Development of a linear ion trap mass spectrometer capable of analyzing megadalton MALDI ions

Detecting megadalton matrix-assisted laser desorption/ionization (MALDI) ions in an ion trap mass spectrometer is a technical challenge. In this study, megadalton protein and polymer ions were successfully measured by MALDI linear ion trap mass spectrometer (LIT-MS) for the first time. The LIT-MS is comprised of a Thermo linear ion trap mass analyzer and a highly sensitive charge-sensing particle detector (CSPD). A newly designed radio frequency (rf) scan mode with dipolar resonance ejection techniques is proposed to extend the mass range of LIT-MS up to one million Thomson (Th). We analyze high mass ions with mass-to charge (m/z) ratios ranging from 100 kTh to 1 MTh, including thyroglobulin, alpha-2-macroglobulin, immunoglobulins (e.g., IgG and IgM), and polymer (∼ 940 kTh) ions. Besides, it is also very challenging for ion trap mass spectrometry to detect megadalton ions at low concentrations. By adopting high affinity carboxylated/oxidized detonation nanodiamonds (oxDNDs) to enrich IgM molecules and form antibody-nanodiamond conjugates, we have successfully reached ∼ 5 nM (5 μg/mL) concentration which is better than that by the other techniques.

High Mass Ion Detection with Charge Detector Coupled to Rectilinear Ion Trap Mass Spectrometer

Conventional linear ion trap mass analyzers (LIT-MS) provide high ion capacity and show their MS ⁿ ability; however, the detection of high mass ions is still challenging because LIT-MS with secondary electron detectors (SED) cannot detect high mass ions. To detect high mass ions, we coupled a charge detector (CD) to a rectilinear ion trap mass spectrometer (RIT-MS). Immunoglobulin G ions (m/z ~150,000) are measured successfully with controlled ion kinetic energy. In addition, when mass-to-charge (m/z) ratios of singly charged ions exceed 10 kTh, the detection efficiency of CD is found to be greater than that of SED. The CD can be coupled to LIT-MS to extend the detection mass range and provide the potential to perform MS ⁿ of high mass ions inside the ion trap. Graphical Abstract ᅟ.

Electron Rephasing in a Laser-Wakefield Accelerator

An important limit for energy gain in laser-plasma wakefield accelerators is the dephasing length, after which the electron beam reaches the decelerating region of the wakefield and starts to decelerate. Here, we propose to manipulate the phase of the electron beam in the wakefield, in order to bring the beam back into the accelerating region, hence increasing the final beam energy. This rephasing is operated by placing an upward density step in the beam path. In a first experiment, we demonstrate the principle of this technique using a large energy spread electron beam. Then, we show that it can be used to increase the energy of monoenergetic electron beams by more than 50%.

Measuring masses of large biomolecules and bioparticles using mass spectrometric techniques

Mass spectrometric techniques can measure the masses and fragments of large biomolecules and bioparticles.

Wavelet-based method for time-domain noise analysis and reduction in a frequency-scan ion trap mass spectrometer

We adopt an orthogonal wavelet packet decomposition (OWPD) filtering approach to cancel harmonic interference noises arising from an AC power source in time domain and remove the resulting rf voltage interference noise from the mass spectra acquired by using a charge detection frequency-scan quadrupole ion trap mass spectrometer. With the use of a phase lock resampling technique, the transform coefficients of the rf interference in signals become a constant, exhibiting a shift of the baseline in different rf phases. The rf interference is therefore removable by shifting the baselines back to zero in OWPD coefficients. The approach successfully reduces the time-domain background noise from 1367 electrons (rms) to 408 electrons (rms) (an improvement of 70 %) and removes the high frequency noise components in the charge detection ion trap mass spectrometry. Unlike other smoothing or averaging methods commonly used in the mass-to-charge (m/Ze) domain, our approach does not cause any distortion of original signals.

Cytomegalovirus drug resistance and clinical implications

Antiviral agents are commonly used for cytomegalovirus (CMV) prophylaxis or therapy after solid organ transplantation. Until recently, the detection of drug-resistant CMV in this setting was rare, but ganciclovir resistance has now been reported to occur in 5-10% of high-risk patient subsets, such as those undergoing primary CMV infection. Persistent viral shedding or progressive CMV disease after several weeks of antiviral therapy may indicate a problem with drug resistance, though laboratory testing is required to confirm this. Rapid genotypic assays for specific mutations in the viral UL97 phosphotransferase or UL54 DNA polymerase genes can be used to detect resistance and predict cross-resistance to other drugs. The emergence of drug resistance may be reduced by optimization of host immunity, use of potent antiviral drug regimens, and adherence to dosing regimens that adequately suppress viral replication.

Vastus medialis obliquus and vastus lateralis activity in open and closed kinetic chain exercises in patients with patellofemoral pain syndrome: an electromyographic study

OBJECTIVES

To evaluate the electromyographic activities of vastus medialis obliquus (VMO) and vastus lateralis (VL) muscles in open and closed kinetic chain exercises in subjects with patellofemoral pain syndrome (PFPS).

DESIGN

Case-controlled study.

SETTING

Rehabilitation science center in a tertiary medical center.

PARTICIPANTS

Ten patients with bilateral knee pain diagnosed with PFPS and 10 healthy volunteers.

INTERVENTIONS

Subjects performed open kinetic chain exercise on an isokinetic dynamometer and closed kinetic chain exercise by squat-to-stand and stand-to-squat tasks. Surface electromyography was done for the VMO and VL muscles.

MAIN OUTCOME MEASURES

VMO/VL ratios were calculated after normalization of muscle activities.

RESULTS

The VMO/VL ratios of PFPS subjects were significantly lower than were those of unimpaired subjects during knee isokinetic closed kinetic chain exercises (p = .047). However, there was no statistical difference in VMO/VL ratio between subjects with and without PFPS during closed kinetic chain exercises (p = .623). Maximum VMO/VL ratio was obtained at 60 degrees knee flexion in closed kinetic chain exercise.

CONCLUSION

In closed kinetic chain exercises, more selective VMO activation can be obtained at 60 degrees knee flexion. Maximal VMO/VL ratio was observed at this knee flexion angle, and muscle contraction intensity was also greatest.

Coordination exercise and postural stability in elderly people: Effect of Tai Chi Chuan

OBJECTIVE

To evaluate the effects of coordination exercise on postural stability in older individuals by Chinese shadow boxing, Tai Chi Chuan (TCC).

DESIGN

Cross-sectional study.

SETTING

Research project in a hospital-based biomechanical laboratory.

PARTICIPANTS

The TCC group (n = 25) had been practicing TCC regularly for 2 to 35 years. The control group (n = 14) included healthy and active older subjects.

INTERVENTION

Static postural stability test: progressively harder sequential tests with 6 combinations of vision (eyes open, eyes closed, sway-referenced) and support (fixed, sway-referenced); and dynamic balance test: 3 tests of weight shifting (left to right, forward-backward, multidirectional) at 3 speeds.

MAIN OUTCOME MEASURES

Static and dynamic balance of Sensory Organization Testing (SOT) of the Smart Balance Master System.

RESULTS

In static postural control, the results showed no differences between the TCC or control group in the more simple conditions, but in the more complicated SOT (eyes closed with sway surface, sway vision with sway surface), the TCC group had significantly better results than the control group. The TCC group also had significantly better results in the rhythmic forward-backward weight-shifting test. Duration of practice did not seem to affect the stability of elder people.

CONCLUSION

The elderly people who regularly practiced TCC showed better postural stability in the more challenged conditions than those who do not (eg, the condition with simultaneous disturbance of vision and proprioception). TCC as a coordination exercise may reduce the risk of a fall through maintaining the ability of posture control.

Motor control assessment for rhizotomy in cerebral palsy

OBJECTIVE

To apply motor control assessment for selection of appropriate spastic cerebral palsy children to receive selective posterior rhizotomy (SPR).

DESIGN

Forty children with spastic cerebral palsy (3-16 yr) were divided into three groups: "independent ambulator," "dependent ambulator," and "nonambulator." Another 18 healthy children were selected as the control group. Both motor control (tested by using polyelectromyography (PEMG)) and clinical ambulatory capability were assessed within 1 mo before SPR and 12 mo after. PEMG patterns were classified into seven patterns according to electromyographic activities during hip/knee flexion and extension. Gait patterns, which were analyzed by computer DynoGraphy, were classified into four patterns for children with ambulatory capability.

RESULTS

PEMG and gait patterns were correlated with ambulatory ability. PEMG patterns 2-3 could predict independent ambulatory ability, whereas patterns 6-7 will interfere with ambulatory ability. PEMG patterns showed significant improvement after SPR in the ambulatory groups (P < 0.05), whereas they did not improve in the nonambulator group. Children with cerebral palsy with co-contraction of proximal/distal muscles had better results after SPR, whereas those with diffuse co-contraction or reduced electromyography activities had poor results.

CONCLUSIONS

PEMG patterns may allow the physician to select the appropriate children with spastic cerebral palsy to receive SPR with good results.

The effect of ankle joint position and effort on quadriceps reflex sensitivity

OBJECTIVE

To investigate a possible ankle-knee synergy, experiments with normal subjects were performed to compare changes of the quadriceps motor pool excitability due to ankle position and effort.

METHODS

Vastus medialis H reflex amplitude was examined during ankle isometric contractions conditioned by different ankle positions (dorsiflexion, neutral, and plantarfiexion) with or without voluntary effort (either in the dorsiflexion or plantarflexion direction). Repeated measures ANOVAs were performed on the mean and standard deviation of the H peak-to-peak amplitude.

RESULTS

Mean vastus medialis H reflex amplitudes were significantly different among the trials of different ankle efforts (P<0.05), and significantly increased during plantarfiexion efforts. In contrast, mean vastus medialis H reflex amplitude did not vary with respect to changes of ankle position (P>0.05).

CONCLUSIONS

The data suggest that (1) the position of the ankle joint did not significantly modify the excitability of the neuromotor pool of the VM muscle, in either static or active cases, and (2) the effort effect from the ankle joint on the VM neuromotor pool is most significant during ankle plantarfiexion effort. Possible mechanisms are central motor irradiation and peripheral force-dependent pathways from the ankle joint that influence the VM neuromotor pool.

The effects of Tai Chi Chuan on postural stability in the elderly: preliminary report

BACKGROUND

Tai chi chuan (TCC) is a traditional Chinese conditioning exercise, consisting of a series of graceful movements linked together in a continuous sequence so that the body is constantly shifting from one foot to the other. We propose that subjects practicing TCC will have better postural control and stability than will active non-practitioners.

METHODS

We compare static and dynamic postural controls in 14 TCC practitioners and 14 healthy active older adults using the Smart Balance Master System. The TCC group, containing 7 male and 7 female subjects (mean age, 70.9 +/- 3.3 years), had been practicing TCC regularly for 2 to 35 years. The control group included 4 male and 10 female healthy and active older subjects (mean age, 69.1 +/- 3.1 years), with age and body size matched to the TCC group.

RESULTS

The results of static postural control tests showed no differences between the TCC and control groups under simple conditions (eyes open, eyes closed, swaying vision, and eyes open with swaying surface), but in the more complicated conditions (eyes closed with sway-referenced support and sway-referenced vision and support), the TCC group had significantly better results than the control group. In the dynamic balance test, the TCC group had significantly better results only in the rhythmic forward-backward weight-shifting test.

CONCLUSION

Our data demonstrate that regular TCC practitioners have better postural stability, especially in the more complicated conditions with disturbed visual and somatosensory conditions.

Microbial dechlorination of polychlorinated biphenyls in anaerobic sewage sludge

The potential of a chlorophenol (CP)-adapted consortium to dechlorinate polychlorinated biphenyls (PCBs) in sewage sludge was investigated. Results show that dechlorination rates differed significantly depending on sludge source and PCB congener. Higher total solid concentrations in sewage sludge and higher concentrations of chlorine in PCB resulted in slower dechlorination rates. No significant difference was found for 2,3,4,5-CB dechlorination from pH 6.0 to pH 8.0; however, dechlorination did not occur at pH 9.0 during a 41-day incubation period. Results show that at concentrations of 1 to 10 mg/L, the higher the PCB concentration, the faster the dechlorination rate. In addition, dechlorination rates were in the following order: methanogenic conditions > sulfate-reducing conditions > denitrifying conditions. The addition of acetate, lactate, pyruvate, and ferric chloride decreased lag times and enhanced dechlorination; however, the addition of manganese dioxide had an inhibitory effect. Dechlorination rates were also enhanced by the addition of PCB congeners, including 2,3,4-CB, 2,3,4,5-CB and 2,3,4,5,6-CB in mixture. Overall results show that the CP-adapted consortium has the potential to enhance PCB dechlorination. The optimal dechlorination conditions presented in this paper may be used as a reference for feasibility studies of PCB removal from sludge.

Cytomegalovirus-induced regulation of major histocompatibility complex class I antigen expression in human aortic smooth muscle cells

Cardiac allograft vasculopathy (accelerated transplant atherosclerosis) is considered by most to involve a chronic allogeneic immune response to one or more constituents in the coronary vascular wall. Recent evidence suggests that there is an association between cytomegalovirus infection and the development of cardiac allograft vasculopathy (CAV). To determine whether CMV directly infects and/or potentially influences immunogenicity of vascular tissue, human umbilical vein (HU-VECs) or human aortic (HAECs) endothelial cells and human aortic smooth muscle cells (HASMCs) were isolated, cultured, and infected with CMV strain AD 169. Infection was detected using an immunoperoxidase-labeled monoclonal antibody to CMV immediate-early antigen (L-14). The presence and relative quantity of MHC class I and II antigens were determined flow cytometrically using monoclonal antibodies to monomorphic class I and class II HLA determinants. Gamma interferon was used as a positive control stimulant for the upregulation of MHC determinants. Both pooled HUVECs as well as 2 cell lines of HAECs served as targets for CMV infection though less than 10% of the cells were infected despite inocula of 10 pfu/cell. Infection of the pooled HUVECs resulted in no significant changes in the cell surface density of either MHC class I or II determinants. In contrast, HASMCs were excellent targets for CMV infection with virtually 100% of cells infected. CMV infection of 2 distinct HASMC cultures resulted in an increase of 254 +/- 158 relative fluorescence units (RFUs) in MHC class I antigen expression, as assessed by fluorescence intensity, in a variable portion of the HASMCs. A second population of cells exhibited a decrease of 73 +/- 16 RFUs in MHC class I antigen expression. No significant change in MHC class II antigen expression was noted. These results demonstrate that while HUVECs and HAECs are targets of CMV infection, human aortic smooth muscle cells can more readily be infected by CMV. Furthermore, CMV can regulate smooth muscle cell MHC class I expression, hence potentially altering immunogenicity. A pathophysiologic link between cardiac allograft vasculopathy and CMV disease can therefore be hypothesized.

Analysis of interstrain variation in cytomegalovirus glycoprotein B sequences encoding neutralization-related epitopes

Nucleotide sequences of a part of the envelope glycoprotein B (gB) gene of human cytomegalovirus (CMV), encoding epitopes recognized by virus-neutralizing monoclonal antibodies, were determined for 12 distinct clinical strains of CMV after amplification of suitable templates using the polymerase chain reaction. Sequence analysis of this region (codons 384-717) revealed that the clinical strains and previously sequenced laboratory strains Towne and AD169 belong to one of four variant groups, each with a characteristic nucleotide and peptide sequence. Peptide homology was greater than 99% for strains within a group, and varied from 91% to 98% for strains in different groups. Variation was most frequent between codons 448 and 480. The gB group of a CMV strain could be determined by restriction analysis of a small target sequence amplified from viral genomic DNA, and an additional 28 clinical strains were grouped in this manner. The existence of a limited number of variants of gB among clinical strains facilitates analysis of biologic function and cross-reactivity of immune responses.

Differentiation of cytomegalovirus strains by restriction analysis of DNA sequences amplified from clinical specimens

DNA sequences of 2.0 to 2.7 kb were amplified by polymerase chain reaction from four genes (major immediate-early, DNA polymerase, and glycoproteins B and H) of 20 distinct strains of cytomegalovirus (CMV). Analysis of the unpurified reaction products using selected restriction enzymes showed sufficient diversity of profiles among strains to differentiate all 20. Sequences suitable for restriction analysis were also amplified directly from clinical urine specimens and showed restriction profiles comparable to those of sequences amplified from corresponding CMV culture isolates. Ability to identify specific strains of CMV in amplification products facilitates molecular epidemiologic studies.

Rises in antibody to human herpesvirus 6 detected by enzyme immunoassay in transplant recipients with primary cytomegalovirus infection

Immunoglobulin G to human herpesvirus 6 (HHV-6) and cytomegalovirus (CMV) in sera from solid organ recipients was measured by an enzyme-linked immunoassay (ELISA) before and after transplant. The HHV-6 ELISA was developed from glycine extracts of HHV-6-infected and uninfected HSB-2 cells. At a serum dilution of 1:500, 80 (91%) of 88 recipients were seropositive for HHV-6 before transplant, while only 14 (16%) were seropositive for CMV. Posttransplant HHV-6 serologic rises were observed in 38 (43%) recipients; rises in 25 of these recipients were associated with primary CMV infection. Titration of sera revealed much higher HHV-6 titer rises among those with primary CMV infection than among those with CMV reactivation or with no CMV infection. Elevated HHV-6 antibody titers persisted for up to 2 years after primary CMV infection. No correlation was noted between CMV and HHV-6 antibody titers in individual serum samples.

Reactivation and recombination of multiple cytomegalovirus strains from individual organ donors

Close examination of restriction enzyme digest profiles of cytomegalovirus (CMV) isolates from corecipients of organs from a common donor revealed instances of intermittent or prolonged shedding of two strains transmitted from the same donor organ. In two corecipients, two distinct donor strains were isolated by end-point dilutions of urine specimens or of cell-free virus stock and were shown by monoclonal antibody staining to differ in their major immediate-early antigen. The separated strains retained stable restriction profiles through greater than 20 passages in cell culture. However, similar passage of the original mixed-strain clinical isolates gave rise to new, recombinant strains of CMV. These findings indicate that more than one strain of CMV can establish latency in normal hosts and suggest that new viral strains arise readily through recombination of existing strains.

Neutralizing antibody responses to reinfecting strains of cytomegalovirus in transplant recipients

Analysis of cytomegalovirus (CMV) isolates shed by 51 recipients of organs from 24 CMV-seropositive donors was used to assess the relative characteristics of primary infection, reactivation of endogenous virus, and reinfection by a donor CMV strain. Reinfection was more frequent than reactivation of endogenous virus. Symptomatic CMV disease was identified in 21 of 25 primary infections, 2 of 16 reinfections, and 1 of 4 cases of endogenous reactivation. Before receiving a transplant, reinfected recipients had detectable neutralizing antibody to the specific reinfecting strain of CMV and to laboratory strain AD169. Following reinfection, rises in neutralizing antibody titers were observed, comparable to the responses of those with reactivation of endogenous CMV. The preexisting level of neutralizing antibody did not appear to predict clinical outcome, and moderately high levels of neutralizing antibody did not prevent viremia. Thus, posttransplant CMV reinfection occurs frequently and appears clinically, serologically, and virologically similar to reactivation of endogenous virus.

Latex agglutination and enzyme-linked immunosorbent assays for cytomegalovirus serologic screening of transplant donors and recipients

The effectiveness of three serologic assays (two enzyme-linked immunosorbent assays [ELISAs] and latex agglutination) for cytomegalovirus (CMV) serologic matching of donors and recipients was assessed over a 2-year period in a major organ transplant program. Sera with equivocal test results were investigated by repeat testing of serum samples and additional specimens from the individuals involved and monitoring of CMV infection in recipients. An in-house ELISA identified all CMV-infective donors as seropositive. Of 63 ELISA-positive donors, 5 were negative by latex agglutination; recipients from 3 of these donors developed primary CMV infection posttransplant. The in-house ELISA and a commercial ELISA (Abbott enzyme immunoassay; Abbott Laboratories, North Chicago, Ill.) had a 93% concordance of results; follow-up testing indicated that the Abbott assay was sensitive but had a false-positive rate of about 11%. One recipient with a false-positive result developed symptomatic primary CMV infection after receiving a seropositive organ. Thus, performance characteristics of currently used screening assays affect recipient outcome.

The influence of donor factors other than serologic status on transmission of cytomegalovirus to transplant recipients

Organs transplanted from donors who are seropositive for CMV are a well-known source of CMV infection in their recipients. Such organs appear to contain latent virus that reactivates following transplantation. However, not all grafts from seropositive donors are observed to transmit CMV, either because of differing immune function among recipients, or content of transmissible virus among donors. To explore these variables, we conducted a 3-year prospective survey involving 140 CMV-seronegative kidney and heart recipients, using a sensitive assay for CMV antibody to classify donors and recipients, and detect posttransplant primary infection. We found that none of 64 recipients of a CMV-seronegative organ, and 40 of 68 (58%) recipients of a CMV-seropositive organ, developed primary CMV infection. Analysis of recipient factors in the latter group showed no significant differences in underlying disease, age, and immunosuppressive therapy between the 58% who did develop CMV infection after receiving a CMV-seropositive organ, and the 42% who did not. In 9 pairs of recipients, each pair of whom received organs from the same CMV-seropositive cadaver donor, there was complete concordance of outcomes within pairs. In 4 pairs, both recipients developed CMV infection, whereas in the remaining 5 pairs, neither recipient did so. These observations suggest that only a subset of CMV-seropositive donors carry latent CMV that reactivates posttransplant, and that donor factors other than seropositivity are important in determining the infectivity of transplanted organs.

Rapid quantitation of cytomegalovirus and assay of neutralizing antibody by using monoclonal antibody to the major immediate-early viral protein

An overnight assay, based on staining cytomegalovirus-infected cells with monoclonal antibody to the 72,000-molecular-weight major immediate-early viral protein, was compared with a conventional 14-day plaque assay for quantitation of cell-free stocks of cytomegalovirus laboratory strain AD-169 and 20 other clinical strains. Viral titers were quantitatively similar when determined by either method, but centrifugation of monolayers during inoculation enhanced viral infectivity an average of 4.1-fold. When used for scoring neutralizing antibody assays, monoclonal antibody staining yielded titers within one dilution of 14-day plaque-reduction assays in 54 of 56 titrations. Of 21 cytomegalovirus strains, 2 were not recognized by the monoclonal antibody used. Assay with monoclonal antibody offers a rapid and accurate alternative to plaque assays for quantitation or neutralization of cytomegalovirus.

Acquisition of donor strains of cytomegalovirus by renal-transplant recipients

To determine the source of post-transplantation cytomegalovirus (CMV) infection in renal-transplant recipients, viral isolates were collected from pairs of patients who received kidneys from the same cadaver. Among 36 pairs of recipients, CMV viruria or viremia occurred in both members of 4 pairs and in one member of 11 pairs. Restriction-enzyme analysis of viral DNA revealed 15 distinct strains of CMV among viral isolates from these 19 patients. In all four pairs in which both members shed CMV, both recipients shed the same strain, suggesting that the virus was of donor origin. In three of these pairs, one member had been seropositive for CMV before transplantation. One seropositive recipient was simultaneously shedding two strains of CMV after transplantation; one strain was of donor origin. Two patients who had CMV viruria before receiving grafts from a seropositive donor shed a different CMV strain two months after grafting. These findings indicate that cadaveric grafts can transmit an identifiable strain of CMV to recipients, and that seropositive recipients can be reinfected by a new CMV strain from the donor after transplantation.

Alpha-interferon administration in cytomegalovirus retinitis

Four patients, including three with the acquired immunodeficiency syndrome (AIDS), were treated with high-dose, buffy coat-derived alpha-interferon for progressive cytomegalovirus retinitis. Two of these patients had decreased viruria during therapy and the other two had increased viruria. There was evidence of progression of disease despite therapy in all patients, although the retinitis eventually became quiescent in the patient without AIDS. The severe immunosuppression encountered in AIDS patients complicates the management of cytomegalovirus and other opportunistic infections.

DNA of 21 clinical cytomegalovirus strains detected by hybridization to cloned DNA fragments of laboratory strain AD-169

Nine distinct DNA probes prepared from cloned DNA fragments of the cytomegalovirus (CMV) strain AD-169, each representing a relatively small portion of the total genome, were able to detect all 21 epidemiologically distinct clinical isolates of CMV that had been passaged in tissue culture. All probes were of comparable sensitivity in the detection of CMV, and under the hybridization conditions used, no probe gave an unusually high background with uninfected host cells.