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From the Clinical Research Centers |
Divisions of Endocrinology, Department of Medicine (C.W., V.M., B.S., R.S.S.) and Pediatrics (N.B.), Harbor-UCLA Medical Center, Torrance, California 90509; Salem Veterans Adminstration Medical Center (A.I.), Salem, Virginia 24153; Southern California Permanente Medical Group (F.Z.), Los Angeles, California 91188; Unimed Pharmaceuticals Inc. (S.M.F., R.E.D.), Buffalo Grove, Illinois 60089; and University of Virginia Health Sciences Center (J.D.V.), Charlottesville, Virginia 22908
Address all correspondence and requests for reprints to: Christina L. Wang, Department of Pediatrics, Clinical Study Center, Harbor UCLA Medical Center, 1000 West Carson Street, Box 16, Torrance, California 90509-2910. E-mail: wang{at}harbor6.humc.edu
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Abstract |
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 Top Abstract IntroductionSubjects and MethodsResultsDiscussionReferences |
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-dihydrotestosterone (DHT) gel (0.7% hydroalcoholic gel
with 2.3 g gel delivering 16 mg DHT) applied daily over one upper
arm (16 mg); both arms and shoulders (32 mg); and bilateral arms,
shoulders, and upper abdomen (64 mg), respectively. Multiple blood
samples for the pharmacokinetic profile for DHT and testosterone (T)
were drawn over a 24-h period before application, after first
application, and after 14 days of daily application of DHT gel.
Additional blood samples for DHT, T, and estradiol were obtained
24 h after application on days 3, 5, 7, and 11 and after
discontinuation of DHT gel for 3, 5, 7, and 14 days (days 17, 19, 21,
and 28 after first instituting treatment). No skin irritation was
observed in any of the subjects. Before treatment, mean serum DHT and T
levels were not different among the three dose groups. The serum DHT
levels increased gradually after gel application on the first day,
reaching a plateau between 12–18 h. During the 14 days of daily
application of DHT gel, the mean baseline DHT levels reached steady
state by day 2 or 3 and were elevated considerably above baseline. Mean
serum DHT levels varied between 8–11, 12–17, and 14–24 nmol/L in the
16-, 32-, and 64-mg groups, respectively. The area under curve (AUC) of
serum DHT levels over 24 h on day 14 were 6.0-, 6.9-, and
16.1-fold above pretreatment levels for the three doses. Concomitant
with the increase in serum DHT levels, the AUC produced by endogenous
serum T levels decreased to 75, 56, and 36% of baseline after 14 days
of 16, 32, and 64 mg/day DHT gel. Similar patterns of decreases in AUC
of serum estradiol levels were found. The calculated mean total
androgen levels (T + DHT) rose with DHT gel application in all groups
(P < 0.0001) on both days 1 and 14. We conclude
that the three doses of DHT gel tested might provide adequate androgen
replacement in hypogonadal men at the low, middle, and high
physiological androgen (T + DHT) range. |
Introduction |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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-reductase enzymes to 5-dihydrotestosterone (DHT).
DHT binds to androgen receptors with a greater affinity than T. Most
efforts to treat men with androgen insufficiency and/or
underresponsiveness have used T as the active steroid. We are presently
exploring the possible advantages of DHT as an androgenic therapeutic
agent. Because DHT cannot be aromatized to estradiol
(E2), when administered as androgen replacement to
hypogonadal men, DHT should have positive anabolic effect while
avoiding the side effect of gynecomastia, which may be a problem
especially in children (1). DHT would be the primary androgen
replacement therapy for patients with 5-reductase 2 deficiency (2).
It is potentially also useful in the treatment of pubertal gynecomastia
(3, 4), microphallus (5), and constitutional delayed puberty. Unlike T,
which has been delivered as injectables, implants, transdermal patches,
and oral and sublingual pills (6), DHT has been used in injectable and
transdermal forms. Injectable DHT heptanoate (enanthate) has only been
used experimentally in boys and men for short-term studies (3, 7) but
is not commercially available. DHT has also been administered as a
percutaneous gel, as a method of androgen replacement, using a
preparation available in some countries in Europe. A new DHT gel
formulation has been prepared for possible application in the United
States and elsewhere, on the premise that DHT gel may have several
advantages over the currently available androgens, including possible
greater pharmacological potency in bioassays (1), single daily
application without a patch, no skin irritation, avoidance of
first-pass hepatic metabolism, and maintenance of stable serum DHT
levels after daily administration. The DHT used in prior studies was formulated as a hydroalcoholic gel containing 2.5% solution of DHT (10 g gel contains 250 mg DHT). When applied to the skin, DHT rapidly penetrated the stratum corneum. The diffusion of DHT through the epidermis and dermis took place over several hours (8). When applied to large areas of skin, although less than 10% of DHT was absorbed, serum DHT was maintained at stable levels both in hypogonadal and eugonadal men (9, 10, 11, 12, 13, 14). DHT administered as a percutaneous gel suppressed pulsatile LH and FSH secretion most likely via negative feedback on hypothalamic GnRH secretion (13, 15, 16).
In patients with hypogonadotropic hypogonadism, DHT gel application resulted in virilization, increased muscle mass, and improved sexual function, without an increase in prostate size (14). When administered for a mean duration of 1.8 yr to older men (55–70 yr), DHT gel led to improved sexual function and a 15 percent decrease in prostate size (17). The explanation for the decreased prostate size was based on the observation that development of benign prostate hyperplasia in dogs (BPH) requires the synergistic stimulation of prostate stromal growth by local availability of both androgen (DHT) and estrogen (E2) (18, 19, 20, 21). Because DHT application suppressed gonadotropins, resulting in decreased endogenous T and E2 secretion, administration of DHT might result in significant decrease in size of the prostate because of the absence of the synergistic effect of intraprostatic E2 and/or intraprostatic DHT formation from T. There are other data in the rat, suggesting that DHT may be less likely than T to induce prostate pathology (22).
Despite reports of these clinical studies, the detailed pharmacokinetics of DHT applied as a gel on the skin have not been reported. The new DHT formulation used in these studies is a 0.7% hydroalcoholic gel administered in metered doses. The present investigations examined the pharmacokinetics of three doses of this newly formulated DHT gel administered daily for 14 days in normal older men. We demonstrated a dose-related increase in serum DHT levels after gel application, which suggests that the doses tested, if administered to hypogonadal men, should provide adequate serum androgen levels (T + DHT) replacement at the low, middle, or high range encountered in normal men.
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Subjects and Methods |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Healthy men, 60 yr of age or older, were recruited into the study after a screening examination to exclude major and chronic medical illness, such as heart, lung, liver, kidney, neurologic, or psychiatric diseases. The subjects, on admission to the study, had normal blood count, urinalysis, and blood chemistry. Their hematocrit was required to be less than 50%. They gave no history of prostate disease or symptoms. They had no abnormalities indicative of prostate cancer on rectal examination, prostate specific antigen levels of less than 4 ng/mL, and a maximum urine flow of over 12 mL per second. Their serum T, LH, and FSH levels were checked at screening but were not used as admission criteria. At the screening visit, five subjects had serum T levels below the normal range (less than 10.1 nmol/L) for young adult males. Of these, two were randomly assigned to the 16-mg group, one to the 32-mg group, and two to the 64-mg group.
Twenty-five subjects participated in the study. Fifteen men were
studied at Harbor-UCLA Medical Center and 10 at the Salem VA Medical
Center. They were randomly assigned to apply 16, 32, or 64 mg DHT gel
every day for 14 days. Their baseline clinical data are given in Table 1
. None of these clinical characteristics
(height, weight, body mass index, testicular volumes) nor serum T
levels was significantly different amongst the three treatment groups.
The protocol was approved by the Institutional Review Board of the
Harbor-UCLA Medical Center and Salem VA Medical Center, and each
subject signed a written consent form.
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DHT gel was prepared by Besins Iscovesco (Paris, France) and obtained through Unimed Pharmaceuticals. It was formulated as a 0.7% hydroalcoholic gel. The gel excipients included carbomer, triethanolamine, isopropyl myristate, absolute ethanol, and purified water. These components were commonly used in the cosmetic industry. The DHT gel was packaged in multidose bottles fitted with a calibrated dispensing pump and administered as a 16-mg metered dose delivered in approximately 2.3 g of gel. Each 16-mg dose was applied by the subject to a single site (arm and shoulders). Higher doses of 32 and 64 mg were applied to two (left and right arms and shoulders) or four (left and right arms and shoulders and left and right abdomen) sites, respectively. This DHT gel was different from that marketed in Europe (Andractim, Besins Iscovesco), which contained 2.5% solution of DHT in the hydroalcoholic gel. The gel was packed in 80-g tubes with graduations indicating each 5 g of gel (125 mg DHT). In the previous studies in Europe, men applied 125 or 250 mg DHT gel per day (14).
All subjects applied the DHT gel on their skin from days 1–14, at approximately the same time each morning, after a shower. After application of the gel, the gel dried rapidly (within 5 min), with no apparent residue left on the skin surface. The subjects were asked to wash their hands after application of the gel.
Study design
On day 0 (before gel application), day 1 (before first
application of DHT gel at time 0 min), and day 14 (after 14 days of
daily DHT gel application), the subjects were admitted to the General
Clinical Research Center at Harbor-UCLA Medical Center or Salem VA
Medical Center for 24 h for detailed pharmacokinetic study. Blood
samples were withdrawn through an in- dwelling catheter at -30, -15,
and 0 min (before) and 0.5, 1, 2, 4, 6, 8, 12, 18, and 24 h after
application of DHT-gel for later serum T, DHT, and E2
measurement. On day 0, no gel was applied. Blood was withdrawn for LH
and FSH measurements only at time 0 min. Serum sex hormone binding
globulin (SHBG) and free T levels were measured in samples on days 0,
7, 14, and 28; and 3-androstanediol glucuronide (3-diol-G) levels
were measured on days 0 and 14. The subjects also returned to the study
centers’ outpatient facilities between 0800 and 1000 h for each
outpatient visit, where blood samples were drawn before DHT application
on days 3, 5, 7, and 11 and after stopping DHT gel application on days
17, 19, 21, and 28. During each admission or outpatient visit, the
sites of DHT gel application were carefully examined for skin
irritation.
Hormone assays
Serum T levels were measured, after extraction with ethylacetate
and hexane, by specific RIA using reagents from ICN (Costa Mesa, CA).
The cross-reactivities of the antiserum used in the T RIA were 3.4%
for DHT, 2.2% for 3-androstanediol, 2.0% for 11 oxotestosterone,
and less than 1% for all other steroids tested. The lower limit of
quantitation of serum T measured by this assay was 0.87 nmol/L (25
ng/dL). The mean accuracy (recovery) of the T assay, determined by
spiking steroid free serum with varying amounts of T (0.9–52 nmol/L),
was 104% (range, 92–117%). The intraassay and interassay
coefficients of the T assay were 7.3 and 11.1% at the normal adult
male range, which, in our laboratory, was 10.1–36.1 nmol/L (290–1042
ng/dL). Serum free T was measured by RIA of the dialysate, after an
overnight equilibrium dialysis, using the same RIA reagents as the T
assay. The lower limit of quantitation of serum free T, using this
equilibrium dialysis method, was estimated to be 22 pmol/L. When
steroid free serum was spiked with increasing doses of T in the adult
male range, increasing amounts of free T were recovered with a
coefficient of variation that ranged from 11–18.5%. The intra- and
interassay precisions of free T were 15% and 16.8% for adult normal
male values (60–250 pmol/L).
Serum DHT was measured by RIA after potassium permanganate treatment of
the sample followed by extraction. The methods and reagents of the DHT
assays were provided by DSL (Webster, TX). The cross-reactivities of
the antiserum used in the DHT-RIA were 1.9% for androstenedine, 1.4%
for E2, 0.02% for T (after potassium permanganate
treatment and extraction), 0.25% for androstanediol, 0.19% for
3-diol-G, and not detectable for other steroids tested. This low
cross-reactivity against T was further confirmed by spiking steroid
free serum with 35 nmol/L (1000 ng/dL) of T and taking the samples
through the DHT assay. The results, even on spiking with over 35 nmol/L
of T, were measured as less than 0.1 nmol/L of DHT. The lower limit of
quantitation of serum DHT in this assay was 0.43 nmol/L. All values
below this value were reported as less than 0.43 nmol/L. The mean
accuracy (recovery) of the DHT assay, determined by spiking steroid
free serum with varying amounts of DHT (0.43–9 nmol/L) was 101%
(range, 83–114%). The intraassay and interassay coefficients of
variation for the DHT assay were 7.8 and 16.6%, respectively, for the
adult normal male range (which, in our laboratory, was 1.3–7.4
nmol/L).
Serum 3-diol-G was measured using an RIA kit from DSL. The assay
measures 5-androstane-3, 17ß-diol-17-glucuronide. The
cross-reactivities of the 3-diol-G antiserum used for the RIA were
1.2% for DHT-glucuronide; 0.9% for T-17-glucuronide
triacetylmethlyester; and nondetectable for 3-diol,
5-androstane-3, 17ß-diol-3-glucuronide, T glucuronide, T,
5-DHT, 5bDHT, and other sex steroids and their glucuronides. The
lower limit of quantitation of serum 3-diol-G with this assay was 1
nmol/L (0.5 ng/mL). The accuracy of the 3-diol-G assay was assessed
by spiking steroid free serum with increasing amounts of 3-diol-G
(1–107 nmol/L) before assay. The mean percent recovery of 3-diol-G
measured, compared with the amount added, was 104.8% (range,
92.1–113%). The intraassay and interassay coefficients of variation
were 4.5 and 12.5%, respectively, for normal adult male range
(6.4–36.8 nmol/L).
Serum E2 levels were measured by a direct assay without extraction with reagents from ICN. The intraassay and interassay coefficients of variation of the E2 assay were 7 and 9%, respectively, for normal adult male range (E2 63–169 pmol/L). The lower limit of quantitation of the E2 was 46 pmol/L. All values below this value were reported as less than 46 pmol/L. The cross-reactivities of the E2 antibody were 20% for estrone, 1.51% for estriol, 0.68% for E2, and less than 0.01% for all other steroids tested. The accuracy of the E2 assay was assessed by spiking steroid free serum with increasing amounts of E2 (46–367 pmol/L). The mean recovery of E2, compared with the amount added, was 98.6% (range, 95–100%).
Serum SHBG levels were measured by assay kits obtained from Delfia, (Wallac, Gaithersberg, MD). The intra- and interassay precisions were 5% and 12%, respectively, for adult normal male range (11–47 nmol/L). Serum FSH and LH were measured by highly sensitive and specific fluroimmunometric assays with reagents provided by Delfia (Wallac). The intraassay coefficient of variations for LH and FSH fluroimmunometric assays were less 4.3 and 5.2%, respectively; and the interassay variations for LH and FSH were 11.0% and 12.0%, respectively (adult normal male range: LH, 1.0–8.1 U/L; FSH, 1.0–6.9 U/L). For both LH and FSH assays, the lower limit of quantitation was determined to be 0.2 IU/L. All samples obtained from the same subject were measured in the same assay.
Statistical analyses
Descriptive statistics for each of the hormone levels for each group were calculated. Before analysis, each variable was examined for its distributional characteristics and, if necessary, transformed to meet the requirements of a normal distribution. The pharmacokinetics of DHT-gel were assessed using area under the curve (AUC) generated by the 24 h of multiple blood sampling for DHT, T, and E2 on days 1 and 14 and were compared with day 0 (baseline). The AUC was computed using the trapezoid method. Pharmacokinetic data were analyzed using repeated measures of ANOVA with three time points (days 0, 1, and 14) as the repeated factor, and treatment groups (3 doses) as a between-subjects factor. If a time effect was found post hoc contrasts were used to determine the characteristics of the time effect. Tests of interaction were used to determine whether the time effect was the same in all treatment groups. If an interaction effect was detected, the analysis was repeated within groups. Pairwise contrasts were used to compare overall group effects. Similar repeated-measures models were used to analyze other variables when there were multiple time points. One-way ANOVA models were used to compare groups when there were data available for two time points (e.g. day 0 and day 14). All data were expressed as mean ± SE.
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Results |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Serum DHT levels
The baseline mean serum DHT levels were not significantly
different amongst the three groups of subjects (16 mg: 1.97 ±
0.43; 32 mg: 2.28 ± 0.28; and 64 mg: 1.63 ± 0.30 nmol/L)
(Fig. 1). After the first application of
DHT gel on day 1, serum DHT levels gradually rose in the three groups
of subjects, reaching a plateau by 12–18 h. At 24 h after the
first application of DHT, mean serum DHT was significantly
(P < 0.001 for all three groups) elevated in all three
groups (16 mg: 7.30 ± 1.31; 32 mg: 12.84 ± 2.16; and 64 mg:
16.31 ± 2.41 nmol/L, respectively). During the 14 days daily
application of DHT gel, the mean DHT levels reached steady-state levels
by day 2 or day 3 and remained elevated and varied between 8–11,
12–17, and 14–24 nmol/L in the 16-, 32-, and 64-mg groups,
respectively.
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) described by
the serum DHT levels over 24 h showed that there was an overall
dose effect (P = 0.0001). This was caused by the 64-mg
dose producing an AUC significantly higher than the 16- and 32-mg doses
on day 1 (P = 0.0007) and day 14 (P =
0.001). Serum DHT AUC also showed an overall time effect, where the AUC
was significantly increased from baseline (day 0), when compared with
days 1 and 14 (P = 0.0001). At the lowest dose of 16
mg, the AUC was significantly increased by 3.5- and 6.0-fold higher on
days 1 and 14, respectively. With the 32-mg dose, the AUC of serum DHT
levels was 4.7- and 6.9-fold higher than basal levels on days 1 and 14.
This increase in serum DHT was most marked with the 64-mg dose, where
the AUC of serum DHT rose 9.6- and 16.1-fold above those on day 0
(baseline).
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, upper panel), then remained
relatively stable during the daily application of DHT gel until the
morning of day 15 (24 h after the last DHT gel application). Serum DHT
AUC calculations were not available from the other days but probably
would have reached a plateau by day 2 or day 3 of study. The serum DHT
levels gradually fell to baseline levels between day 17 and 19. The AUC
of serum DHT (obtained before DHT gel application each morning, days
1–14) from day 1 to day 15 demonstrated an overall dose effect, which
was caused by significantly higher DHT AUC with daily application of 64
mg DHT gel, compared with 16 mg/day (P = 0.046).
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Figure 4 shows the mean serum T
levels on days 0, 1, and 14 after daily application of DHT gel at 16-,
32-, and 64-mg doses for 14 days. Mean serum T levels and the serum
T-AUC (Fig. 2
) were not significantly different on days 0 and 1. On day
14, mean serum total T levels and AUC of serum T levels were
significantly lower than those on day 0 or day 1 at all three doses
(P < 0.0001). The AUC of serum T over 24 h was
suppressed to 75, 56, and 36% of baseline levels on day 14 at 16-,
32-, and 64-mg/day DHT dose, respectively. On day 14 only, there was a
dose effect (P = 0.04), where the AUC of serum T was
significantly lower with 64 mg (105 ± 19 nmol/L/h for 24 h),
compared with 16 mg DHT gel (241 ± 54 nmol/L/h for 24 h)
applied daily for 14 days. When daily serum T levels were examined
during the 14 days of DHT gel application (Fig. 3, middle
panel), serum T progressively decreased until a nadir was reached
on day 7. Thereafter, the serum T levels remained suppressed until DHT
gel was withdrawn. On stopping DHT application, serum T gradually
increased, to reach basal levels by 28 days. Mean AUC described by
serum T from days 1–15 was suppressed by DHT gel administration to
72.3, 56.7, and 52.0% of baseline at 16, 32, and 64 mg/day,
respectively. Because the single blood sample drawn on each clinic
visit showed large inter- and intrasubject variations, these dose
effects were not significantly different.
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After DHT gel application, serum DHT rose, and serum T levels
decreased. The mean serum DHT + T levels (total molar androgen levels)
were also calculated. As shown in Fig. 5, the serum DHT + T levels increased significantly after DHT gel
application on day 1 and day 14 in all dose groups (P =
0.0001). The AUC described by the serum DHT + T levels over 24 h
(Fig. 2) were significantly higher in the 32-mg/day (598 ± 46
nmol/L/h for 24 h) and 64-mg/day (638 ± 69 nmol/Lh for
24 h) groups, compared with the 16-mg/day group (470 ± 82
nmol/L/h for 24 h) on day 1, but the differences were not
statistically significant.
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Serum E2 levels
In general, serum E2 levels followed the same
qualitative pattern as serum T levels (Fig. 6). There was no significant suppression
of serum E2 levels after the first application of DHT gel
(day 1), but significant suppression of serum E2 levels was
noted on day 14 in all three dose groups (P = 0.0001).
The AUC described by serum E2 levels on day 14 was
suppressed to 83, 82, and 71% of baseline levels on 16, 32, and 62
mg/day DHT gel, respectively, which showed no statistical difference
between the doses (Fig. 2). During the 14 days of DHT gel application,
significant suppression of mean serum E2 concentrations
over days 1–15 occurred, with DHT gel application at the 32-mg/day
dose (day 0, 108.7 ± 8.8; day 5, 98.0 ± 9.9; day 7,
91.9 ± 8.9; day 11, 93.5 ± 9.5; day 14, 96.0 ± 10.3,
pmol/L; P = 0.03) and 64-mg/day dose (day 0, 106.6
± 13.8; day 5, 83.9 ± 11.2; day 7, 80.0 ± 103; day 11,
83.9 ± 11.5; and day 14, 74.8 ± 8.5 pmol/L;
P = 0.007). Because some of the levels were suppressed
to beyond the limit of quantitation of the E2 assay (46
pmol/L), the actual degree of suppression might be more than that
reflected in the data.
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-diol-G, free T, and SHBG levels (Table 2)
Serum SHBG levels were not different among the three groups at
baseline and showed no significant change after DHT gel application for
14 days. Serum free T levels were significantly suppressed on days 7
and 14, when compared with baseline values at days 0 or 28, (2 weeks
after stopping DHT gel application) (P = 0.0001).
The-64 mg/day dose seemed to suppress free T levels more than the lower
doses, but the differences were not statistically significant. Serum
3-diol-G levels were significantly increased on day 14 after DHT gel
application in all groups (P = 0.0001). The increase
was particularly marked for the 64-mg/day group, where serum
3-androstanediol levels were significantly higher than the 16-mg/day
group (P = 0.016).
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Both serum LH and FSH levels were suppressed by administration of
DHT gel (Fig. 7, upper panel).
At all dose levels, serum LH (Fig. 7, upper panel) decreased
steadily from day 2 to approximately day 11, reaching a nadir on days
14–15 (P = 0.0001). Serum LH started to increase on
day 17 and then leveled off after day 21. Serum FSH levels followed the
same pattern of serum LH levels (Fig. 7, lower panel). Mean
serum FSH levels decreased from day 2 until day 15, gradually
increased, and then leveled off on day 21 (P = 0.0001).
There was no significant difference in suppression of serum LH or FSH
amongst the three dose groups.
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There was no objective or subjective skin irritation in any of the subjects during and after DHT gel application. There were no other adverse events related to the administration of DHT gel. None of the complete blood counts and routine clinical chemistry changes between screening and day 28 were considered clinically significant. Red blood cell count (screening: 4.7 ± 0.08; day 28: 4.5 ± 0.08 1012/mL; P = 0.0001) and hematocrit (screening: 0.435 ± 0.007; day 28: 0.417 ± 0.008 L/L; P = 0.0001) showed very small (but statistically significant) decreases. This could be explained by the amount of blood withdrawn during the study (approximately 460 mL). The mean serum alanine aminotransferase decreased from 39.4 ± 2.1 at screening to 35.8 ± 20.0 on day 28 (P = 0.003), and mean serum calcium decreased from 2.33 ± 0.02 at screening to 2.30 ± 0.01 nmol/L (P = 0.04) on day 28. These decreases were statistically (but not clinically) significant.
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Discussion |
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TopAbstractIntroductionSubjects and MethodsResultsDiscussionReferences |
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Concomitant with the rise in serum DHT levels after gel application, serum levels of T, free T, E2, FSH, and LH also showed consistent suppression. Previous studies demonstrated that DHT administration suppressed pulsatile LH secretion (13, 15), resulting in decreased production of T and E2. Our study showed that significant suppression of serum T levels was present on day 14, and the suppression was most marked with the 64-mg dose. The degree of suppression of serum T with the 64-mg DHT dose was similar to previous reports by Schaison et al. (14), where 250 mg DHT gel was administered every day. Because of the short duration of DHT gel application (14 days), no significant change in SHBG levels was demonstrated in any of the treatment groups in our study. Administration of the three doses of DHT gel led to dose-dependent increases in serum DHT AUC from 6- to 16-fold and suppression in T-AUC from 75–36% of baseline levels. The calculated total (molar) serum androgen levels, i.e. T + DHT levels, were elevated in all subjects but remained within the normal range of young adult men (13–50 nmol/L) and did not show a clear dose-response. In hypogonadal men, where both basal endogenous serum DHT and T would be suppressed or low, administration of DHT would most likely result in a dose-related response in total androgen levels (primarily DHT), which was not evident in our study of mostly normal men. In future studies of the efficacy of DHT gel in hypogonadal men, our goal will be to study effectiveness when the serum DHT + T level is targeted at the low, medium, or high normal adult range.
Daily application of DHT gel to the skin caused no skin irritation in any of the subjects during the 14 days. There were no reports of rash, itchiness, weals, or redness. Similarly, there were no adverse clinical or biochemical events. Though serum hematocrit and red cell counts were slightly reduced at the end of the study, this could be accounted for by the volume of blood withdrawn during the study period. There were no clinically significant changes in clinical chemistry.
The possible advantages and disadvantages of DHT, over T, as androgen
replacement include the absence of gynecomastia, because DHT is not
aromatizable to E2. A previous uncontrolled study (17)
showed that DHT administration to older men resulted in a 15% decrease
in prostate volume despite high circulating DHT levels. It has been
demonstrated in human prostate cells in vitro and in animal
studies in vivo that E2 acts synergistically
with androgens to stimulate prostatic cell growth and prostatic
hyperplasia (18, 19, 20, 21, 22, 23, 24, 25). Reduced E2 levels, which accompany
percutaneous DHT administration, may result in decreased growth of the
prostate despite high circulating DHT levels. Moreover, the effects of
high serum DHT levels on the intraprostatic hormonal milieu are not
known. Prostatic levels of DHT, T, and E2 have not been
determined during DHT administration. It is also not known whether
prostatic 5-reductase activity will increase or decrease when
circulating DHT levels are elevated.
The effect of DHT, a nonaromatizable androgen, on lipids was previously studied (16). These researchers showed that long-term transdermal DHT in elderly men resulted in moderate decreases in plasma LDL and HDL cholesterol levels. However, Schaison et al. (14) reported that plasma LDL- and HDL-2 cholesterol, as well as apolipoprotein A and B, were not changed after 3 months of DHT treatment in hypogonadal men.
Clinical studies of men with mutations of the estrogen receptor (26) and aromatase enzyme (27) showed that these subjects were markedly osteopenic. The implications of these observations are that androgens exert their effect on bone via conversion to estrogens. Because DHT is not aromatizable, the question is raised whether DHT will have similar positive effects on bone mass and bone mineral density as an aromatizable androgen. A number of considerations may influence the answer to the question and its implication for DHT treatment. Androgen receptors have been demonstrated in human bone cells (28, 29, 30, 31). The models for estrogen deficiency and decreased bone mineral density are based on humans and animals that had congenital, severe decrease in serum estrogens. It is unknown whether acquired deficiency of estrogen, in the presence of normal androgens, will affect bone mass. Because DHT suppression of T and E2 is partial, the residual estrogen levels may be above the threshold for positive effects on bone. Because hypogonadal and older men are not estrogen-deficient from birth, DHT may still have positive actions on maintaining bone mass. These questions will be addressed in longer term efficacy studies of DHT gel administration in androgen deficient men. In addition, T and DHT may exert differential effects on the GH-insulin-like growth factor-I axis, which might affect body composition to different extents (32).
In summary, in this study, administration of graded doses of DHT gel resulted in dose-related increases in DHT levels, which could help to target the therapeutic total androgen levels to the low, medium, or high male range. Studies are in progress to assess the efficacy of DHT as a method of androgen therapy and determine whether its benefit-to-risk ratio is similar, better, or worse than T replacement for various specific endpoints. The long-term effect of DHT on the prostate and lipid profile should be studied in comparison with T administration. Moreover, for DHT to find clinical utility, as androgen replacement therapy in older men, the long-term beneficial effects of DHT administration on bone, muscle and fat mass, sex function, mood, and sense of well-being have to be demonstrated.
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Acknowledgments |
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Footnotes |
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Received December 30, 1997.
Revised April 4, 1998.
Accepted April 23, 1998.
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References |
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