Original Contribution
Differential inflammatory responses in aging and disease: TNF-α and IL-6 as possible biomarkers

https://doi.org/10.1016/j.freeradbiomed.2010.05.019Get rights and content

Abstract

Oxidative stress has been reported to increase during aging and conditions of hypoxia. Although low oxygen saturation has a key role in the development of several age-related diseases, the underlying mechanisms are still unknown. We analyzed the relationship between aging and hypoxia by examining oxidative stress and inflammation-related cytokines. We collected blood samples from three volunteer experimental groups, consisting of one group of normoxic middle-aged people and two groups of individuals older than 75 years, which comprised a subgroup of normoxic subjects and another with oxyhemoglobin saturation lower than 95% (hypoxic). Our results showed a fall in antioxidant defenses in older people with hypoxia. TNF-α, the first element in the cytokine cascade, was significantly increased in the aged population, implying that aging is accompanied by a gradual increase in this inflammatory biomarker. IL-6 was not associated with aging, but it was highly elevated under hypoxia conditions in elderly subjects. Thus, these parameters could be used as biological markers of different inflammatory processes triggered by oxidative stress induced by a decrease in antioxidant defenses in the elderly population, with TNF-α as an indicator of chronic processes, such as aging, and IL-6 as a marker for acute responses, such as hypoxia.

Introduction

Large health care expenditures for a growing elderly population have both stimulated scientific inquiry and heightened public awareness regarding aging-related issues. As a result, many theories have been developed to explain why we age. In the 1950 s, Harman proposed the “free radical theory” of aging, postulating that damage to cellular macromolecules via free radical production in aerobic organisms is a major determinant of life span [1].

Generally, increased oxidative/nitrosative stress describes a condition in which cellular antioxidant defenses are inadequate to completely inactivate reactive oxygen species (ROS)1 and reactive nitrogen species (RNS). Oxidative/nitrosative stress can be caused by excessive ROS/RNS, loss of antioxidant defenses, or both. A major consequence of oxidative/nitrosative stress is damage to nucleic acid bases, lipids, and proteins, which can severely compromise cellular viability and induce a variety of cellular responses through the generation of secondary reactive species, ultimately leading to cell death via necrosis or apoptosis [2]. Substantial evidence suggests that ROS and RNS actively participate in normal aging and have an effect on the onset and progression of age-related diseases [3].

The ability of cells to use oxygen requires adequate cellular oxygen uptake, so abnormal cellular processes can alter cellular oxygen use. Hypoglycemia, for example, can impair the cell's ability to process oxygen and causes hypoxia. In fact, oxyhemoglobin saturation (HbSaO2) can fall to extremely low levels quickly and unexpectedly in association with episodic hypoxemia and is often accompanied by marked changes in heart rate, blood pressure, and respiratory rate [4]. Several high-incidence diseases, including heart failure, chronic obstructive pulmonary disease, and ictus, include hypoxemic incidents among their symptoms. In all instances, this hypoxemic process leads to cellular hypoxia that, in turn, stimulates the generation of ROS [5]. An imbalance between the production and the destruction of ROS, resulting in an increase in ROS, gives rise to oxidative stress, which can inflict direct damage on macromolecules, such as lipids, nucleic acids, and proteins [6]. Previous studies from our laboratory provide evidence that hypoxia-induced ROS cause significant damage to macromolecules in diverse cell types [5].

A modern version of Harman's free radical theory of aging is the “mitochondrial theory of aging,” in which mitochondria are incorporated as critical components that regulate aging. This updated version postulates that electrons from the mitochondrial electron transport chain (ETC) produce ROS, which damage components of the ETC and mitochondrial DNA, leading to a cyclic increase in intracellular ROS levels and a decline in mitochondrial function [7].

An additional theory that has gained increasing attention in recent years is the “molecular inflammatory theory of aging,” which postulates that the activation of redox-sensitive transcription factors by age-related oxidative stress up-regulates the expression of proinflammatory genes [8]. Proinflammatory molecules, such as cytokines, lead to inflammation in various tissues and organs [9]. Cytokines are intercellular signaling proteins that exert pro- and anti-inflammatory activities by binding to specific receptors and stimulating the hepatic production of acute-phase proteins as part of a systemic response that accompanies the local inflammatory response. Cytokines are released at the site of inflammation where they facilitate the influx of lymphocytes, neutrophils, monocytes, and other cells that participate in the clearance of antigens and facilitate healing [10].

The first two cytokines in the inflammatory cascade are tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β), which are produced locally and are considered proinflammatory cytokines. TNF-α and IL-1β stimulate the production of interleukin 6 (IL-6), which has been classified as both a proinflammatory and an anti-inflammatory cytokine. IL-6 inhibits the production of TNF-α and IL-1β, stimulates the release of soluble TNF-α receptors (sTNF-R) [11], and seems to be the primary inducer of hepatocyte-derived acute-phase proteins, many of which have anti-inflammatory properties [12]. C-reactive protein has a role in the induction of anti-inflammatory cytokines in circulating monocytes and in the suppression of proinflammatory cytokines in tissue macrophages [13]. TNF-α and IL-1β represent classic proinflammatory cytokines, whereas sTNF-R and interleukin 10 are anti-inflammatory cytokines [10].

Systemic low-grade inflammation is defined by a two- to threefold increase in the plasma concentration of cytokines and acute-phase proteins [14]. The molecular and physiological significance of systemic low-grade inflammation in chronic disease is not yet fully understood [10]; however, it is associated with age-related diseases including atherosclerosis [15], metabolic syndrome [16], type 2 diabetes mellitus [17], Alzheimer disease [18], and vascular dementia [19].

Although aging is a well-defined process with a familiar set of characteristics, its basis remains poorly understood owing in large part to the difficulty in dissociating normal aging effects from those brought about by age-associated diseases [9]. Likewise, data about the roles of cytokines in aging are conflicting, and most of them are derived from in vitro studies. In vivo studies are necessary to improve the understanding of the roles of inflammatory proteins in the differential responses to aging and age-related pathologies. This study is based on the various hypotheses that relate oxidative stress with aging and the inflammatory response. This is an in vivo study with the aim of defining the effects of aging on the main cytokines TNF-α and IL-6, as well as the effects of acute processes such as hypoxemia on the expression of these cytokines. The ultimate goal of this study is to identify possible differential biomarkers of aging with and without hypoxic episodes.

Section snippets

Subjects

We collected blood samples from three experimental groups of volunteers: a group of healthy and normoxic, middle-aged subjects (middle-aged group, n = 41) and two groups of individuals older than 75 years. The group of older subjects consisted of two subgroups, one group of normoxic subjects with HbSaO2 over 95% (no-hypoxia group, n = 41) and one group with HbSaO2 lower than 95% (hypoxia group, n = 41). The control middle-aged group contained individuals between 18 and 40 years of age (mean age 26 

Results

Protein carbonyls are usually formed by various oxidative mechanisms and have been used as a marker of oxidative stress in human tissues. Here, we show that PD plasma levels were significantly higher in older subjects than in middle-aged persons (P  0.05). When we compared the elderly group with a low HbSaO2 (hypoxia) to an elderly group with physiological HbSaO2 (no hypoxia), we observed a significant increase in protein oxidative damage (P ≤ 0.05; Fig. 1).

TAA is a measurable parameter that

Discussion

Aging is an inherently complex process that is regulated at multiple levels, including genetic, molecular, cellular, organic, and systemic. Although the fundamental mechanisms are still poorly understood, a growing body of evidence points toward ROS as one of the primary determinants of aging [9]. We studied the relationship between oxidative stress, inflammation, and aging and the association between these phenomena and age-related disorders such as hypoxia. Our results support the importance

Acknowledgments

The authors thank the personnel of the Hospital Universitario Central de Asturias and the Centro de Transfusión y Banco de Tejidos del Principado de Asturias for their excellent work. We also thank the Hospital Monte Naranco and the Consejería de Salud Pública del Principado de Asturias. We are part of the INPROTEOLYS group and the National Net RETICEF for Aging study. This work was partly supported by Grants FISS-06-RD06/0013/0011 from the Instituto Carlos III and INIA-RTA2007-00087-C02-02

References (48)

  • C. Tomas-Zapico et al.

    Effects of δ-aminolevulinic acid and melatonin in the Harderian gland of female Syrian hamsters

    Free Radic. Biol. Med.

    (2002)
  • C. Tomas-Zapico et al.

    Melatonin protects against delta-aminolevulinic acid-induced oxidative damage in male Syrian hamster Harderian glands

    Int. J. Biochem. Cell Biol.

    (2002)
  • J. Born et al.

    Cytokine production and lymphocyte subpopulations in aged humans: an assessment during nocturnal sleep

    Mech. Ageing Dev.

    (1995)
  • E.A. Bermudez et al.

    Relation between markers of systemic vascular inflammation and smoking in women

    Am. J. Cardiol.

    (2002)
  • J. Afilalo et al.

    Role of frailty in patients with cardiovascular disease

    Am. J. Cardiol.

    (2009)
  • M. De Martinis et al.

    Inflammation markers predicting frailty and mortality in the elderly

    Exp. Mol. Pathol.

    (2006)
  • H. Bruunsgaard et al.

    Elevated levels of tumor necrosis factor alpha and mortality in centenarians

    Am. J. Med.

    (2003)
  • D. Kastelan et al.

    Possible association of psoriasis and reduced bone mineral density due to increased TNF-alpha and IL-6 concentrations

    Med. Hypotheses

    (2006)
  • D. Harman

    Aging: a theory based on free radical and radiation chemistry

    J. Gerontol.

    (1956)
  • B. Caballero et al.

    Melatonin alters cell death processes in response to age-related oxidative stress in the brain of senescence-accelerated mice

    J. Pineal Res.

    (2009)
  • T. Finkel et al.

    Oxidants, oxidative stress and the biology of ageing

    Nature

    (2000)
  • P.A. McGaffigan

    Hazards of hypoxemia: how to protect your patient from low oxygen levels

    Nursing

    (1996)
  • B. Caballero et al.

    Antioxidant activity in Spalax ehrenbergi: a possible adaptation to underground stress

    J. Comp. Physiol. A Neuroethol. Sens. Neural Behav. Physiol.

    (2006)
  • D.C. Wallace

    A mitochondrial paradigm of metabolic and degenerative diseases, aging, and cancer: a dawn for evolutionary medicine

    Annu. Rev. Genet.

    (2005)
  • Cited by (126)

    • Sexual dimorphism in spatial learning and brain metabolism after exposure to a western diet and early life stress in rats

      2022, Physiology and Behavior
      Citation Excerpt :

      The difference between the initial and final absorbance value at 730 nm is used as an index of antioxidant activity. Finally, the results are transformed into the equivalent of Trolox, which is a vitamin E analogous, in mg Trolox / mL, which produce the same antioxidant effect as the brain sample to be studied [49, 50]. We determined the lipid peroxidation (LP) levels or lipoperoxidation levels, a process that leads to the production of lipid peroxides and their derivatives such as malonyl dialdehyde (MDA) and 4-hydroxynonenal (4-HNE) that provide a convenient lipid peroxidation index.

    View all citing articles on Scopus
    View full text