Biomedical subjects

H M Chan

Publications and source records attributed to H M Chan.

At least 37 records · Page 2Linked to original sources

PubMed2000

Mercury in the traditional diet of indigenous peoples in Canada.

Traditional food of indigenous people in Canada, particularly fish and marine mammal meat, has mercury (Hg) concentrations exceeding the Canadian consumption guideline level of 0.5 microg/g. Health effects of Hg in traditional food are, therefore, a concern. We conducted contaminant exposure assessments in 28 indigenous communities in Canada. Hg exposure was greatest among communities with high use of marine mammals as food. Exposure among other communities was variable. Recent adoption of a lower intake guideline for women of reproductive age and by Health Canada may decrease the use of traditional food, and could result in other health problems, such as increased risk of diabetes and cardiovascular disease.

Journal Article↗

PubMed2000

Functional interaction between nucleosome assembly proteins and p300/CREB-binding protein family coactivators.

The p300/CREB-binding protein (CBP) family of proteins consists of coactivators that influence the activity of a wide variety of transcription factors. Although the mechanisms that allow p300/CBP proteins to achieve transcriptional control are not clear, it is believed that the regulation of chromatin is an important aspect of the process. Here, we describe a new level of p300-dependent control mediated through the functional interaction between p300/CBP and members of the family of nucleosome assembly proteins (NAP), which includes NAP1, NAP2, and TAF1. We find that NAP proteins, which have previously been implicated in the regulation of transcription factor binding to chromatin, augment the activity of different p300 targets, including p53 and E2F, through a process that is likely to involve the physical interaction between p300 and NAP. NAP proteins can form oligomers, and the results show that NAP proteins can bind to both core histones and p300 coactivator proteins, perhaps in a multicomponent ternary complex. We also provide data in support of the idea that histones can influence the interaction between p300 and NAP protein. These results argue that NAP is a functionally important component of the p300 coactivator complex and suggest that NAP may serve as a point of integration between transcriptional coactivators and chromatin.

Adenovirus E2 Proteins↗

PubMed2000

Environment and contaminants in traditional food systems of northern indigenous peoples.

Traditional food resources of indigenous peoples are now recognized as containing a variety of environmental contaminants which reach food species through local or long-range transport avenues. In this chapter we review the published reports of contaminants contained in traditional food in northern North America and Europe as organochlorines, heavy metals, and radionuclides. Usually, multiple contaminants are contained in the same food species. Measurement of dietary exposure to these environmental contaminants is reviewed, as are major issues of risk assessment, evaluation, and management. The dilemma faced by indigenous peoples in weighing the multiple nutritional and socioeconomic benefits of traditional food use against risk of contaminants in culturally important food resources is described.

Chlordan↗

PubMed2000

The influence of nutrition on methyl mercury intoxication.

This article reviews progress in the research of methyl mercury (MeHg) and nutrient interactions during the past two decades. Special emphasis is placed on the following three major areas: a) effects on kinetics, b) effects on toxicity, and c) possible mechanisms. Dietary information is not usually collected in most epidemiologic studies examining of the effects of MeHg exposure. However, inconsistency of the MeHg toxicity observed in different populations is commonly attributed to possible effects of dietary modulation. Even though the mechanisms of interaction have not been totally elucidated, research in nutritional toxicology has provided insights into the understanding of the effects of nutrients on MeHg toxicity. Some of this information can be readily incorporated into the risk assessment of MeHg in the diets of fish-eating populations. It is also clear that there is a need for more studies designed specifically to address the role of nutrition in the metabolism and detoxification of MeHg. It is also important to collect more detailed dietary information in future epidemiologic studies of MeHg exposure.

Animals↗

PubMed1999

The relative estrogenic activity of technical toxaphene mixture and two individual congeners.

Toxaphene is the most abundant persistent organic pollutant in the Arctic and in the Great Lakes. Toxaphene technical mixture (Tox) applied as a pesticide consists of over 800 congeners. Through processes of environmental degradation, selected metabolism, and bioaccumulation, two congeners are prominent in humans; 2-exo,3-endo,5-exo,6-endo,8,8,10,10-octachlorobornane (T2 or Parlar 26) and 2-exo,3-endo,5-exo,6-endo,8,8,9,10, 10-nonachlorocamphene (T12 or Parlar 50). The MCF7-E3 human breast cancer cell model was used to screen for the estrogenic activities of Tox, T2, and T12. A concentration of 10 microM was required by all three compounds to elicit an estrogenic response as indicated by a proliferative effect (PE) upon the cells. The congeners, however, showed significantly different PEs from Tox. Both T2 and T12 had a lower PE (16 and 30%) and than Tox, and T2 had a higher PE than T12 (19%). Results from binary combination studies showed that the effects of Tox, T2, and T12 were additive. Tox, T2, and T12 had no significant effects on estrogen receptor and progesterone receptor levels. Our results suggest that the two environmental prevalent congeners had lower estrogenic activities than Tox and there is no synergistic effect.

Camphanes↗

PubMed1999

Inorganic mercury pre-exposures protect against methyl mercury toxicity in NSC-34 (neuron x spinal cord hybrid) cells.

A neuron spinal chord x hybrid (NSC-34) cell culture derived from neonatal mouse was characterized for studies on mercury toxicity. Exposure of NSC-34 cells to methyl mercury chloride (MeHgCl) (0-16 microM) resulted in significant dose-dependent cell damage and death (P < 0.05). MeHgCl was more toxic than inorganic mercury (Hg2+) for both the NSC-34 cells and its parent neuroblastoma cell line N18TG-2 (P < 0.05). Hg2+, but not ZnCl2 or MeHg exposure induced metallothionein (MT) (P < 0.05). To mimic the increase in Hg2+ in the mammalian brain with long term MeHg exposure, the cells were treated with 1 microM mercuric chloride (HgCl2) for five passages before exposure to MeHgCl (1-16 microM) for 48 h. MeHgCl toxicity was measured by trypan blue exclusion, reduction of resazurin dye and acid phosphatase activity. Pre-exposure to HgCl2 lessened the toxicity as shown by trypan blue exclusion (P = 0.0559) and reduction of resazurin (P = 0.0001). Pre-exposure to HgCl2 also resulted in induction of MT (P = 0.0066) and lessened the decrease of reduced glutathione (GSH) (P = 0.0013). These results suggest that MT and GSH may play a protective role in methyl mercury induced neurotoxicity of neuron spinal chord cells. The NSC-34 hybrid cell line can be a useful model for the study of MeHg neurotoxicity.

Acid Phosphatase↗

PubMed1999

Analysis of metallothioneins by means of capillary electrophoresis coupled to electrospray mass spectrometry with sheathless interfacing.

Capillary electrophoresis (CE) coupled to electrospray mass spectrometry via sheathless interfacing has been applied to the analysis of mammalian metallothionein (MT) extracts. In a rabbit-liver extract, four (MT-2C, MT-2A, MT-2D and MT-2E) out of six known MT sub-isoforms were unambiguously identified under three CE-resolved peaks. A fourth peak was found to contain MT-1A and/or MT-2B, whose molecular masses differ by only 1 Da. Traces of non-N-acetylated MT-2D and MT-2E were observed in a fifth, minor peak. In a rat-liver extract, both MT-1 and MT-2 were resolved and identified. Non-N-acetylated MT-2 was also identified in a resolved, minor peak. Minimum detectable amounts of MTs have been estimated to be approximately 0.6 fmol per sub-isoform.

Animals↗

PubMed1999

Consumption of freshwater fish in Kahnawake: risks and benefits.

Kahnawake is a Mohawk community located on the south shore of the Saint Lawrence River near Montreal. A comprehensive study was conducted in 1996-1997 to address the local concern regarding health risks of contaminant exposure associated with freshwater fish consumption. Forty-two participants, including most of the identified active fishermen (n=33), were interviewed. Walleye, perch, bullhead, and smallmouth bass were the species most consumed. Average daily intake of locally caught fish was 23 g/day. Nutrient and contaminant levels of locally collected fish were analyzed. Fish were good sources of protein, polyunsaturated fatty acids (particularly omega-3 fatty acids), calcium, zinc, and iron. Levels of cadmium, lead, arsenic, polychlorinated biphenyls (PCBs), and other chlorinated pesticides were at least 10 times lower than the guideline levels. Mercury levels of some predatory fish exceeded the guideline of 0.5 microgram/g. Average daily intakes of all contaminants were below the guideline levels by a factor of 10 except for mercury. Average mercury intake rate was about one-third that of the guideline level (200 micrograms/week). Contrary to residents' perception, Kahnawake fish were not particularly contaminated. In view of the nutritional as well as cultural benefits, fishing and fish consumption may be promoted.

Adolescent↗

PubMed1999

Secure placement of continuous ambulatory peritoneal dialysis catheters under laparoscopic assistance.

Laparoscopic surgical procedures were performed in 18 patients with end-stage renal disease for the placement of a Tenckhoff peritoneal dialysis catheter. Among them, 6 patients had received previous lower abdominal surgical treatment and 3 patients underwent laparoscopic rescue of dysfunctional Tenckhoff catheters. The operating time was between 40 and 80 minutes (median, 50 minutes). After a median follow-up period of 11 months, the short-term results revealed that no significant morbidity was associated with this procedure, and all catheters except two functioned well postoperatively. One of the catheters was not functional because of the patient's death, and the other one was removed because of persistent peritonitis. Laparoscopic secure placement of continuous ambulatory peritoneal dialysis catheters appears to be a simple, safe, and viable procedure, even in patients with previous lower-abdominal operations. The same technique can be used to rescue dysfunctional catheters that are displaced or obstructed by adhesion and omental wrapping, thus increasing catheter longevity.

Adult↗

PubMed1999

Biochemical markers for assessment of bone metastases in patients with breast cancer.

Breast cancer commonly metastasizes to bones, producing both osteolytic and osteoblastic deposits. Different markers for quantitative determination of bone turnover have been developed to evaluate bone metastases of breast cancer. The urinary deoxypyridinoline (Dpd), a crosslink product of collagen molecules found in bone and excreted in urine during bone degradation, and bone specific alkaline phosphatase (B-ALP), an isoenzyme localized in the membrane of osteoblasts and released in circulation during bone formation, were recently described as a group of markers of bone turnover in metastatic cancer. The urinary Dpd/creatinine (Cre) ratios and the serum B-ALP activity were determined in the samples from 148 patients who suffered from breast cancer (BC patients) with or without bone metastases, and 42 healthy women. For comparison, other biochemical markers, e.g. carcinoembryonic antigen (CEA), CA15-3, tissue polypeptide antigen (TPA), tissue polypeptide specific antigen (TPSA), and total alkaline phosphatase (T-ALP) in these samples were also evaluated. The results showed that there was a significant difference in urinary Dpd/Cre ratio between the control group and the patients with breast cancer (BC group) (mean +/- S.D., 5.69 +/- 1.26 vs. 8.19 +/- 3.95 nM/mM, P < 0.05). However, there was no significant difference between their B-ALP activities in the two groups. In addition, the BC patients with bone metastases showed elevated urinary Dpd/Cre ratios and B-ALP activities and ratios of (Dpd/Cre)/B-ALP in compare with BC patients without bone metastases (P < 0.05). Meanwhile, the urinary Dpd/Cre ratios (10.50 +/- 5.04 nmol/mmol) in the advanced stage of BC patients were higher than those in an early stage (7.45 +/- 3.23 nmol/mmol) (P < 0.05), but their serum B-ALP activities increased only in stage IV (P < 0.05). The urinary Dpd/Cre ratios also increased progressively according to the degree of bone metastases (P < 0.05), but their serum B-ALP activities only increased in severe bone metastases (P < 0.05). The results showed that the increase of a bone osteolytic activity took place earlier than that of a bone osteoblastic activity in the metastatic BC patients. In compare with other conventional markers, the best diagnostic efficiency of biochemical markers, analyzed by step wise discriminate analysis, was provided by CEA followed by Dpd/Cre ratio, CA15-3, TPA, TPSA, B-ALP and T-ALP. We conclude that showed the urinary Dpd/Cre ratio was a useful tumor marker to evaluate breast cancer with bone metastases.

Adult↗

PubMed1999

Mondor's disease in the breast.

Mondor's disease, superficial thrombophebitis of the breast, is an uncommon self-limiting condition. Surgical procedures and trauma were the common known causes. The objective of this study was to evaluate the incidence of Mondor's disease in different breast operations in lower risk of breast cancer area over a 6-year period and to identify its causes, clinical features, related surgical factors and associated breast cancer. Eighty-four cases of Mondor's disease were obtained from 9657 new patients in the breast clinic of Kaohsiung Medical University Hospital between January 1991 and December 1996. The incidence per year was close (0.84%-0.96%) although the number has been increasing each year. In 23 cases, no definite cause was diagnosed, whereas in 61 cases, the disorder was secondary because the pathogenesis could be discerned. The identified causes included forty-three cases caused by breast surgery, two cases associated with breast cancer and sixteen cases with other benign causes. Although the incidence did not differ significantly between breast surgery (0.95%) and non-surgical causes (0.79%), the highest incidence, 1.52%, occurred when excision through circumareolar incision and tunnel procedure for cosmesis (25 cases in 1634 excisions) were used, and the lowest 0.69% when excisions through direct incision (14 cases in 2004 excisions) were performed. (P < 0.05) The other incidence rates were 1.56% in breast conserving surgery which is higher than 0.37% following mastectomy. The incidence of the disease was higher (4.28%) when the distance of the breast lesion was more than 3 cm from the areolar edge, compared to 1.20% for the 2 cm group and 0.32% for the 1 cm group (P < 0.05) in tunnel procedures. The incidence of Mondor's disease during breast surgery was not significantly different in different breast quardrants. Although Mondor's disease is a benign, self-limiting condition, a high incidence developed in the excision biopsy through circumareolar incision with tunnel procedure when the distance from the breast lesion to the areolar edge was more than 3 cm. To prevent this complication, the tunnel procedure in breast biopsy should be avoided. The incidence of Mondor's disease associated with breast cancer was low (2.4%) in the lower-incidence breast cancer area from this series, but awareness of the condition is recommended.

Adolescent↗

PubMed1998

Dietary exposure to chemical contaminants from traditional food among adult Dene/Métis in the western Northwest Territories, Canada.

Environmental contaminants such as organochlorines and heavy metals have been reported to bioaccumulate in Arctic and subarctic wildlife. The Indigenous Peoples in northern and Arctic Canada rely on local wildlife as an important food source, and it is thus hypothesized that they may have high intakes of these contaminants. Herein, an assessment of dietary exposure to selected organochlorines and heavy metals for Indigenous Peoples of the western Northwest Territories (NWT) is presented. Dietary data were collected from 1012 adults with 24-h recalls in 16 communities in the western NWT (Denendeh). A comprehensive survey of the literature, as well as in-house analysis, formed the basis of a large traditional food-contaminant database. By combining the dietary and contaminant data, dietary exposure to 11 chemical contaminants was calculated. Dietary exposure to chemical contaminants in Denendeh is generally low and there is little, if any, associated health risk. However there are specific contaminants in certain communities for which exposure on a single day approaches the tolerable daily intake levels. These situations are detailed and monitoring needs are described.

Adult↗

PubMed1998

Risk assessment of cadmium exposure in Fort Resolution, Northwest Territories, Canada.

The aim of this study is to investigate the cadmium (Cd) exposure level from traditional food in Fort Resolution, Northwest Territories. We used 24-h dietary recalls and traditional food use frequency to obtain information on traditional food consumption, and analysed cadmium concentrations in traditional food. We also estimated total cadmium intake via market and traditional food, and cigarette smoking. Traditional food accounted for only 10% of the dietary energy. About 30 species of wildlife and plants were used. The most important foods in the community were moose, caribou, and whitefish. The range of cadmium concentrations measured was 0 to 1869 micrograms/g wet weight, with the lowest found in cranberry, and the highest in moose kidney. Cadmium concentrations in traditional food groups were comparable with those of Canadian market food. Highest levels of cadmium were found in the liver and kidney of caribou and moose. Cadmium intakes from traditional food estimated by dietary recall ranged from 0.01 to 1713 micrograms/g/day/person. Average cadmium intakes for women and men from traditional food were estimated to be 9% and 6% respectively, of the Provisional Tolerable Weekly Intake (PTWI, 400-500 micrograms) established by the World Health Organization. The average cadmium inhaled from cigarette smoking was 2.31 +/- 1.00 micrograms/day/person. There was no difference between the total cadmium intakes of smokers and nonsmokers. The total cadmium intake via market and traditional food and cigarette smoking was 136.6 micrograms/ week, which was lower than the PTWI. However, about 20% of the population may consume caribou and moose organ more frequently than the others. The potential health effects on this sub-population needs further clarification.

Animals↗

PubMed1998

Zinc pretreatment inhibits isotretinoin teratogenicity and induces embryonic metallothionein in CD-1 mice.

Isotretinoin (ITR), a teratogen in many species, is associated with increased oxidative stress. Metallothionein (MT) is an important tissue antioxidant whose concentrations are induced by zinc. To study the role of supplemental Zn as an inducer of embryonic MT, we injected pregnant CD-1 mice subcutaneously with saline vehicle, or 20 or 40 mg/kg Zn on gestational day (GD) 6.5. After 48 h, embryonic MT concentrations increased in a dose-related manner (r = 0.64, P < 0.05) with Zn treatment. The possible protective role of Zn pretreatment against ITR teratogenicity was investigated in vivo and in vitro. CD-1 mice were pretreated with saline or Zn (20 and 40 mg/kg) on GD 8.5 and 9.5. ITR was administered to both groups of mice via three intragastric intubations of 100 mg ITR/kg at 4 h intervals on GD 10.5. On GD 18.5, Zn pre-treated mice demonstrated decreased ITR-mediated growth retardation, cleft palates and postpartum mortality. A reduction in embryonic MT concentrations was observed in mice exposed to ITR. Mouse embryos cultured on GD 8.5 with an addition of 15 micromol/L Zn for 48 h had a sixfold greater MT concentration (688 microg/g protein) than controls. The Zn pretreatment of cultured embryos prevented malformations and lessened growth retardation caused by 24 h exposure to 17 micromol/L ITR. These results suggest that Zn-mediated induction of MT in mouse embryos could protect against ITR teratogenicity.

Abnormalities, Drug-Induced↗

PubMed1998

A physical map of the Leishmania major Friedlin genome.

An extensive physical map of the Leishmania major Friedlin genome has been assembled by the combination of fingerprint analysis of a shuttle vector cosmid library and probe hybridization. The integrated data obtained for 9004 fingerprinted clones and 974 probes have placed 91.2% of the 33.58-Mb genome into contigs representing each of the 36 chromosomes. This first-generation map has already provided a suitable framework for both high-throughput DNA sequencing and functional studies of the L. major parasite.

Animals↗

PubMed1998

Ooligan grease: a traditional food fat of western Canada and Alaska.

First Nations Peoples prepare ooligan grease by ripening several tons of the small fish, Thaleichthys pacificus, and rendering the fish oil. Eighteen samples from different family preparations of five cultural areas were analyzed for a spectrum of nutrients, organochlorines, and heavy metals. Ooligan grease was found to be a rich source of retinol (2444 +/- 1198 RE/100 g) and n-3 fatty acids, but had less vitamin A compared to fat of raw fish. There was a 10-fold increase in n-3 fatty acids in grease compared to raw fish fat, which may be attributed to microbial conversion of other fatty acids to DHA. Whole fish were good sources of Ca, Fe, and Zn; heavy metals were below guideline levels in grease. Chlorinated pesticides and PCB increased from north to south locations in British Columbia, with mean levels being 110 ng/g lipid of total chlorinated pesticides and 30 ng/g lipid of PCB. These levels are below regulation limits established by Health Canada. It is concluded that ooligan grease is a superior food fat and safe for human consumption.

Alaska↗

PubMed1998

A database for environmental contaminants in traditional food in northern Canada.

The potential health effects of environmental contaminants in traditional food on indigenous peoples in Northern Canada have been a growing concern. We have conducted an extensive literature review on contaminant levels in Northern Canada through searches of commercial, private, and government databases for the years 1986-1995, including MEDLine, Agricola, Biological Abstracts, Current Contents, Applied Science and Technology, Biosis, CABCD, Aquatic Sciences and Fisheries Abstracts, CRIS/ICAR, and the Northern Aquatic Food Chain Contaminant Database. More than 20,000 data items were identified in over 50 published articles, unpublished data, government reports, and review articles. Ranges of levels of 13 contaminants in major traditional food groups collected from four geographical regions (Yukon, MacKenzie, Keewatin, Baffin and Northern Quebec) were calculated. Exposure levels, particularly according to different dietary patterns, were estimated and discussed in relation to guideline levels.

Animals↗

PubMed1998

Gastric duplication cyst: report of a case.

Gastric duplication cyst is a rare disease entity, especially in the adult population. We report a case of 33-year-old female patient who presented with epigastric pain, postprandial fullness and nausea for the past several months. Gastroendoscopy showed a submucosal mass with normal overlying gastric mucosa. Upper gastrointestinal series confirmed a extrinsic compression of mass in the fundus of the stomach. Endoscopic ultrasonography and computerized tomography demonstrated the lesion to be a cyst in nature. The surgical procedure consisted of total excision without violation of the gastric lumen. Gastric mucosa was found by the histologic study of the excised cyst.

Adult↗