Influence of OCTN2 Variants on Carnitine Status and Plasma Triglycerides

NCT ID: NCT00187733

Last Updated: 2012-09-13

Basic Information

• Recruitment Status: COMPLETED
• Total Enrollment: 16 participants
• Study Classification: OBSERVATIONAL
• Study Start Date: 2005-01-31
• Study Completion Date: 2008-02-29

Brief Summary

The current study is part of a large multi-investigator grant to look at the pharmacogenetics of a number of membrane transporters. Previously, the investigators have recruited a cohort of healthy volunteers (Studies of Pharmacogenetics in Ethnically-Diverse Populations, or SOPHIE) and have resequenced the coding region of a number of membrane transporter genes to identify genetic polymorphisms in these genes. Subjects in this cohort have agreed to be called back for recruitment in further studies based on their own genetic sequence, allowing the investigators the possibility to prospectively study the influence of genetic polymorphisms on particular phenotypes (i.e., genotype-to-phenotype studies). The investigators plan to take a genotype-to-phenotype approach to study the influence of specific polymorphisms in the novel organic cation transporter 2 (OCTN2) gene on carnitine and lipid metabolism in healthy subjects.

Detailed Description

Although OCTN2 is fairly well studied in its relationship with SCD, little is known about the carrier frequency of disease-causing alleles of OCTN2, or of more common functional polymorphisms in this gene. To address these issues, we screened for genetic variants in the OCTN2 coding region by direct sequencing of the exons and flanking intronic region of OCTN2 in a large sample (n = 276) of ethnically diverse subjects. In addition, we established lymphoblastoid cell lines from subjects homozygous for either allele of the previously identified promoter region variant, -207G>C. We found eight amino acid sequence variants of OCTN2, of which three (Phe17Leu, Leu144Phe, and Pro549Ser) were polymorphic in at least one ethnic group. When assayed for functional activity by expression in human embryonic kidney 293 cells, using as probes both the endogenous substrate (l-carnitine) and the organic cation tetraethylammonium, three variants showed functional differences from the reference OCTN2 (Phe17Leu, Tyr449Asp, Val481Phe; p < 0.05). Further studies of the Phe17Leu polymorphism showed a reduced V(max) for l-carnitine transport to approximately 50% of the reference OCTN2. Confocal microscopy studies using an OCTN2-GFP fusion protein showed that Phe17Leu had distinct subcellular localization from the reference OCTN2, with diffuse cytoplasmic retention of Phe17Leu, in contrast to reference OCTN2, which localized specifically to the plasma membrane. Lymphoblasts from subjects homozygous for the -207G allele showed increased l-carnitine transport compared with the -207C/C homozygotes (p < 0.05). This study suggests that although loss-of-function mutations in OCTN2 are likely to be rare, common variants of OCTN2 found in healthy populations may contribute to variation in the disposition of carnitine and some clinically used drugs.

Conditions

Carnitine Transporter Deficiency

Keywords

L-carnitine

Study Design

• Observational Model Type: COHORT
• Study Time Perspective: PROSPECTIVE

Study Groups

Fasting

Other: Fasting blood and urine collection

Fasting blood and urine collection

Intervention Type: OTHER

Not applicable no drugs dispensed

Interventions

Fasting blood and urine collection

Not applicable no drugs dispensed

Intervention Type: OTHER

Eligibility Criteria

Inclusion Criteria

• Previous participation in the "SOPHIE" study
• Between the ages of 18 and 40 years old
• Have a pre-selected genotype for OCTN1 and OCTN2
• Have been selected as healthy by medical history questionnaire and screening blood work (complete blood count [CBC], comprehensive metabolic panel).

Exclusion Criteria

• Pregnant at the time of the study
• Have a new history indicating they are no longer healthy
• Taking a medication that could confound study results
• Individuals with anemia (hemoglobin < 12 g/dL), an elevation in liver enzymes to higher than double the respective normal value, or elevated creatinine concentrations (males ≥ 1.5 mg/dL, females ≥ 1.4 mg/dL).
• Do not consent to participate in the study.

• Minimum Eligible Age: 18 Years
• Maximum Eligible Age: 40 Years
• Eligible Sex: ALL
• Accepts Healthy Volunteers: Yes

Sponsors

University of California, San Francisco

OTHER

Sponsor Role: lead

Responsible Party

Responsibility Role: SPONSOR

Principal Investigators

Kathleen Giacomini, PhD

Role: PRINCIPAL_INVESTIGATOR

University of California, San Francisco

Locations

San Francisco General Hospital

San Francisco, California, United States

Countries

United States

References

Urban TJ, Gallagher RC, Brown C, Castro RA, Lagpacan LL, Brett CM, Taylor TR, Carlson EJ, Ferrin TE, Burchard EG, Packman S, Giacomini KM. Functional genetic diversity in the high-affinity carnitine transporter OCTN2 (SLC22A5). Mol Pharmacol. 2006 Nov;70(5):1602-11. doi: 10.1124/mol.106.028126. Epub 2006 Aug 24.

Reference Type: RESULT

PMID: 16931768 (View on PubMed)

Other Identifiers

1005

Identifier Type: -

Identifier Source: org_study_id