von Willebrand disease type B: a missense mutation selectively abolishes ristocetin-induced von Willebrand factor binding to platelet glycoprotein Ib.

von Willebrand factor (vWF) is a multimeric glycoprotein that mediates the adhesion of platelets to the subendothelium by binding to platelet glycoprotein Ib. For human vWF, this interaction can be induced in vitro by the antibiotic ristocetin or the snake venom protein botrocetin. A missense mutation, Gly-561-->Ser, was identified within the proposed glycoprotein Ib binding domain of vWF in the proband with von Willebrand disease type B, a unique variant characterized by no ristocetin-induced, but normal botrocetin-induced, binding to glycoprotein Ib. The corresponding mutant recombinant protein, rvWF(G561S), formed normal multimers and exhibited the same functional defect as the patient's plasma vWF, confirming that this mutation causes von Willebrand disease type B. These data show that botrocetin and ristocetin cofactor activities of vWF can be dissociated by a point mutation and confirm that these mediators promote vWF binding to platelets by different mechanisms. The normal botrocetin-induced binding and the defective ristocetin-induced binding of rvWF(G561S) suggest that the primary defect in von Willebrand disease type B may be a failure of normal allosteric regulation of the glycoprotein Ib binding function of vWF.     

The J-curve phenomenon and the treatment of hypertension. Is there a point beyond which pressure reduction is dangerous?

We critically appraised the medical literature to evaluate whether there is a point beyond which blood pressure reduction in hypertensive subjects is no longer beneficial and possibly even deleterious. Thirteen studies that stratified cardiovascular outcomes by level of achieved blood pressure in treated hypertensive subjects who had been followed up for at least 1 year were critiqued by four independent reviewers. Data addressing population, protocol, and methodological characteristics were evaluated. Studies did not show a consistent J-shaped relationship between treated blood pressure and stroke, but they did demonstrate a consistent J-shaped relationship for cardiac events and diastolic blood pressure. The beneficial therapeutic threshold point was 85 mm Hg. We conclude that low treated diastolic blood pressure levels, ie, below 85 mm Hg, are associated with increased risk of cardiac events.     

Once-daily topical metronidazole cream formulations in the treatment of the papules and pustules of rosacea

BACKGROUND: The papules and pustules of rosacea can be effectively treated with topical metronidazole. The optimal concentrations of metronidazole and optimum frequencies of application are uncertain. Traditionally, twice-daily applications have been advised, based on the pharmacokinetic profile of metronidazole. Once-daily applications may be safer and less expensive, and they may enhance patient compliance. OBJECTIVE: We compared the efficacy and safety of 2 commercially available topical metronidazole formulations (0.75% metronidazole cream formulation and 1.0% metronidazole cream formulation) when both were used in a once-daily regimen. METHODS: A multicenter, randomized, investigator-blind, parallel group trial was conducted at 3 separate clinical sites located in 3 US cities. The study enrolled 72 rosacea patients with at least 8 to 50 inflammatory facial lesions (pustules and papules) and moderately severe facial erythema. Patients were randomly assigned to receive either 0.75% metronidazole cream or 1.0% metronidazole cream and instructed to apply the medication once daily for 12 weeks. Patients' lesions were evaluated at baseline and at weeks 3, 6, 9, and 12. RESULTS: There were no significant differences between treatment groups for any of the efficacy parameters evaluated. The overall median percentage change in lesion count at end point for patients in the 0.75% metronidazole cream treatment group was -62% compared with -60% for the 1.0% metronidazole cream treatment group. The overall percentage change in erythema scores at endpoint for patients in the 0.75% metronidazole cream treatment group was -26% compared with -30% for patients in the 1.0% metronidazole cream treatment group. Regarding physician assessment of global severity, 57% of subjects (20/35) in the 0.75% metronidazole cream group compared with 37% of subjects (13/35) in the 1.0% metronidazole cream group were rated as having a clear to mild condition at end point. Both drugs were well tolerated; there was no significant difference in the number of drug-related adverse events between the two agents. CONCLUSION: This controlled trial demonstrates that both 0.75% metronidazole cream and 1.0% metronidazole cream, when used once daily, provide well-tolerated efficacy for moderate to severe rosacea.     

Type 1 von Willebrand disease mutation Cys1149Arg causes intracellular retention and degradation of heterodimers: a possible general mechanism for dominant mutations of oligomeric proteins.

Some families affected by von Willebrand disease type 1 show high penetrance with exceptionally low von Willebrand factor (VWF) levels. Previously, a mutation associated with this dominant phenotype, Cys1149Arg, was found to decrease the secretion of coexpressed normal VWF, and the mutation was proposed to cause intracellular retention of pro-VWF heterodimers. To demonstrate heterodimer formation, a model was developed in which subunits could be distinguished immunologically and by size. Recombinant VWF lacking domain A1 (dA1), A3 (dA3), or both (dA13) was secreted efficiently as a full range of multimers. Cotransfection of Cys1149Arg and dA13 resulted in the secretion of multimeric VWF containing about 250 kd (Cys1149Arg) and about 210 kd (dA13). Cell lysates contained pro-VWF forms of Cys1149Arg and dA13. Immunoprecipitation with an antidomain A1 antibody recovered both subunits in heterodimers, and subunit ratios were consistent with random dimerization. Similar results were obtained for cotransfection of Cys1149Arg and dA1. Normal VWF has a Cys1149-Cys1169 intrachain bond. When cotransfected with normal VWF, Cys1149Arg or the double mutant Cys1149Arg+Cys1169Ser caused a similar decrease in VWF secretion, suggesting that an unpaired Cys1169 does not explain the intracellular retention of Cys1149Arg. VWF Cys1149Arg was not secreted from BHK cells but was degraded intracellularly within about 4 hours, and the proteasome inhibitor lactacystin delayed its clearance more than 16 hours. Thus, dominant von Willebrand disease type 1 may be caused by heterodimerization of mutant and normal subunits in the endoplasmic reticulum followed by proteasomal degradation in the cytoplasm. A similar dominant negative mechanism could cause quantitative deficiencies of other multisubunit proteins.     

Operative risk in patients with severe obstructive pulmonary disease.

BACKGROUND--We wanted to determine the risk of postoperative pulmonary complications and mortality in patients with severe chronic obstructive pulmonary disease. METHODS--We reviewed 107 consecutive operations performed in 89 patients with severe chronic obstructive pulmonary disease (forced expiratory volume in 1 second, less than 50% of predicted). RESULTS--Postoperative pulmonary complications occurred in 31 operations (29%) and were significantly related to the type and duration of surgery. Also, American Society of Anesthesiologists class approached significance as a predictor. Postoperative pulmonary complications occurred at higher rates in coronary artery bypass grafting and major abdominal procedures (60% and 56%) than in other operations involving general or spinal anesthesia (27%) or in procedures performed with the patient under regional or local anesthesia (16%). When the durations of the operations were classified as less than 1 hour, 1 to 2 hours, 2 to 4 hours, and more than 4 hours, the rates of postoperative pulmonary complications were 4%, 23%, 38%, and 73%, respectively. Regarding American Society of Anesthesiologists class, postoperative pulmonary complications occurred in 10% of patients in class II, 28% of those in class III, and 46% of those in class IV. In terms of life-threatening complications, there were six deaths and only two cases of nonfatal ventilatory failure. Notably, mortality clustered primarily in coronary artery bypass graft procedures. Five of 10 patients receiving coronary artery bypass grafts died, compared with one death after 97 non-coronary artery bypass graft operations (50% vs 1%). CONCLUSIONS--Although the risk of coronary artery bypass grafting deserves further study, noncardiac surgery carries an acceptable operative risk in patients with severe chronic obstructive pulmonary disease.     

Experimental observations of dry powder inhaler dose fluidisation

Dry powder inhalers (DPIs) are widely used to deliver respiratory medication as a fine powder. This study investigates the physical mechanism of DPI operation, assessing the effects of geometry, inhalation and powder type on dose fluidisation. Patient inhalation through an idealised DPI was simulated as a linearly increasing pressure drop across three powder dose reservoir geometries permitting an analysis of shear and normal forces on dose evacuation. Pressure drop gradients of 3.3, 10 and 30 kPa s(-1)were applied to four powder types (glass, aluminium, and lactose 6 and 16% fines) and high speed video of each powder dose fluidisation was recorded and quantitatively analysed. Two distinct mechanisms are identified, labelled 'fracture' and 'erosion'. 'Fracture' mode occurs when the initial evacuation occurs in several large agglomerates whilst 'erosion' mode occurs gradually, with successive layers being evacuated by the high speed gas flow at the bed/gas interface. The mechanism depends on the powder type, and is independent of the reservoir geometries or pressure drop gradients tested. Both lactose powders exhibit fracture characteristics, while aluminium and glass powders fluidise as an erosion. Further analysis of the four powder types by an annular shear cell showed that the fluidisation mechanism cannot be predicted using bulk powder properties.     

Appendicitis: Higher risk in Mexican Americans?

Objectives. Mexican Americans (MAs), compared to white non‐Hispanics (WNHs), have higher rates of biliary disease, noninsulin dependent diabetes, and endstage renal disease but lower rates of lung cancer, hip fractures, and mortality from coronary heart disease. Relatively little research has been done to identify other ethnic differences in disease incidence. We used surgical procedure rates to confirm known ethnic differences and to explore our clinical suspicion that MAs have higher rates of appendectomy than WNHs.

Methods. We used a registry of surgical procedures at two teaching hospitals in South Texas to calculate proportional operation ratios (PORs) for MAs versus WNHs. These two hospitals are the primary source of acute hospital care for the indigent in the area. The POR is arithmetically identical to proportional incidence and mortality ratios.

Results. MAs underwent appendectomy proportionally more often than WNHs at both hospitals (POR = 1.41 and 1.75, p < 0.0001). Other significant PORs were consistent with known ethnic disease differences in biliary tract operations, vascular access for chronic hemodialysis, lung cancer, and coronary artery bypass.

Conclusions. These findings support the hypothesis that MAs may undergo appendectomy more often than WNHs and so may be at higher risk of appendicitis.     

Expression of von Willebrand factor "Normandy": an autosomal mutation that mimics hemophilia A

von Willebrand disease Normandy (vWD Normandy) is a recently described phenotype in which a mutant von Willebrand factor (vWF) appears structurally and functionally normal except that it does not bind to blood coagulation factor VIII. This interaction is required for normal survival of factor VIII in the circulation; consequently, vWD Normandy can present as apparent hemophilia A but with autosomal recessive rather than X chromosome-linked inheritance. A vWF missense mutation, Thr28----Met, was identified in the propositus in or near the factor VIII binding site. The corresponding mutant recombinant vWF(T28M) formed normal multimers and had normal ristocetin cofactor activity. However, vWF(T28M) exhibited the same defect in factor VIII binding as natural vWF Normandy, confirming that this mutation causes the vWD Normandy phenotype. The distinction between hemophilia A and vWD Normandy is clinically important and should be considered in families affected by apparent mild hemophilia A that fail to show strict X chromosome-linked inheritance and, particularly, in potential female carriers with low factor VIII levels attributed to extreme lyonization.