High Sensitivity Protein Gel Electrophoresis Label Compatible with Mass-Spectrometry

Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) is a widely utilized technique for macromolecule and protein analysis. While multiple methods exist to visualize the separated protein bands on gels, one of most popular methods of staining the proteins is with Coomassie dye. A more recent approach is to use Bio-Rad stain-free technology for visualizing protein bands with UV light and achieve similar or greater sensitivity than that of Coomassie dye. Here, we developed a method to further amplify the sensitivity of stain-free gels using carboxyfluorescein succinimidyl ester (CFSE) staining. We compared our novel method using foetal bovine serum samples with Coomassie dye, standard stain-free gels, and silver staining. Our results show that while silver staining remains a gold-standard method in terms of sensitivity; CFSE staining of samples prior to use with stain-free gels results in a 10–100-fold increase in sensitivity over Coomassie staining and the standard stain-free method. Our method offers a sensitivity similar to that of silver staining which is compatible with downstream mass spectrometry, and therefore more advantageous for further retrieval and analysis of macromolecules in bands.

Towards defining reference materials for measuring extracellular vesicle refractive index, epitope abundance, size and concentration

Accurate characterization of extracellular vesicles (EVs) is critical to explore their diagnostic and therapeutic applications. As the EV research field has developed, so too have the techniques used to characterize them. The development of reference materials are required for the standardization of these techniques. This work, initiated from the ISEV 2017 Biomarker Workshop in Birmingham, UK, and with further discussion during the ISEV 2019 Standardization Workshop in Ghent, Belgium, sets out to elucidate which reference materials are required and which are currently available to standardize commonly used analysis platforms for characterizing EV refractive index, epitope abundance, size and concentration. Due to their predominant use among EV researchers, a particular focus is placed on the optical methods nanoparticle tracking analysis and flow cytometry.

Fluorescence and Light Scatter Calibration Allow Comparisons of Small Particle Data in Standard Units across Different Flow Cytometry Platforms and Detector Settings

Flow cytometers have been utilized for the analysis of submicron-sized particles since the late 1970s. Initially, virus analyses preceded extracellular vesicle (EV), which began in the 1990s. Despite decades of documented use, the lack of standardization in data reporting has resulted in a growing body of literature that cannot be easily interpreted, validated, or reproduced. This has made it difficult for objective assessments of both assays and instruments, in-turn leading to significant hindrances in scientific progress, specifically in the study of EVs, where the phenotypic analysis of these submicron-sized vesicles is becoming common-place in every biomedical field. Methods for fluorescence and light scatter standardization are well established and the reagents to perform these analyses are commercially available. However, fluorescence and light scatter calibration are not widely adopted by the small particle community as methods to standardize flow cytometry (FCM) data. In this proof-of-concept study carried out as a resource for use at the CYTO2019 workshop, we demonstrate for the first-time simultaneous fluorescence and light scatter calibration of small particle data to show the ease and feasibility of this method for standardized FCM data reporting. This data was acquired using standard configuration commercial flow cytometers, with commercially available materials, published methods, and freely available software tools. We show that application of light scatter, fluorescence, and concentration calibration can result in highly concordant data between FCM platforms independent of instrument collection angle, gain/voltage settings, and flow rate; thus, providing a means of cross comparison in standard units. © 2020 International Society for Advancement of Cytometry.

Monolithically-integrated cytometer for measuring particle diameter in the extracellular vesicle size range using multi-angle scattering

Size measurement of extracellular vesicles is hampered by the high cost and measurement uncertainty of conventional flow cytometers which is mainly due to the use of non-specialised free space optics. Integrated cytometry, where the optics and fluidics are embedded in a monolithic chip shows promise for the production of low cost, micro-flow cytometers dedicated for extracellular vesicle (EV) analysis with improved size measurement accuracy and precision. This research demonstrates a unique integrated cytometer for sub-micron particle size measurement using multi-angle scattering analysis. A combination of three technologies is used: (i) Dean-based hydrodynamic focussing to deliver a tight sample core stream to the analysis region, (ii) integrated waveguides with multimode interference devices to focus a narrow excitation beam onto the sample stream, and (iii) an angular array of collection waveguides to measure particle scattering distribution and calculate diameter. Low index 200 nm liposomes could be detected and polystyrene size standards as small as 400 nm diameter could be measured with an uncertainty of ±21 nm (1/2 IQR) demonstrating a first step on the path to high performance integrated cytometry of EVs.

MIFlowCyt-EV: a framework for standardized reporting of extracellular vesicle flow cytometry experiments

Extracellular vesicles (EVs) are small, heterogeneous and difficult to measure. Flow cytometry (FC) is a key technology for the measurement of individual particles, but its application to the analysis of EVs and other submicron particles has presented many challenges and has produced a number of controversial results, in part due to limitations of instrument detection, lack of robust methods and ambiguities in how data should be interpreted. These complications are exacerbated by the field's lack of a robust reporting framework, and many EV-FC manuscripts include incomplete descriptions of methods and results, contain artefacts stemming from an insufficient instrument sensitivity and inappropriate experimental design and lack appropriate calibration and standardization. To address these issues, a working group (WG) of EV-FC researchers from ISEV, ISAC and ISTH, worked together as an EV-FC WG and developed a consensus framework for the minimum information that should be provided regarding EV-FC. This framework incorporates the existing Minimum Information for Studies of EVs (MISEV) guidelines and Minimum Information about a FC experiment (MIFlowCyt) standard in an EV-FC-specific reporting framework (MIFlowCyt-EV) that supports reporting of critical information related to sample staining, EV detection and measurement and experimental design in manuscripts that report EV-FC data. MIFlowCyt-EV provides a structure for sharing EV-FC results, but it does not prescribe specific protocols, as there will continue to be rapid evolution of instruments and methods for the foreseeable future. MIFlowCyt-EV accommodates this evolution, while providing information needed to evaluate and compare different approaches. Because MIFlowCyt-EV will ensure consistency in the manner of reporting of EV-FC studies, over time we expect that adoption of MIFlowCyt-EV as a standard for reporting EV- FC studies will improve the ability to quantitatively compare results from different laboratories and to support the development of new instruments and assays for improved measurement of EVs.

Considerations towards a roadmap for collection, handling and storage of blood extracellular vesicles

There is an increasing interest in exploring clinically relevant information that is present in body fluids, and extracellular vesicles (EVs) are intrinsic components of body fluids ("liquid biopsies"). In this report, we will focus on blood. Blood contains not only EVs but also cells, and non-EV particles including lipoproteins. Due to the high concentration of soluble proteins and lipoproteins, blood, plasma and serum have a high viscosity and density, which hampers the concentration, isolation and detection of EVs. Because most if not all studies on EVs are single-centre studies, their clinical relevance remains limited. Therefore, there is an urgent need to improve standardization and reproducibility of EV research. As a first step, the International Society on Extracellular Vesicles organized a biomarker workshop in Birmingham (UK) in November 2017, and during that workshop several working groups were created to focus on a particular body fluid. This report is the first output of the blood EV work group and is based on responses by work group members to a questionnaire in order to discover the contours of a roadmap. From the answers it is clear that most respondents are in favour of evidence-based research, education, quality control procedures, and physical models to improve our understanding and comparison of concentration, isolation and detection methods. Since blood is such a complex body fluid, we assume that the outcome of the survey may also be valuable for exploring body fluids other than blood.

FCMPASS Software Aids Extracellular Vesicle Light Scatter Standardization

The study of extracellular vesicles (EVs) is a rapidly growing field due to their great potential in many areas of clinical medicine including diagnostics, prognostics, theranostics, and therapeutics. Flow cytometry is currently one of the most popular methods of analyzing EVs due to it being a high-throughput, multiparametric technique, that is readily available in the majority of research labs. Despite its wide use, few commercial flow cytometers are designed specifically for the detection of EVs. Many flow cytometers used for EV analysis are working at their detection limits and are unable to detect the majority of EVs. Currently, very little standardization exists for EV flow cytometry, which is an issue because flow cytometers vary considerably in the way they collect scattered or fluorescent light from particles being interrogated. This makes published research hard to interpret, compare, and in some cases, impossible to reproduce. Here we demonstrate a method of flow cytometer light scatter standardization, utilizing flow cytometer postacquisition analysis software (FCM_PASS ). FCM_PASS is built upon Mie theory and enables the approximation of flow cytometer geometric parameters either by analyzing beads of known diameter and refractive index or by inputting the collection angle if known. The software is then able to create a scatter-diameter curve and scatter-refractive index curve that enables researchers to convert scattering data and instrument sensitivity into standardized units. Furthermore, with the correct controls, light scatter data can be converted to diameter distributions or refractive index distributions. FCM_PASS therefore offers a freely available and ergonomic method of standardizing and further extending EV characterization using flow cytometry.

High-fidelity detection and sorting of nanoscale vesicles in viral disease and cancer

Biological nanoparticles, including viruses and extracellular vesicles (EVs), are of interest to many fields of medicine as biomarkers and mediators of or treatments for disease. However, exosomes and small viruses fall below the detection limits of conventional flow cytometers due to the overlap of particle-associated scattered light signals with the detection of background instrument noise from diffusely scattered light. To identify, sort, and study distinct subsets of EVs and other nanoparticles, as individual particles, we developed nanoscale Fluorescence Analysis and Cytometric Sorting (nanoFACS) methods to maximise information and material that can be obtained with high speed, high resolution flow cytometers. This nanoFACS method requires analysis of the instrument background noise (herein defined as the “reference noise”). With these methods, we demonstrate detection of tumour cell-derived EVs with specific tumour antigens using both fluorescence and scattered light parameters. We further validated the performance of nanoFACS by sorting two distinct HIV strains to >95% purity and confirmed the viability (infectivity) and molecular specificity (specific cell tropism) of biological nanomaterials sorted with nanoFACS. This nanoFACS method provides a unique way to analyse and sort functional EV- and viral-subsets with preservation of vesicular structure, surface protein specificity and RNA cargo activity.

exRNA Atlas Analysis Reveals Distinct Extracellular RNA Cargo Types and Their Carriers Present across Human Biofluids

To develop a map of cell-cell communication mediated by extracellular RNA (exRNA), the NIH Extracellular RNA Communication Consortium created the exRNA Atlas resource (https://exrna-atlas.org). The Atlas version 4P1 hosts 5,309 exRNA-seq and exRNA qPCR profiles from 19 studies and a suite of analysis and visualization tools. To analyze variation between profiles, we apply computational deconvolution. The analysis leads to a model with six exRNA cargo types (CT1, CT2, CT3A, CT3B, CT3C, CT4), each detectable in multiple biofluids (serum, plasma, CSF, saliva, urine). Five of the cargo types associate with known vesicular and non-vesicular (lipoprotein and ribonucleoprotein) exRNA carriers. To validate utility of this model, we re-analyze an exercise response study by deconvolution to identify physiologically relevant response pathways that were not detected previously. To enable wide application of this model, as part of the exRNA Atlas resource, we provide tools for deconvolution and analysis of user-provided case-control studies.

Optimisation of imaging flow cytometry for the analysis of single extracellular vesicles by using fluorescence-tagged vesicles as biological reference material

Extracellular vesicles (EVs) mediate targeted cellular interactions in normal and pathophysiological conditions and are increasingly recognised as potential biomarkers, therapeutic agents and drug delivery vehicles. Based on their size and biogenesis, EVs are classified as exosomes, microvesicles and apoptotic bodies. Due to overlapping size ranges and the lack of specific markers, these classes cannot yet be distinguished experimentally. Currently, it is a major challenge in the field to define robust and sensitive technological platforms being suitable to resolve EV heterogeneity, especially for small EVs (sEVs) with diameters below 200 nm, i.e. smaller microvesicles and exosomes. Most conventional flow cytometers are not suitable for the detection of particles being smaller than 300 nm, and the poor availability of defined reference materials hampers the validation of sEV analysis protocols. Following initial reports that imaging flow cytometry (IFCM) can be used for the characterisation of larger EVs, we aimed to investigate its usability for the characterisation of sEVs. This study set out to identify optimal sample preparation and instrument settings that would demonstrate the utility of this technology for the detection of single sEVs. By using CD63eGFP-labelled sEVs as a biological reference material, we were able to define and optimise IFCM acquisition and analysis parameters on an Amnis ImageStreamX MkII instrument for the detection of single sEVs. In addition, using antibody-labelling approaches, we show that IFCM facilitates robust detection of different EV and sEV subpopulations in isolated EVs, as well as unprocessed EV-containing samples. Our results indicate that fluorescently labelled sEVs as biological reference material are highly useful for the optimisation of fluorescence-based methods for sEV analysis. Finally, we propose that IFCM will help to significantly increase our ability to assess EV heterogeneity in a rigorous and reproducible manner, and facilitate the identification of specific subsets of sEVs as useful biomarkers in various diseases.

Minimal information for studies of extracellular vesicles 2018 (MISEV2018): a position statement of the International Society for Extracellular Vesicles and update of the MISEV2014 guidelines

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles ("MISEV") guidelines for the field in 2014. We now update these "MISEV2014" guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points.

Pathways and mechanisms linking dietary components to cardiometabolic disease: thinking beyond calories

Calories from any food have the potential to increase risk for obesity and cardiometabolic disease because all calories can directly contribute to positive energy balance and fat gain. However, various dietary components or patterns may promote obesity and cardiometabolic disease by additional mechanisms that are not mediated solely by caloric content. Researchers explored this topic at the 2017 CrossFit Foundation Academic Conference 'Diet and Cardiometabolic Health - Beyond Calories', and this paper summarizes the presentations and follow-up discussions. Regarding the health effects of dietary fat, sugar and non-nutritive sweeteners, it is concluded that food-specific saturated fatty acids and sugar-sweetened beverages promote cardiometabolic diseases by mechanisms that are additional to their contribution of calories to positive energy balance and that aspartame does not promote weight gain. The challenges involved in conducting and interpreting clinical nutritional research, which preclude more extensive conclusions, are detailed. Emerging research is presented exploring the possibility that responses to certain dietary components/patterns are influenced by the metabolic status, developmental period or genotype of the individual; by the responsiveness of brain regions associated with reward to food cues; or by the microbiome. More research regarding these potential 'beyond calories' mechanisms may lead to new strategies for attenuating the obesity crisis.

Systematic Methodological Evaluation of a Multiplex Bead-Based Flow Cytometry Assay for Detection of Extracellular Vesicle Surface Signatures

Extracellular vesicles (EVs) can be harvested from cell culture supernatants and from all body fluids. EVs can be conceptually classified based on their size and biogenesis as exosomes and microvesicles. Nowadays, it is however commonly accepted in the field that there is a much higher degree of heterogeneity within these two subgroups than previously thought. For instance, the surface marker profile of EVs is likely dependent on the cell source, the cell’s activation status, and multiple other parameters. Within recent years, several new methods and assays to study EV heterogeneity in terms of surface markers have been described; most of them are being based on flow cytometry. Unfortunately, such methods generally require dedicated instrumentation, are time-consuming and demand extensive operator expertise for sample preparation, acquisition, and data analysis. In this study, we have systematically evaluated and explored the use of a multiplex bead-based flow cytometric assay which is compatible with most standard flow cytometers and facilitates a robust semi-quantitative detection of 37 different potential EV surface markers in one sample simultaneously. First, assay variability, sample stability over time, and dynamic range were assessed together with the limitations of this assay in terms of EV input quantity required for detection of differently abundant surface markers. Next, the potential effects of EV origin, sample preparation, and quality of the EV sample on the assay were evaluated. The findings indicate that this multiplex bead-based assay is generally suitable to detect, quantify, and compare EV surface signatures in various sample types, including unprocessed cell culture supernatants, cell culture-derived EVs isolated by different methods, and biological fluids. Furthermore, the use and limitations of this assay to assess heterogeneities in EV surface signatures was explored by combining different sets of detection antibodies in EV samples derived from different cell lines and subsets of rare cells. Taken together, this validated multiplex bead-based flow cytometric assay allows robust, sensitive, and reproducible detection of EV surface marker expression in various sample types in a semi-quantitative way and will be highly valuable for many researchers in the EV field in different experimental contexts.

Summary of the ISEV workshop on extracellular vesicles as disease biomarkers, held in Birmingham, UK, during December 2017

This report summarises the presentations and activities of the ISEV Workshop on extracellular vesicle biomarkers held in Birmingham, UK during December 2017. Among the key messages was broad agreement about the importance of biospecimen science. Much greater attention needs to be paid towards the provenance of collected samples. The workshop also highlighted clear gaps in our knowledge about pre-analytical factors that alter extracellular vesicles (EVs). The future utility of certified standards for credentialing of instruments and software, to analyse EV and for tracking the influence of isolation steps on the structure and content of EVs were also discussed. Several example studies were presented, demonstrating the potential utility for EVs in disease diagnosis, prognosis, longitudinal serial testing and stratification of patients. The conclusion of the workshop was that more effort focused on pre-analytical issues and benchmarking of isolation methods is needed to strengthen collaborations and advance more effective biomarkers.

Sugar intake by type (added vs. naturally occurring) and physical form (liquid vs. solid) and its varying association with children's body weight, NHANES 2009-2014

BACKGROUND

Sugars and their primary dietary sources (milk, fruits, sweetened foods and beverages) are associated, in different ways, with a range of health outcomes, including obesity. The contribution made to total sugar intake and how the different types and forms of sugar associate with body weight is unclear.

OBJECTIVE

To describe sugar consumption and examine its association with weight status among U.S. children by sugar type [added {AS} vs. naturally occurring {NOS}] and form (solid vs. liquid).

DESIGN

Cross-sectional dietary data (2 24-h recalls) from children 2-19 years in the National Health and Nutrition Examination Survey, 2009-2014 (n = 8136) were used to estimate the amount of each type and form of sugar by age and weight status. Linear regression models tested trends and the multivariate adjusted association between the different sugars and weight status.

RESULTS

Mean total sugar, AS, and NOS was 118.1 g [25.3% total energy {TE}], 71.5 g (14.8% TE), 46.7 g (10.5% TE), respectively. AS in sugar-sweetened (non-dairy) beverages and NOS in juices contributed 6.9% and 2.4% of TE, respectively. Only %TE from AS (controlled for potential demographic, lifestyle confounders) was associated with change in body mass index z-score (BMIz) [AS in beverages: BMIz β + 0.01 {95% CI: 0.002, 0.03}; AS in foods: BMIz β - 0.03 {95% CI: -0.04, -0.02}].

CONCLUSION

Dietary sugars, most of which are AS, are a major contributor of calories in the diets of U.S. children. Only AS in non-dairy sources were associated with weight although the direction differed by the form consumed. AS in beverages were associated positively and those in foods were associated inversely with children's weight status.

Technical challenges of working with extracellular vesicles

Extracellular Vesicles (EVs) are gaining interest as central players in liquid biopsies, with potential applications in diagnosis, prognosis and therapeutic guidance in most pathological conditions. These nanosized particles transmit signals determined by their protein, lipid, nucleic acid and sugar content, and the unique molecular pattern of EVs dictates the type of signal to be transmitted to recipient cells. However, their small sizes and the limited quantities that can usually be obtained from patient-derived samples pose a number of challenges to their isolation, study and characterization. These challenges and some possible options to overcome them are discussed in this review.

Extracellular Vesicle Flow Cytometry Analysis and Standardization

The term extracellular vesicles (EVs) describes membranous vesicles derived from cells, ranging in diameter from 30 to 1,000 nm with the majority thought to be in the region of 100-150 nm. Due to their small diameter and complex and variable composition, conventional techniques have struggled to accurately count and phenotype EVs. Currently, EV characterization using high-resolution flow cytometry is the most promising method when compared to other currently available techniques, due to it being a high-throughput, single particle, multi-parameter analysis technique capable of analyzing a large range of particle diameters. Whilst high resolution flow cytometry promises detection of the full EV diameter range, standardization of light scattering and fluorescence data between different flow cytometers remains an problem. In this mini review, we will discuss the advances in high-resolution flow cytometry development and future direction of EV scatter and fluorescence standardization. Standardization and therefore reproducibility between research groups and instrumentation is lacking, hindering the validation of EVs use as diagnostic biomarkers and therapeutics.

Sugars and adiposity: the long-term effects of consuming added and naturally occurring sugars in foods and in beverages

OBJECTIVE

The aim of this study was to determine if the association with adiposity varies by the type (added vs. naturally occurring) and form (liquid vs. solid) of dietary sugars consumed.

METHODS

Data from the 10-year National Heart, Lung, and Blood Institute (NHLBI) Growth and Health Study (n = 2,021 girls aged 9-10 years at baseline; n = 5,156 paired observations) were used. Using mixed linear models, 1-year changes in sugar intake, body mass index z-score (BMIz) and waist circumference (WC) were assessed.

RESULTS

The results showed mean daily added sugar (AS) intake: 10.3 tsp (41 g) liquid; 11.6 tsp (46 g) solid and naturally occurring sugar intake: 2.6 tsp (10 g) liquid; 2.2 tsp (9 g) solid. Before total energy adjustment, each additional teaspoon of liquid AS was associated with a 0.222-mm increase in WC (p = 0.0003) and a 0.002 increase in BMIz (p = 0.003). Each teaspoon of solid AS was associated with a 0.126-mm increase in WC (p = 0.03) and a 0.001 increase in BMIz (p = 0.03). Adjusting for total energy, this association was maintained only between liquid AS and WC among all and between solid AS and WC among those overweight/obese only. There was no significant association with naturally occurring sugar.

CONCLUSIONS

These findings demonstrate to suggest a positive association between AS intake (liquid and solid) and BMI that is mediated by total energy intake and an association with WC that is independent of it.

Is there a role for PCR-SSCP among the methods for missense mutation detection of TP53 gene?

Mutation analysis methods have increased in variety during the past years. High-throughput microarray methods have especially increased in popularity. However, new methods require reference points, and not all of the methods are equal in sensitivity and specificity. Furthermore, the detection of unknown missense mutations, such as unknown TP53 mutations in human tumors, for clinical purposes requires great accuracy, which may be difficult to acquire with the current high-throughput methods. For these reasons, the classical methods, such as PCR-manual sequencing and PCR-SSCP, are still valuable and necessary.

Alterations of p14ARF, p53, and p73 genes involved in the E2F-1-mediated apoptotic pathways in non-small cell lung carcinoma

Overexpression of E2F-1 induces apoptosis by both a p14ARF-p53- and a p73-mediated pathway. p14ARF is the alternate tumor suppressor product of the INK4a/ARF locus that is inactivated frequently in lung carcinogenesis. Because p14ARF stabilizes p53, it has been proposed that the loss of p14ARF is functionally equivalent to a p53 mutation. We have tested this hypothesis by examining the genomic status of the unique exon 1beta of p14ARF in 53 human cell lines and 86 primary non-small cell lung carcinomas and correlated this with previously characterized alterations of p53. Homozygous deletions of p14ARF were detected in 12 of 53 (23%) cell lines and 16 of 86 (19%) primary tumors. A single cell line, but no primary tumors, harbored an intragenic mutation. The deletion of p14ARF was inversely correlated with the loss of p53 in the majority of cell lines (P = 0.02), but this relationship was not maintained among primary tumors (P = 0.5). E2F-1 can also induce p73 via a p53-independent apoptotic pathway. Although we did not observe inactivation of p73 by either mutation or DNA methylation, haploinsufficiency of p73 correlated positively with either p14ARF or p53 mutation or both (P = 0.01) in primary non-small cell lung carcinomas. These data are consistent with the current model of p14ARF and p53 interaction as a complex network rather than a simple linear pathway and indicate a possible role for an E2F-1-mediated failsafe, p53-independent, apoptotic pathway involving p73 in human lung carcinogenesis.

p53 and K-ras mutations in lung cancers from former and never-smoking women

Somatic p53 mutations are common in lung cancer. Active cigarette smoking is positively correlated with the total frequency of p53 mutations and G:C to T:A transversions on the nontranscribed (DNA coding) strand. Mutational hotspots within the p53 gene, e.g., codon 157, have been identified for tobacco-related lung cancer, whereas these same mutations are found rarely in other cancers. Such data implicate specific p53 mutations as molecular markers of smoking. Because limited data exist concerning the p53 mutation frequency and spectra in ex-smokers and nonsmokers, we have analyzed p53 and K-ras mutations in 126 lung cancers from a population-based case-control study of nonsmoking (n = 117) or ex-smoking (n = 9) women from Missouri with quantitative assessments of exposure to environmental tobacco smoke. Mutations in the p53 gene were found in lung cancers from lifetime nonsmokers (19%) and ex-smokers (67%; odds ratio, 9.08; 95% confidence interval, 2.06-39.98). All deletions were found in tumors from patients who were either ex-smokers or nonsmokers exposed to passive smoking. The G:C to A:T transitions (11 of 28; 39%) were the most frequent p53 mutations found and clustered in tumors from lifetime nonsmokers without passive smoke exposure. The incidence of K-ras codon 12 or 13 mutations was 11% (14 of 115 analyzed) with no difference between long-term ex-smokers and nonsmokers. These and other results indicate that p53 mutations occur more commonly in smokers and ex-smokers than in never-smokers. Such comparisons provide additional evidence of genetic damage caused by tobacco smoke during lung carcinogenesis.