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Biomedical subjects

B X Chen

Publications and source records attributed to B X Chen.

At least 37 records · Page 2Linked to original sources
PubMed1993

Immunoassay of taxol and taxol-like compounds in plant extracts.

A mouse monoclonal anti-taxol antibody (69E4A8E) and a rabbit polyclonal anti-taxol antiserum were used to measure taxol levels in plant extracts in a double-blind experiment in conjunction with assays by HPLC. 69E4A8E was previously shown by ELISA to be specific for taxol with only a slight cross reaction with another bioactive compound, cephalomannine; the antiserum, on the other hand, was, by radioimmunoassay (RIA), essentially equally reactive with taxol and cephalomannine. Immunoassays of the plant extracts gave results in agreement with that found by HPLC, suggesting that the antibodies can be used in simple routine procedures for the quantification of taxol or taxol-like compounds in extracts of plants or other potential natural sources.

Animals↗
PubMed1993

An improved technique for bloodless hepatic resection on in situ cold perfused liver.

An improved technique for bloodless hepatic resection using in situ isolation and asanguinous hypothermic perfusion was described to deal with huge liver tumors involved in the liver hilum, the main hepatic veins and retrohepatic inferior vena cava. The original Fortner's technique was modified, including the choice of incision; semi-isolated perfusion of the liver portion preserved through the single portal vein; suprahepatic outlet of the perfusate and the shortening of the period of hepatic ischemia by reperfusion of hepatic artery prior to the repair or reconstruction of the portal vein. The initial successful experience of the technique applied to 2 pediatric cases with giant liver tumors was reported, and the indications, intraoperative and early postoperative courses were discussed.

Child↗
PubMed1992

Evidence for a functional receptor for cyclosporin A on the surface of lymphocytes.

Cyclosporin A (CsA) is an immunosuppressive agent that inhibits the synthesis of lymphokines by T lymphocytes at the level of transcription. A cytoplasmic protein, cyclophilin, is the most thoroughly studied CsA-binding protein, but its ubiquitous presence in cells of all types raises questions about its role in immunosuppression. In an attempt to ascertain the presence of a cell surface receptor, we synthesized two polyvalent macromolecular CsA derivatives, CsA-BBa-ovalbumin and CsA-BBa-aminodextran (CBD), from the product of the photochemical reaction of CsA and 4-benzoylbenzoic acid (CsA-BBa). (i) They inhibited the peptidylprolyl cis-trans isomerase activity of cyclophilin and the synthesis of interleukin 2 by phorbol ester-activated EL-4 cells. (ii) CBD also inhibited interleukin 2 secretion by Con A-activated T-cell-enriched mouse splenocytes. 4-Benzoylbenzoic acid (BBa)-aminodextran and aminodextran were inactive. (iii) Direct binding and competition studies with [3H]CsA indicated that CBD does not enter EL-4 cells (i.e., it acted at the surface). (iv) CBD caused agglutination of EL-4 cells, murine B and T lymphocytes, human thymocytes, and two T-cell hybridomas. Agglutination was inhibited by a monoclonal antibody to CsA and by CsA and CsA-BBa, but not by BBa. No agglutination was seen with BBa-aminodextran or aminodextran. HeLa cells, Vero (monkey kidney) cells, a mouse plasmacytoma, COS cells, and a poorly differentiated B-cell lymphoma were not agglutinated. (v) EL-4 cells failed to be agglutinated after treatment with trypsin or chymotrypsin. Specific agglutination was again possible after incubation for 5 h at 37 degrees C in the absence of enzyme. (vi) CBD covalently linked to crosslinked agarose beads inhibited interleukin 2 production by phorbol ester-stimulated EL-4 cells. No activity was seen if cell-to-bead contact was prevented by a 0.02-microns microporous filter that did not interfere with the passage of CBD. Our findings support the presence of a functional receptor on the surface of selected cells of the immune system.

Animals↗
PubMed1992

Properties of a monoclonal antibody for the detection of abasic sites, a common DNA lesion.

The abasic site is one of the most frequent changes occurring in DNA and has been shown to be lethal and mutagenic. An abasic site in DNA can be tagged by reaction with O-4-nitrobenzylhydroxylamine (NBHA), resulting in the formation of an oxime linkage between the abasic site and the NBHA moiety. In order to measure NBHA-tagged abasic sites, a monoclonal antibody was elicited against a 5'-phosphodeoxyribosyl O-4-nitrobenzyl hydroxylamine-BSA conjugate. The antibody was specific for the NBHA residue as demonstrated by hapten inhibition, with IC50 values for 5'-phosphodeoxyribosyl-NBHA, deoxyribosyl-NBHA, ribosyl-NBHA and NBHA of 0.3 microM, 5 microM, 5 microM and 7 microM, respectively. Other haptens examined, including benzylhydroxylamine, 5'-phosphodeoxyribosyl-, deoxyribosyl-, and ribosyl-benzylhydroxylamine, showed no inhibition even at 1 mM. The antibody showed high specificity for NBHA-modified AP sites in DNA and exhibited no cross reactivity with normal DNA bases, otherwise-modified DNA bases or unmodified AP sites. Using a direct ELISA assay, the antibody detected 1 AP site (after NBHA-modification) per 10,000 base-pairs or approximately 10 femtomoles of AP sites in DNA. DNA lesions were detectable in 60Co gamma-irradiated DNA at a dose as low as 10 rad (0.1 Gy) and the production of antibody detectable sites was proportional to the gamma-ray dose. Since NBHA reacts with lesions containing an aldehyde group, the simplicity and sensitivity of the antibody assay should provide a useful method for the quantitation of AP sites or other DNA lesions containing an aldehyde group.

Animals↗
PubMed1992

Treatment of hallux valgus in China.

This is a review of the treatment of hallux valgus based on the paper material submitted to the First and Second Sino-American Conferences on Foot Disorders held in Beijing in 1987 and 1990. The data consisted of 676 cases (979 feet) from 10 major hospitals in China. There were 122 men and 554 women, giving a male to female ratio of 1:45. Sixty-nine (10%) cases had a family history of hallux valgus and 120 cases (18%) were associated with hammer toe deformity. The age ranged from 16-85 years with an average of 42. Among the 412 female cases (78.5%) at the age of 20-35, 339 (82.3%) had the history of wearing high heeled and narrow tipped shoes. Osteoarthritis changes of the first M-P joint were seen in 31 cases, all above the age of 60. 615 cases (90.9%) were treated surgically for pain relief and only 25 cases (3.7%) at the age of 20-30 had the deformity corrected for cosmetic purpose. The surgical procedures employed were bunionectomy (Silver's operation, 39 feet), Keller's operation (344 feet), McBride's operation (239 feet) and a variety of osteotomies of the first metatarsal (295 feet). Joplin and Lapidus operations were used by one author in 5 and 2 cases respectively. Overall excellent and good results were obtained in 609 cases (90%) during the follow-up of 1-14 years.

Adolescent↗
PubMed1991

Immunological studies of osteoarthritis in bipedal rats.

Osteoarthritis (OA) models in bipedal rats were used to study the immune response, including the changes of IgG, antibody dependent cytotoxicity tests toward articular chondrocytes and the matrix. The results revealed significant difference between the bipedal and the quadruped rats. Immunological studies have proved that the OA model of bipedal rats is appropriate for the study of OA.

Animals↗
PubMed1990

Pertussis toxin and 4-aminopyridine differentially affect the hypnotic-anesthetic action of dexmedetomidine and pentobarbital.

Dexmedetomidine, a highly selective and potent agonist at alpha-2 adrenoceptors, produces a hypnotic-anesthetic action in rats. The mechanism for this response may involve an inhibitory G-protein and increased conductance through a potassium channel. To investigate this, the effects of pertussis toxin, a specific inactivator of inhibitory G-proteins, and 4-aminopyridine, a blocker of potassium channels, on the hypnotic-anesthetic response to dexmedetomidine were studied in rats. Pertussis toxin and 4-aminopyridine both decreased the hypnotic-anesthetic action of dexmedetomidine in a dose-dependent fashion. To preclude the possibility that pertussis toxin and 4-aminopyridine attenuated the hypnotic-anesthetic action of dexmedetomidine via indirect central nervous system excitation, the effects of pertussis toxin and 4-aminopyridine on the hypnotic-anesthetic action of pentobarbital also were assessed. Pentobarbital-induced hypnosis was not attenuated by either treatment. These results suggest that the receptor-effector mechanism for the hypnotic-anesthetic action of dexmedetomidine involves an inhibitory G-protein and increased conductance through a potassium channel.

4-Aminopyridine↗
PubMed1990

Operative technique for carcinoma of the oesophagus after distal subtotal gastrectomy: a new method using the residual stomach to reconstruct the alimentary tract.

The stomach is the organ most often chosen for substitution following resection of the oesophagus for carcinoma and this method has given good results. The mode of reconstruction of the alimentary tract in oesophageal cancer patients with previous distal gastrectomy presents a surgical problem. Usually the colon or jejunum is chosen as an alternative for substitution in such patients. We report a new technique used in our unit on 30 patients with previous distal subtotal gastrectomy. This involves using the residual stomach for reconstruction and transposing the spleen and tail of the pancreas into the left thoracic cavity in order to preserve the blood supply to the stomach. The entire procedure is performed through the left chest. We explored 35 patients originally, but five were found to be unresectable at operation. Of the remaining 30 patients, the tumour locations were: upper thoracic (1), midthoracic (24) and lower thoracic (5). The anastomotic sites were: above aortic arch (23), below aortic arch (5) and neck (2). The technical success of this procedure was good with no deaths in the immediate post-operative period. There were three anastomotic leakages which all healed after thoracic drainage and a feeding jejunostomy.

Adult↗
PubMed1990

Characterization of a monoclonal antibody to thymidine glycol monophosphate.

A monoclonal antibody specific for thymine glycol (TG) in irradiated or OsO4-treated DNA was obtained by immunizing with thymidine glycol monophosphate (TMP-glycol) conjugated to bovine serum albumin by a carbodiimide procedure. Screening by dot-immunobinding and enzyme-linked immunosorbant assay (ELISA) procedures gave eight clones that bound OsO4- treated DNA. One of them, 2.6F.6B.6C, an IgG2a kappa, was characterized further. Hapten inhibition studies with OsO4-treated DNA showed that the antibody was specific for TMP-glycol. Among the various inhibitors tested, inhibition was in the order TMP-glycol greater than 5,6-dihydrothymidine phosphate greater than TMP greater than thymidine glycol greater than TG. Inhibition by 5,6-dihydrothymidine, thymidine, thymine, AMP, and CMP was negligible. In OsO4-treated DNA, as few as 0.5 TG per 10,000 bp were detectable by direct ELISA. Inhibition assays could detect as few as 1.5 TG per 10,000 bp. The antibody was equally reactive with native or denatured DNA containing TG. Among the X-irradiated homopolymers dC, dA, dG, and dT, only dT reacted with the antibody. Using an ELISA, the antibody could detect damage in irradiated DNA at the level of 20 Gy. Thus the antibody is of potential use in assays for DNA damage caused by X rays or other agents that damage DNA by free radical interactions.

Antibodies, Monoclonal↗
PubMed1989

Dexmedetomidine produces a hypnotic-anesthetic action in rats via activation of central alpha-2 adrenoceptors.

Dexmedetomidine, a highly selective and potent alpha-2 adrenoceptor agonist, reduces halothane anesthetic requirements by over 90% in rats. The present study examined whether dexmedetomidine produces a hypnotic-anesthetic action in rats. Dexmedetomidine induced a hypnotic-anesthetic state in rats characterized by loss of righting reflex at doses greater than or equal to 0.1 mg/kg. This response was dose-dependent between 0.1 and 3 mg/kg. Alpha-2 adrenoceptor antagonists that cross the blood-brain barrier (antipamezole and idazoxan) decreased the hypnotic-anesthetic action of dexmedetomidine in a dose-dependent fashion. In contrast, the alpha-2 antagonist, L-659,066, which does not penetrate into the CNS did not affect dexmedetomidine-induced hypnosis. Antagonists for the other adrenoceptors not only failed to reduce the hypnotic-anesthetic action of dexmedetomidine but in some cases even potentiated this effect. Thus, prazosin, an alpha-1 adrenoceptor antagonist, significantly enhanced the hypnotic-anesthetic property of dexmedetomidine. Antagonists with beta-2 receptor blocking properties also enhanced dexmedetomidine-induced hypnosis. Selective beta-1 receptor antagonists did not affect the hypnotic action of dexmedetomidine. These results suggest that dexmedetomidine produces a hypnotic-anesthetic action in rats via activation of central alpha-2 adrenoceptors.

Adrenergic alpha-Agonists↗
PubMed1989

Oxygen free radical in human osteoarthritis.

The xanthine oxidase catalysed release of superoxide free radicals (O2-) from endogenous hypoxanthine was determined in homogenates of synovium obtained from three groups of patients, those undergoing primary or revision total hip replacement (THR) for osteoarthritis and those undergoing arthroscopy of the knee for semilunar disc injuries. The concentrations of hypoxanthine in homogenates obtained during THR were found to be significantly higher than those in the group with semilunar disc injuries. The results suggest that there is a greater predisposition to free radical release and tissue damage in osteoarthritis.

Free Radicals↗
PubMed1989

Pharmacologic characterization of the receptor mediating the hypnotic action of dexmedetomidine.

The anesthetic-reducing property of medetomidine far exceeds that seen with other alpha 2-adrenergic agonists (e.g., clonidine). This study examined whether medetomidine possesses hypnotic-anesthetic actions. Dexmedetomidine (the d-enantiomer of medetomidine) induced loss of righting reflex in rats (i.e., hypnosis) at doses greater than 100 micrograms/kg i.p.; sleep-time was dose-dependent up to 1000 micrograms/kg i.p. The l-enantiomer of medetomidine (MPV-1441) did not induce hypnosis even when administered up to 30,000 micrograms/kg i.p. The centrally-active alpha 2-receptor antagonists, atipamezole (MPV-1248) and idazoxan, dose-dependently decreased the hypnotic action of dexmedetomidine. The peripherally-active alpha 2-receptor antagonist, DG-5128, did not reduce dexmedetomidine-induced hypnosis. The stereospecificity of dexmedetomidine's hypnotic action and its dose-dependent attenuation by alpha 2-antagonists confirmed the involvement of alpha 2-receptors in this effect. The finding that only alpha 2-antagonists with central activity attenuate the hypnotic action of dexmedetomidine, suggests that the mediating alpha 2-receptor is located in the central nervous system. In summary, this study suggests that dexmedetomidine induces hypnosis in rats by activating central alpha 2-adrenergic receptors. This study also suggests that alpha 2-antagonists can be used to reverse the hypnotic effects of dexmedetomidine.

Adrenergic alpha-Agonists↗
PubMed1985

Semen-induced ovulation in the bactrian camel (Camelus bactrianus).

Bactrian camels (63 female female, 8 male male) were used in the breeding season to determine the factors that will induce ovulation. After insemination of semen samples into the vagina, the ovaries were checked for ovulation by rectal palpation. The results indicated that ovulation was induced by the seminal plasma, but not by the spermatozoa, and the incidence of ovulation after insemination was 87%. Most of the females (66%) had ovulated by 36 h after insemination and the rest by 48 h, as after natural service. The least amount of semen required to elicit ovulation was about 1.0 ml. Intramuscular injections of LH, hCG and LHRH also caused ovulation, even in females that had not ovulated in response to insemination.

Animals↗