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Biomedical subjects

M Xu

Publications and source records attributed to M Xu.

At least 181 records · Page 10Linked to original sources
PubMed1999

Cancer immunotherapy by antisense suppression of Ii protein in MHC-class-II-positive tumor cells.

This study was aimed at creating a more effective tumor cell vaccine by suppressing Ii protein in the presence of MHC class II molecules within a cancer cell. Absence of the Ii protein, which normally blocks the antigenic-peptide-binding site of MHC class II molecules at synthesis in the endoplasmic reticulum, presumably increases the range of cancer-related epitopes presented to CD4+ helper T cells. Effective suppression of Ii protein was achieved with an antisense, phosphorothioate oligonucleotide, which was selected on the basis of (1) the RNase H activation assay, (2) an assay for Ii protein suppression, and (3) a test for potency with respect to the extent of base sequence ("sequence walking"). The SaI murine sarcoma, which is MHC-class-I+ and MHC-class-II-, Ii-protein-, upon transfection with genes for either interferon gamma or the MHC class II transactivator, came to express MHC class II molecules and Ii protein. In each line of transfected tumor cells, the antisense oligonucleotide profoundly suppressed Ii protein in 35%-55% cells, without affecting expression of MHC class II molecules. Inoculation of mice with such Ii-protein-suppressed tumor vaccine cells, after either formaldehyde fixation or X-irradiation, led to much greater protection against challenge with the parental SaI sarcoma than did inoculation with untreated cells. This approach to cancer cell vaccination can be applied in a wide range of human tumors.

Animals↗
PubMed1999

Invariant chain expression in colon neoplasms.

Invariant chain (Ii) is a chaperone molecule that inhibits binding of endogenous antigens to class II molecules. High levels of Ii in cancer cells may prevent tumour antigen expression with class II and render the tumour less immunogenic. To correlate the expression of Ii and class II molecules in colon carcinomas with the density of tumour infiltrating lymphocytes (TILs), surgical specimens from a total of 48 patients with well-(WDAC), moderately (MDAC) and poorly differentiated adenocarcinomas (PDAC), adenoma with high-grade dysplasia (AdHGD) and adenomas were immunostained for Ii and class II antigen (HLA-DR). Aggregates of TILs were graded in H&E-stained sections. Normal colon epithelium was negative for Ii and HLA-DR. Invasive carcinomas showed a linear increase in the expression of Ii in the progression from low- to high-grade tumours, while there was no significant difference in HLA-DR expression across the groups. Invasive carcinomas showed a disproportionate increase in Ii over HLA-DR. Frequency of TILs showed inverse correlation with expression of Ii and tumour grade. This is the first demonstration that expression of Ii increases in the progression from low- to high-grade colon neoplasms and is most marked in the poorly differentiated carcinomas. Ii expression by carcinomas is inversely related to the frequency of TILs. The findings suggest that increased Ii renders the tumour less immunogenic and less likely to stimulate a host immune response.

Adenocarcinoma↗
PubMed1999

Selective neointimal gene transfer in an avian model of vascular injury.

Avian models of atherosclerosis helped pioneer the study of vascular biology, and offer economic and technical advantages over mammalian models. As an initial step towards investigating important molecular pathways involved in avian atherogenesis and restenosis, we developed a recombinant adenovirus (Ad) which expresses the reporter gene beta-galactosidase (beta-gal), and applied it to cultured chicken vascular smooth muscle cells (SMCs) and a rooster model of acute vascular injury. In cultured chicken SMCs, recombinant gene expression increased as a function of multiplicity of infection (MOI) and incubation time. Maximal expression occurred at an MOI of 10(4) plaque-forming units (pfu)/cell with approximately 50% of quiescent and non-quiescent chicken SMCs expressing beta-gal. Human aorta SMCs had two- to four-fold increased beta-gal expression compared with chicken SMCs at all MOI and incubation times. In vivo instillation of recombinant Ad into uninjured rooster femoral artery segments revealed low efficiency endothelial cell expression of the reporter gene. In contrast, recombinant Ad infection of rooster femoral artery segments 3-21 days after balloon injury revealed up to 60% of luminal surface beta-gal expression, confined predominantly to the neointimal layer. Peak reporter gene expression efficiencies occurred in arterial segments infected 3 days after balloon injury. Uninfected and control Ad infected arteries had no detectable beta-gal expression. Rooster neointimal cells targeted by the recombinant Ad were identified as alpha-smooth muscle actin containing cells by immunohistochemistry. We conclude that Ad-mediated gene transfer is efficient and selective for the neointima in the rooster acute vascular injury model, and offers the potential to efficiently introduce exogenous genes that may impact on the injury response. This model of acute vascular injury may also be manipulated into more established avian models of atherosclerosis, permitting the investigation of acute injury progression to chronic injury.

Adenoviridae↗
PubMed1999

Effects of (1DMe)NPYF, a synthetic neuropeptide FF analogue, in different pain models.

The antinociceptive effects of intrathecal (IT) (1DMe)NPYF were studied in adult Sprague-Dawley rats. (1DMe)NPYF produced dose-dependent antinociception that was reduced by subcutaneous injection of naloxone. (1DMe)NPYF (0.5 nmol) also potentiated the antinociceptive effects of intrathecal morphine 7.8 nmol. This suggests that the antinociceptive effects of (1DMe)NPYF are partially mediated by opioid receptor activation. In carrageenan inflammation, 5-10 nmol of (1DMe)NPYF was effective against both thermal hyperalgesia and mechanical allodynia. In the neuropathic pain model, the lowest dose tested (0.5 nmol) showed antiallodynic effects against cold allodynia. The results suggest a potential role for (1DMe)NPYF in the treatment of pain including neuropathic pain.

Amino Acid Sequence↗
PubMed1999

Formation of phosphatidic acid and subclasses of phosphatidylethanol in human neutrophils upon interleukin-8 stimulation.

Previous studies showed that interleukin-8 (IL-8) stimulates phospholipase D hydrolysis of phosphatidylcholine to generate phosphatidic acid in human neutrophils. Phosphatidylcholine in these cells contains diacyl, alkylacyl and alkenylacyl subclasses. No studies have examined phospholipase D hydrolysis of the three subclasses of phosphatidylcholine in interleukin-8-stimulated neutrophils. We used a non-radioactive but very sensitive method to assess the relative distribution of the subclasses in phosphatidylethanol, which is derived from phospholipase D activity in ethanol-exposed neutrophils. We present evidence that the relative abundance of diacyl and alkylacyl subclasses in phosphatidylethanol is similar to that in phosphatidylcholine. Alkenylacyl subclass was also detectable in the phosphatidylethanol fraction, albeit as a minor subclass. Our findings suggest that phospholipase D catalyses the hydrolysis of diacyl, alkylacyl and alkenylacyl subclasses of phosphatidylcholine in neutrophils upon IL-8 stimulation.

Chromatography, Thin Layer↗
PubMed1999

Cancer chemopreventive mechanisms of tea against heterocyclic amine mutagens from cooked meat.

Cooking meat and fish under normal conditions produces heterocyclic amine mutagens, several of which have been shown to induce colon tumors in experimental animals. In our search for natural dietary components that might protect against these mutagens, it was found that green tea and black tea inhibit the formation of heterocyclic amine-induced colonic aberrant crypt foci (ACF) in the rat. Since ACF are considered to be putative preneoplastic lesions, we examined the inhibitory mechanisms of tea against the heterocyclic amines. In the initial studies using the Salmonella mutagenicity assay, green tea and black tea inhibited according to the concentration of tea leaves during brewing and the time of brewing; a 2-3-min brew of 5% green tea (w/v) was sufficient for >90% antimutagenic activity. N-hydroxylated heterocyclic amines, which are direct-acting mutagens in Salmonella, were inhibited by complete tea beverage and by individual components of tea, such as epigallocatechin-3-gallate (EGCG). Inhibition did not involve enhanced mutagen degradation, and EGCG and other catechins complexed only weakly with the mutagens, suggesting electrophile scavenging as an alternative mechanism. Enzymes that contribute to the metabolic activation of heterocyclic amines, namely microsomal NADPH-cytochrome P450 reductase and N, O-acetyltransferase, were inhibited by tea in vitro. Studies in vivo established that tea also induces cytochromes P450 and Phase II enzymes in a manner consistent with the rapid metabolism and excretion of heterocyclic amines. Collectively, the results indicate that tea possesses anticarcinogenic activity in the colon, and this most likely involves multiple inhibitory mechanisms.

Amines↗
PubMed1999

Effect of carcinogen dose fractionation, diet and source of F344 rat on the induction of colonic aberrant crypts by 2-amino-3-methylimidazo[4,5-f]quinoline.

Carcinogen dose fractionation, diet and source of laboratory animal were examined as variables in the induction of colonic aberrant crypt foci (ACF) by the heterocyclic amine 2-amino-3-methylimidazo [4, 5-f]quinoline (IQ). In the first experiment, male F344 rats from the National Cancer Institute (NCI rats) were fed AIN-93G diet and, starting in the third week, IQ was given by gavage on alternating days, the total carcinogen dose of 105 mg being fractionated proportionally over 2, 4, 8 or 14 weeks. Only the high dose (2 week) treatment with IQ was effective for the induction of ACF at 16 weeks, producing on average 3.8 ACF/colon versus 0.5 ACF/colon in all other groups (P < 0.05). The 2 week IQ dosing protocol was used in a second experiment in which male F344 rats from Simonsen Laboratories (SN) or NCI were fed AIN-93G, AIN-76A or chow diet. On average, SN rats on chow diet had twice the number of aberrant crypts compared with NCI rats given the same diet and three to four times as many aberrant crypts as NCI rats fed AIN diets. Hepatic cytochrome P4501A1 (CYP1A1) levels were essentially unaffected by diet, but methoxyresorufin O-demethylase activities and CYP1A2 protein levels were increased 2- to 3-fold in animals fed chow versus AIN diets. During the 2 week period of carcinogen administration, IQ markedly induced CYP1A proteins and negated the differences among groups related to diet. No consistent diet-related changes were detected in the activities of aryl sulfotransferase or N-acetyltransferase, but UDP-glucuronosyltransferase activities were elevated 2- to 3-fold in rats given chow versus AIN diets. In summary, high dose treatment with IQ was required for the induction of ACF, rats on the chow diet had more aberrant crypts than those given AIN diets and male F344 rats purchased from different vendors and fed chow diet differed with respect to their sensitivity to induction of ACF.

Animals↗
PubMed1999

beta-hydroxyisovalerylshikonin inhibits the cell growth of various cancer cell lines and induces apoptosis in leukemia HL-60 cells through a mechanism different from those of Fas and etoposide.

beta-Hydroxyisovalerylshikonin (beta-HIVS), which was isolated from the plant, Lithospermium radix, inhibited the growth of various lines of cancer cells derived from human solid tumors at low concentrations between 10(-8) and 10(-6) M. When HL-60 cells were treated with 10(-6) M beta-HIVS for 3 h, characteristic features of apoptosis, such as DNA fragmentation, nuclear fragmentation, and activation of caspase-3-like activity, were observed. The most characteristic features of the effect of beta-HIVS were the remarkable morphological changes induced upon treatment of HL-60 cells with beta-HIVS, as visualized on the staining of actin filaments with phalloidin labeled with tetramethylrhodamine B isothiocyanate. Moreover, activation of MAP kinases, such as ERK2, JNK and p38, was detected after treatment with 10(-6) M beta-HIVS preceding the appearance of the characteristics of apoptosis, and the features of the activation of these MAP kinases were quite different from those of Fas and anticancer drug-induced apoptosis. The activation of JNK by beta-HIVS was not inhibited by inhibitors of caspases, suggesting that JNK is located either upstream or independent of the caspase signaling pathway. beta-HIVS did not inhibit the activity of topoisomerase II. These results indicate that beta-HIVS induces apoptosis in HL-60 cells through a mechanism unlike those reported for anti-Fas antibodies and etoposide.

Antineoplastic Agents↗
PubMed1999

Systemic physostigmine shows antiallodynic effects in neuropathic rats.

UNLABELLED: The aim of this study was to examine the antiallodynic and antinociceptive effects of subcutaneously administered physostigmine (50, 100, 200 micrograms/kg), compared with morphine (2.5, 5, 10 mg/kg) and NaCl after spinal nerve ligation in rats. The following stimuli were used: acetone (cold allodynia), von Frey hairs (mechanical allodynia), and paw flick test (thermal nociception). Motility boxes were used to investigate the effects of the drugs on motor performance. Physostigmine attenuated both mechanical and cold allodynia dose-dependently but had no effect on the paw flick test. The effect was antagonized by atropine (muscarinic receptor antagonist) but not by mecamylamine (nicotinic receptor antagonist) or naloxone (opioid receptor antagonist). Morphine produced dose-dependent antiallodynic and antinociceptive effects. In the antiallodynic doses, morphine caused severe rigidity. Physostigmine 200 micrograms/kg impaired locomotor activity, but no rigidity was observed. IMPLICATIONS: Physostigmine has different effects on allodynia and nociception, which suggests that different cholinergic (muscarinic) mechanisms may be involved in neuropathic and nociceptive pain.

Analgesics↗
PubMed1999

Renal dysfunction associated with the perioperative use of diclofenac.

UNLABELLED: Postoperative renal dysfunction in rats is induced by ketorolac dosed concurrently with gentamicin. Herein, we report the renal effects of diclofenac in four groups of rats: control (C = anesthesia, surgery); diclofenac (D = anesthesia, surgery, diclofenac 18 mg x kg(-1) x d(-1)); gentamicin (G = anesthesia, surgery, gentamicin 20 mg x kg(-1) x d(-1)); and diclofenac and gentamicin (DG = anesthesia, surgery, diclofenac, gentamicin). Renal function, after three treatment days, was assessed using histology, p-aminohippurate (PAH), and iothalamate (IOT) clearances, serum and urine electrolytes, osmolality, urea, and creatinine. Urine output was increased (from 5.2 to 12.5 mL/24 h), and urine osmolality was decreased (from 2121 to 883 mOsm/kg) in the DG group. PAH and IOT clearances were decreased in the G and DG groups (PAH by 18%, IOT by 22%; PAH by 38%, IOT by 43%, respectively); there were no changes in the C and D groups. Urea and creatinine clearances were decreased by 61% and 43%, respectively, in the DG group. Kidney sections showed the most severe pathologic changes in the DG group. Our data indicate that the perioperative combination of diclofenac and gentamicin was deleterious to renal function. IMPLICATIONS: Diclofenac alone does not result in significant perioperative renal dysfunction, but the combination of gentamicin and diclofenac is deleterious to renal function. Considering this and previous findings, the evidence suggests that treatment with aminoglycosides may be a significant risk factor for inducing perioperative renal failure during treatment with nonsteroidal antiinflammatory drugs.

Animals↗
PubMed1999

Absence of gonadotropin surges and gonadotropin-releasing hormone self-priming in ovariectomized (OVX), estrogen (E2)-treated, progesterone receptor knockout (PRKO) mice.

It is well known that estrogen (E2) stimulates expression of progesterone receptors (PRs), thereby inducing responsiveness of several tissues to the actions of progesterone (P). Recent studies have also suggested, however, that biological actions previously ascribed to E2 alone may also be mediated by activation of E2-induced PRs, even independently of signal changes in P concentrations. In the present experiments, the progesterone receptor knockout (PRKO) mice were used to assess the role of PR activation in the positive feedback actions of E2 on gonadotropin release. Ovariectomized (OVX) PRKO mice were tested for their capacity to mount primary gonadotropin surges in response to exogenous E2, and to exhibit a GnRH self-priming effect in response to sequential injections of the decapeptide. Wild-type (WT) and PRKO mice were OVX, treated with both 17beta-estradiol and estradiol benzoate (EB), and then killed at 1900 h on day 7 postOVX. Plasma LH RIA revealed that WT mice exhibited surges in response to the E2 treatment; the PRKO mice, however, showed no elevation in plasma LH above untreated controls. Instead, plasma LH levels in E2-treated, OVX PRKO mice decreased significantly in comparison to untreated OVX PRKO mice, suggesting that E2 can exert a negative feedback influence on LH release in PRKO mice, despite the absence of positive feedback effects. A slight but significant rise in plasma FSH was observed in E2-treated OVX WT mice in comparison to untreated controls: an effect not seen in E2-treated OVX PRKO mice, reinforcing the observation that estrogen's positive feedback effects are compromised in PRKO mice. In a second experiment, E2-treated OVX WT and PRKO mice were given either one or two pulses of GnRH 60 min apart, and killed 10 min later. The WT mice were found to exhibit a robust GnRH self-priming effect, as WT mice receiving two GnRH pulses displayed LH responses approximately 2-fold greater than those receiving only one pulse. By contrast, PRKO mice receiving two GnRH pulses exhibited no additional increase in plasma LH levels. We conclude that PR activation is obligatory for expression of the GnRH self-priming effect as well as for generation of E2-induced LH and FSH surges. The extent to which failure of LH surge secretion in PRKO mice is due to the absence of GnRH self-priming, lack of hypothalamic GnRH surges, and/or defects in other processes remains to be determined. These observations clearly demonstrate, however, that the presence of PR is an absolute requirement for the transmission of E2-induced signals leading to gonadotropin surges.

Animals↗
PubMed1999

The role of the renin-angiotensin and cardiac sympathetic nervous systems in the development of hypertension and left ventricular hypertrophy in spontaneously hypertensive rats.

To elucidate the relationship between the development of left ventricular hypertrophy (LVH) in hypertension and the development of both the cardiac sympathetic nervous and renin-angiotensin systems, as measured by norepinephrine and angiotensin II levels, respectively. In this longitudinal study, we compared blood pressure (BP), left ventricular weight, and norepinephrine (NE) and angiotensin II (Ang II) concentrations, in Spontaneously Hypertensive Rats (SHR) and age-matched Wistar-Kyoto (WKY) rats at 5, 10, 15, 20, and 28 wk of age. Blood pressure, plasma and ventricular Ang II and tissue NE were measured by the tail-cuff method, radioimmunoassay, and high-performance liquid chromatography (HPLC), respectively. At 5 wk, systolic blood pressure was the same in both strains. But the left ventricular plus septum weight to body weight (LVSW/BW) ratio was higher in SHR than in WKY rats (p < 0.01), which finding may have been related to the increased cardiac tissue NE concentration, and this increase tended to parallel the rise in blood pressure. Both left ventricle and forelimb muscle NE concentrations were significantly higher in SHR than in WKY rats at 5, 10, and 15 wk of age (p < 0.01, respectively), and were similar at 20 and 28 wk of age. The heart and plasma Ang II levels decreased with age, which results were in keeping with the known developmental tendencies of the biological aging progress. There was no significant difference in plasma Ang II levels between the two strains from 5 to 20 wk, whereas these levels were remarkably higher in WKY than in SHR rats at 28 wk (p< 0.01). Otherwise, the left ventricular tissue Ang II concentrations were significantly higher in SHR than in WKY rats at the late stage (from 15 to 28 wk), which may have contributed to the late-stage cardiac hypertrophy. These results suggested that the sympathetic nervous system (SNS) and the renin-angiotensin-system (RAS) in SHR may contribute to the pathogenesis of hypertension and LVH at the early and late stages, respectively.

Animals↗
PubMed1999

Efficacy of recombinant methioninase in combination with cisplatin on human colon tumors in nude mice.

The present treatment of colon cancer is based on 5-fluorouracil (5-FU). Despite promising results of combining leucovorin or levamisole with 5-FU, the 5-year survival rate of patients with advanced colon cancer has not increased significantly. Colon tumors in vitro have been shown previously to have an elevated requirement for methionine, suggesting a new therapeutic target. In this study, targeting the methionine dependence of colon tumors is effected by recombinant methioninase (rMETase), alone and in combination with cisplatin (CDDP). In vitro results demonstrated that CDDP and rMETase act synergistically on the human colon cancer cell line SW 620, with a combination index (CI) of 0.45, as well as on the human colon cancer cell line Colo 205 with a CI of 0.7. Human colon cancer lines HCT 15, HT 29, Colo 205, and SW 620 growing in nude mice were treated with rMETase to determine an effective dose for depletion of tumor methionine. rMETase at 15 units/g/day for 5 days depleted tumor methionine in all four tumor types to approximately 30% of untreated control. rMETase alone arrested growth of HCT 15 and HT29 in nude mice for 1 week after treatment termination. Colo 205 and SW 620 were partially arrested by rMETase. However, CDDP in combination with rMETase resulted in tumor regression of Colo 205 and growth arrest of SW 620 in nude mice. The ratio of the treated:control group (T:C) tumor weights for Colo 205 was 8% when CDDP was given on day-5, followed by treatment on days 5-9 with rMETase. This treatment schedule resulted in two of the six animals having no detectable tumor when the experiment was terminated on day 16. SW620 was resistant to CDDP alone and only partially sensitive to rMETase alone. However, when SW 620 was treated with rMETase from days-5 to -9 and CDDP on day-5, tumor growth was arrested. The results demonstrate that rMETase used simultaneously in combination with CDDP had significant antitumor efficacy in colon cancer in vitro and in vivo. The data suggest a novel and promising therapeutic approach by targeting the elevated methionine dependence of colon cancer.

Animals↗
PubMed1999

Studies on activities of invariant chain peptides on releasing or exchanging of antigenic peptides at human leukocyte antigen-DR1.

An invariant chain peptide (Ii77-92; YRMKLPKSAKPVSQMR; 'Ii-Key') enhances 10-50 times baseline levels, the presentation of synthetic antigenic peptides to murine T cell hybridomas, by an exchange mechanism at cell surface MHC class II molecules. Two differing activities, to promote the release of antigenic peptide in the presence or absence in solution of a second antigenic peptide, were characterized with truncation homologs through assays for release or binding of human myelin basic protein biotinylated (*) peptide 90-102 on purified HLA-DR1: 1) release of bound hMBP *peptide from DR1 in the presence or absence of free hMBP peptide in solution, 2) exchange of hMBP *peptide from solution with hMBP peptide on DR1, and 3) binding of hMBP *peptide to 'empty' DR1. Peptides such as Ii81-88, LPKSAKPV, released prebound hMBP *peptide from DR1 without free hMBP peptide in solution. They also exchanged hMBP *peptide from solution for prebound hMBP peptide. Peptides including hIi77-83, LRMKLPK, released hMBP *peptide only when free hMBP peptide was in solution. Nevertheless, hIi77-85, LRMKLPKPP, released hMBP peptide without hMBP peptide in solution. Either type of peptide accelerated hMBP *peptide binding to 'empty' DR1. Competitive binding assays with hMBP *peptide or several *Ii-Key truncation homologs, with respective not biotinylated forms, demonstrated that the Ii77-83, LRMKLPK, binding site was distinct from the HLA-DR1 antigenic peptide binding site.

Amino Acid Sequence↗
PubMed1999

Hydatid liver disease as a cause of recurrent pancreatitis.

Intrabiliary rupture of a hydatid liver cyst is infrequently reported, but may present with symptoms of choledocholethiasis or cholangitis. We report a case of hydatid liver disease presenting as recurrent pancreatitis, and discuss its clinical, radiological and surgical treatments. Hydatid liver disease has a diverse clinical spectrum, and a diagnosis of acute pancreatitis should be considered in patients with hydatid liver disease presenting with unexplained abdominal pain.

Abdominal Pain↗
PubMed1999

Serum leptin levels and adiposity in adult Chinese: a preliminary observation.

OBJECTIVE: To establish normal serum leptin levels in Chinese and investigate the relationship between serum leptin levels and body fat, gender, age and androgen. METHODS: Serum leptin levels were measured in 77 lean (BMI < 25) and 28 overweight or obese (BMI > or = 25) subjects by a radioimmunoassay (RIA) method. RESULTS: The serum leptin levels in lean Chinese were 2.15 +/- 1.46 ng/ml in male and 7.85 +/- 3.60 ng/ml in female, which are similar to those of Caucasians, while in overweight or obese ones, the levels were 4.87 +/- 3.47 ng/ml and 16.59 +/- 6.92 ng/ml respectively, lower than those in Caucasians. A 2-3 times higher leptin concentrations were found in women than in men in both conditions. Even when the number of lean males was expanded to 79 subjects aged from 17-80 years, no significant leptin-age relationship was found. Despite 25% of obese subjects manifested a relative deficiency of leptin, as a whole, leptin levels in both men and women were significantly correlated with BMI (r = 0.69, P < 0.001 in male and r = 0.63, P < 0.001 in female). CONCLUSIONS: Serum leptin levels in Chinese lean people are similar to those in Caucasians and in both lean and obese groups, the leptin levels are correlated with BMI, suggesting that the great majority of the obese patients are resistant to endogenous leptin. Those who are relatively deficient of leptin may become a group of good candidates for leptin treatment in the future.

Adult↗