Inhibition of the norepinephrine transporter by the venom peptide chi-MrIA: site of action, Na+ dependence, and structure-activity relationship

Chi-conopeptide MrIA (chi-MrIA) is a 13-residue peptide contained in the venom of the predatory marine snail Conus marmoreus that has been found to inhibit the norepinephrine transporter (NET). We investigated whether chi-MrIA targeted the other members of the monoamine transporter family and found no effect of the peptide (100 µm) on the activity of the dopamine transporter and the serotonin transporter, indicating a high specificity of action. The binding of the NET inhibitors, [3H]nisoxetine and [3H]mazindol, to the expressed rat and human NET was inhibited by chi-MrIA with the conopeptide displaying a slight preference toward the rat isoform. For both radioligands, saturation binding studies showed that the inhibition by chi-MrIA was competitive in nature. It has previously been demonstrated that chi-MrIA does not compete with norepinephrine, unlike classically described NET inhibitors such as nisoxetine and mazindol that do. This pattern of behavior implies that the binding site for chi-MrIA on the NET overlaps the antidepressant binding site and is wholly distinct from the substrate binding site. The inhibitory effect of chi-MrIA was found to be dependent on Na+ with the conopeptide becoming a less effective blocker of [3H]norepinephrine by the NET under the conditions of reduced extracellular Na+. In this respect, chi-MrIA is similar to the antidepressant inhibitors of the NET. The structure-activity relationship of chi-MrIA was investigated by alanine scanning. Four residues in the first cysteine-bracketed loop of chi-MrIA and a His in loop 2 played a dominant role in the interaction between chi-MrIA and the NET. H-alpha chemical shift comparisons indicated that side-chain interactions at these key positions were structurally perturbed by the replacement of Gly-6. From these data, we present a model of the structure of chi-MrIA that shows the relative orientation of the key binding residues. This model provides a new molecular caliper for probing the structure of the NET

Outcomes following diagnosis of acute renal failure in U.S. veterans: Focus on acute tubular necrosis

When patients develop acute kidney injury, a small fraction of them will develop end-stage renal disease later. The severity of renal impairment in the remaining patients is uncertain because studies have not carefully examined renal function over time or the precise timing of entry into a late stage of chronic kidney disease. To determine these factors, we used a United States Department of Veterans Affairs database to ascertain long-term renal function in 113,272 patients. Of these, 44,377 had established chronic kidney disease and were analyzed separately. A cohort of 63,491 patients was hospitalized for acute myocardial infarction or pneumonia and designated as controls. The remaining 5,404 patients had diagnostic codes indicating acute renal failure or acute tubular necrosis. Serum creatinine, estimated glomerular filtration rates, and dates of death over a 75-month period were followed. Renal function deteriorated over time in all groups, but with significantly greater severity in those who had acute renal failure and acute tubular necrosis compared to controls. Patients with acute kidney injury, especially those with acute tubular necrosis, were more likely than controls to enter stage 4 chronic kidney disease, but this entry time was similar to that of patients who initially had chronic kidney disease. The risk of death was elevated in those with acute kidney injury and chronic kidney disease compared to controls after accounting for covariates. We found that patients who had an episode of acute tubular necrosis were at high risk for the development of stage 4 disease and had a reduced survival time when compared to control patients

A novel suite of cyclotides from V. odorata: Sequence variation and the implications for structure, function and stability

Venomous animals have evolved a vast array of peptide toxins for prey capture and defence. These peptides are highly prospective for rapid drug discovery as they are active towards a wide variety of pharmacological targets such as ion channels or G-protein coupled receptors (GPCRs) in the nervous system. Here we describe Xenome's drug development process for the chi family, conopeptide _-MrIA[1] of the predatory marine snail Conus marmoreus, leading to a suitable drug candidate (Xen2174). Xen2174 is highly selective for the norepinephrine transporter (NET) compared to other transporters, such as dopamine and serotonin, and inhibits NET via an allosteric mechanism. Xen2174 is currently in a phase I/IIa clinical trial for the treatment of severe pain. An intensive synthetic analogue and screening program around _-MrIA, incorporating early stage animal data, resulted in the identification of Xen2174, a drug with improved plasma stability, linear pharmacokinetics and wide therapeutic window. Xen2174 isomers were synthesized via selective disulfide bond formation to identify the active connectivity. Data from alanine- scans, single amino acid mutations and probing of backbone interactions combined with the full 3D NMR structure, led to the development of a pharmacophore for Xen2174. This model is refined from further studies where STRUCTURE-ACTIVITY RELATIONSHIPs were developed utilising binding and functional assay data for a range of peptides

Spironolactone and Outcomes in Older Patients with Heart Failure and Reduced Ejection Fraction

BackgroundThe efficacy of mineralocorticoid receptor antagonists or aldosterone antagonists in heart failure with reduced ejection fraction (HFrEF) is well known. Less is known about their effectiveness in real-world older patients with HFrEF.MethodsOf the 8206 patients with heart failure and ejection fraction ≤35% without prior spironolactone use in the Medicare-linked OPTIMIZE-HF registry, 6986 were eligible for spironolactone therapy based on serum creatinine criteria (men ≤2.5 mg/dL, women ≤2.0 mg/dL) and 865 received a discharge prescription for spironolactone. Using propensity scores for spironolactone use, we assembled a matched cohort of 1724 (862 pairs) patients receiving and not receiving spironolactone, balanced on 58 baseline characteristics (Creatinine Cohort: mean age, 75 years, 42% women, 17% African American). We repeated the above process to assemble a secondary matched cohort of 1638 (819 pairs) patients with estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73 m2 (eGFR Cohort: mean age, 75 years, 42% women, 17% African American).ResultsIn the matched Creatinine Cohort, spironolactone-associated hazard ratios (95% confidence intervals) for all-cause mortality, heart failure readmission, and combined endpoint of heart failure readmission or all-cause mortality were 0.92 (0.81-1.03), 0.87 (0.77-0.99), and 0.87 (0.79-0.97), respectively. Respective hazard ratios (95% confidence intervals) in the matched eGFR Cohort were 0.87 (0.77-0.98), 0.92 (0.80-1.05), and 0.91 (0.82-1.02).ConclusionsThese findings provide evidence of consistent, albeit modest, clinical effectiveness of spironolactone in older patients with HFrEF regardless of renal eligibility criteria used. Additional strategies are needed to improve the effectiveness of aldosterone antagonists in clinical practice