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Biomedical subjects

L Cheng

Publications and source records attributed to L Cheng.

At least 451 records · Page 25Linked to original sources
PubMed1977

Comparative stereochemistry in the aziridine ring openings of N-methylmitomycin A and 7-methoxy-1,2-(N-methylaziridino)mitosene.

A useful method was found for the conversion of mitomycin C into N-methylmitomycin A. The latter compound gave only two products on acid hydrolysis, the cis- and trans-1-hydroxy-7-methoxy-2-methylaminomitosenes. This selectivity allowed the cis--trans ratio to be quantitatively determined as 4:1. Such a predominance of the cis isomer is unexpected in view of the trans stereochemistry obtained in the opening of simple aziridines. In order to determine if the 9a-methoxy group of mitomycins controlled the direction of aziridine ring opening 7-methoxy-1,2-(N-methylaziridino)mitosene, which lacks this substituent, was prepared and hydrolyzed in acid. It gave the same two products in a 3:1 cis-trans ratio. In the induction of lambda-bacteriophage in Escherichia coli cis-1-hydroxy-7-methoxy-2-methylaminomitosene was more active than the corresponding trans isomer, but both of these compounds were less active than the aziridinomitosene or the mitomycins. Mitomycin A, mitomycin C, and N-methylmitomycin A were active against P388 leukemia in mice.

Animals↗
PubMed1976

Mechanism of the irreversible inhibition of aspartate aminotransferase by the bacterial toxin L-2-amino-4-methoxy-trans-3-butenoic acid.

The naturally occurring toxin L-2-amino-4-methoxy-trans-3-butenoic (AMB) acid irreversibly inhibits pyridoxal phosphate-linked aspartate aminotransferase. The inhibitor is a substrate for the enzyme, and as such is converted into a highly reactive intermediate which chemically reacts with an active site residue, thus irreversibly inactivating the enzyme. Enzymological and model studies on AMB are presented which enable one to determine the precise mechanism of action of this toxin. The mechanism involves Schiff base formation between the enzyme and toxin followed by alpha-C--H bond cleavage and aldimine isomerization to generate a bifunctional Michael acceptor. This molecule alkylates an active site residue by an addition and elimination route.

Aminobutyrates↗
PubMedDate not supplied

Children of yesterday, today and tomorrow: global implications for child language.

The entire global population is waiting for new opportunities of the new millennium. This paper will report selected global trends; describe briefly children of yesterday, today and tomorrow; detail a case study explaining the multiple challenges of working with children in a multicultural environment and probe into the implications for the future of child language.

Child↗
PubMedDate not supplied

Educating speech-language pathologists for a multicultural world.

This paper presents critical elements and current needs in educating speech-language pathologists for a multicultural world. A proposed paradigm shift in clinical teaching using the UK model is also introduced. In addition, a case study on the American Speech Language Hearing Association's efforts in implementing the Multicultural Action Agenda by networking with the Asian Pacific Islander caucus is described. A survey of multicultural elements in programs in Australia and New Zealand is included. Finally, suggestions for collaboration with those in established professional bodies to meet the increasing needs of a multicultural world are provided.

Cultural Diversity↗
PubMedDate not supplied

Diagnosing invasive cystic hypersecretory duct carcinoma of the breast with fine needle aspiration cytology. A case report.

BACKGROUND: Cystic hypersecretory duct carcinoma (CHC) of the breast, first described in 1984, is a rare variant of duct carcinoma. Histologically it is characterized by the formation of dilated ducts and cysts containing an eosinophilic secretory product resembling thyroid colloid. The lining epithelium of the cysts atypically proliferates to form intraductal carcinoma. Only four cases of invasive cystic hypersecretory carcinoma have been reported. CASE: We present a case of invasive CHC with tumor emboli in many lymphatic spaces and axillary nodal metastases. The lesion was also evaluated by fine needle aspiration. Direct smears with Papanicolaou stain were highly cellular and had abundant, intensely staining, orange-to-gray-green thyroid colloid-like material. Epithelial cells, showing a variety of cellular patterns, were indistinguishable from usual ductal carcinoma cells. These cytologic findings may be characteristic enough to suggest cystic hypersecretory carcinoma. CONCLUSION: The cytologic features of CHC are distinctive and correlate with histology. This was the first presentation of colloidlike secretory material in cytologic material with Papanicolaou stain in such a case. Invasive CHC tends to have aggressive behavior. Cystic hypersecretory hyperplasia coexisted in this case.

Adult↗
PubMedDate not supplied

Fine needle aspiration cytology of malignant phyllodes tumor with liposarcomatous stroma of the breast. A case report.

BACKGROUND: Liposarcoma arising within a phyllodes tumor is extremely rare. To the best of our knowledge, a malignant phyllodes tumor with liposarcomatous stroma diagnosed by fine needle aspiration (FNA) has not been reported before. CASE: A 39-year-old female had a malignant phyllodes tumor with liposarcomatous stroma diagnosed by FNA cytology. Two subtypes of liposarcomatous stroma, including lipomalike differentiated and myxoid, were found in the aspirates. The cytologic findings were very representative of the histologic features. CONCLUSION: It is very important to recognize the cytologic features of such rare tumors. An accurate diagnosis preoperatively by FNA permits better therapy planning.

Adult↗
PubMedDate not supplied

Peritoneal washing cytology of ovarian tumors of low malignant potential: correlation with surface ovarian involvement and peritoneal implants.

OBJECTIVE: To correlate the cytologic diagnoses of peritoneal washings (PWs) with histologic findings of ovarian tumors of low malignant potential (LMP). METHODS: PW cytology from 90 patients with histologically confirmed ovarian tumors of LMP were reviewed and correlated with histologic findings. RESULTS: In 90 LMP tumor patients who underwent PW, cytologic diagnoses were reported as positive in 30 (33%) cases, atypical in 5 (6%) cases and negative in 55 (61%) cases. On review of the five atypical cases, three were reclassified as negative and two as positive. Peritoneal washings were positive in 20 (33%) of 60 patients with serous LMP tumors, 12 (44%) of 27 patients with mucinous LMP tumors and none of 3 patients with mixed LMP tumors. The presence of positive cytology was highly indicative of surface ovarian involvement or peritoneal implants in completely staged or selectively biopsied patients (P < .0001). Of 60 (67%) patients who had a staging laparotomy, positive PWs were seen in 3 (75%) of 4 cases with surface involvement only, 13 (94%) of 14 cases with peritoneal implants only, 3 (100%) of 3 cases with both peritoneal implants and ovarian surface involvement, and 9 (23%) of 39 cases without evidence of surface involvement or peritoneal implants. PWs were positive in 4 (13%) of 30 cases without staging laparotomy. CONCLUSION: PW cytology is a sensitive indicator of peritoneal dissemination of ovarian tumors of LMP. In addition, PWs will detect a high percentage of patients with subclinical intraperitoneal extension of such tumors and should be used routinely in the staging of ovarian tumors of LMP.

Female↗
PubMedDate not supplied

Increased expression of membrane-type matrix metalloproteinase and preferential localization of matrix metalloproteinase-2 to the neointima of balloon-injured rat carotid arteries.

BACKGROUND: Remodeling of the injured vascular wall is dependent on the action of several extracellular proteases. Previous studies have shown that expression of matrix metalloproteinases (MMP-2 and MMP-9) is upregulated after vascular injury and that MMP-2 is required for the migration of cultured vascular smooth muscle cells across complex extracellular matrix barriers. The present study examined changes in the expression of membrane-type metalloproteinase (MT-MMP-1), a putative regulator of MMP-2, in the tissue localization of MMP-2, and in the expression of activated and latent forms of MMP-2 and the tissue inhibitor of metalloproteinases, TIMP-2, in rat carotid arteries subjected to balloon catheter injury. METHODS AND RESULTS: MT-MMP-1 mRNA levels increased sixfold after 3 days of injury, coinciding with an increase in MMP-2 activation assessed by gelatin zymography. Western blotting and gelatin zymography showed an increase in MMP-2 protein levels beginning 5 to 7 days after injury; immunocytochemistry and Western blotting showed that the increase occurred preferentially in the developing neointima. CONCLUSIONS: These results show that increased expression of MT-MMP-1 and activation of MMP-2 occurs early after injury to the rat carotid artery and that at later times MMP-2 is preferentially localized to the developing neointima.

Angioplasty, Balloon↗
PubMedDate not supplied

Chemical composition and behavioral responses of the marine insect Halobates hawaiiensis (Heteroptera: Gerridae).

Halobates is the only insect genus with representatives in the open ocean. How adults find one another at sea has long been an intriguing issue. Since chemical communications have been demonstrated in a related marine veliid Trochopus, and laboratory bioassays indicated behavioral differences between males and females when insect extracts were presented, we carried out similar studies on Halobates. Analyses of surface lipid constituents of female and male Halobates hawaiiensis revealed marked differences. Palmitic and oleic acid, major constituents in the male extracts, were absent in the female extract, whereas nonacosenol, dominating the female extracts, was not detected in the male extracts. Analyses of nymphal extracts indicated an intermediate chemical profile. Surface waxes of all insect stages investigated showed nonacosanol and isononacosanol to be main components. "Headspace" analyses of airborne chemicals showed high levels of 4-hydroxy-4-methyl-2-pentanone and benzaldehyde from the male, whereas benzyl alcohol was the main component in the female mixture.

Aldehydes↗
PubMedDate not supplied

Review of latex allergy.

BACKGROUND: Allergy to latex has become an increasing concern to many patients and health care providers. Health care providers should become aware of this problem and develop strategies for treatment and prevention. METHODS: We searched MEDLINE from 1990 to 1998 for the topics of latex allergy using the key words "latex" and "allergy." Other sources were found from back-referencing these references and from the Internet. RESULTS: Latex allergy is emerging as a clinical and occupational health problem. Understanding the clinical and immunologic features, which range from dermatitis to anaphylaxis, can provide the basis of preventive and therapeutic strategies. CONCLUSION: The clinician should be able to recognize latex allergy and educate patients about the potential hazards of latex-containing products. Providers can develop a plan for protecting patients and health care staff from latex exposure as well as treating allergic reactions when they occur.

Humans↗