Hair

Hair follicle development occurs because of ectodermal and mesodermal interactions during epidermal development, beginning at approximately the eighth week of development. The base of the follicle, the dermal papilla, is derived from the mesodermal mesenchyme of the dermis, whereas the remainder of the hair follicle is derived from the ectoderm. The pigmentation of hair and skin is caused by melanocytes, which develop from the neural crest cells. Melanin pigments, eumelanin and pheomelanin, are synthesized and stored in the melanosomes. Eumelanin produces brown and black hair, whereas pheomelanin is responsible for red and blond hair. The proportion of these 2 melanin pigments is what dictates the final color of human hair. The appearance of hair follicles occurs at around the 10th week of fetal development, and continued differentiation results in the formation of various components of the follicle.

Three types of glands are associated with the hair follicle: sebaceous, apocrine, and sweat glands. The sebaceous gland, responsible for the production of sebum, develops on the side of the follicle and is associated with capillary networks, similar to the hair follicle. Sebum is composed of free and combined fatty acids and unsaponifiable material (eg, cholesterol and waxes). Apocrine glands secrete an oily, colorless substance directly into the follicle, and are localized in the axilla, eyelids, and external auditory meatus. Sweat glands, located on most of the body surface, produce sweat, comprising mainly water and salts.

Hair growth occurs in a 3-phase cycle, consisting of anagen, catagen, and telogen phases. The anagen phase represents hair production and begins at the 15th week of fetal development, and the scalp of the fetus is completely covered with anagen phase follicles between the 18th and 20th week of gestation. This phase is characterized by a rapid proliferation of matrix cells, which fill the follicle bulb, extending through epithelial cells. The matrix cells are then keratinized, forming the strand of hair. Growth of the hair continues until expression of epidermal growth factors, resulting in apoptosis of follicular keratinocytes and melanocytes, or the catagen phase. During the catagen phase, the bottom of the hair fiber is fully keratinized. At this point, the hair follicle is dormant and in the telogen phase. In respect to a neonate, the first full cycle of hair growth is complete between the 24th and 28th week of development, with the next cycle starting soon after the first one is completed. Consequently, biomarkers present in hair at birth reflect exposure to toxins during the third trimester, and are able to be tested until approximately 3 months after birth. Therefore, if there is hair present after birth, the window of detection is relatively long.

In children (and adults), the hair growth cycle continues, with each phase having a distinct length of time. The growth of each hair follicle is independent, with approximately 85% of all head hair follicles in the anagen phase (growing phase) at any given time. The remainder of hair follicles are not in the growing phase, and this must be taken into account when interpreting any nonneonatal hair results, because drug incorporation does not occur during the resting phase.

Routes of incorporation of compounds into hair include direct incorporation of a chemical via the capillary networks of the hair follicle, as a result of secretions from the sebaceous and sweat glands, and as a result of environmental or external exposure. Measuring and interpreting biomarkers in hair must properly take these different routes of incorporation into account.

The many factors that determine the concentration of a drug in hair should also be considered. These factors include hair color (melanin content), physicochemical properties of the drug, and cosmetic treatment of hair. For example, it has been found that drugs preferentially incorporate into darker hair, most likely because of the relative amounts of eumelanin. Also, physicochemical properties including lipophilicity, basicity, and membrane permeability affect the ability of drugs to incorporate into hair. Generally, basic, lipophilic drugs tend to accumulate more readily into hair samples than more acidic or polar drugs. Cosmetic treatment of hair has been found to decrease hair concentrations of drugs, mainly because of increased hair damage and the removal of hair color pigment. Hair damage causes drug molecules to be lost more easily from the matrix, whereas removal of pigment reduces the amount of melanin to which the drugs are bound. As a result, clinical interpretations of drug concentrations in hair must take these factors into account.

Hair samples are typically collected from the posterior vertex, because hair from this area of the scalp shows the most constant rate of growth. Analysis of hair provides long-term information on an individual’s drug use or exposure. Taking advantage of the uniform growth rate of human hair, approximately 1 cm/mo, it is possible to segment hair samples to more accurately assess the time and pattern of use or exposure. The window of detection for nonneonatal hair samples is therefore dependent on hair length.

Meconium

The first few bowel movements of a neonate are composed of meconium. This highly complex matrix begins to form approximately during the 12th week of gestation and consists of water, gastrointestinal tract epithelial cells, bile acids and salts, enzymes, sugars, lipids, intestinal secretions, and swallowed amniotic fluid. Fetal swallowing of amniotic fluid is the mechanism believed to concentrate compounds within meconium as fetal urine is deposited into the amniotic fluid and is subject to swallowing again. Determining factors of drug incorporation into meconium and the extent of their concentration are mainly determined on the ability of the drug to cross the placenta. Most drugs are able to transfer across the placenta, and the rate of transfer is then determined by molecule size, ionization state, lipophilicity, and protein binding. Because most drugs are small enough to transfer via passive diffusion, the major limiting factor, in terms of drug transport to the fetus, is placental blood flow. Once meconium is formed in the fetal intestine, it is considered a physically static matrix, becoming a record of fetal exposure to the drugs in question during the second and third trimesters of pregnancy. A positive meconium test indicates intrauterine exposure during the second and third trimesters, but is unable to show time or pattern of use.

Dose-response relationships are difficult to determine using meconium samples, mainly because of urine contamination. If fetal exposure occurs close to term and the compound is incorporated into the urine, contamination of meconium can occur once urine is evacuated into a soiled diaper. This situation increases the sensitivity of meconium testing because of the increased compound levels in the sample. However, it could affect the ratio of drugs and metabolites in the sample, and the development of dose-response relationships.

Collection of meconium specimens is easy and noninvasive. Because it is discarded material and there is usually sufficient quantity for analysis, this matrix is practical and useful. Ninety-nine percent of infants pass their first meconium within 48 hours, giving this matrix a wider window of detection than blood or urine. Once 48 hours have passed, it is necessary to evaluate the texture and odor of the sample to determine whether it still meconium or has changed to postnatal feces. The time allowed for sample collection, 2 days, may be seen as limited, but if the neonate is at high risk for drug or alcohol in utero exposure and in hospital care, obtaining a viable sample is not problematic. Collected samples should be minimally 0.5 g, to provide sufficient sample for all analyses. Storage of samples for analysis should be at –20°C or –80°C.

Hair

Hair follicle development occurs because of ectodermal and mesodermal interactions during epidermal development, beginning at approximately the eighth week of development. The base of the follicle, the dermal papilla, is derived from the mesodermal mesenchyme of the dermis, whereas the remainder of the hair follicle is derived from the ectoderm. The pigmentation of hair and skin is caused by melanocytes, which develop from the neural crest cells. Melanin pigments, eumelanin and pheomelanin, are synthesized and stored in the melanosomes. Eumelanin produces brown and black hair, whereas pheomelanin is responsible for red and blond hair. The proportion of these 2 melanin pigments is what dictates the final color of human hair. The appearance of hair follicles occurs at around the 10th week of fetal development, and continued differentiation results in the formation of various components of the follicle.

Three types of glands are associated with the hair follicle: sebaceous, apocrine, and sweat glands. The sebaceous gland, responsible for the production of sebum, develops on the side of the follicle and is associated with capillary networks, similar to the hair follicle. Sebum is composed of free and combined fatty acids and unsaponifiable material (eg, cholesterol and waxes). Apocrine glands secrete an oily, colorless substance directly into the follicle, and are localized in the axilla, eyelids, and external auditory meatus. Sweat glands, located on most of the body surface, produce sweat, comprising mainly water and salts.

Hair growth occurs in a 3-phase cycle, consisting of anagen, catagen, and telogen phases. The anagen phase represents hair production and begins at the 15th week of fetal development, and the scalp of the fetus is completely covered with anagen phase follicles between the 18th and 20th week of gestation. This phase is characterized by a rapid proliferation of matrix cells, which fill the follicle bulb, extending through epithelial cells. The matrix cells are then keratinized, forming the strand of hair. Growth of the hair continues until expression of epidermal growth factors, resulting in apoptosis of follicular keratinocytes and melanocytes, or the catagen phase. During the catagen phase, the bottom of the hair fiber is fully keratinized. At this point, the hair follicle is dormant and in the telogen phase. In respect to a neonate, the first full cycle of hair growth is complete between the 24th and 28th week of development, with the next cycle starting soon after the first one is completed. Consequently, biomarkers present in hair at birth reflect exposure to toxins during the third trimester, and are able to be tested until approximately 3 months after birth. Therefore, if there is hair present after birth, the window of detection is relatively long.

In children (and adults), the hair growth cycle continues, with each phase having a distinct length of time. The growth of each hair follicle is independent, with approximately 85% of all head hair follicles in the anagen phase (growing phase) at any given time. The remainder of hair follicles are not in the growing phase, and this must be taken into account when interpreting any nonneonatal hair results, because drug incorporation does not occur during the resting phase.

Routes of incorporation of compounds into hair include direct incorporation of a chemical via the capillary networks of the hair follicle, as a result of secretions from the sebaceous and sweat glands, and as a result of environmental or external exposure. Measuring and interpreting biomarkers in hair must properly take these different routes of incorporation into account.

The many factors that determine the concentration of a drug in hair should also be considered. These factors include hair color (melanin content), physicochemical properties of the drug, and cosmetic treatment of hair. For example, it has been found that drugs preferentially incorporate into darker hair, most likely because of the relative amounts of eumelanin. Also, physicochemical properties including lipophilicity, basicity, and membrane permeability affect the ability of drugs to incorporate into hair. Generally, basic, lipophilic drugs tend to accumulate more readily into hair samples than more acidic or polar drugs. Cosmetic treatment of hair has been found to decrease hair concentrations of drugs, mainly because of increased hair damage and the removal of hair color pigment. Hair damage causes drug molecules to be lost more easily from the matrix, whereas removal of pigment reduces the amount of melanin to which the drugs are bound. As a result, clinical interpretations of drug concentrations in hair must take these factors into account.

Hair samples are typically collected from the posterior vertex, because hair from this area of the scalp shows the most constant rate of growth. Analysis of hair provides long-term information on an individual’s drug use or exposure. Taking advantage of the uniform growth rate of human hair, approximately 1 cm/mo, it is possible to segment hair samples to more accurately assess the time and pattern of use or exposure. The window of detection for nonneonatal hair samples is therefore dependent on hair length.

Meconium

The first few bowel movements of a neonate are composed of meconium. This highly complex matrix begins to form approximately during the 12th week of gestation and consists of water, gastrointestinal tract epithelial cells, bile acids and salts, enzymes, sugars, lipids, intestinal secretions, and swallowed amniotic fluid. Fetal swallowing of amniotic fluid is the mechanism believed to concentrate compounds within meconium as fetal urine is deposited into the amniotic fluid and is subject to swallowing again. Determining factors of drug incorporation into meconium and the extent of their concentration are mainly determined on the ability of the drug to cross the placenta. Most drugs are able to transfer across the placenta, and the rate of transfer is then determined by molecule size, ionization state, lipophilicity, and protein binding. Because most drugs are small enough to transfer via passive diffusion, the major limiting factor, in terms of drug transport to the fetus, is placental blood flow. Once meconium is formed in the fetal intestine, it is considered a physically static matrix, becoming a record of fetal exposure to the drugs in question during the second and third trimesters of pregnancy. A positive meconium test indicates intrauterine exposure during the second and third trimesters, but is unable to show time or pattern of use.

Dose-response relationships are difficult to determine using meconium samples, mainly because of urine contamination. If fetal exposure occurs close to term and the compound is incorporated into the urine, contamination of meconium can occur once urine is evacuated into a soiled diaper. This situation increases the sensitivity of meconium testing because of the increased compound levels in the sample. However, it could affect the ratio of drugs and metabolites in the sample, and the development of dose-response relationships.

Collection of meconium specimens is easy and noninvasive. Because it is discarded material and there is usually sufficient quantity for analysis, this matrix is practical and useful. Ninety-nine percent of infants pass their first meconium within 48 hours, giving this matrix a wider window of detection than blood or urine. Once 48 hours have passed, it is necessary to evaluate the texture and odor of the sample to determine whether it still meconium or has changed to postnatal feces. The time allowed for sample collection, 2 days, may be seen as limited, but if the neonate is at high risk for drug or alcohol in utero exposure and in hospital care, obtaining a viable sample is not problematic. Collected samples should be minimally 0.5 g, to provide sufficient sample for all analyses. Storage of samples for analysis should be at –20°C or –80°C.