Mechanism and Kinetics of Fentanyl Dissociation from the mu-Opioid Receptor

Fentanyl is a main driver of the current opioid crisis. As a powerful narcotic, fentanyl initiates biological response through binding to the mu-opioid receptor (mOR); however, the molecular details remain unknown. Here we study the mechanism and predict the kinetics of fentanyl-mOR dissociation by applying an advanced molecular dynamics (MD) technique based on the X-ray structure of the morphinan bound mOR. 144 metadynamics trajectories were performed while accounting for the protonation state of the conserved H29, which has been suggested to modulate ligand-mOR affinity and binding mode. Surprisingly, in some trajectories fentanyl samples a deep pocket 5-10 Angstrom below the level of the conserved D147 before escaping mOR, yielding the calculated residence times of 27 s, 6 s, and 0.6 s, in the presence of the ND-, NE-, and doubly protonated H297, respectively. The former value is within one order of magnitude from the recently measured residence time of about 4 min, suggesting the biological relevance of fentanyl's deep insertion, which is enabled through hydrogen bonding with H297 as well as hydrophobic interactions with transmembrane helix 6. These data support the hypothesis that the molecular mechanism of fentanyl may be distinct from morphinan compounds. Our developed protocol may be used to predict the dissociation rates of other opioids, thereby assisting the evaluation of strategies for drug overdose reversal. Finally, the profound role of the histidine protonation state discovered in this work may shift the paradigm in computational studies of ligand-receptor kinetics.

Analysis of Torque and Force Induced by Rotary Nickel-Titanium Instruments during Root Canal Preparation: A Systematic Review

The aim of this review was to provide a detailed literature analysis of torque and force generation during nickel-titanium rotary root canal instrumentation. We followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. An electronic search was performed using in PubMed and in journals for articles published in English from 1987 to June 2020 on studies that investigated dynamic torque and force in vivo or in vitro. We assessed article titles and abstracts to remove duplicates, and the titles and abstracts of the remaining articles were screened for eligibility. Full texts were read to verify eligibility by considering predetermined inclusion and exclusion criteria. Fifty-two out of 4096 studies met the inclusion criteria, from which we identified 26 factors that influence torque or force generation. Factors associated with higher torque or force generation and supported by multiple studies with mostly consistent results included convex triangle cross-sectional design, regressive taper, short pitch length, large instrument size, small canal size, single-length preparation technique, long preparation time, deep insertion depth, low rate of insertion, continuous rotation (torque), reciprocating motion (force), lower rotational speed and conventional alloy. However, several factors are interrelated, which obscured the independent effect of each factor, and there was insufficient scientific evidence supporting the influence of some factors.

Effect of Depth of Electroacupuncture on the IPSS of Patients with Benign Prostatic Hyperplasia

This study aimed to evaluate the efficacy of electroacupuncture (EA) on Ciliao (BL 32) and Zhongliao (BL 33) acupoints at different depths for the treatment of benign prostatic hyperplasia (BPH) through a single-blind randomized controlled trial. All 120 patients diagnosed with BPH were randomly allocated to an experimental group (deep insertion group, DI group, n = 60) and control group (shallow insertion group, SI group, n = 60) 3 times a week for 4 weeks. The observed results included the International Prostate Symptom Score (IPSS), Quality of Life score (QOL), maximum urine flow rate (Qmax), and postvoid residual urine volume (PVR). After treatment, at both depths, the BPH symptoms of patients were improved by EA. There were significant differences between the IPSS, QOL, and the effective rate of the experimental group and the control group (P<0.05). Although the observed PVR and Qmax were better than those before treatment, there was no statistical significance between two groups (P>0.05). Thus, EA with deep insertion can effectively improve the patients’ urinary symptoms and quality of life, and it will be suitable for clinical application.

Experimental evaluation of a self-propelling bio-inspired needle in single- and multi-layered phantoms

In percutaneous interventions, reaching targets located deep inside the body with minimal tissue damage and patient pain requires the use of long and thin needles. However, when pushed through a solid substrate, a structure with a high aspect ratio is prone to buckle. We developed a series of multi-element needles with a diameter smaller than 1 mm and a length larger than 200 mm, and we experimentally evaluated the performance of a bio-inspired insertion mechanism that prevents needle buckling of such slender structures. The needles consisted of Nitinol wires and advance into a substrate by pushing the wires forward one after the other, followed by pulling all the wires simultaneously backward. The resulting net push force is low, allowing the needles to self-propel through the substrate. We investigated the effect of the needle design parameters (number of wires and their diameter) and substrate characteristics (stiffness and number of layers) on the needle motion. Three needle prototypes (consisting of six 0.25-mm wires, six 0.125-mm wires, and three 0.25-mm wires, respectively) were inserted into single- and multi-layered tissue-mimicking phantoms. The prototypes were able to move forward in all phantoms without buckling. The amount of needle slip with respect to the phantom was used to assess the performance of the prototypes. The six-wire 0.25-mm prototype exhibited the least slip among the three prototypes. Summarizing, we showed that a bio-inspired motion mechanism prevents buckling in very thin (diameter <1 mm), long (length >200 mm) needles, allowing deep insertion into tissue-mimicking phantoms.

Custom Skull Cap With Precision Guides for Deep Insertion of Cellular-Scale Microwire Into Rat Brain

To understand the brain functioning mechanisms, electrophysiological methods represent the most mature approach for recording brain dynamics at millisecond timescales in either local or large spatial scales. Microwire-based microelectrode arrays (MEAs) are a well-established tool for chronic recording of electrophysiologic signals and furthermore have the advantage of minimal brain damage if constructed from cellular-scale (4–100 μm neuron diameter) microwires. However, such cellular-scale MEAs are not widely used by neuroscientists, especially on deep insertion cases, due to the barrier of implantation. Efforts to reduce the size of microwires bring collateral difficulties due to buckling during penetration through membranes (dura/pia) and consequent inability to implant deeply into the brain or in a manner that leaves intact protective biolayers such as the dura mater. In this paper, we developed a custom skull cap with precision guide holes to stabilize the brain and dura, provide sufficient support to microwire along the insertion path, and minimize the unsupported length of microwire during dura penetration and deeper insertion. A cap matched to individual skull anatomy with offset for brain stabilization was designed based on computed tomography (CT) scan of the rat head and fabricated by stereolithography. Micro-milling and wax molding were conducted to fabricate precision insertion guide inside the cap. Animal surgical studies were conducted to test the performance of skull cap and insertion guide. Rats with skull cap attached had survived for multiple weeks until sacrificed by experimenters. Through a test cube with precision guide, a 25 μm diameter tungsten microwire penetrated through the dura mater and was manually inserted over 10 mm into the brain without buckling. In comparison, without the precision guide, insertion of the same microwire caused over 2 mm dimpling of the dura without penetration and finally led to wire buckling. Results showed that the custom skull cap with precision guide holes enabled the insertion of cellular-scale microwire electrodes deep into the brain through the dura mater without buckling.