Side-reactions in peptide synthesis

The impurities which formed in the large-scale synthesis of THF-γ2, an immunomodulatory peptide of formula H-Leu-Glu-Asp-Gly-Pro-Lys-Phe-Leu-OH, were identified by a combination of analytical methods, and their structure confirmed by synthesis. Most impurities originated from side-reactions involving the aspartyl residue (cyclization, β-aspartyl formation and cleavage). Based on this knowledge, modifications were introduced into the work up and the purification procedure which resulted in a very pure final product (>99% by RP-HPLC).     

Synthesis and opioid activity of partial retro-inverso analogs of dermorphin

We studied the effect of partial retro-inverso modification of selected peptide bonds of dermorphin (H-Tyr-d -Ala-Phe-Gly-Tyr-Pro-Ser-NH₂. The modifications concern two consecutive peptide bonds (Phe³-Cly⁴-Tyr⁵, I) or a single one (Gly⁴-Tyr⁵-, II or Phe³-Gly⁴, III). All pseudoheptapeptides showed low opioid activity in the in vitro and in vivo tests. Compound III has a biological potency comparable to that of morphine but only 2–5% of original dermorphin when tested in guinea pig ileum preparation and in mice tail-flick assay after intra-cerebro or subcutaneous administration.     

Synthesis,metabolic stability and chemotactic activity of peptide T and its analogues

Acquired immunodeficiency syndrome (AIDS) is initiated by the attachment of the human immunodeficiency virus (HIV) to a surface glycoprotein CD₄ present on T₄ helper/inducer lymphocytes, monocytes/macrophages and other cells. A simple octapeptide (H-Ala-Ser-Thr-Thr-Thr-Asn-Tyr-Thr-OH, peptide T) seems to inhibit HIV infectivity and to activate human monocyte chemotaxis. In order to study in vitro metabolic stability and structure-activity relationships, peptide T and a number of analogues were prepared and tested on human monocytes by chemotactic assay. Peptide T and the shorter fragments T(3-8)-OH and T(4–8)-OH displayed potent bioactivity (maximal chemotactic activity in the range 10^-11-10^-10M). The C-terminal heptapeptide showed a reduction of potency, while further truncations at N-terminus of T(4–8)-OH abolished the biological action. In the octapeptide series, whereas the α-amino butyric acid (Abu) substitution for Thr⁴ was well tolerated, the same “slight” structural change at Thr⁵ or Thr⁸ was very detrimental. Finally, [d -Asn⁶]T(1-8)-OH analogue has low chemotactic activity. All these results indicate that i) the C-terminal pentapeptide is the minimum sequence required for bioactivity, ii) residues 5 to 8 appear to play a crucial biological role, iii) peptide T chemotaxis is mediated, at least in part, through the polar properties of Thr side chains at the critical positions 5 and 8, while the Thr⁴ does not interfere with biological characteristics of peptides. With regard to the enzymic degradation, the in vitro experiments showed the susceptibility of peptide T to rapid metabolism by human or rat plasma (T1/2 = 5.2 min), rat brain (T1/2 = 2.1 min) and kidney (T1/2 = 0.4 min) enzymes. The main metabolic product appears to be the C-terminal heptapeptide, which retains, in turn, a low enzymatic stability.     

The urinary excretion of prostaglandins E2 and F2α in essential hypertension

The 24 h urinary excretions of prostaglandins E2 (E2/d) and F2 alpha (F2 alpha/d) were measured in twenty-five normal subjects and in thirty-five patients with essential hypertension [seventeen with low renin (LRH) and eighteen with normal renin (NRH) hypertension]. E2/d was lower in patients with LRH than in normal subjects (P less than 0.01), whereas no difference was found between patients with NRH and the controls. F2 alpha/d was similar in patients with LRH and in the normal subjects, but was significantly greater in patients with NRH (P less than 0.02). The ratio of prostaglandin E2 to prostaglandin F2 alpha was decreased in hypertensive patients (P less than 0.02), although in the NRH subgroup the difference was not statistically significant. It appears that LRH is associated with impaired production of prostaglandin E2, while a deranged relationship between the two prostaglandins exists in all the patients with essential hypertension. These changes in prostaglandin production could possibly contribute to the pathogenesis of hypertension, by increasing renal vascular resistance and decreasing sodium excretion. Alternatively, they might be a secondary phenomenon, reflecting changes in renal prostaglandin metabolism induced by the hypertensive state.     

Decrease in Patient Radiation Exposure by a Tantalum Filter during Electrophysiological Procedures

Aim: Minimization of X-ray exposure remains a primary issue in cardiac electrophysiology. The effectiveness of X-ray beam filtration during cardiac electrophysiological procedures was therefore studied, using a 0.05-mm-thick tantalum (Ta) foil, as a filter on the primary X-ray beam, to reduce the patient dose without degradation of image quality.
Method: Preliminary tests were made on a phantom developed with polymethylmethacrylate, catheters, and guide wires. The filter was then used in patients during cardiac procedures. Identical patient images were obtained with and without the Ta filter insertion and the ratio between image quality and patient dose was evaluated. Changes in patient dose and signal-to-noise ratio, as image quality index were measured on the phantom and in patients.
Results and Conclusions: When the Ta filter was used, the mean effective individual patient dose decreased by 3 to 40% (mean reduction = 27%), with no perceivable difference in image quality estimated by electrophysiologists. This Ta filter may be useful to limit the radiation exposure of patients and operators during cardiac procedures.     

A Prospective Randomized Evaluation of VV Delay Optimization in CRT-D Recipients: Echocardiographic Observations from the RHYTHM II ICD Study

Background: All current cardiac resynchronization therapy (CRT) devices allow the programming of the atrioventricular (AV/PV) delays and the sequential stimulation of the ventricles via the inter ventricular (VV) delay.
Aim: This post hoc analysis of the RHYTHM II study was conducted to compare the reverse remodeling associated with VV delay optimization in patients randomly assigned to simultaneous (SIM) biventricular stimulation versus patients assigned to optimized VV delay programming (OPT) (1:3 randomization scheme).
Methods: The analysis included 14 patients assigned to the SIM group and 34 patients to the OPT group who completed the 6-month follow-up period with paired echocardiographic recordings.
Results: In both study groups, changes consistent with left ventricular (LV) remodeling were observed between baseline and 6 months, with significant improvements in LV function and decrease in LV dimensions. In the OPT group, there was also a decrease in left atrial diameter and mitral valve closure to opening time. At 6 months, the overall proportion of echocardiographic responders (≥10% decrease in LV end-systolic volume or ≥5% absolute increase in LV ejection fraction) was similar in both groups. The optimal AV/VV delays, evaluated by maximization of LV outflow tract velocity time integral, changed over time.
Conclusions: Ventriculo-ventricular delay optimization was associated with better immediate hemodynamic function than simultaneous biventricular stimulation, though did not promote additional reverse remodeling at 6 months and did not increase the proportion of echocardiographic responders to CRT. Optimization of both the AV and VV intervals was patient-specific and optimal values changed over time.