Cell renewal patterns

Exercise to Mend Aged-tissue Crosstalk in Bone Targeting Osteoporosis & Osteoarthritis

Aging induces alterations in bone structure and strength through a multitude of processes, exacerbating common aging- related diseases like osteoporosis and osteoarthritis. Cellular hallmarks of aging are examined, as related to bone and the marrow microenvironment, and ways in which these might contribute to a variety of age-related perturbations in osteoblasts, osteocytes, marrow adipocytes, chondrocytes, osteoclasts, and their respective progenitors. Cellular senescence, stem cell exhaustion, mitochondrial dysfunction, epigenetic and intracellular communication changes are central pathways and recognized as associated and potentially causal in aging. We focus on these in musculoskeletal system and highlight knowledge gaps in the literature regarding cellular and tissue crosstalk in bone, cartilage, and the bone marrow niche. While senolytics have been utilized to target aging pathways, here we propose non-pharmacologic, exercise-based interventions as prospective "senolytics" against aging effects on the skeleton. Increased bone mass and delayed onset or progression of osteoporosis and osteoarthritis are some of the recognized benefits of regular exercise across the lifespan. Further investigation is needed to delineate how cellular indicators of aging manifest in bone and the marrow niche and how altered cellular and tissue crosstalk impact disease progression, as well as consideration of exercise as a therapeutic modality, as a means to enhance discovery of bone-targeted therapies.

Cadmium induced-oxidative stress in pituitary gland is reversed by removing the contamination source

Cadmium (Cd2+) is one of the most important environmental contaminants and acts as an endocrine disruptor. Previously, we have demonstrated that the simultaneous administration of Cd2+ and melatonin (Mel) in drinking water impaired metal-induced oxidative stress in rat anterior pituitary gland. The aim of this study was to investigate if a treatment started after the toxic manifestations of Cd 2+ became evident could reverse the effects of the metal. Animals exposed to Cd2+ (5 parts per million [ppm], 30 days) were treated with Mel or without the metal during the next 1 or 2 months. Cd2+ exposure increased the expression of heme oxygenase-1 (HO-1), a biomarker of oxidative stress, and an a posteriori Mel treatment reversed oxidative stress induced by Cd2+. This effect was also observed 1 month after metal removal. The Cd2+-induced increase in metallothionein-1 (MT-1) and nitric oxide synthase 1 (NOS1) expression were also reversed by metal removal. In addition, serum prolactin and luteinizing hormone levels affected by Cd 2+ exposure were normalized. Considering that the manifestations of Cd2+ intoxication become evident only after a certain period of metal accumulation, these results show that metal removal is enough to reverse Cd2+ effects in anterior pituitary gland and bring to light the relevance of moving away the individual from the contamination source.

Evidence for chromosomal replicons as units of sister chromatid exchanges

Chromosomal replicons have been described as the cytological counterpart of DNA replicon clusters and have previously been studied in vitro using premature chromosome condensation-sister chromatid differentiation (PCC-SCD) techniques. Chromosomal replicons are visualized as small SCD segments in S-phase cells, and measurement of these segments can provide estimates of relative chromosomal replicon size corresponding to DNA replicon clusters functioning coordinately in S-phase. Current hypotheses of sister chromatid exchange (SCE) formation postulate that sites of SCE induction are associated with active replicons or replicon clusters. We have applied the PCC-SCD technique to in vivo studies of mouse bone marrow cells that have been treated with cyclophosphamide (CP) for two cell cycles. We have been able to visualize chromosomal replicons, as well as SCEs which have been induced in vivo by CP treatment, simultaneously in the same cells. Chromosomal replicons visualized as small SCD segments were measured in PCC cells classified at early or late S-phase based on SCD segment size prevalence. Early S-phase (E/S) PCC cells contained 90% of the SCD segments measured clustered in a segment size range of 0.1 to 0.8 micron with a peak value around 0.3 to 0.6 micron regardless of CP treatment. As the cells progressed through S-phase, late S-phase (L/S) PCC cells were characterized by the appearance of larger SCD segments and even whole SCD chromosomes in addition to small SCD segments.(ABSTRACT TRUNCATED AT 250 WORDS)

Rodent species and strain specificities for sister-chromatid exchange induction and gene mutagenesis effects from ethyl carbamate, ethyl N-hydroxycarbamate, and vinyl carbamate

Ethyl carbamate (EC) and two related carcinogens, ethyl N-hydroxycarbamate (ENHC) and vinyl carbamate (VC), caused species-specific increases in sister-chromatid exchange (SCE) formation in the bone marrow cells of rodents. Mice exposed to 400 mg/kg of EC had SCE increases of 6-times-baseline, while rats, Chinese hamsters, and golden hamsters showed 3- to 4-times-baseline increases in response to this dose. Lesser, but still significant, differences were found for ENHC and VC; the severest effects consistently occurred in mice. Control bone marrow cell-cycle kinetics among the rodent species were similar. Mouse strains A and C57BL/6, which have high and low susceptibilities to EC induction of lung adenomas, respectively, showed nearly identical levels of SCE induction after in vivo exposure to these carbamates. However, testing of VC, a possible metabolite of EC, in vitro revealed strain-dependent liver enzyme (Aroclor-induced S-9 fraction) capabilities to convert VC to genotoxic products. SCE induction, gene mutation for 6-thioguanine and ouabain resistance, and cytotoxicity in Chinese hamster V79 cells were significantly greater when A strain S-9 enzymes were used as compared with C57BL/6 strain S-9 enzyme preparations. No effect on SCE of reseeding, compared with no reseeding, of VC-treated V79 cells was observed. At a concentration of 25 micrograms/ml, VC caused 6-times-baseline induction of SCE in the presence of A strain S-9 mix and 4-times-baseline induction in the presence of C57BL/6 strain S-9 mix. These in vitro strain-dependent patterns of response are relevant to the current theory that VC may be a proximate carcinogenic metabolite of EC.

The kinetics of in vivo sister chromatid exchange induction in mouse bone marrow cells by alkylating agents: cyclophosphamide

Administration of cyclophosphamide (5, 10, 20 and 25 mg/kg body weight) to male CD-1 mice 2 hr after subcutaneous implantation of a 5-bromo-2'-deoxyuridine (BrdUrd) pellet (55 mg) resulted in a dose-dependent increase in sister chromatid exchanges (SCE) in bone marrow cells. Treatment with cyclophosphamide (15 mg/kg body weight) at the time of BrdUrd implantation and 2, 6.5, and 13 hr post-BrdUrd implantation resulted in the induction of approximately 19 SCE/cell indicating that the bone marrow SCE response was independent of the time of administration. Treatment with cyclophosphamide (15 mg/kg body weight) at 26, 19, 13, and 6 hr prior to BrdUrd implantation resulted in baseline SCE (3.3 SCE/cell) at 26 hr with an increasing number of SCE/cell with decreasing time prior to BrdUrd implantation. These results compare favorably with those obtained by Kram et al [1981] with mitomycin C (MMC) using a similar protocol. The time-dependent induction of SCE is qualitatively similar for CP and MMC, both of which are bifunctional alkylating agents metabolically activated by oxidation and reduction, respectively, and suggests that these two compounds may induce SCE by a similar mechanism.

In vivo sister chromatid exchange in cells of various organs of the mouse

In vivo sister chromatid exchange (SCE) in mouse cells derived from various organs was studied by infusing BrdU from the tail vein. It was found that at BrdU concentrations ranging from 2.2-13.5 micrograms/g/h, the SCE frequency in bone marrow cells seemed to stay at a constant level (1.5-2/cell/two cell cycles) whereas it started to rise as the BrdU dose exceeded this dose range. When BrdU within this dose range was infused continuously from the tail vein for appropriate hours to label chromosomes in various organs, the average SCE frequencies per cell were found to be 1.64 in bone marrow cells, 1.82 in spermatogonia, 1.99 in splenic cells, 2.89 in intestinal cells and 3.69 in cells from adjuvant stimulated lymph nodes. It is suggested that the spontaneous level of the in vivo SCE frequency might be about 1.5-2/cell/two cell cycles in the mouse. In cells derived from intestine and adjuvant stimulated lymph node, some unknown factors might work as a inducer of SCEs resulting in a significant increase in the SCE frequency in these organs.

Bromodeoxyuridine tablet methodology for in vivo studies of DNA synthesis

5-Bromodeoxyuridine (BrdU) tablets with different physical characteristics are useful in a wide variety of studies requiring detection of DNA replication in vivo. These tablets can effect a high substitution of BrdU in DNA, thereby permitting sister chromatid differentiation in chromosomes stained with 33258 Hoechst alone or in conjunction with Giemsa. Baseline and cyclophosphamide-induced in vivo sister chromatid exchange frequencies in mouse spleen, marrow, and thymus were measured and found to be significantly greater than those in spermatogonia. Sister chromatid exchange analysis was also extended to mouse liver and to Chinese hamster and Armenian hamster marrow cells. Sister chromatid differentiation was observed in Armenian hamster meiotic tissue, and evidence for interhomolog chromatid exchange obtained.

Clinicopathologic effects of cancer chemotherapeutic agents on human buccal mucosa

Specimens of buccal mucosa obtained at autopsy from 216 patients were examined for histopathologic alterations. Atrophic oral epithelium was found in thirty cases. A retrospective study of the hospital records revealed that thirteen of these latter patients had been on a cancer chemotherapeutic regimen prior to death. There was a significantly higher incidence of atrophy in the chemotherapy group (p less than 0.001) than in control patients. These findings, as well as the expected inherent susceptibility of rapidly replicating oral epithelial cells to metabolic inhibitors, suggest a causal relationship between oral atrophy and the administration of cancer chemotherapeutic agents. This atrophy may therefore represent a preliminary stage of mucosal alteration that ultimately progresses to the clinical sequelae of stomatitis and oral ulcerations frequently encountered during cancer chemotherapy. Some alternative mechanisms are also discussed.

In vivo BrdU-33258 Hoechst analysis of DNA replication kinetics and sister chromatid exchange formation in mouse somatic and meiotic cells

BrdU (5-bromodeoxyuridine)-33258 Hoechst methods have been adapted for in vivo analyses of replication kinetics, sister chromatid differentiation and sister chromatid exchange (SCE) formation in mice. Sufficient in vivo BrdU substitution for cytological detection was effected with multiple intraperitoneal injections of the analogue. The combination of centromere staining asymmetry and sister chromatid differentiation at metaphase permits unambiguous determination of the number of replications in BrdU and dT (deoxythymidine) undergone by individual cells. Late-replicating regions in marrow and spermatogonial chromosomes are highlighted by bright fluorescence after sequential incorporation of BrdU followed by dT during a single DNA synthesis period. SCEs are analyzed in marrow and spermatogonial metaphases after successive complete cycles of BrdU and dT incorporation. Significant induction of SCE was observed with both mitomycin C and cyclophosphamide; the latter drug requires host-mediated activation to be effective. In meiotic metaphase cells harvested two weeks after BrdU incorporation, satellite DNA asymmetry, sister chromatid differentiation and SCE could be detected in a few chromosomes, most frequently the X and the Y.