Tissue kallikrein-binding protein reduces blood pressure in transgenic mice

Role of human Kallistatin in glucose and energy homeostasis in mice

OBJECTIVE

Kallistatin (KST), also known as SERPIN A4, is a circulating, broadly acting human plasma protein with pleiotropic properties. Clinical studies in humans revealed reduced KST levels in obesity. The exact role of KST in glucose and energy homeostasis in the setting of insulin resistance and type 2 diabetes is currently unknown.

METHODS

Kallistatin mRNA expression in human subcutaneous white adipose tissue (sWAT) of 47 people with overweight to obesity of the clinical trial "Comparison of Low Fat and Low Carbohydrate Diets With Respect to Weight Loss and Metabolic Effects (B-SMART)" was measured. Moreover, we studied transgenic mice systemically overexpressing human KST (hKST-TG) and wild type littermate control mice (WT) under normal chow (NCD) and high-fat diet (HFD) conditions.

RESULTS

In sWAT of people with overweight to obesity, KST mRNA increased after diet-induced weight loss. On NCD, we did not observe differences between hKST-TG and WT mice. Under HFD conditions, body weight, body fat and liver fat content did not differ between genotypes. Yet, during intraperitoneal glucose tolerance tests (ipGTT) insulin excursions and HOMA-IR were lower in hKST-TG (4.42 ± 0.87 AU, WT vs. 2.20 ± 0.27 AU, hKST-TG, p < 0.05). Hyperinsulinemic euglycemic clamp studies with tracer-labeled glucose infusion confirmed improved insulin sensitivity by higher glucose infusion rates in hKST-TG mice (31.5 ± 1.78 mg/kg/min, hKST-TG vs. 18.1 ± 1.67 mg/kg/min, WT, p < 0.05). Improved insulin sensitivity was driven by reduced hepatic insulin resistance (clamp hepatic glucose output: 7.7 ± 1.9 mg/kg/min, hKST-TG vs 12.2 ± 0.8 mg/kg/min, WT, p < 0.05), providing evidence for direct insulin sensitizing effects of KST for the first time. Insulin sensitivity was differentially affected in skeletal muscle and adipose tissue. Mechanistically, we observed reduced Wnt signaling in the liver but not in skeletal muscle, which may explain the effect.

CONCLUSIONS

KST expression increases after weight loss in sWAT from people with obesity. Furthermore, human KST ameliorates diet-induced hepatic insulin resistance in mice, while differentially affecting skeletal muscle and adipose tissue insulin sensitivity. Thus, KST may be an interesting, yet challenging, therapeutic target for patients with obesity and insulin resistance.

Serum kallistatin level is decreased in women with preeclampsia

OBJECTIVES

To evaluate the serum levels of the serine proteinase inhibitor kallistatin in women with preeclampsia (PE).

METHODS

The clinical and laboratory parameters of 55 consecutive women with early-onset PE (EOPE) and 55 consecutive women with late-onset PE (LOPE) were compared with 110 consecutive gestational age (GA)-matched (±1 week) pregnant women with an uncomplicated pregnancy and an appropriate for gestational age fetus.

RESULTS

Mean serum kallistatin was significantly lower in women with PE compared to the GA-matched-controls (27.74±8.29 ng/mL vs. 37.86±20.64 ng/mL, p<0.001); in women with EOPE compared to that of women in the control group GA-matched for EOPE (24.85±6.65 ng/mL vs. 33.37±17.46 ng/mL, p=0.002); and in women with LOPE compared to that of women in the control group GA-matched for LOPE (30.87±8.81 ng/mL vs. 42.25±22.67 ng/mL, p=0.002). Mean serum kallistatin was significantly lower in women with EOPE compared to LOPE (24.85±6.65 ng/mL vs. 30.87±8.81 ng/mL, p<0.001). Serum kallistatin had negative correlations with systolic and diastolic blood pressure, creatinine, and positive correlation with GA at sampling and GA at birth.

CONCLUSIONS

Serum kallistatin levels are decreased in preeclamptic pregnancies compared to the GA-matched-controls. This decrease was also significant in women with EOPE compared to LOPE. Serum kallistatin had negative correlation with systolic and diastolic blood pressure, creatinine and positive correlation with GA at sampling and GA at birth.

Opposing Effects of Oxygen Regulation on Kallistatin Expression: Kallistatin as a Novel Mediator of Oxygen-Induced HIF-1-eNOS-NO Pathway

Oxidative stress has both detrimental and beneficial effects. Kallistatin, a key component of circulation, protects against vascular and organ injury. Serum kallistatin levels are reduced in patients and animal models with hypertension, diabetes, obesity, and cancer. Reduction of kallistatin levels is inversely associated with elevated thiobarbituric acid-reactive substance. Kallistatin therapy attenuates oxidative stress and increases endothelial nitric oxide synthase (eNOS) and NO levels in animal models. However, kallistatin administration increases reactive oxygen species formation in immune cells and bacterial killing activity in septic mice. High oxygen inhibits kallistatin expression via activating the JNK-FOXO1 pathway in endothelial cells. Conversely, mild oxygen/hyperoxia stimulates kallistatin, eNOS, and hypoxia-inducible factor-1 (HIF-1) expression in endothelial cells and in the kidney of normal mice. Likewise, kallistatin stimulates eNOS and HIF-1, and kallistatin antisense RNA abolishes oxygen-induced eNOS and HIF-1 expression, indicating a role of kallistatin in mediating mild oxygen's stimulation on antioxidant genes. Protein kinase C (PKC) activation mediates HIF-1-induced eNOS synthesis in response to hyperoxia/exercise; thus, mild oxygen through PKC activation stimulates kallistatin-mediated HIF-1 and eNOS synthesis. In summary, oxidative stress induces down- or upregulation of kallistatin expression, depending on oxygen concentration, and kallistatin plays a novel role in mediating oxygen/exercise-induced HIF-1-eNOS-NO pathway.

Kallistatin: double-edged role in angiogenesis, apoptosis and oxidative stress

Kallistatin, via its two structural elements – an active site and a heparin-binding domain – displays a double-edged function in angiogenesis, apoptosis and oxidative stress. First, kallistatin has both anti-angiogenic and pro-angiogenic effects. Kallistatin treatment attenuates angiogenesis and tumor growth in cancer-bearing mice. Kallistatin via its heparin-binding site inhibits angiogenesis by blocking vascular endothelial growth factor (VEGF)-induced growth, migration and adhesion of endothelial cells. Conversely, kallistatin via the active site promotes neovascularization by stimulating VEGF levels in endothelial progenitor cells. Second, kallistatin inhibits or induces apoptosis depending on cell types. Kallistatin attenuates organ injury and apoptosis in animal models, and its heparin-binding site is essential for blocking tumor necrosis factor (TNF)-α-induced apoptosis in endothelial cells. However, kallistatin via its active site induces apoptosis in breast cancer cells by up-regulating miR-34a and down-regulating miR-21 and miR-203 synthesis. Third, kallistatin can act as an antioxidant or pro-oxidant. Kallistatin treatment inhibits oxidative stress and tissue damage in animal models and cultured cells. Kallistatin via the heparin-binding domain antagonizes TNF-α-induced oxidative stress, whereas its active site is crucial for stimulating antioxidant enzyme expression. In contrast, kallistatin provokes oxidant formation, leading to blood pressure reduction and bacterial killing. Kallistatin-mediated vasodilation is partly mediated by H2O2, as the effect is abolished by the antioxidant enzyme catalase. Moreover, kallistatin exerts a bactericidal effect by stimulating superoxide production in neutrophils of mice with microbial infection as well as in cultured immune cells. Thus, kallistatin’s dual roles in angiogenesis, apoptosis and oxidative stress contribute to its beneficial effects in various diseases.

The Potential Role of Kallistatin in the Development of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a vascular condition that causes permanent dilation of the abdominal aorta, which can lead to death due to aortic rupture. The only treatment for AAA is surgical repair, and there is no current drug treatment for AAA. Aortic inflammation, vascular smooth muscle cell apoptosis, angiogenesis, oxidative stress and vascular remodeling are implicated in AAA pathogenesis. Kallistatin is a serine proteinase inhibitor, which has been shown to have a variety of functions, potentially relevant in AAA pathogenesis. Kallistatin has been reported to have inhibitory effects on tumor necrosis factor alpha (TNF-α) signaling induced oxidative stress and apoptosis. Kallistatin also inhibits vascular endothelial growth factor (VEGF) and Wnt canonical signaling, which promote inflammation, angiogenesis, and vascular remodeling in various pre-clinical experimental models. This review explores the potential protective role of kallistatin in AAA pathogenesis.

Kallistatin in blood pressure regulation transgenic and somatic gene delivery studies

Kallistatin, first discovered as a human kallikrein-binding protein in the circulation, shares high homology with other plasma serine proteinase inhibitors (serpins). It forms a covalently linked complex with tissue kallikrein and inhibits kallikrein's activity. Substantial evidence has accumulated in recent years indicating that kallistatin may play a role in blood pressure regulation independent of its interaction with tissue kallikrein. Intravenous injection of kallistatin into rats and mice results in a rapid and transient reduction of blood pressure in a dose-dependent manner. Functional analysis in transgenic mice over-expressing rat kallikrein-binding protein, an analogue of human kallistatin, revealed that these mice have significantly lower blood pressure compared with control littermates. Adenovirus-mediated delivery of the human kallistatin gene can cause significant blood pressure reductions for 4 weeks in spontaneously hypertensive rats. Finally, kallistatin can induce vasorelaxation in isolated rat aortic rings and reduce renal perfusion pressure in the isolated, perfused kidney. Together, these findings suggest a direct role for kallistatin in regulating blood pressure and raise the possibility for the development of new pharmacological treatments for hypertension. (Trends Cardiovasc Med 1997;7:307-311). © 1997, Elsevier Science Inc.

Increased serum kallistatin levels in type 1 diabetes patients with vascular complications

BACKGROUND

Kallistatin, a serpin widely produced throughout the body, has vasodilatory, anti-angiogenic, anti-oxidant, and anti-inflammatory effects. Effects of diabetes and its vascular complications on serum kallistatin levels are unknown.

METHODS

Serum kallistatin was quantified by ELISA in a cross-sectional study of 116 Type 1 diabetic patients (including 50 with and 66 without complications) and 29 non-diabetic controls, and related to clinical status and measures of oxidative stress and inflammation.

RESULTS

Kallistatin levels (mean(SD)) were increased in diabetic vs. control subjects (12.6(4.2) vs. 10.3(2.8) μg/ml, p = 0.007), and differed between diabetic patients with complications (13.4(4.9) μg/ml), complication-free patients (12.1(3.7) μg/ml), and controls; ANOVA, p = 0.007. Levels were higher in diabetic patients with complications vs. controls, p = 0.01, but did not differ between complication-free diabetic patients and controls, p > 0.05. On univariate analyses, in diabetes, kallistatin correlated with renal dysfunction (cystatin C, r = 0.28, p = 0.004; urinary albumin/creatinine, r = 0.34, p = 0.001; serum creatinine, r = 0.23, p = 0.01; serum urea, r = 0.33, p = 0.001; GFR, r = -0.25, p = 0.009), total cholesterol (r = 0.28, p = 0.004); LDL-cholesterol (r = 0.21, p = 0.03); gamma-glutamyltransferase (GGT) (r = 0.27, p = 0.04), and small artery elasticity, r = -0.23, p = 0.02, but not with HbA1c, other lipids, oxidative stress or inflammation. In diabetes, geometric mean (95%CI) kallistatin levels adjusted for covariates, including renal dysfunction, were higher in those with vs. without hypertension (13.6 (12.3-14.9) vs. 11.8 (10.5-13.0) μg/ml, p = 0.03). Statistically independent determinants of kallistatin levels in diabetes were age, serum urea, total cholesterol, SAE and GGT, adjusted r2 = 0.24, p < 0.00001.

CONCLUSIONS

Serum kallistatin levels are increased in Type 1 diabetic patients with microvascular complications and with hypertension, and correlate with renal and vascular dysfunction.

Tissue kallikrein in cardiovascular, cerebrovascular and renal diseases and skin wound healing

Tissue kallikrein (KLK1) processes low-molecular weight kininogen to produce vasoactive kinins, which exert biological functions via kinin receptor signaling. Using various delivery approaches, we have demonstrated that tissue kallikrein through kinin B2 receptor signaling exhibits a wide spectrum of beneficial effects by reducing cardiac and renal injuries, restenosis and ischemic stroke, and by promoting angiogenesis and skin wound healing, independent of blood pressure reduction. Protection by tissue kallikrein in oxidative organ damage is attributed to the inhibition of apoptosis, inflammation, hypertrophy and fibrosis. Tissue kallikrein also enhances neovascularization in ischemic heart and limb. Moreover, tissue kallikrein/kinin infusion not only prevents but also reverses kidney injury, inflammation and fibrosis in salt-induced hypertensive rats. Furthermore, there is a wide time window for kallikrein administration in protection against ischemic brain infarction, as delayed kallikrein infusion for 24 h after cerebral ischemia in rats is effective in reducing neurological deficits, infarct size, apoptosis and inflammation. Importantly, in the clinical setting, human tissue kallikrein has been proven to be effective in the treatment of patients with acute brain infarction when injected within 48 h after stroke onset. Finally, kallikrein promotes skin wound healing and keratinocyte migration by direct activation of protease-activated receptor 1.

Novel Role of Kallistatin in Protection Against Myocardial Ischemia–Reperfusion Injury by Preventing Apoptosis and Inflammation

Kallistatin is a serine proteinase inhibitor that has been shown to reduce joint swelling and to inhibit inflammation in a rat model of arthritis. In this study, we investigated the effect and mechanisms of kallistatin on cardiac function after myocardial ischemia-reperfusion (I/R) injury. The human kallistatin gene in an adenoviral vector was delivered locally into rat heart 4 days before 30-min ischemia followed by 24-hr reperfusion. Kallistatin gene transfer significantly reduced myocardial infarct size and left ventricle end-diastolic pressure and improved cardiac contractility. Kallistatin significantly reduced I/R-induced cardiomyocyte apoptosis as identified by TUNEL and Hoechst staining, DNA laddering, cell viability, and caspase-3 activity in ischemic myocardium and in primary cultured cardiomyocytes. Kallistatin also reduced intramyocardial monocyte/macrophage and neutrophil accumulation in conjunction with decreased expression of monocyte chemoattractant protein-1, tumor necrosis factor-alpha, and intercellular adhesion molecule-1. Kallistatin delivery promoted cardiac endothelial nitric oxide synthase activation and increased nitric oxide (NO) formation, but inhibited NADH oxidase activity, p22phox expression, and superoxide production. Moreover, kallistatin reduced the phosphorylation of apoptosis signal-regulating kinase-1 and mitogen-activated protein kinases (MAPKs), but increased Akt and glycogen synthase kinase-3beta phosphorylation. The effects of kallistatin on cardiac function, oxidative stress, and these signal transduction events were all blocked by Nomega-nitro-L-argi-nine methyl ester. These results indicate a novel role of kallistatin in cardiac protection after I/R injury through increased NO formation and Akt-glycogen synthase kinase-3beta signaling and suppression of oxidative stress and MAPK activation.

Kallikrein-binding protein inhibits retinal neovascularization and decreases vascular leakage

AIMS/HYPOTHESIS

Kallikrein-binding protein (KBP) is a serine proteinase inhibitor (serpin). It specifically binds to tissue kallikrein and inhibits kallikrein activity. Our study was designed to test its effects on retinal neovascularization and vascular permeability.

METHODS

Endothelial cell proliferation was determined by [(3)H] thymidine incorporation assay and apoptosis quantified by Annexin V staining and flow cytometry. Effect on retinal neovascularization was determined by fluorescein angiography and count of pre-retinal vascular cells in an oxygen-induced retinopathy (OIR) model. Vascular permeability was assayed by the Evans blue method. Vascular endothelial growth factor (VEGF) was measured by Western blot analysis and ELISA.

RESULTS

Kallikrein-binding protein specifically inhibited proliferation and induced apoptosis in retinal capillary endothelial cells. Intravitreal injection of KBP inhibited retinal neovascularization in an OIR model. Moreover, KBP decreased vascular leakage in the retina, iris and choroid in rats with OIR. Blockade of kinin receptors by specific antagonists showed significantly weaker inhibition of endothelial cells, when compared to that of KBP, suggesting that the anti-angiogenic activity of KBP is not through inhibiting kallikrein activity or kinin production. KBP competed with (125)I-VEGF for binding to endothelial cells and down-regulated VEGF production in endothelial cells and in the retina of the OIR rat model.

CONCLUSION/INTERPRETATION

Kallikrein-binding protein is a multi-functional serpin, and its vascular activities are independent of its interactions with the kallikrein-kinin system. Inhibition of VEGF binding to its receptors and down-regulation of VEGF expression could represent a mechanism for the vascular activities of KBP.

Kallistatin is a new inhibitor of angiogenesis and tumor growth

Kallistatin is a unique serine proteinase inhibitor (serpin) and a heparin-binding protein. It has been localized in vascular smooth muscle cells and endothelial cells of human blood vessels, suggesting that kallistatin may be involved in the regulation of vascular function. Our previous study showed that kallistatin plays a role in neointima hyperplasia. In this study, we investigated the potential role of kallistatin in angiogenesis in vitro and in vivo. Purified human kallistatin significantly inhibited vascular endothelial growth factor (VEGF)- or basic fibroblast growth factor (bFGF)-induced proliferation, migration, and adhesion of cultured endothelial cells. Kallistatin attenuated VEGF- or bFGF-induced capillary density and hemoglobin content in subcutaneously implanted Matrigel plugs in mice. To further investigate the role of kallistatin in angiogenesis, we prepared adenovirus carrying the human kallistatin cDNA (Ad.HKBP) and evaluated the effect of kallistatin gene delivery on spontaneous angiogenesis in a rat model of hind-limb ischemia. Local kallistatin gene delivery significantly reduced capillary formation and regional blood perfusion recovery in the ischemic hind limb after removal of the femoral artery. Furthermore, a single intratumoral injection of Ad.HKBP into pre-established human breast tumor xenografts grown in athymic mice resulted in significant inhibition of tumor growth. CD31 immunostaining of tumor sections showed a decreased number of blood vessels in the kallistatin-treated group as compared to the control. These results demonstrate a novel role of kallistatin in the inhibition of angiogenesis and tumor growth.

Proteomic analysis reveals alterations in the renal kallikrein pathway during hypoxia-induced hypertension

Obstructive sleep apnea syndrome (OSAS), a disorder characterized by episodic hypoxia (EH) during sleep, is associated with systemic hypertension. We used proteomic analysis to examine differences in rat kidney protein expression during EH, and their potential relationship to EH-induced hypertension. Young male Sprague-Dawley rats were exposed to either EH or sustained hypoxia (SH) for 14 (EH14/SH14) and 30 (EH30/SH30) days. Mean arterial blood pressure was significantly increased only in EH30 (p < 0.0002). Kidney proteins were resolved by two-dimensional-PAGE and were identified by MALDI-MS. Renal expression of kallistatin, a potent vasodilator, was down-regulated in all animals. Expression of alpha-1-antitrypsin, an inhibitor of kallikrein activation, was up-regulated in EH but down-regulated in SH. Western blotting showed significant elevation of B(2)-bradykinin receptor expression in all normotensive animals but remained unchanged in hypertensive animals. Proteins relevant to vascular hypertrophy, such as smooth muscle myosin and protein-disulfide isomerase were up-regulated in EH30 but were down-regulated in SH30. These data indicate that EH induces changes in renal protein expression consistent with impairment of vasodilation mediated by the kallikrein-kallistatin pathway and vascular hypertrophy. In contrast, SH-induced changes suggest the kallikrein- and bradykinin-mediated compensatory mechanisms for prevention of hypertension and vascular remodeling. To test the hypothesis suggested by the proteomic data, we measured the effect of EH on blood pressure in transgenic hKLK1 rats that overexpress human kallikrein. Transgenic hKLK1 animals were protected from EH-induced hypertension. We conclude that EH-induced hypertension may result, at least in part, from altered regulation of the renal kallikrein system.

Novel roles of kallistatin, a specific tissue kallikrein inhibitor, in vascular remodeling

We have purified, cloned and characterized kallistatin, a tissue kallikrein-binding protein (KBP) in humans and rodents. Kallistatin is a unique serine proteinase inhibitor (serpin) with Phe-Phe residues at the P2 and P1 positions. Structural and functional analysis of kallistatin by site-directed mutagenesis and protein engineering indicate that wild-type kallistatin is selective for tissue kallikrein. Kallistatin is expressed and localized in endothelial and smooth muscle cells of blood vessels and has multiple roles in vascular function independent of the tissue kallikrein-kinin system. First, kallistatin induces vasorelaxation of isolated aortic rings and reduces renal perfusion pressure in isolated rat kidneys. Transgenic mice overexpressing rat kallistatin are hypotensive, and adenovirus-mediated gene delivery of human kallistatin attenuates blood pressure rise in spontaneously hypertensive rats. Second, kallistatin stimulates the proliferation and migration of vascular smooth muscle cells in vitro and neointima formation in balloon-injured rat arteries. Third, kallistatin inhibits the proliferation, migration and adhesion of endothelial cells in vitro and angiogenesis in the rat model of hindlimb ischemia. These results demonstrate novel roles of kallistatin in blood pressure regulation and vascular remodeling.

Importance of quantitative genetic variations in the etiology of hypertension

Recent progress has been remarkable in identifying mutations which cause diseases (mostly uncommon) that are inherited simply. Unfortunately, the common diseases of humankind with a strong genetic component, such as those affecting cardiovascular function, have proved less tractable. Their etiology is complex with substantial environmental components and strong indications that multiple genes are implicated. In this article, we consider the genetic etiology of essential hypertension. After presenting the distribution of blood pressures in the population, we propose the hypothesis that essential hypertension is the consequence of different combinations of genetic variations that are individually of little consequence. The candidate gene approach to finding relevant genes is exemplified by studies that identified potentially causative variations associated with quantitative differences in the expression of the angiotensinogen gene (AGT). Experiments to test causation directly are possible in mice, and we describe their use to establish that blood pressures are indeed altered by genetic changes in AGT expression. Tests of differences in expression of the genes coding for the angiotensin-converting enzyme (ACE) and for the natriuretic peptide receptor A are also considered, and we provide a tabulation of all comparable experiments in mice. Computer simulations are presented that resolve the paradoxical finding that while ACE inhibitors are effective, genetic variations in the expression of the ACE gene do not affect blood pressure. We emphasize the usefulness of studying animals heterozygous for an inactivating mutation and a wild-type allele, and briefly discuss a way of establishing causative links between complex phenotypes and single nucleotide polymorphisms.

The molecular basis of hypertension

More than 50 million Americans display blood pressures outside the safe physiological range. Unfortunately for most individuals, the molecular basis of hypertension is unknown, in part because pathological elevations of blood pressure are the result of abnormal expression of multiple genes. This review identifies a number of important blood pressure regulatory genes including their loci in the human, mouse, and rat genome. Phenotypes of gene deletions and overexpression in mice are summarized. More detailed discussion of selected gene products follows, beginning with proteins involved in ion transport, specifically the epithelial sodium channel and sodium proton exchangers. Next, proteins involved in vasodilation/natriuresis are discussed with emphasis on natriuretic peptides, guanylin/uroguanylin, and nitric oxide. The renin angiotensin aldosterone system has an important role antagonizing the vasodilatory cyclic GMP system.

Kallikrein-binding protein is induced by growth hormone in the dwarf rat

Rat kallikrein-binding protein (KBP), a member of the serpin family, is a tissue kallikrein inhibitor. It has been shown to be a potential pathogenic factor of diabetic retinopathy and may play a role in animal development and growth. To determine whether reduced KBP expression is involved in retarded animal growth, we examined the in vivo effect of growth hormone (GH) deficiency on the expression of KBP in the Lewis dwarf (dw/dw). We found that serum levels of functionally active KBP were reduced in the dwarf rat (P < 0.05) as determined by complex formation assay between serum KBP and (125)I-labeled rat tissue kallikrein. Enzyme-linked immunosorbent assay showed that KBP levels were significantly reduced in the serum of the dwarf rat compared to the Lewis rat (213.8 ng/ml vs. 413.8 ng/ml, n = 4, P < 0.01). The decreased KBP levels were confirmed by Western blot analysis. Moreover, treatment of the dwarf rat with recombinant human GH for 4 wk resulted in a significant increase in KBP activity (P < 0.01) and serum KBP levels compared with the untreated dwarf rat (549.8 ng/ml, n = 5, vs. 213.8 ng/ml, n = 4, P < 0.02). Northern blot analysis and densitometry showed that liver KBP mRNA levels were reduced by fivefold in the dwarf rat compared to the Lewis rat and the decrease was reversed by the GH treatment. These results indicate that the KBP levels are regulated at the RNA level. Furthermore, in vitro studies using cultured rat hepatocytes showed that GH may have a direct regulatory effect on KBP expression since KBP levels increased in the conditioned media of cells treated with GH. These results demonstrated that KBP is reduced in the genetic dwarf rat and is restored to normal by GH; therefore, KBP is a GH-dependent protein and may be a new target for studying the mechanism of pathological animal growth.

Bradykinin and pituitary-adrenocortical function in the rabbit: in vitro and in vivo studies

Bradykinin (BK) is a 9-amino acid peptide, which has been found to affect adrenocortical secretion in the calf and rat. We investigated the in vitro and in vivo effects of BK and its receptor antagonist [D-Arg, (Hyp3,D-Phe7)]-BK (BK-A) on pituitary-adrenocortical function in the rabbit. BK and BK-A raised basal release of aldosterone, but not of corticosterone by dispersed zona glomeralosa and zona fasciculata-reficularis cells, respectively. Both peptides did not affect ACTH-stimulated aldosterone secretion. Conversely, BK concentration-dependently decreased ACTH-stimulated corticosterone production, and BK-A annulled this effect. The bolus intravenous injection of BK did not alter plasma ACTH concentration. However, BK lowered the blood concentration of both aldosterone and corticosterone, as well as the overall production of the two hormones over a period of 90 min after its administration. The simultaneous injection of BK-A blocked these effects of BK. BK-A alone did not evoke any sizeable change in blood hormonal levels. Collectively, these findings allow us to conclude that in rabbits (i) exogenous BK depresses adrenocortical secretion, through a receptor-mediated mechanism, which does not involve the inhibition of pituitary ACTH release-, and (ii) endogenous BK-like peptides do not play a relevant role in the functional regulation of the pituitary-adrenal axis, at least under basal conditions.

Molecular biology of the kallikrein-kinin system: from structure to function

The participation of the kallikrein-kinin system, comprising the serine proteases kallikreins, the protein substrates kininogens and the effective peptides kinins, in some pathological processes like hypertension and cardiovascular diseases is still a matter of controversy. The use of different experimental set-ups in concert with the development of potent and specific inhibitors and antagonists for the system has highlighted its importance but the results still lack conclusivity. Over the last few years, transgenic and gene-targeting technologies associated with molecular biology tools have provided specific information about the elusive role of the kallikrein-kinin system in the control of blood pressure and electrolyte homeostasis. cDNA and genomic sequences for kinin receptors B2 and B1 from different species were isolated and shown to encode G-protein-coupled receptors and the structure and pharmacology of the receptors were characterized. Transgenic animals expressing an overactive kallikrein-kinin system were established to study the cardiovascular effects of these alterations and the results of these investigations further corroborate the importance of this system in the maintenance of normal blood pressure. Knockout animals for B2 and B1 receptors are available and their analysis also points to the role of these receptors in cardiovascular regulation and inflammatory processes. In this paper the most recent and relevant genetic animal models developed for the study of the kallikrein-kinin system are reviewed, and the advances they brought to the understanding of the biological role of this system are discussed.

Kallistatin is a potent new vasodilator

Kallistatin is a serine proteinase inhibitor which binds to tissue kallikrein and inhibits its activity. The aim of this study is to evaluate if kallistatin has a direct effect on the vasculature and on blood pressure homeostasis. We found that an intravenous bolus injection of human kallistatin caused a rapid, potent, and transient reduction of mean arterial blood pressure in anesthetized rats. Infusion of purified kallistatin (0.07-1.42 nmol/kg) into cannulated rat jugular vein produced a 20-85 mmHg reduction of blood pressure in a dose-dependent manner. Hoe 140, a bradykinin B2-receptor antagonist, had no effect on the hypotensive effect of kallistatin yet it abolished the blood pressure-lowering effect of kinin and kallikrein. Relaxation of isolated aortic rings by kallistatin was observed in the presence (ED50 of 3.4 x 10(-9) M) and in the absence of endothelium (ED50 of 10(-9) M). Rat kallikrein-binding protein, but not kinin or kallikrein, induced vascular relaxation of aortic rings. Neither Hoe 140 nor Nomega-nitro--arginine methyl ester, a nitric oxide synthase inhibitor, affected vasorelaxation induced by kallistatin. Kallistatin also caused dose-dependent vasodilation of the renal vasculature in the isolated, perfused rat kidney. Specific kallistatin-binding sites were identified in rat aorta by Scatchard plot analysis with a Kd of 0.25+/-0.07 nM and maximal binding capacity of 47.9+/-10.4 fmol/mg protein (mean+/-SEM, n = 3). These results indicate that kallistatin is a potent vasodilator which may function directly through a vascular smooth muscle mechanism independent of an endothelial bradykinin receptor. This study introduces the potential significance of kallistatin in directly regulating blood pressure to reduce hypertension.

Adenovirus-mediated delivery of human kallistatin gene reduces blood pressure of spontaneously hypertensive rats

Human kallistatin, or human tissue kallikrein-binding protein (HKBP), is a serine proteinase inhibitor (serpin). Transgenic mice overexpressing rat kallikrein-binding protein are hypotensive. To elucidate therapeutic potentials of kallistatin in hypertension, the human kallistatin gene in an adenoviral vector was directly introduced into spontaneously hypertensive rats (SHR) through portal vein injection. The kallistatin cDNA construct (RSV-cHKBP) under the promoter control of Rous sarcoma virus 3' long terminal repeat (LTR) was incorporated into adenovirus (Ad.RSV-cHKBP). Recombinant kallistatin in 293 cells transfected with RSV-cHKBP or Ad.RSV-cHKBP was measured by ELISA and by its complex formation with tissue kallikrein. A single intraportal vein injection of Ad.RSV-cHKBP at a dose of 8 x 10(10) pfu results in a significant reduction of blood pressure of SHR for 4 weeks. Human kallistatin mRNA was detected in the liver, spleen, kidney, aorta, and lung of rats receiving gene delivery. Immunoreactive human kallistatin in rat serum was detected at the highest level 1 day post injection and at lesser amounts in rat tissues. This study shows that adenovirus harboring Ad.RSV-cHKBP produces functional kallistatin, and adenovirus-mediated transfer of the human kallistatin gene reduces blood pressures of SHR. The results suggest that kallistatin may function as a vasodilator in vivo and provide important information for a potential gene therapy approach to hypertension.

Beneficial effects of kallikrein-binding protein in transgenic mice during endotoxic shock

Rat kallikrein-binding protein (RKBP) is a negative acute phase protein. The potential role of RKBP in inflammation was evaluated in transgenic mice overexpressing the RKBP gene under the control of the mouse metallothionein metal-responsive promoter. Bacterial endotoxic lipopolysaccharide (LPS) was injected intraperitoneally into mice at a dose of 600 microg/25 g body weight. The death toll was recorded every 12 hours for 3 days. The survival rate of transgenic male mice (n=78) was 33.3% while that of control male mice (n=54) was 9.3% 3 days post LPS injection. In comparison, the survival rate of transgenic female mice (n=59) was 55.9% while that of control female mice (n=65) was 30.8%. Recombinant RKBP levels in the circulation of these mice increased by 3-fold after LPS treatment. The results show that RKBP transgenic mice have a higher survival rate than their non-transgenic control littermates after endotoxin shock and female mice are more resistant to lethality induced by endotoxin shock than male mice in both transgenic and control groups. These findings suggest that kallikrein-binding protein has a protective effect during acute phase inflammation.