Polyunsaturated fatty acids and membrane organization: elucidating mechanisms to balance immunotherapy and susceptibility to infection

Polyunsaturated fatty acids (PUFAs), notably of the n-3 series, have immunosuppressive effects which make these molecules candidates for treating inflammatory symptoms associated with cardiovascular disease, obesity, arthritis, and asthma. However, immunosuppression by PUFAs could increase susceptibility to bacterial and viral infection. A detailed molecular picture is required in order to understand the balance between the benefits and risks of utilizing PUFAs as adjuvant immunosuppressants. Here we review evidence that incorporation of PUFAs into membrane lipids of antigen presenting cells (APCs) downregulates APC function. We propose that PUFAs modulate antigen presentation by altering the organization of lipid and protein molecules of the plasma membrane and endomembranes; this alters recognition and responses by T cells. The foundation of our hypothesis is built on data from artificial bilayer experiments which provide the physical principles by which PUFA acyl chains affect membrane architecture. This review also reconciles conflicting results in the literature by discussing the advantages and disadvantages of differing methods of PUFA treatment of cells. We suggest that membrane modulation of immune cells may be an important and overlooked mechanism of immunomodulation. In addition, we propose that mechanistic studies with defined experimental protocols will speed the translation of laboratory studies on PUFAs to the clinic.     

Potential cation and H+ binding sites in acid sensing ion channel-1

Acid sensing ion channels (ASICs) are cation-selective membrane channels activated by H⁺ binding upon decrease in extracellular pH. It is known that Ca²⁺ plays an important modulatory role in ASIC gating, competing with the ligand (H⁺) for its binding site(s). However, the H⁺ or Ca²⁺ binding sites involved in gating and the gating mechanism are not fully known. We carried out a computational study to investigate potential cation and H⁺ binding sites for ASIC1 via all-atom molecular dynamics simulations on five systems. The systems were designed to test the candidacy of some acid sensing residues proposed from experiment and to determine yet unknown ligand binding sites. The ion binding patterns reveal sites of cation (Na⁺ and Ca²⁺) localization where they may compete with protons and influence channel gating. The highest incidence of Ca²⁺ and Na⁺ binding is observed at a highly acidic pocket on the protein surface. Also, Na⁺ ions fill in an inner chamber that contains a ring of acidic residues and that is near the channel entrance; this site could possibly be a temporary reservoir involved in ion permeation. Some acidic residues were observed to orient and move significantly close together to bind Ca²⁺, indicating the structural consequences of Ca²⁺ release from these sites. Local structural changes in the protein due to cation binding or ligand binding (protonation) are examined at the binding sites and discussed. This study provides structural and dynamic details to test hypotheses for the role of Ca²⁺ and Na⁺ ions in the channel gating mechanism.     

Healthcare infrastructure, contraceptive use and infant mortality in Uttar Pradesh, India

This paper analyzes data on approximately 30,000 women from a survey in Uttar Pradesh in 1995 together with the data from surveys of public and private providers of healthcare and family planning services. A framework was developed for analyzing the effects of quality of services on utilization, and for understanding the gradual evolution of the healthcare infrastructure. The empirical results from logistic regressions for use of female sterilization and IUD showed significant effects of quality of services in government and private hospitals, and of socioeconomic variables such as education, caste, and an index of household possessions. Secondly, models for infant mortality of children born in the preceding 3-year period showed significant effects of socioeconomic variables, quality of healthcare services and birth spacing. Lastly, analysis of data at a more aggregated (Primary Sampling Unit) level indicated differential effects of economic development on the quality of services available in the public and private facilities.     

The Catecholaminergic Polymorphic Ventricular Tachycardia Mutation R33Q Disrupts the N-terminal Structural Motif That Regulates Reversible Calsequestrin Polymerization

Calsequestrin undergoes dynamic polymerization with increasing calcium concentration by front-to-front dimerization and back-to-back packing, forming wire-shaped structures. A recent finding that point mutation R33Q leads to lethal catecholaminergic polymorphic ventricular tachycardia (CPVT) implies a crucial role for the N terminus. In this study, we demonstrate that this mutation resides in a highly conserved alternately charged residue cluster (DGKDR; cluster 1) in the N-terminal end of calsequestrin. We further show that this cluster configures itself as a ring system and that the dipolar arrangement within the cluster brings about a critical conformational flip of Lys³¹-Asp³² essential for dimer stabilization by formation of a H-bond network. We additionally show that Ca²⁺-induced calsequestrin aggregation is nonlinear and reversible and can regain the native conformation by Ca²⁺ chelation with EGTA. This study suggests that cluster 1 works as a molecular switch and governs the bidirectional transition between the CASQ2 monomer and dimer. We further demonstrate that mutations disrupting the alternating charge pattern of the cluster, including R33Q, impair Ca²⁺-CASQ2 interaction, leading to altered polymerization-depolymerization dynamics. This study provides new mechanistic insight into the functional effects of the R33Q mutation and its potential role in CPVT.     

Diosgenin from Dioscorea bulbifera: Novel Hit for Treatment of Type II Diabetes Mellitus with Inhibitory Activity against α-Amylase and α-Glucosidase

Diabetes mellitus is a multifactorial metabolic disease characterized by post-prandial hyperglycemia (PPHG). α-amylase and α-glucosidase inhibitors aim to explore novel therapeutic agents. Herein we report the promises of Dioscorea bulbifera and its bioactive principle, diosgenin as novel α-amylase and α-glucosidase inhibitor. Among petroleum ether, ethyl acetate, methanol and 70% ethanol (v/v) extracts of bulbs of D. bulbifera, ethyl acetate extract showed highest inhibition upto 72.06 ± 0.51% and 82.64 ± 2.32% against α-amylase and α-glucosidase respectively. GC-TOF-MS analysis of ethyl acetate extract indicated presence of high diosgenin content. Diosgenin was isolated and identified by FTIR, ¹H NMR and ¹³C NMR and confirmed by HPLC which showed an α-amylase and α-glucosidase inhibition upto 70.94 ± 1.24% and 81.71 ± 3.39%, respectively. Kinetic studies confirmed the uncompetitive mode of binding of diosgenin to α-amylase indicated by lowering of both Km and Vm. Interaction studies revealed the quenching of intrinsic fluorescence of α-amylase in presence of diosgenin. Similarly, circular dichroism spectrometry showed diminished negative humped peaks at 208 nm and 222 nm. Molecular docking indicated hydrogen bonding between carboxyl group of Asp300, while hydrophobic interactions between Tyr62, Trp58, Trp59, Val163, His305 and Gln63 residues of α-amylase. Diosgenin interacted with two catalytic residues (Asp352 and Glu411) from α-glucosidase. This is the first report of its kind that provides an intense scientific rationale for use of diosgenin as novel drug candidate for type II diabetes mellitus.     

Saroglitazar is noninferior to fenofibrate in reducing triglyceride levels in hypertriglyceridemic patients in a randomized clinical trial

Saroglitazar, being a dual PPAR-α/γ agonist, has shown beneficial effect in diabetic dyslipidemia and hypertriglyceridemia. Fibrates are commonly used to treat severe hypertriglyceridemia. However, the effect of saroglitazar in patients with moderate to severe hypertriglyceridemia was not evaluated. We conducted a study to compare the efficacy and safety of saroglitazar (4 mg) with fenofibrate (160 mg) in patients with moderate to severe hypertriglyceridemia. This was a multicenter, randomized, double-blinded, double-dummy, active-control, and noninferiority trial in adult patients with fasting triglyceride (TG) levels of 500–1,500 mg/dl. The patients were randomized in a 1:1 ratio to receive daily dose of saroglitazar or fenofibrate for 12 weeks. The primary efficacy end point was the percent change in TG levels at week 12 relative to baseline. The study comprised of 41 patients in the saroglitazar group and 41 patients in the fenofibrate group. We found that the percent reduction from baseline in TG levels at week 12 was significantly higher in the saroglitazar group (least square mean = ?55.3%; SE = 4.9) compared with the fenofibrate group (least square mean = ?41.1%; SE = 4.9; P = 0.048). Overall, 37 treatment-emergent adverse events (AEs) were reported in 24 patients (saroglitazar: 13; fenofibrate: 11). No serious AEs were reported, and no patient discontinued the study because of AEs. We conclude that saroglitazar (4 mg) is noninferior to fenofibrate (160 mg) in reducing TG levels after 12 weeks of treatment, was safe, and well tolerated.     

Energetics of gating MscS by membrane tension in azolectin liposomes and giant spheroplasts

Mechanosensitive (MS) ion channels are molecular sensors that detect and transduce signals across prokaryotic and eukaryotic cell membranes arising from external mechanical stimuli or osmotic gradients. They play an integral role in mechanosensory responses including touch, hearing, and proprioception by opening or closing in order to facilitate or prevent the flow of ions and organic osmolytes. In this study we use a linear force model of MS channel gating to determine the gating membrane tension (γ) and the gating area change (ΔA) associated with the energetics of MscS channel gating in giant spheroplasts and azolectin liposomes. Analysis of Boltzmann distribution functions describing the dependence of MscS channel gating on membrane tension indicated that the gating area change (ΔA) was the same for MscS channels recorded in both preparations. The comparison of the membrane tension (γ) gating the channel, however, showed a significant difference between the MscS channel activities in these two preparations.