In vivo modulation of androgen receptor by androgens

Aim: To study the effect of androgen and antiandrogen on the level of androgen receptor (AR) mRNA. Methods: The total RNA was extracted from the prostate and analyzed by slot blot analysis. The blots were hybridized with AR cDNA probe and 1A probe (internal control) and autoradiography was performed. The intensity of signal was measured with a densitometer and the ratio of AR RNA and 1A RNA was calculated. Results: Androgenic deprivation produced by castration decreased the weight of the prostate and increased the levels of AR mRNA. Treatment of the castrated rats with testostrone increased the weight of prostate and decreased the levels of AR mRNA. Treatment of normal rats with flutamide decreased the weight of the gland and increased the levels Of AR mRNA. Conclusion: Androgens produce proliferative effect on the prostate and negatively regulate the AR transcription.

One and the same androgen for all?towards designer androgens

The introduction of designer oestrogens as a treatment modality in hormone replacement in women has invited toconsider the concept of compounds with selective androgenic effects for male hormone replacement therapy. The fullspectrum of the actions of testosterone may not be necessary of even undesired for certain indications for testosteronetreatment. To define for what indications certain androgenic properties are desired and undesired more insight in basicandrogen (patho)physiology is required. There is convincing evidence that aromatization of androgenic compounds tooestrogens might be an advantage for maintenance of bone mass and it might also mitigate negative effects of androgenson biochemical parameters of cardiovascular risks; the potentially negative effects of oestrogens on prostate pathology inageing men needs further elucidation. While the role of dihydro-testosterone (DHT) for the male sexual differentiationand for pubertal sexual maturation is evident, its role in mature and ageing males seems less significant or may even beharmful. It is, however, of note that a negative effect of DHT on prostate pathophysiology is certainly not proven.For male contraception a progestational agent with strong androgenic properties might be an asset. For most of theandrogenic actions the critical levels of androgens are not well established. The latter is relevant since the large amountof androgen molecules required for its biological actions (as compared to oestrogens)is an impediment in androgenreplacement modalities. There may be room for more biopotent androgens since delivery of large amounts of androgenmolecules to the circulation poses problems for treatment modalities.

Androgens and prostate disease

A growing body of literature has established the anabolic benefits of testosterone （T） therapy in hypogonadal men. However, there remains a paucity of data regarding the risks of exogenous androgen use in older men and the potential for adverse effects on the prostate gland. Whether T therapy in older, hypogonadal men might worsen lower urinary tract symptoms or exacerbate, unmask, or even incite prostate cancer development has tempered enthusiasm for T therapy, while known prostatic disease has served as a relative contraindication to T therapy. Androgens are necessary for the development and maintenance of the prostate gland. However, epidemiologic studies do not consistently find a positive relationship between endogenous serum androgen concentrations and the risk of prostate disease. Recent data demonstrate that 5α-reductase inhibitors decrease the risk of low-grade prostate cancer, suggesting that modifying androgen metabolism may have beneficial effects on prostate health, yet similar reductions in high-grade disease have not been observed, thereby questioning the true clinical benefits of these agents for chemoprevention. Knowing how to best investigate the relationship between androgens and the development of prostate disease given the lack of large, randomized trials is difficult. Accumulating data challenges the assumption that alterations in serum androgens have parallel effects within the prostate hormonal environment or change androgen-regulated processes within the gland. Long-term intervention studies are needed to truly ascertain the effects of androgen manipulation on prostate tissue and disease risk. However, available data do not support the notion that restoring serum androgens to normal physiologic ranges drives prostate disease.

Androgens and esophageal cancer: What do we know?

Significant disparities exist between genders for the development and progression of several gastrointestinal(GI) diseases including cancer. Differences in incidence between men vs women for colon, gastric and hepatocellular cancers suggest a role for steroid sex hormones in regulation of GI carcinogenesis. Involvement of intrinsic gender-linked mechanisms is also possible for esophageal adenocarcinoma as its incidence is disproportionally high among men. However, the cause of the observed gender differences and the potential role of androgens in esophageal carcinogenesis remains unclear, even though the cancer-promoting role of androgen receptors(AR) shown in other cancers such as prostate and bladder suggests this aspect warrants exploration. Several studies have demonstrated expression of ARs in esophageal cancer. However, only one study has suggested a potential link between AR signaling and outcome- poorer prognosis. Two groups have analyzed data from cohorts with prostate cancer and one of these found a decreased incidence of esophageal squamous and adenocarcinoma after androgen deprivation therapy. However, very limited information is available about the effects of androgen and AR-initiated signaling on esophageal cancer cell growth in vitro and in vivo. Possible mechanisms for androgens/AR involvement in the regulation of esophageal cancer growth are considered, and the potential use of AR as a prognostic factor and clinical target is highlighted, although insufficient evidence is available to support clinical trials of novel therapies. As esophageal adenocarcinoma is a gender linked cancer with a large male predominance further studies are warranted to clarify the role of androgens and ARs in shaping intracellular signaling and genomic responses in esophageal cancer.

Androgens/Androgen Receptor in the Management of Skin Diseases

Beyond regulation of male sexual function, the increasing evidence shows that androgens and androgen receptor (AR) have a variety of physiological and pathological effects on the skin. Skin cells express all androgen metabolizing enzymes that are required for independent skin androgen synthesis and the development of hyperandrogenic related disorders such as acne, hirsutism and androgenetic alopecia. Targeting various elements of androgen function and metabolism is the major goal of medication design for the treatment of androgen-related diseases. Antiandrogen drugs such as clascoterone, flutamide could improve conditions. Even though the involvement of androgens and AR in skin diseases has been investigated for a long time, their molecular mechanisms in skin disorders remain largely insufficient. In this review, recent studies and advances on the role of androgens/AR in several skin-related diseases and their therapeutics are systematically summarized.

Androgens, Male Hypogonadism and Traumatic Brain Injury

Traumatic brain injury (TBI) is a worldwide public health problem. Populations with a growing number of vehicles are experiencing many traumas and accidents. The highest-risk group is young men. Significant advances in neurosurgery and intensive therapy have resulted in increased survival rates of TBI patients. These higher survival rates, in turn, have led to an increasingly higher number of patients with neurological, cognitive, clinical, and social problems. This lack of knowledge about TBI has been called by some “the silent epidemic”. In recent years, studies of patients with moderate and severe TBI are increasing. Glasgow Coma Scale ≤ 8 and abnormal pupils at admission are used to determine the prognosis of patients with moderate or severe TBI. Several biomarkers such as interleukins, thiobarbituric acid reactive species, and some hormones have been studied in an effort to aid prognosis. Testosterone plays a key role in men. Thus, an understanding of androgens in TBI is essential to follow these survivors of head trauma. This review will discuss the epidemiology of TBI, its association with male hypogonadism, and possible treatments.

Androgens and estrogens in skeletal sexual dimorphism

Bone is an endocrine tissue expressing androgen and estrogen receptors as well as steroid metabolizing enzymes. The bioactivity of circulating sex steroids is modulated by sex hormone-binding globulin and local conversion in bone tissue, for example, from testosterone （T） to estradiol （E2） by aromatase, or to dihydrotestosterone by 5（x-reductase enzymes. Our understanding of the structural basis for gender differences in bone strength has advanced considerably over recent years due to increasing use of （high resolution） peripheral computed tomography. These microarchitectural insights form the basis to understand sex steroid influences on male peak bone mass and turnover in cortical vs trabecular bone. Recent studies using Cre/LoxP technology have further refined our mechanistic insights from global knockout mice into the direct contributions of sex steroids and their respective nuclear receptors in osteoblasts, osteoclasts, osteocytes, and other cells to male osteoporosis. At the same time, these studies have reinforced the notion that androgen and estrogen deficiency have both direct and pleiotropic effects via interaction with, for example, insulin-like growth factor 1, inflammation, oxidative stress, central nervous system control of bone metabolism, adaptation to mechanical loading, etc., This review will summarize recent advances on these issues in the field of sex steroid actions in male bone homeostasis.

The physiological and pharmacological basis for the ergogenic effects of androgens in elite sports

Androgen doping in power sports is undeniably rampant worldwide. There is strong evidence that androgen administration in men increases skeletal muscle mass, maximal voluntary strength and muscle power. However, we do not have good experimental evidence to support the presumption that androgen administration improves physical function or athletic performance. Androgens do not increase specific force or whole body endurance measures. The anabolic effects of testosterone on the skeletal muscle are mediated through androgen receptor signaling. Testosterone promotes myogenic differentiation of multipotent mesenchymal stem cells and inhibits their differentiation into the adipogenic lineage. Testosterone binding to androgen receptor induces a conformational change in androgen receptor protein, causing it to associate with beta-catenin and TCF-4 and activate downstream Wnt target genes thus promoting myogenic differentiation. The adverse effects of androgens among athletes and recreational bodybuilders are under reported and include acne, deleterious changes in the cardiovascular risk factors, including a marked decrease in plasma high-density lipoproteins （HDL） cholesterol level, suppression of spermatogenesis resulting in infertility, increase in liver enzymes, hepatic neoplasms, mood and behavioral disturbances, and long term suppression of the endogenous hypothalamic-pituitary-gonadal axis. Androgens are often used in combination with other drugs which may have serious adverse events of their own. In spite of effective methods for detecting androgen doping, the policies for screening of athletes are highly variable in different countries and organizations and even existing policies are not uniformly enforced.

Could androgens maintain specific domains of mental health in aging men by preserving hippocampal neurogenesis

Interest surrounds the role of sex-hormones in regulating brain function outside of reproductive behaviour. Declining androgen production in aging males has been associated with cognitive impairment, depression and increased risk of developing Alzheimer＇s disease. Indication for testosterone replacement therapy is based on biochemically determined low circulating testosterone combined with manifest symptoms. However, which aspects of age-related cognitive decline are attributable to low circulating testosterone remain ambiguous. Studies examining cognition in aging men receiving testosterone replacement therapy have yielded equivocal results. The exact role of testosterone in maintaining cognitive function and the underlying neural mechanisms are largely unknown, though it would appear to be domain specific. Cladty in this area will provide clinical direction toward addressing an increasing healthcare burden of mental health decline coincident with increasing longevity. The premise that androgens contribute to maintaining aspects of mental health in aging men by preserving hippocampal neurogenesis will be used as a forum in this review to discuss current knowledge and the need for further studies to better define testosterone replacement strategies for aging male health.

Reduced mesencephalic astrocyte-derived neurotrophic factor expression by mutant androgen receptor contributes to neurodegeneration in a model of spinal and bulbar muscular atrophy pathology

Spinal and bulbar muscular atrophy is a neurodegenerative disease caused by extended CAG trinucleotide repeats in the androgen receptor gene,which encodes a ligand-dependent transcription facto r.The mutant androgen receptor protein,characterized by polyglutamine expansion,is prone to misfolding and forms aggregates in both the nucleus and cytoplasm in the brain in spinal and bulbar muscular atrophy patients.These aggregates alter protein-protein interactions and compromise transcriptional activity.In this study,we reported that in both cultured N2a cells and mouse brain,mutant androgen receptor with polyglutamine expansion causes reduced expression of mesencephalic astrocyte-de rived neurotrophic factor.Overexpressio n of mesencephalic astrocyte-derived neurotrophic factor amelio rated the neurotoxicity of mutant androgen receptor through the inhibition of mutant androgen receptor aggregation.Conversely.knocking down endogenous mesencephalic astrocyte-derived neurotrophic factor in the mouse brain exacerbated neuronal damage and mutant androgen receptor aggregation.Our findings suggest that inhibition of mesencephalic astrocyte-derived neurotrophic factor expression by mutant androgen receptor is a potential mechanism underlying neurodegeneration in spinal and bulbar muscular atrophy.

Resistance to second generation antiandrogens in prostate cancer: pathways and mechanisms

Androgen deprivation therapy targeting the androgens/androgen receptor(AR)signaling continues to be the mainstay treatment of advanced-stage prostate cancer.The use of second-generation antiandrogens,such as abiraterone acetate and enzalutamide,has improved the survival of prostate cancer patients;however,a majority of these patients progress to castration-resistant prostate cancer(CRPC).The mechanisms of resistance to antiandrogen treatments are complex,including specific mutations,alternative splicing,and amplification of oncogenic proteins resulting in dysregulation of various signaling pathways.In this review,we focus on the major mechanisms of acquired resistance to second generation antiandrogens,including AR-dependent and AR-independent resistance mechanisms as well as other resistance mechanisms leading to CRPC emergence.Evolving knowledge of resistance mechanisms to AR targeted treatments will lead to additional research on designing more effective therapies for advanced-stage prostate cancer.

Treatment of transfusion-dependent nonsevere aplastic anemia with cyclosporine A plus ATG/ALG versus cyclosporine A plus androgens: a retrospective single center study

Objective To determine whether cyclosporine A(CsA)plus andronges was as effective as the current standard immunosuppressive therapy(IST)for transfusion-dependent nonsevere aplastic anemia(TD-NSAA).

Relationship between gene expression of nitric oxide synthase and androgens in rat corpus cavernosum

To clarify the dependence of neural nitric oxide synthase mRNA (nNOSmRNA) and endothelial nitric oxide synthase mRNA (eNOSmRNA) on androgens (testosterone[T] and dihydrotestosterone [DHT]) Methods 160 male Sprague Dawley (SD) rats were divided into Groups A (56 rats,5 weeks old),B (50rats,10 weeks old) and C (54 rats,58 weeks old) Groups A,B and C were all subdivided respectively into five Subgroups Subgroup 1: intact controls; Subgroup 2: castrated;Subgroup 3: castrated with testosterone undecanoate 25mg/kg·mon -1 ,intramuscular injection,Subgroup 4: castrated with testosterone undecanoate 50mg/kg·mon -1 ,intramuscular injection and Subgroup 5: treated with finasteride 4 5 mg/kg·day -1 ,orally Four and ten weeks after treatments described above,one half of the rats were killed Serum samples were taken for measurements of T, free testosterone (FT) and DHT by radioimmunoassay Penile samples were treated with liquid nitrogen and then stored at - 80℃ nNOSmRNA and eNOSmRNA were detected by semiquantitative reverse-transcription polymerase chain reaction (RT-PCR) and Dot blot Results There was no significant difference between Subgroup 1 and Subgroup 2 or Subgroup 5 in all Groups A, B and C The expression of penile eNOSmRNA of Group A was significantly increased (4weeks model) ( P <0 05) or increased (10 weeks model) ( P <0 05) in Subgroup 2 or 5 compared with those in Subgroup 1 There was no significant difference between Subgroup 1 and Subgroup 2 or Subgroup 5 of Group B in 4 weeks model ( P >0 05) There was an elevation when animals were castrated or treated with finasteride in the 10 weeks model The expression of penile eNOSmRNA of Group C was significantly increased (10 weeks model) ( P <0 05) or increased (4 weeks model) in Subgroup 2 compared with those in Subgroup 1 The production of eNOSmRNA in Subgroup 5 was also increased (including 4 and 10 week models) When T was supplied for castration, the penile eNOSmRNA was decreased to some extent;the greater the dose of T given,the lower penile eNOSmRNA was observed Conclusions The expression of eNOSmRNA in SD rat penile tissue increases while T or DHT diminishes Sometimes androgens modulate penile eNOSmRNA in opposite directions There is no correlation between the expression of nNOSmRNA and androgens (including T and DHT) Androgens give rise to penile erection probably not via the NOS pathway

Effects of competitive and noncompetitive 5α-reductase inhibitors on serum and intra-prostatic androgens in beagle dogs

Background 5a-Reductase inhibitors （5a-RI） act by inhibiting the conversion of testosterone to dihydrotestosterone （DHT）, thereby preventing DHT induced benign prostatic hyperplasia. The existing 5a-RIs can be classified into two types： competitive and noncompetitive. Currently, limited evidence is available concerning the effect differences between the two types of 5a-RI on androgens. The purpose of this study was to assess the effects of competitive and noncompetitive 5a-RIs on serum and intra-prostatic androgens in beagle dogs. Methods Twenty beagles with spontaneous benign prostatic hyperplasia were randomly allocated into two groups： epristeride group （n=10） in which beagles were treated with epristeride at 1 mg/kg once a day for 3 months, and finasteride group （n=10） in which beagles were treated with finasteride at 1 mg/kg once a day for 3 months. The levels of intra-prostatic testosterone and DHT were measured before treatment and on day one after three months medication. Serum levels of testosterone and DHT were measured at the same time points. Changes in androgen levels before and after treatment were analyzed, and comparisons were made within each treatment group and between treatment groups. Results After 3-month treatment, serum and intra-prostatic DHT levels all decreased significantly in both the epristeride and finasteride groups. The change of DHT in serum was significantly higher in the finasteride group （-14% and -43% in epdsteride and finasteride groups respectively, with P〈0.001）; however there was no significant difference in the changes of intra-prostatic DHT between the two groups （-47% and -51% in epristeride and finasteride groups, respectively, P=0.304）. The decreases in DHT levels were accompanied by reciprocal increases in serum and intra-prostatic testosterone levels. Changes of testosterone were significantly higher in finasteride group both in serum （20% and 42% in epristeride and finasteride groups, respectively, P〈0.001） and in prostate tissue （18% and 29% in epristeride and finasteride groups, respectively, P=0.004）. Conclusions Two types of 5a-RI have similar effects in reducing DHT in prostate tissue in beagles. Competitive 5a-RI may reduce serum DHT to a greater scale, and significantly increase testosterone in beagle serum and prostate.

The contradictory role of androgens in cutaneous and major burn wound healing

Wound healing is a complex process involving four overlapping phases:haemostasis,inflammation,cell recruitment and matrix remodeling.In mouse models,surgical,pharmacological and genetic approaches targeting androgen actions in skin have shown that androgens increase interleukin-6 and tumor necrosis factor-αproduction and reduce wound re-epithelization and matrix deposition,retarding cutaneous wound healing.Similarly,clinical studies have shown that cutaneous wound healing is slower in men compared to women.However,in major burn injury,which triggers not only local wound-healing processes but also systemic hypermetabolism,the role of androgens is poorly understood.Recent studies have claimed that a synthetic androgen,oxandrolone,increases protein synthesis,improves lean body mass and shortens length of hospital stay.However,the possible mechanisms by which oxandrolone regulates major burn injury have not been reported.In this review,we summarize the current findings on the roles of androgens in cutaneous and major burn wound healing,as well as androgens as a potential therapeutic treatment option for patients with major burn injuries.

Characterization of distinct microbiota associated with androgenetic alopecia patients treated and untreated with platelet-rich plasma(PRP)

Background:Androgenic alopecia(AGA)is the most common type of hair loss in men,and there are many studies on the treatment of hair loss by platelet-rich plasma(PRP).The human scalp contains a huge microbiome,but its role in the process of hair loss remains unclear,and the relationship between PRP and the microbiome needs further study.Therefore,the purpose of this study was to investigate the effect of PRP treatment on scalp microbiota composition.Methods:We performed PRP treatment on 14 patients with AGA,observed their clinical efficacy,and collected scalp swab samples before and after treatment.The scalp microflora of AGA patients before and after treatment was characterized by amplifying the V3-V4 region of the 16 s RNA gene and sequencing for bacterial identification.Results:The results showed that PRP was effective in the treatment of AGA patients,and the hair growth increased significantly.The results of relative abundance analysis of microbiota showed that after treatment,g_Cutibacterium increased and g_Staphylococcus decreased,which played a stable role in scalp microbiota.In addition,g_Lawsonella decreased,indicating that the scalp oil production decreased after treatment.Conclusions:The findings suggest that PRP may play a role in treating AGA through scalp microbiome rebalancing.

Exogenous testosterone therapy on choroid in androgen deficiency

AIM:To investigate the effects of exogenous testosterone treatment on the choroidal parameters in patients with androgen deficiency.METHODS:Right eyes of 24 patients with androgen deficiency and 31 healthy volunteers were included in the study.The eyes were scanned for subfoveal choroidal thickness(SFCT),choroidal vascularity index(CVI),choroidstromal area(C-SA),choroid-luminal area(C-LA),choroidstromal to luminal area ratio(CSLR),and the choroidal parameters within central 1500μm of the macula(CVI1500,C-LA1500,C-SA1500,and CSLR1500)by enhanced-depth imaging optical coherence tomography(EDI-OCT)at baseline,6th and 18th weeks of the exogenous testosterone treatment.RESULTS:The mean SFCT values of the androgen deficient groups and healthy controls were 307.7±27.0 and 303.2±37.2μm(P=0.8).However,CVI,C-SA,CSLR,CVI1500,C-LA1500,and CSLR1500 were significantly different between the groups(all P<0.01).At the 6th week visit after exogenous testosterone treatment,SFCT,CVI,C-LA,and C-SA were significantly decreased,and these parameters returned to baseline levels at the 18th-week visit(all P>0.05).However,CVI1500 and LA1500 significantly increased at the end of the follow-up period(P<0.001).CONCLUSION:CVI is lower in androgen-deficient patients than in healthy subjects.The alterations in the choroid during the testosterone peak are transient in the treatment of patients with androgen deficiency.However,the increase in CVI within the central 1500μm of the macula persists even after 4mo.

Androgen signaling inhibits de novo lipogenesis to alleviate lipid deposition in zebrafish

Testosterone is closely associated with lipid metabolism and known to affect body fat composition and muscle mass in males.However,the mechanisms by which testosterone acts on lipid metabolism are not yet fully understood,especially in teleosts.In this study,cyp17a1-/-zebrafish(Danio rerio)exhibited excessive visceral adipose tissue(VAT),lipid content,and up-regulated expression and activity of hepatic de novo lipogenesis(DNL)enzymes.The assay for transposase accessible chromatinwithsequencing(ATAC-seq)results demonstrated that chromatin accessibility of DNL genes was increased in cyp17a1-/-fish compared to cyp17a1+/+male fish,including stearoyl-CoA desaturase(scd)and fatty acid synthase(fasn).Androgen response element(ARE)motifs in the androgen signaling pathway were significantly enriched in cyp17a1+/+male fish but not in cyp17a1-/-fish.Both androgen receptor(ar)-/-and wildtype(WT)zebrafish administered with Ar antagonist flutamide displayed excessive visceral adipose tissue,lipid content,and up-regulated expression and activity of hepatic de novo lipogenesis enzymes.The Ar agonist BMS-564929 reduced the content of VAT and lipid content,and down-regulated acetyl-CoA carboxylase a(acaca),fasn,and scd expression.Mechanistically,the rescue effect of testosterone on cyp17a1-/-fish in terms of phenotypes was abolished when ar was additionally depleted.Collectively,these findings reveal that testosterone inhibits lipid deposition by down-regulating DNL genes via Ar in zebrafish,thus expanding our understanding of the relationship between testosterone and lipid metabolism in teleosts.

N-acetylcysteine and zinc sulphate abate di-2-ethylhexyl phthalate-mediated reproductive dysfunction in rats:Focus on oxidative and sex hormone receptors mechanisms

Objective:To investigate the potential of N-acetylcysteine(NAC)and zinc sulphate(ZnSO_(4))in mitigating reproductive dysfunction caused by di-2-ethylhexyl phthalate(DEHP)in rats and to understand the underlying mechanisms,specifically oxidative stress and sex hormone receptor activity.Methods:Thirty-five male Wistar rats were randomly divided into five equal groups(n=7 per group).Group 1 was administered 0.5 mL of distilled water and served as the control group.Group 2 was given only DEHP(750 mg/kg/day),while group 3,4 and 5 were given DEHP(750 mg/kg/day)plus NAC(100 mg/kg/day),DEHP(750 mg/kg/day)plus ZnSO_(4)(0.5 mg/kg/day),and DEHP(750 mg/kg/day)plus NAC(100 mg/kg/day)as well as ZnSO_(4)(0.5 mg/kg/day),respectively.All treatments lasted for 21 days.Samples were obtained after the rats were sacrificed,and hormones levels in the serum and markers of oxidative stress in the testicles were analyzed using the enzyme-linked immunosorbent assay.The amount of androgen receptors in the testicles was determined by immunohistochemistry,and the susceptibility of testosterone and DEHP to bind to androgen receptor and 5α-reductase was determined by molecular docking studies.Results:DEHP decreased reproductive hormones,testicular antioxidant enzymes,increased malondialdehyde levels,and negatively impacted histology of the pituitary and testes.NAC or ZnSO_(4) treatment showed a marked improvement in testicular antioxidant status and hormone levels,as well as a positive effect on the histology of the pituitary and testes.The combination of both treatments appeared to be more effective.The affinity of DEHP to bind to androgen receptors may lead to disruption of androgen receptor signaling,which can further result in dysfunction of hormones related to androgen.However,NAC is more likely to form stronger binding interactions with follicle stimulating hormone and luteinizing hormone receptors,as well as gonadotropin-releasing hormone receptors,when compared to DEHP.Conclusions:The possibility that NAC and ZnSO_(4) could downregulate DEHP-induced sex hormone changes is suggested by their potential to reduce toxicity.