Major achievements in cardiology in the past century: influence on Dutch cardiovascular medicine

At the occasion of the 75th anniversary of the Netherlands Society of Cardiology, it is interesting to look back on the major scientific achievements in cardiovascular medicine of the last century and to pay attention to the impact of these achievements on Dutch Cardiology. It might be a nice opportunity not only to mention the ten great discoveries in Cardiology in the past century, but also to address the pioneering work in the Netherlands. When honouring and paying tribute to Dutch individuals, this special article only refers to emeriti-professors in cardiology (and some other closely-related retired experts), as this is a historical reflection rather than a cross-sectional view of current attainments. The practising pioneers of today will hopefully be remembered in 75 years from now. (Neth Heart J 2009;17:136–9.)     

Thrombus Aspiration during Percutaneous coronary intervention in Acute non-ST-elevation myocardial infarction Study (TAPAS II)-Study design

Background and Objective. The Thrombus Aspiration during Percutaneous coronary intervention in Acute myocardial infarction Study (TAPAS) has shown that thrombus aspiration improves myocardial perfusion and clinical outcome compared with conventional primary percutaneous coronary intervention (PCI) in patients with ST-segment-elevation myocardial infarction. Impaired myocardial perfusion due to spontaneous or angioplasty-induced embolisation of atherothrombotic material also occurs in patients with non-ST-elevation myocardial infarction (NSTEMI). The aim of this study is to determine whether thrombus aspiration before stent implantation will result in improved myocardial perfusion in patients with NSTEMI compared with conventional PCI. Study design. The study is a single-centre, prospective, randomised trial with blinded evaluation of endpoints. The planned inclusion is 540 patients with acute NSTEMI who are candidates for urgent PCI. Patients are randomised to treatment with manual thrombus aspiration or to conventional PCI. The primary endpoint is the incidence of myocardial blush grade 3 after PCI. Secondary endpoints are coronary angiographic, histopathological, enzymatic, electrocardiographic and clinical outcomes including major adverse events at 30 days and one year. Implications. If thrombus aspiration leads to significant improvement of myocardial perfusion in patients with acute NSTEMI it may become part of the standard interventional approach. (Neth Heart J 2009;17:409–13.)     

Atrial fibrillation: to map or not to map?

Isolation of the pulmonary veins may be an effective treatment modality for eliminating atrial fibrillation (AF) episodes but unfortunately not for all patients. When ablative therapy fails, it is assumed that AF has progressed from a trigger-driven to a substrate-mediated arrhythmia. The effect of radiofrequency ablation on persistent AF can be attributed to various mechanisms, including elimination of the trigger, modification of the arrhythmogenic substrate, interruption of crucial pathways of conduction, atrial debulking, or atrial denervation. This review discusses the possible effects of pulmonary vein isolation on the fibrillatory process and the necessity of cardiac mapping in order to comprehend the mechanisms of AF in the individual patient and to select the optimal treatment modality.     

Opposite effects of adrenalectomy on eicosanoid release in rat peritoneal macrophages and spleen

The effect of adrenalectomy on the formation of cyclo-oxygenase and lipoxygenase products by activated peritoneal rat macrophages was determined and compared with that of the spleen. After isolation, the cells and tissues were incubated with [1-¹⁴C] arachidonic acid and the Ca-ionophore A23187 and the metabolites isolated by HPLC chromatography. The main components formed in the macrophages of the controls are 6-keto-PGF_1α, TxB₂ and 12-HETE. One peak represents 5, 12 di HETE. Smaller amounts of PGF_2α, PGE₂, PGD₂, LTB₄ and 15-HETE are also present. After adrenalectomy, a considerable increase occurs in the amounts of LTB₄, 15-HETE and 12-HETE. The increase in the PG is smaller. The compounds formed from endogenous arachidonic acid are also determined. In the cells of the controls, the formation of LTB₄ is considerably increased after adrenalectomy. In the spleen, PGD₂ and 12-HETE are decreased after adrenalectomy.The effect of the macrophages is most probably related to a diminished amount or inactivation of lipocortin, a glucocorticosteroid induced peptide with PlA₂ inhibitory activity in adrenalectomized animals. In the decrease in formation in the spleen, the absence of the permissive effect of glucocorticosteroids on the hormone-induced lipolysis may play a role.     

Analysis of hexamethylphosphoramide (HMPA)-induced genetic alterations in relation to DNA damage and DNA repair in Drosophila melanogaster

This paper reports the results of a study on the mutagenic profile of HMPA in Drosophila melanogaster. HMPA produced all types of genetic damage tested for in post-meiotic cells of treated males; at the concentrations used, recessive lethals and ring-X losses were induced at significant rates while 2–3 translocations, entire and partial Y-chromosome losses only occurred at low rates. From a comparison with alkylation-induced mutational spectra, we note a number of peculiarities of HMPA mutagenesis:

1. (1) there is no storage effect on HMPA-induced translocations;

2. (2) the ratio of F₂-lethals: F₃-lethals varies from 6 : 1 to 9 : 1, indicating a low capacity of HMPA for delayed mutations;

3. (3) the use of the DNA-repair-deficient mei-9^L1 females instead of an excision-proficient control strain has no influence on the recovery of mutations )recessive lethals) induced in males;

4. (4) the high frequencies of chromosome loss (CL) induced by HMPA, which are mostly due to ring-X loss, leads us to speculate that one (or more) of its metabolites acts as a DNA-crosslinking agent. In experiments on maternal effects with mei-9^L1 females, there is a 20–40% reduction in the rates of induced CL. Conversely, with mei-41^D5 females, there is a weak increase in CL frequencies.

5. (5) HPLC analysis of DNA reacted with [¹⁴C]HMPA exhibits no methylation at the O⁶ or the N-7 of guanine. This finding, together with the observed inactivity of hexaethylphosphoramide (HEPA) in the recessive lethal assay, suggests that the formation of DNA-bound forms from HMPA may not be the result of simple methylation reactions. This conclusion is supported by the genetic data, i.e., the lack of a storage effect on HMPA-induced chromosome rearrangements.

Consistent with a hypothesis by Brodberg et al. (1983) to explain the action of cisplatin in Drosophila, comparisons of the spectra of genetic alterations produced by HMPA, A 139 (bifunctional) and Thio-TEPA (trifunctional) in the assay for chromosome loss suggest the involvement of two distinct mechanisms in the formation of ring-X loss by crosslinking agents. One pathway concerns induction of chromosome loss as a consequence of sister-chromatid exchanges (SCEs). The second mechanism may be due to DNA adducts or a single adduct responsible for both a fraction of CL and for induced partial Y-loss (PL). Inactivation of the mei-9⁺ function has two consequences: SCE-mediated ring-X loss frequency is lowered in mei-9 females in comparison to the repair-proficient control strain, while the opposite effect is indicated for that fraction of ring-X loss generated by the second mutational pathway. Additional complicating factors include the observation of a dual role of storage in our study: the proportion of SCE-related chromosome losses decreases with increasing time of storage, but that produced by the alternative pathway increases. Thus, the CL frequencies actually recorded under the heading ‘chromosome loss’ appear as the net result of two mechanisms counteracting each other in their effects.     

Determination of leukotriene B4, 6-keto-prostaglandin F1 alpha and thromboxane B2 in peritoneal lavage fluid of sham-operated and adrenalectomized rats

In macrophages, isolated from the peritoneal fluid of rats, after activation, formation of metabolites of arachidonic acid occurs both by the cyclooxygenase and lipoxygenase pathways. The cells of normal animals produce mainly cyclooxygenase products. After adrenalectomy, a considerable increase occurs in the formation of lipoxygenase products, and less in those of the cyclooxygenase (1). In the experiments described here, the effect of adrenalectomy on the presence of leukotriene B4 (LTB4), 6-keto-PGF1 alpha and thromboxane B2 (TxB2) in the peritoneal fluid is determined.     

Influence of inhibition of the metabolic activation on the mutagenicity of some nitrosamines, triazenes, hydrazines and seniciphylline in Drosophila melanogaster

It is determined to what extent certain inhibitors of the xenobiotic metabolizing enzyme systems have an influence on the mutagenicity of various pro-mutagens in Drosophila. 1-Phenylimidazole (PhI) is used as an inhibitor of the cytochrome P-450 (P-450) mediated monooxygenase activities. Iproniazid (Ipr) is a typical monoamine oxidase (MAO) inhibitor which as well seems capable of inhibiting to a certain extent P-450 mediated metabolism. N, N-Dimethyl benzylamine (N, N-DMB) is used as a competitive substrate for the N-oxidizing flavin-containing dimethylaniline monooxygenase (FDMAM). The enzyme-inhibiting activities of PhI and Ipr were determined in vitro using microsomes obtained from Drosophila larvae and adults. Both compounds were capable of inhibiting benzo[a]pyrene (BP) hydroxylation and p-nitroanisole (p-NA) demethylation, although for Ipr 100-fold higher concentrations were required compared to PhI. As model-mutagens were used: the nitrosamines dimethylnitrosamine (DMN) and diethylnitrosamine (DEN), the triazenes 1-(2,4,6-trichlorophenyl)-3,3-dimethyltriazene (Cl3PDMT), 1-(3-pyridyl)-3,3-dimethyltriazene (PyDMT) and dacarbazine (DTIC), the hydrazines procarbazine (PCZ), 1,1-dimethylhydrazine (1,1-DMH) and 1,2-dimethylhydrazine (1,2-DMH) as well as the pyrrolizidine alkaloid seniciphylline (SPh). Simultaneous or pretreatment with Ipr results in a clear decrease of the mutagenicity of Cl3PDMT, while PhI pretreatment leads to an increased mutagenicity. This indicates that these two inhibitors do not inhibit the same enzyme or isozyme. For SPh too, Ipr pretreatment results in some decrease of the mutagenicity. This is in contrast to DEN, where the activation is clearly inhibited by PhI while Ipr has only a minor effect. For DMN, DTIC and PCZ both Ipr and PhI pretreatment caused considerable decreases of the mutagenicity. Inhibition of the FDMAM catalyzed activity by N,N-DMB resulted in an increase of mutagenicity with Cl3PDMT, in a moderate decrease of mutagenicity with DTIC, and a marked decrease with DMN, which was strongly inhibited. In contrast to the clear-cut mutagenicity of PCZ, 1,1-DMH and 1,2-DMH are not mutagenic in Drosophila. No change was observed upon inhibition of the various metabolizing activities. Apart from using strain differences in metabolizing activities and enzyme induction, enzyme inhibition can also be used to determine the influence of metabolism on the in vivo mutagenicity of promutagens in Drosophila.     

Respiration and measurement of cardiac output by thermodilution and central or peripheral dye dilution.

Cardiac output as measured by indicator dilution methods during artificial ventilation shows differences up to +/- 35%. We studied the influence of spontaneous breathing on measurement of cardiac output by thermodilution (TD) and central (CDD) and peripheral dye dilution (PDD) in seven anesthetized dogs. Injection of indicator was timed at one of five chosen moments in a respiratory cycle. The indicator for TD was also used as solvent for indocyanine green. Results were normalized by the value obtained with injection at inspiratory onset. Results of the central dilution methods showed a slight but not significant difference between values measured with injection at 25 and 75% of the respiratory cycle: 105.7 and 98.0%, respectively, (TD) and 102.3 and 97.2% (CDD). Mean cardiac output determined by TD, CDD, or PDD was not significantly different. We conclude that 1) a reasonable estimate of cardiac output may be obtained by means of a single indicator-dilution curve and 2) the choice of the dilution method may be determined by practical considerations.     

Blockade of transgenic gamma delta T cell development in beta 2-microglobulin deficient mice.

The gamma delta T cell receptor (TCR) of the hybridoma KN6 recognizes the self molecule encoded by a class I gene which maps within the TL region of the major histocompatibility complex (MHC) of H-2b mice. Mice transgenic (Tg) for this TCR were crossed with mice genetically deficient in beta 2-microglobulin (beta 2m). No mature Tg gamma delta T cells were detected in the thymus or the spleen of the beta 2m- gamma delta Tg mice. We conclude that interaction between the Tg gamma delta TCR and a beta 2m-associated molecule (probably an MHC class I molecule) is required for the generation of mature Tg gamma delta T cells.     

Influence of metabolic factors on the mutagenic effectiveness of cyclophosphamide in Drosophila melanogaster

This paper describes the influence of changes in metabolic activity on the in-vivo mutagenic effectiveness of cyclophosphamide in Drosophila melanogaster. A dose-dependent increase in mutagenicity was observed until a plateau value is reached which was increased only slightly after enzyme induction with Aroclor 1254, whereas induction with phenobarbital resulted in a decrease, especially when cyclophosphamide was applied by injection. Treatment of the adult males with inhibitors of the monoamine oxidase (MAO, EC 1.4.3.4), such as iproniazid (Ipr), benzimidazole or tryptamine, led to a marked increase of the mutagenic effectiveness of cyclophosphamide especially in spermatocytes. This indicates the importance of metabolic de-activation processes for the limited mutagenicity of cyclophosphamide in Drosophila. The principal active metabolite of cyclophosphamide, phosphoramide mustard, is extensively de-activated by enzymes that can be inhibited by 1-phenylimidazole (PhI), presumably cytochrome P-450 (EC 1.14.14.1), but not by those blocked by MAO inhibitors. Inhibition of the FAD-containing dimethylaniline monooxygenase (FDMAM, EC 1.14.13.8) by N,N-dimethylbenzylamine (N,N-DMB) resulted in some increase in cyclophosphamide mutagenicity only in spermatids. The marginal mutagenicity of cyclophosphamide in Drosophila larvae could not be increased either by cytochrome P-450 induction with phenobarbital or by MAO inhibition with Ipr. In contrast to the failure of cyclophosphamide to induce rod-chromosome loss, a considerable activity was found when a ring-shaped chromosome was used. Similar to the sex-linked recessive lethal (SLRL) test, ring-X loss frequency could be enhanced by simultaneous treatment with MAO inhibitors. The observed ring-X loss frequency declined when males treated with cyclophosphamide were mated to DNA-repair deficient mei-9L1 females. Cyclophosphamide produces chromosome breaks, detected as 2-3 translocations, in Drosophila spermatocytes, the stage in spermatogenesis that is also the most sensitive to the induction of SLRL mutations.