Ingrid Baumgarten

Reversible inhibition of intercellular junctional communication by glycyrrhetinic acid

Intercellular gap-junctional communication was measured using metabolic co-operation in co-cultures of argininosuccinate synthetase-deficient and argininosuccinate lyase-deficient human fibroblasts. 18-alpha-glycyrrhetinic acid (AGA) was found to inhibit communication by more than 95% at concentrations as low as 2 microM. Concentrations up to 100 microM were not cytotoxic over a period of 2 hours. Communication inhibition was of rapid onset and was readily reversible. Communication remained continuously yet reversibly blocked in cells cultured in the presence of AGA for 20 days. The related compounds 18-beta-glycyrrhetinic acid and carbenoxolone also caused communication inhibition. The effect is probably not mediated via mineralocorticoid or glucocorticoid receptors since aldosterone and glucocorticoids had no effect on communication. AGA thus has properties of a useful inhibitor in the study of intercellular junctional communication.

Genetic variation and population structure in remnant populations of black rhinoceros, Diceros bicornis, in Africa.

Black rhinoceros (Diceros bicornis) are one of the most endangered mammal species in Africa, with a population decline of more than 96% by the end of the last century. Habitat destruction and encroachment has resulted in fragmentation of the remaining populations. To assist in conservation management, baseline information is provided here on relative genetic diversity and population differentiation among the four remaining recognized subspecies. Using microsatellite data from nine loci and 121 black rhinoceros individuals, and comparing the results with those of other African species affected in similar ways, Diceros bicornis michaeli retained the most genetic diversity (heterozygosity 0.675) compared with Diceros bicornis minor (0.459) and Diceros bicornis bicornis (0.505), suggesting that the duration of the known bottlenecks in these populations has only had a limited impact on diversity. Comparable and moderate degrees of population differentiation were found between D. b. minor, D. b. bicornis and D. b. michaeli. Results from the single sample available of the most endangered subspecies, Diceros bicornis longipes, showed the least diversity of all individuals examined. This information should assist conservation management decisions, especially those affecting population viability assessments and selection of individuals for translocations, and will also facilitate subspecies identification for ex situ individuals of uncertain origin.

Glutaric aciduria type 1 in South Africa-high incidence of glutaryl-CoA dehydrogenase deficiency in black South Africans.

Glutaric Aciduria type 1 (GA 1) is an inherited disorder of lysine and tryptophan catabolism that typically manifests in infants with acute cerebral injury associated with intercurrent illness. We investigated the clinical, biochemical and molecular features in 14 known GA 1 patients in South Africa, most of whom were recently confirmed following the implementation of sensitive urine organic acid screening at our laboratory. Age at diagnosis ranged from 3days to 5years and poor clinical outcome reflected the delay in diagnosis in all but one patient. Twelve patients were unrelated black South Africans of whom all those tested (n=11) were found homozygous for the same A293T mutation in the glutaryl-CoA dehydrogenase (GCDH) gene. Excretion of 3-hydroxyglutarate (3-OHGA) was >30.1μmol/mmol creatinine (reference range <2.5) in all cases but glutarate excretion varied with 5 patients considered low excretors (glutarate <50μmol/mmol creatinine). Fibroblast GCDH activity was very low or absent in all of five cases tested. Heterozygosity for the A293T mutation was found 1 in 36 (95% CI; 1/54 - 1/24) unrelated black South African newborns (n=750) giving a predicted prevalence rate for GA 1 of 1 in 5184 (95% CI; 1/11664 - 1/2304) in this population. GA 1 is a treatable but often missed inherited disorder with a previously unrecognised high carrier frequency of a single mutation in the South African black population.

A Molecular Phylogeny of Some Bovidae Based on Restriction-Site Mapping of Mitochondrial DNA

Restriction-endonuclease site maps of mitochondrial DNA were constructed for members of the family Bovidae emphasizing species in the Alcelaphinae, Bovinae, and Aepycerotinae. Cladograms weakly supported sister status of the impala, Aepyceros melampus , relative to the Alcelaphinae, and monophyletic status of the Bovini and Tragelaphini. Four members of the Tragelaphini remained an unresolved quadrichotomy, which would be consistent with the inclusion of the eland, Taurotragus oryx , within Tragelaphus . The restriction data are consistent with a radiation for the Tragelaphini at the end of the Miocene.

Metabolic cooperation between argininosuccinate synthetase and argininosuccinate lyase deficient human fibroblasts.

Human fibroblasts deficient in either argininosuccinate synthetase or argininosuccinate lyase show low levels of incorporation of [14C]citrulline into protein. However, when these two cell types are co-cultured [14C]citrulline incorporation is restored to the levels found in control cultures. This metabolic cooperation is cell-density-dependent and does not occur by diffusion of argininosuccinate into the medium. Our results indicate that argininosuccinate passes between the two cell types via intercellular junctions, and this system provides a simple and accurately quantifiable model for the study of intercellular communication.

Inhibition of intercellular junctional communication in human fibroblasts by triphenylmethane, triphenylmethylchloride, tetraphenylboron and related compounds

Intercellular junctional communication was measured using [14C]citrulline incorporation in co-cultures of argininosuccinate synthetase-deficient and argininosuccinate lyase-deficient human fibroblasts. Triphenylmethane, triphenylmethylchloride and tetraphenylboron inhibited communication at concentrations at least 12-fold lower than cytotoxic concentrations. This inhibition was of rapid onset and was rapidly reversible by washing the co-cultures. Refractoriness to inhibition did not develop after prolonged exposure. Several other compounds also induced communication inhibition, but only at concentrations slightly below cytotoxic concentrations. Treatment of co-cultures with calcium ionophore A23187 or cycloheximide did not cause communication inhibition. It is suggested that triphenylmethane, triphenylchloride and tetraphenylboron may be useful inhibitors for studying the roles of intercellular junctional communication in some biological systems.

Effects of extracellular calcium and magnesium on junctional intercellular communication in human fibroblasts

The role of extracellular calcium and magnesium in intercellular communication via permeable junctions was studied by measuring metabolic co-operation between ASS- and ASL- human fibroblasts. Communication through pre-existing junctions was not affected by the removal of extracellular calcium and magnesium from the medium. On the other hand, the establishment of communication through new permeable junctions, when ASS- and ASL- cells were mixed, was dependent on the presence of extracellular calcium and magnesium.

Association Between the 4 bp Proinsulin Gene Insertion Polymorphism (IVS-69) and Body Composition in Black South African Women

The objective of the study was to examine the association between a functional 4 bp proinsulin gene insertion polymorphism (IVS‐69), fasting insulin concentrations, and body composition in black South African women. Body composition, body fat distribution, fasting glucose and insulin concentrations, and IVS‐69 genotype were measured in 115 normal‐weight (BMI <25 kg/m2) and 138 obese (BMI ≥30 kg/m2) premenopausal women. The frequency of the insertion allele was significantly higher in the class 2 obese (BMI ≥35kg/m2) compared with the normal‐weight group (P = 0.029). Obese subjects with the insertion allele had greater fat mass (42.3 ± 0.9 vs. 38.9 ± 0.9 kg, P = 0.034) and fat‐free soft tissue mass (47.4 ± 0.6 vs. 45.1 ± 0.6 kg, P = 0.014), and more abdominal subcutaneous adipose tissue (SAT, 595 ± 17 vs. 531 ± 17 cm2, P = 0.025) but not visceral fat (P = 0.739), than obese homozygotes for the wild‐type allele. Only SAT was greater in normal‐weight subjects with the insertion allele (P = 0.048). There were no differences in fasting insulin or glucose levels between subjects with the insertion allele or homozygotes for the wild‐type allele in the normal‐weight or obese groups. In conclusion, the 4 bp proinsulin gene insertion allele is associated with extreme obesity, reflected by greater fat‐free soft tissue mass and fat mass, particularly SAT, in obese black South African women.