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Biomedical subjects

D Xu

Publications and source records attributed to D Xu.

At least 361 records · Page 20Linked to original sources
PubMed1994

Bombesin protects against bacterial translocation induced by three commercially available liquid enteral diets: a prospective, randomized, multigroup trial.

OBJECTIVE: To test the hypothesis that certain commercially available liquid diets would cause bacterial translocation and that this diet-induced translocation could be reduced with bombesin (an intestinal hormone stimulant). DESIGN: Prospective, multigroup trial in which animals fed each test diet were randomized to receive either bombesin or saline for 7 days. On day 7, the mice were killed and their organs were cultured for translocating bacteria, their cecal bacterial population concentrations were measured, and ileal and jejunal mucosal protein content was determined. SETTING: Small animal laboratory. SUBJECTS: Outbred ICR mice weighing 25 to 35 g. INTERVENTIONS: Mice received bombesin (10 micrograms/kg) or saline subcutaneously three times daily for 7 days before sacrifice. MEASUREMENTS AND MAIN RESULTS: The incidence of bacterial translocation to the mesenteric lymph node was significantly increased (p < .05) in mice fed Vivonex (53%), Criticare (67%), or Ensure (60%) compared with chow-fed controls (0%). All three liquid diets were associated with the development of cecal bacterial overgrowth and loss of jejunal and ileal mucosal protein content. Bombesin reduced the incidence of bacterial translocation and loss of mucosal protein content in all three liquid diet groups (p < .05), but did not prevent diet-induced cecal bacterial overgrowth. CONCLUSIONS: Three different liquid diets induced bacterial translocation to the mesenteric lymph node. Since bombesin was effective in reducing bacterial translocation, it appears that bacterial translocation induced by these liquid diets can be modulated hormonally.

Animals↗
PubMed1994

Evidence favoring the role of the gut as a cytokine-generating organ in rats subjected to hemorrhagic shock.

There is increasing evidence of an association between intestinal injury and the development of a septic state and distant organ failure. Since this phenomenon can occur in the absence of detectable systemic bacterial translocation (BT), we tested the hypothesis that shock-induced intestinal injury will result in the gut becoming a cytokine-generating organ by measuring interleukin 6 (IL-6) and tumor necrosis factor (TNF) levels in the portal blood, cardiac blood, and intestinal lymph of rats subjected to sham, 30, 60, or 90 min of hemorrhagic shock (30 mm Hg). These blood and lymph samples, as well as the mesenteric lymph nodes (MLN), spleens, and livers, were cultured for translocating bacteria. Although all the portal and cardiac blood samples were sterile, the portal blood levels of TNF and IL-6 were increased to a greater extent than simultaneously obtained cardiac blood samples in rats subjected to 60 or 90 min of shock (p < .05). The lymph IL-6 levels increased but were similar between the groups. BT was limited to the MLN and occurred in a dose-dependent fashion with 38, 63, and 100% of the animals having culture-positive MLNs after 30, 60, or 90 min of shock, respectively. In conclusion, after hemorrhagic shock, the gut appears to become a cytokine liberating organ even in the absence of detectable bacteria in the portal circulation.

Animals↗
PubMed1994

Effects of ethanol feeding on the interaction of rat hepatocytes with laminin peptides.

Laminin, a complex glycoprotein of the extracellular matrix, contains a number of biologically active sites. These sites are involved in cell growth, attachment, differentiation, and gene expression. Our previous studies have shown that chronic ethanol consumption by rats impairs hepatocyte attachment to various components of the extracellular matrix including laminin. In this study, three synthetic peptides (PA22-2, YIGSR, and RGD) that correspond to three distinct functional sites on the laminin molecule were used to investigate the effect of ethanol consumption on their cognate receptors. Initially, varying concentrations of each peptide were incubated with isolated hepatocytes from ethanol-fed and pair-fed control rats. These hepatocytes were then assayed for the ability to attach to laminin. The results indicated that all three peptides effectively inhibited laminin-mediated cell adhesion: the degree of inhibition appeared similar between pair-fed controls and ethanol-fed animals. Of the three peptides, PA22-2 showed the most dramatic inhibition of attachment. Therefore, we investigated the ability of hepatocytes to attach directly to PA22-2 itself. Attachment of hepatocytes from ethanol-fed animals to PA22-2 was impaired by 30% after 4 days and 90% by 14 days. Conversely, no significant difference in attachment to the entire laminin molecule was observed in ethanol-fed animals at these early time points. These results indicated that the ethanol-induced impairment of hepatocyte attachment to laminin may be caused by the decreased interaction of hepatocytes with specific functional sites on the laminin molecule and that specific receptors on the hepatocyte may be affected differently.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcoholism↗
PubMed1994

Humanization of the murine anti-human CD3 monoclonal antibody OKT3.

OKT3 is a murine monoclonal antibody which recognizes an epitope on the epsilon-subunit within the human CD3 complex. OKT3 possesses potent immunosuppressive properties in vivo and has been proven effective in the treatment of renal, heart and liver allograft rejection. Despite its efficacy, significant problems remain associated with OKT3 therapy, i.e. T-cell activation and the anti-murine antibody response. To address the problem of the anti-murine antibody response we have constructed humanized versions of OKT3. One of the humanized derivatives, gOKT3-7 incorporating the OKT3 complementarity determining regions plus a small number of alterations to the human framework, has an affinity of 1.4 x 10(9) M-1 compared with 1.2 x 10(9) M-1 for the murine OKT3. A humanized antibody (gOKT3-1) incorporating only the CDRs from OKT3 was found to be functionally inactive, confirming the requirement for nonCDR substitutions. gOKT3-7 retains the ability of mOKT3 to induce T cell proliferation in vitro and appears to be a good candidate for further development for in vivo therapy.

Amino Acid Sequence↗
PubMed1994

[Preliminary observation on the detection of schistosome circulating antigen and the immunocomplex by dot-ELISA].

Serum samples were collected from normal rabbits, normal persons, Schistosoma japonicum-infected rabbits and human cases respectively, and were treated by TCA precipitation and PEG precipitation, and subsequently detected by dot-ELISA. The results showed that both the supernatants of TCA-treated antisera from infected human cases and rabbits and the precipitants of PEG-treated antisera of the same origins showed positive reactions, while no positive reactions were found for sera from normal rabbits and normal persons. It was exhibited that dot-ELISA detected not only the circulating antigen of schistosomes but also the immunocomplex.

Animals↗
PubMed1993

Excitation energy transfer in DNA: duplex melting and transfer from normal bases to 2-aminopurine.

Absorption and fluorescence excitation and emission spectra of the B DNA duplex decamer d[CTGA(2AP)TTCAG]2, where emission from the 2AP (2-aminopurine) base dominates, have been measured as a function of temperature. A low-temperature excitation band in the 260-270-nm region disappears near the duplex melting temperature, Tm = 27 degrees C, but then reappears at higher temperatures. Singlet-singlet energy transfer thus occurs between the normal DNA bases and the 2AP base in the B-helical conformation and to a lesser extent in the structurally-mobile melted conformation. The measured efficiency of transfer is 4-5% at 4 degrees C, near 0 at 30 degrees C, and rises again to 1% at 48 degrees C. Nearest-neighbor-only singlet transfer is likely. Such transfer does not offer a likely explanation for UV damage distributions in DNA.

2-Aminopurine↗
PubMed1993

Repeated induction of nitric oxide synthase and leishmanicidal activity in murine macrophages.

Murine macrophages express high levels of nitric oxide (NO) synthase and produce large amounts of NO when stimulated with interferon-gamma plus lipopolysaccharide in vitro. The expression of NO synthase peaks at 12 h after stimulation and declines rapidly to the background level by 72 h. These macrophages can be repeatedly reactivated to express similar levels of NO synthase. The reactivation is not due to newly divided cells since peritoneal macrophages which do not divide in vitro and J774 cells cultured in the presence of colchicine can also be restimulated to express NO synthase. The reactivation is accompanied by re-expression of NO synthase mRNA, as assessed by polymerase chain reaction analysis. Furthermore, the reactivated macrophages are fully capable of killing the intracellular protozoan parasite Leishmania major.

Amino Acid Oxidoreductases↗
PubMed1993

Pre-exposure of murine macrophages to lipopolysaccharide inhibits the induction of nitric oxide synthase and reduces leishmanicidal activity.

Murine macrophages produce nitric oxide (NO) from L-arginine on stimulation with lipopolysaccharide (LPS), alone or with interferon-gamma (IFN-gamma). The effect of incubation of macrophages with low concentrations of LPS on NO synthesis on subsequent stimulation was investigated, using a murine macrophage cell line, J774, and peritoneal macrophages from CBA mice. Cells which had been incubated with LPS produced significantly lower amounts of NO, and expressed lower levels of NO synthase activity, following stimulation with IFN-gamma and LPS, or with a high concentration of LPS. This effect was not reversed by tumor necrosis factor-alpha. The ability of CBA macrophages to kill the intracellular parasite Leishmania major was markedly reduced by pre-incubation with LPS. Reduced NO production by macrophages previously exposed to LPS is a manifestation of endotoxin tolerance, and may represent an important means of regulation of NO synthesis and thus a survival mechanism for intracellular parasites.

Amino Acid Oxidoreductases↗
PubMed1993

Systemic induction of a potato pin2 promoter by wounding, methyl jasmonate, and abscisic acid in transgenic rice plants.

To address the question whether common signal(s) and transduction pathways are used to mediate a systemic wound response in monocot and dicot plants, a fusion of the potato proteinase inhibitor II gene (pin2) promoter and the bacterial beta-glucuronidase gene (Gus)-coding region was introduced into rice. In transgenic rice plants, the expression of the pin2-Gus fusion gene displays a systemic wound response, although the expression level is relatively low. Incorporation of the first intron from the rice actin 1 gene (Act1) into the 5'-untranslated region of the pin2-Gus construct results in high-level, systemically wound-inducible expression of the modified construct in transgenic rice plants. Histochemical analysis shows that this high-level, wound-inducible expression is associated with the vascular tissue in both leaves and roots. Furthermore, the expression of the pin2-Act1 intron-Gus fusion gene in transgenic rice plants can be systemically induced by both methyl jasmonate (MJ) and the phytohormone abscisic acid (ABA). These results suggest that the signal(s) mediating the observed systemic wound response and certain steps of the transduction pathways are conserved between dicot and monocot plants. Transient expression assays show that the pin2-Act1 intron-Gus construct is also actively expressed in transformed cells and tissues of several other monocot plants. Thus, the wound-inducible pin2 promoter in combination with the rice Act1 intron 1 might be used as an efficient regulator for foreign gene expression in transgenic monocot plants.

Abscisic Acid↗
PubMed1993

Long-term in vivo effects of rapamycin on humoral and cellular immune responses in the rat.

Rapamycin (RAPA) is a strong immunosuppressant and is able to prevent allograft rejection in animal models. We have demonstrated that RAPA could strongly inhibit in vitro immunoglobulin (Ig) production by human lymphocytes. The present study investigated the long-term in vivo effect of RAPA on humoral and cellular immune responses, and the effect of RAPA on accelerated rejection. It was shown that RAPA strongly inhibited antigen (Ag) specific antibody (AB) production (i.e. cytotoxic Ab to donor lymphocytes and Ab to tetanus toxoid) during the period of drug administration. The accelerated rejection of cardiac allografts in presensitized animals was alleviated by RAPA administration. These results suggest the potential application of RAPA in treatment of presensitized candidates for organ transplantation. A little more than two months after the drug withdrawal, the rats were basically competent in Ab response to further Ag challenges. When tested 4 months after the RAPA-treatment, the rats showed uncompromised cardiac allograft rejection, and the cellular immune response in vitro according to mixed lymphocyte reaction (MLR) and mitogen-stimulated proliferation were not hampered. Such results suggest that the immune system can return to normal status without sequelae after discontinuation of RAPA.

Animals↗
PubMed1993

Elemental diet-induced bacterial translocation can be hormonally modulated.

BACKGROUND: The authors have previously documented that feeding mice an elemental diet resulted in bacterial translocation (BT) that could be prevented by the provision of dietary fiber. To test whether the protective effect of fiber was related to the stimulation of trophic gut hormones, the effects of sandostatin and bombesin were tested. METHODS: Mice fed either chow or the elemental diet were stratified into several groups and the ability of bombesin (10 micrograms/kg, tid) or sandostatin (100 micrograms/kg bid) to modulate BT was examined. After 14 days, mice were sacrificed and BT, cecal bacterial population levels, mucosal protein, and small bowel weight was measured. Segments of the ileum and jejunum were examined histologically. RESULTS: Incidence of elemental diet-induced BT (75%) was reduced by fiber (9%) or the administration of bombesin (13%) (p < 0.01). Although sandostatin did not promote BT in chow-fed mice, it reversed the protective effect of fiber on BT (75%) (p < 0.01). CONCLUSION: Elemental diet-induced bacterial translocation can be modulated hormonally and the beneficial effects of fiber on diet-induced BT appears to be hormonally mediated.

Animals↗
PubMed1993

Intracellular localization of membrane-bound endothelin-converting enzyme from rat lung.

Intracellular localization of membrane-bound endothelin-converting enzyme (ECE) was examined in rat lung by sucrose-gradient ultracentrifugation coupled with organelle marker studies. Lung microsomal fraction was prepared and fractionated by ultracentrifugation through a linear sucrose gradient. Sedimentation profiles of marker enzymes for plasma membrane, Golgi, lysosome, and mitochondria showed that these organelles were measurably separated from each other. A major portion of phosphoramidon-sensitive ECE activity was distributed with a single peak at the approximately 1.05-1.2 M sucrose region, where it appeared to be cosedimented with membrane vesicles that contained the two different marker enzymes for Golgi apparatus. These microsomal vesicles also seemed to contain the majority of endogenous immunoreactive ET-1 found in the lung. These findings suggest that a majority of the ECE activity in rat lung may be responsible for the intracellular conversion of big ET-1 during its transit through the secretory pathways.

Animals↗
PubMed1993

Mechanisms of endotoxin-induced intestinal injury in a hyperdynamic model of sepsis.

The goal of this study was to test the hypothesis that endotoxin-induced bacterial translocation is the result of a selective decrease in intestinal blood flow that causes an oxidant-mediated intestinal mucosal injury. To accomplish this goal, 116 instrumented rats receiving a nonlethal dose of endotoxin (5 mg/kg IP) or saline were studied. Organ blood flow and cardiac output were measured using the microsphere technique and intestinal permeability was measured both by the blood to luminal clearance of 51Cr-EDTA and by horseradish peroxidase. Cardiac output was higher in the endotoxin-treated group than in the saline group (76 +/- 12 versus 95 +/- 17 mL/min; p < 0.05). Although endotoxin induced a hyperdynamic state, blood flow to the distal ileum and cecum was selectively decreased by 35%-50% (p < 0.01), whereas blood flow to the rest of the intestine, spleen, pancreas, and liver was normal. Furthermore, blood flow to the ileal mucosa was decreased to a greater extent than to the remainder of the gut wall (p < 0.05). Small bowel permeability to 51Cr-EDTA was increased at sites of decreased blood flow (ileum) but not at sites of normal (jejunum) blood flow. Allopurinol, a competitive inhibitor of xanthine oxidase, ameliorated the endotoxin-induced decrease in ileal blood flow as well as the increase in ileal permeability. Thus these studies support the hypothesis that endotoxin-induced mucosal injury is the result of an ischemia reperfusion-mediated injury of the distal small intestine and cecum.

Allopurinol↗
PubMed1993

Elemental diet-induced bacterial translocation and immunosuppression is not reversed by glutamine.

Previously, we documented that bacterial translocation occurs in rats fed an elemental liquid diet (4.25% amino acids plus 28% glucose) for 7 days. Since controversy exists over the protective effect of glutamine on diet-induced bacterial translocation, we compared the effect of two elemental diets, one containing 0% and the other 30% of amino acids as glutamine. After 7 days on the test diets or chow (307 kcal/kg/day), the rats were killed and half the animals had their organs cultured for translocating bacteria; immune function was quantitated in the other half by measuring the blood, splenic, and mesenteric lymph node (MLN) blastogenic responses to the T-cell mitogens phytohemagglutinin (PHA) and concanavalin A (ConA). The incidence of bacterial translocation was higher in the rats fed the glutamine (88%) or nonglutamine (75%) elemental diets than in the chow-fed rats (13%) (p < 0.05). Both elemental diets equally reduced the blastogenic response of lymphocytes harvested from all three lymphoid compartments (blood, spleen, MLN) (p < 0.01 vs. chow). The percentage of reduction averaged 30% to 40% when PHA was used as the test mitogen and 50% to 70% when ConA was used. These results indicate that glutamine does not prevent elemental diet-induced bacterial translocation or immune suppression.

Animals↗
PubMed1993

Immunosuppressive properties of the benzothiazepine calcium antagonists diltiazem and clentiazem, with and without cyclosporine, in heterotopic rat heart transplantation.

In vitro studies have shown that calcium channel blockers (CCB) exert inhibitory effects on immunocompetent cells but conflicting results have been reported as to the translation of these effects into significant in vivo immunosuppression. In this study we evaluated the effects of the benzothiazepine-like calcium blockers diltiazem and clentiazem, given alone or associated with cyclosporine on survival improvement of heterotopic rat heart transplants. Inbred male rats of the Lewis strain were used as recipients and Wistar-Furth as donors. Following abdominal implantation of the graft, recipients were randomly divided into 9 groups (n = 5). Group 1 were control isografts (Lew-Lew); group 2 were control allografts (WFu-Lew), and group 3 were allografts treated with low-dose oral cyclosporine 2 mg/kg/day. Groups 4 and 5 were allografts treated with oral diltiazem 0.25 and 2.50 mg/kg/day. Groups 6 and 7 were treated with oral clentiazem, 0.25 and 2.50 mg/kg/day. Groups 8 and 9 consisted of allografts receiving low-dose cyclosporine with either diltiazem or clentiazem 2.50 mg/kg/day, all drugs were administered daily by gavage. Graft function was monitored by transabdominal palpation, and rejection was considered to be complete when no contraction of the graft could be detected. Mean survival time of untreated allografts was 6.4 +/- 0.5 days. Cyclosporine alone increased the mean survival time to 10.6 +/- 2.7 days (P < 0.05 vs. group 2). At all doses studied, diltiazem and clentiazem significantly increased mean survival time of allografts, clentiazem being slightly more potent than diltiazem. In addition, the observed beneficial effects of the benzothiazepine-like calcium channel blockers were dose-dependent. When combined with cyclosporine, diltiazem and clentiazem interacted synergistically (mean survival time increased to 16.8 +/- 3.4 days for diltiazem and 15.8 +/- 1.4 days for clentiazem). These results demonstrate that the benzothiazepine-like calcium channel blockers, as opposed to phenylalkylamines or dihydropyridines, afford significant immunosuppression when used alone. These observations, and the fact that they beneficially interact with cyclosporine, suggest that the benzothiazepine-like calcium antagonists should be considered the drugs of choice when CCBs are to be selected in transplanted patients.

Animals↗