PubMed Health⌕ Search

Biomedical subjects

G Marx

Publications and source records attributed to G Marx.

At least 109 records · Page 6Linked to original sources
PubMed1991

[Status of local excision of local deep rectal cancers with curative intention].

103 cases have been analyzed retrospectively to define the indication for local extirpation of small and deep-seated rectum carcinomas with curative purpose. While pedunculated carcinomatous adenomas can be removed by endoscopic loop extraction, the non-sessile polypous carcinomas have to be radically extirpated by excision from intestinal wall resection is a promising procedure. Here, the transanal access by means of a funnel-shaped, lateral fenestrated glass speculum as introduced by Dewey yields better results than the rectotomia posterior.

Adult↗
PubMed1991

Free radical-induced fibrinogen coagulation: modulation of neofibe formation by concentration, pH and temperature.

The reaction of fibrinogen with Cu(II) (10-100 microM) and ascorbate (0.1-2.0 mM) leads to the formation of an insoluble clot-like material, "neofibe", which is dependent on experimental conditions. The reaction is observed with human and bovine fibrinogen, in the presence of 0.1-0.3 N NaCl, is optimal at the pH range of 7.4-7.7, and has characteristics typical of a site-specific Fenton reaction. Thus, it is inhibited by EDTA and catalase. Inhibition by mannitol is observed only at relatively high concentrations of this scavenger (greater than 100 mM). Concomitantly, the rate of oxygen utilization increases linearly with the concentration of reagents. The energy of activation of oxygen utilization by ascorbate and Cu(II) in the absence or presence of fibrinogen is Ea = 6.1 and 7.9 Kcal/mol, respectively. These values suggest that the rate-limiting step is dictated by a reaction of oxygen with "free" or protein-bound copper cations. The temperature dependency of the extent of transformation of human and bovine fibrinogen into neofibe is unusual in that it is biphasic-increasing from 5 to 25 degrees C, and decreasing thereafter, to 43 degrees C. This is not due to the temperature stability of fibrinogen. The essential requirement for copper, ascorbate and oxygen or hydrogen peroxide, as well as the low efficiency of mannitol as a scavenger, are in accord with the most likely interpretation of these data that fibrinogen undergoes a site-specific Fenton reaction. This modifies the protein and results in the formation of insoluble, polymeric, neofibe aggregates.

Animals↗
PubMed1990

Zinc modulates thrombin adsorption to fibrin.

Human thrombin with high affinity to Sepharose insolubilized fibrin monomers (high-affinity thrombin) was used to investigate the effect of Zn(II) on the thrombin adsorption to fibrin. Results showed that at Zn(II) concentrations exceeding 100 mumols/l, thrombin binding to fibrin was decreased concomitant with the Zn(II) concentration and time; at lower Zn(II) concentrations, thrombin adsorption was enhanced. Experimental results were identical by using 125I-labelled high-affinity alpha-thrombin or by measuring the thrombin activity either by chromogenic substrate or by a clotting time method. In contrast, Ca(II) alone (final conc. 3 mmol/l) or in combination with Zn(II) was not effective. However, at higher Ca(II) concentrations (7.5-15 mmol/l), thrombin adsorption was apparently decreased. Control experiments revealed that Zn(II) had no impact on the clottability of fibrinogen, and that the results of the experiments with Ca(II) were not altered by possible cross-linking of fibrin. We conclude that unlike Ca(II), Zn(II) is highly effective in modulating thrombin adsorption to fibrin.

Adsorption↗
PubMed1990

[Noncardiac risk factors in heart surgery--the blood coagulation system].

Diagnostics and therapy in coagulation disorders are presented. A special emphasis is given to alterations of blood coagulation in cardiac surgery. No major rule can be defined for this particular field. All disturbances of blood coagulation may become clinically overt in highly variable combinations, thus representing no or high risk to patients conditions. This implies that the actual risk has to be estimated individually for every patient and that the risk of the cardiac disorder has to be considered in view of the risk of the operation plus potential disturbances in coagulation. The latter in order to be assessed appropriately, clearly requires a laboratory specialised in diagnostics of coagulation, as well as a highly experienced coagulation physiologist for decision making. Following this policy, we have not been forced to disagree about extracorporeal circulation for cardiac surgery in most instances. Problems have been confined to patients suffering from various hepatic disorders or from impaired platelet functions.

Blood Coagulation Disorders↗
PubMed1990

[Adjuvant postoperative irradiation of rectal cancer in a risk group].

The results of the pilot study carried out in 1985 are described. The group with high risk of recurrence is clearly distinguishable by means of prognostic factors. The adjuvant postoperative supervoltage therapy on the former rectum lodge (2 x 5.0 Gy per week up to a total dose of 45.0 Gy) failed to increase the survival rate. The tendency towards reduction of the recurrence rate, 56% vs. 70%, was levelled by post-radiogenic side effects.

Adult↗
PubMed1989

Albumin indirectly modulates fibrin and protofibrin ultrastructure.

Albumin modulation of fibrin and protofibrin coagulation parameters was studied. Cation-depleted, fatty acid free, human and bovine albumins decrease fibrin clot turbidity in a concentration-dependent manner. Albumin also inhibits the formation of protofibrin gels, induced by addition of 25 microM Zn(II) to protofibrils, though it does not bind to (proto)fibrin. In order to verify that competition for cations underlies the influence of albumin, fibrinogen was dialyzed against cation-depleted albumin. Elemental analysis indicates a redistribution of Zn(II) from the fibrinogen to the albumin compartment, and the resultant fibrin clots are less turbid. Apparently, cation-depleted albumin acts as a competitor for divalent cations. The ability of albumin to compete for available Zn(II) was also expressed in gels formed by pH-jump experiments, in which fibrin monomer, maintained soluble at pH 4.9, is induced to change phase by addition of NaOH to pH 7.4. While turbidimetric evidence indicates that individual fibrin fibers simply become thinner with albumin, scanning electron micrographs (SEM) reveal a more complex effect on ultrastructure. Though albumin does not bind to the gels, fibrin gels produced with albumin show major changes in fiber ultrastructure, particularly evident in gels formed in the presence of Zn(II). These structural modifications are discussed within the context of the "excluded volume" effect, in which "crowding" by albumin alters (proto)fibrin reactivity and ultrastructure.

Albumins↗
PubMed1988

Elasticity of fibrin and protofibrin gels is differentially modulated by calcium and zinc.

The mechanical properties of fibrin and protofibrin gels in the presence of physiologic levels of Ca(II) and Zn(II) are described. As monitored with a thrombelastograph, Ca(II) (0.5-2 mM) increases the rate of development and the maximum level of gel elastic modulus (G) of fibrin and protofibrin gels. Zn(II) (10-50 microM) decreases the elastic modulus of those gels, even in the presence of a large excess of Ca(II). This contrasts with the ability of both divalent cations to increase fibrin and protofibrin gel turbidity. Unlike the turbidity or fibre thickness of fibrin and protofibrin gels, both of which are increased by these cations, gel elasticity is increased by Ca(II) but decreased by Zn(II). It is demonstrated that Ca(II) and Zn(II) modulate fibrin and protofibrin gels independently of one another, and that they have opposing effects on the mechanical properties of the gels. The disparity between the visual (turbidity, TEM) and the mechanical (elasticity) properties of (proto)fibrin gels indicates the need for new conceptual and analytic paradigms.

Calcium↗
PubMed1988

Divalent cations induce protofibril gelation.

Soluble fibrin oligomers (protofibrils) undergo phase change merely by adding 1-2 mM Ca2+ or 25-100 microM Zn2+. The cation-induced "protofibrin" clots appear similar to normally formed fibrin gels. Maximal clot turbidity of protofibrin gels increases with cations in a concentration-dependent manner. Magnesium (less than 0.5 mM) is ineffective in inducing protofibril gelation. Turbidity and degree of polymerization (DP) [indirectly expressed as AT (activation time)] appear to be positively correlated, regardless of whether the divalent cation is Ca2+ or Zn2+. Cross sections of Ca2+-induced protofibrin fibers are approximately 6-18-fibrin-monomers-thick. With both Ca2+ and 40 microM Zn2+, fiber cross section increases to 30-50 monomers thick. Negatively stained Zn2+-and Ca2+-induced protofibrin gels exhibit banding periodicity of approximately 240 A, similar to that of normally generated fibrin gels. Regions of lateral merging of individual segments of the protofibrin leads to increased cross section of the fiber and forms a branch required for gelation. These findings indicate that the rate of coagulation and the ultimate thickness of the fibers both relate to lateral associative processes of protofibrils, which are augmented by physiologic concentrations of 2+ and Zn2+.

Biopolymers↗
PubMed1988

Zinc binding to fibrinogen and fibrin.

Zinc binding to fibrinogen and fibrin was studied by two techniques. Scatchard analysis of ultrafiltration eluates reveals that fibrinogen has multiple Zn(II)-binding sites, KD (fibrinogen) = 18 microM; n = 6. The zinc content of the "collapsed" fibrin gel supernatant was also determined by atomic absorption spectroscopy and analyzed by a Scatchard plot (KD (fibrin) = 8 microM, n = 6). In other experiments, Zn(II) did not displace 45Ca(II) from fibrin. It appears that the binding of zinc to fibrinogen or fibrin is distinct from that of calcium, and that the zinc-binding characteristics of fibrinogen and fibrin are not significantly affected by the transformation of one into the other.

Calcium↗
PubMed1987

Zinc alters fibrin ultrastructure.

Turbidimetric studies indicate that Zn(II) accelerates fibrin gelation [decreases clotting time (CT)] and increases maximal fibrin clot turbidity. For any given level of fibrinogen (0.2-2.6 mg/ml), the relative fibrin turbidity of thrombin-induced clots increases with Zn(II) in a concentration dependent manner. Zinc-associated turbidity increases are also observed in the presence of 2 mM (Ca(II). With citrate, similar turbidity increases are observed, though at higher cation levels. Thus, turbidimetry indicates that the gel formed with Zn(II) is coarser, or has thicker fibre strands. SEM micrographs confirm that fibre thickness ranges from 260 A to 2600 A, when Zn(II) levels range from 0-50 uM. With citrate, TEM micrographs reveal a more than 20 X fold increase in fibre diameter (100 A- greater than 2000 A) with higher Zn(II) (less than 1 mM) levels. Based on a fibrin monomer cross-section of approximately 60 A, the electron micrographs indicate that depending on the Zn(II) levels, fibrin strands are composed of between 2 to 40 monomeric fibrin molecules. Thus, at physiologically relevant levels, Zn(II) can drastically modulate fibrin ultrastructure.

Fibrin↗
PubMed1987

[Arguments for regional centralized treatment of stomach cancer. A statistical study of national results].

An analysis was made of therapeutic results obtained from 6,220 cases of primary gastric carcinoma and from 1,308 cases of radical surgery, as listed in the 1976 National Cancer Record of the GDR. Results were examined relative to the number of radical operations per annum. Involved in the above treatment of gastric carcinoma were 237 surgical wards throughout the GDR. Numbers of radical operations were between one and four per annum in 56.1 per cent of all wards (Group I), between 5 and 19 in 40.5 per cent (Group II), and 20 or more in only 3.4 per cent (Group III). Radical removability accounted for 13.2 per cent of all cases in Group I, 28.2 per cent in Group II, and 38.5 per cent in Group III. Better therapeutic results relative to the number of radical operations per annum were reflected in the following absolute five-year survival rates: 3.4 per cent in Group I, 6.8 per cent in Group II, and 10.6 per cent in Group III. These findings are likely to support the advisability of regional centralisation of treatment for stomach carcinoma.

Follow-Up Studies↗
PubMed1987

[Subtotal distal gastrectomy in antral carcinoma: following Billroth I or II?].

In 1976, the National Cancer Registry of the GDR registered 488 cases with radical distal gastrectomy for carcinoma of the gastric antrum. 78.7% of them were treated with Billroth-II and 21.3% with Billroth-I. There were no striking differences regarding the postoperative lethality with 15.1% and 14.4% respectively. With 31.2% and 29.0% the 5-year survival was similar for both surgical methods, too. These results indicate the possibility of performing the Billroth-I-gastrectomy in distal gastric cancer if the principles of surgical oncology are carefully observed.

Carcinoma↗
PubMed1986

Site-specific modification of albumin by free radicals. Reaction with copper(II) and ascorbate.

Exposure of albumin to Cu(II) (10-100 microM) and ascorbate (0.1-2 mM) results in extensive molecular modifications, indicated by decreased fluorescence and chain breaks. The rate of utilization of molecular oxygen and ascorbate as a function of Cu(II) concentration is non-linear at copper/albumin ratios of greater than 1. It appears that Cu(II) bound to the tightest albumin-binding site is less available to the ascorbate than the more loosely bound cation. SDS/polyacrylamide-gel electrophoresis reveals new protein bands corresponding to 50, 47, 22, 18 and 3 kDa. For such a cleavage pattern, relatively few (approximately 3) and rather specific chain breaks occurred. Repeated addition of portions of ascorbate to the albumin/Cu(II) mixture results in increased intensity of the new bands. The absence of Cu(II) or the presence of metal chelating agents is inhibitory. There was no evidence of intermolecular cross-linking or of the formation of insoluble, albumin-derived, material. A mechanism is proposed wherein the loosely bound Cu(II) participates in a Fenton-type reaction. This generates OH. radicals, which rapidly inter-react with the protein and modify it in a 'site-specific' manner.

Ascorbic Acid↗
PubMed1986

Zinc inhibits FPA release and increases fibrin turbidity.

Physiologic concentrations of Zn(II) (4-40 microM) can increase the rate of thrombin-induced fibrin clot formation (decreased clotting time, CT) and increase the turbidity of the fibrin gel. Both the initial and ultimate turbidity (AbS 600 nm) of fibrin gels are increased in the presence of Zn(II). Two techniques were used to elaborate the mechanisms of Zn+2 procoagulant effect. Analytical ultracentrifugation indicates that Zn(II) does not induce the formation of fibrinogen multimers. Radioimmunoassay for FPA indicates that thrombin activation of fibrinogen is decreased by Zn(II), with 50% inhibition of FPA release observed at 35 microM Zn(II). These experiments indicate that the critical feature of Zn(II) procoagulant effect is not due to the induction of fibrinogen proteolysis by thrombin, which is actually decreased. Rather, it appears that Zn(II) accelerates the polymerization step of fibrin assembly and concomitantly modifies fibrin gel structure.

Blood Coagulation Tests↗