The myosuppressin structure-activity relationship for cardiac contractility and its receptor interactions support the presence of a ligand-directed signaling pathway in heart

The structural conservation and activity of the myosuppressin cardioinhibitory peptide across species suggests it plays an important role in physiology, yet much remains unknown regarding its signaling. We previously reported Drosophila melanogaster myosuppressin (dromyosuppressin, DMS; TDVDHVFLRF-NH₂) decreases cardiac contractility through a G protein-coupled receptor, DMS-R2. Our study showed the DMS N-terminus amino acids influence its structure-activity relationship (SAR), yet how they act is not established. We predicted myosuppressin N-terminal amino acids played a role in signaling. Here, we tested our hypothesis in the beetle, Zophobas atratus, using a semi-isolated heart bioassay to explore SAR in a different Order and focus on cardiac signaling. We generated a series of myosuppressin truncated analogs by removing the N-terminal residue and measuring the activity of each structure on cardiac contractility. While DVDHVFLRF-NH₂ decreased cardiac contractility, we found VDHVFLRF-NH₂, DHVFLRF-NH₂, and HVFLRF-NH₂ increased activity. In contrast, VFLRF- NH₂ decreased activity and FLRF-NH₂ was inactive. Next, we analyzed molecular docking data and found the active truncated analogs interacted with the 3-6 lock in DMS-R2, the myosuppressin cardiac receptor, disrupting the salt bridge between H114 and E369, and K289 and Q372. Further, the docking results showed the inhibitory effect on contractility may be associated with contact to Y78, while the analogs that increased contractility lacked this interaction. The data from our study demonstrated N-terminal amino acids played a role in myosuppressin activity and signaling suggesting the cardiac receptor can be targeted by biased agonists. Our myosuppressin cardiac contractility data and predicted receptor interactions describe the presence of functional selectivity in a ligand-directed signaling pathway in heart.

The 5-amino acid N-terminal extension of non-sulfated drosulfakinin II is a unique target to generate novel agonists

The ability to design agonists that target peptide signaling is a strategy to delineate underlying mechanisms and influence biology. A sequence that uniquely characterizes a peptide provides a distinct site to generate novel agonists. Drosophila melanogaster sulfakinin encodes non-sulfated drosulfakinin I (nsDSK I; FDDYGHMRF-NH2) and nsDSK II (GGDDQFDDYGHMRF-NH2). Drosulfakinin is typical of sulfakinin precursors, which are conserved throughout invertebrates. Non-sulfated DSK II is structurally related to DSK I, however, it contains a unique 5-residue N-terminal extension; drosulfakinins signal through G-protein coupled receptors, DSK-R1 and DSK-R2. Drosulfakinin II distinctly influences adult and larval gut motility and larval locomotion; yet, its structure-activity relationship was unreported. We hypothesized substitution of an N-terminal extension residue may alter nsDSK II activity. By targeting the extension we identified, not unexpectedly, analogs mimicking nsDSK II, yet, surprisingly, we also discovered novel agonists with increased (super) and opposite (protean) effects. We determined [A3] nsDSK II increased larval gut contractility rather than, like nsDSK II, decrease it. [N4] nsDSK II impacted larval locomotion, although nsDSK II was inactive. In adult gut, [A1] nsDSK II, [A2] nsDSKII, and [A3] nsDSK II mimicked nsDSK II, and [A4] nsDSK II and [A5] nsDSK II were more potent; [N3] nsDSK II and [N4] nsDSK II mimicked nsDSK II. This study reports nsDSK II signals through DSK-R2 to influence gut motility and locomotion, identifying a novel role for the N-terminal extension in sulfakinin biology and receptor activation; it also led to the discovery of nsDSK II structural analogs that act as super and protean agonists.

Conserved molecular switch interactions in modeled cardioactive RF-NH2 peptide receptors: Ligand binding and activation

Peptides may act through G protein-coupled receptors to influence cardiovascular performance; thus, delineating mechanisms involved in signaling is a molecular-based strategy to influence health. Molecular switches, often represented by conserved motifs, maintain a receptor in an inactive state. However, once the switch is broken, the transmembrane regions move and activation occurs. The molecular switches of Drosophila melanogaster myosuppressin (MS) receptors were previously identified to include a unique ionic lock and novel 3-6 lock, as well as transmission and tyrosine toggle switches. In addition to MS, cardioactive ligands structurally related by a C-terminal RF-NH2 include sulfakinin, neuropeptide F (NPF), short NPF, and FMRF-NH2-containing peptide subfamilies. We hypothesized receptor molecular switch motifs were conserved within a RF-NH2 subfamily and across species. Thus, we investigated RF-NH2 receptor (RFa-R) molecular switches in D. melanogaster, Tribolium castaneum, Anopheles gambiae, Rhodnius prolixus, and Bombyx mori. Adipokinetic hormone (AKH), which does not contain a RF-NH2, was also examined. The tyrosine toggle switch and ionic lock showed a higher degree of conservation within a RF-NH2 subfamily than the transmission switch and 3-7 lock. AKH receptor motifs were not representative of a RF-NH2 subfamily. The motifs and interactions of switches in the RFa-Rs were consistent with receptor activation and ligand-specific binding.

Results of improvement in adequacy of intermittent hemodialysis in uremic patients

PURPOSE

Increasing number of patients, who need intermittent hemodialysis (IHD), is a great challenge for every society. The aim of study is to look if small increase in IHD adequacy is able to improve standard medical parameters.

MATERIAL AND METHODS

In 40 patients, Kt/V was monitored on-line during the middle IHD session in the week, 4 times in each of 6 consecutive months. In the first month of observation Kt/V was lower (1.09 +/- 0.02) than in the further months, in which Kt/V was increasing to 1.17 +/- 0.01. Blood count was estimated every month. At the beginning of study period, after 3 months and at the end of studies, dry body mass, body mass index (BMI), the blood pH and serum concentration of calcium, phosphate, intact parathormone (iPTH), total protein, albumin, cholesterol, iron, ferritin, urea and creatinine were determined.

RESULTS

The increase in Kt/V was accompanied by rising values of hemoglobin (Hb), hematocrit (Hct), mean corpuscular volume, iron, blood pH before and after IHD session as well as by decreasing values of PTH. Statistically unchanged parameters included dry body mass, BMI, serum concentration of total protein, phosphate, cholesterol and ferritin as well as white blood cells and platelet count. There were correlations between Kt/V and serum concentrations of phosphate, PTH, ferritin, Hb and Hct, indicating that higher IHD doses were provided to patients in more advanced uremic state.

CONCLUSIONS

Even small increase in IHD adequacy leads to beneficial changes in management of uremic patients.

Lymphocyte subsets in the course of continuous ambulatory peritoneal dialysis

The present study evaluated whether estimation of lymphocyte subset counts can be more helpful than total lymphocyte count (TLC) in earlier diagnosis of immune and nutritional changes in the course of continuous ambulatory peritoneal dialysis (CAPD). For the study, 50 CAPD patients were divided into four groups depending on dialysis duration. Group I consisted of patients treated for 6-12 months (n = 15); group II, for 13-24 months (n = 16); group III, for 25-36 months (n = 12); and group IV, for more than 36 months (n = 7). Thirteen patients, being 8 +/- 7 days before CAPD initiation, were included in group 0. Flow cytometry was used for estimation of lymphocyte subsets (determination of CD3, CD4, CD8, CD19, and CD16 + 56 antigens). Our uremic patients started CAPD therapy with decreased TLC and lymphocyte subset (excluding CD16 + 56) counts. After 6-12 months of CAPD therapy, a significant increase in TLC, CD4:CD8 ratio, and all examined lymphocyte subset counts was observed. In the next years of CAPD therapy, TLC, CD3, CD4, CD8, and CD19 cell counts decreased. In patients on CAPD for more than 36 months, CD3, CD4, CD8, and CD19 cell counts were below the normal range, but mean TLC was maintained in the normal range, and CD16 + 56 exceeded the upper limit of normal. A significant negative correlation between CD19 cell count and dialysis duration was seen (r = -0.298, p = 0.035, n = 50). In conclusion, the first months of CAPD therapy see an improvement in immune and nutritional status as expressed by an increase in TLC, lymphocyte subset counts, and CD4:CD8 ratio. Repeat determinations of CD3, CD4, CD8, and CD19 cell counts indicate that these counts decrease earlier than an evaluation of TLC indicates. We recommend lymphocyte subset determinations for detection of immune and nutritional abnormalities in the course of CAPD treatment. An increase in natural killer cells above the normal range may reflect chronic sterile or infectious inflammatory response, which deteriorates nutritional status.

Polyglucose dialysis solution induces changes in blood chemistry

In peritoneal dialysis patients, polyglucose dialysis solution (PG-DS) influences serum levels of sodium, amylase, and lipase, and of iron parameters. We aimed to examine, in the blood or serum of continuous ambulatory peritoneal dialysis (CAPD) patients treated with PG-DS, changes in the concentrations of Na+, K+, Ca++, total Ca, phosphorus, urea nitrogen, creatinine, uric acid, total protein, albumin, and intact parathyroid hormone (iPTH); in lipid profile [total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides, HDL:total cholesterol ratio]; and in acid-base status. We started studies in 14 CAPD patients in whom 7.5% PG-DS was applied for the overnight 2-L exchange (duration: about 10 hours). Determinations of blood chemistry were carried out at 1.6 +/- 0.8 months before the introduction of PG-DS (period I, n = 14); after 1.2 +/- 0.6 months (period II, n = 14), 4.4 +/- 0.8 months (period III, n = 11), and 8.8 +/- 2.4 months (period IV, n = 9) of PG-DS administration; and 2.0 +/- 0.6 months after PG-DS discontinuation (period V, n = 11). The most pronounced (significant) differences in the examined parameters were seen between periods I and III or periods I and IV for Na+ (140 +/- 3 mmol/L vs 136 +/- 4 mmol/L), K+ (4.2 +/- 0.6 mmol/L vs 4.8 +/- 0.6 mmol/L), total Ca (9.4 +/- 1.1 mg/dL vs 10.5 +/- 1.3 mg/dL), urea nitrogen (61.3 +/- 25.9 mg/dL vs 79.4 +/- 20.9 mg/dL), creatinine (10.7 +/- 2.6 mg/dL vs 12.8 +/- 4.3 mg/dL), uric acid (4.8 +/- 2.3 mg/dL vs 7.1 +/- 1.7 mg/dL), and total protein (61.7 +/- 10.8 g/L vs 70.5 +/- 8.0 g/L). Serum lipid levels were stable during PG-DS administration, but they increased after discontinuation of the PG-DS. Other studied parameters usually returned to pre-treatment values after PG-DS discontinuation. All patients were in good clinical status during the study. The changes in blood chemistry did not cause clinical intervention. Our results indicate that PG-DS influences blood chemistry. The observed differences need to be clinically analyzed.

Amplification of putative chlorocatechol dioxygenase gene fragments from alpha- and beta-Proteobacteria

Redundant primers were designed for the PCR amplification of DNA from chlorocatechol dioxygenase genes. These primers were used successfully to amplify 270- to 279-bp fragments from a variety of 2,4-dichlorophenoxyacetate- and cholorobenzoate-degrading strains, including species of Sphingomonas. Three groups of closely related sequences were amplified: one from chlorobenzoate degraders that was 86% similar to the amino acid sequence of the protein coded by the tfdC gene of Ralstonia eutropha JMP134 (pJP4), a second from Sphingomonas strains that was 70% similar to this amino acid sequence, and a third from diverse 2,4-D degraders that showed only 53% similarity to the product coded by tfdC from pJP4 but 88-100% similarity to the product of the tfdC gene of the plasmid pEST4011 from a Pseudomonas putida strain. The primers should be useful in further study of this gene and in tracking a variety of degraders of chloroaromatic compounds in natural systems.