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published_or_final_version / Medicine / Doctoral / Doctor of Philosophy

[Truncated abstract] Arachidonic acid is oxidised in vivo by non-enzymatic (free radical) or enzymatic pathways (cyclooxygenase, lipoxygenase, and cytochrome P450) to form a range of biologically active eicosanoids. Specifically, arachidonic acid is metabolised by cytochrome P450 -hydroxylase to produce vasoactive 20-hydroxyeicosatetraenoic acid (20-HETE), and by 5-lipoxygenase to produce proinflammatory leukotriene B4 (LTB4), which can further be metabolised by -hydroxylase to from 20-OH-LTB4 and 20-COOH-LTB4. F2-Isoprostanes (F2-IsoPs) are produced through free radical attack on arachidonic acid and have been recognised as the most reliable markers of lipid peroxidation in vivo. The metabolic syndrome (MetS) is characterised by abdominal obesity, hypertension, insulin resistance, glucose intolerance, and dyslipidemia. It is associated with low-grade inflammation and oxidative stress and an increased risk of developing cardiovascular diseases. Dietary weight loss is strongly recommended for the management of the MetS and can potentially minimise the risk of cardiovascular diseases and diabetes in individuals with the MetS. Little is known regarding the role of these arachidonic acid metabolites in the MetS and the effect of weight loss on their metabolism. Chapter three comprised of three in vitro studies aimed to examine 20-HETE synthesis in human blood cells. 20-HETE acts as a second messenger for vasoconstrictor actions of angiotensin II (Ang II) and endothelin-1 (ET-1) in renal and mesenteric beds. Human neutrophils and platelets are integral to the inflammatory process. ... Production of LTB4 and 20-OH-LTB4 was significantly lower compared with controls (P<0.005) and remained so after adjustment for neutrophil count (P<0.05).The weight loss intervention resulted in a 4.6kg reduction in body weight and a 6.6cm decrease in waist circumference and a significant increase in LTB4 and 20-OH- LTB4 in the weight loss group. Chapter Five continued to investigate the role of other arachidonic acid metabolites, 20-HETE and F2-IsoPs in the MetS and the effect of weight loss. In the case-control study (Human study 1), plasma and urinary 20-HETE and F2-IsoPs were significantly elevated in the MetS group, but no significant difference was found in stimulated-neutrophil 20-HETE. A significant gender x group interaction was observed in that women with the MetS had higher urinary 20-HETE and F2-IsoPs compared to controls (P<0.0001). In a randomised controlled trial (Human study 2), relative to the weight- maintenance group, a 4.6 kg loss in weight resulted in a 2 mmHg fall in blood pressure but did not alter the production of 20-HETE or F2-IsoPs. No significant differences were shown in 20-HETE released from stimulated-neutrophils before and after weight loss. 20-HETE and oxidative stress may be important mediators of cardiovascular disease risk in the MetS. Although a 4% reduction in body weight reduced BP, there were no changes in plasma or urinary 20-HETE or F2-IsoPs. In summary, in vitro studies show that human neutrophils and platelets can produce 20-HETE in response to Ang II and ET-1, and human studies demonstrate that the presence of MetS has a significant impact on arachidonic acid metabolism and effective weight loss can restore leukocyte synthesis of LTB4.

<p>The human cytochrome P450 (CYP) family of monooxygenases is important for metabolism of drugs and endogenous compounds, e.g., vitamin A and D, cholesterol, steroids, fatty acids, and eicosanoids. This thesis describes the tissue distribution, catalytic properties, and possible function of CYP4F8 and CYP4F12. To this respect, methods for immunohistological analysis, and real-time PCR for analysis of their transcripts, were developed.</p><p>CYP4F8 was originally cloned from human seminal vesicles and proposed to catalyze 19-hydroxylation of prostaglandin H₂(PGH₂). This notion could now be supported, as cyclooxygenase-2, CYP4F8, and microsomal prostaglandin E synthase-1 were found to be co-localized in the epithelial linings of seminal vesicles. The three enzymes were also co-localized in the suprabasal layers of epidermis, suggesting a similar function of CYP4F8 in skin. Real-time PCR showed that CYP4F8 mRNA was more than 10-fold increased in psoriatic lesions compared to non-lesional skin. CYP4F8 immunoreactivity was also found in kidney cortex, transitional epithelium, corneal epithelium, and retina. Although transcripts of all three enzymes were detectable in retina, no co-localization was found. Pro inflammatory stimuli were found to increase CYP4F8 mRNA expression in cultured epidermal and corneal keratinocytes. In these tissues CYP4F8 might oxidize fatty acids or other eicosanoids than PGH₂.</p><p>CYP4F12 was originally cloned from the liver and small intestine, and found to oxidize arachidonic acid and two anti-histamines. Immunohistological studies showed that CYP4F12 immunoreactivity was present mainly in the gastrointestinal tract, e.g., stomach, ilium, and colon, but also in placenta. Although CYP4F8 and CYP4F12 have catalytic properties in common, there are important differences. CYP4F12 does not oxidize PGH₂, certain eicosanoids, and fatty acids. The prominent expression in the gut suggests that CYP4F12 might be involved in oxidation of drugs.</p>

The human cytochrome P450 (CYP) family of monooxygenases is important for metabolism of drugs and endogenous compounds, e.g., vitamin A and D, cholesterol, steroids, fatty acids, and eicosanoids. This thesis describes the tissue distribution, catalytic properties, and possible function of CYP4F8 and CYP4F12. To this respect, methods for immunohistological analysis, and real-time PCR for analysis of their transcripts, were developed. CYP4F8 was originally cloned from human seminal vesicles and proposed to catalyze 19-hydroxylation of prostaglandin H2 (PGH2). This notion could now be supported, as cyclooxygenase-2, CYP4F8, and microsomal prostaglandin E synthase-1 were found to be co-localized in the epithelial linings of seminal vesicles. The three enzymes were also co-localized in the suprabasal layers of epidermis, suggesting a similar function of CYP4F8 in skin. Real-time PCR showed that CYP4F8 mRNA was more than 10-fold increased in psoriatic lesions compared to non-lesional skin. CYP4F8 immunoreactivity was also found in kidney cortex, transitional epithelium, corneal epithelium, and retina. Although transcripts of all three enzymes were detectable in retina, no co-localization was found. Pro inflammatory stimuli were found to increase CYP4F8 mRNA expression in cultured epidermal and corneal keratinocytes. In these tissues CYP4F8 might oxidize fatty acids or other eicosanoids than PGH2. CYP4F12 was originally cloned from the liver and small intestine, and found to oxidize arachidonic acid and two anti-histamines. Immunohistological studies showed that CYP4F12 immunoreactivity was present mainly in the gastrointestinal tract, e.g., stomach, ilium, and colon, but also in placenta. Although CYP4F8 and CYP4F12 have catalytic properties in common, there are important differences. CYP4F12 does not oxidize PGH2, certain eicosanoids, and fatty acids. The prominent expression in the gut suggests that CYP4F12 might be involved in oxidation of drugs.

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