Ingolf Cascorbi

Frequency of single nucleotide polymorphisms in the P-glycoprotein drug transporter MDR1 gene in white subjects

P‐glycoprotein, the gene product of MDR1, confers multidrug resistance against antineoplastic agents but also plays an important role in the bioavailability of common drugs in medical treatment. Various polymorphisms in the MDR1 gene were recently identified. A silent mutation in exon 26 (C3435T) was correlated with intestinal P‐glycoprotein expression and oral bioavailability of digoxin.

Modulation of steady‐state kinetics of digoxin by haplotypes of the P‐glycoprotein MDR1 gene

We investigated the effect of polymorphisms in the P‐glycoprotein (P‐gp) MDR1 gene on steady‐state pharmacokinetics of digoxin in Caucasians. According to earlier data, homozygous TT of the exon 26 complementary deoxyribonucleic acid (cDNA) 3435C>T polymorphism was associated with low P‐gp expression in the human intestine.

Mental and physical distress is modulated by a polymorphism in the 5-HT transporter gene interacting with social stressors and chronic disease burden

Previous studies have yielded conflicting results as to the putative role of the functional polymorphism of the promoter region of the serotonin transporter gene (SLC6A4) in the etiology of anxiety-related traits and depressive disorders. Recently, a significant gene–environment interaction was found between life stressors, the short allele of the SLC6A4 polymorphism and depression. The aim of the present study was to investigate if such a gene–environment interaction could be replicated within a different population with a different risk structure. A total of 1005 subjects from a general population sample (Study of Health in Pomerania) were genotyped. Mental and physical distress were assessed on 38 items of the modified complaint scale (BL-38). The interaction between the SLC6A4 genotype, social stressors and chronic diseases with regard to the BL-38 score was evaluated by ANOVA. There was no independent association of genotype with mental and physical distress. However, significant interactions between genotype, unemployment and chronic diseases (F=6.6; df=3, 671; P<0.001) were found in females but not in males. The genotype explained 2% of the total variance of the BL-38 score and 9.1% of the explained variance. The results partly confirm previous findings of a significant gene–environment interaction of the short allele, indicating a higher mental vulnerability to social stressors and chronic diseases. The relevance of this finding is sustained by the fact that the sample characteristics and the risk structure were highly different from previous studies.

Deposition of Alzheimer's β-amyloid is inversely correlated with P-glycoprotein expression in the brains of elderly non-demented humans

Deposition of the beta-amyloid peptide (Abeta) in the brain occurs during normal ageing and is substantially accelerated in patients with Alzheimers disease. Since Abeta is continuously produced in the brain, it has been suggested that a clearance mechanism should exist to prevent its accumulation and subsequent aggregation. Until now, little attention has been paid to the possible role of P-glycoprotein (P-gp), a member of the ATP binding cassette superfamily of transporter proteins, in the pathogenesis of Alzheimers disease. A recent study demonstrated that Abeta40 and Abeta42 interact directly with P-gp. We therefore hypothesized that Abeta accumulation in the brain would correlate inversely with the degree of vascular P-gp expression. To study early pathogenetic factors that influence the deposition of Abeta, at routine autopsies, brain tissue samples were taken from 243 non-demented subjects who died between the ages of 50 and 91 years. Vascular P-gp expression and the number of Abeta40- and Abeta42-positive senile plaques were assessed immunohistochemically in the medial temporal lobe. In addition, the apolipoprotein E (apoE) genotypes, as well as multiple drug resistance gene 1 ( ) polymorphisms (exon 2, G-1A; exon 21, G2677T/A; exon 26, C3436T), were also determined for each case. P-gp expression was not correlated with genotypes, but we found a significant inverse correlation between P-gp expression and the deposition of both Abeta40 and Abeta42 in the medial temporal lobe. Our results provide the first evidence in human brain tissue that the accumulation of Abeta may be influenced by the expression of P-gp in blood vessels, and suggest that P-gp may influence the elimination of Abeta from brain.

The effects of the human MDR1 genotype on the expression of duodenal P-glycoprotein and disposition of the probe drug talinolol

A single‐nucleotide polymorphism (SNP) of the human multidrug‐resistance gene in wobble position of exon 26 reportedly predicts expression and function of P‐glycoprotein in human enterocytes and lymphocytes. Several other allelic variants of MDR1 have been identified, some of which lead to amino acid exchange with as yet unknown functional relevance.

MDR1-P-Glycoprotein (ABCB1) Mediates Transport of Alzheimer’s Amyloid-β Peptides—Implications for the Mechanisms of Aβ Clearance at the Blood–Brain Barrier

Amyloid‐β (Aβ) is the major component of the insoluble amyloid plaques that accumulate intracerebrally in patients with Alzheimer’s disease (AD). It has been suggested that MDR1‐P‐glycoprotein (ABCB1, P‐gp) plays a substantial role in the elimination of Aβ from the brain. In the present study, MDR1‐transfected LLC cells growing in a polarized cell layer were used to characterize the interaction of Aβ1‐40/1‐42 with P‐gp. In this system, P‐gp‐mediated transport can be followed by the efflux of the fluorescent dye rhodamine‐123, or of Aβ itself from the cells into the apical extracellular space. Aβ significantly decreased the apical efflux of rhodamine‐123, and the transcellular transport of Aβ1‐40 and Aβ1‐42 into the apical chamber could be demonstrated using both ELISA and fluorescence (FITC)‐labeled peptides. This transport was inhibited by a P‐gp modulator. Furthermore, ATP‐dependent, P‐gp‐mediated transport of the fluorescence‐labeled peptides could be demonstrated in isolated, inside‐out membrane vesicles. Our data support the concept that P‐gp is important for the clearance of Aβ from brain, and thus may represent a target protein for the prevention and/or treatment of neurodegenerative disorders such as AD.

Glyburide and glimepiride pharmacokinetics in subjects with different CYP2C9 genotypes.

Our objective was to investigate the effects of genetic polymorphisms of cytochrome P450 (CYP) 2C9 on the pharmacokinetics of glyburide (INN, glibenclamide) and glimepiride, two widely used sulfonylurea antidiabetic drugs.

Influence of polymorphisms of ABCB1 and ABCC2 on mRNA and protein expression in normal and cancerous kidney cortex

There is increasing evidence that polymorphisms of the adenosine 5′ triphosphate membrane transporters ABCB1 (P-glycoprotein, MDR1) may affect expression and function, whereas less information is available about the impact of ABCC2 (multidrug resistance-associated protein (MRP2)) single-nucleotide polymorphisms . Particularly, their role in human kidney for drug elimination and in the etiology of renal cell carcinoma is poorly understood. ABCB1 and ABCC2 mRNA and protein expression levels were determined by real-time polymerase chain reaction or immunohistochemistry in kidney cancer and adjacent unaffected cortex tissue of 82 nephrectomized renal cell cancer (RCC) patients (63 clear-cell RCC (CCRCC), 19 non-CCRCC). The DNA of all patients was genotyped for ABCB1 −2352G>A, −692T>C, 2677G>T/A (Ala893Ser/Thr), and 3435C>T, and ABCC2 −24C>T, 1249G>A (Val417Ile) and 3972C>T. ABCB1 and ABCC2 were less expressed in CCRCC than in normal cortex on mRNA as well as on protein level. Although the overall genotype frequency distribution did not differ between the patients and a matched control group, ABCB1 2677T/A and 3435T genotypes were associated with higher (P=0.02 and P=0.04) and ABCC2 −24 T with lower mRNA levels in normal tissues (0.03). The expression of ABCB1 and ABCC2 was not related to genetic variants in RCC tissue. In a reporter gene assay in HepG2 cells, the ABCC2 −24T construct showed an 18.7% reduced activity (P=0.003). In conclusion, ABCB1 and ABCC2 genotypes modulate the expression in the unaffected renal cortex of RCC patients, possibly contributing to inter-individual differences in drug and xenobiotics elimination. Their role in RCC cancer susceptibility or chemotherapy resistance needs further elucidation.

Should We Use N-Acetyltransferase Type 2 Genotyping To Personalize Isoniazid Doses?

ABSTRACT Isoniazid is metabolized by the genetically polymorphic arylamine N-acetyltransferase type 2 (NAT2). A greater number of high-activity alleles are related to increased acetylation capacity and in some reports to low efficacy and toxicity of isoniazid. The objective of this study was to assess individual isoniazid exposure based on NAT2 genotype to predict a personalized therapeutic dose. Isoniazid was administered to 18 healthy Caucasians (age 30 ± 6 years, body weight 74 ± 10 kg, five women) in random order as a 200-mg infusion, a 100-mg oral, and a 300-mg oral single dose. For the assessment of NAT2 genotype, common single nucleotide polymorphisms identifying 99.9% of variant alleles were characterized. Noncompartmental pharmacokinetics and compartmental population pharmacokinetics were estimated from isoniazid plasma concentrations until 24 h postdose by high-pressure liquid chromatography. The influence of NAT2 genotype, drug formulation, body weight, and sex on dose-normalized isoniazid pharmacokinetics was assessed by analysis of variance from noncompartmental data and confirmed by population pharmacokinetics. Eight high-activity NAT2*4 alleles were identified. Sex had no effect; the other factors explained 93% of the variability in apparent isoniazid clearance (analysis of variance). NAT2 genotype alone accounted for 88% of variability. Individual isoniazid clearance could be predicted as clearance (liters/hour) = 10 + 9 × (number of NAT2*4 alleles). To achieve similar isoniazid exposure, current standard doses presumably appropriate for patients with one high-activity NAT2 allele may be decreased or increased by approximately 50% for patients with no or two such alleles, respectively. Prospective clinical trials are required to assess the merits of this approach.

The Role of P-glycoprotein in Cerebral Amyloid Angiopathy; Implications for the Early Pathogenesis of Alzheimer’s Disease

It has been shown in vitro that beta-amyloid (Abeta) is transported by P-glycoprotein (P-gp). Previously, we demonstrated that Abeta immunoreactivity is significantly elevated in brain tissue of individuals with low expression of P-gp in vascular endothelial cells. These findings led us to hypothesize that P-gp might be involved in the clearance of Abeta in normal aging and particularly in Alzheimers disease (AD). As we were interested in the early pathogenesis of Abeta deposition, we studied the correlation between cerebral amyloid angiopathy (CAA) and P-gp expression in brain tissue samples from 243 non-demented elderly cases (aged 50 to 91 years). We found that endothelial P-gp and vascular Abeta were never colocalized, i.e., vessels with high P-gp expression showed no Abeta deposition in their walls, and vice versa. Abeta deposition occurred first in arterioles where P-gp expression was primarily low, and disappeared completely with the accumulation of Abeta. At this early stage, P-gp was upregulated in capillaries, suggesting a compensatory mechanism to increase Abeta clearance from the brain. Capillaries were usually affected only at later stages of CAA, at which point P-gp was lost even in these vessels. We hypothesize that Abeta clearance may be altered in individuals with diminished P-gp expression due, e.g., to genetic or environmental effects (such as drug administration). The impairment of Abeta clearance could lead to the accumulation and earlier deposition of Abeta, both in the walls of blood vessels and in the brain parenchyma, thus elevating the risk of CAA and AD.