3-Chlorodiphenylamine activates cardiac troponin by a mechanism distinct from bepridil or TFP.

Despite extensive efforts spanning multiple decades, the development of highly effective Ca2+ sensitizers for the heart remains an elusive goal. Existing Ca2+ sensitizers have other targets in addition to cardiac troponin (cTn), which can lead to adverse side effects, such as hypotension or arrhythmias. Thus, there is a need to design Ca2+-sensitizing drugs with higher affinity and selectivity for cTn. Previously, we determined that many compounds based on diphenylamine (DPA) were able to bind to a cTnC-cTnI chimera with moderate affinity (Kd ∼10-120 µM). Of these compounds, 3-chlorodiphenylamine (3-Cl-DPA) bound most tightly (Kd of 10 µM). Here, we investigate 3-Cl-DPA further and find that it increases the Ca2+ sensitivity of force development in skinned cardiac muscle. Using NMR, we show that, like the known Ca2+ sensitizers, trifluoperazine (TFP) and bepridil, 3-Cl-DPA is able to bind to the isolated N-terminal domain (N-domain) of cTnC (Kd of 6 µM). However, while the bulky molecules of TFP and bepridil stabilize the open state of the N-domain of cTnC, the small and flexible 3-Cl-DPA molecule is able to bind without stabilizing this open state. Thus, unlike TFP, which drastically slows the rate of Ca2+ dissociation from the N-domain of isolated cTnC in a dose-dependent manner, 3-Cl-DPA has no effect on the rate of Ca2+ dissociation. On the other hand, the affinity of 3-Cl-DPA for a cTnC-TnI chimera is at least an order of magnitude higher than that of TFP or bepridil, likely because 3-Cl-DPA is less disruptive of cTnI binding to cTnC. Therefore, 3-Cl-DPA has a bigger effect on the rate of Ca2+ dissociation from the entire cTn complex than TFP and bepridil. Our data suggest that 3-Cl-DPA activates the cTn complex via a unique mechanism and could be a suitable scaffold for the development of novel treatments for systolic heart failure.

Successful Identification of Cardiac Troponin Calcium Sensitizers Using a Combination of Virtual Screening and ROC Analysis of Known Troponin C Binders.

Calcium-dependent cardiac muscle contraction is regulated by the protein complex troponin. Calcium binds to the N-terminal domain of troponin C (cNTnC) which initiates the process of contraction. Heart failure is a consequence of a disruption of this process. With the prevalence of this condition, a strong need exists to find novel compounds to increase the calcium sensitivity of cNTnC. Desirable are small chemical molecules that bind to the interface between cTnC and the cTnI switch peptide and exhibit calcium sensitizing properties by possibly stabilizing cTnC in an open conformation. To identify novel drug candidates, we employed a structure-based drug discovery protocol that incorporated the use of a relaxed complex scheme (RCS). In preparation for the virtual screening, cNTnC conformations were identified based on their ability to correctly predict known cNTnC binders using a receiver operating characteristics analysis. Following a virtual screen of the National Cancer Institute's Developmental Therapeutic Program database, a small number of molecules were experimentally tested using stopped-flow kinetics and steady-state fluorescence titrations. We identified two novel compounds, 3-(4-methoxyphenyl)-6,7-chromanediol (NSC600285) and 3-(4-methylphenyl)-7,8-chromanediol (NSC611817), that show increased calcium sensitivity of cTnC in the presence of the regulatory domain of cTnI. The effects of NSC600285 and NSC611817 on the calcium dissociation rate was stronger than that of the known calcium sensitizer bepridil. Thus, we identified a 3-phenylchromane group as a possible key pharmacophore in the sensitization of cardiac muscle contraction. Building on this finding is of interest to researchers working on development of drugs for calcium sensitization.

Kinematical analysis of the snatch in elite male junior weightlifters of different weight categories.

The purpose of this study was to analyze the differences in the technical pattern of the snatch in elite junior weightlifters of different weight categories. The sample was a group of 33 men weightlifters from different weight categories. The comparative study included 2 groups, taking into account weight categories. Group A included 17 weightlifters from the lightest categories, 56 and 62 kg; group B included 16 weightlifters from the heaviest categories, 85 and 105 kg. Three-dimensional photogrammetry technique was utilized. Regarding group differences, we can conclude that lifters belonging to heavier categories are more efficient, as they manage to have longer barbell propulsion trajectories, which allows them to exert actions on the barbell for a longer period, especially in the initial lifting phase. They attain greater barbell vertical velocity (p = 0.029), a longer vertical bar trajectory normalized on first pull (p = 0.011), and a greater, although limited, bar height loss on the catch (p = 0.008). Besides, intergroup differences evidence that heavier category lifters observe a different temporal organization of the movement based on a longer first pull (p = 0.000), a shorter transition (p = 0.030), and a longer turnover (p = 0.049). No significant differences were found in the analyzed angular parameters during the first and second pull. We believe the intergroup differences found not to be determining enough to consider a technical model adapted to the characteristics of each body weight category. This confirms that a successful lift is multifactor based and individual dependent. Given its transcendence, this evidence should be taken into account in the technical training of young lifters.

Lymphoscintigraphic study in a case of rheumatoid arthritis-related lymphoedema.

Lymphoedema of the upper limbs is a rare extraarticular manifestation of rheumatoid arthritis (RA). Herein we report a patient with RA who presented two episodes of lymphoedema in the hands and forearms coinciding with flares of polyarthritis. Lymphoscintigraphy showed lymphatic-ectasia. The oedema improved with slow-acting drug treatment.