Dexamethasone Intravitreal Implant for the Treatment of Macular Edema and Uveitis: A Comprehensive Narrative Review

Purpose

The purpose of this review article is to provide a comprehensive review of the current applications of intravitreal DEX implant (Ozurdex^®, Allergan Inc, Irvine, CA) for a variety of ophthalmic conditions – ranging from FDA approved indications to off-label uses. We have attempted to provide relevant evidence from the literature to help a reader develop an understanding of the biological and pharmacokinetic properties of DEX implant, its uses, and potential side effects.

Methods

PubMed searches were performed using the terms “Ozurdex”, or “intravitreal DEX implant”, AND “retinal vein occlusion”, or “diabetic macular edema”, or “uveitis”. The search was performed in July of 2021, with an additional search in October 2021. All original English language articles were considered for this review.

Results

DEX implant has evidence of efficacy in a variety of clinical situations including macular edema associated with retinal vein occlusion, diabetes, uveitis, and others. Safety concerns include cataract formation and progression, intraocular pressure elevation, complications related to intravitreal injection, and opportunistic infections secondary to steroid-induced immune suppression.

Conclusion

DEX implant is a useful tool in the management of several retinal disorders. Further studies are needed for head-to-head comparison with other treatment modalities and to determine its precise place in clinical practice.

Conceptualization of functional single nucleotide polymorphisms of polycystic ovarian syndrome genes: an in silico approach

PURPOSE

Polycystic ovarian syndrome (PCOS) is a multi-faceted endocrinopathy frequently observed in reproductive-aged females, causing infertility. Cumulative evidence revealed that genetic and epigenetic variations, along with environmental factors, were linked with PCOS. Deciphering the molecular pathways of PCOS is quite complicated due to the availability of limited molecular information. Hence, to explore the influence of genetic variations in PCOS, we mapped the GWAS genes and performed a computational analysis to identify the SNPs and their impact on the coding and non-coding sequences.

METHODS

The causative genes of PCOS were searched using the GWAS catalog, and pathway analysis was performed using ClueGO. SNPs were extracted using an Ensembl genome browser, and missense variants were shortlisted. Further, the native and mutant forms of the deleterious SNPs were modeled using I-TASSER, Swiss-PdbViewer, and PyMOL. MirSNP, PolymiRTS, miRNASNP3, and SNP2TFBS, SNPInspector databases were used to find SNPs in the miRNA binding site and transcription factor binding site (TFBS), respectively. EnhancerDB and HaploReg were used to characterize enhancer SNPs. Linkage Disequilibrium (LD) analysis was performed using LDlink.

RESULTS

25 PCOS genes showed interaction with 18 pathways. 7 SNPs were predicted to be deleterious using different pathogenicity predictions. 4 SNPs were found in the miRNA target site, TFBS, and enhancer sites and were in LD with reported PCOS GWAS SNPs.

CONCLUSION

Computational analysis of SNPs residing in PCOS genes may provide insight into complex molecular interactions among genes involved in PCOS pathophysiology. It may also aid in determining the causal variants and consequently contributing to predicting disease strategies.

Dental neglect and adverse birth outcomes: a validation and observational study

OBJECTIVES

The objectives of this study were to validate the Indian translation of the Dental Neglect Scale (DNS) among a sample of parturient Indian women and to investigate dental neglect as a possible risk indicator in adverse birth outcomes.

SUBJECTS AND METHODS

Three hundred and sixteen parturient women were administered the DNS and the Modified Dental Beliefs Scale (MDBS) and were also clinically examined for oral health status. Information regarding socio-economic status, weeks of gestation and birth weight was also collected. A gestation period of less than 37 weeks was considered as preterm and a birth weight of less than 2500 gm as 'low birth weight'.

RESULTS

The Indian version of the DNS was found to be reliable (Cronbach's Alpha = 0.72) and valid for assessing dental neglect among the women. Factor analysis of the DNS revealed a two-factor structure accounting for 56% variance. Dental neglect was higher among those with poorer oral health status, lower socio-economic and educational status. Multinomial logistic regression showed high dental neglect and negative dental beliefs and not poor oral health, as significant risk indicators for occurrence of adverse birth outcomes.

CONCLUSION

The finding of an association of adverse birth outcomes with dental neglect and beliefs, but not with poor oral health could be due to the influence of other more important general factors which had a direct bearing on birth outcomes. There is a need for further research to assess the role of behavioural factors like dental neglect as risk indicators for adverse birth outcomes.

Primary T-cell lymphoma of the retina and cerebellum: immunophenotypic and gene rearrangement confirmation

PURPOSE

To document fully the first credible primary T-cell lymphoma of the retina and central nervous system in a 71-year-old man.

DESIGN

Interventional, retrospective report.

METHODS

Critical analysis of clinical history and findings, which included bilateral vitreitis with anterior chamber reaction, creamy intraretinal infiltrates, and retinal detachment; complete blood counts and other blood studies (anti-neutrophil cytoplasmic antibody [ANCA], angiotensin-converting enzyme levels, and Lyme and fluorescent treponemal antibody absorption titers); magnetic resonance imaging (MRI) scanning of the brain with total body computed tomographic and positron emission tomographic scanning; interleukin (IL) level determinations (IL-10 and IL-6); cytologic and electron microscopic evaluations; immunophenotyping of cells; and polymerase chain reaction studies for viral deoxyribonucleic acid and ribonucleic acid, and immunoglobulin heavy-chain, and T-cell receptor (TCR) gene rearrangements.

RESULTS

The first vitreous specimen was diagnosed mistakenly as cytologically reactive and contained elevated levels of IL-10 and IL-6 in a ratio of 7 to 1. T cells predominated on immunophenotypic analysis. Computed tomographic and positron emission tomographic whole body scanning showed negative results for lymphoma. An MRI scan of the brain eventually revealed a cerebellar lesion. A retinal biopsy harbored cytologically atypical pleomorphic cells that were almost all immunophenotypically T cells; polymerase chain reaction studies demonstrated a clonal TCR gene rearrangement. T-cell lymphocytes in the biopsy specimen of the cerebellum had an identical clonal TCR gene rearrangement.

CONCLUSIONS

This case unequivocally establishes that primary retinal T-cell lymphoma accompanied by central nervous system involvement can occur. Elevation in the IL-10 to IL-6 ratio in the face of inconclusive or confusing vitreous cytologic and immunophenotypic findings (a predominance of "reactive T cells with some atypicality") should lead to gene rearrangement studies on biopsies of involved tissues for the detection of T-cell clonality.

HIV-protease inhibitors alter retinoic acid synthesis

BACKGROUND

An increasing rate of highly-active antiretroviral therapy (HAART)-associated metabolic and morphological abnormalities has been reported in HIV-infected persons. Some of them resemble retinoid-related adverse events, indicating alteration(s) of retinol metabolism or of retinoic acid-mediated signalling.

OBJECTIVE

To evaluate retinol levels in patients with or without HAART and to assess the effect of antiretroviral agents on retinal dehydrogenase (RALDH), a key enzyme involved in retinoic acid synthesis.

DESIGN

Plasma retinol levels, measured in six patients receiving HAART and in five others with no antiretroviral therapy, were correlated with levels of serum retinol-binding proteins. We then studied the effects of seven antiretroviral agents on RALDH activity and gene expression in a kidney-derived cell line (LLCPK).

RESULTS

Plasma retinol levels in patients receiving HAART were decreased in comparison with those not receiving antiretroviral drugs (51 +/- 5 versus 66 +/- 11 microg/dl; P = 0.03), whereas retinol-binding protein levels were increased (68 +/- 18 versus 45 +/- 10 mg/l; P = 0.04). RALDH activity was heightened by ritonavir (24%), indinavir (17%), saquinavir (17%), zalcitabine (14%), delavirdine (12%) and nelfinavir (10%) and decreased (22%) by DMP-450. RALDH gene expression was induced only by indinavir.

CONCLUSIONS

These data indicate that certain retinoid-like adverse effects in HAART-receiving patients are not due to higher retinol levels. Enhanced RALDH activity or/and gene expression by some protease inhibitors could increase retinoic acid concentrations. Elevated retinoic acid levels might be responsible for retinoid-like or other adverse effects due to alterations in the expression of retinoic acid-responsive genes.

Localization of retinal dehydrogenase type 1 in the stomach and intestine

Retinal dehydrogenase type 1 (RALDH1) is involved in the biosynthesis of retinoic acid (RA), a modulator of gene expression and cell differentiation. RALDH1 mRNA transcripts are present in the stomach and small intestine, and their expression is regulated by vitamin A status. In situ hybridization demonstrated RALDH1 mRNA expression in epithelial cells of the stomach, small intestine, and large intestine. Strong hybridization was also seen in the lamina propria of small intestinal mucosa and the smooth muscle layer of the small and large intestines. Immunocytochemical localization revealed RALDH1 staining in parietal cells of the stomach and prismatic cells of the small and large intestines. The presence of RALDH1 protein was also detectable within supportive glial cells around neuronal fibers throughout the muscular layers of the stomach as well as the small and large intestines. These data suggest an important role for RALDH1 in generating RA needed for the differentiation of specific epithelial cells in the stomach and intestines.

Kinetic properties of the human liver cytosolic aldehyde dehydrogenase for retinal isomers

Retinoic acid exerts pleiotropic effects by acting through two families of nuclear receptors, RAR and RXR. All-trans and 9-cis retinoic acid bind RARs, whereas 9-cis retinoic acid binds and activates only the RXRs. To understand the role of human liver cytosolic aldehyde dehydrogenase (ALDH1) in retinoic acid synthesis, we examined the ability of ALDH 1 to catalyze the oxidation of the naturally occurring retinal isomers. ALDH1 catalyzed the oxidation of all-trans, 9-cis, and 13-cis retinal with equal efficiency. However, the affinity to all-trans retinal (Km = 2.2 microM) was twofold higher than to 9-cis (Km = 5.5 microM) and 13-cis (Km = 4.6 microM) retinal. All-trans retinol was a potent inhibitor of ALDH1 activity, and inhibited all-trans retinal oxidation uncompetitively. Comparison of the kinetic properties of ALDH1 for retinal isomers with those of previously reported rat kidney retinal dehydrogenase showed distinct differences, suggesting that ALDH1 may play a different role in retinal metabolism in liver.

Changing patterns of renal retinal dehydrogenase expression parallel nephron development in the rat

We have recently characterized a cytosolic aldehyde dehydrogenase from rat kidney that functions as a retinal dehydrogenase (RALDH) and have cloned the corresponding gene. RALDH catalyzes the oxidation of retinal to retinoic acid, which regulates cell growth and differentiation by activating retinoic acid receptors. In situ hybridization demonstrates that RALDH mRNA expression is prominent in kidney in 2-day-old rats, is detected in lung and in epithelia of several tissues, but is not found in liver tissue. Retinal dehydrogenase activity peaks in kidney at Day 2 after birth and decreases gradually until adulthood, correlating well with RALDH expression. Weaker activity is also detectable in lungs but not in liver. Notably, distribution patterns of RALDH in kidney tissues are dramatically altered during postnatal development (P). From P0 to P6, hybridization is essentially concentrated within the marginal nephrogenic zone of the cortex. Expression progresses to deeper cortical layers from P12 to P16 and is intense in the medulla at P42, and focal expression is still detectable in the cortex. Immunocytochemical localization of RALDH in neonatal kidney shows staining mostly in cortical zone convoluted tubules and in adult rat shows staining in segments of distal and proximal tubules. These data suggest an important role for RALDH in modulating retinoic acid levels in different cell types during rat kidney development. The changing patterns of RALDH expression mirror stages of nephron formation in the developing rat kidney, strongly suggesting a central role for RALDH and thus for retinoids in controlling kidney development.

Differentiation-dependent regulation of retinal dehydrogenase gene expression in the trachea

Retinoic acid (RA), a metabolite of vitamin A, is known to be a key signaling molecule in regulating epithelial cell differentiation. We recently characterized and cloned a retinal dehydrogenase (RALDH) that catalyzes the oxidation of retinal to RA. In this study, we investigated the effects of retinoids on the level of RALDH mRNA and protein as well as RALDH activity in the trachea and cultured tracheal epithelial cells. Vitamin A deficiency induced squamous metaplasia in the tracheal epithelium and down-regulated RALDH expression. Supplementation of retinol and retinoic acid to vitamin A deficient rats restored the normal mucociliary epithelium and up-regulated the RALDH expression. In rat epithelial cells cultured in vitro, RAinhibited squamous differentiation and promoted mucociliary differentiation. Squamous differentiated cultures (RA-) expressed very low levels of RALDH mRNA, whereas mucociliary differentiated cultures (RA+) expressed high levels of RALDH mRNA. Retinal and retinol were poor inducers of mucociliary differentiation as well as RALDH expression. The RALDH expression paralleled the expression of the mucin-1 gene in mucociliary cultures. These results suggest that the expression of RALDH is dependent on the differentiation state of the airway epithelium.

Retinal dehydrogenase gene expression in stomach and small intestine of rats during postnatal development and in vitamin A deficiency

Retinal dehydrogenase (RALDH) catalyzes the oxidation of retinal to all-trans and 9-cis retinoic acid, which function as ligands controlling RAR and RXR nuclear receptor-signaling pathways. We have recently shown the expression of RALDH transcript in the stomach and small intestine by reverse transcription polymerase chain reaction [Bhat, P.V., Labrecque J., Dumas, F., Lacroix, A. and Yoshida, A. (1995) Gene 166, 303-306]. We have examined RALDH expression in the stomach and small intestine before and during postnatal development and in vitamin A deficiency by assaying for mRNA levels and protein as well as for enzyme activity. In -2 day fetuses, RALDH expression was high in the small intestine, whereas RALDH protein was not detectable in the stomach. However, expression of RALDH was seen in the stomach after birth, and gradually increased with age and reached the highest level at postnatal day 42. In the intestine, RALDH expression decreased postnatally. Vitamin A deficiency up-regulated RALDH expression in the stomach and small intestine, and administration of retinoids down-regulated the RALDH expression in these tissues. These results show the differential expression of RALDH in the stomach and small intestine during postnatal development, and that vitamin A status regulates the expression of RALDH gene in these tissues.

Tissue concentrations of retinol, retinyl esters, and retinoic acid in vitamin A deficient rats administered a single dose of radioactive retinol

The tissue concentration of retinol and its metabolites was determined in a group of vitamin A deficient rats after a single dose of 53 micrograms of [11,12-3H]retinol. The sensitive technique of high performance liquid chromatography was used to analyse the metabolites of retinol. The analysis of the metabolites in tissues at different days after the administration of radioactive retinol showed a rapid decrease in the amount of retinol and retinyl esters in the liver tissue, accompanied by an increase in the retinol and retinyl ester values in the kidney. In addition, the content of retinoic acid was higher in liver and kidney compared with intestine, testis, and blood. It reached maximum at 4 and 11 days, respectively. After 17 days the retinoid(s) concentrations decreased markedly in all tissues studied; yet the kidney showed higher concentrations of retinoic acid and retinyl esters. These studies indicate that the kidney retains more vitamin A as vitamin A becomes depleted in the body, probably as a reserve for the production of the active metabolite retinoic acid, needed for the growth and differentiation.

Purification and partial characterization of bovine kidney aldehyde dehydrogenase able to oxidize retinal to retinoic acid

A NAD-dependent enzyme that catalyzes the oxidation of retinal to retinoic acid has been purified to homogeneity from bovine kidney. The procedures used in the purification included ion-exchange chromatography on DEAE-Sepharose, affinity chromatography on Affi-gel blue and chromatography on a Mono-Q anion-exchange column. On the Mono-Q column, the enzyme aldehyde dehydrogenase (ALDH) resolved into two activity peaks designated as ALDH1 and ALDH2. The enzymes ALDH1 and ALDH2 were purified about 114- and 65-fold, respectively. Gel filtration chromatography of the partially purified native enzyme on Sephacryl S-200 HR exhibited a molecular mass of about 108 kDa. Electrophoresis of the purified enzymes under nondenaturing conditions showed a single protein band. However, sodium dodecyl sulfate--polyacrylamide gel electrophorsis indicated three protein bands in the 55, 30, and 22 kDa molecular mass regions. Both enzymes exhibited a broad substrate specificity oxidizing a wide variety of aliphatic and aromatic aldehydes. The ALDH1 enzyme had a pI of 7.45 and exhibited a low Km (6.37 microM) for retinal, while the ALDH2 enzyme was found to have very low Km for acetaldehyde (0.98 microM). Based on its kinetic properties, it is suggested that the ALDH1 enzyme may be the primary enzyme for oxidizing retinal to retinoic acid in bovine kidney.

Cloning of a cDNA encoding rat aldehyde dehydrogenase with high activity for retinal oxidation

Retinoic acid (RA), an important regulator of cell differentiation, is biosynthesized from retinol via retinal by a two-step oxidation process. We previously reported the purification and partial amino acid (aa) sequence of a rat kidney aldehyde dehydrogenase (ALDH) isozyme that catalyzed the oxidation of 9-cis and all-trans retinal to corresponding RA with high efficiency [Labrecque et al. Biochem. J. 305 (1995) 681-684]. A rat kidney cDNA library was screened using a 291-bp PCR product generated from total kidney RNA using a pair of oligodeoxyribonucleotide primers matched with the aa sequence. The full-length rat kidney ALDH cDNA contains a 2315-bp (501 aa) open reading frame (ORF). The aa sequence of rat kidney ALDH is 89, 96 and 87% identical to that of the rat cytosolic ALDH, the mouse cytosolic ALDH and human cytosolic ALDH, respectively. Northern blot and RT-PCR-mediated analysis demonstrated that rat kidney ALDH is strongly expressed in kidney, lung, testis, intestine, stomach and trachea, but weakly in the liver.

A novel isoenzyme of aldehyde dehydrogenase specifically involved in the biosynthesis of 9-cis and all-trans retinoic acid

The pleiotropic effects of retinoids are mediated by two families of nuclear receptors: RAR (retinoic acid receptors) and RXR (retinoid X receptors). 9-cis-Retinoic acid is a specific ligand for RXR receptors, whereas either 9-cis- or all-trans-retinoic acid activates the RAR receptor family. The existence of RXRs suggests a new role for isomerization in the biology of retinoic acid. We report here the identification of an aldehyde dehydrogenase in the rat kidney that catalysed the oxidation of 9-cis- and all-trans-retinal to corresponding retinoic acids with high efficiency, 9-cis-retinal being 2-fold more active than all-trans-retinal. Based on several criteria, such as amino acid sequence, pH optimum, and inhibition by chloral hydrate, this enzyme was found to be a novel isoenzyme of aldehyde dehydrogenase. 9-cis-Retinol, the precursor for the biosynthesis of 9-cis-retinal was identified in the rat kidney. The occurrence of endogenous 9-cis-retinol and the existence of specific dehydrogenase which participates in the catalysis of 9-cis-retinal suggest that all-trans-retinoi(d) isomerization to 9-cis-retinoi(d) occurs at the retinol level, analogous to all-trans-retinol isomerization to 11-cis-retinol in the visual cycle.

Purification and partial characterization of a rat kidney aldehyde dehydrogenase that oxidizes retinal to retinoic acid

A NAD-dependent aldehyde dehydrogenase (EC 1.2.1.3) which catalyzes the oxidation of retinal to retinoic acid was purified to homogeneity from rat kidney by using Affi-Gel blue affinity chromatography and chromatofocusing, followed by Mono-Q anion-exchange chromatography. The apparent molecular weight of the native enzyme determined by size-exclusion fast protein liquid chromatography was 140,000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis gave a subunit molecular weight of 53,000. The isoelectric point as measured by chromatofocusing was 8.5. The enzyme also catalyzed the oxidation of acetaldehyde, but showed much lower Km value for the retinal substrate. We suggest that aldehyde dehydrogenase found in the kidney may be a specific retinal dehydrogenase, involved in vitamin A metabolism.

Dietary restriction reduces the incidence of NMU-induced mammary tumors and alters retinoid tissue concentrations in rats

Previous studies suggested a relationship between dietary restriction (DR) effects on mammary carcinogenesis and DR effects on liver retinoids. Therefore, in this study, retinoid concentrations were measured by high-performance liquid chromatography in the plasma, liver, and peripheral organs of DR rats with chemically induced carcinogenesis. Rats were injected with N-methyl-N-nitrosourea (MNU) and maintained on graded levels of DR (reduction of 10-40% from energy ingested by control animals with free access to food). Mammary tumor incidence and multiplicity induced by MNU were reduced in relation to the degree of DR, with virtual prevention occurring at 30% and 40% DR. Total hepatic retinoid concentrations (retinol + retinyl esters) were significantly greater in rats given MNU and subjected to DR, but liver total retinoid content was comparable between the groups. However, plasma retinol concentrations were significantly lower in DR rats than in controls given the carcinogen without DR. Retinoid concentrations were also elevated in adipose tissue, lungs, and intestine of DR rats, while renal concentrations remained unaltered. Retinoid concentrations in mammary glands and mammary tumors were similar in all groups. Thus, in DR rats, vitamin A concentrations in liver and other target tissues are maintained or increased despite decreases in plasma. It remains to be investigated whether these alterations in retinoid content have any relationship to the cancer-preventive effect of DR.

Effect of dietary restriction on hepatic vitamin A content in aging rats

The size and number of fat-storing cells (FSC), considered to be the main liver storage site of vitamin A, as well as hepatic vitamin A content, were studied in aging female Sprague-Dawley rats subjected soon after weaning to dietary restriction (R), that is, 60% of food consumed by their ad libitum-fed controls (A). In A or R rats, the FSC index (number of cells per 1000 hepatocytes) and volume density (% of hepatic volume) were increased significantly at 24-27 months compared with the younger age groups. The lipocyte index and volume density were also found to be significantly higher, after the first year, in R rats when compared to corresponding age-matched A controls. An increase in total vitamin A content was also noted with age in both groups. R rats exhibited higher retinol, retinyl ester, and total retinoid content than their corresponding controls, but the differences were statistically significant only at 12-14 and 24-27 months. These results indicate that, during aging, dietary restriction markedly increases vitamin A content in liver tissue, a change that may be relevant to the beneficial effect of this dietary manipulation on liver function.

Effects of retinoic acid on the concentrations of radioactive metabolites of retinol in tissues of rats maintained on a retinol-deficient diet

The effects of feeding retinoic acid for 2 and 6 days on the metabolism of labeled retinol in tissues of rats maintained on a vitamin A deficient diet was studied. The metabolites of retinol were analyzed by high performance liquid chromatography. Feeding retinoic acid for 2 days significantly reduced the blood retinol and retinyl ester levels without affecting the vitamin A content of the liver. In intestine and testis the content of labeled retinoic acid was decreased significantly by dietary retinoic acid. Addition of retinoic acid to the diet for 6 days resulted, in addition to decreased blood retinol and retinyl ester values, in an increase in the retinyl ester values in the liver. The accumulation of retinyl ester in the retinoic acid fed rat liver was accompanied by an absence of labeled retinoic acid. Kidney tissue was found to contain the highest levels of labeled retinoic acid, retinol, and retinyl esters; dietary retinoic acid did not alter the concentrations of these retinoids in the kidney during the experimental period. Since kidney retained more vitamin A when the liver vitamin A was low and also dietary retinoic acid did not affect the concentrations of radioactive retinoic acid in the kidney, it is suggested that the kidney may play a major role in the production of retinoic acid from retinol in the body.

Inhibition of growth of established N-methyl-N-nitrosourea-induced mammary cancer in rats by retinoic acid and ovariectomy

Retinoids are effective in the prevention of N-methyl-N-nitrosourea-induced mammary carcinoma; retinoids and hormonal therapy exert synergy in cancer prevention. In this study, we examined the effects of the dietary supplementation with all-trans retinoic acid (RA) alone or in combination with ovariectomy on the growth of established N-methyl-N- nitrosourea-induced mammary carcinomas in rats. In the first experiment, animals (n = 13) were entered in each of the following treatment groups when their tumors reached 2 cm in diameter: 1, control diet; 2, RA 300 mg/kg diet; 3, ovariectomy (OVX); 4, RA 300 mg/kg diet plus OVX. Animals were sacrificed after 28 days of therapy. In the RA-supplemented animals, tumor progression was less than in the control group without signs of toxicity as assessed by total and individual tumor surface area and weight, and animal weight. OVX produced tumor regression that was not enhanced by the addition of RA. In a second experiment, RA 65- and 130-mg/kg diets were dissolved in corn oil with antioxidants prior to mixing to the diet to improve biodisponibility. This resulted in overall stabilization of tumor growth by RA addition to the diet at either of the 2 doses utilized; the addition of RA 65 mg/kg diet did not modify tumor regression induced by OVX. In conclusion, the dietary supplementation with RA decreased the progression or stabilized the growth of the majority of tumors and only rarely (6%) induced tumor regression; no additive or synergistic effects were found with the combination of RA and ovariectomy.

Metabolism of retinol and retinoic acid in N-methyl-N-nitrosourea-induced mammary carcinomas in rats

This study was conducted to examine the in vivo uptake and metabolism of natural retinoids by N-methyl-N-nitrosourea-induced mammary carcinomas. In this study, endogenous retinol and retinyl esters were present in normal mammary epithelial cells, but were undetectable in N-methyl-N-nitrosourea-induced mammary carcinomas in rats as determined by high-pressure liquid chromatography. No differences were found in plasma levels of retinol, in liver retinyl esters, or total content of vitamin A between tumor-bearing and control animals. Administered labeled retinol was taken up and esterified by normal mammary epithelial cells. Tumor-bearing rats were given injections i.p. of either [3H]retinol or [3H]retinoic acid. Radioactivity increased progressively with time in liver and other tissues except in breast tumor, where the uptake fluctuated over the 8 days after the injection of [3H]retinol; in mammary tumors practically no metabolism of [3H]retinol occurred, while in other tissues extensive esterification was detectable. In contrast, in animals given injections of [3H]retinoic acid, the uptake and metabolism of the label in the breast tumors paralleled with those found in other tissues. Neither the activity of acyl coenzyme A:retinol acyl transferase nor the activity of retinyl ester hydrolase was altered in the mammary tumor compared to the normal mammary gland. On the other hand, a significant decrease in the retinal oxidase activity was found in tumor tissue compared to normal mammary tissue. Since no esterification of [3H]retinol occurred in vivo despite the presence of acyl coenzyme A:retinol acyl transferase activity, it is possible that a specific defect in the cellular uptake of retinol may exist in N-methyl-N-nitrosourea-induced mammary carcinomas.

Properties of retinal-oxidizing enzyme activity in rat kidney

An enzyme activity which converts retinal to retinoic acid was found in the cytosol of rat kidney. The oxidation of retinal was pH-, temperature-, time- and protein-dependent. Under the assay conditions employed, the oxidase activity had an apparent Km of 125 microM toward all-trans retinal. n-Propylgallate, butylated hydroxytoluene and quinacrine inhibited the reaction. The inhibition caused by quinacrine can be partly reversed by FAD. p-Hydroxymercuribenzoate, a sulfhydryl cross-linking agent, was a potent inhibitor. 4'-(9-Acridinylamino)methanesulfon-anisidide, an inhibitor of aldehyde oxidase, inhibited the reaction by 77% at a concentration of 3 mM. All-trans retinal reversed the inhibition caused by acetaldehyde and 2-aminobenzaldehyde. Retinol inhibited the reaction, but retinoic acid did not. The specific activity of the enzyme was increased by vitamin A deficiency. These data indicate that retinal-oxidizing enzyme activity found in the kidney is a sulfhydryl flavoprotein and its activity is dependent on the vitamin A levels of the tissues.

Enzymatic oxidation of all-trans retinal to retinoic acid in rat tissues

The 100,000 x g supernatant (cytosolic) fraction of rat tissue homogenates catalyzes the oxidation of all-trans retinal to retinoic acid. Kidney, testis, and lung were the most active of the tissues examined. The presence of enzyme activity in liver and intestine could be detected only when a substrate concentration beyond the saturation point for retinal reductase was used. Spleen, brain, and plasma had no activity. Boiled supernatants did not catalyze the reaction. The enzymatic product was chemically and physically identified as retinoic acid. The cytosol of kidney tissue also catalyzed the conversion of retinol to retinoic acid. These data indicate that kidney tissue has the highest retinal oxidase activity and suggest that it may play a major role in the oxidative metabolism of retinol in the body.

Metabolism of all-trans-retinol and all-trans-retinoic acid in rabbit tracheal epithelial cells in culture

As reported previously squamous cell differentiation of rabbit tracheal epithelial (RTE) cells in culture is a multi-step process. This program of differentiation is inhibited by retinoic acid and retinol; retinoic acid is about 100 times more effective than retinol. To examine the metabolism of these agents in this in vitro model system, RTE cells were grown in the presence of all-trans-[3H]retinol or all-trans-[3H]retinoic acid and their metabolites analyzed by high-pressure liquid chromatography. RTE cells converted most of the retinol to retinyl esters, predominantly retinyl palmitate. A small fraction was metabolized to polar compounds, one of which coeluted with retinoic acid. After methylation this compound eluted as 13-cis-methyl retinoate and as all-trans-methyl retinoate. Conversion to 13-cis-retinol was also observed. All-trans-retinoic acid was rapidly taken up by RTE cells and converted to more polar (peak 1) and less polar (peak 3) metabolites. A proportion of all-trans-[3H]retinoic acid was metabolized to 13-cis-[3H]retinoic acid. These metabolic reactions appeared to be constitutive and were not induced by pretreatment with retinoic acid. The peak 1 metabolites were rapidly secreted into the medium whereas the peak 3 metabolites were retained by the cells and were not detected in the medium. Alkaline hydrolysis of the metabolites in peak 3 yielded retinoic acid, indicating the formation of retinoyl derivatives. Our results establish that RTE cells can convert all-trans-retinol to 13-cis-retinol and retinoic acid. RTE can metabolize all-trans-retinoic acid to 13-cis-retinoic acid and to an unidentified ester of retinoic acid.

Plasma levels of retinol in cancer patients supplemented with retinol

Previous studies have indicated that plasma levels of retinol are decreased in some cancer patients and that lower levels of retinol could be associated with a poor response to chemotherapy. This pilot study was conducted to determine whether it is possible to increase plasma levels of retinol in cancer patients by supplementation with retinol. Plasma levels of retinol were measured by high-performance liquid chromatography in 46 patients treated with chemotherapy for various malignancies and in 43 control individuals; cancer patients were supplemented orally either with 25,000 or 50,000 IU of retinol daily during up to 3 months. Initial levels of retinol were lower in cancer patients than in the control group; the decrease was significant in women with liver metastases but not in men. Women supplemented with 25,000 IU had a significant increase of their retinol levels after 1 month but this effect was not maintained during continued supplementation; in women receiving 50,000 IU daily, a sustained increase in retinol level was maintained during the 3 months of supplementation. In men, a similar trend was produced by the supplementation but the increases were not significant. Retinol levels decreased to initial levels within 1 month of discontinuation of supplementation, indicating the need for continuous supplementation.

Cytoplasmic retinoic acid-binding protein in retinoic acid-resistant human breast cancer sublines

Two sublines resistant to the growth-inhibitory effects of retinoic acid (RA) have been isolated from the parental Hs578T wild-type (W.T.) human breast cancer cell line. These sublines (Hs578T-R-1 and Hs578T-R-2) have been growing normally in 10 microM RA during more than 18 months, and their RA-resistant phenotype has remained stable after the removal of RA. The resistance is specific for RA, since their growth is still inhibited by retinol. The intracellular incorporation of [3H]RA is not deficient in the RA-resistant sublines. Cytoplasmic RA-binding protein (cRABP) is present in Hs578T-R-1 and in Hs578T-R-2 and is not different in terms of maximum binding capacity or binding affinity from cRABP in Hs578T (W.T.). These results indicate that RA resistance in these sublines is not secondary to a defect of RA uptake or of binding of RA to cRABP; the resistance may result from a defect distal to binding to cRABP, or alternatively, cRABP may not mediate this effect of RA.

Metabolism of [11-3H]retinyl acetate in liver tissues of vitamin A-sufficient, -deficient and retinoic acid-supplemented rats

A study was conducted on the incorporation of [11-3H]retinyl acetate into various retinyl esters in liver tissues of rats either vitamin A-sufficient, vitamin A-deficient or vitamin A-deficient and maintained on retinoic acid. Further, the metabolism of [11-3H]retinyl acetate to polar metabolites in liver tissues of these three groups of animals was investigated. Retinol metabolites were analyzed by high-performance liquid chromatography. In vitamin A-sufficient rat liver, the incorporation of radioactivity into retinyl palmitate and stearate was observed at 0.25 h after the injection of the label. The label was further detected in retinyl laurate, myristate, palmitoleate, linoleate, pentadecanoate and heptadecanoate 3 h after the injection. The specific radioactivities (dpm/nmol) of all retinyl esters increased with time. However, the rate of increase in the specific radioactivity of retinyl laurate was found to be significantly higher (66-fold) than that of retinyl palmitate 24 h after the injection of the label. 7 days after the injection of the label, the specific radioactivity between different retinyl esters were found to be similar, indicating that newly dosed labelled vitamin A had now mixed uniformly with the endogenous pool of vitamin A in the liver. The esterification of labelled retinol was not detected in liver tissues of vitamin A-deficient or retinoic acid-supplemented rats at any of the time point studied. Among the polar metabolites analyzed, the formation of [3H]retinoic acid from [3H]retinyl acetate was found only in vitamin A-deficient rat liver 24 h after the injection of the label. A new polar metabolite of retinol (RM) was detected in liver of the three groups of animals. The formation of 3H-labelled metabolite RM from [3H]retinyl acetate was not detected until 7 days after the injection of the label in the vitamin A-sufficient rat liver, suggesting that metabolite RM could be derived from a more stable pool of vitamin A.

Restoration of anchorage regulation in transformed cells by retinoic acid (RA) is independent of the presence of cytoplasmic RA-binding proteins

In an attempt to analyse the cause-effect relationship between anchorage-independent growth (a property which correlates best with in vivo tumorigenicity) and a set of other common transformation-related properties, the effect of retinoic acid (RA) treatment on six unrelated transformed cell lines (including DNA tumor virus, retrovirus, and spontaneously transformed cells) were studied. The data show that the changes in morphology and cellular orientation in culture, loss of cell surface fibronectin, disruption of actin microfilaments, increased hexose uptake, loss of density-dependent growth, and decreased binding of EGF, properties which are often associated with oncogenic transformation of cells, are dissociable from one another and from anchorage-independent growth. RA appears to interfere with anchorage-independent growth of all the retrovirus and spontaneously transformed cell lines (responsive cells) that we examined; however, such treatment failed to inhibit anchorage-independent growth in both of the DNA tumor virus-transformed cell lines (non-responsive cells) that we used in the present study. The presence of RA-binding proteins in both responsive and non-responsive cells suggests that the mechanism of RA action for the inhibition of anchorage-independent growth in transformed cells may be independent of the presence of such cytoplasmic proteins. Finally, the present study clearly indicates that the use of RA treatment, like partial transformation mutants of oncogenic viruses, can be a novel approach in analysing the general mechanism by which transformed cells grow without anchorage.

Effect of 2-alkanols on the separation of geometric isomers of retinol in non-aqueous high-performance liquid chromatography

The effects of 2-alkanols as mobile phase modifiers on the resolution of 11-cis-, 13-cis-, 9-cis- and all-trans-retinol in high-performance liquid chromatography were studied. Partisil-10-ODS and Zorbax CN columns were used in series. The retentions of 9-cis-and all-trans-retinol were significantly influenced by the presence of long-chain 2-alkanols in the mobile phase. Baseline separation of 9-cis-and all-trans-retinol was achieved when 1% 2-heptanol in hexane was used as the eluent. On the other hand, the separation of 11-cis-from 13-cis-retinol required 5% dioxane in hexane. The method is applicable to the separation of retinol isomers present in biological samples. Analysis of normal rat liver lipids showed the presence of a small amount of 13-cis-retinol in addition to all-trans-retinol.

Separation and estimation of retinyl fatty acyl esters in tissues of normal rat by high-performance liquid chromatography

A reversed-phase high-performance liquid chromatography system for the complete separation of naturally occurring retinyl fatty acyl esters (RFAE) is described. The sensitivity of the method allows the detection of as little as 40 pmol of the various RFAE. The procedure was applied to the separation and estimation of endogenous RFAE present in tissues of normal rats; in addition, the incorporation of [3H]retinyl acetate into RFAE was also investigated. Retinyl palmitate is the major fatty acyl ester (79%) present endogenously in various tissues. However, eight other RFAE were also present in some tissues. At 24 hours after the injection of the label, radioactivity present in retinol and its metabolites was recovered mainly in liver tissue followed by kidneys, adrenals, lungs, intestine, trachea, testis, blood, heart and spleen. However, it was found that, in liver tissue, the specific radioactivity (dpm/nmol) of several RFAE was greater than that of retinyl palmitate (retinyl laurate 66-fold, retinyl pentadecanoate 5-fold, retinyl palmitoleate 4-fold).

Ion-pair high-pressure liquid chromatography of cis-trans isomers of retinoic acid in tissues of vitamin A-sufficient rats

Naturally occurring retinoids were separated by reversed-phase high-pressure liquid chromatography on an octadecylsilane column eluted with acetonitrile-potassium phosphate buffer (pH 7.2) mixtures. The order of elution from a mixture of 500 ng each of the following standards was 4-oxo retinoic acid (RA), retinyl phosphate (RP), 13-cis RA, all-trans RA, retinol, retinal, retinyl acetate, anhydroretinol, and retinyl palmitate. This method was employed to investigate the cis-trans isomerization of RA and its metabolism in vitamin A-sufficient male rats. Rats (200 g) were injected intraperitoneally with 50 muCi of either [10-3H]-all-trans RA (5.4 micrograms) or [11-3H]-13-cis RA (8.8 micrograms) and killed after 0.5 and 3 hr. Blood, liver, kidney, small intestines, and testes were removed and lyophilized. All-trans RA was converted at 0.5 hr after injection to 13-cis RA in all the tissues examined, with the exception of the small intestine; the conversion ranged from 2.4 to 6.9% of the total radioactivity. In addition, all-trans RA was converted to metabolites (17.5--47.7%) of greater polarity than 4-oxo RA. After 3 hr, most of the radioactivity (75--90%) was found in the highly polar metabolites. 13-cis RA was also partially isomerized to the all-trans RA and to the highly polar metabolites by 0.5 and 3 hr after injection. Appreciable radioactivity (10--41%) still resided in the 13-cis RA fraction after 3 hr. These results indicate that 13-cis RA is partially isomerized to all-trans RA and that all-trans RA is rapidly metabolized to highly polar compounds in tissues of vitamin A-sufficient rats.

Chemical and biological studies on 5,6-epoxyretinol, retinol, and their phosphoryl esters

Studies are reported on chemical synthesis, ultraviolet absorption spectral characteristics, and mass spectral fragmentation of 5,6-epoxyretinol and 5,6-epoxyretinylphosphate. These compounds were separated from each other and from other retinoids by a reverse phase high pressure liquid chromatographic system. A comparative study on the lability to acid of 5,6-epoxyretinylphosphate and retinylphosphate was conducted. The retroretinoid anhydroretinol is formed chemically from retinylphosphate by acid hydrolysis and biologically from retinal in cultured, spontaneously-transformed mouse fibroblasts, 3T12 cells. Similarly, acid hydrolysis of 5,6-epoxyretinylphosphate (absorption maxima 324, 310, 296 nm) in methanol yielded a low polarity retinoid with absorption maxima at 364, 346, and 330 nm, similar to the absorption spectra of retrovitamin A1 and retrovitamin A2. Mass spectral analysis was found to be in agreement with a retrostructure and permitted identification of the compound as a methoxyretrovitamin A1 methyl ether. A similar retroretinoid was formed biologically from 5,6-epoxyretinol in spontaneously-transformed mouse 3T12 cells. Thus, it appeared that these cells have the ability to convert the primary alcohols into retroretinoids, which are also formed by acid treatment of the phosphate esters. The adhesive properties of 3T12 cells were highly enhanced by culturing in the presence of 10(-6) to 10(-5) M 5,6-epoxyretinol or -retinoic acid, in analogy with the response of these cells to the parent retinoids. Moreover, in another test of biological activity, 5,6-epoxyretinylphosphate functioned as a highly active acceptor of [14C]D-mannose from GDP-[14C]mannose in a reaction catalyzed by rat liver membranes. Thus, 5,6-epoxyretinoids appear to be as active as the parent retinoids in these in vitro tests of biological activity, even though they do not replace vitamin A in its growth function in vivo.

The biosynthesis of a mannolipid containing a metabolite of retinoic acid by 3T12 mouse fibroblasts

Retinol and retinoic acid (RA) increase the adhesive properties of spontaneously transformed mouse fibroblasts (BALB/c 3T12-3 cells) and the incorporation of [2-3H]mannose into cellular glycoconjugates. Therefore we searched for a mannolipid of retinoic acid similar to mannosylretinylphosphate (MRP) in these cells. Radioactively labeled RA was incorporated into a compound of chromatographic characteristics similar to those of standard MRP. This metabolite contained the same 3H:14C ratio as the precursor [11, 12-3H, 15-14C]retinoic acid, demonstrating that no decarboxylation had occurred. A doubly labeled mannolipid was obtained from cells incubated with [2-3H]mannose and [15-14C]retinoic acid. This mannolipid was readily cleaved by mild acid, yielding [3H]mannosephosphate and a compound that migrated as standard anhydroretinol on thin layer of silica gel in toluene:chloroform:methanol (4:1:1) at Rf 0.93. Standard all trans-MRP yields all-trans-anhydroretinol under these conditions. An ion pair reverse phase HPLC system was developed to further characterize the mannolipids obtained from retinol and retinoic acid in 3T12 cells. [15-3H]Retinol and [15-14C]retinoic acid were incorporated into mannolipids that cochromatographed upon HPLC with standard MRP. The mixture of the [15-3H]retinol and [15-14C]retinoic acid derived mannolipids was subjected to mild acid hydrolysis, after purification by HPLC. Nearly 100% of the compounds was hydrolyzed, yielding all-trans-[3H]anhydroretinol and a 14C]labeled product which was eluted from HPLC as a slightly more polar compound than all-trans-anhydroretinol. The retinoic acid-derived mannolipid (MXP) represented approximately 4% of the total radioactivity in the methanolic extract of 3T12 cells incubated for 20 hours in the presence of labeled retinoic acid. However, if the cells were incubated for an additional 20 hours in the absence of the radioactive precursor, MXP represented 40% of the total extracted radioactivity. These results demonstrate that 3T12 cells synthesize mannosylretinylphosphate from retinol and a mannosylretinoidphosphate (MXP) from retinoic acid. These results exclude the possibility of a reduction of retinoic acid to retinol, but suggest that a closely related compound is formed from RA and that this retinol-like compound (X) is incorporated into MXP.

Retinoid metabolism and mode of action

Vitamin A and its derivaties (retinoids) are necessary for the maintenance of normal phenotypic expression. An attempt at understanding the biochemical role of vitamin A had led to the demonstration of a new pathway for retinol. In this pathway, vitamin A is phosphorylated to retinylphosphate (RP), which is then glycosylated to retinylphosphatemannose (MRP). These two derivatives have been found in a variety of tissues in vivo and in vitro and appear to be ubiquitous components of cellular membranes. The suggestion has been made that MRP may mediate specific cellular interactions by functioning as a lipid intermediate in the biosynthesis of specific glycoconjugates. A study on spontaneously-transformed mouse fibroblasts (Balb/c 3T12-3 cells) has shown that retinoids are active in increasing the adhesive properties of these cells as measured in an EDTA-mediated detachment assay. Various retinoids were tested for their activity in the adhesion test, and this activity was found to correlate well with their biological activity in maintaining the expression of normal epithelial differentiation in other systems. Retinoic acid, 5,6-epoxyretinol, and 5,6-epoxyretinoic acid were the most active compounds. Retinoids without biological activity in other systems were also inactive in inducihg adhesive properties of 3T12-3 cells. Among these were the synthetic derivatives of retinol, anhydroretinol, and 4,5-monoeneperhydroretinol, and the phenyl derivative of retinoic acid. Beta-Ionone, abscisic acid, and juvenile hormone, which are devoid of vitamin A activity in other systems, were also inactive in this system. Retinoid-induced changes in cell surface proteins were investigated but no difference in 125I-fibronectin (MW 220,000) was detectable between retinoid-treated and untreated cells. However, these cells synthesized retinylphosphatemannose and the incorporation of 2-3H-mannose into a specific glycoprotein (gp 180) was found to be enhanced specifically by retinoid treatment. Investigations of the involvement of gp 180 in adhesion are in progress.