Aqueously altered igneous rocks sampled on the floor of Jezero crater, Mars

The Perseverance rover landed in Jezero crater, Mars, to investigate ancient lake and river deposits. We report observations of the crater floor, below the crater's sedimentary delta, finding the floor consists of igneous rocks altered by water. The lowest exposed unit, informally named Séítah, is a coarsely crystalline olivine-rich rock, which accumulated at the base of a magma body. Fe-Mg carbonates along grain boundaries indicate reactions with CO₂-rich water, under water-poor conditions. Overlying Séítah is a unit informally named Máaz, which we interpret as lava flows or the chemical complement to Séítah in a layered igneous body. Voids in these rocks contain sulfates and perchlorates, likely introduced by later near-surface brine evaporation. Core samples of these rocks were stored aboard Perseverance for potential return to Earth.

A221 CLINICAL CHARACTERISITICS OF PORTAL VEIN THROMBOSIS AMONG AN INPATIENT COHORT WITH CIRRHOSIS

Background

Portal vein thrombosis (PVT) has a reported prevalence ranging from 0.6 to 26% in cirrhotic patients and yet optimal management in these patients remains unclear [1]. PVT can lead to poor outcomes including increased risk of bleeding, intestinal injury, and deterioration in liver function. Conversely, treatment of PVT in cirrhotic patients increases their risk of bleeding complications, particularly in patients with known varices.

Aims

The aim of this study is to better characterize the prevalence and impact of PVT in cirrhotic inpatients.

Methods

We conducted a retrospective cohort study based on data collected on adult patients admitted to the Ottawa Hospital between January 1, 2011 and December 31, 2015. We included patients with a diagnosis of cirrhosis either before or during index admission. Patients with a radiology report indicating a PVT were compared to those without PVT. Non-Ontario residents were excluded and where there were multiple admissions per patient one admission was randomly selected to be used. Ethics approval was obtained from the Research Ethics Board at the University of Ottawa.

Results

This study found 34 patients with cirrhosis diagnosed with PVT during their hospitalization (3.73%). Of the patients with PVT, 23 were acute and 11 were chronic based on radiologic appearance. Mean age was similar between groups (PVT: 61.7, SD=9.8; No PVT: 62.3, SD=12.3). The mean Na-MELD was also similar (PVT: 17.6, no PVT: 17.3, p=0.82). Among patients with PVT, 11 patients presented with ascites, 10 with hepatic encephalopathy (HE), 5 with abdominal pain and 5 with an upper GI bleed. Spontaneous bacterial peritonitis (SBP) occurred in 11.76% of patients with PVT as compared to 3% of patients without PVT (p value= 0.006). There also seemed to be a trend towards more HE in the cohort with PVT (20.6% vs 10.7%, p value= 0.07). With regards to screening for varices, 2 patients had an EGD in the 6 months prior to admission, 11 had an EGD on admission, 1 after anticoagulation due to bleeding, and 18 had no screening in the 6 months prior to admission. Twelve patients were treated for PVT, 17 were untreated and 5 did not have documentation about treatment. Of the patients that were not treated, 9 were due to palliative goals of care, 1 due to bleeding, 1 due to thrombocytopenia, 2 due to chronicity on imaging and 4 did not have reasons documented.

Conclusions

PVT is a known complication of cirrhosis, however the clinical significance and optimal management of patients with PVT is poorly understood. Although prevalence of PVT was low in this cohort, our data suggests some possible association between liver related complications and PVT, including SBP and HE. Further research is needed to determine how to best manage patients with PVT.

1. Garcia-Pagan JC, Valla DC. Portal vein thrombosis: a predictable milestone in cirrhosis? Journal of hepatology. 2009 Oct 1;51(4):632–4.

Funding Agencies

None

A153 INCIDENCE OF DEEP VEIN THROMBOSIS (DVT) & PROPHYLAXIS PRACTICES IN DECOMPENSATED CIRRHOSIS INPATIENTS

Background

The coagulation cascade is disturbed in cirrhosis. Patients are at risk for bleeding and coagulation through an imbalance of pro and anticoagulant factors.

Aims

We evaluated the incidence of DVTs and prevalence of DVT prophylaxis in hospitalized patients with decompensated cirrhosis.

Methods

A retrospective study of decompensated cirrhotic patients admitted to a tertiary care hospital. We evaluated the incidence of DVTs and use of DVT prophylaxis in this cohort. We also evaluated differences in patient characteristics in those who received DVT prophylaxis and between patients who did or did not develop DVTs.

Results

This study consisted of 520 cirrhotic patients, of which 258 patients (49.6%) received DVT prophylaxis. Of the remaining 262 patients who did not receive DVT prophylaxis, 199 (75.9%) had a documented contraindication to prophylaxis (bleeding, thrombocytopenia, both, or other). Compared to patients without DVT prophylaxis, patients who received prophylaxis were older (61.2 ± 11.2 vs 56.6 ± 10.9, p= 0.00001), had less varices (16.2% vs. 46%, p=0.0048), had more severe liver disease (MELD-Na 21 ± 6.5 vs 19.7 ± 7.3, p = 0.032), and fewer incidents of variceal (3.4% vs. 35.1%, p <0.001) and non-variceal (5.4% vs. 17.1%, p <0.001) gastrointestinal bleeding. DVT prophylaxed patients also had higher mean platelet values (149 ± 89 vs 112 ± 84, p <0.001), but similar baseline INRs (1.6 ± 0.4 vs 1.7 ± 0.8, p= 0.16), and were more likely to be admitted for non-bleeding complications of liver disease, including incidence of hepatic encephalopathy (37.9% vs 25.1%, p = 0.002) and spontaneous bacterial peritonitis (12.1% vs 6.5%, p=0.029). The incidence of radiographically identified DVT events in cirrhotic patients receiving DVT prophylaxis and those not receiving DVT prophylaxis was similar at 1.1 and 0.7%, respectively (OR 1.52, 95% CI 0.254 to 9.1, p = 0.65). There was no difference in liver disease severity between those with DVTs to those who did not develop DVTs, including similar MELD-Na, INR, platelets and hemoglobin values. Compared to patients without DVTs, those who developed DVTs had a higher bilirubin (95.8 ± 78.0 vs. 64.1 ± 24, p = 0.202) and INR (2.1 ± 0.7 vs. 1.6 ± 0.6, p = 0.07), as well as lower platelets (81.8 ± 23.3 vs. 131.4 ± 88.9). These groups had comparatively similar MELD-Na, albumin, creatinine, and hemoglobin levels.

Conclusions

DVT prevalence in this cohort of decompensated liver disease patients was overall low. DVT prophylaxis rates were moderate overall, however taking into account perceived contraindications such as thrombocytopenia or bleeding, patients appeared to be appropriately prophylaxed when indicated. Further study is required to identify which cirrhotic patients are at highest risk for DVTs and the safety of prophylaxis among patients with deranged lab values such as low platelets and elevated INR.

Funding Agencies

None

A70 ASSOCIATION BETWEEN PROTON PUMP INHIBITOR USE IN HOSPITALIZED CIRRHOTICS AND DEVELOPMENT OF HEPATIC ENCEPHALOPATHY AND SPONTANEOUS BACTERIAL PERITONITIS

Background

Proton pump inhibitors (PPI) are commonly prescribed medications which are indicated in various different gastrointestinal (GI) diseases, including peptic ulcer disease, gastroesophageal reflux disorder and upper GI bleeding. There is some evidence to suggest that PPI use in cirrhosis may predispose to the development of hepatic encephalopathy (HE) and spontaneous bacterial peritonitis (SBP), albeit with some controversy.

Aims

We aim to conduct a retrospective epidemiological analysis of the association between PPI use in hospitalized patients with cirrhosis, and prevalence of HE and SBP.

Methods

This was a retrospective cohort study of 600 adult patients (mean age 61.4 (SD=12.2)) admitted the Ottawa Hospital between January 1, 2011 and December 31, 2015 with cirrhosis. A chart review was conducted and relevant information extracted.

Results

Average MELD-Na on admission was 16.2 (sd=6.7). 14.8% of patients had a history of HE, 5.0% SBP, 7.8% with history of hepatocellular carcinoma and 1.0% with history of hepatorenal syndrome. 28.5% of patients had a history of varices, of which 11.0% had previous variceal bleeding. 69.3% of patients were on a PPI during their hospitalization. Not surprisingly, patients admitted with variceal bleeding were more likely to be exposed to PPI in hospital (97.2% vs 63.2%, p<0.01) Patients with a diagnosis of cirrhosis prior to index admission were more likely to be on a PPI in hospital (p=0.001) and on discharge (p=0.001). Patients with ascites were less likely to be on a PPI than those without ascites (64.1% vs 77.6%, p<0.01). There was no significant correlation between in hospital PPI use and MELD score (p=0.42). Amongst patients on PPI in hospital, 85.9% remained on a PPI at discharge. Although numerically greater, no statistically significant differences were observed in terms of prevalence of HE (21.3% in patients on PPI vs 8.3% in those not on PPI (p=0.37)), nor SBP (5.7% on PPI vs. 3.7% in those not on PPI (p=0.29)).

Conclusions

We did not observe a significant difference in HE and SBP among this cohort of cirrhotic patients by in-hospital PPI use. We did however note significantly higher PPI use in patients with previous diagnosis of cirrhosis as compared to those who were newly diagnosed, as well as those whose admissions were related to bleeding. Patients with ascites had lower prevalence of PPI use. Prescribing patterns for PPIs in patients with cirrhosis warrant further attention, including clinical utility and longer-term risks and benefits of this therapy.

Funding Agencies

None

The Development of Integration in Marsupial and Placental Limbs

The morphological interdependence of traits, or their integration, is commonly thought to influence their evolution. As such, study of morphological integration and the factors responsible for its generation form an important branch of the field of morphological evolution. However, most research to date on post-cranial morphological integration has focused on adult patterns of integration. This study investigates patterns of correlation (i.e., morphological integration) among skeletal elements of the fore- and hind limbs of developing marsupial and placental mammals. The goals of this study are to establish how patterns of limb integration vary over development in marsupials and placentals, and identify factors that are likely responsible for their generation. Our results indicate that although the overall pattern of correlation among limb elements is consistent with adult integration throughout mammalian development, correlations vary at the level of the individual element and stage. As a result, the relative integration among fore- and hind limb elements varies dynamically between stages during development in both marsupial and placental mammals. Therefore, adult integration studies of the limbs may not be indicative of developmental integration. Results are also consistent with integration during early limb development being more heavily influenced by genetic and developmental factors, and later by function. Additionally, results are generally consistent with a constraint on marsupial forelimb evolution caused by the functional requirements of the crawl to the teat that operates by limiting morphological variation before and at the time of birth, and not after.

Autophagic dysfunction and autophagosome escape in the mdx mus musculus model of Duchenne muscular dystrophy

AIM

Duchenne muscular dystrophy is caused by the absence of functional dystrophin protein and results in a host of secondary effects. Emerging evidence suggests that dystrophic pathology includes decreased pro-autophagic signalling and suppressed autophagic flux in skeletal muscle, but the relationship between autophagy and disease progression is unknown. The purpose of this investigation was to determine the extent to which basal autophagy changes with disease progression. We hypothesized that autophagy impairment would increase with advanced disease.

METHODS

To test this hypothesis, 7-week-old and 17-month-old dystrophic diaphragms were compared to each other and age-matched controls.

RESULTS

Changes in protein markers of autophagy indicate impaired autophagic stimulation through AMPK, however, robust pathway activation in dystrophic muscle, independent of disease severity. Relative protein abundance of p62, an inverse correlate of autophagic degradation, was dramatically elevated with disease regardless of age. Likewise, relative protein abundance of Lamp2, a lysosome marker, was decreased twofold at 17 months of age in dystrophic muscle and was confirmed, along with mislocalization, in histological samples, implicating lysosomal dysregulation in this process. In dystrophic muscle, autophagosome-sized p62-positive foci were observed in the extracellular space. Moreover, we found that autophagosomes were released from both healthy and dystrophic diaphragms into the extracellular environment, and the occurrence of autophagosome escape was more frequent in dystrophic muscle.

CONCLUSION

These findings suggest autophagic dysfunction proceeds independent of disease progression and blunted degradation of autophagosomes is due in part to decreased lysosome abundance, and contributes to autophagosomal escape to the extracellular space.

Abstract P5-11-02: Breast Cancer Radiation Therapy and the Risk of Developing Bronchiolitis Obliterans Organizing Pneumonia (BOOP): Communication of BOOP Risk by Breast Cancer Information Websites and General Medical Information Websites

Background: BOOP is an inflammatory pulmonary disorder consisting of organized polypoid granulation tissue in the distal airways extending into the alveolar ducts and alveoli. Clinical manifestations of BOOP include fever, cough, dyspnea on exertion, and fatigue. Patients with severe BOOP require hospitalization. The mainstay of BOOP treatment is high dose corticosteroids. Many patients relapse and require long term corticosteroids, often in combination with another immunosuppressant. Significant morbidity and disability may be associated with both the diagnosis of BOOP and the toxicities of treatment. The mortality rate of BOOP has been estimated to be about 5%.

Radiation Therapy (RT) is an important component in the treatment of breast cancer (Breast Ca). Beginning in 1995, reports of BOOP occurring in Breast Ca RT patients began to appear in the medical literature. From 1995 to the present, 43 case study reports described 121 Breast Ca RT patients who developed BOOP within one year of their RT. From 1999 to 2011, seven epidemiological studies were published that suggested that the incidence of BOOP in Breast Ca RT patients was in the range of 2% to 3%.

Objectives: The primary objective of this study was to determine if internet sources of Breast Ca information targeted to Breast Ca patients include BOOP information in their description of RT risks. The secondary objective was to determine if general medical websites conveyed BOOP/Breast Ca RT risk information.

Methods: Eight websites specifically targeted to Breast Ca patients were reviewed. Sponsors of these websites included the US government, Breast Ca advocacy groups, and medical organizations. Seven general medical websites that contained BOOP/Breast Ca RT information were also reviewed.

Results: There was no mention of BOOP in any of the websites targeted to Breast Ca patients. The websites included those from the National Cancer Institute, American Cancer Society, American Society of Therapeutic Radiology and Oncology, Susan G. Komen, and BreastCancer.org. The internet search identified seven general medical websites that did include information about the risk of BOOP from Breast Ca RT.

Discussion: It is perplexing that none of the eight website sources for Breast Ca patients included any mention of the risk of BOOP associated with Breast Ca RT, whereas seven general medical internet sources did disclose this information. This disparity raises important issues and questions. The majority of BOOP/Breast Ca RT reports were published in pulmonology journals. Is this information being disseminated to providers of Breast Ca treatment? Many of the Breast Ca information websites stated that their information was up to date and was reviewed by leading Breast Ca physicians, so it remains an enigma that the BOOP/RT association was not disclosed. The lack of any information about BOOP and Breast Ca RT may indicate Breast Ca physician unawareness. An alternative explanation for this finding may be that these physicans are aware of the BOOP/RT association, but they believe that the rarity of BOOP diagnoses justifies omitting this information in internet-based information sources.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P5-11-02.

Intermediates of the in vitro assembly and disassembly of southern bean mosaic virus

Southern bean mosaic virus (SBMV) was swollen by treatment with EDTA at pH 7.5 and dissociated into RNA and protein in 1 M NaCl. Aliquots of this preparation were diluted with appropriate buffers to obtain samples in varying concentrations of NaCl, and components of these samples were sedimented through sucrose solutions and dissolved in 0.01 M Tris-HCI buffer, pH 7.5. The protein content and sedimentation properties of components in these preparations were determined. When the NaCl molarity in the treatment exceeded 0.6 M the preparations contained RNA with approximately six protein subunits per SBMV RNA molecule. The protein content of the preparations increased from 30 protein subunits per RNA molecule to 145 protein subunits per RNA molecule as the NaCl molarity used in the treatment was decreased from 0.5 to 0.1 M. The positions of sedimentation of components in these preparations in density gradient centrifugation were intermediate between those of RNA and EDTA-swollen virus. The sedimentation rate of these assembled components increased as the NaCl molarity used in the treatment was decreased. Similar components were assembled when preparations of RNA and protein dissociated from SBMV by dialysis in neutral buffers containing EDTA and 1 M NaCl were diluted to lower NaCl molarities. When SBMV was swollen by treatment with EDTA and dissociated in various concentrations of NaCl, the components formed were similar to those obtained by assembly in the same NaCl molarities. Preparations in the pH 7.5 buffer contained single components which sedimented at 56 S, 55 S, 54 S, 51 S, 46 S, 38 S, 33 S, and 24 S. With the exception of the 24 S component, components formed by disassembly in the same NaCl molarities and dissolved in pH 5.0 buffer sedimented faster.

Audit of the management of patients admitted with community acquired pneumonia

Community acquired pneumonia (CAP) is a major cause of morbidity and mortality worldwide. There is evidence that guidelines do guide and standardise management, but with less measurable effect on outcome. We prospectively audited the management of CAP in patients admitted to a Dublin hospital during the winter of 2003/04. The main objective was to evaluate the quality of care for CAP using the BTS guidelines as a standard of management. 164 patients were admitted with CAP during the defined period. Guidelines for assessment of disease severity at presentation were followed in only 56 (34.1%) cases. Appropriate antibiotic therapy was instituted within 8 hours of presentation in 123 (75.0%) cases. The rate of use of a severity assessment score to stratify patients with CAP based on recognized guidelines is low in our hospital. Despite this, the overall mortality rate of 8.5% is comparable with previous results.

Correlates of HIV risk-taking behaviors among African-American college students: the effect of HIV knowledge, motivation, and behavioral skills

This study identifies theoretically based predictors of condom use in a sample of 253 sexually active African-American college students recruited from two historically African-American colleges. The Information-Motivation-Behavioral (IMB) skills model of AIDS-preventive behavior was employed to delineate the roles of HIV/AIDS knowledge, experiences with and attitudes toward condom use, peer influences, perceived vulnerability, monogamy, and behavioral skills. A predictive structural equation model revealed significant predictors of more condom use including: male gender, more sexual HIV knowledge, positive experiences and attitudes about condom use, nonmonogamy, and greater behavioral skills. Results imply that attention to behavioral skills for negotiating safer sex and training in the proper use of condoms are key elements in reducing high risk behaviors. Increasing the specific knowledge level of college students regarding the subtleties of sexual transmission of HIV is important and should be addressed. Heightening students' awareness of the limited protection of serial monogamy, and the need to address gender-specific training regarding required behavior change to reduce transmission of HIV should be an additional goal of college health professionals.

Activity of intrinsic laryngeal muscles in fluent and disfluent speech

The goal of the present experiment was to determine if stuttering is associated with unusually high levels of activity in laryngeal muscles. Qualitative and quantitative analyses of thyroarytenoid and cricothyroid recordings from 4 stuttering and 3 nonstuttering adults revealed the following: Compared to periods of fluent speech, intervals of disfluent speech are not typically characterized by higher levels of activity in these muscles; and when EMG levels during conversational speech are compared to maximal activation levels for these muscles (e.g., those observed during singing and the Valsalva maneuver), normally fluent adults show robust and sometimes near maximal recruitment during conversational speech. The adults who stutter had a lower operating range for these muscles during conversational speech, and their disfluencies did not produce relatively high activation levels. In summary, the present data require us to reject the claim that adults with a history of chronic stuttering routinely produce excessive levels of intrinsic laryngeal muscle activity. These results suggest that the use of botulinum toxin injections into the vocal folds to treat stuttering should be questioned.

Orofacial muscle activity of children who stutter: a preliminary study

This study was a preliminary investigation of the relations between stuttering development and the maturation of speech motor processes. Electromyographic (EMG) activity was recorded from the orofacial muscles of children who stutter and their normally fluent peers during fluent and disfluent speech. Nine children who stutter (8 boys and 1 girl), ranging in age from 2:7 to 14:0, and 9 age- and sex-matched children who do not stutter were subjects. Pairs of surface EMG electrodes were placed on children's faces overlying the anterior belly of the digastric (ABD), levator labii superior (ULIP), and orbicularis oris inferior (LLIP) muscles. Twenty segments of stuttered (for the children who stutter) and perceptually fluent speech were extracted from children's conversational speech samples. Spectra of the amplitude envelopes of the EMG activity were computed. The 3 oldest children who stutter showed evidence of tremorlike oscillations of EMG activity in the 5 to 15 Hz range during stuttering in either ULIP, LLIP, or ABD muscles. The younger children who stutter and the children who do not stutter demonstrated primary spectral peaks in the 1 to 4 Hz range during stuttered and/or perceptually fluent speech. It is hypothesized that the emergence of tremorlike instabilities in the speech motor processes of children who stutter may coincide with aspects of their general neural maturation and with the development of stuttering.

Parents as partners: including mothers and fathers in the treatment of children who stutter

Parents are frequently included in our intervention methods with children who stutter. However, if we examine the research and clinical literature, we find that we do not distinguish between the roles of mothers and fathers in our diagnosis and intervention procedures. Evidence that mothers and fathers may differ in their interactions with children, in general, and children who stutter, in particular, will be presented. Implications of these findings for our clinical practices will be discussed. By doing so, a case will be made for including both mothers and fathers as partners in the treatment of children who stutter.

Speech rates and turn-taking behaviors of children who stutter and their fathers

Paralinguistic behaviors, including speech rates and turn-taking behaviors, of boys who stutter and boys who do not stutter and their fathers were investigated. Subjects were 11 boys who stutter (mean age = 5:1) and their fathers and 11 age-matched (+/- 3 months) nonstuttering boys (mean age = 5:1) and their fathers. Spontaneous conversational speech was obtained from each father and son during approximately 45 minutes of videotaped free play in a clinic setting. Measures of overall, articulatory, and dyadic speaking rates, interruptions, response time latencies, and disfluency characteristics were derived using the videotapes and computer-assisted analyses of the acoustic signal from each conversational sample. Two-factor repeated measures ANOVAs were performed on each of the paralinguistic variables for the 11 sets of age-matched father-son pairs. Fathers produced faster speaking rates, higher frequencies of interruptions and shorter response time latencies than sons. No significant differences were found in comparisons of the two groups of fathers or of the two groups of children for any of the paralinguistic behaviors. A significant positive correlation was found between the SSI scores of children who stutter and the dyadic speaking rates of these children and their fathers. Results partially extend those of Kelly and Conture (1992) for mothers and children, but some potentially important differences emerge between fathers' and mothers' (para)linguistic behaviors in interaction with their children.

Specific-locus experiments show that female mice exposed near the time of birth to low-LET ionizing radiation exhibit both a low mutational response and a dose-rate effect

Female mice were exposed to 300 R of 73-93 R/min X-radiation either as fetuses at 18.5 d post conception (p.c.) or within 9 h after birth. Combining the similar results from these two groups yielded a specific-locus mutation frequency of 9.4 X 10(-8) mutation/locus/R, which is statistically significantly higher than the historical-control mutation frequency, but much lower than the rate obtained by irradiating mature and maturing oocytes in adults. Other females, exposed at 18.5 days p.c. to 300 R of 0.79 R/min gamma-radiation, yielded a mutation frequency that was statistically significantly lower than the frequency at high dose rates. The low-dose-rate group also had markedly higher fertility. It appears that the dose-rate effect for mutations induced near the time of birth may be more pronounced than that reported for mature and maturing oocytes of adults. A hypothesis sometimes advanced to explain low mutation frequencies recovered from cell populations that experience considerable radiation-induced cell killing is that there is selection against mutant cells. The reason for the relatively low mutational response following acute irradiation in our experiments is unknown; however, the finding of a dose-rate effect in these oocytes in the presence of only minor radiation-induced cell killing (as judged from fertility) makes it seem unlikely that selection was responsible for the low mutational response following acute exposure. Had selection been an important factor, the mutation frequency should have increased when oocyte killing was markedly reduced.

Interferometric ether-drift experiment nullified by resynchronization of observer's clocks

In the Marinov coupled rotating-mirror-interferometer experiment [Czech. J. Phys. B 24, 965 (1974)], a comoving observer must synchronize his clocks after an acceleration. As a result of the resynchronization, the mirrors, according to the observer, reach their fiducial points at different times. The observer interprets this as a twist in theapparatus; when this is corrected by adjusting a mirror, a null result follows.

An assessment of the treatment needs of Vietnam-era veterans

A needs assessment was conducted to determine the existence and extent of differences between Vietnam-era veterans and other veterans residing within the catchment area of the Northport Veterans Administration Medical Center. The results of a questionnaire completed by 486 veterans indicated that, compared with World War II and Korean War veterans, a greater percentage of Vietnam-era veterans reported experiencing the symptoms of posttraumatic stress disorder. They also reported more situational adjustment problems. A great number of Vietnam-era veterans expressed a need for psychotherapy and anger-control therapy, and they generally preferred to be treated with other Vietnam-era veterans who have had similar combat experience.

Mutation frequencies in male mice and the estimation of genetic hazards of radiation in men

Estimation of the genetic hazards of ionizing radiation in men is based largely on the frequency of transmitted specific-locus mutations induced in mouse spermatogonial stem cells at low radiation dose rates. The publication of new data on this subject has permitted a fresh review of all the information available. The data continue to show no discrepancy from the interpretation that, although mutation frequency decreases markedly as dose rate is decreased from 90 to 0.8 R/min (1 R = 2.6 x 10(-4) coulombs/kg) there seems to be no further change below 0.8 R/min over the range from that dose rate of 0.0007 R/min. Simple mathematical models are used to compute: (a) a maximum likelihood estimate of the induced mutation frequency at the low dose rates, and (b) a maximum likelihood estimate of the ratio of this to the mutation frequency at high dose rates in the range of 72 to 90 R/min. In the application of these results to the estimation of genetic hazards of radiation in man, the former value can be used to calculate a doubling dose--i.e, the dose of radiation that induces a mutation frequency equal to the spontaneous frequency. The doubling dose based on the low-dose-rate data compiled here is 110 R. The ratio of the mutation frequency at low dose rate to that at high dose rate is useful when it becomes necessary to extrapolate from experimental determinations, or from human data, at high dose rates to the expected risk at low dose rates. The ratio derived from the present analysis is 0.33.

Specific-locus mutation frequencies in mouse stem-cell spermatogonia at very low radiation dose rates

Experiments were undertaken to augment the information on the lowest radiation dose rates feasible for scoring transmitted induced mutations detected by the specific-locus method in the mouse. This is the type of information most suitable for estimating genetic hazards of radiation in man. The results also aid in resolving conflicting possibilities about the relationship between mutation frequency and radiation dose rate at low dose rates. There was no statistically significant difference between mutation frequencies obtained in spermatogonia with 300 R (1 R = 2.6 x 10(-4) coulombs/kg) of gamma radiation at two different dose rates, 0.005 and 0.0007 R/min, or between either of these frequencies and data obtained earlier at dose rates of 0.8 R/min and below. This supports the view in an earlier publication by one of us (W.L.R.) that, at approximately 0.8 R/min and below, mutation frequency is independent of dose rate. Because this independence is now shown to extend over the more than 1000-fold range from 0.8 to 0.0007 R/min, it seems likely that it would hold at still lower dose rates, perhaps even to the much lower dose rates encountered in most human exposures.

Comparison of highly basic cyanogen bromide peptides from strains of southern bean mosaic virus

Electrophoresis patterns of cyanogen bromide (CNBr) peptides from the proteins of the cowpea (SBc), bean (SBb), Mexican (SBm), and Ghana (SBg) strains of southern bean mosaic virus showed a marked similarity between SBc and SBg and between SBb and SBm. A highly basic CNBr peptide from SBc, cCB-1, was isolated by Sephadex and ion-exchange chromatography. The size and amino acid composition of cCB-1 was similar but differed from that of the N-terminal CNBr peptide bCB-1 from SBb described previously.Antisera to cCB-1 or bCB-1 conjugated to tomato bushy stunt virus (TBSV) were used in gel diffusion tests with virus particles of the four SB strains. With the bCB-1–TBSV conjugate antiserum, SBb gave a reaction of identity with SBm and reactions of partial identity with SBc and SBg. With the cCB-1–TBSV conjugate antiserum, SBc gave a reaction of identity with SBg and reactions of partial identity with SBb and SBm. Cross absorption of bCB-1–TBSV conjugate antiserum with TBSV yielded an antiserum that reacted with SBb but not with TBSV. Cross absorption with bCB-1 yielded an antiserum that reacted with TBSV but not with SBb.Limited tryptic proteolysis of SBc in 0.01 M sodium phosphate buffer containing 0.01 M ethylenediaminetetraacetic acid, pH 8.0, resulted in the formation of viruslike particles and smaller spherical particles. Sixteen peptides were isolated from these digests and the compositions of most of them were similar to but not identical to peptides isolated from limited tryptic proteolysis of SBb.

Chemical and serological properties of a cyanogen bromide peptide of southern bean mosaic virus protein

Southern bean mosaic virus (SBMV) protein was cleaved with cyanogen bromide and a highly basic peptide, CB-1, was isolated by ion exclusion and ion-exchange chromatography. Twelve peptides were separated from a tryptic digest of CB-1 by ion-exchange chromatography and the composition of these peptides was similar to that of peptides released from EDTA-swollen virus particles by limited tryptic digestion. The composition and N-termini of the tryptic peptides indicated CB-1 was from the N-terminus of SBMV protein and contained 48 amino acid residues. The CB-1 peptide moved rapidly to the cathode in polyacrylamide gel electrophoresis at pH 3.9 and contained nine arginine residues, three lysine residues, and no acidic amino acid residues. It was shown to interact with purified viral RNA, sodium dextran sulfate, and calf thymus DNA. Antiserum to sodium dodecyl sulfate (SDS)-dissociated virus gave a reaction of partial identity between the CB-1 peptide and the SDS-dissociated virus in SDS gel diffusion tests. The CB-1 peptide did not react with antiserum to SDS-dissociated, trypsin-treated virus. Gel diffusion tests conducted in saline agar gels between trypsin-treated virus and SBMV, with SBMV antiserum, did not show differences in their serological properties. Antiserum to the CB-1 peptide conjugated to tomato bushy shunt virus reacted with SBMV but SBMV antiserum did not react with CB-1 or the CB-1-tomato bushy shunt virus conjugate.

Specific-locus test shows ethylnitrosourea to be the most potent mutagen in the mouse

Use of the specific-locus test to measure the frequency of transmitted gene mutations induced in mouse spermatogonia has shown ethylnitrosourea to be by far the most potent mutagen yet discovered in the mouse. The dose used, 250 mg/kg, gave a mutation rate 5 times as high as had been obtained with 600 R, the most effective acute dose of x-rays. Compared to procarbazine, heretofore the most mutagenic chemical known in the mouse, ethylnitrosourea proved to be 15 times more mutagenic than the peak effect obtained with the most effective dose of procarbazine. Because of its high mutagenicity, ethylnitrosourea can serve as a model compound in exploring the effect of such factors as dose response, dose fractionation, sex, and cell stage on the mutagenic action of a chemical. Ethylnitrosourea is clearly the mutagen of choice for the production of any kind of desired new gene mutations in the mouse.

Analysis of the albino-locus region of the mouse. I. Origin and viability

Numerous specific-locus experiments designed to test the mutagenic effect of external radiation have yielded, in over 3,600,000 animals observed, altogether 119 presumed mutations involving the c locus. Of these, 55 were viable and albino (cav), 13 were viable and of various intermediate pigment types (cxv), four were subvital (cas and cxs), seven were neonatally lethal albinos (cal), 28 prenatally lethal albinos (cal); 12 died untested. All of the prenatally lethal and at least one of the neonatally lethal c-locus mutations (cal classes) are probably deficiencies that we have analyzed extensively in other experiments. Since absence of the locus mimics albino in phenotype, the intermediates (cxv and cxs groups) probably resulted from intragenic changes. The class of viable albino mutants (cav) might include, in addition to intragenic changes, some extremely small deficiencies. --The effects on viability of c-locus lethals (cal's) in heterozygous condition are not drastic enough to be perceived in stocks of mixed genetic background except in the case of the two longest known deficiencies and a few others. --Analysis of the relation between radiation treatment and type of c-locus mutants obtained shows that the relative frequency of viable mutations, for each germ-cell type, is greater for low-LET than for neutron irradiation; however, the difference for any individual cell type is not significant. The majority (66.7%) of mutations derived from X- or gamma-ray irradiated spermatogonia are viable, and the proportion of "intermediates" among these viables is similar to that among presumed spontaneous c-locus mutations. No significant dose-rate effect on the proportion of lethals could be demonstrated within the set of mutants induced by low-LET irradiation of spermatogonia. Although sets from other germ-cell stages are too small for statistical tests, the results for oocytes are similar, as far as they go. Furthermore, most of the c-locus mutations induced in spermatogonia, even by high-dose-rate X-ray or gamma irradiation, are of a type most likely to result from single-tract events (62% cxv, cxs, and cav; plus 16% presumed deficiencies not involving the closest marker). These results support the view that most of the reduction in mutation frequency at low dose rates is not due to a change in relative proportion of two-track and one-track ionizing events.

Contraction Hypothesis Consistent with the Kennedy-Thorndike Experiment

A Lorentz-Fitzgerald contraction augmented by an equal isotropic contraction gives a null result for all interferometric ether-drift experiments.