Structural and molecular bases of angiotensin-converting enzyme inhibition by bovine casein-derived peptides: an in silico molecular dynamics approach

The angiotensin-converting enzyme (ACE) plays a key role in blood pressure regulation process, and its inhibition is one of the main drug targets for the treatment of hypertension. Though various peptides from milk proteins are well-known for their ACE-inhibitory capacity, research devoted to understand the molecular bases of such property remain scarce, specifically for such peptides. Therefore, in this work, computational molecular docking and molecular dynamics calculations were performed to enlighten the intermolecular interactions involved in ACE inhibition by six different casein-derived peptides (FFVAPFPEVFGK, FALPQYLK, ALNEINQFYQK, YLGYLEQLLR, HQGLPQEVLNENLLR and NAVPITPTLNR). Two top ranked docking poses for each peptide (one with N- and the other C-terminal peptide extremity oriented towards the ACE active site) were selected for dynamic simulations (50 ns; GROMOS53A6 force field), and the results were correlated to in vitro ACE inhibition capacity. Two molecular features appeared to be essential for peptides to present high ACE inhibition capacity in vitro: i) to interact with the S1 active site residues (Ala354, Glu384, and Tyr523) by hydrogen bonds; ii) to interact with Zn²⁺ coordinated residues (His383, His387, and Glu411) by short-lenght hydrogen bonds, as observed in the cases of ALNEINQFYQK (IACE = 80.7%), NAVPITPTLNR (IACE = 80.7%), and FALPQYLK (IACE = 79.0%). Regardless of the temporal stability of these strong interactions, they promoted some disruption of Zn²⁺ tetrahedral coordination during the molecular dynamics trajectories, and were pointed as the main reason for the greatest ACE inhibition by these peptides. On the other hand, peptides with intermediate inhibition capacity (50% < I_ACE < 45%) interacted mainly by weaker interactions (e.g.: electrostatic and hydrophobic) with the Zn²⁺ coordinated residues, and were not able to change significantly its tetrahedral coordination structure. These findings may: i) assist the discrimination in silico of "good" and "bad" ACE-inhibitory peptides from other food sources, and/or ii) aid in designing de novo new molecules with ACE-inhibitory capacity. Communicated by Ramaswamy Sarma.

Design of inhibitors of thymidylate kinase from Variola virus as new selective drugs against smallpox: part II

Acknowledging the importance of studies toward the development of measures against terrorism and bioterrorism, this study aims to contribute to the design of new prototypes of potential drugs against smallpox. Based on a former study, nine synthetic feasible prototypes of selective inhibitors for thymidylate kinase from Variola virus (VarTMPK) were designed and submitted to molecular docking, molecular dynamics simulations and binding energy calculations. The compounds are simplifications of two more complex scaffolds, with a guanine connected to an amide or alcohol through a spacer containing ether and/or amide groups, formerly suggested as promising for the design of selective inhibitors of VarTMPK. Our study showed that, despite the structural simplifications, the compounds presented effective energy values in interactions with VarTMPK and HssTMPK and that the guanine could be replaced by a simpler imidazole ring linked to a –NH₂ group, without compromising the affinity for VarTMPK. It was also observed that a positive charge in the imidazole ring is important for the selectivity toward VarTMPK and that an amide group in the spacer does not contribute to selectivity. Finally, prototype 3 was pointed as the most promising to be synthesized and experimentally evaluated.

Communicated by Ramaswamy H. Sarma

The oil-contaminated soil diazotroph Azoarcus olearius DQS-4T is genetically and phenotypically similar to the model grass endophyte Azoarcus sp. BH72

The genome of Azoarcus olearius DQS-4^T , a N₂ -fixing Betaproteobacterium isolated from oil-contaminated soil in Taiwan, was sequenced and compared with other Azoarcus strains. The genome sequence showed high synteny with Azoarcus sp. BH72, a model endophytic diazotroph, but low synteny with five non-plant-associated strains (Azoarcus CIB, Azoarcus EBN1, Azoarcus KH32C, A. toluclasticus MF63^T and Azoarcus PA01). Average Nucleotide Identity (ANI) revealed that DQS-4^T shares 98.98% identity with Azoarcus BH72, which should now be included in the species A. olearius. The genome of DQS-4^T contained several genes related to plant colonization and plant growth promotion, such as nitrogen fixation, plant adhesion and root surface colonization. In accordance with the presence of these genes, DQS-4^T colonized rice (Oryza sativa) and Setaria viridis, where it was observed within the intercellular spaces and aerenchyma mainly of the roots. Although they promote the growth of grasses, the mechanism(s) of plant growth promotion by A. olearius strains is unknown, as the genomes of DQS-4^T and BH72 do not contain genes for indole acetic acid (IAA) synthesis nor phosphate solubilization. In spite of its original source, both the genome and behaviour of DQS-4^T suggest that it has the capacity to be an endophytic, nitrogen-fixing plant growth-promoting bacterium.

Analysis of Coxiela burnetti dihydrofolate reductase via in silico docking with inhibitors and molecular dynamics simulation

Coxiella burnetii is a gram-negative bacterium able to infect several eukaryotic cells, mainly monocytes and macrophages. It is found widely in nature with ticks, birds, and mammals as major hosts. C. burnetii is also the biological warfare agent that causes Q fever, a disease that has no vaccine or proven chemotherapy available. Considering the current geopolitical context, this fact reinforces the need for discovering new treatments and molecular targets for drug design against C. burnetii. Among the main molecular targets against bacterial diseases reported, the enzyme dihydrofolate reductase (DHFR) has been investigated for several infectious diseases. In the present work, we applied molecular modeling techniques to evaluate the interactions of known DHFR inhibitors in the active sites of human and C. burnetii DHFR (HssDHFR and CbDHFR) in order to investigate their potential as selective inhibitors of CbDHFR. Results showed that most of the ligands studied compete for the binding site of the substrate more effectively than the reference drug trimethoprim. Also the most promising compounds were proposed as leads for the drug design of potential CbDHFR inhibitors.

Preventing the return of smallpox: molecular modeling studies on thymidylate kinase fromVariola virus

Smallpox was one of the most devastating diseases in the human history and still represents a serious menace today due to its potential use by bioterrorists. Considering this threat and the non-existence of effective chemotherapy, we propose the enzyme thymidylate kinase from Variola virus (VarTMPK) as a potential target to the drug design against smallpox. We first built a homology model for VarTMPK and performed molecular docking studies on it in order to investigate the interactions with inhibitors of Vaccinia virus TMPK (VacTMPK). Subsequently, molecular dynamics (MD) simulations of these compounds inside VarTMPK and human TMPK (HssTMPK) were carried out in order to select the most promising and selective compounds as leads for the design of potential VarTMPK inhibitors. Results of the docking and MD simulations corroborated to each other, suggesting selectivity towards VarTMPK and, also, a good correlation with the experimental data.

Multi-quantum echoes in GdAl2 zero-field high-resolution NMR

In this paper we present a series of high-resolution zero-field NMR spectra of the polycrystalline intermetallic compound GdAl(2). The spectra were obtained with the sample at 4.2K in the ordered magnetic state and in the absence of an external static magnetic field. Using a sequence composed of two RF pulses, we obtained up to five multi-quantum echoes for the (27)Al nuclei, which were used to construct the zero-field NMR spectra. The spectra obtained from the FID observed after the second pulse and the even echoes exhibited higher resolution than the odd ones. In order to explain such behavior, we propose a model in which there are two regions inside the sample with different inhomogeneous spectral-line broadenings. Moreover, with the enhanced resolution from the FID signal, we were able to determine quadrupolar couplings with great precision directly from the respective spectra. These results were compared with those obtained from the quadrupolar oscillations of the echo signals, and showed good agreement. Similar data were also obtained from (155)Gd and (157)Gd nuclei.

Model for the growth of electrodeposited ferromagnetic aggregates under an in-plane magnetic field

The quasi-two-dimensional deposition of ferromagnetic materials by electrochemical process under the influence of a magnetic field applied in the plane of the growth leads to a surprising symmetry breaking in the dendritic structures found. The reasons for these features are still not completely understood. The original dense circular envelope becomes rectangular, as well as the sparse figures have their shapes elongated. This paper reports the results of a diffusion-limited aggregation (DLA) -like simulation. The model proposed here, a modification of the original DLA model, can deal with ferromagnetic particles under the influence of an electric field and the dipolar interactions between particles, submitted to an applied magnetic field in the plane of growth of such structures. The results were produced varying the applied magnetic field and the magnetic moment of the particles and show that the balance between these interactions is an important mechanisms that can be responsible for the changes in shape of the aggregates observed in the experiments.

Profiling resistance-related mutations in the protease region of the pol gene: single genome sequencing of HIV in plasma and peripheral blood mononuclear cells

Genotypic resistance is currently assessed through direct sequencing, which cannot detect resistant strains below 20%. We compared the genotypic resistance profile of virions and proviruses using population-based analysis and single genome sequencing of the protease region of the pol gene in samples collected from five individuals in whom indinavir monotherapy resulted in treatment failure. Single genome sequencing showed that not all strains present the same resistance mutations, which can be dispersed across different HIV genomes. The resistance profile found in plasma was very similar to that found in peripheral blood mononuclear cells (PBMCs), confirming the utility of assessing proviral DNA as for a means of determining antiretroviral resistance.

No significant association between response to methylphenidate and genes of the dopaminergic and serotonergic systems in a sample of Brazilian children with attention-deficit/hyperactivity disorder

Few studies on pharmacogenetics of Attention-Deficit/Hyperactivity Disorder (ADHD) have been conducted. Most of them evaluated dopaminergic genes resulting in positive and negative findings. We assessed effects of polymorphisms in candidate dopaminergic (DRD4, DAT1) and serotonergic genes (HTR1B, HTR2A, and 5-HTT) on the response to treatment in 111 patients for whom methylphenidate (MPH) was prescribed. Outcome measures (Swanson, Nolan, and Pelham scale-version IV, Children Global Assessment Scale, Barkley's Stimulants Side Effects Rating Scale) were assessed at baseline and 1 month after the intervention. No significant association was detected between polymorphisms assessed and both response and side effects to MPH. Prospective multi-site controlled studies with larger sample sizes are needed in order to disentangle the role of candidate genes in response to ADHD treatment.

Quantum logical operations for spin 3/2 quadrupolar nuclei monitored by quantum state tomography

This article presents the realization of many self-reversible quantum logic gates using two-qubit quadrupolar spin 3/2 systems. Such operations are theoretically described using propagation matrices for the RF pulses that include the effect of the quadrupolar evolution during the pulses. Experimental demonstrations are performed using a generalized form of the recently developed method for quantum state tomography in spin 3/2 systems. By doing so, the possibility of controlling relative phases of superimposed pseudo-pure states is demonstrated. In addition, many aspects of the effect of the quadrupolar evolution, occurring during the RF pulses, on the quantum operations performance are discussed. Most of the procedures presented can be easily adapted to describe selective pulses of higher spin systems (>3/2) and for spin 1/2 under J couplings.

[Squamous cell carcinoma of the canal anal]

BACKGROUND

Anal cancer is an uncommon malignancy accounting for only a small (4%) percentage of intestinal cancer. The authors described the clinical aspects and the treatment of the patients with squamous cell carcinoma of the canal anal.

PATIENTS

Eleven patients with squamous cell carcinoma treated among 1995 and 1999, were analyzed retrospectively. Nine were women and two were men. The mean age was 57.6 years old (range 35-82 years old).

RESULTS

The most common symptoms were rectal bleeding, local tumor and pain. Six of them had previous anal benign disease and two had metastases at the diagnosis. All were submitted to systemic chemotherapy with 5-fluorouracil and mitomycin and radiotherapy with 4500 cGy. Four patients had residual disease after chemo radiation and salvage surgery with abdominoperineal resection was done. Three patients had recurrence and four died from the disease.

CONCLUSION

Most of our patients were women. The chemo radiation can be a curable treatment in patients with local disease; conversely in patients with residual disease, abdominoperineal resection must be done. Although anal cancer is an often curable disease, four patients died because the diagnosis was done in advanced stage.

Croton zehntneri essential oil: effects on behavioral models related to depression and anxiety

Croton zehntneri (Cz), a popular plant used to treat "nervous disturbance", contains a complex mixture of compounds, including substances exhibiting central nervous system activity. The effects of Cz essential oil administration (p.o.) on the rat's central nervous system were studied in behavioral models used to evaluate anxiety and antidepressive drugs. The results showed that administration of Cz essential oil: 1) increased the immobility duration measured in the forced swimming test as compared to control group (control = 89.8 +/- 45.8; 1 microl = 153.0 +/- 48.7; 3 microl = 157.4 +/- 45.3; 10 microl = 145.3 +/- 51.0); 2) reduced the locomotion frequency observed in the open field (control = 62.5 +/- 22.7; 3 microl = 38.0 +/- 13.5; 10 microl = 39.2 +/- 22.2); 3) had no effect on the experimental group (1 microl) observed in open field; 4) had no effect on animals tested in social interactions, plus-maze and holeboard tests. These data suggest that Cz oil produced central depressor effects in rats without any anxiety alterations. These results may explain the popular use of this plant in Brazilian folk medicine for treating "nervous disturbances".

Modulation of carbachol-induced antinociception from the rat periaqueductal gray

The tail-flick latency (TFL) and the vocalisation test (VT) thresholds were all increased by microinjecting CCh into the dorsal periaqueductal gray (dPAG) of rats. The effects on the TFL were mimicked by dimethyl-phenylpiperazinium, and inhibited by local mecamylamine or intraperitoneal (i.p.) phenoxybenzamine. The effects on the VT were mimicked by bethanechol and inhibited by local mecamylamine, atropine or naloxone. The effects on the thresholds for motor defence reaction were inhibited by i.p. methysergide or naloxone, and prolonged by i.p. phenoxybenzamine. The effects on the threshold for vocalisation during the stimulation were blocked by i. p. methysergide and shortened by i.p. phenoxybenzamine or naloxone. No significant effect of CCh was found on open arm exploration of rats in the elevated plus maze paradigm. We conclude that the effects of CCh from the dPAG is not due to an anxiolytic effect, and depends on the activation of local cholinergic and opioid sites for the supraspinal modulation of "affective" component of pain response, and nicotinic sites for the activation of descending pain pathways.

Pharmacological evidence for a periaqueductal gray-nucleus raphe magnus connection mediating the antinociception induced by microinjecting carbachol into the dorsal periaqueductal gray of rats

A previous study demonstrated that microinjection of carbachol (CCh) into the dorsal periaqueductal gray matter (dPAG) of rats increases the latency for the tail flick reflex. Several other studies have implicated the raphe magnus (NRM) and the reticularis paragigantocellularis (NRPG) nuclei as relay stations through which descending pathways from the PAG project to the spinal cord via the dorsolateral funiculus (DLF). In the present study, the effects of microinjecting CCh into the dPAG on the tail flick test were examined in rats in which the ipsilateral DLF was previously lesioned, or saline or lidocaine (2%) was microinjected into the NRM or ipsilateral NRPG. The DLF lesion did not change the baseline threshold of the animals in the test, but abolished the CCh-induced increase in the tail flick latency from the dPAG. The neural block of the NRM or NRPG with lidocaine also did not change significantly the latency for the tail flick reflex. The increase in the tail flick latency produced by CCh from the dPAG was not changed by the neural block of the NRPG, but was significantly reduced by the neural block of the NRM. These results are interpreted as indicative that the central antinociceptive mechanisms activated by CCh from the dPAG depend on a descending pathway that projects to the spinal cord via DLF utilizing at least the NRM, but not the NRPG, as an intermediary relay station.

Metabolism of a chylomicron-like emulsion in rats with Walker 256 tumor: influence of a polyunsaturated (n-6) compared with a saturated fatty acid-rich diet

OBJECTIVE

Defects in lipid metabolism secondary to development of cancer are frequently observed and, in experimental animals, manipulation of the lipid content of the diet can significantly influence tumor growth. The effects of a high polyunsaturated fat vs a high saturated fat diet upon the chylomicron metabolism of rats bearing Walker 256 tumor were examined.

METHODS

Chylomicron-like emulsions labeled with radioactive lipids were injected into rats bearing the tumor and control rats. The two groups were previously given a high polyunsaturated (n-6) (15% fat) or a high saturated fat diet (15% fat) for 6 weeks. Following injection, plasma samples were collected at 8 time intervals in 60 minutes and tissue fragments were excised after the animals were killed, for determination of the plasma fractional clearance rate (FCR, min-1) and organ uptake of radioactive lipids.

RESULTS

FCR of the emulsion triacylglycerols (TG) and cholesteryl oleate ether (CE) decreased in the tumor-bearing rats fed the polyunsaturated fat-rich diet (FCR-TG control = 0.26 +/- 0.09, tumor = 0.11 +/- 0.04; FCR-CE controls = 0.18 +/- 0.05, tumor = 0.10 +/- 0.02), as did activity of the lipoprotein and hepatic lipases (p < 0.05). This indicates that in this group, the presence of the tumor elicited defective lipolysis and delayed removal of the emulsion from the plasma. In the group fed the saturated fatty acid-rich diet, however, these alterations were not observed (FCR-TG control = 0.21 +/- 0.11, tumor = 0.20 +/- 0.08; FCR-CE control = 0.13 +/- 0.06, tumor = 0.10 +/- 0.05). The uptake by several tissues of the emulsion CE was similar in all rat groups.

CONCLUSION

The saturated fat-rich diet avoids the deficiency in chylomicron lipolysis elicited by the implanted Walker 256 tumor.

Antinociceptive effects of carbachol microinjected into different portions of the mesencephalic periaqueductal gray matter of the rat

The changes in tail-flick latency (TFL) to noxious heating of the skin produced by the microinjection of carbachol (CCh) into the dorsal (dPAG), lateral (lPAG), and ventral (vPAG) portions of the mesencephalic periaqueductal gray matter (PAG) were studied in the rat. A significant increase in TFL was produced by CCh (0.2 microgram/0.5 microliter) microinjected into sites widely distributed within the PAG. The effect of CCh was stronger in the most caudal portion of the DPAG. Smaller effects were obtained after injection of CCh into the aqueduct, indicating that drug diffusion from the injection sites to the aqueduct lumen is unlikely to cause the antinociceptive effect of CCh. Dimethyl-phenyl-piperazinium (0.35 microgram/0.5 microliter), but not bethanechol (0.22 and 0.44 microgram/0.5 microliter), produced effects similar to CCh (0.2 microgram/0.5 microliter), when injected into the dPAG. The effects of CCh were inhibited by the previous administration of mecamylamine (1 microgram/0.5 microliter), but not atropine (1 microgram/0.5 microliter) or naloxone (1 microgram/0.5 microliter), into the dPAG. These results are indicative that antinociception produced by CCh from the dPAG depends on nicotinic, but not muscarinic or opioid mechanisms within the dPAG. The intraperitoneal administration of phenoxybenzamine (1 mg/kg) or mecamylamine (1 mg/kg), but not naloxone (1 mg/kg), methysergide (1 mg/kg), or atropine (1 mg/kg), inhibited the effects of CCh injected into the dPAG. In contrast, a higher dose of intraperitoneal phenoxybenzamine (5 mg/kg) was ineffective against the antinociception evoked by CCh when injected into the vPAG. Therefore, the effects of CCh from the dPAG may depend on the activation of centrifugal pathways involving both nicotinic and alpha-adrenergic mechanisms. In addition, the results indicate that different cholinergic substrates in the PAG may mediate both alpha-adrenergic and non-alpha-adrenergic descending pain mechanisms activated by the dPAG and vPAG, respectively.

Involvement of GABA and ACh in retinal spreading depression: effects of "low calcium-high magnesium" solutions

Experiments have been performed on isolated chick retinas to demonstrate the participation of gabaergic and cholinergic systems in spreading depression (SD). Gamma-aminobutyric acid (GABA) and acetylcholine (ACh) were measured in the effluent solution of superfused retinas. The influence of changes in the concentration of calcium/magnesium on the release of these neurotransmitters was studied. GABA and ACh are released in the superfusate of retinas during SD. Such release was observed during experimental periods longer than 2 h during which SD was elicited regularly at 15-20 min intervals. Decreasing calcium concentration from 1.0 to 0.5 mM and simultaneously increasing magnesium from 1.0 to 2.0-4.0 mM led to a decrease in GABA and ACh release during SD. Variations in light-scattering and increases in potassium concentration, usually occurring during SD, also decreased when superfusing with low calcium/high magnesium solutions. Lowering calcium concentration to 0.5 mM and increasing magnesium to 2.0 mM eventually turned the tissue refractory to SD. Sometimes a magnesium concentration of 2.0 mM was not effective in blocking SD. However, this blockage could be attained by increasing the concentration of magnesium to 4.0 mM. The effects of low calcium - high magnesium solutions on GABA and ACh release during SD suggests that the release of the substances is at least partially due to synaptic activity. It is not yet possible to establish whether GABA and ACh release is essential for the occurrence of SD. Nevertheless such release suggest that these neurotransmitters could influence the characteristics of SD manifestations in the retina.