clinical biochemistry II drugs, toxins, and tumor markers

Benign Tumors

• Well differentiated

• Slow-growing

• Smaller (usually)

• Encapsulated

• Non-invasive

• Non-metastastic

• Suffix: "oma" (example: fibroma)

Malignant Tumors

• Poorly differentiated

• Fast-growing

• Larger

• Non-encapsulated

• Invasive

• Metastatic

• Suffix: "carcinoma" or "sarcoma"

Circulating tumor markers

chemicals produced and released by tumors that can be measured in the blood, urine, stool, and other body fluids

Tumor tissue markers

identified directly after collecting the tumor cells.  A sample of the tumor is extracted during a biopsy procedure (or the whole tumor is removed) and the tissue is tested for the presence of various markers associated with a type of cancer.

Prostatic acid phosphatase (ACP)

Elevated serum levels can be seen in patients with a carcinoma that has extended beyond the prostatic capsule. This marker is no longer frequently used as a marker as it has been replaced by another tumor marker, prostate specific antigen (PSA).

Alkaline phosphatase (ALP)

used with other tests in diagnosing bone and liver malignancies. Increased levels of this enzyme is often associated with the presence of tumors in the bone or liver tissue.

Creatine kinase, BB isoenzyme (CK-BB)

has been associated with malignancies of several tissues including the lung, prostate, breast, ovary, kidney, bladder, and brain. It is primarily used to monitor a tumor once the tumor is shown to produce the enzyme.

Neuron specific enolase (NSE)

found in tumors of neurologic origin. Ninety percent of children with neuroblastoma have increased levels that correlate well with disease progression.

Human chorionic gonadotropin (hCG)

The placenta, a trophoblastic tissue, naturally secretes HCG. HCG levels are used extensively as a tumor marker. It is elevated in a high percentage of trophoblastic and testicular tumors.

Calcitonin

Elevated levels can be seen in medullary thyroid cancer.

Alpha-fetoprotein (AFP)

Increased levels after birth have been associated with germ cell tumors and hepatoma (liver cancer).  This marker often rises before other tumor markers in the recurrence of cancer. It is also a reasonably good marker for primary hepatoma because it is elevated in 80% of cases.

Carcinoembryonic antigen (CEA)

Some malignancies that produce elevated levels include colon, breast, gastrointestinal, lung, ovarian, pancreatic, and prostatic cancer. Certain non-malignant conditions may also cause increased production including alcoholism, bowel inflammation, cystic fibrosis, and heavy cigarette smokers. has been proven useful in determining prognosis and monitoring diagnosed patients and may be measured in blood and other body fluids using immunochemical methods.

Prostate specific antigen (PSA)

It is found in small amounts in the normal prostate and elevated in benign prostate hypertrophy (BPH) and adenocarcinoma of the prostate. Elevated levels may not appear until the disease has advanced. It is no longer used as a standard screening test for prostate cancer.

Carbohydrate Antigen 15-3 (CA 15-3)

commonly found on breast tumor cells. is frequently used to monitor therapeutic response and recurrence to breast cancer.

Carbohydrate Antigen 19-9 (CA 19-9)

This marker is used to follow patients' progress with pancreatic, colorectal, lung, and gastric carcinomas

Carbohydrate Antigen 125 (CA 125)

tumor cell antigen that is used as a marker for ovarian and endometrial cancer. Elevated levels of CA 125 have also been described in pregnancy, endometriosis, and other uterine diseases. The highest levels are seen in ovarian cancer

Cell Membrane Receptors

some breast cancer tumor cells have receptors for the hormones estrogen and progesterone and depend on them to grow. The presence and number of cell membrane receptors may determine the degree of responsiveness of certain types of tumors to therapy

Tumor suppressor genes

genes that encode proteins that are involved in controlling unregulated growth. If these genes are mutated, it will likely lead to the formation of a tumor. 

Oncogenes

transform normal cells into tumor cells

minimum effective concentration (MEC)

the lowest concentration of drug in the blood that produces the desired response

Minimum toxic concentration (MTC)

the lowest concentration in the blood that will produce an adverse response

trough drug level

the lowest concentration of the drug measured in blood after the patient has achieved a steady state. trough levels should normally be reached immediately before the next dose of drug and should not fall below the MEC

peak level

represents the highest concentration of drug measured in blood. should not be higher than the MTC.

absorption

the process of a substance entering the blood circulation

drugs that are administered by oral, rectal, or sublingual routes are usually absorbed in the GI tract.

distribution

the dispersion of the drug throughout the fluids and tissues of the body

metabolism / biotransformation

breakdown of the drug from parent compounds into daughter metabolites

The major site of drug metabolism is the liver

Most drugs are metabolized by first-order kinetics

excretion / elimination

the removal of the drug from the body

first-pass effect

• the drug on first pass through the liver is substantially metabolized even before reaching the systemic circulation.

• For some drugs that undergo first pass effects, the blood concentration of the active drug is decreased because of production of inactive metabolites.

• Other drugs may be metabolized to compounds that themselves have pharmacological activity, causing an increased therapeutic effect in patients.

• First-pass effects of a drug must be taken into consideration when determining the dose.

Pharmacokinetic

the study of movement of a drug into, through, and out of the body and therefore it measures rates of absorption, distribution, biotransformation and excretion

Metabolic clearance (CL)

is the sum of all processes by which a drug is cleared from the body per unit time.

CL= rate of elimination/concentration

Volume of distribution (Vd)

is the distribution characteristics of a drug.

Vd= dose/concentration in plasma

Drug Half-Life

the time required for the concentration of a drug to be decreased by one half

t1/2= 0.693 Vd/CL

Digoxin and Digitoxin

function to increase the force of the heart's contraction while decreasing its rate to slow and strengthen the contraction.

Peak levels are usually evaluated 8 hrs after an oral dose. At this time, the serum levels are thought to correlate well with tissue concentrations.

Levels are usually measured with immunoassays

Antiarrhythmic Drugs

lidocaine, quinidine, procainamide, disopyramide

measured using immunoassays, GC, or HPLC

Phenobarbital

Used to treat all seizures except petit mal seizures

Has a long half-life - peak levels should not be drawn before 8-10 hrs have passed

Phenytoin (Dilantin)

Most widely prescribed and is also an antiarrhythmic

Toxic levels cause seizures

Has variable half-life and does not follow first order kinetics

Valproic acid

Has a long half-life

Used to treat most types of seizures often in combination with phenobarbital and phenytoin

Primidone

Metabolized to phenobarbital so phenobarbital must be measured along with it

Carbamazepine (Tegretol)

Generally only used for folks who do not respond to other drugs in this category

Highly protein-bound

Ethosuximide

Only used for petit mal seizures

Theophylline

CNS, respiratory, and cardiac stimulant

Causes smooth muscle relaxation and diuresis

Aminoglycoside Antibiotics

amikacin, streptomycin, gentamicin, kanamycin, tobramycin, neomycin

Used to treat gram-negative aerobic bacteria

Chloramphenicol

Used for gram-negative infections although not frequently prescribed anymore

Vancomycin

Used for gram-positive cocci infections

Trough levels usually monitored

Tricyclic antidepressants (TCA)

Widely used class that includes imipramine, desipramine, amitriptyline, nortriptyline and doxepin

Usually only monitored initially

Lithium

Used for treating bipolar disorders

Ion selective electrode (ISE) measurements are used most often to monitor levels

Cyclosporine

Used to suppress the immune system after transplantation

Current methods for measuring include: immunoassays and HPLC-MS

Tacrolimus (FK-506)

More potent than cyclosporine – smaller dosage

Methotrexate

Interferes with cell metabolism inhibiting cell replication.

Half-life is quite variable so dosage must be adjusted for the individual.

Cisplatin and cyclophosphamide

Alkylating agents that prevent DNA from undergoing replication

Classes of Toxic Substances

1. Gases - gaseous substances inhaled by the subject Example: carbon monoxide

2. Alcohols (Volatiles) - volatile liquids usually ingested by the subject Example: ethyl alcohol (ethanol)

3. Heavy metals - metals which remain in tissues and accumluate over time Example: lead

4. Nonvolatiles - other toxins such as pesticides, drugs of abuse, and therapeutic drugs in overdose

Carbon Monoxide (CO)

An odorless, tasteless gas normally present in small amounts in the atmosphere. Produces hypoxia in brain and heart

Hemoglobin has an affinity for CO as a level 200x greater than that for oxygen. Hemoglobin will preferentially bind CO (in lieu of oxygen). This may lead to reduced oxygen delivery, hypoxia, and anoxia in affected individuals

Whole blood is required for testing

Gas-liquid chromatography is the reference method

Cyanide

Very powerful toxin with many exposure routes (ingestion, inhalation, or absorption). Used in insecticide and rodenticide products

Binds to iron in the cytochrome oxidase complex (electron transport chain) in mitochondria and inhibits cellular production of ATP.

Although there is plenty of oxygen available, the cell cannot make ATP

Ethanol (EtOH)

The liver metabolizes most of the alcohol although a small amount is excreted unchanged through the lungs and kidneys. Alcohol dehydrogenase (ADH) converts EtOH first to acetaldehyde and then to acetic acid, which is capable of entering the TCA cycle

Since alcohol levels may be introduced as evidence in court cases, "chain of custody" must be appropriately documented in these potential cases.

Methanol (wood alcohol)

Used as a topical disinfectant

Metabolism - Methanol is converted to formaldehyde, which is metabolized to formic acid

Propanol (isopropanol)

Used as a topical disinfectant

Metabolism - Propanol is converted to acetone

Ethylene Glycol

Common ingredient of antifreeze

Metabolism - ethylene glycol is converted to glycolic acid and then oxalic acid.

An increased anion gap is characteristic of ethylene glycol poisoning.

Calcium oxalate crystals may also be seen in the urine

Lead

binds to proteins and inhibits (noncompetitive inhibition) many enzymes:

• Inhibits heme synthesis pathway

• Enzymes inhibited : delta aminolevulinic acid dehydrogenase and ferrochetalase

• Results in decreased hemoglobin production

Pesticides 

1. They act by interfering with the action of acetylcholinesterase at neuromuscular junctions and nerve endings.

2. Measurement

   1. Erythrocyte acetylcholinesterase levels

   2. Serum Pseudocholinesterase is often performed because acetylcholinesterase is difficult to measure.

   3. Decreased levels are seen with pesticide poisoning

Amphetamines (stimulants)

include drugs such as pseudoephedrine, ephedrine, and phentermine.

Used to treat narcolepsy and disorders affecting the ability to focus. Also used to provide a sense of mental and physical well-being

Anabolic steroids

1. Function: Used to increase muscle mass and athletic performance

2. Analysis: Gas or liquid chromatograph

Cannabinoids

provide a feeling of mental well-being and euphoria but impair function and short-term memory.

Common substances in this group are marijuana, hashish, sensimilla, pot, and THC

has a relatively long half-life (7-8 days) and accumulates in lipid tissues within the body. – Detectable levels may be evident 1-4 weeks after use

Cocaine

Used as a topical anesthetic for nasal surgery; however, it is most often taken illegally for its stimulant effects

metabolized so quickly it is rare to see the parent compound in the blood or urine of the patient by the time he/she reaches the emergency department.

Hallucinogens

Phencyclidine (PCP): Used as an anesthetic. Has CNS stimulant, depressant, and hallucinogenic properties. Low doses lead to a sense of euphoria. High doses may cause a sense of superhuman strength followed by coma and death.

Lysergic acid diethylamide (LSD: Produces perceptual distortions and rapid emotional changes including panic attacks and hallucinations

Methylenedioxymethamphetamine (MDMA): Probably best known by the street name "ecstasy". Produces feelings of euphoria and heightened sexuality. Can be extremely dangerous in high doses

Opiates

Used as analgesics, sedatives, or anesthetics. Mainly used to relieve pain in moderate doses. Abuse may lead to CNS depression

• Naturally occurring: Opium, morphine, codeine

• Chemically modified: Heroin, dilaudid, oxycodone

• Synthetic: Demerol, methadone, darvon, talwin, fentanyl

Tricyclic antidepressants

1. include a large number of prescription drugs.

2. Function: Used to treat depression, migraine, chronic pain and eating disorders.

3. Toxicity may lead to cardiac arrest.

Tranquilizers

sedative hypnotics that produce depression of CNS, Respiratory depression causes respiratory acidosis

Barbiturates: This group of drugs includes phenobarbital (long-acting), amobarbital (intermediate-acting), secobarbital (short-acting). These drugs are sedatives, depressants, or tranquilizers

Benzodiazepines: to reduce anxiety, treat sleep disorders and seizures. Examples: chlordiazepoxide (Librium), diazepam (Valium), lorazepam (Ativan)

Salicylates (aspirin)

Used as an analgesic (pain relief), antipyretic (fever reducing), and anti-inflammatory

Toxicity initially causes respiratory alkalosis (respiratory center stimulant). This is followed by metabolic acidosis as metabolites are formed

Ferric nitrate method (spectrophotometric)

Acetaminophen (tylenol)

Used as an analgesic

Overdoses will lead to hepatotoxicity due to intermediate metabolite accumulation in the liver.

In-vitro diagnostic clinical research studies

Use human tissues and/or fluids to study disease to contribute to the general body of knowledge of the associated disease

The analysis is not directly linked to any living individual

Patient-oriented research (POR) studies

Used to study mechanisms of disease, therapies, or to develop new technologies related to a disease

Investigator directly interacts with subjects

Reliability

The overall consistency of a measure. A measure is said to have a high reliability if it produces similar results under consistent conditions.

Validity

The degree to which a data instrument measures what it is supposed to measure. The measurement does not always have to be similar, as it does in reliability. However, just because a measure is reliable, it is not necessarily valid (and vice versa).

Generalizability

The extent to which the findings of a clinical trial can be reliably extrapolated from the subjects who participated in the trial to a broader patient population and a broader range of clinical settings.

Observational Studies

Involve humans (cohort or epidemiological studies) but do not specifically tie information to individual patients

Mechanistic Studies

Used to investigate causality

Usually small-population based studies - therefore the results may not be generalizable to a larger population

Therapeutic Studies

Used to determine the efficacy of a medicine or a treatment which is designed to improve a condition or disease.

Smaller and less definitive than large-scale clinical trials

Large-Scale Clinical Trials

Clinical trials conducted over an extended period of time with a large subject pool

Meta-Analysis

Process in which the results of multiple individual studies are statistically combined and analyzed

Formal evaluation of the evidence from two or more trials focused on answering the same question

Translational Research

"Bench to bedside" was formerly used to describe this process; however, translational research is not unidirectional. Once a biological premise or tool is adapted to a medical setting, clinical data derived from patients may inform both patient-oriented and basic investigation

General Sequence of a Clinical Study

1. Observation

2. Generation of a testable hypothesis

3. Design of a study that will test this hypothesis

4. Performance of the study (hypothesis testing)

5. Collection of data from the study

6. Data analysis and interpretation

7. Formulation of conclusions

B-glucuronidase tumor marker

cancer of urinary bladder

leucine amino peptidase (LAP)

liver cell carcinoma