Monoamine Oxidase Activity in the Cerebral Vasculature: Comparison between Fresh Microvessels from Different Structures and Cell Cultures Derived from Microvessels

Abstract

Summary: Monoamine oxidase (MAO) activity was studied in various preparations of porcine brain micro vessels to explore further the role of this enzyme in the blood-brain barrier to catecholamines, No difference was noted (V m and Km) between microvessels isolated from three structures (caudate nucleus, thalamus, and ce rebral cortex) in which the responses to circulating cat echolamines in vivo are markedly different. Large and small microvessels from the caudate nucleus and the thal amus presented the same specific activity. Cell cultures obtained from small microvessels were rich in endothelial cells as identified by the presence of Factor VIII -relatedIn a recent paper (Lasbennes et aI., 1983), we showed that the level of monoamine oxidase (MAO; EC 1.4.3.4) activity in brain microvessels, as mea sured by V m (the maximum activity of the enzyme with respect to a given substrate), was high for both artificial and natural substrates, with a high Km (the concentration of substrate giving one-half V m) ' sug gesting that this enzyme could play an efficient part in blood-brain barrier (BBB) mechanisms. It is generally believed that the cerebrovascular MAO is situated to a great extent in the endothelium, since a characteristic green fluorescence is seen in the endothelium after L-3,4-dihydroxyphenylalanine (L-DOPA) injection in animals treated with a MAO inhibitor (Bertler et al., 1966; Hardebo et aI., 1979). However, in spite of the BBB, circulating cateAddress correspondence and reprint requests to Dr. Sercombe at INSERM U 182, 10 avenue de Verdun, 75010 Paris, France.Abbreviations used: BBB, Blood-brain barrier; BSA, bovine serum albumin; HEPES, N-2-hydroxyethyl piperazine-N'-2-eth anesulfonic acid; 6-k-PGF la , 6-keto-prostaglandin Fla; L-DOPA, L-3,4-dihydroxyphenylalanine; M 199, medium 199; MAO, monoamine oxidase; NA, noradrenaline; PBS, phosphate-buff ered salt solution; PGE2, prostaglandin E2. 415antigen. These preparations displayed an MAO activity about ninefold less than freshly isolated microvessels, al though their prostaglandin synthetase activity appeared normal. These results suggest that MAO activity is not the main factor determining the regional differences in the cerebrovascular reactions to catecholamines, that MAO is not specifically localized in the endothelium but must be also present in the smooth muscle, and that the MAO activity is greatly decreased during cell culture.

Catecholamine‐Metabolizing Enzymes of Bovine Brain Microvessel Endothelial Cell Monolayers

“…In this study two types of MAO, A and B, can be distinguished in bovine cerebral gray matter and brain microvessel endothelial cell monolayers. These results are consistent with previous studies (Lai and Spector, 1978;Sercombe et al, 1984;Maruki et al, 1984). MAO-A preferentially deaminates the endogenous substrates S-hydroxytryptamine, norepinephrine, epinephrine, metanephrine, and normetanephrine as well as P-hydroxylated phenylethylamines such as octopamine.…”

Blood‐Brain Barrier Monoamine Oxidase: Enzyme Characterization in Cerebral Microvessels and Other Tissues from Six Mammalian Species, Including Human

“…Based on our previous findings , and the fact that MPTP has a potent and selective toxic effect on dopamine neurons when infused directly into rat substantia nigra (Harik et al, 19873), we hypothesized that differences among species in their susceptibility to systemic MPTP toxicity may be due to the capacity of the blood-brain barrier to prevent MPTP from reaching the brain in sufficient concentrations. Because MPTP is a known substrate for enzymatic oxidation by MAO-B (Chiba et al, 1984;Heikkila et al, 1985) and because isolated brain capillaries are known to contain MA0 (Lai et al, 1975(Lai et al, , 1978Lai and Spector, 1978;Hardebo et al, 1980;Betz and Goldstein, 1981;Lasbennes et al, 1983Lasbennes et al, , 1985Sercombe et al, 1984;Durand, 1986), we reasoned that MA0 activity of brain microvessels from different species may correlate inversely with their susceptibility to systemic MPTP neurotoxicity. The results presented in this article support this hypothesis (Tables 2 and 3).…”

“…Although M A 0 activity was documented by several groups of investigators in rat, bovine, and avian brain microvessels, there is controversy as to the type of M A 0 present (Lai et al, 1975(Lai et al, , 1978Lai and Spector, 1978;Hardebo et al, 1980;Betz and Goldstein, 198 1 ;Lasbennes et al, 1983Lasbennes et al, , 1985Sercombe et al, 1984;Durand, 1986). In those studies, the type of M A 0 was presumed, based on the relative substrate specificity of the enzyme.…”

“…49,856-864 (1987). able to detect MA0 activity in rat brain capillary walls by using an improved histochemical method. In any case, it is known that isolated brain microvessels have high MA0 activity when studied biochemically using tryptamine, tyramine, norepinephrine, serotonin, and other monoamine substrates (Lai et al, 1975: Lai and Spector, 1978Hardebo et al, 1980;Betz and Goldstein, 1981;Lasbennes et al, 1983Lasbennes et al, , 1985Sercombe et al, 1984;Durand, 1986). Based on these studies of relative substrate specificity, the molecular identity of brain microvessel MA0 remains ambiguous.…”

Correlation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity with blood-brain barrier monoamine oxidase activity.

“…This suggests that the rat's resistance to systemic MPTP may be a property of the blood-brain barrier and other organs that can metabolize MPTP and prevent it from reaching its brain targets in sufficient concentrations. Because MPTP is a known substrate for enzymatic oxidation by MAO-B (6,16), and since brain capillaries possess MAO activity (17)(18)(19)(20)(21)(22), we reasoned that MAO activity in brain microvessels from different species may correlate invrsely with their susceptibility to systemic MPTP neurotoxicity.…”