Elevated plasma homocysteine levels in patients on isotretinoin therapy for cystic acne

Use of Oral Supplements and Topical Adjuvants for Isotretinoin-Associated Side Effects: A Narrative Review

Acne is a chronic inflammatory disease of the pilosebaceous unit with a multifactorial etiology and is one of the most common conditions treated by dermatologists and primary care physicians. Within an extensive and evolving treatment landscape, oral isotretinoin has demonstrated efficacy for treatment of severe, recalcitrant acne. Several side effects of isotretinoin have been reported, including laboratory abnormalities, mucocutaneous, and musculoskeletal effects, which may reduce compliance and patient satisfaction with treatment. In this narrative review, we aim to review the efficacy and safety profile of oral supplements or topical adjuvant therapies in mitigating isotretinoin-associated mucocutaneous and musculoskeletal side effects. Oral supplements reviewed include omega-3 fatty acids, vitamin E, folic acid and vitamin B12, antihistamines, l-carnitine, biotin, and combined oral supplements. Topical adjuvants include a hyaluronic acid, biosaccharide gum-2, and glycerine gel-cream; a nongreasy, noncomedogenic, fragrance-free moisturizing cream; dexpanthenol; trichloroacetic acid; and a combination cream. Most of the supplements and topical adjuvants demonstrated efficacy with an adequate level of supporting evidence and no reported adverse events, indicating an adequate safety profile. Patients on isotretinoin may benefit from using oral supplements and topical adjuvants to minimize primarily mucocutaneous side effects, increase adherence to treatment, and thereby improve overall outcomes.

A Young Patient Presenting with Dilated Cardiomyopathy and Renal Infarction during Treatment with Isotretinoin: Mere Coincidence or Serious Side Effect of a Drug Commonly Used in Adolescence?

Isotretinoin or 13-cis-retinoic acid (RA) is one of the most effective and widely used drugs for the treatment of severe acne vulgaris. Despite being deemed safe, no definite consensus has been reached on the cardiovascular risk of RA derivatives. We report a case of heart failure due to dilated cardiomyopathy (DCM) and concomitant renal infarction occurring after 5 months of isotretinoin use in a previously healthy 18-year-old male. The patient, with a history of acne vulgaris, presented to our emergency department with left iliac fossa pain and effort dyspnea. A trans-thoracic echocardiogram showed DCM and severely reduced left ventricle ejection fraction (LVEF: 29%). During hospitalization, a total body computed tomography (CT) showed an ischemic lesion in the left kidney. Ischemic, autoimmune, infective, and heritable causes of DCM were ruled out. Cardiac magnetic resonance (CMR) evidenced LV circumferential mid-wall late gadolinium enhancement. Heart failure therapy was promptly started and up-titrated, but only poor LVEF improvement was detected overtime. Our case aims to raise awareness on rare life-threatening cardiovascular events possibly associated with isotretinoin use. To the best of our knowledge, this is the first described case of renal thromboembolism and severe DCM leading to implantable cardioverter-defibrillator (ICD) implantation occurring during isotretinoin treatment.

Association between homocysteine and nonalcoholic fatty liver disease: Mendelian randomisation study

BACKGROUND

Many observational studies explore the relationship between homocysteine (Hcy) and nonalcoholic fatty liver disease (NAFLD), whereas the causality of this association remains uncertain, especially in European populations. We performed a bidirectional Mendelian randomisation study to elucidate the causal association between Hcy and NAFLD. Furthermore, we explored the relationship of Hcy with liver enzymes, including alkaline phosphatase (ALP), alanine aminotransferase (ALT) and aspartate aminotransferase (AST).

METHODS

Two-sample Mendelian randomisation study was conducted. Summary statistics for Hcy were obtained from a genome-wide association studies (GWAS) meta-analysis comprising 44,147 subjects. Summary-level data for NAFLD were acquired from a GWAS meta-analysis of 8434 cases and 770,180 noncases and another GWAS meta-analysis of 1483 cases and 17,781 noncases. Summary-level data for three liver enzymes were available from the UK Biobank.

RESULTS

Genetic associations of Hcy concentrations with NAFLD and liver enzymes were observed. Genetically predicted higher Hcy concentrations were consistently associated with an increased NAFLD risk in two data sources. The combined odds ratio of NAFLD was 1.25 (95% confidence interval [CI], 1.05-1.45) per SD increase in Hcy concentrations. Genetically predicted higher Hcy concentrations showed significant association with ALP (Beta .69; 95% CI, 0.04-1.34), ALT (Beta 0.56; 95% CI, 0.15-0.97) and AST levels (Beta .57; 95% CI, 0.10-1.04). Genetic liability to NAFLD was not associated with Hcy concentrations.

CONCLUSIONS

This study has clinical implications as it indicates that increased Hcy concentrations increase the relevant liver enzymes and may play a role in NAFLD risk in European populations.

Adverse Events in Isotretinoin Therapy: A Single-Arm Meta-Analysis

Isotretinoin (ISO) is an oral prescription-only retinoid, well known for its acne-treating effect. However, it affects a substantial number of human cell types, causing a broad spectrum of adverse effects. The purpose of this study is to establish the isotretinoin therapy adverse events among human clinical trials and their prevalence. Two authors (J.K., J.L.) systematically performed the literature review and assessment from December 2021-February 2022. Three databases (PubMed, ClinicalTrials, and Cochrane Library) were searched using the following terms: "isotretinoin acne vulgaris" for published studies in English from 1980-2021. Finally, 25 randomized controlled clinical trials (RCTs) and five open-label clinical trials provided 3274 acne vulgaris suffering patients. Isotretinoin therapy affects almost all of the systems in the human body, causing numerous adverse events. However, they mainly concern mild mucocutaneous conditions (severe cases are rare) and represent individual responses to a drug. In addition, all adverse events are reversible and can be avoided by specific preparations.

Isotretinoin and neuropsychiatric side effects: Continued vigilance is needed

Background

Isotretinoin (13-cis-retinoic acid, marketed under the names Accutane, Roaccutane, and others) is an effective treatment for acne that has been on the market for over 30 years, although reports of neuropsychiatric side effects continue to be reported. Isotretinoin is an isomer of the active form of Vitamin A, 13-trans-retinoic acid, which has known psychiatric side effects when given in excessive doses, and is part of the family of compounds called retinoids, which have multiple functions in the central nervous system.

Methods

The literature was reviewed in pubmed and psychinfo for research related to isotretinoin and neuropsychiatric side effects including depression, suicidal thoughts, suicide, mania, anxiety, impulsivity, emotional lability, violence, aggression, and psychosis.

Results

Multiple case series have shown that successful treatment of acne with isotretinoin results in improvements in measures of quality of life and self esteem However, studies show individual cases of clinically significant depression and other neuropsychiatric events that, although not common, are persistent in the literature. Since the original cases of depression were reported to the United States Food and Drug Administration, numerous cases have been reported to regulatory agencies in the United Kingdom, France, Ireland, Denmark, Australia, Canada, and other countries, making isotretinoin one of the top five medications in the world associated with depression and other neuropsychiatric side effects. Clinicians are advised to warn patients of the risks of neuropsychiatric side effects with isotretinoin which may arise from the medication itself, and not just as a side effect of acne or youth.

Are plasma 25-hydroxyvitamin D and retinol levels and one-carbon metabolism related to metabolic syndrome in patients with a severe mental disorder?

There is a scarcity of studies assessing the influence of biomarkers in metabolic syndrome in psychiatric patients. Our aim was to correlate serum or plasma levels of 25-hydroxyvitamin D (25-OH-VD), retinol, vitamin B12 (VB12), folate and homocysteine (Hcy), with the metabolic status, in a sample of 289 outpatients with Schizophrenia or Bipolar Disorder. Logistic regression and multiple linear regressions were performed to assess the ability of biomarkers to predict the presence of MetS, the number of risk factors for MetS, and insulin resistance indexes (HOMA and QUICKI). Regarding the association between biomarkers and the QUICKI index, the model explained 6.8% of the variance, with folate and 25-OH-VD levels contributing significantly to the model. The model predicting the number of MetS risk factors was significant and explained 21.7% of the variance, being 25-OH-VD and retinol the statistically significant factors. As for the impact of biomarkers on MetS, the model was statistically significant, being 25-OH-VD and retinol levels the significant factors.  We report for the first time an association between MetS and both low 25-OH-VD and high retinol concentrations. Inflammation-related biomarkers may help identify patients with a high risk of MetS who might benefit from healthy lifestyle counselling and early intervention.

Efficacy of Oral Low-Dose Isotretinoin in the Treatment of Acne Vulgaris in Vietnam

BACKGROUND:

Oral isotretinoin is an effective therapy for acne. However, isotretinoin can induce hyperhomocysteinemia and decreased serum folic acid level, which may be a risk for cardiovascular disease and thrombosis, as well as psychoses. Besides, many recent types of research emphasise the safety and effects of the low dose isotretinoin therapy.

AIM:

The aim of our study was to evaluate the effect of the low-dose isotretinoin on the plasma homocysteine and serum folic acid level in the Vietnamese population.

METHODS:

We conducted a longitudinal study to evaluate the effectiveness of the low-dose therapy on the plasma homocysteine and serum folic acid level of 52 acne patients after 6-8-week treatment at University Medical Center Ho Chi Minh City, Viet Nam. Patients had moderate-severe acne with the prolonged course, and most of them had a scar.

RESULTS:

With a low dose of oral isotretinoin (0.37 ± 0.11 mg/kg/day), after 6-8-week treatment, patients dropped the severity of disease, increased the plasma homocysteine level and decreased the serum folic acid level with significant differences in comparison to those before treatment. However, these changes do not exceed the normal range.

CONCLUSION:

In overall, low dose isotretinoin treatment had effectiveness in decrease the severity of disease and no increasing the plasma homocysteine level as well as the serum folic acid level.

Unexpected drug-induced Raynaud phenomenon: Analysis from the French national pharmacovigilance database

OBJECTIVE

To estimate the association between exposure to medicinal products and Raynaud phenomenon.

METHODS

The study used the data of all adverse drug reactions notified to the French national pharmacovigilance database. All cases reported between 1st January 1995 and 10th December 2012 were selected. A case/non-case method was used to measure disproportionality of the association between drug exposure and Raynaud phenomenon. The cases concerned all observations involving Raynaud phenomenon. Non-cases comprised all other reports of adverse drug reactions over the same period.

RESULTS/DISCUSSION

Among the 307,128 adverse drug reaction reports selected from the French national pharmacovigilance database, 175 involved Raynaud phenomenon, most of them affecting women (61.1%). The mean age was 50.1 years, and 8% had a past medical history of Raynaud phenomenon. According to the summaries of product characteristics, 42.3% of these cases were exposed to drugs known to induce Raynaud phenomenon. Unexpected Raynaud phenomenons (unlisted in the summaries of product characteristics) were associated with exposure to drugs for which Raynaud phenomenons are published (interferons, ribavirin, gemcitabine) or for which Raynaud phenomenons are not published (hepatitis B vaccine, isotretinoin, leflunomide, hydroxycarbamide, rofecoxib, telmisartan, zolmitriptan).

CONCLUSION

The case/non-case method is usually used to generate signals. Further epidemiological studies are now necessary to confirm these findings.

Decreased vitamin B12 and folic Acid concentrations in acne patients after isotretinoin therapy: a controlled study

Background:

Oral isotretinoin treatment might influence the levels of vitamin B₁₂ and folic acid.

Aims and Objectives:

The aim of this study is to compare vitamin B₁₂ and folic acid levels in patients with moderate and severe acne vulgaris with those of the healthy control group and to investigate the effect of isotretinoin treatment on these vitamins.

Materials and Methods:

Patients who completed 6 months of isotretinoin therapy for moderate and severe forms of acne vulgaris and a control group consisting of healthy individuals between February 2011 and March 2012 were included in the study. Before isotretinoin therapy and at 6.- months of the therapy, serum vitamin B₁₂ and folic acid levels were measured. In the healthy control group, vitamin B₁₂ and folic acid levels were assessed only once.

Results:

In total, 120 patients with moderate and severe acne vulgaris who completed 6 months isotretinoin therapy and 100 healthy individuals who constituted the control group were included in the study. Pre-treatment vitamin B₁₂ values of the patient group were found to be statistically significantly higher (P = 0.002), but any statistically significant difference was not detected in folic acid measurements (P = 0.566). A statistically significant decrease was detected in post-treatment vitamin B₁₂ and folic acid levels (P < 0.05).

Conclusion:

Vitamin B₁₂/folic acid treatment should be given under medical surveillance before and during isotretinoin therapy. Supplementation of these vitamins should be recommended in cases of their deficiency, so as to decrease the risks of neuropsychiatric and occlusive vascular diseases.

Homocysteine imbalance: a pathological metabolic marker

Perturbations in methyl group metabolism and homocysteine balance have emerged over the past few decades as having defining roles in a number of pathological conditions. Numerous nutritional, hormonal, and genetic factors that are characterized by elevations in circulating homocysteine concentrations are also associated with specific pathological conditions, including cancer development, autoimmune diseases, vascular dysfunction, and neurodegenerative disease. Although much remains to be explored, our understanding of the relationship between disease, methyl balance, and epigenetic control of gene expression has steadily progressed. However, homocysteine balance and its role in health and disease are not as clearly understood. This review presents our current understanding of homocysteine metabolism and its link to specific pathologies.

Effect of isotretinoin treatment on plasma holotranscobalamin, vitamin B12, folic acid, and homocysteine levels: non-controlled study

Isotretinoin (Iso) has been used for the treatment of acne. Some previous studies reported elevated homocysteine (Hcy) levels after treatment with Iso. Some side effects have clinical presentations similar to vitamin B12, folic acid deficiencies, and hyperhomocysteinemia. In the present study we evaluated the plasma Hcy levels, the vitamins involved in its metabolism (vitamin B12 and folic acid), and holotranscobalamin (HoloTC), a transport system for vitamin B12 absorption in patients receiving Iso treatment for acne vulgaris. A total of 66 patients with acne vulgaris between the ages of 18 and 40 years were included. Screening for hemoglobin, creatinine, SGOT, SGPT, total cholesterol, triglycerides, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and very low-density lipoprotein cholesterol (VLDL-C), folic acid, vitamin B12, Hcy, and HoloTC were done just before initiation (pretreatment) and after four months of Iso treatment (posttreatment). Posttreatment vitamin B12, folic acid, and HoloTC levels were significantly lower while Hcy levels were significantly higher compared with initial values. Posttreatment total cholesterol, LDL-C, triglycerides, VLDL-C, SGPT, and SGOT levels were also higher, and HDL-C levels were lower compared with initial values while there was no change in hemoglobin levels during Iso treatment. We found that Iso usage might cause decreased vitamin B12, folic acid, and HoloTC. These Iso side effects might contribute to the missing link between Iso usage, hyperhomocysteinemia, and neuropsychiatric disorders. Trials may be made with the aim of demonstrating (clearly) if starting vitamin B12 and folic acid replacement therapies with Iso treatment initialization could be useful for preventing hyperhomocysteinemia and possibly related disorders.

Retinoic acid and affective disorders: the evidence for an association

OBJECTIVE

Isotretinoin (13-cis-retinoic acid), approved by the US Food and Drug Administration for the treatment of acne, carries a black box warning related to the risk of depression, suicide, and psychosis. Retinoic acid, the active form of vitamin A, regulates gene expression in the brain, and isotretinoin is its 13-cis isomer. Retinoids represent a group of compounds derived from vitamin A that perform a large variety of functions in many systems, in particular the central nervous system, and abnormal retinoid levels can have neurologic effects. Although infrequent, proper recognition and treatment of psychiatric side effects in acne patients is critical given the risk of death and disability. This article reviews the evidence for isotretinoin's relationships with depression and suicidality.

DATA SOURCES

The PsycINFO, MEDLINE, and PubMed searchable database indexes were searched for articles published in the English language from 1960 to June 2010 using the key words isotretinoin, retinoids, retinoic acid, depression, depressive disorders, and vitamin A. Evidence examined includes (1) case reports; (2) temporal association between onset of depression and exposure to the drug; (3) challenge-rechallenge cases; (4) class effect (other compounds in the same class, like vitamin A, having similar neuropsychiatric effects); (5) dose response; and (6) biologically plausible mechanisms.

STUDY SELECTION

All articles in the literature related to isotretinoin, depression, and suicide were reviewed, as well as articles related to class effect, dose response, and biologic plausibility.

DATA EXTRACTION

Information from individual articles in the literature was extracted, including number of episodes of depression, suicidality, suicide, psychosis, violence and aggression, past psychiatric history, time of onset in relation to isotretinoin usage, medication dosage, duration of treatment, and dechallenge and challenge history.

RESULTS

The literature reviewed is consistent with associations of isotretinoin administration with depression and with suicide in a subgroup of vulnerable individuals.

CONCLUSIONS

The relationship between isotretinoin and depression may have implications for a greater understanding of the neurobiology of affective disorders.

Decreased plasma folate concentration in young and elderly healthy subjects after a short-term supplementation with isotretinoin

BACKGROUND

In the last two decades, there has been an increasing use of isotretinoin (13-cis-retinoic acid or 13-CRA) for treatment of severe, and recently mild and moderate, acne in Westernized populations. Recent human and animal studies emphasized alterations caused by 13-CRA administration on folate-dependent, one-carbon metabolism. Folate deficiency and subsequent hyperhomocysteinemia increase the risk of degenerative diseases.

OBJECTIVES

We determine whether a short-term supplementation with 13-CRA alters folate status and homocysteinemia in young and elderly healthy human subjects.

METHODS

Twenty young and 20 elderly (age mean, 26.1 and 65.4 years, respectively) healthy male volunteers were supplemented with approximately 0.5 mg/kg/day of 13-CRA for 28 days. Fasting plasma concentrations of 13-CRA, 5-methyltetrahydrofolate (5-mTHF) as the main circulating form of folate, and homocysteine (Hcy), as well as haematologic parameters and biochemical markers of liver and renal function, were measured at baseline and at the end of supplementation. Statistical analyses were carried out using two-way anova and standard tests.

RESULTS

In both groups, isotretinoin supplementation caused a dramatic increase in the circulating concentration of 13-CRA and its derivatives. It also led to significant increases in serum triglyceride (P < 0.0001) and creatinine (P = 0.002) concentrations and gamma-glutamyltranspeptidase activity (P = 0.0001) and decrease in serum level of urea (P = 0.027). However, the latter four parameters remained within normal ranges. These changes were accompanied by a 17.7% and 13.5% decrease in the plasma level of 5-mTHF (P = 0.001) in the young and elderly volunteers, respectively. Supplementation with 13-CRA did not cause significant variations in their plasma Hcy concentration. However, the latter parameter seemed to respond differently in each group of age (P = 0.046).

CONCLUSIONS

Our data indicate that a 28-day supplementation with isotretinoin alters the plasma folate in young and old healthy individuals. This stresses the necessity of studying the long-term effects of retinoid therapy on folate status and homocysteinemia in acne patients, given that alteration in the latter parameters is known to increase the risk of degenerative diseases.

New Clinical Syndromes in Dermatology

Dermatologists are in the unique position to be able to diagnose serious systemic diseases through skin findings; in addition, cutaneous manifestations can be associated with internal symptoms and clarify the pathogenesis and treatment of challenging new syndromes. Calciphylaxix, now renamed Calcific Uremic Arteriolopathy, primarily affects patients with end-stage renal disease with concomitant hyperphosphatemia, increased calcium-phosphate product and hyperparathyroidism, skin biopsy and wound care are crucial parts of the diagnosis and treatment. Hyperhomocysteinemia may play a very important role in many cutaneous and systemic diseases including, chronic cutaneous wounds, systemic lupus erythematosus, Behcet's disease and psoriasis. Through a skin biopsy and biochemical analysis of the proteoglycans accumulation it may be possible to diagnose a new systemic mucinosis and prevent sudden death in patients with severe mitral valve prolapse. Nephrogenic Fibrosing Dermopathy is a newly described fibrosing disorder occurring in patients with end stage renal disease, the etiology and pathogenesis are still unknown, and the ultimate course of this disease has not been defined.

Reduction of all-trans-retinoic acid–induced teratogenesis in the rat by glycine administration

BACKGROUND

Prenatal rat embryo exposure to retinoids induces severe malformations in various organs; the most active and teratogenic metabolite is all-trans-retinoic acid (atRA). The mechanisms of this embryopathy are only partly known. In the present study, the influence of glycine on the teratogenicity of atRA was investigated.

METHODS

Embryos from 5 groups of white rats were studied: Group 1 remained untreated; Group 2 received glycine 2% in drinking water ad libitum from the first gestational day (GD 1); Group 3 was administered vehicle (corn oil); Group 4 was treated with atRA (50 mg/kg of body weight) injected (IP); and Group 5 was treated with atRA (50 mg/kg of body weight IP) plus glycine 2% in drinking water ad libitum from GD 1. atRA was administrated daily from GD 8-10. Dams were killed on the 21st day of pregnancy, and their fetuses were examined to detect external, visceral, and skeletal malformations.

RESULTS

The results show that the atRA-administered dose is not toxic for the dams, and that although fetal death was not observed, it produced abnormalities in the fetuses. Glycine reduced atRA-induced teratogenic effects (external and skeletal defects).

CONCLUSIONS

The results indicate that glycine effectively reduces the teratogenic effects of atRA. Thus, glycine might be useful for the prevention of vitamin A teratogenicity.

Isotretinoin therapy induces DNA oxidative damage

Background: Isotretinoin (Iso) is currently indicated for the treatment of cystic acne (CA) and is related to marked teratogenicity.

Aim: The aim of the study was to evaluate the relationship between total antioxidant status (TAS) and a serum marker of DNA oxidative damage, 8-hydroxy-2-desoxyguanosine (8-OHdG), in patients on Iso treatment.

Patients and methods: Patients with CA (n=18) were evaluated before and 45days after Iso (0.5mg/kg per day) treatment and non-diseased controls (n=22) were tested only once. Plasma TAS levels and 8-OHdG were measured spectrophotometrically and with an immunoassay, respectively. Liver biochemical parameters and muscle enzymes were measured on a blood chemistry analyzer.

Results: TAS levels were significantly (p<0.0001) lower in patients before treatment (921±124μmol/L) compared with those after treatment (1335±93μmol/L) and in controls (1536±126μmol/L). In contrast, 8-OHdG serum levels were two-fold higher in patients after treatment (0.21±0.03ng/mL) than before treatment (0.11±0.02ng/mL) and three-fold higher than in controls (0.07±0.01ng/mL; p<0.0001). Negative correlations were found between TAS and 8-OHdG (r=−0.754, p<0.0001) in patients before therapy and positive correlations were found between creatine kinase (CK) and 8-OHdG (r=0.488, p<0.001) and liver enzymes after Iso treatment.

Conclusions: High serum levels of 8-OHdG in patients on Iso therapy may be due to a direct effect of Iso on liver, muscle and skin epidermal cells. Regular evaluation of 8-OHdG in sera of patients, especially of women of reproductive age, on Iso treatment could be a sensitive follow-up biomarker of DNA oxidation.

All-trans-retinoic acid rapidly induces glycine N-methyltransferase in a dose-dependent manner and reduces circulating methionine and homocysteine levels in rats

Glycine N-methyltransferase (GNMT) regulates the methyl group supply for S-adenosylmethionine-dependent transmethylation reactions. Retinoids have been shown to perturb methyl group metabolism by increasing the abundance and activity of GNMT, thereby leading to the loss of methyl groups. Previous studies used pharmacologic doses (30 micro mol/kg body weight) of various retinoids administered daily for a total of 10 d. Here, we examined the dose- and time-dependent relationships between all-trans-retinoic acid (ATRA) administration and induction of GNMT, as well as determining additional indices of methyl group and folate metabolism. For the dose-response study, rats were administered 0, 1, 5, 10, 15 or 30 micro mol ATRA/kg body weight for 10 d. For the time-course study, rats were given 30 micromol ATRA/kg body weight for 0, 1, 2, 4, or 8 d. A significant increase (105%) in GNMT activity was observed with doses as low as 5 micromol/kg body weight, whereas maximal induction (231%) of GNMT activity was achieved at 30 micromol/kg body weight. Induction of hepatic GNMT by ATRA was rapid, exhibiting a 31% increase after a single dose (1 d) and achieving maximal induction (95%) after 4 d. Plasma methionine and homocysteine concentrations were decreased 42 and 53%, respectively, in ATRA-treated rats compared with controls. In support of this finding, the hepatic activity of methionine synthase, the folate-dependent enzyme required for homocysteine remethylation, was elevated 40% in ATRA-treated rats. This work demonstrates that ATRA administration exerts a rapid effect on hepatic methyl group, folate and homocysteine metabolism at doses that are within the therapeutic range used by humans.

Activation and induction of glycine N-methyltransferase by retinoids are tissue- and gender-specific

Glycine N-methyltransferase (GNMT) is a key protein in the liver that functions to regulate S-adenosylmethionine (SAM) and the SAM/S-adenosylhomocysteine ratio. Significant GNMT expression is also present in the kidney and pancreas. Inappropriate regulation of GNMT may have negative consequences on methyl group and folate metabolism. We have demonstrated that retinoid compounds significantly elevated hepatic GNMT activity and abundance (approximately 2-fold) in male rats. However, pancreatic GNMT activity and abundance were not altered by retinoid treatment. Likewise, retinoid administration was without effect on renal GNMT activity. Hepatic GNMT activity was also elevated in female rats treated with all-trans-retinoic acid, but to a lesser extent compared to males. Collectively, these results indicate that the modulation of methyl group metabolism by retinoids is tissue- and gender-specific, and may compromise the availability of methyl groups for SAM-dependent transmethylation reactions. In support of this, SAM-dependent synthesis of creatinine was significantly reduced 21% following all-trans-retinoic acid treatment.

Vitamin A and its derivatives induce hepatic glycine N-methyltransferase and hypomethylation of DNA in rats

Regulation of S-adenosylmethionine (SAM) and the SAM/S-adenosylhomocysteine (SAH) ratio by the key cytosolic enzyme glycine N-methyltransferase (GNMT) is essential in optimizing methyl group supply and subsequent functioning of methyltransferase enzymes. Therefore, inappropriate activation of GNMT may lead to the loss of methyl groups vital for many SAM-dependent transmethylation reactions. Previously, we demonstrated that the retinoid derivatives 13-cis- (CRA) and all-trans-retinoic acid (ATRA) mediated both the activity of GNMT and its abundance. The present study was conducted to determine whether vitamin A had a similar ability to up-regulate GNMT and to assess the biological importance of GNMT modulation by examining both the transmethylation and transsulfuration pathways after retinoid treatment. Rats were fed a control (10% casein + 0.3% L-methionine) diet and orally given retinyl palmitate (RP), CRA, ATRA or vehicle daily for 10 d. RP, CRA and ATRA elevated hepatic GNMT activity 32, 74 and 124%, respectively, compared with the control group. Moreover, the retinoid-mediated changes in GNMT activity were reflected in GNMT abundance (38, 89 and 107% increases for RP-, CRA-, and ATRA-treated rats, respectively). In addition, hepatic DNA, a substrate for SAM-dependent transmethylation, was hypomethylated (approximately 100%) after ATRA treatment compared with the control group. In contrast, the transsulfuration product glutathione was unaffected by retinoid treatment. These results provide evidence of the following: 1) vitamin A, like its retinoic acid derivatives, can induce enzymatically active GNMT; and 2) inappropriate induction of GNMT can lead to a biologically important loss of methyl groups and the subsequent impairment of essential transmethylation processes.