Mechanism-Based Targeting of Sickle Cell Pathobiology and Pain with Novel Transdermal Curcumin

Pain is a debilitating consequence of sickle cell disease (SCD). We examined the potential of novel topical transdermal curcumin (TDC) gel with transdermal systemic delivery to target pain and SCD pathobiology. Curcumin is an antioxidant and anti-inflammatory polyphenol with therapeutic potential but has poor oral bioavailability. TDC gel (Vasceptor^TM, Vascarta Inc.), containing 0.1 M of curcuminoids (derived from Curcugen, Dolcas-Biotech, LLC), or vehicle were applied (0.1 mL) topically by gentle rubbing to the abdomen on alternating days for 3 weeks followed by analysis of blood, organ pathology and skin secretome. Using high-performance liquid chromatography, we found that curcumin levels peaked in the plasma (7.87 µg/mL) and blood cells (6.78 µg/mL) 60 min following administration in C57BL/6 mice, thus, showing efficient bioavailability.

Next, we used humanized ‘sickle’, homozygous transgenic mice (HbSS-BERK) expressing >99% human sickle hemoglobin (HbSS) without mouse α- and β-globins. These mice mimic the pathobiology and features of pain observed in persons with SCD. We observed that TDC application in male and female HbSS led to a significant decrease in hyperalgesia over the 21 days (D) of treatment. Mechanical hyperalgesia significantly decreased after 14D of treatment in males and after 21D in females (p<.05 and p<.01, respectively Vs. BL). Similarly, cold hyperalgesia (paw withdrawal frequency on cold plate at 4˚C) decreased significantly in males after 24 hours and in females after 7D of TDC treatment (p<.05 and .01, respectively Vs. BL). Non-evoked cold avoidance showed that males spent significantly more time in the colder chamber at 23ºC on 14D, and females did so on 21D after TDC treatment (p<.001 & p<.01, respectively Vs. BL). Throughout 21D TDC treatment, females showed significantly lower analgesic response in cold hyperalgesia compared to male HbSS, similar to relatively poor response to analgesia in female Vs. male individuals with SCD. The amelioration of hyperalgesia for 21D with TDC suggests a disease-modifying effect. Indeed, we observed a significant increase in hematocrit (p<.05), a reduction in reticulocytes (p<.05), and an appreciable increase (43.2%) in Hb and decreased lactate dehydrogenase activity in the blood of TDC-treated HbSS mice Vs. vehicle (p<.01). RBCs from TDC treated HbSS mice showed enhanced ATP levels (p <.01) and reduced protein carbonylation, both biomarkers of protein oxidation (p<.045) Vs RBCs from vehicle-treated HbSS. Histopathology showed a significant reduction in vascular congestion and iron deposits in TDC-treated male HbSS compared to vehicle in the spleen (p<.0003 & p<.001, respectively) and in % fields involved in hepatic infarcts and iron deposits (p<.02 & p<.044, respectively). Together, decreased hemolysis, increased Hb, hematocrit, and ATP suggest RBC stabilization, improved mitochondrial metabolism, and reduced oxidative stress and organ damage, leading to a disease-modifying effect of TDC.

TDC also significantly reduced global inflammatory marker serum amyloid-P (p<.05) and inflammatory cytokines in the skin secretome with a concomitant reduction in interleukins [2 (p<.05), 4 (p<.01), and 6 (p<.01)], monocyte chemoattractant protein 1 (MCP-1; p<.01), interferon-gamma (IFN-γ; p<.05), granulocyte macrophage-colony stimulating factor (GM-CSF; p<.01), and regulated on activation, normal T-cell expressed and secreted protein (RANTES; p<.05) compared to vehicle. MCP-1 contributes to neuropathic pain and inflammation; GM-CSF stimulates granulocyte differentiation and growth. Both RANTES and MCP-1 may also activate mast cells. TDC led to a significant decrease in cutaneous mast cell degranulation (p<.001) Vs. vehicle in sickle mice. These data strongly suggest an anti-inflammatory effect of TDC by targeting the release of cytokines and inhibiting granulocyte activity.

TDC significantly ameliorates hyperalgesia (chronic pain), inflammation, hemolysis, oxidative stress, and organ damage and improves mitochondrial function and hematological parameters of SCD pathobiology, indicative of disease modifying and anti-nociceptive effects. The results suggest if started early in life, the use of an easy-to-deploy novel TDC formulation, with increased bioavailability and non-toxic properties that directly target sickle cell pathobiology, may prevent chronic pain in SCD.