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Biomedical subjects

R Pathak

Publications and source records attributed to R Pathak.

At least 19 recordsLinked to original sources
PubMed2003

Tandem mass spectra of ammonium ion, metal ion and ligated metal ion adducts of acyclic sugar derivatives.

The tandem mass (MS/MS) spectra of ammonium ion, metal ion and ligated metal ion adducts of chain-extended acyclic nitro-containing deoxyglucose and deoxygalactose derivatives have been studied. The ammonium adducts fragment primarily by elimination of ammonia followed by acetic acid, thus not giving much structural information. In contrast, cationization of these compounds by metal ions and ligated metal ions gave structurally informative and useful fragment ions on MS/MS. The metal ions and ligated metal ions play an important role in controlling and directing fragmentation. Retro-aldol fragmentation is facilitated by metal ions such as Li(+), Na(+), Ag(+) and Cu(+), whereas the adducts with higher alkali metal ions such as Rb(+) and Cs(+) fragment to give only the corresponding metal ions. The divalent metal ions such as Cu(2+) and Ba(2+) also induce retro-aldol fragmentation. However, the charge is carried by the aldehyde fragment in the case of Cu(2+) adducts, whereas the nitroalkane fragment carries the charge in the case of Ba(2+) adducts. Ligated metal ions such as ZnCl(+), CuCl(+), InCl(2) (+) and BaCl(+) also behave similarly and induce retro-aldol fragmentation in these acyclic sugars. Both the metal ion and ligated metal ion adducts can fragment by elimination of metal-containing neutral molecules.

Acetic Acid↗
PubMed2001

Surgery and pancreas divisum: a dwindling role?

Pancreas divisum has generated varying enthusiasm regarding operative intervention. Applying similar principles to divisum surgery as for the surgical treatment of chronic pancreatitis will yield a better outcome than using subjective symptoms.

Humans↗
PubMed2001

A decade of experience with abdominal aortic aneurysm repair in octogenarians.

BACKGROUND: Should abdominal aortic aneurysms (AAA) be electively repaired in octogenarians? METHODS: This was a retrospective review of patients' charts over a ten-year period starting in January 1995. This study was conducted at St. Francis Hospital, Roslyn, New York, which is a tertiary referral center. All octogenarians who underwent AAA repair (elective and emergent) were included in this study (mean age 82.9 years). A total of 71 such patients were identified. Sixty-two patients had elective surgery and nine patients had emergent repair of the ruptured AAA. It was hypothesized before the study was conducted that AAA could be repaired in octogenarians with acceptable morbidity and mortality in an institution with vast experience in dealing with this disease. RESULTS: The mean aneurysm diameter was 6.73 cm. Twenty patients (28%) received bifurcated grafts, while 51 patients (72%) received tubular grafts. Four patients had coronary artery bypass graft before aneurysm surgery. Forty-four patients (62%) were male and 27 (38%) were female. The thirty day mortality rate after elective AAA repair was 1.4%, whereas after the repair of ruptured aneurysms was 44.4%. CONCLUSIONS: We concluded that the elective repair of abdominal aneurysms in most octogenarians is a safe and life-prolonging procedure if performed in an experienced tertiary center.

Aged↗
PubMed2000

Malignancy in HIV/AIDs: a single hospital experience.

BACKGROUND AND OBJECTIVES: Our hospital serves an area with a significant number of patients seropositive for the human immunodeficiency virus (HIV). Intravenous drug abuse and heterosexual exposure are by far the predominant risk factors for HIV and acquired immunodeficiency syndrome (AIDS). Seven percent of these patients develop malignancies. Our aim was to study the types of tumor, their distribution, and to evaluate the patients' outcome. METHODS: Of 3,578 patients with HIV infection or AIDS treated between 1993 and 1998, 245 had 1 or more malignancies. Information was collected on age, sex, race, predisposing risk factors for AIDS, malignancies, symptoms at presentation, the time of the onset of AIDS, CD4 cell counts, pathology findings, and mortality. RESULTS: Although aspects of our patients resembled those of previously studied groups of patients with AIDS, there also were ways in which our patients differed from those other groups. Of our patients, 21. 6% had non-AIDS-defining (NAD) invasive malignancies. This was considerably higher than the rate in most studies. Twenty-seven patients with such malignancies died during the study. Forty-two other patients had pre-invasive cancers. Among patients having AIDS-defining (AD) malignancies, 55.9% died, a fact that was related to patients' low CD4 cell counts and late presentation. Our 97 patients with Kaposi sarcoma included 22 women, a relatively high number that may be related to the fact that most of our patients were intravenous drug abusers or had become infected by heterosexual transmission of HIV. CONCLUSIONS: AIDS is associated with a high risk of malignancy and an unusual spectrum of tumors. Patients with invasive tumors have advanced disease at the time of initial presentation. Those with AD tumors have a worse prognosis than patients with NAD tumors. The impact of highly active antiretroviral therapy on both AD and NAD tumors needs to be further evaluated.

AIDS-Related Complex↗
PubMed1999

Syncytial variant of nodular sclerosing Hodgkin lymphoma.

We report the case history of a 31-year old woman with a rare morphologic form of nodular sclerosing Hodgkin disease (NSHD) termed "syncytial variant." Its histologic features mimic metastatic carcinoma, thymoma, melanoma, non-Hodgkin lymphoma and germ-cell tumor. Antigens expressed on Reed-Sternberg cells, the hallmark of Hodgkin disease, and other neoplastic cells were screened to determine the correct diagnosis. This patient demonstrates the importance of using specific immunohistochemical techniques to clarify the diagnosis of NSHD of the "syncytial variant" subtype.

Adult↗
PubMed1997

A dual affinity tag on the 64-kDa Nlt1p subunit allows the rapid characterization of mutant yeast oligosaccharyl transferase complexes.

Oligosaccharyl transferase catalyzes the glycosylation of selected asparagine residues of nascent polypeptide chains as they are translocated into the lumen of the endoplasmic reticulum. To date, this enzyme has been purified from a number of eukaryotic organisms. Purification of transferase activity has yielded polypeptide complexes of three to six subunits depending on the source organism. Here we present the purification of an affinity-tagged version of the enzyme complex from a membrane protein fraction of the yeast Saccharomyces cerevisiae. A yeast strain was created in which the essential 64-kDa glycoprotein Nlt1p subunit of the oligosaccharyl transferase was modified by the addition of a 22-residue carboxy-terminal affinity tag; the tag included both an 8-residue FLAG epitope and a 6-residue histidine motif. Facile purification of the oligosaccharyl transferase was achieved using affinity chromatography media specific for each segment of the tag. The enzyme was purified as a heteromeric complex of five subunits in agreement with previously reported characterizations of the yeast transferase. Yeast strains bearing affinity-tagged enzyme subunits allow the rapid characterization of native and mutant transferase complexes.

Affinity Labels↗
PubMed1997

Recombinant adeno-associated virus for muscle directed gene therapy.

Although gene transfer with adeno-associated virus (AAV) vectors has typically been low, transduction can be enhanced in the presence of adenovirus gene products through the formation of double stranded, non-integrated AAV genomes. We describe the unexpected finding of high level and stable transgene expression in mice following intramuscular injection of purified recombinant AAV (rAAV). The rAAV genome is efficiently incorporated into nuclei of differentiated muscle fibers where it persists as head-to-tail concatamers. Fluorescent in situ hybridization of muscle tissue suggests single integration sites. Neutralizing antibody against AAV capsid proteins does not prevent readministration of vector. Remarkably, no humoral or cellular immune responses are elicited to the neoantigenic transgene product E. coli beta-galactosidase. The favorable biology of rAAV in muscle-directed gene therapy described in this study expands the potential of this vector for the treatment of inherited and acquired diseases.

Animals↗
PubMed1997

Influence of cultural conditions on lipid production by mutant strain of Rhodotorula glutinis MTCC 1151.

Mutant of Rhodotorula glutinis MTCC 1151 was found to produce high level of lipid (63.6% of biomass) as compared to parent strain (56.7% biomass). The lipid synthesizing capacity of mutant of R. glutinis was evaluated with different glucose concentrations, nitrogen sources, incubation time, and aeration-agitation. Maximum lipid yield (63.6% of biomass) was found with 5% glucose using ammonium sulfate (0.2%) as a nitrogen source under shake-flask conditions (50 ml broth in 250 ml conical flask at 125 rpm) after 4 days of incubation at 28 degrees C. The ability of ammonium sulfate to replace comparatively very costly yeast extract is highly appreciable.

Aerobiosis↗
PubMed1995

Sulfhydryl modification of the yeast Wbp1p inhibits oligosaccharyl transferase activity.

Chemical labeling of the multimeric Saccharomyces cerevisiae oligosaccharyl transferase indicates that the 48 kDa Wbp1p subunit is an integral component of the catalytically active enzyme. The enzyme was purified following chromatography on concanavalin A agarose, heparin agarose, Q-Sepharose, and hydroxyapatite media. The enzyme activity copurified with a tetrameric complex of polypeptide subunits. Two of the subunits have been identified as the yeast proteins Wbp1p and Swp1p by amino-terminal residue sequencing. A third subunit was identified as a variably glycosylated polypeptide near 64 kDa; preliminary amino acid sequencing showed no identity to known yeast proteins. Modification of a cysteine residue by the reagent methyl methanethiolsulfonate (MMTS) caused time-dependent and concentration-dependent inactivation of the enzyme. To identify the modified subunit of the transferase complex, the labeling reagent S-[(N-biotinoylamino)ethyl] methanethiolsulfonate (BMTS) was synthesized. Like MMTS, BMTS inactivated the oligosaccharyl transferase in a time-dependent manner. Additionally, incubation with the substrate (dolichylpyrophosphoryl)-N,N'-diacetylchitobiose [Dol-PP(GlcNAc)2] protected the enzyme from BMTS inactivation. When the purified enzyme complex was incubated with BMTS, Wbp1p alone was specifically labeled, thereby associating this subunit with catalysis and the binding of the dolichylpyrophosphoryl oligosaccharide substrate in the transferase reaction.

Amino Acid Sequence↗
PubMed1995

The essential yeast NLT1 gene encodes the 64 kDa glycoprotein subunit of the oligosaccharyl transferase.

The yeast oligosaccharyl transferase catalyzes the glycosylation of asparagine residues in secreted, vesicular, and membrane proteins. A complex of at least four membrane-bound polypeptides is responsible for oligosaccharyl transferase activity. Amino acid sequences from the 64 kDa glycoprotein subunit of the complex were used to clone the essential NLT1 (N-linked oligosaccharyl transferase) gene. The Nlt1p gene product is a processed, multiply glycosylated type I membrane protein; it has an extensive amino-terminal soluble domain, a potential hydrophobic transmembrane domain, and a short carboxy-terminal soluble domain. The Nlt1p is significantly similar than the mammalian ribophorin I, a component of the mammalian oligosaccharyl transferase complex, and the enzyme is conserved throughout eukaryotic evolution.

Amino Acid Sequence↗
PubMed1995

Automated proton spectroscopic image processing.

An automatic data processing and display protocol for proton magnetic resonance spectroscopic imaging is described. The spectroscopic images are generated using the fitted peak areas of phased metabolite resonances using the Levenberg-Marquardt algorithm. This automated spectroscopic image processing is tested and evaluated using phantom and human brain data. This algorithm is robust, simple to use, and minimizes user bias in processing and quantifying serial changes of metabolite levels in brain tissue.

Algorithms↗
PubMed1991

Scleroderma and central nervous system vasculitis.

We describe a patient with scleroderma (CREST syndrome) and central nervous system vasculitis. While angiography demonstrated segmental symmetrical arterial narrowing characteristic of vasculitis, results of leptomeningeal biopsy were normal. There was no evidence of systemic vasculitis, renal failure, or malignant hypertension previously thought to be required to explain central nervous system dysfunction in patients with scleroderma. Signs and symptoms attributable to vasculitis were reversible with aggressive immunosuppressive therapy.

Cerebrovascular Circulation↗
PubMed1991

Role of a soy-based lactose-free formula in the outpatient management of diarrhea.

The introduction of a soy-based, lactose-free formula during the acute phase of diarrheal illness in infants has been shown to reduce stool output and duration of diarrhea in hospitalized patients. In the United States, most infants with acute diarrhea are treated as outpatients. In the present study, infants with diarrhea who were treated as outpatients were randomly assigned to receive either a soy-based, lactose-free formula alternating with oral rehydration solution from the beginning of therapy ("early feeding") or oral rehydration solution alone for the first 24 hours of therapy, followed by a soy-based, lactose-free formula alternating with oral rehydration solution (control group). Twenty-nine infants were randomly assigned to the early-feeding group and 27 to the control group. Twenty-one (72%) of 29 in the early-feeding group resolved their diarrhea at the end of 48 hours of therapy compared with 12 (44%) of 27 in the group fed oral rehydration solution only (P = .02). It is concluded that the introduction of a soy-based, lactose-free formula from the beginning of therapy for acute diarrhea in children treated as outpatients is safe and may shorten duration of diarrhea while maintaining adequate caloric intake.

Ambulatory Care↗
PubMed1990

Stiff-man syndrome: a GABAergic autoimmune disorder with autoantigenic heterogeneity.

Autoantibodies that reacted with cell bodies and axon terminals of gamma-aminobutyric acid (GABA)ergic neurons were present in the serum and cerebrospinal fluid in a patient with stiff-man syndrome with type I diabetes. Immunoblot experiments using this patient's serum and cerebrospinal fluid did not corroborate an earlier observation that these autoantibodies are directed against the GABAergic cytosolic enzyme, L-glutamic acid decarboxylase. While L-glutamic acid decarboxylase autoantibodies may be associated with this syndrome, they do not appear to be easily demonstrated.

Adult↗
PubMed1986

Angina pectoris and coronary artery disease in isolated, severe aortic regurgitation.

Seventy-eight patients with isolated, severe aortic regurgitation (AR) were studied retrospectively to determine the prevalence of angiographically significant coronary artery disease (CAD) and its relation to angina pectoris (AP). Angiographically, significant CAD was present in 29 of 78 patients (37%), and 36 patients (46%) had AP. Twenty-one of 36 patients (58%) with AP and 8 of 42 patients (19%) without AP had angiographically significant CAD. AP as a predictor of significant CAD had a sensitivity of 73%, specificity of 69% and a risk ratio of 3:1. The predictive accuracy of detecting CAD in the absence of AP was 81%. The benefit from concomitant coronary artery bypass grafting at the time of aortic valve replacement for AR has not been clearly demonstrated; therefore, routine coronary angiography is still recommended for all AR patients older than 40 years undergoing aortic valve replacement.

Adult↗
PubMed1985

Oral rehydration therapy for acute diarrhea in ambulatory children in the United States: a double-blind comparison of four different solutions.

Oral rehydration solutions containing 50 to 90 mmol/L of sodium have recently been recommended for the treatment of diarrhea in both hospitalized and ambulatory children in the United States. Few data are available, however, from ambulatory US children. Therefore, we conducted a randomized double-blind study comparing the use of four different oral rehydration solutions with differing concentrations of sodium, glucose, and base. Ambulatory children less than 2 years of age with acute diarrhea (N = 140) were randomly chosen to receive solutions containing sodium at 90 (solution A), 50 (solution B), and 30 mmol/L (solutions C and D). All oral rehydration solutions contained 20 g/L of glucose except solution D which contained 50 g/L of glucose. Solution A contained bicarbonate as its base source whereas the other three contained citrate. All but three (98%) children were treated uneventfully according to the study protocol, and there were no differences among groups in measurements of clinical outcome. It was concluded that in ambulatory US children, oral rehydration solutions containing 90, 50, or 30 mmol/L of sodium can be used safely for the treatment of mild acute diarrhea and that citrate is as efficacious as bicarbonate in the correction of acidosis.

Ambulatory Care↗