Rodent model systems for studies of HIV-1 associated dementia.

Understanding of HIV-1 neuropathogenesis and development of rationale therapeutic approaches requires relevant animal models. The putative mechanisms of neuroinflammatory and neurotoxic events triggered by HIV-1 brain infection are reflected by a number of rodent models. These include transgenic animals (either expressing viral proteins or pro-inflammatory factors), infection with murine retroviruses, and severe combined immunodeficient (SCID) mice reconstituted with human lymphocytes and injected intracerebrally with HIV-1-infected human monocyte-derived macrophages. The potential importance and limitations of the models in reflecting human disease are discussed with emphasis on their utility for development of therapies to combat HIV-1-associated neurologic impairment.

Alcohol-induced oxidative stress in brain endothelial cells causes blood-brain barrier dysfunction.

Brain microvascular endothelial cells (BMVEC) connected by tight junctions (TJ) form a tight monolayer at the blood-brain barrier (BBB). We investigated the idea that BBB dysfunction seen in alcohol abuse is associated with oxidative stress stemming from ethanol (EtOH) metabolism in BMVEC. Exposure to EtOH induced catalytic activity/expression of EtOH-metabolizing enzymes, which paralleled enhanced generation of reactive oxygen species (ROS). EtOH-mediated oxidative stress led to activation of myosin light chain (MLC) kinase, phosphorylation of MLC and TJ proteins, decreased BBB integrity, and enhanced monocyte migration across BBB. Acetaldehyde or ROS donors mimicked changes induced by EtOH in BMVEC. Thus, oxidative stress resulting from alcohol metabolism in BMVEC can lead to BBB breakdown in alcohol abuse, serving as an aggravating factor in neuroinflammatory disorders.

Determination of total N-nitroso compounds and their precursors in frankfurters, fresh meat, dried salted fish, sauces, tobacco, and tobacco smoke particulates.

Total N-nitroso compounds (NOC) and NOC precursors (NOCP) were determined in extracts of food and tobacco products. Following Walters' method, NOC were decomposed to NO with refluxing HBr/HCl/HOAc/EtOAc and NO was measured by chemiluminescence. NOC were determined after sulfamic acid treatment to destroy nitrite, and NOCP were determined after treatment with 110 mM nitrite and then sulfamic acid. Analysis without HBr gave results < or =20% of those with HBr. This NOC method was efficient for nitrosamines but not nitrosoureas. The standard nitrosation for determining NOCP gave high yields for readily nitrosated amines, including 1-deoxy-1-fructosylvaline, but not for simple amines, dipeptides, and alkylureas. Mean NOC and NOCP results were (respectively, in micromol/kg of product) 5.5 and 2700 for frankfurters, 0.5 and 660 for fresh meat, 5.8 and 5800 for salted, dried fish, and 660 and 2900 for chewing tobacco (all for aqueous extracts) and 220 and 20000 nmol/cigarette for MeCN extracts of cigarette smoke filter pads.

Prevention of pancreatic cancer induction in hamsters by metformin.

BACKGROUND AND AIMS: Our previous study suggested that the known promotional effect of a high fat diet, which in hamsters induces peripheral insulin resistance, is related to a compensatory proliferation of islet cells. The present study was to examine whether the prevention of islet cell proliferation can inhibit the promotional effect of a high-fat diet in pancreatic carcinogenesis. METHODS: Two groups of high fat-fed hamsters were used. One group received Metformin in drinking water for life (HF+Met group), and the other group served as a control (HF group). At the time when the normalization of the plasma insulin level was expected, all hamsters were treated with the pancreatic carcinogen, N-nitrosobis-(2-oxopropyl)amine, and the experiment was terminated 42 weeks later. RESULTS: Although 50% of the hamsters in the high-fat group developed malignant lesions, none was found in the HF+Met group (P < 0.05). Also, significantly more hyperplastic and premalignant lesions, most of which were found within the islets, were detected in the high-fat group (8.6 lesions/hamster) than in the HF+Met group (1.8 lesions/hamster). CONCLUSIONS: The results lend further support on the significant role of islet cells in pancreatic carcinogenesis and may explain the association between pancreatic cancer and obesity, which is usually associated with peripheral insulin resistance.

Nitrate and nitrite concentrations in human saliva for men and women at different ages and times of the day and their consistency over time.

Salivary nitrite arises from nitrate and is the main source of gastric nitrite, a precursor of carcinogenic N-nitroso compounds. We examined nitrate and nitrite levels in unstimulated saliva from subjects consuming low-nitrate low-vitamin C diets. When saliva was collected from six men at nine times of the day (Experiment 1), night time nitrite levels were significantly higher than day time values and nitrite varied more than nitrate. When saliva was collected from 29 subjects aged 19-37 or 60-84 years at four times of the day during 1991-1993 (Experiment 2), all older subjects and older men had significantly higher nitrite levels than the corresponding younger subjects, night time nitrite levels in men were significantly raised, and nitrate and nitrite levels in the same samples were closely correlated. Saliva was collected at 6.00 a.m. on two successive days in 1997 from 16 subjects who had collected saliva in 1991-1993 (Experiment 3). Nitrate and nitrite levels on day 1 of experiment 3 were closely correlated with those on day 2. Nitrate and nitrite levels on days 1 and 2 of Experiment 3 were correlated with the corresponding parameters in Experiment 2 with P = 0.04 and 0.08 for day 1, and 0.10 and 0.28 for day 2, respectively. Hence, saliva nitrite levels rose at night and were higher in older people, especially older men, and saliva nitrate and nitrite levels varied little from day to day, but varied more after 4-6 years.

Diffusion of dialkylnitrosamines into the rat esophagus as a factor in esophageal carcinogenesis.

To indicate how readily nitrosamines (NAms) diffuse into the esophagus, we measured diffusion rate (flux) through rat esophagus of dialkyl-NAms using side-by-side diffusion apparatuses. Mucosal and serosal flux at 37 degrees C of two NAms, each at 50 microM, was followed for 90 min by gas chromatography-thermal energy analysis of NAms in the receiver chamber. Mucosal flux of one or two NAms at a time gave identical results. Mucosal flux was highest for the strong esophageal carcinogens methyl-n-amyl-NAm (MNAN) and methylbenzyl-NAm. Mucosal esophageal flux of 11 NAms was 18-280 times faster and flux of two NAms through skin was 13-28 times faster than that predicted for skin from the molecular weights and octanol:water partition coefficients, which were also measured. Mucosal: serosal flux ratio was correlated (P < 0.05) with esophageal carcinogenicity and molecular weight. For seven NAms tested for carcinogenicity by Druckrey et al. [(1967) Z. Krebsforsch., 69, 103-201], mucosal flux was correlated with esophageal carcinogenicity with borderline significance (P = 0.07). The MNAN:dipropyl-NAm ratio for mucosal esophageal flux was unaffected when rats were treated with phenethylisothiocyanate and was similar to that for forestomach, indicating no involvement by cytochromes P450. Mucosal esophageal flux of MNAN and dimethyl-NAm was reduced by >90% on enzymic removal of the stratum corneum, was unaffected by 0.1 mM verapamil and was inhibited 67-94% by 1.0 mM KCN and 82-93% by 0.23% ethanol. NAm flux through rat skin and jejunum was 5-17% of that through esophagus. Flux through skin increased 5-13 times after enzymic or mechanical removal of the epidermis; the histology probably explained this difference from esophagus. Hence, NAms could be quite rapidly absorbed by human esophagus when NAm-containing foods or beverages are swallowed, the esophageal carcinogenicity of NAms may be partly determined by their esophageal flux and NAm flux probably occurs by passive diffusion.

Effect of ascorbic acid dose taken with a meal on nitrosoproline excretion in subjects ingesting nitrate and proline.

We determined the dose of ascorbic acid (ASC) given to subjects with a standard 400-calorie meal that inhibited N-nitrosoproline (NPRO) formation when we gave 400 mg of nitrate one hour before and 500 mg of L-proline with the standard meal. Volunteers consumed their normal US diets but restricted their intakes of nitrate, proline, NPRO, and ASC. NPRO and N-nitrososarcosine (NSAR) were determined in the 18-hour urines by methylation followed by gas chromatography-thermal energy analysis. Mean NPRO yields were 10.7, 41.9, 33.2, 22.3, and 23.1 nmol for groups of 9-25 subjects taking proline alone, proline + nitrate, and proline + nitrate + 120, 240, and 480 mg of ASC, respectively. There was a significant trend to lower NPRO yields as the ASC dose was raised. These results correspond to inhibitions by ASC of 28%, 62%, and 60%, respectively. Pairwise comparison showed that each group taking ASC formed significantly less NPRO than the group given only proline + nitrate. Mean NSAR yields were 9.0 nmol when proline alone was taken and 16.9-24.0 nmol when proline + nitrate + ASC was taken, with no trend to increase as the ASC dose was raised. However, NPRO and NSAR yields in individual urines were correlated with each other. We concluded that 120 mg of ASC taken with each meal (360 mg/day) would significantly reduce in vivo nitrosamine formation, similar to tests by Leaf and co-workers (Carcinogenesis 8, 791-795, 1987) in which the reactants were taken between meals. The inhibitory dose of ASC may be < 120 mg/meal when doses of nitrate and proline are not taken.