Impaired intestinal vitamin B1 (thiamin) uptake in thiamin transporter-2-deficient mice

BACKGROUND & AIMS

Intestinal thiamin uptake process is vital for maintaining normal body homeostasis of the vitamin; in vitro studies suggest that both thiamin transporter-1 (THTR-1) and -2 (THTR-2) are involved. Mutations in THTR-1 cause thiamin-responsive megaloblastic anemia, a tissue-specific disease associated with diabetes mellitus, megaloblastic anemia, and sensorineural deafness. However, in patients with thiamin-responsive megaloblastic anemia, plasma thiamin levels are within normal range, indicating that THTR-2 (or another carrier) could provide sufficient intestinal thiamin absorption. We tested this possibility and examined the role of THTR-2 in uptake of thiamin in the intestine of mice.

METHODS

THTR-2-deficient mice were generated by SLC19A3 gene knockout and used to examine intestinal uptake of thiamin in vitro (isolated cells) and in vivo (intact intestinal loops). We also examined intestinal thiamin uptake in THTR-1-deficient mice.

RESULTS

Intestine of THTR-2-deficient mice had reduced uptake of thiamin compared with those of wild-type littermate mice (P < .01); this reduction was associated with a decrease (P < .01) in blood thiamin levels in THTR-2-deficient mice. However, intestinal uptake of thiamin in THTR-1-deficient mice was not significantly different from that of wild-type littermate animals. Level of expression of THTR-1 was not altered in the intestine of THTR-2-deficient mice, but level of expression of THTR-2 was up-regulated in the intestine of THTR-1-deficient mice.

CONCLUSIONS

THTR-2 is required for normal uptake of thiamin in the intestine and can fulfill normal levels of uptake in conditions associated with THTR-1 dysfunction.

Nitrofurazone-induced gene expressions in rat hepatocytes and their modification by N-acetylcysteine

The antibiotic nitrofurazone (NF) at a subtoxic dose has been shown to increase hepatocyte DNA synthesis with no preceding cell damage or necrosis. This was suppressed by concomitant administration of the antioxidant N-acetylcysteine (NAC), which suggests that free radical production is involved in the process. In this study, male F344 rats were given a single oral subtoxic dose of NF to investigate the changes in genes implicated in hepatocyte proliferation between 1 and 20h postdose by real-time PCR. Some rats were also given NAC to examine the involvement of free radicals. There were transient and sequential increases in mRNA levels of c-myc and c-jun shortly after the administration, followed by tumor necrosis factor-alpha (TNF-alpha), transforming growth factor-alpha (TGF-alpha), c-Ha-ras, and cyclin E. The increases were blocked by concomitant administration of NAC. In contrast, there were no NF-specific increases in c-fos, hepatocyte growth factor, epidermal growth factor or cyclin D1 mRNAs. These results indicate that the induction of hepatocyte proliferation by NF is triggered by free radicals, with a pathway involving increases in c-jun, c-myc, TNF-alpha, TGF-alpha, c-Ha-ras, and cyclin E. The results also indicate that NF-induced proliferation resembles that of other mitogens.