Uptake Of Porphyrins Research Articles

Interactions of water soluble porphyrins with Z-poly(dG-dC).

The water soluble porphyrin tetrakis(4-N-methylpyridyl)porphine (H2TMpyP) and its copper(II) derivative (CuTMpyP) convert Z-poly(dG-dC) to the B-form. For H2TMpyP, the fraction Z character (fr-Z) is given by fr-Z = 1.0 - 21 rO and for CuTMpyP, fr-Z = .94 - 12 rO where rO identical to [Porphyrin]O/[DNA]O. Neither the manganese(III) derivative of of this porphyrin (MnTMpyP) nor tetrakis(2-N-methylpyridyl)porphine (H2TMpyP-2) is nearly as effective at causing the conversion. The former two porphyrins have been shown to intercalate into B-poly(dG-dC) whereas the latter two porphyrins do not. The kinetics of the Z----B conversion are independent of porphyrin or poly(dG-dC) concentration for 1/rO greater than 6. At smaller values of 1/rO, the conversion rate is greatly increased for H2TMpyP and CuTMpyP. The interaction of these porphyrins with Z-poly(dG-dC) follows simple first order kinetics in this latter concentration range. It is proposed that for small values of 1/rO the sequence of events begins with a porphyrin-unassisted distortion of the Z-duplex (with a rate constant of 0.6 s-1) followed by a rapid uptake of porphyrin in what may be an intercalative mode. The porphyrin thus located in Z-regions brings about rapid conversion to the B-form. Binding of H2TMpyP or CuTMpyP to B-regions of a predominantly Z-strand leads to conversion of Z to B. However, this conversion process is considerably slower than when the porphyrins bind directly to Z-regions.

The interaction of tumour-localizing porphyrins with collagen, elastin, gelatin, fibrin and fibrinogen.

We have already reported in Balb C mouse transplantable mammary carcinoma, that uroporphyrin I and III are superior as tumour localizers when compared to hematoporphyrin derivative and a derivative thereof, photofrin II. This study compares the binding of porphyrins to proteins which may be found in tumour cells or stroma to investigate whether there is a common binding determinant. Coproporphyrin III and deuteroporphyrin IX which are non-tumour localizing porphyrins, were also part of the comparative study. The interaction of these porphyrins with acid soluble collagen and acid insoluble collagen, elastin, and fibrin was evaluated, and the binding of uroporphyrin isomers I and III and deuteroporphyrin IX to gelatin and fibrinogen, was also determined. The results suggest that collagen, especially the acid soluble form, and gelatin preferentially bind the four porphyrins which localize in mammary carcinoma tissue. The well reported observations that malignant epithelial cells, including breast cancer, produce collagen and contain a rate-limiting enzyme in collagen biosynthesis would support the notion that de novo synthesis of this protein may in part govern the tumour uptake and retention of porphyrins. Elastin, fibrinogen and fibrin showed non-discriminant binding to the porphyrins under study.

Augmentation of Hematoporphyrin Uptake and in Vitro-Growth Inhibition of L1210 Leukemia Cells by Succinylacetone

Succinylacetone (SA; 4,6-dioxoheptanoic acid), a specific inhibitor of delta-aminolevulinic acid dehydrase (ALAD) (the second enzyme of the heme biosynthetic pathway), was tested for its effect in L1210 cells from inbred DBA/2 mice. ALAD from broken L1210 cells was completely inhibited by 1 microM SA, but in whole cells activity was decreased only 83% after incubation of the cells with 2.5 mM SA for 3 days. When incubated with hematoporphyrin (HP), L1210 cells rapidly took up porphyrin from the medium, and this uptake could be augmented by pretreatment of the cells with SA; but this enhancement of porphyrin uptake occurred gradually over a period of days. When SA-treated and untreated L1210 cells were incubated with increasing concentrations of HP in the medium, SA-treated cells reached the saturation concentration of cellular porphyrin at lower medium HP concentrations than did untreated cells. Growth of L1210 cells could be inhibited by 2 mM SA or more. Addition of increasing amounts of serum to cultures of cells containing SA did not reverse the growth inhibition due to SA. Porphyrin uptake from HP in the medium in nonmalignant fibroblast line 3T3 was much lower than in L1210 cells and could not be enhanced by incubation of the cells with SA.

Efficient photosensitization of malignant human cells in vitro by liposome-bound porphyrins

Comparative kinetics of porphyrin uptake and release by HeLa cells, incubated with equivalent concentrations of either hematoporphyrin (Hp) in aqueous solution or Hp and its dimethylester (HpDME) bound to unilamellar liposomes, show that liposomal porphyrins are bound at a higher rate and in considerably larger amounts. Moreover, the release of cell-bound porphyrins into the medium is remarkably reduced and slowered after cell loading with liposome-bound porphyrins. The presence of 1% bovine or human serum albumin (but not serum globulins) in the medium has no effect on uptake and release of liposome-bound porphyrins by HeLa cells, whereas it remarkably decreases the uptake of aqueous Hp. Parallel studies of cell photodamages under known concentrations of cell-bound porphyrin unequivocally demonstrate that the photodynamic effect is strictly related to the porphyrin load. As a consequence a dramatic increase of cell-photosensitizing efficiency is obtained by binding Hp (and even more HpDME) with liposomes. Electron microscopy investigations on cell damages caused by loading with liposome-bound porphyrins and subsequent illumination show that the plasmatic membrane is one important cell site of porphyrin interaction and photodynamic effect.

Transferrin as a donor of iron to mitochondria Effect of pyrophosphate and relationship to mitochondrial metabolism and heme synthesis

Rat liver mitochondria accumulate iron mobilized from transferrin by pyrophosphate. The uptake has a very low energy dependence, but it is highly dependent on a functioning respiratory chain. Reduction of the ferric-iron-pyrophosphate complex is not linked to any specific respiratory complex. Half of the amount of iron accumulated is passed into heme. Iron once accumulated is very little accessible to chelation by added ferric or ferrous iron chelators. Iron uptake and heme synthesis are maximal if a suitable porphyrin substrate is added simultaneously with iron. The results represent further evidence that pyrophosphate is a possible candidate for intracellular iron transport. Also, the results suggest that iron uptake is coupled to simultaneous porphyrin uptake and heme synthesis.

Uptake of hematoporphyrin derivative and sensitized photoinactivation of C3H cells with different oncogenic potential

Four types of mouse embryo fibroblast cells of different oncogenic potential were investigated with respect to uptake of the tumor localizing agent hematoporphyrin derivative (Hpd) and sensitized photoinactivation. Cell size and cellular content of Hpd were measured simultaneously for single cells by means of flow cytofluorimetry. The more malignant cell types had a slightly higher porphyrin uptake per unit cellular volume than the untransformed type, while the photosensitivity of cells incubated with Hpd was equal for all the cell types. Since Hpd seems to concentrate in membranes, this may be related to the fact that the membrane areas of malignant cells are relatively larger than that of untransformed cells, due to the presence of more microvilli. The present study indicates that the preferential localization of Hpd in tumors, as well as the high efficiency of phototherapy reported in the literature, are due to extracellular differences between the tumors and normal tissue.

Studies on the efflux of metalloporphyrin from rat liver mitochondria. Effect of K+ and other cations.

The mechanism by which metalloporphyrins synthesized within the mitochondria escape to the incubation medium was studied in isolated rat liver mitochondria. In a low-ionic-strength sucrose medium, the efflux of metalloporphyrins is markedly decreased when K+ (greater than 10 mM) is added. The effect of K+ is not dependent on the energy state of the mitochondria and it can in part be abolished by adding globin, but not albumin. K+ also decreases the uptake of porphyrins by the mitochondria and thereby the rate of synthesis of metalloporphyrins. Qualitatively similar results are found with Na+, Li+, Mg2+ and Ca2+. Quantitatively, however, the efficiency of cations to inhibit the release of metalloporphyrins decreases in the order: Mg2+ greater than Ca2+ greater than K+ greater than Li+ greater than Na+. Co-protoporhyrin behaves essentially as Co-deuteroporphyrin. The results provide further evidence that the efflux of metalloporphyrins from the mitochondria depends on haem-binding ligands of the suspending medium and also on the ionic strength of the incubation medium.

Iron, porphyrin and heme transport in mitochondria

Mitochondria from different tissues and species accumulate iron by two-step mechanism, one energy-dependent, one energy-independent. The uptake of porphyrins is also in part dependent on the mitochondrial energy state. The saturation levels for the uptake of iron and porphyrins are essentially the same, about 7–9 nmol/mg protein. Efflux of heme from the mitochondria increases in inverse to the mitochondrial energy state, and it is markedly stimulated by heme-binding ligands of the medium.

Studies on the uptake of porphyrin by isolated rat liver mitochondria with particular emphasis on the effect of hemin

Studies on the uptake of porphyrin by isolated rat liver mitochondria with particular emphasis on the effect of hemin

Studies on the uptake of porphyrin by isolated rat liver mitochondria

1. 1. The uptake of deuteroporphyrin by isolated rat liver mitochondria proceeds by two different mechanisms, a passive binding, and a mechanism sensitive to CCCP plus valinomycin, with different pH, temperature and time dependencies. 2. 2. The CCCP plus valinomycin-sensitive uptake of deuteroporphyrin parallels the transmembrane potassium gradient ( [ K + in ] [ K + out ]). 3. 3. Only that deuteroporphyrin taken up in parallel to the transmembrane potassium gradient is accessible to ferrochelatase. 4. 4. The uptake of deuteroporphyrin at high concentrations is followed by a series of damaging effcects on the mitochondria: uncoupling, dissipation of the mitochondrial energy potential, increased ion permeability and leakage of endogenous potassium. 5. 5. The detrimental effects of porphyrins at high concentrations on mitochondrial structure might explain the apparently unrelated metabolic aberrations characteristic of certain porphyric diseases.