Differential effects of cross-sex hormonal treatment on plasma asymmetric dimethylarginine (ADMA) in healthy male-to-female and female-to-male transsexuals

Testosterone treatment impacts the intestinal microbiome of transgender individuals

Medical modulation of sex hormone levels is a cornerstone of treatment for many conditions that impact well-being, including cancer, fertility/infertility, gender dysphoria, and chronic metabolic diseases such as diabetes and obesity. The microbial residents of the intestine, known as the microbiota, interact with sex hormones in the intestine, and there is correlative evidence that this interaction is bidirectional. Based on these published findings, we hypothesized that transgender individuals receiving exogenous testosterone as part of their gender-affirming medical treatment might undergo changes in their intestinal microbiome. To test this, we collected 26 stool samples from nine individuals before and up to 8 months after initiation of treatment with exogenous testosterone and subjected these samples to metagenomic analysis. While no species were significantly associated with the duration of testosterone therapy, pathways that generate glutamate increased in abundance, while those that consume glutamate decreased. Glutamate is a precursor of arginine, and testosterone is known to increase levels of arginine and its metabolites in the plasma. We hypothesize that testosterone increases the uptake of glutamate by enterocytes, thus decreasing access of the microbiota to this amino acid. While this pilot study establishes the impact of testosterone therapy on the intestinal microbiome, a more comprehensive study is necessary to establish the impact of testosterone-driven metagenomic shifts on the stool metatranscriptome, the stool metabolome, and the plasma metabolome.IMPORTANCEThe human intestine is inhabited by a large community of microbes known as the microbiome. Members of the microbiome consume the diet along with their human host. Thus, the metabolomes of the host and microbe are intricately linked. Testosterone alters the plasma metabolome. In particular, plasma levels of arginine and its metabolites and testosterone are positively correlated. To investigate the impact of exogenous testosterone on the microbiome, we analyzed the stool metagenomes of transgender individuals before and after the initiation of testosterone treatment. In this pilot project, we found a modest impact on the microbiome community structure but an increase in the abundance of metabolic pathways that generate glutamate and spare glutamate consumption. We propose that the host uses glutamate to generate arginine, decreasing the amount available for the microbiome.

12-months metabolic changes among gender dysphoric individuals under cross-sex hormone treatment: a targeted metabolomics study

Metabolomic analyses in epidemiological studies have demonstrated a strong sexual dimorphism for most metabolites. Cross-sex hormone treatment (CSH) in transgender individuals enables the study of metabolites in a cross-gender setting. Targeted metabolomic profiling of serum of fasting transmen and transwomen at baseline and following 12 months of CSH (N = 20/group) was performed. Changes in 186 serum metabolites and metabolite ratios were determined by targeted metabolomics analysis based on ESI-LC-MS/MS. RandomForest (RF) analysis was applied to detect metabolites of highest interest for grouping of transwomen and transmen before and after initiation of CSH. Principal component analysis (PCA) was performed to check whether group differentiation was achievable according to these variables and to see if changes in metabolite levels could be explained by a priori gender differences. PCA predicted grouping of individuals-determined by the citrulline/arginine-ratio and the amino acids lysine, alanine and asymmetric dimethylarginine - in addition to the expected grouping due to changes in sex steroids and body composition. The fact that most of the investigated metabolites did, however, not change, indicates that the majority of sex dependent differences in metabolites reported in the literature before may primarily not be attributable to sex hormones but to other gender-differences.

Cardiovascular disease in transsexual persons treated with cross-sex hormones: reversal of the traditional sex difference in cardiovascular disease pattern

OBJECTIVE

The incidence of heart disease increases with age, but is lower in women than in men up to 75 years. A protective effect of female sex hormones or, alternatively, acceleration in male heart disease by testosterone at younger ages, could explain this sex difference. In contrast with the above, male-to-female transsexual subjects (MtoF) treated with estrogens (+anti-androgens) show more cardiovascular pathology than female-to-male transsexual subjects (FtoM) receiving testosterone. Why MtoF suffer more frequently from cardiovascular disease than females is as yet unclear. The mode of cross-sex hormone treatment may be a factor, and, if so, it may need adaptations.

SUBJECTS AND METHODS

Studies in transsexual people on the effects of cross-sex hormone treatment on surrogate cardiovascular risks and on clinical endpoints were reviewed. With regard to MtoF, a parallel was sought with men with prostate cancer, undergoing androgen deprivation and estrogen administration.

RESULTS

Exposure of FtoM to testosterone was not associated with a strong increase in cardiovascular events. Aging and pre-existing cardiovascular pathology contributed to the risk of cardiovascular disease in MtoF. Use of the synthetic biopotent compound ethinyl estradiol in a dose two to four times of oral contraceptives increased cardiovascular risk substantially. The route of administration of estrogens (oral vs transdermal) may have impacted on the risks.

CONCLUSION

MtoF should not be treated with oral ethinyl estradiol. Transdermal estrogens are probably safer than oral estrogens. Pre-existing cardiovascular risks should be taken into consideration when prescribing and choosing the type of estrogens in cross-sex hormone administration (oral vs transdermal). In addition, risk factors, as they emerge with aging, should be addressed.

Altered arterial stiffness in male-to-female transsexuals undergoing hormonal treatment

AIM

Male-to-female (MTF) transsexuals are treated with estrogen with and without progestin through a variety of routes. The aim of this study is to evaluate the arterial stiffness in MTF transsexuals undergoing hormonal treatment.

METHODS

We evaluated the arterial stiffness in 156 MTF transsexuals (22 untreated and 129 treated with estrogen only or plus progestin) using a volume-plethysmographic apparatus equipped with a multi-element applanation tonometry sensor.

RESULTS

MTF transsexuals treated with parenteral estrogen were significantly older than untreated MTF transsexuals. Hematocrit, uric acid and activated partial thromboplastin time in treated MTF transsexuals were significantly lower than in untreated MTF transsexuals. The level of high-density lipoprotein cholesterol in MTF transsexuals treated with oral estrogen was significantly higher than in untreated MTF transsexuals or those treated with parenteral estrogen with and without progestin. The systolic blood pressure in MTF transsexuals treated with estrogen only is significantly lower than that in untreated MTF transsexuals. The brachial-ankle pulse wave velocity was significantly decreased in MTF transsexuals treated with estrogen compared to that in untreated MTF transsexuals or in those treated with estrogen plus progestin. The carotid augmentation index in MTF transsexuals treated with oral estrogen was significantly lower than that in MTF transsexuals treated with parenteral estrogen or oral estrogen plus progestin.

CONCLUSIONS

Estrogen treatment is likely to have some beneficial effects on lipid metabolism and vascular function in MTF transsexuals; however, progestin administered with estrogen may have adverse effects on arterial stiffness.

Plasma dimethylarginines during the acute inflammatory response

INTRODUCTION

Asymmetric dimethylarginine (ADMA) concentrations are increased in critically ill patients and may play a role in multiple organ failure. However, plasma ADMA concentrations during the development of the inflammatory response have not been documented. We measured plasma ADMA, as well as urinary excretion of its major metabolite dimethylamine, and nitrate as a marker of nitric oxide synthase (NOS) activity, in a cohort of patients undergoing elective knee arthroplasty that is known to provoke a significant inflammatory response.

METHODS

Thirty-eight patients were recruited. Fasting venous blood samples were obtained pre-operatively and at 12h and daily until the fifth post-operative day. ADMA and symmetric dimethylarginine (SDMA) were measured by high-performance liquid chromatography (HPLC). Urinary dimethylamine and nitrate were measured pre-operatively and on each of the post-operative mornings using HPLC and expressed as a ratio to creatinine.

RESULTS

Plasma ADMA fell by a median of 31% during the post-operative period, reaching a nadir on day 2, and recovering to baseline by the end of the study. SDMA showed no significant changes. No increase in urinary dimethylamine excretion was noted until day 5 post-op, whereupon it doubled. Urinary nitrate showed a small, but nonsignificant decrease on day 2, suggesting no major activation of NOS activity.

CONCLUSIONS

Plasma ADMA concentration decreases rapidly and transiently during the first 48h of acute inflammation. This appears not be caused by increased catabolism and may reflect increased cellular partitioning. This may serve to regulate NOS activity and prevent harmful increases in inducible NOS in situations where it is not appropriate.

Cellular ADMA: regulation and action

Asymmetric (N(G),N(G)) dimethylarginine (ADMA) is present in plasma and cells. It can inhibit nitric oxide synthase (NOS) that generates nitric oxide (NO) and cationic amino acid transporters (CATs) that supply intracellular NOS with its substrate, l-arginine, from the plasma. Therefore, ADMA and its transport mechanisms are strategically placed to regulate endothelial function. This could have considerable clinical impact since endothelial dysfunction has been detected at the origin of hypertension and chronic kidney disease (CKD) in human subjects and may be a harbinger of large vessel disease and cardiovascular disease (CVD). Indeed, plasma levels of ADMA are increased in many studies of patients at risk for, or with overt CKD or CVD. However, the levels of ADMA measured in plasma of about 0.5micromol.l(-1) may be below those required to inhibit NOS whose substrate, l-arginine, is present in concentrations many fold above the Km for NOS. However, NOS activity may be partially inhibited by cellular ADMA. Therefore, the cellular production of ADMA by protein arginine methyltransferase (PRMT) and protein hydrolysis, its degradation by N(G),N(G)-dimethylarginine dimethylaminohydrolase (DDAH) and its transmembrane transport by CAT that determines intracellular levels of ADMA may also determine the state of activation of NOS. This is the focus of the review. It is concluded that cellular levels of ADMA can be 5- to 20-fold above those in plasma and in a range that could tonically inhibit NOS. The relative importance of PRMT, DDAH and CAT for determining the intracellular NOS substrate:inhibitor ratio (l-arginine:ADMA) may vary according to the pathophysiologic circumstance. An understanding of this important balance requires knowledge of these three processes that regulate the intracellular levels of ADMA and arginine.