Leslie Ethridge

Ultrastructural observations on the effect of azelaic acid on normal human melanocytes and a human melanoma cell line in tissue culture.

Azelaic acid has been shown clinically to have a cytotoxic effect on the abnormally active and malignant human melanocyte, but it has no apparent effect upon normal melanocytes. This difference in reactivity between normal and abnormal cells in vivo is further examined here in vitro.

Analytical, ultrastructural, autoradiographic and biochemical studies on [3H]dicarboxylic acid added to cultures of melanoma cells

Lentigo maligna and malignant melanoma can be treated by dicarboxylic acids (C9 and C12, which are competitive inhibitors of tyrosinase. We therefore studied the intracellular location and possible sites of action of dodecanedioic acid (C12) in murine melanoma cells, using EM autoradiography and biochemical analysis of lipid extracts by HPLC. Significant levels of radioactivity were found in the mitochondria and in the nuclei but not in association with membranes of rough endoplasmic reticulum, Golgi‐associated endoplasmic reticulum, or Golgi apparatus, and not in coated vesicles or melanosomes. Biochemical analysis revealed that the diacid underwent β‐oxidation, which occurs only in mitochondria. The results suggest that the toxicity of dicarboxylic acids in melanoma cells is not related to anti‐tyrosinase activity but may be due to interference with oxidoreductase enzymes in the mitochondria and possibly to inhibition of DNA synthesis in the nucleus.

The time sequence of response of the prolactin cells of the freshwater teleost, Poecilia reticulata, to an altered environmental salinity.

SummaryThe time sequence of the ultrastructural changes in the prolactin cells of the adult guppy, Poecilia reticulata, was studied in freshwater fish transferred to 1/3 seawater for 1, 4, 11 and 28 days. The morphological changes were slight and only detectable by quantitative (morphometric) procedures. The secretory granules showed a ‘biphasic’ response to the altered environmental salinity, but the volume density of the Golgi apparatus progressively declined throughout the experiment. After an initial decrease in the volume density of the RER, that organelle regained its original prominence by 11 days in 1/3 seawater. The volume density of the nucleus was markedly higher in fish 28 days after transfer to 1/3 seawater than in any other group. Cell volume estimations showed that a shrinking of the cytoplasm rather than a swelling of the nucleus accounted for the high volume density figure. The changes in the volume density of the mitochondria closely paralleled those of the RER. Profiles of exocytosed granules were rarely found in any of the groups, but were least frequent in fish kept in 1/3 seawater for 28 days, when dense (lysosomal?) bodies were most abundant. The quantitative methods high-lighted some discrepancies in the rate and magnitude of the changes shown by some organelles and have led the authors to suggest that during adaptation of fish to dilute seawater, synthesis and release may not be coupled processes in the prolactin cell of P. reticulata.