Impaired responses to sweet taste in vitamin A-deficient rats

The Roles of Vitamin A in the Regulation of Carbohydrate, Lipid, and Protein Metabolism

Currently, two-thirds of American adults are overweight or obese. This high prevalence of overweight/obesity negatively affects the health of the population, as obese individuals tend to develop several chronic diseases, such as type 2 diabetes and cardiovascular diseases. Due to obesity's impact on health, medical costs, and longevity, the rise in the number of obese people has become a public health concern. Both genetic and environmental/dietary factors play a role in the development of metabolic diseases. Intuitively, it seems to be obvious to link over-nutrition to the development of obesity and other metabolic diseases. However, the underlying mechanisms are still unclear. Dietary nutrients not only provide energy derived from macronutrients, but also factors such as micronutrients with regulatory roles. How micronutrients, such as vitamin A (VA; retinol), regulate macronutrient homeostasis is still an ongoing research topic. As an essential micronutrient, VA plays a key role in the general health of an individual. This review summarizes recent research progress regarding VA's role in carbohydrate, lipid, and protein metabolism. Due to the large amount of information regarding VA functions, this review focusses on metabolism in metabolic active organs and tissues. Additionally, some perspectives for future studies will be provided.

"Functional food" for acceleration of growth in short children born small for gestational age

OBJECTIVE

To assess the effect of nutritional supplementation on growth in short children born small for gestational age (SGA).

PATIENTS

Fifty four short but otherwise healthy children (26 boys), 6.4 +/- 1.8 years of age, were referred for growth retardation.

METHODS

Following a 6 month observation period the participants were randomly allocated to receive growth hormone therapy (GH) 1.26 IU/kg/day (0.042 mg/kg/day) or nutritional program (NUT) or passive observation (OBS). Patients in the nutritional program received 10 mg/day iron, 11 mg zinc-three times a week and 10000 IU/week of vitamin A. The following parameters were obtained 3 monthly: height, weight, dietary intake and serum IGF-1.

RESULTS

Six months of nutritional supplement induced growth acceleration somewhat lower than that seen in the growth hormone treated children, but significantly greater than noted in the observation group (OBS 4.6 +/- 1.3, NUT 7.9 +/- 1.7, GH 9.1 +/- 1.8 cm/yr, P<0.001).

CONCLUSIONS

Six months of vitamin A, iron and zinc supplementation induces growth acceleration in short children born SGA with subnormal nutrients intake similar to growth hormone therapy.

Alterations of taste perception in Crohn's disease and their dependency on disease activity and nutritional behavior

BACKGROUND

The pathogenesis of Crohn's disease (CD) is unknown. Besides immunoregulatory, genetic and environmental aspects, a nutritional impact is also encountered. Whether taste perception exerts any influence on an increased consumption of carbohydrates is unknown.

OBJECTIVE

To evaluate nutritional habits and taste perception in CD patients, either in active or inactive disease stages.

DESIGN

A prospective study was performed with 31 active and 27 inactive CD patients, and 30 age and sex-matched healthy subjects. Nutritional behavior was determined using an extensive optical nutrition questionnaire and taste perception was assessed by a 3-drop method with exceeding dilution tests.

RESULTS

Active and inactive CD patients exhibited a significant increased taste threshold for the detection of all solutions (bitter: P=0.0012; salty: P=0.0198; sour: P=0.0021; and sweet: P=0.0208). For recognition, the determination of bitter solution (P=0.0014) was significantly reduced in CD patients compared with healthy subjects. No impact of clinical or objective parameters of inflammation on taste perception could be established. The consumption of refined sugar in CD patients was higher than in healthy subjects, though not significant.

CONCLUSIONS

An increased taste threshold for the detection of all 4 taste qualities in active and inactive CD patients suggests a systemic pathogenesis, such as an inflammation of the oral cavity, as a manifestation of CD. In this study, changes in taste threshold were not associated with altered sugar consumption.

Old World Nonhuman Primate Models of Type 2 Diabetes Mellitus

Type 2 diabetes mellitus is a major health problem of increasing incidence. To better study the pathogenesis and potential therapeutic agents for this disease, appropriate animal models are needed. Old World nonhuman primates (NHPs) are a useful animal model of type 2 diabetes; like humans, the disease is most common in older, obese animals. Before developing overt diabetes, NHPs have a period of obesity-associated insulin resistance that is initially met with compensatory insulin secretion. When either a relative or absolute deficiency in pancreatic insulin production occurs, fasting glucose concentrations begin to increase and diabetic signs become apparent. Pathological changes in pancreatic islets are also similar to those seen in human diabetics. Initially there is hyperplasia of the islets with abundant insulin production typically followed by replacement of islets with islet-associated amyloid. Diabetic NHPs have detrimental changes in plasma lipid and lipoprotein concentrations, lipoprotein composition, and glycation, which may contribute to progression of atherosclerosis. As both the prediabetic condition (similar to metabolic syndrome in humans) and overt diabetes become better defined in monkeys, their use in pharmacological studies is increasing. Likely due to their genetic similarity to humans and the similar characteristics of the disease in NHPs, NHPs have been used to study recently developed agonists of the peroxisome proliferators-activated receptors. Importantly, agonists of the different receptor subclasses elicit similar responses in both humans and NHPs. Thus, Old World NHPs are a valuable animal model of type 2 diabetes to study disease progression, associated risk factors, and potential new treatments.

Once and again: Retinoic acid signaling in the developing and regenerating olfactory pathway

Retinoic acid (RA), a member of the steroid/thyroid superfamily of signaling molecules, is an essential regulator of morphogenesis, differentiation, and regeneration in the mammalian olfactory pathway. RA-mediated teratogenesis dramatically alters olfactory pathway development, presumably by disrupting retinoid-mediated inductive signaling that influences initial olfactory epithelium (OE) and bulb (OB) morphogenesis. Subsequently, RA modulates the genesis, growth, or stability of subsets of OE cells and OB interneurons. RA receptors, cofactors, and synthetic enzymes are expressed in the OE, OB, and anterior subventricular zone (SVZ), the site of neural precursors that generate new OB interneurons throughout adulthood. Their expression apparently accommodates RA signaling in OE cells, OB interneurons, and slowly dividing SVZ neural precursors. Deficiency of vitamin A, the dietary metabolic RA precursor, leads to cytological changes in the OE, as well as olfactory sensory deficits. Vitamin A therapy in animals with olfactory system damage can accelerate functional recovery. RA-related pathology as well as its potential therapeutic activity may reflect endogenous retinoid regulation of neuronal differentiation, stability, or regeneration in the olfactory pathway from embryogenesis through adulthood. These influences may be in register with retinoid effects on immune responses, metabolism, and modulation of food intake.

Vitamin A deficiency exacerbates inflammation in a rat model of colitis through activation of nuclear factor-kappaB and collagen formation

Inflammatory bowel disease is characterized by oxidative stress, inflammation and tissue damage. Vitamin A is an antioxidant, a regulator of epithelial proliferation and differentiation and vital for optimal immune function. To investigate the effect of vitamin A on the course of colitis, it was induced by administration of trinitrobenzene sulfonic acid (TNBS) into the colons of rats fed for 7 wk vitamin A-deficient (VAD), sufficient (VAS) or supplemented (VASUP) diet, or VAS pair-fed (PF) to the VAD rats. Inflammation and fibrosis were examined by hematoxin and eosin, and Sirius red staining. Activation of nuclear factor-kappaB (NF-kappaB) and oxidative stress were determined by electrophoretic mobility shift and plasma malondialdehyde (MDA) and RBC Cu/Zn-superoxide dismutase activity, respectively. Vitamin A deficiency in the noncolitic rats impaired food consumption and weight gain (P < 0.05) and increased plasma MDA, (P = 0.01) activity of NF-kappaB (P < 0.05) and deposition of collagen in the colon. Our data suggest that vitamin A deficiency induces colonic inflammation. Colitis is amplified by deficiency and ameliorated by supplementation of the vitamin. These findings have implications for the management of inflammatory bowel disease.

Vitamin A during pregnancy

Vitamin A is an essential micronutrient throughout life. In areas of developing countries where vitamin A deficiency is endemic, an estimated 40% of the children are likely to be sub clinically deficient of the vitamin. Yet, the traditional view that preschool age children represent the main population at risk of vitamin A deficiency has been replaced by the growing awareness that sub clinical and even clinical vitamin A deficiency also occurs in women of reproductive age and infants less than 6 month of age. During the period of early foetal development the supply of vitamin A must be carefully managed to ensure that the developing foetus is exposed to neither too little not too much vitamin A because either condition can have teratogenic consequences. Towards the end of gestation, adequate maternal vitamin A status and dietary intakes are important to maximize the vitamin A transferred to the foetus in preparation for parturition and lactation. A review of the current knowledge and prospects for future research is presented.

Vitamin A as an anti-inflammatory agent

Vitamin A is necessary for normal differentiation of epithelial tissues, the visual process and reproduction, and is vital for the optimal maintenance and functioning of the innate and adaptive immune system. Vitamin A deficiency is one of the most profuse nutritional deficiencies worldwide. It is associated with increased susceptibility to infectious diseases in both man and animal models. Vitamin A also has a role as an anti-inflammatory agent. Supplementation with vitamin A has been found to be beneficial in a number of inflammatory conditions, including skin disorders such as acne vulgaris, broncho-pulmonary dysplasia and some forms of precancerous and cancer states. The present review suggests that vitamin A deficiency induces inflammation and aggravates existing inflammatory states. Supplementation with vitamin A in selected cases could ameliorate inflammation. The two main mechanisms which appear to be involved in the prevention of disease are the effects of vitamin A on the immune system and the effect on epithelial integrity.