細懸浮微粒對肥胖與糖尿病大鼠之效應研究

Abstract

流行病學研究顯示，細懸浮微粒與心肺疾病的死亡及罹病有相關，特別是易感族群更容易受到影響。研究也指出糖尿病患者是微粒空氣污染心血管疾病的易感族群。然而細懸浮微粒與糖尿病之發生與其併發症的因果關係並不清楚，也缺乏毒理學之效應研究。為了回答這個問題，我們進行一系列細懸浮微粒暴露的動物實驗，來探討細懸浮微粒對糖尿病大鼠引發之毒性效應。我們首先建立了以高脂食物導致之肥胖大鼠模式。並使用Sprague–Dawley(SD)大鼠，以高脂食物加上單次靜脈注射低劑量(35 mg/kg)的streptozotocin(STZ)，以及高劑量(35 mg/kg)之STZ，分別建立第二型，與第一型糖尿病大鼠動物模式。我們也建立了細懸浮微粒動物暴露系統，進行糖尿病大鼠呼吸暴露。在急性暴露方面，我們以氣管灌注方式，將細懸浮微粒連續暴露肥胖大鼠，探討動物的胰島素阻抗與微粒暴露是否有關。在慢性暴露方面，我們進一步利用非濃縮大氣微粒，暴露健康SD大鼠與糖尿病大鼠3個月，探討細懸浮微粒是否造成心血管毒性與器官的損傷。以氣管灌注連續暴露細懸浮微粒後，我們發現肥胖大鼠的胰島素阻抗上升，而健康SD大鼠並沒有此效應。在亞慢性即時暴露方面，平均細微粒濃度大約13μg/m3，我們發現細懸浮微粒引發第二型糖尿病大鼠的Fibrinogen上升；第一型糖尿病大鼠的長期血糖值(HbA1c)上升；SD大鼠則有氧化壓力(8-OHdG)，發炎反應(IL-6)，與胰島素阻抗上升。組織病理學發現，細懸浮微粒造成在心肌發炎，腹主動脈血管壁增厚，以及腎臟之腎絲球、腎小管病變、以及腫瘤發生。糖尿病並未增強微粒效應，但可能加速腎病變與腫瘤發生。我們發現微粒暴露可造成胰島素阻抗的增加，此結果可以支持流行病學研究結果。我們也發現微粒可造成心血管毒性，與亞慢性病理組織變化，雖然沒有明顯的動脈粥狀硬化，但是有發現心肌發炎與主動脈變化，也支持流行病學對心臟血管疾病的發現。我們的研究也指出腎臟的病變與腫瘤發生，值得未來研究。另外，亞慢性暴露結果指出，在接近目前美國與世界衛生組織之細懸浮微粒法規濃度下，還可以觀察到微粒毒性與病理變化，跟流行病學顯示細懸浮微粒健康效應沒有閾值的觀察是一致的，未來值得進行慢性動物呼吸研究。

Epidemiological studies have shown associations between particulate air pollution and cardiovascular morbidity and mortality. Previous studies suggest that diabetes mellitus (DM) is a sub-population at risk for particulate matters (PM)-associated cardiovascular diseases (CVD). However, the biological plausibility for the relationship remains unclear. We conducted animal studies to determine if particle exposure altered glucose homeostasis and caused cardiovascular damage. First, we investigated the acute, and subacute effects of PM on insulin resistance (IR) in obese and healthy rats. Male Sprague-Dawley (SD) rats were fed with either a high fat diet (HFD) or normal chow diet (NCD). Both groups were then further assigned to receive PM10, PM2.5 or normal saline by intratracheal instillation (IT) once per week for 3 weeks. Homeostasis model assessment-insulin resistance (HOMA-IR) was used to assess IR. Second, to further understand the subchronic effects of ambient PM on IR and target organ damage, we constructed an inhalation system to expose animals to ambient submicron particles. Taipei Air Pollution Exposure System for Health Effects (TAPES), modified from individually ventilated caging (IVC) air handling system, was used for continuous, real-world, non-concentrated straight ambient PM2.5 (s-PM2.5) exposure study. DM rat model was developed after feeding with HFD, and streptozotocin injection. DM and SD rats were randomly assigned to s-PM2.5 or filtered air (FA) for 13-16 weeks in two consecutive winters in Taipei city. Glucose homeostasis was assessed by Hemoglobin A1c (HbA1c) and IR. Biomarkers of oxidative stress, systemic inflammation, endothelium dysfunction, and coagulation were measured. Organ damage was observed by histopathology. PM2.5 increased HOMA-IR after first IT and further increased HOMA-IR at the end of exposure. However, this increase was not observed in NCD rats and after PM10 IT exposure. Increased fibrinogen was also noted after repeated PM2.5 IT exposure in both HFD and NCD rats. The average concentration of s-PM2.5 in the exposure chamber of TAPES during the inhalation study period was 13.3μg/m3. HbA1c was significantly elevated after exposed to s-PM2.5 compared with exposure to FA (mean [SD], 7.4% [3.1%] vs. 5.7% [2.4%], p<.05, respectively) in DM rats. IR was significantly enhanced after exposed to s-PM2.5 compared with exposure to FA in SD rats (mean [SD], 8.1 [4.6] vs 3.9 [1.4] mmol/L*μU/ml, p<.05). Interleukin-6 (IL-6) and urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) were increased in SD rats and fibrinogen was increased in DM rats. S-PM2.5 caused focal myocarditis in the myocardium and increased aortic medial thickness. Morphometric analysis of the kidneys showed a significantly increased proportion of rats with advanced glomerulosclerosis, accentuation of tubular damage, and development of kidney tumors. We conclude that particulate air pollution, even at low concentrations close to current standard, may affect glucose homeostasis and lead to organ damage in susceptible population. Systematic inflammation, coagulation activation and IR may mediate these effects. This may potentially have implications for the policy of air pollution control and management.