Robert M. Russell

β-carotene and other carotenoids as antioxidants

Carotenoids are natural pigments which are synthesized by plants and are responsible for the bright colors of various fruits and vegetables. There are several dozen carotenoids in the foods that we eat, and most of these carotenoids have antioxidant activity. β-carotene has been best studied since, in most countries it is the most common carotenoid in fruits and vegetables. However, in the U.S., lycopene from tomatoes now is consumed in approximately the same amount as β-carotene. Antioxidants (including carotenoids) have been studied for their ability to prevent chronic disease. β-carotene and others carotenoids have antioxidant properties in vitro and in animal models. Mixtures of carotenoids or associations with others antioxidants (e.g. vitamin E) can increase their activity against free radicals. The use of animals models for studying carotenoids is limited since most of the animals do not absorb or metabolize carotenoids similarly to humans.Epidemiologic studies have shown an inverse relationship be...

Enzymatic conversion of β-carotene into β-apo-carotenals and retinoids by human, monkey, ferret, and rat tissues☆☆☆

Whether the conversion of β-carotene into retinoids involves an enzymatic excentric cleavage mechanism was examined in vitro with homogenates prepared from human, monkey, ferret, and rat tissue. Using high-performance liquid chromatography, significant amounts of β-apo-12′-, -10′-, and -8′-carotenals, retinal, and retinoic acid were found after incubation of intestinal homogenates of the four different species with β-carotene in the presence of NAD+ and dithiothreitol. No β-apo-carotenals or retinoids were detected in control incubations done without tissue homogenates. The production of β-apo-carotenals was linear for 30 min and up to tissue protein concentrations of 1.5 mg/ml. The rate of formation of β-apo-carotenals from 2 μm β-carotene was about 7- to 14-fold higher than the rate of retinoid formation in intestinal homogenates, and the rate of β-apo-carotenal production was fivefold greater in primate intestine vs rat or ferret intestine (P < 0.05). The amounts of β-apo-carotenals and retinoids formed were markedly reduced when NAD+ was replaced by NADH, or when dithiothreitol and cofactors were deleted from the incubation mixture. Both β-apo-carotenal and retinoid production from β-carotene were inhibited completely by adding disulfiram, an inhibitor of sulfhydryl-containing enzymes. Incubation of β-carotene with liver, kidney, lung, and fat homogenates from each species also resulted in the appearance of β-apo-carotenals and retinoids. The identification of three unknown compounds which might be excentric cleavage products is ongoing. These data support the existence of an excentric cleavage mechanism for β-carotene conversion.

Fundic atrophic gastritis in an elderly population. Effect on hemoglobin and several serum nutritional indicators

The ratio of pepsinogen I to pepsinogen II in the circulation decreases progressively with increasing severity of atrophic gastritis of the fundic gland mucosa. Fasting blood was obtained from 359 free‐living and institutionalized elderly people (age range, 60 to 99 years). A pepsinogen ***I/pepsinogen II ratio less than 2.9, indicating atrophic gastritis, was found in 113 (31.5%) subjects. The prevalence of atrophic gastritis increased significantly with advancing age (P <.05). Within the atrophic gastritis group, 84 had a pepsinogen I level greater than or equal to 20 μg/L, indicating mild to moderate atrophic gastritis, and 29 had a pepsinogen I level less than 20 μg/L, indicating severe atrophic gastritis or gastric atrophy. A significant increase in the prevalences of elevated serum gastrin levels (P <.005), low serum vitamin B12 levels (P <.005), circulating intrinsic factor antibody (P <.005), and anemia (P <.025) was observed with stepwise increases in severity of atrophic gastritis. Subjects with atrophic gastritis exhibited a lower mean serum vitamin B12 level (P <.05) and a higher mean folate level (P <.05), but no difference was detected in mean hemoglobin levels or serum levels of iron, ferritin, retinal or α‐tocopherol. It is concluded that serum pepsinogen I and pepsinogen II levels can be used to determine the prevalence and severity of atrophic gastritis, that atrophic gastritis is common in an elderly population, and that atrophic gastritis is associated with vitamin B12 deficiency and anemia. Further, higher folate levels in atrophic gastritis may be related to an accumulation of 5‐methyl tetrahydrofolate in serum due to vitamin B12 deficiency and/or greater folate synthesis by the intestinal flora resulting from bacterial overgrowth secondary to hypo‐ or achlorhydria.

The Biochemical Characterization of Ferret Carotene-9′, 10′-Monooxygenase Catalyzing Cleavage of Carotenoids in Vitro and in Vivo*

Previous studies have shown that β-carotene 15,15′-monooxygenase catalyzes the cleavage of β-carotene at the central carbon 15,15′-double bond but cleaves lycopene with much lower activity. However, expressing the mouse carotene 9′,10′-monooxygenase (CMO2) in β-carotene/lycopene-synthesizing and -accumulating Escherichia coli strains leads to both a color shift and formation of apo-10′-carotenoids, suggesting the oxidative cleavage of both carotenoids at their 9′,10′-double bond. Here we provide information on the biochemical characterization of CMO2 of the ferret, a model for human carotenoid metabolism, in terms of the kinetic analysis of β-carotene/lycopene cleavage into β-apo-10′-carotenal/apo-10′-lycopenal in vitro and the formation of apo-10′-lycopenoids in ferrets in vivo. We demonstrate that the recombinant ferret CMO2 catalyzes the excentric cleavage of both all-trans-β-carotene and the 5-cis- and 13-cis-isomers of lycopene at the 9′,10′-double bond but not all-trans-lycopene. The cleavage activity of ferret CMO2 was higher toward lycopene cis-isomers as compared with β-carotene as substrate. Iron was an essential co-factor for the reaction. Furthermore, all-trans-lycopene supplementation in ferrets resulted in significant accumulation of cis-isomers of lycopene and the formation of apo-10′-lycopenol, as well as up-regulation of the CMO2 expression in lung tissues. In addition, in vitro incubation of apo-10′-lycopenal with the post-nuclear fraction of hepatic homogenates of ferrets resulted in the production of both apo-10′-lycopenoic acid and apo-10′-lycopenol, respectively, depending upon the presence of NAD+ or NADH as cofactors. Our finding of bioconversion of cis-isomers of lycopene into apo-10′-lycopenoids by CMO2 is significant because cis-isomers of lycopene are a predominant form of lycopene in mammalian tissues and apo-lycopenoids may have specific biological activities related to human health.

Nutrient Intakes and Adenocarcinoma of the Esophagus and Distal Stomach

We studied the relationship between nutrient intakes and adenocarcinoma of the esophagus and distal stomach among 124 esophageal adenocarcinoma cases, 124 distal stomach cancer cases, and 449 controls in a population-based case-control study in eastern Nebraska. The residual method was used to adjust nutrient intake quartiles or tertiles for energy intake. We observed significant inverse associations with risk of esophageal adenocarcinoma for dietary intakes of total vitamin A [highest vs. lowest quartile, multivariate odds ratio (OR) = 0.5, P for trend = 0.05], β-cryptoxanthin (OR = 0.5, P = 0.05), riboflavin (OR = 0.5, P = 0.01), folate (OR = 0.5, P = 0.03), zinc (OR = 0.5, P = 0.05), dietary fiber (OR = 0.5, P = 0.05), protein (OR = 0.5, P = 0.02), and carbohydrate (OR = 0.4, P = 0.02). For distal stomach cancer, only vitamin C (OR = 0.6, P = 0.04), dietary fiber (OR = 0.4, P = 0.007), and carbohydrate (OR = 0.4, P = 0.004) were inversely associated with risk. Our analyses showed significant interaction between dietary fat intake, but not intakes of other nutrients, and respondent type for both cancer sites. Subgroup analyses among self-respondents revealed positive associations between saturated fat intake and risk of esophageal adenocarcinoma (OR = 1.0, 4.1, and 4.6 for intake tertiles, P for trend = 0.02) and risk of distal stomach cancer (OR = 1.0, 1.2, and 3.6, P = 0.03). However, no such associations were found among proxy respondents. Our data suggest that greater intake of dietary fiber, certain carotenoids, and vitamins may decrease the risk of esophageal adenocarcinoma, whereas greater intake of saturated fat may increase the risk of esophageal adenocarcinoma and distal stomach cancer.

Bacterial overgrowth without clinical malabsorption in elderly hypochlorhydric subjects

BACKGROUND/AIMS Bacterial overgrowth of the small intestine commonly occurs in association with hypochlorhydria caused by atrophic gastritis or during treatment with omeprazole. The purpose of this study was to determine the clinical significance of bacterial overgrowth on small intestinal absorption and permeability and to evaluate the reliability of noninvasive breath tests to detect bacterial overgrowth in subjects with hypochlorhydria. METHODS Seventeen healthy, elderly subjects with atrophic gastritis or omeprazole treatment (40 mg/day) and documented bacterial overgrowth were studied. RESULTS There was no evidence of fat malabsorption (72-hour fecal fat) or clinically significant carbohydrate malabsorption (25 g D-xylose and fecal pH) in any subject. The ratio of lactulose to mannitol excreted was normal in both atrophic gastritis and omeprazole-treated groups. Three subjects in each group had abnormally high alpha 1-antitrypsin clearances. Lactulose (10 g) and glucose (80 g) hydrogen breath tests were only abnormal in 1 out of 17 subjects, whereas the 1 g [14C]D-xylose test was abnormal in 6 out of 17 subjects. CONCLUSIONS Bacterial overgrowth caused by atrophic gastritis or omeprazole treatment is typically not associated with clinically significant fat or carbohydrate malabsorption. Noninvasive breath tests for bacterial overgrowth are not reliable in subjects with hypochlorhydria.

Postprandial plasma vitamin A metabolism in humans: A reassessment of the use of plasma retinyl esters as markers for intestinally derived chylomicrons and their remnants

We investigated postprandial vitamin A metabolism by measuring retinyl ester, triglyceride, and apolipoprotein (apo)B-48 in the plasma lipoproteins of human subjects before and after fat-feeding. Following a 14-hour fast, eight healthy subjects (two men, six women, 28 to 79 years) were given a fat-rich meal (1 g fat/kg body weight) containing vitamin A (40 retinol equivalents per kilogram body weight). Blood was collected every 3 hours for 12 hours and lipoproteins were isolated by sequential ultracentrifugation. Mean plasma retinyl ester concentration peaked 6 hours after the fat-rich meal, whereas mean plasma triglyceride peaked at 3 hours. Data obtained from hourly samples in 3 subjects showed that changes in the postprandial plasma concentration of retinyl ester occurred 1 to 2 hours after changes in the plasma triglyceride concentration. In triglyceride-rich lipoproteins (TRL) of d less than 1.006 g/mL, retinyl ester similarly peaked at 6 hours, whereas triglyceride as well as apoB-48 peaked at 3 hours. Although retinyl esters were found mainly in TRL in the initial postprandial period (84%, 3 hours; 83%, 6 hours), in fasting and postprandial plasma, particularly 9 or more hours after fat-feeding, a large percentage of plasma retinyl esters were in low-density lipoproteins (LDL) (44%, fasting; 9%, 3 hours; 9%, 6 hours; 19%, 9 hours; 32%, 12 hours). A small percentage of retinyl esters were also found in postprandial high-density lipoproteins (HDL) (2% to 7%). ApoB-48 was not detected in LDL of fasting or postprandial plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Postprandial plasma retinyl ester response is greater in older subjects compared with younger subjects. Evidence for delayed plasma clearance of intestinal lipoproteins.

Postprandial vitamin A and intestinal lipoprotein metabolism was studied in 86 healthy men and women, aged 19-76 yr. Three independent experiments were carried out. In the first experiment, a supplement dose of vitamin A (3,000 retinol equivalents [RE]) was given without a meal to 59 subjects, aged 22-76 yr. In the second experiment, 20 RE/kg body wt was given with a fat-rich meal (1 g fat/kg body wt) to seven younger subjects (aged less than 50 yr) and seven older subjects (aged greater than or equal to 50 yr). In both experiments, postprandial plasma retinyl ester response increased significantly with advancing age (P less than 0.05). In the third experiment, retinyl ester-rich plasma was infused intravenously into nine young adult subjects (aged 18-30 yr) and nine elderly subjects (aged greater than or equal to 60 yr), and the rate of retinyl ester disappearance from plasma during the subsequent 3 h was determined. Mean (+/- SE) plasma retinyl ester residence time was 31 +/- 4 min in the young adult subjects vs. 57 +/- 8 min in the elderly subjects (P less than 0.05). These data are consistent with the concept that increased postprandial plasma retinyl ester concentrations in older subjects are due to delayed plasma clearance of retinyl esters in triglyceride-rich lipoproteins of intestinal origin.

Reversal of protein-bound vitamin B12 malabsorption with antibiotics in atrophic gastritis

The role of bacteria in the bioavailability of protein-bound vitamin B12 was examined in eight elderly subjects who had atrophic gastritis and in eight normal controls. On separate days and in random order, vitamin B12 absorption tests were performed using either radiolabeled crystalline or protein-bound vitamin B12. At the same time, bacterial samples were collected from the upper gastrointestinal tract. The tests and gastrointestinal aspirates were performed before and during tetracycline therapy. Crystalline vitamin B12 was absorbed to the same extent in the two study groups. Atrophic gastritis subjects absorbed significantly less protein-bound vitamin B12 than normal controls (mean +/- SEM, 0.7% +/- 0.2% vs. 1.9% +/- 0.5%, respectively). However, protein-bound vitamin B12 absorption in these subjects normalized after antibiotic therapy. These results suggest that the small amounts of vitamin B12 released from the protein binders is readily absorbed (as shown in vitro) and/or metabolized by bacteria.

THE AGING GUT * : Nutritional Issues

With improvements in health care, living standards, and socioeconomic status, more adults are living to old age. As the population ages, it is increasingly important to understand the factors that affect the nutritional status and thus the health status of older adults. Many factors contribute to inadequate nutrition, including health status, financial capacities, mobility, exercise, and physiologic needs. This article considered only the potential changes in nutritional needs because of alterations in the gastrointestinal tract owing to aging. One of the most remarkable changes with aging is the frequent development of atrophic gastritis and the inability to secrete gastric acid. This process affects approximately a third of older adults in the United States and only recently was recognized to be due to infection by H. pylori in the majority of cases. The lack of gastric acid in atrophic gastritis may lead to small intestinal bacterial overgrowth and influences the absorption of a variety of micronutrients, including iron, folate, calcium, vitamin K, and vitamin B12. Lactose maldigestion is a frequent condition in older adults and is extremely common worldwide. The intolerance of dairy products leads to avoidance of these foods and likely contributes to the development of osteopenia. Overall, the small intestine and pancreas undergo astonishingly few clinically significant changes with aging. The relative preservation of overall gastrointestinal function with aging is likely due to the large reserve capacity of this multiorgan system. Further research is needed to define the precise nutritional needs for older adults because simple extrapolation of values from younger adults is now recognized to be insufficient. In addition, it is no longer acceptable to define adequate nutriture in terms of amounts of vitamins needed to maintain serum levels of a nutrient. Further RDAs must consider the functional implications of adequate nutrition. Nutrients in the elderly will be measured as to whether they result in improvements in markers of chronic disease such as homocysteine or, most importantly, in the prevention of chronic disease such as osteoporosis and cardiovascular disease.