Diabetic mice are protected from normally lethal nephrotoxicity of S-1,2-dichlorovinyl-l-cysteine (DCVC): role of nephrogenic tissue repair

Abstract

Streptozotocin (STZ)-induced diabetic (DB) rats are protected from nephrotoxicity of gentamicin, cisplatin and mercuric chloride, although the mechanisms remain unclear. Ninety percent of DB mice receiving a LD90 dose (75 mg/kg, ip) of S-1,2-dichlorovinyl-l-cysteine (DCVC) survived in contrast to only 10% of the nondiabetic (NDB) mice surviving the same dose. We tested the hypothesis that the mechanism of protection is upregulated tissue repair. In the NDB mice, DCVC produced steep temporal increases in blood urea nitrogen (BUN) and plasma creatinine, which were associated with proximal tubular cell (PTC) necrosis, acute renal failure (ARF), and death within 48 h. In contrast, in the DB mice, BUN and creatinine increased less steeply, declining after 36 h to completely resolve by 96 h. HPLC analysis of plasma and urine revealed that DB did not alter the toxicokinetics of DCVC. Furthermore, activity of renal cysteine conjugate β-lyase, the enzyme that bioactivates DCVC, was unaltered in DB mice, undermining the possibility of lower bioactivation of DCVC leading to lower injury. [3H]-thymidine pulse labeling and PCNA analysis indicated an early onset and sustained nephrogenic tissue repair in DCVC-treated DB mice. BRDU immunohistochemistry revealed a fourfold increase in the number of cells in S-phase in the DB kidneys even without exposure to DCVC. Blocking the entry of cells into S-phase by antimitotic intervention using colchicine abolished stimulated nephrogenic tissue repair and nephroprotection. These findings suggest that preplacement of S-phase cells in the kidney due to diabetes is critical in mitigating the progression of DCVC-initiated renal injury by upregulation of tissue repair, leading to survival of the DB mice by avoiding acute renal failure.

Introduction

Modulation of nephrotoxicity in diabetes (DB) has been a topic of several investigations. Risk of contrast media-induced nephropathy (CMN) increases in patients with preexisting renal insufficiency including DB-nephropathy (Lautin et al., 1991, Rudnick et al., 1995, Suen et al., 1998, Andrew and Berg, 2004). Interestingly, Weisberg et al. (1999) report that DB patients are not anymore sensitive to hospital-acquired acute tubular necrosis (ATN) than non-diabetic (NDB) patients unless they suffer from cardiovascular disease. However, incidence of CMN increased in the DB patients when the contrast medium was used in combination with vasodilator and/or diuretic drugs (Weisberg et al., 1994).

Experimental DB has been shown to protect against the nephrotoxic effects of gentamicin, cisplatin, mercuric chloride, and cephaloridine (Vaamonde et al., 1984, Elliott et al., 1985, Valentovic et al., 1991, Cacini et al., 1993, Grover et al., 2002). Detailed investigations have been conducted using gentamicin and cisplatin in DB rats and rabbits (Vaamonde et al., 1984, Elliott et al., 1985, Valentovic et al., 1991, Cacini et al., 1993, Grover et al., 2002). These studies report reduced renal uptake/accumulation of the nephrotoxic drugs in DB kidneys. Although these studies suggested that lower renal concentration of the toxicants may be responsible for the protection in DB, the authors reported that this mechanism does not completely explain the protection in DB.

The possibility of other mechanisms playing a major role has been strongly suggested (Elliott et al., 1985, Gouvea et al., 1989, Scott et al., 1990, Valentovic et al., 1991, Sarangarajan and Cacini, 1996, Najjar and Saad, 2001). Collectively, these reports point out two principal observations: (1) gentamicin- and cisplatin-induced renal dysfunctions assessed by BUN and plasma creatinine elevations are lower in diabetic animals suggesting lower nephrotoxicity in diabetes; and (2) protection against nephrotoxicity of these drugs in diabetes cannot be completely explained by the reduced renal uptake of the toxicants. Time course profiles of renal dysfunction, histopathology, and whether or not DB-induced protection is reflected in animal survival from an ordinarily lethal challenge with nephrotoxicants may shed additional light. Moreover, such studies may reveal the role of other uninvestigated mechanisms such as augmented compensatory renal tissue repair in DB-induced protection, particularly since challenge with nephrotoxicants such as gentamicin, cisplatin, and mercuric chloride is known to stimulate a compensatory tissue repair response in the kidney (Dobyan et al., 1980, Haagsma and Pound, 1980, Laurent et al., 1988, Korrapati et al., 2005). The possibility that such repair mechanisms underlie DB-induced protection from nephrotoxicity is an attractive notion that warrants detailed investigation.

The present study focuses on three main objectives: (1) to study if STZ-induced DB protects against a normally lethal dose of S-1,2-dichlorovinyl-l-cysteine (DCVC) in mice; (2) to quantitate and characterize DCVC-induced renal dysfunction and injury over a time course in order to learn about the onset and recovery profiles of nephrotoxic injury; and (3) to test whether lower bioactivation, altered toxicokinetics, and enhanced compensatory tissue repair or a combination of all these factors play a critical role in this protection. A murine model of type 1 DB (Shankar et al., 2003a, Shankar et al., 2003b) was used to examine whether DB protects against the lethal nephrotoxicity of DCVC. This model of DB has been previously studied using three different strains of mice, which have been shown to be protected from hepatotoxicity of normally lethal challenge with thioacetamide (Shankar et al., 2003a), carbon tetrachloride, bromobenzene, and acetaminophen (Shankar et al., 2003c). Protection against thioacetamide (Shankar et al., 2003a) and acetaminophen-induced hepatic failure (Shankar et al., 2003c) could not be explained by lower bioactivation. Hepatoprotection was found to be due to early onset and robust compensatory hepatic tissue repair associated with stimulated PPAR-α activation in DB (Shankar et al., 2003b).

In the present study, we report that 90% of the DB mice survive a normally LD₉₀ dose of DCVC (75 mg/kg ip). This remarkable protection does not appear to be due to altered disposition, higher elimination, or lower bioactivation of DCVC in the DB mice. Instead, the protection appears to come from a combination of mitigated progression of renal injury and an enhanced and sustained stimulation of tissue repair in DB mice. The mitigation of progressive expansion of renal injury may be attributed to DB-induced advancement of cells into cell division cycle even before challenge with the nephrotoxicant. Blocking this advancement of cells into S-phase using the antimitotic agent colchicine (CLC) resulted in progressive expansion of DCVC-initiated renal injury and abolition of DB-induced protection.