Effect of N-acetylcysteine on hydrogen sulfide in chronic kidney disease

The incidence of cardiovascular morbidity and mortality in patients with
chronic kidney disease (CKD) is high (Go, NEJM 2004).This is partly explained
by the so called traditional risk factors, like hypertension, diabetes
mellitus, and dyslipidemia, but risk factors specific to CKD also contribute
to this high incidence. Nitric oxide (NO) deficiency, oxidative stress,
endothelial dysfunction, and inflammation are considered to be such factors.

NO deficiency has a crucial role in progression of CKD
NO is an important player in the maintenance of target organ health (e.g.
kidney and heart) and blood pressure. Patients with CKD generally show reduced
NO production, reduced NO bioavailability and disturbed redox balance (Baylis,
Am J Physiol Renal Physiol 2008; Kao, J Hum Hypertension 2010). Total NO
production is decreased due to impaired endothelial and renal production of NO.
With less NO, endothelial dysfunction, hypertension, and inflammation occur.
Indeed, NO depletion caused systemic and glomerular hypertension, glomerular
ischemia, glomerulosclerosis, tubulointerstitial injury, and proteinuria (Zatz,
Hypertension 1998, Verhagen, KI 1999, Attia, JASN 2001). It is therefore likely
that CKD-induced NO deficiency contributes to progression of renal damage.
Thus, increasing NO, improving endothelial function, and reducing oxidative
stress and inflammation, are obvious therapeutic targets.

H2S as backup mechanism for NO deficiency in CKD
Previous studies done by our group suggest renal hydrogen sulfide (H2S) and
carbon monoxide (CO) production to be involved during chronic NO depletion
(Attia, JASN 2001; Wesseling, Physiol Genomics 2007). Interestingly, these two
gaseous molecules share the same signaling and vasorelaxant properties as NO,
providing backup for each other in the vascular system (Wang, FASEB J 2002).
H2S is mainly produced by conversion of L-cysteine by cystathionine β-synthase
(CBS) or by g-cystathionase (CTH) and CO is mainly produced by heme oxygenase-1
via degradation of a heme (HO-1) (Li, Amino Acids 2009).
Although there are drugs that enhance CO and NO availability in rodents, none
of them can be applied in humans. Therefore, the focus of our research is on
the potential role of H2S in the protection of the kidneys in patients with
CKD.

Until now, the backup system of NO by H2S is poorly defined. Recently, GFR was
shown to partly depend on H2S blood levels. Renal damage was associated with
diminished H2S levels and this was ameliorated when the H2S level was enhanced
(Xia, J Pharmacol Exp Therap 2009). H2S production may be reduced as renal
function becomes impaired. Indeed, plasma H2S levels were found to be
significantly reduced in hemodialysis patients (Perna, NDT 2009). Whether this
also occurs in patients with CKD, not on dialysis, is unknown.

N-acetylcysteine (NAC) to enhance H2S availability in humans
The readily available drug NAC is used in clinical medicine as a mucolytic
agent, as an antidote for acetaminophen overdose, and in preventing
contrast-induced nephropathy (see also Chapter 6). It is inexpensive, safe, and
well tolerated by patients and could be applied to humans to enhance renal and
systemic H2S. NAC is rapidly absorbed and easily converted to L-cysteine.
L-cysteine is the main substrate for H2S production (and glutathione and
taurine). Therefore, NAC should enable us to stimulate H2S production in
humans. The potential benefits of NAC in CKD were shown in a randomized,
placebo-controlled trial in which hemodialysis patients were treated with NAC
600 mg BID. Treatment with NAC reduced the composite cardiovascular end points
(Tepel, Circulation 2003).

In the proposed study we wish to investigate the effect of NAC on H2S levels.

Primary Objective:
Our primary objective is to investigate the effect of NAC on H2S levels in
plasma in different patient groups, i.e. healthy volunteers, CKD patients, and
dialysis patients. We hypothesize that there is an increase in H2S levels after
treatment with NAC.

Secondary Objective:
Our secondary objective is to investigate differences in plasma H2S levels
between healthy volunteers, CKD patients, and dialysis patients and between
males and females. We hypothesize that there is a reduction in H2S production
when renal function becomes impaired. Furthermore, we will investigate the
effect of NAC on markers of oxidative stress, inflammation, and endothelial
dysfunction.

Study Type: Interventional

Study Design: Allocation: Non-Randomized
Control: Uncontrolled
Endpoint Classification: Efficacy Study
Intervention Model: Single Group Assignment
Masking: Open Label
Primary Purpose: Treatment

Study Duration: 48 hours

All study participants will receive 4 gifts of N-acetylcysteine 600 mg BID.

For this study we need one extra blood collection before NAC treatment and one
blood collection after NAC treatment. NAC in the oral form is safe and well
tolerated.