2.1. Protein

Annona squamosa is a lowland tropical shrub that possesses a high pharmaceutical potential for treating cardiac ailments, thyroid-related disorders, diabetes, and cancer. Phytochemical analysis of ASL extracts revealed the presence of numerous phytochemicals, such as proteins, carbohydrates, saponins, alkaloids, flavonoids, phenolics, and glycosides ^[21]. A study conducted at four different sites in Egypt showed the highest protein content in ASLs compared to seeds and fruit. ASLs from Menofia showed a protein content of 13.47 mg/g on a fresh weight (FW) basis, whereas ASLs from Mansoura demonstrated the highest protein content of 17.26 mg/g FW. ASLs from Alexandria (3.52 mg/g FW) and Giza (6.80 mg/g FW) showed the lowest protein content. Thus, a higher protein content in ASL extracts can harness the nutritional value of the food for use by humans as well as animals ^[22]. Proteins and amino acids were also present in high quantities in the methanolic and aqueous extracts of ASLs ^[23]. The biuret test confirmed the presence of proteins and amino acids in aqueous ASL extracts, while Millon’s test confirmed the presence of proteins and amino acids in methanolic ASL extracts ^[24]. Limited research has been conducted to date regarding the quantification of amino acids and protein in ASLs; hence, more attention is needed to explore its protein and amino acid profiles.

2.2. Minerals and Vitamins

ASLs possess appreciable concentrations of various minerals, such as phosphorus (P), potassium (K), iron (Fe), calcium (Ca), magnesium (Mg), sodium (Na), copper (Cu), selenium (Se), and zinc (Zn), and vitamins, namely, A, C (ascorbic acid), E, B1 (thiamine), B2 (riboflavin), B3 (niacin), and B9 (folic acid). These minerals are required to maintain a healthy human body, as they help to perform various activities, such as maintenance of healthy teeth and bones, muscle contraction and relaxation, blood clotting, blood pressure regulation, nerve functioning, immune system health, energy metabolism, and many enzymes ^[25]. Macro- and microminerals, namely, Mg (65.65 mg/100 g), P (43.1 mg/100 g), Zn (0.455 mg/100 g), Cu (0.312 mg/100 g), and Se (in trace amounts), were reported in extracts of ASLs ^[26]. In another study, Shukry et al. 2019 ^[22] showed the leaf mineral composition of four different varieties of AS: K (252.47–386.98 μmol/g DW), Na (61.2–95.18 μmol/g DW), Ca (78.51–171.65 μmol/g DW), and Fe (37.23–49.55 μmol/g DW).

The concentrations of vitamins B9 and C were reported to be 8.12–11.98 and 11.98–16.78 μg/g FW, respectively, in ASL ^[22]. The vitamin contents of the ASL extract showed the presence of vitamin B1 (0.065 mg/100 g), B2 (0.155 mg/100 g), B3 (1.105 mg/100 g), C (34.4 mg/100 g), and A and E (in traces) ^[26]. HPLC analysis of ASLs revealed a valuable vitamin C concentration of 3.5% ^[27]. These vitamins are involved in many activities in the human body, such as maintaining skin health, epithelial tissue development, bone development, visual sharpness, immune response, wound healing, and strengthening connective tissues. Vitamin B1, B2, B3, and B9 act as cofactors for several enzymes involved in oxidation-reduction reactions and carbohydrate metabolism ^[25].

3.1. Essential Oil Profile

Annona squamosa has been widely grown in India for its fruits, apart from its leaves, stem, and roots, which are also important because they possess nutraceutical and pharmaceutical value. Furthermore, the essential oil extracted from ASLs displays excellent antiparasitic and antimalarial activity ^[28]. Various studies have been conducted to investigate the chemical composition of ASL essential oil (ASLEO). Shade-dried leaves collected from lower regions of the Himalayas yielded 0.13% essential oil through the hydrodistillation method. Altogether, 43 constituents were detected, which represented 88.6% of the total oil extracted from ASLs. Gas chromatography–mass spectrometry (GC-MS) and GC–flame ionisation detection (GC-FID) analyses of ASLEO showed a dominance of sesquiterpenoids (sesquiterpene hydrocarbons, 63.4%, and oxygenated sesquiterpenes, 21.8%) followed by monoterpenes (monoterpene hydrocarbons, 2.0%, and oxygenated monoterpenes, 1.4%). Among the sesquiterpenes, the major constituents were (E)-caryophyllene (15.9%), γ-cadinene (11.2%), and epi-α-cadinol (9.4%) ^[29]. ASLEO composition has also been studied in different parts of the world. (E)-Caryophyllene (27.4%) and germacrene D (17.1%) were major constituents reported in Brazilian ASLEO ^[28]; carvone (24.9%), diacetyl (9.3%), and linalool (7.7%) were major constituents reported in Egyptian ASLEO ^[30]; and leaf essential oil from the closely related plant Annona muricata from France contained germacrene D (15.7%), β-elemene (12.0%), sabinene (8.8%), and α-pinene/β-pinene (8.1%) as major components ^[31]. α-Pinene (1.0–11.9%), limonene (0.8–11.7%), and β-caryophyllene (11.6–24.5%) were the major constituents of ASLEO derived from Vietnam ^[32]. ASLEO is mainly composed of terpenes and sesquiterpenes. It yields approximately 59 chemical compounds, of which β-caryophyllene (31.1%) and δ-cadinene (6.7%) were found to be the major compounds ^[33]. Fresh leaves of Annona squamosa yielded 0.12% (v/w) essential oil through the hydrodistillation method. Eighteen constituents were identified from the ASLEO by using GC and GC/MS, which represented 86% of the total oil extracted. The northern region of India demonstrates a prevalence of β-caryophyllene (23%) and germacrene D (21.3%), while the major components of ASLEO from the southern region of India are β-cedrene (23.3%) and β-caryophyllene (14.1%) ^[34]. The nutritional and essential oil composition of ASLs is presented in Table 1, and Table 2 shows the various essential oil components reported by the scientific community. The structures of essential oil component present in ASLs are depicted in Figure 2.

Figure 2. Major essential oil components in Annona squamosa L. leaves.

3.2. Secondary Metabolite Profile

ASLs are mostly discarded or burnt, as they are considered a worthless agricultural waste product. However, ASLs have been commonly used in tropical and subtropical countries such as India, Vietnam, Malaysia, and Laos as a traditional medicine for the treatment of cardiac problems, dysentery, worm infections, fever, fainting, haemorrhage, constipation, and dysuria. Bioactive phytochemicals investigated in different ASL extracts revealed potential biological and pharmacological activities, such as antidiabetic, antioxidant, antimicrobial, antiviral, antiobesity, antidiarrhoeal, and antitumour activities ^[41][42]. The phytochemical profile of ASLs can be broadly classified as acetogenins, alkaloids, flavonoids, phenols, saponins, tannins, glycosides, sesquiterpenes, anthocyanins, steroids, diterpenes, terpenoids, quinones, amino acids, and fatty acids ^{[43][44][45][46]}. Among them, total phenolic compounds (TPCs), including flavonoids, alkaloids, phenols, saponins, and tannins, are most abundant in ASLs. Epidemiological investigations have proven the role of polyphenolic compounds against various chronic diseases, such as cancer, diabetes, cardiovascular, and neurodegenerative diseases ^[35]. Polyphenolic compounds regulate various biochemical and physiological processes, namely, enzymatic activity, cell proliferation, signal transduction pathways, and cellular redox potential, to fight against chronic pathologies ^[47]. A list of various phytochemicals reported in ASLs is presented in Table 3, and the structures are depicted in Figure 3.

Figure 3. Major phytochemicals from Annona squamosa L. leaves.

In recent years, custard apple cultivation has been gaining much public attention due to the essential oil extracted from its leaves. Kulkarni et al. ^[60] investigated the chemical composition of ASL extracts using the gas chromatography–mass spectroscopy (GC-MS) technique. They reported sodium benzoate (27.50%), 4,4-dimethylcholertrol (10.30%), 4,4-tert-butylcalix(4)areve (12.34%), stigmasterol acetate (2.92), butyloctylpthalate (9.67%), and isoamylacetyate (2.29%) in ASL extracts. Garg and Gupta ^[34] identified 18 compounds from essential oil extracted from ASLs collected from North Indian Plains, which account for 86% of the oil. The major constituents of ASLs oil categorised as β-Caryophyllene (23.0%), germacrene D (21.3%), monoterpene hydrocarbons (2.5%), sesquiterpene hydrocarbons (76.0%) and oxygenated sesquiterpenes (7.1%), β-elemene (7.8%), and bicyclogermacrene (8.5%). Hydro-distillation of ASLs produced red essential oils, with a yield of 0.76% (w/w), and about 95.5% of oil is contributed by sesquiterpenes ^[61]. In this study, 23 compounds were reported in ASLEO using GC-flame ionisation detection (GC-FID) and GC-MS. Among all, (E)-caryophyllene (27.4%), bicyclogermacrene (10.8%), germacrene D (17.1%), β-elemene (6.2%), (Z)-caryophyllene (7.3%), epi-α-cadinol (4.3%), γ-cadinene (4.2%), δ-elemene (4.1%), and α-humulene (5.7%) were found in higher concentrations.

Kumar et al. ^[43] reported the total phenolic content, with a range of 212.8–1478.4 μg/g, in leaf extracts of 30 different Annona squamosa genotypes. A total of seven phenolic compounds, including chlorogenic acid (1.84–5 μg/g), quercetin (0.19–1.60 μg/g), gallic acid (0.45–0.89 μg/g), caffeic acid (0.07–2.57 μg/g), ferullic acid (0.72–2.82 μg/g), cinnamic acid (0.02–0.05 μg/g), and salicylic acid (0.64 μg/g), were detected and quantified from the methanolic extract of ASLs. Similarly, various phytochemicals, such as phenols, anthroquinones, saponins, tannins, glycosides, and flavonoids, were reported by Katole et al. ^[45] in ASL extracts. In another study, Malik et al. ^[46] isolated and characterised rutin (quercetin-3-rhamnosyl glucoside), a flavonoid compound, from ethanolic extracts of ASLs by nuclear magnetic resonance (NMR) and MS techniques. In a recent study of ASL extracts, Nguyen et al. ^[42] reported flavonoid and total phenolic contents of 82.61 ± 0.82 mg of quercetin equivalent (QE)/g and 242.88 ± 6.13 mg of gallic acid equivalent (GAE)/g, respectively. These studies suggested that ASLs may serve as potential food supplements to improve human health.

4.1. Anticancer Activity

The ability to evade apoptosis is a unique property of human cancers that can result in effective cancer progression and tumour formation. The high resistance of cancer cells to apoptosis against a pertinent stimulus is a critical rationale underlying therapy failure. Hence, a number of cancer treatment strategies, including radiation therapy and chemotherapy, are primarily based on cancer cell apoptosis ^[38]. A long history of using natural products as ethnomedicines, which are inexpensive and have minimal side effects, in contrast to exorbitant synthetic drugs with deleterious effects, has instigated the development of natural pharmaceutical drugs ^[39]. In recent decades, naturally derived bioactive compounds with apoptosis-inducing effects have garnered significant interest in the area of anticancer pharmaceuticals.

Leaves of Annona squamosa have a number of chemical compounds belonging to diverse groups, including phenolics, annonaceous acetogenins, saponins, flavonoids, alkaloids, glycosides, alkaloids, steroids, and terpenoids ^[62]. A study was conducted to investigate the in vivo and in vitro anti-breast cancer activity of ASL extracts ^[40]. Leaf extract at a concentration of 100 µg/mL exhibited strong cytotoxic and antiproliferative activities against breast cancer cell lines (MCF-7 and MDA-MB-231). The extracts showed a persistent induction of apoptosis and reduction in wound closure. The authors indicated that the anticancer effects could result from the cell cycle arrest of MCF-7 cells at G1 phase and inhibition of their migration to other parts of the body ^[59]. The inhibition of these cell lines could also be attributable to reactive oxygen species (ROS) generation, DNA fragmentation, and nuclear condensation, resulting from the downregulation of the ratio of Bcl-2 (apoptosis regulator) and Bax (induce apoptosis by instigating the release of mitochondrial cytochrome C). Additionally, the activation of Caspase-3 stimulates the expression of a number of microRNA species that target Bcl-2.

In another study, silver nanoparticles were synthesised by ASL extract (As-Ag NPs) and tested for their anticancer activity against the HeLa (cervical) cancer cell line ^[58]. The results indicated that these As-Ag NPs exhibited strong apoptotic action against HeLa cancer cells. This could result from atypical protein signalling and ROS induction, causing oxidative stress and subsequently inducing apoptosis and cell death ^[63]. A similar study was conducted to test the efficacy of ethanolic ASLs extract integrated with chitosan nanoparticles against human colon cancer cell lines (WiDr) ^[56]. The IC50 value against WiDr cells was estimated to be 292.39 µg/mL. The extracts were found to significantly increase the expression of caspase-3, Bax and bad genes, causing an arrested cell cycle at the G2/M phase and induction of WiDr apoptosis.

4.2. Antidiabetic Activity

Diabetes is an endocrine and metabolic disorder that is primarily characterised by insulin deficiency, insulin resistance, and elevated levels of sugar in the blood. According to the International Diabetes Federation (IDF), the prevalence of diabetes mellitus (DM) is escalating across the globe. In 2016, 415 million people had diabetes, and by 2040, 642 million people are anticipated to suffer from DM ^[57]. For the treatment of DM, numerous oral hypoglycaemic medicinal compounds, such as sulfonylurea (glimepiride), thiazolidinedione (rosiglitazone), and biguanides, are available in addition to insulin. However, counterfeit medicinal compounds have led to critical complications in patients and are harmful to pregnant women ^[64]. In the distant past, medicinal plants and their extracts were used to control diabetes because of their potential to ameliorate hyperglycaemia without any side effects ^[65]. Following the WHO guidelines on DM, investigations into medicinal plants as hypoglycaemic agents have become more relevant ^[66].

The antidiabetic or antihyperglycaemic effects of ASLs and their constituents have been studied in animal models. Panda and Kar ^[49] isolated quercetin-3-O-glucoside (Q3G) from ASL, evaluated its antidiabetic potential in alloxan-induced diabetic rats, and observed that Q3G significantly improved insulin secretion and reduced the level of glucose in the blood. The authors also observed an increase in antioxidant enzyme activity, such as superoxide dismutase (SOD) and catalase (CAT), in renal and hepatic cells. Ranjana and Tripathi ^[53] studied the antidiabetic properties of different extracts of ASL and found that among the methanol and water extracts of ASL, hexane extract showed a better antihyperglycaemic response. Authors reported that hexane extract (400 mg/kg) showed significant intestinal α-glucosidase inhibition with 75.69 ± 1.7% compared to acarbose (10 mg/kg) with 53.60 ± 1.45% and improved the serum insulin level with 16.26 ± 1.20 µU/mL compared to glimepiride (1 mg/kg) with 17.36 ± 0.90 µU/mL, which demonstrated the secretagogue nature of the extract. Davis et al. ^[51] implied that leaves exert their action by promoting glucose uptake as well as by modulating insulin signalling events via inhibition of protein tyrosine phosphatase 1B (PTP1B) and stimulation of the phosphorylation of insulin receptor-β (IR-β) and insulin receptor substrate-1 (IRS-1) accompanied by upregulation of glucose transporter type 4 (GLUT4) and phosphoinositide 3-kinase (PI3 kinase) mRNA expression in vitro. The authors also revealed that oral administration of hexane extract showed a significant reduction of 30.5% in the levels of triglyceride (TG) compared to the antidiabetic drug rosiglitazone (33.5%). Gupta et al. ^[64] evaluated the effects of an ethanol extract of ASLs in alloxan and streptozotocin (STZ)-induced diabetic mice. The authors determined that a dose of 350 mg/kg body weight significantly decreased the fasting blood glucose (FBG) level by 26.8%, reduced the triglyceride (TG) by 28.7%, significantly reduced the low-density lipoprotein (LDL) or “bad cholesterol” by 71.9% along with total cholesterol (TC) by 49.3%, and favourably increased high-density lipoprotein (HDL) or “good cholesterol” by 30.3% in diabetic mice. In several studies, researchers investigated the hypoglycaemic and antidiabetic effects of ASLs and reported that these extracts exerted antidiabetic potential through (i) increasing the amount of insulin by stimulating pancreatic β-cells, (ii) increasing glucose uptake in the muscle, (iii) inhibiting intestinal enzymes such as α-glucosidase responsible for glucose metabolism ^[66], and (iv) inhibiting glucose output from the liver and consequently improving the lipid profile in diabetic mice ^[52][54]. The abovementioned findings suggested that ASLs could be useful to maintain or control normal blood sugar levels and cholesterol levels and could be an effective alternative as a herbal medicine to control diabetes. Antidiabetic and various other bioactivities of ASL extract is presented in Table 4.

4.3. Antioxidant Activity

In the course of metabolic reactions, cells produce free radicals as a byproduct. Free radicals induce oxidative stress in the cell at higher concentrations, which contributes to cell function disruption. Multiple recent studies have shown that deleterious free radicals cause various degenerative diseases, such as diabetes, cancer, and neurodegeneration ^[80]. Several studies have shown the significance of antioxidant compounds from ASLs for mitigating the damaging effects of free radicals ^[82]. Gas chromatography coupled with mass spectrometry (GC-MS) analysis of the methanolic extract of ASLs revealed the presence of sesquiterpene hydrocarbons, such as germacrene-D (22.01%), trans-caryophyllene (12.12%), and bicyclogermacrene (2.80%) ^[18]. Another such preliminary phytochemical screening of ASL extract revealed the presence of alkaloids, flavonoids, phenols, and saponins ^[42]. Several studies were conducted to determine the antioxidant potential of the ASLs. The DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging activities of ASL extracts in acetone, methanol, and water were reported to have moderate antioxidant activity with an IC50 value of 33.9 ± 4.8 μg/mL for acetone, followed by methanol and aqueous extracts with values of 51 ± 1.6 and 98.3 ± 0.4 μg/mL, respectively ^[18]. Another such study of ASL extracts in methanol and ethanol resulted in IC50 = 13.61 µg/mL and IC50 = 15.97 µg/mL, respectively ^[72]. The DPPH free radical scavenging activity of ASL extracts in chloroform, methanol, and water reported IC50 values of 308.3 μg/mL, 342.5 μg/mL, and 439.6 μg/mL, respectively. The NO radical scavenging activity of the extracts reported IC50 values of 185.2 mg/mL, 345.8 mg/mL, and 366.3 mg/mL in methanol, chloroform, and water, respectively. The overall study reported that the methanol extract had higher antioxidant activity than chloroform and water, which was attributed to the presence of a large class of phytochemicals that were absent in chloroform and water extracts. The study also reported phenolic compounds as the main antioxidant components ^[1]. Another study reported the H₂O₂ scavenging activity of different solvent extracts of ASL in methanol, acetone, ethanol, and water, where water extracts exhibited higher activity, i.e., 54.06%, at 25 μg/mL than acetone, ethanol, and methanol extracts. The study also reported the correlation coefficient between the total antioxidant activity and total phenolics, which was found to be 0.8965 ^[3]. A previous study attributed the difference in H₂O₂ scavenging capacity between the solvent extracts to the structural features of their active components, which determine their electron-donating abilities ^[73]. In another study ethanolic extract of ASL was reported to have 133.33 and 264.65 μg/mL DPPH and hydroxyl activity, respectively ^[83]. The authors concluded that polyphenols extracted from the ASL at optimised conditions have excellent antioxidant properties which can be utilised in preparation of functional foods. In a parallel comparative study, methanol and hexane extract of ASL reported IC50 49.64 and 64.01 µg/mL, respectively ^[84]. The authors also showed that ASL extracts have superior antioxidant properties than bark extracts. In summary, many interesting results indicated the potential of ASL extracts as antioxidants, but little research on the application of these extracts has been reported.

4.4. Antimicrobial Activity

Plant-based antimicrobials have substantial prophylactic properties and are considered to be efficient, safe, and cost-effective alternatives for synthetic antimicrobials that possess more notable side effects. Despite being a commercial fruit plant because of its creamy succulent flesh, Annona squamosa is reported to have enormous pharmacological properties, including antimicrobial activity, owing to the presence of different secondary metabolites, such as glycosides, phytosterols, alkaloids, oils, saponins, phenols, and flavonoids ^[85]. In several research studies, the leaf extracts of Annona squamosa were identified to have remarkable antibacterial activity and antifungal activities. Significant antimicrobial activities were exhibited by an active acetogenin compound known as annotemoyin isolated from chloroform leaf extract and by certain flavonoid compounds purified from aqueous leaf extract of the plant ^[44]. Other acetogenins, such as squamocin, squamostatin, and cholesteryl glucopyranoside, showed growth inhibition of gram-positive bacteria, such as Bacillus subtilis, Bacillus cereus, Bacillus megaterium, and Staphylococcus aureus ^[74]. LC-MS/MS analysis of ASL extracts from plants growing in drylands identified the presence of metabolites, including ephedradine A, ergosine, mudanpioside H, and trichosanic acid, exhibiting significant antifungal activity. The same extract was found to inhibit bacterial growth at a concentration of 8–11 µg, and the compound mudanpioside H was possibly responsible for this antibacterial activity ^[81]. Additionally, screening for comparative antimicrobial activity of methanol and petroleum ether leaf extracts of Annona squamosa was performed against two gram-positive (S. aureus and B. subtilis) and two gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria, indicating that the highest zone of inhibition was observed against P. aeruginosa with a minimum inhibitory concentration (MIC) of 131 µg/mL, followed by petroleum ether extract against P. aeruginosa with an MIC of 164 µg/mL and methanol extract against E. coli with an MIC of 179 µg/mL. Here, phytochemical studies proved that some of the essential oil compounds, such as linalool, borneol, eugenol, farnesol, and geraniol, present in the leaf extracts contributed to the antibacterial activity ^[77].

The natural metabolite palmitone purified from leaf cuticular wax of Annona squamosa showed higher antibacterial activity (MIC: 6.24–12.6 µg/mL) than its individual isomeric hydroxyl ketones, i.e., 11-hydroxy-16-hentriacontanone and 10-hydroxy-16-hentriacontanone (MIC: 20–52 µg/mL). For a compound to penetrate the bacterial cell wall, the lipophilicity of the cell wall and the specific compound need to be mutually compatible. Palmitone is a symmetrical ketone compound compared to hydroxy palmitones, and therefore, has a greater penetration ability and higher antimicrobial activity ^[86]. Additionally, antiviral activity was exhibited by kaurane diterpenoid 16β,17-dihydroxy-entkauran-19-oic acid, which inhibited HIV replication in H9 lymphocyte cells ^[78]. The antimicrobial mechanism of action of leaf extracts can be attributed to the major contributors, i.e., phenolic compounds, which induce disruption of the microbial membrane, coagulation of cytoplasmic components, and cytoplasmic leakage, interfering with microbial cellular metabolism and adapting anti-quorum sensing activity ^[79]. A study on the prospective role and applications of ASL extract in the prevention of foodborne bacterial disease indicates that the extract has broad-spectrum but heat-labile activity against foodborne bacterial pathogens because of its ability to scavenge H₂O₂ in a range of 45–55% ^[87]. Detailed research should be performed to explore the myriad of bioactive compounds that combine to give the leaf extract its therapeutic value, their mechanisms of action and more potential benefits of using ASLs as natural food preservatives.

4.5. Hepatoprotective Properties

Hepatosteatosis or fatty liver disease (FLD) is mostly caused by an imbalance in the production and metabolisation of fat in the body, which is caused by dietary habits, sedentary lifestyles, and stress. Moreover, several drugs (e.g., paracetamol) are known to cause damage (as a side effect) to hepatocytes. Due to the effect of a high fat dose and the damage caused by drugs, hepatocytes face oxidative stress, which further leads to hepatosteatosis. Drug-induced liver injury has become a major concern for health-related personnel and industry ^[69]. Therefore, compounds that act as antioxidants, inhibitors of lipid peroxidation, and possess free radical scavenging capacity may show hepatoprotective properties. ASLs exhibit very high antioxidant activity (Section 4.3). The presence of flavonoids, glycosides, saponins, alkaloids, and phenolic compounds was reported by Rajeshkumar et al. ^[71] in ASLs. Paracetamol is the most common medicine used in the treatment of various diseases, but it has many negative impacts on various body parts. Consumption of paracetamol causes hyperlipidaemia, which is a common sign of liver damage. Rajeshkumar et al. ^[71] used paracetamol-treated (2 g/kg b.w.) albino rats to evaluate the hepatoprotective properties of ASLs. The dose of ASL extract (1000 mg/kg body weight (b.w.)) conferred effective protection of hepatic cells by enhancing protein levels and inducing a significant reduction in serum glutamate oxaloacetate transaminase and serum glutamate pyruvate transaminase levels in serum. The presence of a flavone [5,7,40-trihydroxy-6,30 dimethoxy flavone 3-O-a-L-rhamnopyranoside (THDMF-Rha)] was reported in the ASL extract. At a dose of 5.0 mg/kg b.w., THDMF significantly reduced hepatic lipid peroxidation in L-thyroxine-induced rats ^[48]. In another individual experiment, the hepatoprotective properties of ASLs were evaluated in carbon tetrachloride-induced Wistar rats by Sonkar et al. ^[67]. These rats were further treated with ethanolic extract of ASLs (450 mg/kg b.w.), which reduced malondialdehyde (MDA) levels (45.48%), total serum bilirubin (38.82%), alanine aminotransferase (39.51%), and aspartate aminotransferase (11.69%). Moreover, the effect was similar to that of a hepatoprotective compound (silymarin) after 7 days of treatment. The authors speculated that the presence of coumarins may be the chief factor conferring hepatoprotective activity. A significant improvement was observed in islands of Langerhans in rats treated with aqueous and ethanolic extracts at a dose of 300 mg/kg/day ^[70]. In the case of diethylnitrosamine (200 mg/kg)-induced swiss albino mice, the levels of glutamyl oxaloacetate transaminase (GOT), glutamyl pyruvate transaminase (GPT), alkaline phosphatase (ALP), acid phosphatase (ACP), alpha fetoprotein (AFP), and total bilirubin increased in serum and tissue, and these were significantly reduced following treatment with ASL extract (5 g/kg for 30 days) ^[69]. Upon application at 250 and 500 mg/kg b.w., the ASL methanolic extract significantly decreased the serum concentrations of bilirubin, ALP, aspartate amino transferase (AST), gamma glutamate transpeptidase (γ-GT), alanine amino transferase (ALT), and TBARS, but increased the total protein concentration in rifampicin-induced male Wistar albino rats ^[88]. These results demonstrated that ASL extracts can be used as hepatoprotective agents and to improve the condition of hepatocytes.

4.6. Effect of ASLs Extract on the Lipid Profile

A balanced lipid profile or lipid panel is required for the proper metabolic function of the body. An imbalance in the lipid profile (dyslipidaemia) leads to several diseases, such as coronary artery disease, stroke, peripheral arterial disease, cancer, atherosclerosis, and myocardial infarction. Lifestyle, food habits, disease, and drugs are responsible for dyslipidaemia due to the enhanced mobilisation of lipids from adipose tissue to plasma. Diabetes, one of the diseases that affects antioxidant defence systems, causes oxidative stress and alters the lipid profile due to overproduction and/or insufficient removal of ROS ^[52][70]. Diabetic Wistar rats and albino rabbits were treated with ethanolic extract of ASLs at various doses (200, 300, 350, and 400 mg/kg). The most significantly positive result was observed with a dose of 350 mg/kg, which reduced TC, LDL, and TGs by approximately 49.3%, 71.9%, and 28.7%, respectively, and increased the level of HDL (30.3%) ^[64]. In another experiment, streptozotocin (50 mg/kg) induced diabetic albino Wistar rats treated with a water extract of ASLs. Treatment reduced MDA levels, activated antioxidant enzymes, and maintained the lipid profile (lower TGs, TC, and higher HDL) ^[52]. Diabetic mice treated with methanolic extract of ASLs (250 mg/kg body weight) significantly reduced serum TC (34.7%), TGs (50%), and LDL (53%) and improved HDL (53%) levels compared to nontreated mice. The author suggests that the activation of lipoprotein lipase (LPL) and stimulation of β-cells are responsible for hypolipidaemic activity, as they secrete sufficient insulin to clear triglycerides from plasma ^[75]. The application of an alcoholic extract of ASLs in streptozotocin-induced albino rats significantly reduced TC and TGs but increased HDL. Moreover, with the improvement of the lipid profile, a significant weight reduction (19.46%) was reported in the treated rats compared to the control after 28 days of treatment ^[76]. The presence of higher levels of flavonoids in the leaf may be responsible for the same result. Methanolic extract containing THDMF-Rha was found to be effective in reducing lipid concentrations (TC, TGs, VLDL, LDL, and HDL) in serum ^[48]. In another study, the application of both aqueous and ethanolic ASL extracts (300 mg/kg b.w.) significantly decreased the levels of CL, TGs, and LDL cholesterol and significantly increased HDL cholesterol levels in alloxan (150 mg/kg)-induced diabetic rats ^[70]. The present study has shown that ASL extracts potently cause weight loss and maintain the lipid profile in serum.

Extracts from the natural sources are rich in bioactive compounds and perform numerous biological activities, which is key for the formulation of pharmaceutical drugs and innovative food products rich in antioxidants. ASLs have been grossly studied for their health promoting effects using in vivo ad in vitro experiments. However, to establish ASLs as an active ingredient in pharma- and food industry, more clinical trials must be conducted. Furthermore, ASL extracts have been proven to be cytotoxic against cancerous cells, but its toxicity needs more exhaustive studies on the normal cells. Vast molecular diversity of the ASLs have potential to treat other ailments in humans, which needs further attention of the researchers.