Green tea reduces body fat via upregulation of neprilysin.

BACKGROUND/OBJECTIVE: Consumption of green tea has become increasingly popular, particularly because of claimed reduction in body weight. We recently reported that animals with pharmacological inhibition (by candoxatril) or genetic absence of the endopeptidase neprilysin (NEP) develop an obese phenotype. We now investigated the effect of green tea extract (in drinking water) on body weight and body composition and the mediating role of NEP. SUBJECTS/METHODS: To elucidate the role of NEP in mediating the beneficial effects of green tea extract, 'Berlin fat mice' or NEP-deficient mice and their age- and gender-matched wild-type controls received the extract in two different doses (300 or 600 mg kg-1 body weight per day) in the drinking water. RESULTS: In 'Berlin fat mice', 51 days of green tea treatment did not only prevent fat accumulation (control: day 0: 30.5% fat, day 51: 33.1%; NS) but also reduced significant body fat (green tea: day 0: 27.8%, day 51: 20.9%, P<0.01) and body weight below the initial levels. Green tea reduced food intake. This was paralleled by a selective increase in peripheral (in kidney 17%, in intestine 92%), but not central NEP expression and activity, leading to downregulation of orexigens (like galanin and neuropeptide Y (NPY)) known to be physiological substrates of NEP. Consequently, in NEP-knockout mice, green tea extract failed to reduce body fat/weight. CONCLUSIONS: Our data generate experimental proof for the assumed effects of green tea on body weight and the key role for NEP in such process, and thus open a new avenue for the treatment of obesity.

Plasticity and impact of the central renin-angiotensin system during development of ethanol dependence.

Pharmacological and genetic interference with the renin-angiotensin system (RAS) seems to alter voluntary ethanol consumption. However, understanding the influence of the RAS on ethanol dependence and its treatment requires modeling the neuroadaptations that occur with prolonged exposure to ethanol. Increased ethanol consumption was induced in rats through repeated cycles of intoxication and withdrawal. Expression of angiotensinogen, angiotensin-converting enzyme, and the angiotensin II receptor, AT1a, was examined by quantitative reverse transcription polymerase chain reaction. Increased ethanol consumption after a history of dependence was associated with increased angiotensinogen expression in medial prefrontal cortex but not in nucleus accumbens or amygdala. Increased angiotensinogen expression also demonstrates that the astroglia is an integral part of the plasticity underlying the development of dependence. The effects of low central RAS activity on increased ethanol consumption were investigated using either spirapril, a blood-brain barrier-penetrating inhibitor of angiotensin-converting enzyme, or transgenic rats (TGR(ASrAOGEN)680) with reduced central angiotensinogen expression. Spirapril reduced ethanol intake in dependent rats compared to controls. After induction of dependence, TGR(ASrAOGEN)680 rats had increased ethanol consumption but to a lesser degree than Wistar rats with the same history of dependence. These data suggest that the central RAS is sensitized in its modulatory control of ethanol consumption in the dependent state, but pharmacological or genetic blockade of the system appears to be insufficient to halt the progression of dependence.

Effects of kinins on mammalian spermatozoa and the impact of peptidolytic enzymes.

Effects of kinins, mainly bradykinin (Bk), and other components of the kallikrein-kinin system on sperm motility and further fertility-related functions have been described repeatedly. However, reported data are in part controversial and the mechanism of kinin effects on sperm motility is not yet understood. In the present report we describe a significant promoting effect of Bk on sperm motility at subnanomolar concentrations. This effect was stabilized and even increased by suppression of Bk hydrolysis in semen samples. As sperm membrane-bound angiotensin-converting enzyme and neutral metalloendopeptidase are mainly involved in Bk hydrolysis, an effective cocktail of enzyme inhibitors promoting the sperm motility consists of phosphoramidon and lisinopril (both at 10-7 m). The effects of Bk on sperm cells are not mediated by the B2 Bk receptor. Using several biochemical, molecular and genetic methods we could not detect any Bk receptor on spermatozoa.

*NO and oxyradical metabolism in new cell lines of rat brain capillary endothelial cells forming the blood-brain barrier.

To investigate the relevance of *NO and oxyradicals in the blood-brain barrier (BBB), differentiated and well-proliferating brain capillary endothelial cells (BCEC) are required. Therefore, rat BCEC (rBCEC) were transfected with immortalizing genes. The resulting lines exhibited endothelial characteristics (factor VIII, angiotensin-converting enzyme, high prostacyclin/thromboxane release rates) and BBB markers (gamma-glutamyl transpeptidase, alkaline phosphatase). The control line rBCEC2 (mock transfected) revealed fibroblastoid morphology, less factor VIII, reduced gamma-glutamyl transpeptidase, weak radical defence, low prostanoid metabolism, and limited proliferation. Lines transfected with immortalizing genes (especially rBCEC4, polyoma virus large T antigen) conserved primary properties: epitheloid morphology, subcultivation with high proliferation rate under pure culture conditions, and powerful defence against reactive oxygen species (Mn-, Cu/Zn-superoxide dismutase, catalase, glutathione peroxidase, glutathione) effectively controlling radical metabolism. Only 100 microM H2O2 overcame this defence and stimulated the formation of eicosanoids similarly as in primary cells. Some BBB markers were expressed to a lower degree; however, cocultivation with astrocytes intensified these markers (e.g., alkaline phosphatase) and paraendothelial tightness, indicating induction of BBB properties. Inducible NO synthase was induced by a cytokine plus lipopolysaccharide mixture in all lines and primary cells, resulting in *NO release. Comparing the cell lines obtained, rBCEC4 are stable immortalized and reveal the best conservation of properties from primary cells, including enzymes producing or decomposing reactive species. These cells can be subcultivated in large amounts and, hence, they are suitable to study the role of radical metabolism in the BBB and in the cerebral microvasculature.

Elements of the kallikrein-kinin system are present in rat seminiferous epithelium.

Peptide hormones are involved in the paracrine regulation of several physiological processes. A possible function of the kallikrein-kinin system (KKS) in mammalian reproduction has been discussed. To evaluate its putative role in spermatogenesis, we searched for components of the KKS (kallikrein, kininases, kinin receptor) in the rat testis. Specific immunostaining demonstrated that the kininogenase tissue kallikrein was present in round and elongated spermatids. Leydig cells, Sertoli cells, peritubular cells, spermatogonia and spermatocytes were not stained. Bradykinin in the supernatant of Sertoli cell cultures was effectively degraded. The resulting metabolites were analysed by high-performance liquid chromatography (HPLC). Specific protease inhibition in the degrading experiments confirmed the occurrence of several metalloproteases on Sertoli cell membranes, including neutral metalloendopeptidases (NEP 24.11 and NEP 24.15), kininase type II (angiotensin converting enzyme, ACE), and kininase type I (metallocarboxypeptidase). Northern blots hybridized with a bradykinin B2 receptor probe showed the presence of B2 receptor mRNA in testis homogenate and Sertoli cell extract. All components of the kallikrein-kinin system are present within the seminiferous epithelium of the rat. Therefore, this paracrine peptide system may play a role in the regulation of Sertoli cell function or in the Sertoli cell-germ cell crosstalk.

mRNA quantification of C-type natriuretic peptide in brain areas of rodents.

C-type natriuretic peptide (CNP) is regarded as an endothelium-derived vasodilator and might therefore have an important role in controlling vascular tone and remodeling. Because CNP also is expressed in the brain, it is considered to be a neurotransmitter. The present study compares expression levels of CNP mRNA in distinct areas of the mouse brain with the expression pattern in the rat brain. A distinct expression of CNP was found in all investigated areas with the exception of the mouse striatum. In both rodents, high CNP expression was detected in the tegmentum.

Effect of ethanol drinking on the gene expression of opioid receptors, enkephalinase, and angiotensin-converting enzyme in two inbred mice strains.

There is convincing evidence that genetic factors contribute to the predisposition to alcoholism. In this respect, alcohol-preferring (like C57BL/6 mice) and alcohol-avoiding lines (like DBA/2 mice) of animals served as models in the search for neurobiological substrates of excessive ethanol consumption. One of the systems that is thought to be associated with the incidence of alcoholism is the endogenous opioid system. In the first experiment, basal mRNA levels of mu- and delta-opioid receptors, and of opioid-degrading enzymes enkephalinase (neutral endopeptidase 24.11; NEP) and angiotensin-converting enzyme (ACE) in the brain regions of C57BL/6 and DBA/2 mice did not reveal genetically determined differences in these parameters between the two strains. Furthermore, in the brain regions studied, the corresponding enzyme activities of NEP and ACE did not differ significantly between the lines of mice, except for a higher NEP activity in the striatum and olfactory bulb of DBA/2 mice (p < 0.01). In the second experiment, C57BL/6 and DBA/2 mice were offered a free choice between water and 10% ethanol solution for 4 weeks and were killed thereafter; from another group, ethanol was removed for 3 days and from a third group ethanol was removed for 3 weeks before killing. In the striatum, a highly significant increase in the ACE mRNA amount was detected after 3 weeks of removal of ethanol in C57BL/6 mice, whereas in DBA/2 mice the delta-opioid receptor mRNA level was increased at this time when compared with the corresponding ethanol treatment group. The most striking changes were seen in the hypothalamus, where mu-opioid receptor, ACE, and NEP mRNA amounts markedly decreased after ethanol treatment in both strains. Thus, chronic ethanol intake caused significant changes in the gene expression of distinct components of the endogenous opioid system. These findings further underline an involvement of the opioid system in the effects of ethanol.

Stimulation of endothelial angiotensin-converting enzyme by morphine via non-opioid receptor mediated processes.

In this study, we examined the influence of morphine and naloxone on the enzymatic activity of different ecto-peptidases located on the surface of endothelial cells. Morphine increased in a concentration dependent manner the degradation of Leu-enkephalin in cultivated bovine aortic endothelial cells. Naloxone, a morphine antagonist, did not prevent this effect, but caused it as well. The enhanced Leu-enkephalin degradation was due to an increase in the activity of angiotensin-converting enzyme (ACE), whereas the activity of other ecto-peptidases (aminopeptidase N and neutral endopeptidase) was not influenced. Despite a high non-specific binding of [3H]-morphine, no specific opioid receptor binding on the endothelial cells could be detected. Autoradiographic investigations with native, cryostat-sectioned cells demonstrated that [3H]-morphine was nearly exclusively located within the nuclei. The present results suggests that the morphine effect concerning ACE activity is not mediated via opioid receptors but presumably by interactions within the cell nucleus.

Inhibition of corticotropin releasing factor (CRF)-induced adrenocorticotropin (ACTH) secretion in pituitary corticotropic cells by substance P.

Substance P (SP) is one of the three distinct peptides of tachykinin system which possess a common spectrum of biological activities including a modulation of stress. It is assumed that the anterior pituitary is one possible target of SP in attenuation the stress response. Therefore the interaction between the hypothalamic stress hormone corticotropin releasing factor (CRF) and SP was investigated in AtT20/D16v-cells, a cellular model derived from a pituitary tumor. CRF stimulates the release of ACTH from AtT20/D16v cells in a concentration dependent manner. SP (1 microM) was able to abolish the CRF (100 nM)-induced ACTH release. In the same way SP inhibited the CRF-induced accumulation of cyclic adenosine monophosphate (cAMP), indicating that SP influenced the signal transduction pathway of CRF receptor activation. Thus, a direct inhibition of the CRF-mediated stress response by SP at the level of anterior pituitary seems to be likely.

Gene expression and activity of specific opioid-degrading enzymes in different brain regions of the AA and ANA lines of rats.

There is increasing evidence that alcoholism runs in families suggesting that genetic factors may play a role. In support of this hypothesis, the alcohol-preferring (AA) and the alcohol-avoiding (ANA) rat lines have been developed through selective outbreeding. Numerous studies indicate that the endogenous opioid system may be involved in controlling ethanol consumption. Changes in opioid peptides and opioid receptors have been described after ethanol intake. But, the influence of ethanol on peptidolytic degradation of opioid peptides has been largely ignored, although the peptidase-mediated metabolism of neuropeptides is known as an important regulatory site of peptidergic transmission. Neutral endopeptidase 24.11 (NEP) and angiotensin-converting enzyme (ACE) degrade neuropeptides, including enkephalin and are expressed in the brain. Furthermore, a good correspondence between the regional distribution of NEP and opioid receptors in rat brain has already been reported pointing to a possible role of NEP in regulating opioid peptides. For both enzymes studied, the gene expression pattern was found to be in good agreement with the corresponding enzyme activities in the brain regions investigated, showing the highest levels for both specific mRNAs and enzyme activities in the striatum. Differences in both measured parameters were detected in distinct brain regions of AA and ANA rats. Furthermore, in some brain regions discrepancies between ACE and NEP mRNA levels and the corresponding enzyme activities were observed. For example, in olfactory bulb and striatum such discrepancies were found for both enzymes studied. In tegmentum/colliculi a higher NEP gene expression in AA rats was associated with a higher NEP enzyme activity compared to the amounts found in ANA rats.

Ultrastructural localization of angiotensin-converting enzyme in ejaculated human spermatozoa.

Angiotensin-converting enzyme (ACE) is known to be released from human spermatozoa during capacitation. However, it has not yet been localized ultrastructurally in ejaculated sperm cells. Therefore, the purpose of the present study was to demonstrate the location of ACE by means of immunoelectron microscopy and direct immunofluorescence. In addition, ACE activity of spermatozoa was correlated with standard semen parameters. The activity of angiotensin-converting enzyme was measured in spermatozoa from 115 donors and patients attending the andrological outpatient department. Progressive motility was negatively correlated with sperm ACE activity (Spearman rank correlation r=-0.364, P < 0.0001), whereas no statistically significant correlations with sperm concentration, total motility and morphology were observed. Immunoelectron microscopy demonstrated that ACE is mainly located at the plasma membrane of the acrosomal region, equatorial segment, postacrosomal region and midpiece. In contrast, only weak ACE-like immunoreactivity was found at the flagellum. In cases of cells with missing plasma membranes ACE seems also to be located at the surface of the outer acrosomal membrane. By means of immunohistochemical methods, different patterns of ACE-like immunofluorescence were observed: (i) fluorescence of the acrosome or the entire sperm head, midpiece and flagellum; (ii) fluorescence of the postacrosomal region, midpiece and flagellum; (iii) bright fluorescence of the equatorial segment with less intensive labelling of the postacrosomal region and flagellum. Induction of the acrosome reaction by calcium ionophore A23187 resulted in an increase of spermatozoa with weak acrosomal fluorescence, indicating loss of the plasma membrane.

Screening of selected basidiomycetes for inhibitory activity on neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE).

Aqueous extracts of 27 basidiomycetes were investigated for their ability to inhibit the activity of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP). The extracts of 5 fungi inhibited both, ACE and NEP activity, another 18 extracts showed inhibition of the NEP activity whereas only 1 basidiomycete inhibited the ACE activity exclusively. The IC50 values for the ACE inhibition are rather high (between 200 and 1500 micrograms/ml) in comparison to the IC50 of the NEP inhibition (between 40 and 2000 micrograms/ml). These results indicate that the basidiomycetes investigated seem to have a higher potential for the inhibition of the activity of NEP than of ACE. In general, basidiomycetes are a new source for inhibitors of metalloendopeptidases. Resulting from the isolation and characterization of these compounds new leading structures are expectable.

Expression and characterization of the substance P (NK1) receptor in the rat pituitary and AtT20 mouse pituitary tumor cells.

Although substance P is known to take part in the regulation of the anterior pituitary, no conclusive evidence for the expression of the tachykinin NK1 receptor has been found yet in the pituitary or pituitary derived cells. With the reverse transcription-polymerase chain reaction (RT-PCR) method we could detect the low abundant transcripts of the NK1 receptor in the rat pituitary and in the AtT20 cell line (clone D16v). Furthermore, the functional expression of the NK1 receptor in AtT20 cells was confirmed by activation of the phosphatidylinositol-calcium second messenger system when the cells were treated with substance P. In addition, binding studies also indicated the functional expression of this receptor in AtT20 cells. Thus we provide the first evidence that the NK1 receptor is expressed in AtT20 cells and the rat pituitary.

The enzymatic degradation of bradykinin in semen of various species.

The degradation of bradykinin in semen and on washed sperm cells of various species (human, pig, cattle, sheep) is mainly controlled by two peptidases, the angiotensin-converting enzyme (ACE/kininase II; E.C. 3.4.15.1) and neutral metalloendopeptidase (NEP; E.C. 3.4.24.11). In addition, minor activities of kininase I (carboxypeptidase N/CPN; E.C. 3.4.17.3) were measured exclusively in human samples. Samples of the investigated species varied considerably in their ratios of the activities of bradykinin degrading peptidases. This should be considered in any approach aimed at maintaining the promoting effect of bradykinin on sperm motility by use of enzyme inhibitors.

Degradation of bradykinin in semen of ram and boar.

The pattern of bradykinin (BK; Arg1-Pro2-Pro3-Gly4-Phe5-Ser6-Pro7-Phe8-Arg9)-inact iva ting peptidases in semen of boar and ram was investigated. The degradation of BK in semen was completely abolished by the metalloprotease inhibitors EDTA and o-phenanthroline. Inhibitors of angiotensin-converting enzyme (ACE; EC 3.4.15.1) and phosphoramidon, an inhibitor of neutral metalloendopeptidase (NEP; EC 3.4.24.11), were only partially effective in preventing BK degradation in semen. An additive effect was seen with simultaneous inhibition of both enzymes, resulting in complete abolition of BK degradation. HPLC analysis demonstrated that exogenous BK in semen is cleaved at Gly4-Phe5, Phe5-Ser6 and Pro7-Phe8. These results indicate that NEP and ACE are the main peptidases responsible for rapid BK inactivation in semen. The involvement of other peptidases known to be responsible for BK cleavage in other tissues and body fluids, namely carboxypeptidase N (EC 3.4.12.7), post proline cleaving enzyme (EC 3.4.21.26) and aminopeptidase P (EC 3.4.11.9) was excluded. NEP and ACE were shown to be localized mainly in seminal plasma and to a lesser extent on sperm cells.

[Tyrosine splitting aminopeptidases on cultivated anterior hypophyseal and vascular endothelial cells]. / Tyrosin-abspaltende Aminopeptidasen an kultivierten Hypophysenvorderlappen- und Gefässendothelzellen.

Activities of aminopeptidases for a tyrosine peptide hydrolysis were characterized with Tyrosyl-7-amino-4-methyl-coumarin as substrate on in vitro cultivated anterior pituitary cells, respectively, on aortic endothelial cells. Furthermore the corresponding activities were measured in different fractions of the cells. The activities of the enzymes in soluble fractions of the cell homogenates are comparable with aminopeptidases of cytosolic compartments of other tissue samples. On the other hand remarkable differences exist between Km- and IC50-values of the membrane preparations of both cell types. Furthermore, the substrate degradation on intact cells by provable membrane bound ectoenzymes is identically for both cell types and this degradation is insensitive for amastatin. Our results are discussed with special respect for the importance of the degradation of biological active peptides with N-terminal tyrosine by aminopeptidases on their physiological targets.

Investigations on the influence of bradykinin upon the motility of ram spermatozoa.

The influence of bradykinin, a component of the kallikrein-kinin system, on the motility of ram spermatozoa was examined in vitro (photometric motility evaluation, penetration test in cervical mucus of sheep, estimation of the percentage of forward-moving spermatozoa in the thermal resistance test). Whereas the motility was found to be influenced by bradykinin the acrosomal status remained undisturbed by it. With fresh as well as with frozen semen, the drug mainly increased the motility of samples with a low initial motility. With frozen semen, the penetration test revealed greater motility rises at 22 degrees C than at 38 degrees C. The importance of the results in relation to the angiotensin-converting enzyme (kininase) as well as the motility evaluation capabilities of the methods used are discussed. There was, however, no positive drug effect after adding the drug in the course of cryopreservation prior to freezing semen in straws although bradykinin solutions frozen in liquid nitrogen maintained their effectiveness.