Cell loss and the concept of potential doubling time

Characterization of the Safety Profile of Sweet Chestnut Wood Distillate Employed in Agriculture

In organic agriculture, synthetic pesticides and treatments are substituted by natural remedies with interesting success for product yield and environmental outcomes, but the safety of these bio-based products needs to be assessed in vertebrate and human models. Therefore, in this paper we assessed the safety profile of sweet chestnut (Castanea sativa) wood distillate (WD) on the different cellular components of tissues implied in transcutaneous absorption. We investigated the viability of different cell lines mimicking the skin (HaCaT keratinocytes), mucosa (A431), connective (normal human dermal fibroblasts, NHDF) and vascular (human umbilical vein endothelial cells, HUVEC) tissues after exposure to increasing concentrations (0.04–0.5%, v/v, corresponding to 1:2800–1:200 dilutions) of WD. A short exposure to increasing doses of WD was well tolerated up to the highest concentration. Instead, following a prolonged treatment, a concentration dependent cytotoxic effect was observed. Notably, a different behavior was found with the various cell lines, with higher sensitivity to cytotoxicity by the cells with higher proliferation rate and reduced doubling time (human keratinocytes). Moreover, to exclude an inflammatory effect at the not cytotoxic WD concentrations, the expression of the main inducible markers of inflammation, cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase-1 (mPGES-1), were assessed, and no improvement was found both after brief and prolonged exposure. In conclusion, our data exclude any inflammatory and cytotoxic effect at the lowest WD concentrations, namely 0.07% and 0.04%, mimicking some recommended dilutions of the product and the potential exposure doses for the operators in agriculture. Nevertheless, higher concentrations showed a safe profile for short time usage, but caution should be used by farmers following persistent product exposure.

The Physico-Chemical Properties and Exploratory Real-Time Cell Analysis of Hydroxyapatite Nanopowders Substituted with Ce, Mg, Sr, and Zn (0.5-5 at.%)

Cation-substituted hydroxyapatite (HA), standalone or as a composite (blended with polymers or metals), is currently regarded as a noteworthy candidate material for bone repair/regeneration either in the form of powders, porous scaffolds or coatings for endo-osseous dental and orthopaedic implants. As a response to the numerous contradictions reported in literature, this work presents, in one study, the physico-chemical properties and the cytocompatibility response of single cation-doped (Ce, Mg, Sr or Zn) HA nanopowders in a wide concentration range (0.5–5 at.%). The modification of composition, morphology, and structure was multiparametrically monitored via energy dispersive X-ray, X-ray photoelectron, Fourier-transform infrared and micro-Raman spectroscopy methods, as well as by transmission electron microscopy and X-ray diffraction. From a compositional point of view, Ce and Sr were well-incorporated in HA, while slight and pronounced deviations were observed for Mg and Zn, respectively. The change of the lattice parameters, crystallite size, and substituting cation occupation factors either in the Ca(I) or Ca(II) sites were further determined. Sr produced the most important HA structural changes. The in vitro biological performance was evaluated by the (i) determination of leached therapeutic cations (by inductively coupled plasma mass spectrometry) and (ii) assessment of cell behaviour by both conventional assays (e.g., proliferation—3-(4,5-dimethyl thiazol-2-yl) 5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium assay; cytotoxicity—lactate dehydrogenase release assay) and, for the first time, real-time cell analysis (RTCA). Three cell lines were employed: fibroblast, osteoblast, and endothelial. When monophasic, the substituted HA supported the cells’ viability and proliferation without signs of toxicity. The RTCA results indicate the excellent adherence of cells. The study strived to offer a perspective on the behaviour of Ce-, Mg-, Sr-, or Zn-substituted HAs and to deliver a well-encompassing viewpoint on their effects. This can be highly important for the future development of such bioceramics, paving the road toward the identification of candidates with highly promising therapeutic effects.

Cancer recurrence times from a branching process model

As cancer advances, cells often spread from the primary tumor to other parts of the body and form metastases. This is the main cause of cancer related mortality. Here we investigate a conceptually simple model of metastasis formation where metastatic lesions are initiated at a rate which depends on the size of the primary tumor. The evolution of each metastasis is described as an independent branching process. We assume that the primary tumor is resected at a given size and study the earliest time at which any metastasis reaches a minimal detectable size. The parameters of our model are estimated independently for breast, colorectal, headneck, lung and prostate cancers. We use these estimates to compare predictions from our model with values reported in clinical literature. For some cancer types, we find a remarkably wide range of resection sizes such that metastases are very likely to be present, but none of them are detectable. Our model predicts that only very early resections can prevent recurrence, and that small delays in the time of surgery can significantly increase the recurrence probability.

The majority of cancer related deaths are due to the development of secondary tumors called metastases. However, the dynamics of metastases establishment and growth and their relation with the primary tumor evolution are still not clear. A standard treatment starts with the resection of the primary tumor. At this time metastases may have already formed and still be too small to be detected. The presence of only undetectable metastases poses a challenge for deciding on the follow-up therapy. These small metastases could grow to a detectable size—thus leading to a recurrence of the disease—some time after surgery. We are interested in this time until cancer relapse. We present a mathematical model of metastases formation using tools from probability theory and estimate the model parameters for five different cancer types. Our predictions for the probability of visible metastases present at surgery and the mean time to relapse when no visible metastases are found at surgery are both in agreement with clinical data.

Flow cytometry after bromodeoxyuridine labeling to measure S and G2+M phase durations plus doubling times in vitro and in vivo

This protocol describes methods for calculating the proliferative parameters of cell populations. The basis of the technique is to label cells, either in vitro or in vivo, with halogenated thymidine analogs, such as bromodeoxyuridine (BrdU). Bivariate DNA-BrdU flow cytometry is used to analyze the BrdU-labeled and unlabeled cells. The enumeration of specific cohorts of cells that either have or have not divided in the interval between labeling and cell/tissue sampling permits the calculation of the potential doubling time (T(pot)) of the population, plus the durations of DNA synthesis (T(S)) and the G2+M phase (T(G2+M)) of the cell cycle. The method provides information that is not otherwise available, namely inhibition of DNA synthesis and the separate evaluation of cell-cycle effects in BrdU-labeled and unlabeled subpopulations. Ethanol-fixed samples take 1 d to prepare and stain, and reliable parameter estimates might be obtained from measurements made at a single time point after labeling.

Medicolegal liability in surgical pathology: a consideration of underlying causes and selected pertinent concepts

Malpractice actions against surgical pathologists are still relatively uncommon, but they have increased in frequency over time and are associated with sizable indemnity figures. This discussion categorizes areas of liability in surgical pathology into three groups: those that represent health system flaws (problems with specimen identification, or transportation, or both; lack of clinical information or erroneous information; sampling effects and defects; and poorly reproducible or poorly defined diagnostic or prognostic criteria), others that exist at the interface between the system and individuals (allowing clinicians to bypass pathologic review of referred specimens; acceding to clinical demands for inadvisable procedures; and working in a disruptive environment), and truly individual errors by pathologists (lapses in reasoning; deficiencies concerning continuity in the laboratory; invalid assumptions regarding recipients of surgical pathology reports; over-reliance on the results of "special" tests; and problems with peer consultation). Finally, two important topic areas are discussed that commonly enter into lawsuits filed against surgical pathologists; namely, "delay in diagnosis" of malignant neoplasms and "failure to provide adequate prognostic information." Based on a review of the pertinent literature, we conclude that the clinical courses of most common malignancies are not affected in a significant manner by delays in diagnosis. Moreover, the practice of using "personalized external validity" for supposedly prognostic tests is examined, with the resulting opinion that prognostication of tumor behavior in individual patients is not reliable using anything but anatomic staging systems.

Modelling the balance between quiescence and cell death in normal and tumour cell populations

When considering either human adult tissues (in vivo) or cell cultures (in vitro), cell number is regulated by the relationship between quiescent cells, proliferating cells, cell death and other controls of cell cycle duration. By formulating a mathematical description we see that even small alterations of this relationship may cause a non-growing population to start growing with doubling times characteristic of human tumours. Our model consists of two age structured partial differential equations for the proliferating and quiescent cell compartments. Model parameters are death rates from and transition rates between these compartments. The partial differential equations can be solved for the steady-age distributions, giving the distribution of the cells through the cell cycle, dependent on specific model parameter values. Appropriate formulas can then be derived for various population characteristic quantities such as labelling index, proliferation fraction, doubling time and potential doubling time of the cell population. Such characteristic quantities can be estimated experimentally, although with decreasing precision from in vitro, to in vivo experimental systems and to the clinic. The model can be used to investigate the effects of a single alteration of either quiescence or cell death control on the growth of the whole population and the non-trivial dependence of the doubling time and other observable quantities on particular underlying cell cycle scenarios of death and quiescence. The model indicates that tumour evolution in vivo is a sequence of steady-states, each characterised by particular death and quiescence rate functions. We suggest that a key passage of carcinogenesis is a loss of the communication between quiescence, death and cell cycle machineries, causing a defect in their precise, cell cycle dependent relationship.

Estimating cell death in G2M using bivariate BrdUrd/DNA flow cytometry

BACKGROUND

In an accompanying paper (Asmuth et al.) it was found necessary to include cell death explicitly to estimate parameters of cell proliferation. The use of bivariate flow cytometry to estimate the phase durations and the doubling times of cells labeled with thymidine analogues is well established. However, these methods of analysis do not consider the possibility of cell death. This report demonstrates that estimating cell death in G(2)/M is possible.

METHODS

Mathematical models for the experimental quantities, the fraction of labeled undivided cells, the fraction of labeled divided cells, and the relative movement were developed. These models include the possibility that, of the cells with G(2)/M DNA content, only a certain fraction will divide, with the remainder dying after some time T(R). Simulation studies were conducted to test the possibility of using simple methods to estimate phase durations and cell death rates.

RESULTS

Cell death alters the estimates of phase transit times in a rather complex manner that depends on the lifetime of the doomed cells. However, it is still possible to obtain estimates of the phase durations of cells in S and G(2)/M and the death rates of cells in G(2)/M.

CONCLUSIONS

The methods presented herein provide a new way to characterize cell populations that includes cell death rates and common measurements of cell proliferation.

Cell proliferation and cell cycle control: a mini review

Tumourigenesis is the result of cell cycle disorganisation, leading to an uncontrolled cellular proliferation. Specific cellular processes-mechanisms that control cell cycle progression and checkpoint traversation through the intermitotic phases are deregulated. Normally, these events are highly conserved due to the existence of conservatory mechanisms and molecules such as cell cycle genes and their products: cyclins, cyclin dependent kinases (Cdks), Cdk inhibitors (CKI) and extra cellular factors (i.e. growth factors). Revolutionary techniques using laser cytometry and commercial software are available to quantify and evaluate cell cycle processes and cellular growth. S-phase fraction measurements, including ploidy values, using histograms and estimation of indices such as the mitotic index and tumour-doubling time indices, provide adequate information to the clinician to evaluate tumour aggressiveness, prognosis and the strategies for radiotherapy and chemotherapy in experimental researches.

Changes in cell cycle parameters and cell number in the rat midbrain during organogenesis

We employed 5-bromo-2'-deoxyuridine (BrdU) labeling to identify in vivo changes in the cell cycle patterns of the rat midbrain during the major period of midbrain organogenesis, gestational days (gd) 11 to 16. We also used quantitative stereology to determine changes in absolute cell numbers during these gestational time points. Between gd 12 and 16, the length of S-phase did not change significantly while the fraction of cycling cells decreased from 73 to 11%. The average cell cycle length was determined to be 15 h on gd 12 and 17 h on gd 16, the difference not being statistically significant. The cell number in the midbrain increased from 1.3E5 cells on gd 11 to 1.7E7 cells on gd 16. On gd 12 and gd 13, there was a significant negative correlation between litter position and midbrain cell number, the effect diminishing on later days of gestation. The combined use of quantitative stereology and flow cytometry to study brain development represents a novel application that allows for simultaneous evaluation of changes in cell proliferation kinetics and the resulting effect of those kinetic changes on embryonic midbrain development.

Desynchronization rate in cell populations: mathematical modeling and experimental data

We characterize the kinetics of two cancer cell lines: IGROV1 (ovarian carcinoma) and MOLT4 (leukemia). By means of flow cytometry, we selected two populations from exponentially growing in vitro cell lines, depending on the cells' DNA synthesis activity during a preceding labeling period. For these populations we determined the time course of the percentages of cells in different phases of the cycles, sampling every 3 hr for 60 hr. Initially, semi-synchronous populations quickly converged to a stable age distribution, which is typical of the cell line (at equilibrium); this desynchronization reflects the intercell variability in cell cycle duration. By matching these experimental observations to mathematical modelling, we related the convergence rate toward the asymptotic distribution (R) and the period of the phase-percentage oscillations (T), to the mean cell cycle duration and its coefficient of variation. We give two formulas involving the above-mentioned parameters. Since T and R can be drawn by fitting our data to an asymptotic formula obtained from the model, we can estimate the other two kinetic parameters. IGROV1 cells have a shorter mean cell cycle time, but higher intercell variability than the leukemia line, which takes longer to lose synchrony.