Rational Design of Lipid Nanoparticles for Enhanced mRNA Vaccine Delivery via Machine Learning.

Since the coronavirus pandemic, mRNA vaccines have revolutionized the field of vaccinology. Lipid nanoparticles (LNPs) are proposed to enhance mRNA delivery efficiency; however, their design is suboptimal. Here, a rational method for designing LNPs is explored, focusing on the ionizable lipid composition and structural optimization using machine learning (ML) techniques. A total of 213 LNPs are analyzed using random forest regression models trained with 314 features to predict the mRNA expression efficiency. The models, which predict mRNA expression levels post-administration of intradermal injection in mice, identify phenol as the dominant substructure affecting mRNA encapsulation and expression. The specific phospholipids used as components of the LNPs, as well as the N/P ratio and mass ratio, are found to affect the efficacy of mRNA delivery. Structural analysis highlights the impact of the carbon chain length on the encapsulation efficiency and LNP stability. This integrated approach offers a framework for designing advanced LNPs and has the potential to unlock the full potential of mRNA therapeutics.

Microfluidic Bioreactor with Fibrous Micromixers for In Vitro mRNA Transcription.

A new type of microfluidic bioreactor with fibrous micromixers for the ingredient mixing and a long macrochannel for the in vitro transcription reaction was fabricated for the continuous production of mRNA. The diameter of the fibrous microchannels in the micromixers was tuned by using an electrospun microfibrous disc with different microfiber diameters. The micromixer with a larger diameter of fibrous microchannels exhibited a better mixing performance than the others. The mixing efficiency was increased to 0.95 while the mixture was passed through the micromixers, suggesting complete mixing. To demonstrate the continuous production of mRNA, the ingredients for in vitro transcription were introduced into the perfluoropolyether microfluidic bioreactor. The mRNA synthesized by the microfluidic bioreactor had the same sequence and in vitro/in vivo performances as those prepared by the bulk reaction. The continuous reaction in the microfluidic bioreactor with efficient mixing performance can be used as a powerful platform for various microfluidic reactions.

mRNA-HPV vaccine encoding E6 and E7 improves therapeutic potential for HPV-mediated cancers via subcutaneous immunization.

The E6 and E7 proteins of specific subtypes of human papillomavirus (HPV), including HPV 16 and 18, are highly associated with cervical cancer as they modulate cell cycle regulation. The aim of this study was to investigate the potential antitumor effects of a messenger RNA-HPV therapeutic vaccine (mHTV) containing nononcogenic E6 and E7 proteins. To achieve this, C57BL/6j mice were injected with the vaccine via both intramuscular and subcutaneous routes, and the resulting effects were evaluated. mHTV immunization markedly induced robust T cell-mediated immune responses and significantly suppressed tumor growth in both subcutaneous and orthotopic tumor-implanted mouse model, with a significant infiltration of immune cells into tumor tissues. Tumor retransplantation at day 62 postprimary vaccination completely halted progression in all mHTV-treated mice. Furthermore, tumor expansion was significantly reduced upon TC-1 transplantation 160 days after the last immunization. Immunization of rhesus monkeys with mHTV elicited promising immune responses. The immunogenicity of mHTV in nonhuman primates provides strong evidence for clinical application against HPV-related cancers in humans. All data suggest that mHTV can be used as both a therapeutic and prophylactic vaccine.

Marine Submicron Aerosols from the Gulf of Mexico: Polluted and Acidic with Rapid Production of Sulfate and Organosulfates.

We measured submicron aerosols (PM1) at a beachfront site in Texas in Spring 2021 to characterize the "background" aerosol chemical composition advecting into Texas and the factors controlling this composition. Observations show that marine "background" aerosols from the Gulf of Mexico were highly processed and acidic; sulfate was the most abundant component (on average 57% of total PM1 mass), followed by organic material (26%). These chemical characteristics are similar to those observed at other marine locations globally. However, Gulf "background" aerosols were much more polluted; the average non-refractory (NR-) PM1 mass concentration was 3-70 times higher than that observed in other clean marine atmospheres. Anthropogenic shipping emissions over the Gulf of Mexico explain 78.3% of the total measured "background" sulfate in the Gulf air. We frequently observed haze pollution in the air mass from the Gulf, with significantly elevated concentrations of sulfate, organosulfates, and secondary organic aerosol associated with sulfuric acid. Analysis suggests that aqueous oxidation of shipping emissions over the Gulf of Mexico by peroxides in the particles might potentially be an important pathway for the rapid production of acidic sulfate and organosulfates during the haze episodes under acidic conditions.

Synthesis of N-substituted quaternary carbon centers through KOt-Bu-catalyzed aza-Michael addition of pyrazoles to cyclic enones.

This study reports an efficient and mild method for the synthesis of cyclic ß-amino ketones containing N-substituted quaternary carbon centers via the KOt-Bu-catalyzed aza-Michael addition reaction of pyrazoles to ß-substituted cyclic α,ß-enones. The amination was promoted by KOt-Bu (3 mol%) at ambient temperature and a wide range of new and versatile ß-pyrazolyl ketones were obtained in good yields. Furthermore, the KOt-Bu-catalyzed one-pot diamination of a cyclic dienone with pyrazoles via an aza-1,6-conjugate addition followed by an aza-1,4-conjugate addition was also explored.

Applying Protein-Protein Interactions and Complex Networks to Identify Novel Genes in Retinitis Pigmentosa Pathogenesis.

Retinitis Pigmentosa (RP) is a hereditary retinal disorder that causes the atrophy of photoreceptor rod cells. Since individual defective genes converge on the same disease, we hypothesized that all causal genes of RP belong in a complex network. To explore this hypothesis, we conducted a gene connection analysis using 161 genes attributed to RP, compiled from the Retinal Information Network, RetNet. We then examined the protein interaction network (PIN) of these genes. In line with our hypothesis, using STRING, we directly connected 149 genes out of the recognized 159 genes. To uncover the association between the PIN and the ten unrecalled genes, we developed an algorithm to pinpoint the best candidate genes to connect the uncalled genes to the PIN and identified ten such genes. We propose that mutations within these ten genes may also cause RP; this notion is supported by analyzing and categorizing the known causal genes based on cellular locations and related functions. The successful establishment of the PIN among all documented genes and the discovery of novel genes for RP strongly suggest an interconnectedness that causes the disease on the molecular level. In addition, our computational gene search protocol can help identify the genes and loci responsible for genetic diseases, not limited to RP.

Apportioned primary and secondary organic aerosol during pollution events of DISCOVER-AQ Houston.

Understanding the drivers for high ozone (O3) and atmospheric particulate matter (PM) concentrations is a pressing issue in urban air quality, as this understanding informs decisions for control and mitigation of these key pollutants. The Houston, TX metropolitan area is an ideal location for studying the intersection between O3 and atmospheric secondary organic carbon (SOC) production due to the diversity of source types (urban, industrial, and biogenic) and the on- and off-shore cycling of air masses over Galveston Bay, TX. Detailed characterization of filter-based samples collected during Deriving Information on Surface Conditions from Column and VERtically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) Houston field experiment in September 2013 were used to investigate sources and composition of organic carbon (OC) and potential relationships between daily maximum 8 h average O3 and PM. The current study employed a novel combination of chemical mass balance modeling defining primary (i.e. POC) versus secondary (i.e. SOC) organic carbon and radiocarbon (14C) for apportionment of contemporary and fossil carbon. The apportioned sources include contemporary POC (biomass burning [BB], vegetative detritus), fossil POC (motor vehicle exhaust), biogenic SOC and fossil SOC. The filter-based results were then compared with real-time measurements by aerosol mass spectrometry. With these methods, a consistent urban background of contemporary carbon and motor vehicle exhaust was observed in the Houston metropolitan area. Real-time and filter-based characterization both showed that carbonaceous aerosols in Houston was highly impacted by SOC or oxidized OC, with much higher contributions from biogenic than fossil sources. However, fossil SOC concentration and fractional contribution had a stronger correlation with daily maximum 8 h average O3, peaking during high PM and O3 events. The results indicate that point source emissions processed by on- and off-shore wind cycles likely contribute to peak events for both PM and O3 in the greater Houston metropolitan area.

Spatial and Temporal Distributions of Organophosphate Ester Concentrations from Atmospheric Particulate Matter Samples Collected across Houston, TX.

Atmospheric particulate matter (PM) samples were collected from four ground-based sites located in the Houston, TX (September 21-28, 2013) and were analyzed for 12 organophosphate esters (OPEs; current-use plasticizers and flame retardants). Samples analyzed included daytime, nighttime, and 24 h PM of <2.5 µm aerodynamic diameter (PM2.5) and total suspended particulate (TSP) samples. PM2.5 and TSP atmospheric ΣOPE concentrations varied over an order of magnitude and were statistically significantly different between urban and suburban and industrial sites. Additionally, significant temporal variability was also identified; for example, daytime atmospheric concentrations of 2-ethylhexyl diphenyl phosphate (EHDPP; 610 ± 220 pg m-3) measured in TSP samples were significantly higher than nighttime concentrations (280 ± 180 pg m-3; p = 0.03). Detailed discussions of the spatial and temporal distribution are given for Tris-(1-chloro-2-propyl) phosphate (TCiPP), EHDPP, tri-n-butyl phosphate (TnBP), and triphenyl phosphate (TPhP). Correlations to bulk measurements of carbonaceous PM including organic carbon, elemental carbon, and water-soluble organic carbon were used to understand potential sources and urban atmospheric transport. These results highlight the fundamental complexity associated with assessing OPE atmospheric concentrations across a large urban landscape and specific knowledge gaps at the intersection of consumer products and safety with environmental and human health.

Spatial and Temporal Distribution of Current-Use Pesticides in Atmospheric Particulate Matter in Houston, Texas.

The atmospheric concentrations of seven current-use pesticides in particulate matter were determined at four locations throughout the Houston metropolitan area in TSP and PM2.5 samples from September 2013. Atmospheric concentrations in both TSP and PM2.5 ranged from below method detection limits (MDLs) to nearly 1100 pg m-3. The three compounds most frequently detected above MDLs were chlorothalonil, bifenthrin, and λ-cyhalothrin. Atmospheric chlorothalonil concentrations were above 800 pg m-3 in several TSP samples, but

Traffic, transport, and vegetation drive VOC concentrations in a major urban area in Texas.

The population of Texas has increased rapidly in the past decade. The San Antonio Field Study (SAFS) was designed to investigate ozone (O3) production and precursors in this rapidly changing, sprawling metropolitan area. There are still many questions regarding the sources and chemistry of volatile organic compounds (VOCs) in urban areas like San Antonio which are affected by a complex mixture of industry, traffic, biogenic sources and transported pollutants. The goal of the SAFS campaign in May 2017 was to measure inorganic trace gases, VOCs, methane (CH4), and ethane (C2H6). The SAFS field design included two sites to better assess air quality across the metro area: an urban site (Traveler's World; TW) and a downwind/suburban site (University of Texas at San Antonio; UTSA). The results indicated that acetone (2.52 ± 1.17 and 2.39 ± 1.27 ppbv), acetaldehyde (1.45 ± 1.02 and 0.93 ± 0.45 ppbv) and isoprene (0.64 ± 0.49 and 1.21 ± 0.85 ppbv; TW and UTSA, respectively) were the VOCs with the highest concentrations. Additionally, positive matrix factorization showed three dominant factors of VOC emissions: biogenic, aged urban mixed source, and acetone. Methyl vinyl ketone and methacrolein (MVK + MACR) exhibited contributions from both secondary photooxidation of isoprene and direct emissions from traffic. The C2H6:CH4 demonstrated potential influence of oil and gas activities in San Antonio. Moreover, the high O3 days during the campaign were in the NOx-limited O3 formation regime and were preceded by evening peaks in select VOCs, NOx and CO. Overall, quantification of the concentration and trends of VOCs and trace gases in a major city in Texas offers vital information for general air quality management and supports strategies for reducing O3 pollution. The SAFS campaign VOC results will also add to the growing body of literature on urban sources and concentrations of VOCs in major urban areas.

Assessing the atmospheric fate of pesticides used to control mosquito populations in Houston, TX.

During the summer months, urban areas are literal hot spots of mosquito-borne disease transmission and air pollution. Public health authorities release aerosolized pesticides directly into the atmosphere to help control adult mosquito populations and thereby reduce the threat of diseases, such as Zika Virus. The primary adulticides (i.e. pesticides used to control adult mosquito populations) in Houston, TX are permethrin and malathion. These adulticides are typically sprayed at night using ultra-low volume sprayers. Particulate matter (PM) samples including total suspended and fine PM (PM < 2.5 µm in aerodynamic diameter) were collected at four ground-based sites across Houston in 2013 and include daytime, nighttime, and 24 h samples. Malathion is initially sprayed as coarse aerosol (5-25 µm), but is measured in fine aerosol (<2.5 µm) and coarse aerosol in the urban atmosphere. Particle size is relevant both for deposition velocities and for human exposure. Atmospheric permethrin concentrations measured in nighttime samples peak at 60 ng m-3, while malathion nighttime concentrations peak near 40 ng m-3. Malaoxon, an oxidation product of malathion, was also frequently detected at concentrations >10 ng m-3, indicating significant nighttime oxidation. Based on the loss of malathion and the increase in malaoxon, the atmospheric half-life of malathion in Houston was estimated at <12 h, which was significantly shorter than previous half-life estimates (∼days). Importantly, malaoxon is estimated to be 22-33 times more toxic to humans than malathion. Both the aerosol size and the half-life are critical for mosquito control, human exposure, and risk assessment of these routine pesticides.

RNA interference-mediated suppression of TNF-α converting enzyme as an alternative anti-TNF-α therapy for rheumatoid arthritis.

Excessive tumor necrosis factor-α (TNF-α) is associated with the pathogenesis of rheumatoid arthritis (RA). Approximately 90% of patients with RA, who have inadequate response to methotrexate, follow anti-TNF-α therapy as the first-line immuno-treatment. However, ineffective long-term anti-TNF-α antibody cycling for 40% of non-responders to anti-TNF-α antibodies is costly and associated with various side effects, which needs alternative mechanism of action therapies. In the present study, a novel strategy to down-regulate TNF-α level was developed by using an alternative method of suppressing TNF-α converting enzyme (TACE), a transmembrane enzyme involved in cleaving and releasing bioactive soluble TNF-α. TACE suppression can be an effective remedy to block the production of soluble TNF-α, leading to an increased sensitivity to anti-TNF-α non-responders. A disease site-targeted RNA interference system was developed by forming non-viral complex between shRNA against TACE (shTACE) and bone resorption site-specific peptide carrier composed of aspartate repeating and arginine repeating sequences. The shTACE/peptide carrier complex alleviated arthritic symptoms in collagen induced arthritis (CIA) models by demonstrating enhanced anti-inflammatory and anti-osteoclastogenic effects. Similar results were obtained with human primary synovial cells and osteoclast precursor isolated from tissues and synovial fluids of RA patients. Taken together, the shTACE/targeting peptide complex provides a strong potential as an alternative anti-TNF-α therapeutic for RA treatment.

The characterization of fine particulate matter downwind of Houston: Using integrated factor analysis to identify anthropogenic and natural sources.

The interpretation of large air pollution datasets involves a great deal of complexity. To gain a better understanding of the complicated relationships and patterns within datasets, we perform factor analysis. Between December 2015 and December 2017, fine particulate matter (PM2.5) samples were collected at a suburban site northeast of the Houston metropolitan area, TX. A total of 233 filter samples were analyzed for chemical composition. The average of all PM2.5 samples consisted of 38.1% inorganic ions, 28.9% elements, 29.1% organic carbon, and 3.7% elemental carbon and other organic materials. Principal component analysis and positive matrix factorization were utilized to identify eight factors: regional aerosols, biomass burning, gasoline combustion, industry, crustal material, incineration, marine dust, and fireworks. The first three contributed more than 70% of the total PM2.5 mass. The receptor models also captured the impact of fireworks and classified it as a source of PM2.5 over Houston. To identify the origins of air masses transporting PM2.5 to the site, we applied the NOAA hybrid single-particle Lagrangian integrated trajectory model and performed a cluster analysis of back trajectories and determined six cluster source regions: the Gulf of Mexico, the Southeast, two midwestern clusters, the Pacific Northwest, and the Southwest. The results of our analysis show that during the summer months, marine and crustal sources were often associated with an onshore flow from the Gulf of Mexico and that four clusters covering 38% of the West Liberty area were strongly influenced by trajectories originating from biomass burning. The results of this study represented a variety of sources that affect the PM2.5 over the Houston metropolitan area. The quantified contributions of these sources could provide policymakers with useful information for developing more efficient control systems and making more effective decisions to cope with the harmful effects of ambient air pollution.

DKK1 Induced by 1,25D3 Is Required for the Mineralization of Osteoblasts.

1α,25-dihydroxyvitamin D3 (1,25D3), the most popular drug for osteoporosis treatment, drives osteoblast differentiation and bone mineralization. Wnt/ß-catenin signaling is involved in commitment and differentiation of osteoblasts, but the role of the Dickkopf-related protein 1 (DKK1), a Wnt antagonist, in osteoblasts remains unknown. Here, we demonstrate the molecular mechanism of DKK1 induction by 1,25D3 and its physiological role during osteoblast differentiation. 1,25D3 markedly promoted the expression of both CCAAT/enhancer binding protein beta (C/EBPß) and DKK1 at day 7 during osteoblast differentiation. Interestingly, mRNA and protein levels of C/EBPß and DKK1 in osteoblasts were elevated by 1,25D3. We also found that C/EBPß, in response to 1,25D3, directly binds to the human DKK1 promoter. Knockdown of C/EBPß downregulated the expression of DKK1 in osteoblasts, which was partially reversed by 1,25D3. In contrast, overexpression of C/EBPß upregulated DKK1 expression in osteoblasts, which was enhanced by 1,25D3. Furthermore, 1,25D3 treatment in osteoblasts stimulated secretion of DKK1 protein within the endoplasmic reticulum to extracellular. Intriguingly, blocking DKK1 attenuated calcified nodule formation in mineralized osteoblasts, but not ALP activity or collagen synthesis. Taken together, these observations suggest that 1,25D3 promotes the mineralization of osteoblasts through activation of DKK1 followed by an increase of C/EBPß.

Regulation of osteoblasts by alkaline phosphatase in ankylosing spondylitis.

AIM: Ankylosing spondylitis (AS) is characterized by excessive spinal ankylosis and bone formation. Alkaline phosphatase (ALP) activity is reported to be high in AS, but little is known about the molecular relationship between ALP and AS. The aims of this study were to investigate the relevance of ALP to AS and the role of ALP in the regulation of osteoblast differentiation in AS. METHODS: High-throughput data with accession numbers GSE73754 and GSE41038 were downloaded from the Gene Expression Omnibus. We retrospectively collected and compared the ALP levels of male patients with AS to those of sex- and age-matched healthy controls (HC) and rheumatoid arthritis (RA) patients. Total serum ALP and ALP activity were measured in the AS and RA groups. ALP gene expression and intracellular ALP activity were analyzed in microarray data from primary diseases control (Ct) and AS-bone-derived cells (BdCs) and in vitro experiments. Furthermore, the effect of ALP inhibitor was examined in both primary Ct- and AS-BdCs under osteoblast differentiation. Regulation of runt-related transcription factor 2 (RUNX2) by ALP was also analyzed. RESULTS: Alkaline phosphatase level was higher in AS compared with RA and HC and was associated with radiograph progression. ALP expression was also enriched in the bone tissue of AS patients. Furthermore, AS-BdCs exhibited increasing ALP activity, leading to accelerated osteoblastic activity and differentiation. Intriguingly, inhibition of ALP reduced RUNX2 expression, a master transcriptional factor in osteoblasts, and differentiation status of both primary Ct- and AS-BdCs. Treatment of ALP activator or inhibitor modulated RUNX2 protein level and RUNX2 regulated ALP promoter activity, indicating a reciprocal ALP-RUNX2 positive feedback to regulate osteoblast differentiation. CONCLUSION: Alkaline phosphatase was highly expressed in AS patients, may be involved in the ankylosis of AS, and represents a possible therapeutic target for ankylosis.

CCAAT/enhancer-binding protein beta (C/EBPß) is an important mediator of 1,25 dihydroxyvitamin D3 (1,25D3)-induced receptor activator of nuclear factor kappa-B ligand (RANKL) expression in osteoblasts.

Receptor activator of nuclear factor kappa B ligand (RANKL) expression in osteoblasts is regulated by 1,25-dihydroxyvitamin D3 (1,25D3). CCAAT/enhancer-binding protein beta (C/EBPß) has been proposed to function as a transcription factor and upregulate RANKL expression, but it is still uncertain how C/EBPß is involved in 1,25D3-induced RANKL expression of osteoblasts. 1,25D3 stimulation increased the expression of RANKL and C/EPBß genes in osteoblasts and enhanced phosphorylation and stability of these proteins. Moreover, induction of RANKL expression by 1,25D3 in osteoblasts was downregulated upon knockdown of C/EBPß. In contrast, C/EBPß overexpression directly upregulated RANKL promoter activity and exhibited a synergistic effect on 1,25D3-induced RANKL expression. In particular, 1,25D3 treatment of osteoblasts increased C/EBPß protein binding to the RANKL promoter. In conclusion, C/EBPß is required for induction of RANKL by 1,25D3. [BMB Reports 2019; 52(6): 391-396].

Source apportionment of fine particulate matter organic carbon in Shenzhen, China by chemical mass balance and radiocarbon methods.

Chemical mass balance (CMB) modeling and radiocarbon measurements were combined to evaluate the sources of carbonaceous fine particulate matter (PM2.5) in Shenzhen, China during and after the 2011 summer Universiade games when air pollution control measurements were implemented to achieve air quality targets. Ambient PM2.5 filter samples were collected daily at two sampling sites (Peking University Shenzhen campus and Longgang) over 24 consecutive days, covering the controlled and uncontrolled periods. During the controlled period, the average PM2.5 concentration was less than half of what it was after the controls were lifted. Organic carbon (OC), organic molecular markers (e.g., levoglucosan, hopanes, polycyclic aromatic hydrocarbons), and secondary organic carbon (SOC) tracers were all significantly lower during the controlled period. After pollution controls ended, at Peking University, OC source contributions included gasoline and diesel engines (24%), coal combustion (6%), biomass burning (12.2%), vegetative detritus (2%), biogenic SOC (from isoprene, α-pinene, and ß-caryophyllene; 7.1%), aromatic SOC (23%), and other sources not included in the model (25%). At Longgang after the controls ended, similar source contributions were observed: gasoline and diesel engines (23%), coal combustion (7%), biomass burning (17.7%), vegetative detritus (1%), biogenic SOC (from isoprene, α-pinene, and ß-caryophyllene; 5.3%), aromatic SOC (13%), and other sources (33%). The contributions of the following sources were smaller during the pollution controls: biogenic SOC (by a factor of 10-16), aromatic SOC (4-12), coal combustion (1.5-6.8), and biomass burning (2.3-4.9). CMB model results and radiocarbon measurements both indicated that fossil carbon dominated over modern carbon, regardless of pollution controls. However, the CMB model needs further improvement to apportion contemporary carbon (i.e. biomass burning, biogenic SOC) in this region. This work defines the major contributors to carbonaceous PM2.5 in Shenzhen and demonstrates that control measures for primary emissions could significantly reduce secondary organic aerosol (SOA) formation.

Pressurized liquid extraction technique for the analysis of pesticides, PCBs, PBDEs, OPEs, PAHs, alkanes, hopanes, and steranes in atmospheric particulate matter.

An analytical method has been developed for the pressurized liquid extraction (PLE) of a wide range of semi-volatile organic compounds (SVOCs) from atmospheric particulate matter. Approximately 130 SVOCs from eight compound classes were selected as molecular markers of (1) agricultural activity (30 current and historic-use pesticides), (2) industrial activity (18 PCBs), (3) consumer products and building materials (16 PBDEs, 11 OPEs), and (4) motor vehicle exhaust (22 PAHs, 16 alkanes, 9 hopanes, 8 steranes). Currently, there is no analytical method validated for the extraction of all eight compound classes in a single automated technique. The extraction efficiencies of varying solvents and solvent combinations at high temperatures and pressures were examined. Extracts were concentrated and analyzed by gas chromatography coupled with mass spectrometry. The optimized PLE method utilized methylene chloride:acetone (2:1 v/v) at 100 °C with three (5 min) static cycles, flush volume of 80%, and a 100 s N2 purge. Spike and recovery experiments (n=7) provided average percent recoveries for pesticides, PCBs, PBDEs, OPEs, PAHs, alkanes, hopanes, and steranes of 88.8±4.0%, 86.9±2.6%, 83.8±2.9%, 101±6%, 90.3±6.1%, 74.4±8.8%, 104±8%, and 86.5±8.6%, respectively. The developed method was applied to atmospheric particulate matter samples collected in the greater Houston, TX metropolitan area. Ambient concentrations of eight classes of compounds (92 SVOCs) were reported in pg m(-3).