Increasing levels of dietary homocystine with carotid endarterectomy produced proportionate increases in plasma homocysteine and intimal hyperplasia

Purpose: The role that homocysteine may play in post-carotid endarterectomy (CEA) restenosis due to intimal hyperplasia is not well understood. This s tudy was designed to investigate the effects of different levels of dietary homocystine on: (1) plasma homocysteine; (2) post-CEA intimal hyperplasia; and (3) levels of the methyl donor S-adenosylmethionine (SAM) and its coun terpart S-adenosylhomocysteine (SAH) in the homocysteine pathway. Methods: Male rats were fed specialized diets for 2 weeks pre- and post-CEA. Groups included control (0 homocystine added, n = 9), 1.5 (1.5 g/kg homocysteine a dded, n = 10), 3.0 (3.0 g/kg homocystine added, n = 9), and 4.5 (4.5 g/kg h omocystine added, n = 11). The rats underwent a surgical carotid endarterec tomy. Endpoints included; plasma homocysteine, intimal hyperplasia, replica tive index using with a-SM actin and BrdU, hepatic SAM levels, SAH levels, and the hepatic activities of methylenetetrahydrofolate reductase (MTHFR) a nd cystathionine P-synthase (CBS). Results: Increasing dietary homocystine produced a proportionate increase in plasma homocysteine and an increase in intimal hyperplasia. Regression analysis of plasma homocysteine levels and intimal hyperplasia showed a significant correlation (r = 0.71, P = 0.003) . Plasma homocysteine levels above 15 muM were associated with significant increases in intimal hyperplasia above 6.5%, (P = 0.04). Elevation of plasm a homocysteine levels to moderate levels (5-25 muM) resulted in significant post-CEA intimal hyperplasia. Cellular analysis of the area of intimal hyp erplasia in all diet groups showed comparable amounts of cells positive for oc-SM actin. However, with increasing levels of dietary homocystine and pl asma homocysteine there was an increase in replicative index (P < 0.001) as determined by BrdU staining. Increasing dietary homocystine increased plas ma homocysteine and was followed by increases in the replicative index thus producing increased intimal hyperplasia and lumenal stenosis. In hepatic m easurements the 1.5 and 3.0 g/kg homocystine diets caused: increased liver activity of MTHFR (P = 0.03) and decreased hepatic levels of SAM, SAH and S AM/SAH ratios compared to controls. Homocystine treatment did not cause sig nificant alterations in CBS levels (P = 0.992). These studies also showed n o correlation of the MTHFR and CBS enzymes with plasma homocysteine levels or intimal hyperplasia. However, hepatic levels of SAM showed significant n egative correlations with plasma homocysteine (r = -0.58; P = 0.006) and wi th BrdU percentages of cellular proliferation (r = -0.69; P = 0.06). Conclu sion: The degree of post-CEA intimal hyperplasia in a rat model is directly related to the plasma level of homocysteine. The hyperplastic effects of h omocysteine may be mediated in part by a physiological insufficiency of met hyl donors as shown by decreases in SAM. Thus, increasing levels of plasma homocysteine enhanced and accelerated the smooth Muscle cell response after CEA which led to increased intimal hyperplasia and lumenal stenosis. (C) 2 001 Elsevier Science Ireland Ltd. All rights reserved.