Mechanism and specificity of the terminal thioesterase domain from the erythromycin polyketide synthase.

BACKGROUND: Polyketides are important compounds with antibiotic and anticancer activities. Several modular polyketide synthases (PKSs) contain a terminal thioesterase (TE) domain probably responsible for the release and concomitant cyclization of the fully processed polyketide chain. Because the TE domain influences qualitative aspects of product formation by engineered PKSs, its mechanism and specificity are of considerable interest. RESULTS: The TE domain of the 6-deoxyerythronolide B synthase was overexpressed in Escherichia coli. When tested against a set of N-acetyl cysteamine thioesters the TE domain did not act as a cyclase, but showed significant hydrolytic specificity towards substrates that mimic important features of its natural substrate. Also the overall rate of polyketide chain release was strongly enhanced by a covalent connection between the TE domain and the terminal PKS module (by as much as 100-fold compared with separate TE and PKS 'domains'). CONCLUSIONS: The inability of the TE domain alone to catalyze cyclization suggests that macrocycle formation results from the combined action of the TE domain and a PKS module. The chain-length and stereochemical preferences of the TE domain might be relevant in the design and engineered biosynthesis of certain novel polyketides. Our results also suggest that the TE domain might loop back to catalyze the release of polyketide chains from both terminal and pre-terminal modules, which may explain the ability of certain naturally occurring PKSs, such as the picromycin synthase, to generate both 12-membered and 14-membered macrolide antibiotics.

Progressive age-related impairment of cognitive behavior in APP23 transgenic mice.

Transgenic APP23 mice expressing human APP(751) with the K670N/M671L mutation, were compared at ages 3, 18 or 25 months to non-transgenic littermates in passive avoidance and in a small and large Morris maze. The task in the smaller pool habituated their flight response to the platform. Impairments in passive avoidance and small pool performance in APP23 mice were clearly age-related. In the larger Morris maze APP23 mice at all ages were impaired in latency and distance swum before finding the platform. Identical performance of 18-month APP23 and controls in a visible platform condition indicates that the Morris maze performance deficit was not due to sensory, motor or motivational alterations. At age 3 months both groups initially unexpectedly avoided the visible platform, suggesting that in young mice neophobia may contribute significantly to performance in cognitive tests. In conclusion, APP23 mice exhibit both early behavioral impairment in the large Morris maze as well as impairments in passive avoidance and small pool performance that are marked only in old age.

Thrombocytosis following segmental duct-occluded pancreatic transplantation.

The average platelet counts in our patients with functioning SPK were significantly higher during postoperative week 2 and the interval of weeks 5 through 9 compared with a matched group of KTA recipients. The thrombocyte values in the SPK group were consistently elevated above the normal range (except postoperative week 1) but less than a platelet level typically requiring therapeutic intervention (greater than 1 mil/mm3). However, because potential pathology both locally (graft pancreatitis, endothelial damage of preservation and operative trauma, diminished graft blood flow) as well as systemically (atherosclerosis, hypertension) is present in SPK patients, we consider them at high risk for thromboembolic complications and therefore support prophylaxis of post-SPK thrombocytosis with platelet inhibitors.

[Thrombocytosis following pancreas transplantation--a retrospective clinical study]. / Thrombozytose nach Pankreastransplantation--eine retrospektive klinische Studie.

Thrombosis of the pancreas transplant is one of the main causes for the lower success rate of this transplantation compared with other organ transplantations. Approximately one quarter of the pancreas transplantations discussed in this study were unsuccessful for this reason. This work is a retrospective study focussing on the blood platelet measurement from 19 patients with a postoperative combined pancreas and kidney transplant, functioning well for at least 1.5 months. In addition, the drug treatment (immunosuppressive agents, antibiotics, thrombosis prophylaxis), the transfusions and the body temperature were registered. 19 patients with only a kidney transplant, with similar distribution of sex, age and postoperative immunosuppressive treatment, were observed as a control group. After a pancreas transplantation the platelet number increases considerably and is found to be far above the normal level. There are no proven pathophysiological explanations for this thrombocytosis. Different factors such as postoperative infections, inflammations, acute blood losses, side effects of the drugs and the patients postoperative condition were taken into consideration. Other predisposing factors for the thrombosis tendency of the pancreas transplant vessels are its abnormal haemodynamic situation and the endothelial change caused by the preservation of the transplant, by mechanical or surgical traumas or by a possible pancreatitis of the transplant. Because of this increased risk of thrombosis, there are clear indications to use platelet inhibitors during the first two postoperative months.

Haematology, blood chemistry and urine parameters of free-ranging plains viscachas (Lagostomus maximus) in Argentina determined by use of a portable blood analyser (i-STAT) and conventional laboratory methods.

Haematology, blood chemistry and urine values were determined for 44 adult free-ranging plains viscachas (Lagostomus maximus; Rodentia, Chinchillidae) in their pampas habitat in central Argentina. The study animals were captured in the wild and anaesthetized with a ketamine-xylazine combination for physical examination and sampling. Blood was obtained by venipuncture of the saphenous vein. Results for many of the blood parameters fall within the reference ranges for pet chinchillas. Differentiation of white blood cells revealed a predominantly neutrophil count for plains viscachas, while chinchillas have predominantly lymphocytes. Mean values for blood urea nitrogen, creatinine, aspartate aminotransferase and sodium were higher than the upper limit of the reference range for pet chinchillas. The results of seven analytes (haematocrit, haemoglobin, glucose, blood urea nitrogen, sodium, potassium, chloride) were compared by using both a portable blood analyser (i-STAT) in the field and conventional laboratory methods. In general, correlation and agreement between the two methods were low for most parameters.

[Cause of death and autopsy findings in patients of the Swiss HIV Cohort Study (SHCS)]. / Todesursachen und Autopsiebefunde bei Patienten der Schweizerischen HIV-Kohortenstudie (SHCS).

The Swiss HIV Cohort Study (SHCS) is a prospective cohort study of HIV-infected adolescents and adults seen at 7 outpatient clinics (Swiss University Hospitals in Basle, Berne, Geneva, Lausanne, Zurich, the St. Gall Cantonal Hospital and the Civico Hospital in Lugano). The SHCS serves as an infrastructure for different research projects and includes about 70% of all patients with advanced disease in Switzerland. From April 1984 to November 1995 3120 HIV-infected patients of the SHCS died. Autopsies were performed in 314 of these patients. The aim of our study is to analyse autopsy findings as well as causes of death in those 314 HIV-infected patients. An HIV-related cause of death was found in 271 (86%) of the patients, 12 patients (4%) died of a drug overdose, and 3 (1%) of the patients committed suicide. 28 (9%) died either from an HIV unrelated or unidentified cause. The five most frequent causes of death were: bacterial pneumonia (52 patients, 17%), Pneumocystis carinii pneumonia (40 patients, 13%), lymphoma (34 patients, 11%), cytomegalovirus infection (33 patients, 11%), and toxoplasmosis (30 patients, 10%). During our study marked progress occurred in treating HIV-infected patients and preventing opportunistic infections. These improvements have further changed the natural course of acquired immunodeficiency syndrome. They are reflected in the falling rate of Pneumocystis carinii pneumonia and toxoplasmosis, as well as an increase in lymphoma as a cause of death over the period of our study.

[Thrombocytosis following pancreas transplantation]. / Thrombozytose nach Pankreastransplantation.

Thrombosis of the pancreas transplant is one of the main causes for the lower success rate of this procedure compared with that of other organ transplantations. Approximately one quarter of the pancreas transplantations discussed in this study are unsuccessful for this reason. This work is a retrospective study focusing on the postoperative blood platelet counts from 19 patients with a combined pancreas and kidney transplant, functioning well for at least 1.5 months. 19 patients with only a kidney transplantation with similar distribution of sex, age and postoperative immunosuppressive treatment were observed as a control group. After pancreas transplantation the platelet counts increased considerably and were found to be far above the normal level. There are no proven pathophysiological explanations for this thrombocytosis. Because of an increased risk of thrombosis, we recommend to use platelet inhibitors during the first two postoperative months.