Application

Mechanism

Chondrocyte adhesion, growth, and IL-6 secretion

Nabila Mighri et al. compared the chitosan-coated collagen membranes to collagen membranes. They observed more live cell density and higher metabolic activity in chitosan-coated collagen membranes. The pore size of membranes influences the cellular adhesion and growth, chitosan level has a direct correlation with metabolic

activity. This hybrid membranes containing chitosan promote adhesion and proliferation of chondrocytes, as well as interleukin (IL-6) secretion.(9)

Repair of abdominal wall defects (Hernia Repair)

Hernia repair is a very frequent surgery procedure achieved by using conventional prostheses. However, they induce the creation of a peritoneal interface that is not completely desirable. New biomaterials like chitosan are proved to be excellent in terms of peritoneal regeneration, induce a minimal inflammatory response and promote a

good collagen deposition that is crucial to mechanical behavior of the regenerated tissue. (33)

Neuronal disorders

Parkinson's Disease

Dibutyltin (used as a psychedelic drug for Parkinson) induces the release of lactate dehydrogenase (LDH). Wang et al. discovered that this release could be diminished by chitosan, polymer that was able to increase cell viability too. In summary, chitosan inhibits mitochondrial membrane potential (MMP) disruption, cell apoptosis, and

reactive oxygen species (ROS) formation. (5)

Huntington's Disease

There is no cure for Huntington's disease, so therapeutics aim to improve primary symptomatology of this condition. Xu et al. discovered that COSs may decrease

neurotoxicity induced by Cu(II) by interfering with intracellular production of ROS. (5)

Alzheimer's Disease

This condition may be caused by cholinergic neuron death, deposition of amyloid, acetylcholine (ACh) deficiency, metal ion dynamic equilibrium disorder, neuroinflammation, and oxidative stress. As mentioned before, chitosan and COSs have beneficial neuronal effects as they inhibit oxidative stress and neuroinflammation. Unlike this biopolymer, current synthetic materials are ineffective in decreasing oxidative stress and have many side effects. Xao et al. discovered that peracetylated chitosan oligosaccharides (PACOs) reduce lactate dehydrogenase release, reactive oxygen species production, and attenuated the loss of mitochondrial membrane

potential.(5, 15)

Gene therapy

Gene therapy is achieved by introducing exogenous genetic material into a target cell so that the therapeutic effect is achieved. For that purpose, viral or non-viral methods can be used to deliver nucleic acids into cells. Chitosan-based vectors are considered non-viral vectors that must have efficient cell uptake, escape from endolysosomal pathways, have efficient unpacking of the nucleic acid cargo and nuclear import, as well as, protect nucleic acids from nuclease degradation. (16)

Chitosan-based vectors have good appeal for nucleic acid delivery applications due to its the amine groups (such as N-acetylglucosamine). When positively charged, those

amine groups can bind to negatively charged molecules, such as nucleic acid. (16)

Cartilage

Mighri et al. reported in their study that when chitosan is present in the composite chitosan-collagen scaffold, it increases the scaffolds' biostability, which is dependent on the chitosan level. Therefore, chitosan-collagen scaffold may have potential use in the regeneration of cartilage. (9)

Other study shows that chitosan attracts neutrophils and stimulate macrophages in vitro and in vivo. That can play a role in cell proliferation mediated by chitosan and in the chitosan's implants integration in vivo. In the same study, when chitosan solution was used to inject in rat knees' cartilage, the proliferation of chondrocyte increased.

(16)

Hepatitis B

Nowadays, the treatment of Hepatitis B consists in virostatic approaches, so the development of alternative treatments is urgent. Therefore, nonviral vectors such as cell-penetratingg peptides and cationic polymers (like chitosan) have grown of interest, once they facilitate cellular delivery of DNA vaccines or peptide nucleic acids. (34)

In their study, Ndeboko et. al used two animal models. In the first model was investigated the capacity of peptide nucleic acids to inhibit the replication of the virus when they were combined with different cell-penetrating peptides. The authors found that they inhibited the virus replication once they reached the animals' liver. In addition, they found in the other model that the humoral and cellular responses to plasmid-encoded antigen have improved when HBV DNA vaccine was conjugated with modified chitosan. Despite the weak cell specificity of chitosan-based delivery systems (which is a problem), it can be improved to dendritic cells when coupled with mannose. This allows the stimulation of potent immune responses. Altogether, the results show that these nonviral vectors are capable of increasing the uptake and consequently the expression of plasmid DNA, resulting in a specific immune response. The strategies mentioned above could represent a potential alternative treatment in the carriers of chronic hepatitis B. (34)

Chitosan can also be used to produce human skin models. Mieremet et al. develop a human skin model where the dermal matrix was modulated by chitosan. In terms of morphogenesis, this model is the most similar to the native human skin, since it forms an epidermal barrier with composition and organization that decreases the

transepidermal water loss and improves its functionality.(35)

Skin models

Drug delivery

Insulin delivery system

Researchers are trying to develop a different insulin delivery system to reduce the subcutaneous injection in type 1 diabetes mellitus' patients. Through:

• Oral Route: Using nanocarriers (like chitosan), through the liver before reaches the circulation (like the physiological insulin secretion), which reduces the peripheral hyperinsulinemia and other complications that occur with injected insulin. The degradation of insulin in the upper gastrointestinal tract is also protected when chitosan-based particles are used as a carrier. (26, 27)
• Ocular Route: Nanoparticle-based ophthalmic formulations have high interest because of its low irritation, bioavailability, and biocompatibility. (27)

Morphine delivery system

Chitosan's mucoadhesive properties promote retention and permeation of the administered drugs in nasal route. (27) At the moment, a chitosan-based formulation of

morphine for nasal administration is in phase 2 in the UK and EU and phase 3 in USA clinical trials. Probably, it will be released on the market in the next years. (1)