Biomedical subjects

Xiang Wang

Publications and source records attributed to Xiang Wang.

At least 91 records · Page 5Linked to original sources

PubMed2003

An overactivated ATR/CHK1 pathway is responsible for the prolonged G2 accumulation in irradiated AT cells.

Induction of checkpoint responses in G1, S, and G2 phases of the cell cycle after exposure of cells to ionizing radiation (IR) is essential for maintaining genomic integrity. Ataxia telangiectasia mutated (ATM) plays a key role in initiating this response in all three phases of the cell cycle. However, cells lacking functional ATM exhibit a prolonged G2 arrest after IR, suggesting regulation by an ATM-independent checkpoint response. The mechanism for this ataxia telangiectasia (AT)-independent G2-checkpoint response remains unknown. We report here that the G2 checkpoint in irradiated human AT cells derives from an overactivation of the ATR/CHK1 pathway. Chk1 small interfering RNA abolishes the IR-induced prolonged G2 checkpoint and radiosensitizes AT cells to killing. These results link the activation of ATR/CHK1 with the prolonged G2 arrest in AT cells and show that activation of this G2 checkpoint contributes to the survival of AT cells.

Alkaloids↗

PubMed2003

Total synthesis of the salicylate enamide macrolide oximidine II.

The asymmetric synthesis of the salicylate enamide macrolide oximidine II is reported. The synthesis involves a highly regio- and stereoselective ring-closing metathesis of a bis-diene substrate to construct the macrocyclic triene core. Copper(I)-mediated amidation of a (Z)-vinyl iodide was employed to attach the enamide side chain.

Alkenes↗

PubMed2003

Combination therapy of malononitrilamide FK778 with tacrolimus on cell proliferation assays and in rats receiving renal allografts.

BACKGROUND: Malononitrilamide FK778, an analogue of leflunomide's active metabolite, is a promising novel small molecule with immunosuppressive and immunomodulatory properties. In this study, we evaluated the ability of combination therapy of FK778 with tacrolimus to inhibit lymphocyte proliferation and to prevent acute allograft rejection. METHODS: Proliferation assay was used to evaluate the effect of FK778 plus tacrolimus on murine splenocytes, monkey lymphocytes, and human peripheral blood mononuclear cells, after activation with T or B cell-specific mitogens. A rat kidney transplantation model was used to evaluate the ability of FK778 combined with tacrolimus to prolong allograft survival. Median-effect principle and combination index (CI) were used to determine synergism, summation, or antagonism. RESULTS: A total of 58 combinations of FK778 plus tacrolimus were evaluated. Of the combinations tested, 82.8% (24/29) produced additive to synergistic effects in B cells, whereas 79.3% (23/29) produced moderate antagonistic effects in T cells. A concomitant 14-day therapy of FK778 (10 mg/kg/day) and tacrolimus (1 mg/kg/day) synergistically prolonged renal allograft survival to 25.5+/-5.9 days (CI=0.458). However, when addition of FK778 to tacrolimus therapy was delayed to day 7 after transplantation, a strong synergism was obtained (mean survival time=74.9+/-14.8 days, CI<0.001). CONCLUSIONS: This study demonstrates that the combination of FK778 with tacrolimus in vitro produces synergistic inhibition on B-cell proliferation but not on T cell proliferation in mice, nonhuman primates, and humans. When the addition of FK778 treatment was delayed to day 7 after transplantation, a strong synergism was produced in prolongation of renal allograft survival in the rat.

Alkynes↗

PubMed2003

Significant prolongation of renal allograft survival by delayed combination therapy of FK778 with tacrolimus in nonhuman primates.

BACKGROUND: Malononitrilamide 715 (FK778) is a new class of low-molecular-weight immunosuppressant that is a derivative of the active metabolite of leflunomide, A77 1726. In this study, the authors evaluated the combined effect of FK778 with tacrolimus in prevention of renal allograft rejection in Vervet monkeys. METHODS: Male Vervet monkeys were obtained from Caribbean Primates Ltd. Donor and recipient monkeys were from different breeding colonies. Eleven groups (n>or=4 per group) were involved in this study. FK778 and tacrolimus were administered orally for 60 days according to protocol. RESULTS: Naive controls rejected renal grafts, with a median survival time (MST) of 8.0 days in group 1. When recipient monkeys were treated with tacrolimus 1.0 mg/kg/day in group 2 or FK778 2.5 mg/kg/day in group 3, the MST was 16.0 days (P=0.001) and 11.0 days (P=0.266), respectively. Combination therapy of these two agents at the same doses immediately after transplantation resulted in an MST of 25.0 days (P=0.016) in group 4. When tacrolimus was initiated immediately after transplantation and FK778 treatment was delayed until day 7 after surgery in group 5, recipient survivals were significantly prolonged to 38.0 days (P=0.02). These results were repeatable when FK778 5.0 mg/kg/day (9.0 days, P=0.544 in group 6) was combined with tacrolimus 1.0 mg/kg/day immediately after transplantation (8.0 days, P=0.339) in group 7, or when FK778 was delayed 7 days (60.0 days, P=0.002) in group 8. Furthermore, it was also repeatable when FK778 10 mg/kg/day was combined with tacrolimus 1.0 mg/kg/day with a 7-day delay. CONCLUSIONS: A significant prolongation of renal allograft survival was produced when FK778 administration was delayed by 7 days combined with tacrolimus in Vervet monkeys.

Alanine Transaminase↗

PubMed2003

Palladium-catalyzed intramolecular oxidative alkylation of unactivated olefins.

Reaction of 5,5-dimethyl-8-nonene-2,4-dione catalyzed by PdCl2(CH3CN)2 (5 mol %) in the presence of CuCl2 (2.5 equiv) at room temperature for 3 h formed 2-acetyl-3,6,6-trimethyl-2-cyclohexenone in 96% isolated yield. Palladium-catalyzed intramolecular oxidative alkylation tolerated a range of substitution and was applicable to the synthesis of spirobicyclic compounds and to the cyclization of zeta-alkenyl beta-keto esters.

Journal Article↗

PubMed2003

Synergistic effect of vincristine with tacrolimus or sirolimus in prevention of acute heart allograft rejection in the rat.

The application of multiple immunosuppressive therapy for organ transplantation could enhance therapeutic efficacy, while minimizing the toxicity of individual drugs used in the regimen. In this study, the effect of the combined therapy of vincristine (VCR) with tacrolimus (FK506) or sirolimus (rapamycin, RAPA) was tested in prevention of acute heart allograft rejection in the rat. A Brown Norway (BN, RT 1(n)) to Lewis (LEW, RT 1(1)) rat combination was used in a heart allografting model. VCR was administered intraperitoneally once daily, while FK506 and RAPA were given by gavage once daily for 14 days after transplantation. There were dose-related prolongations of mean survival time (MST) to monotherapy of VCR, FK506, or RAPA. The MST in combination therapy indicated that a synergistic interaction was produced when compared with the respective monotherapies: VCR 0.05 mg/kg/day + FK506 0.5 mg/kg/day (16.00 +/- 1.79 days, P = 0.001; combination index (CI) = 0.557); VCR 0.05 mg/kg/day + FK506 1.0 mg/kg/day (29.00 +/- 10.54 days, P = 0.001; CI = 0.598); VCR 0.05 mg/kg/day + RAPA 0.2 mg/kg/day (17.33 +/- 1.97 days, P = 0.001; CI = 0.500); and VCR 0.05 mg/kg/day + RAPA 0.4 mg/kg/day (21.17 +/- 3.19 days, P = 0.001; CI = 0.838). Combination therapy of VCR and FK506 or RAPA produced synergistic effects in prevention of acute heart allograft rejection in the rat.

Acute Disease↗

PubMed2003

Effects of damage on the orthotropic material symmetry of bovine tibial trabecular bone.

The macroscopic mechanical properties of trabecular bone can be predicted by its architecture using theoretical relationships between the elastic and architectural properties. Microdamage caused by overloading or fatigue decreases the apparent elastic moduli of trabecular bone requiring these relationships to be modified to predict the damaged elastic properties. In the case of isotropic damage, the apparent level elastic properties could be determined by multiplying all of the elastic constants by a single scalar factor. If the damage is anisotropic, the elastic constants may change by differing factors and the material coordinate system could become misaligned with the fabric coordinate system. High-resolution finite element models were used to simulate damage overloading on seven trabecular bone specimens subjected to pure shear strain in two planes. Comparison of the apparent elastic moduli of the specimens before and after damage showed that the reduction of the elastic moduli was anisotropic. This suggests that the microdamage within the specimens was inhomogeneous. However, after damage the specimens exhibited nearly orthotropic material symmetry as they did before damage. Changes in the orientation of the orthotropic material coordinate system were also small and occurred primarily in the transverse plane. Thus, while damage in trabecular bone is anisotropic, the material coordinate system remains aligned with the fabric tensor.

Animals↗

PubMed2003

Transplantation of intact rat gonads using vascular anastomosis: effects of cryopreservation, ischaemia and genotype.

BACKGROUND: A limited store of ovarian follicles is present at birth and its progressive decline during ageing is hastened by alkylating agents and ionizing radiation during treatment for cancer or autoimmune disease. Oligo- or azoospermia can arise for similar reasons in men. There is some experimental evidence showing that targeted gene deletion or drugs to produce hypogonadotrophism can protect germ cells from wastage. Another strategy for conserving fertility is to cryopreserve ovarian or testicular tissue for subsequent transplantation. To maximize gonadal function, it is desirable to preserve whole gonads for transplantation using vascular anastomosis. METHODS AND RESULTS: We investigated this strategy in the rat model. All freshly isotransplanted ovaries (n = 8) survived and resumed follicle growth and secretion and, although ischaemia for 24 h at 4 degrees C did not disrupt ovarian function, the organs had fewer follicles. Four out of seven (57%) cryopreserved transplants survived for > or =60 days, were ovulatory and one pregnancy was established, but the ovarian reserve was compromised by fewer follicles. Ovarian allotransplants were vigorously rejected, even with moderate immunosuppression using cyclosporin A. On the other hand, only three out of seven (42%) fresh testicular isotransplants had active spermatogenesis, and none of the cryopreserved testes was functional. CONCLUSIONS: The effects of gonadectomy in rats can be reversed by isotransplants, but the results are more successful with ovaries than testes, and allotransplants were never successful. Intact cryopreserved ovaries can be restored to function after transplantation with vascular anastomoses.

Anastomosis, Surgical↗

PubMed2003

Evidence of gap junctions in the stable nonobstructed human bladder.

PURPOSE: Gap junctions are thought to synchronize muscle cell actions by promoting intercellular communications. Since it is still a matter of debate whether smooth muscle cells in the bladder are electrically coupled, we investigated the occurrence of gap junctions and the gap junction forming protein connexin 45 in normal human detrusor. MATERIALS AND METHODS: Detrusor smooth muscle was obtained during radical cystectomy in 6 patients. For transmission electron microscopy studies samples were high pressure frozen and cryo-fixed. Additional frozen samples were processed for freeze fracture/freeze fracture immunolabeling analyses or for reverse transcriptase-polymerase chain reaction using primers for connexin 45. Furthermore, a set of samples was fixed with Bouin's solution, embedded in paraffin and used for immunohistochemistry with a polyclonal antibody against connexin 45 as well as for in situ hybridization studies with digoxigenin labeled connexin 45 riboprobes. RESULTS: Ultrastructural and freeze fracture studies showed gap junctions at detrusor smooth muscle cells. However, these gap junctions appeared to be small and irregularly shaped. Reverse transcriptase-polymerase chain reaction and in situ hybridization showed that connexin 45 mRNA was expressed in the detrusor muscularis. Furthermore, we detected prominent connexin 45 immunoreactions at detrusor smooth muscle cells. Freeze fracture immunolabeling techniques revealed connexin 45 signals at small gap junctional plaques. CONCLUSIONS: To our knowledge this study is the first to provide morphological, molecular biological and immunohistochemical evidence that smooth muscle cells of stable human detrusor are electrically coupled through gap junctions. These results may contribute to new concepts in the understanding of bladder physiology.

Aged↗

PubMed2003

Caffeine could not efficiently sensitize homologous recombination repair-deficient cells to ionizing radiation-induced killing.

Caffeine inhibits ATM and ATR, two important checkpoint regulators, abolishes ionizing radiation-induced checkpoint response, and radiosensitizes cells. Radiation-induced DNA double-strand breaks (DSBs) are repaired by two major processes, homologous recombination repair (HRR) and nonhomologous end joining (NHEJ). It remains unclear which repair process, HRR or NHEJ, is affected when the checkpoint responses are abolished by caffeine. In this study we observed the effect of caffeine on gene-targeted DT40 chicken lymphoblast cells. We show that caffeine efficiently abolishes S- and G(2)-phase checkpoint responses after irradiation in all cell lines tested and greatly radiosensitizes wild-type and ATM(-/-) cells, the partially checkpoint-deficient cells. However, caffeine has a much smaller radiosensitizing effect on RAD54(-/-) cells and has no effect on RAD51-deficient cells. RAD51 and RAD54 are the important factors for HRR. Our results indicate that the checkpoint responses abolished by caffeine (S and G(2)) mainly affect HRR, which results in cell radiosensitization.

Animals↗

PubMed2003

Caffeine-induced radiosensitization is independent of nonhomologous end joining of DNA double-strand breaks.

After exposure to ionizing radiation, proliferating cells actively slow down progression through the cell cycle through the activation of checkpoints to provide time for repair. Two major complementary DNA double-strand break (DSB) repair pathways exist in mammalian cells, homologous recombination repair (HRR) and nonhomologous end joining (NHEJ). The relationship between checkpoint activation and these two types of DNA DSB repair pathways is not clear. Caffeine, as a nonspecific inhibitor of ATM and ATR, abolishes multi-checkpoint responses and sensitizes cells to radiation-induced killing. However, it remains unknown which DNA repair process, NHEJ or HRR, or both, is affected by caffeine-abolished checkpoint responses. We report here that caffeine abolishes the radiation-induced G(2)-phase checkpoint and efficiently sensitizes both NHEJ-proficient and NHEJ-deficient mammalian cells to radiation-induced killing without affecting NHEJ. Our results indicate that caffeine-induced radiosensitization occurs by affecting an NHEJ-independent process, possibly HRR.

Animals↗

PubMed2003

Vascularity of hepatic VX2 tumors of rabbits: assessment with conventional power Doppler US and contrast enhanced harmonic power Doppler US.

AIM: To investigate the characteristics of the vascularity of hepatic metastasis. METHODS: Six New Zealand rabbits, weighing averagely 2.7+/-0.4 kg, were selected and operated to establish hepatic VX2 tumor carrier model. Hepatic VX2 tumors were then imaged with conventional B mode US, second harmonic imaging (SHI), color Doppler flow imaging (CDFI), power Doppler imaging (PDI) and harmonic PDI by a transducer S8 connected to HP-5 500 ultrasound system. A kind of self made echo contrast agent was intravenously injected at a dose of 0.01 mL/kg through ear vein, and then the venous passage was cleaned with sterilized saline. RESULTS: Totally, 6 hypoechoic lesions and 3 hyperechoic lesions were found in the six carrier rabbits with a mean size about 2.1+/-0.4 cm under conventional B mode ultrasound, they were oval or round in shape with a clear outline or a hypoechoic halo at the margin of the lesions. Contrast agent could not change the echogenicity of the lesions under conventional B mode and SHI, however, it could greatly increase the flow sensitivity of the lesions under PDI and harmonic PDI. Nutrient artery of these metastatic lesions might also be well depicted under contrast enhanced PDI and harmonic PDI. CONCLUSION: Our result suggested that contrast enhanced PDI, especially harmonic PDI, was a promised method in the detection of vascularity of hepatic tumor nodules.

Animals↗

PubMed2003

Assessment of hepatic VX2 tumors of rabbits with second harmonic imaging under high and low acoustic pressures.

AIM: To investigate the possible clinical application value of second harmonic imaging under low acoustic pressure. METHODS: Six New Zealand rabbits, averaging 2.7+/-0.4 kg, were selected and operated upon to construct hepatic VX2 tumor carrier model. Hepatic VX2 tumors were imaged with B mode Ultrasonography (US), and second harmonic imaging (SHI) under high mechanic index (1.6) and low mechanic index (0.1). Echo agent was intravenously injected through ear vein at a dose of 0.01 mL/kg under B mode US and high MI SHI, and 0.05 mL/kg under low MI SHI, and then the venous channel was cleaned with sterilized saline. All the images were recorded by magnetic optics (MO), and they were analyzed further by at least two independent experienced sonographers. RESULTS: Totally 6 hypoechoic and 3 hyperechoic lesions were found in the six carrier rabbits with a mean size about 2.1+/-0.4 under B mode ultrasound, they were oval or round in shape with a clear outline or a hypoechoic halo at the margin of the lesions. Contrast agent could not change the echogenicity of the lesions under B mode US and SHI under high acoustic pressure. However, it could greatly increase the real time visualization sensitivity of the lesions with SHI under low acoustic pressure. CONCLUSION: Our results suggest that contrast enhanced SHI with low MI and a bubble non-destructive method would be much more helpful than conventional SHI in our future clinical applications.

Air↗

PubMed2003

[Sequence variation of mitochondrial cytochrome b gene and phylogenetic relationships among twelve species of Charadriiformes].

Studies of the phylogenetic relationships of the Charadriiformes have been largely based on conservative morphological characters. During the past 10 years, many studies on the evolutionary biology of birds adopted phylogenetic information obtained from mitochondrial DNA, but few work on the Charadriiformes has been reported to date. Therefore, phylogenetic relationships and classification of the Charadriiformes remains controversial. In this study, we try to shed light on these relationships via DNA sequence analysis of the mitochondrial Cyt b gene in 12 species of Charadriiformes. It was a preliminary study of the origin and evolution of the species by using nucleotide sequence data. Using the well-known PCR techniques, the complete mitochondrial Cyt b gene sequences were amplified and sequenced respectively from Charadrius mongolus, Charadrius alexandrinus, Numenius madagascariensis, Numenius arquat, Numenius phaeopus, Tringa totanus, Tringa glareola, Xenus cineres, Arenaria interpres, Calidris tenuirostris, Recurvirostra avosetts and Haematopus ostralensis. The 1143 bp long DNA sequences of the gene from these species were obtained, in which 381 variable sites were identified without insertions or deletions. The nucleic acid sequence variation of the mitochondrial Cyt b gene was 5.16%-16.01% among these species. Phylogenetic trees constructed using the NJ method, MP method and ML method with Ciconia ciconia as the outgroup indicate that the 12 species of Charadriiformes examined in this study are clustered in two major clades. The first clade includes T. totanus, T. glareola, A. interpres, C. tenuirostris, X. cineres, N. madagascariensis, N. arquata and N. phaeopus. The second one includes C. mongolus, C. alexandrinus, R. avosetts and H. ostralensis. Our molecular data show that the phylogenetic relationships among species of Scolopacidae are consistent with the classification based on morphological studies; R. avosetts and H. ostralensis are relatively closer, and form a sister group, and then form paraphyletic group with a sister group which comprised of C. mongolus and C. alexandrinus. The results support Sibley's opinion of assigning R. avosetts and H. ostralensis which form Recurvirostrinae as a taxon of the Charadriidae, and the Charadriidae dividing into two subfamilies: Recurvirostrinae and Charadriinae respectively.

Animals↗

PubMed2002

Ku affects the CHK1-dependent G(2) checkpoint after ionizing radiation.

There are two major pathways for repairing DNA double strand breaks in mammalian cells: nonhomologous end joining (NHEJ) and homologous recombination repair (HRR). The nonhomologous end joining repair is deficient in cells without Ku, whereas HRR is highly efficient in such cells compared with their wild-type counterparts. The mechanism remains unclear. We reported previously that Ku80(-/-) cells show a stronger ATM-dependent S-phase checkpoint response than Ku80(+/+) cells after ionizing radiation (IR; X-Y. Zhou et al., Oncogene, 21:6377-6381, 2002). We report in this study that Ku80(-/-) cells also show a much stronger G(2) accumulation than Ku80(+/+) cells after IR. The stronger G(2) checkpoint response in Ku80(-/-) cells is ATM independent but is accompanied with a higher activity of CHK1 kinase. Treatment with Chk1 antisense oligonucleotide abolishes the stronger G(2) checkpoint response and sensitizes Ku80(-/-) cells to IR. These data indicate that the stronger G(2) checkpoint response shown in Ku80(-/-) cells is CHK1 dependent and suggest that the CHK1-dependent checkpoint response contributes to the highly efficient HRR in such cells.

Animals↗

PubMed2002

Revelation of a cryptic major histocompatibility complex class II-restricted tumor epitope in a novel RNA-processing enzyme.

CD4+ T-cell responses against human tumor antigens are a potentially critical component of the antitumor immune response. Molecular methods have been devised for rapidly identifying MHC class II-restricted tumor antigens and elucidating the recognized epitopes. We describe here the identification of neo-poly(A) polymerase (neo-PAP), a novel RNA processing enzyme overexpressed in a variety of human cancers, by screening a melanoma-derived invariant chain fusion cDNA library with tumor-reactive CD4+ T lymphocytes. A cryptic nonmutated HLA-DRbeta1*0701-restricted neo-PAP epitope was processed through the endogenous MHC class II pathway. A unique point mutation effected a nonconservative substitution of a leucine for a proline residue at a structurally important site in neo-PAP that was remote from the recognized peptide, revealing a normally silent epitope for immune recognition. Genetic aberrations such as the described point mutation can have unexpected immunological consequences, in this case leading to immune recognition of a distant normal self epitope.

Adult↗

PubMed2002

Ku affects the ATM-dependent S phase checkpoint following ionizing radiation.

Following exposure to genotoxic stress, proliferating cells actively slow down DNA replication through an S phase checkpoint to provide time for repair. The ATM-dependent pathway plays an important role in the S phase checkpoint response following ionizing irradiation. We report that there is a stronger S phase checkpoint response in irradiated Ku80(-/-) cells as compared with their wild-type counterparts, which has no relationship to DNA-dependent protein kinase (DNA-PK) activity but correlates with a higher ATM activity and with more ATM bound to chromatin DNA in such cells. Wortmannin, a nonspecific inhibitor of ATM, not only reduces the higher activity of ATM kinase, but also abolishes the stronger S phase checkpoint response in Ku80(-/-) cells. Furthermore, a specific ATM antisense oligonucleotide abolishes the stronger S checkpoint response in Ku80(-/-) cells and renders these cells practically indistinguishable from Ku80(+/+) cells for this endpoint. These results in aggregate indicate that the stronger S checkpoint in irradiated Ku80(-/-) cells is due to the higher ATM kinase activity.

Androstadienes↗

PubMed2002

Cyclization/hydrosilylation of functionalized 1,6-diynes catalyzed by cationic platinum complexes containing bidentate nitrogen ligands.

A 1:1 mixture of the platinum dimethyl diimine complex [PhN[double bond]C(Me)C(Me)[double bond]NPh]PtMe(2) (4a) and B(C(6)F(5))(3) catalyzed the cyclization/hydrosilylation of dimethyl dipropargylmalonate (1) and HSiEt(3) to form 1,1-dicarbomethoxy-3-methylene-4-(triethylsilylmethylene)cyclopentane (3) in 82% isolated yield with 26:1 Z:E selectivity. Platinum-catalyzed diyne cyclization/hydrosilylation tolerated a range of functional groups including esters, sulfones, acetals, silyl ethers, amides, and hindered ketones. Diynes that possessed propargylic substitution underwent facile cyclization/hydrosilylation to form silylated 1,2-dialkylidene cyclopentanes as mixtures of regioisomers. Diynes that possessed an electron-deficient internal alkyne underwent cyclization/hydrosilylation in moderate yield to form products resulting from silyl transfer to the less substituted alkyne. The silylated 1,2-dialkylidenecyclopentanes formed via diyne cyclization/hydrosilylation underwent a range of transformations including protodesilylation, Z/E isomerization, and [4 + 2] cycloaddition with dieneophiles.

Alkynes↗