Julia Cruces

Strategies to Improve the Functions and Redox State of the Immune System in Aged Subjects

The aging process is accompanied by an impairment of the physiological systems including the immune system. This system is an excellent indicator of health. We have also observed that several functions of the immune cells are good markers of biological age and predictors of longevity. In agreement with the oxidation-inflammation theory that we have proposed, the chronic oxidative stress that appears with age affects all cells and especially those of the regulatory systems, such as the nervous, endocrine and immune systems and the communication between them. This fact prevents an adequate homeostasis and, therefore, the preservation of health. We have also proposed an involvement of the immune system in the aging process of the organism, concretely in the rate of aging, since there is a relation between the redox state and functional capacity of the immune cells and the longevity of individuals. A confirmation of the central role of the immune system in oxi-inflamm-aging is that several lifestyle strategies such as the administration of adequate amounts of antioxidants in the diet, physical exercise, physical and mental activity through environmental enrichment and hormetic interventions improve functions of immune cells, decreasing their oxidative stress, and consequently increasing the longevity of individuals. Recent results in mice of investigations on the effects of a new environmental enrichment (bathing in waters) as well as a hormetic intervention with slight infections (caused by injection of E.coli lipopolysaccharide, LPS), on several functions and redox parameters are shown. The advantages and possible problems of the use of those interventions to achieve a healthy aging and longevity are discussed.

Early Maternal Deprivation in Rats : A Proposed Animal Model for the Study of Developmental Neuroimmunoendocrine Interactions

Adult animals that had been subjected to a single prolonged episode of maternal deprivation (MD) [24 h, postnatal day (PND) 9–10] show long‐term behavioral alterations that resemble specific symptoms of schizophrenia. Moreover, at adolescence MD rats showed depressive‐like behavior and altered motor responses. According to the neurodevelopmental hypothesis, certain behavioral abnormalities observed in MD animals may be related to altered neurodevelopmental processes triggered by MD‐induced elevated glucocorticoids in relevant specific brain regions. We review here these neuroendocrine effects and show new data indicating that the MD procedure induces diverse detrimental effects on the immune system that are already revealed in the short term (PND 13) and persist into adulthood. These long‐lasting effects might be related to altered hypothalamus–pituitary–adrenal axis activity and to social as well as nutrition‐related factors. In fact, MD induces long‐lasting decreases in body weight. In view of our findings we propose the present MD procedure as a potentially useful model to analyze developmental interactions between early psychophysiological stress and immunodeficient states.

Immune function parameters as markers of biological age and predictors of longevity

Chronological age is not a good indicator of how each individual ages and thus how to maintain good health. Due to the long lifespan in humans and the consequent difficulty of carrying out longitudinal studies, finding valid biomarkers of the biological age has been a challenge both for research and clinical studies. The aim was to identify and validate several immune cell function parameters as markers of biological age. Adult, mature, elderly and long-lived human volunteers were used. The chemotaxis, phagocytosis, natural killer activity and lymphoproliferation in neutrophils and lymphocytes of peripheral blood were analyzed. The same functions were measured in peritoneal immune cells from mice, at the corresponding ages (adult, mature, old and long lived) in a longitudinal study. The results showed that the evolution of these functions was similar in humans and mice, with a decrease in old subjects. However, the long-lived individuals maintained values similar to those in adults. In addition, the values of these functions in adult prematurely aging mice were similar to those in chronologically old animals, and they died before their non-prematurely aging mice counterparts. Thus, the parameters studied are good markers of the rate of aging, allowing the determination of biological age.

Lifelong treatment with atenolol decreases membrane fatty acid unsaturation and oxidative stress in heart and skeletal muscle mitochondria and improves immunity and behavior, without changing mice longevity

The membrane fatty acid unsaturation hypothesis of aging and longevity is experimentally tested for the first time in mammals. Lifelong treatment of mice with the β1‐blocker atenolol increased the amount of the extracellular‐signal‐regulated kinase signaling protein and successfully decreased one of the two traits appropriately correlating with animal longevity, the membrane fatty acid unsaturation degree of cardiac and skeletal muscle mitochondria, changing their lipid profile toward that present in much more longer‐lived mammals. This was mainly due to decreases in 22:6n‐3 and increases in 18:1n‐9 fatty acids. The atenolol treatment also lowered visceral adiposity (by 24%), decreased mitochondrial protein oxidative, glycoxidative, and lipoxidative damage in both organs, and lowered oxidative damage in heart mitochondrial DNA. Atenolol also improved various immune (chemotaxis and natural killer activities) and behavioral functions (equilibrium, motor coordination, and muscular vigor). It also totally or partially prevented the aging‐related detrimental changes observed in mitochondrial membrane unsaturation, protein oxidative modifications, and immune and behavioral functions, without changing longevity. The controls reached 3.93 years of age, a substantially higher maximum longevity than the best previously described for this strain (3.0 years). Side effects of the drug could have masked a likely lowering of the endogenous aging rate induced by the decrease in membrane fatty acid unsaturation. We conclude that it is atenolol that failed to increase longevity, and likely not the decrease in membrane unsaturation induced by the drug.

The Effect of Psychological Stress and Social Isolation on Neuroimmunoendocrine Communication

The adaptive response to physical or psychological challenges or threats involves the modulation of the three regulatory systems: the nervous, endocrine and immune systems. Correct communication between these systems is required to maintain a homeostatic balance, and to guarantee the health and survival of the individual. While the stress response is essential for survival, failure to cope with a stress can impair the function of these regulatory systems and prevent effective communication between them. Under such circumstances, the loss of homeostasis ultimately leads to the development of pathologies that can compromise survival. Social species live in groups, the maintenance of which ensures the survival of the individual by providing protection from environmental threats. However, the disruption of social bonds in such species constitutes a potent emotional stress. Thus, social isolation is considered a risk factor for morbidity and mortality. The response to isolation or loneliness can vary greatly between individuals due to the influence of many factors, some of which will be considered in this Review. These factors can exert a significant influence on the three regulatory systems throughout the lifespan of the organism, and they include characteristics of the stressor itself (e.g., duration), as well as those of the organism (e.g., biological age), in addition to external factors (e.g., environmental events).

Role of macrophages in age-related oxidative stress and lipofuscin accumulation in mice

The age-related changes in the immune functions (immunosenescence) may be mediated by an increase of oxidative stress and damage affecting leukocytes. Although the “oxidation-inflammation” theory of aging proposes that phagocytes are the main immune cells contributing to “oxi-inflamm-aging”, this idea has not been corroborated. The aim of this work was to characterize the age-related changes in several parameters of oxidative stress and immune function, as well as in lipofuscin accumulation (“a hallmark of aging”), in both total peritoneal leukocyte population and isolated peritoneal macrophages. Adult, mature, old and long-lived mice (7, 13, 18 and 30 months of age, respectively) were used. The xanthine oxidase (XO) activity-expression, basal levels of superoxide anion and ROS, catalase activity, oxidized (GSSG) and reduced (GSH) glutathione content and lipofuscin levels, as well as both phagocytosis and digestion capacity were evaluated. The results showed an age-related increase of oxidative stress and lipofuscin accumulation in murine peritoneal leukocytes, but especially in macrophages. Macrophages from old mice showed lower antioxidant defenses (catalase activity and GSH levels), higher oxidizing compounds (XO activity/expression and superoxide, ROS and GSSG levels) and lipofuscin levels, together with an impaired macrophage functions, in comparison to adults. In contrast, long-lived mice showed in their peritoneal leukocytes, and especially in macrophages, a well-preserved redox state and maintenance of their immune functions, all which could account for their high longevity. Interestingly, macrophages showed higher XO activity and lipofuscin accumulation than lymphocytes in all the ages analyzed. Our results support that macrophages play a central role in the chronic oxidative stress associated with aging, and the fact that phagocytes are key cells contributing to immunosenescence and “oxi-inflamm-aging”. Moreover, the determination of oxidative stress and immune function parameters, together with the lipofuscin quantification, in macrophages, can be used as useful markers of the rate of aging and longevity.

A higher anxiety state in old rats after social isolation is associated to an impairment of the immune response.

Social isolation is common in the elderly exerting negative effects on neuroimmunoendocrine communication. Nevertheless physiological responses to a stressful situation may vary according to diverse factors. This work studies the differences in the immune response of aged male rats socially isolated depending on the anxiety levels produced. Social isolation impaired certain immunological parameters, but a more anxious response to isolation was associated to global severe immunosuppression and greater oxidative state. Thus, responding anxiously to isolation may suppose a more potent risk of morbidity and mortality further than isolation and anxiety by themselves, particularly in elderly subjects.

Improved Measurement of Elastic Properties of Cells by Micropipette Aspiration and Its Application to Lymphocytes

Mechanical deformability of cells is an important property for their function and development, as well as a useful marker of cell state. The classical technique of micropipette aspiration allows single-cell studies and we provide here a method to measure the two basic mechanical parameters, elastic modulus and Poisson’s ratio. The proposed method, developed from finite-element analysis of micropipette aspiration experiments, may be implemented in future technologies for the automated measurement of mechanical properties of cells, based on the micropipette aspiration technique or on the cell transit through flow constrictions. We applied this method to measure the elastic parameters of lymphocytes, in which the mechanical properties depend on their activation state. Additionally, we discuss in this work the accuracy of previous models to estimate the elastic modulus of cells, in particular the analytical model by Theret et al., widely used in the field. We show the necessity of using an improved model, taking into account the finite size of the cells, to obtain new insights that may remain hidden otherwise.

Function and redox state of peritoneal leukocytes as preclinical and prodromic markers in a longitudinal study of triple-transgenic mice for Alzheimer's disease.

The aging process involves the impairment of the immune system (immunosenescence), based on the imbalance of the redox status, as occurs in neurodegenerative diseases such as Alzheimers disease (AD). Since in AD there is a systemic disorder, we aimed to assess longitudinally, from before the onset until the complete establishment of AD, cell populations, several functions, and oxidative stress parameters in peritoneal leukocytes of triple transgenic mice for AD (3xTgAD). These animals mimic the human AD pathophysiology. The results indicate a premature immunosenescence in 3xTgAD at 4 months of age, when the immunoreactivity against intracellular amyloid-β fibrils appears. Thus, decreases in functions such as chemotaxis, phagocytosis, and lymphoproliferation, as well as a lower reduced glutathione content and higher xanthine oxidase activity, appear in leukocytes. Moreover, NK percentage and cytotoxic activity, CD25+ B and naïve CD8 T cells percentage, GSSG/GSH ratio, and GSH content were already changed before the onset of AD, at the age of 2 months. Furthermore, the changes in some parameters such as CD5+ B1 cells, phagocytosis, lymphoproliferation, and xanthine oxidase activity continue at 15 months of age, when AD pathophysiology is completely established. Because the immune system parameters studied are markers of health and longevity, the premature immunosenescence could explain the shorter life span shown by 3xTgAD observed in the present work. These results suggest that peripheral immune cell functions and their oxidative stress status could be good early peripheral markers of the preclinical and prodromal stages and progression of AD.

Improvements in Behavior and Immune Function and Increased Life Span of Old Mice Cohabiting With Adult Animals

The social environment can affect the regulatory systems, and cohabitation with sick subjects is a negative factor for the nervous and immune systems, compromising the life span. Nevertheless, the possible beneficial effects of a positive social environment on nervous and immune functions and longevity have not yet been studied. The aim of this study was to analyze several behavioral and immune function parameters and life span in old mice after their cohabitation with adult animals. Old and adult ICR-CD1 female mice were divided into three experimental groups: adult controls, old controls, and a social environment experimental group. The latter contained two old mice with five adult mice. After 2 months in these conditions, mice were submitted to a behavioral battery of tests to analyze their sensorimotor abilities, anxiety-like behaviors, and exploratory capacities. Peritoneal leukocytes were then collected, and several immune functions as well as oxidative and inflammatory stress parameters were assessed. The animals were maintained in the same conditions until natural death occurred. The results showed that old animals, after cohabitation with adult mice, presented an improvement of behavioral capacities, immune functions, and a lower oxidative and inflammatory stress. Consequently, they exhibited a higher life span.