Biomedical Engineering Reference
In-Depth Information
1
Introduction
1.1
Steroid Hormones: Chemical Structures and Functions
Steroid hormones are composed of 18-21 carbon atoms, which are bonded together
by four fused rings: three cyclohexane rings (designated as rings A, B, and C) and
one cyclopentane ring (as ring D), with an exception of estrogens' ring A as a ben-
zene ring. Hydroxyl and/or ketone groups are attached at C
3
, C
11
, C
17
, C
20
, or C
21
positions, and methyl group(s) is attached at C
18
and/or C
19
positions of the steroid
skeletons, as shown in Fig.
1
. These molecules are neutral, unionized, nonvolatile,
lipid soluble, and stable during extraction and analysis by mass spectrometry.
Originated from cholesterol, the biosynthetic pathways of steroid hormones are well
established [
1-
3
]. The major biotransformation reactions for steroid hormones
include oxidation, reduction, conjugations with glucuronic acid, sulfate, and gluta-
thione [
4,
5
]. As most of the biotransformation pathways and metabolites of steroid
hormones are clearly defined, structure elucidation or identification is not a major
concern for steroid analysis [
6
]. However, since a large portion of endogenous ste-
roid hormones exists as their glucuronide and sulfate conjugates, especially in urine,
deconjugation of the steroid hormones may be needed before LC-MS/MS and
GC-MS analysis [
7,
8
] .
According to bonding receptors and biological functions, steroid hormones are
classified as progestagens (or progestogens, pregnancy hormones), mineralocorti-
coids (mineral retention hormones), glucocorticoids (glucose metabolism and
inflammation hormones), androgens (male hormones), and estrogens (female hor-
mones). Endogenous steroid hormones are chemical messengers regulating many
life functions, such as controlling pregnancy, salt and water balance, metabolism,
inflammation, immune functions, and development of sexual characteristics. Many
serious health problems, diseases, and clinical syndromes are indicated by steroid
hormones deviations from normal levels. Steroid hormone analysis plays important
roles in health care, including disease diagnosis, food safety, and environmental pro-
tection. For example, endogenous steroid hormones are critical biomarkers for clini-
cal diagnoses in endocrinology, physiology, and pathology; and steroid hormones are
also broadly used as medicines for treatment of varieties of diseases, such as
inflammation, malfunctions in immune systems, underdevelopment syndromes, and
disorders in endocrine systems [
2,
9
]. On the other hand, steroid hormones are abused
by some athletes [
10
] and racing horse owners [
11
] to enhance their sport perfor-
mances. Steroid hormones are also found as hazardous residuals in eatable meats
[
12
] and are monitored as environmental pollutants in water and sediments [
13
] .
Therefore, development and application of specific, sensitive, and robust analytical
methods and methodologies for steroid hormone analyses have significant impacts
on clinical analyses, disease diagnoses and treatments, antidoping drug screening,
food safety examination, and environmental quality monitoring. A large number of
articles have been published on analyses of steroid hormones by mass spectrometry
