Endotoxin-tobramycin additive toxicity on renal proximal tubular cells in culture

Detecting early kidney damage in horses with colic by measuring matrix metalloproteinase -9 and -2, other enzymes, urinary glucose and total proteins

Background

The aim of the study was to investigate urine matrix metalloproteinase (MMP-2 and -9) activity, alkaline phosphatase/creatinine (U-AP/Cr) and gamma-glutamyl-transpeptidase/creatinine (U-GGT/Cr) ratios, glucose concentration, and urine protein/creatinine (U-Prot/Cr) ratio and to compare data with plasma MMP-2 and -9 activity, cystatin-C and creatinine concentrations in colic horses and healthy controls. Horses with surgical colic (n = 5) were compared to healthy stallions (n = 7) that came for castration. Blood and urine samples were collected. MMP gelatinolytic activity was measured by zymography.

Results

We found out that horses with colic had significantly higher urinary MMP-9 complex and proMMP-9 activities than horses in the control group. Colic horses also had higher plasma MMP-2 activity than the control horses. Serum creatinine, although within reference range, was significantly higher in the colic horses than in the control group. There was no significant increase in urinary alkaline phosphatase, gamma-glutamyltranspeptidase or total proteins in the colic horses compared to the control group. A human cystatin-C test (Dako Cytomation latex immunoassay^® based on turbidimetry) did not cross react with equine cystatin-C.

Conclusion

The results indicate that plasma MMP-2 may play a role in the pathogenesis of equine colic and urinary MMP-9 in equine kidney damage.

Enhanced cadmium-induced testicular necrosis and renal proximal tubule damage caused by gene-dose increase in a Slc39a8-transgenic mouse line

Resistance to cadmium (Cd)-induced testicular necrosis is an autosomal recessive trait defined as the Cdm locus. Using positional cloning, we previously identified the Slc39a8 (encoding an apical-surface ZIP8 transporter protein) as the gene most likely responsible for the phenotype. In situ hybridization revealed that endothelial cells of the testis vasculature express high ZIP8 levels in two sensitive inbred mouse strains and negligible amounts in two resistant strains. In the present study, we isolated a 168.7-kb bacterial artificial chromosome (BAC), carrying only the Slc39a8 gene, from a Cd-sensitive 129/SvJ BAC library and generated BAC-transgenic mice. The BTZIP8-3 line, having three copies of the 129/SvJ Slc39a8 gene inserted into the Cd-resistant C57BL/6J genome (having its normal two copies of the Slc39a8 gene), showed tissue-specific ZIP8 mRNA expression similar to wild-type mice, mainly in lung, testis, and kidney. The approximately 2.5-fold greater expression paralleled the fact that the BTZIP8-3 line has five copies, whereas wild-type mice have two copies, of the Slc39a8 gene. The ZIP8 mRNA and protein localized especially to endothelial cells of the testis vasculature in BTZIP8-3 mice. Cd treatment reversed Cd resistance (seen in nontransgenic littermates) to Cd sensitivity in BTZIP8-3 mice; reversal of the testicular necrosis phenotype confirms that Slc39a8 is unequivocally the Cdm locus. ZIP8 also localized specifically to the apical surface of proximal tubule cells in the BTZIP8-3 kidney. Cd treatment caused acute renal failure and signs of proximal tubular damage in the BTZIP8-3 but not nontransgenic littermates. BTZIP8-3 mice should be a useful model for studying Cd-induced disease in kidney.

Role of Toll-like receptor 4 in endotoxin-induced acute renal failure

Toll-like receptor 4 (TLR4) is present on monocytes and other cell types, and mediates inflammatory events such as the release of TNF after exposure to LPS. C3H/HeJ mice are resistant to LPS-induced mortality, due to a naturally occurring mutation in TLR4. We therefore hypothesized that LPS-induced acute renal failure (ARF) requires systemic TNF release triggered by LPS acting on extrarenal TLR4. We injected C3H/HeJ mice and C3H/HeOuJ controls with 0.25 mg of LPS, and sacrificed them 6 h later for analysis of blood urea nitrogen (BUN) and kidney tissue (n = 8 per group). In contrast to C3H/HeOuJ controls, C3H/HeJ mice were completely resistant to LPS-induced ARF (6-h BUN of 32.3 +/- 1.1 vs 61.7 +/- 5.6 mg/dl). C3H/HeJ mice released no TNF into the circulation at 2 h (0.00 vs 1.24 +/- 0.16 ng/ml), had less renal neutrophil infiltration (6.4 +/- 1.0 vs 11.4 +/- 1.3 neutrophils per high power field), and less renal apoptosis, as assessed by DNA laddering. Transplant studies showed that C3H/HeJ recipients of wild-type kidneys (n = 9) were protected from LPS-induced ARF, while wild-type recipients of C3H/HeJ kidneys (n = 11) developed severe LPS-induced ARF (24-h BUN 44.0 +/- 4.1 vs 112.1 +/- 20.0 mg/dl). These experiments support our hypothesis that LPS acts on extrarenal TLR4, thereby leading to systemic TNF release and subsequent ARF. Renal neutrophil infiltration and renal cell apoptosis are potential mechanisms by which endotoxemia leads to functional ARF.

Association of nitric oxide production by kidney proximal tubular cells in response to lipopolysaccharide and cytokines with cellular damage

Recent findings suggest that nitric oxide (NO) is an important biologic mediator which exerts a wide variety of effects on numerous physiological and pathophysiological processes. L-Arginine is oxidized to L-citrulline with concomitant NO production; as a result, nitrate and nitrite accumulates. This study was conducted to determine the potential NO production by proximal tubular cells (PTC) in response to bacterial lipopolysac-charides (LPS) and cytokines and to evaluate the cytotoxic effect associated with NO release. After a 7-day stimulation with LPS (100 micrograms/ml), interleukin-1 beta (IL-1 beta) (10 ng/ml), and tumor necrosis factor alpha (TNF-alpha) (10 ng/ml), the nitrate and nitrite levels were determined by a spectrophotometric method based on the Griess reaction. Moreover, alpha-methylglucopyranoside phosphate and lactate dehydrogenase release and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay served as indicators of sodium-dependent hexose transport integrity and cell death, respectively. IL-1 beta and TNF-alpha used alone or together or combined with LPS led to a significant generation of NO by PTC. Our results also demonstrate that NO induced by LPS and cytokines could inhibit sodium-dependent transport and could induce PTC damage.

Parenteral sparfloxacin compared with ceftriaxone in treatment of experimental endocarditis due to penicillin-susceptible and -resistant streptococci

A new, investigational, parenteral form of sparfloxacin was compared with ceftriaxone in the treatment of experimental endocarditis caused by either of three penicillin-susceptible streptococci or one penicillin-resistant streptococcus. Both drugs have prolonged half-lives in serum, allowing single daily administration to humans. Sparfloxacin had relatively low MICs (0.25 to 0.5 mg/liter) for all four organisms and was also greater than or equal to eight times more effective than the other quinolones against 21 additional streptococcal isolates recovered from patients with bacteremia. Ceftriaxone MICs were 0.032 to 0.064 mg/liter for the penicillin-susceptible strains and 2 mg/liter for the resistant isolate. Both antibiotics resulted in moderate bacterial killing in vitro. Rats with catheter-induced aortic vegetations were inoculated with 10(7) CFU of the test organisms. Antibiotic treatment was started 48 h later and lasted either 3 or 5 days. The drugs were injected at doses which mimicked the kinetics in human serum produced by one intravenous injection of 400 mg of sparfloxacin (i.e., the daily dose expected to be given to human adults) and 2 g of ceftriaxone. Both antibiotics significantly decreased the bacterial densities in the vegetations. However, sparfloxacin was slower than ceftriaxone in its ability to eradicate valvular infection caused by penicillin-susceptible bacteria. While this difference was quite marked after 3 days of therapy, it tended to vanish when treatment was prolonged to 5 days. In contrast, sparfloxacin was very effective against the penicillin-resistant isolate, an organism against which ceftriaxone therapy failed in vivo. No sparfloxacin-resistant mutant was selected during therapy. Thus, in the present experimental setting, this new, investigational, parenteral form of sparfloxacin was effective against severe infections caused by both penicillin-susceptible and penicillin-resistant streptococci.

Increased renal uptake of gentamicin in endotoxemic rats receiving concomitant thromboxane A2 antagonist therapy

This report describes the effects of endotoxin and a thromboxane receptor antagonist, L-655,240, on kidney function and the intrarenal pharmacokinetics of aminoglycosides. The rationale for these studies was that thromboxane antagonists may eventually be used in combination with aminoglycosides in patients with gram-negative sepsis and endotoxemia. As aminoglycosides are nephrotoxic and endotoxin has already been shown to increase the renal uptake of gentamicin, we investigated the possibility that thromboxane antagonists might interfere with the nephrotoxic potential of both substances. A decrease in the volume of distribution and an increase in the intracortical concentration of gentamicin were observed in animals given endotoxin. Compared with animals given endotoxin alone, those which received endotoxin plus L-655,240 had significant accumulation of gentamicin in the renal cortex and medulla, as determined by the area under the concentration-time curve, and a significant reduction in the total clearance of the antibiotic (P < 0.05). This difference in uptake could not be attributed to hypotension or changes in the glomerular filtration rate or renal plasma flow. L-655,240 alone did not modify gentamicin pharmacokinetics but did decrease p-aminohippuric acid secretion. Thromboxane antagonists in the context of endotoxemia increase intrarenal uptake of aminoglycosides. If these compounds are to be used as therapeutic agents when endotoxin is present, their influence on renal handling of nephrotoxic drugs needs to be considered. Multiple-dosing regimens deserve investigation.

Isolation and Culture of Proximal Tubular Cells from Porcine Kidney

Porcine proximal tubular cells (PPTC) were isolated from kidneys obtained from slaughterhouse pigs. After disruption of the connective tissue by collagenase, purification was achieved by filtration and centrifugation on a discontinuous density gradient. Single cells and clusters of 10–40 cells were obtained, having a viability of 93–99%. More than 81% of the single cells showed γ-glutamyltranspeptidase (GGT) activity and more than 95% showed non-specific esterase (NE) activity, marker enzymes for proximal tubule cells. One kidney yielded 1 x 107single cells and 3x107cells in clusters. Cells were kept in primary culture on plastic or collagen-coated dishes. In the presence of 10% serum, confluency was reached within four days. The monolayers could be kept in culture for four days after confluency, in serum-free conditions. When seeded in serum-free conditions, PPTC did not reach confluency, but the cells could be kept in culture for at least 16 days. The cells displayed epithelial morphology, i.e. cobblestone shape, dome formation, microvilli, basal infoldings and abundant mitochondria. PPTC in primary culture still displayed NE activity, while 80% of the cells showed GGT activity. In conclusion, the isolated cells are of proximal tubular origin, reach confluency in 3–4 days in the presence of 10% serum, and can be kept as monolayers in serum-free conditions for four additional days and may provide a suitable in vitro model for long-term nephrotoxicity studies.

Efficacy of temafloxacin in experimental Streptococcus adjacens endocarditis and autoradiographic diffusion pattern of [14C]temafloxacin in cardiac vegetations

Temafloxacin, a new fluoroquinolone, alone or in combination with tobramycin, was compared with penicillin, tobramycin, and their combination in the therapy of rabbits with endocarditis caused by Streptococcus adjacens GaDT, a new species of nutritionally variant streptococci. Animals were injected intramuscularly for 4 days with temafloxacin (50 mg/kg of body weight twice daily [b.i.d.]) alone or combined with tobramycin (12 mg/kg once daily), with procaine penicillin (150,000 U/kg b.i.d.) alone or combined with tobramycin (12 mg/kg once daily), or with tobramycin (12 mg/kg once daily) alone. Another group of animals was treated with a higher dose of temafloxacin (100 mg/kg b.i.d.). Temafloxacin, penicillin, and tobramycin MICs and MBCs were 1 and 2, 0.015 and 1, and 8 and 16 micrograms/ml, respectively. Time-kill curves showed that the addition of tobramycin to penicillin or temafloxacin increased the killing rate. In vivo, treatment with temafloxacin (50 and 100 mg/kg b.i.d.) alone reduced the bacterial counts in vegetations (3.9 +/- 0.9 and 3.1 +/- 0.8 log10 CFU/g of vegetation) compared with those in the vegetations of control animals (7.5 +/- 0.9 log10 CFU/g of vegetation). This result was similar to that obtained with penicillin alone (4.5 +/- 0.8 log10 CFU/g of vegetation). The combination of temafloxacin (50 mg/kg) and tobramycin was as effective as penicillin plus tobramycin (2.5 +/- 0.3 versus 2.3 +/- 0.4 log10 CFU/g of vegetation, respectively). The autoradiographic pattern of [14C]temafloxacin diffusion into infected cardiac vegetations was studied. Thirty minutes after the end of infusion of 250 microCi of [14C]temafloxacin, the [14C]temafloxacin was homogeneously distributed throughout the vegetations. These data support further evaluation of quinolones in experimental endocarditis.