High potassium concentrations protect inner and outer hair cells in the newborn rat culture from ischemia-induced damage

An unenhanced 3D-FLAIR sequence using long repetition time and constant flip angle to image endolymphatic hydrops

OBJECTIVES

To evaluate a three-dimensional fluid-attenuated inversion recovery (3D-FLAIR) sequence using a long repetition time (TR) and constant flip angle (CFA) in differentiating between perilymph and endolymph in a phantom study, and unenhanced endolymphatic hydrops (EH) imaging in a patient study.

METHODS

Three solutions in similar ion and protein concentrations with endolymph, perilymph, and cerebrospinal fluid were prepared for variable flip angle (VFA) 3D-FLAIR (TR 10,000 ms) and CFA (120°) 3D-FLAIR using different TR (10,000, 16,000, and 20,000 ms). Fifty-two patients with probable or definite Meniere's disease received unenhanced CFA (120°) 3D-FLAIR using a long TR (20,000 ms) and 4-h-delay enhanced CFA (120°) 3D-FLAIR (TR 16,000 ms). Image quality, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) of them were compared. Agreement in the evaluation of the EH degree between them was analyzed.

RESULTS

In the phantom study, CNRs between perilymphatic and endolymphatic samples of VFA 3D-FLAIR (TR 10,000 ms) and CFA 3D-FLAIR (TR 10,000, 16,000, and 20,000 ms) were 6.66 ± 1.30, 17.90 ± 2.76, 23.87 ± 3.09, and 28.22 ± 3.15 (p < 0.001). In patient study, average score (3.65 ± 0.48 vs. 4.19 ± 0.40), SNR (34.56 ± 9.80 vs. 51.40 ± 11.27), and CNR (30.66 ± 10.55 vs. 45.08 ± 12.27) of unenhanced 3D-FLAIR were lower than enhanced 3D-FLAIR (p < 0.001). Evaluations of the two sequences showed excellent agreement in the cochlear and vestibule (Kappa value: 0.898 and 0.909).

CONCLUSIONS

The CFA 3D-FLAIR sequence using a long TR could be used in unenhanced EH imaging with high accuracy.

CLINICAL RELEVANCE STATEMENT

Unenhanced imaging of endolymphatic hydrops is valuable in the diagnosis and follow-up of patients, especially those who cannot receive contrast-enhanced MRI.

KEY POINTS

Ion and protein concentration differences can be utilized in differentiating endolymph and perilymph on MRI. Endolymphatic and perilymphatic samples could be differentiated in vitro on this 3D-FLAIR sequence. This unenhanced 3D-FLAIR sequence is in excellent agreement with the enhanced constant flip angle 3D-FLAIR sequence.

Regiodivergent Ring-Expansion of Oxindoles to Quinolinones

The development of divergent methods to expedite structure-activity relationship studies is crucial to streamline discovery processes. We developed a rare example of regiodivergent ring expansion to access two regioisomers from a common starting material. To enable this regiodivergence, we identified two distinct reaction conditions for transforming oxindoles into quinolinone isomers. The presented methods proved to be compatible with a variety of functional groups, which enabled the late-stage diversification of bioactive oxindoles as well as facilitated the synthesis of quinolinone drugs and their derivatives.

Resistance to neomycin ototoxicity in the extreme basal (hook) region of the mouse cochlea

Aminoglycoside ototoxicity results in permanent loss of the sensory hair cells in the mammalian cochlea. It usually begins at the basal turn causing high-frequency hearing loss. Here we describe previously unreported resistance of hair cells to neomycin ototoxicity in the extreme basal (hook) region of the developing cochlea of the C57BL/6 mouse. Organ of Corti explants from mice at postnatal day 3 were incubated (37 °C, 5% CO₂) in normal culture medium for 19.5 h prior to and after exposure to neomycin (1 mM, 3 h). To study neomycin uptake in the hair cells, cochlear explants were incubated with Neomycin Texas-red (NTR) conjugate. As expected, exposure to neomycin significantly reduced the survival of inner (IHC) and outer hair cells (OHC). IHC survival rate was high in the apical segment and low in the basal segment. OHC were well preserved in the apical and hook regions, with substantial OHC loss in the basal segment. The NTR uptake study demonstrated that the high survival rate in the extreme basal turn OHC was associated with low NTR uptake. Treatment with a calcium chelator (BAPTA), which disrupts the opening of mechanoelectrical (MET) transduction channels, abolished or reduced NTR uptake in the hair cells throughout the cochlea. This confirmed the essential role of MET channels in neomycin uptake and implied that the transduction channels could be impaired in the hook region of the developing mouse cochlea, possibly as a result of the cadherin 23 mutation responsible for the progressive deafness in C57BL/6 mice.

In Vitro Survival of Human Mesenchymal Stem Cells is Enhanced in Artificial Endolymph with Moderately High Concentrations of Potassium

While mesenchymal stem cells (MSCs) are promising candidates for inner ear hair cell regeneration, to date, there have been no convincing reports indicating whether MSCs can survive in the cochlea for more than a few weeks, as the high levels of potassium (K⁺) in the endolymph (EL) are thought to be toxic to transplanted stem cells. For conditioning the EL for MSC transplantation, we conducted this in vitro study to examine the effects of artificial EL with altered K⁺ concentration levels, in the range of 5-153.8 mM, on proliferation, apoptosis, and morphological changes in MSCs derived from various human tissues. Our findings demonstrate that altering the K⁺ concentration in artificial EL could significantly influence the survival of MSCs in vitro. We discovered that K⁺ concentrations of 55-130 mM in artificial EL could enhance the survival of MSCs in vitro. However, MSCs exhibited reduced proliferation regardless of K⁺ concentration.

Decrease of prestin expression by increased potassium concentration in organotypic cultures of the organ of Corti of newborn rats

Prestin is the motor protein of the outer hair cells of the organ of Corti and a key factor in ensuring a high sensitivity level of mammalian hearing. In the present study, we examined the effects of increased extracellular potassium (K(+)) concentration on the expression of prestin mRNA and the transcription factors Gata-3 and Carf in the organotypic culture of the organ of Corti of newborn rats. Mannitol and NaCl were used to analyze possible effects of hyperosmotic stress or ion-specific changes, respectively. An increase in prestin expression by a factor of 1.5-2.0 was seen in cultures grown in the presence of 5mM K(+). Potassium concentration of 35 and 55 mM induced a parallel decrease in prestin and Carf expression, but Gata-3 expression increased. Mannitol had no effect on gene expression whereas increased NaCl concentrations decreased prestin, but not Carf expression. The data suggest that chronic depolarization might decrease the prestin expression and possibly contribute to hearing loss and tinnitus.

Peptide- and collagen-based hydrogel substrates for in vitro culture of chick cochleae

The overall goal of this work is to improve the culture of the auditory organ of birds for the dual use of developing a hair cell regeneration model and charting a pathway to the eventual replacement of the hearing organ. In doing so, we develop a protocol for removing the auditory organ from its basement membrane in the inner ear, attach the organ to a series of artificial basement membranes, and conduct qualitative and quantitative analysis of how cell morphology, viability and function change with time. Native matrix cultures, where the epithelium was floating in media with the basement membrane and accessory structures attached, were used as a basis of comparison. PuraMatrix, collagen I, collagen I/chondroitin-sulfate and Matrigel were chosen to encompass a diverse range of mechanical properties and macromolecule moieties. Surprisingly, we find that PuraMatrix outperformed the other matrices as a scaffold for sensory organ culture. PuraMatrix a self-assembled peptide hydrogel, is a biochemically specific culture substrate that contains none of the extracellular matrix (ECM) molecules and growth factors contained in the inner ear's basement membrane. Rheological measurements reveal that PuraMatrix may be a closer approximation to the stiffness of the soft tissue supporting the auditory organ. Cell density on the PuraMatrix substrate is comparable to that of the native matrix cultures, despite the absence of the basement membrane and accessory structures. Further studies show that PuraMatrix supports the culture of functional hair cells over a 72 h period, with a significant increase in the number of functional hair cells in comparison to the organ cultured without a matrix. This is the first example of adhesion of the adult auditory epithelium to a biomaterial for an extended period of time. With further optimization, this system will enable the performance of many novel biophysical and pharmacological studies involving hair cells and supporting cells.