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Biomedical subjects

R Krishnamoorthy

Publications and source records attributed to R Krishnamoorthy.

At least 19 recordsLinked to original sources
PubMed1992

DNA sequence variation in a negative control region 5' to the beta-globin gene correlates with the phenotypic expression of the beta s mutation.

The clinical diversity of sickle cell anemia is strongly related to the degree of intracellular hemoglobin S (Hb S) polymerization, which in turn is dependent on the intracellular concentration of Hb S. We have recently defined a region of DNA approximately 500 bp 5' to the human beta-globin gene that acts as a silencer for the transcription of this gene and have shown that a polymorphism in this sequence is associated with a thalassemic phenotype of the beta-globin gene. In this work we have examined the correlation of DNA sequence polymorphisms in this silencer with binding of a previously identified putative repressor protein, BP1, and with the expression of Hb S in individuals heterozygous for the beta s allele. It was found that specific configurations of the motif, (AT)x(T)y, are homogeneous for the major haplotypes of the beta-globin gene cluster described on beta s chromosomes. Binding of BP1 was measured to DNA of three haplotypes: Indian, Benin, and Bantu. BP1 binds most tightly to DNA of the Indian haplotype, and these patients produce less beta s protein than Benin patients, whose DNA exhibits weaker affinity for BP1. Binding of BP1 is the weakest to DNA of the Bantu haplotype, which is associated with clinically more severe sickle cell symptoms. These data are consistent with the hypothesis that these polymorphisms may not be neutral and that the DNA sequence at this site may affect the expression of the beta s gene. Such an effect may be synergistic with other genetic variables, such as fetal hemoglobin levels, F-cell numbers, and the number of alpha-globin genes, in determining intracellular polymerization and, thus, the severity of the sickle cell syndromes.

Africa↗
PubMed1992

Genetic epidemiology of beta-thalassemia in Sicily: do sequences 5' to the G gamma gene and 5' to the beta gene interact to enhance HbF expression in beta-thalassemia?

The present epidemiological study of the molecular characteristics of beta-thalassemia in Sicily was prompted by the disparate phenotypic expression (in clinical status and absolute HbF level) observed in two beta-thalassemic homozygotes who were also homozygous for the beta-like globin gene cluster haplotype III. We suspected that polymorphisms within haplotype III could be the cause for the discrepancy. Based on the association of particular conformations of the (AT)xT(y) motif (-540 5' to the beta gene) with milder forms of thalassemia and sickle cell anemia, 38 homozygous beta-thalassemia patients were studied to define their haplotypes, the -158 site 5' to the G gamma gene (linked to haplotype III) and the structure of the (AT)xT(y) motif. We found that the patient who was phenotypically mild and homozygous for beta-thalassemia, haplotype III, and the -158 C----T mutation was homozygous for the rare (AT)9T5 motif. In contrast, the patient homozygous for beta-thalassemia, haplotype III, and the -158 mutation, but exhibiting a severe clinical course, was homozygous for the (AT)7T7 configuration. Others have suggested that (AT)9T5 is a negative regulatory protein binding sequence, and it is a silent carrier state for beta-thalassemia. The usual configuration (AT)7T7, has considerably less affinity for regulatory protein binding, and it is the most common configuration in Sicilian beta-thalassemics (67 of the 78 chromosomes studied). Within the 38 patients studied, seven were informative because they had various combinations of the (AT)9T5 and (AT)7T7 motif, and the -158 C----T mutation. The results in these patients suggest that only the co-presence of the (AT)9T5 configuration and a C----T change at -158 5' to the G gamma gene is associated with high HbF expression and a mild clinical phenotype. We postulate that these two regions of the beta-like globin gene cluster interact, when endowed with the proper sequences, to enhance the expression of HbF secondary to anemia.

Adolescent↗
PubMed1992

Presence of an African beta-globin gene cluster haplotype in normal chromosomes in Sicily.

African admixture in Sicily has been long suspected because of the presence of the sickle gene. Nevertheless, the degree of African admixture cannot be derived from the study of HbS frequency, since this gene was most likely expanded by the selective pressure of malaria, for a long time endemic to the region. We have examined 142 individuals from the Sicilian town of Butera (12% sickle trait) to search for other markers of the globin gene cluster less likely to be selected for by malaria. The TaqI polymorphism in the intervening sequences between the two gamma genes is informative. We have found only two instances of this African marker (TaqI(-)) among 267 normal chromosomes, demonstrating that the admixture occurred at a much lower level than previously thought.

Adolescent↗
PubMed1992

A novel sickle cell mutation of yet another origin in Africa: the Cameroon type.

The sickle cell mutation (beta s) arose as at least three independent events in Africa and once in Asia, being termed the Senegal, Benin, Bantu and Indian types respectively. An investigation in Cameroon was carried out to determine whether the atypical sickle genes observed in the neighboring countries are the result of recombination or the presence of a sickle cell mutation of a different genetic origin. It was conducted on 40 homozygous SS patients followed at the Blood Transfusion Center in the capital city of Yaoundé. On 80 beta s chromosomes, 13 exhibited a novel polymorphic pattern that was observed three times in the homozygous state. This chromosome contains an A gamma T gene. The restriction fragment length polymorphism haplotype is different from all the other beta s chromosomes in both the 5' and 3' regions, but has previously been reported in sporadic cases. The (AT)8(T)5 sequence in the -500 region of the beta gene is specific and different from that of the Senegal, Benin, Bantu or Indian beta s genes. All the carriers of this specific chromosome belong to the Eton ethnic group and originate from the Sanaga river valley. This observation strongly argues for yet another independent origin of the sickle cell mutation in Africa, here referred to as the "Cameroon type". The Benin haplotype and a Benin/Bantu recombinant haplotype have been observed in the other studied populations: Ewondo, Bamiléké, Bassa, Yambassa and Boulou.

Anemia, Sickle Cell↗
PubMed1992

Extensive study of DRB, DQA, and DQB gene polymorphism in 23 DR2-positive, insulin-dependent diabetes mellitus patients.

To gain insight into the HLA subregions involved in protection against insulin-dependent diabetes mellitus (IDDM) we investigated the polymorphism of HLA-DR and -DQ genes in 23 DR2 IDDM patients. Results show the following. (1) Fourteen patients (61%) possess the DRB1, DRB5, and DQB1 alleles found in DRw16/DQw5 healthy people. These data contrast with the 5% of DRw16 normally found in DR2 populations and are in agreement with former observations supporting that the DRw16 haplotype is not protective. (2) Nine DR2 patients, i.e., 39% versus 95% in published DR2 controls, possess the DRB alleles found in DRw15 unaffected people. Among them, six patients have also DQA1 and DQB1 alleles identical to those found in DRw15/DQw6 healthy individuals. These data confirm that the DRw15/DQw6 haplotype is protective but indicate that none of the DR or DQ alleles, alone or in association, confers an absolute protection. (3) Our most striking results concern the very high frequency of recombinant haplotypes among the DRw15 patients: 3 of 9. In these three patients recombinations led to the elimination of both DQB1 and DQA1 alleles usually associated with DRw15. This strongly suggests that the occurrence of IDDM in these DRw15 patients is due to the absence of the usual DQ product and thus reinforces the assumption that DQ rather than DR region is involved in the protection conferred by the DRw15/DQw6 haplotype. Finally, analysis of the non-DRw15 haplotypes in heterozygous patients showed that IDDM can occur in the absence of any DQ alpha beta heterodimer of susceptibility.

DNA Probes, HLA↗
PubMed1992

Kinetics and mechanism of degradation of a cyclic hexapeptide (somatostatin analogue) in aqueous solution.

A highly active cyclic hexapeptide analogue of somatostatin, Cyclo(N-Me-L-Ala-L-Tyr-D-Trp-L-Lys-L-Val-L-Phe), L-363,586, was found to improve the control of postprandial hyperglycemia in diabetic animals when given in combination with insulin. The compound is reported to be relatively stable in blood, nasal cavity, and intestinal lumen but undergoes rapid degradation in aqueous solution. The objective of this study was to elucidate the degradation mechanisms based on the kinetic data and the structure of the degradation products. Both pH and temperature had a profound influence on the instability of the peptide in aqueous solution. The data indicated that the peptide was most stable at a pH of about 4.7. The pH-rate profile exhibited specific acid catalysis at a pH less than 3.0 and base catalysis above pH 10.5. The kinetic pKa was determined to be 9.7. This pKa could be attributed to the tyrosine residue. The mechanisms of degradation under acidic and alkaline conditions appear to be different. Identification of the fragments obtained using mass spectrometry and amino acid sequencing suggest that the cyclic compound was cleaved to yield a linear fragment, which underwent further cleavage at both peptide linkages alpha to the tryptophanyl residue. The indole group of that residue is probably the potential nucleophile attacking the adjacent carbonyls. A rate equation for the degradation of the hexapeptide has been proposed.

Amino Acid Sequence↗
PubMed1992

Cyclodextrins as nasal absorption promoters of insulin: mechanistic evaluations.

The safety and effectiveness of cyclodextrins (CD) as nasal absorption promoters of peptide-like macromolecules have been investigated. The relative effectiveness of the cyclodextrins in enhancing insulin nasal absorption was found to be in the descending order of dimethyl-beta-cyclodextrin (DM beta CD) greater than alpha-cyclodextrin (alpha-CD) greater than beta-cyclodextrin (beta-CD), hydroxypropyl-beta-cyclodextrin (HP beta CD) greater than gamma-cyclodextrin (gamma-CD). A direct relationship linking absorption promotion to nasal membrane protein release is evident, which in turn correlates well with nasal membrane phospholipid release. The magnitude of the membrane damaging effects determined by the membrane protein or phospholipid release may provide an accurate, simple, and useful marker for predicting safety of the absorption enhancers. In order to estimate further the magnitude of damage and specificity of cyclodextrin derivatives in solubilizing nasal membrane components, the enzymatic activities of membrane-bound 5'-nucleotidase (5'-ND) and intracellular lactate dehydrogenase (LDH) in the perfusates were also measured. HP beta CD at a 5% concentration was found to result in only minimal removal of epithelial membrane proteins as evidenced by a slight increase in 5'-ND and total absence of LDH activity. On the other hand, 5% DM beta CD caused extensive removal of the membrane-bound 5'-ND. Moreover, intracellular LDH activity in the perfusate increased almost linearly with time. The cyclodextrins are also capable of dissociating insulin hexamers into smaller aggregates, and this dissociation depends on cyclodextrin structure and concentration. Enhancement of insulin diffusivity across nasal membrane through dissociation may provide an additional mechanism for cyclodextrin promotion of nasal insulin absorption.

5'-Nucleotidase↗
PubMed1992

Study of CYP2D6 gene in children with autoimmune hepatitis and P450 IID6 autoantibodies.

Cytochrome P450 IID6 is an autoantigen recognized by the sera of children affected with a subtype of autoimmune hepatitis. It was hypothesized that a mutation in the CYP2D6 gene could explain the autoimmune response in these patients. To examine this question, genomic DNA from peripheral lymphocytes (n = 9) and liver (n = 1) of 10 patients with anti-LKM-1 antibody was analysed by Southern blot for genetic association studies between a particular CYP2D6 haplotype and autoimmune hepatitis. In addition, a region of CYP2D6, from the same genomic DNA, was amplified by polymerase chain reaction (PCR) and digested by BstNI, in a search for the most prevalent 29B mutation, described in subjects who do not express the P450 IID6. Total RNA and proteins, prepared from the liver of an anti-LKM-1+ patient, were analysed by Northern and Western (immunoblot) blots respectively. Our results do not reveal any major structural change in the DNA of this patient at the CYP2D6 locus that could explain their autoimmune response. Corroborating this observation, no changes were noted either in P450 IID6 mRNA size or in the corresponding protein. However, these data do not exclude the possibility of subtle changes in the protein due to point mutations in critical regions that might trigger an autoimmune response.

Autoantibodies↗
PubMed1991

Characterization of highly virulent Escherichia coli strains by ribosomal DNA restriction fragment length polymorphism.

Patterns of ribosomal DNA polymorphism were examined to compare carboxylesterase B type B1 strains and B2 strains of Escherichia coli isolated from extra-intestinal infections. DNA from 14 type B2 strains showing the presence of alpha-haemolysin and mannose-resistant haemagglutinin and lethality to mice and 14 type B1 strains lacking these characteristics, was digested with HindIII, EcoRI, BamHI or BglII restriction enzymes and analysed by Southern blotting. The obtained ribotypes clearly differentiated the B2 strains from the B1 strains. These results indicate that genotypes of the highly virulent B2 strains are different from that of the less virulent B1 strains.

Blotting, Southern↗
PubMed1991

Application of silver staining to the rapid typing of the polymorphism of HLA-DQ alleles by enzymatic amplification and allele-specific restriction fragment length polymorphism.

A rapid and highly sensitive silver staining method, originally developed for the detection of proteins, was slightly modified to detect nucleic acids in polyacrylamide gels. The second exons of the histocompatibility antigen HLA-DQA 1 and DQB 1 genes were selectively amplified from genomic DNA by the polymerase chain reaction (PCR). Digestion of the PCR products by endonucleases, followed by their size-separation on polyacrylamide gels and visualization by silver staining, allowed us to define the HLA-DQ alleles of the genomic DNA. The intensity of staining of digested PCR-amplified DNA is linear from at least 8 to 18 ng for fragments of lengths ranging from approximately 40 to 200 bp. Thus, silver staining in combination with PCR and allele-specific restriction fragment length polymorphism provides a simple, safe, and rapid method for accurate definition of HLA-DQ alleles at the nucleotide level in the clinical typing laboratory.

Base Sequence↗
PubMed1991

A simple nonradioactive method of DNA typing for subsets of HLA-DR4: prevalence data on HLA-DR4 subsets in three diabetic population groups.

The molecular basis of eight DR4 subtypes resides in several nucleotide substitutions in the third hypervariable region of the DR beta 1 chain. The typing of DR4 subsets using the mixed lymphocyte culture (MLC) assay or allele-specific oligonucleotide hybridization is expensive, cumbersome, and requires the use of radioisotopes. We have therefore developed a rapid and safe procedure for subtyping DR4-alleles that involves selective amplification of the second exon of the DR4-DRBI gene followed by unambiguous subtype discrimination after digestion with five allele-specific endonucleases [polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP)] and visualization of the polymorphic fragments with silver or ethidium bromide staining. Validity of this subtyping procedure was initially examined by the use of cell lines of known subtypes. Three groups of DR4 patients with insulin-dependent diabetes mellitus (IDDM) from Chinese, Tunisian, and Caucasian populations were subtyped and the prevalence of subtype associations with IDDM was compared.

Alleles↗
PubMed1991

Comparison of molecular epidemiological tools for Branhamella catarrhalis typing.

Twenty-one Branhamella catarrhalis strains selected for their diversity by esterase electrophoretic polymorphism, and belonging to 20 distinct zymotypes, were studied by restriction fragment length polymorphism (RFLP) of total DNA after ethidium bromide staining and of ribosomal DNA regions (ribotyping). The former analysis allowed the distinction of 20 patterns and the latter the delineation of 19 ribotypes. The three methods were correlated and showed a clonal diversity of the species. Esterase electrophoresis and Hinfl RFLP patterns after ethidium bromide staining appeared to be simple tools for use in B. catarrhalis epidemiology.

Bacterial Typing Techniques↗
PubMed1991

Origin and spread of beta-globin gene mutations in India, Africa, and Mediterranea: analysis of the 5' flanking and intragenic sequences of beta S and beta C genes.

Nucleotide polymorphisms of both the 5' flanking and intragenic regions of the human beta-globin gene were investigated by directly sequencing genomic DNA after amplification by the polymerase chain reaction in 47 subjects homozygous for the beta S or the beta C mutation. The sickle-cell mutation was found in the context of five different haplotypes defined by eight nucleotide substitutions and various structures of a region of the simple repeated sequence (AT) chi Ty. All subjects from the same geographic origin bear an identical chromosomal structure, defining the Senegal-, Bantu-, Benin-, Cameroon-, and Indian-type chromosomes. These results strengthen our previous conclusions about the multiple occurrence of the sickle-cell mutation. The Benin-type chromosome was also found among Algerian and Sicilian sickle-cell patients, whereas the Indian-type chromosome was observed in two geographically distant tribes, illustrating the spread of these sickle-cell genes. We also found that the intragenic sequence polymorphisms (frameworks) are not always in linkage disequilibrium with the BamH I polymorphism downstream from the beta-globin gene, as had been previously observed. Finally, we present a tentative phylogenetic tree of the different alleles at this locus. Some polymorphisms of this sequence might be contemporary with our last common ancestor, the great apes, that is, about 4-6 millions years old.

Africa↗