The ENIGMATIC Side of NITRIC OXIDE

Insights from New Research

Nitric Oxide in Physiology

Since my discovery that endothelial production of the vasodilator, nitric oxide, is a critical driver for cardiovascular disease back in the ‘80s (Deficiency in NO drives Hypertension), there has been a myriad of efforts to correct the deficiency and restore balanced, cardiovascular health. This includes various NO donors, antioxidants to limit is rapid degradation, as well as supplementing the nitrogen cycle with supplemental dietary nitrate.

Success has been somewhat limited, but efforts persist.

One aspect that various biomedical audiences routinely forget, is that there 3 different enzyme pathways to generate nitric oxide. There is the endothelial form (eNOS) that is the focus of vascular health, but in addition, there is a neuronal form (nNOS) which influences central nervous system actions linked to memory, as well as sphincter tone in the peripheral nervous system. Indeed, my research noted that “failure to thrive” states in neonates may accompany a lack of nitric oxide regulating gastric emptying and generating the condition called Hypertrophic Pyloric Stenosis (Neonatal Failure to Thrive & nNOS).

These two constitutive forms of nitric oxide synthase are regulated by their activation by a calcium/calmodulin complex that slips in & out of the enzymes as they release nitric oxide from L-arginine, in an episodic form of activity. These constitutive forms of nitric oxide synthase are constantly functioning in an ON/OFF modality.

Changing the Rules: The Effects of iNOS

However, the isoform that is most often dropped from discussions is the role of inducible nitric oxide synthase (iNOS). This form of nitric oxide synthase produces vast amounts of nitric oxide as it comes pre-equipped with the calcium/calmodulin subunit. The only thing that slows it down is the availability of the substrate L-arginine. It this characteristic that leads to the classification that L-arginine is a semi-essential amino acid, meaning that it is essential in states of infection and cancer, but not at other times when there are ample levels (as needed by eNOS and nNOS).

Normally iNOS is absent, its gene suppressed and rendered dormant. The reactive nitrogen species when generated by iNOS are in substantial amounts are quite dangerous. That is the biochemical intent is to help fight infections and cancer. Once those issues are addressed the iNOS gene returns to its dormant state. It works on an entirely different scale of NO production, for longer time frames and with an entirely different pattern of reactive nitrogen species generated from NO.

The love-fest for nitric oxide was thrown into a far more complex state in the early 90’s when I demonstrated for the first time, that iNOS generated nitric oxide drove chronic inflammation (Chronic Inflammation Driven by iNOS). This enigmatic role was a shock to the community, as until then we only thought of NO as a good thing and one that we need more of. My cautionary tale still upsets some that are happy and content with a focus on the endothelial isoform and all it brings to the table.

Indeed, the systemic production of nitric oxide in conditions like bacterial sepsis may be so overwhelming that blood pressure can be drop dramatically (septic shock). Some 27 years ago, I demonstrated that experimental septic shock can be treated with NO-scavengers like vitamin B12 (Septic Shock reversal by Vit B12). This concept has been now been validated in clinical trials (Treatment of septic shock with Vita B12 ), albeit decades later.

One aspect of these interactions that needs attention are mitochondria. These energy-producing organelles are replete in membranes and so their lipid environment is prime real estate for the interaction between NO and O2. Not surprisingly high levels of NO and its biochemical children, the reactive nitrogen species like peroxynitrite, have profound effects that compromise mitochondrial function (Reactive Nitrogen species & MItochondria). As mitochondria generate the currency of cellular energy, ATP, it is clear that compromise mitochondrial performance the cellular and tissue consequences can be profound.

Cancer

As noted above, iNOS is part of the biochemical weaponry that the body throws at cancer (Cancer Therapies & iNOS ) in order to eliminate the offending cancer cells. Invading micro-organisms are similar stimulants as I discussed in the COVID newsletter (Nitric Oxide and COVID-19). Nitric oxide itself is not that reactive (toxic), despite being a free radical, but it readily reacts with oxygen to form nitrogen dioxide (NO2) and in turn, dinitrogen trioxide (N2O3), which everyone knows as the brown gases in smog (Smog in Lipids via NO and O2). We calculated that 90% of the interaction between oxygen and NO occurs in lipids, with this reaction being 300x more rapid in lipids than in the aqueous environment.

“Yes the immune system uses SMOG to kill cancer cells and infections”.

One recent paper that really caught my attention was aimed at how the victim (cancer cells) respond to this onslaught (ADMA as Cancer Defense). The question posed in the research was how do cancer cells circumvent this gasotransmitter attack of NO, NO2 and N2O3?

In war, there are offenses, defenses and counter-offenses and if we can negate the defensive strategy of cancer cells, then maybe we can win the battle and be rid of cancer. The researchers chose to focus on ADMA (asymmetric dimethyl arginine), an analog of L-arginine, which competes with arginine for nitric oxide synthase but yet, does not yield nitric oxide. Asymmetric Dimethyl Arginine (ADMA) has been implicated in numerous pathologies including hypertension (ADMA and Hypertension), insulin resistance (Insulin Resistance & ADMA), obesity (ADMA, Nitric Oxide & Obesity), heart failure (ADMA lowering NO is a driver or Heart Failure) and even the litany of deleterious consequences and side-effects of taking acid reflux medicines that work by inhibiting acid production in the stomach. The substantial cardiovascular side-effects arise from an accidental inhibition of another enzyme, DDAH1 that functions to degrade ADMA (Proton Pump Inhibitors & ADMA), that then results in excessive levels of ADMA.

So there is precedence for ADMA levels having a massive influence on the production of nitric oxide. Under normal circumstances, when only the constitutive forms of NOS are active, the consequences are based around compromised vascular events (hypertensions, stroke, dementia, kidney disease). In the case of cancer, the ability of cancer cells to create high levels of ADMA means that the immune onslaught with reactive nitrogen species is compromised, conferring a survival method to the cancer cells.

Interpretation is not always clear. Some researchers note that while ADMA levels are a predictor of metastasis, they proposed that inhibitors of nitric oxide synthesis may be an ideal approach to treating colon cancer (ADMA raised in Tumors). While the data is intriguing I believe the therapeutic approach is the exact opposite - lower ADMA levels to allow the iNOS part of the immune system to do its thing - kill the cancer cells.

Summary

Nitric oxide has captured the attention of many that desire to create superior health, wellness and combat disease. Sadly, we got stuck in our thinking of only taking into account the endothelial enzyme eNOS, laying aside the importance of nNOS and in particular iNOS. The latter source changes the playing field with its role in inflammation, cancer and immunity. There is also a slew or reactive nitrogen species that dictate outcomes and need to be accounted for. There are true targets we can approach for superior health, but we need to understand the entire vista, not simply endothelial function and performance.