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Biomedical subjects

B Das

Publications and source records attributed to B Das.

At least 145 records · Page 8Linked to original sources
PubMed1988

The kinetic mechanism of human placental aldose reductase and aldehyde reductase II.

The kinetic mechanism of NADPH-dependent aldehyde reductase II and aldose reductase, purified from human placenta, has been studied using L-glucuronate and DL-glyceraldehyde as their respective substrates. For aldehyde reductase II, the initial velocity and product inhibition studies (using NADP and gulonate) indicate that the enzyme reaction sequence is ordered with NADPH binding to the free enzyme and NADP being the last product to be released. Inhibition patterns using menadione (an analog of the aldehydic substrate) and ATP-ribose (an analog of NADPH) are also consistent with a compulsory ordered reaction sequence. Isotope effects of deuterium-substituted NADPH (NADPD) also corroborate the above reaction scheme and indicate that hydride transfer is not the sole rate-limiting step in the reaction sequence. For aldose reductase, initial velocity patterns, product, and dead-end inhibition studies indicate a random binding pattern of the substrates and an ordered release of product; the coenzyme is released last. A steady-state random mechanism is also consistent with deuterium isotope effects of NADPD on the reaction sequence catalyzed by this enzyme. However, the hydride transfer step seems to be more rate determining for aldose reductase than for aldehyde reductase II.

Aldehyde Reductase↗
PubMed1988

Surgical experience with intracardiac myxomas.

Eighteen patients underwent surgery for intracardiac myxoma (16 left atrial and 2 right atrial) during the last 10 years. Seventeen patients had tumour stalk attached to the oval fossa. The myxoma was excised along with a cuff of the atrial septum, which was reconstructed using a Dacron patch in 15 patients and by direct suture in 2 patients. In the remaining case the myxoma was attached to the left atrial wall and adjacent atrioventricular junction. There was only one early death in a patient who underwent a concomitant lobectomy for lung abscess and one late death due to a noncardiac cause. During the follow-up period of 3-96 months (average 36 months) all the survivors were in New York Heart Association Class I. Scanning electron microscopy of tumour tissue was done in 8 cases. The morphological findings did not help in categorizing the tumours into any pathological subgroups. Postoperative cardiac catheterization done in 3 patients (30-50 months postoperatively) showed return of haemodynamics to normal. Echocardiographic studies done postoperatively have not revealed recurrence of tumour in any patient. Surgical excision of myxomas is possible with very gratifying long-term results.

Adolescent↗
PubMed1988

Nifedipine prevents the pressor response to laryngoscopy and tracheal intubation in patients with coronary artery disease.

The efficacy of sublingual nifedipine, administered one minute before anaesthetic induction, in order to minimise the pressor response to laryngoscopy and tracheal intubation was studied in a group of 15 patients who underwent coronary artery bypass surgery. Another group of 15 similar patients served as control. Premedication consisted of oral diazepam 5-10 mg, intramuscular morphine 0.2 mg/kg and promethazine 0.4 mg/kg. Anaesthesia was induced with morphine 0.1-0.15 mg/kg and thiopentone 3-5 mg/kg. Laryngoscopy and tracheal intubation were facilitated with suxamethonium 1.5 mg/kg. A significant increase in blood pressure occurred during and after laryngoscopy and tracheal intubation in the control group. This increase was absent in the patients pretreated with nifedipine. The nifedipine group also maintained a lower rate-pressure-product than the control group during the period of study. It is concluded that nifedipine 10 mg is a useful pretreatment to prevent the pressor response to laryngoscopy and tracheal intubation in patients with coronary artery disease.

Adult↗
PubMed1988

Closed mitral valvotomy during pregnancy. A 20-year experience.

Closed mitral valvotomy for rheumatic mitral stenosis was performed on 126 pregnant women (average duration of pregnancy c. 21 weeks), 91% of whom were in NYHA functional class III or IV. Associated functional tricuspid regurgitation was present in 47 (37%) of the women, and 102 (81%) had critical mitral stenosis (digitally assessed valve area less than 1 cm2). There was no surgical mortality. Postoperatively 84% of the women were in NYHA class I. Clinical evidence of pulmonary artery hypertension and tricuspid regurgitation regressed postoperatively in most patients. Full-term normal delivery was achieved in 82% of the pregnancies, with total fetal mortality 6%. There were no congenital abnormalities and the infants' progress was normal. At 5-year follow-up 86% of the women were in NYHA class I or II and at 10 years the figure was 60%. The restenosis rate was 2%/year and the late mortality 3.3%. Closed mitral valvotomy during pregnancy thus was safe and reliable, giving significant functional and clinical improvement without adversely affecting the fetus.

Adult↗
PubMed1988

Pregnancy in patients with prosthetic cardiac valve. A 10-year experience.

Pregnancy after valve replacement has been considered hazardous because of maternal and fetal complications secondary to anticoagulant medication, in addition to basic myocardial problems. Of 229 females aged 15-45 years with prosthetic valve replacement, 37 (including 34 with Björk-Shiley valve and anticoagulants) subsequently had a total of 47 pregnancies. Fullterm delivery of a normal infant was achieved in 40 cases. There were three premature births, two spontaneous abortions, one stillbirth and one ectopic pregnancy. The fetal mortality was 8.5%. Valve thrombosis developed in two cases, but surgical treatment was successful. Oral anticoagulants (acenocoumarin and dipyridamole) were continued throughout pregnancy. Heparin was substituted before labour began, but discontinued after delivery, when effective oral anticoagulation was resumed. Our experience showed that pregnancy in women with mechanical heart valve prosthesis and continued oral intake of anticoagulants is safe and successful in most cases.

Acenocoumarol↗
PubMed1988

Chest injuries: a clinical and autopsy profile.

The clinical profiles and management of 236 consecutive chest injury patients treated and followed up at All India Institute of Medical Sciences between January 1983 and July 1985 were analyzed prospectively. There were 149 blunt and 87 penetrating injuries; 21 patients (9%) required thoracotomy. Single- or multiple-tube thoracostomy was performed in 141 patients (60%). The remaining 74 patients (31%) required only observation for a period of 24-48 hours. Fifteen patients (6.3%) died, the mortality being related to head injury in four, irreversible hypovolemic shock in four, pulmonary embolism in three, septicemia in two, and respiratory failure in two. Nonfatal complications included residual hemothorax in 18 cases, persistent air leak in 13, pulmonary infection in eight, pulmonary embolism in one, and empyema in one. The average hospital stay was 6.9 days. Evidence of chest injury of various magnitudes was found in 756 of 2,286 autopsies conducted for trauma-deaths during the same study period analyzed retrospectively; however, it was the major cause of death in only 147 (19%). Cardiac injuries accounted for 41% of the deaths resulting primarily from chest trauma. Only 10% of the patients who sustained cardiac injury reached hospital alive.

Adolescent↗
PubMed1987

Diethyl pyrocarbonate inactivation of human placental aldehyde reductase II.

Diethyl pyrocarbonate inactivated aldehyde reductase II (L-gulonate:NADP+ 6-oxidoreductase, EC 1.1.1.19) from human placenta. A concentration of 0.5-1.0 mM diethyl pyrocarbonate caused 40-65% loss of activity. The inactivation of the enzyme by diethyl pyrocarbonate was reversed by hydroxylamine and was accompanied by a large change in the absorbance of the protein at 242 nm, but not at 278 nm, indicating that only the histidine residues were modified. NADPH, but not glucuronate afforded significant protection to the enzyme from inactivation by diethyl pyrocarbonate. With 0.2-1.0 mM diethyl pyrocarbonate, 4-5 histidine residues were modified with a pseudo-first-order rate process. A double log plot of the fraction of the unmodified residues indicates that only one functional histidine residue is essential for the catalytic activity of aldehyde reductase II.

Carbohydrate Dehydrogenases↗
PubMed1987

Microdetermination of aldose and aldehyde reductases from human tissues.

Microfluorometric method has been described for the determination of aldose reductase and aldehyde reductase II activities in human erythrocyte, brain, and lens. The enzyme activity determined by the microfluorometric method was compared with the activity determined spectrophotometrically by following the oxidation of NADPH and fluorometrically by the formation of sorbitol. The activity of aldose reductase in homogenous preparations from human lens, brain, and erythrocyte was identical when determined by NADPH oxidation, NADP formation, and sorbitol formation using glucose as substrate and NADPH as co-factor. This indicated that NADPH oxidation by aldose reductase is not due to a non-specific oxidation by oxidants generated as a result of interaction of aldose reductase and glucose. Similarly, the activity of aldehyde reductase II obtained by NADPH oxidation and that by NADP formation were in good agreement. The microfluorescent method is convenient and accurate and can be used for the determination of aldose reductase in human tissues using glucose as substrate even when the sample size is small.

Alcohol Dehydrogenase↗
PubMed1986

Hyperglycemia-induced activation of human erythrocyte aldose reductase and alterations in kinetic properties.

Incubation of human erythrocytes with varying concentrations of glucose resulted in a several-fold increase in aldose reductase (alditol:NADP+ 1-oxidoreductase, EC 1.1.1.21) activity as determined by the rate of NADPH oxidation and the rate of sorbitol formation. As compared to aldose reductase from human erythrocytes not incubated with glucose (native enzyme), aldose reductase from 30 mM glucose-incubated erythrocytes (activated enzyme) exhibited altered kinetic and inhibition properties. Native enzyme showed biphasic kinetics with substrates (glucose and glyceraldehyde), was strongly inhibited by 15 microM ADP, 1,3-diphosphoglycerate, 2,3-diphosphoglycerate and 3-phosphoglycerate, and aldose reductase inhibitors such as sorbinil and alrestatin. The activated enzyme, on the other hand, exhibited monophasic kinetics, low Km for substrates, was not inhibited by the phosphorylated intermediates, and was less susceptible to inhibition by aldose reductase inhibitors. In erythrocytes of the diabetic subjects, we have found an excellent correlation between aldose reductase activity and plasma glucose levels and have observed that whenever the blood glucose level was higher than 15 mM, all of the erythrocyte aldose reductase was present in the activated form and exhibited properties similar to those observed with aldose reductase obtained from 30 mM glucose-incubated erythrocytes.

Aldehyde Reductase↗
PubMed1986

Activation of human erythrocyte, brain, aorta, muscle, and ocular tissue aldose reductase.

Based upon kinetic, structural, and immunologic properties, we have demonstrated that human tissues have three major forms of aldo-keto reductases: aldose reductase (AR), and aldehyde reductases I (AR I) and II (AR II). The proposed subunit compositions are AR, alpha; AR I, alpha-beta; and AR II, delta. Only AR can effectively reduce glucose to sorbitol. The beta subunits in AR I alter the substrate specificity of AR and prevent conformational changes required for the activation of alpha subunits. Partially purified AR (by DE-52) from human erythrocytes expresses biphasic kinetics with glucose and glyceraldehyde. The enzyme can be activated with glucose + glucose-6-P + NADPH and is strongly inhibited by sorbinil, alrestatin, and quercetrin, and by ADP, 2,3DPG, 1,3DPG, and 3PGA. The activated enzyme expresses monophasic kinetics with substrates (Km glucose less than 1 mmol/L) and is less susceptible to inhibition by synthetic AR inhibitors and phosphorylated intermediates. The enzyme from human brain, aorta, muscle, and ocular tissues was also activated under similar conditions. Erythrocyte enzyme was activated by incubation of blood with 30 to 50 mmol/L glucose. In diabetic subjects with blood sugar levels higher than 250 mg%, almost all the erythrocyte enzyme exists in the activated form. As demonstrated by enzyme-linked immunosorbent assay (ELISA), the increase in AR activity (in vivo and in vitro) was due to the activation of the enzyme and not to the de novo synthesis. In each case, the activation of the enzyme was confirmed by NADPH oxidation and the formation of proportionate amounts of sorbitol.

Aldehyde Reductase↗
PubMed1986

Dual left coronary systems.

Dual left coronary systems, one originating normally and the other anomalously from the right sinus of Valsalva, is described in a 53-year-old patient with atypical chest pain with exercise-induced ST-depression in the anteroseptal area (V2-4). Clinical consequences of this hitherto undescribed anomaly are discussed.

Angiography↗
PubMed1986

Fate of thrombectomized Björk-Shiley valves. A long-term cinefluoroscopic, echocardiographic, and hemodynamic evaluation.

Fourteen patients underwent thrombectomy for thrombosis of implanted Björk-Shiley valves (13 in the mitral and one in the aortic position) between January, 1975, and July, 1984. There was no operative mortality or perioperative embolism. Over a follow-up period of 1 to 96 months (average 23.5 months), there was no late mortality. Serial evaluation of valve function by cinefluoroscopy and echocardiography has shown no evidence of rethrombosis or valve dysfunction in any of the patients. Cardiac catheterization and angiocardiography done in 10 patients at various intervals (1 month to 6 years) postoperatively have shown normal valve function in all and normalization of elevated preoperative intracardiac pressures in the majority. Our experience suggests that thrombectomy of thrombosed Björk-Shiley valves provides excellent early and long-term results in terms of patient survival and valve function.

Adult↗
PubMed1985

Purification and properties of aldehyde reductases from human placenta.

Aldehyde reductases (alcohol: NADP+-oxidoreductase, EC 1.1.1.2) I and II from human placenta have been purified to homogeneity. Aldehyde reductase I, molecular weight about 74 000, is a dimer of two nonidentical subunits of molecular weights of about 32 500 and 39 000, whereas aldehyde reductase II is a monomer of about 32 500. Aldehyde reductase I can be dissociated into subunits under high ionic concentrations. The isoelectric pH for aldehyde reductases I and II are 5.76 and 5.20, respectively. Amino acid compositions of the two enzymes are significantly different. Placenta aldehyde reductase I can utilize glucose with a lower affinity, whereas aldehyde reductase II is not capable of reducing aldo-sugars. Similarly, aldehyde reductase I does not catalyse the reduction of glucuronate while aldehyde reductase II has a high affinity for glucuronate. Both enzymes, however, exhibit strong affinity towards various other aldehydes such as glyceraldehyde, propionaldehyde, and pyridine-3-aldehyde. The pH optima for aldehyde reductases I and II are 6.0 and 7.0, respectively. Aldehyde reductase I can use both NADH and NADPH as cofactors, whereas aldehyde reductase II activity is dependent on NADPH only. Both enzymes are susceptible to inhibition by sulfhydryl group reagents, aldose reductase inhibitors, lithium sulfate, and sodium chloride to varying degrees.

Alcohol Oxidoreductases↗
PubMed1985

Interrelationships among human aldo-keto reductases: immunochemical, kinetic and structural properties.

We have proposed earlier a three gene loci model to explain the expression of the aldo-keto reductases in human tissues. According to this model, aldose reductase is a monomer of alpha subunits, aldehyde reductase I is a dimer of alpha, beta subunits, and aldehyde reductase II is a monomer of delta subunits. Using immunoaffinity methods, we have isolated the subunits of aldehyde reductase I (alpha and beta) and characterized them by immunocompetition studies. It is observed that the two subunits of aldehyde reductase I are weakly held together in the holoenzyme and can be dissociated under high ionic conditions. Aldose reductase (alpha subunits) was generated from human placenta and liver aldehyde reductase I by ammonium sulfate (80% saturation). The kinetic, structural and immunological properties of the generated aldose reductase are similar to the aldose reductase obtained from the human erythrocytes and bovine lens. The main characteristic of the generated enzyme is the requirement of Li2SO4 (0.4 M) for the expression of maximum enzyme activity, and its Km for glucose is less than 50 mM, whereas the parent enzyme, aldehyde reductase I, is completely inhibited by 0.4 M Li2SO4 and its Km for glucose is more than 200 mM. The beta subunits of aldehyde reductase I did not have enzyme activity but cross-reacted with anti-aldehyde reductase I antiserum. The beta subunits hybridized with the alpha subunits of placenta aldehyde reductase I, and aldose reductase purified from human brain and bovine lens. The hybridized enzyme had the characteristic properties of placenta aldehyde reductase I.

Alcohol Oxidoreductases↗