Dietary fatty acid composition affects aminopeptidase activities in the testes of mice

The Type of Fat in the Diet Influences Regulatory Aminopeptidases of the Renin-Angiotensin System and Stress in the Hypothalamic-Pituitary-Adrenal Axis in Adult Wistar Rats

(1) Background: Prolonged feeding with a high-fat diet (HFD) acts as a stressor by activating the functions of the hypothalamic-pituitary-adrenal gland (HPA) stress axis, accompanied of hypertension by inducing the renin-angiotensin-aldosterone system. Angiotensinases enzymes are regulatory aminopeptidases of angiotensin metabolism, which together with the dipeptidyl peptidase IV (DPP-IV), pyroglutamyl- and tyrosyl-aminopeptidase (pGluAP, TyrAP), participate in cognitive, stress, metabolic and cardiovascular functions. These functions appear to be modulated by the type of fat used in the diet. (2) Methods: To analyze a possible coordinated response of aminopeptidases, their activities were simultaneously determined in the hypothalamus, adenohypophysis and adrenal gland of adult male rats fed diets enriched with monounsaturated (standard diet (S diet) supplemented with 20% virgin olive oil; VOO diet) or saturated fatty acids (diet S supplemented with 20% butter and 0.1% cholesterol; Bch diet). Aminopeptidase activities were measured by fluorimetry using 2-Naphthylamine as substrates. (3) Results: the hypothalamus did not show differences in any of the experimental diets. In the pituitary, the Bch diet stimulated the renin-angiotensin system (RAS) by increasing certain angiotensinase activities (alanyl-, arginyl- and cystinyl-aminopeptidase) with respect to the S and VOO diets. DPP-IV activity was increased with the Bch diet, and TyrAP activity decrease with the VOO diet, having both a crucial role on stress and eating behavior. In the adrenal gland, both HFDs showed an increase in angiotensinase aspartyl-aminopeptidase. The interrelation of angiotensinases activities in the tissues were depending on the type of diet. In addition, correlations were shown between angiotensinases and aminopeptidases that regulate stress and eating behavior. (4) Conclusions: Taken together, these results support that the source of fat in the diet affects several peptidases activities in the HPA axis, which could be related to alterations in RAS, stress and feeding behavior.

High-Fat Diets Modify the Proteolytic Activities of Dipeptidyl-Peptidase IV and the Regulatory Enzymes of the Renin-Angiotensin System in Cardiovascular Tissues of Adult Wistar Rats

(1) Background: The replacement of diets high in saturated fat (SAFA) with monounsaturated fatty acids (MUFA) is associated with better cardiovascular function and is related to the modulation of the activity of the local renin–angiotensin system (RAS) and the collagenase activity of dipeptidyl peptidase IV (DPP-IV). The objective of the work was to verify the capacity of different types of dietary fat on the regulatory activities of RAS and DPP-IV. (2) Methods: Male Wistar rats were fed for 24 weeks with three different diets: the standard diet (S), the standard diet supplemented with virgin olive oil (20%) (VOO), or with butter (20%) plus cholesterol (0.1%) (Bch). The proteolytic activities were determined by fluorometric methods in the soluble (sol) and membrane-bound (mb) fractions of the left ventricle and atrium, aorta, and plasma samples. (3) Results: With the VOO diet, angiotensinase values were significantly lower than with the Bch diet in the aorta (GluAP and ArgAP (mb)), ventricle (ArgAP (mb)) and atrium (CysAP (sol)). Significant decreases in DPP-IV (mb) activity occurred with the Bch diet in the atrium and aorta. The VOO diet significantly reduced the activity of the cardiac damage marker LeuAP (mb) in the ventricle and aorta, except for LeuAP (sol) in the ventricle, which was reduced with the Bch diet. (4) Conclusions: The introduction into the diet of a source rich in MUFA would have a beneficial cardiovascular effect on RAS homeostasis and cardiovascular functional stability.

Effects of Virgin Olive Oil on Blood Pressure and Renal Aminopeptidase Activities in Male Wistar Rats

High saturated fat diets have been associated with the development of obesity and hypertension, along with other pathologies related to the metabolic syndrome. In contrast, the Mediterranean diet, characterized by its high content of monounsaturated fatty acids, has been proposed as a dietary factor capable of positively regulating cardiovascular function. These effects have been linked to changes in the local renal renin angiotensin system (RAS) and the activity of the sympathetic nervous system. The main goal of this study was to analyze the role of two dietary fat sources on aminopeptidases activities involved in local kidney RAS. Male Wistar rats (six months old) were fed during 24 weeks with three different diets: the standard diet (S), the standard diet supplemented with virgin olive oil (20%) (VOO), or the standard diet enriched with butter (20%) plus cholesterol (0.1%) (Bch). Kidney samples were separated in medulla and cortex for aminopeptidase activities (AP) assay. Urine samples were collected for routine analysis by chemical tests. Aminopeptidase activities were determined by fluorometric methods in soluble (sol) and membrane-bound (mb) fractions of renal tissue, using arylamide derivatives as substrates. After the experimental period, the systolic blood pressure (SBP) values were similar in standard and VOO animals, and significantly lower than in the Bch group. At the same time, a significant increase in GluAP and IRAP activities were found in renal medulla of Bch animals. However, in VOO group the increase of GluAP activity in renal medulla was lower, while AspAP activity decreased in the renal cortex. Furthermore, the VOO diet also affected other aminopeptidase activities, such as TyrAP and pGluAP, related to the regulation of the sympathetic nervous system and the metabolic rate. These results support the beneficial effect of VOO in the regulation of SBP through changes in local AP activities of the kidney.

The Role of High Fat Diets and Liver Peptidase Activity in the Development of Obesity and Insulin Resistance in Wistar Rats

High-fat diets (HFD) have been widely associated with an increased risk of metabolic disorders and overweight. However, a high intake of sources that are rich in monounsaturated fatty acids has been suggested as a dietary agent that is able to positively influence energy metabolism and vascular function. The main objective of this study was to analyze the role of dietary fats on hepatic peptidases activities and metabolic disorders. Three diets: standard (S), HFD supplemented with virgin olive oil (VOO), and HFD supplemented with butter plus cholesterol (Bch), were administered over six months to male Wistar rats. Plasma and liver samples were collected for clinical biochemistry and aminopeptidase activities (AP) analysis. The expression of inducible nitric oxide synthase (iNOS) was also determined by Western blot in liver samples. The diet supplement with VOO did not induce obesity, in contrast to the Bch group. Though the VOO diet increased the time that was needed to return to the basal levels of plasma glucose, the fasting insulin/glucose ratio and HOMA2-%B index (a homeostasis model index of insulin secretion and valuation of β-cell usefulness (% β-cell secretion)) were improved. An increase of hepatic membrane-bound dipeptidyl-peptidase 4 (DPP4) activity was found only in VOO rats, even if no differences in fasting plasma glucagon-like peptide 1 (GLP-1) were obtained. Both HFDs induced changes in hepatic pyroglutamyl-AP in the soluble fraction, but only the Bch diet increased the soluble tyrosyl-AP. Angiotensinase activities that are implicated in the metabolism of angiotensin II (AngII) to AngIV increased in the VOO diet, which was in agreement with the higher activity of insulin-regulated-AP (IRAP) in this group. Otherwise, the diet that was enriched with butter increased soluble gamma-glutamyl transferase (GGT) and Leucyl-AP, iNOS expression in the liver, and plasma NO. In summary, VOO increased the hepatic activity of AP that were related to glucose metabolism (DPP4, angiotensinases, and IRAP). However, the Bch diet increased activities that are implicated in the control of food intake (Tyrosine-AP), the index of hepatic damage (Leucine-AP and GGT), and the expression of hepatic iNOS and plasma NO. Taken together, these results support that the source of fat in the diet affects several peptidases activities in the liver, which could be related to alterations in feeding behavior and glucose metabolism.

Influence of a Virgin Olive Oil versus Butter Plus Cholesterol-Enriched Diet on Testicular Enzymatic Activities in Adult Male Rats

The aim of the present work was to improve our knowledge on the mechanisms underlying the beneficial or deleterious effects on testicular function of the so-called Mediterranean and Western diet by analyzing glutamyl aminopeptidase (GluAP), gamma glutamyl transpeptidase (GGT) and dipeptidyl peptidase IV (DPP IV) activities in testis, as enzymes involved in testicular function. Male Wistar rats (6 months old) were fed for 24 weeks with three different diets: standard (S), an S diet supplemented with virgin-olive-oil (20%) (VOO), or a S diet enriched with butter (20%) plus cholesterol (0.1%) (Bch). At the end of the experimental period, plasma lipid profiled (total triglycerides, total cholesterol and cholesterol fractions (HDL, LDL and VDL)) were measured. Enzymatic activities were determined by fluorimetric methods in soluble (sol) and membrane-bound (mb) fractions of testicular tissue using arylamide derivatives as substrates. Results indicated an increase in plasmatic triglycerides, total cholesterol, LDL and VLDL in Bch. A significant increase of mb GluAP and GGT activities was also found in this diet in comparison with the other two diets. Furthermore, significant and positive correlations were established between these activities and plasma triglycerides and/or total cholesterol. These results support a role for testicular GluAP and GGT activities in the effects of saturated fat (Western diet) on testicular functions. In contrast, VOO increased sol DPP IV activity in comparison with the other two diets, which support a role for this activity in the effects of monounsaturated fat (Mediterranean diet) on testicular function. The present results strongly support the influence of fatty acids and cholesterol on testicular GluAP and GGT activities and also provide support that the reported beneficial influence of the Mediterranean diet in male fertility may be mediated in part by an increase of testicular sol DPP IV activity.

Role of central and peripheral aminopeptidase activities in the control of blood pressure: a working hypothesis

Although there is a large body of knowledge on protein synthesis, the available data on protein catabolism, although quite substantial, are still inadequate. This is due to the marked differences in the activity of proteolytic enzymes, compounded by different substrate specificities and multiple environmental factors. Understanding enzyme behavior under physiological and pathological conditions requires the identification of specific proteolytic activities, such as aminopeptidases, as able to degrade certain peptidergic hormones or neuropeptides. Another requirement is the isolation, purification and characterization of the enzymes involved. In addition, systematic studies are needed to determine each enzyme's subcellular location, tissue distribution, and the influence of environmental factors such as diurnal rhythm, age, gender, diet, cholesterol, or steroids. Central and peripheral aminopeptidases may play a role in the control of blood pressure by coordinating the effect of the different peptides of the renin-angiotensin system cascade, acting through the AT(1), AT(2), and AT(4) receptors. Our review of the available data suggests the hypothesis that cholesterol or steroids, particularly testosterone, significantly influence aminopeptidase activities, their substrate availability and consequently their functions. These observations may have relevant clinical implications for a better understanding of the pathophysiology of cardiovascular diseases, and thus for their treatment with aminopeptidase inhibitors.