Bone marrow-cellularity

Blood dyscrasias Any abnormality in blood or bone marrow cellular components such as low white blood cells, red blood cells, or platelets. 

Tier 3 is the evaluation of bone marrow after in vivo exposure to determine in vivo applicability of the in vitro results (tiers 1 and 2) and predict clinical target- and chemistry-related toxidties. Historically, the bone marrow toxicity potential of compounds was evaluated by microscopic assessment of rat bone marrow cellularity from decalcified sternum bone slides, hematology and in some cases bone marrow differentials [55] only when a compound reached development. 

Tunek, A., Hflgstedt. B. Olofsson, T. (1982) Mechanism of benzene toxicity. Effects of benzene and benzene metabolites on bone marrow cellularity, number of granulopoietic stem cells and frequency of micronuclei in mice. Chem.-biol. Interact., 39, 129-138... 

Hedli, C.C.. Snyder, R. Witmer, C.M. (1990) Bone marrow DNA adducts and bone marrow cellularity following treatment with benzene metabolites in vivo. In Witmer, C.M., Snyder, R.R.. Jollow, D.J., Kalf, G.F., Kocsis, J.J. Sipes, LG, eds, Biological Reactive Intermediates IV. New York, Plenum Press, pp. 745-748... 

NMRI male mice exposed to benzene at concentrations ranging from 1 to 200 ppm, exhibited a reduction in bone marrow cellularity (nucleated cells per tibia), a reduction in the number of colony-forming granulopoietic stem cells (CFU-C) per tibia, and an increase in frequency of micronucleated polychromatic erythrocytes (MN-PCE) that varied with dose and duration of exposure as explained below (Toft et al. 1982). Mice exposed continually (24 hours/day) to 21 ppm or more benzene in air for 4-10 days showed significant changes in all of the parameters. No adverse effects on hematological parameters were noted in mice exposed to 14 ppm benzene continuously for 1-8 weeks (Toft et al. 1982). 

A continuation of this line of studies for 6 days to 23 weeks at 300 ppm showed continued decreases in numbers of mature B- and T-lymphocytes produced in the bone marrow, spleen, and thymus (Rozen and Snyder 1985). Abnormalities of humoral and cell-mediated immune responses following benzene exposure are presumably caused by a defect in the lymphoid stem cell precursors of both T- and B-lymphocytes. Bone marrow cellularity increased 3-fold, and the number of thymic T-cells increased 15-fold in benzene-exposed mice between the 6th and the 30th exposure. No corresponding increase in splenic cells was noted. The marked increase in the numbers of cells in bone marrow and thymus was interpreted by the authors to indicate a compensatory proliferation in these cell lines in response to... 

Other studies have also shown similar effects on immune functions following acute-duration exposure to benzene. These include decreased numbers of circulating leukocytes and decreases in bone marrow cellularity in mice exposed to 100 ppm and higher, 24 hours per day for up to 8 days (Gill et al. 1980) decreased leukocytes and increased leukocyte alkaline phosphatase in rats exposed to 100 ppm for 7 days (Li et al. 1986) decreased leukocytes and bone marrow cellularity in DBA/2 mice exposed to 300 ppm benzene for 2 weeks (Chertkov et al. 1992) and decreased leukocytes in mice exposed to 300 ppm for 10 days (Ward et al. 1985). These studies are more fully described in Section 2.2.1.2. Decreased spleen weight and levels of B- and T-lymphocytes have also been noted in the blood and spleen of mice exposed 6 hours per day to 47-48 ppm of benzene for 7 or 14 days (Aoyama 1986). Decreased thymus weights were also noted at the 48 ppm dose after 14-day exposure (Aoyama 1986). 

Benzene, administered intraperitoneally at 600 mg/kg in com oil, 2 times per day for 2 days to male C57BL/6J mice, caused a significant depression in the total number of nucleated bone marrow cells per femur, when measured on day 3 (Niculescu and Kalf 1995). Additional experiments with 7-day exposure revealed that there was an initial depression in erythroid cells on day 3 which remained constant lymphocytes exhibited a progressively depressive effect, and the numbers of intermediate and terminally differentiated granulocytes exhibited a progressive increase over the 7 days of exposure. Upon cessation of the benzene treatment, the bone marrow appeared to begin recovery, with the number of nucleated cells equal to control animals by day 7 after treatment ended. Concomitant administration of IL-la prevented the decrease in nucleated bone marrow cells, whereas IL-la administered after 2 days of benzene exposure significantly increased the rate of recovery of bone marrow cellularity. 

Experimental data in animals and studies of human cases of benzene intoxication indicate a link between the decrease in bone marrow cellularity and the development of leukemia. Many cases of benzene-induced leukemia appear to have been preceded by aplastic anemia (Toft et al. 1982). The compensatory response (regenerative hyperplasia) observed in the bone marrow, thymus, and spleen of exposed animals may play a role in the carcinogenic response (Rozen and Snyder 1985 Snyder 1987 Snyder and Koscis 1975 Snyder etal. 1984). 

Ethanol can increase the severity of benzene-induced anemia, lymphocytopenia, and reduction in bone marrow cellularity, and produce transient increases in normoblasts in the peripheral blood and atypical cellular morphology (Baarson et al. 1982). The enhancement of the hematotoxic effects of benzene by ethanol is of particular concern for benzene-exposed workers who consume alcohol (Nakajima et al. 

Hedli CC, Snyder R, Witmer CM. 1990. Bone marrow DNA adducts and bone marrow cellularity following treatment with benzene metabolites in vivo. Adv Exp Med Biol 283 745-748. 

Tunek A, Olofsson T, Berlin M. 1981. Toxic effects of benzene and benzene metabolites on granulopoietic stem cells and bone marrow cellularity in mice. Toxicol Appl Pharmacol 59 149-156. 

Klein et alP also assessed the protective properties of swainsonine in vivo with the myelosuppressive agent 3 -azido-3 -deoxythymidine (known as Zidovudine or AZT), which is often used in therapy for the acquired immune deficiency syndrome (AIDS). Swainsonine administered by intraperitoneal injection increased both total bone marrow cellularity and the number of circulating white blood cells in mice treated with doses of AZT that typically lead to severe myelosuppression, which is the major dose-limiting... 

Oral LD50 values range from 1 to 3gkg in rodents. A dermal LD50 of 1.3gkg was determined in rabbits. An inhalation LC50 of 4600 ppm was determined in mice. In animals, systemic effects from sublethal, or short-term exposures, are kidney damage, thymic involution, depression of blood cell counts, and depression of bone marrow cellularity. 

Atkinson, T.G., Barker, H.J., and Meckling-Gill, K.A. 1997. Incorporation of long-chain n-3 fatty acids in tissues and enhanced bone marrow cellularity with docosahexaenoic acid feeding in post-weanling Fischer 344 rats. Lipids 32, 293-302. 

Mathew and Kuttan [16] have found that the methanolic extract of Tinospora cordifolia inhibited lipid peroxide formation and scavenged hydroxyl and superoxide radicals in vitro. For 100% inhibition 50 mg/ml were required. This was associated with increased bone marrow cellularity as well as an ablation of neutropenia. 

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