Overexpression of cytosolic malate dehydrogenase (MDH2) causes overproduction of specific organic acids in Saccharomyces cerevisiae

Saccharomyces cerevisiae accumulates L-malic acid through a cytosolic pathway starting from pyruvic acid and involving the enzymes pyruvate carboxylase and malate dehydrogenase. In the present study, the role of malate dehydrogenase in the cytosolic pathway was studied. Overexpression of cytosolic malate dehydrogenase (MDH2) under either the strong inducible GAL10 or the constitutive PGK promoter causes a 6- to 16-fold increase in cytosolic MDH activity in growth and production media and up to 3.7-fold increase in L-malic acid accumulation in the production medium. The high apparent Km of MDH2 for L-malic acid (11.8 mM) indicates a low affinity of the enzyme for this acid, which is consistent with the cytosolic function in the enzyme and differs from the previously published Km of the mitochondrial enzyme (MDH1, 0.28 mM). Under conditions of MDH2 overexpression, pyruvate carboxylase appears to be a limiting factor, thus providing a system for further metabolic engineering of L-malic acid production. The overexpression of MDH2 activity also causes an evaluation in the accumulation of fumaric acid and citric acid. Accumulation of fumaric acid is presumably caused by high intracellular L-malic acid concentrations and the activity of the cytosolic fumarase. The accumulation of citric acid may suggest the intriguing possibility that cytosolic L-malic acid is a direct precursor of citric acid in yeast.

The cloning and characterization of a murine secretory leukocyte protease inhibitor cDNA

Human secretory leukocyte protease inhibitor (hSLPI) is produced by epithelial cells at mucosal surfaces, where it regulates both the neutrophil-mediated inflammation that characterizes inflammatory diseases, and pathogens themselves via both antiprotease and "defensin-like" activities. Additionally, hSLPI may regulate other processes such as cutaneous desquamation and placental invasiveness. To better understand the primary physiologic roles of SLPI, it will be important to establish a genetically tractable animal model, the most attractive candidate being the mouse. In this report, the cloning and characterization of murine (m) SLPI is described. mSLPI is encoded by a single copy gene, and appears structurally highly similar to hSLPI. At the same time, significant differences between mSLPI and hSLPI are presented, notably a difference in expression pattern, and a structural difference in the protease binding site that correlates with a difference in the spectrum of protease inhibiton. Such species-specific evolution of this protease inhibitor is notable given that species-specific structure-function differences have previously been reported for the alpha-1 antitrypsin family.

Differential cytokine regulation of complement proteins in human glomerular epithelial cells

We have previously shown in inbred strains of mice which naturally develop systemic lupus erythematosus that kidney C3, C2, C4 and factor B gene expression increases coincidently with the occurrence of glomerulonephritis, suggesting that local tissue complement gene expression could contribute to the pathogenesis of immune complex injury. In this study, we investigated the synthesis of complement proteins in glomerular epithelial cells (GECs) and its regulation. Using biosynthetic labelling, immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, we demonstrated that GECs synthesized C1r, C1s, C1 inhibitor, C3, C2 and factor B. Interferon-gamma induced increases in the synthesis of all these proteins. Both factor B and C3 proteins were increased following addition of either IL-1beta, IL-6 or TNF-alpha to GEC cultures; however, these cytokines did not increase either C2, C1r, C1s or C1-inhibitor biosynthesis. Lipopolysaccharide affected the biosynthesis of these proteins in a similar way. A semiquantitative analysis of the mRNA expression of some of these proteins by reverse-transcriptase polymerase chain reaction showed that these cytokine effects were pretranslational as there was enhancement of factor B mRNA expression by IL-1, TNF-alpha, IFN-gamma, IL-6 and endotoxin, but only IFN-gamma enhanced C1-inhibitor and C4 mRNA expression. These results may be of significance in the immunopathogenesis of glomerulonephritis, where it is likely that local complement production in GECs is independently regulated by cytokines, derived from resident glomerular mesangial cells or infiltrating monocyte/macrophages and T cells.

The cytosolic pathway of L-malic acid synthesis in Saccharomyces cerevisiae: the role of fumarase

Saccharomyces cerevisiae accumulates L-malic acid but not only minute amounts of fumaric acid. A 13C-nuclear magnetic resonance study following the label from glucose to L-malic acid indicates that the L-malic acid is synthesized from pyruvic acid via oxaloacetic acid. From this, and from previously published studies, we conclude that a cytosolic reductive pathway leading from pyruvic acid via oxaloacetic acid to L-malic acid is responsible for the L-malic acid production in yeast. The non-production of fumaric acid can be explained by the conclusion that, in the cell, cytosolic fumarase catalyzes the conversion of fumaric acid to L-malic but not the reverse. This conclusion is based on the following findings. (a) The cytosolic enzyme exhibits a 17-fold higher affinity towards fumaric acid than towards L-malic acid; the Km for L-malic acid is very high indicating that L-malic acid is not an in vivo substrate of the enzyme. (b) Overexpression of cytosolic fumarase does not cause accumulation of fumaric acid (but rather more L-malic acid). (c) According to 13C NMR studies there is no interconversion of cytosolic L-malic and fumaric acids.

Postgraduate medical education and flexible training

The importance of opportunities to train and work on a flexible basis are emphasized, particularly in the light of current medical staffing shortages in the NHS and the need to use resources effectively. The profile of the medical workforce is very different now compared with 40 years ago, and career pathways must therefore be modified.

Activated protein C resistance--low incidence in glaucomatous optic disc haemorrhage and central retinal vein occlusion

PURPOSE

Activated protein C (APC) resistance has recently been reported as conferring a sevenfold increase in the risk of venous thrombosis. It is linked to a genetic mutation in the factor V gene which occurs commonly (about 2% to 4% of the community have the mutation). Glaucoma patients with nerve fibre layer (NFL) haemorrhages on the optic disc and patients with central retinal vein occlusion (CRVO) were tested for APC resistance to determine if there was an association.

METHODS

Twenty-three patients with glaucomatous NFL haemorrhages and 23 patients with CRVO were tested. The CRVO cases included 11 with relatively young age of onset (mean 45.1 +/- 6.9 years) without conventional vascular risk factors. Eighty randomly selected Red Cross blood donor samples and 33 staff members were tested as controls. Clotting times with and without exogenous APC were recorded and an APC ratio determined. Cases with APC resistance were tested to confirm that they had the factor V Leiden gene.

RESULTS

No cases of APC resistance were identified in the glaucoma patients and only one of the younger CRVO patients tested positive, but four of 113 controls tested positive. The difference in prevalence between groups is not significant. The mean APC ratios for the three groups were very similar: NFL haemorrhages 5.46(+/- 1.62), CRVO 5.70(+/- 1.56), controls 5.34 ( +/- 1.19) p > 0.5.

CONCLUSION

There was not clear association detected between glaucomatous NFL haemorrhages or CRVO and APC resistance in this sample of patients. This negative finding is important due its known association with venous thrombosis elsewhere in the body.

Pathogenic role of anti-endothelial cell antibodies in vasculitis. An idiotypic experimental model

Idiotypic manipulation of naive mice has previously been used for induction of systemic autoimmune diseases (e.g., antiphospholipid syndrome, systemic lupus erythematosus, and Wegener's granulomatosis). The aim of this study focused on the utilization of this technique to induce the production of anti-endothelial cells Abs (AECA) and autoimmune vasculitis in a murine model. AECA were derived from a Wegener's granulomatosis patient's plasma. IgG was purified by absorption on a proteinase-3 affinity column resulting in the depletion of anti-neutrophil cytoplasmic Ab activity. The absorbed IgG fraction displayed a high titer of AECA as evidenced by a cyto-ELISA against unfixed human umbilical vein endothelial cells. BALB/c mice were actively immunized with the purified AECA. Three months after a boost injection with the human AECA, mice developed endogenous AECA (AB), but not Abs to proteinase-3, cardiolipin, or DNA. Histologic examination of lungs and kidneys revealed both lymphoid cell infiltration surrounding arterioles and venules; as well as deposition of Igs at the outer part of blood vessel walls. This experimental animal model of vasculitis, a product of our method of idiotypic manipulation, provides the first direct proof for the pathogenicity of AECA.

Pathogenic role of anti-endothelial cell antibodies in vasculitis. An idiotypic experimental model

Idiotypic manipulation of naive mice has previously been used for induction of systemic autoimmune diseases (e.g., antiphospholipid syndrome, systemic lupus erythematosus, and Wegener's granulomatosis). The aim of this study focused on the utilization of this technique to induce the production of anti-endothelial cells Abs (AECA) and autoimmune vasculitis in a murine model. AECA were derived from a Wegener's granulomatosis patient's plasma. IgG was purified by absorption on a proteinase-3 affinity column resulting in the depletion of anti-neutrophil cytoplasmic Ab activity. The absorbed IgG fraction displayed a high titer of AECA as evidenced by a cyto-ELISA against unfixed human umbilical vein endothelial cells. BALB/c mice were actively immunized with the purified AECA. Three months after a boost injection with the human AECA, mice developed endogenous AECA (AB), but not Abs to proteinase-3, cardiolipin, or DNA. Histologic examination of lungs and kidneys revealed both lymphoid cell infiltration surrounding arterioles and venules; as well as deposition of Igs at the outer part of blood vessel walls. This experimental animal model of vasculitis, a product of our method of idiotypic manipulation, provides the first direct proof for the pathogenicity of AECA.

Libman-Sacks endocarditis in the antiphospholipid syndrome: immunopathologic findings in deformed heart valves

OBJECTIVE

To examine the potential immunologic mechanism and involvement of antiphospholipid antibodies in the pathogenesis of heart valve lesions in patients with the antiphospholipid syndrome (APS).

METHODS

Immunoperoxidase and immunofluorescence staining methods were used to evaluate 13 heart valve specimens derived from eight patients with the APS, either primary or secondary to systemic lupus erythematosus. Primary antibodies to human immunoglobulins, complement components, serum albumin and a monoclonal anti-idiotypic antibody to human anticardiolipin antibodies (aCL) were employed. Various tissue specimens from a patient with the APS as well as deformed and normal valves from subjects without the APS were used as controls.

RESULTS

Linear subendothelial deposition consisting of immunoglobulins with complement components but not of a non-specific serum protein was found in deformed valves from patients with the APS. None of the control valves or tissues disclosed similar deposition. The same pattern and location of staining was obtained by the anti-idiotypic antibody to aCL. A significant amount of IgG immunoglobulins that bound to cardiolipin was eluted from a valve of a patient with secondary APS.

CONCLUSION

Deposits of immunoglobulins including aCL, and of complement components, are common in affected valves of patients with primary and secondary APS. Such deposits may be involved in the pathogenesis of valvular lesions.

Increased insulin-like growth factor binding protein-2 (IGFBP-2) gene expression and protein production lead to high IGFBP-2 content in malignant ovarian cyst fluid

Expression of insulin-like growth factor-I (IGF-I), its receptor and IGF-binding proteins (IGFBPs) by ovarian cancer cells and its mitogenic effect on these cells in vitro, suggest that IGF-I may have a role in regulation of human ovarian cancer. We have recently shown IGFBP-2 to be markedly elevated in malignant ovarian cyst fluid in vivo. To identify the origin of increased IGFBP-2 in these cyst fluids, the gene expression and protein content of IGFBP-2 were investigated in 14 malignant and four benign epithelial ovarian neoplasms. IGFBP-2 mRNA was detected in all ovarian specimens and was 2- to 30-fold higher in malignant than in benign neoplasms. Within the malignant tissues IGFBP-2 mRNA levels correlated with the aggressiveness of the tumour and were higher in invasive tumours than in those with borderline pathology. Southern blot analysis revealed no amplification of IGFBP-2 gene in the DNA samples from ovarian tumours regardless of their nature. IGFBP-2 was the major binding protein in tissue extracts, as measured by both Western ligand blotting and immunoblotting, and was significantly higher in malignant than in benign neoplasms. These findings were further supported by immunohistochemical detection of IGFBP-2 in tumour sections. Our data suggest that increased local production by the tumour in vivo is responsible for the increased IGFBP-2 levels in the cyst fluid bathing the ovarian malignancy. This may represent an autocrine regulatory mechanism for IGF-I proliferative effect of ovarian cancer.

The safety of topical beta-blockers in glaucoma treatment

While adverse effects are uncommon in patients who are otherwise fit and well, doctors should be aware of the implications of the systemic effects of these drugs, particularly the non-selective types, and particularly in the elderly.

C3, C4, factor B and HLA-DR alpha mRNA expression in renal biopsy specimens from patients with IgA nephropathy

The deposition of complement in the kidney mesangium is a constant finding associated with renal injury in IgA nephropathy, even though IgA does not bind complement. We have previously reported that complement gene expression in the kidney increases concurrently with the progression of immune complex disease in murine lupus nephritis. We have now studied the expression of C3, C4, factor B and HLA-DR alpha mRNA by in situ hybridization in renal biopsy specimens of patients with IgA nephropathy and compared these findings to those in patients with other immune-mediated diseases of the kidney, hereditary nephritis and normal kidney. In IgA nephropathy, C3 and factor B mRNA were expressed in the renal tubular epithelial cells, while no expression of either C3 or factor B mRNA was apparent in the glomerulus. Specimens from patients with other immune-mediated forms of chronic glomerulonephritis also showed a similar pattern of expression of C3 and factor B mRNA only in the tubules, but not in the glomerules. However, C3 and factor B mRNA were not found in normal kidney tissue or biopsy specimens from patients with hereditary nephritis. C4 mRNA was expressed in the tubular epithelial cells in all specimens examined, indicating that C4 mRNA is constitutively expressed in the human kidney. In IgA nephropathy HLA-DR alpha mRNA was observed in the interstitium, but not the tubules or glomerular cells. In contrast, HLA-DR alpha mRNA was present in the glomerulus and scattered in the interstitium in other immune-mediated kidney diseases. There was no expression of HLA-DR alpha mRNA in hereditary nephritis or normal kidney. Our findings, which reflect the immunopathogenic events in vivo, provide new insights as to the interpretation of the molecular immunology of this immune complex disease.

Exogenous insulin-like growth factor II enhances post-infarction regional myocardial function in swine

OBJECTIVES

Insulin-like growth factor II (IGF-II) promotes cardiac myocyte growth and contractility in vitro. This study was designed to investigate the effect of exogenous IGF-II on regional myocardial function at the area of infarct in the pig.

METHODS

Myocardial infarction was induced in 12 female anaesthetized pigs by affigel blue beads, embolizing microvessels of the left anterior descending coronary artery distribution. In the experimental group (n = 6), IGF-II (0.12 microgram.kg-1 in two animals and 0.6 microgram.kg-1 in four) was incorporated into the beads and delivered by them to the infarct area. Myocardial function was followed echocardiographically, and the excised heart was analysed immunohistochemically and histopathologically.

RESULTS

Myocardial function in injured zones, inversely related to an echocardiographic segmental wall motion score (mean +/- SEM), was similar between the two groups at baseline, but at 4 weeks post-infarction was significantly (P = 0.008) reduced in the control group (0.58 +/- 0.38 vs 3.42 +/- 0.84), in contrast to nearly baseline values in the experimental group (0.58 +/- 0.33 vs 1.17 +/- 0.42, P = 0.41). Cardiac performance in injured segments was significantly better after myocardial injury in the experimental group (P = 0.04). Tissue samples from both groups (4 weeks post-infarction), stained with haematoxylin and eosin demonstrated peri-infarct myocyte hypertrophy, corresponding to regions selectively stained by an antibody for CD56, which highlights growing cardiac myocytes. By image analysis semi-quantification, staining for CD56 was significantly (P = 0.04) higher in the peri-infarct region of the experimental group, as compared with controls (106.5 +/- 2.8 vs 92 +/- 4.4 gray level units). Microvessels stained for von-Willebrand factor were similar in number in both groups (P = 0.8), as were mesenchymal cells stained for vimentin (P = 0.7).

CONCLUSIONS

Exogenous IGF-II, delivered to the infarct area ameliorates regional cardiac function in the pig, perhaps by inducing peri-infarct myocyte growth.

Sodwanones G, H, and I, new cytotoxic triterpenes from a marine sponge

Three cytotoxic triterpenes, sodwanones G [5], H [6], and I [7], have been isolated from a marine sponge. The three structures were determined by interpretation of nmr spectra, and in the case of 5, also on the basis of the X-ray diffraction analysis. The X-ray diffraction analysis of two other earlier reported sodwanones, E [3] and F [4] is also discussed. The cytotoxic activity against several cancer cell lines, has been tested. IC50 values between 20 and 0.02 microM were obtained. Compounds 5 and 6 were 10- and 500-fold, respectively, more cytotoxic to A-549 cells than to any of the other cell lines tested (HT-29, MEL-28, P-388).