Anti-Inflammatory and Anti-Fibrotic Effects of Thymosin Beta4 Fragment Ac-SDKP.

Table of Contents

Ac-SDKP is a Peptide Fragment of Thymosin Beta 4 (TB-500)

“Tβ4 is a naturally occurring peptide consisting of 43 base pairs of amino acids and generates the N-terminal tetrapeptide AcSDKP.” (14)

Peptide Ac-SDKP was isolated from the whole Thymosin Beta 4 Peptide Sequence.

Ac-SDKP Reduced Kidney Fibrosis.

“Treatment of cultured cells with ACEi alone or in combination with AcSDKP prevented the downregulated expression of miR-29s and miR-let-7s induced by TGFβ stimulation. Interestingly, ACEi also restored miR-29 and miR-let-7 family cross-talk in endothelial cells, an effect that is shared by AcSDKP suggesting that AcSDKP may be partially involved in the anti-mesenchymal action of ACEi. The results of the present study promise to advance our understanding of how ACEi regulates antifibrotic microRNAs crosstalk and DPP-4 associated-fibrogenic processes which is a critical event in the development of diabetic kidney disease.” (14)

“Western blot analysis revealed higher protein levels of DPP-4, TGFβR1, smad3 phosphorylation, fibroblast specific protein 1 (FSP-1), αSMA, collagen I and fibronectin in the kidneys of diabetic mice. Moreover, we observed remarkable higher immuno-labeled CD31/DPP-4 positive cells DPP-4/αSMA in kidneys of diabetic mice as compared to kidneys of non-diabetic control mice. ACEi and combination treatment significantly reduced the protein level of DPP-4, TGFβR1, smad3 phosphorylation, FSP-1, αSMA, collagen I and fibronectin; suppressed the higher expression level of CD31/DPP-4 and DPP-4/ αSMA positive cells in the kidneys of diabetic mice… ACEi significantly downregulated gene expression of ACE mRNA whereas, ARB suppressed the gene expression level of AT1R in the kidneys of diabetic mice… Inhibition of ACE restored the TGFβ2-associated disruption of cross-talk regulation between miR-29 and miR-let-7 family members in the endothelial cells.” (5)

“…there is a lack of comparative studies on the effects of ACEi versus ARB on renal fibrosis. Here, we observed that ACEi ameliorated renal fibrosis by mitigating DPP-4 and TGFβ signaling, whereas, ARB did not show. Moreover, the combination of N-acetyl-seryl-aspartyl-lysyl-proline (AcSDKP), one of the substrates of ACE, with ACEi slightly enhanced the inhibitory effects of ACEi on DPP-4 and associated-TGFβ signaling.” (5)

“Our data suggests that miR-29 and miR-let-7 identify as key antifibrotic players. Members of miR-29 family negatively regulate DPP-4, so we tried to find out functional significance in between TGFβRs and DPP-4 with respect to renal fibrosis. In previous studies, TGFβ2 treatment in the HMVECs caused gain of features of myo-fibroblasts and reported to show down-regulated expression level of miR-29 and miR-let-7. MiR-let-7 family members were key anti-fibrotic players targeting TGFβR1 in the HMVECs as evidenced by our results. AcSDKP is the key essential peptide that regulates the antifibrotic crosstalk between miR-29s and miR-let-7s in the endothelial cells and this antifibrotic microRNA crosstalk is critical for its anti-EndMT effect. Moreover, inhibition of ACE caused up-regulation of antifibrotic microRNAs (miR-29 and miR-let-7 family members) and restored the antifibrotic cross-talk in the cultured endothelial cells while ARB has minimal effect suggesting that ACEi has a critical anti-EndMT effect.” (5)

“In conclusion, these data supporting the idea that inhibition of ACE protects renal fibrosis by its ability to induce the AcSDKP-associated renal protections, either by suppressing DPP-4-associated mesenchymal transformations or by elevating the gene expression of antifibrotic microRNAs in the kidneys of diabetic mice, whereas, ARB did not show such effects. The study adds valuable information in the significance of ACEi and DPP-4 biology in the kidneys of diabetic mice.” (5)

Anti-Fibrotic Effects in Lungs and Heart.

“Decreased Endogenous Levels of Ac-SDKP Promote Organ Fibrosis: When we treated rats with a specific oral rolyl oligopeptidase inhibitor, Ac-SDKP decreased significantly in the plasma, heart, and kidney. In the present study, we tested the hypothesis that endogenous Ac-SDKP at basal levels plays a physiological role, antagonizing and/or preventing excessive collagen deposition. We studied whether chronic blockade of Ac-SDKP promotes collagen accumulation and/or accelerates this process in the presence of a profibrotic stimulus such as angiotensin II. We found that decreased basal levels of Ac-SDKP increased cardiac and renal perivascular fibrosis and promoted glomerulosclerosis. Moreover, in the presence of angiotensin II decreasing basal levels of Ac-SDKP accelerated interstitial cardiac fibrosis attributable to an increase in cells that produce collagen. We concluded that Ac-SDKP participates in the regulation of collagen content under normal conditions. We believe this is the first study showing that this peptide plays a physiological role at basal concentrations, preventing organ collagen accumulation.” (13)

“N-acetyl-Ser-Asp-Lys-Pro (Ac-SDKP) is specifically cleared by ACE. This process has been reported to be carried out predominantly by the N-domain… findings indicated that Ac-SDKP also possesses potent anti-fibrotic and anti-inflammatory effects in numerous tissues including heart, liver, kidney and lung. Ac-SDKP is able to blunt the Smad signalling effects of transforming growth factor-β, a prominent fibrosis marker. Thus, Ac-SDKP appears to have a prominent physiological role.” (1)

“The results of the present study suggest a novel mechanism of action for Ac-SDKP’s beneficial effect in silicosis, which involves attenuation of TGF-β1 and its receptors, SRF and Ang II type 1 receptor (AT₁) expression, collagen deposition and myofibroblast differentiation.” (3)

“Ac-SDKP increases α-TAT 1 and promotes the apoptosis in lung fibroblasts and epithelial cells double-stimulated with TGF-β1 and silica.” (6)

Prevents Cardiomyopathy by Blocking TGF-β1-induced Differentiation of Cardiac Fibroblasts into Fibrosis-producing Myofibroblasts.

“Presence of DNA degenerative changes and cardiomyocyte loss… Increased number of TUNEL positive cells were identified in rats after thoracic radiation exposure. Ac-SDKP therapy significantly decreased the number of TUNEL positive cells. Numerical density of cardiomyocytes nuclei was identified in each cross sectional image captured at high magnification. Connective tissue staining was subtracted from the total tissue area to determine the percentage that was represented by myocytes (% myocyte area). There was significant decrease in the nuclear density in radiation exposed rats compared to control. Ac-SDKP therapy prevented the myocyte nuclear drop.” (12)

Inhibited fibrotic factors a-SMA and MRTF-A in the Heart.

“Myofibroblast differentiation could be induced by Ang II from MRC-5 cells with a dose- and time-dependent manner. The up-regulation of SRF and MRTF-A were observed in MRC-5 cells induced by Ang II and accompanied with collagen I and α-SMA increased. Pre-treatment with 8-Me-cAMP or Ac-SDKP could attenuated all these changes induced by Ang II, and promoted the expression of Epac1.” (9)

“The expressions of collagen, TGF-β1 and RAS signaling were also assessed. The results revealed that TGF-β1 strongly induced myofibroblast differentiation and collagen synthesis in vitro, and that pre-treatment with Ac-SDKP markedly attenuated myofibroblast activation, as well as induction of TGF-β1 and its receptor. Similar results were observed in vivo in the pathologically relevant rat model of silicosis. Ac-SDKP treatment in vivo strongly attenuated 1) silicosis-induced increased expressions of TGF-β1 and RAS signaling, 2) myofibroblast differentiation as indicated by a robust decrease of SRF and α-SMA-positive myofibroblast localization in siliconic nodules in the lung, 3) collagen deposition.” (10)

“We have used a rat model of radiation induced cardiomyopathy, which shows cardiomyocyte apoptosis, increased extracellular matrix, macrophage infiltration, and Mac-2 expression. We also report that treatment with a small peptide, Ac-SDKP limits the fibroinflammatory cascade triggered by radiation exposure, specifically involving macrophage activity. The results of this study demonstrate strong therapeutic promise, which can potentially benefit large number of cancer survivors… Because Mac-2 is a crucial macrophage-derived mediator of fibrosis, we performed studies to determine Mac-2 synthesis by macrophages in response to radiation, and change in profibrotic responses by Mac-2 gene depleted cardiac fibroblasts after radiation. Cardiac irradiation diminished myocardial contractile velocities and enhanced extracellular matrix deposition. This was accompanied by macrophage infiltration, fibrosis, cardiomyocyte apoptosis, and cardiac Mac-2 expression. Ac-SDKP strongly inhibited these detrimental effects. Ac-SDKP migrated into the perinuclear cytoplasm of the macrophages and inhibited radiation-induced Mac-2 release. Cardiac fibroblasts lacking the Mac-2 gene showed reduced transforming growth factor β1, collagen I, and collagen III expression after radiation exposure.” (12)

“Ac-SDKP significantly blocked TGF-β1-induced pSmad2 but had no effect on Smad7 expression.” (8)

“We found that phosphorylation of ERK1/2 increased in TGF-β1-stimulated fibroblasts ( P = 0.001) but was significantly blunted by pretreatment with Ac-SDKP.” (8)

“Treatment with TGF-β1 for 48 h increased collagen production from control levels of 12.1 ± 0.8 μg/mg protein to 19.8 ± 1.1 ( P = 0.002). Ac-SDKP inhibited TGF-β1-stimulated collagen production in a dose-dependent manner.” (8)

“Absorbance in untreated fibroblasts (controls) was 0.21 ± 0.02 arbitrary units. It increased to 1.13 ± 0.04 after 48 h of incubation with 5% FGS and 0.53 ± 0.03 with TGF-β1. Ac-SDKP inhibited cell proliferation stimulated with both FGS and TGF-β1, with more pronounced inhibitory effect against FGS’s effect.” (8)

Keeps Stem Cells in a Quiescent State.

“Ac-SDKP was originally discovered as a potent inhibitor of bone marrow derived stem cell differentiation through inhibition of the G1-S phase transition. This suggested a possible role of Ac-SDKP as a co-treatment to reduce the treatment associated severity of some chemotherapies due to this peptide being able to keep stem cells in the quiescent state.” (1)

“More recently, the tetrapetide N-acetyl-Ser–Asp–Lys–Pro (Ac-SDKP) has emerged as a potent antifibrotic agent and negative regulator of haematopoietic stem cell differentiation which is processed exclusively by ACE.” (1)

Reduced Inflammation, M1 Macrophages, ER Stress, and Atherosclerotic Lipid Peroxidation.

“Ac-SDKP reduced M1 macrophages in cardiac tissue after MI, without affecting M2 macrophages and neutrophils.” (2)

“Ac-SDKP reduced M1 macrophages in cardiac tissue after MI, without affecting M2 macrophages and neutrophils. Ac-SDKP decreased MMP-9 activation in infarcted hearts with no changes on MPO expression. Ac-SDKP prevents cardiac rupture and decreases mortality post-acute MI. These protective effects of Ac-SDKP are associated with decreased pro-inflammatory M1 macrophage infiltration and MMP-9 activation.” (2)

“There was a trend toward the reduction of lymphocyte count in radiated rats, which was compensated by an increase in the number of monocytes. Although platelet counts were significantly decreased post-radiation, Ac-SDKP therapy did not change platelets or white cell counts compared with the radiation group.” (12)

“Ac-SDKP treatment led to a substantial decrease in the infiltration of CD4+ T cells into the hippocampus of mice with EAE… After treatment with Ac-SDKP, the intensity of inflammatory infiltration, neuronal apoptosis and CD4+ T cells activation was attenuated. Additionally, Iba1 and GFAP immunoreactivity as well as IL-1β levels were considerably increased following EAE induction, which trigger inflammation. Ac-SDKP-treated mice showed a reduction in EAE-induced activation of microglia and upregulation of IL-1β… sections were labeled with anti-GFAP to detect active astrocytes, which a remarkable rise in the number of active astrocytes was seen in EAE samples that was reduced in response to Ac-SDKP treatment.” (11)

“Our results displayed that Ac-SDKP down regulates caspase-12 and CHOP expression in the hippocampus resident oligodendrocytes of EAE mice. Further, treatment with Ac-SDKP decreased oxidative stress markers and caspase-3 activation in the hippocampus of EAE mice. According to our findings, Ac-SDKP showed beneficial effects against ER stress and oxidative stress in addition to inflammation in the hippocampus of EAE mice… Ac-SDKP weakens expression of CHOP and caspase-12-induced ER stress in microglia, astrocyte and oligodendrocyte cells…” (11)

Antioxidant Effect.

“Ac-SDKP-treated EAE mice show a reduction in ROS and NO production… Ac-SDKP recovers antioxidant potential and antioxidant enzymes activity… Ac-SDKP blocks inflammatory cell infiltration in the hippocampus of EAE mice… The presence of oxidative stress following EAE induction was demonstrated in our study and Ac-SDKP showed a profound impact against oxidative stress by decrease in ROS production and lipid peroxidation.” (11)

“EAE group also showed marked attenuation of anti-apoptotic protein Bcl2. Administration of Ac-SDKP declined the activation of IL-6 and IL-1β in EAE mice, while levels of Bcl2 increased in Ac-SDKP group. Discovery of the increased expression of ER stress-related caspase-12 and CHOP proteins in the hippocampus of EAE mice invited us for more evaluations into the role of ER stress in oligodendrocytes death. Interpreting the quantified double immunofluorescence images in Fig. 4 provided evidence that the increased protein expression of caspase-12 and CHOP is found predominantly in the hippocampus-resident oligodendrocytes but to a lesser extent in microglia and astrocytes… Notably, the treatment of EAE mice with Ac-SDKP raised the antioxidant capacity and the reduced glutathione levels of the hippocampus. The results also revealed that AcSDKP increases sharply GPx enzyme activity and the heme oxygenase levels.” (11)

Reversed Demyelination Caused By Inflammatory Multiple Sclerosis

“Ac-SDKP reversed EAE-induced demyelination and apoptosis after EAE: Treatment of EAE mice with Ac-SDKP reversed the hippocampus demyelination partially. We next observed the effect of Ac-SDKP on decrease in EAE-induced apoptosis using TUNEL staining. The increase in the TUNEL positive cells in the hippocampus of EAE mice revealed that the hippocampus subjects to apoptosis after EAE induction, which was reduced in the presence of Ac-SDKP.” (11)

“Cumulatively, our data depicts that oxidative stress and ER stress might be the fundamental players in progress of EAE and even in MS. In this study, we extended our analysis of the protective effect of Ac-SDKP on EAE-induced ER stress and oxidative stress by providing evidence that Ac-SDKP attenuates caspase-12 and CHOP expression in the hippocampal glial cells of EAE mice, especially oligodendrocytes. On the other hand, we found that Ac-SDKP treatment ameliorates EAE by reducing ROS production. Since Ac-SDKP revealed the beneficial functions at low dose, it might be an alternative therapeutic strategy for weakening the progress of EAE.” (11)

Inhibits Loss of Bones by Blocking Osteoclasts

“Ac-SDKP also attenuated the reduction in femoral bone mineral density in silicotic rats by inhibiting osteoclast differentiation via the RANKL signaling pathway.” (3)

“Osteoclast differentiation is characterized by increased bone absorbability and positive expression of tartrate-resistant acid phosphatase (TRAP), and it is regulated by several signaling pathways: receptor activator of nuclear factor kappa-B ligand (RANKL), osteoclast stimulatory transmembrane protein (OC-STAMP), nuclear factor-activated T-cell cytoplasmic 1 (NFATc1), activator protein-1 (AP-1), and nuclear factor kappa-B (NF-κB) signaling pathways. Positivity of TRAP in alveolar macrophages is also found in the lungs of patients with chronic obstructive pulmonary disease and asthma compared with controls, and high TRAP activity is observed in the lungs of mice with experimental chronic obstructive pulmonary disease or asthma. TRAP-positive macrophages produce various matrix metalloproteinases (MMPs) such as MMP-2 (gelatinase A), MMP-9 (gelatinase B), MMP-12 (macrophage metalloelastase), and MMP-14 (MT1-MMP). Therefore, TRAP-positive lung macrophages might display some molecular signatures of osteoclast differentiation regulated by the RANKL signaling pathway.” (3)

“We used NR8383 rat alveolar macrophages to explore the anti-inflammatory effect of Ac-SDKP… silica promoted an increase in TRAP-positive cells and activated RANKL, RANK, OC-STAMP, AP-1, NFATc1, and NF-κB expression as well as increase of TLR4, MyD88, p-IκB, TNF-α, and MMP-12 in NR8383 macrophages. Treatment with Ac-SDKP reversed all of the silica-induced effects…” (3)

“Preclinical studies have shown that the naturally occurring tetrapeptide N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) has greatly beneficial effects with respect to modulation of inflammatory activities in heart, kidney, brain, and lung injury. Evidence from clinical trials suggests that Ac-SDKP exerts anti-inflammatory, anti-fibrotic, and pro-angiogenic potential and is well tolerated in humans. The anti-inflammatory effects of Ac-SDKP on macrophages indicate that Ac-SDKP may have a potential role in activation of lung macrophages or osteoclast differentiation.” (3)