Role of Q190 of MuLV RT in ddNTP resistance and fidelity of DNA synthesis: a molecular model of interactions with substrates

Gln190 of MuLV reverse transcriptase (RT) plays an important role in the catalytic mechanism of MuLV RT for its conservative and non-conservative mutant derivatives exhibit low catalytic activity. We now report that both Q190N and Q190A MuLV RTs are more efficient in their activity to incorporate ddNTPs and exhibit higher fidelity than the wild-type (WT) enzyme of DNA synthesis in both RNA- and DNA-directed reactions. To obtain some insight into the structural basis for the differential utilization of dNTP and ddNTP by the mutant enzymes, we modeled the binary and the ternary complexes of MuLV RT using corresponding HIV-1 RT structures and available structure of the fragment of MuLV RT. Q190 of MuLV RT appears to be essential for the interaction with 3'OH of dNTP. The lack of a 3'OH moiety in ddNTP does not permit the binding of ddNTPs to WT MuLV RT. However, the shorter side chain of Q190N (or A) mutant MuLV RT and the absence of 3'OH in ddNTP result in the rearrangement of hydrophobic interactions favoring the binding and limited incorporation of ddNTPs. In addition, while modeling the binary and ternary complexes of MuLV RT, we noted that in the formation of the ternary complex, an interaction of Q190 with dNTP substrate requires a shift from its interaction with the template base. This may be achieved by a small conformational change or motion of the loop between beta9 and alphaH containing Q190, which may correspond to the conformational change step requiring participation of Q190 during the catalytic reaction as reported in an earlier biochemical investigation.

Diagnostic value of ileoscopy: a report from India

Our aim was to present a report about the usefulness of ileoscopy as an adjunct to colonoscopy, as studied in India, in the face of a dearth of such reports from the developing countries and to study the role of ileoscopy in increasing the yield of diagnosis reached and modified. In a prospective study in 66 consecutive patients undergoing colonoscopy for various indications, colonoscopy/ileoscopy was performed with a forward viewing fiberoptic colonoscope. Details of ileal mucosa, time taken to reach ileum, and length of ileum intubated were noted. Of the 66 patients undergoing colonoscopy, cecum could be reached in 62, whereas ileum was successfully intubated in 57 (86.4%). In 13 (22.5%) cases, additional information was obtained. In eight (14.4%) cases, diagnosis was established on ileoscopy. Of these, two were of lower gastrointestinal (GI) bleed (typhoid ulcer and nonsteroidal antiinflammatory drug ulcer), one had lymphoma, two had tuberculosis, and three were cases of reactive arthritis with ulcers in terminal ileum. After ileoscopy, the diagnosis was altered in five (8.7%) cases. Time taken to reach ileum from cecum was 3.3 +/- 2.5 minutes and the length of examined ileum was 17.3 +/- 7.5 cm. Ileoscopy is a useful adjunct to colonoscopy that not only helps to modify the diagnosis but also established them.

Preparation of the cervix for surgical termination of pregnancy in the first trimester

Worldwide, surgical vacuum aspiration is the method of choice of terminating first trimester unwanted pregnancy. Cervical priming prior to surgical evacuation reduces the risks of cervical injury by making the cervix softer and easier to dilate. Over the years, a number of effective methods of cervical priming have became available: osmotic dilators; antiprogesterone and prostaglandins. Of these, prostaglandins remain the most widely used method of cervical preparation. However many of the natural and synthetic analogues of prostaglandins are either expensive or associated with troublesome side-effects. More recently, misoprostol, a synthetic 15-deoxy-16 hydroxy 16-methyl analogue of naturally occurring prostaglandin E, used in the management of peptic ulcers, has established a lead for cervical priming in terms of availability, ease of administration, cost and effectiveness. In fact it appears that both oral and vaginal misoprostol given at dosages of 400 microg are effective for cervical priming when administered 3 h prior to surgical vacuum aspiration. Now that the use of misoprostol for cervical priming has been validated, its widespread use in gynaecological practice is expected.

Recruitment properties of intramuscular and nerve-trunk stimulating electrodes

Functionally useful reanimation of paralyzed limbs generally requires reliable, finely graded control of muscle recruitment and force with minimal fatigue. We used force and electromyographic (EMG) recordings in combination with myofibrillar adenosine triphosphatase activity and glycogen depletion analysis to investigate the recruitment properties of intramuscular (IM) and nerve cuff (NC) stimulating electrodes implanted acutely or chronically in cat hindlimbs. Overall, 32 muscles were submaximally stimulated with current intensities producing approximately 20% of maximal twitch force using 330 ms trains of pulses at 20 and 40 pps. Both the glycogen-depletion and fatigue-test results were found to be difficult to interpret because NC stimulation resulted in surprisingly unstable recruitment during such trains. Fluctuations of force and M-waves within trains of identical stimuli were significantly greater for NC than for IM stimulation. NC stimulation produced much steeper recruitment curves and a reduced tetanus/twitch ratio compared to IM stimulation. IM stimulation produced more reliable and less fatigable recruitment of a mix of motor unit types that tended to be localized in neuromuscular compartments containing, or adjacent to, the IM electrode. We hypothesize that trains of submaximal stimulation applied through NC electrodes resulted in fluctuating recruitment because this electrode configuration magnifies the effects of refractoriness and small changes in axonal excitability during pulse trains.

The J-helix of Escherichia coli DNA polymerase I (Klenow fragment) regulates polymerase and 3'- 5'-exonuclease functions

To assess the functional importance of the J-helix region of Escherichia coli DNA polymerase I, we performed site-directed mutagenesis of the following five residues: Asn-675, Gln-677, Asn-678, Ile-679, and Pro-680. Of these, the Q677A mutant is polymerase-defective with no change in its exonuclease activity. In contrast, the N678A mutant has unchanged polymerase activity but shows increased mismatch-directed exonuclease activity. Interestingly, mutation of Pro-680 has a Q677A-like effect on polymerase activity and an N678A-like effect on the exonuclease activity. Mutation of Pro-680 to Gly or Gln results in a 10-30-fold reduction in k(cat) on homo- and heteropolymeric template-primers, with no significant change in relative DNA binding affinity or K(m)((dNTP)). The mutants P680G and P680Q also showed a nearly complete loss in the processive mode of DNA synthesis. Since the side chain of proline is generally non-reactive, mutation of Pro-680 may be expected to alter the physical form of the J-helix itself. The biochemical properties of P680G/P680Q together with the structural observation that J-helix assumes helical or coiled secondary structure in the polymerase or exonuclease mode-bound DNA complexes suggest that the structural alteration in the J-helix region may be responsible for the controlled shuttling of DNA between the polymerase and the exonuclease sites.

Syntheses and biological evaluation of 3-substituted amino-1-aryl-6-hydroxy-hex-2-ene-1-ones as antioxidant and hypolipidemic agents

A new series of compounds belonging to 3-substituted amino-1-aryl-6-hydroxy-hex-2-ene-1-ones (4-12a-e) have been synthesized and evaluated for antioxidant and hypolipidemic activities. Amongst all the synthesized compounds, seven compounds, namely 5b, 5d, 6e, 8a, 8b, 10b and 11a, exhibit better antioxidant activity than probucol. Two compounds, 5d and 10b, have been evaluated in detail for antioxidant and hypolipidemic activities and show comparable activity profile to that of probucol and guggulipid. From the present study it may be postulated that the mechanism of action of these compounds could be through activation of lecithin cholesterol acyltransferase (LCAT), liver lipolytic activity, increased faecal bile acid secretion and inhibition of hepatic cholesterol biosynthesis.

Reversible portal hypertension due to tuberculosis

Presentation of abdominal tuberculosis with portal hypertension is rare. We report a 25-year-old man with portal hypertension due to compression of the portal vein by tuberculous lymph nodes at the hepatic hilum. After antitubercular therapy, features of portal hypertension disappeared as the nodes regressed.

A carboxylate triad is essential for the polymerase activity of Escherichia coli DNA polymerase I (Klenow fragment). Presence of two functional triads at the catalytic center

The catalytic roles of two essential active-site aspartates at positions 705 and 882 of Escherichia coli DNA polymerase I have been well established (Steitz, T. A. (1998) Nature 391, 231-232). We now demonstrate that the participation of at least one additional carboxylate, a glutamate at position 710 or 883, is obligatory for catalysis. This conclusion has been drawn from our investigation of the properties of single (E710D, E710A, E883D, and E883A) and double (E710D/E883D and E710A/E883A) substitutions of residues Glu(710) and Glu(883). While single substitutions of either of the glutamates resulted in some reduction in polymerase activity, the mutant enzyme with simultaneous substitution of both glutamates with alanine exhibited a nearly complete loss of activity. Interestingly, substitution with two aspartates in place of the glutamates resulted in an enzyme species that catalyzed DNA synthesis in a strictly distributive mode. Pyrophosphorolytic activity of the mutant enzymes reflected their polymerase activity profiles, with markedly reduced pyrophosphorolysis by the double mutant enzymes. Moreover, an evaluation of Mg(2+) and salt optima for all mutant enzymes of Glu(710) and Glu(883) revealed significant deviations from that for the wild type, implying a possible role of these glutamates in metal coordination as well as in maintaining the structural integrity of the active site.

p38 mitogen-activated protein kinase pathway protects adult rat ventricular myocytes against beta -adrenergic receptor-stimulated apoptosis. Evidence for Gi-dependent activation

We have shown that stimulation of beta-adrenergic receptors (beta-AR) by norepinephrine (NE) increases apoptosis in adult rat ventricular myocytes (ARVMs) via a cAMP-dependent mechanism that is antagonized by activation of G(i) protein. The family of mitogen-activated protein kinases (MAPKs) is involved in the regulation of cardiac myocyte growth and apoptosis. Here we show that beta-AR stimulation activates p38 kinase, c-jun N-terminal kinases (JNKs), and extracellular signal-regulated kinase (ERK1/2) in ARVMs. Inhibition of p38 kinase with SB-202190 (10 micrometer) potentiated beta-AR-stimulated apoptosis as measured by flow cytometry and terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) staining. SB-202190 at this concentration specifically blocked beta-AR-stimulated activation of p38 kinase and its downstream substrate MAPK-activated protein kinase-2 (MAPKAPK2). Pertussis toxin, an inhibitor of G(i)/G(o) proteins, blocked the activation of p38 kinase and potentiated beta-AR-stimulated apoptosis. Activation of G(i) protein with the muscarinic receptor agonist carbachol protected against beta-AR-stimulated apoptosis. Carbachol also activated p38 kinase, and the protective effect of carbachol was abolished by SB-202190. PD-98059 (10 micrometer), an inhibitor of ERK1/2 pathway, blocked beta-AR-stimulated activation of ERK1/2 but had no effect on apoptosis. These data suggest that 1) beta-AR stimulation activates p38 kinase, JNKs, and ERK1/2; 2) activation of p38 kinase plays a protective role in beta-AR-stimulated apoptosis in cardiac myocytes; and 3) the protective effects of G(i) are mediated via the activation of p38 kinase.

Optical encryption by double-random phase encoding in the fractional Fourier domain

We propose an optical architecture that encodes a primary image to stationary white noise by using two statistically independent random phase codes. The encoding is done in the fractional Fourier domain. The optical distribution in any two planes of a quadratic phase system (QPS) are related by fractional Fourier transform of the appropriately scaled distribution in the two input planes. Thus a QPS offers a continuum of planes in which encoding can be done. The six parameters that characterize the QPS in addition to the random phase codes form the key to the encrypted image. The proposed method has an enhanced security value compared with earlier methods. Experimental results in support of the proposed idea are presented.

Comparison of seven and fourteen days of lansoprazole, clarithromycin, and amoxicillin therapy for eradication of Helicobacter pylori: a report from India

BACKGROUND

In developed countries, a 1-week regimen of combined proton pump inhibitors and two antibiotics is considered adequate for Helicobacter pylori eradication. However, there is a paucity of reports from developing countries on treatment duration of less than 14 days. We compared efficacy of 7 and 14 days of lansoprazole (L), clarithromycin (C), and amoxicillin (A) combinations for eradication of H. pylori.

PATIENTS AND METHODS

Forty-six consecutive patients who presented with upper gastrointestinal symptoms and tested positive for H. pylori infection were included in the study. In every patient, after performance of upper gastrointestinal endoscopy, antral biopsies were obtained. H. pylori infection was diagnosed by positive rapid urease test and identification of organisms on antral histology. Patients were randomly selected to receive lansoprazole, 30 mg once daily, plus clarithromycin, 250 mg twice daily, plus amoxicillin, 500 mg three times daily for 2 weeks (group 1; n = 24; age, 36 +/- 12 years; 18 men) or 1 week (group 2; n = 22; age, 45 +/- 15 years; 12 men). One month after completion of treatment, repeat upper gastrointestinal endoscopy was performed. H. pylori eradication was defined as absence of organism on histopathological examination of both antrum and body of stomach and negative rapid urease test.

RESULTS

Eradication rate was higher in group 1 (23 of 24; 96%) as compared to group 2 (12 of 22; 54%; p <.05). One patient in group 1 had diarrhea, and one patient in group two had skin rash and itching.

CONCLUSIONS

Fourteen-day therapy with lansoprazole, clarithromycin, and amoxicillin is highly effective in eradication of H. pylori. Reducing duration of therapy to 7 days significantly lowers eradication rates.

Endoscopic dilation for treatment of anastomotic leaks following transhiatal esophagectomy

BACKGROUND AND STUDY AIMS

Anastomotic leak is a known complication after transhiatal esophagectomy (THE) and cervical esophagogastric anastomosis. Conservative management takes a long time to heal such leaks. We assessed the role of endoscopic dilation in patients with anastomotic leak following THE.

PATIENTS AND METHODS

Eight consecutive patients (seven men, one woman; mean age 51) with anastomotic leak following THE were subjected to endoscopic dilation using Savary Gilliard dilators of 7-15 mm diameter. The mean interval between surgery and detection of leak was 9 days (range 5-22 days) and dilation was performed at a mean interval of 11.4 days (range 1-20 days) after detection of the leak.

RESULTS

Drainage from fistulas stopped completely after 1-8 days (mean 3 days). X-ray with water soluble contrast showed closure of the fistula in all cases. Duration of follow-up ranged from 2 to 12 months. Anastomotic strictures developed in three patients. These patients required three sessions each of repeat dilation, and were alive at follow-up periods of 2, 4, and 12 months, respectively. One patient developed recurrence of growth at an anastomotic site. Four patients died because of distant metastasis.

CONCLUSIONS

Bougie dilation of anastomotic sites is a safe and effective technique for the healing of anastomotic leaks following THE. However there is a need for a prospective randomized trial comparing endoscopic dilation with no dilation in patients with anastomotic leaks following THE.

Adrenergic overload and apoptosis in heart failure: implications for therapy

Sympathetic nervous system activity to the myocardium is increased in patients with heart failure. It is now appreciated that norepinephrine (NE), the primary sympathetic neurotransmitter, can exert direct adverse effects on cardiac myocytes and might thereby contribute to pathological remodeling, a chronic process which leads to progressive left ventricular (LV) chamber dilation and loss of contractile function. The demonstration of apoptosis in failing human hearts has led to the thesis that continuing loss of viable myocytes is a mechanism for progressive myocardial failure. For many years it has been appreciated that chronic exposure to catecholamines can exert a toxic effect on the myocardium. In vitro studies in cultured cardiac myocytes show that tonic exposure to NE increases the number of apoptotic myocytes via stimulation of the beta-adrenergic receptor (beta-AR) pathway. Interestingly, a beta1-AR selective antagonist completely prevented NE-stimulated apoptosis, whereas a beta2-AR selective antagonist increased the amount of apoptosis, suggesting that beta1- versus beta2-AR may couple to different signaling pathways. In rats, isoproterenol infusion for as little as 12 hours increased the frequency of terminal deoxynucleotidyltransferase-mediated nick end-labeling (TUNEL)-positive myocytes. Likewise, mice that overexpress beta1-AR or G alpha s in the myocardium develop left ventricular dilation, contractile dysfunction and apoptosis. Although the link between apoptosis and myocardial failure remains to be proven, these in vitro and in vivo observations provide a rational mechanism by which beta-AR antagonists may help to prevent or slow LV remodeling and failure in patients.

Gynaecology in the new millennium

Great challenges await the gynaecologist in the 21st century. While advances in medical technology necessitate that gynaecology move more towards a medical discipline than a surgical one, gynaecologists will be expected to play an increasingly important role in the modern woman's life. This fundamental change is influenced by four main factors, namely, the world's aging population, spread of information technology, advances in molecular based medical therapy, and the changing lifestyle of the woman in the next century. Our role cannot get any lesser as we continue to advise, educate and facilitate the lives of women, and we must aspire a new generation of responsible gynaecologists to continue this ambition.

Budd-Chiari syndrome: our experience of 71 patients

BACKGROUND

Hepatic venous outflow obstruction (Budd-Chiari syndrome) is frequently encountered as a cause of portal hypertension at our centre.

METHODS AND RESULTS

We studied the clinical presentation, therapeutic modalities and outcome of 71 patients with hepatic venous outflow obstruction between 1992 and 1997. Twenty-seven patients presented with acute disease, while 44 had chronic presentation. Abdominal pain, distension, jaundice and upper gastrointestinal bleeding were the commonest presenting symptoms. The majority of patients had distended veins, hepatomegaly, splenomegaly, ascites and ankle oedema. The diagnosis was made on the basis of inferior vena cavography/functional hepatography and pulsed Doppler ultrasonography and/or liver biopsy in 39 patients and pulsed Doppler ultrasonography and/or liver biopsy in 32 patients. Pulsed Doppler ultrasonography accurately detected the site of the block in 31 of 39 patients (79.4%). The obstruction was in the hepatic vein in 20 patients, in the inferior vena cava in 10, and in both in 41 patients. Aetiologically, four had pregnancy-related disease, four tumour-related, three hypercoagulable states, 18 inferior vena cava membranes and 42 were idiopathic. Of 30 patients in whom liver biopsy was carried out, eight had centrizonal congestion and necrosis, 13 had mixed features and nine had established cirrhosis. Seven patients underwent a shunt operation and surgical membranotomy was carried out in one. Three patients (4.2%) died in the hospital.

CONCLUSIONS

Hepatic venous outflow obstruction is a common problem; patients present with abdominal pain, distension, jaundice, distended veins, ascites and ankle oedema. Chronic presentation is more frequent. Pulsed Doppler ultrasound, venography and liver biopsy are very helpful in diagnosis.

Myocardial-directed overexpression of the human beta(1)-adrenergic receptor in transgenic mice

The beta(1)-adrenergic receptor (AR) is the dominant subtype in non-failing and failing myocardium. beta(1)-AR signaling, by the endogenous neurotransmitter norepinephrine, is central to the regulation of myocardial contractility. In heart failure, the beta(1)-AR undergoes subtype-selective downregulation which may protect against the increased cardiac adrenergic drive associated with this pathophysiological state. To examine the hypothesis that chronically increased beta(1)-AR mediated signaling has adverse myocardial effects, transgenic mice overexpressing the human beta(1)-AR in a cardiac-selective context were produced, utilizing an alpha-myosin heavy chain (MHC) promoter. In these mice, beta(1)-AR protein abundance was approximately 24-46-fold (1-2 pmol/mg protein) that of wild-type mice. Histopathological examination of young (4 months old) and old (approximately 9 months old) transgenic mouse hearts consistently demonstrated large areas of interstitial replacement fibrosis, marked myocyte hypertrophy and myofibrilar disarray. In addition, increased expression of the pre-apoptotic marker, Bax, was observed coincident with regions of fibrosis accompanied by an increased apoptotic index, as measured by TUNEL assay. Older non-transgenic mice exhibited a slight tendency towards a decreased fractional shortening, whereas older beta(1)-AR transgenic mice had a marked reduction in fractional shortening (%FS approximately 30) as determined by echocardiography. Additionally, older beta(1)-AR transgenic mice had an increased left ventricular chamber size. In summary, cardiac-directed overexpression of the human beta(1)-AR in transgenic mice leads to a significant histopathological phenotype with no apparent functional consequence in younger mice and a variable degree of cardiac dysfunction in older animals. This model system may ultimately prove useful for investigating the biological basis of adrenergically-mediated myocardial damage in humans.

Protective efficacy of trypsin inhibitor on the the gut following rotavirus infection in malnourished infant mice

Epidemiologic data suggest a close relationship between protein energy malnutrition (or protein energy malnourished) (PEM) and development of infectious diarrheal diseases. In the present studies, the impact of trypsin inhibitor (TI) on the gut following rotavirus (RV) infection was investigated in PEM young growing inbred balb/c mice. The animals were divided into four groups: (1) control; (2) PEM; (3) PEM+RV and (4) PEM+ RV+TI. Control and PEM animals were orally inoculated with normal saline, PEM+RV animals were given 50 microl RV (100ID50) and PEM+RV+TI animals were inoculated with 0.6 mg TI/g body weight + 50 micronl RV. The body weight of each animal was recorded. Six animals from each group were sacrificed on days 0, 1, 3, 5, 7 and 10 post inoculation by cervical dislocation. The intestines were removed, everted and homogenized in ice-cold saline. Leucine aminopeptidase (LAP), glutathione (GSH) levels and L-leucine uptake were determined in the jejunum and ileum. Body weight was decreased in PEM and PEM+RV groups compared to the controls. LAP and leucine uptake levels were elevated in the PEM group but decreased in the PEM+RV group. GSH levels were decreased in the PEM+RV group. Enzyme activity, GSH and LAP uptake levels were restored in the PEM+RV+TI group. The study shows the protective role of soybean TI against RV infection in malnourished mice.

Helicobacter pylori infection in chronic smokers with non ulcer dyspepsia

BACKGROUND/AIMS

Both H. pylori infection and smoking are risk factors for acid peptic disorders. There is paucity of data on relationship between smoking and H. pylori infection. Therefore, we studied prevalence of H. pylori infection in smokers with non-ulcer dyspepsia (NUD).

PATIENTS AND METHODS

30 smokers with NUD (age 29.5 +/- 1.2 years; all men) and 30 non-smokers with NUD (age 29.2 +/- 1.6 years; all men) were included. None was on antiulcer drugs or antibiotics for more than 2 weeks. Upper gastrointestinal endoscopy was performed and antral biopsies obtained were subjected to rapid urease test, Gram's staining, culture and histopathology. Patient was considered H. pylori positive, if culture was positive or combination of histopathology plus rapid urease test or Gram's staining plus rapid urease test was positive.

RESULTS

24 of 30 (80%) smokers and 13 of 30 (43%) non smokers were positive for H. pylori infection (p < 0.001). There was no significant difference in the positivity of H. pylori in light (78%), moderate (81%) and heavy smokers (80%). All the 37 patients who were positive for H. pylori had histological gastritis compared to 65% in H. pylori negative patients. However there was no difference in presence of histological gastritis among H. pylori negative smokers (33%) and non smokers (70%; p = NS).

CONCLUSIONS

H. pylori infection is more common in smokers with NUD than in non-smokers. However duration and amount of smoking has no relationship with H. pylori positivity.