Sulfation of minoxidil by multiple human cytosolic sulfotransferases

Low-dose Oral Minoxidil in the Treatment of Alopecia: Evidence and Experience-based Consensus Statement of Indian Experts

Alopecia is a highly prevalent condition worldwide including in India. There are different types of alopecia with differing etiology, presentation, and hence treatment. Androgenetic alopecia represents the most common form of hair loss affecting male as well as female population termed as male and female pattern hair loss, respectively. Several treatment options are available for the treatment of alopecia with often unsatisfactory results resulting in psychological distress among such patients. Topical minoxidil is known to be effective in the treatment of alopecia. However, oral minoxidil is not currently approved for the treatment of alopecia. This expert consensus is prepared to provide guidance to the clinicians regarding the use of oral minoxidil in the treatment of alopecia. Extensive literature review was performed to prepare the draft consensus which was then revised based on the suggestions and comments from the experts. The final draft was circulated to the experts for review and approval. This consensus document provides overview of evidence related to oral minoxidil and consensus from the experts for its use in the treatment of minoxidil.

Systemic Minoxidil Accidental Exposure in a Paediatric Population: A Case Series Study of Cutaneous and Systemic Side Effects

Oral minoxidil is an approved treatment for high blood pressure which is also used as an off-label drug for alopecia. Knowledge about the effects of systemic minoxidil in the paediatric population is limited. A retrospective case series study of paediatric patients with history of systemic minoxidil intake due to contaminated sets of omeprazole was performed to describe side effects of high dose oral minoxidil intake in children. Twenty patients aged between 2 months and 13 years joined the study. They had received high doses of oral minoxidil (mean dose 0.90 mg/kg/day) during a mean time of 38.3 days. Hypertrichosis appeared in 65%, with a mean latency time of 24.31 days. Treatment time was associated with the appearance of hypertrichosis (p < 0.05). Most common initial zone of hypertrichosis was the face. Systemic effects developed in 15%, with no cases of severe disorders. The present study shows a novel insight into the side effects of high doses of oral minoxidil in children.

Minoxidil: a comprehensive review

Topical minoxidil (5% foam, 5% solution, and 2% solution) is FDA-approved for androgenetic alopecia (AGA) in men and women.Mechanism of action: Minoxidil acts through multiple pathways (vasodilator, anti-inflammatory agent, inducer of the Wnt/β-catenin signaling pathway, an antiandrogen), and may also affect the length of the anagen and telogen phases.Pharmacokinetics: Approximately 1.4% of topical minoxidil is absorbed through the skin. Minoxidil is a prodrug that is metabolized by follicular sulfotransferase to minoxidil sulfate (active form). Those with higher sulfotransferase activity may respond better than patients with lower sulfotransferase activity.Clinical efficacy (topical minoxidil): In a five-year study, 2% minoxidil exhibited peak hair growth in males at year one with a decline in subsequent years. Topical minoxidil causes hair regrowth in both frontotemporal and vertex areas. The 5% solution and foam were not significantly different in efficacy from the 2% solution.Oral and Sublingual minoxidil (not FDA approved; off-label): After 6 months of administration, minoxidil 5 mg/day was significantly more effective than topical 5% and 2% in male AGA. Low-dose 0.5-5 mg/day may also be safe and effective for female pattern hair loss and chronic telogen effluvium. Sublingual minoxidil may be safe and effective in male and female pattern hair loss.

Minoxidil and its use in hair disorders: a review

Minoxidil was first introduced as an antihypertensive medication and the discovery of its common adverse event, hypertrichosis, led to the development of a topical formulation for promoting hair growth. To date, topical minoxidil is the mainstay treatment for androgenetic alopecia and is used as an off-label treatment for other hair loss conditions. Despite its widespread application, the exact mechanism of action of minoxidil is still not fully understood. In this article, we aim to review and update current information on the pharmacology, mechanism of action, clinical efficacy, and adverse events of topical minoxidil.

Xenobiotic-metabolizing enzymes in the skin of rat, mouse, pig, guinea pig, man, and in human skin models

The exposure of the skin to medical drugs, skin care products, cosmetics, and other chemicals renders information on xenobiotic-metabolizing enzymes (XME) in the skin highly interesting. Since the use of freshly excised human skin for experimental investigations meets with ethical and practical limitations, information on XME in models comes in the focus including non-human mammalian species and in vitro skin models. This review attempts to summarize the information available in the open scientific literature on XME in the skin of human, rat, mouse, guinea pig, and pig as well as human primary skin cells, human cell lines, and reconstructed human skin models. The most salient outcome is that much more research on cutaneous XME is needed for solid metabolism-dependent efficacy and safety predictions, and the cutaneous metabolism comparisons have to be viewed with caution. Keeping this fully in mind at least with respect to some cutaneous XME, some models may tentatively be considered to approximate reasonable closeness to human skin. For dermal absorption and for skin irritation among many contributing XME, esterase activity is of special importance, which in pig skin, some human cell lines, and reconstructed skin models appears reasonably close to human skin. With respect to genotoxicity and sensitization, activating XME are not yet judgeable, but reactive metabolite-reducing XME in primary human keratinocytes and several reconstructed human skin models appear reasonably close to human skin. For a more detailed delineation and discussion of the severe limitations see the “Overview and Conclusions” section in the end of this review.

Phase II metabolism in human skin: skin explants show full coverage for glucuronidation, sulfation, N-acetylation, catechol methylation, and glutathione conjugation

Although skin is the largest organ of the human body, cutaneous drug metabolism is often overlooked, and existing experimental models are insufficiently validated. This proof-of-concept study investigated phase II biotransformation of 11 test substrates in fresh full-thickness human skin explants, a model containing all skin cell types. Results show that skin explants have significant capacity for glucuronidation, sulfation, N-acetylation, catechol methylation, and glutathione conjugation. Novel skin metabolites were identified, including acyl glucuronides of indomethacin and diclofenac, glucuronides of 17β-estradiol, N-acetylprocainamide, and methoxy derivatives of 4-nitrocatechol and 2,3-dihydroxynaphthalene. Measured activities for 10 μM substrate incubations spanned a 1000-fold: from the highest 4.758 pmol·mg skin(-1)·h(-1) for p-toluidine N-acetylation to the lowest 0.006 pmol·mg skin(-1)·h(-1) for 17β-estradiol 17-glucuronidation. Interindividual variability was 1.4- to 13.0-fold, the highest being 4-methylumbelliferone and diclofenac glucuronidation. Reaction rates were generally linear up to 4 hours, although 24-hour incubations enabled detection of metabolites in trace amounts. All reactions were unaffected by the inclusion of cosubstrates, and freezing of the fresh skin led to loss of glucuronidation activity. The predicted whole-skin intrinsic metabolic clearances were significantly lower compared with corresponding whole-liver intrinsic clearances, suggesting a relatively limited contribution of the skin to the body's total systemic phase II enzyme-mediated metabolic clearance. Nevertheless, the fresh full-thickness skin explants represent a suitable model to study cutaneous phase II metabolism not only in drug elimination but also in toxicity, as formation of acyl glucuronides and sulfate conjugates could play a role in skin adverse reactions.

Clinical utility and validity of minoxidil response testing in androgenetic alopecia

Clinical response to 5% topical minoxidil for the treatment of androgenetic alopecia (AGA) is typically observed after 3-6 months. Approximately 40% of patients will regrow hair. Given the prolonged treatment time required to elicit a response, a diagnostic test for ruling out nonresponders would have significant clinical utility. Two studies have previously reported that sulfotransferase enzyme activity in plucked hair follicles predicts a patient's response to topical minoxidil therapy. The aim of this study was to assess the clinical utility and validity of minoxidil response testing. In this communication, the present authors conducted an analysis of completed and ongoing studies of minoxidil response testing. The analysis confirmed the clinical utility of a sulfotransferase enzyme test in successfully ruling out 95.9% of nonresponders to topical minoxidil for the treatment of AGA.

Interactions of cytosolic sulfotransferases with xenobiotics

Cytosolic sulfotransferases are a superfamily of enzymes that catalyze the transfer of the sulfonic group from 3'-phosphoadenosine-5'-phosphosulfate to hydroxy or amine groups in substrate molecules. The human cytosolic sulfotransferases that have been most studied, namely SULT1A1, SULT1A3, SULT1B1, SULT1E1 and SULT2A1, are expressed in different tissues of the body, including liver, intestine, adrenal, brain and skin. These sulfotransferases play important roles in the sulfonation of endogenous molecules such as steroid hormones and neurotransmitters, and in the elimination of xenobiotic molecules such as drugs, environmental chemicals and natural products. There is often overlapping substrate selectivity among the sulfotransferases, although one isoform may exhibit greater enzyme efficiency than other isoforms. Similarly, inhibitors or enhancers of one isoform often affect other isoforms, but typically with different potency. This means that if the activity of one form of sulfotransferase is altered (either inhibited or enhanced) by the presence of a xenobiotic, the sulfonation of endogenous and xenobiotic substrates for other isoforms may well be affected. There are more examples of inhibitors than enhancers of sulfonation. Modulators of sulfotransferase enzymes include natural products ingested as part of the human diet as well as environmental chemicals and drugs. This review will discuss recent work on such interactions.

Sulfotransferase activity in plucked hair follicles predicts response to topical minoxidil in the treatment of female androgenetic alopecia

Two percent topical minoxidil is the only US Food and Drug Administration-approved drug for the treatment of female androgenetic alopecia (AGA). Its success has been limited by the low percentage of responders. Meta-analysis of several studies reporting the number of responders to 2% minoxidil monotherapy indicates moderate hair regrowth in only 13-20% of female patients. Five percent minoxidil solution, when used off-label, may increase the percentage of responders to as much as 40%. As such, a biomarker for predicting treatment response would have significant clinical utility. In a previous study, Goren et al. reported an association between sulfotransferase activity in plucked hair follicles and minoxidil response in a mixed cohort of male and female patients. The aim of this study was to replicate these findings in a well-defined cohort of female patients with AGA treated with 5% minoxidil daily for a period of 6 months. Consistent with the prior study, we found that sulfotransferase activity in plucked hair follicles predicts treatment response with 93% sensitivity and 83% specificity. Our study further supports the importance of minoxidil sulfation in eliciting a therapeutic response and provides further insight into novel targets for increasing minoxidil efficacy.

Promotive effect of topical ketoconazole, minoxidil, and minoxidil with tretinoin on hair growth in male mice

Recently topical use of 2% Ketoconazole solution has been reported to have a therapeutic effect on androgenic alopecia. Minoxidil is a vasodilatory medication used primarily as antihypertensive drug. It was discovered to have the side effect of hair growth and reversing baldness. Tretinoin is commonly used topically for acne treatment and in the treatment of photoaging. It is used by some as hair loss treatment. Objective. To compare the stimulatory effect of Ketoconazole, Minoxidil, and Minoxidil with Tretinoin on hair growth in a mouse model. Materials and Methods. Coat hairs on the dorsal skin of seven weeks old male mice were gently clipped and then stained by using commercial dye. These mice were divided into four groups each of five treated with topical application of ethanol 95%, Ketoconazole solution 2%, Minoxidil solution 5%, and Minoxidil with Tretinoin solution 0.1%, respectively. The drugs were applied once daily for three weeks, the clipped area was photographed, and the ratio of regrown coat area was calculated. Results. The results demonstrated that Ketoconazole, Minoxidil, and Minoxidil with Tretinoin had a significant stimulatory effect on hair growth compared with the control group and Minoxidil was the most effective drug among them.

Idiosyncratic adverse drug reactions: current concepts

Idiosyncratic drug reactions are a significant cause of morbidity and mortality for patients; they also markedly increase the uncertainty of drug development. The major targets are skin, liver, and bone marrow. Clinical characteristics suggest that IDRs are immune mediated, and there is substantive evidence that most, but not all, IDRs are caused by chemically reactive species. However, rigorous mechanistic studies are very difficult to perform, especially in the absence of valid animal models. Models to explain how drugs or reactive metabolites interact with the MHC/T-cell receptor complex include the hapten and P-I models, and most recently it was found that abacavir can interact reversibly with MHC to alter the endogenous peptides that are presented to T cells. The discovery of HLA molecules as important risk factors for some IDRs has also significantly contributed to our understanding of these adverse reactions, but it is not yet clear what fraction of IDRs have a strong HLA dependence. In addition, with the exception of abacavir, most patients who have the HLA that confers a higher IDR risk with a specific drug will not have an IDR when treated with that drug. Interindividual differences in T-cell receptors and other factors also presumably play a role in determining which patients will have an IDR. The immune response represents a delicate balance, and immune tolerance may be the dominant response to a drug that can cause IDRs.

In-vitro sulfation of piceatannol by human liver cytosol and recombinant sulfotransferases

Objectives

The aim of this study was to investigate the concentration-dependent sulfation of piceatannol, a dietary polyphenol present in grapes and wine and known for its promising anticancer and anti-inflammatory activity.

Methods

Sulfation of piceatannol was investigated in human liver cytosol as well as using a panel of recombinant sulfotransferase isoforms. Furthermore, the chemical structures of novel sulfates were identified by liquid chromatography/mass spectrometry (LC/MS).

Key findings

In the presence of 3′-phosphoadenosine-5′-phosphosulfate, three metabolites could be detected whose structures were identified by LC/MS/MS as piceatannol disulfate (M1) and two monosulfates (M2, M3). The kinetics of M1 formation exhibited a pattern of substrate inhibition with a Ki of 21.8 ± 11.3 μM and a Vmax/Km of 7.63 ± 1.80 μl/mg protein per min. Formation of M2 and M3 showed sigmoidal kinetics with apparent Km and Vmax values of 27.1 ± 2.90 μM and 118.4 ± 4.38 pmol/mg protein per min, respectively, for M2; and 35.7 ± 2.70 μM and 81.8 ± 2.77 pmol/mg protein per min, respectively, for M3. Incubation in the presence of human recombinant sulfotransferases (SULTs) demonstrated that M1 was formed equally by SULT1A1*1 and SULT1B1 and to a lesser extent by SULT1A1*2. M2 was preferentially catalysed by SULT1A1*2, 1A3 and 1E1. The formation of M3, however, was mainly catalysed by SULT1A2*1 and SULT1A3.

Conclusions

Our results elucidate the importance of piceatannol sulfation in human liver, which must be taken into account in humans after dietary intake of piceatannol.

Changes in global gene expression in rat myometrium in transition from late pregnancy to parturition

The process of parturition involves the complex interplay of factors that change the excitability and contractile activity of the uterus. We have compared the relative gene expression profile of myometrium from rats before parturition (21 days pregnant) and during delivery, using high-density DNA microarray. Of 8,740 sequences available in the array, a total of 3,782 were detected as present. From the sequences that were significantly altered, 59 genes were upregulated and 82 genes were downregulated. We were able to detect changes in genes described to have altered expression level at term, including connexin 43 and 26, cyclooxygenase 2, and oxytocin receptor, as well as novel genes that have been not previously associated with parturition. Quantitative real-time PCR on selected genes further confirmed the microarray data. Here we report for the first time that aquaporin5 (AQP5), a member of the aquaporin water channel family, was dramatically downregulated during parturition (approximately 100-fold by microarray and approximately 50-fold by real-time PCR). The emerging profile highlights biochemical cascades occurring in a period of approximately 36 h that trigger parturition and the initiation of myometrium reverse remodeling postpartum. The microarray analysis uncovered genes that were previously suspected to play a role in parturition. This regulation involves genes from immune/inflammatory response, steroid/lipid metabolism, calcium homeostasis, cell volume regulation, cell signaling, cell division, and tissue remodeling, suggesting the presence of multiple and redundant mechanisms altered in the process of birth.

Sulfation of resveratrol in human liver: Evidence of a major role for the sulfotransferases SULT1A1 and SULT1E1

Sulfation of resveratrol, a polyphenolic compound present in grapes and wine with anticancer and cardioprotective activities, was studied in human liver cytosol. In the presence of 3'-phosphoadenosine-5'-phosphosulfate, three metabolites (M1-3) whose structures were identified by mass spectrometry and NMR as trans-resveratrol-3-O-sulfate, trans-resveratrol-4'-O-sulfate, and trans-resveratrol-3-O-4'-O-disulfate, respectively. The kinetics of M1 formation in human liver cytosol exhibited an pattern of substrate inhibition with a K(i) of 21.3 +/- 8.73 microM and a V(max)/K(m) of 1.63 +/- 0.41 microLmin(-1)mg(-1) protein. Formation of M2 and M3 showed sigmoidal kinetics with about 56-fold higher V(max)/K(m) values for M3 than for M2 (2.23 +/- 0.14 and 0.04 +/- 0.01 microLmin(-1)mg(-1)). Incubation in the presence of human recombinant sulfotransferases (SULTs) demonstrated that M1 is almost exclusively catalysed by SULT1A1 and only to a minor extent by SULT 1A2, 1A3 and 1E1, whereas M2 is selectively formed by SULT1A2. M3 is mainly catalysed by SULT1A2 and 1A3. In conclusion, the results elucidate the enzymatic pathways of resveratrol in human liver, which must be considered in humans following oral uptake of dietary resveratrol.

Drug-metabolizing enzymes in the skin of man, rat, and pig

The mammalian skin has long been considered to be poor in drug metabolism. However, many reports clearly show that most drug metabolizing enzymes also occur in the mammalian skin albeit at relatively low specific activities. This review summarizes the current state of knowledge on drug metabolizing enzymes in the skin of human, rat, and pig, the latter, because it is often taken as a model for human skin on grounds of anatomical similarities. However only little is known about drug metabolizing enzymes in pig skin. Interestingly, some cytochromes P450 (CYP) have been observed in the rat skin which are not expressed in the rat liver, such as CYP 2B12 and CYP2D4. As far as investigated most drug metabolizing enzymes occur in the suprabasal (i.e. differentiating) layers of the epidermis, but the rat CYP1A1 rather in the basal layer and human UDP-glucuronosyltransferase rather in the stratum corneum. The pattern of drug metabolizing enzymes and their localization will impact not only the beneficial as well as detrimental properties of drugs for the skin but also dictate whether a drug reaches the blood flow unchanged or as activated or inactivated metabolite(s).

Role of pharmacologically active metabolites in drug discovery and development

Pharmacologically active metabolites can contribute significantly to the overall therapeutic and adverse effects of drugs. Therefore, to fully understand the mechanism of action of drugs, it is important to recognize the role of active metabolites. Active metabolites can also be developed as drugs in their own right. Using illustrative examples, this paper discusses a variety of biotransformation reactions that produce active metabolites and their structure-activity relationships. The paper also describes the role and significance of active metabolites in drug discovery and development, various experimental observations that can be used as indicators of their presence, and methods that can be used to assess their biological activities and contribution to the overall therapeutic and adverse effects of drugs.

Simultaneous effects of tocopheryl polyethylene glycol succinate (TPGS) on local hair growth promotion and systemic absorption of topically applied minoxidil in a mouse model

In this study, topical minoxidil solutions supplemented with TPGS in cosolvent systems of various compositions consisting of water, alcohol, and polyethylene glycol 400 were designed to evaluate the efficacy of promoting hair growth after topical application and the safety in terms of the amount of minoxidil absorbed through the skin into the circulation using C57BL/6J mice as a model. The commercial product of 2% Regaine) was used as the positive control. The role, which sulfotransferase activity plays in hair growth with treatment using minoxidil, was determined as well. The results revealed that the addition of 0.5% TPGS was able to enhance the proliferation of hair, but an increase in the amount of TPGS to 2% led to deterioration in the enhancement of hair growth. At the higher added amount (2.0%) of TPGS, the promotion of hair growth was slightly reduced for both cosolvent formulations F1 (100% water) and F3 (100% PEG 400), whereas it was reduced to a greater extent for the cosolvent formulations F8-F10. In comparison, the influences of cosolvent compositions with TPGS amounts of 0.0 and 2.0% on the promotion of hair growth were similar. On the contrary, variability in the promotion of hair growth by different solvent formulations was minimal when the added amount of TPGS was 0.5%. In general, a relationship between hair growth and sulfotransferase activities after topical application of 2% Regaine and minoxidil formulations containing various amounts of TPGS was not demonstrated. Plasma concentrations of minoxidil with 2% Regaine were found to be greater than those of 2% minoxidil in those cosolvent formulations containing various amounts of TPGS, while showing insignificant differences among those 10 cosolvent formulations with a fixed amount of TPGS. A tendency for the plasma concentration of minoxidil to increase after the topical administration of minoxidil formulations containing the higher amount of TPGS (2%) was noted.

Novel and Established Potassium Channel Openers Stimulate Hair Growth In Vitro: Implications for their Modes of Action in Hair Follicles

Although ATP-sensitive potassium (K(ATP)) channel openers, e.g., minoxidil and diazoxide, can induce hair growth, their mechanisms require clarification. Improved drugs are needed clinically. but the absence of a good bioassay hampers research. K(ATP) channels from various tissues contain subtypes of the regulatory sulfonylurea receptor, SUR, and pore-forming, K(+) inward rectifier subunits, Kir6.X, giving differing sensitivities to regulators. Therefore, the in vitro effects of established potassium channel openers and inhibitors (tolbutamide and glibenclamide), plus a novel, selective Kir6.2/SUR1 opener, NNC 55-0118, were assessed on deer hair follicle growth in serum-free median without streptomycin. Minoxidil (0.1-100 microM, p<0.001), NNC 55-0118 (1 mM, p<0.01; 0.1, 10, 100 microM, p<0.001), and diazoxide (10 microM, p<0.01) increased growth. Tolbutamide (1 mM) inhibited growth (p<0.001) and abolished the effect of 10 microM minoxidil, diazoxide and NNC 55-0118; glibenclamide (10 microM) had no effect, but prevented stimulation by 10 microM minoxidil. Phenol red stimulated growth (p<0.001), but channel modulator responses remained unaltered. Thus, deer follicles offer a practical, ethically advantageous in vitro bioassay that reflects clinical responses in vivo. The results indicate direct actions of K(ATP) channel modulators within hair follicles via two types of channels, with SUR 1 and SUR 2, probably SUR2B, sulfonylurea receptors.

Synergistic effect of antioxidant phenolic acids on human phenolsulfotransferase activity

Sulfate conjugation by phenolsulfotransferases (PSTs) is an important process in the detoxification of xenobiotics and endogenous compounds. There are two forms of PSTs for the sulfation of small phenols (PST-P) and monoamines (PST-M). Phenolic acids are known to increase the activities of PST-P and PST-M. The purpose of this study is to investigate the synergistic effect of the combinations of phenolic acids on human PSTs activities. The combinations of p-hydroxybenzoic acid, gentisic acid, ferulic acid, gallic acid, and coumaric acid in a random order for their effects on PSTs activities were evaluated at concentrations of 2.5, 5.0, and 7.5 microM. The PST-M activity was significantly increased when gentisic acid was combined with each of the other phenolic acids. When p-hydroxybenzoic acid was combined with each of the other phenolic acids, a synergistic effect with respect to the promotion of PST-P activity was obtained. A potential synergistic effect for the PST-P activity was also found in the following combination: p-hydroxybenzoic acid + gallic acid + gentisic acid, p-hydroxybenzoic acid + gallic acid + m-coumaric acid, p-hydroxybenzoic acid + o-coumaric acid + p-coumaric acid, p-hydroxybenzoic acid + o-coumaric acid + m-coumaric acid, gallic acid + gentisic acid + p-coumaric acid, and gallic acid + o-coumaric acid + m-coumaric acid. Therefore, the activities of both forms of PSTs can be promoted by all of these combinations of phenolic acids. These results provide a better understanding regarding the effect of phenolic acids on human PSTs activities, as well as more information on the intake of antioxidant phenolic acids for human health.

Minoxidil: mechanisms of action on hair growth

We have known for over 30 years that minoxidil stimulates hair growth, yet our understanding of its mechanism of action on the hair follicle is very limited. In animal studies, topical minoxidil shortens telogen, causing premature entry of resting hair follicles into anagen, and it probably has a similar action in humans. Minoxidil may also cause prolongation of anagen and increases hair follicle size. Orally administered minoxidil lowers blood pressure by relaxing vascular smooth muscle through the action of its sulphated metabolite, minoxidil sulphate, as an opener of sarcolemmal KATP channels. There is some evidence that the stimulatory effect of minoxidil on hair growth is also due to the opening of potassium channels by minoxidil sulphate, but this idea has been difficult to prove and to date there has been no clear demonstration that KATP channels are expressed in the hair follicle. A number of in vitro effects of minoxidil have been described in monocultures of various skin and hair follicle cell types including stimulation of cell proliferation, inhibition of collagen synthesis, and stimulation of vascular endothelial growth factor and prostaglandin synthesis. Some or all of these effects may be relevant to hair growth, but the application of results obtained in cell culture studies to the complex biology of the hair follicle is uncertain. In this article we review the current state of knowledge on the mode of action of minoxidil on hair growth and indicate lines of future research.

Pharmacogenetics of Antihypertensive Drug Responses

The blood pressure (BP) response to any single antihypertensive drug is characterized by marked interindividual variation, and the known predictors of response are of limited value in identifying the optimum drug for an individual patient. Analysis of genetic variation has the potential to improve our understanding of determinants of antihypertensive drug response in order to individualize drug selection. Genetic variation can influence both pharmacokinetic and pharmacodynamic mechanisms underlying variation in drug response. Classic pharmacogenetic investigations have identified variations in single genes that have a large effect on antihypertensive drug metabolism and are inherited in a Mendelian fashion. These include a polymorphism in the CYP2D6 gene, encoding a cytochrome p450 family member involved in phase I drug metabolism, and polymorphisms in genes encoding enzymes involved in phase II drug metabolism, including N-acetyltransferase (NAT2), catechol-O-methyltransferase (COMT), and phenol sulfotransferase (P-PST, SULT1A1). Although these polymorphisms have major effects on the pharmacokinetic profiles of both commonly used antihypertensive drugs such as metoprolol (CYP2D6), and lesser used drugs such as hydralazine (NAT2), methyldopa (COMT), and minoxidil (SULT1A1), they have not been shown to influence variation in the antihypertensive effect of these drugs at conventional doses. Interest is now focused on identifying genetic polymorphisms that influence the pharmacodynamic determinants of antihypertensive response. Using a candidate gene approach, such polymorphisms have been identified in genes encoding alpha-adducin (ADD1), subunits of G-proteins (GNB3 and GNAS1), the beta(1)-adrenergic receptor (ADRB1), endothelial nitric oxide synthase (NOS3), and components of the renin-angiotensin-aldosterone system (angiotensinogen [AGT], angiotensin converting enzyme [ACE], the angiotensin type I receptor [AGTR1], and aldosterone synthase [CYP11B2]). These polymorphisms have been shown to influence the BP response to diuretics (ADD1, GNB3, NOS3, and ACE), beta-blockers (GNAS1 and ADRB1), ACE inhibitors (AGT, ACE, and AGTR1), angiotensin receptor blockers (ACE and CYP11B2), and clonidine (GNB3).An emerging consensus from these studies is that single gene effects on antihypertensive drug responses are small, and even the combined effects of all presently known polymorphisms do not account for enough variation in response to be clinically useful. New genome-wide scanning techniques may lead to the identification of genes previously unsuspected of influencing drug response. Additional requirements for pharmacogenetic approaches to become clinically useful are the characterization of the effects of haplotypes and multi-locus genotypes on drug response, and consideration of gene-by-environment interactions. Such studies will require huge sample sizes and novel statistical methods, but the theoretical and technical framework is in place to make this possible.

Transdermal delivery of paracetamol for paediatric use: effects of vehicle formulations on the percutaneous penetration

Paracetamol is a safe and effective analgesic and antipyretic agent, and is one of the most widely used medications for infants and children. The formulations currently available have been designed for oral and rectal administration. However, they are not practical in young patients with vomiting and diarrhoea, or in those who refuse to take the full dose. An alternative route of administration would be a significant contribution to the paediatric pharmacopoeia. The aim of this study was to develop a new transdermal system for optional therapeutic administration of paracetamol in infants and children. In-vivo studies were carried out in animals using a transdermal system of high-loaded, soluble paracetamol in a hydrogel patch, which was also tested in-vitro for 8 h. Although the beneficial contribution of glyceryl oleate to the transdermal penetration of paracetamol seemed to be significant in-vitro, it was shown to be insufficient in-vivo. To improve the penetration of the drug, 4% PEG-40 stearate and 10% ethanol were incorporated as absorption enhancers into the dermal patches. A few hours after application of the improved patches to rats, plasma drug concentrations were elevated to levels comparable with those obtained after oral and subcutaneous administration of a high dose of paracetamol. Since plasma drug concentrations did not reach a constant steady state (as a peak or plateau) during the short-term animal experiments, longer pharmacokinetic studies in conscious animals are necessary.

Effects of phenolic acids on human phenolsulfotransferases in relation to their antioxidant activity

Sulfate conjugation by phenolsulfotransferase (PST) enzyme is an important process in the detoxification of xenobiotics and endogenous compounds. There are two forms of PST that are specific for the sulfation of small phenols (PST-P) and monoamines (PST-M). Phenoilc acids have been reported to have important biological and pharmacological properties and may have benefits to human health. In the present study, human platelets were used as a model to investigate the influence of 13 phenolic acids on human PST activity and to evaluate the relationship to their antioxidant activity. The results showed that chlorogenic acid, syringic acid, protocatechuic acid, vanillic acid, sinapic acid, and caffeic acid significantly (p < 0.05) inhibited the activities of both forms of PST by 21-30% at a concentration of 6.7 microM. The activity of PST-P was enhanced (p < 0.05) by p-hydroxybenzoic acid, gallic acid, gentisic acid, o-coumaric acid, p-coumaric acid, and m-coumaric acid at a concentration of 6.7 microM, whereas the activity of PST-M was enhanced by gentisic acid, gallic acid, p-hydroxybenzoic acid, and ferulic acid. The phenolic acids exhibited antioxidant activity as determined by the oxygen radical absorbance capacity (ORAC) assay and Trolox equivalent antioxidant capacity (TEAC) assay, especially gallic acid, p-hydroxybenzoic acid, gentisic acid, and coumaric acid, which had strong activity. The overall effect of phenolic acids tested on the activity of PST-P and PST-M was well correlated to their antioxidant activity of ORAC value (r = 0.71, p < 0.01; and r = 0.66, p < 0.01). These observations suggest that antioxidant phenolic acids might alter sulfate conjugation.

Human cytosolic sulphotransferases: genetics, characteristics, toxicological aspects

Cytosolic sulphotransferases transfer the sulpho moiety from the cofactor 5'-phosphoadenosine-3'-phosphosulphate (PAPS) to nucleophilic groups of xenobiotics and small endogenous compounds (such as hormones and neurotransmitters). This reaction often leads to products that can be excreted readily. However, other sulpho conjugates are strong electrophiles and may covalently bind with DNA and proteins. All known cytosolic sulphotransferases are members of an enzyme/gene superfamily termed SULT. In humans, 10 SULT genes are known. One of these genes encodes two different enzyme forms due to the use of alternative first exons. Different SULT forms substantially differ in their substrate specificity and tissue distribution. Genetic polymorphisms have been described for three human SULTs. Several allelic variants differ in functional properties, including the activation of promutagens. Only initial results are available from the analysis of SULT allele frequencies in different population groups, e.g. subjects suffering from specific diseases and corresponding controls.

Relationship of phenol sulfotransferase activity (SULT1A1) genotype to sulfotransferase phenotype in platelet cytosol

Sulfation catalysed by human cytosolic sulfotransferases is generally considered to be a detoxification mechanism. Recently, it has been demonstrated that sulfation of heterocyclic aromatic amines by human phenol sulfotransferase (SULT1A1) can result in a DNA binding species. Therefore, sulfation capacity has the potential to influence chemical carcinogenesis in humans. To date, one genetic polymorphism (Arg213His) has been identified that is associated with reduced platelet sulfotransferase activity. In this study, data on age, race, gender, SULT1A1 genotype and platelet SULT1A1 activity were available for 279 individuals. A simple colorimetric phenotyping assay, in conjunction with genotyping, was employed to demonstrate a significant correlation (r = 0.23, P < 0.01) of SULT1A1 genotype and platelet sulfotransferase activity towards 2-naphthol, a marker substrate for this enzyme. There was also a difference in mean sulfotransferase activity based on gender (1.28 nmol/min/mg, females; 0.94 nmol/min/mg, males, P = 0.001). DNA binding studies using recombinant SULT1A1*1 and SULT1A1*2 revealed that SULT1A1*1 catalysed N-hydroxy-aminobiphenyl (N-OH-ABP) DNA adduct formation with substantially greater efficiency (5.4 versus 0.4 pmol bound/mg DNA/20 min) than the SULT1A1*2 variant. A similar pattern was observed with 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5b]pyridine (N-OH-PhIP) (4.6 versus 1.8 pmol bound/mg DNA/20 min).

Expression profiling of human sulfotransferase and sulfatase gene superfamilies in epithelial tissues and cultured cells

The bioavailability of drugs administered topically or orally depends on their metabolism by epithelial enzymes such as the cytosolic sulfotransferases (SULT). Reverse transcriptase-polymerase chain reaction (RT-PCR) methods were established to detect expression of 8 SULT genes and 4 arylsulfatase (ARS) genes in human tissues of epithelial origin and in cultures of normal and transformed (cancer) cells. The results indicate: (i) SULT 1A1, 1A3, ARSC, and ARSD genes are ubiquitously expressed; (ii) expression is frequently similar between cell lines and corresponding tissues; (iii) SULT gene expression in normal cultured cells is generally comparable to the expression in associated transformed (cancer) cell lines; (iv) SULT 1A1 promoter usage is mainly tissue specific; however, both promoters are frequently used in SULT 1A3 expression; and (v) the expression profile of SULT 1A1, 1A3, 1E1, and 2B1a/b suggests that one or more of these isoforms may be involved in the cutaneous sulfoconjugation of minoxidil and cholesterol.

Induction of rat hepatic aryl sulfotransferase (SULT1A1) gene expression by triamcinolone acetonide: impact on minoxidil-mediated hypotension

The hypotensive agent minoxidil (6-imino-1, 2-dihydro-1-hydroxy-2-imino-4-piperidinopyrimidine) depends upon aryl sulfotransferase (SULT1)-catalyzed sulfation for its bioactivation. Previous reports suggest that glucocorticoids induce class-specific SULT1 and isoform-specific SULT1A1 gene expression in rat liver. In the present study, rats were treated with the glucocorticoid triamcinolone acetonide (TA, 5 mg/kg/day i.p. x 3 days) or its vehicle, 2% Tween-20, prior to minoxidil, and subsequent effects on mean arterial pressure (MAP), heart rate (HR), and hepatic SULT1 gene expression were characterized. Minoxidil treatment (1.5 mg/kg) resulted in a steady decline in MAP values of 16.3 to 18.6% relative to basal control levels at 35 to 60 min following minoxidil injection. Pentachlorophenol (PCP, 40 micromol/kg i.p.), an inhibitor of SULT1 enzyme activity, effectively ablated the hypotensive effects of minoxidil. By contrast, pretreatment with TA significantly enhanced minoxidil-induced hypotension. Relative to vehicle-treated controls, TA-treated rats displayed a steeper rate of decline in MAP and more profound levels of hypotension with decreases in MAP following minoxidil administration of 27.8%. TA also produced significant increases in hepatic SULT1 mRNA expression (of 271%) and SULT1A1 immunoreactive protein levels (of 273%), relative to vehicle-treated controls. These results provide physiological evidence to support the biological relevance of SULT1A1 induction by glucocorticoids. The data indicate that steroid treatment induces SULT1A1 gene expression and, as a consequence, accentuates the hypotensive effects of minoxidil.

Sulfation of iodothyronines by recombinant human liver steroid sulfotransferases

Sulfation is an important pathway in the metabolism of thyroid hormones. Sulfated iodothyronines are elevated in nonthyroidal illnesses and in the normal human fetal circulation. We assayed and characterized COS-1 cell expressed recombinant human liver dehydroepiandrosterone sulfotransferase (DHEA ST or SULT2A1) and estrogen sulfotransferase (EST or SULT1E1) activities for the first time with triiodothyronine (T(3)) as the substrate. Several biochemical properties that included apparent K(m) values, thermal stabilities, and responses to the inhibitors 2, 6-dichloro-4-nitrophenol and NaCl were tested. SULT2A1, a member of the hydroxysteroid sulfotransferase family, used 3,3'-T(2) more readily than T(3) and 3,5-T(2) as substrates, but had the lowest apparent K(m) value for T(3) of any reported human SULT. SULT1E1, a member of the phenol sulfotransferase family, used 3,3'-T(2) and rT(3) more readily than T(3), and also displayed the greatest specificity for T(4) among human SULTs. SULT2A1 may contribute more to iodothyronine sulfation than previously suspected. Potential roles of both steroid sulfotransferases in the enhanced sulfation of nonthyroidal illnesses and fetal development invite further investigation.