The antiproliferative effects of DV extracts, most often demonstrated using in vitro cell viability assays, have been reported on a range of cancer cell types, primarily of epithelial origin, namely colon, cervical, ovarian, and breast cancers (23-28) (Table I). Studies using the breast cancer cell lines MCF-7 and MDA-MB231 found that DV leaf extracts, prepared using dried leaves ground to a powder and thereafter suspended in solvent, potently inhibited proliferation, via S phase arrest, with an IC₅₀ of 75 µg/ml (23,24). In a study assessing crude ethanolic extracts of DV leaves, as well as purified fractions (hexane, chloroform, ethyl acetate, butanol and aqueous fractions), the growth of the established human colorectal adenocarcinoma cell line HT29 was found to be inhibited (25). The mouse 3T3 embryonic non-malignant cell line was also included for comparison. The crude ethanol extract and the chloroform fraction in particular showed significant selectivity towards the cancer cell line, with the chloroform fraction displaying an impressive 12-fold reduced IC₅₀ value relative to the 3T3 cells. However, the two major limitations of the study were inclusion of only one representative cancer cell line, and the lack of directly comparable non-malignant cell lines as controls (25). In a subsequent study, the same researchers fractionated and analysed hydroethanolic extracts of DV leaves and identified over 50 individual chemical constituents, a majority of which were flavonoids and diterpenoids (26). They found the hydroethanolic DV extract to be slightly more selective towards the two human colorectal cancer cell lines SW480 and SW620, compared with Chinese hamster ovary cells (CHO-1) and the human benign keratinocyte cell line HaCaT. The effects on cell proliferation and cell death were demonstrated using several standard assays, including analysis of cell morphology using microscopy, induction of apoptosis using Annexin V-PI labelling, and assessment of mitochondrial membrane potential disruptions (26). Extractions using a range of solvents, as well as combinations of solvents, found the flowers and leaves of the plant to yield the highest percentage extract, relative to the stems and roots (27). Notably, the yield varied depending on the solvent type, indicating a richness of phytoconstituents with diverse chemical composition. Except for the flower-derived extract, fractions showed potent cytotoxicity against human leukemic (THP-1) and liver (Hep-G2) cell lines, although selectivity towards cancer cells remains undetermined due to the absence of non-malignant control cells (27). In yet another study, the antiproliferative activity of two purified root extracts, both triterpenoid saponins, was demonstrated against the human ovarian cancer cell line A2780(28), while fractions from ethanolic crude extracts prepared from leaves showed growth inhibition in the human lung adenocarcinoma cell line A549(29). These studies are summarized in Fig. 2, and provide strong evidence for the DV plant as a potential lead source of anticancer bioactive phytochemicals, although limitations remain including the robustness of some of the data especially related to selectivity towards malignant cells. To date, few studies have reported on the cellular pathways mediating the cytotoxic mechanism of action of DV extracts. A recent study revealed potent and selective killing of Burkitt lymphoma cells, mediated, in part, through inhibition of the oncogenic P13K/Akt pathway (30).

The use of nanotechnology in the delivery of DV-derived compounds has shown promising results. Advances in nanotechnology research have allowed for improved drug delivery, demonstrating increased efficacy and specificity of treatment, and reduced adverse effects (31,32). As a result, several nano-based treatment modalities have been translated into clinical trials, including silver nanoparticles (AgNPs), which are widely used in clinical applications due to their antimicrobial, antioxidant, antiviral, and antidiabetic properties, and as conjugates with chemotherapeutic drugs (33). Notably, AgNps synthesized from DV leaf extracts have exhibited potent anti-proliferative properties in vitro against ovarian (SKOV-3) and lung (A549) cancer cell lines (34,35). In both of these studies, DVE-AgNPs were significantly more toxic to the cancer cells compared with non-cancerous control cells or cancer cells treated with the crude extract alone. Furthermore, cancer cells were markedly more sensitive to AgNPs synthesized from solvents such as petroleum ether, acetone, methanol, and acetonitrile compared with those synthesized from an aqueous solvent (34,35). The use of zinc oxide nanoparticle (ZnO NP) preparations from ethanol-, petroleum ether-, chloroform-, and methanol-derived DV leaf extracts have also yielded promising results, demonstrating significant inhibition of cell viability towards liver (HepG2) and colorectal (HCT-116) cancer cell lines compared with fibroblast cells (3T3), showing superior cytotoxicity relative to Tamoxifen-treated cancer cells (36). ZnO NPs exhibited superior cytotoxicity relative to chloroform-derived DV fractions (IC₅₀ values of ZnO NPs: HepG2, 16.4±4 µg/ml and HCT116, 29.07±2.7 µg/ml vs. IC₅₀ values of chloroform DV fractions: HepG2, 26.4±3.3 µg/ml and HCT116, 39.8±13 µg/ml) (36).

To date, only a few studies have made use of preclinical models to evaluate the efficacy and safety of DV extracts. Nevertheless, these have yielded promising outlooks on anticancer efficacy, bioavailability and toxicity. For instance, AgNPs synthesized from ethanolic DV leaf extracts inhibited the development of tumours induced by N-nitrosodiethylamine in the liver of Wistar rats (37). Serum levels of enzymatic markers indicative of liver damage, alanine transaminase and aspartate aminotransferase, were significantly reduced, while albumin levels, a marker of less aggressive tumour progression, were reduced. While DNA damage was reduced in hepatic tissues of rats which received the DV-AgNPs, the apoptosis rate was increased. Overall, DV AgNPs exhibited protective effects against liver damage and significantly inhibited hepatocellular carcinoma progression in rats receiving DV extracts compared with controls (37).

Oxidative damage to proteins and DNA resulting from disrupted reactive oxygen species (ROS) homeostasis is a major contributor to genomic alterations that enhance oncogenic phenotypes in cancer cells. Numerous natural products are rich sources of antioxidants able to act as effective scavengers of free radicals and ROS (38). The administration of extracts from DV, both organic and aqueous, proved protective towards carbon tetrachloride (CCL4)-induced hepatotoxicity in rats (39). CCL4 is known to cause liver damage through the formation of ROS, and in that particular study, hautriwaic acid was suggested as the main DV-derived protective compound identified via HPLC fingerprinting (39). In a more recent study (40), through the use of the DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging in vitro assay, stem and leaf extracts of DV were found to have strong antioxidant activities, which corroborated an earlier study where stem extracts of the plant showed strong scavenging activities (27).

The innate inflammatory response is the first line of defense against damaging agents and invading pathogens, but its effects are mitigated by the use anti-inflammatory medicines to mitigate tissue damage caused by prolonged or excessive responses. Naturally occurring agents with anti-inflammatory properties offer potentially safer and more effective alternatives to synthetic options for managing inflammation. The carrageenan rat paw edema model was used to demonstrate that hydroalcoholic (DVHA) and n-hexane (DVH) extracts from DV leaves were more effective compared with the anti-inflammatory drug indomethacin, in reducing inflammation (41). The study demonstrated that the DVHA and DVH extracts effectively suppressed carrageenan-induced inflammation in rats compared with control rats which either did not receive DV or received indomethacin. In another study, this time using mice ear edema as a model to measure inflammation, a 64% reduction in ear edema was observed in mice receiving DV dichloromethane extracts, compared with a 40% reduction in mice receiving indomethacin (42). A potential mechanism mediating these anti-inflammatory effects was suggested to be through the action of the phytochemical viscosine. Using molecular docking simulations, viscosine was found to impair the activity of lipoxygenase, an enzyme responsible for generating pro-inflammatory mediators and implicated in inflammatory diseases (43). Another notable observation was the potent reduction of nitric oxide production, prostaglandin E2 and tumor necrosis factor-α in the culture medium of lipopolysaccharide-induced murine macrophages (RAW264.7), once again suggesting that extracts from DV possess significant anti-inflammatory activity (43).

Extracts from the DV plants have been reported to inhibit the growth and biofilm formation of several bacterial and fungal pathogens including Staphylococcus aureus, Streptococcus mutans, Candida albicans, Salmonella typhi, Shigella flexneri, Escherichia coli, Vibrio cholera, Mycobacterium tuberculosis and Pseudomonas fluorescens (18,27,29,35,44-46). In rats infected with S. aureus, those receiving oral administration of ethanolic DV extracts for 30 days had improved kidney histopathology with normal glomeruli and convoluted tubules compared with untreated mice who developed thickening of the wall of renal vessels, infiltrating lymphocytes in the kidneys, and damaged glomeruli (44). Notably, extracts from the DV plant have been shown to display inhibitory effects against strains of Mycobacterium tuberculosis (M. tuberculosis), the organism responsible for multidrug-resistant tuberculosis which remains a public health concern worldwide. Using the resazurin microtiter assay the anti-mycobacterial efficacy of methyl alcohol and chloroform extracts of DV was assessed against three distinct strains of M. tuberculosis namely bg 1972, bg 206, and H37Rv (47). A dose-dependent decrease in the growth of the bacteria was observed, with the most pronounced effect exerted against the H37Rv strain.

The antifungal activity of the acetone-derived DV extract was evaluated against 40 Candida albicans (C. albicans) strains, 20 of which were isolated from individuals living with HIV and 20 from individuals without HIV (48). Although no discernible difference in effect was observed between the C. albicans isolates from the two groups, all strains were potently inhibited by the extracts. Notably, another study demonstrated that planktonic cells of C. albicans exposed to acetone DV extracts and DV bioactive compound (5, 6, 8-trihydroxy-7, 4' dimethoxy flavone) could not form germ tubes (49). These findings lend credence to the use of DV extracts by traditional medical practitioners to treat oral thrush and related infections, and suggest that DV may serve as a natural source of antifungal agents. Collectively, these results indicated that DV is a promising source of phytochemicals possessing antibacterial and antimycobacterial properties.

Viral diseases such as Zika, Ebola, AIDS, SARS, MERS, influenza, and pneumonia are major contributors to mortality and disability around the world. In low-income countries, chronic viral infections are attributable to up to 26% of cancer cases, where cancer incidence and related deaths are expected to increase significantly by 2050, highlighting the urgent need for effective prevention and treatment of viral infections (50). In a study by Rashed et al (51), the human CD4⁺ lymphoid cell line C8166 was used to demonstrate DV-induced inhibition of HIV-1 infection. Chromatographic separation of the extract with the highest anti-HIV-1 activity (petroleum ether-derived) identified two compounds, β-sitosterol and stigmasterol, as active antiviral agents (51). In yet another study, the effects of five different extracts from DV leaves were examined against coxsackievirus B3 and rotavirus SA-11 viral infections (52).

The hypoglycaemic activity of DV leaf extracts (derived from chloroform, methanol, butanol, and aqueous) was analysed in normal and alloxan-induced diabetic rabbits in several independent studies, all of which reported hypoglycaemic effects within 1-2 h after oral administration (53-56). A significant reduction in the blood glucose levels was observed in diabetic rabbits receiving DV compared with those treated with glibenclamide or untreated normal rabbits (53). Prolonged treatment, for 10/15/30 days, potently and consistently reduced blood glucose levels in alloxan-induced diabetic rabbits compared with normal and untreated controls, and a significant increase in plasma insulin levels and a reduction in urea, total cholesterol and triglycerides were observed during the treatment period (54,55). In a different animal model, that of streptozotocin-induced diabetic rats, a significant reduction in blood glucose, pyruvic transaminase, glutamic oxaloacetic transaminase, creatine, and urea was observed in DV-treated animals compared with untreated ones, accompanied by reduced levels of total cholesterol, triglycerides, low-density lipoprotein-cholesterol and pro-inflammatory biomarkers in serum, while no significant change was observed in high-density lipoprotein-cholesterol serum levels (56). Histopathological analysis of the liver and renal tissues from the DV-treated animals showed significant liver protection as evidenced by the regeneration of hepatocytes with a lack of fatty lobulation and necrosis, and lack of renal tubular necrosis which was evident in animals that did not receive the plant extracts (56). The cumulative findings from these studies provide strong support for the consideration of DV extract as a viable antidiabetic treatment.

The application of DV-derived products to assist in wound healing has been reported in alternative therapy, prompting investigation of this potential therapeutic benefit in laboratory-based in vivo studies using rats. Ethyl acetate flavonoid-rich fractions extracted from DV leaves were shown to significantly increase levels of hydroxyproline and hexosamine, important constituents of the extracellular matrix, improve collagen formation, and fasten epithelialization and vascularization of wounds, relative to control groups (57). In a separate but similar study using the same in vivo model and approach, DV extracts were found to perform similarly to the known and approved antibiotic nitrofurazone in preventing infection and accelerating wound healing (58). These findings warrant further investigations aimed at isolating the bioactive constituents with wound healing and antibiotic properties from the crude extracts of DV.

Extracts from DV leaves were shown to have gastroprotective effects and protect against the development of ulcers in a rodent model (59). Pretreatment with DV hexane extracts blocked the formation of ethanol/indomethacin-induced gastric ulcer lesions in the Charles Wister rats which displayed reduced gastric glutathione levels, inhibition in the accumulation of alkaline phosphatase and increased gastric pH. These effects were similar to those observed in rats treated with the proton-pump inhibitor drug, omeprazole. In a separate study, the anti-diarrheal activity of DV root extracts (alcohol and aqueous) was analysed in male albino mice fed castor oil to induce diarrhea (60). Both alcohol and aqueous DV extracts significantly reduced diarrhea episodes and stool weight in the mice in a dose-dependent manner, similar to what was observed in the groups receiving the anti-diarrheal drug, loperamide. Additionally, the DV extracts were found to be non-toxic to the mice at a dose of up to 2,000 mg/kg. No clinical signs of weakness or other adverse events were observed in the animals after DV treatment (60).