Crystal Structure of the Bacterial Ribosomal Decoding Site Complexed with a Synthetic Doubly Functionalized Paromomycin Derivative: a New Specific Binding Mode to an A-Minor Motif Enhances in vitro Antibacterial Activity

The crystal structure of the complex between oligonucleotide containing the bacterial ribosomal decoding site (A site) and the synthetic paromomycin analogue 1, which contains the gamma-amino-alpha-hydroxybutyryl (L-haba) group at position N1 of ring II (2-DOS ring), and an ether chain with an O-phenethylaminoethyl group at position C2'' of ring III, is reported. Interestingly, next to the paromomycin analogue 1 specifically bound to the A site, a second molecule of 1 with a different conformation is observed at the crystal packing interface which mimics the A-minor interaction between two bulged-out adenines from the A site and the codon-anticodon stem of the mRNA-tRNA complex. Improved antibacterial activity supports the conclusion that analogue 1 might affect protein synthesis on the ribosome in two different ways: 1) specific binding to the A site forces maintenance of the "on" state with two bulged out adenines, and 2) a new binding mode of 1 to an A-minor motif which stabilizes complex formation between the ribosome and the mRNA-tRNA complex regardless of whether the codon-anticodon stem is of the cognate or near-cognate type.

Crystallographic studies of Homo sapiens ribosomal decoding A site complexed with aminoglycosides

Aminoglycosides are highly effective antibacterial drugs that decrease translation accuracy by binding to the aminoacyl-tRNA decoding site (A site) of 16S ribosomal RNA. On the other hand, they are highly toxic to mammals through kidney and ear-associated illnesses by binding to ribosomal A sites. To understand the mechanism of toxicity of aminoglycosides to mammals at atomic level, crystallographic studies have been carried out with a number of Homo sapiens mitochondrial and cytoplasmic A sites complexed with aminoglycosides. Several X-ray diffraction data sets were successfully collected. Initial phases of mitochondrial A site with tobramycin and cytoplasmic A site with paromomycin were derived by the molecular replacement method. Refinements of atomic parameters are now under progress.

Structure-based design, synthesis, and A-site rRNA cocrystal complexes of functionally novel aminoglycoside antibiotics: C2" ether analogues of paromomycin

A series of 2"-O-substituted ether analogues of paromomycin were prepared based on new site-selective functionalizations. X-ray cocrystal complexes of several such analogues revealed a new mode of binding in the A-site rRNA, whereby rings I and II adopted the familiar orientation and position previously observed with paromomycin, but rings III and IV were oriented differently. With few exceptions, all of the new analogues showed potent inhibitory activity equal or better than paromomycin against a sensitive strain of S. aureus. Single digit microM MIC values were obtained against E. coli, with some of the ether appendages containing polar or basic end groups. Two analogues showed excellent survival rate in a mouse septicemia protection assay. Preliminary histopathological analysis of the kidney showed no overt signs of toxicity, while controls with neomycin and kanamycin were toxic at lower doses.

Structure-based design, synthesis, and A-site rRNA cocrystal complexes of functionally novel aminoglycoside antibiotics: C2" ether analogues of paromomycin

A series of 2"-O-substituted ether analogues of paromomycin were prepared based on new site-selective functionalizations. X-ray cocrystal complexes of several such analogues revealed a new mode of binding in the A-site rRNA, whereby rings I and II adopted the familiar orientation and position previously observed with paromomycin, but rings III and IV were oriented differently. With few exceptions, all of the new analogues showed potent inhibitory activity equal or better than paromomycin against a sensitive strain of S. aureus. Single digit microM MIC values were obtained against E. coli, with some of the ether appendages containing polar or basic end groups. Two analogues showed excellent survival rate in a mouse septicemia protection assay. Preliminary histopathological analysis of the kidney showed no overt signs of toxicity, while controls with neomycin and kanamycin were toxic at lower doses.

Crystal structure of the bacterial ribosomal decoding site complexed with amikacin containing the gamma-amino-alpha-hydroxybutyryl (haba) group

Amikacin is the 4,6-linked aminoglycoside modified at position N1 of the 2-deoxystreptamine ring (ring II) by the L-haba group. In the present study, the crystal structure of a complex between oligonucleotide containing the bacterial ribosomal A site and amikacin has been solved at 2.7 A resolution. Amikacin specifically binds to the A site in practically the same way as its parent compound kanamycin. In addition, the L-haba group interacts with the upper side of the A site through two direct contacts, O2*...H-N4(C1496) and N4*-H...O6(G1497). The present crystal structure shows how the introduction of the L-haba group on ring II of aminoglycoside is an effective mutation for obtaining a higher affinity to the bacterial A site.

Binding of neomycin-class aminoglycoside antibiotics to mutant ribosomes with alterations in the A site of 16S rRNA

Aminoglycoside antibiotics that bind to the aminoacyl-tRNA site (A site) of the ribosome are composed of a common neamine core in which a glycopyranosyl ring is attached to position 4 of a 2-deoxystreptamine moiety. The core is further substituted by one (ribostamycin), two (neomycin and paromomycin), or three (lividomycin A) additional sugars attached to position 5 of the 2-deoxystreptamine. To study the role of rings III, IV, and V in aminoglycoside binding, we used isogenic Mycobacterium smegmatis DeltarrnB mutants carrying homogeneous populations of mutant ribosomes with alterations in the 16S rRNA A site. MICs were determined to investigate drug-ribosome interactions, and the results were compared with that of the previously published crystal structure of paromomycin bound to the ribosomal A site. Our analysis demonstrates that the stacking interaction between ring I and G1491 is largely sequence independent, that rings III and IV each increase the strength of drug binding to the ribosome, that ring IV of the 6'-NH3+ aminoglycosides compensates for loss of interactions between ring II and U1495 and between ring III and G1491, that the aminoglycosides rely on pseudo-base pairing between ring I and A1408 for binding independently of the number of sugar rings attached to the neamine core, that addition of ring V to the 6'-OH 4,5-aminoglycoside paromomycin does not alter the mode of binding, and that alteration of the U1406.U1495 wobble base pair to the Watson-Crick interaction pair 1406C-1495G yields ribosomal drug susceptibilities to 4,5-aminoglycosides comparable to those seen with the wild-type A site.

Crystal structures of complexes between aminoglycosides and decoding A site oligonucleotides: role of the number of rings and positive charges in the specific binding leading to miscoding

The crystal structures of six complexes between aminoglycoside antibiotics (neamine, gentamicin C1A, kanamycin A, ribostamycin, lividomycin A and neomycin B) and oligonucleotides containing the decoding A site of bacterial ribosomes are reported at resolutions between 2.2 and 3.0 A. Although the number of contacts between the RNA and the aminoglycosides varies between 20 and 31, up to eight direct hydrogen bonds between rings I and II of the neamine moiety are conserved in the observed complexes. The puckered sugar ring I is inserted into the A site helix by stacking against G1491 and forms a pseudo base pair with two H-bonds to the Watson-Crick sites of the universally conserved A1408. This central interaction helps to maintain A1492 and A1493 in a bulged-out conformation. All these structures of the minimal A site RNA complexed to various aminoglycosides display crystal packings with intermolecular contacts between the bulging A1492 and A1493 and the shallow/minor groove of Watson-Crick pairs in a neighbouring helix. In one crystal, one empty A site is observed. In two crystals, two aminoglycosides are bound to the same A site with one bound specifically and the other bound in various ways in the deep/major groove at the edge of the A sites.

Extrapericardial cardiac tamponade caused by traumatic retrosternal hematoma

Cardiac tamponade is an uncommon complication of blunt chest trauma, resulting typically from hemorrhage into the pericardial space. We report a case of hemodynamic compromise secondary to an extrapericardial compression caused by the acute formation of a retrosternal hematoma associated with a sternal fracture. The patient was involved in a violent deceleration accident. Initially, he only complained of an anterior thoracic pain, but subsequently became restless, pale, and dyspneic. A severe hypotension associated with sinus bradycardia (45 bpm) rapidly occurred. Both jugular veins became markedly turgescent, but no significant pulsus paradoxus was noted. Echocardiography disclosed a large hematoma, compressing anteriorly both the right ventricular cavity and outflow tract. Surgical evacuation of the retrosternal hematoma related to a bifocal fracture of the manubrium was followed by instantaneous hemodynamic improvement. Regional extrapericardial tamponade secondary to the acute formation of compressive retrosternal hematoma is an unusual cause of circulatory failure after severe blunt chest trauma. Since conventional clinical signs associated with typical tamponade physiology may be lacking in this setting, echocardiography is ideally suited for early recognition of this unusual condition.

[Hemophagocytosis during multiple organ failure: M-CSF overproduction or viral reactivation?]

OBJECTIVE

This study was aimed to assess the potential role of M-CSF and viral reactivation in the genesis of haemophagocytosis during the multiple organ failure (MOF) syndrome.

METHODS

Twenty-five patients (mean age: 60 +/- 16 years; Apache II: 23 +/- 5) sustaining MOF with an unexplained thrombocytopenia were studied. In each patient, a bone marrow aspirate, serum M-CSF concentration, and a virological examination (Herpes viruses) were obtained on admission. In addition, 20 patients (mean age: 57 +/- 15 years; Apache II: 24 +/- 7) with at least two organ failures but no thrombocytopenia constituted the control group. Circulating M-CSF levels and the frequency of virus reactivation were compared between groups.

RESULTS

Haemophagocytosis was diagnosed in 11/25 patients (44%). No viral reactivation was found. Serum M-CSF concentrations were higher in the presence of haemophagocytosis (699 +/- 242 vs 438 +/- 157 IU.mL-1; p < 0.05). Ferritin levels were also increased in the presence of a macrophage activation (3,258 +/- 2,807 vs. 520 +/- 280 mg.L-1; p < 0.0001). In contrast, both circulating M-CSF and ferritin levels were similar between thrombocytopenic patients with no hemophagocytosis and controls.

CONCLUSIONS

This study confirmed the high incidence of haemophagocytosis in critically ill patients sustaining MOF. In this setting, circulating M-CSF levels were markedly elevated, whereas no Herpes viruses reactivation was found.

Comparison of multiplane transesophageal echocardiography and contrast-enhanced helical CT in the diagnosis of blunt traumatic cardiovascular injuries

BACKGROUND

Multiplane transesophageal echocardiography (TEE) and helical computed tomography (CT) of the chest have been validated separately against aortography for the diagnosis of acute traumatic aortic injuries (ATAI). However, their respective diagnostic accuracy in identifying blunt traumatic cardiovascular lesions has not been compared.

METHODS

During a 3-yr period, 110 consecutive patients with severe blunt chest trauma (age: 41 +/- 17 yr; injury severity score: 34 +/- 14) prospectively underwent TEE and chest CT as part of their initial evaluation. Results of both imaging methods were interpreted independently by experienced investigators and subsequently compared. All cases of subadventitial acute traumatic aortic injury were surgically confirmed.

RESULTS

Seventeen patients had vascular injury and 11 had cardiac lesions. TEE and CT identified all subadventitial disruptions involving the aortic isthmus (n = 10) or the ascending aorta (n = 1) that necessitated surgical repair. In contrast, CT only depicted one disruption of the innominate artery. TEE detected injuries involving the intimal or medial layer, or both, of the aortic isthmus in four patients with apparently normal CT results who underwent successful conservative treatment. All cardiac injuries but two were identified only by TEE.

CONCLUSIONS

In patients with severe blunt chest trauma, TEE and CT have similar diagnostic accuracy for the identification of surgical acute traumatic aortic injuy. TEE also allows the diagnosis of associated cardiac injuries and is more sensitive than CT for the identification of intimal or medial lesions of the thoracic aorta.

A new simple technique for the insertion of cuffed central venous catheters: an initial experience

BACKGROUND

Although tunneled polyurethane catheters with polyester cuffs are useful when prolonged central venous access is necessary but their insertion still remains challenging at times. We report the first study of a new cuffed polyurethane catheter (Seldicuff) that can be easily inserted using the Seldinger technique without the need of a vein dilator and that incorporates a tunneling needle onto the catheter. A Seldicuff catheter was placed in 15 patients (mean age: 53 +/- 11 years) who required prolonged parenteral nutrition. All catheters were inserted into the right subclavian vein. The procedure lasted 6.4 +/- 0.8 minutes and no complication directly related to catheter placement was noted. Catheters remained in position for a mean duration of 103 days (range, 58 to 220 days). During this period, no infectious or mechanical complications were observed.

CONCLUSION

These results demonstrate that placement of this novel cuffed catheter is as simple as inserting a conventional central venous catheter.

Reactivation of human herpesvirus type 6 in multiple organ failure syndrome

Human herpesvirus type 6 (HHV-6) and cytomegalovirus (CMV) are known to interact with the production of cytokines. In this study, we sought to determine the incidence of HHV-6 and CMV reactivation during multiple organ failure syndrome (MOFS) and to evaluate the potential effects of viral replication on both the morbidity and mortality associated with MOFS. Viral reactivation was assessed by use of specific polymerase chain reaction (PCR) analysis of the serum samples obtained from 48 consecutive patients with MOFS (the MOFS group) and from 48 sex- and age-matched patients with <2 organ failures (the control group). In addition, HHV-6 replication was assessed in 106 blood donors (the normal group). The incidence of HHV-6 replication was higher in the MOFS group than in the control and normal groups (26 [54%] of 48 vs. 7 [15%] of 48 and 5 [5%] of 106, respectively; P<.0001), with apparently no influence on morbidity and mortality rates. In contrast, reactivation of CMV was found in a single patient. Further studies are needed to evaluate the pathogenesis of HHV-6 replication in critically ill patients.

Intrathecal baclofen after traumatic brain injury: early treatment using a new technique to prevent spasticity

BACKGROUND

In the early course of severe head trauma, the clinical value of intrathecal administration of baclofen to reduce autonomic disorders and spasticity has not been established.

METHODS

We studied four patients (Glasgow Coma Scale score 3 or 4) with autonomic disorders and spasticity who failed to respond to conventional treatment during the early course of head injury. Baclofen (25 microg/mL) was infused continuously through an intrathecal catheter inserted at patient bedside and subcutaneously tunneled. When this treatment was successful, the spinal catheter was removed and surgically replaced by another catheter connected to a subcutaneous pump. Clinical follow-up was obtained at 6 months after the head injury.

RESULTS

Mean delay for the initiation of intrathecal baclofen was 25 days (range, 21 to 31 days), and optimal dose was 385 +/- 185 microg/day. In all patients, the Ashworth score was consistently reduced (3.5 +/- 0.5 vs. 4.5 +/- 0.5 for upper limbs and 2 +/- 0.5 vs. 4.5 +/- 0.5 for lower limbs), as were both the frequency and intensity of autonomic disorders. The spinal catheters were used during a mean period of 9.5 +/- 1.7 days without complications. All three survivors were equipped with a programmable pump and had a lower Ashworth score at 6 months. Autonomic disorders had disappeared in two patients and remained modest in the remaining patient.

CONCLUSION

Continuous administration of baclofen via the intrathecal route using this new technique seems to reduce autonomic disorders and spasticity during the early course of severe traumatic head injury.