Nuclear magnetic resonance characterization of peptide models of collagen-folding diseases

Misfolding of the triple helix has been shown to play a critical role in collagen diseases. The substitution of a single Gly by another amino acid breaks the characteristic repeating (Gly-X-Y)n sequence pattern and results in connective tissue disease such as osteogenesis imperfecta. Nuclear magnetic resonance (NMR) studies of normal and mutated collagen triple-helical peptides offer an opportunity to characterize folding and conformational alterations at the substitution site, as well as at positions upstream and downstream of a Gly mutation. The NMR studies suggest that the local sequences surrounding the substitution site, and the renucleation sequences N-terminal to and adjacent to the substitution site, may be critical in defining the clinical phenotype of osteogenesis imperfecta. These studies may pave the way to understanding the mechanism by which a single Gly substitution in collagen can lead to pathological conditions.

Minimal flow sevoflurane and isoflurane anaesthesia and impact on renal function

BACKGROUND AND AIM

Compound A generation and accumulation in sevoflurane anaesthesia is dependent on fresh gas flow. We investigated the extent of generation of compound A.

METHODS

After Institutional Review Board approval and informed consent, patients with normal renal function were randomized to receive either sevoflurane (n = 33) or isoflurane (n = 43) minimal flow anaesthesia (0.5 L min-1) for at least 2 h under standardized conditions. Compound A concentrations were quantified and blood and urine samples were taken to assess renal involvement. Both groups were comparable.

RESULTS

No significant differences concerning blood chemistry and urine measurements were found. The maximum mean compound A concentration was observed 90 min after flow reduction being 40 +/- 9 p.p.m. at a corresponding mean sevoflurane concentration of 2.1 +/- 0.5 vol%. Mean inspiratory compound A exposure was 102 +/- 33 p.p.m h-1.

CONCLUSION

Compound A concentrations using 0.5 L min-1 fresh gas flow and a heated absorber were higher than previously published values using an inflow of 1 L min-1. Compound A exposure was similar to other clinical studies which did not show changes in renal and hepatic function.

Pathogenesis and treatment of "sterile" midperipheral corneal infiltrates associated with soft contact lens use

PURPOSE

To demonstrate the sterile nature of presumed sterile midperipheral corneal infiltrates associated with soft contact lens (SCL) use and to show that withholding antibiotics or the occasional use of a topical corticosteroid alone may, with strict guidelines, have a role in the treatment of this entity.

METHODS

Nine consecutive patients presenting with typical midperipheral corneal infiltrates after SCL wear were seen in the office (O.H.D.) during a 2-year period, 1996-1998. All patients were initially placed on topical fluorometholone as the only treatment.

RESULTS

Eight of the nine patients experienced a rapid relief of symptoms and the infiltrates were noted to be smaller and less dense in 34 days. Therapy was discontinued after 7 days, by which time the lesions had cleared. The ninth patient developed a microbial keratitis from which Pseudomonas aeruginosa was cultured. With appropriate therapy, visual acuity returned to 20/25. Two different algorithms are offered for the treatment of a putative sterile infiltrate associated with SCL use.

CONCLUSION

The use of a topical corticosteroid alone may have a role in the treatment of presumed sterile midperipheral corneal infiltrates associated with SCLs when strict guidelines are followed. Such therapy suggests that the infiltrates are not the result of infection.

[Nitrous oxide free low-flow anesthesia]

The routine use of nitrous oxide as a component of the carrier gas has been unanimously called into question in recent surveys, in fact, its use is now recommended in indicated cases only. Whereas a lot of contraindications are listed in the surveys, precise definitions of justified indications are not given. In clinical routine practice, there are absolutely no problems in carrying out inhalational anaesthesia without nitrous oxide. The missing analgetic effect can be compensated for by moderately increasing the additively used amount of opioids, while the missing hypnotic effect can be achieved by raising the expired concentration of the inhalational anaesthetic by not more than 0.2-0.25 x MAC. Thus, when isoflurane is used, an expired concentration of 1.2 vol% is desired, in the case of sevoflurane of 2.2 vol% and with desflurane of 5.0 vol%. In addition, doing without nitrous oxide facilitates the performance of low flow anaesthetic techniques considerably. Since the patient only inhales oxygen and the volatile anaesthetic, the total gas uptake is reduced significantly. Washing out nitrogen is no longer necessary. This means that the initial phase of low flow anaesthesia, during which high fresh gas flows have to be used, can be kept short. Its duration is now determined by the wash-in of the volatile anaesthetic. Since there is no uptake of nitrous oxide, a considerably greater volume of gas is circulating within the breathing system, minimizing the possibility of accidental gas volume deficiency. Thus, if anaesthesia machines with highly gas-tight breathing systems are used, even the performance of non-quantitative closed system anaesthesia becomes possible in routine clinical practice. The carrier gas flow can be reduced to just that amount of oxygen which is really taken up by the patient. This oxygen volume can be roughly calculated by applying the Brody's formula. Using fresh gas flows as low as 0.25 l/min, however, will result in a significant decrease of the output of conventional vaporizers outside the circuit. Thus, it becomes nearly impossible to maintain an expired isoflurane concentration of 1.2 vol%. With respect to their pharmcokinetic properties, the newer low soluble volatile agents sevoflurane and desflurane are better suited for use with flows corresponding to the basal oxygen uptake. Our own clinical experience, gained in the last six months from a trial involving over 1,800 patients, shows that the increase in opioid consumption resulted in additional costs of about 0.25-0.50 DM per patient. The increased concentration of inhalational agents brought additional costs of 3.00 to 5.00 DM for a two-hour anaesthesia. On the other hand, doing without nitrous oxide saved 2.61 DM per one-hour anaesthesia, whereby our consumption of nitrous oxide is extremely low as minimal flow anaesthesia is performed consistently. Furthermore, these calculations disregard the cost of the technical maintenance fo the central gas piping system and of the regular measurement of workplace contamination with nitrous oxide by a certified institute, which in Germany, ad least, is obligatory. The additional costs of nitrous oxide-free inhalational anaesthesia seem to be balanced by the savings. Given the numerous justified arguments against the routine use of nitrous oxide, the lack of precisely-defined indications and the clinical experience showing that doing without nitrous oxide is uncomplicated, self-financing and ecologically beneficial, the use of nitrous oxide should be given up completely.

The evolution of antibiotic therapy for bacterial conjunctivitis and keratitis: 1970-2000

The editors of this Festschrift asked us to review the use of antibiotics for the treatment of bacterial conjunctivitis and keratitis over the past 25 years, a period coinciding with the life of the Castroviejo Corneal Society. We believe it is more appropriate to begin our review in the late 1960s. about the time that experimental and clinical studies and algorithms for the clinical care derived from these studies helped shape a more rigorous approach to therapy. Those years saw the introduction of antibiotics that were adapted for ophthalmic use, many of which are still being used today. We will give more weight to our review of keratitis than conjunctivitis.

Multicenter evaluation of the Glucometer Elite XL meter, an instrument specifically designed for use with neonates

OBJECTIVE

To evaluate the clinical performance of the Glucometer Elite XL Diabetes Care System in neonatal settings using a multicenter study

RESEARCH DESIGN AND METHODS

A total of 388 blood specimens from 333 neonates were included in the study. A capillary or arterial sample was analyzed for determination of glucose with the Glucometer Elite XL system by an attending trained nurse. Through the same sampling site, a specimen was collected and sent to the laboratory for measurement of plasma glucose, bilirubin, and hematocrit.

RESULTS

The regression analysis between the results of the Glucometer Elite XL system and comparative methods resulted in the following: Glucometer Elite XL meter = 1.01 x laboratory method + 0.02 mmol/l (n = 388). For the 1.1-4.0 mmol/l plasma glucose range, the regression was Glucometer Elite XL meter = 1.07 x laboratory method + 0.12 mmol/l (n = 150). A difference plot indicated a mean bias of 0.04 mmol/l (95% CI -0.01 to 0.10). No relationship was found between meter glucose biases and hematocrit levels (r = 0.10, P = 0.14). Although a statistically significant correlation existed between bilirubin levels and the glucose meter biases (r = 0.14, P = 0.005), the predicted mean biases were of little clinical significance.

CONCLUSIONS

The Glucometer Elite XL system showed a good performance when used in neonatal settings.

Treatment of persistent corneal epithelial defect with extended wear of a fluid-ventilated gas-permeable scleral contact lens

PURPOSE

To report treatment of persistent corneal epithelial defects unresponsive to other therapies by extended wear of a fluid-ventilated gas-permeable scleral contact lens.

METHODS

In this retrospective study, 14 eyes of 13 consecutive patients referred for the treatment of persistent corneal epithelial defects that failed to heal with conventional therapies or developed epithelial defects after penetrating keratoplasty for persistent corneal epithelial defects were fitted with an extended-wear gas-permeable scleral lens. These included seven eyes of six patients with Stevens-Johnson syndrome and seven eyes of seven patients who did not have Stevens-Johnson syndrome. Twelve eyes had undergone recent penetrating keratoplasty. All 14 eyes were fitted with a gas-permeable scleral contact lens designed to avoid the intrusion of air bubbles under its optic. An antibiotic and corticosteroid were added to the lens fluid reservoir or instilled before each lens insertion in 12 of 14 eyes. The lenses were worn continuously except for brief periods of removal for purposes of cleaning, replacement of the lens fluid reservoir, and examination and photography of the cornea.

RESULTS

Five of the seven persistent corneal epithelial defects associated with Stevens-Johnson syndrome healed. The persistent corneal epithelial defects of four of these eyes re-epithelialized within 7 days, and a fifth healed in 27 days of gas-permeable scleral lens extended wear. A sixth persistent corneal epithelial defect that failed to heal initially re-epithelialized after a subsequent penetrating keratoplasty and gas-permeable scleral lens extended wear. The seventh eye healed after 3 days of gas-permeable scleral lens extended wear, but the persistent corneal epithelial defect subsequently recurred. Three of seven non-Stevens-Johnson syndrome persistent corneal epithelial defects re-epithelialized within 36 hours, 6 days, and 36 days, respectively. Of the six (six of 14) persistent corneal epithelial defects that failed to heal with a gas-permeable scleral lens extended wear, one subsequently healed after multiple amniotic membrane grafts. Microbial keratitis occurred in four eyes (four of 14) and graft failure in one eye, all of which required repeat penetrating keratoplasty.

CONCLUSION

Extended wear of an appropriately designed gas-permeable scleral contact lens was effective in promoting the healing of persistent corneal epithelial defects in some eyes that failed to heal after other therapeutic measures. Re-epithelialization appears to be aided by a combination of oxygenation, moisture, and protection of the fragile epithelium afforded by the scleral lens. However, microbial keratitis represents a significant risk.

Conformational characterization of a helix-nucleated bicyclic GCN4 decapeptide by proton NMR

A bicyclic decapeptide, GCN4brM1, which was designed to be a helix-locked analog of the DNA-binding basic region from the yeast transcription factor GCN4, was synthesized and characterized using circular dichroism (CD) spectropolarimetry and 1H-NMR. This peptide has two Lys(i), Asp(i+4) side chain lactam bridges incorporated into its structure in overlapping positions in the peptide chain, linking residues 3 and 7 and residues 4 and 8. CD spectra of GCN4brM1 in aqueous solution are consistent with the expected helical conformation, and indicate that this conformation is remarkably resistant to heat denaturation and is essentially unchanged by addition of 50% (v/v) trifluoroethanol (TFE) as cosolvent. NMR spectra measured in aqueous solution at -5 degrees C show long-range nuclear Overhauser effects (NOEs) that are consistent with an alpha-helical conformation throughout the peptide structure. The measured 3J(HN) coupling constants are also in agreement with an alpha-helical structure. Extremely slow proton-deuterium exchange rates measured for backbone amides in the middle of the peptide indicate that this helix is highly stabilized and rarely unfolds within the side chain bridged sequence. NOE-constrained molecular dynamics simulations gave rise to a single family of converged structures that are fully alpha-helical throughout the GCN4brM1 backbone, and show a single, well-defined conformation for the two side chain bridges. This study demonstrates that two overlapping Lys(i), Asp(i+4) lactam bridges, positioned in consecutive residue positions in a hexapeptide segment, form a rigid alpha-helical structure in aqueous solution that is propagated in both the N-terminal and C-terminal directions.

[Climatization of anesthetic gases using different breathing hose systems]

BACKGROUND

During general anaesthesia gas climate significantly is improved by performance of low flow techniques. Gas climatisation, however, markedly also will be influenced by the temperature loss at, and corresponding water condensation within the hoses, factors which are related to the technical design and material of the patient hose system. The objective of this prospective study was to investigate 1. how anaesthetic gas climatisation during minimal flow anaesthesia is influenced by the technical design of different breathing hose systems in clinical practice. 2. to investigate, whether a sufficient gas climatisation also can be gained with higher fresh gas flows if that hose system is used, proven beforehand to optimally warming and humidifying the anaesthetic gases.

METHODS

Three different systems, a conventional two-limb hosing consisting of smooth silicone hoses, a coaxial hosing, and a hosing consisting of actively heated breathing hoses, attached to a Dräger Cicero EM anaesthesia machine, were used during minimal flow anaesthesia with a fresh gas flow of 0.5 l/min. Gas temperature and absolute humidity were measured at the tapered connection between the inspiratory limb and the breathing system as well as at its connection to the endotracheal tube. The best gas climatisation was observed if heated breathing hoses were used. Thus, using this hosing, additionally gas temperature and humidity in the inspiratory limb were taken at fresh gas flow rates of 1.0, 2.0 and 4.4 l/min respectively. Measurements were performed in all groups at all general anaesthesias lasting at least 45 minutes during the lists of eight different days each.

RESULTS

In minimal flow anaesthesia, with all hose systems likewise, generally an absolute humidity between 17 to 30 mgH2O/l is reached at the endotracheal tube's connector during the course of the list. Only in the first cases of the day there was a short delay of 15 to 30 minutes before reaching a humidity of at least 17 mgH2O/l. Only with heated hoses, however, humidity frequently even exceeded 30 mgH2O/l. If conventional or coaxial hosings were used, during minimal flow anaesthesia gas temperatures in an acceptable range between 23 to 30 degrees C were measured at the tube connector. With heated hoses, however, warming of the gases was excellent with gas temperatures between 28 to 32 degrees C. In minimal flow anaesthesia climatisation of the anaesthetic gases proved to be best if heated hoses were used. Thus, using heated hose systems another three trials with increasing fresh gas flow rates of 1.0, 2.0 and 4.4 l/min respectively were performed. Whereas climatisation of the anaesthetic gases still was found to be optimal with a fresh gas flow of 1.0 l/min, the humidity dropped drastically to values lower than 17 mgH2O/l at 2.0 l/min and even down to 10 mgH2O/l at a flow rate of 4.4 l/min. Gas temperatures, however, turned out to be independent of the flow and remained at 28-32 degrees C, even at a flow as high as 4.4 l/min.

CONCLUSIONS

Using conventional hose systems and coaxial hosings acceptable, but not optimal climatisation of the anaesthetic gases can be gained if minimal flow anaesthesia is performed. The use of a coaxial hose system seems to lead to improved climatisation in long lasting procedures only. In routine clinical practice, however, conventional and coaxial hose systems are similar in respect to the climatisation of breathing gases. Heated breathing hoses performed markedly better in terms of climatisation of the breathing gas than the coaxial and the conventional hose system. With this hosing not only sufficient but optimal moisture and temperature values are realized. Optimal climatisation, however, only can be gained if low flow anesthetic techniques with fresh gas flows equal or less than 1 l/min are performed. With higher fresh gas flow rates the humidity decreases markedly while high gas temperatures are maintained. (ABSTRACT TRUNCATED)

Site-specific NMR monitoring of cis-trans isomerization in the folding of the proline-rich collagen triple helix

Understanding the folding of the proline-rich collagen triple helix requires consideration of the effects of proline cis-trans isomerization and may shed light on the misfolding of collagen in connective tissue diseases. Folding was monitored in real time by heteronuclear 2D NMR spectroscopy for the (15)N labeled positions in the triple-helical peptide T1-892 [GPAGPAGPVGPAGARGPAGPOGPOGPOGPOGV]. In the equilibrium unfolded monomer form, each labeled residue showed multiple peaks with interconversion rates consistent with cis-trans isomerization of Gly-Pro and Pro-Hyp bonds. Real-time NMR studies on the folding of T1-892 showed slow decay of monomer peaks and a concomitant increase in trimer peaks. Gly25 in the C-terminal rich (Gly-Pro-Hyp)(4) domain folds first, consistent with its being a nucleation domain. Analysis of the kinetics indicates that the folding of Gly25 is biphasic and the slower step represents cis-trans isomerization of imino acids. This illustrates that nucleation is limited by cis-trans isomerization. Monitoring Gly6, Gly10, Ala12, and Gly13 monomer and trimer peaks captures the C- to N-terminal propagation of the triple helix, which is also limited by Gly-Pro cis-trans isomerization events. The zipper-like nature of the propagation process is confirmed by the slower rate of folding of Ala6 compared to Gly13, reflecting the larger number of isomerization events encountered by the more N-terminal Ala6. The cis-trans isomerization events at multiple proline residues is a complex statistical process which can be visualized by these NMR studies.

Characterization of millisecond time-scale dynamics in the molten globule state of alpha-lactalbumin by NMR

The motional dynamics of the molten globule (MG) state of alpha-lactalbumin have been characterized using (15)N transverse relaxation rates (R2). A modified version of the Carr-Purcell-Meiboom-Gill (CPMG) R2 pulse sequence is proposed in order to overcome the loss of sensitivity that arises from extreme line broadening due to complex dynamics on the millisecond time-scale. Using this pulse sequence, chemical exchange rates were extracted by examining the (15)N transverse relaxation rates as a function of CPMG delay values. The results clearly illustrate that pervasive conformational exchange of 0.2-0.5 ms in the (15)N backbone resonances of the molten globule state of alpha-lactalbumin. The temperature dependence of the conformational exchange rates display standard Arrhenius kinetic behavior between 10 and 30 degrees C. Estimates of the activation energies range from 0.8 to 4. 4 kcal/mol, indicating a low energetic barrier to conformational fluctuations relative to native state proteins. The fluctuations and low energetic barriers may be critical for directing the search for contacts that will result in the transition from the MG state to the native state.

Folding of peptide models of collagen and misfolding in disease

The misfolding of the triple helix has been shown to play a critical role in collagen diseases. Normal and mutated collagen triple helices can be modeled by short, synthetic peptides of varying design. NMR spectroscopy and circular dichroism studies on the assembly of these peptide models have recently been used to isolate specific steps in the folding pathway and have provided information on the alterations resulting from mutations.

Nuclear magnetic resonance shows asymmetric loss of triple helix in peptides modeling a collagen mutation in brittle bone disease

To investigate a human folding disease, NMR studies were carried out on collagen-like peptides to define the structural consequences of a single amino acid change found in patients with osteogenesis imperfecta (OI), a disease characterized by fragile bones. One peptide included a normal collagen sequence, while a second peptide included a Gly --> Ser substitution as found in a nonlethal case of OI. Residue specific internal dynamics and conformational studies indicate that the normal collagen-like sequence forms a triple helix which is rigid along its entire length. The introduction of a Gly --> Ser substitution induces an asymmetric disruption of the uniform triple helix. While the C-terminal end of the peptide retains the triple helix, the Ser substitution site and residues N-terminal to it exhibit the mobility of a random chain. This equilibrium state indicates that a Gly substitution can terminate the C to N propagation of the triple helix and suggests that renucleation is required for folding to continue. Defective folding has been implicated in brittle bone disease, and these results begin to characterize the folding process in OI collagens. OI collagen studies may also provide insights about defective protein folding, assembly, and aggregation in other human diseases.

[Low-flow and minimal-flow anesthesia with sevoflurane]

Due to its low solubility and the high maximum concentration delivered by the vaporizer sevoflurane is especially suitable for the performance of low flow anaesthetic techniques. High flow phases for wash-in or wash-out of anaesthetic gases can be kept short, the difference between the volatile's concentration in the fresh gas and within the breathing system is comparatively small, and the time constants are short even during low flow anaesthesia. The monitoring, required to sufficiently ensure the safety of the patients, corresponds to the current obliging technical safety standards. As compound A may accumulate in the breathing system, sevoflurane should not be administered with fresh gas flows lower than 1.0 l/min, until the scientific discussion on nephrotoxicity of this substance in humans is solved. Low flow anaesthesia guarantees a sufficient and continuous wash-out of trace gases. Thoroughly the use of sevoflurane with dry soda lime must be avoided, as this volatile in an extreme exothermic reaction is absorbed nearly totally and degraded to a considerable degree by dry carbon dioxide absorbent. The gaseous degradation products are pungent and possibly may be harmful to the patients. Only by low flow anaesthesia the use of sevoflurane will gain an economically and ecologically acceptable range of efficiency.

Tertiary contacts in alpha-lactalbumin at pH 7 and pH 2: a molecular dynamics study

Molecular dynamics simulations of alpha-lactalbumin were performed under conditions of neutral pH and low pH in order to study the acid-induced molten globule state. Through the use of experimental techniques such as NMR and CD spectroscopy, molten globules have been characterized as being compact intermediates with secondary structure similar to that of the native protein but with tertiary structure that is disordered. The detailed structure of the molten globule state is unknown, however. Through the use of computer simulations we can study the structural changes which occur upon lowering pH. The simulations presented here differ from previous unfolding simulations in two important ways: the electrostatic interactions are treated more accurately than ever before, and artificially high temperatures are not used to force the protein to unfold. Simulations of 880 psec each were run at pH 7 (control simulation) and pH 2. We concentrate on the interesting changes in the tertiary interactions within the protein with lowering of pH. In particular, there is a loss of native tertiary contacts in the beta domain and interdomain region, and a large decrease in interdomain hydrogen bonds.