Left ventricular myocardial work in patients with secondary mitral regurgitation

Background

Assessment of left ventricular (LV) function in patients with secondary mitral regurgitation (SMR) remains challenging because LV ejection fraction (LVEF) reflects changes in LV volume without taking into account the direction of the blood flow. LV global longitudinal strain better reflects active LV myocardial deformation but does not incorporate afterload. LV myocardial work derived from pressure-strain loops integrates speckle tracking echocardiography with non-invasive blood pressure measurement.

Purpose

To evaluate LV myocardial work components to better characterize LV function in patients with SMR.

Methods

378 patients (72% men, median age 68 [range 60 to 74 years]) with various grades of SMR were retrospectively analysed. LV myocardial constructive work, wasted work and work efficiency were measured with speckle tracking echocardiography.

Results

145 patients had mild SMR, 130 moderate SMR and 103 severe SMR. Patients with severe SMR had larger LV volumes, lower LVEF and more impaired LV GLS (Table 1). While LV constructive work was more impaired in patients with severe SMR, wasted work was lower as compared to mild SMR (Table 1). Consequently, patients with severe SMR had better myocardial work efficiency than patients with mild MR. This could reflect, the regurgitant volume which is pumped into a low pressure chamber (the left atrium) resulting in less myocardial wasted work and preservation of myocardial efficiency.

Conclusion

In patients with severe SMR, LVEF, LV GLS and myocardial constructive work are more impaired when compared to mild SMR. However, myocardial wasted work is lower, resulting in higher better LV myocardial work efficiency.

Funding Acknowledgement

Type of funding source: None

Prognostic value of global myocardial constructive work in patients with secondary mitral regurgitation

Background

Left ventricular (LV) myocardial contractility evaluation is of crucial importance in patients with secondary mitral regurgitation (SMR). The most widespread echocardiographic tool, left ventricular ejection fraction (LVEF), might overestimate LV function, since it calculates the volume changes regardless of the flow direction. Global myocardial constructive work (GMCW) might be a more suitable tool, as LV myocardial work derived from pressure-strain loops obtained with speckle tracking echocardiography incorporates non-invasive blood pressure measurements.

Purpose

To evaluate the prognostic value of LV GMCW in patients with SMR.

Methods

378 patients (72% men, median age 68 [range 60 to 74 years]) with various grades of SMR were retrospectively analysed. LV global myocardial constructive work, wasted work and work efficiency were measured with speckle tracking echocardiography.

Results

There were 145 patients with mild SMR, 130 with moderate SMR and 103 with severe SMR. Patients with severe SMR had larger LV volumes, lower LVEF and more impaired LV GLS. GMCW was more impaired in patients with severe SMR, compared with mild MR (678 mmHg% vs. 845 mmHg% p<0.001 respectively). After a mean follow-up of 59±37 months, 162 patients died. When dividing the population according to prognostically relevant cut offs derived by spline curve analysis, patients with a GMCW≤700 mmHg% had a worse prognosis, compared with their counterparts (Figure 1).

Conclusion

Global myocardial constructive work ≤700 mmHg% is associated with worse long-term survival in patients with SMR.

Kaplan-Meier survival curves

Funding Acknowledgement

Type of funding source: None

Age-dependent changes in intervertebral disc cell mitochondria and bioenergetics

Robust cellular bioenergetics is vital in the energy-demanding process of maintaining matrix homeostasis in the intervertebral disc. Age-related decline in disc cellular bioenergetics is hypothesised to contribute to the matrix homeostatic perturbation observed in intervertebral disc degeneration. The present study aimed to measure how ageing impacted disc cell mitochondria and bioenergetics. Age-related changes measured included matrix content and cellularity in disc tissue, as well as matrix synthesis, cell proliferation and senescence markers in cell cultures derived from annulus fibrosus (AF) and nucleus pulposus (NP) isolated from the discs of young (6-9 months) and older (36-50 months) New Zealand White rabbits. Cellular bioenergetic parameters were measured using a Seahorse XFe96 Analyzer, in addition to quantitating mitochondrial morphological changes and membrane potential. Ageing reduced mitochondrial number and membrane potential in both cell types. Also, it significantly reduced glycolytic capacity, mitochondrial reserve capacity, maximum aerobic capacity and non-glucose-dependent respiration in NP. Moreover, NP cells exhibited age-related decline in matrix synthesis and reduced cellularity in older tissues. Despite a lack of changes in mitochondrial respiration with age, AF cells showed an increase in glycolysis and altered matrix production. While previous studies report age-related matrix degenerative changes in disc cells, the present study revealed, for the first time, that ageing affected mitochondrial number and function, particularly in NP cells. Consequently, age-related bioenergetic changes may contribute to the functional alterations in aged NP cells that underlie disc degeneration.

The effect of long-term bisphosphonate therapy on trabecular bone strength and microcrack density

Objectives

Bisphosphonates (BP) are the first-line treatment for preventing fragility fractures. However, concern regarding their efficacy is growing because bisphosphonate is associated with over-suppression of remodelling and accumulation of microcracks. While dual-energy X-ray absorptiometry (DXA) scanning may show a gain in bone density, the impact of this class of drug on mechanical properties remains unclear. We therefore sought to quantify the mechanical strength of bone treated with BP (oral alendronate), and correlate data with the microarchitecture and density of microcracks in comparison with untreated controls.

Methods

Trabecular bone from hip fracture patients treated with BP (n = 10) was compared with naïve fractured (n = 14) and non-fractured controls (n = 6). Trabecular cores were synchrotron scanned and micro-CT scanned for microstructural analysis, including quantification of bone volume fraction, microarchitecture and microcracks. The specimens were then mechanically tested in compression.

Results

BP bone was 28% lower in strength than untreated hip fracture bone, and 48% lower in strength than non-fractured control bone (4.6 MPa vs 6.4 MPa vs 8.9 MPa). BP-treated bone had 24% more microcracks than naïve fractured bone and 51% more than non-fractured control (8.12/cm²vs 6.55/cm²vs 5.25/cm²). BP and naïve fracture bone exhibited similar trabecular microarchitecture, with significantly lower bone volume fraction and connectivity than non-fractured controls.

Conclusion

BP therapy had no detectable mechanical benefit in the specimens examined. Instead, its use was associated with substantially reduced bone strength. This low strength may be due to the greater accumulation of microcracks and a lack of any discernible improvement in bone volume or microarchitecture. This preliminary study suggests that the clinical impact of BP-induced microcrack accumulation may be significant.

Cite this article: A. Jin, J. Cobb, U. Hansen, R. Bhattacharya, C. Reinhard, N. Vo, R. Atwood, J. Li, A. Karunaratne, C. Wiles, R. Abel. The effect of long-term bisphosphonate therapy on trabecular bone strength and microcrack density. Bone Joint Res 2017;6:602–609. DOI: 10.1302/2046-3758.610.BJR-2016-0321.R1.

Complex high-resolution linkage disequilibrium and haplotype patterns of single-nucleotide polymorphisms in 2.5 Mb of sequence on human chromosome 21

One approach to identify potentially important segments of the human genome is to search for DNA regions with nonrandom patterns of human sequence variation. Previous studies have investigated these patterns primarily in and around candidate gene regions. Here, we determined patterns of DNA sequence variation in 2.5 Mb of finished sequence from five regions on human chromosome 21. By sequencing 13 individual chromosomes, we identified 1460 single-nucleotide polymorphisms (SNPs) and obtained unambiguous haplotypes for all chromosomes. For all five chromosomal regions, we observed segments with high linkage disequilibrium (LD), extending from 1.7 to>81 kb (average 21.7 kb), disrupted by segments of similar or larger size with no significant LD between SNPs. At least 25% of the contig sequences consisted of segments with high LD between SNPs. Each of these segments was characterized by a restricted number of observed haplotypes,with the major haplotype found in over 60% of all chromosomes. In contrast, the interspersed segments with low LD showed significantly more haplotype patterns. The position and extent of the segments of high LD with restricted haplotype variability did not coincide with the location of coding sequences. Our results indicate that LD and haplotype patterns need to be investigated with closely spaced SNPs throughout the human genome, independent of the location of coding sequences, to reliably identify regions with significant LD useful for disease association studies.

Acetylation of nuclear hormone receptor-interacting protein RIP140 regulates binding of the transcriptional corepressor CtBP

CtBP (carboxyl-terminal binding protein) participates in regulating cellular development and differentiation by associating with a diverse array of transcriptional repressors. Most of these interactions occur through a consensus CtBP-binding motif, PXDLS, in the repressor proteins. We previously showed that the CtBP-binding motif in E1A is flanked by a Lys residue and suggested that acetylation of this residue by the p300/CBP-associated factor P/CAF disrupts the CtBP interaction. In this study, we show that the interaction between CtBP and the nuclear hormone receptor corepressor RIP140 is regulated similarly, in this case by p300/CBP itself. CtBP was shown to interact with RIP140 in vitro and in vivo through a sequence, PIDLSCK, in the amino-terminal third of the RIP140 protein. Acetylation of the Lys residue in this motif, demonstrated in vivo by using an acetylated RIP140-specific antibody, dramatically reduced CtBP binding. Mutation of the Lys residue to Gln resulted in a decrease in CtBP binding in vivo and a loss of transcriptional repression. We suggest that p300/CBP-mediated acetylation disrupts the RIP140-CtBP complex and derepresses nuclear hormone receptor-regulated genes. Disruption of repressor-CtBP interactions by acetylation may be a general mode of gene activation.

Acetylation of adenovirus E1A regulates binding of the transcriptional corepressor CtBP

Adenovirus E1A mediates its effects on cellular transformation and transcription by interacting with critical cellular proteins involved in cell growth and differentiation. The amino terminus of E1A binds to CBP/p300 and associated histone acetyltransferases such as P/CAF. The carboxyl terminus binds to the carboxyl-terminal binding protein (CtBP), which associates with histone deacetylases. We show that 12S E1A can be acetylated by p300 and P/CAF and map one of the acetylation sites to Lys-239. This Lys residue is adjacent to the consensus CtBP binding motif, PXDLS. Mutation of Lys-239 to Gln or Ala blocks CtBP binding in vitro and disrupts the E1A-CtBP interaction in vivo. Peptide competition assays demonstrated that the interaction of E1A with CtBP is also blocked by Lys-239 acetylation. Supporting a functional role for Lys-239 in CtBP binding, mutation of this residue to Ala decreases the ability of E1A to block cAMP-regulated enhancer (CRE)-binding protein (CREB)-stimulated gene expression. Finally, we demonstrate that Lys-239 is acetylated in cells by using an antibody directed against an acetyl-Lys-239 E1A peptide. CtBP interacts with a wide variety of other transcriptional repressors through the PXDLS motif, and, in many instances, this motif is followed by a Lys residue. We suggest that acetylation of this residue by histone acetyltransferases, and the consequent disruption of repressor complexes, might be a general mechanism for gene activation.

Histone binding protein RbAp48 interacts with a complex of CREB binding protein and phosphorylated CREB

A CREB-CREB binding protein (CBP) complex was used as bait to screen a mouse embryo cDNA library in yeast. One of the strongest interactions identified the histone binding protein RbAp48. RbAp48 also interacted weakly with CBP alone but did not interact with phosphorylated or nonphosphorylated CREB. CBP (or its homologue p300) from HeLa cell nuclear extracts coimmunoprecipitated with RbAp48 and its homologue RbAp46 and bound to a glutathione S-transferase-RbAp48 fusion protein. This interaction was stimulated by the addition of phosphorylated CREB and allowed the association of core histones and mononucleosomes in an acetylation-dependent manner. RbAp48 lowered the K(m) of CBP histone acetylase activity and facilitated p300-mediated in vitro transcription of a chromatinized template in the presence of acetylcoenzyme A. These data indicate that the association of phosphorylated CREB with CBP promotes the binding of RbAp48 and its homologue RbAp46, allowing the formation of a complex that facilitates histone acetylation during transcriptional activation.

Recruitment of CREB binding protein is sufficient for CREB-mediated gene activation

Phosphorylation of the transcription factor CREB leads to the recruitment of the coactivator, CREB binding protein (CBP). Recent studies have suggested that CBP recruitment is not sufficient for CREB function, however. We have identified a conserved protein-protein interaction motif within the CBP-binding domains of CREB and another transcription factor, SREBP (sterol-responsive element binding protein). In contrast to CREB, SREBP interacts with CBP in the absence of phosphorylation. We have exploited the conservation of this interaction motif to test whether CBP recruitment to CREB is sufficient for transcriptional activation. Substitution of six nonconserved amino acids from SREBP into the activation domain of CREB confers high-affinity, phosphorylation-independent CBP binding. The mutated CREB molecule, CREB(DIEDML), activates transcription in F9 teratocarcinoma and PC12 cells even in the absence of protein kinase A (PKA). Addition of exogenous CBP augments the level of transcription mediated by CREB(DIEDML), and adenovirus 12S E1A blocks transcription, implicating CBP in the activation process. Thus, recruitment of CBP to CREB is sufficient for transcriptional activation. Addition of PKA stimulates transcription induced by CREB(DIEDML) further, suggesting that a phosphorylation event downstream from CBP recruitment augments CREB signaling.

Reversal of prolonged isoniazid-induced coma by pyridoxine

Isoniazid overdose is known to result in the rapid onset of seizures, metabolic acidosis, and prolonged obtundation. Pyridoxine has been reported to be effective in treating isoniazid-induced seizures. We report three cases of obtundation secondary to isoniazid overdose that was immediately reversed by intravenous pyridoxine. In two of these cases, status seizures were stopped by intravenous pyridoxine administration, but the patients remained comatose for prolonged periods. The comas were immediately reversed by the administration of additional pyridoxine. In the third case, the patient's lethargy was treated by intravenous pyridoxine on presentation and was followed by immediate awakening. Pyridoxine is effective in treating not only isoniazid-induced seizures, but also the mental status changes associated with this overdose. The dose required to induce awakening may be higher than that required to control seizures.

Delayed hypersensitivity on a surgical service

Two hundred patients assessed for nutritional deficiencies were analyzed for reaction to skin testing with common antigens and the incidence of sepsis and death. Only 39% of all skin tests were positive, though 50% of the patients had at least one positive test. Associated diagnoses revealed a high incidence of malnutrition, cancer, radiation therapy, and chemotherapy. Analysis using Chi-square and Gamma shows good statistical correlation between skin tests and sepsis and death. Those with negative tests (anergic) using PPD, Candida, and mumps had a threefold higher mortality. Major sepsis also increased in the skin negative group (+80%), but here the incidence varied directly with the number of positive skin tests. Mortality, unlike sepsis, was influenced only by the presence of delayed hypersensitivity and was not related to the number of positive reactions. The basic rate of infection or mortality was not influenced by major surgery.

Differentiation of vascular and neurogenic claudication

Lower extremity pain caused by exercise but relieved by rest is usually a reliable symptom of chronic arterial insufficiency. However, similar discomfort often occurs in patients who have neurospinal compression. Furthermore, both arterial occlusive disease and neurogenic causes of lower extremity discomfort may present simultaneously. Forty patients with symptoms that suggested intermittent claudication comprised our study group. All had non-arterial cause of their complaint. The nonvascular origin of the symptoms was suggested initially by clinical evaluation in 30 patients and by noninvasive evaluation in 25 patients. The neurospinal origin of symptoms was obscured in 15 patients because of the concomitant presence of significant arterial occlusive disease as demonstrated by noninvasive arterial testing. Twelve of these 15 patients underwent arterial reconstruction, which did not relieve their symptoms. Subsequently, the neurospinal origin of their symptoms was proven by appropriate evaluation and therapy. Forms of evaluation that proved helpful in the differential diagnosis were lumbosacral spine x-rays, electromyography, nerve conduction velocity studies, computerized tomography, Doppler noninvasive assessment and, at times arteriography and contrast myelography.

Systemic organ assessment using computerized profiles

Clinical monitoring of isolated parameters may lead to erroneous conclusions or conflicting speculations about the patient's general physiological status. Data derived from two or three primary parameters may provide a better understanding of the patient's overall status. Four automated profiles have been designed to aid in the management of critically ill patients. Data obtained from simple blood and urinary tests are used to compute parameters for various physiologic, renal, respiratory, and metabolic functions. The derived data are plotted in hard-copy form. A sequential series of each profile assists the physician in making intelligent and rapid therapeutic decisions and in evaluating the effectiveness of this therapy.

Severe postappendectomy bleeding

Postappendectomy bleeding is a rare and occasionally catastrophic phenomenon. Three cases of bleeding, two into the retroperitoneum and one into the gastrointestinal tract, are reported, and 13 other cases collected from the literature are reviewed. Retroperitoneal hematoma may require reoperation because of infection. Bleeding in the gastrointestinal tract may occur early (mean, 4 days), or late (mean, 7 years). An unligated stump or slippage of the tie around the stump are the main causes of early bleeding. Sixty-six per cent of the patients recovered without further bleeding. All six patients with late rectal bleeding required surgery for control of the bleeder. Causes included ulceration, vascular malformation, or granuloma.