**3. Toxicological concern with oral nanoparticles**

#### **3.1 Polymer-based nanoparticles**

Polymer-based NPs (PNPs) can interact with GIT cells and tissues, resulting in inflammation, oxidative stress, and damage to the intestinal barrier. Various poly(lactide-co-glycolic acid) NPs (PLGA) were examined for toxicity in THP-1 macrophages similar to human cells. When used as an NPs stabiliser, chitosan polymer conferred significant cytotoxicity to PLGA NPs, despite being slightly cytotoxic [73]. Research has shown that NPs exhibit varying levels of impact on intestinal cells, intestinal flora, and the intestinal barrier, confirming that NPs cause damage to the digestive system [45, 74]. Polystyrene NPs administration has been found to trigger the TOS-MAPK/NF-kB signalling pathway in macrophage RAW 264.7, leading to inflammation with pro-inflammatory and cytotoxic potential activity [35]. Furthermore, exposure to polystyrene NPs have been shown to disrupt the balance of cell populations within the intestinal cells of zebrafish [75]. Existing data on the toxic effects of ingested zinc oxide (ZnO) NPs on intestinal models need to be more consistent. Several studies have found negative biological effects, such as increased intestinal inflammation, reduced cell viability, and mitochondrial membrane depolarization, resulting from the treatment with ZnO NPs. However, modified ZnO NPs do not cause significant cell damage [76, 77].

#### **3.2 Lipid-based nanoparticles**

Lipid-based nanoparticles (LNPs) have gained attention as potential DDS due to their ability to encapsulate hydrophobic medications and shield them from degradation [78]. Cationic lipids, for instance, show significant potential as carriers for delivering delicate substances such as nucleic acids, but certain cationic lipids can lead to cytotoxicity [36]. The impact of hydrophobic chains on lipid toxicity has yet to be thoroughly investigated, impeding the development of less harmful lipids [79]. Solid lipid nanoparticles (SLNs) are among the most prevalent types of LNPs employed in drug delivery. SLNs have been discovered to cause toxicity in the GIT, resulting in inflammation, oxidative stress, and damage to the intestinal barrier [80]. Numerous studies have indicated that the interaction between LNPs and GIT can trigger an immune response, modify the gut microbiota, and induce toxicity [79, 81]. A recent study discovered that oral administration of altered RNA-LNPs led to the expression of pro-inflammatory cytokines (such as interleukin (IL) -6 and macrophage inflammation protein 2 (MIP-2)) and chemokines in the intestines of unexposed mice [39]. Ball et al. [82] documented that LNPs can compromise the stability of the intestinal epithelial barrier and result in intestinal inflammation.

#### **3.3 Silica-based nanoparticles**

Silicon-based nanoparticles (SiNPs) can interact with GIT cells and tissues, causing inflammation, oxidative stress, and damage to the intestinal barrier [83]. Various factors influence the toxicity of SiNPs in GIT, including their dimensions, surface area, surface charge, and chemical makeup [84]. Cellular absorption of silica dioxide NPs (SiO2NPs) depends on the size of the particles, particularly in the range of 30-50 nm. SiO2 NPs within the 30-50 nm size range can be carriers in multiple applications [40, 41]. An *in vivo* study revealed that ingesting SiO2NPs led to GIT inflammation and increased permeability, causing intestinal contents to leak into the bloodstream and disrupting the microbiota-gut-brain axis [85]. Guo et al. [83] discovered that exposure to SiO2NPs affected nutrient transportation, ROS production, barrier function, gene expression, and microvilli structure. To assess the potential toxicity of SiNPs, examining their interactions with gut cells, uptake, and impact on GIT function and microbiota is important. The nanoscale SiO2 found in the E551 food additive could uniquely impact the absorption and distribution of SiO2 within the human body [86]. Numerous in vitro studies have shown that SiO2NPs can produce cytotoxic effects in cultured human cell lines, such as glioblastoma cells, depending on their size, shape, and dose [87]. Furthermore, SiO2NPs, inhaled or ingested, can infiltrate cells and engage with cellular membranes or organelles, leading to mammalian cell death through oxidative stress, endoplasmic reticulum stress, and apoptosis [42, 43]. A different instance of SiNPs that exhibit toxicity in the GIT involves mesoporous silica NPs (M-SiNPs) [44]. M-SiNPs have been identified to induce toxicity in the GIT, with inflammation, oxidative stress, and harm to the intestinal barrier. SiNPs administration has been found to cause intestinal inflammation by interfering with the hydrolysis and metabolism of nutrient peptides in *Caenorhabditis elegans* (an invertebrate nematode) [45]. Furthermore, Ogawa et al. [88] revealed that administering 10-nm SiNPs provoked intestinal inflammation by activating an apoptosis-associated speck-like protein with a CARD (caspase activation and recruitment domain) inflammasome.

#### **3.4 Metallic-based nanoparticles**

Numerous scientific investigations have been conducted on the therapeutic applications of gold nanoparticles (AuNPs), silver nanoparticles (AgNPs) and superparamagnetic iron oxide nanoparticles (SPIONPs) [55, 89]. They possess several characteristics

#### *Potential Toxicity of Nanoparticles for the Oral Delivery of Therapeutics DOI: http://dx.doi.org/10.5772/intechopen.111946*

that make them attractive as DDS. Specifically, they can be easily synthesised in various sizes and shapes, their surfaces can be functionalized with different elements such as polymers, peptides, targeting ligands, imaging probes, and more, and they are generally considered safe for certain *in vivo* biological applications [55].

AgNPs exhibit distinct properties related to toxicity, surface plasmon resonance, and electrical resistance [90]. In a study by Vandebriel et al. [91], repeated exposure to AgNPs resulted in cytotoxic effects on various rat cells. Intending to create new anticancer treatments, Azizi et al. [92] developed albumin-coated AgNPs, which were found to be specifically taken up by cancerous cells and trigger apoptosis. Furthermore, through numerous pathways, AgNPs are highly effective against gram-positive and gram-negative bacteria. They help address the problem of drug resistance often seen with traditional antibiotics due to their unique mode of action [54]. Clear evidence of systemic toxicity from AgNPs ingested orally or through intravenous routes has been demonstrated, and the toxic effects are related to the amount of Ag+ released during exposure [93]. Moreover, the significant surface area of AgNPs that release Ag+ ions is a critical aspect that contributes to the cytotoxic behaviour. As widely recognised, smaller AgNPs exhibit a faster pace of silver ion (Ag+ ) dissolution in the nearby microenvironment, owing to their greater surface area-to-volume ratio. This results in increased bioavailability, improved distribution, and increased toxicity compared to larger AgNPs [40, 94]. Research examining the anti-inflammatory properties of AgNPs has shown a considerable decrease in wound inflammation, adjustment of fibrogenic cytokines, a reduction of pro-inflammatory cytokines, and cell death in inflammatory cells [52, 53]. NPs with diameters below 100 nm have been documented to be mainly taken up by endocytosis in epithelial cells. Within these cells, AgNPs can induce oxidative stress, DNA damage, and inflammation [95]. Jeong et al. [96] observed an increase in goblet cells in the intestines and a significant release of mucus granules in mice treated with oral AgNPs (60 nm) at a 30 mg/kg body weight per day for 28 days. Furthermore, AgNPs administered orally (5-20 nm) for 21 days in mice (20 mg/kg body weight) disrupted the microvilli of epithelial cells and affected the intestinal glands [93].

Various *in vivo* studies have been conducted to assess the possible toxic effects of AuNPs, but the findings still need to be definitive [51]. Factors such as size, shape, surface properties, stabilising coatings, and administration aspects (dosage, duration, and method of administration) can lead to the varying toxic effects of AuNP *in vivo* [46]. Research has shown that smaller AuNPs (5–15 nm) exhibit a more extensive organ distribution in rodents compared to larger AuNPs (50–100 nm), suggesting a higher risk of toxicity *in vivo* for smaller AuNPs [47]. Research conducted by Goodman and colleagues [97] indicated that cationic AuNPs interact with the negatively charged cellular membrane, causing damage to the intestinal membrane. Furthermore, citrate-capped AuNP (13 nm in diameter) were harmful to human lung carcinoma cells while not affecting human liver carcinoma cells at the same dose [98]. As additional information is collected, it has been recommended that proper consideration be given to surface chemistry and dosages of Au and AgNPs to utilise them in biomedical applications efficiently [49, 50].

SPIONPs have become increasingly popular in numerous biomedical applications, such as magnetic resonance imaging, targeted drug or gene delivery, and hyperthermia [57]. However, SPIONPs can potentially cause cytotoxicity, negatively impacting vital cellular components such as mitochondria, the nucleus, and DNA [99]. Research examining the influence of various surface coatings on cell behaviour and structure revealed that dextran-magnetite (Fe3O4) NPs lead to cell death and decreased proliferation,

similar to the effects of uncoated iron oxide particles [56]. Contact with SPIONPs has been linked to considerable harmful consequences, including inflammation, developing apoptotic structures, compromised mitochondrial functioning (MTT), membrane leakage, ROS production, extensive chromosomal aberration, and condensation [57].
