The aim of this work is to analyze relevant endogenous lipid processing pathways, in the context of the impact that lipids have on drug absorption, their therapeutic use, and utilization in drug delivery. Lipids may serve as biomarkers of some diseases, but they can also provide endogenous therapeutic effects for certain pathological conditions. Current uses and possible clinical benefits of various lipids (fatty acids, steroids, triglycerides, and phospholipids) in cancer, infectious, inflammatory, and neurodegenerative diseases are presented. Lipids can also be conjugated to a drug molecule, accomplishing numerous potential benefits, one being the improved treatment effect, due to joined influence of the lipid carrier and the drug moiety. In addition, such conjugates have increased lipophilicity relative to the parent drug. This leads to improved drug pharmacokinetics and bioavailability, the ability to join endogenous lipid pathways and achieve drug targeting to the lymphatics, inflamed tissues in certain autoimmune diseases, or enable overcoming different barriers in the body. Altogether, novel mechanisms of the lipid role in diseases are constantly discovered, and new ways to exploit these mechanisms for the optimal drug design that would advance different drug delivery/therapy aspects are continuously emerging.

Treatment of Crohn’s disease (CD) with anti-tumor necrosis factor α (TNFα) decreases intestinal inflammation, but the effect on fibrosis remains unclear. We hypothesized that treatment with rat-specific anti-TNFα will decrease the development of intestinal fibrosis in a rat model of CD. We further hypothesized that magnetization transfer magnetic resonance imaging (MT-MRI) will be sensitive in detecting these differences in collagen content. Rats were injected in the distal ileum and cecum with peptidoglycan–polysaccharide (PG-PS) or human serum albumin (control) at laparotomy and then received intraperitoneal injections of rat-specific anti-TNFα or vehicle daily for 21 days after laparotomy. Rats underwent MT-MRI abdominal imaging on day 19 or 20. MT ratio was calculated in the cecal wall. Cecal tissue histologic inflammation was scored. Cecal tissue procollagen, cytokine, and growth factor messenger RNAs were measured by quantitative real-time PCR. PG-PS–injected rats treated with anti-TNFα had less histologic inflammation, and cecal tissue expressed lower levels of proinflammatory cytokine messenger RNAs than vehicle-treated PG-PS–injected rats (IL-1β: 5.59 ± 1.53 versus 10.41 ± 1.78, P = 0.02; IL-6: 23.23 ± 9.33 versus 45.89 ± 11.79, P = 0.07). PG-PS–injected rats treated with anti-TNFα developed less intestinal fibrosis than vehicle-treated PG-PS–injected rats by tissue procollagen I (2.87 ± 0.66 versus 9.28 ± 1.11; P = 0.00002), procollagen III (2.25 ± 0.35 versus 7.28 ± 0.76; P = 0.0000009), and MT-MRI (MT ratio: 17.79 ± 1.61 versus 27.95 ± 1.75; P = 0.0001). Insulin-like growth factor I (2.52 ± 0.44 versus 5.14 ± 0.60; P = 0.0007) and transforming growth factor β1 (2.34 ± 0.29 versus 3.45 ± 0.29; P = 0.006) were also decreased in anti-TNFα–treated PG-PS–injected rats. Anti-TNFα prevents the development of bowel wall inflammation and fibrosis in the PG-PS rat model of CD. MT-MRI measurably demonstrates this decrease in intestinal fibrosis.

Nowadays, the prodrug approach is used already at the early stages of drug development. Lipidic prodrug approach is a growing field for improving a number of drug properties/delivery/therapy aspects, and can offer solutions for various unmet needs. This approach includes drug moiety bound to the lipid carrier, which can be triglyceride, fatty acids, steroid, or phospholipid (PL). The focus of this article is PL-based prodrugs, which includes a PL carrier covalently bound to the active drug moiety. An overview of relevant physiological lipid processing pathways and absorption barriers is provided, followed by drug delivery/therapeutic application of PL-drug conjugates, as well as computational modeling techniques, and a modern bioinformatics tool that can aid in the optimization of PL conjugates. PL-based prodrugs have increased lipophilicity comparing to the parent drug, and can therefore significantly improve the pharmacokinetic profile and overall bioavailability of the parent drug, join the endogenous lipid processing pathways and therefore accomplish drug targeting, e.g., by lymphatic transport, drug release at specific target site(s), or passing the blood-brain barrier. Moreover, an exciting gateway for treating inflammatory diseases and cancer is presented, by utilizing the PL sn-2 position in the prodrug design, aiming for PLA₂-mediated activation. Overall, a PL-based prodrug approach shows great potential in improving different drug delivery/therapy aspects, and is expected to grow.

Parkinson's Disease (PD) is a multisystem disorder in which dysregulated neuroimmune crosstalk and inflammatory relay via the gut-blood-brain axis have been implicated in PD pathogenesis. Although alterations in circulating inflammatory cytokines and reactive oxygen species (ROS) have been associated with PD, no biomarkers have been identified that predict clinical progression or disease outcome. Gastrointestinal (GI) dysfunction, which involves perturbation of the underlying immune system, is an early and often-overlooked symptom that affects up to 80 % of individuals living with PD. Interestingly, 50-70 % of individuals with inflammatory bowel disease (IBD), a GI condition that has been epidemiologically linked to PD, display chronic illness-induced anemia - which drives toxic accumulation of iron in the gut. Ferroptotic (or iron loaded) cells have small and dysmorphic mitochondria-suggesting that mitochondrial dysfunction is a consequence of iron accumulation. In pro-inflammatory environments, iron accumulates in immune cells, suggesting a possible connection and/or synergy between iron dysregulation and immune cell dysfunction. Peripheral blood mononuclear cells (PBMCs) recapitulate certain PD-associated neuropathological and inflammatory signatures and can act as communicating messengers in the gut-brain axis. Additionally, this communication can be modulated by several environmental factors; specifically, our data further support existing literature demonstrating a role for non-steroidal anti-inflammatory drugs (NSAIDs) in modulating immune transcriptional states in inflamed individuals. A mechanism linking chronic gut inflammation to iron dysregulation and mitochondrial function within peripheral immune cells has yet to be identified in conferring risk for PD. To that end, we isolated PBMCs and simultaneously evaluated their directed transcriptome and bioenergetic status, to investigate if iron dysregulation and mitochondrial sensitization are linked in individuals living with PD or IBD because of chronic underlying remittent immune activation. We have identified shared features of peripheral inflammation and immunometabolism in individuals living with IBD or PD that may contribute to the epidemiological association reported between IBD and risk for PD.

In ulcerative colitis (UC), the inflammation is localized in the colon, and one of the successful strategies for colon-targeting drug delivery is the prodrug approach. In this work, we present a novel phospholipid (PL)-based prodrug approach, as a tool for colonic drug targeting in UC. We aim to use the phospholipase A₂ (PLA₂), an enzyme that is overexpressed in the inflamed colonic tissues of UC patients, as the PL-prodrug activating enzyme, to accomplish the liberation of the parent drug from the prodrug complex at the specific diseased tissue(s). Different linker lengths between the PL and the drug moiety can dictate the rate of activation by PLA₂, and subsequently determine the amount of free drugs at the site of action. The feasibility of this approach was studied with newly synthesized PL-Fmoc (fluorenylmethyloxycarbonyl) conjugates, using Fmoc as a model compound for testing our hypothesis. In vitro incubation with bee venom PLA₂ demonstrated that a 7-carbon linker between the PL and Fmoc has higher activation rate than a 5-carbon linker. 4-fold higher colonic expression of PLA₂ was demonstrated in colonic mucosa of colitis-induced rats when compared to healthy animals, validating our hypothesis of a colitis-targeting prodrug approach. Next, a novel molecular dynamics (MD) simulation was developed for PL-based prodrugs containing clinically relevant drugs. PL-methotrexate conjugate with 6-carbon linker showed the highest extent of PLA₂-mediated activation, whereas shorter linkers were activated to a lower extent. In conclusion, this work demonstrates that for carefully designed PL-drug conjugates, PLA₂ overexpression in inflamed colonic tissues can be used as prodrug-activating enzyme and drug targeting strategy, including insights into the activation mechanisms in a PLA₂ binding site.