The effect of vitamin B6 deficiency on food intake, growth, and renal function in chronically azotemic rats

Detrimental effects of 6 months exposure to very low doses of a mixture of six pesticides associated with chronic vitamin deficiency on rats

This study aimed to evaluate the long-term low-dose effects of exposure to a mixture of 6 pesticide active substances (diquat, imazamox, imazethapyr, tepraloxydin, bentazone, acifluorfen) and to elucidate if chronic vitamin deficiency can influence their toxicity. Two hundred Wistar rats were divided in 4 groups: a vitamin-sufficiency control group, a vitamin-deficiency control group, a vitamin sufficiency test group and a vitamin-deficiency test group. The test groups were treated with the aforementioned pesticides at doses 100 times lower than the corresponding NOAEL. After 6 months, ten rats from each group were sacrificed and a complete evaluation of blood and urine biochemistry, biomarkers of oxidative stress, xenobiotic detoxification enzymes and lysosomal enzymes and organ histopathology was performed. The pesticides mixture and vitamin deficiency determined an increase in alkaline phosphatase levels and urinary calcium levels, abnormal serum lipid profile, and a decrease of total blood proteins levels, red blood cells, haematocrit and haemoglobin. The combination of the two stressors up-regulated CYP1A1, CYP1A2, CYP2B1 and GST levels. This study provides a new proof for the need to move forward from single chemical testing to a more complex approach to account for the multitude of stressors that can challenge the setting of real safety levels.

A Vitamin B-6 Antagonist from Flaxseed Perturbs Amino Acid Metabolism in Moderately Vitamin B-6-Deficient Male Rats

BACKGROUND

Pyridoxal 5'-phosphate (PLP) plays a crucial role as a cofactor in amino acid metabolism. There is a prevalence of moderate vitamin B-6 deficiency in the population that may be exacerbated through the ingestion of 1-amino d-proline (1ADP), a vitamin B-6 antagonist found in flaxseed.

OBJECTIVE

Given prior evidence of the impact of synthetic 1ADP on indexes of pyridoxine metabolism, the current study was designed to investigate the effects of 1ADP derived from flaxseed on amino acid metabolism in moderately vitamin B-6-deficient rats.

METHODS

Male weanling rats (n = 8/treatment) consumed a semipurified diet containing either 7 mg pyridoxine hydrochloride/kg diet [optimum vitamin B-6 (OB)] or 0.7 mg pyridoxine hydrochloride/kg diet [moderately vitamin B-6 deficient (MB)], each with 0 or 10 mg vitamin B-6 antagonist/kg diet, in either a synthetic form (1ADP) or as a flaxseed extract (FE), for 5 wk. At the end of the experiment, plasma vitamin B-6 and amino acid concentrations and the activities of hepatic PLP-dependent enzymes were analyzed.

RESULTS

Compared with the MB control group, plasma PLP concentrations were 26% and 69% lower, respectively, in the MB+FE and MB+1ADP rats (P ≤ 0.001). In the MB+FE group, the plasma cystathionine concentration was 100% greater and the plasma α-aminobutyric acid and glutamic acid concentrations were 59% and 30% lower, respectively, than in the MB control group. Both synthetic 1ADP and FE significantly (P < 0.001) inhibited the in vitro hepatic activities of 2 PLP-dependent enzymes, cystathionine β-synthase (up to 44%) and cystathionine γ-lyase (up to 60%), irrespective of vitamin B-6 concentrations. Because of vitamin B-6 antagonist exposure, observed perturbations in plasma biomarkers and hepatic enzyme activities were not evident or of lesser magnitude in rats consuming adequate vitamin B-6.

CONCLUSION

The current data from a rat model provide evidence that a vitamin B-6 antagonist now prevalent in the human food supply may pose challenges to individuals of moderate vitamin B-6 status.

Oral exposure to the anti-pyridoxine compound 1-amino D-proline further perturbs homocysteine metabolism through the transsulfuration pathway in moderately vitamin B₆ deficient rats

Pyridoxal 5'-phosphate (PLP; a B₆ vitamer) serves as an important cofactor in a myriad of metabolic reactions, including the transsulfuration (TS) pathway, which converts homocysteine (Hcy) to cysteine. While overt vitamin B₆ deficiency is rare, moderate deficiency is common and may be exacerbated by anti-pyridoxine factors in the food supply. To this end, we developed a model of moderate B₆ deficiency and a study was conducted to examine the in vivo effect of 1-amino D-proline (1ADP), an anti-pyridoxine factor found in flaxseed, on indices of Hcy metabolism through the TS pathway in moderately B₆ deficient rats. Male weaning rats received a semi-purified diet containing either 7 mg/kg (control; CD) or 0.7 mg/kg (moderately deficient; MD) diet of pyridoxine·hydrochloride (PN∙HCl), each with 1 of 4 levels of 1ADP, viz. 0, 0.1, 1 and 10 mg/kg diet for 5 weeks. Perturbations in vitamin B₆ biomarkers were more pronounced in the MD group. Plasma PLP was significantly reduced, while plasma Hcy (8-fold) and cystathionine (11-fold) were increased in rats consuming the highest amount of 1ADP in the MD group. The activities of hepatic cystathionine β-synthase and cystathionine γ-lyase enzymes were significantly reduced in rats consuming the highest 1ADP compared to the lowest, for both levels of PN∙HCl. Dilation of hepatic central veins and sinusoids, mild steatosis and increased liver triglycerides were present in MD rats consuming the highest 1ADP level. The current data provide evidence that the consumption of an anti-pyridoxine factor linked to flaxseed may pose a risk for subjects who are moderate/severe vitamin B₆ deficient.

Vitamin B6 deficiency and dietary fats: effects on lipid composition and glutathione peroxidase activity in rat liver

Dietary selenium, vitamin B6 and fatty acids modulate both tissue acyl composition by regulating polyunsaturated fatty acid metabolism and antioxidant defences by influencing glutathione peroxidase activity. Alteration in the intake of one of them could therefore lead to different results depending on the intake of the others. To clarify this complex relationship, in the present study we have evaluated the modifications occurring in fatty acid composition and glutathione peroxidase activity in total liver and liver microsomes of rats fed diets containing the same amount of selenium, but different vitamin B6 content and fatty acid composition. Our data indicate that both acyl composition and glutathione peroxidase activity are greatly influenced not only by vitamin B6 deficiency, but also by the diet unsaturation degree. This study underlines that not only selenium availability but also other nutrients can modulate glutathione peroxidase activity.

Vitamin B6 status in uremia

We have studied vitamin B6 status in 26 uremic patients, 18 on maintenance hemodialysis and 8 nonhemodialyzed. The vitamin B6 status was estimated by an assay of erythrocyte aspartate aminotransferase and coenzyme stimulation. Hemodialyzed uremic patients were found to have vitamin B6 deficiency. Patients were treated with 150 mg pyridoxine hydrochloride daily for 4 weeks. Erythrocyte aspartate aminotransferase increased significantly in both groups of uremic patients, the increase being greater in hemodialyzed patients. In vitro pyridoxal phosphate stimulation produces an erythrocyte aspartate aminotransferase activity greater than that obtained before pyridoxine hydrochloride administration. After cessation of pyridoxine hydrochloride treatment, erythrocyte aspartate aminotransferase decreases in hemodialyzed patients, while it remains elevated in nonhemodialyzed patients. The data obtained appear to indicate that vitamin B6 administration to patients with chronic renal insufficiency must be appraised not only for correcting the deficit but also for increasing the intracellular pyridoxal phosphate concentration, which could modify the possible functional impairment at the level of apoenzymes that use pyridoxal phosphate.