Determination of alpha-helix propensity within the context of a folded protein. Sites 44 and 131 in bacteriophage T4 lysozyme

To determine the effects of different amino acids on the structure and stability of an alpha-helix in the context of a globular protein, all 19 naturally-occurring amino acids were substituted for Ser44 in phage T4 lysozyme. A more restricted set of nine replacements was also made for Val131. Ser44 and Val131 are two of a very limited number of possible sites in T4 lysozyme that are well within alpha-helices, are solvent-exposed and relatively free of interactions with neighboring residues, and are not involved in crystal contacts. High resolution structures for the majority of the mutants, some of which crystallized non-isomorphously with wild-type, were determined. With the exception of proline, the amino acid substitutions caused little if any perturbation of the alpha-helix backbone. Also the beta-branched residues Thr, Val and Ile show no indication of either side-chain or backbone distortion. Therefore, other than proline, there is no evidence that differences in helix propensities are associated with different amounts of strain introduced into the helix. For reference, and also to allow estimates of side-chain entropy, a survey was made of side-chain conformations in 100 well-refined protein structures. As noted previously all side-chains within alpha-helices strongly avoid the g- conformation (chi 1 approximately 60 degrees). This restricts the beta-branched residues Thr, Val and Ile to a single conformer (g+, chi 1 approximately -60 degrees). Asp, Asn, Met and Ser within helices also overwhelmingly prefer the g+ conformation. For Arg, Cys, Gln, Glu, Leu and Lys the t (chi 1 approximately 180 degrees) and g+ conformers are populated roughly equally. Only the aromatic residues, His, Tyr, Trp and Phe prefer the t conformation. These preferences are the same whether the side-chain is buried or solvent-exposed. In general, the side-chain conformations adopted by the residues substituted at positions 44 and 131 correspond to the most commonly observed conformation for the same amino acid in helices in known protein structures. The changes in protein stability for the replacements at site 131 in general agree well with those at site 44 (correlation r = 0.97), suggesting that these may be representative of substitutions at fully solvent-exposed sites in the middle of alpha-helices. The free energy values also agree quite well with those observed for equivalent replacements in a number of soluble alpha-helical model peptides and with data from "host-guest" studies and statistical surveys (r = 0.69 to 0.93).(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanisms by which dichloroacetate lowers lactic acid levels: the kinetic interrelationships between lactate, pyruvate, alanine, and glucose

Dichloroacetate (DCA) is gaining use as an alternative to bicarbonate therapy in the treatment of lactic acidosis. To determine the mechanism(s) by which DCA lowers blood lactate levels, we studied its effect on the kinetic interrelationships between pyruvate, lactate, alanine, and glucose in the hindlimb of dogs during hormonal stimulation of pyruvate production (Ra) and its conversion to lactate. Three groups of dogs (n = 6) were infused with 1-13C-pyruvate to measure whole body pyruvate Ra, and pyruvate Ra and utilization (Rd) across the hindlimb during either a 4-hr infusion of saline (controls), or somatostatin, glucagon, and epinephrine (SGE), or SGE plus dichloroacetate (SGE + DCA). Pyruvate Ra was used as an index of rate of glycolysis and Rd as an index of pyruvate oxidation. In the controls, all kinetic parameters were constant during the saline infusion. Hindlimb pyruvate Ra and Rd were almost equal, and lactate release negligible. Compared to controls, SGE administration significantly increased (P < 0.05) wholebody pyruvate Ra (48.5 +/- 6.2 vs 33.6 +/- 2.4 mumol/kg/min) and blood lactate levels (P < 0.05). Hindlimb pyruvate Ra increased by approximately 150%, but Rd remained unchanged resulting in marked increases in lactate and alanine effluxes. Adding DCA to the SGE infusion significantly reduced wholebody pyruvate Ra (P < 0.05) and blood lactate levels (P < 0.01). In the hindlimb, however, there was no decrease in lactate output, despite a 91% increase in pyruvate utilization because pyruvate Ra also increased. These results suggest that during stimulation of rate of glycolysis, DCA lowers lactate levels by reducing the overall availability of pyruvate for lactate synthesis. This is accomplished by suppressing the rate of glycolysis in tissues other than skeletal muscle and stimulating pyruvate oxidation.

Guinea pig ileitis is attenuated by the leumedin N-(fluorenyl-9- methoxycarbonyl)-leucine (NPC 15199)

Anti-inflammatory properties have been ascribed to a series of N-(fluorenyl-9-methoxycarbonyl) amino acids called leumedins that inhibit the activity of granulocytes and T-lymphocytes. We evaluated one of these leumedins, N-(fluorenyl-9-methoxycarbonyl) leucine (NPC 15199), in a model of ileitis in guinea pigs. Ileitis was induced by intraluminal trinitrobenzenesulfonic acid (TNBS 30 mg/kg in 50% ethanol) in anesthetized guinea pigs. NPC 15199 was administered daily (10 or 100 mg/kg, s.c.). After 7 days, the guinea pigs were anesthetized, and saline was administered intraluminally into an ileal loop created at the site of TNBS administration and was withdrawn after 30 min. The changes in lavage protein, nitrite levels, myeloperoxidase (MPO) activity and mast cell numbers were used as indices of inflammation and injury. NPC 15199 (10 or 100 mg/kg) attenuated or abolished TNBS-induced elevations in lavage protein and nitrite content. Only the high dose of NPC 15199 (100 mg/kg) attenuated ileal MPO activity and mast cell hyperplasia. Histological disturbances induced by TNBS administration included crypt hypertrophy, mucosal and submucosal fibrosis and smooth-muscle hyperplasia. These disturbances were reversed by high-dose NPC 15199 (100 mg/kg) but were minimally affected by low-dose NPC 15199 (10 mg/kg). We conclude that NPC 15199 prevents mucosal injury and dysfunction in this model of intestinal inflammation. Inhibition of granulocyte infiltration does not appear to be essential for the beneficial effects of NPC 15199 and suggests that the alternative actions of NPC 15199 may be pertinent to this model.

Structural basis of amino acid alpha helix propensity

The propensity of an amino acid to form an alpha helix in a protein was determined by multiple amino substitutions at positions 44 and 131 in T4 lysozyme. These positions are solvent-exposed sites within the alpha helices that comprise, respectively, residues 39 to 50 and 126 to 134. Except for two acidic substitutions that may be involved in salt bridges, the changes in stability at the two sites agree well. The stability values also agree with those observed for corresponding amino acid substitutions in some model peptides. Thus, helix propensity values derived from model peptides can be applicable to proteins. Among the 20 naturally occurring amino acids, proline, glycine, and alanine each have a structurally unique feature that helps to explain their low or high helix propensities. For the remaining 17 amino acids, it appears that the side chain hydrophobic surface buried against the side of the helix contributes substantially to alpha helix propensity.

[Role of oxygen-derived free radicals in stress-induced gastric ulceration]

In the present work, the role of oxygen-derived free radicals in the pathogenesis of the gastric mucosal injury induced by cold-restraint stress was studied in rats. The results were as follows. (1) In rats pretreated with superoxide dismutase (SOD), a scavenger of superoxide anions, or with dimethyl sulfoxide and mannitol, scavengers of hydroxyl radicals, the gastric lesions induced by stress became much less extensive. (2) The mucosal content of malondialdehyde, a metabolic product of lipid peroxides, was significantly increased during stress. (3) Histochemical study revealed that the gastric mucosa abounded in xanthine oxidase (XO), the enzymic activity of which was increased during stress. In the rats pretreated with allopurinol, to inhibit XO activity, the extent of gastric mucosal lesions was decreased significantly. These suggested that oxygen free radicals might be one of the important factors in inducing gastric mucosal injury during stress and the increase of XO activity might be responsible for the production of the radicals.

Nitric oxide: the Jekyll and Hyde of gut inflammation

We studied the effects of seven day treatment with the nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine (L-NAME), administered in the drinking water (100 micrograms/ml ad lib) of female guinea pigs. The effects of NOS inhibition were evaluated in naive animals and in guinea pigs with ileitis induced by intraluminal trinitrobenzenesulfonic acid (TNBS). After 7 days, animals were anesthetized, a sterile saline lavage injected into an ileal loop and removed after 30 min for analysis. In naive guinea pigs, L-NAME caused a marked increase in ileal myeloperoxidase activity and conversion of the mucosa from an absorptive to a secretory state. TNBS-treated guinea pigs has a similar, marked increase in granulocyte infiltration and a mucosal secretory response. However, in contrast to naive animals, L-NAME treatment was anti-inflammatory, reverting all responses to the basal state. We conclude that intestinal nitric oxide serves an anti-inflammatory role under basal conditions, whereas in the TNBS model of chronic ileitis, nitric oxide is a critical mediator of gut injury.

Nitric oxide release in response to gut injury

We evaluated nitric oxide release in several models of intestinal inflammation through luminal nitrite concentrations. In anesthetized rabbits, piglets, and guinea pigs, luminal lavages were collected from loops of normal or injured small intestine. Lavages were analyzed spectrophotometrically for nitrite (Griess reagent) and protein. Myeloperoxidase (MPO) content of intestinal segments was used as an index of granulocyte infiltration and intestinal inflammation. Acute ileal inflammation was induced by luminal acetic acid + casein in rabbits and luminal deoxycholate in neonatal piglets and adult rabbits. Chronic ileitis was induced in guinea pigs by intraluminal trinitrobenzenesulfonic acid. In each model nitrite levels in ileal lavages were significantly greater than control loops/animals. Increased luminal protein and intestinal MPO activity paralleled the changes in nitrite levels. To determine whether nitric oxide production influenced mucosal repair, segments of ileum were perfused with the L-arginine antagonist NG-nitro-L-arginine methyl ester (L-NAME, 10 mg/ml) after acute acetic acid + casein exposure. L-NAME administration reversed the decline in epithelial permeability characteristic of epithelial restitution, causing an increase in epithelial permeability which was readily reversible. These results suggest that nitrite production is a useful index of gut injury and that nitric oxide may contribute to the functional repair of the epithelial barrier under acute conditions.

[An investigation on the freshwater crab as the host of Paragonimus in Hunan province]

Through an investigation of the freshwater crabs in 39 counties of Hunan province, 20 species of fresh water crabs were found as the intermediate hosts of Paragonimus. They belong to three genus and two families, in which 10 are new species (including 4 new subspecies). Besides, the natural infection with lung fluke metacercariae was also observed in some of the fresh water crabs.

Single-dose toxicokinetics of aluminum in the rat

The toxicokinetics of aluminum (Al) in male Wistar rats was studied after single intragastric (IG) doses of 1000 and 12,000 micrograms Al/kg and intravenous (IV) doses of 10, 100, 1000, and 12,000 micrograms Al/kg. Serial blood samples, daily samples of urine and feces as well as brain, liver, kidney, spleen, quadriceps muscle, and femur samples were collected. Al was measured by atomic absorption spectrometry. Al blood profiles after IV doses were adequately described by a two-compartment open model. Al toxicokinetics was dose dependent and appeared to plateau at 12,000 micrograms/kg. At IV doses between 10 and 1000 micrograms/kg the terminal half-life of elimination from whole blood (t1/2 beta) increased from 29.9 +/- 7.8 to 209.3 +/- 32.6 min, and the total body clearance (CL) decreased from 2.45 +/- 0.64 to 0.28 +/- 0.03 ml min-1 kg-1. Following an IV bolus of 10 and 100 micrograms/kg the administered Al was recovered completely from urine (94.4% +/- 9.9% and 98.5% +/- 3.2%). Twenty-nine days after the IV dose of 1000 micrograms/kg daily renal excretion decreased to baseline values while only 55.1% +/- 8.0% of the dose was excreted. Nineteen days after the single IV dose of 1000 micrograms/kg Al accumulated in liver (28.1 +/- 7.7 versus 1.7 +/- 0.5 micrograms/g of control rats) and spleen (72.5 +/- 21.1 versus < 0.4 microgram/g). After the single 1000 micrograms/kg IG dose no absorption of Al was detectable. The IG dose of 12,000 micrograms/kg resulted in a maximum blood Al level of 47.9 +/- 12.4 micrograms/l after 50 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Rabbit gut permeability in response to histamine chloramines and chemotactic peptide

Granulocyte-derived chlorinated amines and bacterial formyl peptides are thought to enhance epithelial permeability. In the current study, gut permeability to [51Cr]ethylenediaminetetraacetic acid (EDTA) was monitored in response to luminal formyl-methionyl-leucyl-phenylalanine (fMLP) and histamine monochloramine and dichloramine. Responses were determined in rabbits during states of basal and elevated permeability. Luminal fMLP had minimal effects of gut permeability in control and injured states. Histamine monochloramine or dichloramine enhanced epithelial permeability under basal conditions; this effect was exaggerated by a pre-existing injury. Both histamine monochloramine and dichloramine retained full histamine agonist properties, and a combination of antioxidant and antihistamine therapy was required to block this increase in gut permeability. Whereas histamine chloramines caused a dose-dependent cytotoxicity in rat-cultured enterocytes, marked histological changes to the mucosa were not evident, nor were mucosal glutathione levels depleted. As histamine chloramines retain the histaminergic and oxidizing potential of their precursors, they represent a unique form of inflammatory mediator, although their highly reactive nature precludes in vivo confirmation of their formation.

[Role of sulfhydryl compounds in the oxygen radical induced injury of isolated gastric mucosal cells]

Gastric mucosal cells were separated by pronase-EDTA method and cultured. The cellular injury was produced by oxygen radicals provided by xanthine oxidase(XO)-xanthine(X) system. When the cells were subjected to the action of XO-X system, the cellular viability was decreased and leakage of lactate dehydrogenase (LDH) from the cells was significantly increased. In addition, the cellular contents of nonprotein sulfhydryls (NPSH) and protein sulfhydryls (PSH) were decreased. When the intracellular sulfhydryl content was decreased by N-ethylmaleimide (NEM, a depletor of endogenous sulfhydryls), the cell mortality and LDH leakage were increased in a time-dependent and dose-dependent manner. If glutathione or cysteamine (compounds containing-SH) was administered into the media, the cellular injury induced by XO-X system was notably inhibited, also in a dose-dependent manner. The above results suggest that sulfhydryls may play an important role in the cell defending mechanism against injury of gastric mucosal cells by oxygen radicals.

Harry M. Vars Research Award. A new model to determine in vivo the relationship between amino acid transmembrane transport and protein kinetics in muscle

The bidirectional transmembrane transport rates of leucine (Leu), valine (Val), phenylalanine (Phe), lysine (Lys), and alanine (Ala) were measured in vivo in the hindlimb muscle of five dogs and related to the rates of protein synthesis and degradation. The compartmental model was based on the systemic continuous infusion of stable isotopic tracers of the amino acids, and the measurement of the enrichment and concentration in the arterial and femoral vein plasma and the intracellular free water in muscle (obtained by biopsy). The transport rate from plasma to tissue (in micromoles per minute) was: Leu, 18.1 +/- 1.8; Val, 26.9 +/- 3.5; Phe, 10.5 +/- 1.6 Lys; 12.2 +/- 1.8; and Ala, 10.7 +/- 3.4. The transport rate from tissue to plasma (in micromoles per minute) was: Leu, 25.5 +/- 2.5; Val, 32.4 +/- 2.8; Phe, 17.0 +/- 2.8; Lys, 24.9 +/- 3.4; Ala, 34.4 +/- 9.0. When the transmembrane transport rate was normalized per unit of amino acid concentration in the source pool, we found that the transport of Leu, Val, and Phe was significantly faster (p less than .05) than the transport of Lys and Ala. The calculated rates of incorporation into hindlimb muscle protein of Phe and Lys (in micromoles per minute) were 4.2 +/- 1.3 and 19.4 +/- 5.3, respectively, and the rates of intracellular appearance from breakdown were 10.7 +/- 1.9 and 32.1 +/- 6.6, respectively. We concluded, therefore, that (1) the transmembrane amino acid transport rate can be measured in vivo in muscle with a relatively noninvasive technique, (2) in the dog hindlimb the equilibration between tissue and plasma free amino acid pool is different for each amino acid depending on the kinetics of the transmembrane transport systems, and (3) the transport rates of amino acids and their rate of appearance from protein breakdown are roughly comparable, suggesting that variations in transport rates could play a role in controlling the rate of protein synthesis.

Multiple alanine replacements within alpha-helix 126-134 of T4 lysozyme have independent, additive effects on both structure and stability

In a systematic attempt to identify residues important in the folding and stability of T4 lysozyme, five amino acids within alpha-helix 126-134 were substituted by alanine, either singly or in selected combinations. Together with three alanines already present in the wild-type structure this provided a set of mutant proteins with up to eight alanines in sequence. All the variants behaved normally, suggesting that the majority of residues in the alpha-helix are nonessential for the folding of T4 lysozyme. Of the five individual alanine substitutions it is inferred that four result in slightly increased protein stability and one, the replacement of a buried leucine with alanine, substantially decreased stability. The results support the idea that alanine is a residue of high helix propensity. The change in protein stability observed for each of the multiple mutants is approximately equal to the sum of the energies associated with each of the constituent substitutions. All of the variants could be crystallized isomorphously with wild-type lysozyme, and, with one trivial exception, their structures were determined at high resolution. Substitution of the largely solvent-exposed residues Asp 127, Glu 128, and Val 131 with alanine caused essentially no change in structure except at the immediate site of replacement. Substitutions of the partially buried Asn 132 and the buried Leu 133 with alanine were associated with modest (< or = 0.4 A) structural adjustments. The structural changes seen in the multiple mutants were essentially a combination of those seen in the constituent single replacements. The different replacements therefore act essentially independently not only so far as changes in energy are concerned but also in their effect on structure. The destabilizing replacement Leu 133-->Ala made alpha-helix 126-134 somewhat less regular. Incorporation of additional alanine replacements tended to make the helix more uniform. For the penta-alanine variant a distinct change occurred in a crystal-packing contact, and the "hinge-bending angle" between the amino- and carboxy-terminal domains changed by 3.6 degrees. This tends to confirm that such hinge-bending in T4 lysozyme is a low-energy conformational change.

Comparison of constant infusion and flooding dose techniques to measure muscle protein synthesis rate in dogs

The exact relationship between the constant infusion and flooding dose techniques for measuring fractional muscle protein synthesis (FMPS) rates was determined in anesthetized dogs during the postabsorptive period, using different isotopes of leucine as tracers. First, [1,2-13C]- and [U-14C]leucine were given simultaneously by prime-constant infusion for 5 h to establish that both isotopes gave comparable FMPS rate values. The tracers gave almost identical FMPS rates and the values obtained after 3 and 5 h were not different. Next, the constant infusion and flooding dose methods were compared in the same animal by first measuring FMPS rate with a prime-constant infusion of [U-14C]leucine, then with a flooding dose of 376 mumol/kg [1,2-13C]leucine. The flooding dose method gave FMPS rates that were markedly greater than the constant infusion values. Finally, the effect of a 376 mumol/kg leucine flooding dose on FMPS rate was assessed using the prime-constant infusion of [U-14C]lysine. The large dose of leucine decreased FMPS rate by approximately 50% because acid-soluble muscle lysine (precursor) specific activity increased while the rate of incorporation of labeled lysine into protein decreased. These results indicate that the flooding dose method gives FMPS rates that are markedly greater than those obtained with the constant infusion method and that the latter method is not valid when a large dose of leucine is given.

Response of a protein structure to cavity-creating mutations and its relation to the hydrophobic effect

Six "cavity-creating" mutants, Leu46----Ala (L46A), L99A, L118A, L121A, L133A, and Phe153----Ala (F153A), were constructed within the hydrophobic core of phage T4 lysozyme. The substitutions decreased the stability of the protein at pH 3.0 by different amounts, ranging from 2.7 kilocalories per mole (kcal mol-1) for L46A and L121A to 5.0 kcal mol-1 for L99A. The double mutant L99A/F153A was also constructed and decreased in stability by 8.3 kcal mol-1. The x-ray structures of all of the variants were determined at high resolution. In every case, removal of the wild-type side chain allowed some of the surrounding atoms to move toward the vacated space but a cavity always remained, which ranged in volume from 24 cubic angstroms (A3) for L46A to 150 A3 for L99A. No solvent molecules were observed in any of these cavities. The destabilization of the mutant Leu----Ala proteins relative to wild type can be approximated by a constant term (approximately 2.0 kcal mol-1) plus a term that increases in proportion to the size of the cavity. The constant term is approximately equal to the transfer free energy of leucine relative to alanine as determined from partitioning between aqueous and organic solvents. The energy term that increases with the size of the cavity can be expressed either in terms of the cavity volume (24 to 33 cal mol-1 A-3) or in terms of the cavity surface area (20 cal mol-1 A-2). The results suggest how to reconcile a number of conflicting reports concerning the strength of the hydrophobic effect in proteins.

[Study on significance of lymphocyte chemiluminescence measurements in cancer patients]

Chemiluminescent responses of peripheral blood lymphocytes were measured in patients with carcinomas and healthy donors. The intensity of lymphocyte chemiluminescence (Ly-CL) in 54 preoperative patients was significantly lower than that in 97 healthy donors (P less than 0.05). Compared to that before treatment, the Ly-CL intensity in 14 patients after radiotherapy was decreased (P less than 0.05). However, Ly-CL intensity in 12 patients after 6-8 days of thymosin therapy was significantly increased (P less than 0.05), and exceeded that of healthy donors (P less than 0.01). These data suggest that Ly-CL measurements may become a new method for monitoring lymphocyte activity or function, and evaluating therapeutic effectiveness in cancer patients.

Dissection of protein structure and folding by directed mutagenesis

The lysozyme from bacteriophage T4 is being used as a model system to determine the roles of individual amino acids in the folding and stability of a typical globular protein. One general finding is that the protein is very adaptable, being able to accommodate many potentially destabilizing replacements. In order to determine the importance of 'alpha-helix propensity' in protein stability, different replacements have been made within alpha-helical segments of T4 lysozyme. Several such substitutions of the form Xaa-->Ala increase the stability of the protein, supporting the idea that alanine is a strongly helix-favouring amino acid. It is possible to engineer a protein that has up to ten alanines in succession, yet still folds and has normal activity. This illustrates the redundancy that is present in the amino acid sequence. A number of 'cavity-creating' mutants of the form Leu-->Ala have been constructed to understand better the nature of hydrophobic stabilization. The structural consequences of these mutations differ from site to site. In some cases the protein structure hardly changes at all; in other cases removal of the wild-type side-chain allows surrounding atoms to move in and occupy the vacated space, although a cavity always remains. The destabilization of the protein associated with these cavity-creating mutations also varies from case to case. The results suggest how to reconcile recent conflicting reports concerning the strength of the hydrophobic effect in proteins.

Histamine is a transient marker of small intestinal injury induced by luminal acetic acid and casein

We compared the time course of histamine release with other markers of intestinal injury in a rabbit model of necrotizing enterocolitis. Injury was induced by luminal acetic acid (200 mM) and casein (10 mg/ml) and experiments terminated after 45 min or 3 hr. Compared to saline controls there was a significant elevation of epithelial permeability (51Cr-EDTA clearance) and luminal protein levels at both time points. Luminal fluid histamine levels were approximately 120-fold greater than saline controls at 45 min but were indistinguishable from control values at 3 hr. We conclude that although mast cell activation is a characteristic of this model, elevations in histamine levels are transient.

Misoprostol attenuates acetic acid-induced damage in rabbit distal small intestine

The influence of misoprostol pretreatment (100 micrograms/loop intraluminally) on small intestinal damage induced by acetic acid was evaluated in anesthetized rabbits. In this model injury was induced by intraluminal administration into loops of distal small intestine, of a solution of calcium gluconate (50 mg/ml) and acetic (200 mM). After 3 hr damage was associated with increase in loop fluid volume, loop fluid protein levels and epithelial permeability to 51Cr-EDTA, all of which were attenuated by misoprostol pretreatment. Similar protective effects were noted 45 min after the insult, suggesting that misoprostol may be therapeutically useful in conditions where the epithelial barrier is compromised.

Potential role of histamine monochloramine in a rabbit model of ileitis

Histamine chloramines, derived from the chlorination of histamine by granulocyte-derived oxidants, are potential mediators of intestinal injury and dysfunction in states of atopy or inflammation. We assessed the ability of histamine monochloramine to increase epithelial permeability in rabbit distal small intestine and determined whether the conditions for histamine chloramine formation are favorable in a rabbit model of ileitis. Epithelial permeability, quantified by the blood-to-lumen clearance of 51Cr-labeled ethylenediaminetetraacetic acid, was enhanced by luminal perfusion with either histamine or histamine monochloramine (10 microM), although the latter was twice as effective (p less than 0.05). In a rabbit model of ileitis induced by a luminal solution of acetic acid (200 mM) and casein (10 mg/ml) there was a marked increase in epithelial permeability and in the release into the lumen of histamine, myeloperoxidase, 6-keto-prostaglandin F1 alpha and protein. These results suggest that the conditions are favorable for histamine chloramine formation and that histamine and histamine chloramine may impair the integrity of the epithelial barrier.

Acute intestinal injury induced by acetic acid and casein: prevention by intraluminal misoprostol

Acute injury was established in anesthetized rabbits by intraluminal administration of acetic acid with and without bovine casein, into loops of distal small intestine. Damage was quantified after 45 minutes by the blood-to-lumen movement of 51Cr-labeled ethylenediaminetetraacetic acid (EDTA) and fluorescein isothiocyanate-tagged bovine serum albumin as well as luminal fluid histamine levels. The amount of titratable acetic acid used to lower the pH of the treatment solutions to pH 4.0 was increased by the addition of calcium gluconate. Luminal acetic acid caused a 19-fold increase in 51Cr-EDTA accumulation over saline controls; casein did not modify this effect. In saline controls, loop fluid histamine levels bordered on the limits of detection (1 ng/g) but were elevated 19-fold by acetic acid exposure and markedly increased (118-fold) by the combination of acid and casein. Intraluminal misoprostol (3 or 30 micrograms/mL), administered 30 minutes before acetic acid, significantly attenuated the increase in epithelial permeability (luminal 51Cr-EDTA, fluorescein isothiocyanate-bovine serum albumin accumulation) and histamine release (P less than 0.05). Diphenhydramine, alone or in combination with cimetidine, and indomethacin (5 mg/kg IV) were not protective. It is concluded that exposure of the epithelium to acetic acid promotes the transepithelial movement of casein leading to enhanced mast cell activation and mucosal injury. Damage to the epithelial barrier can be prevented by misoprostol.

Role of basal insulin in the regulation of protein kinetics and energy metabolism in septic patients

We have investigated the role of basal insulin concentration on leucine kinetics (determined by means of 1-[13C]leucine) and energy metabolism (determined by indirect calorimetry) in eight septic patients by reducing insulin (and glucagon) secretion by somatostatin infusion. Basal glucagon concentration was elevated (744 +/- 381 pg/mL), and insulin concentration was normal (10 +/- 4 microU/mL). Basal resting energy expenditure (REE) was 151 +/- 8% that of predicted basal energy expenditure, and leucine appearance (Ra), oxidation, and nonoxidative disposal rates were all elevated above the normal ranges. Somatostatin infusion reduced insulin concentration by 52% and glucagon concentration by 64%. This resulted in a significant increase in the rate of leucine oxidation from 0.96 +/- 0.08 to 1.18 +/- 0.14 mumol/kg/min (p less than 0.01), and nonoxidative leucine disposal decreased from 2.95 +/- 0.18 to 2.67 +/- 0.17 mumol/kg/min (p less than 0.01). Somatostatin infusion also caused significant increases in REE and fat oxidation from 1310 +/- 100 to 1505 +/- 128 kcal/m2/day (p less than 0.05) and from 1.72 +/- 0.24 to 2.41 +/- 0.41 mg/kg/min, respectively, and a slight decrease of carbohydrate oxidation from 1.51 +/- 0.49 to 1.31 +/- 0.49 mg/kg/min. These metabolic responses can be attributed to the reduction in insulin concentration, because they are in the opposite direction of changes that would occur as a consequence of a reduction in glucagon concentration. We conclude that the basal insulin plays an important role in attenuating net protein loss and energy expenditure.

Exaggerated intestinal histamine release by casein and casein hydrolysate but not whey hydrolysate

Loops of rabbit distal small intestine received luminal acetic acid (pH 4.0) alone or in combination with bovine casein, casein hydrolysate, or whey hydrolysate. Blood-to-lumen movement of 51Cr-labeled ethylenediaminetetraacetic acid (EDTA) (an index of epithelial permeability) and loop fluid histamine levels were quantified after 45 min. Luminal acetic acid caused a marked increase in 51Cr-EDTA accumulation which was not modified by the addition of bovine casein or hydrolysates by of casein or whey. However, acetic acid-induced histamine release was potentiated by casein and casein hydrolysate (six- and four-fold respectively) but was not altered by whey hydrolysate. Casein hydrolysate-dependent histamine release was evident in naloxone-pretreated rabbits, suggesting that beta-casomorphins were not solely responsible. We conclude that luminal casein or casein hydrolysate, but not whey hydrolysate. can activate intestinal mast cells under conditions of enhanced epithelial permeability. This effect appears to involve components other than beta-casomorphins.

[An electron microscopic study on the structural alteration of the coronary artery of rats induced by vitamin D3]

Ultrastructural alteration of the coronary artery of the rat induced by a single oral administration of varying doses of vitamin D3 was examined by electron microscopy. Three groups of rats were orally administered 175,000 IU, 350,000 IU and 700,000 IU of vitamin D3/kg body wt. in 1 ml of olive oil, respectively. Another group of rats received 1 ml of olive oil alone as controls. In either group of rats receiving vitamin D3, a significant elevation of serum calcium level was observed at 12, 24 and 48 hours as a maximum level after a single oral administration of vitamin D3, as compared with that of the control group. Ultrastructural changes were first observed mainly in the medial smooth muscle cells of the coronary artery at 24 hours after administration of 700,000 IU of vitamin D3. These were characterized by dissociation of myofilaments, focal necrosis of the cytoplasm and karyolysis. At 48 hours after administration, the coronary arteries of the rats receiving 350,000 IU and 700,000 IU of vitamin D3 showed ultrastructural alteration of medial smooth muscle cells. In the latter group of rats, irregular precipitations of fine, needle-like materials with high electron density were observed in the areas of medial degeneration, and were proved to be calcium salts by X-ray microanalysis. At 72 hours after administration of vitamin D3, such medial structural changes as above were enhanced in the rats receiving both 350,000 IU and 700,000 IU of vitamin D3, but not 175,000 IU. The present study demonstrated that ultrastructural changes of the coronary artery induced by vitamin D3 were, in onset and degree, closely dependent upon the dose of this agent and suggests that the arteriosclerosis induced by vitamin D3 is not initiated by hypercalcemia produced by this agent, but with its direct toxic action to the medial smooth muscle cells.

Toward a simplification of the protein folding problem: a stabilizing polyalanine alpha-helix engineered in T4 lysozyme

In an attempt to simplify the protein folding problem, and also to further investigate the role of alanine as a helix-stabilizing residue, a series of alanines was introduced within the alpha-helix that includes residues 126-134 of T4 lysozyme. In wild-type lysozyme this alpha-helix contains alanine residues at positions 129, 130, and 134. Mutant lysozymes with alanines substituted at positions 128, 131, 132, and 133, either as single substitutions or in selected combinations, were constructed by oligonucleotide-directed mutagenesis. With the exception of the replacement of Leu 133, which is buried within the hydrophobic core of the protein, all the variants were more stable than wild-type lysozyme. The variant with alanines substituted at positions 128, 131, and 132 (E128A/V131A/N132A), which incorporates the sequence Ala 128-Ala 129-Ala 130-Ala 131-Ala 132-Leu 133-Ala 134, has a melting temperature 3.3 degrees C above that of wild-type lysozyme. Determination of the crystal structure of this mutant lysozyme shows that the replacement of Glu 128, Val 131, and Asn 132 with alanine causes alpha-helix 126-134 to rotate 3.4 degrees about an axis parallel to its own axis. This rotation seems to be triggered primarily by the loss of a hydrogen bond between Asn 132 and Ser 117 and is associated with the repacking of several side chains at the interface between alpha-helix 126-134 and the adjacent alpha-helix 115-122.(ABSTRACT TRUNCATED AT 250 WORDS)

[The relationship between protection of regenerating rat liver against carbon tetrachloride and change of its mitochondrial respiratory activity]

Protection of regenerating rat liver against carbon tetrachloride (CCl4) poisoning 96 h after partial hepatectomy was observed, and the respiratory activity of its mitochondria was determined by using oxygen electrode method. The results were as follows: (1) Mortality in partial hepatectomized rats (PHR) caused by CCl4 (50%, 10 ml/kg) was reduced significantly as compared with sham operated rats. (2) Following hepatic damage induced by CCl4 (50%, 5 ml/kg), the levels of serum bilirubin and sGPT in PHR were significantly lower than those in sham operated rats. Histological examination of the liver also showed a significant extent of repair. (3) Respiratory activity of regenerating liver mitochondria in PHR with or without CCl4 poisoning was higher than that in sham operated rats, and the respiratory activity went parallel with the degree of repair of histological damage, the reduction of serum bilirubin, sGPT and mortality. The results mentioned above indicate that increase of respiratory activity of regenerating liver mitochondria and resistance to CCl4 may play an important role in the protection of regenerating liver against CCl4.

Comparison of the crystal structure of bacteriophage T4 lysozyme at low, medium, and high ionic strengths

Crystals of bacteriophage T4 lysozyme used for structural studies are routinely grown from concentrated phosphate solutions. It has been found that crystals in the same space group can also be grown from solutions containing 0.05 M imidazole chloride, 0.4 M sodium choride, and 30% polyethylene glycol 3500. These crystals, in addition, can also be equilibrated with a similar mother liquor in which the sodium chloride concentration is reduced to 0.025 M. The availability of these three crystal variants has permitted the structure of T4 lysozyme to be compared at low, medium, and high ionic strength. At the same time the X-ray structure of phage T4 lysozyme crystallized from phosphate solutions has been further refined against a new and improved X-ray diffraction data set. The structures of T4 lysozyme in the crystals grown with polyethylene glycol as a precipitant, regardless of the sodium chloride concentration, were very similar to the structure in crystals grown from concentrated phosphate solutions. The main differences are related to the formation of mixed disulfides between cysteine residues 54 and 97 and 2-mercaptoethanol, rather than to the differences in the salt concentration in the crystal mother liquor. Formation of the mixed disulfide at residue 54 resulted in the displacement of Arg-52 and the disruption of the salt bridge between this residue and Glu-62. Other than this change, no obvious alterations in existing salt bridges in T4 lysozyme were observed. Neither did the reduction in the ionic strength of the mother liquor result in the formation of new salt bridge interactions. These results are consistent with the ideas that a crystal structure determined at high salt concentrations is a good representation of the structure at lower ionic strengths, and that models of electrostatic interactions in proteins that are based on crystal structures determined at high salt concentrations are likely to be relevant at physiological ionic strengths.

[Involvement of sulfhydryls in the protective mechanism of gastric mucosa]

The present work have studied the role of nonproteinsulfhydryl (NPSH) in the protective mechanism of gastric mucosa. During the development of gastric injury induced by acidified ethanol (AE) gavage or restraint-cold stress (RCS), NPSH content in gastric mucosa markedly decreased. Pretreatment with cysteamine (cys) or reductive glutathione (GSH) could prevent gastric mucosa from injury induced by AE. The activity of glutathione reductase in gastric mucosa was inhibited consistently in the time course with NPSH decrease after AE gavage or RCS. Malondialdehyde (MDA) level in the mucosa increased after AE gavage and dimethyl suloxide, a free radical scavenger, could reduce AE induced injury. The above results suggest that NPSH in gastric mucosa might be involved in the local protective mechanism through its free radical scavenging activity, and the decrease of NPSH in gastric mucosa resulted by the inhibition of glutathione reductase activity and the increase of free radical production may be an important step in the development of injury.

Hemodynamic and permeability characteristics of acute experimental necrotizing enterocolitis

We examined the local hemodynamic response of intestinal loops during acute necrotizing enterocolitis (NEC) in anesthetized rabbits. NEC was induced in ileal loops by transmural injection of a solution containing casein (10 mg/ml) and calcium gluconate (50 mg/ml) acidified to pH 4.0 with propionic or acetic acid. Control loops received casein only (pH 5.0). Mucosal damage was quantified by the blood-to-lumen movement of [51Cr]EDTA, fluid shifts into the lumen, and histology. Mean arterial pressure and loop blood flow were steady over the 3-hr period, loop fluid volume decreased, and there was no evidence of necrosis or epithelial damage. In loops receiving acidified casein and calcium gluconate, there was an immediate dramatic increase in loop blood flow that returned to baseline by 50 min. In addition, loop fluid volume was dramatically increased, necrosis was noted in the form of blunting and loss of villi, and sevenfold increase in [51Cr]EDTA permeability was evident. Administration of CV 1808 (30 mg/kg/hr), a selective adenosine2 agonist, which maintained and elevated loop blood flow throughout the 3 hr protocol, failed to alter the changes in loop fluid volume or prevent necrosis. Histamine levels in loop fluid levels were significantly elevated 20-30 min after NEC induction when compared to saline controls, indicating an early activation of mucosal defenses with this luminal insult. Thus, this model of NEC is characterized by a transient, acute hyperemia, increased intestinal permeability, and histamine release. As mucosal damage was independent of ischemia and could not be prevented by vasodilatory therapy, this model supports the clinical findings that NEC is correlated with luminal factors related to feeding and independent of cardiovascular stress.

[Effects of indomethacin on 45Ca uptake and membrane fluidity of mitochondria and microsomes from rat liver]

We have reported previously that indomethacin-pretreatment could induce marked hepatic protection in rats. The present work reported effects of indomethacin on calcium regulation and membrane fluidity of mitochondria and microsomes of hepatocytes. The results showed that calcium uptake and membrane fluidity increased significantly in mitochondria and microsomes of hepatocytes isolated from the rats pretreated with indomethacin in vivo as compared with that from the control; adding indomethacin directly to isolated mitochondria and microsomes from normal rats in vitro, on the contrary, decreased membrane fluidity. These changes may be related to the protective effect of indomethacin.

[Observing cytoprotection of indomethacin on primary cultured hepatocytes of rats]

We observed previously that indomethacin induced hepatic protection against CCl4 and galactosamine in rats. In this work we further investigated this phenomenon on primary cultured rat hepatocytes. The results showed that cultured hepatocytes of rats pretreated with indomethacin in vivo still retained the ability resisting CCl4-induced cytotoxicity, as indicated by lower leakage of enzymes. However, cultured hepatocytes of normal rats treated with indomethacin in vitro had no obvious resistance to CCl4-induced cytotoxicity. The results suggest that indomethacin pretreatment in vivo enables hepatocytes to resist injury, which probably also needs participation of other factors.

[Studies on the mechanism of acute gastric ulceration induced by high spinal cord transection]

Spinal cord of the rat was transected at C7 level to produce acute gastric ulcer. It was observed as follows: (1) The body temperature (B.T.) of the cord transected animals fell in a good agreement with ambient temperature. It appears that the fall in B.T. is one of the main causes inducing ulceration. (2) Administration of epinephrine decreased ulceration and prevented the fall in B.T. both in a dose-dependent manner. (3) Cord transection induced ulcer formation was markedly attenuated by adrenalectomy and exacerbated again by displacement with dexamethasone, but the fall in B.T. was unaffected at all in either case. (4) The variations in acid secretory and endocrine function of gastric mucosa after transection might be involved in ulcer formation.

[The role of sulfhydryls in indomethacin-induced gastric mucosal injury in rats]

The possible role of sulfhydryls in indomethacin-induced gastric mucosal injury was studied. No significant decrease of the contents of both non-protein and protein-binding sulfhydryls was observed in the gastric mucosa during injury. Indomethacin-induced gastric ulcer was inhibited by cysteamine of 132 and 264 mumol, i.g. or of 132 mumol, s.c. by 82%, 92% and 75% respectively. Such protective effect was not observed with cysteine in equal molar dose. Subcutaneously injected cysteamine (132 mumol) inhibited gastric acid secretion by 46% in indomethacin-treated rats, while no effect was observed on acid secretion when cysteamine was given intragastrically. Cysteamine, given through both routes, did not affect gastric barrier mucus secretion. It is suggested that sulfhydryls in gastric mucosa are not involved in the mechanism of indomethacin-induced injury and that the potent cytoprotective effect of cysteamine against indomethacin-induced ulcer maybe not caused by its sulfhydryl group.

[Effects of buzhong yiqi decoction on the anticancer activity and toxicity induced by cyclophosphamide]

Effects of Buzhong Yiqi decoction on anticancer activity and toxicity induced by cyclophosphamide were investigated. The results showed that the decoction significantly increased the anticancer activity and simultaneously decreased the toxicity of cyclophosphamide. These data suggest that anticancer chemotherapeutic drugs combined with traditional Chinese medicine Buzhong Yiqi decoction can raise curative effect and reduce toxicity.

Glial epiretinal membranes and contraction. Immunohistochemical and morphological studies

It has been suggested that glial cells do not contribute substantially to the contractile forces generated by epiretinal membranes. We have established a rabbit model in which epiretinal membranes form on the inferior peripheral retina after the injection of activated macrophages into the vitreous. By two months, the membranes were extensive but without evidence of traction. At four months, however, full-thickness retinal folds were present beneath the thick epiretinal membrane. A homogeneous glial cell composition was suggested by light microscopic examination of serial sections through several membranes. Immunohistochemical staining with anti-glial fibrillary acidic protein and antivimentin and immunoelectron microscopy confirmed that these thick epiretinal membranes were composed entirely of glial cells, which may cause mild traction on the retina; this traction is associated with cell alignment and the tissue bridges connecting the membrane and the retina. The fusiform densities and indented nuclei suggested that the glial cells within the membrane may possess some characteristics of myofibroblasts.