'Late onset' ornithine transcarbamylase deficiency: function of three purified recombinant mutant enzymes

Although many mutations in the ornithine transcarbamylase gene have been correlated with 'late onset' of hyperammonemia in patients, the effects of these mutations on enzyme function are largely unknown. Three recurrent mutations (R40H, R277W and R277Q) found in patients with 'late onset' disease were incorporated into 'mature' human ornithine transcarbamylase cDNA and overexpressed in Escherichia coli. The three recombinant mutant enzymes were purified to homogeneity on an affinity column and their biochemical characteristics were compared to the wild type enzyme. The R277W and R277Q mutants display markedly reduced affinity for L-ornithine, loss of substrate inhibition, alkaline shift of pH optimum, and reduced thermal stability compared to the wild type enzyme. These differences, particularly the reduced affinity for L-ornithine, are sufficient to account for their biochemical effects. In contrast, the 'mature' R40H mutant was biochemically indistinguishable from the wild type enzyme in vitro.      

Contaminant Loading in Drainage and Fresh Water Used for Wetland Management at Stillwater National Wildlife Refuge

Throughout the western United States, studies have identified various detrimental effects of contaminants to aquatic biota from the use of agricultural drainage water for management of arid wetlands. However, little is known about the relative contributions of contaminant loading from pollutants dissolved in water compared with those carried by drifting material (e.g., detritus) associated with drainage water. Consequently, we determined loading rates for contaminants dissolved in water and those incorporated by drifting material for drainage (Diagonal Drain) as well as fresh (S-Line Canal) water used for wetland management at Stillwater National Wildlife Refuge (SNWR), Nevada during the early, middle, and late periods of the irrigation season (June through mid-November) in 1993. We found loading rates for trace elements throughout the irrigation season were almost entirely (> 98%) associated with contaminants dissolved in the water rather than incorporated by drift. Although drift contributed little to the total loading for trace elements to SNWR wetlands, contaminant concentrations were much greater in drift compared with those dissolved in water. Loading rates for dissolved As, B, Hg, and total dissolved solids (TDS) differed among periods for the Diagonal Drain. Along the Diagonal Drain, loading rates for dissolved As, B, Hg, Mo, unionized ammonia (NH₃-N), TDS, and Zn differed among its three sampling sites. B was the only trace element with differences in loading rates for drift among periods from the Diagonal Drain. In contrast, loading rates for As, B, Cr, Cu, Hg, Se, and Zn in drift differed among periods for the S-Line Canal. Along Diagonal Drain, loading rates in drift for B (middle and late periods), Cr, Cu, and Zn differed among sites. Hg (xˉ ≥ 12.0 ng/L) and NH₃-N (xˉ ≥ 0.985 mg/L) dissolved in water as well as B (xˉ ≥ 97.4 μg/g DW) and Hg (xˉ ≥ 0.461 μg/g DW) in drift from the Diagonal Drain and S-Line Canal exceeded screening levels (SLs) for protection of aquatic biota throughout the irrigation season. Dissolved As (xˉ ≥ 0.0426 mg/L) in water from the Diagonal Drain during all periods exceeded the SL for protection of aquatic biota. Dissolved B (xˉ = 1.03 mg/L) in water from the Diagonal Drain during the early period exceeded the SL for protection of aquatic biota. Received: 18 September 1997/Accepted: 5 February 1998     

Hypertrophic osteoarthropathy: An unusual manifestation in nasopharyngeal cancer

A patient with nasopharyngeal carcinoma developed clubbing and hypertrophic osteoarthropathy 6 months before radiological detection of secondary deposits in the lung. Another patient with nasopharyngeal carcinoma developed digital clubbing and hypertrophic osteoarthropathy 6 months after the discovery of lung metastases. Development of a paraneoplastic syndrome in the form of hypertrophic osteoarthropathy and digital clubbing is very rare. This manifestation of nasopharyngeal cancers is presented, with a short review of its biology and pathogenesis.     

The oral mucosa: A barrier site participating in tissue‐specific and systemic immunity

In the oral cavity, the immune system is constantly exposed to unique tissue‐specific signals, including a rich community of commensal microbes and their metabolites, continuous tissue damage from mastication, and antigens from food and airborne particles. How this unique combination of signals participates in the training of specialized immunity at this site is not well understood, yet imbalance of local responses is linked to tissue‐specific disease susceptibilities with the prototypic disease being periodontitis. However, the oral mucosa is also well recognized as a site where systemic inflammatory and autoimmune diseases often manifest, indicating that systemic immune deregulation is reflected in the function of the oral immune system. This commentary will discuss both aspects of compartmentalized and systemic immunity at the oral mucosa.     

Risk and significance of endoscopic/radiological evidence of recurrent Crohn's disease

BACKGROUND & AIMS: The aim of this study was to determine the risk of endoscopic/radiological recurrence of Crohn's disease postoperatively and the long-term outcome. METHODS: A randomized placebo-controlled trial was performed to determine the effectiveness of mesalamine in preventing recurrent Crohn's disease postoperatively. Patients in the control group were examined endoscopically/radiologically before entry into and annually during the trial. Findings were classified as minimal or severe. RESULTS: There were 76 patients (49 men and 37 women; mean age, 37.1 +/- 13.2 years). Fifty (61.7%) had terminal ileal resections. Overall, 55 endoscopic/radiological recurrences were observed in 51 patients (67.1%). Expressed actuarially, the recurrence rate was 27.5% at 1 year (95% confidence interval [CI], 15.8%-37.6%), 60.8% at 2 years (95% CI, 46%-71.3%), and 77.3% at 3 years (95% CI, 62.7%-86.3%). Nineteen (37%) were symptomatic and 12 (24%) were initially asymptomatic but later became symptomatic (mean, 13.0 +/- 8.8 months), whereas 20 (39%) remained asymptomatic (mean, 16.9 +/- 17.4 months). Patients with severe endoscopic/radiological disease were significantly more likely to be or become symptomatic than those with minimal disease (23 of 32 vs. 8 of 19, respectively; P = 0.0437). CONCLUSIONS: This study suggests that postoperative endoscopic/radiological recurrences occur later than previously reported. Furthermore, many of these patients, especially with minimal disease, will remain asymptomatic. (Gastroenterology 1997 Dec;113(6):1823-7)     

Impaired interleukin-3 response in Pim-1-deficient bone marrow-derived mast cells

The mouse Pim-1 gene encodes two cytoplasmic serine-threonine-specific protein kinases. The gene has been found to be activated (overexpressed) by retroviral insertion in hematopoietic tumors in mice. Transgenic mice that overexpress Pim-1 (E mu-Pim-1) have a low incidence of spontaneous T-cell lymphomas and an increased susceptibility to Moloney murine leukemia virus and N-ethyl-N- nitrosourea-induced lymphomas. Apart from a slight enlargement of the spleen, no abnormalities were found in prelymphomatous transgenic mice. Inactivation of the Pim-1 gene in the germline of mice resulted in mice with a surprisingly subtle phenotype. Therefore, we investigated whether subtle effects of the absence of Pim-1 could be made visible during in vitro culturing of hematopoietic cells. We found that bone marrow-derived mast cells (BMMC) lacking Pim-1 had a distinct growth disadvantage when grown on interleukin (IL)-3, but not when stimulated by the factors IL-4, IL-9, or Steel factor (SF). This indicates a role for Pim-1 as a modulator of the IL-3 signal transduction pathway.     

Biologic effects of leukocytes present in transfused cellular blood products

A considerable literature has accumulated over the past decade indicating that leukocytes present in allogeneic cellular blood components, intended for transfusion, are associated with adverse effects to the recipient. These include the development of febrile transfusion reactions, graft-versus-host disease, alloimmunization to leukocyte antigens, and the immunomodulatory effects that might influence the prognosis of patients with a malignancy. Moreover, it has become evident that such leukocytes may be the vector of infectious agents such as CMV, HTLV-I/II, and EBV as well as other viruses. An interesting development that has occurred coincidentally in transfusion medicine is that agencies responsible for the provision of blood products are being designated manufacturers of biologicals. The trend among manufacturers of biologicals is to try to produce pure products to provide for the specific therapeutic need of patients. Thus, with the realization that allogeneic leukocytes and their products may have adverse biologic activities, there is increasing pressure from various sources for the reduction of the leukocyte content in allogeneic blood components to minimize the occurrence of their adverse effects. Although the threshold leukocyte number below which these effects might no longer occur is still to be determined, a 2 to 3 log10 leukocyte reduction, provided by the currently available commercial leukocyte filters, has been shown to reduce the frequency of many of such reactions. On the other hand, the immunosuppressive effects produced by the infusion of allogeneic leukocytes might be beneficial for some patients, ie, for the maintenance of kidney allografts, in possibly reducing the relapse rate in patients with inflammatory bowel diseases, and in ameliorating recurrent spontaneous abortion. Moreover, therapeutic granulocyte transfusions may be of benefit in certain well- defined categories of patients infected with bacteria, yeast, and/or fungi. These include neonates with bacterial sepsis associated with bone marrow failure as well as severely neutropenic leukemic patients with an infection unresponsive to appropriate and specific antibiotic therapy. Many of the results obtained with the use of leukocyte depletion filters are tantalizing, but the actual clinical benefit of leukodepletion has not been established in most instances, because much of the available data are retrospective or from uncontrolled clinical trials. Moreover, issues of cost-effectiveness and quality control have not been considered adequately. Properly designed prospective clinical trials are essential to provide data with which to answer such questions and also to help define the optimal conditions required for the preparation of blood components ultimately destined for clinical use. Only with the availability of such data can sound decisions be made about the clinical value of leukodepletion.     

Post‐Transplantation Immunoadsorption Can Be Withheld in ABO‐Incompatible Kidney Transplant Recipients

After ABO‐incompatible kidney transplantation, postoperative plasma exchange (PE) or immunoadsorption (IA) is performed per protocol or depending on postoperative A/B‐titers to prevent acute rejection. However, the need for postoperative PE or IA is not known. Since 2006, 30 consecutive patients received three standard postoperative IAs. Starting from 2009, the last 46 patients received only preoperative IA. Preoperative desensitization consisted of rituximab, tacrolimus, mycophenolate mofetil, prednisone and intravenous immunoglobulins. Antigen‐specific IA was performed pre‐operatively with the Glycosorb device. Biopsy‐proven acute rejections either antibody‐mediated (AMR) or mixed cellular and antibody‐mediated (MAR) within 3 months were recorded. The postoperative titer in patients with postoperative IA did not exceed 1:16 (IgG 1:4 [<2–16] median and range). The postoperative IgG titer was not significantly different after abandoning postoperative IA, although three patients had titers of 1:32 and one patient even 1:128. Rejections tended to be more frequent in the group with postoperative IA: 6 AMR and 3 MAR were recorded in 30 patients, vs. 4 AMR and 1 MAR in the 46 patients without postoperative IA (30 vs. 11%, P = 0.067). Baseline characteristics differed however: in the group with postoperative IA the vast majority had blood group O (87 vs. 52%, P = 0.003). Also, the IgG titer on the day of transplantation was higher (1:4 [<2–16] vs. 1:2 [<2–32], P = 0.007). All 14 patients with AMR and MAR rejections had postoperative IgG titers ≤1:16. Postoperative removal of A/B‐antibodies can be safely removed from the ABOi transplantation protocol using strict preoperative criteria for antibody lowering.