This study investigated the relative contribution of ion-trapping, microsomal binding, and distribution of unbound drug as determinants in the hepatic retention of basic drugs in the isolated perfused rat liver. The ionophore monensin was used to abolish the vesicular proton gradient and thus allow an estimation of ion-trapping by acidic hepatic vesicles of cationic drugs. In vitro microsomal studies were used to independently estimate microsomal binding and metabolism. Hepatic vesicular ion-trapping, intrinsic elimination clearance, permeability-surface area product, and intracellular binding were derived using a physiologically based pharmacokinetic model. Modeling showed that the ion-trapping was significantly lower after monensin treatment for atenolol and propranolol, but not for antipyrine. However, no changes induced by monensin treatment were observed in intrinsic clearance, permeability, or binding for the three model drugs. Monensin did not affect binding or metabolic activity in vitro for the drugs. The observed ion-trapping was similar to theoretical values estimated using the pHs and fractional volumes of the acidic vesicles and the pK a values of drugs. Lipophilicity and pK a determined hepatic drug retention: a drug with low pK a and low lipophilicity (e.g., antipyrine) distributes as unbound drug, a drug with high pK a and low lipophilicity (e.g., atenolol) by ion-trapping, and a drug with a high pK a and high lipophilicity (e.g., propranolol) is retained by ion-trapping and intracellular binding. In conclusion, monensin inhibits the ion-trapping of high pK a basic drugs, leading to a reduction in hepatic retention but with no effect on hepatic drug extraction.Basic lipophilic compounds are characterized by a high volume of distribution as a result of extensive tissue uptake. The main mechanisms of such a distribution pattern are nonspecific binding to membrane phospholipids (Bickel and Steele, 1974;Francesco and Bickel, 1977;Romer and Bickel, 1979), binding to microsomal protein (Hung et al., 2002), and the sequestration of the compounds into acidic vesicular compartments such as lysosomes or mitochondria (Daniel et al., 1995). A potential consequence of an apparent irreversible sequestration of basic drugs into acidic vesicles is a potentially reduced drug bioavailability (de Duve et al., 1974;Ohkuma and Poole, 1978) or drug interactions (Daniel and Wojcikowski, 1999b;Nebbia et al., 1999). Lysosomal trapping of basic lipophilic drugs has also been demonstrated to be an important determinant of disposition for desipramine and chloroquine and psychotropic compounds such as the piperidine and piperazine-type neuroleptics (Daniel et al., 2001). The lysosomotropic properties of basic drugs are particularly important determining drug disposition and pharmacokinetics in lysosome-rich organs such as lungs, kidneys, or the liver.Specific studies determining the relative contribution of ion-trapping and microsomal binding to the hepatic retention of drugs or relating the relative uptake to the ph...
A family history of Parkinson's disease (PD) is the most commonly reported risk factor after age, suggesting a genetic component to the disease in a sub-group of patients. Mutations in at least six genes have been identified that can lead to monogenic forms of PD. We screened a sample of 74 early-onset PD cases out of a cohort of 950 patients (onset <50 years) for genetic abnormalities in known familial Parkinsonism genes. A self-reported family history of PD existed for 30 patients (40.5%). Of these, 13 each had a first- or a second-degree relative with PD and four reported a more distant relative with PD. The entire coding region of the PRKN (MIM 602544), DJ-1 (MIM 602533) and PINK1 (MIM 698309) genes, and exon 41 of the LRRK2 gene (MIM 609007) were screened by direct sequencing. All exons of PRKN were examined for gene-dosage abnormalities. Screening identified five patients with putative genetic disease: two patients carried PRKN mutations (p.G12R heterozygous and p.G430D homozygous), one patient carried a p.G411S heterozygous amino acid change in the PINK1 gene and two individuals were heterozygous for the common p.G2019S mutation in LRRK2. No alpha-synuclein or DJ-1 variants were observed. Our data suggest that approximately 7% of early-onset PD cases seen in Queensland movement disorders clinics have mutations involving known PARK genes.
kinetics of [ 3 H]palmitate and its low-molecular-weight metabolites in perfused rat livers were studied using the multiple-indicator dilution technique, a selective assay for [ 3 H]palmitate and its low-molecular-weight metabolites, and several physiologically based pharmacokinetic models. The level of liver fatty acid binding protein (L-FABP), other intrahepatic binding proteins (microsomal protein, albumin, and glutathione S-transferase) and the outflow profiles of [ 3 H]palmitate and metabolites were measured in four experimental groups of rats: 1) males; 2) clofibrate-treated males; 3) females; and 4) pregnant females. A slow-diffusion/bound model was found to better describe the hepatic disposition of unchanged [3 H]palmitate than other pharmacokinetic models. The L-FABP levels followed the order: pregnant female Ͼ clofibrate-treated male Ͼ female Ͼ male. Levels of other intrahepatic proteins did not differ significantly. The hepatic extraction ratio and mean transit time for unchanged palmitate, as well as the production of low-molecular-weight metabolites of palmitate and their retention in the liver, increased with increasing L-FABP levels. Palmitate metabolic clearance, permeability-surface area product, retention of palmitate by the liver, and cytoplasmic diffusion constant for unchanged [3 H]palmitate also increased with increasing L-FABP levels. It is concluded that the variability in hepatic pharmacokinetics of unchanged [ 3 H]palmitate and its lowmolecular-weight metabolites in perfused rat livers is related to levels of L-FABP and not those of other intrahepatic proteins.clofibrate; pregnancy; multiple indicator dilution; hepatic extraction ratio; cytoplasmic diffusion constant NONESTERIFIED, LONG-CHAIN fatty acids (hereafter referred to as fatty acids) play a vital role in many cellular processes. They are an important source for cellular energy and form the building blocks from which various cellular components are synthesized. Some fatty acids are precursors for biological mediators, whereas others may interact with the cell membrane to regulate various cellular functions. Uptake of fatty acids has been shown to parallel the level of liver fatty acid binding protein (L-FABP) (22).L-FABP levels are known to be gender dependent, with females showing higher levels than males (25). L-FABP is also altered in various conditions, such as pregnancy and clofibrate treatment (6,26,31). Although the variation in the content of various intrahepatic proteins in liver disease has been used to account for the uptake, binding, and metabolism of solutes (20), the influence of intrahepatic proteins other than L-FABP [e.g., microsomal protein (MP), cytochrome P-450 (CYP), albumin (Alb), and glutathione S-transferase (GST)] on the hepatic disposition of [ 3 H]palmitate has been studied to a limited extent. Most studies investigating the fatty acid uptake into the liver have used isolated hepatocytes with some studies using intact livers (26,38).In this work, we examined the relationship between the hepatic pharma...
Alzheimer's disease (AD) and Parkinson's disease (PD) are the two most common neurodegenerative disorders. Why some individuals develop one disease rather than the other is not clear. Association studies with a case-control design are the time-honored approach to identifying risk factors. Extensive association studies have been carried out in both diseases creating a large knowledge database, however, reproducible risk factors remain rare. This general lack of knowledge of pathogenesis prevents us from reducing the worldwide burden of these diseases. Case-control studies are reductionist paradigms that assume, for maximum power, that the two populations being compared are exclusive and homogenous. The common occurrence of incidental AD and PD-type pathology combined with 'intermediate phenotypes' such as dementia with Lewy bodies suggest that aging itself, AD, and PD are part of a complex continuum characterized by variable amounts of amyloid-β, tau, and α-synuclein pathology. This heterogeneity may be a contributor to the lack of reproducibility in association studies to date. Here, we speculate on alternative experimental approaches to the case-control paradigm and consider how the association-study literature for AD and PD might be re-interpreted in terms of a disease spectrum.
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