Cell Renewal Systems Research Articles

Structure and function of bone marrow hemopoiesis: mechanisms of response to ionizing radiation exposure.

It is the purpose of this presentation to review the unique structure and function of bone marrow anchored hematopoiesis in their significance for its response mechanisms to an exposure to ionizing radiation. The ultimate objective of bone marrow hematopoiesis is to maintain in the peripheral blood a constant level of the different blood cell types (erythrocytes, granulocytes, platelets, lymphocytes, etc.). All of them have their particular turnover kinetics (such as granulocytes 120 x 10(9)/d, erythrocytes 200 x 10(9)/d or thrombocytes 150 x 10(9)/d), are semi-autonomous in their steady state regulatory mechanisms and dependent on a life-long supply of mature cells from a stem cell pool with unlimited replicative and pluripotent differentiative potential. The present knowledge of hematopoietic cellular renewal is the result of years of basic experimental and clinical studies using radionuclides in various metabolic forms including (59)Fe, (32)P (DF (32)P), (51)Cr, (131)I, (60)Co, (3)H ((3)HTdR) and (14)C ((14)CTdR). To understand the physiology but in particular the radiation-pathophysiology, it is essential to recognize in detail the infrastructure of the bone marrow as a distinct unit. Indispensable for a life-long cell production is the capsule of the marrow - the bone cortex -, the arterial supply of blood connected to the sinusoidal microvascular architecture with its sinusoids contorti and recti as well as the central (cell collecting) sinusoids. It is further of importance to recognize the significance of nerval regulation of blood flow, characterized by myelinated and unmyelinated nerve fibers. The type of unique lining cells of the sinusoids is the prerequisite for the cell traffic between the hemopoietic parenchyma and the blood. This in turn cannot be achieved without an alternative opening and closing of the sinusoidal segments which - in turn - requires a rigid long capsule to assure an - in toto - constant volume of each bone marrow unit. If a bone marrow unit is exposed to ionizing radiation, a perturbance of the balance between cellular growth pressure and blood flow dynamics can be observed, resulting in a special type of bone marrow hemorrhage and an "excess cell loss" that may result in an non-thrombopenic exhaustion of the stem cell pool. Of great importance is the question as to the mechanisms that allow the bone marrow hemopoiesis to act as one cell renewal system although the bone marrow units are distributed throughout more than 100 bone marrow areas or units in the skeleton. The observation that "the bone marrow" acts and reacts as "one organ" is due to the regulatory mechanisms: the humeral factors (such as erythropoietins, granulopoietins, thrombopoietins etc.), the nerval factors (central nervous regulation) and cellular factors (continuous migration of stem cells through the blood to assure a sufficient stem cell pool size in each bone marrow "sub-unit"). It should be recalled that the bone marrow functions as a physiological chimera and becomes established by the hematogeneic seeding of stem cells to a mesenchymal matrix during embryogenesis. The repopulation of the bone marrow after partial body irradiation, after strongly inhomogeneous radiation exposure or after total body exposure with stem cell transplantation can well be considered as a repetition of the embryogenesis of bone marrow hemopoiesis with the key element of stem cells migrating via the blood to stromal sites of the marrow prepared to accept stem cells to home and start their replication and differentiation if the micro-environmental quality permits. In summary, the radiation biology of bone marrow hemopoiesis requires a thorough understanding of the physiology and pathophysiology of structure, function and regulation not only of the process of cellular renewal but also of the intricate infrastructure.

Apoptosis and parasitism: from the parasite to the host immune response

Apoptosis, a form of programmed cell death (PCD), plays a central role in normal tissue development as well as in the pathogenesis of different diseases. PCD is responsible for the non-inflammatory physiological elimination of potentially harmful or unnecessary cells during embryogenesis, and for the proper functioning of continuous cell renewal systems in adult organisms. Maturation of the immune system and the specific immune response are examples of situations where PCD plays important roles. This review discusses the importance of apoptosis in two fundamental elements of a host-parasite interaction: the parasite (Section 1), and the host's immune response (Section 2). Section 1 discusses questions raised by the description of apoptosis in unicellular eukaryotes, such as the evolutionary origin of the molecular components of PCD, its role in the emergence and maintenance of parasitism, and the constraints of a multicellular organization for the proper operation of a cell death programme. The proposal is that PCD can occur in any situation where living cells display features of an organized network which operates through interactions within themselves and/or with elements of their environment. The possibility is also discussed that evolutionary relics of a complete cell death system may operate in unicellular parasites with functions other than inducing cell death. Section 2 reviews data on the mechanisms of host-cell PCD and the consequences of this phenomenon in host defence and pathogenesis. Infectious agents, from viruses to parasites, can either delay or induce apoptosis of different types of host cells. Apoptosis following lymphocyte polyclonal activation and stimulation of peripheral T lymphocytes, as a result of the engagement of specific counter-receptor systems, is of special interest for defining host immunocompetence and mechanisms of immunopathology.

Treatment of a radiation-induced sigmoid stricture with an expandable metal stent

Rectosigmoid strictures are a late complication following radiation therapy for cancers of the cervix, prostate, testes, urinary bladder, and uterus. Radiation therapy uses high-energy x-rays that ionize tissues and disrupt the epithelial cell renewal system, thereby leading to acute mucosal damage.1,2 Over years, the submucosa becomes injured as endarteritis obliterans progresses from inflammation to ischemia and eventually fibrosis.1 As a result, stricturing may occur, resulting in obstruction decades after the initial radiation treatment.

Apoptosis in parasites and parasite-induced apoptosis in the host immune system: a new approach to parasitic diseases.

Apoptosis, a form of programmed cell death (PCD), has been described as essential for normal organogenesis and tissue development, as well as for the proper function of cell-renewal systems in adult organisms. Apoptosis is also pivotal in the pathogenesis of several different diseases. In this paper we discuss, from two different points of view, the role of apoptosis in parasitic diseases. The description of apoptotic death in three different species of heteroxenic trypanosomatids is reviewed, and considerations on the phylogenesis of apoptosis and on the eventual role of PCD on their mechanism of pathogenesis are made. From a different perspective, an increasing body of evidence is making clear that regulation of host cell apoptosis is an important factor on the definition of a host-pathogen interaction. As an example, the molecular mechanisms by which Trypanosoma cruzi is able to induce apoptosis in immunocompetent cells, in a murine model of Chagas' disease, and the consequences of this phenomenon on the outcome of the experimental disease are discussed.

Folliculo-stellate cells and intercellular communication within the rat anterior pituitary gland.

Folliculo-stellate (FS) cell are agranular and arranged around a follicle. They contain the S-100 protein and beta-adrenergic receptors. It has been suggested that they can act as stem cells, since they show mitotic figures, and could transform into granular or chromophilic cells according to the concept of a "cell renewal system." Cell-to-cell interactions among pituitary cells have been described, and recent progress with freeze-fracture electron microscopy has provided novel observations of the cell surface and gap junctions within the rat or teleost fish pituitary gland, or in cultured rat pituitary cells. In adult rats, the anterior pituitary was composed of lobules incompletely separated by a basement membrane. Follicles consisted exclusively of FS cells. Gap junctions were observed only between adjacent FS cells, in rare cases on the tips of their cytoplasmic processes. Thus, the FS cells, connected by gap junctions, made up a dense cellular network throughout the pituitary. Gap and tight junctions were absent on granular cells. Elongated follicles with columnar FS cells were observed in 10-day-old rats and were separated into smaller units. The number of gap junctions rapidly increased with age until 40-45 days of age. Few S-100 protein positive cells were observed on day 10, along the marginal cell layer and near the so-called postero-lateral wing. The frequency of positive cells increased with age and by day 40; numerous cells were observed throughout the anterior lobe. Gap junction number also varied with the stage of the estrous cycle, and frequency; during diestrus, they were half of that during proestrus or estrus. The number of gap junctions increased in late pregnancy and in lactating rats, probably due to changes in estrogen and progesterone. Hormone (LH-RH and testosterone) treated groups of rats showed accelerated development by almost 10 days, compared with controls. In castrated male rats, the ultrastructure of the pituitary remained immature even at 40 days of age, when the number of gap junctions was a quarter or less than the number in intact rats. Testosterone treatment restored the frequency of gap junctions to a normal level. We conclude that the appearance of gap junctions in the pituitary cells and maturation of the gland are dependent to a large degree upon gonadal steroids.

Apoptosis and cell proliferation in the Xenopus small intestine during metamorphosis

In the amphibian small intestine, the epithelial transformation from the larval to adult type is mainly the result of degeneration of the larval epithelium and development of the new (adult) epithelium. In this analysis at the cellular level, we chronologically examined apoptosis and cell proliferation in the Xenopus intestine by using in situ nick end-labeling of genomic DNA (TUNEL) and bromodeoxyuridine (BrdU) immunohistochemistry. During pre- and prometamorphosis, few apoptotic cells were detected by TUNEL, and a small number of proliferating cells randomly distributed in the larval epithelium were labeled by BrdU. At the beginning of the metamorphic climax, when primordia of the adult epithelium were first detected, numbers of apoptotic cells suddenly increased in the larval epithelium, whereas numbers of proliferating cells increased only in the adult epithelium. Subsequently, a dramatic cell loss of the larval epithelium and a rapid growth of the adult epithelium occurred. Following complete epithelial replacement, the adult epithelium became differentiated into a simple columnar epithelium possessing a cell renewal system similar to that of mammalian intestinal epithelium. These results indicate that larval epithelial apoptosis progresses simultaneously with active proliferation of the adult epithelium during the early period of metamorphic climax, which coincides with the modification of the basement membrane lining both types of epithelia.

Interval analysis as a tool for sensitivity analysis of a hemopoietic model

In this article a method for sensitivity analysis of dynamic models based on interval analysis is introduced and illustrated for a simple model of a cell renewal system. This system is an important subsystem in the hemopoietic system, which is one of the most important cell renewal systems in the human body. The basic tool used is interval analysis, which is briefly introduced in this article. Simulation results showing the successful application of the method conclude the paper.

Radioresistance in Murine Solid Tumors Induced by Interleukin-1

Interleukin-1 (IL-1) has radioprotective activity in hematopoietic lineages and in other normal cell renewal systems, but little is known about the effects of IL-1 alpha on the radiosensitivity of tumor cell populations. The present studies were conducted to investigate the effects of IL-1 alpha on the radiosensitivity of clonogenic cells in RIF-1 and SCC-7 tumors. Radioresistance was detected within 2-4 after administration of IL-1 alpha (0.5 micrograms/mouse, ip) and characterized by increases in D(o), Dq, alpha/beta and SF2. This radioresistance was similar to that seen in tumors rendered totally hypoxic before X irradiation. Tirapazamine, a hypoxic cell cytotoxin, and IL-1 alpha had synergistic schedule-dependent antitumor activity in vivo, suggesting that IL-1-induced radioresistance in vivo is due to hypoxia. Radioresistance induced by IL-1 alpha was transient, and the data suggested reoxygenation within 12 h. In vitro, IL-1 alpha had no direct effect on the radiosensitivity of SCC-7 cells in tissue culture under aerobic conditions. However, an increase in D(o), alpha/beta and SF2 was seen in clonogenic tumor cells from primary cultures treated with IL-1 alpha under aerobic conditions. Superoxide dismutase and catalase prevented the induction of radioresistance by IL-1 alpha in vitro, suggesting that oxidative responses from tumor macrophages after administration of IL-1 alpha may be responsible for induced radioresistance by IL-1 in vitro. Although oxidant stress induced by IL-1 and in vitro in our models, the mechanisms by which such responses modulate tumor radiosensitivity in vivo and in vitro are likely quite different.

A biomathematical model of granulocytopoiesis for estimation of stem cell numbers.

In this paper a dynamic model of granulocytopoiesis is used to estimate stem cell numbers after acute and chronic irradiation. Regeneration data from irradiation accidents and bone marrow transplantation are investigated in the case of acute irradiation. Data from dogs living in a low-dose irradiation field are investigated for the case of chronic irradiation. The effects of acute irradiation and bone marrow transplantation are interpreted as a change of the initial conditions of the model, while the effect of chronic irradiation is interpreted as a continuous cell loss in the proliferating cell compartments of the model. The unknown initial conditions of the model are computed on the basis of real patient and dog data with the help of a suitably constructed optimization problem. The numerical solution of this optimization problem will only be sketched in this paper. In all cases discussed in this paper, a very good agreement between the model and the real data is achieved.

Modeling of radiogenic responses induced by fractionated irradiation in malignant and normal tissue.

The aim of this contribution is to outline how methods of system analysis, control theory and computer science can be applied to simulate malignant and normal cell growth and to optimize cancer treatment. Based on biological observations and cell kinetic data, our group has constructed three types of computer models: 1) A cell cycle model describing the spatial (3D) and temporal growth of tumor spheroids; 2) A compartment model describing the growth of rapidly proliferating normal cells; 3) A compartment model simulating slowly proliferating normal tissues. These growth models have been extended by an irradiation model based on the linear-quadratic survival function. Different clinical fractionation schemes (standard-, super-, hyperfractionation and weekly high single dose) have been applied to the tissues mentioned above. The simulation results show that in the case of irradiating a rapidly growing tumor spheroid the hyperfractionation (3 x 1-1.5 Gy per day) leads to a particularly good anti-tumor effectiveness. On the other hand, the radiogenic response of rapidly growing normal tissue to a hyperfractionated treatment schedule is severe. The same result is observed when simulating the late reaction on slowly growing parenchymal tissue. Therefore, this therapeutic modality is ensured only if the overall dose is reduced from DTOTAL = 60 Gy to DTOTAL = 50 Gy.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiological and pathophysiological aspects of the immune system contributing to a biomathematical model of lymphocytes.

The effects of chronic low-dose irradiation on the immune system and the lymphocytes are largely unknown. The uranium miners in the former German Democratic Republic (GDR) were exposed mainly to a local low-dose irradiation in the lung by radon and its progeny, but also to some whole-body gamma irradiation. The local irradiation led to an increased rate of lung cancer and perhaps to some increase in extrapulmonary neoplasms. But little is known about the effects on the lymphocytes circulating and recirculating to the lung. As a prerequisite for the establishment of a biomathematical model to estimate lymphocyte fluxes, and to assess the radiation effects on the lymphocytic (and stem cell) populations passing through the lung, it was necessary to establish the current knowledge with respect to the physiology and pathophysiology of the lymphocytic cell renewal systems. The data concerning lymphopoiesis and lymphocyte kinetics, which are important for the development of this model, are summarized. The distribution of lymphocytes between different compartments including the lung is taken into consideration, as well as the effects of acute and chronic irradiation on the immune system. The extracorporeal irradiation of the blood (ECIB) may serve as a model of irradiation of blood in the lung. This review shows that many data necessary for development of a detailed biomathematical model are still missing, especially data concerning details on lymphocyte production rates of their different subsets and regulatory mechanisms of the lymphocytic system.

Response of hemopoiesis in dogs to continuous low dose rate total body irradiation.

Among the cytotoxic agents which particularly cause damage to cell renewal systems, ionizing radiation is one of the most effective ones since it leads to inactivation of all types of proliferating cells including resting stem cells. It is the aim of this paper to present the effects of continuous low dose rate total body irradiation (TBI) on hemopoiesis in dogs. The animals were exposed to gamma-rays from a 60-Co source, receiving a daily radiation dose of 0.0188 Gy for indefinite times. Sequential hematological studies performed included determinations of peripheral blood cell counts and of total cell numbers in standardized bone marrow samples, assessments of progenitor cells GM-CFC in the blood and bone marrow, and of colony-stimulating activity (CSA) in the serum. The lymphocytes, the thrombocytes and neutrophilic granulocytes uniformly showed early decreases within the first 200 to 500 days corresponding to cumulative radiation doses in the range up to 3.8 to 9 Gy, but remained stable at subnormal levels in the period up to 1,700 days of exposure. The GM-CFC numbers in bone marrow samples from the rib clearly showed a strong decrease within the first 150 days of exposure preceding the changes in the blood granulocyte concentration. A transient partial recovery of the GM-CFC was observed at later times between 700 and 1,200 days of exposure, followed by another decrease to extremely low values at cumulative doses in the range of 32 Gy.(ABSTRACT TRUNCATED AT 250 WORDS)

Misoprostol-Induced Radioprotection of Syrian Hamster Embryo Cells In Utero from Cell Death and Oncogenic Transformation

Misoprostol, a PGE1 analog, is an effective radioprotector of murine intestine and hematopoietic and hair cell renewal systems. The radioprotective nature of misoprostol was extended to examine its ability to influence clonogenic cell survival and induction of oncogenic transformation in Syrian hamster embryo cells exposed to X rays in utero and assayed in vitro. Hamsters in their 12th day of pregnancy were injected subcutaneously with misoprostol, and 2 h later the pregnant hamsters were exposed to graded doses of X rays. Immediately after irradiation, hamsters were euthanized and embryonic tissue was explanted into culture dishes containing complete growth medium. After a 2-week incubation period, clonogenic cell survival and morphologically transformed foci were determined. Survival of misoprostol-treated SHE cells was increased and yielded a dose reduction factor of 1.5 compared to SHE cells treated with X rays alone. In contrast, radiation-induced oncogenic transformation of misoprostol-treated cells was reduced by a factor of 20 compared to cells treated with X rays alone. These studies suggest that misoprostol not only protects normal tissues in vivo from acute radiation injury, but also protects cells, to a large extent, from injury leading to transforming events.

Speculations on the roles of RB1 in tissue‐specific differentiation, tumor initiation, and tumor progression

Studies of retinoblastoma clearly identify mutation of the RB1 gene on chromosome 13 as the primary cause of this cancer. However, all retinoblastoma tumors have an abnormal karyotype (1, 2) indicating the presence of additional mutations and suggesting that mutation of both RB1 alleles is insufficient for development of retinoblastoma. In addition, analysis of RB1 expression and of RB1 mutations in different tumors leads to the following dilemma: while the RB1 gene product, p110RB1, is expressed in most dividing cells, germline mutations inactivating the function of p110RB1 predispose primarily to retinoblastoma and to a lesser extent to osteosarcoma, but do not predispose to cancer in general. However, many tumors contain somatic mutations that disrupt RB1 function. Thus, we are faced with the unusual situation in which germline mutations in the RB1 gene predispose to a very limited set of cancers, but somatic mutations in RB1 appear to contribute to malignancy in many tissues. We propose that the role of the RB1 gene is to maintain the cells in a stable, quiescent state required for terminal differentiation and that the effect of RB1 mutations in different tissues depends on the pattern of differentiation in that tissue. In tissues where differentiation follows a linear process from undifferentiated precursors to fully differentiated cells, loss of RB1 function during early stages of differentiation may lead to uncontrolled growth and the development of cancer. On the other hand, in cell renewal systems where cell number is usually maintained by a process of programmed cell death (PCD) or apoptosis, loss of RB1 function may lead to cell death.

A Clinical Decision Support System for the Treatment of Irradiated Persons Based on Mathematical Model of Granulocytopoiesis

In this paper a decision support system to assist the medical doctor in the treatment of irradiated persons is presented. The nucleus of this system is a biomathematical model of granulocytopoiesis. This special cell renewal system contains fundamental biological information and, consequently, serves as one of the most important biomedical indicators to judge the severeness of irradiation cases. Two representative example cases conclude the paper.

Streaming kidney

Twenty-five male young adult random bred rats, weighing 250-300 g, were injected with 18.5 kBq/g body weight tritiated thymidine (specific activity 185 GBq/mM). The rats were then killed in groups of five, at the following times: 1 h and 14, 30, 60 and 120 days. The kidneys were processed histologically and dipped into liquid emulsion, exposed for 3 weeks and developed. Kinetic measurements were restricted to juxta-medullary glomeruli, their adjacent convoluted tubules and medullary tubuli. All other nephrons were ignored. The medullary pole of the juxta-medullary glomerulus served as reference point for all measurements and was referred to as the origin. The distance of a labelled cell from the origin was measured with an eye-piece micrometer and expressed in terms of two units: distance (microns) and cell location, defined as the number of cells separating a labelled cell from origin. Since only medullary nephrons were considered, these measurements represent distances directed toward the papilla. One hour after labelling, most cells were in the vicinity of the juxta-medullary glomerulus, not further than 800 microns from the origin in the direction of the papilla. During the following days labelled cells advanced toward the papilla at a daily velocity of 13.8 microns, covering 1.1 locations/day. Kinetically, the juxta-medullary nephron is a two-compartment cell renewal system. Its compartments, the progenitor (P) and the functional (Q), cover locations 0-80 and 81-150, respectively. The first feeds the second with cells. Morphologically, the progenitor compartment includes proximal and distal convoluted epithelia and a part of thick straight tubules. Other nephron portions belong to the Q-compartment. It is assumed that the nephrocyte is a part of a cell stream directed toward the papilla, which probably also includes stroma and vasculature.

Modulation of bone marrow cell functions in vitro by Bestatin (ubenimex)

Bestatin (ubenimex), the microbial leucil-aminopeptidase B inhibitor, has been shown previously to stimulate both interleukin-1 (IL-1) and IL-2 production and to enhance T-cell, as well as macrophage mediated immunoreaction when administered in vivo in mice [10, 15, 23]. Here we show that although Bestatin has no direct growth stimulatory activity, it enhances the growth of GM-CFU populations in semisolide culture and stimulates the cell production in liquide organotypic Hematon cultures in synergy with recombinant human GM-CSF. In long term human bone marrow culture Bestatin accelerated the adipocytic differentiation among colony forming stroma cells (F-CFU). Our data provide further evidences that Bestatin may interact with the hemopoietic cell renewal system at different levels of biological organisation. Bestatin/bone marrow/cell culture

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There are two problems in the application of Auger electrons derived from 125IUdR for cancer treatment. One is cell cycle dependency (effective only for S phase cells), the other is side effects for the cell renewal systems(e. g. bone marrow, intestine). We tried intratumoral injection of 125IUdR oil suspension using Ehrlich ascites tumors in the thighs of mice. Oil suspension was more effective in tumor growth delay than saline solution. Single injection of oil suspension at the dose of 0.46 MBq resulted in 21.5 days growth delay while 1.85 MBq of saline solution resulted in 11.5 days growth delay relative to control growth delay. At 40 days after treatment, higher radioactivities were observed in the tumor and the skin of the mice treated with oil suspension, which represented prolongation of 125IUdR oil suspension within the tumors. No normal tissue toxicities were observed. This method can be a new treatment for brain tumors and radioresistant head and neck tumors by further improvements of drug delivery systems

Heterochrony of tooth root initiation in rabbits

AbstractOne of the considerable evolutionary modifications to the dentition of rabbits and other lagomorphs has been the transition from teeth of finite growth, characterized by the presence of brachydontic roots in ancestral species, to teeth in which their generative parts operate as cell renewal systems to maintain a continuous growth of teeth in contemporary species. In contemporary lagomorphs evidence for the existence of vestigial roots in the “rootless”, continuously growing permanent cheek teeth has not been described. It was the purpose of this study to examine developing molariform teeth for evidence of such structures. The basis for the examination was serial histological sections of maxillae and mandibles of contemporary rabbits (Oryctolagus cuniculus L.) harvested from foetuses and postnatals aged from the 15th day postconception to birth and from birth to the 90th postnatal day respectively. The fossil teeth of the Miocene lagomorphs from the genus Amphilagus and Titanomys were used for direct comparisons together with evidence from the literature. It was found that of the 3 root openings which appeared during the early development of permanent molariform teeth, the two lateral ones were homologous with the 2 lateral brachydontic roots present in adult molariform teeth of ancestral lagomorphs. The time required for initiation of the root openings, counted from the day of appearance of the cap stage, was found to be 6 days for deciduous teeth and 3 to 4 days for permanent ones. Four stages in the ontogenesis and evolution of the odontogenic cell renewal system of lagomorphs have been described.

The differentiation-promoting potential of a cytostatic fluoro-pyranosyl adriamycin analog (FAD 104)

Acute toxicity to the hematopoietic cell renewal system is a critical side effect of most anticancer agents. Here we compared the effects of FAD-104 to those of the parent compound adriamycin (ADM) and of epi-adriamycin (epi-ADM) on the growth and differentiation of normal as well as leukemic human myeloid progenitor cells. FAD-104 was less toxic to myeloid colony-forming cells (GM-CFU) than ADM or epi-ADM. In addition, FAD-104 but not ADM induced a clonal down-grading in both normal and leukemic blast cells, and it stimulated the terminal differentiation of myeloid leukemia cells. Therefore, FAD-104 may be useful in the treatment of some forms of myeloid leukemia.