David Kram

The effects of high and low fluoride diets on the frequencies of sister chromatid exchanges

A recent report suggests that fluoride has mutagenic activity in mice. To examine the potential clastogenic effect of ingested fluoride, we examined the frequencies of baseline SCE and mitomycin C induced SCE as well as baseline chromsomal aberrations and cell-cycle kinetics in mice raised on high and low fluoride diets. The lack of significant differences in any of these parameters between the two groups of animals indicates that dietary fluoride is not clastogenic and supports the continued use of water fluoridation.

The effect of aging on sister chromatid exchange.

The advent of the bromodeoxyuridine(BrdU)-differential staining techniques has greatly facilitated the detection of sister chromatid exchanges (SCE). These SCE have been demonstrated to be an accurate reflection of DNA damage both in vitro in cultured cells and in vivo in mouse and rate bone marrow and spleen cells. In this review, we examine the effect of cellular aging on both baseline and mutagen-induced SCE levels. In all systems examined, aging did not appear to significantly affect the baseline levels of SCE. However, in human fibroblast cultures we have found a significant decrease in the levels of mutagen-induced SCE as a function of both in vitro passage level (in vitro aging) and the age of the cell culture donor (in vivo aging). In addition we have found a similar decrease in mutagen-induced SCE levels in both mouse and rat bone marrow cells and mouse spleen cells where examinations were performed entirely in vivo. Diminished mutagen-induced SCE levels were obtained with a wide variety of agents including mitomycin-C, cyclophosphamide, adriamycin, ethyl methanesulfonate and N-acetyl-2-acetoxyamino-fluorene. These decreased SCE levels were accompanied by increased frequencies of chromosomal aberrations in the older cell populations. If SCE represents a form of DNA repair as has been suggested by several investigators, our finding would indicate impaired DNA repair occurring in old cells.

Spontaneous and mitomycin-C induced sister-chromatid exchanges: Comparison of in vivo and in vitro systems

Frequencies of sister-chromatid exchanges (SCE) were measured in vitro in mouse fibroblasts and in vivo in mouse bone-marrow cells. SCE levels in these cell systems were measured in response to varying concentrations of bromode-oxyuridine (BrdU) and mitomycin-C (MMC). Although BrdU was found to induce SCE in both cellular systems, baseline SCE levels were 2- to 3-fold higher in vitro than in vivo. SCE induction was found to be a linear function of MMC concentration in vivo and in vitro; however the slope of the vivo curve was 5-fold higher. The interaction of BrdU substituted DNA and MMC was examined by administering a fixed dose of MMC with increasing concentrations of BrdU. The induced SCE frequencies appeared to be additive. In addition to measuring drug-induced SCE, the BrdU differential staining technique allows concomitant measurement of the inhibition of cellular replication by the test drugs.

Reduced frequencies of mitomycin-c induced sister chromatid exchanges in akr mice.

SummaryThe frequencies of base-line and Mitomycin-C (MMC) induced sister chromatid exchanges (SCE) were surveyed in four inbred strains of mice. In contrast to the C57B1/6J, CBA/J, and A/J strains where frequencies of SCE increased linearly with increasing dose of MMC, levels of SCE were significantly lower in AKR/J mice at high MMC concentrations. At a dose of 5 mg/kg MMC, chromosomal aberrations were more frequent in bone marrow cells of AKR/J mice than in C57B1/6J mice. These observations suggest an altered response to DNA damage in the AKR mouse strain.

Aging and sister chromatid exchange. I. The effect of aging on mitomycin-c induced sister chromatid exchange frequencies in mouse and rat bone marrow cells in vivo.

Abstract Utilizing the differential staining of chromatids containing BUdR, it was demonstrated that frequencies of mitomycin-C induced sister chromatid exchanges decline with age. The concomitant increase in chromosomal aberrations suggest an altered response to DNA damage with aging.

CELLULAR REPLICATION AND AGING

Controversy exists concerning the effect of aging on replicating cell systems. This review summarizes a number of studies which indicate that both in vivo and in vitro, cell replication is significantly altered during aging. In vitro, studies of both human lymphocytes and fibroblasts indicated that a number of replication kinetic parameters are influenced by the age of the cell donor. In vivo, the application of the bromodeoxyuridine-(BrdU)-differential chromatid staining techniques to the analysis of cellular replication kinetics has permitted us to demonstrate that cellular replication is also significantly diminished with aging in mouse and rat cell populations. Therefore, both in vivo and in vitro in human as well as rodent cell populations, the rates of cellular replication are significantly decreased with cellular aging.

Sister-chromatid exchange induction by carcinogens in HTC cells An in vitro system which does not require addition of activating factors

The hepatic tumor cell line (HTC) was tested for the ability to produce sister chromatid exchanges (SCEs) in response to chemical carcinogens which require activation. Without the addition of exogenous microsomal enzyme preparations, cyclophosphamide, N-nitrosodiethylamine (DEN) and aflatoxin B1 (AFB1) induced significant levels of SCEs in these cells. Mitomycin C (MMC) and ultraviolet light, which do not require activation, also produced significant levels of SCEs. The induction of SCEs in HTC cells by AFB1 was shown to be inhibited by estradiol, a known inhibitor of microsomal activating enzymes. For the carcinogens tested, the HTC cell SCE assay was quite sensitive and comparable to other mammalian test systems. Exceptional sensitivity was found in the case of AFB1. SCE analysis of HTC cells offers a simplified system of detecting carcinogens requiring activation. This system also has the potential of investigating interactions between agents such as steroid hormones and carcinogens.

Parental-Age Effects: Increased Frequencies of Genetically Abnormal Offspring

In the previous chapters, the authors have discussed at length the effect of genotype on aging. In this chapter, we will focus on the effect of aging on human genotype—the increased risk faced by the older parent of having a child with a genetic disorder. This increased risk of genetically abnormal offspring with parental aging represents a sizable socioeconomical as well as clinical problem. The magnitude of this problem is reflected in the cost of one parental-age-related disorder, the Down syndrome. If the number of annual Down syndrome births (approximately 8000) is multiplied by the average life expectancy of a newborn with the Down syndrome (30 years) and by the average cost of specialized care for these persons (

Relationship between in vivo mitomycin c exposure, sister chromatid exchange induction and in vitro mitogenic proliferation. II. Effect of aging on spleen cell mitogenesis and sister chromatid exchange induction

5000 per year is a modest estimate), the staggering annual cost of 1.2 billion dollars is obtained (Swanson, 1970). In addition to the economic burden, one must consider the emotional and psychological problems that occur in a family with a Down syndrome child. The high frequency of parental-age-related disorders is also seen in institutions for the mentally retarded, where Down syndrome patients may comprise as much as one third of the entire patient population.

Relationship between in vivo mitomycin c exposure, sister chromatid exchange induction and in vitro mitogenic proliferation. I. Development of murine splenic cell system

In vivo administration of mitomycin C (MMC) produces an increase in both the frequencies of sister chromatid exchange (SCE) as well as inhibition of in vitro mitogenic responses. At low concentrations of MMC (2 mg/kg) spleen cell suspensions from both young and old mice showed similar patterns of mitogen inhibition and increased SCE frequencies. At high MMC concentrations (5 mg/kg) significant differences between young and old responses were observed. Spleen cells from young animals displayed mitogen-inhibition curves which plateaued with increasing doses of MMC, while the cells from old animals displayed a continuing increase in mitogenic inhibition. MMC-induced SCE frequencies revealed a complementary pattern: increasing SCE frequencies as a function of MMC concentration in young spleen cells while SCE levels plateaued in old spleen cell populations. The results of these studies suggest (1) that an inverse relationship exists between sister chromatid exchange induction and mitogenic response, (2) that cells from older animals may have an increased sensitivity to high levels of DNA damage (5 mg/kg MMC), and (3) that this sensitivity may be expressed functionally by increased inhibition of in vitro mitogenic responses.