Transcranial magnetic stimulation enhances the specificity of multiple sclerosis diagnostic criteria: a critical narrative review.

Background: Multiple sclerosis (MS) is an immune-mediated neurodegenerative disease that involves attacks of inflammatory demyelination and axonal damage, with variable but continuous disability accumulation. Transcranial magnetic stimulation (TMS) is a noninvasive method to characterize conduction loss and axonal damage in the corticospinal tract. TMS as a technique provides indices of corticospinal tract function that may serve as putative MS biomarkers. To date, no reviews have directly addressed the diagnostic performance of TMS in MS. The authors aimed to conduct a critical narrative review on the diagnostic performance of TMS in MS. Methods: The authors searched the Embase, PubMed, Scopus, and Web of Science databases for studies that reported the sensitivity and/or specificity of any reported TMS technique compared to established clinical MS diagnostic criteria. Studies were summarized and critically appraised for their quality and validity. Results: Seventeen of 1,073 records were included for data extraction and critical appraisal. Markers of demyelination and axonal damage-most notably, central motor conduction time (CMCT)-were specific, but not sensitive, for MS. Thirteen (76%), two (12%), and two (12%) studies exhibited high, unclear, and low risk of bias, respectively. No study demonstrated validity for TMS techniques as diagnostic biomarkers in MS. Conclusions: CMCT has the potential to: (1) enhance the specificity of clinical MS diagnostic criteria by "ruling in" true-positives, or (2) revise a diagnosis from relapsing to progressive forms of MS. However, there is presently insufficient high-quality evidence to recommend any TMS technique in the diagnostic algorithm for MS.

CT features of cutaneous and subcutaneous canine mast cell tumors and utility of conventional and indirect lymphography to detect clinically unknown mast cell tumors and to map the sentinel lymph nodes.

Computed tomography is frequently used to stage canine mast cell tumors (MCTs). The aims of this prospective, observational study were to describe the CT features of MCTs, to evaluate the performance of CT in detecting additional or incidental MCTs, to distinguish between cutaneous (cMCT) or subcutaneous (scMCT) MCTs, and to identify one or multiple sentinel lymph nodes (SLNs) by indirect CT lymphography (ICTL). Seventy-two dogs affected by 111 MCTs were included. The recorded parameters were: shape, size, attenuation (Hounsfield units [HU]), location (cutaneous or subcutaneous), and presence of fat stranding. The SLNs were compared with the regional lymph nodes and supplementary MCTs were registered. Mast cell tumors mostly appeared with well-defined margins (89%), round/oval shape (71%), homogeneous enhancement (90%) with a mean postcontrast density of 62.0 ± 23.4 HU and associated with fat stranding (43%). Cutaneous mast cell tumors were more frequently round (P = .003), whereas scMCTs were oval (P = .011) with a larger mean maximal diameter (2.91 ± 1.57 cm vs 1.46 ± 1.28 cm, P = .002) and more feeding vessels (77% vs 39% P = .044). Compared with histopathology, CT accuracy in differentiating cMCTs and sMCTs was 57%, with an interobserver agreement of 88% (three reviewers). Indirect CT lymphography showed the SLN in 82 of 85 (97%) cases, 32% of them not corresponding to the regional node. CT showed additional or incidental MCTs in 23 of 72 (32%) dogs. In conclusion, the common CT appearance of canine cMCTs and scMCTs is reported with some statistical differences between the two categories. CT is useful in identifying clinically undetected MCTs and SLNs, although it shows low accuracy in distinguishing between cMCT and scMCT.

Primary preputial reconstruction following surgical excision of cutaneous mast cell tumours without penile amputation in eight dogs.

CASE HISTORY: Medical records from a single referral hospital (Davies Veterinary Specialists, Hitchin, UK) were reviewed to identify dogs (n = 8) with preputial cutaneous mast cell tumours (CMCT) that underwent surgical excision and primary preputial reconstruction, preserving the penis and urethra, after clients declined alternatives such as penile amputation and urethrostomy, from June 2017-June 2022. CLINICAL FINDINGS: Tumours had a median diameter of 21.5 (min 15, max 30) mm, were located cranioventrally (3/8), caudoventrally (1/8), laterally (2/8) and dorsally (2/8) relative to the prepuce and were diagnosed as CMCT based on cytology. No dogs had hepatic or splenic metastasis on cytology but inguinal lymph node metastasis was identified in 3/4 dogs sampled. TREATMENT AND OUTCOME: The owners of all dogs had declined penile amputation and scrotal urethrostomy. The CMCT were excised and primary reconstruction of the prepuce performed. Surgical lateral margins of 10, 20 or 30 mm were used and the deep margin excised the inner preputial lamina or underlying muscular fascia. The deep margin for caudoventral CMCT involved excision of the underlying SC adipose tissue. Preputial advancement was performed in 3/8 dogs to achieve adequate penile coverage. Histopathology confirmed all CMCT were Kiupel low grade, Patnaik grade II with complete margins in 6/8 dogs but identified metastasis only in one inguinal lymph node from one dog. Two dogs encountered minor complications (infection and a minor dehiscence) and one dog had a major complication (infection with major dehiscence). Median follow-up duration was 125 weeks, excluding one dog with 4 weeks of follow-up. None of the dogs experienced local recurrence or died of mast cell disease during the available follow-up period. CLINICAL RELEVANCE:  This clinical study evaluated a surgical alternative to penile amputation and advanced reconstructive techniques for Kuipel low/Patnaik grade II preputial CMCT when these procedures were declined by owners. Surgical excision of preputial CMCT with lateral margins of 10, 20 or 30 mm with primary preputial reconstruction is achievable with low morbidity and a good outcome when penile amputation and scrotal urethrostomy is not an option.

Clinical study on low-frequency repetitive transcranial magnetic stimulation for the treatment of walking dysfunction following stroke through three-dimensional gait analysis.

BACKGROUND: The recovery of walking capacity is of great significance in stroke rehabilitation. We evaluated changes in post-stroke gait function after low-frequency repetitive transcranial magnetic stimulation (LF-rTMS) treatment. METHODS: Stroke patients were randomly assigned to control (conventional treatment)/LF-rTMS (LF-rTMS treatment based on conventional treatment) groups. Gait spatiotemporal parameters/affected side joint motion angle/affected side dynamic parameters were analyzed by 3D gait analyses. Motor evoked potential (MEP)/central motor conduction time (CMCT) changes were detected. Correlations between MEP latency/CMCT and gait parameters after LF-rTMS were analyzed by Pearson analysis. RESULTS: The two groups exhibited boosted stride speed/frequency/length, affected side stride length/swing phase percentage/hip/knee/ankle joint plantar flexion angle, and affected side ahead ground reaction force/ upward ground reaction force (AGRF/UGRF)/ankle joint plantar flexion moment, along with reduced affected side gait period/stance phase percentage after treatment, and the LF-rTMS group manifested better efficacy. MEP latency/CMCT of stroke patients treated with LF-rTMS was adversely linked to stride speed, affected side stride length/swing phase percentage/knee flexion angle, AGRF and UGRF, and positively correlated with affected side stance phase percentage. CONCLUSION: LF-rTMS significantly improved gait spatiotemporal parameters/affected joint motion angles/neurophysiologic parameters (MEP latency/CMCT) in patients with post-stroke walking dysfunction. MEP latency/CMCT after LF-rTMS treatment were prominently correlated with gait parameters. Relative to the traditional scale assessment, we provided a more accurate, objective and reliable evaluation of the effects of LF-rTMS on lower limb mobility and functional recovery effects in stroke patients from the perspective of 3D gait analysis and neurophysiology, which provided more evidence to support the clinical application of LF-rTMS in post-stroke walking dysfunction treatment.

Abnormal cortical excitability in patients with spinocerebellar ataxia type 12.

BACKGROUND: Spinocerebellar ataxia type 12 (SCA-12) is an uncommon autosomal dominant cerebellar ataxia characterized by action tremors in the upper limbs, dysarthria, head tremor, and gait ataxia. We aimed to evaluate the motor cortical excitability in patients with SCA-12 using transcranial magnetic stimulation (TMS). METHODS: The study was done in the department of Neurology at the National Institute of Mental Health and Neuro Sciences (NIMHANS), Bangalore. Nine patients with SCA-12 (2 females) and 10 healthy controls (2 females) were included in the study. TMS was performed in all the subjects and various parameters such as resting motor threshold (RMT), central motor conduction time (CMCT) and contralateral silent period (cSP) were recorded. The left motor cortex was stimulated and the recording was done from right first dorsal interossei muscle. The severity of ataxia was assessed using the scale for assessment and rating in ataxia (SARA). RESULTS: The mean age of the patients was 58.11 ± 7.56 years mean age at onset: 51.67 ± 4.18 years. The mean duration of illness was 9.44 ± 4.88 years. The mean SARA score was 13.83 ± 3.60. Patients with SCA-12 had significantly increased RMT (88.80 ± 12.78 %) compared to HC (44.90 ± 9.40 %, p < 0.05). A significantly prolonged CMCT was observed in patients (13.70 ± 2.52 msec) compared to HC (7.31 ± 1.21 msec, p < 0.05). In addition, cSP was significantly increased in SCA-12 patients (144.43 ± 25.79 msec) compared to HC (82.14 ± 28.90 msec, p < 0.05). CONCLUSIONS: Patients with SCA-12 demonstrate a reduced cortical excitability and increased cortical inhibition suggesting an increase in the GABAergic neurotransmission.

Resting-state functional magnetic resonance imaging indices are related to electrophysiological dysfunction in degenerative cervical myelopathy.

The age-related degenerative pathologies of the cervical spinal column that comprise degenerative cervical myelopathy (DCM) cause myelopathy due spinal cord compression. Functional neurological assessment of DCM can potentially reveal the severity and pathological mechanism of DCM. However, functional assessment by conventional MRI remains difficult. This study used resting-state functional MRI (rs-fMRI) to investigate the relationship between functional connectivity (FC) strength and neurophysiological indices and examined the feasibility of functional assessment by FC for DCM. Preoperatively, 34 patients with DCM underwent rs-fMRI scans. Preoperative central motor conduction time (CMCT) reflecting motor functional disability and intraoperative somatosensory evoked potentials (SEP) reflecting sensory functional disability were recorded as electrophysiological indices of severity of the cervical spinal cord impairment. We performed seed-to-voxel FC analysis and correlation analyses between FC strength and the two electrophysiological indices. We found that FC strength between the primary motor cortex and the precuneus correlated significantly positively with CMCT, and that between the lateral part of the sensorimotor cortex and the lateral occipital cortex also showed a significantly positive correlation with SEP amplitudes. These results suggest that we can evaluate neurological and electrophysiological severity in patients with DCM by analyzing FC strengths between certain brain regions.

SIRT6 deficiency in endothelial cells exacerbates oxidative stress by enhancing HIF1α accumulation and H3K9 acetylation at the Ero1α promoter.

BACKGROUND: SIRT6, an important NAD+ -dependent protein, protects endothelial cells from inflammatory and oxidative stress injuries. However, the role of SIRT6 in cardiac microvascular endothelial cells (CMECs) under ischemia-reperfusion injury (IRI) remains unclear. METHODS: The HUVECs model of oxygen-glucose deprivation/reperfusion (OGD/R) was established to simulate the endothelial IRI in vitro. Endoplasmic reticulum oxidase 1 alpha (Ero1α) mRNA and protein levels in SIRT6-overexpressing or SIRT6-knockdown cells were measured by qPCR and Western blotting. The levels of H2 O2 and mitochondrial reactive oxygen species (ROS) were detected to evaluate the status of oxidative stress. The effects of SIRT6 deficiency and Ero1α knockdown on cellular endoplasmic reticulum stress (ERS), inflammation, apoptosis and barrier function were detected by a series of molecular biological experiments and functional experiments in vitro. Chromatin immunoprecipitation, Western blotting, qPCR, and site-specific mutation experiments were used to examine the underlying molecular mechanisms. Furthermore, endothelial cell-specific Sirt6 knockout (ecSirt6-/- ) mice were subjected to cardiac ischemia-reperfusion surgery to investigate the effects of SIRT6 in CMECs in vivo. RESULTS: The expression of Ero1α was significantly upregulated in SIRT6-knockdown endothelial cells, and high Ero1α expression correlated with the accumulation of H2 O2 and mitochondrial ROS. In addition, SIRT6 deficiency increased ERS, inflammation, apoptosis and endothelial permeability, and these effects could be significantly attenuated by Ero1α knockdown. The deacetylase catalytic activity of SIRT6 was important in regulating Ero1α expression and these biological processes. Mechanistically, SIRT6 inhibited the enrichment of HIF1α and p300 at the Ero1α promoter through deacetylating H3K9, thereby antagonizing HIF1α/p300-mediated Ero1α expression. Compared with SIRT6-wild-type (SIRT6-WT) cells, cells expressing the SIRT6-H133Y-mutant and SIRT6-R65A-mutant exhibited increased Ero1α expression. Furthermore, ecSirt6-/- mice subjected to ischemia-reperfusion surgery exhibited increased Ero1α expression and ERS in CMECs and worsened injuries to microvascular barrier function and cardiac function. CONCLUSIONS: Our results revealed an epigenetic mechanism associated with SIRT6 and Ero1α expression and highlighted the therapeutic potential of targeting the SIRT6-HIF1α/p300-Ero1α axis.

Cutaneous mastocytosis in 8 young dogs and review of literature.

Cutaneous mastocytosis (CM) is a rare condition in young dogs characterized by multicentric cutaneous proliferation of neoplastic mast cells. Clinical data from 8 dogs that met inclusion criteria (age of onset less than 1.5 years, greater than 3 lesions) were obtained via a standardized survey. Biopsy samples were classified by the Kiupel/Patnaik grading systems and analyzed for c-KIT mutations. The median age of onset was 6 months (range: 2-17 months). Dogs had 5 to more than 50 lesions characterized as nodules, plaques, and papules. Seven dogs were pruritic. Clinical staging in 2 dogs did not reveal visceral involvement. No dogs had systemic illnesses at diagnosis. Histologically, CM was similar to cutaneous mast cell tumor (cMCT). Two dogs had neoplasms classified as high-grade/grade II while 6 dogs had low-grade/grade II neoplasms. No dogs had mutations in c-KIT exons 8 and 11. Treatment included antihistamines (8/8), corticosteroids (7/8), lokivetmab (3/8), and toceranib (1/8). Six dogs were alive with lesions at the end of the study with a median follow-up time of 898 days, while 2 dogs were euthanized. In dogs with high-grade/grade II neoplasms, one continued to develop lesions at 1922 days post-diagnosis, while the other dog was euthanized at 56 days post-diagnosis. One dog was euthanized 621 days post-diagnosis due to rupture of a neoplasm. CM occurs in young dogs and is histologically indistinguishable from cMCT. Current histologic grading systems did not apply uniformly to the dogs of the study and further studies are needed.

Endothelial-cell-mediated mechanism of coronary microvascular dysfunction leading to heart failure with preserved ejection fraction.

Although the prevalence of heart failure with preserved ejection fraction (HFpEF) is growing worldwide, its complex pathophysiology has yet to be fully elucidated, and multiple hypotheses have all failed to produce a viable target for therapeutic action or provide effective treatment. Cardiac remodeling has long been considered an important mechanism of HFpEF. Strong evidence has been reported over the past years that coronary microvascular dysfunction (CMD), manifesting as structural and functional abnormalities of coronary microvasculature, also contributes to the evolution of HFpEF. However, the mechanisms of CMD are still not well understood and need to be studied further. Coronary microvascular endothelial cells (CMECs) are one of the most abundant cell types in the heart by number and active players in cardiac physiology and pathology. CMECs are not only important cellular mediators of cardiac vascularization but also play an important role in disease pathophysiology by participating in the inception and progression of cardiac remodeling. CMECs are also actively involved in the pathogenesis of CMD. Numerous studies have confirmed that CMD is closely related to cardiac remodeling. ECs may serve a critical function in mediating the connection between CMD and HFpEF. It follows that CMECs participate in the mechanism of CMD leading to HFpEF. In this review article, we focus on the role of CMD in the pathogenesis of HFpEF resulting from cardiac remodeling and highlight the subsequent complexity of the EC-mediated correlation between CMD and HFpEF.

Expression of cannabinoid receptors CB1 and CB2 in canine cutaneous mast cell tumours.

Cannabinoid receptors (CB1 and CB2) belong to endocannabinoid system (ECS), which is also composed from endocannabinoids and the enzymatic systems involved in their biosynthesis and degradation. The expression of CB1 and CB2 have been previously identified in normal canine mast cell and in atopic dermatitis. Canine cutaneous mast cell tumours (cMCTs) are among the most common cutaneous neoplasms in dogs and have a highly variable clinical behaviour. Expression of CB1-CB2 was assessed by means of immunohistochemistry in thirty-seven dogs (from 2019 to 2021) with proven histological diagnosis of cMCT. Dogs were divided in two groups according to the Kiupel's grading system: high-grade (HG) cMCT and low-grade (LG) cMCT. A semiquantitative (score 0-3) and quantitative assessment of immunoreactivity (IR) was performed for each case. Our results show that there CB1 and CB2 are highly expressed in LG- cMCT, in contrast to HG- cMCT.

RNA Secondary Structure Study by Chemical Probing Methods Using DMS and CMCT.

RNA folds into secondary structures that can serve in understanding various RNA functions (Weeks KM. Curr Opin Struct Biol 20(3):295-304, 2010). Chemical probing is a method that enables the characterization of RNA secondary structures using chemical reagents that specifically modify RNA nucleotides that are located in single-stranded areas. In our protocol, we used Dimethyl Sulfate (DMS) and Cyclohexyl-3-(2-Morpholinoethyl) Carbodiimide metho-p-Toluene sulfonate (CMCT) that are both base-specific modifying reagents (Behm-Ansmant I, et al. J Nucleic Acids 2011:408053, 2011). These modifications are mapped by primer extension arrests using 5' fluorescently labeled primers. In this protocol, we show a comprehensive method to identify RNA secondary structures in vitro using fluorescently labeled oligos. To demonstrate the efficiency of the method, we give an example of a structure we have designed which corresponds to a part of the 5'-UTR regulatory element called Translation Inhibitory Element (TIE) from Hox a3 mRNA (Xue S, et al. Nature 517(7532):33-38, 2015).

RNA Remodeling by RNA Chaperones Monitored by RNA Structure Probing.

RNA structure probing enables the characterization of RNA secondary structures by established procedures such as the enzyme- or chemical-based detection of single- or double-stranded regions. A specific type of application involves the detection of changes of RNA structures and conformations that are induced by proteins with RNA chaperone activity. This chapter outlines a protocol to analyze RNA structures in vitro in the presence of an RNA-binding protein with RNA chaperone activity. For this purpose, we make use of the methylating agents dimethyl sulfate (DMS) and 1-cyclohexyl-3-(2-morpholinoethyl) carbodiimide metho-p-toluenesulfonate (CMCT). DMS and CMCT specifically modify nucleotides that are not involved in base-pairing or tertiary structure hydrogen bonding and that are not protected by a ligand such as a protein. Modified bases are identified by primer extension. As an example, we describe how the RNA chaperone activity of an isoform of the RNA-binding protein AUF1 induces the flaviviral RNA switch required for viral genome cyclization and viral replication.This chapter includes comprehensive protocols for in vitro synthesis of RNA, 32P-5'-end labeling of DNA primers, primer extension, as well as the preparation and running of analytical gels. The described methodology should be applicable to any other RNA and protein of interest to identify protein-directed RNA remodeling.

RNA Structure Analysis by Chemical Probing with DMS and CMCT.

RNA structure is important for understanding RNA function and stability within a cell. Chemical probing is a well-established and convenient method to evaluate the structure of an RNA. Several structure-sensitive chemicals can differentiate paired and unpaired nucleotides. This chapter specifically addresses the use of DMS and CMCT. Although exhibiting different affinities, the combination of these two chemical reagents enables screening of all four nucleobases. DMS and CMCT are only reactive with exposed unpaired nucleotides. We have used this method to analyze the effect of the RNA chaperone Hfq on the conformation of the 16S rRNA. The strategy here described may be applied for the study of many other RNA-binding proteins and RNAs.

Plin5/p-Plin5 Guards Diabetic CMECs by Regulating FFAs Metabolism Bidirectionally.

BACKGROUND: Hyper-free fatty acidemia (HFFA) impairs cardiac capillaries, as well as type 2 diabetes mellitus (T2DM). Perilipin 5 (Plin5) maintains metabolic balance of free fatty acids (FFAs) in high oxidative tissues via the states of nonphosphorylation and phosphorylation. However, when facing to T2DM-HFFA, Plin5's role in cardiac microvascular endothelial cells (CMECs) is not defined. METHODS: In mice of WT or Plin5-/-, T2DM models were rendered by high-fat diet combined with intraperitoneal injection of streptozocin. CMECs isolated from left ventricles were incubated with high glucose (HG) and high FFAs (HFFAs). Plin5 phosphorylation was stimulated by isoproterenol. Plin5 expression was knocked down by small interfering RNA (siRNA). We determined cardiac function by small animal ultrasound, apoptotic rate by flow cytometry, microvessel quantity by immunohistochemistry, microvascular integrity by scanning electron microscopy, intracellular FFAs by spectrophotometry, lipid droplets (LDs) by Nile red staining, mRNAs by quantitative real-time polymerase chain reaction, proteins by western blots, nitric oxide (NO) and reactive oxygen species (ROS) by fluorescent dye staining and enzyme-linked immunosorbent assay kits. RESULTS: In CMECs, HFFAs aggravated cell injury induced by HG and activated Plin5 expression. In mice with T2DM-HFFA, Plin5 deficiency reduced number of cardiac capillaries, worsened structural incompleteness, and enhanced diastolic dysfunction. Moreover, in CMECs treated with HG-HFFAs, both ablation and phosphorylation of Plin5 reduced LDs content, increased intracellular FFAs, stimulated mitochondrial ß-oxidation, added ROS generation, and reduced the expression and activity of endothelial nitric oxide synthase (eNOS), eventually leading to increased apoptotic rate and decreased NO content, all of which were reversed by N-acetyl-L-cysteine. CONCLUSION: Plin5 preserves lipid balance and cell survival in diabetic CMECs by regulating FFAs metabolism bidirectionally via the states of nonphosphorylation and phosphorylation.

The interplay between molecular flexibility and RNA chemical probing reactivities analyzed at the nucleotide level via an extensive molecular dynamics study.

Determination of the tridimensional structure of ribonucleic acid molecules is fundamental for understanding their function in the cell. A common method to investigate RNA structures of large molecules is the use of chemical probes such as SHAPE (2'-hydroxyl acylation analyzed by primer extension) reagents, DMS (dimethyl sulfate) and CMCT (1-cyclohexyl-3-(2-morpholinoethyl) carbodiimide metho-p-toluene sulfate), the reaction of which is dependent on the local structural properties of each nucleotide. In order to understand the interplay between local flexibility, sugar pucker, canonical pairing and chemical reactivity of the probes, we performed all-atom molecular dynamics simulations on a set of RNA molecules for which both tridimensional structure and chemical probing data are available and we analyzed the correlations between geometrical parameters and the chemical reactivity. Our study confirms that SHAPE reactivity is guided by the local flexibility of the different chemical moieties but suggests that a combination of multiple parameters is needed to better understand the implications of the reactivity at the molecular level. This is also the case for DMS and CMCT for which the reactivity appears to be more complex than commonly accepted.

Pseudouridines have context-dependent mutation and stop rates in high-throughput sequencing.

The abundant RNA modification pseudouridine (Ψ) has been mapped transcriptome-wide by chemically modifying pseudouridines with carbodiimide and detecting the resulting reverse transcription stops in high-throughput sequencing. However, these methods have limited sensitivity and specificity, in part due to the use of reverse transcription stops. We sought to use mutations rather than just stops in sequencing data to identify pseudouridine sites. Here, we identify reverse transcription conditions that allow read-through of carbodiimide-modified pseudouridine (CMC-Ψ), and we show that pseudouridines in carbodiimide-treated human ribosomal RNA have context-dependent mutation and stop rates in high-throughput sequencing libraries prepared under these conditions. Furthermore, accounting for the context-dependence of mutation and stop rates can enhance the detection of pseudouridine sites. Similar approaches could contribute to the sequencing-based detection of many RNA modifications.

Ion/ion reactions with "onium" reagents: an approach for the gas-phase transfer of organic cations to multiply-charged anions.

The use of ion/ion reactions to effect gas-phase alkylation is demonstrated. Commonly used fixed-charge "onium" cations are well-suited for ion/ion reactions with multiply deprotonated analytes because of their tendency to form long-lived electrostatic complexes. Activation of these complexes results in an SN2 reaction that yields an alkylated anion with the loss of a neutral remnant of the reagent. This alkylation process forms the basis of a general method for alkylation of deprotonated analytes generated via electrospray, and is demonstrated on a variety of anionic sites. SN2 reactions of this nature are demonstrated empirically and characterized using density functional theory (DFT). This method for modification in the gas phase is extended to the transfer of larger and more complex R groups that can be used in later gas-phase synthesis steps. For example, N-cyclohexyl-N'-(2-morpholinoethyl)carbodiimide (CMC) is used to transfer a carbodiimide functionality to a peptide anion containing a carboxylic acid. Subsequent activation yields a selective reaction between the transferred carbodiimide group and a carboxylic acid, suggesting the carbodiimide functionality is retained through the transfer process. Many different R groups are transferable using this method, allowing for new possibilities for charge manipulation and derivatization in the gas phase.

Cyclodextrin-grafted chitosan hydrogels for controlled drug delivery.

A series of ß-cyclodextrin-grafted carboxymethyl chitosan hydrogels (CD-g-CMCs) were prepared from carboxymethyl chitosan (CMC) and carboxymethyl ß-chitosan (CMCD) using a water-soluble carbodiimide as a crosslinker in the presence of N-hydroxysuccinimide. Details of the hydrogel structures were determined via FTIR and solid-state NMR spectroscopic analyses. Increasing the feed ratio of CMCD to CMC in the reaction mixture led to an increase in CD grafting within the gel networks comprising CMC; this was confirmed by SEM observations and rheological analysis of the swollen hydrogels. The prepared CD-g-CMC hydrogels exhibited absorption properties toward acetylsalicylic acid (ASA, or Aspirin) due to the presence of CD in the structure; the amount of ASA absorbed into the hydrogels was enhanced with an increase in the amount of CD incorporated within the hydrogels. In addition, CD-g-CMC hydrogels provided a slower release of the entrapped ASA in comparison to the ASA release profile of a solely CMC-containing hydrogel. From these results, CD-g-CMC hydrogels have the potential to function as a biodegradable active material with controlled drug release ability.

RNA recognition by the DNA end-binding Ku heterodimer.

Most nucleic acid-binding proteins selectively bind either DNA or RNA, but not both nucleic acids. The Saccharomyces cerevisiae Ku heterodimer is unusual in that it has two very different biologically relevant binding modes: (1) Ku is a sequence-nonspecific double-stranded DNA end-binding protein with prominent roles in nonhomologous end-joining and telomeric capping, and (2) Ku associates with a specific stem-loop of TLC1, the RNA subunit of budding yeast telomerase, and is necessary for proper nuclear localization of this ribonucleoprotein enzyme. TLC1 RNA-binding and dsDNA-binding are mutually exclusive, so they may be mediated by the same site on Ku. Although dsDNA binding by Ku is well studied, much less is known about what features of an RNA hairpin enable specific recognition by Ku. To address this question, we localized the Ku-binding site of the TLC1 hairpin with single-nucleotide resolution using phosphorothioate footprinting, used chemical modification to identify an unpredicted motif within the hairpin secondary structure, and carried out mutagenesis of the stem-loop to ascertain the critical elements within the RNA that permit Ku binding. Finally, we provide evidence that the Ku-binding site is present in additional budding yeast telomerase RNAs and discuss the possibility that RNA binding is a conserved function of the Ku heterodimer.

Mass spectrometry-based quantification of pseudouridine in RNA.

Direct detection of pseudouridine (ψ), an isomer of uridine, in RNA is challenging. The most popular method requires chemical derivatization using N-cyclohexyl-N'-ß-(4-methylmorpholinum ethyl) carbodiimide p-tosylate (CMCT) followed by radiolabeled primer extension mediated by reverse transcriptase. More recently, mass spectrometry (MS)-based approaches for sequence placement of pseudouridine in RNA have been developed. Nearly all of these approaches, however, only yield qualitative information regarding the presence or absence of pseudouridine in a given RNA population. Here, we have extended a previously developed liquid chromatography tandem mass spectrometry (LC-MS/MS) method to enable both the qualitative and quantitative analysis of pseudouridine. Quantitative selected reaction monitoring (SRM) assays were developed using synthetic oligonucleotides, with or without pseudouridine, and the results yielded a linear relationship between the ion abundance of the pseudouridine-specific fragment ion and the amount of pseudouridine-containing oligonucleotide present in the original sample. Using this quantitative SRM assay, the extent of pseudouridine hypomodification in the conserved T-loop of tRNA isolated from two different Escherichia coli strains was established.