Platelet phosphatidylcholine turnover in experimental hypertension

Antihypertensive effect and underlying mechanism of tripeptide NCW on spontaneously hypertensive rats using metabolomics analysis

Tripeptide NCW identified in our previous study displayed a strong ACE inhibitory activity, but whether it has any antihypertensive effect in vivo remains unknown. Thus, in this study, we aimed to investigate the protective effects of tripeptide NCW in spontaneously hypertensive rats (SHRs) and to further figure out the serum metabolic profiling variations due to its oral administration via UPLC-Q-TOF-MS/MS-based metabolomics analysis to clarify the underlying hypotensive mechanism. After three weeks of oral administration, the tripeptide NCW-treated group (NCW/SHR group, 80 mg per kg BW per d) showed significantly reduced systolic and diastolic blood pressure by 48.08 ± 3.84 mmHg and 48.92 ± 5.77 mmHg, respectively. Additionally, a total of 25 blood pressure-related metabolites were identified as being significantly changed in SHRs given tripeptide NCW after three weeks. These 25 metabolites might be biomarkers that indicated that the tripeptide NCW exhibits antihypertensive activity via regulating bile acid metabolism, lipid metabolism, amino acid metabolism, purinergic signaling, pantothenate and CoA biosynthesis, and the citrate cycle. Collectively, tripeptide NCW has a protective effect on SHRs associated with serum metabolite abnormalities.

Liver oleic acid biogenesis is impaired during the prehypertensive period in the spontaneously hypertensive rat

In the present study, we have investigated the liver microsomal stearic acid delta9 desaturation, and the fatty acid composition of liver microsomal total lipids in 10- and 30-day-old spontaneously hypertensive rats (SHRs), compared to the normotensive Wistar Kyoto (WKY) control rats. So as to avoid any influence related to the diet, the composition of the milk being different in SHR and WKY strains, the pups were suckled by adoptive normotensive female Wistar. After weaning, the 30-day-old rats were fed a standard commercial diet and then killed. Our results show lower liver microsomal delta9 desaturase activities in the 10- and 30-day-old SHR versus the WKY of the same age. The fatty acid composition of the SHR liver microsomal total lipids are not in agreement with the changes in the delta9 desaturase activities at the two studied ages. This phenomenon depends not only on desaturation/elongation but also on other interacting aspects of lipid metabolism including oxidation, substrate availability, acyl exchange, and eicosanoid synthesis, as well as hormonal status.

Composition en acides gras des hémisphères cérébraux de rats spontanément hypertendus allaités par des femelles Wistar

Total lipid fatty acid composition was investigated in brain hemispheres of male Spontaneously Hypertensive Rats (SHR), compared with normotensive Wistar Kyoto rats (WKY) used as controls. Both strains were suckled by adoptive Wistar mothers, and then fed a standard diet after weaning. No difference was observed between the two hemispheres of WKY killed either at 10 or 30 days. In SHR killed at 10 days, the two hemispheres showed differences, SHR left hemispheres exhibiting greater fatty acid composition changes than those of WKY, phenomenon that toned down at 30 days. Hence, SHR pups showed a different total lipid fatty acid composition of their brain hemispheres when compared with their WKY controls, though the two strains received the same diet. Genetically programmed hypertension might be, directly or not, involved in these changes.

Desaturase activities are depleted before and after weaning in liver microsomes of spontaneously hypertensive rats

In the present study, we have investigated the microsomal linoleic acid desaturation steps into arachidonic acid in 10- and 30-day-old spontaneously hypertensive rats (SHR), as compared to their normotensive control rats, Wistar Kyoto (WKY). Suckled by adoptive Wistar normotensive female, the SHR and WKY were fed the same diet. Our results show lower Delta 6 and Delta 5 desaturase activities (the limiting steps in the bioconversion of linoleic acid into arachidonic acid) in the young SHR, as compared to the WKY normotensive rats. The fatty acid composition of liver microsomal total lipids evidences a higher proportion of linoleic acid in SHR than in WKY, in agreement with the partially depleted desaturase activities. Such a loss of desaturase activities may be under the control of hormones involved in the regulation of SHR blood pressure.

Age-related depletion of linoleic acid desaturation in liver microsomes from young spontaneously hypertensive rats

The present study was designed to investigate the microsomal interconversion of linoleic acid (LA) into arachidonic acid (AA) in young spontaneously hypertensive rats (SHR), in relation to the pathogenesis of hypertension. Our results show lower delta 6 and delta 5 desaturase activities (the limiting steps in the bioconversion of LA into AA) in young SHR, as compared to Wistar Kyoto normotensive rats. This impairment of desaturase activities is raised when the blood pressure increases and is related to the age of animals. The fatty acid composition of liver lipids shows a lower proportion of AA and a higher proportion of LA in SHR than in normotensive rats, confirming the depletion of the enzymatic system studied. Such a loss of desaturase activity may be under the control of hormones involved in the regulation of SHR blood pressure.

Evidence for phosphatidylcholine hydrolysis by phospholipase C in rat platelets

Production of [3H]1,2-dipalmitoylglycerol ([3H]DAG) from 1-palmitoyl-2-[9,10-3H]palmitoyl-sn-glycero-3-phosphocholine and [3H]phosphorylcholine from 1,2-dipalmitoyl-sn-glycero-3-[Me-3H]phosphocholine was studied using sonicated rat platelets. The formation of [3H]DAG and [3H]phosphorylcholine occurred at a comparable rate. [3H]Phosphorylcholine formation was dependent on the concentration of the substrate, platelet sonicates and calcium in the incubation medium. The [3H]phosphorylcholine formation increased in presence of 0.01% deoxycholate and 0.01% Triton X-100. The phosphatidylcholine-phospholipase C (PC-PLC) in the platelet sonicates was recovered in both the supernatant and particulate fractions obtained after ultracentrifugation at 105,000 x g for 1 h. The PC-PLC activity in both fractions was inhibited by 2 mM EDTA. In the presence of 0.01% deoxycholate and 0.01% Triton X-100 the activity in the particulate fraction increased compared to the activity in the supernatant, which was inhibited by 0.01% Triton X-100. The pH optima for PC-PLC in both fractions was between pH 7.2 and 7.6. PC-PLC activity was also found in rabbit and human platelet sonicates, but the activity was significantly lower than in rat platelet sonicates. There was no evidence to suggest presence of phosphatidylcholine-specific phospholipase D activity in rat sonicated platelets. This data, therefore, provides direct evidence for the presence of PC-PLC activity in rat platelets.

Protein kinase C and cell proliferation in spontaneously hypertensive rats

Cultured aortic fibroblasts from spontaneously hypertensive rats (SHR) exhibit increased proliferation rate compared with cells from normotensive Wistar Kyoto (WKY) rats. The present study was designed to investigate whether this growth abnormality could be accounted for by alteration in protein kinase C (PKC). The enzyme activation by 12-O-tetradecanoyl phorbol 13-acetate (TPA) promoted 3H-thymidine incorporation which was higher in SHR-derived fibroblasts compared with WKY-derived cells. Likewise, 3H-phorbol 12,13-dibutyrate (PDBu) binding to intact cells was markedly increased in SHR-derived fibroblasts. These findings suggest a difference in PKC activity between the two cell types. In both cell types, serum-induced 3H-thymidine incorporation was enhanced by PKC down-regulation, which was obtained by prolonged treatment of cells with high dose of TPA, whereas it was inhibited in a dose-dependent manner by activation of the enzyme. The changes in serum-induced 3H-thymidine incorporation elicited either by activation or desensitization of PKC, did not differ between SHR and WKY fibroblasts. Our results indicate therefore i) that in the presence of serum PKC exerts an antiproliferative effect in rat aortic fibroblasts and ii) that the increase in PKC activity and in sensitivity to TPA exhibited by SHR-derived fibroblasts, is not involved in the increased proliferation rate displayed by SHR-derived fibroblasts in serum-containing medium.

Variation of choline-substituted lipid metabolism in doxorubicin-resistant leukemia cells

In adriamycin-resistant murine (FLC) and human (K562) leukemia cells, phosphatidylcholine increases and phosphatidylethanolamine decreases compared to adriamycin-sensitive lines. This change is due to an increase in phosphatidylethanolamine methylation. The choline pathway of phosphatidylcholine biosynthesis is also disturbed in resistant cells with a blocking step of CDP-phosphocholine transferase and a decrease in sphingomyelinase activity. These changes in phospholipid metabolism are suggested to be responsible for the changes in membrane fluidity reported previously (Tapiero et al, 1986) for resistant cells.

Rise and fall of agonist-evoked platelet Ca2+ in hypertensive rats

We previously reported an enhanced peak response of intracellular free Ca2+ to thrombin in platelets of spontaneously hypertensive rats in comparison with normotensive Wistar-Kyoto rats. In the present study, we compared the platelet intracellular Ca2+ response to the receptor-linked agonist thrombin with the response to the Ca2+ ionophore ionomycin. Basal intracellular Ca2+ was higher in hypertensive platelets as was leakage of fura-2. We confirmed the previous finding that the thrombin-induced intracellular Ca2+ peak is greater in platelets of hypertensive rats and noted that the rate of recovery from peak intracellular Ca2+ is significantly greater in this model. In contrast, the peak platelet intracellular Ca2+ response to ionomycin (50 nM and 5 microM) was not different between the two strains, and the rate of recovery from the peak response was only slightly depressed in hypertensive rats after the low dose of ionomycin. Internal Ca2+ discharge capacity, assessed by the intracellular Ca2+ response to a maximal dose of ionomycin in Ca(2+)-free medium, was not different between platelets of the two strains. Thus, activated platelet intracellular Ca2+ is not altered in the hypertensive rat when the nonphysiological ionophore ionomycin is used as agonist. However, a heightened intracellular Ca2+ response is observed when the receptor-mediated agonist thrombin is used. These results are consistent with the hypothesis that differences in receptor-linked second messenger pathways underlie the altered intracellular Ca2+ response in platelets of genetically hypertensive rats and may contribute to differences both in the mobilization of Ca2+ and in its fall.

Lipid bilayer in genetic hypertension

Membrane microviscosity, phospholipid composition, and turnover were measured in cultured vascular smooth muscle cells isolated from mesenteric arteries of stroke-prone spontaneously hypertensive and age-matched, normotensive Wistar-Kyoto rats. Membrane microviscosity, measured with fluorescence polarization, revealed greater microviscosity (lower fluidity) of the membranes isolated from smooth muscle cells from hypertensive as compared with those isolated from normotensive rats (p less than 0.01). Preincubation of membranes from hypertensive rats with 5 mM calcium reduced membrane microviscosity in "core" and in "surface" regions of the bilayer toward values observed in Wistar-Kyoto rats. Phospholipid composition did not differ between intact aortas and cultured mesenteric cells or between those tissues obtained from normotensive and from hypertensive rats. The total lipid-associated radioactivity was significantly lower in cells from stroke-prone spontaneously hypertensive rats than in those from Wistar-Kyoto controls (p less than 0.01). Phosphatidylcholine incorporated 70% and phosphatidylinositol 16% of total lipid-associated radioactivity, with no difference between cells from hypertensive and normotensive animals. Turnover of phosphatidylethanolamine was greater in cells from Wistar-Kyoto rats (p = 0.02), whereas turnover of phosphatidylserine was greater in cells from stroke-prone spontaneously hypertensive rats (p = 0.04). The greater microviscosity of the lipid bilayer in hypertension is a generalized defect of the matrix in which the transport proteins function. We hypothesize that this defect is responsible for the multiple abnormalities of membrane transport systems that have been described in genetic hypertension.

Pathogenesis of the essential hypertensions

The pathogenesis of essential hypertension (EH) is reviewed with a special focus on the development phase or the pre-hypertensive period. Three animal models are presented: the spontaneously hypertensive rat, the Dahl's salt-sensitive rat, and the Milan hypertensive rat. Some of the findings in animal models have inspired new fields and technical approaches for studying EH in man. From the original idea of Page, a new mosaic of various etiological parameters serves as a basis for reviewing the multiple facets of EH in man. One must conclude that EH is heterogeneous disease and most likely every single hypertensive patient belongs to a subgroup of the whole population of hypertensives.

Many membrane abnormalities in hypertension result from one primary defect

Evidence has been presented that: 1.) Changes in lipid bilayer alter the function of integral membrane proteins. 2.) There is less calcium bound to the plasma membrane in hypertension. 3.) Structural and functional abnormalities of the lipid bilayer have been reported in genetic hypertension. We hypothesize that multiple abnormalities of membrane transport systems in hypertension are secondary to an inherent abnormality of the lipid bilayer in which these transport proteins reside.