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Correlation between Testosterone and the Inflammatory Marker Soluble Interleukin-6 Receptor in Older Men

Longitudinal Studies Section (M.M., S.Bas., A.B., L.F.) and Translational Research and Medical Support Section (S.Bas., S.M.L.), Clinical Research Branch, National Institute on Aging, Intramural Research Program, National Institutes of Health, Baltimore, Maryland 21225; Department of Medicine, Division of Endocrinology, Johns Hopkins University School of Medicine, Bayview Medical Center (S.Bas.), Baltimore, Maryland; Tuscany Regional Health Agency (F.L.,), 50134 Florence, Italy; Geriatric Rehabilitation, Azienda Sanitaria di Firenze (S.Ban.), 50125 Florence, Italy; and Department of Internal Medicine and Biomedical Sciences, Section of Geriatrics, University of Parma (G.P.C., G.V.), 43100 Parma, Italy

Address all correspondence and requests for reprints to: Dr. Luigi Ferrucci, National Institute on Aging, National Institutes of Health, National Institute on Aging, Advanced Studies in Translational Research on Aging at Harbor Hospital, 3001 South Hanover Street, Baltimore, Maryland 21225. E-mail: ferruccilu{at}grc.nia.nih.gov.

	Abstract

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Context: An age-associated decline in testosterone (T) levels and an increase in proinflammatory cytokines contribute to chronic diseases in older men. Whether and how these changes are related is unclear.

Objective: We hypothesized that T and inflammatory markers are negatively correlated in older men.

Design: This was a cross-sectional study.

Setting: A population-based sample of older men was studied.

Participants and Measures: After excluding participants taking glucocorticoids or antibiotics or those with recent hospitalization, 467 men, aged 65 yr or older, had complete determinations of total T, bioavailable T, SHBG, albumin, IL-6, soluble IL-6 receptor (sIL-6r), TNF-, IL-1ß, and C-reactive protein.

Results: After adjusting for potential confounders, sIL-6r was significantly and inversely correlated with total T (r = –0.20; P < 0.001) and bioavailable T (r = –0.12; P < 0.05). T was not correlated with any other inflammatory marker.

Conclusions: These preliminary findings suggest an inverse relationship between T and sIL-6r. Longitudinal studies are needed to establish the causality of this association.

	Introduction

Top Abstract Introduction Subjects and Methods Results Discussion References

 
A WEALTH OF data suggest that the age-associated decline in sex hormones may facilitate the development of a mild proinflammatory state (1). In aging men, a decline in testosterone (T) and an increase in IL-6, TNF-, and IL-1ß (2, 3) may contribute to sarcopenia, osteoporosis, arthritis, cardiovascular disease, and frailty (4).

In vitro studies suggest that T down-regulates the IL-6 gene through androgen receptors (5), although conflicting data are available regarding the effects of IL-6 on T production and biological activity in humans (6) (7). The induction of hypogonadism in older men is followed by a significant increase in IL-6, soluble IL-6 receptor (sIL-6r), and TNF- (8). In contrast, T replacement in hypogonadal men results in decreased levels of TNF- and IL-1ß without significant changes in IL-6 (9). It is unclear whether the progressive reduction of T that occurs in a large percentage of older men influences inflammatory status. Using data from a representative sample of older men enrolled in an epidemiological study, we tested the hypothesis that low T is associated with higher levels of inflammatory markers, including IL-1ß, IL-6, sIL-6r, TNF-, and C-reactive protein (CRP).

	Subjects and Methods

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Study population

The study population included 497 male InCHIANTI participants, aged 65 yr and older, who were representative of male residents in the Chianti geographic area (10). We excluded 22 men taking glucocorticoids, exogenous androgens, or antibiotic treatment and eight who had been recently hospitalized. The final analysis included 467 men (mean age, 74.8 ± 7.0 yr; range, 65–97 yr).

Our institutional review board approved the study protocol, and participants consented to participate in the study.

Hormone assays

Fasting blood samples were processed immediately after collection, and 0.5-ml serum aliquots were stored at –80 C until analysis. T was assayed using a radioimmunological kit (Diagnostic Systems Laboratories, Webster, TX) with a minimum detection limit of 0.03 nmol/liter and intra- and interassay coefficients of variation of 9.6% and 8.6%, respectively. SHBG was measured by RIA (Diagnostic Products Corp., Los Angeles, CA), with a minimum detectable concentration of 0.04 nmol/liter and inter- and intraassay coefficients of variation of 3.1% and 2.8%, respectively (11). Bioavailable T (Bio-T) was calculated using the Vermeulen formula (12).

Cytokine assays

Serum IL-6, sIL-6r, TNF-, and IL-1ß were measured in duplicate by high-sensitivity ELISAs (BioSource International, Camarillo, CA). The lower detectable limit was 0.1 pg/ml for IL-6, 8.00 pg/ml for sIL-6r, 0.09 pg/ml for TNF-, and 0.01 pg/ml for IL-1ß. The interassay coefficient of variation was 7% for all cytokines (3). CRP was measured with a high-sensitivity ELISA, a competitive immunoassay that uses purified protein and polyclonal anti-CRP antibodies. The interassay coefficient of variation was 5.0%. The minimum detectable concentration was 0.03 mg/liter.

Assessment of covariates

Body mass index was calculated as: weight (kilograms)/height (meters)². Physical activity in the year before the interview was coded as: 1) sedentary: completely inactive or light-intensity activity less than 1 h/wk; 2) light physical activity: light-intensity activity 2–4 h/wk; and 3) moderate-high physical activity: light activity at least 5 h/wk or more or moderate activity at least 1–2 h/wk. Daily total energy (kilocalories) and alcohol (grams) intake were estimated by the European Prospective Investigation into Cancer and Nutrition food frequency questionnaire (13). Smoking was assessed by self-report and expressed as pack-years (packs smoked per day x years of smoking). Diabetes, angina, myocardial infarction, cancer, and chronic obstructive pulmonary disease were ascertained according to standard criteria. Independence in basic activities of daily living was assessed by self-report (14).

Statistical analysis

Values are reported as the mean ± SD or the median and interquartile range when appropriate. Differences in T among age groups were tested using ANOVA; differences in Bio-T and cytokines were determined by using Kruskal-Wallis ranking test and P for trend on log-transformed values. Associations of T with proinflammatory markers were tested using partial correlation coefficient adjusted for age, body mass index, physical activity, smoking, alcohol consumption, disability, and medical conditions.

	Results

Top Abstract Introduction Subjects and Methods Results Discussion References

 
T and Bio-T levels were significantly lower in older compared with younger participants. Older men tended to have higher levels of IL-6, TNF-, IL-1ß, and CRP, but the levels of sIL-6r were not different (Table 1).

View this table: [in this window] [in a new window]   TABLE 1. Serum total T, Bio-T, IL-6, sIL-6r, TNF-, IL-1ß, and CRP levels according to age groups

After adjusting for age and multiple confounders, the negative correlation between log(sIL-6r) and T and log(Bio-T) was maintained. We found no independent association of T and log(Bio-T) with log(TNF-), log(IL-1ß), or log(CRP) (Table 2).

View this table: [in this window] [in a new window]   TABLE 2. Partial correlation coefficients evaluating the independent relationship of T to IL-6, sIL-6r, TNF-, IL-1ß, and CRP

	Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

Inflammation is risk factor for disability (15) and mortality (16). The higher incidence and prevalence of autoimmune diseases in women and androgen deficient men suggest that androgens may have an immunosuppressive role (17). The antiinflammatory activity of T may explain why hypogonadal men have a higher risk of metabolic syndrome (18) and coronary artery disease (19). Our findings suggest that T may decrease inflammation by reducing the production of sIL-6r. The IL-6r is composed of two subunits, a membrane-bound glycoprotein 130 and an extramembrane domain (IL-6r), which also exists in a soluble form (sIL-6r). sIL-6r enhances the IL-6 activity by making cells that have a glycoprotein 130 membrane domain sensitive to IL-6 signaling (20).

We did not observe any significant change in sIL-6r levels with age. However, in a previous study we demonstrated that after adjusting for cardiovascular risk factors and morbidity, there was a substantial increase in sIL-6r with age (3).

Given the cross-sectional nature of this study, a mechanism of reverse causality, namely, that T might be negatively affected by sIL6r or IL-6, cannot be excluded. However, Tsigos et al. (6) have shown that a suppressive effect of rIL-6 on T was possible with doses that resulted in serum levels greater than 65 ± 22 pg/dl, much higher than the levels seen in our study population.

Our findings contrast, at least in part, with some recent literature. In one study, induction of hypogonadism with GnRH agonists in elderly men resulted in significant increases in IL-6 and sIL-6r (8). Another study found that T replacement therapy in hypogonadal men was associated with reductions in IL-1ß and TNF-, but not IL-6 (9). However, acute (8) and chronic androgen ablation, such as androgen deprivation therapy in metastatic prostate cancer (unpublished observations from our group), may have a different effect on the immune system. Additionally, an intervention study (9) may be different from the slow and progressive adaptation in response to the decline in T in aging men.

In conclusion, our findings suggest that the biological activities of T and sIL-6r are inversely related. These findings should be verified in prospective studies.

	Footnotes

 
The InCHIANTI study was supported as a targeted project (ICS 110.1/RS97.71) by the Italian Ministry of Health and in part by the U.S. National Institute of Aging (Contracts 263-MD-916413 and 263-MD-821336).

All authors declare they have no conflict of interest to disclose concerning this manuscript.

First Published Online November 1, 2005

Abbreviations: Bio-T, Bioavailable testosterone; CRP, C-reactive protein; sIL-6r, soluble IL-6 receptor; T, testosterone.

Received May 18, 2005.

Accepted October 21, 2005.

	References

Top Abstract Introduction Subjects and Methods Results Discussion References

 

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