Topological knots and links in proteins.

Twenty years after their discovery, knots in proteins are now quite well understood. They are believed to be functionally advantageous and provide extra stability to protein chains. In this work, we go one step further and search for links-entangled structures, more complex than knots, which consist of several components. We derive conditions that proteins need to meet to be able to form links. We search through the entire Protein Data Bank and identify several sequentially nonhomologous chains that form a Hopf link and a Solomon link. We relate topological properties of these proteins to their function and stability and show that the link topology is characteristic of eukaryotes only. We also explain how the presence of links affects the folding pathways of proteins. Finally, we define necessary conditions to form Borromean rings in proteins and show that no structure in the Protein Data Bank forms a link of this type.

Noninvasive cardiac hemodynamics monitoring of acute myocardial ischemia in rats using near-infrared spectroscopy: A pilot study.

Noninvasive and real-time optical detection of cardiac hemodynamics dysfunction during myocardial ischemia remains challenging. In this study, we developed a near-infrared spectroscopy device to monitor rats' myocardial hemodynamics. The well-designed system can accurately reflect the hemodynamics changes by the classic upper limb ischemia test. Systemic hypoxia by disconnecting to the ventilator and cardiac ischemia by coronary artery slipknot ligation was conducted to monitor myocardial hemodynamics. When systemic hypoxia occurred, ΔHbR and ΔtHb increased significantly, whereas ΔHbO decreased rapidly. When coronary blood flow was obstructed by slipknots, cardiothoracic ΔHbO immediately begins to decline, while ΔHbR also significantly increases. Simultaneously, SpO2 did not show any obvious changes during myocardial ischemia, while SpO2 decreased significantly during systemic hypoxia. These results demonstrated that cardiothoracic hemodynamics stemmed from myocardial ischemia. This pilot study demonstrated the practicality of noninvasive, low-cost optical monitoring for cardiac oxygenation dysfunction in rats.

Biomechanical analysis of four different meniscus suturing techniques for posterior meniscal root pull-out repair: A human cadaveric study.

Purpose: To compare the biomechanical properties of the slip-knot technique with three other transtibial pullout suture repair constructs for meniscal root tears. Method: Thirty-two fresh-frozen cadaveric menisci were randomly allocated to four meniscus-suture fixation constructs: Two simple-sutures (TSS), two slip-knot (TSK) sutures, two cinch-loop (TCL) sutures, and two modified Mason-Allen (TMMA) sutures. Cyclic loading from 5 to 20 N was conducted for 1000 cycles at 0.5 Hz, and then loaded to failure at 0.5 mm/s. Parametric data (displacement during cyclic loading, ultimate load, yield load, and displacement at failure) were analysed using a one-way analysis of variance (ANOVA), whereas nonparametric data (stiffness) were analysed using the Kruskal-Wallis test. Results: After 1000 cycles, the TCL construct significantly displaced the most (mean ± SD, 6.78 ± 1.32 mm; p < 0.001), followed by the TMMA (2.83 ± 0.90 mm), TSK (2.33 ± 0.57 mm), and TSS (2.03 ± 0.62 mm) groups. On ultimate failure load, there was no significant difference between the TSK group (123.48 ± 27.24 N, p > 0.05) and the other three groups (TSS, 94.65 ± 25.33 N; TMMA, 168.38 ± 23.24 N; TCL, 170.54 ± 57.32 N); however, it exhibited the least displacement (5.53 ± 1.25 mm) which was significantly shorter than those of the TCL (11.82 ± 4.25 mm, p < 0.001) and TMMA (9.53 ± 2.18 mm, p = 0.03) constructs. No significant difference in stiffness was observed among the four meniscus-suture constructs. Conclusion: The slip-knot technique has proven to be a simple, yet robust and stable meniscal root fixation option; moreover, it exhibited superiority over the more complex modified Mason-Allen suture construct in resisting displacement at the ultimate failure load. Level of Evidence: Not applicable.

Single-port laparoscopic ovariectomy using a pre-tied loop ligature in Santa Ines ewes / Ovariectomia por um portal laparoscópico com aplicação de ligaduras pré-montadas em ovelhas Santa Inês

ABSTRACT:The aim of the study was to develop and assess the feasibility, postoperative pain and inflammatory response of the single-port laparoscopic ovariectomy in ewes, using a simple pre-tied loop ligature technique. Pre-tied Meltzer's knot was employed for prophylactic hemostasis of the ovarian pedicle. Slipknot was inserted within the abdominal cavity through a 14-gauge needle and tied surrounding the ovarian pedicle. Mean surgical time, manipulation, ligature and resection of each ovary and anesthesia time were 63±20, 20±10 and 91±26 minutes, respectively. No bleeding occurred during the surgeries. Ewes showed low scores pain (0.5±0.5) at all time-points. Postsurgical plasma fibrinogen was within the normal range for sheep specie at all time-points. The ewes showed a significant weight gain in comparison to the basal scaling (one day before the surgery). Single-port laparoscopic ovariectomy using a pre-tied loop ligature is feasible in the ovine specie and provided minimal postoperative distress and quick weight gain.

RESUMO:Objetivou-se com este trabalho desenvolver e descrever uma técnica de ovariectomia por videolaparoscopia utilizando um portal laparoscópico e um sistema de ligadura pré-montada, avaliando a sua viabilidade, o desconforto doloroso e o processo inflamatório provocado em ovelhas. O nó de Meltzer pré-montado foi utilizado para hemostasia profilática do pedículo ovariano. O nó corrediço foi inserido na cavidade abdominal através de uma agulha 14G e atado em torno do pedículo ovariano. O tempo médio de cirurgia foi de 63±20min, o de manipulação, ligadura e ressecção para cada ovário foi de 20±10min, e o de anestesia 91±26min. Não houve hemorragia durante as cirurgias. As ovelhas apresentaram escores de dor considerados baixos (0,5±0,5). Todos os valores do fibrinogênio plasmático estiveram dentro do padrão de normalidade, não havendo diferença estatística entre os momentos avaliados. Houve aumento significativo nas médias de peso das fêmeas, quando comparados ao momento controle (um dia anterior ao experimento). A ovariectomia por um portal laparoscópico com aplicação de ligaduras pré-montadas é factível para a espécie ovina, provocando mínimo estresse, desconforto doloroso e rápido ganho de peso nos animais.