Impaired hepatic and intestinal ATP-binding cassette transporter G5/8 was associated with high exposure of β-sitosterol and the potential risks to blood-brain barrier integrity in diabetic rats

Sitosterolemia: Twenty Years of Discovery of the Function of ABCG5ABCG8

Sitosterolemia is a lipid disorder characterized by the accumulation of dietary xenosterols in plasma and tissues caused by mutations in either ABCG5 or ABCG8. ABCG5 ABCG8 encodes a pair of ABC half transporters that form a heterodimer (G5G8), which then traffics to the surface of hepatocytes and enterocytes and promotes the secretion of cholesterol and xenosterols into the bile and the intestinal lumen. We review the literature from the initial description of the disease, the discovery of its genetic basis, current therapy, and what has been learned from animal, cellular, and molecular investigations of the transporter in the twenty years since its discovery. The genomic era has revealed that there are far more carriers of loss of function mutations and likely pathogenic variants of ABCG5 ABCG8 than previously thought. The impact of these variants on G5G8 structure and activity are largely unknown. We propose a classification system for ABCG5 ABCG8 mutants based on previously published systems for diseases caused by defects in ABC transporters. This system establishes a framework for the comprehensive analysis of disease-associated variants and their impact on G5G8 structure-function.

Critical Analysis on Characterization, Systemic Effect, and Therapeutic Potential of Beta-Sitosterol: A Plant-Derived Orphan Phytosterol

Beta-sitosterol (BS) is a phytosterol, widely distributed throughout the plant kingdom and known to be involved in the stabilization of cell membranes. To compile the sources, physical and chemical properties, spectral and chromatographic analytical methods, synthesis, systemic effects, pharmacokinetics, therapeutic potentials, toxicity, drug delivery and finally, to suggest future research with BS, classical as well as on-line literature were studied. Classical literature includes classical books on ethnomedicine and phytochemistry, and the electronic search included Pubmed, SciFinder, Scopus, the Web of Science, Google Scholar, and others. BS could be obtained from different plants, but the total biosynthetic pathway, as well as its exact physiological and structural function in plants, have not been fully understood. Different pharmacological effects have been studied, but most of the mechanisms of action have not been studied in detail. Clinical trials with BS have shown beneficial effects in different diseases, but long-term study results are not available. These have contributed to its current status as an "orphan phytosterol". Therefore, extensive research regarding its effect at cellular and molecular level in humans as well as addressing the claims made by commercial manufacturers such as the cholesterol lowering ability, immunological activity etc. are highly recommended.

Altered Expression of Transporters, its Potential Mechanisms and Influences in the Liver of Rodent Models Associated with Diabetes Mellitus and Obesity

Diabetes mellitus is becoming an increasingly prevalent disease that concerns patients and healthcare professionals worldwide. Among many anti-diabetic agents in clinical uses, numerous reports are available on their altered pharmacokinetics because of changes in the expression of drug transporters and metabolic enzymes under diabetic states. These changes may affect the safety and efficacy of therapeutic agents and/or drug-drug interaction with co-administered agents. Therefore, the changes in transporter expression should be identified, and the underlying mechanisms should be clarified. This review summarizes the progress of recent studies on the alterations in important uptake and efflux transporters in liver of diabetic animals and their regulatory pathways.

ABCG5 and ABCG8 gene polymorphisms in type 2 diabetes mellitus in the Turkish population

OBJECTIVE

The aim of the present study was to investigate the relationship between ABCG5 and ABCG8 gene polymorphisms and plasma lipid concentrations in Turkish patients with type 2 diabetes mellitus.

METHODS

Included in this study were 80 patients with type 2 diabetes and 73 healthy controls. Two selected single nucleotide polymorphisms in ABC transporter genes, ABCG5 (rs6720173) and ABCG8 (rs4148211), were genotyped by using the polymerase chain reaction-restriction fragment length polymorphism technique.

RESULTS

The rate of having the ABCG8 AA genotype (p=0.001) was significantly higher in the patients than in the control subjects. Correspondingly, the rates of having the AG genotype (p=0.001) and the G allele (p=0.001) were significantly lower in the patients than in controls. Upon comparing the groups regarding ABCG5, the frequencies of occurrence of the GG genotype (p=0.031) and G allele (p=0.003) were considerably higher in patients than in control subjects. In the patients, the rates of having the CC genotype (p=0.003) and the C allele (p=0.031) were also significantly lower than those in control subjects. There was no significant difference between G5 and G8 polymorphism and lipid levels in the study groups. The ABCG8 AA genotype carriers had higher triglyceride (p=0.045) and very low-density-cholesterol (p=0.045) levels than the ABCG8 GG genotype carriers in all study populations.

CONCLUSIONS

These results indicate that the AA genotype for ABCG8 and the GG genotype and G allele for ABCG5 are risk factors for diabetes. This study reveals the first data concerning the ABCG5 and ABCG8 gene polymorphisms in Turkish patients with diabetes.