Detection of retinyl palmitate and retinol in the liver of mice injected with excessive amounts of retinyl acetate

A simple and robust quantitative analysis of retinol and retinyl palmitate using a liquid chromatographic isocratic method

Vitamin A is a vital nutritional substances that regulates biological activities including development, but is also associated with disease onset. The extent of vitamin A intake influences the retinoid content in the liver, the most important organ for the storage of vitamin A. Measurement of endogenous retinoid in biological samples is important to understand retinoid homeostasis. Here we present a reliable, highly sensitive, and robust method for the quantification of retinol and retinyl palmitate using a reverse-phase HPLC/ UV isocratic method. We determined the impact of chronic dietary vitamin A on retinoid levels in livers of mice fed an AIN-93G semi-purified diet (4 IU/g) compared with an excess vitamin A diet (1000 IU/g) over a period from birth to 10 weeks of age. Coefficients of variation for intra-assays for both retinoids were less than 5%, suggesting a higher reproducibility than any other HPLC/UV gradient method. Limits of detection and quantification for retinol were 0.08 pmol, and 0.27 pmol, respectively, which are remarkably higher than previous results. Supplementation with higher doses of vitamin A over the study period significantly increased liver retinol and retinyl palmitate concentrations in adult mice. The assays described here provide a sensitive and rigorous quantification of endogenous retinol and retinyl palmitate, which can be used to help determine retinoid homeostasis in disease states, such as toxic hepatitis and liver cancer.

Liver autofluorescence properties in animal model under altered nutritional conditions

Autofluorescence spectroscopy is a promising and powerful approach for an in vivo, real time characterization of liver functional properties. In this work, preliminary results on the dependence of liver autofluorescence parameters on the nutritional status are reported, with particular attention to vitamin A and lipid accumulation in liver tissue. Normally fed and 24 h starving rats were used as animal models. Histochemical and autofluorescence analysis showed that lipids and vitamin A colocalize in the liver parenchyma. Fasting condition results in a parallel increase in both lipids and vitamin A. Autofluorescence imaging and microspectrofluorometric analysis carried out on unfixed, unstained tissue sections under 366 nm excitation, evidenced differences in both spectral shape and response to continuous irradiation between liver biopsies from fed and starving rats. As to photobleaching, in particular, fitting analysis evidenced a reduction of about 85% of the signal attributable solely to vitamin A during the first 10 s of irradiation. The tissue whole emission measured in fed and starving rat livers exhibited reductions of about 35% and 52%, respectively, that are closely related to vitamin A contents. The findings open interesting perspectives for the set up of an in situ, real time diagnostic procedure for the assessment of liver lipid accumulation, exploiting the photophysical properties of vitamin A.

High, but not low, dietary retinoids aggravate manifestation of rat liver fibrosis

BACKGROUND

Although there is strong implication that retinoids regulate Ito cell proliferation and collagen synthesis, results from in vivo studies on the relationship between vitamin A and liver fibrosis are conflicting. The present study focuses on the role of vitamin A in carbon tetrachloride (CCl4)-induced fibrosis by chronic feeding of rats with either a vitamin A-supplemented or -depleted diet.

METHODS AND RESULTS

In animals with high dietary hepatic retinoid levels, liver fibrosis was more pronounced and was associated with an increased CCl4-toxicity resulting in high mortality (73%). Enhanced liver fibrosis was confirmed by in vivo fluorescence microscopic determination of both collagen deposits (7.4 +/- 1.1 vs 3.9 +/- 0.3% in high vitamin A diet-fed and standard diet-fed fibrotic animals, respectively; P < 0.05) and rarefication of sinusoids (1.5 +/- 0.2 vs 2.4 +/- 0.2 sinusoids/200 microm in high vitamin A diet-fed and standard diet-fed fibrotic animals, respectively; P < 0.05). It was further associated with decreased bile flow and increased parenchymal cell damage. CCl4 reduced hepatic retinoid levels in high vitamin A diet-fed animals, but restored hepatic retinoid levels in animals fed with a vitamin A-deficient diet, implying major interference of vitamin A metabolism with hepatotoxic agents such as CCl4. Low vitamin A feeding did not modulate liver fibrogenesis and caused no mortality.

CONCLUSIONS

These results show that the vitamin A status of the liver plays an important role in liver fibrogenesis. While dietary vitamin A shortage does not promote liver fibrogenesis, high levels of vitamin A have the potential to increase systemic and hepatic toxicity of CCl4. Thus, the narrow therapeutic window for nutritional vitamin A substitution must take into account that liver fibrotic patients may display enhanced susceptibility to the adverse effects of vitamin A.