Virtual Screening of Physicochemical and Pharmacokinetic Parameters of Selected Bryophyllum Pinnatum Constituents

Medicinal plants have been known since ages and esteemed as rich source of therapeutic agents, thus utilized in preventing and treating various diseases and ailments. Despite of advancement in drug industry and drug products, about 75% of world population rely on traditional plant products for healing. Traditionally, Bryophyllum pinnatum has been noted for its versatile medicinal properties.¹

 Bryophyllum pinnatum is a succulent and perennial plant mostly found at tropical and subtropical areas. The species is native to Madagascar. Bryophyllum pinnatum is also known as Kalanchoe pinnata. Some of the common names for these herbs are as follows: air plant, cathedral bells, miracle leaf, devils backbone.²

Taxonomy:

Kingdom: Plantae

Class: Dicotyledon

Family: Crassulaceae

Genus: Bryophyllum.³

Description of plant:

The plant grows up to 150cm(1-1.5m) in height and leaves grow 10-30cm long. The lower leaves differentiate from upper leaves of plant such that the lower leaves are simple and dark green in color while the upper leaves are 3-7 foliated, long petiolate, with characteristic odour, bitter taste and thick⁴.  Flowers are cymose, unisexual, regular and pendent with large spreading panicles. Petals are as sepals, reddish-purple in color, while sepals are 25-55mm long, red striated with base green. The fruits are follicles, contain a few seeds. These seeds are small and oblong in shape with smooth surface and brownish in color. The Bryophyllum  pinnatum plant flowers in Nov-Mar and produce fruits in April.           

Pharmacological Actions

The  Bryophyllum pinnatum shows various pharmacological actions such as anti-inflammatory, antidiabetic, anticancer, analgesic, antipyretic, antiulcer, astringent, antiseptic, hepatoprotective, antileishmanial, antioxidant, wound healing activity, antibacterial, antituberculosis, antihypertensive, tocolytic agent, CNS depressant, anxiolytic, neurosedative, insecticidal, immunomudulatory agent, antiallergic, antimicrobial, hepatoprotective, antiurolithic, diurectic, anticonvulsant, uterine relaxant, muscle relaxant, antimalarial, carminative, antigout.^4,5,6,7

Chemical Constituents Of Bryophyllum Pinnatum

 Bryophyllum pinnatum is rich in various phytocontituents such as alkaloids, flavonoids, steroids, triterpenes, phenanthrenes, bufadienolides, cardienolides, lipids, glycosides. The leaves are concentrated with majority of bufadienolides and cardiac glycosides. From aerial parts of plant Phenolic acids such as syringic acid, caffeic acid, 2-4-hydroxy-3-methoxy cinnamic acid, etc have been isolated. Flavanoids are rich in leaves mainly quercetin and kaempferol glycosides and few flavone glycosides i.e., luteolin, diosmetin. The plant also showed the presence of triterpenes such as alpha amyrin, beta amyrin, alpha amyrin acetate, beta amyrin acetate, taraxerone, etc. and phytosterols such as stigmast-24-enol, 5-methylerogost-24(28)-enol, etc. Bryophyllum pinnatum possessed high content of mallic acids, carboxylic acids such as oxalic acids, citric acid, isocitric acid, etc.⁷ U. Rosemary et.al, performed ethanolic extraction of leaves obtained from Bryophyllum pinnatum, 3,5-dihydroxy-6-methyl-2,3-dihydroxy-4H-pyran-4-one showed anticancer activity, alpha-D-Glucopyranoside methyl possessed anti-tuberculosis, antioxidant and anticonvulsant activities, n-Hexadecanoic acid was effective against rheumatism and inflammation, oleic acid decreased risk of breast cancer and decreased blood pressure.⁶ C. Lucas et.al, carried out ethanolic extraction of Bryophyllum pinnatum. The   flavonoids such as rutin, quercetin, luteolin-7-o-beta-o-glusoide were detected. The study revealed that ethanolic extraction of of  Bryophyllum pinnatum leaves is effective as topical anti-inflammatory for acute and chronic inflammation conditions.⁸ M. Afzal et.al, isolated a steroidal derivative Stigmast-4,20 (21),23-trien-3-one from Bryophyllum pinnatum leaves. This compound was evaluated for anti-inflammatory activity in carrageenan induced paw edema model and was capable of reducing inflammation.⁹ Ogidigo.J.O.et.al, performed In-silico molecular docking and pharmacokinetic studies of selected constituents from Bryophyllum pinnatum. Patuletin, luteolin, kaempferol and acacetin passed the Lipinski’s rule of five and showed good binding scores and considerable drug likeness.¹⁰ Literature survey revealed that there is a lack of computational studies on virtual screening of selected phytoconstituents from Bryophyllum pinnatum plant, to investigate its physicochemical and ADME properties. Hence, in this context, in the current research work, we aim at virtually screening some phytoconstituents from Bryophyllum pinnatum plant for various physicochemical and pharmacokinetic parameters.

METHODOLOGY

Physicochemical properties and drug likeness

Drug likeness score is determined from molecular properties i.e molecular weight, number of hydrogen bond donors, number of hydrogen bond acceptors, LogP and polar surface area by Molsoft online server.

ADME predictive study

Various ADME parameters of all the selected chemical constituents of Brophyllum pinnatum were calculated by using Qik Prop module of the Schrodinger molecular modeling software. These parameters were then compared with the recommended values of the Qik Prop properties mentioned in the Qik Prop User Manual.

A] Determination Of Physicochemical Properties And Drug Likeness Of Selected Chemical Constituents From   Bryophyllum Pinnatum

Lipinski’s Rule Of 5

Lipinski’s rule of 5 or Pfizer rule of 5 or rule of 5 is a thumb rule which postulates whether a drug is orally active in humans or not. This rule was worked out by Christopher A. Lipinski in 1997.¹¹

Components Of Rule Of 5:

Lipinski’s rule of 5 intends that no orally active drug should show more than 1 violation for following norms:

• No more than 5 hydrogen bond donors
• No more than 10 hydrogen bond acceptors
• Molecular weight of drug should be less than 500
• Log P valve should not exceed more than 5

Since all numbers are multiple of 5, thus contributes to name “RULE OF 5”^11,12

B] Determination of Pharmacokinetic Properties of Selected Chemical Constituents from Bryophyllum Pinnatum

Pharmacokinetics Studies (Adme Studies)

Pharmacology is categorized into 2 groups: Pharmacodynamics and Pharmacokinetics. Pharmacodynamics is defined as study of effect of drug on body (what the drug does to body). Pharmacokinetics is study of effect of body on drug or is also defined as movement of drug within body and excretion from body (what body does to the drug).The term Pharmacokinetics is coined by Leslie Benet. In order to understand the concept of pharmacokinetics, it is grouped into 4 phases of drugs movement i.e., absorption, distribution, metabolism and excretion (ADME). ADME of drug depends on various properties of drug such as molecular weight, chemical structure, chemical space, degree of ionization, lipophilicity, water solubility, etc. Majority of compounds lack these properties, thus ADME studies are conducted priorily in order to eliminate such compounds. The assessment of ADME is an important part during various stages of drug development such as drug discovery, preclinical and clinical stage, as it determines the drug efficacy, safety and toxicity. About 80% of investigational new drugs are ruled out during drug development process because of undesirable ADME and toxicity characteristics. Most of the Pharmaceutical companies possess hundreds – thousands of potential drugs, but are not FDA approved due to undesirable properties.¹³

Absorption: Absorption is the movement of drug from its site of administration into circulation. When a drug is administered through oral route, the drug reaches the liver via hepatic portal vein after the drug passes out of Gastrointestinal tract. The drug moves from liver into the blood. Poor absorption of drug likely occurs if the drug has more than      

• 5H-bond donors
• 10H- bond acceptors
• Molecular weight more than 500 Daltons
• Log P greater than 5

The amount of drug absorbed from the site of absorption evaluates the bioavailability of drug at site of action.

Distribution: The distribution of drug involves its movement into, through, and out of body compartments. Once the drug enters into systemic circulation by absorption, it gets distributed to various organs and muscles. Distribution pattern of drug depends on factors like:

• Lipid solubility
• Ionisation at physiological pH
• Extent of binding to plasma and tissue proteins
• Presence of tissue specific transporters
• Difference in regional blood flow

Metabolism: In this process the drug gets converted into metabolites through enzymes. It converts non polar compounds to polar compounds, so that excretion process takes place eliminating the reabsorption of compounds in renal tubules. The converted metabolites may be either active or inactive. This process may either increase or decrease parent drugs activity.

If the drugs activity increases, then the metabolite is active and if drugs activity decreases then the metabolite is inactive.

Excretion: The body excretes metabolites and remaining drug through kidney and other organs such as lungs and skin. If the drug is not completely excreted from body, the remaining traces of body may cause adverse reactions. Drugs and their metabolites are excreted in urine, faeces, exhaled air, saliva, sweat and milk.

Toxicity: The ADME studies includes toxicity studies to calculate Maximum therapeutic dose and minimum toxic dose.^13,14,15

The pharmacokinetic parameters of selected chemical constituents from  Bryophyllum pinnatum, were calculated by using QikProp module of Schrodinger molecular modeling software and the data obtained was verified with QikProp manual. The recommended ranges for different ADME parameters are as follows: CNS: predicted central nervous system,-2 to +2, dipole: computed dipole moment of the molecule,1.0-12.5, volume: total solvent-accessible volume in cubic angstroms using a probe with a 1.4angstroms radius,500-2000, QPlogPC16: predicted hexadecane/gas partition coefficient,4.0-18.0, QPlogPoct: predicted octanol/gas partition coefficient,8.0-35.0, QPlogPw: predicted water/gas partition coefficient,4.0-45.0, QPlogPo/w: predicted octanol/water partition coefficient,-2.0-6.5, QPlogS: predicted aqueous solubility,-6.5-0.5, QPlogHERG: predicted IC₅₀ value for blockage of HERG K⁺ channels,below-5, QPPCaco: predicted apparent Caco-2 cell permeability in nm/sec,<25>500 great, QPlogBB: predicted brain/blood partition coefficient,-3.0-1.2, QPPMDCK: predicted apparent MDCK cell permeability in nm/sec,<25poor>500great, QPlogKp: predicted skin permeability,     -8.0-1.0, QPlogKhsa: prediction of binding to human serum albumin,-1.5-1.5, %HOA: predicted human oral absorption on 0 to 100% scale,>80% is high <25>Table 2. Quercitrin, isoquercitrin, rutin, myricitrin, astragalin, kaempferitrin, thesiuside and misquelianin showed poor HOA. Results shown in Table 2.

Table 1. Physicochemical parameters and drug likeness of selected chemical constituents from  Bryophyllum pinnatum

Table 2. Pharmacokinetic parameters of selected chemical constituents from Bryophyllum pinnatum