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LE Magazine November 2000

Continued from Medical Abstracts, November 2000

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Heterocyclic Amines

Cancer chemopreventive mechanisms of tea against heterocyclic amine mutagens from cooked meat

Cooking meat and fish under normal conditions produces heterocyclic amine mutagens, several of which have been shown to induce colon tumors in experimental animals. In our search for natural dietary components that might protect against these mutagens, it was found that green tea and black tea inhibit the formation of heterocyclic amine-induced colonic aberrant crypt foci (ACF) in the rat. Since ACF are considered to be putative preneoplastic lesions, we examined the inhibitory mechanisms of tea against the heterocyclic amines. In the initial studies using the Salmonella mutagenicity assay, green tea and black tea inhibited according to the concentration of tea leaves during brewing and the time of brewing; a 2-3-min brew of 5% green tea (w/v) was sufficient for >90% antimutagenic activity. N-hydroxylated heterocyclic amines, which are direct-acting mutagens in Salmonella, were inhibited by complete tea beverage and by individual components of tea, such as epigallocatechin-3-gallate (EGCG). Inhibition did not involve enhanced mutagen degradation, and EGCG and other catechins complexed only weakly with the mutagens, suggesting electrophile scavenging as an alternative mechanism. Enzymes that contribute to the metabolic activation of heterocyclic amines, namely microsomal NADPH-cytochrome P450 reductase and N, O-acetyltransferase, were inhibited by tea in vitro. Studies in vivo established that tea also induces cytochromes P450 and Phase II enzymes in a manner consistent with the rapid metabolism and excretion of heterocyclic amines. Collectively, the results indicate that tea possesses anticarcinogenic activity in the colon, and this most likely involves multiple inhibitory mechanisms.

Proc Soc Exp Biol Med 1999 pr;220(4):239-43

Antimutagenicity of flavones and flavonols to heterocyclic amines by specific and strong inhibition of the cytochrome P450 1A family

We found the mechanism in flavonoids that can strongly suppress the mutagenicity of one of the food-derived and carcinogenic heterocyclic amines, 3-amino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2). The antimutagenicity was evaluated by IC50 value, the amount required for 50% inhibition of the mutagenicity of 0.1 nmol Trp-P-2, with Salmonella typhimurium TA98 strain in the presence of S9 mix. The flavones and flavonols were two orders stronger as antimutagens that such antimutagenic phytochemicals as chlorophylls and catechins. We had previously found flavonoids to be a desmutagen to neutralize Trp-P-2 before or during attack of DNA, because they had no effect on either the ultimate mutagenic form of Trp-P-2 (N-hydroxy-Trp-P-2) or the mutated cells. The desmutagenicity of the flavonoids did not depend on the hydroxy number or position that should be associated with antioxidative potency, and was also unaffected by the solubility of Trp-P-2 in the assay solution. The inhibitory effect of the flavonoids on the metabolic activation of Trp-P-2 to N-hydroxy-Trp-P-2 was almost in parallel with the antimutagenic IC50 value, when determined with a Saccharomyces cerevisiae AH22 cell simultaneously expressing both rat cytochrome P450 1A1 and yeast reductase. The Ki values of flavones and flavonols for the enzyme were less than 1 microM, while the K(m) value of Trp-P-2 was 25 microM. The antimutagenicity of the flavones and flavonols was thus concluded to be due to inhibition of the activation process of Trp-P-2 by P450 1A1 to the ultimate carcinogenic form. They were also able to act as antimutagens toward other indirect mutagens that were activated by P450 1A1.

Biosci Biotechnol Biochem 1998 May;62(5):970-7

Effects of marinating on heterocyclic amine carcinogen formation in grilled chicken

This study compared heterocyclic aromatic amines in marinated and unmarinated chicken breast meat flame-broiled on a propane grill. Chicken was marinated prior to grilling and the levels of several heterocyclic amines formed during cooking were determined by solid-phase extraction and HPLC. Compared with unmarinated controls, a 92-99% decrease in 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was observed in whole chicken breast marinated with a mixture of brown sugar, olive oil, cider vinegar, garlic, mustard, lemon juice and salt, then grilled for 10, 20, 30 or 40 min. Conversely, 2-amino-3, 8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) increased over 10-fold with marinating, but only at the 30 and 40 min cooking times. Marinating reduced the total detectable heterocyclic amines from 56 to 1.7 ng/g, from 158 to 10 ng/g and from 330 to 44 ng/g for grilling times of 20, 30 and 40 min, respectively. The mutagenic activity of the sample extracts was also measured, using the Ames/Salmonella assay. Mutagenic activity was lower in marinated samples cooked for 10, 20 and 30 min, but higher in the marinated samples cooked for 40 min, compared with unmarinated controls. Although a change in free amino acids, which are heterocyclic amine precursors, might explain the decrease in PhIP and increase in MeIQx, no such change was detected. Marinating chicken in one ingredient at a time showed that sugar was involved in the increased MeIQx, but the reason for the decrease in PhIP was unclear. PhIP decreased in grilled chicken after marinating with several individual ingredients. This work shows that marinating is one method that can significantly reduce PhIP concentration in grilled chicken.

Food Chem Toxicol 1997 May;35(5):433-41

Well-done meat intake and the risk of breast cancer

BACKGROUND: Heterocyclic amines, mutagens formed in meats cooked at high temperatures, have been demonstrated as mammary carcinogens in animals. We conducted a nested, case-control study among 41836 cohort members of the Iowa Women's Health Study to evaluate the potential role of heterocyclic amines and intake of well-done meat in the risk for human breast cancer. METHODS: A questionnaire was mailed to individuals in the cohort who had breast cancer diagnosed during the period from 1992 through 1994 and a random sample of cancer-free cohort members to obtain information on usual intake of meats and on meat preparation practices. Color photographs showing various doneness levels of hamburger, beefsteak, and bacon were included. Multivariate analysis was performed on data from 273 case subjects and 657 control subjects who completed the survey. RESULTS: A dose-response relationship was found between doneness levels of meat consumed and breast cancer risk. The adjusted odds ratios (ORs) for very well-done meat versus rare or medium-done meat were 1.54 (95% confidence interval [CI]=0.96-2.47) for hamburger, 2.21 (95% CI=1.30-3.77) for beef steak, and 1.64 (95% CI=0.92-2.93) for bacon. Women who consumed these three meats consistently very well done had a 4.62 times higher risk (95% CI=1.36-15.70) than that of women who consumed the meats rare or medium done. Risk of breast cancer was also elevated with increasing intake of well-done to very well-done meat. CONCLUSIONS: Consumption of well-done meats and, thus, exposures to heterocyclic amines (or other compounds) formed during high-temperature cooking may play an important role in the risk of breast cancer.

J Natl Cancer Inst 1998 Nov 18;90(22):1724-9


Ibuprofen suppresses plaque pathology and inflammation in a mouse model for Alzheimer's disease

The brain in Alzheimer's disease (AD) shows a chronic inflammatory response characterized by activated glial cells and increased expression of cytokines and complement factors surrounding amyloid deposits. Several epidemiological studies have demonstrated a reduced risk for AD in patients using nonsteroidal anti-inflammatory drugs (NSAIDs), prompting further inquiries about how NSAIDs might influence the development of AD pathology and inflammation in the CNS. We tested the impact of chronic orally administered ibuprofen, the most commonly used NSAID, in a transgenic model of AD displaying widespread microglial activation, age-related amyloid deposits, and dystrophic neurites. These mice were created by overexpressing a variant of the amyloid precursor protein found in familial AD. Transgene-positive (Tg+) and negative (Tg-) mice began receiving chow containing 375 ppm ibuprofen at 10 months of age, when amyloid plaques first appear, and were fed continuously for 6 months. This treatment produced significant reductions in final interleukin-1beta and glial fibrillary acidic protein levels, as well as a significant diminution in the ultimate number and total area of beta-amyloid deposits. Reductions in amyloid deposition were supported by ELISA measurements showing significantly decreased SDS-insoluble Abeta. Ibuprofen also decreased the numbers of ubiquitin-labeled dystrophic neurites and the percentage area per plaque of anti-phosphotyrosine-labeled microglia. Thus, the anti-inflammatory drug ibuprofen, which has been associated with reduced AD risk in human epidemiological studies, can significantly delay some forms of AD pathology, including amyloid deposition, when administered early in the disease course of a transgenic mouse model of AD.

J Neurosci 2000 Aug 1;20(15):5709-14

Differential effects of inhibitors of cyclooxygenase (cyclooxygenase 1 and cyclooxygenase 2) in acute inflammation

The anti-inflammatory activity of drugs more selective for cyclooxgenase isoform inhibition (cyclooxygenase 1, cyclooxygenase 2), were compared in rat carrageenin-induced pleurisy. Suppression of inflammation by cyclooxygenase 2-selective inhibitors, NS-398 (N-[-2-cyclohexyloxy]-4-nitrophenyl methanesulphonamide) and nimesulide (4-nitro-2-phenoxy-methanesulfonanilide), and by piroxicam and aspirin, more selective for cyclooxygenase 1, was measured. Piroxicam and aspirin significantly inhibited inflammatory cell influx, exudate and prostaglandin E2 formation, 6 h after carrageenin injection. Cyclooxygenase 2 inhibitors had little effect on these parameters with NS-398 alone reducing prostaglandin E2 levels, but increasing levels of leukotriene B4. In contrast, at 3 h after carrageenin injection, cyclooxygenase 2 inhibitors significantly inhibited all inflammatory parameters however suppression with piroxicam and aspirin was greater, and more pronounced than at 6 h. NS-398 and nimesulide dosing did not reduce thromboxane B2 production from platelets isolated from rats with carrageenin-induced pleurisy, demonstrating that at the doses used, cyclooxygenase 2 inhibitors did not inhibit cyclooxygenase 1, as platelets contain only this isoform. Therefore, in the rat carrageenin-induced pleurisy, drugs more selective for the inhibition of cyclooxygenase 1 attenuate inflammation over a wider time frame than cyclooxygenase 2-selective drugs, suggesting a significant role for cyclooxygenase 1 in this model. Inhibition of cyclooxygenase 2 by NS-398 however, resulted in an increase in the potent chemoattractant leukotriene B4.

Eur J Pharmacol 1998 Aug 21;355(2-3):211-7

Inhibition of Alzheimer's beta-amyloid induced vasoactivity and proinflammatory response in microglia by a cGMP-dependent mechanism

Beta-amyloid (Abeta) peptides are the major protein components of senile plaques in Alzheimer's disease (AD) brains. Vascular damage and reactive gliosis are found colocalized with amyloid deposits in AD brains, suggesting that the vasculature may be a clinically significant site of AD pathology. Our results show that freshly solubilized Abeta1-40 enhances the vasoconstriction induced by endothelin-1 (ET-1) and increases resistance to relaxation triggered by nitric oxide (NO), suggesting that Abeta may oppose the NO/cGMP pathway. Using specific inhibitors and activators of the NO/cGMP pathway, we show that Abeta vasoactivity is not due to a modulation of nitric oxide synthase (NOS) or soluble guanylyl cyclase (sGC). However, we find that a selective cGMP phosphodiesterase (cGMP-PDE) inhibitor (dipyridamole) is able to interactively block the enhanced vasoconstriction as well as the opposition to relaxation induced by Abeta, suggesting that Abeta could effect the activity of this enzyme. Cyclic GMP levels, but not cAMP concentrations, are reduced after Abeta treatment of rat aortic rings, further substantiating this hypothesis. Moreover, in examination of this pathway in another cell type pertinent to AD, we find that Abeta induces a proinflammatory response in microglia as evidenced by increased leukotriene B4 release. We show that both dipyridamole and compounds which increase cGMP levels prevent Abeta-induced microglial inflammation. Our results suggest that therapeutic intervention aimed at reduction of microglial-mediated inflammation via inhibition of cGMP-PDE or elevation of cGMP may be beneficial in the treatment of AD.

Exp Neurol 1999 May;157(1):211-21


Metabolic difference between visceral fat and subcutaneous abdominal fat

Obesity stands as a public health issue. Obesity prevalence is increasing throughout every industrialized country. Android obesity is linked with an increased cardiovascular mortality and with type 2 diabetes mellitis, thus calling for an early management of this disease. Several studies showed a significant association between an android fat distribution and an increased cortisol secretion, raising the still debated question of a causal relationship between the development of android obesity and hypercorticism. Moreover, android obese subjects exhibit reduced plasma testosterone and growth hormone levels, meaning complex hormonal abnormalities in these subjects. Current hypotheses suggest that android fat distribution depends on the association of these hormonal abnormalities. Android obese patients have supranormal free fatty acid plasma concentrations. Visceral fat tissue, through its portal drainage, could be an important source for free fatty acids that may exert complex metabolic effects: involvement in hepatic lipogenesis, increase in hepatic neoglucogenic flux, reduction in insulin metabolic clearance and involvement in peripheral insulin resistance through a competition mechanism described by Randle. Technics in vitro (isolated adipocytes) and in vivo in human (labeled fatty acid flux) showed that visceral fatty acid flux was increased in obese patients and subcutaneous adipose tissue, as opposed to common opinion, was also involved in free fatty acid pool in obese patients. Thus, visceral obesity and diabetes could be linked through an enhanced fatty acid availability from adipose tissues (visceral and subcutaneous) in otherwise genetically type 2 diabetes-prone individuals.

Diabetes Metab 2000 Jun;26 Suppl 3:10-2

Low serum testosterone level as a predictor of increased visceral fat in Japanese-American men

OBJECTIVE: To examine the association between baseline testosterone levels and changes in visceral adiposity in Japanese-American men. DESIGN: Prospective observational study. SUBJECTS: Second-generation Japanese-American males enrolled in a community-based population study. MEASUREMENTS: At baseline, 110 men received a 75g oral glucose tolerance test (OGTT), and an assessment of body mass index (BMI); visceral adiposity measured as intra-abdominal fat area (IAF) using computed tomography (CT); fasting insulin and C-peptide levels; and total testosterone levels. IAF was re-measured after 7.5 y. Subcutaneous fat areas were also measured by CT in the abdomen, thorax and thigh. The total fat (TF) was calculated as the sum of IAF and total subcutaneous fat areas (SCF). RESULTS: After 7.5y, IAF increased by a mean of 8.0 cm2 (95% CI: 0.8, 15.3). Baseline total testosterone was significantly correlated with change in IAF (r= -0.26, P= 0.006), but not to any appreciable degree with change in BMI, TF, or SCF. In a linear regression model with change in IAF as the dependent variable, baseline testosterone was significantly related to this outcome while adjusting for baseline IAF, SCF, BMI, age, diabetes mellitus status (OGTT by the WHO diagnostic criteria) and fasting C-peptide (regression coefficient for baseline testosterone [nmol/l] = -107.13, P = 0.003). CONCLUSIONS: In this Japanese-American male cohort, lower baseline total testosterone independently predicts an increase in IAF. This would suggest that by predisposing to an increase in visceral adiposity, low levels of testosterone may increase the risk of type 2 diabetes mellitus.

Int J Obes Relat Metab Disord 2000 Apr;24(4):485-91

Saw Palmetto

Effects of a saw palmetto herbal blend in men with symptomatic benign prostatic hyperplasia

PURPOSE: We tested the effects of a saw palmetto herbal blend in men with symptomatic benign prostatic hyperplasia (BPH) via a randomized, placebo controlled trial. MATERIALS AND METHODS: We randomized 44 men 45 to 80 years old with symptomatic BPH into a trial of a saw palmetto herbal blend versus placebo. End points included routine clinical measures (symptom score, uroflowmetry and post-void residual urine volume), blood chemistry studies (prostate specific antigen, sex hormones and multiphasic analysis), prostate volumetrics by magnetic resonance imaging, and prostate biopsy for zonal tissue morphometry and semiquantitative histology studies. RESULTS: Saw palmetto herbal blend and placebo groups had improved clinical parameters with a slight advantage in the saw palmetto group (not statistically significant). Neither prostate specific antigen nor prostate volume changed from baseline. Prostate epithelial contraction was noted, especially in the transition zone, where percent epithelium decreased from 17.8% at baseline to 10.7% after 6 months of saw palmetto herbal blend (p <0.01). Histological studies showed that the percent of atrophic glands increased from 25. 2% to 40.9% after treatment with saw palmetto herbal blend (p <0.01). The mechanism of action appeared to be nonhormonal but it was not identified by tissue studies of apoptosis, cellular proliferation, angiogenesis, growth factors or androgen receptor expression. We noted no adverse effects of saw palmetto herbal blend. When the study was no longer blinded, 41 men elected to continue therapy in an open label extension. CONCLUSIONS: Saw palmetto herbal blend appears to be a safe, highly desirable option for men with moderately symptomatic BPH. The secondary outcome measures of clinical effect in our study were only slightly better for saw palmetto herbal blend than placebo (not statistically significant). However, saw palmetto herbal blend therapy was associated with epithelial contraction, especially in the transition zone (p <0.01), indicating a possible mechanism of action underlying the clinical significance detected in other studies.

J Urol 2000 May;163(5):1451-6

Benign prostatic hyperplasia treated with saw palmetto: a literature search and an experimental case study

European physicians treat benign prostatic hyperplasia (BPH) with saw palmetto extract (SPE), while American physicians generally disregard SPE because "research is lacking." The authors investigated this discrepancy with a literature search and a clinical trial. The literature search began with MEDLINE, then expanded to "alternative" databases, including AGRICOLA, EMBASE, IBIS, and Cochrane, plus a manual search of unindexed herbal journals. The clinical trial was an experimental case study in which a 67-year-old man with symptomatic BPH was randomly administered SPE (160 mg standardized extract twice daily) or placebo. Outcome measures included the American Urological Association Symptom Index (AUASI), serum prostate-specific antigen, and prostate volume. Our expanded literature search revealed 58 clinical trials, whereas MEDLINE yielded only 19 clinical trials, or 33% of the total. Our clinical trial measured a baseline AUASI score of 20, which improved to 7 after unblinded administration of SPE. Subsequent double-blinded placebo produced a score of 14, and final single-blinded allotment of SPE produced a score of 11. Prostate-specific antigen was 10.3 ng/mL at baseline and 10.7 ng/mL at trial's conclusion. Baseline prostatic volume was 92 mL, and end volume was 75 mL. In conclusion, MEDLINE proved inadequate as a stand-alone search engine for locating information about an herbal medicine. Our experimental case study, similar to N = 1 research methodology, proved suitable for clinical evaluation of an herbal medicine in a rural private practice. SPE improved the patient's BPH. Unstandardized look-alike herbs may act as nontherapeutic placebos and may undermine consumer confidence in herbal medicine.

J Am Osteopath Assoc 2000 Feb;100(2):89-96

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