Hans Niedermüller

Models of the biological age of the rat. I. A factor model of age parameters.

The hypothesis of biological age postulates a fixed pattern in the aging of the multicellular organism. As a test of this hypothesis 23 age parameters of the rat were submitted to factor analysis. The data used in this study were a result of a long-term cohort study on 240 male Sprague-Dawley rats, which covered an age range of 10-30 months. The age parameters were obtained from various systems and levels of organization. The analysis revealed that there is a fixed pattern in the variations of the parameters. In this factor pattern the parameters are grouped into six factors, five of which can be attributed to the aging process. The first factor is interpreted as representing primary aging, factors 2-5 are interpreted as an expression of system-specific secondary processes of multicellular aging. Approximately 40% of the total variation of all parameters turned out to be random or due to processes other than aging.

Immune modulation following immunization with polyvalent vaccines in dogs.

A decline in T-cell-mediated immunity and transient state of immunosuppression after immunization has been reported in dogs. Nevertheless, dogs are still routinely vaccinated with polyvalent live vaccines and severe disease does not generally occur. In order to investigate these effects on the canine immune system and to elucidate possible mechanisms we determined the following immune parameters in the blood of 33 clinically sound German shepherd dogs before and after standard vaccination with a polyvalent vaccine against distemper, parvovirus, viral hepatitis, leptospirosis, kennel cough and rabies: white and differential blood cell count, the serum concentrations and/or activities of IL-1, IL-2, IFN-gamma, TNF-alpha, neopterin and IgG, natural killer (NK) cell activity, bactericidal activity and complement hemolytic activity, lymphocyte proliferation test (LPT) and nitroblue tetrazolium test (NBT). Our major findings were that significant postvaccinal decreases in T-cell mitogenic response to PHA and in neutrophil function and neopterin serum concentration were accompanied by simultaneous increase in plasma IgG and hemolytic complement activity. This suggests a transient shift in the balance between cell-mediated and humoral (T(H)1/T(H)2) immunity rather than immunosuppression. These results do not imply that dogs should not receive live vaccines, as the response to vaccines just seems to create a state of altered homeostasis when immunization elicits protection by humoral and cell-mediated immunity. However, these recognized compromises of immune function should be considered and vaccines still be applied only in healthy animals and strictly according to the rules and regulations given by the manufacturer.

Investigations on the kinetics of collagen-metabolism in young and old rats

Abstract Collagen is one of the most important body-proteins (about 30%) whose structure, function and turnover depends on certain diseases and on the aging process. After designing a general model of collagen-metabolism the course of the specific activity of hydroxyproline in three different collagen-modifications of skin and tail-tendon was investigated for 32 days in Sprague-Dawley rats with an age of 3 resp. 20–24 months. These modifications are typical for the structure of collagen. From this course and from the specific activity in blood and urine the turnover rates of one single modification into one another were calculated. From the size of these determined constants conclusions could be drawn upon the different ways of collagen-biosynthesis in young and old animals. Moreover this model should give information about the nature of this way of collagen-synthesis in different diseases of connective tissue.

Changes of DNA repair mechanisms during the aging of the rat

Recent studies have shown a significant reduction in DNA repair capacity in aging rats. Therefore we were interested in investigating which repair mechanism is concerned in this reduction. We investigated: excision repair (ER); single-strand break repair (SSBR); double-strand break repair (DSBR); and gamma-endonuclease susceptibility (ES) by means of the following methods: [3H]thymidine ([3H]dThd) incorporation into DNA after damage by N-methyl-N-nitrosourea (MNU); nucleoid sedimentation after damage by methyl methanesulfonate (MMS); neutral elution techniques after damage by 4-nitroquinoline-1-oxide (NQO); and determination of ES sites by velocity sedimentation in an alkaline sucrose gradient after damage by gamma-irradiation. Studies were done with male Sprague-Dawley rats aged 9, 18 and 28 months using nine different organs. We were able to determine a distinct age dependency of excision repair, a slight reduction of single-strand break repair, an elevation of gamma-endonuclease susceptible sites and no significant change in double-strand break repair in the course of aging. Therefore we see a shift in the pattern of DNA repair: in old age strand break repair mechanisms become more important, while repair replication is reduced. From this we can conclude that genetic expression is altered during the aging process, with all the consequences for the disposition toward certain diseases.

A simple method for the simultaneous separation of peripheral blood mononuclear and polymorphonuclear cells in the dog

A simple method for the simultaneous separation and purification of peripheral blood mononuclear cells (PBMC) and polymorphonuclear neutrophil cells (PMNC) was developed for comparative and functional studies in the immune system of the dog. Purity and cell viability were > 95%, yields were similar to those obtained by other techniques but without red blood cell contamination. Differential blood cell count studies of the isolated cells in blood samples of beagle dogs and German shepherd dogs demonstrated that the 1.077/1.119 double density centrifugation is an effective method of acquiring both highly purified blood mononuclear cells and polymorphonuclear cells as separate entities from the same sample. The interface between plasma and 1.077 contained an average 97% blood mononuclear cells vs. 3% polymorphonuclear cells, and the interface between 1.077 and 1.119 an average 96% polymorphonuclear cells vs. 4% blood mononuclear cells. These data indicate that Histopaque 1.077/1.119 double density gradient allows the purification and physical separation of lymphocytes and phagocytes from a blood sample in the dog, enabling the investigator to examine both cell types from the same sample simultaneously.

Age dependence of signal transduction and cell signaling as a major factor of intervention into the aging process

Nowadays, it has become necessary to investigate the mechanisms underlying aging changes and their modulation. Of particular interest are the cellular and molecular level cell-cell and cell-matrix interactions. Thus, we partly determined in rats aged 9 and 31 months (a) the concentrations and the activities of signal molecules, such as G-proteins, cyclic adenosine monophosphate (cAMP) and kinases (cellular) and collagens, proteoglycans (PG) and fibronectin (extracellular) in vivo in the skin of the back, as well as in isolated fibroblasts and keratinocytes; (b) the cell proliferation and (c) we tried to retard the aging process in the skin by topical application (or by addition to cell cultures) of fetal mesenchymal cells, PGs, and soya matrix and we compared the above mentioned parameters with those obtained by stimulation of skin cells with growth factors. There are indications that there is (a) no change in the quantity of Gs-proteins but a reduction of the binding capacity. We found lower concentrations of cAMP, a reduced activity of protein kinase C in vivo, a higher collagen crosslinking, a lower PG concentration and no change of the amount of fibronectin in the old rats skin and (b) there is a more or less extensive restoration of these parameters by all the above mentioned stimuli. So, we conclude that all the above mentioned influences modulate the aging process of the skin and its cells by intervention into the signaling pathways, by mediating new signals to the cells and hence by readjusting damaged feedforward systems in the cells.

Age-related changes in plasma IgM level after SRBC-stimulation in the rat

The aim of our investigation was to detect age-related changes in the immune system and immune response of the rat in order to establish a system of biological markers of aging in the immune system. Our results demonstrate significant changes with increasing age in the immune system of Sprague-Dawley rats. Immunoglobulin M (IgM) plasma concentrations showed significant age-related differences after immunization with sheep red blood cells (SRBC). An increase in IgM plasma concentration after exogenous stimulation was found only in young and adult animals but not in old ones. Furthermore, we were able to demonstrate an age-dependent decrease in the peripheral blood lymphocyte count (PBL) and the W3/13-cell count, whereas plasma IgM concentration and polymorphonuclear cell count (PMNC) increased with age in the animals between 12 and 32 months of age. Because of these data, we suggest that the observed decline in humoral immune response with age indicates a decline in cell-mediated immunity.

Assessment of modifications of the rate of aging in the rat.

Multivariate models of BA are, at present, the only way of measuring the main subject of gerontological research, namely, aging of the organism as a whole. Aging is obviously not a completely random process without any regularity, but shows a pattern which is determined by the organisms principles of order and its answer to the stochastic events of primary aging. Based on this theoretical concept, which is supported by results of factor analysis, multicellular aging may be described by a single complex variable, BA. However, the non-linearity of age changes and the different extent to which primary and secondary aging are involved, as well as factors other than aging, restrict the sensitivity of multiple regression models. Sensitivity may be increased by selecting parameters according to their discriminating power revealed by discriminant analysis. Wherever influences on aging are to be tested, a combination of the three types of multivariate methods will allow for an objectivation of effects and provide clues to a possible mode of action.

Lebensdauer: Genetische Determinierung und lebensverlängernde Strategien

Altern ist ein grundlegender physiologischer Prozess, der ausnahmslos in allen arbeitsteiligen multizellularen Organismen auftritt. In dieser Arbeit werden wir uns beim Begriff „Spezies“ besonders auf Mammalia beziehen—auf Abweichungen wird hingewiesen. Aus medizinisch-biologischer Sicht umfasst der Begriff „Altern“ die regressive Phase des stetigen Wandels von Struktur und Funktion, den Burger (1947) als Biomorphose bezeichnete (Abb. 1.2.1).