Effect of cigarette smoke condensate and vitamin A depletion on keratin expression patterns in cultured hamster tracheal epithelium. An immunohistomorphological study using monoclonal antibodies to keratins

Keratin expression in hamster tracheal epithelium was investigated during organ culture in serum-free, hormone-supplemented medium using monospecific monoclonal antibodies. Generally, tracheal basal cells expressed keratins detected by antibodies RCK102 and RCK103, while columnar epithelial cells were stained positively by RGE53, RCK103, RCK105 and HCK19. Metaplastic squamous cell foci reacted with antibodies RKSE60, RCK103 and HCK19. Early metaplastic alterations were more clearly RKSE60-positive than the mature lesions. In the vitamin A-depleted tracheas basal cells were clearly RCK102-positive. Superficial cells in the central part of areas of squamous metaplasia induced by cigarette smoke condensate expressed the basal cell keratins, and were negative for the columnar cell keratin 18 detected by the RGE53 antibody. This finding suggests that in cigarette smoke condensate-induced squamous metaplasia basal cells play an important role. The mucus-producing cells at the edges of metaplastic squamous cell foci expressed the keratins specific to columnar cells. Cigarette smoke condensate exposure accelerated epithelial keratinization compared to the vitamin A-depleted epithelium. It was concluded that not only small mucous granule cells, but also basal cells are involved in the development and maintenance of induced squamous metaplasia in tracheal epithelium. Furthermore, in vitro vitamin A-depleted epithelium did not coexpress vimentin in addition to the different keratins.

Uptake and cellular transport of [11-3H] all-trans-retinoic acid in the liver of vitamin A-deficient hamsters

In this study, we examined, by ultrastructural autoradiography, the uptake and intracellular transport of [3H]all-trans-retinoic acid ([3H]RA) in the livers of vitamin A-deficient hamsters. Four-week-old animals were administered 25 microCi of [3H]RA by gavage, and, at different intervals thereafter, one animal was sacrificed. Their livers were excised and processed for autoradiography. Radioactive grains were observed to pass randomly through the plasma membrane by diffusion. No evidence of retinoid internalization by endocytosis was observed. Between 1 and 30 min after gavage, the radioactivity in parenchymal cells was associated mainly with rough endoplasmic reticulum (RER) and mitochondria. The labeling over nuclei was apparent at 1 min, remained relatively high up to 30 min, and subsequently decreased. At 2 and 5 hr, only a few grains were observed over nuclei, RER and mitochondria. At 24 hr, most of the labeling was associated with endothelial cells and sinusoidal spaces, indicating mobilization of [3H]RA from the liver. The results indicate that [3H]RA is transported through the plasma membrane by transmembrane diffusion without endocytosis and, after entering the cells, the ligand is rapidly translocated into nuclei.

Study on the mechanism of interference of 3,4,3',4'-tetrachlorobiphenyl with the plasma retinol-binding proteins in rodents

The mechanism of plasma retinol reduction in rodents by 3,4,3',4'-tetrachlorobiphenyl (TCB) was investigated by radioimmunochemical analysis of the amounts of circulating and hepatic retinol-binding protein (RBP) and transthyretin (TTR) in exposed and control animals. Plasma RBP concentrations were markedly reduced in C57BL/Rij mice (50%) at 4 days, in DBA/2 mice (37-41%) at 4 and 8 days, and in Sprague-Dawley rats (58%) at 2 days after exposure to TCB. These reductions paralleled the time course of reduction of plasma retinol after exposure to TCB. Hepatic RBP concentrations were somewhat increased in TCB-treated animals, especially in the C57BL/Rij mouse and Sprague-Dawley rat. However, the release of hepatic RBP into the circulation was not blocked by TCB treatment, as analysed in vitamin A deficient rats. In addition, the amount of plasma TTR was in the normal range in TCB-treated rats. The dissociation constants of the RBP-TTR complex as analysed by polarization of fluorescence appeared to be significantly increased (from 0.5 x 10(-7) M-1 to 2.4 x 10(-7) M-1) in the presence of a TCB metabolite, isolated from plasma of TCB-treated rats. In addition, the estimated number of binding sites for RBP on the TTR molecule was reduced (from 2.8 to 1.7 sites) upon treatment of TTR with the TCB metabolite. These data support the hypothesis that plasma retinol reduction by TCB might result from a weakening of the RBP-TTR complex, in the presence of the TCB metabolite bound to the TTR.

Novel aspects of vitamin A metabolism in the dog: distribution of lipoprotein retinyl esters in vitamin A-deprived and cholesterol-fed animals

Retinyl ester concentrations in plasma from fasting humans, rabbits and rats are usually negligible. In contrast, plasma from fasting dogs contains appreciable amounts of retinyl esters, associated almost entirely with the low-density lipoproteins. This study was undertaken to gather additional information about the nature and origin of canine retinyl ester-containing lipoproteins. We examined the metabolism of endogenous lipoprotein retinyl esters in adult mongrel dogs with moderate vitamin A deficiency. Four animals were fed a diet of oatmeal and tuna fish that provided only 4% of the vitamin A contained in their control rations (15 vs. 367% of the canine recommended daily intake). There was an initial rapid decline in plasma retinyl esters. However, measurable concentrations persisted in plasma for up to 1 year of restricted vitamin A intake. Total plasma retinyl ester concentrations after 6 months of vitamin A deprivation, extrapolated from best-fit monoexponential decay curves for each animal, ranged from 11 to 89% of control, suggesting that there was sustained secretion of retinyl esters from endogenous stores. Density gradient ultracentrifugation of plasma from fasting vitamin A-deprived dogs showed retinyl esters in the very-low- and low-density lipoproteins. After fat and vitamin A feeding retinyl esters appeared among the very-low-, intermediate- and low-density lipoproteins, consistent with the suggestion that chylomicron retinyl esters are first taken up by the liver, and then resecreted as density less than 1.006-1.063 g/ml lipoproteins. Maximal incorporation of dietary retinyl esters into low-density lipoproteins was not reached until 24-48 h. Intermediate-density and beta-migrating low-density lipoprotein retinyl esters were increased markedly in fasting animals maintained on cholesterol- and saturated fat-enriched diets. These observations provide further evidence for the proposal that the canine liver secretes retinyl ester-containing particles, in amounts governed by dietary composition and vitamin A content. What selective advantage this unusual transport pathway might provide is not apparent.

Effect of vitamins A, C and glutathione on the mutagenicity of benzo[a]pyrene mediated by S9 from vitamin A-deficient rats

Vitamin A deficiency has been shown to enhance the mutagenicity of benzo[a]pyrene (Narbonne et al., 1985). Here we report that this is not a result of increased benzo[a]pyrene metabolism but might be a consequence of either a lack of vitamin A or a decreased level of scavengers (ascorbic acid and glutathione) in the liver. However, the addition of vitamin A in vitro in the form of retinyl palmitate strongly inhibits the benzo[a]pyrene mutagenicity. An enhancing effect on the mutagenicity of benzo[a]pyrene is observed with addition of ascorbic acid when incubated with high amounts of the precarcinogen. In vivo addition of high levels of glutathione also reduces the mutagenicity of benzo[a]pyrene.

Effect of short term vitamin A deficiency on organ weights, blood glucose and lactate levels and, tissue protein and glycogen contents of albino rats: a preliminary study

The effect of short term dietary vitamin A deficiency in post-pubertal female rats in terms of weight gain, food consumption, organ weights, haemoglobin content, blood glucose and lactate levels and, tissue protein and glycogen contents has been evaluated to gain insight into the possible interrelationship between vitamin A and general metabolism. Significant elevation in blood glucose level and reduction in blood lactate and haemoglobin along with a tendency of reduction in weights of spleen, adrenals and ovaries have been noted. Lowered tissue protein and glycogen contents and reduced body weight gain have also been revealed. Obviously, reduced functional competence of some of the organs and certain alterations in general metabolism especially of carbohydrates are suspected and hence is discussed in relation to supportive evidences available.

Induction of ceruloplasmin synthesis by retinoic acid in rats: influence of dietary copper and vitamin A status

Ceruloplasmin, a copper-containing acute phase plasma protein, has been shown to be regulated by 13-cis retinoic acid in rats. Ceruloplasmin activity was significantly increased within 24 h and remained elevated for at least 72 h after a single injection of 13-cis retinoic acid. With daily injections of retinoic acid, the ceruloplasmin activity continued to increase for at least 4 d. After 4 d, the activity was four times control levels. In copper-deficient rats, the ceruloplasmin activity did not increase in response to retinoic acid unless copper was also given to these rats 8 h after retinoic acid. Actinomycin D blocked the retinoic acid-induced stimulation of ceruloplasmin activity in copper-sufficient rats, but in copper-deficient rats only about half of the increase was blocked when the rats were given copper or copper and retinoic acid. By use of pulse-labeling techniques, ceruloplasmin synthesis was shown to increase 1.5-fold after retinoic acid and this increase was blocked by actinomycin D. When vitamin A-deficient rats were repleted with 13-cis retinoic acid for 3 or 5 d, both the ceruloplasmin activity and synthesis were significantly stimulated when compared to the nonrepleted, deficient rats. Therefore, the dietary components, copper and vitamin A, play an important role in the regulation of plasma ceruloplasmin levels.

Liver takes up retinol-binding protein from plasma

Retinol is transported in plasma bound to a specific transport protein, retinol-binding protein. We prepared 125I-tyramine cellobiose-labeled rat retinol-binding protein and studied its tissue uptake 1, 5, and 24 h after intravenous injection into rats. The liver was the organ containing most radioactivity at all time points studied. After 5 and 24 h, 30 and 22% of the injected dose were recovered in liver, respectively. After separating the liver into parenchymal and nonparenchymal cells in the 5-h group, we found that both cell fractions contained approximately the same amount of radioactivity (per gram of liver). Most of the retinol-binding protein radioactivity in the nonparenchymal cell fraction was in the stellate cells. The implication of these results for a possible transfer mechanism for retinol between parenchymal and stellate cells is discussed.

Vitamin A status needed to maintain vitamin A concentrations in nonhepatic tissues of the pregnant rat

Vitamin A-depleted pregnant rats were fed diets containing 0, 1, 10 or 100 retinol equivalents (REq)/d during gestation. Maternal tissues of these dams, their placentas and fetuses were assayed for total vitamin A (retinol and its esters) at gestational ages 10, 13, 16 or 19 d. The vitamin A concentrations in placenta and fetuses of dams fed 10 REq/d were significantly different from those of dams fed no vitamin A. This difference was not seen in any of the six other maternal tissues assayed. We suggest that the fetus is at greater risk than other maternal tissues during severe vitamin A deprivation. For vitamin A-deprived dams, linear regression analysis indicated strong relationships between the vitamin A concentrations of nonhepatic tissues and their liver vitamin A concentrations. In contrast, among vitamin A-replete dams, these relationships were not statistically significant. An estimate was made of the minimal vitamin A status corresponding to tissue repletion by solving linear equations described by the data of the depleted dams for the vitamin A concentrations found in tissues of replete dams. This analysis revealed that a maternal vitamin A status of 3 micrograms/g liver was needed to provide the level of vitamin A found in the placenta, whole fetus and maternal tissues of vitamin A-replete dams.

Effect of ethanol and vitamin A deficiency on epithelial cell proliferation and structure in the rat esophagus

An increased risk of cancer of the esophagus has been reported in alcoholics and in populations with low dietary vitamin A consumption. As cancer is a disorder of cell proliferation and differentiation, we have assessed the combined effects of ethanol and vitamin A deficiency on cell proliferation and structure of the esophagus. Weanling male rats were fed liquid diets with either a standard amount of vitamin A or lacking vitamin A for 8 wk. Littermates were pair-fed the same diets with carbohydrate (36% of calories) replaced by ethanol. Rats were given [3H]thymidine 1 h before death, and the labeling index of the proliferative basal cells was determined on radioautographs. In rats fed the normal vitamin A diet with or without ethanol, plasma vitamin A was normal. Hepatic vitamin A was markedly decreased, whereas esophageal vitamin A was increased after ethanol feeding. Ethanol feeding resulted in a twofold increase in basal cell labeling index (14.6 +/- 0.7 vs. 6.8 +/- 0.8; p less than 0.001). The thickness of the epithelium and the morphology of basal cells were not altered by ethanol feeding. In rats fed the vitamin A-deficient diet with or without ethanol, plasma vitamin A was extremely low, and hepatic and esophageal vitamin A were unmeasurable. The epithelium was thin (with a 50% reduction in thickness) and showed abnormalities of basal cells and increased production of keratohyalin granules, changes suggesting a disorder in the epithelial differentiation. This altered differentiation caused by vitamin A deficiency was not affected by ethanol consumption. Ethanol feeding again resulted in an increase in the basal cell labeling index (13.2 +/- 1.6 vs. 4.8 +/- 0.7; p less than 0.001). Vitamin A deficiency had no effect on basal cell proliferation. Therefore, the stimulatory effect of ethanol on cell proliferation is independent of vitamin A deficiency. Nevertheless, the combined actions of ethanol and vitamin A deficiency may have a synergistic effect on the susceptibility of the esophagus to carcinogens.

Rapid induction of vitamin A deficiency in rabbits

Clinical and biochemical evidence of vitamin A deficiency was produced in rabbits as early as 4-5 weeks after weaning to a vitamin A deficient diet from dams maintained during lactation on the deficient diet. Mean serum retinol levels at the time of weaning for the deficient dams were 25 +/- 6 micrograms/dl compared with 74 +/- 8 micrograms/dl for the controls. Five weeks after weaning, 25% of pups fed the vitamin A deficient diet had ocular lesions characterized by the accumulation of sloughed epithelium on the cornea. At this time, mean serum values of the pups were 10 +/- 4 micrograms/dl for the deficient group and 73 +/- 8 micrograms/dl for the controls. Evidence of critically depleted liver stores was documented in the deficient rabbits by an elevated relative dose response test (54 +/- 18%) that did not occur in the control group (6 +/- 5%). Although food consumption was similar, weight gain was lower in the deficient group when compared to the control group.

Liver microsomal membrane fluidity and lipid characteristics in vitamin A-deficient rats

Rat liver microsomes (microsomal fraction) were isolated from vitamin A-deficient and -sufficient rats and analysed for membrane lipid characteristics. Membrane fluidity was found to be significantly decreased in microsomes from the vitamin A-deficient rats, but not in liposomes prepared from lipid extracts. Microsomes from vitamin A-deficient animals showed a significant decrease in C18:2, omega 6 and an increase in C22:5, omega 6 fatty acids.

Effect of vitamin A nutriture on experimental esophageal carcinogenesis

The effect of mild vitamin A deficiency or vitamin A supplementation on methylbenzylnitrosamine (MBN; CAS: 937-40-6)-induced esophageal carcinogenesis was examined in Sprague-Dawley rats. The animals were fed semipurified diets containing levels of retinyl acetate, which were adequate (2.2 mg/kg diet), deficient (0.30 mg/kg diet), or supplemented (29.9 mg/kg diet) with respect to vitamin A content. Carcinogen-treated rats received 2.5 mg MBN/kg (body wt) twice a week for 5 weeks; they were then sacrificed for evaluation of esophageal tumorigenesis 15 weeks later. Liver levels of retinol reflected vitamin A nutriture, but there were no clinical signs of deficiency or toxicity. There were no significant differences in the frequency or incidence of esophageal tumors (either carcinomas or papillomas) among the dietary groups. There was also no indication that either vitamin A deficiency or vitamin A supplementation influenced the formation of preneoplastic lesions. Although the time was short for the neoplastic development, tumors were observed. These data suggest that vitamin A is selective in tissues it may protect from cancer induction and that the esophagus is less involved than other tissues.

[Effect of vitamin A deficiency on surfactants and enzymes of xenobiotic metabolism in the rat lung]

Experiments were conducted on 128 male rats kept on a retinol-deprived diet during 12-14 weeks, that resulted in vitamin A deficiency. The content of phospholipids, total lipids, proteins and the activity of esterase, glutamate dehydrogenase, catalase, glutathione-S-transferase, aldehyde dehydrogenase and aldehyde oxidase were assayed in the bronchoalveolar lavage fluid, in homogenates and microsomes of the lungs. The content of phospholipids in the bronchoalveolar lavage fluid was reduced up to 63.9%, as compared to that in the control rats, while the protein content was unchanged. The levels of phospholipids, total lipids and protein rose in the homogenates and microsomes of the lungs. Esterase activity decreased up to 38.6% of the control level, catalase--up to 73.2%, glutamate dehydrogenase--up to 79%. There was a tendency to decrease in glutathione-S-transferase activity, while aldehyde dehydrogenase and aldehyde oxidase activities remained unchanged. It is suggested that the disorders in the enzymatic activity and lipid content in the surfactant can be responsible for the changes in the xenobiotic biotransformation and for the rise in xenobiotic toxicity.

Regulation of levels of specific Sertoli cell mRNAs by vitamin A

The regulation of Sertoli cell transferrin and sulfated glycoprotein-2 (SGP-2) mRNA levels by vitamin A was studied in vitamin A deficient rats. Vitamin A deficiency differentially affected the levels of these mRNAs. Sertoli cells from vitamin A deficient rats contained 3-fold less transferrin mRNA and 1.8-fold more SGP-2 mRNA than Sertoli cells from normal rats. Vitamin A deficiency did not result in changes in the amount of transferrin mRNA per liver cell. When vitamin A deficient rats were fed a retinol supplemented diet, Sertoli cell transferrin and SGP-2 mRNA levels returned to normal. In contrast, dietary retinoic acid did not support recovery of the levels of the two mRNAs. The regulation of transferrin and SGP-2 mRNA levels was further examined in vitamin A deficient rats that had received subcapsular testicular injections of vitamin A and in vitamin A supplemented cultures of Sertoli cells from vitamin A deficient rats. Under these conditions, retinol and retinoic acid both stimulated transferrin mRNA levels but did not affect SGP-2 mRNA levels. Retinol did not inhibit the turnover of transferrin mRNA in Sertoli cell cultures suggesting that the stimulation of transferrin mRNA levels by retinol is due to increased transcription of the transferrin gene. A mathematical correlation between the Sertoli cell transferrin mRNA levels and the weight of the testes or the number of germinal cells was observed.

[Activity of glutathione-dependent enzymes, catalase and superoxide dismutase in the liver and myocardium of rats with vitamin A deficiency]

The alimentary deficiency of vitamin A causes marked shifts in the metabolism of GSH: the levels of GSH, GSSG and cysteine in the liver increase, while the activities of glutathione-S-transferase (using glycerol as substrate) and gamma-glutamyltransferase in the liver show a rise. At the same time, vitamin A deficiency causes a decrease of the glutathione peroxidase and catalase activity in the liver. The data obtained are discussed in terms of the role of GSH and enzymes of GSH metabolism in the protection of cells against the damaging influence of lipid peroxidation.

The effects of vitamin A nutritional status on glutathione, glutathione transferase and glutathione peroxidase activities in rat intestine

In rat intestine, the glutathione level was increased, glutathione peroxidase activity decreased and glutathione-S-transferase unchanged by vitamin A deficiency.

Vitamin-A-dependent zinc-binding protein and intestinal absorption of Zn in chicks

It was demonstrated that the development of experimental avitaminosis A in chicks led to secondary zinc deficiency. The balance of Zn in the chick became negative, while the Zn content of various tissues decreased. Thus in vitamin-A-deficient chicks the serum Zn content was 1258 (SD 26.3) micrograms/l which was considerably lower than 1652 (SD 97.8) micrograms/l in controls. Zn absorption was considerably reduced throughout the entire small intestine of vitamin-A-deficient chicks and most markedly in the ileal region. Within 72 h after retinyl acetate administration Zn absorption was fully restored in this region of the intestine. The 65Zn-binding capacity of soluble proteins, present in the supernatant fraction of ileal-mucosa homogenates of vitamin-A-deficient chicks, was found to increase 2.6 times by 72 h after the administration of a single dose of retinyl acetate. A vitamin-A-dependent Zn-binding protein (ZnBP), absent in vitamin-A-deficient chicks, was isolated from the ileal mucosa after their repletion with vitamin A. Competitive-binding studies (calcium, cadmium, copper) showed the protein to be highly specific for Zn ions. The molecular weight of ZnBP was 83 kDa. The association constant of the protein-Zn complex was 0.8 X 10(6)/mol. The protein was acidic with approximately 20% of its amino acid residues belonging to dicarboxylic acids. ZnBP was found to be a glycoprotein, and it contained hexose as a carbohydrate component. It is suggested that ZnBP is involved in the binding of Zn in the ileal mucosa of chicks.

[Effect of vitamin A deficiency on the macromolecular permeability of small intestine mucosa in the adult rat]

Adult rats with experimental vitamin A deficiency and control animals were intraperitoneally injected with chicken ovalbumin (OA) solution and the entrance of native OA into the blood was assessed 3 hours later by competitive radioimmunoassay. The OA amounts circulating in the blood of control animals averaged (0.39 +/- 0.06) X 10(-4)% of the consumed dose, while in the experimental group it averaged (1.33 +/- 0.42) 10(-4)%. Electron microscopy, using colloid lanthanum hydroxide, has shown vitamin A deficiency to give rise to an abrupt reduction in glycocalix layer, as compared to the control, without increasing erythrocyte membrane permeability for tracer particles. It is concluded that vitamin A deficiency leads to a considerable damage of small intestinal permeability for protein macromolecules.

Studies on the metabolism of retinol-binding protein by primary hepatocytes from retinol-deficient rats

Studies were conducted to explore the regulation of retinol-binding protein (RBP) metabolism in cultured primary hepatocytes from retinol-deficient rats. Newly isolated hepatocytes from retinol-deficient rats contained elevated levels (3.4-fold) of RBP, compared to hepatocytes from normal (retinol-adequate) rats. Addition of retinol to retinol-depleted hepatocytes stimulated RBP secretion by the cells in a concentration-dependent manner. Maximal stimulation of RBP secretion was seen with a retinol level of 0.3 micrograms/ml. The effect of retinol was quite rapid, and was evident by 20 minutes after addition of retinol to the medium. Stimulation of RBP secretion was only seen during the first few hours after retinol addition. The effect of retinol was specific for RBP; thus, retinol had no effect on the secretion rates of transthyretin or albumin. Addition of retinoic acid also stimulated RBP secretion by retinol-deficient hepatocytes. Addition of dexamethasone to retinol-deficient cells did not maintain the initial rate of RBP secretion. Dexamethasone also had no effect on the secretion of transthyretin or albumin by these cells. The effects of retinol and of dexamethasone seen here with retinol-depleted cells differed dramatically from effects seen in other studies with normal (retinol-adequate) hepatocytes. Thus, with normal cells, dexamethasone maintains RBP, TTR, and albumin production and secretion rates close to initial rates. Also in normal hepatocytes, with ample retinol available within the cell, addition of exogenous retinol does not appear to influence RBP secretion. In contrast, and as shown previously in intact rats, in retinol deficiency the availability of retinol specifically regulates the secretion of RBP by hepatocytes.

Effects of vitamin A deficiency and repletion on rat insulin secretion in vivo and in vitro from isolated islets

We studied the effects of vitamin A deficiency and repletion on rat insulin release and islet cellular retinol binding protein (CRBP) and cellular retinoic acid binding protein (CRABP). Biphasic insulin release from vitamin A-deficient perifused islets was markedly impaired. Release remained impaired with retinoic acid (RA) repletion, 2 micrograms/g diet compared to release from islets of rats repleted with retinol in the form of retinyl palmitate, 4 micrograms/g diet. Release normalized with RA, 8 micrograms/g diet. Vitamin A deficiency did not affect islet insulin content, cell size, number or structure. In vivo, vitamin A-deficient rats had impaired glucose-induced acute insulin release and glucose intolerance, which improved with repletion. Normal islets had greater concentrations of CRBP than CRABP; vitamin A deficiency reduced CRBP but not CRABP levels. We conclude retinol is required for normal insulin secretion. Retinoic acid may substitute for retinol in this function.

In vivo and in vitro study of the effects of vitamin A deficiency on rat third molar development

We have examined the effect of in vivo vitamin A status on subsequent rat third molar formation and mineralization in an in vitro organ culture system. Vitamin A deficiency imposed during an eight-day in vitro period caused effects very similar to those of vitamin A deficiency imposed on rats in vivo. Analysis of the data also demonstrates that retinoic acid is capable of reversing the interference in mineralization of third molars induced by vitamin A deficiency in the organ culture system.