Franco Tropea

In vivo accumulation of sulfated glycoprotein 2 mRNA in rat thymocytes upon dexamethasone-induced cell death.

Two hours after a single intraperitoneal injection of dexamethasone (20 micrograms/Kg b.w.) into adult male rats, a typical ladder of DNA fragments was detectable upon separation on agarose gels of DNA from thymocytes. This became maximally evident at 4 hours. Accumulation of sulfated glycoprotein-2 (SGP-2) mRNA, whose rate of expression has been associated to the processes of programmed cell death, preceded the appearance of DNA degradation, starting to increase as early as 30 min after steroid injection, and maintained higher than controls until 8 hrs; a different time course was shown by changes in the levels of beta-actin mRNA. In the spleen, under the same conditions, the SGP-2 message also increased at 30 min, prior to DNA fragmentation, but decreased thereafter below the control value.

Apoptosis—programmed cell death: a role in the aging process?

Cells continuously exposed to genotoxic agents, such as oxygen free radicals (OFRs), deeply involved in the aging process use a variety of cellular defense mechanisms. These defense mechanisms include DNA repair enzymes, antioxidants, poly(ADP-ribosyl)polymerase (pADPRP), and stress proteins and they constitute an integrated network. An age-related failure of the efficiency of this network can affect cell proliferation and cell death, two phenomena tightly linked and regulated. Recent data from our laboratory on the role of DNA damage and pADPRP activation and on the type of cell death induced by OFRs in human lymphocytes are reviewed. In vitro and in vivo data on possible strategies to reduce oxidative stress in lymphocytes from normal and Down syndrome subjects, by using natural compounds and trace elements, are presented. They indicate that nicotinamide and L-carnitine protect human cells from OFR-induced damage and suggest that they are possible candidates as antiaging substances.

Cell Proliferation and Cell Death in Immunosenescence

Aging is characterized by a variety of alterations that occur in most organs and cell types. Loss of proliferative vigor is considered a marker of the aging process and is related to the Hayflick phenomenon, that is, the limited number of replications that normal cells can undergo. A correlation between proliferative capability and maximum lifespan in different species, and an inverse correlation between proliferative capability and donor age have been dem~nstrated.l-~ Thus, a decreased capability to proliferate may be considered a characteristic of cellular senescence. In a recent paper we argued that an intriguing relation exists among cellular senescence, tumor growth, and 10ngevity.~ All these phenomena are deeply related to programmed cell death or apopto~is.~ A possible scenario is the following: cells may be equipped with genes that actively promote cellular senescence, thus controlling cell death in order and escaping transformation.68 This situation is balanced by other genes responsible for survival and viability, as depicted in FIGURE 1. Circumstantial evidence suggests that cellular senescence may be considered a peculiar type of cell differentiation whose biological function is to counteract uncontrolled cell proliferation. (For an example, see ref. 9.) From this point of view, cellular senescence can be considered one of the most important mechanisms in avoiding the continuous onset of tumors. The most effective evolutive way for a cell to control neoplastic growth is likely to set up genes that promote apoptotic cell death.1s24

Effects of Pulsed Electromagnetic Fields on the Proliferation of Lymphocytes from Aids Patients, HIV-Seropositive Subjects, and Seronegative Drug Users

The effect of the exposure of mitogen-stimulated lymphocytes from subjects infected by human immunodeficiency virus to extremely low frequency pulsed electromagnetic fields (PEMFs) was studied, by evaluating the incorporation of tritiated thymidine, the expression of IL-2 receptor, and the amount of activated T lymphocytes. Four groups of subjects were considered patients with acquired immunodeficiency syndrome (AIDS), asymptomatic seropositive subjects, seronegative drug users, and young healthy controls. PEMFs increased cell proliferation only in the group of healthy controls, as measured at the 72nd hour of culture, but an increase in the number of activated T lymphocytes was observed by cytofluorimetric analysis after 18 hrs of PEMF exposure in cultures from AIDS patients.

DNA AND CELL DEATH

The type of DNA damage and the role of poly (ADP-ribosyl) polymerase (ADPRP) and sulphated glyprotein 2 (SGP-2) in programmed cell death (apoptosis) was investigated in the following model systems: i) rat thymocytes treated with dexamethasone (DEX) eitherin vitro orin vivo; ii) human perypheral blood mononuclear cells (hPBMCs) exposed to oxygen free radicals (OR); iii) K562 cell line killed by hPBCs during spontaneous (NK) or interleukin-2 (IL-2)-induced (LAK) cytotoxic activity. The results suggest that ADPRP and SGP-2 are involved in the apoptotic process, but their role probably differs according to the type of cell and the inducing damage/stimulus. Moreover, no simple correlation appears to exist between the extent of DNA damage and cell survival or cell death.