Use of antioxidant nutrients in the prevention and treatment of type 2 diabetes.

Type 2 diabetes, or non-insulin dependent diabetes mellitus (NIDDM), is increasingly common throughout the world. The World Health Organization has predicted that between 1997 and 2025, the number of diabetics will double from 143 million to about 300 million. The incidence of NIDDM is highest in economically developed nations, particularly the U.S., where approximately 6.5% of the population (17 million people) have either diagnosed or undiagnosed diabetes. The two most important factors contributing to the development of NIDDM are obesity and physical inactivity. The leading cause of mortality and morbidity in people with NIDDM is cardiovascular disease caused by macro- and microvascular degeneration. Current therapies for NIDDM focus primarily on weight reduction. Indeed, several investigations indicate that 65% to 75% of cases of diabetes in Caucasians could be avoided if individuals in this subgroup did not exceed their ideal weight. The success of this approach has been, at best, modest. An alternate approach to the control of Type 2 diabetes is to arrest the progress of the pathology until a cure has been found. To this end, some investigators suggest that dietary antioxidants may be of value. Several studies in humans and laboratory animals with NIDDM indicate that vitamin E and lipoic acid supplements lessen the impact of oxidative damage caused by dysregulation of glucose metabolism. In this brief review, we discuss the incidence, etiology, and current therapies for NIDDM and further explore the usefulness of dietary antioxidants in treating this disorder.

Reduced feeding response to neuropeptide Y in senescent Fischer 344 rats.

The anorexia of aging syndrome in humans is characterized by spontaneous body weight loss reflecting diminished food intake. We reported previously that old rats undergoing a similar phenomenon of progressive weight loss (i.e., senescent rats) also display altered feeding behavior, including reduced meal size and duration. Here, we tested the hypothesis that blunted responsiveness to neuropeptide Y (NPY), a feeding stimulant, occurs concurrently with senescence-associated anorexia/hypophagia. Young (8 mo old, n = 9) and old (24-30 mo old, n = 11) male Fischer 344 rats received intracerebroventricular NPY or artificial cerbrospinal fluid injections. In response to a maximum effective NPY dose (10 microg), the net increase in size of the first meal after injection was similar in old weight-stable (presenescent) and young rats (10.85 +/- 1.73 and 12.63 +/- 2.52 g/kg body wt (0.67), respectively). In contrast, senescent rats that had spontaneously lost approximately 10% of body weight had significantly lower net increases at their first post-NPY meal (1.33 +/- 0.33 g/kg body wt (0.67)) than before they began losing weight. Thus altered feeding responses to NPY occur in aging rats concomitantly with spontaneous decrements in food intake and body weight near the end of life.

Description of the long-term lipogenic effects of dietary carbohydrates in male Fischer 344 rats.

The introduction of high fructose corn syrup as a substitute sweetener for sucrose in the mid-1970s has contributed to a general increase in fructose consumption in the U.S. diet. Although several previous investigations suggested that dietary fructose increases serum triglyceride concentration and body fat, these studies have, in general, evaluated this effect in young rats fed the experimental diets for a relatively short period of the life span of the animals. Moreover, these investigations did not control for the possible effects that increased adiposity due to fructose feeding may have on serum triglyceride concentration. The purpose of the current investigation was to describe the long-term effects of specific dietary carbohydrates on serum lipid concentrations and body composition. To this end, we measured serum triglyceride, total cholesterol and HDL cholesterol concentrations and body composition of rats aged 9, 18 and 26 mo that had free access to or were restricted to 60% of free access intake of one of five diets that varied in carbohydrate source (cornstarch, sucrose, glucose, fructose or equimolar fructose plus glucose) starting at 3 mo of age. Dietary fructose significantly increased serum triglyceride concentration across the life span in rats that had free access to food or were calorie restricted. The source of dietary carbohydrate did not have a significant effect on body composition, total cholesterol or the distribution of the cholesterol fractions. These data suggest that dietary fructose per se and not the interaction between fructose and the energy content of the diet increases serum triglyceride concentration in rats.

Accumulation of advanced glycation endproducts in aging male Fischer 344 rats during long-term feeding of various dietary carbohydrates.

The observation of accelerated collagen glycation in association with enhanced progression of many age-associated diseases in hyperglycemic subjects has led researchers to propose a role of glycation in the aging process. Although short-term studies in healthy animals suggest that feeding a diet high in fructose may increase serum glucose concentrations and increase glycemic stress, the effects of a long-term feeding, i.e., life span, are unknown. This study was designed to evaluate the long-term effects of dietary carbohydrates on serum and tissue markers of glycemic stress. Three-month-old male Fischer 344 rats were given free access to or restricted to 60% caloric intake of one of five isocaloric diets that contained as their carbohydrate source either cornstarch, glucose, sucrose, fructose or equimolar amounts of fructose and glucose. Rats were killed at 9-, 18- or 26-mo of age. Glycated hemoglobin, serum glucose and fructosamine levels were measured as markers of serum glycemic stress. Collagen-associated fluorescence and pentosidine concentrations were measured in skin, aortic, tracheal and tail tendon collagen as markers of advanced glycation endproducts (AGE). The source of dietary carbohydrate had little effect on markers of glycemic stress and the accumulation of AGE. Restricting the amount of calories consumed resulted in lower serum glucose concentrations, glycated hemoglobin levels and pentosidine concentrations in tail tendon collagen. Our data suggest that the rate of collagen glycation is tissue-specific. These results suggest that long-term feeding of specific dietary carbohydrates does not alter serum glucose concentrations or the rate of collagen glycation. Rather, age-related accumulation of AGE is more closely related to caloric intake.

Neurochemical alterations during age-related anorexia.

Unexplained weight loss during the latter stages of aging is commonly preceded by a spontaneous diminution in food intake. Multiple etiologies of age-related anorexia in humans, ranging from social isolation to impaired gastrointestinal function, have been proposed. The observation of this phenomenon in older laboratory animals suggests that physiological changes play a significant causal role. A continually expanding body of information on the neurochemical control of food intake supports a contribution of altered neurochemistry to dysregulated feeding behavior. This review provides an update on the relationship between declining food intake during advanced age and physiological (specifically neurochemical) function. The complexity of the control of food intake as well as the variety of investigative methods used in this field of study render the identification of definitive causes difficult. Evidence presented here is evaluated and possible etiologic factors are suggested.

Alterations in endogenous circadian rhythm of core temperature in senescent Fischer 344 rats.

We assessed whether alterations in endogenous circadian rhythm of core temperature (CRT) in aging rats are associated with chronological time or with a biological marker of senescence, i.e., spontaneous rapid body weight loss. CRT was measured in male Fischer 344 (F344) rats beginning at age 689 days and then continuously until death. Young rats were also monitored. The rats were housed under constant dim red light at 24-26 degrees C, and core temperature was recorded every 10 min via biotelemetry. The CRT amplitude of the body weight-stable (presenescent) old rats was significantly less than that of young rats at all analysis periods. At the onset of spontaneous rapid weight loss (senescence), all measures of endogenous CRT differed significantly from those in the presenescent period. The suprachiasmatic nucleus (a circadian pacemaker) of the senescent rats maintained its light responsiveness as determined by an increase in c-fos expression after a brief light exposure. These data demonstrate that some characteristics of the CRT are altered slowly with chronological aging, whereas others occur rapidly with the onset of senescence.

Brown adipose tissue thermogenesis during aging and senescence.

We have found that cold- and norepinephrine-induced brown adipose tissue (BAT) nonshivering thermogenesis (NST) is significantly lower in old male Fischer 344 rats and is associated with the decreased ability of these animals to maintain homeothermy. This decline in BAT thermogenesis is not as great in females. Although the mechanism(s) underlying this gender difference in the age-related decrease in brown fat NST are not completely elucidated, they do not appear to reflect decreased sympathetic neural activity of BAT in the older males vs. females. Rather, our investigations, strongly suggest that the blunted cold-induced heat production of BAT reflects less functional BAT. The fact that the older animals have less functional BAT than do their younger counterparts may predispose them to the accumulation of excess body fat. Our studies have also found that near the end of the natural life of these rats, they enter a state of senescence that can be identified by spontaneous rapid body weight loss, resulting from decreased food intake. In this state, the rats are considerably more susceptible to cold than are comparably aged presenescent (body weight stable) rats of the same chronological age. The greater hypothermia exhibited by the senescent vs. presenescent rats during cold exposure is associated with a significant reduction in the amount of functional brown fat and in the amount of heat each brown fat cell can generate. It is the intent of this review to discuss the findings of these investigations.

Meal patterns associated with the age-related decline in food intake in the Fischer 344 rat.

We previously reported that aging Fischer 344 (F344) rats display a spontaneous, rapid loss in body weight associated with decreased food intake near the end of life. Here, we describe the specific changes in feeding patterns underlying this reduced intake. Nine male F344 rats, aged 25 mo, were monitored continuously until 7 days after the onset of spontaneous rapid weight loss (i.e., senescence). Regardless of age at death (25.5-32.5 mo), all senescent rats demonstrated a similar pattern of decreased food intake. They ate significantly smaller meals (g/meal) of shorter duration during spontaneous rapid weight loss compared with their period of weight stability (presenescence). However, no differences occurred in the number of meals eaten per day. Rapid weight loss had no effect on the rats' selection of preferred diets. Serum levels of the hormone leptin were not higher in the senescent vs. age-matched presenescent rats, nor was the incidence of common disease different in senescent animals. Moreover, the area of the pituitary-hypothalamus interface, measured to identify possible hypothalamic compression, was similar in the senescent rats and an age-matched, presenescent control group despite significantly greater pituitary size in the former. Our data show that simultaneous with rapid spontaneous weight loss, aging rats demonstrate significant changes in feeding patterns suggestive of earlier satiation. These feeding alterations do not result from loss of ability to select for palatable food, elevated serum leptin levels, specific pathology, or hypothalamic compression.

Market-stage analysis enhances strategic planning.

Changing market conditions are challenging healthcare organizations to determine how to allocate resources and make operational planning decisions to prepare for future changes. A vital part of meeting these challenges is understanding the impact of market stages, and using that knowledge to build effective business strategies. Financial modeling that includes market-stage information provides insight into market opportunities and presents a clearer picture of the organizational changes that will need to be implemented at each stage. Effective strategic action should take into account critical success factors in market responsiveness, organizational responsiveness, operational effectiveness, and financial strength.

Effects of age, gender, and senescence on beta-adrenergic responses of isolated F344 rat brown adipocytes in vitro.

We previously reported greater age-related attenuation of cold-induced thermoregulation and brown adipose tissue thermogenic capacity in male vs. female F344 rats. With onset of the rapid weight loss that occurs near the end of the lifespan, this age-related attenuation becomes severe. We refer to this "end-of-life" physiological state of older rats as senescence. Here, we measured oxygen consumption of isolated brown adipocytes and found no age (6 vs. 12 vs. 26 mo) or gender effects on maximal norepinephrine (NE)- or CL-316,243 (beta 3-adrenergic agonist)-induced responses. In contrast, brown adipocytes from 22- to 26-mo-old senescent rats (males and females) consumed 51-60% less oxygen during maximal stimulation with NE and CL-316,243 than did cells from 26-mo-old presenescent rats. This attenuation was associated with lower (65-72%) uncoupling protein 1 concentrations but no alterations in NE-induced cAMP levels or lipolysis. Our data indicate that senescence, but not chronological age, significantly impacts NE-/beta 3-mediated thermogenesis of isolated brown adipocytes and that this effect involves altered mitochondrial rather than altered membrane or cytosol events.

Cold-induced thermoregulation and biological aging.

Aging is associated with diminished cold-induced thermoregulation (CIT). The mechanisms accounting for this phenomenon have yet to be clearly elucidated but most likely reflect a combination of increased heat loss and decreased metabolic heat production. The inability of the aged subject to reduce heat loss during cold exposure is associated with diminished reactive tone of the cutaneous vasculature and, to a lesser degree, alterations in the insulative properties of body fat. Cold-induced metabolic heat production via skeletal muscle shivering thermogenesis and brown adipose tissue nonshivering thermogenesis appears to decline with age. Few investigations have directly linked diminished skeletal muscle shivering thermogenesis with the age-related reduction in cold-induced thermoregulatory capacity. Rather, age-related declines in skeletal muscle mass and metabolic activity are cited as evidence for decreased heat production via shivering. Reduced mass, GDP binding to brown fat mitochondria, and uncoupling protein (UCP) levels are cited as evidence for attenuated brown adipose tissue cold-induced nonshivering thermogenic capacity during aging. The age-related reduction in brown fat nonshivering thermogenic capacity most likely reflects altered cellular signal transduction rather than changes in neural and hormonal signaling. The discussion in this review focuses on how alterations in CIT during the life span may offer insight into possible mechanisms of biological aging. Although the preponderance of evidence presented here demonstrates that CIT declines with chronological time, the mechanism reflecting this attenuated function remains to be elucidated. The inability to draw definitive conclusions regarding biological aging and CIT reflects the lack of a clear definition of aging. It is unlikely that the mechanisms accounting for the decline in cold-induced thermoregulation during aging will be determined until biological aging is more precisely defined.

Cellular proliferation and UCP content in brown adipose tissue of cold-exposed aging Fischer 344 rats.

Previous investigations have demonstrated that older vs. younger rats respond to cold exposure with blunted cold-induced nonshivering thermogenesis of brown adipose tissue (BAT). This reduction in nonshivering thermogenesis is associated with reduced mass and blunted nonshivering thermogenic capacity of BAT. The purpose of this study was to test the hypothesis that brown fat in 26-mo-old Fischer 344 (F344) male rats has an impaired capacity to respond to the trophic stimulus of chronic cold exposure with increases in cell number, mass, and uncoupling protein (UCP) content. To test this hypothesis, the response of BAT to chronic cold exposure was evaluated in young and old rats. We exposed 6-, 12-, and 26-mo-old F344 male rats to 10 degrees C for 5 days and measured interscapular BAT (IBAT) mass, cell size and proliferation, and mitochondrial UCP1 content. Plasma concentrations of insulin-like growth factor I (IGF-I) and norepinephrine IBAT mass, cell proliferation, or UCP1 content in response to chronic cold, whereas the 6-mo-old rats had a nearly 2-fold cold-induced increase in IBAT mass, a 26-fold increase in cell proliferation, and a 4-fold increase in UCP1 content. Cold exposure also produced an increase of 29, 19, and 20% in mature brown adipocyte cell size of the 6-, 12-, and 26-mo-old animals, respectively. Plasma levels of IGF-I were unaffected by cold at all ages, whereas NE levels were increased by the cold exposure and by increasing age. These data support the hypothesis that brown fat in old F344 rats does not respond to the trophic stimulus of chronic cold exposure to the same degree as younger animals. Moreover, these data indicate that the observed cold- or age-induced changes in levels of growth factors evaluated in this study were not associated with the lack of cold-induced preadipocyte proliferation or increased UCP1 in brown fat of the 26-mo-old rats.

Some considerations for the development of diets for mature rodents used in long-term investigations.

Nutritional requirements for mature rodents used in long-term investigations are virtually unknown. The limited knowledge of the dietary needs of mature rodents is due in part to overreliance on weanling animals fed an experimental diet for relatively short periods. Generalizations made from observations of weanling rodents are not appropriate for all ages. Dietary recommendations for rodents have been established, for the most part, by using the nutritional benchmark of maximal growth rate in animals fed ad libitum. Although this method provides valuable insight into the understanding of nutritional deficiency, it is less effective in determining nutrient requirements for mature animals used for the long term. The implication that maximal growth resulting from ad libitum feeding may not indicate the best dietary regimen in the long term is consistent with the observation that energy-restricted rodents live significantly longer and have lower incidence of disease that do their ad libitum-fed counterparts. These and other findings discussed in the review suggest that nutrient requirements established for young rodents may need re-evaluation to determine their applicability to the dietary recommendations for older animals used in long-term investigations.

Altered cellular heterogeneity as a possible mechanism for the maintenance of organ function in senescent animals.

We tested the hypothesis that an alteration in the functional heterogeneity of cell populations (i.e., changes occurring in sensitivity and responsiveness to external stimuli among individual cells) may be a mechanism by which some organs are able to resist age-related decrements in function. To this end, changes in cytoplasmic free calcium concentration ([Ca2+]i) following glucose stimulation of individual pancreatic beta cells isolated from male F344 rats of ages 6, 12, and 26 mo were used as a model for evaluating responsiveness and sensitivity. Changes in [Ca2+]i of individual beta cells were monitored using fura-2 microspectrofluorimetry. No differences were observed in [Ca2+]i or in insulin secretion per beta cell among the age groups at any of the glucose concentrations. However, the percentage of beta cells that were responsive to a stimulatory glucose concentration (> 5.5 mM) was significantly greater in islets from the 26-mo-old rats (76%) as compared to the 6- and 12-mo-old animals (63% and 65%, respectively). Of the responsive beta cells, a significantly greater percentage of those from the 26-mo-old rats (72%) responded at the lowest stimulatory glucose concentration (7.5 mM) as compared to the 6- and 12-mo-old animals (58% and 60%, respectively). These data suggest that the maintenance of organ function in older rats at a level comparable to that of younger animals may be accomplished, in part, by an increase in the percentage of cells that are responsive to stimuli and/or by an increase in the sensitivity of the responsive cells.

Relationship between cold-induced thermoregulation and spontaneous rapid body weight loss of aging F344 rats.

We previously showed that, although cold-induced thermoregulation is attenuated in 26-mo-old male Fischer 344 (F344) rats, not all rats this age exhibit the same degree of cold-exposed hypothermia or diminished brown adipose tissue nonshivering thermogenic capacity. Examination of this heterogeneity suggested the hypothesis that it was associated with a difference in the physiological state between aged rats that were maintaining stable body weight versus those showing the rapid weight loss often occurring near the end of the rat's natural life span. To test this, we acutely exposed male F344 rats to cold (4 h at 6 degrees C) beginning at 24 mo of age. This exposure was weekly for the first 2 wk and then on alternate weeks as long as the rat's body weight was stable. If body weight progressively declined for 3-5 consecutive days, the rat's response to the acute cold exposure was again measured, as was that of two additional rats not displaying this rapid loss in body weight. If body temperature decreased during the cold exposure to intraperitoneal temperatures < or = 32.5 degrees C, the rat was killed with pentobarbital sodium and interscapular brown adipose tissue was removed. One of the age-matched controls was also killed at this time. The age at which body weight showed a spontaneous rapid decline ranged from 24.5 to 29 mos. All eight rats displaying spontaneous rapid weight loss had significant hypothermia during the acute cold exposure, whereas none of the eight weight-stable rats did. The development of hypothermia in the spontaneous rapid weight loss group was not, in general, observed before their weight loss. The weight loss and hypothermia were associated with lower levels of brown fat uncoupling protein and significant changes in body fat and protein. These data suggest that the development of senescence-related hypothermia occurs rapidly and is not a simple function of chronological age or the median life span of the animals. Furthermore, these data imply that the rate of aging in terms of maintenance of thermoregulatory homeostasis has both a gradual and rapid component, the latter being associated with a different physiological state than the former.

Effects of caloric restriction and source of dietary carbohydrate on glycemic status of the Fischer 344 rat.

The effects of caloric restriction and dietary carbohydrate source on the regulation of insulin secretion were evaluated in vivo and using islets of Langerhans isolated from 9-month-old male Fischer 344 rats. Serum glucose and insulin concentrations of rats fed a calorie-restricted diet for 6 months were significantly less than those of rats fed ad libitum, regardless of carbohydrate source. Rats fed diets containing fructose, either as a monosaccharide or as a component of a disaccharide, had generally greater serum insulin and glucose concentrations than rats fed diets containing no fructose. Glucose-stimulated insulin secretion by islets isolated from rats fed the restricted diet was significantly less than those of rats fed ad libitum. No differences in islet insulin secretion associated with carbohydrate source were observed. These results suggest that caloric restriction and the source of dietary carbohydrate can have significant effects on the glycemic status of the rat.

Effect of participation in congregate-site meal programs on nutritional status of the healthy elderly.

OBJECTIVE: This study was designed to evaluate whether participation in a congregate-site meal program influenced the nutritional status of a group of healthy elderly. DESIGN: Nutritional status, as defined by dietary intake and biochemical indexes, was assessed in free-living persons (aged 60 to 89 years) who either did (n = 70) or did not (n = 65) participate in the meal program. Three-day mean intakes of 17 nutrients and serum levels of 13 indexes of nutritional status were measured. STATISTICAL ANALYSES: Multifactorial analysis of variance was used to determine differences in nutrient intake data and biochemical indexes between the groups. By means of correlation analysis, relationships between income and main outcome measures were examined. chi 2 Analysis was used to determine differences in response to categorical variables of the questionnaire. RESULTS: In general, dietary intakes of participants did not differ significantly from those of nonparticipants, nor did the meal provided at the site significantly affect the overall dietary intake of participants. Mean biochemical indexes of nutritional status were within normal ranges for participants and nonparticipants, except for iron. However, 26% of the population consumed diets that may place them at risk for nutritional inadequacy. CONCLUSIONS: Mean dietary intake data and biochemical indexes of nutritional status suggest that the congregate-site meal program did not significantly affect the nutritional status of the population surveyed. Additional studies focusing on the nutritional intake and status of low-income, ethnic minority, and socially isolated participants in the congregate-site meal program are needed to assess which populations are at risk for nutritional deficiencies.

Influence of dietary sucrose on biological aging.

The segment of the population aged > 65 y is the fastest growing age segment in most developed countries. The increasing numbers of individuals living into their eighth and ninth decades of life have shifted the focus of biomedical research from seeking mechanisms for extending life to finding ways to improve health and to reduce age-related morbidity. One area of research that has shown considerable promise for improving the health of elderly people is nutrition. I review recent literature pertinent to the influences of nutrition on biological aging by discussing the effects of dietary sucrose and other carbohydrates on glucose homeostasis, age-related disorders and pathology, and life span. Although critical gaps remain in our understanding of how dietary sucrose can affect biological aging, evidence exits that the type and amount of dietary carbohydrate can significantly affect the health and life span of elderly people.