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Biomedical subjects

J T Chan

Publications and source records attributed to J T Chan.

51 records · Page 3Linked to original sources
PubMed1976

Distribution of cholesterol-5alpha,6alpha-epoxide formation and its metabolism in mouse skin.

The distribution of cholesterol-5alpha,6alpha-epoxide in ultraviolet light-irradiated mouse skin was determined. Highest levels of cholesterol-5alpha,6alpha-epoxide were found in the epidermis and distributed rather evenly throughout all subcellular fractions. Low but potentially significant levels of the compound diffused from the epidermis. Metabolic studies demonstrated that cholesterol-5alpha,6alpha-epoxide was converted to cholestane-3ss,5alpha,6ss-triol by an enzyme, cholesterol-5alpha,6alpha-epoxide hydrase, which was localized in the epidermal fractions sedimenting at 10,000 and 100,000 X g. Comparative studies indicated a much higher capacity for metabolism of cholesterol-5alpha,6alpha-expoide in liver than in skin. The effect of the epoxide and its metabolic product on the skin is discussed.

Animals↗
PubMed1976

Etiologic related studies of ultraviolet light-mediated carcinogenesis.

Comparisons were made of cholesterol-5alpha, 6alpha-epoxide (CAE) levels in skin of hairless mice maintained on a regular or antioxidant supplemented diet and receiving chronic ultraviolet light (UVL) radiation over an 18-week period. Cholesterol-5alpha, 6alpha-epoxide levels in skin of animals on antioxidant supplemented diet, while reaching a peak four weeks after that of animals on regular diet, thereafter were consistently higher. Dietary antioxidants nevertheless had an inhibitory effect on UVL-induced tumors. These data are inconsistent with the theory of CAE involvement as an ultimate carcinogen in UVL-mediated carcinogenesis.

Animals↗
PubMed1975

Suppression of ultraviolet light-induced tumor formation by dietary antioxidants.

Dietary antioxidants were effective in reducing the number and severity of ultraviolet light-induced squamous cell carcinomas in skin of hairless mice. This and previous studies suggest that antioxidants may play a role in both inhibition of the primary event(s) involved in ultraviolet light-mediated tumor induction and the subsequent development of precancerous lesions into tumors.

Animals↗
PubMed1974

Skin carcinogenesis: cholesterol-5alpha,6alpha-epoxide hydrase activity in mouse skin irradiated with ultraviolet light.

Cholesterol-5alpha,6alpha-epoxide hydrase activity was 96 percent greater in skin of hairless mice that were receiving suberythemic ultraviolet light irradiation for 15 weeks than in nonirradiated controls. This enzyme system, which metabolizes cholesterol-5alpha,6alpha-epoxide (a known carcinogen), appears to be substrateinducible and is apparently responsible for the concomitant reduction of the sterol carcinogen that occurs prior to tumor induction.

Animals↗
PubMed1974

Inhibition of Sterol Biosynthesis in Chlorella sorokiniana by Triparanol.

When Chlorella sorokiniana was cultured in the presence of 1 mg/1 triparanol succinate, there was a 42% reduction in total sterol concentration. Algal biomass was reduced by approximately the same amount. In addition to the cycloartenol, cyclolaudenol, 24-methyl-pollinastanol, ergosta-5, 7-dien-3beta-ol, and ergosterol that occur in control culture, pollinastanol, 14alpha-methyl-5alpha-ergost-8-en-3beta-ol, 5alpha-ergosta-8, 14, 22-trien-3beta-ol, 5alpha-ergosta-8(14), 22-dien-3beta-ol, 5alpha-ergosta-8(9), 22-dien-3beta-ol, 5alpha-ergosta-8, 14-dien-3beta-ol, 5alpha-ergost-8(9)-3n-3beta-ol, 5alpha-ergost-8(14)-en-3beta-ol, 5alpha-ergosta-7, 22-dien-3beta-ol, and 5alpha-ergost-7-en-3beta-ol were isolated and identified from triparanol succinate-treated cells. A biosynthetic pathway for sterol biosynthesis in this organism is postulated based on all the sterols that were isolated and identified in triparanol-treated cultures of C. sorokiniana. Cyclolaudenol appears to be the product of the first alkylation at C-24 in this organism rather than the more common 24-methylene cycloartanol. Since 24-methylene sterols are needed for the second alkylation reaction, this would explain the absence of C-29 sterols in C. sorokiniana. Four of the sterols identified in C. sorokiniana are reported for the first time in a living organism. They are: 24-methyl pollinastanol, 5alpha-ergosta-8, 14, 22-trien-3beta-ol, 5alpha-ergosta-8(14), 22-dien-3beta-ol and 5alpha-ergost-8(14)-en-3beta-ol.

Journal Article↗
PubMed1973

Triparanol Inhibition of Sterol Biosynthesis in Chlorella ellipsoidea.

The sterol composition of C. ellipsoidea was markedly changed when this alga was grown in the presence of 1 mug/g triparanol. Triparanol appears to inhibit the removal of 14alpha-methyl group, the second alkylation at C-24, Delta(7)-reductase, and Delta(8) --> Delta(7)-isomerase. The effect of triparanol in Chlorella is much more diversified than the specific effect originally assigned to it in animals.

Journal Article↗
PubMedDate not supplied

Influence of vitamins and iron on plasma fluoride levels in rats.

Thirty female Sprague-Dawley rats (250 +/- 10 g) were divided randomly into five equal groups. After overnight fasting, a silastic catheter was placed in the jugular vein of each rat. Each group was intragastrically administered 0.25 mg F/250 g rat weight in 1 ml of one of the following forms of fluoride supplements: Pediaflor (Abbott/Ross, Columbus, OH), Tri-Vi-Flor, Tri-Vi-Flor + iron; Poly-Vi-Flor or Poly-Vi-Flor + iron (Mead Johnson Nutritionals, Bristol-Myers Squibb Co., Evansville, IN). Timed blood samples were collected and plasma fluoride concentration was determined using the microdiffusion method. The presence of iron and vitamins affect the bioavailability of fluoride as measured by the area under the time-plasma fluoride concentration curve.

Animals↗
PubMedDate not supplied

Topical fluorides: efficacy, administration, and safety.

Fluoride's role in decreasing dental caries has been recognized for decades. The professional fluoride treatment has recently been augmented with home-use fluoride products. The introduction of many attractive products makes it difficult for dental professionals to know which are effective. Both professional and home-use products are described, as are proven techniques for their use. Recognition of fluoride toxicity, and its prevention and treatment, are also discussed.

Child↗
PubMedDate not supplied

Impact of imported beverages on fluoridated and nonfluoridated communities.

In order to compare the effect of beverages "imported" from nearby communities on the fluoride intake of a fluoridated community with that of a nonfluoridated community, 45 different carbonated and juice drinks were sampled from Houston (fluoridated) and San Antonio (nonfluoridated) and examined for their fluoride concentrations. In spite of the fact that an individual lives in a low fluoride community, the risk of fluorosis exists through fluoride consumption in beverages as well as from the water supply and fluoride therapy. It is therefore important for dental practitioners to carefully evaluate their patients' entire fluoride exposure before prescribing fluoride supplements.

Adolescent↗
PubMedDate not supplied

Effects of topical fluoride treatment on tensile bond strength of pit and fissure sealants.

Clinicians often do not place pit and fissure sealants immediately after topical fluoride treatment because fluoride treatment might reduce bonding to enamel. The effect of NaF, SnF2, and APF on the in-vitro bond strength of two sealants to enamel was determined. The fluoride treatments and control (artificial saliva) were applied to enamel surfaces for four minutes and rinsed. A filled sealant (FluoroShield) and an unfilled sealant (Concise) were bonded to the etched enamel and debonded in tension using a universal testing machine. NaF increased the bond strength of the unfilled sealant; SnF2 and APF had no significant effect. NaF and APF decreased the bond strength of filled sealant while SnF2 had no significant effect. The bond strength of the filled sealant was higher than or equal to that of the unfilled sealant. Exposure of enamel to NaF, SnF2, or APF prior to placement of unfilled or filled sealants has no effect on in vitro bond strength between the enamel and the sealants.

Acidulated Phosphate Fluoride↗