Impact of cholesterol reduction on peripheral arterial disease in the Program on the Surgical Control of the Hyperlipidemias (POSCH)

BACKGROUND: Few lipid/atherosclerosis intervention trials have assessed the impact of cholesterol reduction on peripheral arterial disease. The 838 patients evaluated in the Program on the Surgical Control of the Hyperlipidemias (POSCH) trial represent more than the total number of patients in the seven previously reported studies. METHODS: Peripheral arterial disease in POSCH was assessed by progression of clinical disease, serial changes in the systolic blood pressure ankle/brachial index (ABI), and changes on sequential peripheral arteriograms. RESULTS: At the time of formal closure of the POSCH trial on July 19, 1990, claudication or limb-threatening ischemia was exhibited in 72 of 417 control group (CG) patients and in 54 of 421 intervention group (IG) patients (IG relative risk [RR] 0.702, 95% confidence interval [CI] 0.169 to 1.000, p = 0.049). With additional follow-up evaluation to September 30, 1994, clinical peripheral arterial disease was evident in 91 CG patients and 64 IG patients (RR 0.656, 95% CI 0.200 to 0.903, p = 0.009). At the 5-year follow-up evaluation, an ABI of less than 0.95 was present in 41 of 120 CG patients and in 24 of 126 IG patients, all of whom had an ABI of 0.95 or greater at baseline (RR in the IG of 0.557, 95% CI 0.360 to 0.863, p < 0.01). No appreciable differences were noted in the progression or regression of arteriographic peripheral arterial disease between the two groups. CONCLUSIONS: Effective cholesterol reduction in POSCH led to statistically significant differences between the control and the intervention groups in the development of clinically evident peripheral arterial disease and in the ABI values, but not in the peripheral arteriograms. Additional studies need to assess the correlation between peripheral arterial changes and coronary arterial changes and clinical atherosclerosis events. Intervention trials that study peripheral arterial disease have intrinsic value in the evaluation of the impact of risk factor modification on progression of atherosclerotic peripheral arterial disease.     

Infection by Mycobacterium tuberculosis promotes human alveolar macrophage apoptosis

The effect of Mycobacterium tuberculosis infection on the viability of healthy (control) human alveolar macrophages was evaluated by staining with ethidium homodimer and calcein to discriminate live from dead cells. Infection with M. tuberculosis H37Ra or H37Rv increased macrophage mortality at 6 days from the control level of 3.8% +/- 0.7% to 28.7% +/- 6.9% or 12.6% +/- 3.1%, respectively (P < 0.001 for comparisons of all conditions). A role for tumor necrosis factor alpha (TNF-alpha) in the M. tuberculosis-induced cytolysis of alveolar macrophages was demonstrated by increased cytotoxicity following the addition of exogenous TNF-alpha to the cultures and by enhancement of macrophage survival when M. tuberculosis-infected alveolar macrophages were treated with pentoxifylline or anti-TNF-alpha antibody. The cytolytic mechanism was determined to be apoptosis by the demonstration of a characteristic internucleosomal ladder of genomic DNA by agarose gel electrophoresis, by finding nuclear fragmentation and condensation by electron microscopy, and by in situ terminal transferase-mediated nick end labeling of fragmented DNA in alveolar macrophages infected with M. tuberculosis in vitro. The latter technique was employed to reveal extensive apoptosis within caseating granulomas from lung tissue samples from clinical tuberculosis cases. The induction of apoptosis in alveolar macrophages by M. tuberculosis may play a role in the macrophage-pathogen interaction of tuberculosis in vivo.     

Mutational analysis of potential zinc-binding residues in the active site of the enterococcal D-Ala-D-Ala dipeptidase VanX

VanX, one of the five proteins required for the vancomycin-resistant phenotype in clinically pathogenic Enterococci, is a zinc-containing d-Ala-d-Ala dipeptidase. To identify potential zinc ligands and begin defining the active site residues, we have mutated the 2 cysteine, 5 histidine, and 4 of the 28 aspartate and glutamate residues in the 202 residue VanX protein. Of 10 mutations, 3 cause inactivation and greater than 90% loss of zinc in purified enzyme samples, implicating His116, Asp123, and His184 as zinc-coordinating residues. Homology searches using the 10 amino acid sequence SxHxxGxAxD, in which histidine and aspartate residues are putative zinc ligands, identified the metal coordinating ligands in the N-terminal domain of the murine Sonic hedgehog protein, which also exhibits an architecture for metal coordination identical to that observed in thermolysin from Bacillus thermoproteolyticus. Furthermore, this 10 amino acid consensus sequence is found in the Streptomyces albus G zinc-dependent N-acyl-d-Ala-d-Ala carboxypeptidase, an enzyme catalyzing essentially the same d-Ala-d-Ala dipeptide bond cleavage as VanX, suggesting equivalent mechanisms and zinc catalytic site architectures. VanX residue Glu181 is analogous to the Glu143 catalytic base in B. thermoproteolyticus thermolysin, and the E181A VanX mutant has no detectable dipeptidase activity, yet maintains near-stoichiometric zinc content, a result consistent with the participation of the residue as a catalytic base.     

Asterlingulatosides C and D, cytotoxic triterpenoid saponins from Aster lingulatus

Over the last few decades, European courses in which 'classical' tropical medicine (i.e. parasitology, entomology, and clinical aspects of tropical diseases) is taught have largely become anachronisms. Most countries in the tropics have their own medical schools and few have much need of expatriate doctors. There do, however, appear to be other ways in which Europeans may still help improve health in the tropics. One is to control the quality of the expatriate nurses who are still in demand in the tropics (often as cheaper, generally less demanding substitutes for doctors). This may be achieved by only training the best, insisting they spend some time after graduation gaining maturity before they leave for the tropics, ensuring they realise that their clinical skills will probably be inferior to their local counterparts in the tropics, and encouraging them to continue studying once abroad. The second way Europeans may help is to change the bias of their courses from teaching to training. There seems little doubt that the intellectual personalities of the brightest young men and women in the tropics often develop far better when they spend a period in a foreign environment, especially when they are allowed to function within a team, with trainees and trainers from other countries. Some 'international' courses may offer such benefits, especially if closely tailored to the needs of the trainees and their home countries.     

Construction and characterization of a radio-iodinatable mutant of recombinant human CD4

Drug-selected intrachromosomal gene amplification by breakage-fusion-bridge (BFB) cycles is well documented in mammalian cells, but factors governing this mechanism are not clear. Here, we show that only some clastogenic drugs induce drug resistance through intrachromosomal amplification. We strictly correlate triggering of BFB cycles to induction of fragile site expression. We demonstrate a dual role for fragile sites in intrachromosomal amplification: a site telomeric to the selected gene is involved in initiation, while a centromeric site defines the size and organization of early amplified units. The positions of fragile sites relative to boundaries of amplicons found in human cancers support the hypothesis that fragile sites play a key role in the amplification of at least some oncogenes during tumor progression.     

The diagnosis and management of gall bladder in private patients in Harare

Gall bladder disease is getting more and more common in Africans. Some present with typical right upper quadrant pain but some are found on routine examination of the abdomen. The diagnosis is now very easy with ultrasound scan of the abdomen. The treatment used to be laparotomy and cholecystectomy but now is with laparoscopic surgery which leaves very little scarring. The results of the Harare study show chronic cholecystitis with cholesterol stones and very few bilirubinate stones.     

Alteration of Ca2+ dependence of neurotransmitter release by disruption of Ca2+ channel/syntaxin interaction

Presynaptic N-type calcium channels interact with syntaxin and synaptosome-associated protein of 25 kDa (SNAP-25) through a binding site in the intracellular loop connecting domains II and III of the alpha1 subunit. This binding region was loaded into embryonic spinal neurons of Xenopus by early blastomere injection. After culturing, synaptic transmission of peptide-loaded and control cells was compared by measuring postsynaptic responses under different external Ca2+ concentrations. The relative transmitter release of injected neurons was reduced by approximately 25% at physiological Ca2+ concentration, whereas injection of the corresponding region of the L-type Ca2+ channel had virtually no effect. When applied to a theoretical model, these results imply that 70% of the formerly linked vesicles have been uncoupled after action of the peptide. Our data suggest that severing the physical interaction between presynaptic calcium channels and synaptic proteins will not prevent synaptic transmission at this synapse but will make it less efficient by shifting its Ca2+ dependence to higher values.