Inhibition of riboflavin metabolism in rat tissues by chlorpromazine, imipramine, and amitriptyline

Flavins and Flavoproteins in the Neuroimmune Landscape of Stress Sensitization and Major Depressive Disorder

Major Depressive Disorder (MDD) is a common and severe neuropsychiatric condition resulting in irregular alterations in affect, mood, and cognition. Besides the well-studied neurotransmission-related etiologies of MDD, several biological systems and phenomena, such as the hypothalamic-pituitary-adrenal (HPA) axis, reactive oxygen species (ROS) production, and cytokine signaling, have been implicated as being altered and contributing to depressive symptoms. However, the manner in which these factors interact with each other to induce their effects on MDD development has been less clear, but is beginning to be understood. Flavins are potent biomolecules that regulate many redox activities, including ROS generation and energy production. Studies have found that circulating flavin levels are modulated during stress and MDD. Flavins are also known for their importance in immune responses. This review offers a unique perspective that considers the redox-active cofactors, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), as vital substrates for linking MDD-related maladaptive processes together, by permitting stress-induced enhancement of microglial interleukin-1 beta (IL-1β) signaling.

Mechanistic and structural insights into vitamin B2 metabolizing enzyme riboflavin kinase from Leishmania donovani

Leishmania donovani relies on specific vitamins and cofactors crucial for its survival and pathogenesis. Tailoring therapies to disrupt these pathways offers a promising strategy for the treatment of Visceral Leishmaniasis. Current treatment regimens are limited due to drug resistance and high costs. The dependency of Leishmania parasites on Vitamin B2 and its metabolic products is not known. In this study, we have biochemically and biophysically characterized a Vitamin B2 metabolism enzyme, riboflavin kinase from L. donovani (LdRFK) which converts riboflavin (vitamin B2) into flavin mononucleotide (FMN). Sequence comparison with human counterpart reflects 31.58 % identity only, thus opening up the possibility of exploring it as drug target. The rfk gene was cloned, expressed and the recombinant protein was purified. Kinetic parameters of LdRFK were evaluated with riboflavin and ATP as substrates which showed differential binding affinity when compared with the human RFK enzyme. Thermal and denaturant stability of the enzyme was evaluated. The rfk gene was overexpressed in the parasites and its role in growth and cell cycle was evaluated. In the absence of crystal structure, homology modelling and molecular dynamic simulation studies were performed to predict LdRFK structure. The data shows differences in substrate binding between human and parasite enzyme. This raises the possibility of exploring LdRFK for specific designing of antileishmanial molecules. Gene disruption studies can further validate its candidature as antileishmanial target.

Origin and functional diversification of PAS domain, a ubiquitous intracellular sensor

Signal perception is a key function in regulating biological activities and adapting to changing environments. Per-Arnt-Sim (PAS) domains are ubiquitous sensors found in diverse receptors in bacteria, archaea, and eukaryotes, but their origins, distribution across the tree of life, and extent of their functional diversity are not fully characterized. Here, we show that using sequence conservation and structural information, it is possible to propose specific and potential functions for a large portion of nearly 3 million PAS domains. Our analysis suggests that PAS domains originated in bacteria and were horizontally transferred to archaea and eukaryotes. We reveal that gas sensing via a heme cofactor evolved independently in several lineages, whereas redox and light sensing via flavin adenine dinucleotide and flavin mononucleotide cofactors have the same origin. The close relatedness of human PAS domains to those in bacteria provides an opportunity for drug design by exploring potential natural ligands and cofactors for bacterial homologs.

Biological Properties of Vitamins of the B-Complex, Part 1: Vitamins B1, B2, B3, and B5

This review summarizes the current knowledge on essential vitamins B1, B2, B3, and B5. These B-complex vitamins must be taken from diet, with the exception of vitamin B3, that can also be synthetized from amino acid tryptophan. All of these vitamins are water soluble, which determines their main properties, namely: they are partly lost when food is washed or boiled since they migrate to the water; the requirement of membrane transporters for their permeation into the cells; and their safety since any excess is rapidly eliminated via the kidney. The therapeutic use of B-complex vitamins is mostly limited to hypovitaminoses or similar conditions, but, as they are generally very safe, they have also been examined in other pathological conditions. Nicotinic acid, a form of vitamin B3, is the only exception because it is a known hypolipidemic agent in gram doses. The article also sums up: (i) the current methods for detection of the vitamins of the B-complex in biological fluids; (ii) the food and other sources of these vitamins including the effect of common processing and storage methods on their content; and (iii) their physiological function.

Fundamental Role of Methylenetetrahydrofolate Reductase 677 C → T Genotype and Flavin Compounds in Biochemical Phenotypes for Schizophrenia and Schizoaffective Psychosis

The Mental Health Biomarker Project (2010-2016) explored variables for psychosis in schizophrenia and schizoaffective disorder. Blood samples from 67, highly characterized symptomatic cases and 67 gender and age matched control participants were analyzed for methyl tetrahydrofolate reductase (MTHFR) 677C → T gene variants and for vitamin B6, B12 and D, folate, unbound copper, zinc cofactors for enzymes in the methylation cycle, and related catecholamine pathways. Urine samples were analyzed for indole-catecholamines, their metabolites, and oxidative-stress marker, hydroxylpyrolline-2-one (HPL). Rating scales were Brief Psychiatric Rating Scale, Positive and Negative Syndrome Scale, Global Assessment of Function scale, Clinical Global Impression (CGI) score, and Social and Occupational Functioning Assessment Scale (SOFAS). Analysis used Spearman's correlates, receiver operating characteristics and structural equation modeling (SEM). The correlative pattern of variables in the overall participant sample strongly implicated monoamine oxidase (MAO) enzyme inactivity so the significant role of MAO's cofactor flavin adenine nucleotide and its precursor flavin adenine mononucleotide (FMN) within the biochemical pathways was investigated and confirmed as 71% on SEM of the total sample. Splitting the data sets for MTHFR 677C → T polymorphism variants coding for the MTHFR enzyme, discovered that biochemistry variables relating to the wild-type enzyme differed markedly in pattern from those coded by the homozygous variant and that the hereozygous-variant pattern resembled the wild-type-coded pattern. The MTHFR 677C → T-wild and -heterozygous gene variants have a pattern of depleted vitamin cofactors characteristic of flavin insufficiency with under-methylation and severe oxidative stress. The second homozygous MTHFR 677TT pattern related to elevated copper:zinc ratio and a vitamin pattern related to flavin sufficiency and risk of over-methylation. The two gene variants and their different biochemical phenotypes govern findings in relationship to case-identification, illness severity, duration of illness, and functional disability in schizophrenia and schizoaffective psychosis, and establish a basis for trials of gene-guided precision treatment for the management of psychosis.

MetMaxStruct: A Tversky-Similarity-Based Strategy for Analysing the (Sub)Structural Similarities of Drugs and Endogenous Metabolites

BACKGROUND

Previous studies compared the molecular similarity of marketed drugs and endogenous human metabolites (endogenites), using a series of fingerprint-type encodings, variously ranked and clustered using the Tanimoto (Jaccard) similarity coefficient (TS). Because this gives equal weight to all parts of the encoding (thence to different substructures in the molecule) it may not be optimal, since in many cases not all parts of the molecule will bind to their macromolecular targets. Unsupervised methods cannot alone uncover this. We here explore the kinds of differences that may be observed when the TS is replaced-in a manner more equivalent to semi-supervised learning-by variants of the asymmetric Tversky (TV) similarity, that includes α and β parameters.

RESULTS

Dramatic differences are observed in (i) the drug-endogenite similarity heatmaps, (ii) the cumulative "greatest similarity" curves, and (iii) the fraction of drugs with a Tversky similarity to a metabolite exceeding a given value when the Tversky α and β parameters are varied from their Tanimoto values. The same is true when the sum of the α and β parameters is varied. A clear trend toward increased endogenite-likeness of marketed drugs is observed when α or β adopt values nearer the extremes of their range, and when their sum is smaller. The kinds of molecules exhibiting the greatest similarity to two interrogating drug molecules (chlorpromazine and clozapine) also vary in both nature and the values of their similarity as α and β are varied. The same is true for the converse, when drugs are interrogated with an endogenite. The fraction of drugs with a Tversky similarity to a molecule in a library exceeding a given value depends on the contents of that library, and α and β may be "tuned" accordingly, in a semi-supervised manner. At some values of α and β drug discovery library candidates or natural products can "look" much more like (i.e., have a numerical similarity much closer to) drugs than do even endogenites.

CONCLUSIONS

Overall, the Tversky similarity metrics provide a more useful range of examples of molecular similarity than does the simpler Tanimoto similarity, and help to draw attention to molecular similarities that would not be recognized if Tanimoto alone were used. Hence, the Tversky similarity metrics are likely to be of significant value in many general problems in cheminformatics.

Transcriptional regulation of the albumin gene depends on the removal of histone methylation marks by the FAD-dependent monoamine oxidase lysine-specific demethylase 1 in HepG2 human hepatocarcinoma cells

Lysine-specific demethylase (LSD) 1 is an FAD-dependent demethylase that catalyzes the removal of methyl groups from lysine-4 in histone H3, thereby mediating gene repression. Here we tested the hypothesis that riboflavin deficiency causes a loss of LSD1 activity in HepG2 human hepatocarcinoma cells, leading to an accumulation of lysine-4-dimethylated histone H3 (H3K4me2) marks in the albumin promoter and aberrant upregulation of albumin expression. Cells were cultured in riboflavin-defined media providing riboflavin at concentrations representing moderately deficient (3.1 nmol/L), sufficient (12.6 nmol/L), and supplemented (301 nmol/L) cells in humans for 7 d. The efficacy of treatment was confirmed by assessing glutathione reductase activity and concentrations of reduced glutathione as markers of riboflavin status. LSD activity was 21% greater in riboflavin-supplemented cells compared with riboflavin-deficient and -sufficient cells. The loss of LSD activity was associated with a gain in the abundance of H3K4me2 marks in the albumin promoter; the abundance of H3K4me2 marks was ∼170% higher in riboflavin-deficient cells compared with sufficient and supplemented cells. The abundance of the repression mark, K9-trimethylated histone H3, was 38% lower in the albumin promoter of riboflavin-deficient cells compared with the other treatment groups. The expression of albumin mRNA was aberrantly increased by 200% in riboflavin-deficient cells compared with sufficient and supplemented cells. In conclusion, riboflavin deficiency impairs gene regulation by epigenetic mechanisms, mediated by a loss of LSD1 activity.

From cholesterogenesis to steroidogenesis: role of riboflavin and flavoenzymes in the biosynthesis of vitamin D

Flavin-dependent monooxygenases and oxidoreductases are located at critical branch points in the biosynthesis and metabolism of cholesterol and vitamin D. These flavoproteins function as obligatory intermediates that accept 2 electrons from NAD(P)H with subsequent 1-electron transfers to a variety of cytochrome P450 (CYP) heme proteins within the mitochondria matrix (type I) and the (microsomal) endoplasmic reticulum (type II). The mode of electron transfer in these systems differs slightly in the number and form of the flavin prosthetic moiety. In the type I mitochondrial system, FAD-adrenodoxin reductase interfaces with adrenodoxin before electron transfer to CYP heme proteins. In the microsomal type II system, a diflavin (FAD/FMN)-dependent cytochrome P450 oxidoreductase [NAD(P)H-cytochrome P450 reductase (CPR)] donates electrons to a multitude of heme oxygenases. Both flavoenzyme complexes exhibit a commonality of function with all CYP enzymes and are crucial for maintaining a balance of cholesterol and vitamin D metabolites. Deficits in riboflavin availability, imbalances in the intracellular ratio of FAD to FMN, and mutations that affect flavin binding domains and/or interactions with client proteins result in marked structural alterations within the skeletal and central nervous systems similar to those of disorders (inborn errors) in the biosynthetic pathways that lead to cholesterol, steroid hormones, and vitamin D and their metabolites. Studies of riboflavin deficiency during embryonic development demonstrate congenital malformations similar to those associated with genetic alterations of the flavoenzymes in these pathways. Overall, a deeper understanding of the role of riboflavin in these pathways may prove essential to targeted therapeutic designs aimed at cholesterol and vitamin D metabolism.

Differentiation-dependent regulation of intestinal vitamin B(2) uptake: studies utilizing human-derived intestinal epithelial Caco-2 cells and native rat intestine

Intestinal epithelial cells undergo differentiation as they move from the crypt to the villi, a process that is associated with up- and downregulation in expression of a variety of genes, including those involved in nutrient absorption. Whether the intestinal uptake process of vitamin B(2) [riboflavin (RF)] also undergoes differentiation-dependent regulation and the mechanism through which this occurs are not known. We used human-derived intestinal epithelial Caco-2 cells and native rat intestine as models to address these issues. Caco-2 cells showed a significantly higher carrier-mediated RF uptake in post- than preconfluent cells. This upregulation was associated with a significantly higher level of protein and mRNA expression of the RF transporters hRFVT-1 and hRFVT-3 in the post- than preconfluent cells; it was also accompanied with a significantly higher rate of transcription of the respective genes (SLC52A1 and SLC52A3), as indicated by the higher level of expression of heterogeneous nuclear RNA and higher promoter activity in post- than preconfluent cells. Studies with native rat intestine also showed a significantly higher RF uptake by epithelial cells of the villus tip than epithelial cells of the crypt; this again was accompanied by a significantly higher level of expression of the rat RFVT-1 and RFVT-3 at the protein, mRNA, and heterogeneous nuclear RNA levels. These findings show, for the first time, that the intestinal RF uptake process undergoes differentiation-dependent upregulation and suggest that this is mediated (at least in part) via transcriptional mechanisms.

Chlorpromazine oligomer is a potentially active substance that inhibits human D-amino acid oxidase, product of a susceptibility gene for schizophrenia

D-amino acid oxidase (DAO), a potential risk factor for schizophrenia, has been proposed to be involved in the decreased glutamatergic neurotransmission in schizophrenia. Here we show the inhibitory effect of an antipsychotic drug, chlorpromazine, on human DAO, which is consistent with previous reports using porcine DAO, although human DAO was inhibited to a lesser degree (K(i) = 0.7 mM) than porcine DAO. Since chlorpromazine is known to induce phototoxic or photoallergic reactions and also to be transformed into various metabolites, we examined the effects of white light-irradiated chlorpromazine on the enzymatic activity. Analytical methods including high-resolution mass spectrometry revealed that irradiation triggered the oligomerization of chlorpromazine molecules. The oligomerized chlorpromazine showed a mixed type inhibition with inhibition constants of low micromolar range, indicative of enhanced inhibition. Taken together, these results suggest that oligomerized chlorpromazine could act as an active substance that might contribute to the therapeutic effects of this drug.

Transport functions of riboflavin carriers in the rat small intestine and colon: site difference and effects of tricyclic-type drugs

The present study was aimed at kinetically characterizing the newly found carrier-mediated riboflavin transport system in the rat colon, comparing it with that in the small intestine, and also probing the potential roles of these transport systems in intestinal drug absorption. Riboflavin transport, evaluated by measuring the initial uptake into everted intestinal tissue sacs, was saturable with a Michaelis constant (Km) of 0.13 microM and a maximum transport rate (Jmax) of 0.74 pmol/min/100 mg wet tissue weight (wtw) in the colon. Both the Km and the Jmax were smaller than those (0.57 microM and 4.26 pmol/min/100 mg wtw, respectively) in the small intestine, suggesting that the transport system in the colon has a higher affinity to substrates and a smaller transport capacity than its counterpart in the small intestine. The carrier-mediated riboflavin transport in the colon, similarly to that in the small intestine, was Na+-dependent and inhibited by lumiflavin, a riboflavin analogue with an isoalloxazine ring, but not by D-ribose, which forms the side-chain attached to the isoalloxazine ring in riboflavin. To further clarify the substrate specificities of the transport systems, we examined the effects of several drugs with a tricyclic structure similar to isoalloxazine ring on riboflavin transport. Chlorpromazine, a phenothiazine derivative, was found to inhibit riboflavin transport in both the small intestine and the colon. Methylene blue also was found to be a potent inhibitor in both sites. These results suggest that some tricyclic-type drugs could interfere with intestinal riboflavin absorption by specific carrier-mediated transport systems. These transport systems may play roles in the absorption of tricyclic-type drugs.

Riboflavin transport by isolated perfused rabbit renal proximal tubules

Rabbit renal proximal tubular transport of riboflavin (RF) was examined by using the in vitro isolated tubule perfusion technique. We found that proximal tubules actively reabsorbed (J(lb)) and secreted (J(bl)) RF. At 0.1 microM RF concentration, J(bl) was significantly higher than J(lb), resulting in a net secretion. This net secretion of RF was decreased at 0.01 microM RF concentration and increased at 1 microM RF concentration. Both J(lb) and J(bl) were inhibited by lowering temperature or by adding iodoacetate, a metabolic inhibitor, and lumichrome, an RF analog, suggesting the involvement of carrier-mediated transport mechanisms. J(bl) was inhibited by probenecid, an anion transport inhibitor, and by para-aminohippuric acid, an organic anion, suggesting the relevance of RF secretion to renal organic anion transport. J(bl) was also inhibited by alkaline pH (8.0) and by the calmodulin inhibitor trifluoperazine, indicating the influence of pH and Ca(2+)/calmodulin-dependent pathway on RF secretion. Finally, we found that addition of chlorpromazine, a phenothiazine derivative, inhibited both J(lb) and J(bl), raising the concern about the nutritional status in patients receiving such a type of medication.

Low thyroxine levels in female psychiatric inpatients with riboflavin deficiency: implications for folate-dependent methylation

Intermediates in the folate-dependent methylation pathways may play a role in the etiology and treatment of such mental disorders as major depression. These pathways include a step dependent on a riboflavin (B2)-derived coenzyme, flavin adenine dinucleotide (FAD), which is reportedly sensitive to thyroid status and to phenothiazine and tricyclic drug exposure. In a sample of 52 male and female acute psychiatric inpatients, 17% (n = 9) showed B2 deficiency (i.e., insufficient FAD activity) on a functional red blood cell enzyme assay, but only one B2-deficient individual showed deficiency in another B-complex vitamin (folate). All patients with B2 deficiency were women, who were also significantly younger than the rest of the sample. The B2-deficient women had significantly lower thyroxine levels, even when controlling for sex and covarying for age. B2-deficient patients exhibited a nonsignificant trend toward more unipolar depression (44% vs 14%), but not toward bipolar or schizophrenic disorders. As in a previous study, drug exposure did not show a relationship to riboflavin deficiency in this sample. The findings suggest that B2 (FAD) activity may serve as a sensitive marker of thyroxine status in certain female psychiatric inpatients and that B2 deficiency may play an etiological role in defects of the methylation pathways in a subset of mentally ill individuals.

B complex vitamin patterns in geriatric and young adult inpatients with major depression

This study compared the B complex vitamin status at time of admission of 20 geriatric and 16 young adult non-alcoholic inpatients with major depression. Twenty-eight percent of all subjects were deficient in B2 (riboflavin), B6 (pyridoxine), and/or B12 (cobalamin), but none in B1 (thiamine) or folate. The geriatric sample had significantly higher serum folate levels. Psychotic depressives had lower B12 than did non-psychotic depressives. Poorer blood vitamin status was not associated with higher scores on the Hamilton Depression Rating Scale or lower scores on the Mini-Mental State Examination in either age group. The data support the hypothesis that poorer status in certain B vitamins is present in major depression, but blood measures may not reflect central nervous system vitamin function or severity of affective syndromes as measured by the assays and scales in the present study.

Antimalarial properties of imipramine and amitriptyline

Dietary riboflavin deficiency is known to diminish malarial parasitemia. In this study, we determined whether imipramine and amitriptyline, drugs which inhibit riboflavin metabolism, have antimalarial efficacy. In addition, we evaluated whether these drugs, like other antimalarial agents, increase the hemolytic response to ferriprotoporphyrin IX (FP). The growth of Plasmodium falciparum (FCR3) in the absence and presence of these drugs (10 to 75 microM) was measured by determining (3H)hypoxanthine uptake by intra-erythrocytic parasites for 48 h in RPMI 1640 medium. The uptake of (3H)hypoxanthine was significantly reduced in a dose-dependent manner by both imipramine and amitriptyline. The IC50 values of imipramine and amitriptyline at 48 h were 56 and 45 microM, respectively. Both drugs enhanced hemolysis induced by FP (10 or 20 microM). No hemolysis by these drugs was detected in the absence of FP. It is concluded that the tricyclic antidepressants, imipramine and amitriptyline, possess substantial antimalarial properties.

Inhibition of flavin metabolism by adriamycin in skeletal muscle

Adriamycin (ADR), a potent antineoplastic agent, has been shown to interact with flavin derivatives and to compete with flavin coenzymes for their respective binding sites on flavin-containing enzymes. The present investigation determined that ADR administration inhibited flavin adenine dinucleotide (FAD) biosynthesis from riboflavin in rat skeletal muscle in a dose-related manner compared to results in pair-fed controls. Five groups of adult Holtzman rats of both sexes were given twice daily intraperitoneal injections of ADR for 3 days, representing cumulative doses of 6, 12, 18, 24, and 30 mg/kg body weight. At the cumulative dose of 6 mg/kg, there was no significant effect, but at 12, 18, 24, and 30 mg/kg levels significant increases in [14C]FAD formation from [14C]riboflavin occurred. ADR-induced myopathy may be due, at least in part, to inhibition of FAD formation, ultimately leading to changes in energy metabolism and oxidative capacity.

Mechanisms underlying the differential effects of ethanol on the bioavailability of riboflavin and flavin adenine dinucleotide

Chronic alcoholism is associated with a high prevalence of riboflavin deficiency. Experiments were designed in an animal model to determine whether ethanol alters selectively the absorption of riboflavin and flavin adenine dinucleotide (FAD), the predominant dietary form of the vitamin. Rats received by gavage a liver homogenate to which either [14C]riboflavin or [14C]FAD was added with either ethanol or isocaloric sucrose solutions. Ethanol markedly diminished the bioavailability of [14C]FAD to a greater degree than that of [14C]riboflavin. Corroboration of an ethanol-impaired intraluminal hydrolysis of FAD was provided by using everted jejunal segments and measuring mucosal uptake of [14C]riboflavin together with nonradiolabeled FAD. In subsequent studies with mucosal cell extracts, ethanol markedly inhibited activities of FAD pyrophosphatase and flavin mononucleotide (FMN) phosphatase. These findings suggest that dietary sources of riboflavin (FMN and FAD) are not absorbed as well in the presence of ethanol than are vitamin preparations containing riboflavin, which is utilized more readily.

New approaches to the possible prevention of side effects of chemotherapy by nutrition

In an effort to develop new methods for preventing side effects of chemotherapy, the authors initiated studies to determine whether Adriamycin (doxorubicin) inhibits the metabolism of riboflavin (vitamin B2). Adriamycin has been shown to form a 1:1 stoichiometric complex with riboflavin, as well as to compete for binding to tissue proteins. Adult rats treated with Adriamycin in clinically relevant doses were compared to control animals in ability to convert riboflavin into flavin adenine dinucleotide (FAD), the active flavin coenzyme derivative, in heart, skeletal muscle, liver, and kidney. Rats treated with Adriamycin exhibited diminished formation of carbon 14 (14C)FAD in skeletal muscle to nearly 50% that of controls, and in heart to about 70% to 80% of controls. Under these conditions, (14C)FAD formation in liver and kidney was largely unaffected by Adriamycin. In preliminary studies, riboflavin-deficient animals treated with Adriamycin had accelerated mortality rates compared to those of food restricted controls treated with similar doses of Adriamycin. The data as a whole suggest a potential mechanism for Adriamycin-induced cardiac and skeletal myopathy, i.e., inhibition of synthesis of FAD, a flavin coenzyme which is involved in electron transport, lipid metabolism, and energy generation. These findings in an animal model raise the possibility that defects of riboflavin nutriture, either dietary or drug-induced, may be a determinant of Adriamycin toxicity. Further studies are required to explore the potential for preventing side effects due to Adriamycin by administration of this vitamin.

Effects of riboflavin deficiency upon prostaglandin biosynthesis in rat kidney

The effects of riboflavin deficiency on the activity in vitro of prostaglandin synthetase were determined in rat kidney homogenates. For a period of two to five months, weaning rats were fed either a diet deficient in riboflavin or equal amounts of a diet identical in composition except for the addition of riboflavin at four times the RDA for this vitamin. In further experiments, each group of rats was treated for 10 days with either an inhibitor of cyclooxygenase (flurbiprofen) or buffer. Following sacrifice, prostaglandin biosynthesis in vitro was measured both in the absence and presence of reduced glutathione, and subsequently in the presence of reduced glutathione with and without flurbiprofen. Reaction products were extracted from supernatant solutions with diethylether, and the PGE2 and PGF2 alpha formed were measured by radioimmunoassay. Dietary riboflavin deficiency increased biosynthesis rates in vitro of both PGE2 and PGF2 alpha in rat renal medulla and papilla. When both control and riboflavin deficient rats were treated with flurbiprofen for a 10 day period, PGE2 biosynthesis in vitro was markedly inhibited. This inhibition of PGE2 biosynthesis was partially overcome by the addition of reduced glutathione in vitro. The addition of flurbiprofen in vitro to samples containing reduced glutathione prevented the restoration of PGE2 biosynthesis by the latter. The rate of prostaglandin biosynthesis in kidney homogenates from riboflavin deficient rats remained higher than that of controls with each experimental manipulation. These data in their entirety suggest a possible role for riboflavin in the regulation of renal prostaglandin biosynthesis in the rat.

Inhibition by chlorpromazine of thyroxine modulation of flavin metabolism in liver, cerebrum and cerebellum

In livers of adult rats that have been treated with thyroxine, the rate of incorporation of radiolabeled riboflavin into both flavin adenine dinucleotide (FAD) and FAD covalently attached to specific apoflavoenzymes was enhanced markedly. By contrast, thyroxine diminished riboflavin incorporation into FAD in cerebrum and cerebellum but continued to enhance incorporation into the covalently bound fraction of FAD. Diminished net incorporation of riboflavin into FAD in brains of adult rats may reflect increased utilization of this fraction for covalent attachment into specific apoflavoenzymes rather than down regulation of the FAD biosynthetic enzymes, flavokinase and FAD pyrophosphorylase, inasmuch as covalent attachment of FAD occurs subsequent to the formation of FAD. The psychotropic drug, chlorpromazine, over a wide dose range, exerted an inhibitory effect on both incorporation of riboflavin into FAD and the utilization of FAD for incorporation into covalently bound flavoenzymes in liver, cerebrum, and cerebellum. Thus, chlorpromazine inhibition of FAD metabolism occurred regardless of the direction of the thyroxine effect and was compatible with an observed inhibitory effect by this drug upon the flavin biosynthetic enzymes.

Nutrition and cancer

Nutrition and cancer interact at several levels. Both dietary deficiencies and dietary excesses have been linked with changes in prevalence of certain human cancers. With respect to one particular nutrient, riboflavin, a dietary deficiency may decrease the development of spontaneous tumors in experimental animals but increase carcinogenesis due to certain agents. Cancer itself has profound effects upon nutritional status, and neoplastic tissue appears in general to resist dietary deficiency more effectively than normal tissues. Nutrition has a major role in therapy of cancer, but as an adjunct to the treatment plan rather than as an alternative. Parenteral nutrition, either peripheral or total, can provide support that is critically needed when patients cannot eat or swallow, have obstruction or malabsorption, or are otherwise unable to utilize dietary nutrients in adequate amounts. The advent of home parenteral nutrition now provides a means for long-term rehabilitation of cancer patients.

Accelerated development of riboflavin deficiency by treatment with chlorpromazine

The present study was undertaken to determine whether treatment with chlorpromazine accelerates the depletion of tissue stores of flavin adenine dinucleotide during dietary riboflavin deficiency. These investigations derived their impetus from earlier findings that low doses of chlorpromazine in rats fed abundant riboflavin increase urinary riboflavin excretion and reduce hepatic flavin stores. From 6 to 10 days after beginning to feed on a riboflavin-deficient diet, rats treated with chlorpromazine, 2 mg/kg body weight twice daily, had approximately twice the urinary riboflavin excretion of that of pair-fed saline-treated controls. When the riboflavin-deficient diets and chlorpromazine treatments were extended for 3 weeks and the animals killed, FAD levels in liver, kidney, and heart were markedly lower in drug-treated than in saline-treated animals. When studies were extended for 7 weeks, tissue FAD levels in saline-treated animals declined further and were equal to those of chlorpromazine-treated rats after only 3 weeks of dietary deficiency. Thus, chlorpromazine treatment accelerated urinary riboflavin loss and accelerated tissue depletion of FAD levels during dietary riboflavin deficiency. Brain levels of FAD by contrast were relatively resistant to both dietary riboflavin withdrawal and treatment with chlorpromazine. Subsequent studies showed that urinary riboflavin excretion began to increase within 6 hr of treatment with chlorpromazine. It is concluded that significant riboflavin depletion occurs following treatment with low doses of chlorpromazine, both in animals fed a normal diet and in animals fed a riboflavin-deficient diet, particularly during the early stages of deficiency.

Cardiac sensitivity to the inhibitory effects of chlorpromazine, imipramine and amitriptyline upon formation of flavins

Chlorpromazine, imipramine and amitriptyline, drugs structurally related to riboflavin, each inhibited the formation in vivo of flavin adenine dinucleotide (FAD) from riboflavin in rat heart at 2-5 mg/kg body weight, doses comparable on a weight basis to those used clinically. All three drugs inhibited FAD formation in heart within 5 hr after a single dose of 25 mg/kg. Chlorpromazine under these conditions also inhibited FAD formation in liver, cerebrum and cerebellum. A series of psychoactive agents structurally unrelated to riboflavin did not inhibit flavin formation in the organs tested. These findings indicate that the inhibitory effects of the drugs studied have organ specificity with respect to FAD formation.