Age-related increases in mitogenic responses and natural immunity to a syngeneic fibrosarcoma in rats

The effect of aging on the growth of colon cancer

Reports on the effect of patient age on the prognosis for colon cancer vary. We have tested the effect of aging using a model of murine colon adenocarcinoma in groups of mice of different ages. In experiment A, Balb/c mice of age groups 3-4 weeks, 10-12 weeks, 24-32 weeks and 40-48 weeks (13 mice/group) were injected with 5 X 10(4) MC-26 cells subcutaneously in the right flank. Tumors were measured twice weekly, and the rate of occurrence of tumor, mortality rate, and growth rate were calculated. In experiment B, the same plan as experiment A was used, except mice of age groups I (14 days), II (3-4 weeks), and III (20-22 months) were used with tumor doses of 1 X 10(4) cells and 5 X 10(5) cells (9-15 mice/group). In both experiments, the rate of growth of tumor, mortality rate, and sizes of tumors obtained were the same. In experiment A, the rate of occurrence of the tumors was the same in all groups, but in experiment B the occurrence of the tumor varied. A palpable tumor appeared earliest in the weanling mice (14 days), next in old mice (20-22 months), and last in the young adult group (3-4 weeks). Tumor doubling time was longest in the young adult mice (7 days), intermediate in the old mice (6.1 days), and shortest in the weanling mice (5.5 days). Established tumors grew at similar rates (as assessed by doubling time), independent of host age. Mortality rates were similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of polyclonal, tumor cell and alloantigen-induced proliferation: identification of cyclooxygenase pathway dependent and independent mechanisms

Polyclonal T cell activation, syngeneic tumor cell and alloantigen-induced proliferative responses were studied to determine if the regulation of these responses in normal and tumor-bearing NBR rats is mediated through products of the cyclooxygenase pathway and prostaglandin E2 (PGE2) in particular. Young rats and tumor-bearing rats have previously been shown to produce poor proliferative responses to PHA, Con A and syngeneic methylcholanthrene (MCA)-induced fibrosarcoma cells. The poor responses to PHA and Con A are mediated by PGE2 in unfractionated ( UNF ) and nylon wool adherent (ADH) cells. The same relationship was also established in the mixed leukocyte tumor cell (MLTC) response to MCA tumor cells although it appears to be of only minor significance as the enhancement following indomethacin (IND) treatment is still a relatively poor response. Indomethacin generally had no effect on the proliferative responses of tumor-bearing animals indicating that the suppression was not mediated through the cyclooxygenase pathway. We have also extended a previous observation in which UNF cells were found to be unresponsive to alloantigen stimulation. This suppression does not appear to be mediated through cyclooxygenase products as IND treatment does not enhance the UNF response although it does enhance the ADH response. These data indicate that a complex network of cyclooxygenase dependent and independent regulation exists in normal and tumor-bearing NBR rats.

Changes in spleen cell proliferative responses and resistance to syngeneic tumor challenge in aging NBR rats

New Zealand Black rats are shown to have a mean longevity of 102.9 weeks. The 90%, 50% and 10% survival age are 81 weeks, 108 weeks and 126 weeks, respectively. Resistance to syngeneic tumor challenge is significantly lower in young rats (3-35 weeks) and very old rats (126-140 weeks) compared to middle-aged rats (36-85 weeks). The in vitro spleen cell proliferative response to syngeneic tumor cells is decreased in old rats. No decrease is observed in spleen cell proliferation induced by the mitogens concanavalin A or phytohemagglutinin. Young (4 weeks) rat spleens contain suppressor cells which affect the mitogen and syngeneic tumor cell induced proliferation of responsive spleen cells (from 50-week-old rats). Spleen cells from old rats (130 weeks) do not demonstrate analogous suppressor cell activity.

Carcinogenesis and aging

Figure 2 illustrates a suggested mechanism of carcinogenesis. This scheme takes into account the effect of carcinogens at different integration levels: subcellular, tissue, and organism. Any of these levels may be age dependent. Age-associated changes in the activity of enzymes responsible for activation and inactivation of carcinogens, and variations in concentrations of lipids and proteins contributing to the transport of carcinogenic agents into cells, may play an important role in the modifying effect of age on carcinogenesis. The effects of age-associated changes in DNA repair need clarification. However, they are thought to exert a permissive influence on the age-associated rise in tumor incidence. It seems that proliferative activity of target tissues is the important modifying factor of carcinogenesis. Age-related changes of regulation at tissue and organism levels are also powerful factors in carcinogenesis modification. Age-dependent changes in the neuroendocrine system provide conditions for metabolic immunodepression and promotion of carcinogenesis. On the other hand, carcinogens per se (especially chemical and radiological) may intensify aging processes in the organism. Normalization, by drugs, of age-associated shifts requiring synthetic and energetic changes of a transformed tumor cells, and of immunological shifts, may exert both antitumor and geroprotective effects.