Successful management of maternal anti-PP1Pk alloimmunization in pregnancy with therapeutic plasma exchange and intravenous immunoglobulin

Anti-PP1PK alloimmunization is rare given ubiquitous P1PK expression. Prevention of recurrent miscarriages and hemolytic disease of the fetus and newborn (HDFN) in pregnant individuals with anti-PP1PK antibodies has relied upon individual reports. Here, we demonstrate the successful management of maternal anti-PP1PK alloimmunization in a 23-year-old, G2P0010, with therapeutic plasma exchange (TPE), intravenous immunoglobulin (IVIG), and monitoring of anti-PP1Pk titers. Twice-weekly TPE (1.5 plasma volume [PV], 5% albumin replacement) with weekly titers and IVIG (1 g/kg) was initiated at 9 weeks of gestation (WG). The threshold titer was ≥16. Weekly middle cerebral artery-peak systolic velocities (MCA-PSV) for fetal anemia monitoring was initiated at 16 WG. PVs were adjusted throughout pregnancy based on treatment schedule, titers, and available albumin. Antigen-negative, ABO-compatible RBCs were obtained through the rare donor program and directed donation. An autologous blood autotransfusion system was reserved for delivery. Titers decreased from 128 to 8 by 10 WG. MCA-PSV remained stable. At 24 WG, TPE decreased to once weekly. After titers increased to 32, twice-weekly TPE resumed at 27 WG. Induction of labor was scheduled at 38 WG. Vaginal delivery of a 2950 g neonate (APGAR score: 9, 9) occurred without complication (Cord blood: 1+ IgG DAT; Anti-PP1Pk eluted). Newborn hemoglobin and bilirubin were unremarkable. Discharge occurred postpartum day 2. Anti-PP1Pk alloimmunization is rare but associated with recurrent miscarriages and HDFN. With multidisciplinary care, a successful pregnancy is possible with IVIG and TPE adjusted to PV and titers. We also propose a patient registry and comprehensive management plan.

Predicting the CD34 content of mobilized peripheral blood leukapheresis products: single institution experience over 20 years

BACKGROUND AIMS

Since the standardization of CD34 measurement by flow cytometry, predictors of leukapheresis CD34 yield have played a pivotal role in planning donor leukaphereses. We describe here a single institution's experience with a multivariate predictor that was used for 2,929 products without alteration for 20 years.

METHODS

The ordinary least squares regression model variables included log peripheral CD34 count, collection duration (3- versus 4-hours), collection number, donor sex, and transplant type.

RESULTS

During the study period we changed flow cytometers twice and leukapheresis instruments once. During the Cobe Spectra era the predictor explained 90% of the variability in CD34 collection yield for autologous transplants (r2 = 0.90), and 70% for allogeneic transplants with an overall sensitivity to predict a CD34 yield of ≥ 1 × 106/kg of 97.7%, and specificity of 81.4%.

CONCLUSIONS

Implemented prospectively with real-time result reporting, the model allowed us to predict CD34 yield with both 3- and 4-hour collection scenarios. Given this guidance, 3-hour collections were selected by the clinical team 25% of the time, saving patient leukapheresis time and resources. When faced with a prediction of < 1 × 106 CD34/kg, the clinical team chose to defer collection 72% of the time. In instances where leukapheresis was performed despite a poor predicted outcome, 85% of patients collected on the Cobe Spectra, and 92% of patients collected on the Optia, failed to collect at least 1 × 106 CD34/kg. A revised model is tested retrospectively on Optia data, and suggestions for further improvements are discussed.

Effective peripheral blood stem cell collection in a 4.6-kg child

BACKGROUND

Due to unique technical challenges, effective peripheral blood stem cell collections (PBSCs) have not been consistently reported in patients weighing less than 5 kg. We describe three PBSCs performed in a 4.6-kg child undergoing myeloablative chemotherapy for high-grade glioma.

STUDY DESIGN AND METHODS

A multidisciplinary group representing the clinical and apheresis teams adapted a PBSC protocol to accommodate the patient's size and collection targets. Special considerations included timing of the collection relative to chemotherapy, vascular access, strategies for monitoring adverse events during collection, and contingencies.

RESULTS AND DISCUSSION

The patient underwent three PBSC procedures over 2 days due to suboptimal collection after the first two procedures. For procedure 1, a conservative inlet: anticoagulant (AC) ratio and AC infusion rate of 15 and 0.6 mL/min/L total blood volume (TBV) resulted in premature discontinuation due to clotting. A ratio of 8 and AC infusion rate of 1.5-1.7 mL/min/L TBV with subsequent titration to higher levels were adopted for the second and third procedures. These changes resulted in greater acid-citrate-dextrose exposure, that was managed by continuous calcium chloride infusion. There was no hypocalcemia, hypotension, or distress during any procedure. A total of 15 × 106 CD34+ cells/kg were collected. This retrospective review illustrates that PBSC can be safely undertaken in children weighing less than 5 kg.

How do we operate a large monthly red blood cell exchange program

BACKGROUND

Red blood cell (RBC) exchange for sickle cell disease presents unique difficulties due to RBC phenotyping, complex antibody work-ups, large number of RBC units required, and vascular access considerations, any of which can delay the procedure. Multidisciplinary coordination and systemic processes ensure that monthly appointments remain on schedule.

STUDY DESIGN AND METHODS

A high-volume chronic RBC exchange program is described, highlighting the importance of multidisciplinary coordination and process improvement strategies involving initial referral, vascular access, order sets, and allocation of antigen-negative or phenotypically matched RBCs.

RESULTS

Approximately 50 outpatient RBC exchanges are performed each month with an 82% kept-appointment rate. Specific factors for program success include open communication across services and improvements to referrals and standardized order sets.

CONCLUSION

A combination of multidisciplinary coordination and process improvement can ensure the success of a high volume RBC exchange program. Frequent communication of upcoming appointments between the referring hematologists, the hemapheresis clinic, transfusion service, and interventional radiology is critical. Advance notice to the immunohematology reference lab of upcoming appointments is needed to allow enough time for allocating antigen-negative RBCs. Order sets can be leveraged to standardize and streamline RBC exchanges. Lastly, numerous mechanisms help patients compensate for the cognitive sequelae of stroke.

Benchmarking the centralized urgent plasma exchange service for patients admitted with a diagnosis of suspected acquired thrombotic thrombocytopenic purpura at a large healthcare system

BACKGROUND

Consensus guidelines recommend that therapeutic plasma exchange (TPE) should be started within 4 to 8 hours after the diagnosis of suspected acquired thrombotic thrombocytopenic purpura (aTTP). This study aimed to audit the steps from diagnosis to initiation of plasma exchange at a centralized apheresis service.

METHODS

A retrospective review of the electronic medical record and laboratory information systems from January 1, 2014 to August 31, 2017 was conducted to identify all patients with suspected aTTP undergoing TPE. Demographics, comorbidities, pertinent laboratory tests, and temporal TPE procedural data were collected.

RESULTS

The median (5th-95th percentile) time from request to initiation of TPE was 5.4 (3.2-10.6) hours. TPE was initiated within 8 hours in 94 of the 108 patients (87.0%). The median (5th-95th percentile) time from request to central venous access was 2.5 (0.5-6.9) hours and from request to plasma product issuance from the blood bank was 3.4 (1.6-8.1) hours. aTTP patients in whom TPE was initiated greater than 6 hours from request did not have worse outcomes compared to those with TPE initiation within 6 hours: in-hospital mortality (2/14 [14.3%] vs 2/21 [9.5%], P = 0.66), median length of stay (9.0 [4.7-44.1] vs 8.3 [3.9-27.0] days, P = 0.76), and median number of days to durable platelet count recovery (4.5 [2.0-9.0] vs 4.0 [2.0-18.0] days, P = 0.66).

CONCLUSIONS

The 4 to 8-hour target window from TPE request to initiation appears feasible for a centralized apheresis program servicing a large healthcare system.

Process mapping of the urgent red cell exchange procedure for patients with severe complications of sickle cell disease at a centralized hemapheresis service

Sickle cell disease (SCD) patients require urgent red cell exchange (RCE) procedures for acute chest syndrome (ACS), demanding a coordinated effort of multiple clinical services. Execution of RCE is a multistep process from the time the procedure is requested to the time the procedure is initiated. A retrospective review of patients with SCD requiring urgent RCE for ACS and stroke from 2012 to 2017 was performed at a centralized hemapheresis service covering a multihospital healthcare system. A total of 30 urgent RCE procedures performed on 28 patients were evaluated. The time required for red blood cell (RBC) preparation was the longest step in the process (median 3.8 hours). Furthermore, RBC preparation time was longer for sickle cell patients with RBC alloimmunization compared with nonalloimmunized patients (8.6 vs 3.8 hours, P = .03). One mortality event occurred in Ab- group. This study identified potentially modifiable factors, which impact the time to implementation of RCE in one service area. It highlights the importance of a structured and coordinated approach for the efficient and timely delivery of this vital treatment modality.

Influence of dihydropyrimidine dehydrogenase gene (DPYD) coding sequence variants on the development of fluoropyrimidine-related toxicity in patients with high-grade toxicity and patients with excellent tolerance of fluoropyrimidine-based chemotherapy

Alterations in dihydropyrimidine dehydrogenase gene (DPYD) coding for the key enzyme (DPD) of fluoropyrimidines (FPs) catabolism contribute to the development of serious FPs-related toxicity. We performed mutation analysis of DPYD based on cDNA sequencing in 76 predominantly colorectal cancer patients treated by FPs with early development of high (grade 3-4) hematological and/or gastrointestinal toxicity. Six previously described [85T>C (C29R), 496A>G (M166V), 775A>G (K259E), 1601G>A (S534N), 1627A>G (I543V), IVS14+1G>A, 2194G>A (V732I)] and two novel [187A>G (K63E) and 1050 G>A (R357H)] non-synonymous DPYD variants were found in 56/76 (73.7%) high-toxicity patients. Subsequently, these alterations were analyzed in 48 patients with excellent long-term tolerance of FPs and in 243 controls and were detected in 37/48 (77.1%) and 166/243 (68.3%) cases, respectively. Analysis of these alterations as risk factors for development of toxicity in pooled FPs-treated population demonstrated that C29R negatively correlated with overall gastrointestinal toxicity (OR = 0.48; 95%CI 0.23-1.0) and M166V in women protected against overall hematological toxicity and neutropenia (both OR = 0.26; 95%CI 0.07-0.89), whereas IVS14+1G>A (found in five high-toxicity patients only) increased risk of mucositis in overall population (OR = 7.0; 95%CI 1.1-44.53), and thrombocytopenia in women (OR = 10.8; 95%CI 1.24-93.98). Moreover, we identified a strong association of V732I with leucopenia (OR = 8.17; 95%CI 2.44 - 27.31) and neutropenia (OR=2.78; 95% CI 1.03-7.51). Our data enabled characterization of "high risk" haplotypes (carriers of IVS14+1G>A or V732 lacking M166V) representing small (22% female and 11% male patients), population in high risk of serious hematological toxicity development, and in patients with "lower risk" that unlikely develop serious hematological toxicity [carriers of M166V without IVS14+1G>A and V732I in females (32% women), and non-carriers of C29R, M166V, IVS14+1G>A, and V732I in males (46% men)]. Our results indicate that genotyping of several DPYD variants may lead to stratification of patients with respect to the risk of serious hematological toxicity development during FPs treatment.

Long-term BRCA1 down-regulation by small hairpin RNAs targeting the 3' untranslated region

Mutations in the BRCA1 gene are responsible for the majority of hereditary breast/ovarian cancers. The functional significance of many mutations/splicing variants identified during the screening of high-risk individuals is difficult to predict due to the lack of in vitro functional tests correlating sequence variants with a risk of cancer development. RNA interference is a promising tool in analyzing functional properties of BRCA1 mutations. Here we designed and functionally analyzed shRNAs directed to 3'-UTR of BRCA1 mRNA that may be used to knock-down expression of endogenous BRCA1. Using retroviral infection, we achieved long-term down-regulation of BRCA1 in a cell-type specific manner. We propose that 3'-UTR-directed shRNAs, coupled with up-regulation of exogenous mutated BRCA1 variants, may constitute a versatile system for the functional analysis of BRCA1 gene alterations.

Intrinsically disordered tau protein in Alzheimer's tangles: a coincidence or a rule?

Tau protein, the major constituent of neurofibrillary tangles in Alzheimer's disease (AD) and related tauopathies, is classified as intrinsically disordered protein (IDP). IDPs in contrast to globular proteins contain high proportion of polar and charged amino acids in their sequence, which results in the absence of a well-defined three-dimensional structure of the free protein. Structural flexibility of IDPs is required to perform their important role in many cellular processes. In the course of tauopathies, highly soluble disordered tau protein acquires rigid fold and forms highly insoluble filaments. Beneficial intrinsic disorder transforms into a fatal order: is it a coincidence, or is there an underlying reason for preferential IDPs assembly? In this review we present the structural characteristics of tau protein filamentous lesions in AD and discuss the tendency of IDPs to assembly and to form amyloid deposits (Ref: 65).

Ribonuclease from Streptomyces aureofaciens at atomic resolution

Crystals of ribonuclease from Streptomyces aureofaciens diffract to atomic resolution at room temperature. Using synchrotron radiation and an imaging-plate scanner, X-ray data have been recorded to 1.20 A resolution from a crystal of native enzyme and to 1.15 A from a crystal of a complex with guanosine-2'-monophosphate. Refinement with anisotropic atomic temperature factors resulted in increased accuracy of the structure. The R factors for the two structures are 10.6 and 10.9%. The estimated r.m.s. error in the coordinates is 0.05 A, less than half that obtained in the previous analysis at 1.7 A resolution. For the well ordered part of the main chain the error falls to below 0.02 A as estimated from inversion of the least-squares matrix. The two independent molecules in the asymmetric unit allowed detailed analysis of peptide planarity and some torsion angles. The high accuracy of the analysis revealed density for a partially occupied anion in the nucleotide binding site of molecule A in the native structure which was not seen at lower resolution. The anisotropic model allowed correction of the identity of the residue at position 72 from cysteine to threonine. Cys72 SG had been modelled in previous analyses with two conformations. The solvent structure was modelled by means of an automated procedure employing a set of objective criteria. The solvent structure for models refined using different programs with isotropic and anisotropic description of thermal motion is compared.

Complex of ribonuclease from Streptomyces aureofaciens with 2'-GMP at 1.7 A resolution

The crystal structure of a complex of ribonuclease from Streptomyces aureofaciens (RNase Sa) with guanosine-2'-monophosphate (2'-GMP) has been refined against synchrotron data recorded from a single crystal using radiation from beamline X31 at EMBL, Hamburg, and an imaging plate scanner. The crystals are in space group P2(1)2(1)2(1) with cell dimensions a = 64.7, b = 78.8 and c = 39.1 A. The structure has two enzyme molecules in the asymmetric unit, complexed with 2'-GMP inhibitor with occupancies of 1 and 2/3 (different to the 3'-GMP complex crystal structure where only one of the two independent RNase Sa molecules binds nucleotide), 492 associated water molecules and one sulfate ion, and was refined using all data between 10.0 and 1.7 A to a final crystallographic R factor of 13.25%. Binding of the base to the enzyme confirms the basis for the guanine specificity but the structural results still do not provide direct evidence of the identity and role of the particular residues involved in the catalytic process. New native RNase Sa data to 1.8 A were recorded to provide a reference set measured under comparable experimental conditions. The crystals are in the same space group and have the same lattice as those of the 2'-GMP complex. The native structure with 423 water molecules was refined in a similar manner to the complex to a final R factor of 13.87%. 1.77 A resolution data were independently measured on a 2'-GMP complex crystal at UCLA using an R-AXIS II image plate scanner mounted on a conventional source. The cell dimensions were essentially the same as above. 2'-GMP was bound more fully to molecule A than to molecule B of the RNase Sa. The structure was refined to an R factor of 14.64% with 388 water molecules. This work follows on from the structure determination of native RNase Sa and its complex with 3'-GMP [Sevcik, Dodson & Dodson (1991). Acta Cryst. B47, 240-253].

Tyrosine hydrogen bonds make a large contribution to protein stability

The aim of this study was to gain a better understanding of the contribution of hydrogen bonds by tyrosine -OH groups to protein stability. The amino acid sequences of RNases Sa and Sa3 are 69 % identical and each contains eight Tyr residues with seven at equivalent structural positions. We have measured the stability of the 16 tyrosine to phenylalanine mutants. For two equivalent mutants, the stability increases by 0.3 kcal/mol (RNase Sa Y30F) and 0.5 kcal/mol (RNase Sa3 Y33F) (1 kcal=4.184 kJ). For all of the other mutants, the stability decreases with the greatest decrease being 3.6 kcal/mol for RNase Sa Y52F. Seven of the 16 tyrosine residues form intramolecular hydrogen bonds and the average decrease in stability for these is 2.0(+/-1.0) kcal/mol. For the nine tyrosine residues that do not form intramolecular hydrogen bonds, the average decrease in stability is 0.4(+/-0.6) kcal/mol. Thus, most tyrosine -OH groups contribute favorably to protein stability even if they do not form intramolecular hydrogen bonds. Generally, the stability changes for equivalent positions in the two proteins are remarkably similar. Crystal structures were determined for two of the tyrosine to phenylalanine mutants of RNase Sa: Y80F (1.2 A), and Y86F (1.7 A). The structures are very similar to that of wild-type RNase Sa, and the hydrogen bonding partners of the tyrosine residues always form intermolecular hydrogen bonds to water in the mutants. These results provide further evidence that the hydrogen bonding and van der Waals interactions of polar groups in the tightly packed interior of folded proteins are more favorable than similar interactions with water in the unfolded protein, and that polar group burial makes a substantial contribution to protein stability.

Contribution of a conserved asparagine to the conformational stability of ribonucleases Sa, Ba, and T1

The contribution of hydrogen bonding by peptide groups to the conformational stability of globular proteins was studied. One of the conserved residues in the microbial ribonuclease (RNase) family is an asparagine at position 39 in RNase Sa, 44 in RNase T1, and 58 in RNase Ba (barnase). The amide group of this asparagine is buried and forms two similar intramolecular hydrogen bonds with a neighboring peptide group to anchor a loop on the surface of all three proteins. Thus, it is a good model for the hydrogen bonding of peptide groups. When the conserved asparagine is replaced with alanine, the decrease in the stability of the mutant proteins is 2.2 (Sa), 1.8 (T1), and 2.7 (Ba) kcal/mol. When the conserved asparagine is replaced by aspartate, the stability of the mutant proteins decreases by 1.5 and 1.8 kcal/mol for RNases Sa and T1, respectively, but increases by 0.5 kcal/mol for RNase Ba. When the conserved asparagine was replaced by serine, the stability of the mutant proteins was decreased by 2.3 and 1.7 kcal/mol for RNases Sa and T1, respectively. The structure of the Asn 39 --> Ser mutant of RNase Sa was determined at 1.7 A resolution. There is a significant conformational change near the site of the mutation: (1) the side chain of Ser 39 is oriented differently than that of Asn 39 and forms hydrogen bonds with two conserved water molecules; (2) the peptide bond of Ser 42 changes conformation in the mutant so that the side chain forms three new intramolecular hydrogen bonds with the backbone to replace three hydrogen bonds to water molecules present in the wild-type structure; and (3) the loss of the anchoring hydrogen bonds makes the surface loop more flexible in the mutant than it is in wild-type RNase Sa. The results show that burial and hydrogen bonding of the conserved asparagine make a large contribution to microbial RNase stability and emphasize the importance of structural information in interpreting stability studies of mutant proteins.

Conformational stability and thermodynamics of folding of ribonucleases Sa, Sa2 and Sa3

Ribonucleases Sa, Sa2, and Sa3 are three small, extracellular enzymes produced by different strains of Streptomyces aureofaciens with amino acid sequences that are 50% identical. We have studied the unfolding of these enzymes by heat and urea to determine the conformational stability and its dependence on temperature, pH, NaCl, and the disulfide bond. All three of the Sa ribonucleases unfold reversibly by a two-state mechanism with melting temperatures, Tm, at pH 7 of 48.4 degrees C (Sa), 41.1 degrees C (Sa2), and 47.2 degrees C (Sa3). The Tm values are increased in the presence of 0.5 M NaCl by 4.0 deg. C (Sa), 0.1 deg. C (Sa2), and 7.2 deg. C (Sa3). The Tm values are decreased by 20.0 deg. C (Sa), 31.5 deg. C (Sa2), and 27.0 deg. C (Sa3) when the single disulfide bond in the molecules is reduced. We compare these results with similar studies on two other members of the microbial ribonuclease family, RNase T1 and RNase Ba (barnase), and with a member of the mammalian ribonuclease family, RNase A. At pH 7 and 25 degrees C, the conformational stabilities of the ribonucleases are (kcal/mol): 2.9 (Sa2), 5.6 (Sa3), 6.1 (Sa), 6.6 (T1), 8.7 (Ba), and 9.2 (A). Our analysis of the stabilizing forces suggests that the hydrophobic effect contributes from 90 to 110 kcal/mol and that hydrogen bonding contributes from 70 to 105 kcal/mol to the stability of these ribonucleases. Thus, we think that the hydrophobic effect and hydrogen bonding make large but comparable contributions to the conformational stability of these proteins.

Crystallization and preliminary X-ray investigation of the complex of RNase Sa with wild-type barstar

RNase Sa, an extracellular ribonuclease produced by Streptomyces aureofaciens, is inhibited by barstar, the natural protein inhibitor of barnase, the ribonuclease of Bacillus amyloliquefaciens. The complex of RNase Sa with wild-type barstar was crystallized by hanging-drop vapour diffusion. It was shown by sodium dodecyl sulfate polyacrylamide gel electrophoresis that RNase Sa and barstar are present in equimolar proportions in the crystals. The crystals are in the hexagonal space group P65 with unit cell dimensions a = b = 56.95, c = 135.8 A. They diffract to 1.7 A resolution at the DESY synchronton source. The asymmetric unit contains one molecule of the complex.

Isolation and purification of two novel streptomycete RNase inhibitors, SaI14 and SaI20, and cloning, sequencing, and expression in Escherichia coli of the gene coding for SaI14

Two new RNase inhibitors, SaI14 (Mr, approximately 14,000) and SaI20 (Mr, approximately 20,000), were isolated and purified from a Streptomyces aureofaciens strain. The gene sai14, coding for SaI14 protein, was cloned and expressed in Escherichia coli. The alignment of the deduced amino acid sequence of SaI14 with that of barstar, the RNase inhibitor from Bacillus amyloliquefaciens, showed significant similarity between them, especially in the region which contains most of the residues involved in barnase-barstar complex formation.

Purification of ribonucleases Sa, Sa2, and Sa3 after expression in Escherichia coli

The genes for three small ribonucleases from different strains of Streptomyces aureofaciens have been cloned and expressed in Escherichia coli. The purification of these ribonucleases from the periplasmic space is described. The yields range from 10 to 50 mg of protein per liter of culture medium. The molar absorption coefficients, isoelectric pH values, and pH of optimum activity are reported.

Hypoxic changes in rat locus coeruleus neurons in vitro

1. Intracellular recordings were made in a pontine slice preparation of the rat brain containing the nucleus locus coeruleus (LC). Locus coeruleus neurons responded to brief hypoxic stimuli (replacement of 95% O2-5% CO2 with 95% N2-5% CO2) with hyperpolarization and a cessation of spontaneous action potentials. When the cells were continuously hyperpolarized by about 15 mV in order to abolish spontaneous firing, hypoxia induced an early depolarization (HD), followed by a hypoxic hyperpolarization (HH) and after reoxygenation, a posthypoxic hyperpolarization (PHH). These responses were accompanied by a decrease in input resistance, which was larger during HH than during HD but, thereafter, became smaller during PHH. 2. The hypoxia-induced currents associated with the changes in membrane potential, at a holding potential of -70 mV, were an early inward current (HIC), a subsequent outward current (HOC) and after reoxygenation, another outward current (PHOC). The HIC did not change with an increasing holding potential. In contrast, the HOC reversed its amplitude at about -95 mV. Finally, the PHOC decreased, but did not reverse its polarity at more negative holding potentials. When the external K+ was elevated from 2.5 to 10.5 mM, the current-voltage (I-V) relation of the HOC and its reversal potential were shifted to the right. 3. In the presence of tetrodotoxin, the HH decreased. A low Ca(2+)-high Mg2+ medium depressed both the HH and PHH. Rauwolscine did not alter either response to hypoxia, while 8-cyclopentyl-1,3-dipropylxanthine decreased the PHH only. S-(p-Nitrobenzyl)-6-thioguanosine potentiated both HH and PHH. 4. Whereas tolbutamide markedly lowered the HH and PHH, glibenclamide was ineffective. Tetraethylammonium also failed to alter the hypoxic responses. Furthermore, ouabain or the removal of K+ from the superfusion medium, depressed PHH. 5. Pressure application of adenosine inhibited the spontaneous firing of LC neurons. DPCPX did not alter the firing, but antagonized the effect of adenosine. Tolbutamide also counteracted the inhibitory effect of adenosine and, additionally, facilitated the firing rate in some neurons. Moreover, tolbutamide abolished the adenosine-induced outward current. 6. Early hypoxic depolarization and PHH are mostly due to the blockade and subsequent reactivation of the K(+)-Na+ pump, respectively. The HH is caused by the opening of ATP-sensitive K+ (KATP) channels in response to the hypoxia-induced decline of intracellular ATP. Adenosine released by hypoxic stimuli may lead to an adenosine A1-receptor-mediated opening of (KATP) channels during the HH and more markedly during the PHH.

Modulation of locus coeruleus neurons by extra- and intracellular adenosine 5'-triphosphate

The cell membrane of rat locus coeruleus (LC) neurons is sensitive to both extra- and intracellular ATP. Extracellular ATP or its enzymatically stable analogues activate membrane receptors of the P2 type. These receptors inhibit a persistent potassium current and simultaneously activate a nonselective cationic conductance. The resulting depolarization increases the spontaneous firing rate. A decrease in the concentration of intracellular ATP during hypoxia or hypoglycemia opens ATP-sensitive K+ (KATP) channels of LC neurons. The resulting hyperpolarization depresses the discharge of action potentials and conserved energy. The hypoxia-induced hyperpolarization is additionally due to the release of adenosine from neighboring neurons or glial cells. A certain class of compounds, termed potassium channel openers, also decrease the firing, while sulphonylurea antidiabetics known to block KATP channels increase it. Sulphonylurea antidiabetics antagonize the excitability decrease induced both by potassium channel openers and metabolic damage.

Effects of the central analgesic tramadol and its main metabolite, O-desmethyltramadol, on rat locus coeruleus neurones

1. Tramadol is a centrally acting analgesic with low opioid receptor affinity and, therefore, presumably additional mechanisms of analgesic action. Tramadol and its main metabolite O-desmethyltramadol were tested on rat central noradrenergic neurones of the nucleus locus coeruleus (LC), which are involved in the modulation of nociceptive afferent stimuli. 2. In pontine slices of the rat brain the spontaneous discharge of action potentials of LC cells was recorded extracellularly. (-)-Tramadol (0.1-100 microM), (+)-tramadol (0.1-100 microM), (-)-O-desmethyl-tramadol (0.1-100 microM) and (+)-O-desmethyltramadol (0.01-1 microM) inhibited the firing rate in a concentration-dependent manner. (+)-O-desmethyltramadol had the highest potency, while all other agonists were active at a similar range of concentrations. 3. (-)-Tramadol (10, 100 microM) was less inhibitory in brain slices of rats pretreated with reserpine (5 mg kg-1, 5 h before decapitation) than in controls. 4. The effect of (-)-tramadol (10 microM) was abolished in the presence of the alpha 2-adrenoceptor antagonist, rauwolscine (1 microM), whilst that of (+)-O-desmethyltramadol (0.3 microM) virtually disappeared in the presence of the opioid antagonist, naloxone (0.1 microM). (+)-Tramadol (30 microM) and (-)-O-desmethyl-tramadol (10 microM) became inactive only in the combined presence of naloxone (0.1 microM) and rauwolscine (1 microM). 5. In another series of experiments, the membrane potential of LC neurones was determined with intracellular microelectrodes. (-)-Tramadol (100 microM) inhibited the spontaneous firing and hyper-polarized the cells; this effect was abolished by rauwolscine (1 microM). (+)-O-desmethyltramadol (10 microM)had a similar but somewhat larger effect on the membrane potential than (-)-tramadol. The (+)-O-desmethyltramadol-(10 microM) induced hyperpolarization was abolished by naloxone (0.1 microM).6. The hyperpolarizing effect of noradrenaline (30 microM) was potentiated in the presence of (-)-tramadol(100 microM), but not in the presence of (+)-O-desmethyltramadol (10 microM). There was no potentiation of the noradrenaline (30 microM) effect, when the cells were hyperpolarized by current injection to an extent similar to that produced by (-)-tramadol (100 microM).7. Both noradrenaline (100 microM) and (- )-tramadol (100 microM) decreased the input resistance.8. The results confirm that the analgesic action of tramadol involves both opioid and non-opioid components. It appears that (-)-tramadol inhibits the uptake of noradrenaline and via a subsequent increase in the concentration of endogenous noradrenaline indirectly stimulates alpha2-adrenoceptors. (+)-0-desmethyltramadol seems to stimulate directly opioid micro-receptors. The effects of (+)-tramadol and(-)-O-desmethyltramadol consist of combined micro-opioid and alpha2-adrenergic components.

Complex of ribonuclease Sa with a cyclic nucleotide and a proposed model for the reaction intermediate

The structure of the complex of ribonuclease from Streptomyces aureofaciens (RNase Sa) with exo guanosine 2',3'-cyclophosphorothioate has been refined against 0.2-nm resolution synchrotron data using, as a starting model, coordinates from the RNase Sa: 2'-GMP complex. The refinement was based on all data over 1.0-0.2 nm and converged to a crystallographic R factor of 11.9%. This is the first structure of a microbial ribonuclease complexed with a 2',3'-cyclophosphorothioate, which is a thio analogue of the intermediate of the two-step reaction. However, exo guanosine 2',3'-cyclophosphorothioate is bound in a non-functional mode and is not hydrolysed. This structure therefore does not provide direct evidence on the identity of the amino acid residues responsible for catalytic cleavage of the substrate. However, based on present and previous results, a plausible model is proposed for the complex of the cyclic intermediate which acts as substrate for the second step of the catalysis.

Effects of potassium channel openers and their antagonists on rat locus coeruleus neurones

1. Intracellular recordings were obtained from a pontine slice preparation of the rat brain containing the locus coeruleus (LC). Two openers of ATP-sensitive potassium (K(ATP)) channels, RO 31-6930 (10 microM) and cromakalim (100 microM) decreased the spontaneous discharge of action potentials without altering their amplitude or duration. Neither compound changed the resting membrane potential. 2. Of two K(ATP) channel blockers, tolbutamide (300 microM) increased the firing rate, while glibenclamide (3 microM) only tended to do so. In addition, both compounds antagonized the effect of RO 31-6930 (10 microM). Neither glibenclamide (3 microM) nor tolbutamide (300 microM) altered the resting membrane potential. 3. Tetrodotoxin (0.5 microM) depressed the firing, but did not influence the inhibitory action of RO 31-6930 (10 microM). The excitatory amino acid antagonist, kynurenic acid (500 microM), did not change the spontaneous discharge of action potentials. 4. Small shifts (2-4 mV) of the membrane potential by hyper- or depolarizing current injections markedly decreased and increased the firing rate, respectively. 5. Noradrenaline (100 microM) hyperpolarized the cells and decreased their input resistance. This effect was not antagonized by glibenclamide (3 microM) or tolbutamide (300 microM). Ba2+ (2 mM), a blocker of both ATP-sensitive and inwardly rectifying potassium channels, abolished the effects of RO 31-6930 (10 microM) and noradrenaline (100 microM). 6. These data suggest that K(ATP) channels are present on the noradrenergic LC neurones, but are not coupled to alpha 2-adrenoceptors.

Galanin receptors inhibit the spontaneous firing of locus coeruleus neurones and interact with mu-opioid receptors

Electrophysiological experiments were performed in a pontine slice preparation of rat brain containing the locus coeruleus (LC). The extracellular part of this study showed that galanin (0.003-0.1 mumol/l), [Met5]enkephalin (0.01-10 mumol/l) and noradrenaline (0.1-100 mumol/l) concentration dependently inhibited the firing rate. Noradrenaline (1 and 3 mumol/l) had the same effect both before and during the application of galanin (0.001 or 0.01 mumol/l). Similarly, [Met5]enkephalin (0.03 and 0.1 mumol/l) produced identical inhibition, regardless of the presence or absence of 0.01 mumol/l galanin. Whereas rauwolscine (1 mumol/l) potentiated the effect of galanin (0.03 mumol/l), idazoxan (1 mumol/l) was inactive. In contrast, both naloxone (0.1 mumol/l) and beta-funaltrexamine (0.1 mumol/l) facilitated the galanin-induced inhibition. In the intracellular experiments, galanin (0.3 mumol/l) abolished the spontaneous discharge of action potentials, hyperpolarized the cells and decreased their input resistance. In conclusion, galanin may depress the firing rate by increasing a potassium permeability. Moreover, galanin receptors appear to interact with mu-opioid receptors but not with alpha 2-adrenoceptors.

Cloning and sequencing of the gene encoding a ribonuclease from Streptomyces aureofaciens CCM3239

A ribonuclease-encoding gene (rnaSa3) from Streptomyces aureofaciens CCM3239 has been isolated and sequenced. The deduced amino acid sequence shows 77% homology with RNase Sa from S. aureofaciens.

A comparative study on the catalytic properties of guanyl-specific ribonucleases

The kinetic parameters of reactions catalyzed by four guanyl-specific RNases T1, Pb1, Th1 and Sa were studied comparatively using three types of substrates; guanosine-2',3'-cyclophosphates, GpN dinucleoside phosphates and synthetic polyribonucleotides. The kinetic parameters were shown to be similar in spite of considerable differences in primary structures of these RNases, including amino acid residues of the active sites. Therefore, primary structures of guanyl RNases allow for a considerable number of substitutions (both in the 'recognising' and catalytical parts of the active site) without changes in the catalytical parameters.

Specificity of guanylic RNases to polynucleotide substrates

Kinetic parameters kcat and KM were measured for cleavage of poly I, poly A, poly U, poly C and poly I poly C by guanyl-specific RNases Sa, Pb1 and T1 and compared with that of guanyl-preferential RNase Bi. Catalytic efficiencies of the investigated enzymes to polynucleotide substrates vary considerably. The structural basis for specificity of these RNases is discussed. A hypothesis is suggested that Ser-56 plays an important role in recognition of poly A by RNase Bi.

Determination and restrained least-squares refinement of the structures of ribonuclease Sa and its complex with 3'-guanylic acid at 1.8 A resolution

The crystal structures of ribonuclease from Streptomyces aureofaciens (RNase Sa) and its complex with 3'-guanylic acid (guanosine 3'-monophosphate, 3'-GMP) have been determined by the method of isomorphous replacement. The atomic parameters have been refined by restrained least-squares minimization using data in the resolution range 10.0-1.8 A. All protein atoms and more than 230 water atoms in the two crystal structures have been refined to crystallographic R factors of 0.172 and 0.175 respectively. The estimated r.m.s. error in the atomic positions ranges from 0.2 A for well-defined atoms to about 0.5 A for more poorly defined atoms. There are two enzyme molecules in the asymmetric unit, built independently, and referred to as molecules A and B. The value of the average B factor for protein atoms in both structures is about 19 A2 and for water molecules about 35 A2. Electron density for the substrate analogue 3'-GMP was found only at the active site of molecule A. The density was very clear and the positions of all 3'-GMP atoms were refined with precision comparable to that of the protein.

Comparison of active sites of some microbial ribonucleases: structural basis for guanylic specificity

Crystallographic studies of enzymes complexed with suitable ligands are an important tool to aid our understanding of biological catalysis. To this goal, a contribution is made by analysing structures of complexes formed by three guanyl-specific ribonucleases with guanosine 3'-monophosphate.

The effect of substance P on nerve action potential propagation and cholinergic transmission in the myenteric plexus of the guinea-pig ileum

The effect of substance P on nerve terminals in myenteric plexus of the guinea-pig ileum was investigated. Neurogenic twitches of the myenteric plexus longitudinal muscle strip were recorded. Twitches of the strip portion where excitation involved the most distal parts of cholinergic nerve terminals were more increased by local application of substance P (0.1 and 0.4 nmol/l) than twitches of the portion where excitation involved both distal and proximal parts of nerve terminals. Substance P addition to a portion of the strip conducting nerve action potentials to invade the neighbouring strip portion also augmented twitches of the latter portion so that the interference with the propagation process was considered. The effect of substance P was poorly antagonized by the addition of a substance P antagonist, (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-substance P. Compound nerve action potentials were evoked in strands of fibres of the myenteric plexus by low-frequency train stimulation (1 Hz). The addition of substance P prevented a decrease of the amplitude of responses observed under control conditions. Using high-frequency train stimulation (30 Hz) the amplitude of responses to impulses 2-7 was augmented over that to the first impulse; substance P further increased such facilitation regularly. It seems that substance P might promote nerve action potential invasion of the distal parts of nerve terminals.

The topographical basis of cholinergic transmission in guinea-pig ileum myenteric plexus

Myenteric plexus-longitudinal muscle strips were used to study nerve action potential propagation and transmission and their differences between the proximal and the distal regions of cholinergic terminals. Neurogenic twitches of a portion of the strip were evoked by focal electrical stimulation. Twitches mediated by the distal regions of cholinergic nerve terminals were more influenced by drugs affecting Ca2+ "utilization" (Bay K 8644, kappa opiate ligand ethylketocyclazocine, changes in extracellular Ca2+ or Co2+ concentration) in contrast to twitches mediated by proximal regions of these terminals which were more influenced by drugs affecting sodium-potassium spike (tetrodotoxin, dendrotoxin, 4-aminopyridine, tetraethylammonium). Post-tetanic potentiation of twitches was prominent with that portion of the strip where the distal regions of nerve terminals were involved. Drugs interfering with Na+/K+ spikes indiscriminately influenced both the twitch height and post-tetanic potentiation whereas changes in extracellular Ca2+ concentration affected selectively only post-tetanic potentiation. Release of [3H]acetylcholine from pre-labelled strips evoked by 1 Hz continuous stimulation or by train stimulation at 30 Hz was measured selectively from portions containing either proximal and distal or only distal regions of nerve terminals. The release from portions containing the distal regions was relatively higher when evoked by 30 Hz than by 1 Hz. The distal regions of nerve terminals might be thus recruited to participate in transmission by a frequency-dependent process. Nerve impulses were recorded from strands of nerve fibres in the myenteric plexus. At 1 and 5 mm distance from the stimulation focus nerve impulses were completely suppressed by tetrodotoxin. At 5 mm, in some strands the amplitude of nerve impulses was also subject to the effect of drugs affecting Ca2+ "utilization"; facilitation of nerve impulse amplitude during 30 Hz train stimulation was always influenced by drugs affecting Ca2+ "utilization". Propagation of nerve impulses in the distal region of cholinergic nerve terminals was found to be Ca-sensitive and frequency-dependent; this might form the basis for facilitation and post-tetanic potentiation of muscarinic transmission.