Shinji Takai

Non-alcoholic steatohepatitis (NASH) is characterized by inflammation and fibrosis, in addition to steatosis, of the liver, but no therapeutic agents have yet been established. The mast cell protease chymase can generate angiotensin II, matrix metalloproteinase-9 and transforming growth factor-β, all of which are associated with liver inflammation or fibrosis. In animal models of NASH, augmented chymase has been observed in the liver. In histological analysis, chymase inhibitor prevented hepatic steatosis, inflammation, and fibrosis. Chymase inhibitor also attenuated the augmentation of angiotensin II, matrix metalloproteinase-9, and transforming growth factor-β observed in the liver of NASH. Oxidative stress, inflammatory markers, and collagen were attenuated by chymase inhibition. Moreover, chymase inhibitor showed a mitigating effect on established NASH, and survival rates were significantly increased by treatment with chymase inhibitor. In this review, we propose that chymase inhibitor has potential as a novel therapy for NASH.

Summary: Chymase has been identified as an angiotensin II‐forming enzyme found in cardiovascular tissues. Angiotensin II is involved not only in the regulation of blood pressure, but also in the progression of cardiovascular remodelling. Interestingly, chymase inhibitors prevent cardiovascular remodelling without lowering blood pressure. The reason why chymase inhibitors do not affect blood pressure may depend on the localization of chymase in vivo. In normal tissues, chymase is stored in mast cell granules and has no enzymatic function; whereas, in damaged tissues, chymase exhibits enzymatic activity immediately following its release from the granules. Chymase also activates transforming growth factor‐β and matrix metalloproteinase‐9, both of which are involved in cardiovascular remodelling, and their enzymatic functions are also observed only in damaged tissues. In animal models of hypertension, diabetes and hypercholesterolaemia, chymase inhibitors improve cardiovascular remodelling without a general circulatory effect, including blood pressure. Thus, it is proposed that chymase is a potentially important target for preventing cardiovascular diseases.

Introduction: To clarify the importance of the vascular concentration of an angiotensin II receptor blocker (ARB) to its hypotensive effect, the relationships between the drug concentrations in plasma and vascular tissues and the hypotensive effect after administration of an ARB were compared. Materials and methods: In spontaneously hypertensive/NDmcr-cp rats (SHR/NDmcr-cp), systolic blood pressure (SBP) and angiotensin II-induced vascular contraction were measured 2 h and 24 h after administration of telmisartan (3 mg/kg). Plasma and vascular concentrations of telmisartan were also measured at 2 h and 24 h. Results: SBP was significantly lower 2 h after administration of telmisartan, and the significant hypotensive effect was continued until 24 h. A significant attenuation of angiotensin II-induced vascular contraction at 2 h was also continued until 24 h. No significant difference between 2 h and 24 h was observed both in SBP and angiotensin II-induced vascular contraction. Vascular concentration at 24 h was 90.0% when the concentration at 2 h was assumed to be 100%, and no significant difference was observed. However, the plasma concentration of telmisartan at 2 h was significantly decreased by 88.2% at 24 h. Conclusion: The vascular drug concentration, not the plasma drug concentration, may be related to the hypotensive effect after administration of telmisartan.

Chymase stored in mast cells activates matrix metalloproteinase (MMP)-9, which may relate to the progression of sinusoidal obstruction syndrome (SOS). We investigated the preventive effect of a chymase inhibitor, TY-51469, on monocrotaline-induced SOS in hamsters. Hamsters were orally administrated with a single dose of monocrotaline (120 mg/kg) to induce SOS. Treatment with TY-51469 (1 mg/kg per day) or placebo had started 3 days before the monocrotaline administration. Two days after the monocrotaline administration, significant increases in aspartate aminotransferase, alanine aminotransferase and total bilirubin and a significant reduction of albumin were observed in plasma, but their changes were significantly attenuated by treatment with TY-51469. The numerous hepatic necrosis areas were observed in the placebo-treated group, but the ratio of necrotic area to total area in liver had been significantly reduced by treatment with TY-51469. Both chymase activity and MMP-9 level in liver were significantly augmented in the placebo-treated group. Furthermore, tumor necrosis factor (TNF)-α level in liver was also augmented in the placebo-treated group. However, the chymase activity and levels of MMP-9 and TNF-α were significantly attenuated in the TY-51469-treated group. Until 14 days after monocrotaline administration, survival rates in the placebo- and TY-51469-treated groups were 25% and 70%, respectively, and a significant difference was observed. In conclusion, chymase inhibition by TY-51469 may prevent the accelerating of severity in monocrotaline-induced SOS in hamsters.

To clarify the matrix metalloproteinase (MMP)-9 inhibitory effect of an angiotensin-converting enzyme (ACE) inhibitor in vivo, we evaluated the effect of an ACE inhibitor against elastase-induced abdominal aortic aneurysm (AAA) progression in mice. Molecular models showed that imidapril bound directly to the mouse MMP-9 active center. An active form of imidapril, imidaprilat, dose-dependently inhibited MMP-9 activity in the extract from elastase-induced AAA in wild-type mice. Imidapril (10 mg/kg per day) was administered to wild-type or angiotensin II type 1 (AT₁) receptor knockout mice. Blood pressure was significantly lower in AT₁ receptor–knockout mice than in wild-type mice, but imidapril did not affect blood pressure in AT₁ receptor–knockout mice. The aortic diameter was significantly expanded after elastase application, but the expansion was significantly lower in AT₁ receptor–knockout mice than in wild-type mice. In AT₁ receptor–knockout mice, the aortic expansion was further attenuated by imidapril. MMP-9 activity in aorta was significantly augmented after elastase application. The MMP-9 activity was significantly lower in AT₁ receptor–knockout mice than in wild-type mice, and it was further attenuated by imidapril. In conclusion, MMP-9 inhibition by imidapril might contribute to the attenuation of AAA progression in AT₁ receptor–knockout mice.

To clarify the hypotensive mechanism of angiotensin II receptor–blockers (ARBs), drug concentrations in plasma and vascular tissues were measured using matrix-assisted laser desorption ionization time-of-flight mass spectrometry and imaging mass spectrometry. In spontaneously hypertensive rats, systolic blood pressure (SBP) was measured 2 and 24 h after administration of candesartan cilexetil (0.3, 1, or 3 mg/kg) or azilsartan (0.3, 1, or 3 mg/kg). SBP was similarly lowered 2 h after administration of azilsartan or candesartan cilexetil, but it was significantly lower in the azilsartan-treated group than in the candesartan cilexetil-treated group at 24 h. Angiotensin II–induced vascular contractions were similarly attenuated 2 h after administration of these drugs, and the contractions were significantly lower in the azilsartan-treated group at 24 h. Although plasma concentration was significantly lower in the azilsartan-treated group at 24 h, vascular concentration of azilsartan was significantly greater than that of candesartan. Significant correlations between SBP and vascular concentrations were observed both at 2 and 24 h, while no significant correlation was observed between plasma and vascular concentrations. In conclusion, the mechanism of ARB-induced hypotension is likely to depend on vascular concentrations rather than plasma concentrations.

Aim: Chymase plays a role in the augmentation of angiotensinIIformation, which is involved in liver fibrosis. The therapeutic effects of a chymase inhibitor,TY‐51469, on established hepatic steatosis and fibrosis were investigated in a model of developed non‐alcoholic steatohepatitis.Methods: Hamsters were fed a normal diet or methionine‐ and choline‐deficient (MCD) diet for 12 weeks. Then, treatment withTY‐51469 (1 mg/kg per day) or placebo was initiated, and the treatment was continued concurrently with theMCDdiet for an additional 12 weeks.Results: At 12 weeks after initiating theMCDdiet, marked hepatic steatosis and fibrosis were observed inMCDdiet‐fed hamsters. Malondialdehyde and gene expression levels of collagenI, collagenIII, α‐smooth muscle actin (α‐SMA) andRac‐1 in liver extracts were also increased in theMCD‐diet‐fed hamsters at 12 weeks. At 24 weeks, hepatic steatosis and fibrosis were more prominent in the placebo‐treated hamsters that were fed theMCD‐diet for 24 weeks versus 12 weeks. Hamsters treated withTY‐51469 for 12 weeks after being on a 12‐weekMCDdiet had significant ameliorations in both hepatic steatosis and fibrosis, and there were no significant differences compared to normal diet‐fed hamsters. There were significant augmentations in angiotensinIIand malondialdehyde, and gene expressions of collagenI, collagenIII, α‐SMAandRac‐1 in the placebo‐treated hamsters at 24 weeks; however, these levels were reduced to normal levels in theTY‐51469‐treated hamsters.Conclusion: TY‐51469 not only prevented the progression of hepatic steatosis and fibrosis, but also ameliorated hepatic steatosis and fibrosis.

Cilnidipine is an L- and N-type calcium channel blocker (CCB), and amlodipine is an L-type CCB. Valsartan (10 mg kg⁻¹), valsartan (10 mg kg⁻¹) and amlodipine (1 mg kg⁻¹), and valsartan (10 mg kg⁻¹) and cilnidipine (1 mg kg⁻¹) were administered once daily for 2 weeks to stroke-prone, spontaneously hypertensive rats (SHR-SPs). Blood pressure was significantly reduced by valsartan, and it was further reduced by the combination therapies. Vascular endothelial dysfunction was significantly attenuated in all therapeutic groups, and further significant attenuation was observed in the valsartan+cilnidipine-treated group, but not in the valsartan+amlodipine-treated group. Vascular nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunit NOX1 gene expression was significantly attenuated in all therapeutic groups, and significantly greater attenuation was observed in the valsartan+cilnidipine-treated group than in the valsartan-treated group. Compared with the valsartan-treated group, the positive areas for 4-hydroxy-2-nonenal were significantly lower only in the valsartan+cilnidipine-treated group. Plasma renin activity was significantly augmented in the valsartan-treated group, and it was significantly attenuated in the valsartan+cilnidipine-treated group. A significant increase in the ratio of plasma angiotensin-(1-7) to angiotensin II was observed only in the valsartan+cilnidipine-treated group. Vascular angiotensin-converting enzyme (ACE) gene expression was significantly attenuated only in the valsartan+cilnidipine-treated group, but ACE2 gene expression was significantly higher in all of the therapeutic groups. Thus, valsartan and cilnidipine combination therapy might have a powerful protective effect in the vascular tissues via increases in the angiotensin-(1-7)/angiotensin II ratio in plasma.