1.Kinetics of cellular retention during Caco-2 permeation experiments: role of lysosomal sequestration and impact on permeability estimates.
Heikkinen AT1, Mönkkönen J, Korjamo T. J Pharmacol Exp Ther. 2009 Mar;328(3):882-92. doi: 10.1124/jpet.108.145797. Epub 2008 Dec 16.
The permeability estimation from cell monolayer permeation data is usually based on 100% recovery assumption. However, poor recovery is often seen in such experiments in practice but often neglected in data interpretation. In the present study, the cellular retention kinetics during Caco-2 permeation experiments of three passively transported compounds, weakly basic propranolol [(+/-)-1-isopropylamino-3-(1-naphthyloxy)-2-propanol], weakly acidic ibuprofen [alpha-methyl-4-(isobutyl)phenylacetic acid], and neutral testosterone (17beta-hydroxy-4-androsten-3-one), were determined. Furthermore, the effects of cellular retention kinetics on apparent permeability were evaluated, and the role of lysosomal sequestration in cellular retention of propranolol was explored. The cellular retention profiles were observed to be direction and concentration dependent, which may cause erroneous directionality and concentration dependence in permeability estimates.
2.Role for dopamine in malonate-induced damage in vivo in striatum and in vitro in mesencephalic cultures.
Moy LY1, Zeevalk GD, Sonsalla PK. J Neurochem. 2000 Apr;74(4):1656-65.
Defects in mitochondrial energy metabolism have been implicated in the pathology of several neurodegenerative disorders. In addition, the reactive metabolites generated from the metabolism and oxidation of the neurotransmitter dopamine (DA) are thought to contribute to the damage to neurons of the basal ganglia. We have previously demonstrated that infusions of the metabolic inhibitor malonate into the striata of mice or rats produce degeneration of DA nerve terminals. In the present studies, we demonstrate that an intrastriatal infusion of malonate induces a substantial increase in DA efflux in awake, behaving mice as measured by in vivo microdialysis. Furthermore, pretreatment of mice with tetrabenazine (TBZ) or the TBZ analogue Ro 4-1284 (Ro-4), compounds that reversibly inhibit the vesicular storage of DA, attenuates the malonate-induced DA efflux as well as the damage to DA nerve terminals. Consistent with these findings, the damage to both DA and GABA neurons in mesencephalic cultures by malonate exposure was attenuated by pretreatment with TBZ or Ro-4.
3.Role of adenylate cyclase in the modulation of the release of dopamine: a microdialysis study in the striatum of the rat.
Santiago M1, Westerink BH. J Neurochem. 1990 Jul;55(1):169-74.
In the present study, we have applied the brain microdialysis technique to investigate the effect of the stimulation of adenylate cyclase on the extracellular levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in the striatum of freely moving rats. Infusion of 8-bromo-adenosine 3',5'-cyclic monophosphate (8-Br-cAMP), 3-isobutyl-1-methylxanthine, or forskolin produced a significant increase in the release of DA. The effect of 8-Br-cAMP was tetrodotoxin, Ca2+, and dose dependent and was saturable. 8-Br-cAMP also caused an increase in the output of DOPAC and HVA. No effects were seen on the output of 5-HIAA, except at the highest 8-Br-cAMP concentration studied. Infusion of 8-Br-cAMP (25 microM, 1.0 mM, and 3.3 mM) together with infusion of (-)-sulpiride (1 microM) or systemic administration of (+/-)-sulpiride (55 mumol/kg i.p.) produced an additive effect on the release of DA.
4.Errors introduced by a tritium label in position 8 of catecholamines.
Grohmann M, Henseling M, Cassis L, Trendelenburg U. Naunyn Schmiedebergs Arch Pharmacol. 1986 Jan;332(1):34-42.
The neuronal and extraneuronal disposition of 3H-7,8- and 3H-7-labelled (-)-noradrenaline and dopamine was compared in in vitro studies. In agreement with earlier studies, the present results show that the presence of a tritium label in position 8 (i.e., on the alpha-carbon) has two consequences: a) the rate of deamination declines and b) part of the deamination results in the formation of an unlabelled aldehyde plus tritium water; tritium water is recovered from the OMDA-fraction of the column chromatographic procedure of Graefe et al. (1973). Whenever the deamination of a 3H-catecholamine is reduced (by tritium in position 8), the intraneuronal 3H-catecholamine concentration is increased. This increase, in turn, partly masks the decline in neuronal deamination (rat vas deferens). Irrespective of whether one determines the spontaneous efflux, the release of 3H-noradrenaline by nerve stimulation or the release of 3H-(-)-noradrenaline by the reserpine-like compound Ro 4-1284, the presence of tritium in position 8 distorts the results (experiments with rat vasa deferentia and/or rabbit aorta).