Human aging is associated with altered TNF-alpha production during hyperglycemia and hyperinsulinemia

John P. Kirwan1,2, Raj K. Krishnan3, James A. Weaver3, Luis F. Del Aguila3, and William J. Evans4

1 Departments of Reproductive Biology and 2 Nutrition, Case Western Reserve University School of Medicine at MetroHealth Medical Center, Cleveland, Ohio 44109; 3 Noll Physiological Research Center, Pennsylvania State University, University Park, Pennsylvania 16802; and 4 Nutrition, Metabolism, and Exercise Division, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72114


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Changes in tumor necrosis factor-alpha (TNF-alpha ) may provide a mechanism to explain impaired glucose metabolism with advancing age. Hyperglycemic clamps (180 min, 10 mM) were performed on seven older [67 ± 2 yr; body mass index (BMI) 24.7 ± 1.0 kg/m2] and seven younger (22 ± 1 yr; BMI 21.8 ± 1.3 kg/m2) healthy sedentary males with normal glucose tolerance. TNF-alpha production at basal and at the end of 180 min of hyperglycemia and hyperinsulinemia was measured ex vivo from lipopolysaccharide-stimulated (1 ng/ml) peripheral blood mononuclear cells. Plasma glucose, insulin, and C-peptide levels were similar in both groups at basal and during the last 30 min of the hyperglycemic clamp. Glucose infusion rates were lower (P < 0.004) in the older group compared with the young, indicating decreased insulin action among the older subjects. Basal TNF-alpha secretion was similar in older and younger subjects. TNF-alpha was suppressed (P < 0.02) in the younger group (230 ± 46 vs. 126 ± 49 pg/ml; basal vs. clamp) but not in the older group (153 ± 37 vs. 182 ± 42 pg/ml), with significant group differences in response (P < 0.05). A significant correlation was observed between the level of suppression in TNF-alpha production and insulin action (Kendall's rank, tau  = 0.40, P < 0.05). Furthermore, the TNF-alpha response during the clamp was related to fat mass (r = 0.88, P < 0.001) and abdominal fat (r = 0.81, P < 0.003). In conclusion, these findings suggest a possible mechanism by which TNF-alpha may modulate glucose metabolism in younger people. Aging and modest increases in adiposity prevent the "normal" suppression of TNF-alpha production after a sustained postprandial-like hyperglycemic-hyperinsulinemic stimulus, which may contribute in part to the decline in insulin sensitivity in older men.

insulin resistance; obesity; diabetes; abdominal adiposity


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

HUMAN AGING is associated with the development of glucose intolerance (2), abnormal pancreatic beta -cell secretion (3, 18, 25, 32), and insulin resistance (6, 8, 26). However, it is unclear as to the mechanism responsible for these changes as people age. Recent investigations have implicated the cytokine tumor necrosis factor (TNF)-alpha as a modulator of glucose metabolism. Particularly, TNF-alpha has been associated with the metabolic defects related to insulin resistance. In vitro studies show that TNF-alpha can induce insulin resistance and downregulate insulin receptor signaling in cultured adipocytes (22), hepatocytes (14), and skeletal muscle (10). Furthermore, increased TNF-alpha is associated with insulin resistance in obesity (23), sepsis (29), after muscle damage (11), and with age-associated muscle wasting (17). Interestingly, elevated plasma TNF-alpha levels have been observed in older men and women (37), and increased TNF-alpha protein expression has been reported in adipose tissue and skeletal muscle of obese and diabetic humans (24, 35, 40). Indeed, TNF-alpha may provide a link to explain the impaired glucose metabolism that is seen with advancing age. Furthermore, the normal age-related increases in body fat and abdominal adiposity (41) may be related to the effects of age on TNF-alpha and its role as a glucoregulatory modulator.

The purpose of this investigation was to determine the effects of physiologically elevated levels of glucose and insulin on TNF-alpha production in healthy sedentary older men. To determine the effects of age on TNF-alpha production, the responses among these older men were compared with those of a group of healthy sedentary younger men. Because the focus of the investigation was to examine underlying abnormalities in TNF-alpha and glucoregulation among successfully aging older adults, the older and younger men had normal glucose tolerance and pancreatic beta -cell secretion and were not obese.


    METHODS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Subjects. Fourteen men (7 younger, age 21-28 yr, and 7 older, age 59-75 yr) participated in this study. All subjects were screened for acute and chronic diseases, and none was taking medications that would affect carbohydrate metabolism or immune function. In addition, all of the subjects were sedentary, with a similar activity level between groups, as assessed by a physical activity questionnaire. None of the subjects was involved in any regular exercise regimen for at least 6 mo before the time of testing. All participants had a normal plasma glucose response to a 75-g oral glucose tolerance test (1). All of the subjects provided written informed consent in accordance with The Pennsylvania State University guidelines for the protection of human subjects.

Height without shoes was measured to the nearest 1.0 cm. Body weight was measured to the nearest 0.1 kg. Body circumferences were measured at the waist (level of the umbilicus) and hip (point of widest circumference around the buttocks). Waist circumference and waist-to-hip ratio were used to estimate abdominal adiposity (26). Body density and body fat were determined by hydrostatic weighing after an overnight fast as previously described (28).

Study design. All of the trials included residence at the General Clinical Research Center (GCRC) for three nights and two consecutive days (day 1 and day 2). Subjects consumed a balanced diet and received all of their meals from the GCRC for the 2 days before the clamp (young, 3,704 ± 94 kcal; old, 2,613 ± 130 kcal). During these 2 days, the subjects maintained a normal level of activity and did not exercise. Hyperglycemic clamps were performed on day 3 of residence.

Hyperglycemic clamp. The hyperglycemic clamp (180 min, 10.0 mM) was performed as described by DeFronzo et al. (9). After an overnight fast (~12 h), the subjects voided morning urine and were weighed. An 18-gauge polyethylene catheter was inserted in an antecubital vein for the infusion of glucose (20% dextrose). A second 20-gauge polyethylene catheter was inserted in retrograde fashion in a dorsal hand vein, and the hand was warmed in a heated box (~65°C) for sampling of arterialized venous blood. Baseline blood samples were drawn for glucose, insulin, and C-peptide determination. Subsequently, plasma glucose concentrations were raised to 10.0 mM within 15 min by using a primed glucose infusion with a variable-speed infusion pump (Harvard Apparatus, South Natick, MA). Plasma glucose concentrations were maintained at 10.0 mM for a further 165 min by a variable-rate infusion based on the prevailing plasma glucose concentration. Blood samples (0.5 ml) were drawn every 5 min and were assayed immediately by the glucose oxidase method (Beckman Instruments, Fullerton, CA). The glucose concentrations were used to adjust the infusion rate throughout the clamp procedure. In addition, blood samples (3.0 ml) were drawn every 2 min for the first 10 min (0-10 min) and every 15 min for the remainder of the clamp procedure (15-180 min) to determine insulin and C-peptide concentrations during the first (0-10 min) and second (10-180 min) phases of pancreatic secretion. At the conclusion of the clamp, a urine sample was obtained for the determination of glucose concentration.

Analytical methods. Mononuclear cell (MNC) isolation and culture were performed on 20 ml of arterialized venous blood, which was obtained at 0 and 180 min of the clamp. The cells were isolated by Ficoll-Hypaque centrifugation (4), washed two times in pyrogen-free saline, suspended in RPMI (100 U/ml penicillin, 100 µg/ml streptomycin, and 0.3 mg/ml L-glutamine) with serum substitute TCH, and seeded in coated culture plates (2.5 × 106 cells/ml). The cells were then incubated (humidified, 5% CO2, 37°C) for 24 h with lipopolysaccharide endotoxin (LPS, 1 ng/ml). After incubation, supernatants (10,000 g for 1 min) were obtained and stored at -70°C until analysis. TNF-alpha concentrations were measured in duplicate by ELISA (Endogen, Woburn, MA). Complete blood counts were obtained using a Coulter Counter (Coulter Instruments). Plasma insulin and C-peptide concentrations were determined in duplicate by double-antibody RIA using commercial kits (Linco Research, St. Charles, MO, and Diagnostic Products, Los Angeles, CA). To reduce interassay variability, all samples for each subject were run in the same assay.

Statistics. The MIXED procedure for the Statistical Analysis System (SAS Institute, Cary, NC) was used for ANOVA by the rank transformation (nonparametric) approach to identify statistical differences in the data. Primary dependent variables were analyzed by two-way repeated-measures ANOVA with the following main effects: group (young and old) and trial (basal and clamp). Descriptive data were analyzed using a one-way ANOVA. Model-adjusted P values from a comparison of the least-squared means were used to determine differences between basal and clamp within groups. Group-by-trial interaction was used to demonstrate group differences in measured responses when the basal was compared with the clamp within groups. Spearman product-moment correlations were used to determine the relationship between the TNF-alpha response and body composition. Kendall's rank, tau , was used to determine the relationship between the change in TNF-alpha production and estimated insulin action. All values are expressed as means ± SE. An alpha -level of 0.05 was used to determine statistical significance.


    RESULTS
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

Subjects were similar in weight, fat-free mass, and body mass index (BMI), but the older group had a higher fat mass, waist circumference, and waist-to-hip ratio (Table 1). All subjects had a normal response to an oral glucose tolerance test (2-h value, 5.6 ± 0.4 mM for the older group and 5.7 ± 0.5 mM for the younger group). Basal glucose, insulin, and C-peptide levels were within normal limits and were similar between the two age groups (Table 2). Both groups were clamped at similar glucose levels, and there was no difference in the insulin and C-peptide response to hyperglycemia (Table 2). However, the glucose infusion rate that was required to maintain hyperglycemia in the older group was less than the rate in the younger group (10.0 ± 0.1 vs. 6.7 ± 0.6 mg · kg fat-free mass-1 · min-1, P < 0.004). To estimate insulin action in the two groups, the glucose disposal rate (M value, calculated from the glucose infusion rate from 150 to 180 min and adjusted for the glucose equivalent space and urinary glucose loss, if any) was divided by the corresponding insulin concentration (I). Insulin action was reduced (P < 0.02) in the older men (Fig. 1).

                              
View this table:
[in this window]
[in a new window]
 
Table 1.   Subject characteristics


                              
View this table:
[in this window]
[in a new window]
 
Table 2.   Plasma glucose, insulin, C-peptide, and TNF-alpha levels and monocyte TNF-alpha production at rest and during the hyperglycemic clamp in older and younger men



View larger version (60K):
[in this window]
[in a new window]
 
Fig. 1.   Estimate of insulin sensitivity based on the ratio of the glucose disposal rate (M) to insulin concentration (I) during the hyperglycemic-hyperinsulinemic clamp. M and I were calculated for the final 150-180 min of the clamp. Units are expressed relative to fat-free mass (FFM). *Significantly lower sensitivity in the older group, P < 0.02.

TNF-alpha production was similar for both groups in the basal state. However, hyperglycemia and hyperinsulinemia resulted in a suppression of TNF-alpha secretion in the young subjects but no change in the older men (Table 2 and Fig. 2). The response between the two groups was significantly different (P < 0.05). Univariate analysis revealed a direct relationship between TNF-alpha production after hyperglycemia-hyperinsulinemia and both fat mass (r = 0.88, P < 0.001) and waist circumference (r = 0.81, P < 0.003) for the combined groups (Figs. 3 and 4). In addition, the amount of suppression in TNF-alpha production during hyperglycemia-hyperinsulinemia was directly associated with insulin action, estimated from the M-to-I ratio during the clamp (Kendall's rank, tau  = 0.40, P < 0.05). As shown in Table 2, plasma TNF-alpha concentrations followed similar trends as monocyte TNF-alpha production in both groups; however, the decrease after hyperglycemia-hyperinsulinemia for the young was not significant (P = 0.20). Basal plasma TNF-alpha concentrations were not significantly increased in the older compared with younger men (P = 0.18).


View larger version (34K):
[in this window]
[in a new window]
 
Fig. 2.   Tumor necrosis factor (TNF)-alpha production from monocytes cultured with lipopolysaccharide for 24 h. Basal samples were collected before the clamp, and clamp samples were collected at the end of 180 min of the glucose infusion. *Clamp TNF-alpha production was significantly lower than basal in the young group, P < 0.02. **TNF-alpha response to hyperglycemia-hyperinsulinemia in the older group was significantly different from that of the young group, P < 0.05.



View larger version (19K):
[in this window]
[in a new window]
 
Fig. 3.   Correlation between abdominal adiposity and the suppression of TNF-alpha production during the clamp. Data are shown for 14 men with normal glucose tolerance. open circle , Older men; , younger men. TNF-alpha was measured from lipopolysaccaride-stimulated monocytes obtained at 0 and 180 min of the clamp. Abdominal adiposity was estimated from waist circumference.



View larger version (16K):
[in this window]
[in a new window]
 
Fig. 4.   Correlation between fat mass and the suppression of TNF-alpha production during the clamp. Data are shown for 14 men with normal glucose tolerance. open circle , Older men; , younger men. TNF-alpha was measured from lipopolysaccharide-stimulated monocytes obtained at 0 and 180 min of the clamp. Fat mass was estimated from hydrostatic weighing.

Total MNC, lymphocyte, monocyte, and granulocyte numbers were similar for both the older and younger groups under basal conditions (Table 3). The hyperglycemic-hyperinsulinemic conditions that prevailed during the clamp resulted in a significant decrease in total MNC and lymphocyte numbers in both groups. Monocyte number was decreased in the older group but not the young. Granulocyte number was not changed in either group.

                              
View this table:
[in this window]
[in a new window]
 
Table 3.   Blood cell counts at rest and during the hyperglycemic clamp in older and younger men


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

The present study is the first to show that, although older healthy men may have normal glucose tolerance, there is an underlying abnormality in TNF-alpha production when presented with a sustained physiological hyperglycemic and hyperinsulinemic challenge. Compared with a group of healthy young men, the older men failed to show a "normal" suppression in TNF-alpha production under postprandial-like conditions. Our data provide further support for the role of TNF-alpha as a modulator of insulin-mediated glucose metabolism, and, indeed, TNF-alpha may contribute to the decline in insulin action observed among these older men. Although the older men were relatively lean, fat mass and abdominal fat were significantly greater than in the young group. Furthermore, the independent associations between TNF-alpha and both fat mass and waist circumference suggest that the increased body fat, particularly abdominal fat, may be a key determinant of the observed differences in TNF-alpha secretion and its potential role in modulating insulin action.

The effect of in vivo hyperglycemia, or simultaneous hyperglycemia and hyperinsulinemia, on TNF-alpha secretion in humans remains unknown, despite the fact that these conditions are most reflective of the postprandial state and may have a considerable bearing on the development of insulin resistance. Indeed, much of what we know about the relationship between TNF-alpha and glucose metabolism is based on studies that have examined how TNF-alpha affects insulin receptor signaling and consequently glucose uptake or how TNF-alpha stimulates insulin secretion from beta -cells (19, 20, 36). In vitro studies using supraphysiological glucose concentrations (>22 mM) have reported an increase in TNF-alpha secretion from healthy human peripheral blood MNCs (20, 36). The exact mechanism by which hyperglycemia alters TNF-alpha secretion in these cells is unknown, but hyperglycemia can stimulate transcription of TNF-alpha mRNA and protein turnover, with a possible mechanism being the increased osmolarity that is associated with high glucose (36).

In contrast to these in vitro studies with hyperglycemia, healthy sedentary young men in the present study showed an ~45% decrease in TNF-alpha secretion after hyperglycemia and hyperinsulinemia. We took these data to represent the normal in vivo TNF-alpha response to 3 h of hyperglycemia coupled with hyperinsulinemia in males. So, is there a physiological benefit to decreased TNF-alpha secretion after hyperglycemia and hyperinsulinemia in these young men? It is now well documented that TNF-alpha can impair insulin receptor signaling in adipose tissue and skeletal muscle, thereby decreasing insulin-mediated glucose uptake (10, 11, 14, 22, 23, 29). It was recently shown that TNF-alpha promotes Ser307 phosphorylation of insulin receptor substrate (IRS)-1, which impairs IRS-1 association with the insulin receptor, thus inhibiting downstream insulin signaling (39). Furthermore, TNF-alpha production by monocytes from healthy young men is positively correlated with the activity of the downstream protein phosphatidylinositol 3-kinase in skeletal muscle during transient insulin resistance (11). Because TNF-alpha appears to play an important role in reducing insulin-stimulated glucose metabolism, it may be beneficial to be able to control TNF-alpha production when there is a need to increase glucose disposal. The decrease in TNF-alpha secretion among the younger group suggests a novel mechanism whereby TNF-alpha suppression may help to modulate and facilitate glucose disposal.

In contrast, healthy sedentary older men failed to suppress TNF-alpha secretion during similar hyperglycemic and hyperinsulinemic conditions. Furthermore, even though the older men had normal glucose tolerance and a similar insulin secretion as the younger subjects, glucose infusion rates were lower in the older group. The glucose infusion rates were calculated relative to the prevailing insulin concentration (M-to-I ratio) and were used as a surrogate measure of insulin resistance. As shown previously (13, 25, 28), insulin resistance was increased among the older group. The correlation between the degree of TNF-alpha suppression and insulin action suggests that the mechanism responsible for impaired glucose metabolism in the older men may be related to TNF-alpha . It has been shown that plasma TNF-alpha is increased with advancing age, and the increase is associated with insulin resistance (37). A similar observation has been reported when comparing plasma TNF-alpha levels in young and old rats (33). Furthermore, when old rats are infused with TNF-alpha , they experience increased insulin resistance (33). When these observations are coupled with TNF-alpha production data from the present study, the emerging hypothesis is that the decline in insulin sensitivity with advancing age may be related to impaired suppression of TNF-alpha secretion, particularly during postprandial periods when glucose and insulin levels are elevated.

The effect of aging per se on TNF-alpha secretion under basal conditions has not been clearly established (38). In the present study, data collected before the clamp allowed us to compare TNF-alpha production in older vs. younger men. Although TNF-alpha secretion was ~33% lower in the older compared with the younger group, the difference was not significant. Mooradian et al. (34) also reported ~40% lower TNF-alpha secretion when comparing young men with an older group of subjects, which again was not significantly different. Roubenoff et al. (38) found that LPS-stimulated TNF-alpha secretion was not increased with age. In contrast, several studies report a decrease in LPS-induced TNF-alpha production with age (5, 12, 16). The similarity in the TNF-alpha response between the young and old groups under fasting conditions in the present study, and the difference between these results and the findings of other investigators who have shown a decrease in TNF-alpha secretion with age, may be a function of the relative health status of the study subjects. The older subjects in our study were very healthy, took no medications, and had no acute or chronic cardiovascular or metabolic abnormalities. They were in the healthy category according to NHANES III data, were not overweight, and had a BMI of <25 kg/m2. Approximately 30% of 65- to 74-yr-old men in the United States have a BMI <25 kg/m2 (27). We also controlled for the activity level before the procedures and standardized the diet and residence before testing. Thus these data are relevant to healthy aging per se and are not influenced by age-related diseases or antecedent diet and physical activity.

The change in TNF-alpha secretion after hyperglycemia and hyperinsulinemia was directly related to fat mass and abdominal fat. Although both groups of men were relatively lean, the older men did have greater fat mass and waist circumference compared with the younger group. Thus it appears that, with advancing age, even modest increases in adiposity, especially in the abdominal region, may contribute to the inability to suppress TNF-alpha secretion during hyperglycemia and hyperinsulinemia. These data extend our previous observations (25, 26) and those of Coon et al. (7) showing that age-related changes in insulin resistance were a function of abdominal adiposity. The present data are particularly interesting because they provide a potential mechanism to explain these observations and are supported by earlier reports linking obesity, elevated TNF-alpha expression, and insulin resistance (21, 23, 24, 40). The issue of body fat distribution is particularly important in light of a recent report that TNF-alpha secretion from subcutaneous adipose tissue of obese women is related to insulin-stimulated glucose transport in adipocytes (30). Data from the present study suggest that abdominal adiposity is also associated with altered TNF-alpha secretion from monocytes in nonobese older men who have experienced an age-related increase in insulin resistance. Additional studies will be required to determine whether being overweight or obese increases or decreases TNF-alpha further and whether these changes are associated with glucose metabolism.

Fasting MNC numbers were similar in older and younger men and were suppressed to the same extent in both groups after the clamp. Monocytes were reduced in older, but not younger, men after the clamp. The reason for the decrease in the older men is unclear, but it is known that hyperglycemia can induce monocyte adherence to endothelium in diabetic rats through an increase in nonenzymatic glycation adducts (15). It is also known that there is an increased accumulation of advanced glycation end products (AGE) with advancing age, particularly in the presence of diabetes (31, 42). Although we did not measure AGEs in the present study, it is quite likely that there was greater accumulation in the older men, which would in turn facilitate greater adherence of monocytes in response to hyperglycemia and hyperinsulinemia compared with the younger group. Because the binding of AGEs to monocytes initiates cytokine-mediated processes (31), it is also possible that this mechanism may help to explain the different TNF-alpha response between the young and old groups. It is important to note that, despite differences between pre- and postclamp whole blood monocyte number, the in vitro component of the study allowed us to evaluate TNF-alpha secretion from equal numbers of monocytes in each group.

In conclusion, we observed an age-related impairment in TNF-alpha production during hyperglycemia and hyperinsulinemia. The failure to suppress TNF-alpha secretion among healthy older individuals compared with a younger group represents a unique observation in light of the decline in insulin action with age. Moreover, the association between TNF-alpha production and both total and abdominal fat suggests that modest increases in adiposity may be responsible for the different TNF-alpha responses in our groups. Thus the present data add to the growing body of literature drawing relationships between aging, glucose intolerance, changes in body composition, and modulatory factors such as TNF-alpha . These data raise the intriguing possibility that, during postprandial periods when glucose and insulin are elevated, TNF-alpha production is decreased to facilitate glucose uptake by insulin-sensitive tissues. The loss of this postprandial response may be one of the factors contributing to insulin resistance with advancing age.


    ACKNOWLEDGEMENTS

We thank the nursing/dietary staff of the General Clinical Research Center and the technical/engineering staff of the Noll Physiological Research Center for supporting the implementation of the study and assisting with data collection. We also thank David Williamson, Donal O'Gorman, Christiana Lakatta, Jazmir Hernandez, Chris Marchetti, and Cormac Ryan for assistance. We are grateful to Allen R. Kunselman at the Center for Biostatistics and Epidemiology at the Hershey Medical Center for assistance in data analysis and interpretation.


    FOOTNOTES

This research was supported by National Institutes of Health Grants AG-12834 to J. P. Kirwan, AG-11811 to W. J. Evans, and MO1 RR-10732.

Address for reprint requests and other correspondence: J. P. Kirwan, Case Western Reserve Univ. School of Medicine at MetroHealth Medical Center, Depts. of Reproductive Biology & Nutrition, Bell Greve Bldg., Rm G-232E, 2500 MetroHealth Dr., Cleveland, OH 44109-1998 (E-mail: jkirwan{at}metrohealth.org).

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Received 28 June 2001; accepted in final form 1 August 2001.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES

1.   American Diabetes Association. Screening for type 2 diabetes (Position Statement). Diabetes Care 22: S20-S23, 1999[ISI].

2.   Andres, R, and Tobin JD. Aging and the disposition of glucose. Adv Exp Med Biol 61: 239-249, 1975[Medline].

3.   Bourey, RE, Kohrt WM, Kirwan JP, Staten MA, King DS, and Holloszy JO. Relationship between glucose tolerance and glucose-stimulated insulin response in 65-year olds. J Gerontol A Biol Sci Med Sci 48: M122-M127, 1993.

4.   Boyum, A. Isolation of mononuclear cells and granulocytes from human blood. Scand J Clin Lab Invest 21, Suppl97: 77-89, 1968[ISI][Medline].

5.   Bruunsgaard, H, Pedersen AN, Schroll M, Skinhoj P, and Pedersen BK. Impaired production of proinflammatory cytokines in response to lipopolysaccharide (LPS) stimulation in elderly humans. Clin Exp Immunol 118: 235-241, 1999[ISI][Medline].

6.   Chen, M, Bergman RN, Pacini G, and Porte JD. Pathogenesis of age-related glucose intolerance in man: insulin resistance and decreased beta -cell function. J Clin Endocrinol Metab 60: 13-20, 1985[Abstract].

7.   Coon, PJ, Rogus EM, Drinkwater D, Muller DC, and Goldberg AP. Role of body fat distribution in the decline in insulin sensitivity and glucose tolerance with age. J Clin Endocrinol Metab 75: 1125-1132, 1992[Abstract].

8.   DeFronzo, RA. Glucose intolerance and aging: evidence for tissue insensitivity to insulin. Diabetes 28: 1095-1101, 1979[ISI][Medline].

9.   DeFronzo, RA, Tobin JD, and Andres R. Glucose clamp technique: a method for quantifying insulin secretion and resistance. Am J Physiol Endocrinol Metab Gastrointest Physiol 237: E214-E223, 1979[Abstract/Free Full Text].

10.   Del Aguila, LF, Claffey KP, and Kirwan JP. TNF-alpha impairs insulin signaling and insulin stimulation of glucose uptake in C2C12 muscle cells. Am J Physiol Endocrinol Metab 276: E849-E855, 1999[Abstract/Free Full Text].

11.   Del Aguila, LF, Krishnan RK, Ulbrecht JS, Farrell PA, Correll PH, Lang CH, Zierath JR, and Kirwan JP. Muscle damage impairs insulin stimulation of IRS-1, PI 3-kinase, and Akt-kinase in human skeletal muscle. Am J Physiol Endocrinol Metab 279: E206-E212, 2000[Abstract/Free Full Text].

12.   Effros, RB, Svoboda K, and Walford RL. Influence of age and caloric restriction on macrophage IL-6 and TNF production. Lymphokine Cytokine Res 10: 347-351, 1991[ISI][Medline].

13.   Elahi, D, Muller D, McAloon-Dyke M, Tobin J, and Andres R. The effect of age on insulin response and glucose utilization during four hyperglycemic plateaus. Exp Gerontol 28: 393-409, 1993[ISI][Medline].

14.   Feinstein, R, Kanety H, Papa MZ, Lunefeld B, and Karasik A. Tumor necrosis factor-alpha suppresses insulin-induced tyrosine phosphorylation of insulin receptor and its substrates. J Biol Chem 268: 26055-26058, 1993[Abstract/Free Full Text].

15.   Gilcrease, MZ, and Hoover RL. Examination of monocyte adherence to endothelium under hyperglycemic conditions. Am J Pathol 139: 1089-1097, 1991[Abstract].

16.   Gon, Y, Hashimoto S, Hayashi S, Koura T, Matsumoto K, and Horie T. Lower serum concentrations of cytokines in elderly patients with pneumonia and the impaired production of cytokines by peripheral blood monocytes in the elderly. Clin Exp Immunol 106: 120-126, 1996[ISI][Medline].

17.   Greiwe, JS, Cheng B, Rubin DC, Yarasheski KE, and Semenkovich CF. Resistance exercise decreases skeletal muscle tumor necrosis factor alpha  in frail elderly humans. FASEB J 15: 475-482, 2001[Abstract/Free Full Text].

18.   Gumbiner, B, Polonsky KS, Beltz WF, Wallace P, Brechtel G, and Fink RI. Effects of aging on insulin secretion. Diabetes 38: 1549-1556, 1989[Abstract].

19.   Haller, H, Drab M, and Luft FC. The role of hyperglycemia and hyperinsulinemia in the pathogenesis of diabetic angiopathy. Clin Nephrol 46: 246-255, 1996[ISI][Medline].

20.   Hancu, N, Netea MG, and Baciu I. High glucose concentrations increase the tumor necrosis factor-alpha production capacity by human peripheral blood mononuclear cells. Rom J Physiol 35: 325-330, 1998[Medline].

21.   Hotamisligil, GS, Arner P, Caro JF, Atkinson RL, and Spiegelman BM. Increased adipose tissue expression of tumor necrosis factor-alpha in human obesity and insulin resistance. J Clin Invest 95: 2409-2415, 1995[ISI][Medline].

22.   Hotamisligil, GS, Murray DL, Choy LN, and Spiegelman BM. Tumor necrosis factor alpha inhibits signaling from the insulin receptor. Proc Natl Acad Sci USA 91: 4854-4858, 1994[Abstract].

23.   Hotamisligil, GS, Peraldi P, Budavari A, Ellis R, White MF, and Spiegelman BM. IRS-1 mediated inhibition of insulin receptor tyrosine kinase activity in TNF-alpha and obesity-induced insulin resistance. Science 271: 665-668, 1996[Abstract].

24.   Kern, PA, Ranganathan S, Li C, Wood L, and Ranganathan G. Adipose tissue tumor necrosis factor and interleukin-6 expression in human obesity and insulin resistance. Am J Physiol Endocrinol Metab 280: E745-E751, 2001[Abstract/Free Full Text].

25.   Kirwan, JP, Kohrt WM, Wojta DM, Bourey RE, and Holloszy JO. Endurance exercise training reduces glucose-stimulated insulin levels in 60- to 70-year-old men and women. J Gerontol A Biol Sci Med Sci 48: M84-M90, 1993.

26.   Kohrt, WM, Kirwan JP, King DS, Staten MA, and Holloszy JO. Insulin resistance of aging is related to abdominal obesity. Diabetes 42: 273-281, 1993[Abstract].

27.   Kramarow, E, Lentzner H, Rooks R, Weeks J, and Saydah S. Health and Aging Chartbook. Hyattsville, MD: National Center for Health Statistics, 1999, p. 51.

28.   Krishnan, RK, Hernandez JM, Williamson DL, O'Gorman DJ, Evans WJ, and Kirwan JP. Age-related differences in the pancreatic beta -cell response to hyperglycemia after eccentric exercise. Am J Physiol Endocrinol Metab 275: E463-E470, 1998[Abstract/Free Full Text].

29.   Ling, PR, Bistrian BR, Mendez B, and Istfan NW. Effects of systemic infusions of endotoxin, tumor necrosis factor, and interleukin-1 on glucose metabolism in the rat: relationship to endogenous glucose production and peripheral tissue glucose uptake. Metabolism 43: 279-284, 1994[ISI][Medline].

30.   Lofgren, P, van Harmelen V, Reynisdottir S, Naslund E, Ryden M, Rossner S, and Arner P. Secretion of tumor necrosis factor-alpha shows a strong relationship to insulin-stimulated glucose transport in human adipose tissue. Diabetes 49: 688-692, 2000[Abstract].

31.   Makita, Z, Vlassara H, Rayfield E, Cartwright K, Freidman E, Rdoby R, Cerami A, and Bucala R. Hemoglobin-AGE: a circulating marker of advanced glycosylation. Science 258: 651-653, 1992[ISI][Medline].

32.   Meneilly, GS, and Elliott T. Metabolic alterations in middle-aged and elderly obese patients with type 2 diabetes. Diabetes Care 22: 112-118, 1999[Abstract].

33.   Mondon, CE, and Starnes HF. Differential metabolic responses to tumor necrosis factor with increase in age. Metabolism 41: 970-981, 1992[ISI][Medline].

34.   Mooradian, AD, Reed RL, and Scuderi P. Serum levels of tumor necrosis factor alpha, interleukin-1 alpha and beta in healthy elderly subjects. Age Ageing 14: 61-64, 1991.

35.   Morin, CL, Pagliassotti MJ, Windmiller D, and Eckel RH. Adipose tissue-derived tumor necrosis factor-alpha activity is elevated in older rats. J Gerontol B Psychol Sci Soc Sci 52: B190-B195, 1997.

36.   Morohoshi, M, Fujisawa K, Uchimura I, and Numano F. Glucose-dependent interleukin 6 and tumor necrosis factor production by human peripheral blood monocytes in vitro. Diabetes 45: 954-959, 1996[Abstract].

37.   Paolisso, G, Rizzo MR, Mazziotti G, Tagliamonte MR, Gambardella A, Rotondi M, Carella C, Giugliano D, Varricchio M, and D'Onofrio F. Advancing age and insulin resistance: role of plasma tumor necrosis factor-alpha . Am J Physiol Endocrinol Metab 275: E294-E299, 1998[Abstract].

38.   Roubenoff, R, Harris TB, Abad LW, Wilson PWF, Dallal GE, and Dinarello CA. Monocyte cytokine production in an elderly population: effect of age and inflammation. J Gerontol 53A: M20-M26, 1998[ISI].

39.   Rui, L, Aguirre V, Kim JK, Shulman GI, Lee A, Corbould A, Dunaif A, and White MF. Insulin/IGF-1 and TNF-alpha stimulate phosphorylation of IRS-1 at inhibitory Ser307 via distinct pathways. J Clin Invest 107: 181-189, 2001[Abstract/Free Full Text].

40.   Saghizadeh, M, Ong JM, Garvey WT, Henry RR, and Kern PA. The expression of TNFalpha by human muscle. J Clin Invest 97: 1111-1116, 1996[Abstract/Free Full Text].

41.   Schwartz, RS, Shuman WP, Bradbury VL, Cain KC, Fellingham GW, Beard JC, Kahn SE, Stratton JR, Cerqueira MD, and Abrass IB. Body fat distribution in healthy young and older men. J Gerontol A Biol Sci Med Sci 45: M181-M185, 1990.

42.   Vlassara, H. Cell-mediated interactions of advanced glycosylation end products and the vascular wall. In: Hyperglycemia, Diabetes, and Vascular Disease (1st ed.), edited by Ruderman N, Williamson J, and Brownlee M.. New York: Oxford Univ. Press, 1992, p. 228-242.


Am J Physiol Endocrinol Metab 281(6):E1137-E1143
0193-1849/01 $5.00 Copyright © 2001 the American Physiological Society