Geographic distribution of liver and stomach cancers in Thailand in relation to estimated dietary intake of nitrate, nitrite, and nitrosodimethylamine.

It is our working hypothesis that the high rate of the liver and gastric cancers in North and Northeast Thailand is associated with increased daily dietary intake of nitrate, nitrite, and nitrosodimethylamine (NDMA). Samples of fresh and preserved Thai foods were systematically collected and analyzed from 1988 to 1996 and from 1998 to 2005. Consumption frequencies of various food items were determined on the basis of a dietary questionnaire given to 467 adults (212 males and 255 females) from 1998 to 2005. Food consumption data for the preceding and current year were collected and intakes (day, week, and month) of nitrate, nitrite, and NDMA were calculated. The trends in liver and stomach cancer age-standardized incidence rates (ASR) in four regions of Thailand were compared with the dietary intake of nitrate, nitrite, and NDMA in those same geographic regions. Mean daily intakes of nitrate of 155.7 mg/kg, of nitrite of 7.1 mg/kg, and of NDMA of 1.08 microg/kg per day were found. Significant differences in dietary nitrate, nitrite, and NDMA intakes were seen between various Thai regions (P < 0.0001), and these corresponded to the variations in liver and stomach cancer ASR values between the regions. Dietary factors are likely to play key roles in different stages of liver and stomach carcinogenesis in Thailand.

Novel DNA staining method and processing technique for the quantification of undamaged double-stranded DNA in epidermal tissue sections by PicoGreen probe staining and microspectrophotometry.

Histotechnological processing of DNA can cause damage to and loss of DNA and can change its structure. DNA probes have severe tissue-staining limitations. New DNA probes and improved histotechnology are needed to enhance the characterization of fixed tissue-bound DNA. Our team developed a novel DNA staining technique and histotechnological processing procedure that improves tissue-bound DNA retention and the qualification and quantification of intact double-stranded (ds)-B-DNA. We used the ultrasensitive PicoGreen ds-DNA probe for the histochemical characterization of ds-DNA. Fifteen fixatives were examined to determine which were best for preventing DNA denaturation and retaining original DNA content and structures. Our use of a microwave-vacuum oven reduced heating temperatures, shortened heating and processing times, and enhanced fixation. We achieved better qualitative and quantitative results by using superior tissue-acquisition techniques (e.g., reduced prefixation times) and improved histotechnology. We also compared our novel approach with archival tissues, delayed fixation, less sophisticated and conventional histological processing techniques, and by experimenting with preservation of tissue-bound ds-Z-DNA. Results demonstrate that our histotechnological procedure and nucleic acid staining method significantly improve the retention of intact, undamaged ds-DNA which, in turn, allows the investigator to more precisely quantify the content and structures of unaltered and undamaged tissue-bound ds-B-DNA.

Rising leukemia rates in Thailand: the possible role of benzene and related compounds in cigarette smoke.

Epidemiological studies suggest that cigarette smoking is associated with an increased risk of leukemia and that benzene and related compounds in cigarette smoke may contribute to this elevated risk. This report presents new findings on selected components of cigarette smoke (including benzene and 1,3-butadiene) from major brands of cigarettes sold in Thailand, which represent about 80% of market share. Tested were also two major and popular brands of U.S. cigarettes sold in Thailand, representing about 100% of market share. The cigarettes tested were filter and non-filter, and with high and 'low' tar and nicotine levels. The observed range for benzene, toluene and 1,3-butadiene were found in the range of 25.5-63.7, 36.4-79.8 and 44.6-78.7 microg/cigarette, respectively. The amount of acrolein ranged from 79.9-181 microg/cigarette and for isoprene from 313-694 microg/cigarette. Yields of these substances showed no correlation with tar deliveries in mainstream smoke. Consumption of tobacco products increased in Thailand since 1970. This study also showed increases in leukemia mortality rates in Thailand, and in the relative frequency of leukemia among incident cancers diagnosed at a large hospital in Bangkok. Exposure to benzene and related compounds in cigarette smoke may have contributed to these trends. Analytic epidemiological studies are needed on the relationship between these compounds in smoke from tobacco products used in Thailand. These preliminary findings support the need for voluntary and/or government-regulated reduction in smoke yields of benzene and related compounds in tobacco products, and for expanded smoking prevention and cessation efforts, in Thailand.