**3. Mechanism of action: fumaric acid esters**

Despite the numerous *in vitro* and *in vivo* studies that have been conducted over the years, the mechanism of action of FAE is still not fully understood and novel aspects continue to emerge. The generic hypothesis to explain the benefits of FAE is that DMF/MMF interferes with the cellular redox system by inducing a strong antioxidant response. Indeed, the robust induction of Nrf2 (nuclear factor E2 (erythroid-derived 2)-related factor) by DMF/MMF has been well described (**Figure 2**). In cells, DMF/MMF leads to the nuclear translocation of Nrf2, a phenomenon that is known to in turn, enhance the expression of antioxidant enzymes [26]. Specifically, it has been shown that MMF induces alkylation of a critical reactive thiol, Cys151, on Keap1 (Kelch-like ECH associated protein 1) which results in the release of Nrf2 [26, 27]. Once dissociated from Keap-1, Nrf2 translocates to the

#### **Figure 2.**

*Involvement of Nrf2-dependent and independent mechanisms in FAE-mediated antioxidant and antiinflammatory effects. Fumaric acid esters (DMF/MMF) disrupt Keap1-Nrf2 binding to induce nuclear translocation of Nrf2 which in turn, activates a number of downstream antioxidant response genes. This mode of action of FAE is well known and is purported to be responsible for the positive actions of FAE in neurotoxicity, nephrotoxicity, and spinal cord injury. Additionally, however, MMF, the major bioactive ingredient of FAE, is an agonist of HCAR2, a Gi-protein coupled membrane receptor that potentiates robust anti-inflammatory signaling. Various studies have shown that while FAE-mediated Nrf2 signaling elicits both antioxidant and anti-inflammatory responses, HCAR2-dependent signaling predominantly provides an anti-inflammatory effect. The HCAR2-mediated actions of FAE have been implicated its protective effects in gastrointestinal diseases, pancreatitis and neuroinflammation. Importantly however, the combined actions (Nrf2- and HCAR2-mediated) have been demonstrated in several pathologic conditions (sickle cell disease, retinal degeneration, sepsis and stroke). FAE, fumaric acid esters; HCAR2 or HCA2, hydroxycarboxylic acid receptor 2; DMF, dimethyl fumarate; MMF, monomethyl fumarate; Keap1; kelch-like ECH associated protein 1; Nrf2, nuclear factor erythroid 2-related factor 2; ARE; antioxidant responsive element.*

**201**

provided in **Table 1**.

*Repurposing Fumaric Acid Esters to Treat Conditions of Oxidative Stress and Inflammation…*

nucleus and therein, binds to the antioxidant response element (ARE) of an array of antioxidant target genes thereby upregulating their expression and related activity. This effect was corroborated in Nrf2-deficient cells in which the antioxidant effects

*The role of FAE in regulating microglia activation. FAE (DMF/MMF) are known to induce Nrf2 and to activate HCAR2. Various studies have shown that via these mechanisms, FAE prevent the polarization of microglia from the M1 (resting) phenotype to the M2 (active and thereby pro-inflammatory) phenotype, the consequences of which are reduced free radical and pro-inflammatory cytokine production. This action of FAE is thought to underlie the neuroprotective effects of the drug in conditions like HIV-induced neuroinflammation, Parkinson's disease, retinal degeneration, and stroke. FAE, fumaric acid esters, HCAR2, hydroxycarboxylic acid receptor 2; DMF, dimethyl fumarate; MMF, monomethyl fumarate; Nrf2, nuclear* 

*factor erythroid 2-related factor 2; HIV, human immunodeficiency virus.*

The majority of preclinical studies of DMF/MMF, highlight the Nrf2-mediated mechanism of the drug as the principal factor underlying its therapeutic effects. However, DMF/MMF has also been shown to elicit a robust anti-inflammatory response. This additional desirable effect is thought to be accomplished via the inhibition of NF-kB translocation into the nucleus, an action that impacts negatively the expression of a plethora of inflammatory cytokine, chemokine, and adhesion molecule genes. Relevant also to the anti-inflammatory effects of DMF/ MMF, is hydroxycarboxylic acid receptor 2 (HCAR2; GPR109A)-dependent signaling (**Figure 2**). MMF is a strong agonist of HCAR2. DMF activates the receptor as well although with a comparably lower affinity [28]. In a study by Chen et al. 2014 it was shown that DMF treatment reduced pathological features of experimental autoimmune encephalomyelitis in WT mice, but not in *Hcar2−/−* mice, indicating the importance of HCAR2-mediated signaling by DMF [29]. In another study, Parodi et al. [30] demonstrated the importance of HCAR2 to the anti-inflammatory effects of MMF in microglia. Specifically, it was reported that MMF could modulate microglia activation through inhibition of the NF-κB pathway via the AMPK/SIRT-1 axis. MMF treatment to microglia cells resulted in the activation of the HCAR2 receptor via enhanced intracellular calcium levels, an effect that prevents microglial polarization into an inflammatory phenotype (**Figure 3**). Downstream, it induced CAMKK (Calcium/calmodulin-dependent protein kinase kinase 2) dependent activation of AMPK/SIRT-1 axis which also contributes to reduced inflammation. Several other studies have also reported on the HCAR2 receptor-dependent and independent anti-inflammatory effects of FAE in additional cell types including

keratinocytes [31–33] and epithelial cells of the retina [34, 35].

**4. Role of FAE in inflammatory and oxidative stress conditions**

Herein we highlight the findings of preclinical studies on the use of DMF/MMF to counter inflammation and oxidative stress associated with the pathogenesis of pathological conditions other than psoriasis and MS (**Figure 2**). A summary is

*DOI: http://dx.doi.org/10.5772/intechopen.91915*

of DMF/MMF were lost [27].

**Figure 3.**

*Repurposing Fumaric Acid Esters to Treat Conditions of Oxidative Stress and Inflammation… DOI: http://dx.doi.org/10.5772/intechopen.91915*

#### **Figure 3.**

*Drug Repurposing - Hypothesis, Molecular Aspects and Therapeutic Applications*

Despite the numerous *in vitro* and *in vivo* studies that have been conducted over the years, the mechanism of action of FAE is still not fully understood and novel aspects continue to emerge. The generic hypothesis to explain the benefits of FAE is that DMF/MMF interferes with the cellular redox system by inducing a strong antioxidant response. Indeed, the robust induction of Nrf2 (nuclear factor E2 (erythroid-derived 2)-related factor) by DMF/MMF has been well described (**Figure 2**). In cells, DMF/MMF leads to the nuclear translocation of Nrf2, a phenomenon that is known to in turn, enhance the expression of antioxidant enzymes [26]. Specifically, it has been shown that MMF induces alkylation of a critical reactive thiol, Cys151, on Keap1 (Kelch-like ECH associated protein 1) which results in the release of Nrf2 [26, 27]. Once dissociated from Keap-1, Nrf2 translocates to the

*Involvement of Nrf2-dependent and independent mechanisms in FAE-mediated antioxidant and antiinflammatory effects. Fumaric acid esters (DMF/MMF) disrupt Keap1-Nrf2 binding to induce nuclear translocation of Nrf2 which in turn, activates a number of downstream antioxidant response genes. This mode of action of FAE is well known and is purported to be responsible for the positive actions of FAE in neurotoxicity, nephrotoxicity, and spinal cord injury. Additionally, however, MMF, the major bioactive ingredient of FAE, is an agonist of HCAR2, a Gi-protein coupled membrane receptor that potentiates robust anti-inflammatory signaling. Various studies have shown that while FAE-mediated Nrf2 signaling elicits both antioxidant and anti-inflammatory responses, HCAR2-dependent signaling predominantly provides an anti-inflammatory effect. The HCAR2-mediated actions of FAE have been implicated its protective effects in gastrointestinal diseases, pancreatitis and neuroinflammation. Importantly however, the combined actions (Nrf2- and HCAR2-mediated) have been demonstrated in several pathologic conditions (sickle cell disease, retinal degeneration, sepsis and stroke). FAE, fumaric acid esters; HCAR2 or HCA2, hydroxycarboxylic acid receptor 2; DMF, dimethyl fumarate; MMF, monomethyl fumarate; Keap1; kelch-like ECH associated protein* 

*1; Nrf2, nuclear factor erythroid 2-related factor 2; ARE; antioxidant responsive element.*

**3. Mechanism of action: fumaric acid esters**

**200**

**Figure 2.**

*The role of FAE in regulating microglia activation. FAE (DMF/MMF) are known to induce Nrf2 and to activate HCAR2. Various studies have shown that via these mechanisms, FAE prevent the polarization of microglia from the M1 (resting) phenotype to the M2 (active and thereby pro-inflammatory) phenotype, the consequences of which are reduced free radical and pro-inflammatory cytokine production. This action of FAE is thought to underlie the neuroprotective effects of the drug in conditions like HIV-induced neuroinflammation, Parkinson's disease, retinal degeneration, and stroke. FAE, fumaric acid esters, HCAR2, hydroxycarboxylic acid receptor 2; DMF, dimethyl fumarate; MMF, monomethyl fumarate; Nrf2, nuclear factor erythroid 2-related factor 2; HIV, human immunodeficiency virus.*

nucleus and therein, binds to the antioxidant response element (ARE) of an array of antioxidant target genes thereby upregulating their expression and related activity. This effect was corroborated in Nrf2-deficient cells in which the antioxidant effects of DMF/MMF were lost [27].

The majority of preclinical studies of DMF/MMF, highlight the Nrf2-mediated mechanism of the drug as the principal factor underlying its therapeutic effects. However, DMF/MMF has also been shown to elicit a robust anti-inflammatory response. This additional desirable effect is thought to be accomplished via the inhibition of NF-kB translocation into the nucleus, an action that impacts negatively the expression of a plethora of inflammatory cytokine, chemokine, and adhesion molecule genes. Relevant also to the anti-inflammatory effects of DMF/ MMF, is hydroxycarboxylic acid receptor 2 (HCAR2; GPR109A)-dependent signaling (**Figure 2**). MMF is a strong agonist of HCAR2. DMF activates the receptor as well although with a comparably lower affinity [28]. In a study by Chen et al. 2014 it was shown that DMF treatment reduced pathological features of experimental autoimmune encephalomyelitis in WT mice, but not in *Hcar2−/−* mice, indicating the importance of HCAR2-mediated signaling by DMF [29]. In another study, Parodi et al. [30] demonstrated the importance of HCAR2 to the anti-inflammatory effects of MMF in microglia. Specifically, it was reported that MMF could modulate microglia activation through inhibition of the NF-κB pathway via the AMPK/SIRT-1 axis. MMF treatment to microglia cells resulted in the activation of the HCAR2 receptor via enhanced intracellular calcium levels, an effect that prevents microglial polarization into an inflammatory phenotype (**Figure 3**). Downstream, it induced CAMKK (Calcium/calmodulin-dependent protein kinase kinase 2) dependent activation of AMPK/SIRT-1 axis which also contributes to reduced inflammation. Several other studies have also reported on the HCAR2 receptor-dependent and independent anti-inflammatory effects of FAE in additional cell types including keratinocytes [31–33] and epithelial cells of the retina [34, 35].

### **4. Role of FAE in inflammatory and oxidative stress conditions**

Herein we highlight the findings of preclinical studies on the use of DMF/MMF to counter inflammation and oxidative stress associated with the pathogenesis of pathological conditions other than psoriasis and MS (**Figure 2**). A summary is provided in **Table 1**.


**203**

**4.1 Gastrointestinal diseases**

*Repurposing Fumaric Acid Esters to Treat Conditions of Oxidative Stress and Inflammation…*

MMF (i.p.)

100 mg/kg MMF (i.p.)

15 mg/kg of DMF (i.g.)

50 mg/kg MMF (i.p.)

30 mg/kg DMF (i.g.)

1 mM (intravitreal) and 15 mg/ ml MMF (in drinking water)

30 mg/kg (i.g.)

2.5 and 5 mg/ kg MMF (i.p.)

**Effective dose Outcomes References**

MMF reduced retinal I/R injury in mice via induction

MMF-mediated HCAR2 signaling provided neuroprotection via reduced microglial activation, inflammation, and oxidative

DMF reduced inflammation and oxidative stress in heart, liver, lung, kidney, and brain, and improved cognitive function

MMF alleviated sepsis-induced hepatic dysfunction by reducing oxidative and inflammatory via the inhibition of the TLR-4/ NF-κB signaling pathway.

DMF increased expression of nuclear Nrf2 in the liver and kidney to decreases oxidative stress and inflammation

MMF treatment-induced fetal hemoglobin production and reduced oxidative stress and inflammation via Nrf2 activation

DMF and MMF improved SCI

MMF restored monoamine, corticosterone, and cytokine homeostasis by regulating neuroendocrine-immune systems

injury in mice.

[51]

[52]

[53, 54]

[55]

[56]

[34, 35]

[57]

[39]

of Nrf2 signaling

stress.

Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the colon and small intestine that includes Crohn's disease and ulcerative colitis [58, 59]. Treatments for IBD range from symptomatic treatment with anti-diarrheal medications, anti-inflammatory agents or immunosuppressive drugs to more radical surgical interventive strategies (e.g. partial or complete colectomy). These strategies are effective in a number of patients however given the complex etiology of IBD, the need for new and/or improved therapeutic strategies remains high. Given the well-established link between inflammation and IBD development and progression, it is not surprising that several groups have sought to test the efficacy of FAE in this condition. For the most part, these studies have been conducted using experimental models of colitis; rodents treated with dinitrobenzene sulfuric acid (DNBS) or dextran sodium sulfate (DSS), etc. [60, 61]. Casili et al. induced colitis in mice via intrarectal administration of DNBS (4 mg/mouse). DMF (10, 30 or 100 mg/kg) was then administered orally

*Some important* in vivo *studies showing the use of fumaric acid esters for the treatment of oxidative stress and* 

*DOI: http://dx.doi.org/10.5772/intechopen.91915*

**Experimental model**

Light-induced retinal damage in

to cecal ligation and puncture procedure

HbSS-Townes and NY1DD mice

HbSS-Townes mice

SCI injury in mice using aneurysm

to chronic footshock stress

clip

Ulcer Rats exposed

mice

Sepsis Rats subjected

I/R injury in mice 50 mg/kg

**Disease condition**

Retinal degeneration

Sickle cell disease

Sickle cell retinopathy

Spinal cord injury

**Table 1.**

*inflammation.*


*Repurposing Fumaric Acid Esters to Treat Conditions of Oxidative Stress and Inflammation… DOI: http://dx.doi.org/10.5772/intechopen.91915*

#### **Table 1.**

*Drug Repurposing - Hypothesis, Molecular Aspects and Therapeutic Applications*

25 and 50 mg/ kg DMF (i.g.)

30 and 45 mg/ kg DMF and MMF (i.p.)

30 and 60 mg/ kg DMF (i.g.)

15 mg/kg DMF (i.g.)

100 mg/kg (i.p.)

50 mg / kg DMF (i.g.)

60 and 200 mg/kg DMF (i.g.)

25 mg/kg DMF (i.g.)

25 mg/Kg DMF (i.g.)

50 mg/kg DMF (i.g.)

100 mg/kg MMF/ DMF (i.g.)

100 and 300 mg/kg DMF (i.g.)

10, 30, and 100mg/kg DMF (i.g.)

30 and 100 mg/kg DMF (i.g.)

**Effective dose Outcomes References**

DMF and MMF suppressed glial activation via increasing the expression of Nrf2

DMF induced antioxidant response by regulating SOD-2 and inflammation by Nf-kB signaling to reduce colitis.

DMF alleviated DSS-induced colitis by regulating Nrf2 mediated inhibition of NLRP3

DMF can ameliorate ICHmediated injury with a therapeutic window of at least

DMF-induced dissociation of Nrf2 from Keap1, and the consequent casein kinase 2 phosphorylation of Nrf2, resulted in neuroprotection after ICH

DMF reduced nephrotoxicity by inhibiting oxidative stress and

DMF reduced neurotoxicity by

inflammasome

inflammation

activating HO-1.

DMF was effective in ameliorating the histological lesions and biochemical abnormalities and improving

beta-cell function

and cell necrosis

response.

DMF treated rats showed reductions in the severity of inflammatory cell infiltration, acinar damage, perilobar edema,

DMF reduced neurotoxicity by Nrf2 mediated antioxidant

DMF prevented Synucleinopathy in a mouse model of PD by activating Nrf2 signaling

DMF and MMF exhibit neuroprotective effects via Nrf2-mediated antioxidant, antiinflammatory, and mitochondrial functional/biogenetic effects.

DMF protected against experimental PD via regulation of the NF-κB/Nrf-2 pathway

24 h

[36]

[37]

[38]

[39]

[40]

[41]

[42]

[43]

[44, 45]

[46]

[47]

[48]

[49]

[50]

DMF protected against experimental stroke by inducing immunomodulatory and antioxidant response

**Experimental model**

Middle cerebral artery occlusion in rats

Middle cerebral artery occlusion in mice

a. Mice treated with DNBS. b. IL-10<sup>−</sup>/<sup>−</sup> mice.

Mice treated with 3% (w/v) DSS drinking water

Intra-striatal injection of autologous blood in rats and mice

Mice using either the collagenase injection model (cICH) or the autologous blood (bICH)

with 20 mg/kg Cyclosporin A for 28 days

10 nmol sodium nitroprusside

Rats treated with 3 g/Kg L-arginine

6-OHDA-induced neurotoxicity in

Mice treated with

Mice treated with a viral vector expressing human

MPTP-treated mice

mice

MPTP

α-SYN

with 2.5 g/ kg L-arginine

**Disease condition**

Cerebral ischemia–

Experimental colitis

Intracerebral hemorrhage

Nephrotoxicity Rats treated

Pancreatitis Rats treated

Parkinson's disease

Neurotoxicity Mice treated with

**202**

*Some important* in vivo *studies showing the use of fumaric acid esters for the treatment of oxidative stress and inflammation.*

#### **4.1 Gastrointestinal diseases**

Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the colon and small intestine that includes Crohn's disease and ulcerative colitis [58, 59]. Treatments for IBD range from symptomatic treatment with anti-diarrheal medications, anti-inflammatory agents or immunosuppressive drugs to more radical surgical interventive strategies (e.g. partial or complete colectomy). These strategies are effective in a number of patients however given the complex etiology of IBD, the need for new and/or improved therapeutic strategies remains high. Given the well-established link between inflammation and IBD development and progression, it is not surprising that several groups have sought to test the efficacy of FAE in this condition. For the most part, these studies have been conducted using experimental models of colitis; rodents treated with dinitrobenzene sulfuric acid (DNBS) or dextran sodium sulfate (DSS), etc. [60, 61]. Casili et al. induced colitis in mice via intrarectal administration of DNBS (4 mg/mouse). DMF (10, 30 or 100 mg/kg) was then administered orally

every 24 h, starting 3 h after the administration of DNBS and continuing over the course of 4 days. DMF treatment to DNBS treated mice significantly improved colon injury and histological score. Further DMF also reduced lipid peroxidation by regulating the expression of SOD2 (superoxide dismutase 2, mitochondrial) and Nrf2. The anti-inflammatory effect of DMF was evident by a reduction in the expression of TNF-α (tumor necrosis factor- α), IL-1β (Interleukin 1 beta) and ICAM-1 (intercellular adhesion molecule 1) and P- selectin. This effect was thought to be a result of reduced IκB-α degradation to prevent nuclear translocation of p65 NF-κB (Nuclear factor-κB). Moreover, *in vitro* DMF treatment improved hydrogen peroxide-induced barrier dysfunction of human intestinal epithelial cells. The authors also confirmed the protective effect of DMF on experimental colitis using another model (9-weekold IL-10KO mice). Collectively, this study demonstrated that DMF could reduce experimental colitis by regulating inflammation and oxidative stress [38]. In another study, Liu et al., 2016 evaluated the efficacy of DMF in reducing DSS-induced murine colitis. Wild-type and *Nrf2−/−* mice received either vehicle or 3% (w/v) DSS in drinking water for 7 days and thereafter provided with only drinking water for another 3 days. Groups of mice were also given 30 or 60 mg/kg DMF (i.g.) from day 1 to 10. DMF treatment significantly reduced oxidative stress and inflammation and thereby improved signs/symptoms of colitis in DSS-treated mice. However, these effects were lost in *Nrf2<sup>−</sup>/<sup>−</sup>* mice, highlighting the importance of the Nrf2-mediated mechanism of action of the drug. This was supported by additional *in vitro* studies in which the authors showed that DMF-mediated Nrf2 activation reduces NLRP3 (NLR family pyrin domain containing 3) inflammasome activation to control intestinal inflammation.

Consistent with the above gastrointestinal benefits derived from DMF/MMF treatment, the efficacy of MMF treatment in improving stomach ulcers in rats has also been described. Although the detailed mechanism of action was not evaluated, the authors attributed the protective effect of the compound in this condition to be due primarily to the anti-inflammatory activity of MMF [39]. Collectively, these studies indicate that DMF/MMF therapy may be of benefit the clinical management of inflammatory gastrointestinal disorders. This is interesting given that gastrointestinal (GI) side effects (e.g., nausea, vomiting, diarrhea, and upper abdominal pain) are one of the most commonly reported complaints in patients receiving DMF therapy [62, 63]. Indeed, during phase 3 clinical trials for multiple sclerosis, adverse events (AEs) involving the GI system were reported in 40% of patients treated with DMF compared with 30% of patients treated with placebo [64, 65]. Though the adverse GI events are generally mild in severity and typically resolve within the first 2 months of treatment, these issues may impact patient quality of life and ultimately medication adherence. Thus, while a number of experimental studies have reported gastroprotective effects of DMF, there is some concern as to whether such therapy could reliably be extrapolated to clinical management of gastrointestinal disorders in human patients. However, the increasing number of additional reports of DMF/MMF benefit in the digestive system that continue to arise in the scientific literature suggests that perhaps efforts to implement DMF/MMF therapy for use in this regard should not be dismissed completely. For example, Rao and Mishra [66] performed a preliminary study demonstrating the hepatoprotective effects of MMF isolated from *Fumaria Indica* extract in various models of hepatotoxicity. Although the study was preliminary and had some limitations, it does introduce a possible hepatoprotective effect of MMF. This is supported also by a recent study by Abdelrahman et al. [67] that reported the protective effects of DMF treatment on acetaminophen-induced hepatic injury in mice. Acetaminophen-treated mice receiving a single or double dose of DMF (100 mg/kg) showed reduced oxidative stress, inflammation, and associated liver damage compared to non-DMF treated

**205**

**4.3 Nephrotoxicity**

*Repurposing Fumaric Acid Esters to Treat Conditions of Oxidative Stress and Inflammation…*

animals. Hence, additional studies in larger animal models and at some point, in humans, to test, develop and/or refine DMF/MMF formulations to improve potential suitability for use in the treatment of gastrointestinal or liver diseases are

With improvements in treatments for HIV (human immunodeficiency virus), lifespan has increased significantly affected persons. However, neuroinflammation and/or toxicity remain major concerns in this disease. The critical relevance of neuroinflammation to the etiology of MS, a disease for which DMF/MMF therapy is already approved, is undeniable [68]. Further, patients with MS are at considerably higher risk for neurotoxicity than are patients without the demyelinating disease [69]. Given these commonalities between MS and HIV-induced neurologic disease, preclinical testing of DMF/MMF in the latter is of interest. Using an *in vitro* model of HIV-mediated neurotoxicity, Cross et al. 2011 [70] showed that HIV infection dysregulates macrophage antioxidant response and reduces the expression of heme oxygenase-1 (HO-1). Importantly, DMF and MMF (5–30 μM) dose-dependently suppressed HIV replication, improved antioxidant response and reduced neurotoxin release, effects that the authors proposed to be mediated via a two-way action of DMF: (1) inhibition of NF-kB nuclear translocation and consequent suppression of HIV replication, and (2) decreased neurotoxin release stemming from HO-1 induction. Further, they also found that DMF reduces CCL2 (C-C Motif Chemokine

Ligand 2)-induced monocyte chemotaxis, suggesting that DMF additionally decreased the recruitment of activated monocytes to the CNS (central nervous system) in response to inflammatory mediators. Based on the above, the authors concluded that dysregulation of the antioxidant response during HIV infection drives macrophage-mediated neurotoxicity and DMF could serve as an adjunctive neuroprotectant. In a separate study, Ambrosius et al. [71] evaluated the effect of MMF on microglia activation and subsequent neurotoxicity. MMF treatment (10–30 μM) significantly reduced HIV-mediated neurotoxicity in microglia cells (**Figure 3**). A similar but prior study by a different group showed MMF to be capable of inducing a phenotypic shift from pro-inflammatory to anti-inflammatory macrophages [72] however, Ambrosius et al. did not observe such effects. These differences could be model-dependent or related to methodological differences in the two studies and therefore require further investigation since the authors did not comprehensively evaluate the possible mechanism of action in these short reports. Notwithstanding, however, the opposing effects of DMF/MMF on microglial responses, particularly those of an inflammatory nature, appear to be solidly supported by several other studies [30] which in turn, collectively support additional effort to advance DMF/ MMF therapy for potential use in HIV-associated neuroinflammation and toxicity.

Very little information exists on the protective effect of FAEs on renal function. A study by Takasu et al. [42] evaluated the effect of DMF treatment on CsA (calcineurin inhibitor)-induced nephrotoxicity. Male *Sprague–Dawley* rats were treated with 20 mg/kg CsA or CsA + 50 mg/kg DMF (i.g.) for 28 days. At the end of the treatment schedule, renal function, histopathology, malondialdehyde (MDA), myeloperoxidase levels, and antioxidant enzyme expression were determined. DMF co-treatment ameliorated CsA-induced renal dysfunction as evidenced by a significant decrease in serum creatinine and urea levels, as well as improvement of creatinine clearance. DMF also significantly decreased serum and renal MDA

**4.2 HIV-induced neuroinflammation and neurotoxicity**

*DOI: http://dx.doi.org/10.5772/intechopen.91915*

warranted.

animals. Hence, additional studies in larger animal models and at some point, in humans, to test, develop and/or refine DMF/MMF formulations to improve potential suitability for use in the treatment of gastrointestinal or liver diseases are warranted.
