 10-min time-out-10-min time-in fixed-ratio 15 (FR15) schedule of food reinforcement. Free-feeding was measured in a 3-cycle 10-min food jar-out-10-min food jar-in test conducted in the operant chambers. Three hours of restraint stress did not significantly affect response rate or food reinforcement in the operant FR15 task or in the free-feeding condition. In contrast, 3 h of RWI completely abolished operant food reinforcement and suppressed response rate, whereas free-feeding was significantly reduced but not abolished in food-restricted, hungry rats. We conclude that acute restraint stress in food-restricted, hungry rats does not affect their appetite or motor ability to lever-press for food nor did it affect their ability to feed in a free-feeding situation. In contrast, RWI stress may have induced a motor impairment, or some other aspect of motivation independent of hunger, that disrupted their performance in the operant FR15 task.

Prevention of arterial thrombosis using a novel heparin with enhanced antiplatelet activity and reduced anticoagulant activity

PURPOSE

Thrombosis after arterial injury is often initiated by von Willebrand factor (vWF)-dependent platelet accumulation. A promising antithrombotic strategy is the interruption of platelet/vWF interactions. Previously, we demonstrated how chemical and affinity modification can enhance heparin's anti-vWF activity while reducing conventional anticoagulation. Here, we investigated whether a modified heparin can block platelet-dominated arterial thrombosis.

METHODS

Standard heparin was oxidized with periodate, refined to have high vWF affinity and inhibitory potency, and tested in a guinea pig model of platelet-dependent arterial thrombosis. In this model, a controlled mechanical arterial injury yields cyclic flow variations (CFVs) caused by recurrent accumulation of platelet thrombi.

RESULTS

All six control animals developed CFVs (mean, 10.4 +/- 2.6 CFVs), and six of seven animals treated with standard heparin also developed CFVs (mean, 7.6 +/- 4.6). Only one of six animals treated with the anti-vWF heparin and one of six treated with AJvW-2 (an anti-vWF antibody) developed CFVs (mean, 2.0 +/- 4.9 and 0.5 +/- 1.2, respectively). Thus both the modified heparin and AJvW-2 were more effective than standard heparin (p < 0.03). Bleeding times and platelet counts were unaffected. A modified activated partial thromboplastin time was less prolonged by the modified high-affinity heparin (91 +/- 17) seconds) than by standard heparin (144 +/- 30 seconds; p < 0.01).

CONCLUSIONS

The modified heparin with high vWF affinity was a more effective arterial antithrombotic agent, with fewer conventional anticoagulant effects than standard heparin. Interruption of the vWF/platelet interaction is a promising antithrombotic strategy that may be met by novel heparin-based antithrombotic drugs.

High molecular weight kininogen peptides inhibit the formation of kallikrein on endothelial cell surfaces and subsequent urokinase-dependent plasmin formation

A sequence of 31 amino acids (S565-K595) in domain 6 of the light chain of high molecular weight kininogen (HK) has previously been shown to be responsible for the binding of plasma prekallikrein (PK) or kallikrein. To find effective peptides that might block binding between HK and PK on cell surfaces, a new series of synthetic peptides has now been prepared that incorporates portions of this binding domain sequence. For mapping the minimal sequence within HK, these new peptides were tested for their ability to compete with HK for binding PK in a cell-free system and on human umbilical vein endothelial cells (HUVEC). In the former, at pH 7.4, the kds for binding between kallikrein and either D567-K595, S565-P594, D567-S593, or D567-T591 were all similar to that for the binding of S565-K595 (0.2 to 0.4 micromol/L), but those for the binding of D568-K595, W569-K595, and D567-P589 were an order of magnitude greater (kd = 2 to 5 micromol/L). D567-S586, the shortest chain length of the N- and C-terminal truncation sequences tested, does not effectively compete with kininogen for kallikrein binding (kd = 100 micromol/L). These results imply that D567-T591, a 25-residue peptide (HK25c), contains sufficient structural information for binding kallikrein in solution. D567-T591 also is the minimum structural sequence to block binding of kallikrein to HUVEC-bound HK (IC50 = 50 nmol/L) and to inhibit PK activation to kallikrein on the cell surface (IC50 = 80 nmol/ L). In addition, D567-T591 also inhibits the generation of kallikrein-activated urokinase, which activates plasminogen to plasmin (IC50 = 100 nmol/L). Thus, HK-derived peptides may be useful compounds for modulating excessive fibrinolysis and hypotension in sepsis and multiple trauma.

Voluntary wheel running decreases adipose tissue mass and expression of leptin mRNA in Osborne-Mendel rats

The purpose of this study was to assess the effects of voluntary wheel running on the expression of leptin mRNA in rats that are either sensitive (OM) or resistant (S5B/Pl) to diet-induced obesity. Male OM and S5B/Pl rats had ad libitum access to standard rodent diet and water. At 3-5 weeks of age, animals of both strains were randomly assigned to either an exercise or sedentary control group. The exercise groups had 24-h access to a running wheel, and they trained for 7 weeks. During weeks 1-4, animals in both OM and S5B/Pl exercise groups progressively increased their running. During weeks 5-7, S5B/Pl exercisers tended to run more than did OM (approximately 60 vs. 45 km/week), but by the end of the study both groups had an equally greater heart weight (mg/g body weight) and planteris citrate synthase activity than their sedentary controls. Oral glucose tolerance tests performed during the last week of training revealed that compared with their appropriate controls, insulin sensitivity was enhanced (P < 0.05) in OM but not in the S5B/Pl wheel-running groups. Inguinal, epididymal, and retroperitoneal fat pads weighed less in the running than in the nonrunning groups of both strains (P < 0.01). Additionally, exercised animals had an increased percentage of smaller cells (40-60 microm; P < 0.05) and a decreased percentage of larger cells (120-160 microm; P < 0.05) in the epididymal fat depot. Epididymal leptin mRNA measured by Northern blot analysis was reduced in the exercise-trained rats of both strains (P < 0.05). Furthermore, serum leptin was reduced in exercise-trained compared with the control animals of both strains. In comparison to S5B/Pl, control OM animals exhibited both a higher expression and higher circulating levels of leptin (P < 0.05). While serum leptin levels were decreased and food intake was increased in the exercise-trained animals of both strains (P < 0.05), the exact relationship between exercise, leptin, and food intake in this rat model of dietary obesity remains to be determined. Nonetheless, these results suggest that the expression and secretion of leptin can be influenced by exercise training and that these changes (i.e., reduced expression and secretion of protein) can occur independently of changes in whole-body insulin sensitivity and susceptibility to diet-induced obesity.

Physical and biological significance of peptide sequences mediating the interaction between high molecular weight kininogen and plasma prekallikrein

HK31 (S565-K595) has previously been shown to encompass the binding domain for plasma prekallikrein (PK) within domain 6 of high molecular weight kininogen (HK). The complementary binding domain for HK within PK is mapped to PK56 (F56-G86), in the Apple 1 domain and to PK266 (K266-C295) in the Apple 4 domain. Isothermal titration calorimetry demonstrated that either PK peptide binds to HK31 in 1:1 stoichiometry. Binding of the alternate PK peptide into a ternary complex is facilitated nearly 2-fold. Fluorescence emission spectroscopy revealed that only the binding of PK56 caused a limited decrease in intrinsic tryptophane fluorescence emission intensity of HK31. We conclude that the two PK peptides bind to the HK peptide at different sites. To map the minimal sequence within HK31, truncated new peptides were tested for their ability to compete with HK for binding PK in a cell-free system. D567-T591, a 25-residue peptide which contains sufficient structural information for binding kallikrein in solution, blocked the binding of kallikrein to HK bound to endothelial cells and inhibited PK activation to kallikrein and the generation of kallikrein-activated urokinase on endothelial cell surfaces. HK-derived peptides could modulate excessive fibrinolysis and hypotension in sepsis and multiple trauma.

Recombinant leptin exchanges between parabiosed mice but does not reach equilibrium

Parabiosis experiments suggest that ob/ob mice are deficient in a circulating "lipostatic" signal but respond to such a signal when it is delivered in the cross circulation from their parabiotic partner. Identification of leptin as the mutation in ob/ob mice leads to the assumption that leptin is the lipostatic signal. The objective of these experiments was to determine the circulating half-life of leptin and to demonstrate whether it exchanged between parabiosed mice. Measurement of disappearance of recombinant leptin from serum in SWRJ mice indicated a circulating half-life of approximately 36 min. Single ob/ob mice or one member of a parabiosed pair of ob/ob mice received 50 micrograms recombinant murine leptin in two intraperitoneal injections a day for 10 days, starting 40 days after parabiosis surgery. Control mice and pairs received equivalent injections of vehicle. In single mice, leptin significantly reduced food intake, body weight, serum insulin, and pancreatic and liver weight. Leptin treatment of one member of a parabiosed pair of ob/ob mice reduced serum insulin, gut content (an index of food intake), and body fat in both partners. The injected parabiont lost more fat than its partner, and body temperature was increased only in the injected mouse, indicating that leptin did not reach equilibrium in the two animals. This was confirmed by Western blot analysis of serum leptin measured 2 h after injection. Therefore, although leptin can exchange between parabionts, its half-life is inadequate to allow equilibrium when a large concentration gradient exists between partners.

Loss of body fat in lean parabiotic partners of ob/ob mice

The objective of this experiment was to confirm whether changes in serum leptin and leptin expression were consistent with it being the "lipostatic" factor implicated by earlier parabiosis studies. Lean (+/?) and obese (ob/ob) female C57B1/6J-ob mice were parabiosed (lean-ob/ob) at 7 wk of age. Controls were ob/ob-ob/ob and lean-lean pairs, and single lean and ob/ob mice. Pairs were maintained for 50 days. In ob/ob members of lean-ob/ob pairs serum insulin was normalized, food intake was suppressed, and body fat was reduced by 14%. Lean partners of ob/ob mice had a reduced rectal temperature and experienced a 37% reduction in body fat. Despite loss of fat, serum leptin and adipose leptin mRNA expression were unchanged in lean partners of ob/ob mice. These results suggest that, in lean-ob/ob parabiotic pairs, the ob/ob mouse responds to leptin originating in the lean parabiont, whereas the lean partner responds to a circulating signal, originating in the ob/ob mouse, that maintains leptin expression at inappropriate levels for the degree of adiposity of the lean animal.

Appropriate animal models for clinical studies

Results from experiments with animal models can provide useful information relevant to human diet studies. They may indicate approximate levels of supplementation required to see an effect on the end-point measure of interest. They also allow investigation of metabolic responses that require invasive tissue sampling inappropriate for human studies. Animal studies carry the advantages of cost-effectiveness, speed, and control of potential confounding variables. However, results from animal studies cannot be directly extrapolated to clinical trials due to the absence of potential nutrient interactions, environmental stimuli, and learned food preferences and aversions that are experienced by human subjects.

Structural aspects of heparin responsible for interactions with von Willebrand factor

Unfractionated heparin (UFH) binds von Willebrand factor (vWF) and inhibits the vWF-platelet GP Ib interaction. For vWF, a heparin-binding domain has been identified, but for heparin, the structures that confer such activity are unknown. To investigate this, UFH was depolymerized by methods that yield structurally distinct fragments. The glycosaminoglycans (GAGs) produced were separated into five groups of homogeneous molecular weight (MW). Anti-Xa activity, vWF binding affinity, and vWF-dependent platelet agglutination were measured. Periodate oxidation but not heparinase digestion destroyed anti-Xa activity. At all MWs, periodate conferred greater vWF binding affinity and greater ability to inhibit platelet agglutination than heparinase. As an example, at MW 6100, the binding IC50 was 100+/-19 micromol/L for a periodate-derived GAG and 527+/-70 micromol/L for a heparinase-derived GAG. At the same MW, the agglutination IC50 was 17+/-5 micromol/L for periodate and 135+/-18 micromol/L for heparinase. This suggests that the disaccharide GlcNS[6S]-IdoA2S, destroyed by heparinase but not periodate, is crucial to heparin-vWF interactions. An MW dependency was also noted, with a minimum dodecasaccharide required for activity inhibition. To further investigate the heparin/vWF interaction, affinity fractionation of heparins was performed with an immobilized peptide derived from a heparin-binding domain of vWF. Disaccharide analysis of high-affinity heparins revealed an increased ratio of IdoA2S-GlcN[S/Ac]6S to IdoA2S-GlcN[S/Ac]. Affinity fractionation of oligosaccharides (MW 3500) diminished the relative content of all disaccharides except IdoA2S-GlcNS6S, which was increased. These data suggest that the disaccharide structures IdoA2S-GlcNS6S and GlcNS6S-IdoA2S are crucial to heparin/vWF interactions. Understanding the structural aspects that confer such activity may be useful in designing heparin-based antithrombotic drugs.

Sleep deprivation by the "flower pot" technique and spatial reference memory

This study investigated whether paradoxical, or rapid eye movement (REM), sleep deprivation (SD) affected spatial memory. SD was induced in male Wistar rats by housing them on small platforms over water. They fell into the water if they lost muscle tone. Controls were either housed in tanks with large platforms (TC) or in normal cages (CC). All rats had free access to food and water. Each day they were tested in a place-learning set task using a Morris water maze. The rats were released from 6 different starting points (sets) and allowed 2 min to find a submerged platform. Two trials were conducted from each starting point. SD caused a significant decrement in performance in Trial 1 from Day 2. By Day 4, when distance swum to find the platform was plotted against set, area under the curve was doubled in SD compared to that in TC and CC rats, indicating a significant impairment in reference spatial memory. There was no consistent effect on working memory, indicated by Trial 2. SD caused weight loss and increased serum corticosterone compared to that in CC rats. There were no differences in concentrations of hypothalamic, hippocampal, or cortical catecholamines or their metabolites. Serotonin metabolism was elevated in the hypothalamus and hippocampus in SD rats. These results indicate that SD induced in rats housed on small platforms causes a substantial impairment of reference memory. The memory deficit may not be specific to SD because the rats are physically stressed and lose some nonREM sleep when housed in these conditions.

CRF receptor antagonist attenuates immobilization stress-induced norepinephrine release in the prefrontal cortex in rats

Neuroanatomical, neurophysiological, and behavioral studies suggest that brain stem nucleus locus coeruleus (LC) plays an important role in stress response. The present study was designed to clarify, whether infusion of CRF antagonist, alpha hCRF, into LC could attenuate or block stress-induced changes in norepinephrine (NE) concentrations in microdialysates collected from the medial prefrontal cortex (PFM). Rats were implanted with a bilateral cannulae assembly aimed in the LC and a microdialysis probe (4 mm active membrane length) into the LC. Immobilization of animals significantly increased the concentration of NE in microdialysates from PFM to a maximum of 170.8 +/- 12.8% of the baseline ten minutes after the onset of stressor. Concentration of NE in dialysates remained significantly elevated for the next 40 min. Infusion of alpha hCRF into the LC significantly attenuated stress-induced increase in PFM NE concentration in samples collected at 10, 20, 30, and 50 min after the onset of immobilization. Infusion of alpha hCRF alone (no immobilization) did not change concentrations at any time during sample collection. These results are consistent with other studies and suggest that stress can facilitate NE release in the PFM through the activation of the CRF system in the brain.

Ectopic production and processing of atrial natriuretic peptide in a small cell lung carcinoma cell line and tumor from a patient with hyponatremia

BACKGROUND

Tumors and tumor cell lines from two patients with small cell lung carcinoma (SCLC) (one with and one without hyponatremia) were studied. Ectopic production and prohormone processing of atrial natriuretic peptide (ANP) were investigated to determine if a biologically active peptide was produced in a tumor cell line from a patient with hyponatremia and no evidence of arginine vasopressin (AVP) production.

METHODS

Ribonuclease (RNase) protection assays were performed on mRNA isolated from tumors and tumor cell lines established from two SCLC patients, one with and one without hyponatremia. Cellular extracts and conditioned media were studied using reversed-phase high performance liquid chromatography (HPLC) to determine the immunoreactive form of ANP. Tumor cell line sonicates were studied for subcellular localization of enzymatic activity that cleaved pro-ANP peptide substrates.

RESULTS

RNase protection assays showed a 200-base pair protected fragment in the mRNA isolated from the tumor and tumor cell line from the patient with hyponatremia (Patient 4). HPLC characterization of the cellular extract and conditioned medium from the tumor and tumor cell line from Patient 4 demonstrated ANP immunoreactivity in the same fraction as ANP- (S99-Y126). The tumor cell line extract that localizes to a subcellular fraction enriched for lysosomes and secretory organelles contains a 60-kilodalton molecular weight protein with enzyme activity that hydrolyzes synthetic pro-ANP substrates and catalyzes the formation of ANP-(S99-Y126).

CONCLUSIONS

A tumor cell line from a patient with hyponatremia was able ectopically to produce, process, and secrete ANP in the same immunoreactive form as the biologically active molecule. Preliminary studies show that tumor cell line NCI-H1284 contains an enzyme that can cleave precursors at the same amino acid sequences needed to produce ANP-(S99-Y126) from pro-ANP.

Corticotropin-releasing factor receptor antagonist infused into the locus coeruleus attenuates immobilization stress-induced defensive withdrawal in rats

It has been proposed that corticotropin-releasing factor (CRF) released during stress in the region of the locus coeruleus (LC) induces changes in behavior that are typical indices of anxiety. The experiments tested the ability of a CRF antagonist, alpha hCRF9-41, to attenuate stress-induced defensive withdrawal in rats. 1 microgram of alpha hCRF in 300 nl was infused bilaterally in the LC of rats 10 min prior to 30 min immobilization. The apparatus consisted of a small chamber set on one side of a 1 m open field, into which the rat was placed to start the test. Restraint induced defensive withdrawal in rats familiar with the apparatus and significantly increased latency time to emerge from the chamber, total time and mean time spent in the chamber. Infusion of alpha hCRF into the LC prior to restraint significantly decreased total and mean time spent in the chamber comparing to stressed animals. These results are consistent with anatomical, electrophysiological and neurochemical evidence that CRF receptors located in, or close to, the LC region influence behaviors induced by stress.

Structure/activity studies of anti-inflammatory peptides based on a conserved peptide region of the lectin domain of E-, L- and P-selectin

Previously, it was established that the peptide YYWIGIRK-NH2 inhibits both myeloid cell adhesion to selectins in vitro and neutrophil influx into inflammatory sites in vivo (Briggs et al., 1995). Initial structure/activity studies revealed that at least one Y residue at the N-terminus of the peptide was essential for these bioactivities but that the C-terminal K residue was unnecessary for inhibitory activity. We have now synthesized a new series of peptides which contain single residue substitutions at each position of the reference peptide, YYWIGIR-NH2, and have tested these peptides for inhibitory activity in a selectin cell binding assay. In addition, peptides containing single D-amino acids at selected positions, or an all D-configured reference peptide sequence, or the retro-inverso version (rigiwyy-NH2) of the reference peptide sequence have also been analyzed for inhibitory activity in the same assays. Finally, the ability of the reference peptide and a specifically designed control sequence (YY(AIB)IGIR-NH2) to discriminate between potential synthetic saccharide ligands, including sialyl-Lewis x, Lewis x, and sialyl-N-acetyl-lactosamine, was investigated using isothermal titration calorimetry. The results of these studies demonstrate that whereas many single amino acid substitutions are tolerated in the peptide without complete loss of inhibitory activity, substitution at some positions (e.g., the W residue) results in relatively inactive compounds, clearly pointing to the importance of these residues in making critical contacts with the appropriate saccharide ligand. Titration calorimetry revealed that the reference peptide does not discriminate between Lewis x or sialyl-Lewis x in vitro, but binds these saccharides with nearly 40-fold higher affinity (KD 25 microM) than the nonfucosylated trisaccharide, sialyl-N-acetyl-lactosamine. We can infer from these studies that the presence of a sialyl group per se, is not a requisite for complex formation between the reference peptide and its saccharide ligand. Substitution of single D-amino acid residues at various positions in the reference peptide sequence reduces or eliminates all inhibitory properties. However, the all D-configured peptide or the retro-inverso peptide sequence have greater activity than the all L-configured reference peptide in the in vitro biological assays, and each was an effective inhibitor of neutrophil infiltration in a thioglycolate-induced mouse peritonitis model. These results, combined with the results of titration, allow us to conclude that binding between the reference peptide and its saccharide ligand, which affords its inhibitory properties, is mediated by the presence of a contiguous, nonpolar surface, or face, presented at the N-terminus of the reference peptide, likely encompassing the sequence YYWI. Furthermore, the W plays a critical role in binding, probably through formation of an essential hydrogen bond with a suitably juxtaposed group carried on the saccharide ligand.

The effect of preexisting long-term diabetes on the outcome after islet transplantation in rats

Studies of islet transplantation conducted immediately following diabetes induction may not accurately reflect the clinical situation. Long term preexisting diabetes with generalized microvasculature complication might adversely affect the outcome after islet transplantation. The present study testing this hypothesis by evaluating the effect of long-term preexisting diabetes on glucose-induced insulin secretion up to 6 months after transplantation of two different quantities of islets. One thousand two hundred or 2,400 islets were isotransplanted into the left renal subcapsular space at 10 days (acute diabetes), 3 months (chronic diabetes), or 6 months (long-term diabetes) after diabetes induction by streptozotocin in the rat. In addition, one group of diabetic rats in which normoglycemia was maintained with exogenous insulin treatment for 6 months was then transplanted with 1,200 islets. Intravenous glucose tolerance tests were performed at 10, 90, and 180 days after islet transplantation. Islet transplantation normalized the basal blood glucose levels within 24-48 h in all transplanted groups that remained normal for the entire study period of 6 months, with no differences among acute, chronic, or long-term diabetes. Basal plasma insulin levels were also normalized in all transplanted groups. Diabetic (acute, chronic, or long-term) rats transplanted with 2,400 islets achieved normal glucose-induced insulin secretion at 10 and 90 days after transplantation. In contrast, glucose-induced insulin secretion was impaired in rats transplanted with only 1,200 islets, with no differences among acute, chronic, and long term diabetes. However, at 180 days after transplantation, long term diabetic rats transplanted with 2,400 islets had impaired insulin secretion compared to normal controls. Insulin-treated long-term diabetic rats transplanted with 1,200 islets had normal glucose-induced insulin secretion at 10 days after transplantation. However, at 90 and 180 days after transplantation, insulin-treated long-term diabetic rats had impaired glucose-induced insulin secretion which was not different from nontreated transplanted long-term diabetic rats. It is concluded that long-term preexisting diabetes has no impact on the early outcome after islet transplantation. However, it may adversely affect the long-term function of the transplanted islets. Also, transplantation of a sufficient islet mass is the critical factor in achieving complete glucose homeostasis.

Physician advice and tobacco use: a survey of 1st-year college students

First-year college students were surveyed by telephone to determine their current level of tobacco use and find out what advice they had previously received from physicians regarding tobacco products. Current tobacco use reported in this 1st-year population was 19% in men and 17% in women. Although 99.6% of the students reported having had a medical visit within the last 5 years and 89% reported a visit within the past 12 months, only 26% remembered being asked at the last visit about their use of tobacco. Women were significantly more likely than men to have been asked about tobacco (31% compared with 21%), perhaps because of oral contraceptive counseling and the women's medical history. It appeared that healthcare providers are not fully using the opportunities available to them to educate young adults about using tobacco.

Structure-function relations of antithrombin III-heparin interactions as assessed by biophysical and biological assays and molecular modeling of peptide-pentasaccharide-docked complexes

The serine proteinase inhibitor antithrombin III (ATIII) is a key regulatory protein of intrinsic blood coagulation. ATIII attains its full biological activity only upon binding polysulfated glycosaminoglycans, such as heparin. Peptide K121-A134, based on the sequence of ATIII in the D helix region, was previously shown by us (Tyler-Cross et al., Protein Sci. 3, 620-627, 1994) to encompass part (or all) of the purported high-affinity heparin binding region of ATIII. A series of peptide analogs has now been prepared whose sequences are identical to K121-A134 except that single cationic residues of K121-A134 have been successively replaced with Ala. In one case, the Arg residue of the reference peptide corresponding to R129 of ATIII has been replaced by Gln (R129deltaQ peptide), thus mimicking the naturally occurring mutant protein, ATIII Geneva. The heparin affinity of all peptides was quantitated by isothermal titration calorimetry and by peptide/ATIII competition binding assays. Replacement of any single cationic residue with Ala had a deleterious effect on heparin binding. The greatest reduction in heparin affinity (more than 30-fold) was observed with the R129deltaQ peptide (KD = 1.5 +/- 0.06 microM vs 51 +/- 2 nM for the reference peptide, K121-A134). Furthermore, each of the Ala-replacement peptides was a less-effective inhibitor of ATIII-heparin complex formation than the reference peptide. The poorest inhibitor was the R129deltaQ peptide which showed nearly 30% decrease in inhibition potency (60% inhibition at 100 microM peptide vs 90% inhibition with the reference peptide). The relative heparin affinities of the peptides measured by biological assay were the same as determined by titration calorimetry. Consequently, we modeled the complexes formed between the pentasaccharide unit structure and the R129deltaQ peptide or the reference peptide, K121-A134. In the "docked" complex, the assumed conformation of K121-A134 permitted juxtaposition of the cationic residues of the peptide with functional anionic groups of the pentasaccharide known to be involved in binding. A docked complex could also be formed between the R129deltaQ peptide and the pentasaccharide, but misalignment of critical peptide and saccharide functional groups was observed. The structure of the R129deltaQ-pentasaccharide complex was highly irregular because F123 and Y131 were completely surface exposed, likely yielding an unfavorable structure in aqueous solution. The observations from molecular modeling allow us to suggest that ATIII Geneva displays decreased heparin binding affinity due to its inability to form a productive binding complex in which essential electrostatic contacts are made between suitably juxtaposed saccharide anionic functional groups and cationic amino acid side chains.

Direct evidence for multifacial contacts between high molecular weight kininogen and plasma prekallikrein

HK31 (S565-K595) has previously been shown to encompass the binding domain for plasma prekallikrein (PK) within domain 6 of high molecular weight kininogen (HK). The complementary binding domain for HK within PK is mapped to PK56 (F56-G86), in the apple 1 domain, and to PK266 (K266-C295), in the apple 4 domain. Isothermal titration calorimetry was used to directly monitor binding among HK31, PK56, and PK266. Either PK peptide binds to HK31 in 1:1 stoichiometry, regardless of whether a binary complex is first formed between PK266 and HK31 or between PK56 and HK31. Binding of the alternate PK peptide into a ternary complex is facilitated nearly 2-fold. The ternary complex consists of 1:1:1 HK31:PK56:PK266. Furthermore, binary and ternary complex formation is entropically driven and thermodynamically favored, suggesting that the conformational changes accompany binding. Fluorescence emission spectroscopy revealed that binding of PK56 caused a limited decrease in intrinsic tryptophan fluorescence emission intensity of HK31 while binding of PK266 to HK31 or the complex of HK31/PK56 had no such effect. We conclude that the two PK peptides bind to the HK peptide at different sites. The binding between HK and PK is likely due to conformational changes which serve to juxtapose the PK binding domain within HK with the HK binding site involving two spatial proximity segments.

Early and late stimulation of ob mRNA expression in meal-fed and overfed rats

ob protein is hypothesized to be a circulating feedback signal in the regulation of energy balance. Obese, overfed rats have high levels of ob mRNA expression and suppressed voluntary food intake, indicating the presence of a potent satiety factor. The objectives of this experiment were to determine whether feeding rats their normal daily intake in three meals, compared with ad libitum feeding, increased ob mRNA expression and to determine the degree of obesity required to stimulate expression of ob mRNA. Rats were fed ad libitum, were tube-fed their normal intake in three meals a day, or were tube-fed twice normal intake, ob mRNA was measured by Northern blot analysis after 0, 2, 7, 14, 21, and 32 d of tube-feeding. After only 2 d ob mRNA was threefold higher in tube-fed animals than in ad libitum controls. By day 21 there was a further increase in ob mRNA expression in overfed rats which were at 130% control weight. These results suggest that a metabolic consequence of meal-feeding increases ob mRNA expression in the absence of increased food intake or weight gain. There is a further increase in ob mRNA expression once significant obesity is established.

Heparins designed to specifically inhibit platelet interactions with von Willebrand factor

BACKGROUND

Platelet interactions with the injured vessel wall may contribute significantly to the early and late failures of many cardiovascular interventions; the adhesive protein von Willebrand factor (vWF) is thought to play an important role. Previously, we demonstrated that heparin interfered with platelet/vWF hemostatic mechanisms by binding to vWF within the proteins's domain responsible for binding the platelet vWF receptor, glycoprotein Ib. The purpose of the present study was to develop and refine heparins with greater potency to inhibit platelet/vWF interactions.

METHODS AND RESULTS

Immobilized synthetic peptides based on a known heparin-binding domain of vWF were used to yield novel fractions of standard heparin that demonstrated a sevenfold increase in their ability to inhibit vWF-dependent platelet agglutination and vWF/platelet binding. The high vWF affinity heparin showed enhanced anti-factor Xa activity but comparable activated partial thromboplastin time activity. Chemical modification of a standard heparin by periodate oxidation and borohydride reduction enhanced its ability to inhibit platelet/vWF interactions by threefold, while eliminating more than 90% of its activated partial thromboplastin time and anti-factor Xa activity. Affinity chromatography of the chemically modified heparin yielded a heparin with an eightfold higher inhibitory potency than the original heparin.

CONCLUSIONS

Subspecies of heparin can be developed with significantly enhanced potency to inhibit vWF/platelet interactions. The vWF-inhibiting property of heparin can be dissociated from its antithrombin-binding activity. Based on a growing understanding of heparin/vWF interactions, combinations of affinity separations and chemical modifications could be designed to yield heparins uniquely suitable for prevention of arterial thrombosis.

The role of neutrophils in peritoneal adhesion formation

The most common cause of intraperitoneal adhesions is previous abdominal surgery. Postoperative adhesion formation results from a fibroproliferative inflammatory reaction that begins with an influx of polymorphonuclear leukocytes (PMNs) into the peritoneal cavity. Adherence of the PMNs to the endothelial cells (EC) is necessary for PMN migration into the tissue in response to a stimulus. Several receptor-counterreceptor pairs of ligands such as CD11/CD18 on the PMN and ICAM-1 (CD54) on EC have been identified. Monoclonal antibody against CD11/CD18 (R15.7) inhibits PMN adherence and migration and consequently protects against PMN-induced tissue injuries. We therefore studied the effect of preventing PMN-EC adherence, using anti-CD18 monoclonal antibody, on postoperative adhesion formation in rabbits. Group 1 was a control receiving physiologic saline, and group 2 received anti-CD18 antibody (R15.7, 2 mg/kg). The treatment was administered iv at the end of surgery and repeated on the first and second postoperative days. Peritoneal adhesions were induced at laparotomy by repairing two peritoneal defects, by oversewing the defect (model 1), and by resuturing the removed parietal peritoneum in its place as an ischemic graft (model 2). Adhesions were evaluated blindly at 10 days after operation by measuring the percentage of the suture line covered with adhesions (model 1) or by a scoring system (model 2). All control animals developed intraperitoneal adhesions and the percentage of the suture line covered with adhesions was 25 +/- 5.9% (mean +/- SEM) and the mean score in model 2 was 0.9 +/- 0.2. Anti-CD18 antibody, R15.7, increased the degree of postoperative adhesion formation in both models, but the results were significant only in model 2. Also, anti-CD18 antibody significantly decreased peritoneal neutrophils from 11.1 x 10(7) +/- 1.8 x 10(7) to 2.2 x 10(7) +/- 0.4 x 10(7) (P < 0.001) on the first postoperative day. It is concluded that inhibition of PMN-EC adherence does influence the postoperative adhesion formation. These results might suggest that PMNs have a role in modulating postoperative adhesion formation.

Antibody characteristics for a continuous response fiber optic immunosensor for theophylline

A self-contained fiber optic immunosensor was developed to measure continuously theophylline concentrations. The analytical signal was derived from the non-radiative energy transfer quench of fluorescence following binding of a fluorescence donor, B-phycoerythrin labeled theophylline, to an energy acceptor, Texas Red labeled antibody. Increases in free theophylline analyte concentrations resulted in a shift in antibody binding equilibrium between labeled and unlabeled theophylline that elicited a proportional increase in the fluorescence. The selection criteria for a monoclonal antibody as a molecular recognition element, and the optimization of labeling conditions to maximize the dynamic range and minimize sensor response time are described. Under one or more Texas Red labeling conditions, five antibody clones exhibited significant quenching when mixed with labeled analyte and also demonstrated 95% or greater reversible binding to labeled analyte. Two clones failed to exhibit fluorescence quenching when mixed with labeled analyte. The response time of the indicator chemistry system was dependent on the dissociation rate constant of the antibody. The equilibrium response time of intact sensors was limited by analyte diffusion across the containment membrane.

N-terminal sequence analysis of atrial granule serine proteinase purified by affinity chromatography

Atrial granule serine proteinase is considered the leading candidate endoproteolytic processing enzyme of pro-atrial natriuretic factor. Its cleavage specificity is directed toward a monobasic amino acid processing site, and as such, the atrial enzyme is distinguished from the family of prohormone convertases which act at dibasic amino acid processing sites. To delineate the molecular mechanisms which distinguish monobasic from dibasic amino acid-directed processing enzymes, pure atrial enzyme is needed for sequence determination leading to molecular cloning, and for preparation of antisera. An affinity chromatography purification scheme seemed a logical modification of our established procedures to yield suitable amounts of enzyme for further studies [Damodaran and Harris (1995, J. Protein Chem., this issue] formed ineffective affinity ligands, even though these compounds contain essential residues on either side of what would be the scissile bond in a peptide substrate. On the other hand, tripeptide aldehydes (based on the substrate recognition sequence of the atrial enzyme) linked to Sepharose formed effective affinity matrices, permitting purification of the enzyme in a single step from a subcellular fraction enriched for atrial granules and lysosomes. Hence, the enzyme was purified 2000-fold in 90% overall yield, and subjected to N-terminal sequence analysis through 26 residues. The sequence determined, XXPEAAGLPG[R,L]GNPVP[F,G]R[Q,I]XY[G,E]XR(N,A]V, indicates that the atrial enzyme is unique, showing little sequence homology to other proteins in the database.

Preparations of psi-peptide bond and peptide-aldehyde inhibitors of atrial granule serine proteinase, a candidate processing enzyme of pro-atrial natriuretic factor

Pseudo-peptide bond inhibitors (psi-bond inhibitors) and peptide-aldehyde inhibitors of atrial granule serine proteinase, the candidate processing enzyme of pro-atrial natrieuretic factor, are prepared in high yield and purity by novel synthetic routes. The psi-bond compounds retain essential residues for enzyme binding, but place the enzyme inhibition site in the midst of the peptide sequence. Thus, Bz-APR-psi-LR and Bz-APR-psi-SLRR can be considered "readthrough inhibitors" of atrial granule serine proteinase. The most potent psi-peptide, Bz-APR-psi-SLRR (IC50=250 microM), is about fivefold less potent than the best peptide-aldehyde inhibitor (EACA-APR-CHO), and both the psi-bond and peptide-aldehyde compounds are competitive, reversible inhibitors of the enzyme. The psi-bond peptides containing two C-terminal Arg residues are three- to tenfold more potent than the analogous compounds containing only one C-terminal Arg residue, confirming the importance of both Arg residues in the enzyme processing recognition site. As expected, because of their moderate potencies, the psi-peptides are not useful affinity ligands for purification of atrial granule serine proteinase, but both peptide aldehydes are effective affinity ligands.