Early kidney damage induced by subchronic exposure to PM2.5 in rats

Abstract

Background: Particulate matter exposure is associated with respiratory and cardiovascular system dysfunction. Recently, we demonstrated that fine particles, also named PM_2.5, modify the expression of some components of the angiotensin and bradykinin systems, which are involved in lung, cardiac and renal regulation. The endocrine kidney function is associated with the regulation of angiotensin and bradykinin, and it can suffer damage even as a consequence of minor alterations of these systems. We hypothesized that exposure to PM_2.5 can contribute to early kidney damage as a consequence of an angiotensin/bradykinin system imbalance, oxidative stress and/or inflammation.

Results: After acute and subchronic exposure to PM_2.5, lung damage was confirmed by increased bronchoalveolar lavage fluid (BALF) differential cell counts and a decrease of surfactant protein-A levels. We observed a statistically significant increment in median blood pressure, urine volume and water consumption after PM_2.5 exposure. Moreover, increases in the levels of early kidney damage markers were observed after subchronic PM_2.5 exposure: the most sensitive markers, β-2-microglobulin and cystatin-C, increased during the first, second, sixth and eighth weeks of exposure. In addition, a reduction in the levels of specific cytokines (IL-1β, IL-6, TNF-α, IL-4, IL-10, INF-γ, IL-17a, MIP-2 and RANTES), and up-regulated angiotensin and bradykinin system markers and indicators of a depleted antioxidant response, were also observed. All of these effects are in concurrence with the presence of renal histological lesions and an early pro-fibrotic state.

Conclusion: Subchronic exposure to PM_2.5 induced an early kidney damage response that involved the angiotensin/bradykinin systems as well as antioxidant and immune imbalance. Our study demonstrates that PM_2.5 can induce a systemic imbalance that not only affects the cardiovascular system, but also affects the kidney, which may also overall contribute to PM-related diseases.

Keywords: Angiotensin and bradykinin systems; Antioxidant response; Cardiovascular diseases; Inflammation; Kidney biomarkers.

Fig. 1

Particulate exposure description. Animal exposure was performed in the raining season in Mexico City. Ambient parameters such as relativity humidity and temperature was monitored by a weather station, it was not observed raining during the schedule exposure. We report the median and the range for each week (a). During eight weeks animals exposure (input concentrator) and ambient air were monitored simultaneous, each week was defined as 4 days/week, 5 h/ day. The particulate concentrator enrichment have a minimum enrichment of 9.5 and a maximum of 20.7 times (b). Particulate scraped dust from each week was used to determinate the endotoxin content and the oxidative capability of particles by DTT oxidation assay, our data showed that Endotoxin and DTT have the same pattern and the weeks 2, 3 and 8 have the highest values during the exposure (c). Each graph point represent the triplicate average ± standar desviation

Fig. 2

PM_2.5 exposure induces inflammatory response and a reduction in SPA levels in rat lungs. Rats were acutely (3 days, 5 h/day) and subchronically exposed to concentrated PM_2.5 (8 weeks, 4 days/week, 5 h/day), and filtered air (FA) as a control group. Subcellular population counts of macrophagues (Mφ), monocytes and lymphocytes from PM_2.5 bronchialveolar lavage showed an augment after the acute exposure (a); however, in subchronic exposure only Mφ count augment in the PM_2.5 group was observed (b). Surfactant protein type-A (SPA) showed a marginal down regulation in the acute exposure to PM_2.5 (c), on the other hand, SPA levels after subchronic exposure to PM_2.5 decrease statistically (d). *in boxplot graphyc indicates statistical significant differences (p < 0.05)

Fig. 3

The PM_2.5 continuous exposure affects the hydric state. Rats were subchronically exposed to concentrated PM_2.5 (8 weeks, 4 days/week, 5 h/ day). Particulate exposure does not modify the body weight of animals during the eight weeks (a). However, the water consumption (b) and the urinary flow rate (c) increase significantly weekly at the end each exposure week. On boxplot graphyc* indicates statistical differences (p < 0.05)

Fig. 4

Exposure to PM_2.5 induces the release of kidney early damage markers in urine. Rats were exposed to concentrated PM_2.5 (8 weeks, 4 days/week, 5 h/ day). At the end of each week twelve hours-urine was collected by metabolic cage. Six early kidney markers were evaluated by Luminex technology. Albumin does not show statistical differences at any time evaluated (a). α-1-glycoprotein (b), β-2-Microglobulin (c), Cistatin-C (d), epithermal growth factor (e) and lipocalin-2/NGAL (f) have the highest increment in urine levels in the second week. The most sensitive early markers a long to the particle exposure were β-2-Microglobulin and Cistatin-C showed increments on the first, second, sixth, and eighth week. At week 4 any early damage kidney marker showed statistical differences. On boxplot graphyc * indicate statistical differences (p < 0.05)

Fig. 5

Proteins of angiotensin-, and bradykinin- systems respond at the end of eight weeks to PM_2.5 exposure. After eight exposure weeks (4 days/week, 5 h/ day) in kidney rats, we observed an augment in angiotensin-converter enzyme (ACE) and angiotensin-receptor type-I (AT₁R), (a) and (b) respectively. Bradykinin receptor type-1 (B₁R) increase and tissue kallikrein (KLK-1) decrease, (c) and (d) respectively. On boxplot graphyc * indicates statistical differences (p < 0.05)

Fig. 6

Kidney antioxidants decreased at the end of the eight weeks of PM_2.5 exposure. After eight exposure weeks (4 days/week, 5 h/ day) in kidney rats we observed a decrement of the antioxidant nuclear transcription factor (Nrf-2) (a), and antioxidant enzymes such as mitochondrial superoxide dismutase (SOD-2) and hemoxygenase type-1 (HO-1), (b) and (c) respectively. However, the gamma-glutamil cysteine ligase heavy chain the catalytic subunit (γ-GCLc) was up-regulated showed the kidney dependence of glutathione resource (d) On boxplot graphyc * indicates statistical differences (p < 0.05)

Fig. 7

Exposure to PM_2.5 induces early kidney lesions with the presence of tubular deterioration. After eight exposure weeks (4 days/week, 5 h/ day) in kidney histology we observed tubular lesion of hematoxylin and eosin staining slides (a). Tubular damage was corroborate by the immunodetection of Kidney injury molecule-1 (KIM-1) (b). On boxplot graphic * indicates statistical differences (p < 0.05)

Fig. 8

Exposure to PM_2.5 induces an early pro-fibrosis state. After eight exposure weeks (4 days/week, 5 h/ day) in kidney rat we observed the promotion of fibrosis by the detection of beta- transforming growth factor (TGF-β) (a) and the evaluation of pro-collagen-III mRNA (Col3a1) by q-PCR, (b) Premature deposit of collagen in tubular and glomerulli by the Masson’s trichromic staining (c). Yellow and red arrows indicate deposit of colagen in control (FA) and PM_2.5 groups, respectivetly. On boxplot graphic *indicates statistical differences (p < 0.05)