TY - JOUR
T1 - Enzymes involved in l-carnitine biosynthesis are expressed by small intestinal enterocytes in mice
T2 - Implications for gut health
AU - Shekhawat, Prem S.
AU - Sonne, Srinivas
AU - Carter, A. Lee
AU - Matern, Dietrich
AU - Ganapathy, Vadivel
N1 - Funding Information:
PS conceived the project, carried out the scientific work with SS and wrote the manuscript under supervision of VG, AL helped with carnitine biosynthesis assay, DM did tandem mass assays and actively participated in manuscript preparation and all authors approve the final version of manuscript. This work was supported by NIH grant HD 048867 to PS.
PY - 2013/7/1
Y1 - 2013/7/1
N2 - Background: Carnitine is essential for mitochondrial β-oxidation of long-chain fatty acids. Deficiency of carnitine leads to severe gut atrophy, ulceration and inflammation in animal models of carnitine deficiency. Genetic studies in large populations have linked mutations in the carnitine transporters OCTN1 and OCTN2 with Crohn's disease (CD), while other studies at the same time have failed to show a similar association and report normal serum carnitine levels in CD patients. Methods: In this report, we have studied the expression of carnitine-synthesizing enzymes in intestinal epithelial cells to determine the capability of these cells to synthesize carnitine de novo. We studied expression of five enzymes involved in carnitine biosynthesis, namely 6-N-trimethyllysine dioxygenase (TMLD), 4-trimethylaminobutyraldehyde dehydrogenase (TMABADH), serine hydroxymethyltransferase 1 and 2 (SHMT1 and 2) and γ-butyrobetaine hydroxylase (BBH) by real-time PCR in mice (C3H strain). We also measured activity of γ-BBH in the intestine using an ex vivo assay and localized its expression by in situ hybridization. Results: Our investigations show that mouse intestinal epithelium expresses all five enzymes required for de novo carnitine biosynthesis; the expression is localized mainly in villous surface epithelial cells throughout the intestine. The final rate-limiting enzyme γ-BBH is highly active in the small intestine; its activity was 9.7 ± 3.5. pmol/mg/min, compared to 22.7 ± 7.3. pmol/mg/min in the liver. Conclusions: We conclude that mouse gut epithelium is able to synthesize carnitine de novo. This capacity to synthesize carnitine in the intestine may play an important role in gut health and can help explain lack of clinical carnitine deficiency signs in subjects with mutations with OCTN transporters.
AB - Background: Carnitine is essential for mitochondrial β-oxidation of long-chain fatty acids. Deficiency of carnitine leads to severe gut atrophy, ulceration and inflammation in animal models of carnitine deficiency. Genetic studies in large populations have linked mutations in the carnitine transporters OCTN1 and OCTN2 with Crohn's disease (CD), while other studies at the same time have failed to show a similar association and report normal serum carnitine levels in CD patients. Methods: In this report, we have studied the expression of carnitine-synthesizing enzymes in intestinal epithelial cells to determine the capability of these cells to synthesize carnitine de novo. We studied expression of five enzymes involved in carnitine biosynthesis, namely 6-N-trimethyllysine dioxygenase (TMLD), 4-trimethylaminobutyraldehyde dehydrogenase (TMABADH), serine hydroxymethyltransferase 1 and 2 (SHMT1 and 2) and γ-butyrobetaine hydroxylase (BBH) by real-time PCR in mice (C3H strain). We also measured activity of γ-BBH in the intestine using an ex vivo assay and localized its expression by in situ hybridization. Results: Our investigations show that mouse intestinal epithelium expresses all five enzymes required for de novo carnitine biosynthesis; the expression is localized mainly in villous surface epithelial cells throughout the intestine. The final rate-limiting enzyme γ-BBH is highly active in the small intestine; its activity was 9.7 ± 3.5. pmol/mg/min, compared to 22.7 ± 7.3. pmol/mg/min in the liver. Conclusions: We conclude that mouse gut epithelium is able to synthesize carnitine de novo. This capacity to synthesize carnitine in the intestine may play an important role in gut health and can help explain lack of clinical carnitine deficiency signs in subjects with mutations with OCTN transporters.
KW - Carnitine
KW - Crohn's disease
KW - Gut inflammation
KW - Ulcerative colitis
KW - γ-Butyrobetaine hydroxylase
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U2 - 10.1016/j.crohns.2012.08.011
DO - 10.1016/j.crohns.2012.08.011
M3 - Article
C2 - 22999781
AN - SCOPUS:84877028600
SN - 1873-9946
VL - 7
SP - e197-e205
JO - Journal of Crohn's and Colitis
JF - Journal of Crohn's and Colitis
IS - 6
ER -