A case of severe hyponatremia due to linezolid-induced SIADH.

WHAT IS KNOWN AND OBJECTIVE: Hyponatremia is the most common electrolyte disorder. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is the main cause of euvolemic hyponatremia and is often associated with medications or underlying diseases. Linezolid is a potent antibiotic against resistant Gram-positive microorganisms that has been associated with mild hyponatremia, yet with a mechanism different from SIADH. CASE SUMMARY: We present the case of a patient who developed severe hyponatremia during treatment with linezolid for an ampicillin-resistant E. faecium bacteremia. A thorough work-up during the hyponatremia, as well as after it resolved, firmly identified SIADH as its cause. Importantly, SIADH occurred after linezolid was started and resolved after it was stopped, and a work-up for another cause of SIADH was negative, suggesting that linezolid was the cause of SIADH in this patient. WHAT IS NEW AND CONCLUSION: This is the second case of a linezolid-induced SIADH, diagnosed with a thorough work-up so to correctly differentiate between SIADH from other causes of hyponatremia.

Frequent COL4 mutations in familial microhematuria accompanied by later-onset Alport nephropathy due to focal segmental glomerulosclerosis.

Familial microscopic hematuria (FMH) is associated with a genetically heterogeneous group of conditions including the collagen-IV nephropathies, the heritable C3/CFHR5 nephropathy and the glomerulopathy with fibronectin deposits. The clinical course varies widely, ranging from isolated benign familial hematuria to end-stage renal disease (ESRD) later in life. We investigated 24 families using next generation sequencing (NGS) for 5 genes: COL4A3, COL4A4, COL4A5, CFHR5 and FN1. In 17 families (71%), we found 15 pathogenic mutations in COL4A3/A4/A5, 9 of them novel. In 5 families patients inherited classical AS with hemizygous X-linked COL4A5 mutations. Even more patients developed later-onset Alport-related nephropathy having inherited heterozygous COL4A3/A4 mutations that cause thin basement membranes. Amongst 62 heterozygous or hemizygous patients, 8 (13%) reached ESRD, while 25% of patients with heterozygous COL4A3/A4 mutations, aged >50-years, reached ESRD. In conclusion, COL4A mutations comprise a frequent cause of FMH. Heterozygous COL4A3/A4 mutations predispose to renal function impairment, supporting that thin basement membrane nephropathy is not always benign. The molecular diagnosis is essential for differentiating the X-linked from the autosomal recessive and dominant inheritance. Finally, NGS technology is established as the gold standard for the diagnosis of FMH and associated collagen-IV glomerulopathies, frequently averting the need for invasive renal biopsies.

Limited impact of colistin resistance on mortality of intensive care patients with carbapenem-resistant bacteraemia.

BACKGROUND: Increasing incidence of carbapenem-resistant Gram-negative bacteraemia (CR-GNB) has triggered increased use of polymyxins, likely fuelling the emergence and spread of colistin resistance. AIM: To estimate the excess clinical burden of colistin resistance in intensive care patients with CR-GNB. METHODS: A cohort of patients with CR-GNB during their stay in the intensive care unit (ICU) of a university hospital in Greece over a 4-year period (2020-2023) was constructed. Competing risks survival analysis was performed to estimate the burden associated with colistin resistance. FINDINGS: Of the 177 ICU patients with CR-GNB, 134 (76%) had colistin-resistant isolates, predominantly Acinetobacter baumannii (79%), identified by broth microdilution. Patients with colistin-resistant infection were similar to those with colistin-susceptible infection with respect to age, sex, APACHE II score, Charlson comorbidity index score, Pitt bacteraemia score, prior surgery and the occurrence of polymicrobial cultures. However, patients in the colistin-resistant group had lower risk of mortality compared with those in the colistin-susceptible group (31% vs 44%, P = 0.004 at 14 days, respectively; 46% vs 56% at 28 days, respectively; P = 0.173). Multi-variable regression analysis confirmed that colistin-resistant CR-GNB was associated with significantly lower risk of inpatient death compared with colistin-susceptible CR-GNB within 14 days [cause-specific hazard ratio (csHR) 0.53, 95% CI 0.28-1.01) and 28 days (csHR 0.55, 95% CI 0.31-0.95) of infection onset. CONCLUSION: Limited impact of colistin resistance on mortality was demonstrated in a large contemporary cohort of ICU patients with CR-GNB, possibly reflecting the recent shift away from colistin-based treatment regimens.

A new bacteriophage P1-derived vector for the propagation of large human DNA fragments.

We have designed a P1 vector (pCYPAC-1) for the introduction of recombinant DNA into E. coli using electroporation procedures. The new cloning system, P1-derived artificial chromosomes (PACs), was used to establish an initial 15,000 clone library with an average insert size of 130-150 kilobase pairs (kb). No chimaerism has been observed in 34 clones, by fluorescence in situ hybridization. Similarly, no insert instability has been observed after extended culturing, for 20 clones. We conclude that the PAC cloning system will be useful in the mapping and detailed analysis of complex genomes.

Metabolic profile of patients with isolated systolic hypertension.

PURPOSE/OBJECTIVE: While hypertension is an important contributor to cardiovascular disease (CVD) and its treatment has well-established mortality benefits, there is uncertainty as regards the management of isolated systolic hypertension (ISH). Furthermore, the association of ISH with CVD and mortality has been established, but the metabolic characteristics of the affected population have not as yet been adequately described. The aim of this study was to describe the metabolic profiles of patients with ISH. METHODS: An observational study of patients attending the Hypertension Unit of the University Hospital of Heraklion, Crete, Greece, was performed. RESULTS: In total, 809 hypertensive patients not on any antihypertensive treatment were identified. Among them, 44.7% were men, aged 55.6 ± 12.5 years, while 29.7% of both men and women were smokers. Systolic blood pressure was 161.3 ± 15.8 mmHg and diastolic blood pressure was 96.1 ± 11.3 mmHg. Body mass index (BMI) was 31 ± 5.3 kg/m2, while 9.6% had type 2 diabetes (T2D). A comparison of patients with ISH with those with hypertension, but not ISH, revealed that patients with ISH were older and had lower SBP and higher pulse pressure, while they also had lower total cholesterol and LDL and were more likely to have T2D, albeit they had a slightly lower BMI. On the other hand, they did not have any difference in terms of gender, smoking status, HDL, triglycerides, liver biochemistry, uric acid, or prevalence of impaired fasting glucose. CONCLUSION: Patients with ISH were older, with lower SBP, total cholesterol, and LDL and higher pulse pressure and higher prevalence of diabetes.

Gram-negative bacteria as emerging pathogens affecting mortality in skin and soft tissue infections.

INTRODUCTION: Skin and soft tissue infections (SSTIs) are commonly encountered in clinical practice and mainly caused by gram-positive cocci such as S.aureus and ß-hemolytic streptococci. Complicated SSTIs involving deeper tissues often necessitate surgical intervention and occur in patients with significant comorbidities such as diabetes or immunocompromising conditions. METHODS: In this study, we retrospectively reviewed the epidemiology, clinical characteristics, microbiology, and treatment of patients admitted with SSTI during a five-year period in the Internal Medicine Department of a tertiary hospital. RESULTS: During the study period, 317 patients were recorded, with a mean age of 72.1 years. The most common underlying medical conditions were diabetes mellitus, chronic kidney disease, and heart failure. Cultures were positive in 23.3 % of cases, 62.2 % of which were polymicrobial. The most frequently isolated microorganisms were Enterococci, Escherichia coli, and Pseudomonas aeruginosa. Significant antimicrobial resistance rates were noted, in particular for gram-negative microorganisms. Mortality was higher than described in the literature and associated with age, comorbidities, and infection by gram-negative microorganisms. CONCLUSION: This study denotes the role of gram-negative bacteria in SSTI epidemiology. Therapeutic protocols regarding the empiric treatment of SSTIs should necessarily take into account the local epidemiology of isolated pathogens and antimicrobial resistance. HIPPOKRATIA 2018, 22(1): 23-28.

A statistical state dynamics approach to wall turbulence.

This paper reviews results obtained using statistical state dynamics (SSD) that demonstrate the benefits of adopting this perspective for understanding turbulence in wall-bounded shear flows. The SSD approach used in this work employs a second-order closure that retains only the interaction between the streamwise mean flow and the streamwise mean perturbation covariance. This closure restricts nonlinearity in the SSD to that explicitly retained in the streamwise constant mean flow together with nonlinear interactions between the mean flow and the perturbation covariance. This dynamical restriction, in which explicit perturbation-perturbation nonlinearity is removed from the perturbation equation, results in a simplified dynamics referred to as the restricted nonlinear (RNL) dynamics. RNL systems, in which a finite ensemble of realizations of the perturbation equation share the same mean flow, provide tractable approximations to the SSD, which is equivalent to an infinite ensemble RNL system. This infinite ensemble system, referred to as the stochastic structural stability theory system, introduces new analysis tools for studying turbulence. RNL systems provide computationally efficient means to approximate the SSD and produce self-sustaining turbulence exhibiting qualitative features similar to those observed in direct numerical simulations despite greatly simplified dynamics. The results presented show that RNL turbulence can be supported by as few as a single streamwise varying component interacting with the streamwise constant mean flow and that judicious selection of this truncated support or 'band-limiting' can be used to improve quantitative accuracy of RNL turbulence. These results suggest that the SSD approach provides new analytical and computational tools that allow new insights into wall turbulence.This article is part of the themed issue 'Toward the development of high-fidelity models of wall turbulence at large Reynolds number'.

Insertion of disease-causing mutations in BACs by homologous recombination in Escherichia coli.

We have used GET Recombination, an inducible homologous recombination system for Escherichia coli, to insert one of the most common thalassaemia mutations into the intact beta-globin locus in a second generation BAC vector. We first inserted a PCR fragment carrying the tetracycline resistance gene (TetR) into the beta-globin gene. All recombinant clones examined contained the TetR gene at the correct target site. Next, a PCR fragment with the IVS I-110 G-->A splicing mutation but no selectable marker was used to replace the TetR gene in a second round of GET Recombination. Recombinant clones were selected by plating on medium containing chlorotetracycline and fusaric acid. Although counterselection for the TetR gene is not very efficient, four recombinant colonies with the IVS I-110 mutation were identified among 480 clones screened. Analysis of the recombinant clones did not show any other modifications or rearrangements. Thus the TetR gene can be used in combination with GET Recombination to introduce point mutations and other modifications in BACs without leaving behind any operational sequences, in order to generate accurate cell and transgenic mouse models for various diseases.

Engineering EGFP reporter constructs into a 200 kb human beta-globin BAC clone using GET Recombination.

GET Recombination, a simple inducible homologous recombination system for Escherichia coli, was used to target insertion of an EGFP cassette between the start and termination codons of the beta-globin gene in a 200 kb BAC clone. The high degree of homology between the promoter regions of the beta- and delta-globin genes also allowed the simultaneous generation of a delta-globin reporter construct with the deletion of 8.8 kb of intervening sequences. Both constructs expressed EGFP after transient transfection of MEL cells. Similarly, targeting of the EGFP cassette between the promoter regions of the gamma-globin genes and the termination codon of the beta-globin gene enabled the generation of reporter constructs for both (A)gamma- and (G)gamma-globin genes, involving specific deletions of 24 and 29 kb of genomic sequence, respectively. Finally the EGFP cassette was also inserted between the epsilon- and beta-globin genes, with the simultaneous deletion of 44 kb of intervening sequence. The modified constructs were generated at high efficiency, illustrating the usefulness of GET Recombination to generate large deletions of specific sequences in BACs for functional studies. The establishment of stable erythropoietic cell lines with these globin constructs will facilitate the search for therapeutic agents that modify the expression of the individual globin genes in a physiologically relevant manner.

Phase transition characteristics of diphosphatidyl-glycerol (cardiolipin) and stereoisomeric phosphatidyldiacylglycerol bilayers. Mono- and divalent metal ion effects.

Synthesis and phase transition chaaracteristics of aqueous dispersions of the homologous (12 : 0, 14 : 0, 16 : 0) diphosphatidylglycerols (cardiolipins) and phosphatidyldiacylglycerols are reported. Electron microscopy of the negatively stained aqueous dispersions reveals a characteristic lamellar structure suggesting that these phospholipid molecules are organized as bilayers in the aqueous dispersions. The phase transition temperature (Tm) and the enthalpy of transition (delta H) increase monotonically with chain length in the cardiolipin and phosphatidyldiacylglycerol series; Tm for phosphatidyldiacylglycerol is higher than that for cardiolipin of the same chain-length. The transition temperatures for the enantiomeric sn-3,3- and sn-1,1-phosphatidyldiacylglycerol and for the diastereomeric, meso-sn-1,3-phosphatidyldiacylglycerol are approximately the same. The molar enthalpy for the transition of cardiolipin-NH+4 bilayers is approximately twice the value for the phosphatidylcholines of the same chain length, i.e., the molar enthalpy per acyl chain is approximately the same in the two systems. The transition temperatures for metal ion salts of C16-cardiolipin exhibit a biphasic dependence upon the unhydrated ionic radii, i.e., the highest Tm is observed for Ca2+-cardiolipin and decreases for the salts of ions with smaller and larger ionic radii than that of Ca2+. The lowest Tm is observed for Rb+-cardiolipin. Monovalent metal salts of cardiolipin exhibit two phase transitions. This effect may result from different conformational packing of the four acyl chains due to differences in metal-phosphate binding.

Phosphatidylcholesterol bilayers. A model for phospholipid-cholesterol interaction.

Aqueous dispersions of monovalent and divalent cations salts of O-(1,2-dipalmitosyl-sn-glycero-3-phosphoryl)cholesterol form multilamellar vesicles as shown by freeze-fracture electron microscopy, by electron micrographs of the negatively stained liposomes, and by swelling curves of liposomes in hypo-osmotic medium. Differential scanning calorimetry reveals that aqueous dispersions of divalent metal salts of O-(1,2-dipalmitoyl-sn-glycero-3-phosphoryl)cholesterol undergo a characteristic thermotropic phase transition with a relatively large cooperative unit (n greater than 250 for the calcium salt). In contrast, monovalent cation salts of O-(1,2-dipalmitoyl-sn-glycero-3-phosphoryl)cholesterol do not show a thermotropic phase transition under comparable conditions. The molecular area of 0-(1,2-dipalmitoyl-sn-glycero-3-phosphoryl)cholesterol in a monolayer is the same in the presence and absence of Ca2+, and is virtually equal to the area of an equimolar mixture of dipalmitoyl phosphatidic acid and cholesterol. To account for the novel state induced by Ca2+, on aqueous dispersions of O-(1,2-dipalmitoyl-sn-glycero-3-phosphoryl)cholesterol (i.e., bilayer organization and highly cooperative phase transition), a linear array model is proposed in which Ca2+ bridges adjacent arrays of O-(1,2-dipalmitoyl-sn-glycero-3-phosphoryl)cholesterol molecules, thus freezing the acyl chains in their normal state. One of the main corollaries of the model is that the cooperative unit for a thermotropic phase transition is essentially one-dimensional, rather than a two-dimensional matrix. O-(1,2-Dipalmitoyl-sn-glycero-3-phosphoryl)cholesterol is proposed as an orientationally and conformationally restricted analog of glycerophospholipid plus cholesterol in bilayers.

Physical stability of sonicated arsonoliposomes: effect of calcium ions.

The physical stability of sonicated arsonoliposomes in the absence and presence of Ca(2+) ions is evaluated. Cholesterol-containing arsonoliposomes composed of arsonolipids [having different acyl chains (C(12)-C(18))], or mixtures of arsonolipids with phospholipids (phosphatidylcholine or distearoyl-phosphatidylcholine) were prepared, and physical stability was evaluated in the absence and presence of CaCl(2), by vesicle dispersions turbidity measurements and cryo-electron microscopy morphological assessment. In some cases, vesicle zeta-potential was measured, under identical conditions. Results demonstrate that self-aggregation of the vesicles studied is low and influenced by the acyl chain length of the arsonolipid used, whereas calcium-induced aggregation is higher, correlating well with the decreased values of vesicle zeta-potential in the presence of Ca(2+) ions (weaker electrostatic repulsion). Acyl chain length of arsonolipids used has a significant quantitative effect on Ca(2+)-induced vesicle aggregation mainly for arsonoliposomes that contain phospholipids (mixed), compared with the vesicles that consist of plain arsonolipids (significant effect only for initial aggregation at time 0). Another difference between plain and mixed arsonoliposomes is that for mixed arsonoliposomes Ca(2+)-induced increases in turbidity are irreversible by ethylenediaminotetraacetic acid, suggesting that vesicle fusion is taking place. This was confirmed by cryo-electron microscopy observations. Finally, when phosphatidylcholine is replaced by distearoyl-phosphatidylcholine, arsonoliposomes are more stable in terms of self-aggregation, but in the presence of calcium, the turbidity and morphology results are similar.

The effect of pH on the electrophoretic behaviour of a new class of liposomes: arsonoliposomes.

Herein we report the effect of pH on the surface charge of a new class of liposomes: arsonoliposomes. Plain or mixed arsonoliposomes with cholesterol (Chol) and distearoyl-phosphatidylcholine (DSPC) in 1:1 molar ratio were prepared with lauryl-(C12), myristoyl-(C14) and palmitoyl-(C16) acyl side chain arsonolipids. The one step hydration method was used for vesicle preparation and zeta potential measurements were performed in the pH range from 3 to 9. The results revealed that these lipids hold a negative surface charge at all pH values investigated. The presence of cholesterol in 1:1 molar ratio results in higher zeta potential compared with plain arsonoliposomes with the exception of palmitoyl-(C16) acyl chain arsonolipids in neutral and slightly basic pH values. Oppositely, the DSPC (1:1 molar ratio) containing arsonoliposomes had lower values of zeta potential compared with plain arsonoliposomes. Concluding, the experimental results reveal that zeta potential of arsonoliposomes is indeed modified when the vesicles are incubated in environments with different acidity. In most cases these changes are in accordance with the ionization pattern of the arsonolipid headgroup, while some peculiar deviations may be connected with the known difference in the structure between some of the vesicle types studied.

Regulated systemic activation of rat plasma prorenin.

Nephrectomized rats have above-normal plasma prorenin levels, presumably of extra-renal origin, but essentially no renin, suggesting a lack of "convertase" for prorenin activation. Adrenalectomized rats have low plasma prorenin levels accompanied by high renin activity, suggesting enhanced prorenin activation by the action of a stimulated "convertase" mechanism. Cross-circulation between adrenalectomized and nephrectomized rats for 15 or 30 minutes, dramatically lowered prorenin and raised renin levels in both types of rats, suggesting extensive activation of prorenin to renin. Similarly, in vitro mixing of these bloods (without cross-circulation) raised renin activity over five times the expected calculated level, while prorenin essentially disappeared. In both cases, prorenin from nephrectomized rat plasma apparently was activated to renin by the enhanced action of "convertase" in the adrenalectomized rat plasma. This newly generated renin activity was, like normal plasma renin, almost completely inhibited by a monoclonal antibody against hog renin and generated an immunoreactive angiotensin I. In contrast, cross-circulation or in vitro mixing of blood from normal control and nephrectomized rats produced little detectable activation of prorenin and only modest increments of renin, suggesting relative inactivity of the "convertase" mechanism in normal plasma. Our data suggest that activation of plasma prorenin is a significant regulated pathway for renin production, as it is greatly stimulated after adrenalectomy and deficient after nephrectomy, thereby implicating the kidney as an important contributor to the "convertase" mechanism operating within the circulation.

Use of matrix-immobilised recombinant plasmids to purify chain-specific rabbit globin complementary DNAs.

The cloning of DNA sequences in plasmid recombinants has made it possible to amplify specific sequences to an extent that they can be used for preparative purposes. We describe the use of rabbit globin DNA sequences cloned in the plasmid pCR1 and covalently bound to Sepharose 4B for the purification of chain-specific rabbit alpha- and beta-globin cDNAs. These purified probes were then used to estimate the length of the alpha- and beta-globin DNA sequences inserted into the recombinant plasmid. The technique should allow the rapid isolation of sequence-specific cDNA, RNA and genomic DNA.

Detection of Duchenne and Becker muscular dystrophy carriers by quantitative multiplex polymerase chain reaction analysis.

We developed a method for the detection of Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) carriers. The method is based on the quantitative analysis of the products of standard multiplex polymerase chain reaction (PCR) from 18 different exons of the dystrophin gene, and is designated "QM-PCR." We detected deletions of one or more exons by standard multiplex PCR in DMD/BMD patients in 14 of 18 families examined (77.7%). The same deletions were readily demonstrated by QM-PCR in nine of 14 mothers (64.3%) and in another six of 22 possible carriers in these families. In five families where deletions were detectable in DMD/BMD patients, the mothers did not exhibit any deletions in their peripheral blood (35.7%). We obtained evidence for germinal mosaicism in at least two of these families and confirmed carrier identification by haplotype analysis using CA repeat polymorphisms at the 5' and 3' ends of the dystrophin gene. Furthermore, analysis of 17 coded DNA samples from normal females and obligatory carriers by QM-PCR showed that this technique could directly identify carriers of deletions in any of 18 different exons of the dystrophin gene. Its application in combination with existing techniques is expected to significantly improve the accuracy of carrier diagnosis in many families, and it may also be applicable to families in which pedigree and polymorphism information is insufficient for carrier diagnosis.