Effect of hemin and Protoporphyrin IX on the protein-synthesizing activity of human granulocytes, lymphocytes and platelets

Protein synthesis by platelets: historical and new perspectives

In the late 1960s, numerous investigators independently demonstrated that platelets are capable of synthesizing proteins. Studies continued at a steady pace over the next 30 years and into the 21st century. Collectively, these investigations confirmed that platelets synthesize proteins and that the pattern of protein synthesis changes in response to cellular activation. More recent studies have characterized the mechanisms by which platelets synthesize proteins and have shown that protein synthesis alters the phenotype and functions of platelets. Here, we chronologically review our increased understanding of protein synthetic responses in platelets and discuss how the field may evolve over the next decade.

Distribution of 5-aminolevulinic acid-induced porphyrins in noduloulcerative basal cell carcinoma

Microscopic fluorescence photometry incorporating a light-sensitive thermo-electrically cooled charge-coupled device (CCD) camera was employed to investigate the fluorescence distribution of 5-aminolevulinic acid (ALA)-induced porphyrins in 22 patients with a total number of 52 noduloulcerative basal cell carcinomas (BCC) after topical ALA application with or without dimethylsulfoxide (DMSO)/ethylenediaminetetraacetic acid (EDTA) or after intravenous administration of ALA. Both localization patterns and amounts of ALA-induced porphyrins in the BCC were studied. The ALA-induced porphyrins were localized only in the superficial layers of the noduloulcerative BCC lesions after topical application of 20% ALA alone for 3 h. However, both the penetration of ALA into deep lesions and the production of the ALA-induced porphyrin fluorescence were increased after topical administration of 20% ALA and 20% DMSO/4% EDTA for 3 h. Prior treatment with 99% DMSO for 15 min further enhanced the ALA penetration into the BCC lesions after topical application of the ALA/DMSO/EDTA mixture and produced more ALA-induced porphyrins by a factor of about three compared with those treated with ALA alone. The penetration of ALA into the deep BCC lesions could also be increased by prolonging the time of topical application of 20% ALA/4% EDTA to 29-48 h (without DMSO). Intravenous injection of ALA led to a more homogeneous distribution of the ALA-derived porphyrins in the whole noduloulcerative BCC lesions.

Heme inhibits cartilage metabolism and growth in vitro

The present study was designed to investigate the potential role of heme as a direct inhibitor of cartilage metabolism and growth. We used the embryonic chick pelvic rudiment bioassays and the hypophysectomized rat cartilage sulfation bioassay, both sensitive to growth factors and growth inhibitors. In the chick bioassay pelvic rudiment growth was inhibited when heme was added to the culture medium at 0.1 mmol/L (after five days in culture, cartilage weight 224% +/- 11% of initial with normal serum, but 141% +/- 3% of initial with serum plus heme 0.25 mmol/L); the heme-induced growth inhibition was promptly reversible when cartilages were placed in heme-free medium. This was due, at least in part, to heme-induced inhibition of (1) [35S] sulfate incorporation into proteoglycans by as little as 0.05 mmol/L heme (66% +/- 5% of assay buffer); (2) [14C] leucine incorporation into proteins by greater than or equal to 0.05 mmol/L heme (85% +/- 6% of assay buffer); and (3) [3H] uridine incorporation by greater than or equal to 0.10 mmol/L heme (50% +/- 4% of assay buffer). In the rat cartilage sulfation bioassay (the literature "standard" bioassay for skeletal growth studies) a dose-dependent inhibition of [35S] sulfate incorporation occurred with greater than or equal to 0.01 mmol/L added heme (82% +/- 3% of assay buffer). Heme caused a dose-dependent and reversible inhibition of cartilage metabolism and growth, and it may have a novel role in the pathophysiology of growth retardation associated with some chronic disease.

Tetrapyrroles as inhibitors of normal cartilage metabolism: relative potency of different compounds

The present study was designed to explore the role of different tetrapyrroles as inhibitors of cartilage metabolism. We studied the effects of tetrapyrroles on the incorporation of [35S]sulfate into proteoglycans, [14C]-leucine into protein, and [3H]uridine into the RNA of normal cartilage from two different vertebrate classes using the embryonic chicken pelvic rudiment bioassay and the hypophysectomized rat costal cartilage bioassay, both very sensitive to cartilage growth factors and growth inhibitors. We compared the relative potencies of the following compounds: both metalloporphyrins (heme and chlorophyllin), linear tetrapyrroles (bilirubin), and heme proteins (hemoglobin, myoglobin, and cytochrome c). Hemoglobin and heme were the most potent inhibitors of rat cartilage metabolism, and bilirubin was a far more potent inhibitor of embryonic chick cartilage metabolism. Chlorophyllin had moderate inhibitory activity, especially on chick cartilage, whereas cytochrome c was inactive in these bioassays. Surprisingly, myoglobin was relatively ineffective despite its close similarity to heme and hemoglobin. The bilirubin-induced inhibition of sulfate incorporation into chick cartilage was partially prevented when glutathione was included in the incubation medium, suggesting that a free-radical mechanism may be involved. There were significant differences in the sensitivity of the two cartilages studied, indicating there may be species-dependent sensitivity to different tetrapyrroles.

Lysine binding to activated human platelets and its similarity to fibrinogen binding

Platelet surface glycoproteins IIb-IIIa are considered to function as the binding site for fibrinogen. Fibrinogen binding is essential for platelet aggregation and several amines have been shown to inhibit this binding. The present study compares the binding properties of 125I-fibrinogen and [3H]lysine with platelets activated by the Ca2+ ionophore A23187. Many lines of similarities in the binding properties are apparent; however, several differences were also found. The similarities are listed below and the differences are pointed out in parentheses. Marked enhancement by platelet activation; deficiency of binding by thrombasthenic platelets lacking the glycoproteins IIb-IIIa; saturability (fibrinogen binding approaches saturation at more than 12 microM, within 10 min; lysine binding at more than 100 mM within 1 min); Ca2+-dependence (at 1 mM Ca2+ lysine binding is minute and fibrinogen binding is half-saturated); reversibility; the binding achieved within 10 min is exchangeable; dissociation depends upon time and external ligand concentration; inhibition by the oligoamines His-Lys and Lys4; inhibition by serum from a thrombasthenic patient who developed anti-glycoproteins IIb-IIIa antibodies; specificity; alanine neither binds to activated platelets nor inhibits fibrinogen binding; it thus appears that the lysine which associates with activated platelets is mostly bound onto the surface of the cells rather than being incorporated. Moreover, the major site of lysine binding seems to be the complexed glycoproteins IIb-IIIa.

Destruction of erythroleukemia, myelocytic leukemia and Burkitt lymphoma cells by photoactivated protoporphyrin

The effect of protoporphyrin on erythroid, myeloid and lymphoid leukemic cells and their destruction induced by the photoactivated porphyrin was studied. Friend erythroleukemic cells (FL) and myelocytic leukemic cells (ML) accumulated protoporphyrin in a cap or patch-like pattern observed by fluorescence microscopy. Photoactivated protoporphyrin induced the appearance of "holes" on the cell membrane demonstrated by scanning electron microscopy. On the other hand, Burkitt lymphoma (BL) and mastocytoma (MS) cells accumulated porphyrin intracellularly around the nuclear envelope and as circular profiles, respectively. Photoactivated protoporphyrin induced development of multiple blebs on the cell membrane, and even complete cell destruction. Cytotoxicity of protoporphyrin at short-term incubation periods was determined by [3H]thymidine and [3H]uridine incorporation. Protoporphyrin, unexposed to light, reduced the incorporation of both precursors only to a moderate extent. On the other hand, porphyrin-treated cells exposed to light showed complete inhibition of RNA and DNA synthesis. Long-term exposure of ML and BL cells to porphyrin in the dark induced a nearly 50% inhibition of RNA and DNA synthesis. Although the cytotoxic effect of protoporphyrin in the dark was lower than that of photoactivated porphyrin, this may possess a potential activity in vivo even without illumination.