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R E Das

Publications and source records attributed to R E Das.

At least 19 recordsLinked to original sources
PubMed1996

Therapeutic botulinum type A toxin: factors affecting potency.

The type A neurotoxin produced by Clostridium botulinum is a potent neuromuscular blocking agent which causes paralysis by preventing the release of neurotransmitter from motor neurons. This property has resulted in the use of the toxin in the treatment of a number of neuromuscular diseases involving muscle spasms. At present, the only recognised assay to estimate accurately the potency of botulinum toxin in clinical preparations is bioassay, in which lethality is used as the endpoint. Such bioassay is inherently variable and large interlaboratory variability has been reported, highlighting problems for standardisation of activity in the absence of any commonly used reference preparation. In the present study, we have confirmed that many different assay conditions can affect potency estimates of clinical formulations of type A botulinum toxin. Further, our studies indicate that different preparations, because of their unique formulation and stability, are differentially affected by some of these assay conditions and that these differences might well contribute to the differences observed in their clinical use.

Analysis of Variance↗
PubMed1995

Enhanced potency of human calcitonin when fibrillation is avoided.

The peptide hormone calcitonin (CT) is a potent drug for the therapy of different bone diseases. Salmon CT (sCT) is reported to be more active than human CT (hCT). Human CT, but not sCT, has a strong tendency to aggregate and fibrillate in aqueous solutions. Recent investigations of the fibrillation mechanisms contributed to the development of hCT solutions in which fibrillation is inhibited. Taking into consideration these new findings, we tested the relative activities of hCT handled so as to avoid aggregation/fibrillation, sCT handled in exactly the same way, and hCT handled carefully but without regard to possible fibrillation (denoted R-hCT). The effect of the CTs on bone resorption by isolated osteoclasts was measured. This assay measures the activity of interest (bone resorption) by the cell (the osteoclast) at which therapy is directed. The concentration that inhibits 50% of resorption (EC50) for hCT is 10(-5)-10(-4) pg/mL, compared with 10(-2)-1 pg/mL for R-hCT and 10(-3)-10(-1) pg/mL for sCT. The results show that when aggregation and fibrillation are avoided, hCT at the EC50 is 2-4 orders of magnitude more active than R-hCT. Thus, earlier reports of lower potency of hCT compared with sCT may have been based on inadvertent use of partially aggregated/fibrillated samples of hCT. This finding may have implications for the dose and dosage forms advised for human therapy.

Analgesics↗
PubMed1994

International collaborative study of the candidate international standards for human tumour necrosis factors alpha (hTNF-alpha) and beta (hTNF-beta) and for murine tumour necrosis factor alpha (mTNF-alpha).

Four ampouled preparations of human tumour necrosis factor alpha (hTNF-alpha), one ampoule of human tumour necrosis factor beta (hTNF-beta) and one ampoule of mouse tumour necrosis factor alpha (mTNF-alpha) were evaluated by 20 laboratories in nine countries for their suitability to serve as international standards for these materials. A further three preparations of recombinant hTNF-alpha were included in the study so that hTNF-alpha preparations from different sources and with various structures could be compared. The preparations were assayed using in vitro bioassays and immunoassays. On the basis of the results reported here, with the agreement of participants in the study and with the authorisation of the Expert Committee on Biological Standardization (ECBS) of the World Health Organization (WHO), the preparation of hTNF-alpha in ampoules designated 87/650 was established as the international standard for hTNF-alpha with a defined potency of 40,000 international units per ampoule. Estimates relative to hTNF-alpha for both hTNF-beta and mTNF-alpha showed a substantial inter-laboratory variability in cytotoxic activity indicating that no preparations of hTNF-alpha would be suitable as a reference standard for either hTNF-beta or mTNF-alpha. However, given the current need for reference preparations for these materials, the ampouled preparations of hTNF-beta (87/640) and mTNF-alpha (88/532) were assigned potencies in arbitrary units and are available as reference reagents.

Animals↗
PubMed1994

Elevated cytosolic calcium levels in human lymphocytes during surface virus infections.

Generalised metabolic and electrolyte disturbances are known to accompany both plasma and surface virus infections. We have investigated whether these infections could impair the transport of Ca2+ from cells under conditions of controlled concentrations of the energy substrate glucose. Thus, cytosolic calcium levels ([Ca2+]i) were measured in single isolated lymphocytes obtained from healthy volunteers or those suffering from coryza. Before making measurements using a Ca(2+)-sensitive fluorescent dye indo 1, we incubated lymphocytes in buffers containing 0 mM-, 5.6 mM- or 11.2 mM-[glucose]. We found that [Ca2+]i of lymphocytes obtained from the sick were significantly higher than those from healthy controls both at 0 mM and 5.6 mM-[glucose], and that [Ca2+]i was inversely related to the media glucose concentration for both groups. These results suggest a diminished capacity of cation pumping in viral infections, such as coryza, in relationship to the available glucose as energy substrate.

Calcium↗
PubMed1994

Botulinum toxin.

Explore the source record for details and available documents.

Animals↗
PubMed1992

Serum immunoreactive erythropoietin in patients with idiopathic aplastic and Fanconi's anaemias.

In patients with idiopathic aplastic anaemia (n = 34) and Fanconi's anaemia (n = 8), sampled once or on several occasions, serum erythropoietin (Epo) increased with increasing severity of anaemia with apparently similar rates of increase in each group. However, after adjustment for Hb, log Epo values for the Fanconi's anaemics tended to be greater than those for the idiopathic aplastic anaemics (P < 0.01). Erythropoietin concentrations in serum samples from patients with Fanconi's and idiopathic aplastic anaemias tended to be greater than in samples from patients with anaemias from protein energy malnutrition, myelodysplasia and iron deficiency. The results suggest that there is no deficiency of erythropoietin in Fanconi's and idiopathic aplastic anaemias and that if exogenous erythropoietin is of any benefit it would need to be administered in doses large enough to induce a significant increase in log Epo. Results of the study illustrate the need to take account of the assumptions which underlie interpretation of the statistical analysis. Use of erythropoietin values in place of log Epo gives misleading conclusions demonstrable as invalid as the conditions for normality of distribution of the data and homogeneity of variances were not satisfied.

Adolescent↗
PubMed1992

Peripheral analgesic activities of peptides related to alpha-melanocyte stimulating hormone and interleukin-1 beta 193-195.

1. The hyperalgesic effects of interleukin-1 beta (IL-1 beta) and prostaglandin E2 (PGE2) were measured in rats. 2. Hyperalgesic responses to IL-1 beta were inhibited in a dose-dependent manner by alpha-melanocyte stimulating hormone (alpha-MSH)-related peptides with the following order of potency: [N1(4),D-Phe7]alpha-MSH greater than alpha-MSH greater than Lys-D-Pro-Val greater than Lys-Pro-Val greater than Lys-D-Pro-Thr greater than D-Lys-Pro-Thr. 3. Hyperalgesic responses to PGE2 were not inhibited by Lys-D-Pro-Thr and D-Lys-Pro-Thr but were inhibited in a dose-dependent manner by the other peptides with the same order of potency as against IL-1 beta. 4. The potencies of [N1(4), D-Phe7]alpha-MSH and alpha-MSH were greatly diminished by deletion of their C-terminal tripeptide, Lys11-Pro-Val13. 5. Nor-binaltorphimine (Nor-BNI) largely reversed the analgesic effects of alpha-MSH, [N1(4), D-Phe7]alpha-MSH, Lys-Pro-Val and Lys-D-Pro-Val indicating that kappa-opioid receptors mediated the analgesic activity of these peptides. 6. Nor-BNI did not antagonize the inhibition by Lys-D-Pro-Thr and D-Lys-Pro-Thr of IL-1 beta evoked hyperalgesia indicating that these peptides were not acting via kappa-opioid receptors.

Amino Acid Sequence↗
PubMed1991

A collaborative assay of the proposed third British Reference Preparation for Pertussis Vaccine and of the relative potencies of the second International Standard and the second British Reference Preparation for Pertussis Vaccine.

A collaborative assay has been carried out to estimate the mouse protective potency of a freeze-dried preparation of Bordetella pertussis (88/522) intended to serve as the third British Reference Preparation for Pertussis Vaccine (third BRP). The opportunity was also taken of reassessing the relationship between the second International Standard for Pertussis Vaccine and the second British Reference Preparation for Pertussis Vaccine (second BRP). Workers in nine laboratories took part in the study and together completed 19 assays which were considered to be statistically valid. Based on the results of the study it is proposed that ampouled preparation code number 88/522 be established as the third BRP with an assigned potency of 50 IU per ampoule. The evidence of this study also suggests that the relationship between the second International Standard for Pertussis Vaccine and the second BRP has not changed significantly since they were originally established.

Animals↗
PubMed1990

The International Reference Reagent for insulin-like growth factor-I.

Three preparations of recombinant DNA-derived insulin-like growth factor-I (IGF-I) were obtained, prepared in ampoules coded 86/522, 86/720 or 87/518, and evaluated as candidate International Reference Reagents in an international collaborative study (nine laboratories in four countries) in response to a request by the World Health Organization (WHO). Immunoassay dose-response curves for each of the three preparations did not in general differ significantly from those of local standards or from those of ampouled preparations of serum-derived IGF-I which were included in the study. The estimates of ampoule contents in terms of local standards showed considerable heterogeneity; the between-laboratory variability of estimates in terms of local standards was ten times greater than the inherent variability of estimates from these systems as estimated from comparisons of coded duplicates. Bioassay data were limited, and those available were inconsistent with immunoassay data. Of the three preparations, ampoules coded 86/720 were derived from an IGF-I preparation that was heterogeneous by high-performance liquid chromatography, and stability data for the preparation 86/522 were anomalous. As a result, the ampouled preparation coded 87/518 has been established by WHO as the International Reference Reagent for IGF-I for immunoassay, with an assigned ampoule content of 3.1 micrograms/ampoule, and is available from the National Institute for Biological Standards and Control.

Biological Assay↗
PubMed1988

World Health Organization International Standards for highly purified human, porcine and bovine insulins.

The 4th International Standard (IS) for Insulin, established in 1958, consists of a mixture of relatively impure bovine and porcine insulins and is not suitable as a standard for the assay of highly purified single-species insulins presently used in the treatment of diabetes. Preparations of human, bovine and porcine crystalline insulins, representative of current highly purified therapeutic insulins, have now been studied in an international collaborative study carried out by twenty-three laboratories in fifteen countries. In the collaborative study described here, each of the three preparations was found to be suitable for use as a standard for insulin for bioassay and each was established by WHO in 1986 as an international standard. The 4th IS of Insulin bovine/porcine (code numbered 58/6) has been discontinued. Insulin preparations should now be calibrated in terms of International Units defined by the standard for the appropriate species: the International Standard for Insulin, Human, the International Standard for Insulin, Bovine, or the International Standard for Insulin, Porcine.

Animals↗
PubMed1988

WHO international reference reagents for human proinsulin and human insulin C-peptide.

Candidate preparations for international reference reagents for immunoassays of human proinsulin and human insulin C-peptide were evaluated in an international collaborative study. With the authorization of the Expert Committee on Biological Standardization of WHO, the following preparations were established as international reference reagents: human proinsulin (84/611, nominal ampoule content 6 micrograms) and human insulin C-peptide (84/510, 10 micrograms). Each preparation is intended as a primary reference reagent for the calibration of immunoassays.

C-Peptide↗
PubMed1988

WHO international reference reagents for bovine and porcine proinsulins.

Candidate preparations for International Reference Reagents (IRR) for immunoassays of bovine and porcine proinsulin were evaluated in an international collaborative study. With the authorization of the Expert Committee on Biological Standardization of WHO, the following preparations were established as IRRs: bovine proinsulin (code 84/514, defined ampoule content 25 micrograms) and porcine proinsulin (84/528, 20 micrograms). The content of ampoules of these materials is defined in terms of mass rather than international units of activity, therefore they are IRR rather than International Standards. Both preparations are intended as primary reference reagents for the calibration of immunoassays.

Animals↗
PubMed1983

Stability of four steroids in lyophilised human serum.

The stability of a preparation of lyophilised serum and its suitability for use as a reference material for routine assays of cortisol, oestradiol, and progesterone have been studied in four laboratories with a variety of assay systems. Cortisol and oestradiol were also measured by gas chromatography-mass spectrometry. The lyophilised serum was suitable for use in all routine and reference assay methods examined, with between-method variability no greater than that for frozen serum pools. The concentrations of cortisol, oestradiol, and progesterone were predicted by accelerated degradation studies to decline by 0.01% per annum if the preparations were to be stored at --20 degrees C. The testosterone content of the preparation, determined in one laboratory, provided no evidence for degradation. The preparation can be shipped for use at ambient temperature without deleterious effect.

Drug Stability↗
PubMed1983

Interim report of results from an international collaborative study of the Proposed International Reference Preparation of porcine pancreatic kininogenase.

A collaborative study of the ampouled preparation of porcine pancreatic kininogenase, the Proposed International Reference Preparation (PIRP), was carried out, on behalf of the World Health Organization, by 19 laboratories in seven countries. The PIRP was studied using in vivo bioassays, immunoassays and in vitro enzyme assays involving natural protein substrate and small molecular ester and peptide substrates. An analysis of results obtained from a majority of the participating laboratories is presented. Comparison of the PIRP with the widely used Bayer house standard of porcine pancreatic kininogenase showed general agreement for estimates of relative activity, although differences were detected in some assay systems. The PIRP was shown to be stable and appears to be suitable to serve as an international reference preparation. Comparison of the PIRP with a preparation of highly purified human urinary kininogenase showed a wide diversity of estimates so that no general comparison of activities for these preparations is possible.

Animals↗
PubMed1978

The stability of standards for radioimmunoassay of human TSH: research standard A and the international reference preparation initially 68/38.

The stability of the International Reference Preparation of human TSH for immunoassay (previously distributed in ampoules coded 68/38) and of Research Standard A for HTSH has been examined by radioimmunoassay of accelerated degradation samples (stored as the dry ampouled preparations). Potency estimates on degradation samples suggest a high order of stability of immunopotency recognisable by two antisera (MRC 72/356 and Hunter 3A). For the International Reference Preparation the loss of immunopotency during storage at -20 degrees C is predicted to have been 0.56% per year.

Drug Stability↗