With the advent of very sensitive chemical techniques, scientists have discovered that drugs such as cocaine, morphine, nicotine, and amphetamine can be detected in human hair. Do the drugs get into the hair from inside the body or from the air? The answer is both, depending on the volatility of the drug. This poses a dilemma. For example, drug testing of athletes in sports or job applicants might involve hair samples, which are easier to collect than urine. If the subject has a positive test, how do the testers know if the drug came from the environment or from drug use? These questions must be answered if drug testing in hair is to become a standard procedure. Let’s consider both possibilities.
In order for a drug to get into the hair from inside the body, it must be distributed throughout the bloodstream. Drugs like morhpine, for example, get into the bloodstream directly by injecting them into a vein. If a person snorts cocaine, smokes a cigarette or swallows an amphetamine pill, the drug must pass first through several barriers to get into the bloodstream.
1. Create a drawing to show how a drug gets into the bloodstream for each of the situations just described; injection, snorting, smoking and swallowing.
Once these drugs reach the bloodstream, they travel throughout the body, wherever the blood goes. As the heart pumps blood, the drugs are carried in the arteries to organs and tissues. The arteries branch off to become very small (these are called arterioles) as they enter tissues. Each cell must be close to the blood vessels in order to receive oxygen and glucose. These 2 substances are required for cells to live. The arterioles branch off again to form capillaries. The capillaries are extremely small so that they can reach all cells. Capillaries deliver nutrients dissolved in the blood such as oxygen and glucose to the hair follicles so that hair will grow. The hair follicle is made up of different kinds of cells that have different functions.
2. Make a diagram of a hair follicle. Show where the different kinds of cells are found in the hair follicle and indicate their major functions.
3. On your diagram, indicate where the capillaries come in contact with the hair follicle. How does the structure of capillaries make them so good at delivering nutrients to cells?
4. How easily can drugs such as morphine, cocaine, nicotine or amphetamine cross the capillary membrane to enter hair follicles?
The hair follicle gives rise to hair, which grows from the bottom of the follicle. Hair is composed of several substances, but mostly of protein.
5. What is the principle protein found in hair? What is so special about this protein that it is an ideal protein for hair?
6. What other biological components are found in hair?
Once drugs such as morphine, cocaine, nicotine or amphetamine get into the hair follicle, they bind to melanin, the pigment that gives hair color. Each of these drugs shares a common chemical property that makes them likely to bind to hair melanin. They are all weak bases. So, they tend to accept a H+ when they are in an acidic environment (where there is a high concentration of H+).
7. Which is more acidic, blood or hair? Why?
8. What kind of molecule is melanin? What is it made from and where is it made?
9. What is the major force that binds these drugs to melanin?
The amount and type of melanin determines the color of hair. More melanin gives rise to darker hair. Blond-haired people have little melanin. People with red hair have a different type of melanin compared to people with brown hair. People with black hair have the most melanin.
10. Would drug-testing of hair from people with different color hair (blonde vs brown or black) or from people of different races reveal different amounts of drugs, even if they all had taken the same dose? What kinds of dilemmas does this pose in cases of drug-testing in sporting events or in the workplace?
It is also possible to detect drugs such as nicotine and cocaine in hair of individuals that do not smoke or do not use cocaine. The drugs do not reach the hair through the bloodstream; instead, they enter hair from the environment surrounding the user or people nearby. This happens when drugs are heated or volatilized so that they can be smoked. Most drugs that are smoked are weak bases. Examples of weak bases that are smoked are nicotine, cocaine and heroin. However, when people smoke drugs, a large portion of the smoke does not enter the lungs. The smoke stays in the air surrounding the smoker and other people nearby. The drugs dissolved in the smoke easily penetrate the hair to bind to melanin.
11. Weak bases can exist in 2 forms – a charged form (the drug has accepted a H+) and an uncharged form (the free base). Which form is easily volatilized?
12. Why does this form make it easier to penetrate into the hair?
The pattern of drug binding within the hair can help distinguish between a user and a person exposed through second-hand smoke.
13. Is this easier for short hair or long hair? Why?
Another way to distinguish the ways in which drugs enter hair is to analyze the hair for not only the drug but also its metabolites. When drugs enter the bloodstream, they travel to the liver before they go to the rest of the body. There, enzymes participate in chemical reactions to change some of the drug into another form, called a metabolite. For example, some enzymes oxidize the drug by adding an OH group, making the metabolite more polar than the parent compound. Most of the time, these polar metabolites are inactive, although some drugs have active metabolites. The metabolites of drugs travel throughout the bloodstream along with the drugs themselves and can be distributed to some of the same tissues.
14. Where do metabolites go once they leave the liver?
15. What allows the polar metabolites to leave the bloodstream and enter the hair?
16. Can metabolites reach the hair from second-hand smoke?
