Atropa Belladonna
Drugs

Alberto Peano and Damiano Maria Vallero
Academic year 2013-2014
Course of Laboratory Medicine

ATROPINE

Introduction
Atropine is a natural alkaloid originally extracted from Atropa belladonna (Figure 1) and then found in others plants of the family Solanaceae. It is a drug with a wide range of effects in humans including anesthesia, anti-arhythmia, bronchodilatation, mydriasis and parasympathicolysis. Brand names of atropine include Atropair, Atropen, Atropine sulfate, Atropinol and Atropisol (University of Alberta database - DrugBank , Wikipedia)

Figure 1: Atropa belladonna

History
The term “alkaloid” derives from the Arabic al-qali, the plant from which soda was first obtained. Alkaloids are nitrogenous compounds that constitute the pharmacologically active principles of several flowering plants. The use of alkaloid-containing plant extracts as potions, medicines, and poisons date back to the start of civilization. Famous examples include Socrates’ death in 399 B.C. by ingestion of hemlock (scientific name Conium maculatum). Medieval european women utilized extracts of deadly nightshade (the common name of Atropa belladonna) for the same purpose, hence the name “belladonna” (Alkaloid biosynthesis - The basis for metabolic engineering of medicinal plants, 1995)

Biochemistry
Atropine is a racemic mixture of equal parts of D- and L-hyoscyamine (Figure 2). Hyoscyamine (IUPAC name: (1R,3S,5S)-8-methyl-8azabicyclo [3.2.1] octan-3-yl 3-hydroxy-2-phenylpropanoate) is a compound with molecular weight of 289 Da and chemical formula C ₁₇ H ₂₃ NO ₃

Figure 2: structural formula of D- and L-hyoscyamine

Hereafter the biosynthesis pathway:
I. L-phenylalanine is transaminated to phenylpyruvic acid and then reduced to phenyl-lactic acid (Figure 3)
II. putrescine-N-methyltransferase catalyzes the transfer of a methyl group from S-adenosyl-L-methionine to an amino group of putrescine, which is the first committed step in the biosynthesis of nicotine and tropane alkaloids. This enzyme is expressed in tobacco plant such as in Atropa belladonna because first steps of nicotine biosynthesis, obtained from tobacco plant, are the same of atropine biosynthesis. N-methyl-putrescine is then converted to tropinone, whose keto group is in turn converted by the tropinone reductase-I to the alpha-hydroxyl of tropine (Figure 4)
III. phenyl-lactic acid binds to coenzyme A and reacts with tropine to form littorine, that go through a radical transposition to make hyoscyamine aldehyde. At last, a dehydrogenase reduces the aldehyde to alcool forming hyoscyamine (Figure 3)
IV. is also possible to obtain atropine through a chemical synthesis. This process, first discovered by Richard Willstater, is based on the reaction of tropine with tropic acid while in the presence of hydrochloric acid (Figure 4) (Synthesis of essential drugs, 1st edition (R. Vardanyan, V. Hruby), PubChem database, Alkaloid biosynthesis - The basis for metabolic engineering of medicinal plants, 1995)

Figure 3: biosynthesis of atropine

Figure 4: biosynthesis of tropine and chemical synthesis of atropine

Pharmacokinetic
Atropine is rapidly and well absorbed after oral or intramuscular administration. Atropine disappears rapidly from the blood and is distributed throughout the various body tissues and fluids. It can readily cross the blood-brain (about 95% of intestinal absorbed quota) and the placental barrier. Much of the drug is destroyed by enzymatic hydrolysis, particularly in the liver (atropine is a substrate of cytochrome P450 3A4). At last, from 13 to 50% of the drug is excreted unchanged in the urine (University of Alberta database - DrugBank)

Pharmacodynamic
Muscarinic acetylcholine receptors (M1-5) mediates various cellular responses, including inhibition of adenylate cyclase, breakdown of phosphoinositides and modulation of potassium channels through the action of G proteins. Atropine is a competitive muscarinic receptor antagonist (Figure 5) that determine a wide range of anti-cholinergic effects:
- mild vagal stimulation
- transient cardiac slowing (mechanism unknown) followed by tachycardia as a result of vagal blockade at the sinoatrial node
- decrease of bronchial secretions
- relaxation of bronchial smooth muscle
- reduction of tone and motility of the gastrointestinal tract and urinary bladder
- depression of salivary and sweat secretion
- mydriasis
- restlessness, excitement, irritability and hallucinations (University of Nebraska database - Autonomic and cardiovascular pharmacology)

Figure 5: mechanism of action of atropine

Therapeutic uses
Thanks to its anticholinergic effects atropine is recommended in a lot of pathological states and clinical situations, relating to a wide range of medical specialties:
- analgesic spasmolytic in the treatment of gastro-intestinal spasms and biliary or hepatic colic
- antispasmodic in asthma
- cough medicine (in association with codeine and dyphylline)
- treatment of tremor and rigidity in Parkinson's disease
- mydriatic and cycloplegic (to perform ophthalmoscopy)
- preanesthetic (to inhibit salivation and respiratory secretions and to prevent the risk of vagal inhibition of the heart)
- during ophthalmic surgery (to reduce the incidence of the oculocardiac reflex)
- treatment of bradycardia and cardiac arrest in intensive care medicine
- antidote to nerve agent poisoning (this is the reason why soldiers at risk are equipped with atropine loaded in autoinjectors) (Miller's Anesthesia, 7th edition (R. D. Miller), University of Nebraska database - Autonomic and cardiovascular pharmacology)

Side effects and toxicity
The anticholinergic effects of atropine can produce tachycardia, pupil dilation, dry mouth, urinary retention, inhibition of sweating (anhidrosis), blurred vision, constipation and depression. However, most of these side effects are only manifested with repeated or excessive dosing. In instance of overdose, therapy includes removal of the drug from stomach, artificial respiration and, if body temperature is high, administration of physostigmine (which counteracts both central and peripheral blockade of cholinergic nerves) (Cardiovascular pharmacology concepts, PubMed Health database, United States National Library of Medicine - Toxnet)

Examples of clinical cases
During the work we have found several papers relating to interesting clinical cases, some of which hereafter summarized:
* a 20-year-old man was diagnosed with a carotid tumor and underwent surgery. When the operation was initiated, the patient developed sudden cardiac arrest. Chest compression was immediately initiated, and atropine 0.5 mg was administered. Subsequently circulation was restored and the surgery was successfully performed (Case report of cardiac arrest during carotid body tumor resection, 2014)
* a 44-year-old female was scheduled for a varicosectomy. Two hours after the administration of the spinal anesthesia, the heart rate dropped to 42-45 beats/min, and 0.5 mg of atropine was injected intravenously. Shortly after ventricular tachycardia occurred, making necessary the transfer to the intensive care unit. In consequence, further considerations should be taken in regards to the benefits found from the use of atropine in bradycardia not accompanied by hypotension (Atropine injection followed by coronary artery spasm with ventricular tachycardia during spinal anesthesia, 2013)
* a 20-day-old male infant developed generalized tonic–clonic seizures after the administration of a homeopathic medicine containing Atropa belladonna for infantile colic. His clinical signs and symptoms disappeared after a dose of benzodiazepine, instilling the suspect of central anticholinergic intoxication (Seizures caused by ingestion of Atropa belladonna in a homeopathic medicine in a previously well infant: case report and review of the literature, 2013)
* a 11-years-old girl, under Rifampicin and Isoniazid for lymph node tuberculosis, was given Atropa belladona by an herbalist. She developed an anti-cholinergic toxidrome, a condition characterized by mydriasis, blurred vision, photophobia, dry mouth, tachycardia, decreased bowel sounds, difficulty in swallowing and speaking, hyperthermia, hypertension, seizures, loss of consciousness and coma. The patient was monitored in a critical care unit for vital findings and received a symptomatic treatment based on oxygenotherapy, antiemetic, stomach protection and hydroelectrolytic supply. The anti tuberculosis treatments was stopped because of its hepatic side effect. The evolution was marked by neurological improvement and disappearance of delirium (Atropa Belladonna intoxication: a case report, 2012, Belladonna alkaloid intoxication: the 10-year experience of a large tertiary care pediatric hospital, 2013)
* a 38-year-old primiparous woman was administered epidural analgesia. The patient showed progressive changes in mental status, respiratory depression, bradycardia, and hypotension; accidental subdural injection was inferred as the cause of these complications. Since the fetus showed severe bradycardia (70 beats/min), despite being in the normal range (100-150 beats/min) before this event, 0.5 mg of atropine were injected. At 5 min after intrauterine fetal resuscitation, the fetal heart rate was 100 beats/min (Intrauterine fetal bradycardia after accidental administration of the anesthetic agent in the subdural space during epidural labor analgesia, 2013)
* the body of a 51-year-old man was found in the boot of his car, which had been left in a public car park in France. The autopsy failed to determine the cause of death, and samples were collected and submitted for toxicological analysis; routine toxicological analyses were performed on the peripheral blood and urine, and in light of these first results atropine was specifically quantified in all the biologic samples, showing the presence of the drug in all the victim’s samples. The postmortem concentrations measured in the victim are consistent with a massive overdose of atropine, proving that this is a case of murder by atropine poisoning (Atropine eye drops: an unusual homicidal poisoning, 2014.)