PubMed Health⌕ Search

Biomedical subjects

A K Das

Publications and source records attributed to A K Das.

At least 55 records · Page 3Linked to original sources
PubMed2001

Positional candidate gene cloning of CLN1.

Mutations in the CLN1 gene encoding palmitoyl-protein thioesterase (PPT) underlie the recessive neurodegenerative disorder, infantile Batten disease, or infantile neuronal ceroid lipofuscinosis (INCL). The CLN1 gene was mapped to chromosome 1p32 in the vicinity of a microsatellite marker HY-TM1 in a cohort of Finnish INCL families, and mapping of the PPT gene to the CLN1 critical region (and the discovery of mutations in PPT in several unrelated families) led to conclusive identification of PPT as the disease gene. PPT is a lysosomal thioesterase that removes fatty acids from fatty-acylated cysteine residues in proteins. The accumulation of fatty acyl cysteine thioesters can be reversed in INCL cells by the exogenous administration of recombinant PPT, which enters the cells through the mannose 6-phosphate receptor pathway. Over two dozen PPT mutations have been found in PPT-deficient patients worldwide. In the United States, all PPT-deficient patients show "GROD" histology but the age of onset of symptoms is later in some children due to the presence of missense mutations that result in enzymes with residual PPT activity. Now that INCL is known to be caused by a defect in a soluble lysosomal enzyme, appropriate therapies may be forthcoming. Prospects for therapy include enzyme replacement, stem cell transplantation, gene therapy, and metabolic therapy aimed at depleting the abnormal substrate accumulation in the disease.

Cloning, Molecular↗
PubMed2001

Infantile neuronal ceroid lipofuscinosis: no longer just a 'Finnish' disease.

The neuronal ceroid lipofuscinoses (NCLs) are a group of enigmatic neurodegenerative disorders of children that have in common the storage of autofluorescent lipofuscin, or aging pigment, in the brain. With the identification of the three major genes involved in the disorder, the NCLs are now appreciated to represent true lysosomal storage disorders. The most severe (infantile) form of NCL is caused by mutations in a lysosomal thioesterase that removes fatty acids from modified cysteine residues in proteins. Although the disorder was first described in Finland (and the identification of the underlying gene (CLN1) made in this population) defects in CLN1 and the underlying deficiency have been widely reported outside of Scandinavia. In this report, we summarize the relationship of genotype to phenotype in the disorder and evaluate known mutations in light of the recently solved crystal structure of defective enzyme, palmitoyl-protein thioesterase (PPT). We also discuss progress in identifying the fatty acyl cysteine thioesters that accumulate in PPT deficiency and in working toward animal models of NCL. Recent progress in these areas holds promise for the eventual treatment of the disorder.

Animals↗
PubMed2001

Anesthetic management of acquired tracheoesophageal fistula: a brief report.

IMPLICATIONS: Tracheoesophageal fistula may be either a congenital lesion or an acquired condition, most often resulting from foreign body ingestion. Location of the lesion has implications for anesthetic management and single lung ventilation may be required to facilitate surgical repair. In pediatric patients, intentional mainstem intubation may be required.

Anesthesia, Inhalation↗
PubMed2001

Effect of chronic bladder outlet obstruction on blood flow of the rabbit bladder.

PURPOSE: Previous studies have shown that the initial reaction of the rabbit bladder to partial bladder outlet obstruction is increased blood flow at day 1 and a return to baseline blood flow at 1 week. Mucosal and muscle blood flow followed this pattern but mucosal blood flow was always 4 to 5-fold greater. In this study we examined the effect of 4 weeks of outlet obstruction on bladder blood flow and correlated it with the severity of bladder contractile dysfunction. MATERIALS AND METHODS: A total of 14 male New Zealand White rabbits underwent partial outlet obstruction creation by standard methods. After 4 weeks the rabbits were anesthetized, and blood flow to the muscle and mucosa was determined by standard fluorescent microsphere technique. A section of each detrusor was used for in vitro contractility studies. Contractile responses to field stimulation, carbachol and potassium chloride were determined. A section of each detrusor tissue was fixed in formalin and used to determine the smooth muscle volume fraction. RESULTS: Four weeks of partial bladder outlet obstruction caused a significant and variable increase in bladder weight and a decrease in blood flow to bladder muscle without changes in the blood flow to mucosa. There was a clear correlation between the severity of contractile dysfunction, bladder weight and the magnitude of the decrease in blood flow in muscle. The smooth muscle volume fraction remained stable at approximately 40%. CONCLUSIONS: Bladder decompensation was associated with decreased blood flow to bladder smooth muscle. Because compensated obstructed bladders with relatively normal contractile function are also hypertrophied but have normal blood flow, decreased blood flow in decompensated bladders is not simply a response to bladder hypertrophy. From this study we hypothesize that decreased blood flow to bladder smooth muscle is an etiological factor in bladder contractile dysfunction (bladder decompensation) secondary to partial outlet obstruction.

Animals↗
PubMed2001

Malignant priapism associated with metastatic urethral carcinoma.

We present a 40-year-old man with malignant priapism secondary to urethral squamous cell carcinoma. Magnetic resonance imaging revealed the tumor originating from the bulbous urethra, extending into the penile urethra and corpora spongiosa and cavernosa. A penile biopsy confirmed poorly differentiated squamous cell carcinoma of the urethra. Despite administration of systemic chemotherapy, the prognosis of the patient has worsened due to the extensive metastatic disease.

Adult↗
PubMed2001

Metastatic sweat gland carcinoma.

Sweat gland tumours are very rare. They lack distinctive clinical features and the histological appearences are often varied. Hence, diagnosis is difficult and usually late. We report a case of sweat gland adenocarcinoma with bony and lymphnode metastases, and possibly secondary involvement of 7th cranial nerve. This is probably the first case in Indian literature.

Adenocarcinoma↗
PubMed2001

A formal method to resolve temporal mismatches in clinical databases.

Overcoming data heterogeneity is essential to the transfer of decision-support programs to legacy databases and to the integration of data in clinical repositories. Prior methods have focused primarily on problems of differences in terminology and patient identifiers, and have not addressed formally the problem of temporal data heterogeneity, even though time is a necessary element in storing, manipulating, and reasoning about clinical data. In this paper, we present a method to resolve temporal mismatches present in clinical databases. This method is based on a foundational model of time that can formalize various temporal representations. We use this temporal model to define a novel set of twelve operators that can map heterogeneous time-stamped data into a uniform temporal scheme. We present an algorithm that uses these mapping operators, and we discuss our implementation and evaluation of the method as a software program called Synchronus.

Algorithms↗
PubMed2001

Merits of performing coronary artery by-pass grafts on the beating heart.

A retrospective study of 1006 patients was undertaken to evaluate the benefit of a change of strategy in performing coronary artery by-pass grafting surgery. Group A consisted of 500 patients who were consecutively operated on cardiopulmonary by-pass and group B consisted of 506 patients who were consecutively operated on using "off pump" techniques. Pre-operative risk profile in both groups were similar as was as in the operating time. There was distinct benefit in amount of homologous transfusion, period of ICU stay, increased usage of radial artery conduit and improvement in transoesophageal echocardiography assessment of ischaemic mitral incompetence immediately after revascularisation in off pump (group B). Though there was a lower mortality in group B ie, 3/506 vis-a-vis 10/500 in group A this is not of statistical significance. Improvement in left ventricular ejection fraction >5.0% occurred more frequently in one month follow-up visits of group B patients. Period of return to active life was also shorter (28 versus 56 days). Based on observations, we conclude that there is a distinct benefit in avoiding cardiopulmonary by-pass while performing coronary artery by-pass grafting.

Coronary Artery Bypass↗
PubMed2000

Absorption of oxybutynin from vaginal inserts: drug blood levels and the response of the rabbit bladder.

OBJECTIVES: Oxybutynin has been used for treatment of urge urinary incontinence for more than 20 years. However, one of the major problems with its use is uncomfortable anticholinergic side effects that can lead to discontinuation of treatment. Alternative forms of drug administration may reduce side effects and thus improve patient compliance. METHODS: A cylinder-shaped, curved silicone elastomer insert containing oxybutynin was anchored in the vagina of female rabbits. The inserts were designed to release oxybutynin at rates of 0.5, 1.0, and 5.0 mg/day, respectively. Blood drug and metabolite levels were monitored for 1 to 7 days and cystometry was carried out after 7 days of treatment. RESULTS: There was a consistent dose-dependent absorption of the oxybutynin resulting in stable plasma concentrations by 3 days. Levels of N-desethyloxybutynin, the active metabolite that is thought to be responsible for side effects, were less than 1.0 ng/mL in all groups. The cystometrograms showed a decrease in the detrusor pressures for the higher oxybutynin groups and a dose-dependent decrease in micturition pressure. The vaginal wall in contact with the insert showed no irritation. CONCLUSIONS: The inserts produced stable blood levels and released sufficient amounts of oxybutynin to have measurable effects on the bladder. There was no irritating effect of the insert on the vaginal wall after a 1-week treatment. Vaginal inserts containing oxybutynin may be an interesting alternative method for the chronic delivery of oxybutynin.

Absorption↗
PubMed2000

An antitumor pectic polysaccharide from Feronia limonia.

An acidic heteropolysaccharide has been isolated from the tropical angiosperm Feronia limonia syn. F. elephantum (family: Rutaceae). A partially carboxymethylated alpha-(1-4) polygalacturonan backbone structure with 2- and 2,4-O-alpha-L-rhamnopyranosyl, 2- and 2, 3-O-alpha-L-arabinofuranosyl and 3-, 2,4-and terminal alpha-D-galactopyranosyl bearing side chains has been tentatively assigned. The preliminary study in the murine model showed some significant in vivo Ehrlich ascites carcinoma cell growth inhibition.

Antineoplastic Agents, Phytogenic↗
PubMed2000

Molecular cloning and expression of mammalian peroxisomal trans-2-enoyl-coenzyme A reductase cDNAs.

Chain elongation of fatty acids is an important cellular process and is believed to occur in the endoplasmic reticulum of all eukaroytic cells. Herein we describe the cloning and characterization of a peroxisomal NADPH-specific trans-2-enoyl-CoA reductase, the key enzyme for a proposed peroxisomal chain elongation pathway. The reductase was solubilized and partially purified from guinea pig liver peroxisomes by affinity chromatography. On SDS-polyacrylamide gel electrophoresis, a 40-kDa band was identified as the enzyme, and its partial amino acid sequence (27 amino acids) was determined. A full-length cDNA for the reductase was cloned from a guinea pig liver cDNA library. The open reading frame of this nucleotide sequence encodes a 302-amino acid polypeptide with a calculated molecular mass of 32.5 kDa. Full-length mouse and human cDNA clones encoding homologous proteins have also been isolated. All of these translated polypeptides have the type I peroxisomal targeting signal, AKL, at the carboxyl terminus. The identity of the cloned enoyl-CoA reductase cDNAs was confirmed by expressing the guinea pig and human cDNAs in Escherichia coli. The His-tagged recombinant enzymes were found to have very high NADPH-specific 2-enoyl-CoA reductase activity with similar properties and specificity as the liver peroxisomal reductase. Both the natural and the recombinant enzyme catalyze the reduction of trans-2-enoyl-CoAs of varying chain lengths from 6:1 to 16:1, having maximum activity with 10:1 CoA. Northern blot analysis demonstrated that a single transcript of 1.3 kilobases is present in most mouse tissues, with particularly high concentrations in liver and kidney.

Amino Acid Sequence↗
PubMed2000

Structural basis for the insensitivity of a serine enzyme (palmitoyl-protein thioesterase) to phenylmethylsulfonyl fluoride.

Palmitoyl-protein thioesterase-1 (PPT1) is a newly described lysosomal enzyme that hydrolyzes long chain fatty acids from lipid-modified cysteine residues in proteins. Deficiency in this enzyme results in a severe neurodegenerative storage disorder, infantile neuronal ceroid lipofuscinosis. Although the primary structure of PPT1 contains a serine lipase consensus sequence, the enzyme is insensitive to commonly used serine-modifying reagents phenylmethylsulfonyl fluoride (PMSF) and diisopropylfluorophosphate. In the current paper, we show that the active site serine in PPT1 is modified by a substrate analog of PMSF, hexadecylsulfonylfluoride (HDSF) in a specific and site-directed manner. The apparent K(i) of the inhibition was 125 micrometer (in the presence of 1.5 mm Triton X-100), and the catalytic rate constant for sulfonylation (k(2)) was 3.3/min, a value similar to previously described sulfonylation reactions. PPT1 was crystallized after inactivation with HDSF, and the structure of the inactive form was determined to 2.4 A resolution. The hexadecylsulfonyl was found to modify serine 115 and to snake through a narrow hydrophobic channel that would not accommodate an aromatic sulfonyl fluoride. Therefore, the geometry of the active site accounts for the reactivity of PPT1 with HDSF but not PMSF. These observations suggest a structural explanation as to why certain serine lipases are resistant to modification by commonly used serine-modifying reagents.

Acylation↗
PubMed2000

The crystal structure of palmitoyl protein thioesterase 1 and the molecular basis of infantile neuronal ceroid lipofuscinosis.

Mutations in palmitoyl-protein thioesterase 1 (PPT1), a lysosomal enzyme that removes fatty acyl groups from cysteine residues in modified proteins, cause the fatal inherited neurodegenerative disorder infantile neuronal ceroid lipofuscinosis. The accumulation of undigested substrates leads to the formation of neuronal storage bodies that are associated with the clinical symptoms. Less severe forms of PPT1 deficiency have been found recently that are caused by a distinct set of PPT1 mutations, some of which retain a small amount of thioesterase activity. We have determined the crystal structure of PPT1 with and without bound palmitate by using multiwavelength anomalous diffraction phasing. The structure reveals an alpha/beta-hydrolase fold with a catalytic triad composed of Ser115-His289-Asp233 and provides insights into the structural basis for the phenotypes associated with PPT1 mutations.

Amino Acid Sequence↗
PubMed2000

Induction of the peroxisomal glycerolipid-synthesizing enzymes during differentiation of 3T3-L1 adipocytes. Role in triacylglycerol synthesis.

The glycerophosphate backbone for triglyceride synthesis is commonly believed to be created through the conversion of dihydroxyacetone phosphate (DHAP) by glycerophosphate dehydrogenase (GPD) to sn-glycerol 3-phosphate (GP), which is then converted by glycerophosphate acyltransferase (GPAT) to 1-acyl-GP. Consistent with this, GPD and GPAT are highly induced during differentiation of mouse 3T3-L1 preadipocytes. While the acyl dihydroxyacetone phosphate (acyl-DHAP) pathway for glycerolipid synthesis is commonly believed to be involved only in glycerol ether lipid synthesis, we report here that during conversion of 3T3-L1 preadipocytes to adipocytes, the specific activity of peroxisomal DHAP acyltransferase (DHAPAT) is increased by 9-fold in 6 days, while acyl-DHAP:NADPH reductase is induced by 5-fold. A parallel increase in the catalase (the peroxisomal marker enzyme) activity is also seen. In contrast, the specific activity of alkyl-DHAP synthase, the enzyme catalyzing the synthesis of the ether bond, is decreased by 60% during the same period. Unlike microsomal GPAT, the induced DHAPAT is found to have high activity at pH 5.5 and is resistant to inhibition by sulfhydryl agents, heat, and proteolysis. On subcellular fractionation, DHAPAT is found to be associated with microperoxisomes whereas GPAT activity is mainly present in microsomes. Northern blot analyses reveal that induction of DHAPAT can be largely explained through increases in DHAPAT mRNA. A comparison of microsomal and peroxisomal glycerolipid synthetic pathways, using D-[3-(3)H, U-(14)C]glucose as the precursor of the lipid glycerol backbone shows that about 40-50% of triglyceride is synthesized via the acyl-DHAP pathway. These results indicate that the acyl-DHAP pathway is important not only for the synthesis of ether lipids, but also for the synthesis of triacylglycerol and other non-ether glycerolipids.

3T3 Cells↗
PubMed2000

The crystal structure of human eukaryotic release factor eRF1--mechanism of stop codon recognition and peptidyl-tRNA hydrolysis.

The release factor eRF1 terminates protein biosynthesis by recognizing stop codons at the A site of the ribosome and stimulating peptidyl-tRNA bond hydrolysis at the peptidyl transferase center. The crystal structure of human eRF1 to 2.8 A resolution, combined with mutagenesis analyses of the universal GGQ motif, reveals the molecular mechanism of release factor activity. The overall shape and dimensions of eRF1 resemble a tRNA molecule with domains 1, 2, and 3 of eRF1 corresponding to the anticodon loop, aminoacyl acceptor stem, and T stem of a tRNA molecule, respectively. The position of the essential GGQ motif at an exposed tip of domain 2 suggests that the Gln residue coordinates a water molecule to mediate the hydrolytic activity at the peptidyl transferase center. A conserved groove on domain 1, 80 A from the GGQ motif, is proposed to form the codon recognition site.

Amino Acid Sequence↗
PubMed2000

Identification of three novel mutations of the palmitoyl-protein thioesterase-1 (PPT1) gene in children with neuronal ceroid-lipofuscinosis.

Eight unrelated children with progressive neurological deterioration and granular osmiophilic deposits (GROD) due to an underlying palmitoyl-protein thioesterase deficiency were analyzed for mutations in the PPT1 gene. Three novel mutations (G118D, Q291X and F84del) were identified. The novel Q291X mutation was observed in an African-American child. The G118D and Q291X mutations occurred in infantile-onset subjects. These two mutations would be predicted to have severe effects on enzyme activity. The novel F84del mutation involves an invariant phenylalanine residue. A missense mutation, Q177E, occurred in three subjects from two families with late-infantile NCL, confirming an association of the Q177E mutation with a late-infantile phenotype. Other previously described mutations were R151X (5/16 alleles), T75P (3/16 alleles), R164X (1/16 alleles), and V181M (1/16 alleles). The current study expands the spectrum of mutations in PPT1 deficiency and further confirms the broad range of age of onset of symptoms resulting from an enzyme deficiency previously associated only with infantile NCL.

Child↗
PubMed2000

A scientific basis for the therapeutic effects of Pygeum africanum and Serenoa repens.

In Europe, phytotherapeutic preparations have been prescribed for the treatment of symptomatic benign prostatic hyperplasia (BPH) for over 20 years [1-4]. In these countries, phytotherapeutic preparations represent approximately 1/3 of total sales of all therapeutic agents sold for the treatment of BPH. In France, and other countries, phytotherapeutic preparations are the most widely used drugs for the treatment of BPH. In Asia, Africa, and India, phytotherapy is considered a first-line treatment for BPH and has been utilized effectively for centuries. In the United States, the multimillion dollar sales of phytotherapeutic preparations for "the health of the prostate and bladder" attests to the widespread utilization of these agents [3, 4]. Two of the most popular phytotherapeutic agents that have undergone both clinical studies to determine their efficacy, and have been the subject of basic science studies to identify the mechanism(s) of action are Pygeum africanum (Tadenan), an extract from the bark of the African plum tree, and Serenoa repens (Permixon), a lipido-sterol extract of dwarf palm. Tadenan and Permixon are registered therapeutic agents of Debat Pharmaceuticals, and Pierre Fabre Medicament, respectively. Manufacture of both preparations are tightly controlled and subjected to strict quality control for stability of component composition. In regard to phytotherapeutic agents, each individual preparation (even from the same plant source) must be considered individually because of differences in the extraction techniques, preparation of products, composition, and biological activities. Thus, the clinical and biological activities of one preparation cannot be extrapolated to other preparations of the same plant source. Thus, studies described in this review which utilize the preparations that are manufactured by DEBAT (Pygeum africanum) or Pierre Fabre Medicament (Serenoa repens) are referred to by their trade names, Tadenan and Permixon, to differentiate them from other nonstandardized preparations of the same plants.

Androgen Antagonists↗