Melanin potentiates daunorubicin-induced inhibition of collagen biosynthesis in human skin fibroblasts.

One of the recognized side effects of antineoplastic anthracyclines is poor wound healing, resulting from an impairment of collagen biosynthesis. The most affected tissue is skin. The mechanism underlying the tissue specificity of the side effects of anthracyclines has not been established. In view of the fact that a number of pharmacologic agents are known to form complexes with melanin and melanins are abundant constituents of the skin, we determined whether daunorubicin interacts with melanin and how this process affects collagen biosynthesis in cultured human skin fibroblasts. Results indicated that daunorubicin forms complexes with melanin. Scatchard analysis showed that the binding of daunorubicin to melanin was heterogeneous, suggesting the presence of two classes of independent binding sites with K1 = 1.83 x 10(5) M(-1) and K2 = 5.52 x 10(3) M(-1). The number of strong binding sites was calculated as n1 = 0.158 micromol/mg of melanin and the number of weak binding sites as n2 = 0.255 micromol/mg of melanin. We have suggested that prolidase, an enzyme involved in collagen metabolism, may be one of the targets for anthracycline-induced inhibition of collagen synthesis. We found that daunorubicin induced inhibition of prolidase activity (IC50 = 10 microM), collagen biosynthesis (IC50 = 70 microM) and DNA biosynthesis (IC50= 10 microM) in human skin fibroblasts. Melanin (100 microg/ml) by itself produced about 25% inhibition of DNA synthesis and prolidase activity but it had no effect on collagen biosynthesis in cultured fibroblasts. However, the addition of melanin (100 microg/ml) to daunorubicin-treated cells (at IC50 concentration) augmented the inhibitory action of daunorubicin on collagen and DNA biosynthesis without having any effect on prolidase activity. The same effect was achieved when the cells were treated with daunorubicin at one-fourth of the IC50 given at 0, 6, 12 and 18 h during a 24-h incubation. The data suggest that the melanin-induced augmentation of the inhibitory effects of daunorubicin on collagen and DNA biosynthesis may result from: (i) accumulation of the drug in the extracellular matrix, (ii) gradual dissociation of the complex, and (iii) constant action of the released drug on cell metabolism. The phenomenon may explain the potential mechanism for the organ specificity of daunorubicin-induced poor wound healing in patients administered this drug.

The prostacyclin analogue iloprost and prostaglandin E1 suppress sterol synthesis in freshly isolated human mononuclear leukocytes.

The effects of the stable prostacyclin analogue iloprost, prostaglandin E1 and prostaglandin F2 alpha on sterol synthesis were investigated in freshly isolated human mononuclear leukocytes. Incubation of cells for 6 h in a medium containing lipid-depleted serum led to a 3-fold rise in the rate of sterol synthesis from [14C]acetate or tritiated water. Iloprost and prostaglandin E1 added in increasing concentrations at zero time resulted in an inhibition of the synthesis of sterols, the suppression being 50 and 55% at a concentration of 1 mumol/1, respectively. Both prostaglandins yielded a sigmoidal log dose-effect curve. In contrast, prostaglandin F2 alpha had no influence on sterol synthesis up to a concentration of 1 mumol/1. The action of the prostacyclin analogue and prostaglandin E1 on the relative rate of sterol synthesis was not immediate, since the prostaglandins had no effect when given at 6 h to the incubation medium, and the incorporation of [14C]acetate into sterols was measured thereafter. The results suggest that prostacyclin and prostaglandin E1 affect cholesterol synthesis and therefore may play a role in the regulation of cellular cholesterol homeostasis and in the development of atherosclerosis.

Low platelet MAO activity in psychiatric patients and plasma factors: no evidence for inhibitory influences on MAO in the circulating platelet population.

The influence of plasma and low and high molecular weight plasma fraction on MAO activity in platelets from controls were studied. Plasmas were obtained from patients with decreased platelet MAO activity and suffering from chronic schizophrenia of different syndrome subtypes, unipolar depressions, and alcoholism. Up to 50% inhibition and activation of MAO activity alterations were not different between the plasmas from schizophrenic, depressive, and alcoholic patients. Plasmas from schizophrenic patients without medication or on neuroleptics showed similar inhibition and/or activation of MAO activity in platelets from controls. The results indicate, in accordance with recent findings, that a number of low and high molecular weight substances can trigger platelet MAO activity changes. These plasma factors do not appear to be characteristic of schizophrenic patients with low platelet MAO activity.

3,4,5-Trimethoxybenzoic acid, a new mescaline metabolite in humans.

After ingestion of 400 mg of mescaline sulfate by human volunteers, 3,4,5-trimethoxybenzoic acid was isolated from urine and identified by gas chromatography-mass spectrometry. The amount of this anionic mescaline metabolite was found to be very low as compared with that of the well-konwn 3,4,5-trimethoxyphenylacetic acid. The significance of this finding is discussed.