Khella

Khella (Ammi visnaga L.): A Comprehensive Reference

1. Identity, Botanical Classification, and Common Forms

Botanical and Chemical Names

Ammi visnaga L. (synonym: Visnaga daucoides Gaertn.), family Apiaceae, is also known as Khella Baldi or toothpick weed, and is an annual or biennial herb indigenous to the Mediterranean region of North Africa, Asia, and Europe. Commonly known as Khella and Bishop's Weed, it is an annual aromatic herb belonging to the Apiaceae family. Its scientific names include Ammi majus L. and Ammi visnaga Lam., and it carries common names including Ammi, Bisnaga, Khella, Khellin, Toothpickweed, and Visnaga.

The genus name "Ammi" derives from the Greek term "ammos" meaning "sand" and refers to the plant's habitat. Khella is a member of the celery, carrot, or parsley family (Apiaceae) and has been used as a medicinal herb since ancient times for a variety of ailments.

Plant Description and Distribution

Khella is an annual plant found primarily in Egypt, other regions of the Middle East, and the Mediterranean. A. visnaga has been naturalized to parts of the southeastern United States. The plant can grow to approximately 1 m in height and has a slightly aromatic odor and a very bitter taste. Khella is native to the Mediterranean region and cultivated in Egypt, Morocco, India, and parts of the USA, among other locations.

Plant Part Used and Common Preparations

The fruits (seeds) of khella are used in herbal medicine. The fruits are collected in summer before they fully mature and dried for later use. Ammi visnaga is traditionally used for medical purposes in the form of a decoction (extraction of plant materials in water by boiling) of its dried seeds or tincture of its fruits. Khellin is rarely found in its pure form; instead it is found in Visnaga daucoides (khella) extract. Preparations of Visnaga daucoides are commercially available and very common; however, the amount of khellin and other ingredients varies greatly between brands and even batches of the same brand. The extract is commonly found as a tea or in pill form.

Flowers, seeds, and leaves of Ammi visnaga are good sources of both khellin and visnagin. Ammi majus only contains khellin in its seeds and flowers.

Other Common Names

The dried umbels of khella are often found in markets in the Middle and the Far East, where the flower stalks are used as toothpicks, a use which is reflected in the plant's other common name "toothpick plant." In Arabic tradition it is known as bisr-el-khella. Additional synonyms and translations appearing in the literature include: Ammi daucoides, Bischofskrautfruchte, Bishop's Weed Fruit, Biznaga, Fenouil Annuel, Fruits de Khella, Herbe aux Cure-Dents, Herbe aux Gencives, Khellin, Khelline, Noukha, Toothpick Ammi, Toothpick Plant, Visnaga, Visnagafruchte, Visnaga Fruit, and Visnagin.

2. Traditional and Historical Use

Ancient Egypt and the Earliest Records

Khella is one of the oldest medicinal plants documented in the Ebers Papyrus of Egypt. It is known that the ancient Egyptians cultivated the plant and used it mainly for conditions related to the urinary tract system, a practice still in use today. The majority of early experiments with A. visnaga came from Egypt, where it had been used in practice to treat urinary stones. Egyptian clinicians such as Dr. Ibrahim, the dean of the medical school at the University of Egypt in 1933, had many years of clinical experience with khella—known to the public as bisr-el-khelle.

Back in 1879, Mostapha et al. investigated the chemistry of khella and isolated an impure crystalline substance. At a later date, Samaan et al. extracted six distinct crystalline principles from A. visnaga. He stated that among these, visammin is the most active compound. In subsequent papers, visammin was called khellin.

Traditional Uses Across Cultures

The khella plant has been cultivated for hundreds of years and was known by the Assyrians. Both species of Ammi have been used in traditional medicine for millennia, particularly for the management of angina and respiratory diseases. The fruit has been used in Egyptian folk medicine as a diuretic and for the treatment of kidney and bladder stones. Khella has also traditionally been used for the management of diabetes in Israel and to treat urinary tract infections in Palestine.

A. visnaga L. has been used in folk medicine by the Middle Eastern population since ancient times. The fruit decoction was used for the treatment of renal colic by the ancient Egyptians, as a treatment of kidney inflammation in Iraq and Palestine, and in the treatment of urolithiasis and prostatic pain in Algeria. Its use had spread to the extent that it was regarded as the most recommended species for the treatment of urinary tract infections.

Traditionally, khella (Ammi visnaga L.) has been described as emetic, purgative, antispasmodic, and diuretic, and was used to treat renal colic, bronchial asthma, and whooping cough by Unani physicians. During the middle ages, it was not uncommon to use the herb as a diuretic.

A. visnaga L. has earned recognition in the literature and works of diverse Arab chemists and physicians, attesting to its well-documented medicinal and therapeutic characteristics.

3. Key Constituents and Active Compounds

Principal Phytochemicals

Peer-reviewed studies show that the pharmacological activities of A. visnaga are due to its valuable chemical constituents, which include mainly essential oil, polyphenolic compounds including flavonoids, as well as γ-pyrones, represented mainly by khellin and visnagin.

Ammi visnaga contains γ-pyrones (furanochromones, up to 4%), the principal compounds being khellin (0.3–1.2%), visnagin (0.05–0.30%), khellinol, ammiol, khellol, and khellinin. Ammi visnaga also contains fixed oils (up to 18%) and coumarins (0.2–0.5%), the main one being the pyranocoumarin visnadin (0.3%).

The most important active substances in the khella fruits are believed to be the furanocoumarins khellin, visnagin, khellol, and khellol glucoside, and the pyranocoumarins visnadine and samidin. Furthermore, the herb contains flavonoids (including quercetin and isorhamnetin), plant sterols, and a minimal amount (0.2%) of essential oil.

Khellin: Structure and Significance

Khellin is the key furanocoumarin of Ammi visnaga L. that exhibits various biological properties. This unique natural product has inspired the discovery of two first-in-class drugs, amiodarone and sodium cromoglycate.

Khellin and visnagin can be quantitatively determined in aqueous extract prepared from the crushed fruits of Ammi visnaga L. using HPLC. The quantitative amounts of the marker compounds khellin and visnagin were 2.88 and 1.72 mg per 100 mg of the extract, respectively.

Visnagin: Structure and Significance

Visnagin, a bioactive compound found in the fruit of Ammi visnaga, belongs to the furanochromone class of natural substances and possesses a distinctive molecular structure characterized by a chromone backbone fused with a furan ring. Visnagin (4-methoxy-7-methyl-5H-furo[3,2-g][1]-benzopyran-5-one) is an active principle of the fruit of Ammi visnaga, a plant traditionally used in cardiovascular disorders, and its vasodilator effects have been studied in rat vascular smooth muscle.

Visnadin

The seeds of Ammi visnaga exhibit notable cardioprotective properties primarily due to three key constituents—khellin, visnagin, and visnadin—known for their calcium channel blocking activities. These constituents improve coronary circulation and alleviate pain associated with decreased blood flow to the heart. Visnadin, in particular, has shown significant efficacy in dilating coronary and peripheral vessels, while visnagin supports similar vasodilatory effects.

4. Mechanisms of Action

Smooth Muscle Relaxation and Calcium Channel Blocking

Khellin and the structurally related furanochromone visnagin are the major active principles found in Ammi visnaga, whose dried fruits have been traditionally used in Asia and the Middle East for treatment of coronary diseases, bronchial asthma, renal colics, and muscle spasms. Both compounds exhibit vasodilatory activities due to their calcium channel blocking properties and act in an anti-inflammatory manner by inhibiting AP-1 and NF-κB signaling.

The γ-pyrone content of A. visnaga has a powerful effect on facilitating the passage of kidney stones and relieving renal colic, in addition to having a relaxant effect on smooth muscle including that of the coronary arteries.

Visnadin is the most active compound and can inhibit vascular smooth muscle contraction and may dilate peripheral and coronary vessels and increase coronary circulation. Visnagin also has negative chronotropic and inotropic effects and reduces peripheral vascular resistance.

Renal and Urinary Mechanisms

Khellin was found to be a smooth muscle relaxant, induces diuresis, increases excretion of citrate, and decreases the excretion of oxalate in urine, which improves nephrolithiasis and passage of ureteric stones. Khellin was thought to slow or prevent calcium oxalate nucleation, preventing stones from forming. However, studies have shown that khellin is not the sole active ingredient in Visnaga daucoides extract. Upon studying calcium oxalate nucleation, Visnaga daucoides extract as a whole was shown to prolong nucleation time as well as change stone conformation, while khellin alone had no effect.

Antioxidant and Anti-inflammatory Mechanisms

The essential oil of A. visnaga is reported to have antiviral, antibacterial, and larvicidal effects, while its flavonoid content is responsible for its antioxidant activity. Both khellin and visnagin act in an anti-inflammatory manner by inhibiting AP-1 and NF-κB signaling.

CYP1A Enzyme Modulation

Khellin and visnagin have been identified as activators of the aryl hydrocarbon receptor (AHR) in human primary hepatocytes and HepG2 hepatocarcinoma cells. Both compounds increased the expression of several AHR target genes, but simultaneously acted as potent inhibitors of CYP1A monooxygenases. This finding has significant implications for drug–drug interactions (see Safety section below).

Cardioprotection Against Doxorubicin

Visnagin is known for its vasodilatory and anti-inflammatory properties, and recent studies suggest its cardioprotective efficacy against doxorubicin-induced cardiotoxicity through mitochondrial protection, the modulation of key signaling pathways, and the inhibition of apoptosis. High-throughput chemical screening performed in zebrafish embryos identified visnagin as a potential novel therapy for doxorubicin-induced cardiotoxicity.

5. Scientific Evidence by Area of Use

5.1 Urolithiasis (Kidney Stones) and Renal Colic

Teas prepared from the fruits of Ammi visnaga L. have been traditionally used in Egypt as a remedy to treat kidney stones. Several lines of evidence — primarily preclinical and case-based — support this use.

In vitro evidence: A study evaluated the effect of a Khella extract (KE) as well as the two major constituents khellin and visnagin on renal epithelial injury using LLC-PK1 and Madin-Darby canine kidney (MDCK) cells as model systems to study cellular processes involved in the development of a renal stone.

Animal evidence: Researchers investigated the effect of Ammi visnaga seeds on experimentally induced kidney stones in male Wistar albino rats. Several studies have focused on the diuretic activity of A. visnaga; it has been shown to be effective in the treatment of nephrolithiasis and uremia in animal models.

Clinical/case evidence: A published case report highlighted a patient with recurrent urethral stones and hypertriglyceridemia. The patient was treated with A. visnaga seeds and recovered completely from ureteral stones, with high-density lipoprotein (HDL)-cholesterol levels returning to normal after using A. visnaga seeds for 10 days. The case showed the effect of A. visnaga seeds in treating urolithiasis with an extended effect on raising HDL-cholesterol. The dosage used was a teaspoon size (10 g) of seeds boiled in 200 mL of water twice daily for 10 days.

Evidence strength: The clinical evidence for khella in urolithiasis is limited to case reports and small series. No large, randomized, placebo-controlled trials in humans have been published. The in vitro and animal data are supportive but cannot substitute for rigorously controlled human studies. The whole-plant extract appears more effective than isolated khellin alone for anti-nucleation effects.

5.2 Vitiligo and Skin Repigmentation (KUVA Therapy)

Khellin is a furanochromone extracted from the seeds of Ammi visnaga (khella), a plant common in the Eastern Mediterranean region, and has a chemical structure close to psoralens with similar phototherapeutic properties but with less phototoxic and carcinogenic effects.

Mechanism: When khellin is applied topically in combination with UVA light, it is able to stimulate melanocytes (cells that produce melanin) in hair follicles for successful treatment of vitiligo.

Clinical evidence — randomized trial: In a randomized, double-blind trial, 60 patients with vitiligo took 100 mg khellin once daily or placebo, followed 45 minutes later by 15 minutes of sun exposure.

Clinical evidence — gel formulation study: A total of 36 patients suffering from different types of vitiligo underwent a 6-month period of treatment. A 1% gel formulation of khellin in a water/2-propanol/propylene glycol (WPG) ternary system was applied to one side of the body, and as a control only the WPG vehicle to the other side, 30 minutes before UVA exposure. The khellin-WPG preparation showed increased solubility with enhanced patient compliance. Repigmentation (>10% of the initially affected area) occurred in 86.1% of the khellin-WPG-treated sides vs. 66.6% of the placebo-treated sides (P < 0.01). Young patients with a short duration of disease demonstrated a better response.

Open-label prospective study: The combination of 308-nm excimer light and khellin is a safe and effective treatment and represents a new alternative therapy for vitiligo. Further comparative controlled randomized investigations are needed to confirm these promising results with the appropriate therapeutic protocols.

Topical vs. systemic effects: When khellin is applied topically and treated with UV light, pigmentation returns to treated areas. When taken systemically, khellin induces elevated liver enzyme levels and broad photosensitivity; however, topical application reduces these side effects.

Evidence strength: Multiple controlled and open-label human trials support the combination of khellin with UV light (KUVA therapy) for vitiligo, with statistically significant repigmentation in one randomized controlled trial. Evidence is moderate in strength but comes from studies with relatively small populations. Topical khellin-UVA compares favorably to psoralen-based PUVA therapy in terms of side-effect profile.

5.3 Psoriasis

A trial in Egyptian patients with psoriasis found that 6 of 8 had a significant response to therapy with khellin combined with sun exposure, compared to none of the 10 subjects randomized to placebo after 4 months, and results were durable to 3 years in the treatment group. Early research also suggests that taking khellin, a chemical in khella, by mouth in combination with sunlight exposure helps clear skin lesions in people with psoriasis.

Evidence strength: The clinical evidence for psoriasis is limited to small trials. The study populations are very small, and independent replication in larger, well-controlled trials is lacking. Evidence is preliminary.

5.4 Cardiovascular: Angina Pectoris and Coronary Vasodilation

Khellin (C₁₄H₁₂O₅) is a vasodilator that also has bronchodilatory activity; its active ingredient was found to increase coronary blood flow. Khellin has been used to relieve the pain associated with angina pectoris by acting as a selective coronary vasodilator.

Observations of a laboratory technician being cured of anginal symptoms after taking khellin led to efforts by European pharmaceutical industries to isolate an active compound. Amiodarone was initially developed in 1961 at the Labaz company, Belgium, by chemists Tondeur and Binon, who were working on preparations derived from khellin. It became popular in Europe as a treatment for angina pectoris.

Evidence strength: The direct use of khella/khellin for angina in modern human clinical trials is limited. Much of the cardiovascular evidence comes from preclinical work and the legacy of derived pharmaceuticals (amiodarone). The direct plant preparation has no large-scale, modern, randomized controlled trial evidence for cardiovascular indications.

5.5 Respiratory: Asthma and Bronchospasm

Some good effects were reported in the literature on the use of khellin, an extract of seeds of Ammi visnaga, by intramuscular route in bronchial asthma. Authors tried 7 mg of khellin by aerosol spray for 5 minutes on 10 patients with bronchial asthma, with very satisfying clinical results. Control of vital capacity showed an increase in all cases (average 404.8 ccm).

Intramuscular injections of khellin can also be used to treat asthma. Khellin acts as a bronchodilator; however, the common side effects including nausea present difficulties.

Connection to modern pharmacology: The discovery of the anti-asthma drug sodium cromoglycate arose from a Fisons program aimed at studying the anti-spasmodic properties of an Egyptian herb called khellin. Two khellin-derived analogues, amiodarone (an anti-anginal drug) and cromolyn sodium (an anti-asthmatic drug), were approved by the US Food and Drug Administration (FDA) in 1985 and 1973, respectively.

Evidence strength: The evidence for the direct use of whole khella or isolated khellin as an anti-asthmatic in modern clinical trials is very limited and largely historical. The most compelling evidence for asthma derives indirectly from the development of sodium cromoglycate, a structurally related pharmaceutical. The existing human data on the direct use of khellin for asthma are from small, older studies.

5.6 Cardioprotection Against Anthracycline Chemotherapy

Visnagin emerges as a potential cardioprotective solution; a review aimed to provide a comprehensive overview of the cardioprotective properties of visnagin against doxorubicin (DOX)-induced cardiotoxicity, summarizing molecular mechanisms and providing experimental evidence from various studies, and discussing the potential for integration of visnagin into cancer therapeutic regimens.

Although much remains to be learned about the mechanisms by which visnagin provides cell type-specific protection from doxorubicin, its discovery offers compelling evidence that doxorubicin-induced cell death can be mitigated in a cell-specific fashion. The discovery that MDH2 (mitochondrial malate dehydrogenase) inhibition is sufficient for cardioprotection provides not only a potential new therapeutic target, but also a new entrance point for investigating the fundamental differences in responsiveness to doxorubicin by cardiac and tumor cells.

Evidence strength: Evidence is currently preclinical (animal models, zebrafish embryos, cell lines). No human clinical trial data are yet available. This represents an active area of emerging research.

5.7 Antimicrobial Activity

Khella possesses substantial antimicrobial properties attributed to its primary constituents, khellin and visnagin, which exhibit antifungal, antibacterial, and antiviral activities. Research indicates that Ammi visnaga can inhibit the growth of threats such as Mycobacterium tuberculosis and various pathogenic fungi when its extracts are used.

Evidence strength: Antimicrobial activity has been demonstrated in vitro. No human clinical trials have been conducted to evaluate khella as an antimicrobial therapeutic agent.

6. Body Systems and Health Areas Associated with Khella

• Urinary / Renal System: The plant is used directly as a herb or as a component for production of a number of herbal medicines for the cure of renal colic and ureteric stones.
• Cardiovascular System: Khella is a potent coronary vasodilator with antispasmodic effects, making it useful in treating angina.
• Respiratory System: Khella is used for respiratory conditions including asthma, bronchitis, cough, and whooping cough.
• Dermatology / Skin: It is used as a folk medicine for vitiligo and psoriasis.
• Metabolic / Lipid: The case evidence showed that A. visnaga seeds have an effect in treating urolithiasis with an extended effect on raising HDL-cholesterol.
• Oncology (Emerging/Preclinical): Recent studies have identified derivatives of khellin and visnagin as suitable agents to treat different types of tumors, epileptic seizures, kidney stones, and inflammatory diseases.

7. Dosage Forms and Dosages Reported in Studies

A typical dose of khella is an amount that provides 20 mg of the khellin constituent per day.

In safety and efficacy studies of khellin use in combination with ultraviolet (UV) light therapy for treatment of vitiligo, pure compound khellin was applied topically as a 5% preparation and as 100 mg administered orally. In a study evaluating effects of khellin on cholesterol regulation, khellin 200 mg/day orally was administered for 4 weeks.

An aerosol study administered 7 mg of khellin by aerosol spray for 5 minutes in 10 patients with bronchial asthma.

In a 36-patient vitiligo gel study, a 1% gel formulation of khellin in a WPG ternary solvent system was applied to one side of the body 30 minutes before UVA exposure over a 6-month treatment period.

In the published urolithiasis case report, the dose was a teaspoon-sized amount (10 g) of seeds boiled in 200 mL of water, taken twice daily for 10 days.

An infusion preparation for experimental study used 20 g of fruits ground to medium powder size, with 200 mL of boiling water poured over the ground fruits and steeped for 5 minutes at room temperature.

8. Safety Considerations and Drug Interactions

Systemic Adverse Effects

Unwanted side effects include dizziness, reversible cholestatic jaundice, pseudoallergic reaction, and elevated levels of liver enzymes (transaminases and gamma-glutamyltransferase). Its oral use is limited by its potential toxicity (e.g., elevated liver enzymes, phototoxicity, dermatitis). In experimental animals, the median lethal dose (LD₅₀) was 3.6 g/kg for intraperitoneal administration and 10.1 g/kg for oral administration.

When taken systemically, khellin induces elevated liver enzyme levels and broad photosensitivity; however, topical application reduces these side effects.

Hepatotoxicity Risk

Unwanted side effects include dizziness, reversible cholestatic jaundice, pseudoallergic reaction, and elevated levels of liver enzymes (transaminases and gamma-glutamyltransferase). The available case-level and study data indicate that long-term or high-dose oral use carries a documented risk of hepatic enzyme elevation.

CYP1A Enzyme Inhibition and Drug Interactions

Both khellin and visnagin act as potent inhibitors of CYP1A monooxygenases. Therefore, with regard to the potential health risk for individuals under KUVA therapy, both the putative adverse effects as well as possible drug–drug interactions of khellin and structurally related chemicals need to be carefully elucidated in future toxicological studies to minimize unpredicted side effects.

Despite the frequent usage of khellin and visnagin, their potential toxic properties are not well characterized. Many natural compounds modulate the expression and activity of cytochrome P450 1A1 (CYP1A1), which is well-known to bioactivate pro-carcinogens.

Interaction with Digoxin

There is a reported moderate interaction with digoxin (Lanoxin). Digoxin helps the heart beat more strongly. Khella appears to slow the heartbeat. Taking khella along with digoxin might decrease the effectiveness of digoxin.

Pregnancy

It is considered likely unsafe to take khella if pregnant. It contains khellin, a chemical that can cause the uterus to contract and may cause a miscarriage.

Photosensitivity

When taken systemically, khellin induces elevated liver enzyme levels and broad photosensitivity; however, topical application reduces these side effects. The photosensitizing properties of khellin are also central to its therapeutic use in KUVA therapy for vitiligo.

Product Variability

As a result of khellin being found only as part of the broader khella extract, many healing properties have been attributed to khellin that are actually due to other constituents of the extract. Visnaga daucoides preparations are commercially available and very common; however, the amount of khellin and other ingredients varies greatly between brands and even batches of the same brand.

9. Derived Pharmaceuticals: Khellin's Legacy in Modern Medicine

Khellin's structural scaffold has given rise to two major pharmaceutical agents in current medical practice:

• Amiodarone (anti-arrhythmic): Amiodarone was initially developed in 1961 at the Labaz company, Belgium, by chemists Tondeur and Binon, who were working on preparations derived from khellin. It became popular in Europe as a treatment for angina pectoris. As a doctoral candidate at Oxford University, Bramah Singh determined that amiodarone and sotalol had antiarrhythmic properties and belonged to a new class of antiarrhythmic agents (what would become the class III antiarrhythmic agents).
• Sodium Cromoglycate (anti-asthma/mast cell stabilizer): The anti-allergic cromones were originally synthesized in the 1960s by Fisons Plc, and the first drug to emerge from this program, disodium cromoglycate, was subsequently marketed for the treatment of asthma and other allergic conditions. Early studies demonstrated that the ability of the cromones to prevent allergic reactions was due to their mast cell stabilizing properties. It arose from a Fisons program aimed at studying the anti-spasmodic properties of an Egyptian herb called khellin.

Khellin, from Ammi visnaga (L) Lamk., led to the development of chromolyn (in the form of sodium chromoglycate) as a bronchodilator, representing one of the most notable plant-to-pharmaceutical translations in modern pharmacology.

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