Theoretical Sum Frequency Generation Spectra of Protein Amide with Surface-Specific Velocity-Velocity Correlation Functions

Vibrational sum frequency generation (vSFG) spectroscopy is widely used to probe the protein structure at interfaces. Because protein vSFG spectra are complex, they can only provide detailed structural information if combined with computer simulations of protein molecular dynamics and spectra calculations. We show how vSFG spectra can be accurately modeled using a surface-specific velocity-velocity scheme based on ab initio normal modes. Our calculated vSFG spectra show excellent agreement with the experimental sum frequency spectrum of LTα14 peptide and provide insight into the origin of the characteristic α-helical amide I peak. Analysis indicates that the peak shape can be explained largely by two effects: (1) the uncoupled response of amide groups located on opposite sides of the α-helix will have different orientations with respect to the interface and therefore different local environments affecting the local mode vibrations and (2) vibrational splitting from nearest neighbor coupling evaluated as inter-residue vibrational correlation. The conclusion is consistent with frequency mapping techniques with an empirically based ensemble of peptide structures, thus showing how time correlation approaches and frequency mapping techniques can give independent yet complementary molecular descriptions of protein vSFG. These models reveal the sensitive relationship between protein structure and their amide I response, allowing exploitation of the complicated molecular vibrations and their interference to derive the structures of proteins under native conditions at interfaces.

Nature of Cations Critically Affects Water at the Negatively Charged Silica Interface

Understanding the collective behavior of ions at charged surfaces is of paramount importance for geological and electrochemical processes. Ions screen the surface charge, and interfacial fields break the centro-symmetry near the surface, which can be probed using second-order nonlinear spectroscopies. The effect of electrolyte concentration on the nonlinear optical response has been semi-quantitatively explained by mean-field models based on the Poisson–Boltzmann equation. Yet, to explain previously reported ion-specific effects on the spectroscopic response, drastic ion-specific changes in the interfacial properties, including surface acidities and dielectric permittivities, or strong ion adsorption/desorption had to be invoked. Here, we use sum-frequency generation (SFG) spectroscopy to probe the symmetry-breaking of water molecules at a charged silica surface in contact with alkaline metal chloride solutions (LiCl, NaCl, KCl, and CsCl) at various concentrations. We find that the water response varies with the cation: the SFG response is markedly enhanced for LiCl compared to CsCl. We show that within mean-field models, neither specific ion–surface interactions nor a reduced dielectric constant of water near the interface can account for the variation of spectral intensities with cation nature. Molecular dynamics simulations confirm that the decay of the electrochemical potential only weakly depends on the salt type. Instead, the effect of different salts on the optical response is indirect, through the reorganization of the interfacial water: the salt-type-dependent alignment of water directly at the interface can explain the observations.

Elucidating Conformation and Hydrogen-Bonding Motifs of Reactive Thiourea Intermediates

Substituted diphenylthioureas (DPTUs) are efficient hydrogen-bonding organo-catalysts, and substitution of DPTUs has been shown to greatly affect catalytic activity. Yet, both the conformation of DPTUs in solution and the conformation and hydrogen-bonded motifs within catalytically active intermediates, pertinent to their mode of activation, have remained elusive. By combining linear and ultrafast vibrational spectroscopy with spectroscopic simulations and calculations, we show that different conformational states of thioureas give rise to distinctively different N–H stretching bands in the infrared spectra. In the absence of hydrogen-bond-accepting substrates, we show that vibrational structure and dynamics are highly sensitive to the substitution of DPTUs with CF₃ groups and to the interaction with the solvent environment, allowing for disentangling the different conformational states. In contrast to bare diphenylthiourea (0CF-DPTU), we find the catalytically superior CF₃-substituted DPTU (4CF-DPTU) to favor the trans–trans conformation in solution, allowing for donating two hydrogen bonds to the reactive substrate. In the presence of a prototypical substrate, DPTUs in trans–trans conformation hydrogen bond to the substrate’s C=O group, as evidenced by a red-shift of the N–H vibration. Yet, our time-resolved infrared experiments indicate that only one N–H group forms a strong hydrogen bond to the carbonyl moiety, while thiourea’s second N–H group only weakly interacts with the substrate. Our data indicate that hydrogen-bond exchange between these N–H groups occurs on the timescale of a few picoseconds for 0CF-DPTU and is significantly accelerated upon CF₃ substitution. Our results highlight the subtle interplay between conformational equilibria, bonding states, and bonding lifetimes in reactive intermediates in thiourea catalysis, which help rationalize their catalytic activity.

Serum phosphate as an independent factor associated with cholesterol metabolism in patients undergoing hemodialysis: a cross-sectional analysis of the DREAM cohort

Background

Hyperphosphatemia is a risk factor for cardiovascular outcomes in patients with chronic kidney disease. In an experimental model, hyperphosphatemia promotes atherosclerosis by activating sterol regulatory element-binding protein 2 which controls cholesterol homeostasis. In the present study, we hypothesized that serum phosphate level is associated with cholesterol metabolism in patients with kidney failure.

Methods

We conducted a single center cross-sectional study including 492 patients undergoing hemodialysis and 100 healthy controls not on statin or ezetimibe treatment. Serum lathosterol and campesterol levels were measured as a marker of cholesterol synthesis and absorption, respectively. As compared to the control group, the hemodialysis patients had higher median (interquartile range) phosphate [5.8 (5.0 to 6.6) vs. 3.3 (3.0 to 3.6) mg/dL, P < 0.001], lower lathosterol [1.2 (0.8 to 1.7) vs. 2.6 (1.9 to 3.4) µg/mL, P < 0.001] and higher campesterol levels [4.5 (3.6 to 6.0) vs. 4.1 (3.2 to 5.4) µg/mL, P = 0.02]. Serum phosphate correlated positively to campesterol in the control group (Spearman's r = 0.21, P = 0.03) and in the hemodialysis patients (Spearman's r = 0.19, P < 0.001). The positive association between phosphate and campesterol levels in the hemodialysis group remained significant in multivariable-adjusted linear regression analysis. There was no significant association between phosphate and lathosterol in either group.

Conclusions

An independent association was found between phosphate and campesterol levels in patients with kidney failure. This study suggests a novel relationship between phosphate and cholesterol metabolism, both of which could affect cardiovascular outcomes in this population.

Polarization-Dependent Heterodyne-Detected Sum-Frequency Generation Spectroscopy as a Tool to Explore Surface Molecular Orientation and Ångström-Scale Depth Profiling

Sum-frequency generation (SFG) spectroscopy provides a unique optical probe for interfacial molecules with interface-specificity and molecular specificity. SFG measurements can be further carried out at different polarization combinations, but the target of the polarization-dependent SFG is conventionally limited to investigating the molecular orientation. Here, we explore the possibility of polarization-dependent SFG (PD-SFG) measurements with heterodyne detection (HD-PD-SFG). We stress that HD-PD-SFG enables accurate determination of the peak amplitude, a key factor of the PD-SFG data. Subsequently, we outline that HD-PD-SFG can be used not only for estimating the molecular orientation but also for investigating the interfacial dielectric profile and studying the depth profile of molecules. We further illustrate the variety of combined simulation and PD-SFG studies.

Identification of clinical factors related to antibody-mediated immune response to the subfornical organ

OBJECTIVE

We recently reported cases of adipsic hypernatremia caused by autoantibodies against the subfornical organ in patients with hypothalamic-pituitary lesions. This study aimed to clarify the clinical features of newly identified patients with adipsic hypernatremia whose sera displayed immunoreactivity to the mouse subfornical organ.

DESIGN

Observational cohort study of patients diagnosed with adipsic hypernatremia in Japan, United States, and Europe.

METHODS

The study included 22 patients with adipsic hypernatremia but without overt structural changes in the hypothalamic-pituitary region and congenital disease. Antibody response to the mouse subfornical organ was determined using immunohistochemistry. The clinical characteristics were compared between the patients with positive and negative antibody responses.

RESULTS

Antibody response to the mouse subfornical organ was detected in the sera of 16 patients (72.7%, female/male ratio, 1:1, 12 pediatric and 4 adult patients). The prolactin levels at the time of diagnosis were significantly higher in patients with positive subfornical organ (SFO) immunoreactivity than in those with negative SFO immunoreactivity (58.9 ± 33.5 vs. 22.9 ± 13.9 ng/ml, p < .05). Hypothalamic disorders were found in 37.5% of the patients with positive SFO immunoreactivity. Moreover, six patients were diagnosed with rapid-onset obesity with hypothalamic dysfunction, hypoventilation, and autonomic dysregulation/neural tumor syndrome after the diagnosis of adipsic hypernatremia. Plasma renin activity levels were significantly higher in patients with serum immunoreactivity to the Na_x channel.

CONCLUSIONS

The patients with serum immunoreactivity to the SFO had higher prolactin levels and hypothalamic disorders compared to those without the immunoreactivity. The clinical characteristics of patients with serum immunoreactivity to the subfornical organ included higher prolactin levels and hypothalamic disorders, which were frequently associated with central hypothyroidism and the presence of retroperitoneal tumors.

Polarization-Dependent Sum-Frequency Generation Spectroscopy for Ångstrom-Scale Depth Profiling of Molecules at Interfaces

The three-dimensional spatial distribution of molecules at soft matter interfaces is crucial for processes ranging from membrane biophysics to atmospheric chemistry. While several techniques can access surface composition, obtaining information on the depth distribution is challenging. We develop a noninvasive, polarization-resolved, surface-specific sum-frequency generation spectroscopy providing quantitative depth information. We demonstrate the technique on formic acid molecules at the air-water interface. With increasing molar fraction from 2.5% to 10%, the formic acid molecules shift, on average, ∼0.9  Å into the bulk. The consistency with the simulation data manifests that the technique allows for probing the Ångstrom-scale depth profile.

Where Lennard-Jones Potentials Fail: Iterative Optimization of Ion-Water Pair Potentials Based on Ab Initio Molecular Dynamics Data

The use of the Lennard-Jones (LJ) potential in computer simulations of aqueous electrolyte solutions is widespread. The standard approach is to parametrize LJ potential parameters against thermodynamic solution properties, but problems in representing the local structural and dynamic properties of ion hydration shells remain. The r^-12-term in the LJ potential is responsible for this as it leads to overly repulsive ion-water interactions at short range. As a result, the LJ potential predicts blue-shifted vibrational peaks of the cations' rattling mode and too large negative ion hydration entropies. We demonstrate that cation-water effective pair potentials derived from ab initio MD data have softer short-range repulsions and represent hydration shell properties significantly better. Our findings indicate that replacing the LJ potential with these effective pair potentials offers a promising route to represent thermodynamic solution properties and local interactions of specific ions with nonpolarizable force field models.

Minimizing plasma temperature for antimatter mixing experiments

The ASACUSA collaboration produces a beam of antihydrogen atoms by mixing pure positron and antiproton plasmas in a strong magnetic field with a double cusp geometry. The positrons cool via cyclotron radiation inside the cryogenic trap. Low positron temperature is essential for increasing the fraction of antihydrogen atoms which reach the ground state prior to exiting the trap. Many experimental groups observe that such plasmas reach equilibrium at a temperature well above the temperature of the surrounding electrodes. This problem is typically attributed to electronic noise and plasma expansion, which heat the plasma. The present work reports anomalous heating far beyond what can be attributed to those two sources. The heating seems to be a result of the axially open trap geometry, which couples the plasma to the external (300 K) environment via microwave radiation.

Accurate molecular orientation at interfaces determined by multimode polarization-dependent heterodyne-detected sum-frequency generation spectroscopy via multidimensional orientational distribution function

Many essential processes occur at soft interfaces, from chemical reactions on aqueous aerosols in the atmosphere to biochemical recognition and binding at the surface of cell membranes. The spatial arrangement of molecules specifically at these interfaces is crucial for many of such processes. The accurate determination of the interfacial molecular orientation has been challenging due to the low number of molecules at interfaces and the ambiguity of their orientational distribution. Here, we combine phase- and polarization-resolved sum-frequency generation (SFG) spectroscopy to obtain the molecular orientation at the interface. We extend an exponentially decaying orientational distribution to multiple dimensions, which, in conjunction with multiple SFG datasets obtained from the different vibrational modes, allows us to determine the molecular orientation. We apply this new approach to formic acid molecules at the air–water interface. The inferred orientation of formic acid agrees very well with ab initio molecular dynamics data. The phase-resolved SFG multimode analysis scheme using the multidimensional orientational distribution thus provides a universal approach for obtaining the interfacial molecular orientation.

Parathyroid Hormone Regulates Circulating Levels of Sclerostin and FGF23 in a Primary Hyperparathyroidism Model

Parathyroid hormone (PTH) increases fibroblast growth factor 23 (FGF23), mediated both by protein kinase A (PKA) and Wnt signaling, and decreases expression of sclerostin, a Wnt antagonist derived from osteocytes. Patients with primary hyperparathyroidism (PHPT) have lower serum sclerostin levels than healthy controls, consistent with the idea of SOST downregulation by PTH. Nevertheless, the relationship between FGF23 and sclerostin in PHPT is still unclear. We examined this issue in a mouse model of PHPT. PHPT mice had increased FGF23 and decreased sclerostin expression in calvaria and in their serum concentrations compared with wild-type (WT) mice. In UMR106 osteoblasts, PTH increased Fgf23 expression and decreased Sost expression, as well as forskolin, a PKA agonist, whereas inhibition of PKA reversed the changes in Fgf23 and Sost expression, stimulated by PTH. Sclerostin treatment had no effect on Fgf23 expression, but when it was added together with PTH, it statistically significantly abrogated the increase in Fgf23 expression. By contrast, there was no statistically significant correlation between serum FGF23 and sclerostin, whereas PTH was positively and negatively correlated with serum FGF23 and sclerostin, respectively. These results indicate that the high level of PTH in PHPT mice leads to increased FGF23 and decreased sclerostin expression in serum and calvaria. A decrease of sclerostin may further augment FGF23 in vitro; however, there was no statistically significant association between circulating FGF23 and sclerostin. It is suggested that the pathogenesis of increased FGF23 expression in PHPT mice may be modified by not only sclerostin, but also other regulatory factors modulated by PTH.

Scratch-Healing Behavior of Ice by Local Sublimation and Condensation

We show that the surface of ice is scratch healing: micrometer-deep scratches in the ice surface spontaneously disappear by thermal relaxation on the time scale of roughly an hour. Following the dynamics and comparing it to different mass transfer mechanisms, we find that sublimation from and condensation onto the ice surface is the dominant scratch-healing mechanism. The scratch-healing kinetics shows a strong temperature dependence, following an Arrhenius behavior with an activation energy of ΔE = 58.6 ± 4.6 kJ/mol, agreeing with the proposed sublimation mechanism and at odds with surface diffusion or fluid flow or evaporation-condensation from a quasi-liquid layer.

Nutritional disorder evaluated by geriatric nutritional risk index predicts death after hospitalization for infection in patients undergoing maintenance hemodialysis

OBJECTIVE

Infection is related to higher rate of hospitalization and subsequent death in patients undergoing hemodialysis. Limited data are available about factors associated with death after hospitalization for infection. Nutritional disorder also known as protein-energy wasting is profoundly associated with poor consequences. Geriatric nutritional risk index (GNRI) is a simple but useful nutritional screening tool to predict mortality. We examined whether GNRI could predict hospitalization for infection and subsequent death.

DESIGN AND METHODS

This was a prospective cohort study in hemodialysis patients. The predictor was GNRI. The patients were divided into tertiles of GNRI (T1 to T3), with the highest tertile of T3 as referent. The outcomes of interest were all-cause mortality, hospitalization for infection and subsequent death.

RESULTS

Of 518 patients, 107 patients died (median follow-up period, 5.0 years; interquartile range 3.6-5.0) and 169 patients experienced new hospitalization for infection (median follow-up period, 4.5 years; interquartile range 3.4-5.0) during the follow-up period from December 2004 to December 2009. A lower GNRI was a significant predictor for all-cause mortality in multivariable Cox models (hazard ratio [HR] 2.9, 95% confidential interval [CI] 1.5-5.5, p < 0.001 for T1 vs. T3). However, GNRI was not associated with hospitalization for infection in multivariable Fine-Gray models with death as a competing risk (subdistributional HR 1.5, 95% CI 1.0-2.3, p = 0.056 for T1 vs. T3). After hospitalization for infection, 38 patients died during subsequent 2.5-year follow-up period. GNRI was a significant predictor of death after hospitalization for infection in multivariable Cox models (HR 2.7, 95% CI 1.3-5.6, p = 0.006 for T1 vs. T2+T3).

CONCLUSIONS

A lower GNRI predicted a higher risk of all-cause mortality but not hospitalization for infection. However, a lower GNRI was significantly associated with a higher risk of mortality after hospitalization for infection. These findings suggest that long-term mortality after hospitalization for infection was predicted by nutritional disorder evaluated by GNRI.

Bexarotene-induced central hypothyroidism assessed by TRH stimulation test in cutaneous T-cell lymphoma patients

Bexarotene-induced central hypothyroidism (CH), for which levothyroxine (LT4) replacement is recommended, has been shown to be caused by pituitary but not hypothalamic disorder experimentally, though the underlying mechanism in humans remains unclear. Here, the pathophysiology of bexarotene-induced CH was examined using a TRH stimulation test in cutaneous T-cell lymphoma (CTCL) patients. In this retrospective longitudinal observational study, serum TSH and free T4 (F-T4) levels were measured in 10 euthyroid patients with CTCL during 24 weeks of bexarotene treatment. TRH stimulation testing was performed following CH diagnosis, with LT4 replacement dosage adjusted to maintain F-T4 at the pre-treatment level. After one week of bexarotene administration, all 10 patients developed CH, based on combined findings of low or low-normal F-T4 with low or normal TSH levels. TSH peak response after a stimulation test at one week was reached at 30 minutes. However, that was <4 μIU/mL in all patients, indicating a blunted though not exaggerated and delayed TSH response. In eight who continued bexarotene for 24 weeks, median LT4 replacement dosage was 125 (range, 75-150) μg/day. TSH level at 30 as well as 15, 60, 90, and 120 minutes after TRH stimulation was significantly correlated with LT4 replacement dosage (ρ = -0.913, p = 0.002), whereas TSH and F-T4 basal levels at one week were not. These results suggest that pituitary hypothyroidism is responsible for bexarotene-induced CH, while TSH levels after TRH stimulation precisely reflect residual pituitary-thyroid function in patients receiving bexarotene.

Ovariectomy-Induced Dysbiosis May Have a Minor Effect on Bone in Mice

We determined the bone mineral density (BMD) and the expression of serum bone formation marker (procollagen type I N-terminal propeptide: PINP) and bone resorption marker (C-terminal telopeptide of collagen: CTX) by ELISA to evaluate ovariectomy-induced osteoporosis in ovariectomized (OVX) mice. The intestinal microbiota of the mice was assessed using 16S rRNA gene sequencing. OVX mice exhibited a lower BMD of 87% with higher serum levels of CTX and PINP compared to sham-operated (sham) mice. The cecum microbiome of OVX mice showed lower bacterial diversity than that of sham mice. TNFα mRNA levels in the colon were 1.6 times higher, and zonula occludens-1 mRNA and protein expression were lower in OVX mice than in sham mice, suggesting that ovariectomy induced inflammation and increased intestinal permeability. Next, we used antibiotic treatment followed by fecal microbiota transplantation (FMT) to remodel the gut microbiota in the OVX mice. A decrease in PINP was observed in antibiotic-treated mice, while there was no change in BMD or CTX between mice with and without antibiotic treatment. Oral transplantation of the luminal cecal content of OVX or sham mice to antibiotic-treated mice did not affect the BMD or PINP and CTX expression. Additionally, transplantation of the luminal contents of OVX or sham mice to antibiotic-treated OVX mice had similar effects on BMD, PINP, and CTX. In conclusion, although ovariectomy induces dysbiosis in the colon, the changes in the gut microbiota may only have a minor role in ovariectomy-induced osteoporosis.

Thermally-modulated cell separation columns using a thermoresponsive block copolymer brush as a packing material for the purification of mesenchymal stem cells

Cell therapy using mesenchymal stem cells (MSCs) is used as effective regenerative treatment. Cell therapy requires effective cell separation without cell modification and cellular activity reduction. In this study, we developed a temperature-modulated mesenchymal stem cell separation column. A temperature-responsive cationic block copolymer, poly(N,N-dimethylaminopropylacrylamide)-b-poly(N-isopropylacrylamide)(PDMAPAAm-b-PNIPAAm) brush with various cationic copolymer compositions, was grafted onto silica beads via two-step atom transfer radical polymerization. Using the packed beads, the elution behavior of the MSCs was observed. At 37 °C, the MSCs were adsorbed onto the column via both hydrophobic and electrostatic interactions with the PNIPAAm and PDMAPAAm segments of the copolymer brush, respectively. By reducing the temperature to 4 °C, the adsorbed MSCs were eluted from the column by reducing the hydrophobic and electrostatic interactions attributed to the hydration and extension of the PNIPAAm segment of the block copolymer brush. From the temperature-modulated adsorption and elution behavior of MSCs, a suitable DMAPAAm composition of the block copolymer brush was determined. Using the column, a mixture of MSC and BM-CD34⁺ cells was separated by simply changing the column temperature. The column was used to purify the MSCs, with purities of 78.2%, via a temperature change from 37 °C to 4 °C. Additionally, the cellular activity of the MSCs was retained throughout the column separation step. Overall, the obtained results show that the developed column is useful for MSC separation without cell modification and cellular activity reduction.