Human Pluripotent Stem Cells to Assess Developmental Toxicity in the Osteogenic Lineage

Human Pluripotent Stem Cell-Based Assays to Predict Developmental Toxicity

Human beings are continuously exposed to various toxic substances throughout their lives, which affect their reproductive health and eventually the offspring they give birth to. Mainly, these toxins damage the heart and neurological development of the newborn, but most recently, they have begun to affect the musculoskeletal system as well. These toxins are usually present in food, pharmaceuticals, cosmetics, or even the polluted air that people breathe; as a result, the prevalence of birth defects is steadily rising. For this reason, it becomes a necessity to deploy a new set of assays to test for such toxins in industries to decrease the occurrence of developmental toxicity. These assays are exceedingly expensive when carried out conventionally using animal models or cells from such sources and have a lower predictive value due to the vast variation between animals and humans. To overcome such major problems, human pluripotent stem cells are now frequently used for these assays. These cells are easily available, are quickly generated from somatic cells (induce pluripotent stem cells), can be of human origin without harming people, and eliminate animal harm, which makes them the top choice of scientists for carrying out any in vitro developmental toxicity assays.This chapter, therefore, provides an overview of several steps that can be used to predict a compound's developmental toxicity by utilizing human pluripotent stem cells. Here, the easiest and most effective procedure has been outlined that can screen many compounds simultaneously.

Sidestream Smoke Extracts from Harm-Reduction and Conventional Camel Cigarettes Inhibit Osteogenic Differentiation via Oxidative Stress and Differential Activation of intrinsic Apoptotic Pathways

Epidemiological studies suggest cigarette smoking as a probable environmental factor for a variety of congenital anomalies, including low bone mass, increased fracture risk and poor skeletal health. Human and animal in vitro models have confirmed hypomineralization of differentiating cell lines with sidestream smoke being more harmful to developing cells than mainstream smoke. Furthermore, first reports are emerging to suggest a differential impact of conventional versus harm-reduction tobacco products on bone tissue as it develops in the embryo or in vitro. To gather first insight into the molecular mechanism of such differences, we assessed the effect of sidestream smoke solutions from Camel (conventional) and Camel Blue (harm-reduction) cigarettes using a human embryonic stem cell osteogenic differentiation model. Sidestream smoke from the conventional Camel cigarettes concentration-dependently inhibited in vitro calcification triggered by high levels of mitochondrially generated oxidative stress, loss of mitochondrial membrane potential, and reduced ATP production. Camel sidestream smoke also induced DNA damage and caspase 9-dependent apoptosis. Camel Blue-exposed cells, in contrast, invoked only intermediate levels of reactive oxygen species insufficient to activate caspase 3/7. Despite the absence of apoptotic gene activation, damage to the mitochondrial phenotype was still noted concomitant with activation of an anti-inflammatory gene signature and inhibited mineralization. Collectively, the presented findings in differentiating pluripotent stem cells imply that embryos may exhibit low bone mineral density if exposed to environmental smoke during development.

Exposure to Cigarette Smoke Impedes Human Osteoblast Differentiation Independently of Nicotine

INTRODUCTION

Tobacco smoking has been implicated in an array of adverse health outcomes, including those that affect adult bone. However, little is known about the impact of tobacco products on developing bone tissue as it develops in the embryo.

AIMS AND METHODS

Here, human embryonic stem cells were differentiated into osteoblasts in vitro and concomitantly exposed to various concentrations of smoke solutions from two conventional, one additive-free and two harm-reduction brands of cigarettes. Differentiation inhibition was determined by calcium assays that quantified matrix mineralization and compared to the cytotoxicity of the tobacco product.

RESULTS

Exposure to mainstream smoke from conventional and additive-free cigarettes caused no inhibition of cell viability or mineralization, while sidestream smoke (SS) concentration-dependently produced cell death. In contrast, mineralization was inhibited only by the highest mainstream concentration of harm-reduction smoke solution. Additionally, sidestream smoke solution from the harm-reduction cigarettes impeded calcification at concentrations lower than those determined to be cytotoxic for conventional products.

CONCLUSIONS

Sidestream smoke impaired in vitro osteogenesis at subtoxic concentrations. In addition, though often perceived as safer, smoke from harm-reduction cigarettes was more potent in inhibiting in vitro osteogenesis than smoke from conventional cigarettes.

IMPLICATIONS

This study adds to a growing list of adverse outcomes associated with pre-natal tobacco exposure. Specifically, in vitro exposure to tobacco products interfered with osteogenic differentiation of human embryonic stem cells, a well-established surrogate model for human embryonic bone development. Contrasting a diverse array of tobacco products unveiled that sidestream smoke was generally more developmentally osteotoxic than mainstream smoke and that harm-reduction products may not be less harmful than conventional products, adverse effects that were seemingly independent of nicotine.

Pluripotent stem cell assays: Modalities and applications for predictive developmental toxicity

This manuscript provides a review focused on embryonic stem cell-based models and their place within the landscape of alternative developmental toxicity assays. Against the background of the principles of developmental toxicology, the wide diversity of alternative methods using pluripotent stem cells developed in this area over the past half century is reviewed. In order to provide an overview of available models, a systematic scoping review was conducted following a published protocol with inclusion criteria, which were applied to select the assays. Critical aspects including biological domain, readout endpoint, availability of standardized protocols, chemical domain, reproducibility and predictive power of each assay are described in detail, in order to review the applicability and limitations of the platform in general and progress moving forward to implementation. The horizon of innovative routes of promoting regulatory implementation of alternative methods is scanned, and recommendations for further work are given.

An Evaluation of Human Induced Pluripotent Stem Cells to Test for Cardiac Developmental Toxicity

To prevent congenital defects arising from maternal exposure, safety regulations require pre-market developmental toxicity screens for industrial chemicals and pharmaceuticals. Traditional embryotoxicity approaches depend heavily on the use of low-throughput animal models which may not adequately predict human risk. The validated embryonic stem cell test (EST) developed in murine embryonic stem cells addressed the former problem over 15 years ago. Here, we present a proof-of-concept study to address the latter challenge by updating all three endpoints of the classic mouse EST with endpoints derived from human induced pluripotent stem cells (hiPSCs) and human fibroblasts. Exposure of hiPSCs to selected test chemicals inhibited differentiation at lower concentrations than observed in the mouse EST. The hiPSC-EST also discerned adverse developmental outcomes driven by novel environmental toxicants. Evaluation of the early cardiac gene TBX5 yielded similar toxicity patterns as the full-length hiPSC-EST. Together, these findings support the further development of hiPSCs and early molecular endpoints as a biologically relevant embryotoxicity screening approach for individual chemicals and mixtures.