The capacity for biosynthesis of prostaglandin F2alpha (PGF2alpha) and prostaglandin E2 (PGE2) from endogenous precursors by brain tissue slices and homogenates was measured by a gas chromatography - mass fragmentography method using deuterated prostaglandins as internal standards. Mean biosynthesis in rat cerebral cortex slices incubated for 60 min was 60.2 ng PGF2alpha and 17.4 ng PGE2 per 100 mg of tissue. The corresponding values for homogenates were 78.1 ng and 28.9 ng. Synthetic capacity of cat cerebral cortex was considerably greater but that of human tissue was smaller than that found in rat brain. Cat cerebellum in contrast to other regions synthesized more PGE2 than PGF2alpha. The time-course of prostaglandin formation in slices was linear for the initial 60 min. Catabolism in cerebral tissues was found to be very small. Prostaglandins formed or added to the incubation media distributed between tissue and medium in a manner indicating some specific binding as well as nonspecific solubilization in tissue lipids. Norepinephrine, 3,4-L-dihydroxyphenylalanine, dopamine, adrenochrome and apomorphine greatly stimulated PGF2alpha formation probably through a nonenzymatic reduction of endoperoxides. Norepinephrine added to homogenates appeared to stabilize the fatty acid cyclo-oxygenase preventing it from inactivation. Indomethacin and Ketoprofen were potent inhibitors of biosynthesis. Paracetamol was found to be a less potent synthetase inhibitor than aspirin. The biosynthetic capacity of brain tissue in vitro appears to be orders of magnitude more than that of normal brain in situ.

Previous studies from this laboratory have demonstrated that protein kinase C (PKC) enzyme activity is highly correlated with the proliferation rate of glioma cells, and that glioma cells of both human and rat origin have very high PKC enzyme activity when compared to non-malignant glia including astrocytes, the antecedents of most gliomas. In the present study, by contrasting the rat C6 glioma cells with non-malignant rat astrocytes, we have sought to determine whether the high PKC enzyme activity of glioma cells was due to the overexpression of a specific isoform of PKC. By Western blot analyses, both C6 glioma cells and astrocytes were found to express PKC alpha, beta, delta, epsilon and zeta, but not gamma. Enzyme activity measurements revealed that the elevated PKC activity of glioma cells compared to glia was calcium-dependent, thereby implicating abnormal activity of the alpha or beta isoforms. On Western blots, when compared to astrocytes, glioma cells were determined to overexpress PKC alpha but not beta. An antisense oligonucleotide to PKC alpha, directed at the site of initiation of translation, inhibited the proliferation rate of glioma cells when compared to cells treated with control oligonucleotides; PKC enzyme activity and PKC alpha protein expression were significantly reduced by the antisense treatment. These results suggest that the high PKC enzyme activity of glioma cells, and its correspondence with proliferation rate, is the result of overexpression of isozyme alpha. Targetting PKC alpha in glioma cells may provide a refinement of therapy of glioma patients, some of which are already showing clinical stabilization when treated with drugs with PKC-inhibitory effects.

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