Riboflavin deficiency reduces bone mineral density in rats by compromising osteoblast function.

Insufficient riboflavin intake has been associated with poor bone health. This study aimed to investigate the effect of riboflavin deficiency on bone health in vivo and in vitro. Riboflavin deficiency was successfully developed in rats and osteoblasts. The results indicated that bone mineral density, serum bone alkaline phosphatase, bone phosphorus, and bone calcium were significantly decreased while serum ionized calcium and osteocalcin were significantly increased in the riboflavin-deficient rats. Riboflavin deficiency also induced the reduction of Runx2, Osterix, and BMP-2/Smad1/5/9 cascade in the femur. These results were further verified in cellular experiments. Our findings demonstrated that alkaline phosphatase activities and calcified nodules were significantly decreased while intracellular osteocalcin and pro-collagen I c-terminal propeptide were significantly increased in the riboflavin-deficient osteoblasts. Additionally, the protein expression of Osterix, Runx2, and BMP-2/Smad1/5/9 cascade were significantly decreased while the protein expression of p-p38 MAPK were significantly increased in the riboflavin-deficient cells compared to the control cells. Blockage of p38 MAPK signaling pathway with SB203580 reversed these effects in riboflavin-deficient osteoblastic cells. Our data suggest that riboflavin deficiency causes osteoblast malfunction and retards bone matrix mineralization via p38 MAPK/BMP-2/Smad1/5/9 signaling pathway.

Dietary riboflavin deficiency induces genomic instability of esophageal squamous cells that is associated with gut microbiota dysbiosis in rats.

SCOPE: Epidemiologic evidence suggests that riboflavin (RBF) deficiency is a specific nutritional predisposition for esophageal cancer. The aim of this study is to investigate the potential roles of gut microbiota in esophageal tumorigenesis caused by the RBF deficiency. METHODS: Male F344 rats were subcutaneously injected with the chemical carcinogen N-nitrosomethylbenzylamine (NMBA, 0.35 mg kg-1). Rats were assigned to 4 groups, denoted as R6 (normal RBF, 6 mg kg-1), R6N (normal RBF combined with NMBA), R6N → R0N (normal RBF conversion to RBF-deficiency), and R0N → R6N (RBF-deficiency conversion to normal RBF). Bacterial communities were analyzed based on high-throughput 16S rRNA gene sequencing. Oxidative DNA damage and double-strand break markers were studied by immunohistochemistry. RESULTS: The R6N → R0N diet enhanced the incidence of esophageal intraepithelial neoplasia (EIN, 40 weeks 66.7% vs. 25 weeks 16.7%, P < 0.05). RBF deficiency and replenishment modulated the gut microbiota composition. The gut microbiota (e.g. Caulobacteraceae, Sphingomonas and Bradyrhizobium) affected xenobiotic biodegradation and the genomic instability of the host. Furthermore, the RBF deficiency aggravated oxidative DNA damage and DNA double-strand breaks (immunohistochemistry) in the esophageal epithelium, whereas the RBF replenishment had the opposite effect (P < 0.05, respectively). CONCLUSIONS: RBF deficiency promotes NMBA-induced esophageal tumorigenesis, which is associated with gut microbiota-associated genomic instability, and offers new insights into the role of RBF deficiency in esophageal carcinogenesis.

Adaptive regulation of riboflavin transport in heart: effect of dietary riboflavin deficiency in cardiovascular pathogenesis.

Deficiency or defective transport of riboflavin (RF) is known to cause neurological disorders, cataract, cardiovascular anomalies, and various cancers by altering the biochemical pathways. Mechanisms and regulation of RF uptake process is well characterized in the cells of intestine, liver, kidney, and brain origin, while very little is known in the heart. Hence, we aimed to understand the expression and regulation of RF transporters (rRFVT-1 and rRFVT-2) in cardiomyocytes during RF deficiency and also investigated the role of RF in ischemic cardiomyopathy and mitochondrial dysfunction in vivo. Riboflavin uptake assay revealed that RF transport in H9C2 is (1) significantly higher at pH 7.5, (2) independent of Na+ and (3) saturable with a Km of 3.746 µM. For in vivo studies, male Wistar rats (110-130 g) were provided riboflavin deficient food containing 0.3 ± 0.05 mg/kg riboflavin for 7 weeks, which resulted in over expression of both RFVTs in mRNA and protein level. RF deprivation resulted in the accumulation of cardiac biomarkers, histopathological abnormalities, and reduced mitochondrial membrane potential which evidenced the key role of RF in the development of cardiovascular pathogenesis. Besides, adaptive regulation of RF transporters upon RF deficiency signifies that RFVTs can be considered as an effective delivery system for drugs against cardiac diseases.

Riboflavin Deficiency in Rats Decreases de novo Formate Production but Does Not Affect Plasma Formate Concentration.

Background: The one-carbon metabolism pathway is highly dependent on a number of B vitamins in order to provide one-carbon units for purine and thymidylate biosynthesis as well as homocysteine remethylation. Previous studies have examined folate and vitamin B-12 deficiency and their effects on formate metabolism; as of yet, to our knowledge, no studies on the effects of riboflavin deficiency on formate metabolism have been published.Objective: Our objective was to determine the effects of riboflavin deficiency on formate metabolism.Methods: Weanling male rats were randomly assigned either to control, riboflavin-replete (RR) or to experimental, riboflavin-deficient (RD) versions of the AIN-93G diet for 13 d, at which time a constant infusion of [13C]-formate was carried out to ascertain the effects of deficiency on formate production. Gas chromatography-mass spectrometry was used to measure plasma formate concentration and [13C]-formate enrichment. HPLC, LC-mass spectrometry (MS)/MS, and enzymatic assays were used for the measurement of one-carbon precursors and other metabolites.Results: RD rats had significantly lower rates of formate production (15%) as well as significantly reduced hepatic methylenetetrahydrofolate reductase activity (69%) and protein concentration (54%) compared with RR rats. There was no difference in plasma formate concentrations between the groups. Plasma serine, a potential one-carbon precursor, was significantly higher in RD rats (467 ± 73 µM) than in RR rats (368 ± 52 µM).Conclusions: Although deficiencies in folate and vitamin B-12 lead to major changes in plasma formate concentrations, riboflavin deficiency results in no significant difference; this disagrees with the prediction of a published mathematical model. Our observation of a lower rate of formate production is consistent with a role for flavoproteins in this process.

Intestinal immune function, antioxidant status and tight junction proteins mRNA expression in young grass carp (Ctenopharyngodon idella) fed riboflavin deficient diet.

This study investigated the effects of riboflavin on intestinal immunity, tight junctions and antioxidant status of young grass carp (Ctenopharyngodon idella). Fish were fed diets containing graded levels of riboflavin (0.63-10.04 mg/kg diet) for 8 weeks. The study indicated that riboflavin deficiency decreased lysozyme, acid phosphatase, copper/zinc superoxide dismutase, glutathione reductase and glutathione peroxidase activities, and contents of complement component 3 and reduced glutathione in the intestine of fish (P < 0.05). Meanwhile, riboflavin deficiency increased reactive oxygen species, malondialdehyde and protein carbonyl contents and catalase activity (P < 0.05) in the intestine of fish. Furthermore, real-time polymerase chain reaction analysis was used to investigate mRNA expression patterns and found that the mRNA levels of interleukin 10 and transforming growth factor ß1, Occludin, zonula occludens 1, Claudin-b and Claudin-c, inhibitor protein κBα, target of rapamycin, ribosomal S6 protein kinase 1 and NF-E2-related factor 2, copper/zinc superoxide dismutase, glutathione peroxidase and glutathione reductase were decreased (P < 0.05) in the intestine of fish fed riboflavin-deficient diet. Conversely, the mRNA levels of tumor necrosis factor α, interleukin 1ß, interleukin 8, nuclear factor kappa B p65, Ikappa B kinase ß, Ikappa B kinase γ, Kelch-like-ECH-associated protein 1b, p38 mitogen-activated protein kinase, myosin light chain kinase and Claudin-12 were increased (P < 0.05) in the intestine of fish fed riboflavin-deficient diet. In conclusion, riboflavin deficiency decreased immunity and structural integrity of fish intestine. The optimum riboflavin level for intestinal acid phosphatase activity of young grass carp was estimated to be 6.65 mg/kg diet.

Dietary riboflavin deficiency decreases immunity and antioxidant capacity, and changes tight junction proteins and related signaling molecules mRNA expression in the gills of young grass carp (Ctenopharyngodon idella).

This study investigated the effects of dietary riboflavin on the growth, gill immunity, tight junction proteins, antioxidant system and related signaling molecules mRNA expression of young grass carp (Ctenopharyngodon idella). Fish were fed six diets containing graded levels of riboflavin (0.63-10.04 mg/kg diet) for 8 weeks. The study indicated that riboflavin deficiency decreased lysozyme and acid phosphatase activities, and complement component 3 content in the gills of fish (P < 0.05). Moreover, riboflavin deficiency caused oxidative damage, which might be partly due to decrease copper, zinc superoxide dismutase, catalase, glutathione reductase, glutathione peroxidase and glutathione-S-transferase activities and reduced glutathione content in the gills of fish (P < 0.05). Furthermore, the relative mRNA levels of antimicrobial peptides (liver expressed antimicrobial peptide 2 and Hepcidin), anti-inflammatory cytokines (interleukin 10 and transforming growth factor ß1), tight junction proteins (Occludin, zonula occludens 1, Claudin-c and Claudin-3), signaling molecules (inhibitor of κBα, target of rapamycin and NF-E2-related factor 2) and antioxidant enzymes (copper, zinc superoxide dismutase and glutathione reductase) were significantly decreased (P < 0.05) in the gills of fish fed riboflavin-deficient diet. Conversely, the mRNA levels of pro-inflammatory cytokines (tumor necrosis factor α, interleukin 8, interferon γ2, and interleukin 1ß), signaling molecules (nuclear factor kappa B p65, IκB kinase ß, IκB kinase γ, Kelch-like-ECH-associated protein 1b and myosin light chain kinase) and tight junction protein Claudin-12 were significantly increased (P < 0.05) in the gills of fish fed riboflavin-deficient diet. In addition, this study indicated for the first time that young fish fed a riboflavin-deficient diet exhibited anorexia and poor growth. In conclusion, riboflavin deficiency decreased growth and gill immunity, impaired gill antioxidant system, as well as regulated mRNA expression of gill tight junction proteins and related signaling molecules of fish. Based on percent weight gain, gill lysozyme activity and reduced glutathione content, the dietary riboflavin requirements for young grass carp (275-722 g) were estimated to be 5.85, 7.39 and 6.34 mg/kg diet, respectively.

Riboflavin (vitamin B2 ) deficiency impairs NADPH oxidase 2 (Nox2) priming and defense against Listeria monocytogenes.

Riboflavin, also known as vitamin B2 , is converted by riboflavin kinase (RFK) into flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which are essential cofactors of dehydrogenases, reductases, and oxidases including the phagocytic NADPH oxidase 2 (Nox2). Riboflavin deficiency is common in young adults and elderly individuals, who are at the coincidental risk for listeriosis. To address the impact of acute riboflavin deficiency on host defense against Listeria monocytogenes (L.m.), we generated conditional RFK knockout (KO) strains of mice. Phagocyte-specific RFK KO impaired the capability of phagocytes to control intracellular L.m., which corresponded to a greater susceptibility of mice to in vivo challenge with L.m. The oxidative burst of RFK-deficient phagocytes in response to L.m. infection was significantly reduced. Mechanistically, TNF-induced priming of Nox2, which is needed for oxidative burst, was defective in RFK-deficient phagocytes. Lack of riboflavin in wild-type macrophages for only 6 h shut down TNF-induced, RFK-mediated de novo FMN/FAD generation, which was accompanied by diminished ROS production and impaired anti-listerial activity. Vice versa, ROS production by riboflavin-deprived macrophages was rapidly restored by riboflavin supplementation. Our results suggest that acute riboflavin deficiency immediately impairs priming of Nox2, which is of crucial relevance for an effective phagocytic immune response in vivo.

Biosynthesis of flavin cofactors in man: implications in health and disease.

The primary role of the water-soluble vitamin B2, i.e. riboflavin, in cell biology is connected with its conversion into FMN and FAD, the cofactors of a large number of dehydrogenases, reductases and oxidases involved in energetic metabolism, redox homeostasis and protein folding as well as in diverse regulatory events. Deficiency of riboflavin in men and experimental animal models has been linked to several diseases, including neuromuscular and neurological disorders and cancer. Riboflavin at pharmacological doses has been shown to play unexpected and incompletely understood regulatory roles. Besides a summary on riboflavin uptake and a survey on riboflavin-related diseases, the main focus of this review is on discovery and characterization of FAD synthase (EC 2.7.7.2) and other components of the cellular networks that ensure flavin cofactor homeostasis.Special attention is devoted to the problem of sub-cellular compartmentalization of cofactor synthesis in eukaryotes, made possible by the existence of different FAD synthase isoforms and specific molecular components involved in flavin trafficking across sub-cellular membranes.Another point addressed in this review is the mechanism of cofactor delivery to nascent apo-proteins, especially those localized into mitochondria, where they integrate FAD in a process that involves additional mitochondrial protein(s) still to be identified. Further efforts are necessary to elucidate the role of riboflavin/FAD network in human pathologies and to exploit the structural differences between human and microbial/fungal FAD synthase as the rational basis for developing novel antibiotic/antimycotic drugs.

Influence of preconditioning-like hypoxia on the liver of developing methyl-deficient rats.

Deficiency in nutritional determinants of homocysteine (HCY) metabolism, such as vitamin B(12) and folate, during pregnancy is known to influence HCY levels in the progeny, which in turn may exert adverse effects during development, including liver defects. Since short hypoxia has been shown to induce tolerance to subsequent stress in various cells including hepatocytes, and as vitamins B deficiency and hypoxic episodes may simultaneously occur in neonates, we aimed to investigate the influence of brief postnatal hypoxia (100% N(2) for 5 min) on the liver of rat pups born from dams fed a deficient regimen, i.e., depleted in vitamins B(12), B(2), folate, and choline. Four experimental groups were studied: control, hypoxia, deficiency, and hypoxia + deficiency. Although hypoxia transiently stimulated HCY catabolic pathways, it was associated with a progressive increase of hyperhomocysteinemia in deficient pups, with a fall of cystathionine beta-synthase activity at 21 days. At this stage, inducible NO synthase activity was dramatically increased and glutathione reductase decreased, specifically in the group combining hypoxia and deficiency. Also, hypoxia enhanced the deficiency-induced drop of the S-adenosylmethionine/S-adenosylhomocysteine ratio. In parallel, early exposure to the methyl-deficient regimen induced oxidative stress and led to hepatic steatosis, which was found to be more severe in pups additionally exposed to hypoxia. In conclusion, brief neonatal hypoxia may accentuate the long-term adverse effects of impaired HCY metabolism in the liver resulting from an inadequate nutritional regimen during pregnancy, and our data emphasize the importance of early factors on adult disease.

Riboflavin metabolism--relevance to human nutrition.

Studies in developing countries like India have revealed a very high incidence of biochemical riboflavin deficiency, particularly in women and children as judged by erythrocyte glutathione reductase activation test (EGR-AC). Riboflavin deficiency can cause conditioned deficiency of vitamin B6 and the mucocutaneous lesions observed in these two vitamins deficiencies could be due to impaired skin collagen maturity. Subclinical riboflavin deficiency impairs psychomotor function and vitamin B2 requirement may be enhanced during increased physical activity. Riboflavin status is not dependent exclusively on dietary intake of the vitamin, certain non-dietary factors can modify riboflavin status. Respiratory infection, certain diseases, drugs and hormones can influence riboflavin metabolism.

Changes in iron, calcium, magnesium, copper, and zinc levels in different tissues of riboflavin-deficient rats.

To clarify the changes of mineral levels in different tissues of riboflavin-deficient rats, Wistar rats were separated into three groups. One group was fed a diet ad libitum that was deficient in riboflavin. The other two were fed either the complete diet that was weight-matched to the riboflavin-deficient group or fed a complete diet ad libitum. In riboflavin-deficient rats, the hemoglobin concentration and riboflavin contents of blood, liver, and kidney were significantly decreased, compared with weight-matched and ad libitum-fed controls. The mineral concentrations of tissues are summarized as follows: The iron (Fe) concentration in the heart, liver, and spleen was decreased in the riboflavin-deficient group compared with the other groups. Calcium (Ca) and magnesium (Mg) concentrations in tibia were decreased in the riboflavin-deficient group compared with the other two groups. Copper (Cu) concentration was increased in the heart and liver, when the riboflavin-deficient group was compared with the other groups. Zinc (Zn) concentration was increased in tibia when the riboflavin-deficient group was compared with the other groups.

Acute ethanol exposure alters hepatic glutathione metabolism in riboflavin deficiency.

Since acute ethanol consumption and riboflavin deficiency each induces oxidative stress within tissues, we examined whether their combined effects compromise the major antioxidative system in liver, namely, reduced glutathione (GSH) metabolism. Four hours before sacrifice, half the riboflavin-deficient (RD) and riboflavin-sufficient (RS) rats were treated with ethanol (3 g/kg). Livers were excised and analyzed for GSH and enzymes that control its metabolism. In RD rats, GSH increased while glucose-6-phosphate dehydrogenase (G6PD) activity decreased. Ethanol had no effect on these measurements in RS rats. In RD rats, ethanol administration decreased GSH along with the activities of GSH peroxidase, glutathione reductase, and G6PD. These data suggest that riboflavin deficiency alone does not compromise hepatic GSH metabolism. By contrast, ethanol consumption together with riboflavin deficiency depletes hepatic GSH, blunts enzyme activities controlling GSH metabolism and may enhance alcohol-induced liver injury.

Enhanced growth of mammary adenocarcinoma in rats by chloroquine and quinacrine.

This study investigated whether the growth of transplanted mammary tumors is altered in rats by treatment with the antimalarial drugs chloroquine (CQ) and quinacrine (QN). Female inbred F344 rats were divided into three experimental groups. Animals were injected i.p. with either CQ, QN or normal saline for 5 days a week throughout the entire experimental period (25 days). After 7 days of drug treatment each rat received subcutaneously one 2-mm2 aliquot of R3230AC mammary adenocarcinoma in the mid-thoracic region. Eighteen days after implantation, all rats were sacrificed and tumors were excised, weighed and measured. The results indicate that weights and volumes of tumors as well as tumor-to-body weight ratios were significantly higher in CQ and QN-treated animals than those in saline-treated animals. The final body weights of rats treated with QN were significantly lower than those treated with saline. The prostaglandin E2 content of tumors was significantly reduced by CQ treatment. Erythrocyte glutathione reductase activity coefficient and reduced glutathione concentrations remained unaffected by both treatments. These results suggest that CQ and QN have significant stimulatory effects on the growth of mammary adenocarcinoma in rats.

Effects of riboflavin deficiency and riboflavin administration on carcinogen-DNA binding.

A study was conducted to assess the effects of riboflavin deficiency and riboflavin supplementation on carcinogen-DNA binding. After 12 wk on a riboflavin-sufficient or a riboflavin-deficient diet male Wistar rats were administered 3H-labelled benzo[a]pyrene (BP) ip. [3H]BP was given either at a uniform dose of 450 muCi/rat irrespective of body weight or at a dose adjusted to body weight. After 17 hr the animals were killed, various organs were dissected and the level of [3H]BP bound to DNA was quantified in organs that are known to be the seats of drug metabolism (i.e. the liver, lungs and intestinal mucosa). In a separate experiment, the effect of riboflavin supplementation on BP-DNA binding was also investigated. When [3H]BP was administered at 450 microCi/rat, BP-DNA binding was markedly increased in the livers and intestinal mucosae of the pair-fed and deficient groups compared with controls. With the administration of [3H]BP adjusted to body weight, no differences in BP-DNA binding between groups were observed in any tissue. However, on administration of riboflavin there was a decrease in the level of [3H]BP bound to DNA in almost all tissues, especially in the lungs, where the reduction was significant. The results suggest that undernutrition/riboflavin deficiency may increase the risk of carcinogenesis by way of an increase in carcinogen binding, which however can be reversed by riboflavin supplementation.

Comparison of changes in the uptake and mucosal processing of iron in riboflavin-deficient rats.

Riboflavin deficiency in rats resulted in a reduction in the transfer of 59Fe from an intragastric dose to plasma compared to age-matched or weight-matched controls. The uptake of iron by brush-border membrane vesicles made from intestinal mucosa of riboflavin-deficient rats was much less than identically-prepared vesicles from control groups. Although the mucosal content of 59Fe was smaller in riboflavin-deficient rats thirty minutes after dosing, the relative distribution of 59Fe between the mucosal iron-binding proteins, ferritin and transferrin, was not changed compared to the control groups. These studies suggest that the impairment in iron absorption in riboflavin deficiency is primarily the result of a reduced uptake of iron into the mucosal cell and not a redistribution of iron between iron-binding proteins inside the mucosal cell.

A proposed intestinal mechanism for the effect of riboflavin deficiency on iron loss in the rat.

The effect of riboflavin deficiency on gastrointestinal Fe distribution and loss was studied in weanling rats. Riboflavin deficiency was associated with a significant increase in crypt depth in the upper and mid small intestine and a twofold increase in the rate of crypt cell production compared with weight-matched and ad lib.-fed control rats. The rate of loss of endogenous Fe, measured as faecal 59Fe after intraperitoneally administered 59Fe, was twice that from riboflavin-deficient rats compared with weight-matched controls. We suggest that while there may be a contribution from turnover of enterocytes with an enhanced Fe content, enhanced Fe loss associated with riboflavin deficiency is due predominantly to an accelerated rate of small-intestinal epithelial turnover.

[Use of the magnitude of vitamin and vitamin metabolite excretion as indicators of availability of vitamins B2, B6, and niacin]. / Ob ispol'zovanie velichin ékskretsii vitaminov i ikh metabolitov v kachestve pokazatelei obespechennosti vitaminami B2, B6 i niatsinom.

Alimentary deficiency of riboflavin in rats caused a decrease in excretion of vitamin B2 with urine simultaneously with lowering in daily excretion of 4-pyridoxylic acid (4-PA) and N1-methyl nicotinamide (N1-MNA); these patterns are usually used as indicators of pyridoxine and niacin availability. The similar decrease in excretion of 4-PA and N1-MNA with urine but without alterations in NAD+NADP concentrations in erythrocytes was detected in women deficient in vitamin B2. Content of nicotinamide coenzymes in erythrocytes correlated with excretion of N1-MNA with urine only under normal conditions of riboflavin availability. Use of the criteria involving rates of 4-PA and N1-MNA excretion for evaluation of pyridoxine and niacin deficiency is discussed.

Riboflavin deficiency and iron absorption in adult Gambian men.

Iron absorption from 3.38 mg 58Fe was measured in riboflavin-deficient Gambian men with haemoglobin (Hb) less than 11.5 g/dl before and after oral riboflavin therapy, and the results compared with a group not receiving riboflavin. Riboflavin status (as determined by erythrocyte glutathione reductase activation coefficient) and Hb increased in teh riboflavin-supplemented but not placebo group. Plasma ferritin levels were low and did not change in either group. There was very wide variation in percentage iron absorption between individuals and also within single individuals on two separate occasions but no measurable change with riboflavin supplementation. The results of the study indicate that the efficiency of iron utilization is impaired in riboflavin deficiency, but that iron absorption is unaffected.