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Biomedical subjects

S Vemuri

Publications and source records attributed to S Vemuri.

17 recordsLinked to original sources
PubMed2005

Comparison of assays for determination of peptide content for lyophilized thymalfasin.

Precise determination of the peptide content in drug substance samples depends highly upon the particular peptide compound and methodology used. Four independent methods were evaluated and compared to determine which would produce the best experimental precision for analysis of thymalfasin (thymosin alpha-1). Four different methods were evaluated including elemental analysis (CHN), quantitative amino acid analysis (AAA), high-performance liquid chromatography (HPLC), and Kjeldahl. This study demonstrates that the AAA method is highly variable in one laboratory while quite precise in another laboratory. Similarly, HPLC results depended on the laboratory conducting the study with more precise values obtained under cGMP. On the contrary, the CHN method yielded highly precise [i.e. <2% coefficient of variation (CV)] values. As precise knowledge of protein content is fundamental for the compounding of final pharmaceutical product of a specific potency, the CHN analysis is recommended for peptide content determination of the drug substance thymalfasin.

Amino Acid Sequence↗
PubMed2000

A screening technique to study the mechanical strength of gelatin formulations.

A semiquantitative method for measuring the mechanical strength of gelatin ribbons was demonstrated using a universal tensile testing machine (Instron, model 1122). Molten gelatin formulations comprised of acid-bone gelatin, limed-hide gelatin, or their combinations were made, pored as gelatin films, and aged at 50% relative humidity (RH). Viscoelastic properties (mechanical strength) of five gelatin formulations were evaluated by determining elastic modulus, tensile strength, and ratio of tensile strength to elastic modulus of gelatin ribbons. This study demonstrated that a 3:1 ratio of acid-bone to limed-hide gelatin combination showed better viscoelastic properties than the other formulations studied.

Chemistry, Pharmaceutical↗
PubMed1999

The inhibition of capacitative calcium entry due to ATP depletion but not due to glucosamine is reversed by staurosporine.

The capacitative Ca2+ entry pathway in J774 macrophages is rapidly inhibited by the amino sugar glucosamine. This pathway is also inhibited by treatments such as 2-deoxy-D-glucose (2dGlc) or glucose deprivation that inhibit glycolysis and lead to significant decreases in cellular ATP and other trinucleotides. We sought to determine whether glucosamine's effect on capacitative Ca2+ entry was also due to ATP depletion, as has been suggested recently for its link to insulin resistance. In contrast to brief treatments with 2dGlc, there was no significant decrease in ATP following exposure to glucosamine. In addition, the 2dGlc-mediated inhibition of capacitative Ca2+ influx was reversed by staurosporine, a microbial alkaloid that inhibits a broad range of protein kinases. Staurosporine was also able to reverse the inhibition of capacitative Ca2+ entry seen following other treatments that decreased cellular ATP levels, including cytochalasin B and iodoacetic acid. Other inhibitors of protein kinase C, including bisindolylmaleimide, K252a, H-7, and calphostin C, were unable to mimic this effect of staurosporine. However, the inhibition of capacitative Ca2+ influx in the presence of glucosamine was not reversed by staurosporine. These data indicate that the inhibitory action on capacitative Ca2+ entry of glucosamine is distinct from that caused by ATP depletion.

Adenosine Triphosphate↗
PubMed1995

Preparation and characterization of liposomes as therapeutic delivery systems: a review.

Liposome drug delivery systems are being developed for a variety of drugs. Scale-up process to larger size batches is often a monumental task for the process development scientists. This article reviews various aspects of process development work pertinent to aseptic process techniques for liposomes. This article also has discussed the bilayer properties of liposomes and showed the nomenclature used to classify the liposomes. Discussed is the pH gradient method to load liposomes. Issues and challenges involved in prolonging the shelf-life of liposomes is presented. This review covered the importance of complete removal of organic solvent that is used in the process. Finally the authors presented an HPLC method for quick identification and assay of various phospholipids in a mixture of phospholipids.

Drug Carriers↗
PubMed1994

Development and characterization of a liposome preparation by a pH-gradient method.

A pH gradient across liposome bilayers was established in order to load a model drug (orciprenaline sulphate) into liposome vesicles. This method of liposome loading resulted in yields as high as 80-85% encapsulation. An eight-step process was designed to scale-up the process and was evaluated. In this process a diafiltration technique was successfully used to remove the excess orciprenaline sulphate present in the external medium. Finally, drug-loaded liposomes were lyophilized using lactose as an internal and external liposomal cryoprotectant. Five-month stability data for the liposomes is reported. An HPLC technique was used to determine the drug concentration and a laser light-scattering technique was employed to determine the liposome vesicle size and polydispersity factor. Liposomes prepared by the pH-gradient method showed high encapsulation efficiency. Upon storage at 2-8 degrees C the vesicle size increased and encapsulation efficiency decreased with time. These phenomena are attributed to gradual fusion of liposomes and loss of drug to the extra-liposomal media.

Capsules↗
PubMed1994

The stability of bFGF against thermal denaturation.

The influence of sulphated ligand and pH on thermal denaturation of basic fibroblast growth factor (bFGF) was investigated by differential scanning calorimetry (DSC), and verified by fluorescence spectrophotometry. Purity of bFGF before and after heat denaturation was assessed by SDS-PAGE analysis. In DSC studies the samples were heated to 95 degrees C. The midpoint of the temperature change in the thermogram was designated as Tm. Sulphated ligand experiments were undertaken in potassium phosphate (pH 6.5) and sodium acetate buffers. Control thermograms (with no ligand) showed a Tm at 59 degrees C in potassium phosphate buffer. Higher Tm values were noted as sulphated ligand concentration was increased. Similarly when heparin was added, the Tm moved to a higher temperature. A ratio as low as 0.3:1 of heparin to bFGF, increased the Tm to 90 degrees C, which is a 31 degrees C shift in Tm. The effect of pH on thermal denaturation of bFGF was studied in a citrate-phosphate-borate buffer system. A shift in Tm from 46 to 65 degrees C was observed as the pH is changed from 4 to 8. Changes in protein conformation as a function of pH were monitored by fluorescence spectroscopy. It was found that a pH range from 5 to 9 is optimal for the stability of bFGF formulations. In a stability study it was noted that heparin protected bFGF from thermal denaturation only at high temperature.

Buffers↗
PubMed1992

A correlation between digoxin plasma concentrations and systolic time intervals in hospitalized congestive heart failure patients.

Plasma digoxin level is at best an indirect measure of pharmacological response to digoxin in patients being treated for congestive heart failure. Systolic time interval (STI) measurement reflecting left ventricular function at the physiological site of action of digoxin, is both more direct and non-invasive. With a portable instrument to measure systolic time intervals, the measurement can also be convenient for hospital staff. A portable electrocardiogram (ECG) machine was modified to mimic the capabilities of a large, multichannel model. Upon satisfactory evaluation, it was employed in the collection of systolic time interval data from five hospitalized patients undergoing digoxin treatment. An attempt was made to show a relationship between STI indices and digoxin plasma concentrations. Additionally, a statistical comparison was made of change in STI (delta STI) and plasma digoxin concentration both before and after drug administrations. The change in pre-ejection period (delta PEP) values show a significant difference over the changes in total electromechanical systole (delta QS2) and the changes in left ventricular ejection time (delta LVET). In three congestive heart failure patients, the time course of the change in plasma concentration showed good correspondence with delta PEP.

Adolescent↗
PubMed1992

Lyophilization cycle development for interleukin-2.

The effects of temperature and pressure variation on the lyophilization of interleukin-2 (IL-2) were studied. The human recombinant IL-2 used in this study was synthesized in and purified from E. coli, formulated, and then submitted to experimental lyophilization procedures. The collapse temperature of the formulation was first determined to be -25 degrees C by differential scanning calorimetry. The effects of chamber pressure and shelf temperature on IL-2 during lyophilization were evaluated. Lyophilization chamber pressures were varied from 100 mu to 300 mu in combination with the different chamber pressures. Lyophilized cake quality was assessed by evaluating three of its properties: residual moisture, by the Karl Fischer method; the monomeric content of the protein, by RP-HPLC; and oligomeric content, by SDS-PAGE. Process uniformity was checked by determining residual moisture in cakes collected from various locations in the chamber. The experimental data show that IL-2 can be lyophilized in a pilot unit within 30 hours. The IL-2 lyophilized at various primary drying conditions retained its purity and potency throughout the stability study period (12 months).

Calorimetry, Differential Scanning↗
PubMed1991

The experience of pain and perceptions of quality of life: validation of a conceptual model.

Pain is a common symptom of terminally ill cancer patients and a major challenge for hospice care. This paper presents a conceptual model of the relationship between pain and quality of life that was derived from the authors' previous research. The model should prove useful to hospice clinicians and researchers in evaluating the impact of palliative care on the quality of life.

Evaluation Studies as Topic↗
PubMed1990

MacProMass: a computer program to correlate mass spectral data to peptide and protein structures.

A program known as MacProMass has been written for Macintosh computers to assist in the analysis of mass spectral data of peptides and proteins. The program employs a user friendly, graphical interface and accommodates a variety of protein structures including cyclic peptides and multiple chain proteins. In addition to molecular mass calculations for positive and negative molecular ions, MacProMass also calculates elemental composition, amino acid composition, isoelectric point, surface free energy, and high-performance liquid chromatography index values for whole structures and peptide fragments resulting from enzymatic or chemical degradation. Users can program their own amino acid residues and terminal groups. In addition to search routines for both mass and sequence, theoretical fragment ions for peptide mass spectra can be calculated. Analysis of variant proteins is facilitated with a subroutine that systematically catalogs single amino acid substitutions that correspond to mass differences between observed and expected molecular ions. Interchain and intrachain disulfide bonds and other types of linkages are maintained throughout the chemical and enzymatic degradation operations.

Amino Acid Sequence↗
PubMed1984

Simulated analysis of patient waiting time in an outpatient pharmacy.

The cost of various options for reducing patient waiting time in an outpatient pharmacy was studied through computer simulation. The time required to complete prescription filling tasks was recorded for a baseline of five pharmacy employees: technicians A, B, and C, a typist , and a pharmacist. A fixed factorial design of 12 configurations was used in which the number of pharmacy employees was varied (one, two, or three technician As; one or two typists ; and one or two technician Bs). Patient waiting time for each configuration was determined through computer simulation. Pharmacy employee salaries were used to calculate the relative cost of six of the configurations that were predicted to reduce waiting time to less than 10 minutes. Configurations with additional technician Bs or typists , or both, exhibited reductions in total waiting time of comparable magnitude. One of these configurations was identified as the least expensive per daily hours saved. Without disturbing the operation of the pharmacy, computer simulation was found useful in identifying the least expensive method of reducing patient waiting time in an outpatient pharmacy.

Appointments and Schedules↗
PubMedDate not supplied

Effect of cryoprotectants on freezing, lyophilization, and storage of lyophilized recombinant alpha 1-antitrypsin formulations.

Stabilizing effect of several commonly used cryoprotectants, namely lactose, sucrose, and polyvinyl-pyrrolidone (PVP), on recombinant alpha 1-antitrypsin (rAAT) were studied. A solution of rAAT in a phosphate/citrate buffer (pH 7.0) was made with and without a given cryoprotectant and filled into small vials. The vials were frozen on shelf, at -40 degrees C in a lyophilizer. At the end of the freezing cycle, half of the batch was thawed at ambient temperature and the other half was continued to the completion of lyophilization. Sample vials taken before freezing, after thawing, and after lyophilization were analyzed for total rAAT protein, monomeric content, and elastase-inhibitory activity. Results indicated that neither freeze-and-thaw nor lyophilization caused any damage to rAAT, contrary to what was generally believed. The control formulation (i.e., without a cryoprotectant) performed as good as those containing cryoprotectants. Freezing rates and protein concentration in formulation did not influence the stability of rAAT either. Lyophilized rAAT samples retained the activity and purity during the 12 month stability period, at room temperature and 2-8 degrees C.

Buffers↗