Orientation and immersion depth of a helical lipopeptaibol in membranes using TOAC as an ESR probe

Trichogin GA IV is a lipopeptaibol antibiotic characterized by the sequence nOct-Aib1-Gly-Leu-Aib4-Gly-Gly-Leu-Aib8-Gly-Ile- Lol (nOct: n-octanoyl; Aib: alpha-aminoisobutyric acid; Lol, leucinol), which exhibits membrane-modifying properties. We synthesized step-by-step by solution methods three trichogin analogues, each with a single Aib --> 2,2,6,6-tetramethylpiperidin-1-oxyl-4-amino-4-carboxylic acid (TOAC) substitution. The similarity in the conformational propensities of the Calpha-tetrasubstituted alpha-amino acids Aib and TOAC allowed us to exploit these analogues to investigate the orientation and therefore the mechanism of action of trichogin in the membranes by the electron spin resonance (ESR) technique. A conformational analysis by Fourier transform ir absorption and CD in different organic solvents and in a membrane-mimetic environment indicated that the conformation of the natural lipopeptaibol remains almost unchanged in the three analogues. Moreover, for all of the analogues permeability measurements revealed membrane-modifying properties comparable to those of trichogin. Our ESR investigation demonstrated that, in liposomes based on phosphatidylcholine, trichogin lays parallel to the membrane surface with its hydrophobic face oriented toward the membrane interior. These results suggest that trichogin might modify membrane permeability via a carpet-like mechanism, at least in liposomes and in the absence of a transmembrane potential.

Identification and characterization of a novel high affinity metal-binding site in the hammerhead ribozyme

A novel metal-binding site has been identified in the hammerhead ribozyme by 31P NMR. The metal-binding site is associated with the A13 phosphate in the catalytic core of the hammerhead ribozyme and is distinct from any previously identified metal-binding sites. 31P NMR spectroscopy was used to measure the metal-binding affinity for this site and leads to an apparent dissociation constant of 250-570 microM at 25 degrees C for binding of a single Mg2+ ion. The NMR data also show evidence of a structural change at this site upon metal binding and these results are compared with previous data on metal-induced structural changes in the core of the hammerhead ribozyme. These NMR data were combined with the X-ray structure of the hammerhead ribozyme (Pley HW, Flaherty KM, McKay DB. 1994. Nature 372:68-74) to model RNA ligands involved in binding the metal at this A13 site. In this model, the A13 metal-binding site is structurally similar to the previously identified A(g) metal-binding site and illustrates the symmetrical nature of the tandem G x A base pairs in domain 2 of the hammerhead ribozyme. These results demonstrate that 31P NMR represents an important method for both identification and characterization of metal-binding sites in nucleic acids.

Axillary schwannoma masquerading as cervical radiculopathy

A 58-year-old woman, suffering from radicular-like pain in the left arm for 3 years, presented an entirely negative cervical imaging. Careful clinical examination disclosed Tinel's sign in the axilla. This clinical finding led to further investigation of this region. Computed tomography and magnetic resonance imaging disclosed a small tumour highly suggestive of a schwannoma. Surgical exploration and microscopic examination confirmed a diagnosis of schwannoma located on the radial trunk of the left brachial plexus. After tumour excision, the patient had immediate relief of pain without sensitive or motor sequelae. No recurrence has been observed after 3 years.

Cervical spinal cord injury in sapho syndrome

Cervical spinal fracture and pseudarthrosis are previously described causes of spinal cord injury (SCI) in patients with spondylarthropathy. SAPHO (Synovitis Acne Pustulosis Hyperostosis Osteitis) syndrome is a recently recognized rheumatic condition characterized by hyperostosis and arthro-osteitis of the upper anterior chest wall, spinal involvement similar to spondylarthropathies and skin manifestations including palmoplantar pustulosis and pustular psoriasis. We report the first case of SAPHO syndrome disclosed by SCI related to cervical spine ankylosis.

Anatomical differences in the psoas muscles in young black and white men

The anatomy of the psoas major muscle (PMA) in young black and white men was studied during routine autopsies. The forensic autopsies included 44 fresh male cadavers (21 black, 23 white) with an age span of 14 to 25 y. The range for weight was 66-76 kg and for height 169-182 cm. The PMA was initially measured in its entire length before measuring the diameter and circumference at each segmental level (L1-S1). At each segmental level, the calculated anatomical cross-sectional area (ACSA) was more than 3 times greater in the black group compared with the white (P < 0.001). The psoas minor muscle (PMI) was absent in 91% of the black subjects, but only in 13% of the white subjects. These data show that the PMA is markedly larger in black than white subjects. The marked race specific difference in the size of the PMA may have implications for hip flexor strength, spine function and race specific incidence in low back pathology, and warrants further investigation.

Determining the occurrence of a 3(10)-helix and an alpha-helix in two different segments of a lipopeptaibol antibiotic using TOAC, a nitroxide spin-labeled C(alpha)-tetrasubstituted alpha-aminoacid

Trichogin GA IV is a 11-residue lipopeptaibol antibiotic exhibiting membrane modifying properties. We synthesized step-by-step by solution methods three trichogin analogues, each with a double Aib (alpha-aminoisobutyric acid)-->TOAC (2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid) replacement. The strict similarity in the conformational propensities of Aib and TOAC allowed us to exploit these analogues in a detailed investigation of the conformation of this lipopeptaibol in different organic solvents and in a membrane-mimetic environment using in particular the double spin labeling ESR technique. We conclude that the secondary structure in solution remains essentially unchanged if compared to that previously found in the crystal state for trichogin. More specifically, the N-terminal region of the peptide folds in a 3(10)-helix, while the central and C-terminal regions are mainly alpha-helical. An additional, significant proof for the modest plasticity of the trichogin structure was obtained by an X-ray diffraction analysis of the nOct-[TOAC4,8, Leu-OMe11] analogue. For the three analogues permeability measurements revealed membrane-modifying properties comparable to those of natural trichogin.

The difference in anatomy of the lumbar anterior longitudinal ligament in young African-Americans and Scandinavians

OBJECTIVE

To examine possible structural differences in the lumbar anterior longitudinal ligament between young African-American and Scandinavian people.

DESIGN

The lumbar anterior longitudinal ligament was examined in 48 African-American and Scandinavian young men and women (17 to 30 years old). Apart from the selection of gender, age, height, and weight, all subjects were recruited consecutively during routine forensic autopsies. Sections of the ligament were obtained from the L1 and the L5 vertebra for thickness and width measurements and histologic preparations. The measurements were performed with a digital vernier caliper with an accuracy of 0.1 mm.

RESULTS

The width of the L1 part of the lumbar anterior longitudinal ligament in the African-American group (27.5+/-1.8mm) was greater than that in the Scandinavian group (17.7+/-1.5mm) (p < .001), and the thickness of the L1 part in the African-American group (3.8+/-0.4mm) was greater than that in the Scandinavian group (3.3+/-0.3mm) (p < .001). The width of the L5 part in the African-American group (34.1+/-2.0mm) was greater than that in the Scandinavian group (25.0+/-1.5mm) (p < .001), and the thickness of the L5 part in the African-American group (3.3+/-0.3mm) was greater than that in the Scandinavian group (2.2+/-0.3mm) (p < .001). The cross-sectional area was greater in the African-American group in both sections (L1, African-American 106.4+/-13.7mm2 vs Scandinavian 52.8+/-7.9mm2; L5, African-American 112.2+/-14.6mm2 vs Scandinavian 55.6+/-6.7mm2) (p < .001). No histologic differences between the two groups were observed.

CONCLUSIONS

The lumbar anterior longitudinal ligament was considerably wider and thicker, which yielded a markedly greater cross-sectional area, in African-American than in Scandinavian subjects. In contrast, the ligament appears to be histologically similar in the two groups. These are previously unrecognized differences in anatomy between young African-American and Scandinavian people.

Effects of respiratory muscle work on cardiac output and its distribution during maximal exercise

We have recently demonstrated that changes in the work of breathing during maximal exercise affect leg blood flow and leg vascular conductance (C. A. Harms, M. A. Babcock, S. R. McClaran, D. F. Pegelow, G. A. Nickele, W. B. Nelson, and J. A. Dempsey. J. Appl. Physiol. 82: 1573-1583, 1997). Our present study examined the effects of changes in the work of breathing on cardiac output (CO) during maximal exercise. Eight male cyclists [maximal O2 consumption (VO2 max): 62 +/- 5 ml . kg-1 . min-1] performed repeated 2.5-min bouts of cycle exercise at VO2 max. Inspiratory muscle work was either 1) at control levels [inspiratory esophageal pressure (Pes): -27.8 +/- 0.6 cmH2O], 2) reduced via a proportional-assist ventilator (Pes: -16.3 +/- 0.5 cmH2O), or 3) increased via resistive loads (Pes: -35.6 +/- 0.8 cmH2O). O2 contents measured in arterial and mixed venous blood were used to calculate CO via the direct Fick method. Stroke volume, CO, and pulmonary O2 consumption (VO2) were not different (P > 0.05) between control and loaded trials at VO2 max but were lower (-8, -9, and -7%, respectively) than control with inspiratory muscle unloading at VO2 max. The arterial-mixed venous O2 difference was unchanged with unloading or loading. We combined these findings with our recent study to show that the respiratory muscle work normally expended during maximal exercise has two significant effects on the cardiovascular system: 1) up to 14-16% of the CO is directed to the respiratory muscles; and 2) local reflex vasoconstriction significantly compromises blood flow to leg locomotor muscles.

Constitutive nitric oxide synthases in rat gastric mucosa: subcellular distribution, relative activity and different carboxyl-terminal antigenicity of the neuronal form compared with cerebellum

BACKGROUND/AIMS

To investigate whether the neuronal form of nitric oxide (NO) synthase (nNOS) in gastric mucosa differed from nNOS in the brain in subcellular distribution or antigenicity, and to determine the relative activity of the endothelial form of NO synthase (eNOS) and nNOS in gastric mucosa.

METHODS

Subcellular fractionation, assay of enzyme activity by conversion of arginine to citrulline, and immunoblotting were employed.

RESULTS

10% of NO synthase activity in gastric mucosa was particulate compared with 31% in the cerebellum. Immunoblotting demonstrated that gastric mucosal nNOS protein was essentially cytosolic and that eNOS was largely particulate. Combination of these results with measurements of enzyme activity suggested that 96% of gastric mucosal activity was contributed by nNOS. Experiments with an antiserum raised against the carboxyl-terminal hexadecapeptide of rat brain NO synthase suggested a difference in antigenicity between forms of nNOS from the cerebellum and gastric mucosa. This difference did not seem to result from alternative splicing of the primary transcript, and was not present after enrichment of nNOS by affinity chromatography using 2',5'-ADP agarose.

CONCLUSION

The form of nNOS in rat gastric mucosa is largely cytosolic and is the major constitutive activity. When first isolated gastric nNOS differs in antigenicity from the equivalent brain enzyme, probably as a result of an unstable post-translational modification, close to the carboxyl-terminus.

An NMR investigation of the conformational effect of nitroxide spin labels on Ala-rich helical peptides

Nitroxide spin labels, in conjunction with electron spin resonance (ESR) experiments, are extensively employed to probe the structure and dynamics of biomolecules. One of the most ubiquitous spin labeling reagents is the methanethiosulfonate spin label which attaches a spin label selectively to Cys residues via a disulfide bond (Cys-SL). However, the actual effect of the nitroxide spin label upon the conformation of the peptide or protein cannot be unambiguously determined by ESR. In this study, a series of 16-residue Ala-rich helical peptides was characterized by nuclear magnetic resonance techniques. The C alpha H chemical shift analysis, NOEs, and 3JNH alpha coupling constants for peptides with no Cys, free Cys, and Cys-SL (with the N-O group reduced) were compared. These results indicate that while replacement of an Ala with a Cys residue causes a loss of overall helical structure, the Cys-SL residue is helix supporting, as would be expected for a non-beta-branched aliphatic amino acid. Thus, the Cys-SL residue does not perturb helical structure and, instead, exhibits helix-stabilizing characteristics similar to that found for Ala, Met, and Leu.

The influence of skin temperature on latency and amplitude of the sympathetic skin response in normal subjects

The influence of skin temperature on latency and amplitude of the sympathetic skin response (SSR) was studied in 10 normal subjects. SSRs were elicited in all four limbs of each subject by electrical stimulation after cooling of the right arm and after cooling of the right hand only. At low skin temperature, the latency was prolonged and the amplitude decreased. Latency and amplitude were linearly correlated with skin temperature of the right arm. There were no changes in the left arm and the legs, which basically excludes involvement of central pathways in these response parameters. With regard to the skin temperature of the arm, a temperature correction factor of 0.088 s/degrees C was calculated for latency. With regard to the skin temperature of the hand, latency prolongation was significantly greater after cooling of the whole arm. This suggests that not only the neuroglandular junction, but also the postganglionic sympathetic C fibers were responsible for latency modifications. In contrast, amplitude was reduced similarly after cooling of the whole arm and the hand only, suggesting that mainly the neuroglandular junction is responsible for amplitude modifications. We conclude that skin temperature is a mandatory measurement in the study of the SSR.

Preliminary study of large and small peripheral nerve fibers in Charcot-Marie-Tooth disease, type I

Histologic studies of Charcot-Marie-Tooth disease, type I, show a contrast between the lesions of myelinated fibers and the normality of unmyelinated fibers. Conventional electrophysiologic tests only demonstrate the alteration of myelinated fibers but do not study unmyelinated fiber function. We present routine clinical tests that are easily available and effective for the evaluation of small unmyelinated fibers: thermal threshold testing for warmth to evaluate small C unmyelinated somatic fibers and sympathetic skin responses to evaluate small C unmyelinated sympathetic fibers. Five unrelated patients with a diagnosis of Charcot-Marie-Tooth disease, type I, confirmed by biopsy were investigated. All of these patients showed marked reduction or absence of motor and sensory conduction velocities and severe denervation at needle examination. By contrast, thermal threshold testing for warmth and sympathetic skin responses were normal, confirming the normality of small C unmyelinated somatic and sympathetic fibers. We conclude that these noninvasive tests are helpful in the diagnosis of Charcot-Marie-Tooth disease, type I.

Acute corticosteroid myopathy in intensive care patients

Several recent studies have attributed the occurrence of acute myopathy in intensive care unit patients to the combination of corticosteroids and neuromuscular junction blocking agents (NMBAs) used for mechanical ventilation. We present 4 patients who developed acute myopathy after administration of high doses of glucocorticoids during sedation with propofol without any NMBAs. All patients had elevated creatine kinase levels. Electrophysiological studies indicated normal motor and sensory nerve conduction velocities but reduced motor nerve response amplitudes. Needle electromyography identified abnormal spontaneous activity; motor unit potentials were polyphasic of low amplitude and short duration, characteristic of a myopathic process. Muscle biopsy demonstrated a prominent acute necrotizing myopathy in all 4 patients with a loss of thick filaments. Our observations support glucocorticoids rather than NMBAs as the main offending drug in acute corticosteroid myopathy. The predisposing factor should be the hypersensitivity of paralyzed muscles to corticosteroids regardless of the drug inducing paralysis: NMBAs or propofol.

Estimating the relative populations of 3(10)-helix and alpha-helix in Ala-rich peptides: a hydrogen exchange and high field NMR study

Recent experimental and theoretical work suggests that alanine-rich peptides fold as a mixture of 3(10)-helix (i --> i + 3 hydrogen bonding) and alpha-helix (i --> i + 4 hydrogen bonding). In order to assess the relative proportions of the two conformers, NMR studies were performed on the 16 residue sequences: Ac-AAAAKAAAAKAAAAKA-NH2 (3K) and Ac-AMAAKAWAAKAAAARA-NH2 (MW). Hydrogen/deuterium-exchange kinetics measured for the first three amide protons of the 3K peptide indicate that the NH of Ala3 is partially protected from exchange. This result is consistent with the presence of an i --> i + 3 hydrogen bond between the carbonyl group of the acetyl blocking group and the NH group of Ala3. The MW peptide is a modified version of the 3K peptide, designed to increase alphaH signal dispersion. 1H NMR spectra of the MW peptide at 750 MHz reveal a series of intermediate range (NOEs) consistent with a mixture of 3(10)-helix and alpha-helix. The relative intensities of the alphaN(i,i + 3) and alphabeta(i,i + 3) (nuclear Overhauser enhancements) NOEs suggest that 3(10)-helix is present throughout the peptide, but with the greatest contribution at the termini. A model was developed to determine the relative contributions of 3(10)-helix and alpha-helix. Lower bounds for the population of 3(10)-helix are approximately 50% at the termini and 25% in the middle of the peptide. The greatest alpha-helical content is between the middle of the peptide and the N terminus.

Reverse cholesterol transport in the rat following a short-term intravenous infusion of fat emulsion

The effect on cholesterol transport of an intravenous infusion of a fat emulsion (10%) Intralipid or 10% Lipovenös) in vivo was investigated in the rat. Intralipid (1.85 ml/hr/kg body weight in rts for 3 hr) caused a reduction (P < 0.05) in free cholesterol in the aorta (by 25%), in plasma high-density lipoproteins (64%) and in erythrocytes (11%) with a concomitant enrichment of liver free cholesterol (16%), suggesting an enhanced reverse cholesterol transport in this species. Lipovenös under the same conditions gave similar results. Our data support our previous in vivo study in man indicating that infusion of a fat emulsion is able even to remove cholesterol from the arterial wall and thereby possibly be considered as an antiatherosclerotic agent.

Lyme borreliosis neuropathy. A case report

Lyme borreliosis is responsible for a large variety of peripheral neurologic manifestations including axonal polyneuropathy, radiculopathy, and facial nerve palsy. The prevalence of the disease must draw our attention on the possible responsibility of Borrelia burgdorferi in the pathogenesis of such symptomatology. Electrophysiologic studies demonstrate a proximal and distal axonal involvement, whereas neuropathologic studies suggest that vasculitis might be one of the primary pathophysiologic mechanisms. Electromyography provides a useful diagnostic tool and an important measure of response to treatment. Although peripheral neuropathy usually improves, our case report confirms the fact that chronic neurologic manifestations may not consistently resolve with appropriate treatment.

Hemodynamic patterns and duration of post-dynamic exercise hypotension in hypertensive humans

We investigated: 1) the mechanism of the hypotensive effect of a single bout of dynamic exercise in hypertensive subjects by measuring hemodynamic parameters before and for 2 h after treadmill exercise, and 2) the duration of the effect using ambulatory blood pressure (BP) monitoring once the subjects left the test site. Ten minutes after exercise there was a significant decrease from baseline systolic pressure (SP; -14 +/- 3 mm Hg), mean arterial pressure (MAP; -7 +/- 2 mm Hg), total peripheral resistance (TPR; -3.7 +/- 1.2 units), calf vascular resistance (CVR; -25.4 +/- 4.1 units), and an increase in HR (19 +/- 2 bpm). The changes in SP, DP, MAP, and HR were maintained during the 2 h of post-exercise monitoring; CVR remained decreased for 1 h; TPR returned to baseline within 20 min and then tended to be slightly elevated. CO was significantly decreased at 50, 60, and 120 min after exercise. We conclude that the early decline in BP after dynamic exercise in hypertensive subjects follows a biphasic pattern: 1) an initial decrease in total and regional vascular resistance with maintained CO, 2) followed by increasing resistance and decrease CO. Pre-exercise hypertensive BP values returned during subsequent ambulatory monitoring.

Squatting revisited: comparison of haemodynamic responses in normal individuals and heart transplantation recipients

BACKGROUND

Squatting produces a prompt increase in cardiac output and arterial blood pressure which is accompanied by an immediate decrease in heart rate and forearm vascular resistance. The rise in cardiac output and blood pressure has been attributed to augmented venous return from compression of leg veins, while the decreases in heart rate and forearm vascular resistance are probably due to activation of cardiopulmonary and arterial baroreflexes. Haemodynamic patterns in nine normal men and six heart transplant recipients during 2 min of squatting were examined to determine the role of cardiac innervation in the mediation of these responses.

METHODS

Stroke volume was monitored by ensemble averaged thoracic impedance cardiography and blood pressure was determined with an Ohmeda fingertip plethysmograph. These techniques provided continuous measurements which were capable of detecting transient and non-steady state changes. Forearm blood flow was measured with venous occlusion plethysmography. Measurements were obtained after 3 min of quiet standing, immediately after squatting, and at 20, 60, and 120 s of sustained squatting.

RESULTS

Both groups exhibited similar increases in stroke volume index (normal individuals 10.5 ml/m2; heart transplant recipients 10.3 ml/m2) and mean arterial pressure (normal individuals 8.5 mm Hg; heart transplant recipients 5.0 mm Hg) which were sustained throughout squatting. Each group also showed an initial decrease in peripheral resistance (normal individuals 3.6 units; heart transplant recipients 7.7 units) followed by a return to baseline values after 20 s. Heart rate decreased in normal individuals (10 beats/min) but was unchanged or minimally increased (2 beats/min) in heart transplant recipients. Forearm vascular resistance was conspicuously decreased in normal individuals (47.8 units) but only minimally (20.9 units) and not significantly in heart transplant recipients.

CONCLUSIONS

The major haemodynamic responses to squatting (increased cardiac output and blood pressure) are similar in normal individuals and heart transplant recipients. These responses are primarily due to augmented venous return and are not altered by cardiac denervation. Both groups also exhibited a transient decline in peripheral vascular resistance which is most likely mediated by arterial baroreflexes activated by the acute rise in arterial blood pressure. The absence of a significant decrease in forearm vascular resistance in heart transplant recipients suggests that this response is partially mediated by cardiopulmonary or ventricular baroreflexes or that local forearm flow mediated vasodilatation remains impaired after heart transplantation.

Comparison of arterial occlusion and ischaemic exercise for the study of vasodilatation in the human calf

1. Calf blood flow was measured by venous occlusion plethysmography to compare two stimuli for eliciting maximal calf vascular conductance: (i) 10 min of arterial occlusion and (ii) isolated exhaustive calf exercise with ischaemic occlusion. The subjects were semi-supine with the calf in position for immediate blood flow measurements after release of the occluding cuff. Three groups of subjects were studied: young [35 years (SD 9, n = 9)], old [57 years (SD 5, n = 10)] and patients with congestive heart failure [63 years (SD 7, n = 7)]. 2. Occlusion and ischaemic exercise were equally effective in producing maximal calf vascular conductance in each of the subject groups. Maximal calf vascular conductance (ml min-1 100 ml-1 mmHg-1) was equivalent in the young [ischaemic exercise 0.54 (SEM 0.03), occlusion 0.54 (SEM 0.05)] and old [ischaemic exercise 0.47 (SEM 0.05), occlusion 0.48 (SEM 0.04)] subjects. However, patients with congestive heart failure exhibited significantly reduced maximal calf vascular conductance [ischaemic exercise 0.20 (SEM 0.02), occlusion 0.20 (SEM 0.01)]. 3. Analysis of the curves, generated by plotting serial calf vascular conductance values obtained immediately and every 15 s after occlusion cuff release for 165 s, revealed differences in the pattern of vasodilatation after occlusion and ischaemic exercise.(ABSTRACT TRUNCATED AT 250 WORDS)