This study demonstrated that clinical use of MTX for treating rheumatoid arthritis is associated with elevated expressions of atheroprotective protein HY27 and ABCA1 in human PBMCs. This is the first in vivo evidence in humans that the commonly used low-dose MTX in rheumatoid arthritis might induce the mRNA expression of antiatherogenic reverse cholesterol transporter expression in humans. Via the induction of these proteins, low-dose MTX treatment has the potential to protect against dyslipidemia through facilitation of cholesterol outflow in patients on this medication.
In the present study, no significant differences in blood lipids were observed between MTX(+) and MTX(-) subjects, possibly attributed to low prevalence of dyslipidemia in the study subjects. Although no differences were observed in the blood lipid profiles, the potential impacts of MTX on cholesterol metabolism should not be overlooked. The majority of our subjects had relatively normal cholesterol intake, and their lipid indicators fell within the normal range of healthy humans. We suggest that the potential impacts of altered HY27 and ABCA1 might be compensated by relatively normal cholesterol intake in these subjects. It is plausible that the potential atheroprotective effects from HY27 and ABCA1 inductions occur only in those persons with elevated blood lipids. This postulation needs to be investigated further in animals or subjects with abnormal blood lipids in the future.
According to the latest 2005-2008 NAHSIT, the prevalence of hyperlipidemia, hypertriglyceridemia, elevated LDL-C, and low HDL-C in females at the same age group were 4.7%, 11.8%, 18.6%, and 2.9%, respectively . The prevalence of abnormal lipid profiles was determined by the standard for the threshold limit value of disease (TC ≥240 mg/dl, TG ≥200 mg/dl, HDL-C <35 mg/dl, LDL-C≥160 g/dl) . When the same standard was applied to subjects in the present study, less than 5% of our subjects had elevated TC (4%) or TG (2%), elevated LDL-C (2%) or low HDL-C (2%), indicating that the prevalence of abnormal blood lipid profile in these subjects was indeed lower than that of the general Taiwanese population of the same age. When we looked at the prevalence of marginal elevated blood lipid profiles using the normal range of healthy humans (mean TC <200 mg/dl; TG <150 mg/dl; HDL-C >40 mg/dl; LDL-C <130 g/dl), the prevalence of dyslipidemia in our subjects was also lower than that in the NAHSIT . Only 24.2% of our subjects had elevated TC, 6.1% had elevated TG, 5.1% had low HDL-C, and 12.1% had elevated LDL-C. Consistently, we found a lower prevalence of being overweight (24≤BMI <27 kg/m2) and obesity (≥27 kg/m2) in our study subjects (19% for being overweight and 16% for obesity) that was also lower than that of the general population at a similar age (39% for being overweight and 23% for obesity) in Taiwan .
The therapeutic strategies for dyslipidemia include a healthy diet with reduced intake of saturated fat and cholesterol. With regard to cholesterol intake, most of our subjects (79.6%) had a daily cholesterol intake below 300 mg (Table 4). In addition, only approximately one-fifth of these subjects had fat intake exceeding 30% of their total calories and, on average, 29% of the total energy came from fat. In the general population of the same age, the prevalence of high fat intake was up to 46.5%, and the energy from fats was 35% . The mean intake of saturated fat in our study subjects was also significantly lower than that of the population . We concluded that lower cholesterol and fat intake accounted for the relatively normal blood lipid profiles in these subjects.
In vitro MTX treatment was shown to increase HY27 mRNA expression  and reverse the COX2 inhibitor-induced downregulation of HY27 and ABCA1 in human THP-1 monocyte/macrophages . Despite no differences being observed in the blood lipid profiles between MTX(-) and MTX(+) subjects, we found that clinical use of low-dose MTX was associated with increased HY27 and ABCA1 mRNA in the PBMCs. These results implied that under certain conditions, clinical use of MTX might induce the gene expression of atheroprotective protein HY27 and ABCA1. This is the first in vivo evidence that the commonly used DMARD MTX may increase the expression of antiatherogenic reverse cholesterol transport protein in human PBMCs. However, the potential impacts of MTX induced HY27 and ABCA1 expressions might be compensated by relatively normal to low cholesterol intake in these subjects; and that the potential atheroprotective effects from HY27 and ABCA1 may only be present in those persons with pre-existing dyslipidemia. Whether MTX induced HY27 and ABCA1 expressions can protect against cardiovascular disease in patients with chronic inflammation through the facilitation of cholesterol export remains to be established. Further studies pertaining to the potential benefits of low-dose MTX in hypercholesterolemic subjects are warranted.