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Reversion of prion protein conformational changes by synthetic β-sheet breaker peptides Prions: A lone killer or a vital accomplice?
286 overgrowth. They therefore set about to study whether supplemental oxygen would affect the incidence of postoperative wound infection. Five hundred adult patients undergoing elective colorectal resection were randomized to receive either 30% or 80% inspired oxygen during surgery and for the first 2 hours of the postoperative period. Care of the patients was otherwise standardized. Blinded observers assessed whether postoperative wound infection had developed. As expected, the pO2 was higher in the group given more supplemental oxygen. Among the 250 patients who received 80% oxygen, 5% (confidence interval, 2.4% to 8.0%) developed surgical wound infections. In contrast, among those given less oxygen, 11% (confidence interval, 7.3% to 15.1%) developed infections (P = .01). Most positive wound cultures contained multiple organisms typical of those found in this setting. In addition, 12 patients in the 30% oxygen group and only 5 patients in the 80% oxygen group required admission to intensive care for complications such as wound dehiscence, anastomotic leak, and peritonitis. A greater number of patients assigned to the 30% oxygen group died. Transfusion support was not statistically different for the two groups. This interesting study suggests that a very simple, nontoxic, and inexpensive treatment is able to significantly decrease postoperative wound infections in patients undergoing coldrectal surgery. For transfusion medicine professionals, the study also raises a flag of concern about the extent to which oxygen support was controlled and balanced in prior studies of leukoreduction. (S.D. )
Solvent/detergent-treated plasma has decreased antitrypsin activity and absent antiplasmin activity. A,E. Mast, J.E. Stadanlick, M. Lockett, et aL Blood 94:39223927, 1999. See also: Solvent/detergent treated plasma: Is its decreased protein S activity clinically significant in the treatment of thrombotic thrombocytopenic purpura? Blood 94:1999 (abstr #1092). Hospitals across North America have debated whether to offer solvent/detergent-treated plasma (SD-FFP) to their patients. Most concerns regarding SD-FFP have focused on the fact that this is a pooled product and that the solvent/detergent treatment is not capable of inactivating nonenveloped viruses. Compared with regular FFP, SD-FFP also is recognized to be deficient in high-molecular-weight forms of yon Willebrand factor. Otherwise, SD-FFP was considered to be relatively similar to regular FFR This paper and abstract identify other potential shortcomings of SD-FFP. The investigation in the published paper focused on serpins--a family of proteins that are all serine protease inhibitors. Serpins contain a protein loop that is sensitive to detergent and heat treatment. Excess treatment can convert the molecules from their native "active" state to an inactive or polymerized conformation. Three serpins were studied--antithrombin, antitrypsin, and antiplasmin. The authors report that both antitrypsin and antiplasmin were affected by the SD process. SD-FFP contained nearly 0% active arltiplasmin and approximately 50% active antitrypsin. Antithrombin was not affected by the SD process. The loss of active antiplasmin activity in SD-FFP is of some concern for those who wish to use FFP in the treatment of patients with fibrinolytic conditions, patients undergoing liver transplantation (where plasmin levels can become extremely elevated) or patients undergoing massive replacement with FFP as occurs during plasma exchange. Conversely, a recent abstract (cited above)
CURRENT LITERATURE noted deficiency of protein S in SD-plasma and thrombotic complications in 2 patients with underlying hypercoagulation disorders who received plasma exchange with SD-plasma. This report comes at the same time as the cited abstract, which reports on 2 patients with TTP who were treated with SD-plasma and developed thromboses.
Recombinant factor Vlla is effective for bleeding and surgery in patients with Glanzmann thrombasthenia. M,C. Poon, C. Demers, E Jobin, et al. Blood 94:39513953, 1999. Factor VII combines with tissue factor, and this complex is considered to be the primary initiator of blood coagulation. Factor VII plays an essential role in coagulation, and deficien cies of factor VII represent serious coagnlopathies. With the recent availability of a recombinant activated factor VII suitable for intravenous injection, rVIIa is being tried for a number of related coagulation defects. This brief repolnt suggest that rVIIa may be of value in the treatment of bleeding patients with thrombasthenia. Glanzmann's thrombasthenia results from a deficiency or abnormality of platelet glycoprotein lYo-IIIa. The disorder can result in life-threatening bleeding. Patients with Glanzmann's thrombasthenia who become refractory to platelet transfusions can be very difficult to treat. Four children (ages 1 to 6) with Glanzmann's thrombasthenia were treated. The 4 children experienced a total of 24 separate bleeding episodes, mostly occurring in the nose and oropharynx, rVIIa was administered in large doses (89 to 116 gg/kg) every 2 hours and in conjunction with antifibrinolytic therapy. Antifibdnolytics were continued for up to 9 days after rVIIa treatment, and the authors consider this to have been an important means to promote clot stabilization and avoid maintenance therapy with rVIla. There was no control group. In 7 bleeding episodes, transfusion of red cells was needed. In two thirds of bleeding episodes, the bleeding stopped with 6 hours of starting rVIIa. One patient with a gastrointestinal bleed did not stop bleeding despite 48 hours of repeated rVIIa injections and then promptly stopped bleeding after a platelet transfusion. Although the results of this study are quite preliminary, they provide a promising new alternative to achieve hemostasis in patients with Glanzmann's thrombasthenia. Whether rVIIa will prove beneficial in the treatment of other platelet disorders remains to be seen. The usefulness of this new recombinant is also being explored among patients with hemophilia and inhibitors and among those with severe liver disease. (S.D.)
Reversion of prion protein conformational changes by synthetic ~-sheet breaker peptides. C. Soto, R.J. Kascsak, G.R Saborio, et al. Lancet 355:192-197, 2000. Also, interested readers should see: Prions: A lone killer or a vital accomplice.'? M. Baiter. Science 286:660662, 1999. An essential aspect of the prion protein hypothesis for transmissable spongiform encephalopathies is that abnormal prions are able to "convert" normal prions PrP c to the pathological PrP sc form. This conversion results in a critical change in the prion molecule from the normal form, which contains an c~-helix, to the abnormal form, which contains a [3-pleted sheet. This extremely interesting early report seeks to reverse this process and convert pathological PrP sc back to the normal PrP c
CURRENT LITERATURE
form. The method is based on the use of highly engineered small peptides--known as [3-sheet breakers--which interrupt the conversion step. Previous research had discovered that amino acids 115 to 222 of the prion molecule played a central role in the conversion from normal to pathological form. The investigators designed small peptide molecule homologous to this region but with an important difference. The newly engineered peptides contained proline amino acid substitutions because proline interferes with the folding of peptides into [3-pleated sheets. First, the investigators partially purified PrP sc from scrapieinfected mouse brain or from the brains of humans who died of spongiform encephalopathy and showed that the usual protease resistance of this prion was abolished after incubation with the PrP inhibitor peptide. The effect was dose dependent and required both a molar excess of the inhibitory peptide and a 48-hour period of incubation. Using infrared spectroscopy, they also showed that the conversion effect produced a decrease in the amount of 13-sheet forms present. In addition, the investigators added the inhibitory peptide to cell cultures of cells that
287
produced a prpsc-like prion. Compared with control cultures, the treated cultures expressed less than 10% of the enzymatically resistant prpsc-like form. Finally, in an in vivo study in mice, they found that mice who were injected with PrP sc that had been "treated" with inhibitory peptide developed scrapietype symptoms much more slowly than mice injected with infectious material that had not been treated. Serial experiments allowed for an estimate that the inhibitory peptide treatment reduced the infectious concentration by 1 log. The effect would be expected to be even greater if the starting material were in low concentration. Although the authors noted the obvious potential therapeutic value of this treatment, they acknowledged that peptides do not cross the blood-brain barrier easily--a limitation that could seriously affect the therapeutic value of this approach. Surprisingly, they did not mention in their publication the even more exciting possibility of using this peptide technology to inactivate any potential PrP sc that might exist in donor blood. (S.D. )
Solvent/detergent-treated plasma has decreased antitrypsin activity and absent antiplasmin activity. A,E. Mast, J.E. Stadanlick, M. Lockett, et aL Blood 94:39223927, 1999. See also: Solvent/detergent treated plasma: Is its decreased protein S activity clinically significant in the treatment of thrombotic thrombocytopenic purpura? Blood 94:1999 (abstr #1092). Hospitals across North America have debated whether to offer solvent/detergent-treated plasma (SD-FFP) to their patients. Most concerns regarding SD-FFP have focused on the fact that this is a pooled product and that the solvent/detergent treatment is not capable of inactivating nonenveloped viruses. Compared with regular FFP, SD-FFP also is recognized to be deficient in high-molecular-weight forms of yon Willebrand factor. Otherwise, SD-FFP was considered to be relatively similar to regular FFR This paper and abstract identify other potential shortcomings of SD-FFP. The investigation in the published paper focused on serpins--a family of proteins that are all serine protease inhibitors. Serpins contain a protein loop that is sensitive to detergent and heat treatment. Excess treatment can convert the molecules from their native "active" state to an inactive or polymerized conformation. Three serpins were studied--antithrombin, antitrypsin, and antiplasmin. The authors report that both antitrypsin and antiplasmin were affected by the SD process. SD-FFP contained nearly 0% active arltiplasmin and approximately 50% active antitrypsin. Antithrombin was not affected by the SD process. The loss of active antiplasmin activity in SD-FFP is of some concern for those who wish to use FFP in the treatment of patients with fibrinolytic conditions, patients undergoing liver transplantation (where plasmin levels can become extremely elevated) or patients undergoing massive replacement with FFP as occurs during plasma exchange. Conversely, a recent abstract (cited above)
CURRENT LITERATURE noted deficiency of protein S in SD-plasma and thrombotic complications in 2 patients with underlying hypercoagulation disorders who received plasma exchange with SD-plasma. This report comes at the same time as the cited abstract, which reports on 2 patients with TTP who were treated with SD-plasma and developed thromboses.
Recombinant factor Vlla is effective for bleeding and surgery in patients with Glanzmann thrombasthenia. M,C. Poon, C. Demers, E Jobin, et al. Blood 94:39513953, 1999. Factor VII combines with tissue factor, and this complex is considered to be the primary initiator of blood coagulation. Factor VII plays an essential role in coagulation, and deficien cies of factor VII represent serious coagnlopathies. With the recent availability of a recombinant activated factor VII suitable for intravenous injection, rVIIa is being tried for a number of related coagulation defects. This brief repolnt suggest that rVIIa may be of value in the treatment of bleeding patients with thrombasthenia. Glanzmann's thrombasthenia results from a deficiency or abnormality of platelet glycoprotein lYo-IIIa. The disorder can result in life-threatening bleeding. Patients with Glanzmann's thrombasthenia who become refractory to platelet transfusions can be very difficult to treat. Four children (ages 1 to 6) with Glanzmann's thrombasthenia were treated. The 4 children experienced a total of 24 separate bleeding episodes, mostly occurring in the nose and oropharynx, rVIIa was administered in large doses (89 to 116 gg/kg) every 2 hours and in conjunction with antifibrinolytic therapy. Antifibdnolytics were continued for up to 9 days after rVIIa treatment, and the authors consider this to have been an important means to promote clot stabilization and avoid maintenance therapy with rVIla. There was no control group. In 7 bleeding episodes, transfusion of red cells was needed. In two thirds of bleeding episodes, the bleeding stopped with 6 hours of starting rVIIa. One patient with a gastrointestinal bleed did not stop bleeding despite 48 hours of repeated rVIIa injections and then promptly stopped bleeding after a platelet transfusion. Although the results of this study are quite preliminary, they provide a promising new alternative to achieve hemostasis in patients with Glanzmann's thrombasthenia. Whether rVIIa will prove beneficial in the treatment of other platelet disorders remains to be seen. The usefulness of this new recombinant is also being explored among patients with hemophilia and inhibitors and among those with severe liver disease. (S.D.)
Reversion of prion protein conformational changes by synthetic ~-sheet breaker peptides. C. Soto, R.J. Kascsak, G.R Saborio, et al. Lancet 355:192-197, 2000. Also, interested readers should see: Prions: A lone killer or a vital accomplice.'? M. Baiter. Science 286:660662, 1999. An essential aspect of the prion protein hypothesis for transmissable spongiform encephalopathies is that abnormal prions are able to "convert" normal prions PrP c to the pathological PrP sc form. This conversion results in a critical change in the prion molecule from the normal form, which contains an c~-helix, to the abnormal form, which contains a [3-pleted sheet. This extremely interesting early report seeks to reverse this process and convert pathological PrP sc back to the normal PrP c
CURRENT LITERATURE
form. The method is based on the use of highly engineered small peptides--known as [3-sheet breakers--which interrupt the conversion step. Previous research had discovered that amino acids 115 to 222 of the prion molecule played a central role in the conversion from normal to pathological form. The investigators designed small peptide molecule homologous to this region but with an important difference. The newly engineered peptides contained proline amino acid substitutions because proline interferes with the folding of peptides into [3-pleated sheets. First, the investigators partially purified PrP sc from scrapieinfected mouse brain or from the brains of humans who died of spongiform encephalopathy and showed that the usual protease resistance of this prion was abolished after incubation with the PrP inhibitor peptide. The effect was dose dependent and required both a molar excess of the inhibitory peptide and a 48-hour period of incubation. Using infrared spectroscopy, they also showed that the conversion effect produced a decrease in the amount of 13-sheet forms present. In addition, the investigators added the inhibitory peptide to cell cultures of cells that
287
produced a prpsc-like prion. Compared with control cultures, the treated cultures expressed less than 10% of the enzymatically resistant prpsc-like form. Finally, in an in vivo study in mice, they found that mice who were injected with PrP sc that had been "treated" with inhibitory peptide developed scrapietype symptoms much more slowly than mice injected with infectious material that had not been treated. Serial experiments allowed for an estimate that the inhibitory peptide treatment reduced the infectious concentration by 1 log. The effect would be expected to be even greater if the starting material were in low concentration. Although the authors noted the obvious potential therapeutic value of this treatment, they acknowledged that peptides do not cross the blood-brain barrier easily--a limitation that could seriously affect the therapeutic value of this approach. Surprisingly, they did not mention in their publication the even more exciting possibility of using this peptide technology to inactivate any potential PrP sc that might exist in donor blood. (S.D. )