Background

Integrity of the tight junction (TJ) which seals the gap between the epithelial cells of the gastrointestinal tract is critical in preventing the entry of the microbial toxins, antigens, and other harmful products in the subepithelial tissues and the internal milieu. By enabling the absorption of these products, impairment of the intestinal epithelial barrier leads to local and systemic inflammation. We have recently found depletion of the key protein constituents of colonic epithelial TJ in animals with chronic kidney disease (CKD). Postmortem studies have revealed the presence of inflammation throughout the gastrointestinal tract in uremic humans. This observation suggests that uremia may cause disruption of the epithelial barrier in all segments of the gastrointestinal tract including the stomach, jejunum, and ileum. The present study was undertaken to explore this possibility.

Methods

Sprague-Dawley rats were randomized to CKD or control groups. The CKD group was subjected to 5/6 nephrectomy while the control group underwent a sham operation. The animals were observed for 10 weeks at which time they were euthanized and their stomachs, jejunums, and ileums were removed and processed for measurement of TJ proteins.

Results

The CKD rats showed marked azotemia, systemic oxidative stress, and marked depletion of the key protein constituents of the epithelial TJ (claudin-1, occludin, and ZO1) in the stomach, jejunum, and ileum.

Conclusions

The present study extends the earlier finding of uremia-induced disruption of colonic epithelial TJ by documenting the involvement of the stomach, jejunum, and ileum as well.

An elevation of mean blood pressure was found in rats treated with low lead (0.01% lead acetate) for 3 months, as contrasted to paired Sprague-Dawley control rats. In these rats, measurement of plasma and urine endothelins-1 and -3 revealed that plasma concentration and urinary excretion of endothelin-3 increased significantly after 3 months (plasma: lead group, 31.8+/-2.2, versus controls, 23.0+1.7 pg/mL, P<.001; urinary excretion: lead group, 46.6+11.7, versus controls, 35.6+6.7 pg/24 h, P<.05), whereas endothelin-1 was unaffected. Plasma and urinary nitric oxide (NO) and cyclic GMP concentrations were not significantly changed. However, assay of plasma and kidney cortex malondialdehyde by high-pressure liquid chromatography, as a measure of reactive oxygen species, was elevated in lead-treated rats compared with that in control rats (plasma: lead group, 4.74+1.27, versus controls, 2.14+.49 micromol/L, P<.001; kidney cortex: lead group, 28.75+3.46, versus controls, 16.38+2.37 nmol/g wet weight, P<.001). There was increased NO synthase activity in lead-treated rat brain cortex and cerebellum. In lead-treated rat kidney cortex, the endothelial constitutive NO synthase protein mass was unaffected, whereas the inducible NO synthase protein mass was increased. These data suggest a balance between increased NO synthesis and degradation (by reactive oxygen species) in lead-treated rats, which results in normal levels of NO. Thus, the hypertension may be related to an increase in the pressure substances, endothelin-3 and reactive oxygen species, rather than to an absolute decrease in nitric NO.

The potential utility of dietary supplementation in order to prevent some of the oxidative and inflammatory changes occurring in the brain with age, has been studied. The cerebral cortex of 27-month-old male B6C3F1 mice had elevated levels of nitric oxide synthase 1 (EC 1.14.13.39) (nNOS) and peptide nitrotyrosine relative to cortices of younger (4-month-old) animals. After 25-month-old mice received basal diet together with 300 mg/l acetyl L-carnitine in the drinking water for 8 weeks, these levels were fully restored to those found in younger animals. A partial restoration was found when old animals received basal diet supplemented with 200 ppm melatonin in the diet. Levels of mRNA (messenger RNA) for nNOS were unchanged following these treatments implying translational regulation of nNOS activity. Behavioral indices indicative of exploratory behavior were also depressed in aged animals. Dietary supplementation with melatonin or acetyl L-carnitine partially reversed these changes. These findings suggest that dietary supplementation cannot merely arrest but indeed reverse some age-related increases in markers of oxidative and inflammatory events occurring with the cortex.

Background

Chronic renal failure (CRF) is associated with hypertriglyceridemia and impaired clearance of very low density lipoprotein (VLDL) and chylomicrons which are largely due to lipoprotein lipase (LPL) deficiency/dysfunction. After its release from myocytes and adipocytes, LPL binds to the endothelium in the adjacent capillaries where it catalyzes hydrolysis of triglycerides in VLDL and chylomicrons. The novel endothelium-derived molecule, glycosylphosphatidylinositol-anchored binding protein 1 (GPIHBP1), plays a critical role in LPL metabolism and function by anchoring LPL to the endothelium and binding chylomicrons. GPIHBP1-deficient mice and humans exhibit severe hypertriglyceridemia and diminished heparin-releasable LPL, pointing to the critical role of GPIHBP1 in regulation of LPL activity. Given its central role in regulation of LPL activity and triglyceride metabolism, we explored the effect of chronic kidney disease (CKD) on GPIHBP1 expression.

Methods

Expression of GPIHBP1 and LPL were determined by reverse transcriptase-polymerase chain reaction, Western blot and immunohistochemical analyses in the adipose tissue, skeletal muscle and myocardium of rats 12 weeks after 5/6 nephrectomy (CRF) or sham-operation (control).

Results

Compared to the controls, the CRF group exhibited severe hypertriglyceridemia, significant reduction of the skeletal muscle, myocardium and adipose tissue LPL mRNA and protein abundance. This was accompanied by parallel reductions of GPIHBP1 mRNA abundance and immunostaining in the tested tissues.

Conclusions

LPL deficiency in CKD is associated with and compounded by GPIHBP1 deficiency. Together these abnormalities contribute to impaired clearance of triglyceride-rich lipoproteins, diminished availability of lipid fuel for energy storage in adipocytes and energy production in myocytes and consequent hypertriglyceridemia, cachexia, muscle weakness and atherosclerosis.

Background

Gut inflammation is prevalent in chronic kidney disease (CKD) and likely contributes to systemic inflammation via disruption of the epithelial tight junction with subsequent endotoxin and bacterial translocation.

Aims

To study the expression profile of inflammatory and tight junction proteins in the colon from CKD rats compared to healthy controls, and demonstrate the role of Nrf2 (transcription factor nuclear factor erythroid 2-related factor 2) using a potent Nrf2 activator.

Methods

CKD was induced via 5/6 nephrectomy in Sprague-Dawley rats, and dh404 (2 mg/kg/day) was used to study the effects of systemic Nrf2 activation. The experimental groups included sham, CKD and CKD+ dh404 rats. Blood and colon tissues were analyzed after a 10-week study period.

Results

Colon from CKD rats showed histological evidence of colitis, depletion of epithelial tight junction proteins, significant reduction of Nrf2 and its measured target gene products (NQO1, catalase, and CuZn SOD), activation of NFkB, and upregulation of pro-inflammatory molecules (COX-2, MCP-1, iNOS, and gp91(phox)). Treatment with dh404 attenuated colonic inflammation, restored Nrf2 activity and levels of NQO1, catalase and CuZn SOD, decreased NFkB and lowered expression of COX-2, MCP-1, iNOS, and gp91(phox). This was associated with restoration of colonic epithelial tight junction proteins (occludin and claudin-1).

Conclusions

CKD rats exhibited colitis, disruption of colonic epithelial tight junction, activation of inflammatory mediators, and impairment of Nrf2 pathway. Treatment with an Nrf2 activator restored Nrf2 activity, attenuated colonic inflammation, and restored epithelial tight junction proteins.