MTHFR and hyperhomocysteinemia: More recent studies reported impaired endothelial function and a decrease in eNOS dimer/monomer ratio by CRP treatment of rats [137], in old rats with improvement by arginase inhibition [138], in mild hyperhomocysteinemia in mice with heterozygous gene deletion of methylenetetrahydrofolate reductase (Mthfr+/−) [139], and in 8-nitro-cGMP treated mice [140].