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Open Access Publications from the University of California

Scholarly Works (67 results)

  • Thesis
  • Peer Reviewed
UC San Diego Electronic Theses and Dissertations (2010)
Occasional (non-daily) smokers pose difficulties for classic withdrawal-based addiction theory because they can regularly go without cigarettes for days with no apparent discomfort. Occasional smokers can be further divided into two subgroups: (1) occasional smokers who used to smoke daily, also known as former-daily occasional smokers (FDO) and (2) occasional smokers who never smoked daily (NDO). Little is known about the situations under which occasional smokers typically smoke their cigarettes, and even less is known about how daily smokers transition to occasional smoking. Three exploratory studies were conducted to examine the following questions. (1) What proportions of smokers are occasional and daily smokers, and how have the respective proportions changed as social norms become increasingly anti-smoking and as smoking continues to decline? (2) When are occasional smokers most likely to smoke, and how do they compare with daily smokers? (3) How do daily smokers transition to smoking occasionally? When they first cut back to smoking only about half the days in a month, which days are they most likely to forgo? The first study analyzed data from the 1996, 1999, 2002, and 2005 California Tobacco Surveys (CTS); the second used data from the 2002 CTS Young Adult Supplement, which includes questions on smoking situations; and the third focused on 152 occasional smokers recruited from the Internet for detailed interviews on smoking situations. The studies found that occasional smokers represent substantial proportions of all current smokers. Moreover, as the overall smoking prevalence declined from 17.7% in 1996 to 14.2% in 2005, the proportions of occasional smokers did not decrease, as would be predicted by their significantly higher cessation rates compared to that of daily smokers. The proportion of FDO smokers increased, though not significantly, from 1996 to 2005: 12.3% to 14.2% for men and 12.9% to 16.8% for women. The NDO proportion increased from 11.9% to 15.3% for men and decreased slightly from 10.6% to 9.5% for women; but again neither change is statistically significant. The pattern of smoking situations for FDO smokers was quite similar to that of NDO smokers, with greater overall likelihood of smoking in social or episodic situations (i.e., socializing with friends or going out) rather than solitary or routine situations (i.e., working or driving). Both differed significantly from that of daily smokers who tended to smoke across a variety of situations. Most FDO smokers (64.3%) had converted to occasional smoking through quitting smoking completely and then returning to smoking non-daily, rather than by cutting down their consumption gradually. Based on these findings we propose a model explaining how daily smokers could transition to occasional smoking. The minority of daily smokers who cut down gradually to non- daily smoking first forgo those days involving routine, solitary situations, such as at home with no other smokers present. The majority who quit daily smoking and later relapse to occasional smoking restrict their smoking mostly to days that involve episodic social situations, such as at parties. In either case, the results from the present three studies show that FDO smokers are virtually indistinguishable from NDO smokers in their current smoking situations, suggesting their previous smoking pattern has very limited influence on their current smoking behavior
    Cover page: Two groups of occasional smokers : different pathways with the same outcome
    • Thesis
    • Peer Reviewed
    UC Davis Electronic Theses and Dissertations (2021)

    Electronic cigarettes (e-cigarettes) are battery-operated devices for nicotine delivery that operate by vaping or aerosolizing an “e-liquid” that contains propylene glycol (PG), vegetable glycerin (VG), nicotine, and different flavoring chemicals. E-cigarettes have been regarded as a “less-harm” alternative to combustible tobacco cigarettes, and their worldwide market share has been increasing exponentially in recent years. In the e-cigarette device vessel, the e-liquid is heated by an atomizer (metal coil) to create an e-cigarette aerosol mixture, which includes both gas and particle phases. Both nicotine-based and cannabinoid-based e-liquids are common in e-cigarette use. Due to their relative novelty, e-cigarettes have not been subject to significant regulatory action until the outbreak of e-cigarette or vaping use-associated lung injury (EVALI) starting from 2019 that killed more than 60 people. In the EVALI outbreak, cannabis vapes (mainly from extracted tetrahydrocannabinol oil) that were adulterated with vitamin E acetate (VEA) in the black market are thought, but not yet confirmed, to be causal agents. After the EVALI outbreak, e-cigarette flavors were banned in closed-tank systems.

    During the heat-induced aerosolization process of e-liquid, many thermal degradation products have been identified and characterized (e.g., formaldehyde, acetaldehyde, acetone) that are produced from the thermal degradation of PG and VG, as well as flavorant mixtures. Previous research studies indicate that the production of thermal degradation products depends on puff regimen, coil temperature, e-liquid composition, and possibly other factors. However, knowledge gaps still exist regarding the large variety of thermal degradation products that remain unidentified or unquantified, and the intrinsic relationship between actual coil temperature and e-liquid composition to the thermal degradation of e-liquid. In addition, the thermal degradation mechanism of VEA and THC is still unknown.

    In this work, high performance liquid chromatography (HPLC) coupled with electrospray ionization (ESI) high resolution mass spectrometry (HRMS) are used for the chemical analysis of thermal degradation carbonyl compounds and organic acids. Both carbonyls and acids are derivatized with 2,4-dinitrophenylhydrazine (2,4-DNPH) prior to mass spectrometry analysis. A novel theoretical chemistry model was developed to predict the analytical sensitivities of carbonyl(acid)-DNPH derivatives in ESI negative mode for the analyte compounds for which corresponding DNPH derivatives standards are unavailable. This characterization method enabled an untargeted analysis and the most comprehensive picture, to date, of the carbonyls and acids that are generated from both PG/VG and VEA/THC vaping systems. Over 40 thermal degradation carbonyls and acids were characterized from the thermal degradation of PG, VG, VEA and THC, while nearly 20 cannabinoids and derivatives were also identified by the same methods. PG, VG, and VEA were analyzed by gas chromatography to enable mass closure for the aerosolization process.

    Moreover, this work systematically studies how changing the vaping parameters, including coil temperature, e-liquid composition and puff regimen, alters the production of aerosol mass and carbonyl degradation products. The thermal degradation mechanism of PG and VG is proposed from the results, including differences between heat-induced dehydration and oxidant-induced decomposition. The thermal degradation chemistry of THC and VEA is also studied, and the corresponding mechanisms proposed. In summary, this work provides important chemical-specific information that may be helpful for the fundamental understanding of chemistry in e-cigarettes and for guiding regulatory action. Corresponding toxicology and in vivo studies are needed to further evaluate the health risk of e-cigarette use.

      Cover page: Aerosolization and Thermal Degradation Chemistry of Electronic Cigarettes
      • Thesis
      • Peer Reviewed
      UC Berkeley Electronic Theses and Dissertations (2019)

      Lipid droplets (LDs) are ubiquitous organelles that play a critical role in lipid homeostasis by regulating the storage and mobilization of fatty acids. When nutrient supplies are limited, the fatty acids stored in LDs are transferred to the mitochondria for the generation of energy. As starvation persists however, autophagy is triggered to degrade and recycle damaged organelles. Autophagy releases FAs into the cytosol to replenishing LDs with new FAs, increasing LD abundance. Interestingly, the autophagy-dependent LDs cluster in close proximity to mitochondria, forming membrane contact sites (MCSs). MCSs are areas of close apposition between the membranes of two organelles mediated by tethering forces that arise from protein-protein interaction. However, the identity of a LD-mitochondrial tethering complex and the functional importance of the LD-mitochondrial contacts in FA transfer and energy homeostasis are unknown.

      In chapter one, we observed an increase in LD abundance during prolonged nutrient deprivation. Starvation-induced LDs are not required for fatty acid delivery to mitochondria, but instead LDs sequester fatty acids that are released during autophagy to prevent lipotoxic dysregulation of mitochondrial function. In chapter two, we established an inducible heterodimer tethering system to temporally and spatially regulate LD-mitochondrial contact to study the functional importance of the interorganelle contact. Finally, in chapter three we employed proximity-labeling proteomics to identify protein tethers that mediate the close positioning of LDs and mitochondria. Together, our studies advance our understanding of organelle communication in the maintenance of lipid and energy homeostasis.

        Cover page: The Role of Lipid Droplets in Cellular Energy Homeostasis and Interorganelle Communication
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2019)
        Lipid droplets (LDs) are hubs for lipid metabolism that form membrane contact sites with multiple organelles. In this issue, Hariri et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201808119) reveal the functions of Mdm1-mediated endoplasmic reticulum (ER)-LD tethering in yeast and Datta et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201808133) identify a role for the Mdm1 orthologue, Snx14, as an ER-LD tether that regulates lipid metabolism in human cells.
          Cover page: Getting a handle on lipid droplets: Insights into ER–lipid droplet tethering
          • Article
          • Peer Reviewed
          UC Berkeley Previously Published Works (2017)
          Lipid droplets (LDs) are neutral lipid storage organelles that provide a rapidly accessible source of fatty acids (FAs) for energy during periods of nutrient deprivation. Surprisingly, lipids released by the macroautophagic/autophagic breakdown of membranous organelles are packaged and stored in new LDs during periods of prolonged starvation. Why cells would store FAs during an energy crisis was unknown. In our recent study, we demonstrated that FAs released during MTORC1-regulated autophagy are selectively channeled by DGAT1 (diacylglycerol O-acyltransferase 1) into triacylglycerol (TAG)-rich LDs. These DGAT1-dependent LDs sequester FAs and prevent the accumulation of acylcarnitines, which otherwise directly disrupt mitochondrial integrity. Our findings establish LD biogenesis as a general cellular response to periods of high autophagic flux that provide a lipid buffering system to mitigate lipotoxic cellular damage.
            Cover page: Lipid droplets and lipotoxicity during autophagy
            • Article
            • Peer Reviewed
            Proceedings of the Annual Meeting of the Cognitive Science Society, Volume 44 (2022)
            Beyond seemingly lower-level features such as color and motion, visual perception also recovers properties that are more commonly associated with higher-level thought — as when an upwardly accelerating object is seen as self-propelled, and resisting the force of gravity. Past work has explored how speed changes drive the perception of physical forces, but might the reverse also be true? Does seeing a speed change as resisting the force of gravity make us more likely to notice it in the first place? In four experiments, observers were more sensitive to objects’ accelerations when they moved upward (i.e. when those accelerations were opposite to gravity), and they were more sensitive to objects’ decelerations when they moved downward (i.e. when those decelerations appeared as ‘braking’ against gravity). We conclude that the perception of physical forces is not merely an outcome of visual processing, but also determines the perception of other, seemingly lower-level, features of how objects move.
              Cover page: May the Force be against you: Better sensitivity to speed changes opposite to gravityCreative Commons 'BY' version 4.0 license
              • Article
              • Peer Reviewed
              UC Davis Previously Published Works (2021)
              The hydroxyl radical (OH) oxidation of the most abundant nonmethane volatile organic compound emitted to the atmosphere, isoprene (C5H8), produces a number of chemical species that partition to the condensed phase via gas-particle partitioning or form condensed-phase compounds via multiphase/heterogeneous chemistry to generate secondary organic aerosols (SOA). The SOA species in aerosol water or cloud/fog droplets may oxidize further via aqueous reaction with OH radicals, among other fates. Rate coefficients for compounds in isoprene's photochemical cascade are well constrained in the gas phase; however, a gap of information exists for the aqueous OH rate coefficients of the condensed-phased products, precluding the atmospheric modeling of the oxidative fate of isoprene-derived SOA. This work investigated the OH-initiated oxidation kinetic rate coefficients (kOH) for six major SOA compounds formed from the high-NO and low-NO channels of isoprene's atmospheric oxidation and one analog, most of which were synthesized and purified for study: (k1) 2-methyltetrol [MT: 1.14 (±0.17) × 109 M-1 s-1], (k2) 2-methyl-1,2,3-trihydroxy-4-sulfate [MT-4-S: 1.52 (±0.25) × 109 M-1 s-1], (k3) 2-methyl-1,2-dihydroxy-3-sulfate [MD-3-S: 0.56 (±0.15) × 109 M-1 s-1], (k4) 2-methyl-1,2-dihydroxy-but-3-ene [MDE: 4.35 (±1.16) × 109 M-1 s-1], (k5) 2-methyl-2,3-dihydroxy-1,4-dinitrate [MD-1,4-DN: 0.24 (±0.04) × 109 M-1 s-1], (k6) 2-methyl-1,2,4-trihydroxy-3-nitrate [MT-3-N: 1.12 (±0.15) × 109 M-1 s-1], and (k7) 2-methylglyceric acid [MGA: pH 2:1.41 (±0.49) × 109 M-1 s-1; pH 5:0.97 (±0.42) × 109 M-1 s-1]. The second-order rate coefficients are determined against the known kOH of erythritol in pure water. The decays of each reagent were measured with nuclear magnetic resonance (NMR) and high-performance liquid chromatography-high resolution mass spectrometry (HPLC-HRMS). The aqueous photooxidation fates of isoprene-derived SOA compounds are substantial and may impact the SOA budget when implemented into global models.
                Cover page: Second-Order Kinetic Rate Coefficients for the Aqueous-Phase Hydroxyl Radical (OH) Oxidation of Isoprene-Derived Secondary Organic Aerosol Compounds at 298 K
                • Article
                • Peer Reviewed
                UC Davis Previously Published Works (2013)
                Sources and chemical composition of brown carbon are poorly understood, and even less is known about the mechanisms of its atmospheric transformations. This work presents molecular-level investigations of the reactive compound ketolimononaldehyde (KLA, C9H14O3), a second-generation ozonolysis product of limonene (C10H16), as a potent brown carbon precursor in secondary organic aerosol (SOA) through its reactions with reduced nitrogen compounds, such as ammonium ion (NH4+), ammonia, and amino acids. The reactions of synthesized and purified KLA with NH4+ and glycine resulted in the formation of chromophores nearly identical in spectral properties and formation rates to those found in similarly-aged limonene/O3 SOA. Similar chemical reaction processes of limononaldehyde (LA, C10H16O2) and pinonaldehyde (PA, C10H16O2), the first-generation ozonolysis products of limonene and alpha-pinene, respectively, were also studied, but the resulting products did not exhibit the light absorption properties of brown carbon, suggesting that the unique molecular structure of KLA produces visible-light-absorbing compounds. The KLA/NH4+ and KLA/GLY reactions produce water-soluble, hydrolysis-resilient chromophores with high mass absorption coefficients (MAC = 2000-4000 cm2 g(-1)) at lambda - 500 nm, precisely at the maximum of the solar emission spectrum. Liquid chromatography was used to isolate the light-absorbing fraction, and UV-Vis, FTIR, NMR and high-resolution mass spectrometry (HR-MS) techniques were used to investigate the structures and chemical properties of the light-absorbing compounds. The KLA browning reaction generates a diverse mixture of light-absorbing compounds, with the majority of the observable products containing 1-4 units of KLA and 0-2 nitrogen atoms. Based on the HR-MS product distribution, conjugated aldol condensates, secondary imines (Schiff bases), and N-heterocycles like pyrroles may contribute in varying degree to the light-absorbing properties of the KLA brown carbon. The results of this study demonstrate the high degree of selectivity of organic compound structures on the light-absorbing properties of SOA.
                  Cover page: Brown carbon formation from ketoaldehydes of biogenic monoterpenest.
                  • Article
                  • Peer Reviewed
                  UC Davis Previously Published Works (2021)
                  1,2-Dihydroxy isoprene (1,2-DHI), a product of isoprene oxidation from multiple chemical pathways, is produced in the atmosphere in large quantities; however, its chemical fate has not been comprehensively studied. Here, we perform chamber experiments to investigate its gas-phase reactions. We find that the reactions of 1,2-DHI with OH radicals and ozone are rapid (kOH = 8.0 (±1.3) × 10-11 cm3 molecule-1 s-1; kO3 = 7.2 (±1.1) × 10-18 cm3 molecule-1 s-1). Reaction with OH, which dominates 1,2-DHI loss, leads primarily to fragmentation and radical recycling; major products under both high- and low-NO conditions include hydroxyacetone, glycolaldehyde, and 2,3-dihydroxy-2-methyl-propanal (DHMP). Radical-terminating hydroperoxide formation from the peroxy radical (RO2) reaction with HO2 and organonitrate formation from RO2 + NO are not observed in the gas phase, possibly due to low volatility; constraints for their branching ratios are instead derived by mass balance. We also measure secondary organic aerosol mass yields from 1,2-DHI (0-23%) and show that oxidation in the presence of aqueous particles leads to formic and acetic acid production. Finally, we incorporate results into GEOS-Chem, a global chemical transport model, to compute the global production (25.3 Tg a-1) and gas-phase loss (20.2 Tg a-1) of 1,2-DHI and show that its oxidation provides non-negligible contributions to the atmospheric budgets of hydroxyacetone, glycolaldehyde, hydroxymethyl hydroperoxide, formic acid, and DHMP.
                    Cover page: Gas-Phase Oxidation Rates and Products of 1,2-Dihydroxy Isoprene
                    • Article
                    • Peer Reviewed
                    UC San Francisco Previously Published Works (2022)
                    The use of muscle flaps, such as the sartorius muscle, for groin coverage in high-risk vascular patients has been shown to reduce complication rates. However, it remains unknown whether earlier postoperative ambulation is associated with improved postoperative outcomes for groin muscle flaps following infrainguinal vascular surgery.

                    Methods

                    We performed a pilot randomized trial to analyze the effect of early ambulation on postoperative outcomes in patients who had groin reconstruction with sartorius muscle flaps following infrainguinal vascular surgery at our academic institution.

                    Results

                    Fourteen patients were randomized to standard ambulation (on postoperative day 6), and 14 patients were randomized to early ambulation (on postoperative day 2). The treatment arms were similar with respect to age, body mass index, risk category, smoking status, and comorbidities. Median length of stay was 6 days in the early group versus 7 days in the standard group. Immediate and long-term physical function and general health were better in the early group There were slightly more wound complications in the standard (57.1%) versus the early group (42.9%), and the early group had more lymphatic complications (35.7% versus 14.3%).

                    Conclusions

                    The decision to ambulate a patient after this surgery continues to be a decision between the vascular and plastic surgeons. However, this pilot trial has shown the safety profile of early ambulation and that it should be considered for specific patients. Additionally, this trial has provided valuable information for performing a larger scale randomized controlled trial to determine the optimal postoperative protocol for patients with these reconstructions.
                      Cover page: A Pilot Randomized Clinical Trial of Early Ambulation after Groin Reconstruction with Sartorius Muscle Flaps
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