A multigene family of Heteractis magnificalysins (HMgs).

Sea anemones are passive predators. They use their specialized stinging cells (nematocysts) to immobilize any prey that blunders into them. A cnida fires, everting a tubule which delivers toxins that may stick to a prey. These toxins include neurotoxins, cytotoxins, cardiotoxins and haemolysins. Heteractis magnificalysins (HMgs) belong to a family of cytolysins from the sea anemone Heteractis magnifica. HMgs are 19.5kDa basic proteins of 177 amino acids with pI values ranging from 8 to 10. From 52 cloned HMg gene sequences, we showed that HMgs are encoded by a multigene family whose members are highly homologous to each other. HMg genes are intronless, and may have arisen by gene duplication, gene conversion or mutation. By modifying the extraction procedure, we purified more natural HMg proteins from H. magnifica, thus demonstrating that H. magnifica are naturally competent to produce a large number of HMg cytolysins. Native and recombinant HMg proteins differed from each other in their amino acid sequences and biological activities. In each H. magnifica, many cytolysin isoforms are produced. H. magnifica appeared to have evolved a survival mechanism whereby a large number of cytolysins of different biological properties are produced for defense and offence.

The effects of problem-based learning during medical school on physician competency: a systematic review.

BACKGROUND: Systematic reviews on the effects of problem-based learning have been limited to knowledge competency either during medical school or postgraduate training. We conducted a systematic review of evidence of the effects that problem-based learning during medical school had on physician competencies after graduation. METHODS: We searched MEDLINE, EMBASE, CINAHL, PsycINFO, Cochrane Databases, and the tables of contents of 5 major medical education journals from earliest available date through Oct. 31, 2006. We included studies in our review if they met the following criteria: problem-based learning was a teaching method in medical school, physician competencies were assessed after graduation and a control group of graduates of traditional curricula was used. We developed a scoring system to assess the quality of the studies, categorized competencies into 8 thematic dimensions and used a second system to determine the level of evidence for each competency assessed. RESULTS: Our search yielded 102 articles, of which 15 met inclusion criteria after full text review. Only 13 studies entered final systematic analysis because 2 studies reported their findings in 2 articles. According to self-assessments, 8 of 37 competencies had strong evidence in support of problem-based learning. Observed assessments had 7 competencies with strong evidence. In both groups, most of these competencies were in the social and cognitive dimensions. Only 4 competencies had moderate to strong levels of evidence in support of problem-based learning for both self-and observed assessments: coping with uncertainty (strong), appreciation of legal and ethical aspects of health care (strong), communication skills (moderate and strong respectively) and self-directed continuing learning (moderate). INTERPRETATION: Problem-based learning during medical school has positive effects on physician competency after graduation, mainly in social and cognitive dimensions.

Nitric oxide synthase and heme oxygenase expressions in human liver cirrhosis.

AIM: Portal hypertension is a common complication of liver cirrhosis. Intrahepatic pressure can be elevated in several ways. Abnormal architecture affecting the vasculature, an increase in vasoconstrictors and increased circulation from the splanchnic viscera into the portal system may all contribute. It follows that endogenous vasodilators may be able to alleviate the hypertension. We therefore aimed to investigate the levels of endogenous vasodilators, nitric oxide (NO) and carbon monoxide (CO) through the expression of nitric oxide synthase (NOS) and heme oxygenase (HO). METHOD: Cirrhotic (n=20) and non-cirrhotic (n=20) livers were obtained from patients who had undergone surgery. The mRNA and protein expressions of the various isoforms of NOS and HO were examined using competitive PCR, Western Blot and immunohistochemistry. RESULTS: There was no significant change in either inducible NOS (iNOS) or neuronal NOS (nNOS) expressions while endothelial NOS (eNOS) was up-regulated in cirrhotic livers. Concomitantly, caveolin-1, an established down-regulator of eNOS, was up-regulated. Inducible HO-1 and constitutive HO-2 were found to show increased expression in cirrhotic livers albeit in different localizations. CONCLUSION: The differences of NOS expression might be due to their differing roles in maintaining liver homeostasis and/or involvement in the pathology of cirrhosis. Sheer stress within the hypertensive liver may induce increased expression of eNOS. In turn, caveolin-1 is also increased. Whether this serves as a defense mechanism against further cirrhosis or is a consequence of cirrhosis, is yet unknown. The elevated expression of HO-1 and HO-2 suggest that CO may compensate in its role as a vasodilator albeit weakly. It is possible that CO and NO have parallel or coordinated functions within the liver and may work antagonistically in the pathophysiology of portal hypertension.

Replacement of tyrosine 181 by phenylalanine in gentisate 1,2-dioxygenase I from Pseudomonas alcaligenes NCIMB 9867 enhances catalytic activities.

xlnE, encoding gentisate 1,2-dioxygenase (EC 1.13.11.4), from Pseudomonas alcaligenes (P25X) was mutagenized by site-directed mutagenesis. The mutant enzyme, Y181F, demonstrated 4-, 3-, 6-, and 16-fold increases in relative activity towards gentisate and 3-fluoro-, 4-methyl-, and 3-methylgentisate, respectively. The specific mutation conferred a 13-fold higher catalytic efficiency (k(cat)/Km) on Y181F towards 3-methylgentisate than that of the wild-type enzyme.

Adenosine induced apoptosis in BHK cells via P1 receptors and equilibrative nucleoside transporters.

Adenosine, as a ubiquitous metabolite, mediates many physiological functions via activation of plasma membrane receptors. Mechanisms of most of its physiological roles have been studied extensively, but research on adenosine-induced apoptosis (AIA) has only started recently. In this study we demonstrate that adenosine dose-dependently triggered apoptosis of cultured baby hamster kidney (BHK) cells. Adenosine-induced apoptotic cell death was characterized by DNA laddering, changes in nuclear chromatin morphology and phosphatidylserine staining. Apoptosis was also quantified by flow cytometry. Results suggest the involvement of adenosine A1 and A3 receptors as well as equilibrative nucleoside transporters in apoptosis induced by adenosine. These results indicate a receptor-transporter co-signaling mechanism in AIA in BHK cells. The involvement of A1 and A3 receptors also implies a possible apoptotic pathway mediated by G protein-coupled receptors.

Chronic administration of aminoguanidine reduces vascular nitric oxide production and attenuates liver damage in bile duct-ligated rats.

BACKGROUND: Nitric oxide (NO) has been implicated in the pathogenesis of liver cirrhosis. This study investigated the activity of nitric oxide synthase (NOS) in cirrhosis induced by bile duct-ligation (BDL) with NOS inhibitors. METHOD: Three days after operation, rats were randomized to receive aminoguanidine (AG, 25 mg/kg/day) or L-N(G)-nitro-L-arginine methyl ester (L-NAME, 10 mg/kg/day) for 21 days. RESULTS: Vascular NO production, which was increased in BDL cirrhotic rats, was reduced by 75% with AG but not L-NAME chronic administration. AG treatment attenuated liver damage, while L-NAME aggravated it. AG significantly suppressed inducible NOS (iNOS) expression in aorta of BDL rats at both mRNA and protein level, but much less efficient in reducing it in liver. In contrast, endothelial NOS (eNOS) expression was not markedly affected. Calcium-independent NOS activity, which was dramatically increased in aorta of BDL rats, was abolished by AG treatment. In liver, however, both calcium-dependent and -independent NOS activity were increased by AG treatment. CONCLUSION: Chronic administration of AG could reduce systemic NO levels as well as suppress iNOS expression and activity in aorta of BDL rats. It also improved liver function, possibly because of its ability to increase hepatic NOS activity, and to correct the systemic hemodynamic disorders by decreasing vascular NO production.

Cloning and molecular characterization of the first aquatic hyaluronidase, SFHYA1, from the venom of stonefish (Synanceja horrida).

We report here for the first time the molecular characterization of a hyaluronidase from an aquatic source. SFHYA1 is the hyaluronidase found in the venom gland of stonefish, Synanceja horrida. Using a cDNA segment amplified with degenerate oligonucleotides based on the amino acid sequences of a conserved region in testicular-type hyaluronidases and a tryptic fragment of SFHYA1, clones encoding the precursor of this enzyme were isolated from a cDNA library prepared from stonefish venom glands. The deduced amino acid sequence of SFHYA1 shows that SFHYA1 is expressed as a precursor peptide with a 28-residue signal peptide for targeting it into endoplasmic reticulum. Mature SFHYA1 is a polypeptide composed of 449 residues containing three potential N-glycosylation sites, four putative hyaluronan-binding motifs [B(X)7B] and various residues implicated in substrate binding and catalysis. This cDNA was expressed in an active form in insect-cells but not in E. coli. Homology-based computational analyses suggested that SFHYA1 closely resembles the PH-20 family of hyaluronidases.

Temporal expression of hepatic inducible nitric oxide synthase in liver cirrhosis.

AIM: Nitric oxide (NO) has been implicated in the pathogenesis of liver cirrhosis. We have found inducible nitric oxide synthase (iNOS) can be induced in hepatocytes of cirrhotic liver. This study further investigated the temporal expression and activity of hepatic iNOS in cirrhosis development. METHODS: Cirrhosis was induced in rats by chronic bile duct ligation (BDL). At different time points after the operation, samples were collected to examine NO concentration, liver function, and morphological changes. Hepatocytes were isolated for determination of iNOS mRNA, protein and enzymatic activity. RESULTS: Histological examination showed early cirrhosis 1-2 wk after BDL, with advanced cirrhosis at 3-4 wk. Bilirubin increased dramatically 3 d after BDL, but decreased by 47% on d 14. Three weeks after BDL, it elevated again. Systemic NO concentration did not increase significantly until 4 wk after BDL, when ascites developed. Hepatocyte iNOS mRNA expression was identified 3 d after BDL, and enhanced with time to 3 wk, but reduced thereafter. iNOS protein showed a similar pattern to mRNA expression. iNOS activity decreased from d 3 to d 7, but increased again thereafter till d 21. CONCLUSION: Hepatic iNOS can be induced in the early stage, which increases with time as cirrhosis develops. Its enzymatic activity is significantly correlated with protein expression and histological alterations of the liver, but not with systemic NO levels, nor with absolute values of liver function markers.

Expression pattern of neuronal nitric oxide synthase in embryonic zebrafish.

Nitric oxide synthase catalyzes the production of nitric oxide, a multifunctional signaling molecule that affects diverse aspects of animal physiology such as cell proliferation, differentiation, neurotransmission and apoptosis. Here, we report the cloning and expression pattern of the zebrafish nnos. This gene was mapped to zebrafish linkage group 5. The spatial and temporal expression pattern of nnos in embryonic zebrafish was analyzed by whole mount in situ hybridization. nnos is widely expressed in the embryonic nervous system. Expression of zebrafish nnos appeared at 16 hours post-fertilization in the hypothalamus and by 3 days post-fertilization was present in discrete locations in the central nervous system as well as the enteric nervous system. Some nnos-positive cells were mapped to specific locations in the central nervous system using tyrosine hydroxylase as a specific marker indicating that nnos transcripts were present in the olfactory bulb, anterior diencephalon, posterior hypothalamus and anterior hindbrain.

Implementation of problem-based learning in Asian medical schools and students' perceptions of their experience.

BACKGROUND: Since the introduction of problem-based learning (PBL) at McMaster University in 1969, many medical schools in the USA, Canada and Europe have included PBL in their curricula. In the past decade, many medical schools in Asia have also done so. However, so far no one has questioned whether the outcomes expected of the learner in a PBL setting are applicable to students from different cultural upbringings. AIM: The aim of this study was to investigate the implementation of PBL in Asian medical schools, their students' perceptions of this new mode of teaching/learning and how the problems that have arisen may be overcome. METHOD: Published reports and conference presentations were gathered on the implementation of PBL in some Asian medical schools and comparisons of the experiences in PBL of Asian and students of other ethnic backgrounds. RESULTS: Most Asian medical schools and their students appear to be positive about adapting to PBL in their curriculum. The positive and negative observations appear to be similar to those experienced in non-Asian medical schools. The problems that arose for students in Asian medical schools in the early stages of implementing PBL appear to have been overcome after a period of adjustment with the help of supportive and open-minded tutors. The reports also suggested that trigger problems should be carefully designed to make them relevant and interesting for the students. CONCLUSION: Strong support from the academic administrators (dean and other staff responsible for implementation of the curriculum) in the introduction of PBL into the curriculum and careful training of both faculty and students appear to be key factors to ensure the successful implementation of PBL in Asian medical schools.

Expression of haem oxygenase in cirrhotic rat liver.

The haem oxygenase (HO)/carbon monoxide (CO) system has been implicated as a modulator of hepatobiliary function. This study investigated HO expression in the process of cirrhosis development, as well as its relationship to nitric oxide synthase (NOS). Liver cirrhosis was induced in rats by chronic bile duct ligation (BDL). HO mRNA expression was evaluated by competitive RT-PCR, while protein expression was determined by immunoblotting and immunohistochemistry. In liver tissue where cirrhosis had fully developed, the expression levels of HO-1 were greatly enhanced at both mRNA and protein level compared with sham livers. Immunohistochemistry showed that HO-1 was induced in hepatocytes and enhanced in some of the Kupffer-like cells in BDL livers. In contrast, there was no difference between the sham and the BDL livers for the expression levels of HO-2. Interestingly, administration of the NOS inhibitor aminoguanidine (AG) or N(G)-nitro-L-arginine methyl ester inhibited HO-1 expression. To study further the role of HO-1 in the development of liver cirrhosis, hepatocytes were isolated from the rats at different time points after BDL operation. HO-1 was expressed in hepatocytes at high levels during the early onset of cirrhosis but dropped slightly at a later stage of cirrhosis. Zinc protoporphyrin IX (ZnPP), an HO inhibitor, blocked HO-1 expression in hepatocytes from BDL cirrhotic rats, but enhanced the activity of inducible NOS (iNOS) in BDL hepatocytes. In conclusion, HO-1 was induced in the hepatocytes of rats undergoing cirrhosis, suggesting that HO-1 plays a role in the development of liver cirrhosis. Induction of HO-1 may be mediated partially by iNOS. However, once it is induced, HO-1 may be important in modulating iNOS activity, thus playing a protective role in liver cirrhosis.

Differential expression and localization of nitric oxide synthases in cirrhotic livers of bile duct-ligated rats.

Increased vascular nitric oxide (NO) production has been implicated in the pathogenesis of the hyperdynamic circulation in liver cirrhosis. This study investigated the expression of three isoforms of NO synthase (NOS) in rat cirrhotic livers. Cirrhosis was induced by chronic bile duct ligation (BDL). NOS enzyme activity was assessed by L-citrulline generation. Competitive RT-PCR was performed to detect the mRNA levels of NOS. In situ hybridization was done to localize NOS mRNA. Protein expression of NOS was evaluated by Western blotting and immunohistochemistry. The L-citrulline assay showed that constitutive NOS (cNOS) enzymatic activity was decreased, while inducible NOS (iNOS) activity was increased in BDL livers. Both endothelial NOS (eNOS) and neuronal NOS (nNOS) mRNA were detected in BDL and sham rats, but with enhanced expression in BDL rats. eNOS protein was redistributed with less expression in sinusoidal endothelial cells, but the total levels in liver were not changed. nNOS was induced in hepatocytes of BDL rats, in contrast to only a weak signal observed around some blood vessels in sham livers. Intense mRNA and protein expression of iNOS was induced in livers of BDL rats and was localized in hepatocytes, with no or a negligible amount in control livers. In conclusion, iNOS was induced in cirrhotic liver with its activity increased. In contrast, cNOS activity was impaired, regardless of unchanged eNOS protein levels and enhanced nNOS expression. These results suggest that all three types of NOS have a role in cirrhosis, but their expression and regulation are different.

Autonomic effects of some scorpion venoms and toxins.

1. The autonomic effects of venoms and toxins from several species of scorpions, including the Indian red scorpion Mesobuthus tamulus, the Chinese scorpion Buthus martensi Karsch and the Israeli scorpion Leiurus quinquestriatus quinquestriatus, all belonging to Buthidae, and the Asian black scorpions Heterometrus longimanus and Heterometrus spinifer, belonging to Scorpionidae, are reviewed. 2. The effects of the venoms of M. tamulus and L. q. quinquestriatus on noradrenergic and nitrergic transmission in the rat isolated anococcygeus muscle revealed that both venoms mediated their pharmacological effects via a prejunctional mechanism involving the activation of voltage-sensitive sodium channels with consequent release of neurotransmitters that mediate target organ responses, similar to the effects mediated by other alpha-scorpion toxins. 3. Two new toxins, Makatoxin I and Bukatoxin, were purified to homogeneity from the venom of B. martensi Karsch. Determination of their complete amino acid sequences confirmed that both toxins belonged to the class of alpha-scorpion toxins. The effects of both toxins on noradrenergic and nitrergic transmission in the rat anococcygeus muscle provided firm evidence that their pharmacological actions also closely resembled those mediated by other alpha-scorpion toxins on neuronal voltage-sensitive sodium channels. 4. The venoms of H. longimanus and H. spinifer were found to have high concentrations of noradrenaline (1.8 +/- 0.3 mmol/L) and relatively high concentrations of acetylcholine (79.8 +/- 1.7 micromol/L) together with noradrenaline (146.7 +/- 19.8 micromol/L), respectively, which can account for their potent direct cholinergic and noradrenergic agonist actions in the rat anococcygeus muscle. 5. Our studies confirmed that the rat anococcygeus muscle is an excellent nerve-smooth muscle preparation for investigating the effects of bioactive agents on noradrenergic and nitrergic transmission, as well as the direct agonist actions of these agents on post-synaptic alpha-adrenoceptors and M3 muscarinic cholinoceptors. Although many studies, including our own, have documented that scorpion venoms and toxins mediate their primary effects via a prejunctional mechanism that leads to the marked release of various autonomic neurotransmitters, our studies have shown that there are exceptions to this generally accepted phenomenon. In particular, we have provided firm evidence to show that the venoms from H. longimanus and H. spinifer do not have such a prejunctional site of action but, instead, the venoms mediate their autonomic effects through direct agonist actions on post-junctional muscarinic M3 cholinoceptors and alpha-adrenoceptors.

Bioactive proteins from stonefish venom.

1. Of all the venomous fish known, the stonefish is one of the most commonly encountered by man. Studies on its venom started in the 1950s, but little work was performed after that until several groups revived interest in the venom in the 1980s after easier accessibility to the fish. 2. Stonefish venom is a mixture of proteins, containing several enzymes, including hyaluronidase of high specific activity. A purified stonefish hyaluronidase has been characterized. 3. Several of the effects of the crude venom have been isolated to a protein lethal factor that has cytolytic, neurotoxic and hypotensive activity. This protein is stonustoxin from Synanceja horrida, trachynilysin from Synanceja trachynis and verrucotoxin from Synanceja verrucosa. 4. The biochemical properties and activities of these protein lethal factors are reviewed.

Nitric oxide in liver diseases: friend, foe, or just passerby?

Research on the free radical gas, nitric oxide (NO), during the past twenty years is one of the most rapid growing areas in biology. NO seems to play a part in almost every organ and tissue. However, there is considerable controversy and confusion in understanding its role. The liver is one organ that is clearly influenced by NO. Acute versus chronic exposure to NO has been associated with distinct patterns of liver disease. In this paper we review and discuss the involvement of NO in various liver diseases collated from observations by various researchers. Overall, the important factors in determining the beneficial versus harmful effects of NO are the amount, duration, and site of NO production. A low dose of NO serves to maximize blood perfusion, prevent platelet aggregation and thrombosis, and neutralize toxic oxygen radicals in the liver during acute sepsis and reperfusion events. NO also demonstrates antimicrobial and antiapoptosis properties during acute hepatitis infection and other inflammatory processes. However, in the setting of chronic liver inflammation, when a large sustained amount of NO is present, NO might become genotoxic and lead to the development of liver cancer. Additionally, during prolonged ischemia, high levels of NO may have cytotoxic effects leading to severe liver injury. In view of the various possible roles that NO plays, the pharmacologic modulation of NO synthesis is promising in the future treatment of liver diseases, especially with the emergence of selective NO synthase inhibitors and cell-specific NO donors.

Induction of arginase II in livers of bile duct-ligated rats.

Nitric oxide (NO) has been implicated in playing a role in liver cirrhosis, but the regulatory mechanisms are still unclear. As arginase shares a common substrate with NO synthase (NOS), the aim of this study was to investigate the expression of arginase I and II in cirrhotic liver. Liver cirrhosis was induced in rats by chronic bile duct ligation (BDL). Controls were sham-operated. Competitive polymerase chain reaction was performed to assay the expression of messenger RNA of arginase I and II. Protein expression was detected by immunohistochemistry and western-blotting. The level of arginine in plasma was lower in BDL rats, while the ornithine level in plasma was correspondingly higher (r= -0.96, P<0.0001). Arginase I messenger RNA was reduced significantly in BDL rats (3.34+/-0.32 vs. 1.32+/-0.21 x 10(4) attomole/microg of total RNA, sham vs. BDL, P<0.001), as well as arginase I protein. In contrast, arginase II mRNA was induced in the livers of BDL rats, with negligible expression in controls (0.35+/-0.11 vs. 3.64+/-0.54 attomole/microg of total RNA, sham vs. BDL, P<0.001). Arginase II protein was localized in some hepatocytes and hyperplastic bile ductular epithelial cells of cirrhotic livers but not in control livers. In conclusion, arginase II was induced in BDL livers, while the expression of arginase I was down-regulated. These data suggest that arginase I and II are regulated differently and may have different functions in the livers of BDL rats. Reduction of arginase I in BDL livers may be responsible for the lowering of arginine levels in the plasma, while induction of arginase II could be important in regulating NO synthesis as well as other important mechanisms involved in liver cirrhosis.