Mapping the Morphology of DNA on Carbon Nanotubes in Solution Using X-ray Scattering Interferometry

Single-walled carbon nanotubes (SWCNTs) with adsorbed single-stranded DNA (ssDNA) are applied as sensors to investigate biological systems, with potential applications ranging from clinical diagnostics to agricultural biotechnology. Unique ssDNA sequences render SWCNTs selectively responsive to target analytes such as (GT)n-SWCNTs recognizing the neuromodulator, dopamine. It remains unclear how the ssDNA conformation on the SWCNT surface contributes to functionality, as observations have been limited to computational models or experiments under dehydrated conditions that differ substantially from the aqueous biological environments in which the nanosensors are applied. We demonstrate a direct mode of measuring in-solution ssDNA geometries on SWCNTs via X-ray scattering interferometry (XSI), which leverages the interference pattern produced by AuNP tags conjugated to ssDNA on the SWCNT surface. We employ XSI to quantify distinct surface-adsorbed morphologies for two (GT)n ssDNA oligomer lengths (n = 6, 15) that are used on SWCNTs in the context of dopamine sensing and measure the ssDNA conformational changes as a function of ionic strength and during dopamine interaction. We show that the shorter oligomer, (GT)6, adopts a more periodically ordered ring structure along the SWCNT axis (inter-ssDNA distance of 8.6 ± 0.3 nm), compared to the longer (GT)15 oligomer (most probable 5'-to-5' distance of 14.3 ± 1.1 nm). During molecular recognition, XSI reveals that dopamine elicits simultaneous axial elongation and radial constriction of adsorbed ssDNA on the SWCNT surface. Our approach using XSI to probe solution-phase morphologies of polymer-functionalized SWCNTs can be applied to yield insights into sensing mechanisms and inform future design strategies for nanoparticle-based sensors.

Correlating Conformational Equilibria with Catalysis in the Electron Bifurcating EtfABCX of Thermotoga maritima

Electron bifurcation (BF) is an evolutionarily ancient energy coupling mechanism in anaerobes, whose associated enzymatic machinery remains enigmatic. In BF-flavoenzymes, a chemically high-potential electron forms in a thermodynamically favorable fashion by simultaneously dropping the potential of a second electron before its donation to physiological acceptors. The cryo-EM and spectroscopic analyses of the BF-enzyme Fix/EtfABCX from Thermotoga maritima suggest that the BF-site contains a special flavin-adenine dinucleotide and, upon its reduction with NADH, a low-potential electron transfers to ferredoxin and a high-potential electron reduces menaquinone. The transfer of energy from high-energy intermediates must be carefully orchestrated conformationally to avoid equilibration. Herein, anaerobic size exclusion-coupled small-angle X-ray scattering (SEC-SAXS) shows that the Fix/EtfAB heterodimer subcomplex, which houses BF- and electron transfer (ET)-flavins, exists in a conformational equilibrium of compacted and extended states between flavin-binding domains, the abundance of which is impacted by reduction and NAD(H) binding. The conformations identify dynamics associated with the T. maritima enzyme and also recapitulate states identified in static structures of homologous BF-flavoenzymes. Reduction of Fix/EtfABCX's flavins alone is insufficient to elicit domain movements conducive to ET but requires a structural "trigger" induced by NAD(H) binding. Models show that Fix/EtfABCX's superdimer exists in a combination of states with respect to its BF-subcomplexes, suggesting a cooperative mechanism between supermonomers for optimizing catalysis. The correlation of conformational states with pathway steps suggests a structural means with which Fix/EtfABCX may progress through its catalytic cycle. Collectively, these observations provide a structural framework for tracing Fix/EtfABCX's catalysis.

A round-robin approach provides a detailed assessment of biomolecular small-angle scattering data reproducibility and yields consensus curves for benchmarking

Through an expansive international effort that involved data collection on 12 small-angle X-ray scattering (SAXS) and four small-angle neutron scattering (SANS) instruments, 171 SAXS and 76 SANS measurements for five proteins (ribonuclease A, lysozyme, xylanase, urate oxidase and xylose isomerase) were acquired. From these data, the solvent-subtracted protein scattering profiles were shown to be reproducible, with the caveat that an additive constant adjustment was required to account for small errors in solvent subtraction. Further, the major features of the obtained consensus SAXS data over the q measurement range 0-1 Å-1 are consistent with theoretical prediction. The inherently lower statistical precision for SANS limited the reliably measured q-range to <0.5 Å-1, but within the limits of experimental uncertainties the major features of the consensus SANS data were also consistent with prediction for all five proteins measured in H2O and in D2O. Thus, a foundation set of consensus SAS profiles has been obtained for benchmarking scattering-profile prediction from atomic coordinates. Additionally, two sets of SAXS data measured at different facilities to q > 2.2 Å-1 showed good mutual agreement, affirming that this region has interpretable features for structural modelling. SAS measurements with inline size-exclusion chromatography (SEC) proved to be generally superior for eliminating sample heterogeneity, but with unavoidable sample dilution during column elution, while batch SAS data collected at higher concentrations and for longer times provided superior statistical precision. Careful merging of data measured using inline SEC and batch modes, or low- and high-concentration data from batch measurements, was successful in eliminating small amounts of aggregate or interparticle interference from the scattering while providing improved statistical precision overall for the benchmarking data set.

Structural plasticity enables evolution and innovation of RuBisCO assemblies

Oligomerization is a core structural feature that defines the form and function of many proteins. Most proteins form molecular complexes; however, there remains a dearth of diversity-driven structural studies investigating the evolutionary trajectory of these assemblies. Ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) is one such enzyme that adopts multiple assemblies, although the origins and distribution of its different oligomeric states remain cryptic. Here, we retrace the evolution of ancestral and extant form II RuBisCOs, revealing a complex and diverse history of oligomerization. We structurally characterize a newly discovered tetrameric RuBisCO, elucidating how solvent-exposed surfaces can readily adopt new interactions to interconvert or give rise to new oligomeric states. We further use these principles to engineer and demonstrate how changes in oligomerization can be mediated by relatively few mutations. Our findings yield insight into how structural plasticity may give rise to new oligomeric states.

Monitoring Nuclease Activity by X-Ray Scattering Interferometry Using Gold Nanoparticle-Conjugated DNA

The biologically critical, exquisite specificity and efficiency of nucleases, such as those acting in DNA repair and replication, often emerge in the context of multiple other macromolecules. The evolved complexity also makes biologically relevant nuclease assays challenging and low-throughput. Meiotic recombination 11 homolog 1 (MRE11) is an exemplary nuclease that initiates DNA double-strand break (DSB) repair and processes stalled DNA replication forks. Thus, DNA resection by MRE11 nuclease activity is critical for multiple DSB repair pathways as well as in replication. Traditionally, in vitro nuclease activity of purified enzymes is studied either through gel-based assays or fluorescence-based assays like fluorescence resonance energy transfer (FRET). However, adapting these methods for a high-throughput application such as inhibitor screening can be challenging. Gel-based approaches are slow, and FRET assays can suffer from interference and distance limitations. Here we describe an alternative methodology to monitor nuclease activity by measuring the small-angle X-ray scattering (SAXS) interference pattern from gold nanoparticles (Au NPs) conjugated to 5'-ends of dsDNA using X-ray scattering interferometry (XSI). In addition to reporting on the enzyme activity, XSI can provide insight into DNA-protein interactions, aiding in the development of inhibitors that trap enzymes on the DNA substrate. Enabled by efficient access to synchrotron beamlines, sample preparation, and the feasibility of high-throughput XSI data collection and processing pipelines, this method allows for far greater speeds with less sample consumption than conventional SAXS techniques. The reported metrics and methods can be generalized to monitor not only other nucleases but also most other DNA-protein interactions.

Chemical crystallography by serial femtosecond X-ray diffraction

Inorganic-organic hybrid materials represent a large share of newly reported structures, owing to their simple synthetic routes and customizable properties1. This proliferation has led to a characterization bottleneck: many hybrid materials are obligate microcrystals with low symmetry and severe radiation sensitivity, interfering with the standard techniques of single-crystal X-ray diffraction2,3 and electron microdiffraction4-11. Here we demonstrate small-molecule serial femtosecond X-ray crystallography (smSFX) for the determination of material crystal structures from microcrystals. We subjected microcrystalline suspensions to X-ray free-electron laser radiation12,13 and obtained thousands of randomly oriented diffraction patterns. We determined unit cells by aggregating spot-finding results into high-resolution powder diffractograms. After indexing the sparse serial patterns by a graph theory approach14, the resulting datasets can be solved and refined using standard tools for single-crystal diffraction data15-17. We describe the ab initio structure solutions of mithrene (AgSePh)18-20, thiorene (AgSPh) and tethrene (AgTePh), of which the latter two were previously unknown structures. In thiorene, we identify a geometric change in the silver-silver bonding network that is linked to its divergent optoelectronic properties20. We demonstrate that smSFX can be applied as a general technique for structure determination of beam-sensitive microcrystalline materials at near-ambient temperature and pressure.

Investigation of Nucleation and Growth at a Liquid-Liquid Interface by Solvent Exchange and Synchrotron Small-Angle X-Ray Scattering

Hybrid nanomaterials possess complex architectures that are driven by a self-assembly process between an inorganic element and an organic ligand. The properties of these materials can often be tuned by organic ligand variation, or by swapping the inorganic element. This enables the flexible fabrication of tailored hybrid materials with a rich variety of properties for technological applications. Liquid-liquid interfaces are useful for synthesizing these compounds as precursors can be segregated and allowed to interact only at the interface. Although procedurally straightforward, this is a complex reaction in an environment that is not easy to probe. Here, we explore the interfacial crystallization of mithrene, a supramolecular multi-quantum well. This material sandwiches a well-defined silver-chalcogenide layer between layers of organic ligands. Controlling mithrene crystal size and morphology to be useful for applications requires understanding details of its crystal growth, but the specific mechanism for this reaction remain only lightly investigated. We performed a study of mithrene crystallization at an oil-water interfaces to elucidate how the interfacial free energy affects nucleation and growth. We exchanged the oil solvent on the basis of solvent viscosity and surface tension, modifying the dynamic contact angle and interfacial free energy. We isolated and characterized the reaction byproducts via scanning electron microscopy (SEM). We also developed a high-throughput small angle X-ray scattering (SAXS) technique to measure crystallization at short reaction timescales (minutes). Our results showed that modifying interfacial surface energy affects both the reaction kinetics and product size homogeneity and yield. Our SAXS measurements reveal the onset of crystallinity after only 15 min. These results provide a template for exploring directed synthesis of complex materials via experimental methods.

Albumin in patients with liver disease shows an altered conformation

Human serum albumin (HSA) constitutes the primary transporter of fatty acids, bilirubin, and other plasma compounds. The binding, transport, and release of its cargos strongly depend on albumin conformation, which is affected by bound ligands induced by physiological and pathological conditions. HSA is both highly oxidized and heavily loaded with fatty acids and bilirubin in chronic liver disease. By employing small-angle X-ray scattering we show that HSA from the plasma of chronic liver disease patients undergoes a distinct opening compared to healthy donors. The extent of HSA opening correlates with clinically relevant variables, such as the model of end-stage liver disease score, bilirubin, and fatty acid levels. Although the mild oxidation of HSA in vitro does not alter overall structure, the alteration of patients’ HSA correlates with its redox state. This study connects clinical data with structural visualization of albumin dynamicity in solution and underlines the functional importance of albumin’s inherent flexibility.

Paar et al. propose a SAXS-based approach to study conformations of human serum albumin (HSA) from patients with liver disease and a structural understanding of HSA dynamicity and its correlation with clinical variables are provided. Using it on real clinical samples, this study has concrete practical implications too.

Rigid monoclonal antibodies improve detection of SARS-CoV-2 nucleocapsid protein

Monoclonal antibodies (mAbs) are the basis of treatments and diagnostics for pathogens and other biological phenomena. We conducted a structural characterization of mAbs against the N-terminal domain of nucleocapsid protein (NP NTD ) from SARS-CoV-2 using small angle X-ray scattering (SAXS). Our solution-based results distinguished the mAbs' flexibility and how this flexibility impacts the assembly of multiple mAbs on an antigen. By pairing two mAbs that bind different epitopes on the NP NTD , we show that flexible mAbs form a closed sandwich-like complex. With rigid mAbs, a juxtaposition of the Fabs is prevented, enforcing a linear arrangement of the mAb pair, which facilitates further mAb polymerization. In a modified sandwich ELISA, we show the rigid mAb-pairings with linear polymerization led to increased NP NTD detection sensitivity. These enhancements can expedite the development of more sensitive and selective antigen-detecting point-of-care lateral flow devices (LFA), key for early diagnosis and epidemiological studies of SARS-CoV-2 and other pathogens.

Quantitative Protein Corona Composition and Dynamics on Carbon Nanotubes in Biological Environments

When nanoparticles enter biological environments, proteins adsorb to form the "protein corona" which alters nanoparticle biodistribution and toxicity. Herein, we measure protein corona formation on DNA-functionalized single-walled carbon nanotubes (ssDNA-SWCNTs), a nanoparticle used widely for sensing and delivery, in blood plasma and cerebrospinal fluid. We characterize corona composition by mass spectrometry, revealing high-abundance corona proteins involved in lipid binding, complement activation, and coagulation. We investigate roles of electrostatic and entropic interactions driving selective corona formation. Lastly, we study real-time protein binding on ssDNA-SWCNTs, obtaining agreement between enriched proteins binding strongly and depleted proteins binding marginally, while highlighting cooperative adsorption mechanisms. Knowledge of protein corona composition, formation mechanisms, and dynamics informs nanoparticle translation from in vitro design to in vivo application.

Visualizing functional dynamicity in the DNA-dependent protein kinase holoenzyme DNA-PK complex by integrating SAXS with cryo-EM

Assembly of KU and DNA-dependent protein kinase catalytic subunit (DNA-PKcs) at DNA double strand breaks (DSBs) forms DNA-PK holoenzyme as a critical initiating step for non-homologous end joining (NHEJ) repair of DSBs produced by radiation and chemotherapies. Advanced cryo-electron microscopy (cryo-EM) imaging together with breakthrough macromolecular X-ray crystal (MX) structures of KU and DNA-PKcs recently enabled visualization of the ∼600 kDa DNA-PK assembly at near atomic resolution. These important static structures provide the foundation for definition and interpretation of functional movements crucial to mechanistic understanding that can be tested through solution state structure analysis. We herein therefore leverage Cryo-EM and MX structures for the interpretation of synchrotron small-angle X-ray scattering (SAXS) data on DNA-PK conformations in solution to inform the structural mechanism for NHEJ initiation. SAXS, which measures thermodynamic solution-state conformational states and assemblies outside of cryo- and solid-state conditions, unveils the inherent flexibility of KU, DNA-PKcs and DNA-PK. The combined structural measurements reveal mobility of KU80 C-terminal region (KU80CTR), motion/plasticity of HEAT (DNA-PKcs Huntingtin, Elongation Factor 3, PP2 A, and TOR1) regions, allosteric switching upon DNA-PKcs autophosphorylation, and dimeric arrangements of DNA-PK assembly. Importantly, the results uncover displacement of the N-terminal HEAT domain during autophosphorylation as suitable for a regulated release mechanism of DNA-PKcs from DNA-PK to control unproductive access to toxic and mutagenic DNA repair intermediates. These integrated analyses show that the marriage of SAXS with cryo-EM leverages the strengths of both techniques to enable assessment of functional conformations and flexibility defining atomic-resolution molecular mechanisms for DSB repair.

Synthesis of microporous silica nanoparticles to study water phase transitions by vibrational spectroscopy

Silica can take many forms, and its interaction with water can change dramatically at the interface. Silica based systems offer a rich tapestry to probe the confinement of water as size and volume can be controlled by various templating strategies and synthetic procedures. To this end, microporous silica nanoparticles have been developed by a reverse microemulsion method utilizing zinc nanoclusters encapsulated in hydroxyl-terminated polyamidoamine (PAMAM-OH) dendrimers as a soft template. These nanoparticles were made tunable within the outer diameter range of 20-50 nm with a core mesopore of 2-15 nm. Synthesized nanoparticles were used to study the effects of surface area and microporous volumes on the vibrational spectroscopy of water. These spectra reveal contributions from bulk interfacial/interparticle water, ice-like surface water, liquid-like water, and hydrated silica surfaces suggesting that microporous silica nanoparticles allow a way to probe silica water interactions at the molecular scale.

Allosteric activation of the nitric oxide receptor soluble guanylate cyclase mapped by cryo-electron microscopy

Soluble guanylate cyclase (sGC) is the primary receptor for nitric oxide (NO) in mammalian nitric oxide signaling. We determined structures of full-length Manduca sexta sGC in both inactive and active states using cryo-electron microscopy. NO and the sGC-specific stimulator YC-1 induce a 71° rotation of the heme-binding β H-NOX and PAS domains. Repositioning of the β H-NOX domain leads to a straightening of the coiled-coil domains, which, in turn, use the motion to move the catalytic domains into an active conformation. YC-1 binds directly between the β H-NOX domain and the two CC domains. The structural elongation of the particle observed in cryo-EM was corroborated in solution using small angle X-ray scattering (SAXS). These structures delineate the endpoints of the allosteric transition responsible for the major cyclic GMP-dependent physiological effects of NO.

In humans and other animals, as the heart pumps blood around the body, the blood exerts pressure on the walls of the blood vessels, much like water flowing through a hose. Our blood pressure naturally varies over the day, generally increasing when we are active and decreasing when we rest. However, if blood pressure remains high for extended periods of time it can lead to heart attacks, strokes and other serious health conditions.

In 2013, a new drug known as Adempas was approved to treat high blood pressure in the lungs. This drug helps a signaling molecule in the body called nitric oxide to activate an enzyme that widens blood vessels and in turn lower blood pressure. Previous studies have found that the enzyme – called soluble guanylate cyclase (sGC) – contains several distinct domains and that nitric oxide binds to a domain known as β H-NOX. However, it was not clear how β H-NOX and the other three domains fit together to make the three-dimensional structure of the enzyme, or how nitric oxide and Adempas activate it.

To address this question, Horst, Yokom et al. used a technique called cryo-electron microscopy to determine the three-dimensional structures of the inactive and active forms of a soluble guanylate cyclase from a moth known as Manduca sexta. To produce the active form of the enzyme, soluble guanylate cyclase was incubated with both nitric oxide and a molecule called YC-1 that works in similar way to Adempas. The structures revealed that nitric oxide and YC-1 caused β H-NOX and another domain to rotate by 71. This in turn caused the remaining two domains – known as the coiled-coil domains – to change shape, and all of these movements together led to the activated enzyme. The structures also revealed that YC-1 bound to a site on the enzyme between β H-NOX and the coiled-coil domains.

Understanding how a drug for a particular condition works makes it much easier to develop new drugs that are more effective at treating the same condition or are tailored to treat other diseases. Therefore, these findings will allow pharmaceutical companies and other organizations to develop new drugs for high blood pressure and other cardiovascular diseases in a much more precise way.

Structural basis for AcrVA4 inhibition of specific CRISPR-Cas12a

CRISPR-Cas systems provide bacteria and archaea with programmable immunity against mobile genetic elements. Evolutionary pressure by CRISPR-Cas has driven bacteriophage to evolve small protein inhibitors, anti-CRISPRs (Acrs), that block Cas enzyme function by wide-ranging mechanisms. We show here that the inhibitor AcrVA4 uses a previously undescribed strategy to recognize the L. bacterium Cas12a (LbCas12a) pre-crRNA processing nuclease, forming a Cas12a dimer, and allosterically inhibiting DNA binding. The Ac. species Cas12a (AsCas12a) enzyme, widely used for genome editing applications, contains an ancestral helical bundle that blocks AcrVA4 binding and allows it to escape anti-CRISPR recognition. Using biochemical, microbiological, and human cell editing experiments, we show that Cas12a orthologs can be rendered either sensitive or resistant to AcrVA4 through rational structural engineering informed by evolution. Together, these findings explain a new mode of CRISPR-Cas inhibition and illustrate how structural variability in Cas effectors can drive opportunistic co-evolution of inhibitors by bacteriophage.

Hydrothermal synthesis and characterization under dynamic conditions of cobalt oxide nanoparticles supported over magnesium oxide nano-plates

Surface evolution of a nano-catalyst comprised of oxidized Co NPs and MgO nano-plates was studied under O₂, H₂ and H₂ + CO atmospheres using synchrotron-based X-ray spectroscopies.

Association between coronary heart disease and cancers of the breast, prostate, and colon

Coronary heart disease (CHD) and cancers of the breast, prostate, and colon are more common in industrialized countries than in the developing world, and to some degree, these conditions appear to share risk factors. To investigate whether there is an association between these cancers and a prior history of CHD, a hospital-based case-control study was conducted at Columbia-Presbyterian Medical Center in New York. The study was based on 252 breast cancer cases, 256 colorectal cancer cases, and 322 benign surgical controls, all of whom underwent biopsy or surgery between January 1989 and December 1992, and on 319 prostate cancer cases and 189 benign prostatic hypertrophy controls diagnosed between January 1984 and December 1986 (prior to widespread use of prostate-specific antigen screening). Medical records were reviewed on each, focusing on the preoperative anesthesia and surgical clearances. No association was found between a history of CHD and breast or colorectal cancer, but an elevated risk was found for prostate cancer (odds ratio, 2.00; 95% confidence interval, 1.18-3.39), using unconditional logistic regression with adjustment for appropriate confounders. No association was found between cigarette smoking and any of the three cancers. Aspirin use was protective for colorectal cancer (odds ratio, 0.35; 95% confidence interval, 0.17-0.73) but had no association with breast or prostate cancer. The study suggests that individuals with CHD are at elevated risk for prostate cancer but not breast or colorectal cancer. Etiological risk factors associated with CHD should be investigated with regard to prostate cancer. Patients with CHD may represent a high-risk group for prostate cancer and potential future targets for prostate cancer screening interventions.

The role of cyclic nucleotides in guinea-pig bladder contractility

1. The effects of phosphodiesterase (PDE) inhibition and forskolin pretreatment on the contractile responses of guinea-pig urinary bladder strips to electrical field stimulation, carbachol, ATP and KCl were studied. 2. Inhibition of cyclic AMP-specific PDE4 isozymes by rolipram significantly reduced the contractile response of bladder strips to field stimulation. Rolipram also suppressed the contractile response to low concentrations of carbachol, but potentiated the response to high concentrations. The contractile response to ATP was significantly reduced by rolipram treatment, but that to KCl was unaltered. 3. Inhibition of cyclic GMP-specific PDE5 isozymes by zaprinast had no effects on the contractile response of bladder strips to field stimulation, ATP or KCl. Zaprinast suppressed the contractile responses to 1 microM carbachol and potentiated the response to high concentrations. 4. Contractile responses to field stimulation and to carbachol after pretreatment with the adenylyl cyclase activator, forskolin, were qualitatively similar to those caused by rolipram treatment. beta-Adrenoceptor blockade with propranolol partially reversed the inhibitory effects of rolipram on the response to field stimulation. 5. Rolipram significantly reduced the contractile response of bladder strips from sensitized guinea-pigs to ovalbumin challenge, but zaprinast was ineffective. PDE inhibition had similar effects on the responsiveness of control and of sensitized guinea-pig bladder strips to field stimulation, carbachol, ATP and KCl. 6. The data suggest that the contractile response of guinea-pig bladder strips can be modified by increases in cyclic AMP levels.

Diagnosis of postoperative bile leaks

Bile leaks are the most common biliary complication of laparoscopic cholecystectomy. Cholescintigraphy has been utilized in the past to diagnose postoperative bile leaks after open cholecystectomy. However, the sensitivity and specificity of this imaging technique has not been defined or compared to other clinical tests. We have retrospectively studied 30 patients over a 2-yr period who underwent cholescintigraphy for a possible postoperative bile leak. This study reviewed the cholescintigraphy images, clinical presentations, and abdominal ultrasonography/CT scanning. Using a gold standard that consisted of the findings of cholangiography and clinical outcome, we determined the diagnostic accuracy of these tests. Symptoms, laboratory testing, and physical examination were found to be poor predictors for the presence of postoperative bile leaks. Ultrasound and CT imaging were less sensitive and nonspecific. In contrast, cholescintigraphy was found to be quite accurate (83-87%) for predicting the presence of bile leaks after laparoscopic cholecystectomy, as well as other biliary surgeries.

Improved results of extracorporeal shock wave lithotripsy with the Dornier MPL 9000 for single gallstones

Our aim was to compare the results of extracorporeal shock wave lithotripsy with the Dornier MPL 9000 for patients with single radiolucent gallstones less than or equal to 20-mm diameter using higher power (kV) and more shock waves during lithotripsy with our results during the Dornier National Biliary Lithotripsy Study using lower power and fewer shock waves. Nineteen patients were treated at higher power (mean +/- SE, 21.0 +/- 0.4 kV) vs 11 patients at lower power (18.8 +/- 0.5 kV). In the higher power group, the actuarial rate for complete clearance of gallstone fragments was 39 +/- 9%, 63 +/- 9% and 78 +/- 9% after 6 weeks, 3- and 6-months follow-up, respectively, versus only 19 +/- 12% after 6 months in the lower power group. We conclude that the use of higher power and more shock waves during extracorporeal shock wave lithotripsy with the MPL 9000 results in fragment clearance rates over 6 months for patients with single gallstones that are significantly higher than those previously achieved in the Dornier National Biliary Lithotripsy Study.

Dental health of homeless adults

As part of a community-based study, we were able to assess the number of grossly decayed and missing teeth, as well as recent use of dental services, among 529 homeless adults. We found that 27% reported having had a toothache during the previous month (only one-tenth of these individuals had sought help from a dentist for their toothache). Homeless adults, as compared with a general population, were half as likely to have made a dental visit within the preceding year (26.7% versus 55.0%) and had more grossly decayed teeth (means = 2.3 versus means = 1.4). Individuals with more tooth decay and missing teeth were more likely to be older, have physical health problems, smoke more cigarettes, use more alcohol, and have worse personal hygiene. Age, not length of homelessness, was the most important predictor variable of missing teeth. Thus, homeless adults have a higher degree of dental pathosis as well as a lower use of dental services than the general population. On the basis of these findings, more accessible dental services need to be designed for the homeless population.

Estimating treatment and treatment times for special and nonspecial patients in hospital ambulatory dental clinics

Increased time to treat the special patient is often cited as a barrier to dental care. The purpose of this study was to analyze the separate and combined effects of differences in dental services planned, services actually performed, and differences in treatment time requirements between special and nonspecial patients in a hospital ambulatory clinical setting. Data for this study were obtained from the UCLA evaluators of the RWJ-funded Hospital-Sponsored Ambulatory Dental Services Program (HSADSP). The results show that special patients require more dental treatment than nonspecial patients for advanced dental disease (i.e., periodontics, surgery, and removable prosthetics) and that they receive more of such services. The study also found that special patients should not be viewed as a homogeneous group when evaluating dental needs and required time resources for treatment. Three subgroups of special patients were identified: developmentally disabled, severely compromised, and moderately compromised. The developmentally disabled as compared to the nonspecial patients required significantly more (20 percent) provider time in completing a "representative" treatment plan.

Prevalence of anxiety disorder among alcoholics

A preliminary study of the prevalence of DSM-III anxiety disorders in a group of inpatients treated for alcohol detoxification is presented. The rating was performed in accordance with the Structured Clinical Interview for DSM-III (SCID). The results showed that nineteen of 84 subjects (22.6%) met criteria for one or more anxiety disorders. In 12 of these subjects drinking followed the onset of anxiety by as long as 19 years. No conclusions can be drawn about the etiologic role of anxiety in alcoholism. However, to the extent that patients with treatable phobic and anxious states can be identified, there is a potential for prevention of alcoholism in some of these individuals.