A. Zaia

Insulin receptors in the brain cortex of aging mice

The aim of the present study was to analyze whether aging also affects central insulin receptors in brain cortex as it does in whole brain of BALB/c-nu mice. Results showed statistically significant decrease of number and increase of affinity of insulin high affinity binding sites in old animals. As a consequence, central insulin actions, among which neuromodulation of monoaminergic system, can result altered during aging.

Use of mathematical models of survivorship in the study of biomarkers of aging : the role of heterogeneity

An ever increasing number of people have been engaging in aging research using various interventions aimed to modify aging processes, and/or life span, of experimental animals. Since this type of studies needs outcome parameters for assessing the efficacy of such interventions, research on biomarkers of aging (ABs) has received new stimuli. In the present paper, the problem of the occurrence of a vicious circle any time we study ABs and determinants of aging is addressed. In fact, while ABs would represent the standard reference to be used in the study of the main causes of processes of aging, these very determinants should already be known in order to get reliable ABs. A feasible way to overcome this impasse is proposed, using mathematical models of survivorship or mortality based on biological hypotheses and accounting for inter-individual heterogeneity, a necessary ingredient for a correct interpretation of survival results. Specific kinetics of experimental parameters that are candidates as ABs can be compared to the kinetics hypothesized for general biological functions entering the model. We have built a model of this type that can also be used to perform a reliable overall gross estimate of the rate of aging, R(a), in the population, a parameter useful when judging the success of interventions aimed to act on determinants of aging. The perspective that theory of complex systems can be of help in the search for ABs is also discussed.

Influence of L‐Deprenyl Treatment on Mouse Survival Kinetics

The study of the mechanisms of aging received an important momentum from the use of animal models whose life span can be modified by definite controlled interventions. These models present, however, their limits when the interpretation of the results is attempted. At present, in fact, there is no agreement about how to measure the aging rate of a population or the biological age of an individual.’ Even when the findings seem clear-cut as happens in caloric restricted rats, caution is necessary in extrapolating results to animals living in unrestricted conditions. Despite the limitation that any model may have, manipulations able to prolong life span, and maximal life span in particular, remain among the most powerful tools to gain insights into basic aging processes. Thus, any new way of extending life is welcome, as from a multifaceted view a more complete and understandable picture can stem. In this framework, the observations of some authors on the effects of the monoamine oxidase inhibitor L-deprenyl on aged animals sound very interesting.24 It has been observed that this drug can prolong the life span of treated rats and improve their sexual activity at the same time.5*6 Interestingly, the treatment was effective when started at the end of the second year of life?,’ It is also worth stressing that L-deprenyl can be considered a safe drug, thus very useful in long-term experiments.“.6 In addition to the interest due to these characteristics, our attention was drawn by the possible relationships of its mechanism of action with that at the basis of our previous findings in old mice: age-related alterations of the adrenergic system in different tissues of aging animals.a*l These changes were demonstrated to be not definitive, being corrected by endocrine manipulation exerted just a little before two years of age.I2-l4 Since our previous experimental work on aging was done on mice, first of all a survival experiment was planned with the strain of mice of our own laboratory. The drug was administered to 22-month-old mice, as one of the most interesting characteristic to verify was the efficacy of a treatment starting late in life.

Differential Regulation of Brain β‐Adrenoceptor Subpopulations in Aging Rodents

P-Adrenergic receptors (PARS), widely distributed among animal tissues, play a key role in the action of catecholamines.l.2 PI-Adrenoceptor (P,AR) and P2adrenoceptor (j3,AR) subtypes have been demonstrated to have heterogeneous distribution among brain regions, with differences in the relative amounts of each ~ u b t y p e , ~ . ~ suggesting that each subtype may mediate different neuronal responses to biogen amines. Other studies have demonstrated that P,ARs and P2ARs may also be differentially regulated in various brain areas by homologous and heterologous agents, such as endogenous and synthetic catecholamines, antidepressants, and hormones. 5 lo During aging many P-adrenergic system functions are impaired,”-” often due to or associated with alterations of PARs.I4*I5 In this paper changes in PAR characteristics in the rodent brain have been focused on, showing areaand receptor subpopulation-selective impairments. Particular attention has been devoted to age-related changes of the regulatory capacity of PARS, which may reveal subtle but relevant alterations not evident in unstimulated conditions.

Alterations of brain insulin receptor characteristics in aging mice.

An interesting role of insulin and insulin receptors (InsRs) in the brain is neuromodulation of monoaminergic systems. Since our previous studies showed age-dependent alterations of alpha- and beta-adrenoceptors in mouse brain cortex, the intriguing role of brain InsRs per se and their involvement in adrenergic modulation prompted us to check their eventual changes with aging. Thus, brain InsR characteristics were studied in young (3 months) and old (27 months) Balb/c-nu mice by direct binding with (125)I-insulin. A two-sites model analysis of data shows a statistically significant age-related decrease of receptor density (39%) and k(d) (57%) in the high affinity population. The low affinity receptor subset also shows a decreasing trend of its characteristics; however, differences are not statistically significant and show a high degree of interindividual variability in both groups of mice.

Long-live euthymic BALB/c-nu mice. II : spontaneous tumors and other pathologies

This paper is the second of a series aimed to show the main physiological and pathological characteristics of male euthymic BALB/c-nu mice, a long-live strain of BALB/c mice bred in our own Institute. The previous paired paper Piantanelli (Mech. Ageing Dev. (2001)) has been devoted to a survival study up to advanced ages highly interesting for studies on successful aging. In the present paper we report first data of a cross-sectional study on 4,15,22,28 and 34 months-old mice, dealing with tumors and other relevant pathologies. Results have shown that tumors or other pathologies can hardly be detected up to the age of 22 months. At 34 months of age about 40% of mice revealed a variety of neoplasia and other diseases are clearly detectable. These results suggest that a significant increase in longevity could be a factor increasing the risk of tumor development; thus, caution has to be paid in studies on mice utilized for long term carcinogenicity assay, where animals are sacrificed at the age of 18 months, according to the International Program. Finally, animals of the same chronological age have been subdivided in clusters according to their presumptive longevity, estimated taking advantage of the relationship between body weight and age-at-death found in the paired longitudinal study. This subdivision will be helpful in interpreting inter-individual variability of the biological parameters checked in these animals.

Long-live euthymic BALB/c-nu mice. I. Survival study suggests body weight as a life span predictor.

This paper is the first of a series aimed to show the main physiological and pathological characteristics of male euthymic BALB/c-nu mice, a long-live strain of BALB/c mice bred in our own Institute. In particular, the first two paired papers are respectively devoted to general survival information and disease characteristics, also taking into account very old animals that are of high interest for studies on successful aging. In this paper we report the analysis of survival kinetics, the time course of body weight and the correlation between body weight and time-at-death. The longitudinal study has been performed on 88 male mice, checking individually their body weight and date of death and analyzing survival data by a model built by our own. Survival analysis shows quite higher longevity (median age: about 29 months) in this population when compared with other BALB/c strains. The most relevant finding on body weight is its correlation with longevity until the age of 22 months: thinner subjects live longer and lose weight at a lower rate than their heavier mates. Results have formed the basis on which to plan the cross-sectional experiment to study pathologies and biological parameters at different ages, including a group of mice at very advanced ages (34 months).

Insulin receptors in mouse brain: age-related modifications are corrected by thymus graft

Recently, we have shown that insulin receptors (InsRs) in the brain undergo impairment with aging, as happens for other receptors such as alpha- and beta-adrenoceptors. Age-related alterations of adrenoceptors, which are modulated by brain InsRs, are not definitive as they can be recovered by a thymus graft. In this study we verified the possibility that the thymus graft can also recover the age-dependent modifications of brain InsRs. InsR characteristics were assayed in a group of 27 months old Balb/c-nu mice grafted with a neonatal thymus, under renal capsule, one month before the animals were killed. Another two groups of young (3 months) and old (27 months) mice were used as controls. A two-sites model analysis of receptor data confirmed the age-dependent decrease of InsR density previously observed in the high affinity population. Furthermore, a statistically significant recovery of this impairment was shown in thymus grafted animals. The low affinity receptor subset also showed some differences among the three animal models; however, they were not statistically significant. Thymus graft induced recovery of the age-related changes found in brain InsRs, together with the similar one observed on the adrenergic system, calls for deeper studies of their interaction and the role they can play on aging processes.

Functional interrelationships in aging processes: alterations and reversibility.

The problem of assessing the relevance of the reversibility of age-related functional alterations for aging studies has been presented. Transduction mechanisms of adrenergic stimulation have been chosen as the target of age-related changes and thymus as the effector of some corrective interventions performed at advanced age. Both alterations of adrenoceptor characteristics and their reversibility have been reviewed. beta-adrenoceptors have been studied in organs bearing only one subtype of receptors or both, revealing an age-related decrease in density only in the beta1-subtype. It has been shown that a similar age-related decrease is present in alpha1-adrenoceptor density. Such alterations are corrected by grafting a neonatal thymus into old mice. On the contrary, thymus fails to correct the alteration of T4-induced upregulation of beta-adrenoceptors indicating some limits to its corrective effect when the net of functional interrelationships becomes relatively complex. Both failures and successes of thymic grafts and thymic extracts in reversing age-related changes are discussed taking into account the effects induced on the life span of the animals. Different unsolved problems stemming from the previous considerations are also presented. Among them the controversial question about linearity and non-linearity of biological parameters presumed to be good indices of aging is discussed, with the aid of a simple model as a schematic example.

The human lymphocyte as a model of β-adrenoceptor reculation in aging and disease

Summary Extensive experimental evidence suggests that human lymphocytes may model the behavior of other tissues as far as β-adrenoceptor characteristics are concerned. In fact, although lymphocytes bear only β2-adrenoceptor subtype, they may mirror other tissues in various physiological and pathological conditions. In the present paper examples are given demonstrating receptor regulations after drug or surgical stimulus. Age-related changes have also been taken into account. Treatment with β1-selective β-blockers without or with intrinsic sympathomimetic activity induces, respectively, up- or down-regulation of β-adrenoceptors of lymphocytes in agreement with other tissues, as suggested by clinical findings. Data on the influence of thyroidectomy are also in agreement with clinical observations and animal experimental findings on other tissues. Preliminary results on old subjects also suggest a possible role of the human lymphocyte in modelling other tissues or organs in relation to aging processes. The clinical application could be of paramount importance due to the impossibility to directly monitor the receptor status in most of human tissues.