Novel Treatment Option for Rheumatoid Arthritis through Bone‐Targeted Delivery of Novokinin
Authors: Ranjit Arina , Khajehpour Sana , Aghazadeh‐Habashi Ali 
Published: May 2022

ObjectiveRheumatoid arthritis (RA) is an autoimmune inflammatory disorder affecting about 1‐2% of the world population. RA is known to be a major cause of disability which progresses eventually to systemic complexities with high chances of early morbidity. This complex dynamic situation of inflammation is orchestrated by multiple systems in the body, including the Renin‐Angiotensin System (RAS). Angiotensin II (Ang II), a main effector peptide in the RAS, predominantly binds to Angiotensin II Type (I) receptor (AT1R). When it overproduced can result in inflammation, vasoconstriction, and oxidative stress. Ang II also binds to Angiotensin II Type (II) receptor (AT2R), which provides functional antagonism to AT1R activation. Novokinin, a synthetic peptide, promotes beneficial effects through activation of AT2R, and can be considered a potential drug candidate for alternative therapy in RA if its plasma stability and half‐life could be improved. Here, we developed a novel bone‐targeting novokinin Conjugate (Novo Conj), which binds to the bone, utilizes it as a reservoir while protecting it from enzymatic and hydrolytic degradation. We hypothesized that this delivery approach would extend the peptide half‐life and provide sustained plasma levels to elicit anti‐inflammatory activity.MethodHealthy male, Sprague Dawley rats, were induced adjuvant arthritis (AA) by administering 0.2mL of 50mg/mL of Mycobacterium butyricum through the tail base injection. Arthritic rats were divided into three groups (n=5/group) and dosed with saline (Inflamed), novokinin of 400 µg/kg (Novokinin), or an equivalent dose of 400 µg/kg of novokinin (Novo Conj). A group of healthy rats (n=5) received saline and was taken as a healthy control (Control) group. After the emergence of arthritis (i.e., 10‐12 days after adjuvant arthritis induction), animals were dosed with assigned treatment every other day for two weeks. Animals were monitored three times a week for their body weight, paw, and joint diameters. At the end of the experiment, rats were euthanized, plasma/tissues were harvested and analyzed for plasma nitric oxide (NO) and the RAS components by western blot.ResultsThe induction of AA led to a significant reduction in percent body weight gain over time, increased paws and joints swelling, and elevated plasma NO levels. AA brought an imbalance in the RAS enzymatic inflammatory axis indicator, i.e., Angiotensin‐Converting Enzyme (ACE) and ACE2 causing a reduction in ACE2/ACE and AT2R/AT1R ratio. The treatment of arthritic rats by novokinin and Novo Conj restored their body weight gain, reduced paws and joints' swelling, lowered the plasma NO level, and reinstated the imbalanced ratios of enzymes and receptors. These observed anti‐inflammatory effects were significantly higher in the Novo Conj group.ConclusionThis result indicates that the novokinin and its bone‐targeted conjugate shows anti‐inflammatory effects through the RAS. The observed enhanced impacts could be attributed to improved stability and extension of the half‐life of novokinin through its conjugation and binding to the bone. Our novel bone‐targeting delivery of novokinin offers effective alternative therapy for managing RA signs and symptoms and could be further utilized for various RAS disorders.